Revealing the Ion Regulation Effect of Zwitterionic All‐Solid‐State Electrolytes in Lithium Metal Batteries

ABSTRACT Uniform lithium deposition is crucial for the development of lithium metal batteries, but uncontrolled lithium dendrite growth remains a major challenge. While zwitterionic materials show promise in modulating metal‐ion deposition, their underlying mechanisms remain unclear. Here, we synthesize four all‐solid‐state electrolytes with different functional groups, including a tertiary amine‐based zwitterionic polymer electrolyte (ZPE), to probe the distinct functions of its cationic and anionic sites. The “anti‐polyelectrolyte effect” is identified as a key factor governing the unique behavior of ZPE. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) reveals a zwitterion‐mediated, salt‐induced phase separation process that generates “ion‐enrichment pathway”‐like domains in ZPE. This heterogeneous structure gives ZPE a high Li ⁺ transference number (t _Li ⁺ = 0.62) and a Li ₂ O‐rich inner layer in solid electrolyte interphase (SEI), enabling uniform Li ⁺ deposition. As a result, the assembled all‐solid‐state lithium metal batteries exhibit exceptional cycling stability, retaining 95% capacity retention after 500 cycles under bending. The mechanistic insight into ion regulation within ZPE provides guiding principles for next‐generation energy storage devices.