Anion Modulation: Enabling Highly Conductive Stable Polymer Electrolytes for Solid‐State Li‐Metal Batteries

Solid polymer electrolytes (SPEs) are promising ionic conductors for developing high-specific-energy solid-state lithium metal batteries. However, developing SPEs with both high ionic conductivity and interfacial compatibility remains a challenge. Here, we propose a design concept of an anion-modulated polymer electrolyte (termed AMPE) for high-voltage Li metal batteries. Specifically, we design the AMPE by incorporating high-voltage-resistant and high charge density units with an anion receptor unit. The high-voltage-resistant and high charge density segments contribute to achieving a decent voltage tolerance of the polymer chains and ensure sufficient carrier ions. The anion receptor, represented by a boron-containing molecule, promotes the generation of free Li⁺ by dissociating anion-cation pairs. More importantly, the strong interaction between the electron-deficient B and the TFSI^- in the matrix promotes the anion reduction to form a stable anion-derived mosaic-like solid electrolyte interphase on the Li-metal anode. As a result, the AMPE exhibits a high ionic conductivity of 3.80×10^-4 S cm^-1 and effectively suppresses lithium dendrites, enabling an all-solid-state Li|AMPE|LiCoO₂ cell to achieve a cycle life of 700 cycles at an operating voltage of 4.40 V. This design concept would inspire efforts to develop high-performance SPEs for high-specific-energy solid-state lithium metal batteries.