Lithium- manganese-rich oxides are believed to be suitable candidate for cathode materials in the next generation of lithium-ion batteries. However, they have some disadvantages such as low initial coulombic efficiency, low rate capacity, and deficient cyclability. Different approaches such as elemental doping and surface coating have been adopted to overcome these shortcomings. In this study, Cu-doped Li1.25Mn0.50Ni0.125Co0.125O2 was synthesized by sol-gel method. The prepared samples were characterized using thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, surface area analysis, and field emission scanning electron microscopy. Galvanostatic charge-discharge measurement and electrochemical impedance spectroscopy were also conducted to investigate the electrochemical performance of the prepared samples. The XRD patterns revealed that all the samples had two phase structures. By doping Cu, the lattice parameters and the volume of the samples changed. The first discharge capacity of the doped samples was found to be lower than that of the undopped sample. In comparison with the pristine material, Cu-doped ones displayed better cycling performance and rate capability. The Li1.25Mn0.50Ni0.125Co0.125-xCuxO2 sample (with x = 0.05), which delivers an initial discharge capacity of 225.2 mAhg−1 at 0.1 C, was found to have the highest capacity retention with the best cycling performance (207.4 mAhg−1), after 50 cycles. The optimum performance of the doped samples could be related to its lower charge transfer resistance and better structural stability.

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