Alkaline zinc-iron flow battery electrolyte and zinc-iron flow battery

Abstract

The invention discloses an alkaline zinc-iron flow battery electrolyte and a zinc-iron flow battery, and belongs to the field of flow batteries. According to the alkaline zinc-iron flow battery electrolyte, LiOH is adopted as a supporting electrolyte, so that the freezing point of a Na4Fe (CN) 6 or K4Fe (CN) 6 solution can be remarkably reduced, and the solubility and low-temperature stability of Fe (CN) 6 < 4-> are improved. According to the zinc-iron flow battery adopting the alkaline zinc-iron flow battery electrolyte, the solubility of Fe (CN) 64 <-> / Fe (CN) 63 <-> is improved by regulating and controlling the solvation structure of Fe (CN) 64 <->, and the stability of Fe (CN) 64 <-> / Fe (CN) 63 <-> at a lower temperature (-10 DEG C) is enhanced.

Description

TECHNICAL FIELD

[0001] The application relates to an alkaline zinc-iron flow battery electrolyte and a zinc-iron flow battery, and belongs to the field of flow batteries. BACKGROUND

[0002] Ferrocyanide / ferrocyanide (Fe(CN)6 4- / Fe(CN)6 3- ) redox couples are ideal positive redox couples for alkaline flow batteries due to their low cost and excellent electrochemical properties. However, flow batteries based on Fe(CN)6 4- / Fe(CN)6 3- redox couples are limited by their solubility, resulting in low energy density of the battery. For example, the solubility of sodium ferrocyanide (Na4Fe(CN)6) and potassium ferrocyanide (K4Fe(CN)6) in water is only 0.56 mol L -1 and 0.76 mol L -1 , respectively. In alkaline media, the concentration of Fe(CN)6 4- is usually only 0.4 mol L -1 (mol L -1 , abbreviated as M) (Table 1, Angewandte Chemie International Edition, 2024, DOI: https: / / doi.org / 10.1002 / anie.202403607), which is significantly lower than the concentration of vanadium ions in a full vanadium flow battery (1.5 mol L -1 ). Moreover, affected by the "common ion effect", the higher the salt concentration in the solution, the lower the solubility of Fe(CN)6 4- / Fe(CN)6 3- . Currently, the low solubility of Fe(CN)6 4- / Fe(CN)6 3- results in a low energy density of the alkaline zinc-iron flow battery. In addition, Fe(CN)6 4- / Fe(CN)6 3- is sensitive to temperature, resulting in that flow batteries based on Fe(CN)6 4- / Fe(CN)6 3- couples generally work at room temperature (Table 1).

[0003] Table 1 Comparison of Fe(CN)6 3- / Fe(CN)6 4- concentration in different alkaline flow batteries

[0004]

[0005]

[0006] Angew. Chem. Int. Ed. 2023, 62, e202304667; Cell Reports Physical Science, 2023, 4, 101215; Joule 2019, 3, 149-163 employed a neutral supporting electrolyte or replaced the counterions (K 4- , Na 3- ) of Fe(CN)6 + / Fe(CN)6 + with NH4 + , Li + , which is an effective strategy to improve the solubility of Fe(CN)6 4- / Fe(CN)6 3- at room temperature. The solubility of K4Fe(CN)6 in the solution containing potassium ions (potassium hydroxide (KOH)) will be reduced due to the same ion effect (iScience, 2018, 3, 40-49). However, when K4Fe(CN)6 is mixed with sodium hydroxide (NaOH) in water, the solubility of Fe(CN)6 4- can be improved due to the interaction between different ions. The results of the study show that the interaction between K4Fe(CN)6 and Na + in the NaOH solution is stronger than that between K4Fe(CN)6 and K + in the KOH solution, resulting in a higher adsorption energy between Fe(CN)6 4- and Na + in the NaOH solution, which reduces the lattice energy of K4Fe(CN)6 and further improves its solubility (Materials Today Energy, 2022, 28, 101061). In the NaOH solution, mixing equal molar amounts of K4Fe(CN)6 and Na4Fe(CN)6 can increase the solubility of Fe(CN)6 4- to 1.46 mol L -1 (Materials Today Energy, 2022, 28, 101061). Mixing K4Fe(CN)6 and Na4Fe(CN)6 in equal molar proportions in water can also increase the solubility of Fe(CN)6 4- to 1.5 mol L -1 (US9929425B2[P].2018-03-27); a complex mixture of K4Fe(CN)6, Na4Fe(CN)6, NaOH, and KOH can increase the solubility of Fe(CN)6 4- to 1.0 mol L -1(US9929425B2[P].2018-03-27). However, there is currently no research on the solubility and stability of Fe(CN)6 4- / Fe(CN)6 3- The research on redox couples mainly focuses on regulating their solubility and chemical stability at room temperature. There is a lack of research on the solubility and stability of Fe(CN)6 4- / Fe(CN)6 3- at low temperatures, especially at 0℃ or below for a long time, which poses a serious challenge to the stable operation of this type of flow battery at low temperatures. SUMMARY

