Vanadium flow battery electrolyte and battery

Abstract

The application belongs to the technical field of all-vanadium liquid flow electrolyte, and discloses an all-vanadium liquid flow battery electrolyte and a battery, wherein the electrolyte comprises VOSO4 or V2(SO4)3, H2SO4 and an electrolyte additive, the concentration of the electrolyte additive is 0.01mol / L-1mol / L, and the electrolyte additive is selected from at least one of the following substances: or X is F, Br or I. The electrolyte additive used in the application makes the pentavalent vanadium ion have better high-temperature stability, and the prepared battery has better cycle stability and better electrical performance, such as higher average coulomb efficiency, voltage efficiency and energy efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of all-vanadium redox flow electrolyte, and relates to an all-vanadium redox flow battery electrolyte and a battery. BACKGROUND

[0002] The statements herein are provided only to enhance understanding of the application and are not necessarily intended to constitute the prior art.

[0003] The global energy consumption growth promotes the development of renewable energy, and new energy storage is the key to supporting the energy transformation and industrial upgrading. At present, solar energy and wind energy are limited by natural conditions and have the disadvantages of instability and discontinuity, and lithium battery energy storage also faces capacity and safety bottlenecks. The all-vanadium redox flow battery has become an important choice for grid peak shaving, renewable energy consumption and large-scale energy storage due to its inherent safety, flexibility, long service life, fast response and environmental friendliness.

[0004] The all-vanadium redox flow battery is a kind of redox battery with vanadium as active substance in the form of circulating flow liquid. The electric energy of the all-vanadium redox flow battery is stored in the form of chemical energy in the sulfuric acid electrolyte of different valence vanadium ions. The electrolyte is transported to the half-cell stack by a pump, and circulates in the closed loop of different liquid storage tanks and half-cells under the action of mechanical power. A proton exchange membrane is used as the separator of the half-cell. The electrolyte solution flows through the porous electrode and undergoes electrochemical reaction. The current is collected and conducted through the bipolar plate, so as to realize the mutual conversion of chemical energy and electric energy.

[0005] The electrolyte is an energy storage medium of the all-vanadium redox flow battery. Vanadium ions (V 2+ / V 3+ and V 4+ / V 5+ ) in the electrolyte undergo oxidation-reduction reaction on the electrode surface to realize the conversion of electric energy and chemical energy. The solvation structure of pentavalent vanadium ions is easy to lose protons to form vanadium pentoxide precipitate under high temperature conditions, which reduces the concentration of active substances in the electrolyte and causes irreversible decay of the battery performance. The generated vanadium pentoxide precipitate will block the electrode and pipeline.

[0006] Some existing technologies use organic ligands and halides to cooperate to improve the defect problem of V 5+ hydration structure change to generate V2O5 precipitate, but the degree of solving this problem is limited. Therefore, the high-temperature stability of pentavalent vanadium ions needs to be improved. SUMMARY

[0007] In view of the deficiencies in the prior art, the purpose of the present application is to provide an all-vanadium redox flow battery electrolyte and battery to improve the stability and efficiency of the all-vanadium redox flow battery under high temperature conditions.

[0008] To achieve the above object, the present application is realized by the following technical solutions:

[0009] In a first aspect, the present application provides a vanadium redox flow battery electrolyte, which comprises VOSO4 or V2(SO4)3, H2SO4 and an electrolyte additive, wherein the concentration of the electrolyte additive is 0.01 mol / L to 1 mol / L.

[0010] The electrolyte additive is selected from at least one of the following substances:

[0011] or ;

[0012] X is F, Br or I.

[0013] In a second aspect, the present application provides a vanadium redox flow battery, wherein the positive electrolyte and / or the negative electrolyte of the vanadium redox flow battery is the vanadium redox flow battery electrolyte.

[0014] The beneficial effects achieved by one or more embodiments of the present application are as follows:

[0015] (1) In the additive of the present application, halogen ions (F - , Br - , I - , etc.) participate in the solvation structure of pentavalent vanadium ions ([VO2(H2O)3] + ) in the positive electrolyte, which inhibits the deprotonation process at high temperature by changing the charge distribution and steric hindrance of vanadium ions, and can improve the stability of pentavalent vanadium ions at high temperature.

