A method for preparing negative electrode electrolyte for aqueous iron-based liquid flow battery and its application

Abstract

A method for preparing an aqueous iron-based liquid flow battery negative electrode electrolyte and its application, belonging to the field of liquid flow battery energy storage. In the present invention, the electrolyte mainly comprises a multidentate ligand chelating agent, an iron-based salt, a supporting electrolyte and an auxiliary electrolyte. The multidentate ligand chelating agent is selected from one or more 1,2-cyclohexanediaminetetraacetic acid chemicals. 1,2-cyclohexanediaminetetraacetic acid chemicals have a wide range of coordination properties and can be well coordinated with Fe in an alkaline environment. 3+ / Fe 2+ The complexation forms a stable complex, inhibits the hydrolysis of Fe ions to form hydroxide precipitates, and has a high solubility, thus realizing a new alkaline all-iron negative electrode electrolyte with low cost, high energy density and high power density, which shows excellent cycle stability and has good application prospects in the field of liquid flow batteries.

Description

Technical Field

[0001] The invention relates to the technical field of liquid flow batteries, and in particular to a method for preparing a negative electrode electrolyte of an aqueous iron-based liquid flow battery. Background Art

[0002] With the rapid development of renewable energy technologies (such as solar energy, wind energy, etc.), in order to solve the intermittency of renewable energy, there has been an obvious demand for large-scale energy storage systems in recent years. Aqueous redox flow battery (ARFB) technology has attracted global attention due to its long life, safety and reliability, and flexible power and capacity design. In the past few decades, various organic and metal-based redox active materials have been proposed. However, to date, only all-vanadium and zinc-based flow batteries among metal-based redox flow batteries have been commercialized. However, all-vanadium flow batteries face the challenge of high vanadium raw material costs, while zinc-based flow batteries have the risk of metal dendrites, which largely hinders their widespread application. In this case, iron-based flow batteries with low-cost conditions are expected to become an attractive candidate battery in flow batteries.

[0003] Electrodes, ion exchange membranes and electrolytes are the basic components of flow battery stacks. The active substances contained in the electrolyte are crucial to flow batteries. The active substances in the electrolyte must have the characteristics of high solubility, good stability and low cost. 2+ / Fe 3+ Redox substances have obvious redox reversibility. In contrast, the negative electrode reaction is the deposition / stripping reaction of Fe on the electrode, which has poor reversibility, and there are many hydrogen evolution side reactions in an acidic environment, which greatly limits the long-term operation of the flow battery. The present invention uses fully soluble iron salts and multidentate ligand chelates to achieve a low-cost, high-energy-density, high-power-density aqueous iron-based flow battery negative electrode electrolyte, which exhibits excellent cycle stability. Summary of the invention

[0004] The purpose of the present invention is to solve the existing shortcomings of iron-based liquid flow battery technology, overcome the limitations of acidic environment, and provide an aqueous iron-based liquid flow battery negative electrode electrolyte solution in the pH range of 7 to 14. The method adopts a complexation method with trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA) and its derivative salt chemicals, and adds a large sterically hindered chelating agent to change the coordination environment around the iron element, wherein the N element and the O element of the trans-CyDTA provide 6 coordination sites to chelate with Fe, avoiding the combination of Fe and -OH to form precipitation, thereby improving the cycle life of the liquid flow battery.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A negative electrode electrolyte for an aqueous iron-based liquid flow battery, characterized in that the raw material components of the electrolyte include a complex formed by an iron salt chemical and a multidentate ligand chelating agent, a supporting electrolyte, and an auxiliary electrolyte; the multidentate ligand chelating agent is one or more of 1,2-cyclohexanediaminetetraacetic acid chemicals.

[0007] The iron salt chemicals are selected from one or more of ferric chloride, ammonium ferric sulfate, ferric sulfate, ferric nitrate, and ferric acetate; the 1,2-cyclohexanediaminetetraacetic acid chemicals are selected from one or more of trans-1,2-cyclohexanediaminetetraacetic acid (i.e., trans-CyDTA), cis-1,2-cyclohexanediaminetetraacetic acid (i.e., cis-CyDTA), 1,2-cyclohexanediaminetetraacetic acid monohydrate, disodium 1,2-cyclohexanediaminetetraacetic acid, tetrasodium 1,2-cyclohexanediaminetetraacetic acid hydrate, and potassium 1,2-cyclohexanediaminetetraacetic acid hydrate, preferably trans-1,2-cyclohexanediaminetetraacetic acid. The supporting electrolyte in the electrolyte is selected from one or more of potassium carbonate, sodium carbonate, lithium carbonate, lithium hydroxide, sodium hydroxide, and potassium hydroxide; the auxiliary electrolyte is selected from one or more of potassium chloride, potassium nitrate, sodium nitrate, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate.

