Partial crystallisation in liquid polymer electrolytes based on co-polymers of ethylene oxide/propylene oxide

Solutions of lithium perchlorate in a low molecular weight ethylene oxide/propylene oxide (EO/PO) co-polymer were studied by differential scanning calorimetry. The pure co-polymer was found to crystallise partially, while addition of the salt impaired crystallisation first by slowing crystal growth then by slowing nucleation. At high salt concentrations (～1·0 molal) no crystallisation occurred. The solvation of Li⁺-ions and the introduction of ‘transient crosslinking’ between cations and anions effectively suppresses the separation of the polymer into microregions of EO and PO. The crystallisation phenomena are relevant to the use of these copolymers as ‘model’ polymer electrolyte systems.