CN106450404A - Flow battery stack - Google Patents

Abstract

The present invention discloses a liquid flow battery stack, which is composed of a plurality of single cells connected in series, each of which includes a bipolar plate, an electrode, an electrode frame, and an ion conduction membrane. The component structure of the first and/or last single cell in the stack is the same as the component structure of other single cells. By improving the structure of the first and last single cells, including replacing the bipolar plates of the first and last single cells with materials with lower conductivity and greater roughness; replacing the ion conduction membranes of the first and last single cells with membrane materials with lower resistance and better performance, the voltage extreme difference of the liquid flow battery stack is effectively reduced, the voltage consistency of the single cells in the stack is greatly improved, the negative impact of the long-term operation of the stack under a higher voltage extreme difference on the battery system is avoided, and the long-term operation stability of the battery system is improved.

Description

Flow battery stack

technical field

The invention relates to the field of manufacturing liquid flow batteries, in particular to a liquid flow battery electric stack.

Background technique

The increasing demand for traditional energy in the development of modern economy and society has made the problem of insufficient supply increasingly prominent. People have to look for renewable energy such as wind energy and solar energy. In recent years, new energy represented by wind energy and solar energy has occupied a place in energy supply. With the increase of demand, the proportion is still increasing, but it is affected by the weather. The contradiction between supply and demand that causes intermittent power generation is relatively prominent, and the development of large-scale energy storage is imperative.

As a way of large-scale energy storage--the production and development of flow batteries provide a good supplement for the above-mentioned defects of new energy sources. Liquid flow batteries have the characteristics of good safety, long life, large storage capacity, separate and adjustable power and capacity, free site selection, clean and environmental protection, etc., which can ensure the stable output of new energy such as wind energy and solar energy after storage adjustment, and realize scale The important role of chemical power management, grid auxiliary, voltage control, and large uninterruptible power supply.

The electric stack is the core component of the flow battery. At present, the electric stack is connected in series with multiple single cells, and each single cell has the same structure; a diaphragm separates the positive and negative electrodes, and the positive and negative electrodes have the same structure; Each side is followed by electrodes and bipolar plates (positive and negative common).

The electric stack is a place where chemical energy and electric energy are mutually converted, and the rationality of its structure is directly related to the efficiency and operation reliability of the flow battery system. The stack improves the overall working voltage and power of the stack by connecting the positive and negative electrodes in series, but it also reduces the voltage uniformity between the single cells in the stack.

In the prior art, the preferred method is to use single cells with the same structure to assemble a high-power stack, but the position of the first and last single cells of the stack has a certain specificity compared with other cells: it is different from the current collector plate. The components are in direct contact, and the strong clamping force of the bolts on the end plate first acts on the first and last cells, resulting in greater contact resistance and compression force of the first and last cells than cells in other positions in the stack, resulting in The performance of the first and last single cells is poor, and the damage rate is relatively high. After testing, during the charging and discharging operation of the stack, the voltage of the first and last single cells has a large voltage deviation compared with other single cells, up to tens of millivolts. With the increase of the current density in the process of charging and discharging, this voltage deviation will increase exponentially, and the voltage inhomogeneity between the single cells will cause the flow battery system to make the first and last electrodes of the stack in the long-term operation. Different degrees of overvoltage phenomenon occurred and burned down, resulting in a decrease in the overall efficiency of the battery system, and the battery stack was scrapped and unusable.

Contents of the invention

Aiming at the technical defect of the extremely poor voltage of the current flow battery stack in the prior art, the present invention provides a flow battery stack capable of reducing the extreme voltage difference of the stack.

After research, the present invention finds that the excessive voltage difference between the first and last single cells of the stack is due to the contact between the bipolar plate and the current collector plates (usually copper plates) on both sides, and the contact between two materials with different structures and different surface topography is inevitable. This increases the contact resistance between the two.

The present invention provides the following technical solutions to solve the defects of the prior art: the electric flow battery stack is composed of several single cells connected in series, and each single cell includes a bipolar plate, an electrode, an electrode frame, and an ion-conducting membrane. The structure of the components of the first and/or last cell is different from that of the components of other cells.

A specific technical solution is to increase the electrical conductivity of the bipolar plate material of the first and/or last cell.

Preferably, the electrical conductivity of the bipolar plate material of the first and/or last single cell is at least 120% of the conductivity of the bipolar plate material of other single cells. By increasing the conductivity of the bipolar plate, the conductivity of the body of the bipolar plate is improved, and the overall resistance of the first and last cells is reduced.

Preferably, the bipolar plate material of the first section and/or the last single cell is subjected to surface modification treatment; the modification treatment method includes surface deposition catalysis, surface coating, etc., and the catalyst used for surface deposition catalysis is preferably Bi or Mn.

