Normal
Pacific pattern: Warm pool in the west drives deep atmospheric
convection. In the east local winds cause nutrient-rich cold water to
upwell at the Equator and along the South American coast. (NOAA / PMEL / TAO)
El
Niño conditions: warm water and atmospheric convection move eastwards.
In strong El Niños the deeper thermocline off S. America means upwelled
water is warm and nutrient poor.
El Niño is accompanied by high air pressure
in the western Pacific and low air pressure in the eastern Pacific. El
Niño phases are known to last close to four years; however, records
demonstrate that the cycles have lasted between two and seven years.
During the development of El Niño, rainfall develops between
September–November. The cool phase of ENSO is La Niña,
'The Girl', with sea surface temperatures (SSTs) in the eastern Pacific
below average, and air pressure high in the eastern Pacific and low in
the western Pacific. The ENSO cycle, including both El Niño and La Niña,
causes global changes in temperature and rainfall.
Developing countries
that depend on their own agriculture and fishing, particularly those
bordering the Pacific Ocean, are usually most affected. In this phase of
the Oscillation, the pool of warm water in the Pacific near South
America is often at its warmest about Christmas. The original phrase, El Niño de Navidad, arose centuries ago, when Peruvian fishermen named the weather phenomenon after the newborn Christ.
Concept
Originally, the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time. However, over time the term has evolved and now refers to the warm and negative phase of the El Niño–Southern Oscillation and is the warming of the ocean surface or above-average sea surface temperatures in the central and eastern tropical Pacific Ocean.
This warming causes a shift in the atmospheric circulation with
rainfall becoming reduced over Indonesia, India and northern Australia,
while rainfall and tropical cyclone formation increases over the
tropical Pacific Ocean. The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.
It is believed that El Niño has occurred for thousands of years. For example, it is thought that El Niño affected the Moche in modern-day Peru.
Scientists have also found chemical signatures of warmer sea surface
temperatures and increased rainfall caused by El Niño in coral specimens
that are around 13,000 years old. Around 1525, when Francisco Pizarro made landfall in Peru, he noted rainfall in the deserts, the first written record of the impacts of El Niño. Modern day research and reanalysis techniques have managed to find at least 26 El Niño events since 1900, with the 1982–83, 1997–98 and 2014–16 events among the strongest on record.
Currently, each country has a different threshold for what
constitutes an El Niño event, which is tailored to their specific
interests. For example, the Australian Bureau of Meteorology
looks at the trade winds, Southern Oscillation Index, weather models
and sea surface temperatures in the Niño 3 and 3.4 regions, before
declaring an El Niño. The United States Climate Prediction Center (CPC) and the International Research Institute for Climate and Society
(IRI) looks at the sea surface temperatures in the Niño 3.4 region, the
tropical Pacific atmosphere and forecasts that NOAA's Oceanic Niño
Index will equal or exceed +.5 °C (0.90 °F) for several seasons in a
row. However, the Japan Meteorological Agency
declares that an El Niño event has started when the average five month
sea surface temperature deviation for the Niño 3 region, is over 0.5 °C
(0.90 °F) warmer for six consecutive months or longer.
The Peruvian government declares that a coastal El Niño is under way if
the sea surface temperature deviation in the Niño 1+2 regions equal or
exceed 0.4 °C (0.72 °F) for at least three months.
There is no consensus on whether climate change
will have any influence on the strength or duration of El Niño events,
as research alternately supports El Niño events becoming stronger and
weaker, longer and shorter. However, recent scholarship has found that climate change is increasing the frequency of extreme El Niño events.
Occurrences
Timeline of El Niño episodes between 1900 and 2023.
El Niño events are thought to have been occurring for thousands of years.
For example, it is thought that El Niño affected the Moche in
modern-day Peru, who sacrificed humans in order to try to prevent the
rains.
It is thought that there have been at least 30 El Niño events since 1900, with the 1982–83, 1997–98 and 2014–16 events among the strongest on record.Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10, 2014–16, 2018–19, and beginning in 2023.
Major ENSO events were recorded in the years 1790–93, 1828, 1876–78, 1891, 1925–26, 1972–73, 1982–83, 1997–98, and 2014–16.
Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.
The average period length is five years. When this warming occurs for
seven to nine months, it is classified as El Niño "conditions"; when its
duration is longer, it is classified as an El Niño "episode".
During strong El Niño episodes, a secondary peak in sea surface
temperature across the far eastern equatorial Pacific Ocean sometimes
follows the initial peak.
Cultural history and prehistoric information
ENSO conditions have occurred at two- to seven-year intervals for at
least the past 300 years, but most of them have been weak. Evidence is
also strong for El Niño events during the early Holocene epoch 10,000 years ago.
El Niño may have led to the demise of the Moche and other pre-Columbian Peruvian cultures.
A recent study suggests a strong El Niño effect between 1789 and 1793
caused poor crop yields in Europe, which in turn helped touch off the French Revolution. The extreme weather produced by El Niño in 1876–77 gave rise to the most deadly famines of the 19th century. The 1876 famine alone in northern China killed up to 13 million people.
An early recorded mention of the term "El Niño" to refer to climate occurred in 1892, when Captain Camilo Carrillo told the geographical society congress in Lima that Peruvian sailors named the warm south-flowing current "El Niño" because it was most noticeable around Christmas. Although pre-Columbian societies were certainly aware of the phenomenon, the indigenous names for it have been lost to history. The phenomenon had long been of interest because of its effects on the guano
industry and other enterprises that depend on biological productivity
of the sea. It is recorded that as early as 1822, cartographer Joseph
Lartigue, of the French frigate La Clorinde under Baron Mackau, noted the "counter-current" and its usefulness for traveling southward along the Peruvian coast.
Charles Todd, in 1888, suggested droughts in India and Australia tended to occur at the same time; Norman Lockyer noted the same in 1904.
An El Niño connection with flooding was reported in 1894 by Victor
Eguiguren (1852–1919) and in 1895 by Federico Alfonso Pezet (1859–1929). In 1924, Gilbert Walker (for whom the Walker circulation is named) coined the term "Southern Oscillation". He and others (including Norwegian-American meteorologist Jacob Bjerknes) are generally credited with identifying the El Niño effect.
The major 1982–83 El Niño led to an upsurge of interest from the
scientific community. The period 1990–95 was unusual in that El Niños
have rarely occurred in such rapid succession.
An especially intense El Niño event in 1998 caused an estimated 16% of
the world's reef systems to die. The event temporarily warmed air
temperature by 1.5 °C, compared to the usual increase of 0.25 °C
associated with El Niño events. Since then, mass coral bleaching has become common worldwide, with all regions having suffered "severe bleaching".
Diversity
It is thought that there are several different types of El Niño
events, with the canonical eastern Pacific and the Modoki central
Pacific types being the two that receive the most attention.
These different types of El Niño events are classified by where the
tropical Pacific sea surface temperature (SST) anomalies are the
largest. For example, the strongest sea surface temperature anomalies associated with the canonical eastern Pacific event are located off the coast of South America. The strongest anomalies associated with the Modoki central Pacific event are located near the International Date Line. However, during the duration of a single event, the area with the greatest sea surface temperature anomalies can change.
The traditional Niño, also called Eastern Pacific (EP) El Niño,
involves temperature anomalies in the Eastern Pacific. However, in the
last two decades, atypical El Niños were observed, in which the usual
place of the temperature anomaly (Niño 1 and 2) is not affected, but an
anomaly arises in the central Pacific (Niño 3.4). The phenomenon is called Central Pacific (CP) El Niño, "dateline" El Niño (because the anomaly arises near the International Date Line), or El Niño "Modoki" (Modoki is Japanese for "similar, but different").
The effects of the CP El Niño are different from those of the
traditional EP El Niño—e.g., the recently discovered El Niño leads to
more frequent Atlantic hurricanes.
There is also a scientific debate on the very existence of this
"new" ENSO. Indeed, a number of studies dispute the reality of this
statistical distinction or its increasing occurrence, or both, either
arguing the reliable record is too short to detect such a distinction, finding no distinction or trend using other statistical approaches, or that other types should be distinguished, such as standard and extreme ENSO.
The first recorded El Niño that originated in the central Pacific and moved toward the east was in 1986. Recent Central Pacific El Niños happened in 1986–87, 1991–92, 1994–95, 2002–03, 2004–05 and 2009–10. Furthermore, there were "Modoki" events in 1957–59, 1963–64, 1965–66, 1968–70, 1977–78 and 1979–80. Some sources say that the El Niños of 2006-07 and 2014-16 were also Central Pacific El Niños.
