Iron-chromium flow battery electrolyte as well as preparation method and application thereof

Abstract

The invention relates to an iron-chromium flow battery electrolyte as well as a preparation method and application thereof. The iron-chromium flow battery electrolyte is prepared from the following raw materials: a chromium salt solution, a complexing agent, ferrite, an acidic reagent and a solvent, the complexing agent is a complexing agent capable of providing ammonia molecules; the complexing agent capable of providing the ammonia molecules comprises any one or a combination of at least two of NH4HCO3, NH4HSO3, NH4HS, NH4F or ammonia gas. According to the invention, specific weak acid ammonium and / or ammonia gas is adopted as a complexing agent, and is preferentially complexed with chromium ions in a high-concentration chromium salt solution to form a complex with electrochemical activity, so that the chromium ions are prevented from forming inactivated [Cr (H2O) 6] < 3 + >, and the electrochemical activity attenuation of Cr < 2 + > / Cr < 3 + > couple is effectively slowed down, thereby improving the electrochemical activity of the iron-chromium flow battery electrolyte.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow battery electrolyte, in particular to an iron-chromium flow battery electrolyte and a preparation method and application thereof. BACKGROUND

[0002] Iron-chromium flow battery is an electrochemical energy storage system based on the redox reaction of metal ions in the positive and negative electrodes to realize energy storage and release. It has the advantages of low cost, high safety performance, long cycle life and wide temperature adaptation range, and can be applied to the fields of grid-level energy storage, industrial and commercial energy storage, military and aerospace, etc. The electrolyte, as the core component of the iron-chromium flow battery, plays a multiple key role in the process of energy storage and conversion. However, the development of the electrolyte of the current iron-chromium flow battery is not yet perfect, and there is still a lot of room for improvement. Due to the immaturity of the technology, the commercialization of the iron-chromium flow battery is hindered.

[0003] Research has found that there is mutual transformation between [Cr(H2O)6] 3+ , [Cr(H2O)5Cl] 2+ and [Cr(H2O)4Cl2] + in the electrolyte of the iron-chromium flow battery. [Cr(H2O)5Cl] 2+ with electrochemical activity and [Cr(H2O)6] 3+ without electrochemical activity exist in dynamic equilibrium. Under normal conditions, [Cr(H2O)5Cl] 2+ is converted into [Cr(H2O)6] 3+ at a slow speed, but Cr 2+ appearing in the charging and discharging process will accelerate this conversion, and electrolyte deactivation becomes a key problem that the iron-chromium flow battery needs to address.

[0004] CN114865066A discloses an iron-chromium flow battery electrolyte containing a complexing agent. The electrolyte containing the complexing agent is obtained by simultaneously adding diethylenetriamine pentaacetic acid (DTPA) or its salt and bromide into the electrolyte containing Cr 3+ / Cr 2+ ions in the negative electrode and the electrolyte containing Fe 3+ / Fe 2+ ions in the positive electrode, respectively, to obtain a negative electrolyte containing (Br)Cr(DTPA) 3+ / (Br)Cr(DTPA) 2+ and a positive electrolyte containing (Br)Fe(DTPA) 3+ / (Br)Fe(DTPA) 2+ . The electrolyte can effectively improve the reaction activity of the positive and negative redox couples and inhibit Cr 3+Deactivation, increase the size of metal ion complex, avoid electrolyte cross contamination across the membrane, improve the efficiency and life of iron-chromium flow battery. However, the addition of organic matter will inevitably sacrifice the conductivity of the electrolyte and increase the viscosity of the electrolyte, thereby affecting the operation effect of the iron-chromium flow battery.

[0005] CN117174978A discloses an iron-chromium flow battery electrolyte with ammonium chloride and ammonia as complexing agent. The prepared electrolyte can reduce the hydrogen evolution of iron-chromium flow battery and realize low attenuation charge-discharge operation under high current density. However, the nitrogen atoms in ammonium chloride and ammonia in the solution exist in the form of NH4 + , it is difficult to dissociate NH3 molecules and chromium ions to form complex reaction, thereby hindering the improvement of electrolyte performance.

