An electrolyte and an iron-based mixed liquid flow battery using the electrolyte

Abstract

This invention relates to an electrolyte for iron-based hybrid flow batteries, comprising 0-5 mol / L iron salt, 1-5 mol / L hydrochloride, 0-2 mol / L fluoroborate, 0.05-2 mol / L H3BO3 or borate, and 0-0.5 mol / L ZnCl2; wherein the hydrochloride is a mixture of NH4Cl and NaCl in a molar ratio of 1:10 to 10:1. This electrolyte can be used as the negative electrode electrolyte in conventional iron-based hybrid flow batteries, and also as the negative electrode electrolyte in a novel iron-based hybrid flow battery with a connected positive and negative electrode electrolyte circulation structure. Compared with existing technologies, this invention has advantages such as lower cost and better performance.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to an electrolyte and an iron-based hybrid flow battery using the electrolyte. Background Technology

[0002] Inexpensive, powerful, and efficient large-scale energy storage systems are crucial for a stable supply of electricity generated from solar and wind energy resources.

[0003] In the field of low-cost, large-scale energy storage, flow battery technology has received widespread attention due to its advantages such as high safety, high cycle life and long service life, high depth of discharge, and ease of modular production and installation, which are achieved by using aqueous electrolytes.

[0004] Given that iron is one of the most abundant metallic elements on Earth's surface, and is low-cost, non-toxic, and environmentally friendly, it is an ideal source of active material for flow batteries, and a great deal of research has been conducted on it both domestically and internationally.

[0005] Among long-term grid energy storage batteries, aqueous iron-based ferrite flow batteries are made from materials with abundant reserves such as iron, salt, and water, and are particularly attractive and noteworthy for their safety, low cost, sustainability, and environmental friendliness.

[0006] Inexpensive and long-lasting aqueous iron-based flow batteries can help alleviate the supply pressure of renewable energy and expand the use of clean energy. It has been reported that ESS Corporation in the United States is engaged in the research and development of iron-based flow batteries and has already achieved some commercial applications. For example, ESS's invention patent CN110301060B discloses an electrolyte for iron flow batteries, wherein the electroplating electrolyte and the redox electrolyte include one or more of FeCl2, KCl, and H3BO3, and the ductile electroplating additive includes one or more of MnCl2, InCl2, and BiCl2. The inventors also recognized that "during battery operation, the concentration gradient on both sides of the barrier layer drives some Fe..." 3+ The transition from redox electrolyte to electroplating electrolyte. The abrupt pH change (from 1 to 3-6) from electroplating electrolyte to redox electrolyte leads to Fe(OH)2... + Fe(OH)3 forms and precipitates. These precipitates degrade the ion exchange membrane by poisoning the organic functional groups or clogging the pores of the microporous membrane. As a result, the ohmic resistance of the battery increases. The precipitates can be removed by acid washing the battery, but this requires continuous maintenance and limits its commercial use, as it also relies on conventional electrolyte preparation. However, the disclosed method inhibits these reactions by adding a specific organic acid to the electrolyte in response to the pH of the electrolyte (which indicates and facilitates these reactions). "On the reverse side of the IFB, during charging, Fe..." 2+It accepts two electrons and forms Fe 0 Competitive reaction on the reverse side of the battery (H) + The tendency of the electrolyte on the reverse side of the IFB to rise from pH 2 to pH 6 during cycling (accepting an electron and forming H2) exacerbates the problems of electrolyte precipitation and proton exchange membrane blockage, and also increases the internal resistance of the flow battery and reduces the energy cycling efficiency.

[0007] Furthermore, research shows that during the electrolysis or discharge of the iron electrode at the negative electrode, compounds such as ferrous hydroxide are generated, which hinder further reactions. In addition, the boric acid electrolyte used alone is prone to associate into polyboric acid and its corresponding salts. The polarization effect during the charging and discharging process of the electrode reduces the voltage efficiency of the flow battery, resulting in a significant decrease in the energy efficiency of the flow battery.

