Positive electrode electrolyte, preparation method thereof and all-vanadium redox flow battery

Abstract

The invention provides a positive electrode electrolyte and a preparation method thereof, and an all-vanadium redox flow battery, the positive electrode electrolyte comprises: an active material, the active material comprising + 5-valent vanadium ions; a first additive, wherein the first additive comprises an organic phosphonate; the second additive comprises a high-molecular compound containing amino and hydroxyl. The synergistic effect of the first additive and the second additive can significantly improve the stability of the positive electrode electrolyte and the solubility of + 5-valent vanadium ions, and is beneficial to improving the battery performance and prolonging the battery life.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of all-vanadium redox flow battery, in particular, the present application relates to the positive electrolyte and its preparation method and all-vanadium redox flow battery. BACKGROUND

[0002] With the increasingly serious problems of fossil energy resources depletion and environmental pollution, finding new energy and energy storage technology has become an urgent problem in the development of energy. All-vanadium redox flow battery is a new type of high-efficiency electrochemical energy storage battery, which has super-long cycle, flexible capacity design, fast response rate, high safety and other characteristics, which also makes it widely concerned in the field of new energy. Many research institutions and scholars have also carried out a lot of research work, and strive to improve and perfect the performance of all-vanadium redox flow battery. Electrolyte as the energy storage medium of all-vanadium electrolyte, it determines the capacity and energy density of all-vanadium redox flow battery, therefore, the research of electrolyte has very important significance for the development of all-vanadium redox flow battery.

[0003] In the charging and discharging process of all-vanadium redox flow battery, there will be different valence state of vanadium ion conversion in electrolyte, in the positive electrolyte, +5 valence and +4 valence vanadium ions are active substances, +5 valence and +4 valence vanadium ions exist in the form of VO2 + ion and VO 2+ ion in acidic solution respectively, among them, the solubility of +5 valence vanadium ion is low, and it is greatly affected by temperature, when the temperature is higher than 40℃, the positive electrolyte after charging is easy to hydrolyze and precipitate V2O5(2VO2 + +H2O=V2O5+2H + ). And +5 valence vanadium ion is the main component of all-vanadium redox flow battery positive electrolyte, in the process of charging and discharging of the battery, the conversion between +4 valence vanadium ion and +5 valence vanadium ion occurs constantly, therefore, the instability of +5 valence vanadium ion will lead to precipitation, loss of vanadium ion, affect the capacity and cycle life of the battery. The positive electrolyte with good stability is the basis for the normal work of the battery and good charging and discharging performance.

[0004] Therefore, it is urgent to develop a positive electrolyte with good stability and can improve the solubility of +5 valence vanadium ion and avoid its precipitation, the development of this electrolyte is beneficial to improve the capacity and energy density of all-vanadium redox flow battery, and can solve the problem of capacity disadvantage of all-vanadium redox flow battery. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the prior art at least to some extent.

[0006] A first aspect of this application discloses a positive electrode electrolyte comprising: an active material including pentavalent vanadium ions; a first additive including an organophosphonate; and a second additive including a polymeric compound containing amino and hydroxyl groups. This improves the solubility of pentavalent vanadium ions and enhances the stability of the positive electrode electrolyte.

[0007] According to embodiments of this application, the positive electrode electrolyte may further include at least one of the following additional technical features:

[0008] According to an embodiment of this application, the mass ratio of the first additive to the second additive is 1:(0.2-1.2). Therefore, by keeping the mass ratio of the first additive and the second additive within the above range, the synergistic effect of the first additive and the second additive is improved. This enhances the complexation effect on +5 vanadium ions and increases the solubility of +5 vanadium ions, while reducing the content of the first additive and the second additive in the positive electrode electrolyte that do not undergo complexation, thus reducing the impact on battery capacity, cycle stability, and charge / discharge efficiency.

[0009] According to an embodiment of this application, the mass percentage of the first additive is 0.3% to 1% based on the total mass of the positive electrode electrolyte. Therefore, while improving the complexation effect on +5 vanadium ions and increasing the solubility of +5 vanadium ions, the content of the first additive that does not undergo complexation in the positive electrode electrolyte is reduced, thereby minimizing the impact on battery capacity and cycle stability.

[0010] According to an embodiment of this application, the mass percentage of the second additive is 0.05% to 1% based on the total mass of the positive electrode electrolyte. Therefore, while improving the complexation effect on +5 vanadium ions and increasing the solubility of +5 vanadium ions, the content of the second additive that does not undergo complexation in the positive electrode electrolyte is reduced, thereby minimizing the impact on battery capacity and cycle stability.

[0011] According to embodiments of this application, the molar concentration of +5-valent vanadium ions in the positive electrode electrolyte is not less than 0.5 mol / L. This increases the concentration of +5-valent vanadium ions in the positive electrode electrolyte, thereby increasing the energy density of the battery.

