Synthesis and electrochemical characterization of Ni- and Ti-substituted Li2MnO3 positive electrode material using coprecipitation-hydrothermal-calcination method

Homogeneous solid solutions of Ni- and Ti-substituted Li2MnO3 (Li1+x(Ni0.3Mn0.7-yTiy)1-xO2, 0 < x < 1/3, y = 0, 0.1, 0.2) have been prepared using coprecipitation-hydrothermal-calcination method. With increasing Ti contents, the randomly-distributed transition metal structure became stable. The average valence state of Ni and Mn ions was reduced and additional transition metal ion was introduced in Li-layer by calcining in N2 atmosphere at the same Ti content. The electrochemical performance depended on the Ti content and calcination atmosphere. By incorporating Ti ion, although the initial capacity and initial cycle efficiency worsened, cyclability was drastically improved. By changing from air to N2 atmosphere, the initial capacity, initial cycle efficiency, voltage decay with cycle and cyclability improved. A combination of Ti substitution and calcination in N2 atmosphere, optimized composition, Li1+x(Ni0.3Mn0.5Ti0.2)1-xO2 is proposed because the sample exhibited high cyclability up to 30 cycles (95%) under a full-cell configuration.