A membrane-free static alkaline zinc-iron battery

Abstract

This invention relates to a membrane-free static alkaline zinc-iron battery. On one hand, this invention utilizes a vacuum filtration method to deposit high-specific-surface-area carbon material with a specific concentration gradient into the electrode. The adsorption of ferricyanide ions by the carbon material ensures that the active material generated during charging is mainly concentrated at the bottom of the electrode, reducing self-discharge caused by ferricyanide ions diffusing to the negative electrode and reacting directly with zinc. On the other hand, it utilizes the magnetic property of ferricyanide by applying an external magnetic field to the membrane-free static alkaline zinc-iron battery. The magnetic field induces ferricyanide ions, reducing their diffusion to the negative electrode. Through these methods, a high-efficiency membrane-free static zinc-iron battery is constructed.

Description

Technical Field

[0001] This invention relates to a membraneless static alkaline zinc-iron battery. Background Technology

[0002] With the increasing depletion of fossil fuels, the development and utilization of renewable energy sources such as wind and solar power have become a focus of attention for countries worldwide. However, wind and solar power are discontinuous and unstable due to weather and other factors, which can impact the power grid during grid connection, affecting power quality and grid stability. Energy storage technology can solve this problem, ensuring the efficient and stable operation of renewable energy generation connected to the grid. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among them, chemical energy storage, represented by flow batteries, has the greatest advantage in large-scale energy storage due to its many advantages, such as independent power and capacity, rapid response, simple structure, ease of design, long cycle life, and environmental friendliness. Alkaline zinc-iron flow batteries use abundant zinc and iron as active materials, featuring low cost (~$100 / kWh) and high open-circuit voltage (1.74V), showing great application prospects in the energy storage field, especially in distributed energy storage. However, zinc-iron flow batteries require circulation pumps at both the positive and negative electrodes to drive the electrolyte circulation, which increases system losses, reduces battery energy density, and also complicates the system and increases costs. The use of separators in the battery further increases system costs and affects cycle life. In addition, the limited variety of separators available for alkaline flow batteries restricts the development of alkaline zinc-iron flow batteries.

[0003] Membrane-less batteries have attracted widespread attention due to their advantages such as low cost, simple structure, and ease of design. Currently developed systems include hydrobromide membrane-less batteries, zinc-bromide membrane-less batteries, zinc-cerium membrane-less batteries, zinc-nickel membrane-less batteries, and lead-acid membrane-less batteries. Summary of the Invention

[0004] The technical problem to be solved by this invention (the purpose of the invention)

[0005] This invention proposes a membrane-free static zinc-iron battery. To achieve this, the invention employs two methods: First, a high-specific-surface-area carbon material with a specific concentration gradient is deposited in the electrode using a vacuum filtration method. The adsorption of ferricyanide by the carbon material concentrates the active material generated during charging primarily at the bottom of the electrode, reducing self-discharge caused by ferricyanide diffusing to the negative electrode and reacting directly with zinc. Second, the magnetic property of ferricyanide is utilized by applying an external magnetic field to the membrane-free static alkaline zinc-iron battery. The magnetic field induces ferricyanide diffusion to reduce its diffusion to the negative electrode. Through these methods, a high-efficiency membrane-free static zinc-iron battery is constructed.

[0006] The complete technical solution provided by this invention

[0007] A membraneless static alkaline zinc-iron battery includes a storage box, a positive electrode current collector, a positive electrode, a negative electrode, and a negative electrode current collector;

[0008] The positive and negative electrodes are placed alternately in a sealed storage box. A positive electrode current collector is provided on the side of the positive electrode away from the negative electrode, and the positive electrode current collector is in contact with the positive electrode. A negative electrode current collector is provided on the side of the negative electrode away from the positive electrode, and the negative electrode current collector is in contact with the negative electrode.

[0009] The electrolyte is filled in the storage box, so that the space between the positive and negative electrodes is filled with electrolyte;

[0010] A magnetic field generating device is installed on the outside of the liquid storage box on the side away from the negative electrode and the positive electrode.

[0011] An electrolyte inlet with a sealed cap is provided above the storage box. Electrolyte is added into the storage box through the inlet so that all or part of the positive and negative electrodes are in the electrolyte.

[0012] Grooves with the same or equivalent thickness as the current collector are provided on the inner wall of the liquid storage box near the positive and negative electrodes respectively. One edge or opposite two edges of the flat positive electrode current collector and the negative electrode current collector are inserted into the grooves respectively to fix the positive electrode current collector and the negative electrode current collector respectively.

