ИСТИНА

In our group a novel series of vanadium-based AVPO4F (A = Li, K, Rb) cathode materials adopting the KTP-type structure was designed and synthesized using various soft-chemistry approaches including hydrothermal technique and freeze-drying. The peculiarities of the KTP-type “VPO4F” framework enabled excellent rate capability demonstrated in Li cells. The material exhibited remarkable capacity retention maintaining more than 75% of the initial specific capacity in Li-ion cells at 40C and an average potential of 4.0 V vs Li/Li+ with maximal theoretical energy density of more than 650 mWh/g. The materials also offer a reversible intercalation of Na+, K+ and even Rb+ ions preserving the host structure. Both electrochemical behaviour and solid-state transport were found quite different for Li+, Na+, K+ and Rb+ ions. The alkali ion diffusion coefficients measured by PITT were the lowest for Li+ (10-12 – 10-14 cm2/s) and highest for K+ (10-11 – 10-12 cm2/s). Moreover, the full de/intercalation of K+ in KVPO4F occurs at the highest potentials comparing to Li+, Na+ and Rb+ exceeding 4.6 V vs K/K+, which defines KVPO4F as the most high-voltage cathode material for K-ion batteries investigated so far. The possibility to de/intercalate four types of alkali ions proves the versatility of the “VPO4F” framework and opens up new opportunities in designing polyanion-based cathodes for alternative metal-ion batteries. In this report we will focus on our recent activities on KTP-type fluoride-phosphates considered as promising candidates for Na and K-ion rechargeable batteries with special attention to the structure-property relationships.