Lithium-ion battery

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Lithium-ion battery
Nokia Battery.jpg
Nokia Li-ion battery for powering a mobile phone
Specific energy

100–265 W·h/kg[1][2]

(0.36–0.95 MJ/kg)
Energy density

250–730 W·h/L[2]

(0.90–2.23 MJ/L)
Specific power ~250-~340 W/kg[1]
Charge/discharge efficiency 80–90%[3]
Energy/consumer-price 2.5 W·h/US$
Self-discharge rate 8% at 21 °C
15% at 40 °C
31% at 60 °C
(per month)[4]
Cycle durability

400–1200 cycles

[5]
Nominal cell voltage NMC 3.6 / 3.7 V, LiFePO4 3.2 V

A lithium-ion battery (sometimes Li-ion battery or LIB) is a member of a family of rechargeable battery types 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 the electrode material, compared to the metallic lithium used in non-rechargeable lithium battery.

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, no memory effect (note, however, that new studies have shown signs of memory effect in lithium-ion batteries[6]), and only a slow loss of charge when not in use. Beyond consumer electronics, LIBs are also growing in popularity for military, electric vehicle and aerospace applications.[7] 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 a lightweight lithium/carbon negative electrodes and lithium iron phosphate positive electrodes. Lithium-ion batteries can provide the same voltage as lead-acid batteries, so no modification to the vehicle's drive system is required.[8]

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO
2
), which offers high energy density, but presents safety risks, especially when damaged. Lithium iron phosphate (LFP), lithium manganese oxide (LMO) and lithium nickel manganese cobalt oxide (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 (NCA) and lithium titanate (LTO) are specialty designs aimed at particular niche roles.

Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also 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.[9] This is in response to reported accidents and failures, and there have been battery-related recalls by some companies.

History[edit]

Before commercial introduction[edit]

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

Lithium batteries were first proposed by M. S. Whittingham, now at Binghamton University, while working for Exxon in the 1970s.[10] Whittingham used titanium(IV) sulfide and lithium metal as the electrodes.

Reversible intercalation in graphite[11][12] and intercalation into cathodic oxides[13][14] was discovered in the 1970s by J. O. Besenhard at TU Munich. Besenhard proposed its application in lithium cells.[15][16] Electrolyte decomposition and solvent co-intercalation into graphite were severe early drawbacks for battery life.

Primary lithium batteries with metallic lithium negative electrodes pose safety issues. As a result, lithium-ion batteries were developed in which both electrodes are made of a material containing lithium ions.[clarification needed][citation needed]

At Oxford University, England, in 1979, John Goodenough and Koichi Mizushima demonstrated a rechargeable cell with voltage in the 4 V range using lithium cobalt oxide (LiCoO
2
) as the positive electrode and lithium metal as the negative electrode.[17][clarification needed] This innovation provided the positive electrode material that made LIBs possible. LiCoO
2
is a stable positive electrode material which acts as a donor of lithium ions, which means that it can be used with a negative electrode material other than lithium metal. By enabling the use of stable and easy-to-handle negative electrode materials, LiCoO
2
opened a whole new range of possibilities for novel rechargeable battery systems.

In 1977, Samar Basu demonstrated electrochemical intercalation of lithium in graphite at the University of Pennsylvania.[18][19] This led to the development of a workable lithium intercalated graphite electrode at Bell Labs (LiC
6
)[20] to provide an alternative to the lithium metal electrode battery.

In 1980, Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite.[21][22] 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. The graphite electrode discovered by Yazami is currently (2011-03-20) the most commonly used electrode in commercial lithium ion batteries.

In 1983, Michael M. Thackeray, Goodenough, and coworkers identified manganese spinel as a positive electrode material.[23] 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.[24] As of 2013 manganese spinel was used in commercial cells.[25]

In 1985, Akira Yoshino assembled a prototype cell using carbonaceous material into which lithium ions could be inserted as one electrode, and lithium cobalt oxide (LiCoO
2
), which is stable in air, as the other.[26] By using materials without metallic lithium, safety was dramatically improved. LiCoO
2
enabled industrial-scale production and represents the birth of the current lithium-ion battery.

