Electrolyte, method for preparing the same, and all-vanadium redox flow battery

Abstract

The application belongs to the field of liquid flow batteries, and particularly relates to an electrolyte, a preparation method thereof and a full vanadium liquid flow battery. The electrolyte comprises vanadium ions, bismuth ions, an N-vinyl amide polymer and an acid; a monomer of the N-vinyl amide polymer contains an amide bond and a carbon-carbon double bond connected to an N atom of the amide bond. By introducing the N-vinyl amide polymer, the catalytic activity of a catalyst is ensured, the stability of the electrolyte is improved, and the efficiency, stability and cycle performance of the full vanadium liquid flow battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of flow batteries, specifically relating to an electrolyte, its preparation method, and an all-vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries are energy storage technologies based on the redox reaction of vanadium ions. They utilize the reversible conversion of vanadium ions in different valence states in the electrolyte to achieve energy storage and release. They have advantages such as ultra-long cycle life, high safety, independently adjustable capacity and power, and environmental friendliness.

[0003] In existing technologies, bismuth salts (such as bismuth chloride (BiCl3) and bismuth nitrate (Bi(NO3)3)) are often used as catalysts in electrolytes. However, they are unstable during cycling and easily form insoluble hydrolysis products (such as bismuth oxychloride (BiOCl) and bismuth oxynitrate (BiONO3)), leading to catalyst failure, poor electrolyte stability, and performance degradation of vanadium redox flow batteries. At the same time, due to the transmembrane migration of vanadium ions in the electrolyte, electrolyte deterioration occurs, reducing the efficiency and stability of vanadium redox flow batteries.

[0004] Therefore, there is an urgent need to develop an electrolyte with stable catalytic activity to improve the efficiency and stability of vanadium redox flow batteries. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an electrolyte, its preparation method, and an all-vanadium redox flow battery. By introducing N-vinylamide polymers, this invention effectively solves the technical challenges of bismuth salt stability and vanadium ion permeation, ensuring the catalytic activity of the catalyst, improving the stability of the electrolyte, and enhancing the efficiency, stability, and cycle performance of the all-vanadium redox flow battery.

[0006] Specifically, the present invention provides an electrolyte comprising vanadium ions, bismuth ions, an N-vinylamide polymer, and an acid; wherein the monomer of the N-vinylamide polymer contains an amide bond and a carbon-carbon double bond connected to the N atom of the amide bond.

[0007] In one or more embodiments, the N-vinylamide polymer is selected from one or more of poly(N-vinylacetamide), polyvinylpyrrolidone, and poly(N-vinylcaprolactam).

[0008] In one or more embodiments, the acid is sulfuric acid.

[0009] In one or more embodiments, the electrolyte further includes water.

[0010] In one or more embodiments, the concentration of vanadium ions in the electrolyte is 1-2 mol / L.

[0011] In one or more embodiments, the concentration of hydrogen ions in the electrolyte is 3.7-5.4 mol / L.

[0012] In one or more embodiments, the concentration of bismuth ions in the electrolyte is 0.001-0.003 mol / L.

[0013] In one or more embodiments, the concentration of the monomer units of the N-vinylamide polymer in the electrolyte is 0.0003-0.015 mol / L.

[0014] In one or more embodiments, the molar ratio of monomer units of the N-vinylamide polymer to bismuth ions in the electrolyte is (0.2-10):1.

[0015] In one or more embodiments, the concentration of sulfuric acid is 3-5 mol / L.

[0016] In one or more embodiments, the concentration of bismuth ions in the electrolyte is 0.001-0.002 mol / L.

[0017] In one or more embodiments, the concentration of the monomer units of the N-vinylamide polymer in the electrolyte is 0.001-0.002 mol / L.

[0018] In one or more embodiments, the molar ratio of monomer units to bismuth ions of the N-vinylamide polymer in the electrolyte is (0.5-2):1.

[0019] In one or more embodiments, the molar ratio of monomer units of the N-vinylamide polymer to bismuth ions in the electrolyte is (0.8-1.2):1.

[0020] The present invention provides a method for preparing any of the electrolytes described herein, the method comprising: mixing a vanadium source, a bismuth salt, an N-vinylamide polymer and an acid to obtain an electrolyte.

[0021] In one or more embodiments, the bismuth salt is bismuth chloride and / or bismuth nitrate.

[0022] In one or more embodiments, (1) a bismuth salt is dissolved in an acidic solution to obtain a bismuth ion-containing solution A, an N-vinylamide polymer is prepared to form an N-vinylamide polymer-containing solution B, and solutions A and B are mixed to obtain an electrolyte.

