Single Potassium-Ion Conducting Polymer Electrolytes: Preparation, Ionic Conductivities, and Electrochemical Stability

Potassium batteries have recently attracted the attention of many researchers. To date, however, most common K-ion electrolytes for potassium secondary batteries are still liquid electrolytes, which may give rise to safety problems. In this work, a new single potassium-ion conducting polymer, potassium poly((trifluoromethyl)sulfonyl)(4-vinylphenyl)amide (KPSTFSA), was synthesized via a facile method. The electrolyte, which is composed of dimethoxyethane (DME)-swollen KPSTFSA with Al2O3 filler electrolyte, has a high ionic conductivity of 6.0 × 10–2 mS cm–1 at 20 °C and high potassium ion transference number of 0.87. On the contrary, traditional KPF6-DME liquid electrolyte only shows an ion transference number of 0.11. The electrochemical stability of the polymer gel electrolyte was systematically studied by using KC8. The decomposition products were characterized to illustrate the degradation mechanism. We conclude that the polystyrene structure of KPSTFSA is the most unstable motif of the molecule and readily reacts with KC8.