[0012] According to embodiments of this application, the molar concentration of the +5-valent vanadium ions in the positive electrode electrolyte is 0.5 mol / L to 1.5 mol / L. This increases the concentration of +5-valent vanadium ions in the positive electrode electrolyte, thereby improving the energy density of the battery.

[0013] According to embodiments of this application, the first additive includes at least one of hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, and diethylenetriaminepentamethylidenephosphonic acid. Thus, the aforementioned type of first additive can increase the solubility of +5 vanadium ions in the electrolyte through complexation, reduce the probability of +5 vanadium ions forming precipitates, thereby improving the stability of the electrolyte and increasing the energy density and cycle life of the battery.

[0014] According to an embodiment of this application, the first additive includes the hydroxyethylidene diphosphonic acid.

[0015] According to embodiments of this application, the second additive includes at least one of chitosan and cellulose.

[0016] According to an embodiment of this application, the second additive includes chitosan.

[0017] The second additive can form a cage-like structure to complex +5 vanadium ions, thereby increasing the solubility of +5 vanadium ions in the electrolyte and reducing the probability of +5 vanadium ions forming precipitates.

[0018] According to embodiments of this application, the positive electrode electrolyte further comprises an aqueous sulfuric acid solution. Therefore, it can maintain a low pH of the electrolyte, inhibit the hydrolysis of +5 vanadium ions, increase the conductivity of the electrolyte, and improve the energy efficiency of the battery.

[0019] According to embodiments of this application, the molar concentration of the sulfuric acid aqueous solution is 2 mol / L to 4 mol / L. Therefore, it can maintain a low pH of the electrolyte, inhibit the hydrolysis of +5 vanadium ions, increase the conductivity of the electrolyte, and improve the energy efficiency of the battery.

[0020] A second aspect of this application discloses a method for preparing the positive electrode electrolyte described in the first aspect. According to an embodiment of this application, the method includes: subjecting a vanadium solution, a first additive, and a second additive to a first mixing treatment, followed by electrolysis to obtain the positive electrode electrolyte, wherein the vanadium solution comprises +4 valent vanadium ions. Therefore, the positive electrode electrolyte prepared by this method exhibits excellent stability and can improve the cycle stability of the battery.

[0021] According to embodiments of this application, the method for preparing the positive electrode electrolyte may further include at least one of the following additional technical features:

[0022] According to embodiments of this application, the molar concentration of the +4 vanadium ions is not less than 1 mol / L. Therefore, increasing the concentration of +5 vanadium ions in the positive electrode electrolyte after charging improves the energy density of the battery.

[0023] According to embodiments of this application, the molar concentration of the +4 vanadium ions is 1 mol / L to 3 mol / L. Therefore, increasing the concentration of +5 vanadium ions in the positive electrode electrolyte after charging improves the energy density of the battery.

[0024] According to embodiments of this application, the current for the electrolytic treatment is 100mA to 1000mA. Therefore, the conversion rate of +4 vanadium ions to +5 vanadium ions can be increased.

[0025] According to embodiments of this application, the electrolysis treatment time is 1 hour to 10 hours. Therefore, the conversion rate of +4 vanadium ions to +5 vanadium ions can be increased.

[0026] A third aspect of this application discloses an all-vanadium redox flow battery. This all-vanadium redox flow battery possesses all the characteristics and advantages of the aforementioned positive electrode electrolyte, which will not be repeated here. In general, it exhibits at least high energy density and cycle life.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Fig. 1 This is a comparison of the ultraviolet spectra of positive electrode electrolytes with different mass concentrations of hydroxyethylidene diphosphonic acid (HEDP) and chitosan according to embodiments of this application.

[0030] Fig. 2 This is a comparison of the ultraviolet spectra of positive electrode electrolytes with the same mass concentration of hydroxyethylidene diphosphonic acid (HEDP) and different mass concentrations of chitosan according to embodiments of this application.

[0031] Fig. 3 This is a comparison chart of the ultraviolet spectra of the positive electrode electrolytes according to the embodiments and comparative examples of this application. Detailed Implementation

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0034] 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 pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0036] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] A vanadium redox flow battery (VRB), also known as a vanadium battery, is a type of flow battery that uses vanadium ions as the active material in a liquid redox regenerative circuit. The VRB uses a solution of vanadium ions in the +4 and +5 valence states as the active material for the positive electrode, and a solution of vanadium ions in the +2 and +3 valence states as the active material for the negative electrode, both stored in their respective electrolyte tanks. During charging and discharging, the electrolytes at the positive and negative electrodes undergo a redox reaction across the ion exchange membrane. Simultaneously, an external pump continuously pumps electrolyte from the storage tanks into the positive and negative electrode chambers to maintain ion concentration and achieve the charging and discharging process.

