In this paper, we report on a novel RbVPO₄F fluoride phosphate, which adopts the KTiOPO₄(KTP) type structure and complements the AVPO₄F (A = alkali metal) family of positive electrode (cathode) materials for metal-ion batteries.

For successful development of novel rechargeable batteries, considerable efforts should be devoted to identifying suitable cathode materials that will ensure a proper level of energy output, structural stability, and affordable cost. Among various compounds explored as electrode materials, structural analogues of minerals–natural stable inorganic solids–occupy a prominent place. The largest number of varieties of phosphate minerals occurs in rare metal granite pegmatites, and many of which contain transition metals as essential components. Transition metal phosphates are promising candidates for exploration as cathode materials due to a perfect combination of easily scalable synthesis, moderate-to-high voltage operation, thermal/chemical stability, and environmental safety. However, impurities usually presented in natural objects, and often inappropriate sample morphologies, do not permit the use of minerals as battery electrode materials. Nevertheless, the minerals of different classes, especially phosphates, are considered as prototypes for developing novel materials for battery applications. The crystal chemical peculiarities of the phosphate representatives that are most relevant in this aspect and the electrochemical characteristics of their synthetic analogues are discussed here.

Introducing 4d-elements into a transition metal subsystem activates the diffusion of Na ⁺ ions in an anti-NASICON framework.