Method for repairing unbalanced battery electrolyte and method for determining repair endpoint thereof

Abstract

The present invention relates to electrolyte repair, and discloses a method for repairing an unbalanced battery electrolyte and a method for determining the repair endpoint thereof. The repair method comprises: S1, mixing the positive and negative electrolytes of the unbalanced battery to obtain a mixed electrolyte I; preparing a pentavalent ion suspension of metal cations contained in the mixed electrolyte I; S2, mixing the mixed electrolyte I and the pentavalent ion suspension to obtain a mixed electrolyte II; S3, dividing the mixed electrolyte II into two parts, one of which serves as the repair anode electrolyte and the other as the repair cathode electrolyte, and performing constant current electrolysis. When the battery terminal voltage undergoes a step and the first-order differential of the terminal voltage is maximized, the repair endpoint is reached. This repair method has a good repair effect and can improve the utilization efficiency of the unbalanced battery electrolyte.

Description

Technical Field

[0001] The present invention relates to electrolyte repair, and more particularly to a method for repairing an unbalanced electrolyte. Furthermore, the present invention provides a method for determining the end point of electrolyte repair in an unbalanced battery. Background Art

[0002] All-vanadium liquid flow batteries are considered to be one of the most advantageous large-scale energy storage methods due to their unique safety. The charge and discharge capacity of vanadium batteries is determined by the volume of the electrolyte, the vanadium concentration therein, and the utilization rate of vanadium ions. During long-term operation, the positive and negative electrolytes of vanadium batteries cross-link with each other, resulting in volume and concentration differences. Usually, the negative electrode electrolyte migrates to the positive electrode side, causing an imbalance in vanadium concentration and valence state, resulting in a substantial attenuation of the charge and discharge capacity. The capacity attenuation of vanadium batteries is one of the main bottlenecks affecting the large-scale application of vanadium batteries.

[0003] At present, the rebalancing of unbalanced electrolytes is mainly divided into complete rebalancing and partial rebalancing. Both complete (remixing) rebalancing and partial (mixing) rebalancing are considered from the perspective of restoring the volume and concentration of the electrolyte, and cannot solve the oxidation imbalance and reduction imbalance problems of the electrolyte.

[0004] Although some repair methods are provided in the prior art, no final method for determining the repair endpoint is provided, and the repair endpoint of the electrolyte cannot be determined, which ultimately affects subsequent applications. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that the prior art does not provide a final determination method for the repair endpoint, and to provide a method for repairing an unbalanced battery electrolyte and a method for determining the repair endpoint thereof. The repair method has a good repair effect and can improve the utilization efficiency of the unbalanced battery electrolyte.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for repairing an unbalanced battery electrolyte, comprising the following steps:

[0007] S1, mixing the positive electrolyte and the negative electrolyte of the unbalanced battery to obtain a mixed electrolyte I;

[0008] preparing a pentavalent ion suspension of metal cations contained in the mixed electrolyte solution I;

[0009] S2, mixing the mixed electrolyte I and the pentavalent ion suspension to obtain a mixed electrolyte II;

[0010] S3. Divide the mixed electrolyte II into two parts, one of which is used as the anolyte and the other as the catholyte, and perform constant current electrolysis. When the battery terminal voltage has a step and the first-order differential of the terminal voltage is the largest, it is the repair end point.

[0011] Preferably, in step S1, the volume of the mixed electrolyte I is determined and recorded as V1, and the molar concentration of the trivalent cations, the molar concentration of the tetravalent cations and the molar concentration of the sulfate ions in the mixed electrolyte I are determined, wherein the molar concentration of the trivalent cations is recorded as c 3价 The molar concentration of tetravalent cations is denoted as c 4价 The molar concentration of sulfate ions is c 酸根离子 .

[0012] Further preferably, in step S1 , the method for preparing the pentavalent ion suspension includes: mixing a pentavalent metal oxide for forming metal cations in the pentavalent ion suspension, a sulfuric acid solution, and water.

[0013] Preferably, in the pentavalent ion suspension of step S1, the amount of the pentavalent metal oxide used to form the metal cation in the pentavalent ion suspension is calculated according to formula (I), and the amount of the sulfuric acid solution is calculated according to formula (II).

[0014] n 5价 =c 3价 ×V1÷2 formula (I);

[0015] V2=2×n 5价 ×c 酸根离子 ÷(c 4价 +c 3价 )÷V m Formula (II);

[0016] Among them, n 5价 is the amount of pentavalent metal oxide, V2 is the volume of sulfuric acid solution, V m is the volume molar concentration of sulfuric acid solution.

[0017] Preferably, the amount of water is calculated according to formula (III),

[0018] V3=[n 5价 ÷(c 4价 +c 3价 )-V2]×a formula (III);

[0019] Among them, V3 is the volume of water, and a is the proportional coefficient, which is 0.6-0.8.

[0020] More preferably, the metal is vanadium metal, the trivalent cation of the metal is a trivalent cation of vanadium, the tetravalent cation of the metal is a tetravalent cation of vanadium, and the oxide of the pentavalent metal is V2O5.

[0021] More preferably, the step S2 further comprises fixing the volume of the mixed solution after the mixing is completed so that the volume of the mixed solution is 0.99[V1+n5价 ÷(c 4价 +c 3价 )]-1.01[V1+n 5价 ÷(c 4价 +c 3价 )].

[0022] More preferably, in step S2, the mixing conditions at least include: a stirring rate of 200-500 r / min.

[0023] Preferably, in step S3, the volume ratio of the repair anode electrolyte to the repair cathode electrolyte is 1:2.

[0024] Further preferably, the conditions for the constant current electrolysis include: a current density of 30-60 mA / cm 2 .

[0025] Preferably, the constant current electrolysis is carried out in a repair device, which includes a constant current electrolysis instrument, an anode electrolysis chamber, a cathode electrolysis chamber, a separator, an anode electrode structure and a cathode electrode structure, the anode electrode structure is connected to the anode electrolysis chamber, the cathode electrode structure is connected to the cathode electrolysis chamber, the anode electrode structure and the cathode electrode structure are both connected to the constant current electrolysis instrument, and the separator is arranged between the anode electrode structure and the cathode electrode structure.

