High-conductivity vanadium redox flow battery electrolyte and preparation method thereof

Abstract

The invention relates to the technical field of redox flow batteries, in particular to a high-conductivity vanadium redox flow battery electrolyte and a preparation method thereof.The electrolyte is prepared from, by weight, 0.06-0.25 part of carbon nanotubes, 9-14 parts of phosphoric acid, 0.45-0.7 part of erbium oxide, 137-200 parts of vanadium pentoxide, 536-618 parts of sulfuric acid, 1.34-4.95 parts of a dispersing agent and 11.2-102 parts of a reducing agent. The electrolyte has the effect of comprehensively improving the conductivity, the stability and the reaction activity of the electrolyte. The three-dimensional conductive network is constructed through the carbon nanotubes, so that the electron conduction capability is remarkably improved; phosphoric acid is used for complexing and stabilizing high-valence vanadium ions, precipitation generation is inhibited, and thermal stability and cycling stability are enhanced. Erbium oxide is used for regulating and controlling a vanadium ion solvation structure, ion transmembrane migration is slowed down, active sites are provided on an electrode interface, and reaction kinetics is optimized. Through the synergistic effect of the three components, the conductivity, the stability and the electrochemical activity of the electrolyte are comprehensively improved.

Description

Technical Field

[0001] This application relates to the field of flow battery technology, and in particular to a highly conductive vanadium redox flow battery electrolyte and its preparation method. Background Technology

[0002] Vanadium redox flow batteries, as a promising large-scale energy storage technology, have shown broad application potential in areas such as grid connection of renewable energy sources like wind and solar power, and grid peak shaving, due to their advantages such as long cycle life, high safety, environmental friendliness, and deep charge / discharge capability. Vanadium redox flow batteries primarily utilize the redox reactions of vanadium ions between different valence states to achieve the storage and release of electrical energy.

[0003] As a core component of vanadium redox flow batteries, the electrolyte's performance directly determines the battery's energy density, cycle stability, efficiency, and lifespan. An ideal electrolyte should possess high conductivity, good thermal stability, excellent electrochemical activity, and structural stability under long-term cycling. However, at high temperatures, pentavalent vanadium ions easily precipitate, leading to electrolyte deactivation and battery performance degradation. Furthermore, the electrolyte's low conductivity increases internal resistance, reducing voltage and energy efficiency.

[0004] To improve electrochemical performance, the industry modifies electrolytes with additives, but these strategies each have significant limitations: adding inorganic salts (chlorides, sulfates) to increase conductivity may introduce impurity ions, affecting electrochemical reversibility; increasing sulfuric acid concentration to enhance vanadium solubility may cause side reactions and compromise electrolyte stability due to excessive acid. Summary of the Invention

[0005] To improve electrochemical performance, this application provides a highly conductive vanadium redox flow battery electrolyte and its preparation method.

[0006] In a first aspect, this application provides a highly conductive vanadium redox flow battery electrolyte, employing the following technical solution: A highly conductive vanadium redox flow battery electrolyte comprises the following raw materials in parts by weight: Carbon nanotubes 0.06-0.25 parts, phosphoric acid 9-14 parts, erbium oxide 0.45-0.7 parts, vanadium pentoxide 137-200 parts, sulfuric acid 536-618 parts, dispersant 1.34-4.95 parts, reducing agent 11.2-102 parts.

[0007] By employing the above technical solutions, carbon nanotubes, acting as a conductive framework, can interconnect to form a three-dimensional continuous electronic conduction network in the electrolyte, significantly reducing the ohmic resistance of the electrolyte. Phosphate ions can complex with high-valent vanadium ions, especially pentavalent vanadium ions, effectively reducing the concentration of free pentavalent vanadium ions and thermodynamically and kinetically inhibiting the formation of vanadium pentoxide precipitate, thereby enhancing the thermal stability and long-term cycling stability of the electrolyte. Erbium oxide can regulate the solvation structure of vanadium ions, slow down the transmembrane migration rate of vanadium ions, and adsorb on the electrode surface to optimize the double-layer structure or provide active sites, thus comprehensively improving the reaction kinetics of vanadium ions. The synergistic effect of these components can comprehensively improve the conductivity, stability, and reactivity of the electrolyte.

