Dielectric Filler‐Induced Hybrid Interphase Enabling Robust Solid‐State Li Metal Batteries at High Areal Capacity

Abstract The fillers in composite solid‐state electrolyte are mainly responsible for the enhancement of the conduction of Li ions but barely regulate the formation of solid electrolyte interphase (SEI). Herein, a unique filler of dielectric NaNbO₃ for the poly(vinylidene fluoride) (PVDF)‐based polymer electrolyte, which is subjected to the exchange of Li⁺ and Na⁺ during cycling, is reported and the substituted Na⁺ is engaged in the construction of a fluorinated Li/Na hybrid SEI with high Young's modulus, facilitating the fast transport of Li⁺ at the interface at a high areal capacity and suppressing the Li dendrite growth. The dielectric NaNbO₃ also induces the generation of high‐dielectric β phase of PVDF to promote the dissociation of Li salt. The Li/Li symmetrical cell exhibits a long‐term dendrite‐free cycling over 600 h at a high areal capacity of 3 mA h cm⁻². The LiNi_0.8Mn_0.1Co_0.1O₂/Li solid‐state cells with NaNbO₃ stably cycle 2200 times at 2 C and that paired with high‐loading cathode (10 mg cm⁻²) can stably cycle for 150 times and exhibit excellent performances at −20 °C. This work provides a novel design principle of fillers undertaking interfacial engineering in composite solid‐state electrolytes for developing the safe and stable solid‐state lithium metal battery.