Effects on the global climate
El Niño affects the global climate and disrupts normal weather
patterns, which as a result can lead to intense storms in some places
and droughts in others.
Tropical cyclones
Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies. Areas west of Japan and Korea
tend to experience many fewer September–November tropical cyclone
impacts during El Niño and neutral years. During El Niño years, the
break in the subtropical ridge tends to lie near 130°E, which would favor the Japanese archipelago.
Within the Atlantic Ocean
vertical wind shear is increased, which inhibits tropical cyclone
genesis and intensification, by causing the westerly winds in the
atmosphere to be stronger.
The atmosphere over the Atlantic Ocean can also be drier and more
stable during El Niño events, which can also inhibit tropical cyclone
genesis and intensification. Within the Eastern Pacific basin: El Niño events contribute to decreased easterly vertical wind shear and favours above-normal hurricane activity. However, the impacts of the ENSO state in this region can vary and are strongly influenced by background climate patterns. The Western Pacific basin
experiences a change in the location of where tropical cyclones form
during El Niño events, with tropical cyclone formation shifting
eastward, without a major change in how many develop each year.
As a result of this change, Micronesia is more likely to be affected by
tropical cyclones, while China has a decreased risk of being affected
by tropical cyclones.
A change in the location of where tropical cyclones form also occurs
within the Southern Pacific Ocean between 135°E and 120°W, with tropical
cyclones more likely to occur within the Southern Pacific basin than
the Australian region.
As a result of this change tropical cyclones are 50% less likely to
make landfall on Queensland, while the risk of a tropical cyclone is
elevated for island nations like Niue, French Polynesia, Tonga, Tuvalu, and the Cook Islands.
Remote influence on tropical Atlantic Ocean
A
study of climate records has shown that El Niño events in the
equatorial Pacific are generally associated with a warm tropical North
Atlantic in the following spring and summer. About half of El Niño events persist sufficiently into the spring months for the Western Hemisphere Warm Pool to become unusually large in summer.
Occasionally, El Niño's effect on the Atlantic Walker circulation over
South America strengthens the easterly trade winds in the western
equatorial Atlantic region. As a result, an unusual cooling may occur in
the eastern equatorial Atlantic in spring and summer following El Niño
peaks in winter. Cases of El Niño-type events in both oceans simultaneously have been linked to severe famines related to the extended failure of monsoon rains.
Regional impacts
Observations of El Niño events since 1950 show that impacts associated with El Niño events depend on the time of year.
However, while certain events and impacts are expected to occur during
events, it is not certain or guaranteed that they will occur.
The impacts that generally do occur during most El Niño events include
below-average rainfall over Indonesia and northern South America, while
above average rainfall occurs in southeastern South America, eastern
equatorial Africa, and the southern United States.
Africa
In Africa, East Africa—including Kenya, Tanzania, and the White Nile
basin—experiences, in the long rains from March to May,
wetter-than-normal conditions. Conditions are also drier than normal
from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana.
Antarctica
Many ENSO linkages exist in the high southern latitudes around Antarctica. Specifically, El Niño conditions result in high-pressure anomalies over the Amundsen and Bellingshausen Seas, causing reduced sea ice and increased poleward heat fluxes in these sectors, as well as the Ross Sea. The Weddell Sea,
conversely, tends to become colder with more sea ice during El Niño.
The exact opposite heating and atmospheric pressure anomalies occur
during La Niña.
This pattern of variability is known as the Antarctic dipole mode,
although the Antarctic response to ENSO forcing is not ubiquitous.
Asia
As warm water spreads from the west Pacific and the Indian Ocean
to the east Pacific, it takes the rain with it, causing extensive
drought in the western Pacific and rainfall in the normally dry eastern
Pacific. Singapore experienced the driest February in 2010 since
records began in 1869, with only 6.3 mm of rain falling in the month and
temperatures hitting as high as 35 °C on 26 February. The years 1968
and 2005 had the next driest Februaries, when 8.4 mm of rain fell.
During El Niño events, the shift in rainfall away from the Western Pacific may mean that rainfall across Australia is reduced.
Over the southern part of the continent, warmer than average
temperatures can be recorded as weather systems are more mobile and
fewer blocking areas of high pressure occur. The onset of the Indo-Australian Monsoon
in tropical Australia is delayed by two to six weeks, which as a
consequence means that rainfall is reduced over the northern tropics.
The risk of a significant bushfire season in south-eastern Australia is
higher following an El Niño event, especially when it is combined with a
positive Indian Ocean Dipole event.
During an El Niño event, New Zealand tends to experience stronger or
more frequent westerly winds during their summer, which leads to an
elevated risk of drier than normal conditions along the east coast.
There is more rain than usual though on New Zealand's West Coast,
because of the barrier effect of the North Island mountain ranges and
the Southern Alps.
Fiji generally experiences drier than normal conditions during an
El Niño, which can lead to drought becoming established over the
Islands. However, the main impacts on the island nation is felt about a year after the event becomes established.
Within the Samoan Islands, below average rainfall and higher than
normal temperatures are recorded during El Niño events, which can lead
to droughts and forest fires on the islands.
Other impacts include a decrease in the sea level, possibility of coral
bleaching in the marine environment and an increased risk of a tropical
cyclone affecting Samoa.
Europe
El Niño's effects on Europe
are controversial, complex and difficult to analyse, as it is one of
several factors that influence the weather over the continent and other
factors can overwhelm the signal.
Over North America, the main temperature and precipitation impacts of
El Niño generally occur in the six months between October and March.
In particular, the majority of Canada generally has milder than normal
winters and springs, with the exception of eastern Canada where no
significant impacts occur.
Within the United States, the impacts generally observed during the
six-month period include wetter-than-average conditions along the Gulf Coast between Texas and Florida, while drier conditions are observed in Hawaii, the Ohio Valley, Pacific Northwest and the Rocky Mountains.
Historically, El Niño was not understood to affect U.S. weather patterns until Christensen et al. (1981) used entropy minimax
pattern discovery based on information theory to advance the science of
long range weather prediction. Previous computer models of weather
were based on persistence alone and reliable to only 5–7 days into the
future. Long range forecasting was essentially random. Christensen et
al. demonstrated the ability to predict the probability that
precipitation will be below or above average with modest but
statistically significant skill one, two and even three years into the
future.
Study of more recent weather events over California and the
southwestern United States indicate that there is a variable
relationship between El Niño and above-average precipitation, as it
strongly depends on the strength of the El Niño event and other factors.
Though it has been historically associated with high rainfall in
California, the effects of El Niño depend more strongly on the "flavor"
of El Niño than its presence or absence, as only "persistent El Niño"
events lead to consistently high rainfall.
The synoptic condition for the Tehuano wind, or "Tehuantepecer", is associated with a high-pressure area forming in Sierra Madre of Mexico in the wake of an advancing cold front, which causes winds to accelerate through the Isthmus of Tehuantepec.
Tehuantepecers primarily occur during the cold season months for the
region in the wake of cold fronts, between October and February, with a
summer maximum in July caused by the westward extension of the Azores High. Wind magnitude is greater during El Niño years than during La Niña years, due to the more frequent cold frontal incursions during El Niño winters. Its effects can last from a few hours to six days. Some El Niño events were recorded in the isotope signals of plants, and that had helped scientists to study his impact.
South America
Because
El Niño's warm pool feeds thunderstorms above, it creates increased
rainfall across the east-central and eastern Pacific Ocean, including
several portions of the South American west coast. The effects of El
Niño in South America are direct and stronger than in North America. An
El Niño is associated with warm and very wet weather months in
April–October along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme. The effects during the months of February, March, and April may become critical along the west coast of South America, El Niño reduces the upwelling of cold, nutrient-rich water that sustains large fish populations, which in turn sustain abundant sea birds, whose droppings support the fertilizer industry. The reduction in upwelling leads to fish kills off the shore of Peru.
