CN115939475A - Simple low-cost method for reducing concentration polarization of flow battery and application - Google Patents

Abstract

The invention belongs to the field of flow batteries and discloses a simple method for reducing concentration polarization of a flow battery and application thereof, wherein electrodes with different n block body densities rho are sequentially arranged in an electrolyte reaction area of a positive electrode and a negative electrode along the flowing direction of the electrolyte, the sum of the combined areas of the n electrodes is consistent with the area of the electrolyte reaction area, n is more than or equal to 2 and less than or equal to 10,0.07g/cm ³ ≤ρ≤0.15g/cm ³ . The method for reducing the concentration polarization of the flow battery is simple to operate, low in cost, obvious in effect and suitable for large-scale popularization; can reduce the shape constraint of the galvanic pile, improve the effective utilization rate of the ion exchange membrane and the bipolar plate material to a certain extent, and does not need to bring additional pump consumption.

Description

A simple and low-cost method and application for reducing the concentration polarization of a flow battery

technical field

The invention relates to the field of liquid flow batteries, in particular to a simple method and application for reducing the concentration polarization of a liquid flow battery.

Background technique

Flow battery is a new type of energy storage technology, which has been developed to a certain extent in the field of energy storage in recent years. In a flow battery, the electrolyte is the energy unit, which is the medium for storing electric energy, and the stack is the power unit, which is the place where the active substances in the electrolyte participate in the conversion of electrical energy and chemical energy. During the conversion of electrical energy and chemical energy in a flow battery, energy loss is unavoidable. The energy loss of the energy storage system is mainly the energy loss of the stack during the charging and discharging process and the energy loss caused by the operation of auxiliary equipment (circulation pumps, refrigeration equipment, lighting equipment, etc.). During the charging and discharging process of the stack, in addition to side reactions In addition, various polarization losses are the most important source of energy loss. For flow batteries, the polarization loss is mainly divided into ohmic polarization, electrochemical polarization and concentration polarization. Among them, ohmic polarization is mainly composed of various conductive materials and contact resistance, and electrochemical polarization is mainly composed of electrical The chemical reaction electron transfer rate is determined, and the concentration polarization is mainly determined by whether the reactants are sufficient and the mass transfer rate. For the concentration polarization, in the actual application process, the method to reduce the concentration polarization is mainly to shorten the flow distance of the electrolyte in the stack (that is, the short flow structure) and increase the flow rate of the pump, so that the activity after the reaction Substances are capable of rapid transfer. However, the short-flow structure will constrain the shape of the stack to a certain extent (the ratio of length and width is large), and under the same ion-exchange membrane and bipolar plate area usage conditions, the ion-exchange membrane and bipolar plate of the short-flow structure The utilization rate of the pump is relatively low; increasing the flow rate of the pump will increase the energy consumption of the pump and cause additional energy loss, which will be limited in actual use. Therefore, developing a new method to reduce concentration polarization is one of the main research directions in this field.

Contents of the invention

In order to make up for the deficiencies of the prior art, the present invention provides a simple and low-cost method for reducing the concentration polarization of the flow battery to reduce the concentration polarization during the operation of the flow battery and improve the voltage efficiency and energy efficiency of the battery .

In the prior art, a whole electrode with the same volume density is placed in the electrolyte reaction area. When assembling the stack, the electrode is placed flat on the electrolyte reaction area, and its position is limited by the part framed in the middle of the electrode frame. The size of the middle part of the electrode frame is consistent with the electrolyte reaction area. In the present invention, the electrode assembled by using multiple electrodes with different volume densities has the same overall external size as the size of the electrolyte reaction zone, and the others remain unchanged. The electrode is limited by the electrode frame. When the stack is assembled, the external pressure The electrode can be fixed by the limitation of the electrode frame.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A simple and low-cost method for reducing the concentration polarization of a flow battery. In the electrolyte reaction zone of the positive and negative electrodes, n blocks of electrodes with different densities ρ are sequentially arranged along the flow direction of the electrolyte, and the n blocks of electrodes are combined The sum of the areas is consistent with the area of the electrolyte reaction zone.

