Eternal inflation

From Wikipedia, the free encyclopedia

Eternal inflation is a hypothetical inflationary universe model, which is itself an outgrowth or extension of the Big Bang theory.

According to eternal inflation, the inflationary phase of the universe's expansion lasts forever throughout most of the universe. Because the regions expand exponentially rapidly, most of the volume of the universe at any given time is inflating. Eternal inflation, therefore, produces a hypothetically infinite multiverse, in which only an insignificant fractal volume ends inflation.
Paul Steinhardt, one of the original architects of the inflationary model, introduced the first example of eternal inflation in 1983,^[1] and Alexander Vilenkin showed that it is generic.^[2]

Alan Guth's 2007 paper, "Eternal inflation and its implications",^[3] states that under reasonable assumptions "Although inflation is generically eternal into the future, it is not eternal into the past." Guth detailed what was known about the subject at the time, and demonstrated that eternal inflation was still considered the likely outcome of inflation, more than 20 years after eternal inflation was first introduced by Steinhardt.

Overview

Development of the theory

Inflation, or the inflationary universe theory, was originally developed as a way to overcome the few remaining problems with what was otherwise considered a successful theory of cosmology, the Big Bang model.

In 1979, Alan Guth introduced the inflationary model of the universe to explain why the universe is flat and homogeneous (which refers to the smooth distribution of matter and radiation on a large scale).^[4] The basic idea was that the universe underwent a period of rapidly accelerating expansion a few instants after the Big Bang. He offered a mechanism for causing the inflation to begin: false vacuum energy. Guth coined the term "inflation," and was the first to discuss the theory with other scientists worldwide.

Guth's original formulation was problematic, as there was no consistent way to bring an end to the inflationary epoch and end up with the hot, isotropic, homogeneous universe observed today. Although the false vacuum could decay into empty "bubbles" of "true vacuum" that expanded at the speed of light, the empty bubbles could not coalesce to reheat the universe, because they could not keep up with the remaining inflating universe.

In 1982, this "graceful exit problem" was solved independently by Andrei Linde and by Andreas Albrecht and Paul J. Steinhardt^[5] who showed how to end inflation without making empty bubbles and, instead, end up with a hot expanding universe. The basic idea was to have a continuous "slow-roll" or slow evolution from false vacuum to true without making any bubbles. The improved model was called "new inflation."

In 1983, Paul Steinhardt was the first to show that this "new inflation" does not have to end everywhere.^[1] Instead, it might only end in a finite patch or a hot bubble full of matter and radiation, and that inflation continues in most of the universe while producing hot bubble after hot bubble along the way. Alexander Vilenkin showed that when quantum effects are properly included, this is actually generic to all new inflation models.^[2]

Using ideas introduced by Steinhardt and Vilenkin, Andrei Linde published an alternative model of inflation in 1986 which used these ideas to provide a detailed description of what has become known as the Chaotic Inflation theory or eternal inflation.^[6]

Quantum fluctuations

New inflation does not produce a perfectly symmetric universe due to quantum fluctuations during inflation. The fluctuations cause the energy and matter density to be different in different points in space.

Quantum fluctuations in the hypothetical inflation field produce changes in the rate of expansion that are responsible for eternal inflation. Those regions with a higher rate of inflation expand faster and dominate the universe, despite the natural tendency of inflation to end in other regions. This allows inflation to continue forever, to produce future-eternal inflation. As a simplified example, suppose that during inflation, the natural decay rate of the inflaton field is slow compared to the effect of quantum fluctuation. When a mini-universe inflates and "self-reproduces" into, say, twenty causally-disconnected mini-universes of equal size to the original mini-universe, perhaps nine of the new mini-universes will have a larger, rather than smaller, average inflaton field value than the original mini-universe, because they inflated from regions of the original mini-universe where quantum fluctuation pushed the inflaton value up more than the slow inflation decay rate brought the inflaton value down. Originally there was one mini-universe with a given inflaton value; now there are nine mini-universes that have a slightly larger inflaton value. (Of course, there are also eleven mini-universes where the inflaton value is slightly lower than it originally was.) Each mini-universe with the larger inflaton field value restarts a similar round of approximate self-reproduction within itself. (The mini-universes with lower inflaton values may also reproduce, unless its inflaton value is small enough that the region drops out of inflation and ceases self-reproduction.) This process continues indefinitely; nine high-inflaton mini-universes might become 81, then 729... Thus, there is eternal inflation.^[7]

In 1980, quantum fluctuations were suggested by Viatcheslav Mukhanov and Gennady Chibisov^[8][9] in the Soviet Union in the context of a model of modified gravity by Alexei Starobinsky^[10] to be possible seeds for forming galaxies.

In the context of inflation, quantum fluctuations were first analyzed at the three-week 1982 Nuffield Workshop on the Very Early Universe at Cambridge University.^[11] The average strength of the fluctuations was first calculated by four groups working separately over the course of the workshop: Stephen Hawking;^[12] Starobinsky;^[13] Guth and So-Young Pi;^[14] and James M. Bardeen, Paul Steinhardt and Michael Turner.^[15]

The early calculations derived at the Nuffield Workshop only focused on the average fluctuations, whose magnitude is too small to affect inflation. However, beginning with the examples presented by Steinhardt^[1] and Vilenkin,^[2] the same quantum physics was later shown to produce occasional large fluctuations that increase the rate of inflation and keep inflation going eternally.

Further developments

In analyzing the Planck Satellite data from 2013, Anna Ijjas and Paul Steinhardt showed that the simplest textbook inflationary models were eliminated and that the remaining models require exponentially more tuned starting conditions, more parameters to be adjusted, and less inflation. Later Planck observations reported in 2015 confirmed these conclusions.^[16][17]

A 2014 paper by Kohli and Haslam called into question the viability of the eternal inflation theory, by analyzing Linde's chaotic inflation theory in which the quantum fluctuations are modeled as Gaussian white noise.^[18] They showed that in this popular scenario, eternal inflation in fact cannot be eternal, and the random noise leads to spacetime being filled with singularities. This was demonstrated by showing that solutions to the Einstein field equations diverge in a finite time. Their paper therefore concluded that the theory of eternal inflation based on random quantum fluctuations would not be a viable theory, and the resulting existence of a multiverse is "still very much an open question that will require much deeper investigation".

Inflation, eternal inflation, and the multiverse

In 1983, it was shown that inflation could be eternal, leading to a multiverse in which space is broken up into bubbles or patches whose properties differ from patch to patch spanning all physical possibilities.

Paul Steinhardt, who produced the first example of eternal inflation,^[1] eventually became a strong and vocal opponent of the theory. He argued that the multiverse represented a breakdown of the inflationary theory, because, in a multiverse, any outcome is equally possible, so inflation makes no predictions and, hence, is untestable. Consequently, he argued, inflation fails a key condition for a scientific theory.^[19][20]

Both Linde and Guth, however, continued to support the inflationary theory and the multiverse. Guth declared:

It's hard to build models of inflation that don't lead to a multiverse. It's not impossible, so I think there's still certainly research that needs to be done. But most models of inflation do lead to a multiverse, and evidence for inflation will be pushing us in the direction of taking the idea of a multiverse seriously.^[21]

According to Linde, "It's possible to invent models of inflation that do not allow a multiverse, but it's difficult. Every experiment that brings better credence to inflationary theory brings us much closer to hints that the multiverse is real."^[21]

Global Warming Alarmists Caught Doctoring '97-Percent Consensus' Claims

From https://www.forbes.com/sites/jamestaylor/2013/05/30/global-warming-alarmists-caught-doctoring-97-percent-consensus-claims/#277ab972485d

 

James Taylor , Contributor I am president of the Spark of Freedom Foundation. Opinions expressed by Forbes Contributors are their own.

 

 (Photo credit: Wikipedia)

Global warming alarmists and their allies in the liberal media have been caught doctoring the results of a widely cited paper asserting there is a 97-percent scientific consensus regarding human-caused global warming. After taking a closer look at the paper, investigative journalists report the authors’ claims of a 97-pecent consensus relied on the authors misclassifying the papers of some of the world’s most prominent global warming skeptics. At the same time, the authors deliberately presented a meaningless survey question so they could twist the responses to fit their own preconceived global warming alarmism.

Global warming alarmist John Cook, founder of the misleadingly named blog site Skeptical Science, published a paper with several other global warming alarmists claiming they reviewed nearly 12,000 abstracts of studies published in the peer-reviewed climate literature. Cook reported that he and his colleagues found that 97 percent of the papers that expressed a position on human-caused global warming “endorsed the consensus position that humans are causing global warming.”


As is the case with other ‘surveys’ alleging an overwhelming scientific consensus on global warming, the question surveyed had absolutely nothing to do with the issues of contention between global warming alarmists and global warming skeptics. The question Cook and his alarmist colleagues surveyed was simply whether humans have caused some global warming. The question is meaningless regarding the global warming debate because most skeptics as well as most alarmists believe humans have caused some global warming. The issue of contention dividing alarmists and skeptics is whether humans are causing global warming of such negative severity as to constitute a crisis demanding concerted action.


Either through idiocy, ignorance, or both, global warming alarmists and the liberal media have been reporting that the Cook study shows a 97 percent consensus that humans are causing a global warming crisis. However, that was clearly not the question surveyed.

Investigative journalists at Popular Technology looked into precisely which papers were classified within Cook’s asserted 97 percent. The investigative journalists found Cook and his colleagues strikingly classified papers by such prominent, vigorous skeptics as Willie Soon, Craig Idso, Nicola Scafetta, Nir Shaviv, Nils-Axel Morner and Alan Carlin as supporting the 97-percent consensus.

Cook and his colleagues, for example, classified a peer-reviewed paper by scientist Craig Idso as explicitly supporting the ‘consensus’ position on global warming “without minimizing” the asserted severity of global warming. When Popular Technology asked Idso whether this was an accurate characterization of his paper, Idso responded, “That is not an accurate representation of my paper. The papers examined how the rise in atmospheric CO2 could be inducing a phase advance in the spring portion of the atmosphere's seasonal CO2 cycle. Other literature had previously claimed a measured advance was due to rising temperatures, but we showed that it was quite likely the rise in atmospheric CO2 itself was responsible for the lion's share of the change. It would be incorrect to claim that our paper was an endorsement of CO2-induced global warming."

