Highly conductive vanadium flow battery electrolyte and method of making same

Abstract

The application relates to the technical field of liquid flow batteries, in particular to a vanadium liquid flow battery electrolyte with high conductivity and a preparation method thereof, the electrolyte is prepared from the following raw materials in parts by weight: 0.06-0.25 parts of carbon nanotubes, 9-14 parts of phosphoric acid, 0.45-0.7 parts 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 application has the effects of comprehensively improving the conductivity, stability and reaction activity of the electrolyte. The three-dimensional conductive network is constructed by the carbon nanotubes, and the electron conduction capacity is significantly improved; the high-valence vanadium ions are complexed and stabilized by the phosphoric acid, the precipitation generation is inhibited, and the thermal stability and cycle stability are enhanced; the vanadium ion solvation structure is regulated by the erbium oxide, the ion transmembrane migration is slowed down, and the active sites are provided at the electrode interface, and the reaction kinetics is optimized. The three synergistic effects comprehensively improve the conductivity, stability and electrochemical activity of the electrolyte.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of liquid flow batteries, in particular to a vanadium liquid flow battery electrolyte with high conductivity and a preparation method thereof. BACKGROUND

[0002] As a promising large-scale energy storage technology, the all-vanadium redox flow battery has a wide application potential in the fields of renewable energy grid connection and power grid peak shaving due to its long cycle life, high safety, environmental friendliness and deep charge-discharge capability. The all-vanadium redox flow battery is mainly based on the redox reaction of vanadium ions between different valence states to realize the storage and release of electric energy.

[0003] The electrolyte is a core component of the all-vanadium redox flow battery, and its performance directly determines the energy density, cycle stability, efficiency and service life of the battery. An ideal electrolyte should have high conductivity, good thermal stability, excellent electrochemical activity and structural stability under long-term cycling. However, at high temperatures, pentavalent vanadium ions are prone to precipitation, resulting in deactivation of the electrolyte and degradation of the battery performance. In addition, the electrolyte has low conductivity, which leads to increased internal resistance of the battery and reduced voltage and energy efficiency.

[0004] In order to improve the electrochemical performance, the industry modifies the electrolyte by adding additives, but such strategies have significant limitations: adding inorganic salts (chlorides, sulfates) to improve conductivity, but may introduce impurity ions, affecting electrochemical reversibility; increasing the concentration of sulfuric acid to enhance vanadium solubility, but excessive acid will trigger side reactions and destroy the stability of the electrolyte. SUMMARY

[0005] In order to improve the electrochemical performance, the application provides a vanadium liquid flow battery electrolyte with high conductivity and a preparation method thereof.

[0006] In the first aspect, the application provides a vanadium liquid flow battery electrolyte with high conductivity, which adopts the following technical scheme:

[0007] A vanadium liquid flow battery electrolyte with high conductivity comprises the following weight parts of raw materials:

[0008] 0.06-0.25 parts of carbon nanotubes, 9-14 parts of phosphoric acid, 0.45-0.7 parts 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.

[0009] By adopting the technical scheme, the carbon nanotubes are used as a conductive framework, can be connected with each other to form a three-dimensional continuous electron conduction network in the electrolyte, and greatly reduces the ohmic resistance of the electrolyte; the phosphate ions can be complexed with the high-valence vanadium ions, especially the pentavalent vanadium ions, effectively reduces the concentration of free pentavalent vanadium ions, and inhibits the generation of vanadium pentoxide precipitate from the thermodynamic and kinetic aspects, thereby enhancing the thermal stability and long-term cycle stability of the electrolyte; the erbium oxide can regulate the solvation structure of the vanadium ions, slow down the transmembrane migration rate of the vanadium ions, and be adsorbed on the electrode surface to optimize the double-layer structure or provide active sites, and then comprehensively improve the reaction kinetics of the vanadium ions. The above components can synergistically improve the conductivity, stability and reaction activity of the electrolyte.

[0010] Optionally, the weight ratio of the carbon nanotubes to the erbium oxide is 1: (2-5.3).

