The Effect of Polyanion-Doping on the Structure and Electrochemical Performance of Li-Rich Layered Oxides as Cathode for Lithium-Ion Batteries

Li-rich layered oxides as cathode materials have attracted considerable attention worldwide owing to their high capacity and low cost. However, one of the inherent drawbacks of Li-rich layered oxides is the gradual capacity fading and potential decline during long cycling, caused by the slow structure transition from layered structure to spinel. Therefore, slowing down the intrinsic structure transition is an effective strategy to stabilize the discharge energy density of Li-rich layered oxides. In this work, SiO44− and SO42− polyanions with large radii are introduced into Li-rich layered oxides. The polyanion-doping can slightly change the local environment in the layered structure and enhance the binding energy of cations to anions. In addition, some crystal defects are induced inside the lattice by doping with large polyanions. The further extension of the structure transition from the surface region to the bulk phase can be blocked by the defect structure to a certain extent. Consequently, polyanion-doped oxides present much better cycle performance, including stable discharge capacity, much less potential decline, as well as more stable thermal stability. These results imply that the polyanion doping is an effective method to stabilize energy density of Li-rich layered oxide for advanced lithium ion batteries.