[0039] Vanadium batteries store electrical energy as chemical energy in a sulfuric acid electrolyte containing vanadium ions in different valence states. An external pump forces the electrolyte into the battery stack, where it circulates within closed loops of different storage tanks and half-cells under mechanical force. A proton exchange membrane serves as the separator in the battery pack. The electrolyte solution flows parallel across the electrode surfaces, undergoing electrochemical reactions. Current is collected and conducted through dual electrode plates, thus converting the chemical energy stored in the solution into electrical energy. This reversible reaction process allows the vanadium battery to smoothly complete charging, discharging, and recharging. The positive electrode electrolyte consists of vanadium ions in +4 and +5 valence states, while the negative electrode electrolyte consists of vanadium ions in +2 and +3 valence states. After charging, the positive electrode material is a +5 valence vanadium ion solution, and the negative electrode is a +2 valence vanadium ion solution. After discharging, the positive and negative electrodes are +4 and +3 valence vanadium ion solutions, respectively. Internally, the battery uses H₂O to dissipate the vanadium ions. + Conductive. Vanadium ions in the +5 and +4 oxidation states react in acidic solutions as VO2+ and vanadium ions, respectively. + Ions and VO 2+ Since vanadium exists in ionic form, the positive and negative electrode reactions of a vanadium battery can be described as follows:

[0040] Positive terminal during charging: VO 2+ +H2O→VO2 + +2H + +e -

[0041] Negative terminal during charging: V 3+ +e - →V 2+

[0042] Positive electrode during discharge: VO2 + +2H + +e - →VO 2+ +H2O

[0043] Negative electrode during discharge: V 2+ →V 3+ +e -

[0044] Vanadium ions (+5 valent) have low solubility in electrolytes and are highly temperature-dependent. Under high temperatures and excessively high concentrations, they easily precipitate, reducing the concentration of +5 vanadium ions in the positive electrode electrolyte and consequently lowering the battery's energy density and cycle life. Related technologies have improved the electrolyte; for example, acetonitrile is used as an additive in the preparation of the positive electrode electrolyte, which can effectively improve the electrolyte's stability. However, acetonitrile has high toxicity, limiting its application in vanadium batteries.

[0045] This application proposes a positive electrode electrolyte in which two additives are added. The first additive includes an organophosphonate, and the second additive includes a polymer compound containing amino and hydroxyl groups. The polymer compound can form a cage-like structure. The two additives can significantly increase the solubility of +5 vanadium ions and the stability of the positive electrode electrolyte through synergistic effect.

[0046] Positive Electrolyte

[0047] This application discloses a positive electrode electrolyte. According to an embodiment of this application, the electrolyte includes an active substance comprising +5 vanadium ions; a first additive comprising an organophosphonate; and a second additive comprising a polymeric compound containing amino and hydroxyl groups.

[0048] It should be noted that the main component of the positive electrode electrolyte of the all-vanadium redox flow battery in this application is a vanadium ion (vanadium oxide)-sulfuric acid system, wherein the +5 vanadium ions are mainly composed of VO2+. + Vanadium ions exist in the form of +4 valence ions as VO 2+ It exists in form.

[0049] The positive electrode electrolyte proposed in this application is prepared by simultaneously adding a first additive and a second additive, wherein the first additive, an organophosphonate, contains phosphite ions (H₂PO₃). - Able to work with VO2 + Complexation occurs, forming a stable complex [V(H2PO3)] 4+ This prevents VO2 + Hydrolysis occurs to form V2O5 precipitate, and the specific reaction formula is as follows: VO2 + +H2PO3 - +4H + →[V(H2PO3)] 4+ +2H₂O, complex [V(H₂PO₃)] 4+ It has high solubility in the positive electrode electrolyte, thus enhancing the solubility of +5 vanadium ions; the amino and hydroxyl groups on one unit of the second additive will first form hydrogen bonds with the hydrogen atoms on the other unit (for example, the second additive is (R)). n (The amino and hydroxyl groups on one of the R atoms will combine with the hydrogen atoms on the other R atoms to form hydrogen bonds), repeating this process multiple times, causing the second additive to form a cage-like structure. The amino and hydroxyl groups on the cage-like structure will combine with VO2... +The additive complexes with vanadium ions in the electrolyte, allowing them to enter the cage-like structure and improving their stability. Simultaneously, the first additive, also a complexing agent, interacts with vanadium ions. Through the combined action of the small-molecule first additive and the large-molecule second additive, a more stable coordination cage structure is formed. This demonstrates a synergistic effect between the large-molecule and small-molecule additives, jointly enhancing the capture of vanadium ions and reducing free VO2 in the positive electrode electrolyte. + The concentration of VO2 is reduced. + The probability of hydrolysis to generate V2O5 is increased, which improves the stability of the positive electrode electrolyte, thereby improving the cycle stability and capacity retention of the vanadium redox flow battery.