[0011] By adopting the technical scheme, the carbon nanotubes and the erbium oxide are used in a specific ratio in the application, the carbon nanotubes construct an effective three-dimensional conductive network to improve the conductivity, and the erbium oxide fully modifies the electrode / electrolyte interface to optimize the reaction kinetics, thereby realizing the synchronous optimization of the battery energy efficiency, cycle life and energy density.

[0012] Optionally, the carbon nanotubes are nitrogen-doped modified carbon nanotubes.

[0013] Optionally, the preparation steps of the nitrogen-doped modified carbon nanotubes include: mixing the carbon nanotubes and a nitrogen-containing precursor, heat treating under inert gas protection, and then acid treating and purifying to obtain the nitrogen-doped modified carbon nanotubes.

[0014] Optionally, the nitrogen-containing precursor is one or more of urea and melamine.

[0015] By adopting the technical scheme, the nitrogen atoms are introduced into the graphite lattice of the carbon nanotubes by heat treating the nitrogen-containing precursor, and nitrogen doping is realized. This modification improves the performance in two aspects: first, the electrons provided by the nitrogen atoms act as carriers, change the surface charge distribution of the carbon nanotubes, optimize the interface interaction between the carbon nanotubes and the ions in the electrolyte, thereby significantly reducing the charge transfer resistance and improving the conductivity; second, the introduced nitrogen atoms enhance the polarity of the surface of the carbon nanotubes, which is beneficial to improving the compatibility of the carbon nanotubes with the aqueous electrolyte, and then realizes more excellent and stable dispersibility.

[0016] Optionally, the carbon nanotubes are single-walled carbon nanotubes.

[0017] By adopting the technical scheme, the single-walled carbon nanotube is adopted, a larger specific surface area and a higher length-diameter ratio are provided, a more compact and efficient conductive network is formed, and thus the ohmic polarization is further reduced, and more active sites are provided for the oxidation and reduction of vanadium ions, and the electrochemical polarization is reduced.

[0018] Optionally, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol 400 and sodium dodecyl sulfonate.

[0019] By adopting the technical scheme, the polyvinylpyrrolidone, polyethylene glycol 400 or sodium dodecyl sulfonate can promote the carbon nanotube to be stably and uniformly dispersed in the electrolyte in the form of nanometer scale single or small bundle, so as to build a continuous three-dimensional conductive network. The network significantly reduces the ohmic resistance of the electrolyte, improves the uniformity of current distribution, slows down the polarization and side reaction of the electrode in the cycle process, and thus is beneficial to guarantee the long-term cycle stability of the battery.

[0020] Optionally, the reducing agent is one or more of oxalic acid, citric acid, glycerol and glucose.

[0021] In a second aspect, the application provides a preparation method of a high-conductivity vanadium flow battery electrolyte, which adopts the following technical scheme:

[0022] A preparation method of a high-conductivity vanadium flow battery electrolyte, comprising the following steps:

[0023] S1, dispersion: purifying the carbon nanotube by acid treatment, then adding a dispersant, and performing high-speed shearing dispersion and ultrasonic dispersion to obtain a carbon nanotube dispersion liquid;

[0024] S2, preparation of a 3.5-valence state basic vanadium electrolyte: mixing vanadium pentoxide, sulfuric acid and a reducing agent, heating and stirring, cooling, constant volume, and then performing electrolysis by using an electrolytic cell to obtain a 3.5-valence state basic vanadium electrolyte;

[0025] S3, homogenization: mixing the carbon nanotube dispersion liquid obtained in step S1 and the 3.5-valence state basic vanadium electrolyte obtained in step S2, dispersing, and then sequentially adding erbium oxide and phosphoric acid and mixing uniformly to obtain the electrolyte.