[0008] Currently disclosed iron-based flow batteries, such as those in invention patents CN114388859A, CN113328124A, CN112467179A, CN110212228A, CN110301060A, and CN107978775A, all use electrolytes containing organic compounds, resulting in higher costs and poor cycle stability during charge-discharge processes. Furthermore, the hydrogen evolution reaction (HER) at the negative electrode during charging reduces the system energy efficiency of iron-based flow batteries, limiting their deployment. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art by providing an electrolyte for iron-based hybrid flow batteries, which reduces the hydrogen evolution reaction (HER) at the negative electrode during charging and improves the system energy efficiency of iron-based flow batteries.

[0010] The objective of this invention can be achieved through the following technical solution: an electrolyte for an iron-based mixed flow battery, characterized in that the electrolyte contains 0-5 mol / L iron salt, 1-5 mol / L hydrochloride, 0-2 mol / L fluoroborate, 0.05-2 mol / L H3BO3 or borate, and 0-0.5 mol / L ZnCl2; wherein the hydrochloride is a mixture of NH4Cl and NaCl in a molar ratio of 1:10 to 10:1, preferably in a molar ratio of 1:4 to 4:1.

[0011] Furthermore, the electrolyte also contains a supporting electrolyte, which is any one or more of hydrochloric acid, ammonia, boric acid, hydrofluoric acid, HBF4, and NaOH, with a total concentration of 0-3 mol / L.

[0012] Further, the iron salt is FeCl2 and / or FeCl3; the fluoroborate includes NaBF4 and / or NH4BF4; and the borate includes NaBO2 and / or NH4BO2.

[0013] Furthermore, the concentration of fluoroborate is 0.05-0.5 mol / L, and even further, the fluoroborate is 0.1-1 mol / L NaBF4.

[0014] Furthermore, the electrolyte is the negative electrode electrolyte of an iron-based mixed flow battery, and the active component of the negative electrode is elemental iron. During charging, iron is deposited from the electrolyte and adheres to the negative electrode, and during discharging, elemental iron dissolves in the electrolyte.

[0015] An iron-based hybrid flow battery using the electrolyte includes a flow battery casing, a negative electrode containing elemental iron and a negative electrode electrolyte storage tank, a positive electrode and a positive electrode electrolyte storage tank, a proton exchange membrane, a positive electrode delivery pump, and a negative electrode delivery pump.

[0016] During use, the circulation pump pumps the positive and negative electrolytes into the positive and negative electrodes inside the flow battery casing, respectively, to participate in the battery's redox reaction.

[0017] Furthermore, the positive and negative electrodes are installed inside the flow battery casing, and the positive and negative electrodes and their corresponding electrolytes are separated by a proton exchange membrane.

[0018] The electrolyte in the negative electrode electrolyte storage tank is pumped to the negative electrode electrolyte inlet by a circulation pump; the electrolyte in the positive electrode electrolyte storage tank is pumped to the positive electrode electrolyte inlet by a circulation pump.

[0019] An iron-based hybrid flow battery using the electrolyte includes a flow battery casing, a magnetic negative electrode containing elemental iron and a negative electrode electrolyte storage tank, a positive electrode and a positive electrode electrolyte storage tank, a proton exchange membrane, and a circulation pump.

[0020] The positive and magnetic negative electrodes are installed inside the flow battery casing, and the positive and negative electrodes, along with their respective electrolytes, are separated by a proton exchange membrane.

[0021] The magnetic negative electrode includes a magnet, iron powder, and a negative electrode current collector, wherein the iron powder is adsorbed on the magnet, the magnet is placed in the negative electrode current collector, and the magnetic field lines of the magnet pass through the negative electrode current collector.

[0022] Furthermore, during the charging process, the electrolyte enters the magnetic negative electrode of the flow battery from the negative electrode electrolyte storage tank, electrolyzes out elemental iron, and the electrolyzed elemental iron is adsorbed on the negative electrode current collector with a magnetic structure; then it is transported into the positive electrode region by a circulation pump, where the remaining ferrous ions are oxidized into iron ions in the positive electrode structure and enter the positive electrode electrolyte storage tank.

[0023] During the discharge process, the electrolyte containing iron ions is transported from the positive electrode electrolyte storage tank, where the iron ions are reduced to ferrous ions and the acidity increases. The electrolyte is then transported to the negative electrode structure through a circulation pump to react with elemental iron.

