Aqueous total-iron flow battery negative electrode electrolyte and aqueous total-iron flow battery

Abstract

The invention discloses an aqueous all-iron flow battery negative electrode electrolyte and an aqueous all-iron flow battery, and belongs to the fields of an electrochemical energy storage technology and a flow battery. The aqueous total iron flow battery negative electrode electrolyte comprises an iron ion-containing active substance, a first complexing agent, a second complexing agent and hydrogen evolution inhibitor, a supporting electrolyte and water, and the first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined to iron ions to form a stable chelate with a saturated six-coordinate structure. The first complexing agent is selected from triethanolamine or analogues thereof, and the second complexing agent and hydrogen evolution inhibitor is selected from organic acids having a chelation effect and salts thereof. According to the invention, two complexing agents are combined with the same iron ion at the same time to form a stable six-coordinate structure, so that the problems of capacity fading, low energy efficiency and poor cycling stability caused by iron separation and hydrogen separation due to dissociation of organic matters and ferrous ions in the operation process of the battery are effectively relieved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage technology and liquid flow batteries, and specifically relates to an aqueous all-iron liquid flow battery negative electrode electrolyte and an aqueous all-iron liquid flow battery. Background Art

[0002] As the most promising large-scale energy storage technology, flow batteries can store the electricity generated by renewable energy in the form of chemical energy, and then convert the chemical energy into stable electrical energy output during discharge. The basic components of flow batteries include modules such as electrodes, electrolytes, diaphragms, electrolyte storage tanks, circulation pumps, circulation pipelines and control systems. When the flow battery is working, the electrolyte in the battery is continuously renewed and circulated on the surface of the electrode through the circulation pump. The diaphragm separates the positive and negative electrolytes to prevent cross-contamination caused by electrolyte mixing. The electrochemical redox reaction of the battery occurs on the surface of the electrode. At present, all-vanadium flow batteries have been commercialized, but due to the high cost of their electrolytes, their large-scale application is also limited to a certain extent. In addition to all-vanadium flow batteries, iron-chromium flow batteries, all-iron flow batteries, zinc-bromine flow batteries and zinc-iron flow batteries have also been developed. Among them, all-iron flow batteries have attracted widespread attention because both the positive and negative electrodes use abundant and cheap iron salts as raw materials; its principle is that the positive and negative active materials use Fe 2+ , positive electrode Fe 3+ / Fe 2+ As a redox couple, the negative electrode Fe 2+ / Fe 0 As a redox couple, the negative electrode has solid iron to participate in the reaction, which requires the electrolyte to be an acidic solution. It is easy to cause the occurrence of hydrogen evolution side reaction, affecting the cycle stability of the battery, resulting in low efficiency of traditional all-iron liquid flow batteries and severe capacity attenuation.

[0003] In response to these problems, scientists have tried to make the positive and negative electrodes of all-iron flow batteries both Fe 2+ and Fe 3+ On the negative electrode side, different complexes are used to chelate Fe 3+ / Fe 2+ , changing its redox potential and improving the stability of the active substance; using organic matter with a larger molecular weight as a ligand can effectively reduce the cross-reaction between the ligand and the positive electrode material.

[0004] Chinese patent CN113328124A discloses a negative electrode electrolyte for all-iron liquid flow battery, the negative electrode of which still uses the traditional Fe 2+ / Fe 0The redox couple reacts. By adding a complexing agent such as citric acid or trisodium citrate to the negative electrolyte to chelate ferrous ions and remove the bound water originally coordinated by the ferrous ions, the surrounding structure is regulated, the hydrolysis of ferrous ions is inhibited, the iron deposition becomes more uniform, and the reversibility of the deposition / dissolution reaction is improved. However, the precipitation of metallic iron will inevitably lead to problems such as hydrogen evolution and iron dendrites piercing the membrane, resulting in low battery efficiency and rapid capacity decay.

[0005] Chinese Patent CN112467179A discloses an alkaline all-iron flow battery. Its positive electrode uses ferricyanide / ferrocyanide as the redox couple, and its negative electrode uses gluconic acid as a chelating agent to form a complex with iron as the electroactive substance. The semi-permeable membrane used is a SPEEK membrane, and the battery has good stability. However, the SPEEK membrane is prone to swelling in an aqueous flow battery, has poor mechanical properties, and the proton exchange ability of the SPEEK membrane is much lower than that of the Nafion membrane, resulting in low battery energy efficiency.

[0006] Chinese Patent CN114709459A discloses a negative electrolyte for an aqueous all-iron flow battery. The negative electrolyte adopts a strategy of simultaneously complexing two ligands to the same iron ion or ferrous ion in an alkaline environment. This complexing method can achieve saturated six-coordination of iron and effectively reduce the phenomena of hydrogen evolution and iron precipitation. However, the proportion of the second complex in this patent is relatively small, and more is the role played by triethanolamine or its analogs. Therefore, this electrolyte will inevitably face attenuation during long-term cyclic voltammetry testing and also has problems of capacity decay and efficiency reduction in battery testing.

[0007] The complex formed by ferric ions and ferrous ions with triethanolamine and its analogs has a negative redox potential and low raw material costs, and is a negative electrolyte for an all-iron flow battery with development potential. Chinese Patent CN113764714A discloses an electrolyte for an aqueous flow battery, an all-iron aqueous flow battery and its application. The negative electrolyte uses bis(2-hydroxyethyl)amino(tris(hydroxymethyl)methane) or 3-[N-N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid as ligands to form complexes with ferric ions or ferrous ions. These two ligands are both analogs of triethanolamine. The binding force between triethanolamine and ferrous ions is weak and will fall off during long-term operation, resulting in partial reduction of ferrous ions to metallic iron. The functional groups of these two ligands acting on ferric ions or ferrous ions are the same as those of triethanolamine. Therefore, there are also problems of attenuation faced during long-term cyclic voltammetry testing and capacity decay and efficiency reduction in battery testing.

[0008] The most stable coordination mode of metal iron ions and ferrous ions is a six-coordination structure. Triethanolamine and its analogues mostly form a five-coordination structure with iron. During the operation of the battery, some coordination bonds will break, resulting in the dissociation of ferrous ions from triethanolamine and its analogues, and then being reduced to metallic iron. The deposition of iron will cause a series of problems such as hydrogen evolution and capacity decay. Eventually, it will lead to low battery efficiency and poor stability.

[0009] The present invention adopts a strategy of combining a complexing agent and a hydrogen evolution inhibitor. The complexing agent forms a stable coordination structure with iron ions and ferrous ions, improving the solubility and electrochemical activity of the negative electrode electrolyte. At the same time, the hydrogen evolution inhibitor can stabilize the Coulombic efficiency and cycling performance of the battery in the case of a small amount of iron precipitation, thereby improving the capacity retention rate and long-term cycling stability of the aqueous all-iron redox flow battery. Summary of the Invention

[0010] Aiming at the problems of metal iron precipitation caused by the weak chelation of iron ions with different valence states and ligands in the prior art of all-iron redox flow batteries, which lead to hydrogen evolution side reactions, battery capacity decay and poor long-cycle performance, the purpose of the present invention is to provide an aqueous negative electrode electrolyte for an all-iron redox flow battery and an aqueous all-iron redox flow battery. Based on the negative electrode electrolyte combined with a complexing agent and a hydrogen evolution inhibitor, the solubility and electrochemical activity of the active substances in the negative electrode electrolyte are greatly improved, the hydrogen evolution reaction is reduced, and the energy efficiency and cycle life of the aqueous all-iron redox flow battery are improved.

