Iron-chromium flow battery electrolyte, preparation method thereof and iron-chromium flow battery

Abstract

The invention relates to an iron-chromium flow battery electrolyte, a preparation method thereof and an iron-chromium flow battery. The iron-chromium flow battery electrolyte comprises a trivalent chromium ion organic complex, ferrous ions, hydrogen ions, lithium ions, metal ions except lithium, iron and chromium, and a solvent. An organic ligand in the trivalent chromium ion organic complex comprises a compound containing a carboxylic acid group and / or a compound containing an amino group. According to the iron-chromium flow battery electrolyte disclosed by the invention, the organic ligand and the trivalent chromium ions are complexed, and the catalytic action of the lithium ions and other metal ions except lithium, iron and chromium is combined, so that the reaction activity of chromium couple in the negative electrode electrolyte can be remarkably improved, the phenomenon that a large amount of trivalent chromium ions are aged is improved, the hydrogen evolution side reaction is reduced, and the service life of the iron-chromium flow battery is prolonged. And the charge-discharge capacity, the cycle stability and the energy efficiency of the iron-chromium flow battery are comprehensively improved, so that the purpose of high-efficiency operation of the iron-chromium flow battery is achieved.

Description

Technical Field

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

[0002] Due to the gradual depletion of fossil fuel resources and the increasingly serious environmental pollution caused by them, renewable energy such as wind power and solar energy are widely used. However, the intermittent and unstable output of this renewable energy makes it difficult to meet the requirements of power quality and safe operation of the power grid. Therefore, it is necessary to develop large-scale energy storage systems to achieve continuous power supply and grid stability. As the earliest proposed and applicable flow battery, the iron-chromium redox flow battery has significant advantages such as independent system energy and power, low material cost, easy expansion, high safety, fast response speed, long cycle life, and high energy efficiency. It is a very promising large-scale energy storage technology.

[0003] As a carrier of active substances in flow batteries, electrolyte plays a vital role in the performance of batteries. In actual operation, iron-chromium flow batteries generally use hydrochloric acid aqueous solution containing iron ions and chromium ions. In an acidic environment, unlike the iron ions in the positive electrolyte, the electrode potential of the active substance chromium in the negative electrolyte is close to the hydrogen evolution potential. The higher hydrogen ion concentration will intensify the hydrogen evolution reaction during charging. This side reaction will not only reduce the coulomb efficiency of the battery, but also cause the battery capacity to decay rapidly due to the charge imbalance in the positive and negative electrolytes. In addition, another problem of iron-chromium batteries is the aging of chromium ions, that is, chromium ions will complex with water molecules in aqueous solution to form inactive molecules that are not easy to react, resulting in capacity loss. In addition, iron-chromium flow batteries usually use higher operating temperatures, which intensifies the hydrogen evolution reaction, resulting in a more significant capacity decay of the battery after long-term cyclic operation.

[0004] CN117133957A discloses an iron-chromium liquid flow battery, comprising: a battery electrolyte, wherein the battery electrolyte comprises Fe 2+ Cr 3+ , H + and metal ions, wherein the metal ions include Li + 、Na + , K + and NH4 + At least one of; a battery electrode, comprising an electrode material and a catalyst located on the surface of the electrode material, wherein the catalyst comprises Pb and X, wherein X comprises at least one of Bi, In and Au, and the catalyst is deposited on the negative electrode material to increase Cr 3+Although the above-mentioned iron-chromium flow battery can avoid hydrogen evolution side reaction without sacrificing energy conversion efficiency, its electrolyte system can only be used with electrode materials containing the above-mentioned specific catalysts, and it does not improve the Cr reaction efficiency from the perspective of the iron-chromium flow battery electrolyte system itself. 3+ The reaction efficiency at the negative electrode makes its universality poor. In addition, the average energy efficiency it can achieve is not very high.

[0005] Therefore, how to provide an iron-chromium flow battery electrolyte system to improve the reaction activity of chromium ions in the iron-chromium flow battery electrolyte and reduce the occurrence of hydrogen evolution side reactions during the use of the iron-chromium flow battery is a problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an iron-chromium flow battery electrolyte, a preparation method thereof and an iron-chromium flow battery. The iron-chromium flow battery electrolyte of the present invention uses organic ligands to complex with trivalent chromium ions, and then combines the catalytic effect of lithium ions and other metal ions except lithium, iron and chromium, which can significantly improve the reaction activity of chromium pairs in the negative electrode electrolyte, improve the phenomenon of large-scale aging of trivalent chromium ions, and reduce the side reaction of hydrogen evolution, so as to comprehensively improve the charge and discharge capacity, cycle stability and energy efficiency of the iron-chromium flow battery, so as to achieve the purpose of efficient operation of the iron-chromium flow battery.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an iron-chromium flow battery electrolyte, the iron-chromium flow battery electrolyte comprising a trivalent chromium ion organic complex, ferrous ions, hydrogen ions, lithium ions, other metal ions except lithium, iron and chromium, and a solvent;

[0009] The organic ligand in the trivalent chromium ion organic complex comprises a compound containing a carboxylic acid group and / or a compound containing an amino group.

[0010] In the electrolyte of the iron-chromium flow battery, there is [Cr(H2O)6] in the acid-containing aqueous solution of trivalent chromium ions. 3+ 、[Cr(H2O)5Cl] 2+ and [Cr(H2O)4Cl] 2+ Three complexes, and [Cr(H2O)6] 3+ Due to its symmetrical structure, it has extremely strong stability. The electrons are not easily exposed to the trivalent chromium ions, so it is not chemically active. The other two complex ions will gradually transform into [Cr(H2O)6] as the reaction proceeds. 3+ , resulting in a large amount of aging of trivalent chromium ions.