[0026] By adopting the technical scheme, the application ensures that the functional components are compounded in the best state through step-by-step preparation and ordered compounding, thereby synchronously improving the conductivity, stability and reactivity of the electrolyte. The stable dispersion liquid capable of forming a three-dimensional conductive network is prepared by adding a hydrophilic group to the carbon nanotube through acid treatment and dispersion, thereby laying a foundation for improving the conductivity; the electrolyte is prepared through chemical reduction-electrolysis coupling, thereby obtaining a 3.5-valence vanadium electrolyte base with the most stable thermodynamics, thereby fundamentally guaranteeing the stability of the system; finally, the electrolyte is compounded with erbium oxide and phosphoric acid, the erbium oxide optimizes the electrode interface reaction kinetics, and the phosphoric acid further consolidates the chemical stability of the electrolyte.

[0027] Optionally, the mass relationship between the reducing agent and the vanadium pentoxide is:

[0028] (I)

[0029] m1 is the mass of vanadium pentoxide (unit: g);

[0030] m2 is the mass of the reducing agent (unit: g);

[0031] z is the molar coefficient ratio of the reducing agent and vanadium pentoxide during reaction;

[0032] M2 is the molar mass of the reducing agent (unit: g / mol);

[0033] ω2 is the purity of the reducing agent (unit: %);

[0034] 181.88 is the molar mass of vanadium pentoxide (unit: g / mol).

[0035] Optionally, the time used during electrolysis of the electrolytic cell is:

[0036] (II)

[0037] m1 is the mass of vanadium pentoxide (unit: g);

[0038] 181.88 is the molar mass of vanadium pentoxide (unit: g / mol);

[0039] i is the current value used during electrolysis (unit: A);

[0040] k is the total number of single cells of the electrolysis stack during electrolysis;

[0041] T is the electrolysis time used during electrolysis (unit: h).

[0042] Optionally, in S1, the high-speed shearing stirring speed is 8000-15000 rpm, and the ultrasonic power is 300-500 W.

[0043] By adopting the technical scheme, the strong fluid shear force generated by high-speed stirring and the cavitation effect generated by ultrasonic can effectively disperse the agglomeration of carbon nanotubes and promote the adsorption of dispersant molecules on the surface of the carbon nanotubes, so that a uniform and stable system is formed, and a continuous and dense three-dimensional conductive network is constructed.

[0044] Optionally, in the S2, the heating temperature is 60-80 DEG C, the stirring speed is 300-500 rpm, and the cooling temperature is 20-30 DEG C.

[0045] Optionally, in the S3, the ultrasonic power is 300-500 W.

[0046] In a third aspect, the application provides a vanadium flow battery, which adopts the following technical scheme: a vanadium flow battery electrolyte with high conductivity.

[0047] In summary, the application has at least one of the following beneficial technical effects:

[0048] 1. By using carbon nanotubes as a conductive framework, a three-dimensional continuous electron conduction network can be formed in the electrolyte, greatly reducing the ohmic resistance of the electrolyte; phosphate ions can form a complex with high-valence vanadium ions, especially pentavalent vanadium ions, effectively reducing the concentration of free pentavalent vanadium ions, and inhibiting the generation of vanadium pentoxide precipitate from the thermodynamic and kinetic aspects, thereby enhancing the thermal stability and long-term cycle stability of the electrolyte; erbium oxide can regulate the solvation structure of vanadium ions, slow down the transmembrane migration rate of vanadium ions, and be adsorbed on the electrode surface to optimize the double-layer structure or provide active sites, thereby comprehensively improving the reaction kinetics of vanadium ions; the synergistic effect of the above components can comprehensively improve the conductivity, stability and reaction activity of the electrolyte;

[0049] 2. By using carbon nanotubes and erbium oxide in a specific ratio, the carbon nanotubes can construct an effective three-dimensional conductive network to improve the conductivity, and the erbium oxide can fully modify the electrode / electrolyte interface to optimize the reaction kinetics, thereby achieving simultaneous optimization of battery energy efficiency, cycle life and energy density;

[0050] 3. By using urea heat treatment to introduce nitrogen atoms into the graphite lattice of carbon nanotubes, nitrogen doping is achieved. This modification improves performance in two ways: first, the electrons provided by the nitrogen atoms act as carriers, changing the surface charge distribution of the carbon nanotubes and optimizing their interface interaction with ions in the electrolyte, thereby significantly reducing the charge transfer resistance and improving the conductivity; second, the introduced nitrogen atoms enhance the polarity of the carbon nanotube surface, which is beneficial to improving the compatibility of the carbon nanotubes with the aqueous electrolyte, thereby achieving more excellent and stable dispersibility;

