Electrolyte of high-capacity aqueous iron-europium flow battery and preparation method of electrolyte

Abstract

The invention discloses an electrolyte of a high-capacity aqueous iron europium flow battery and a preparation method of the electrolyte, and belongs to the technical field of flow battery energy storage. The main component of the positive electrode electrolyte is iron-containing salt. And the supporting electrolyte is used for adjusting and stabilizing the pH environment of the electrolyte. After the trivalent europium is coordinated with the organic phosphine chelating agent, the solubility is relatively high, and the characteristics of high capacity and high performance are realized. A battery voltage window of about 1.5 V may be provided. When trivalent europium is reduced into divalent europium, good reversibility is shown, and redox reaction kinetics is improved. The chelating agent is large in molecular size, and after the chelating agent is stably coordinated with metal ions, transmembrane transportation of active substances is reduced, so that the stability and efficiency of the flow battery are improved, and the service life of the flow battery is prolonged. The device can be widely applied to large-scale energy storage in the new energy fields of wind power, photovoltaic and the like, and has a wide application prospect in small energy storage devices such as new energy electric vehicles, industrial standby power supplies, charging stations and the like.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically an electrolyte for a high-capacity aqueous iron-europium flow battery. This patented solution can be widely applied to large-scale energy storage in new energy fields such as wind power and photovoltaics, accelerating the utilization of renewable energy. It also has broad application prospects in small-scale energy storage devices such as new energy electric vehicles, industrial backup power supplies, and charging station energy storage. Background Art

[0002] Currently, fossil energy is becoming increasingly depleted. To meet this severe challenge, building a new power system based on renewable energy is a major trend. In this system, energy storage technology plays a vital role in the efficient utilization of renewable energy. As renewable energy (solar, wind, hydro, hydrogen, biomass, etc.) continues to grow in share of energy consumption, the development of new electrochemical energy storage technologies is urgent. This technology can store large amounts of electrical energy while mitigating the intermittent fluctuations of renewable energy, and is crucial to the survival and development of the national power grid. Redox flow batteries are an electrochemical energy storage technology that operates primarily on the reversible electrochemical reaction of redox-active substances in the negative and positive electrode regions.

[0003] Currently, the most mature and commercially viable flow battery on the market is the all-vanadium flow battery. However, due to the relatively high production and development costs of vanadium, and the need to fully utilize renewable energy and meet its energy storage requirements, the design and development of new flow battery electrolytes remains a critical task. China possesses the world's largest rare earth reserves and production, accounting for 35.4% and 69.2% of the global total, respectively. Its abundant rare earth element resources play a crucial role in the rare earth industry chain. Rare earth elements can be widely used in large-scale energy storage in new energy sectors such as wind power and photovoltaics, accelerating the utilization of renewable energy. They also have broad application prospects in small-scale energy storage devices, such as new energy electric vehicles, industrial backup power supplies, and charging station energy storage.

[0004] The electrolyte of aqueous iron-europium flow battery is a rare earth redox flow battery composed of trivalent europium and organic phosphine chelating agent as negative electrode and ferrocyanide as positive electrode. 3+The organic phosphine chelate added to the electrolyte shifts the electrochemical window of trivalent europium and improves the kinetics of redox reactions. The large molecular size of the chelate reduces the transmembrane transport of active substances after stable coordination with metal ions, avoiding cross-contamination of active substances, thereby improving the stability, efficiency, and life of the flow battery. Its performance was tested using an electrochemical workstation and a blue light system. The electrochemical workstation showed that after trivalent europium was coordinated with the organic phosphine chelate, the theoretical voltage shifted by -0.6V compared to the uncoordinated state. Test results in the blue light system also showed that the iron-europium flow battery has high energy density and power density. Summary of the Invention

[0005] The present invention develops a method for preparing an electrolyte for a high-capacity aqueous iron-europium flow battery. An organic phosphine chelating agent is added to the electrolyte, and the chelating agent forms a stable coordination structure with active ions, thereby improving the stability, efficiency and cycle life of the battery.

