Electrostatic Templating of Transport Networks in Polymer-Based Solid Electrolytes

Polymer-based solid electrolytes offer a promising route to safe, flexible energy-storage devices, but their performance is often limited by sluggish ion transport and unstable electrode interfaces. The polymer-in-salt (PiS) regime, in which the salt content exceeds that of the host polymer, provides a route to enhanced ionic conduction, yet the relationship between salt-rich domain organization and transport behavior is still not fully understood. Here we investigate a polymer-in-salt electrolyte in which excess salt phase-separates into a continuous, ion-rich network within a fluoropolymer host. Spectroscopic and molecular-dynamics analyses reveal how the self-assembled salt-rich domains govern ion coordination and transport, and how electrostatic interactions shape the organization of these domains. We further examine how this microstructure influences the electrode–electrolyte interface during operation. The resulting electrolyte exhibits favorable ion transport and stable interfacial behavior in condensed-phase electrodes over prolonged cycling. This work highlights self-assembled salt-rich domains in polymer-in-salt matrices as a versatile platform for designing multifunctional soft materials with tunable interfacial and transport properties.