LITHIUM ION (Li-Ion / LIB) BATTERY INFORMATION

A lithium-ion battery or Li-ion battery (abbreviated as LIB) is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the constituent components of a lithium-ion battery cell. Lithium-ion batteries are common in home electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, tiny memory effect and low self-discharge. Beyond consumer electronics, LIBs are also growing in popularity for military, battery electric vehicle and aerospace applications. For example, lithium-ion batteries are becoming a common replacement for the lead–acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolyte, the trend is to use lightweight lithium-ion battery packs that can provide the same voltage as lead-acid batteries, so no modification to the vehicle's drive system is required.

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO2, which offers high energy density, but presents safety risks, especially when damaged. Lithium iron phosphate (LiFePO4), lithium ion manganese oxide battery (LiMn2O4, Li2MnO3, or LMO) and lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) offer lower energy density, but longer lives and inherent safety. Such batteries are widely used for electric tools, medical equipment and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (LiNiCoAlO2 or NCA) and lithium titanate (Li4Ti5O12 or LTO) are specialty designs aimed at particular niche roles. The newer lithium–sulfur batteries promise the highest performance-to-weight ratio.

Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they, unlike other rechargeable batteries, contain a flammable electrolyte and are kept pressurized. Because of this, the testing standards for these batteries are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests. This is in response to reported accidents and failures, and there have been battery-related recalls by some companies.

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

Reversible intercalation in graphite and intercalation into cathodic oxides was discovered in the 1970s by J. O. Besenhard at TU Munich. Besenhard proposed its application in lithium cells. Electrolyte decomposition and solvent co-intercalation into graphite were severe early drawbacks for battery life.
  • 1973 - Adam Heller Proposes the lithium thionyl chloride battery, still used in implanted medical devices and in defense systems where greater than a 20-year shelf life, high energy density, or extreme operating temperatures are encountered.
  • 1977 - Samar Basu demonstrated electrochemical intercalation of lithium in graphite at the University of Pennsylvania. This led to the development of a workable lithium intercalated graphite electrode at Bell Labs (LiC 6) to provide an alternative to the lithium metal electrode battery.
  • 1979 - Working in separate groups, at Stanford University Ned A. Godshall et al., and the following year in 1980 at Oxford University, England, John Goodenough and Koichi Mizushima, both demonstrated a rechargeable lithium cell with voltage in the 4v range using lithium cobalt oxide (LiCoO2) as the positive electrode and lithium metal as the negative electrode. This innovation provided the positive electrode material that made lithium batteries commercially possible. LiCoO2 is a stable positive electrode material which acts as a donor of lithium ions, which means that it can be used with a negative electrode material other than lithium metal. By enabling the use of stable and easy-to-handle negative electrode materials, LiCoO2 opened a whole new range of possibilities for novel rechargeable battery systems. Godshall et al. further identified in 1979, along with LiCoO2, the similar value of ternary compound lithium-transition metal-oxides such as the spinel LiMn2O4, Li2MnO3, LiMnO2, LiFeO2, LiFe5O8, and LiFe5O4 (and later lithium-copper-oxide and lithium-nickel-oxide cathode materials in 1985)
  • 1980 - Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite. The organic electrolytes available at the time would decompose during charging with a graphite negative electrode, slowing the development of a rechargeable lithium/graphite battery. Yazami used a solid electrolyte to demonstrate that lithium could be reversibly intercalated in graphite through an electrochemical mechanism. (As of 2011, the graphite electrode discovered by Yazami is the most commonly used electrode in commercial lithium ion batteries).
  • 1982 - Godshall et al. were awarded the U.S. Patent on the use of LiCoO2 as cathodes in lithium batteries, based on Godshall's Stanford University Ph.D. thesis Dissertation and 1979 publications.
  • 1983 - Michael M. Thackeray, John Goodenough, and coworkers further developed manganese spinel as a positive electrode material, after its 1979 identification as such by Godshall et al. in 1979 (above). Spinel showed great promise, given its low-cost, good electronic and lithium ion conductivity, and three-dimensional structure, which gives it good structural stability. Although pure manganese spinel fades with cycling, this can be overcome with chemical modification of the material. As of 2013, manganese spinel was used in commercial cells.
  • 1985 - Akira Yoshino assembled a prototype cell using carbonaceous material into which lithium ions could be inserted as one electrode, and lithium cobalt oxide (LiCoO2), which is stable in air, as the other. By using materials without metallic lithium, safety was dramatically improved. LiCoO2 enabled industrial-scale production and represents the birth of the current lithium-ion battery.
  • 1989 - John Goodenough and Arumugam Manthiram of the University of Texas at Austin showed that positive electrodes containing polyanions, e.g., sulfates, produce higher voltages than oxides due to the induction effect of the polyanion.
There were two main trends in the research and development of electrode materials for lithium ion rechargeable batteries. One was the approach from the field of electrochemistry centering on graphite intercalation compounds, and the other was the approach from the field of new nano-carbonaceous materials.

