Multi-layer electrode for flow battery, preparation method of multi-layer electrode and flow battery

Abstract

The invention belongs to the technical field of electrochemical energy storage, and discloses a multi-layer electrode for a flow battery, a preparation method of the multi-layer electrode and the flow battery, the multi-layer electrode comprises a first carbon layer, a carbon felt base material layer and a second carbon layer which are sequentially stacked, the first carbon layer is a carbon layer with a hydrophilic surface and a volume resistivity of less than or equal to 5 * 10 <-Omega > cm < 3 >, and the second carbon layer is a carbon layer with a hydrophilic surface and a volume resistivity of less than or equal to 5 * 10 <-Omega > cm < 3 >. And the second carbon layer is a perforated carbon layer. The multi-layer electrode for the flow battery can solve the problems that an existing flow battery electrode is large in contact resistance and insufficient in ionic membrane side mass transfer, and ohmic polarization cannot be reduced and mass transfer efficiency cannot be improved at the same time, and the energy efficiency of the flow battery under high current density can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a multilayer electrode for flow batteries, its preparation method, and the flow battery itself. Background Technology

[0002] As one of the core directions of large-scale energy storage technology, the electrode performance of flow batteries directly affects their energy efficiency and power density. Currently, the commonly used electrode material in flow batteries is carbon felt, which has the characteristics of large specific surface area and moderate conductivity. However, there are two major problems: (1) The contact interface between carbon felt and bipolar plates has high contact resistance, which leads to increased ohmic polarization of the battery, especially at high current densities (such as above 200 mA / cm²), resulting in significant energy loss; (2) In the carbon felt near the ion membrane side, the diffusion and convection of active materials (such as vanadium ions) are insufficient, resulting in large mass transfer resistance, which leads to limited reaction kinetics and reduced voltage efficiency. The core defect of the existing technology is that it cannot synergistically optimize contact resistance and mass transfer efficiency, resulting in generally low battery energy efficiency at high current densities.

[0003] In existing technologies, the main improvement methods fall into two categories: The first category involves altering the porosity distribution of the carbon felt body. For example, CN117525447A restructures and weaves the carbon felt body to construct a three-level gradient porous electrode, thereby changing the porosity distribution of the carbon felt, promoting the uniform distribution of active materials, and overcoming the constraint between reaction area and mass transport. Another example is CN117059828A, which uses pre-oxidized felt as a precursor for an integrated gradient porosity electrode material. It utilizes thermosetting resins and freeze-drying technology to form different porosities in different thickness regions, followed by carbonization, graphitization, and activation to obtain an integrated gradient porosity electrode material. This results in a more uniform electrolyte flow distribution, improved electrode mass transfer, and reduced battery internal resistance. However, this method only enhances mass transfer and does not solve the interfacial contact problem, resulting in relatively high ohmic polarization. Moreover, the method is relatively complex, costly, and energy-intensive, making large-scale batch production difficult. The second approach involves reducing the contact resistance between the carbon felt and the bipolar plate. For example, CN117423881A coats the surface of a graphite paper bipolar plate with an adhesive, then composites and cures the porous graphite felt electrode with the graphite paper bipolar plate to obtain a composite electrode plate. Finally, the composite electrode plate undergoes carbonization and graphitization treatments to obtain a tightly bonded composite electrode plate where the graphite felt and graphite paper are integrated, increasing the effective contact area between the porous electrode and the bipolar plate and effectively reducing the overall resistance. While this method can reduce contact resistance, methods that solely reduce contact resistance (such as coating modification) often sacrifice electrode porosity, leading to increased mass transfer resistance. However, neither of the above two methods synergistically optimizes contact resistance and mass transfer efficiency.

[0004] Therefore, providing an electrode for flow batteries that solves the problems of high contact resistance, insufficient mass transfer on the ion membrane side, and inability to simultaneously reduce ohmic polarization and improve mass transfer efficiency in existing flow battery electrodes is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, the present invention aims to provide a multilayer electrode for flow batteries, a method for preparing the same, and a flow battery. The multilayer electrode for flow batteries of the present invention solves the problems of high contact resistance, insufficient mass transfer on the ion-membrane side, and the inability to simultaneously reduce ohmic polarization and improve mass transfer efficiency in existing flow battery electrodes, enabling a significant improvement in battery energy efficiency at high current densities.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a multilayer electrode for a flow battery, the multilayer electrode comprising a first carbon layer, a carbon felt substrate layer, and a second carbon layer sequentially stacked thereon, wherein the first carbon layer is hydrophilic and has a volume resistivity ≤5×10⁻⁻⁻⁻⁴ ... 4 Ω・cm 3 The first carbon layer is a carbon layer with perforations.

