Iron-chromium flow battery electrolyte and recovery method thereof

Abstract

The invention provides an iron-chromium flow battery electrolyte and a recovery method thereof. A positive electrode electrolyte of the iron-chromium flow battery electrolyte contains iron ions, chromium ions, a supporting electrolyte and recovery ions; the negative electrode electrolyte contains iron ions, chromium ions and supporting electrolyte; the recovery ions are one or more of vanadium ions, manganese ions, bromide ions and cobalt ions. The recovery method of the electrolyte of the iron-chromium flow battery comprises the following steps: charging the battery until recovery ions in a positive electrode electrolyte reach an oxidation state, and adding a reducing agent to reduce the recovery ions to a reduction state; and continuously charging, continuously monitoring the valence states and the concentrations of iron ions and chromium ions in the positive electrode electrolyte and the negative electrode electrolyte, and finishing recovery when the positive electrode electrolyte and the negative electrode electrolyte are recovered to an initial test state. The iron-chromium flow battery electrolyte is scientific and reasonable in composition, and the electrolyte can utilize high reaction potential of recovery ions to realize chemical reduction, namely recovery of the electrolyte; the recovery process has no residue, and does not affect the performance of the battery.

Description

Technical Field

[0001] The invention relates to liquid flow battery technology, and in particular to an iron-chromium liquid flow battery electrolyte and a recovery method thereof. Background Art

[0002] Due to the high hydrogen evolution rate of chromium, liquid flow batteries using chromium as the negative electrode active material decay rapidly, which is manifested as continuous hydrogen evolution at the negative electrode and a continuous increase in the valence of ions in the positive electrode electrolyte. This leads to a gradual decrease in the concentration of active ions that can play a role in the battery, severely limiting the commercialization of such liquid flow batteries.

[0003] Usually, after the capacity of a flow battery is lost, reducing substances can be added to the positive electrode to reduce the active ions of the positive electrode to achieve recovery. However, for batteries with iron ions as the positive electrode reaction, the redox potential of iron ions is low, and it is difficult to completely oxidize organic reducing substances. After the reaction is completed, a large amount of organic matter remains in the positive electrode solution, which damages the performance of the battery, which is manifested in a decrease in the battery's voltage efficiency and severe battery polarization.

[0004] The recovery methods of iron-chromium flow batteries that have been reported so far include the commonly used indirect reduction method, (1) using a solution containing ferrous ions as the anode, and using the positive or negative electrode in the iron-chromium battery as the cathode, and reducing the valence state of the electrolyte of the iron-chromium battery by electrolysis to achieve the purpose of recovery. In essence, this is to replace the trivalent ferrous ions in the iron-chromium battery with new ferrous ions, thereby achieving battery recovery. Therefore, it is not economical in the industrialization process. Because the recovery process will produce a large amount of trivalent ferrous solution, it cannot be processed on-site at the project site and needs to be transported to a third party for the treatment of the trivalent ferrous ion solution. (2) Using the electrolyte of a vanadium battery as the anode and the electrolyte of an iron-chromium battery as the cathode, the valence state of the iron-chromium electrolyte is reduced by electrolysis, and then a reducing agent is added to the oxidized vanadium electrolyte to restore it to its initial state. Although this method can achieve the recovery of the iron-chromium electrolyte, it can also be continuously cycled. However, vanadium ions will continue to enter the iron-chromium electrolyte through the diaphragm of the electrolytic cell, resulting in the loss of vanadium. In addition, a system for electrolytic reduction and recovery needs to be built, which requires complex equipment and huge investment. Summary of the invention

[0005] The purpose of the present invention is to propose an electrolyte for an iron-chromium liquid flow battery in view of the many problems existing in the recovery of the current iron-chromium liquid flow battery. The electrolyte has a scientific and reasonable composition and can utilize the high reaction potential of the recovery ions to achieve chemical reduction, that is, to achieve electrolyte recovery. The recovery process has no residue and does not affect the performance of the battery.