[0006] Therefore, how to provide an iron-chromium flow battery electrolyte to avoid the aging and deactivation of chromium ions in the electrolyte and reduce the capacity attenuation of the electrolyte has become a problem to be solved at present. SUMMARY

[0007] To solve the above technical problems, the purpose of the present application is to provide an iron-chromium flow battery electrolyte and its preparation method and application. The present application uses specific weak acid ammonium and / or ammonia gas as complexing agent, which can be complexed with chromium salt to form a complex with electrochemical activity, thereby improving the electrochemical activity of the iron-chromium flow battery electrolyte.

[0008] To achieve this purpose, the present application adopts the following technical solutions:

[0009] In the first aspect, the present application provides an iron-chromium flow battery electrolyte, the raw materials of the iron-chromium flow battery electrolyte include chromium salt solution, complexing agent, ferrous salt, acidic reagent and solvent;

[0010] The complexing agent is a complexing agent that can provide ammonia molecules;

[0011] The complexing agent that can provide ammonia molecules includes any one or a combination of at least two of NH4HCO3, NH4HSO3, NH4HS, NH4F or ammonia gas.

[0012] The present application introduces a complexing agent into the iron-chromium flow battery electrolyte, which can be complexed with chromium ions in chromium salt to form a complex. Ammonia gas or specific weak acid ammonium as complexing agent will undergo hydrolysis in the solution to produce ammonia molecules. Ammonia molecules can be complexed with chromium ions to form chromium ion complexes [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ , which prevents the formation of deactivated [Cr(H2O)6] 3+ , effectively slows down the Cr2+ / Cr 3+ electrochemical activity of the electric pair. In addition, NH4HCO3, NH4HSO3, NH4HS or NH4F as the complexing agent can undergo double hydrolysis in aqueous solution, which produces ammonia molecules, and also forms CO2, SO2, H2S and HF, which are easy to escape from the surface of the solution to the external environment, thereby further promoting the double hydrolysis reaction in the complexing agent solution to form ammonia molecules, increasing the content of ammonia molecules in the solution, and being more conducive to the reaction with the chromium salt solution to form [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ chromium ion complex, thereby improving the electrochemical activity of the iron-chromium flow battery electrolyte and reducing the capacity attenuation of the electrolyte.

[0013] Preferably, the complexing agent capable of providing ammonia molecules includes any one or a combination of at least two of NH4HCO3, NH4HSO3, NH4HS or NH4F.

[0014] Preferably, in the raw material of the iron-chromium flow battery electrolyte, the concentration of chromium ions in the chromium salt solution is 1.8-2.5 mol / L, such as 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L or 2.5 mol / L, etc.

[0015] The chromium salt used in the raw material of the electrolyte of the present application is a high-concentration chromium salt solution. On the one hand, the water content inside the solution is relatively small, and the chromium ion hydration aging speed is slow, which is not easy to be inactivated. On the other hand, the chromium ion concentration is high, which increases the contact probability of chromium ions and ammonia molecules in the complexing reaction process, thereby improving the reaction efficiency and increasing the electrochemical activity of the chromium electric pair.

[0016] Preferably, the chromium salt solution includes a chromium salt and a solvent.

[0017] Preferably, in the chromium salt solution, the solvent includes water.

[0018] Preferably, in the raw material of the iron-chromium flow battery electrolyte, the ratio of the molar amount of chromium ions in the chromium salt solution to the molar amount of ammonia in the complexing agent is 1:(0.1-1.2), such as 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1.0 or 1:1.2, etc.

[0019] In the present application, the "molar amount of ammonia in the complexing agent" refers to the molar amount of ammonia gas introduced and / or the molar amount of NH4+ molar amount.

[0020] Preferably, in the iron-chromium liquid flow battery electrolyte, the chromium ions in the chromium salt solution are complexed into chromium complexes with the complexing agent.

[0021] The iron-chromium liquid flow battery electrolyte provided by the present application does not limit the content of chromium ions complexed into complexes with the complexing agent. Some chromium ions in the chromium salt can be complexed with the complexing agent, and the other part of the chromium ions can exist in the electrolyte in the form of free state.

[0022] Preferably, in the iron-chromium liquid flow battery electrolyte, the concentration of ferrous ions in the ferrous salt is 1-1.5 mol / L, such as 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, etc.

[0023] Preferably, in the iron-chromium liquid flow battery electrolyte, the concentration of the acidic agent is 1-5 mol / L, such as 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 4.0 mol / L, 4.5 mol / L or 5.0 mol / L, etc.

