Positive electrode electrolyte of all-vanadium redox flow battery and preparation method of positive electrode electrolyte

Abstract

The invention belongs to the technical field of a positive electrode electrolyte of an all-vanadium redox flow battery, and particularly relates to a positive electrode electrolyte of an all-vanadium redox flow battery and a preparation method of the positive electrode electrolyte. The method comprises the following steps: dissolving VOSO4 in water, adding concentrated sulfuric acid, stirring in a magnetic stirrer, performing ultrasonic treatment in an ultrasonic cleaner, and finally fixing the volume in a volumetric flask; and then taking out part of the solution with the constant volume, mixing the solution with a NaCl solution, and uniformly stirring to obtain the positive electrode electrolyte of the all-vanadium redox flow battery. According to the positive electrode electrolyte of the all-vanadium redox flow battery, the reversibility of electrochemical reaction of the electrolyte is improved, the electron transfer rate in the electrochemical reaction process of VO < 2 + > / VO < 2 + > is accelerated, and the diffusion coefficient of active substances in the electrolyte is improved, so that the positive electrode electrolyte has higher electrochemical activity.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytes for all-vanadium redox flow batteries, and in particular relates to a positive electrode electrolyte for all-vanadium redox flow batteries and a preparation method thereof. Background Art

[0002] As an important component of all-vanadium liquid flow batteries, electrolyte is the core material for energy storage and conversion of all-vanadium liquid flow batteries, and determines the energy density of all-vanadium liquid flow batteries. Its positive and negative active substances are different valence states of vanadium ions, and the storage and release of charge are achieved through the redox reaction between vanadium ions of different valence states. The electrolyte has high requirements for the control of impurities and valence states during the preparation process. How to achieve high purity at low cost requires long-term process accumulation. At present, the preparation methods of vanadium electrolyte mainly include three categories: physical dissolution method, chemical reduction method and electrolysis method. Among them, large-scale preparation mainly adopts electrolysis method. However, the existing electrolyte solutions have the problems of low electrochemical activity, poor reversibility of electrochemical reaction, and unstable electrolyte. Therefore, it is urgent to develop a positive electrolyte for all-vanadium liquid flow batteries with high electrochemical activity and stability. Summary of the invention

[0003] The purpose of the present invention is to provide a positive electrode electrolyte for an all-vanadium liquid flow battery and a preparation method thereof, so as to solve the problems of low electrochemical activity, poor reversibility of electrochemical reaction and unstable electrolyte in existing electrolytes.

[0004] The implementation process of the present invention is as follows:

[0005] A positive electrode electrolyte for an all-vanadium liquid flow battery comprises the following components: vanadyl sulfate (VOSO4), sulfuric acid (H2SO4), and sodium chloride (NaCl).

[0006] Furthermore, the concentration of VOSO4 in the positive electrode electrolyte is 0.24 to 0.4 mol / L, the concentration of H2SO4 is 1.6 to 3.2 mol / L, and the concentration of the NaCl solution is 0.02 to 0.04 mol / L.

[0007] Furthermore, the positive electrode electrolyte of the all-vanadium redox flow battery can reduce the charge transfer resistance at the interface between the electrode and the electrolyte.

[0008] Furthermore, the positive electrode electrolyte of the all-vanadium redox flow battery can increase the active material VO in the positive electrode electrolyte. 2+ / VO2 + The diffusion coefficient.

[0009] Furthermore, the positive electrode electrolyte of the all-vanadium redox flow battery can increase the peak current of the oxidation peak and the reduction peak of the all-vanadium redox flow battery.

[0010] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0011] (1) Dissolve VOSO4 in water, add concentrated H2SO4, and adjust the volume in a volumetric flask after stirring and ultrasonication;

[0012] (2) Taking out part of the solution after the volume is fixed in step (1) and mixing it with the NaCl solution, and obtaining the positive electrode electrolyte of the all-vanadium liquid flow battery after stirring and ultrasonication.

[0013] Furthermore, in step (1), the concentration of VOSO4 after volume adjustment in the volumetric flask is 0.3-0.5 mol / L; the concentration of H2SO4 after volume adjustment in the volumetric flask is 2-4 mol / L.

[0014] Furthermore, the concentration of the NaCl solution in step (2) is 0.1-0.2 mol / L.