[0008] Optionally, the weight ratio of the carbon nanotubes to erbium oxide is 1:(2-5.3).

[0009] By adopting the above technical solution, this application uses a specific ratio of carbon nanotubes and erbium oxide to ensure that the carbon nanotubes construct an effective three-dimensional conductive network and improve the conductivity, while also enabling the erbium oxide to fully modify the electrode / electrolyte interface to optimize the reaction kinetics, thereby achieving simultaneous optimization of battery energy efficiency, cycle life and energy density.

[0010] Optionally, the carbon nanotubes are nitrogen-doped modified carbon nanotubes.

[0011] Optionally, the preparation steps of the nitrogen-doped modified carbon nanotubes include: mixing carbon nanotubes and a nitrogen-containing precursor, heat-treating under inert gas protection, and then purifying by acid treatment to obtain nitrogen-doped modified carbon nanotubes.

[0012] Optionally, the nitrogen-containing precursor is one or more of urea and melamine.

[0013] By employing the above-mentioned technical solution, this application introduces nitrogen atoms into the graphite lattice of carbon nanotubes through nitrogen-containing precursor heat treatment, achieving nitrogen doping. This modification improves performance in two ways: First, the electrons provided by the nitrogen atoms act as charge carriers, altering the surface charge distribution of the carbon nanotubes and optimizing their interfacial interaction with ions in the electrolyte, thereby significantly reducing charge transfer resistance and improving conductivity; Second, the introduced nitrogen atoms enhance the polarity of the carbon nanotube surface, which is beneficial for improving the compatibility of carbon nanotubes with aqueous electrolytes, thus achieving superior and stable dispersion.

[0014] Optionally, the carbon nanotubes are single-walled carbon nanotubes.

[0015] By adopting the above technical solution, this application uses single-walled carbon nanotubes, which can provide a larger specific surface area and a higher aspect ratio, which is conducive to forming a denser and more efficient conductive network, thereby further reducing ohmic polarization and providing more active sites for the redox of vanadium ions, thus reducing electrochemical polarization.

[0016] Optionally, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol 400, and sodium dodecyl sulfonate.

[0017] By employing the above-mentioned technical solutions, polyvinylpyrrolidone, polyethylene glycol 400, or sodium dodecyl sulfonate can promote the stable and uniform dispersion of carbon nanotubes in the electrolyte in the form of single nanotubes or small bundles at the nanoscale, thereby constructing a continuous three-dimensional conductive network. This network significantly reduces the ohmic resistance of the electrolyte, improves the uniformity of current distribution, and mitigates electrode polarization and side reactions during cycling, thus contributing to ensuring the long-term cycling stability of the battery.

[0018] Optionally, the reducing agent is one or more of oxalic acid, citric acid, glycerol, and glucose.

[0019] Secondly, this application provides a method for preparing a highly conductive vanadium redox flow battery electrolyte, employing the following technical solution: A method for preparing a highly conductive vanadium redox flow battery electrolyte includes the following steps: S1. Dispersion: Carbon nanotubes are purified by acid treatment, then a dispersant is added, and the mixture is dispersed by high-speed shearing and ultrasonication to obtain a carbon nanotube dispersion. Preparation of S2 and 3.5 valence basic vanadium electrolyte: Vanadium pentoxide, sulfuric acid, and reducing agent are mixed, heated and stirred, cooled, and brought to a constant volume. Then, electrolysis is carried out in an electrolytic cell to obtain 3.5 valence basic vanadium electrolyte. S3. Homogenization: The carbon nanotube dispersion obtained in step S1 is mixed with the 3.5 valence state basic vanadium electrolyte obtained in step S2 and dispersed. Then, erbium oxide and phosphoric acid are added in sequence and mixed evenly to obtain the electrolyte.

