prolong lithium-ion battery's life

prolong lithium-ion battery's life(一)

Battery research is focusing heavily on lithium chemistries, so much so that one could presume

that all portable devices will be powered with lithium-ion batteries in the future. In many ways,

lithium-ion is superior to nickel and lead-based chemistries and the applications for lithium-ion

batteries are growing as a result.Lithium-ion has not yet fully matured and is being improved

continuously. New metal and chemical combinations are being tried every six months to increase

energy density and prolong service life. The improvements in longevity after each change will

not be known for a few years. A lithium-ion battery provides 300-500 discharge/charge cycles.

The battery prefers a partial rather than a full discharge. Frequent full discharges should be

avoided when possible. Instead, charge the battery more often or use a larger battery. There is

no concern of memory when applying unscheduled charges.Although lithium-ion is memory-free

in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to

as "digital memory". Here is the reason: Short discharges with subsequent recharges do not

provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-

charge. A deliberate full discharge and recharge every 30 charges corrects this problem. Letting

the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge

will become increasingly less accurate. (Read more in 'Choosing the right battery for portable

computing', Part Two.) Aging of lithium-ion is an issue that is often ignored. A lithium-ion

battery in use typically lasts between 2-3 years. The capacity loss manifests itself in increased

internal resistance caused by oxidation. Eventually, the cell resistance reaches a point where the

pack can no longer deliver the stored energy although the battery may still have ample charge.

For this reason, an aged battery can be kept longer in applications that draw low current as

opposed to a function that demands heavy loads. Increasing internal resistance with cycle life

and age is typical for cobalt-based lithium-ion, a system that is used for cell phones, cameras and

laptops because of high energy density. The lower energy dense manganese-based lithium-ion,

also known as spinel, maintains the internal resistance through its life but loses capacity due to

chemical decompositions. Spinel is primarily used for power tools.