Electrostatic Suspension of Lithium Ions in Mg _1‐x Li _x F ₂ /PEO Electrolytes Enables all‐Solid‐S

ABSTRACT

All‐solid‐state lithium metal batteries (SSLMBs) are promising next‐generation energy‐storage devices, but their practical application is hindered by the low ionic conductivity, low Li ⁺ transference number, and poor interfacial stability of solid‐state electrolytes, particularly under near‐room‐temperature conditions. To address these challenges, we developed PEO/LiTFSI‐Mg _1‐x Li _x F ₂ composite electrolytes based on a novel electrostatic suspension strategy. At the filler/polymer interface, Mg _1‐x Li _x F ₂ and PEO generate dynamically balanced yet oppositely directed electrostatic fields, in which Li ⁺ remains in a “suspended” state. The continuous low‐energy transport channels formed by these interfacial suspension sites enable directional and rapid Li ⁺ slip migration along the interface under an external electric field. The optimized composite electrolyte exhibits an ionic conductivity of 0.158 mS cm ⁻¹ and a Li ⁺ transference number of 0.56 at 30°C. Benefiting from the electrostatic suspension effect and the in situ formed LiF‐rich SEI, Li||Li symmetric cells cycle stably for over 2650 h at 0°C. Moreover, SSLMBs with LFP cathodes deliver excellent rate capability and cycling stability, with 98% capacity retention after 300 cycles at 0°C. This work establishes an electrostatic suspension mechanism for the design of polymer electrolytes and provides new insights into high‐performance SSLMBs operating over a wide temperature range.