In 1989, 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.[27]

From commercial introduction[edit]

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

In 1991 Sony and Asahi Kasei released the first commercial lithium-ion battery.

In 1996 Goodenough, Akshaya Padhi and coworkers proposed lithium iron phosphate (LiFePO
4
) and other phospho-olivines (lithium metal phosphates with the same structure as mineral olivine) as positive electrode materials.[28]

In 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[citation needed] with aluminium, niobium and zirconium. The exact mechanism causing the increase became the subject of widespread debate.[29]

In 2004 Chiang again increased performance by utilizing iron 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 Goodenough.[29]

As of 2011, lithium-ion batteries accounted for 66% of all portable secondary (i.e., rechargeable) battery sales in Japan.[30]

In June 2012 John Goodenough, Rachid Yazami and Akira Yoshino received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the lithium ion battery.

By 2013 the lithium rechargeable battery had progressed to a lithium vanadium phosphate battery to increase energy efficiency in the forward and reverse reaction.

In 2014 John Goodenough, Yoshio Nishi, Rachid Yazami and Akira Yoshino were rewarded by The National Academy of Engineering for pioneering and leading the groundwork for today’s lithium ion battery. The prize, which is in its 25th year, includes a $500,000 award.[31]

In 2014 batteries stated to have 20% higher capacity than those previously available, with a silicon anode rather than graphite (carbon) anode, were being delivered to smartphone manufacturers.[32]

Construction[edit]

Cylindrical 18650 lithium iron phosphate cell before closing

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.[33] 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).[34]

The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions.[35] These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF
6
), lithium hexafluoroarsenate monohydrate (LiAsF
6
), lithium perchlorate (LiClO
4
), lithium tetrafluoroborate (LiBF
4
) and lithium triflate (LiCF
3
SO
3
).

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

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

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

For notebooks or laptops, lithium-ion cells are supplied as part of a battery pack with temperature sensors, voltage converter/regulator circuit, voltage tap, battery charge state monitor and the main connector. These components monitor the state of charge and current in and out of each cell, capacities of each individual cell (drastic change can lead to reverse polarities which is dangerous),[36] temperature of each cell and minimize the risk of short circuits.[37]

Shapes[edit]

Nissan Leaf's lithium-ion battery pack.

Li-ion cells (as distinct from entire batteries) are available in various shapes, which can generally be divided into four groups:[38][full citation needed]

  • 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)
  • Prismatic (semi-hard plastic case with large threaded terminals, such as vehicles' traction packs)

The absence of a case gives pouch cells the highest energy density; however, batteries using pouch and prismatic cells require an external means of containment to prevent expansion when their state-of-charge (SOC) level is high.[39]

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.[40]

Electrochemistry[edit]

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) 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 units of moles, making it possible to use coefficient x.

The positive electrode half-reaction is:[41]

{LiCoO_2}\leftrightarrows\mathrm{Li}_{1-x}\mathrm{CoO_2}+x\mathrm{Li^+}+x\mathrm{e^-}


The negative electrode half reaction is:

x\mathrm{Li^+} + x\mathrm{e^-} + x\mathrm{C_6} \leftrightarrows\ x\mathrm{LiC_6}


The overall reaction has its limits. Overdischarge supersaturates lithium cobalt oxide, leading to the production of lithium oxide,[42] possibly by the following irreversible reaction:

\mathrm{Li^+} + \mathrm{e^-} + \mathrm{LiCoO_2} \rightarrow \mathrm{Li_2O} + \mathrm{CoO}

Overcharge up to 5.2 volts leads to the synthesis of cobalt(IV) oxide, as evidenced by x-ray diffraction:[43]

 \mathrm{LiCoO_2} \rightarrow \mathrm{Li^+} + \mathrm{CoO_2} +\mathrm{e^-}

In a lithium-ion battery the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li
1-x
CoO
2
from Co3+
to Co4+
during charge, and reduced 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[edit]

The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze. Given lithium metal's high reactivity to water, nonaqueous or aprotic solutions are used.

Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF
6
, LiBF
4
or LiClO
4
in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. A liquid electrolyte acts as a carrier between the positive and negative electrodes when current flows through an external circuit. Typical conductivities of liquid electrolyte at room temperature (20 °C (68 °F)) are in the range of 10 mS/cm (1 S/m), increasing by approximately 30–40% at 40 °C (104 °F) and decreasing slightly at 0 °C (32 °F).[44]

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),[45] 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.[46]

Composite electrolytes based on POE (poly(oxyethylene)) developed by Syzdek et al., provide a relatively stable interface.[47][48] 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.[49]

Charge and discharge[edit]

During discharge, lithium ions Li+
carry the current from the negative to the positive electrode, through the non-aqueous electrolyte and separator diaphragm.[50]

During charging, an external electrical power source (the charging circuit) applies an over-voltage (a higher voltage but of the same polarity) than that produced by the battery, forcing the current to pass in the reverse direction. 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.

Charging procedure[edit]

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:[36]
  1. Constant current (CC)
  2. Voltage source (CV)
  • A Li-ion battery (a set of Li-ion cells in series) is charged in three stages:
  1. Constant current
  2. Balance (not required once a battery is balanced)
  3. Voltage source

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 cycle 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.

Lithium-ion is charged at approximately 4.2 ± 0.05 V/cell except for "military long life" that uses 3.92 V to extend battery life. Most protection circuits cut off if voltage greater than 4.3 V or temperature greater than 90 °C is reached. Below 2.50 V/cell the battery protection circuit may render the battery unchargeable with regular charging equipment. Most battery circuits stop at 2.7–3.0 V/cell.

Failure to follow current and voltage limitations can result in an explosion.[51]

Charging at high and low temperatures[edit]

Charging temperature limits for Li-ion are stricter than operational limits. Lithium-ion performs well at elevated temperatures; however, prolonged exposure to heat reduces longevity.

Li‑ion batteries offer reasonably good charging performance at cooler temperatures and allow fast-charging in a temperature bandwidth of 5 to 45 °C[citation needed] (41 to 113 °F).[52] 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 low-temperature charge the slight temperature rise above ambient due to the internal cell resistance is beneficial. Higher temperatures during charging may lead to battery degradation while charging at temperatures above 45 °C will degrade battery performance, whereas at lower temperatures the internal resistance of the battery will increase, resulting in less charging and longer charging times.[52]

Consumer-grade lithium-ion batteries cannot be charged at temperatures below 0 °C (32 °F). Although the pack appears to be charging normally, permanent plating of metallic lithium can occur on the anode during a subfreezing charge, and cannot be removed with cycling. Batteries with lithium plating are known to be more vulnerable to failure if exposed to vibration or other stressful conditions.[53] Most devices equipped with Li-ion batteries do not allow charging outside of 0-45 °C for safety reasons, except for mobile phones that allow some degree of charging when they detect an emergency call in progress.[54]

Production[edit]

Industry produced about 660 million cylindrical lithium-ion cells in 2012; the 18650 format 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 7,000 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.[55] Production is gradually shifting to higher-capacity 3,000+ mAh cells. Annual flat polymer cell demand was expected to exceed 700 million in 2013.[56]

Specifications[edit]

  • Specific energy density: 100 to 250 W·h/kg (360 to 900 kJ/kg)[57]
  • Volumetric energy density: 250 to 620 W·h/L (900 to 1900 J/cm³)[2]
  • Specific power density: 300 to 1500 W/kg (@ 20 seconds and 285 W·h/l)[1][not in citation given]

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

The open circuit voltage is higher than aqueous batteries (such as lead acid, nickel-metal hydride and nickel-cadmium).[58] The internal resistance of widely used LiCoO
2
batteries is higher than that of nickel-metal hydride, nickel-cadmium, LiFePO
4
and lithium-polymer cells.[59] Internal resistance increases with both cycling and age.[58][60] 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 3.2 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 and some types can reach 90% of full charge in as little as 10 minutes.[61]

Materials of commercial cells[edit]

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 solutions. The following materials have been used in commercially available cells. Research into other materials continues.