[0015] Furthermore, in step (2), the volume ratio of the solution after volume adjustment in step (1) and the NaCl solution is 4:1.

[0016] The working principle of the all-vanadium liquid flow battery described in the present invention is:

[0017] During the charging process of the vanadium battery, the positive electrolyte undergoes the following reactions:

[0018] VO 2+ +H2O→VO2 + +2H + +e - ,E o =+1.00V vs.SHE

[0019] During the discharge process of the vanadium battery, the positive electrolyte undergoes the following reactions:

[0020] VO 2+ +H2O←VO2 + +2H + +e - ,E o =+1.00V vs.SHE

[0021] Positive effects of the present invention:

[0022] (1) In the positive electrode electrolyte of the all-vanadium redox flow battery described in the present invention, H2SO4 is a strong acid with extremely strong corrosiveness. When selected, its concentration should be as low as possible. The reason for selecting it is that, first, it provides the acidic environment required for the electrochemical reaction, and second, the same acid is selected as the anion of the active substance VOSO4, which can avoid introducing other ions into the system and forming a complex electrochemical system. Therefore, this system uses H2SO4 as the supporting electrolyte, and the concentration does not exceed 3.2 mol / L. NaCl is used as an additive to enhance the electrochemical activity of the positive electrode electrolyte of the all-vanadium redox flow battery in the present invention.

[0023] (2) The cathode electrolyte of the all-vanadium liquid flow battery of the present invention improves the electrochemical activity of the electrolyte and the reversibility of the electrochemical reaction, accelerating the VO 2+ / VO2 + The electron transfer process during the electrochemical reaction increases the diffusion coefficient of the active substance in the electrolyte.

[0024] (3) The positive electrode electrolyte of the all-vanadium liquid flow battery of the present invention can reduce the peak current of the oxidation peak and reduction peak of the vanadium battery from -9.622×10 -4 A and 4.916×10 -4 A increased to -13.39×10 -4 A and 7.358×10 -4 A;

[0025] (4) The positive electrode electrolyte of the all-vanadium liquid flow battery of the present invention can convert the active material VO in the positive electrode electrolyte into 2+ / VO2 + The diffusion coefficient ranges from 2.09 to 2.59×10 -10 cm 2 ·s -1 Increased to 4.67~5.77×10 -10 cm 2 ·s -1 ;

[0026] (5) The positive electrode electrolyte of the all-vanadium liquid flow battery described in the present invention can reduce the charge transfer resistance at the interface between the electrode and the electrolyte from 149.8Ω to 34.34Ω.

[0027] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention and to enable one of ordinary skill in the relevant art to make and use the invention.

[0029] Figure 1 CV graphs of graphite electrodes in the electrolytes of the control experiment and Example 1;

[0030] Figure 2 CV graphs of graphite electrodes in the electrolytes of the control experiment and comparative example 1;

[0031] Figure 3 CV graphs of graphite electrodes in the electrolytes of the control experiment and comparative example 2;

[0032] Figure 4 CV graphs of graphite electrodes in the electrolytes of Example 1, Comparative Example 1 and Comparative Example 2;

[0033] Figure 5 CV graphs of graphite electrode in the electrolyte of the control experiment at different scan rates;

[0034] Figure 6 CV graphs of the graphite electrode in the positive electrode electrolyte of Example 1 at different scan rates;

[0035] Figure 7 It is a fitting curve diagram of the peak current versus the square root of the scan rate of the control experiment and Example 1;

[0036] Figure 8 1 is an EIS graph of the graphite electrode in the electrolyte of the control experiment, Example 1, Comparative Example 1 and Comparative Example 2;

[0037] Fig. 9 1 is the EIS graph of the graphite electrode in the electrolyte of the control experiment and Example 1;

[0038] Fig.10 for Fig. 9 Equivalent circuit diagram of

[0039] Fig.11 is the EIS graph of the graphite electrode in the electrolyte of the control experiment and comparative example 3;

[0040] Fig.12 is the EIS graph of the graphite electrode in the electrolyte of Comparative Example 4;

[0041] Fig.13 CV diagram of the graphite electrode after repeated scanning for 30 cycles in the positive electrode electrolyte of Example 1. DETAILED DESCRIPTION

[0042] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments may be implemented in a variety of forms and should not be construed as being limited to the examples set forth herein; rather, the description of these embodiments is intended to make the present invention more comprehensive and complete and to fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a deeper understanding of the embodiments of the present invention.

