Electrochemical Performance of Highly Ion-Conductive Polymer Electrolyte Membranes Based on Polyoxide-tetrathiol Conetwork for Lithium Metal Batteries

A copolymer network consisting of poly(trimethylolpropane ethoxylate triacrylate) oligomer (TMPETA) and pentaerythritol tetrakis (3-mercaptopropionate) cross-linker (PETMP, tetrathiol) was photo-cross-linked via “thiol–ene click” reaction. The conetwork (TMPETA-co-PETMP) exhibited a single glass transition temperature (Tg) shifting systematically to a lower temperature with increasing content of tetrathiol cross-linker from −22 °C at 100:0 to −36 °C at the composition of 60:40 ratio by weight %. Polymer electrolyte membranes (PEMs) containing various contents of lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt and succinonitrile (SCN) plasticizer were investigated in order to obtain optimum PEM formulation having high ionic conductivity and good mechanical support for use in lithium metal batteries. The optimized PEM composition of (70:30) 20/40/40 (TMPETA-co-PETMP)/SCN/LiTFSI exhibited high room-temperature ionic conductivity of ∼1.8 × 10–3 S/cm, good mechanical performance, and high Li+ transference number of ∼0.76 suggestive of domination by the lithium cation transport, which would alleviate some drawbacks encountered in conventional liquid electrolyte systems. Moreover, the PEM was found to be electrochemically stable up to 5.3 V with excellent cyclability. The specific capacity of 147 mA h g–1 was obtained at 0.1 C from the Li-PEM-LFP cell, exhibiting excellent capacity retention of about 94%. Given the excellent ionic conductivity at ambient, good mechanical integrity, thermal stability, and outstanding electrochemical performance at various operating conditions, the present all-solid-state PEM is an excellent candidate for potential application in high-energy lithium metal batteries.