[0050] In some embodiments of this application, the mass ratio of the first additive to the second additive can be 1:(0.2-1.2). For example, it can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc., or a range of any of the above values. By keeping the mass ratio of the first additive and the second additive within the above range, the synergistic effect of the first additive and the second additive is improved, thereby increasing the concentration of VO2 in the electrolyte. + The chelation effect reduces VO2 + The probability of hydrolysis forming a precipitate increases the solubility of +5 vanadium ions, thereby improving the stability of the cathode electrolyte, battery energy density, and cycle performance.

[0051] In some embodiments of this application, the mass percentage of the first additive can be 0.3% to 1% based on the total mass of the positive electrode electrolyte. For example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., or a range of any of the above values. By keeping the content of the first additive within the above range, the phosphate ion content in the positive electrode electrolyte is increased, and the resistance to VO2+ is improved. + While achieving complexation, it reduces the content of phosphate ions that have not undergone complexation in the positive electrode electrolyte, thereby reducing the impact on electrolyte viscosity and thus reducing the impact on battery cycle performance.

[0052] In some embodiments of this application, the mass percentage of the second additive can be 0.05% to 1% based on the total mass of the positive electrode electrolyte. For example, it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any range of the above values. By keeping the content of the second additive within the above range, the complexation effect of the second additive on +5 vanadium ions is improved. Simultaneously, the content of the second additive that does not undergo complexation in the positive electrode electrolyte is reduced, thus reducing the impact on electrolyte viscosity and consequently reducing the impact on battery cycle performance.

[0053] In some embodiments of this application, the molar concentration of +5-valent vanadium ions in the positive electrode electrolyte is not less than 0.5 mol / L. For example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L, or any range of the above values. This increases the molar concentration of +5-valent vanadium ions in the positive electrode electrolyte, thereby improving the energy density and cycle life of the battery.

[0054] In some embodiments of this application, the molar concentration of the +5 vanadium ions in the positive electrode electrolyte is 0.5 mol / L to 1.5 mol / L. For example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc., or any range of the above values. By keeping the concentration of +5 vanadium ions within the above range, both a large output current and the normal occurrence of the electrochemical reaction can be ensured.

[0055] It should be noted that when the molar concentration of +5 vanadium ions in the positive electrode electrolyte is between 0.5 mol / L and 1.5 mol / L, the addition of the first and second additives can reduce the probability of precipitation in the electrolyte and electrode during charging and discharging. This is because +5 vanadium ions within this concentration range provide sufficient reactants, allowing the positive and negative electrode reactions to proceed smoothly. Furthermore, the added first and second additives can effectively complex with +5 vanadium ions within this concentration range, improving their stability and thus reducing the probability of precipitation formation. However, when the concentration of +5 vanadium ions is too high, even with the addition of the first and second additives, while their addition may reduce precipitation, it may not prevent precipitation formation altogether. This is because an excessively high concentration of +5 vanadium ions increases the likelihood of their interaction and aggregation. Additionally, the phosphite ions, amino groups, and hydroxyl groups in the first and second additives cannot sufficiently complex with the excessive amount of +5 vanadium ions, failing to improve the overall stability of the positive electrode electrolyte. Therefore, even with the presence of additives, it is difficult to reduce the probability of precipitation formation.

[0056] In some embodiments of this application, the first additive comprises an organophosphonate. The organophosphonate comprises at least one of hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylenephosphonic acid (ATMP), and diethylenetriaminepentamethylidenephosphonic acid (DTPMPA). Specifically, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, and diethylenetriaminepentamethylidenephosphonic acid all contain phosphite ions, which are H₂PO₃. - Able to work with VO2 + Complexation occurs, forming a stable complex [V(H2PO3)] 4+ The specific reaction formula is as follows: VO2 + +H2PO3 - +4H + →[V(H2PO3)] 4+ +2H2O. Therefore, hydroxyethylidene diphosphonic acid, aminotrimethylene phosphonic acid, and diethylenetriaminepentamethylidene phosphonic acid can all improve the solubility of +5 vanadium ions and the stability of the cathode electrolyte, thereby enhancing the cycle performance of the battery.

[0057] In some embodiments of this application, the first additive includes hydroxyethylidene diphosphonic acid. Hydroxyethylidene diphosphonic acid exhibits excellent dissociation in water, capable of releasing a large number of phosphite ions to form a stable complex [V(H₂PO₃)] with +5 valent vanadium ions. 4+ Therefore, compared to other phosphonates, hydroxyethylidene diphosphonic acid can significantly increase the solubility of +5 vanadium ions.

[0058] In some embodiments of this application, the second additive comprises a polymeric compound containing amino and hydroxyl groups, wherein the polymeric compound containing amino and hydroxyl groups comprises at least one of chitosan and cellulose.