When Popular Technology asked physicist Nicola Scafetta whether Cook and his colleagues accurately classified one of his peer-reviewed papers as supporting the ‘consensus’ position, Scafetta similarly criticized the Skeptical Science classification.

“Cook et al. (2013) is based on a straw man argument because it does not correctly define the IPCC AGW theory, which is NOT that human emissions have contributed 50%+ of the global warming since 1900 but that almost 90-100% of the observed global warming was induced by human emission,” Scafetta responded. “What my papers say is that the IPCC [United Nations Intergovernmental Panel on Climate Change] view is erroneous because about 40-70% of the global warming observed from 1900 to 2000 was induced by the sun.”

“What it is observed right now is utter dishonesty by the IPCC advocates. … They are gradually engaging into a metamorphosis process to save face. … And in this way they will get the credit that they do not merit, and continue in defaming critics like me that actually demonstrated such a fact since 2005/2006,” Scafetta added.

Astrophysicist Nir Shaviv similarly objected to Cook and colleagues claiming he explicitly supported the ‘consensus’ position about human-induced global warming. Asked if Cook and colleagues accurately represented his paper, Shaviv responded, “Nope... it is not an accurate representation. The paper shows that if cosmic rays are included in empirical climate sensitivity analyses, then one finds that different time scales consistently give a low climate sensitivity. i.e., it supports the idea that cosmic rays affect the climate and that climate sensitivity is low. This means that part of the 20th century [warming] should be attributed to the increased solar activity and that 21st century warming under a business as usual scenario should be low (about 1°C).”

“I couldn't write these things more explicitly in the paper because of the refereeing, however, you don't have to be a genius to reach these conclusions from the paper," Shaviv added.

To manufacture their misleading asserted consensus, Cook and his colleagues also misclassified various papers as taking “no position” on human-caused global warming. When Cook and his colleagues determined a paper took no position on the issue, they simply pretended, for the purpose of their 97-percent claim, that the paper did not exist.

Morner, a sea level scientist, told Popular Technology that Cook classifying one of his papers as “no position” was "Certainly not correct and certainly misleading. The paper is strongly against AGW [anthropogenic global warming], and documents its absence in the sea level observational facts. Also, it invalidates the mode of sea level handling by the IPCC."

Soon, an astrophysicist, similarly objected to Cook classifying his paper as “no position.”
"I am sure that this rating of no position on AGW by CO2 is nowhere accurate nor correct,” said Soon.

“I hope my scientific views and conclusions are clear to anyone that will spend time reading our papers. Cook et al. (2013) is not the study to read if you want to find out about what we say and conclude in our own scientific works,” Soon emphasized.

Viewing the Cook paper in the best possible light, Cook and colleagues can perhaps claim a small amount of wiggle room in their classifications because the explicit wording of the question they analyzed is simply whether humans have caused some global warming. By restricting the question to such a minimalist, largely irrelevant question in the global warming debate and then demanding an explicit, unsolicited refutation of the assertion in order to classify a paper as a ‘consensus’ contrarian, Cook and colleagues misleadingly induce people to believe 97 percent of publishing scientists believe in a global warming crisis when that is simply not the case.

Misleading the public about consensus opinion regarding global warming, of course, is precisely what the Cook paper sought to accomplish. This is a tried and true ruse perfected by global warming alarmists. Global warming alarmists use their own biased, subjective judgment to misclassify published papers according to criteria that is largely irrelevant to the central issues in the global warming debate. Then, by carefully parsing the language of their survey questions and their published results, the alarmists encourage the media and fellow global warming alarmists to cite these biased, subjective, totally irrelevant surveys as conclusive evidence for the lie that nearly all scientists believe humans are creating a global warming crisis.

These biased, misleading, and totally irrelevant “surveys” form the best “evidence” global warming alarmists can muster in the global warming debate. And this truly shows how embarrassingly feeble their alarmist theory really is.

Two Degree Temperature Target Has Little Scientific Basis

The two degree temperature target (beyond which we will face an existential climate crisis) is inaccurate, irrelevant, and vague.  It appears to be based on the claim that modern humans (Homo sapiens) never existed when the average global temperature was two degrees above the mid-nineteenth century, and therefor, since this is an "unprecedented" state of affairs, must lead to catastrophe.

But, first, it is incorrect, as shown below.  Modern humans evolved before the last interglacial period, the Eemian, which was at least a degree warmer than the present at times, and perhaps more.  Second, it is a non sequitur, for two reasons:  one, that an unprecedented global climate condition does not logically or scientifically predict catastrophe; second, that human beings do not live in an average global climate but a local one -- there is little doubt, for example, that Europe and the North Atlantic climate region has undergone temperature swings of two and more degrees during the Holocene, yet the millions who have lived there during this period survived and even thrived -- despite possessing little more than Stone Age technology for much of this time, while being subject to famines, droughts, contagions, warfare, and invasions -- conditions which no longer prevail even today, let alone 50 or 100 years from now.

That the claim is vague, and lacking in any scientific specificity, I hope is clear.

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Prof. Roger Pielke Jr. on origins of 2 degree temp target: ‘Has little scientific basis’

By: Marc Morano - Climate Depot September 20, 2017 4:03 PM

Original link:  http://www.climatedepot.com/2017/09/20/prof-roger-pielke-jr-on-origins-of-2-degree-temp-target-has-little-scientific-basis/

Via: Roger Pielke Jr.’s The Climate Fix website: https://theclimatefix.wordpress.com/2017/09/18/pielke-on-climate-5/

Do you want to know the origins of the 2 degree temperature target that underpins much of climate policy discussions and action?

• As is often the case, it is an arbitrary round number that was politically convenient. So it became a sort of scientific truth. However, it has little scientific basis but is a hard political reality.
• Jaeger and Jaeger (2011) explain that it came from “a marginal remark in an early paper about climate policy”
• That “marginal paper” was a 1975 working paper by economist William Nordhaus (here in PDF and a second version is from 1977, with the figure shown below). At p. 23, “If there were global temperatures of more than 2 or 3 C. above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.”
  
  
• Nordhaus’ claim was sourced to climatologist Hubert Lamb (1972) who in turn calculated long-term variations in temperature based on record kept in Central England.
• So: The 2 degree temperature target that sits at the center of current climate policy discussions originated in a local, long-term record of temperature variation in England, which was adapted by an economist in a “what if?” exercise.
• The 2 degree target is today far more politically “real” than its grounding in science or policy. That won’t change, but it is nonetheless a fascinating look at the arbitrariness of policy and how it is that issues are framed shapes what options are deemed relevant and appropriate.
• As an example, check out this paper just out today in Nature — it argues that we can emit more than we thought and still hit a 1.5 degree temperature target. People will argue about the results, many because of its perceived political implications. But this argument is only tenuously related to actual energy policies, instead it is related to how we should think about arguments that might be used to motivate people to think about energy policies and thus demand action and so on. Tenuous, like I said.

Related Link: 
Flashback Climategate emails: Phil Jones says critical 2-degree C limit was ‘plucked out of thin air’

Via: https://junkscience.com/2011/11/climategate-2-0-jones-says-2o-limit-plucked-out-of-thin-air/

From the Climategate 2.0 collection, to a European Peoples Party officials who is trying to eliminate skepticism from the EPP’s position paper on climate, Phil Jones describes the origin of the 2^o limit:

“The 2 deg C limit is talked about by a lot within Europe. It is never defined though what it means. Is it 2 deg C for the globe or for Europe? Also when is/was the base against which the 2 deg C is calculated from? I know you don’t know the answer, but I don’t either! I think it is plucked out of thin air. I think it is too high as well. If it is 2 deg C globally, this could be more in Europe – especially the northern part. A better limit might be maintaining some summer Arctic sea ice!”

German Scientists: ‘2°C Target Purely Political’ – Prof. Dr. Christian Schönwiese told German public television: ‘They formulated a 2°C target. It is not from a climate scientist, or a physicist, or a chemist, but from an outside person who simply plucked it out of thin air and said ‘2°C’

Warmist father Hans Joachim Schellnhuber of 2C temperature limit admits it’s ‘a political goal’– Hans Joachim Schellnhuber, a top German climate scientist who helped establish the 2-degree threshold, stressed it was a policy marker: “Two degrees is not a magical limit — it’s clearly a political goal,” says Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research (PIK). “The world will not come to an end right away in the event of stronger warming, nor are we definitely saved if warming is not as significant. The reality, of course, is much more complicated.” Schellnhuber ought to know. He is the father of the two-degree target. “Yes, I plead guilty,” he says, smiling. The idea didn’t hurt his career. In fact, it made him Germany’s most influential climatologist. Schellnhuber, a theoretical physicist, became Chancellor Angela Merkel’s chief scientific adviser — a position any researcher would envy.

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Out of Africa: When Did Prehistoric Humans Actually Leave—and Where Did They Go?

By Katherine Hignett On 1/26/18 at 9:11 AM 
Original link:  http://www.newsweek.com/out-africa-prehistoric-humans-791822

Scientists have discovered the oldest human fossil ever found outside of Africa in Misliya Cave, Israel. The find means our current timing for human migration—and evolution—could be off by at least 50,000 years.

So when did humans really start exploring the rest of the world?
 
The jawbone fossil was found in Misliya Cave in Israel. The newly discovered fossil is estimated to be between 170,000 and 190,000 years old.

Scientists think our modern human species (Homo sapiens) emerged approximately 200,000 years ago in Africa. In the 1980s, fossil and DNA evidence pointed to the continent as the cradle of humanity.

Where humans went next, however, is still a big mystery.

Out of Africa

The traditional “Out of Africa” model holds that humans first traveled from the continent between 130,000 and 115,000 years ago, toward the Middle East.

The newly discovered fossil is estimated to be between 170,000 and 190,000 years old. Before now, the earliest remains found in Israel were dated between 90,000 and 120,000 years old. This means humans reached the region at least 50,000 years earlier than expected.

Chris Stringer of London’s Natural History Museum, who was not involved in the latest discovery, told the BBC: “The find breaks the long-established 130,000-year-old limit on modern humans outside of Africa.... The new dating hints that there could be even older Homo sapien finds to come from the region of western Asia.”

