Homogeneous and Fast Ion Conduction of PEO‐Based Solid‐State Electrolyte at Low Temperature

Abstract Poly(ethylene oxide) (PEO)‐based electrolytes are promising for all‐solid‐state batteries but can only be used above room temperature due to the high‐degree crystallization of PEO and the intimate affinity between ethylene oxide (EO) chains and lithium ions. Here, a homogeneous‐inspired design of PEO‐based solid‐state electrolytes with fast ion conduction is proposed. The homogeneous PEO‐based solid‐state electrolyte with an adjusted succinonitrile (SN) and PEO molar ratio simultaneously suppresses the PEO crystallization and mitigates the affinity between EO and Li + . By adjusting the molar ratio of SN to PEO (SN:EO ≈ 1:4), channels providing fast Li + transport are formed within the homogeneous solid‐state polymer electrolyte, which increases the ionic conductivity by 100 times and enables their application at a low temperature (0–25 °C), together with the uniform lithium deposition. This modified PEO‐based electrolyte also enables a LiFePO 4 cathode to achieve a superior Coulombic efficiency (>99%) and have a long life (>750 cycles) at room temperature. Moreover, even at a low temperature of 0 °C, 82% of its room‐temperature capacity remains, demonstrating the great potential of this electrolyte for practical solid‐state lithium battery applications.