[0043] The present invention uses NaCl as an additive and VOSO4 and H2SO4 as the positive electrode electrolyte of the all-vanadium liquid flow battery, thereby improving the electrochemical activity of the positive electrode electrolyte of the vanadium battery and the reversibility of the electrochemical reaction, accelerating the VO 2+ / VO2 + The electron transfer process during the electrochemical reaction increases the diffusion coefficient of the active substance in the electrolyte.

[0044] In the first aspect, the present invention provides a positive electrode electrolyte for an all-vanadium liquid flow battery, comprising the following components: VOSO4, H2SO4, and NaCl, wherein the concentration of VOSO4 in the positive electrode electrolyte is 0.24-0.4 mol / L, the concentration of H2SO4 is 1.6-3.2 mol / L, and the concentration of NaCl solution is 0.02-0.04 mol / L. The positive electrode electrolyte of the all-vanadium liquid flow battery can reduce the charge transfer resistance at the interface between the electrode and the electrolyte. The positive electrode electrolyte of the all-vanadium liquid flow battery can increase the active substance VO in the positive electrode electrolyte. 2+ / VO2 + The positive electrode electrolyte of the all-vanadium liquid flow battery can increase the peak current of the oxidation peak and the reduction peak of the all-vanadium liquid flow battery.

[0045] In a second aspect, the present invention provides a method for preparing a positive electrolyte of an all-vanadium redox flow battery, comprising the following steps:

[0046] (1) Dissolve VOSO4 in water, add concentrated H2SO4, and adjust the volume in a volumetric flask after stirring and ultrasonication; the concentration of VOSO4 after adjustment in the volumetric flask is 0.3-0.5 mol / L; the concentration of H2SO4 after adjustment in the volumetric flask is 2-4 mol / L.

[0047] (2) The volume ratio of the solution fixed in step (1) to the NaCl solution is 4:1, the solution fixed in step (1) is taken out and mixed with a NaCl solution with a concentration of 0.1 to 0.2 mol / L, and the positive electrode electrolyte of the all-vanadium redox flow battery is obtained after stirring and ultrasonication.

[0048] The stirring in the method of the present invention is performed on a magnetic stirrer, and the present invention does not limit the stirring rate and stirring time, as long as the mixture is mixed evenly. The ultrasound is performed on an ultrasonic cleaner, and the present invention does not limit the ultrasound frequency and ultrasound time, as long as the mixture is mixed evenly.

[0049] Example 1

[0050] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0051] (1) Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated sulfuric acid, and stir on a magnetic stirrer for 5 minutes, then ultrasonicate on an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask;

[0052] (2) 40 mL of the solution prepared in step (1) was taken out and mixed with 10 mL of 0.1 mol / L NaCl solution, followed by stirring on a magnetic stirrer for 5 minutes, and then ultrasonicated on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 was 0.32 mol / L, the concentration of H2SO4 was 2.4 mol / L, and the concentration of NaCl solution was 0.02 mol / L.

[0053] Controlled experiment

[0054] Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated sulfuric acid, and then stir on a magnetic stirrer for 5 minutes, then ultrasonicate on an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask. The resulting solution is used as a control experiment.

[0055] Comparative Example 1

[0056] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0057] (1) Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated H2SO4, and stir on a magnetic stirrer for 5 minutes, then ultrasonicate in an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask;

[0058] (2) 40 mL of the solution prepared in step (1) was taken out and mixed with 10 mL of a 0.1 mol / L FeCl3 solution, followed by stirring on a magnetic stirrer for 5 minutes, and then ultrasonicated on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 was 0.32 mol / L, the concentration of H2SO4 was 2.4 mol / L, and the concentration of the FeCl3 solution was 0.02 mol / L.

[0059] Comparative Example 2

[0060] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0061] (1) Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated H2SO4, and stir on a magnetic stirrer for 5 minutes, then ultrasonicate in an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask;

[0062] (2) 40 mL of the solution obtained by dilution in step (1) was taken out and mixed with 10 mL of 0.1 mol / L MgCl2 solution, followed by stirring on a magnetic stirrer for 5 minutes, and then ultrasonicated on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 was 0.32 mol / L, the concentration of H2SO4 was 2.4 mol / L, and the concentration of MgCl2 solution was 0.02 mol / L.