[0024] Preferably, the total concentration of chromium ions in the iron-chromium liquid flow battery electrolyte is 1-1.5 mol / L, such as 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, etc.

[0025] In the present application, the "total concentration of chromium ions in the iron-chromium liquid flow battery electrolyte" refers to the total concentration of free chromium ions in the solution and chromium elements in the chromium complexes.

[0026] Preferably, the total concentration of ammonia in the iron-chromium liquid flow battery electrolyte is 0.1-1 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1.0 mol / L, etc.

[0027] In the present application, the "total ammonia" refers to the sum of the ammonia molecules in the complexes formed after the chromium salt and the complexing agent are complexed, and the uncomplexed NH4 + and / or ammonia gas.

[0028] Preferably, the solvent in the raw material of the iron-chromium liquid flow battery electrolyte comprises water.

[0029] In a second aspect, the present application provides a preparation method of the iron-chromium liquid flow battery electrolyte according to the first aspect, the preparation method comprising the following steps:

[0030] (1) complexing the chromium salt solution with a complexing agent to obtain a complexing solution;

[0031] (2) mixing the complexing solution with a ferrous salt, an acidic reagent and a solvent to obtain the iron-chromium liquid flow battery electrolyte;

[0032] The complexing agent is a complexing agent capable of providing ammonia molecules; the complexing agent capable of providing ammonia molecules includes any one or a combination of at least two of NH4HCO3, NH4HSO3, NH4HS, NH4F or ammonia gas.

[0033] The preparation method of the iron-chromium liquid flow battery electrolyte provided by the present application uses a complexing agent capable of providing ammonia molecules to form a complexing solution through complexing reaction with a chromium salt solution. The ammonia gas in the complexing agent capable of providing ammonia molecules and / or the hydrolysis of specific weak acid ammonium to produce ammonia molecules contacts with chromium ions in the solution, and complexing reaction occurs, which can form [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ chromium ion complexes, hinder the aging and deactivation reaction of chromium ions with water molecules, improve the activity of chromium ions, and the complexing solution formed is mixed with a ferrous salt and an acidic reagent to prepare an iron-chromium liquid flow battery electrolyte, which improves the electrochemical activity of the electrolyte and effectively reduces the capacity attenuation of the iron-chromium liquid flow battery electrolyte during operation.

[0034] Preferably, the temperature of the complexing reaction in step (1) is 50-80℃, such as 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, etc.

[0035] Preferably, the time of the complexing reaction in step (1) is 30-120min, such as 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, etc.

[0036] Preferably, the complexing reaction in step (1) is accompanied by simultaneous stirring and dispersion.

[0037] In the present application, the complexing reaction of the chromium salt solution and the complexing agent is carried out in a reaction kettle with a stirring paddle and a dispersion disc.

[0038] The complexing reaction provided by the present application is also accompanied by stirring and dispersion process, which can promote the sufficient contact between the ammonia molecules produced in the hydrolysis process of the complexing agent and the chromium ions in the solution, improve the sufficiency of the complexing reaction, and further improve the Cr 2+ / Cr 3 + Electrochemical activity of the electric pair.

[0039] Preferably, the rotation speed of the stirring is 20-70 r / min, such as 20 r / min, 30 r / min, 40 r / min, 50 r / min, 60 r / min, or 70 r / min, etc.

[0040] Preferably, the rotation speed of the dispersion is 500-3000 r / min, such as 500 r / min, 600 r / min, 800 r / min, 1000 r / min, 1200 r / min, 1400 r / min, 1600 r / min, 1800 r / min, 2000 r / min, 2200 r / min, 2400 r / min, 2600 r / min, 2800 r / min, or 3000 r / min, etc.

[0041] Preferably, the preparation method of the chromium salt solution in step (1) comprises: mixing a chromium salt with a solvent to obtain the chromium salt solution.

[0042] Preferably, the solvent used in the preparation process of the chromium salt solution comprises water.

[0043] Preferably, the concentration of chromium ions in the chromium salt solution is 1.8-2.5 mol / L, such as 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, or 2.5 mol / L, etc.

[0044] Preferably, the ratio of the molar amount of chromium ions in the chromium salt solution to the molar amount of ammonia in the complexing agent in step (1) is 1:(0.1-1.2), such as 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1.0, or 1:1.2, etc.