The local fishing industry along the affected coastline can
suffer during long-lasting El Niño events. The world's largest fishery
collapsed due to overfishing during the 1972 El Niño Peruvian anchoveta reduction. During the 1982–83 event, jack mackerel and anchoveta populations were reduced, scallops increased in warmer water, but hake followed cooler water down the continental slope, while shrimp and sardines moved southward, so some catches decreased while others increased. Horse mackerel
have increased in the region during warm events. Shifting locations and
types of fish due to changing conditions create challenges for the
fishing industry. Peruvian sardines have moved during El Niño events to Chilean
areas. Other conditions provide further complications, such as the
government of Chile in 1991 creating restrictions on the fishing areas
for self-employed fishermen and industrial fleets.
The ENSO variability may contribute to the great success of
small, fast-growing species along the Peruvian coast, as periods of low
population removes predators in the area. Similar effects benefit migratory birds that travel each spring from predator-rich tropical areas to distant winter-stressed nesting areas.
Southern Brazil and northern Argentina
also experience wetter than normal conditions, but mainly during the
spring and early summer. Central Chile receives a mild winter with large
rainfall, and the Peruvian-Bolivian Altiplano is sometimes exposed to unusual winter snowfall events. Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America.
Galapagos Islands
The Galapagos Islands are a chain of volcanic islands, nearly 600 miles west of Ecuador, South America.
Located in the Eastern Pacific Ocean, these islands are home to a wide
diversity of terrestrial and marine species including sharks, birds,
iguanas, turtles, penguins, and seals.
This robust ecosystem is fueled by the normal trade winds which
influence upwelling of cold, nutrient rich waters to the islands.
During an El Niño an event where the trade winds weaken and sometimes
push from west to east. This causes the Equatorial current to weaken,
thus raising surface water temperatures and decreasing nutrients in
waters surrounding the Galapagos. El Niño causes a trophic cascade which
impacts entire ecosystems starting with primary producers and ending
with critical animals such as sharks, penguins, and seals.
The effects of El Niño can become detrimental to populations that often
starve and die off during these years. Rapid evolutionary adaptations
are displayed amongst animal groups during El Niño years to mitigate El
Niño conditions.
Socio-ecological effects for humanity and nature
Economic effects
When El Niño conditions last for many months, extensive ocean warming
and the reduction in easterly trade winds limits upwelling of cold
nutrient-rich deep water, and its economic effect on local fishing for
an international market can be serious.
More generally, El Niño can affect commodity prices and the
macroeconomy of different countries. It can constrain the supply of
rain-driven agricultural commodities; reduce agricultural output,
construction, and services activities; create food-price and generalised
inflation; and may trigger social unrest in commodity-dependent poor
countries that primarily rely on imported food.
A University of Cambridge Working Paper shows that while Australia,
Chile, Indonesia, India, Japan, New Zealand and South Africa face a
short-lived fall in economic activity in response to an El Niño shock,
other countries may actually benefit from an El Niño weather shock
(either directly or indirectly through positive spillovers from major
trading partners), for instance, Argentina, Canada, Mexico and the
United States. Furthermore, most countries experience short-run
inflationary pressures following an El Niño shock, while global energy
and non-fuel commodity prices increase.
The IMF estimates a significant El Niño can boost the GDP of the
United States by about 0.5% (due largely to lower heating bills) and
reduce the GDP of Indonesia by about 1.0%.
Health and social impacts
Extreme weather conditions related to the El Niño cycle correlate with changes in the incidence of epidemic diseases. For example, the El Niño cycle is associated with increased risks of some of the diseases transmitted by mosquitoes, such as malaria, dengue fever, and Rift Valley fever. Cycles of malaria in India, Venezuela, Brazil, and Colombia have now been linked to El Niño. Outbreaks of another mosquito-transmitted disease, Australian encephalitis (Murray Valley encephalitis—MVE),
occur in temperate south-east Australia after heavy rainfall and
flooding, which are associated with La Niña events. A severe outbreak of
Rift Valley fever occurred after extreme rainfall in north-eastern
Kenya and southern Somalia during the 1997–98 El Niño.
ENSO conditions have also been related to Kawasaki disease incidence in Japan and the west coast of the United States, via the linkage to tropospheric winds across the north Pacific Ocean.
ENSO may be linked to civil conflicts. Scientists at The Earth Institute of Columbia University,
having analyzed data from 1950 to 2004, suggest ENSO may have had a
role in 21% of all civil conflicts since 1950, with the risk of annual
civil conflict doubling from 3% to 6% in countries affected by ENSO
during El Niño years relative to La Niña years.
Ecological consequences
In
terrestrial ecosystems, rodent outbreaks were observed in northern
Chile and along the Peruvian coastal desert following the 1972-73 El
Niño event. While some nocturnal primates (western tarsiers Tarsius bancanus and slow loris Nycticebus coucang) and the Malayan sun bear (Helarctos malayanus) were locally extirpate or suffered drastic reduction in numbers within these burned forests.
Lepidoptera outbreaks were documented in Panamá and Costa Rica. During
the 1982–83, 1997–98 and 2015–16 ENSO events, large extensions of
tropical forests experienced a prolonged dry period that resulted in
widespread fires, and drastic changes in forest structure and tree
species composition in Amazonian and Bornean forests.
Their impacts do not restrict only vegetation, since declines in
insect populations were observed after extreme drought and terrible
fires during El Niño 2015–16.
Declines in habitat-specialist and disturbance-sensitive bird species
and in large-frugivorous mammals were also observed in Amazonian burned
forests, while temporary extirpation of more than 100 lowland butterfly
species occurred at a burned forest site in Borneo.
Most critically, global mass bleaching events were recorded in
1997-98 and 2015–16, when around 75-99% losses of live coral were
registered across the world. Considerable attention was also given to
the collapse of Peruvian and Chilean anchovy populations that led to a
severe fishery crisis following the ENSO events in 1972–73, 1982–83,
1997–98 and, more recently, in 2015–16. In particular, increased surface
seawater temperatures in 1982-83 also lead to the probable extinction
of two hydrocoral species in Panamá, and to a massive mortality of kelp
beds along 600 km of coastline in Chile, from which kelps and associated
biodiversity slowly recovered in the most affected areas even after 20
years. All these findings enlarge the role of ENSO events as a strong
climatic force driving ecological changes all around the world –
particularly in tropical forests and coral reefs.
In seasonally dry tropical forests, which are more drought
tolerant, researchers found that El Niño induced drought increased
seedling mortality. In a research published in October 2022, researchers
studied seasonally dry tropical forests in a national park in Chiang Mai
in Thailand for 7 years and observed that El Niño increased seedling
mortality even in seasonally dry tropical forests and may impact entire
forests in long run.
A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithiumions to store energy. The negative electrode of a conventional lithium-ion cell is typically graphite, a form of carbon. This negative electrode is sometimes called the anode as it acts as an anode during discharge. The positive electrode is typically a metal oxide; the positive electrode is sometimes called the cathode as it acts as a cathode during discharge.
Positive and negative electrodes remain positive and negative in normal
use whether charging or discharging and are therefore clearer terms to
use than anode and cathode which are reversed during charging.
Chemistry, performance, cost, and safety characteristics vary
across types of lithium-ion batteries. Most commercial Li-ion cells use intercalation compounds as active materials. The anode or negative electrode is usually graphite, although silicon-carbon is also being increasingly used. Cells can be manufactured to prioritize either energy or power density. Handheld electronics mostly use lithium polymer batteries (with a polymer gel as electrolyte), a lithium cobalt oxide (LiCoO 2) cathode material, and a graphite anode, which together offer a high energy density. Lithium iron phosphate (LiFePO 4), lithium manganese oxide (LiMn 2O 4 spinel, or Li 2MnO 3-based lithium rich layered materials, LMR-NMC), and lithium nickel manganese cobalt oxide (LiNiMnCoO 2 or NMC) may offer longer lives and may have better rate capability. NMC and its derivatives are widely used in the electrification of transport, one of the main technologies (combined with renewable energy) for reducing greenhouse gas emissions from vehicles.
M. Stanley Whittingham discovered the concept of intercalation electrodes in the 1970s and created the first rechargeable lithium-ion battery, which was based on a titanium disulfide anode and a lithium-aluminum cathode, although it suffered from safety issues and was never commercialized. John Goodenough expanded on this work in 1980 by using lithium cobalt oxide as a cathode. The first prototype of the modern Li-ion battery, which uses a carbonaceous anode rather than lithium metal, was developed by Akira Yoshino in 1985, which was commercialized by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991.
Lithium-ion batteries can be a safety hazard if not properly
engineered and manufactured since cells have flammable electrolytes and
if damaged or incorrectly charged, can lead to explosions and fires.