[0006] The present invention adopts the following technical solutions:

[0007] A high-capacity aqueous iron-europium flow battery electrolyte, characterized in that: the negative electrode electrolyte is an aqueous solution of europium, which contains trivalent europium ions and a chelating agent, and the chelating agent is one or more of ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, and aminotrimethylenephosphonic acid; the negative electrode electrolyte also contains a supporting electrolyte.

[0008] The positive electrode electrolyte is an aqueous solution of ferrocyanide, and the ferrocyanide used in the positive electrode is one or more of potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, and ammonium ferrocyanide. The positive electrode electrolyte also contains an auxiliary electrolyte.

[0009] In the negative electrode electrolyte: the molar concentration corresponding to the trivalent europium ion is 0 to 2.0 mol / L and is not 0, preferably 0.2 to 1.6 mol / L; the chelating agent is selected from one or more of ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, and aminotrimethylenephosphonic acid, and the molar concentration of the chelating agent is 0 to 5.0 mol / L and is not 0, preferably 0.2 to 3.2 mol / L; the molar concentration of the supporting electrolyte is 0 to 15.0 mol / L, preferably 0.8 to 12.8 mol / L; and oxygen-free deionized water is used as the solvent.

[0010] In the positive electrode electrolyte: the molar concentration of divalent iron ions is 0 to 5.0 mol / L and not 0, preferably 0.1 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 8.0 mol / L, preferably 0.1 to 4.0 mol / L, and oxygen-free deionized water is used as the solvent.

[0011] The europium salt chemicals are one or more of europium phosphonate, europium chloride, europium nitrate, europium sulfate, europium oxalate and europium citrate.

[0012] The ferrocyanide chemicals are one or more of potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, and ammonium ferrocyanide.

[0013] The supporting electrolyte is one or more of potassium carbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, potassium hydroxide, and sodium hydroxide; the auxiliary electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate.

[0014] The high-capacity aqueous iron-europium flow battery electrolyte is prepared according to the following process: adding a trivalent europium active substance to the negative electrode reactor, then adding an organic phosphine chelating agent, adding a ferrocyanide active substance to the positive electrode reactor, adding a supporting electrolyte and an auxiliary electrolyte to each reactor respectively, adding deionized water after mixing, and fully stirring at 10°C to 90°C for 3 to 24 hours to prepare a uniform solution, which is then left to stand for 6 hours before use.

[0015] Furthermore, the pH of the negative electrode electrolyte and the positive electrode electrolyte is 6 to 9, which is neutral.

[0016] The suitable operating temperature of the aqueous iron-europium liquid flow battery electrolyte is 10-90°C.

[0017] A high-capacity aqueous iron-europium flow battery, comprising the negative electrode electrolyte and the positive electrode electrolyte described in the above-mentioned high-capacity aqueous iron-europium flow battery electrolyte; comprising positive and negative electrodes, a battery separator, and a current collector; the positive and negative electrode materials are selected from one of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth inert materials, and one of Nafion117, Nafion115, Nafion212, and Nafion211 is used as the battery separator.

[0018] Negative electrode reaction: Eu 3+ +e - →Eu 2+

[0019] Positive electrode reaction: Fe 2+ -e - →Fe 3+

[0020] The total battery reaction is: Eu 3+ +Fe 2+ →Eu 2+ +Fe 3+

[0021] Discharge is the reverse reaction of the above reaction.

[0022] Beneficial results of the present invention:

[0023] 1. The present invention coordinates a europium salt with a chelating agent to form a stable coordination structure. This coordination effect increases the solubility of the europium salt and, consequently, the capacity of the electrolyte, resulting in a high-capacity electrolyte. This improves battery efficiency, stability, and cycle life.

[0024] 2. The negative electrode electrolyte of the present invention is rare earth metal ions, which are coordinated by a chelating agent with a large molecular size to solve the cross-contamination caused by the transmembrane transport of active ions and improve the energy efficiency of the battery.

[0025] 3. The negative electrode electrolyte of the present invention has slow kinetics. After modification by the chelating agent, the redox kinetics are accelerated. Compared with the iron-europium flow battery without the chelating agent, the Eu 3+ Electrochemical window, steadily improving battery performance.

[0026] 4. The negative electrode electrolyte used in the present invention is low-cost and easy to operate. Europium, as a rare earth metal, has abundant reserves and production in China and can be widely used in large-scale energy storage in new energy fields such as wind power and photovoltaics, accelerating the utilization of renewable energy.

