Physical-Chemical and Structural Properties of V₂O₅, Synthesized by Electrolysis from Metavanadate Solution and Features of Its Electrochemical Performance in Redox Reactions with Lithium

CZU 544.643-621.157

DOI  https://doi.org/10.5281/zenodo.3369714

V₂O₅ oxide was obtained in thin layers on an anode of 18Н12Х9Т stainless steel from an aqueous solution of ammonium metavanadate followed by treatment at 300 and 500°C. It was investigated in the redox reaction with lithium to be compared with analogues obtained from oxovanadium sulfate solution to be used in a lithium thin layer battery. The physical-chemical and structural properties, the morphology of the surface of the deposits were determined using X-ray phase analysis, IR absorption spectroscopy, thermoanalytical study, and atomic force microscopy. Large-block deposits with a smooth surface structure precipitated from a solution of NH₄VO₃ differ significantly from the deposits with a branched surface structure obtained from a solution of oxovanadium sulfate. The hydrated electrolysis product VO₂ nV₂O₅(n = 1–3) with the presence of NH₄⁺ after high-temperature treatment is transformed into orthorhombic V₂O₅. The discharge characteristics of V₂O₅ in the redox reaction with lithium in a liquid-phase electrolyte 1 mole/l LiClO₄, propylene carbonate, dimethoxyethane differ from those in a polymer electrolyte with a polyvinyl chloride matrix including propylene carbonate, LiN(CF₃SO₂)₂. The discharge capacity of V₂O₅ obtained from the metavanadate solution at the treatment T = 300 С (7 h) decreases in a liquid-phase electrolyte from 250 mAh/g to 110 mAh/g in the 40th cycle, while in a polymer electrolyte - from 210 mAh/g to 100 mAh/g at an earlier cycling stage. The reversibility of the electrode process is lost at the stage of phase transition (δ-γ) in V₂O₅ near a voltage of 2.3 V. Annealing the deposits at 500°С increases the discharge capacity of V₂O₅ obtained from a solution of oxovanadium sulfate. The large-block structure of the deposits obtained from the metavanadate electrolyte does not allow increasing their heating to 500°С due to the loss of adhesion of the deposits to the metal base. The branched structure of the deposits obtained from the solution of oxovanadium sulfate promotes their better adhesion to the base than a large-block structure of the deposits obtained from the metavanadate solution. For the usage of V₂O₅ obtained from the metavanadate solution in the lithium battery system, it is necessary to find ways to modify the morphology of the deposit surface. V₂O₅ deposition in the presence of Co²⁺ can contribute to the fragmentation of the block structure.

Keywords: V₂O₅ oxide, electrolysis synthesis, metavanadate electrolyte, Li-accumulator, discharge capacity, oxovanadium sulfate.