Surface Structural Transition Induced by Gradient Polyanion Doping in Li Rich Layered Oxides: Implications for Enhanced Electrochemical Performance
Lithium rich layered oxides (LLOs) exhibit great potential as high capacity cathode materials for lithium ion batteries, but usually suffer from capacity/voltage fade during electrochemical cycling. Herein, a gradient polyanion doping strategy is developed to initiate surface structural transition to form a spinel like surface nanolayer and a polyanion doped layered core material in LLOs simultaneously. This strategy integrates the advantages of both bulk doping and surface modification as the oxygen close packed structure of LLOs is stabilized by polyanion doping, and the LLO cathodes are protected from steady corrosion induced by electrolytes. A LLO material modified with 5 at% phosphate (5%P@LLO) shows a high reversible discharge capacity of 300 mAh g 1 at 0.1 C, excellent cycling stability with a capacity retention of 95% after 100 cycles, and enhanced electrode kinetics. This gradient doping strategy can be further extended to other polyanion doped LLO materials, such as borate and silicate polyanions.