Another specific solution is that the surface roughness of the bipolar plate material of the first and/or last single cell is at least 120% of the surface roughness of the bipolar plate material of other single cells. By increasing the roughness of the surface of the bipolar plate, the bipolar plate has more contact area with the electrode material, the contact resistance between the two is reduced, and the performance of the first and last cells is improved.

Another specific solution is to replace the ion-conducting membrane of the first and last cells with an ion-conducting membrane with better performance (smaller thickness, more ion-conducting groups, or larger ion-transporting pore size) to reduce the cost of the first and last cells. The single cell voltage improves the performance of the first and last single cells.

Preferably, the resistance of the ion-conducting membrane material of the first and/or last unit cell is at most 80% of the resistance of the ion-conducting membrane of other unit cells, preferably 50% to 70%, which can be achieved by reducing the resistance of the ion-conducting membrane material It can be realized by surface resistance or volume resistance. By improving the electrical conductivity of the membrane material of the first and last sections, the contact resistance between the membrane material and the electrode material or the overall resistance of the single cells of the first and last sections is reduced.

Preferably, the number of ion-exchange groups on the surface of the ion-conducting membrane of the first and/or last unit cell is at least 20% greater than the number of ion-exchange groups on the surface of the ion-conducting membrane of other unit cells. The number of ion-exchange groups on the surface of the membrane material can be increased by surface treatment of the membrane material, such as soaking in an oxidizing liquid, and then the exchange capacity and speed of active groups on the surface of the membrane material can be improved. Preferably, the ion exchange groups are sulfonic acid groups and/or carboxylic acids.

Preferably, the pore size of the ion-conducting membrane of the first and/or last unit cell is at least 10% larger than the pore size of the ion-conducting membrane of other unit cells, preferably 15%-30%. By selecting a membrane material with a larger pore size, the migration rate of hydrogen ions permeating the membrane material of the first and last single cells can be increased, thereby improving the reaction speed and overall performance of the first and last single cells.

Preferably, the thickness of the ion-conducting membrane of the first and/or last unit cell is at most 90% of the thickness of the ion-conducting membrane of other unit cells. By reducing the thickness of the membrane material, the bulk resistance of the membrane material is effectively reduced, thereby reducing the overall resistance of the first and last single cells.

The beneficial effects of the present invention are as follows:

1. By improving the structure of the first and last cells of the stack, the problem of excessive voltage at the first and last cells in the stack is effectively solved, which has the advantages of easy operation and good effect.

2. The structure of the bipolar plates of the first and last single cells is improved, and the conductivity and roughness of the bipolar plates of the first and last single cells are changed, so that the bipolar plates are in closer contact with the electrode material and the current collector plate on the other side , greatly reducing the contact resistance between the electrode and the bipolar plate, between the bipolar plate and the current collector, and improving the overall performance and long-term operation stability of the stack.

3. Through surface treatment on the surface of the bipolar plate of the first and last single cells, the conductivity and catalyst content of the surface of the bipolar plate are increased, the reactivity of the bipolar plate side of the electrode material is improved, and the redox reaction speed of the first and last single cells is accelerated. Improve the energy efficiency, coulombic efficiency and voltage efficiency of the first and last single cells, and improve the stability of the long-term operation of the stack.

4. Through the improvement of the membrane material of the first and last single cells, the reaction speed on the surface of the membrane material is accelerated, the hydrogen ion transmission speed is accelerated, the body resistance and polarization resistance of the first and last single cells are effectively reduced, and the overall performance of the first and last single cells is improved. , greatly reducing the voltage difference of the stack.

5. There is no need to make structural improvements to the other single cells of the stack, making it possible to realize batch processing and manufacturing of the first and last single cells, effectively reducing the assembly and production costs of the stack, and promoting the full industrialization and commercialization of the flow battery application is important.

Description of drawings

1 piece of accompanying drawing of the present invention,

Figure 1 is a schematic diagram of the structure of the flow battery stack device;

In Fig. 1, 1 end plate, 2 current collector plate, 3 bipolar plate, 4 electrode frame, 5 electrode, 6 ion conducting membrane.

detailed description

The following non-limiting examples can enable those skilled in the art to understand the present invention more fully, but do not limit the present invention in any way.

Example 1 The first and last cells use bipolar plates with higher conductivity

Voltage range test method: Connect the assembled cell stack with the electrolyte circulation system and the battery management system, charge and discharge it at a fixed current density, and record the last charge after multiple charge and discharge cycles. The voltage of the discharge cycle is extremely poor. The specific method is to record the actual voltage value of each single battery when the battery is charged to a certain voltage value during the charging process (for example: the all-vanadium redox flow battery is 1.50V average voltage multiplied by the number of single cells), and all The voltage difference between the two single cells with the maximum voltage and the minimum voltage in the single cell is the voltage range of the stack at the corresponding current density.

