Positive electrode electrolyte, preparation method and flow battery

Abstract

The invention provides a positive electrode electrolyte, a preparation method of the positive electrode electrolyte and a flow battery, the positive electrode electrolyte comprises: an active material suitable for providing positive pentavalent vanadium ions; a dispersant; the cations comprise at least one of calcium ions, magnesium ions, sodium ions, barium ions, strontium ions and ammonium ions; and chloride ions. Therefore, the positive electrode electrolyte has relatively good stability, the solubility and the dispersity of positive pentavalent vanadium ions in the positive electrode electrolyte can be improved, precipitation is avoided, and the capacity and the energy density of the battery are further improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a positive electrode electrolyte, a method for preparing the positive electrode electrolyte, and a flow battery. Background Technology

[0002] With the continuous depletion of fossil fuels worldwide and the increasing awareness of environmental protection, renewable energy power generation technologies are gaining popularity. Renewable energy sources mainly include wind, solar, biomass, and ocean energy, which are typically converted into electricity. However, due to factors such as location and weather, these renewable energy power generation methods exhibit significant discontinuity and instability. To smooth and stabilize renewable energy power output, resolve the time lag between power generation and consumption, and improve power quality and grid reliability, it is essential to develop efficient energy storage technologies. Flow batteries, such as vanadium redox flow batteries (VFBs), offer significant advantages including independently adjustable system capacity and power, rapid response, safety and reliability, environmental friendliness, long cycle life, and ease of maintenance and regeneration, making them suitable for renewable energy power generation.

[0003] In flow batteries, such as vanadium redox flow batteries, vanadium ions in different valence states undergo transformation in the electrolyte during charging and discharging. For example, in the positive electrode electrolyte, pentavalent (also known as "+5 valence state") vanadium ions and tetravalent (also known as "+4 valence state") vanadium ions serve as active materials. The +5 and +4 valence vanadium ions react in acidic solutions as VO2+ and vanadium ions, respectively. + Ions and VO 2+ Vanadium ions exist in ionic form, with the +5 valence state exhibiting low solubility. In particular, after charging, the positive electrode electrolyte is prone to hydrolysis, resulting in the precipitation of V₂O₅ (₂VO₂). + +H₂O=V₂O₅+2H + This results in the loss of vanadium ions, affecting the battery's capacity and cycle life.

[0004] Therefore, the current positive electrode electrolyte still needs improvement. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art, to at least some extent.

[0006] A first aspect of this application discloses a positive electrode electrolyte. According to an embodiment of this application, the positive electrode electrolyte includes an active material suitable for providing pentavalent vanadium ions; a dispersant; a cation including at least one of calcium, magnesium, sodium, barium, strontium, and ammonium ions; and chloride ions. Therefore, this positive electrode electrolyte exhibits good stability, improving the solubility and dispersibility of pentavalent vanadium ions in the electrolyte, preventing precipitation, and further enhancing the battery's capacity and energy density. According to an embodiment of this application, in a flow battery, such as a vanadium redox flow battery, +5 valence vanadium ions are the main component of the positive electrode electrolyte. During the charging and discharging process of the battery, continuous conversion between +4 and +5 valence vanadium ions occurs. Therefore, the instability of +5 valence vanadium ions leads to precipitation. The inventors of this application have discovered that by using the positive electrode electrolyte according to the embodiments of this application, the +5 valence vanadium ions in the electrolyte can have better stability, thereby ensuring normal battery operation and obtaining good charge and discharge performance.

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

[0008] According to embodiments of this application, the dispersant is lignin sulfonate or a derivative thereof. Using this dispersant can improve the dispersibility of vanadium ions and further enhance the shielding effect of cations through the complexation between the dispersant and the cations.

[0009] According to embodiments of this application, the dispersant includes at least one of sodium lignosulfonate and calcium lignosulfonate. Therefore, according to embodiments of this application, using the above-mentioned dispersant can further ensure uniform dispersion of pentavalent vanadium ions in the positive electrode electrolyte, increase the solubility of pentavalent vanadium ions in the positive electrode electrolyte, reduce the probability of pentavalent vanadium ions forming precipitates, thereby improving the stability of the positive electrode electrolyte and increasing the energy density and cycle life of the battery.

