The effect of chromium substitution on improving electrochemical performance of low-cost Fe-Mn based Li-rich layered oxide as cathode material for lithium-ion batteries

Novel lithium-rich cathode materials, LiFe_1-xCr _xO₂·Li₂MnO₃ (x = 0, 0.1, 0.25, 0.5), have been successfully synthesized using a co-precipitation method followed by hydrothermal and calcination treatment. The effects of Cr substitution on the structure and electrochemical properties of these materials are investigated. These composite materials with layered structure are mainly composed of agglomerated spherical particles with uniform particle size distribution. The sample with x = 0.1 delivers higher initial discharge capacity and higher initial Coulombic efficiency, which is believed to be associated with the oxidation of Cr³⁺ suggested by the CV curve. This sample also exhibits better rate capability than samples with other "x" values due to its low charge transfer resistance. The best cycling stability and highest reversible discharge capacity (226 mAh g^-1 after 50 cycles) are obtained for the sample with x = 0.25. Excessive Cr substitution of Fe in the composite may suppress the oxygen release from Li₂MnO₃ on the first charging, which is helpful to stabilize the composite structure. This study not only provides a rational design approach for high-capacity cathode materials, but also demonstrates that the LiFe_1-xCr _xO₂·Li₂MnO₃, is very attractive as cathode materials for lithium-ion batteries, providing that the amount of Cr substitution can be controlled appropriately.