A negative electrode electrolyte for a liquid iron flow energy storage battery

Abstract

This invention belongs to the field of electrochemical energy storage technology, and more specifically, relates to a negative electrode electrolyte for a liquid iron flow battery. This invention addresses the issue of traditional liquid iron flow batteries using Fe as the negative electrode. 2+ / Fe 0 To address the problem of short battery life caused by active electrodes, a first, second, and third complexing agent are simultaneously coordinated and complexed onto the same iron or ferrous ion, stabilizing its structure and forming a new Fe... 3+[ Complex 123] / Fe 2+ [Complex 123] Active couple: This reaction only involves liquid-liquid phase reaction and does not involve phase transformation. It does not deposit metallic iron, which fundamentally solves the problem of short life caused by iron dendrites in the negative electrode and improves the cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a negative electrode electrolyte for a liquid iron flow energy storage battery. Background Technology

[0002] In the 21st century, with the massive use of primary energy sources such as coal, oil, and natural gas, serious environmental problems have become increasingly prominent. As primary energy resources become increasingly scarce, the demand for clean and renewable energy has reached unprecedented levels. This has led to greater attention being paid to inexpensive renewable energy sources such as solar, wind, and tidal power. However, renewable energy has a significant drawback: its intermittent and fluctuating nature prevents it from being directly integrated into the power grid to supply normal human needs. Furthermore, some renewable energy sources are highly geographically specific. Therefore, the demand for high-performance energy storage technologies has become particularly prominent. Among these, battery technologies in chemical energy storage, such as flow batteries, demonstrate superior performance and application prospects compared to other energy storage technologies due to their advantages of low cost, easy scalability, high safety, good stability, and lack of geographical limitations.

[0003] As an electrochemical device that fulfills energy storage requirements through redox reactions between positive and negative electrode active materials, the electrolyte in a flow battery is continuously refreshed and circulated on the electrode surface via a power delivery system. To prevent capacity loss caused by the mixing of positive and negative electrode electrolytes, a separator is used to separate the electrolytes. Because the active materials and the stack of a flow battery are separated, the charge and discharge capacity and power of the flow battery can be flexibly designed according to needs, which is very suitable for large-scale, long-term energy storage requirements. Currently, vanadium redox flow batteries have become one of the better-developed and more mature flow battery technologies due to their advantages such as no cross-contamination of different ions and large capacity. However, vanadium redox flow batteries have a fatal problem: the cost of the electrolyte is too high. Vanadium ore is a rare resource, and its purchase cost is much higher than that of ordinary metals. Therefore, how to reduce the cost of flow batteries has become a major challenge for their application.

[0004] To address the high cost of vanadium redox flow batteries, numerous researchers have investigated other flow battery systems, such as iron-chromium flow batteries, quinone-bromine flow batteries, all-iron flow batteries, and zinc-iron flow batteries. Among these, the all-iron flow battery has attracted significant attention because both the positive and negative electrodes utilize abundant and inexpensive iron / iron salts as raw materials. Its basic principle is that both the positive and negative electrode active materials use Fe... 2+ And, respectively, redox reactions occur at the positive and negative electrodes. Among them, Fe... 3+ / Fe 2+ As a redox couple at the positive electrode, Fe 2+Fe serves as the redox couple at the negative electrode. However, all-iron flow batteries still face several significant challenges: firstly, the energy efficiency of current acidic iron-based flow batteries is generally low, meaning the electrolyte utilization rate is low; secondly, iron deposition easily occurs in the negative electrode electrolyte during charge and discharge, significantly impacting the flow battery's capacity and cycle stability, thus reducing its lifespan. To address these issues, researchers both domestically and internationally have conducted further research on the negative electrode electrolyte for all-iron flow batteries.

[0005] Shanghai Jiao Tong University has disclosed an all-iron redox energy storage battery, its electrolyte, and its preparation method. It utilizes non-toxic and harmless inorganic iron salts as the active materials for both the positive and negative electrodes, achieving different redox potentials based on different valence states, thereby realizing the storage and release of electrical energy (CN102332596A). This is an earlier patent, and its innovation lies solely in replacing the vanadium electrolyte with an iron electrolyte. The hydrogen and iron evolution problems in the negative electrode electrolyte are severe, resulting in low battery stability and efficiency.

