A pH buffer-based wide-adaptability neutral all-iron flow battery electrolyte and a preparation method thereof

Abstract

This invention discloses a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte and its preparation method, relating to the field of electrochemical energy storage technology. The electrolyte comprises: a soluble trivalent iron salt, a chelating agent, and a pH buffer system; the solvent is deionized water; the pH buffer system is used to stabilize the electrolyte's pH value within the range of 6.0 to 9.0. The neutral all-iron flow battery constructed based on this electrolyte dynamically neutralizes H₂ generated by side reactions during charging and discharging through the buffer system. + or OH ‑ It avoids local pH fluctuations, significantly improves cycle life and operational stability, and is suitable for large-scale, long-term energy storage applications.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte and its preparation method. Background Technology

[0002] With the accelerating global energy transition, developing low-cost, long-life flow battery energy storage systems has become a key support for technological development. Among existing flow battery technologies, vanadium redox flow batteries are relatively mature, but their large-scale commercialization faces significant bottlenecks due to high costs caused by the scarcity of vanadium resources and poor thermal stability. In contrast, iron-based flow batteries, with their abundant iron resources and low raw material costs, have become a research hotspot and key development direction in the energy storage field.

[0003] To address the severe hydrogen evolution side reaction problem in acidic iron-based batteries, neutral or near-neutral all-iron flow batteries have gradually become a research focus in recent years. In this system, ligands (i.e., chelating agents) need to be introduced to coordinate with iron ions, thereby inhibiting the hydrolysis reaction of iron ions and the formation of hydroxide precipitates under near-neutral conditions, ensuring the basic working performance of the battery. However, existing neutral all-iron flow battery technology still suffers from two major shortcomings that hinder its industrialization: First, the selection of chelating agents is severely limited. Not all potential chelating agents can remain stable throughout the pH range of battery operation. Currently, the types of chelating agents available are scarce, mostly limited to a few strong ligands. Moreover, these chelating agents cannot simultaneously meet the core requirements of high solubility, suitable redox potential, and low cost. Many chelating agents with low cost or high activity potential are highly sensitive to pH values; they will fail or precipitate if they deviate slightly from a specific pH range, making them unsuitable for practical applications.

[0004] Secondly, pH fluctuations lead to poor battery cycle stability. During long-cycle charge and discharge, side reactions such as hydrogen evolution and oxygen evolution, as well as ion transmembrane transport, can easily cause pH drift in the electrolyte. Once the pH of the existing electrolyte system exceeds the stable coordination window of the chelating agent, the coordination balance between iron ions and the chelating agent will be disrupted, leading to irreversible precipitation of active materials, which in turn causes rapid capacity decay and a significant reduction in coulombic efficiency.

[0005] Therefore, how to improve the electrolyte to improve the performance of all-iron flow batteries has become a key technical problem that urgently needs to be solved in the field of neutral all-iron flow batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte and its preparation method, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a pH-buffered neutral all-ferrous flow battery electrolyte, comprising: a soluble trivalent iron salt, a chelating agent, and a pH buffer system; the solvent is deionized water. The pH buffer system is used to stabilize the pH value of the electrolyte in the range of 6.0 to 9.0, more preferably 6.0 to 7.5.

[0008] Furthermore, the chelating agent is an aminocarboxylic acid chelating agent or an organophosphonic acid chelating agent.

[0009] Further, the aminocarboxylic acid chelating agent includes one or more of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), aminotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), glutamic acid diacetic acid (GLDA), methylglycine diacetic acid (MGDA), and cyclohexanediaminetetraacetic acid (CDTA); The organophosphonic acid chelating agents include one or more of the following: hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylenephosphonic acid (ATMP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), diethylenetriaminepentamethylenephosphonic acid (DTPMP), ethylenediaminetetramethylenephosphonic acid (EDTMP), 2-hydroxyphosphonoacetic acid (HPAA), polyaminopolyethermethylenephosphonic acid (PAPEMP), hexamethylenediaminetetramethylenephosphonic acid (HDTMP), bis(hexamethylene)triaminepentamethylenephosphonic acid (BHMTPMP), hydroxyethylaminodimethylenephosphonic acid (HEMPA), and trimethylenephosphonic acid (TMPA).

[0010] Furthermore, the pH buffer system is an inorganic buffer system, an organic buffer system, or a biological buffer system; The inorganic buffer system includes a phosphate system, a carbonate system, or a borate system; The organic buffer system includes amino acids, hydroxyethylpiperazine ethanesulfonic acid, morpholine ethanesulfonic acid, or piperazine-N,N'-di(2-ethanesulfonic acid); The biological buffer system includes PBS buffer, Tris buffer, or Good's buffer.