[0008] The volume resistivity of the first carbon layer in this invention is ≤5×10⁻ 4 Ω・cm 3 For example, it could be 5×10⁻ 4 Ω・cm 3 4.5×10⁻ 4 Ω・cm 3 4×10⁻ 4 Ω・cm 3 3.5×10⁻ 4 Ω・cm 3 3×10⁻ 4 Ω・cm 3 2.5×10⁻ 4 Ω・cm 3 2×10⁻ 4 Ω・cm 3 1.5×10⁻ 4 Ω・cm 3 Or 1×10⁻ 4 Ω・cm 3 wait.

[0009] This invention, for the first time, addresses the differentiated needs of low contact resistance on the bipolar plate side and high mass transfer efficiency on the ion-exchange membrane side by providing a multilayer electrode with a gradient functional design, achieving synergistic optimization of reduced contact resistance and enhanced mass transfer. The technical principle is as follows: The first carbon layer has high conductivity, enabling ohmic polarization of the bipolar plate-electrode interface. Furthermore, the first carbon layer has surface hydrophilicity, allowing the electrolyte to more uniformly wet the electrode surface, increasing the solid-liquid contact area, and promoting the diffusion and mass transfer of active ions (such as vanadium ions) on the electrode surface, thereby reducing concentration polarization and improving battery efficiency. The carbon felt substrate, as the main reaction region, undertakes the electron conduction of the first carbon layer and the transport of active materials from the second carbon layer. The carbon felt substrate provides sufficient reaction surface area to ensure efficient electrochemical reactions. The second carbon layer has a porous structure, which enhances the diffusion and convection of active materials on the ion-exchange membrane side, reducing mass transfer resistance, and retains the conductivity of the carbon layer, resolving the contradiction of simultaneously achieving conductivity and mass transfer.

[0010] The multilayer electrode of this invention simultaneously satisfies low ohmic loss and high mass transfer efficiency. When applied to flow batteries, it can maintain high energy efficiency and voltage efficiency even at high current densities (e.g., 200 mA / cm²), breaking through the performance bottleneck of existing technologies at high current densities.

[0011] Preferably, the first carbon layer is carbon paper or carbon cloth that has undergone high-temperature activation treatment.

[0012] In this invention, the conductivity and porosity of carbon paper or carbon cloth can be optimized by adjusting the weaving density.

[0013] Preferably, the temperature of the high-temperature activation treatment is 700℃~900℃, for example, it can be 700℃, 720℃, 725℃, 750℃, 760℃, 780℃, 800℃, 825℃, 850℃, 875℃ or 900℃, etc.

[0014] By activating carbon paper or carbon cloth at high temperature, a first carbon layer with high conductivity and hydrophilic surface can be obtained, which is conducive to its close contact with the bipolar plate and reduces the ohmic polarization of the bipolar plate and electrode interface.

[0015] Preferably, the specific surface area of ​​the first carbon layer is 700 m² / g to 900 m² / g, for example, it can be 700 m² / g, 720 m² / g, 740 m² / g, 750 m² / g, 760 m² / g, 780 m² / g, 800 m² / g, 825 m² / g, 850 m² / g, 875 m² / g, or 900 m² / g, etc.

[0016] Preferably, the thickness of the first carbon layer is 0.05 mm to 0.2 mm, for example, it can be 0.05 mm, 0.07 mm, 0.1 mm, 0.12 mm, 0.15 mm, 0.16 mm, 0.18 mm, or 0.2 mm. If the thickness of the first carbon layer is too small, it will increase the brittleness of the carbon layer, making it easy to break and increasing the difficulty of assembly; if the thickness of the first carbon layer is too large, it will increase the contact resistance, thereby reducing the performance of the flow battery.

[0017] Preferably, the specific surface area of ​​the carbon felt substrate is ≥1m² / g, for example, it can be 1m² / g, 1.5m² / g, 2m² / g, 2.5m² / g, 3m² / g, 3.5m² / g, 4m² / g, 4.5m² / g, 5m² / g, 5.5m² / g, 6m² / g, 6.5m² / g, 7m² / g, 7.5m² / g, 8m² / g, 8.5m² / g, 9m² / g, 9.5m² / g, or 10m² / g, etc.

