Anisotropic Mechanical Responses of Poly(Ethylene Oxide)‐Based Lithium Ions Containing Solid Polymer Electrolytes

Development of mechanically deformable solid state devices is receiving tremendous attention, and high ionic conductivity solid polymer electrolytes (SPEs) are highly sought after for their development. The process history-induced polymer alignment anisotropy can lead to anisotropic conductivity to the SPEs. Here, a Li ion SPE membrane developed using poly(ethylene oxide) (PEO) and LiClO4 is demonstrated for its microstructure variations while applying external stress and the corresponding variations in the ionic conductivity are also calculated. The microstructural evolution shows that larger strain values induce large dislocations in the crystallites of PEO leading to the formation of larger amorphous regions which soften the matrix. The anisotropic mechanical responses are observed while applying cyclic strain to thicker SPEs, where the compressive measurements show softening of the matrix while tensile measurements harden the matrix. The ionic conductivities of the softened matrix are found to be enhanced while those of toughened matrix are found to be decreased. This detailed mechanical analysis along with the in situ ionic conductivity studies of PEO-based Li ion SPE show that along with the thermal history of the polymers, process history and the anisotropic mechanical responses of the polymers also need to be considered while developing SPEs for flexible devices.