Lithium ion battery
Encyclopedia : L : LI : LIT : Lithium ion battery
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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 they may have a shorter lifespan compared to other battery types. A more advanced lithium-ion battery design is the lithium polymer cell.
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HistoryGilbert N. Lewis pioneered lithium batteries in 1912; the first non-rechargable cells were created in the early 1970s. The rechargable 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 by Sony in 1991, following research by a team led by John B. Goodenough. Advantages and disadvantagesAdvantagesLi batteries are lighter than equivalents in other chemistries — often much lighter. This is because lithium ions have an extremely high charge density — the highest of all known naturally occurring ions. Li ions are small and mobile, but more readily stored than hydrogen. Thus a battery based on lithium is smaller than one with hydrogen elements, such as nickel metal hydride, 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. DisadvantagesA 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 °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. 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 nickel metal hydride or nickel-cadmium designs and can be extremely dangerous if mistreated. They are usually more expensive, since they use a newer chemistry and have more advanced applications. Specifications and design
Li0.5CoO2 + Li0.5C6 ↔ C6 + LiCoO2 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 interfaceA 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 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 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 decomposed 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 cations is the same as the way in which the cathode in many lithium ion cells work. Guidelines for prolonging Li-ion battery life
Storage temperature and chargeStoring 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.
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. WarningLithium-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. See example: [Dell laptop explodes at Japanese conference]New technologyIn February 2005, Altair NanoTechnology[], 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.[link] In November 2005, A123Systems announced[link] a new higher power, faster recharging Li-Ion battery system[link] [link] 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 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 (Amp-hours) is increased only slightly. 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) [link] 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 [link]. See alsoExternal links
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