Lithium-ion battery Totally Explained

Everything about Lithium-ion Battery totally explained

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Lithium-ion batteries (sometimes abbreviated Li-ion batteries) are a type of rechargeable battery in which a lithium ion moves between the anode and cathode. The lithium ion moves from the anode to the cathode during discharge and from the cathode to the anode when charging.
Lithium ion batteries are commonly used in consumer electronics. They are currently one of the most popular types of battery for portable electronics, with one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. Certain kinds of mistreatment may cause Li-ion batteries to explode. In addition to uses for consumer electronics, lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density.
The three primary functional components of a lithium ion battery are the anode, cathode, and electrolyte, for which a variety of materials may be used. Commercially, the most popular material for the anode is graphite, although materials such as TiS₂ were originally used. However, the cathode is generally one of three materials: a layered oxide, such as cobalt oxide, a polyanion, such as lithium iron phosphate, or a spinel, such as manganese oxide. Depending on the choice of material for the anode, cathode, and electrolyte, the voltage, capacity, life, and safety of a lithium ion battery can change dramatically. Lithium ion batteries are not to be confused with lithium batteries, the key difference being that lithium batteries are primary batteries containing metallic lithium while lithium-ion batteries are secondary batteries containing an intercalation anode material.

History

Lithium ion batteries were first proposed by M.S. Whittingham, then at Exxon, in the 1970s. Whittingham used titanium sulfide as the cathode and lithium metal as the anode.
   Lithium batteries in which the anode is made from metallic lithium pose severe safety issues. As a result, lithium-ion batteries were developed in which the anode, like the cathode, is made of a material containing lithium ions. Lithium-ion batteries came into reality when Bell Labs developed a workable graphite anode to provide an alternative to lithium metal, the lithium battery. Following groundbreaking cathode research by a team led by John Goodenough, the first commercial lithium-ion battery was released by Sony in 1991. The cells utilised layered oxide chemistry, specifically lithium cobalt oxide. These batteries revolutionised consumer electronics.
   In 1983, Michael Thackeray and coworkers identified manganese spinel as a cathode material. Spinel showed great promise, since it's a low-cost material, has good electronic and lithium ion conductivity, and possesses a three-dimensional structure which gives it good structural stability. Although pure manganese spinel fades with cycling, this can be overcome with additional chemical modification of the material. Manganese spinel is currently used in commercial cells.
   In 1989, Arumugam Manthiram and John Goodenough of the University of Texas at Austin showed that cathodes containing polyanions, eg. sulfates, produce higher voltage than oxides due to the inductive effect of the polyanion. Following this, in 1996 Goodenough and co-workers discovered the electrochemical utility of the olivine material lithium iron phosphate, LiFePO₄. It is an important and emerging cathode material for lithium-ion batteries due in part to its enhanced safety compared to other lithium-ion chemistries. Cells containing lithium iron phosphate cathodes have been commercialised by multiple companies, including Phostech, Valence Technology, A123Systems, Aleees and Lithium Technology Corp.

Electrochemistry

The three participants in the electrochemical reactions in a lithium ion battery are the anode, cathode, and electrolyte.
   Both the anode and cathode are materials into which and from which lithium can migrate. The process of lithium moving into the anode or cathode is referred to as insertion (or intercalation), and the reverse process, in which lithium moves out of the anode or cathode is referred to as extraction (or deintercalation). When a cell is discharging, the lithium is extracted from the anode and inserted into the cathode. When the cell is charging, the reverse process occurs: lithium is extracted from the cathode and inserted into the anode.
   The anode of a conventional Li-ion cell is made from carbon, the cathode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent.
   Useful work can only be extracted if electrons flow through an external circuit. Therefore the half reactions are enlightening. The following equations are written in units of moles, making it possible to use the coefficient

x

. The cathode half reaction (with charging being forwards) is:

mathrm_2

being oxidized from Co³⁺ to Co⁴⁺ during charging, and reduced from Co⁴⁺ to Co³⁺ during discharge.