[0011] The organic ligand in the trivalent chromium ion organic complex of the present invention includes a compound containing a carboxylic acid group and / or a compound containing an amino group. The organic ligand can replace part / all of the water molecules to coordinate with the trivalent chromium ion to form a trivalent complex ion organic complex, thereby breaking the [Cr(H2O)6] 3+ The low activity can achieve the purpose of inhibiting the aging of trivalent chromium ions; at the same time, some carboxyl groups and amino groups can also be absorbed on the electrode to form N-containing groups and O-containing groups with stronger peak intensity, which increases the hydrophilicity of the electrode, is also beneficial to the diffusion and absorption of the electrolyte, and reduces the solution ion diffusion resistance. In addition, the iron-chromium liquid flow battery electrolyte system of the present invention also includes lithium ions and other metal ions other than lithium, iron and chromium that play a catalytic role. The addition of lithium ions and other metal ions other than lithium, iron and chromium can promote the complexation of trivalent chromium ions with organic ligands on the one hand, and on the other hand, it is beneficial to improve the redox activity of the negative electrode chromium electrode and reduce the occurrence of hydrogen evolution side reactions. Therefore, the use of organic ligands to complex with trivalent chromium ions, combined with the catalytic effect of lithium ions and other metal ions other than lithium, iron and chromium, can synergistically improve the charge and discharge capacity, cycle stability and energy efficiency of the iron-chromium liquid flow battery, so as to achieve the purpose of efficient operation of the iron-chromium liquid flow battery.

[0012] It should be noted that part of the trivalent chromium ions in the electrolyte of the iron-chromium flow battery of the present invention are complexed with an organic ligand to form a trivalent chromium ion organic complex containing an organic ligand, and the other part is still in the form of [Cr(H2O)4Cl2] + 、[Cr(H2O)5Cl] 2+ and [Cr(H2O)6] 3+ exists in the electrolyte.

[0013] As a preferred technical solution of the present invention, the compound containing a carboxylic acid group includes any one of glycolic acid, malic acid or aminoacetic acid, or a combination of at least two of them.

[0014] Preferably, the compound containing an amino group comprises urea and / or glycine.

[0015] Preferably, in the iron-chromium flow battery electrolyte, the concentration of the organic ligand in the trivalent chromium ion organic complex is 0.01mol / L-4.5mol / L, for example, 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 2.5mol / L, 3.5mol / L or 4.5mol / L, etc., preferably 0.1mol / L-3mol / L, and more preferably 0.5mol / L-1.5mol / L.

[0016] In the present invention, by regulating the concentration of the organic ligand in the trivalent chromium ion complex, the capacity decay rate of the iron-chromium flow battery can be better reduced, which plays a role in improving the long-term operation stability of the electrolyte, and makes the electrochemical performance of the battery better. If the concentration of the organic ligand is too high, the viscosity of the electrolyte will be too large and the conductivity will be reduced; if the concentration of the organic ligand is too low, the complex with the trivalent chromium ion will be insufficient, and the corresponding complex ion concentration will be too low, which cannot achieve the purpose of effectively improving the aging of the trivalent chromium ion and effectively improving the activity of the trivalent chromium ion.

[0017] Preferably, in the iron-chromium flow battery electrolyte, the concentration of trivalent chromium ions is 0.01mol / L-5mol / L, for example, 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.8mol / L, 2mol / L, 3mol / L, 4mol / L or 5mol / L, etc., preferably 0.1mol / L-2mol / L, and more preferably 0.8mol / L-1.6mol / L.

[0018] As a preferred technical solution of the present invention, the other metal ions except lithium, iron and chromium include tin ions and / or titanium ions.

[0019] In the present invention, lithium ions and other metal ions except lithium, iron and chromium cooperate to play a catalytic role, wherein lithium ions can promote the complexation of trivalent chromium ions with organic ligands, and the addition of tin ions and / or titanium ions can improve the activity of trivalent chromium ions. On this basis, the redox activity of the negative electrode chromium electrode pair can be further improved, showing a higher hydrogen evolution energy barrier, and further reducing the occurrence of hydrogen evolution side reactions.

[0020] Preferably, the tin ions include tetravalent tin ions and / or stannous ions.

[0021] Preferably, the titanium ions include tetravalent titanium ions and / or titanous ions.

[0022] Preferably, in the iron-chromium flow battery electrolyte, the concentration of lithium ions is 0.001mol / L-1mol / L, for example, 0.001mol / L, 0.005mol / L, 0.01mol / L, 0.03mol / L, 0.05mol / L, 0.1mol / L, 0.15mol / L, 0.2mol / L, 0.25mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L or 1mol / L, etc., preferably 0.01mol / L-0.5mol / L, and further preferably 0.05mol / L-0.3mol / L.

[0023] In the present invention, regulating the concentration of lithium ions can better achieve the complexation of trivalent chromium ions with organic ligands, while also avoiding the problems of increased electrolyte viscosity and reduced conductivity caused by excessively high lithium ion concentration.

[0024] Preferably, in the iron-chromium flow battery electrolyte, the concentration of the other metal ions except lithium, iron and chromium is 0.001mol / L-1mol / L, for example, 0.001mol / L, 0.005mol / L, 0.01mol / L, 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, 0.06mol / L, 0.07mol / L, 0.08mol / L, 0.09mol / L, 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L or 1mol / L, etc., preferably 0.01mol / L-0.5mol / L, and further preferably 0.05mol / L-0.1mol / L.

[0025] In the present invention, regulating the concentration of other metal ions except lithium, iron and chromium is more conducive to improving the redox electrochemical activity of the chromium electrode. If the concentration of other metal ions except lithium, iron and chromium is too low, the redox electrochemical activity of the chromium electrode will be limited, and it will not be able to compete with the hydrogen evolution reaction; if the concentration of other metal ions except lithium, iron and chromium is too high, the amount of hydrogen evolution increases during charging of the iron-chromium liquid flow battery, and the capacity decays rapidly, thereby affecting the battery life.

