ИСТИНА

In the pursuit of low-cost, eco-friendly and chemically stable cathode materials, a huge variety of candidates was thoroughly inspected starting from layered oxides to complex polyanion and mixed anion compounds. At the same time the crystal structure of the cathodes have evolved from close packages into much more sophisticated arrangements, which opened up opportunities to tune the electrochemical properties of the resulting electrode materials. Fluoride phosphates based cathode materials with AxMPO4F and general formula (x = 1, 2; A – alkali metal; M – 3d transition metal)1,2,3 are in focus due to the several advantages arising from the combination of phosphate and fluoride anion moieties as well as the richer structural diversity. The phosphate group is responsible for a structural, chemical and thermal stability; fluoride anion anticipates a better kinetics of the mobile ion and brings about an increase of the working potential. Within the scope of this work we investigated mixed (Li,Na)2Co1-xMxPO4F (M = Mn, Fe) and AVPO4F fluoride-phosphates as cathode materials for Li-ion batteries and found two new polymorphs crystallizing in the orthorhombic system with quasi-2D and 3D structures respectively.