Aqueous iron europium flow battery and preparation method of electrolyte

Abstract

The invention discloses a water-based iron europium flow battery and a preparation method of electrolyte, and belongs to the field of batteries. The positive electrode electrolyte comprises ferric salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte and oxygen-free deionized water. The negative electrode electrolyte comprises europium salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte and oxygen-free deionized water; the chelating agent is at least one of iminodisuccinic acid, succinic acid, N, N '-ethylenediamine disuccinic acid, aspartic acid, nitrilotriacetic acid, ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, trans-1, 2-cyclohexanediamine tetraacetic acid, 1, 3-propanediamine tetraacetic acid, N-(2-ethoxyl) ethylenediamine-N, N', N '-triacetic acid, iminodiacetic acid or derivative chemicals thereof. The iron-europium flow battery can be used under a neutral condition, is low in cost and simple to prepare, practically ensures stable output of a power system, can also be used as a power supply system of a new energy automobile, and realizes instant recharging by replacing electrolyte.

Description

Technical Field

[0001] The present invention relates to the field of liquid flow battery energy storage technology, specifically a method for preparing an aqueous iron-europium liquid flow battery and an electrolyte. This liquid flow battery can be widely used in power supplies, power grids, user sides and special scenarios, can stabilize the output of power systems, can be combined with solar energy, wind energy, and electric vehicle charging stations to improve the stability of new energy vehicle power systems, and has broad application prospects in the development of new power vehicles. Background Art

[0002] The growing global population and the rapid development of industrial society are accelerating the demand for energy, while the large-scale consumption of fossil fuels will pollute the environment and have an adverse impact on climate change. Renewable energy such as solar energy and wind energy are the focus of solving the above problems. In recent years, the installed capacity of renewable energy has increased faster than ever before. However, renewable energy has the problems of intermittency and volatility and cannot be directly incorporated into the power grid system. It must be stored in the energy storage system and released stably to supply the power grid when necessary. Liquid flow batteries have attracted much attention in the field of energy storage due to their decoupling of power and capacity, high safety, and freedom of site selection.

[0003] It is worth noting that in aqueous flow batteries, water is used as a solvent, which not only reduces costs but also ensures safety. Among them, all-vanadium flow batteries have attracted much attention and related research is very extensive. This type of battery uses the redox reaction of vanadium ions to complete the storage and release of electrical energy. There is no cross-contamination in the whole process, and the cycle life is quite impressive. However, the existing production capacity is limited and it is difficult to meet the huge demand in the field of flow battery electrolytes. In view of this, it is urgent to develop low-cost flow battery electrolyte technology to fill the energy storage needs of flow batteries. All-iron flow batteries have attracted research due to their abundant resources, low cost and safety.

[0004] The electrolyte of the all-iron liquid flow battery can construct a full-solution flow battery through the chelation effect between iron ions and ligands, and the size of the iron complex is larger, thereby reducing the crossover of active substances. In the all-solution all-iron liquid flow battery, the positive electrode electrolyte is generally ferrocyanide, and the negative electrode electrolyte is a chelate formed by trivalent iron ions and other ligands. However, we found that some ligands have limited ability to regulate the negative electrode potential, and the potential of the chelate formed by them moves negatively, and the voltage difference with the battery composed of ferrocyanide is small, which affects the energy density and power density of the battery. At the same time, the negative electrode ligand will cross the ion exchange membrane, causing the occurrence of side reactions in the positive electrode electrolyte and the battery capacity to decay. Summary of the invention

[0005] In view of the problems existing in the above-mentioned flow battery, the present invention provides an aqueous iron-europium flow battery and a method for preparing an electrolyte. The negative electrode electrolyte uses europium ions as active substances. The low redox potential itself is further negatively migrated through the chelation of the ligand, and the electrochemical activity and reversibility between trivalent europium and divalent europium are improved. The active substance of the positive electrode electrolyte is iron ions, and the ligand is consistent with the negative electrode ligand, so as to avoid side reactions of the ligand across the membrane.

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

[0007] An aqueous iron-europium flow battery electrolyte, characterized in that: the positive electrode electrolyte comprises an iron salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte, and oxygen-free deionized water; and the negative electrode electrolyte comprises an europium salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte, and oxygen-free deionized water.