[0026] As a preferred technical solution of the present invention, in the iron-chromium flow battery electrolyte, the ferrous ion concentration is 0.01mol / L-5mol / L, for example, 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.8mol / L, 2mol / L, 3mol / L, 4mol / L or 5mol / L, etc., preferably 0.1mol / L-2mol / L, and more preferably 0.8mol / L-1.6mol / L.

[0027] Preferably, in the iron-chromium flow battery electrolyte, the concentration of hydrogen ions is 0.01mol / L-5mol / L, for example, 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.8mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, 2mol / L, 3mol / L, 4mol / L or 5mol / L, etc., preferably 0.1mol / L-3mol / L, and more preferably 1mol / L-2mol / L.

[0028] In the present invention, regulating the concentration of the hydrogen ions is more conducive to enhancing the reaction activity of the electrolyte, making the battery coulomb efficiency, voltage efficiency and energy efficiency higher. If the hydrogen ion concentration is too high, the hydrogen evolution of the electrolyte will increase, the coulomb efficiency will decrease, and the stability will decrease; if the hydrogen ion concentration is too low, the electrochemical activity of the trivalent chromium ions will be poor.

[0029] Preferably, the solvent comprises deionized water.

[0030] In a second aspect, the present invention further provides a method for preparing the iron-chromium liquid flow battery electrolyte according to the first aspect, the preparation method comprising the following steps:

[0031] (1) mixing an organic complexing agent, a ferrous salt, a trivalent chromium salt and a solvent to obtain a first mixed solution;

[0032] The structural formula of the organic complexing agent includes a carboxyl group and / or an amino group;

[0033] (2) Mixing lithium salt, other metal salts except lithium, iron and chromium, acid solution and the first mixed solution of step (1) to obtain an iron-chromium liquid flow battery electrolyte.

[0034] In the present invention, an organic ligand, a ferrous salt, a trivalent chromium salt and a solvent are first mixed, which can promote the complexation of trivalent chromium ions in the organic ligand and the trivalent chromium salt, and then lithium salt and other metal salts except lithium, iron and chromium are added as catalysts and an acid solution, which can avoid the occurrence of hydrolysis reactions of other metal salts except lithium, iron and chromium, thereby affecting the preparation of the iron-chromium liquid flow battery electrolyte.

[0035] As a preferred technical solution of the present invention, the organic ligand in step (1) includes any one of glycolic acid, malic acid, urea or aminoacetic acid, or a combination of at least two of them, such as a combination of glycolic acid and malic acid, a combination of malic acid and urea, or a combination of urea and aminoacetic acid.

[0036] Preferably, the ferrous salt comprises FeCl2·4H2O.

[0037] Preferably, the purity of the ferrous salt is ≥99.0%.

[0038] Preferably, the trivalent chromium salt comprises CrCl3·6H2O.

[0039] Preferably, the purity of the trivalent chromium salt is ≥99.0%.

[0040] Preferably, the acid solution comprises concentrated HCl.

[0041] Preferably, the mass concentration of the acid solution is 36%-38%, such as 36%, 36.5%, 37%, 37.5% or 38%.

[0042] Preferably, the mixing in step (1) comprises: firstly mixing the organic complexing agent and the solvent for a first time, then adding a trivalent chromium salt for a second time, and then adding a ferrous salt for a third time.

[0043] As a preferred technical solution of the present invention, the first mixing includes heating to dissolve and stirring.

[0044] Preferably, the heating and dissolving includes microwave-enhanced heating and dissolving and / or ultrasound-enhanced heating and dissolving.

[0045] Preferably, the temperature of the heating and dissolving is 25°C-80°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., preferably 25°C-65°C.

[0046] In the present invention, the temperature of heating and dissolving is regulated to be 25° C.-80° C., which is beneficial to promoting the dissolution process and thus shortening the dissolution time.

[0047] Preferably, the heating and dissolving time is 5 min-30 min, for example, 5 min, 10 min, 15 min, 20 min, 25 min or 30 min, etc.

[0048] Preferably, the second mixing includes heating complexation and stirring.

[0049] Preferably, the temperature of the heating complexation is 25°C-80°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., preferably 25°C-65°C.

[0050] In the present invention, the temperature of the heating complexation is regulated to be 25° C.-80° C., which is beneficial to promoting the complexation process, allowing more organic complexing agent molecules to complex with trivalent chromium ions, and further increasing the concentration of the trivalent chromium ion organic complex.

[0051] Preferably, the heating complexation time is 10 min-30 min, for example, 10 min, 15 min, 20 min, 25 min or 30 min.

[0052] Preferably, the third mixing comprises stirring.

[0053] Preferably, the temperature of the third mixing is 10°C-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C.

[0054] In the present invention, the temperature of the third mixing is 10°C-40°C, which is conducive to promoting the dissolution process and dissolving all the ferrous ions within a reasonable time range. If the dissolution temperature is lower than 10°C, the dissolution time will be prolonged; if the dissolution temperature is higher than 40°C, the ferrous ions will undergo an oxidation reaction with oxygen in the air during the dissolution process, thereby causing a loss of electrolyte capacity.

[0055] Preferably, the third mixing time is 10 min-30 min, for example, 10 min, 15 min, 20 min, 25 min or 30 min.

[0056] Preferably, the pH value of the first mixed solution is ≤3, for example, 3, 2.8, 2.5, 2.2, 2, 1.8, 1.5, 1.2 or 1.

[0057] In the present invention, the pH value of the first mixed solution is regulated to be ≤3, which is conducive to the effective entry of ferrous ions into the liquid phase.

[0058] As a preferred technical solution of the present invention, the lithium salt in step (2) includes any one of LiCl, LiNO3, Li2SO4 or CHCOOLi, or a combination of at least two thereof.

