Boron Surface Treatment of Li7La3Zr2O12 Enabling Solid Composite Electrolytes for Li‐Metal Battery Applications

Abstract Despite being promoted as a superior Li‐ion conductor, lithium lanthanum zirconium oxide (LLZO) still suffers from a number of shortcomings when employed as an active ceramic filler in composite polymer–ceramic solid electrolytes for rechargeable all‐solid‐state lithium metal batteries. One of the main limitations is the detrimental presence of Li 2 CO 3 on the surface of LLZO particles, restricting Li‐ion transport at the polymer–ceramic interfaces. In this work, a facile way to improve this interface is presented, by purposely engineering the LLZO particle surfaces for a better compatibility with a PEO:LiTFSI solid polymer electrolyte matrix. It is shown that a surface treatment based on immersing LLZO particles in a boric acid solution can improve the LLZO surface chemistry, resulting in an enhancement in the ionic conductivity and cation transference number of the CPE with 20 wt % of boron‐treated LLZO particles compared to the analogous CPE with non‐treated LLZO. Ultimately, an improved cycling performance and stability in Li//LiFePO 4 cells was also demonstrated for the modified material.