Synthesis and charge-discharge properties of Li1+xNi1-x-yCoyO2-zFz

LiNiO2 is one of the best cathode active materials for applying to lithium rechargeable batteries because of large capacity. However, its unsatisfactory cycling properties and difficulties in handling are not yet to be improved. It was found by some groups [M.G.S.R. Thomas, W.I.F. David, J.B. Goodenough, P. Groves, Mater. Res. Bull. 20 (1985) 1137; J.R. Dahn, U. von Sacken, C.A. Michal, Solid State Ionics 44 (1990) 87] that cation substitution reduces the lattice deformation during charging or discharging and improves the cycling properties. On the other hand, we reported [T. Ohzuku, A. Ueda, M. Kouguchi, J. Electrochem. Sec. 12 (1995) 4033] that addition of LiF to the starting materials, causing fluorine substitution for the anion, is also effective to obtain a better cycling life for LiNiO2, though the problem of the lattice deformation is not alleviated. Thus, it was expected that simultaneous substitution of cation- and anion sites might be useful. We synthesized Li1+xNi1-x-yCoyO1-zFz by an ordinary solid state reaction and evaluated the charge-discharge properties of this series of samples. The initial discharge capacity of Li1.075Ni0.755Co0.017O1.9F0.1 was 182 mAh/g. The capacity decrease rate was only 2.8% in the first 100 cycles, and became even smaller as the cycle number increased. The result suggests that each of the Co- and F substitution independently contributes to the improvement of cycling properties of LiNiO2. (C) 1999 Elsevier Science S.A. All rights reserved.