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Conditioning controversy

There is a belief that Li+ batteries need to be "conditioned" before first use. One is told to plug the battery/device into a charger and leave it there for seven or eight hours, even if fully charged. But this may simply be a confusion of the battery software calibration instructions with the "conditioning" instructions for NiCd and NiMH batteries. The software of a typical smart phone, for example, learns how to accurately gauge the battery's life by watching it discharge, and leaving it on the charger produces a series of "micro discharges" that the software can watch and learn from.

Lithium ion batteries do not need the "conditioning" of being fully discharged and charged the way NiCd and NiMH batteries do. In fact, there is a similar debate over whether discharging an Li+ battery as low as the protection circuit allows will cause the very sort of problem that is "fixed" by doing so with the older battery types.

Multicell devices

Li-ion batteries require a battery management system to prevent operation outside each cell's safe operating area (over-charge, under-charge, safe temperature range) and to balance cells to eliminate state of charge mismatches, significantly improving battery efficiency and increasing overall capacity. As the number of cells and load currents increase, the potential for mismatch increases. There are two kinds of mismatch in the pack: state-of-charge (SOC) and capacity/energy ("C/E") mismatch. Though SOC is more common, each problem limits pack current capacity (mAh) to that of the weakest cell.

Safety

Lithium-ion batteries can rupture, ignite, or explode when exposed to high temperature. Short-circuiting a battery will cause the cell to overheat and possibly to catch fire. Adjacent cells may then overheat and fail, possibly causing the entire battery to ignite or rupture. In the event of a fire, the device may emit dense irritating smoke. The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ per Ah, most of it chemical. Authorities and handlers lack knowledge on how to treat Li-Ion battery fire.

Replacing the lithium cobalt oxide cathode material in lithium-ion batteries with a lithium metal phosphate such as lithium iron phosphate improves cycle counts, shelf life and safety, but lowers capacity. Currently, these 'safer' lithium-ion batteries are mainly used in electric cars and other large-capacity battery applications, where safety issues are critical.

Lithium-ion batteries normally contain safety devices to protect the cells from disturbance. However, contaminants inside the cells can defeat these safety devices.

Recalls

In March 2007, Lenovo recalled approximately 205,000 batteries at risk of explosion. In August 2007, Nokia recalled over 46 million batteries at risk of overheating and exploding. One such incident occurred in the Philippines involving a Nokia N91, which uses the BL-5C battery.



In December 2006, Dell recalled approximately 22,000 laptop batteries from the US market. Approximately 10 million Sony batteries used in Dell, Sony, Apple, Lenovo/IBM, Panasonic,Toshiba, Hitachi, Fujitsu and Sharp laptops were recalled in 2006. The batteries were found to be susceptible to internal contamination by metal particles during manufacture. Under some circumstances, these particles could pierce the separator, causing a short-circuit.

In October 2004, Kyocera Wireless recalled approximately 1 million mobile phone batteries to identify counterfeits.


Date: 2015-12-11; view: 507


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