A vanadium redox flow battery structure for protecting an ion exchange membrane

Abstract

The present invention belongs to the technical field of all-vanadium redox flow batteries, and discloses an all-vanadium redox flow battery structure for protecting an ion exchange membrane. The specific structure is that carbon cloth electrodes are covered on both sides of the ion exchange membrane, and carbon felt electrodes are covered on the other side of the carbon cloth electrodes. The carbon felt electrodes are composed of carbon felt electrode longitudinal fibers and carbon felt electrode transverse fibers, and the carbon cloth electrodes are composed of carbon cloth transverse fibers. The carbon felt electrodes are not in direct contact with the membrane, the carbon cloth electrodes are in direct contact with the membrane, and the carbon felt electrodes are in contact with the carbon cloth electrodes. It effectively avoids the contact between the longitudinal carbon felt fibers and the ion exchange membrane. When using the carbon cloth electrodes to contact the membrane, more reaction sites are provided, and the electrochemical reaction rate is further improved, that is, the battery conversion efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-vanadium redox flow batteries, and particularly relates to an all-vanadium redox flow battery structure for protecting an ion exchange membrane. Background Art

[0002] In today's society, with the improvement of living standards, various electronic device products such as mobile phones, computers, TVs, electric vehicles and other high-end devices are constantly developing, greatly enriching the lives of the majority of users. The development of these high-tech products has an increasingly strong demand for high-quality energy (mainly electrical energy).

[0003] At the same time, the gradual reduction of energy sources such as coal, oil, and natural gas and the environmental pollution caused by their use have made the research and development of large-scale renewable energy the first choice. Since the power generation of renewable energy (such as wind energy, solar energy, tidal energy, etc.) has the characteristics of instability and discontinuity, a supporting energy storage system is required for balancing to ensure its continuous and stable use.

[0004] The energy storage battery is the heart of the energy storage system. Among the existing energy storage batteries, the flow battery is the best choice for realizing large-scale energy storage solutions due to its advantages such as good safety, high power, long service life, and environmental friendliness.

[0005] The structure of a single-stack of an all-vanadium redox flow battery stack is generally: end plate, liquid inlet plate, current collector plate, bipolar plate, electrode, separator, electrode, bipolar plate, current collector plate, liquid inlet plate, end plate. The structure of a multi-stack battery stack can be obtained by correspondingly increasing the combination of bipolar plates, electrodes, separators, electrodes, and bipolar plates.

[0006] The electrode is generally a carbon felt electrode. The carbon fiber is woven into a carbon felt through a knitting process, which has the characteristics of high porosity, high conductivity, high specific surface area, etc. After carbonization and activation treatment, the specific surface area is further increased and the activity is increased, and it is widely used as the electrode material of the all-vanadium redox flow battery.

[0007] Under the current stack structure, in order to ensure the performance of the stack, the compression ratio of the stack electrode is usually controlled at 10-20%. After charge and discharge cycles, there is a probability of internal leakage in the stack, resulting in a rapid decrease in the performance of the stack until it is completely damaged. Most of the reasons for internal leakage are that the ion exchange membrane is pierced by the longitudinal fibers of the carbon felt (such as Figure 2 ), resulting in the contact of the positive and negative electrolyte solutions, that is, internal leakage, causing a rapid decrease in the short-circuit performance.

[0008] In the structure of the ion exchange membrane and the carbon felt electrode of the existing all-vanadium redox flow battery stack, the following defects and problems exist:

[0009] 1. To ensure the performance of the stack, the compression ratio of the stack electrodes is usually controlled between 10% and 20%. At this time, there is a probability that the carbon felt fibers will pierce the ion exchange membrane, causing internal leakage, resulting in a rapid decline in the stack performance, and even causing the stack to be damaged;

[0010] 2. To avoid the carbon felt fibers from piercing the ion exchange membrane, the compression ratio of the carbon felt electrodes can be reduced. The compression ratio of the carbon felt electrodes can be reduced from 10% - 20% to 0% - 5%, reducing the piercing pressure of the carbon felt fibers on the membrane to achieve the purpose of protecting the membrane. However, at this time, because the compression ratio of the carbon felt electrodes is too small, the resistance of the carbon felt electrode body is too large, and the contact resistance between the carbon felt electrode and the bipolar plate is too large, resulting in a stack performance decline of more than 10%, making it of no use value;

[0011] 3. To improve the stack performance, one way can be achieved by increasing the carbon felt compression ratio. When the carbon felt compression ratio increases to 50%, the stack performance can be improved by 3% - 5% in a short time. However, due to the increase in the compression ratio, the force of the carbon felt electrode fibers pressing on the membrane further increases, resulting in more serious and frequent internal leakage situations. Summary of the Invention

[0012] In order to overcome the deficiencies of the prior art, the present invention provides a vanadium redox flow battery structure for protecting the ion exchange membrane, effectively avoiding the contact between the longitudinal carbon felt fibers and the ion exchange membrane, thereby preventing the carbon fiber from piercing the ion exchange membrane.

