Rational design of a double-layer Janus solid electrolyte for high voltage lithium metal battery

Interfacial side reaction is a major problem faced by solid state electrolyte (SSE), especially the oxidation reaction between high-voltage cathode materials and SSE. Herein, a double-layer PVCA-ETPTA|LAGP-PPC Janus solid electrolyte (JSE) with ultra-high interfacial stability is successfully designed. An oxidation tolerant cross-linked poly (Vinylene Carbonate) (PVCA)-Ethoxylated trimethylolpropane triacrylate (ETPTA) electrolyte is used on the cathode side, resulting in a stable interfacial layer under high-voltage. To enhance the stability of SSE|Li interface, a protective Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP)-Poly (propylene carbonate) (PPC) layer is adhered to Li metal. The obtained dual-layer structure shows great thermal stability with an electrochemical stable window of 0–4.5 V. Moreover, the PVCA-ETPTA layer fabricated by in-situ polymerization helps building an integrated structure, which can significantly reduce the interfacial resistance. The ionic conductivity of LP|PE can reach 1.2 × 10⁻⁴ S cm⁻¹ at 55 °C. As a consequence, the assembled NCM622|LP|PE|Li solid state cell shows exceptional electrochemical performance, with 70 % cycle retention for 100 cycles at 0.2 C.