[0051] 4. The application ensures that each functional component is compounded in the best state through step-by-step preparation and ordered compounding, thereby synchronously improving the conductivity, stability and reaction activity of the electrolyte. The stable dispersion liquid capable of forming a three-dimensional conductive network is pre-prepared through purification and dispersion of the carbon nanotubes, thereby laying a foundation for improving the conductivity; the thermodynamically most stable 3.5-valence vanadium electrolyte base is obtained through precise electrochemical valence state regulation, thereby fundamentally guaranteeing the stability of the system; and the erbium oxide and phosphoric acid are compounded, the erbium oxide optimizes the electrode interface reaction kinetics, and the phosphoric acid further consolidates the chemical stability of the electrolyte. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0053] The application designs a high-conductivity vanadium flow battery electrolyte, which comprises the following preparation raw materials in parts by weight:

[0054] The carbon nanotubes are 0.06-0.25 parts, the phosphoric acid is 9-14 parts, the erbium oxide is 0.45-0.7 parts, the vanadium pentoxide is 137-200 parts, the sulfuric acid is 536-618 parts, the dispersant is 1.34-4.95 parts, and the reducing agent is 11.2-102 parts.

[0055] A preparation method of a high-conductivity vanadium flow battery electrolyte comprises the following steps:

[0056] 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, and heat treatment is performed at 600-1000°C under inert gas protection for 2-4h;

[0057] S1, dispersion: the carbon nanotubes treated in the S0 step are placed in concentrated sulfuric acid (≥98%) for refluxing for 1-2h, the mass ratio of the carbon nanotubes treated in the S0 step to the concentrated sulfuric acid is 1:(500-700), impurities are removed, the sulfuric acid is washed away with water after refluxing and low-temperature drying is performed for standby use, a dispersant is added, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol 400 and sodium dodecyl sulfonate, the mass ratio of the carbon nanotubes to the dispersant is 1:(10-30), water is further added to the mixture containing the carbon nanotubes and the dispersant, the liquid-solid volume ratio is (1-3):1; a magnetic stirrer is used for stirring at 8000-15000rpm for 30-50min, and 300-500W ultrasonic dispersion is performed for 30-50min, to obtain a dispersion liquid;

[0058] S2, Preparation of 3.5 valence state basic vanadium electrolyte: Vanadium pentoxide and sulfuric acid solution were mixed and activated, a reducing agent was added, the reducing agent was one or more of oxalic acid, glycerol, and glucose, heated to 60-80℃, stirred at 300-500rpm for 1-2h, cooled to 20-30℃, and then diluted to the target concentration, electrolyzed using an electrolytic cell, and a 3.5 valence state basic vanadium electrolyte was obtained;

[0059] S3, Homogenization: The dispersion liquid was added to the 3.5 valence state basic vanadium electrolyte, the dispersion liquid was added at 0.2%-0.8% of the mass of the electrolyte, and ultrasonic dispersion was performed at 300-500W for 30-50min, then erbium oxide and phosphoric acid were sequentially added, the erbium oxide was added at 0.008%-0.05% of the mass of the 3.5 valence state basic vanadium electrolyte, and the phosphoric acid was added at 0.05mol / L-0.15mol / L, and then mixed uniformly to obtain the electrolyte.