[0016] (2) In the additive of the present application, the nitrogen-methyl alkyl imidazole or nitrogen-methyl alkyl pyridine cation onium salt can attract free halogen anions (such as F - , Br - , I - , etc.) in the positive electrolyte through electrostatic interaction, reduce the electrochemical reaction of free halogen anions (such as F - , Br - , I - , etc.), and reduce the corrosion of the positive electrode; the additive in the present application can be adsorbed on the electrode surface in the negative electrolyte, forming a double-layer structure and reducing the negative electrode interfacial resistance. The electrolyte additive used in the present application makes the pentavalent vanadium ions have better high-temperature stability, and the prepared battery has better cycle stability and better electrical performance, such as better average coulombic efficiency, voltage efficiency and energy efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated herein by reference. The illustrations are of exemplary embodiments of the application and explain the principles of the application, but do not limit the application.

[0018] Figure 1 is the performance of the all-vanadium redox flow battery with brominated nitrogen-methyl alkyl imidazole as the positive electrolyte additive, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0019] Figure 2 is the performance of the all-vanadium redox flow battery with iodinated nitrogen-methyl alkyl pyridine as the positive electrolyte additive, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0020] Figure 3 is the performance of the all-vanadium redox flow battery with blank electrolyte, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0021] Figure 4 is the performance of the all-vanadium redox flow battery in Example 4, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0022] Figure 5 is the performance of the all-vanadium redox flow battery in Comparative Example 1, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0023] Figure 6 is the performance of the all-vanadium redox flow battery in Comparative Example 2, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0024] Figure 7 is the performance of the all-vanadium redox flow battery in Comparative Example 3, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0025] Figure 8 is the performance of the all-vanadium redox flow battery in Comparative Example 4, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0026] Figure 9 is the performance of the all-vanadium redox flow battery in Comparative Example 5, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance;

[0027] Figure 10 is the performance of the all-vanadium redox flow battery in Comparative Example 6, wherein (a) is the charge-discharge efficiency of the all-vanadium redox flow battery; (b) is the discharge capacity retention performance. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0029] In the sulfuric acid system, the pentavalent vanadium ion does not simply exist in the form of VO2 + , but in a variety of complex vanadium-oxygen ion hydration structures. Under general conditions, when the temperature of the system increases, the pentavalent vanadium ion hydration ion will undergo deprotonation, as shown in equations (1) and (2), to form vanadium pentoxide solid precipitate.

[0030] [VO2(H2O)3] + →[VO(OH)3] + H3O + (1);

[0031] [VO(OH)3] → V2O5•3H2O (precipitate) (2).

[0032] The pentavalent vanadium ion is an active substance in the electrolyte, and after forming a precipitate in the form of vanadium pentoxide, it will no longer participate in the redox reaction, which will directly lead to a decrease in the total energy storage capacity of the electrolyte. Moreover, the generated vanadium pentoxide is a solid particle, which will block the porous electrode, the pores of the carbon felt electrode will be blocked, reducing the specific surface area for reaction, increasing the electrochemical polarization, leading to a decrease in the charging / discharging efficiency; the precipitate will wear the pump, block the filter and small-diameter pipeline in the circulation system, affect the normal circulation of the electrolyte, and even cause the system to shut down; the precipitate adheres to the ion exchange membrane, increasing the ion transmission resistance, greatly increasing the internal resistance of the battery, leading to an increase in energy consumption and a decrease in efficiency.

[0033] Since vanadium pentoxide is a solid and difficult to re-melt, once formed, it cannot be eliminated by simple circulation, so the performance loss caused is irreversible.

[0034] To solve the above technical problems, the application provides a full vanadium redox flow battery electrolyte, which comprises VOSO4 or V2(SO4)3, H2SO4 and an electrolyte additive, and the concentration of the electrolyte additive is 0.01 mol / L to 1 mol / L.

[0035] The electrolyte additive is selected from at least one of the following substances:

[0036] or ;

[0037] X is F, Br or I.

[0038] The pentavalent vanadium ion formed in the positive electrolyte (usually in the form of dioxovanadate ion, which can be written as [VO2] + ) will interact with the surrounding water molecules and anions in the sulfuric acid solution to form a stable "solvation shell". The original solvation structure is [VO2(H2O)3] + , that is, surrounded by water molecules.

