Europium-cerium flow battery electrolyte and preparation method thereof

Abstract

This invention relates to a europium-cerium flow battery electrolyte and its preparation method, belonging to the field of flow battery technology. The negative electrode electrolyte comprises europium salt and additives, while the positive electrode electrolyte comprises cerium salt and additives. The additives include phosphate-containing chelating agents and supporting and auxiliary electrolytes. The chelating agents provided in this invention have large molecular weights, avoiding cross-contamination caused by active ions crossing the membrane. Furthermore, the additives at both ends are identical, resulting in essentially consistent viscosity of the electrolytes at both electrodes, which helps maintain the consistency and stability of conductivity, allowing for more uniform electrochemical reactions within the battery. As a novel type of flow battery, the europium-cerium flow battery has a higher voltage window, thereby improving the battery's energy density and power density. Moreover, the combination of europium and cerium ions with chelating agents further enhances the redox kinetics, showing broad application prospects in new energy vehicles.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, and relates to a novel electrolyte for europium-cerium flow batteries and its preparation method. In particular, it relates to a method for preparing an electrolyte in which metal ions are coordinated with a chelating agent. Background Technology

[0002] Flow battery technology is an effective energy storage technology for addressing the volatility and intermittency of new energy systems, primarily wind and solar power, and has attracted widespread attention due to its freely adjustable power and capacity. Currently, the most mature flow battery systems include vanadium redox flow batteries. The application scenarios for vanadium redox flow batteries are becoming increasingly diversified, playing a crucial role in grid energy storage for grid stabilization, peak shaving and valley filling to reduce electricity costs in industrial and commercial sectors, and in distributed energy systems. This will further expand the market space for vanadium redox flow batteries and drive the industry's continued development. However, the high price of vanadium and the low energy density caused by the low voltage of individual cells limit the further development and application of vanadium redox systems. In contrast, europium-cerium redox flow batteries have lower costs and a higher voltage window, resulting in higher energy and power densities. Europium-cerium redox flow batteries are all rare-earth flow batteries with a theoretically high voltage, improving the battery's power and energy densities. However, after charging, the divalent europium ions in the negative electrode electrolyte are oxidized by the air, causing self-discharge, rapid degradation, and difficulty in continuous operation. Furthermore, europium-cerium batteries typically exhibit slow oxidation kinetics, leading to low coulombic efficiency and short cycle life. Adding chelating agents to the electrolyte allows them to coordinate and encapsulate metal ions, preventing them from reacting with water and increasing the electrolyte concentration. The coordination between the chelating agent and the metal ions alters the 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, with broad prospects for use in new energy 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 a simple composition and high acid-base stability. Adding a chelating agent to the electrolyte allows it to form a stable coordination structure with the active ions, potentially solving the problem of europium ion deactivation, improving battery stability and cycle life, and ensuring long-term stable operation of the europium-cerium flow battery.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] This invention provides a novel negative electrode electrolyte for a europium-cerium flow battery. The solute in the negative electrode electrolyte includes europium salts and additives. The additives include chelating agents formed from one or more of N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphate, ethylenediaminetetramethylene phosphate, and diethylenetriaminepentamethylene phosphate or their derivatives. The electrolyte also contains a supporting electrolyte and an auxiliary electrolyte.

[0006] This invention provides a novel positive electrode electrolyte for europium-cerium flow batteries. The solute in the positive electrode electrolyte includes cerium salt and additives. The additives include chelating agents formed from one or more of N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylene phosphoric acid, and diethylenetriaminepentamethylene phosphoric acid or their derivatives. The electrolyte also contains a supporting electrolyte and an auxiliary electrolyte.

[0007] In the negative electrode electrolyte: the europium salt corresponds to trivalent europium, with a molar concentration of 0–2.0 mol / L and not 0, preferably 0.1–1.0 mol / L; the chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphate, ethylenediaminetetramethylene phosphate, and diethylenetriaminepentamethylene phosphate or their derivatives have a molar concentration of 0–4.0 mol / L and not 0, preferably 0.5–2.0 mol / L; the supporting electrolyte has a molar concentration of 0–8.0 mol / L, preferably 1.0–4.0 mol / L; the auxiliary electrolyte has a molar concentration of 0–3.0 mol / L, preferably 0.5–1.5 mol / L; and deionized water is used as the solvent.

