Salt‐Segregated Solid Polymer Electrolytes for High‐Rate Solid‐State Lithium Batteries

Abstract Solid‐polymer electrolytes (SPEs) demonstrate great potential for solid‐state lithium batteries (SSLBs), however, interfacial instability and sluggish ion transport at the interface critically hinder their high‐rate capability and long‐term stability. Here, a novel salt‐segregation methodology with spatial salt grade for SPEs is introduced. This approach leverages the differential solubility of lithium salts and PVDF matrix in a commercially available fluoroethylene carbonate during fabrication, which drives the formation of an ion‐enriched surface layer. The strategy simultaneously enhances interfacial and bulk ionic conductivity while effectively mitigating parasitic reactions. These advancements optimize Li⁺ flux at the lithium metal interphase, promoting a spherical Li growth with minimized surface area and leading to dense lithium deposition. Consequently, the engineered SPE achieves a remarkable cycling of 500 h in Li||Li cells at 2 mA cm⁻². Solid‐state Li||LiFePO₄ cells exhibit a record stability for 20 000 cycles at 1.12 A g⁻¹ (2 mg cm⁻² LiFePO₄ cathode), and a high capacity of 147 mAh g⁻¹ over 300 cycles at 0.84 mA cm⁻² under a high‐loading 2 mAh cm⁻² cathode. The strategy addresses interfacial limitations in SPEs and further introduces a paradigm shift by emphasizing the critical role of spatial salt‐graded engineering at the surface over uniform ion distribution for stabilizing high‐rate SSLBs.