Positive electrode[edit]

Positive electrode
Technology Company Target application Date Benefit
Lithium Nickel Manganese Cobalt Oxide ("NMC", LiNixMnyCozO2) Imara Corporation, Nissan Motor,[62][63] Microvast Inc. 2008 density, output, safety
Lithium Manganese Oxide ("LMO", LiMn2O4) Lucky Goldstar Chemical,[64] NEC, Samsung,[25] Hitachi,[65] Nissan/AESC,[66] EnerDel[67] Hybrid electric vehicle, cell phone, laptop 1996 durability, cost
Lithium Iron Phosphate ("LFP", LiFePO4) University of Texas/Hydro-Québec,[68] Phostech Lithium Inc., Valence Technology, A123Systems/MIT[69][70] Segway Personal Transporter, power tools, aviation products, automotive hybrid systems, PHEV conversions 1996 moderate density (2 A·h outputs 70 amperes) operating temperature >60 °C (140 °F)
Oxygen ("Li-Air") IBM, Polyplus[71] Automotive 2012 Energy density: up to 10,000 mA·h per gram of positive electrode material. Rechargeable.

Negative electrode[edit]

Negative electrode
Technology Density Durability Company Target application Date Benefit
Graphite The dominant negative electrode material used in lithium ion batteries. 1991 Low cost and good energy density
Lithium Titanate ("LTO", Li4Ti5O12) 9,000 Toshiba, Altairnano automotive (Phoenix Motorcars), electrical grid (PJM Interconnection Regional Transmission Organization control area,[72] United States Department of Defense[73]), bus (Proterra) 2008 output, charging time, durability (safety, operating temperature −50–70 °C (−58–158 °F))[74][dead link]
Hard Carbon Energ2[75] Consumer electronics 2013 greater storage capacity
Tin/Cobalt Alloy Sony Consumer electronics (Sony Nexelion battery) 2005 Larger capacity than a cell with graphite (3.5Ah 18650-type battery)
Silicon/Carbon Volumetric: 580 W·h/l Amprius[76] Smartphones, providing 1850 mA·h capacity 2013 Uses silicon and other electrochemicals. Energy density

Uses[edit]

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[77] and more efficient than connecting a single large battery.[citation needed] Such devices include:

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.[78]

Self-discharge[edit]

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

Batteries gradually self-discharge even if not connected and delivering current. Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month.[79][80] 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.[81] Self-discharge rates may increase as batteries age.[82]

For comparison, the self-discharge rate is over 30% per month for common nickel metal hydride (NiMH) batteries,[83] dropping to about 1.25% per month for low self-discharge NiMH batteries, and 10% per month in nickel-cadmium batteries.

Battery life[edit]

Rechargeable battery life is often stated in number of charge cycles, but depth of discharge is usually not explicitly stated. Apple Inc. clarify that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle.[84]

It is widely stated on Web sites and other sources, without citing any evidence or source, that "lithium-ion batteries deteriorate over time, whether they're being used or not. So a spare battery won't last much longer than the one in use."[85] Manufacturers' information implies that the life of a battery that is not abused depends upon the number of charge cycles it undergoes, specifying typical battery capacity in terms of number of cycles (e.g., capacity dropping linearly to 80% over 500 cycles), with no mention of age of the battery.[86] Research by Professor Jeff Dahn of Dalhousie University suggests this common industry practice of merely counting cycles, ignoring the effect of age, is a poor predictor real-world battery life. In particular, a major contributor to the degradation of Li-Ions cell is the length of time they spend sitting at full charge, and with continuous cycle testing the cells are not left sitting with a full state of charge for any significant length of time. [87] Battery performance is rarely specified over 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. But it is also quite possible to obtain lithium-ion batteries based on carbon anodes with more than 10.000 cycles.[88]

All rechargeable batteries degrade with use, the capacity decreasing until it is unusably small. Li+ batteries last longer[85][unreliable source?][dubious ] if not deeply discharged (depleted) before recharging.

