A novel europium-cerium flow battery electrolyte and preparation method thereof

Abstract

A novel europium-cerium flow battery electrolyte and its preparation method belong to the technical field of flow battery energy storage. The theoretical voltage of the novel europium-cerium flow battery is 1.9 V, with higher energy density and power density. The synthesis strategy is to add a chelating agent to a solution containing europium or cerium. The formed chelate has a large molecular size, avoiding cross-contamination caused by the transmembrane of active ions. The presence of the chelating agent can stabilize the reduced state of metal ions and slow down the oxidation reaction of the electrolyte with oxygen. The electrolyte has a low cost, is suitable for use in a neutral environment, and europium and cerium are rare earth metals with rich resource reserves, a complete industrial chain, advanced technology accumulation, and government policy support in China. When combined with a chelating agent to enhance its own redox kinetics, it can be widely applied to photovoltaic energy storage systems and also has broad application prospects in new energy vehicles.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow battery energy storage, and specifically to a preparation method of a novel europium-cerium liquid flow battery electrolyte. The electrolyte has a low cost, is suitable for use in a neutral environment, can be widely applied to photovoltaic energy storage systems, and also has broad application prospects in new energy vehicles. Background Art

[0002] Limited fossil fuel resources and global climate change have stimulated great interest in generating electrical energy from renewable resources. Among them, solar energy and wind energy are the most abundant and easily accessible energy sources. Capturing a small portion of the potential solar and wind energy can greatly contribute to meeting the world's electrical energy demand. However, solar and wind energies are not constant and reliable energy sources, and are characterized by dispersion and intermittency. To ensure the stability and reliability of the power grid, it has become increasingly important to seek efficient and large-scale electrical energy storage systems. Redox flow batteries are considered suitable for large-scale applications due to their modular design, good scalability, and flexible operation.

[0003] Currently, all-vanadium flow batteries have entered the commercial operation stage, are relatively mature, and have received extensive research. However, the demand for liquid flow battery energy storage is large, and developing a preparation method for a novel liquid flow electrolyte can better meet the demand for electrical energy storage. China has rich resource reserves, a complete industrial chain, advanced technology accumulation, and government policy support in rare earth resources, and can be widely applied to photovoltaic energy storage systems.

[0004] The europium-cerium flow battery is an all-rare-earth flow battery with a high theoretical voltage, which improves the power density and energy density of the battery. However, after charging is completed, the divalent europium ions in the solution will be oxidized by air in the negative electrolyte, resulting in self-discharge of the battery, rapid attenuation, and difficulty in continuous operation. Moreover, in general, the oxidation kinetics of europium-cerium batteries is slow, resulting in low Coulomb efficiency and short cycle life. After adding a chelating agent to the electrolyte, not only can the reaction kinetics be accelerated, the electrochemical window be shifted, but also the reduced state of europium ions can be stabilized, and the capacity attenuation caused by reaction with oxygen can be slowed down. Summary of the Invention

[0005] The present invention has developed a preparation method of a novel europium-cerium liquid flow battery electrolyte. By adding a chelating agent to the electrolyte, the chelating agent forms a stable coordination structure with the active ions, which is expected to solve the inactivation of europium ions and improve the stability and cycle life of the battery.

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

[0007] A preparation method of a novel europium-cerium flow battery electrolyte, characterized in that: the negative electrolyte is an aqueous solution of europium, which contains trivalent europium ions and a chelating agent selected from one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals to form a chelate, and also contains a supporting electrolyte and an auxiliary electrolyte.

[0008] The positive electrolyte is an aqueous solution of cerium, which contains trivalent cerium ions and a chelating agent selected from one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals to form a chelate, and also contains a supporting electrolyte and an auxiliary electrolyte.

[0009] In the negative electrolyte: the molar concentration of trivalent europium ions is 0 to 2.0 mol / L and not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of the chelating agent nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals is 0 to 4.0 mol / L and 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; and the solvent is anaerobic deionized water.

[0010] In the positive electrolyte: the molar concentration of trivalent cerium ions is 0 to 2.0 mol / L and not 0, preferably 0.1 to 1.0 mol / L; the molar concentration of chelating agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans - 1,2 - cyclohexanediaminetetraacetic acid, 1,3 - propanediaminetetraacetic acid, N-(2 - hydroxyethyl)ethylenediamine - N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or their derivative chemicals is 0 to 4.0 mol / L and 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; and the solvent is anaerobic deionized water.