[0020] By adopting the above technical solution, this application ensures that each functional component is combined in its optimal state through stepwise preparation and ordered composite, thereby simultaneously improving the conductivity, stability, and reactivity of the electrolyte. First, carbon nanotubes are purified by acid treatment, hydrophilic groups are added, and dispersion is performed to pre-prepare a stable dispersion capable of forming a three-dimensional conductive network, laying the foundation for improved conductivity. Then, the electrolyte is prepared through a chemical reduction-electrolysis coupling method, obtaining a thermodynamically stable 3.5 valence vanadium electrolyte substrate, fundamentally ensuring the stability of the system. Finally, it is composited with erbium oxide and phosphoric acid; erbium oxide optimizes the reaction kinetics at the electrode interface, while phosphoric acid further consolidates the chemical stability of the electrolyte.

[0021] Optionally, the mass relationship between the reducing agent and vanadium pentoxide is as follows: (I) Where: m1 is the mass of vanadium pentoxide used (unit: g); m2 is the mass of the reducing agent used (unit: g); z is the molar ratio of the reducing agent to vanadium pentoxide during the reaction; M2 is the molar mass of the reducing agent used (unit: g / mol); ω2 represents the purity of the reducing agent used (in %). 181.88 is the molar mass of vanadium pentoxide (in g / mol).

[0022] Optionally, the electrolytic cell takes the following time for electrolysis: (II) Where: m1 is the mass of vanadium pentoxide used (unit: g); 181.88 is the molar mass of vanadium pentoxide (in g / mol). i represents the current value used during electrolysis (unit: A); k is the total number of individual cells in the electrolytic cell stack during electrolysis; T represents the electrolysis time (in hours).

[0023] Optionally, in S1, the high-speed shear stirring speed is 8000-15000 rpm, and the ultrasonic power is 300-500W.

[0024] By adopting the above technical solution, the strong fluid shear force generated by high-speed stirring and the cavitation effect generated by ultrasound can effectively break up the agglomeration of carbon nanotubes and promote the adsorption of dispersant molecules on the surface of carbon nanotubes, which is conducive to the formation of a uniform and stable system and the construction of a continuous and dense three-dimensional conductive network.

[0025] Optionally, in step S2, the heating temperature is 60-80℃, the stirring speed is 300-500rpm, and the cooling temperature is 20-30℃.

[0026] Optionally, in S3, the ultrasonic power is 300-500W.

[0027] Thirdly, this application provides a vanadium redox flow battery, which adopts the following technical solution: including a highly conductive vanadium redox flow battery electrolyte.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. Using carbon nanotubes as a conductive framework, they can interlock to form a three-dimensional continuous electronic conduction network in the electrolyte, greatly reducing the ohmic resistance of the electrolyte. Phosphate ions can complex with high-valent vanadium ions, especially pentavalent vanadium ions, effectively reducing the concentration of free pentavalent vanadium ions and thermodynamically and kinetically inhibiting the formation of vanadium pentoxide precipitate, thereby enhancing the thermal stability and long-term cycling stability of the electrolyte. Erbium oxide can regulate the solvation structure of vanadium ions, slow down the transmembrane migration rate of vanadium ions, and adsorb on the electrode surface to optimize the double-layer structure or provide active sites, thus comprehensively improving the reaction kinetics of vanadium ions. The synergistic effect of the above components can comprehensively improve the conductivity, stability, and reactivity of the electrolyte. 2. By using a specific ratio of carbon nanotubes and erbium oxide, while ensuring that the carbon nanotubes construct an effective three-dimensional conductive network and improve the conductivity, the erbium oxide can also fully modify the electrode / electrolyte interface to optimize the reaction kinetics, thereby achieving simultaneous optimization of battery energy efficiency, cycle life and energy density. 3. Nitrogen doping was achieved by introducing nitrogen atoms into the graphite lattice of carbon nanotubes through urea heat treatment. This modification improved performance in two ways: first, the electrons provided by nitrogen atoms act as charge carriers, altering the surface charge distribution of carbon nanotubes and optimizing their interfacial interaction with ions in the electrolyte, thereby significantly reducing charge transfer resistance and increasing conductivity; second, the introduced nitrogen atoms enhanced the polarity of the carbon nanotube surface, which is beneficial for improving the compatibility of carbon nanotubes with aqueous electrolytes, thus achieving better and more stable dispersion. 4. This application employs stepwise preparation and ordered composite processes to ensure that each functional component is composited in its optimal state, thereby simultaneously improving the conductivity, stability, and reactivity of the electrolyte. First, by purifying and dispersing carbon nanotubes, a stable dispersion capable of forming a three-dimensional conductive network is pre-prepared, laying the foundation for improved conductivity. Then, through precise electrochemical valence state control, a thermodynamically stable 3.5 valence vanadium electrolyte substrate is obtained, fundamentally ensuring the system's stability. Finally, it is composited with erbium oxide and phosphoric acid; erbium oxide optimizes the electrode interface reaction kinetics, while phosphoric acid further consolidates the electrolyte's chemical stability. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] This application designs a highly conductive vanadium redox flow battery electrolyte, comprising the following raw materials in parts by weight: Carbon nanotubes 0.06-0.25 parts, phosphoric acid 9-14 parts, erbium oxide 0.45-0.7 parts, vanadium pentoxide 137-200 parts, sulfuric acid 536-618 parts, dispersant 1.34-4.95 parts, reducing agent 11.2-102 parts.