[0007] To solve the above technical problems, the present application aims to provide a basic zinc-iron flow battery electrolyte and a zinc-iron flow battery with low-temperature adaptability. By regulating the solvation structure of Fe(CN)6 4- , the solubility of Fe(CN)6 4- / Fe(CN)6 3- is improved, and its stability at lower temperatures (-10℃) is enhanced.

[0008] According to the first aspect of the present application, a basic zinc-iron flow battery electrolyte is provided. LiOH is used as a supporting electrolyte, which can significantly lower the freezing point of Na4Fe(CN)6 or K4Fe(CN)6 solution. Li + can enter the solvation layer of Fe(CN)6 4- , break the tight adsorption between Na + or K + and Fe(CN)6 4- , and promote more Fe(CN)6 4- to diffuse into the bulk solution, thereby inhibiting the formation of ice crystals in the salt solution, improving the solubility of Fe(CN)6 4- and its low-temperature stability.

[0009] A basic zinc-iron flow battery electrolyte includes a positive electrolyte and a negative electrolyte.

[0010] The positive electrolyte is composed of Na4Fe(CN)6, K4Fe(CN)6, and LiOH.

[0011] The negative electrolyte includes zinc ions, ligands, and a supporting electrolyte.

[0012] The supporting electrolyte is composed of LiOH and KOH

[0013] or

[0014] The supporting electrolyte is composed of LiOH and NaOH.

[0015] In the positive electrode electrolyte, the molar ratio of Na4Fe(CN)6 to K4Fe(CN)6 is 1:1;

[0016] The positive electrode electrolyte has its pH adjusted to 11-14 using LiOH.

[0017] The pH of the negative electrode electrolyte is adjusted to be the same as that of the positive electrode electrolyte by a supporting electrolyte.

[0018] Optionally, the pH of the positive electrode electrolyte is adjusted to 12 using LiOH.

[0019] Optionally, the concentration of Na4Fe(CN)6 in the positive electrode electrolyte is 0.2 mol / L. -1 ~0.85 mol L -1 .

[0020] Optionally, the concentration of Na4Fe(CN)6 in the positive electrode electrolyte is 0.4 mol / L. -1 ~0.5 mol L -1 .

[0021] Optionally, the concentration of Na4Fe(CN)6 in the positive electrode electrolyte is independently selected from 0.2 mol / L. -1 0.25 mol L -1 0.3 mol L -1 0.35 mol L -1 0.4 mol L -1 0.45 mol L -1 0.5 mol L -1 0.55 mol L -1 0.6 mol L -1 0.65 mol L -1 0.7 mol L -1 0.75 mol L -1 0.8 mol L -1 0.85 mol L -1 Any value in the range or any value between the two.

[0022] Optionally, the concentration of LiOH in the positive electrode electrolyte is 0.05–2.0 mol / L. -1 .

[0023] Optionally, the concentration of LiOH in the positive electrode electrolyte is independently selected from 0.05 mol L. -1 0.1 mol L -1 0.3 mol L -1 0.5 mol L -10.7 mol L -1 1 mol L -1 1.3 mol L -1 1.5 mol L -1 1.7 mol L -1 2.0 mol / L -1 Any value in the range or any value between the two.

[0024] Optionally, the concentration of LiOH in the negative electrode electrolyte is 0.05–3.0 mol / L. -1 .

