An all-vanadium redox flow battery asymmetric electrolyte and all-vanadium redox flow battery

Abstract

The application provides a kind of full vanadium redox flow battery asymmetric electrolyte and full vanadium redox flow battery, belong to electrolyte technical field.The full vanadium redox flow battery asymmetric electrolyte includes positive electrode electrolyte and negative electrode electrolyte, positive electrode electrolyte includes positive electrode supporting electrolyte, positive electrode electrolyte, positive electrode additive and deionized water, negative electrode electrolyte includes negative electrode supporting electrolyte, negative electrode electrolyte, negative electrode additive and deionized water.The full vanadium redox flow battery asymmetric electrolyte meets the following conditions: the concentration of vanadium ions in the positive electrode electrolyte is greater than the concentration of vanadium ions in the negative electrode electrolyte;And the concentration of positive electrode supporting electrolyte in the positive electrode electrolyte is greater than the concentration of negative electrode supporting electrolyte in the negative electrode electrolyte.The full vanadium redox flow battery asymmetric electrolyte provided by the application can comprehensively improve the concentration, working temperature and cycle performance of the electrolyte, thereby significantly improving the energy storage density, cycle life and thermal stability of the full vanadium redox flow battery.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to an asymmetric electrolyte for a full vanadium redox flow battery and a full vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow battery (VRFB) is one of the core technologies for realizing large-scale electrochemical energy storage. The electrolyte, as its core energy storage medium, directly determines the battery's energy density, cycle life, and operating temperature range. Currently, the preparation technology of vanadium redox flow battery electrolytes is based on sulfuric acid systems, and generally adopts a symmetrical design scheme with the same concentration of vanadium ions in both the positive and negative electrodes and the same concentration of sulfuric acid supporting electrolyte. Furthermore, the vanadium ion concentration in the vanadium redox flow battery electrolyte is mostly below 2.0 mol / L, and the operating temperature range of the assembled battery is only 0℃~40℃.

[0003] Specifically, existing technical solutions mainly fall into two categories: One category, for example, CN117712438A discloses a method for directly obtaining high-concentration vanadium electrolytes for both positive and negative electrodes through dissolution-reduction. This method involves calcining vanadium slag under a CO and CO2 atmosphere, preparing VOCl2 crystals using a chlorinating agent, dissolving them to obtain V(IV) electrolyte, and then reducing them with H2 to obtain V(III) electrolyte. Impurities are used as additives to further improve the electrochemical performance of the battery. However, this technical solution requires precise control of the calcination temperature and time, and the vanadium conversion rate is prone to fluctuation. Furthermore, the high-temperature calcination process is complex. The other category, for example, CN121394479A discloses an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds and its preparation method. By adding a single-type stabilizer to suppress vanadium ion precipitation, the operating temperature range can be slightly broadened, but the problem of imbalance in the positive and negative electrode liquids caused by the difference in the transmembrane diffusion rate of vanadium ions of different valence states remains unresolved, resulting in rapid capacity decay of the battery after long-term cycling. In addition, traditional vanadium redox flow battery electrolytes based on sulfuric acid systems have the following inherent defects: In the Nafion ion exchange membrane, the diffusion rate difference between V(V) and low-valence vanadium ions is more than 30%. After long-term cycling, the volume of the positive electrode electrolyte continues to increase and the volume of the negative electrode continues to decrease, resulting in rapid capacity decay and difficulty in improving cycle life.

[0004] (1) Limited adaptability of electrolyte concentration and temperature: In traditional vanadium redox flow battery electrolytes based on sulfuric acid system, the coordination structure of vanadium ions is prone to change at high and low temperatures. Specifically, the coordination compound formed by V(V) ions and sulfate ions is prone to decompose and precipitate V2O5 at high temperatures above 40℃, and low-valence vanadium ions such as V(II), V(III) and V(IV) are prone to form crystalline hydrates at low temperatures below 0℃. However, existing single additives can only improve the stability in a single temperature range and cannot take into account both high and low temperature performance, resulting in the difficulty of the vanadium ion concentration to exceed 2.0 mol / L and the narrow operating temperature range of the electrolyte.

[0005] (2) Long-term cycling leads to imbalance of positive and negative electrode electrolytes and rapid capacity decay: Existing technologies all use a symmetrical concentration system for positive and negative electrodes, without considering the differences in the transmembrane diffusion rate of vanadium ions of different valence states. For example, Nafion membranes have stronger selective permeability to high-valence vanadium ions, which causes them to migrate in a directional manner during long-term cycling, thereby causing an imbalance in the volume and concentration of the positive and negative electrode electrolytes. This is the core reason for the rapid capacity decay of the battery.

[0006] (3) The preparation process is complex and the parameters are difficult to optimize: Most of the existing high-concentration electrolyte preparation technologies involve roasting, chlorination or gas phase reduction processes. Furthermore, the parameters such as roasting temperature, chlorinating agent ratio and reduction time are highly coupled and difficult to control precisely, resulting in low vanadium conversion rate and poor batch stability of products. At the same time, the high temperature and high pressure process increases production costs and equipment wear.

[0007] (4) Lack of quantitative analysis model: In the existing technology, the composition design of vanadium redox flow battery electrolyte still largely follows empirical formulation methods, lacking an effective quantitative analysis model, and thus unable to accurately measure the effectiveness of optimization.

