Nucleophilic cleavage of C-F bonds by Brønsted base for rapid synthesis of fluorophosphate materials.

Abstract

Fluorochemicals are a rapidly expanding class of materials used in a variety of fields including pharmaceuticals, metallurgy, agrochemicals, refrigerants, and in particular, alkali metal ion batteries. However, achieving one-step synthesis of pure fluorophosphate compounds in a well-controlled manner remains a formidable challenge due to the volatilization of fluorine during the heat treatment process. One feasible method is to cleave the C-F bond in polytetrafluoroethylene (PTFE) during synthesis to create a fluorine-rich atmosphere and strongly reducing environment. However, the inert nature of the C-F bond in PTFE presents a significant obstacle, as it is the strongest single bond in organic compounds. To address this predicament, we propose a fluorine-compensating strategy that involves cleavage of the C-F bonds by nucleophilic S_N2-type reactions of Brønsted base (ammonia) enabling fluorine compensation. The decomposed products (NH₂· and C·) also result in the formation of micropores (via NH₃ escape) and in-situ carbon coating (via C· polymerization). The resultant cathode delivers a superior potassium storage capability including high rate performance and capacity retention. This contribution not only overcomes the obstacles associated with the inert C-F bond in fluororesin, but also represents a significant step forward in the development of fluorine-containing compounds.