[0011] The dissociation constant (pKa) of the buffer needs to ensure that the pH of the system remains stable within a specific "safe window" below the iron ion hydrolysis precipitation threshold and within the optimal coordination range of the chelating agent.

[0012] Further, the concentration of the soluble ferric salt is 0.1 mol / L to 2.0 mol / L, the concentration of the chelating agent is 0.2 mol / L to 4.0 mol / L, and the concentration of the pH buffer system is 0.01 mol / L to 4.0 mol / L.

[0013] Furthermore, the electrolyte also includes a supporting electrolyte, wherein the supporting electrolyte ions are sodium ions and / or potassium ions, with a concentration of 2 mol / L to 4 mol / L, and the anion is selected from at least one of sulfate ions, chloride ions, or perchlorate ions.

[0014] This invention fundamentally solves the core problem of unstable iron ion coordination in electrolytes by constructing a pH buffering system using organic buffers (such as amino acids, hydroxyethylpiperazine ethanethioic acid, morpholine ethanethioic acid, piperazine-N,N'-bis(2-ethanethioic acid), etc.), inorganic buffers (such as phosphate systems, carbonate systems, borate systems, etc.), and biological buffers (such as PBS phosphate buffer, Tris tris(hydroxymethyl)aminomethane, Good's buffer, etc.). This innovation not only breaks through the performance bottleneck of single chelating agents and avoids the disadvantages of difficult and costly synthesis of novel chelating agents in traditional technologies, but also significantly broadens the selection range of chelating agents.

[0015] Traditional non-buffered systems have stringent requirements for the pH tolerance of chelating agents. However, the buffering strategy of this invention can stabilize the electrolyte pH within the optimal coordination window, allowing many low-cost, highly active chelating agents, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), aminotriacetic acid (NTA), and hydroxyethylethylenediaminetriacetic acid (HEDTA), which were originally unable to be used for long periods due to high pH sensitivity, to function stably in this system. This significantly reduces the raw material cost of all-iron flow batteries. At the same time, unlike existing technologies that passively withstand capacity decay caused by pH changes, the buffering mechanism of this invention can actively offset pH fluctuations during charge and discharge, effectively suppress the formation of iron hydroxide precipitation, significantly improve the battery's capacity retention and cycle life, and achieve long-term dynamic stability.

[0016] This invention also provides a method for preparing the above-mentioned pH-buffered neutral all-iron flow battery electrolyte, comprising the following steps: The chelating agent and the pH buffer system are mixed in deionized water, the pH is adjusted to the target buffer zone, and then the soluble ferric salt is added to obtain the electrolyte.

[0017] When a supporting electrolyte is present, the iron salt is added to the system to further increase the supporting electrolyte. Sodium / potassium ions are used to improve the conductivity of the solution and maintain the osmotic pressure balance of the positive and negative electrode electrolytes.

[0018] The present invention further provides an all-iron flow battery, wherein the electrolyte is the above-mentioned pH-buffered neutral all-iron flow battery electrolyte.

[0019] Furthermore, the all-iron flow battery includes a positive electrode, a negative electrode, an ion-selective membrane, and an electrolyte.

[0020] The reaction principle of the positive and negative electrodes of the battery is as follows: .

[0021] Both the negative and positive electrodes are made of porous carbon materials, including but not limited to graphite felt, carbon felt, carbon cloth or carbon paper; the battery separator is a polymer separator with ion selective permeability, including but not limited to perfluorosulfonic acid proton exchange membrane, sulfonated polyether ether ketone membrane, polyethylene porous membrane or anion exchange.