[0011] The purpose of the present invention is achieved by the following technical solutions: An aqueous negative electrode electrolyte for an all-iron redox flow battery, comprising an iron ion active substance, a first complexing agent, a second complexing agent and hydrogen evolution inhibitor, a supporting electrolyte and water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable chelate with a saturated six-coordination structure. The first complexing agent is selected from triethanolamine or its analogues, and the second complexing agent and hydrogen evolution inhibitor are selected from organic acids with chelating effects and their salts.

[0012] Further, the iron ion active substance is selected from at least one of iron sulfate, iron nitrate, iron chloride and iron phosphate; The concentration of iron ions is 0.1 mol / L - 1.5 mol / L.

[0013] Further, the first complexing agent is selected from one of triethanolamine, 3-bis(2-hydroxyethyl)amino-2-hydroxypropanesulfonic acid and bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane.

[0014] Further, the second complexing agent and hydrogen evolution inhibitor are selected from one of gluconic acid and its salts, tartaric acid and its salts, trisodium nitrilotriacetate, glycine and its salts or L-lactic acid and its salts.

[0015] Further, the gluconate is selected from one of sodium gluconate, zinc gluconate, potassium gluconate and calcium gluconate; The tartrate is selected from one of sodium tartrate, calcium tartrate, potassium tartrate and magnesium tartrate; The glycinate is selected from one of sodium glycinate, zinc glycinate and magnesium glycinate; The L-lactate is selected from one of zinc L-lactate, calcium L-lactate, lithium L-lactate and sodium L-lactate.

[0016] Further, the concentrations of the first complexing agent, the second complexing agent and the hydrogen evolution inhibitor are all 0.1 mol / L - 2 mol / L.

[0017] Further, the supporting electrolyte is selected from at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0018] Further, the concentration of the supporting electrolyte is 0.1 mol / L - 6 mol / L.

[0019] Further, the molar concentration ratio of ferric ions, the first complexing agent and the second complexing agent and the hydrogen evolution inhibitor is 1:(0.5 - 2):(1 - 3).

[0020] An all-aqueous iron flow battery includes electrodes, a positive electrolyte, a negative electrolyte, a separator, a positive electrolyte storage tank, a negative electrolyte storage tank, a positive peristaltic pump, a negative peristaltic pump, pipelines and a battery testing system; the positive and negative electrolytes are respectively transported and circulated by the positive and negative peristaltic pumps and are separated by the separator in the battery cavity; The negative electrolyte adopts a negative electrolyte of an all-aqueous iron flow battery of the present invention; The electrode material is selected from one of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper and carbon cloth inert materials; The separator is selected from one of perfluorosulfonic acid membranes Nafion117, Nafion115, Nafion212 and Nafion211.

[0021] Advantages and effects of the present invention: 1. The present invention uses two complexing agents to simultaneously combine with the same ferric ion to form a stable six-coordination structure, effectively reducing the iron precipitation and hydrogen evolution caused by the dissociation of organic matter and ferrous ions during the operation of the battery, thereby solving the problems of capacity attenuation, low energy efficiency and poor cycle stability. For the all-aqueous iron flow battery of the present invention, the Coulomb efficiency ≥ 98.5%, the voltage efficiency ≥ 84.8%, the energy efficiency ≥ 84.2% after 300 cycles, and the number of cycles when the battery capacity decays to 70% ≥ 1005 cycles.

[0022] 2. The present invention adopts a strategy that combines a complexing agent with hydrogen evolution inhibition. On the one hand, in an alkaline environment, iron ions form stable complexes with the complexing agent, ultimately obtaining a relatively negative redox potential, which matches the positive electrode electrolyte to form a relatively high battery voltage. On the other hand, it improves the solubility of the active substances in the negative electrode electrolyte, and the formed complex effectively inhibits the penetration of the negative electrode active substances to the positive electrode electrolyte side, alleviating the problems of cross-contamination between the positive and negative electrolytes and capacity attenuation. Description of the Drawings

[0023] Figure 1 Cyclic voltammogram curves of the complex solution of triethanolamine (0.25 mol / L) - iron ions (0.5 mol / L) - potassium gluconate (0.5 mol / L) - sodium hydroxide (2 mol / L) in Example 1 within the scanning rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 2 Cyclic voltammogram curves of the complex solution of triethanolamine (0.1 mol / L) - iron ions (0.1 mol / L) - potassium gluconate (0.125 mol / L) - sodium hydroxide (0.1 mol / L) in Example 2 within the scanning rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 3 Cyclic voltammogram curves of the complex solution of 3-bis(2-hydroxyethyl)amino-2-hydroxypropane sulfonic acid (0.75 mol / L) - iron ions (1.5 mol / L) - sodium gluconate (1.5 mol / L) - potassium hydroxide (6 mol / L) in Example 3 within the scanning rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 4 Cyclic voltammogram curves of the complex solution of bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane (0.9 mol / L) - iron ions (0.60 mol / L) - sodium glycinate (1.8 mol / L) - lithium hydroxide (3 mol / L) in Example 4 within the scanning rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 5 Cyclic voltammogram curves of the complex solution of triethanolamine (0.25 mol / L) - iron ions (0.5 mol / L) - sodium glycinate (1.5 mol / L) - sodium hydroxide (2 mol / L) in Example 5 within the scanning rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 6For the cyclic voltammogram of the complex solution of triethanolamine (2 mol / L) - iron ion (1 mol / L) - zinc glycinate (2 mol / L) - sodium hydroxide (2 mol / L) in Example 6 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 7 For the cyclic voltammogram of the complex solution of triethanolamine (1 mol / L) - iron ion (1 mol / L) - sodium tartrate (2 mol / L) - sodium hydroxide (3 mol / L) in Example 7 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 8 For the cyclic voltammogram of the complex solution of 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid (0.1 mol / L) - iron ion (0.1 mol / L) - potassium tartrate (0.1 mol / L) - potassium hydroxide (3 mol / L) in Example 8 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 9 For the cyclic voltammogram of the complex solution of bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane (0.5 mol / L) - iron ion (0.5 mol / L) - trisodium nitrilotriacetate (1 mol / L) - sodium hydroxide (3 mol / L) in Example 9 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 10 For the cyclic voltammogram of the complex solution of triethanolamine (0.5 mol / L) - iron ion (0.5 mol / L) - sodium L - lactate (1.25 mol / L) - potassium hydroxide (2 mol / L) in Example 10 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 11 For the cyclic voltammogram of the complex solution of bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane (0.5 mol / L) - iron ion (1.0 mol / L) - lithium L - lactate (2 mol / L) - lithium hydroxide (2 mol / L) in Example 11 within the scan rate range of 10 mV·s -1 -50 mV·s -1 ; Figure 12 For the comparison chart of Coulombic efficiency between Examples 1 to 11 and Comparative Examples 1 to 2; Figure 13 For the comparison chart of voltage efficiency between Examples 1 to 11 and Comparative Examples 1 to 2; Figure 14 Energy efficiency comparison charts for Examples 1 to 11 and Comparative Examples 1 to 2; Figure 15 Cycling times comparison charts for Examples 1 to 11 and Comparative Examples 1 to 2 when the capacity decays to 70%. Detailed implementation manners

[0024] The present invention will be described in detail below in conjunction with examples.