[0008] In the positive electrode electrolyte: cerium corresponds to trivalent cerium, and the molar concentration of trivalent cerium is 0–2.0 mol / L and not 0, preferably 0.1–1.0 mol / L; the molar concentration of chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylene phosphoric acid, and diethylenetriaminepentamethylene phosphoric acid or their derivatives is 0–4.0 mol / L and not 0, preferably 0.5–2.0 mol / L; the molar concentration of supporting electrolyte is 0–8.0 mol / L, preferably 1.0–4.0 mol / L; the molar concentration of auxiliary electrolyte is 0–3.0 mol / L, preferably 0.5–1.5 mol / L; and 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, other unlisted values ​​within this 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, other unlisted values ​​within this range are also applicable.

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

[0012] The substances corresponding to trivalent cerium are 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] This invention provides a method for preparing the electrolyte according to the first aspect, the method comprising:

[0015] The negative or positive electrode electrolyte is obtained by mixing europium salt or cerium salt, chelating agent and solvent; the solvent is water.

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

[0017] Preferably, the mixing process includes: first, 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 preliminary mixture; and finally, mixing a supporting electrolyte and an auxiliary electrolyte with the obtained preliminary mixture to obtain an electrolyte.

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

[0019] The final mixing temperature described in this invention is 10 to 80°C, for example, it can be 10°C, 25°C, 30°C, 40°C, 50°C, 55°C, 60°C, 70°C or 80°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] The mixing time described in this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] A novel europium-cerium flow battery is characterized by comprising the above-mentioned positive electrolyte and negative electrolyte, wherein the chelating agent in the positive electrolyte and the chelating agent in the negative electrolyte are the same: including the same substances and the same concentration.

[0022] The electrolyte provided by this invention includes a chelating agent. Firstly, 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 / oxygen evolution side reactions; thus improving the battery's energy and power density. Secondly, the chelating agent contains amino groups; the positively charged amino groups adsorb onto the nucleation sites of europium or cerium, preventing them from reacting with water and increasing the electrolyte concentration, thereby further improving the electrolyte's stability.

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

[0024] (1) The electrolyte provided by this invention includes a chelating agent. Firstly, 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 / oxygen evolution side reactions; thus improving the energy and power density of the battery. Secondly, the chelating agent contains amino groups, and the positively charged amino groups adsorb onto 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 a simple composition and high acid and alkali stability. It includes the addition of a chelating agent to the electrolyte. The chelating agent forms a stable coordination structure with the active ions, which 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 europium cerium redox flow battery.

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

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

[0028] (5) The positive and negative electrode electrolytes used in this invention are inexpensive and easy to operate. Europium and cerium are rare earth metals with abundant resources in China. They can be applied on a large scale to urban energy storage systems to reduce energy costs and improve energy utilization. They also have broad application prospects in the development of new energy vehicles.

[0029] (6) The positive and negative electrode electrolytes used in this invention are suitable for use under mild conditions, reducing the energy consumption of the temperature control system. The novel europium-cerium redox flow battery has a high voltage window, which improves the energy density and power density of the battery. Attached Figure Description

[0030] Figure 1 The cyclic voltammetry curves of the positive electrode electrolyte in Example 1 are shown in the range of 10–50 mV / s.

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

[0032] Figure 3 The cyclic voltammetry curves of the negative electrode electrolyte in Example 2 are shown within 30 mV / s.

[0033] Figure 4 Example 2 is at 10–50 mA / cm 2 Capacity-voltage curve within. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0035] Example 1

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

[0037] The method for preparing the negative electrode electrolyte is as follows:

[0038] Nitrogen gas was introduced into the reactor to purge air. 7.3 g of europium chloride and 13.6 g of N-(phosphorylmethyl)iminodiacetic acid were mixed and added to the reactor containing deionized water. The mixture was heated and stirred at 80°C for 2.5 hours. 13.8 g of potassium carbonate and 3.7 g of potassium chloride were then added, followed by deionized water. The mixture was stirred for 4 hours to form a homogeneous solution, which was then brought to a final volume of 100 mL. The solution was allowed to stand for 24 hours, and the pH was adjusted to approximately 7.

