Negative electrode electrolyte of near-neutral total iron flow battery and preparation method of negative electrode electrolyte

Abstract

The invention belongs to the technical field of flow battery energy storage, and more specifically relates to a near-neutral total iron flow battery negative electrode electrolyte and a preparation method thereof, the negative electrode electrolyte is prepared from an iron salt, a chelating agent, a stabilizing agent, a supporting electrolyte and water at a certain temperature, the total iron concentration is 0.1-1.0 M, the molar ratio of the chelating agent to the iron salt is 1.2-2.0, the molar ratio of the stabilizing agent to the supporting electrolyte is 1.2-2.0, and the total iron concentration is 0.1-1.0 M. The molar ratio of the stabilizer to Fe is 0.25-1.0, the supporting electrolyte concentration is 0-2.0 mol / L, and the pH value is 7.0-8.5. The near-neutral negative electrode electrolyte for the total-iron flow battery is high in stability, can effectively inhibit generation of ferric hydroxide precipitates under a neutral condition, improves the stability of iron ions, greatly prolongs the cycle life of the total-iron flow battery, and can be widely applied to various aqueous flow batteries.

Description

Technical Field

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

[0002] Liquid flow battery is a liquid electrochemical energy storage device, whose active material is completely dissolved in the electrolyte, and energy storage and release are achieved through changes in the oxidation state of the active elements. It is a redox battery. As a typical representative of liquid flow batteries, all-vanadium liquid flow battery has the advantages of good stability, long cycle life, and fast response. It is a relatively mature liquid flow battery that has initially moved towards commercial application prospects. However, the electrolyte cost of all-vanadium liquid flow battery is relatively high, accounting for more than 60% of the total energy storage cost, which to a certain extent limits the application of all-vanadium liquid flow battery in the field of energy storage.

[0003] All-iron flow batteries are divided into acidic, neutral and alkaline systems. Acidic all-iron flow batteries are relatively mature in commercial development. Both positive and negative electrolytes use cheap iron as the raw material to make the active material of the electrolyte. The open circuit voltage is 1.21V, which is close to that of all-vanadium flow batteries. It can avoid cross-contamination. In addition, the active material raw materials are cheap and widely available. The structure is simple and the cost is low. It is a very promising flow battery. However, the hydrolysis and deposition / dissolution reactions of ferrous ions in the negative electrode electrolyte are poorly reversible, and the hydrogen evolution reaction is serious, resulting in low energy efficiency, severe capacity decay, and poor cycle stability of all-iron flow batteries, which limits their application in energy storage technology. Patents such as CN113328124A, CN116598552A, and CN114388859B disclose acidic iron-based negative electrode electrolytes. Although citric acid, N,N-dimethylacetamide, dimethyl sulfoxide, and other substances are added to the electrolyte to inhibit the hydrolysis of ferrous ions, the negative electrode reaction is still the traditional Fe 2+ / Fe deposition / dissolution reaction, the existence of side reactions such as iron dendrites and hydrogen evolution, leads to low battery efficiency and rapid capacity decay.

[0004] In recent years, alkaline all-iron flow batteries have developed rapidly. By the end of 2023, there have been commercial energy storage application demonstration projects, which are likely to surpass the development trend of acidic all-iron flow batteries. Gong et al. 6 3- / 4-The first fully soluble all-iron flow battery was made for the redox couple, and the battery energy efficiency has been greatly improved compared with the traditional acidic all-iron. The alkaline iron-based negative electrode electrolytes disclosed in patents such as CN118336062A, CN113764714B, CN114709459A, CN118738483A and CN116259810A all use TEA or TEA derivatives as the main ligands, and use small molecule organic imidazoles, polysaccharide alcohols, malonic acid, citric acid or glycine as auxiliary ligands to form a stable six-coordinate complex with iron ions. However, during the long-life cycle of the battery, these small molecule organics are easy to fall off and pass through the diaphragm, resulting in the conversion of Fe-TEA / TEA derivatives into five-coordinate complexes, which are easy to form iron hydroxide precipitation and iron element, resulting in rapid battery capacity decay and short cycle life. The alkaline iron-based negative electrode electrolytes disclosed in patents such as CN118712441A, CN118588997A, CN117154113A, CN117096406A, and CN117164485B, although the ligands and iron ions in the negative electrode electrolytes can form a six-coordination structure, the negative electrode electrolytes are still in a strongly alkaline environment, and problems such as hydrogen evolution and iron hydroxide precipitation still exist during long-cycle charge and discharge processes and cannot be solved.