Cathodes

Material	Average Voltage	Gravimetric Capacity
LiCoO₂	3.7 V	140 mAh/g
LiMnO₂	4.0 V	100 mAh/g
LiFePO₄	3.3 V	170 mAh/g
Li₂FePO₄F	3.6 V	115 mAh/g

Electrolytes

Liquid electrolytes in Li-ion batteries consist of solid lithium-salt electrolytes, such as LiPF₆, LiBF₄, or LiClO₄, and organic solvents, such as ether. A liquid electrolyte conducts Li ions, which acts as a carrier between the cathode and the anode when a battery passes an electric current through an external circuit. However, organic solvents are easily decomposed on anodes during charging, thus preventing battery activation. Nevertheless, when appropriate organic solvents are used for electrolytes, the electrolytes are decomposed and form a solid electrolyte interphase (SEI) at first charge that's electrically insulating and high Li-ion conducting. The interphase prevents decomposition of the electrolyte after the second charge. For example, ethylene carbonate is decomposed at a relatively high voltage, 0.7 V vs. Li, and forms a dense and stable interface.
See uranium trioxide for some details of how the cathode works. While uranium oxides are not used in commercially made batteries, the way in which uranium oxides can reversibly insert cations is the same as the way in which the cathode in many lithium-ion cells work.

Advantages and disadvantages

Advantages

Lithium-ion batteries can be formed into a wide variety of shapes and sizes so as to efficiently fill available space in the devices they power.
   Li-ion batteries are lighter than other equivalent secondary batteries—often much lighter. The energy is stored in these batteries through the movement of lithium ions. However, the bulk of the electrodes are effectively "housing" for the ions and add weight, and in addition "dead weight" from the electrolyte, current collectors, casing, electronics and conductivity additives reduce the charge per unit mass to little more than that of other rechargeable batteries. A key advantage of using Li-ion chemistry is the high open circuit voltage that can be obtained in comparison to aqueous batteries (such as lead acid, nickel metal hydride and nickel cadmium).
   Li-ion batteries don't suffer from the memory effect. They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in common nickel metal hydride batteries (Low self-discharge NiMH batteries have much lower values; they can still hold 85% of their charge, after one year) and 10% per month in nickel cadmium batteries.
   According to one manufacturer, Li-ion cells (and, accordingly, "dumb" Li-ion batteries) don't have any self-discharge in the usual meaning of this word. What looks like a self-discharge in these batteries is a permanent loss of capacity, described in more detail below. On the other hand, "smart" Li-ion batteries do self-discharge, due to the small constant drain of the built-in voltage monitoring circuit. This drain is the most important source of self-discharge in these batteries.