[0063] Comparative Example 3

[0064] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0065] (1) Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated H2SO4, and stir on a magnetic stirrer for 5 minutes, then ultrasonicate in an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask;

[0066] (2) 40 mL of the solution prepared in step (1) was taken out and mixed with 10 mL of a 0.05 mol / L NaCl solution, followed by stirring on a magnetic stirrer for 5 minutes, and then ultrasonicated on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 was 0.32 mol / L, the concentration of H2SO4 was 2.4 mol / L, and the concentration of the NaCl solution was 0.01 mol / L.

[0067] Comparative Example 4

[0068] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0069] (1) Dissolve 0.02 mol of VOSO4 in 10 mL of water, add 8.3 mL of concentrated H2SO4, and stir on a magnetic stirrer for 5 minutes, then ultrasonicate in an ultrasonic cleaner for 5 minutes, and then make up to volume in a 50 mL volumetric flask;

[0070] (2) 40 mL of the solution prepared in step (1) was taken out and mixed with 10 mL of a 0.25 mol / L NaCl solution, followed by stirring on a magnetic stirrer for 5 minutes, and then ultrasonicated on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 was 0.32 mol / L, the concentration of H2SO4 was 2.4 mol / L, and the concentration of the NaCl solution was 0.05 mol / L.

[0071] The electrochemical performance tests are as follows:

[0072] Test method: A three-electrode system was composed of a graphite electrode (3 mm in diameter, Tianjin Aida Hengsheng Technology Development Co., Ltd.), a saturated calomel electrode (SCE, Shanghai Russell Technology Co., Ltd.) and a platinum sheet (Tianjin Aida Hengsheng Technology Development Co., Ltd.). An electrochemical workstation (Shanghai Chenhua Co., Ltd., CHI760E) was used to perform cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests on the positive electrode electrolyte of the all-vanadium liquid flow battery obtained in Example 1, the control solution obtained in the control experiment, and the positive electrode electrolyte of the all-vanadium liquid flow battery obtained in Comparative Examples 1-2. All the following potentials are relative to the potential values ​​of SCE.

[0073] (1) Cyclic voltammetry study

[0074] The purpose of CV test is to study the oxidation and reduction reactions of the working electrode in a specific electrolyte. The potential corresponding to each current peak represents a specific Faraday reaction, the peak height represents the activity of the Faraday reaction, the peak width represents the reversibility of the Faraday reaction, and the peak area represents the capacity of the Faraday reaction. CV tests were performed on the electrolytes of the control experiment, Example 1, Comparative Example 1 and Comparative Example 2, respectively, with a scanning potential range of 0.4 to 1.4 V and a scanning rate of 10 mV / s. The test results are shown in Figure 1-4 .

[0075] from Figure 1-3 It can be seen that compared with the CV curve of the electrolyte in the control experiment, the reduction peak current and oxidation peak current of the CV curve after the addition of NaCl, FeCl3 or MgCl2 have been significantly improved, indicating that these three metal ions as additives have increased the electrochemical activity of the electrolyte. Figure 4 It is the superposition of the CV curves of the graphite electrode in the electrolyte of Example 1 and Comparative Examples 1-2. It can be seen from the figure that the peak current of the CV curve of the graphite electrode in the electrolyte of Example 1 is higher than the peak current of the CV curve in the electrolyte of Comparative Examples 1-2, indicating that the electrochemical activity of the positive electrode electrolyte of the all-vanadium liquid flow battery with NaCl as an additive is the highest. Figure 1 The test curve can be obtained in Table 1.

[0076] Table 1 CV curve parameters of electrolyte with NaCl as additive

[0077]

[0078] As can be seen from Table 1, compared with the electrolyte of the control experiment, the graphite electrode was tested in the electrolyte of Example 1 for CV, and the redox peak current of the vanadium battery was increased from -9.622×10 -4 A and 4.916×10 -4 A increased to -13.39×10 -4 A and 7.358×10 -4 A, indicating that the electrochemical activity is improved; at the same time, in the electrolyte of Example 1, the peak current ratio is reduced and the peak potential difference is reduced, indicating that the addition of NaCl to the positive electrode electrolyte improves VO 2+ / VO2 + The reversibility of the electrochemical reaction occurs because the addition of NaCl accelerates the VO 2+ / VO2 + The electron transfer process during electrochemical reaction.

