Effect of thermal pre-compressing on ionic conductivity and mechanical properties of PEO-based solid-state electrolytes

Polyethylene oxide (PEO)-based solid polymer electrolytes are regarded as promising electrolyte materials because of their safety and flexibility. However, low ionic conductivity at ambient temperature and poor mechanical properties have been a hindrance to its development. In this work, we thermally compressed the PEO-based electrolytes and explored the ionic conductivity, mechanical performance, free volume, and thermal properties of the electrolyte under different thermal pre-compressing strains (TPC-strains). The results show that TPC-strain can significantly improve the ionic conductivity, in-plane strength, stiffness, and cell specific capacity as well as the mechanical integrity of solid polymer electrolytes within the battery environment. However, it also results in a reduction in the modulus and stiffness of the SPEs in the through-plane. In particular, applying a TPC-strain of 10%–20% to the SPEs by thermal compressing may be a suitable option, which can increase the ionic conductivity of the through-plane to a factor of 3.4 compared with the uncompressed electrolyte, and increase the in-plane strength by up to 141%, resulting in better mechanical integrity during charging/discharging processes. At the same time, the compression modulus can be maintained at 80% or higher.