Investigation Of High Concentrated Electrolyte For All Vanadium Flow Battery

Today, the electrical industries are facing new challenges as the market isbeing liberalized and deregulated in many countries. Electricity storage isundoubtedly a disruptive technology that will play, in the near future, a majorrole in the energy exploitation and usage. All-vanadium redox flow battery hasrecently received considerate attention as it possesses many features thatprovide for long life, flexible design, high reliability and low operation andmaintenance costs.In this paper, we mainly discussed preparation of electrolyte and itsperformance. preparation of high concentrated electrolyte, analysis ofelectrolyte, the fundamental performance of electrolyte, and stability andelectrochemical performance of catholyte and anolyte were studied in detail inthis dissertation. The main points can be summarized as follows:The four different valences of high concentrated V-H₂SO₄solutions canbe prepared by electrolysis of VOSO₄solutions. The cyclic voltammetry（CV）tests show that the best concentration of sulphuric acid is3M for vanadiumelectrolyte; and the positive and negative reaction are electrochemicalquasi-reversible and are controlled by diffusion. The conductivity test showsthat as the vanadium concentration is increased, the electrolyte conductivitydecreases for each of the vanadium oxidation states. So to thevanadium-H₂SO₄solution, the best concentration of vanadium ions is about1.5～2M. Oxalic acid, ammonium oxalate, EDTA, glucose, D-fructose, α-lactoseare explored as additives in negative electrolyte for vanadium battery,respectively. The effects of additives on electrolyte are studied for the thermalstability of the V （III） sulfuric acid solution and by cyclic voltammetry,electrochemical impedance spectroscopy（EIS）, electric and charge-dischargetest. The results show that these additives can improve the thermal stability ofV （III） sulfuric acid solution. But CV and EIS show that organic additivesoxalic acid, ammonium oxalate, ethylenediamine tetraacetate containingcarboxyl groups are better than glucose, D-fructose, α-lactose containinghydroxyl groups for improving the electrochemical activity and reversible ofV （III） sulfuric acid solution. This is because-COOH is easier to leave H than-C-OH, thus-COOH is more advantageous to the V （II）/V （III） electrodereaction.Pentavalent vanadium ion, as the positive active material, suffers fromprecipitation with increased temperature or concentration. This thesis select aseries of inorganic and organic substances and surfactants to examine itsinfluence to the thermal stability of V （V） ions, and its mechanism ispreliminary analysed in this paper. The results show that the addition of1%sodium sulfate, betaine, glucose, glycerin etc have positive effect to thestability of V （V） solution. These solution can exist without pricipition morethan30days in50℃. The CV and EIS show that sodium can improve thereversibility of V （IV）/V （V） electrode reaction, glucose can improve thecapacity of the battery.