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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.
History
Gilbert N. Lewis pioneered lithium batteries in 1912; the first non-rechargeable cells were created in the early 1970s. The rechargeable lithium-ion battery required nearly 20 years of development before it was safe enough to be used on a mass market level, and the first commercial version was created in 1991.
Advantages and disadvantages
Advantages
Li batteries are lighter than equivalents in other chemistries - often much lighter. This is because Lithium battery chemistry has a 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 elements, such as nickel metal hydride or nickel cadmium, and with fewer volatile gases. The ions need fewer storage intermediaries, so more battery weight is usable as charge, instead of overhead.
Li-ion batteries do not suffer from the memory effect. They also have a low self-discharge rate of 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 advantage is that their lifespan remains relatively unaffected if they are kept "plugged in" after they have been fully charged. Other rechargeable batteries may degrade in these circumstances.
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. This drawback is not widely publicized.
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 ¡ãC, 20% at 25 ¡ãC, and 35% at 40 ¡ãC. When stored at 40% charge level, these figures are reduced to 2%, 4%, 15% at 0, 25 and 40 degrees Celsius respectively.
If the battery is used and fully depleted to 0 %, this is called a "deep discharge" cycle, and this decreases its capacity. Approximately 100 deep discharge cycles leave the battery with about 75% to 85% capacity. 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.
Li-ion batteries do not suffer from the memory effect, but they are not as durable as Ni-MH or Ni-CD designs and can be extremely dangerous if mistreated.
Li batteries are usually more expensive, since they use a newer chemistry and have more advanced applications.
Specifications and design
¡ñ Specific energy density: 150 to 200 W¡¤h/kg (540 to 720 kJ/kg)
¡ñ Volumetric energy density: 250 to 530 W¡¤h/L (900 to 1900 J/cm3)
¡ñ 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 is as follows:
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.
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.
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 cation is the same as the way in which the cathode in many lithium ion cells work.
Guidelines for prolonging Li-ion battery life
Unlike Ni-CD batteries or Ni-MH 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.
Avoid running the battery through "deep discharge" cycles ¡ª that is using it until it's fully depleted to 0 %.
Many authors suggest that freezing Li-ion batteries may be detrimental. However, most Li-ion battery electrolytes freeze at approximately -40¡ãC. Household freezers rarely reach below -20¡ãC. Published experiments demonstrate that freezing (even below -40¡ãC) is unharmful if the battery is fully warmed to room temperature before use.
Buy Li-ion batteries only when needed. Look at the manufacturing date. That is when the ageing process begins.
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.
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 and 100% Charg
|
| 0¡æ(32¡ãF) |
2% loss after 1 year |
6% loss after 1 year |
| 25¡æ(77¡ãF) |
4% loss after 1 year |
20% loss after 1 year |
| 40¡æ(104¡ãF) |
15% loss after 1 year |
35% loss after 1 year |
| 60¡æ (140¡ãF) |
25% loss after 1 year |
40% loss after 3 months |
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 unrecoverable 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 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.
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.
New Technology
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.
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