[0026] Further preferably, the anode electrode structure and the cathode electrode structure independently include an electrode, a current collecting plate and an end plate in sequence from the inside to the outside, the electrode is in contact with the separator, and the constant current electrolysis instrument is connected to the current collecting plate.

[0027] Preferably, the repair device further comprises a data acquisition system and a nitrogen supply structure, the data acquisition system is connected to the constant current electrolysis instrument, and the nitrogen supply structure is connected to the cathode electrolysis chamber.

[0028] Preferably, the anode electrode structure is arranged outside the anode electrolyzer, and the cathode electrode structure is arranged outside the cathode electrolyzer.

[0029] Preferably, the battery terminal voltage is the potential difference between the anode electrode structure and the cathode electrode structure.

[0030] Preferably, the repaired cathode electrolyte obtained in step S3 is the repaired electrolyte.

[0031] When the battery is unbalanced again, the positive electrolyte and the negative electrolyte of the unbalanced battery are mixed to obtain a mixed electrolyte III; the repaired anode electrolyte obtained in step S3 is added dropwise to the mixed electrolyte III until the electrolyte turns bright blue, and step S3 is repeated to repair the unbalanced electrolyte again; or,

[0032] When the battery becomes unbalanced again, steps S1 to S3 are repeated to repair the unbalanced electrolyte.

[0033] A second aspect of the present invention provides a method for determining the end point of repair of an unbalanced battery electrolyte, comprising: during constant current electrolysis of the unbalanced electrolyte, when a step occurs in the battery terminal voltage and the first-order differential of the terminal voltage is maximum, the repair end point is determined.

[0034] Through the above technical solution, the present invention mixes the positive electrolyte and negative electrolyte of the unbalanced battery, and mixes them with a pentavalent ion suspension of metal cations contained in the electrolyte, and uses them as the repair anode electrolyte and the repair cathode electrolyte for constant current electrolysis. When the battery terminal voltage has a step and the first-order differential of the terminal voltage is maximum, it is the repair endpoint. The repair endpoint can be quickly and accurately determined while repairing the unbalanced battery electrolyte, reducing repair errors, improving repair quality, and thereby improving the utilization efficiency of the unbalanced battery electrolyte.

[0035] In addition, the method for determining the end point of repair of an unbalanced battery electrolyte provided by the present invention is that during the constant current electrolysis process, when a step occurs in the battery terminal voltage and the first-order differential of the terminal voltage is maximized, it is the repair end point, which has a high accuracy rate, effectively reduces the repair error, and improves the repair quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of a repair device provided by one embodiment of the present invention;

[0037] Figure 2 This is the repair endpoint determination diagram of Example 1;

[0038] Figure 3 is a UV-visible spectrum detection diagram of the cathode electrolyte after repair in Example 1;

[0039] Figure 4 1 is a cyclic voltammogram of the catholyte and the unbalanced electrolyte after repair in Example 1;

[0040] Figure 5 This is a picture of the electrolyte that appears bright blue;

[0041] Figure 6 This is a UV-visible spectrum detection diagram of the bright blue electrolyte obtained in step (2) of Example 2;

[0042] Figure 7is a UV-visible spectrum detection diagram of the catholyte after repair in Example 2;

[0043] Figure 8 1 is the cyclic voltammogram of the cathode electrolyte and the unbalanced electrolyte after repair in Example 2.

[0044] Description of Reference Numerals

[0045] 1. Data acquisition system; 2. Constant current electrolysis instrument; 3. Anode electrolysis chamber; 4. Cathode electrolysis chamber; 5. End plate; 6. Current collecting plate; 7. Electrode; 8. Separator membrane; 9. Pumping structure; 10. Nitrogen supply structure; 11. Gas flow meter. DETAILED DESCRIPTION

[0046] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0047] As mentioned above, the present invention provides a method for repairing an unbalanced battery electrolyte, comprising the following steps:

[0048] S1, mixing the positive electrolyte and the negative electrolyte of the unbalanced battery to obtain a mixed electrolyte I;

[0049] preparing a pentavalent ion suspension of metal cations contained in the mixed electrolyte solution I;

[0050] S2, mixing the mixed electrolyte I and the pentavalent ion suspension to obtain a mixed electrolyte II;

[0051] S3. Divide the mixed electrolyte II into two parts, one of which is used as the repair anode electrolyte and the other as the repair cathode electrolyte, and perform constant current electrolysis. When the battery terminal voltage has a step and the first-order differential of the terminal voltage is the largest, it is the end point of the repair.

[0052] Chemical analysis (UV-visible spectroscopy and concentration determination) and cyclic voltammetry tests confirmed that the repaired electrolyte was a 3.5-valent electrolyte with good electrochemical activity, demonstrating that this method can accurately determine the repair endpoint.

[0053] The repair method provided by the present invention mixes the positive electrode electrolyte and the negative electrode electrolyte of the unbalanced battery, and mixes them with a pentavalent ion suspension of the metal cations described in the electrolyte, and uses them as the repair anode electrolyte and the repair cathode electrolyte for constant current electrolysis. When a step occurs in the battery terminal voltage and the first-order differential of the terminal voltage is maximized, it is the repair endpoint. The repair endpoint can be quickly and readily determined while the unbalanced battery electrolyte is being repaired, thereby reducing repair errors, improving repair quality, and thereby improving the utilization efficiency of the unbalanced battery.

[0054] Preferably, in step S1, the volume of the mixed electrolyte I is determined and recorded as V1, and the molar concentration of the trivalent cations, the molar concentration of the tetravalent cations and the molar concentration of the sulfate ions in the mixed electrolyte I are determined, wherein the molar concentration of the trivalent cations is recorded as c 3价 The molar concentration of tetravalent cations is denoted as c 4价 The molar concentration of sulfate ions is c 酸根离子 .

[0055] The volume of the mixed electrolyte I can be directly measured, and the molar concentration of the trivalent cation of the metal, the molar concentration of the tetravalent cation and the molar concentration of the sulfate ion can be measured by titration. The reagent used in the titration can be a reagent conventionally used in the art to titrate the molar concentration of the trivalent cation of the metal, the molar concentration of the tetravalent cation and the molar concentration of the sulfate ion. Taking the trivalent cation of the metal as a trivalent vanadium ion and the tetravalent cation of the metal as a tetravalent vanadium ion as an example, with reference to national standard GBT8704.5-2020, the trivalent vanadium ions and tetravalent vanadium ions in the solution are titrated by potentiometric titration, and the sulfate concentration in the solution is titrated by gravimetric method with reference to industry standard T / QAS 004-2019.