Moving back the date of that first migration has big consequences for our understanding of human evolution. “The entire narrative of the evolution of Homo sapiens must be pushed back by at least 100,000 to 200,000 years,” study author Israel Hershkovitz from Tel Aviv University explained in a statement. “In other words, if modern humans started traveling out of Africa some 200,000 years ago, it follows that they must have originated in Africa at least 300,000 to 500,000 years ago.”
 
A micro-CT reconstruction of the jawbone fossil found in Misliya Cave in Israel. Scientists believe the jawbone to be the oldest human fossil ever found outside of Africa. The discovery means our current timings for human migration—and evolution—could be off by at least 50,000 years. Gerhard Weber/University of Vienna

What path did early humans take?

The early excursions into Eurasia responsible for the Misliya fossil likely ended in extinction. Scientists had believed a second exodus occurred about 60,000 years ago.

This idea was brought under scrutiny last year, when a team of scientists reviewed human bones from China. The bones were estimated to be up to 120,000 years old. The team argued that multiple dispersals might explain a growing body of evidence finding humans in the wrong place, at the wrong time.

They produced a map (below) describing the human journey from Africa as a series of smaller migrations around the globe.
 
This map shows the early human migration charted by researchers. It reflects the human journey from Africa as a series of smaller migrations around the globe. Katerina Douka/Michelle O'Reilly/Science
The question of when humans left Africa is far from solved. The Misliya jawbone has once again thrown the question of human origins wide open.

Hershkovitz explains: “This finding—that early modern humans were present outside of Africa earlier than commonly believed—completely changes our view on modern human dispersal and the history of modern human evolution.”

Every Black Hole Contains Another Universe – Equations Predict

April 19, 2018 Original article posted on National Geographic.
 

Like part of a cosmic Russian doll, our universe may be perfectly nested inside a black hole that is itself part of a larger universe. In turn, all the black holes found so far in our universe—from the microscopic to the supermassive—may be ultimate doorways into alternate realities.

According to a mind-bending new theory, a black hole is actually a tunnel between universes—a type of wormhole. The matter the black hole attracts doesn’t collapse into a single point, as has been predicted, but rather gushes out a “white hole” at the other end of the black one, the theory goes.

In a paper published in the journal Physics Letters B, Indiana University physicist Nikodem Poplawski presents new mathematical models of the spiraling motion of matter falling into a black hole. His equations suggest such wormholes are viable alternatives to the “space-time singularities” that Albert Einstein predicted to be at the centers of black holes. According to Einstein’s equations for general relativity, singularities are created whenever matter in a given region gets too dense, as would happen at the ultra-dense heart of a black hole. 

Einstein’s theory suggests singularities take up no space, are infinitely dense, and are infinitely hot—a concept supported by numerous lines of indirect evidence but still so outlandish that many scientists find it hard to accept. If Poplawski is correct, they may no longer have to. According to the new equations, the matter black holes absorb and seemingly destroy is actually expelled and becomes the building blocks for galaxies, stars, and planets in another reality.

The notion of black holes as wormholes could explain certain mysteries in modern cosmology, Poplawski said. For example, the big bang theory says the universe started as a singularity. But scientists have no satisfying explanation for how such a singularity might have formed in the first place. If our universe was birthed by a white hole instead of a singularity, Poplawski said:

“It would solve this problem of black hole singularities and also the big bang singularity.”

Wormholes might also explain gamma ray bursts, the second most powerful explosions in the universe after the big bang. Gamma ray bursts occur at the fringes of the known universe. They appear to be associated with supernovae, or star explosions, in faraway galaxies, but their exact sources are a mystery.

Poplawski proposes that the bursts may be discharges of matter from alternate universes. The matter, he says, might be escaping into our universe through supermassive black holes—wormholes—at the hearts of those galaxies, though it’s not clear how that would be possible. The wormhole theory may also help explain why certain features of our universe deviate from what theory predicts, according to physicists. 

“It’s kind of a crazy idea, but who knows?” he said. There is at least one way to test Poplawski’s theory: Some of our universe’s black holes rotate, and if our universe was born inside a similarly revolving black hole, then our universe should have inherited the parent object’s rotation. If future experiments reveal that our universe appears to rotate in a preferred direction, it would be indirect evidence supporting his wormhole theory, Poplawski said.

Based on the standard model of physics, after the big bang the curvature of the universe should have increased over time so that now—13.7 billion years later—we should seem to be sitting on the surface of a closed, spherical universe. But observations show the universe appears flat in all directions.

What’s more, data on light from the very early universe show that everything just after the big bang was a fairly uniform temperature. That would mean that the farthest objects we see on opposite horizons of the universe were once close enough to interact and come to equilibrium, like molecules of gas in a sealed chamber. 

Again, observations don’t match predictions, because the objects farthest from each other in the known universe are so far apart that the time it would take to travel between them at the speed of light exceeds the age of the universe. Inflation states that shortly after the universe was created, it experienced a rapid growth spurt during which space itself expanded at faster-than-light speeds. The expansion stretched the universe from a size smaller than an atom to astronomical proportions in a fraction of a second.

The universe therefore appears flat, because the sphere we’re sitting on is extremely large from our viewpoint—just as the sphere of Earth seems flat to someone standing in a field. Inflation also explains how objects so far away from each other might have once been close enough to interact. But—assuming inflation is real—astronomers have always been at pains to explain what caused it. That’s where the new wormhole theory comes in.

According to Poplawski, some theories of inflation say the event was caused by “exotic matter,” a theoretical substance that differs from normal matter, in part because it is repelled rather than attracted by gravity. Based on his equations, Poplawski thinks such exotic matter might have been created when some of the first massive stars collapsed and became wormholes.

“There may be some relationship between the exotic matter that forms wormholes and the exotic matter that triggered inflation,” he said.

The new model isn’t the first to propose that other universes exist inside black holes. Damien Easson, a theoretical physicist at Arizona State University, has made the speculation in previous studies.

“What is new here is an actual wormhole solution in general relativity that acts as the passage from the exterior black hole to the new interior universe.In our paper, we just speculated that such a solution could exist, but Poplawski has found an actual solution,” said Easson, referring to Poplawski’s equations (who was not involved in the new study). Nevertheless, the idea is still very speculative, Easson said in an email.

“Is the idea possible? Yes. Is the scenario likely? I have no idea. But it is certainly an interesting possibility. Future work in quantum gravity—the study of gravity at the subatomic level—could refine the equations and potentially support or disprove Poplawski’s theory”, Easson said.

Overall, the wormhole theory is interesting, but not a breakthrough in explaining the origins of our universe, said Andreas Albrecht, a physicist at the University of California, Davis, who was also not involved in the new study. By saying our universe was created by a gush of matter from a parent universe, the theory simply shifts the original creation event into an alternate reality. In other words, it doesn’t explain how the parent universe came to be or why it has the properties it has—properties our universe presumably inherited.

“There’re really some pressing problems we’re trying to solve, and it’s not clear that any of this is offering a way forward with that,” he said.

Still, Albrecht doesn’t find the idea of universe-bridging wormholes any stranger than the idea of black hole singularities, and he cautions against dismissing the new theory just because it sounds a little out there.

“Everything people ask in this business is pretty weird,” he said. “You can’t say the less weird [idea] is going to win, because that’s not the way it’s been, by any means.”

Lithium-ion battery

From Wikipedia, the free encyclopedia

Lithium-ion battery

An example of a Li-ion battery (used in various Nokia mobile phones)
Specific energy	100–265 W·h/kg[1][2] (0.36–0.875 MJ/kg)
Energy density	250–693 W·h/L[3][4] (0.90–2.43 MJ/L)
Specific power	~250-~340 W/kg[1]
Charge/discharge efficiency	80–90%[5]
Energy/consumer-price	2.5 W·h/US$[6]
Self-discharge rate	2% per month[7]
Cycle durability	400–1200 cycles [8]
Nominal cell voltage	NMC 3.6 / 3.85 V, LiFePO4 3.2 V

A lithium-ion battery or Li-ion battery (abbreviated as LIB) is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the constituent components of a lithium-ion battery cell.

Lithium-ion batteries are common in home electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, tiny memory effect^[9] and low self-discharge. LIBs are also growing in popularity for military, battery electric vehicle and aerospace applications.^[10]

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO
₂), which offers high energy density but presents safety risks, especially when damaged. Lithium iron phosphate (LiFePO
₄), lithium ion manganese oxide battery (LiMn
₂O
₄, Li
₂MnO
₃, or LMO), and lithium nickel manganese cobalt oxide (LiNiMnCoO
₂ or NMC) offer lower energy density but longer lives and less likelihood of unfortunate events in real-world use (e.g., fire, explosion, etc.). Such batteries are widely used for electric tools, medical equipment, and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (LiNiCoAlO
₂ or NCA) and lithium titanate (Li
₄Ti
₅O
₁₂ or LTO) are specialty designs aimed at particular niche roles. The newer lithium–sulfur batteries promise the highest performance-to-weight ratio.

Lithium-ion batteries can pose unique safety hazards since they contain a flammable electrolyte and may be kept pressurized. A battery cell charged too quickly could cause a short circuit, leading to explosions and fires.^[11] Because of these risks, testing standards are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests.^[12][13][14] There have been battery-related recalls by some companies, including the 2016 Samsung Galaxy Note 7 recall for battery fires.^[15][16]

Research areas for lithium-ion batteries include life extension, energy density, safety, cost reduction, and charging speed,^[17] among others.

Terminology

Battery versus cell

International industry standards differentiate between a "cell" and a "battery".^[14][18] A "cell" is a basic electrochemical unit that contains the electrodes, separator, and electrolyte. A "battery" or "battery pack" is a collection of cells or cell assemblies which are ready for use, as it contains an appropriate housing, electrical interconnections, and possibly electronics to control and protect the cells from failure.^[19][20] ("Failure" in this case is used in the engineering sense and may include thermal runaway, fire, and explosion as well as more benign events such as loss of charge capacity.) In this regard, the simplest "battery" is a single cell.