Disadvantages

A unique drawback of the Li-ion battery is that its life span is dependent upon aging from time of manufacturing (shelf life) regardless of whether it was charged, and not just on the number of charge/discharge cycles. So an older battery won't last as long as a new battery due solely to its age, unlike other batteries. This drawback isn't widely published.
   At a 100% charge level, a typical Li-ion laptop battery that's full most of the time at 25 degrees Celsius or 77 degrees Fahrenheit will irreversibly lose approximately 20% capacity per year. However, a battery stored inside a poorly ventilated laptop may be subject to a prolonged exposure to much higher temperatures than 25 °C, which will significantly shorten its life. The capacity loss begins from the time the battery was manufactured, and occurs even when the battery is unused. Different storage temperatures produce different loss results: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40% - 60% charge level, these figures are reduced to 2%, 4%, 15% at 0, 25 and 40 degrees Celsius respectively.
   Under certain temperature conditions, the batteries have a tendency to become damaged and can sometimes never fully recharge again. In certain situations where the temperature is too cold (below the recommended battery temperature) the battery will still hold its charge but can't be recharged as a result of the cold temperature. This is most common in smaller batteries such as cellular phones and handheld devices.
   As batteries age, their internal resistance rises. This causes the voltage at the terminals to drop under load, reducing the maximum current that can be drawn from them. Eventually they reach a point at which the battery can no longer operate the equipment it's installed in for an adequate period.
   High drain applications such as powertools may require the battery to be able to supply a current of (15 h^-1)C - 15/hour times "C" - the battery capacity in Ampere hours, whereas MP3 players may only require (0.1 h^-1)C (discharging in 10 hours). With similar technology, the MP3 battery can tolerate a much higher internal resistance, so will have an effective life of many more cycles.
   Li-ion batteries can even go into a state that's known as deep discharge. At this point, the battery may take a very long time to recharge. For example, a laptop battery that normally charges fully in 3 hours may take up to 42 hours to recharge. Or the deep discharge state may be so severe that the battery will never come back to life. Deep discharging only takes place when products with rechargeable batteries are left unused for extended periods of time (often 2 or more years) or when they're fully discharged so often that they can no longer hold a charge. This makes Li-ion batteries unsuitable for back-up applications where they may become completely discharged.
   A stand-alone Li-ion cell must never be discharged below a certain voltage to avoid irreversible damage. Therefore all Li-ion battery systems are equipped with a circuit that shuts down the system when the battery is discharged below the predefined threshold. .
   The number of safety features can be compared with that of a nickel metal hydride cell, which only has a hydrogen/oxygen recombination device (preventing damage due to mild overcharging) and a back-up pressure valve.

Specifications and design

Specific energy density: 150 to 200 Wh/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 Wh/l (900 to 1900 J/cm³)
Specific power density: 300 to 1500 W/kg (@ 20 seconds and 285 Wh/l)

Because lithium-ion batteries can have a variety of cathode and anode materials, cell specifications, such as the energy density and voltage vary from chemistry to chemistry. Lithium ion batteries with a lithium iron phosphate cathode and graphite anode have a nominal open-circuit voltage of 3.6 V and a typical charging voltage of 4.2 V. The charging procedure is done at constant voltage with current limiting circuitry. This means charging with constant current until a voltage of 4.2 V is reached by the cell and continuing with a constant voltage applied until the current drops close to zero. Typically the charge is terminated at 7% of the initial charge current. In the past, lithium-ion batteries couldn't be fast-charged and typically needed at least two hours to fully charge. Current generation cells can be fully charged in 45 minutes or less; some Lithium-Ion variants can reach 90% in as little as 10 minutes.

Commercialization of Lithium Ion Batteries

Lithium Cobalt Oxide Cathodes

Lithium ion batteries were first commercialized by Sony in 1991. The cells utilized a lithium cobalt oxide cathode and a graphite anode. Sony and Sanyo are the leading producers of lithium ion batteries. A variety of Chinese, Japanese, and South Korean companies produce cells based on the lithium cobalt oxide cathode chemistry.

Manganese Spinel Cathodes

LG, which is the third largest producer of lithium ion batteries, uses the lithium manganese spinel for its cathode. It is working with its subsidiary CPI to commercialize lithium ion batteries containing manganese spinel for HEV applications. Several other companies are also working on manganese spinel, including NEC and Samsung.

Lithium Iron Phosphate Cathodes

The University of Texas first licensed its patent for lithium iron phosphate cathodes to HydroQuebec. Phostech was later spun-off from Hydroquebec for the sole development of lithium iron phosphate. Valence Technology, located in Austin, TX, is also working on lithium iron phosphate cells. Since March 2005, the Segway Personal Transporter has been shipping with extended-range lithium-ion batteries made by Valence Technology using iron phosphate cathode materials. Segway, Inc. chose to build their large-format battery with this cathode material because of its improved safety over metal-oxide materials.
In November 2005, A123Systems announced the development of lithium iron phosphate cells based on research licensed from MIT. While the battery has slightly lower energy density that other competing Lithium Ion technologies, a 2 Ahr cell can provide a peak of 70 Amps without damage and operate at temperatures above 60 degrees C. Their first cell is in production (1Q/2006) and being used in consumer products including DeWalt power tools, aviation products, automotive hybrid systems and PHEV conversions.

