Solid-state lithium batteries using solid polymer electrolytes can improve the safety and energy density of batteries. Smoother lithium-ion channels are necessary for solid polymer electrolytes with high ionic conductivity. The porosity and channel structure of the polymer film affect the transfer of lithium ions. However, their controllable synthesis remains a big challenge. Here, we developed a simple synthesis approach toward wrinkled microporous polymer electrolytes by combining the amphoteric (water solubility and organic solubility) polymer in three polymer blends. The homogeneous blend solution spontaneously wrinkled to vertical fold channels as the solvent evaporated. Two minor polymers, poly(vinyl pyrrolidone) (PVP) and polyetherimide (PEI), formed close stacks, and Janus PVP was dispersed in the poly(vinylidene fluoride) (PVDF) matrix. The interfacial tensions between the three polymers were different, so stress was produced when they solidified. The solvent was evaporated to the top layer of the polymers when the temperature increased. The bottom layer wrinkled owing to the stress during solidification. The evaporation of the solvent generated micropores to form the lithium-ion channel. They helped Li + transference and created a wrinkled microporous PVDF-based polymer electrolyte, which achieved an ionic conductivity of 5.1 × 10 −4 S cm −1 and a lithium-ion transference number of 0.51 at room temperature. Meanwhile, the good flame retardancy and tensile strength of the polymer electrolyte film can improve the safety of the battery. At 0.5C and room temperature, the batteries with a LiFePO 4 cathode and the wrinkled microporous LiTFSI/PEI/PVP/PVDF electrolyte reached a high discharge specific capacity of 122.1 mAh g −1 at the 100th cycle with a Coulombic efficiency of above 99%. The results of tensile and self-extinguishing tests show that the polymer electrolyte film has good safety application prospects.
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 1butyl-1-methyl pyrrolidine bis-trifluoromethyl sulfonimide (Py 14 TFSI) was used as the solid electrolyte. The ionic conductivity of the LiTFSI/Py 14 TFSI/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/Py 14 TFSI/CA/PVDF | LiFePO 4 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 m 2 g −1 . The solid-state lithium−sulfur battery (Li | LiTFSI/ Py 14 TFSI/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 Py 14 TFSI cation and Li 2 S 8 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.
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