[0023] In one or more embodiments, (1') a bismuth salt and an N-vinylamide polymer are dissolved together in an acidic solution to obtain an electrolyte.

[0024] In one or more embodiments, in step (1), the concentration of hydrogen ions in the acidic solution is 1-5.4 mol / L.

[0025] The present invention provides an all-vanadium redox flow battery comprising any of the electrolytes described in the present invention.

[0026] In one or more embodiments, the electrolyte is used as the negative electrode electrolyte in a vanadium redox flow battery.

[0027] Compared with the prior art, the present invention has the following technical effects:

[0028] (1) This invention introduces N-vinylamide polymers into the electrolyte, which significantly improves the solubility and stability of bismuth salts through the coordination between bismuth ions and N-vinylamide polymers, effectively inhibiting precipitation formation and solving the key problem of hydrolysis and precipitation of bismuth salts as catalysts. This significantly improves the stability of the electrolyte and the cycle performance of the battery. At the same time, through the coordination between N-vinylamide polymers and vanadium ions, ion penetration is reduced, cross-contamination of positive and negative electrode active materials is reduced, the stability of the electrolyte is improved, and the coulombic efficiency and energy efficiency are further improved. This dual coordination mechanism not only maintains the catalytic activity of the catalyst and improves the stability of the electrolyte, but also improves the efficiency and cycle life of the vanadium redox flow battery, breaking through the main technical bottleneck of the commercialization of vanadium redox flow batteries.

[0029] (2) The N-vinylamide polymers introduced in this invention have low cost and high engineering potential. Attached Figure Description

[0030] Figure 1 For a single cell containing the electrolyte prepared in Example 1 or Comparative Example 1, at 200 mA / cm 2 Figure showing the test results of long-cycle stability under electrical density. Detailed Implementation

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0033] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0034] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0035] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0036] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0037] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0038] This invention provides an electrolyte comprising vanadium ions, bismuth ions, an N-vinylamide polymer, and an acid. In this invention, the N-vinylamide polymer reacts with the Bi ions through its amide groups. 3+ Forming coordination bonds prevents bismuth salt aggregation and precipitation, inhibits hydrolysis and precipitation, and significantly improves the stability of the electrolyte and the cycle performance of the vanadium redox flow battery; at the same time, N-vinylamide polymers and V 2+ V 3+ Coordination occurs, inhibiting vanadium ion penetration; the above-mentioned dual coordination synergy ensures the catalytic activity of the catalyst, improves the stability of the electrolyte, and enhances the efficiency, stability, and cycle performance of the all-vanadium redox flow battery.

[0039] In the electrolyte of this invention, the concentration of vanadium ions can be 1-2 mol / L, for example, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2 mol / L. In this invention, the valence state of vanadium ions can be +3.5.

[0040] In this invention, the monomers of the N-vinylamide polymers contain an amide bond and a carbon-carbon double bond bonded to the nitrogen atom of the amide bond. The N-vinylamide polymers of this invention can be one or more selected from poly(N-vinylacetamide) (PNVA), poly(N-vinylpyrrolidone) (PVP), and poly(N-vinylcaprolactam) (PNVCL). Using the above-mentioned N-vinylamide polymers in this invention can more effectively achieve dual coordination, thereby helping to ensure the catalytic activity of the catalyst, improve the stability of the electrolyte, and enhance the efficiency, stability, and cycle performance of the vanadium redox flow battery.

[0041] In the electrolyte of this invention, the concentration of the monomer units of the N-vinylamide polymer can be 0.0003-0.015 mol / L, preferably 0.001-0.002 mol / L. Controlling the concentration of the N-vinylamide polymer monomer units within the above range in this invention helps to ensure the catalytic activity of the catalyst, improve the stability of the electrolyte, and enhance the efficiency, stability, and cycle performance of the vanadium redox flow battery.

[0042] In the electrolyte of this invention, the concentration of hydrogen ions is 3.7-5.4 mol / L, for example, 3.7 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, and 5.4 mol / L. In this invention, the acid can be sulfuric acid. In the electrolyte of this invention, the concentration of sulfuric acid can be 3-5 mol / L, for example, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, and 5 mol / L. In this invention, the second-step ionization of sulfuric acid is incomplete. In this invention, the electrolyte may also include water.