[0059] In some embodiments of this application, the second additive comprises chitosan. Chitosan contains abundant amino and hydroxyl groups, and its chemical formula is (C6H2O). 11 NO4) n One unit of chitosan is C6H. 11 NO4, with the specific structure shown in Formula I, has a hydroxyl and amino group on one unit that can form hydrogen bonds with the hydrogen on another unit. This process is repeated multiple times, allowing multiple chitosans to connect and form a cage-like structure. The amino and hydroxyl groups on the cage-like structure can react with VO2. + The vanadium ions in the electrolyte are complexed, allowing them to enter the cage-like structure, as shown in Formula II. Therefore, the addition of chitosan can improve the stability of the vanadium ions and the electrolyte, further enhancing the electrochemical activity and cycle stability of the battery.

[0060]

[0061] Organophosphates also have the ability to complex with vanadium ions, and they can stabilize the cage-like structure formed by chitosan, working synergistically with chitosan to improve the solubility of +5 vanadium ions in the electrolyte.

[0062] In some embodiments of this application, the positive electrode electrolyte further includes an aqueous sulfuric acid solution. The electrolyte matrix of a vanadium redox flow battery is generally an aqueous sulfuric acid solution, which serves to maintain a low pH in the electrolyte, inhibit the hydrolysis of vanadium ions, increase the conductivity of the electrolyte, reduce ohmic polarization, and improve battery energy efficiency.

[0063] In some embodiments of this application, the molar concentration of the sulfuric acid aqueous solution can be from 2 mol / L to 4 mol / L. For example, it can be 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, or any range of the above values. Therefore, a molar concentration of sulfuric acid aqueous solution within this range can balance the relationship between the viscosity, conductivity, and electrochemical activity of the electrolyte, achieving optimal battery performance and cycle stability, and improving battery energy efficiency.

[0064] Methods for preparing positive electrode electrolyte

[0065] This application discloses a method for preparing a positive electrode electrolyte. According to an embodiment of this application, the method includes: subjecting a vanadium solution, a first additive, and a second additive to a first mixing treatment, followed by electrolysis to obtain the positive electrode electrolyte, wherein the vanadium solution comprises +4 valent vanadium ions.

[0066] In the method described in this application, vanadium ions in the vanadium solution are converted to vanadium ions in the form of VO2+ ions through electrolysis. + It exists in the form of vanadium ions. By adding a first additive and a second additive to the electrolyte, the solubility of +5 valent vanadium ions formed after electrolysis can be increased, preventing them from forming precipitates and further improving the stability of the electrolyte. Among them, the first additive contains phosphite ions (H2PO3). - Able to work with VO2 + Complexation occurs, forming a stable complex [V(H2PO3)] 4+ This prevents VO2 + Hydrolysis occurs to form V2O5 precipitate, and the specific reaction formula is as follows: VO2 + +H2PO3 - +4H + →[V(H2PO3)] 4+ +2H₂O, complex [V(H₂PO₃)] 4+ It has high solubility in the positive electrode electrolyte, thus enhancing the solubility of +5 vanadium ions; the amino and hydroxyl groups on one unit of the second additive will first combine with the hydrogen ions on the other unit to form hydrogen bonds (for example, the second additive is (R)). n (The amino and hydroxyl groups on one of the R atoms will combine with the hydrogen ions on the other R atoms to form hydrogen bonds), repeating this process multiple times, causing the second additive to form a cage-like structure. Then, the amino and hydroxyl groups on the cage-like structure will combine with VO2... + The process involves complexing the +5 vanadium ions in the electrolyte, allowing them to enter the cage-like structure and improving their stability. Simultaneously, the second additive is a macromolecular additive, while the first additive is a small molecule additive. The first additive can enter the gaps between multiple second additives to complex the +5 vanadium ions present within these gaps. This synergistic effect of macromolecular and small molecule additives enhances the complexation effect on +5 vanadium ions, reducing free VO2 in the positive electrode electrolyte. + The concentration of VO2 is reduced. + The probability of hydrolysis to generate V2O5 is increased, which improves the stability of the positive electrode electrolyte, thereby improving the cycle stability and capacity retention of the vanadium redox flow battery.

[0067] When both additives are present, they together form a cage-like structure. Under the influence of organophosphates, the cage-like structure formed by chitosan becomes more stable, resulting in a more stable positive electrolyte for high-concentration vanadium redox flow batteries. This phenomenon generally holds true within a certain concentration range. If the concentrations of the two additives are too low, a stable cage-like structure cannot be formed; if the concentrations are too high, it will actually disrupt the increased solubility of pentavalent vanadium ions due to complexation, thus resulting in a decreased absorption peak in UV testing. Experiments were conducted in the examples to illustrate the concentrations of the two additives.

