Allylimidazolium-Based Poly(ionic liquid) Anodic Binder for Lithium-Ion Batteries with Enhanced Cyclability

An allylimidazolium-based poly(ionic liquid), poly-[vinylbenzylallylimidazolium bis(trifluoromethane)sulfonylimide] (PVBCAImTFSI) was used as a binder for graphite anodes in lithium-ion batteries. The anodes with the synthesized binder exhibited lesser electrolyte degradation and higher lithium-ion diffusion. Electrochemical impedance spectroscopy (EIS) results showed decreased interfacial and diffusion resistance for PVBCAImTFSI-based electrodes after cycling compared to PVDF-based anodes. Dynamic electrochemical impedance spectroscopy (DEIS) results indicated the interfacial resistance of the interface formed for the PVBCAImTFSI-based anodes to be 3 times lesser than the PVDF-based anodes. Suppression of electrolyte degradation and decrease in the intercalation-deintercalation potential and improved Li-ion diffusion coefficient for PVBCAImTFSI-based half-cells were observed from cyclic voltammetry measurements. DFT-based theoretical studies also speculated the suppression in the electrolyte degradation in the case of PVBCAImTFSI binder due to the positioning of its HOMO-LUMO levels. A reversible discharge capacity of 210 mAh/g was obtained for PVBCAImTFSI-based half-cells at 1C rate as compared to the 140 mAh/g obtained for PVDF-based anodic half-cells. After 500 cycles, 95% retention in the discharge capacity was observed. Also, PVBCAImTFSI-based anodes exhibited better charge- discharge stability than the PVDF-based anodes. Suppression of electrolyte degradation, reduction in the interfacial resistance, enhanced wettability, and an optimal SEI layer formed in the case of PVBCAImTFSI-based anodes cumulatively led to an enhanced stability and cyclability during the charge-discharge studies as compared to the commercially employed PVDF-based anodes. Thus, the tuning of the interfacial properties leads to the improvement in the performance of the lithium-ion batteries with PVBCAImTFSI as a binder.