[0056] Preferably, in step S1, the method for preparing the pentavalent ion suspension comprises: mixing a pentavalent metal oxide for forming metal cations in the pentavalent ion suspension, a sulfuric acid solution, and water. Further preferably, the amount of the pentavalent metal oxide for forming metal cations in the pentavalent ion suspension is calculated according to formula (I), and the amount of the sulfuric acid solution is calculated according to formula (II).

[0057] n 5价 =c 3价 ×V1÷2 formula (I);

[0058] V2=2×n 5价 ×c 酸根离子 ÷(c 4价 +c 3价 )÷V m Formula (II);

[0059] Among them, n5价 is the amount of pentavalent metal oxide, V2 is the volume of sulfuric acid solution, V m By controlling the amount of pentavalent metal oxide and concentrated sulfuric acid in the above manner, the amount of pentavalent metal ions can be effectively controlled, thereby further improving the repair effect, while also ensuring that the metal ion concentration and acid radical ion concentration of the electrolyte remain unchanged.

[0060] According to the present invention, the units of the above parameters are all international standard units, such as the unit of molar concentration is mol / L, the unit of volume is L, and the unit of amount of substance is mol. m is the molar concentration of the added sulfuric acid solution, such as when the sulfuric acid solution is concentrated sulfuric acid, the molar concentration of the sulfuric acid is 18.4 mol / L. Preferably, the molar concentration of the sulfuric acid solution is 15-18.4 mol / L, more preferably 17.5-18.4 mol / L.

[0061] Preferably, the amount of water is calculated according to formula (III),

[0062] V3=[n 5价 ÷(c 4价 +c 3价 )-V2]×a formula (III);

[0063] Where V3 is the volume of water and a is the proportional coefficient, which is 0.6-0.8. By controlling the amount of water in the above manner, the repair effect can be further improved.

[0064] Preferably, the metal is vanadium metal, the trivalent cation of the metal is a trivalent cation of vanadium, the tetravalent cation of the metal is a tetravalent cation of vanadium, and the oxide of the pentavalent metal is V2O5. The repair method provided by the present invention has a good repair effect on all-vanadium redox flow batteries.

[0065] Preferably, the step S2 further comprises fixing the volume of the mixed solution after the mixing is completed so that the volume of the mixed solution is 0.99[V1+n 5价 ÷(c 4价 +c 3价 )]-1.01[V1+n 5价 ÷(c 4价 +c 3价 )]. By controlling the volume of the mixed solution within the above range, the concentrations of tetravalent vanadium ions and sulfate ions can be guaranteed to be the target concentrations, thereby further ensuring the repair effect.

[0066] Preferably, in step S2, the mixing conditions include at least a stirring rate of 200-500 r / min, which may be 200 r / min, 300 r / min, 400 r / min, 500 r / min, or any value therebetween. These mixing conditions provide a good mixing effect. The stirring time is not particularly limited, as long as the two are mixed into a solution, and is generally 8-12 minutes.

[0067] Preferably, in step S3, the volume ratio of the repair anolyte to the repair catholyte is 1: 2. Controlling the repair catholyte and the repair anolyte under the above conditions can further improve the repair effect.

[0068] According to the present invention, the volume ratio here may not be absolutely 1:2, and experimental errors may be allowed.

[0069] Preferably, the conditions for constant current electrolysis include: a current density of 30-60 mA / cm 2 , can be 30mA / cm 2 , 40mA / cm 2 , 50mA / cm 2 、60mA / cm 2 , or any value between the above values. Controlling the current density within the above range can further improve the repair effect.

[0070] Preferably, the method further comprises: the repaired cathode electrolyte obtained in step S3 is the repaired electrolyte, which can be used as the cathode electrolyte and the anolyte of the battery;

[0071] If the battery becomes unbalanced again, the positive and negative electrolytes of the unbalanced battery are mixed to obtain a mixed electrolyte III. The repaired anolyte obtained in step S3 is added dropwise to the mixed electrolyte III until the electrolyte turns bright blue. Step S3 is then repeated to repair the unbalanced electrolyte again. The anolyte produced during the repair process can be reused, achieving recycling of the anolyte produced during the repair of the unbalanced electrolyte. The electrolyte of the unbalanced battery can be repaired again, and the method is simple, convenient, and effective.

[0072] Alternatively, when the battery is unbalanced again, steps S1 to S3 can be repeated to repair the unbalanced electrolyte, thereby achieving the restoration of the electrolyte.

[0073] Preferably, the constant current electrolysis is carried out in a repair device, which includes a constant current electrolysis instrument 2, an anode electrolysis chamber 3, a cathode electrolysis chamber 4, a separator 8, an anode electrode structure and a cathode electrode structure, the anode electrode structure is connected to the anode electrolysis chamber 3, the cathode electrode structure is connected to the cathode electrolysis chamber 4, the anode electrode structure and the cathode electrode structure are both connected to the constant current electrolysis instrument 2, and the separator 8 is arranged between the anode electrode structure and the cathode electrode structure.

[0074] The constant current electrolysis instrument 2 can be any instrument capable of achieving constant current electrolysis, such as a charge-discharge instrument, an electrochemical workstation, etc. In a specific embodiment of the present invention, the constant current electrolysis instrument 2 is a charge-discharge instrument.

[0075] The above device can directly repair the unbalanced electrolyte without the need for additional repair devices, further reducing the cost of repairing the electrolyte.

[0076] The anode and cathode electrode structures can each be independently selected from any electrode structure, as long as they can achieve constant-current electrolysis of an unbalanced electrolyte. In one embodiment of the present invention, the anode and cathode electrode structures each independently comprise, from the inside out, an electrode 7, a current collecting plate 6, and an end plate 5. The electrode 7 contacts a separator 8, and the constant-current electrolysis apparatus 2 is connected to the current collecting plate 6. This arrangement of electrode structures improves energy efficiency while ensuring effective repair.

