Single-Ion Polymer-in-Salt Electrolytes Enabling Percolating Ionic Nanoaggregates for Ambient-Temperature Solid-State Batteries

Solid polymer electrolytes (SPEs) with high ion conduction and interfacial stability are crucial for advancing high-performance solid-state batteries. While tuning electrolytes with weak solvation structures shows promise in enhancing interfacial stability, it remains challenging to concurrently achieve high Li⁺ conductivity. Herein, we introduce a single-ion polymer-in-salt (SIP-in-salt) electrolyte, which not only provides additional charge carriers and enhanced salt compatibility via an ionic polymer backbone but also forms nanometric percolating ionic aggregates (p-AGGs) at high salt concentrations. Unlike state-of-the-art weak solvation structures, p-AGGs are found to be homogeneous, interconnected, and possess enhanced Li⁺-anion dissociation, allowing structural diffusion over reduced distances and continuous Li⁺ transport pathways. The SIP-in-salt electrolyte enables a 100-fold improvement in Li⁺ conductivity compared to traditional polymer-in-salt electrolytes, lowering the operational temperature of SPE-based solid-state batteries to 25 °C. This work demonstrates a promising strategy for advancing SPEs by tuning ionic solvation structures, paving the way for next-generation high-performance batteries.