[0010] According to an embodiment of this application, the dispersant is lignin sulfonate, and the cations and chloride ions are provided in the form of magnesium chloride, wherein the mass ratio of the lignin sulfonate to the magnesium chloride is (3-14):1. This improves the synergistic effect of the dispersant, cations, and chloride ions, increasing the dispersion of pentavalent vanadium ions while simultaneously improving the dispersion of cations and chloride ions, promoting their interaction with pentavalent vanadium ions, reducing the probability of pentavalent vanadium ions forming precipitates, thereby improving the stability of the electrolyte and increasing the energy density and cycle life of the battery.

[0011] According to an embodiment of this application, based on the total mass of the positive electrode electrolyte, the positive electrode electrolyte contains 0.2% to 0.8% of the lignin sulfonate. Therefore, by maintaining the mass percentage of lignin sulfonate within the aforementioned range, it helps to uniformly disperse pentavalent vanadium ions in the electrolyte, improves the solubility of pentavalent vanadium ions, and reduces the content of undispersed lignin sulfonate in the positive electrode electrolyte, thereby reducing the impact on battery capacity and cycle stability.

[0012] According to an embodiment of this application, the positive electrode electrolyte contains 0.55 g / L to 1.35 g / L of magnesium chloride. Therefore, by maintaining the mass percentage of magnesium chloride within the above range, the probability of pentavalent vanadium ions hydrolyzing to form a precipitate can be reduced, while simultaneously reducing the impact of magnesium chloride on the reversibility of the electrode reaction.

[0013] According to an embodiment of this application, the positive electrode electrolyte contains not less than 0.9 mol / L of pentavalent vanadium ions. According to an embodiment of this application, the positive electrode electrolyte contains 0.9 mol / L to 1.5 mol / L of pentavalent vanadium ions. Therefore, because the positive electrode electrolyte contains a high concentration of dissolved pentavalent vanadium ions, the energy density of the battery can be effectively improved by using this positive electrode electrolyte.

[0014] According to embodiments of this application, the positive electrode electrolyte further comprises sulfuric acid. According to embodiments of this application, the concentration of the sulfuric acid is 2 mol / L to 4 mol / L. Therefore, by using sulfuric acid, the acidic conditions of the electrolyte can be maintained, thereby further suppressing the hydrolysis of pentavalent vanadium ions, improving the conductivity of the electrolyte, and thus effectively improving the energy efficiency of the battery.

[0015] 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 providing the active material in the presence of the dispersant, the cation, and the chloride ion, the active material being adapted to provide pentavalent vanadium ions to obtain the positive electrode electrolyte. Thus, the positive electrode electrolyte prepared by this method exhibits excellent stability, improving the cycle stability of the battery. As mentioned above, according to embodiments of this application, in flow batteries, such as vanadium redox flow batteries, +5 valence vanadium ions are the main component of the positive electrode electrolyte. During the charge and discharge process of the battery, continuous conversion between +4 valence vanadium ions and +5 valence vanadium ions occurs. Therefore, the instability of +5 valence vanadium ions leads to precipitation. The inventors of this application have discovered that by using the positive electrode electrolyte according to embodiments of this application, the +5 valence vanadium ions in the electrolyte can have better stability, thereby ensuring normal battery operation and obtaining good charge and discharge performance.

[0016] According to embodiments of this application, the above-described method for preparing the positive electrode electrolyte may further include at least one of the following additional technical features:

[0017] According to embodiments of this application, the active material is provided by electrolyzing a solution containing tetravalent vanadium ions. According to embodiments of this application, the method includes: mixing magnesium chloride, sodium lignosulfonate, and VOSO4; and electrolyzing the resulting mixture to convert at least a portion of the tetravalent vanadium ions into pentavalent vanadium ions to obtain the positive electrode electrolyte. This effectively improves the preparation efficiency of the positive electrode electrolyte.

[0018] According to embodiments of this application, the electrolysis is performed using a current of 100mA to 1000mA for 1 hour to 10 hours. Therefore, the conversion rate of tetravalent vanadium ions to pentavalent vanadium ions can be increased.

[0019] A third aspect of this application discloses a flow battery, which, according to an embodiment of this application, includes the positive electrode electrolyte described in the first aspect. According to an embodiment of this application, the flow battery is an all-vanadium redox flow battery.