[0068] In some embodiments of this application, the molar concentration of +4 vanadium ions in the vanadium solution is not less than 1 mol / L. For example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L, or any range of the above values. Therefore, a sufficient concentration of +4 vanadium ions can provide ample reactants, enabling the formation of sufficient +5 vanadium ions after electrolysis, thereby improving the battery energy density.

[0069] In some embodiments of this application, the molar concentration of the +4 vanadium ions can be from 1 mol / L to 3 mol / L. For example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, or any range of the above values. By keeping the +4 vanadium ions within this range, they can provide sufficient reactants, enabling the formation of enough +5 vanadium ions after electrolysis, thereby increasing the energy density of the battery.

[0070] In some embodiments of this application, electrolysis is carried out under conditions of 100mA to 1000mA for 1h to 10h. Therefore, it can promote the conversion of +4 vanadium ions to +5 vanadium ions, ensuring the normal occurrence of the electrochemical reaction.

[0071] In some embodiments of this application, electrolysis may be carried out under conditions such as 100mA, 200mA, 300mA, 400mA, 500mA, 600mA, 700mA, 800mA, 900mA, 1000mA, or a range of any of the above values.

[0072] In some embodiments of this application, the electrolysis time can be, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or a range of any of the above values.

[0073] In some embodiments of this application, the vanadium solution is obtained by: subjecting a compound containing tetravalent vanadium ions and an aqueous sulfuric acid solution to a second mixing treatment; and then heating the product of the second mixing treatment to obtain the vanadium solution. Here, the tetravalent vanadium ions serve as the active material in the positive electrode electrolyte, participating in the redox reaction of the battery and, under the influence of an external power source, achieving the conversion of tetravalent vanadium ions to pentavalent vanadium ions. The aqueous sulfuric acid solution serves as the electrolyte, used to conduct vanadium ions.

[0074] In some embodiments of this application, the compounds containing tetravalent vanadium ions include, but are not limited to, vanadium oxysulfate (VOSO4) or vanadium dichloride (VOCl2), wherein the tetravalent vanadium ions in the positive electrode electrolyte are in the form of VO4. 2+ It exists in the form of.

[0075] In some embodiments of this application, the molar concentration of the sulfuric acid aqueous solution can be from 2 mol / L to 4 mol / L. For example, it can be 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, or any range of the above values. The concentration of the sulfuric acid aqueous solution affects the viscosity, conductivity, and electrochemical activity of the electrolyte by changing the hydrogen ion concentration in the electrolyte. Therefore, a molar concentration of sulfuric acid aqueous solution within this range can balance the relationship between the viscosity, conductivity, and electrochemical activity of the electrolyte, resulting in optimal battery performance and cycle stability.

[0076] To ensure the rapid and uniform dissolution of compounds containing tetravalent vanadium ions in an aqueous sulfuric acid solution, magnetic stirring was performed concurrently with heat treatment. The heat treatment was conducted at 50°C-100°C for 15-60 minutes.

[0077] In some embodiments of this application, the heat treatment may be carried out under conditions such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or may be a range of any of the above values.

[0078] In some embodiments of this application, the heating treatment time can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc., or can be a range of any of the above values.

[0079] Vanadium redox flow battery

[0080] This application proposes an all-vanadium redox flow battery. According to an embodiment of this application, the all-vanadium redox flow battery includes the aforementioned positive electrode electrolyte. As mentioned earlier, the superior stability of the positive electrode electrolyte in this application not only reduces side reactions during charge and discharge, extending the battery's cycle life, but also helps improve the battery's energy conversion efficiency. Furthermore, the increased solubility of +5 vanadium ions in the positive electrode electrolyte allows for better transport during charge and discharge, thereby contributing to improved energy efficiency and cycle stability, and ultimately enhancing battery performance.

[0081] In some embodiments of this application, the vanadium redox flow battery further includes a negative electrode electrolyte, a positive electrode, a negative electrode, and a separator.

[0082] In some embodiments of this application, the negative electrode electrolyte includes an active substance, a matrix, and additives. The active substance includes +2 valent vanadium ions and / or +3 valent vanadium ions. The matrix includes, but is not limited to, an aqueous sulfuric acid solution. The additives are not limited here, as long as they can promote the overall redox reaction and promote charge transport.

[0083] In some embodiments of this application, the positive or negative electrode material includes metals, carbon materials, or composite materials, wherein metals may be selected from Pb, Ti, etc.; carbon materials may be selected from graphite, carbon cloth, carbon felt, etc.; and composite materials may be selected from conductive polymers, polymer composite materials, etc.

[0084] In some embodiments of this application, the membrane may be selected from ion exchange membranes, as long as it can suppress the cross-mixing of vanadium ions of different valence states in the positive and negative electrode electrolytes without hindering hydrogen ions from passing through the membrane and transferring charge.

