• A novel sandwich-structured solid electrolyte (SSE) integrates a perovskite-type LSZT ceramic core with composite solid polymer electrolyte (CSPE) layers, reducing interfacial resistance and suppressing Li-induced degradation.
• The SSE achieves high ionic conductivity of 8.76 × 10⁻⁵ S·cm⁻¹ at 30°C and 1.13 × 10⁻³ S·cm⁻¹ at 100°C, with a low activation energy of 0.36 eV and electrochemical stability up to 4.58 V vs Li⁺/Li.
• Li | SSE | Li symmetric cells operate stably for 500 h at 0.3 mA·cm⁻² without short circuit, confirming excellent interfacial compatibility and significant suppression of Li dendrite growth.
• An all-solid-state LiFePO₄ | SSE | Li battery delivers an initial discharge capacity of 109.8 mAh·g⁻¹ and retains 118.1 mAh·g⁻¹ after 50 cycles at 0.1C (30°C), demonstrating good cycling performance.