A method for inhibiting electrolyte capacity fade in a all-vanadium redox flow battery

Abstract

This application discloses a method for suppressing the capacity decay of the electrolyte in a vanadium redox flow battery, belonging to the field of electrochemical energy storage technology. The method for suppressing the capacity decay of the electrolyte in a vanadium redox flow battery includes the following steps: (1) constructing mass transfer equations for vanadium ions of various valence states, where temperature and SOC are independent variables; (2) calculating the Vc in the negative electrode storage tank based on the mass transfer equations. 2+ and V 3+ The total rate of diffusion to the positive electrode storage tank J n VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion to the negative electrode storage tank J p Calculate the net diffusion rate J = J n -J p (3) Adjust the temperature and charge / discharge SOC range to minimize the difference J. This application studies the influence of electrolyte temperature and SOC on ion transmembrane mass transfer by establishing a mass transfer equation, optimizes the mass transfer coefficient, reduces the degree of side reactions, improves the utilization rate of vanadium electrolyte, suppresses the capacity decay of vanadium redox flow battery, and can restore the capacity of the battery that has already decayed.

Description

Technical Field

[0001] This application relates to a method for suppressing the capacity decay of electrolyte in a vanadium redox flow battery, belonging to the field of electrochemical energy storage technology. Background Technology

[0002] Vanadium redox flow batteries (VRBs) possess advantages such as high safety, long lifespan, deep charge / discharge capability, and independently adjustable capacity and power, making them promising candidates for large-scale energy storage. However, due to factors such as vanadium ion transmembrane permeation imbalance, side reactions, water migration, and vanadium ion temperature stability in the electrolyte, VRBs suffer from capacity decay during operation, affecting their cycle life and economic viability. Therefore, it is necessary to research and develop methods to suppress electrolyte capacity decay.

[0003] Currently, the main engineering approach to address capacity decay caused by imbalance of positive and negative electrode active materials is periodic mixing and reactivation. This results in reduced utilization and high activation energy consumption. It is necessary to address the specific causes of capacity decay and propose targeted solutions to reduce the rate of capacity decay and decrease the frequency of mixing and reactivation.

[0004] To address the problem of transmembrane permeation imbalance in electrolytes, patent (CN114744253A) analyzed the reasons why the transmembrane permeation rate of active ions in the negative electrode electrolyte is greater than that of the positive electrode electrolyte in the perfluorosulfonic acid cation membrane system. It proposed a stack structure using a mixture of anion and cation membranes, which utilizes the opposite permeation characteristics of the anion membrane to neutralize the quantitative deviation of permeate caused by the cation membrane, thus ensuring the overall transmembrane permeation balance of the electrolyte. However, this method affects the consistency of the stack.

[0005] Patent (CN114497665A) addresses the transmembrane permeation of vanadium ions from the negative electrode to the positive electrode during charge-discharge cycles by adding a composite permeation-enhancing solute to the negative electrode electrolyte in a perfluorosulfonic acid cation exchange membrane system, thus maintaining electrode balance. However, this introduces acid-soluble sugars and metal complexing agents such as glycolic acid, increasing the organic component of the electrolyte and affecting viscosity control. Current methods for improving electrolyte stability primarily involve adding compounds with hydroxyl, amino, and mercapto groups, organic phosphoric acids, ammonium salts, phosphoric acids and various salts, polysaccharide compounds, carboxylic acids, and chelates containing other functional groups. These methods also alter the electrolyte composition, increasing the risk of changes in the overall performance of vanadium redox flow batteries and complicating electrolyte recovery processes.