[0018] Preferably, the thickness of the carbon felt substrate is 2mm to 3mm, for example, it can be 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm or 3mm.

[0019] In a preferred embodiment of the multilayer electrode for flow batteries described in this invention, the second carbon layer is perforated carbon paper or carbon cloth. In this invention, the conductivity and porosity can be optimized by adjusting the weaving density of the carbon paper or carbon cloth.

[0020] Preferably, the perforation process is laser perforation. Laser perforation can create pores that penetrate the second carbon layer, forming a directional mass transfer channel, enhancing the diffusion rate of active materials (e.g., increasing the diffusion coefficient of active materials by more than 30% compared to an unperforated carbon layer) and convection effect, and reducing mass transfer resistance.

[0021] Preferably, the pore size in the perforated carbon layer is 30μm to 250μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 47μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 1 The pore sizes are 90μm, 200μm, 210μm, 220μm, 230μm, 240μm, or 250μm, etc.; the pore spacing is 0.3mm to 1.5mm, for example, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, or 1.5μm, etc. Here, the pore spacing refers to the distance between the center points of adjacent pores. Those skilled in the art can adjust the pore size and pore spacing according to the mass transfer requirements of flow batteries with different active materials (such as iron-based flow batteries and zinc-based flow batteries).

[0022] In one embodiment, the pores in the perforated carbon layer are arranged in an orderly matrix.

[0023] Preferably, the open porosity of the perforated carbon layer is 25% to 35%, for example, it can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34% or 35%, etc.

[0024] Preferably, the thickness of the second carbon layer is 0.1 mm to 0.2 mm, for example, it can be 0.1 mm, 0.12 mm, 0.14 mm, 0.16 mm, 0.18 mm, or 0.2 mm. If the thickness of the second carbon layer is too small, it will lead to processing difficulties and the carbon layer will be easily damaged; if the thickness of the second carbon layer is too large, it will increase the electrolyte transport distance and reduce the mass transfer efficiency.

[0025] Preferably, the first carbon layer, the carbon felt substrate layer, and the second carbon layer are bonded together by hot pressing. Hot pressing ensures a tight bond between the layers, guaranteeing unobstructed electron conduction paths.

[0026] Preferably, the overall porosity of the multilayer electrode is ≥90%, for example, it can be 90%, 91%, 92%, 93%, 94% or 95%, etc.

[0027] In a second aspect, the present invention provides a method for preparing a multilayer electrode for a flow battery as described in the first aspect, the method comprising the following steps:

[0028] (1) Prepare the first carbon layer and the second carbon layer respectively:

[0029] The carbon paper or carbon cloth is activated at high temperature to obtain the first carbon layer; the carbon paper or carbon cloth is then laser-drilled to obtain the second carbon layer.

[0030] (2) Composite:

[0031] The first carbon layer, carbon felt, and second carbon layer are stacked sequentially and then hot-pressed to obtain the multilayer electrode for the flow battery.

[0032] In the method of this invention, the preparation of the first carbon layer and the second carbon layer does not have a specific order.

[0033] The method of the present invention has the advantages of simple preparation process and is easy to industrialize.

[0034] Preferably, the temperature of the high-temperature activation treatment in step (1) is 700℃~900℃, for example, it can be 700℃, 720℃, 725℃, 750℃, 760℃, 780℃, 800℃, 825℃, 850℃, 875℃ or 900℃, etc.

[0035] Preferably, the atmosphere for the high-temperature activation treatment in step (1) is an oxygen atmosphere.

[0036] Preferably, the temperature of the hot pressing in step (2) is 120℃~150℃, for example, it can be 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, etc.; the pressure of the hot pressing is 0.5MPa~1MPa, for example, it can be 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa or 1MPa, etc.

[0037] In this invention, the hot pressing conditions affect the tightness of the interlayer contact and the porosity of the final multilayer electrode.

[0038] Thirdly, the present invention provides a flow battery, the flow battery comprising the multilayer electrode described in the first aspect, or the multilayer electrode prepared by the method described in the second aspect, wherein a first carbon layer in the multilayer electrode is in contact with a bipolar plate, and a second carbon layer in the multilayer electrode is in contact with an ion-exchange membrane.

