Abstract:

This study prepares the elastic solid polymer electrolyte with polyvinylidene fluoride (PVDF) nanofiber as the base membrane by thermal initiation in-situ polymerization, with Li ditrifluoromethyl sulfonate imide as the Li salt, and butyl acrylate and fluoro-ethylene carbonate (FEC) as the raw materials of the composite solid electrolyte. The introduction of PBA elastomer can enhance the toughness of the composite film and provide buffer space for Li dendrite puncture. The addition of the FEC flame retardant additive can effectively increase the thermal stability and interface stability of the composite film. Furthermore, according to its synergistic effect, problems, such as poor interface contact and low ion conductivity, can be effectively solved. Moreover, the utilization of the functional groups containing C—F in PVDF can facilitate the adsorption of Li ions and the dissociation of Li salts. In addition, the three-dimensional interconnected network structure of PVDF nanofiber membranes can provide a larger specific-surface area, thereby contributing more Li-ion adsorption sites and providing sufficient ordered interconnected Li-ion transfer channels. The introduction of PVDF nanofiber membranes can greatly improve the strength of composite solid-electrolyte membranes, and this is beneficial for inhibiting the growth of Li dendrites. The results show that the ionic conductivity of the elastic, composite solid-electrolyte membrane containing PVDF nanofibers is 3.9 × 10^-4 S/cm at 25 ℃, with tensile strength of 13.8 MPa, thermal decomposition temperature of 200 ℃, and Li⁺ transference number of 0.75. Furthermore, Lithium iron phosphate (LFP)|SPE|Li solid-state battery possesses an initial discharge capacity of 167 mAh/g at 0.1 C, and 122.3 mAh/g after 120 cycles at 0.5 with a capacity retention rate of 95.9%.

Key words: solid polymer electrolyte, nanofiber membrane, elastic matrix, ion transport, solid-state battery