Method for reducing internal resistance of all-vanadium redox flow battery

Abstract

The invention discloses a method for reducing the internal resistance of an all-vanadium redox flow battery. The method comprises the following steps: pre-treating a graphite felt electrode and a bipolar plate; pretreating the conductive silver paste; uniformly coating the pretreated conductive silver paste on the pretreated bipolar plate; and pressing and molding the pretreated graphite felt electrode and the bipolar plate coated with the conductive silver paste to obtain the integrated electrode. The treatment process is simple, and the operation process is convenient; compared with the prior art that the interface resistance is reduced by increasing the contact surface or directly pressing tightly, the bipolar plate and the graphite felt electrode are pressed and cured into the integrated electrode through the modified conductive silver paste, and the interface resistance is directly and almost eliminated.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid flow batteries, and in particular relates to a method for reducing the internal resistance of an all-vanadium liquid flow battery. Background Art

[0002] All-vanadium flow battery is a large-scale and efficient electrochemical energy storage technology. Compared with mainstream lithium-ion batteries, it has many advantages such as intrinsic safety, decoupling of output power and capacity, flexible system design, long battery cycle life, and deep discharge without damaging the battery. At present, the main direction of all-vanadium flow battery is to improve efficiency and reduce costs. The redox activity of the electrode reaction can be improved by modifying the electrode and electrolyte, thereby improving the coulombic efficiency of the battery. The polarization of the electrode reaction and the charge and discharge voltage difference can be reduced by increasing the conductivity of the raw materials and reducing the internal resistance of the battery, thereby improving the voltage efficiency of the battery. At present, the assembly of the battery is through mechanical compression between the graphite felt electrode and the bipolar plate, so that the graphite felt reaches a certain compression ratio, but the direct physical compression between the untreated graphite felt and the bipolar plate interface often has a large interface contact resistance, and the size of this resistance can be appropriately reduced by the degree of compression, but the degree of ohmic polarization in the electrode reaction process is still large, and the battery still exhibits a high charging voltage and a low discharge voltage, which greatly affects the voltage efficiency and comprehensive energy efficiency of the electrode reaction. Summary of the invention

[0003] In view of the above problems, the present invention discloses a method for reducing the internal resistance of an all-vanadium liquid flow battery, comprising:

[0004] Pre-treat graphite felt electrodes and bipolar plates;

[0005] Pre-treating the conductive silver paste;

[0006] Uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate;

[0007] The pre-treated graphite felt electrode and the bipolar plate coated with conductive silver paste are pressed into shape to obtain an integrated electrode.

[0008] Furthermore, the specific steps of pre-treating the graphite felt electrode and the bipolar plate are as follows:

[0009] Wipe the surface of the bipolar plate clean with alcohol or acetone;

[0010] Dry the graphite felt electrode and bipolar plate at 60-100°C for 30-60 minutes.

[0011] Furthermore, the specific steps of pre-treating the conductive silver paste are as follows:

[0012] The carbon material is added to the conductive silver paste, followed by thorough stirring at 50 to 80° C. for 30 to 50 minutes.

[0013] Furthermore, 0.005-0.02 g of carbon material is mixed into every 10 ml of the conductive silver paste.

[0014] Furthermore, the conductive silver paste contains 70% to 90% silver powder and 10% to 30% curing agent.

[0015] Furthermore, the carbon material is one or more of carbon fiber, carbon nanotube, graphene, and fullerene.

[0016] Furthermore, the specific steps of uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate are as follows:

[0017] The pretreated conductive silver paste is immediately coated on the pretreated bipolar plate, and the coating thickness of the conductive silver paste is 0.05 to 0.25 mm.

[0018] Furthermore, the coating is one of spraying, dipping and brushing.

[0019] Furthermore, the specific steps of pressing the pre-treated graphite felt electrode and the bipolar plate coated with the conductive silver paste to obtain the integrated electrode are as follows:

[0020] The pre-treated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and pressed by a tooling, and then placed in a vacuum drying oven at 100-180° C. for curing for 30-60 minutes to obtain an integrated electrode;

[0021] The curing temperature rise rate in the vacuum drying oven is 150-200°C / h.