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

[0012] The substances corresponding to trivalent cerium ions include 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 preparation method of the novel europium - cerium redox flow battery electrolyte is prepared as follows: in a reactor, add the corresponding active substances of europium or cerium, then add the chelating agent, mix and then add deionized water, heat, and at 20°C to 90°C, add the supporting electrolyte and the auxiliary electrolyte, and stir well for 3 to 24 hours to form a homogeneous solution, and use it after standing for 6 hours.

[0015] Furthermore, the pH of the negative electrolyte or the positive electrolyte is 4 to 9, being slightly neutral.

[0016] The suitable operating temperature of the novel europium - cerium redox flow battery electrolyte is 10 to 80°C.

[0017] The beneficial effects of the present invention:

[0018] 1. In the present invention, cerium salts or europium salts are coordinated with chelating agents to form a stable coordination structure, which is difficult to oxidize in the air, thereby improving the stability and cycle life of the battery.

[0019] 2. The positive and negative electrolytes of the present invention are rare earth metal ions, coordinated with the same chelating agent to form chelate molecules with large sizes, solving the cross - contamination caused by the transmembrane transport of active ions and improving the efficiency of the battery.

[0020] 3. The kinetics of the positive and negative electrolytes of the present invention is slow by itself. After being modified by the chelating agent, the redox kinetics is accelerated. Compared with the europium - cerium flow battery without the chelating agent, a large current density can be adopted, and the current density can be doubled, stably improving the battery performance.

[0021] 4. 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 rich resource reserves in China. They can be widely used in urban energy storage systems, reducing energy costs and improving energy utilization efficiency. They also have broad application prospects in the development of new - type electric vehicles.

[0022] 5. The positive and negative electrolytes used in the present invention are suitable for use under mild conditions, have no corrosion, have low requirements for equipment, effectively improving the operation stability of the battery. The theoretical voltage of the new europium - cerium flow battery is 1.9V, improving the energy density and power density of the battery. Description of the Drawings

[0023] Figure 1 Cyclic voltammogram of the positive and negative electrolytes in Example 2 at 50 mV·s -1

[0024] Figure 2 Coulomb efficiency - cycle curve of the comparative example within 1 - 10 cycles.

[0025] Figure 3 Charge - discharge capacity - cycle curve of the comparative example within 1 - 10 cycles.

[0026] Figure 4 Charge - discharge efficiency and capacity - cycle curve of Example 1 within 1 - 10 cycles.

[0027] Figure 5 Charge - discharge efficiency and capacity - cycle curve of Example 2 within 1 - 40 cycles. Detailed Embodiments

[0028] The present invention will be described in detail below through specific examples. However, the uses and purposes of these exemplified embodiments are only used to illustrate the present invention, and do not constitute any form of limitation to the actual protection scope of the present invention, nor will the protection scope of the present invention be limited thereto.

[0029] Comparative Example:

[0030] In this comparative example, the main components of the negative electrode electrolyte include: europium chloride, methanesulfonic acid, and sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of methanesulfonic acid is 1.0 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0031] The main components of the positive electrode electrolyte include: cerium chloride, methanesulfonic acid, and sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of methanesulfonic acid is 1.0 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0032] The specific steps for preparing the negative electrode electrolyte are as follows:

[0033] Add 7.3 g of europium chloride, 9.6 g of methanesulfonic acid, and 2.9 g of sodium chloride in sequence, add anaerobic deionized water after mixing, stir for 6 hours to make a homogeneous solution, make up the volume to 100 mL, and use it after standing for 24 hours.

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

[0035] Add 7.5 g of cerium chloride, 9.6 g of methanesulfonic acid, and 2.9 g of sodium chloride in sequence, add anaerobic deionized water after mixing, stir for 6 hours to make a homogeneous solution, make up the volume to 100 mL, and use it after standing for 24 hours.

[0036] The single cell components include an aluminum end plate, a polytetrafluoroethylene gasket, a current collector plate, a graphite bipolar plate, a graphite felt electrode, a fluororubber gasket, and a proton exchange membrane. Assemble the single cell and form a battery test system with positive and negative liquid storage tanks, positive and negative peristaltic pumps, and a circulation pipeline.