[0006] Currently, methods to reduce capacity decay include strictly controlling the range of the cutoff voltage, such as lowering the charging cutoff voltage from 1.8V to 1.6V or even 1.55V, which is far from the potential range of side reactions. While this reduces capacity decay, it also reduces electrolyte utilization. In summary, existing methods for suppressing capacity decay in vanadium redox flow batteries cannot effectively solve the problem, and engineering practice still relies mainly on reactivation of the mixed electrolyte. There is an urgent need to develop a method that can both improve the utilization rate of vanadium electrolyte and suppress capacity decay and restore battery capacity in vanadium redox flow batteries. Summary of the Invention

[0007] To address the aforementioned issues, a method for suppressing the capacity decay of the electrolyte in vanadium redox flow batteries is provided. This method establishes a mass transfer equation to study the effects of electrolyte temperature and state of charge (SOC) on ion transmembrane mass transfer, selects an appropriate temperature range and SOC state, optimizes the mass transfer coefficient, reduces the degree of side reactions, and simultaneously improves the utilization rate of vanadium electrolyte while suppressing the capacity decay of vanadium redox flow batteries. Furthermore, it can restore the capacity of batteries that have already decayed.

[0008] According to one aspect of this application, a method for suppressing capacity decay of an all-vanadium redox flow battery electrolyte is provided, comprising the following steps:

[0009] (1) Construct mass transfer equations for vanadium ions in various valence states, where temperature and SOC are independent variables in the mass transfer equations;

[0010] (2) Calculate V in the negative electrode storage tank according to the mass transfer equation. 2+ and V 3+ The total rate of diffusion to the positive electrode storage tank J n VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion to the negative electrode storage tank J p Calculate the net diffusion rate J = J n -J p ;

[0011] (3) Adjust the temperature and charge / discharge SOC range to minimize the difference J.

[0012] Since the battery is a new battery or a recyclable battery, the SOC range during charging and discharging can be controlled to suppress battery degradation. For example, the battery SOC range can be controlled between 30% and 80% during charging and discharging. Combined with temperature control, this can suppress battery degradation. The above-mentioned SOC range of 30% to 80% is only an example and does not constitute a limitation of this application.

[0013] According to another aspect of this application, a method for restoring the capacity of a vanadium redox flow battery is provided, comprising the following steps:

[0014] (1) Measure the ion concentration in the negative electrode reservoir and the ion concentration in the positive electrode reservoir, and compare them with the ion concentration in the initial state to determine the direction of battery permeation.

[0015] (2) Construct mass transfer equations for vanadium ions in various valence states, where temperature and SOC are independent variables in the mass transfer equations;

[0016] (3) Adjust the temperature and SOC range according to the mass transfer equation to determine the difference J for reverse osmosis. The difference J = J n -J p J n V in the negative electrode storage tank 2+ and V 3+ The total rate of diffusion into the positive electrode storage tank, J p VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion into the negative electrode storage tank;

[0017] (4) When the ion concentration in the negative electrode storage tank and the ion concentration in the positive electrode storage tank differ from the initial state by no more than 10%, reverse osmosis shall be stopped.

[0018] When restoring the capacity of a degraded battery, it is necessary to control the initial temperature and state of charge (SOC) to allow vanadium ions in the degraded battery to diffuse in reverse, thereby achieving the purpose of capacity recovery. The recovery process is equivalent to self-discharge, and its SOC changes as the capacity is restored. Therefore, when restoring a battery, the capacity is mainly restored by controlling the temperature. The temperature is adjusted in real time according to the change in SOC to achieve the purpose of reverse recovery.

[0019] Optionally, the mass transfer equations for the vanadium ions in each valence state are as follows:

[0020] J2=D2(T)·SOC·C n / δ+α·A·e B / T ;

[0021] J3=D3(T)·(1-SOC)·C n / δ+α·A·e B / T ;

[0022] J4=D4(T)·(1-SOC)·C p / δ+α·A·e B / T ;

[0023] J5=D5(T)·SOC·C p / δ+α·A·e B / T ;

