prolong lithium-ion battery's life

prolong lithium-ion battery's life (三)

The voltage level to which the cells are charged also plays an important role to longevity. For

safety reasons, most lithium-ion cannot exceed 4.20 volts per cell. While a higher voltage boosts

capacity, the disadvantage is lower cycle life. Figure 2 shows the cycle life as a function of charge

voltage.

(Figure 2: Effects on cycle life at different float charge levels (Choi et al., 2002)Higher charge

voltages boost capacity but lower cycle life.)

There are no remedies to restore lithium-ion once

worn out. A momentary improvement in performance is noticeable when heating up the battery.

This lowers the internal resistance momentarily but the condition reverts back to its former

state when the temperature drops. Cold temperature will increase the internal resistance.If

possible, store the battery in a cool place at about a 40% state-of-charge. Some reserve charge is

needed to keep the battery and its protection circuit operational during prolonged storage. Avoid

keeping the battery at full charge and high temperature. This is the case when placing a cell

phone or spare battery in a hot car. Running a laptop computer on the mains has a similar

temperature problem. While the battery is kept fully charged, the inside temperature during

operation rises to 45°C (113°F). Removing the battery from the laptop when running on fixed

power protects the battery from heat. With the concern of the battery overheating and causing

fire, a spokesperson for the U.S. Consumer Product Safety Commission advises to eject the

battery of affected laptops and to run the machines on a power cord. It should be noted that on a

power outage, unsaved works will be lost.The question is often asked, should the laptop be

disconnected from the main when not in use? Under normal circumstances, it should not matter

with lithium-ion. Once the battery is fully charged, no further charge is applied. However, there

is always the concern is malfunction of the AC adapter, the laptop or the battery.A large number

of lithium-ion batteries for cell phones are being discarded under the warranty return policy.

Some failed batteries are sent to service centers or the manufacturer, where they are

refurbished. Studies show that 80%-90% of the returned batteries can be repaired and returned

to service.Some lithium-ion batteries fail due to excessive low discharge. If discharged below 2.5

volts per cell, the internal safety circuit opens and the battery appears dead. A charge with the

original charger is no longer possible. Some battery analyzers (Cadex) feature a boost function

that reactivates the protection circuit of a failed battery and enables a recharge. However, if the

cell voltage has fallen below 1.5V/cell and has remained in that state for a few months, a

recharge should be avoided because of safety concerns. To prevent failure, never store the

battery fully discharged. Apply some charge before storage, and then charge fully before use.All

personal computers (and some other electronic devices) contain a battery for memory back up.

This battery is commonly a small non-rechargeable lithium cell, which provides a small current

when the device is turned off. The PC uses the battery to retain certain information when the

power is off. These are the BIOS settings, current date and time, as well as resource assignment

for Plug and Play systems. Storage does shorten the service life of the backup battery to a few

years. Some say 1-2 years. By keeping the computer connected to the main, albeit turned off, a

battery on the PC motherboards should be good for 5-7 years. A PC should give the advanced

warning when battery gets low. A dead back-up battery will wipe out the volatile memory and

erase certain settings. After battery is replaced, the PC should again be operational.