Titanate Anodes

Altairnano, a small firm based in Reno, Nevada, has announced a nano-sized titanate electrode material for lithium-ion batteries. It is claimed the prototype battery has three times the power output of existing batteries and can be fully charged in six minutes. However the energy capacity is about half that of normal li-ion cells. The company also says the battery can handle approximately 20,000 recharging cycles, so durability and battery life are much longer, estimated to be around 20 years or four times longer than regular lithium-ion batteries. The batteries can operate from -50 °C to over 75 °C and won't explode or result in thermal runaway even under severe conditions because they don't contain graphite-coated-metal anode electrode material. The batteries are currently being tested in a new production car made by Phoenix Motorcars which was on display at the 2006 SEMA motorshow. Enerdel, which is jointly owned by Ener1 and Delphi, is working to commercialize cells containing a titanate anode and manganese spinel cathode. Although the cells show excellent thermal properties and cyclability, their low voltage may mitigate commercial success.
All these formulations involve new electrodes (anodes or cathodes). By increasing the effective electrode area — thus decreasing the internal resistance of the battery — the current can be increased during both use and charging. This is similar to developments in ultracapacitors. Therefore, the battery is capable of delivering more power (watts); however, the battery's capacity (ampere-hours) is increased only slightly.

Breakthrough Research

In April 2006, a group of scientists at MIT announced a process which uses viruses to form nano-sized wires. These can be used to build ultrathin lithium-ion batteries with three times the normal energy density.
As of June 2006, researchers in France have created nanostructured battery electrodes with several times the energy capacity, by weight and volume, of conventional electrodes.
In the September 2007 issue of Nature, researchers from the University of Waterloo, Canada, reported a new cathode chemistry, whereby the hydroxide group in the iron phosphate cathode was replaced by fluorine. (External Link

) The advantages seem to be two-fold. First, there's less volume change in the cathode over a charge cycle which indicates a possibility for longer battery life. Second, the chemistry allows the substitution of Sodium or a Sodium/Lithium mixture for the Lithium in the battery (hence their reference to it as an Alkali-Ion battery).
In November 2007, Subaru unveiled their concept G4e electric vehicle with a lithium vanadium oxide based lithium ion battery, promising double the energy density of a conventional lithium ion battery (lithium cobalt oxide and graphite).(External Link

) In the lab, Lithium vanadium oxide anodes, paired with lithium cobalt oxide cathodes, have achieved 745Wh/l, nearly three times the volumetric energy density of conventional lithium ion batteries. (External Link

) In December 2007, researchers at Stanford university reported creating a lithium ion battery with ten times the energy density (amount of energy available by weight) through using silicon nanowires deposited on stainless steel as the anode. The battery takes advantage of the fact that silicon can hold large amounts of lithium, and helps alleviate the longstanding problem of cracking by the small size of the wires. (External Link

) To gain a tenfold improvement in energy density, the cathode would need to be improved as well; however, just improving the anode as such could provide "several" times the energy density, according to the team. The team leader, Yi Cui, expects to be able to commercialize the technology in about five years.(External Link

)

Guidelines for prolonging Li-ion battery life

Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they're not used for a long time, they should be brought to a charge level of around 40% - 60%. Lithium-ion batteries shouldn't be frequently fully discharged and recharged ("deep-cycled") like Ni-Cd batteries, but this is necessary after about every 30th recharge to recalibrate any external electronic "fuel gauge" (for example State Of Charge meter). This prevents the fuel gauge from showing an incorrect battery charge. (most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers).

Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured. and stored in a cool place so that it isn't affected by the heat produced by the computer.

Storage temperature and charge

Storing a Li-ion battery at the correct temperature and charge makes all the difference in maintaining its storage capacity. The following table shows the amount of permanent capacity loss that will occur after storage at a given charge level and temperature.

Further Information

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