[0024] Where J2 is V in the negative electrode storage tank. 2+ The rate of diffusion into the positive electrode storage tank, D2(T), is V.2+ The empirical equation for the diffusion coefficient versus temperature, where J3 is the V in the negative electrode storage tank. 3+ The rate of diffusion into the positive electrode storage tank, D3(T), is V. 3+ The empirical equation for the diffusion coefficient versus temperature, where J4 is the VO in the positive electrode storage tank. 2+ The rate of diffusion into the negative electrode storage tank, D4(T) is VO 2+ The empirical equation for the diffusion coefficient versus temperature, where J5 is the VO2 in the positive electrode storage tank. + The rate of diffusion into the negative electrode storage tank, D5(T) is VO2 + The empirical equation for the diffusion coefficient versus temperature, where SOC represents the state of charge, ranging from 0% to 100%, and C n V in the negative electrode storage tank 2+ and V 3+ Total ion concentration, C p VO in the positive electrode storage tank 2+ and VO2 + Total ion concentration, δ is membrane thickness, T is temperature in °C, A is the pre-index, B is the Arrhenius temperature dependence parameter, and α is the viscosity influence factor, ranging from 0 to 0.2.

[0025] Optionally, the empirical formulas for D2(T), D3(T), D4(T), and D5(T) in the mass transfer equation are obtained through multinomial fitting, specifically as follows:

[0026] D n (T)=aT 2 +bT+c, where a, b, and c are polynomial fitting coefficients, and n is 2, 3, 4, and 5 respectively. When n is different, a, b, and c take different values.

[0027] Optionally, the empirical formula multinomial fitting steps for D2(T), D3(T), D4(T), and D5(T) are as follows:

[0028] S1: Prepare a vanadium ion permeation apparatus containing a diaphragm. The diaphragm is connected to tanks A and B on either side, where tank A contains vanadium ion permeation material. 2+ V 3+ VO 2+ VO2 + The solution in container A is vanadium, and container B is sulfuric acid solution. The sulfuric acid concentration in containers A and B is the same, and the volumes in containers A and B are the same.

[0029] S2: Calculate V at different temperatures using the following formula. 2+ V 3+ VO 2+ VO2 + diffusion coefficient:

[0030] Where D is the diffusion coefficient, and C A Where C is the vanadium ion concentration in container A. B denoted as vanadium ion concentration in tank B, t as time, S as effective permeable membrane area of ​​the diaphragm, δ as membrane thickness, and V as volume of tank A or tank B.

[0031] S3: The diffusion coefficients obtained at different temperatures are fitted using a polynomial to obtain empirical formulas for D2(T), D3(T), D4(T), and D5(T).

[0032] Optionally, the membrane is an anion exchange membrane or a cation exchange membrane.

[0033] Optionally, the cation exchange membrane is a Nafion 115 membrane.

[0034] Optionally, when n is 2, a is 0.1365 × 10 -7 b is 0.9495 × 10 -7 c is 3.674 × 10 -7 ;

[0035] When n is 3, a is 0.056 × 10 -7 b is 0.3184 × 10 -7 c is 1.4 × 10 -7 ;

[0036] When n is 4, a is 0.1068 × 10 -7 b is 0.7211 × 10 -7 c is 2.8947 × 10 -7 ;

[0037] When n is 5, a is 0.0893 × 10 -7 b is 0.6449 × 10 -7 c is 2.4748 × 10 -7 .

[0038] Optionally, in step (4) of the method for restoring the capacity of a vanadium redox flow battery, reverse osmosis is stopped when the ion concentration in the negative electrode reservoir and the ion concentration in the positive electrode reservoir differ from the initial state by no more than 5%.

[0039] The beneficial effects of this application include, but are not limited to:

[0040] 1. Since the four valence states of vanadium ions have different transmembrane permeation rates in the separator of a vanadium redox flow battery, this application studies the electrolyte temperature, SOC, and viscosity, and establishes transmembrane mass transfer equations for vanadium ions of each valence state. By controlling the mass transfer function of active ions, the operating parameters of the vanadium redox flow battery can be optimized. When the battery operating temperature and SOC state are different, timely adjustments can be made. This can both suppress the capacity decay caused by the imbalance of ion transmembrane permeation and reversely control the migration of active ions to achieve capacity recovery, thus expanding the application prospects of vanadium redox flow batteries.

