Highly conductive solvent-free polymer electrolyte membrane for lithium-ion batteries: Effect of prepolymer molecular weight

• Achieved solvent-free polymer electrolyte membrane with superionic conductivity.
• Ionic conductivity was increased with increasing molecular weight of prepolymer.
• Mechanical toughness of the membrane was also improved.
• High thermal (140 °C) and electrochemical stability (4.8 V/Li/Li+) were achieved.
• The present PEMs are compatible to both LiFePO4 and Li4Ti5O12 electrodes.

The present article demonstrates the effects of molecular weight of network precursor on properties of solid-state polymer electrolyte membrane (PEM) comprised of poly (ethylene glycol) diacrylate (PEGDA) prepolymer, succinonitrile (SCN) plasticizer, and lithium bis(trifluoromethane sulphonyl) imide (LiTFSI) salt using two different PEGDA molecular weights. To provide guidance for crosslinking reaction, ternary phase diagrams of the PEM precursor mixtures were established. Upon photopolymerization within the wide isotropic region, completely amorphous membranes were obtained in several compositions. The PEM having a higher PEGDA molecular weight (i.e., 6000 g/mol) revealed both improved impact strength with an elongation at break of ~80 % and higher ambient temperature ionic conductivity (~1.4×10−3 S cm−1) relative to the low molecular weight counterpart (i.e., 700 g/mol). Both PEMs exhibited excellent electrochemical (4.8 V/Li/Li+) and thermal (140 °C) stabilities. Specific discharge capacities of the PEM containing half-cells using LiFePO4 or Li4Ti5O12 electrodes against lithium electrode reached the level of ~140 mAh g−1 at 0.2 °C, indicating potential applications in all solid-state lithium-ion batteries.