[0008] Therefore, there is an urgent need to develop a vanadium redox flow battery electrolyte to solve the above problems. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide an asymmetric electrolyte for vanadium redox flow batteries. By asymmetrically controlling the concentration of vanadium ions and the concentration of supporting electrolyte in the positive and negative electrode electrolytes, the concentration, operating temperature, and cycle performance of the electrolyte can be comprehensively improved, thereby significantly improving the energy storage density, cycle life, and thermal stability of vanadium redox flow batteries.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides an asymmetric electrolyte for a vanadium redox flow battery, the vanadium redox flow battery asymmetric electrolyte comprising a positive electrode electrolyte and a negative electrode electrolyte, the positive electrode electrolyte comprising a positive electrode supporting electrolyte, a positive electrode electrolyte, a positive electrode additive and deionized water, and the negative electrode electrolyte comprising a negative electrode supporting electrolyte, a negative electrode electrolyte, a negative electrode additive and deionized water;

[0012] The asymmetric electrolyte of the all-vanadium redox flow battery satisfies the following conditions:

[0013] The concentration of vanadium ions in the positive electrode electrolyte is greater than the concentration of vanadium ions in the negative electrode electrolyte;

[0014] Furthermore, the concentration of the positive electrode supporting electrolyte in the positive electrode electrolyte is greater than the concentration of the negative electrode supporting electrolyte in the negative electrode electrolyte.

[0015] The present invention provides an asymmetric electrolyte with high concentration, wide temperature range, and long cycle life. Its vanadium ion concentration can exceed 2 mol / L, which is beneficial for improving the energy density of the battery. Furthermore, it has a wide operating temperature range (-10℃ to 60℃), does not precipitate at high temperatures, and does not crystallize at low temperatures. In addition, this asymmetric electrolyte effectively solves the problem of vanadium ion transmembrane diffusion imbalance, improving the cycle stability of the battery, as detailed below:

[0016] (1) In the positive electrode electrolyte, a higher sulfuric acid concentration can provide sufficient sulfate ligands for V(V) ions and form stable multi-component coordination compounds in synergy with positive electrode additives, which greatly improves the thermal stability of V(V) ions and inhibits the decomposition and precipitation of V2O5 at high temperature. This successfully breaks through the limitation that the vanadium concentration of traditional electrolytes does not exceed 2.0 mol / L. At the same time, the high sulfuric acid system can improve the ionic conductivity of the positive electrode electrolyte and improve the electrochemical reaction kinetics on the positive electrode side.

[0017] (2) In the negative electrode electrolyte, a suitable sulfuric acid concentration can ensure the solubility and conductivity of vanadium ions in the negative electrode while avoiding the adverse effects of increased differences in transmembrane diffusion caused by high sulfuric acid concentration. At the same time, the use of negative electrode additives can further regulate the interfacial reaction kinetics of vanadium ions in the negative electrode electrolyte, reduce the difference in transmembrane diffusion rates between V(II) / V(III) and V(V) / V(IV) ions, alleviate the imbalance of positive and negative electrode liquids during long-term cycling, and facilitate the improvement of the cycle stability of the battery.

[0018] Preferably, the concentration of vanadium ions in the positive electrode electrolyte is 1.6 mol / L to 2.2 mol / L, for example, it can be 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L or 2.2 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the concentration of the positive electrode supporting electrolyte in the positive electrode electrolyte is 3.5 mol / L to 5.2 mol / L, for example, it can be 3.5 mol / L, 3.8 mol / L, 4.0 mol / L, 4.2 mol / L, 4.5 mol / L, 4.8 mol / L, 5.0 mol / L or 5.2 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] As an example, the positive electrode supporting electrolyte in the positive electrode electrolyte is a sulfuric acid solution.

[0021] Preferably, the positive electrode additive in the positive electrode electrolyte includes at least one of a phosphate compound, a carboxylic acid compound, or a sulfate compound.

[0022] As an example, the phosphate compounds include, but are not limited to, phytic acid, hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylphosphonic acid (ATMP), ethylenediaminetetramethylidene phosphonic acid (EDTMP), diethylenetriaminepentamethylidene phosphonic acid (DTPMP), phosphonobutane tricarboxylic acid (PBTC), glycine dimethylidene phosphonic acid, methylphosphonic acid, phenylphosphonic acid, methylene diphosphonic acid, ammonium hydrogen phosphate, or at least one of the ammonium, potassium, or sodium salts corresponding to the above-mentioned organic phosphonic acids or inorganic phosphates; the carboxylic acid compounds include, but are not limited to, oxalic acid, malonic acid, succinic acid, and at least one of their soluble salts; the sulfate compounds include, but are not limited to, at least one of manganese sulfate, magnesium sulfate, zinc sulfate, or sodium sulfate.

[0023] Preferably, the concentration of the positive electrode additive in the positive electrode electrolyte is 0.05 mol / L to 0.75 mol / L, for example, it can be 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, or 0.75 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, so as to form a stable coordination compound in synergy with high-concentration sulfuric acid.

[0024] In this invention, by controlling the concentrations of vanadium ions and supporting electrolytes in the positive electrode electrolyte to be relatively high, the conductivity and electrochemical reaction kinetics of the positive electrode electrolyte can be balanced. At the same time, it works synergistically with the positive electrode additive to achieve the technical effect of resisting high-temperature precipitation, and significantly improves the thermal stability of V(V) ions.

