Solid-State Polymer Electrolyte Solves the Transfer of Lithium Ions between the Solid–Solid Interface of the Electrode and the Electrolyte in Lithium–Sulfur and Lithium-Ion Batteries

The use of secondary batteries has been on the rise in recent years, especially solid-state batteries. However, security issues have become a major challenge in practical applications. Both lithium-ion batteries and lithium–sulfur batteries have safety problems that need to be solved. Herein, a polymer electrolyte suitable for the two types of batteries was easily synthesized. A polyvinylidene fluoride (PVDF)-based polymer electrolyte with 1-butyl-1-methyl pyrrolidine bis-trifluoromethyl sulfonimide (Py14TFSI) was used as the solid electrolyte. The ionic conductivity of the LiTFSI/Py14TFSI/cellulose acetate (CA)/PVDF polymer electrolyte was 1.45 × 10–4 S cm–1. The electrochemical stability window was 4.95 V. The transference number of the lithium ion was 0.231. The constant-current polarization test results showed that the polarization voltage was only 0.04 V when the current density was 1 mA cm–2. The first discharge specific capacity of the Li | LiTFSI/Py14TFSI/CA/PVDF | LiFePO4 battery was 125.7 mA h g–1 (0.5 C), and the capacity retention rate was 95.22% after 50 cycles at room temperature. A multistage porous conductive carbon (M-PCC) material with micropores and mesopores was applied as the host of the sulfur cathode of lithium–sulfur batteries. The M-PCC material provided a carrier for sulfur and sulfide with a specific surface area of 1132.68 m2 g–1. The solid-state lithium–sulfur battery (Li | LiTFSI/Py14TFSI/CA/PVDF | S@M-PCC) had excellent electrochemical performance. The first discharge specific capacity was 1245.9 mA h g–1 with an average Coulombic efficiency of 97.34%. The energy of Py14TFSI cation and Li2S8 calculated by DFT was 8.8345 eV, which indicated that the polysulfide cannot adsorb onto the polymer electrolyte. XPS was used to measure the elemental composition of the anode–electrolyte interface after charge–discharge cycling. The uniform growth of lithium dendrite was observed by the SEM image of the anode after cycles. The results showed that a solid-state lithium–sulfur battery produced uniform solid electrolyte interface films and completely suppressed the shuttle effect.