Much progress has been made in the development and manufacturing of
safe lithium-ion batteries. Lithium ion all solid state batteries are being developed to eliminate the flammable electrolyte. Improperly recycled batteries can create toxic waste, especially from toxic metals and are at risk of fire. Moreover, both lithium
and other key strategic minerals used in batteries have significant
issues at extraction, with lithium being water intensive in often arid
regions and other minerals often being conflict minerals such as cobalt. Both environmental issues have encouraged some researchers to improve mineral efficiency and alternatives such as iron-air batteries.
Research areas for lithium-ion batteries include extending
lifetime, increasing energy density, improving safety, reducing cost,
and increasing charging speed,
among others. Research has been under way in the area of non-flammable
electrolytes as a pathway to increased safety based on the flammability
and volatility of the organic solvents used in the typical electrolyte.
Strategies include aqueous lithium-ion batteries, ceramic solid electrolytes, polymer electrolytes, ionic liquids, and heavily fluorinated systems.
Research on rechargeable Li-ion batteries dates to the 1960s; one of the earliest examples is a CuF 2/Li battery developed by NASA in 1965. The breakthrough that produced the earliest form of the modern Li-ion battery was made by British chemist M. Stanley Whittingham in 1974, who first used titanium disulfide (TiS 2) as a cathode material, which has a layered structure that can take in lithium ions without significant changes to its crystal structure. Exxon tried to commercialize this battery in the late 1970s, but found the synthesis expensive and complex, as TiS 2 is sensitive to moisture and releases toxic H 2S
gas on contact with water. More prohibitively, the batteries were also
prone to spontaneously catch fire due to the presence of metallic
lithium in the cells. For this, and other reasons, Exxon discontinued
the development of Whittingham's lithium-titanium disulfide battery.
In 1980 working in separate groups Ned A. Godshall et al., and, shortly thereafter, Koichi Mizushima and John B. Goodenough, after testing a range of alternative materials, replaced TiS 2 with lithium cobalt oxide (LiCoO 2,
or LCO), which has a similar layered structure but offers a higher
voltage and is much more stable in air. This material would later be
used in the first commercial Li-ion battery, although it did not, on its
own, resolve the persistent issue of flammability. The same year, Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite, and invented the lithium graphite electrode (anode).
These early attempts to develop rechargeable Li-ion batteries
used lithium metal anodes, which were ultimately abandoned due to safety
concerns, as lithium metal is unstable and prone to dendrite formation, which can cause short-circuiting.
The eventual solution was to use an intercalation anode, similar to
that used for the cathode, which prevents the formation of lithium metal
during battery charging. A variety of anode materials were studied; in
1987, Akira Yoshino patented what would become the first commercial lithium-ion battery using an anode of "soft carbon" (a charcoal-like material) along with Goodenough's previously reported LCO cathode and a carbonate ester-based electrolyte. In 1991, using Yoshino's design, Sony began producing and selling the world's first rechargeable lithium-ion batteries. The following year, a joint venture between Toshiba and Asashi Kasei Co. also released their lithium-ion battery.
Significant improvements in energy density were achieved in the
1990s by replacing the soft carbon anode first with hard carbon and
later with graphite, a concept originally proposed by Jürgen Otto Besenhard in 1974 but considered unfeasible due to unresolved incompatibilities with the electrolytes then in use.
In 2010, global lithium-ion battery production capacity was 20 gigawatt-hours. By 2016, it was 28 GWh, with 16.4 GWh in China. Global production capacity was 767 GWh in 2020, with China accounting for 75%.
Production in 2021 is estimated by various sources to be between 200
and 600 GWh, and predictions for 2023 range from 400 to 1,100 GWh.
In 2012 John B. Goodenough, Rachid Yazami and Akira Yoshino
received the 2012 IEEE Medal for Environmental and Safety Technologies
for developing the lithium-ion battery; Goodenough, Whittingham, and
Yoshino were awarded the 2019 Nobel Prize in Chemistry "for the development of lithium-ion batteries".
In April 2023 CATL announced that it would begin scaled-up production of its semi-solid condensed matter battery that produces a then record 500 Wh/kg.
They use electrodes made from a gelid material, requiring fewer binding
agents. This in turn shortens the manufacturing cycle. One potential
application is in battery-powered airplanes.
Design
Generally, the negative electrode of a conventional lithium-ion cell is graphite made from carbon. The positive electrode is typically a metal oxide. The electrolyte is a lithiumsalt in an organicsolvent. The anode (negative electrode) and cathode (positive electrode) are prevented from shorting by a separator. The anode and cathode are separated from external electronics with a piece of metal called a current collector.
The electrochemical roles of the electrodes reverse between anode and
cathode, depending on the direction of current flow through the cell.
The most common commercially used anode is graphite, which in its fully lithiated state of LiC6 correlates to a maximal capacity of 1339 C/g (372 mAh/g). The cathode 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). More experimental materials include graphene-containing electrodes, although these remain far from commercially viable due to their high cost.
The electrolyte salt is almost always lithium hexafluorophosphate (LiPF 6), which combines good ionic conductivity with chemical and electrochemical stability. Hexafluorophosphate is essential for passivating the aluminum current collector used for the cathode. A titanium tab is ultrasonically welded to the aluminum current collector.
Other salts like lithium perchlorate (LiClO 4), lithium tetrafluoroborate (LiBF 4), and lithium bis(trifluoromethanesulfonyl)imide (LiC 2F 6NO 4S 2) are frequently used in research in tab-less coin cells, but are not usable in larger format cells, often because they are not compatible with the aluminum current collector. Copper (with a spot-welded nickel tab) is used as the anode current collector.
Current collector design and surface treatments may take various
forms: foil, mesh, foam (dealloyed), etched (wholly or selectively), and
coated (with various materials) to improve electrical characteristics.
Depending on materials choices, the voltage, energy density, life, and safety of a lithium-ion cell can change dramatically. Current effort has been exploring the use of novel architectures using nanotechnology to improve performance. Areas of interest include nano-scale electrode materials and alternative electrode structures.
Electrochemistry
The
reactants in the electrochemical reactions in a lithium-ion cell are
materials of anode and cathode, both of which are compounds containing
lithium atoms. During discharge, an oxidation half-reaction
at the anode produces positively charged lithium ions and negatively
charged electrons. The oxidation half-reaction may also produce
uncharged material that remains at the anode. Lithium ions move through
the electrolyte, electrons move through the external circuit, and then
they recombine at the cathode (together with the cathode material) in a
reduction half-reaction. The electrolyte and external circuit provide
conductive media for lithium ions and electrons, respectively, but do
not partake in the electrochemical reaction. During discharge, electrons
flow from the negative electrode (anode) towards the positive electrode
(cathode) through the external circuit. The reactions during discharge
lower the chemical potential of the cell, so discharging transfers energy
from the cell to wherever the electric current dissipates its energy,
mostly in the external circuit. During charging these reactions and
transports go in the opposite direction: electrons move from the
positive electrode to the negative electrode through the external
circuit. To charge the cell the external circuit has to provide electric
energy. This energy is then stored as chemical energy in the cell (with
some loss, e. g. due to coulombic efficiency lower than 1).
Both electrodes allow lithium ions to move in and out of their structures with a process called insertion (intercalation) or extraction (deintercalation), respectively.
As the lithium ions "rock" back and forth between the two
electrodes, these batteries are also known as "rocking-chair batteries"
or "swing batteries" (a term given by some European industries).
The following equations exemplify the chemistry.
The positive electrode (cathode) half-reaction in the lithium-doped cobalt oxide substrate is
The negative electrode (anode) half-reaction for the graphite is
The full reaction (left to right: discharging, right to left: charging) being
The overall reaction has its limits. Overdischarging supersaturates lithium cobalt oxide, leading to the production of lithium oxide, possibly by the following irreversible reaction:
In a lithium-ion cell, 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.
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 kilogram of lithium. 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.
The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze.
Charging and discharging
During discharge, lithium ions (Li+ ) carry the current within the battery cell from the negative to the positive electrode, through the non-aqueouselectrolyte and separator diaphragm.
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 each cell 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.
Energy losses arising from electrical contact resistance at interfaces between electrode
layers and at contacts with current collectors can be as high as 20% of
the entire energy flow of batteries under typical operating conditions.
