A Zwitterion Coupled All-Solid-State Single Ion Conducting Polymer Electrolyte via Photoinitiated Thiol-Ene Click Polymerization

Abstract

The all-solid-state single ion conducting polymer electrolyte has a bottleneck in ionic conductivity even though it can prevent concentration polarization. Here, lithium 3,3′-(diallylammonio)bis(propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAA(PSI)₂) with a symmetrical “one positive, two negative” structure and unsaturated double bonds for propagation, is synthesized. LiDAA(PSI)₂ is copolymerized with 1,2-ethanedithiol and poly(ethylene glycol) diacrylate via photoinitiated thiol-ene click polymerization and forms a random copolymer, SPZ for short. For comparison, lithium 3-(diallylamino)propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAAPSI) and corresponding copolymer SP are synthesized. The ⁷Li resonance peak position of LiDAA(PSI)₂ shifts to a low-field compared to that of LiDAAPSI, indicating a weaker electrostatic attraction. The symmetrical “one positive, two negative” structure is responsible for the low-field shift, taking effect of charge conjugation. Unsurprisingly, the ionic conductivity of SPZ is 1.69e-5 S cm⁻¹ at 60 °C, which is 1.9 times that of SP. Lithium electroplating and stripping at 0.0125 mA cm⁻²@0.05 mAh cm⁻² at 60 °C are performed. An all-solid-state single ion conducting lithium metal secondary battery is demonstrated. Zwitterion coupled LiDAA(PSI)₂ possesses a symmetrical “one positive, two negative” structure, charge conjugation to weaken electrostatic interaction, and unsaturated double bonds for propagation, which inspires the design and synthesis of single ion conducting polymer electrolytes with zwitterion effect.