Soft‐Rigid Sandwich‐Structured Hybrid Electrolytes Based on Polymer‐in‐Ceramic Electrolytes for Stable‐Cycle Solid‐State Lithium‐Metal Batteries

Abstract Solid‐state lithium (Li) batteries are regarded as a promising candidate for next‐generation energy storage because of their high capacity and the intrinsic safety of solid‐state electrolytes (SSEs). Building an improved solid‐state battery has two main challenges, namely, to improve the ionic conductivity of solid electrolytes and to reduce interfacial problems. In particular, interfacial issues between SSEs and electrodes are critical factors that affect the performance of SSEs. Accordingly, a soft‐rigid sandwich‐structured hybrid electrolyte, wherein polymer‐in‐ceramic electrolytes (rigid inner structure) are sandwiched in between Celgard separator membranes (soft outer structure), was used to meet the above‐mentioned requirements. Results show that the hybrid electrolyte exhibits high ionic conductivity (4.76×10−4 S cm−1 at room temperature), low interfacial resistance (below 300 Ω for two sides), high thermal stability, and effective inhibition of Li dendrite growth due to its distinct structural advantages. Moreover, the solid‐state LiFePO4||Li battery that used this sandwich‐structured hybrid electrolyte has an initial discharge capacity of 125.8 mAh g−1, a high capacity retention of 94.9 % after 200 cycles, a good rate capability, and excellent Coulombic efficiency (close to 100 % except for the value of the initial cycle, which is 84 %) of 0.2 C at room temperature. Hence, the as‐synthesized sandwich‐structured hybrid electrolyte has great potential for practical application of solid‐state Li‐metal batteries.