[0020] As mentioned above, according to embodiments of this application, in flow batteries such as vanadium redox flow batteries, +5 valence vanadium ions are the main component of the positive electrode electrolyte. During the charging and discharging process of the battery, the conversion between +4 valence vanadium ions and +5 valence vanadium ions occurs continuously. Therefore, the instability of +5 valence vanadium ions leads to precipitation. The inventors of this application have discovered that by using the positive electrode electrolyte according to embodiments of this application, the +5 valence vanadium ions in the electrolyte can have better stability, thereby ensuring normal battery operation and obtaining good charge and discharge performance.

[0021] It should be noted that those skilled in the art will understand that the features and advantages described in various aspects of this application are applicable to each other, and will not be repeated hereafter.

[0022] 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

[0023] 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:

[0024] Figure 1 These are comparison diagrams of the ultraviolet spectra of Examples 1-5 of this application;

[0025] Figure 2 These are comparison diagrams of the ultraviolet spectra of Examples 1 and 6-9 of this application;

[0026] Figure 3 These are comparison diagrams of the ultraviolet spectra of Examples 1 and 10-12 of this application;

[0027] Figure 4 These are comparison diagrams of the ultraviolet spectra of Example 12 and Comparative Examples 1-7 of this application;

[0028] Figure 5 These are comparison diagrams of the ultraviolet spectra of Example 1 and Comparative Examples 2 and 4 of this application;

[0029] Figure 6 These are comparison diagrams of the ultraviolet spectra of Example 1 and Comparative Examples 3 and 4 of this application. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Flow batteries are high-performance batteries that typically use independently configured positive and negative electrolytes for separate cycling. They are characterized by high capacity, wide application range, and long cycle life, making them a type of new energy product. Unlike batteries that typically use solid or gaseous electrodes, the active material in a flow battery is a flowing electrolyte solution. Its most significant feature is its ability to store energy on a large scale. Flow batteries can be classified into vanadium redox flow batteries, lithium-ion flow batteries, and lead-acid flow batteries, depending on the active material used in their electrodes.

[0036] 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.

[0037] 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:

[0038] Positive terminal during charging: VO 2+ +H2O→VO2 + +2H + +e -

[0039] Negative terminal during charging: V3+ +e - →V 2+

[0040] Positive electrode during discharge: VO2 + +2H + +e - →VO 2+ +H2O

[0041] Negative electrode during discharge: V 2+ →V 3+ +e -

[0042] 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 vanadium ions in the positive electrode electrolyte and consequently lowering the battery's energy density and cycle life. It has been reported that acetonitrile can be used as an additive to improve electrolyte stability during preparation; however, acetonitrile is highly toxic, hindering its widespread industrial application.

[0043] In view of this, the inventors of this application, through in-depth research, unexpectedly proposed an electrolyte formulation that can effectively improve the solubility of +5 vanadium ions and the stability of the positive electrode electrolyte through synergistic effects. The electrolyte and its application will be described in detail below.

[0044] Positive Electrolyte

[0045] In a first aspect, this application provides a positive electrode electrolyte. According to an embodiment of this application, the positive electrode electrolyte includes an active material, a dispersant, cations, and chloride ions, wherein the active material is adapted to provide pentavalent vanadium ions, and the cations may include at least one of calcium ions, magnesium ions, sodium ions, barium ions, strontium ions, and ammonium ions.

[0046] According to an embodiment of this application, the inventors of this application unexpectedly discovered that pentavalent vanadium ions can exist stably in the positive electrode electrolyte. In other words, the positive electrode electrolyte can improve the dispersibility and stability of vanadium ions and reduce the tendency of pentavalent vanadium ions to precipitate in the active material.

[0047] In some embodiments of this application, the inventors have discovered that dispersants, cations, and chloride ions, as additives, can work together in the positive electrode electrolyte to improve the stability of pentavalent vanadium ions. Specifically, according to embodiments of this application, the dispersant can increase the repulsive force between pentavalent vanadium ions in the positive electrode electrolyte, thereby improving the dispersion stability of pentavalent vanadium ions in the positive electrode electrolyte.