For example, battery electric vehicles,^[21] may have a battery system of 400 V, made of many individual cells. The term "module" is often used, where a battery pack is made of modules, and modules are composed of individual cells.^[20][21]

Anode, cathode, electrode

In electrochemistry, the anode is the electrode where oxidation is taking place in the battery, i.e. electrons get free and flow out of the battery (technical current flowing into it). However, this happens on opposite electrodes during charge vs. discharge. The less ambiguous terms are positive (cathode on discharge) and negative (anode on discharge). This is the positive-negative polarity which is displayed on a volt meter.^[22] For rechargeable cells, the term "cathode" designates the positive electrode in the discharge cycle, even when the associated electrochemical reactions change their places when charging and discharging, respectively. For lithium-ion cells the positive electrode ("cathode") is the lithium based one.

History

Invention and development

Varta lithium-ion battery, Museum Autovision, Altlussheim, Germany

Lithium batteries were proposed by British chemist M Stanley Whittingham, now at Binghamton University, while working for Exxon in the 1970s.^[23] Whittingham used titanium(IV) sulfide and lithium metal as the electrodes. However, this rechargeable lithium battery could never be made practical. Titanium disulfide was a poor choice, since it has to be synthesized under completely sealed conditions, also being quite expensive (~$1000 per kilogram for titanium disulfide raw material in 1970s). When exposed to air, titanium disulfide reacts to form hydrogen sulfide compounds, which have an unpleasant odour and are toxic to most animals. For this, and other reasons, Exxon discontinued development of Whittingham's lithium-titanium disulfide battery.^[24] Batteries with metallic lithium electrodes presented safety issues, as lithium is a highly reactive element; it burns in normal atmospheric conditions because of spontaneous reactions with water and oxygen.^[25] As a result, research moved to develop batteries in which, instead of metallic lithium, only lithium compounds are present, being capable of accepting and releasing lithium ions.

Reversible intercalation in graphite^[26][27] and intercalation into cathodic oxides^[28][29] was discovered during 1974–76 by J. O. Besenhard at TU Munich. Besenhard proposed its application in lithium cells.^[30][31] Electrolyte decomposition and solvent co-intercalation into graphite were severe early drawbacks for battery life.

• 1973 – Adam Heller Proposes the lithium thionyl chloride battery, still used in implanted medical devices and in defense systems where greater than a 20-year shelf life, high energy density, or extreme operating temperatures are encountered.^[32]
• 1977 – Samar Basu demonstrated electrochemical intercalation of lithium in graphite at the University of Pennsylvania.^[33][34] This led to the development of a workable lithium intercalated graphite electrode at Bell Labs (LiC
  ₆)^[35] to provide an alternative to the lithium metal electrode battery.
• 1979 – Working in separate groups, at Stanford University Ned A. Godshall et al.,^[36][37][38] and the following year in 1980 at Oxford University, England, John Goodenough and Koichi Mizushima, both demonstrated a rechargeable lithium cell with voltage in the 4 V range using lithium cobalt oxide (LiCoO
  ₂) as the positive electrode and lithium metal as the negative electrode.^[39][40] This innovation provided the positive electrode material that made lithium batteries commercially possible. LiCoO
  ₂ is a stable positive electrode material which acts as a donor of lithium ions, which means that it can be used with a negative electrode material other than lithium metal.^{[citation needed]} By enabling the use of stable and easy-to-handle negative electrode materials, LiCoO
  ₂ opened a whole new range of possibilities for novel rechargeable battery systems. Godshall et al. further identified in 1979, along with LiCoO₂, the similar value of ternary compound lithium-transition metal-oxides such as the spinel LiMn₂O₄, Li₂MnO₃, LiMnO₂, LiFeO₂, LiFe₅O₈, and LiFe₅O₄ (and later lithium-copper-oxide and lithium-nickel-oxide cathode materials in 1985)^[41][41]
• 1980 – Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite.^[42][43] The organic electrolytes available at the time would decompose during charging with a graphite negative electrode, slowing the development of a rechargeable lithium/graphite battery. Yazami used a solid electrolyte to demonstrate that lithium could be reversibly intercalated in graphite through an electrochemical mechanism. (As of 2011, the graphite electrode discovered by Yazami is the most commonly used electrode in commercial lithium ion batteries).
• 1982 – Godshall et al. were awarded the U.S. Patent^[44] on the use of LiCoO₂ as cathodes in lithium batteries, based on Godshall's Stanford University Ph.D. thesis Dissertation and 1979 publications.
• 1983 – Michael M. Thackeray, John B. Goodenough, and coworkers further developed manganese spinel as a positive electrode material, after its 1979 identification as such by Godshall et al. in 1979 (above).^[45] Spinel showed great promise, given its low-cost, good electronic and lithium ion conductivity, and three-dimensional structure, which gives it good structural stability. Although pure manganese spinel fades with cycling, this can be overcome with chemical modification of the material.^[46] As of 2013, manganese spinel was used in commercial cells.^[47]
• 1985 – Akira Yoshino assembled a prototype cell using carbonaceous material into which lithium ions could be inserted as one electrode, and lithium cobalt oxide (LiCoO
  ₂), which is stable in air, as the other.^[48] By using materials without metallic lithium, safety was dramatically improved. LiCoO
  ₂ enabled industrial-scale production and represents the birth of the current lithium-ion battery.
• 1989 – John Goodenough and Arumugam Manthiram of the University of Texas at Austin showed that positive electrodes containing polyanions, e.g., sulfates, produce higher voltages than oxides due to the induction effect of the polyanion.^[49]

There were two main trends in the research and development of electrode materials for lithium ion rechargeable batteries. One was the approach from the field of electrochemistry centering on graphite intercalation compounds,^[50] and the other was the approach from the field of new nano-carbonaceous materials.^[51]

The negative electrode of today’s lithium ion rechargeable battery has its origins in PAS (polyacenic semiconductive material) discovered by Tokio Yamabe and later by Shjzukuni Yata in the early 1980s.^{[52][53][54][55]} The seed of this technology, furthermore, was the discovery of conductive polymers by Professor Hideki Shirakawa and his group, and it could also be seen as having started from the polyacetylene lithium ion battery developed by Alan MacDiarmid and Alan J. Heeger et al.^[56]

Commercial production

The performance and capacity of lithium-ion batteries increases as development progresses.

• 1991 – Sony and Asahi Kasei released the first commercial lithium-ion battery.^[57]
• 1996 – John Goodenough, Akshaya Padhi and coworkers proposed lithium iron phosphate (LiFePO
  ₄) and other phospho-olivines (lithium metal phosphates with the same structure as mineral olivine) as positive electrode materials.^[58]
• 2001 – Zhonghua Lu and Jeff Dahn file a patent^[59] for the lithium nickel manganese cobalt oxide (NMC) class of positive electrode materials, which offers safety and energy density improvements over the widely used lithium cobalt oxide.
• 2002 – Yet-Ming Chiang and his group at MIT showed a substantial improvement in the performance of lithium batteries by boosting the material's conductivity by doping it^[60] with aluminium, niobium and zirconium. The exact mechanism causing the increase became the subject of widespread debate.^[61]
• 2004 – Chiang again increased performance by utilizing lithium iron(II) phosphate particles of less than 100 nanometers in diameter. This decreased particle density almost one hundredfold, increased the positive electrode's surface area and improved capacity and performance. Commercialization led to a rapid growth in the market for higher capacity LIBs, as well as a patent infringement battle between Chiang and John Goodenough.^[61]
• 2011 – lithium-ion batteries accounted for 66% of all portable secondary (i.e., rechargeable) battery sales in Japan.^[62]
• 2012 – John Goodenough, Rachid Yazami and Akira Yoshino received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the lithium ion battery.
• 2014 – commercial batteries from Amprius Corp. reached 650 Wh/L (a 20% increase), using a silicon anode and were delivered to customers.^[63] The National Academy of Engineering recognized John Goodenough, Yoshio Nishi, Rachid Yazami and Akira Yoshino for their pioneering efforts in the field.^[64]

As of 2016, global lithium-ion battery production capacity was 28 gigawatt-hours, with 16.4 GWh in China.^[65]

Market

Industry produced about 660 million cylindrical lithium-ion cells in 2012; the 18650 size is by far the most popular for cylindrical cells. If Tesla meets its goal of shipping 40,000 Model S electric cars in 2014 and if the 85-kWh battery, which uses 7,104 of these cells, proves as popular overseas as it was in the U.S., in 2014 the Model S alone would use almost 40 percent of global cylindrical battery production.^[66] Production is gradually shifting to higher-capacity 3,000+ mAh cells. Annual flat polymer cell demand was expected to exceed 700 million in 2013.^[67]

In 2015 cost estimates ranged from $300–500/kWh.^[68]

In 2016 GM revealed they will be paying $145 / kWh for the batteries in the Chevy Bolt EV.^[69]

Price-fixing conspiracy

Information came to light in 2011 regarding a long-term antitrust violating price-fixing conspiracy among the world's major lithium-ion battery manufacturers that kept prices artificially high from 2000 to 2011, according to a class action complaint that was tentatively settled with one of the defendants, Sony, in 2016.^[70] The complaint provided evidence that participants included LG, Samsung SDI, Sanyo, Panasonic, Sony, and Hitachi, and notes that Sanyo and LG had "pled guilty to the criminal price-fixing of Lithium Ion Batteries".^[70]

Sony agreed to settle for $20 million, and also cooperate by, among other things, making employees chosen by plaintiffs available for interviews, depositions and testimony, as well as provide clarifying information regarding the scheme and the documents provided to date, including responding to authentication and clarification questions.^{[71]Cooperation clause: pp. 23–25.}

Construction

Cylindrical Panasonic 18650 lithium-ion battery cell before closing. Several thousand of them form the Tesla Model S battery (see Gigafactory).

Lithium-ion battery monitoring electronics (over-charge and deep-discharge protection)

An 18650 size lithium ion battery, with an alkaline AA for scale. 18650 are used for example in notebooks or Tesla Model S

The three primary functional components of a lithium-ion battery are the positive and negative electrodes and electrolyte. Generally, the negative electrode of a conventional lithium-ion cell is made from carbon. The positive electrode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent.^[72] The electrochemical roles of the electrodes reverse between anode and cathode, depending on the direction of current flow through the cell.