[0043] In the electrolyte of this invention, the concentration of bismuth ions can be 0.001-0.003 mol / L, preferably 0.001-0.002 mol / L, for example, 0.001 mol / L, 0.002 mol / L, or 0.003 mol / L. In this invention, vanadium ions need to be adsorbed onto the active sites of bismuth to react. If the vanadium ion concentration is very high, but the bismuth catalyst loading is low (few active sites), then the number of vanadium ions that can react per unit time is limited, which may lead to increased polarization and reduced battery efficiency. Therefore, bismuth, as a catalyst, has an optimal matching relationship with vanadium ions in the system. In this invention, controlling the concentration of bismuth ions within the above range ensures the catalytic activity of the catalyst, which is beneficial to improving the stability of the electrolyte and enhancing the three major efficiencies, stability, and cycle performance of the vanadium redox flow battery.

[0044] In the electrolyte of this invention, the molar ratio of N-vinylamide polymer monomer units to bismuth ions can be (0.2-10):1, preferably (0.5-2):1, and more preferably (0.8-1.2):1. Controlling the molar ratio of N-vinylamide polymer monomer units to bismuth ions within the above range in this invention helps to ensure the catalytic activity of the catalyst, improve the stability of the electrolyte, and enhance the efficiency, stability, and cycle performance of the vanadium redox flow battery.

[0045] The present invention provides a method for preparing the electrolyte of the present invention, the method comprising mixing a vanadium source, a bismuth salt, an N-vinylamide polymer and an acid to obtain an electrolyte.

[0046] In this invention, the bismuth salt can be a water-soluble bismuth salt, preferably bismuth chloride (BiCl3) and / or bismuth nitrate (Bi(NO3)3).

[0047] The method for preparing the electrolyte of the present invention can be as follows: (1) dissolve bismuth salt in an acidic solution to obtain a solution A containing bismuth ions, prepare an N-vinylamide polymer to form a solution B containing an N-vinylamide polymer, mix solution A and solution B to obtain the electrolyte.

[0048] Because soluble bismuth salts readily hydrolyze to form insoluble precipitates, such as bismuth oxychloride white precipitate and bismuth oxynitrate white precipitate, soluble bismuth salts must be directly dissolved in a strong acid and cannot be dissolved in water; a strong acid environment can effectively inhibit the hydrolysis of soluble bismuth salts. In step (1), the concentration of hydrogen ions in the acidic solution can be 1-5.4 mol / L. In this invention, a hydrogen ion concentration above 1 mol / L can inhibit the hydrolysis of bismuth salts, but an excessively high hydrogen ion concentration may accelerate the hydrogen evolution side reaction, increase the viscosity of the sulfuric acid system, and potentially decrease the solubility of vanadium.

[0049] The method for preparing the electrolyte of the present invention can be as follows: (1') dissolving bismuth salt and N-vinylamide polymer together in an acidic solution to obtain the electrolyte.

[0050] In this invention, the electrolyte can be prepared using conventional techniques in the field.

[0051] This invention provides a vanadium redox flow battery comprising the electrolyte of this invention. The electrolyte of this invention is used as the negative electrode electrolyte in the vanadium redox flow battery.

[0052] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0053] In this invention, the vanadium electrolyte used in Examples 1-5 and Comparative Examples 1-4 had a total vanadium concentration of 1.7 mol / L and V 3+ / V 4+ The concentration ratio is 1, and the supporting electrolyte is 4 mol / L sulfuric acid.

[0054] Example 1

[0055] 1. Take a 250mL beaker and accurately measure 100mL of vanadium electrolyte to be used using a graduated cylinder; accurately weigh 0.0015mol of bismuth chloride (BiCl3) powder using an analytical balance; slowly add 0.0015mol of bismuth chloride powder to 100mL of vanadium electrolyte while stirring; continue stirring until the bismuth chloride powder is completely dissolved to obtain a homogeneous solution A.

[0056] 2. Take a 100mL beaker and add 50mL of vanadium electrolyte to be used; accurately weigh 0.0015mol of poly(N-vinylacetamide) (PNVA) (Sigma-Aldrich; CAS: 28408-65-3) powder using an analytical balance; add 0.0015mol of PNVA powder to 50mL of vanadium electrolyte and stir until the PNVA powder is completely dissolved to obtain a homogeneous solution B.