[0077] In one embodiment of the present invention, the anode electrode structure is disposed outside the anode electrolysis chamber 3, and the cathode electrode structure is disposed outside the cathode electrolysis chamber 4. Both ends of the anode electrode structure are connected to the anode electrolysis chamber 3, and both ends of the cathode electrode structure are connected to the cathode electrolysis chamber 4, to achieve circuit circulation. Preferably, a pumping structure 9 is independently disposed between the anode electrode structure and the anode electrolysis chamber 3, and between the cathode electrode structure and the cathode electrolysis chamber 4. This can further improve repair efficiency.

[0078] According to the present invention, the pumping structure 9 can be any structure that can improve the delivery effect, for example, it can be a peristaltic pump.

[0079] In one embodiment of the present invention, the repair device further includes a data acquisition system 1, which is connected to a constant current electrolysis instrument 2 so as to transmit voltage information collected by the constant current electrolysis instrument 2 to the data acquisition system 1 in real time. The data acquisition system 1 then converts the voltage information into a first-order differential of voltage-time in real time, thereby rapidly determining the repair endpoint. This further improves the timeliness of confirming the repair endpoint and enhances the repair effect.

[0080] In a specific real-time mode of the present invention, the repair device also includes a nitrogen supply structure 10, which is connected to the cathode electrolysis chamber 4 so that the cathode electrolysis chamber 4 can be filled with nitrogen so that the cathode electrolysis chamber 4 is in a nitrogen atmosphere, thereby avoiding the divalent metal ions generated during the repair process from being oxidized by air and causing the error in the repair valence state, thereby further improving the repair effect. Preferably, a gas flow meter 11 is also provided between the nitrogen supply structure 10 and the cathode electrolysis chamber 4, which can effectively control the amount of nitrogen entering the cathode electrolysis chamber 4, ensuring the cost while keeping the cathode electrolysis chamber 4 in a nitrogen atmosphere at all times.

[0081] In a specific embodiment of the present invention, the separation membrane 8 is a proton exchange membrane, and the proton exchange membrane can be any membrane that can only achieve proton exchange.

[0082] In addition, the present invention also provides a method for determining the end point of repair of an unbalanced battery electrolyte, comprising: during the process of constant current electrolysis of the unbalanced electrolyte, when a step occurs in the battery terminal voltage and the first-order differential of the terminal voltage is the largest, the repair end point is determined.

[0083] The judgment method provided by the present invention has high accuracy, effectively reduces repair errors, and improves repair quality.

[0084] According to the present invention, the repair device used in the constant current electrolysis process can be the repair device mentioned in the above-mentioned repair method, and the conditions of the constant current electrolysis can be consistent with the conditions in the repair method.

[0085] According to a particularly preferred embodiment of the present invention, a method for repairing an unbalanced battery electrolyte comprises the following steps:

[0086] S1, mixing the positive electrolyte and the negative electrolyte of the unbalanced battery to obtain a mixed electrolyte I; determining the volume of the mixed electrolyte I and recording it as V1; determining the molar concentration of the trivalent cation of vanadium, the molar concentration of the tetravalent cation and the molar concentration of the sulfate ion in the mixed electrolyte I, wherein the molar concentration of the trivalent cation is recorded as c 3价 The molar concentration of tetravalent cations is denoted as c 4价 The molar concentration of sulfate ions is c 酸根离子 ;

[0087] S2. Prepare a pentavalent ion suspension using V2O5, concentrated sulfuric acid and water; wherein the amount of V2O5 is calculated according to formula (I), the amount of concentrated sulfuric acid is calculated according to formula (II), and the amount of water is calculated according to formula (III).

[0088] n 5价 =c 3价 ×V1÷2 formula (I);

[0089] V2=2×n 5价 ×c 酸根离子 ÷(c 4价 +c 3价 )÷V m Formula (II);

[0090] V3=[n 5价 ÷(c 4价 +c 3价 )-V2]×a formula (III);

[0091] Among them, n 5价 is the amount of V2O5, V2 is the volume of concentrated sulfuric acid, V m is the molar concentration of concentrated sulfuric acid added (18.4 mol / L), V3 is the volume of water, and a is the proportional coefficient, with a value of 0.6-0.8;

[0092] S3, the mixed electrolyte I and the pentavalent ion suspension were mixed at a stirring rate of 400-500 r / min for 8-12 min, and then the volume was fixed to 0.99 [V1 + n 5价 ÷(c 4价 +c 3价 )]-1.01[V1+n 5价 ÷(c 4价 +c 3价 )], to obtain a mixed electrolyte II;

[0093] S4, the mixed electrolyte II is divided into two parts, one of which is used as the repair electrode anolyte, and the other is used as the repair electrode catholyte, at 30-60mA / cm 2 Constant current electrolysis is performed at a current density of , and when a step occurs in the battery terminal voltage and the first-order differential of the terminal voltage is the maximum, it is the repair end point; the repair cathode electrolyte obtained by constant current electrolysis is the repaired electrolyte;

[0094] The volume ratio of the repair electrode anolyte to the repair electrode catholyte is 1:2;

[0095] S5. When the battery is unbalanced again, the positive electrolyte and the negative electrolyte of the unbalanced battery are mixed to obtain a mixed electrolyte III. The repaired anode electrolyte obtained in step S4 is added dropwise to the mixed electrolyte III until the electrolyte turns bright blue (see Figure 5 ), continue to repeat step S4 to repair the unbalanced electrolyte again;

[0096] The repair device used in step S4 is as follows: Figure 1As shown, it includes a data acquisition system 1, a constant current electrolysis instrument 2, an anode electrolysis chamber 3, a cathode electrolysis chamber 4, a separator 8, an anode electrode structure, a cathode electrode structure and a nitrogen supply structure 10. The anode electrode structure and the cathode electrode structure each include an electrode 7, a current collecting plate 6 and an end plate 5 from the inside to the outside. The separator 8 is arranged between the two electrodes 7. The anode electrolysis chamber 3 is connected to the electrode 7 of the anode electrode structure, and the cathode electrolysis chamber 4 is connected to the electrode 7 of the cathode electrode structure. The anode electrode structure is arranged outside the anode electrolysis chamber 3, and the cathode electrode structure is arranged outside the cathode electrolysis chamber 4. The anode electrode structure A pumping structure 9 is also provided between the electrodes 7, and between the cathode electrolysis chamber 4 and the electrode 7 of the cathode electrode structure. The current collecting plate 6 of the anode electrode structure and the current collecting plate 6 of the cathode electrode structure are both connected to the constant current electrolysis instrument 2, so that the constant current electrolysis of the entire repair device can be controlled by the constant current electrolysis instrument 2 and the electrolysis information (the potential difference between the two electrodes 7) can be collected. The data receiving end of the data acquisition system 1 is connected to the signal output end of the constant current electrolysis instrument 2 to receive the electrolysis information collected by the constant current electrolysis instrument 2 in real time, and convert it into a time (h)-voltage first-order differential diagram in real time to quickly and accurately determine the electrolysis end point.

