Influence of Ti substitution on the structure and electrochemical properties of lithium-excess layered manganese based oxide for lithium ion batteries

Abstract

A series of pure solid solution between Li2MO3 and LiNi1/2M1/2O2 (M=Ti, Mn) described as Li5/3Ni1/6Mn5/6-xTixO8/3(0≤x≤5/6) have been successfully prepared. Their hexagonal lattice parameters, a and c, change monotonously with the increase in x value. Tremendous change in their I003/I104 values indicates that Ti substitution causes cation mixing in the solid solution. The shapes in initial charge curve of solid solutions are similar to each other though charge capacities decrease for x≥4/6. On the other hand, initial discharge curve of the as synthesized solid solution are commonly composed of three plateaus which located at high voltage (>3.5V), low voltage and 2.8V plateau. Well separation of high and low voltage plateau is observed for x>4/6 and lower voltage plateau shifts dramatically to lower potential with increasing x value (3/6≤x≤5/6). Detailed analysis of initial charge/discharge and following reversible capacities indicates that peroxide type species in the solid solution play an important role in electrochemical reaction. It was found that the discharge curves of Li5/3Ni1/6Mn2/6Ti3/6O8/3 maintain its original shape after prolonged cycles, even though it is accompanied with capacity loss. Such behavior might be related with migration of metal ion into Li layer during initial charge process and result in rock salt like structure during prolonged cycling.