[0060] The raw materials used in the embodiments of the present application can be obtained through commercial channels, wherein:

[0061] Carbon nanotubes, Qingdao Haoxin New Energy Technology Co., Ltd.;

[0062] Concentrated sulfuric acid, 98%, Xinhua Pharmaceutical Shouguang Co., Ltd.;

[0063] Erbium oxide, analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.;

[0064] Phosphoric acid, Qingdao Jinghang Chemical Co., Ltd.;

[0065] Polyvinylpyrrolidone, Shanghai Aladdin Bio-Chem Technology Co., Ltd.;

[0066] Polyethylene glycol 400, PEG400, Shanghai Aladdin Bio-Chem Technology Co., Ltd.;

[0067] Sodium dodecyl sulfate, Shanghai Aladdin Bio-Chem Technology Co., Ltd.;

[0068] Urea, Henan Zhongyuan Dahua Group Co., Ltd.;

[0069] Vanadium pentoxide, Shanghai Aladdin Bio-Chem Technology Co., Ltd. Specific embodiments

[0070] Preparation Example 1

[0071] Preparation of nitrogen-doped modified carbon nanotubes: 1g of urea and 1g of single-walled carbon nanotubes were mixed, heated to 800℃ in a tube furnace under argon protection for 3h, and then refluxed in concentrated sulfuric acid for 1h to obtain nitrogen-doped modified carbon nanotubes. Example 1

[0072] 0.06 g carbon nanotubes (single wall) were placed in 36 g concentrated sulfuric acid and refluxed for 1 h, after refluxing, the sulfuric acid was washed away with water and dried at 30°C for standby use, 0.06 g of the carbon nanotubes treated above were weighed and added into 1.34 g of polyvinylpyrrolidone, 2.5 ml of water was added, stirred at 8000 rpm for 50 min, and dispersed by ultrasonic at 300 W for 50 min to obtain a dispersion liquid; 544 g of water and 500 g of concentrated sulfuric acid were prepared into a sulfuric acid solution, 137 g of vanadium pentoxide was added into the sulfuric acid solution, the temperature was kept at 60°C, stirred at 300 rpm for 1 h of activation reaction, 70 g of oxalic acid was added for further reaction for 1 h, cooled to 25°C, and diluted to 1 L, electrolysis was carried out by using an electrolytic cell, the electrolysis was carried out according to formula (II) to obtain a 3.5 valence state basic vanadium electrolyte; the 1 L 3.5 valence state basic electrolyte was added into the dispersion liquid, dispersed by ultrasonic at 300 W for 50 min, 0.45 g of erbium oxide was added and mixed uniformly, 9 g of phosphoric acid was added and mixed uniformly to obtain an electrolyte. Example 2

[0073] 0.13 g carbon nanotubes (single wall) were placed in 78 g concentrated sulfuric acid and refluxed for 1 h, after refluxing, the sulfuric acid was washed away with water and dried at 30°C for standby use, 0.13 g of the carbon nanotubes treated above were weighed and added into 2.75 g of polyethylene glycol 400, 4 ml of water was added, stirred at 10000 rpm for 40 min, and dispersed by ultrasonic at 400 W for 40 min to obtain a dispersion liquid; 508 g of water and 468 g of concentrated sulfuric acid were prepared into a sulfuric acid solution, 155 g of vanadium pentoxide was added into the sulfuric acid solution, the temperature was kept at 70°C, stirred at 400 rpm for 1 h of activation reaction, 11.2 g of glycerol was added for further reaction for 1 h, cooled to 25°C, diluted to 1 L, electrolysis was carried out by using an electrolytic cell, the electrolysis was carried out according to formula (II) to obtain a 3.5 valence state basic vanadium electrolyte; the 1 L 3.5 valence state basic electrolyte was added into the dispersion liquid, dispersed by ultrasonic at 400 W for 40 min, 0.69 g of erbium oxide was added and mixed uniformly, 11.5 g of phosphoric acid was added and mixed uniformly to obtain an electrolyte. Example 3