[0045] Preferably, after the complexing reaction in step (1), standing is further performed to obtain the complexing solution.

[0046] Preferably, the standing time is 20-30 h, such as 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, or 30 h, etc.

[0047] Preferably, the solvent in the mixing process in step (2) comprises water.

[0048] In a third aspect, the present application provides an iron-chromium flow battery electrolyte comprising the iron-chromium flow battery electrolyte as described in the first aspect.

[0049] Compared with the prior art, the present application has at least the following beneficial effects:

[0050] (1) The present application introduces a complexing agent into the iron-chromium flow battery electrolyte, which can complex with chromium ions in a high-concentration chromium salt solution to form a complex, using ammonia gas or a specific weak acid ammonium that can provide ammonia molecules as the complexing agent. Hydrolysis occurs in the solution to produce ammonia molecules, which can complex with chromium ions to form electrochemically active chromium ion complexes [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ , preventing the formation of inactive [Cr(H2O)6] 3+ , effectively slowing down the electrochemical activity decay of the Cr 2+ / Cr 3+ redox pair. In addition, NH4HCO3, NH4HSO3, NH4HS, or NH4F as a complexing agent undergoes double hydrolysis in aqueous solution, producing ammonia molecules while also forming CO2, SO2, H2S, and HF, which easily escape from the solution surface to the external environment, further promoting the double hydrolysis reaction of the complexing agent in the solution, increasing the production of ammonia molecules in the solution, and more conducive to the reaction with the chromium salt solution to form electrochemically active [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ chromium ion complexes, thereby improving the electrochemical activity of the iron-chromium flow battery electrolyte and reducing the capacity decay of the electrolyte.

[0051] (2) The preparation method of the iron-chromium flow battery electrolyte provided by the present application uses a complexing agent that can provide ammonia molecules to form a complexing solution through a complexing reaction with a chromium salt solution. The ammonia water and / or specific weak acid ammonium in the complexing agent that can provide ammonia molecules undergoes hydrolysis to produce ammonia molecules that contact with chromium ions in the solution, undergo a complexing reaction, and can form electrochemically active [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ chromium ion complexes, hindering the aging and inactivation reaction of chromium ions with water molecules, improving the activity of chromium ions, and the complexing solution formed is mixed with ferrous salt and acidic reagents to prepare an iron-chromium flow battery electrolyte, improving the electrochemical activity of the electrolyte, and effectively reducing the capacity decay of the iron-chromium flow battery electrolyte during operation. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 This is a cycle performance diagram of the iron-chromium flow battery electrolyte provided by Example 1 and Comparative Example 1 applied to the iron-chromium flow battery. DETAILED DESCRIPTION

[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0054] Example 1

[0055] This embodiment provides a method for preparing an electrolyte for an iron-chromium flow battery, comprising the following steps:

[0056] S1. Mix chromium chloride hexahydrate with deionized water to prepare a chromium chloride solution. The Cr in the chromium chloride solution 3+ The concentration is 1.8 mol / L.

[0057] S2. Add NH4HCO3 to the chromium chloride solution obtained in step S1 and perform a complexation reaction for 60 min, wherein the Cr in the chromium chloride solution 3+ The molar amount of NH4 in the added NH4HCO3 + The molar ratio is 1:0.4, the temperature of the complex reaction is 60°C, and the complex reaction is carried out in a reactor equipped with a stirring paddle and a dispersion disk. The stirring speed of the stirring paddle is 70r / min, and the dispersion speed of the dispersion disk is 1000r / min. Then, the product after the complex reaction is allowed to stand for 24h to obtain a complex solution.

[0058] S3. The complex solution obtained in step S2 is mixed with ferrous chloride, hydrochloric acid and deionized water to prepare an iron-chromium flow battery electrolyte, wherein the iron-chromium flow battery electrolyte has a ferrous ion concentration of 1 mol / L, a hydrochloric acid concentration of 3 mol / L, a total chromium ion concentration of 1 mol / L, and a total ammonia concentration of 0.3 mol / L.

[0059] Example 2

[0060] This embodiment provides a method for preparing an electrolyte for an iron-chromium flow battery, comprising the following steps:

[0061] S1. Mix chromium chloride hexahydrate with deionized water to prepare a chromium chloride solution. The Cr in the chromium chloride solution 3+ The concentration is 2mol / L.