Table 1

The specific parameters of the electric stack of embodiment 1 are shown in Table 1. A 30-section battery stack is adopted. The single cells of the electric stack are connected in series. The conductivity of the bipolar plate is 0.5s/cm, and the conductivity of the bipolar plates of other cells is 0.2s/cm. Connect the assembled 3kW stack to the electrolyte circulation system and the battery management system, charge and discharge it at a current density of 110mA/cm ² , and record the 20th charging cycle after the battery runs stably for 19 charge and discharge cycles. The voltage at the end of the discharge cycle charge is extremely poor.

Comparative example 1

The components listed in Table 1 are used to assemble a 3kW battery stack. The single cells of the stack are connected in such a way that the structure of each single cell in series is exactly the same, that is, the thickness of the bipolar plate is 2 mm, and the conductivity is 0.2 s/cm.

The test method of voltage extreme difference is the same as embodiment 1, and test result is as shown in table 2:

Table 2

Example 2 The bipolar plates of the first and last single cells are treated by electrochemical deposition

table 3

Part Name performance characteristics power 20kW configuration solution 1.0mol/L sulfuric acid/hydrochloric acid mixed acid system vanadium electrolyte Number of cells 46 knots Collector plate copper plate electrode Thickness 5.5mm bipolar plate The thickness is 1.5mm, and the first and last sections are treated with electrochemical deposition ion conducting membrane Thickness 150μm, surface resistance 0.5Ω/cm ² . Electrode frame Thickness 5mm, with flow channel

The specific parameters of the battery stack in Example 2 are shown in Table 7. A 46-cell battery stack is used. The single cells of the battery stack are connected in series. The thickness of the ion-conducting membrane is 150 μm, and the measured value of the surface resistance is 0.5Ω/cm ² . The first and last bipolar plates are treated with chemical deposition catalyst, and the treatment process is shown in Table 4.

Table 4

deposition process parameter 1 parameter 2 deposited metal ions Bi ³⁺ Mn ²⁺ Electrolyte BiCl ₃ +HCl MnSO ₄ +H ₂ SO4 Sedimentation 100mg/ ^m2 200mg/ ^m2 current density, time 10mA/cm ² , 30min 30mA/cm ² , 30min

Connect the assembled 20kW stack to the electrolyte circulation system and the battery management system, charge and discharge it at a current density of 50mA/cm ² , and record the 50th charging cycle after the battery runs stably for 49 cycles. The voltage at the end of the discharge cycle charge is extremely poor.

Comparative example 2

The components listed in Table 3 are used to assemble a 20kW battery stack. The single cells of the stack are connected in series, and the structure of each single cell is exactly the same (the first and last sections of the bipolar plate are not treated with electrochemical deposition).

The test method of voltage extreme difference is the same as embodiment 1, and test result is as shown in table 5:

table 5

Example 3 The first and last cells use bipolar plates with relatively high roughness

Table 6

The specific parameters of the battery stack in Example 3 are shown in Table 6. The assembled 1kW battery stack is connected to the electrolyte circulation system and the battery management system, and it is charged and discharged at a current density of 150mA/ ^cm2 . When the battery runs stably After 19 charge-discharge cycles, record the voltage extreme difference at the end of the 20th charge-discharge cycle.

Comparative example 3

Use the components listed in Table 5 to assemble a 1kW battery stack. The single cells of the stack are connected in series, and the structure of each single cell is exactly the same (the surface roughness of the bipolar plate: Ra 3.2 μm).

The test method of voltage extreme difference is the same as embodiment 1, and the test results are as shown in table 7:

Table 7

Example 4 The first and last batteries use different structural membrane materials

4.1 The surface resistance of the membrane material of the first and last single cell is different from that of other sections

Table 8

The battery parameters are shown in Table 8. Connect the assembled 10kW stack to the electrolyte circulation system and battery management system, and charge and discharge it at a current density of 120mA/cm2. When the battery runs stably for 29 charge-discharge cycles Afterwards, the voltage extreme difference of the 30th charge-discharge cycle was detected and recorded according to the method of Example 1.

Example 4.2 The number of ion exchange groups of the membrane material of the first and last single cell is different from that of other sections

The parameters of the stack are the same as in Example 4.1 except that the structure of the membrane material is different. The parameters of the ion-conducting membrane are shown in Table 9. The operating conditions of the battery are the same as in Example 4.1.

