Molecular Design of Difluorinated Polyether Electrolyte for Ultrastable High-Voltage All-Solid-State Lithium Metal Batteries

Solid polymer electrolytes with high interfacial stability are considered among the most promising alternatives for replacing liquid electrolytes in high-voltage lithium (Li) metal batteries. However, their application faces significant challenges, such as random dendrite deposition, interfacial side reactions, and sluggish ion transport, leading to performance degradation and safety hazards. Herein, an inherently stable difluorinated polyether electrolyte (DPE) is proposed that exhibits superior interfacial stability and ion conductivity, enabling the reliable operation of high-voltage all-solid-state Li metal batteries (ASSLMBs). Due to the synergistic electron-withdrawing and ion solvation effects of difluorinated functional groups, DPE shows an improved oxidation voltage of 4.9 V and high Li⁺ conductivity of 2.0 × 10⁻⁴ S cm⁻¹. The generated LiF-rich electrolyte/electrode interphase further improves the stability of DPEs against both Li metal anode and high-voltage cathode. Consequently, the assembled all-solid-state Li||LFP battery retains 73.17% of its capacity after 700 cycles. The high-voltage all-solid-state Li||LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) battery remains stable over 300 cycles with a high capacity retention of 76.02%. Moreover, the high-voltage ASSLMB shows negligible capacity degradation during 3000 bending cycles at a small radius curvature of 4.0 mm. This work provides a feasible strategy for designing antioxidant polymer electrolytes for the stable operation of high-voltage Li metal batteries.