Europium-cerium flow battery electrolyte and preparation method thereof

Abstract

The invention discloses europium-cerium flow battery electrolyte and a preparation method thereof, and belongs to the technical field of flow batteries. The negative electrolyte comprises europium salt and an additive, the positive electrolyte comprises cerium salt and an additive, and the additive comprises a chelating agent containing a phosphate group and supporting and auxiliary electrolyte. The chelating agent provided by the invention is large in molecular weight, and cross contamination caused by active ion transmembrane is avoided. And the additives at the two ends are the same, and the viscosities of the electrolytes at the two electrodes are basically consistent, so that the consistency and stability of the conductivity can be maintained, and the electrochemical reaction in the battery can be performed more uniformly. As a novel flow battery, the europium-cerium flow battery has a higher voltage window in battery voltage, so that the energy density and the power density of the battery are improved. Furthermore, europium ions and cerium ions are matched with the chelating agent, so that the oxidation-reduction kinetics of the catalyst can be improved, and the catalyst also has a wide application prospect in the aspect of novel power automobiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow batteries and relates to a novel electrolyte for europium-cerium liquid flow batteries and a preparation method thereof, and in particular to a preparation method of an electrolyte in which metal ions are coordinated with a chelating agent. Background Art

[0002] Flow battery technology is an effective energy storage technology for addressing the volatility and intermittency of renewable energy systems, primarily wind and photovoltaic power. Its power and capacity are regulated freely, attracting widespread attention. Currently, the more mature flow battery systems primarily include all-vanadium flow batteries. Their application scenarios are becoming increasingly diverse, playing a key role in grid energy storage to stabilize the power grid, peak load shifting and valley shifting in industrial and commercial sectors to reduce electricity costs, and distributed energy systems. This will further expand the market for all-vanadium flow batteries and promote the sustainable development of the industry. However, the high price and cost of vanadium in all-vanadium systems, as well as the low energy density resulting from the low voltage of individual cells, limit their further development and application. Europium-cerium flow battery electrolytes, on the other hand, are inexpensive and have a higher voltage window, resulting in higher energy and power densities. Europium-cerium flow batteries are all-rare earth flow batteries with a high theoretical voltage, which improves the battery's power and energy density. However, after charging, the divalent europium ions in the negative electrode electrolyte are oxidized by air, causing the battery to self-discharge, rapidly degrade, and struggle to maintain sustained operation. Europium-cerium batteries generally exhibit slow oxidation kinetics, resulting in low coulombic efficiency and short cycle life. Adding a chelating agent to the electrolyte increases the electrolyte concentration by coordinating and encapsulating the metal ions, preventing them from reacting with water. The coordination of the chelating agent with the metal ions also alters their redox potential, thereby adjusting the battery's operating voltage and potentially increasing energy density. This electrolyte is suitable for use in neutral environments and can be widely applied in photovoltaic energy storage systems. It also has broad application prospects in new electric vehicles. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a novel europium-cerium flow battery electrolyte and its preparation method. The electrolyte provided by the present invention has simple composition and high acid-base stability. The addition of a chelating agent to the electrolyte forms a stable coordination structure with active ions, potentially resolving europium ion deactivation, improving battery stability and cycle life, and ensuring the long-term stable operation of europium-cerium flow batteries.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] The present invention provides a novel negative electrode electrolyte for a europium-cerium liquid flow battery. The negative electrode electrolyte comprises a solute containing a europium salt and an additive, wherein the additive comprises a chelating agent formed by one or more of N-(phosphomethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid, and diethylenetriaminepentamethylenephosphoric acid or their derivative chemicals, and further comprises a supporting electrolyte and an auxiliary electrolyte.

[0006] The present invention provides a novel cathode electrolyte for a europium-cerium liquid flow battery. The cathode electrolyte comprises a solute of a cerium salt and an additive, wherein the additive comprises a chelating agent formed by one or more of N-(phosphomethyl)iminodiacetic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and diethylenetriaminepentamethylenephosphonic acid or their derivative chemicals, and further comprises a supporting electrolyte and an auxiliary electrolyte.

[0007] In the negative electrode electrolyte: the europium salt corresponds to: trivalent europium, the molar concentration of trivalent europium is 0 to 2.0 mol / L and is not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of the chelating agent N-(phosphomethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or its derivative chemicals is 0 to 4.0 mol / L and is not 0, preferably 0.5 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L, preferably 1.0 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L, preferably 0.5 to 1.5 mol / L; oxygen-free deionized water is used as the solvent.

[0008] In the positive electrode electrolyte: the cerium corresponds to trivalent cerium, the molar concentration of trivalent cerium is 0 to 2.0 mol / L and is not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of the chelating agent N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or their derivative chemicals is 0 to 4.0 mol / L and is not 0, preferably 0.5 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L, preferably 1.0 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L, preferably 0.5 to 1.5 mol / L; oxygen-free deionized water is used as the solvent.