[0025] Example 1 A negative electrolyte for an all - iron aqueous flow battery of the present invention includes iron - ion active substance ferric chloride, a first complexing agent triethanolamine, a second complexing agent and hydrogen evolution inhibitor potassium gluconate, a supporting electrolyte sodium hydroxide, and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable triethanolamine - iron ion - potassium gluconate complex with a saturated six - coordination structure; the iron ion concentration is 0.5 mol / L, the first complexing agent concentration is 0.25 mol / L, the second complexing agent and hydrogen evolution inhibitor is 0.5 mol / L, the supporting electrolyte concentration is 2 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:0.5:1; The preparation method of a negative electrolyte for an all - iron aqueous flow battery in Example 1 is as follows: Weigh 13.515 g of FeCl3·6H2O, 3.32 mL of triethanolamine, 11.71 g of potassium gluconate, and 8 g of sodium hydroxide and add them to a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant - temperature water bath, and stir magnetically until completely dissolved. Then transfer it to a 100 - mL volumetric flask and make up the volume to obtain 100 mL of triethanolamine (0.25 mol / L) - iron ion (0.5 mol / L) - potassium gluconate (0.5 mol / L) - sodium hydroxide (2 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 1 shown, for a negative electrolyte of an all - iron aqueous flow battery in Example 1, within the scanning rate range of 10 mV·s -1 -50 mV·s -1 During the cyclic voltammetry curve scanning, there is a linear relationship between the peak current density and the square root of the scanning rate, and the cyclic voltammetry curve is relatively symmetric, indicating good reversibility.

[0026] An all - iron aqueous flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a separator, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system; the positive and negative electrolytes are circulated by pumps and are separated by a separator in the battery cavity; The electrode is made of carbon felt, and the membrane is made of perfluorosulfonic acid membrane Nafion212; The negative electrolyte is a kind of aqueous all-iron redox flow battery negative electrolyte of Example 1 of the present invention; The preparation method of the positive electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 8 g of NaOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for constant volume to obtain a 100 mL 0.5 mol / L K4[Fe(CN)6] solution for use.

[0027] Performance test of the aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min, at 80 mA / cm 2 Charge and discharge tests are carried out, and the charge and discharge cut-off voltages are set to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, the Coulomb efficiency of a kind of aqueous all-iron redox flow battery of Example 1 after 300 cycles is 99.1%, the voltage efficiency is 85.3%, the energy efficiency is 84.5%, and the number of cycles when the battery capacity decays to 70% is 1120 cycles.

[0028] Example 2 A kind of aqueous all-iron redox flow battery negative electrolyte of the present invention includes iron ion active substance iron phosphate, first complexing agent triethanolamine, second complexing agent and hydrogen evolution inhibitor potassium gluconate, supporting electrolyte sodium hydroxide and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable triethanolamine-iron ion-potassium gluconate complex with a saturated six-coordinate structure; the iron ion concentration is 0.1 mol / L, the first complexing agent concentration is 0.1 mol / L, the second complexing agent and hydrogen evolution inhibitor is 0.125 mol / L, the supporting electrolyte concentration is 0.1 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1:1.25; The preparation method of a kind of aqueous all-iron redox flow battery negative electrolyte of Example 2 is as follows: Weigh 1.51 g of FePO4, 1.33 mL of triethanolamine, 2.93 g of potassium gluconate, and 0.4 g of sodium hydroxide, add them to a beaker in sequence, add 60 mL of deionized water, heat in a constant temperature water bath at 40 °C, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for constant volume to obtain a 100 mL triethanolamine (0.1 mol / L)-iron ion (0.1 mol / L)-potassium gluconate (0.125 mol / L)-sodium hydroxide (0.1 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 2 shown, the cyclic voltammogram curve of the negative electrolyte of the all-iron aqueous flow battery in Example 2 is scanned within a sweep rate of 10 mV·s -1 -50 mV·s -1 The result shows that there is a linear relationship between the peak current density and the square root of the scan rate, and the cyclic voltammogram curve is relatively symmetric, with good reversibility.

[0029] An all-iron aqueous flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a separator, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines and a battery testing system; the positive and negative electrolytes are circulated by pumps and separated by the separator in the battery cavity; The electrodes are made of carbon felt, and the separator is made of perfluorosulfonic acid membrane Nafion115; The negative electrolyte is the negative electrolyte of the all-iron aqueous flow battery in Example 2; The preparation method of the positive electrolyte is as follows: Weigh 4.22 g of K4[Fe(CN)6]·3H2O and 0.4 g of NaOH and add them to 80 mL of deionized water. After magnetic stirring until completely dissolved, transfer it to a 100 mL volumetric flask and make up the volume to obtain 100 mL of 0.1 mol / L K4[Fe(CN)6] solution for use.

[0030] Performance test of the all-iron aqueous flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min. For charge and discharge tests, the charge and discharge cut-off voltages are set to 1.6 V and 0.5 V respectively; 2 Test results: As shown, the Coulombic efficiency of the all-iron aqueous flow battery in Example 2 after 300 cycles is 99.7%, the voltage efficiency is 85.4%, the energy efficiency is 85.2%, and the number of cycles when the battery capacity decays to 70% is 1050 cycles. Figures 12 - 15

[0031] Example 3 A negative electrolyte for an all - iron aqueous flow battery of the present invention includes an iron - ion active substance ferric phosphate, a first complexing agent 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid, a second complexing agent and hydrogen evolution inhibitor sodium gluconate, a supporting electrolyte potassium hydroxide, and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid - iron ion - sodium gluconate complex with a saturated six - coordinate structure. The concentration of iron ions is 1.5 mol / L, the concentration of the first complexing agent is 0.75 mol / L, the second complexing agent and hydrogen evolution inhibitor is 1.5 mol / L, the concentration of the supporting electrolyte is 6.0 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:0.5:1; The preparation method of a negative electrolyte for an all - iron aqueous flow battery in Example 3 is as follows: Weigh 22.62 g of FePO4, 18.25 g of 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid, 32.72 g of sodium gluconate, and 33.67 g of potassium hydroxide and add them to a beaker in sequence. Add 60 mL of deionized water, heat in a constant - temperature water bath at 40 °C, and stir magnetically until completely dissolved. Then transfer it to a 100 - mL volumetric flask and make up the volume to obtain a 100 - mL solution of 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid (0.75 mol / L)-iron ion (1.5 mol / L)-sodium gluconate (1.5 mol / L)-potassium hydroxide (6 mol / L) complex; Electrochemical performance test of the electrolyte: As Figure 3 shown, for the negative electrolyte of an all - iron aqueous flow battery in Example 3, within the scanning rate range of 10 mV·s -1 -50 mV·s -1 in the cyclic voltammetry curve scanning, there is a linear relationship between the peak current density and the square root of the scanning rate. The cyclic voltammetry curve is relatively symmetric, indicating good reversibility, and the peak current density is relatively large, indicating good electrochemical activity.