[0041] 2. This application guides the use and operation of the battery through the mass transfer equation. It does not introduce other substances into the electrolyte and will not affect the stack or the overall battery system. It can effectively solve the problem of capacity decay in the existing vanadium redox flow battery and is conducive to engineering use.

[0042] 3. Based on the mass transfer equation established in this application, temperature and SOC can be controlled to reverse the online recovery of batteries with degraded capacity, slow down or reverse the battery capacity decay process, and the recovered battery can approach the initial state, thereby extending the battery life, saving battery production costs, and reducing environmental pollution caused by battery scrapping.

[0043] 4. This application can monitor the capacity performance of vanadium redox flow batteries and suppress economic losses caused by battery capacity decay, reducing maintenance costs, especially in terms of improving battery life, reducing the operating costs of energy storage systems, and reducing the need for replacement and maintenance.

[0044] 5. This application addresses the diffusion imbalance of vanadium ions of different valences by controlling various factors in the mass transfer equation. This technical concept can be applied to different types of membranes and electrolytes of different concentrations or compositions, and plays an important guiding role for current all-vanadium redox flow batteries. Attached Figure Description

[0045] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0046] Figure 1 A schematic diagram of the vanadium ion permeation device used in establishing the mass transfer equation for this application.

[0047] List of components and reference numerals:

[0048] 1. Fuel cell stack; 2. Diaphragm; 3. Tank A; 4. Tank B; 5. Pump. Detailed Implementation

[0049] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0050] Unless otherwise specified, the embodiments in this application use carbon felt as the reaction electrode and a Nafion 115 ion exchange membrane (DuPont, USA) as the separator to assemble the experimental battery. The positive and negative electrode electrolytes are 1.7 mol / L VOSO4 + 4.78 mol / L H2SO4, respectively, and the effective electrode area is 25 cm². 2 .

[0051] Example 1

[0052] This embodiment relates to a method for suppressing the capacity decay of electrolyte in a vanadium redox flow battery, comprising the following steps:

[0053] (1) First, construct the mass transfer equations for vanadium ions in each valence state:

[0054] Step 1: Establish empirical equations for the diffusion coefficient of vanadium ions in various valence states versus temperature:

[0055] S1: Preparation Figure 1 A vanadium ion permeation device is described, comprising an electrode stack 1, a diaphragm 2, a tank A 3, a tank B 4, and a pump 5. Tank A 3 and tank B 4 are connected to opposite sides of the diaphragm 2, respectively. Tank A 3 contains vanadium ion permeation material. 2+ V 3+ VO 2+ VO2 + The solution contains vanadium, and container B contains sulfuric acid. Containers A and B have the same sulfuric acid concentration and the same volume.

[0056] S2: Calculate the diffusion coefficient of vanadium ions in different valence states at different temperatures:

[0057] According to Fick's diffusion law, the concentration differences dc and dx in the original formula are specifically expressed by the vanadium ion concentration difference on both sides of membrane 2 and the thickness of membrane 2, resulting in the following formula (1):

[0058]

[0059] The left side of the formula represents the concentration of vanadium ions migrating from tank A3 to tank B4 per unit time. On the right side, S represents the effective permeable membrane area of ​​diaphragm 2, δ represents the membrane thickness, and C... A C represents the vanadium ion concentration in container A, 3. B This indicates the vanadium ion concentration in container B4. Since the vanadium ion concentration in container A3 is much greater than that in container B4, C... A It can be considered a constant, and without considering electrolyte water migration, the volume V of the solution in both chambers remains unchanged. Integrating the time term in equation (1) yields the final diffusion coefficient, equation (2):

[0060]

[0061] Where D is the diffusion coefficient, and C A The concentration of vanadium ions in container A is 3, and C is... B denoted as vanadium ion concentration in tank B4, t as time, S as effective permeable membrane area of ​​diaphragm 2, δ as membrane thickness, and V as volume of tank A3 or tank B4.