[0059] Preferably, the other metal salts except lithium, iron and chromium in step (2) include tin salts and / or titanium salts.

[0060] Preferably, the tin salt comprises a tetravalent tin salt and / or a stannous salt.

[0061] Preferably, the tetravalent tin salt includes any one of SnCl4, Sn(SO4)2 or Sn(NO3)4, or a combination of at least two thereof.

[0062] Preferably, the stannous salt comprises SnCl2 and / or SnSO4.

[0063] Preferably, the titanium salt comprises a tetravalent titanium salt and / or a titanous salt.

[0064] Preferably, the tetravalent titanium salt includes any one of TiCl4, TiOSO4 or Ti(NO3)4 or a combination of at least two thereof.

[0065] Preferably, the titanous salt comprises TiCl2.

[0066] The mixing in step (2) includes: firstly performing a fourth mixing on the acid solution and the first mixed solution in step (1), and then adding lithium salt and other metal salts except lithium, iron and chromium to perform a fifth mixing.

[0067] Preferably, the fourth mixing comprises stirring.

[0068] Preferably, the temperature of the fourth mixing is 10°C-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C.

[0069] Preferably, the fifth mixing comprises stirring.

[0070] Preferably, the fifth mixing temperature is 10°C-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C.

[0071] Preferably, the fifth mixing time is 10 min-30 min, for example, 10 min, 15 min, 20 min, 25 min or 30 min.

[0072] Preferably, after the mixing in step (2) is completed, a heat preservation treatment is also included.

[0073] Preferably, the temperature of the heat preservation treatment is 45°C-70°C, such as 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, etc., preferably 55°C-65°C.

[0074] In the present invention, the iron-chromium liquid flow battery electrolyte can be kept in a high electrochemical activity state at all times through heat preservation treatment, and the aging rate of the electrolyte can be reduced, thereby obtaining a stable iron-chromium liquid flow battery electrolyte.

[0075] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0076] (1) firstly, the organic complexing agent and the solvent are heated and dissolved at 25° C.-80° C. for 5 min-30 min, to perform a first mixing; then, under the condition of stirring at 25° C.-80° C., a trivalent chromium salt is added and heated for complexation for 10 min-30 min, to perform a second mixing; then, under the condition of stirring at 10° C.-40° C., a ferrous salt is added and mixed and dissolved for 10 min-30 min, to perform a third mixing, to obtain a first mixed solution with a pH value of ≤3;

[0077] The structural formula of the organic complexing agent includes a carboxyl group and / or an amino group;

[0078] (2) Mixing the acid solution with the first mixed solution in step (1) for the fourth time under the stirring condition of 10°C-40°C; adding lithium salt and other metal salts except lithium, iron and chromium and dissolving them for 10min-30min under the stirring condition of 10°C-40°C, mixing for the fifth time, and heat-treating at 45°C-70°C to obtain an iron-chromium liquid flow battery electrolyte.

[0079] In a third aspect, the present invention further provides an iron-chromium flow battery, which comprises the iron-chromium flow battery electrolyte as described in the first aspect, or the iron-chromium flow battery electrolyte prepared by the preparation method as described in the second aspect.

[0080] Compared with the prior art, the present invention has at least the following beneficial effects:

[0081] (1) The iron-chromium liquid flow battery electrolyte provided by the present invention can inhibit the aging of trivalent chromium ions by complexing trivalent chromium ions with organic ligands instead of water molecules; at the same time, adding a small amount of lithium ions and other metal ions except lithium, iron and chromium can accelerate the complexation of trivalent chromium ions with organic ligands, reduce the energy barrier of the redox reaction of the negative electrode chromium electrode, improve the activity and reversibility of the redox reaction of the chromium electrode, inhibit the hydrogen evolution side reaction, and reduce the polarization potential of the electrolyte; therefore, by using organic ligands to complex trivalent chromium ions, combined with the catalytic effect of lithium ions and other metal ions except lithium, iron and chromium, the charge and discharge capacity, cycle stability and energy efficiency of the iron-chromium liquid flow battery can be synergistically improved, so as to achieve the purpose of efficient operation of the iron-chromium liquid flow battery.

[0082] (2) The iron-chromium liquid flow battery electrolyte provided by the present invention is used in the iron-chromium liquid flow battery. The initial charging capacity of the iron-chromium liquid flow battery is between 1.02Ah and 1.22Ah. During 50 cycles of charge and discharge, the average attenuation per cycle is ≤0.5%. At the same time, the energy efficiency can reach between 77.2% and 81.9%. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 This is a process flow chart of the method for preparing the iron-chromium liquid flow battery electrolyte provided in Example 1 of the present invention.

[0084] Figure 2 This is a comparison chart of the energy efficiency of the iron-chromium liquid flow battery provided by Application Example 1 of the present invention and Comparative Application Example 1.

[0085] Figure 3 This is a comparison chart of the charging capacity of the iron-chromium liquid flow battery provided by Application Example 1 of the present invention and Comparative Application Example 1. DETAILED DESCRIPTION

[0086] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only 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.