[0025] Preferably, the concentration of vanadium ions in the negative electrode electrolyte is 1.3 mol / L to 1.7 mol / L, for example, it can be 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L or 1.7 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the concentration of the negative electrode supporting electrolyte in the negative electrode electrolyte is 3.0 mol / L to 4.5 mol / L, for example, it can be 3.0 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4.0 mol / L, 4.2 mol / L or 4.5 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] As an example, the negative electrode supporting electrolyte in the negative electrode electrolyte is a sulfuric acid solution.

[0028] Preferably, the negative electrode additive in the negative electrode electrolyte includes at least one of amino acid compounds, sulfonic acid compounds, or metal oxides.

[0029] As an example, the amino acid compounds include, but are not limited to, at least one of cysteine, methionine, glycine, serine, glutamic acid, proline, and their soluble salts; the sulfonic acid compounds include, but are not limited to, at least one of 1,3-propanedisulfonic acid, 2-amino-1,4-benzenedisulfonic acid, methanesulfonic acid, sulfosalicylic acid, or lignin sulfonate; and the metal oxides include, but are not limited to, at least one of copper oxide, iron oxide, cobalt oxide, nickel oxide, or iron(II,III) oxide.

[0030] Preferably, the concentration of the negative electrode additive in the negative electrode electrolyte is 0.01 mol / L to 0.7 mol / L, for example, it can be 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, or 0.7 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, thereby balancing the ion migration rate.

[0031] In this invention, by adjusting the negative electrode electrolyte to a system with a medium vanadium concentration combined with an appropriate sulfuric acid concentration, the vanadium ion solubility, conductivity and ion migration stability of the negative electrode electrolyte can be taken into account. At the same time, it works synergistically with the negative electrode additives to regulate the negative electrode ion migration kinetics.

[0032] Preferably, the positive electrode electrolyte or the negative electrode electrolyte satisfies the following relationship:

[0033] ;

[0034] in, This is the critical stability temperature of the electrolyte. This is a correction term for the reference temperature of the electrolyte;

[0035] This is the vanadium concentration coefficient. To support the electrolyte concentration coefficient, This refers to the additive concentration coefficient.

[0036] This represents the concentration of vanadium ions in the electrolyte. This refers to the concentration of the supporting electrolyte in the electrolyte solution. This represents the concentration of additives in the electrolyte.

[0037] In this invention, by utilizing the above-mentioned relationship, the limiting operating temperature at which the electrolyte will not precipitate or crystallize can be directly predicted, thereby achieving quantitative design of the formulation.

[0038] It should be noted that in the above formula, the positive electrode electrolyte corresponds to... For example, it can be 40°C; the corresponding negative electrode electrolyte For example, it can be 5°C.

[0039] Preferably, in the positive electrode electrolyte and the negative electrode electrolyte, the... The range is from -2.0 to 1.4, and can include, for example, -2.0, -1.5, -1.0, -0.5, -0.2, 0.2, 0.5, 0.75, 0.8, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1.0, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.3, 1.35, or 1.4, etc. It is not limited to the listed values; other unlisted values ​​within this range also apply.

[0040] Preferably, in the positive electrode electrolyte and the negative electrode electrolyte, the... The range is -2.5 to 2.5, and can include, for example, -2.5, -2.0, -1.5, -1.0, -0.5, -0.2, 0.2, 0.5, 0.9, 0.92, 0.95, 0.98, 1.0, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 2.0, 2.2, 2.4, or 2.5, etc. It is not limited to the listed values; other unlisted values ​​within this range also apply.

[0041] Preferably, in the positive electrode electrolyte and the negative electrode electrolyte, the... The range is -3.1 to 4.0, and can include, for example, -3.1, -2.5, -2.0, -1.5, -1.0, -0.5, -0.2, 0.2, 0.5, 0.8, 1.0, 1.1, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, or 4.0, etc. It is not limited to the listed values, and other unlisted values ​​within this range also apply.

[0042] It should be noted that the above , and Multiple gradient electrolytes were prepared using a three-factor, three-level orthogonal experiment. The critical stability temperature of the positive electrode was determined by the high-temperature turbidity precipitation method, and the critical stability temperature of the negative electrode was determined by the low-temperature crystallization observation method. The specific orthogonal experimental factor levels are shown in Table 1.

[0043] Table 1

[0044]

[0045] As a preferred technical solution of the present invention, a method for preparing the asymmetric electrolyte of the all-vanadium redox flow battery described in the first aspect is provided, the preparation method comprising the following steps:

[0046] (1) Preparation of positive electrode electrolyte

[0047] High-concentration vanadium solution and positive electrode additive are mixed at a mass ratio of 1:(0.05~0.2). Concentrated sulfuric acid or deionized water with a mass fraction of 98% is added to adjust the concentration of sulfuric acid to 3.5mol / L~5.2mol / L. The volume is then adjusted to 2.0 times~2.5 times the original volume of the solution.

[0048] (2) Preparation of negative electrode electrolyte

[0049] Mix the low-concentration vanadium solution with the negative electrode additive at a mass ratio of 1:(0.05~0.1), add concentrated sulfuric acid (98% mass fraction) or deionized water to adjust the sulfuric acid concentration to 3.0mol / L~4.5mol / L, and bring the volume to a preset value that matches the volume of the positive electrode electrolyte.