[0062] S3: As shown in equation (2), by measuring the vanadium ion concentration in tank B4 at different times, the relationship curve between time and concentration can be obtained. Substituting this into the formula, the vanadium ion diffusion coefficient D at different temperatures can be calculated. The vanadium ion diffusion coefficient is non-linearly related to temperature. By using polynomial fitting to correlate the vanadium ion diffusion coefficient D with temperature T, the following empirical formula is obtained:

[0063] D n (T)=aT 2 +bT+c Equation (3);

[0064] Where a, b, and c are polynomial fitting coefficients, and n is 2, 3, 4, and 5 respectively. When n is different, a, b, and c take different values. When using cation membrane 2, the above a, b, and c take positive values; when using anion membrane 2, the above a, b, and c take negative values.

[0065] When using Nafion 115 membrane as separator 2, the empirical formulas for polynomial fitting of D2(T), D3(T), D4(T), and D5(T) are as follows:

[0066] D2(T) = 10 -7 ×(0.1365T 2 +0.9495T+3.674) R 2 =1

[0067] D3(T) = 10 -7 ×(0.056T 2 +0.3184T+1.4) R 2 =1

[0068] D4(T) = 10 -7 ×(0.1068T 2 +0.7211T+2.8947) R 2 =1

[0069] D5(T) = 10 -7 ×(0.0893T 2 +0.6449T+2.4748) R 2 =1

[0070] Step 2: Establish the mass transfer equations for vanadium ions in various valence states:

[0071] Since temperature affects not only the diffusion coefficient of vanadium ions on membrane 2, but also the increase or decrease in viscosity, leading to changes in osmotic pressure and thus influencing the diffusion process of vanadium ions, the empirical formulas for the viscosity of the positive and negative electrode electrolytes in a full vanadium redox flow battery are as follows:

[0072] η=A·e (B / T) Equation (4);

[0073] Equation (4) can be used to describe the relationship between viscosity and temperature. It is a simplified Arrhenius formula, where η is the viscosity of the electrolyte, T is the temperature (in °C), A and B are constants related to the properties of the electrolyte, A is the exponent, and B is the Arrhenius temperature dependence parameter.

[0074] In the actual cycle of the vanadium redox flow battery, vanadium ions of four valence states coexist. The migration of vanadium ions of each valence state is not only determined by the diffusion coefficient controlled by temperature, but also by the concentration of vanadium ions of each valence state in the positive and negative electrode electrolytes. The concentration of vanadium ions of each valence state can be represented by the SOC state at this time, i.e., the following formula (5).

[0075]

[0076] Therefore V 2+ V 3+ VO 2+ VO2 + The concentrations were SOC·Cn, (1-SOC)·Cn, (1-SOC)·Cp, and SOC·Cp, respectively. n V in the negative electrode storage tank 2+ and V 3+ Total ion concentration, C p VO in the positive electrode storage tank 2+ and VO2 + Total ion concentration.

[0077] Therefore, considering the combined effects of temperature, viscosity, and concentration on vanadium ion transmembrane mass transfer, the diffusion coefficient equations for the four valence states of vanadium ions at different temperatures (Equation 3), the relationship between the concentration of each valence state of vanadium ions in the electrolyte and SOC (Equation 5), and the influence of the Arrhenius equation on diffusion regarding viscosity, are used. Based on Fick's law J = -D·(dc / dx), D in the formula can be expressed using the relationship D(T), thus introducing temperature as the independent variable in the mass transfer equation. dc is the concentration difference across the membrane, i.e., the difference between the vanadium ions of different valence states in the positive and negative electrode storage tanks; in the negative electrode tank of the vanadium battery, it is V. 2+ and V 3+ Vanadium ions, in the positive electrode container, are VO 2+ and VO2 +Vanadium ions, in all valence states, undergo side reactions and are consumed after crossing the membrane. Therefore, it is assumed that VO will not appear in the negative electrode tank. 2+ and VO2 + Vanadium ions will not appear in the positive electrode container. 2+ and V 3+ Vanadium ions, then the concentration difference dc is the V in the tank at this time. 2+ V 3+ VO 2+ VO2 + The concentrations, expressed in terms of SOC, are SOC·Cn, (1-SOC)·Cn, (1-SOC)·Cp, and SOC·Cp, respectively, while dx is still expressed in terms of membrane thickness δ.

