Lithium-ion batteries are a type of rechargeable battery 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. They can be dangerous if mistreated and unless care is taken their lifespan may be reduced. Although originally intended for consumer electronics, Lithium-ion batteries are growing in popularity with the defense and aerospace industries because of their high energy density. A more advanced lithium-ion battery design is the lithium polymer cell.
Li-ion Battery History
Lithium-ion batteries, first proposed in the 1960s, came into reality once 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. Used in numerous commercial applications these batteries revolutionized consumer electronics.
One of the latest uses is in hybrid electric cars and eventually electric vehicles, as commodity cells. Tesla Motors, Reva and Kewet are all releasing new lithium ion battery electric car models in 2007.
Li-ion Battery Specifications & 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 and 285 W·h/L)
Lithium-ion batteries 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 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.
Guidelines for prolonging Li-ion battery life
- Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40%. Lithium-ion batteries should never be “deep-cycled” like Ni-Cd batteries.
- Lithium-ion batteries should never be depleted to below their minimum voltage, 2.4v to 3.0v.
- Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
- According to one book, li-ion batteries should not be frozen, because most lithium-ion battery electrolytes freeze at approximately −40 °C.
- Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.
- When using a notebook computer running from fixed line power over extended periods, the battery should be removed and stored in a cool place so that it is not affected by the heat produced by the computer.
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.