Negative electrode electrolyte, preparation method and total iron flow battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a negative electrode electrolyte, a preparation method and an all-iron flow battery. The negative electrode electrolyte comprises a negative electrode active material, a complexing agent, a negative electrode electrolyte and deionized water; the complexing agent is a sulfonate organic matter; the sulfonate organic matter contains lone pair electrons which are coordinated and complexed with iron ions. The sulfonic acid complexing agent provided by the invention is combined with Fe < 3 + > and Fe < 2 + > to regulate and control the potential and binding force of Fe < 3 + > / Fe < 2 + > active couple, so that the sulfonic acid complexing agent can be used as a negative electrode complexing agent to prepare a negative electrode electrolyte suitable for an aqueous total iron flow battery. The negative electrode active material is prevented from permeating towards the positive electrode electrolyte side, and the problem of capacity fading caused by the fact that a small-molecule unstable ligand penetrates through the diaphragm to enter the positive electrode electrolyte is relieved. The solubility of iron ions is improved, precipitation of the iron ions in the electrolyte is inhibited, and the capacity retention ratio and the energy efficiency are improved.

Description

Technical Field

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

[0002] Battery storage technologies include lead-acid batteries, lithium-ion batteries, sodium-based batteries, and redox flow batteries (ARFBs). These technologies offer a potential solution for large-scale energy storage and act as a buffer between intermittent power production and customer demand for immediate power delivery. For large-scale energy storage in the 10kW-10MW range, redox flow batteries have advantages over lithium-ion batteries and sodium-sulfur batteries in terms of cost, mobility, flexibility, depth of discharge, fast response, and safety.

[0003] Compared with traditional lead-acid batteries that have been widely used in transportation, aqueous redox flow batteries have become one of the most popular low-cost energy storage technologies, especially all-vanadium aqueous redox flow batteries, which are currently the most mature and widely used energy storage system. However, the material scarcity and price fluctuations of vanadium highlight the urgent need to develop technologies beyond all-vanadium flow batteries. Redox flow batteries have advantages in cost, performance, mobility and flexibility. Due to their prefabrication, modular design and long life performance, the construction and maintenance costs of redox flow batteries tend to be the lowest among all other energy storage systems. In addition, in most cases, flow batteries can be fully discharged without damaging the electrodes or electrolytes. Designed for large-scale energy storage, with long operating life and long rated power discharge duration.

[0004] So far, iron-based redox-active materials have cost and environmental advantages for use in redox flow batteries, and many inorganic, organic and metal organic materials with oxidation activity have been studied, including but not limited to iron, chromium, vanadium ions, quinones, nitrogen heteroaromatics, nitrogen oxide radicals and iron complexes. However, due to limited resource supply, strong electrolyte corrosion and slow redox kinetics, the network-scale application of traditional ARFBs is challenged and restricted. The advantage of iron redox flow batteries (Fe-RFBs) is that they use abundant iron as the redox active material in their electrolyte. In recent years, great progress has been made in the research of iron complexes. Using Fe 3+ / Fe 2+ The redox couple is used as the polar electrolyte in the iron redox flow battery (the positive electrode is Fe 3+ / Fe 2+ Redox couple, the negative electrode is Fe 2+ / Fe redox pair), known organic ligands such as ethylenediaminetetraacetate (EDTA), 2,2'bipyridine (bpy), triethanolamine (TEOA) and cyanide (CN) can form stable soluble redox active substances with iron ions. However, the complex strength of such substances with iron ions is weak, and the equilibrium potential reached is low, which makes the capacity and cycle performance of the battery unsatisfactory. The redox potential of Fe(II) and Fe(III) complexes can be changed by changing the ligands bound to them, and their standard redox potential E0 Fe(III) / Fe(II). Therefore, organic molecules with large peak intensity and good structural adjustability are expected to become the most promising active ingredients in new redox flow batteries.