[0009] Preferably, the concentration of the chelating agent is 0.5 to 2.0 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L or 2.0 mol / L, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0010] Preferably, the concentration of the supporting electrolyte is 1.0 to 4.0 mol / L, for example, it can be 1.0 mol / L, 1.5 mol / L, 1.7 mol / L, 2.0 mol / L, 2.5 mol / L, 2.7 mol / L, 3.0 mol / L, 3.5 mol / L or 4.0 mol / L, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0011] The active substance corresponding to trivalent europium is one or more of europium phosphonate, europium chloride, europium nitrate, europium acetate, europium sulfate, and europium carbonate.

[0012] The substance corresponding to trivalent cerium is one or more of cerium chloride, cerium phosphonate, cerium nitrate, cerium carbonate, cerium acetate, and cerium sulfate.

[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, potassium sulfate, sodium sulfate, potassium nitrate, and sodium nitrate to improve the conductivity of the electrolyte.

[0014] The present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising:

[0015] Europium salt or cerium salt, a chelating agent and a solvent are mixed to obtain the negative electrode or positive electrode electrolyte; the solvent is water.

[0016] Preferably, the mixing further includes mixing of a supporting electrolyte.

[0017] Preferably, the mixing includes: firstly mixing europium salt or cerium salt with a solvent to obtain a neutral solution, then mixing a chelating agent with the obtained neutral solution to obtain a primary mixed solution, and finally mixing a supporting electrolyte and an auxiliary electrolyte with the obtained primary mixed solution to obtain an electrolyte.

[0018] Preferably, the final mixing method includes stirring at a temperature of 10 to 80° C. for 3 to 24 hours.

[0019] The final mixing temperature in the present invention is 10-80°C, for example, 10°C, 25°C, 30°C, 40°C, 50°C, 55°C, 60°C, 70°C or 80°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0020] The mixing time in the present invention is 3 to 24 hours, for example, it can be 3 hours, 5 hours, 8 hours, 10 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0021] A novel europium-cerium liquid flow battery is characterized in that it comprises the above-mentioned positive electrode electrolyte and negative electrode electrolyte, and the chelating agent in the positive electrode electrolyte is the same as the chelating agent in the negative electrode electrolyte, including the same substance and the same concentration.

[0022] The electrolyte provided by the present invention includes a chelating agent. First, the chelating agent contains functional groups such as phosphate and carboxyl groups, which have excellent buffering properties, protecting metal ions from excessive protonation and reducing hydrogen and oxygen evolution side reactions, thereby improving the energy and power density of the battery. Second, the chelating agent contains amino groups. The positively charged amino groups adsorb to the nucleation sites of europium or cerium, preventing them from reacting with water and increasing the electrolyte concentration, thereby further improving the stability of the electrolyte.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The electrolyte provided by the present invention includes a chelating agent. First, the chelating agent contains functional groups such as phosphate and carboxyl groups, which have excellent buffering effects, can protect metal ions from excessive protonation, reduce hydrogen evolution and oxygen evolution side reactions, and improve the energy and power density of the battery. Second, the chelating agent contains amino groups. The positively charged amino groups will adsorb to the nucleation sites of europium or cerium, preventing them from reacting with water and increasing the electrolyte concentration, thereby further improving the stability of the electrolyte.

[0025] (2) The electrolyte provided by the present invention has simple components and high acid-base stability. It includes the addition of a chelating agent to the electrolyte, which forms a stable coordination structure with the active ions, and is expected to solve the deactivation of europium ions and cerium ions, improve the stability and cycle life of the battery, and ensure the long-term stable operation of the europium-cerium liquid flow battery.

[0026] (3) When the positive and negative electrolytes of the present invention use the same chelating agent, their viscosity, ion mobility and pH are easier to control to similar levels, reducing uneven pumping energy consumption or concentration polarization caused by differences in fluid properties.

[0027] (4) The positive and negative electrolytes of the present invention have slow kinetics. After modification by the chelating agent, the ion size is increased, the cross contamination of the positive and negative active substances through the membrane is reduced, and the cycle life is extended.

[0028] (5) The positive and negative electrolytes used in the present invention are low-cost and easy to operate. Europium and cerium are rare earth metals with abundant reserves in China. They can be widely used in urban energy storage systems to reduce energy costs and improve energy utilization. They also have broad application prospects in the development of new power vehicles.

[0029] (6) The positive and negative electrolytes used in the present invention are suitable for use under mild conditions, reducing the energy consumption of the temperature control system. The new europium-cerium liquid flow battery has a high voltage window, which improves the energy density and power density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the cyclic voltammetry curve of the positive electrode electrolyte in Example 1 within the range of 10 to 50 mV / s.