[0022] Furthermore, the compression ratio of the graphite felt electrode after pressing is 20% to 50%.

[0023] Compared with the prior art, the embodiments of the present invention have at least the following advantages:

[0024] 1. The treatment process is simple and the operation process is convenient (substrate purification, conductive silver paste modification spraying, pressing and curing integration). The core of the present invention is to only apply the pre-treated conductive silver paste on the bipolar plate to achieve the effect of reducing resistance;

[0025] 2. The present invention does not use toxic and harmful gases and reagents, making the process environmentally friendly, pollution-free, green, low-carbon, clean and efficient;

[0026] 3. The resistance reduction effect of the present invention is very significant. Compared with other existing technologies that still reduce the interface resistance by increasing the contact surface or directly pressing, the present invention presses and solidifies the bipolar plate and the graphite felt electrode into an integrated electrode through modified conductive silver paste, which directly and almost eliminates the interface resistance;

[0027] 4. The conductive silver paste and other reagent materials used are cheaper than the precious catalysts used for graphite felt electrodes and bipolar plate resistance reduction modification (in the prior art, carbon materials are coated on the surface of bipolar plates, and precious metal catalysts are modified on the graphite felt interface to achieve the effect of reducing internal resistance), which can improve battery performance without incurring huge costs;

[0028] 5. There is no need to change the bulk properties of the bipolar plates and graphite felt electrodes (in the prior art, the bipolar plates are heated and softened and the graphite felt electrodes are fused into an integrated electrode. This process easily leads to aging of the polyethylene plastic in the bipolar plates, which in turn increases resistance), thereby ensuring the activity of the electrode redox reaction and the capacity efficiency of the battery.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A flow chart showing a method for reducing the internal resistance of an all-vanadium liquid flow battery according to an embodiment of the present invention is shown;

[0032] Figure 2 A charge and discharge voltage curve diagram according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Figure 1 FIG. 1 is a flow chart showing a method for reducing the internal resistance of an all-vanadium liquid flow battery according to an embodiment of the present invention. Figure 1As shown, in view of the performance defects of the prior art all-vanadium liquid flow battery, such as large interface contact internal resistance, high degree of ohmic polarization of electrode reaction, resulting in large charge and discharge voltage difference and low voltage efficiency, after a large number of experimental studies, the present invention proposes a method for reducing the internal resistance of the all-vanadium liquid flow battery, comprising the following steps:

[0035] Pre-treat graphite felt electrodes and bipolar plates;

[0036] Pre-treating the conductive silver paste;

[0037] Uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate;

[0038] The pre-treated graphite felt electrode and the bipolar plate coated with conductive silver paste are pressed together to obtain an integrated electrode. The specific structure of the integrated electrode is bipolar plate / conductive silver paste / graphite felt electrode.

[0039] The present invention provides a method for reducing the internal resistance of an all-vanadium liquid flow battery. The conductive silver paste that has been optimized and pretreated is uniformly coated on the bipolar plate, and is pressed and cured with a graphite felt electrode to form a shape, thereby significantly reducing the internal resistance of the all-vanadium liquid flow battery and improving the voltage efficiency of the battery, thereby achieving a significant improvement in the battery's power storage performance.

[0040] In some embodiments, the specific steps of pre-treating the graphite felt electrode and the bipolar plate are as follows:

[0041] Wipe the surface of the bipolar plate clean with alcohol or acetone;

[0042] Dry the graphite felt electrode and bipolar plate at 60-100°C for 30-60 minutes.

[0043] The purpose of drying is to keep the bipolar plates and graphite felt electrodes dry, which is beneficial to the solidification of the conductive silver paste and improve the bonding strength.

[0044] In some embodiments, the specific steps of pre-treating the conductive silver paste are as follows:

[0045] The carbon material is added to the conductive silver paste, followed by thorough stirring at 50 to 80° C. for 30 to 50 minutes.

[0046] The above conditions are used to stir the mixture sufficiently to ensure that the carbon material is evenly dispersed in the conductive silver paste.

