Synthesis and characterization of LiCoyNi(1−y)VO4 lithium insertion materials

A family of mixed LiCoyNi(1−y)VO4 (y=0.2, 0.5 and 0.8) compounds of potential use as high voltage cathode materials in lithium batteries, has been synthesized and characterized. The X-ray diffraction analysis showed that these compounds adopt an inverse spinel structure where in average 85% of the Ni2+ and Co2+ ions occupy octahedral sites and the other 15% occupy tetrahedral sites with the V5+ ions, although this occupation share is somewhat influenced by the preparation temperature. The annealing temperature plays also a key role in determining the particle size, as demonstrated by scanning electron microscope analysis. Cycling voltammetry tests showed that the lithium insertion–deinsertion process in the LiCoyNi(1−y)VO4 electrode materials occurs reversibly around 4.3–4.4 V vs. Li, as also confirmed by cycling tests. The cycling capacity is somewhat modest; however, the trend of the cycling curves leads to foresee that a consistent increase in capacity may be obtained by extending the charging process beyond 4.6 V vs. Li, once a stable electrolyte will be available.