Conductive slurry and preparation method therefor, composite electrode, and flow battery

Abstract

A conductive slurry and a preparation method therefor, a composite electrode, and a flow battery. The conductive slurry is prepared from a conductive carbon black, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone. The composite electrode comprises a first electrode, a bipolar plate, a second electrode, and the conductive slurry as described above, wherein the conductive slurry is disposed between the first electrode and the bipolar plate and disposed between the second electrode and the bipolar plate. The conductive slurry is not only stable in the initial chemical state of a vanadium electrolyte of a common flow battery, but also has electrochemical stability during charging and discharging after a voltage is applied thereto. The conductive slurry has a long service life and does not degrade over time as the battery is used. The conductive slurry has a good bonding effect, and also enables the contact resistance to be reduced after the bipolar plate and carbon felt electrodes are compounded. Moreover, the conductive slurry itself has a good electrocatalytic activity, thereby providing reaction sites for a vanadium electrolyte commonly used in a flow battery and thus improving the efficiency and performance of the battery.

Description

Conductive slurry, preparation method thereof, composite electrode and flow battery Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a conductive slurry, a preparation method thereof, a composite electrode and a flow battery. Background Art

[0002] With the increase in renewable clean energy generation, the industry's demand for energy storage is gaining increasing attention. Energy storage technologies are now experiencing a state of "a hundred schools of thought contending," ranging from well-known pumped hydro storage based on physical principles to electrochemical lithium battery energy storage systems. Each technology is beginning to play its role in different application scenarios. Flow batteries, among them, are a type of electrochemical energy storage technology. They primarily consist of a separate energy storage electrolyte and a battery stack, and feature a separation between capacity and power. This characteristic also determines the inherent safety of flow batteries, making them increasingly popular in practical applications.

[0003] With the explosive growth in demand for flow batteries in energy storage projects and the gradual formation of its upstream industrial chain, the market's expectations for the performance and production capacity of flow battery stacks have also reached new heights. The main components of a flow battery stack include exchange membranes, bipolar plates, and electrodes. These three materials are mostly stacked in the stack. Electrode materials usually use porous carbon material carbon felt, and bipolar plates usually use water-isolating flexible graphite plates. Studies have found that the simple stacking structure of carbon felt and bipolar plates will form contact resistance in the gap, reducing the charge and discharge efficiency of the stack and thus affecting its performance. Therefore, the industry usually uses physical or chemical methods to bond carbon felt and bipolar plates together to form a composite electrode. The formation of a composite electrode will also reduce the steps in the production and assembly process of the stack, increasing the manufacturer's production capacity.

[0004] Among the reported composite electrode technologies, several technologies adopt the idea of ​​preparing resin bipolar plates and their composite electrodes from the source, such as: Patent Application 1-CN102738479A, Patent Application 2-CN102569824A, Patent Application 3-CN207993964U, Patent 4-CN102891324B and Patent 5-CN113809339B. These technologies involve the preparation process of bipolar plates, which increases the workload of forming composite electrodes. In addition, Patent Applications 1 to 3 all use the method of hot pressing pure plastic resin. The pure plastic material sandwiched between the electrodes will increase the resistance value. In Patent 4, the homemade bipolar plate / skeleton layer is the electrode material filled with resin. In order to fix it with the outer electrode, a conductive agent must also be added in the middle and then hot pressed. Patent 5 adds an organic solvent to the surface of the prepared bipolar plate and passes an electric current, bonding it to the carbon felt through the changes in the bipolar plate interface caused by electrical heat generation. Whether it is mechanical hot pressing or pressing by generating heat after power is applied, these processes damage the surface of the bipolar plate and affect its stability.