[0022] The application of existing all-iron flow batteries faces the following technical problems: First, iron ions readily undergo hydrolysis in neutral or alkaline environments, generating insoluble iron hydroxide (Fe(OH)3) or iron oxide precipitates, interfering with normal battery operation; second, during battery cycling, OH- ions appear on the electrodes. - Localized aggregation leads to increased pH, which not only further induces iron ion hydrolysis and precipitation but also damages the structure of some pH-sensitive chelating agents, causing rapid capacity decay in a short period. Thirdly, chelating agents are too expensive; some specially modified ligands, while having good stability, are costly, even exceeding the price advantage of iron itself, contradicting the core principle of "low cost" in all-iron batteries and becoming a significant obstacle to technology promotion. To address these issues, this invention provides an electrolyte containing a buffer solute that establishes a strong acid-base buffer capacity within the electrolyte, strictly locking the pH value of the microenvironment below the iron ion hydrolysis threshold while remaining within the optimal coordination range of the chelating agent. This fundamentally prevents precipitate formation, avoids electrode flow channel blockage and ion exchange membrane contamination, and constructs a reliable safety barrier for the long-term safe operation of the battery system, significantly improving the physical stability of the electrolyte. Secondly, the buffering strategy of this invention possesses a "dynamic neutralization" active self-healing function; when pH fluctuations occur during charging and discharging, the buffer can rapidly release protons or capture OH groups. -This system effectively mitigates pH changes, maintains the integrity of the chelating agent's coordination structure, and prevents coordination bond breakage and active material shedding caused by pH runaway. This significantly reduces the battery capacity decay rate and enables long-term stable cycling. Furthermore, the highly stable pH environment greatly broadens the selection window for chelating agents, allowing many low-cost conventional chelating agents (such as common aminocarboxylates) that were previously unusable due to high pH sensitivity and weak anti-interference capabilities to exhibit stability comparable to expensive specialty ligands in this system. This successfully reduces the system cost of all-iron flow batteries, laying a solid foundation for their large-scale industrial application.

[0023] The present invention discloses the following technical effects: The buffer system in the electrolyte of this invention can strictly stabilize the electrolyte pH below the iron ion hydrolysis threshold and within the optimal coordination range of the chelating agent, thereby inhibiting Fe from the source. 3+ Hydrolysis produces ferric hydroxide precipitate, which avoids blockage of electrode channels and contamination of ion exchange membranes, and significantly improves the physical stability of the electrolyte.

[0024] The electrolyte of this invention has a "dynamic neutralization" function, which can immediately suppress pH fluctuations caused by side reactions and ion transmembrane transport during charging and discharging, maintain the integrity of the chelating agent coordination structure, prevent the shedding of active materials, significantly reduce the battery capacity decay rate, and achieve long-term stable cycling. At the same time, the stable pH environment breaks the strict limitations of traditional systems on the pH tolerance of chelating agents, enabling low-cost conventional chelating agents such as EDTA and NTA to play a stable role without relying on expensive special ligands, greatly broadening the selection window of chelating agents and reducing system costs.

[0025] The all-iron flow battery using the electrolyte of this invention can maintain high coulombic efficiency, voltage efficiency and energy efficiency over a wide current density range, providing key support for the large-scale industrial application of all-iron flow batteries. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The all-iron flow battery prepared in Example 1 operates at 20 mA·cm⁻¹. -2 ~100mA•cm -2 Efficiency characteristics at current density.

[0028] Figure 2The all-iron flow battery prepared in Example 1 operates at 20 mA·cm⁻¹. -2 Long-cycle performance at current density.

[0029] Figure 3 The all-iron flow battery prepared in Example 2 was tested at 20 mA·cm⁻¹. -2 ~100mA•cm -2 Efficiency characteristics at current density.

[0030] Figure 4 The all-iron flow battery prepared in Example 3 was tested at 20 mA·cm⁻¹. -2 ~100mA•cm -2 Efficiency characteristics at current density.

[0031] Figure 5 The all-iron flow battery prepared in Example 4 was tested at 20 mA·cm⁻¹. -2 ~100mA•cm -2 Efficiency characteristics at current density.

[0032] Figure 6 The all-iron flow battery prepared for Comparative Example 1 was tested at 20 mA•cm. -2 ~100mA•cm -2 Efficiency characteristics at current density.

[0033] Figure 7 The all-iron flow battery prepared for Comparative Example 2 was tested at 20 mA•cm. -2 ~100mA•cm -2 Efficiency characteristics at current density. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0040] Example 1 This embodiment provides a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte with the following components and concentrations: Ferric chloride 0.5 mol / L, ethylenediaminetetraacetic acid (EDTA) 0.5 mol / L, sodium chloride 2 mol / L and glycine (an amino acid buffer solute) 0.1 mol / L, with deionized water as the solvent.

[0041] The electrolyte preparation steps are as follows: (1) Add 5.844 g of ethylenediaminetetraacetic acid and 0.15 g of glycine to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safety window of 8 (below the iron ion hydrolysis precipitation threshold and within the optimal coordination range of EDTA). (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0042] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (2 2cm 2 The positive and negative electrode electrolytes were both prepared using the electrolyte obtained in Example 1, and the battery separator was a Nafion 212 membrane (4). 4cm 2 ).

[0043] Battery performance test: (1) Ratio performance test Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0044] Test results: such as Figure 1 As shown, the battery operates at 20 mA•cm -2 Up to 100mA•cm -2 It maintains high coulombic efficiency, voltage efficiency and energy efficiency across the entire current density range, demonstrating excellent rate adaptability.