[0005] Compared with the widely used lithium-ion batteries, the limited energy density of ARFBs is another obstacle to their widespread application in the consumer market. The energy density of ARFBs depends on the operating voltage, the concentration of electroactive substances and the number of electrons involved in the redox reaction. Another challenge that hinders the widespread application of aqueous all-iron flow batteries is how to design systems with high energy density, power density and excellent cycle stability. The current technical problems and hazards of all-iron flow batteries mainly include: (1) Hydrogen evolution reaction at the negative electrode: This will not only reduce the operating efficiency of the battery, but may also lead to a reduction in battery capacity, and the generated hydrogen may pose a safety hazard. (2) Precipitation of iron hydroxide: The formation of precipitation may block the ion conduction membrane, affect the normal operation of the battery, and reduce battery performance and service life. (3) Poor reversibility of the electrochemical reaction of the iron negative electrode: It affects the charge and discharge efficiency and cycle performance of the battery. (4) Iron dendrite problem: Iron dendrites may grow at the negative electrode, causing damage to the electrode structure, increasing the internal resistance of the battery, affecting the charge and discharge performance and life of the battery, and dendrites may also penetrate the diaphragm, causing safety problems such as internal short circuit of the battery. (5) Irreversible capacity loss: During the battery cycle, irreversible capacity loss may occur, resulting in a gradual decrease in the actual available capacity of the battery, affecting the long-term use and energy storage effect of the battery. (6) Limited low-temperature performance: Aqueous electrolytes tend to solidify at low temperatures, limiting the application of all-iron flow batteries in cold areas or low-temperature environments.

[0006] Introducing a suitable chelating agent is one of the effective ways to solve the above problems. Due to the challenge of designing a suitable iron complex, the research on feasible iron complexes for the anode electrolyte of aqueous all-iron flow batteries has been stagnant. Studies have shown that organic electroactive molecules are superior to inorganic materials due to their high adjustability of redox potential, solubility and electrochemical stability. Triethanolamine can be used as a chelating agent to form a complex with iron ions. For example, when used in combination with 3-(NN-bis(2-hydroxyethyl)amino)-2-hydroxypropanesulfonic acid, it can bind to the same iron ion and ferrous ion at the same time. However, the pH concentrations suitable for the positive and negative electrodes in this system are different, and side reactions are prone to occur at the diaphragm. Oxalic acid and its salts, such as sodium oxalate and potassium oxalate, can form stable complexes with iron ions and can be used as chelating agents to improve the performance of all-iron flow batteries to a certain extent. However, such substances have weak chelating ability with iron ions and are easily separated from iron ions during the cycle, thereby affecting the electrochemical performance of the battery. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a negative electrode electrolyte and a preparation method thereof and an all-iron liquid flow battery.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A negative electrode electrolyte comprises a negative electrode active material, a complexing agent, a negative electrode electrolyte and a solvent; the complexing agent is a sulfonate organic matter; the sulfonate organic matter contains a lone pair of electrons and is coordinated and complexed with iron ions.

[0010] The complexing agent is a mixture of one or more of 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt, 4-hydroxy-1-naphthalenesulfonic acid sodium salt (1-naphthol-4-sulfonate sodium), sodium allyl sulfonate, sulfosalicylic acid and sodium lignin sulfonate;

[0011] Preferably, the solvent is water, preferably deionized water.

[0012] The molecular structure of 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt contains multiple hydroxyl groups, sulfonic acid groups, nitrogen atoms and other groups with lone pair electrons. These groups can act as ligands to coordinate with iron ions to form a stable complex.

[0013] The molecules of 4-hydroxy-1-naphthalenesulfonic acid sodium salt and sulfosalicylic acid contain hydroxyl groups and sulfonic acid groups. The oxygen atoms on the hydroxyl groups and the oxygen atoms in the sulfonic acid groups have lone pairs of electrons, which can coordinate with the empty orbitals of iron ions to form stable complexes. In the complexation reaction, the iron ion serves as the central ion, and the sodium 4-hydroxy-1-naphthalenesulfonic acid salt, sodium allyl sulfonate or sulfosalicylic acid serves as ligands surrounding the iron ion, forming a relatively stable complex structure through coordination bonds.

