Appearance of Lithium-Excess LiNiO₂with High Cyclability Synthesized by Thermal Decomposition Route from LiNiO₂-Li₂NiO₃Solid Solution

Abstract

Hexagonal (Rm Li-excess LiNiO2 with a primary particle size smaller than 0.5 μm was formed above 625°C as a result of thermal decomposition of a monoclinic LiNiO2-Li2NiO3 solid solution (C2/m, nominal Li/Ni ratio up to 1.5) using precipitation–calcination. Although the initial electrochemical properties of the monoclinic solid solution resemble those of the well-known LiNi1/2Mn1/2O2-Li2MnO3-based one, it exhibited poor discharge characteristics including initial discharge capacity and cyclability because of its low thermal stability. However, hexagonal Li-excess LiNiO2 with Ni-deficient in Ni-layer exhibited high-capacity above 210 mAh/g and better cyclability under high upper voltage up to 4.8 V than that of typical LiNiO2 against both Li metal and graphite negative electrodes. The rate performance of the hexagonal phase was comparable to that of typical LiNiO2. A relation between the structure and cyclability was constructed for the hexagonal phase to improve the future electrochemical performance.