Modification Strategy for Constructing Li Gradient Combined with Spinel Phase Coating on Li-Rich Mn-Based Materials

Li-rich layered oxides (LLOs) are considered as the cathode materials for the next generation of lithium-ion batteries because of their high specific capacity. However, due to the structural rearrangement in the charging and discharging process, the initial Coulombic efficiency (ICE) is low and accompanied by serious voltage attenuation and bad cycle performance. In this work, the Li-gradient layer on the surface of the rod-like LLOs is constructed by the treatment of (NH4)2SiF6 under high temperature and subsequent washing. XRD, HRTEM, and Raman spectra verify the existence of the spinel phase of Li1–xMn2O4 on the surface of LLOs by the modification. The results of electrochemical measurements show that the modified LLOs exhibit a higher ICE of 87% with an excellent cycling retention of 90.4% (after 100 cycles at 1 C). These improvements on the electrochemical performance are caused by the high Li+ diffusion and improved the redox reversibility of oxygen ions on the LLOs with the unique structure of the Li-gradient and spinel coating layer on the surface.