[0031] Figure 2 The charge-discharge efficiency and capacity-cycle curves for cycles 1 to 10 of Example 1 are shown.

[0032] Figure 3 This is the cyclic voltammetry curve of the negative electrode electrolyte in Example 2 within 30mV / s.

[0033] Figure 4 For Example 2, the temperature is 10-50 mA / cm 2 The capacity-voltage curve inside. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0035] Example 1

[0036] This embodiment provides a negative electrode electrolyte for a europium-cerium flow battery, wherein the solutes of the negative electrode electrolyte include 0.2 mol / L europium chloride, 0.6 mol / L N-(phosphorylmethyl)iminodiacetic acid, 1.0 mol / L potassium carbonate, and 0.5 mol / L potassium chloride, and the solvent is oxygen-free deionized water; the pH of the negative electrode electrolyte is 7;

[0037] The preparation method of the negative electrode electrolyte is:

[0038] After purging the reactor with nitrogen to remove all air, a mixture of 7.3 g of europium chloride and 13.6 g of N-(phosphorylmethyl)iminodiacetic acid was added to a reactor containing oxygen-free deionized water. The mixture was heated with stirring at 80°C for 2.5 hours. A mixture of 13.8 g of potassium carbonate and 3.7 g of potassium chloride was added, followed by addition of oxygen-free deionized water. The mixture was stirred for 4 hours to form a homogeneous solution. The solution was then diluted to 100 mL and allowed to stand for 24 hours. The pH was adjusted to approximately 7.

[0039] The positive electrode electrolyte mainly comprises: 0.2 mol / L cerium chloride, 0.6 mol / L N-(phosphorylmethyl)iminodiacetic acid, 1.0 mol / L potassium carbonate and 0.5 mol / L potassium chloride, and the solvent is oxygen-free deionized water; the pH of the negative electrode electrolyte is 7;

[0040] The method for preparing the positive electrode electrolyte is:

[0041] After nitrogen was introduced into the reactor to expel air, a mixture of 7.5 g of cerium chloride and 13.6 g of N-(phosphorylmethyl)iminodiacetic acid was added to a reactor containing oxygen-free deionized water. The mixture was heated with stirring at 80°C for 2.5 hours. A mixture of 13.8 g of potassium carbonate and 3.7 g of potassium chloride was added, followed by addition of oxygen-free deionized water. The mixture was stirred for 4 hours to form a homogeneous solution. The solution was then diluted to 100 mL and allowed to stand for 24 hours. The pH was adjusted to approximately 7.

[0042] The electrochemical test of the above cathode electrolyte was carried out, and the results were as follows: Figure 1 The cyclic voltammetry curves were scanned at a scan rate of 10-50 mV / s, and the CV curves showed symmetrical oxidation and reduction peaks, reflecting higher redox reversibility.

[0043] 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.

[0044] After assembling the above components, an inert gas is circulated through the battery system to prevent the active materials from deactivating. The battery is then connected to the battery testing system and testing begins.

[0045] The volume of positive and negative electrolytes is 40 ml each, and the positive and negative electrodes are 3×3 cm -2 The porous carbon felt electrode and the proton membrane are Nafion 117 membrane. 2 Charged to 1.8V at a current density of 20mA / cm 2 The battery is discharged to 0.65V at a current density of 180mA. The single battery has a high charge and discharge cut-off voltage. It has a high power density at a charge and discharge current of 180mA and a high energy density per unit volume. Figure 2 Within 1 to 10 cycles, the battery coulombic efficiency remains at around 80%, and the voltage efficiency and energy efficiency can be stabilized at around 60% and 75% respectively.

[0046] Example 2

[0047] This embodiment provides a negative electrode electrolyte for a europium-cerium flow battery, wherein the solutes of the negative electrode electrolyte include 0.2 mol / L europium chloride, 0.4 mol / L ethylenediaminetetramethylenephosphoric acid, 1.0 mol / L potassium carbonate, and 0.5 mol / L potassium chloride, and the solvent is oxygen-free deionized water; the pH of the negative electrode electrolyte is 7;

[0048] The positive electrode electrolyte mainly comprises: 0.2 mol / L cerium chloride, 0.4 mol / L ethylenediaminetetramethylenephosphoric acid, 1.0 mol / L potassium carbonate and 0.5 mol / L potassium chloride, and the solvent is oxygen-free deionized water; the pH of the negative electrode electrolyte is 7;

[0049] The electrolyte preparation method is shown in Example 1.

[0050] To prevent the active material from deactivating, the negative electrode electrolyte was electrochemically tested after the inert gas filled the entire system. The results are as follows: Figure 3 .