[0087] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0088] Example 1

[0089] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte includes 1 mol / L Cr 3+ (including Cr not complexed by organic ligands 3+ and the complexed Cr in the trivalent chromium ion organic complex 3+ , where the organic ligands include 0.5 mol / L glycolic acid, 0.5 mol / L urea), 1 mol / L Fe 2+ , 1.5mol / LH + 、0.2mol / L Li + 、0.05mol / L Sn 2+ and deionized water;

[0090] The process flow chart of the preparation method is as follows Figure 1 As shown, according to the above recipe, the following steps are included:

[0091] (1) Add glycolic acid and urea to deionized water, and dissolve them in a water bath at 65° C. and under continuous stirring for 20 minutes, at which time the glycolic acid and urea are completely dissolved; then, add CrCl3·6H2O and dissolve it in a water bath at 65° C. and under continuous stirring for 15 minutes, and after the CrCl3·6H2O is completely dissolved, continue to stir and complex for 30 minutes to fully complex it; then, add FeCl2·4H2O and dissolve it in a water bath at 25° C. and under continuous stirring for 15 minutes, at which time the FeCl2·4H2O is completely dissolved, to obtain a first mixed solution;

[0092] (4) Adding concentrated HCl with a mass concentration of 37% to the first mixed solution at 25°C with continuous stirring, and then adding LiCl and SnCl2 to dissolve for 10 minutes at 25°C with continuous stirring. At this time, when LiCl and SnCl2 are completely dissolved, add deionized water to make the volume 100 mL, and put it into a 65°C water bath for heat preservation to obtain an iron-chromium liquid flow battery electrolyte.

[0093] Example 2

[0094] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that, in the iron-chromium flow battery electrolyte, in the trivalent chromium ion organic complex, the ligand includes 0.8 mol / L glycolic acid and 0.7 mol / L urea, and the remaining composition and content are consistent with those of Example 1;

[0095] The difference between the preparation method and Example 1 is that the addition amounts of glycolic acid and urea are adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0096] Example 3

[0097] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that, in the iron-chromium flow battery electrolyte, the ligand 0.5 mol / L glycolic acid is replaced with 0.5 mol / L malic acid, and the remaining composition and content are consistent with those of Example 1;

[0098] The difference between the preparation method and Example 1 is that glycolic acid is replaced by malic acid, and the rest of the preparation method and parameters are the same as those in Example 1.

[0099] Example 4

[0100] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the ligand 0.5 mol / L urea is replaced by 0.5 mol / L aminoacetic acid in the iron-chromium flow battery electrolyte, and the remaining composition and content are consistent with those in Example 1;

[0101] The difference between the preparation method and Example 1 is that urea is replaced by aminoacetic acid, and the other preparation methods and parameters are consistent with Example 1.

[0102] Example 5

[0103] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the ligand 0.5 mol / L urea is replaced with 0.9 mol / L aminoacetic acid, and the remaining composition and content are consistent with those of Example 1.

[0104] The difference between the preparation method and Example 1 is that urea is replaced by aminoacetic acid, and a corresponding mass of aminoacetic acid is added according to the change in concentration, and the rest of the preparation method and parameters are consistent with Example 1.

[0105] Example 6

[0106] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that: + The concentration of is 1.999 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0107] The difference between the preparation method and Example 1 is that the amount of concentrated HCl added is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0108] Example 7

[0109] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that: Li + The concentration is 0.001 mol / L, Sn 2+ The concentration is 0.1 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0110] The difference between the preparation method and Example 1 is that the addition amount of LiCl and SnCl2 is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0111] Example 8

[0112] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that: Li + The concentration is 0.3 mol / L, Sn 2+ The concentration is 0.01 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0113] The difference between the preparation method and Example 1 is that the addition amount of LiCl and SnCl2 is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0114] Example 9

[0115] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that it also includes Sn 4+ , Sn 2+ and Sn 4+ The total concentration is 0.025 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0116] The difference between the preparation method and Example 1 is that SnCl4 is added and the addition amount is adjusted according to the concentration, and the other preparation methods and parameters are consistent with Example 1.

[0117] Example 10

[0118] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that Sn 2+ Replaced with an equal concentration of Ti 2+ , the other compositions and contents are consistent with those in Example 1;

[0119] The difference between the preparation method and Example 1 is that SnCl2 is replaced by TiCl2, and the rest of the preparation method and parameters are consistent with Example 1.

[0120] Embodiment 11

[0121] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that Sn 2+ Replaced with an equal concentration of Ti 2+ and Ti 4+ (Ti 2+ and Ti 4+ Total concentration and Sn in Example 1 2+ The other compositions and contents are the same as those in Example 1;

[0122] The difference between the preparation method and Example 1 is that SnCl2 is replaced by TiCl2 and TiCl4, and the rest of the preparation method and parameters are consistent with Example 1.

[0123] Example 12

[0124] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is consistent with that of embodiment 1;

[0125] The difference between the preparation method and Example 1 is that the temperature remains constant at 35° C. throughout the preparation process, and the other preparation methods and parameters remain consistent with Example 1.

[0126] Embodiment 13

[0127] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of Example 1 in that the ligand in the trivalent chromium ion organic complex includes 1 mol / L glycolic acid, and the remaining composition and content are consistent with those of Example 1;

[0128] The difference between the preparation method and Example 1 is that urea is omitted according to the change in concentration, and the addition amount of glycolic acid is adaptively adjusted. The other preparation methods and parameters are consistent with Example 1.

[0129] Embodiment 14

[0130] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of Example 1 in that the ligand in the trivalent chromium ion organic complex includes 1 mol / L urea, and the remaining composition and content are consistent with those of Example 1;

[0131] The difference between the preparation method and Example 1 is that the addition amount of glycolic acid is omitted according to the change in concentration, and the addition amount of urea is adaptively adjusted. The other preparation methods and parameters are consistent with Example 1.

[0132] Embodiment 15

[0133] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of embodiment 1 in that the iron-chromium flow battery electrolyte only includes 1 mol / L Cr 3+ (including Cr not complexed by organic ligands 3+ and the complexed Cr in the trivalent chromium ion organic complex 3+ , where the organic ligands include 0.5 mol / L glycolic acid, 0.5 mol / L urea), 1 mol / L Fe 2+ , 1.5mol / LH +、0.25mol / L Sn 2+ and deionized water;

[0134] The difference between the preparation method and Example 1 is that LiCl is omitted, and 0.2 mol / L LiCl in Example 1 is completely replaced by 0.2 mol / L SnCl2, and the rest of the preparation method and parameters are consistent with Example 1.