The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different:
During the constant current phase, the charger applies a
constant current to the battery at a steadily increasing voltage, until
the top-of-charge voltage limit per cell is reached.
During the balance phase, the charger/battery 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. Balancing typically occurs whenever one
or more cells reach their top-of-charge voltage before the other(s), as
it is generally inaccurate to do so at other stages of the charge cycle.
This is most commonly done by passive balancing, which dissipates
excess charge via resistors connected momentarily across the cell(s) to
be balanced. Active balancing is less common, more expensive, but more
efficient, returning excess energy to other cells (or the entire pack)
through the means of a DC-DC converter
or other circuitry. Some fast chargers skip this stage. Some chargers
accomplish the balance by charging each cell independently. This is
often performed by the battery protection circuit/battery management system
(BPC or BMS) and not the charger (which typically provides only the
bulk charge current, and does not interact with the pack at the
cell-group level), e.g., e-bike and hoverboard
chargers. In this method, the BPC/BMS will request a lower charge
current (such as EV batteries), or will shut-off the charging input
(typical in portable electronics) through the use of transistor
circuitry while balancing is in effect (to prevent over-charging
cells). Balancing most often occurs during the constant voltage stage of
charging, switching between charge modes until complete. The pack is
usually fully charged only when balancing is complete, as even a single
cell group lower in charge than the rest will limit the entire battery's
usable capacity to that of its own. Balancing can last hours or even
days, depending on the magnitude of the imbalance in the battery.
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.
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).
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.
Batteries gradually self-discharge even if not connected and delivering current. Li-ion rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5–2% per month.
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. Self-discharge rates may increase as batteries age. In 1999, self-discharge per month was measured at 8% at 21 °C, 15% at 40 °C, 31% at 60 °C. By 2007, monthly self-discharge rate was estimated at 2% to 3%, and 2–3% by 2016.
By comparison, the self-discharge rate for NiMH batteries dropped, as of 2017, from up to 30% per month for previously common cells to about 0.08–0.33% per month for low self-discharge NiMH batteries, and is about 10% per month in NiCd batteries.
Cathode
Cathode materials are generally constructed from LiCoO 2 or LiMn 2O 4. The cobalt-based material develops a pseudo tetrahedral structure that allows for two-dimensional lithium-ion diffusion.
The cobalt-based cathodes are ideal due to their high theoretical
specific (per-mass) charge 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. The manganese-based materials adopt a cubic crystal lattice system, which allows for three-dimensional lithium-ion diffusion.
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.
Cobalt-based cathodes are the most common, however other materials are
being researched with the goal of lowering costs and improving cell
life.
As of 2017, LiFePO 4
is a candidate for large-scale production of lithium-ion batteries such
as electric vehicle applications due to its low cost, excellent safety,
and high cycle durability. For example, Sony Fortelion batteries have
retained 74% of their capacity after 8000 cycles with 100% discharge. A carbon conductive agent is required to overcome its low electrical conductivity.
It is worth mentioning so-called "lithium-rich" cathodes, that
can be produced from traditional NCM layered cathode materials upon
cycling them to voltages/charges higher than those corresponding to
Li:M=1. Under such conditions a new semi-reversible redox transition at a
higher voltage with ca. 0.4-0.8 electrons/metal site charge appears.
This transition involves non-binding electron orbitals centered mostly
on O atoms. Despite significant initial interest, this phenomenon did
not result in marketable products because of the fast structural
degradation (O2 evolution and lattice rearrangements) of such
"lithium-rich" phases.
Negative electrode materials are traditionally constructed from
graphite and other carbon materials, although newer silicon-based
materials are being increasingly used (see Nanowire battery).
In 2016, 89% of lithium-ion batteries contained graphite (43%
artificial and 46% natural), 7% contained amorphous carbon (either soft
carbon or hard carbon), 2% contained lithium titanate (LTO) and 2% contained silicon or tin-based materials.
These materials are used because they are abundant, electrically conducting and can intercalate lithium ions to store electrical charge with modest volume expansion (~10%).
Graphite is the dominant material because of its low intercalation
voltage and excellent performance. Various alternative materials with
higher capacities have been proposed, but they usually have higher
voltages, which reduces energy density. Low voltage is the key requirement for anodes; otherwise, the excess capacity is useless in terms of energy density.
The dominant negative electrode material used in lithium ion batteries, limited to a capacity of 372 mAh/g.
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
that constitute graphite. 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.
Improved output, charging time, durability (safety, operating temperature −50–70 °C (−58–158 °F)).
Hard carbon
Energ2
Home electronics
Greater storage capacity.
Tin/cobalt alloy
Sony
Consumer electronics (Sony Nexelion battery)
Larger capacity than a cell with graphite (3.5 Ah 18650-type cell).
Silicon/carbon
730 Wh/L 450 Wh/kg
Amprius
Smartphones, providing 5000 mAh capacity
Uses < 10% with 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 1200 mAh/g over 800 cycles.
As graphite is limited to a maximum capacity of 372 mAh/g
much research has been dedicated to the development of materials that
exhibit higher theoretical capacities and overcoming the technical
challenges that presently encumber their implementation. The extensive
2007 Review Article by Kasavajjula et al.
summarizes early research on silicon-based anodes for lithium-ion secondary cells. In particular, Hong Li et al.
showed in 2000 that the electrochemical insertion of lithium ions in
silicon nanoparticles and silicon nanowires leads to the formation of an
amorphous Li-Si alloy. The same year, Bo Gao and his doctoral advisor,
Professor Otto Zhou described the cycling of electrochemical cells with
anodes comprising silicon nanowires, with a reversible capacity ranging
from at least approximately 900 to 1500 mAh/g.
To improve the stability of the lithium anode, several approaches to installing a protective layer have been suggested.
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%), which causes catastrophic failure for the cell. Silicon has been used as an anode material but the insertion and extraction of
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 , and degrade the capacity and cycling stability of the anode.
In addition to carbon- and silicon- based anode materials for
lithium-ion batteries, high-entropy metal oxide materials are being
developed. These conversion (rather than intercalation) materials
comprise an alloy (or subnanometer mixed phases) of several metal oxides
performing different functions. For example, Zn and Co can act as
electroactive charge-storing species, Cu can provide an electronically
conducting support phase and MgO can prevent pulverization.
Electrolyte
Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF 6, LiBF 4 or LiClO 4 in an organicsolvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate.
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). The combination of linear and cyclic carbonates (e.g., ethylene carbonate (EC) and dimethyl carbonate (DMC)) offers high conductivity and solid electrolyte interphase (SEI)-forming ability. 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,
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. Composite electrolytes based on POE (poly(oxyethylene)) provide a relatively stable interface. 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.
Recent advances in battery technology involve using a solid as
the electrolyte material. The most promising of these are ceramics. 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. 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. 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.
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 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.
An efficient and economic way to tune targeted electrolytes properties
is by adding a third component in small concentrations, known as an
additive.
By adding the additive in small amounts, the bulk properties of the
electrolyte system will not be affected whilst the targeted property can
be significantly improved. The numerous additives that have been tested
can be divided into the following three distinct categories: (1) those
used for SEI chemistry modifications; (2) those used for enhancing the
ion conduction properties; (3) those used for improving the safety of
the cell (e.g. prevent overcharging).
Electrolyte alternatives have also played a significant role, for example the lithium polymer battery.
Polymer electrolytes are promising for minimizing the dendrite
formation of lithium. Polymers are supposed to prevent short circuits
and maintain conductivity.
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
In this equation, D is the diffusion coefficient for the lithium ion. It has a value of 7.5×10−10 m2/s in the LiPF 6 electrolyte. The value for ε, the porosity of the electrolyte, is 0.724.
Formats
Lithium-ion batteries are organized into multiple sub-units. The largest unit is the battery itself, also called the battery pack. Depending on the application, multiple battery packs are sometimes wired together in series to increase the voltage. Each pack consists of several battery modules connected both in series and in parallel. Each module is in turn made of multiple cells connected in parallel.
Cells
Li-ion cells are available in various shapes, which can generally be divided into four groups:
Large cylindrical (solid body with large threaded terminals)
Flat or pouch (soft, flat body, such as those used in cell phones and newer laptops; these are lithium-ion polymer batteries.