[0008] The selected europium salt is one or more of europium chloride, europium sulfate, europium carbonate, europium acetate, europium nitrate, and europium oxalate, and the selected iron salt is one or more of ferrous chloride, ferrous sulfate, ferrous sulfate, ferrous nitrate, and ferrous acetate. The selected chelating agent is at least one of iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid, aminotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1.2-cyclohexanediaminetetraacetic acid, 1,3-propylenediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, or its derivative chemicals; the positive electrode chelating agent is consistent with the negative electrode chelating agent.

[0009] The selected auxiliary electrolyte is one or more of sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate, potassium nitrate, ammonium chloride, ammonium sulfate, and ammonium carbonate.

[0010] The selected supporting electrolyte is one or more of potassium carbonate, sodium carbonate, lithium carbonate, ammonium carbonate, potassium hydroxide, sodium hydroxide and lithium hydroxide.

[0011] In the positive electrolyte, the concentration of ferrous salt is 0.1-4 mol / L, preferably 0.2-1.5 mol / L, and the molar ratio of the selected chelating agent to ferrous iron is 0.5-4, preferably 1-3. In the negative electrolyte, the concentration of europium salt is 0.1-3 mol / L, preferably 0.2-1.5 mol / L, and the molar ratio of the selected chelating agent to europium is 0.5-4, preferably 1-3.

[0012] The molar concentration of the supporting electrolyte is 0-8.0 mol / L, preferably 1.0-4.0 mol / L, and the dissociated ligand chelates with the active ions; the molar concentration of the auxiliary electrolyte is 0-3.0 mol / L, preferably 0.5-1.5 mol / L, and the conductivity is improved.

[0013] The above-mentioned method for preparing an aqueous iron-europium flow battery and an electrolyte is characterized in that it comprises the following steps:

[0014] 1) adding iron salt or europium salt and chelating agent into a corresponding reactor containing oxygen-free deionized water, heating the reactor to a temperature of 20 to 100° C., and stirring the reactor for 2 to 10 hours;

[0015] 2) Then, add the supporting electrolyte into the corresponding reactor, heat to 20-100° C., stir for 2-10 hours, adjust the volume, and let stand;

[0016] 3) Add auxiliary electrolyte, measure and adjust pH to obtain the required electrolyte.

[0017] The suitable pH range of the electrolyte is 4-9.

[0018] The electrolyte is used at a temperature of 10 to 70°C.

[0019] An aqueous iron-europium flow battery, characterized in that it comprises the above-mentioned positive and negative electrolytes, a positive electrode, a negative electrode and a diaphragm. The electrodes and the electrolyte are separated by a diaphragm into two positive and negative chambers, and the electrolyte is transported and circulated by a pump. The positive or negative electrode material is a porous carbon material electrode, selected from one of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth inert materials. The diaphragm is a Nafion membrane, selected from one of Nafion117, Nafion115, Nafion212, and Nafion211.

[0020] Beneficial results of the present invention:

[0021] 1. The novel iron-europium liquid flow battery of the present invention uses a ligand compound formed by the chelation of the ligand in the positive and negative electrolytes, which avoids the metal dendrite problem of the iron in the positive electrolyte and improves the electrochemical activity and reversibility of the europium ions in the negative electrolyte. At the same time, the chelate itself has a large molecular size and is difficult to pass through the ion exchange membrane, thereby improving the stability of the iron-europium liquid flow battery.

[0022] 2. In the present invention, the positive and negative electrolytes are prepared using the same chelating agent ligand, thereby eliminating electrolyte contamination caused by transmembrane transport of the ligand and reducing capacity loss caused by side reactions.

[0023] 3. The chelating agent ligand adjusts the negative movement of the iron ion potential to a smaller extent, but when combined with the low-potential europium ion, it can be adjusted to a more negative potential, and its ligand compound is more suitable as the negative electrode electrolyte. The iron-europium liquid flow battery has a high power density and can maintain a high coulombic efficiency at a high current density. After that, the performance remains stable when the current density is changed to a low current density.

[0024] 4. The iron-europium liquid flow battery in the present invention can be used in a neutral environment, has low cost, and a simple preparation method. It can be widely used in power supplies, power grids, user sides, and special scenarios to achieve stable output of power systems and improve the stability of new energy power generation systems. It can also be used in new energy vehicle power systems to achieve instant recharging by replacing the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The working principle and structural diagram of the iron-europium liquid flow battery

[0026] Figure 2 Before and after adding the ligand to the negative electrode electrolyte of Example 1, the -1 Cyclic voltammetry curves inside.