[0039] The multilayer electrode of this invention is compatible with various flow battery systems, such as vanadium-based flow batteries, iron-based flow batteries, and zinc-based flow batteries.

[0040] Compared with existing technologies, the present invention has the following beneficial effects:

[0041] (1) This invention, for the first time, addresses the differentiated needs of low contact resistance on the bipolar plate side and high mass transfer efficiency on the ion membrane side by providing a multilayer electrode with a gradient functional design, achieving synergistic optimization of reduced contact resistance and enhanced mass transfer. The technical principle is as follows: The first carbon layer has high conductivity, enabling ohmic polarization of the bipolar plate-electrode interface. Furthermore, the first carbon layer has surface hydrophilicity, allowing the electrolyte to more uniformly wet the electrode surface, increasing the solid-liquid contact area, and promoting the diffusion and mass transfer of active ions (e.g., vanadium ions) on the electrode surface, thereby reducing concentration polarization and improving battery efficiency. The carbon felt substrate, as the main reaction area, undertakes the electron conduction of the first carbon layer and the transport of active materials from the second carbon layer. The carbon felt substrate provides sufficient reaction surface area to ensure efficient electrochemical reactions. The second carbon layer has a porous structure, which enhances the diffusion and convection of active materials on the ion membrane side, reducing mass transfer resistance. Moreover, it retains the conductivity of the carbon layer, resolving the contradiction of simultaneously achieving conductivity and mass transfer.

[0042] (2) The multilayer electrode of the present invention simultaneously satisfies low ohmic loss and high mass transfer efficiency. When applied to flow batteries, it can still maintain high energy efficiency, voltage efficiency and cycle performance at high current density (e.g., 200 mA / cm²). Its energy efficiency is above 81%, voltage efficiency is above 84.8%, and efficiency retention rate after 500 cycles is above 98%, breaking through the performance bottleneck of the prior art at high current density. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of a multilayer electrode for a vanadium redox flow battery according to one embodiment of the present invention.

[0044] Figure 2 This is a plan view of the second carbon layer in a multilayer electrode according to one embodiment of the present invention.

[0045] Figure 3 This is a diagram showing the positional relationship of the multilayer electrodes, bipolar plates, and ion-exchange membrane in an all-vanadium redox flow battery according to one embodiment of the present invention.

[0046] Among them, 1. multilayer electrode; 11. first carbon layer; 12 carbon felt substrate layer; 13. second carbon layer; 2. bipolar plate; 3. ion membrane. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0048] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0050] Example 1

[0051] This embodiment provides a multilayer electrode 1 for an all-vanadium redox flow battery (see schematic diagram for its structure). Figure 1 The carbon paper comprises a first carbon layer 11, a carbon felt substrate layer 12, and a second carbon layer 13, which are stacked sequentially. The first carbon layer 11 is carbon paper that has been activated at 800°C (its surface is hydrophilic and its volume resistivity is ≤5×10⁻⁻⁻⁶). 4 Ω・cm 3 The first carbon layer has a specific surface area of ​​800 m² / g and a thickness of 0.2 mm; the second carbon layer 12 is a polyacrylonitrile-based carbon felt (porosity of 95% and thickness of 2.5 mm); the third carbon layer 13 is laser-drilled carbon paper (pore size of 100 μm, pore spacing of 0.8 μm, porosity of 30%, and thickness of 0.15 mm). See the top plan view of the second carbon layer. Figure 2 The overall porosity of the multilayer electrode 1 used in vanadium redox flow batteries is ≥90%.

[0052] This embodiment also provides a method for preparing the above-mentioned multilayer electrode for an all-vanadium redox flow battery, including the following steps:

[0053] The carbon paper is heat-treated at 800℃ to obtain the first carbon layer 11; the carbon paper is perforated using a laser perforation process to obtain the second carbon layer 13.

[0054] The three layers are stacked sequentially in the order of first carbon layer 11, carbon felt substrate layer 12, and second carbon layer 13, and hot-pressed for 30 minutes at a temperature of 130°C and a pressure of 0.8 MPa to form a multilayer electrode 1 for vanadium redox flow batteries.