[0039] Halide ions (X - ) can participate in the solvation structure of pentavalent vanadium ions, forming stable neutral structures with hydrated vanadium oxygen cations, inhibiting the deprotonation process at high temperatures.

[0040] Halide ions (X - ) are Lewis bases, and their electronegativity is weaker than that of oxygen in water molecules (except for F). When X - coordinates to the vanadium ion, it will provide electrons to the central vanadium atom more easily than water molecules.

[0041] Vanadium is in the highest valence state (+5), with a strong electron-withdrawing tendency. The electron density provided by halide ions partially neutralizes the strong positive charge of vanadium, weakening the bond between vanadium and oxygen (V=O), reducing the electrophilicity of oxygen: the electron cloud density of oxygen increases, reducing its ability to extract protons (H + ) from water molecules. "Deprotonation" is the first step in generating highly active vanadate ions and is the rate-determining step of the precipitation reaction. If this step is inhibited, the entire hydrolysis and precipitation reaction will be inhibited.

[0042] In addition, halide ions have a certain volume, and when they enter the coordination structure of vanadium ions, their volume effect hinders the approach of water molecules to vanadium ions, and to some extent, hinders the precipitation of vanadium ions.

[0043] Through the above analysis, it can be seen that halide ions play an important role, but if high concentrations of halides (such as KBr, NaF, etc.) are directly added, a large number of X - will freely move to the electrode surface, triggering a series of side reactions, such as: when the battery is charging, the positive electrode potential is very high, Br - or I - may be oxidized to Br2 or I2 on the electrode surface. Strongly oxidizing halogen elements will cause some corrosion to the electrode, leading to an increase in oxygen-containing functional groups on the electrode surface, a decrease in electrochemical activity, and a reduction in service life. In addition, the redox reaction of halide ions at the electrode interface to form neutral molecules will no longer participate in the coordination of the vanadium ion hydration structure, reducing the temperature stability of the electrolyte.

[0044] In the present application, when nitrogen methyl imidazolium fluoride salt, nitrogen methyl pyridinium fluoride salt, nitrogen methyl imidazolium bromide salt, nitrogen methyl pyridinium bromide salt, nitrogen methyl imidazolium iodide salt or nitrogen methyl pyridinium iodide salt and the like are selected as electrolyte additives in the positive electrolyte, these additives are completely dissociated in the electrolyte, but due to the large volume of organic cations and the dispersion of electric charge, while the halide anion has small volume and concentrated electric charge, there is strong electrostatic attraction between them, forming ion pairs, which significantly reduces the concentration of free halide anions in the electrolyte; and the presence of these cations significantly slows down the diffusion rate and reaction kinetics of halide ions.

[0045] In addition, in the negative electrolyte, at the electrode / electrolyte interface, positively charged organic cations tend to be adsorbed on the negatively charged electrode surface, and through the amphiphilic nature of the organic cation and electrostatic adsorption, a stable double-layer structure is formed at the electrode interface, which is beneficial to improve the ion electrochemical reaction process at the interface and reduce the electrochemical polarization.

[0046] Therefore, when the above additives are added to the electrolyte of the all-vanadium redox flow battery, not only can the high-temperature stability of pentavalent vanadium ions be better improved, but also a double-layer structure can be formed in the negative electrolyte to improve the electrochemical reaction process, so that the prepared battery has better cycle stability and better electrical performance, such as higher average coulombic efficiency, voltage efficiency and energy efficiency.

[0047] In some embodiments, the concentration of the electrolyte additive is 0.02 mol / L to 1 mol / L. For example, it can be 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L.

[0048] Preferably, the concentration of the electrolyte additive is 0.1 mol / L to 1 mol / L, more preferably 0.05 mol / L to 0.2 mol / L. For example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L.

[0049] In some embodiments, the electrolyte additive is nitrogen methyl imidazolium bromide salt or nitrogen methyl pyridinium iodide salt.

[0050] In some embodiments, the total concentration of vanadyl oxo is 0.5-3 mol / L in the electrolyte of the all-vanadium redox flow battery; preferably 1-3 mol / L.

[0051] In some embodiments, the total concentration of sulfate is 1-5 mol / L in the electrolyte of the all-vanadium redox flow battery; preferably 2-5 mol / L.

