Negative electrolyte, preparation method and all-iron flow battery

Abstract

This invention belongs to the field of batteries, specifically relating to a negative electrode electrolyte and its preparation method, and an all-iron flow battery. The negative electrode electrolyte includes a negative electrode active material, a complexing agent, a negative electrode electrolyte, and deionized water; the complexing agent is a sulfonate organic compound; the sulfonate organic compound contains lone pair electrons that coordinate with iron ions for complexation. The all-iron flow battery negative electrode electrolyte provided by this invention uses a sulfonate complexing agent and Fe... 3+ and Fe 2+ Combined, regulating Fe 3+ / Fe 2+ The potential and binding force of the active redox couple allow it to act as a negative electrode complexing agent, enabling the preparation of a negative electrode electrolyte suitable for aqueous all-iron flow batteries. This prevents the negative electrode active material from permeating into the positive electrode electrolyte side, mitigating the problem of capacity decay caused by unstable small molecule ligands crossing the separator into the positive electrode electrolyte. It also improves iron ion solubility, inhibits iron ion precipitation in the electrolyte, and enhances capacity retention and energy efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of batteries, and particularly relates to a negative electrolyte, a preparation method and a full-iron flow battery. BACKGROUND

[0002] Battery storage technologies include lead-acid batteries, lithium-ion batteries, sodium-based batteries, and redox flow batteries (ARFBs). These technologies provide 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 range of 10 kW-10 MW, 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 promising low-cost energy storage technologies, especially all-vanadium aqueous redox flow batteries, which are the most mature and widely used energy storage systems. However, the scarcity of vanadium materials and price fluctuations highlight the urgent need to develop technologies beyond all-vanadium flow batteries. Redox flow batteries have advantages in terms of cost, performance, mobility, and flexibility. Due to their prefabricated, modular design and long service life performance, the construction and maintenance costs of redox flow batteries are often the lowest among all other energy storage systems. In addition, in most cases, flow batteries can be completely discharged without damaging the electrodes or electrolytes. Designed for large-scale energy storage, with long service life and long duration of power discharge at rated power.

[0004] So far, iron-based redox active materials have cost and environmental advantages for redox flow batteries, and many inorganic, organic, and metal-organic compounds with oxidation activity have been studied, including but not limited to iron, chromium, vanadium ions, quinones, nitrogen heteroarenes, nitroxide radicals, and iron complexes. However, due to limited resource supply, strong corrosive electrolytes, and slow redox kinetics, the network-scale application of traditional ARFBs is challenged and limited. The advantage of iron redox flow batteries (Fe-RFB) is that iron, an abundant resource, is used as a redox active material in the electrolyte. In recent years, iron complexes have made great progress. Fe 3+ / Fe 2+ Redox couples as polar electrolytes for iron redox flow batteries (the positive electrode is Fe 3+ / Fe 2+ Redox couples, the negative electrode is Fe 2+It is known that 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 complexing 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 not ideal. The redox potential of Fe(II) and Fe(III) complexes can be changed by changing the ligand bound to them, thus changing the standard redox potential E0 Fe(III) / Fe(II). Therefore, organic molecules with high peak intensity and good structural adjustability are expected to become the most promising active ingredients in new redox flow batteries.

