Non-Fluorinated Polymers with Dual Weak-Solvation Sites for High-Voltage Lithium Metal Batteries

Solid-state lithium-metal batteries (LMBs) using polymer electrolytes emerge as highly promising next-generation systems. They offer enhanced safety and high energy density (>400 Wh kg⁻¹) by replacing flammable liquids with flexible, solid-state separators. However, conventional polymers face oxidation susceptibility at high voltages (<4.3 V). While fluorinated polymers extend the electrochemical window and induce robust, LiF-rich interfaces, they are hindered by environmental persistence and high manufacturing costs. To overcome these limitations, we introduce PMDX-Li, a non-fluorinated polymer electrolyte designed via a dual weak-solvation strategy. PMDX-Li achieves a superior 5.3 V window, a high Li⁺ transference number of 0.77, and an ionic conductivity of 0.48 mS cm⁻¹. In high-voltage tests, Ni-rich cathode cells cycle stably for 900 cycles at 4.3 V with 75.6% retention. Remarkably, cells using 4.6 V lithium-rich manganese-based (LRMO) cathodes maintain 80.4% capacity over 120 cycles at a low N/P ratio. Furthermore, an Ah-level pouch cell demonstrates a high energy density of 415 Wh kg⁻¹ and retains over 400 Wh kg⁻¹ after initial cycling. This proves that high-voltage performance is achievable without the environmental or cost penalties of fluorination.