[0051] After the battery system is assembled, other reference conditions are the same as in Example 1. To prevent the active material from deactivating, wait until the inert gas fills the entire battery system. Then connect it to the battery testing system and start testing.

[0052] The volume of positive and negative electrolytes is 40 ml each, and the positive and negative electrodes are 3×3 cm -2 The porous carbon felt electrode and the proton membrane are Nafion 117 membrane. 2 The capacity-voltage graph is obtained by charging to 2V at a current density of 1000V and then discharging to 0.65V at a corresponding current density. The results are as follows: Figure 4 .

Claims

1. A europium-cerium flow battery electrolyte, characterized in that: A negative electrode electrolyte, wherein the solute of the negative electrode electrolyte includes a europium salt and an additive, wherein the additive includes a chelating agent formed by one or more of N-(phosphomethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or their derivative chemicals, and further contains a supporting electrolyte and an auxiliary electrolyte.

2. A europium-cerium flow battery electrolyte, characterized in that: The positive electrode electrolyte comprises a solute of a cerium salt and an additive, wherein the additive comprises a chelating agent formed by one or more of N-(phosphomethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or their derivative chemicals, and further comprises a supporting electrolyte and an auxiliary electrolyte.

3. The europium-cerium flow battery electrolyte according to claim 1, characterized in that: In the negative electrode electrolyte: the europium salt corresponds to: trivalent europium, the molar concentration of trivalent europium is 0 to 2.0 mol / L and is not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of the chelating agent N-(phosphomethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or its derivative chemicals is 0 to 4.0 mol / L and is not 0, preferably 0.5 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L, preferably 1.0 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L, preferably 0.5 to 1.5 mol / L; oxygen-free deionized water is used as the solvent.

4. The europium-cerium flow battery electrolyte according to claim 1, characterized in that: In the positive electrode electrolyte: the cerium corresponds to trivalent cerium, the molar concentration of trivalent cerium is 0 to 2.0 mol / L and is not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of the chelating agent N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylenephosphoric acid and diethylenetriaminepentamethylenephosphoric acid or their derivative chemicals is 0 to 4.0 mol / L and is not 0, preferably 0.5 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L, preferably 1.0 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L, preferably 0.5 to 1.5 mol / L; oxygen-free deionized water is used as the solvent.

5. The europium-cerium flow battery electrolyte according to claim 3 or 4, characterized in that: The concentration of the chelating agent is 0.5 to 2.0 mol / L, and can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L or 2.0 mol / L; The concentration of the supporting electrolyte is 1.0 to 4.0 mol / L, and can be 1.0 mol / L, 1.5 mol / L, 1.7 mol / L, 2.0 mol / L, 2.5 mol / L, 2.7 mol / L, 3.0 mol / L, 3.5 mol / L or 4.0 mol / L.

6. The europium-cerium flow battery electrolyte according to claim 1 or 2, characterized in that: The active substance corresponding to trivalent europium is one or more of europium phosphonate, europium chloride, europium nitrate, europium acetate, europium sulfate, and europium carbonate; The substance corresponding to trivalent cerium is one or more of cerium chloride, cerium phosphonate, cerium nitrate, cerium carbonate, cerium acetate, and cerium sulfate; 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, potassium sulfate, sodium sulfate, potassium nitrate, and sodium nitrate.

7. The europium-cerium flow battery electrolyte according to any one of claims 1 to 6, characterized in that: The operating temperature of the electrolyte is 10-80°C.

8. A method for preparing an electrolyte for a europium-cerium flow battery according to any one of claims 1 to 6, characterized in that: include: The negative electrode or positive electrode electrolyte is obtained by mixing europium salt or cerium salt, a chelating agent and a solvent; the solvent is water; and the mixing also includes mixing of a supporting electrolyte.

9. The method according to claim 8, characterized in that The mixing comprises: firstly mixing the europium salt or the cerium salt with a solvent to obtain a neutral solution, then mixing a chelating agent with the obtained neutral solution to obtain a primary mixed solution, and finally mixing a supporting electrolyte and an auxiliary electrolyte with the obtained primary mixed solution to obtain an electrolyte; The final mixing method includes stirring at a temperature of 10 to 80°C for 3 to 24 hours; The final mixing temperature is 10-80°C, for example, 10°C, 25°C, 30°C, 40°C, 50°C, 55°C, 60°C, 70°C or 80°C. The mixing time is 3 to 24 hours, and can be 3 hours, 5 hours, 8 hours, 10 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours.

10. A new type of europium-cerium flow battery, characterized in that: The invention comprises a positive electrode electrolyte and a negative electrode electrolyte corresponding to any one of claims 1 to 6, wherein the chelating agent in the positive electrode electrolyte is the same as the chelating agent in the negative electrode electrolyte, including the same substance and the same concentration.

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