[0062] S2. Add NH4HCO3 to the chromium chloride solution obtained in step S1 and perform a complexation reaction for 30 minutes, wherein the Cr in the chromium chloride solution 3+the molar amount of NH4 in the added NH4HCO3 + the ratio of the molar amount of NH4 in the added NH4HCO3 to the molar amount of Cr3+ in the CrCl3 solution is 1:0.1, the temperature of the complexing reaction is 50℃, the complexing reaction is carried out in a reaction kettle with a stirring paddle and a dispersion disc, the stirring speed of the stirring paddle is 20r / min, the dispersion speed of the dispersion disc is 500r / min, then the product after the complexing reaction is allowed to stand for 20h to obtain a complexing solution.

[0063] S3. The complexing solution obtained in step S2 is mixed with ferrous chloride, hydrochloric acid and deionized water to configure an iron-chromium liquid flow battery electrolyte, wherein in the iron-chromium liquid flow battery electrolyte, the concentration of ferrous ions is 1.5mol / L, the concentration of hydrochloric acid is 1mol / L, the total concentration of chromium ions is 1.5mol / L, and the total concentration of ammonia is 0.1mol / L.

[0064] Example 3

[0065] The embodiment provides a preparation method of an iron-chromium liquid flow battery electrolyte, comprising the following steps:

[0066] S1. Chromium chloride hexahydrate is mixed with deionized water to configure a chromium chloride solution, and the concentration of Cr3+ in the chromium chloride solution is 2.4mol / L. 3+

[0067] S2. NH4HCO3 is added to the chromium chloride solution obtained in step S1 to carry out a complexing reaction for 120min, wherein the ratio of the molar amount of NH4 in the added NH4HCO3 to the molar amount of Cr3+ in the CrCl3 solution is 1:0.1, the temperature of the complexing reaction is 50℃, the complexing reaction is carried out in a reaction kettle with a stirring paddle and a dispersion disc, the stirring speed of the stirring paddle is 20r / min, the dispersion speed of the dispersion disc is 500r / min, then the product after the complexing reaction is allowed to stand for 20h to obtain a complexing solution. 3+ + the ratio of the molar amount of NH4 in the added NH4HCO3 to the molar amount of Cr3+ in the CrCl3 solution is 1:1.2, the temperature of the complexing reaction is 80℃, the complexing reaction is carried out in a reaction kettle with a stirring paddle and a dispersion disc, the stirring speed of the stirring paddle is 50r / min, the dispersion speed of the dispersion disc is 2000r / min, then the product after the complexing reaction is allowed to stand for 30h to obtain a complexing solution.

[0068] S3. The complexing solution obtained in step S2 is mixed with ferrous chloride, hydrochloric acid and deionized water to configure an iron-chromium liquid flow battery electrolyte, wherein in the iron-chromium liquid flow battery electrolyte, the concentration of ferrous ions is 1.2mol / L, the concentration of hydrochloric acid is 2mol / L, the total concentration of chromium ions is 1.3mol / L, and the total concentration of ammonia is 1mol / L.

[0069] Example 4

[0070] The embodiment differs from the embodiment 1 only in that in step S2, NH4HSO3 is added to the chromium chloride solution obtained in step S1. The rest is the same as the embodiment 1.

[0071] Example 5​​

[0072] The difference between this example and Example 1 is only that in step S2, NH4HS is added into the chromium chloride solution obtained in step S1. The rest is the same as Example 1.

[0073] Example 6

[0074] The difference between this example and Example 1 is only that in step S2, NH4F is added into the chromium chloride solution obtained in step S1. The rest is the same as Example 1.

[0075] Example 7

[0076] The difference between this example and Example 1 is only that in step S2, ammonia gas is filled into the bottom of the container containing the chromium chloride solution obtained in step S1 until the concentration of ammonia gas in the solution is 1 mol / L. The rest is the same as Example 1.

[0077] Example 8

[0078] The difference between this example and Example 1 is only that the concentration of Cr 3+ in the chromium chloride solution prepared in step S1 is 1.5 mol / L. The rest is the same as Example 1.

[0079] Example 9

[0080] The difference between this example and Example 1 is only that the concentration of Cr 3+ in the chromium chloride solution prepared in step S1 is 3 mol / L. The rest is the same as Example 1.

