TTE-Mediated Anode/Electrolyte Interface Modification of SN-Plasticized PEO/PVDF-HFP Solid Polymer Electrolyte for Room-Temperature Applications

Abstract

Polyethylene oxide (PEO)-based polymer electrolytes hold promise for application in solid-state lithium metal batteries. However, the high crystallinity of PEO poses a significant challenge to ion transport, particularly limiting its room-temperature performance. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a semi-crystalline polymer with rigid fluorocarbon chains, can provide robust mechanical support to the electrolyte system. Herein, a quasi-solid electrolyte (QSE) was fabricated by using PEO and PVDF-HFP, in which succinonitrile (SN) was introduced as a plasticizer to enhance the electrochemical properties at room temperature. Innovatively, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was employed as a shield layer to prevent direct contact between the Li anode and the prepared SN-modified PEO/PVDF-HFP-QSE, thus forming a stable anode/electrolyte interface. The obtained TTE-P8P2S(12%)-QSE exhibits high room-temperature electrochemical properties, with an ionic conductivity of 4.02 × 10–4 S cm–1, a lithium-ion transport number of 0.47, and a wide electrochemical window of 5.4 V vs. Li+/Li. By interfacial modification, TTE-P8P2S(12%)-QSE can enable long-term cycling of LiCoO2 cathodes and Li anodes, with an initial discharge capacity of 126.9 mAh g–1, and achieve an average capacity of 142.8 mAh g–1 within 100 cycles at room temperature. Characterizations reveal that the incorporation of TTE preserves the structural integrity of the lithium electrodes, promotes efficient utilization of active lithium ions, and tailors the composition and structure of the solid-electrolyte interphase (SEI) on the lithium metal anode, thereby substantially enhancing interfacial stability. This work provides a feasible strategy for building high-energy-density lithium metal batteries for room-temperature applications.