Rigid plastic case with large threaded terminals (such as electric vehicle 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 the positive electrode, separator, negative
electrode, and separator rolled into a single spool. One advantage of
cylindrical cells compared to cells with stacked electrodes is the
faster production speed. One disadvantage of cylindrical cells can be a
large radial temperature gradient inside the cells developing at high
discharge currents.
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,
and for general structural stability of the battery pack of which they
are part. Both rigid plastic and pouch-style cells are sometimes
referred to as prismatic cells due to their rectangular shapes.
Battery technology analyst Mark Ellis of Munro & Associates sees
three basic Li-ion battery types used in modern (~2020) electric vehicle
batteries at scale: cylindrical cells (e.g., Tesla), prismatic pouch (e.g., from LG), and prismatic can cells (e.g., from LG, Samsung, Panasonic, and others). Each form factor has characteristic advantages and disadvantages for EV use.
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.
In 2014, Panasonic created the smallest Li-ion cell. It is pin shaped. It has a diameter of 3.5mm and a weight of 0.6g. A coin cell form factor resembling that of ordinary lithium batteries is available since as early as 2006 for LiCoO2 cells, usually designated with a "LiR" prefix.
Batteries
A battery pack consists of multiple connected lithium-ion cells.
Battery packs for large consumer electronics like laptop computers also
contain temperature sensors, voltage regulator circuits, voltage taps, and charge-state monitors. These components minimize safety risks like overheating and short circuiting. To power larger devices, such as electric cars, connecting many small batteries in a series-parallel circuit is more effective.
Uses
Lithium ion batteries are used in a multitude of applications from consumer electronics, toys, power tools and electric vehicles.
More niche uses include backup power in telecommunications
applications. Lithium-ion batteries are also frequently discussed as a
potential option for grid energy storage, although as of 2020, they were not yet cost-competitive at scale.
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 in aqueous batteries (such as lead–acid, nickel–metal hydride and nickel-cadmium). Internal resistance increases with both cycling and age, although this depends strongly on the voltage and temperature the batteries are stored at.
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.
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. In the period from 2011 to 2017, progress has averaged 7.5% annually.
Overall, between 1991 and 2018, prices for all types of lithium-ion cells (in dollars per kWh) fell approximately 97%. Over the same time period, energy density more than tripled.
Efforts to increase energy density contributed significantly to cost reduction.
Differently sized cells with similar chemistry can also have different energy densities. The 21700 cell has 50% more energy than the 18650 cell, and the bigger size reduces heat transfer to its surroundings.
Round-trip efficiency
Based on an experimental evaluation of a "high-energy" type 3.0Ah
18650 NMC cell in 2021, round-trip efficiency which compared the energy
going into the cell and energy extracted from the cell from 100% (4.2v)
SoC to 0% SoC (cut off 2.0v):
Another characterization of a cell in 2017 reported round-trip efficiency of 85.5% at 2C and 97.6% at 0.1C
The lifespan of a lithium-ion battery is typically defined as the
number of full charge-discharge cycles to reach a failure threshold in
terms of capacity loss or impedance rise. Manufacturers' datasheet
typically uses the word "cycle life" to specify lifespan in terms of the
number of cycles to reach 80% of the rated battery capacity.
Simply storing lithium-ion batteries in the charged state also reduces
their capacity (the amount of cyclable Li+) and increases the cell
resistance (primarily due to the continuous growth of the solid electrolyte interface on the anode).
Calendar life is used to represent the whole life cycle of battery
involving both the cycle and inactive storage operations. Battery cycle
life is affected by many different stress factors including temperature,
discharge current, charge current, and state of charge ranges (depth of
discharge). Batteries are not fully charged and discharged in real applications
such as smartphones, laptops and electric cars and hence defining
battery life via full discharge cycles can be misleading. To avoid this
confusion, researchers sometimes use cumulative discharge defined as the total amount of charge (Ah) delivered by the battery during its entire life or equivalent full cycles,
which represents the summation of the partial cycles as fractions of a
full charge-discharge cycle. Battery degradation during storage is
affected by temperature and battery state of charge (SOC) and a
combination of full charge (100% SOC) and high temperature (usually
> 50 °C) can result in sharp capacity drop and gas generation.
Multiplying the battery cumulative discharge by the rated nominal
Voltage gives the total energy delivered over the life of the battery.
From this one can calculate the cost per kWh of the energy (including
the cost of charging).
Over their lifespan batteries degrade gradually leading to
reduced capacity (and, in some cases, lower operating cell voltage) due
to a variety of chemical and mechanical changes to the electrodes.
Several degradation processes occur in lithium-ion batteries, some during cycling, some during storage, and some all the time: Degradation is strongly temperature-dependent: degradation at room
temperature is minimal but increases for batteries stored or used in
high temperature or low temperature environments. High charge levels also hasten capacity loss.
In a study, scientists provided 3D imaging and model analysis to
reveal main causes, mechanics, and potential mitigations of the
problematic degradation of the batteries over charge cycles.
They found "[p]article cracking increases and contact loss between
particles and carbon-binder domain are observed to correlate with the
cell degradation" and indicates that "the reaction heterogeneity within
the thick cathode caused by the unbalanced electron conduction is the
main cause of the battery degradation over cycling".
The most common degradation mechanisms in lithium-ion batteries include:
Reduction of the organic carbonate electrolyte at the anode, which results in the growth of Solid Electrolyte Interface
(SEI), where Li+ ions get irreversibly trapped, i.e. loss of lithium
inventory. This shows as increased ohmic impedance and reduced Ah
charge. At constant temperature the SEI film thickness (and therefore,
the SEI resistance and the lost in cyclable Li+) increases as a square
root of the time spent in the charged state. The number of cycles is not
a useful metrics in characterizing this main degradation pathway. Under
high temperatures or in the presence of a mechanical damage the
electrolyte reduction can proceed explosively.
Lithium metal plating also results in the loss of lithium inventory
(cyclable Ah charge), as well as internal short-circuiting and ignition
of a battery. Once Li plating commences during cycling, it results in
larger slopes of capacity loss per cycle and resistance increase per
cycle. This degradation mechanism become more prominent as fast charging
and low temperatures.
Loss of the (negative or positive) electroactive materials due to
dissolution (e.g. of Mn(3+) species), cracking, exfoliation, detachment
or even simple regular volume change during cycling. It shows up as both
charge and power fade (increased resistance). Both positive and
negative electrode materials are subject to fracturing due to the
volumetric strain of repeated (de)lithiation cycles.
Structural degradation of cathode materials, such as Li+/Ni2+ cation
mixing in nickel-rich materials. This manifests as “electrode
saturation", loss of cyclable Ah charge and as a "voltage fade".
Other material degradations. Negative copper current collector is
particularly prone to corrosion/dissolution at low cell voltages. PVDF
binder also degrades, causing the detachment of the electroactive
materials, and the loss of cyclable Ah charge.
These are shown in the figure on the right. A change from one main
degradation mechanism to another appears as a knee (slope change) in the
capacity vs. cycle number plot.
Most studies of lithium-ion battery aging have been done at
elevated (50-60 °C) temperatures in order to complete the experiments
sooner. Under these storage conditions, fully charged
nickel-cobalt-aluminum and lithium-iron phosphate cells lose ca. 20% of
their cyclable charge in 1-2 year. It is believed that the
aforementioned anode aging is the most important degradation pathways in
these cases. On the other hand, manganese-based cathodes show a (ca.
20-50%) faster degradation under these conditions, probably due to the
additional mechanism of Mn ion dissolution.
At 25 °C the degradation of lithium-ion batteries seems to follow the
same pathway(s) as the degradation at 50 °C, but with half the speed.
In other words, based on the limited extrapolated experimental data,
lithium-ion batteries are expected to lose irreversibly ca. 20% of their
cyclable charge in 3–5 years or 1000-2000 cycles at 25 °C.
Lithium-ion batteries with titanate anodes do not suffer from SEI
growth, and last longer (>5000 cycles) than graphite anodes. However,
in complete cells other degradation mechanisms (i.e. the dissolution of
Mn3+ and the Ni3+/Li+ place exchange, decomposition of PVDF binder and
particle detachment) show up after 1000–2000 days, and the use titanate
anode does not improve full cell durability in practice.