[0008] The concentration of iron salt chemicals in the electrolyte is 0-2 mol / L and not 0, preferably in the range of 0.5-1.0 mol / L; the multidentate ligand chelating agent is 0.8-1.2 times the molar number of the iron element, preferably 1 times. The concentration of the supporting electrolyte is 0-10 mol / L, preferably 0-6 mol / L, and more preferably 1-4 mol / L; the concentration of the auxiliary electrolyte is 0-1 mol / L; and the pH range of the electrolyte is 7-14.

[0009] The method for preparing the negative electrode electrolyte of the all-iron aqueous liquid flow battery is characterized by comprising the following process steps:

[0010] Step 1) nitrogen is introduced into the reactor to exhaust the air, and an appropriate amount of supported electrolysis is added to deionized water and stirred thoroughly until completely dissolved;

[0011] Step 2) Add appropriate amounts of iron salt, multidentate ligand chelating agent and auxiliary electrolyte to the supporting electrolyte solution obtained in step 1, stir thoroughly until completely dissolved, mix thoroughly and let stand for 6 to 48 hours before use.

[0012] The operating temperature of the aqueous iron-based liquid flow battery is 10-70°C.

[0013] Compared with the prior art, the present invention has the following significant advantages and beneficial effects:

[0014] 1. The present invention uses chelation coordination to form a ligand compound between an iron-containing salt and a CyDTA-type chelating agent in an alkaline environment. Since CyDTA itself contains 6 coordination sites, which just meet the coordination structure of Fe, the amount of ligand used is reduced, thereby reducing the process cost.

[0015] 2. The chelate compound formed by the synthesized CyDTA and Fe in the present invention has high solubility, which increases the concentration of active substances, thereby increasing the energy density of the flow battery and reducing the overall investment cost; at the same time, the chelate compound is stable in nature and is not easy to precipitate iron.

[0016] 3. The improvement of the overall ionic strength in the present invention improves the conductivity of the electrolyte, reduces the ohmic polarization of the flow battery, and improves the energy efficiency of the battery.

[0017] In summary, the present invention prepares an aqueous iron-based liquid flow battery negative electrode electrolyte by complexing an iron-containing salt with a price advantage and a CyDTA-type chelating agent. This electrolyte can maintain a stable solution state for a long time in a neutral or alkaline environment without precipitation, has stable performance, high conductivity, and a simple synthesis process and low cost, and has the potential for large-scale application in iron-based liquid flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the coordination of the chelate synthesized in Example 1.

[0019] Figure 2 The cyclic voltammetry test results of the negative electrode electrolyte in Example 1 are shown.

[0020] Figure 3 The cyclic voltammetry results of the negative electrode electrolyte in Example 1 are 500 times.

[0021] Figure 4 The charge and discharge capacity-cycle curve of the electrolyte in Example 1 within 100 cycles

[0022] Figure 5 The charge and discharge efficiency-cycle curve of the electrolyte in Example 1 within 100 cycles.

[0023] Figure 6 The energy efficiency test results of Examples 2 and 3 are shown. DETAILED DESCRIPTION

[0024] The present invention is described in detail below through specific examples, but the use and purpose of these exemplary embodiments are only used to illustrate the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to these.

[0025] Embodiment 1:

[0026] In this embodiment, the negative electrode electrolyte iron salt uses ferric chloride, the chelating agent is trans-1,2-cyclohexanediaminetetraacetic acid, potassium carbonate is the supporting electrolyte, sodium chloride is the auxiliary electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of ferric chloride is 0.5 mol / L, the concentration of trans-1,2-cyclohexanediaminetetraacetic acid is 0.5 mol / L, and the final pH of the solution is ~9.

[0027] The specific steps for preparing the electrolyte are as follows: weigh 207g of potassium carbonate in a reactor filled with an inert gas atmosphere, add an appropriate amount of oxygen-free deionized water and stir thoroughly for 0.5h, then put the weighed 135g of ferric chloride, 182g of trans-1,2-cyclohexanediaminetetraacetic acid and 58g of sodium chloride into the above reactor to dissolve and stir thoroughly for 1h to prepare an electrolyte solution with an active substance of 0.5mol / L, and let it stand for 12h before use.

