Manufacturers of lithium-ion cells have very strict guidelines in charge procedures, charging these cells incorrectly can cause great safety concerns. It is very important that you get advice from the supplier or manufacturer of the battery at time of purchase. This way the proper recommendations can be made to ensure that you have the correct charger for your application.
This next chapter outlines some of the basics behind charging Lithium-Ion batteries for standard applications. Again, it must be stressed that manufactures guidance should always be sought.
The charge time of most chargers is about 3 hours. Smaller batteries used for cell phones can be charged at 1C; the larger cells used for laptops should be charged at 0.8C or less. The charge efficiency is 99.9% and the battery remains cool during charge. Full charge is attained after the voltage threshold has been reached and the current has dropped to 3% of the rated current or has levelled off.
Lithium-ion batteries cannot be trickle charged; this would causes plating of metallic lithium that could lead to instabilities and compromise safety.
It is also very important not to overcharge Lithium-ion batteries; Lithium-ion is designed to operate safely within their normal operating voltage but become unstable if charged to higher voltages. Overcharging the cell causes plating of metallic lithium on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up. If left unattended, the cell could vent with flame.
General Charging Tips
* Your Charger should apply full charge. Avoid economy chargers that advertise one-hours charge. Fastest full-charge time: 2-3 hours.
* Recharge often as apposed to frequent full discharges, however on batteries with a fuel gauge, allow a full discharge once a month.
* Partial charge-recharge cycles will not affect the performance of the battery.
* It is recommended to store your battery at 40% charge if not in regular use, but do not let the battery fully deplete.
Charging Lithium-ion batteries by CellPack Solutions
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11 February 2009
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