[0045] (2) Long-cycle stability test: Test conditions: at 20mA•cm -2 Under a constant current density, continuous charge-discharge cycle tests were conducted.

[0046] Test results: such as Figure 2 As shown, the battery can be stably cycled 1000 times without significant capacity decay during the cycle, and the coulombic efficiency remains stable, fully demonstrating that the electrolyte and battery of this invention have excellent long-term cycle stability.

[0047] Example 2 This embodiment provides a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte with the following components and concentrations: Ferric chloride 0.5 mol / L, diethylenetriaminepentaacetic acid (DTPA) 1.0 mol / L, sodium chloride 2 mol / L, and sodium bicarbonate / sodium carbonate buffer pair (carbonate system buffer solute) 0.10 mol / L, with deionized water as solvent.

[0048] The electrolyte preparation steps are as follows: (1) Add 4.970g of diethylenetriaminepentaacetic acid and 0.12g of carbonate buffer solute to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safety window of 8 (below the iron ion hydrolysis precipitation threshold and within the optimal coordination range of DTPA). (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0049] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (3 3cm 2 The positive and negative electrode electrolytes were both prepared using the electrolyte obtained in Example 2, and the battery separator was a Nafion 212 membrane (4). 4cm 2 ).

[0050] Ratio performance test: Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0051] Test results: such as Figure 3 As shown, the battery operates at 20 mA•cm -2 Up to 100mA•cm -2 It maintains high coulombic efficiency, voltage efficiency and energy efficiency across the entire current density range, demonstrating excellent rate adaptability.

[0052] Example 3 This embodiment provides a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte with the following components and concentrations: Ferric chloride 0.5 mol / L, aminotriacetic acid (NTA) 0.5 mol / L, sodium chloride 2 mol / L and β-alanine (an amino acid buffer solute) 0.05 mol / L, with deionized water as the solvent.

[0053] The electrolyte preparation steps are as follows: (1) Add 1.914 g of nitric acid and 0.089 g of β-alanine to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safety window of 8 (below the ferric ion hydrolysis precipitation threshold and within the optimal coordination range of NTA). (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0054] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (2 2cm 2The positive and negative electrode electrolytes were both prepared using the electrolyte obtained in Example 3, and the battery separator was a Nafion 212 membrane (4). 4cm 2 ).

[0055] Ratio performance test: Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0056] Test results: such as Figure 4 As shown, the battery operates at 20 mA•cm -2 Up to 100mA•cm -2 It maintains high coulombic efficiency, voltage efficiency and energy efficiency across the entire current density range, demonstrating excellent rate adaptability.

[0057] Example 4 This embodiment provides a pH-buffered, wide-adaptability neutral all-iron flow battery electrolyte with the following components and concentrations: Ferric chloride 0.5 mol / L, glutamate diacetic acid (GLDA) 0.5 mol / L, sodium chloride 2 mol / L, and sodium hydrogen phosphate / sodium dihydrogen phosphate buffer pair (phosphate system buffer solute) 0.01 mol / L, with deionized water as solvent.

[0058] The electrolyte preparation steps are as follows: (1) Add 3.511g of glutamic acid diacetic acid and 0.142g of phosphate buffer solute to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safety window of 8 (below the iron ion hydrolysis precipitation threshold and within the optimal coordination range of GLDA). (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0059] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (4 4cm 2 The positive and negative electrode electrolytes were both prepared using the electrolyte obtained in Example 4, and the battery separator was a Nafion 212 membrane (5). 5cm 2 ).

[0060] Ratio performance test: Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0061] Test results: such as Figure 5 As shown, the battery operates at 20 mA•cm -2 Up to 100mA•cm -2 It maintains high coulombic efficiency, voltage efficiency and energy efficiency across the entire current density range, demonstrating excellent rate adaptability.

[0062] Comparative Example 1 This comparative example provides an all-iron flow battery electrolyte with the following composition and concentration: Ferric chloride 0.5 mol / L, glutamic acid diacetic acid (GLDA) 0.5 mol / L, sodium chloride 2 mol / L, with no buffer solute and water as solvent.

[0063] The electrolyte preparation steps are as follows: (1) Add 2.87g of glutamic acid diacetic acid to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safe window of 8; (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0064] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (4 4cm 2 The positive and negative electrode electrolytes were both prepared using the electrolytes obtained in Comparative Example 1, and the battery separator was a Nafion 212 membrane (5). 5cm 2 ).

[0065] Ratio performance test: Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0066] Test results: As shown in Figure 6, the battery performs well at 20 mA•cm. -2 Up to 100mA•cm -2The capacity decays rapidly across the entire current density range.