[0031] A method for preparing a highly conductive vanadium redox flow battery electrolyte includes the following steps: S0, Preparation of nitrogen-doped modified carbon nanotubes (single-walled): Nitrogen-containing precursors and carbon nanotubes are mixed at a mass ratio of (1-20):1. The nitrogen-containing precursors are one or more of urea and melamine. The mixture is heat-treated at 600-1000℃ under inert gas protection for 2-4 hours. S1. Dispersion: Place the carbon nanotubes treated in step S0 into concentrated sulfuric acid (≥98%) and reflux for 1-2 hours. The mass ratio of the carbon nanotubes treated in step S0 to concentrated sulfuric acid is 1:(500-700). Remove impurities, wash off the sulfuric acid with water after reflux, and dry at low temperature for later use. Add a dispersant, which is one or more of polyvinylpyrrolidone, polyethylene glycol 400, and sodium dodecyl sulfonate. The mass ratio of carbon nanotubes to dispersant is 1:(10-30). Add water to the mixture containing carbon nanotubes and dispersant. The liquid-to-solid volume ratio is (1-3):1. Stir with a magnetic stirrer at 8000-15000 rpm for 30-50 minutes and ultrasonically disperse at 300-500W for 30-50 minutes to obtain a dispersion. Preparation of S2, 3.5 valence basic vanadium electrolyte: Vanadium pentoxide and sulfuric acid solution are mixed and activated, a reducing agent is added, which is one or more of oxalic acid, glycerol, and glucose. The mixture is heated to 60-80℃, stirred at 300-500 rpm for 1-2 hours, cooled to 20-30℃, and brought to a final volume according to the target concentration. Electrolysis is then carried out in an electrolytic cell to obtain 3.5 valence basic vanadium electrolyte. S3. Homogenization: Add the dispersion to the 3.5 valence vanadium electrolyte at a concentration of 0.2%-0.8% of the electrolyte mass. Disperse the electrolyte using ultrasonication at 300-500W for 30-50 minutes. Then, add erbium oxide and phosphoric acid sequentially. The amount of erbium oxide added is 0.008%-0.05% of the 3.5 valence vanadium electrolyte mass, and the amount of phosphoric acid added is 0.05mol / L-0.15mol / L. Mix thoroughly to obtain the electrolyte.