[0025] Optionally, the concentration of LiOH in the negative electrode electrolyte is independently selected from 0.05 mol / L. -1 0.1 mol L -1 0.3 mol L -1 0.5 mol L -1 0.7 mol L -1 1 mol L -1 1.3 mol L -1 1.5 mol L -1 1.7 mol L -1 2.0 mol / L -1 2.3 mol L -1 2.5 mol L -1 2.7 mol L -1 3.0 mol L -1 Any value in the range or any value between the two.

[0026] Optionally, in the negative electrode electrolyte, the molar ratio of LiOH to KOH is 3:20 to 6:1.

[0027] or

[0028] The molar ratio of LiOH to NaOH is 3:20 to 6:1.

[0029] Optionally, in the negative electrode electrolyte, the molar ratio of LiOH to KOH is 1:1 to 6:1 or

[0030] The molar ratio of LiOH to NaOH is 1:1 to 6:1.

[0031] Optionally, in the negative electrode electrolyte, the molar ratio of LiOH to KOH is independently selected from any value or a range between any two of 0.15:1, 0.2:1, 0.3:1, 0.5:1, 0.7:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, and 6:1.

[0032] Optionally, in the negative electrode electrolyte, the molar ratio of LiOH to NaOH is independently selected from any value or a range between any two of 0.15:1, 0.2:1, 0.3:1, 0.5:1, 0.7:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, and 6:1.

[0033] Optionally, the concentration of zinc ions is 0.2 mol / L. -1 -0.8mol L -1 .

[0034] Optionally, the concentration of zinc ions is independently selected from 0.2 mol L. -1 0.3 mol L -1 0.4 mol L -1 0.5 mol L -1 0.6 mol L -1 0.7 mol L -1 0.8 mol L -1 Any value in the range or any value between the two.

[0035] Optionally, the molar ratio of the concentration of zinc ions to the concentration of ligands is 1 to 1.3.

[0036] Optionally, the zinc ions are selected from at least one of zinc chloride, zinc nitrate, zinc acetate, zinc bromide, and zinc iodide.

[0037] Optionally, the ligand is selected from at least one of diethylenetriaminepentaacetic acid (DTPA), hydroxyethylidene diphosphonic acid (HEDP), ethylenediaminetetraacetic acid (EDTA), and ethylenediaminedisuccinic acid (EEDS).

[0038] According to a second aspect of this application, a zinc-iron flow battery is provided. This zinc-iron flow battery uses LiOH as the supporting electrolyte and exhibits excellent low-temperature stability, operating stably at -10°C.

[0039] A zinc-iron flow battery comprises an alkaline zinc-iron flow battery electrolyte, an ion-conducting membrane, electrodes, and a current collector;

[0040] The alkaline zinc-iron flow battery electrolyte is selected from the alkaline zinc-iron flow battery electrolyte described above.

[0041] In this application, the ion-conducting membrane, electrode, and current collector can be constructed using conventional existing technologies.

[0042] The beneficial effects that this application can produce include:

[0043] 1) The alkaline zinc-iron flow battery electrolyte provided in this application can significantly lower the freezing point of Na₄Fe(CN)₆ or K₄Fe(CN)₆ solutions, even at -10℃ and 0.8 mol / L. -1 Fe(CN)6 4- The solution remains stable, and its ionic conductivity remains at 70 mS / cm. -1 At -10℃, Fe(CN)6 4- / Fe(CN)6 3- The redox couple still exhibits excellent electrochemical activity and reversibility in the LiOH supported electrolyte.

[0044] 2) The zinc-iron flow battery provided in this application, at 25°C, utilizes the addition of LiOH as a supporting electrolyte to enhance the Fe(CN)6 content. 4- The solubility at room temperature increased to 1.7 mol L. -1 And increased the energy density of zinc-iron flow batteries to 49Wh / L. -1 Based on 0.8 mol L -1 Fe(CN)6 4- The zinc-iron flow battery with LiOH-supported electrolyte maintained stable performance for ~4200 hours and ~800 hours at 25℃ and -10℃, respectively, significantly improving the energy density, operating temperature range and stability of the zinc-iron flow battery.