[0097] The repair method provided by the preferred embodiment described above can quickly and accurately determine the repair endpoint while repairing the unbalanced battery electrolyte, reducing repair errors, improving repair quality, and thereby increasing the utilization efficiency of the unbalanced battery electrolyte. Furthermore, the repair device used during the repair process is simple, eliminating the need for additional repair equipment, thus reducing costs.

[0098] The present invention is described in detail below through examples. In the following examples, the data acquisition system 1 is a Dell microcomputer; the constant current electrolysis device 2 is a Neware, CT-4008Tn-5V12A; the end plate 5 is a stainless steel end plate with an internal insulating sheet; the current collector 6 is a gold-plated copper plate; the electrode 7 is a 4.6 mm thick carbon felt electrode (GFD 4.6EA, SGL) fixed by a hard graphite plate with a serpentine channel; and the proton exchange membrane 8 is a Nafion membrane (NF-117) from Suzhou Kerun Group. The end plate 5, current collector 6, electrode 7, and proton exchange membrane 8 are sealed using screws, O-rings, and face seals to prevent electrolyte leakage.

[0099] Repair device: such as Figure 1As shown, it includes a data acquisition system 1, a constant current electrolysis instrument 2, an anode electrolysis chamber 3, a cathode electrolysis chamber 4, a separator 8, an anode electrode structure, a cathode electrode structure and a nitrogen supply structure 10. The anode electrode structure and the cathode electrode structure each include an electrode 7, a current collecting plate 6 and an end plate 5 from the inside to the outside. The separator 8 is arranged between the two electrodes 7. The anode electrolysis chamber 3 is connected to the electrode 7 of the anode electrode structure, and the cathode electrolysis chamber 4 is connected to the electrode 7 of the cathode electrode structure. The anode electrode structure is arranged outside the anode electrolysis chamber 3, and the cathode electrode structure is arranged outside the cathode electrolysis chamber 4. The anode electrode structure A pumping structure 9 is also provided between the electrodes 7, and between the cathode electrolysis chamber 4 and the electrode 7 of the cathode electrode structure. The current collecting plate 6 of the anode electrode structure and the current collecting plate 6 of the cathode electrode structure are both connected to the constant current electrolysis instrument 2, so that the constant current electrolysis of the entire repair device can be controlled by the constant current electrolysis instrument 2 and the electrolysis information (the potential difference between the two electrodes 7) can be collected. The data receiving end of the data acquisition system 1 is connected to the signal output end of the constant current electrolysis instrument 2 to receive the electrolysis information collected by the constant current electrolysis instrument 2 in real time, and convert it into a time (h)-voltage first-order differential diagram in real time to quickly and accurately determine the electrolysis end point.

[0100] Example 1

[0101] (1) The unbalanced electrolytes were blended to obtain 100 mL of mixed electrolyte I. The concentrations of sulfate and vanadium ions of different valence states in the mixed electrolyte I were measured by titration, as shown in Table 1.

[0102]

[0103] Table 1 Titration results of vanadium ions of different valence states in mixed electrolyte I

[0104] c(Vanadium (III)) c(vanadium 4) c(total vanadium) 0.7026 0.9974 1.7

[0105] (2) Take 6.389 g of V2O5, 8.984 mL of concentrated sulfuric acid and 22.642 mL of deionized water, dilute the concentrated sulfuric acid first, and then mix the V2O5 with the dilute sulfuric acid to obtain a suspension. The amount of V2O5, the volume of concentrated sulfuric acid and the volume of water are calculated according to formula (I), formula (II) and formula (III), where c 酸0 It is 18.4mol / L, and a is 0.7.

[0106] (3) Suspension II and electrolyte I were mixed and stirred at a stirring speed of 200 r / min. After mixing, the suspension became a solution and the volume was fixed to 141.329 mL with deionized water (according to V1+n 5价 ÷(c 4价 +c 3价 ) is calculated), which is the mixed electrolyte II.

[0107] (4) Divide 141.329 mL of mixed electrolyte II into three equal parts by volume, place one part in the anode electrolysis chamber 3 of the above-mentioned repair device, and place two parts in the cathode electrolysis chamber 4 of the above-mentioned repair device;

[0108] (5) At 60 mA / cm 2 Repair is performed under the current density, and the terminal voltage of the repair device is recorded by the data acquisition system 1. When the terminal voltage of the repair device jumps and the first-order differential of the terminal voltage is the largest, the repair reaches the end point. Figure 2 The cathode electrolyte obtained by repair is the repair electrolyte, which can be injected into the cathode and anode of the battery for reuse.

[0109] Test Example 1

[0110] The cathode electrolyte after the electrolysis of Example 1 was subjected to UV-visible spectroscopy analysis to obtain Figure 3 .Depend on Figure 3 It can be seen that there is an absorption peak of tetravalent vanadium ions at around 780nm, and absorption peaks of trivalent vanadium ions at around 600nm and 400nm, proving the presence of trivalent and tetravalent vanadium ions in the solution. Although it is difficult to accurately measure pentavalent and divalent vanadium ions using UV-visible spectroscopy, trivalent and pentavalent vanadium ions cannot coexist in the same solution, and tetravalent and divalent vanadium ions cannot coexist. Therefore, it can be determined that trivalent and tetravalent vanadium ions are present in the repaired electrolyte, but not pentavalent vanadium ions, indicating that the repair method provided by this method can accurately determine the repair endpoint and improve the repair effect.

[0111] Test Example 2

[0112] The concentrations of trivalent vanadium ions and tetravalent vanadium ions in the cathode electrolyte after the electrolysis of Example 1 were titrated using an automatic potentiometric titrator to obtain the values ​​shown in Table 2.