[0052] In some embodiments, the electrolyte of the all-vanadium redox flow battery is a positive electrolyte or a negative electrolyte; when it is a positive electrolyte, the electrolyte comprises VOSO4, H2SO4 and an electrolyte additive;

[0053] When it is a negative electrolyte, the electrolyte comprises V2(SO4)3, H2SO4 and an electrolyte additive.

[0054] The electrochemical reaction of the negative electrode of the all-vanadium redox flow battery is that the trivalent vanadium ion is reduced to divalent vanadium ion by obtaining electrons, and the reduction potential is close to that of the reduction of hydrogen by water, so at the end of charging, when the local current density is too high or the temperature rises, the hydrogen evolution side reaction is prone to occur, which in turn has the following adverse effects: consumption of electrolyte and charge, reduction of coulombic efficiency.

[0055] The organic cation in the additive has amphiphilic properties, which can improve the electrode and electrolyte interface, and at the same time form a double-layer structure at the negative electrode interface due to electrostatic adsorption, thereby improving the efficiency of the electrochemical reaction at the interface.

[0056] In a second aspect, the present application provides an all-vanadium redox flow battery, wherein the positive electrolyte and / or the negative electrolyte of the all-vanadium redox flow battery is the electrolyte of the all-vanadium redox flow battery.

[0057] In some embodiments, the positive electrolyte comprises VOSO4, H2SO4 and an electrolyte additive; the negative electrolyte comprises V2(SO4)3, H2SO4 and an electrolyte additive.

[0058] The present application is further described below in conjunction with embodiments.

[0059] In the following embodiments, the electrolyte additive added is at least one selected from the group consisting of fluorinated nitrogen-methyl imidazolium salt, fluorinated nitrogen-methyl pyridinium salt, brominated nitrogen-methyl imidazolium salt, brominated nitrogen-methyl pyridinium salt, iodinated nitrogen-methyl imidazolium salt or iodinated nitrogen-methyl pyridinium salt, and the structural formula is as shown below:

[0060] Or ;

[0061] X is F, Br or I.

[0062] The preparation method of the electrolyte additive is as follows:

[0063] ;

[0064] ;

[0065] wherein X is F, Br or I;

[0066] Into a 250 mL volumetric flask, 50 mL of imidazole / pyridine in diethyl ether solution and 50 mL of methyl halide in diethyl ether solution (molar ratio of imidazole / pyridine to methyl halide is 1:1.5) were added, and the reaction was carried out under magnetic stirring at a heating temperature of 40-55°C for 5-8 h. After the reaction was completed, the solvent and excess methyl halide were removed by rotary evaporation to obtain a white / yellowish solid halogenated nitrogen-methyl imidazole / pyridinium salt additive.

[0067] In the above preparation method, the concentration of the solute in the imidazole / pyridine in diethyl ether solution and the methyl halide in diethyl ether solution is between 5% and 30% by weight.

[0068] Example 1

[0069] Into a prepared 60 mL positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4), a nitrogen-methyl imidazolium bromide salt additive was added, and after being fully stirred and completely dissolved, a positive electrolyte containing 0.1 mol / L of nitrogen-methyl imidazolium bromide salt additive was prepared.

[0070] The structural formula of the nitrogen-methyl imidazolium bromide salt is:

[0071] X is Br.

[0072] A 1.6 mol / L V2(SO4)3+3 mol / L H2SO4solution was matched as a negative electrolyte, and a full vanadium flow energy storage single cell was assembled. Among them, a porous carbon felt (thickness of 4.3 mm) was used as an electrode; a graphite plate (thickness of 2 mm) was used as a bipolar plate; Nafion115 was used as a battery ion conducting film (effective area of the film was 48 cm 2 , 6 cm x 8 cm); and the cutoff voltage was 1.0-1.55 V.

[0073] The full vanadium flow energy storage single cell was tested at an ambient temperature of 50°C in a constant current charge and discharge mode at a current density of 80 mA / cm 2 .

[0074] The average coulombic efficiency refers to the ratio of the actual discharge capacity to the charging capacity during the charging and discharging process, and reflects the efficiency of the electrochemical reaction and the degree of side reaction.

[0075] The voltage efficiency refers to the ratio of the average discharge voltage to the average charging voltage of the battery.

[0076] Battery system energy efficiency is an important indicator to measure the energy conversion capacity of the battery pack, which is defined as the ratio of the energy output to the inverter when the battery pack is discharged to the energy input to the battery pack when it is charged under the condition of constant power charging and discharging, expressed in percentage form.