History described above is based on the former stand point. On the other hand, in the recent interview article concerning the first stage of scientific research activity directly related to the LIB developments, it is stated that looking at the major streams in research development, the negative-electrode of today’s lithium ion rechargeable battery has its origins in PAS (polyacenic semi-conductive material) discovered by Professor Tokio Yamabe and later Shjzukuni Yata at the beginning of 1980’s. The seed of this technology, furthermore, was the discovery of conductive polymers by Professor Hideki Shirakawa and his group, and it could also be seen as having started from the polyacetylene lithium ion battery developed by MacDiarmid and Heeger et al.

Commercial Production
The performance and capacity of lithium-ion batteries increases as development progresses.
  • 1991 - Sony and Asahi Kasei released the first commercial lithium-ion battery.
  • 1996 - John Goodenough, Akshaya Padhi and coworkers proposed lithium iron phosphate (LiCoO4) and other phospho-olivines (lithium metal phosphates with the same structure as mineral olivine) as positive electrode materials.
  • 2001 - Zhonghua Lu and Jeff Dahn file a patent for the lithium nickel manganese cobalt oxide (NMC) class of positive electrode materials, which offer's safety and energy density improvements over the widely used lithium cobalt oxide.
  • 2002 - Yet-Ming Chiang and his group at MIT showed a substantial improvement in the performance of lithium batteries by boosting the material's conductivity by doping it with aluminium, niobium and zirconium. The exact mechanism causing the increase became the subject of widespread debate.
  • 2004 - Chiang again increased performance by utilizing iron(III) phosphate particles of less than 100 nanometers in diameter. This decreased particle density almost one hundredfold, increased the positive electrode's surface area and improved capacity and performance. Commercialization led to a rapid growth in the market for higher capacity LIBs, as well as a patent infringement battle between Chiang and John Goodenough.
  • 2011 - lithium-ion batteries accounted for 66% of all portable secondary (i.e., rechargeable) battery sales in Japan.
  • 2012 - John Goodenough, Rachid Yazami and Akira Yoshino received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the lithium ion battery.
  • 2014 - commercial batteries from Amprius Corp. reached 650 Wh/L (a 20% increase), using a silicon anode and were delivered to customers. The National Academy of Engineering recognized John Goodenough, Yoshio Nishi, Rachid Yazami and Akira Yoshino for their pioneering efforts in the field.
  • 2016 - Nov. 22nd. Yasunaga (TYO:7271) Japanese technology firm, which is also a battery manufacturing equipment manufacturer revealed that they had developed a special positive electrode surface treatment which would allow the battery to have more than 1200% cycle life over the conventional lithium ion batteries. It tested 60000cycles to 102400cycles over the conventional battery that would only do 5000cycles before reaching 70% capacity compared to new. Yasunaga has commented the life is expected to be even longer when the negative electrodes get the same technology applied to them. This technology also showed 12% reduction in cell resistance as well. This is also expected to improve once negative side is treated.
PRICE-FIXING CONSPIRACY
Information came to light in 2011 regarding a long-term antitrust violating price-fixing conspiracy amongst the world's major lithium-ion battery manufacturers that kept prices artificially high from 2000 to 2011, according to a class action complaint that was tentatively settled with one of the defendants, Sony, in 2016. The complaint provided evidence that participants included LG, SD, Sanyo, Panasonic, Sony, and Hitachi, and notes that Sanyo and LG had pled guilty to the criminal price-fixing of Lithium Ion Batteries. "p. Sony agreed to settle for $20 million, and also cooperate by, among other things, making employees chosen by plaintiffs available for interviews, depositions and testimony, as well as provide clarifying information regarding the scheme and the documents provided to date, including responding to authentication and clarification questions." Cooperation clause: page 23 - 25.

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

The most commercially popular negative electrode is graphite. The positive electrode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as lithium manganese oxide). Recently, graphene based electrodes ( based on 2D and 3D structures of graphene) have also been used as electrodes for lithium batteries. The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions. These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium triflate (LiCF3SO3).