[0057] 3. Pour all of solution B into solution A. Rinse the beaker containing solution B with the vanadium electrolyte to be used, and pour the rinsing solution into the beaker as well, ensuring complete transfer. Turn on the stirrer and mix the two thoroughly. Then transfer the mixed solution to a 1L volumetric flask. Rinse the beaker containing solution A several times with the existing vanadium electrolyte to be used, and pour the rinsing solution into the volumetric flask. Slowly add the vanadium electrolyte to the volumetric flask until the liquid level is close to the 1L mark. Use a dropper to add the vanadium electrolyte drop by drop until the lowest point of the concave meniscus is tangent to the mark. Tighten the stopper of the volumetric flask, invert and shake it repeatedly 10 times to ensure the solution is completely homogeneous, obtaining 1L of vanadium electrolyte, in which the concentration of bismuth chloride is 0.0015mol / L, the concentration of poly(N-vinylacetamide) monomer units is 0.0015mol / L, the concentration of vanadium ions is 1.7mol / L, and the concentration of sulfuric acid is 4mol / L.

[0058] Example 2

[0059] The other conditions in this embodiment are the same as in Embodiment 1, except that the bismuth chloride powder in Embodiment 1 is replaced with bismuth nitrate (Bi(NO3)3) powder.

[0060] Example 3

[0061] The other conditions in this embodiment are the same as in Example 1, except that the polyvinyl acetamide powder in Example 1 is replaced with polyvinylpyrrolidone (PVP) powder (Aladdin, K16-K90, CAS No.: 9003-39-8) with a monomer unit amount of 0.0015 mol.

[0062] Example 4

[0063] The other conditions in this embodiment are the same as in Embodiment 1, except that the amount of monomer unit substance of the polyethylene acetamide powder in Embodiment 1 is adjusted to 0.0003 mol.

[0064] Example 5

[0065] The other conditions in this embodiment are the same as in Embodiment 1, except that the amount of monomer unit substance of the polyethylene acetamide powder in Embodiment 1 is adjusted to 0.015 mol.

[0066] Example 6

[0067] The other conditions in this embodiment are the same as in Example 1, except that the polyvinylacetamide powder in Example 1 is replaced with poly(N-vinylcaprolactam) (PNVCL) powder with a monomer unit amount of 0.0015 mol (purchased from Beijing Spectrum Technology Co., Ltd., CAS No.: 25189-83-7).

[0068] Comparative Example 1

[0069] The electrolyte used in this comparative example is a vanadium electrolyte that is ready for use.

[0070] Comparative Example 2

[0071] 1. Take a 250mL beaker and accurately measure 100mL of vanadium electrolyte to be used using a graduated cylinder; accurately weigh 0.0015mol of bismuth chloride (BiCl3) powder using an analytical balance; slowly add 0.0015mol of bismuth chloride powder to 100mL of vanadium electrolyte while stirring; continue stirring until the bismuth chloride powder is completely dissolved to obtain a homogeneous solution A.

[0072] 2. Transfer all of solution A to a 1L volumetric flask; rinse the beaker containing solution A with the available vanadium electrolyte and pour all the rinsing solution into the volumetric flask; slowly add the vanadium electrolyte to the volumetric flask until the liquid level is close to the 1L mark; then add the electrolyte dropwise using a dropper until the lowest point of the concave meniscus is tangent to the mark; tightly stopper the volumetric flask, invert and shake it repeatedly at least 10 times to ensure the solution is completely homogeneous, resulting in 1L of vanadium electrolyte, in which the concentration of bismuth chloride is 0.0015mol / L, the concentration of vanadium ions is 1.7mol / L, and the concentration of sulfuric acid is 4mol / L.

[0073] Comparative Example 3

[0074] 1. Take a 100mL beaker and add 50mL of vanadium electrolyte to be used; accurately weigh 0.0015mol of poly(N-vinylacetamide) (PNVA) (Sigma-Aldrich; CAS: 28408-65-3) powder using an analytical balance; add 0.0015mol of PNVA powder to 50mL of vanadium electrolyte and stir until the PNVA powder is completely dissolved to obtain a homogeneous solution B.

[0075] 2. Transfer all of solution B to a 1L volumetric flask; rinse the beaker containing solution B with the available vanadium electrolyte and pour all the rinsing solution into the volumetric flask; slowly add the vanadium electrolyte to the volumetric flask until the liquid level is close to the 1L mark; then add the electrolyte dropwise using a dropper until the lowest point of the concave meniscus is tangent to the mark; tightly stopper the volumetric flask, invert and shake it repeatedly at least 10 times to ensure the solution is completely homogeneous, resulting in 1L of vanadium electrolyte, wherein the monomer concentration of poly(N-vinylacetamide) is 0.0015mol / L, the vanadium ion concentration is 1.7mol / L, and the sulfuric acid concentration is 4mol / L.

[0076] Comparative Example 4

[0077] The conditions for this comparative example are the same as those for Example 1, except that the bismuth chloride powder in Example 1 is replaced with nickel chloride (NiCl2) powder.

