Factors that affect cycle-life and possible degradation mechanisms of a Li-ion cell based on LiCoO2

An extensive test has been conducted on a lithium-ion (Li-ion) cell under a variety of cycling conditions in order to evaluate factors that affect its cycle-life. The study is performed on a 900-mAh wound prismatic cell with contains a LiCoO2 positive electrode (cathode) and a synthetic graphite negative electrode (anode). Cycle-life is greatly influenced by the charge conditions, but is relatively insensitive to the discharge conditions. High charge cut-off voltages and a long float-charge period at 4.2 V or above have the most severe effects on cycle-life. Another damaging condition is high charge rates above the 1C rate, but reduction in the depth-of-discharge does not improve the cycle-life unlike the situation with other rechargeable batteries such as alkaline and lead–acid batteries. The dependence of the degradation rate on the charge voltage and the period of high charge voltage suggests that an electrochemical oxidation may be the cause.