[0027] 5. The positive and negative electrolytes used in the present invention are suitable for use at room temperature, are non-toxic and corrosive, and effectively improve the operating stability and safety of the battery. The theoretical voltage of the iron-europium liquid flow battery can reach 1.5V, which improves the energy density and power density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a high-capacity aqueous iron-europium flow battery device.

[0029] Figure 2 This is the cyclic voltammogram of the positive and negative electrode electrolytes in Example 1 at 10mV / s.

[0030] Figure 3 The cyclic voltammetry curve of Example 1 within 10-50 mV / s is shown in FIG.

[0031] Figure 4 The cyclic voltammetry curve of Example 2 within 10-50 mV / s is shown in FIG.

[0032] Figure 5 The charge and discharge efficiency-cycle curve of the electrolyte of Example 1 within 1 to 50 cycles.

[0033] Figure 6 It is a visual comparison chart of the dissolution stability of electrolytes without and with chelates;

[0034] On the left is an electrolyte with a temperature of 25°C and a concentration of 1.6 mol / L of europium chloride without the addition of a chelate, and on the right is an electrolyte with a temperature of 25°C and a concentration of 1.6 mol / L of europium chloride with the addition of ethylenediaminetetramethylenephosphonic acid. It can be seen that the electrolyte with the addition of a chelate forms a stable solution and can be used as an electrolyte efficiently, while the europium chloride without the addition of a chelate does not form a stable solution. The solubility of europium chloride in water is very low, and the effective europium ion concentration is low, so a high-capacity electrolyte cannot be formed. DETAILED DESCRIPTION

[0035] 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 do they limit the protection scope of the present invention to them.

[0036] Example 1:

[0037] In this embodiment, the negative electrolyte solution mainly comprises europium chloride, ethylenediaminetetramethylenephosphonic acid, and potassium carbonate, and the solvent is oxygen-free deionized water. The concentration of europium chloride is 1.6 mol / L, the concentration of ethylenediaminetetramethylenephosphonic acid is 3.2 mol / L, and the concentration of potassium carbonate is 12.8 mol / L.

[0038] The positive electrolyte solution mainly comprises potassium ferrocyanide and potassium chloride, and the solvent is oxygen-free deionized water. The concentration of potassium ferrocyanide is 4.0 mol / L, and the concentration of potassium chloride is 4.0 mol / L.

[0039] The specific steps for preparing the negative electrode electrolyte are as follows:

[0040] 58.4 g of europium chloride, 140 g of ethylenediaminetetramethylenephosphonic acid, and 176.8 g of potassium carbonate were added in sequence, mixed, and then added with oxygen-free deionized water. The mixture was stirred for 6 hours to form a uniform solution, which was then diluted to 100 mL and allowed to stand for 24 hours before use.

[0041] The specific steps for preparing the positive electrode electrolyte are as follows:

[0042] 176.8 g of potassium ferrocyanide and 29.6 g of potassium chloride were added in sequence, mixed, and then oxygen-free deionized water was added. The mixture was stirred for 6 hours to make a uniform solution, and the volume was adjusted to 100 mL. The solution was allowed to stand for 24 hours before use.

[0043] Figure 6 On the left is the electrolyte of trivalent europium without chelate at a temperature of 25°C and a concentration of 1.6 mol / L. It is relatively turbid, indicating that there are too many solutes and it is difficult to dissolve. Figure 6The right side shows the negative electrolyte of the iron-europium flow battery with trivalent europium added with ethylenediaminetetramethylenephosphonic acid at a temperature of 25°C and a concentration of 1.6 mol / L. Its color is clear and transparent, indicating that the solute has high solubility. Figure 6 From the comparison between the left and right, we can see that adding chelates to trivalent europium to form coordination can greatly increase the active substance Eu. 3+ The solubility of the active material in water is related to the battery capacity, the number of electrons transferred, and the volume of the solution. Therefore, the number of electrons transferred per unit volume in an aqueous iron-europium flow battery is 1. Adding a chelate to the negative electrolyte can increase the battery capacity by increasing the solubility of the active material, thereby achieving a high-capacity aqueous iron-europium flow battery.