[0024] Furthermore, the elemental iron decomposed by electrolysis is equivalent to 1 / 3 or less of the total molar amount of ferrous ions.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The negative electrode electrolyte of the iron-based mixed flow battery of the present invention contains NH4Cl, which can be used as a hydrogen ion carrier to enhance the proton penetration performance and reduce the hydrogen evolution reaction.

[0027] (2) The present invention uses a mixture of NH4Cl and NaCl, which has a lower cost, to increase the total electrolyte concentration and replace the more expensive KCl, thereby reducing the cost. Moreover, the electrolyte concentration of the present invention is higher, forming a "salt-in-water" electrolyte, with NaCl as the main "salt-in-water" electrolyte; NH4Cl is added to improve the hydrogen ion penetration balance performance and increase the total solubility.

[0028] (3) The mixture of H3BO3 and HBF4 (or salt) used in this invention can synergistically generate hydroxyfluoroboric acid and its corresponding salt, such as HBF3(OH), HBF2(OH)2, and HBF(OH)3, which can prevent boric acid from further associating into polyboric acid and its corresponding salt, reduce the viscosity of the electrolyte, reduce the polarization of the electrode during the charging and discharging process, and improve the conductivity of the electrolyte, thereby significantly improving the voltage efficiency and energy efficiency of the flow battery.

[0029] (4) The present invention incorporates ZnCl2 and Fe 2+ Competitive hydrolysis to suppress the electrode indication of Fe 2+ The surface iron ions hydrolyze, and the free ammonia generated in a high pH environment forms a complex, preventing precipitation caused by excessively high pH.

[0030] (5) The electrolyte of the present invention is applied to the structure of a novel magnetic iron-based hybrid flow battery. The negative electrode structure of the battery includes a magnet, iron powder, a negative electrode current collector, and a negative electrode electrolyte. The iron powder is adsorbed on the magnet, and the magnet is placed in the negative electrode current collector so that the magnetic field lines of the magnet pass through the negative electrode current collector. This prevents the iron powder from falling off the negative electrode of the battery with the flow of the electrolyte during charging and discharging, and avoids short circuits caused by the iron powder connecting the positive and negative electrode structures; thereby improving the reliability of the electrodes and the energy efficiency of the flow battery. Attached Figure Description

[0031] Figure 1This is a schematic diagram of the iron-based hybrid flow battery of Example 1;

[0032] Figure 2 This is a schematic diagram of the iron-based hybrid flow battery of Example 2.

[0033] The diagram is labeled as follows:

[0034] 1: Battery casing 2: Negative electrode 3: Positive electrode

[0035] 4: Circulation pump; 5: Negative electrode electrolyte storage tank; 6: Proton exchange membrane / ion exchange membrane; 7: Positive electrode electrolyte storage tank; 8: Magnetic negative electrode structure. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] The present invention aims to develop an electrolyte for iron-based hybrid flow batteries to reduce hydrogen evolution reaction (HER) at the negative electrode during charging and improve the system energy efficiency of iron-based flow batteries.

[0038] In hybrid flow battery systems, the negative electrode can be referred to as the electroplated electrode. The principle of an iron-based hybrid redox flow battery, which uses iron as the active material for the reaction, is as follows: At the negative electrode, during charging, Fe... 2+ It accepts two electrons and deposits as iron metal; during the discharge process, the iron metal loses two electrons and dissolves back into Fe. 2+ As shown in equation (1); at the positive electrode, during the charging process, two Fe... 2+ Losing two electrons to form two Fe 3+ During the discharge process, two Fe 3+ Two electrons are gained to form two Fe atoms. 2+ As shown in equation (2):

[0039] Fe 2+ +2e- <==> Fe0 E0= - 0.44 vs. SHE (1)

[0040] 2Fe 2+ 2Fe 3+ +2e- E0= 0.77 vs. SHE (2)

[0041] Simultaneously, a hydrogen evolution reaction occurs, as shown in equation (3). At pH = 4, the hydrogen evolution potential is -0.24V.

[0042] 2H + +2e - <==> H2 ↑ E = - 0.24 vs. SHE (3)

[0043] Studies have shown that since the iron electrode potential is lower than the hydrogen evolution potential, the pH needs to be increased to reduce the hydrogen evolution reaction; however, excessively high pH can easily cause iron ions to hydrolyze and precipitate. Under normal circumstances, the iron coating exhibits an overpotential of 200mV. The operating window of the electroplating electrolyte for the battery is between pH 3 and 4 to maintain stable battery operation and reduce hydrogen evolution.