[0045] 3) The zinc-iron flow battery provided in this application reduces the alkaline concentration of the positive and negative electrode electrolytes, which can reduce the requirements for the alkaline stability of key battery materials and has good practical application value. Attached Figure Description

[0046] Figure 1 middle, Figure 1 The left image of Figure a is a photograph of the electrolyte used in Comparative Example 1, which was left to stand at -10°C for 4 hours after being supported by KOH. Figure 1 The right image of a is a photograph of the electrolyte of Example 1, which uses LiOH as the supporting electrolyte, after standing at -10°C for 4 hours. Figure 1 b is the zinc-iron flow battery assembled in Example 2 at 40 mA / cm. -2 Battery efficiency test graph at operating current density.

[0047] Figure 2 The diagram shows the cyclic voltammetry test results of the zinc-iron flow battery assembled in Example 3. Figure 2 'a' represents the conditions at 25℃. Figure 2 b represents the conditions at -10℃.

[0048] Figure 3The zinc-iron flow battery assembled in Example 4 was tested at 40 mA cm⁻¹. -2 The cycle performance and partial charge-discharge curves were obtained by testing at the operating current density. Figure 3 a represents the conditions at 25℃; Figure 3 b represents the conditions at -10℃; Figure 3 c represents the temperature at 25℃, using 1.7 mol L... -1 Fe(CN)6 4- . Detailed Implementation

[0049] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0050] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0051] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0052] The analysis method in the embodiments of this application is as follows:

[0053] The zinc-iron flow battery consists of an alkaline zinc-iron flow battery electrolyte, an ion-conducting membrane, electrodes, and current collectors, specifically a sulfonated polyether ether ketone (SPEEK) ion exchange membrane, a carbon felt electrode, and a graphite plate current collector.

[0054] Electrochemical performance analysis of zinc-iron flow batteries was conducted using an Arbin BT 2000 or a Xinwei battery testing system (CT-4008Tn-5V12A-S1-F, Shenzhen, China).

[0055] Comparative Example 1

[0056] KOH was used as the supporting electrolyte in a 0.4 mol L solution. -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A solution of K4Fe(CN)6 (pH=12) freezes and precipitates after standing at -10℃ for 4 hours. Figure 1 The left figure of a is shown.

[0057] Comparative Example 2

[0058] 0.4 mol L of KOH as the supporting electrolyte -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A 0.4 mol / L solution of K4Fe(CN)6 (pH = 12) was used as the positive electrode electrolyte, and NaOH was used as the supporting electrolyte. -1 EDTA + 0.4 mol L -1The minimum operating temperature of a zinc-iron flow battery assembled with a ZnBr2 solution (pH=12) as the negative electrode electrolyte is 0℃. When the temperature is further reduced to -2℃, the positive electrode electrolyte precipitates and blocks the pipeline, preventing the positive electrode electrolyte from flowing into the positive electrode, thus causing the battery to fail.

[0059] Comparative Example 3

[0060] At 0.8 mol L -1 Fe(CN)6 4- +3mol L -1 KOH is used as the positive electrode electrolyte, 0.4 mol / L. -1 Zn(OH)4 2- +3mol L - 1 Using KOH as the negative electrode electrolyte, the minimum operating temperature of the assembled strongly alkaline zinc-iron flow battery is 15℃. When the temperature is further reduced to 1℃, the positive electrode electrolyte precipitates and blocks the pipeline, preventing the positive electrode electrolyte from flowing into the positive electrode, leading to battery failure.

[0061] Comparative Example 4

[0062] 0.4 mol L of LiOH as the supporting electrolyte -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A solution of K4Fe(CN)6 (pH = 12) is used as the positive electrode electrolyte, and LiOH and NaOH are used as supporting electrolytes at a concentration of 0.4 mol / L. -1 EDTA + 0.4 mol L -1 In a zinc-iron flow battery assembled with a ZnBr2 solution (pH=14) as the negative electrode electrolyte, during battery operation, the pH on both sides of the positive and negative electrodes reaches equilibrium due to transmembrane carrier transfer. The positive electrode OH... - Increased concentration will affect Fe(CN)6 4- The solvation structure reduces the temperature stability of the battery, increasing the minimum stable operating temperature from -10°C in a pH=12 solution to -5°C.