[0006] BYD Company Limited discloses an all-iron flow battery electrolyte and a single-electrolyte all-iron flow battery, using 2,2'-bipyridine as a complexing agent, and the complexing agent reacts with Fe in an organic solvent. 2+ The complexation of iron with organic compounds was used, and this solution was used as the positive and negative electrolyte for a flow battery (CN102237541A). This method addresses the low open-circuit voltage of existing aqueous electrolyte all-iron flow batteries by combining aqueous and organic systems, resulting in a significant increase in open-circuit voltage and mitigating iron deposition to some extent. However, the system change significantly reduces the safety of the all-iron flow battery, and the battery efficiency remains relatively low.

[0007] Dalian University of Technology has disclosed a high open-circuit voltage all-iron complex flow battery. The main research focus remains on the positive and negative electrode electrolytes, with o-phenanthroline used as the Fe... 2+ The complexing agent is triethanolamine, and the negative electrode uses Fe. 3+ A complexing agent is used to create a potential difference between the positive and negative electrodes by complexing with iron ions, thereby assembling an all-iron flow battery (CN103700872A). This method results in a high open-circuit voltage for the all-iron flow battery, and the iron complex also inhibits the hydrogen evolution reaction to some extent. However, this method also has the drawback of a large pH difference between the positive and negative electrolytes, which can lead to water migration, causing capacity decay and affecting the battery's stability and lifespan.

[0008] The Institute of Metal Research, Chinese Academy of Sciences, has disclosed a negative electrode electrolyte for all-iron flow batteries. Citric acid / citrate is used as an additive, and a complexation reaction is employed to regulate the coordination structure of ferrous ions, further eliminating water molecules surrounding the ferrous ions, thus serving as the negative electrode electrolyte for traditional all-iron flow batteries (CN113328124A). This method solves the problem of poor reversibility in ferrous ion hydrolysis and deposition / dissolution reactions, further improving battery cycle life. However, this method is still an improvement on traditional iron-based flow batteries and does not break free from the framework of reducing ferrous ions to elemental iron. Therefore, the problem of iron deposition in the negative electrode electrolyte still exists, and battery efficiency remains limited.

[0009] The Institute of Metal Research, Chinese Academy of Sciences, has disclosed another negative electrode electrolyte for all-iron flow batteries. This method involves adding dimethyl sulfoxide (DMSO) or its derivatives to the ferrous ions and supporting electrolyte, allowing DMSO to act as a complexing agent to complex the ferrous ions. This solution is then applied to traditional iron-based flow batteries. This method results in more uniform and dense ferrous ion deposition in the negative electrode electrolyte, reducing hydrogen evolution reaction and improving the reversibility of the negative electrode reaction. However, this method suffers from the same problem as the aforementioned patent: it still produces iron dendrites, affecting battery efficiency and lifespan.

[0010] In summary, researchers are currently suppressing the formation of iron dendrites by modifying complexing agents and solvent systems. However, based on current research progress, problems such as short battery life, low efficiency, and iron dendrite formation still exist, preventing the further application of all-iron flow batteries.

[0011] Based on the above analysis, this patent addresses the issue by altering the redox couple at the negative electrode and applying a complexing agent without changing the solvent system. It leverages the coordination ability of the complexing agent with iron / ferrous ions to simultaneously coordinate iron / ferrous ions with multiple complexing agents, forming a more stable structure suitable for use as the negative electrode electrolyte in an all-iron flow battery. The advantage of this electrolyte is that the reaction involves only Fe. 3+ / Fe 2+ The liquid-liquid phase reaction does not involve a phase transformation process, thus fundamentally solving the problem of iron dendrites and further addressing the issue of poor battery cycle stability. Summary of the Invention

[0012] To fundamentally solve the problem of short battery life caused by iron dendrites in the negative electrode, this invention utilizes the simultaneous action of iron ions or ferrous ions with three complexing agents to achieve a balance between iron and ferrous oxide in the negative electrode. 3+ [Complex 123] / Fe 2+ [Complex 123] The active couple exhibits higher electrochemical activity and increases the size of the liquid particle complex, thereby suppressing migration. It also improves the efficiency and stability of aqueous all-iron flow batteries, showing promising application prospects.

