Weakly alkaline all-iron flow battery electrolyte and preparation method thereof

Abstract

The invention relates to an alkalescent total-iron flow battery electrolyte and a preparation method thereof. The lithium ion battery comprises a positive electrode electrolyte and a negative electrode electrolyte, the positive electrode electrolyte is a weakly alkaline aqueous solution of ferrocyanate, the negative electrode electrolyte is a weakly alkaline aqueous solution of ferric salt and an ethylenediamine di-o-hydroxyphenyl acetate complex, and the pH value of the positive electrode electrolyte and the pH value of the negative electrode electrolyte are kept consistent and are 8.0-11.0. In the negative electrode electrolyte, ethylenediamine di-o-hydroxyphenyl acetate is adopted as a complexing agent and forms a stable hexa-coordination structure with iron ions, so that the stability of the negative electrode electrolyte is enhanced; under the weak alkaline condition, generation of ferric hydroxide precipitates in positive and negative electrolyte can be effectively inhibited, and the stability of iron ions is improved; besides, the ligand molecules are large in size, the steric effect of the formed chelate is large, the transmembrane migration degree of iron ions / ferrous ions is reduced, the cycle life of the total-iron flow battery is greatly prolonged, and the total-iron flow battery can be widely applied to various aqueous flow batteries.

Description

Technical Field

[0001] The present invention relates to the field of liquid flow batteries, and in particular to a weak alkaline all-iron liquid flow battery electrolyte and a preparation method thereof Background Art

[0002] All-iron flow batteries are divided into acidic, neutral and alkaline systems. Acidic all-iron flow batteries are relatively mature in commercial development. Both the positive and negative electrolytes use cheap iron as the raw material to make the active material of the electrolyte. The open circuit voltage is 1.21V, which is close to that of all-vanadium flow batteries. It can avoid cross-contamination, and the active material raw materials are cheap and widely available. The structure is simple and the cost is low. It is a very promising flow battery. However, the reversibility of the hydrolysis and deposition / dissolution reactions of ferrous ions in the negative electrode electrolyte is poor, and the hydrogen evolution reaction is serious, resulting in low energy efficiency, severe capacity attenuation and poor cycle stability of the all-iron flow battery, which limits its application in energy storage technology. Patent CN113328124A discloses an acidic iron-based negative electrode electrolyte. Although additives such as citric acid are added to the electrolyte to inhibit the hydrolysis of ferrous ions, the negative electrode reaction is still the traditional Fe 2+ / Fe deposition / dissolution reaction, the existence of side reactions such as iron dendrites and hydrogen evolution, leads to low battery efficiency and rapid capacity decay.

[0003] In recent years, alkaline all-iron flow batteries have developed rapidly. By the end of 2023, there have been commercial energy storage application demonstration projects, which are likely to surpass the development trend of acidic all-iron flow batteries. Gong et al. 3- / 4- The first fully soluble all-iron flow battery is made for the redox couple, and the battery energy efficiency has been greatly improved compared with the traditional acidic all-iron. The alkaline iron-based negative electrode electrolytes disclosed in patents such as CN118336062A, CN113764714B, CN114709459B and CN116259810A all use TEA or TEA derivatives as the main ligands, and use small molecule organic imidazoles, polysaccharide alcohols, malonic acid, citric acid or glycine as auxiliary ligands to form a stable six-coordinate complex with iron ions. However, during the long-life cycle of the battery, these small molecule organics are easy to fall off and penetrate the diaphragm, resulting in the conversion of Fe-TEA / TEA derivatives into five-coordinate complexes. Under strong alkaline conditions (pH greater than 13.0), iron hydroxide precipitation and iron element are easily formed, and the battery capacity decays quickly and the cycle life is short.

[0004] Ferrocyanate will slowly decompose into ferric hydroxide precipitate in a strong alkaline environment (pH>13.0), causing the concentration of active substances in the electrolyte to decrease. At the same time, the precipitated ferric hydroxide will adhere to the surface of the electrode and the diaphragm, increasing the internal resistance of the battery, thus affecting the long-term cycle stability of the battery stack. At the same time, in a strong alkaline environment (pH>13.0), the oxygen evolution potential of the positive electrode electrolyte is about 0.4V, which is close to the electrode potential of the active substance ferrocyanate. When the active substance (ferrocyanate) loses electrons, OH - Ions will also lose electrons and become oxygen, causing instability in the charge and discharge capacity of the positive and negative electrolyte active substances, and reducing the capacity retention rate of the alkaline all-iron flow battery, limiting the industrial prospects of the flow battery of this system.

