Lithium-ion rechargeable batteries with LiCoO2 and carbon electrodes: the LiCoO2/C system

Lithium-ion rechargeable battery with LiCoO2 cathode and non-graphitizable carbon anode has high energy density (253 Wh/ ℓ in 18650). By using LiPF6 containing propylene carbonate/diethyl carbonate electrolyte solution, excellent cycle performance can be obtained even at a moderately high temperature, because (1) LiCoO2 remains stable, and (2) non-graphitizable carbon exhibits a good cyclability with respect to Li-doping/undoping capability. Although a thin film is formed on the carbon surface during charge and discharge cycling, the discharge capacity degradation is only 10 to 20% after 500 cycles. Furthermore, even if the cell is overcharged, safety can be attained (1) by providing an anti-overcharging safety device which operates when Li2CO3 in the cathode is decomposed and (2) by using a polyolefin separator which shuts down at a high temperature due to overcharge current.