[0135] Example 16

[0136] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of embodiment 1 in that the iron-chromium flow battery electrolyte only includes 1 mol / L Cr 3+ (including Cr not complexed by organic ligands 3+ and the complexed Cr in the trivalent chromium ion organic complex 3+ , where the organic ligands include 0.5 mol / L glycolic acid, 0.5 mol / L urea), 1 mol / L Fe 2+ , 1.5mol / LH + 、0.25mol / L Li + and deionized water;

[0137] The difference between the preparation method and Example 1 is that SnCl2 is omitted, and 0.05 mol / L SnCl2 in Example 1 is completely replaced by 0.05 mol / L LiCl, and the rest of the preparation method and parameters are consistent with Example 1.

[0138] Embodiment 17

[0139] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that: Li + The concentration of is 0.4 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0140] The difference between the preparation method and Example 1 is that the amount of concentrated LiCl added is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0141] Embodiment 18

[0142] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that: Li + The concentration of is 0.025 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0143] The difference between the preparation method and Example 1 is that the amount of concentrated LiCl added is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0144] Embodiment 19

[0145] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that Sn 2+ The concentration of is 0.015 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0146] The difference between the preparation method and Example 1 is that the amount of concentrated SnCl2 added is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters remain consistent with Example 1.

[0147] Embodiment 20

[0148] This embodiment provides an iron-chromium liquid flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium liquid flow battery electrolyte is different from that of embodiment 1 in that Sn 2+ The concentration of is 0.2 mol / L, and the other compositions and contents are consistent with those in Example 1;

[0149] The difference between the preparation method and Example 1 is that the amount of concentrated SnCl2 added is adaptively adjusted according to the change in concentration, and the other preparation methods and parameters remain consistent with Example 1.

[0150] Embodiment 21

[0151] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the concentration of the ligand glycolic acid is 1.0 mol / L, the concentration of urea is 1.0 mol / L, and the other compositions and contents are consistent with those of Example 1.

[0152] The difference between the preparation method and Example 1 is that the addition amounts of glycolic acid and urea are adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0153] Embodiment 22

[0154] This embodiment provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the concentration of the ligand glycolic acid is 0.2 mol / L, the concentration of urea is 0.2 mol / L, and the other compositions and contents are consistent with those of Example 1.

[0155] The difference between the preparation method and Example 1 is that the addition amounts of glycolic acid and urea are adaptively adjusted according to the change in concentration, and the other preparation methods and parameters are consistent with Example 1.

[0156] Comparative Example 1

[0157] This comparative example provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the iron-chromium flow battery electrolyte only includes 1 mol / L Cr 3+ 、1mol / L Fe 2+ , 1.5mol / LH + and deionized water;

[0158] The difference between the preparation method and Example 1 is that the step of adding glycolic acid, urea, LiCl and SnCl2 is omitted, and the other preparation methods and parameters are consistent with Example 1.

[0159] Comparative Example 2

[0160] This comparative example provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the iron-chromium flow battery electrolyte only includes 1 mol / L Cr 3+ (including Cr not complexed by organic ligands 3+ and the complexed Cr in the trivalent chromium ion organic complex 3+ , where the organic ligands include 0.5 mol / L glycolic acid, 0.5 mol / L urea), 1 mol / L Fe 2+ , 1.5mol / LH + and deionized water;

[0161] The difference between the preparation method and Example 1 is that the step of adding LiCl and SnCl2 is omitted, and the other preparation methods and parameters are consistent with Example 1.

[0162] Comparative Example 3

[0163] This comparative example provides an iron-chromium flow battery electrolyte and a preparation method thereof. The composition of the iron-chromium flow battery electrolyte is different from that of Example 1 in that the iron-chromium flow battery electrolyte only includes 1 mol / L Cr 3+ 、1mol / L Fe 2+ , 1.5mol / LH + 、0.2mol / L Li + 、0.05mol / L Sn 2+ and deionized water;

[0164] The difference between the preparation method and Example 1 is that the step of adding glycolic acid and urea is omitted, and the other preparation methods and parameters are consistent with Example 1.

[0165] Application Example 1-22 and Comparative Application Example 1-3

[0166] The iron-chromium liquid flow battery electrolyte provided by Examples 1-22 and Comparative Examples 1-3 is divided into two equal parts, namely the positive electrode electrolyte and the negative electrode electrolyte, respectively, poured into the positive electrode storage tank and the negative electrode storage tank, respectively, and assembled with N212 perfluorosulfonic acid proton membrane, 4.3mm thick graphite felt electrode, graphite plate and other accessories into an iron-chromium liquid flow battery, corresponding to Application Examples 1-22 and Comparative Application Examples 1-3 respectively.

[0167] The iron-chromium liquid flow battery provided in Application Example 1-22 and Comparative Application Example 1-3 was operated at a current density of 100 mA / cm at 50 °C. 2 The constant current charge and discharge experiment was carried out, the charge start voltage and the discharge cut-off voltage were 0.7V, the charge cut-off voltage was 1.2V, and the battery capacity test and battery energy efficiency test were carried out on each iron-chromium liquid flow battery with different charge and discharge cycle numbers. The test results are shown in Table 1.

[0168] Figure 2 A comparison diagram of the energy efficiency of the iron-chromium liquid flow battery provided by Application Example 1 of the present invention and Comparative Application Example 1 is shown. Figure 3 A comparison chart of the charging capacity of the iron-chromium liquid flow battery provided by Application Example 1 of the present invention and Comparative Application Example 1 is shown. It can be seen from the figure that the charging capacity and energy efficiency of the iron-chromium liquid flow battery provided by Application Example 1 of the present invention are significantly higher than those of Comparative Application Example 1, indicating that the electrochemical performance of the iron-chromium liquid flow battery can be significantly improved by complexing trivalent chromium ions with organic ligands and combining the catalytic effect of lithium ions and other metal ions except lithium, iron and chromium.

