In situ construction of 3D Li channels high-temperature-resistant polymer electrolyte and Li3N-rich interface enabling stable solid-state Li metal battery

Abstract

High safety, high ion conductivity, and stable interface contacts are of significant importance for the application of solid-state electrolytes (SSEs) in solid-state lithium metal batteries (SSLMBs). In this study, SSEs with high ion conductivity and safety were constructed by in-situ polymerization of poly butyl acrylate (PBA) based electrolytes in the three-dimensional (3D) pores of a polyvinylidene fluoride (PVDF) nanofiber membrane, and embedded with ion conductor succinonitrile (SN), fluorinated ethylene carbonate (FEC), and imidazolium-based ionic liquid (IL). The test results and microscopic structural analysis indicate that SN is uniformly dispersed in PVDF, effectively reducing the crystallinity of solid polymer electrolytes (SPEs) and constructing a 3D interconnected lithium-ion conduction network. Consequently, an ion conductivity of 4.89 mS cm−1 was achieved at 25°C. Meanwhile, density functional theory (DFT) calculations demonstrated that imidazolium-based ionic liquid can adjust the dissolution characteristics of Li+ through weak interactions with the polymer framework and strong coordination with TFSI-. X-ray photoelectron spectroscopy (XPS) characterization revealed that the imidazolium-based ionic liquid can form a stable solid electrolyte interface enriched with Li3N on the lithium-metal surface. The resulting SPEs demonstrated excellent ion conductivity, a high Li+ transfer number (tLi+ = 0.739), and a nanofiber-reinforced interpenetrating framework with a tensile strength of 17.15 MPa. Furthermore, the LiFePO4 (LFP)||Li battery equipped with PBA-PVDF-SN (modified with IL) exhibited excellent electrochemical performance at room temperature with a capacity retention of 87.4 % after 800 cycles at 0.5C.