The most commercially popular negative electrode is graphite. The positive electrode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as lithium manganese oxide).^[73] Recently, graphene based electrodes (based on 2D and 3D structures of graphene) have also been used as electrodes for lithium batteries.^[74]

The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions.^[75] These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF
₆), lithium hexafluoroarsenate monohydrate (LiAsF
₆), lithium perchlorate (LiClO
₄), lithium tetrafluoroborate (LiBF
₄), and lithium triflate (LiCF
₃SO
₃).

Depending on materials choices, the voltage, energy density, life, and safety of a lithium-ion battery can change dramatically. Recently, novel architectures using nanotechnology have been employed to improve performance.

Pure lithium is highly reactive. It reacts vigorously with water to form lithium hydroxide and hydrogen gas. Thus, a non-aqueous electrolyte is typically used, and a sealed container rigidly excludes moisture from the battery pack.

Lithium-ion batteries are more expensive than NiCd batteries but operate over a wider temperature range with higher energy densities. They require a protective circuit to limit peak voltage.

For notebooks or laptops, lithium-ion cells are supplied as part of a battery pack with temperature sensors, voltage converter/regulator circuit, voltage tap, battery charge state monitor and the main connector. These components monitor the state of charge and current in and out of each cell, capacities of each individual cell (drastic change can lead to reverse polarities which is dangerous),^{[76][unreliable source?]} and temperature of each cell and minimize the risk of short circuits.^[77]

Shapes

Nissan Leaf's lithium-ion battery pack.

Li-ion cells (as distinct from entire batteries) are available in various shapes, which can generally be divided into four groups:^{[78][full citation needed]}

• Small cylindrical (solid body without terminals, such as those used in older laptop batteries)
• Large cylindrical (solid body with large threaded terminals)
• Pouch (soft, flat body, such as those used in cell phones and newer laptops; also referred to as li-ion polymer or lithium polymer batteries)
• Prismatic (semi-hard plastic case with large threaded terminals, such as vehicles' traction packs)

Cells with a cylindrical shape are made in a characteristic "swiss roll" manner (known as a "jelly roll" in the US), which means it is a single long sandwich of positive electrode, separator, negative electrode and separator rolled into a single spool. The main disadvantage of this method of construction is that the cell will have a higher series inductance.

The absence of a case gives pouch cells the highest gravimetric energy density; however, for many practical applications they still require an external means of containment to prevent expansion when their state-of-charge (SOC) level is high,^[79] and for general structural stability of the battery pack of which they are part.

Since 2011, several research groups have announced demonstrations of lithium-ion flow batteries that suspend the cathode or anode material in an aqueous or organic solution.^[80]

In 2014, Panasonic created the smallest Li-ion battery. It is pin shaped. It has a diameter of 3.5mm and a weight of 0.6g.^[81]

Electrochemistry

The reactants in the electrochemical reactions in a lithium-ion battery are the negative and positive electrodes and the electrolyte providing a conductive medium for lithium ions to move between the electrodes. Electrical energy flows out from or in to the battery when electrons flow through an external circuit during discharge or charge, respectively.

Both electrodes allow lithium ions to move in and out of their structures with a process called insertion (intercalation) or extraction (deintercalation), respectively. During discharge, the (positive) lithium ions move from the negative electrode (usually graphite = "${\displaystyle {\ce {C_{6}}}}$" as below) to the positive electrode (forming a lithium compound) through the electrolyte while the electrons flow through the external circuit in the same direction.^[82] When the cell is charging, the reverse occurs with the lithium ions and electrons moved back into the negative electrode in a net higher energy state. The following equations exemplify the chemistry.

The positive (cathode) electrode half-reaction in the lithium-doped cobalt oxide substrate is:^[83][84]

${\displaystyle {\ce {{CoO2}+{Li+}+{e^{-}}<=>{LiCoO2}}}}$

The negative (anode) electrode half-reaction for the graphite is:

${\displaystyle {\ce {{LiC6}<=>{C6}+{Li+}+{e^{-}}}}}$

The full reaction (left: charged, right: discharged) being:

${\displaystyle {\ce {{LiC6}+{CoO2}<=> {C6}+{LiCoO2}}}}$

The overall reaction has its limits. Overdischarge supersaturates lithium cobalt oxide, leading to the production of lithium oxide,^[85] possibly by the following irreversible reaction:

${\displaystyle {\ce {{Li+}+{e^{-}}+{LiCoO2}->{Li2O}+{CoO}}}}$

Overcharge up to 5.2 volts leads to the synthesis of cobalt(IV) oxide, as evidenced by x-ray diffraction:^[86]

${\displaystyle {\ce {{LiCoO2}->{Li+}+{CoO2}+{e^{-}}}}}$

In a lithium-ion battery the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li
_1-xCoO
₂ from Co³⁺ to Co⁴⁺ during charge, and reducing from Co⁴⁺ to Co³⁺ during discharge. The cobalt electrode reaction is only reversible for x < 0.5 (x in mole units), limiting the depth of discharge allowable. This chemistry was used in the Li-ion cells developed by Sony in 1990.^[87]

The cell's energy is equal to the voltage times the charge. Each gram of lithium represents Faraday's constant/6.941 or 13,901 coulombs. At 3 V, this gives 41.7 kJ per gram of lithium, or 11.6 kWh per kg. This is a bit more than the heat of combustion of gasoline, but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.

Electrolytes

The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze.

Liquid Electrolytes

Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF
₆, LiBF
₄ or LiClO
₄ in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate.^[88] A liquid electrolyte acts as a conductive pathway for the movement of cations passing from the negative to the positive electrodes during discharge. Typical conductivities of liquid electrolyte at room temperature (20 °C (68 °F)) are in the range of 10 mS/cm, increasing by approximately 30–40% at 40 °C (104 °F) and decreasing slightly at 0 °C (32 °F).^[89]

The combination of linear and cyclic carbonates (e.g., ethylene carbonate (EC) and dimethyl carbonate (DMC)) offers high conductivity and SEI-forming ability. A mixture of a high ionic conductivity and low viscosity carbonate solvents is needed, because the two properties are mutually exclusive in a single material.^[22]

Organic solvents easily decompose on the negative electrodes during charge. When appropriate organic solvents are used as the electrolyte, the solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase (SEI),^[90] which is electrically insulating yet provides significant ionic conductivity. The interphase prevents further decomposition of the electrolyte after the second charge. For example, ethylene carbonate is decomposed at a relatively high voltage, 0.7 V vs. lithium, and forms a dense and stable interface.^[91]

Composite electrolytes based on POE (poly(oxyethylene)) provide a relatively stable interface.^[92][93] It can be either solid (high molecular weight) and be applied in dry Li-polymer cells, or liquid (low molecular weight) and be applied in regular Li-ion cells.

Room temperature ionic liquids (RTILs) are another approach to limiting the flammability and volatility of organic electrolytes.^[94]

Solid Electrolytes

Recent advances in battery technology involve using a solid as the electrolyte material. The most promising of these being ceramics.^[95]

Solid ceramic electrolytes are mostly lithium metal oxides which allow lithium ion transport through the solid more readily due to the intrinsic lithium. The main benefit of solid electrolytes is that there is no risk of leaks, which is a serious safety issue for batteries with liquid electrolytes.^[96]

Solid ceramic electrolytes can be further broken down into two main categories: ceramic and glassy. Ceramic solid electrolytes are highly ordered compounds with crystal structures that usually have ion transport channels.^[97] Common ceramic electrolytes are lithium super ion conductors (LISICON) and perovskites. Glassy solid electrolytes are amorphous atomic structures made up of similar elements to ceramic solid electrolytes, but have higher conductivities overall due to higher conductivity at grain boundaries.^[98]

Both glassy and ceramic electrolytes can be made more ionically conductive by substituting sulfur for oxygen. The larger radius of sulfur and its higher ability to be polarized allow for higher conductivity of lithium. This contributes to conductivities of solid electrolytes are nearing parity with their liquid counterparts, with most on the order of 0.1 mS/cm and the best at 10 mS/cm.^[99]

Charge and discharge

During discharge, lithium ions (Li⁺) carry the current within the battery from the negative to the positive electrode, through the non-aqueous electrolyte and separator diaphragm.^[100]
During charging, an external electrical power source (the charging circuit) applies an over-voltage (a higher voltage than the battery produces, of the same polarity), forcing a charging current to flow within the battery from the positive to the negative electrode, i.e. in the reverse direction of a discharge current under normal conditions. The lithium ions then migrate from the positive to the negative electrode, where they become embedded in the porous electrode material in a process known as intercalation.

Procedure

The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different.

• A single Li-ion cell is charged in two stages:^{[76][unreliable source?]}

1. Constant current (CC)
2. Constant Voltage (CV)

• A Li-ion battery (a set of Li-ion cells in series) is charged in three stages:

1. Constant current
2. Balance (not required once a battery is balanced)
3. Constant Voltage

During the constant current phase, the charger applies a constant current to the battery at a steadily increasing voltage, until the voltage limit per cell is reached.

During the balance phase, the charger reduces the charging current (or cycles the charging on and off to reduce the average current) while the state of charge of individual cells is brought to the same level by a balancing circuit, until the battery is balanced. Some fast chargers skip this stage. Some chargers accomplish the balance by charging each cell independently.

During the constant voltage phase, the charger applies a voltage equal to the maximum cell voltage times the number of cells in series to the battery, as the current gradually declines towards 0, until the current is below a set threshold of about 3% of initial constant charge current.

Periodic topping charge about once per 500 hours. Top charging is recommended to be initiated when voltage goes below 4.05 V/cell.