[0077] The test results are shown in Figs. (a) and (b) of the accompanying drawings. Figure 1 As shown in Figs. (a) and (b) of the accompanying drawings, the battery cycle performance is stable within 100 charge-discharge cycles, the capacity retention rate is 84%, the average coulomb efficiency is 97.9%, the voltage efficiency is 88.5%, and the energy efficiency is 86.6%.

[0078] Example 2

[0079] The prepared 60 mL positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4) was added with a nitrogen methyl imidazolium bromide additive, and after being fully stirred and completely dissolved, a positive electrolyte containing 0.1 mol / L of the nitrogen methyl imidazolium bromide additive was prepared.

[0080] The same electrolyte (0.1 mol / L of nitrogen methyl imidazolium bromide + 1.6 mol / L V2(SO4)3+ 3 mol / L H2SO4) was used as the negative electrolyte to assemble a full vanadium redox flow battery. Among them, the porous carbon felt (thickness of 4.3 mm) was used as the electrode; the graphite plate (thickness of 2 mm) was used as the bipolar plate; Nafion115 was used as the battery ion conducting film (effective area of the film was 48 cm 2 , 6 cm x 8 cm); the cutoff voltage was 1.0-1.55 V.

[0081] The full vanadium redox flow battery was tested at an ambient temperature of 50°C under a constant current charge-discharge mode at a current density of 80 mA / cm 2 .

[0082] The test results are shown in Figs. (a) and (b) of the accompanying drawings. Figure 2 As shown in Figs. (a) and (b) of the accompanying drawings, the battery cycle performance is stable within 100 charge-discharge cycles, the capacity retention rate is 95.6%, the average coulomb efficiency is 98.2%, the voltage efficiency is 88.7%, and the energy efficiency is 87.1%.

[0083] Example 3

[0084] The iodomethyl pyridinium salt was used as an additive to configure the positive electrolyte of the full vanadium redox flow battery: the iodomethyl pyridinium salt was added to 60 mL of the blank positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4), and after being fully stirred and completely dissolved, a positive electrolyte containing 0.1 mol / L of the iodomethyl pyridinium salt was prepared.

[0085] The structural formula of nitrogen methylpyridinium salt of iodide is:

[0086] X is I.

[0087] Using the same negative electrode electrolyte (1.6 mol / L V2(SO4)3 + 3mol / L H2SO4), Nafion115 was used as the ion-conducting membrane, porous carbon felt (4.3 mm thick) was used as the electrode, and graphite plate (2 mm thick) was used as the bipolar plate to assemble a vanadium redox flow cell with a cutoff voltage of 1.0~1.55 V.

[0088] A vanadium redox flow battery, operating at an ambient temperature of 50°C in constant current charge-discharge mode, achieves a current of 80 mA / cm². 2 The current density was tested.

[0089] Test results are as follows Figure 3 As shown in (a) and (b), after 100 charge-discharge cycles, the average coulombic efficiency of the vanadium redox flow battery is 96.8%, the average voltage efficiency is 87.9%, and the average energy efficiency is 85.1%, and the capacity remains stable during the 100 charge-discharge cycles with a capacity retention rate of 95.8%.

[0090] Example 4

[0091] A positive electrode electrolyte for a vanadium redox flow battery was prepared using nitrogen-methylpyridinium iodide as an additive: Nitrogen-methylpyridinium iodide was added to 60 mL of blank positive electrode electrolyte (1.6 mol / L VOSO4 + 3 mol / L H2SO4), and after thorough stirring and complete dissolution, a positive electrode electrolyte containing 0.1 mol / L nitrogen-methylpyridinium iodide was obtained.

[0092] Using the same electrolyte as the negative electrode electrolyte (0.1 mol / L methylpyridinium iodide + 1.6 mol / L V2(SO4)3 + 3 mol / L H2SO4), Nafion 115 was used as the ion conducting membrane, porous carbon felt (4.3 mm thick) was used as the electrode, and graphite plate (2 mm thick) was used as the bipolar plate to assemble an all-vanadium redox flow cell with a cutoff voltage of 1.0~1.55 V.

[0093] A vanadium redox flow battery, operating at an ambient temperature of 50°C in constant current charge-discharge mode, achieves a current of 80 mA / cm². 2 The current density was tested.