[0048] Generally, pentavalent vanadium ions hydrolyze to form V₂O₅, and the reaction equation is 2VO₂. + +H₂O=V₂O₅+2H + The generated V2O5 will gradually form V2O5 crystal precipitate. The crystal growth of V2O5 is achieved by the continuous deposition of V2O5 molecules from the solution onto the surface of the crystal nucleus. According to embodiments of this application, the cations in the electrolyte can adsorb onto the surface of the V2O5 crystal nucleus, acting as a "growth shield." Specifically, when cations adsorb onto the crystal nucleus surface, V2O5 will stop growing because it cannot find effective adsorption sites on the nucleus surface, thereby inhibiting the formation of V2O5 precipitate.

[0049] In some embodiments of this application, chloride ions in the electrolyte can react with VO2 in the positive electrode electrolyte. + The reaction produces soluble VO₂Cl, and the reaction equation is VO₂ + +Cl - →VO2Cl, which can reduce VO2 + The probability of hydrolysis forming a precipitate. Furthermore, the inventors discovered that chloride ions help the generated VO2Cl bind more firmly with water, increasing the solubility of pentavalent vanadium ions and reducing the probability of pentavalent vanadium ions forming a precipitate. This may be due to the high electronegativity and ionization degree of chloride ions.

[0050] In addition, in some embodiments of this application, the inventors have found that there is a synergistic effect between the dispersant, cations and chloride ions. Specifically, the dispersant can further improve the dispersibility of cations and chloride ions, promote the interaction between cations, chloride ions and pentavalent vanadium ions respectively, improve the stability of the positive electrode electrolyte, and thus improve the cycle stability and capacity retention of the vanadium redox flow battery.

[0051] It should be noted that the expression "the active material is suitable for providing pentavalent vanadium ions" used herein means that the active material can form pentavalent vanadium ions during the operation of the electrolyte. This active material may include pentavalent vanadium ions, or it may include substances that can be converted into pentavalent vanadium ions during the operation of the electrolyte, such as tetravalent vanadium ions, for example, under electrolytic regulation. In some embodiments of this application, the active materials that can be used include, but are not limited to: NaVO3, KVO3, NH4VO3, ammonium polyvanadate, and VOSO4. According to specific embodiments of this application, the main component of the positive electrode electrolyte for a vanadium redox flow battery is a vanadium ion (vanadium oxide)-sulfuric acid system, wherein the pentavalent vanadium ions are mainly composed of VO2. + Vanadium ions exist in the form of tetravalent vanadium ions as VO 2+ It exists in various forms. Among them, the tetravalent vanadium ions in VOSO4 can be converted into pentavalent vanadium ions under electrolytic conditions.

[0052] In some embodiments of this application, the dispersant may be lignin sulfonate or a derivative thereof. Therefore, this dispersant can improve the dispersion stability of pentavalent vanadium ions in the positive electrode electrolyte, and simultaneously can complex with cations, improving the dispersibility of cations. According to some specific embodiments of this application, the dispersant includes at least one of sodium lignin sulfonate and calcium lignin sulfonate. Thus, the dispersant can improve the dispersibility of pentavalent vanadium ions, cations, and chloride ions in the positive electrode electrolyte, promote the interaction between cations and chloride ions and pentavalent vanadium ions, improve the stability of the positive electrode electrolyte, and enhance the cycle performance of the battery.

[0053] In some embodiments of this application, magnesium chloride can be used in the electrolyte, thereby providing both cations and chloride ions simultaneously. Magnesium ions can shield the crystal growth of V₂O₅, reducing the formation of V₂O₅ precipitates; chloride ions can react with VO₂ in the positive electrode electrolyte. + The reaction produces soluble VO2Cl, specifically VO2Cl. + +Cl - →VO2Cl reduces the precipitation of pentavalent vanadium ions, improves the stability of the positive electrode electrolyte, and enhances the cycle performance of the battery.

[0054] In some embodiments of this application, the dispersant is lignin sulfonate, and the cations and chloride ions are provided in the form of magnesium chloride. According to embodiments of this application, the mass ratio of lignin sulfonate to magnesium chloride is (3-14):1. For example, it can be 3:1, 5:1, 8:1, 10:1, 12:1, 14:1, or any range of the above values. By keeping the mass ratio of lignin sulfonate to magnesium chloride within the above range, the synergistic effect of lignin sulfonate and magnesium chloride can be promoted. This not only improves the dispersion of pentavalent vanadium ions in the positive electrode electrolyte but also promotes the interaction between magnesium chloride and pentavalent vanadium ions, reducing the probability of hydrolysis of pentavalent vanadium ions to form precipitates, increasing the solubility of pentavalent vanadium ions, and improving the stability of the positive electrode electrolyte, as well as the battery energy density and cycle performance.