[0005] Although both acidic all-iron flow batteries and alkaline all-iron flow batteries have commercial demonstration devices, the system still has essential problems such as hydrogen evolution, iron dendrites and iron hydroxide precipitation that cannot be solved. Therefore, it is urgent to develop a near-neutral all-iron flow battery that can perfectly solve a series of problems existing under strong acid and strong alkaline conditions. The iron chelating ability of organic phosphine complexing agents (HEDP, EDTMPS, DETPMPS, etc.) is stronger than that of EDTA and phosphates, with high complexing capacity, large stability constant, good chemical stability, and will not be inactivated even at high temperatures (200°C); its complexing reaction with iron ions can be completed under weak alkalinity (7.5-8.5), and does not require protonation in a strong alkaline environment. The near-neutral all-iron flow battery composed of the positive electrolyte (ferrocyanide) has good stability, and will not have essential problems such as hydrogen and oxygen evolution, iron dendrites and iron hydroxide precipitation that affect the long-term operation of the battery, which greatly extends the cycle life of the all-iron flow battery and can be widely used in various aqueous flow batteries. Summary of the invention

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

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

[0008] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery, characterized in that: the active component of the negative electrode electrolyte is organic complex iron, the total iron concentration is 0.1-1.0 mol / L, the molar ratio of the organic complexing agent to iron is 1.2-2.0, the molar ratio of the stabilizer to iron is 0.25-1.0, the concentration of the auxiliary electrolyte is 0-2.0 mol / L, and the pH value is 7.0-8.5; the organic complexing agent is one or more of aminotrimethylphosphonic acid (NTMPA), hydroxyethylidene diphosphonic acid (HEDP), ethylenediaminetetramethylenephosphonic acid (EDTMPA), diethylenetriaminepentamethylphosphonic acid (DTPMPA), polyaminopolyethermethylenephosphonic acid (PAPEMP), and hexamethylenediaminetetramethylenephosphonic acid (HDTMPA).

[0009] The iron salt is one or more of ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate, ferric hydroxide or ferric carbonate, wherein the iron ion concentration is 0.1-1.0 mol / L.

[0010] The stabilizer is polysaccharide alcohol, glycerol and citric acid. The polysaccharide alcohol is one or more of sorbitol, mannitol, gluconic acid and glucoheptanoic acid. The molar ratio of stabilizer to Fe is 0.25 to 1.0.

[0011] The auxiliary electrolyte is selected from one or more of ammonium chloride, potassium chloride, sodium chloride, ammonium sulfate, potassium sulfate, sodium sulfate, potassium nitrate, and sodium nitrate, wherein the auxiliary electrolyte concentration is 0-2.0 mol / L.

[0012] The pH value of the negative electrode electrolyte is selected to be 7.0 to 8.5. The pH value of the negative electrode electrolyte is adjusted by using an inorganic base.

[0013] The organic complexing agent is preferably selected from one or more of aminotri(methylene)phosphonic acid (NTMPA), hydroxyethylidene diphosphonic acid (HEDP), ethylenediaminetetra(methylene)phosphonic acid (EDTMPA), and diethylenetriaminepenta(methylene)phosphonic acid (DTPMPA), wherein the molar ratio of the organic complexing agent to iron is 1.2-2.0.