[0027] Figure 3 The positive electrode electrolyte of Example 2 is 10-50 mV·s -1 Cyclic voltammetry curves inside.

[0028] Figure 4 Example 1: Fe-Eu liquid flow battery at 100 mA cm -2 Efficiency and capacity-cycle curves.

[0029] Figure 5 Example 1 Iron-Europium flow battery at 40 mA cm -2 Efficiency and capacity-cycle curves. DETAILED DESCRIPTION

[0030] 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.

[0031] Embodiment 1:

[0032] like Figure 1 As shown, the novel iron-europium flow battery system of the present invention includes a single cell, positive and negative electrode storage tanks, positive and negative electrode peristaltic pumps, a circulation pipeline and a battery testing system. During the charging process, the divalent iron chelate in the positive electrode electrolyte loses electrons and becomes a trivalent iron chelate; the trivalent europium chelate in the negative electrode electrolyte gains electrons and becomes a divalent europium chelate. The discharge process is the opposite.

[0033] In this embodiment, the main components of the positive electrolyte include: ferrous sulfate, diethylenetriaminepentaacetic acid, a supporting electrolyte of potassium carbonate, an auxiliary electrolyte of sodium chloride, and a solvent of oxygen-free deionized water. Among them, the concentration of ferrous chloride is 0.2 mol / L, the concentration of diethylenetriaminepentaacetic acid is 0.4 mol / L, the concentration of potassium carbonate is 1 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0034] The specific steps for configuring the positive electrode electrolyte are as follows:

[0035] Nitrogen was introduced into the reactor to exhaust the air, 5.5 g of ferrous chloride and 15.8 g of diethylenetriaminepentaacetic acid were mixed and added to the reactor containing oxygen-free deionized water, heated and stirred, and the heating temperature was set to 40°C for 1 hour. 13.8 g of potassium carbonate and 2.9 g of sodium chloride were mixed and added, and oxygen-free deionized water was added after mixing, and stirred for 6 hours to make a uniform solution, and the volume was adjusted to 100 mL, and it was allowed to stand for 24 hours, and the pH was adjusted to about 7.

[0036] The main components of the negative electrode electrolyte include: europium chloride, diethylenetriaminepentaacetic acid, supporting electrolyte is potassium carbonate, auxiliary electrolyte is sodium chloride, and the solvent is oxygen-free deionized water. Among them, the concentration of europium chloride is 0.2mol / L, the concentration of diethylenetriaminepentaacetic acid is 0.4mol / L, the concentration of potassium carbonate is 1mol / L, and the concentration of sodium chloride is 0.5mol / L.

[0037] The specific steps for configuring the negative electrode electrolyte are as follows:

[0038] Nitrogen was introduced into the reactor to exhaust the air, 7.3 g of europium chloride and 15.8 g of diethylenetriaminepentaacetic acid were mixed and added to the reactor containing oxygen-free deionized water, heated and stirred, and the heating temperature was set to 40°C for 1 hour. 13.8 g of potassium carbonate and 2.9 g of sodium chloride were mixed and added, and after mixing, oxygen-free deionized water was added, stirred for 6 hours to make a uniform solution, fixed to 100 mL, and allowed to stand for 24 hours, and the pH was adjusted to about 7.

[0039] No ligand was added to the negative electrode electrolyte. 7.3 g of europium chloride was added to a reactor containing oxygen-free deionized water and the volume was fixed to 100 ml. Only electrochemical testing was performed.

[0040] The above negative electrode electrolyte was divided into two parts according to whether there was a ligand or not, and electrochemical tests were performed on each part for comparison. The results are shown in Figure 2. Figure 2 As shown in the figure, after the europium electrolyte is chelated by the ligand, the redox potential moves negatively and can eventually reach about -1.35 V. And when the cyclic voltammetry curve is scanned at a scan rate of 10 to 50 mV / s, the curve shape is symmetrical, the peak ratio of the oxidation peak to the reduction peak is close, the peak potential difference is small, and it has good reversibility.

[0041] The above-mentioned negative electrode and positive electrode electrolytes were subjected to battery testing.