[0169] Table 1

[0170]

[0171]

[0172] The test results show that:

[0173] (1) It can be seen from Application Examples 1 to 14 that the present invention can significantly improve the reaction activity of the chromium electrode in the negative electrode electrolyte, prevent chromium aging, reduce hydrogen evolution side reactions, and improve the battery charge and discharge capacity and cycle stability by utilizing organic ligands to complex with trivalent chromium ions, and then combining the catalytic effects of lithium ions and other metal ions except lithium, iron and chromium, so as to achieve the purpose of efficient operation of the iron-chromium liquid flow battery. Specifically, the initial charging capacity of the iron-chromium liquid flow battery is between 1.02Ah and 1.22Ah, and the average attenuation per cycle during 50 charge and discharge cycles is ≤0.5%. At the same time, the energy efficiency can reach between 77.2% and 81.9%. It can be concluded that the use of the iron-chromium liquid flow battery electrolyte formulated by the present invention can greatly improve the electrochemical performance of the liquid flow battery.

[0174] (2) It can be seen from Application Examples 1 and 15-16 that the present invention Li + and Sn 2+ There is a synergistic effect between them, among which Li + It can promote the complexation of trivalent chromium ions with glycolic acid and urea. On this basis, Sn 2+ The addition of can further improve the redox activity of the negative electrode chromium pair, showing a higher hydrogen evolution energy barrier and further reducing the occurrence of hydrogen evolution side reactions; if Li is used alone + , trivalent chromium ion organic complex will increase the internal resistance of the electrolyte, resulting in reduced energy efficiency; if Sn is used alone 2+ , it will lead to lower inhibition of hydrogen evolution reaction and faster capacity decay, thus failing to achieve the corresponding effect.

[0175] (3) It can be seen from Application Examples 1 and 17-18 that the present invention regulates Li + The concentration of Li + If the concentration is too high, the viscosity of the electrolyte will increase, and the corresponding internal resistance will increase, which will have a negative impact on the overall performance, especially reducing the energy efficiency. + If the concentration is too low, the complexation degree of trivalent chromium ions will be insufficient, thus reducing the initial capacity.

[0176] (4) It can be seen from Application Examples 1 and 19-20 that the present invention regulates Sn 2+ The concentration of Sn is more conducive to the improvement of the electrochemical activity of chromium electrode redox and energy efficiency. 2+ If the concentration is too high, the amount of hydrogen evolution will increase during charging of the iron-chromium flow battery, and the capacity will decay rapidly, with an average decay of up to 0.76% per cycle. 2+If the concentration is too low, the electrochemical activity of chromium electrode for redox reaction will be limited, and it will not be able to compete with the hydrogen evolution reaction, resulting in a decrease in coulombic efficiency, voltage efficiency and energy efficiency.

[0177] (5) It can be seen from Application Examples 1 and 21-22 that by regulating the concentration of organic ligands in the trivalent chromium ion organic complex, the capacity decay rate of the iron-chromium flow battery can be reduced, the long-term operation stability of the electrolyte can be improved, and the electrochemical performance of the battery can be improved. If the concentration of the organic ligand is too high, the viscosity of the electrolyte will be too high and the energy efficiency will be reduced; if the concentration of the organic ligand is too low, the complex with the trivalent chromium ion will be insufficient, and the corresponding complex ion concentration will be too low, which cannot effectively improve the aging of the trivalent chromium ion and effectively improve the activity of the trivalent chromium ion, and the capacity decay is faster, with an average decay of up to 0.58% per cycle, and the energy efficiency is also reduced.

[0178] (6) It can be seen from Application Example 1 and Comparative Application Example 1 that if no organic ligand, lithium ions and other metal ions other than lithium, iron and chromium are added to the electrolyte of the iron-chromium flow battery of the present invention as catalysts, the trivalent chromium ions will age severely, and the capacity will decay rapidly, with an average decay of up to 0.78% per cycle, and the energy efficiency will also be greatly reduced.

[0179] (7) It can be seen from Application Example 1 and Comparative Application Example 2 that, if only organic ligands are added to the electrolyte of the iron-chromium liquid flow battery of the present invention, although the capacity decay rate can be slowed down, the redox activity of the chromium electrode cannot be effectively improved, so the initial charging capacity and energy efficiency are both low.

[0180] (8) It can be seen from Application Example 1 and Comparative Application Example 3 that if only lithium ions and other metal ions except lithium, iron and chromium are added as catalysts to the electrolyte of the iron-chromium liquid flow battery of the present invention, although the activity of the chromium-electrode reaction can be improved, the battery capacity and energy efficiency can be increased, but at the same time, the hydrogen evolution side reaction is aggravated, and the capacity decay is not improved, with an average decay of up to 1.1% per cycle.

[0181] In summary, the iron-chromium liquid flow battery electrolyte of the present invention utilizes organic ligands to complex with trivalent chromium ions, and then combines the catalytic effects of lithium ions and other metal ions except lithium, iron and chromium, so as to significantly improve the reaction activity of the chromium electrode in the negative electrode electrolyte, improve the phenomenon of large-scale aging of trivalent chromium ions, and reduce the hydrogen evolution side reaction, so as to comprehensively improve the charge and discharge capacity, cycle stability and energy efficiency of the iron-chromium liquid flow battery, so as to achieve the purpose of efficient operation of the iron-chromium liquid flow battery.