[0014] A method for preparing a negative electrode electrolyte for a near-neutral all-iron liquid flow battery is as follows:

[0015] 1) Add iron salt and distilled water into a reactor with stirring and jacket, then continuously introduce high-purity nitrogen into the reactor as a protective gas, and heat to 40-45°C while stirring;

[0016] 2) Slowly adding the stabilizer to the solution in step 1) until it is completely dissolved, and continuing to stir the reaction for 30 minutes;

[0017] 3) adding the organic complexing agent to the mixture of step 2) and stirring to dissolve;

[0018] 4) slowly adding the inorganic base to the mixture of step 3) until it is completely dissolved, and continue stirring for 1 to 2 hours;

[0019] 5) slowly adding the auxiliary electrolyte to step 4), and continuing stirring for 30 minutes after it is completely dissolved;

[0020] 6) Slowly adding an inorganic base to step 5), adjusting the pH value of the solution to a set value, and cooling to room temperature under nitrogen protection to obtain a negative electrode electrolyte.

[0021] The inorganic base for adjusting the pH of the negative electrode electrolyte is selected from sodium hydroxide, potassium hydroxide, and ammonia water.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention adopts an organic phosphine chelating agent (amino trimethylene phosphonic acid, hydroxyethylidene diphosphonic acid, ethylenediaminetetramethylene phosphonic acid, diethylenetriaminepentamethylene phosphonic acid, polyaminopolyether methylene phosphonic acid, hexamethylenediaminetetramethylene phosphonic acid, etc.) as the negative electrode electrolyte active substance, most of which contain multiple hydroxyl groups (-OH), 2-4 phosphonic acid groups and multiple amino groups. Due to the high electronegativity of atoms such as N, P, and O, it is easy to form a coordination bond with the outermost d orbital of the central ion iron, and timely supplement the vacant coordination site of the ferrous ion. The organic phosphine chelating agent chelates with the iron ion to form a six-coordinate or eight-coordinate stable structure, which solves the problem that the ferrous triethanolamine and its derivative system form a five-coordinate structure and is unstable, and greatly improves the cycle stability of the negative electrode electrolyte.

[0024] Organic complex iron

[0025] (2) The present invention uses polysaccharide alcohols, glycerol, and citric acid as stabilizers. According to the spatial structure analysis of polysaccharide alcohols and glycerol, their molecules contain multiple hydroxyl groups (-OH). When combined with iron ions, d 2 sp 3 Hybridization forms 6 empty hybrid orbitals with an octahedral configuration, forming a stable hexacoordinate structure. Citric acid contains three carboxyl groups and one amino group, which also form a stable hexacoordinate structure with iron ions through coordination bonds. Even if the pH value of the negative electrode electrolyte changes drastically, iron hydroxide will not precipitate, causing rapid capacity decay, thereby improving the stability of the negative electrode electrolyte.

[0026] (3) The molecular size of organic phosphine-containing complex iron is generally relatively large, and the permeability through the ion exchange membrane is greatly reduced. The ion exchange membrane can effectively block the migration of active substances by treating it with distilled water alone. The assembled battery has high coulombic efficiency, good stability, and low capacity attenuation rate.

[0027] (4) The pH value of the negative electrode electrolyte of the present invention is selected to be 7.0-8.5, which is a near-neutral environment. Together with the neutral positive electrode electrolyte (ferrocyanide, etc.), the near-neutral all-iron liquid flow battery is basically free of hydrogen and oxygen evolution, iron hydroxide and iron dendrite problems during battery operation, which greatly extends the cycle life of the all-iron liquid flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Cyclic voltammetry curves at different scan rates of Example 5

[0029] Figure 2 500 sets of cyclic voltammetry curves of Example 5

[0030] Figure 3 Capacity retention rate of near-neutral all-iron flow batteries composed of Examples 1 to 6

[0031] Figure 4 Capacity retention rate of all-iron flow batteries composed of comparative examples 1 to 7 DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the implementation scheme of the present invention is further described below in conjunction with examples.