Detailed degradation description
A more detailed description of some of these mechanisms is provided below:
(1) The negative (anode) SEI layer, a passivation coating formed
by electrolyte (such as ethylenecarbonate) reduction products, is
essential for providing Li+ ion conduction, while preventing electron
transfer (and, thus, further solvent reduction). Under typical operating
conditions, the negative SEI layer reaches a fixed thickness after the
first few charges (formation cycles), allowing the device to operate for
years. However, at elevated temperatures or due to mechanical
detachment of the negative SEI, this exothermic electrolyte reduction can proceed violently and lead to an explosion via several reactions. Lithium-ion batteries are prone to capacity fading over hundreds
to thousands of cycles. Formation of the SEI consumes lithium ions,
reducing the overall charge and discharge efficiency of the electrode
material.
as a decomposition product, various SEI-forming additives can be added
to the electrolyte to promote the formation of a more stable SEI that
remains selective for lithium ions to pass through while blocking
electrons.
Cycling cells at high temperature or at fast rates can promote the
degradation of Li-ion batteries due in part to the degradation of the
SEI or lithium plating. Charging Li-ion batteries beyond 80% can drastically accelerate battery degradation.
Depending on the electrolyte and additives, common components of the SEI layer that forms on the anode include 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 species such as Li 2CO 3 that increases the film thickness. This increases cell impedance and reduces cycling capacity.
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.
Below 25 °C, plating of metallic Lithium on the anodes and subsequent
reaction with the electrolyte is leading to loss of cyclable Lithium. Extended storage can trigger an incremental increase in film thickness and capacity loss. Charging at greater than 4.2 V can initiate Li+ plating on the anode, producing irreversible capacity loss.
Electrolyte degradation mechanisms include hydrolysis and thermal decomposition.
At concentrations as low as 10 ppm, water begins catalyzing a host of
degradation products that can affect the electrolyte, anode and cathode. 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. 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 potentially causing thermal runaway.
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.
Batteries generate heat when being charged or discharged,
especially at high currents. Large battery packs, such as those used in
electric vehicles, are generally equipped with thermal management
systems that maintain a temperature between 15 °C (59 °F) and 35 °C
(95 °F). Pouch and cylindrical cell temperatures depend linearly on the discharge current.
Poor internal ventilation may increase temperatures. For large
batteries consisting of multiple cells, non-uniform temperatures can
lead to non-uniform and accelerated degradation. In contrast, the calendar life of LiFePO 4 cells is not affected by high charge states.
Positive SEI layer in lithium-ion batteries is much less
understood than the negative SEI. It is believed to have a low-ionic
conductivity and shows up as an increased interfacial resistance of the
cathode during cycling and calendar aging.
(2) 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. Lithium plating is the most serious concern, when Li-ion batteries are charged at cold temperatures.
(3) Certain manganese containing cathodes can degrade by the
Hunter degradation mechanism resulting in manganese dissolution and
reduction on the anode. By the Hunter mechanism for LiMn 2O 4,
hydrofluoric acid catalyzes the loss of manganese through
disproportionation of a surface trivalent manganese to form a
tetravalent manganese and a soluble divalent manganese:
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. 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.
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. 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.
(4) Cation mixing is the main reason for the capacity decline of
the Ni-rich cathode materials. As the Ni content in the NCM layered
material increases the capacity will increase, which is the result of
two-electron of Ni2+/Ni4+ redox reaction (please note, that Mn remains
electrochemically inactive in the 4+ state) but, increasing the Ni
content results in a significant degree of mixing of Ni2+ and Li+
cations due to the closeness of their ionic radius (Li+ =0.076 nm and
Ni2+ =0.069 nm). During charge/discharge cycling, the Li+ in the cathode
cannot be easily be extracted and the existence of Ni2+ in the Li layer
blocks the diffusion of Li+, resulting in both capacity loss and
increased ohmic resistance.
(5) Discharging below 2 V can also result in the dissolution of
the copper anode current collector and, thus, in catastrophic internal
short-circuiting on recharge.
Recommendations
The IEEE
standard 1188–1996 recommends replacing Lithium-ion batteries in an
electric vehicle, when their charge capacity drops to 80% of the nominal
value.
In what follows, we shall use the 20% capacity loss as a comparison
point between different studies. We shall note, nevertheless, that the
linear model of degradation (the constant % of charge loss per cycle or
per calendar time) is not always applicable, and that a “knee point”,
observed as a change of the slope, and related to the change of the main
degradation mechanism, is often observed.
Characterization
Rechargeable
batteries are complex and heterogeneous devices with numerous
interfaces, which are essential as they are at the core of the battery
function. The redox reactions used to store and release energy necessitate the (triple) contact of electrons, redox centres, and ions (commonly lithium) for charge balance. Side reaction also take place at interfaces and they are therefore of key importance for the battery lifetime. Two main families of measurements, ex situ and in situ, can be performed to study the solid interphases in batteries.
Nuclear magnetic resonance (NMR)
Nuclear magnetic resonance
is traditionally not a routine characterization tool in the field of
rechargeable batteries. However, the ability to selectively address the
interfaces, through chemical or spatial selectivity has recently
triggered a lot of interest. One of the main assets exploited in the
last years was the quantification in ex situ Magic Angle Spinning
NMR (MAS-NMR) studies of the SEI and in situ NMR studies of Li or Na
plating. This ability is powerful, but it should be exploited with care
as several conditions must be fulfilled for the measurements to be
accurate. The development of Dynamic nuclear polarization (DNP) for sensitivity and Magnetic resonance imaging
(MRI) for spatially localized information should also result in a
continued progress of NMR implementation in the battery field in the
future.
For ex situ NMR, the part of interest is extracted from the battery in an argonglovebox
and transferred into the NMR sample holder. Ex situ NMR is
traditionally performed to study the bulk changes in the solid parts for
various state of charge
of the battery and more recently, it was applied to gain insight into
the interface components of Lithium-ion battery, especially the solid
electrode-electrolyte interface (SEI) for the anode, the solid electrolyte reactivity and dynamics and the cathode-electrolyte interface (CEI) for the cathode.
The liquid electrolyte stability (decomposition products on the
surface) and the plating and stripping of metal (lithium) on negative
electrodes are of particular interest.
For in situ NMR, the full battery is placed within the NMR magnet and radiofrequency coil
for the measurement. In situ NMR is advantageous as it is
non-destructive - the battery does not need a destructive opening for
the measurement - and it allows measuring the spectra for several states
of charge on the same battery. Operando spectroscopy
(while the current is flowing for the charge/discharge) enables
detecting transient phases in real-time which is of particular interest
in batteries because of the strongly reducing environment, especially at
the negative electrode on top of charge.
Lithium-ion batteries can be a safety hazard since they contain a
flammable electrolyte and may become pressurized if they become damaged.
A battery cell charged too quickly could cause a short circuit, leading to explosions and fires.
A Li-ion battery fire can be started due to (1) thermal abuse, e.g.
poor cooling or external fire, (2) electrical abuse, e.g. overcharge or
external short circuit, (3) mechanical abuse, e.g. penetration or crash,
or (4) internal short circuit, e.g. due to manufacturing flaws or
aging.
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, and there are shipping
limitations imposed by safety regulators. There have been battery-related recalls by some companies, including the 2016 SamsungGalaxy Note 7 recall for battery fires.
Lithium-ion batteries have a flammable liquid electrolyte. A faulty battery can cause a serious fire.
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.
Short-circuiting a battery will cause the cell to overheat and possibly to catch fire. Smoke from thermal runaway in a Li-ion battery is both flammable and toxic. The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ/(A·h), most of it chemical.
Around 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. UPS Airlines Flight 6 crashed in Dubai after its payload of batteries spontaneously ignited.
To reduce fire hazards, research projects are intended to develop non-flammable electrolytes.
Damaging and overloading
If
a lithium-ion battery is damaged, crushed, or is subjected to a higher
electrical load without having overcharge protection, then problems may
arise. External short circuit can trigger a battery explosion.
If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture.
During thermal runaway, internal degradation and oxidization processes
can keep cell temperatures above 500 °C, with the possibility of
igniting secondary combustibles, as well as leading to leakage,
explosion or fire in extreme cases.
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,
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.
Voltage limits
Lithium-ion
cells are susceptible to stress by voltage ranges outside of safe ones
between 2.5 and 3.65/4.1/4.2 or 4.35V (depending on the components of
the cell). Exceeding this voltage range results in premature aging and
in safety risks due to the reactive components in the cells.
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 battery management system
(BMS) may retain a record of this battery (or charger) "failure". Many
types of lithium-ion cells cannot be charged safely below 0 °C,
as this can result in plating of lithium on the anode of the cell,
which may cause complications such as internal short-circuit paths.