[0078] In addition, the Arrhenius equation regarding viscosity affects diffusion α·A·e (B / T) The mass transfer equations for vanadium ions in various valence states are obtained as follows:

[0079] J2=D2(T)·SOC·C n / δ+α·A·e B / T Equation (6);

[0080] J3=D3(T)·(1-SOC)·C n / δ+α·A·e B / T Equation (7);

[0081] J4=D4(T)·(1-SOC)·C p / δ+α·A·e B / T Equation (8);

[0082] J5=D5(T)·SOC·C p / δ+α·A·e B / T Equation (9);

[0083] In equations (6)-(9), J2 represents the V in the negative electrode storage tank. 2+ The rate of diffusion into the positive electrode storage tank, D2(T), is V. 2+ The empirical equation for the diffusion coefficient versus temperature, where J3 is the V in the negative electrode storage tank. 3+ The rate of diffusion into the positive electrode storage tank, D3(T), is V. 3+ The empirical equation for the diffusion coefficient versus temperature, where J4 is the VO in the positive electrode storage tank. 2+ The rate of diffusion into the negative electrode storage tank, D4(T) is VO 2+ The empirical equation for the diffusion coefficient versus temperature, where J5 is the VO2 in the positive electrode storage tank. + The rate of diffusion into the negative electrode storage tank, D5(T) is VO2 +The empirical equation for the diffusion coefficient versus temperature, where SOC represents the state of charge, ranging from 0% to 100%, and C n V in the negative electrode storage tank 2+ and V 3+ Total ion concentration, C p VO in the positive electrode storage tank 2+ and VO2 + Total ion concentration, δ is membrane thickness, T is temperature in °C, A is the pre-index, B is the Arrhenius temperature dependence parameter, and α is the viscosity influence factor, ranging from 0 to 0.2. Since α varies under different conditions, the median value of 0.1 is taken here.

[0084] (2) Calculate V in the negative electrode storage tank according to the mass transfer equation. 2+ and V 3+ The total rate of diffusion to the positive electrode storage tank J n VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion to the negative electrode storage tank J p J n The size is J2 + J3, J p The magnitude is J4 + J5, and the net diffusion rate J = J n -J p ;

[0085] (3) Adjust the temperature and charge / discharge SOC range according to actual needs to minimize the difference J.

[0086] The method described in this embodiment controls the temperature and state of charge (SOC) during the charging and discharging processes of three different types of vanadium redox flow batteries, named Battery 1#, Battery 2#, and Battery 3#, respectively, with a charging and discharging current density of 60 mA / cm². 2 The coulombic efficiency, voltage efficiency, energy efficiency, and capacity decay after 50 and 100 cycles of the battery were calculated. A control group was also set up, in which vanadium redox flow batteries of the same type, batch, and specifications were subjected to natural charge and discharge without any control, and their coulombic efficiency, voltage efficiency, energy efficiency, and capacity decay after 50 and 100 cycles were calculated. The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] According to the data in Table 1, the method of this embodiment for controlling the temperature and SOC of the vanadium redox flow battery can suppress the capacity decay caused by the transmembrane permeation imbalance of the battery electrolyte and extend the battery's service life. After 50 cycles, the capacity decay is reduced by an average of 62.15% compared to the control group, and after 100 cycles, the capacity decay is reduced by an average of 56.41% compared to the control group. The difference between the average decay of the control group in batteries 1#, 2#, and 3# and the average decay in Example 1 is the average reduction.