[0032] All raw materials used in the embodiments of this application are commercially available, wherein: Carbon nanotubes, Qingdao Haoxin New Energy Technology Co., Ltd.; Concentrated sulfuric acid, 98%, Xinhua Pharmaceutical Shouguang Co., Ltd.; Erbium oxide, analytical grade, Sinopharm Chemical Reagent Co., Ltd. Phosphoric acid, Qingdao Jinghang Chemical Co., Ltd.; Polyvinylpyrrolidone, Shanghai Aladdin Biochemical Technology Co., Ltd.; Polyethylene glycol 400, PEG400, Shanghai Aladdin Biochemical Technology Co., Ltd.; Sodium dodecyl sulfonate, Shanghai Aladdin Biochemical Technology Co., Ltd.; Urea, Henan Zhongyuan Dahua Group Co., Ltd.; Vanadium pentoxide, Shanghai Aladdin Biochemical Technology Co., Ltd. Specific Implementation

[0033] Preparation Example 1 Preparation of nitrogen-doped modified carbon nanotubes: 1g of urea and 1g of single-walled carbon nanotubes were mixed and heat-treated at 800℃ for 3h in a tube furnace under argon protection, and then refluxed in concentrated sulfuric acid for 1h to obtain nitrogen-doped modified carbon nanotubes. Example 1

[0034] 0.06 g of carbon nanotubes (single-walled) were refluxed in 36 g of concentrated sulfuric acid for 1 h. After reflux, the sulfuric acid was washed off with water and dried at 30 °C for later use. 0.06 g of the treated carbon nanotubes were weighed and added to 1.34 g of polyvinylpyrrolidone and 2.5 ml of water. The mixture was stirred at 8000 rpm for 50 min and ultrasonically dispersed at 300 W for 50 min to obtain a dispersion. 544 g of water and 500 g of concentrated sulfuric acid were mixed to prepare a sulfuric acid solution. 137 g of vanadium pentoxide was added to the sulfuric acid solution. The temperature was maintained at 60 °C and the mixture was stirred at 300 rpm to activate the reaction for 1 h. 70 g of oxalic acid was added and the reaction continued for 1 h. The mixture was cooled to 25 °C and brought to a final volume of 1 L. Electrolysis was performed in an electrolytic cell according to formula (II) to obtain a 3.5 valence vanadium electrolyte. 1 L of the electrolyte was then... Add the 3.5 valence state basic electrolyte to the dispersion, sonicate at 300W for 50 min, add 0.45 g of erbium oxide, mix well, add 9 g of phosphoric acid, mix well, and obtain the electrolyte. Example 2

[0035] 0.13g of carbon nanotubes (single-walled) were refluxed in 78g of concentrated sulfuric acid for 1 hour. After reflux, the sulfuric acid was washed off with water and dried at 30°C for later use. 0.13g of the treated carbon nanotubes were weighed and added to 2.75g of polyethylene glycol 400 and 4ml of water. The mixture was stirred at 10000rpm for 40min and ultrasonically dispersed at 400W for 40min to obtain a dispersion. 508g of water and 468g of concentrated sulfuric acid were mixed to prepare a sulfuric acid solution. 155g of vanadium pentoxide was added to the sulfuric acid solution. The temperature was maintained at 70°C, and the mixture was stirred at 400rpm to activate the reaction for 1 hour. 11.2g of glycerol was added, and the reaction was continued for 1 hour. The mixture was cooled to 25°C and brought to a final volume of 1L. Electrolysis was performed in an electrolytic cell according to formula (II) to obtain a 3.5 valence vanadium electrolyte. 1L of the electrolyte was then... Add the 3.5 valence state basic electrolyte to the dispersion, ultrasonically disperse at 400W for 40 min, add 0.69 g of erbium oxide, mix well, add 11.5 g of phosphoric acid, mix well, and obtain the electrolyte. Example 3