[0037] Battery test:

[0038] The volume of the positive and negative electrolytes is 20 ml each, and the positive and negative electrodes are both 3×3 cm 2 porous carbon felt electrodes, and the proton membrane is Nafion 212 membrane. Charge to 50 mAh at a current density of 20 mA / cm 2 and discharge to 0.1 V at a current density of 20 mA / cm 2 .

[0039] Without the protection of inert gas, the electrolyte will come into contact with air. For example, Figure 2 , within 1 to 10 cycles, the Coulomb efficiency of the battery decreases from 80% in the first cycle to 20%. For example, Figure 3 , within 1 to 10 cycles, the battery capacity decays rapidly because during the charging process, trivalent europium ions are reduced to divalent europium ions, and the divalent europium ions are quickly oxidized by air and cannot be discharged.

[0040] Example 1:

[0041] In this embodiment, the main components of the negative electrode electrolyte include: europium chloride, diethylenetriaminepentaacetic acid, potassium carbonate, sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of diethylenetriaminepentaacetic acid is 0.2 mol / L, the concentration of potassium carbonate is 0.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0042] The main components of the positive electrode electrolyte include: cerium chloride, diethylenetriaminepentaacetic acid, potassium carbonate, sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of diethylenetriaminepentaacetic acid is 0.2 mol / L, the concentration of potassium carbonate is 0.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0043] The specific steps for preparing the negative electrode electrolyte are as follows:

[0044] In a reactor, 7.3 g of europium chloride and 7.9 g of diethylenetriaminepentaacetic acid are added in sequence. After mixing, deionized water is added, and the mixture is heated. At 90 °C, 6.91 g of potassium carbonate and 2.9 g of sodium chloride are added, and the mixture is stirred well for 3 hours to form a homogeneous solution, which is transferred to a 100 ml volumetric flask for volume fixation and allowed to stand for 6 hours before use.

[0045] The specific steps for preparing the positive electrode electrolyte are as follows:

[0046] In a reactor, 7.5 g of cerium chloride and 7.9 g of diethylenetriaminepentaacetic acid are added in sequence. After mixing, deionized water is added, and the mixture is heated. At 90 °C, 6.91 g of potassium carbonate and 2.9 g of sodium chloride are added, and the mixture is stirred well for 3 hours to form a homogeneous solution, which is transferred to a 100 ml volumetric flask for volume fixation and allowed to stand for 6 hours before use.

[0047] Battery test:

[0048] The volume of the positive and negative electrode electrolytes is 20 ml each, and the positive and negative electrodes are both 3×3 cm 2 porous carbon felt electrodes, and the proton membrane is Nafion 212 membrane. Charge to 50 mAh at a current density of 20 mA / cm 2 and discharge to 0.1 V at a current density of 20 mA / cm 2 .

[0049] Without the protection of inert gas, the electrolyte will come into contact with air. As Figure 4 , within 1 to 10 cycles, the Coulomb efficiency of the battery remains at about 90%, the voltage efficiency and energy efficiency can be stabilized at about 70% and 60% respectively, and the capacity of the battery will not decay. After adding the chelating agent, the divalent europium ions are not easily oxidized, and the performance indicators of the battery in Example 1 are higher than those in the comparative example.

[0050] Example 2:

[0051] In this example, the main components of the negative electrode electrolyte include: europium chloride, nitrilotriacetic acid, potassium carbonate, sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of nitrilotriacetic acid is 0.2 mol / L, the concentration of potassium carbonate is 0.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0052] The main components of the positive electrode electrolyte include: cerium chloride, diaminotriacetic acid, potassium carbonate, sodium chloride, and the solvent is anaerobic deionized water. Among them, the concentration of europium chloride is 0.2 mol / L, the concentration of nitrilotriacetic acid is 0.2 mol / L, the concentration of potassium carbonate is 0.5 mol / L, and the concentration of sodium chloride is 0.5 mol / L.

[0053] The method for preparing the electrolyte refers to Example 1.

[0054] The positive and negative electrode electrolytes are respectively subjected to cyclic voltammetry tests at 50 mV·s -1 As Figure 1 , the theoretical voltage of the single cell is 1.9 V, which can provide higher power density and energy density.