[0005] Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0007] The present application provides a conductive slurry, a preparation method thereof, a composite electrode and a flow battery. The conductive slurry provided in the present application can composite the bipolar plate and the electrode together with the smallest possible force. The conductive slurry of the present application adheres well to the flat surface of the bipolar plate, and the bipolar plate does not crack under the flushing of the liquid at a high flow rate. In addition, the conductive slurry of the present application has strong chemical and electrochemical corrosion resistance and is stable under different charge and discharge states of the flow battery electrolyte. The bonding of the conductive slurry not only reduces the contact resistance between the electrode and the bipolar plate, but also has excellent electrocatalytic activity, which is beneficial to the electrochemical reaction efficiency of the flow battery electrolyte and can improve the battery performance. The composite electrode of the present application uses the common carbon felt electrodes and bipolar plates on the market as the main body, adopts a short process to prepare the conductive slurry, and uses common temperature and pressure to achieve the composite of the bipolar plate and the carbon felt electrode without damaging the surface of the bipolar plate. The conductive paste formulation in this application is not only stable in the initial chemical state of common vanadium flow battery electrolytes, but also electrochemically stable during charge and discharge when voltage is applied, resulting in a long lifespan and resistance to degradation over battery life. The conductive paste in this application not only exhibits excellent bonding properties, reducing contact resistance when the bipolar plate is composited with the carbon felt electrode, but also exhibits excellent electrocatalytic activity, providing reaction sites for the vanadium electrolyte commonly used in flow batteries, thereby improving battery efficiency and performance.

[0008] In one aspect, the present application provides a conductive paste, which is made of conductive carbon black, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone.

[0009] In an embodiment of the present application, the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84-1.1:1:0.93.

[0010] In an embodiment of the present application, the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1-0.2 kg / L; or

[0011] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0012] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0013] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0014] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 kg / L; or

[0015] The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes was 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent was 0.2 kg / L.

[0016] In another aspect, the present application provides a method for preparing the conductive paste according to the above, the method comprising the following steps:

[0017] 1) Grind conductive carbon black and polyvinylidene fluoride in a mortar until no obvious white particles remain in the powder. Then transfer the mixture to a mixing tank of a vacuum mixer and inject half the required amount of N-methylpyrrolidone solvent.

[0018] 2) Place the carbon nanotubes in another container, add the remaining amount of N-methylpyrrolidone and stir evenly, then transfer the mixture to the stirring tank of the same vacuum mixer;

[0019] 3) Using a stirrer, stirring at a rotation speed of 500-700 RPM for 30-60 min, then stirring at a rotation speed of 100-300 RPM for 30-60 min under vacuum, and finally stirring at a rotation speed of 200-400 RPM for 5-10 h to obtain a conductive slurry.

[0020] In an embodiment of the present application, the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84-1.1:1:0.93.

[0021] In an embodiment of the present application, the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1-0.2 kg / L; or

[0022] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0023] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0024] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0025] The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes was 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent was 0.1 kg / L.

[0026] The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes was 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent was 0.2 kg / L.

[0027] In yet another aspect, the present application provides a composite electrode, comprising a first electrode, a bipolar plate, a second electrode, and the above-mentioned conductive paste or a conductive paste prepared by the above-mentioned method, wherein the conductive paste is arranged between the first electrode and the bipolar plate and between the second electrode and the bipolar plate.

[0028] In an embodiment of the present application, the first electrode and the second electrode are carbon felt.

[0029] In an embodiment of the present application, the material of the bipolar plate is flexible carbon.

[0030] In yet another aspect, the present application provides a flow battery comprising the composite electrode.

[0031] Beneficial effects of this application:

[0032] 1. The conductive paste formula of the present application is not only stable in the initial chemical state of the common liquid flow battery vanadium electrolyte, but also has electrochemical stability during the charge and discharge process when voltage is applied. It has a long life and will not degrade with the use of the battery.

[0033] 2. The conductive paste of the present application not only has good bonding effect, but also reduces contact resistance after the bipolar plate and carbon felt electrode are composited. In addition, the conductive paste itself has good electrocatalytic activity, providing reaction sites for the vanadium electrolyte commonly used in liquid flow batteries, thereby improving battery efficiency and performance.

[0034] 3. The composite electrode of this application uses carbon felt electrodes and bipolar plates commonly found on the market as the main body, adopts a short process to prepare the conductive slurry, and uses common temperature and pressure to achieve the composite of the bipolar plate and the carbon felt without damaging the surface of the bipolar plate.

[0035] Other features and advantages of the present application will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present application. Other advantages of the present application can be realized and obtained by the solutions described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 shows a schematic exploded view of the composite electrode of the present application.

[0037] FIG2 shows the resistance measurement results of the composite electrode according to Example 1 of the present application before and after being coated with the conductive paste.

[0038] FIG3 shows the charge and discharge curves of the flow battery of the present application at different currents.

