Toward practical lithium metal batteries via a solvation structure regulation strategy in in situ polymerized fluorinated gel polymer electrolytes

Abstract

Developing electrolytes that enable stable lithium metal anodes and high-voltage cathodes is critical for next-generation lithium metal batteries (LMBs). In situ polymerized gel polymer electrolytes (GPEs) offer notable advantages in high-energy-density LMBs due to their unique rigid–flexible structure and superior interfacial contact. However, the solvation structure of GPEs remains underexplored, which is crucial as it significantly influences ion transport and interfacial stability. Here, we employ fluorinated polymer backbones, TF, in a high-concentration ether-based liquid electrolyte (HCE) as pseudo-diluents, featuring low Li⁺ desolvation barriers and balanced ion transport via –CF₃ group modulation of Li⁺ solvation structures in a non-coordinating manner. The weak solvation structure of TF + HCE promotes uniform deposition, while facilitating the formation of a robust, inorganic-rich solid electrolyte interphase (SEI)/cathode electrolyte interphase (CEI). Consequently, TF + HCE exhibits high ionic conductivity (4.02 mS cm⁻¹) at 30 °C and supports long-term cycling in Li||Cu cells at 2 mAh cm⁻² with 300 cycles and 1 mAh cm⁻² with 1000 cycles (CE 98.73%). Additionally, when assembled with lean lithium (45 μm) and high areal capacity (2.09 mAh cm⁻²) in Li||NCM811 full cells, it enables stable cycling under high voltage (4.4 V). Notably, over 500 cycles are achieved at high rates (2–3C) with ≥80% capacity retention. Additionally, a high energy density of 465.63 Wh kg⁻¹ is achieved in lithium pouch cells. Importantly, a 2.5 A h Gr||NCM811 pouch demonstrates ∼95% capacity retention over 200 cycles, underscoring the oxidative stability, manufacturability, and practical compatibility of the fluorinated GPE system.