Cation-Deficient Li_<i>x</i>WO₃ Surface Coating on Ni-Rich Cathodes Materials for Lithium-Ion Batteries

In the pursuit to increase the energy density of lithium-ion batteries (LIBs), considerable efforts have focused on developing high-capacity cathode materials. While Ni-rich (Ni ≥ 80 at. %) layered cathode materials are considered a viable commercial option, surface engineering is crucial for enhancing their cycle performance for successful implementation in commercial LIBs. Various functional materials have been explored for effective surface protection and stabilization to reduce interfacial resistance and enhance the structural stability of Ni-rich cathode materials. In this context, we propose a surface coating with a nonstoichiometric lithium hexagonal tungsten bronze (Li_<i>x</i>WO₃) for Ni-rich cathode materials via simple wet-coating. We demonstrate that the distinctive physicochemical properties of Li_<i>x</i>WO₃, such as its high ionic conductivity (∼10^-6 S cm^-1) and mechanical strength (∼236.0 MPa), are beneficial for enhancing the cycle performance of Ni-rich cathode materials by modulating the interfacial reactions without undesirable loss of reversible capacity. In practice, the Li_<i>x</i>WO₃ surface layer induces a significant reduction in interfacial resistance and effective strain relaxation upon repeated Li⁺ insertion and extraction. Our findings provide insights into the development of highly reliable Ni-rich cathode materials for high-energy LIBs.