[0013] One side surface of the flat positive electrode current collector is attached to the inner wall of the liquid storage box; so that the flat positive electrode current collector is placed between the magnetic field generating device and the positive electrode, forming a magnetic field region on the positive electrode side facing the negative electrode.

[0014] The positive electrode is bonded and fixed to the plate-shaped positive electrode current collector using conductive adhesive, and the negative electrode is bonded and fixed to the negative electrode current collector using conductive adhesive.

[0015] Above the positive and negative current collectors, there is an electrode tab that extends through the upper wall of the liquid storage box and out of the liquid storage box. The position where the electrode tabs intersect with the liquid storage box through the upper wall of the liquid storage box is sealed with epoxy resin.

[0016] The positive and negative electrode materials are respectively flat carbon felt or flat graphite felt, placed parallel to each other in a storage box. The positive and negative current collectors are respectively graphite plates. One surface of the flat carbon felt or flat graphite felt serving as the positive electrode material is deposited with carbon material; the side with the deposited carbon material faces the positive current collector. The carbon material is one or more of porous activated carbon, graphene, carbon nanotubes, fullerene, and carbon black.

[0017] The deposition process involves depositing carbon materials dispersed in a solution onto a carbon felt or graphite felt electrode as a positive electrode using vacuum filtration. Before filtration, the carbon materials are uniformly dispersed in an ultrasonic cleaner using isopropanol as a solvent and Nafion as a binder. The mass ratio of carbon materials to binder is 10:1-5:1, and the mass-volume ratio of carbon materials to solvent is 1:15-1:30 (g:ml).

[0018] A magnetic field generating device is provided on the positive electrode side away from the negative electrode; the magnetic field generating device is a permanent magnet and / or an electromagnet, with a magnetic field strength between 100-600 mT, preferably between 500-600 mT. The distance between the positive and negative electrodes of the membraneless alkaline zinc-iron flow battery is 3-9 mm.

[0019] The positive and negative electrodes of the membraneless alkaline zinc-iron flow battery use the same electrolyte; static means that the electrolyte filled in the storage box is in a non-flowing state.

[0020] Beneficial effects of the technical solution of this invention

[0021] 1. A separator-less alkaline zinc-iron battery is proposed to solve the problem of separator limitations in alkaline zinc-iron batteries. The battery reduces costs by eliminating the need for a separator.

[0022] 2. During the charging and discharging operation of the diaphragm-less alkaline zinc-iron battery, the battery does not use a circulation pump, reducing system losses and simplifying the battery system structure; at the same time, the end-plate-less structure design simplifies the battery structure and eliminates the need for fasteners.

[0023] 3. By combining the pre-deposition of high specific surface area carbon materials with a certain concentration gradient with the application of an external magnetic field, the diffusion of ferricyanide to the negative electrode is reduced, the battery self-discharge is reduced, and the battery cycle performance is improved. Attached Figure Description

[0024] Figure 1 A schematic diagram of a membrane-free static alkaline zinc-iron battery;

[0025] Among them: 1. Magnetic field generating device; 2. Positive electrode tab; 3. Liquid storage box groove; 4. Positive electrode; 5. Liquid storage box; 6. Negative electrode; 7. Negative electrode tab; 8. Liquid filling port. Detailed Implementation

[0026] A zinc-iron battery includes a storage box, a positive electrode current collector, a positive electrode, a negative electrode, and a negative electrode current collector. The electrodes are in contact with the current collector through conductive adhesive.

[0027] Example 1

[0028] Weigh 2g of porous activated carbon, 4.44g of 5% Nafion solution, and 40ml of isopropanol, and ultrasonically disperse until homogeneous. Pour the dispersion evenly onto a surface with an effective area of ​​9cm².2 Vacuum filtration is performed on the carbon felt, and the material is dried for use as the positive electrode. The negative electrode is a flat carbon felt.

[0029] The composition of both the positive and negative electrode electrolytes is 0.7 mol / L. -1 Na₄Fe(CN)₆ + 0.7 mol L -1 K4Fe(CN)6+0.1ol L - 1 KOH + 0.1 mol L -1 NaOH and 0.6 mol L -1 Na₂Zn(OH)₄ + 5mol L -1 A 1:1 volume ratio NaOH solution was used, and a magnetic field of 500 mT was applied externally to the battery. The magnetic field was at 10 mA / cm². -2 Charge for 10 minutes under the given current density, then cut off the voltage, at 10 mA / cm². -2 Discharged to 0.1V under the current density conditions.