[0044] However, during the charging (electroplating) process of a flow battery, elemental iron is released from the solution, generating hydrogen ions. If rapid exchange of hydrogen ions cannot be achieved through a proton exchange membrane to maintain pH stability, the pH will decrease, increasing the hydrogen evolution reaction, or external adjustment will be required. Similarly, the same applies during battery discharge. Furthermore, increasing the pH to reduce the hydrogen evolution reaction lowers the hydrogen ion concentration and consequently reduces the hydrogen ion exchange rate. Therefore, this invention incorporates ammonium ions, which can serve as a hydrogen ion carrier.

[0045] To reduce the hydrogen evolution problem, this invention increases the concentration of electrolyte in the electrolyte solution to form a "salt-in-water" electrolyte, that is, increases the concentration of salt ions, which is equivalent to reducing the "concentration" of water in the solution, thereby reducing the hydrogen evolution reaction.

[0046] Example 1

[0047] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, and 0.4 mol / L H3BO3.

[0048] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, and 0.4 mol / L H3BO3.

[0049] The structure of a general iron-based hybrid flow battery is as follows: Figure 1 As shown:

[0050] The battery includes a flow battery casing 1, a negative electrode 2 containing elemental iron and a negative electrode electrolyte storage tank 5, a positive electrode 3 and a positive electrode electrolyte storage tank 7, a proton exchange membrane 6 (or ion exchange membrane), and a circulation pump 4 (including a positive electrode transfer pump and a negative electrode transfer pump). The positive electrode 3 and the negative electrode 2 are installed inside the flow battery casing 1. The positive and negative electrodes and their corresponding electrolytes are separated by the proton exchange membrane 6. The electrolyte in the negative electrode electrolyte storage tank 5 is transported to the electrolyte inlet of the negative electrode by the negative electrode transfer pump. The electrolyte in the positive electrode electrolyte storage tank 7 is transported to the electrolyte inlet of the positive electrode by the positive electrode transfer pump.

[0051] During use, the positive electrode delivery pump and the negative electrode delivery pump pump the positive electrode electrolyte and the negative electrode electrolyte into the positive electrode and the negative electrode inside the flow battery casing, respectively, to participate in the redox reaction of the battery.

[0052] A magnetic structure is added to the negative electrode to prevent the shedding of elemental iron.

[0053] Example 2

[0054] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, and 0.4 mol / L H3BO3.

[0055] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, and 0.4 mol / L H3BO3.

[0056] The structure of a novel iron-based hybrid flow battery employing a positive and negative electrode electrolyte interconnected circulation structure, such as... Figure 2 As shown: It includes a flow battery casing 1, a magnetic negative electrode containing elemental iron 8 and a negative electrode electrolyte storage tank 5, a positive electrode 3 and a positive electrode electrolyte storage tank 7, a proton exchange membrane 6, and a circulation pump 4;

[0057] The positive electrode 3 and the magnetic negative electrode 8 are installed inside the flow battery casing 1. A proton exchange membrane 6 separates the positive and negative electrodes and their corresponding electrolytes. The magnetic negative electrode 8 includes a magnet, iron powder, and a negative electrode current collector. The iron powder is adsorbed onto the magnet, which is placed within the current collector, allowing its magnetic field lines to pass through it. The magnet is a U-shaped magnet, and multiple U-shaped magnets are placed within the current collector. The current collector is made of stainless steel and has an open-top groove shape. Its length matches the length of the multiple U-shaped magnets arranged side-by-side, and its height is the same as the height of a single U-shaped magnet. Since the magnetic field lines of the magnet pass through the current collector, and the distance between the magnet and the battery's ion exchange membrane is greater than the distance between the poles of the U-shaped magnets, the magnetic field strength is significantly reduced at the proton exchange membrane or the positive electrode structure of the battery.

[0058] The positive electrode electrolyte storage tank 7 and the negative electrode electrolyte storage tank 5 are circulated by the circulation pump 4 to achieve electrolyte circulation.