[0063] Comparative Example 5

[0064] 0.4 mol L of LiOH as the supporting electrolyte -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A 0.4 mol / L solution of K4Fe(CN)6 (pH = 12) was used as the positive electrode electrolyte, and NaOH was used as the supporting electrolyte. -1 EDTA + 0.4 mol L -1In a zinc-iron flow battery assembled with a ZnBr2 solution (pH=12) as the negative electrode electrolyte, during battery operation, due to transmembrane carrier transfer, the Na+ on the negative electrode side... + It will be transferred to the positive electrode electrolyte through the diaphragm, which will also affect Fe(CN)6. 4- Due to the solvation structure, as the battery cycles, when the battery operates at -10°C for 100 cycles, precipitates gradually appear in the positive electrode reservoir.

[0065] Comparative Example 6

[0066] Using LiOH and NaOH (in a molar ratio of 1:1) as the supporting electrolyte, 0.4 mol L... -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A solution of K4Fe(CN)6 (pH = 12) is used as the positive electrode electrolyte, and LiOH and NaOH are used as supporting electrolytes at a concentration of 0.4 mol / L. -1 EDTA + 0.4 mol L -1 In a zinc-iron flow battery assembled with a ZnBr2 solution (pH=12) as the negative electrode electrolyte, during battery operation, due to Fe(CN)6... 4- with Na + The strong intermolecular interactions hinder the dissociation of ferrocyanide, thus leading to Fe(CN)6 4- It accumulates in the solution, reducing the battery's temperature stability; the lowest stable operating temperature is -3℃.

[0067] Example 1

[0068] Using LiOH as the supporting electrolyte, 0.4 mol L -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A solution of K4Fe(CN)6 (pH=12) remained stable after standing at -10℃ for 4 hours. Figure 1 The right figure of a is shown.

[0069] Example 2

[0070] During the charging and discharging process of a zinc-iron flow battery, the cations (Na+) in the positive and negative electrode electrolytes... + K + Li + Transmembrane transport of ions alters the salt ion concentration in the positive electrode electrolyte. Therefore, to ensure the optimal concentration of salt ions in a 0.4 mol L⁻¹ electrolyte based on LiOH as the supporting electrolyte, [further measures are needed]. - 1 Na₄Fe(CN)₆ + 0.4 mol L -1The low-temperature stability of K4Fe(CN)6 solution (pH=12) during the cycling process of zinc-iron flow battery was improved by optimizing the molar ratio of LiOH to NaOH in the supporting electrolyte of the negative electrode.

[0071] At -5℃ and -10℃, the negative electrode uses 0.4 mol L. -1 EDTA + 0.4 mol L -1 ZnBr2 (the pH of the solution was adjusted to 12 using LiOH and NaOH, with LiOH concentrations of 2.8, 2.0, 1.5, and 1.2 mol / L). -1 The molar ratios of LiOH to NaOH were 4:1, 2:1, 1:1, and 0.67:1, respectively; the positive electrode electrolyte was a 0.4 mol / L solution with LiOH as the supporting electrolyte. -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A zinc-iron flow cell assembled in a K4Fe(CN)6 solution (pH=12) at 40 mA cm⁻¹ -2 Battery efficiency at operating current density, such as Figure 1 As shown in b.

[0072] When the molar ratio of LiOH to NaOH in the negative electrode electrolyte is less than 1:1, there will be more NaOH in the solution. + Surrounding Fe(CN)6 4- Surrounding, and Fe(CN)6 4- with Na + The strong intermolecular interactions hinder the dissociation of ferrocyanide, thus leading to Fe(CN)6 4- Aggregation in the solution affects the low-temperature stability of the positive electrode electrolyte at -10℃ (but does not affect stable operation at -5℃). Figure 1 (b) This leads to the failure of zinc-iron flow batteries due to the freezing and precipitation of the positive electrode electrolyte. Because sodium hydroxide is more soluble in water and has stronger alkalinity, while lithium hydroxide has relatively lower solubility and slightly weaker alkalinity, when the negative electrode supporting electrolyte is entirely LiOH, the solution conductivity is low. Batteries tested with this method exhibited a conductivity of 40 mA cm⁻¹. -2 The operating current density and energy efficiency at -10℃ are only 75%; however, the battery exhibits optimal efficiency when the molar ratio of LiOH to NaOH is 1:1. The same beneficial effect can be achieved when a mixed solution of LiOH and KOH is used as the supporting electrolyte for the negative electrode. Considering that NaOH is cheaper than KOH, in practical applications, NaOH and LiOH are mainly used as the supporting electrolyte to regulate the pH of the negative electrode solution.

