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

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 Li₂O-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.