[0074] Put 0.25 g carbon nanotubes (single wall) in 150 g concentrated sulfuric acid and reflux for 1 h, then wash the sulfuric acid away with water and dry at 30°C to obtain a product for use, take 0.25 g of the carbon nanotubes treated as above and add 4.95 g sodium dodecyl sulfonate, 6 ml water, stir at 15000 rpm for 30 min, and disperse ultrasonically at 500 W for 30 min to obtain a dispersion; prepare a sulfuric acid solution by mixing 635 g water with 468 g concentrated sulfuric acid, accurately weigh 200 g vanadium pentoxide and add to the sulfuric acid solution, keep the temperature at 80°C, stir at 500 rpm for 1 h to activate the reaction, add 102 g oxalic acid and continue to react for 1 h, cool to 25°C, dilute to 1 L, and electrolyze using an electrolytic cell, the electrolysis is carried out according to formula (II) to obtain a 3.5 valence state basic vanadium electrolyte; add the 1 L 3.5 valence state basic electrolyte to the dispersion, disperse ultrasonically at 300 W for 30 min, add 0.7 g erbium oxide, mix well, add 14 g phosphoric acid, mix well, and obtain an electrolyte.

[0075] The electrolytes obtained in Examples 1-3 are subjected to conductivity, coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization rate, energy density, and capacity retention rate tests. The water meets the third grade water standard in GB 6682-92 "Water Specifications and Test Methods for Analytical Laboratories", the pH value is in the range of 5.0-7.5, the conductivity is ≤5 μS / m, and the resistivity is ≥0.2 MΩ·cm. The test items and test methods are as follows:

[0076] Charge-discharge performance test: the battery assembled with the electrolyte is subjected to constant current charge-discharge test at a current density of 4 A and 160 mA / cm 2 , and the conductivity is determined by the electrochemical workstation CHI660E using the alternating current impedance method. Battery assembly: carbon felt is used as the positive and negative electrodes, 240 ml of the electrolyte is evenly divided into two equal parts as the positive electrolyte and the negative electrolyte of the battery, N212 perfluorosulfonic acid ion exchange membrane is used as the separator, a magnetic drive circulating pump is used as the power device for transporting the electrolyte, and silica gel sheets are used for sealing to obtain the battery. The charge-discharge test is carried out at a current density of 160 mA / cm 2 for constant current charging / constant current discharging, and the cycle is repeated for 200 times to obtain the coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization rate, energy density, and capacity retention rate.

[0077] The test results of Examples 1-3 according to the above test methods are shown in Table 1:

[0078] Table 1 Performance test of the electrolyte of Examples 1-3

[0079]

[0080] As can be seen from Examples 1-3 and Table 1, the conductivity of the electrolyte of Examples 1-3 of the application is above 391 mS / cm, the energy efficiency is above 86.83%, the vanadium utilization rate is above 71%, the energy density is above 20.71 wh / L, and the capacity retention rate is above 84%, indicating that the electrolyte of the application can significantly improve the conductivity and has a higher capacity retention rate, vanadium utilization rate and energy density. Carbon nanotubes can be interconnected in the electrolyte to form a three-dimensional continuous electron conduction network, thereby improving the conductivity; phosphate ions can form a complex with high-valence vanadium ions, especially pentavalent vanadium ions, effectively reducing the concentration of free pentavalent vanadium ions, and inhibiting the generation of vanadium pentoxide precipitate from the thermodynamic and kinetic aspects, thereby enhancing the capacity retention rate of the electrolyte; erbium oxide can regulate the solvation structure of vanadium ions, slow down the transmembrane migration rate of vanadium ions, and be adsorbed on the electrode surface to optimize the double-layer structure or provide active sites, thereby improving the energy efficiency and vanadium utilization rate. The synergistic effect of the above components can comprehensively improve the conductivity, stability and reactivity of the electrolyte. The increase of the proportion of vanadium pentoxide can improve the energy density of the electrolyte, but will cause the conductivity, coulombic efficiency and voltage efficiency to decrease. The increase of the proportion of carbon nanotubes can increase the conductivity and vanadium utilization rate of the electrolyte, but will cause the energy density to decrease at the same time.

[0081] Comparative Example 1

[0082] The difference between the present comparative example and Example 2 is that the present comparative example replaces the carbon nanotubes in Example 2 with erbium oxide in equal mass.

[0083] Comparative Example 2

[0084] The difference between the present comparative example and Example 2 is that the present comparative example replaces the erbium oxide in Example 2 with carbon nanotubes in equal mass.