[0055] In some embodiments of this application, based on the total mass of the positive electrode electrolyte, the positive electrode electrolyte contains 0.2% to 0.8% of the lignin sulfonate. For example, it can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, etc., or a range of any of the above values. By keeping the lignin sulfonate content within the above range, the dispersibility of pentavalent vanadium ions, as well as cations and chloride ions in the positive electrode electrolyte is improved, while the content of undispersed lignin sulfonate in the positive electrode electrolyte is reduced, thus reducing its impact on electrolyte viscosity and consequently reducing the impact on battery cycle performance.

[0056] In some embodiments of this application, the positive electrode electrolyte contains magnesium chloride at a concentration of 0.55 g / L to 1.35 g / L. For example, the concentration can be 0.55 g / L, 0.75 g / L, 0.95 g / L, 1.15 g / L, 1.35 g / L, or any range of the above values. By maintaining the magnesium chloride content within the above range, the probability of pentavalent vanadium ions hydrolyzing to form a precipitate can be reduced, while simultaneously reducing the impact of magnesium chloride in the electrolyte that does not react with pentavalent vanadium ions on the reversibility of the electrode reaction.

[0057] In some embodiments of this application, the positive electrode electrolyte contains at least 0.9 mol / L of the aforementioned pentavalent vanadium ions. For example, the concentration can be 0.9 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. Therefore, because the positive electrode electrolyte contains a high concentration of pentavalent vanadium ions, the energy density of the battery can be effectively increased by using this positive electrode electrolyte.

[0058] In some embodiments of this application, the positive electrode electrolyte contains 0.9 mol / L to 1.5 mol / L of the aforementioned pentavalent vanadium ions. For example, the concentration can be 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, or any range of the above values. By maintaining the concentration of pentavalent vanadium ions within the above range, both a large output current and the normal occurrence of the electrochemical reaction can be ensured.

[0059] It should be noted that when the concentration of pentavalent vanadium ions in the positive electrode electrolyte is between 0.9 mol / L and 1.5 mol / L, the addition of dispersant, cations, and chloride ions can reduce the probability of precipitation in the electrolyte and electrode during charging and discharging. This is because pentavalent vanadium ions within this concentration range provide sufficient reactants, allowing the positive and negative electrode reactions to proceed smoothly. Furthermore, the added dispersant, cations, and chloride ions can effectively act on pentavalent vanadium ions within this concentration range, improving their dispersibility and stability, thereby reducing the probability of precipitation formation.

[0060] In some embodiments of this application, the positive electrode electrolyte further includes sulfuric acid. In some embodiments of this application, the concentration of sulfuric acid 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, etc., or any range of the above values. Therefore, by using sulfuric acid, the acidic conditions of the electrolyte can be maintained, the hydrolysis of vanadium ions can be suppressed, the conductivity of the electrolyte can be increased, ohmic polarization can be reduced, and the battery energy efficiency can be improved.

[0061] Therefore, the concentration of sulfuric acid within this range can balance the relationship between the viscosity, conductivity and electrochemical activity of the electrolyte, thereby achieving optimal battery performance and cycle stability and improving battery energy efficiency.

[0062] Methods for preparing positive electrode electrolyte

[0063] In a second aspect, this application proposes a method for preparing a positive electrode electrolyte. According to an embodiment of this application, the method includes providing an active material suitable for providing pentavalent vanadium ions in the presence of a dispersant, cations, and chloride ions, thereby obtaining the positive electrode electrolyte. Thus, the positive electrode electrolyte prepared by this method exhibits excellent stability, improving the cycle stability of the battery. As mentioned above, according to embodiments of this application, in flow batteries such as vanadium redox flow batteries, +5 valence vanadium ions are the main component of the positive electrode electrolyte. During the charge and discharge process of the battery, continuous conversion between +4 valence vanadium ions and +5 valence vanadium ions occurs. Therefore, the instability of +5 valence vanadium ions leads to precipitation. The inventors of this application have discovered that by using the positive electrode electrolyte of the embodiments of this application, the +5 valence vanadium ions in the electrolyte can have better stability, thereby ensuring normal battery operation and obtaining good charge and discharge performance.