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

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

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

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

SHAPES
Li-ion cells (as distinct from entire batteries) are available in various shapes, which can generally be divided into four groups:
  • Small cylindrical (solid body without terminals, such as those used in laptop batteries)
  • Large cylindrical (solid body with large threaded terminals)
  • Pouch (soft, flat body, such as those used in cell phones; also referred to as li-ion polymer or lithium polymer batteries)
  • Prismatic (semi-hard plastic case with large threaded terminals, such as vehicles' traction packs)
Cells with a cylindrical shape are made in a characteristic "swiss roll" manner (known as a "jelly roll" in the US), which means it is a single long sandwich of positive electrode, separator, negative electrode and separator rolled into a single spool. The main disadvantage of this method of construction is that the cell will have a higher series inductance.

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

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

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

ELECTROCHEMISTRY
The participants in the electrochemical reactions in a lithium-ion battery are the negative and positive electrodes with the electrolyte providing a conductive medium for lithium ions to move between the electrodes.

Both electrodes allow lithium ions to move in and out of their interiors. During insertion (or intercalation) ions move into the electrode. During the reverse process, extraction (or deintercalation), ions move back out. When a lithium-ion based cell is discharging, the positive lithium ion moves from the negative electrode (usually graphite = "C6 below) and enters the positive electrode (lithium containing compound). When the cell is charging, the reverse occurs.

Useful work is performed when electrons flow through a closed external circuit. The following equations show one example of the chemistry. In a lithium-ion battery the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li1-xCoO2 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, 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 kg. This is a bit more than the heat of combustion of gasoline, but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.

ELECTROLYTES
The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze. Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF6, LiBF4 or LiClO4 in an organic solvent, 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 SEI-forming ability. A mixture of a high ionic conductivity and low viscosity carbonate solvents is needed, because the two properties are mutually exclusive in a single material.

Organic solvents easily decompose on the negative electrodes during charge. When appropriate organic solvents are used as the electrolyte, the solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase (SEI), 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, 0.7v 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.

CHARGE & DISCHARGE
During discharge, lithium ions (Li+) carry the current within the battery from the negative to the positive electrode, through the non-aqueous electrolyte and separator diaphragm.

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

PROCEDURE
The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different. A single Li-ion cell is charged in two stages:
  • Constant current (CC)
  • Voltage source (CV)
A Li-ion battery (a set of Li-ion cells in series) is charged in three stages:
  • Constant current (CC)
  • Balance (not required once a battery is balanced)
  • Voltage source (CV)
During the constant current phase, the charger applies a constant current to the battery at a steadily increasing voltage, until the voltage limit per cell is reached.

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

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

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

Failure to follow current and voltage limitations can result in an explosion.

EXTREME TEMPERATURES
Charging temperature limits for Li-ion are stricter than the operating limits. Lithium-ion chemistry performs well at elevated temperatures but prolonged exposure to heat reduces battery life. Li-ion batteries offer good charging performance at cooler temperatures and may even allow 'fast-charging' within a temperature range of 5 to 45°C (41 to 113°F). 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.

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

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

In 2015 cost estimates ranged from $300-500/kwh.

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

PERFORMANCE
  • Specific energy density: 100 to 250 W·h/kg (360 to 900 kJ/kg)
  • Volumetric energy density: 250 to 620 W·h/L (900 to 2230 J/cm3)
  • Specific power density: 300 to 1500 W/kg (at 20 seconds and 285 W·h/L)
Because lithium-ion batteries can have a variety of positive and negative electrode materials, the energy density and voltage vary accordingly.

The open circuit voltage is higher than aqueous batteries (such as lead acid, nickel-metal hydride and nickel-cadmium). Internal resistance increases with both cycling and age. Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually increasing resistance means that the battery can no longer operate for an adequate period.

Batteries with a lithium iron phosphate positive and graphite negative electrodes have a nominal open-circuit voltage of 3.2v and a typical charging voltage of 3.6 V. Lithium nickel manganese cobalt (NMC) oxide positives with graphite negatives have a 3.7v nominal voltage with a 4.2v 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 4.2v 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 Wh/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 0.3Wh per dollar to over 3Wh per dollar.

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

Cathode materials are generally constructed out of two general materials: LiCoO22 and LiMn2O2. 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 heat capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. Limitations include the high cost of the material, slight toxicity, 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 less toxic than other materials used. 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 beginning to be developed to make cheaper and less toxic cathodes.