[0050] (3) Mixing of positive and negative electrode solutions and concentration calibration

[0051] The positive and negative electrolytes were mixed at a volume ratio of 1:(1~2.5) at 25℃~40℃. The total vanadium concentration of the mixture was determined by inductively coupled plasma atomic emission spectrometry. The total vanadium concentration was adjusted to 1.8mol / L~2.2mol / L by adding high-concentration or low-concentration vanadium solution. The mixture was stirred at room temperature or medium temperature (32℃~38℃) for 3h~4h until the system was homogeneous.

[0052] (4) Electrolyte balance and regeneration

[0053] The mixed electrolyte is allowed to stand and equilibrate. Excess overflow electrolyte from the positive electrode side is separated and recovered. V(V) ions in the recovered solution are reduced to V(III) ions by chemical reduction or electrolytic reduction. The sulfuric acid concentration of the reduced solution is adjusted to 3.0 mol / L~4.5 mol / L and then added back to the negative electrode electrolyte system to form a stable 1.3 mol / L~1.7 mol / L negative electrode electrolyte, which is directly used in vanadium redox flow batteries.

[0054] Preferably, the reducing agent used in the chemical reduction process includes, but is not limited to, at least one of zinc sulfate, sodium sulfate, sodium sulfite, or ferrous sulfate. After reduction, the sulfuric acid concentration in the negative electrode electrolyte is calibrated by adding sulfuric acid or deionized water.

[0055] Preferably, the electrolytic reduction can be exemplarily performed using a constant current electrolysis method, with the current density controlled at 5 mA / cm². 2 ~10mA / cm 2 The reduction efficiency can reach over 95%, and the sulfuric acid concentration is simultaneously calibrated after reduction.

[0056] As a preferred technical solution of the present invention, an apparatus for preparing the asymmetric electrolyte of the all-vanadium redox flow battery described in the first aspect is provided. The apparatus includes a positive electrode electrolyte preparation unit, a negative electrode electrolyte preparation unit, a mixing and calibration unit, a temperature-controlled stirring and balancing unit, a positive electrode electrolyte recovery unit, a reduction reaction unit, a sulfuric acid concentration calibration unit, and a finished electrolyte output unit.

[0057] Preferably, the positive electrode electrolyte preparation unit includes a positive electrode mixing tank with an online sulfuric acid concentration detection module, into which a supporting electrolyte, electrolyte, positive electrode additive, and deionized water are added.

[0058] Furthermore, the outlet end of the positive electrode mixing tank is connected to the battery stack.

[0059] Preferably, the negative electrode electrolyte preparation unit includes a negative electrode mixing tank with an online sulfuric acid concentration detection module, into which a supporting electrolyte, electrolyte, negative electrode additive, and deionized water are added.

[0060] Furthermore, the outlet end of the negative electrode mixing tank is connected to the battery stack.

[0061] Preferably, the hybrid calibration unit includes a hybrid calibration container with an ICP vanadium concentration detection module.

[0062] Preferably, the temperature-controlled stirring and balancing unit includes a temperature-controlled stirring vessel with a temperature control and stirring device.

[0063] Preferably, the positive electrode electrolyte recovery unit includes a positive electrode electrolyte recovery tank for recovering excess high-valence vanadium ion solution from the positive electrode mixing tank.

[0064] Preferably, the reduction reaction unit includes a reduction reaction vessel for converting high-valence vanadium ions into low-valence vanadium ions.

[0065] Furthermore, the outlet end of the reduction reaction unit is connected to the negative electrode mixing tank in the negative electrode electrolyte preparation unit, for replenishing the negative electrode mixing tank with low-valent vanadium ion solution.

[0066] Preferably, the sulfuric acid concentration calibration unit includes a sulfuric acid concentration calibration tank with an online sulfuric acid concentration detection module.

[0067] Preferably, the finished electrolyte output unit includes a finished positive electrolyte storage tank or a negative electrolyte storage tank.

[0068] Preferably, the device further includes a metering pump and a pipeline system. The positive electrode electrolyte preparation unit, negative electrode electrolyte preparation unit, mixing and calibration unit, temperature control stirring and balancing unit, positive electrode electrolyte recovery unit, reduction reaction unit, sulfuric acid concentration calibration unit and finished electrolyte output unit are connected by pipelines to realize continuous preparation of electrolyte. The online sulfuric acid concentration detection module is a core supporting device to ensure accurate control of sulfuric acid concentration at the positive and negative electrodes.

[0069] In a second aspect, the present invention provides a vanadium redox flow battery, the vanadium redox flow battery comprising the asymmetric electrolyte of the vanadium redox flow battery described in the first aspect.

[0070] Preferably, the cycle life prediction equation for the all-vanadium redox flow battery satisfies the following relationship:

[0071] ;

[0072] in, The cycle life of the vanadium redox flow battery;

[0073] To determine the cycle life of an all-vanadium redox flow battery using an additive-free symmetrical electrolyte, the... The value range is 300 to 600.

[0074] The average diffusion coefficient of vanadium ions measured in the symmetrical electrolyte;

[0075] The average diffusion coefficient of vanadium ions measured in the asymmetric electrolyte of the all-vanadium redox flow battery;

[0076] The additive synergistic gain coefficient, the The value range is 0.8 to 1.1;

[0077] The temperature correction factor is... The value range is 0.1 to 1.0.

