Coupled Evolution of Network Structure and Electrolyte Permeation in Butyl-Rubber Sealing Membranes under Thermal-Oxidative Stress

Butyl Rubber (IIR) and Brominated Butyl Rubber (BIIR) are potential candidates for the sealing solutions in the lithium-ion battery area. In this work, the electrolyte resistance of IIR- and BIIR-based membranes under various thermo-oxidative conditions is characterized by the evolution of macromolecular structures, mechanical properties, and fluid transport performance. The changes in mechanical properties of the BIIR are more evident than those of IIR after aging under various conditions. FTIR analysis reveals that -Br groups induce aberrant cross-linking and oxidation of BIIR, generating carbonyl groups at 1710 cm^-1. Transport kinetics indicates that BIIR exhibits a higher diffusion coefficient and permeability coefficient, while IIR maintains a lower uptake ratio and dimensional stability within the range of 45-80 °C. The electrolyte swelling experiment shows that the residual electrolyte crystal powder on the surface of IIR and BIIR samples increases with the temperature. The permeation activation energies (<i>E</i>_P) accounting for the electrolyte resistance are fitted by the Arrhenius equation for IIR and BIIR samples, being in the range of 177.4-208.8 kJ mol^-1 and 170.8-203.0 kJ mol^-1, respectively. Theoretical support can be obtained from this work for the selection of sealing membrane materials and prediction of service life in the lithium-ion battery area under enhanced thermal-oxidative conditions.