USES
Li-ion batteries provide lightweight, high energy density power sources for a variety of devices. To power larger devices, such as electric cars, connecting many small batteries in a parallel circuit is more effective and more efficient than connecting a single large battery. Such devices include:
  • Portable devices: these include mobile phones and smart phones, laptops and tablets, digital cameras and camcorders, electronic cigarettes, hand held game consoles and flashlights.
  • Power tools: Li-ion batteries are used in tools such as cordless drills, sanders, saws and a variety of garden equipment including whipper-snippers and hedge trimmers.
  • Electric vehicles: Because of their light weight Li-ion batteries are used for propelling a wide range of electric vehicles such as aircraft, electric cars, Pedelecs, hybrid vehicles, advanced electric wheel chairs, radio-controlled models, model aircraft and the Mars Curiosity rover.
Li-ion batteries are used in telecommunications applications. Secondary non-aqueous lithium batteries provide reliable backup power to load equipment located in a network environment of a typical telecommunications service provider. Li-ion batteries compliant with specific technical criteria are recommended for deployment in the Outside Plant (OSP) at locations such as Controlled Environmental Vaults (CEVs), Electronic Equipment Enclosures (EEEs), and huts, and in uncontrolled structures such as cabinets. In such applications, li-ion battery users require detailed, battery-specific hazardous material information, plus appropriate fire-fighting procedures, to meet regulatory requirements and to protect employees and surrounding equipment.

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

For comparison, the self-discharge rate is over 30% per month for common nickel metal hydride (NiMH) batteries, dropping to about 1.25% per month for low self-discharge NiMH batteries, and 10% per month in nickel-cadmium batteries.

BATTERY LIFE
Rechargeable battery life is typically defined as the number of full charge-discharge cycles before significant capacity loss. Storage also reduces capacity. Manufacturers' information typically specify lifespan in terms of the number of cycles (e.g., capacity dropping linearly to 80% over 500 cycles), with no mention of chronological age. Research rejects this common industry practice. On average, lifetimes consist of 1000 cycles, although battery performance is rarely specified for more than 500 cycles. This means that batteries of mobile phones, or other hand-held devices in daily use, are not expected to last longer than three years. Some batteries based on carbon anodes offer more than 10,000 cycles.

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

In November 2016, Yasunaga, a Japanese battery manufacturer, revealed that they had developed a special positive electrode surface treatment which would allow the battery to have more than twelve times the cycle life of conventional lithium-ion batteries. It tested 60,000 cycles to 102,400 cycles over the conventional battery that would only do 5000 to 6000 cycles before reaching 70% capacity compared to new. Yasunaga has commented that the life is expected to be even longer when the negative electrodes get the same technology applied to them. This technology also showed 12% reduction in cell resistance.

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

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

Degradation is strongly temperature-dependent; increasing if stored or used at higher temperatures. High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss. Carbon anodes generate heat when in use. Batteries may be refrigerated to reduce temperature effects. Pouch and cylindrical cell temperatures depend linearly on the discharge current. Poor internal ventilation may increase temperatures. Loss rates vary by temperature: 6% loss at 0°C (32°F), 20% at 25°C (77°F), and 35% at 40°C (104°F). In contrast, the calendar life of LiFePO4 cells is not affected by high charge states.

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

SAFETY
If overheated or over-charged, Li-ion batteries may suffer thermal runaway and cell rupture. In extreme cases this can lead to combustion. To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range of 3-4.2v per cell. Lithium-ion cells are very susceptible to damage outside the allowed voltage range that is typically within (2.5 to 3.65v) for most LFP cells. Exceeding this voltage range results in premature aging of the cells and, furthermore, results 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. Many types of lithium-ion cells cannot be charged safely below 0°C.

Other safety features are required in each cell:
  • Shut-down separator (for overheating)
  • Tear-away tab (for internal pressure)
  • Vent (pressure relief)
  • Thermal interrupt (overcurrent/over-charging)
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 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 can not be equipped with a vent or thermal interrupt. High current cells must not produce any excessive heat or oxygen. Instead they must be equipped with internal thermal fuses which act before the anode and cathode reaches their thermal runaway limits.

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

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

Lithium-ion batteries, unlike other rechargeable batteries, have a potentially hazardous pressurized flammable electrolyte, and require strict quality control during manufacture. 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.

While fire is often serious, it may be catastrophically so. In about 2010 large lithium-ion batteries were introduced in place of other chemistries to power systems on some aircraft; as of January 2014 there had been at least four serious lithium-ion battery fires, or smoke, on the Boeing 787 passenger aircraft, introduced in 2011, none of which caused crashes but had the potential to do so.

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

ENVIRONMENTAL CONCERNS & RECYCLING
Since Li-ion batteries contain less toxic metals than other types of batteries which may contain lead or cadmium they are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, but mining generally remains cheaper than recycling. At present, not much money and research has been invested into recycling Li-ion batteries due to costs, complexities and low yield. The most expensive metal involved in the construction of the cell is cobalt. Lithium iron phosphate is cheaper but has other drawbacks. Lithium is less expensive than other metals used, but recycling could prevent a future shortage. The manufacturing processes of nickel and cobalt for the positive electrode as well as the solvent, present potential environmental and health hazards. Manufacturing a kg of Li-ion battery takes the energy equivalent to 1.6 kg of oil.