[0032] An all - iron aqueous flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a separator, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system. The positive and negative electrolytes are pumped to circulate and are separated by a separator in the battery cavity; The electrodes are made of graphite plates, and the separator is a perfluorosulfonic acid membrane Nafion117; The negative electrolyte is the negative electrolyte of an all - iron aqueous flow battery in Example 3; The preparation method of the positive electrolyte is as follows: Weigh 31.68 g of K4[Fe(CN)6]·3H2O, 22.80 g of Na4[Fe(CN)6] and 33.67 g of KOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for constant volume to obtain 100 mL of K4[Fe(CN)6] (0.75 mol / L) + Na4[Fe(CN)6] (0.75 mol / L) solution for use.

[0033] Performance test of aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrode electrolytes are both 100 mL / min, and at 80 mA / cm 2 Charge-discharge test, set the charge-discharge cut-off voltages to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, the Coulombic efficiency of an aqueous all-iron redox flow battery in Example 3 after 300 cycles is 99.3%, the voltage efficiency is 84.8%, the energy efficiency is 84.2%, and the number of cycles when the battery capacity decays to 70% is 1135 cycles.

[0034] Example 4 The negative electrode electrolyte of an aqueous all-iron redox flow battery of the present invention includes iron ion active substance ferric nitrate, the first complexing agent bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane, the second complexing agent and hydrogen evolution inhibitor sodium glycinate, supporting electrolyte lithium hydroxide and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane-iron ion-sodium glycinate complex with a saturated six-coordinate structure; the iron ion concentration is 0.6 mol / L, the first complexing agent concentration is 0.9 mol / L, the second complexing agent and hydrogen evolution inhibitor is 1.8 mol / L, the supporting electrolyte concentration is 3 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1.5:3; The preparation method of the negative electrode electrolyte of an aqueous all-iron redox flow battery in Example 4 is as follows: Weigh 24.24 g of Fe(NO3)3·9H2O, 18.83 g of bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane, 17.47 g of sodium glycinate, and 7.19 g of lithium hydroxide, add them to a beaker in sequence, add 60 mL of deionized water, heat in a 40 °C constant temperature water bath, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for constant volume to obtain 100 mL of bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane (0.9 mol / L)-iron ion (0.6 mol / L)-sodium glycinate (1.8 mol / L)-lithium hydroxide (3 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 4 shown, for the negative electrolyte of the all - iron aqueous flow battery in this Example 4, within the scanning rate range of 10 mV·s -1 - 50 mV·s -1 during cyclic voltammetry scanning, there is a linear relationship between the peak current density and the square root of the scanning rate, and the cyclic voltammogram is relatively symmetric, indicating good reversibility.

[0035] An all - iron aqueous flow battery of the present invention includes electrodes, positive electrolyte, negative electrolyte, diaphragm, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery testing system; the positive and negative electrolytes are circulated by pumps and separated by a diaphragm in the battery cavity; Graphite felt is selected as the electrode, and Nafion211, a perfluorosulfonic acid membrane, is selected as the diaphragm; The negative electrolyte is the negative electrolyte of the all - iron aqueous flow battery in this Example 4; The preparation method of the positive electrolyte is as follows: Weigh 25.34 g of K4[Fe(CN)6]·3H2O and 7.19 g of LiOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 - mL volumetric flask for volume fixation to obtain 100 mL of 0.6 mol / L K4[Fe(CN)6] solution for use.

[0036] Performance test of the all - iron aqueous flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min. For charge - discharge testing, the charge - discharge cut - off voltages are set to 1.6 V and 0.5 V respectively; 2 Test results: As Figures 12 - 15 shown, for the all - iron aqueous flow battery in this Example 4, the Coulombic efficiency after 300 cycles is 99.2%, the voltage efficiency is 85.9%, the energy efficiency is 85.3%, and the number of cycles when the battery capacity decays to 70% is 1120 cycles.

[0037] Example 5 ​A negative electrolyte for an all - iron aqueous flow battery of the present invention comprises iron - ion active substance ferric chloride, a first complexing agent triethanolamine, a second complexing agent and hydrogen evolution inhibitor sodium glycinate, a supporting electrolyte sodium hydroxide, and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor simultaneously bind to iron ions to form a stable triethanolamine - iron ion - sodium glycinate complex with a saturated six - coordination structure. The concentration of iron ions is 0.5 mol / L, the concentration of the first complexing agent is 0.25 mol / L, the second complexing agent and hydrogen evolution inhibitor is 1.5 mol / L, the concentration of the supporting electrolyte is 2 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:0.5:3; The preparation method of a negative electrolyte for an all - iron aqueous flow battery in Example 5 is as follows: Weigh 13.515 g of FeCl3·6H2O, 3.32 mL of triethanolamine, 14.56 g of sodium glycinate, and 8 g of sodium hydroxide and add them into a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant - temperature water bath, and stir magnetically until completely dissolved. Then transfer it to a 100 - mL volumetric flask and make up the volume to obtain 100 mL of a triethanolamine (0.25 mol / L) - iron ion (0.5 mol / L) - sodium glycinate (1.5 mol / L) - sodium hydroxide (2 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 5 shown, for the negative electrolyte of an all - iron aqueous flow battery in Example 5, within the scanning rate range of 10 mV·s -1 - 50 mV·s -1 in the cyclic voltammetry curve scanning, there is a linear relationship between the peak current density and the square root of the scanning rate, and the cyclic voltammetry curve is relatively symmetric, indicating good reversibility.<{

[0038] An all - iron aqueous flow battery of the present invention comprises electrodes, a positive electrolyte, a negative electrolyte, a diaphragm, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system. The positive and negative electrolytes are pumped for circulation and are separated by a diaphragm in the battery cavity; The electrodes are made of carbon paper, and the diaphragm is made of perfluorosulfonic acid membrane Nafion117; The negative electrolyte is the negative electrolyte of an all - iron aqueous flow battery in Example 5; The preparation method of the positive electrolyte is as follows:[[ID=!24]] Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 8 g of NaOH and add them to 80 mL of deionized water. Stir magnetically until completely dissolved, then transfer it to a 100 - mL volumetric flask and make up the volume to obtain 100 mL of 0.5 mol / L K4[Fe(CN)6] solution for use.