[0014] Sodium lignin sulfonate is an anionic surfactant, and its molecular structure contains multiple oxygen-containing functional groups such as hydroxyl, carboxyl, and sulfonic acid groups. The oxygen atoms in these oxygen-containing functional groups have lone pairs of electrons, which can be coordinated with the empty orbitals of iron ions as coordinating atoms. Iron ions have empty valence electron orbitals, which can accept the lone pairs of electrons of oxygen atoms in sodium lignin sulfonate molecules, thereby forming coordination bonds and producing complexes. This complexation allows iron ions to be tightly combined with sodium lignin sulfonate. The above negative electrode electrolyte additives can all be used as water quality stabilizers. After complexation with iron ions, they reduce the deposition of iron ions and avoid clogging electrodes and diaphragms.

[0015] The molar concentration of the complexing agent in the negative electrode electrolyte is 1-4 times the molar concentration of the negative electrode active material, preferably 2 times.

[0016] Preferably, the negative electrode active material is an iron salt; preferably a mixture of one or more of ferric chloride, ferric sulfate, ferric nitrate, and ferric acetate; preferably, the molar concentration of the negative electrode active material is 0.1-2 mol / L, preferably 0.2-1 mol / L.

[0017] Preferably, the negative electrode electrolyte is an alkaline substance, preferably, the negative electrode electrolyte is a mixture of one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and lithium carbonate;

[0018] Preferably, the molar concentration of the negative electrode electrolyte is in the range of 1.5-6 mol / L, preferably 1-4 mol / L; more preferably 3 mol / L.

[0019] The present invention also includes a method for preparing the negative electrode electrolyte, comprising the following steps:

[0020] Adding a solvent into a reactor, and then adding a negative electrode active material to dissolve to obtain an iron ion solution;

[0021] Adding a complexing agent to the iron ion solution and dissolving it to obtain a complexing solution;

[0022] The negative electrode electrolyte is dissolved in a solvent to form an electrolyte solution, which is then added to the complex solution and mixed evenly to obtain a negative electrode electrolyte. The present invention also includes an alkaline all-iron liquid flow battery, including the negative electrode electrolyte, an electrode, a diaphragm, and a positive electrode electrolyte.

[0023] The positive electrode electrolyte comprises ferrocyanide and a positive electrode electrolyte;

[0024] Preferably, the ferrocyanide salt comprises one or a mixture of ferrocyanide or ferrocyanide;

[0025] Preferably, the ferrocyanide is a mixture of one or more of sodium ferrocyanide, potassium ferrocyanide, and lithium ferrocyanide; the ferrocyanide is a mixture of one or more of sodium ferrocyanide, potassium ferrocyanide, and lithium ferrocyanide. Preferably, potassium ferrocyanide is used as the positive electrode electrolyte, and the molar concentration of ferrocyanide is 0.1-2.0 mol / L.

[0026] The positive electrode electrolyte is an alkaline substance. Preferably, the positive electrode electrolyte is a mixture of one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the molar concentration range of the positive electrode electrolyte is 0.1-2.0 mol / L.