[0013] A negative electrode electrolyte for an iron-liquid flow energy storage battery is characterized by comprising iron ions, a first complexing agent, a second complexing agent, a third complexing agent, a supporting electrolyte, and water. The first complexing agent, the second complexing agent, and the third complexing agent can simultaneously bind to the same iron ion or ferrous ion. The first complexing agent is citric acid and its salt, the second complexing agent is oxalic acid and its salt, and the third complexing agent is phosphate or bromide ions.

[0014] The iron-containing liquid flow energy storage battery negative electrode electrolyte is characterized in that the iron-containing substance is selected from one or more of ferric chloride, ferric sulfate, and ferric nitrate, and the concentration of iron ions is 0.1-1.6 mol / L.

[0015] The negative electrode electrolyte of the iron-liquid flow energy storage battery is characterized in that the first complexing agent is one or more of citric acid, sodium citrate, and potassium citrate, with a concentration of 0.1-2.4 mol / L.

[0016] The negative electrode electrolyte of the iron-liquid flow energy storage battery is characterized in that the oxalate used as the second complexing agent is selected from one or more of sodium oxalate, potassium oxalate, and lithium oxalate, and the concentration is 0.1-2.4 mol / L.

[0017] The negative electrode electrolyte of the iron-liquid flow energy storage battery is characterized in that the third complexing agent is one or more of sodium phosphate, potassium phosphate, lithium phosphate, sodium bromide, potassium bromide, and lithium bromide, with a concentration of 0.1-2.4 mol / L.

[0018] The iron-based liquid flow energy storage battery negative electrode electrolyte is characterized in that the molar ratio of iron / ferrous ions, the first complexing agent, the second complexing agent, and the third complexing agent is 1:(1-1.5):(1-1.5):(1-1.5).

[0019] The iron-liquid flow energy storage battery negative electrode electrolyte is characterized in that the electrolyte is used to adjust the pH value and conductivity of the solution, and the electrolyte is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium chloride, and ammonium sulfate, and the concentration of the electrolyte is 0.1-8 mol / L.

[0020] Advantages of the present invention

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention employs a first complexing agent, a second complexing agent, and a third complexing agent to simultaneously complex with ferric ions or ferrous ions, forming structurally stable Fe. 3+ [Complex 123] / Fe 2+[Complex 123] active electrode couple is used as the negative electrode electrolyte in an all-iron flow battery. This electrolyte replaces the Fe anode of a conventional iron-based flow battery. 2+ The / Fe active couple fundamentally solves the problem of short battery life caused by iron dendrites in the negative electrode, and significantly improves the cycle stability and efficiency of the battery. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an all-iron flow battery and its structure based on the present invention. The components in the diagram are as follows: 1. Negative electrode storage tank, 2. Negative electrode power pump, 3. Negative electrode end plate, 4. Negative electrode current collector, 5. Negative electrode, 6. Ion exchange membrane, 7. Positive electrode, 8. Positive electrode current collector, 9. Positive electrode end plate, 10. Positive electrode power pump, 11. Positive electrode inlet tank. Detailed Implementation

[0024] Example 1: Negative Electrolyte and All-Iron Flow Battery Based on Citrate-Oxalate-Phosphate-Iron Ion Complex

[0025] 1. Preparation method of negative electrode electrolyte based on citrate-oxalate-phosphate-iron ion complex:

[0026] 1) First, add 0.05 mol FeCl3 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner. Once the solution is evenly dispersed, you will get solution 1.

[0027] 2) Weigh 0.05 mol of trisodium citrate and add it to solution 1. Stir evenly with a glass rod and sonicate until the solid is completely dissolved. After the solution is evenly dispersed, you will get solution 2.

[0028] 3) Weigh 0.05 mol of potassium oxalate, add an appropriate amount of deionized water, stir continuously with a glass rod, and sonicate until the solid is completely dissolved. Once the solution is evenly dispersed, add it to solution 2 to obtain solution 3.

[0029] 4) Weigh 0.05 mol of potassium phosphate into a beaker, add an appropriate amount of deionized water, stir evenly with a glass rod, and sonicate until the solid is completely dissolved. After the solution is evenly dispersed, add it to solution 3 to obtain solution 4.

[0030] 5) Weigh 0.2 mol of NH4Cl solid and add it to solution 4. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution. After the solution is evenly dispersed, you will get solution 5.