[0039] Performance Test of Aqueous All-Iron Redox Flow Battery: Test Conditions: During the operation of the battery, the flow rates of the positive and negative electrolyte solutions are both 100 mL / min. During the charge and discharge test, the cut-off voltages for charge and discharge are set at 1.6 V and 0.5 V respectively at 80 mA / cm 2 charge and discharge test, the cut-off voltages for charge and discharge are set at 1.6 V and 0.5 V respectively; Test Results: As Figures 12 - 15 shown, for an aqueous all-iron redox flow battery of Example 5, the Coulombic efficiency after 300 cycles is 98.5%, the voltage efficiency is 85.9%, the energy efficiency is 84.7%, and the number of cycles when the battery capacity decays to 70% is 1500 cycles.

[0040] Example 6 The negative electrolyte of an aqueous all-iron redox flow battery of the present invention includes iron ion active substance ferric nitrate, first complexing agent triethanolamine, second complexing agent and hydrogen evolution inhibitor zinc glycinate, supporting electrolyte sodium hydroxide and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable triethanolamine-iron ion-zinc glycinate complex with a saturated six-coordinate structure; the iron ion concentration is 1 mol / L, the first complexing agent concentration is 2 mol / L, the second complexing agent and hydrogen evolution inhibitor is 2 mol / L, the supporting electrolyte concentration is 2 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:2:2; The preparation method of the negative electrolyte of an aqueous all-iron redox flow battery of Example 6 is as follows: Weigh 40.4 g of Fe(NO3)3·9H2O, 26.55 ml of triethanolamine, 42.7 g of zinc glycinate, and 8 g of sodium hydroxide and add them to a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant temperature water bath, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for volume fixation to obtain 100 mL of triethanolamine (2 mol / L)-iron ion (1 mol / L)-zinc glycinate (2 mol / L)-sodium hydroxide (2 mol / L) complex solution; Electrochemical Performance Test of the Electrolyte: As Figure 6 shown, for the negative electrolyte of an aqueous all-iron redox flow battery of Example 6, when scanning the cyclic voltammetry curve within the sweep rate range of 10 mV·s -1 -50 mV·s -1 there is a linear relationship between the peak current density and the square root of the scan rate, and the cyclic voltammetry curve is relatively symmetric, indicating good reversibility.

[0041] An aqueous all-iron redox flow battery of the present invention includes electrodes, positive electrolyte, negative electrolyte, diaphragm, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines and a battery test system; the positive and negative electrolytes are circulated by pumps and separated by a diaphragm in the battery cavity; The electrode is made of graphite paper, and the separator is made of perfluorosulfonic acid membrane Nafion115; The negative electrolyte is a kind of negative electrolyte of aqueous all-iron redox flow battery in Example 6 of this embodiment; The preparation method of the positive electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O, 15.20 g of Na4[Fe(CN)6] and 8 g of NaOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for constant volume to obtain a 100 mL solution of K4[Fe(CN)6] (0.5 mol / L) + Na4[Fe(CN)6] (0.5 mol / L) for use.

[0042] Performance test of aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min, at 80 mA / cm 2 Charge and discharge tests are carried out, and the charge and discharge cut-off voltages are set to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, for a kind of aqueous all-iron redox flow battery in Example 6 of this embodiment, the Coulomb efficiency after 300 cycles is 99.6%, the voltage efficiency is 85.2%, the energy efficiency is 84.9%, and the number of cycles when the battery capacity decays to 70% is 1005 cycles.

[0043] Example 7 A kind of negative electrolyte of aqueous all-iron redox flow battery of the present invention includes iron ion active substance ferric sulfate, the first complexing agent triethanolamine, the second complexing agent and hydrogen evolution inhibitor sodium tartrate, supporting electrolyte sodium hydroxide and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable triethanolamine-iron ion-sodium tartrate complex with a saturated six-coordination structure; the iron ion concentration is 1 mol / L, the first complexing agent concentration is 1 mol / L, the second complexing agent and hydrogen evolution inhibitor is 2 mol / L, the supporting electrolyte concentration is 3 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1:2; The preparation method of a kind of negative electrolyte of aqueous all-iron redox flow battery in Example 7 of this embodiment is as follows: Weigh 19.99 g of Fe2(SO4)3, 13.27 mL of triethanolamine, 46.02 g of sodium tartrate dihydrate, and 12 g of sodium hydroxide and add them to a beaker in sequence. Then add 60 mL of deionized water, heat in a 40 °C constant temperature water bath, and stir magnetically until completely dissolved. Then transfer it to a 100 mL volumetric flask and make up the volume to obtain a 100 mL triethanolamine (1 mol / L)-iron ion (1 mol / L)-sodium tartrate (2 mol / L)-sodium hydroxide (3 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 7 shown, the cyclic voltammogram of the negative electrolyte of the aqueous all-iron redox flow battery in Example 7 of the present invention is scanned within a sweep rate of 10 mV·s -1 -50 mV·s -1 There is a linear relationship between the peak current density and the square root of the scan rate. The cyclic voltammogram is relatively symmetric, indicating good reversibility. The large peak current density indicates high electrochemical activity.

[0044] An aqueous all-iron redox flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a separator, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system; the positive and negative electrolytes are circulated by pumps and separated by a separator in the battery cavity; The electrode is made of carbon cloth, and the separator is made of perfluorosulfonic acid membrane Nafion115; The negative electrolyte is the negative electrolyte of the aqueous all-iron redox flow battery in Example 7 of the present invention; The preparation method of the positive electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O, 15.2 g of Na4[Fe(CN)6], and 12 g of NaOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, then transfer it to a 100 mL volumetric flask and make up the volume to obtain a 100 mL K4[Fe(CN)6] (0.5 mol / L) + Na4[Fe(CN)6] (0.5 mol / L) solution for use.

[0045] Performance test of the aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min, and charge-discharge tests are carried out at 80 mA / cm 2 Set the charge-discharge cut-off voltages to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, the Coulombic efficiency of the aqueous all-iron redox flow battery in Example 7 after 300 cycles is 99.2%, the voltage efficiency is 85.8%, the energy efficiency is 85.2%, and the number of cycles when the battery capacity decays to 70% is 1125 cycles.

[0046] Example 8 A negative electrolyte for an all - iron aqueous flow battery of the present invention includes an iron - ion active substance ferric phosphate, a first complexing agent triethanolamine, a second complexing agent and hydrogen evolution inhibitor potassium tartrate, a supporting electrolyte potassium hydroxide, and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid - iron ion - potassium tartrate complex with a saturated six - coordination structure; the iron ion concentration is 0.1 mol / L, the first complexing agent concentration is 0.1 mol / L, the second complexing agent and hydrogen evolution inhibitor is 0.1 mol / L, the supporting electrolyte concentration is 3 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1:1; The preparation method of the negative electrolyte for an all - iron aqueous flow battery in Example 8 is as follows: Weigh 1.51 g of FePO4, 2.43 g of 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid, 2.35 g of potassium tartrate hemihydrate, and 16.83 g of potassium hydroxide and add them to a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant - temperature water bath, and stir magnetically until completely dissolved. Then transfer it to a 100 - mL volumetric flask and make up the volume to obtain 100 mL of a 3 - bis(2 - hydroxyethyl)amino - 2 - hydroxypropane sulfonic acid (0.1 mol / L)-iron ion (0.1 mol / L)-potassium tartrate (0.1 mol / L)-potassium hydroxide (3 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 8 shown, for the negative electrolyte of an all - iron aqueous flow battery in Example 8, within the scanning rate range of 10 mV·s -1 -50 mV·s -1 the cyclic voltammogram shows a linear relationship between the peak current density and the square root of the scanning rate, and the cyclic voltammogram is relatively symmetric, indicating good reversibility.