[0013] The above object of the present invention is achieved by the following technical solutions: A vanadium redox flow battery structure for protecting the ion exchange membrane, the specific structure is that carbon cloth electrodes are covered on both sides of the ion exchange membrane, and carbon felt electrodes are covered on the other side of the carbon cloth electrodes. The carbon felt electrodes are composed of carbon felt electrode longitudinal fibers and carbon felt electrode transverse fibers, and the carbon cloth electrodes are composed of carbon cloth transverse fibers.

[0014] Further, the carbon cloth electrodes are pretreated by graphitization and activation in sequence.

[0015] Further, the graphitization step of the carbon cloth electrodes is: under the condition of isolating oxygen, the carbon cloth electrodes are heated at a programmed rate, rising to 1800 - 2400 °C at a heating rate of 1 - 5 °C / min, and then holding for 1 - 5 h. Naturally cool to room temperature.

[0016] Further, the activation step of the carbon cloth electrodes is: continuously conveying ozone, water vapor, air or carbon dioxide to the carbon cloth electrodes, while the carbon cloth electrodes are heated at a programmed rate, rising to 400 - 700 °C at a heating rate of 1 - 5 °C / min, and then holding for 1 - 10 h, and then naturally cooling to room temperature.

[0017] Further, the carbon cloth electrodes and the carbon felt electrodes are assembled by any one of stacking, knitting, and winding.

[0018] Furthermore, the carbon cloth electrode and the ion exchange membrane are assembled in a stacked manner.

[0019] The beneficial effects of the present invention compared with the prior art are as follows:

[0020] 1. The carbon felt electrode does not directly contact the membrane, the carbon cloth electrode directly contacts the membrane, and the carbon felt electrode contacts the carbon cloth electrode. This effectively avoids the contact between the longitudinal carbon felt fibers and the ion exchange membrane, thereby preventing the carbon fibers from piercing the ion exchange membrane; reducing the failure rate of the stack due to carbon fiber piercing of the ion exchange membrane from 7% to 0%.

[0021] 2. After adding the carbon cloth electrode, since the contact between the longitudinal carbon fibers and the ion exchange membrane is avoided and the ion exchange membrane is protected, the compression ratios of the carbon felt electrode and the carbon cloth electrode can be increased to 50%, further reducing the bulk resistance of the electrode and the contact resistance between the electrode and the bipolar plate, and improving the stack performance by 3% - 5%.

[0022] 3. The fiber bulk density of the carbon cloth electrode is much higher than that of the carbon felt electrode, usually 5 - 50 times that of the carbon felt electrode. Most of the electrochemical reactions occurring in the flow battery take place at the interface between the electrode and the membrane. Therefore, when using the carbon cloth electrode to contact the membrane, more reaction sites are provided, and the rate of the electrochemical reaction is further increased, that is, the battery conversion efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0024] Figure 1 It is a schematic diagram of the internal structure of the battery: carbon felt electrode + carbon cloth electrode + membrane + carbon cloth electrode + carbon felt electrode;

[0025] Figure 2 : Schematic diagram of the cross-sectional structure of the carbon felt electrode;

[0026] Figure 3 : Schematic diagram of the cross-sectional structure of the carbon cloth electrode;

[0027] Figure 4 : Surface morphology of the carbon felt electrode (SEM photo);

[0028] Figure 5 : Surface morphology of the carbon cloth electrode (SEM photo);

[0029] Figure 6 : Apparent morphology of the ion exchange membrane after 1000 cycles in Comparative Example 1 (SEM photo);

[0030] Figure 7 : Apparent morphology of the ion exchange membrane after 1000 cycles in Example 1 (SEM photo);

[0031] Figure 8 : Apparent morphology of the ion exchange membrane after 1000 cycles in Comparative Example 2 (SEM photograph);

[0032] Figure 9 : Apparent morphology of the ion exchange membrane after 1000 cycles in Example 2 (SEM photograph);

[0033] Figure 10 : Apparent morphology of the ion exchange membrane after 1000 cycles in Example 3 (SEM photograph);

[0034] In the figure: 1. Ion exchange membrane; 2. Carbon cloth electrode; 3. Carbon felt electrode; 4. Longitudinal fibers of the carbon felt electrode; 5. Transverse fibers of the carbon felt electrode; 6. Transverse fibers of the carbon cloth; 7. Hole in the ion exchange membrane pierced by carbon felt fibers. Detailed implementation manners

[0035] The present invention will be described in detail below through specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0036] Example 1