Batteries may last longer if not stored fully discharged. As the battery self-discharges over time, its voltage gradually reduces. When depleted below the low-voltage threshold of the protection circuit (2.4 to 2.9 V/cell, depending on chemistry) it will be disabled and cannot be further discharged until recharged.[85] This because as the discharge progresses, the metallic contents of the cell are plated onto its internal structure creating an unwanted discharge path. It is recommended to store batteries at 40% charge level.[85][dubious ]

The rate of degradation of lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures. The carbon negative electrode of the cell also generates heat. High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss.[58] Poor ventilation may increase temperatures, further shortening battery life. 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 LiFePO
4
cells is not affected by high charge states.[89] They may be stored in a refrigerator.[90][91]

Charging forms deposits inside the electrolyte that inhibit ion transport. The increase in internal resistance reduces the cell's ability to deliver current. This problem is more pronounced in high-current applications. Older batteries also do not charge as much as new ones (charging time required decreases).

Conditioning[edit]

The need to "condition" NiCd and NiMH batteries has incorrectly leaked into folklore surrounding Li-ion batteries. The recommendation for the older technologies is to leave the device plugged in for seven or eight hours, even if fully charged.[92] This may be a confusion of battery software calibration instructions with the "conditioning" instructions for NiCd and NiMH batteries.[93] The software of a typical smart phone, for example, learns how to accurately gauge the battery's life by watching it discharge and leaving it on the charger produces a series of "micro discharges" that the software can watch and learn from.[citation needed]

Multicell devices[edit]

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

Safety[edit]

If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture.[94] In extreme cases this can lead to combustion. To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that shuts down the battery when its voltage is outside the safe range of 3–4.2 V per cell.[41][83] When stored for long periods the small current draw of the protection circuitry may drain the battery below its shutdown voltage; normal chargers are then ineffective. Many types of lithium-ion cells cannot be charged safely below 0 °C.[95]

Other safety features are required in each cell:[41]

  • Shut-down separator (for overheating)
  • Tear-away tab (for internal pressure)
  • Vent (pressure relief)
  • Thermal interrupt (overcurrent/overcharging)

These devices occupy useful space inside the cells, add additional points of failure and irreversibly disable the cell when activated. They are required because the negative electrode produces heat during use, while the positive electrode may produce oxygen. These devices and improved electrode designs reduce/eliminate the risk of fire or explosion. Further, these features increase costs compared to nickel metal hydride batteries, which require only a hydrogen/oxygen recombination device (preventing damage due to mild overcharging) and a back-up pressure valve.[96] Contaminants inside the cells can defeat these safety devices.[clarification needed]

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.[97] The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ per A·h, most of it chemical. Extinguishing this fire is dangerous as lithium burns violently when it comes in contact with water or moisture in the air; a suitable waterless fire extinguisher is recommended.[36][98]

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.[99]

Lithium-ion batteries, unlike other rechargeable batteries, have a potentially hazardous pressurised flammable electrolyte, and require strict quality control during manufacture.[100] 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. Battery packs which are not branded by a reputable manufacturer may not be built to the same safety standard as branded ones.

While fire is often serious, it may be catastrophically so. In about 2010 large lithium-ion batteries were introduced in place of other chemistries to power systems on some aircraft; as of January 2014 there had been at least four serious lithium-ion battery fires, or smoke, on the Boeing 787 passenger aircraft, introduced in 2011, which did not cause crashes but had the potential to do so.[101][102]

Environmental concerns and recycling[edit]

Since Li-ion batteries contain no toxic metals (unlike other types of batteries which may contain lead or cadmium)[41] 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.[103] At present, not much is 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. The manufacturing processes of nickel and cobalt for the positive electrode and also the solvent, present potential environmental and health hazards.[104][105]

Recalls[edit]

In October 2004 Kyocera Wireless recalled approximately 1 million mobile phone batteries to identify counterfeits.[106]

In December 2006 Dell recalled approximately 22,000 laptop computer batteries.[107] Approximately 10 million Sony batteries used in Dell, Sony, Apple, Lenovo, Panasonic, Toshiba, Hitachi, Fujitsu and Sharp laptops were recalled in 2006. 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.[108]

In March 2007 computer manufacturer Lenovo recalled approximately 205,000 batteries at risk of explosion. In August 2007 mobile phone manufacturer Nokia recalled over 46 million batteries at risk of overheating and exploding.[109] One such incident occurred in the Philippines involving a Nokia N91, which used the BL-5C battery.[110]