[0182] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An iron-chromium flow battery electrolyte, characterized in that: The iron-chromium flow battery electrolyte comprises trivalent chromium ion organic complex, ferrous ion, hydrogen ion, lithium ion, other metal ions except lithium, iron and chromium, and solvent; The organic ligand in the trivalent chromium ion organic complex comprises a compound containing a carboxylic acid group and / or a compound containing an amino group.

2. The iron-chromium flow battery electrolyte according to claim 1, characterized in that: The compound containing a carboxylic acid group includes any one of glycolic acid, malic acid or aminoacetic acid or a combination of at least two thereof; Preferably, the compound containing an amino group comprises urea and / or glycine; Preferably, in the iron-chromium flow battery electrolyte, the concentration of the organic ligand in the trivalent chromium ion organic complex is 0.01 mol / L-4.5 mol / L, preferably 0.1 mol / L-3 mol / L, and more preferably 0.5 mol / L-1.5 mol / L; Preferably, in the iron-chromium flow battery electrolyte, the concentration of trivalent chromium ions is 0.01 mol / L-5 mol / L, preferably 0.1 mol / L-2 mol / L, and more preferably 0.8 mol / L-1.6 mol / L.

3. The iron-chromium flow battery electrolyte according to claim 1 or 2, characterized in that: The other metal ions besides lithium, iron and chromium include tin ions and / or titanium ions; Preferably, the tin ions include tetravalent tin ions and / or stannous ions; Preferably, the titanium ions include tetravalent titanium ions and / or titanous ions; Preferably, in the iron-chromium flow battery electrolyte, the concentration of lithium ions is 0.001 mol / L-1 mol / L, preferably 0.01 mol / L-0.5 mol / L, and more preferably 0.05 mol / L-0.3 mol / L; Preferably, in the iron-chromium flow battery electrolyte, the concentration of the other metal ions except lithium, iron and chromium is 0.001 mol / L-1 mol / L, preferably 0.01 mol / L-0.5 mol / L, and further preferably 0.05 mol / L-0.1 mol / L.

4. The iron-chromium flow battery electrolyte according to any one of claims 1 to 3, characterized in that: In the iron-chromium flow battery electrolyte, the concentration of ferrous ions is 0.01 mol / L-5 mol / L, preferably 0.1 mol / L-2 mol / L, and more preferably 0.8 mol / L-1.6 mol / L; Preferably, in the iron-chromium flow battery electrolyte, the concentration of hydrogen ions is 0.01 mol / L-5 mol / L, preferably 0.1 mol / L-3 mol / L, and more preferably 1 mol / L-2 mol / L.

5. A method for preparing an electrolyte for an iron-chromium flow battery according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) mixing an organic complexing agent, a ferrous salt, a trivalent chromium salt and a solvent to obtain a first mixed solution; The structural formula of the organic complexing agent includes a carboxyl group and / or an amino group; (2) Mixing lithium salt, other metal salts except lithium, iron and chromium, acid solution and the first mixed solution of step (1) to obtain an iron-chromium liquid flow battery electrolyte.

6. The preparation method according to claim 5, characterized in that: The organic complexing agent in step (1) includes any one of glycolic acid, malic acid, urea or aminoacetic acid, or a combination of at least two thereof; Preferably, the mixing in step (1) comprises: firstly mixing the organic complexing agent and the solvent for a first time, then adding a trivalent chromium salt for a second time, and then adding a ferrous salt for a third time.

7. The preparation method according to claim 6, characterized in that: The first mixing includes heating to dissolve and stirring; Preferably, the temperature of the heating and dissolving is 25°C-80°C, preferably 25°C-65°C; Preferably, the heating and dissolving time is 5 min-30 min; Preferably, the second mixing includes heating complexation and stirring; Preferably, the temperature of the heating complexation is 25°C-80°C, preferably 25°C-65°C; Preferably, the heating complexation time is 10min-30min; Preferably, the temperature of the third mixing is 10°C-40°C; Preferably, the third mixing time is 10min-30min; Preferably, the pH value of the first mixed solution is ≤3.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The other metal salts in step (2) except lithium, iron and chromium include tin salts and / or titanium salts; Preferably, the tin salt comprises a tetravalent tin salt and / or a stannous salt; Preferably, the titanium salt comprises a tetravalent titanium salt and / or a titanous salt; Preferably, the mixing in step (2) comprises: firstly mixing the acid solution with the first mixed solution in step (1) for a fourth time, and then adding lithium salt and other metal salts except lithium, iron and chromium for a fifth time; Preferably, after the mixing in step (2) is completed, a heat preservation treatment is also included; Preferably, the temperature of the heat preservation treatment is 45°C-70°C, preferably 55°C-65°C.

9. The preparation method according to claim 5, characterized in that: The preparation method comprises the following steps: (1) firstly, the organic complexing agent and the solvent are heated and dissolved at 25° C.-80° C. for 5 min-30 min, to perform a first mixing; then, under the condition of stirring at 25° C.-80° C., a trivalent chromium salt is added and heated for complexation for 10 min-30 min, to perform a second mixing; then, under the condition of stirring at 10° C.-40° C., a ferrous salt is added and mixed and dissolved for 10 min-30 min, to perform a third mixing, to obtain a first mixed solution with a pH value of ≤3; The structural formula of the organic complexing agent includes a carboxyl group and / or an amino group; (2) Mixing the acid solution with the first mixed solution in step (1) for the fourth time under the stirring condition of 10°C-40°C; adding lithium salt and other metal salts except lithium, iron and chromium and dissolving them for 10min-30min under the stirring condition of 10°C-40°C, mixing for the fifth time, and heat-treating at 45°C-70°C to obtain an iron-chromium liquid flow battery electrolyte.

10. An iron-chromium flow battery, characterized in that: The iron-chromium flow battery comprises the iron-chromium flow battery electrolyte as described in any one of claims 1 to 4, or the iron-chromium flow battery electrolyte prepared by the preparation method as described in any one of claims 5 to 9.

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