Dual doping in transition metal site of polyanionic Na3V2 PO4 x OyFz intercalation cathodes

Abstract

The electronic industry is largely fuelled by lithium-ion batteries (LIBs) owing to their outstanding attributes such as high reversible capacity, high energy density, and prolonged cycle life. There is currently a higher demand for sodium-ion batteries due to the restricted supply of lithium resources and the higher costs related to manufacturing LIBs. Furthermore, because of its easier accessibility, lithium-like electrochemistry, and ecologically friendly characteristics, sodium is seen as the next major energy storage element. However, the larger ionic size and higher mass of sodium compared to lithium restrict the diffusion through the electrolyte which decreases the specific capacity as well as energy density and also hinders the rate performance and cycling stability. The key benefit of sodium, aside from these drawbacks, is that it does not alloy with aluminium, which can be used as current collector for both cathode and anode, increasing the value of sodium batteries in the commercial market. However, sodium-ion batteries are unable to entirely substitute lithium-ion batteries due to the benefits they provide. However, SIBs can be applied to complement LIBs such as, grid-storage applications where energy density and battery size are not primary factors. Cathode materials play a decisive role in the electrochemical performance of alkali-ion batteries since they are the primary source of ions. The development of diverse cathode materials for sodium-ion batteries, such as layered oxides, Prussian blue, and polyanionic materials, is greatly aided by research. Among these, NASICON-type materials which belong to polyanionic cathodes garnered much attention due to their robust 3D network, higher voltage as well as reasonable theoretical capacity. The covalent bonds between the oxygen and transition metal give rise to higher thermal stability for this class of material and also the inductive effect from the polyanionic group results in higher voltage compared to their oxide counterparts. However...