[0042] 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. Assemble the single cell and form a battery test system with the positive and negative electrode storage tanks, positive and negative electrode peristaltic pumps, and circulation pipelines.

[0043] Prior to testing, an inert gas is circulated through the battery system to prevent deactivation of the active substances.

[0044] The volume of positive and negative electrolyte is 20ml each, and the positive and negative electrodes are 3×3cm 2 The porous carbon felt electrode and the proton membrane are Nafion 212 membrane. At 100 mA / cm 2 Charged to 1.7V at a current density of 100mA / cm 2 The battery was discharged to 0.4V at a current density of 1.5V and 15 cycles were performed. Figure 4 As shown, the CE of the battery is maintained at about 95%, and the VE and EE are maintained at about 60%. After the test is completed, the test procedure is changed to 40mA / cm 2 The current density is charged to 30 mAh at 40 mA / cm 2 Discharge to 0.4V at a current density of Figure 5 As shown in the figure, the CE of the battery is maintained at about 95%, and the VE and EE are maintained at about 80% and 70% respectively. 2 The performance is excellent at high current density, and it is changed to 40mA / cm 2 The current density remains stable.

[0045] Embodiment 2:

[0046] In this embodiment, the main components of the positive electrolyte include: ferrous chloride, ethylenediaminetetraacetic acid, a supporting electrolyte of potassium carbonate, an auxiliary electrolyte of sodium chloride, and a solvent of oxygen-free deionized water. Among them, the concentration of ferrous chloride is 0.5 mol / L, the concentration of ethylenediaminetetraacetic acid is 1.0 mol / L, the concentration of potassium carbonate is 1.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0047] The main components of the negative electrode electrolyte include: europium chloride, ethylenediaminetetraacetic acid, supporting electrolyte is potassium carbonate, auxiliary electrolyte is sodium chloride, and the solvent is oxygen-free deionized water. Among them, the concentration of europium chloride is 0.5 mol / L, the concentration of ethylenediaminetetraacetic acid is 1.0 mol / L, the concentration of potassium carbonate is 1.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0048] Configuration process reference example 1

[0049] The above electrolyte was subjected to electrochemical and battery tests. The results of the positive electrode electrolyte cyclic voltammetry test are as follows: Figure 3 As shown, the redox potential is around -0.1 V, which is not negative enough, so it is suitable to be the positive electrode electrolyte in the present invention.

[0050] The volume of positive and negative electrolyte is 30ml each, and the positive and negative electrodes are 3×3cm 2 Porous carbon felt electrode, proton membrane is Nafion 117 membrane. At 40mA / cm 2 The current density was charged to 1.7V at 40mA / cm 2 The battery was discharged to 0.4 V at a current density of 1.5 V. The first cycle battery test results are shown in Table 1.

[0051] Embodiment 3:

[0052] In this embodiment, the main components of the positive electrolyte include: ferrous chloride, aminotriacetic acid, a supporting electrolyte of potassium carbonate, an auxiliary electrolyte of sodium chloride, and a solvent of oxygen-free deionized water. Among them, the concentration of ferric chloride is 0.5 mol / L, the concentration of aminotriacetic acid is 1.0 mol / L, the concentration of potassium carbonate is 1.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0053] The main components of the negative electrode electrolyte include: europium chloride, aminotriacetic acid, supporting electrolyte is potassium carbonate, auxiliary electrolyte is sodium chloride, and the solvent is oxygen-free deionized water. Among them, the concentration of europium chloride is 0.5 mol / L, the concentration of aminotriacetic acid is 1.0 mol / L, the concentration of potassium carbonate is 1.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0054] Configuration process reference example 1

[0055] The above electrolytes were subjected to electrochemical and battery tests.

[0056] The volume of positive and negative electrolyte is 30ml each, and the positive and negative electrodes are 3×3cm 2 Porous carbon felt electrode, proton membrane is Nafion 117 membrane. At 40mA / cm 2 The current density was charged to 1.7V at 40mA / cm 2 The battery was discharged to 0.4 V at a current density of 1.5 V. The first cycle battery test results are shown in Table 1.