Other safety features are required in each cell:
Shut-down separator (for overheating)
Tear-away tab (for internal pressure relief)
Vent (pressure relief in case of severe outgassing)
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.
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.
Replacing the lithium cobalt oxide
positive electrode material in lithium-ion batteries with a lithium
metal phosphate such as lithium iron phosphate (LFP) 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.
Recalls
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.
IATA estimates that over a billion lithium metal and lithium-ion cells are flown each year. Some kinds of lithium batteries may be prohibited aboard aircraft because of the fire hazard. Some postal administrations restrict air shipping (including EMS) of lithium and lithium-ion batteries, either separately or installed in equipment.
Supply chain
The electric vehicle supply chain comprises the mining and refining of raw materials and the manufacturing processes that produce lithium ion batteries and other components for electric vehicles. The lithium-ion battery supply chain is a major component of the overall EV supply chain, and the battery accounts for 30%-40% of the value of the vehicle. Lithium, cobalt, graphite, nickel, and manganese are all critical minerals that are necessary for electric vehicle batteries.
There is rapidly growing demand for these materials because of growth
in the electric vehicle market, which is driven largely by the proposed transition to renewable energy. Securing the supply chain for these materials is a major world economic issue.
Recycling and advancement in battery technology are proposed strategies
to reduce demand for raw materials. Supply chain issues could create
bottlenecks, increase costs of EVs and slow their uptake.
The battery supply chain faces many challenges. Battery minerals
typically travel 50,000 miles from where they are extracted to
downstream manufacturing facilities. Deposits of critical minerals are
concentrated in a small number of countries, mostly in the Global South.
Mining these deposits presents dangers to nearby communities because of
weak regulation, corruption, and environmental degradation. These
communities face human rights violations, environmental justice issues, problems with child labour, and potentially generational legacies of contamination from mining activities.
Manufacture of battery technology is largely dominated by China.
Extraction of lithium, nickel, and cobalt, manufacture of solvents,
and mining byproducts present significant environmental and health
hazards.
Lithium extraction can be fatal to aquatic life due to water pollution.
It is known to cause surface water contamination, drinking water
contamination, respiratory problems, ecosystem degradation and landscape
damage. It also leads to unsustainable water consumption in arid regions (1.9 million liters per ton of lithium).
Massive byproduct generation of lithium extraction also presents
unsolved problems, such as large amounts of magnesium and lime waste.
Lithium mining takes place in North and South America, Asia, South Africa, Australia, and China.
Manufacturing a kg of Li-ion battery takes about 67 megajoule (MJ) of energy. The global warming potential
of lithium-ion batteries manufacturing strongly depends on the energy
source used in mining and manufacturing operations, and is difficult to
estimate, but one 2019 study estimated 73 kg CO2e/kWh. Effective recycling can reduce the carbon footprint of the production significantly.
Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, usually by burning away the other materials, but mining generally remains cheaper than recycling; recycling may cost $3/kg, and in 2019 less than 5% of lithium ion batteries were being recycled.
Since 2018, the recycling yield was increased significantly, and
recovering lithium, manganese, aluminum, the organic solvents of the
electrolyte, and graphite is possible at industrial scales. The most expensive metal involved in the construction of the cell is cobalt. Lithium is less expensive than other metals used and is rarely recycled, but recycling could prevent a future shortage.
Accumulation of battery waste presents technical challenges and health hazards.
Since the environmental impact of electric cars is heavily affected by
the production of lithium-ion batteries, the development of efficient
ways to repurpose waste is crucial.
Recycling is a multi-step process, starting with the storage of
batteries before disposal, followed by manual testing, disassembling,
and finally the chemical separation of battery components. Re-use of the
battery is preferred over complete recycling as there is less embodied energy
in the process. As these batteries are a lot more reactive than
classical vehicle waste like tire rubber, there are significant risks to
stockpiling used batteries.
Pyrometallurgical recovery
The pyrometallurgical
method uses a high-temperature furnace to reduce the components of the
metal oxides in the battery to an alloy of Co, Cu, Fe, and Ni. This is
the most common and commercially established method of recycling and can
be combined with other similar batteries to increase smelting
efficiency and improve thermodynamics. The metal current collectors aid the smelting process, allowing whole cells or modules to be melted at once. The product of this method is a collection of metallic alloy, slag,
and gas. At high temperatures, the polymers used to hold the battery
cells together burn off and the metal alloy can be separated through a
hydrometallurgical process into its separate components. The slag can be
further refined or used in the cement industry. The process is relatively risk-free and the exothermic reaction from polymer combustion reduces the required input energy. However, in the process, the plastics, electrolytes, and lithium salts will be lost.
Hydrometallurgical metals reclamation
This method involves the use of aqueous solutions to remove the desired metals from the cathode. The most common reagent is sulfuric acid. Factors that affect the leaching rate include the concentration of the acid, time, temperature, solid-to-liquid-ratio, and reducing agent. It is experimentally proven that H2O2 acts as a reducing agent to speed up the rate of leaching through the reaction:
Once leached, the metals can be extracted through precipitation
reactions controlled by changing the pH level of the solution. Cobalt,
the most expensive metal, can then be recovered in the form of sulfate,
oxalate, hydroxide, or carbonate. More recently recycling methods
experiment with the direct reproduction of the cathode from the leached
metals. In these procedures, concentrations of the various leached
metals are premeasured to match the target cathode and then the cathodes
are directly synthesized.
The main issues with this method, however, is that a large volume of solvent
is required and the high cost of neutralization. Although it's easy to
shred up the battery, mixing the cathode and anode at the beginning
complicates the process, so they will also need to be separated.
Unfortunately, the current design of batteries makes the process
extremely complex and it is difficult to separate the metals in a
closed-loop battery system. Shredding and dissolving may occur at
different locations.
Direct recycling
Direct
recycling is the removal of the cathode or anode from the electrode,
reconditioned, and then reused in a new battery. Mixed metal-oxides can
be added to the new electrode with very little change to the crystal
morphology. The process generally involves the addition of new lithium
to replenish the loss of lithium in the cathode due to degradation from
cycling. Cathode strips are obtained from the dismantled batteries, then
soaked in NMP, and undergo sonication to remove excess deposits. It is treated hydrothermally with a solution containing LiOH/Li2SO4 before annealing.
This method is extremely cost-effective for noncobalt-based
batteries as the raw materials do not make up the bulk of the cost.
Direct recycling avoids the time-consuming and expensive purification
steps, which is great for low-cost cathodes such as LiMn2O4 and LiFePO4. For these cheaper cathodes, most of the cost, embedded energy, and carbon footprint is associated with the manufacturing rather than the raw material. It is experimentally shown that direct recycling can reproduce similar properties to pristine graphite.
The drawback of the method lies in the condition of the retired
battery. In the case where the battery is relatively healthy, direct
recycling can cheaply restore its properties. However, for batteries
where the state of charge is low, direct recycling may not be worth the
investment. The process must also be tailored to the specific cathode
composition, and therefore the process must be configured to one type of
battery at a time.
Lastly, in a time with rapidly developing battery technology, the
design of a battery today may no longer be desirable a decade from now,
rendering direct recycling ineffective.
Human rights impact
Extraction
of raw materials for lithium ion batteries may present dangers to local
people, especially land-based indigenous populations.
Cobalt sourced from the Democratic Republic of the Congo is often
mined by workers using hand tools with few safety precautions,
resulting in frequent injuries and deaths.
Pollution from these mines has exposed people to toxic chemicals that
health officials believe to cause birth defects and breathing
difficulties. Human rights activists have alleged, and investigative journalism reported confirmation, that child labor is used in these mines.
A study of relationships between lithium extraction companies and
indigenous peoples in Argentina indicated that the state may not have
protected indigenous peoples' right to free prior and informed consent,
and that extraction companies generally controlled community access to
information and set the terms for discussion of the projects and benefit
sharing.
Development of the Thacker Pass lithium mine
in Nevada, USA has met with protests and lawsuits from several
indigenous tribes who have said they were not provided free prior and
informed consent and that the project threatens cultural and sacred
sites. Links between resource extraction and missing and murdered indigenous women have also prompted local communities to express concerns that the project will create risks to indigenous women. Protestors have been occupying the site of the proposed mine since January, 2021.
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.