Polyoxometalate Li3PW12O40 and Li3PMo12O40 Electrolytes for High‐energy All‐solid‐state Lithium Batteries

Solid‐state lithium (Li) batteries promise both high energy density and safety while existing solid‐state electrolytes (SSEs) fail to satisfy the rigorous requirements of battery operations. Herein, novel polyoxometalate SSEs, Li₃PW₁₂O₄₀ and Li₃PMo₁₂O₄₀, are synthesized, which exhibit excellent interfacial compatibility with electrodes and chemical stability, overcoming the limitations of conventional SSEs. A high ionic conductivity of 0.89 mS cm⁻¹ and a low activation energy of 0.23 eV are obtained due to the optimized three‐dimensional Li⁺ migration network of Li₃PW₁₂O₄₀. Li₃PW₁₂O₄₀ exhibits a wide window of electrochemical stability that can both accommodate the Li anode and high‐voltage cathodes. As a result, all‐solid‐state Li metal batteries fabricated with Li/Li₃PW₁₂O₄₀/LiNi_0.5Co_0.2Mn_0.3O₂ display a stable cycling up to 100 cycles with a cutoff voltage of 4.35 V and an areal capacity of more than 4 mAh cm⁻², as well as a cost‐competitive SSEs price of $5.68 kg⁻¹. Moreover, Li₃PMo₁₂O₄₀ homologous to Li₃PW₁₂O₄₀ was obtained via isomorphous substitution, which formed a low‐resistance interface with Li₃PW₁₂O₄₀. Applications of Li₃PW₁₂O₄₀ and Li₃PMo₁₂O₄₀ in Li‐air batteries further demonstrate that long cycle life (650 cycles) can be achieved. This strategy provides a facile, low‐cost strategy to construct efficient and scalable solid polyoxometalate electrolytes for high‐energy solid‐state Li metal batteries.