Lithium ion battery

From Free net encyclopedia

Lithium ion batteries (sometimes abbreviated Li-Ion) are a type of rechargeable battery commonly used in consumer electronics. They are currently one of the most popular types of battery, with one of the best energy-to-weight ratios, no memory effect and a slow loss of charge when not in use. They can be dangerous if mistreated, however, and unless care is taken may have a short lifespan compared to other battery types. A more advanced lithium-ion battery design is the lithium polymer cell.

1 History
2 Advantages and disadvantages
3 Specifications and design
- 3.1 Solid electrolyte interface
4 Guidelines for prolonging Li-ion battery life
- 4.1 Storage Temperature and Charge
5 Warning
6 New Technology
7 See also
8 External links

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History

Gilbert N. Lewis pioneered lithium batteries in 1912; the first non-rechargable cells were created in the early 1970s. The first commercial lithium ion battery was created by Sony in 1991, following research by a team led by John B. Goodenough.

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Advantages and disadvantages

The immediate advantage to Lithium battery chemistry is higher charge density. Li ions are small and mobile, but more readily stored than hydrogen. Thus a battery based on Li is smaller than one with hydrogen, such as a NiMH or NiCd, and with fewer volatile gases. Because the ions need fewer storage intermediaries, more battery weight is usable as charge, instead of overhead. Thus, Li batteries are lighter than equivalents in other chemistries - often much lighter.

The Li-ion battery does not lose quality when recharging during laptop use; it is capable of easily regulating back and forth movement of energy from powercell to powercell.

A unique drawback of the Li-ion battery is that its life cycle 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. This drawback is not widely publicized.

As a newer chemistry, with more advanced applications, Li batteries command a higher price.

The Li-ion battery required nearly 20 years of development before it was safe enough to be used on a mass market level. While Li-ion batteries do not suffer from the memory effect, they are not as durable as NiMH or NiCd designs and can be extremely dangerous if mistreated. At a 100% charge level, a typical Li-ion laptop battery that's full most of the time at 25 degrees Celsius, will irreversibly lose approximately 20% capacity per year. This capacity loss begins from the time it was manufactured, and occurs even when the battery is unused. Different storage temperatures produce different loss results: 6% loss at 0 °C, 20% at 25 °C, and 35% at 40 °C. When stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at 0, 25 and 40 degrees Celsius respectively. Every deep discharge cycle decreases its capacity, and the degradation is sloped such that 100 cycles leave the battery with about 75% to 85% of the original. When used in laptop computers or cellular phones, this rate of deterioration means that after three to five years the battery will have capacities that are too low to be usable.

One great advantage of Li-ion batteries is their low self-discharge rate of only approximately 5% per month, compared with over 30% per month and 20% per month in nickel metal hydride batteries and nickel cadmium batteries, respectively.

Another great advantage is the fact that, unlike other types of rechargeable batteries, the lifespan of a Li-ion battery remains relatively unaffected if they remain "plugged in" after they have been fully charged.

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Specifications and design

Specific energy density: 150 to 200 W·h/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 W·h/L (900 to 1900 J/cm³)
Specific power density: 300 to 1500 W/kg (@ 20 seconds [1] and 285 W·h/L)

A typical chemical reaction of the Li-ion battery ia as follows: <math>Li0.5CoO3 + Li0.5C6 <--> C6 + LiCoO2\,</math>

Lithium-ion batteries have a nominal voltage of 3.6 V and a typical charging voltage of 4.2 V. The charging procedure is one of constant voltage with current limiting. 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 could not 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 reach 90% in as little as 10 minutes.

Lithium ion internal design is as follows. The anode is made from carbon, the cathode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent. Since the lithium metal which might be produced under irregular charging conditions is very reactive and might cause explosion, Li-ion cells usually have built-in protective electronics and/or fuses to prevent polarity reversal, over-voltage and over-heating.

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Solid electrolyte interface

A particularly important element for activating Li-ion batteries is the solid electrolyte interface (SEI). 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 act as a carrier between the cathode and the anode when a battery passes an electric current through an external circuit. However, solid electrolytes and organic solvents are easily dissolved on anodes during charging, thus preventing battery activation. Nevertheless, when appropriate organic solvents are used for electrolytes, the electrolytes are dissolved and form a solid electrolyte interface at first charge that is electrically insulating and high Li-ion conducting. The interface prevents decomposition of electrolytes after the second charge. For example, ethylene carbonate is dissolved at relatively high voltage, 0.7 V vs. Li, and forms a tight and stable interface. This interface is called an SEI.

