An Improved Li / Li x CoO2 Rechargeable Cell

Abstract

Improvement of the cycling behavior of the cell has been brought about by the use of esters and alkyl carbonate‐based mixed solvents, and by physical modifications of the cathode structure. Binary solvent mixtures of methyl formate with either dimethyl carbonate, diethyl carbonate, or and electrolyte exhibit superior resistance towards solvent oxidation as well as improved lithium cycling efficiencies. Use of these mixed solvents with newly developed thin cathodes has resulted in stable cells which can be cycled more than 100 times at current densities of 1–10 mA cm−2, and at an average cell discharge voltage of between 3.9 and 3.7 V. Due to the high rate of solid‐state diffusion of Li+, the cathode can be charged at rates of up to 2 mA cm−2 over at least 100 deep charge and discharge cycles.