[0094] Test results are as follows Figure 4The test results are as follows: after 100 cycles of charge and discharge, the average coulombic efficiency of the all-vanadium redox flow battery is 97.3%, the average voltage efficiency is 88.7%, the average energy efficiency is 86.3%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 99.7%.

[0095] Example 5

[0096] The positive electrolyte of the all-vanadium redox flow battery is configured by adding fluorinated nitrogen methyl imidazolium salt as an additive: 0.1 mmol / L fluorinated nitrogen methyl imidazolium salt is added to 60 mL of blank positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4), and the positive electrolyte is prepared after being fully stirred and completely dissolved.

[0097] The structural formula of the fluorinated nitrogen methyl imidazolium salt is:

[0098] X is F.

[0099] The same negative electrolyte (1.6 mol / L V2(SO4)3+3 mol / L H2SO4) is matched, Nafion115 is used as an ion conduction film, porous carbon felt (thickness of 4.3 mm) is used as an electrode, and a graphite plate (thickness of 2 mm) is used as a bipolar plate, and an all-vanadium redox flow energy storage single cell is assembled, and the cutoff voltage is 1.0-1.55 V.

[0100] The all-vanadium redox flow energy storage single cell is tested at an ambient temperature of 50°C in a constant current charge and discharge mode at a current density of 80 mA / cm 2 .

[0101] The test results are as follows: after 100 cycles of charge and discharge, the average coulombic efficiency of the all-vanadium redox flow battery is 97.2%, the average voltage efficiency is 88.1%, the average energy efficiency is 85.6%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 85.3%.

[0102] Example 6

[0103] The positive electrolyte of the all-vanadium redox flow battery is configured by adding fluorinated nitrogen methyl imidazolium salt as an additive: 0.1 mmol / L fluorinated nitrogen methyl imidazolium salt is added to 60 mL of blank positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4), and the positive electrolyte is prepared after being fully stirred and completely dissolved.

[0104] The structural formula of the fluorinated nitrogen methyl imidazolium salt is:

[0105] , X is F.

[0106] The same negative electrolyte (1.6 mol / L V2(SO4)3+3 mol / L H2SO4) was matched, Nafion 115 was used as an ion conductive film, porous carbon felt (thickness of 4.3 mm) was used as an electrode, and a graphite plate (thickness of 2 mm) was used as a bipolar plate to assemble a full vanadium flow energy storage single cell, and the cutoff voltage was 1.0-1.55 V.

[0107] The full vanadium flow energy storage single cell was tested at an ambient temperature of 50 DEG C in a constant current charge and discharge mode at a current density of 80 mA / cm 2 .

[0108] The test results are as follows: after 100 cycles of charge and discharge, the average coulombic efficiency of the full vanadium flow battery is 97.1%, the average voltage efficiency is 88.7%, the average energy efficiency is 86.1%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 84.2%.

[0109] Example 7

[0110] A full vanadium flow battery positive electrolyte was prepared by adding a nitrogen methyl pyridine onium bromide salt as an additive to 60 mL of a blank positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4), and after being fully stirred and completely dissolved, a positive electrolyte containing 0.1 mmol / L nitrogen methyl pyridine onium bromide salt was prepared.

[0111] The structural formula of the nitrogen methyl pyridine onium bromide salt is:

[0112] , X is Br.

[0113] The same negative electrolyte (1.6 mol / L V2(SO4)3+3 mol / L H2SO4) was matched, Nafion 115 was used as an ion conductive film, porous carbon felt (thickness of 4.3 mm) was used as an electrode, and a graphite plate (thickness of 2 mm) was used as a bipolar plate to assemble a full vanadium flow energy storage single cell, and the cutoff voltage was 1.0-1.55 V.

[0114] The full vanadium flow energy storage single cell was tested at an ambient temperature of 50 DEG C in a constant current charge and discharge mode at a current density of 80 mA / cm 2 .

[0115] The test results are as follows: after 100 cycles of charge and discharge, the average coulombic efficiency of the full vanadium flow battery is 95.8%, the average voltage efficiency is 89.0%, the average energy efficiency is 85.3%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 82.2%.