[0078] Test case

[0079] Ten sets of single cells were assembled: the positive electrode electrolyte of each cell was a spare electrolyte, and the negative electrode electrolyte was the vanadium electrolyte prepared in Examples 1-6 and Comparative Examples 1-4, respectively; the ion-exchange membrane was a perfluorosulfonic acid proton exchange membrane, and the electrode was a 2.5 mm carbon felt electrode with an effective electrode area of ​​48 cm². 2 The compression ratio is 20%, and the volumes of both the positive and negative electrolytes are 70 mL.

[0080] Three efficiency performance tests: The single cells containing the electrolytes prepared in Examples 1-6 and Comparative Examples 1-4 were tested for rate performance under constant capacitance mode, using 110, 160, 180, 200, and 250 mA / cm², respectively. 2 The test was conducted with a charging limit of 1.55V and a discharging limit of 1.00V, and was performed for 5 cycles. The data from the 4th cycle was used as the result. The test results of the three efficiencies (Coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE)) are shown in Table 1.

[0081] Table 1: Three major efficiencies of single cells containing electrolytes prepared in Examples 1-6 and Comparative Examples 1-4

[0082]

[0083] Cyclic performance testing: Single cells containing the electrolytes prepared in Example 1 and Comparative Example 1 were tested at 200 mA / cm². 2 Long-cycle stability tests were conducted in electrical density mode, with a charging upper limit of 1.55V and a discharging lower limit of 1.00V. The test results of the three efficiencies (Coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE)) are shown in Table 2.

[0084] Table 2: Cycle performance of single cells containing the electrolyte prepared in Example 1 or Comparative Example 1

[0085]

Claims

1. An electrolyte, characterized in that, The electrolyte comprises vanadium ions, bismuth ions, an N-vinylamide polymer, and an acid; the monomer of the N-vinylamide polymer contains an amide bond and a carbon-carbon double bond connected to the N atom of the amide bond; The molar ratio of monomer units to bismuth ions of the N-vinylamide polymer in the electrolyte is (0.2-10):

1.

2. The electrolyte as described in claim 1, characterized in that, The electrolyte has one or more of the following characteristics: The N-vinylamide polymers are selected from one or more of poly(N-vinylacetamide), polyvinylpyrrolidone, and poly(N-vinylcaprolactam); The acid is sulfuric acid; The electrolyte also includes water; The concentration of vanadium ions in the electrolyte is 1-2 mol / L; The concentration of hydrogen ions in the electrolyte is 3.7-5.4 mol / L; The concentration of bismuth ions in the electrolyte is 0.001-0.003 mol / L; The concentration of the monomer units of the N-vinylamide polymer in the electrolyte is 0.0003-0.015 mol / L.

3. The electrolyte as described in claim 2, characterized in that, The electrolyte has one or more of the following characteristics: The concentration of sulfuric acid is 3-5 mol / L; The concentration of bismuth ions in the electrolyte is 0.001-0.002 mol / L; The concentration of the monomer units of the N-vinylamide polymer in the electrolyte is 0.001-0.002 mol / L; The molar ratio of monomer units to bismuth ions of the N-vinylamide polymer in the electrolyte is (0.5-2):

1.

4. The electrolyte as described in claim 2, characterized in that, The molar ratio of monomer units to bismuth ions of the N-vinylamide polymer in the electrolyte is (0.8-1.2):

1.

5. A method for preparing the electrolyte according to any one of claims 1-4, characterized in that, The method includes mixing a vanadium source, a bismuth salt, an N-vinylamide polymer, and an acid to obtain an electrolyte.

6. The method as described in claim 5, characterized in that, The bismuth salt is bismuth chloride and / or bismuth nitrate.

7. The method as described in claim 5, characterized in that, The method includes: (1) Dissolve bismuth salt in an acidic solution to obtain solution A containing bismuth ions, prepare N-vinylamide polymer to form solution B containing N-vinylamide polymer, mix solution A and solution B to obtain electrolyte; or (1') Dissolve bismuth salt and N-vinylamide polymer together in an acidic solution to obtain an electrolyte.

8. The method as described in claim 7, characterized in that, In step (1), the concentration of hydrogen ions in the acidic solution is 1-5.4 mol / L.

9. A vanadium redox flow battery comprising the electrolyte of any one of claims 1-4.

10. The all-vanadium redox flow battery as described in claim 9, characterized in that, The electrolyte is used as the negative electrode electrolyte in the vanadium redox flow battery.

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