[0031] 5) Transfer the mixed solution 5 to a 100 mL volumetric flask, let it cool to room temperature, make up to volume, shake well, and prepare a citrate (0.5 mol / L)-oxalate (0.5 mol / L)-phosphate (0.5 mol / L)-iron (0.5 mol / L) complex solution. Use this solution as the negative electrode electrolyte for the all-iron flow battery.

[0032] 2. Preparation of the positive electrode electrolyte:

[0033] 1) Add 0.05 mol FeCl2 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner until the solution is evenly dispersed.

[0034] 2) Weigh 0.2 mol of NH4Cl solid and add it to the above solution. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution until it is evenly dispersed.

[0035] 3) Transfer the mixed solution to a 100 mL volumetric flask, allow it to cool to room temperature, then dilute to volume, shake well, and prepare a 0.5 mol / L FeCl2 solution. This solution will be used as the positive electrode electrolyte for the all-iron flow battery.

[0036] 3. Assembly of an all-ferric flow battery:

[0037] according to Figure 1 The vanadium redox flow battery is assembled with the following components from the outside in: stainless steel end plates, current collectors, carbon felt electrodes, and ion exchange membranes. A magnetically driven circulation pump serves as the power delivery device for the electrolyte. The ion exchange membrane is a Nafion 212 model. The carbon felt electrodes, with an electrode area of ​​3cm × 3cm × 6mm, are used for both positive and negative electrodes. The current collectors for both electrodes are graphite plates with a serpentine flow field.

[0038] 4. Performance testing of all-iron flow batteries:

[0039] Constant current charge / discharge test: using 100mA / cm 2 Current density, charge / discharge cutoff voltage is 1.2–0.4V.

[0040] Cyclic stability test: using 100 mA / cm 2 The current density and charge / discharge cutoff voltage are 1.2–0.4V. After the test, the battery's coulombic efficiency, voltage efficiency, energy efficiency, and capacity are obtained.

[0041] Example 2: Negative Electrolyte and All-Iron Flow Battery Based on Citrate-Oxalate-Bromide-Iron Ion Complex

[0042] 1. Preparation method of negative electrode electrolyte based on citrate-oxalate-bromine-ferric ion complex:

[0043] 1) First, add 0.05 mol FeCl3 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner. Once the solution is evenly dispersed, you will get solution 1.

[0044] 2) Weigh 0.05 mol of trisodium citrate and add it to solution 1. Stir evenly with a glass rod and sonicate until the solid is completely dissolved. After the solution is evenly dispersed, you will get solution 2.

[0045] 3) Weigh 0.05 mol of potassium oxalate, add an appropriate amount of deionized water, stir continuously with a glass rod, and sonicate until the solid is completely dissolved. Once the solution is evenly dispersed, add it to solution 2 to obtain solution 3.

[0046] 4) Weigh 0.05 mol of potassium bromide and place it in a beaker. Add an appropriate amount of deionized water, stir evenly with a glass rod, and sonicate until the solid is completely dissolved. After the solution is evenly dispersed, add it to solution 3 to obtain solution 4.

[0047] 5) Weigh 0.2 mol of NH4Cl solid and add it to solution 4. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution. After the solution is evenly dispersed, you will get solution 5.

[0048] 5) Transfer the mixed solution 5 to a 100 mL volumetric flask, let it cool to room temperature, make up to volume, shake well, and prepare a citrate (0.5 mol / L)-oxalate (0.5 mol / L)-bromine (0.5 mol / L)-ferric (0.5 mol / L) complex solution. Use this solution as the negative electrode electrolyte for the all-ferric flow battery.

[0049] 2. Preparation of the positive electrode electrolyte:

[0050] 1) Add 0.05 mol FeCl2 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner until the solution is evenly dispersed.

[0051] 2) Weigh 0.2 mol of NH4Cl solid and add it to the above solution. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution until it is evenly dispersed.

[0052] 3) Transfer the mixed solution to a 100 mL volumetric flask, let it cool to room temperature, make up to volume, shake well, and prepare a 0.5 mol / L FeCl2 solution. Use this solution as the positive electrode electrolyte for the all-iron flow battery.