[0113] Table 2 Catholyte titration results

[0114] c(trivalent vanadium ion) c(quaternary vanadium ion) c(trivalent vanadium ion):c(quaternary vanadium ion) 0.8486 0.8514 0.9967

[0115] As can be seen from Table 2, c(trivalent vanadium ion):c(quaternary vanadium ion)=0.9967, which is in line with the national standard GB / T37204-2018 that the ratio of trivalent and quadrivalent vanadium ions in 3.5-valent electrolyte is 1±0.1, indicating that the repair method provided by this method can accurately determine the repair endpoint and improve the repair effect.

[0116] Test Example 3

[0117] Cyclic voltammetry was performed on the unbalanced electrolyte and the repaired electrolyte (the cathode electrolyte after electrolysis in Example 1) at 0-1.7 V and a scan rate of 40 mV / s in the same three-electrode system, and the results were as follows: Figure 4 .

[0118] Depend on Figure 4 It can be seen that after the electrolyte was repaired, the oxidation peak current density and reduction peak current density increased, indicating an increase in the electrolyte's electrochemical activity; the area of ​​the redox peak increased, indicating an increase in the electrochemical reaction capacity in the electrolyte; and the difference in the height of the oxidation peak and reduction peak decreased, indicating a significant improvement in the reversibility of the electrolyte. Therefore, compared to the unbalanced electrolyte, the electrochemical activity, electrochemical reaction capacity, and reversibility of the repaired electrolyte were significantly increased, demonstrating the feasibility of this repair method.

[0119] Example 2

[0120] (1) The repaired electrolyte obtained in step (5) of Example 1 was re-imbalanced to obtain an unbalanced electrolyte and mixed to obtain 80 mL of mixed electrolyte III;

[0121] (2) The anolyte obtained in step (5) of Example 1 was slowly added dropwise to the mixed electrolyte III and stirred continuously on a magnetic stirrer until the electrolyte turned bright blue. Figure 5 ;

[0122] (3) The electrolyte is divided into three parts, one part is placed in the anode electrolysis chamber 3 of the above-mentioned repair device, and the other two parts are placed in the cathode electrolysis chamber 4 of the above-mentioned repair device;

[0123] (4) At 60 mA / cm 2 Repair is performed at a constant current density while the terminal voltage of the repair device is recorded by the data acquisition system 1. When the terminal voltage of the repair device experiences a step change and the first-order differential of the terminal voltage is maximized, the repair has reached the end point. The catholyte obtained from the repair is the repair electrolyte and can be injected into the cathode and anode of the battery for reuse.

[0124] Test Example 4

[0125] The bright blue electrolyte in step (2) of Example 2 was subjected to UV-visible spectroscopy and automatic potentiometric titration to analyze the vanadium ion composition and valence state in the bright blue electrolyte, and the obtained Figure 6 and Table 3. Figure 6It can be seen that there are no absorption peaks for trivalent vanadium ions at around 600nm and 400nm, while there is an absorption peak for tetravalent vanadium ions at around 780nm. Trivalent vanadium ions are absent in the electrolyte, and a pentavalent vanadium ion absorption peak appears in the 200-300nm range. Therefore, only tetravalent and pentavalent vanadium ions are present in the electrolyte. Based on this conclusion, the bright blue electrolyte was subjected to automatic potentiometric titration, yielding the results in Table 3. The automatic potentiometric titration instrument was a Leici ZDJ-4B automatic potentiometric titrator. The pentavalent vanadium ion concentration was titrated using ammonium ferrous sulfate. The minimum volume per drop of ammonium ferrous sulfate was 0.01mL. From the start of the titration to the potential step, the potential was around half a drop of ammonium ferrous sulfate solution. Therefore, the tetravalent vanadium ion content in the solution was >99.5%. It can be concluded that the tetravalent vanadium ion purity in this electrolyte is high, and it is essentially a pure tetravalent electrolyte.

[0126] Table 3

[0127] c(quaternary vanadium ion) c(pentavalent vanadium ion) Content of tetravalent vanadium ions >1.67 <0.01 >99.5％

[0128] Test Example 5

[0129] The cathode electrolyte after the electrolysis of Example 2 was subjected to UV-visible spectroscopy analysis to obtain Figure 7 .Depend on Figure 7 It can be seen that there is an absorption peak of tetravalent vanadium ions at around 780nm, and absorption peaks of trivalent vanadium ions at around 600nm and 400nm, proving the presence of trivalent and tetravalent vanadium ions in the solution. Although it is difficult to accurately measure pentavalent and divalent vanadium ions using UV-visible spectroscopy, trivalent and pentavalent vanadium ions cannot coexist in the same solution, and tetravalent and divalent vanadium ions cannot coexist. Therefore, it can be determined that trivalent and tetravalent vanadium ions are present in the repaired electrolyte, but not pentavalent vanadium ions, indicating that the repair method provided by this method can accurately determine the repair endpoint and improve the repair effect.

[0130] Test Example 6

[0131] The concentrations of trivalent vanadium ions and tetravalent vanadium ions in the cathode electrolyte after the electrolysis of Example 2 were titrated using an automatic potentiometric titrator to obtain the values ​​shown in Table 4.

[0132] Table 4

[0133] c(trivalent vanadium ion) c(quaternary vanadium ion) c(trivalent vanadium ion):c(quaternary vanadium ion) 0.8352 0.8448 0.9886

[0134] As shown in Table 4, c(trivalent vanadium ion):c(quaternary vanadium ion)=0.9886, which is in line with the national standard GB / T37204-2018 that the ratio of trivalent and quadrivalent vanadium ions in 3.5-valent electrolyte is 1±0.1, indicating that the repair method provided by this method can accurately determine the repair endpoint and improve the repair effect.

[0135] Test Example 7

[0136] Cyclic voltammetry was performed on the unbalanced electrolyte and the repaired electrolyte (the cathode electrolyte after electrolysis in Example 2) at 0-1.7 V and a scan rate of 40 mV / s in the same three-electrode system, and the results were as follows: Figure 8 .