Failure to follow current and voltage limitations can result in an explosion.^[12][101]

Extreme temperatures

Charging temperature limits for Li-ion are stricter than the operating limits. Lithium-ion chemistry performs well at elevated temperatures but prolonged exposure to heat reduces battery life.  Li‑ion batteries offer good charging performance at cooler temperatures and may even allow 'fast-charging' within a temperature range of 5 to 45 °C (41 to 113 °F).^{[102][better source needed]} Charging should be performed within this temperature range. At temperatures from 0 to 5 °C charging is possible, but the charge current should be reduced. During a low-temperature charge the slight temperature rise above ambient due to the internal cell resistance is beneficial. High temperatures during charging may lead to battery degradation and charging at temperatures above 45 °C will degrade battery performance, whereas at lower temperatures the internal resistance of the battery may increase, resulting in slower charging and thus longer charging times.^{[102][better source needed]}

Consumer-grade lithium-ion batteries should not be charged at temperatures below 0 °C (32 °F). Although a battery pack^[103] may appear to be charging normally, electroplating of metallic lithium can occur at the negative electrode during a subfreezing charge, and may not be removable even by repeated cycling. Most devices equipped with Li-ion batteries do not allow charging outside of 0–45 °C for safety reasons, except for mobile phones that may allow some degree of charging when they detect an emergency call in progress.^[104]

Performance

• Specific energy density: 100 to 250 W·h/kg (360 to 900 kJ/kg)^[105]
• Volumetric energy density: 250 to 620 W·h/L (900 to 2230 J/cm³)^[2]
• Specific power density: 300 to 1500 W/kg (at 20 seconds and 285 W·h/L)^{[1][not in citation given]}

Because lithium-ion batteries can have a variety of positive and negative electrode materials, the energy density and voltage vary accordingly.

The open circuit voltage is higher than aqueous batteries (such as lead acid, nickel-metal hydride and nickel-cadmium).^{[106][not in citation given]} Internal resistance increases with both cycling and age.^{[106][not in citation given][107]} Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually, increasing resistance will leave the battery in a state such that it can no longer support the normal discharge currents requested of it without unacceptable voltage drop or overheating.

Batteries with a lithium iron phosphate positive and graphite negative electrodes have a nominal open-circuit voltage of 3.2 V and a typical charging voltage of 3.6 V. Lithium nickel manganese cobalt (NMC) oxide positives with graphite negatives have a 3.7 V nominal voltage with a 4.2 V maximum while charging. The charging procedure is performed at constant voltage with current-limiting circuitry (i.e., charging with constant current until a voltage of 4.2 V is reached in the cell and continuing with a constant voltage applied until the current drops close to zero). Typically, the charge is terminated at 3% of the initial charge current. In the past, lithium-ion batteries could not be fast-charged and needed at least two hours to fully charge. Current-generation cells can be fully charged in 45 minutes or less. In 2015 researchers demonstrated a small 600 mAh capacity battery charged to 68 percent capacity in two minutes and a 3,000 mAh battery charged to 48 percent capacity in five minutes. The latter battery has an energy density of 620 W·h/L. The device employed heteroatoms bonded to graphite molecules in the anode.^[108]

Performance of manufactured batteries has improved over time. For example, from 1991 to 2005 the energy capacity per price of lithium ion batteries improved more than ten-fold, from 0.3 W·h per dollar to over 3 W·h per dollar.^[109] In the period from 2011-2017, progress has averaged 7.5% annually.^[110]

Materials

The increasing demand for batteries has led vendors and academics to focus on improving the energy density, operating temperature, safety, durability, charging time, output power, and cost of lithium ion battery technology. The following materials have been used in commercially available cells. Research into other materials continues.

Cathode materials are generally constructed out of two general materials: LiCoO
₂ and LiMn
₂O
₄. The cobalt-based material develops a pseudo tetrahedral structure that allows for two-dimensional lithium ion diffusion.^[111] The cobalt-based cathodes are ideal due to their high theoretical specific heat capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. Limitations include the high cost of the material, and low thermal stability.^[112] The manganese-based materials adopt a cubic crystal lattice system, which allows for three-dimensional lithium ion diffusion.^[111] Manganese cathodes are attractive because manganese is cheaper and because it could theoretically be used to make a more efficient, longer-lasting battery if its limitations could be overcome. Limitations include the tendency for manganese to dissolve into the electrolyte during cycling leading to poor cycling stability for the cathode.^[112] Cobalt-based cathodes are the most common, however other materials are being researched with the goal of lowering costs and improving battery life.^[113]

As of 2017 a candidate for large-scale production of lithium-ion batteries such as electric vehicle applications is LiFePO
₄ due to its low cost, excellent safety, high cycle durability (74% after 8000, 100% discharge for Sony Fortelion batteries)^[114] and excellent performance, though a carbon conductive agent is required to overcome its low electrical conductivity.^[115]

Electrolyte alternatives have also played a significant role, for example the lithium polymer battery.

Positive electrode

Positive electrode

Technology	Company	Target application	Date	Benefit
Lithium Nickel Manganese Cobalt Oxide ("NMC", LiNixMnyCozO2)	Imara Corporation, Nissan Motor,[116][117] Microvast Inc., LG Chem[118]	Electric vehicles, power tools, grid energy storage	2008	good specific energy and specific power density
Lithium Manganese Oxide ("LMO", LiMn2O4)	LG Chem,[119] NEC, Samsung,[47] Hitachi,[120] Nissan/AESC,[121] EnerDel[122]	Hybrid electric vehicle, cell phone, laptop	1996
Lithium Iron Phosphate ("LFP", LiFePO4)	University of Texas/Hydro-Québec,[123] Phostech Lithium Inc., Valence Technology, A123Systems/MIT[124][125]	Segway Personal Transporter, power tools, aviation products, automotive hybrid systems, PHEV conversions	1996	moderate density (2 A·h outputs 70 amperes) High safety compared to Cobalt / Manganese systems. Operating temperature >60 °C (140 °F)
Lithium Cobalt Oxide (LiCoO2)	Sony first commercial production[57][87]	broad use	1991	High specific energy
Lithium Nickel Cobalt Aluminum Oxide ("NCA", LiNiCoAlO2)	Panasonic,[118] Saft Groupe S.A.[126]	Electric vehicles	1999	High specific energy, good life span

Negative electrode

Negative electrode materials are generally constructed from graphite and other carbon materials. These materials are used because they are abundant and are electrically conducting and can intercalate lithium ions to store electrical charge with modest volume expansion (ca. 10%).^[127] The reason that graphite is the dominant material is because of its low voltage and excellent performance. Various materials have been introduced but their voltage is high leading to a low energy density.^[128] Low voltage of material is the key requirement; otherwise, the excess capacity is useless in terms of energy density.

Negative electrode

Technology	Density	Durability	Company	Target application	Date	Comments
Graphite			Targray	The dominant negative electrode material used in lithium ion batteries.	1991	Low cost and good energy density. Graphite anodes can accommodate one lithium atom for every six carbon atoms. Charging rate is governed by the shape of the long, thin graphene sheets. While charging, the lithium ions must travel to the outer edges of the graphene sheet before coming to rest (intercalating) between the sheets. The circuitous route takes so long that they encounter congestion around those edges.[129]
Lithium Titanate ("LTO", Li4Ti5O12)			Toshiba, Altairnano	automotive (Phoenix Motorcars), electrical grid (PJM Interconnection Regional Transmission Organization control area,[130] United States Department of Defense[131]), bus (Proterra)	2008	output, charging time, durability (safety, operating temperature −50–70 °C (−58–158 °F))[132]
Hard Carbon			Energ2[133]	Home electronics	2013	greater storage capacity
Tin/Cobalt Alloy			Sony	Consumer electronics (Sony Nexelion battery)	2005	Larger capacity than a cell with graphite (3.5Ah 18650-type battery)
Silicon/Carbon	Volumetric: 580 W·h/l		Amprius[134]	Smartphones, providing 5000 mA·h capacity	2013	Uses < 10wt% Silicon nanowires combined with graphite and binders. Energy density: ~74 mAh/g. Another approach used carbon-coated 15 nm thick crystal silicon flakes. The tested half-cell achieved 1.2 Ah/g over 800 cycles.[135]

Anode research

Silicon is beginning to be looked at as an anode material because it can accommodate significantly more lithium ions, storing up to 10 times the electric charge, however this alloying between lithium and silicon results in significant volume expansion (ca. 400%),^[127] which causes catastrophic failure for the battery.^[136] Silicon has been used as an anode material but the insertion and extraction of ${\displaystyle {\ce {\scriptstyle Li+}}}$ can create cracks in the material. These cracks expose the Si surface to an electrolyte, causing decomposition and the formation of a solid electrolyte interphase (SEI) on the new Si surface (crumpled graphene encapsulated Si nanoparticles). This SEI will continue to grow thicker, deplete the available ${\displaystyle {\ce {\scriptstyle Li+}}}$, and degrade the capacity and cycling stability of the anode.
There have been attempts using various Si nanostructures that include nanowires, nanotubes, hollow spheres, nanoparticles, and nanoporous with the goal of them withstanding the (${\displaystyle {\ce {\scriptstyle Li+}}}$)-insertion/removal without significant cracking. Yet the formation of SEI on Si still occurs. So a coating would be logical, in order to account for any increase in the volume of the Si, a tight surface coating is not viable. In 2012 researchers from Northwestern University created an approach to encapsulate Si nanoparticles using crumpled r-GO, graphene oxide. This method allows for protection of the Si nanoparticles from the electrolyte as well as allow for the expansion of Si without expansion due to the wrinkles and creases in the graphene balls.^[137]

These capsules began as an aqueous dispersion of GO and Si particles, and are then nebulized into a mist of droplets that pass through a tube furnace. As they pass through the liquid evaporates, the GO sheets are pulled into a crumpled ball by capillary forces and encapsulate Si particles with them. There is a galvanostatic charge/discharge profile of 0.05 ${\displaystyle {\ce {\scriptstyle mA/cm^{2}}}}$ to 1 ${\displaystyle {\ce {\scriptstyle mA/cm^{2}}}}$ for current densities 0.2 to 4 A/g, delivering 1200 mAh/g at 0.2 A/g.^[137]

Diffusion

The ions in the electrolyte diffuse because there are small changes in the electrolyte concentration. Linear diffusion is only considered here. The change in concentration, c, as a function of time t and distance x, is

${\displaystyle {\frac {\partial c}{\partial t}}=-{\frac {D}{\varepsilon }}{\frac {\partial ^{2}c}{\partial x^{2}}}}$

The negative sign indicates the ions are flowing from high concentration to low concentration. In this equation, D is the diffusion coefficient for the lithium ion. It has a value of 7.5 × 10⁻¹⁰ m/s in the LiPF
₆ electrolyte. The value for ε, the porosity of the electrolyte, is 0.724.^[138]

Uses

Li-ion batteries provide lightweight, high energy density power sources for a variety of devices. To power larger devices, such as electric cars, connecting many small batteries in a parallel circuit is more effective^[139] and more efficient than connecting a single large battery.^[140] Such devices include:

• Portable devices: these include mobile phones and smartphones, laptops and tablets, digital cameras and camcorders, electronic cigarettes, handheld game consoles and torches (flashlights).
• Power tools: Li-ion batteries are used in tools such as cordless drills, sanders, saws and a variety of garden equipment including whipper-snippers and hedge trimmers.
• Electric vehicles: including electric cars,^[141] hybrid vehicles, electric bicycles, personal transporters and advanced electric wheelchairs. Also radio-controlled models, model aircraft, aircraft,^{[142][143][144]} and the Mars Curiosity rover.