[0005] Although both acidic all-iron flow batteries and strong alkaline all-iron flow batteries have commercial demonstration devices, the system still has problems such as hydrogen evolution, iron dendrites and iron hydroxide precipitation that are difficult to solve. Therefore, it is urgent to develop a weakly alkaline all-iron flow battery that can perfectly solve a series of problems existing under strong acid and strong alkaline conditions. There are multiple hydrophilic groups (-OH and -COOH) in the ethylenediamine di-o-phenylacetic acid molecule, which chelate with iron ions to form a stable six-membered ring network structure. The complex constant of ethylenediamine di-o-phenylacetic acid iron is high (pKa = 33.9). Even under high temperature alkaline conditions, it is difficult to dissociate metallic iron ions and has good chemical stability. The weakly alkaline all-iron flow battery composed of the positive electrode electrolyte (ferrocyanate) under weakly alkaline conditions (pH = 8.0 ~ 11.0) has good stability, and basically does not have essential problems that affect the long-term operation of the battery, such as hydrogen and oxygen evolution, iron dendrites and iron hydroxide precipitation, which greatly prolongs the cycle life of the all-iron flow battery and can be widely used in various aqueous flow batteries. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned acidic or strongly alkaline all-iron liquid flow batteries, the present invention provides an electrolyte for a weakly alkaline all-iron liquid flow battery and a preparation method thereof, which can effectively inhibit the formation of iron hydroxide precipitation under weakly alkaline conditions, improve the stability of iron ions, and greatly extend the cycle life of the all-iron liquid flow battery.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0008] A weakly alkaline all-iron liquid flow battery electrolyte, characterized in that it comprises a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte is a weakly alkaline aqueous solution composed of ferrocyanate and a supporting electrolyte, and the total iron concentration is 0.1-0.5 mol / L; the negative electrode electrolyte is a weakly alkaline aqueous solution composed of iron salt, ethylenediamine di-o-phenyl acetate, a stabilizer, and a supporting electrolyte, and the total iron concentration is 0.1-0.5 mol / L, the molar ratio of ethylenediamine di-o-phenyl acetate to iron is 1.0-2.0, and the molar ratio of stabilizer to Fe is 0.25-1.0; the concentration of the supporting electrolyte is 0-2.0 mol / L, and the pH value is adjusted to 8.0-11.0 by an inorganic base.

[0009] The ferrocyanide is one or more of sodium ferrocyanide, potassium ferrocyanide, lithium ferrohydride, and ammonium ferrocyanide.

[0010] The iron salt is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric hydroxide and ferric carbonate.

[0011] The ethylenediamine di-o-phenylacetic acid ion is one or more of ethylenediamine di-o-phenylacetic acid, ethylenediamine di-o-phenylacetic acid disodium, ethylenediamine di-o-phenylacetic acid diammonium, and ethylenediamine di-o-phenylacetic acid dipotassium.

[0012] The stabilizer is one or more of sorbitol, mannitol, gluconic acid and glucoheptanoic acid.

[0013] The supporting electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate.

[0014] The alkali solution is one or more of ammonia water, sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0015] The pH values ​​of the positive electrode electrolyte and the negative electrode electrolyte are kept consistent and adjusted with alkaline solution to a pH value of 8.0 to 11.0.

[0016] The positive electrode electrolyte preparation method comprises the following steps: weighing a certain mass of ferrocyanide, a stabilizer and a supporting electrolyte and dissolving them in an appropriate amount of distilled water, then adjusting the pH value of the solution to 8.0-11.0 with an alkali solution, stirring at 40-60° C. for 24 hours, and cooling to room temperature to obtain a positive electrode electrolyte.

[0017] The negative electrode electrolyte preparation method comprises the following steps: weighing a certain mass of iron salt, ethylenediamine di-o-phenylacetate, a stabilizer and a supporting electrolyte and dissolving them in an appropriate amount of distilled water, then adjusting the pH value of the solution to 8.0-11.0 with an alkali solution, stirring at 40-60° C. for 24 hours, and cooling to room temperature to obtain the negative electrode electrolyte.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention uses ethylenediamine di-o-phenylacetic acid iron as the negative electrode electrolyte active material, which has multiple hydrophilic groups (-OH and -COOH) and chelates with iron ions to form a stable six-membered ring network structure. The complex constant of ethylenediamine di-o-phenylacetic acid iron is high, and it is difficult to dissociate metallic iron ions even under high temperature alkaline conditions, thereby greatly improving the cycle stability of the negative electrode electrolyte.