[0137] Depend on Figure 8 It can be seen that after the electrolyte was repaired, the oxidation peak current density and reduction peak current density increased, indicating an increase in the electrolyte's electrochemical activity; the area of ​​the redox peak increased, indicating an increase in the electrochemical reaction capacity in the electrolyte; and the difference in the height of the oxidation peak and reduction peak decreased, indicating a significant improvement in the reversibility of the electrolyte. Therefore, compared to the unbalanced electrolyte, the electrochemical activity, electrochemical reaction capacity, and reversibility of the repaired electrolyte were significantly increased, demonstrating the feasibility of this repair method.

[0138] Example 3

[0139] (1) The unbalanced electrolytes were blended to obtain 200 mL of mixed electrolyte I. The concentrations of sulfate and vanadium ions of different valence states in the mixed electrolyte I were measured by titration, as shown in Table 5.

[0140]

[0141] Table 5 Titration results of vanadium ions of different valence states in mixed electrolyte I

[0142] c(Vanadium (III)) c(vanadium 4) c(total vanadium) 0.6052 0.8948 1.5000

[0143] (2) Take 11.007 g of V2O5, 13.156 mL of concentrated sulfuric acid, and 40.522 mL of deionized water. Dilute the concentrated sulfuric acid first, then mix the V2O5 with the dilute sulfuric acid to obtain a suspension. The amount of V2O5, the volume of concentrated sulfuric acid, and the volume of water are calculated according to formula (I), formula (II), and formula (III), where c 酸0 It is 18.4mol / L, and a is 0.6.

[0144] (3) Suspension II and electrolyte I were mixed and stirred at a stirring speed of 400 r / min. After mixing, the suspension became a solution and the volume was fixed to 280.693 mL with deionized water (according to V1+n 5价 ÷(c 4价 +c 3价 ) is calculated), which is the mixed electrolyte II.

[0145] (4) Divide 280.693 mL of the mixed electrolyte II into two portions at a volume ratio of 1:2, place the smaller portion in the anode electrolysis chamber 3 of the above-mentioned repair device, and place the larger portion in the cathode electrolysis chamber 4 of the above-mentioned repair device;

[0146] (5) At 45 mA / cm2 Repair is performed at a constant current density while the terminal voltage of the repair device is recorded by the data acquisition system 1. When the terminal voltage of the repair device experiences a step change and the first-order differential of the terminal voltage is maximized, the repair has reached the end point. The catholyte obtained from the repair is the repair electrolyte and can be injected into the cathode and anode of the battery for reuse.

[0147] Example 4

[0148] (1) The unbalanced electrolytes were blended to obtain 100 mL of mixed electrolyte I. The concentrations of sulfate and vanadium ions of different valence states in the mixed electrolyte I were measured by titration, as shown in Table 6.

[0149]

[0150] Table 6 Titration results of vanadium ions of different valence states in mixed electrolyte I

[0151] c(Vanadium (III)) c(vanadium 4) c(total vanadium) 0.6908 0.8326 1.5234

[0152] (2) Take 6.282 g of V2O5, 9.858 mL of concentrated sulfuric acid and 28.390 mL of deionized water, dilute the concentrated sulfuric acid first, and then mix the V2O5 with the dilute sulfuric acid to obtain a suspension. The amount of V2O5, the volume of concentrated sulfuric acid and the volume of water are calculated according to formula (I), formula (II) and formula (III), where c 酸0 It is 18.4mol / L, and a is 0.8.

[0153] (3) Suspension II and electrolyte I were mixed and stirred at a stirring speed of 500 r / min. After mixing, the suspension became a solution and the volume was fixed to 145.346 mL with deionized water (according to V1+n 5价 ÷(c 4价 +c 3价 ) is calculated), which is the mixed electrolyte II.

[0154] (4) Divide 145.346 mL of mixed electrolyte II into two portions at a volume ratio of 1:2, place the smaller portion in the anode electrolysis chamber 3 of the above-mentioned repair device, and place the larger portion in the cathode electrolysis chamber 4 of the above-mentioned repair device;

[0155] (5) At 30 mA / cm 2 Repair is performed at a constant current density while the voltage at the repair device terminal is recorded by the data acquisition system 1. When the voltage at the repair device terminal jumps and the first-order differential of the terminal voltage reaches a maximum, the repair has reached its endpoint. The catholyte obtained from the repair is the repair electrolyte and can be injected into the battery's cathode and anode for reuse.

[0156] After the electrolysis was completed, the cathode electrolytes of Example 3 and Example 4 were tested, and both met the national standard GB / T37204-2018, which stated that the ratio of trivalent and tetravalent vanadium ions in the 3.5-valent electrolyte was 1±0.1.

[0157] Experimental example

[0158] Using 1.6 mol / L tetravalent vanadium electrolyte as raw material, 100 mL of 1.6 mol / L V 3.5+ Electrolyte, the electrolysis end point is determined by controlling the electrolysis time and voltage step as the end point.

[0159] Take controlling the electrolysis time as an example:

[0160] Electrolysis time calculation: t = V × c × F ÷ 2 ÷ I ÷ η, where V is V 3.5+ The volume of the electrolyte is in L, c is the electrolyte concentration in mol / L, F is the Faraday constant: 96485, in C, I is the electrolysis current in A, and η is the Coulomb efficiency, which is generally 0.94-0.99;

[0161] If electrolysis is carried out at a current density of 0.36 A and the coulombic efficiency is 0.95, then t = 0.1 × 1.6 × 96485 ÷ 2 ÷ 0.36 ÷ 0.95 = 22569.59 s;

[0162] After the electrolysis was completed, the concentration and content of trivalent vanadium ions and tetravalent vanadium ions in the electrolyte were titrated using automatic potentiometric titration. The results are shown in Table 7.

[0163] Table 7

[0164] c(Vanadium (III)) c(vanadium 4) c(total vanadium) 0.8421 0.7571 1.5992

[0165] c(trivalent vanadium ion):c(quaternary vanadium ion)=1.1122, which does not meet the national standard GB / T 37204-2018 that the ratio of trivalent and quadrivalent vanadium ions in 3.5-valent electrolyte is 1±0.1. There are quality problems with the electrolyte.

[0166] Determine the electrolysis endpoint by voltage step:

[0167] Place 50 mL of IV electrolyte at the anode and 100 mL at the cathode. The repair endpoint is when the battery terminal voltage undergoes a step and the first-order differential of the terminal voltage is the largest.

