Solid acrylonitrile-based copolymer electrolytes and their potential application in solid state battery

Two solid acrylonitrile-based polymer electrolytes (SPE1-21 and SPE2-31) were investigated. SPE1-21 comprises the acrylonitrile/2-ethylhexyl acrylate copolymer and 33 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In contrast, SPE2-31 comprises the AN/vinyl acetate (VAC) copolymer and 25 wt% LiTFSI. SPEP1-21 shows inferior ionic conductivity and transference number to SPE2-31. However, SPE1-21 has higher oxidation potential and better interfacial stability against Li metal than SPE2-31. These SPEs were used as the separator in solid-state batteries with LiFePO4 as the cathode and Li foil as the anode. For SPE1-21 cell, the charge/discharge cycling remained relatively stable up to 223rd cycle, at which point the coulombic efficiency (CE) drops to 95.0% and the corresponding capacity retention is 98.1%. On the other hand, SPE2-31 cell exhibited very poor cycling performance; the CE rapidly dropped to 55.5% at 10th cycle. This indicates that undesired side reaction occurs during the cycling process, which is attributed to the oxidation reaction of acetate group of the VAC unit in the AN-VAC copolymer.

Automated summary

Two solid acrylonitrile-based polymer electrolytes (SPE1-21 and SPE2-31) were compared in this study. It was found that SPE1-21 had lower ionic conductivity and transference number compared to SPE2-31, but had higher oxidation potential and better interfacial stability against Li metal. Additionally, SPE1-21 exhibited better cycling performance and capacity retention.