Improving the rate performance of LiNi0.5Mn0.5O2 material at high voltages by Cu-doping

A series of LiNi0.5-xCuxMn0.5O2 (0 ≤ x ≤ 0.05) samples were synthesized through a combination of co-precipitation (CP) and solid-state reaction. The synthesized cathode materials were systematically investigated by X-ray diffraction (XRD), Rietveld refinement, inductively coupled plasma (ICP) spectroscopy, X-ray photoelectron spectroscopy (XPS), and charge-discharge tests. The structural measurements indicated that Cu2+ was successfully doped into the structure of the LiNi0.5Mn0.5O2 material. The results of the electrochemical measurements suggest that the electrochemical performances of LiNi0.5Mn0.5O2 can be obviously improved by Cu -doping, and the best doping amount is 1 mol%. Specifically, the capacity retention of a 1 mol% Cu-doped sample is 18% higher than that of pure LiNi0.5Mn0.5O2 in the range of 2.5~4.6 V at 0.2 C. Most importantly, the cycle stability of LiNi0.5Mn0.5O2 at high currents can also be improved by Cu-doping. We found that Cu-doping can lower the Li/Ni cation mixing, enlarge the migration channels of lithium ions, reduce migration resistance, and retard polarization, and in turn, it can improve the electrochemical properties of LiNi0.5Mn0.5O2.