Li-ion batteries

Lithium Ion batteries are supposed to be the best type available at this time. They provide good energy storage in a small space. There are also new versions coming available that will increase the energy capacity and the charge/discharge rate. I was doing some checking to find out why a camera did not run for more than a few minutes on battery and discovered some interesting things about Li-ion batteries. They offer the highest practical energy density (provide the most power for size/weight). The first commercial Li-ion battery came out in about 1991. They are environmentally hazardous. They can be dangerous if mistreated. It took about 20 years of research to make them safe enough for mass market use. They reduce in capacity from the date of manufacture (even if not used). They are very easily damaged by even the slightest overcharging. The charge process is complex and precise to ensure reasonable life. The biggest negative seems to be that they deteriorate from the date of manufacture at a reasonable speed. They don't tell you this in the sales brochures.   Technical Details Cell voltage is about 3.6V. Charging is typically by constant current up to this voltage and then constant voltage until the current drops to zero. A very small over-charge can destroy the battery and a small under-charge will leave it with little stored energy. Charge current is recommended to be 0,7CmA. If below 2,9V per cell then 0,1CmA. Charging environment must be 0-40 degC. Maximum discharge current must not exceed 1.0CmA and discharge voltage must not drop below 3,0V Because of the constant-current charging they usually charge quite quickly. At 100% charge, the typical Li-ion laptop battery that's usually fully charged, at 25 degC, will lose about 20% capacity per year. These batteries do not suffer from the memory effect associated with Ni-cad and Ni-Mh. They also have a lower self-discharge rate; about 5% per month, (30% /month Ni-Mh, 20% /month Ni-cad). You can also leave then plugged in without affecting the life span. Note: overcharging should not normally be possible. Chargers are designed to prevent it.   So; What does this mean? To get the best life you should use the manufacturers recommended charger or power supply for the equipment; we have to assume that the manufacturer has a good charger design. Store batteries at about 40% charge and in a cool place. Some say freezing is OK but thaw before use. If not in use charge and cycle back to 40% once a year. Avoid deep discharge cycles and don't keep batteries in hot places like cars. Buy only when needed and check the manufacture date. Don't buy old stock or surplus. There's no point buying a spare battery for the laptop, camera, cellphone etc. because it will age almost as fast as the one in use.   The dangers The danger from Li-ion batteries is probably quite small. These batteries can explode and burn if shorted, damaged or overheated. Cool pictures of exploding laptop link It makes you think twice about "lap"-top.

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last updated: 25 July 2006