[0073] Example 3

[0074] Cyclic voltammetry (CV) was used to study the effect of LiOH supporting electrolyte on Fe(CN)6. 4- / Fe(CN)6 3- The effect of redox electrochemical pair on electrochemical properties. Using LiOH as the supporting electrolyte, 0.4 mol L... -1 Na₄Fe(CN)₆ + 0.4 mol L -1 A solution of K4Fe(CN)6 (pH = 12) at 25℃ Figure 2 a) and -10℃ ( Figure 2 b) Cyclic voltammetry test, such as Figure 2 As shown, the results indicate that Fe(CN)6 4- / Fe(CN)6 3- The redox couple retains good reversibility and electrochemical activity in the LiOH supported electrolyte and follows a standard diffusion-controlled process. At 25 °C ( Figure 2 a) Fe(CN)6 was calculated using the Randles-Sevcik equation. 4- / Fe(CN)6 3- The redox diffusion coefficients of the redox couple in the LiOH supported electrolyte are 2.35 × 10⁻⁶. -6 cm 2 S -1 and 2.16×10 -6 cm 2 S -1 Even at temperatures as low as -10°C ( Figure 2 b), Fe(CN)6 4- / Fe(CN)6 3- The redox couple still exhibits a high diffusion coefficient. Furthermore, analysis based on the Nicholson equation reveals that in LiOH solution, Fe(CN)6... 4- / Fe(CN)6 3- The redox rate constant k0 is 2.92 × 10⁻⁶. -4 cm s -1 This indicates that Fe(CN)6 4- / Fe(CN)6 3- It exhibits good reversibility and electrochemical activity in LiOH-supported electrolytes.

[0075] Example 4

[0076] To investigate the effects of LiOH on the cycle stability and low-temperature stability of zinc-iron flow batteries, a zinc-iron flow battery based on LiOH-supported electrolyte was assembled. Figure 3 As shown in figure a, at 25℃ and 40mA cm -2 Under the operating current density conditions, 0.8 mol L -1Fe(CN)6 4- (0.4 mol L) -1 Na₄Fe(CN)₆ + 0.4 mol L -1 K4Fe(CN)6) and 0.4 mol L -1 LiOH is used as the positive electrode electrolyte (pH = 12), and LiOH and NaOH (molar ratio 1:1) form 0.4 mol L⁻¹ of supporting electrolyte. -1 EDTA + 0.4 mol / L -1 Zinc-iron flow batteries using ZnBr2 as the negative electrode electrolyte (pH=12) exhibit excellent cycle performance, operating stably for approximately 4200 hours (each cycle is approximately 1 hour; charge-discharge curves are shown below). Figure 3 As shown in a), the average coulombic efficiency (CE) is ~99.62% and the average energy efficiency (EE) is ~88.57%.

[0077] A zinc-iron flow battery using the same electrolyte was tested at -10°C and 40 mA cm⁻¹. -2 It can still operate continuously and stably for ~800 hours at the operating current density, with an average energy efficiency of ~81.41%. Figure 3 b) For the first time, a method based on 0.8 mol L... -1 Fe(CN)6 4- The electrolyte-based flow battery operates stably for extended periods at -10°C. At -10°C, the utilization rate and discharge capacity (approximately 0.96 Ah) of the positive and negative electrolytes are the same as at 25°C.

[0078] Taking advantage of the LiOH system, 0.85 mol L of LiOH was used as the supporting electrolyte. -1 Na₄Fe(CN)₆ + 0.85 mol / L -1 A solution of K4Fe(CN)6 (pH = 12) is used as the positive electrode electrolyte, and LiOH and NaOH are used as supporting electrolytes at a concentration of 0.4 mol / L. -1 EDTA + 0.4 mol L -1 A ZnBr2 solution (pH = 12) is used as the negative electrode electrolyte. At 25℃, Fe(CN)6... 4- The solubility in LiOH solution can be further increased to 1.7 mol L. -1 At 25℃, using 1.7 mol L... -1 Fe(CN)6 4- and 0.4 mol L -1 Zinc-iron flow batteries using LiOH as the positive electrode electrolyte have operated stably for over 500 cycles (approximately 1100 hours, with each cycle lasting approximately 2 hours), achieving a discharge capacity of 25 Ah / L. -1The average coulombic efficiency of the battery is ~99.05%, and the energy efficiency is ~87.44%. Figure 3 c) This significantly improves the energy density of zinc-iron flow batteries, making them more advantageous in practical applications.