[0005] Compared with widely used lithium-ion batteries, the limited energy density of ARFB is another obstacle to its wide application in the consumer market. The energy density of ARFB depends on the working voltage, the concentration of electroactive substances and the number of electrons involved in the redox reaction. Another challenge that hinders the widespread application of water-based all-iron flow batteries is how to design a system with high energy density, power density and excellent cycle stability. The technical problems and hazards existing in the current all-iron flow battery mainly include: (1) hydrogen evolution reaction at the negative electrode: this not only reduces the operating efficiency of the battery, but also can lead to a decrease in battery capacity, and the generated hydrogen can pose a safety hazard. (2) Generation of iron hydroxide precipitate: the generation of precipitate can block the ion-conducting membrane, affect the normal operation of the battery, and reduce the performance and service life of the battery. (3) Poor reversibility of iron negative electrode electrochemical reaction: affects the charge and discharge efficiency and cycle performance of the battery. (4) Iron dendrite problem: the growth of iron dendrites may occur at the negative electrode, leading to the destruction of the electrode structure, increasing the internal resistance of the battery, affecting the charge and discharge performance and life of the battery, and the dendrites may also penetrate the separator, causing internal short circuit and other safety problems. (5) Irreversible loss of capacity: during the cycle use of the battery, irreversible loss of capacity may occur, leading to 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: the aqueous electrolyte is prone to solidification at low temperatures, limiting the application of all-iron flow batteries in cold regions or low-temperature environments.

[0006] Introducing a suitable complexing agent is one of the effective ways to solve the above problems. The research on the feasible iron complex of the anolyte of the aqueous all-iron flow battery has been stagnant due to the challenge of designing a suitable iron complex. Studies have shown that organic electroactive molecules are superior to inorganic materials due to their high tunability of redox potential, solubility and electrochemical stability. Triethanolamine can be used as a complexing agent to form a complex with iron ions, for example, it can be used in combination with 3-(N-N-bis(2-hydroxyethyl)amino)-2-hydroxypropanesulfonic acid to bind to both iron ions and ferrous ions at the same time. However, the pH concentration of the positive and negative electrodes in this system is different, and side reactions are prone to occur at the separator. Oxalic acid and its salts, such as sodium oxalate and potassium oxalate, can form stable complexes with iron ions and can be used as complexing agents to improve the performance of the all-iron flow battery to some extent. However, the complexing ability of such substances with iron ions is weak, and they are prone to separate from iron ions during the cycling process, thereby affecting the electrochemical performance of the battery. SUMMARY

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

[0008] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0009] A negative electrolyte comprises a negative active material, a complexing agent, a negative electrolyte and a solvent; the complexing agent is a sulfonate organic compound; the sulfonate organic compound contains lone pair electrons for coordination complexation with iron ions.

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

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

[0012] The 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt molecule contains multiple hydroxyl groups, sulfonic acid groups and nitrogen atoms with lone pair electrons, which can act as ligands to coordinate and bind with iron ions to form stable complexes.

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

[0014] Sodium lignosulfonate is an anionic surfactant, and the molecular structure contains multiple oxygen-containing functional groups such as hydroxyl, carboxyl, and sulfonic acid group. The oxygen atoms in these oxygen-containing functional groups have lone pair electrons, which can act as coordination atoms to coordinate with the empty orbital of iron ions. Iron ions have empty valence electron orbitals, which can accept the lone pair electrons of oxygen atoms in sodium lignosulfonate molecules, thereby forming coordination bonds and generating complexes. This complexation makes iron ions and sodium lignosulfonate tightly combined together. The above negative electrolyte additives can all act as water quality stabilizers, and after complexing with iron ions, the deposition of iron ions is reduced, thereby avoiding the blockage of electrodes and separators.

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

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

[0017] Preferably, the negative electrolyte is an alkaline substance, and preferably the negative 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 electrolyte is in the range of 1.5-6 mol / L, preferably 1-4 mol / L; more preferably 3 mol / L.

[0019] The present application also includes a preparation method of the negative electrolyte, comprising the following steps:

[0020] A solvent is added to the reactor, and then the negative active material is dissolved to obtain an iron ion solution;

[0021] The complexing agent is dissolved in the iron ion solution to obtain a complex solution;

[0022] The negative electrolyte is dissolved in the solvent to form an electrolyte solution, which is then added to the complex solution and mixed uniformly to obtain the negative electrolyte. The present application also includes an alkaline full-iron flow battery, which comprises the negative electrolyte, an electrode, a separator, and a positive electrolyte.