[0116] Example 8

[0117] The positive electrolyte of the all-vanadium redox flow battery was prepared by adding iodine methylimidazolium salt as an additive to 60 mL of blank positive electrolyte (1.6 mol / L VOSO4+3 mol / L H2SO4). After being stirred and dissolved completely, the positive electrolyte containing 0.1 mmol / L iodine methylimidazolium salt was prepared.

[0118] The structural formula of the iodine methylimidazolium salt is as follows:

[0119] X is I.

[0120] The same negative electrolyte (1.6 mol / L V2(SO4)3+3 mol / L H2SO4) was matched, Nafion 115 was used as an ion-conducting membrane, porous carbon felt (4.3 mm in thickness) was used as an electrode, and a graphite plate (2 mm in thickness) was used as a bipolar plate to assemble an all-vanadium redox flow battery cell, and the cutoff voltage was 1.0-1.55 V.

[0121] The all-vanadium redox flow battery cell was tested at an ambient temperature of 50°C under a constant current charging and discharging mode at a current density of 80 mA / cm 2 .

[0122] The test results were as follows: after 100 cycles of charging and discharging, the average coulombic efficiency of the all-vanadium redox flow battery was 96.4%, the average voltage efficiency was 88.9%, the average energy efficiency was 85.7%, the capacity remained stable during the 100 cycles of charging and discharging, and the capacity retention rate was 84.1%.

[0123] Example 9

[0124] The difference between Example 1 and the present example is that the electrolyte additive is 0.05 mmol / L of bromine methylimidazolium salt and 0.05 mmol / L of fluorine methylimidazolium salt, and the other conditions are the same as those in Example 1.

[0125] The test results were as follows: after 100 cycles of charging and discharging, the average coulombic efficiency of the all-vanadium redox flow battery was 97.6%, the average voltage efficiency was 88.2%, the average energy efficiency was 86.1%, the capacity remained stable during the 100 cycles of charging and discharging, and the capacity retention rate was 87.4%.

[0126] Example 10

[0127] The difference from Example 1 is that the electrolyte additive is 0.05 mmol / L of bromide nitrogen methyl imidazolium salt and 0.05 mmol / L of bromide nitrogen methyl pyridine onium salt, and the others are the same as Example 1.

[0128] The test results are that after 100 cycles of charge and discharge, the average coulombic efficiency of the all-vanadium redox flow battery is 97.5%, the average voltage efficiency is 88.0%, the average energy efficiency is 85.8%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 86.5%.

[0129] Example 11

[0130] The difference from Example 1 is that the electrolyte additive is 0.05 mmol / L of bromide nitrogen methyl imidazolium salt and 0.05 mmol / L of iodide nitrogen methyl imidazolium salt, and the others are the same as Example 1.

[0131] The test results are that after 100 cycles of charge and discharge, the average coulombic efficiency of the all-vanadium redox flow battery is 96.7%, the average voltage efficiency is 88.3%, the average energy efficiency is 85.4%, and the capacity remains stable during the 100 cycles of charge and discharge, and the capacity retention rate is 84.6%.

[0132] Comparative Example 1

[0133] 1.6 mol / L VOSO4+3 mol / L H2SO4 solution as the positive electrolyte and 1.6 mol / L V 3+ +3 mol / L H2SO4 solution as the negative electrolyte; Nafion115 (effective area 48 cm 2 , 6 cm x 8 cm) is used as an ion conductive membrane; porous carbon felt (thickness of 4.3 mm) is used as an electrode; graphite plate (thickness of 2 mm) is used as a bipolar plate, and an all-vanadium redox flow battery is assembled. The single battery is tested at room temperature in a constant current charge and discharge mode at a current density of 80 mA / cm 2 , and the cutoff voltage is 1.0-1.55 V.

[0134] As shown in Figs. Figure 5 (a) and (b), the blank electrolyte is tested in the all-vanadium redox flow battery, and the battery efficiency fluctuates frequently during 25 cycles, the average coulombic efficiency is 95.8%, the voltage efficiency is 85.3%, the energy efficiency is 81.7%, and the discharge capacity decays rapidly, and after 25 cycles of test, it decays to about 50% of the initial capacity.

[0135] Comparative Example 2

[0136] The difference from Example 1 is that the electrolyte additive is 0.1 mol / L N-methylimidazole, while all other aspects are the same as in Example 1.

