Exploring 1,3-dioxolane polymerization initiated by NOPF6: a universal approach to self-solidifying electrolytes for high-capacity retention potassium batteries†

Abstract

Sustainable development of the energy storage market requires a gradual shift from lithium-ion batteries to other types of devices. While potassium-ion batteries attracted a lot of attention during the last decade, they are still far from real practical implementation, since basically all the cell components are not optimized. In particular, gel polymer electrolytes commonly used in advanced lithium batteries are very rare for their potassium analogs. The cost-effective and technologically very convenient approach to form quasi-solid polymer electrolytes in situ by polymerization of 1,3-dioxolane induced by the electrolyte salt (LiPF₆) is not applicable for potassium batteries since KPF₆ does not initiate the polymerization. Herein, we have addressed this challenge and proposed using NOPF₆ as an additive launching the dioxolane polymerization reaction resulting in electrolyte gelation directly within the cell. The first potassium batteries with a dioxolane-derived gel polymer electrolyte were fabricated and a spectacular enhancement in the battery cyclability upon addition of NOPF₆ has been demonstrated. Furthermore, a thorough investigation of the dioxolane polymerization reaction by GC-MS allowed us to identify a series of key intermediates and by-products and unravel important mechanistic details, such as the oxonium ion stabilization pathway and the nature of the formed terminal groups in the polymer chains. Both newly generated fundamental knowledge and the proposed self-solidifying electrolyte formulation are expected to be particularly valuable for the further development of advanced gel polymer electrolytes for different types of batteries.