[0020] (2) The molecular sizes of the active substances in the electrolyte of the all-iron liquid flow battery, ethylenediamine di-o-phenylacetic acid ferric and ferrocyanate, are relatively large, and their permeability through the ion exchange membrane is greatly reduced. The ion exchange membrane can effectively block the migration of active substances by simply treating it with distilled water. The assembled battery has high coulombic efficiency, good stability, and low capacity attenuation rate.

[0021] (3) The pH value of the electrolyte of the all-iron liquid flow battery of the present invention is selected to be 8.0-11.0, which is a weakly alkaline environment. The weakly alkaline all-iron liquid flow battery composed of a weakly alkaline positive electrode electrolyte (such as ferrocyanide) will basically not have the problems of hydrogen and oxygen evolution, iron hydroxide and iron dendrites during battery operation, which greatly extends the cycle life of the all-iron liquid flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The structure of ethylenediamine di-o-phenylacetate ferric

[0023] Figure 2 Cyclic voltammetry curves (CV curves) of 500 groups of negative electrode electrolytes in Example 1

[0024] Figure 3 Capacity retention rate of weakly alkaline all-iron flow batteries composed of Examples 1 to 5

[0025] Figure 4 Capacity retention rate of all-iron flow batteries composed of Example 1 and Comparative Examples 1 to 4 DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the preferred implementation schemes of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0027] The present invention is further described in detail below through comparative examples and embodiments.

[0028] 1 Preparation process of all-iron liquid flow battery electrolyte

[0029] 1.1 Positive Electrolyte Preparation Process:

[0030] Weigh a certain mass of ferrocyanide, stabilizer and supporting electrolyte and dissolve them in an appropriate amount of distilled water, then adjust the pH value of the solution to 8.0-11.0 with alkali solution, stir at 40-60°C for 24 hours, and cool to room temperature to obtain a positive electrode electrolyte.

[0031] 1.2 Negative electrolyte preparation process:

[0032] Weigh a certain mass of iron salt, ethylenediamine di-o-phenylacetate, stabilizer and supporting electrolyte and dissolve them in an appropriate amount of distilled water, then adjust the pH value of the solution to 8.0-11.0 with alkali solution, stir at 40-60°C for 24 hours, and cool to room temperature to obtain a negative electrode electrolyte.

[0033] Example 1

[0034] Positive electrolyte: 0.1 mol sodium ferrocyanide, 2 mol potassium chloride, adjust the pH to 8.0 with sodium hydroxide, and adjust the volume to 1 L to prepare a positive electrolyte containing 0.1 M ferrocyanide.

[0035] Negative electrode electrolyte: 0.1 mol ferric chloride, 0.2 mol ethylenediamine di-o-phenylacetic acid, 0.1 mol sorbitol, 2 mol potassium chloride, adjust the pH value to 8.0 with sodium hydroxide, and adjust the volume to 1 L to prepare a negative electrode electrolyte containing 0.1 M ethylenediamine di-o-phenylacetic acid ferric.

[0036] Example 2

[0037] Positive electrolyte: 0.2 mol potassium ferrocyanide, 1 mol sodium chloride, 1 mol sodium sulfate, adjust the pH to 9.0 with potassium hydroxide, and adjust the volume to 1 L to prepare a positive electrolyte containing 0.2 M ferrocyanide.

[0038] Negative electrode electrolyte: 0.2 mol ferric sulfate, 0.3 mol disodium ethylenediamine di-o-phenylacetate, 0.1 mol mannitol, 1 mol sodium chloride, 1 mol sodium sulfate, adjust the pH value to 9.0 with potassium hydroxide, fix the volume to 1 L, and prepare a negative electrode electrolyte containing 0.2 M ethylenediamine di-o-phenylacetate iron.

[0039] Example 3

[0040] Positive electrolyte: 0.3 mol lithium ferrocyanide, 0.5 mol potassium sulfate, 0.5 mol potassium nitrate, adjust the pH to 10.0 with lithium hydroxide, fix the volume to 1 L, and prepare a positive electrolyte containing 0.3 M ferrocyanide.