[0044] The electrochemical test of the above negative electrode electrolyte was carried out using an electrochemical workstation, and the results are as follows: Figure 2 , Figure 3 shown.

[0045] Figure 2 The cyclic voltammograms of the positive and negative electrolytes at 10 mV / s show a voltage difference of 1.5 V between the positive and negative electrolytes. Compared to the iron-europium flow battery without the chelating agent, the theoretical voltage shift is -0.6 V. According to the formula "Energy density = (battery theoretical capacity × average voltage) ÷ electrolyte volume; power density = (voltage × current) ÷ electrode area," the iron-europium flow battery with the addition of the chelate can increase its energy density and power density per unit area / unit volume by increasing the voltage under certain current density conditions.

[0046] Figure 3 The cyclic voltammetry curve of the negative electrode electrolyte was scanned at a scan rate of 10 to 50 mV / s. The scanning results showed that it had good reversibility and the redox reaction kinetics of the battery was high.

[0047] The components of a single cell include aluminum end plates, polytetrafluoroethylene gaskets, collector plates, graphite bipolar plates, graphite felt electrodes, fluororubber gaskets, and proton exchange membranes. The single cell is assembled and combined with the positive and negative electrode liquid storage tanks, positive and negative electrode peristaltic pumps, and circulation piping to form a battery testing system.

[0048] Use the BluePower system to test the battery:

[0049] The volume of positive and negative electrolytes is 20 ml each, and the positive and negative electrodes are 3×3 cm 2 Porous carbon felt electrode, proton exchange membrane is Nafion212 membrane. 2 Charged to 1.6V at a current density of 20mA / cm 2 The battery was discharged to 0.01 V at a current density of 100 Ω.

[0050] The reaction needs to be carried out under the protection of inert gas. After 50 cycles, the charge and discharge are still stable. At a high concentration of 1.6 mol / L of active material, it has a high capacity in a volume of 20 mL, and Figure 5 As shown, within 50 cycles, the battery coulombic efficiency remains at 90%, the voltage efficiency and energy efficiency can be stabilized at 80% and 70%, and the battery capacity does not decay.

[0051] Example 2:

[0052] In this embodiment, the negative electrode electrolyte mainly comprises europium chloride, diethylenetriamine penta (methylene phosphonic acid), potassium carbonate, and the solvent is oxygen-free deionized water. The concentration of europium chloride is 0.8 mol / L, the concentration of diethylenetriamine penta (methylene phosphonic acid) is 1.6 mol / L, and the concentration of potassium carbonate is 8.0 mol / L.

[0053] The positive electrolyte solution mainly comprises potassium ferrocyanide and potassium chloride, and the solvent is oxygen-free deionized water. The concentration of potassium ferrocyanide is 4.0 mol / L, and the concentration of potassium chloride is 4.0 mol / L.

[0054] The specific steps for preparing the negative electrode electrolyte are as follows:

[0055] In the reactor, 28.8g of europium chloride and 92.0g of diethylenetriamine penta (methylene phosphonic acid) were added in sequence, mixed, and oxygen-free deionized water was added, followed by 110.4g of potassium carbonate. The mixture was stirred for 3 hours to form a uniform solution, which was transferred to a 100ml volumetric flask, fixed to volume, and allowed to stand for 6 hours before use.

[0056] The specific steps for preparing the positive electrode electrolyte are as follows:

[0057] 168.8 g of potassium ferrocyanide and 29.6 g of potassium chloride were added in sequence, mixed, and then oxygen-free deionized water was added. The mixture was stirred for 6 hours to make a uniform solution, and the volume was adjusted to 100 mL. The solution was allowed to stand for 24 hours before use.

[0058] The electrochemical test of the above negative electrode electrolyte was carried out using an electrochemical workstation, and the results are as follows: Figure 4 The cyclic voltammetry curve was scanned at a scan rate of 10 to 50 mV / s, and the scanning results showed that it had good redox reaction kinetics.

[0059] Use the BluePower system to test the battery:

[0060] The volume of positive and negative electrolytes is 20 ml each, and the positive and negative electrodes are 3×3 cm 2 Porous carbon felt electrode, proton exchange membrane is Nafion212 membrane. 2 Charged to 1.6V at a current density of 20mA / cm 2The battery was discharged to 0.01 V at a current density of 100 Ω.