[0081] Example 10

[0082] The difference between this example and Example 1 is only that the ratio of the molar amount of Cr 3+ in the chromium chloride solution to the molar amount of NH4 + in the NH4HCO3 added in step S2 is 1:1.5. The rest is the same as Example 1.

[0083] Example 11

[0084] The difference between this example and Example 1 is only that the ratio of the molar amount of Cr 3+ in the chromium chloride solution to the molar amount of NH4 + in the NH4HCO3 added in step S2 is 1:0.01. The rest is the same as Example 1.

[0085] Example 12

[0086] The difference between this example and Example 1 is only that the stirring and dispersion process in step S2 is omitted. The rest is the same as Example 1.

[0087] Example 13

[0088] The difference between this example and Example 1 is that the temperature of the complexation reaction in step S2 is 40℃. The rest is the same as Example 1.

[0089] Example 14

[0090] The difference between this example and Example 1 is that the temperature of the complexation reaction in step S2 is 90℃. The rest is the same as Example 1.

[0091] Example 15

[0092] The present example provides a preparation method of an iron-chromium liquid flow battery electrolyte, comprising the following steps:

[0093] S1. Mixing chromium chloride hexahydrate with deionized water to prepare a chromium chloride solution, the concentration of Cr 3+ in the chromium chloride solution is 1.8 mol / L.

[0094] S2. Mixing the chromium chloride solution obtained in step S1 with NH4HCO3, ferrous chloride, hydrochloric acid and deionized water, and performing a complexation reaction for 60 min, the ratio of the molar amount of Cr 3+ in the chromium chloride solution to the molar amount of NH4 + in NH4HCO3 is 1:0.4, the complexation reaction temperature is 60℃, the complexation reaction is carried out in a reaction kettle with a stirring paddle and a dispersion disc, the stirring speed of the stirring paddle is 70 r / min, the dispersion speed of the dispersion disc is 1000 r / min, then, standing for 24 h, to prepare an iron-chromium liquid flow battery electrolyte, wherein, in the iron-chromium liquid flow battery electrolyte, the concentration of ferrous ions is 1 mol / L, the concentration of hydrochloric acid is 3 mol / L, the total concentration of chromium ions is 1 mol / L, and the total ammonia concentration is 0.3 mol / L.

[0095] Example 16

[0096] The difference between this example and Example 1 is that CH3COONH4 is added to the chromium chloride solution obtained in step S1 in step S2. The rest is the same as Example 1.

[0097] Comparative Example 1

[0098] The iron-chromium liquid flow battery electrolyte provided in this comparative example comprises ferrous chloride, chromium chloride, hydrochloric acid and a solvent, wherein the concentration of Cr 3+ is 1 mol / L, the concentration of ferrous ions is 1 mol / L, the concentration of hydrochloric acid is 3 mol / L, and the total concentration of chromium ions is 1 mol / L.

[0099] Take equal volume of the above-mentioned iron-chromium liquid flow battery electrolyte provided in the examples and comparative examples, respectively, into the iron-chromium liquid flow battery positive and negative electrode storage tanks, to form an iron-chromium liquid flow battery, and perform charge-discharge test in the voltage range of 1.18V-0.6V, with a current density of 100mA / cm 2 . The test results are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] From the test results, it can be seen that:

[0104] (1) From Examples 1 to 7, it can be seen that the introduction of complexing agent in the iron-chromium liquid flow battery electrolyte can complex with chromium ions in the chromium salt to form a complex, and with ammonia gas or a specific weak acid ammonium as the complexing agent, hydrolysis will occur in the solution to produce ammonia molecules, which can complex with chromium ions to form electrochemically active chromium ion complexes [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ , preventing the formation of inactive [Cr(H2O)6] 3+ , effectively slowing down the electrochemical activity decay of Cr 2+ / Cr 3+ electrochemical pair.

[0105] (2) From the comparison between Example 1 and Examples 8-9, it can be seen that if the concentration of Cr 3+ in the chromium chloride solution prepared in step S1 of the present application is too low, the solution will have a higher water content, the chromium ion hydration aging rate will be faster, and the contact effect with ammonia molecules will be poorer, resulting in a decrease in reaction efficiency, thereby leading to a decrease in the electrochemical activity of the electrolyte and a decrease in the performance of the battery; if it is too high, precipitation will occur, thereby leading to a decrease in the electrochemical performance of the iron-chromium liquid flow battery.