[0033] 1 Preparation process of all-iron flow battery

[0034] 1.1 Negative electrolyte preparation process:

[0035] Examples 1 to 6 and Comparative Examples 1 to 3 were prepared in the following manner:

[0036] 1) Add iron salt and distilled water into a reactor with stirring and jacket, then continuously introduce high-purity nitrogen into the reactor as a protective gas, and heat to 40-45°C while stirring;

[0037] 2) Slowly adding the stabilizer to the solution in step 1) until it is completely dissolved, and continuing to stir the reaction for 30 minutes;

[0038] 3) adding the organic complexing agent to the mixture of step 2) and stirring to dissolve;

[0039] 4) slowly adding the inorganic base to the mixture of step 3) until it is completely dissolved, and continue stirring for 1 to 2 hours;

[0040] 5) slowly adding the auxiliary electrolyte to step 4), and continuing stirring for 30 minutes after it is completely dissolved;

[0041] 6) Slowly adding an inorganic base to the solution in step 5) to adjust the pH value of the solution to a set value, and cooling to room temperature under nitrogen protection to obtain a negative electrode electrolyte.

[0042] 1.2 Positive Electrolyte Preparation Process:

[0043] Accurately weigh 0.5 mol potassium ferrocyanide, 0.5 mol sodium ferrocyanide, and 1.0 mol ammonium chloride and dissolve them in distilled water. Adjust the pH value to about 8.0 with ammonia water and adjust the volume to 1 L to prepare a neutral positive electrode electrolyte.

[0044] Example 1

[0045] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 0.1 mol ferric chloride, 0.2 mol polyaminopolyether methylenephosphonic acid (PAPEMP), 0.1 mol sorbitol, 1 mol ammonium chloride and 1 mol potassium chloride, the pH value is adjusted to 8.5 with potassium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing Fe (0.1M)-PAPEMP (0.2M)-sorbitol (0.1M) is prepared.

[0046] Example 2

[0047] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 0.1 mol ferric sulfate, 0.3 mol hexamethylenediaminetetramethylenephosphonic acid (HDTMPA), 0.025 mol gluconic acid, 0.025 mol mannitol, 0.5 mol sodium chloride and 0.5M sodium sulfate, the pH value is adjusted to 8.0 with sodium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing Fe (0.2M)-HDTMPA (0.3M)-gluconic acid / mannitol (0.025M / 0.025M) is prepared.

[0048] Example 3

[0049] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 0.15 mol ferric nitrate, 0.15 mol ferric carbonate, 0.45 mol diethylenetriaminepenta(methylenephosphonic acid) (DTPMPA), 0.05 mol gluconic acid, 0.05 mol propylene glycol, 0.5 mol potassium sulfate, 0.5 mol sodium nitrate, the pH value is adjusted to 7.5 with potassium hydroxide, the volume is fixed to 1L, and a negative electrode electrolyte containing Fe(0.3M)-DTPMPA(0.45M)-gluconic acid / propylene glycol (0.05M / 0.05M) is prepared.

[0050] Example 4

[0051] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 0.3 mol ferrous sulfate, 0.3 mol ferrous chloride, 0.8 mol ethylenediaminetetramethylenephosphonic acid (EDTMPA), 0.15 mol citric acid, 0.5 mol potassium nitrate, the pH value is adjusted to 7.0 with ammonia water, the volume is fixed to 1L, and a negative electrode electrolyte containing Fe (0.6M)-EDTMPA (0.8M)-citric acid (0.15M) is prepared.

[0052] Example 5

[0053] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 0.7 mol ferrous sulfate, 1.4 mol aminotri(methylenephosphonic acid) (NTMPA), 0.2 mol sorbitol, 0.2 mol ammonium sulfate, the pH value is adjusted to 7.8 with aqueous ammonia, the volume is fixed to 1 L, and a negative electrode electrolyte containing Fe (0.7 M)-NTMPA (1.4 M)-sorbitol (0.2 M) is prepared.