[0027] The diaphragm is a SPEEK diaphragm or a perfluorosulfonic acid membrane; since the complex molecules formed by sulfonic acid substances and iron are relatively large, the above diaphragm can achieve a good barrier effect. In order to improve the permeability of SPEEK and perfluorosulfonic acid membranes, improve battery energy efficiency, and inhibit liquid cross-linking; preferably, the diaphragm is a diaphragm that has been pre-treated by soaking in a strong alkaline aqueous solution with a pH of 14 at 25°C for 24 hours.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The technical solution of this application uses sulfonate organic matter as a complexing agent to solve multiple technical problems at the same time. First, sulfonate organic matter has good solubility, which allows them to be well dispersed and dissolved in aqueous electrolytes. Secondly, sulfonate organic matter has high surface activity: it can reduce the surface tension of the liquid, has functions such as dispersion, and improves the dispersibility of iron ions in the electrolyte. The most important thing is that sulfonate organic matter has certain electrochemical activity: in specific electrochemical systems such as all-iron liquid flow batteries, iron ions have specific coordination geometry requirements. For example, Fe 3+ Usually tend to form a hexacoordinated octahedral structure, while Fe 2+ A tetracoordinate or hexacoordinate structure may be formed. The structure and spatial orientation of the sulfonic acid organic compound can meet the coordination geometry requirements of the iron ion, thereby forming a stable complex and improving the energy density and cycle life of the flow battery.

[0030] The present invention provides a sulfonic acid complexing agent for the negative electrode electrolyte of the all-iron liquid flow battery and Fe 3+ and Fe 2+ Binding and regulation of Fe 3 + / Fe 2+The potential and binding force of the active electrode pair allow it to be used as a negative electrode complexing agent to prepare a negative electrode electrolyte suitable for aqueous all-iron liquid flow batteries. It avoids the penetration of negative electrode active substances into the positive electrode electrolyte side, and alleviates the problem of small molecule unstable ligands passing through the diaphragm into the positive electrode electrolyte causing capacity decay. It improves the solubility of iron ions, inhibits the precipitation of iron ions in the electrolyte, improves the capacity retention rate and energy efficiency, and at the same time, the efficiency and stability of aqueous all-iron liquid flow batteries using this electrolyte are greatly improved. Aqueous all-iron liquid flow batteries based on this technology cost less than existing lithium-ion batteries, and have better safety and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the efficiency diagram of the embodiment of the present invention and the comparative example;

[0032] Figure 2 Graphs showing the cycle capacity of the embodiments of the present invention and the comparative example. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0034] Example 1

[0035] 1. Preparation of negative electrode electrolyte

[0036] 1) Add 0.04 mol of negative electrode active material FeCl3 to 50 ml of solvent deionized water and stir until dissolved;

[0037] 2) slowly adding 0.08 mol of complexing agent 3-[N-trimethylolmethylamine]-2-hydroxypropanesulfonic acid sodium salt to step 1), and continuing to stir and react for 1.5 hours;

[0038] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours;

[0039] 4) The above solution was transferred to a 100 ml volumetric flask to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (final concentration, the same below, 0.4 mol / L)-complexing agent 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt (final concentration, the same below, 0.8 mol / L)-negative electrode electrolyte NaOH (final concentration, the same below, 3 mol / L).

[0040] 2. Preparation of positive electrolyte

[0041] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0042] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0043] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (final concentration, the same below, 0.4 mol / L)-positive electrode electrolyte NaOH (final concentration, the same below, 3 mol / L) for standby use.

[0044] Example 2

[0045] 1. Negative Electrolyte

[0046] 1) Add 0.04 mol of negative electrode active material FeCl3 into 50 ml of deionized water and stir until dissolved;

[0047] 2) slowly adding 0.08 mol of complexing agent 4-hydroxy-1-naphthalenesulfonic acid sodium salt to step 1), and continuing to stir and react for 1.5 hours;

[0048] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours.

[0049] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent 4-hydroxy-1-naphthalenesulfonic acid sodium salt (0.8 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0050] 2. Preparation of positive electrolyte

[0051] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0052] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0053] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0054] Example 3

[0055] 1. Negative Electrolyte

[0056] 1) Add 0.04 mol of negative electrode active material FeCl3 to 50 ml of solvent deionized water and stir until dissolved;

[0057] 2) Slowly add 0.08 mol of complexing agent sodium allyl sulfonate to step 1), and continue stirring the reaction for 1.5 hours;

[0058] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours.