Further, the value range of n is: 2≤n≤10. It is worth noting here that under similar conditions, the increase of the n value will improve the battery efficiency to a certain extent. This is due to the more detailed distribution of the electrode to the electrolyte, which is more conducive to reducing the concentration polarization. However, it is not recommended to take a relatively larger value for n, because an increase in n means an increase in the number of electrodes, which will increase the difficulty of assembling the stack to a certain extent and reduce work efficiency. In actual work, it can be determined according to the specific situation ( Consider comprehensive consideration of factors such as stack size, electrode body density, and area) to select an appropriate value of n.

Further, the volume density ρ of the n blocks of electrodes with different volume densities ρ arranged sequentially along the flow direction of the electrolyte decreases successively.

Further, the bulk density of each electrode is the density after assembly and compression of the stack, and satisfies 0.07g/cm ³ ≤ρ≤0.15g/cm ³ .

Further, the electrode is a porous carbon material electrode.

Further, the electrodes are carbon felt electrodes, carbon fiber cloth electrodes, carbon paper electrodes, foam carbon electrodes, 3D printed carbon electrodes, etc.

Another object of the present invention is to protect the electrode prepared by the above method suitable for the field of redox flow battery.

In order to make this program easier to understand, here is a further elaboration:

In a conventional flow battery, in order to ensure that the electrolyte can be evenly distributed to each unit of the stack, and that the electrodes can completely contact the electrolyte to participate in the reaction, and there is no dead zone, the electrolyte is fed from the bottom to the top. . Therefore, at the bottom of the electrode (close to the electrolyte inlet), the active material participating in the reaction is the most sufficient. In order to ensure the maximum reaction, the electrode should provide more active sites and a larger contact area with the electrolyte. At this time, the electrode with a larger bulk density meets the requirements. With the progress of the active material reaction and the upward transport of the electrolyte, the concentration of the active material participating in the reaction decreases, the requirement for the number of active sites on the electrode is reduced, and lower resistance is required to electrolyze The liquid is transported out of the stack, at which point the electrodes with lower bulk density can play a role. That is to say, the density of the electrode body is high, which can provide more active sites and has a larger contact area with the electrolyte, which is conducive to the active material to participate in the reaction, but at the same time, the resistance of the liquid to the liquid will also If it becomes larger, it will hinder the transmission of the electrolyte; the density of the electrode body is small, and the active sites that can be provided are relatively few (but enough), and the resistance to the electrolyte is small, which helps the rapid transmission of the electrolyte and reduces the battery life of the flow battery. concentration polarization. It is worth mentioning that the material of the electrode is preferably carbon felt, and the smaller the density of carbon felt may reduce the bulk resistance of carbon felt to a certain extent, but because carbon felt is an electronic conductor, its own surface resistance is very low. Low (<0.2Ω·cm ² ), so the reduction of the bulk density basically does not affect the ohmic polarization of the battery.

Compared with the prior art, the beneficial effects of the present invention are as follows:

A method for reducing the concentration polarization of a liquid flow battery provided by the present invention has simple operation, low cost and obvious effect, and is suitable for large-scale promotion;

The invention provides a method for reducing the concentration polarization of the liquid flow battery, which can reduce the constraint of the stack shape, improve the effective utilization rate of the ion exchange membrane and bipolar plate materials to a certain extent, and does not need to bring additional pump consumption.

Description of drawings

Figure 1 is a schematic diagram of the assembly structure of a bipolar plate, an electrode frame and an electrode in Example 1 of the present invention;

Fig. 2 is a schematic diagram of electrode frame and electrode structure in Embodiment 1 of the present invention;

Fig. 3 is a schematic diagram of electrode frame and electrode structure in Embodiment 2 of the present invention;

Fig. 4 is a schematic diagram of electrode frame and electrode structure in Embodiment 3 of the present invention;

Fig. 5 is a schematic diagram of the electrode frame and electrode structure in Embodiment 4 of the present invention.