[0041] Negative electrode electrolyte: 0.2 mol ferric nitrate, 0.3 mol dipotassium ethylenediamine di-o-phenylacetate, 0.1 mol gluconic acid, 0.5 mol potassium sulfate, 0.5 mol potassium nitrate, adjust the pH value to 10.0 with lithium hydroxide, fix the volume to 1L, and prepare a negative electrode electrolyte containing 0.3M ethylenediamine di-o-phenylacetate ferric.

[0042] Example 4

[0043] Positive electrolyte: 0.4 mol ammonium ferrocyanide, 0.25 mol sodium nitrate, 0.25 mol ammonium sulfate, adjust the pH to 11.0 with potassium hydroxide, and adjust the volume to 1 L to prepare a positive electrolyte containing 0.4 M ferrocyanide.

[0044] Negative electrode electrolyte: 0.4 mol ferric carbonate, 0.5 mol dipotassium ethylenediamine di-o-phenylacetate, 0.1 mol gluconic acid, 0.25 mol sodium nitrate, 0.25 mol ammonium sulfate, adjust the pH value to 11.0 with potassium hydroxide, fix the volume to 1 L, and prepare a negative electrode electrolyte containing 0.4 M ethylenediamine di-o-phenylacetate iron.

[0045] Example 5

[0046] Positive electrolyte: 0.5 mol ammonium ferrocyanide, 0.5 mol ammonium chloride, adjust the pH to 8.5 with ammonia water, and adjust the volume to 1 L to prepare a positive electrolyte containing 0.5 M ferrocyanide.

[0047] Negative electrode electrolyte: 0.5 mol ferric hydroxide, 0.5 mol ethylenediamine diammonium o-phenylacetate, 0.15 mol sorbitol, 0.5 mol ammonium chloride, adjust the pH value to 8.5 with ammonia water, fix the volume to 1 L, and prepare a negative electrode electrolyte containing 0.5 M ethylenediamine di-o-phenylacetate iron.

[0048] Comparative Example 1

[0049] Positive electrolyte: 0.1 mol sodium ferrocyanide, 2 mol potassium chloride, adjust the pH to 8.0 with sodium hydroxide, and adjust the volume to 1 L to prepare a positive electrolyte containing 0.1 M ferrocyanide.

[0050] Negative electrode electrolyte: 0.1 mol ferric chloride, 0.2 mol ethylenediaminedi-o-phenylacetic acid, 2 mol potassium chloride, adjust the pH value to 8.0 with sodium hydroxide, fix the volume to 1 L, and prepare a negative electrode electrolyte containing 0.1 M ethylenediaminedi-o-phenylacetic acid ferric.

[0051] Comparative Example 2

[0052] Positive electrolyte: Accurately weigh 0.5 mol sodium ferrocyanide, 1.0 mol potassium chloride, and 1 mol potassium hydroxide and dissolve them in distilled water to make a volume of 1 L to prepare a positive electrolyte.

[0053] Negative electrode electrolyte: 0.5 mol ferric chloride, 1.0 mol triethanolamine (TEA), 4 mol KOH, 1 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1 L to prepare a negative electrode electrolyte containing 0.5 M Fe-TEA.

[0054] Comparative Example 3

[0055] Positive electrolyte: Accurately weigh 0.5 mol sodium ferrocyanide, 1.0 mol potassium chloride, and 1 mol potassium hydroxide and dissolve them in distilled water to make a volume of 1 L to prepare a positive electrolyte.

[0056] Negative electrolyte: 0.5 mol ferric chloride, 1.0 mol triethanolamine (TEA), 0.5 mol dimethylimidazole (MM), 4 mol KOH, 1 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1L to prepare a negative electrolyte containing 0.5M Fe-TEA-MM

[0057] Comparative Example 4

[0058] The positive and negative electrolytes are both ferrous chloride (total iron concentration: 1.0M), hydrochloric acid concentration: 2.0M.

[0059] 2 Electrochemical performance test of all-iron liquid flow battery

[0060] 2.1 Cyclic voltammetry curve (CV curve)

[0061] Experimental conditions: Cyclic voltammetry curve (CV curve): three-electrode mode (electrochemical workstation: Shanghai Chenhua Instrument Co., Ltd. CHI660E), working electrode: glassy carbon electrode (diameter 6mm), counter electrode: platinum sheet electrode (15*15*0.1mm), reference electrode: Ag / AgCl, scanning voltage range: 0~-1.0V; scanning voltage: 50mv / s, number of cycles: 500 groups, the electrolyte changes after 500 groups of CV curves of the negative electrode electrolyte in Examples 1 to 5 and Comparative Examples 1 to 4 are as follows Table 1, and the 500 groups of CV curves of the negative electrode electrolyte in Example 1 are as follows Figure 2 .