[0079] (2) Kinetic analysis of mass transfer process

[0080] For the electrode reaction of the reversible process, the diffusion coefficient of the active material is calculated according to the Randles-Sevcik equation (1) combined with the CV test graph, and the peak current is:

[0081] I p = 2.69×10 5 AD 1 / 2 n 2 / 3 v 1 / 2 C (1)

[0082] In equation (1), n ​​represents the number of electrons transferred in the electrochemical reaction. In this system, n = 1, and A represents the electroactive area of ​​the electrode (cm 2 ), D represents the diffusion coefficient of the active substance (at 25°C, D = 6.70 × 10 -6 cm 2 ·s -1 ), v represents the scan rate (mV·s -1 ), C represents the concentration of active substances (mol cm -1 ).

[0083] For the irreversible Faraday reaction, the diffusion coefficient of the active substance is obtained by combining the CV test graph with equation (2).

[0084] I p = 2.99 × 10 5 AD 1 / 2 n2 / 3 v 1 / 2 C (2)

[0085] The meanings and units of the parameters in formula (2) and formula (1) are the same. In this research system, VO 2+ / VO2 + The electrochemical reaction is a quasi-reversible process, which indicates that the active substance VO in the electrolyte 2+ The diffusion coefficient of should be between the diffusion coefficient obtained in the reversible system and the diffusion coefficient obtained in the irreversible system. Combining equations (1) and (2), the diffusion coefficient of the active substance is obtained by calculation, see Table 2.

[0086] Table 2 Diffusion coefficients of active substances in the electrolyte before and after the addition of additives

[0087] Sample name Control experiment Example 1 <![CDATA[D(×10 -10 cm 2 ·s -1 )]]> 2.09～2.59 4.67～5.77

[0088] Figure 5-6 CV curves of graphite electrode in the electrolyte of control experiment and Example 1 at different scanning speeds, with the potential scanning range of 0.4 to 1.4 V. Figure 5 and Figure 6 It can be seen that as the scan rate increases, the oxidation peak and reduction peak currents are increasing; the oxidation peak potential gradually shifts positively, and the reduction peak potential gradually shifts negatively. Due to the enhancement of electrochemical polarization, the redox peak potential difference increases. However, the CV curve limits the peak potential difference and presents a more symmetrical redox peak. Combined with the data in Table 1, it shows that the redox reaction on the graphite electrode surface is a quasi-reversible reaction. Figure 7 It can be seen that the peak current of the control experiment and Example 1 is proportional to the square root of the scan rate (linear relationship), indicating that VO 2+ / VO2 + The electrochemical reaction is a diffusion-controlled process. Compared with the electrolyte in the control experiment, the slope of the linear relationship curve fitted in the positive electrode electrolyte of Example 1 is greater than the slope of the linear relationship curve fitted in the electrolyte in the control experiment. The addition of NaCl makes the active substance VO in the electrolyte 2+ / VO2 + The diffusion coefficient ranges from 2.09 to 2.59×10 -10 cm 2 ·s -1 Increased to 4.67~5.77×10 -10 cm 2 ·s -1 , indicating that the mass transfer process is faster in the positive electrode electrolyte of Example 1. It can be seen that the parameters proposed by the present invention can bring about a doubled diffusion coefficient, that is, the active substances in the electrochemical system diffuse faster, thereby achieving better results.

[0089] (3) Analysis of AC impedance and electrolyte cycling stability

[0090] Figure 8 1 is an EIS graph of the graphite electrode in the electrolyte of the control experiment, Example 1, Comparative Example 1 and Comparative Example 2; Fig. 9 is the EIS graph of the graphite electrode in the electrolyte of the control experiment and Example 1, Fig.10 is the equivalent circuit diagram. Figure 8 and Fig. 9 It can be seen that compared with the control experiment, the cathode electrolyte of the all-vanadium liquid flow battery of Example 1 can reduce the charge transfer resistance at the interface between the electrode and the electrolyte from 149.8Ω to 34.34Ω. It can be seen that the condition parameters used in the present invention can reduce the charge transfer resistance by 4 / 5, thereby significantly accelerating the charge transfer of the electrochemical system, indicating that the charge transfer speed of the cathode electrolyte of Example 1 is accelerated, and further indicating that NaCl can effectively improve the electrochemical activity of the cathode electrolyte.

