Stabilized Lithium, Manganese-Rich Layered Cathode Materials Enabled by Integrating Co-Doping and Nanocoating.

While lithium, manganese-rich (LMR) layered oxide cathode materials offer high energy density (>900 Wh kg-1) and low cost, LMR is susceptible to continuous capacity and voltage decay from the oxygen migration and side reaction with aqueous electrolyte at high voltage. Herein, the integration of Na/F co-doping (CD) and AlF3 coating on LMR is achieved without the need of complex atomic layer deposition. Akin to pristine and CD samples, CD with 1 wt % AlF3 (CD-1.0 wt %) shows excellent electrochemical performance with the capacity and voltage retentions of 93 and 91% after 150 cycles at 0.5C, respectively, and increased ionic conductivity. Spectroscopic analysis indicates that the coating mainly influences the Co distribution, where Co is enriched on the surface, and partial diffusion of Al3+ ions toward the bulk, leading to a slight change of transition-metal (TM) valence states at the nanometer scale and the formation of a stable Lix(CoAl)Oy phase. Post-cycling analysis reveals that CD-1.0 wt % can alleviate the formation of rock-salt structure and Mn dissolution. Besides, little to no metal segregation is detected for the cycled CD-1.0 wt % sample. This finding presents the first instance to apply co-doping and AlF3 coating as a new strategy to enhance the structural homogeneity and takes another step toward their commercial viability.