Improved cycling and rate performance of Sm-doped LiNi_0.5Mn _1.5O₄ cathode materials for 5 v lithium ion batteries

Spinel powders of Sm-doped LiNi_0.5Sm_xMn _1.5-xO₄ with different Sm contents (x = 0, 0.01, 0.03, and 0.05) have been synthesized by a gelatin-assisted solid-state method. The structural and electrochemical properties of the electrode materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), cyclic voltammetry (CV), charge/discharge testing and electrochemical impedance spectroscopy (EIS). The partial substitution of Sm³⁺ for Mn³⁺ in LiNi_0.5Mn_1.5O ₄ leads to a decrease in the lattice parameter and unit cell volumes, resulting in an improvement of structural stability, enhance the electronic conductivity and diminish the polarization and the charge transfer resistance. As a result, the cyclic ability at 25 C performances and rate performances of LiNi_0.5Mn_1.5O₄ electrode materials are significantly improved with the increasing Sm addition, compared to the pristine LiNi_0.5Mn_1.5O₄, though high doping gives rise to a small reduction of the initial discharge capacity.