Synergistic effect of MOF fillers and succinonitrile in PEO-based electrolytes for long-cycle all-solid-state Li–CO₂batteries

Li–CO₂ batteries have emerged as promising candidates for next-generation energy storage systems due to their ultrahigh theoretical energy density. However, some safety issues primarily arising from the volatility and leakage of liquid electrolytes within semi-open cell configurations remain a critical challenge. Herein, we develop a novel solid polymer electrolyte (SPE) based on a poly(ethylene oxide) (PEO) matrix, incorporated with zeolitic imidazolate framework-8 (ZIF-8) and succinonitrile (SN). ZIF-8 with ample open metal sites (OMSs) can function as a Lewis acidic center to anchor anions effectively, while SN reduces the crystallinity of the polymer. Benefiting from the synergistic effect between ZIF-8 and SN, the SPE exhibits high ionic conductivity (3.6 × 10⁻⁴ S cm⁻¹ at 30 °C), an enhanced Li⁺ transference number (0.36), and an extended electrochemical window (>5.2 V vs. Li/Li⁺). As a result, the assembled all-solid-state Li–CO₂ battery with the SPE delivers a high discharge capacity of 15 016 mAh g⁻¹ at 100 mA g⁻¹ and demonstrates exceptional cycling stability exceeding 1600 h at 200 mA g⁻¹. This work provides an innovative strategy for developing safe and high-performance Li–CO₂ batteries.