[0085] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0086] Example 1

[0087] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (heating at 70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% HEDP (first additive) and 0.5 wt% chitosan (second additive) were added to the mixture. After mixing evenly, the mixture was placed in the anode tank of an H-type electrolytic cell and subjected to constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0088] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0089] Example 2

[0090] The electrolyte was prepared according to the method described in Example 1, except that the first additive used in Example 2 was nitrogen-based trimethylenephosphonic acid (ATMP).

[0091] Example 3

[0092] The electrolyte was prepared according to the method described in Example 1, except that in Example 3, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.05 wt% chitosan (second additive) were added.

[0093] Example 4

[0094] The electrolyte was prepared according to the method described in Example 1, except that in Example 4, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.1 wt% chitosan (second additive) were added.

[0095] Example 5

[0096] The electrolyte was prepared according to the method described in Example 1, except that in Example 5, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.2 wt% chitosan (second additive) were added.

[0097] Example 6

[0098] The electrolyte was prepared according to the method described in Example 1, except that in Example 6, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.25 wt% chitosan (second additive) were added.

[0099] Example 7

[0100] The electrolyte was prepared according to the method described in Example 1, except that in Example 7, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.3 wt% chitosan (second additive) were added.

[0101] Example 8

[0102] The electrolyte was prepared according to the method described in Example 1, except that in Example 8, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.4 wt% chitosan (second additive) were added.

[0103] Example 9

[0104] The electrolyte was prepared according to the method described in Example 1, except that in Example 9, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.6 wt% chitosan (second additive) were added.

[0105] Example 10

[0106] The electrolyte was prepared according to the method described in Example 1, except that in Example 10, 0.1 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.05 wt% chitosan (second additive) were added.

[0107] Example 11

[0108] The electrolyte was prepared according to the method described in Example 1, except that in Example 11, 1 wt% hydroxyethylidene diphosphonic acid (first additive) and 0.5 wt% chitosan (second additive) were added.

[0109] Example 12

[0110] The electrolyte was prepared according to the method described in Example 1, except that in Example 12, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) and 1 wt% chitosan (second additive) were added.

[0111] Example 13

[0112] The electrolyte was prepared according to the method described in Example 1, except that in Example 13, 0.5 wt% HEDP and 0.5 wt% cellulose were added.

[0113] Example 14

[0114] The electrolyte was prepared according to the method described in Example 1, except that in Example 14, 0.3 wt% HEDP and 0.15 wt% chitosan were added.

[0115] Example 15

[0116] The electrolyte was prepared according to the method described in Example 1, except that in Example 15, 0.8 wt% HEDP and 0.4 wt% chitosan were added.

[0117] Comparative Example 1

[0118] The electrolyte was prepared according to the method described in Example 1, except that no additives were added in Comparative Example 1. The specific method is as follows:

[0119] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar added, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (70℃ for 30 min). After the VOSO4 was fully dissolved, it was placed in the anode tank of an H-type electrolytic cell and subjected to constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0120] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0121] Comparative Example 2

[0122] The electrolyte was prepared according to the method described in Example 1, except that only the first additive, hydroxyethylidene diphosphonic acid, was added in Comparative Example 2. The specific method is as follows:

[0123] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (heating at 70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% hydroxyethylidene diphosphonic acid (first additive) was added to the mixture. After mixing thoroughly, the mixture was placed in the anode tank of an H-type electrolytic cell and subjected to constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0124] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0125] Comparative Example 3

[0126] The electrolyte was prepared according to the method described in Example 1, except that only the first additive ATMP was added in Comparative Example 3. The specific method is as follows:

[0127] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% ATMP (first additive) was added to the mixture, and after thorough mixing, it was placed in the anode tank of an H-type electrolytic cell and subjected to constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0128] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0129] Comparative Example 4

[0130] The electrolyte was prepared according to the method described in Example 1, except that only the second additive, chitosan, was added in Comparative Example 4. The specific method is as follows:

[0131] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (heating at 70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% chitosan (second additive) was added to the mixture, and after thorough mixing, it was placed in the anode tank of an H-type electrolytic cell for constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0132] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0133] Comparative Example 5

[0134] The electrolyte was prepared according to the method described in Example 1, except that Comparative Example 5 only added glucosamine as a second additive. The specific method is as follows:

[0135] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% glucosamine (second additive) was added to the mixture, and after thorough mixing, it was placed in the anode tank of an H-type electrolytic cell for constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0136] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0137] Comparative Example 6

[0138] The electrolyte was prepared according to the method described in Example 1, except that Comparative Example 6 only added cellulose as a second additive. The specific method is as follows:

[0139] Electrolyte formulation: A certain amount of VOSO4 was dissolved in a 3.0 mol / L sulfuric acid aqueous solution to prepare a mixed solution with a +4 vanadium ion concentration of 2.5 mol / L. The mixture was placed on a magnetic stirrer with a stir bar, and the VOSO4 was dissolved in the sulfuric acid under heating conditions (70℃ for 30 min). After the VOSO4 was fully dissolved, 0.5 wt% cellulose (second additive) was added to the mixture, and after thorough mixing, it was placed in the anode tank of an H-type electrolytic cell and subjected to constant current electrolysis for 4 h. During this process, an oxidation reaction occurs at the anode, converting +4 vanadium ions into +5 vanadium ions, thus preparing the positive electrode electrolyte. The precipitation in the electrolytic cell after preparation was observed, and a small amount of electrolyte was diluted and subjected to UV testing.