[0059] During charging, a solution containing ferrous ions enters the negative electrode structure of the flow battery from the negative electrode electrolyte tank and electrolytically decomposes elemental iron. The molar ratio of the electrolytically decomposed portion is approximately 1 / 3 or less of the ferrous ion content. The precipitated elemental iron is adsorbed onto the negative electrode current collector, which has a magnetic structure. Then, it is transported to the positive electrode region by an insulated circulation pump, where the remaining ferrous ions are oxidized into iron ions in the positive electrode structure and enter the positive electrode electrolyte tank.

[0060] During the discharge process, an electrolyte containing iron ions is transported from the positive electrode electrolyte storage tank. The iron ions are reduced to ferrous ions, and the acidity increases. The electrolyte is then transported to the negative electrode structure through an insulated circulation pump to react with elemental iron.

[0061] A magnetic structure is added to the negative electrode to prevent the shedding of elemental iron.

[0062] Before charging, the positive electrode electrolyte is empty and is generated by the corresponding negative electrode electrolyte during the charging process.

[0063] Example 3

[0064] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, and 0.2 mol / L NaBF4.

[0065] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, and 0.2 mol / L NaBF4.

[0066] The structure of the iron-based hybrid flow battery with a general structure is the same as in Example 1.

[0067] Example 4

[0068] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, and 0.2 mol / L NaBF4.

[0069] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, and 0.2 mol / L NaBF4.

[0070] The structure of the novel magnetic iron-based hybrid flow battery is the same as in Example 2.

[0071] Example 5

[0072] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0073] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0074] The structure of the iron-based hybrid flow battery with a general structure is the same as in Example 1.

[0075] Example 6

[0076] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0077] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0078] The structure of the novel magnetic iron-based hybrid flow battery is the same as in Example 2.

[0079] Example 7

[0080] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 2.0 mol / L NH4Cl, 1.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0081] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0082] The structure of the iron-based hybrid flow battery with a general structure is the same as in Example 1.

[0083] Example 8

[0084] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 2.0 mol / L NH4Cl, 1.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0085] The positive electrode electrolyte used is: 1.0 mol / L FeCl3, 1.0 mol / L NH4Cl, 2.0 mol / L NaCl, 0.2 mol / L H3BO3, 0.2 mol / L NaBF4, and 0.05 mol / L ZnCl2.

[0086] The structure of the novel magnetic iron-based hybrid flow battery is the same as in Example 2.

[0087] Comparative Example 1

[0088] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 3.0 mol / L KCl, and 0.4 mol / L H3BO3.

[0089] The positive electrode electrolyte is a solution of 1.0 mol / L FeCl3, 3.0 mol / L KCl, and 0.4 mol / L H3BO3.

[0090] The structure of the iron-based hybrid flow battery with a general structure is the same as in Example 1.

[0091] Comparative Example 2

[0092] The negative electrode electrolyte is a solution containing 1.0 mol / L FeCl2, 3.0 mol / L KCl, and 0.4 mol / L H3BO3.

[0093] The positive electrode electrolyte is a solution of 1.0 mol / L FeCl3, 3.0 mol / L KCl, and 0.4 mol / L H3BO3.

[0094] The structure of the novel magnetic iron-based hybrid flow battery is the same as in Example 2.

[0095] The performance of the flow batteries constructed in Examples 1-6 and Comparative Examples 1-2 was tested as follows:

[0096]

[0097]

[0098] Therefore, by using NaCl and NH4Cl as the main "salt-in-water" electrolytes and introducing the synergistic effects of boric acid, fluoroboric acid, and ZnCl2, the system energy efficiency of the resulting iron-based flow battery is improved by more than 5%. Furthermore, when used in a novel magnetic iron-based flow battery, the system energy efficiency is improved by more than 10% compared to a general flow battery using KCl as the base electrolyte.

[0099] Furthermore, the cost comparison of the main electrolytes in the electrolyte solution, KCl, NaCl, and NH4Cl, is as follows:

[0100] electrolytes Unit price (¥ / kg)* relative atomic mass Unit price (¥ / mol) KCl 44.1 74.5 3.28 NaCl 13.4 58.5 0.79 <![CDATA[NH4Cl]]> 22.3 53.5 1.19

[0101] *Note: All substances are compared with the price of 25kg / drum of AR (Shanghai Test) purity sold on the National Pharmaceutical Reagent Network (www.reagent.com.cn).