[0054] Example 6

[0055] A negative electrode electrolyte for a near-neutral all-iron liquid flow battery: 1.0 mol ferric hydroxide, 1.2 mol hydroxyethylidene diphosphonic acid (HEDP), 0.25 mol sorbitol, the pH value is adjusted to 8.2 with ammonia water, the volume is fixed to 1L, and a negative electrode electrolyte containing Fe (1.0M)-HEDP (1.2M)-sorbitol (0.25M) is prepared.

[0056] Comparative Examples 1 to 3

[0057] To simplify the description and enhance the comparison effect, Comparative Examples 1 to 3 are based on Examples 1 to 3, respectively, without adding stabilizer (polysaccharide alcohols, glycerol or citric acid), and the other conditions are exactly the same as those of Comparative Example 1.

[0058] Comparative Example 4

[0059] Negative electrode electrolyte: 0.5 mol ferric chloride, 1.0 mol triethanolamine (TEA), 4 mol NaOH, 1 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1 L to prepare a negative electrode electrolyte containing Fe (0.5 M)-TEA (1.0 M).

[0060] Positive electrolyte: Accurately weigh 0.5 mol sodium ferrocyanide, 1.0 mol potassium chloride, and 1 mol potassium hydroxide and dissolve them in distilled water to make a volume of 1 L to prepare a positive electrolyte.

[0061] Comparative Example 5

[0062] Negative electrode electrolyte: 0.5 mol ferric chloride, 1.0 mol 3-[NN-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), 4 mol NaOH, 1 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1 L to prepare a negative electrode electrolyte containing Fe (0.5 M)-DIPSO (1.0 M).

[0063] Positive electrolyte: Accurately weigh 0.5 mol sodium ferrocyanide, 1.0 mol potassium chloride, and 1 mol potassium hydroxide and dissolve them in distilled water to make a volume of 1 L to prepare a positive electrolyte.

[0064] Comparative Example 6

[0065] Negative electrolyte: 0.5 mol ferric chloride, 1.0 mol bis(2-hydroxyethyl)amino-tris(hydroxymethyl)methane (BISTRIS), 4 mol NaOH, 1 mol potassium chloride and a certain amount of deoxygenated distilled water were fixed to 1 L to prepare a negative electrolyte containing Fe(0.5M)-BISTRIS(1.0M).

[0066] Positive electrolyte: Accurately weigh 0.5 mol sodium ferrocyanide, 1.0 mol potassium chloride, and 1 mol potassium hydroxide and dissolve them in distilled water to make a volume of 1 L to prepare a positive electrolyte.

[0067] Comparative Example 7

[0068] The positive and negative electrolytes are both ferrous chloride (total iron concentration: 1.0M), hydrochloric acid concentration: 2.0M.

[0069] 2 Electrochemical performance test of all-iron liquid flow battery

[0070] 2.1 Cyclic voltammetry curve (CV curve)

[0071] Experimental conditions: Cyclic voltammetry curve (CV curve): three-electrode mode (electrochemical workstation: Shanghai Chenhua Instrument Co., Ltd. CHI660E), working electrode: graphite felt (diameter 6mm, thickness 4.35mm), counter electrode: platinum sheet electrode (15*15*0.1mm), reference electrode: Ag / AgCl, scanning voltage range: 0.2~-0.6V; scanning voltage: 5mv / s, number of cycles: 500 groups, the electrolyte changes after 500 groups of CV curves of the negative electrode electrolyte in Examples 1 to 6 and Comparative Examples 1 to 7 are as follows Table 1, the CV curves of Example 5 and 500 groups of CV curves at different scanning rates are as follows Figure 1 and Figure 2 .

[0072] Table 1 Electrochemical experimental phenomena of negative electrode electrolyte

[0073]

[0074] Note: The total iron concentration in Examples 1 to 6 and Comparative Examples 1 to 7 was diluted to 0.1 mol / L with deoxygenated distilled water.