[0023] The positive electrolyte comprises ferricyanide and a positive electrolyte;

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

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

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

[0027] The separator is a SPEEK separator or a perfluorosulfonic acid membrane; since the sulfonic acid substance forms a complex molecule with iron, the above-mentioned separator can achieve good barrier effect. In order to improve the permeability of the SPEEK and the perfluorosulfonic acid membrane, improve the energy efficiency of the battery, and inhibit the liquid leakage phenomenon; preferably, the separator is a separator treated by being immersed in a strong alkaline aqueous solution with a pH of 14 at 25°C for 24h.

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] The technical scheme of the present application selects sulfonate organic compounds as complexing agents to solve a variety of technical problems. First, sulfonate organic compounds have good solubility, which makes them well dispersed and dissolved in aqueous electrolyte. Second, sulfonate organic compounds have high surface activity: they can reduce the surface tension of the liquid, have dispersion and other functions, and improve the dispersibility of iron ions in the electrolyte. Most importantly, sulfonate organic compounds have certain electrochemical activity: in specific electrochemical systems such as full-iron flow batteries, iron ions have specific coordination geometry requirements. For example, Fe 3+ Generally tends to form a six-coordinated octahedral structure, while Fe 2+ May form a four-coordinated or six-coordinated structure. The structure and spatial orientation of the sulfonic acid organic compound can meet the coordination geometry requirements of iron ions, thereby forming a stable complex and improving the energy density and cycle life of the flow battery.

[0030] The full-iron flow battery negative electrolyte sulfonic complexing agent provided by the present application combines with Fe 3+ And Fe 2+ To regulate Fe 3 + / Fe 2+The potential and binding force of the active electric pair enable it to be used as a negative complexing agent to prepare a negative electrolyte suitable for water-based full-iron flow batteries. The negative active material is prevented from penetrating to the positive electrolyte side, and the problem of capacity attenuation caused by small molecule unstable ligands crossing the diaphragm into the positive electrolyte is alleviated. The solubility of iron ions is improved, the precipitation of iron ions in the electrolyte is inhibited, the capacity retention rate and energy efficiency are improved, and the efficiency and stability of the water-based full-iron flow battery using the electrolyte are greatly improved. The water-based full-iron flow battery based on the technology has lower cost than the existing lithium ion battery, and has better safety and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Efficiency chart for the examples and comparative examples of the present application;

[0032] Figure 2 Cycle capacity chart for the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in combination with the drawings and the best embodiments.

[0034] Example 1

[0035] 1. Preparation of negative electrolyte

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

[0037] 2) Slowly add 0.08 mol of complexing agent 3-[N-trihydroxymethylmethylamine]-2-hydroxypropanesulfonic acid sodium salt to step 1), and continue stirring for 1.5 hours;

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

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

[0040] 2. Preparation of positive electrolyte

[0041] 1) Weigh 0.04 mol of ferricyanide K4[Fe(CN)6] into 50 ml of deionized water, stir at room temperature until the solid is completely dissolved (about 10 mins) to obtain a complex solution.

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

[0043] 3) Transfer the above solution into a 100 ml volumetric flask, add deionized water to constant volume, finally obtain 100 ml of positive electrolyte, ferricyanide K4[Fe(CN)6] (final concentration, same below, 0.4 mol / L) - positive electrolyte NaOH (final concentration, same below, 3 mol / L) for use.

[0044] Example 2

[0045] 1. Negative electrolyte

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

[0047] 2) Slowly add 0.08 mol of complexing agent 4-hydroxy-1 naphthalene sulfonic acid sodium salt to step 1), continue stirring for 1.5 hours;

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

[0049] 4) Transfer the above solution to a 100 ml volumetric flask to constant volume to obtain negative active material FeCl3 (0.4 mol / L) - complexing agent 4-hydroxy-1 naphthalene sulfonic acid sodium salt (0.8 mol / L) - negative electrolyte NaOH (3 mol / L) negative electrolyte.

