New inverse spinel cathode materials for rechargeable lithium batteries

The synthesis, characterization, and electrochemical properties of LiNiyCo1 − yVO4 (0 ≤ y ≤ 1) as the new cathode materials for rechargeable lithium batteries were investigated. A series of LiNiyCo1 − yVO4 (y = 0.1 − 0.9) compounds were synthesized by either a solid-state reaction of LiNiyCo1 − yO2 and V2O5 at 800 °C for 12 h or a solution coprecipitation of LiOH · H2O, Ni(NO3)2 · 6H2O, Co(NO3)2 · 6H2O and NH4VO3, followed by heating the precipitate at 500 °C for 48 h. The products from both preparation methods were analyzed by scanning electron microcopy and inductively-coupled plasma-atomic emission spectroscopy. These compounds are inverse spinels based on the results from Rietveld analysis and the fact that the cubic lattice constant a is a linear function of stoichiometry y in LiNiyCo1 −yVO4. Either a 1 M LiC1O4-EC + PC (1:1) or 1 M LiBF4-EC + PC + DMC (1:1:4) electrolyte can be used as the electrolyte for Li/LiNiyCo1 − yVO4 cells up to y = 0.7. The charge and discharge capacity of a Li/1 M LiBF4-EC + PC + DMC (1:1:4) /LiNi0.5Co0.5VO4 cell were 43.8 and 34.8 mAh/g, respectively, when the cathode material was prepared by the low temperature coprecipitation method.