[0055] This embodiment also provides an all-vanadium redox flow battery, including the aforementioned multilayer electrode 1. The first carbon layer 11 of the multilayer electrode 1 is in contact with the bipolar plate 2, and the second carbon layer 13 of the multilayer electrode 1 is in contact with the ion-exchange membrane 3. The all-vanadium redox flow battery adopts a symmetrical structure, with an electrode area of ​​30 cm². 2 The electrolyte composition is 1.7 mol / L VOSO4 and 3 mol / L H2SO4. For a diagram showing the positional relationship between the multilayer electrode 1, bipolar plate 2, and ion-exchange membrane 3 in the vanadium redox flow battery, please refer to [reference needed]. Figure 3 .

[0056] Example 2

[0057] This embodiment provides a multilayer electrode for a vanadium redox flow battery, comprising a first carbon layer, a carbon felt substrate layer, and a second carbon layer stacked sequentially. The first carbon layer is carbon paper activated at 750°C (its surface is hydrophilic, and its volume resistivity is ≤5×10⁻⁻⁻⁻⁴). 4 Ω・cm 3The specific surface area is 900 m² / g and the thickness is 0.1 mm; the carbon felt substrate layer is polyacrylonitrile-based carbon felt (porosity is 95% and thickness is 2 mm); the second carbon layer is carbon paper that has been laser-drilled (pore size is 150 μm, pore spacing is 1 μm, porosity is 25% and thickness is 0.1 mm).

[0058] This embodiment also provides a method for preparing the above-mentioned multilayer electrode for an all-vanadium redox flow battery, including the following steps:

[0059] The carbon paper is heat-treated at 750℃ to obtain the first carbon layer; the carbon paper is then perforated using a laser perforation process to obtain the second carbon layer.

[0060] The three layers are stacked sequentially in the order of the first carbon layer, the carbon felt substrate layer, and the second carbon layer, and hot-pressed together for 25 minutes at a temperature of 120°C and a pressure of 1 MPa to form a multilayer electrode for vanadium redox flow batteries.

[0061] This embodiment also provides an all-vanadium redox flow battery, including the aforementioned multilayer electrode. The first carbon layer in the multilayer electrode is in contact with a bipolar plate, and the second carbon layer in the multilayer electrode is in contact with an ion-exchange membrane. The all-vanadium redox flow battery adopts a symmetrical structure, with an electrode area of ​​30 cm². 2 The electrolyte consists of 1.7 mol / L VOSO4 and 3 mol / L H2SO4.

[0062] Example 3

[0063] This embodiment provides a multilayer electrode (overall porosity ≥90%) for a vanadium redox flow battery, comprising a first carbon layer, a carbon felt substrate layer, and a second carbon layer stacked sequentially. The first carbon layer is carbon cloth activated at 850°C (its surface is hydrophilic, and its volume resistivity is ≤5×10⁻⁻⁻⁻⁵). 4 Ω・cm 3 The surface area is 750 m² / g and the thickness is 0.07 mm; the carbon felt substrate layer is polyacrylonitrile-based carbon felt (porosity 90%, thickness 3 mm); the second carbon layer is carbon cloth with laser perforation treatment (pore diameter 70 μm, pore spacing 0.5 μm, porosity 35%, thickness 0.2 mm).

[0064] This embodiment also provides a method for preparing the above-mentioned multilayer electrode for an all-vanadium redox flow battery, including the following steps:

[0065] The carbon cloth is heat-treated at 850℃ to obtain the first carbon layer; the carbon cloth is perforated using a laser perforation process to obtain the second carbon layer.

[0066] The three layers are stacked sequentially in the order of the first carbon layer, the carbon felt substrate layer, and the second carbon layer. They are then hot-pressed together for 15 minutes at a temperature of 150°C and a pressure of 0.5 MPa to form a multilayer electrode for vanadium redox flow batteries.

[0067] This embodiment also provides an all-vanadium redox flow battery, including the aforementioned multilayer electrode. The first carbon layer in the multilayer electrode is in contact with a bipolar plate, and the second carbon layer in the multilayer electrode is in contact with an ion-exchange membrane. The all-vanadium redox flow battery adopts a symmetrical structure, with an electrode area of ​​30 cm². 2 The electrolyte consists of 1.7 mol / L VOSO4 and 3 mol / L H2SO4.

[0068] Example 5

[0069] This embodiment provides a multilayer electrode for a vanadium redox flow battery and a vanadium redox flow battery. The difference between the multilayer electrode for the vanadium redox flow battery and that in Embodiment 1 is that the thickness of the first carbon layer is 0.25 mm.