[0028] In the flow battery test, the positive electrolyte uses a solution containing 0.5 mol / L potassium ferrocyanide and 3 mol / L potassium hydroxide. Take a suitable volume of the prepared electrolyte and put it into the positive and negative electrode storage tanks of the all-iron flow battery for testing. The all-iron flow battery system includes a single cell, positive and negative electrode storage tanks, a peristaltic pump, a corrosion-resistant circulation pipeline, and a battery testing system. Among them, the single cell components include: aluminum end plate, polytetrafluoroethylene gasket, collector plate, graphite bipolar plate, fluororubber gasket, proton exchange membrane, and graphite felt electrode. The graphite felt electrode size is 3cm×3cm, and a 2mm empty groove is left between the upper and lower edges and the gasket to act as a buffer. Nafion212 is used as the proton exchange membrane. After the battery is assembled, the inert gas is filled into the entire battery system pipeline to avoid inactivation of active substances and deterioration of alkaline electrolyte. Connect to the battery test system and start the peristaltic pump test.

[0029] The schematic diagram of the chelate coordination in this embodiment is as follows Figure 1 As shown, the Fe atom coordinates with 2 N atoms and 4 O atoms respectively to form a stable chelate structure.

[0030] The above negative electrode electrolyte was subjected to cyclic voltammetry test (25°C), and the results are as follows Figure 2 As shown. In 2~50mV·s -1 In the scan rate range of , the peak current density shows a regular linear change relationship, and the ratio is close to 1, proving that its redox reversibility is good. In addition, the cyclic voltammetry curve of the electrolyte after 500 cycles is shown in Figure 3 As shown, the results show that the CV curves have almost no change within 500 cycles, demonstrating its excellent redox stability.

[0031] The assembled flow battery was subjected to 100 charge and discharge cycle tests. The charge and discharge capacity curves of the 100 cycles are shown in Figure 4As shown in Figure 1, the capacity first decreases and then stabilizes in 100 cycles. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of the 100 charge and discharge cycle tests are shown in Figure 1. Figure 5 As shown in the figure, CE is close to 100% within 100 cycles, proving its good stability. As VE gradually decreases, EE also decreases. During the reaction, polarization increases slightly, resulting in a gradual increase in voltage efficiency loss.

[0032] Embodiment 2:

[0033] In this embodiment, the negative electrode electrolyte iron salt uses ferric nitrate, the chelating agent is cis-1,2-cyclohexanediaminetetraacetic acid, sodium hydroxide is the supporting electrolyte, sodium nitrate is the auxiliary electrolyte, and oxygen-free deionized water is the solvent. Among them, the concentration of ferric nitrate is 0.8 mol / L, the concentration of cis-1,2-cyclohexanediaminetetraacetic acid is 0.8 mol / L, and the final pH of the solution is ~10.

[0034] The specific steps for preparing the electrolyte are as follows: weigh 180g of sodium hydroxide in a reactor filled with an inert gas atmosphere, add an appropriate amount of oxygen-free deionized water and stir thoroughly for 0.5h, then put the weighed 194g of ferric nitrate, 292g of cis-1,2-cyclohexanediaminetetraacetic acid and 43g of sodium chloride into the above reactor to dissolve and stir thoroughly for 2h to prepare an electrolyte solution with an active substance of 0.8mol / L, and let it stand for 12h before use.

[0035] In the flow battery test, the positive electrode electrolyte used was a solution containing 0.5 mol / L potassium ferrocyanide and 3 mol / L potassium hydroxide. After all the components of the single cell were assembled, the remaining conditions were the same as in Example 1. The inert gas filled the entire battery system to avoid inactivation of active substances and deterioration of alkaline electrolyte. The battery test system was connected and the peristaltic pump was started to start the test. The energy efficiency results of the test are shown in Figure 1. Figure 6 shown.

[0036] Embodiment 3:

[0037] In this embodiment, the main components of the negative electrode electrolyte include: ferric sulfate, disodium cyclohexanediaminetetraacetic acid as a ligand, lithium hydroxide as a supporting electrolyte, sodium sulfate as an auxiliary electrolyte, and oxygen-free deionized water as a solvent. Among them, the concentration of ferric sulfate is 0.8 mol / L, the concentration of disodium cyclohexanediaminetetraacetic acid is 1.2 mol / L, and the final pH is ~12.