[0030] By employing pre-deposited carbon material electrodes and applying an external magnetic field, the membraneless zinc-iron flow battery exhibited excellent performance, with a CE of 95%, VE of 84%, and EE of 80%. The battery showed no significant performance degradation after 100 cycles.

[0031] Example 2

[0032] Weigh 2g of porous activated carbon, 4.44g of 5% Nafion solution, and 40ml of isopropanol, and ultrasonically disperse until homogeneous. Pour the dispersion evenly onto a surface with an effective area of ​​9cm². 2 Vacuum filtration is performed on the carbon felt, and the material is dried for use as the positive electrode. The negative electrode is a flat carbon felt.

[0033] The composition of both the positive and negative electrode electrolytes is 0.7 mol / L. -1 Na₄Fe(CN)₆ + 0.7 mol L -1 K4Fe(CN)6+0.1ol L - 1 KOH + 0.1 mol L -1 NaOH and 0.6 mol L -1 Na₂Zn(OH)₄ + 5mol L -1 A 1:1 volume ratio NaOH solution was used, and magnetic field strengths of 0 mT, 100 mT, 200 mT, 300 mT, 400 mT, 500 mT, and 600 mT were applied externally to the battery. The magnetic field strength was 10 mA / cm². -2 Charge for 10 minutes under the given current density, then use voltage cutoff as the condition, 10mA cm -2 Discharged to 0.1V under the current density conditions.

[0034] The battery performance is as follows when different magnetic fields are applied:

[0035] 0 85 84 71 100 90 84 76 200 91 84 76 300 92 84 77 400 94 84 79 500 95 84 80 600 95 84 80

[0036] When the magnetic field strength is 0 mT, the battery's charge-discharge (CE) is only 85%, mainly due to the ferricyanide ions generated during charging diffusing to the negative electrode and reacting directly with zinc, causing self-discharge. As the magnetic field strength increases, the battery's CE gradually increases, primarily because the introduction of the magnetic field reduces the diffusion of ferricyanide ions to the negative electrode, thus reducing self-discharge. When the magnetic field strength exceeds 500 mT, the battery performance remains unchanged.

[0037] Comparative Example 1 (Blank carbon felt + magnetic field 500mT)

[0038] The composition of both the positive and negative electrode electrolytes is 0.7 mol / L. -1 Na₄Fe(CN)₆ + 0.7 mol L -1 K4Fe(CN)6+0.1ol L - 1 KOH + 0.1 mol L -1 NaOH and 0.6 mol L -1 Na₂Zn(OH)₄ + 5mol L -1 A 1:1 volume ratio NaOH solution was used, and a magnetic field of 500 mT was applied externally to the battery. The positive and negative electrodes were flat carbon felt plates. The magnetic field strength was 10 mA cm⁻¹. -2 Charge for 10 minutes under the given current density, then use voltage cutoff as the condition, 10mA cm -2 Discharged to 0.1V under the current density conditions.

[0039] Under a 500mT magnetic field, when no carbon material is deposited inside the positive electrode, the battery's emission coefficient (CE) is only 89%. This is mainly because the diffusion of ferricyanide to the negative electrode is intensified when no carbon material is pre-deposited inside the electrode, leading to self-discharge caused by the direct reaction of ferricyanide with zinc. When carbon material is deposited on the electrode, the battery's CE increases by 6%, indicating that the deposition of carbon material further reduces the diffusion of ferricyanide to the negative electrode and reduces the battery's self-discharge.

[0040] Comparative Example 2 (Immersed Electrode + Magnetic Field 500mT)

[0041] Weigh 2g of porous activated carbon, 4.44g of 5% Nafion solution, and 40ml of isopropanol, and ultrasonically disperse until homogeneous. The effective area is 9cm². 2 The carbon felt is immersed in the dispersion and then dried for later use.

[0042] The composition of both the positive and negative electrode electrolytes is 0.7 mol / L. -1Na₄Fe(CN)₆ + 0.7 mol L -1 K4Fe(CN)6+0.1ol L - 1 KOH + 0.1 mol L -1 NaOH and 0.6 mol L -1 Na₂Zn(OH)₄ + 5mol L -1 A 1:1 volume ratio NaOH solution was used, and a magnetic field of 500 mT was applied externally to the battery. The positive and negative electrodes were flat carbon felt plates. The magnetic field strength was 10 mA cm⁻¹. -2 Charge for 10 minutes under the given current density, then use voltage cutoff as the condition, 10mA cm -2 Discharged to 0.1V under the current density conditions.