[0090] Example 2

[0091] This embodiment relates to a method for restoring the capacity of a vanadium redox flow battery, including the following steps:

[0092] (1) Measure the ion concentration in the negative electrode reservoir and the ion concentration in the positive electrode reservoir, and compare them with the ion concentration in the initial state to determine the direction of battery permeation and whether the battery permeates from the positive electrode to the negative electrode or from the negative electrode to the positive electrode.

[0093] (2) Constructing mass transfer equations for vanadium ions in each valence state: This step is the same as step (1) in Example 1;

[0094] (3) Adjust the temperature and SOC range according to the mass transfer equation to determine the difference J for reverse osmosis. The difference J = J n -J p J n V in the negative electrode storage tank 2+ and V 3+ The total rate of diffusion into the positive electrode storage tank, J p VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion into the negative electrode storage tank;

[0095] (4) When the ion concentration in the negative electrode storage tank and the ion concentration in the positive electrode storage tank differ from the initial state by no more than 10%, reverse osmosis shall be stopped.

[0096] Preferably, in step (4), reverse osmosis is stopped when the ion concentration of the negative electrode storage tank and the ion concentration of the positive electrode storage tank differ from the initial state by no more than 5%.

[0097] The method described in this embodiment was used to conduct charge-discharge tests on five different types of vanadium redox flow batteries, which were named Battery 1#, Battery 2#, Battery 3#, Battery 4#, and Battery 5#, respectively. The initial capacity, recovered capacity, and calculated capacity recovery rate of the above five different batteries were recorded, as shown in Table 2 below:

[0098] Table 2

[0099] Test number Initial capacity (Ah) Restored capacity (Ah) Capacity recovery rate (%) Battery #1 1.158 1.082 93.43 Battery #2 1.084 1.076 99.26 Battery #3 1.079 1.055 97.78 Battery #4 1.561 1.381 88.49 Battery #5 1.251 1.145 91.56

[0100] As shown in Table 2, the method of this embodiment can control the temperature and SOC of the degraded vanadium redox flow battery, thereby reversing the capacity decay process and turning waste into treasure, thus extending the battery's lifespan. The battery capacity recovery rate is above 88%, and can reach up to 99% or more.

[0101] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for suppressing capacity decay of electrolyte in a vanadium redox flow battery, characterized in that, Includes the following steps: (1) Construct mass transfer equations for vanadium ions in various valence states, where temperature and SOC are independent variables in the mass transfer equations; (2) Calculate V in the negative electrode storage tank according to the mass transfer equation. 2+ and V 3+ The total rate of diffusion to the positive electrode storage tank J n VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion to the negative electrode storage tank J p Calculate the net diffusion rate J = J n -J p ; (3) Adjust the temperature and charge / discharge SOC range to minimize the difference J; The mass transfer equations for the vanadium ions in each valence state are as follows: ； ； ； ； Where J2 is V in the negative electrode storage tank. 2+ The rate of diffusion into the positive electrode storage tank, D2(T), is V. 2+ The empirical equation for the diffusion coefficient versus temperature, where J3 is the V in the negative electrode storage tank. 3+ The rate of diffusion into the positive electrode storage tank, D3(T), is V. 3+ The empirical equation for the diffusion coefficient versus temperature, where J4 is the VO in the positive electrode storage tank. 2+ The rate of diffusion into the negative electrode storage tank, D4(T) is VO 2+ The empirical equation for the diffusion coefficient versus temperature, where J5 is the VO2 in the positive electrode storage tank. + The rate of diffusion into the negative electrode storage tank, D5(T) is VO2 + The empirical equation for the diffusion coefficient versus temperature, where SOC represents the state of charge, ranging from 0% to 100%, and C n V in the negative electrode storage tank 2+ and V 3+ Total ion concentration, C p VO in the positive electrode storage tank 2+ and VO2 + Total ion concentration, δ is membrane thickness, T is temperature in °C, A is the pre-index, B is the Arrhenius temperature-dependent parameter, and α is the viscosity influence factor, ranging from 0 to 0.