[0055] Battery test:

[0056] The volumes of the positive and negative electrode electrolytes are each 20 ml. The positive and negative electrodes are both 3×3 cm 2 porous carbon felt electrodes, and the proton exchange membrane is Nafion 212 membrane. After the modification with the chelating agent, the reaction kinetics of the electrolyte is accelerated, doubling the current density in the battery test of the comparative example. When charging to 50 mAh at a current density of 40 mA / cm 2 and discharging to 0.1 V at a current density of 40 mA / cm 2 .

[0057] Without the protection of inert gas, the electrolyte will contact with air. As Figure 5 , within 1 to 40 cycles, the Coulombic efficiency of the battery is about 80%, the voltage efficiency and energy efficiency can be stabilized at about 80% and 60% respectively, and the capacity of the battery will not decay.

Claims

1. An electrolyte for an europium-cerium flow battery, characterized in that: The negative electrode electrolyte is an aqueous solution of europium, which contains trivalent europium ions and a chelating agent selected from one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals to form a chelate, and also contains a supporting electrolyte and an auxiliary electrolyte; The positive electrode electrolyte is an aqueous solution of cerium, which contains trivalent cerium ions and a chelating agent selected from one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals to form a chelate, and also contains a supporting electrolyte and an auxiliary electrolyte; The positive and negative electrode electrolytes are coordinated with the same chelating agent; In the negative electrode electrolyte: the molar concentration of trivalent europium ions is 0 to 2.0 mol / L and not 0; the molar concentration of the chelating agent nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals is 0 to 4.0 mol / L and not 0; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L; and the solvent is anaerobic deionized water; In the positive electrode electrolyte: the molar concentration of trivalent cerium ions is 0 to 2.0 mol / L and not 0; the molar concentration of the chelating agent nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid, iminodiacetic acid, iminodisuccinic acid, succinic acid, N,N'-ethylenediaminedisuccinic acid, aspartic acid or its derivative chemicals is 0 to 4.0 mol / L and not 0; the molar concentration of the supporting electrolyte is 0 to 8.0 mol / L; the molar concentration of the auxiliary electrolyte is 0 to 3.0 mol / L; and the solvent is anaerobic deionized water.

2. The europium-cerium flow battery electrolyte according to claim 1, wherein: In the negative electrode electrolyte: the molar concentration of trivalent europium ions is 0.1 to 1.0 mol / L; the molar concentration of the chelating agent is 0.5 to 2.0 mol / L; the molar concentration of the supporting electrolyte is 1.0 to 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0.5 to 1.5 mol / L.

3. The europium-cerium flow battery electrolyte according to claim 1, characterized in that: In the positive electrode electrolyte: the molar concentration of cerium(III) ions is 0.1 - 1.0 mol / L; the molar concentration of the chelating agent is 0.5 - 2.0 mol / L; the molar concentration of the supporting electrolyte is 1.0 - 4.0 mol / L; the molar concentration of the auxiliary electrolyte is 0.5 - 1.5 mol / L.

4. The europium-cerium flow battery electrolyte according to claim 1, characterized in that: The active substance containing europium(III) ions is one or more of europium phosphate, europium chloride, europium nitrate, europium acetate, europium sulfate, and europium carbonate.

5. A europium-cerium flow battery electrolyte according to claim 1, characterized in that: The substance containing cerium(III) ions is one or more of cerium chloride, cerium phosphate, cerium nitrate, cerium carbonate, cerium acetate, and cerium sulfate.

6. The europium-cerium flow battery electrolyte according to claim 1, characterized in that: 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. A method for preparing an electrolyte of an europium-cerium flow battery according to any one of claims 1-6, characterized in that: It is prepared by the following process: in a reactor, add the corresponding active substance of europium or cerium, then add the chelating agent, mix and add deionized water, heat, and at 20°C - 90°C, add the supporting electrolyte and the auxiliary electrolyte, and stir well for 3 - 24 hours to form a homogeneous solution, and use it after standing for 6 hours.

8. The method according to claim 7, wherein The pH of the negative electrode electrolyte or the positive electrode electrolyte is 4 - 9.

9. The method according to claim 7, characterized in that, The operating temperature of the electrolyte is 10 - 80 °C.

10. A europium-cerium flow battery, characterized in that, It includes a europium-cerium redox flow battery electrolyte according to any one of claims 1 - 6; the theoretical voltage of the europium-cerium redox flow battery is 1.9 V.

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