Detailed ways

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples. Unless otherwise specified, the experimental methods used in the present invention are conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial sources.

The flow battery of the present invention selects the all-vanadium flow battery with the most mature technology for the embodiment description, but does not limit the specific type of the flow battery. Applications in flow batteries are also within the protection scope of the present invention.

All-vanadium redox flow battery stack performance test conditions: use graphite carbon felts with different volume densities produced by Liaoyang Jingu Carbon Materials Co., Ltd. as reaction electrodes, and the positive and negative electrolytes are VO ²⁺ /VO ₂ ⁺ and V ²⁺ respectively /V ³⁺ sulfuric acid solution, the battery operating temperature is 37°C.

In the present invention, the total size of the n electrodes may be consistent with the size of the electrolyte reaction zone, and the width of each electrode may be the same or different, and there is no requirement for the width ratio of each electrode. In the following embodiments, taking the same width of each electrode as an example is only for convenience of description.

Example 1

The number, size and bulk density of the electrodes are shown in Table 1.

The carbon felt electrode parameter in the embodiment 1 of table 1

Assemble into a 44-cell stack, charge and discharge at a constant current (average discharge power 5kW) at a current fluid density of 100mA/cm ² , and select the data of the fifth cycle as the initial performance data. Note, the dimensions of the ion exchange membrane and bipolar plate are the same as the outer edge of the electrode frame.

Example 2

The number, size and bulk density of the electrodes are shown in Table 2.

Carbon felt electrode parameter in table 2 embodiment 2

Assemble into a 44-cell stack, charge and discharge at a constant current (average discharge power 5kW) at a current fluid density of 100mA/cm ² , and select the data of the fifth cycle as the initial performance data. Note, the dimensions of the ion exchange membrane and bipolar plate are the same as the outer edge of the electrode frame.

Example 3

The number, size and bulk density of the electrodes are shown in Table 3.

Carbon felt electrode parameter in table 3 embodiment 3

Assemble into a 44-cell stack, charge and discharge at a constant current (average discharge power 5kW) at a current fluid density of 100mA/cm ² , and select the data of the fifth cycle as the initial performance data.

Example 4

The number, size and bulk density of the electrodes are shown in Table 4.

Carbon felt electrode parameter in table 4 embodiment 4

Assemble a 40-cell stack, perform constant current charge and discharge (average power 5kW) at a current fluid density of 100mA/cm ² , and select the data of the fifth cycle as the initial performance data. Note, the dimensions of the ion exchange membrane and bipolar plate are the same as the outer edge of the electrode frame.

Comparative example 1

Using the same electrode frame structure as in Example 1 or 2, replace the electrode with a single carbon felt with a size of 200mm×460mm and a bulk density of 0.07g/cm ³ . /cm ² for constant current charge and discharge (average discharge power 5kW), select the data of the fifth cycle as the initial performance data.

Comparative example 2

Use the same electrode frame structure as in Example 1 or 2, replace the electrode with a single carbon felt with a size of 200mm×460mm and a bulk density of 0.12g/ ^cm3 , and other conditions unchanged, assemble a 44-cell stack, and use 100mA /cm ² for constant current charge and discharge (average discharge power 5kW), select the data of the fifth cycle as the initial performance data.

Comparative example 3

Use the same electrode frame structure as in Example 1 or 2, replace the electrode with a single carbon felt with a size of 200mm×460mm and a bulk density of 0.15g/ ^cm3 , and other conditions unchanged, assemble a 44-cell stack, and use 100mA /cm ² for constant current charge and discharge (average discharge power 5kW), select the data of the fifth cycle as the initial performance data.