[0006] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0007] To achieve the above object, the technical solution adopted by the present invention is: an iron-chromium liquid flow battery electrolyte, including a positive electrode electrolyte and a negative electrode electrolyte; the positive electrode electrolyte contains iron ions, chromium ions, a supporting electrolyte and recovery ions; the negative electrode electrolyte contains iron ions, chromium ions and a supporting electrolyte;

[0008] The restoring ions are vanadium ions (VO 2+ ), manganese ion (Mn 2+ ), bromide ion (Br - ) and cobalt ions (Co 2+ )

[0009] Furthermore, the recovery ion concentration in the positive electrode electrolyte is 0.2-3M.

[0010] Furthermore, the restoring ions are preferably vanadium ions, and the preferred concentration is 0.5-2M.

[0011] Furthermore, the restoring ions are preferably manganese ions, and the preferred concentration is 0.51-2M.

[0012] Furthermore, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, wherein the concentration is 0.1 to 3M, preferably 0.3 to 2M, measured as hydrogen ions.

[0013] Furthermore, the concentration of the iron ions is 0.5-2M, and the concentration of the chromium ions is 0.5-2M.

[0014] Another object of the present invention is to disclose an iron-chromium liquid flow battery, comprising a positive electrode, a separator, a negative electrode and the iron-chromium liquid flow battery electrolyte.

[0015] Another object of the present invention is to disclose a method for preparing an iron-chromium liquid flow battery electrolyte, comprising the following steps: positive electrode electrolyte: mixing an iron source, a chromium source, a supporting electrolyte and a recovery ion source; negative electrode electrolyte: mixing an iron source, a chromium source and a supporting electrolyte recovery ion source.

[0016] Furthermore, the recovery ion source is one or more of ammonium metavanadate (AMV), V2O4, V2O3, V2O5, VCl3, VOCl2, VOSO4, V2(SO4)3, manganese sulfate (MnSO4), manganese chloride (MnCl2), manganese phosphate, MnO, hydrobromic acid, bromine water, cobalt sulfate and cobalt chloride.

[0017] Furthermore, the iron source is one or more of ferrous sulfate, ferrous chloride, iron powder, ferrochromium alloy, ferrous oxide FeO and ferric oxide Fe2O3.

[0018] Furthermore, the chromium source is one or more of chromium trichloride CrCl3, iron-chromium alloy and chromium sulfate CrSO4.

[0019] Furthermore, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid.

[0020] Another object of the present invention is to disclose a recovery method of an iron-chromium flow battery, comprising the following steps:

[0021] Step 1, charging the battery until the recovery ions in the positive electrode electrolyte reach an oxidized state;

[0022] Step 2, adding a reducing agent to the positive electrode electrolyte to restore the recovery ions to a reduced state. If the recovery reaches the initial capacity of the battery, the recovery is terminated, otherwise, returning to step 1;

[0023] Further, when the unbalanced capacity of the battery decays to 70-90% (preferably 80%) of the initial capacity, recovery begins and the process enters step 1.

[0024] Furthermore, the average current density of the recovery process is 50-200 mA / cm 2 .

[0025] Furthermore, when the restoring ion is a vanadium ion, its oxidation state is a pentavalent vanadium ion VO2 + , its reduced state is tetravalent vanadium ion VO 2+ When the recovery ion is a manganese ion, its oxidation state is Mn 3+ , its reduced state is Mn 2+ When the recovery ion is a bromide ion, its oxidation state is Br 2+ , its reduced state is Br - When the recovery ion is a cobalt ion, its oxidation state is Co 3+ , its reduced state is Co 2+ .

[0026] Furthermore, the reducing agent is one or more of formaldehyde, formic acid, acetic acid, citric acid, glucose, fructose, tartaric acid and vitamin C.

[0027] Furthermore, the amount of the reducing agent added is 1 to 1.2 times the stoichiometric amount corresponding to the required amount of restored electricity.

[0028] Taking glucose as the reducing agent as an example, the theoretical chemical reduction coefficient is 24 mol electrons / mol. If the battery recovers 2 Ah of charging time, the required glucose is：

[0029] 2 / 96485*3600 / 24*180.156*1=0.56g.