[0075] It can be clearly seen from Table 1 above that after 500 sets of cyclic voltammetry curves (CV curves) of the negative electrode electrolytes in Examples 1 to 6 and Comparative Examples 1 to 3, neither iron elemental substance nor bubbles were generated on the graphite felt, and there was no red flocculent precipitate in the electrolyte; however, in Comparative Example 4, there was obviously iron elemental substance on the graphite felt of the negative electrode electrolyte, accompanied by a large number of bubbles, and the electrolyte became obviously turbid; in Comparative Examples 5 and 6, there was only a very small amount of iron elemental substance on the graphite felt of the negative electrode electrolyte, and there was only a trace amount of red flocculent precipitate in the electrolyte; in Comparative Example 7, there was a large amount of iron elemental substance on the graphite felt of the negative electrode electrolyte.

[0076] from Figure 1 and Figure 2 It can be seen that the CV curves of 500 groups of negative electrode electrolytes of Example 5 overlap very well, which indicates that the negative electrode electrolytes of Examples 1 to 6 have very good stability. In summary, the stability of the negative electrode electrolytes of Examples 1 to 6 is significantly higher than that of Comparative Examples 1 to 7.

[0077] 2.2 All-iron flow battery performance test

[0078] (1) Assembly of all-iron flow battery

[0079] The single cell was assembled in the following order: positive electrode aluminum end plate, gold-plated copper plate, graphite current collector, positive electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), ion exchange membrane Nafion212 (soaked in the negative electrode electrolyte for 1 day and then repeatedly washed with distilled water before use), negative electrode 4cm*4cm*4.35mm graphite felt (Liaoning Jingu Carbon Materials Co., Ltd.), graphite current collector, gold-plated copper plate and negative electrode aluminum end plate.

[0080] Liquid flow battery: It is composed of the above-mentioned positive electrode electrolyte and negative electrode electrolyte, positive electrode electrolyte tank, negative electrode electrolyte tank, circulation pump, circulation pipeline and single battery circuit connected in series.

[0081] (2) All-iron flow battery test conditions

[0082] Charge and discharge tester: CT-4008T from Dongguan Xinwei Testing Technology Co., Ltd., charge and discharge mode: constant current charging mode, the volume of the positive and negative electrolytes is 35ml, the flow rate of the positive and negative electrolytes is 150ml / min, nitrogen is introduced before charging and discharging to remove oxygen, current density: 50mA / cm 2 , temperature: 35°C, the charge and discharge cut-off voltages of Examples 1 to 6 and Comparative Examples 1 to 3 are 1.0V and 0.1V respectively, the charge and discharge cut-off voltages of Comparative Examples 4 to 6 are 0.7 to 1.7V respectively, and the charge and discharge times are 500 times. Table 2 shows the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1 to 6 and Comparative Examples 1 to 7. Figure 3The capacity retention rate of the neutral flow batteries of Examples 1 to 6 is shown. Figure 4 It represents the capacity retention rate of the all-iron liquid flow batteries composed of Comparative Examples 1 to 7.

[0083] Table 2 All-iron flow battery performance

[0084]

[0085]

[0086] It can be clearly seen from Table 2 above that the coulombic efficiency, voltage efficiency and energy efficiency of Examples 1-6 are significantly higher than those of Comparative Examples 1-7.

[0087] from Figure 3 and Figure 4 It can be seen that the capacity retention rate of the all-iron liquid flow battery composed of Examples 1 to 6 is still higher than 90% after 500 sets of charge and discharge, and the capacity retention rate is relatively high; however, the capacity retention rate of the all-iron liquid flow battery composed of Comparative Examples 1 to 7 is relatively low after 500 sets of charge and discharge, and the capacity decay is fast. This shows that the charge and discharge performance of the neutral all-iron liquid flow battery composed of Examples 1 to 6 is significantly better than that of Comparative Examples 1 to 7. This also shows that the neutral negative electrode electrolyte has high charge and discharge activity, few side reactions, low ion permeability, and good cycle stability.

