Abstract:

Vanadium redox flow battery (VRFB) is one of the most promising chemical electric source technologies for large scale stationary energy storage. Currently, since a large share of the VRFB costs is attributed to the cost of the electrolyte, vanadium pentoxide was usually chosen as the raw materials of vanadium. However, due to the low solubility of vanadium pentoxide in sulfuric acid, the direct dissolution of vanadium pentoxide in sulfuric acid is unable to prepare an electrolyte with high vanadium concentration. In this study, pentavalent vanadium electrolyte is directly prepared from vanadium pentoxide solid by activating vanadium pentoxide with sulfuric acid at elevated temperatures. The composition, structure, and dissolution processes of the activated solid mixture are analyzed by XRD, Raman, and FT-IR. The results indicate that when the activating temperature is 180°C and the molar ratio of sulfuric acid to vanadium pentoxide of 4, the dissolution performance of vanadium pentoxide after activation is greatly enhanced, and its dissolution mass percentage is up to 98.5%. And the vanadium ion concentration can be dissolved successfully up to 3 mol·L^-1. After activation, sulfuric acid and vanadium pentoxide form V₂O₃(SO₄)₂. The original structure of vanadium pentoxide is changed and the solubility of the substance is increased. At the same time, it is found that V(Ⅴ) ions with high concentration will react with \mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}-} to produce \mathrm{V}{\mathrm{O}}_{\mathrm{2}}\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{-}, while \mathrm{V}{\mathrm{O}}_{\mathrm{2}}^{+} in solution would also polymerize to form polymers such as {\mathrm{V}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{4}+} and {\mathrm{V}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}+}.

Key words: vanadium pentoxide, positive electrolyte, vanadium redox flow battery, solubility, activation at elevated temperature

摘要：

全钒液流电池是大规模储能领域首选的化学储能技术之一。因电解液成本占比较高，通常采用成本相对较低的五氧化二钒作为原料来制备全钒液流电池电解液。针对五氧化二钒在硫酸中溶解度较小、直接使用硫酸溶解五氧化二钒难以制备出高浓度电解液的问题，本研究通过将硫酸与五氧化二钒进行升温活化处理，水溶后即可实现高浓度五价钒电解液的制备。采用XRD、Raman、FT-IR等手段对活化后固体的组成、结构和溶解过程进行分析。结果表明，在活化温度为180℃、活化时间为3 h、硫酸与五氧化二钒摩尔比为4时，五氧化二钒溶解质量分数高达98.5%，溶解的钒离子浓度高达3 mol·L^-1。硫酸与五氧化二钒升温活化后生成V₂O₃(SO₄)₂，改变原有的五氧化二钒的结构，导致活化后的物质水溶时溶解性增加，并且溶解后的钒离子价态以V(Ⅴ)形式存在。溶液中高浓度的V(Ⅴ)离子会与\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}-}络合反应生成\mathrm{V}{\mathrm{O}}_{\mathrm{2}}\mathrm{S}{\mathrm{O}}_{\mathrm{4}}^{-}，同时溶液中\mathrm{V}{\mathrm{O}}_{\mathrm{2}}^{+}也会发生聚合形成{\mathrm{V}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{4}+}、{\mathrm{V}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{2}+}等多聚体。

关键词: 五氧化二钒, 正极电解液, 全钒液流电池, 溶解度, 升温活化