[0137] like Figure 6 As shown in (a) and (b), the test results are as follows: after 25 charge-discharge cycles, the average coulombic efficiency of the vanadium redox flow battery is 96.3%, the average voltage efficiency is 84.1%, the average energy efficiency is 81.0%, and the capacity retention rate is 65.9% during the 25 charge-discharge cycles.

[0138] Comparative Example 3

[0139] The difference from Example 1 is that the electrolyte additive is 0.1 mol / L potassium bromide, while everything else is the same as in Example 1.

[0140] like Figure 7 As shown in (a) and (b), the test results are as follows: after 25 charge-discharge cycles, the average coulombic efficiency of the vanadium redox flow battery is 94.9%, the average voltage efficiency is 85.5%, the average energy efficiency is 81.1%, and the capacity retention rate is 84.2% during the 25 charge-discharge cycles.

[0141] Comparative Example 4

[0142] The difference from Example 1 is that the electrolyte additive is 0.1 mol / L N-methylpyridine, while all other aspects are the same as in Example 1.

[0143] The test results are as follows: After 25 charge-discharge cycles, the vanadium redox flow battery exhibits an average coulombic efficiency of 95.7%, an average voltage efficiency of 85.5%, and an average energy efficiency of 81.8%. Furthermore, the capacity retention rate during these 25 charge-discharge cycles is 65.9%. Figure 8 As shown in (a) and (b).

[0144] Comparative Example 5

[0145] The difference from Example 1 is that the electrolyte additive is 0.1 mol / L potassium iodide, while everything else is the same as in Example 1.

[0146] The test results are as follows: After 25 charge-discharge cycles, the average coulombic efficiency of the vanadium redox flow battery is 95.7%, the average voltage efficiency is 85.5%, and the average energy efficiency is 81.8%. Furthermore, the capacity retention rate during the 25 charge-discharge cycles is 83.5%. Figure 9 As shown in (a) and (b).

[0147] Comparative Example 6

[0148] The difference from example 1 is that the electrolyte additive is 0.1 mmol / L of potassium bromide and 0.1 mmol / L of N-methyl imidazole, and the others are the same as example 1.

[0149] The test results are that the average coulombic efficiency of the all-vanadium redox flow battery is 95.6%, the average voltage efficiency is 88.2%, the average energy efficiency is 84.4%, and the capacity retention rate is 84.6% during 25 charge-discharge cycles, as shown in Figs. Figure 10 (a) and (b) in the middle.

[0150] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte for a vanadium redox flow battery, characterised in that: The electrolyte additive is selected from at least one of the following substances: VOSO4 or V2(SO4)3, H2SO4 and an electrolyte additive. or ; X is F, Br or I; The concentration of the electrolyte additive is 0.02-1 mol / L. The total concentration of vanadium oxyanions in the electrolyte of the all-vanadium redox flow battery is 1-3 mol / L.

2. The vanadium redox flow battery electrolyte of claim 1, wherein: The concentration of the electrolyte additive is 0.1-1 mol / L.

3. The vanadium redox flow battery electrolyte of claim 1, wherein: The electrolyte additive is a nitrogen-methyl imidazolium bromide or a nitrogen-methyl pyridinium iodide.

4. The vanadium redox flow battery electrolyte of claim 1, wherein: The total concentration of sulfate in the electrolyte of the all-vanadium redox flow battery is 1-5 mol / L.

5. The vanadium redox flow battery electrolyte of claim 4, wherein: The total concentration of sulfate in the electrolyte of the all-vanadium redox flow battery is 2-5 mol / L.

6. The vanadium redox flow battery electrolyte of claim 4, wherein: The all-vanadium redox flow electrolyte is a positive electrolyte or a negative electrolyte, when being the positive electrolyte, the electrolyte comprises VOSO4, H2SO4 and an electrolyte additive; When being the negative electrolyte, the electrolyte comprises V2(SO4)3, H2SO4 and an electrolyte additive.

7. An all-vanadium redox flow battery characterised in that: The positive electrolyte and / or the negative electrolyte of the all-vanadium redox flow battery is the electrolyte of any one of claims 1-6.

8. The all-vanadium redox flow battery according to claim 7, characterized in that: The positive electrolyte and the negative electrolyte are both the electrolyte of any one of claims 1-6. The positive electrolyte comprises VOSO4, H2SO4 and an electrolyte additive. The negative electrolyte comprises V2(SO4)3, H2SO4 and an electrolyte additive.

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