[0106] (3) From the comparison between Example 1 and Examples 10-11, it can be seen that if the ratio of the molar amount of Cr 3+ in the chromium chloride solution in step S2 to the molar amount of NH4 + in the added NH4HCO3 is too low, the content of the ammonium compound added will be relatively high, which will result in a higher concentration of ammonium ions in the electrolyte, affecting the electrochemical performance of the electrolyte; if it is too high, the amount of the ammonium compound added will be relatively low, which will not be able to effectively alleviate the inactivation of chromium ions, thereby leading to a decrease in the electrochemical activity of the electrolyte.

[0107] (4) By comparing Example 1 and Example 12, it can be seen that if the stirring and dispersion process of step S2 is omitted in the present application, the contact effect between ammonia molecules and chromium ions during the complexation reaction will be poor, the complexation reaction will be insufficient, and the electrochemical activity of the chromium ion electric pair will decrease.

[0108] (5) By comparing Example 1 and Examples 13-14, it can be seen that if the temperature of the complexation reaction is too low in the present application, the destruction of the deactivated [Cr(H2O)6] 3+ cannot be achieved, resulting in the presence of a large number of [Cr(H2O)6] 3+ in the electrolyte, thereby causing the electrochemical activity of the electrolyte to decrease and the electrochemical performance of the flow battery to decrease; if the temperature of the complexation reaction is too high, the ammonia molecules released by hydrolysis will overflow too quickly, and there will not be enough time for the complexation reaction with chromium ions in the solution, resulting in a low complexation reaction efficiency, and even no complexation reaction, thereby causing the electrochemical performance of the iron-chromium flow battery to deteriorate.

[0109] (6) By comparing Example 1 and Example 15, it can be seen that if the chromium chloride solution is mixed with NH4HCO3, ferrous chloride, hydrochloric acid, and deionized water in the present application, the presence of hydrochloric acid will inhibit the double hydrolysis process of NH4HCO3, resulting in a decrease in the content of ammonia molecules in the solution, thereby affecting the mitigation of the electrochemical activity decay of Cr 2+ / Cr 3+ electric pairs, and causing the electrochemical performance of the flow battery to decrease significantly.

[0110] (7) By comparing Example 1 and Example 16, it can be seen that if NH4HCO3 is replaced by CH3COONH4 in the present application, the hydrolysis process of CH3COONH4 cannot produce volatile acids or gases, thereby failing to effectively promote the formation of ammonia molecules, resulting in a low content of ammonia molecules in the solution, and causing the performance of the electrolyte to decrease.

[0111] (8) By comparing Example 1 and Comparative Example 1, it can be seen that if the complexing agent is omitted in the present application, the chromium ions will form deactivated [Cr(H2O)6] 3+ , the electrochemical activity decay of Cr 2+ / Cr 3+ electric pairs will be significant, and the cycle performance of the flow battery will decrease significantly.

[0112] Figure 1 The cycle performance chart of the electrolyte provided by Example 1 and Comparative Example 1 applied to the iron-chromium flow battery is given, and from the chart, it can be seen that compared with Comparative Example 1 which omits the addition of a complexing agent, the specific weak acid ammonium used as a complexing agent in Example 1 can complex with chromium ions to form a chromium ion complex-[Cr(H2O)5(NH3)] 3+and [Cr(H2O)4(NH3)2] 3+ , improve the electrochemical activity of the electrolyte of the iron-chromium flow battery.