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Guidelines for prolonging Li-ion battery life

Unlike NiCad batteries or NiMH batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a longer time, they should be brought to a charge level of around 40%. Never use the battery care functions some cellular phones provide for nickel based batteries. (This will deep cycle the batteries.)
Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. Keeping them in very hot cars can kill lithium-ion batteries.
Many authors suggest freezing Li-ion batteries may be detrimental. However, most Li-ion battery electrolytes freeze at approximately -40°C. Houshold freezers rarely reach below -20°C. Published experiments demonstrate freezing (even below -40°C) is unharmful if the battery is fully warmed to room temperature before use. See "Characteristics and Behavior of 1M LiPF6 1EC:1DMC Electrolyte at Low Temperatures, L. M. Cristo, T. B. Atwater, U.S. Army Research, Fort Monmouth, NJ."
Buy Li-ion batteries only when needed. Look at the manufacturing date. That is when the aging process commenced.
When using a notebook computer running from fixed line power over extended periods, it is advisable to remove the battery and store it in a cool place.
However, many laptop manufacturers recommend against removing the battery from a laptop while it is plugged in, as this can damage a laptop designed to operate with the battery installed. Some manufacturers are also concerned about dust accumulation with the battery removed. Therefore, check the manufacturer's instructions before removing the battery.

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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.

Permanent Capacity Loss versus Storage Conditions
Storage Temperature	40% Charge	100% Charge
0 °C (32 °F)	2% loss after 1 year	6% loss after 1 year
25 °C (77 °F)	4% loss after 1 year	20% loss after 1 year
40 °C (104 °F)	15% loss after 1 year	35% loss after 1 year
60 °C (140 °F)	25% loss after 1 year	40% loss after 3 months
Source: BatteryUniversity.com

Note that it is very important not to store your battery at full charge. A Li-ion battery stored at 40% charge will last many times longer than one stored at 100% charge, particularly at higher temperatures.

If a Li-ion battery is stored with too low a charge, you run the risk of allowing the charge to drop below the battery's low-voltage threshold, and ending up with an unrecoverably dead battery. Once the charge has dropped to this level, recharging it can be dangerous. An internal safety circuit will therefore open to prevent charging, and the battery will be (for all practical purposes) dead.

If you already have two Li-ion batteries for a given device, charge (or discharge) one battery to 40% and place it in the refrigerator or freezer. If freezing, batteries must be allowed to completely warm to room temperature over up to 24 hours before any discharge or charge. Use the other until it "dies", which may be a few years. In the mean time, you may want to check on your cold battery now and again to make sure that its charge does not get too low. Once your primary battery is used to its fullest, take your cold battery out of storage, warm it to room temperature, charge it completely, and use as normal. This will give you the greatest total life out of the pair of them. Better still, don't buy the second battery until you've exhausted the useful life of the first.

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Warning

Lithium-ion batteries can easily rupture, ignite, or explode when exposed to high temperatures or direct sunlight. Never store them inside of a car during hot weather. Short-circuiting a Li-ion battery can also cause it to ignite or explode. Never open a Li-ion battery's casing. Li-ion batteries contain safety devices that, if damaged, can cause the battery to ignite or explode.

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New Technology

In February 2005, Altair NanoTechnology[2], a small firm based in Reno, Nevada, announced a new kind of lithium-ion battery. Its prototype has three times the capacity of existing batteries and can be fully charged in six minutes.

In March of 2005, Toshiba announced another fast charging lithium-ion battery, based on new nano-material technology, that provides even faster charge times, greater capacity, and a longer life cycle. The battery may be used in commercial products in 2006 or early 2007, primarily in the industrial and automotive sectors.[3]

In November 2005, A123Systems announced[4] a new higher power, faster recharging Li-Ion battery system[5] [6] based on research licensed from MIT. Their first battery is in production (1Q/2006) and being sold in DeWalt power tools.

All these formulations involve new electrodes. By increasing effective electrode area, decreasing the internal resistance of the battery, the current can be increased during both use and charging. This is similar to developments in ultracapacitors. Typically, battery power is increased in terms of wattage, but amp-hours are increased only slightly, from higher process efficiency.

In April 2006, a group of scientists at MIT announced that they had figured out a way to use viruses to form nano-sized wires that can be used to build ultrathin lithium-ion batteries with three times the normal energy density. Science Express (preprint) [7]

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