Finite elastic-viscoplastic deformation behaviour of PEO-based solid polymer electrolyte: Experimental investigation and constitutive modelling

Polyethene oxide (PEO) has emerged as a preferred candidate for solid electrolytes due to its excellent solubility towards lithium salts, stable chemical properties, high flexibility, and low cost. However, the poor knowledge of the mechanical behaviours of PEO electrolytes leads to the road facing vast challenges in developing all-solid-state lithium batteries. In this study, we conducted the uniaxial tensile tests on PEO-LiTFSI films at 20–40 °C, and the strain rate ranges from 0.001 s−1 to 0.01 s−1 while investigating the potential effect mechanisms. Based on a rheological scheme of semi-crystalline polymers, we developed a new constitutive model for simulating the stress-strain curves of PEO-based electrolytes. The results indicate that PEO-LiTFSI exhibits the finite viscoelastic-plastic deformation characteristic with a minimal elastic strain range, low elastic modulus and yield strength. Increasing LiTFSI content and temperature can reduce the crystallinity of the PEO, resulting in significant softening of the polymer electrolyte; the opposite is true with raising the strain rate. Notably, the present model can capture the mechanical response of PEO electrolytes across a range of temperatures and strain rates, and the predicted tensile curves align closely with the experimental results. In addition, the simulation reveals that subpar mechanical performance would occur for PEO-LiTFSI under the recommended electrochemical operation conditions (0.05–5 C and 50 °C).