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

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.