[0047] In some embodiments, 0.005-0.02 g of carbon material is mixed in every 10 ml of the conductive silver paste. This addition amount can achieve the best bonding strength. If the addition amount of carbon material is too little, the graphite felt electrode and the bipolar plate are easily delaminated. If the addition amount of carbon material is too high, the conductive silver paste is too little, resulting in insufficient interface bonding strength.

[0048] In some embodiments, the silver powder content of the conductive silver paste is 70% to 90%, and the curing agent content is 10% to 30%. Under this ratio, the bonding strength between the graphite felt electrode and the bipolar plate is the highest, and the conductivity of the integrated electrode can be guaranteed to be the maximum.

[0049] Exemplarily, the curing agent is ethylene triamine DETA, diaminocyclohexane DACH, methylene biscyclohexylamine 4,4'-PACM, and the like.

[0050] In some embodiments, the carbon material is one or more of carbon fiber, carbon nanotube, graphene, and fullerene. The above carbon materials added to the conductive silver paste can enhance the bonding strength between the graphite felt electrode and the bipolar plate, which are both carbon materials. The pure conductive silver paste is easy to delaminate at the interface.

[0051] In some embodiments, the specific steps of uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate are as follows:

[0052] The pre-treated conductive silver paste is immediately applied evenly and flatly on the pre-treated bipolar plate, and the coating thickness of the conductive silver paste is 0.05-0.25mm. On the one hand, the coating thickness ensures the original size of the integrated electrode as much as possible, because the graphite felt electrode needs to be compressed during later use. If the conductive silver paste layer is too thick, it will affect the compression ratio of the graphite felt electrode; secondly, the thickness can ensure the bonding strength and conductivity between the graphite felt electrode and the bipolar plate. If it is too thick, the cost will increase and the conductive silver paste will be wasted.

[0053] In some embodiments, the coating is one of spraying, dipping, and brushing.

[0054] In some embodiments, the specific steps of pressing the pre-treated graphite felt electrode and the bipolar plate coated with the conductive silver paste to obtain the integrated electrode are as follows:

[0055] The pre-treated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and pressed by a tooling, and then placed in a vacuum drying oven at 100-180° C. for curing for 30-60 minutes to obtain an integrated electrode;

[0056] The curing temperature rise rate in the vacuum drying oven is 150-200°C / h.

[0057] Drying and curing under the above conditions is conducive to the rapid curing and forming of the integrated electrode, preventing the displacement of the two electrodes and the generation of bubbles or pores in the conductive silver paste due to the long curing process, and also preventing the change of the properties of the conductive silver paste due to too long a time.

[0058] In some embodiments, the compression ratio of the graphite felt electrode after pressing is 20% to 50%. This compression ratio can reduce the volume of the battery cavity while ensuring that the circulation and diffusion of the electrolyte are not affected.

[0059] The method for reducing the internal resistance of an all-vanadium liquid flow battery of the present invention has the advantages of simple processing technology and convenient operation process, and no toxic and harmful gases and reagents are used, so that the process is environmentally friendly and pollution-free, green, low-carbon, clean and efficient; the resistance reduction effect of the present invention is very significant, compared with other existing technologies that still reduce the interface resistance by increasing the contact surface or directly pressing, the present invention presses and solidifies the bipolar plate and the graphite felt electrode into an integrated electrode through modified conductive silver paste, and directly almost eliminates the interface resistance; the conductive silver paste and other reagent materials used are cheaper than the precious catalysts used for the resistance reduction modification of the graphite felt electrode and the bipolar plate (in the prior art, carbon materials are coated on the surface of the bipolar plate, and precious metal catalysts are modified on the graphite felt interface to achieve the effect of reducing the internal resistance), and the battery performance is improved without incurring huge costs; there is no need to change the bulk properties of the bipolar plate and the graphite felt electrode (in the prior art, the bipolar plate is heated and softened and the graphite felt electrode is fused into an integrated electrode, and this process easily leads to the aging of the polyethylene plastic in the bipolar plate, which will increase the resistance), thereby ensuring the activity of the electrode redox reaction and the capacity efficiency of the battery.

