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 LiFePO4 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.