[0091] Fig.11 is the EIS graph of the graphite electrode in the electrolyte of the control experiment and comparative example 3; Fig.12 It is the EIS diagram of the graphite electrode in the electrolyte of Comparative Example 4. Fig.11 It can be seen that compared with the control experiment, adding 0.01 mol / L NaCl to the positive electrolyte leads to a larger charge transfer resistance at the interface between the positive electrolyte electrode and the electrolyte, which is about 250 ohms. Fig.12 It can be seen that in the positive electrode electrolyte containing 0.05 mol / L NaCl, the charge transfer resistance (greater than 400 ohms) at the interface between the graphite electrode and the electrolyte is greater than the resistance of the graphite electrode in the positive electrode electrolyte containing 0.01 mol / L NaCl. Therefore, in the positive electrode electrolyte of the all-vanadium liquid flow battery of the present invention, the concentration of the NaCl solution is 0.02-0.04 mol / L, and the selection of this parameter range plays an important role in the electrochemical activity of the positive electrode electrolyte of the all-vanadium liquid flow battery of the present invention. In the positive electrode electrolyte, when the concentration of NaCl solution is outside the concentration range of 0.02-0.04 mol / L, the charge transfer resistance at the interface between the graphite electrode and the electrolyte is greater than the resistance within this range, regardless of whether it is in the low concentration or high concentration direction. This indicates that only within this concentration range can the charge transfer resistance at the interface between the electrode and the electrolyte be minimized, that is, the active material is transferred fastest, thereby making the electrochemical activity of the positive electrode electrolyte containing NaCl in the concentration range of 0.02-0.04 mol / L the best.

[0092] The reason for this result is that when the concentration of NaCl as an additive is too small or too large, the desired synergistic effect of the additive and the active material cannot be achieved. It only increases the total ion concentration in the electrolyte, and then increases the charge transfer resistance at the interface between the electrode and the electrolyte, that is, it reduces the diffusion of the active material (high-valent vanadium ions), causing the charge transfer rate of the active material to decrease, thereby reducing the electrochemical activity of the positive electrode electrolyte. When the concentration of the additive NaCl is in the range of 0.02-0.04 mol / L, NaCl can form a perfect synergistic effect with the active material, inhibit the association reaction between vanadium ions, and at the same time improve the stability of high-valent vanadium ions, reduce the precipitation of vanadium ions in the positive electrode electrolyte (which will lead to a decrease in the energy density of the vanadium battery), thereby ensuring that the positive electrode electrolyte has good electrochemical activity.

[0093] Fig.13 The graphite electrode is subjected to 30 cycles of repeated scanning in the positive electrode electrolyte of Example 1, with a scanning rate of 20 mV / s. Fig.11 It can be seen that except for the first curve at the beginning of scanning (in the first scan, the electrochemical system is not stable enough at the beginning of scanning, and thereafter, the three-electrode electrochemical system becomes more and more stable. Therefore, the cyclic voltammetry curve obtained by scanning does not change much and tends to overlap), the other scanning curves are basically consistent, indicating that the positive electrode electrolyte of the all-vanadium liquid flow battery obtained in Example 1 is very stable.

[0094] Example 2

[0095] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0096] (1) Dissolve 0.015 mol of VOSO4 in 10 mL of water, add 5.53 mL of concentrated sulfuric acid, and stir on a magnetic stirrer for 3 minutes, then ultrasonicate on an ultrasonic cleaner for 6 minutes, and then make up to volume in a 50 mL volumetric flask;

[0097] (2) 40 mL of the solution obtained after the dilution in step (1) was taken out and mixed with 10 mL of 0.2 mol / L NaCl solution, followed by stirring on a magnetic stirrer for 8 minutes, and then ultrasonicating on an ultrasonic cleaner for 10 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 is 0.24 mol / L, the concentration of H2SO4 is 1.6 mol / L, and the concentration of NaCl solution is 0.04 mol / L.

