Potential‐Gated Polymer Integrates Reversible Ion Transport and Storage for solid‐state Batteries

Abstract The development of practical solid‐state batteries is hindered by their high interfacial resistance and sluggish diffusion properties, primarily due to the heterogeneous interfaces between the solid electrolyte and the electrode. Here, an all‐in‐one polymer electrode‐electrolyte material (P(EO 2 ‐S 3 )) is presented, which covalently integrates ethylene oxide groups for Li + transport and trisulfide linkages for redox‐active sites. This material exhibits favorable ionic conductivity as a solid electrolyte, while its reversible redox activity activates below 2.5 V versus Li⁺/Li, delivering a high reversible capacity of 491.7 mAh g −1 . Leveraging P(EO 2 ‐S 3 ) as both cathode and electrolyte, integrated cells (P(EO 2 ‐S 3 )@CP|P(EO 2 ‐S 3 )|Li) exhibit accelerated electrochemical kinetics while maintaining cycling stability in flexible devices over 20 000 bending cycles. As a redox‐active catholyte of LiFePO 4 , P(EO 2 ‐S 3 ) increases the capacity of the composite cathode to 358.3 mAh g −1 based on LiFePO 4 mass, achieving an electrode energy density of 585.9 Wh kg −1 . This work establishes a new paradigm for multifunctional polymers that integrates ion transport and storage, offering a versatile platform for flexible, high‐energy solid‐state batteries.