Enhancing the performance of Li-rich oxide cathodes through multifunctional surface engineering

Abstract

The commercial development of lithium-rich manganese-based cathode materials is limited by severe capacity decay, voltage attenuation and poor rate capability. Herein, a multifunctional surface engineering is successfully applied to improve Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ materials by a facile method of solution pretreatment followed by high-temperature thermal treatment. Gradient fluorine doping on the near-surface region is demonstrated to induce the higher ratio of Mn³⁺/Mn⁴⁺, the increasing amounts of oxygen vacancies and the decreasing Li⁺ diffusion energy barrier. Fast-ion-conductivity spinel phase of LiMn₂O₄ is spontaneously formed on the subsurface and the outmost coating layer that consists of Li₃PO₄ and LiF is constructed on the surface. The formed heterogeneous layers could not only facilitate Li ⁺ rapid transport but also effectively stabilize the surficial structure. The optimal sample is demonstrated to exhibit superior cycling stability and rate capability. The capacity retention after 200 cycles at 1 C is improved from 67.7 % to 91.0 % and the specific capacity at 8 C is increased from 81.9 to 140.8 mAh/g. The voltage attenuation is significantly mitigated, decreasing from 2.02 to 1.05 mV per cycle. The encouraging results may promote the practical application of lithium-rich manganese-based cathode materials in high-energy-density lithium-ion batteries.