[0047] An all - iron aqueous flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a separator, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system; the positive and negative electrolytes are circulated by pumps and are separated by a separator in the battery cavity; The electrodes are made of carbon felt, and the separator is made of perfluorosulfonic acid membrane Nafion212; The negative electrolyte is the negative electrolyte for an all - iron aqueous flow battery in Example 8; The preparation method of the positive electrolyte is as follows: Weigh 4.22 g of K4[Fe(CN)6]·3H2O and 12 g of NaOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask to make up the volume to obtain 100 mL of 0.1 mol / L K4[Fe(CN)6] solution for use.

[0048] Performance test of aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolyte solutions are both 100 mL / min, and at 80 mA / cm 2 Charge-discharge test, set the charge-discharge cut-off voltages to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, for an aqueous all-iron redox flow battery in Example 8, the Coulombic efficiency after 300 cycles is 99.5%, the voltage efficiency is 85.4%, the energy efficiency is 85%, and the number of cycles when the battery capacity decays to 70% is 1009 cycles.

[0049] Example 9 The negative electrolyte of an aqueous all-iron redox flow battery of the present invention includes an iron ion active substance ferric chloride, a first complexing agent bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane, a second complexing agent and hydrogen evolution inhibitor trisodium nitrilotriacetate, a supporting electrolyte sodium hydroxide and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane-iron ion-trisodium nitrilotriacetate complex with a saturated six-coordinate structure; the iron ion concentration is 0.5 mol / L, the first complexing agent concentration is 0.5 mol / L, the second complexing agent and hydrogen evolution inhibitor iron ion is 1 mol / L, the supporting electrolyte concentration is 3 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1:2; The preparation method of the negative electrolyte of an aqueous all-iron redox flow battery in Example 9 is as follows: Weigh 13.515 g of FeCl3·6H2O, 10.462 g of bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane, 25.71 g of trisodium nitrilotriacetate monohydrate, and 12 g of sodium hydroxide in sequence and add them to a beaker. Add 60 mL of deionized water, heat in a 40 °C constant temperature water bath, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask to make up the volume to obtain 100 mL of bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane (0.5 mol / L)-iron ion (0.5 mol / L)-trisodium nitrilotriacetate (1 mol / L)-sodium hydroxide (3 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 9As shown in Example 9, the negative electrode electrolyte of an aqueous all-iron flow battery is 10mV·s -1 -50mV·s -1 In the cyclic voltammetry curve within the scan rate, there is a linear relationship between the peak current density and the square root of the scan rate, and the cyclic voltammetry curve is relatively symmetrical, indicating good reversibility.

[0050] The present invention discloses an aqueous all-iron flow battery, comprising electrodes, a positive electrolyte, a negative electrolyte, a diaphragm, positive and negative electrode liquid storage tanks, positive and negative electrode peristaltic pumps, piping, and a battery testing system. The positive and negative electrode electrolytes are circulated by the pumps and separated by the diaphragm in the battery cavity. The electrode is made of carbon felt and the diaphragm is made of perfluorosulfonic acid membrane Nafion117; The negative electrode electrolyte is an aqueous all-iron flow battery negative electrode electrolyte of Example 9; The configuration method of the positive electrode electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 12 g of NaOH and add them to 80 mL of deionized water. After magnetic stirring until completely dissolved, transfer to a 100 mL volumetric flask and make up to volume to obtain 100 mL of 0.5 mol / L K4[Fe(CN)6] solution for later use.

[0051] Aqueous all-iron flow battery performance test: Test conditions: During battery operation, the flow rate of the positive and negative electrolytes was 100 mL / min, and the flow rate was 80 mA / cm 2 For charge and discharge tests, set the charge and discharge cut-off voltages to 1.6V and 0.5V respectively; Test results: Figures 12 - 15 As shown, the coulombic efficiency of an aqueous all-iron liquid flow battery of Example 9 after 300 cycles is 99.4%, the voltage efficiency is 85.7%, the energy efficiency is 85.2%, and the number of cycles for the battery capacity to decay to 70% is 1130 cycles.

[0052] Example 10 The present invention discloses an aqueous all-iron liquid flow battery negative electrode electrolyte, comprising ferric chloride as an iron ion active substance, a first complexing agent triethanolamine, a second complexing agent and hydrogen evolution inhibitor L-sodium lactate, a supporting electrolyte potassium hydroxide, and deionized water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor simultaneously bind to the iron ion to form a stable triethanolamine-iron ion-L-sodium lactate composite complex with a saturated hexacoordinate structure. The iron ion concentration is 0.5 mol / L, the first complexing agent concentration is 0.5 mol / L, the second complexing agent and hydrogen evolution inhibitor concentration is 1.25 mol / L, the supporting electrolyte concentration is 2 mol / L, and the molar concentration ratio of the iron ion, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:1:2.5. The preparation method of the negative electrolyte of the all - iron aqueous flow battery in this Example 10 is as follows: Weigh 13.515 g of FeCl3·6H2O, 6.5 mL of triethanolamine, 14.01 g of sodium L - lactate, and 11.22 g of potassium hydroxide and add them to a beaker in sequence. Then add 60 mL of deionized water, heat in a 40 °C constant - temperature water bath, and stir magnetically until completely dissolved. After that, transfer it to a 100 - mL volumetric flask and make up the volume to obtain a 100 - mL complex solution of triethanolamine (0.5 mol / L) - iron ion (0.5 mol / L) - sodium L - lactate (1.25 mol / L) - potassium hydroxide (2 mol / L); Electrochemical performance test of the electrolyte: As Figure 10 shown, for the negative electrolyte of the all - iron aqueous flow battery in this Example 10, within the scanning rate range of 10 mV·s -1 -50 mV·s -1 during the cyclic voltammetry curve scanning, there is a linear relationship between the peak current density and the square root of the scanning rate, and the cyclic voltammetry curve is relatively symmetric, indicating good reversibility.

[0053] An all - iron aqueous flow battery of the present invention includes electrodes, positive electrolyte, negative electrolyte, diaphragm, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system; the positive and negative electrolytes are circulated by pumps and are separated by the diaphragm in the battery cavity; The electrodes are made of carbon felt, and the diaphragm is made of Nafion212 perfluorosulfonic acid membrane; The negative electrolyte is the negative electrolyte of the all - iron aqueous flow battery in this Example 10; The preparation method of the positive electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 11.22 g of KOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer it to a 100 - mL volumetric flask and make up the volume to obtain 100 mL of 0.5 - mol / L K4[Fe(CN)6] solution for use.