[0085] Comparative Example 3

[0086] The difference between the present comparative example and Example 2 is that the present comparative example replaces the single-walled carbon nanotubes in Example 2 with multi-walled carbon nanotubes in equal mass.

[0087] The electrolytes obtained in Examples 2 and Comparative Examples 1-2 were detected for conductivity, coulombic efficiency, voltage efficiency, energy efficiency, vanadium utilization rate, energy density and capacity retention rate. The detection results are shown in Table 2:

[0088] Table 2 Performance detection of electrolytes of Example 2 and Comparative Examples 1-3

[0089]

[0090] As can be seen from Example 2, Comparative Examples 1-2 and Table 2, the conductivity of the electrolyte of Example 2 is 401 mS / cm, the energy efficiency is 87.97%, the vanadium utilization rate is 80%, the energy density is 22.97 wh / L, and the capacity retention rate is 86%, which are significantly better than the electrolytes prepared by using carbon nanotubes or erbium oxide alone. The carbon nanotubes can improve the conductivity of the electrolyte by constructing a three-dimensional conductive network, and the erbium oxide can optimize the electrode interface reaction kinetics, avoid uneven current density distribution and local overcharge / overdischarge on the electrode surface, thereby reducing side reactions and electrode corrosion, and ultimately improving the capacity retention rate. Although the use of carbon nanotubes alone can construct an electron conductive network, the high redox reaction energy barrier and slow speed of vanadium ions at the interface make the electrochemical polarity large, resulting in a decrease in vanadium ion utilization rate and energy density. Although the use of erbium oxide alone can optimize the interface reaction kinetics, the electron transmission depends on the ion path and the electrode with poor conductivity, which increases the ohmic resistance of the system, resulting in a significant decrease in conductivity and capacity retention rate.

[0091] As can be seen from Example 2, Comparative Example 3 and Table 2, compared with the use of multi-walled carbon nanotubes, single-walled carbon nanotubes can significantly improve the conductivity and capacity retention rate. Single-walled carbon nanotubes are curled from a single layer of graphene, have a larger specific surface area, can provide more contact points and a wider interface in the electrolyte, and are more likely to form an interwoven and tight "nanometer grid", thereby constructing a more efficient and more comprehensive three-dimensional conductive path to improve the conductivity.

[0092] Example 4-5

[0093] Based on Example 2, except for the weight ratio of carbon nanotubes and erbium oxide, the other components and preparation methods are consistent with those of Example 2, and the total weight of carbon nanotubes and erbium oxide remains unchanged.

[0094] Example 4

[0095] The difference between this example and Example 2 is that the weight ratio of carbon nanotubes and erbium oxide in this example is 1:3, specifically, the weight of carbon nanotubes is 0.205 g, and the weight of erbium oxide is 0.615 g.

[0096] Example 5

[0097] The difference between this example and Example 2 is that the weight ratio of carbon nanotubes and erbium oxide in this example is 1:2, specifically, the weight of carbon nanotubes is 0.273 g, and the weight of erbium oxide is 0.547 g.

[0098] The conductivity, vanadium utilization rate, energy density, and capacity retention rate of the electrolytes obtained in Example 2, Examples 4-5 were detected. The detection results are shown in Table 3:

[0099] Table 3 Performance detection of electrolytes of Example 2, Examples 4-5

[0100]

[0101] As can be seen from Example 2, Example 4-5 and Table 3, the vanadium utilization rate of the electrolyte of Example 4 is 84.92%, the energy density is 24.40 wh / L, and the capacity retention rate is 87%, which is significantly better than Example 2 and Example 5. In the present application, carbon nanotubes and erbium oxide in a specific ratio are used. On the one hand, the carbon nanotubes ensure the construction of an effective three-dimensional conductive network and improve the electrical conductivity. On the other hand, the erbium oxide fully modifies the electrode / electrolyte interface to optimize the reaction kinetics, thereby achieving the simultaneous optimization of battery energy efficiency, cycle life and energy density. If the proportion of erbium oxide is too high, the erbium oxide particles may be excessively adsorbed or aggregated on the surface of the electrode, blocking the active sites, affecting the normal transmission and reaction of vanadium ions, and reducing the vanadium utilization rate and the capacity retention rate. If the proportion of carbon nanotubes is too high, the carbon nanotubes may be aggregated in the electrolyte, making it difficult to form a uniform and stable nanodispersion system, blocking the electrode pores or the separator, and reducing the capacity retention rate.