[0038] The specific steps for preparing the negative electrode electrolyte are as follows:

[0039] The specific steps for preparing the electrolyte are as follows: weigh 72g of lithium hydroxide in a reactor filled with an inert gas atmosphere, add an appropriate amount of deionized water to dissolve and stir thoroughly for 1h, put the weighed 160g of ferric sulfate, 468g of disodium cyclohexanediaminetetraacetate and 58g of sodium chloride into a reactor filled with an inert gas atmosphere, stir thoroughly for 2h, prepare an electrolyte solution with an active substance of 0.8mol / L, and use it after standing for 24h.

[0040] The positive electrode electrolyte is mainly composed of 0.8 mol / L lithium ferrocyanide and 3 mol / L lithium hydroxide. After all the components of the single cell are assembled, the remaining conditions are the same as in Example 1. The inert gas fills the entire battery system to avoid inactivation of active substances and deterioration of alkaline electrolyte. Connect the battery test system and start the peristaltic pump test. The energy efficiency results of the test are as follows: Figure 6 shown.

Claims

1. An aqueous iron-based liquid flow battery negative electrode electrolyte, characterized in that: The raw material components of the negative electrode electrolyte are a complex formed by an iron salt chemical and a multidentate ligand chelating agent, a supporting electrolyte, and an auxiliary electrolyte; the multidentate ligand chelating agent is one or more of 1,2-cyclohexanediaminetetraacetic acid chemicals; The iron salt chemical is selected from one or more of ferric chloride, ammonium ferric sulfate, ferric sulfate, ferric nitrate, and ferric acetate; The 1,2-cyclohexanediaminetetraacetic acid chemicals are selected from one or more of trans-1,2-cyclohexanediaminetetraacetic acid, cis-1,2-cyclohexanediaminetetraacetic acid, 1,2-cyclohexanediaminetetraacetic acid salt monohydrate, 1,2-cyclohexanediaminetetraacetic acid disodium, 1,2-cyclohexanediaminetetraacetic acid tetrasodium hydrate, and 1,2-cyclohexanediaminetetraacetic acid potassium hydrate; The supporting electrolyte in the electrolyte is selected from one or more of potassium carbonate, sodium carbonate, lithium carbonate, lithium hydroxide, sodium hydroxide and potassium hydroxide; The auxiliary electrolyte is selected from one or more of potassium chloride, potassium nitrate, sodium nitrate, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate; At the same time, the pH range of the electrolyte is 9~14.

2. The negative electrode electrolyte of an aqueous iron-based liquid flow battery according to claim 1, characterized in that: The concentration of iron salt chemicals in the electrolyte is 0 ~ 2 mol / L and not 0; the multidentate ligand chelating agent is 0.8 ~ 1.2 times the molar number of iron element; the concentration of supporting electrolyte is 0 ~ 10 mol / L; and the concentration of auxiliary electrolyte is 0 ~ 1 mol / L.

3. The negative electrode electrolyte of an aqueous iron-based liquid flow battery according to claim 2, characterized in that: The concentration of iron salt chemicals in the electrolyte is 0.5 ~ 1.0 mol / L; the multidentate ligand chelating agent is 1 times the molar number of iron element; and the concentration of supporting electrolyte is 0 ~ 6 mol / L.

4. The negative electrode electrolyte of an aqueous iron-based liquid flow battery according to claim 2, characterized in that: The concentration of supporting electrolyte is 1 ~ 4 mol / L.

5. A method for preparing a negative electrode electrolyte for an aqueous iron-based liquid flow battery according to any one of claims 1 to 4, characterized in that: The process steps include: Step 1) nitrogen is introduced into the reactor to exhaust the air, and an appropriate amount of supported electrolysis is added to deionized water and stirred thoroughly until completely dissolved; Step 2) Add appropriate amounts of iron salt, multidentate ligand chelating agent and auxiliary electrolyte to the supporting electrolyte solution obtained in step 1, stir thoroughly until completely dissolved, mix thoroughly and let stand for 6 to 48 hours before use.

6. Use of the negative electrode electrolyte of an aqueous iron-based liquid flow battery as claimed in any one of claims 1 to 4, as the negative electrode electrolyte of an aqueous iron-based liquid flow battery, with an operating temperature of 10 to 70 °C.

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