Effect of bication (Cu-Cr) substitution on the structure and electrochemical performance of LiMn2O4 spinel cathodes at low and high current rates

This report describes the detailed structural and electrochemical characterization of a series of low content (0.01 to 0.05) Cu-Cr bi-metal doped LiMn₂O₄ cathode material synthesized by sol–gel method. The structural and morphological features were described using XRD, SEM, TEM, EDAX and FTIR techniques. The electron transfer and its feasibility were discussed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge–discharge studies were performed to evaluate the capacity fading and rate capability. It was found that the electrochemical performance is very much dependent on the amount of Cu-Cr bi-metal doping and interestingly decreased the capacity fading with high cycleability. The sample with the least amount of dopants (i.e., LiCu_0.01Cr_0.01Mn_1.98O₄) demonstrated much improved capacity, cycleability and high rate capability. The LiCu_0.01Cr_0.01Mn_1.98O₄ cathode exhibited a discharge capacity of 112 mA h g^?1 at very first cycle and retained 93 mA h g^?1 after 100 cycles at a C rate of 0.3. Further, the same material at very high current density (5 C) retained 83% of the initial discharge capacity. The Cu-Cr doping stabilized the spinel structure by suppressing the Jahn-Teller distortion effect and Mn dissolution and the resultant material showed the workability of the cathodes for devices which work at substantially high C-rate of 5C.