[0060] The flow battery system used in the charge and discharge tests in the following examples is an all-vanadium flow battery. The specific description is as follows:

[0061] 1. It is composed of single battery;

[0062] 2. The battery electrode area is 24cm 2 ;

[0063] 3. The vanadium ion concentration in the electrolyte is 1.60 mol / L and the sulfate concentration is 4.0 mol / L;

[0064] 4. The current density of the battery constant current charge and discharge is 100-150mA / cm 2 ;

[0065] 5. The charge and discharge cut-off voltages of single cells are 1.65V and 1.0V respectively;

[0066] 6. The volume of positive / negative electrolyte is 100mL each.

[0067] Implementation 1:

[0068] Wipe the surface of the bipolar plate clean with alcohol, and dry the graphite felt electrode and the bipolar plate at 60°C for 30 minutes. The selected conductive silver paste contains 70% silver powder and 30% ethylenetriamine DETA. Add carbon fiber to the conductive silver paste to reduce the fluidity of the conductive silver paste and increase the bonding strength with the bipolar plate and graphite felt electrode. Mix 0.005g of carbon fiber in every 10ml of conductive silver paste, then stir thoroughly at 50°C for 30 minutes, and then immediately spray the pretreated conductive silver paste evenly and evenly on the pretreated bipolar plate, with a coating thickness of 0.05mm. The pretreated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and the tooling is pressed to make the compression ratio of the graphite felt electrode 20%. After pressing, put it in a vacuum drying oven and cure it at 100°C for 30 minutes. The curing heating rate of the vacuum drying oven is 150°C / h to obtain an integrated electrode.

[0069] Implementation 2:

[0070] Wipe the surface of the bipolar plate clean with alcohol, and dry the graphite felt electrode and the bipolar plate at 100°C for 60 minutes. The selected conductive silver paste contains 90% silver powder and 10% ethylenetriamine DETA. Add carbon fiber to the conductive silver paste to reduce the fluidity of the conductive silver paste and increase the bonding strength with the bipolar plate and graphite felt electrode. Mix 0.02g of carbon fiber in every 10ml of conductive silver paste, then stir thoroughly at 80°C for 50 minutes, and then immediately spray the pretreated conductive silver paste evenly and evenly on the pretreated bipolar plate, with a coating thickness of 0.25mm. The pretreated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and the tooling is pressed to make the compression ratio of the graphite felt electrode 50%. After pressing, put it in a vacuum drying oven and cure it at 180°C for 60 minutes. The curing heating rate of the vacuum drying oven is 200°C / h to obtain an integrated electrode.

[0071] Implementation three:

[0072] Wipe the surface of the bipolar plate clean with alcohol, and dry the graphite felt electrode and the bipolar plate at 80°C for 45 minutes. The selected conductive silver paste contains 80% silver powder and 20% ethylenetriamine DETA. Add carbon nanotubes to the conductive silver paste to reduce the fluidity of the conductive silver paste and increase the bonding strength with the bipolar plate and graphite felt electrode. Mix 0.01g of carbon fiber in every 10ml of conductive silver paste, then stir thoroughly at 65°C for 40 minutes, and then immediately spray the pretreated conductive silver paste evenly and evenly on the pretreated bipolar plate, with a coating thickness of 0.15mm. The pretreated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and the tooling is pressed to make the compression ratio of the graphite felt electrode 35%. After pressing, put it in a vacuum drying oven and cure it at 140°C for 45 minutes. The curing heating rate of the vacuum drying oven is 180°C / h to obtain an integrated electrode.

[0073] Comparative Example

[0074] The preparation method of the comparative example is the same as that of Example 1, except that the pre-treated conductive silver paste is not coated on the surface of the bipolar plate and between the graphite felt electrodes.

[0075] The integrated electrodes prepared in the above-mentioned Examples 1, 2 and 3 and the electrodes prepared in the comparative example were tested.