[0088] In summary, the negative electrode electrolyte of a near-neutral all-iron liquid flow battery provided by the present invention selects an organic phosphine chelating agent that chelates with iron ions to form a stable structure such as hexacoordinate or octacoordinate as a complexing agent, and uses polysaccharide alcohols, propylene glycol, and citric acid as stabilizers. It is easy to form a stable structure such as hexacoordinate or octacoordinate with the outermost d orbital of the central ion iron, thereby solving the problem of the unstable five-coordinate structure formed by ferrous triethanolamine and its derivative system; the all-iron liquid flow battery adopts a near-neutral environment, and basically no problems of hydrogen and oxygen evolution, iron hydroxide, and iron dendrites will occur during the operation of the battery, thereby greatly extending the cycle life of the all-iron liquid flow battery.

Claims

1. A negative electrode electrolyte for a near-neutral all-iron liquid flow battery, characterized in that: The active component of the negative electrode electrolyte is organic complex iron, the total iron concentration is 0.1-1.0 mol / L, the molar ratio of the organic complexing agent to iron is 1.2-2.0, the molar ratio of the stabilizer to iron is 0.25-1.0, the concentration of the auxiliary electrolyte is 0-2.0 mol / L, and the pH value is 7.0-8.5; the organic complexing agent is one or more of aminotri (methylene phosphonic acid), hydroxyethylidene diphosphonic acid, ethylenediaminetetra (methylene phosphonic acid), diethylenetriaminepenta (methylene phosphonic acid), polyaminopolyether (methylene phosphonic acid), and hexamethylenediaminetetra (methylene phosphonic acid).

2. The negative electrode electrolyte of a near-neutral all-iron liquid flow battery according to claim 1, characterized in that: The iron salt is one or more of ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate, ferric hydroxide or ferric carbonate.

3. The negative electrode electrolyte of a near-neutral all-iron liquid flow battery according to claim 1, characterized in that: The stabilizer is one or more of polysaccharide alcohols, glycerol and citric acid.

4. The negative electrode electrolyte of a near-neutral all-iron liquid flow battery according to claim 3, characterized in that: The polysaccharide alcohols are one or more of sorbitol, mannitol, gluconic acid and glucoheptanoic acid.

5. The negative electrode electrolyte of a near-neutral all-iron liquid flow battery according to claim 1, characterized in that: The auxiliary electrolyte is selected from one or more of ammonium chloride, potassium chloride, sodium chloride, ammonium sulfate, potassium sulfate, sodium sulfate, potassium nitrate, and sodium nitrate.

6. The negative electrode electrolyte of a near-neutral all-iron liquid flow battery according to claim 1, characterized in that: The pH value of the negative electrode electrolyte is 7.0-8.

5.

7. A method for preparing a negative electrolyte for a near-neutral all-iron liquid flow battery according to claim 1, comprising the following steps: 1) Add iron salt and distilled water into a reactor with stirring and jacket, then continuously introduce high-purity nitrogen into the reactor as a protective gas, and heat to 40-45°C while stirring; 2) slowly adding the stabilizer to the solution in step 1) until it is completely dissolved, and continuing to stir the reaction for 30 minutes; 3) adding the organic complexing agent to the mixture of step 2) and stirring to dissolve; 4) slowly adding the inorganic base to the mixture of step 3) until it is completely dissolved, and continue stirring for 1 to 2 hours; 5) slowly adding the auxiliary electrolyte to step 4), and continuing stirring for 30 minutes after it is completely dissolved; 6) Slowly adding an inorganic base to step 5), adjusting the pH value of the solution to a set value, and cooling to room temperature under nitrogen protection to obtain a negative electrode electrolyte.

8. The method for preparing a negative electrode electrolyte for a near-neutral all-iron liquid flow battery according to claim 7, characterized in that: The inorganic base used to adjust the pH of the negative electrode electrolyte is one of sodium hydroxide, potassium hydroxide and ammonia water.

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