[0079] Example 5

[0080] A zinc-iron flow battery based on LiOH-supported electrolyte was assembled and tested at -5℃ and 40 mA cm⁻¹. -2 Under the operating current density conditions, using 1.0 mol L -1 Fe(CN)6 4- (0.5mol L -1 Na₄Fe(CN)₆ + 0.5 mol L -1 K4Fe(CN)6) and 0.4 mol L -1 LiOH is used as the positive electrode electrolyte (pH = 12), and LiOH and NaOH (molar ratio 1:1) form a supporting electrolyte of 0.5 mol L⁻¹. - 1 EDTA + 0.5 mol L -1 Zinc-iron flow batteries using ZnBr2 as the negative electrode electrolyte (pH=12) exhibit excellent cycle performance, maintaining stable performance for up to 120 cycles, with no active material precipitation in the positive electrode electrolyte.

[0081] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An alkaline zinc-iron flow battery electrolyte, characterized in that, comprise a positive electrolyte and a negative electrolyte; the positive electrolyte is composed of Na4Fe(CN)6, K4Fe(CN)6, LiOH; the negative electrolyte comprises zinc ions, ligands, and a supporting electrolyte; the supporting electrolyte is composed of LiOH and KOH or the supporting electrolyte is composed of LiOH and NaOH; wherein, in the positive electrolyte, the molar concentration ratio of Na4Fe(CN)6 to K4Fe(CN)6 is 1:1; the positive electrolyte has a pH of 11-14 adjusted by LiOH; the negative electrolyte has a pH identical to that of the positive electrolyte adjusted by the supporting electrolyte.

2. The alkaline zinc-iron flow battery electrolyte of claim 1, wherein, The concentration of Na4Fe(CN)6 in the positive electrolyte is 0.2-0.85 mol / L -1 . -1 ; Preferably, in the positive electrolyte, the concentration of Na4Fe(CN)6 is 0.4 mol / L -1 ~ 0.5 mol / L -1 .

3. The alkaline zinc-iron flow battery electrolyte of claim 1, wherein, The concentration of LiOH in the positive electrolyte is 0.05-2.0 mol / L -1 .

4. The alkaline zinc-iron flow battery electrolyte of claim 1, wherein, The concentration of LiOH in the negative electrolyte is 0.05-3.0 mol / L -1 .

5. The alkaline zinc-iron flow battery electrolyte of claim 1, wherein, in the negative electrolyte, the molar ratio of LiOH to KOH is 3:20-6:1 or the molar ratio of LiOH to NaOH is 3:20-6:1; preferably, in the negative electrolyte, the molar ratio of LiOH to KOH is 1:1-6:1 or the molar ratio of LiOH to NaOH is 1:1-6:

1.

6. The alkaline zinc-iron liquid flow battery electrolyte of claim 1, wherein, The concentration of the zinc ions is 0.2 mol L -1 -0.8 mol L -1 .

7. The alkaline zinc-iron flow battery electrolyte of claim 1, wherein, the molar ratio of the concentration of zinc ions to the concentration of ligands is 1-1.

3.

8. The alkaline zinc-iron liquid flow battery electrolyte of claim 1, wherein, the source of zinc ions is selected from at least one of zinc chloride, zinc nitrate, zinc acetate, zinc bromide, and zinc iodide.

9. The alkaline zinc-iron liquid flow battery electrolyte of claim 1, wherein, the ligand is selected from any one of diethylenetriamine pentaacetic acid, hydroxyethylenediphosphonic acid, ethylenediaminetetraacetic acid, and ethylenediamine disuccinic acid.

10. A zinc-iron flow battery, characterized in that, consist of an alkaline zinc-iron flow battery electrolyte, an ion-conducting membrane, an electrode, and a current collector; the alkaline zinc-iron flow battery electrolyte is selected from any one of the alkaline zinc-iron flow battery electrolytes according to claims 1-9.

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