Material balance of petroleum coke/LiNiO2 lithium-ion cells

A method is described for the estimation of the volumetric specific capacity of balanced Li-ion cells. The effect of the material balance or the cathode/anode mass ratio, r, in Li-ion cells on the volumetric specific capacity, qv, of the electrode pair is studied in the example of a petroleum coke/LiNiO2 couple. The values of qv of several electrode pairs used in Li-ion cells, calculated on the basis of present experimental and previously published data are juxtaposed. A good agreement between calculated and experimentally determined qv values is found. The qv value of the natural graphite/LiNiO2 pair exceeds by nearly 28% that of the commercialized PFA-C/LiCoO2 pair, considered so far as the best available. This advantage will however be reduced by 30 to 50% in a real cell, when the volumes of all cell components are taken into account. The influence of r on the cycling stability is also demonstrated experimentally. The possibility of using unbalanced cells with moderately overcharged anodes appears feasible, while cells with precharged anodes from an auxiliary Li source seem impractical.