[0078] It should be noted that, The arithmetic mean of the individual diffusion coefficients of divalent, trivalent, tetravalent, and pentavalent vanadium ions were obtained by testing them separately at the same vanadium ion and sulfate concentrations (symmetric electrolyte). The value range is ≥3.0×10. - 8 cm 2 / s.

[0079] The arithmetic mean of the individual diffusion coefficients of divalent, trivalent, tetravalent, and pentavalent vanadium ions under different vanadium ion and sulfate concentrations (in an asymmetric electrolyte) was obtained.

[0080] For example, the above The membrane sample was pretreated by immersing it in a 3 mol / L sulfuric acid solution at 25°C for 24 hours. The pretreated sample was then placed between two constant-temperature conductive cells at 25°C and secured with bolts. A blank reference solution was poured into the permeate side chamber of the conductive cell. An equivalent volume of symmetrical electrolyte was measured and poured into the electrolyte side chamber, ensuring the solution height and volume on both sides were consistent and completely submerged the effective area of ​​the membrane sample. The volumes of the positive and negative electrolytes were recorded. Stirring rods were placed in both chambers of the conductive cell, and the magnetic stirrer was powered on at 200 rpm with a stirrer diameter of 5 mm to 10 mm. Before testing, the solution was removed from the permeate side using a pipette, and the initial concentration (theoretically 0) was measured using a UV spectrophotometer. After testing, the solution was returned to the permeate side of the conductive cell. Subsequently, samples were taken and their concentration values ​​recorded every 1 hour, resulting in a total of 8 to 10 data points. The experimental setup was disassembled, the membrane sample was removed, and the average thickness of the membrane sample was measured to obtain... Taking tetravalent vanadium ions as an example, the composition of the symmetrical electrolyte is: a 1.5 mol / L VOSO4+ aqueous solution and a 3.0 mol / L sulfuric acid aqueous solution; the composition of the blank reference solution is: a 1.5 mol / L MgSO4+ aqueous solution and a 3.0 mol / L sulfuric acid aqueous solution. Similarly, the individual diffusion coefficients for the other divalent, trivalent, and pentavalent vanadium ions can be obtained by simply replacing VOSO4 with VSO4, V2(SO4)3, and (VO2)2SO4, respectively.

[0081] The above The results were obtained using the diffusion cell method. The specific testing process included the following steps: Multiple gradient experiments were set up to change the concentrations of vanadium ions and sulfate ions in the asymmetric electrolyte. Taking tetravalent vanadium ions as an example, the composition of the asymmetric electrolyte was: 0.5 mol / L to 2.3 mol / L VOSO4 + 2.0 mol / L to 5.5 mol / L sulfuric acid aqueous solution; the composition of the blank reference solution was: 0.5 mol / L to 2.3 mol / L MgSO4 + 2.0 mol / L to 5.5 mol / L sulfuric acid aqueous solution; the results were calculated using orthogonal experiments to determine the concentrations of vanadium ions and sulfate ions corresponding to different concentrations. Similarly, the individual diffusion coefficients for the remaining divalent, trivalent, and pentavalent vanadium ions can be obtained by simply replacing VOSO4 with VSO4, V2(SO4)3, and (VO2)2SO4, respectively.

[0082] Furthermore, and The following relationship exists between them: ;in, This represents the vanadium ion concentration difference between the positive and negative electrode electrolytes. This represents the concentration difference of the supporting electrolyte between the positive and negative electrode electrolytes. It is an asymmetric regulatory factor.

[0083] The cycle life ratio of electrolytes with and without additives at the same concentration can be obtained by comparing them.

[0084] It is calculated from the difference between the critical stable temperature of the positive electrode electrolyte and the actual operating temperature. A positive temperature difference of 15℃ is set as the coefficient of 0.1, and a difference greater than or equal to the critical stable temperature of the positive electrode electrolyte is set as the coefficient of 1.

[0085] Specifically, the For example, it can be 300 times, 350 times, 400 times, 450 times, 500 times, 550 times, or 600 times, etc., not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0086] The For example, it can be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05 or 1.1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] The For example, it can be 0.1, 0.2, 0.4, 0.5, 0.6, 0.8 or 1.0, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0088] Preferably, the cycle life of the vanadium redox flow battery and the vanadium redox flow battery using an additive-free symmetrical electrolyte is the cycle life when the capacity decays to 80% of the initial capacity.

[0089] Preferably, during the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using additive-free symmetrical electrolyte, the battery voltage range is controlled to be 1.0V~1.55V, for example, it can be 1.0V, 1.15V, 1.2V, 1.25V, 1.3V, 1.35V, 1.4V, 1.45V, 1.5V or 1.55V, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0090] Preferably, during the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using an additive-free symmetrical electrolyte, the test current density is controlled to be 80 mA / cm². 2 ~200mA / cm 2 For example, it can be 80mA / cm 2 100mA / cm 2120mA / cm 2 150mA / cm 2 180mA / cm 2 Or 200mA / cm 2 The term "etc." is not limited to the listed values; it also applies to other unlisted values ​​within the range.

[0091] Preferably, during the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using additive-free symmetrical electrolyte, the test temperature is controlled to be 25℃~50℃, for example, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0092] Preferably, the all-vanadium redox flow battery comprises a single cell or a battery stack.