[0070] Example 7

[0071] This embodiment provides a multilayer electrode for a vanadium redox flow battery and a vanadium redox flow battery. The difference between the multilayer electrode for the vanadium redox flow battery and that in Embodiment 1 is that the thickness of the second carbon layer is 0.25 mm.

[0072] Example 8

[0073] This embodiment provides a multilayer electrode for an iron-chromium flow battery and an iron-chromium flow battery.

[0074] The difference between the multilayer electrode in this embodiment and the multilayer electrode in Example 1 is that the pore size of the second carbon layer is 50 μm and the pore spacing is 0.5 μm. By adjusting the pore size and pore spacing, rapid mass transfer of iron ions is facilitated. The thickness of the first carbon layer is adjusted from 0.2 mm to 0.3 mm. By adjusting the thickness of the first carbon layer, conductivity is enhanced to match the high polarization characteristics of the iron-chromium system.

[0075] Comparative Example 1

[0076] This comparative example provides a two-layer electrode for a vanadium redox flow battery and a vanadium redox flow battery. The difference between the two-layer electrode for the vanadium redox flow battery and Example 1 is that the first carbon layer is not provided, and the thickness of the carbon felt substrate layer is adjusted so that the total thickness of the electrode in this comparative example is the same as the total thickness of the multilayer electrode in Example 1.

[0077] In this comparative example of a vanadium redox flow battery, the carbon felt substrate layer is in contact with the bipolar plate, and the second carbon layer is in contact with the ion exchange membrane.

[0078] Comparative Example 2

[0079] This comparative example provides a two-layer electrode for a vanadium redox flow battery and a vanadium redox flow battery. The difference between the two-layer electrode for the vanadium redox flow battery and Example 1 is that a second carbon layer is not provided, and the thickness of the carbon felt substrate layer is adjusted so that the total thickness of the electrode in this comparative example is the same as the total thickness of the multilayer electrode in Example 1.

[0080] In this comparative example of a vanadium redox flow battery, the first carbon layer is in contact with the bipolar plate, and the carbon felt substrate layer is in contact with the ion exchange membrane.

[0081] Comparative Example 3

[0082] This comparative example provides a single-layer electrode for a vanadium redox flow battery and a vanadium redox flow battery. The difference between the single-layer electrode for the vanadium redox flow battery and Example 1 is that the first carbon layer and the second carbon layer are not provided, and the thickness of the carbon felt substrate layer is the same as the total thickness of the multilayer electrode in Example 1.

[0083] In this comparative example of a full vanadium redox flow battery, the carbon felt substrate layer is in contact with the bipolar plate and the ion exchange membrane on both sides, respectively.

[0084] The following performance tests were performed on the flow batteries of Examples 1-8 and Comparative Examples 1-3:

[0085] (1) Control the ambient temperature to 25±1℃, and conduct the test under constant current charge and discharge mode with a cutoff voltage range of 1.55V-1V and a current density of 200mA / cm². Record the coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) of the battery. Calculate the voltage efficiency and the efficiency retention rate after 500 cycles. The calculation formula is: Voltage efficiency = Energy efficiency / Coulombic efficiency × 100%, Efficiency retention rate after 500 cycles = Energy efficiency of the 500th cycle / Energy efficiency of the first cycle × 100%.

[0086] (2) The contact resistance of the bipolar plates in the flow battery was tested using a contact resistance tester. The contact resistance was tested using the limiting current method, and the specific steps were as follows: Connect the positive and negative terminals of the single cell to the positive and negative terminals of the charge-discharge tester respectively, and measure the contact resistance at a low flow rate (e.g., 25 mL / min). -1 The limiting current of a single cell directly reflects the maximum diffusion rate at which vanadium ions can reach the electrode surface under the test conditions.

[0087] (3) The limiting current of the flow battery is tested by connecting the positive and negative terminals of the single cell to the positive and negative terminals of the charge-discharge tester respectively, and measuring the current at a low flow rate (e.g., 30 mL / min). -1The limiting current of a single cell is determined as follows: First, at a given voltage, record the current value after it stabilizes. After resting for 30 seconds, increase the voltage to a new given value (in 50mV increments) and record the new stable current value. Continue this process until the current value no longer increases with voltage, then stop the test. The average current value corresponding to this plateau is the limiting current, which directly reflects the maximum diffusion rate of vanadium ions to the electrode surface under these test conditions. The higher the limiting current, the higher the diffusion coefficient of the active material.

