Synthesis and properties of gallium-doped LiNiO2 as the cathode material for lithium secondary batteries

Gallium-doping to LiNiO2 was investigated, and we found that it is effective to improve the cycling behavior of LiNiO2. The obtained specimen is single phase with hexagonal structure without any other foreign matters such as LiGaO2 by X-ray diffraction measurement. The crystal structure during charging process is stabilized by gallium doping. Hexagonal structure is retained all over the charging state without monoclinic phase and without two hexagonal phase regions which are observed in undoped LiNiO2. Consequently, the crystal lattice parameters change continuously and gradually. The gallium-doped LiNiO2 shows superior rechargeable capacity of 190 mAh/g and retention of more than 95% after 100 cycles in the cycling test between 3.0 and 4.3 V at room temperature. In the cycling test with higher charging voltage (4.4 or 4.5 V), the rechargeable capacity reaches more than 200 mAh/g without significant degradation of cycling behavior. It also demonstrates excellent over-charge resistance.