[0053] 3. Assembly of an all-ferric flow battery:

[0054] according to Figure 1The vanadium redox flow battery is assembled with the following components from the outside in: stainless steel end plates, current collectors, carbon felt electrodes, and ion exchange membranes. A magnetically driven circulation pump serves as the power delivery device for the electrolyte. The ion exchange membrane is a Nafion 212 model. The carbon felt electrodes, with an electrode area of ​​3cm × 3cm × 6mm, are used for both positive and negative electrodes. The current collectors for both electrodes are graphite plates with a serpentine flow field.

[0055] 4. Performance testing of all-iron flow batteries:

[0056] Constant current charge / discharge test: using 100mA / cm 2 Current density, charge / discharge cutoff voltage is 1.2–0.4V.

[0057] Cyclic stability test: using 100 mA / cm 2 The current density and charge / discharge cutoff voltage are 1.2–0.4V. After the test, the battery's coulombic efficiency, voltage efficiency, energy efficiency, and capacity are obtained.

[0058] Examples 3-7: Negative electrode electrolytes and all-iron flow batteries with different concentrations of citrate-oxalate-phosphate-iron ion complexes

[0059] To simplify the description and enhance the comparative effect, Examples 3-7 describe the negative electrode electrolytes prepared at different concentrations and their performance in an all-iron flow battery. The only variables are the contents of FeCl2, FeCl3, trisodium citrate, potassium oxalate, and potassium phosphate. The concentration of FeCl2 in the positive electrode electrolyte is the same as that in the negative electrode electrolyte. The remaining steps are exactly the same as in Example 1. The specific formulations and battery performance are shown in Table 1:

[0060] Table 1. Performance of negative electrode electrolytes and all-iron flow batteries with different concentrations of citrate-oxalate-phosphate-iron ion complexes.

[0061]

[0062] Examples 8-12: Negative electrode electrolytes and all-iron flow batteries of different concentrations of citrate-oxalate-bromine-iron complexes

[0063] To simplify the description and enhance the comparative effect, Examples 8-12 describe the negative electrode electrolytes prepared at different concentrations and their performance in an all-iron flow battery. The only variables are the contents of FeCl2, FeCl3, trisodium citrate, potassium oxalate, and potassium bromide. The concentration of FeCl2 in the positive electrode electrolyte is the same as that in the negative electrode electrolyte. The remaining steps are exactly the same as in Example 2. The specific formulations and battery performance are shown in Table 1:

[0064] Table 2. Performance of negative electrode electrolytes and all-iron flow batteries with different concentrations of citrate-oxalate-bromine-iron complexes.

[0065]

[0066] Comparative Example 1:

[0067] 1. Preparation method of negative electrode electrolyte based on citrate-iron ion complex:

[0068] 1) First, add 0.05 mol FeCl3 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner. Once the solution is evenly dispersed, you will get solution 1.

[0069] 2) Weigh 0.05 mol of trisodium citrate and add it to solution 1. Stir evenly with a glass rod and sonicate until the solid is completely dissolved. After the solution is evenly dispersed, you will get solution 2.

[0070] 5) Weigh 0.2 mol of NH4Cl solid and add it to solution 2. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution. After the solution is evenly dispersed, solution 3 is obtained.

[0071] 5) Transfer mixed solution 3 to a 100mL volumetric flask, let it cool to room temperature, make up to volume, shake well, and prepare a citrate (0.5mol / L)-iron (0.5mol / L) complex solution. Use this solution as the negative electrode electrolyte for the all-iron flow battery.

[0072] 2. Preparation of the positive electrode electrolyte:

[0073] 1) Add 0.05 mol FeCl2 to a beaker containing 60 ml of deionized water and disperse it using an ultrasonic cleaner until the solution is evenly dispersed.

[0074] 2) Weigh 0.2 mol of NH4Cl solid and add it to the above solution. Stir evenly with a glass rod and use an ultrasonic cleaner to evenly disperse the solution until it is evenly dispersed.

[0075] 3) Transfer the mixed solution to a 100 mL volumetric flask, allow it to cool to room temperature, then dilute to volume, shake well, and prepare a 0.5 mol / L FeCl2 solution. This solution will be used as the positive electrode electrolyte for the all-iron flow battery.

[0076] 3. Assembly of an all-ferric flow battery:

[0077] This process is the same as step 3 in Example 1.

