Vanadium phosphate materials cobalt

Further evidence for the catalytic importance of amorphous material comes from experiments carried out with cobalt-doped catalysts. Hutchings et al. (217) found that doping of the catalysts with cobalt improved their performance. Moreover, Sajip et al. (148) found that the cobalt-promoted catalysts are far more disordered than the undoped catalysts. In the doped catalysts, the promoter is dispersed in the amorphous phase, and cobalt is not found in the vanadyl pyrophosphate crystals. It is thought that one of the properties of the cobalt promoter is to stabilize the disordered phase and V -containing phases in the final catalysts, which leads to improved performance. This suggestion implies that the disordered material is the catalytically active vanadium phosphate phase. 

The metal oxides used to make positive electrode materials for lithium-ion batteries commonly include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, vanadium oxide, and various others, such as iron oxides. Positive electrode materials of 5 V and polyanion-type positive electrode materials (so far mainly referring to lithium iron phosphate, LiFeP04) have also been investigated. Among the primary materials for these positive electrode materials, cobalt is the most expensive, followed by nickel and then manganese and vanadium. As a result, the prices of positive electrode materials are basically in line with the market prices of the primary materials. The structures of these positive electrode materials are mainly layered, spinel, and oliven. 

EDX characterisation of the 2 and 5at% Co-doped VPO samples showed similar concentrations of Co in the disordered regions of the platelet to that observed in the lat%Co-doped VPO sample. In the former of the two materials, the excess Co was found to be present as a secondary phase of vanadium doped cobalt phosphate. This suggests that there is a limited solubility of Co in the disordered VPO material and explains why increasing the Co loading does not necessarily lead to improved catalytic performance. 

---