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 Li 3 N on the lithium-metal surface. The resulting SPEs demonstrated excellent ion conductivity, a high Li + transfer number (t Li + = 0.739), and a nanofiber-reinforced interpenetrating framework with a tensile strength of 17.15 MPa. Furthermore, the LiFePO 4 (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.
Polymer electrolytes (PEs) synthesized from an in situ polymerization strategy are considered as promising candidates to improve interfacial compatibility. However, most in situ formed PEs still suffer from problems such as low lithium-ion transference number (tLi+) and insufficient ionic conductivity at room temperature (RT). Herein, a series of copolymer electrolytes (CPEs) consisting of 1,3-dioxolane (DOL) and 1,3,5-trioxane (TXE) monomers are synthesized. Due to the additive of succinonitrile (SN), and the promoted dissociation of lithium salt, the obtained polymer electrolyte (SN-CPE) exhibits an excellent ionic conductivity (4.06 × 10−4 S cm−1) and a high lithium-ion transference number (tLi+ = 0.881) at RT, as well as a high voltage oxidation window of 5.1 V. Thanks to the in situ formed intimate contacted electrode/electrolyte interface, the symmetric Li/Li cell can achieve long-term cycling stability over 1500 h without a short circuit. A LiF-rich organic–inorganic composite layer is formed on both the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) as demonstrated by XPS, TEM, and SEM analyses. Thereafter, the LiFePO4/Li cell has a high capacity retention of 84.1% after 900 cycles at RT, and it can still work effectively at high temperatures (e.g. 80 °C). Furthermore, SN-CPE exhibits excellent electrochemical performance and safety in the LiCoO2/Li cell and LiFePO4/graphite pouch cell, which again supports the promising application of SN-CPE.
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