Effect of Molecular Weight on Mechanical and Electrochemical Performance of All Solid-State Polymer Electrolyte Membranes

Guided by ternary phase diagrams of polyethylene glycol diacrylate (PEGDA), succinonitrile plasticizer, and LiTFSI salt, completely amorphous solid-state transparent polymer electrolyte membranes (ss-PEM) were fabricated by UV irradiation in the isotropic melt state. Effects of PEGDA molecular weight (700 vs 6000 g/mol) on ss-PEM performance were investigated. These amorphous PEMs have superionic room temperature ionic conductivity of $\sim$10$^{-3}$ S/cm, whereby PEGDA6000-PEM outperforms its PEGDA700 counterpart, which may be ascribed to lower crosslinking density and greater segmental mobility. The longer chain between crosslinked points of PEGDA6000-PEM is responsible for greater extensibility of $\sim$80\% versus $\sim$7\% of PEGDA700-PEM. Besides, both PEMs exhibited thermal stability up to 120 $^{\circ}$C and electrochemical stability versus Li$^{+}$/Li up to 4.7V. LiFePO$_{4}$/PEM/Li and Li$_{4}$Ti$_{5}$O$_{12}$ /PEM/Li half-cells exhibited stable cyclic behavior up to 50 cycles tested with a capacity of $\sim$140mAh/g, suggesting that LiFePO$_{4}$/PEM/Li$_{4}$Ti$_{5}$O$_{12}$ may be a promising full-cell for all solid-state lithium battery.