[0140] Conditions for constant current electrolysis: Electrode: graphite felt electrode, area 1.5cm×3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane; Constant current electrolysis current density 500mA; Electrolyte volume: 25mL; Electrolysis time: 4h.

[0141] Comparative Example 7

[0142] The electrolyte was prepared according to the method described in Example 1, except that 0.5 wt% HEDP and 0.5 wt% glucosamine were added to Comparative Example 7.

[0143] The types and mass fractions of the first and second additives in Examples 1-15 and Comparative Examples 1-7, as well as the mass ratio of the first and second additives, are shown in Table 1.

[0144] Table 1

[0145]

[0146]

[0147] Performance testing

[0148] Ultraviolet-Vis spectrophotometry detection

[0149] The characteristic peak position of +5 vanadium ions is at 270-290 nm. The UV test results of the electrolyte under different additive conditions are as follows: Figs. 1-3 As shown in Table 1, the peak intensities of the ultraviolet characteristic peaks in Examples 1-15 all appeared at this position. This indicates that after the constant current electrolysis reduction process in these examples, the +4 valence vanadium ions in the original electrolyte were all converted into +5 valence vanadium ions. In contrast, no peak was observed in Comparative Example 1 at 270-290 nm (the peak intensity was very weak), indicating that the addition of the additive did indeed increase the concentration of +5 valence vanadium ions in the vanadium electrolyte.

[0150] The results of Examples 1-15 and Comparative Examples 1-7 show that the combination of the first additive and the second additive can improve the solubility of vanadium ions in the +5 valence. In particular, the first additive and the second additive need to meet certain ratios and concentrations (the mass percentage of the first additive is 0.3-0.8 wt%, and the mass percentage of the second additive is 0.05%-1%) to significantly improve the solubility of vanadium ions in the +5 valence.

[0151] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0152] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrolyte, characterized by comprising: The active substance comprises +5 valence vanadium ions. The first additive comprises an organic phosphonate. The second additive comprises a high-molecular compound containing amino and hydroxyl groups. The mass ratio of the first additive to the second additive is 1:(0.2-1.2).

2. The positive electrolyte according to claim 1, characterized in that, The mass percentage of the first additive in the total mass of the positive electrolyte is 0.3%-1%.

3. The positive electrolyte according to claim 2, characterized in that, And / or, the mass percentage of the second additive in the total mass of the positive electrolyte is 0.05%-1%. The molar concentration of the +5 valence vanadium ions in the positive electrolyte is not less than 0.5 mol / L; optionally, the molar concentration of the +5 valence vanadium ions in the positive electrolyte is 0.5 mol / L-1.5 mol / L.

4. The positive electrolyte according to claim 1, characterized in that, The first additive comprises at least one of hydroxyethylidene diphosphonic acid, aminotri(methylene) phosphonic acid, and diethylene triamine penta(methylene) phosphonic acid; optionally, the first additive comprises the hydroxyethylidene diphosphonic acid.

5. The positive electrolyte according to any one of claims 1 to 4, characterized in that, The second additive comprises at least one of chitosan and cellulose.

6. The positive electrolyte according to any one of claims 1 to 4, characterized in that, Further comprising a sulfuric acid aqueous solution; optionally, the molar concentration of the sulfuric acid aqueous solution is 2 mol / L-4 mol / L.

7. The positive electrolyte according to any one of claims 1 to 4, characterized in that, The vanadium solution, the first additive, and the second additive are subjected to a first mixing treatment and electrolysis to obtain the positive electrolyte, the vanadium solution comprising +4 valence vanadium ions.

8. A method of preparing the positive electrolyte according to any one of claims 1 to 7, characterized in that, The molar concentration of the +4 valence vanadium ions in the vanadium solution is not less than 1 mol / L; optionally, the molar concentration of the +4 valence vanadium ions is 1 mol / L-3 mol / L. The current for the electrolysis is 100 mA-1000 mA.

9. The method of claim 8, wherein, And / or, the time for the electrolysis is 1 h-10 h.

10. The method of claim 8, wherein, The positive electrolyte of any one of claims 1-7. ​ 11. An all-vanadium redox flow battery characterised in that, ​

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