[0102] Compared with KCl, a mixture of NaCl and NH4Cl in a 2:1 ratio results in a cost saving of over 70% per mole.

[0103] Considering that a relatively high concentration of "salt-in-water" electrolyte (approximately 3 mol / L) needs to be added to the electrolyte, the economic benefits of this invention are quite considerable.

Claims

1. An electrolyte for iron-based hybrid flow batteries, characterized in that, The electrolyte contains 1-5 mol / L iron salt, 1-5 mol / L hydrochloride, 0.1-1 mol / L NaBF4, 0.05-2 mol / L H3BO3 or borate, and 0.05-0.5 mol / L ZnCl2; wherein the hydrochloride is a mixture of NH4Cl and NaCl in a molar ratio of 1:10 to 10:

1.

2. The electrolyte for an iron-based hybrid flow battery according to claim 1, characterized in that, The electrolyte also contains a supporting electrolyte, which is any one or more of hydrochloric acid, ammonia, boric acid, hydrofluoric acid, HBF4, and NaOH, with a total concentration of 0-3 mol / L.

3. The electrolyte for an iron-based hybrid flow battery according to claim 1, characterized in that, The iron salt is FeCl2 and / or FeCl3; the borate includes NaBO2 and / or NH4BO2.

4. An electrolyte for an iron-based hybrid flow battery according to claim 1 or 2, characterized in that, The electrolyte is the negative electrode electrolyte of an iron-based mixed flow battery. The active component of the negative electrode is elemental iron. During charging, iron is deposited from the electrolyte and adheres to the negative electrode. During discharging, elemental iron dissolves in the electrolyte.

5. An iron-based mixed liquid flow battery using the electrolyte of claim 1, characterized in that, It includes a flow battery casing, a negative electrode containing elemental iron and a negative electrode electrolyte storage tank, a positive electrode and a positive electrode electrolyte storage tank, as well as a proton exchange membrane, a positive electrode transfer pump, and a negative electrode transfer pump; During use, the circulation pump pumps the positive and negative electrolytes into the positive and negative electrodes inside the flow battery casing, respectively, to participate in the battery's redox reaction.

6. The iron-based mixed liquid flow battery with the electrolyte according to claim 5, characterized in that, The positive and negative electrodes are installed inside the flow battery casing, and are separated from their electrolytes by a proton exchange membrane. The electrolyte in the negative electrode electrolyte storage tank is pumped to the negative electrode electrolyte inlet by a circulation pump; the electrolyte in the positive electrode electrolyte storage tank is pumped to the positive electrode electrolyte inlet by a circulation pump.

7. An iron-based mixed liquid flow battery using the electrolyte of claim 1, characterized in that, It includes a flow battery casing, a magnetic negative electrode containing elemental iron and a negative electrode electrolyte storage tank, a positive electrode and a positive electrode electrolyte storage tank, as well as a proton exchange membrane and a circulation pump; The positive and magnetic negative electrodes are installed inside the flow battery casing, and the positive and negative electrodes, along with their respective electrolytes, are separated by a proton exchange membrane. The magnetic negative electrode includes a magnet, iron powder, and a negative electrode current collector, wherein the iron powder is adsorbed on the magnet, the magnet is placed in the negative electrode current collector, and the magnetic field lines of the magnet pass through the negative electrode current collector.

8. The iron-based mixed liquid flow battery with the electrolyte according to claim 7, characterized in that, During charging, the electrolyte enters the magnetic negative electrode of the flow battery from the negative electrolyte storage tank, electrolyzes out elemental iron, and the electrolyzed elemental iron is adsorbed on the negative electrode current collector with a magnetic structure; then it is transported into the positive electrode area by a circulation pump, where the remaining ferrous ions are oxidized into iron ions in the positive electrode structure and enter the positive electrolyte storage tank. During the discharge process, the electrolyte containing iron ions is transported from the positive electrode electrolyte storage tank, where the iron ions are reduced to ferrous ions and the acidity increases. The electrolyte is then transported to the negative electrode structure through a circulation pump to react with elemental iron.

9. The iron-based mixed liquid flow battery with the electrolyte according to claim 8, characterized in that, During the charging process, the amount of elemental iron electrolytically decomposed is equivalent to 1 / 3 or less of the total molar amount of ferrous ions.

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