[0036] 0.25g of carbon nanotubes (single-walled) were refluxed in 150g of concentrated sulfuric acid for 1 hour. After reflux, the sulfuric acid was washed off with water and dried at 30°C for later use. 0.25g of the treated carbon nanotubes were weighed and added to 4.95g of sodium dodecyl sulfonate and 6ml of water. The mixture was stirred at 15000rpm for 30min and ultrasonically dispersed at 500W for 30min to obtain a dispersion. 635g of water and 468g of concentrated sulfuric acid were mixed to prepare a sulfuric acid solution. 200g of vanadium pentoxide was accurately weighed and added to the sulfuric acid solution. The temperature was maintained at 80°C, and the mixture was stirred at 500rpm to activate the reaction for 1 hour. 102g of oxalic acid was added and the reaction continued for 1 hour. The mixture was cooled to 25°C and brought to a final volume of 1L. Electrolysis was performed in an electrolytic cell according to formula (II) to obtain a 3.5 valence vanadium electrolyte. 1L of the electrolyte was then... Add the 3.5 valence state basic electrolyte to the dispersion, sonicate at 300W for 30 min, add 0.7g erbium oxide, mix well, add 14g phosphoric acid, mix well, and obtain the electrolyte.

[0037] The electrolytes obtained in Examples 1-3 were tested for conductivity, coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization, energy density, and capacity retention. The water used met the Class III water standard in GB 6682-92 "Specifications and Test Methods for Water Used in Analytical Laboratories," with a pH range of 5.0–7.5, conductivity ≤5 μS / m, and resistivity ≥0.2 MΩ·cm. The testing items and methods are as follows: Charge-discharge performance test: The battery assembled with electrolyte was subjected to a constant current of 4A and a discharge rate of 160mA / cm. 2Constant current charge-discharge tests were conducted at a current density of 160 mA / cm², and the conductivity was determined using AC impedance spectroscopy with a CHI660E electrochemical workstation. Battery assembly: Carbon felt was used as the positive and negative electrodes. 240 ml of electrolyte was divided into two equal portions, serving as the positive and negative electrolytes respectively. An N₂¹₂ perfluorosulfonic acid ion exchange membrane was used as the separator, and a magnetically driven circulation pump was used to transport the electrolyte. The battery was sealed with a silicone sheet. Charge-discharge tests were conducted at 160 mA / cm². 2 Constant current charging / discharging was performed at the specified current density for 200 cycles to obtain coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization, energy density, and capacity retention.

[0038] The test results of Examples 1-3 obtained according to the above test methods are shown in Table 1: Table 1 Electrolyte performance testing in Examples 1-3

[0039] As shown in Examples 1-3 and Table 1, the electrolytes of Examples 1-3 of this application exhibit conductivity above 391 mS / cm, energy efficiency above 86.83%, vanadium utilization above 71%, energy density above 20.71 Wh / L, and capacity retention above 84%. This indicates that the electrolyte of this application can significantly improve conductivity and has high capacity retention, vanadium utilization, and energy density. Carbon nanotubes can interlock to form a three-dimensional continuous electron conduction network in the electrolyte, thereby improving conductivity. Phosphate ions can complex with high-valent vanadium ions, especially pentavalent vanadium ions, effectively reducing the concentration of free pentavalent vanadium ions and thermodynamically and kinetically inhibiting the formation of vanadium pentoxide precipitate, thus enhancing the capacity retention of the electrolyte. Erbium oxide can improve energy efficiency and vanadium utilization by regulating the solvation structure of vanadium ions, slowing down the transmembrane migration rate of vanadium ions, and adsorbing on the electrode surface to optimize the double-layer structure or provide active sites. The synergistic effect of the above components can comprehensively improve the conductivity, stability, and reactivity of the electrolyte. Increasing the proportion of vanadium pentoxide can improve the energy density of the electrolyte, but it will lead to decreased conductivity, coulombic efficiency, and voltage efficiency. Increasing the proportion of carbon nanotubes can increase the conductivity and vanadium utilization of the electrolyte, but it will simultaneously lead to a decrease in energy density.

[0040] Comparative Example 1 The difference between this comparative example and Example 2 is that the carbon nanotubes in Example 2 are replaced with erbium oxide.

[0041] Comparative Example 2 The difference between this comparative example and Example 2 is that the erbium oxide in Example 2 is replaced by carbon nanotubes.