[0078] 4. Test conditions for all-iron flow batteries:

[0079] This process is the same as step 4 in Example 1.

[0080] Comparative Example 2:

[0081] 1. Preparation method based on ferric sulfate negative electrode electrolyte:

[0082] 1) Measure 0.1 mol / L HCl solution using a graduated cylinder, adjust the pH of the solution to ≈3.5 using a pH meter, and prepare 80 ml of weakly acidic solution.

[0083] 2) Weigh 0.1 mol of ferric sulfate and slowly add it to the above solution. Adjust the pH of the solution to 3.5 by adding deionized water and a trace amount of 0.1 mol / L HCl to obtain an acidic solution.

[0084] 3) Transfer the mixed solution to a 100 mL volumetric flask, make up to volume, shake well, and prepare a 1.0 mol / L ferric sulfate solution. This solution will be used as the negative electrode electrolyte for the all-ferric flow battery.

[0085] 2. Preparation of positive electrode electrolyte:

[0086] 1) Measure 0.1 mol / L HCl solution using a graduated cylinder, adjust the pH of the solution to ≈3.5 using a pH meter, and prepare 80 ml of weakly acidic solution.

[0087] 2) Weigh 0.1 mol of ferrous sulfate and slowly add it to the above solution. Adjust the pH of the solution to 3.5 by adding deionized water and a trace amount of 0.1 mol / L HCl to obtain an acidic solution.

[0088] 3) Transfer the mixed solution to a 100 mL volumetric flask, make up to volume, shake well, and prepare a 1.0 mol / L ferrous sulfite solution. Use this solution as the positive electrode electrolyte for the all-iron flow battery.

[0089] 3. Assembly of an all-ferric flow battery:

[0090] This process is the same as step 3 in Comparative Example 1.

[0091] 4. Test conditions for all-ferric flow batteries:

[0092] This process is the same as step 4 in Example 1.

[0093] Table 3. Performance of different comparative ratio negative electrode electrolytes and all-iron flow batteries

[0094]

[0095] As can be seen from the above embodiments and comparative examples, the energy efficiency of the all-iron flow battery assembled with the electrolyte of this patent is improved by 2-7%, the capacity retention rate after 50 cycles is improved by more than 20%, which fundamentally solves the problem of short battery life caused by iron dendrites in the negative electrode, and greatly improves the cycle stability and efficiency of the battery.

Claims

1. A negative electrode electrolyte for a liquid iron flow energy storage battery, characterized in that, It includes iron ions, a first complexing agent, a second complexing agent, a third complexing agent, a supporting electrolyte, and water. The first, second, and third complexing agents can simultaneously bind to the same iron ion. The first complexing agent is citric acid and its salt, the second complexing agent is oxalic acid and its salt, and the third complexing agent is phosphate or bromide ions. The molar ratio of iron ions, the first complexing agent, the second complexing agent, and the third complexing agent is 1:(1-1.5):(1-1.5):(1-1.5).

2. The negative electrode electrolyte for a liquid iron flow energy storage battery as described in claim 1, characterized in that, The substance containing iron ions is selected from one or more of ferric chloride, ferric sulfate, and ferric nitrate, and the concentration of iron ions is 0.1-1.6 mol / L.

3. The negative electrode electrolyte for a liquid iron flow energy storage battery as described in claim 1, characterized in that, The first complexing agent is one or more of citric acid, sodium citrate, and potassium citrate, with a concentration of 0.1-2.4 mol / L.

4. The negative electrode electrolyte for a liquid iron flow energy storage battery as described in claim 1, characterized in that, The oxalate used in the second complexing agent is selected from one or more of sodium oxalate, potassium oxalate, and lithium oxalate, with a concentration of 0.1-2.4 mol / L.

5. The negative electrode electrolyte for a liquid iron flow energy storage battery as described in claim 1, characterized in that, The third complexing agent is one or more of sodium phosphate, potassium phosphate, lithium phosphate, sodium bromide, potassium bromide, and lithium bromide, with a concentration of 0.1-2.4 mol / L.

6. The negative electrode electrolyte for a liquid iron flow energy storage battery as described in claim 1, characterized in that, The electrolyte is used to adjust the pH and conductivity of the solution. The electrolyte is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium chloride, and ammonium sulfate. The concentration of the electrolyte is 0.1-8 mol / L.

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