[0059] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent sodium allyl sulfonate (0.8 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0060] 2. Preparation of positive electrolyte

[0061] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0062] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0063] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0064] Example 4

[0065] 1. Negative Electrolyte

[0066] 1) Add 0.04 mol of negative electrode active material FeCl3 into 50 ml of deionized water and stir until dissolved;

[0067] 2) slowly adding 0.08 mol of complexing agent sulfosalicylic acid to step 1), and continuing to stir and react for 1.5 hours;

[0068] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours.

[0069] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent sulfosalicylic acid (0.8 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0070] 2. Preparation of positive electrolyte

[0071] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0072] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0073] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0074] Example 5

[0075] 1. Negative Electrolyte

[0076] 1) Add 0.04 mol of negative electrode active material FeCl3 into 50 ml of deionized water and stir until dissolved;

[0077] 2) slowly adding 0.08 mol of complexing agent sodium lignin sulfonate to step 1), and continuing to stir and react for 1-2 hours;

[0078] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1-2 hours.

[0079] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent sodium lignin sulfonate (0.8 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0080] 2. Preparation of positive electrolyte

[0081] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0082] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0083] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0084] Example 6

[0085] 1. Preparation of negative electrode electrolyte

[0086] 1) Add 0.04 mol of negative electrode active material FeCl3 to 50 ml of solvent deionized water and stir until dissolved;

[0087] 2) slowly adding 0.04 mol of complexing agent 3-[N-trimethylolmethylamine]-2-hydroxypropanesulfonic acid sodium salt to step 1), and continuing to stir and react for 1.5 hours;

[0088] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours;

[0089] 4) The above solution was transferred to a 100 ml volumetric flask to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt (0.4 mol / L)-negative electrode electrolyte NaOH (, 3 mol / L).

[0090] 2. Preparation of positive electrolyte

[0091] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0092] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0093] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0094] Example 7

[0095] 1. Preparation of negative electrode electrolyte

[0096] 1) Add 0.04 mol of negative electrode active material FeCl3 to 50 ml of solvent deionized water and stir until dissolved;

[0097] 2) Slowly add 0.16 mol of complexing agent 3-[N-trimethylolmethylamine]-2-hydroxypropanesulfonic acid sodium salt to step 1), and continue stirring and reacting for 1.5 hours;

[0098] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours;

[0099] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt (1.6 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0100] 2. Preparation of positive electrolyte

[0101] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0102] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0103] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume, finally obtaining 100 ml positive electrode electrolyte, ferrocyanide K4[Fe(CN)6] (0.4 mol / L)-positive electrode electrolyte NaOH (3 mol / L) for standby use.

[0104] Comparative Example 1

[0105] 1. Preparation of negative electrode electrolyte

[0106] 1) Add 0.04 mol of negative electrode active material FeCl3 to 50 ml of solvent deionized water and stir until dissolved;

[0107] 2) Slowly add 0.08 mol of complexing agent triethanolamine to step 1), and continue stirring to react for 1.5 hours;

[0108] 3) Weigh 0.3 mol of negative electrode electrolyte NaOH and dissolve it in 20 ml of distilled water, add it to the above complex solution and stir for 1.5 hours;

[0109] 4) The above solution was transferred to a 100 ml volumetric flask and fixed to volume to obtain a negative electrode electrolyte solution of negative electrode active material FeCl3 (0.4 mol / L)-complexing agent triethanolamine (0.8 mol / L)-negative electrode electrolyte NaOH (3 mol / L).

[0110] 2. Preparation of positive electrolyte

[0111] 1) Weigh 0.04 mol ferrocyanide K4[Fe(CN)6] and add it to 50 ml deionized water. Stir at room temperature until the solid is completely dissolved (about 10 minutes) to obtain a complex solution.

[0112] 2) Dissolve 0.3 mol of positive electrode electrolyte NaOH in 20 ml of deionized water, add it to the complex solution and stir for 1 hour.