[0042] Comparative Example 3 The difference between this comparative example and Example 2 is that the single-walled carbon nanotubes in Example 2 are replaced with multi-walled carbon nanotubes.

[0043] The electrolytes obtained in Example 2 and Comparative Examples 1-2 were tested for conductivity, coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization, energy density, and capacity retention. The test results are shown in Table 2. Table 2 Electrolyte performance testing of Examples 2 and Comparative Examples 1-3

[0044] As shown in Example 2, Comparative Examples 1-2, and Table 2, the electrolyte in Example 2 exhibits a conductivity of 401 mS / cm, an energy efficiency of 87.97%, a vanadium utilization rate of 80%, an energy density of 22.97 Wh / L, and a capacity retention rate of 86%, significantly superior to electrolytes prepared using only carbon nanotubes or erbium oxide. Carbon nanotubes can improve electrolyte conductivity by constructing a three-dimensional conductive network. Erbium oxide can optimize electrode interface reaction kinetics, avoiding uneven current density distribution and local overcharging / over-discharging on the electrode surface, thereby reducing side reactions and electrode corrosion, ultimately improving capacity retention. While carbon nanotubes alone can construct an electronic conductive network, the high energy barrier and slow speed of the redox reaction at the vanadium ion interface result in high electrochemical polarity, leading to reduced vanadium ion utilization and energy density. Although erbium oxide alone optimizes interface reaction kinetics, electron transport relies on poorly conductive ion pathways and electrodes, increasing the system's ohmic resistance and significantly reducing conductivity and capacity retention.

[0045] As shown in Example 2, Comparative Example 3, and Table 2, single-walled carbon nanotubes significantly improve conductivity and capacity retention compared to multi-walled carbon nanotubes. Single-walled carbon nanotubes are formed by rolling up a single layer of graphene, resulting in a larger specific surface area. This provides more contact points and a wider interface in the electrolyte, making it easier to form a tightly interwoven "nanoscale network," thereby constructing a more efficient and comprehensive three-dimensional conductive pathway and improving conductivity.

[0046] Examples 4-5 Based on Example 2, except for the weight ratio of carbon nanotubes and erbium oxide, the other components and preparation methods are the same as in Example 2, and the total weight of carbon nanotubes and erbium oxide remains unchanged.

[0047] Example 4 The difference between this embodiment and Embodiment 2 is that the weight ratio of carbon nanotubes to erbium oxide in this embodiment is 1:3. Specifically, the weight of carbon nanotubes is 0.205g and the weight of erbium oxide is 0.615g.

[0048] Example 5 The difference between this embodiment and Embodiment 2 is that the weight ratio of carbon nanotubes to erbium oxide in this embodiment is 1:2. Specifically, the weight of carbon nanotubes is 0.273g and the weight of erbium oxide is 0.547g.

[0049] The electrolytes obtained in Examples 2 and 4-5 were tested for conductivity, vanadium utilization, energy density, and capacity retention. The test results are shown in Table 3. Table 3 Electrolyte performance testing results for Examples 2 and 4-5

[0050] As shown in Examples 2, 4-5, and Table 3, the electrolyte in Example 4 exhibits a vanadium utilization rate of 84.92%, an energy density of 24.40 Wh / L, and a capacity retention rate of 87%, significantly superior to Examples 2 and 5. This application utilizes a specific ratio of carbon nanotubes and erbium oxide. While ensuring the construction of an effective three-dimensional conductive network by carbon nanotubes and improving conductivity, it also allows erbium oxide to fully modify the electrode / electrolyte interface to optimize reaction kinetics, thereby achieving simultaneous optimization of battery energy efficiency, cycle life, and energy density. An excessively high proportion of erbium oxide may lead to excessive adsorption or aggregation of erbium oxide particles on the electrode surface, blocking active sites and affecting the normal transport and reaction of vanadium ions, resulting in reduced vanadium utilization and capacity retention. Conversely, an excessively high proportion of carbon nanotubes may cause carbon nanotubes to agglomerate in the electrolyte, making it difficult to form a uniform and stable nano-dispersion system, blocking electrode pores or the separator, and leading to reduced capacity retention.