[0062] Table 1 Electrochemical experimental phenomena of negative electrode electrolyte

[0063]

[0064]

[0065] Note: The total iron concentration in Examples 1 to 5 and Comparative Examples 1 to 4 was diluted to 0.1 mol / L with deoxygenated distilled water.

[0066] It can be clearly seen from Table 1 above that after 500 sets of cyclic voltammetry curves (CV curves) of the negative electrode electrolyte in Examples 1 to 5 and Comparative Example 1, no iron element was generated on the working electrode, no bubbles were generated, and no red flocculent precipitation was present in the electrolyte; however, the negative electrode electrolyte in Comparative Example 2 and Comparative Example 3 clearly had iron element on the working electrode, accompanied by a large number of bubbles, and the electrolyte became obviously turbid; the negative electrode electrolyte in Comparative Example 4 had a large amount of iron element on the working electrolyte. Figure 2 It can be seen that the CV curves of 500 groups of negative electrode electrolytes in Example 1 have very good coincidence, which indicates that the negative electrode electrolyte in Example 1 has very good stability.

[0067] In summary, this indicates that the negative electrode electrolytes in Examples 1 to 5 and Comparative Example 1 have good stability, while the negative electrode electrolytes in Comparative Examples 2 to 4 have poor cycle stability.

[0068] 2.2 All-iron flow battery performance test

[0069] (1) Assembly of all-iron flow battery

[0070] The single cell was assembled in the following order: positive electrode aluminum end plate, gold-plated copper plate, graphite current collector, positive electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), ion exchange membrane Nafion212 (soaked in the negative electrode electrolyte for 1 day and then repeatedly washed with distilled water before use), negative electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), graphite current collector, gold-plated copper plate and negative electrode aluminum end plate.

[0071] Liquid flow battery: It is composed of the above-mentioned positive electrode electrolyte and negative electrode electrolyte, positive electrode electrolyte tank, negative electrode electrolyte tank, circulation pump, circulation pipeline and single battery circuit connected in series.

[0072] (2) All-iron flow battery test conditions

[0073] Charge and discharge tester: CT-4008T from Dongguan Xinwei Testing Technology Co., Ltd., charge and discharge mode: constant current charging mode, the volume of the positive and negative electrolytes is 35ml, the flow rate of the positive and negative electrolytes is 150ml / min, nitrogen is introduced before charging and discharging to remove oxygen, current density: 50mA / cm 2 , temperature: 35°C, the charge and discharge cut-off voltages of Examples 1 to 5 and Comparative Example 1 are 1.2V and 0.5V respectively, the charge and discharge cut-off voltages of Comparative Examples 2 to 4 are 0.5 to 1.7V respectively, and the charge and discharge times are 1000 times. Table 2 shows the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1 to 5 and Comparative Examples 1 to 4. Figure 3 The capacity retention rate of the weak alkaline flow batteries of Examples 1 to 5 is shown. Figure 4It represents the capacity retention rate of the all-iron liquid flow batteries composed of Comparative Examples 1 to 4.

[0074] Table 2 All-iron flow battery performance

[0075]

[0076]

[0077] It can be clearly seen from Table 2 above that the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1-5 are significantly higher than those of Comparative Examples 1-4.

[0078] from Figure 3 and Figure 4 It can be seen that the capacity retention rate of the all-iron liquid flow battery composed of Examples 1 to 5 is still higher than 90% after 1000 charge and discharge cycles, and the capacity retention rate is relatively high; however, the capacity retention rate of the all-iron liquid flow battery composed of Comparative Examples 1 to 4 is relatively low after 1000 charge and discharge cycles, and the capacity decay is fast, especially the all-iron liquid flow battery composed of Comparative Examples 2 to 4 has decayed by more than 60% after 500 cycles.

[0079] After the experiment was completed, the all-iron liquid flow battery stacks composed of Examples 1 to 5 and Comparative Examples 1 to 4 were disassembled. We found that the ion exchange membranes and graphite felts in the liquid flow batteries composed of Examples 1 to 5 were clean, no iron hydroxide precipitation, no iron element was generated, and the electrolyte was still clear and transparent; however, in the liquid flow batteries composed of Comparative Examples 1 to 4, there were obvious iron elements or red flocculent precipitation of iron hydroxide on the graphite felt, and obvious red flocculent precipitation on the ion exchange membrane, and the positive and negative electrolytes were turbid. This shows that the charge and discharge performance of the weakly alkaline all-iron liquid flow battery composed of Examples 1 to 5 is significantly better than that of Comparative Examples 1 to 4, and the positive and negative electrolytes of the present invention have high charge and discharge activity, few side reactions, low ion permeability, and good cycle stability.

