Effect of Li ion in transition metal sites on electrochemical behavior of layered lithium manganese oxides solid solutions

Two solid solutions of Li[Li1/5Ni1/10Co1/5Mn1/2]O2 and Li[Ni1/4Co1/2Mn1/4]O2 compositions were synthesized using a sol–gel method. The solid solutions with layered manganese oxides were both formed with typical hexagonal structure with maintaining the manganese oxidation state of 4+. The electrochemical characterization of the synthesized materials showed a monotonous discharge curve shape without structural transformation to spinel during charge–discharge processes. The Li[Li1/5Ni1/10Co1/5Mn1/2]O2 and Li[Ni1/4Co1/2Mn1/4]O2 delivered 190 and 184 mA h/g, respectively, at the 1st cycle. The subsequent capacities of the samples were 229 and 169 mA h/g after the 40th cycle with the capacity fading ratios of 0.032% and 0.19%/cycle, respectively, for maximum capacities of the samples. The different electrochemical behaviors of the two samples were intensively discussed based on various experimental observations.