[0064] It should be noted that, in the method described in this application, the active material, pentavalent vanadium ions, is provided by electrolyzing a solution containing tetravalent vanadium ions. By adding a dispersant, cations, and chloride ions to the electrolyte, where the dispersant, cations, and chloride ions have a synergistic effect, the dispersant can improve the dispersion of vanadium ions, cations, and chloride ions in the positive electrode electrolyte, promote the interaction of cations and chloride ions with pentavalent vanadium ions, reduce the aggregation and precipitation of pentavalent vanadium ions, improve the stability of the electrolyte, and enhance the cycle stability and capacity retention of the vanadium redox flow battery.

[0065] In some embodiments of this application, the method includes: mixing magnesium chloride, sodium lignosulfonate, and VOSO4; and electrolyzing the resulting mixture to convert at least a portion of tetravalent vanadium ions into pentavalent vanadium ions to obtain the positive electrode electrolyte. Therefore, the positive electrode electrolyte prepared by the method of this application has good stability, can improve the dispersibility and stability of pentavalent vanadium ions, and reduce the probability of hydrolysis to form precipitates.

[0066] In some embodiments of this application, the concentration of VOSO4 in the VOSO4 solution is not less than 1 mol / L. According to embodiments of this application, the concentration of VOSO4 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, etc., or a range of any of the above values. Therefore, VOSO4 can provide a sufficient concentration of tetravalent vanadium ions, enabling the formation of sufficient pentavalent vanadium ions after electrolysis, thereby improving the battery energy density.

[0067] In some embodiments of this application, electrolysis is performed using a current of 100mA to 1000mA for 1 hour to 10 hours. According to embodiments of this application, electrolysis can be performed using currents such as 100mA, 200mA, 300mA, 400mA, 500mA, 600mA, 700mA, 800mA, 900mA, and 1000mA, or any range of these values. According to embodiments of this application, the electrolysis time can be, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, and 10 hours, or any range of these values. Therefore, the conversion of tetravalent vanadium ions to pentavalent vanadium ions can be promoted, ensuring the normal occurrence of the electrochemical reaction.

[0068] In some embodiments of this application, the concentration of the sulfuric acid 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 solution affects the viscosity, conductivity, and electrochemical activity of the electrolyte by changing the hydrogen ion concentration in the electrolyte. Therefore, a sulfuric acid solution molar concentration within this range can balance the relationship between the viscosity, conductivity, and electrochemical activity of the electrolyte, achieving optimal battery performance and cycle stability.

[0069] Flow battery

[0070] This application discloses a flow battery. According to an embodiment of this application, the 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 stability and solubility of pentavalent 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.

[0071] In some embodiments of this application, the flow battery is a vanadium redox flow battery.

[0072] In some embodiments of this application, the flow battery further includes a negative electrolyte, a positive electrode, a negative electrode, and a separator.

[0073] In some embodiments of this application, the negative electrode electrolyte includes an active material and a matrix, wherein the active material includes +2 valent vanadium ions and / or +3 valent vanadium ions, and the matrix includes, but is not limited to, an aqueous sulfuric acid solution.

[0074] 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.

[0075] 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.

[0076] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0077] Example 1

[0078] First, an electrolyte containing tetravalent vanadium ions was prepared under room temperature and pressure conditions. A 3.0M sulfuric acid solution was placed in a beaker, and an appropriate amount of VOSO4 was weighed and dissolved in the 3.0M sulfuric acid solution to prepare a 1.5M VOSO4 solution. The beaker was then heated (70°C for approximately 30 minutes) with magnetic stirring until the VOSO4 was completely dissolved. Sodium lignosulfonate (first additive) and magnesium chloride (second additive) were then added to the beaker, with the concentration of sodium lignosulfonate being 0.5 wt% and the concentration of magnesium chloride being 0.95 g / L, and the mixture was dispersed evenly. This solution was then transferred to the anode cell of an H-type electrolytic cell. In another beaker, an equal volume of 3.0M sulfuric acid solution was prepared and poured into the cathode cell.