[0030] The working principle of the recovery method of the iron-chromium liquid flow battery of the present invention is as follows, taking manganese ions as the recovery ions:

[0031] When the battery is operating normally, the charge and discharge cut-off voltage is controlled so that the positive electrode only utilizes the conversion between divalent iron and trivalent iron, while the manganese ions always remain divalent. The charge cut-off voltage in this process is usually around 1.2V.

[0032] When the battery unbalanced capacity decays to 80% of the initial capacity, recovery operations are required:

[0033] 1. When charging to a cut-off voltage of about 2V, the reaction of converting divalent iron into trivalent iron first occurs at the positive electrode of the battery. At this time, a potential jump occurs, and the reaction of converting divalent manganese into trivalent manganese occurs at the positive electrode; during the recovery process, the reduction reaction of trivalent chromium to divalent chromium ions occurs at the negative electrode;

[0034] 2. Add a reducing agent to the positive electrolyte to reduce the trivalent manganese ions to divalent manganese ions;

[0035] 3. Repeat steps 1-2 until the battery capacity is restored.

[0036] The iron-chromium liquid flow battery electrolyte and the recovery method thereof of the present invention have the following advantages compared with the prior art:

[0037] 1) The electrolyte of the iron-chromium liquid flow battery of the present invention contains recovery ions, and the battery can be independently recovered by the battery itself without the need for an external recovery device;

[0038] 2) The method for recovering the electrolyte of the iron-chromium liquid flow battery of the present invention utilizes the high reaction potential of the recovery ions to achieve chemical reduction, that is, to achieve electrolyte recovery, and the recovery process has no residue and does not affect the performance of the battery;

[0039] The iron-chromium liquid flow battery electrolyte of the present invention has good application prospects and large-scale production potential in the field of liquid flow batteries. DETAILED DESCRIPTION

[0040] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0041] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0042] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0043] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0044] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0045] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0046] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0047] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0048] Example 1

[0049] This embodiment discloses an iron-chromium flow battery electrolyte and a recovery method:

[0050] The iron-chromium liquid flow battery electrolyte comprises:

[0051] 100ml positive electrolyte, Fe 2+ 1.5M, Mn 2+ 0.6M,Cr 3+ 0.8M, Cl - 7M, SO4 2- 0.6M, H3PO4 0.2M;

[0052] 100ml negative electrolyte, Fe 2+ 0.8M, Mn 2+ 0.6M,Cr 3+ 1.5M, Cl - 7M, SO4 2- 0.6M, H3PO4 0.2M;

[0053] During the charge and discharge process of the iron-chromium flow battery, the average current density is 100 mA / cm 2, charge and discharge cut-off voltage 0.6V-1.2V, constant power 5W continuous charge and discharge, initial charge and discharge capacity is 3Ah, cycle until the capacity decays to below 2.5Ah, restore the battery, the recovery method is as follows:

[0054] 1. Charge according to the charging strategy to a cut-off voltage of 1.2V to convert the divalent iron in the electrolyte into trivalent iron;

[0055] Continue constant current 150mA / cm 2 After charging for 0.5 Ah, the divalent manganese at the positive electrode is oxidized to trivalent manganese, and the chromium at the negative electrode is further reduced.

[0056] 2. Add 0.15 g fructose to the cathode solution and stir at 50 °C for 8 h;

[0057] The battery capacity is restored to 3Ah;

[0058] In this embodiment, since the amount of manganese ions exceeds the ampere-hour capacity that needs to be restored, the cycle recovery operation is not performed.

[0059] Example 2

[0060] This embodiment discloses an iron-chromium liquid flow battery electrolyte and a recovery method.