[0076] Test results: Figure 2 The charge and discharge voltage curves of the electrode without resistance reduction (comparative example) and the integrated electrode of implementation three are shown in FIG. Figure 2 The contact resistance of the bipolar plates and graphite felt electrodes of the all-vanadium liquid flow battery without interface treatment is large, and the ohmic polarization of the electrode reaction process is high, which makes the battery charging voltage high and the discharge voltage low, thereby only obtaining a low voltage efficiency. At the same time, the polarization degree of the electrode without resistance reduction in the comparative example is large, so that the voltage rises rapidly during the charging process to reach the cut-off voltage, so that the overall all-vanadium liquid flow battery only obtains a low charge and discharge capacity, and the utilization rate of the electrolyte is also significantly reduced. However, by implementing the three-treatment bipolar plate and graphite felt electrode interface of the present invention, the contact resistance between the two and the ohmic polarization of the electrode reaction process are greatly reduced, so that a lower charging voltage and a higher discharge voltage are obtained as shown in the figure, so that the all-vanadium liquid flow battery can obtain higher voltage efficiency and energy efficiency. In addition, the charge and discharge capacity of the liquid flow battery and the utilization rate of the electrolyte are greatly improved. Table 1 shows the integrated electrode resistance and battery voltage efficiency of the electrode without resistance reduction and implementation cases one, two, and three. The conductivity of the bipolar plate and graphite felt electrode of the electrode without resistance reduction is 55.13S·cm -1 , while the voltage efficiency of the assembled all-vanadium liquid flow battery is only 77.4%. The conductivity of the bipolar plate and graphite felt electrode integrated electrode treated by the present invention is generally increased to 320-410S·cm -1The maximum conductivity of 416.89 S·cm was obtained under the three parameter optimization conditions. -1 The voltage efficiency of the all-vanadium liquid flow battery assembled with integrated electrodes treated by the scheme of the present invention is generally improved to 85% to 92%, among which the maximum voltage efficiency of 90.5% is obtained under the three parameter optimization conditions, thereby greatly improving the overall energy efficiency of the all-vanadium liquid flow battery.

[0077] Table 1 Electrode conductivity and cell voltage efficiency

[0078]

[0079] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the internal resistance of an all-vanadium liquid flow battery, characterized in that: include: Pre-treat graphite felt electrodes and bipolar plates; Pre-treating the conductive silver paste; Uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate; The pre-treated graphite felt electrode and the bipolar plate coated with conductive silver paste are pressed into shape to obtain an integrated electrode.

2. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 1, characterized in that: The specific steps of pre-treating the graphite felt electrode and the bipolar plate are as follows: Wipe the surface of the bipolar plate clean with alcohol or acetone; Dry the graphite felt electrode and bipolar plate at 60-100°C for 30-60 minutes.

3. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 1, characterized in that: The specific steps of pre-treating the conductive silver paste are as follows: The carbon material is added to the conductive silver paste, followed by thorough stirring at 50 to 80° C. for 30 to 50 minutes.

4. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 3, characterized in that: 0.005-0.02 g of carbon material is mixed into every 10 ml of the conductive silver paste.

5. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 3 or 4, characterized in that: The conductive silver paste contains 70% to 90% silver powder and 10% to 30% curing agent.

6. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 3 or 4, characterized in that: The carbon material is one or more of carbon fiber, carbon nanotube, graphene and fullerene.

7. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 1, characterized in that: The specific steps of uniformly coating the pre-treated conductive silver paste on the pre-treated bipolar plate are as follows: The pretreated conductive silver paste is immediately coated on the pretreated bipolar plate, and the coating thickness of the conductive silver paste is 0.05 to 0.25 mm.

8. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 7, characterized in that: The coating is one of spraying, dipping and brushing.

9. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 1, characterized in that: The specific steps of pressing the pre-treated graphite felt electrode and the bipolar plate coated with the conductive silver paste to obtain the integrated electrode are as follows: The pre-treated graphite felt electrode is vertically attached to the bipolar plate coated with the conductive silver paste, and pressed by a tooling, and then placed in a vacuum drying oven at 100-180° C. for curing for 30-60 minutes to obtain an integrated electrode; The curing temperature rise rate in the vacuum drying oven is 150-200°C / h.

10. The method for reducing the internal resistance of an all-vanadium redox flow battery according to claim 9, characterized in that: The compression ratio of the graphite felt electrode after pressing is 20% to 50%.

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