Fluoroacetonitrile‑Based Gel Polymer Electrolytes for Fast‑Charging Lithium Metal Batteries

ABSTRACT Gel polymer electrolytes (GPEs) are promising electrolyte candidates for lithium metal batteries (LMBs) due to their favorable interfacial contact and enhanced safety. However, GPE electrolytes suffer from severe interfacial instability against lithium metal anodes (LMAs) and limited lithium‑ion transference number ( t _Li+ ), which significantly restricts the fast‑charging performance of LMBs. Herein, we propose a fast‑charging gel polymer electrolyte (GPE‑FN) using fluoroacetonitrile (FAN) as the solvent, with fluoroethylene carbonate (FEC) and LiNO ₃ as reduction additives. The GPE‑FN electrolyte addresses the interfacial incompatibility issues of FAN in LMBs by forming a stable solid electrolyte interphase (SEI) layer through the reduction of FEC and LiNO ₃ on LMA, which effectively prevents the continuous consumption of FAN. Furthermore, this SEI layer also effectively enhances the interfacial Li ⁺ transport. The results show that the GPE‑FN electrolyte demonstrates a high ionic conductivity (σ) of 1.66 mS cm ⁻¹ and a high t _Li+ of 0.848 at 25°C. Both LiFePO ₄ (LFP)||Li and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811)||Li cells based on the GPE‑FN electrolyte achieve 4100 cycles with 80.3% capacity retention and 800 cycles with 79.5% capacity retention at 5C, respectively, exhibiting excellent fast‑charging performance. Furthermore, full cells incorporating high‑loading cathodes demonstrate stable cycling, highlighting the promising potential of the GPE‑FN electrolyte.