Study of electrode materials for lithium-ion batteries

Electrochemical behaviour of both positive and negative electrodes materials of lithium-ion cells have been studied. Li1-zNi1+zO2 positive material exhibits the best electrochemical performances for low values of z (Z<0.03) corresponding to material having a small amount of extra Ni2+ ions in the interslab space. The loss of reversibility at the first cycle is related to the oxidation process of these Ni2+ ions which induces a "spot welding" of the slabs. X-rays characterization of lithium nickel oxide having undergone 1200 charge/discharge cycles shows no evidence of structural modification. Reversible intercalation of unsolvated lithium into graphite electrodes has been carried out using electrolytes containing up to 95% of propylene carbonate (PC). Moreover reversible charge/discharge cycling may be performed in pure PC based electrolyte by using graphite electrodes treated by : (i) previously forming a passivating layer by reducing graphite in ethylene CEC) or chloroethylene (ClEC) carbonate based electrolytes (ii) previously wetting graphite in ClEC.