[0080] In summary, the weakly alkaline all-iron flow battery electrolyte provided by the present invention adopts ethylenediamine di-o-phenylacetic acid iron as the negative electrode electrolyte active substance, has multiple hydrophilic groups (-OH and -COOH), and chelates with iron ions to form a stable six-membered ring network structure. The complex constant of ethylenediamine di-o-phenylacetic acid iron is high, and it is difficult to dissociate metallic iron ions even under high temperature alkaline conditions, which greatly improves the cycle stability of the negative electrode electrolyte; polysaccharide alcohols are used as stabilizers, which are easy to form six-coordinate or eight-coordinate stable structures with the outermost d orbital of the central ion iron, further improving the stability of the all-iron flow battery electrolyte; the pH value of the all-iron liquid flow battery electrolyte of the present invention is selected to be 8.0-11.0, a weakly alkaline environment, and the weakly alkaline all-iron liquid flow battery composed of a weakly alkaline positive electrode electrolyte (such as ferrocyanate) will basically not have the problems of hydrogen and oxygen evolution, iron hydroxide and iron dendrites during battery operation, which greatly extends the cycle life of the all-iron liquid flow battery.

Claims

1. A weak alkaline all-iron flow battery electrolyte, comprising a positive electrode electrolyte and a negative electrode electrolyte, characterized in that: The positive electrode electrolyte is a weak alkaline aqueous solution composed of ferrocyanide and a supporting electrolyte, and the negative electrode electrolyte is a weak alkaline aqueous solution composed of iron salt, ethylenediamine di-o-phenyl acetate, a stabilizer, and a supporting electrolyte.

2. The weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The total iron concentration of the positive electrode electrolyte is 0.1-0.5 mol / L; the total iron concentration of the negative electrode electrolyte is 0.1-0.5 mol / L, the molar ratio of ethylenediamine di-o-phenylacetate to iron is 1.0-2.0, the molar ratio of stabilizer to Fe is 0.25-1.0, the supporting electrolyte concentration is 0-2.0 mol / L, and the inorganic base is used to adjust the pH value to 8.0-11.

0.

3. The weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The ferrocyanide in the positive electrode electrolyte is one or more of sodium ferrocyanide, potassium ferrocyanide, lithium ferrohydride, and ammonium ferrocyanide.

4. The weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The iron salt in the negative electrode electrolyte is one or more of ferric chloride, ferric sulfate, ferric nitrate, ferric hydroxide and ferric carbonate.

5. The weak alkaline all-iron flow battery electrolyte according to claim 2, characterized in that: The ethylenediaminedi-o-phenylacetic acid ion in the negative electrode electrolyte is one or more of ethylenediaminedi-o-phenylacetic acid, disodium ethylenediaminedi-o-phenylacetic acid, diammonium ethylenediaminedi-o-phenylacetic acid, and dipotassium ethylenediaminedi-o-phenylacetic acid.

6. The weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The stabilizer in the negative electrode electrolyte is one or more of sorbitol, mannitol, gluconic acid, and gluconic acid.

7. The weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The supporting electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate.

8. A weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The inorganic base is one or more of ammonia water, sodium hydroxide, potassium hydroxide and lithium hydroxide.

9. A weak alkaline all-iron flow battery electrolyte according to claim 1, characterized in that: The pH values ​​of the positive electrode electrolyte and the negative electrode electrolyte are kept consistent and adjusted with inorganic alkali to a pH value of 8.0 to 11.

0.

10. An electrolyte for a weakly alkaline all-iron flow battery according to claim 1, 2, 4, 5 or 6, characterized in that: The negative electrode electrolyte preparation method comprises the following steps: weighing a certain mass of iron salt, ethylenediamine di-o-phenylacetate, a stabilizer and a supporting electrolyte and dissolving them in an appropriate amount of distilled water, then adjusting the pH value of the solution to 8.0-11.0 with an alkali solution, stirring at 40-60° C. for 24 hours, and cooling to room temperature to obtain the negative electrode electrolyte.

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