Na/W co-doping enhances the electrochemical performance of Li-rich Mn-based cathode through improved electronic conductivity and promoted cationic migration

Abstract

The study aimed to improve the performance of a cathode material (Li1.16Na0.01Mn0.5Ni0.15Co0.15Al0.025W0.01O2) by co-doping with Na and W. The X-ray diffraction and scanning electron microscopy results indicate that both Na+ and W6+ cations are introduced into the lattice, and further investigation with scanning transmission electron microscopy reveals that Na + occupy the original Li sites while W6+ are placed in the transition metal layer. First principle calculations suggest that the band structure of the cathode material is primarily influenced by the incorporation of W6+ in the lattice, which decreases the bandgap and increases the electronic conductivity of the cathode powder. The Rietveld refinements suggest that the introduction of Na+ increases the thickness of the Li slab, thereby promoting the diffusion of Li+ within the layer. Based on the synergistic effect of Na and W co-doping, the electrochemical performance of LNCMA-Na/W cathode is significantly improved. The sample LNCMA displays an initial capacity of 277.7 mAh·g−1 at 0.1C and a capacity retention of 86.3 % after 100 cycles at 0.5C. By comparison, the initial capacity of sample LNCMA-Na/W increases to 326 mAh·g−1 at 0.1C, and the capacity retention reaches 93.4 % after 100 cycles at 0.5C, LNCMA-Na/W cathode exhibits a higher specific capacity of 167.3 mAh·g−1 at 5C compared to the undoped cathode (110.8 mAh·g−1).