[0050] 2. Preparation of positive electrolyte

[0051] 1) Weigh 0.04 mol of ferricyanide K4[Fe(CN)6] into 50 ml of deionized water, stir at room temperature until the solid is completely dissolved (about 10 mins) to obtain a complex solution.

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

[0053] 3) The above solution was transferred into a 100 ml volumetric flask and diluted with deionized water to the mark. Finally, 100 ml of positive electrolyte, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) was obtained.

[0054] Example 3

[0055] 1. Negative electrolyte

[0056] 1) 0.04 mol of negative active material FeCl3 was added to 50 ml of solvent, deionized water, and stirred until dissolved;

[0057] 2) 0.08 mol of complexing agent, sodium allyl sulfonate, was slowly added to step 1), and the stirring reaction was continued for 1.5 hours;

[0058] 3) 0.3 mol of negative electrolyte NaOH was weighed and dissolved in 20 ml of distilled water, and added to the above complexing solution and stirred for 1.5 hours.

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

[0060] 2. Preparation of positive electrolyte

[0061] 1) 0.04 mol of ferricyanide K4[Fe(CN)6] was weighed and added to 50 ml of deionized water, and stirred at room temperature until the solid was completely dissolved (about 10 mins) to obtain a complexing solution.

[0062] 2) 0.3 mol of positive electrolyte NaOH was dissolved in 20 ml of deionized water, and after dissolution, was added to the complexing solution and stirred for 1 h.

[0063] 3) The above solution was transferred into a 100 ml volumetric flask and diluted with deionized water to the mark. Finally, 100 ml of positive electrolyte, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) was obtained.

[0064] Example 4

[0065] 1. Negative electrolyte

[0066] 1) 0.04 mol of negative active material FeCl3 was added to 50 ml of deionized water, and stirred until dissolved;

[0067] 2) To the solution of step 1) slowly add 0.08 moles of complexing agent sulfosalicylic acid and continue stirring the reaction for 1.5 hours;

[0068] 3) Weigh 0.3 moles of negative electrolyte NaOH into 20 ml of distilled water and add to the above complex solution and stir for 1.5 hours.

[0069] 4) Transfer the above solution to a 100 ml volumetric flask and make up to volume to obtain the negative active material FeCl3(0.4 moles / L) - complexing agent sulfosalicylic acid (0.8 moles / L) - negative electrolyte NaOH (3 moles / L) negative electrolyte.

[0070] 2. Positive electrolyte preparation

[0071] 1) Weigh 0.04 moles of ferricyanide K4[Fe(CN)6] into 50 ml of deionized water and stir at room temperature until the solid is completely dissolved (about 10 mins) to obtain a complex solution.

[0072] 2) Dissolve 0.3 moles of positive electrolyte NaOH in 20 ml of deionized water and add to the complex solution after dissolution and stir for 1 h.

[0073] 3) Transfer the above solution to a 100 ml volumetric flask and add deionized water to make up to volume to finally obtain 100 ml of positive electrolyte, ferricyanide K4[Fe(CN)6] (0.4 moles / L) - positive electrolyte NaOH (3 moles / L) ready for use.

[0074] Example 5

[0075] 1. Negative electrolyte

[0076] 1) Add 0.04 moles of negative active material FeCl3to 50 ml of deionized water and stir until dissolved;

[0077] 2) To the solution of step 1) slowly add 0.08 moles of complexing agent sodium lignosulfonate and continue stirring the reaction for 1-2 hours;

[0078] 3) Weigh 0.3 moles of negative electrolyte NaOH into 20 ml of distilled water and add to the above complex solution and stir for 1-2 h.

[0079] 4) Transfer the above solution to a 100 ml volumetric flask and make up to volume to obtain the negative active material FeCl3(0.4 moles / L) - complexing agent sodium lignosulfonate (0.8 moles / L) - negative electrolyte NaOH (3 moles / L) negative electrolyte.