[0113] 3) Transfer the above solution into a 100 ml volumetric flask and add deionized water to make up to volume to obtain 100 ml

[0114] The positive electrode electrolyte, ferrocyanide K4[Fe(CN)6](0.4mol / L)-positive electrode electrolyte NaOH(3mol / L) is set aside.

[0115] The positive electrode electrolyte and the negative electrode electrolyte obtained in Examples 1-7 and Comparative Example 1 were assembled into an all-iron liquid flow battery:

[0116] The all-iron liquid flow battery provided by the present invention comprises a negative electrode electrolyte storage tank, a positive electrode electrolyte storage tank, a diaphragm, a negative electrode, a positive electrode, a negative terminal plate, a positive terminal plate, a negative electrode pump, and a positive electrode pump. The battery unit is assembled in the order of a positive terminal plate, a graphite current collector, a positive electrode 6mm×3cm×3cm carbon felt, an ion exchange membrane Nafion 115 as a diaphragm, a negative electrode 6mm×3cm×3cm carbon felt, a graphite current collector, and a negative terminal plate.

[0117] All-iron flow battery testing:

[0118] During the battery operation, the flow rate of the positive and negative electrolytes was 100 mL / min, and the flow rate was 30 mA / cm 2 For the charge and discharge test, the charge and discharge cut-off voltages were set to 1.65 V and 0.8 V respectively, and 100 cycles were performed.

[0119] The volume of the positive and negative electrolytes is 100 ml, the flow rate of the positive and negative electrolytes is 100 ml / min, and the current density is 50 mA / cm 2 , test temperature: 30℃, argon was used as protective gas during the charge and discharge process, the charge and discharge cut-off voltages were 1.6V and 0.7V respectively, and the charge and discharge times were 100 times.

[0120] Table 1 shows the coulombic efficiency, voltage efficiency and energy efficiency of alkaline flow batteries with different negative electrode electrolyte compositions in Examples 1 to 7 and Comparative Example 1 after 100 cycles. The molar concentration ratio in Table 1 is the ratio of the molar concentration of the complexing agent in the negative electrode electrolyte to the molar concentration of the negative electrode active material; Figure 1 The efficiency diagram of alkaline liquid flow batteries with different negative electrode electrolyte compositions of Examples 1 to 7 and Comparative Examples is shown in FIG. Figure 2 The capacity diagram of the alkaline liquid flow battery with different negative electrode electrolyte compositions of Examples 1 to 7 and the comparative example after 100 cycles.

[0121] Table 1

[0122]

[0123]

[0124] As can be seen from the table, in Comparative Examples 1, 6, and 7, there are too few additives, and the ability to complex with iron ions is reduced. The iron ions in the solution are more likely to precipitate, affecting the capacity and cycle performance of the battery. There are too many additives, and there are redundant additives in the solution, which increases the viscosity of the solution and reduces the activity of the iron ions. By comparing Comparative Example 1 with Example 1, it can be seen that the triethanolamine without sulfonic acid group selected in Comparative Example 1 cannot form a complete six-coordinate structure with iron ions, and the stability of the iron complex is poor. The iron ions easily fall off from the triethanolamine group to form a precipitate. Therefore, the battery efficiency and stability are not as good as the implementation scheme of the present application. As can be seen from Examples 1-5, the sulfonic acid complexing agent of the negative electrode electrolyte of the all-iron liquid flow battery provided by the present invention is compatible with Fe 3+ and Fe 2+ Binding and regulation of Fe 3+ / Fe 2+ The potential and binding force of the active electrode pair allow it to be used as a negative electrode complexing agent to prepare a negative electrode electrolyte suitable for aqueous all-iron liquid flow batteries. It avoids the penetration of negative electrode active substances into the positive electrode electrolyte side, and alleviates the problem of small molecule unstable ligands passing through the diaphragm into the positive electrode electrolyte causing capacity decay. It improves the solubility of iron ions, inhibits the precipitation of iron ions in the electrolyte, improves the capacity retention rate and energy efficiency, and at the same time, the efficiency and stability of aqueous all-iron liquid flow batteries using this electrolyte are greatly improved. Aqueous all-iron liquid flow batteries based on this technology cost less than existing lithium-ion batteries, and have better safety and cycle stability.