[0093] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0094] Compared with the prior art, the present invention has the following beneficial effects:

[0095] This invention provides a high-concentration, wide-temperature-range, and long-cycle asymmetric electrolyte for vanadium redox flow batteries. Its vanadium ion concentration can exceed 2 mol / L, which is beneficial for improving the battery's energy density. Furthermore, it has a wide operating temperature range (-10℃ to 60℃), does not precipitate at high temperatures, and does not crystallize at low temperatures. In addition, this asymmetric electrolyte effectively solves the problem of vanadium ion transmembrane diffusion imbalance, improving the battery's cycle stability, as detailed below:

[0096] (1) In the positive electrode electrolyte, a higher sulfuric acid concentration can provide sufficient sulfate ligands for V(V) ions and form stable multi-component coordination compounds in synergy with positive electrode additives, which greatly improves the thermal stability of V(V) ions and inhibits the decomposition and precipitation of V2O5 at high temperature. This successfully breaks through the limitation that the vanadium concentration of traditional electrolytes does not exceed 2.0 mol / L. At the same time, the high sulfuric acid system can improve the ionic conductivity of the positive electrode electrolyte and improve the electrochemical reaction kinetics on the positive electrode side.

[0097] (2) In the negative electrode electrolyte, a suitable sulfuric acid concentration can ensure the solubility and conductivity of vanadium ions in the negative electrode while avoiding the adverse effects of increased differences in transmembrane diffusion caused by high sulfuric acid concentration. At the same time, the use of negative electrode additives can further regulate the interfacial reaction kinetics of vanadium ions in the negative electrode electrolyte, reduce the difference in transmembrane diffusion rates between V(II) / V(III) and V(V) / V(IV) ions, alleviate the imbalance of positive and negative electrode liquids during long-term cycling, and facilitate the improvement of the cycle stability of the battery. Detailed Implementation

[0098] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0099] Example 1

[0100] This embodiment provides an asymmetric electrolyte for a vanadium redox flow battery and a vanadium redox flow battery containing the same. The asymmetric electrolyte for the vanadium redox flow battery includes a positive electrode electrolyte and a negative electrode electrolyte.

[0101] The positive electrode electrolyte consists of: a concentration of 2.0 mol / L for [V5+ / 4+], a concentration of 4.5 mol / L for sulfuric acid supporting electrolyte, and positive electrode additives including a concentration of 0.15 mol / L for zinc phosphate and a concentration of 0.3 mol / L for citric acid.

[0102] The negative electrode electrolyte consists of: a concentration of 1.5 mol / L for [V3+ / 2+], a concentration of 3.8 mol / L for sulfuric acid supporting electrolyte, and negative electrode additives including a concentration of 0.1 mol / L for glycine and a concentration of 0.2 mol / L for sulfonic acid.

[0103] This embodiment also provides a method for preparing the above-mentioned asymmetric electrolyte for the all-vanadium redox flow battery, which includes the following steps:

[0104] (1) Preparation of positive electrode electrolyte

[0105] Vanadium pentoxide was dissolved in a 4.5 mol / L sulfuric acid aqueous solution according to the formula, and then the positive electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0106] (2) Preparation of negative electrode electrolyte

[0107] Vanadium trioxide was dissolved in a 3.8 mol / L sulfuric acid aqueous solution according to the formula, and then the negative electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0108] (3) Assemble an all-vanadium redox flow battery

[0109] The positive and negative electrolytes are injected separately into the vanadium redox flow battery stack and isolated using a Nafion ion exchange membrane to facilitate subsequent electrochemical performance testing.

[0110] Example 2

[0111] This embodiment provides an asymmetric electrolyte for a vanadium redox flow battery and a vanadium redox flow battery containing the same. The asymmetric electrolyte for the vanadium redox flow battery includes a positive electrode electrolyte and a negative electrode electrolyte.

[0112] The positive electrode electrolyte consists of: a concentration of 1.6 mol / L for [V5+ / 4+], a concentration of 3.5 mol / L for sulfuric acid supporting electrolyte, and positive electrode additives including a concentration of 0.05 mol / L for zinc phosphate and a concentration of 0.2 mol / L for citric acid.

[0113] The negative electrode electrolyte consists of: a concentration of 1.3 mol / L for [V3+ / 2+], a concentration of 3.0 mol / L for sulfuric acid supporting electrolyte, and negative electrode additives including a concentration of 0.02 mol / L for glycine and a concentration of 0.15 mol / L for sulfonic acid.

[0114] This embodiment also provides a method for preparing the above-mentioned asymmetric electrolyte for the all-vanadium redox flow battery, which includes the following steps:

[0115] (1) Preparation of positive electrode electrolyte

[0116] Vanadium pentoxide was dissolved in a 3.5 mol / L sulfuric acid aqueous solution according to the formula, and then the positive electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0117] (2) Preparation of negative electrode electrolyte

[0118] Vanadium trioxide was dissolved in a 3.0 mol / L sulfuric acid aqueous solution according to the formula, and then the negative electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0119] (3) Assemble an all-vanadium redox flow battery

[0120] The positive and negative electrolytes are injected separately into the vanadium redox flow battery stack and isolated using a Nafion ion exchange membrane to facilitate subsequent electrochemical performance testing.