Comparative example 4

Use the same electrode frame structure as in Example 3, replace the electrode with a single carbon felt with a size of 300mm×335mm and a bulk density of 0.07g/cm ³ , and other conditions remain unchanged, assemble into a 40-cell stack, and use 100mA/cm The electric fluid density of ² is charged and discharged at a constant current (average discharge power 5kW), and the data of the fifth cycle is selected as the initial performance data.

Comparative example 5

Using the same electrode frame structure as in Example 3, the electrode was replaced with a single carbon felt with a size of 300mm×335mm and a bulk density of 0.12g/cm ³ , and other conditions remained unchanged, assembled into a 40-cell stack, and a 100mA/cm The electric fluid density of ² is charged and discharged at a constant current (average discharge power 5kW), and the data of the fifth cycle is selected as the initial performance data.

Comparative example 6

Using the same electrode frame structure as in Example 3, the electrode was replaced with a single carbon felt with a size of 300mm×335mm and a bulk density of 0.15g/cm ³ , and other conditions remained unchanged, and assembled into a 40-cell stack. The electric fluid density of ² is charged and discharged at a constant current (average discharge power 5kW), and the data of the fifth cycle is selected as the initial performance data.

Table 5 embodiment 1-3, the test data of comparative example 1-6 stack

As can be seen from Examples 1-3 and Comparative Examples 1-3 (or Example 4 and Comparative Examples 4-6), under other conditions such as the same electrode frame, using the method of the present invention can significantly reduce the concentration of the stack. Poor polarization improves voltage efficiency and energy efficiency; as can be seen from Comparative Examples 1-3 and Comparative Examples 4-6, when increasing the flow distance of the electrolyte in the stack, the short flow structure is not used (Comparative Examples 4- 6), the effective utilization of the area of ion exchange membrane and bipolar plate (under the same premise of total use area) can increase (from 61.3% to 67.0%), and under this condition, from embodiment 4 and comparative example 1-3 It can be seen that with the method of the present invention, when the stack does not use a short-flow structure, the efficiency of the stack can still reach or even exceed the effect of a short-flow structure stack, which shows that the method of the present invention is useful for reducing It is effective to improve the voltage efficiency and energy efficiency of the battery by concentration polarization of the flow battery, and to a certain extent, it can get rid of the constraints of the stack shape.

The above are typical embodiments and comparative examples of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field shall, within the technical scope disclosed in the present invention, according to the technical scheme of the present invention and its design Any equivalent replacement or change shall fall within the protection scope of the present invention.

Claims (7)

1. A simple low-cost method for reducing concentration polarization of a flow battery is characterized in that electrodes with different n block densities rho are sequentially arranged in electrolyte reaction areas of a positive electrode and a negative electrode along the flowing direction of electrolyte, and the sum of the combined areas of the n electrodes is consistent with the area of the electrolyte reaction area.

2. The simple low-cost method for reducing concentration polarization of a flow battery as claimed in claim 1, wherein the value range of n is: n is more than or equal to 2 and less than or equal to 10.

3. The simple and low-cost method for reducing concentration polarization of a flow battery as claimed in claim 1, wherein the n electrodes with different bulk densities ρ arranged in sequence along the electrolyte flow direction have sequentially reduced bulk densities ρ.

4. The simple low-cost method for reducing concentration polarization of the flow battery as claimed in claim 1, wherein the bulk density is the density after the stack is assembled and compressed, and the density meets 0.07g/cm ³ ≤ρ≤0.15g/cm ³ 。

5. The simple and low-cost method for reducing concentration polarization of a flow battery as claimed in claim 1, wherein said electrode is a porous carbon material electrode.

6. The simple and low-cost method for reducing concentration polarization of a flow battery as claimed in claim 1, wherein the electrode is a carbon felt electrode, a carbon fiber cloth electrode, a carbon paper electrode, a foam carbon electrode, or a 3D printed carbon electrode.

7. The electrode prepared by the simple low-cost method for reducing the concentration polarization of the flow battery according to claim 1 is suitable for the field of redox flow batteries.

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