[0168] After the electrolysis was completed, the concentration and content of trivalent vanadium ions and tetravalent vanadium ions in the electrolyte were titrated using automatic potentiometric titration. The results are shown in Table 8.

[0169] Table 8

[0170] c(Vanadium (III)) c(vanadium 4) c(total vanadium) 0.8011 0.8012 1.6023

[0171] c(trivalent vanadium ion):c(quaternary vanadium ion)=0.9999, which is in line with the national standard GB / T 37204-2018 that the ratio of trivalent and quadrivalent vanadium ions in 3.5-valent electrolyte is 1±0.1.

[0172] When controlling the electrolysis time to prepare the electrolyte, there is a problem of unstable Coulomb efficiency. Although it is generally taken as 0.94-0.99, a slight deviation will cause the electrolysis time to deviate too much, and the preparation endpoint is difficult to control. The voltage step control is based on the principle that the electrode potential is different when the vanadium ions in the electrolyte undergo different reactions. The voltage step actually reflects the change in the reaction occurring in the electrolyte in the anode tank, and can reflect the state of the electrolyte in the anode tank in real time. It can avoid the problem of difficult to control the electrolysis time due to unstable Coulomb efficiency, accurately control the repair endpoint and improve the repair efficiency.

[0173] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for repairing an unbalanced battery electrolyte, characterized in that: The steps include: S1. Mixing the positive electrolyte and the negative electrolyte of the unbalanced battery to obtain a mixed electrolyte I; determining the volume of the mixed electrolyte I and recording it as V1; Determine the molar concentration of trivalent cations of vanadium, the molar concentration of tetravalent cations of vanadium and the molar concentration of sulfate ions in the mixed electrolyte I, wherein the molar concentration of trivalent cations of vanadium is denoted as c 3价 The molar concentration of the tetravalent cation of vanadium is denoted as c 4价 The molar concentration of sulfate ions is c 酸根离子 ; Mix V2O5, sulfuric acid solution and water to obtain a pentavalent ion suspension; the amount of V2O5 is calculated according to formula (I), and the amount of sulfuric acid solution is calculated according to formula (II). n 5价 =c 3价 ×V1÷2 formula (I); V2=2×n 5价 ×c 酸根离子 ÷(c 4价 +c 3价 )÷V m Formula (II); Among them, n 5价 is the amount of V2O5, V2 is the volume of sulfuric acid solution, V m is the volume molar concentration of sulfuric acid solution; The amount of water is calculated according to formula (III), V3=[n 5价 ÷(c 4价 +c 3价 )-V2]×a formula (III); Where V3 is the volume of water, a is the proportional coefficient, which is 0.6-0.8; S2, mixing the mixed electrolyte I and the pentavalent ion suspension to obtain a mixed electrolyte II; S3. Divide the mixed electrolyte II into two parts, one of which is used as the repair anode electrolyte and the other as the repair cathode electrolyte, and perform constant current electrolysis. When the battery terminal voltage has a step and the first-order differential of the terminal voltage is the largest, it is the end point of the repair.

2. The repair method according to claim 1, characterized in that: The step S2 further comprises fixing the volume of the mixed solution after the mixing is completed so that the volume of the mixed solution is 0.99[V1+n 5价 ÷(c 4价 +c 3价 )]-1.01[V1+n 5价 ÷(c 4价 +c 3价 )].

3. The repair method according to claim 2, characterized in that: In step S2, the mixing conditions at least include: a stirring rate of 200-500 r / min.

4. The repair method according to any one of claims 1 to 3, characterized in that: In step S3, the volume ratio of the repair anode electrolyte to the repair cathode electrolyte is 1:

2.

5. The repair method according to claim 4, characterized in that: The conditions of the constant current electrolysis include: a current density of 30-60 mA / cm 2 .

6. The repair method according to any one of claims 1 to 3, characterized in that: The constant current electrolysis is carried out in a repair device, which includes a constant current electrolysis instrument (2), an anode electrolysis chamber (3), a cathode electrolysis chamber (4), a separator (8), an anode electrode structure and a cathode electrode structure, wherein the anode electrode structure is connected to the anode electrolysis chamber (3), the cathode electrode structure is connected to the cathode electrolysis chamber (4), the anode electrode structure and the cathode electrode structure are both connected to the constant current electrolysis instrument (2), and the separator (8) is arranged between the anode electrode structure and the cathode electrode structure.

7. The repair method according to claim 6, characterized in that: The anode electrode structure and the cathode electrode structure independently include an electrode (7), a current collecting plate (6) and an end plate (5) in sequence from the inside to the outside, the electrode (7) is in contact with the separator (8), and the constant current electrolysis instrument (2) is connected to the current collecting plate (6); and / or, The anode electrode structure is arranged outside the anode electrolysis chamber (3), and the cathode electrode structure is arranged outside the cathode electrolysis chamber (4).

8. The repair method according to claim 6, characterized in that: The repair device further comprises a data acquisition system (1) and a nitrogen supply structure (10), wherein the data acquisition system (1) is connected to the constant current electrolysis instrument (2), and the nitrogen supply structure (10) is connected to the cathode electrolysis chamber (4).

9. The repair method according to claim 6, characterized in that: The battery terminal voltage is the potential difference between the anode electrode structure and the cathode electrode structure.

10. The repair method according to any one of claims 1 to 3, characterized in that: The repaired cathode electrolyte obtained in step S3 is the repaired electrolyte; When the battery is unbalanced again, the positive electrolyte and the negative electrolyte of the unbalanced battery are mixed to obtain a mixed electrolyte III; the repaired anode electrolyte obtained in step S3 is added dropwise to the mixed electrolyte III until the electrolyte turns bright blue, and step S3 is repeated to repair the unbalanced electrolyte again; or, When the battery becomes unbalanced again, steps S1 to S3 are repeated to repair the unbalanced electrolyte.

11. A method for determining the end point of electrolyte repair in an unbalanced battery, characterized in that: include: During the constant current electrolysis of the unbalanced electrolyte as claimed in any one of claims 1 to 10, when a step occurs in the terminal voltage of the battery and the first-order differential of the terminal voltage is maximized, the repair endpoint is reached.

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