Li-ion batteries are used in telecommunications applications. Secondary non-aqueous lithium batteries provide reliable backup power to load equipment located in a network environment of a typical telecommunications service provider. Li-ion batteries compliant with specific technical criteria are recommended for deployment in the Outside Plant (OSP) at locations such as Controlled Environmental Vaults (CEVs), Electronic Equipment Enclosures (EEEs), and huts, and in uncontrolled structures such as cabinets. In such applications, li-ion battery users require detailed, battery-specific hazardous material information, plus appropriate fire-fighting procedures, to meet regulatory requirements and to protect employees and surrounding equipment.^[145]

Self-discharge

A lithium-ion battery from a laptop computer (176 kJ)

Batteries gradually self-discharge even if not connected and delivering current. Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month.^[146][147]

The rate increases with temperature and state of charge. A 2004 study found that for most cycling conditions self-discharge was primarily time-dependent; however, after several months of stand on open circuit or float charge, state-of-charge dependent losses became significant. The self-discharge rate did not increase monotonically with state-of-charge, but dropped somewhat at intermediate states of charge.^[148] Self-discharge rates may increase as batteries age.^[149] In 1999, self-discharge per month was measured at 8% at 21 °C, 15% at 40 °C, 31% at 60 °C.^[150] By 2007, monthly self-discharge rate was estimated at 2% to 3%,^[151] and 2^[7]-3% by 2016.^[152]

By comparison, the self-discharge rate for metal hydride (NiMH) batteries dropped, as of 2017, from up to 30% per month for previously common cells^[153] to about 1.25% per month for low self-discharge NiMH batteries, and is about 10% per month in nickel-cadmium batteries.^{[citation needed]}

Battery life

Rechargeable battery life is typically defined as the number of full charge-discharge cycles before significant capacity loss. Inactive storage may also reduce capacity.

Manufacturers' information typically specify lifespan in terms of the number of cycles (e.g., capacity dropping linearly to 80% over 500 cycles), with no mention of chronological age.^[154] On average, lifetimes consist of 1000 cycles,^[155] although battery performance is rarely specified for more than 500 cycles. This means that batteries of mobile phones, or other hand-held devices in daily use, are not expected to last longer than three years. Some batteries based on carbon anodes offer more than 10,000 cycles.^[156]

As a battery discharges, its voltage gradually diminishes. When depleted below the protection circuit's low-voltage threshold (2.4 to 2.9 V/cell, depending on chemistry) the circuit disconnects and stops discharging until recharged. As discharge progresses, metallic cell contents plate onto its internal structure, creating an unwanted discharge path.^{[citation needed]}

Defining battery life via full discharge cycles, is the industry standard, but may be biased, since full depth of discharge (DoD)/recharge may itself diminish battery life, compared to cumulative Ah partial discharge/charge performance. Projection from the standard to specific use patterns may require additional factors, e.g. DoD, rate of discharge, temperature, etc.

Multiplying the battery life (at rated cycle depth) by the capacity gives a total energy delivered over the life of the battery. From this one can calculate the cost per kWh of the power (including the cost of charging). This value reveals that battery power is currently expensive compared to other power sources.

Variability

A 2015 study by Andreas Gutsch of the Karlsruhe Institute of Technology found that lithium-ion battery lifespan could vary by a factor of five, with some Li-ion cells losing 30% of their capacity after 1,000 cycles, and others having better capacity after 5,000 cycles. The study also found that safety standards for some batteries were not met. For stationary energy storage it was estimated that batteries with lifespans of at least 3,000 cycles were needed for profitable operation.^{[citation needed]}

Degradation

Over their lifespan, batteries degrade progressively with reduced capacity, cycle life, and safety due to chemical changes to the electrodes. Capacity loss/fade is expressed as a percentage of initial capacity after a number of cycles (e.g., 30% loss after 1,000 cycles). Fade can be separated into calendar loss and cycling loss. Calendar loss results from the passage of time and is measured from the maximum state of charge. Cycling loss is due to usage and depends on both the maximum state of charge and the depth of discharge.^[22] Increased rate of self-discharge can be an indicator of internal short-circuit.^[157]

Degradation is strongly temperature-dependent; increasing if stored or used at above or below 25 °C.^[158] High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss.^{[106][not in citation given]} Carbon anodes generate heat when in use. Batteries may be refrigerated to reduce temperature effects.^{[159][not in citation given]}

Pouch and cylindrical cell temperatures depend linearly on the discharge current.^[160] Poor internal ventilation may increase temperatures. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F).^{[citation needed]} In contrast, the calendar life of LiFePO
₄ cells is not affected by high charge states.^{[161][162][not in citation given]}

The advent of the SEI layer improved performance, but increased vulnerability to thermal degradation. The layer is composed of electrolyte – carbonate reduction products that serve both as an ionic conductor and electronic insulator. It forms on both the anode and cathode and determines many performance parameters. Under typical conditions, such as room temperature and the absence of charge effects and contaminants, the layer reaches a fixed thickness after the first charge, allowing the device to operate for years. However, operation outside such parameters can degrade the device via several reactions.^[22]

Reactions

Five common exothermic degradation reactions can occur:^[22]

• Chemical reduction of the electrolyte by the anode.
• Thermal decomposition of the electrolyte.
• Chemical oxidation of the electrolyte by the cathode.
• Thermal decomposition by the cathode and anode.
• Internal short circuit by charge effects.

Anode

The SEI layer that forms on the anode is a mixture of lithium oxide, lithium fluoride and semicarbonates (e.g., lithium alkyl carbonates).

At elevated temperatures, alkyl carbonates in the electrolyte decompose into insoluble Li
₂CO
₃ that increases film thickness, limiting anode efficiency. This increases cell impedance and reduces capacity.^[158] Gases formed by electrolyte decomposition can increase the cell's internal pressure and are a potential safety issue in demanding environments such as mobile devices.^[22]

Below 25 °C, plating of metallic Lithium on the anodes and subsequent reaction with the electrolyte is leading to loss of cyclable Lithium.^[158]

Extended storage can trigger an incremental increase in film thickness and capacity loss.^[22]

Charging at greater than 4.2 V can initiate Li⁺ plating on the anode, producing irreversible capacity loss. The randomness of the metallic lithium embedded in the anode during intercalation results in dendrites formation. Over time the dendrites can accumulate and pierce the separator, causing a short circuit leading to heat, fire or explosion. This process is referred to as thermal runaway.^[22]

Discharging beyond 2 V can also result in capacity loss. The (copper) anode current collector can dissolve into the electrolyte. When charged, copper ions can reduce on the anode as metallic copper. Over time, copper dendrites can form and cause a short in the same manner as lithium.^[22]

High cycling rates and state of charge induces mechanical strain on the anode's graphite lattice. Mechanical strain caused by intercalation and de-intercalation creates fissures and splits of the graphite particles, changing their orientation. This orientation change results in capacity loss.^[22]

Electrolytes

Electrolyte degradation mechanisms include hydrolysis and thermal decomposition.^[22]

At concentrations as low as 10 ppm, water begins catalyzing a host of degradation products that can affect the electrolyte, anode and cathode.^[22] LiPF
₆ participates in an equilibrium reaction with LiF and PF
₅. Under typical conditions, the equilibrium lies far to the left. However the presence of water generates substantial LiF, an insoluble, electrically insulating product. LiF binds to the anode surface, increasing film thickness.^[22]

LiPF
₆ hydrolysis yields PF
₅, a strong Lewis acid that reacts with electron-rich species, such as water. PF
₅ reacts with water to form hydrofluoric acid (HF) and phosphorus oxyfluoride. Phosphorus oxyfluoride in turn reacts to form additional HF and difluorohydroxy phosphoric acid. HF converts the rigid SEI film into a fragile one. On the cathode, the carbonate solvent can then diffuse onto the cathode oxide over time, releasing heat and thermal runaway.^[22]

Decomposition of electrolyte salts and interactions between the salts and solvent start at as low as 70 C. Significant decomposition occurs at higher temperatures. At 85 C transesterification products, such as dimethyl-2,5-dioxahexane carboxylate (DMDOHC) are formed from EC reacting with DMC.^[22]

Cathode

Lithium cobalt oxide (LiCoO
₂) is the most widely used cathode material. Lithium manganese oxide (LiMn2O
₄) is a potential alternative because of its low cost and ease of preparation, but its relatively poor cycling and storage capabilities has prevented it from commercial acceptance.^[22]

Cathode degradation mechanisms include manganese dissolution, electrolyte oxidation and structural disorder.^[22]

In LiMnO
₄ hydrofluoric acid catalyzes the loss of metallic manganese through disproportionation of trivalent manganese:^[22]

2Mn³⁺ → Mn²⁺+ Mn⁴⁺

Material loss of the spinel results in capacity fade. Temperatures as low as 50 °C initiate Mn²⁺ deposition on the anode as metallic manganese with the same effects as lithium and copper plating.^[158] Cycling over the theoretical max and min voltage plateaus destroys the crystal lattice via Jahn-Teller distortion, which occurs when Mn⁴⁺ is reduced to Mn³⁺ during discharge.^[22]

Storage of a battery charged to greater than 3.6 V initiates electrolyte oxidation by the cathode and induces SEI layer formation on the cathode. As with the anode, excessive SEI formation forms an insulator resulting in capacity fade and uneven current distribution.^[22]

Storage at less than 2 V results in the slow degradation of LiCoO
₂ and LiMn
₂O
₄ cathodes, the release of oxygen and irreversible capacity loss.^[22]