[0121] Example 3

[0122] This embodiment provides an asymmetric electrolyte for a vanadium redox flow battery and a vanadium redox flow battery containing the same. The asymmetric electrolyte for the vanadium redox flow battery includes a positive electrode electrolyte and a negative electrode electrolyte.

[0123] The positive electrode electrolyte consists of: a concentration of 2.2 mol / L for [V5+ / 4+], a concentration of 5.2 mol / L for sulfuric acid supporting electrolyte, and positive electrode additives including a concentration of 0.25 mol / L for zinc phosphate and a concentration of 0.5 mol / L for citric acid.

[0124] The negative electrode electrolyte consists of: a concentration of 1.7 mol / L for [V3+ / 2+], a concentration of 4.5 mol / L for sulfuric acid supporting electrolyte, and negative electrode additives including a concentration of 0.2 mol / L for glycine and a concentration of 0.5 mol / L for sulfonic acid.

[0125] This embodiment also provides a method for preparing the above-mentioned asymmetric electrolyte for the all-vanadium redox flow battery, which includes the following steps:

[0126] (1) Preparation of positive electrode electrolyte

[0127] Vanadium pentoxide was dissolved in a 5.2 mol / L sulfuric acid aqueous solution according to the formula, and then the positive electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0128] (2) Preparation of negative electrode electrolyte

[0129] Vanadium trioxide was dissolved in a 4.5 mol / L sulfuric acid aqueous solution according to the formula, and then the negative electrode additive was added. After stirring evenly, the solution was brought to the required concentration range.

[0130] (3) Assemble an all-vanadium redox flow battery

[0131] The positive and negative electrolytes are injected separately into the vanadium redox flow battery stack and isolated using a Nafion ion exchange membrane to facilitate subsequent electrochemical performance testing.

[0132] Example 4

[0133] The difference between this embodiment and Example 1 is that the concentration of [V5+ / 4+] in the positive electrode electrolyte is 2.2 mol / L, and the concentration of sulfuric acid supporting electrolyte is 6.0 mol / L. All other aspects are the same as in Example 1.

[0134] Example 5

[0135] The difference between this embodiment and Example 1 is that the concentration of [V3+ / 2+] in the negative electrode electrolyte is 0.5 mol / L, and the concentration of sulfuric acid supporting electrolyte is 2.5 mol / L. Everything else is the same as in Example 1.

[0136] Example 6

[0137] The difference between this embodiment and Example 1 is that the positive electrode additive only includes citric acid at a concentration of 0.45 mol / L, while everything else is the same as in Example 1.

[0138] Example 7

[0139] The difference between this embodiment and Example 1 is that the negative electrode additive includes glycine at a concentration of 0.02 mol / L and sulfonic acid at a concentration of 0.15 mol / L, while all other aspects are the same as in Example 1.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that the composition of the positive electrode electrolyte includes: a concentration of [V5+ / 4+] of 1.5 mol / L, a concentration of sulfuric acid supporting electrolyte of 3.8 mol / L, and positive electrode additives including a concentration of 0.15 mol / L of zinc phosphate and a concentration of 0.3 mol / L of citric acid.

[0142] The composition of the negative electrode electrolyte includes: a concentration of 1.5 mol / L for [V3+ / 2+], a concentration of 3.8 mol / L for sulfuric acid supporting electrolyte, and negative electrode additives including a concentration of 0.1 mol / L for glycine and a concentration of 0.2 mol / L for sulfonic acid, all of which are the same as in Example 1.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 1 is that the concentration of [V5+ / 4+] in the positive electrode electrolyte is 1.0 mol / L, and the concentration of sulfuric acid supporting electrolyte is 3.0 mol / L. All other aspects are the same as in Example 1.

[0145] Comparative Example 3

[0146] The difference between this comparative example and Example 1 is that the concentration of [V3+ / 2+] in the negative electrode electrolyte is 2 mol / L, and the concentration of sulfuric acid supporting electrolyte is 5.0 mol / L. All other aspects are the same as in Example 1.

[0147] Performance testing

[0148] (a) Critical stability temperature of electrolyte

[0149] To verify the practical application of the critical stability temperature relationship of the electrolyte described above, the positive and negative electrode electrolytes provided in the above examples and comparative examples were subjected to stability tests at different temperatures (0℃, 25℃, 50℃, and 60℃), and the precipitation of substances in the solution was monitored using a high-precision conductivity meter and a microscopic imaging system. The parameters in the specific relationship and the measured values ​​of the actual critical stability temperatures are shown in Table 2.

[0150] Table 2

[0151]

[0152] As shown in Table 2, the critical stability temperature relationship satisfied by the positive or negative electrode electrolyte provided by the technical solution of this invention is simple to operate, easy to implement, and low in cost. Furthermore, the accuracy of this critical stability temperature relationship is high, further enabling more precise control of the battery's operating state in the battery energy storage system and achieving quantitative design of the formulation.

[0153] (II) Cycle life of all-vanadium redox flow batteries

[0154] To verify the practical application effect of the cycle life prediction equation for the vanadium redox flow battery described above, the vanadium redox flow batteries provided in the above embodiments and comparative examples were subjected to charge-discharge cycles at a current density of 140 mA / cm² under conditions of 25°C and a voltage range of 1.0V~1.55V until the capacity decayed to 80% of the initial capacity. The parameters in the specific relationship and the measured number of cycles are shown in Table 3:

[0155] Table 3

[0156]

[0157] As can be seen from Table 3, the cycle life prediction equation for the all-vanadium redox flow battery provided by the technical solution of the present invention can accurately predict the cycle life of the battery, and is not affected by the preparation method, site or electrolyte type. It has strong adaptability, high accuracy of prediction results, small error value, and is easy to promote.