Transport restrictions[edit]

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

IATA estimates that over a billion lithium cells are flown each year.[98] The United States Department of Transportation has not allowed passengers on commercial aircraft to carry spare lithium batteries (i.e., not installed in a device) in their checked baggage since 1 January 2008. Types of batteries covered by this rule are those containing small amounts of lithium, including Li-ion, lithium polymer, and lithium cobalt oxide chemistries. Lithium-ion batteries containing more than 25 grams (0.88 oz) equivalent lithium content (ELC) are forbidden in US air travel.[111]

Replacement batteries may be transported in carry-on luggage. Tips are provided on safe packaging and carriage of batteries; e.g., such batteries should be in their original protective packaging or in individual containers or plastic bags.[111][112]

Some postal administrations restrict air shipping (including EMS) of lithium and lithium-ion batteries, either separately or installed in equipment. Such restrictions apply in Hong Kong,[113] Australia and Japan.[114]

On 16 May 2012 the United States Postal Service (USPS) banned shipping anything containing a lithium battery to an overseas address, after fires from transport of batteries.[115] This restriction made it difficult to send anything containing lithium batteries to military personnel overseas, as the USPS was the only method of shipment to these addresses; the ban was lifted on 15 November 2012.[116]

The Boeing 787 Dreamliner uses large lithium cobalt oxide[117] batteries, which are more reactive than newer types of batteries such as LiFePO
4
.[118]

Research[edit]

Researchers are working to improve the research methods, power density, safety, cycle durability, recharge time, cost, flexibility and other characteristics of these batteries.

Solid-state design (no electrolyte)[edit]

Solid-state lithium-ion batteries designs[119] have the potential to deliver three times the energy density of typical 2011 lithium-ion batteries at less than half the cost per kilowatt-hour. This approach eliminates binders, separators and liquid electrolytes. By eliminating these, "you can get around 95% of the theoretical energy density of the active materials."[120] Solid-state designs do not overheat or catch fire like traditional lithium-ion batteries can. They are much safer because they do not use liquid electrolyte. Plans are to have products ready for field testing as early as March 2015.[121] Solid-state lithium-ion batteries are probably going to become the standard for electronics that are capable of operating in multiples of 3.2, 3.6 and 3.7 volts, respectively.

Tin electrode[edit]

Washington State University researchers developed a tin negative electrode technology that they predicted would triple the energy capacity of lithium ion batteries. The technology involves using standard electroplating process to create tin nanoneedles that do not shortciruit when the tin expands by one third during charging.[122][123]

Microporous tin has been used as a substrate for negative and positive electrodes that exhibit high energy density, power and fast recharge. The substrate self-assembles. Small spheres are packed onto a surface, forming a lattice. The area between the spheres is coated with the substrate material (nickel). The spheres are dissolved/melted and the resulting surface is electro-polished to enlarge the pores. Finally the substrate is coated with a thin film of the active material (Ni/Sn for negative electrode, LiMnO
2
for positive).[124][125]

Higher lithium content electrode[edit]

Researchers at Nissan are investigating lithium-rich batteries that may increase energy density by 150% and improve cycle durability.[126]

Silicon anode[edit]

Researchers at Amprius have created a lithium-ion battery that holds 20% more energy than the standard lithium-ion battery and they are in the process of producing higher levels of energy density. Theoretically, they can create a battery that can contain up to ten times as much energy density.[127] They are using a silicon anode, rather than standard graphite (carbon). These new batteries are being produced with all the same materials as the standard.[128]

Pomegranate style electrode for silicon anode[edit]

Researchers have discovered that using a pomegranate-inspired electrode with a silicon anode can reduce swelling while charging and reduce the gunk from the reaction with the electrolyte. This technique involves gathering yolk shells into clusters and then applying another coat of carbon around the cluster.