[0061] The iron-chromium flow battery electrolyte comprises: 100 ml of positive electrode electrolyte, Fe 2+ 1.8MCo 2+ 0.3M,Cr 3+ 1.1M, Cl - 2.5M, SO4 2- 2.8M;

[0062] 100ml negative electrolyte, Fe 2+ 1M,Co 2+ 0.3M,Cr 3+ 1.8M, Cl - 2.5M, SO4 2- 3M;

[0063] During the charge and discharge process of the iron-chromium flow battery, the average current density is 80 mA / cm 2 , the charge and discharge cut-off voltage is 0.65V-1.18V, the constant power is 10W, the initial charge and discharge capacity is 3.5Ah, and the cycle is performed until the capacity decays to below 2.8Ah, and the battery is restored. The recovery method is as follows:

[0064] 1. Charge according to the charging strategy to a cut-off voltage of 1.18V to convert the divalent iron in the electrolyte into trivalent iron;

[0065] Continue constant current 120mA / cm2 After charging for 0.8 Ah, the cobalt ions at the positive electrode are oxidized to pentavalent, and the chromium at the negative electrode is further reduced.

[0066] 2. Add 0.25 g of glucose to the cathode solution and stir at 55 °C for 10 h to reduce the cobalt ions back to tetravalent;

[0067] The battery capacity is restored and the valence state of vanadium returns to its initial state.

[0068] Example 3

[0069] This embodiment discloses an iron-chromium liquid flow battery electrolyte and a recovery method.

[0070] The iron-chromium liquid flow battery electrolyte comprises:

[0071] 100ml positive electrolyte, Fe 2+ 1.2M, VO 2+ 1M,Cr 3+ 0.6M, Cl - 7M, PO4 3- 0.2M;

[0072] 100ml negative electrolyte, Fe 2+ 0.6M, VO 2+ 0.4M,Cr 3+ 1.5M, Cl - 7M, PO4 3- 0.2M;

[0073] During the charge and discharge process of the iron-chromium flow battery, the average current density is 150 mA / cm 2 , the charge and discharge cut-off voltage is 0.65V-1.21V, the constant power is 15W, the initial charge and discharge capacity is 6Ah, and the cycle is performed until the capacity decays to below 4.2Ah, and the battery is restored. The recovery method is as follows:

[0074] 1. Charge according to the charging strategy to a cut-off voltage of 1.21V, so that the divalent iron in the electrolyte is converted into trivalent iron;

[0075] 2. Continue with constant current of 100mA / cm 2 , charged for 1Ah, at this time, the tetravalent vanadium in the positive electrode is partially oxidized to pentavalent, and the chromium in the negative electrode is further reduced, and the capacity is restored to 5.2Ah;

[0076] 3. Add 0.45g of citric acid to the positive electrode solution, stir and react at 60℃ for 15h to reduce pentavalent vanadium to tetravalent vanadium;

[0077] 4. Continue charging for 0.8Ah. At this time, the tetravalent vanadium in the positive electrode is partially oxidized to pentavalent, and the chromium in the negative electrode is further reduced.

[0078] 5. Add 0.35 g of citric acid to the cathode solution and stir at 60°C for 15 h to reduce pentavalent vanadium to tetravalent vanadium;

[0079] The battery capacity is restored and the valence state of vanadium returns to its initial state.

[0080] Comparative Example 1

[0081] This comparative example discloses an iron-chromium liquid flow battery electrolyte and a recovery method

[0082] The iron-chromium flow battery electrolyte comprises: 100 ml of positive electrode electrolyte, Fe 2+ 1.5M, Mn 2+ 0.2M,Cr 3+ 0.8M, Cl - 7M, SO4 2- 0.6M;

[0083] 100ml negative electrolyte, Fe 2+ 0.8M, Mn 2+ 0.2M,Cr 3+ 1.5M, Cl - 7M, SO4 2- 0.6M;

[0084] During the charge and discharge process of the iron-chromium flow battery, the average current density is 100 mA / cm 2 , charge and discharge cut-off voltage 0.6V-1.2V, constant power 5W continuous charge and discharge, initial charge and discharge capacity is 3Ah, cycle until the capacity decays to below 2.5Ah, restore the battery, the recovery method is as follows:

[0085] 1. Charge according to the charging strategy to convert the divalent iron in the electrolyte into trivalent iron;