[0079] A constant-current electrolysis process of 500 mA for 4 hours yielded the positive electrode electrolyte for a vanadium redox flow battery from the anode tank. During electrolysis, a rotor was added to the anode tank, and the additives were evenly dispersed in the anode under magnetic stirring.

[0080] Conditions for constant current electrolysis: Electrode: graphite felt electrode with an area of ​​1.5cm × 3cm; Electrolytic cell: H type; Proton exchange membrane: perfluorosulfonic acid membrane.

[0081] Example 2

[0082] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the concentration of the second additive, magnesium chloride, was 0.55 g / L in this example.

[0083] Example 3

[0084] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the concentration of the second additive, magnesium chloride, was 0.75 g / L in this example.

[0085] Example 4

[0086] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the concentration of the second additive, magnesium chloride, was 1.15 g / L in this example.

[0087] Example 5

[0088] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the concentration of the second additive, magnesium chloride, was 1.35 g / L in this example.

[0089] Example 6

[0090] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the amount of the first additive, sodium lignosulfonate, was 0.2 wt% in this example.

[0091] Example 7

[0092] The positive electrode electrolyte for the vanadium redox flow battery was prepared using a method essentially the same as that in Example 1, except that the amount of the first additive, sodium lignosulfonate, was 0.4 wt%.

[0093] Example 8

[0094] The positive electrode electrolyte for the vanadium redox flow battery was prepared using a method essentially the same as that in Example 1, except that the amount of the first additive, sodium lignosulfonate, was 0.6 wt% in this example.

[0095] Example 9

[0096] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the amount of the first additive, sodium lignosulfonate, was 0.8 wt% in this example.

[0097] Example 10

[0098] The positive electrode electrolyte for the vanadium redox flow battery was prepared using a method essentially the same as that in Example 1, except that the first additive in this example was calcium lignosulfonate.

[0099] Example 11

[0100] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the second additive in this example was calcium chloride.

[0101] Example 12

[0102] The positive electrode electrolyte for the vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the second additive in this example was sodium chloride.

[0103] Comparative Example 1

[0104] The positive electrode electrolyte for the all-vanadium redox flow battery was prepared using essentially the same method as in Example 1, except that the first additive and the second additive were not added in this example.

[0105] Comparative Example 2

[0106] The positive electrode electrolyte for the vanadium redox flow battery was prepared using a method essentially the same as that in Example 1, except that only the first additive, sodium lignosulfonate, was added in this example.

[0107] Comparative Example 3

[0108] The electrolyte for the positive electrode of the all-vanadium redox battery was prepared using a method essentially the same as that in Example 1, except that only the first additive, calcium lignosulfonate, was added in this example.

[0109] Comparative Example 4

[0110] The electrolyte for the positive electrode of the vanadium redox battery was prepared using a method essentially the same as that in Example 1, except that only the second additive, magnesium chloride, was added in this example.

[0111] Comparative Example 5

[0112] The electrolyte for the positive electrode of the vanadium redox battery was prepared using a method essentially the same as that in Example 1, except that only the second additive, calcium chloride, was added in this example.

[0113] Comparative Example 6

[0114] The electrolyte for the positive electrode of the vanadium redox battery was prepared using a method essentially the same as that in Example 1, except that only the second additive, sodium chloride, was added in this example.

[0115] Comparative Example 7

[0116] The electrolyte for the positive electrode of the vanadium redox battery was prepared using a method essentially the same as that in Example 1, except that only the second additive, magnesium sulfate, was added in this example.

[0117] The types and mass percentages or mass concentrations of the first and second additives in Examples 1-12 and Comparative Examples 1-7, as well as the mass ratio of the first and second additives, are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] Performance testing

[0122] Ultraviolet-Vis spectrophotometry detection

[0123] After electrolysis, the collected electrolyte was diluted and tested using a UV-Vis spectrophotometer. The position and intensity of the UV absorption peaks were used to determine the valence state and concentration of vanadium ions. The characteristic peak of pentavalent vanadium ions was located at 270-290 nm, and peaks appeared at this position in Examples 1-12. This indicates that pentavalent vanadium ions were formed in the electrolyte after constant current electrolysis.