[0088] The results are shown in Table 1.

[0089]

[0090] As can be seen from the comparison of Examples 1-6 and Comparative Examples 1-3, the multilayer electrode of the present invention, through the synergistic cooperation of the first carbon layer, the second carbon layer and the carbon felt substrate layer, can simultaneously meet the requirements of low ohmic loss and high mass transfer efficiency. When applied to flow batteries, it can still maintain high energy efficiency, voltage efficiency and cycle performance at high current densities (e.g., 200 mA / cm²), with an energy efficiency of over 81%, a voltage efficiency of over 84.8%, and an efficiency retention rate of over 98% after 500 cycles, breaking through the performance bottleneck of the prior art at high current densities.

[0091] Meanwhile, a comparison between Example 1 and Example 4 shows that the thickness of the first carbon layer should not be too large, otherwise it will increase the contact resistance on the bipolar plate side and reduce the performance of the flow battery.

[0092] A comparison between Example 1 and Example 5 shows that the thickness of the second carbon layer should not be too large, otherwise it will reduce the diffusion coefficient of the active material and reduce the performance of the flow battery.

[0093] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A multilayer electrode for a flow battery, characterized in that, The multilayer electrode comprises a first carbon layer, a carbon felt substrate layer, and a second carbon layer stacked sequentially. The first carbon layer is hydrophilic and has a volume resistivity ≤5×10⁻⁻⁻⁻⁻⁵. 4 Ω・cm 3 The first carbon layer is a carbon layer with perforations.

2. The multilayer electrode for a flow battery according to claim 1, characterized in that, The first carbon layer is carbon paper or carbon cloth that has undergone high-temperature activation treatment; Preferably, the temperature of the high-temperature activation treatment is 700℃~900℃.

3. The multilayer electrode for a flow battery according to claim 1 or 2, characterized in that, The specific surface area of ​​the first carbon layer is 700 m² / g to 1000 m² / g; Preferably, the thickness of the first carbon layer is 0.05 mm to 0.2 mm.

4. The multilayer electrode for a flow battery according to any one of claims 1-3, characterized in that, The specific surface area of ​​the carbon felt substrate is ≥1m² / g; Preferably, the thickness of the carbon felt substrate is 2mm to 3mm.

5. The multilayer electrode for a flow battery according to any one of claims 1-4, characterized in that, The second carbon layer is perforated carbon paper or carbon cloth; Preferably, the drilling process is laser drilling; Preferably, the carbon layer with perforation treatment has a pore size of 30μm to 250μm and a pore spacing of 0.3mm to 1.5mm; Preferably, the porosity of the perforated carbon layer is 25% to 35%. Preferably, the thickness of the second carbon layer is 0.1 mm to 0.2 mm.

6. The multilayer electrode for a flow battery according to any one of claims 1-5, characterized in that, The first carbon layer, the carbon felt substrate layer, and the second carbon layer are bonded together by hot pressing.

7. The multilayer electrode for a flow battery according to any one of claims 1-6, characterized in that, The overall porosity of the multilayer electrode is ≥90%.

8. A method for preparing a multilayer electrode for a flow battery as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Prepare the first carbon layer and the second carbon layer respectively: The carbon paper or carbon cloth is activated at high temperature to obtain the first carbon layer; the carbon paper or carbon cloth is then laser-drilled to obtain the second carbon layer. (2) Composite: The first carbon layer, carbon felt, and second carbon layer are stacked sequentially and then hot-pressed to obtain the multilayer electrode for the flow battery.

9. The method for preparing a multilayer electrode for a flow battery according to claim 8, characterized in that, The temperature of the high-temperature activation treatment in step (1) is 700℃~900℃; Preferably, the atmosphere for the high-temperature activation treatment in step (1) is an oxygen atmosphere; Preferably, the temperature of the hot pressing in step (2) is 120℃~150℃, and the pressure of the hot pressing is 0.5MPa~1MPa.

10. A flow battery, characterized in that, The flow battery includes a multilayer electrode as described in any one of claims 1-7, or a multilayer electrode prepared by the method described in claim 8 or 9, wherein the first carbon layer of the multilayer electrode is in contact with the bipolar plate, and the second carbon layer of the multilayer electrode is in contact with the ion membrane.

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