Table 9

Ion Conducting Membrane Parameters value thickness 150μm Surface resistance 0.40Ω/ ^cm2 thickness 150μm Pore diameter (mean) 15nm Ion exchange content of first and last section 0.83mmol/g Other Sections Ion Exchange Content 0.45mmol/g

Example 4.3 The pore size of the membrane material of the first and last single cell is different from that of other sections

The parameters of the stack are the same as in Example 4.1 except that the structure of the membrane material is different. The parameters of the ion-conducting membrane are shown in Table 10. The operating conditions of the battery are the same as in Example 4.1.

Table 10

Ion Conducting Membrane Parameters value thickness 150μm Surface resistance 0.40Ω/ ^cm2

ion exchange content 0.45mmol/g Pore diameter of first and last segment membrane (mean value) 20nm Other membrane aperture (mean) 15nm

Example 4.4 The thickness of the membrane material of the first and last single cell is different from that of other sections

The parameters of the stack are the same as those in Example 4.1 except that the structure of the membrane material is different. The parameters of the ion-conducting membrane are shown in Table 11. The operating conditions of the battery are the same as in Example 4.1.

Table 11

Ion Conducting Membrane Parameters value thickness 150μm Surface resistance 0.40Ω/ ^cm2 Pore diameter (mean) 15nm ion exchange content 0.45mmol/g Thickness of first and last section 120μm Other section thickness 150μm

Comparative example 4

The components listed in Table 7 are used to assemble the stack with the same specifications, and the structure of the first and last ion-conducting membrane is exactly the same as that of other sections, the surface resistance is 0.40Ω/cm2, the thickness is 150μm, the ion exchange content is 0.45mmol/g, and the pore diameter The size is 15nm. The battery operation method is exactly the same as that in Example 4.1.

The test method of voltage extreme difference is the same as embodiment 1, and the test results are as shown in table 12:

Table 12

Example 5 Flow battery structure with bipolar plates and membrane materials of different structures used in the first and last batteries

Table 13

The battery parameters are shown in Table 13. The structures of the bipolar plates and ion-conducting membranes in the first and last sections (sections 1 and 5) of the stack are different from those of other single cells. Connect the assembled 100W stack to the electrolyte circulation system and the battery management system, charge and discharge it at a current density of 110mA/cm ² , and record the 100th charging cycle after the battery runs stably for 99 charge and discharge cycles. The voltage at the end of the discharge cycle charge is extremely poor.

Comparative example 5

The components listed in Table 12 are used to assemble the electric stack with the same specifications, and the structure of the bipolar plate and ion-conducting membrane of the first and last single cells is exactly the same as that of other single cells. The measured value of the surface roughness of the bipolar plate is Ra 3.2 μm, and the conductivity The rate is 0.1s/cm, and the ion exchange content of the membrane material is 0.8mmol/g. The battery operation method is completely consistent with that of Example 5.

The test method of voltage extreme difference is the same as embodiment 1, and the test results are as shown in table 14:

Table 14

Claims (10)

1. The electric flow battery stack is composed of several single cells connected in series, and each single cell includes a bipolar plate, an electrode, an electrode frame, and an ion-conducting membrane. It is characterized in that the first and/or last section of the stack The structure of the cell components is different from that of other cell components. 2. The flow battery stack according to claim 1, characterized in that, the electrical conductivity of the bipolar plate material of the first and/or last single cell is at least half of the conductivity of the bipolar plate material of other single cells 120%. 3 . The flow battery stack according to claim 2 , wherein the bipolar plate material of the first and/or last single cell is subjected to surface modification treatment. 4 . 4. The flow battery stack according to claim 1, characterized in that, the surface roughness of the bipolar plate material of the first and/or last single cell is at least as rough as the surface roughness of the bipolar plate material of other single cells 120% of the degree. 5 . The flow battery stack according to claim 1 , wherein the performance of the ion-conducting membrane material of the first and/or last unit cell is better than that of other unit cells. 6 . 6 . The flow battery stack according to claim 5 , wherein the resistance of the material of the ion-conducting membrane of the first and/or last unit cell is at most 80% of the resistance of the ion-conducting membrane of other unit cells. 7. The flow battery stack according to claim 5, wherein the number of ion exchange groups on the surface of the ion-conducting membrane of the first and/or last unit cell is at least greater than that on the surface of the ion-conducting membrane of other unit cells 20% of the number of ion exchange groups. 8. The flow battery stack according to claim 7, wherein the ion exchange group is a sulfonic acid group and/or a carboxylic acid. 9. The flow battery stack according to claim 5, wherein the pore size of the ion-conducting membrane of the first and/or last unit cell is at least 10% larger than the pore size of the ion-conducting membrane of other unit cells . 10 . The flow battery stack according to claim 5 , wherein the thickness of the ion-conducting membrane of the first and/or last unit cell is at most 90% of the thickness of the ion-conducting membrane of other unit cells. 11 .