[0067] Comparative Example 2 This comparative example provides an aminophosphonate chelating agent neutral all-iron flow battery electrolyte, with the following components and concentrations: Ferric chloride 0.5 mol / L, triazinetrimethylenephosphonic acid 0.5 mol / L, sodium chloride 2 mol / L, unbuffered solute, water as solvent.

[0068] The electrolyte preparation steps are as follows: (1) Add 2.99g of nitrotrimethylenephosphonic acid to 10 ml of deionized water and stir until completely dissolved, so that the pH of the mixed solution is within the preset safe window of 8; (2) Add 2.334g of sodium chloride and 2.703g of ferric chloride hexahydrate to the mixed solution obtained in step (1) and stir until fully dissolved; (3) Transfer the mixed solution obtained in step (2) to a 20ml volumetric flask, dilute to volume with deionized water, and shake well to obtain the electrolyte.

[0069] Battery assembly: Both positive and negative electrodes use graphite felt electrodes (4 4cm 2 The positive and negative electrode electrolytes were both prepared using the electrolytes obtained in Comparative Example 2, and the battery separator was a Nafion 212 membrane (5). 5cm 2 ).

[0070] Ratio performance test: Test conditions: The battery capacity was fixed at 20mAh, and the test was conducted at 20mA•cm. -2 Up to 100mA•cm -2 Charge-discharge tests were conducted over a wide current density range to evaluate the battery's coulombic efficiency, voltage efficiency, and energy efficiency.

[0071] Test results: such as Figure 7 As shown, the battery operates at 20 mA•cm -2 Up to 100mA•cm -2 Throughout the entire current density range, the performance of Comparative Example 2, which uses a high-cost chelating agent, is almost identical to that of the low-cost chelating agents with added buffer solvents in Examples 1-4 of this invention, demonstrating that the technical solution of this invention has significant economic benefits and excellent technical effects.

[0072] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A pH-buffered neutral all-iron flow battery electrolyte, characterized in that, include: A system of soluble ferric salts, chelating agents, and pH buffers; the solvent is deionized water. The pH buffer system is used to stabilize the pH value of the electrolyte within the range of 6.0 to 9.

0.

2. The pH-buffered neutral all-iron flow battery electrolyte according to claim 1, characterized in that, The chelating agent is an aminocarboxylic acid chelating agent or an organophosphonic acid chelating agent.

3. The pH-buffered neutral all-iron flow battery electrolyte according to claim 2, characterized in that, The aminocarboxylic acid chelating agents include one or more of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, aminotriacetic acid, hydroxyethylethylenediaminetriacetic acid, glutamic acid diacetic acid, methylglycine diacetic acid, and cyclohexanediaminetetraacetic acid; The organophosphonic acid chelating agents include one or more of the following: hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, 2-hydroxyphosphonoacetic acid, polyaminopolyethermethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, bis(hexamethylene)triaminepentamethylenephosphonic acid, hydroxyethylaminodimethylenephosphonic acid, and trimethylenephosphonic acid.

4. The pH-buffered neutral all-iron flow battery electrolyte according to claim 1, characterized in that, The pH buffer system is an inorganic buffer system, an organic buffer system, or a biological buffer system; The inorganic buffer system includes a phosphate system, a carbonate system, or a borate system; The organic buffer system includes amino acids, hydroxyethylpiperazine ethanesulfonic acid, morpholine ethanesulfonic acid, or piperazine-N,N'-di(2-ethanesulfonic acid); The biological buffer system includes PBS buffer, Tris buffer, or Good's buffer.

5. The pH-buffered neutral all-iron flow battery electrolyte according to claim 1, characterized in that, The concentration of the soluble ferric salt is 0.1 mol / L to 2.0 mol / L, the concentration of the chelating agent is 0.2 mol / L to 4.0 mol / L, and the concentration of the pH buffer system is 0.01 mol / L to 4.0 mol / L.

6. The pH-buffered neutral all-iron flow battery electrolyte according to claim 1, characterized in that, The electrolyte also includes a supporting electrolyte, wherein the supporting electrolyte consists of sodium ions and / or potassium ions at a concentration of 2 mol / L to 4 mol / L.

7. The method for preparing the pH-buffered neutral all-iron flow battery electrolyte according to any one of claims 1-6, characterized in that, Includes the following steps: The chelating agent and the pH buffer system are mixed in deionized water, the pH is adjusted to the target buffer zone, and then the soluble ferric salt is added to obtain the electrolyte.

8. An all-ferrofluid flow battery, characterized in that, The electrolyte is the pH-buffered neutral all-iron flow battery electrolyte as described in any one of claims 1-6.

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