Zwitterion‐Induced Interfacial‐Potential Regulation Stabilizes Micron‐Sized Silicon Anodes in Quasi‐Solid‐State Lithium‐Ion Batteries

Micron-sized silicon (μ-Si) is an attractive anode material for high-energy lithium-ion batteries owing to its high tap density, large specific capacity, and compatibility with scalable manufacturing. Its practical deployment, however, is impeded by an uncontrolled interfacial-potential landscape that drives heterogeneous Li⁺ transport, spatially non-uniform reduction and recurrent solid-electrolyte interphase (SEI) rupture, thereby accelerating capacity fade. Here, we report a zwitterion-modified quasi-solid-state electrolyte that regulates the interfacial-potential distribution at the μ-Si/electrolyte interface. In situ polymerization of 3-(1-vinyl-3-imidazolyl)propanesulfonate (VIPS) within a conventional carbonate electrolyte yields PVIPSE, whose spatially proximate imidazolium and sulfonate groups stabilize μ-Si anodes through synergistic effects: (i) electrostatic screening that equalizes potential across the inner/outer Helmholtz planes and homogenizes Li⁺ flux; (ii) Li⁺-sulfonate coordination that restructures the solvation environment and biases reduction pathways toward an inorganic-rich, electronically insulating SEI; and (iii) selective partitioning of fluoroethylene carbonate at the interface to promote uniform LiF-rich passivation. Scanning electrochemical microscopy directly visualizes the reduced interfacial-potential heterogeneity and improved SEI uniformity. As a result, the quasi-solid-state PVIPSE enables stable long-term cycling of μ-Si anodes, establishing interfacial-potential regulation as a distinct and effective design principle, orthogonal to solvation engineering and mechanical reinforcement, for stabilizing high-capacity alloying anodes.