Improved Electrochemical Performance of W6+-Doped Li-Rich Cathode Li1.17Mn0.51Ni0.15Co0.15Al0.025O2: Combined Results from the Reduced Residual Li2MnO3 Phase and Promoted Li Intercalation

Li-rich Mn-based cathode material suffers from severe capacity decay, voltage attenuation, and low initial coulombic efficiency, which hinder its commercialization in Li secondary batteries. In our previous work, Li1.17Mn0.51Ni0.15Co0.15Al0.025O2 (LNCMA-O) synthesized in an oxygen atmosphere presented an improved electrochemical performance due to the reduced amount of the unfavorable Li2MnO3 phase. In this work, 1 wt % W-doped Li1.17Mn0.5Ni0.15Co0.15Al0.025W0.01O2 (LNCMA-W) is synthesized to further facilitate the electrochemical performance. The W-doped cathode exhibits an excellent specific capacity of 247.3 mAh g–1 at 0.5C, with a further facilitated coulombic efficiency of 76.5% at the first cycle and an outstanding rate performance of 150.1 mAh g–1 at 5C. Such significant improvements can be attributed to the following points: (1) W6+ doping reduces the amount of residual Li2MnO3 C2/m phase in the cathode, thereby inhibiting the oxygen loss caused by Li2MnO3 activation and decreasing the irreversible capacity at the first cycle so that the initial coulombic efficiency of the material is improved. (2) The incorporation of W6+ increases the amount of LiMO2 R3m solid solution, which can effectively increase the amount of reversible Li+ and improve the specific capacity of the material. (3) The stronger W–O bond can facilitate the stability of the crystal structure and suppress the volume change during the redox process, which further leads to an enhanced capacity retention. (4) The suppressed Li/Ni mixing and increased interplanar thickness of the Li layer after W6+ doping causes an improved diffusion coefficient of Li+, so that the rate performance of the cathode is significantly improved. In summary, a prospective approach for improving the electrochemical performance discovered in this work offers an instructive significance to Li-rich Mn-based cathode materials.