[0039] The main components of the positive electrode electrolyte include: 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, with deionized water as the solvent; the pH of the negative electrode electrolyte is 7.

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

[0041] Nitrogen gas was introduced into the reactor to purge air. 7.5g of cerium chloride and 13.6g of N-(phosphorylmethyl)iminodiacetic acid were mixed and added to the reactor containing deionized water. The mixture was heated and stirred at 80℃ for 2.5 hours. 13.8g of potassium carbonate and 3.7g of potassium chloride were then added, followed by deionized water. The mixture was stirred for 4 hours to form a homogeneous solution, which was then brought to a final volume of 100mL. The solution was allowed to stand for 24 hours, and the pH was adjusted to approximately 7.

[0042] Electrochemical tests were performed on the above-mentioned positive electrode electrolyte, and the results are as follows: Figure 1 Cyclic voltammetry curves were scanned within a scan rate of 10–50 mV / s, and their CV curves showed symmetrical oxidation and reduction peaks, demonstrating higher redox reversibility.

[0043] The single-cell components include aluminum end plates, polytetrafluoroethylene gaskets, current collectors, graphite bipolar plates, graphite felt electrodes, fluororubber gaskets, and proton exchange membranes. The single-cell is assembled and, together with positive and negative electrode reservoirs, positive and negative electrode peristaltic pumps, and circulation piping, forms a battery testing system.

[0044] After assembling the above components, an inert gas is first circulated within the battery system to prevent deactivation of the active materials. Then, the battery testing system is connected, and testing begins.

[0045] The electrolyte volume for both positive and negative electrodes is 40 ml, and both electrodes are 3×3 cm. -2 A porous carbon felt electrode with a Nafion 117 proton exchange membrane was used. At 20 mA / cm²... 2 Charged to 1.8V at a current density of 20mA / cm 2 It discharges to 0.65V at a current density, has a high single-cell charge / discharge cutoff voltage, high power density at a charge / discharge current of 180mA, and high energy density per unit volume. For example... Figure 2 Within 1 to 10 cycles, the battery coulombic efficiency remains at around 80%, while the voltage efficiency and energy efficiency remain stable at around 60% and 75%, respectively.

[0046] Example 2

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

[0048] The main components of the positive electrode electrolyte include: 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, with deionized water as the solvent; the pH of the negative electrode electrolyte is 7.

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

[0050] To prevent deactivation of the active material, after the inert gas had completely filled the entire system, an electrochemical test was performed on the above-mentioned negative electrode electrolyte. The results are as follows: Figure 3 .

[0051] After assembling the battery system, other reference conditions are the same as in Example 1. To prevent deactivation of active materials, wait until the entire battery system is filled with inert gas. Then connect to the battery testing system and begin testing.

[0052] The electrolyte volume for both positive and negative electrodes is 40 ml, and both electrodes are 3×3 cm. -2 A porous carbon felt electrode with a Nafion 117 proton exchange membrane was used. The values ​​ranged from 10 to 50 mA / cm². 2 The capacitor is charged to 2V at a given current density, and then discharged to 0.65V at the corresponding current density. The capacity-voltage diagram is then obtained, and the results are as follows: Figure 4 .

Claims

1. A europium-cerium flow battery electrolyte, characterized in that, The negative electrode electrolyte, wherein the solute comprises europium salts and additives, the additives comprising chelating agents formed from one or more of N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphate, ethylenediaminetetramethylene phosphate, and diethylenetriaminepentamethylene phosphate or their derivatives, and further comprising a supporting electrolyte and an auxiliary electrolyte, wherein the supporting electrolyte is one or more of potassium carbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, potassium hydroxide, and sodium hydroxide; and the auxiliary electrolyte is one or more of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, potassium nitrate, and sodium nitrate.