[0098] Example 3

[0099] A method for preparing a positive electrolyte for an all-vanadium liquid flow battery comprises the following steps:

[0100] (1) Dissolve 0.025 mol of VOSO4 in 10 mL of water, add 11.1 mL of concentrated H2SO4, and stir on a magnetic stirrer for 7 minutes, then ultrasonicate on an ultrasonic cleaner for 6 minutes, and then make up to volume in a 50 mL volumetric flask;

[0101] (2) 40 mL of the solution obtained after the dilution in step (1) was taken out and mixed with 10 mL of 0.1 mol / L NaCl solution, followed by stirring on a magnetic stirrer for 6 minutes, and then ultrasonicating on an ultrasonic cleaner for 5 minutes to obtain a positive electrode electrolyte for an all-vanadium liquid flow battery, wherein the concentration of VOSO4 is 0.4 mol / L, the concentration of H2SO4 is 3.2 mol / L, and the concentration of NaCl solution is 0.02 mol / L.

[0102] In summary, in the positive electrode electrolyte of the present invention, the role of each component is: VOSO4 provides active substances, H2SO4 serves as a supporting electrolyte, and NaCl is an additive to enhance electrochemical activity. When the concentration of NaCl in the electrolyte is in the range of 0.02 to 0.04 mol / L, it can bring about a multiple better effect, and the concentration range of NaCl is relatively difficult to obtain. It cannot be obtained by simply performing multiple experiments. The concentration range of the synergistic effect between the additive NaCl and the active substance precursor VOSO4 must be considered. Outside this range, the activity of the positive electrode electrolyte will be significantly reduced. The highly active vanadium battery positive electrode electrolyte provided by the present invention lays the foundation for the further commercial application of vanadium batteries.

[0103] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing what is disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and embodiments are to be considered as exemplary only, and the present invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from the scope thereof.

Claims

1. A positive electrolyte for an all-vanadium redox flow battery, characterized in that: It includes the following components: VOSO4, H2SO4, and NaCl.

2. The positive electrode electrolyte of the all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of VOSO4 in the positive electrode electrolyte is 0.24-0.4 mol / L, the concentration of sulfuric acid is 1.6-3.2 mol / L, and the concentration of NaCl is 0.02-0.04 mol / L.

3. The positive electrolyte of the all-vanadium redox flow battery according to claim 1, characterized in that: The positive electrode electrolyte of the all-vanadium liquid flow battery can reduce the charge transfer resistance at the interface between the electrode and the electrolyte.

4. The positive electrode electrolyte of the all-vanadium redox flow battery according to claim 1, characterized in that: The positive electrode electrolyte of the all-vanadium liquid flow battery can increase the active material VO in the positive electrode electrolyte. 2+ / VO2 + The diffusion coefficient.

5. The positive electrode electrolyte of the all-vanadium redox flow battery according to claim 1, characterized in that: The positive electrode electrolyte of the all-vanadium liquid flow battery can increase the peak current of the oxidation peak and the reduction peak of the all-vanadium liquid flow battery.

6. A method for preparing a cathode electrolyte for an all-vanadium redox flow battery, characterized in that: The steps include: (1) Dissolve VOSO4 in water, add concentrated sulfuric acid, and adjust the volume in a volumetric flask after stirring and ultrasonication; (2) Taking out part of the solution after the volume is fixed in step (1) and mixing it with the NaCl solution, and obtaining the positive electrode electrolyte of the all-vanadium liquid flow battery after stirring and ultrasonication.

7. The method for preparing the positive electrolyte of the all-vanadium redox flow battery according to claim 6, characterized in that: In step (1), the concentration of VOSO4 after volume adjustment in the volumetric flask is 0.3-0.5 mol / L; the concentration of sulfuric acid after volume adjustment in the volumetric flask is 2-4 mol / L.

8. The method for preparing the positive electrolyte of the all-vanadium redox flow battery according to claim 6, characterized in that: The concentration of the NaCl solution in step (2) is 0.1-0.2 mol / L.

9. The method for preparing the positive electrolyte of the all-vanadium redox flow battery according to claim 6, characterized in that: In step (2), the volume ratio of the solution after volume adjustment in step (1) and the NaCl solution is 4:1.

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