[0054] Performance test of the all - iron aqueous flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrolytes are both 100 mL / min. For the charge - discharge test, set the charge - discharge cut - off voltages to 1.6 V and 0.5 V respectively; 2 Test results: As Figures 12 - 15 shown, for the all - iron aqueous flow battery in this Example 10, the Coulomb efficiency after 300 cycles is 98.7%, the voltage efficiency is 85.7%, the energy efficiency is 84.6%, and the number of cycles when the battery capacity decays to 70% is 1250 cycles. ​

[0055] Example 11 A negative electrolyte for an all - iron aqueous flow battery of the present invention includes an iron - ion active substance ferric phosphate, a first complexing agent bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane, a second complexing agent and hydrogen evolution inhibitor lithium L - lactate, a supporting electrolyte lithium hydroxide, and deionized water. The first complexing agent and the second complexing agent (also acting as a hydrogen evolution inhibitor) are simultaneously combined with iron ions to form a stable bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane - iron ion - lithium L - lactate complex with a saturated six - coordination structure. The iron - ion concentration is 1 mol / L, the first complexing agent concentration is 0.5 mol / L, the second complexing agent (also acting as a hydrogen evolution inhibitor) is 2 mol / L, the supporting electrolyte concentration is 2 mol / L, and the molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent (also acting as a hydrogen evolution inhibitor) is 1:0.5:2; The preparation method of the negative electrolyte for an all - iron aqueous flow battery in this Example 11 is as follows: Weigh 15.08 g of FePO4, 10.46 g of bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane, 19.2 g of lithium L - lactate, and 4.79 g of lithium hydroxide and add them into a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant - temperature water bath, and stir magnetically until completely dissolved. Then transfer it to a 100 - mL volumetric flask for volume - fixing to obtain 100 mL of a bis(2 - hydroxymethyl)amino - tris(hydroxymethyl)methane (0.5 mol / L) - iron ion (1 mol / L) - lithium L - lactate (2 mol / L) - lithium hydroxide (2 mol / L) complex solution; Electrochemical performance test of the electrolyte: As Figure 11 shown, for the negative electrolyte of an all - iron aqueous flow battery in this Example 11, when scanning the cyclic voltammetry curve within a sweep rate of 10 mV·s -1 - 50 mV·s -1 There is a linear relationship between the peak current density and the square root of the scan rate, and the cyclic voltammetry curve is relatively symmetric, indicating good reversibility.

[0056] An all - iron aqueous flow battery of the present invention includes electrodes, a positive electrolyte, a negative electrolyte, a diaphragm, positive and negative liquid storage tanks, positive and negative peristaltic pumps, pipelines, and a battery test system. The positive and negative electrolytes are pumped for circulation and are separated by a diaphragm in the battery cavity; The electrodes are made of carbon felt, and the diaphragm is made of perfluorosulfonic acid membrane Nafion212; The negative electrolyte is the negative electrolyte for an all - iron aqueous flow battery in this Example 11; The preparation method of the positive electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O, 15.2 g of Na4[Fe(CN)6] and 12 g of NaOH, add them to 80 mL of deionized water, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for volume fixation to obtain 100 mL of K4[Fe(CN)6] (0.5 mol / L) + Na4[Fe(CN)6] (0.5 mol / L) solution for standby.

[0057] Performance test of aqueous all-iron redox flow battery: Test conditions: During the operation of the battery, the flow rates of the positive and negative electrode electrolytes are both 100 mL / min, at 80 mA / cm 2 Charge-discharge test, set the charge-discharge cut-off voltages to 1.6 V and 0.5 V respectively; Test results: As Figures 12 - 15 shown, the coulombic efficiency of an aqueous all-iron redox flow battery in Example 11 after 300 cycles is 99.1%, the voltage efficiency is 85.3%, the energy efficiency is 84.5%, and the number of cycles when the battery capacity decays to 70% is 1345 cycles.

[0058] Comparative Example 1 A negative electrode electrolyte for an aqueous all-iron redox flow battery, which is different from that in Example 1 in that it does not contain a second complexing agent and hydrogen evolution inhibitor. It includes an iron ion active substance ferric chloride, a complexing agent triethanolamine, a supporting electrolyte sodium hydroxide and deionized water. The complexing agent binds to the iron ions to form a triethanolamine-iron ion complex; the iron ion concentration is 0.5 mol / L, the triethanolamine concentration is 0.25 mol / L, and the supporting electrolyte concentration is 2 mol / L; The preparation method of a negative electrode electrolyte for an aqueous all-iron redox flow battery in this Comparative Example 1 is as follows: Weigh 13.515 g of FeCl3·6H2O, 3.32 mL of triethanolamine, and 8 g of sodium hydroxide and add them to a beaker in sequence. Add 60 mL of deionized water, heat in a 40 °C constant temperature water bath, stir magnetically until completely dissolved, and then transfer to a 100 mL volumetric flask for volume fixation to obtain 100 mL of triethanolamine (0.25 mol / L)-iron ion (0.5 mol / L)-sodium hydroxide (2 mol / L) complex solution; An aqueous all-iron redox flow battery includes electrodes, a positive electrode electrolyte, a negative electrode electrolyte, a separator, positive and negative electrode storage tanks, positive and negative electrode peristaltic pumps, pipelines and a battery test system; the positive and negative electrode electrolytes are circulated by pumps and are separated by a separator in the battery cavity; The electrodes are made of carbon felt, and the separator is made of perfluorosulfonic acid membrane Nafion212; The negative electrode electrolyte is a negative electrode electrolyte for an aqueous all-iron redox flow battery in this Comparative Example 1; The preparation method of the positive electrode electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 8 g of NaOH and add them to 80 mL of deionized water. After magnetic stirring until completely dissolved, transfer to a 100 mL volumetric flask and make up to volume to obtain 100 mL of 0.5 mol / L K4[Fe(CN)6] solution for later use.

[0059] Aqueous all-iron flow battery performance test: Test conditions: During battery operation, the flow rate of the positive and negative electrolytes was 100 mL / min, and the flow rate was 80 mA / cm 2 For charge and discharge tests, set the charge and discharge cut-off voltages to 1.6V and 0.5V respectively; Test results: Figures 12 - 15 As shown, the coulombic efficiency of an aqueous all-iron flow battery in this comparative example 1 after 50 cycles is 85.8%, the voltage efficiency is 84.6%, and the energy efficiency is 72.6%. The number of cycles in which the battery capacity decays to 70% is only 50 cycles; when the number of cycles is relatively small, the coulombic efficiency, voltage efficiency, and energy efficiency are all low, indicating that the chelation between triethanolamine and iron ions is not tight enough. During the battery charging process, the process of trivalent iron being reduced to divalent iron will be accompanied by the precipitation of elemental iron, and the molecular size of triethanolamine is small, and it is easy to pass through the diaphragm and react with the positive electrode electrolyte, which eventually leads to capacity decay, reduced coulombic efficiency, and poor long-cycle performance of the battery; and as the number of cycles increases, the coulombic efficiency continues to decline and the capacity continues to decay.