[0080] 2. Positive electrolyte preparation

[0081] 1) 0.04 mol of ferricyanide salt K4[Fe(CN)6] was weighed and added to 50 ml of deionized water, stirred at room temperature until the solid was completely dissolved (about 10 mins), to obtain a complex solution.

[0082] 2) 0.3 mol of positive electrolyte NaOH was dissolved in 20 ml of deionized water, after dissolution it was added to the complex solution and stirred for 1 h.

[0083] 3) The above solution was transferred into a 100 ml volumetric flask and deionized water was added to constant volume, finally 100 ml of positive electrolyte was obtained, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) was ready for use.

[0084] Example 6

[0085] 1. Preparation of negative electrolyte

[0086] 1) 0.04 mol of negative active material FeCl3 was added to 50 ml of solvent deionized water, stirred until dissolved;

[0087] 2) 0.04 mol of complexing agent 3-[N-trishydroxymethylmethylamine]-2-hydroxypropane sulfonic acid sodium salt was slowly added to step 1), continue to stir for 1.5 hours;

[0088] 3) 0.3 mol of negative electrolyte NaOH was weighed and dissolved in 20 ml of distilled water, added to the above complex solution and stirred for 1.5 hours;

[0089] 4) The above solution was transferred to a 100 ml volumetric flask and constant volume was obtained, to obtain negative active material FeCl3 (0.4 mol / L) - complexing agent 3-[N-trishydroxymethylmethylamine]-2-hydroxypropane sulfonic acid sodium salt (0.4 mol / L) - negative electrolyte NaOH (3 mol / L) negative electrolyte.

[0090] 2. Preparation of positive electrolyte

[0091] 1) 0.04 mol of ferricyanide salt K4[Fe(CN)6] was weighed and added to 50 ml of deionized water, stirred at room temperature until the solid was completely dissolved (about 10 mins), to obtain a complex solution.

[0092] 2) 0.3 mol of positive electrolyte NaOH was dissolved in 20 ml of deionized water, after dissolution it was added to the complex solution and stirred for 1 h.

[0093] 3) The above solution was transferred into a 100 ml volumetric flask and diluted with deionized water to obtain 100 ml of positive electrolyte solution, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) ready for use.

[0094] Example 7

[0095] 1. Preparation of negative electrolyte solution

[0096] 1) 0.04 mol of negative active material FeCl3 was added to 50 ml of solvent deionized water and stirred until dissolved;

[0097] 2) 0.16 mol of complexing agent 3-[N-trihydroxymethyl methylamine]-2-hydroxypropane sulfonic acid sodium salt was slowly added to step 1) and the reaction was continued for 1.5 hours with stirring;

[0098] 3) 0.3 mol of negative electrolyte NaOH was weighed and dissolved in 20 ml of distilled water and added to the above complexing solution and stirred for 1.5 hours;

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

[0100] 2. Preparation of positive electrolyte solution

[0101] 1) 0.04 mol of ferricyanide K4[Fe(CN)6] was weighed and added to 50 ml of deionized water and stirred at room temperature until the solid was completely dissolved (about 10 mins) to obtain a complexing solution.

[0102] 2) 0.3 mol of positive electrolyte NaOH was dissolved in 20 ml of deionized water and added to the complexing solution after dissolution and stirred for 1 h.

[0103] 3) The above solution was transferred into a 100 ml volumetric flask and diluted with deionized water to obtain 100 ml of positive electrolyte solution, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) ready for use.

[0104] Comparative Example 1

[0105] 1. Preparation of negative electrolyte solution

[0106] 1) 0.04 mol of negative active material FeCl3 was added to 50 ml of solvent deionized water and stirred until dissolved;

[0107] 2) To the solution of step 1), 0.08 mol of complexing agent triethanolamine was added slowly and the reaction was continued for 1.5 h with stirring;

[0108] 3) 0.3 mol of negative electrolyte NaOH was weighed in 20 ml of distilled water and added to the above complexing solution and stirred for 1.5 h;

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

[0110] 2. Positive electrolyte preparation

[0111] 1) 0.04 mol of ferricyanide K4[Fe(CN)6] was weighed and added to 50 ml of deionized water and stirred at room temperature until the solid was completely dissolved (about 10 mins) to obtain a complexing solution.