[0125] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode electrolyte, characterized in that: The invention comprises a negative electrode active material, a complexing agent, a negative electrode electrolyte and a solvent; the complexing agent is a sulfonate organic matter; the sulfonate organic matter contains a lone pair of electrons and is coordinated and complexed with iron ions.

2. The negative electrode electrolyte according to claim 1, characterized in that: The complexing agent is a mixture of one or more of 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt, 4-hydroxy-1-naphthalenesulfonic acid sodium salt (1-naphthol-4-sulfonate sodium), sodium allyl sulfonate, sulfosalicylic acid and sodium lignin sulfonate; Preferably, the solvent is water, preferably deionized water.

3. The negative electrode electrolyte according to claim 1, characterized in that: The molar concentration of the complexing agent in the negative electrode electrolyte is 1-4 times the molar concentration of the negative electrode active material, preferably 2 times.

4. The negative electrode electrolyte according to claim 1, characterized in that: The negative electrode active material is an iron salt; preferably a mixture of one or more of ferric chloride, ferric sulfate, ferric nitrate and ferric acetate; Preferably, the molar concentration of the negative electrode active material is 0.1-2 mol / L, preferably 0.2-1 mol / L; more preferably 0.8 mol / L.

5. The negative electrode electrolyte according to claim 1, characterized in that: The negative electrode electrolyte is an alkaline substance. Preferably, the negative electrode electrolyte is a mixture of one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and lithium carbonate; Preferably, the molar concentration of the negative electrode electrolyte is in the range of 1.5-6 mol / L, preferably 1-4 mol / L; more preferably 3 mol / L.

6. A method for preparing the negative electrode electrolyte according to any one of claims 1 to 5, characterized in that: The steps include: Adding a solvent into a reactor, and then adding a negative electrode active material to dissolve to obtain an iron ion solution; Adding a complexing agent to the iron ion solution and dissolving it to obtain a complexing solution; The negative electrode electrolyte is dissolved in a solvent to form an electrolyte solution, which is then added into the complex solution and mixed evenly to obtain a negative electrode electrolyte.

7. An alkaline all-iron flow battery, characterized in that: It comprises the negative electrode electrolyte, electrode, separator, and positive electrode electrolyte as described in any one of claims 1 to 5.

8. The all-iron liquid flow battery according to claim 7, characterized in that: The positive electrode electrolyte comprises ferrocyanide and a positive electrode electrolyte; Preferably, the ferrocyanide comprises one or a mixture of ferrocyanide or ferrocyanide; Preferably, the molar concentration of the ferricyanide is 0.1-2.0 mol / L; preferably 0.4 mol / L.

9. The all-iron liquid flow battery according to claim 8, characterized in that: The ferrocyanide is a mixture of one or more of sodium ferrocyanide, potassium ferrocyanide and lithium ferrocyanide; Preferably, the ferrocyanide is a mixture of one or more of sodium ferrocyanide, potassium ferrocyanide and lithium ferrocyanide; Preferably, the positive electrode electrolyte is an alkaline substance; Preferably, the positive electrode electrolyte is a mixture of one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide; Preferably, the molar concentration of the cathode electrolyte is in the range of 0.1-4.0 mol / L, preferably 3 mol / L.

10. The all-iron liquid flow battery according to claim 8, characterized in that: The diaphragm is a SPEEK diaphragm or a perfluorosulfonic acid membrane; Preferably, the diaphragm is a diaphragm that has been pre-treated by soaking in a strong alkaline aqueous solution with a pH of 14 at 25° C. for 24 hours.

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