[0086] Continue charging for 0.5Ah, at which time the divalent manganese at the positive electrode is oxidized to trivalent, and the chromium at the negative electrode is further reduced;

[0087] 2. Add 0.15 g fructose to the cathode solution and stir at 50 °C for 8 h;

[0088] The battery capacity only reached 2.8Ah when the heavy discharge cycle was continued, and bubbles appeared in the positive electrode solution during the charging process, causing the battery to be unable to be fully charged;

[0089] Compared with Example 1, in Comparative Example 1, due to the lower manganese concentration in the positive electrode solution, the reduction reaction of fructose added after charging was not sufficient, and more trivalent manganese and fructose remained in the solution, and the capacity of the battery was not fully restored.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An iron-chromium flow battery electrolyte, characterized in that: It comprises a positive electrode electrolyte and a negative electrode electrolyte; the positive electrode electrolyte contains iron ions, chromium ions, a supporting electrolyte and recovery ions; the negative electrode electrolyte contains iron ions, chromium ions and a supporting electrolyte; The restoring ions are one or more of vanadium ions, manganese ions, bromide ions and cobalt ions.

2. The iron-chromium flow battery electrolyte according to claim 1, characterized in that: The recovery ion concentration in the positive electrode electrolyte is 0.2-3M.

3. The iron-chromium flow battery electrolyte according to claim 1, characterized in that: The supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid; And / or, the concentration of the iron ions is 0.5-2M, and the concentration of the chromium ions is 0.5-2M.

4. An iron-chromium flow battery, characterized in that: The invention comprises a positive electrode, a separator, a negative electrode and the iron-chromium liquid flow battery electrolyte according to any one of claims 1 to 3.

5. A method for preparing an electrolyte for an iron-chromium flow battery according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: positive electrode electrolyte: mixing an iron source, a chromium source, a supporting electrolyte and a recovery ion source; negative electrode electrolyte: mixing an iron source, a chromium source and a supporting electrolyte recovery ion source.

6. The method for preparing the electrolyte of the iron-chromium flow battery according to claim 5, characterized in that: The recovery ion source is one or more of ammonium metavanadate, V2O4, V2O3, V2O5, VCl3, VOCl2, VOSO4, V2(SO4)3, manganese sulfate, manganese chloride, manganese phosphate, MnO, hydrobromic acid, bromine water, cobalt sulfate and cobalt chloride; And / or, the iron source is one or more of ferrous sulfate, ferrous chloride, iron powder, ferrochromium alloy, ferrous oxide FeO and ferric oxide Fe2O3; And / or, the chromium source is one or more of chromium trichloride CrCl3, iron-chromium alloy and chromium sulfate CrSO4; And / or, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid.

7. A method for recovering an iron-chromium flow battery according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, charging the battery until the recovery ions in the positive electrode electrolyte reach an oxidized state; Step 2: Add a reducing agent to the positive electrode electrolyte to restore the recovery ions to a reduced state. If the capacity of the battery is restored to its initial state, the recovery is terminated; otherwise, return to step 1.

8. The recovery method of the iron-chromium flow battery according to claim 7, characterized in that: When the battery unbalanced capacity decays to 70-90% of the initial capacity, recovery begins.

9. The recovery method of the iron-chromium flow battery according to claim 7, characterized in that: When the restoring ion is a vanadium ion, its oxidation state is pentavalent vanadium ion VO2 + , its reduced state is tetravalent vanadium ion VO 2+ When the recovery ion is a manganese ion, its oxidation state is Mn 3+ , its reduced state is Mn 2+ When the recovery ion is a bromide ion, its oxidation state is Br 2+ , its reduced state is Br - When the recovery ion is a cobalt ion, its oxidation state is Co 3+ , its reduced state is Co 2+ .

10. The recovery method of the iron-chromium flow battery according to claim 7, characterized in that: The reducing agent is one or more of formaldehyde, formic acid, acetic acid, citric acid, glucose, fructose, tartaric acid and vitamin C.