[0112] 2) 0.3 mol of positive electrolyte NaOH was dissolved in 20 ml of deionized water and added to the complexing solution after dissolution and stirred for 1 h.

[0113] 3) The above solution was transferred to a 100 ml volumetric flask and made up to volume with deionized water to obtain finally 100 ml

[0114] positive electrolyte, ferricyanide K4[Fe(CN)6] (0.4 mol / L) - positive electrolyte NaOH (3 mol / L) ready for use.

[0115] The positive electrolyte and negative electrolyte obtained from Examples 1-7 and Comparative Example 1 were assembled into a full iron flow battery:

[0116] The full iron flow battery provided by the present application includes a negative electrolyte storage tank, a positive electrolyte storage tank, a separator, a negative electrode, a positive electrode, a negative end plate, a positive end plate, a negative pump, and a positive pump. The battery unit is assembled in the order of positive end plate, graphite current collector, positive 6 mm x 3 cm x 3 cm carbon felt, ion exchange membrane Nafion 115 as separator, negative 6 mm x 3 cm x 3 cm carbon felt, graphite current collector, and negative end plate.

[0117] Full iron flow battery test:

[0118] During the operation of the battery, the flow rates of the positive and negative electrolytes were both 100 mL / min, and the charge and discharge current densities were 30 mA / cm 2 Charge and discharge test, set the charge and discharge cut-off voltage to 1.65 V and 0.8 V respectively, and perform 100 cycles.

[0119] The volume of the positive electrolyte and the negative electrolyte is 100 ml, the flow rate of the positive electrolyte and the negative electrolyte is 100 ml / min, and the current density is 50 mA / cm 2 The test temperature is 30°C, argon is used as the protective gas during the charging and discharging process, the charging and discharging cut-off voltage is 1.6 V and 0.7 V, respectively, and the charging and discharging number is 100.

[0120] Table 1 shows the coulombic efficiency, voltage efficiency and energy efficiency of the alkaline flow battery with different negative electrolyte compositions of Examples 1-7 and Comparative Example 1 after 100 cycles. In Table 1, the molar concentration ratio is the ratio of the molar concentration of the complexing agent to the molar concentration of the negative active material in the negative electrolyte; Figure 1 Fig. 1 is a graph of the efficiency of the alkaline flow battery with different negative electrolyte compositions of Examples 1-7 and Comparative Example 1. Figure 2 Fig. 2 is a graph of the capacity of the alkaline flow battery with different negative electrolyte compositions of Examples 1-7 and Comparative Example 1 after 100 cycles.

[0121] Table 1

[0122]

[0123]

[0124] As can be seen from the table, in Comparative Examples 1, 6 and 7, the amount of additive is too small, the complexing ability with iron ions is reduced, and the iron ions in the solution are more likely to form precipitates, affecting the capacity and cycle performance of the battery. If the amount of additive is too large, there is excess additive in the solution, the viscosity of the solution increases, and the activity of iron ions is reduced. As can be seen from the comparison between Comparative Example 1 and Example 1, in Comparative Example 1, triethanolamine without a sulfonic acid group is selected, which cannot form a complete six-coordination structure with iron ions, the stability of the iron complex is poor, and iron ions are easily detached from the triethanolamine group to form precipitates. Therefore, the efficiency and stability of the battery are not as good as the embodiments of the present application. As can be seen from Examples 1-5, the sulfonic acid complexing agent provided by the present application combines with Fe 3+ and Fe 2+ , regulates the potential and binding force of the Fe 3+ / Fe 2+ active electrode pair, so that it can be used as a negative complexing agent to prepare a negative electrolyte suitable for a water-based full-iron flow battery. This avoids the penetration of the negative active material to the positive electrolyte side, alleviates the problem of capacity decay caused by small molecules of unstable ligands passing through the separator into the positive electrolyte, improves the solubility of iron ions, suppresses the precipitation of iron ions in the electrolyte, improves the capacity retention rate and energy efficiency, and greatly improves the efficiency and stability of the water-based full-iron flow battery using the electrolyte. The water-based full-iron flow battery based on the present technology has lower cost than existing lithium-ion batteries, and has better safety and cycle stability.