[0158] Furthermore, the technical solution of this invention is not limited to the cycle test conditions mentioned above for predicting the cycle life of vanadium redox flow batteries. It can also arbitrarily select cycle test conditions with known parameters such as cycle temperature, current density, and cycle charge-discharge depth. Based on the cycle life test data of vanadium redox flow batteries using additive-free symmetrical electrolytes, the cycle life of the target object can be accurately predicted for the entire life cycle.

[0159] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An asymmetric electrolyte for a vanadium redox flow battery, wherein the vanadium redox flow battery asymmetric electrolyte comprises a positive electrode electrolyte and a negative electrode electrolyte, characterized in that, The positive electrode electrolyte includes a positive electrode supporting electrolyte, a positive electrode electrolyte, a positive electrode additive, and deionized water; the negative electrode electrolyte includes a negative electrode supporting electrolyte, a negative electrode electrolyte, a negative electrode additive, and deionized water. The asymmetric electrolyte of the all-vanadium redox flow battery satisfies the following conditions: The concentration of vanadium ions in the positive electrode electrolyte is greater than the concentration of vanadium ions in the negative electrode electrolyte; Furthermore, the concentration of the positive electrode supporting electrolyte in the positive electrode electrolyte is greater than the concentration of the negative electrode supporting electrolyte in the negative electrode electrolyte.

2. The asymmetric electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, The concentration of vanadium ions in the positive electrode electrolyte is 1.6 mol / L to 2.2 mol / L; And / or, the concentration of the positive electrode supporting electrolyte in the positive electrode electrolyte is 3.5 mol / L to 5.2 mol / L; And / or, the positive electrode additive in the positive electrode electrolyte includes at least one of phosphate compounds, carboxylic acid compounds, or sulfate compounds; And / or, the concentration of the positive electrode additive in the positive electrode electrolyte is 0.05 mol / L to 0.75 mol / L.

3. The asymmetric electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, The concentration of vanadium ions in the negative electrode electrolyte is 1.3 mol / L to 1.7 mol / L; And / or, the concentration of the negative electrode supporting electrolyte in the negative electrode electrolyte solution is 3.0 mol / L to 4.5 mol / L; And / or, the negative electrode additive in the negative electrode electrolyte includes at least one of amino acid compounds, sulfonic acid compounds, or metal oxides; And / or, the concentration of the negative electrode additive in the negative electrode electrolyte is 0.01 mol / L to 0.7 mol / L.

4. The asymmetric electrolyte for a full vanadium redox flow battery according to claim 2 or 3, characterized in that, The positive electrode electrolyte or the negative electrode electrolyte satisfies the following relationship: ； in, This is the critical stability temperature of the electrolyte. This is a correction term for the reference temperature of the electrolyte; This is the vanadium concentration coefficient. To support the electrolyte concentration coefficient, This refers to the additive concentration coefficient. This represents the concentration of vanadium ions in the electrolyte. This refers to the concentration of the supporting electrolyte in the electrolyte solution. This represents the concentration of additives in the electrolyte.

5. The asymmetric electrolyte for a full vanadium redox flow battery according to claim 4, characterized in that, In the positive electrode electrolyte and the negative electrode electrolyte, The value ranges from -2.0 to 1.

4. And / or, in the positive electrode electrolyte and the negative electrode electrolyte, the The value is -2.5 to 2.

5. And / or, in the positive electrode electrolyte and the negative electrode electrolyte, the The value ranges from -3.1 to 4.

0.

6. A vanadium redox flow battery, characterized in that, The vanadium redox flow battery includes the vanadium redox flow battery asymmetric electrolyte as described in any one of claims 1-5.

7. The all-vanadium redox flow battery according to claim 6, characterized in that, The cycle life prediction equation for the all-vanadium redox flow battery satisfies the following relationship: ； in, The cycle life of the vanadium redox flow battery; To determine the cycle life of an all-vanadium redox flow battery using an additive-free symmetrical electrolyte, the... The value range is 300 to 600. The average diffusion coefficient of vanadium ions measured in the symmetrical electrolyte; The average diffusion coefficient of vanadium ions measured in the asymmetric electrolyte of the all-vanadium redox flow battery; The additive synergistic gain coefficient, the The value range is 0.8 to 1.1; The temperature correction factor is... The value range is 0.1 to 1.

0.

8. The all-vanadium redox flow battery according to claim 7, characterized in that, The cycle life of the vanadium redox flow battery and the vanadium redox flow battery using an additive-free symmetrical electrolyte is the cycle life when the capacity decays to 80% of the initial capacity.

9. The all-vanadium redox flow battery according to claim 8, characterized in that, During the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using additive-free symmetrical electrolyte, the battery voltage range was controlled to be 1.0V~1.55V. And / or, during the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using an additive-free symmetrical electrolyte, the test current density is controlled to be 80 mA / cm². 2 ~200mA / cm 2 ; And / or, during the cycle life test of the vanadium redox flow battery and the vanadium redox flow battery using additive-free symmetrical electrolyte, the test temperature is controlled to be 25℃~50℃.

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