2. A europium-cerium flow battery electrolyte, characterized in that, The positive electrode electrolyte comprises a cerium salt and additives, wherein the additives include chelating agents formed from one or more of N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphate, ethylenediaminetetramethylene phosphate, and diethylenetriaminepentamethylene phosphate or their derivatives, and further comprises a supporting electrolyte and an auxiliary electrolyte. 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.

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, with a molar concentration of 0–2.0 mol / L and not equal to 0; the chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphate, ethylenediaminetetramethylene phosphate, and diethylenetriaminepentamethylene phosphate or their derivatives have a molar concentration of 0–4.0 mol / L and not equal to 0; the supporting electrolyte has a molar concentration of 0–8.0 mol / L; the auxiliary electrolyte has a molar concentration of 0–3.0 mol / L; and deionized water is used as the solvent.

4. The europium-cerium flow battery electrolyte according to claim 3, characterized in that, The molar concentration of trivalent europium is 0.1–1.0 mol / L; the molar concentration of chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylene phosphoric acid, and diethylenetriaminepentamethylene phosphoric acid or their derivatives is 0.5–2.0 mol / L; the molar concentration of supporting electrolyte is 1.0–4.0 mol / L; and the molar concentration of auxiliary electrolyte is 0.5–1.5 mol / L.

5. A europium-cerium flow battery electrolyte according to claim 2, characterized in that, In the positive electrode electrolyte: cerium corresponds to trivalent cerium, with a molar concentration of 0–2.0 mol / L and not equal to 0; the molar concentration of chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylene phosphoric acid, and diethylenetriaminepentamethylene phosphoric acid or their derivatives is 0–4.0 mol / L and not equal to 0; the molar concentration of supporting electrolyte is 0–8.0 mol / L; the molar concentration of auxiliary electrolyte is 0–3.0 mol / L; and deionized water is used as the solvent.

6. The europium-cerium flow battery electrolyte according to claim 5, characterized in that, The molar concentration of trivalent cerium is 0.1–1.0 mol / L; the molar concentration of chelating agents N-(phosphorylmethyl)iminodiacetic acid, aminotrimethylene phosphoric acid, ethylenediaminetetramethylene phosphoric acid, and diethylenetriaminepentamethylene phosphoric acid or their derivatives is 0.5–2.0 mol / L; the molar concentration of supporting electrolyte is 1.0–4.0 mol / L; and the molar concentration of auxiliary electrolyte is 0.5–1.5 mol / L.

7. The europium-cerium flow battery electrolyte according to claim 3, characterized in that, The active substances corresponding to trivalent europium are one or more of europium phosphonate, europium chloride, europium nitrate, europium acetate, europium sulfate, and europium carbonate.

8. A europium-cerium flow battery electrolyte according to claim 5, characterized in that, The substances corresponding to trivalent cerium are one or more of cerium chloride, cerium phosphonate, cerium nitrate, cerium carbonate, cerium acetate, and cerium sulfate.

9. A europium-cerium flow battery electrolyte according to any one of claims 1-2, characterized in that, The electrolyte operates at a temperature of 10–80 °C.

10. A method for preparing a europium-cerium flow battery electrolyte according to any one of claims 1-2, characterized in that, include: Europium salt or cerium salt, chelating agent and solvent are mixed to obtain the negative or positive electrode electrolyte; the solvent is water; the mixing also includes mixing a supporting electrolyte and an auxiliary electrolyte.

11. The method according to claim 10, characterized in that, The mixing process includes: first, 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 preliminary mixture; and finally, mixing a supporting electrolyte and an auxiliary electrolyte with the obtained preliminary mixture to obtain an electrolyte. The final mixing method includes stirring at a temperature of 10–80 °C for 3–24 h; The final mixing temperature is 10–80 °C; The mixing time is 3 to 24 hours.

12. A novel europium-cerium flow battery, characterized in that, It includes the positive electrode electrolyte corresponding to any one of claims 1, 3-4 and the negative electrode electrolyte corresponding to any one of claims 2, 5-6, wherein the chelating agent in the positive electrode electrolyte and the chelating agent in the negative electrode electrolyte are the same: including the same substance and the same concentration.

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