[0125] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A negative electrolyte for an alkaline all-iron flow battery, characterized by, The negative active material, complexing agent, negative electrolyte and solvent are included; the complexing agent is 3-[N-trihydroxymethyl methylamine]-2-hydroxypropane sulfonic acid sodium salt; the molar concentration of the complexing agent in the negative electrolyte is 2 times the molar concentration of the negative active material; the negative electrolyte is an alkaline substance; the negative active material is an iron salt; the molar concentration of the negative active material is 0.4 mol / L; and the solvent is water.

2. The negative electrolyte according to claim 1, wherein The negative active material is one or a mixture of several of iron chloride, iron sulfate, iron nitrate and iron acetate.

3. The negative electrolyte of claim 1, wherein The negative electrolyte is one or a mixture of several of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate and lithium carbonate.

4. The negative electrolyte of claim 1, wherein The molar concentration of the negative electrolyte is in the range of 1.5-6 mol / L.

5. The negative electrolyte of claim 1, wherein The molar concentration of the negative electrolyte is in the range of 1-4 mol / L.

6. The negative electrolyte of claim 1, wherein The molar concentration of the negative electrolyte is 3 mol / L.

7. A method for preparing the negative electrolyte according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: adding a solvent into a reactor, then adding the negative active material to dissolve, to obtain an iron ion solution; adding a complexing agent into the iron ion solution to dissolve, to obtain a complexing solution; dissolving a negative electrolyte in a solvent to form an electrolyte solution, then adding the electrolyte solution into the complexing solution to mix uniformly, to obtain a negative electrolyte solution.

8. An alkaline full iron liquid flow battery characterized by, The method comprises the negative electrolyte solution, electrode, separator and positive electrolyte solution as claimed in any one of claims 1-6.

9. The all-iron flow battery of claim 8, wherein, The positive electrolyte solution comprises an iron cyanide salt and a positive electrolyte.

10. The all-iron flow battery of claim 9, wherein, The iron cyanide salt comprises one or a mixture of iron cyanide or ferrocyanide.

11. The all-iron flow battery of claim 9, wherein, The molar concentration of the iron cyanide salt is in the range of 0.1-2.0 mol / L.

12. The all-iron flow battery of claim 9, wherein, The molar concentration of the iron cyanide salt is 0.4 mol / L.

13. The all-iron flow battery of claim 10, wherein, The iron cyanide is one or a mixture of several of sodium ferricyanide, potassium ferricyanide and lithium ferricyanide.

14. The all-iron flow battery of claim 10, wherein, The ferrocyanide is one or a mixture of several of sodium ferrocyanide, potassium ferrocyanide and lithium ferrocyanide.

15. The all-iron flow battery of claim 9, wherein, The positive electrolyte is an alkaline substance.

16. The all-iron flow battery of claim 9, wherein, The positive electrolyte is one or a mixture of several of sodium hydroxide, potassium hydroxide and lithium hydroxide.

17. The all-iron flow battery of claim 9, wherein, The molar concentration of the positive electrolyte is in the range of 0.1-4.0 mol / L.

18. The all-iron flow battery of claim 9, wherein, The molar concentration of the positive electrolyte is 3 mol / L.

19. The all-iron flow battery of any one of claims 8-18, wherein, The separator is a SPEEK separator or a perfluorosulfonic acid membrane.

20. The all-iron flow battery of claim 19, wherein, The separator is a separator that has been previously soaked in a strong alkaline aqueous solution at 25℃ and pH 14 for 24 h.

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