[0060] Comparative Example 2 An aqueous all-iron liquid flow battery negative electrode electrolyte, which differs from Example 1 in that it does not contain a first chelating agent. The electrolyte comprises ferric chloride, an iron ion-containing active substance, potassium gluconate, a chelating agent and hydrogen evolution inhibitor, sodium hydroxide, a supporting electrolyte, and deionized water. The chelating agent and hydrogen evolution inhibitor combines with iron ions to form a chelate, forming a potassium gluconate-iron ion composite complex. The iron ion concentration is 0.5 mol / L, the chelating agent and hydrogen evolution inhibitor concentration is 0.5 mol / L, and the supporting electrolyte concentration is 2 mol / L.

[0061] The configuration method of the negative electrode electrolyte of an aqueous all-iron liquid flow battery in this comparative example 2 is as follows: Weigh 13.515 g FeCl₃·6H₂O, 11.71 g potassium gluconate, and 8 g sodium hydroxide into a beaker, add 60 mL of deionized water, heat in a 40°C constant temperature water bath, and stir magnetically until completely dissolved. Transfer to a 100 mL volumetric flask and adjust to volume to obtain 100 mL of potassium gluconate (0.5 mol / L)-iron ion (0.5 mol / L)-sodium hydroxide (2 mol / L) complex solution. An aqueous all-iron flow battery comprises electrodes, a positive electrolyte, a negative electrolyte, a diaphragm, positive and negative electrode liquid storage tanks, positive and negative electrode peristaltic pumps, piping, and a battery testing system. The positive and negative electrode electrolytes are circulated by the pumps and separated by the diaphragm within the battery cavity. The electrode is made of carbon felt and the diaphragm is made of perfluorosulfonic acid membrane Nafion212; The negative electrode electrolyte is an aqueous all-iron flow battery negative electrode electrolyte of Comparative Example 2; The configuration method of the positive electrode electrolyte is as follows: Weigh 21.12 g of K4[Fe(CN)6]·3H2O and 8 g of NaOH and add them to 80 mL of deionized water. After magnetic stirring until completely dissolved, transfer to a 100 mL volumetric flask and make up to volume to obtain 100 mL of 0.5 mol / L K4[Fe(CN)6] solution for later use.

[0062] Aqueous all-iron flow battery performance test: Test conditions: During battery operation, the flow rate of the positive and negative electrolytes was 100 mL / min, and the flow rate was 80 mA / cm 2 For charge and discharge tests, set the charge and discharge cut-off voltages to 1.6V and 0.5V respectively; Test results: Figures 12 - 15 As shown, the coulombic efficiency of an aqueous all-iron liquid flow battery in Comparative Example 2 after 100 cycles is 90.3%, the voltage efficiency is 78.4%, and the energy efficiency is 70.8%. The number of cycles in which the battery capacity decays to 70% is 90 cycles; when the number of cycles is relatively small, the coulombic efficiency, voltage efficiency, and energy efficiency are all low, indicating that the gluconate ion also has a weak chelating ability with iron ions. During the battery charging process, iron is precipitated and catalyzes the hydrogen evolution reaction, resulting in capacity decay, reduced coulombic efficiency, and unstable long-cycle performance of the battery; and as the number of cycles increases, the coulombic efficiency and capacity continue to decay.

[0063] Comparative Example 3 A solution was prepared using the same recipe as in Example 1: triethanolamine (1 mol / L) - iron ions (1 mol / L) - sodium hydroxide (2 mol / L). However, a clear aqueous solution could not be obtained. Therefore, this solution could not be used as the negative electrolyte for an all-iron flow battery. This indicates that a single complex cannot achieve high solubility because, at high concentrations, triethanolamine and iron ions cannot form a stable coordination structure.

Claims

1. An aqueous negative electrolyte for an all-iron redox flow battery, characterized in that, It includes an iron ion-containing active substance, a first complexing agent, a second complexing agent and hydrogen evolution inhibitor, a supporting electrolyte, and water. The first complexing agent and the second complexing agent and hydrogen evolution inhibitor are simultaneously combined with iron ions to form a stable chelate with a saturated six-coordination structure. The first complexing agent is selected from triethanolamine or its analogs, and the second complexing agent and hydrogen evolution inhibitor are selected from organic acids with chelating effects and their salts.

2. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, wherein The iron ion-containing active substance is selected from at least one of iron sulfate, iron nitrate, iron chloride, and iron phosphate; the concentration of iron ions is 0.1 mol / L - 1.5 mol / L.

3. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, wherein The first complexing agent is selected from one of triethanolamine, 3-bis(2-hydroxyethyl)amino-2-hydroxypropanesulfonic acid, and bis(2-hydroxymethyl)amino-tris(hydroxymethyl)methane.

4. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, characterized in that, The second complexing agent and hydrogen evolution inhibitor are selected from one of gluconic acid and its salts, tartaric acid and its salts, trisodium nitrilotriacetate, glycine and its salts, or L-lactic acid and its salts.

5. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 4, wherein, The gluconate is selected from one of sodium gluconate, zinc gluconate, potassium gluconate, and calcium gluconate; The tartrate is selected from one of sodium tartrate, calcium tartrate, potassium tartrate, and magnesium tartrate; The glycinate is selected from one of sodium glycinate, zinc glycinate, and magnesium glycinate; The L-lactate is selected from one of zinc L-lactate, calcium L-lactate, lithium L-lactate, and sodium L-lactate.

6. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, wherein The concentrations of the first complexing agent and the second complexing agent and hydrogen evolution inhibitor are both 0.1 mol / L - 2 mol / L.

7. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, wherein The supporting electrolyte is selected from at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

8. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, wherein, The concentration of the supporting electrolyte is 0.1 mol / L - 6 mol / L.

9. The negative electrode electrolyte of an all-iron aqueous flow battery according to claim 1, characterized in that, The molar concentration ratio of iron ions, the first complexing agent, and the second complexing agent and hydrogen evolution inhibitor is 1:(0.5 - 2):(1 - 3).

10. A water-based all-iron flow battery, characterized in that, It includes an electrode, a positive electrode electrolyte, a negative electrode electrolyte, a separator, a positive electrode liquid storage tank, a negative electrode liquid storage tank, a positive electrode peristaltic pump, a negative electrode peristaltic pump, pipelines, and a battery test system; the positive and negative electrode electrolytes are respectively transported and circulated by the positive and negative electrode peristaltic pumps and are separated by the separator in the battery cavity; The negative electrode electrolyte uses an aqueous all-iron redox flow battery negative electrode electrolyte according to any one of claims 1 - 9; The electrode material is selected from one of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth inert materials; The separator is selected from one of perfluorosulfonic acid membranes Nafion117, Nafion115, Nafion212, and Nafion211.

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