Synthesis and cathode properties of a cubic rocksalt-type Si-doped Li ₂NiTiO₄ for lithium-ion batteries

Li₂NiSi_xTi_1-xO₄ was obtained by the sol-gel method under ambient pressure in the whole 0 ≤ x ≤ 0.2 regions. The lattice constant did not change, but the crystallinity decreased by increasing the Si doping level. The discharge capacities at the rate of 0.32 mA g^-1 for the obtained Li₂NiTiO₄ and Li ₂NiSi_0.1Ti_0.9O₄ were 153.4 mAh g^-1 and 145.5 mAh g^-1, respectively. The energy densities of the Li₂NiTiO₄ (598 mWh g^-1) and Li ₂NiSi_0.1Ti_0.9O₄ (567 mWh g ^-1) obtained at the rate of 0.32 mA g^-1 were equivalent to that of LiCoO₂. Moreover, the discharge capacities of Li ₂NiTiO₄ and Li₂NiSi_0.1Ti _0.9TiO₄ remained at 57.1 mAh g^-1 and 75.6 mAh g^-1 even after 20 cycles, respectively. In addition, the framework of Li₂NiTiO₄ and Li₂NiSi_xTi _1-xO₄ was stable enough to maintain its charge-discharge processes at the first cycle by expansion and contraction of the lattice accompanying the extraction/insertion of lithium.