[0043] Under a 500 mT magnetic field, the cell using carbon-impregnated electrodes exhibited a CE of 92%, VE of 84%, and EE of 77%. Compared to electrodes prepared using a vacuum filtration method, the cell CE was reduced by 3%. This is mainly because the vacuum filtration method, with the carbon-deposited side of the electrode facing the positive current collector, better helps reduce Fe(CN)6 content. 3- Diffusion towards the negative electrode side.

Claims

1. A diaphragm-less static alkaline zinc-iron flow battery, characterized in that: Includes a liquid storage box, a positive electrode current collector, a positive electrode, a negative electrode, and a negative electrode current collector; Static refers to the electrolyte filling the storage box being in a non-flowing state; The positive and negative electrodes are placed alternately in a sealed storage box. A positive electrode current collector is provided on the side of the positive electrode away from the negative electrode, and the positive electrode current collector is in contact with the positive electrode. A negative electrode current collector is provided on the side of the negative electrode away from the positive electrode, and the negative electrode current collector is in contact with the negative electrode. The electrolyte is filled in the storage box, so that the space between the positive and negative electrodes is filled with electrolyte; A magnetic field generating device is installed outside the liquid storage box on the side away from the negative electrode; an external magnetic field is applied to the outside of the diaphragm-free static alkaline zinc-iron flow battery to reduce the diffusion of ferricyanide to the negative electrode by the induction effect of the magnetic field on ferricyanide; the magnetic field strength is between 100-800mT. The positive electrode material and the negative electrode material are respectively flat carbon felt or flat graphite felt. The positive and negative electrodes are placed parallel to each other in the liquid storage box. The positive electrode current collector and the negative electrode current collector are respectively graphite plates. Carbon material is deposited on one side of the flat carbon felt or flat graphite felt that serves as the positive electrode material. The side with the deposited carbon material faces the side of the positive electrode current collector. The carbon material is one or more of porous activated carbon, graphene, carbon nanotubes, fullerene, and carbon black; the deposition process involves depositing the carbon material dispersed in the solution onto a carbon felt or graphite felt electrode as a positive electrode using vacuum filtration. Before filtration, the carbon material is uniformly dispersed in an ultrasonic cleaner using isopropanol as a solvent and Nafion as a binder; the mass ratio of carbon material to binder is 10:1-5:1, and the mass-volume ratio of carbon material to solvent (g:ml) is 1:15-1:

30.

2. The battery according to claim 1, characterized in that: The storage box is a sealed container with a filling port with a sealing cap on the top. Electrolyte is added into the storage box through the filling port so that all or part of the positive and negative electrodes are in the electrolyte.

3. The battery according to claim 1, characterized in that: On the inner wall of the liquid storage box, grooves with the same or equivalent thickness as the plate-shaped current collector are provided on both sides near the positive and negative electrodes. One edge or opposite two edges of the plate-shaped positive electrode current collector and the plate-shaped negative electrode current collector are respectively inserted into the grooves to fix the positive electrode current collector and the negative electrode current collector respectively. One side surface of the flat positive electrode current collector is attached to the inner wall of the liquid storage box; so that the flat positive electrode current collector is placed between the magnetic field generating device and the positive electrode, forming a magnetic field region on the positive electrode side facing the negative electrode. The positive electrode is bonded and fixed to the plate-shaped positive electrode current collector using conductive adhesive, and the negative electrode is bonded and fixed to the negative electrode current collector using conductive adhesive.

4. The battery according to claim 1, characterized in that: Above the positive and negative current collectors, there is an electrode tab that extends through the upper wall of the liquid storage box and out of the liquid storage box. The position where the electrode tabs intersect with the liquid storage box through the upper wall of the liquid storage box is sealed with epoxy resin.

5. The battery according to claim 1, characterized in that: The magnetic field generating device is a permanent magnet and / or an electromagnet, with a magnetic field strength between 500-600 mT.

6. The battery according to any one of claims 1-5, characterized in that: The distance between the positive and negative electrodes of the membraneless static alkaline zinc-iron flow battery is 3-9 mm.

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