Researchers have previously overcome these problems by using silicon nanoparticles, which are already too small to break. They place the silicon nanoparticles in yolk shells made from carbon, with enough spare room inside for them to swell and shrink without causing damage.[129]

Silicon-carbon anode[edit]

Researchers have developed a battery that blends silicon and carbon that has a dramatic energy density improvement and five times the life cycle improvement than regular silicon anode lithium-ion batteries. The new silicon-anode batteries will allow electric vehicles to go 200–300 miles on a single charge. They are also cost effective and can be produced large scale.[130]

Sticky liquid electrolyte[edit]

Researchers have developed a chewing gum like substance to replace liquid electrolytes. This new material contain liquid electrolyte but is sticky and thus eliminates the fire hazard. This material is also flexible so it can be used with bendable electronics in the future.[131]

Disorder in battery materials[edit]

Creating lithium-ion batteries with disorder in the materials they are composed of has achieved 660 watt-hours per kilogram at 2.5 volts, a result rarely observed even in perfectly structured devices. Lithium-ion batteries are most commonly made of meticulously arranged rigid patterns of materials.[132]

Flexibility[edit]

Researchers have discovered a way to make li-ion batteries flexible, bendable, twistable and crunchable using the Miura fold. This discovery comes on the heels of using all the same material of conventional lio-ion batteries and could be commercialized for foldable smartphones and other applications.[133]

Nonflammable perfluoropolyether electrolyte[edit]

Researchers found a way to replace the electrolyte’s flammable organic solvent with nonflammable perfluoropolyether (PFPE), which eliminate the fire hazard. PFPE is usually used as an industrial lubricant. Researchers had originally been looking at using PFPE on the bottom of ships to prevent marine life from sticking, which is a serious problem in the world of shipping. More testing to see if the nonflammable electrolyte can withstand the rigors of everyday use, but they also exhibit unprecedented high transference numbers and low electrochemical polarization, indicative of longer battery life.[134]

Germanium nanowire-based anode[edit]

Researchers have found that germanium nanowire-based anodes more than double the capacity of standard graphite anodes while still retaining high capacity even after being charged and discharged over 1,000 times.[135][136]

Uniformity of li-ions into and out of cathode[edit]

Researchers have discovered a way to raise the charge durability to last four times more than traditional lithium-ion batteries while still maintaining adequate capacity. The process used maintains the lithium-ion diffusion at optimal levels and eliminates concentration polarization and thus allows the Li-ions to be more uniformly extracted from or reinserted into the cathode materials. This maintains the SEI layer at a stable state and prevents battery capacity fading.

Some of the companies interested in this new technology are concerned that this would mean fewer products are sold because the batteries would last so long.[137] This lack of interest in bringing new technology is part of a corporate eco-system that holds technology back.

Architecture and controlling algorithm[edit]

Researchers have discovered a way to store 10-40% more capacity (specific energy of 110 – 175 Wh/kg) using their special battery pack architecture and controlling algorithm that allows it to fully utilize the active materials in battery cells.[138]

Lithium iron phosphate cathode[edit]

Scientists at Massachusetts Institute of Technology have created Nanoball batteries that are capable re-charging 100 times faster than traditional li-ion batteries. They are capable of a 10 second re-charge in the size of a cell phone battery and a 5 minute re-charge in the size of an electric car battery. The cathode portion of the battery is composed of nanosized balls of lithium iron phosphate and the batteries can be charged much faster because the li-ion nanoballs transmit electrons to the surface of the cathode at a much higher rate. The batteries have also shown higher energy density and cycle durability than traditional li-ions. The issue is that the batteries also discharge at the much faster rate.[139][140]

Single-walled carbon nanotubes[edit]

Researchers at Northwestern University have made discoveries about Single-walled carbon nanotubes (SWCNTs) that could help boost their energy density and cycle durability. They found that metallic SWCNTs accommodate lithium much more efficiently than their semiconducting counterparts. Another important discovery was that, if made denser, the semiconducting SWCNT films also begin to take up lithium at levels comparable to metallic SWCNTs. The team is also looking into other nanomaterials for research.[141]

Analysis of cathode[edit]

Researchers at Nissan have developed a way to observe electrode material in the cathode during charging and discharging. This type of analysis could lead to higher energy density and higher cycle durability.[142]

See also[edit]


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