Conditioning

The need to "condition" NiCd and NiMH batteries has leaked into folklore surrounding Li-ion batteries, but is unfounded. The recommendation for the older technologies is to leave the device plugged in for seven or eight hours, even if fully charged.^[163] This may be a confusion of battery software calibration instructions with the "conditioning" instructions for NiCd and NiMH batteries.^[164]

Multicell devices

Li-ion batteries require a battery management system to prevent operation outside each cell's safe operating area (max-charge, min-charge, safe temperature range) and to balance cells to eliminate state of charge mismatches. This significantly improves battery efficiency and increases capacity. As the number of cells and load currents increase, the potential for mismatch increases. The two kinds of mismatch are state-of-charge (SOC) and capacity/energy ("C/E"). Though SOC is more common, each problem limits pack charge capacity (mA·h) to that of the weakest cell.^{[citation needed]}

Safety

If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture.^[165][166] In extreme cases this can lead to leakage, explosion or fire. To reduce these risks, many lithium-ion cells (and battery packs) contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range of 3–4.2 V per cell.^[87][153] or when overcharged or discharged. Lithium battery packs, whether constructed by a vendor or the end-user, without effective battery management circuits are susceptible to these issues. Poorly designed or implemented battery management circuits also may cause problems; it is difficult to be certain that any particular battery management circuitry is properly implemented. Lithium-ion cells are susceptible to damage outside the allowed voltage range that is typically within (2.5 to 3.65) V for most LFP cells. Exceeding this voltage range, even by small voltages (millivolts) results in premature aging of the cells and, furthermore, results in safety risks due to the reactive components in the cells.^[167] When stored for long periods the small current draw of the protection circuitry may drain the battery below its shutoff voltage; normal chargers may then be useless since the BMS may retain a record of this battery (or charger) 'failure'. Many types of lithium-ion cells cannot be charged safely below 0 °C.^[168]

Other safety features are required in each cell:^[87]

• Shut-down separator (for overheating)
• Tear-away tab (for internal pressure relief)
• Vent (pressure relief in case of severe outgassing)
• Thermal interrupt (overcurrent/overcharging/environmental exposure)

These features are required because the negative electrode produces heat during use, while the positive electrode may produce oxygen. However, these additional devices occupy space inside the cells, add points of failure, and may irreversibly disable the cell when activated. Further, these features increase costs compared to nickel metal hydride batteries, which require only a hydrogen/oxygen recombination device and a back-up pressure valve.^[153] Contaminants inside the cells can defeat these safety devices. Also, these features can not be applied to all kinds of cells, e.g. prismatic high current cells cannot be equipped with a vent or thermal interrupt. High current cells must not produce excessive heat or oxygen, lest there be a failure, possibly violent. Instead, they must be equipped with internal thermal fuses which act before the anode and cathode reach their thermal limits.

Short-circuiting a battery will cause the cell to overheat and possibly to catch fire. Adjacent cells may then overheat and fail, possibly causing the entire battery to ignite or rupture. In the event of a fire, the device may emit dense irritating smoke.^[169] The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ/(A·h), most of it chemical.^{[76][unreliable source?][170]}

Replacing the lithium cobalt oxide positive electrode material in lithium-ion batteries with a lithium metal phosphate such as lithium iron phosphate improves cycle counts, shelf life and safety, but lowers capacity. As of 2006 these 'safer' lithium-ion batteries were mainly used in electric cars and other large-capacity battery applications, where safety is critical.^[171]

Lithium-ion batteries, unlike rechargeable batteries with water-based electrolytes, have a potentially hazardous pressurised flammable liquid electrolyte, and require strict quality control during manufacture.^[172] A faulty battery can cause a serious fire.^[11] Faulty chargers can affect the safety of the battery because they can destroy the battery's protection circuit. While charging at temperatures below 0 °C, the negative electrode of the cells gets plated with pure lithium, which can compromise the safety of the whole pack.

While fire is often serious, it may be catastrophically so. In about 2010 large lithium-ion batteries were introduced in place of other chemistries to power systems on some aircraft; as of January 2014 there had been at least four serious lithium-ion battery fires, or smoke, on the Boeing 787 passenger aircraft, introduced in 2011, which did not cause crashes but had the potential to do so.^[173][174]

In addition, several aircraft crashes have been attributed to burning Li-Ion batteries. UPS Airlines Flight 6 crashed in Dubai after its payload of batteries spontaneously ignited, progressively destroying critical systems inside the aircraft which eventually rendered it uncontrollable.

Environmental concerns and recycling

Since Li-ion batteries contain less of toxic metals than other types of batteries which may contain lead or cadmium^[87] they are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled,^[175][176] but mining generally remains cheaper than recycling.^[177] At present, not much is invested into recycling Li-ion batteries due to cost, complexity and low yield. The most expensive metal involved in the construction of the cell is cobalt. Lithium iron phosphate is cheaper but has other drawbacks. Lithium is less expensive than other metals used, but recycling could prevent a future shortage.^[175] The manufacturing processes of nickel and cobalt, and the solvent, present potential environmental and health hazards.^[178][179] Manufacturing a kg of Li-ion battery takes energy equivalent to 1.6 kg of oil.^[180][181]

Recalls

• In October 2004 Kyocera Wireless recalled approximately 1 million mobile phone batteries to identify counterfeits.^[182]
• In December 2005 Dell recalled approximately 22,000 laptop computer batteries, and 4.1 million in August 2006.^[183]
• In 2006 approximately 10 million Sony batteries used in Dell, Sony, Apple, Lenovo, Panasonic, Toshiba, Hitachi, Fujitsu and Sharp laptops were recalled. The batteries were found to be susceptible to internal contamination by metal particles during manufacture. Under some circumstances, these particles could pierce the separator, causing a dangerous short-circuit.^[184]
• In March 2007 computer manufacturer Lenovo recalled approximately 205,000 batteries at risk of explosion.
• In August 2007 mobile phone manufacturer Nokia recalled over 46 million batteries at risk of overheating and exploding.^[185] One such incident occurred in the Philippines involving a Nokia N91, which used the BL-5C battery.^[186]
• In September 2016 Samsung recalled approximately 2.5 million Galaxy Note 7 phones after 35 confirmed fires.^[16] The recall was due to a manufacturing design fault in Samsung's batteries which caused internal positive and negative poles to touch.^[187]

Transport restrictions

Japan Airlines Boeing 787 lithium cobalt oxide battery that caught fire in 2013

IATA estimates that over a billion lithium cells are flown each year.^[170]

The maximum size of each battery (whether installed in a device or as spare batteries) that can be carried is one that has an equivalent lithium content (ELC) not exceeding 8 grammes per battery. Except, that if only one or two batteries are carried, each may have an ELC of not more than 25 grammes each.^[188] The ELC for any battery is found by multiplying the ampere-hour capacity of each cell by 0.3 and then multiplying the result by the number of cells in the battery.^[188] The resultant calculated lithium content is not the actual lithium content but a theoretical figure solely for transportation purposes. When shipping lithium ion batteries however, if the total lithium content in the cell exceeds 1.5 g, the package must be marked as "Class 9 miscellaneous hazardous material".

Although devices containing lithium-ion batteries may be transported in checked baggage, spare batteries may be only transported in carry-on baggage.^[188] They must be protected against short circuiting, and example tips are provided in the transport regulations on safe packaging and carriage; e.g., such batteries should be in their original protective packaging or, "by taping over the exposed terminals or placing each battery in a separate plastic bag or protective pouch".^[188][189] These restriction do not apply to a lithium-ion battery that is a part of a wheelchair or mobility aid (including any spare batteries) to which a separate set of rules and regulations apply.^[188]

Some postal administrations restrict air shipping (including EMS) of lithium and lithium-ion batteries, either separately or installed in equipment. Such restrictions apply in Hong Kong,^[190] Australia and Japan.^[191] Other postal administrations, such as the United Kingdom's Royal Mail may permit limited carriage of batteries or cells that are operative but totally prohibit handling of known defective ones, which is likely to prove of significance to those discovering faulty such items bought through mail-order channels.^[192] The IATA provides details in its Lithium Battery Guidance document which the Royal Mail makes available.

On 16 May 2012, the United States Postal Service (USPS) banned shipping anything containing a lithium battery to an overseas address, after fires from transport of batteries.^[193] This restriction made it difficult to send anything containing lithium batteries to military personnel overseas, as the USPS was the only method of shipment to these addresses; the ban was lifted on 15 November 2012.^[194] United Airlines and Delta Air Lines excluded lithium-ion batteries in 2015 after an FAA report on chain reactions.^{[195][196][197]}

The Boeing 787 Dreamliner uses large lithium cobalt oxide^[198] batteries, which are more reactive than newer types of batteries such as LiFePO
₄.^[199][12]

Research

Researchers are actively working to improve the power density, safety, cycle durability (battery life), recharge time, cost, flexibility, and other characteristics, as well as research methods and uses, of these batteries.

• Researchers at IBM India have come up with an experimental power supply using lithium-ion cells from discarded laptop battery packs for use in unelectrified regions in developing nations.^[200]
• In November 2016, Yasunaga, a Japanese battery manufacturer, revealed that they had developed a special positive electrode surface treatment which would allow the battery to have more than twelve times the cycle life of conventional lithium-ion batteries. Batteries were tested to 60,000 to 102,400 cycles before falling to 70% of the original new capacity, compared to the conventional battery that would only do 5000 to 6000 cycles. This technology also showed 12% reduction in cell resistance. Yasunaga also commented that the life is expected to be even longer when the same technology is applied to negative electrodes.^[201]
• In March 2017, American Lithium Energy in California revealed plans for mass marketing of its branded Safe Core technology that was developed for use by the US Department of Defense, Department of Energy and national research labs. The technology was initially devoted to vehicle batteries that would not catch fire if damaged in a crash and led to bullet-safe batteries for troops. "What we did was put a fuse inside the cell, so when something is wrong inside, our fuse will kick in and break the current [before it reaches a critical temperature] and then the battery will be safe," said Jiang Fan, PhD, founder and chief technology officer for the company. Fan also provided a useful perspective on lithium-ion development. "As people try to put more energy into the cell, they end up making compromises. Each one is just a little compromise in terms of safety, but it makes the whole system less robust. So the level of manufacturing defects (the battery) can withstand is lower."^[202][203]