2. The empirical formulas for D2(T), D3(T), D4(T), and D5(T) in the mass transfer equation were obtained through multinomial fitting, specifically as follows: D n (T) = aT 2 +bT+c, where a, b, and c are polynomial fitting coefficients, and n is 2, 3, 4, and 5 respectively. When n is different, a, b, and c take different values.

2. A method for restoring the capacity of a vanadium redox flow battery, characterized in that, Includes the following steps: (1) Measure the ion concentration in the negative electrode reservoir and the ion concentration in the positive electrode reservoir, and compare them with the ion concentration in the initial state to determine the direction of battery permeation; (2) Construct mass transfer equations for vanadium ions in various valence states, where temperature and SOC are independent variables in the mass transfer equations; (3) Adjust the temperature and SOC range according to the mass transfer equation to determine the difference J for reverse osmosis. The difference J = J n -J p J n V in the negative electrode storage tank 2+ and V 3+ The total rate of diffusion into the positive electrode storage tank, J p VO in the positive electrode storage tank 2+ and VO2 + The total rate of diffusion into the negative electrode storage tank; (4) When the ion concentration in the negative electrode storage tank and the ion concentration in the positive electrode storage tank differ from the initial state by no more than 10%, reverse osmosis shall be stopped; The mass transfer equations for the vanadium ions in each valence state are as follows: ； ； ； ； Where J2 is V in the negative electrode storage tank. 2+ The rate of diffusion into the positive electrode storage tank, D2(T), is V. 2+ The empirical equation for the diffusion coefficient versus temperature, where J3 is the V in the negative electrode storage tank. 3+ The rate of diffusion into the positive electrode storage tank, D3(T), is V. 3+ The empirical equation for the diffusion coefficient versus temperature, where J4 is the VO in the positive electrode storage tank. 2+ The rate of diffusion into the negative electrode storage tank, D4(T) is VO 2+ The empirical equation for the diffusion coefficient versus temperature, where J5 is the VO2 in the positive electrode storage tank. + The rate of diffusion into the negative electrode storage tank, D5(T) is VO2 + The empirical equation for the diffusion coefficient versus temperature, where SOC represents the state of charge, ranging from 0% to 100%, and C n V in the negative electrode storage tank 2+ and V 3+ Total ion concentration, C p VO in the positive electrode storage tank 2+ and VO2 + Total ion concentration, δ is membrane thickness, T is temperature in °C, A is the pre-index, B is the Arrhenius temperature-dependent parameter, and α is the viscosity influence factor, ranging from 0 to 0.

2. The empirical formulas for D2(T), D3(T), D4(T), and D5(T) in the mass transfer equation are obtained through multinomial fitting, specifically as follows: D n (T) = aT 2 +bT+c, where a, b, and c are polynomial fitting coefficients, and n is 2, 3, 4, and 5 respectively. When n is different, a, b, and c take different values.

3. The method according to claim 2, characterized in that, In step (4), reverse osmosis is stopped when the ion concentration in the negative electrode storage tank and the ion concentration in the positive electrode storage tank differ from the initial state by no more than 5%.

4. The method according to claim 1 or 2, characterized in that, When n is 2, a is 0.1365 × 10 -7 b is 0.9495 × 10 -7 c is 3.674 × 10 -7 ; When n is 3, a is 0.056 × 10 -7 b is 0.3184 × 10 -7 c is 1.4 × 10 -7 ; When n is 4, a is 0.1068 × 10 -7 b is 0.7211 × 10 -7 c is 2.8947 × 10 -7 ; When n is 5, a is 0.0893 × 10 -7 b is 0.6449 × 10 -7 c is 2.4748 × 10 -7 .

Images