[0061] The reaction needs to be carried out under the protection of inert gas. Table 1 shows the comparison of battery test results after 50 cycles of various embodiments.

[0062] Table 1 is a comparison of the battery test results after 50 cycles of each embodiment.

[0063] sample CE / % VE / % EE / % Example 1 90.2％ 79.4％ 70.2％ Example 2 89.6％ 68.2％ 65.3％ .

Claims

1. A high-capacity aqueous iron-europium flow battery electrolyte, characterized in that: The negative electrode electrolyte is an aqueous solution of europium, which contains trivalent europium ions and one or more chelating agents selected from ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, and aminotrimethylenephosphonic acid; and further contains a supporting electrolyte. The positive electrode electrolyte is a ferrocyanide aqueous solution; the iron salt chemicals used in the positive electrode are one or more of potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, and ammonium ferrocyanide; and it also contains auxiliary electrolytes.

2. The high-capacity aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: In the negative electrode electrolyte: the molar concentration corresponding to the trivalent europium ion is 0 to 2.0 mol / L and is not 0, preferably 0.2 to 1.5 mol / L; the molar concentration of the chelating agent is 0 to 4.0 mol / L and is not 0, preferably 0.2 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L, preferably 0.8 to 6.4 mol / L; and oxygen-free deionized water is used as the solvent.

3. The high-capacity aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: In the positive electrode electrolyte: the molar concentration of divalent iron ions is 0-2.0 mol / L and not 0, preferably 0.1-2.0 mol / L; the molar concentration of the auxiliary electrolyte is 0-8.0 mol / L, preferably 0.1-2.0 mol / L, and oxygen-free deionized water is used as the solvent.

4. A high-capacity aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 3, characterized in that: The europium salt chemicals are one or more of europium phosphonate, europium chloride, europium nitrate, europium sulfate, europium oxalate, and europium citrate; Ferrocyanide chemicals are one or more of potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, and ammonium ferrocyanide; The supporting electrolyte is one or more of potassium carbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, potassium hydroxide, and sodium hydroxide; the auxiliary electrolyte is one or more of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, ammonium sulfate, potassium nitrate, and sodium nitrate.

5. A high-capacity aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 4, characterized in that: The pH of the negative electrode electrolyte and the positive electrode electrolyte is 6 to 9, which is neutral.

6. A high-capacity aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 4, characterized in that: The operating temperature of the electrolyte is 10-90°C.

7. A method for preparing a high-capacity aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 4, characterized in that: In the negative electrode reactor, add the active substance of trivalent europium, then add the organic phosphine chelating agent, add the supporting electrolyte and the auxiliary electrolyte, add deionized water after mixing, stir thoroughly for 3 to 24 hours at 10°C to 90°C to make a uniform solution, let it stand for 6 hours before use; in the positive electrode reactor, add the active substance of ferrocyanide, add the supporting electrolyte and the auxiliary electrolyte, add deionized water after mixing, stir thoroughly for 3 to 24 hours at 10°C to 90°C to make a uniform solution, let it stand for 6 hours before use.

8. A high-capacity aqueous iron-europium flow battery, comprising the negative electrode electrolyte and the positive electrode electrolyte described in any one of claims 1 to 4; comprising positive and negative electrodes, a battery separator, and a current collector; the positive and negative electrode materials are selected from one of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth inert materials, and one of Nafion117, Nafion115, Nafion212, and Nafion211 is used as the battery separator.

9. The high-capacity aqueous iron-europium flow battery according to claim 8, characterized in that: Negative electrode reaction: Eu 3+ +e - →Eu 2+ Positive electrode reaction: Fe 2+ -e - →Fe 3+ The total battery reaction is: Eu 3+ +Fe 2+ →Eu 2+ +Fe 3+ Discharge is the reverse reaction of the above reaction.

10. The high-capacity aqueous iron-europium flow battery according to claim 8, characterized in that: It is used in large-scale energy storage in new energy fields such as wind power and photovoltaics, as well as in small energy storage devices such as new energy electric vehicles, industrial backup power supplies, and charging stations.

Images