[0037] Two 0.5-mm-thick carbon cloth electrodes 2 that have been carbonized and activated are respectively placed between the ion exchange membrane 1 and the carbon felt electrodes 3 at the positive and negative poles to assemble a single cell, and the compression ratio of the carbon cloth electrode 2 and the carbon felt electrode 3 is 20%. The comparison results with Comparative Example 1 are shown in Table 1. After 1000 cycles of 160 mA / cm 2 constant current charge-discharge test, the battery performance does not decrease significantly; the battery is disassembled, and the ion exchange membrane 1 is taken out for SEM analysis of the apparent morphology, and there is no obvious damage. This shows that the carbon cloth electrode 2 can well protect the ion exchange membrane 1 from being pierced by the fibers of the carbon felt electrode 3, thereby improving the battery stability. At the same time, it is noted that the initial performance of the battery assembled with carbon cloth is also improved compared with the comparative example, indicating that when using the carbon cloth electrode 2 in contact with the membrane, more reaction sites are provided, and the electrochemical reaction rate is further increased, that is, the battery conversion efficiency is improved.

[0038] Comparative Example 1

[0039] Except for not having the carbon cloth in Example 1, the other structures are the same.

[0040] Table 1

[0041]

[0042]

[0043] Example 2

[0044] Two carbon cloth electrodes 2 with a thickness of 0.5 mm that have been carbonized and activated are respectively placed between the ion exchange membrane 1 and the carbon felt electrodes 3 at the positive and negative poles to assemble a single cell. The compression ratio of the carbon cloth electrode 2 and the carbon felt electrode 3 is 50%. The comparison results with Comparative Example 2 are shown in Table 2. After 1000 cycles of constant current charge and discharge tests at 160 mA / cm2, the battery performance shows no obvious decline; when the battery is disassembled, the ion exchange membrane 1 is taken out and its apparent morphology is analyzed by electron microscopy, showing no obvious damage. This shows that after adding the carbon cloth electrode 2, the compression ratio of the electrode can be greatly increased to improve the battery performance, and at the same time, it will not damage the membrane.

[0045] Comparative Example 2

[0046] Except for not having the carbon cloth in Example 2, the rest of the structure is the same.

[0047] Table 2

[0048]

[0049] Example 3

[0050] Two carbon cloth electrodes 2 with a thickness of 1.0 mm that have been carbonized and activated are respectively placed between the ion exchange membrane 1 and the carbon felt electrodes 3 at the positive and negative poles to assemble a single cell. The compression ratio of the carbon cloth electrode 2 and the carbon felt electrode 3 is 20%. The comparison results with Comparative Example 3 are shown in Table 3. After 1000 cycles of constant current charge and discharge tests at 160 mA / cm2, the battery performance shows no obvious decline; when the battery is disassembled, the ion exchange membrane 1 is taken out and its apparent morphology is analyzed by electron microscopy, showing no obvious damage. This shows that batteries can be assembled using carbon cloth electrodes 2 with different thicknesses. The thicker the carbon cloth electrode 2, due to the increase in the bulk resistance, the battery performance will be slightly lower than that of the thinner carbon cloth.

[0051] Comparative Example 3

[0052] Except for not having the carbon cloth in Example 3, the rest of the structure is the same.

[0053] Table 3

[0054]

[0055] The above-described embodiments are only the preferred embodiments of the present invention, and not all the feasible embodiments of the present invention. For those of ordinary skill in the art, any obvious modifications made without departing from the principle and spirit of the present invention should be considered to be included within the scope of the claims of the present invention.

Claims

1. A vanadium redox flow battery structure for protecting an ion exchange membrane, characterized in that, The specific structure is that carbon cloth electrodes (2) are covered on both sides of the ion exchange membrane (1), and a carbon felt electrode (3) is covered on the other side of the carbon cloth electrode (2). The carbon felt electrode (3) is composed of carbon felt electrode longitudinal fibers (4) and carbon felt electrode transverse fibers (5), and the carbon cloth electrode (2) is composed of carbon cloth transverse fibers (6); the carbon cloth electrode (2) is pretreated by graphitization and activation in sequence; the graphitization step is: under the condition of isolating oxygen, the carbon cloth electrode (2) is heated at a heating rate of 1-5 °C / min to 1800-2400 °C, then held for 1-5 h, and naturally cooled to room temperature; the activation step is: ozone, water vapor, air or carbon dioxide is continuously fed to the carbon cloth electrode (2), and at the same time the carbon cloth electrode (2) is heated at a heating rate of 1-5 °C / min to 400-700 °C, then held for 1-10 h, and then naturally cooled to room temperature.

2. The all-vanadium redox flow battery structure for protecting an ion exchange membrane according to claim 1, wherein The carbon cloth electrode (2) and the carbon felt electrode (3) are assembled by any one of a stacked type, a knitted type, and a wound type.

3. The all-vanadium redox flow battery structure for protecting an ion exchange membrane according to claim 1, wherein The carbon cloth electrode (2) and the ion exchange membrane (1) are assembled by a stacked type.

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