[0102] Example 6

[0103] The difference between the present example and Example 4 is that the carbon nanotubes in Example 4 are replaced by the nitrogen-doped modified carbon nanotubes obtained in Preparation Example 1.

[0104] The electrolytes obtained in Example 4 and Example 6 are subjected to conductivity, vanadium utilization rate, energy density and capacity retention rate detection. The detection results are shown in Table 4:

[0105] Table 4 Performance detection of electrolytes of Example 4 and Example 6

[0106]

[0107] As can be seen from Example 4, Example 6 and Table 4, the conductivity of the electrolyte of Example 6 is 418 mS / cm, the vanadium utilization rate is 87.04%, the energy density is 25.01 wh / L, and the capacity retention rate is 89%, which is significantly better than Example 4. The introduction of nitrogen atoms into the graphite lattice of the carbon nanotubes changes the surface charge distribution of the carbon nanotubes, optimizes the interface interaction between the carbon nanotubes and the ions in the electrolyte, thereby significantly reducing the charge transfer resistance and improving the electrical conductivity. In addition, the introduced nitrogen atoms enhance the polarity of the surface of the carbon nanotubes, which is beneficial to improving the compatibility of the carbon nanotubes with the aqueous electrolyte, and thus realizing more excellent and stable dispersibility.

[0108] The above are preferred embodiments of the present application, which do not limit the protection scope of the present application, therefore: any equivalent changes made on the basis of the structure, shape, principle of the present application should be covered into the protection scope of the present application.

Claims

1. A high conductive vanadium flow battery electrolyte, characterized in that, The preparation raw materials include the following weight parts: 0.06-0.25 parts of carbon nanotubes, 9-14 parts of phosphoric acid, 0.45-0.7 parts of erbium oxide, 137-200 parts of vanadium pentoxide, 536-618 parts of sulfuric acid, 1.34-4.95 parts of a dispersant, and 11.2-102 parts of a reducing agent; The weight ratio of the carbon nanotubes to the erbium oxide is 1:(2-5.3); the carbon nanotubes are single-walled carbon nanotubes; and the preparation steps of the electrolyte solution include: S1, dispersion: purifying the carbon nanotubes by acid treatment, adding a dispersant, and dispersing by high-speed shearing and ultrasonic dispersion to obtain a carbon nanotube dispersion liquid; S2, preparation of a 3.5-valence basic vanadium electrolyte solution: mixing vanadium pentoxide, sulfuric acid, and a reducing agent, heating and stirring, cooling, constant volume, and then electrolyzing by using an electrolytic cell to obtain a 3.5-valence basic vanadium electrolyte solution; S3, homogenization: mixing the carbon nanotube dispersion liquid obtained in step S1 with the 3.5-valence basic vanadium electrolyte solution obtained in step S2, dispersing, and then sequentially adding erbium oxide and phosphoric acid and mixing uniformly to obtain the electrolyte solution.

2. The high conductivity vanadium flow battery electrolyte of claim 1, wherein, The carbon nanotubes are nitrogen-doped modified carbon nanotubes.

3. The high conductivity vanadium flow battery electrolyte of claim 2, wherein, 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.

4. The high conductivity vanadium flow battery electrolyte of claim 1, wherein, The dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol 400, and sodium dodecyl sulfonate.

5. The high conductivity vanadium flow battery electrolyte of claim 1, wherein, The reducing agent is one or more of oxalic acid, citric acid, glycerol, and glucose.

6. The high conductivity vanadium flow battery electrolyte of claim 1, wherein, In the S1, the high-speed shearing stirring speed is 8000-15000 rpm.

7. A vanadium flow battery characterised in that, The high-conductivity vanadium flow battery electrolyte solution of any one of claims 1-6.

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