[0113] In summary, the present application introduces a complexing agent into the electrolyte of the iron-chromium flow battery, which can complex with chromium ions in the high-concentration chromium salt solution to form a complex. The ammonia gas or specific weak acid ammonium that can provide ammonia molecules is used as the complexing agent, and hydrolysis occurs in the solution to produce ammonia molecules. The ammonia molecules can complex with chromium ions to form a chromium ion complex [Cr(H2O)5(NH3)] with electrochemical activity. 3+ and [Cr(H2O)4(NH3)2] 3+ , prevent the formation of inactive [Cr(H2O)6] 3+ , effectively slow down the electrochemical activity decay of the Cr 2+ / Cr 3+ electrochemical pair. In addition, NH4HCO3, NH4HSO3, NH4HS, or NH4F as a complexing agent will undergo double hydrolysis in an aqueous solution, producing ammonia molecules while also forming CO2, SO2, H2S, and HF, which are easily released from the solution surface to the external environment, thereby further promoting the double hydrolysis reaction of the complexing agent in the solution, increasing the production of ammonia molecules in the solution, and more conducive to the reaction with the chromium salt solution to form a chromium ion complex [Cr(H2O)5(NH3)] 3+ and [Cr(H2O)4(NH3)2] 3+ with electrochemical activity, thereby improving the electrochemical activity of the electrolyte of the iron-chromium flow battery and reducing the capacity decay of the electrolyte.

[0114] The applicant states that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by any person skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. An iron-chromium flow battery electrolyte, characterized in that: The raw materials of the iron-chromium flow battery electrolyte include chromium salt solution, complexing agent, ferrous salt, acidic reagent and solvent; The complexing agent is a complexing agent that can provide ammonia molecules; The complexing agent capable of providing ammonia molecules may include any one of NH4HCO3, NH4HSO3, NH4HS, NH4F or ammonia gas, or a combination of at least two thereof.

2. The iron-chromium flow battery electrolyte according to claim 1, characterized in that The complexing agent capable of providing ammonia molecules includes any one of NH4HCO3, NH4HSO3, NH4HS or NH4F, or a combination of at least two thereof; Preferably, in the raw materials of the iron-chromium flow battery electrolyte, the concentration of chromium ions in the chromium salt solution is 1.8-2.5 mol / L; Preferably, in the raw materials of the iron-chromium flow battery electrolyte, the ratio of the molar amount of chromium ions in the chromium salt solution to the molar amount of ammonia in the complexing agent is 1:(0.1-1.2).

3. The iron-chromium flow battery electrolyte according to claim 1 or 2, characterized in that: In the iron-chromium flow battery electrolyte, chromium ions in the chromium salt solution are complexed with the complexing agent to form a chromium complex; Preferably, in the iron-chromium flow battery electrolyte, the concentration of ferrous ions in the ferrous salt is 1-1.5 mol / L; Preferably, in the iron-chromium flow battery electrolyte, the concentration of the acidic reagent is 1-5 mol / L.

4. The iron-chromium flow battery electrolyte according to any one of claims 1 to 3, characterized in that: The total concentration of chromium ions in the iron-chromium flow battery electrolyte is 1-1.5 mol / L; Preferably, the total ammonia concentration in the iron-chromium flow battery electrolyte is 0.1-1 mol / L.

5. A method for preparing an iron-chromium flow battery electrolyte according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) performing a complex reaction on a chromium salt solution and a complexing agent to obtain a complex solution; (2) mixing the complex solution with a ferrous salt, an acidic reagent, and a solvent to obtain the iron-chromium flow battery electrolyte; The complexing agent is a complexing agent that can provide ammonia molecules; the complexing agent that can provide ammonia molecules includes any one of NH4HCO3, NH4HSO3, NH4HS, NH4F or ammonia gas, or a combination of at least two of them.

6. The preparation method according to claim 5, characterized in that The temperature of the complexation reaction in step (1) is 50-80° C.; Preferably, the complexation reaction time in step (1) is 30-120 min.

7. The preparation method according to claim 5 or 6, characterized in that: The complexation reaction in step (1) is also accompanied by simultaneous stirring and dispersion; Preferably, the stirring speed is 20-70 r / min; Preferably, the dispersion rotation speed is 500-3000 r / min.

8. The preparation method according to any one of claims 5 to 7, characterized in that The concentration of chromium ions in the chromium salt solution of step (1) is 1.8-2.5 mol / L; Preferably, the ratio of the molar amount of chromium ions in the chromium salt solution in step (1) to the molar amount of ammonia in the complexing agent is 1:(0.1-1.2).

9. The preparation method according to any one of claims 5 to 8, characterized in that After the complexation reaction in step (1), the mixture is allowed to stand to obtain the complexation solution; Preferably, the standing time is 20-30 hours.

10. An iron-chromium flow battery, characterized in that: The iron-chromium flow battery comprises the iron-chromium flow battery electrolyte according to any one of claims 1 to 4.

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