The physicochemical and electrochemical performance of electrolytes prepared with different grades of V₂O₅ raw materials were investigated systematically for a vanadium redox flow battery. Physicochemical tests showed that the conductivity of electrolytes prepared with lower grades of V₂O₅ raw materials obviously decreased, while the viscosity increased. The results of electrochemical experiments showed that the electrochemical activity and reversibility of electrolytes decreased, and the solution resistance increased obviously, as the grade of V₂O₅ raw materials gradually decreased. In addition, the battery efficiency and charge–discharge capacity were negatively affected by impurities in the lower grade V₂O₅ raw materials, due to an increase of polarization on the charge–discharge voltage. Moreover, the performance of electrolytes was related to the total concentration of impurities in the electrolyte, and Na, K impurity ions were the main factors that adversely affected the electrochemical activity and reversibility, mass transfer, and capacity of the electrolytes. Based on the economic analysis, the impurities in V₂O₅ raw materials would not only reduce the performance of electrolytes, but also affect the production costs of electrolytes and the economic profits. Through this fundamental research, people can better understand the influence of V₂O₅ raw materials on electrolyte properties, and direct more attention to research how to effectively use lower grade V₂O₅ raw materials to reduce the costs of electrolyte preparation.

Glucose, sucrose, D(+)-xylose and α-lactose monohydrate are selected as additives relative to the negative electrolyte of Vanadium Redox Flow Battery (VRFB), with the aim of reducing vanadium permeation and improving electrochemical performance to mitigate capacity decay. The results of a charge–discharge test show that the cell with α-Lactose monohydrate in the negative electrolyte exhibits the best capacity retention. The capacity retention of a single cell employing 1 wt% α-Lactose monohydrate in the negative electrolyte was 71% after 30 cycles, which is 41.5% higher than 29.5% of the control group. Correspondingly, adding α-Lactose monohydrate into the negative electrolyte also significantly inhibits vanadium crossover and water transfer. Furthermore, the effects of additives on the performance of the negative electrolyte are studied by thermal stability experiments, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The stability experiments indicate that the introduction of 1 wt% α-Lactose monohydrate can elevate the stability of the negative electrolyte at low temperatures. The electrochemical measurements indicate that V(III) electrolyte with 1 wt% α-Lactose monohydrate obtains superior electrochemical activity and reversibility, which can be ascribed to the fact that the hydroxyl group carried by the additive provides more active sites for the redox reaction. Herein, the study provides a meaningful reference for mitigating the capacity decay of VRFB.

The vanadium redox flow battery (VRFB) is a highly favorable tool for storing renewable energy, and the catalytic activity of electrode materials is crucial for its development. Taurine-functionalized carbon nanotubes (CNTs) were prepared with the aim of augmenting the redox process of vanadium ions and enhancing the efficiency of the VRFB. Sulfonated CNTs were synthesized through a simple modification process in a taurine solution and used as electrocatalysts for redox reactions involving VO²⁺/VO₂⁺ and V²⁺/V³⁺. The SO₃H-CNTs modified at 60 °C for 2 h exhibit the best electrocatalytic activity, showing higher redox peak current values compared to pristine carboxylated CNTs (COOH-CNTs). Sulfonic acid groups added to the surface of CNTs increase active sites for redox reactions and act as carriers for mass transfer and bridges for charge transfer, accelerating the rate of the electrode reactions. A battery consisting of SO₃H-CNTs as catalysts demonstrates the outstanding charge–discharge performance at a current density of 300 mA∙cm⁻². This configuration displays voltage and energy efficiencies of 81.46% and 78.83%, respectively, representing enhancements of 6.15% and 6.12% compared to that equipped with conventional graphite felts (75.31%, 72.71%). This study illustrates that taurine-functionalized carbon nanotubes serve as an efficient and promising catalyst for both the anode and cathode, leading to the improved performance of the VRFB.

Traditional vanadium electrolyte production faces challenges of complex processes, high costs, and inefficient impurity removal. This study developed an integrated crystallization-solvent extraction method to directly produce high-performance electrolyte from high-aluminum vanadium shale leachate (Al: 21.2 g/L, V: 54.2 g/L). Through ammonium alum crystallization under optimal conditions (NH ₄ ⁺ /Al ^{3 +} =1:1, 5°C, 6 h), 51.67% aluminum was removed with <1% vanadium loss. Subsequent five-stage countercurrent extraction achieved 96.04% vanadium recovery, while four-stage stripping produced a 2.0 mol/L V electrolyte. The obtained electrolyte exhibited excellent properties: viscosity of 5.00 mm ² /s, conductivity of 253.7 mS/cm, and electrochemical performance comparable to commercial standards. Battery tests demonstrated outstanding stability with average coulombic efficiency of 87.86%, voltage efficiency of 93.00%, and energy efficiency of 81.70% over 80 cycles at 40 mA/cm ² . This short process offers strong potential for industrial application in vanadium redox flow batteries.

Capacitive deionization (CDI) based on LSC-957 resin/carbon composite electrodes was used to remove Fe impurity ions from a spent vanadium electrolyte, which enabled simple and efficient regeneration of the electrolyte. The experiments conducted in this study demonstrated that 3:1 was the optimal mass ratio of LSC-957 resin to activated carbon for the preparation of the composite electrodes, and the optimal operating voltage and operating time were 0.9 V and 6 h, respectively. After five stages of CDI tandem treatment, the adsorption rate of Fe impurity ions was 86.84% and the loss rate of V was only 3.8%. The energy efficiency of the regenerated electrolyte was 84.49%, and its performance was significantly improved compared to the spent vanadium electrolyte. The adsorption process of composite electrodes was analyzed by kinetic and isothermal models’ fit, SEM-EDS, and FTIR. This work has provided an effective and novel method for removing impurity ions from a spent electrolyte.