Fluorophosphate compounds are an important class of cathode materials; however, the one-step synthesis of phase-pure fluorophosphate compounds in a well-controlled manner remains challenging owing to the facile volatilization of fluorine during heat treatment. Herein, the rapid, facile, and scalable preparation of phase-pure fluorophosphates (e.g. KVPOF) was successfully realized via a one-step solid-state reaction through the addition of PVDF, which served as an effective fluorine-compensating, vanadium-reducing, and in situ carbon-coating agent. In-depth mechanistic study showed that carbene (:CH) generated upon PVDF decomposition could be easily recombined to form a ˙CH(CH)CH˙ alkyl biradical, and both were able to catalyze C-F bond breakage in fluorocarbon gases (CF) and therefore plays a pivotal role in promoting the formation of phase-pure fluorophosphate. The resultant cathode enabled a superior potassium-storage capability, including high specific capacity, excellent rate capability, and good cycling stability. The generality of the as-proposed synthetic strategy was also validated through the successful preparation of other fluorophosphate compounds.