[0124] Figure 1 This indicates the effect of different concentrations of the second additive, MgCl2, on the concentration of pentavalent vanadium ions when the first additive is sodium lignosulfonate at a concentration of 0.5 wt%.

[0125] Figure 2 This indicates the effect of different concentrations of MgCl2 (0.95 g / L) on the concentration of pentavalent vanadium ions when the second additive is sodium lignosulfonate and the first additive is sodium lignosulfonate.

[0126] Figure 3 The effects of different lignosulfonate additives and chloride salt additives on enhancing the concentration of pentavalent vanadium ions in the electrolyte were compared. It can be seen that the lignosulfonate additives selected from sodium lignosulfonate or calcium lignosulfonate, and the chloride salt selected from magnesium chloride, have better effects.

[0127] Figure 4 This demonstrates the effects of using a single additive versus no additive. The results show that the effect of a single additive is significantly weaker than that of a dual additive, indicating a synergistic effect between the two additives in increasing the concentration of pentavalent vanadium ions in the electrolyte.

[0128] Figure 5 The study showed the vanadium ion concentration in the electrolyte when sodium lignosulfonate and MgCl2 were used as single additives, as well as the vanadium ion concentration in the electrolyte when they were added together. The results indicate that the combined use of the two additives significantly improved the concentration of vanadium ions in the electrolyte compared to their individual use.

[0129] Figure 6 The study showed the vanadium ion concentration in the electrolyte when calcium lignosulfonate and MgCl2 were used as single additives, respectively, as well as the vanadium ion concentration in the electrolyte when both additives were used together. Similarly, the combined use of the two additives had a more significant effect on increasing the vanadium ion concentration in the electrolyte.

[0130] 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.

[0131] 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: include: An active substance, wherein the active substance is adapted to provide pentavalent vanadium ions; Dispersant; Cations, said cations including at least one of calcium ions, magnesium ions, sodium ions, barium ions, strontium ions, and ammonium ions; and Chloride ions.

2. The positive electrolyte according to claim 1, characterized in that, The dispersant is lignin sulfonate or its derivative.

3. The positive electrode electrolyte according to claim 1, characterized in that, The dispersant includes at least one of sodium lignosulfonate and calcium lignosulfonate.

4. The positive electrode electrolyte according to claim 1, characterized in that, The dispersant is lignin sulfonate, and the cation and the chloride ion are provided in the form of magnesium chloride, wherein the mass ratio of the lignin sulfonate to the magnesium chloride is (3-14):

1.

5. The positive electrode electrolyte according to claim 4, characterized in that, The positive electrode electrolyte contains: 0.2% to 0.8% of the lignin sulfonate; and / or The magnesium chloride concentration is 0.55 g / L to 1.35 g / L.

6. The positive electrode electrolyte according to claim 1, characterized in that, The positive electrode electrolyte contains not less than 0.9 mol / L of the pentavalent vanadium ions, and optionally, the positive electrode electrolyte contains 0.9 mol / L to 1.5 mol / L of the pentavalent vanadium ions.

7. The positive electrode electrolyte according to claim 1, characterized in that, The positive electrode electrolyte further contains: sulfuric acid, Optionally, the concentration of the sulfuric acid is 2 mol / L to 4 mol / L.

8. A method for preparing the positive electrode electrolyte according to any one of claims 1 to 7, characterized in that, include: The active material is provided in the presence of the dispersant, the cation, and the chloride ion, the active material being adapted to provide pentavalent vanadium ions in order to obtain the positive electrode electrolyte.

9. The method according to claim 8, characterized in that, The active substance is provided by electrolyzing a solution containing tetravalent vanadium ions.

10. The method according to claim 8, characterized in that, include: Mix magnesium chloride, sodium lignosulfonate and VOSO4; The resulting mixture is electrolyzed to convert at least a portion of the tetravalent vanadium ions into pentavalent vanadium ions in order to obtain the positive electrode electrolyte.

11. The method according to any one of claims 9 to 10, characterized in that, The electrolysis is performed using a current of 100mA to 1000mA for 1 hour to 10 hours.

12. A flow battery, characterized in that, Includes the positive electrode electrolyte as described in any one of claims 1 to 7.

13. The flow battery according to claim 12, characterized in that, The flow battery is a vanadium redox flow battery.

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