Cycle-life improvement of Li/LiCoO2 batteries

The inherently good electronic conductivity and high lithium mobility of LixCoO2 make it a prime candidate cathode material for high-power rechargeable lithium batteries. We have studied the ageing of Li/LiCoO2 cells with LiPF6 in propylene carbonate electrolyte during cycling between fixed voltage limits. The polarization increases with cycle number and the useful capacity decreases by 0.5 to 1% per cycle. Although some of the results seem to reflect a structural change of LixCoO2, analysis of the data shows that degradation of the electrolyte is a more likely explanation for both the increase in polarization and the apparent structural change. Reduction of the maximum voltage from 4.3 to 4.1 V results in a lower initial capacity, but also in a higher remaining capacity after 100 cycles.