Electrochemical characteristics of layered-spinel 0.7li₂mno₃·0.3li₄mn₅o₁₂ composite powders with spherical shape and porous nanostructure

Layered-spinel 0.7li₂mno₃·0.3li₄mn₅o₁₂ composite cathode powders are prepared by spray pyrolysis. Composite powders post-treated at temperatures below 800°C have spherical shapes and porous nanostructures. The BET surface areas of the composite powders decrease from 18.8 to 1.8 mm² g^-1 when the post-treatment temperature is increased from 550°C to 850°C. The composite powders post-treated at temperatures below 700°C have similar charge capacities due to the Mn^3+/4+ redox reaction of the spinel component when they are initially charged to 4.5 V (about 41 mAh g^-1). However, the initial charge capacities of the composite powders post-treated at 550°C, 600°C, 650°C, and 700°C are 203, 197, 166, and 105 mAh g^-1, respectively, when they are charged to 4.95 V. The elimination of Li2O from the layered Li2MnO3 component is affected by the crystallite size of the Li2MnO3 phase as well as the grain size in the composite powders. The discharge capacities of the composite powders post-treated at 600°C increase from 220 to 263 mAh g^-1 after 3 cycles. Then, the discharge capacities monotonically decrease to 201 mAh g^-1 after 30 cycles.