[0051] Example 6 The difference between this embodiment and Example 4 is that in this embodiment, the carbon nanotubes in Example 4 are replaced with nitrogen-doped modified carbon nanotubes obtained in Preparation Example 1.

[0052] The electrolytes obtained in Examples 4 and 6 were tested for conductivity, vanadium utilization, energy density, and capacity retention. The test results are shown in Table 4. Table 4 Electrolyte performance testing in Examples 4 and 6

[0053] As shown in Examples 4 and 6 and Table 4, the electrolyte of Example 6 has a conductivity of 418 mS / cm, a vanadium utilization rate of 87.04%, an energy density of 25.01 Wh / L, and a capacity retention rate of 89%, which are significantly better than those of Example 4. The introduction of nitrogen atoms into the graphite lattice of carbon nanotubes alters the surface charge distribution of the carbon nanotubes, optimizes their interfacial interaction with ions in the electrolyte, thereby significantly reducing charge transfer resistance and improving conductivity. Furthermore, the introduced nitrogen atoms enhance the polarity of the carbon nanotube surface, which is beneficial for improving the compatibility of carbon nanotubes with aqueous electrolytes, thus achieving superior and more stable dispersion.

[0054] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A highly conductive vanadium redox flow battery electrolyte, characterized in that, The raw materials include the following parts by weight: Carbon nanotubes 0.06-0.25 parts, phosphoric acid 9-14 parts, erbium oxide 0.45-0.7 parts, vanadium pentoxide 137-200 parts, sulfuric acid 536-618 parts, dispersant 1.34-4.95 parts, reducing agent 11.2-102 parts.

2. The highly conductive vanadium redox flow battery electrolyte according to claim 1, characterized in that, The weight ratio of the carbon nanotubes to erbium oxide is 1:(2-5.3).

3. The highly conductive vanadium redox flow battery electrolyte according to claim 1, characterized in that, The carbon nanotubes are nitrogen-doped modified carbon nanotubes.

4. The highly conductive vanadium redox flow battery electrolyte according to claim 3, characterized in that, The preparation steps of the nitrogen-doped modified carbon nanotubes include: mixing carbon nanotubes and a nitrogen-containing precursor, heat-treating under inert gas protection, and then purifying by acid treatment to obtain nitrogen-doped modified carbon nanotubes.

5. The highly conductive vanadium redox flow battery electrolyte according to claim 1, characterized in that, The carbon nanotubes are single-walled carbon nanotubes.

6. The highly conductive vanadium redox flow battery electrolyte according to claim 1, characterized in that, The dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol 400, and sodium dodecyl sulfonate.

7. The highly conductive vanadium redox flow battery electrolyte according to claim 1, characterized in that, The reducing agent is one or more of oxalic acid, citric acid, glycerol, and glucose.

8. A method for preparing a highly conductive vanadium redox flow battery electrolyte according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Dispersion: Carbon nanotubes are purified by acid treatment, a dispersant is added, and high-speed shear dispersion and ultrasonic dispersion are performed to obtain a carbon nanotube dispersion. Preparation of S2 and 3.5 valence basic vanadium electrolyte: Vanadium pentoxide, sulfuric acid, and reducing agent are mixed, heated and stirred, cooled, and brought to a constant volume. Then, electrolysis is carried out in an electrolytic cell to obtain 3.5 valence basic vanadium electrolyte. S3. Homogenization: The carbon nanotube dispersion obtained in step S1 is mixed with the 3.5 valence state basic vanadium electrolyte obtained in step S2 and dispersed. Then, erbium oxide and phosphoric acid are added in sequence and mixed evenly to obtain the electrolyte.

9. The method for preparing the highly conductive vanadium redox flow battery electrolyte according to claim 8, characterized in that, In S1, the high-speed shear stirring speed is 8000-15000 rpm.

10. A vanadium redox flow battery, characterized in that, The electrolyte includes the highly conductive vanadium redox flow battery electrolyte as described in any one of claims 1-7.

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