Oxygen vacancies with localized electrons direct a functionalized separator toward dendrite-free and high loading LiFePO4 for lithium metal batteries

The pursuit of high energy density has promoted the development of high-performance lithium metal batteries (LMBs). However, the underestimated but non-negligible dendrites of Li anode have been observed to shorten battery lifespan. Herein, a composite separator (TiO2−x@PP), in which TiO2 with electron-localized oxygen vacancies (TiO2−x) is coated on a commercial PP separator, is fabricated to homogenize lithium ion transport and stabilize the lithium anode interface. With the utilization of TiO2−x@PP separators, the symmetric lithium metal battery displays enhanced cycle stability over 800 h under a high current density of 8 mA cm−2. Moreover, the LMBs assembled with high-loading LiFePO4 (9.24 mg cm−2) deliver a stable cycling performance over 900 cycles at a rate of 0.5 C. Comprehensive theoretical studies based on density functional theory (DFT) further unveil the mechanism. The favorable TiO2−x is beneficial for facilitating fast Li+ migration and impeding anions transfer. In addressing the Li dendrite issues, the use of TiO2−x@PP separator potentially provides a facile and attractive strategy for designing well-performing LMBs, which are expected to meet the application requirements of rechargeable batteries.