[0057] Table 1 is a comparison of the first cycle battery test results of each embodiment

[0058]

[0059] The negative adjustment range of the chelating agent ligand on the potential of iron ions alone is small, but after combining with low-potential europium ions, it can accurately adjust the potential more suitable for the negative electrode, making the ligand compound more in line with the needs of the negative electrode. With the help of ligand chelation, the positive and negative electrolytes form chelates, which not only effectively solves the problem of iron metal dendrites at the positive electrode, but also significantly enhances the electrochemical performance of europium ions at the negative electrode. In addition, the chelate molecules are difficult to penetrate the membrane, greatly improving the stability of the battery. The positive and negative electrodes use the same chelating agent ligand to prepare the electrolyte, completely eliminating the pollution caused by the transmembrane transport of the ligand and reducing the capacity loss caused by side reactions. The iron-europium liquid flow battery can be used under neutral conditions, with low cost and simple preparation. It can be widely used in power supplies, power grids, user sides and special scenarios to effectively ensure the stable output of the power system. It can also serve as a power system for new energy vehicles. By replacing the electrolyte, it can be recharged instantly.

Claims

1. An aqueous iron-europium flow battery electrolyte, characterized in that: The positive electrode electrolyte comprises an iron salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte, and oxygen-free deionized water; the negative electrode electrolyte comprises a europium salt, a chelating agent, a supporting electrolyte, an auxiliary electrolyte, and oxygen-free deionized water; The selected chelating agent is at least one of iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid, aminotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propylenediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid or its derivative chemicals; the positive electrode chelating agent is consistent with the negative electrode chelating agent.

2. The aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: The selected europium salt is one or more of europium chloride, europium sulfate, europium carbonate, europium acetate, europium nitrate, and europium oxalate; the selected iron salt is one or more of ferrous chloride, ferrous sulfate, ferrous sulfate, ferrous nitrate, and ferrous acetate.

3. The aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: The selected auxiliary electrolyte is one or more of sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate, potassium nitrate, ammonium chloride, ammonium sulfate, and ammonium carbonate; The selected supporting electrolyte is one or more of potassium carbonate, sodium carbonate, lithium carbonate, ammonium carbonate, potassium hydroxide, sodium hydroxide and lithium hydroxide.

4. The aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: In the positive electrode electrolyte, the concentration of ferrous salt is 0.1-4 mol / L, preferably 0.2-1.5 mol / L, and the molar ratio of the selected chelating agent to ferrous iron is 0.5-4, preferably 1-3.

5. The aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: In the negative electrode electrolyte, the concentration of europium salt is 0.1-3 mol / L, preferably 0.2-1.5 mol / L, and the molar ratio of the selected chelating agent to europium is 0.5-4, preferably 1-3.

6. The aqueous iron-europium flow battery electrolyte according to claim 1, characterized in that: The molar concentration of the supporting electrolyte is 0-8.0 mol / L, preferably 1.0-4.0 mol / L, and the dissociated ligand chelates with the active ions; the molar concentration of the auxiliary electrolyte is 0-3.0 mol / L, preferably 0.5-1.5 mol / L, and the conductivity is improved.

7. A method for preparing an aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: 1) adding iron salt or europium salt and chelating agent into a corresponding reactor containing oxygen-free deionized water, heating the reactor to a temperature of 20 to 100° C., and stirring the reactor for 2 to 10 hours; 2) Then, add the supporting electrolyte into the corresponding reactor, heat to 20-100° C., stir for 2-10 hours, adjust the volume, and let stand; 3) Add auxiliary electrolyte, measure and adjust pH to obtain the required electrolyte. Adjust the pH range to 4-9.

8. Use of an aqueous iron-europium flow battery electrolyte according to any one of claims 1 to 6, which is used in an aqueous iron-europium flow battery, and the operating temperature of the electrolyte is 10 to 70°C.

9. An aqueous iron-europium flow battery, characterized in that: The invention comprises positive and negative electrolytes, a positive electrode, a negative electrode and a diaphragm of an aqueous iron-europium flow battery electrolyte as described in any one of claims 1 to 6; the electrodes and the electrolyte are separated into positive and negative chambers by the diaphragm, and the electrolyte is transported and circulated by a pump.

10. An aqueous iron-europium flow battery according to claim 9, characterized in that: The positive electrode or negative electrode material is a porous carbon material electrode, selected from one of the inert materials of carbon felt, graphite felt, graphite plate, graphite paper, carbon paper, and carbon cloth; the diaphragm is a Nafion membrane, selected from one of Nafion117, Nafion115, Nafion212, and Nafion211.

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