[0039] FIG4 shows the charge and discharge test efficiency changes of different composite electrode samples.

[0040] Figure 5 shows the electrochemical stability of different slurry coating formulations.

[0041] FIG6(a) shows the effect of the addition of carbon nanotubes on the electrocatalytic activity of the flow battery electrolyte, and FIG6(b) shows the effect of the amount of carbon nanotubes added on the electrocatalytic activity of the flow battery electrolyte.

[0042] Figure 7 shows a performance comparison between a battery using the composite electrode of the present application and a battery not using the composite electrode of the present application. 1 - first electrode; 2 - bipolar plate; 3 - second electrode; 4 - conductive slurry. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and advantages of this application more clear, the embodiments of this application will be described in detail below. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other in any way.

[0044] An embodiment of the present application provides a conductive paste, which is made of conductive carbon black, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone.

[0045] In an embodiment of the present application, the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84-1.1:1:0.93.

[0046] In an embodiment of the present application, the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to the N-methylpyrrolidone as a solvent is 0.1-0.2 kg / L; or

[0047] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0048] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0049] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0050] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 kg / L; or

[0051] The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes was 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent was 0.2 kg / L.

[0052] The present invention also provides a method for preparing the conductive paste, which comprises the following steps:

[0053] 1) Grind conductive carbon black and polyvinylidene fluoride in a mortar until no obvious white particles remain in the powder. Then transfer the mixture to a mixing tank of a vacuum mixer and inject half the required amount of N-methylpyrrolidone solvent.

[0054] 2) Place the carbon nanotubes in another container, add the remaining amount of N-methylpyrrolidone and stir evenly, then transfer the mixture to the stirring tank of the same vacuum mixer;

[0055] 3) Using a stirrer, stirring at a rotation speed of 500-700 RPM for 30-60 min, then stirring at a rotation speed of 100-300 RPM for 30-60 min under vacuum, and finally stirring at a rotation speed of 200-400 RPM for 5-10 h to obtain a conductive slurry.

[0056] In an embodiment of the present application, the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84-1.1:1:0.93.

[0057] In an embodiment of the present application, the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to the N-methylpyrrolidone as a solvent is 0.1-0.2 kg / L; or

[0058] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0059] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0060] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or

[0061] The mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 kg / L; or

[0062] The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes was 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent was 0.2 kg / L.

[0063] An embodiment of the present application also provides a composite electrode, which includes a first electrode, a bipolar plate, a second electrode, and the above-mentioned conductive paste or a conductive paste prepared by the above-mentioned method, wherein the conductive paste is arranged between the first electrode and the bipolar plate and between the second electrode and the bipolar plate.

[0064] In an embodiment of the present application, the first electrode and the second electrode are carbon felt.

[0065] In an embodiment of the present application, the material of the bipolar plate is flexible carbon.

[0066] An embodiment of the present application further provides a liquid flow battery, which includes the above-mentioned composite electrode.

[0067] Figure 1 shows a schematic exploded view of the composite electrode of the present application. As shown in Figure 1, in an exemplary embodiment of the present application, a composite electrode includes a first electrode 1, a bipolar plate 2, a second electrode 3 and the conductive paste 4 as described above, and the conductive paste 4 is arranged between the first electrode 1 and the bipolar plate 2 and between the second electrode 3 and the bipolar plate 2.

[0068] In the examples of the present application, the composite electrode of the present application is manufactured as follows:

[0069] Step 1: Prepare the conductive paste. The conductive paste is made by dissolving conductive carbon black Super P (Hefei Kejing), carbon nanotubes (CNT) (5% carbon content, Harbin Jinna Technology), and polyvinylidene fluoride (PVDF) (Hefei Kejing) in N-methylpyrrolidone (NMP) (Hefei Kejing). The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1:1:0.84-1.1:1:0.93, and the ratio of the conductive carbon black, carbon nanotubes, and polyvinylidene fluoride as solids to the N-methylpyrrolidone solvent is 0.1-0.2 kg / L. The specific preparation method is as follows: first, conductive carbon black and polyvinylidene fluoride are placed in a mortar and ground until there are no obvious white particles in the powder, and then the mixture is transferred to the stirring tank of a vacuum mixer and half of the NMP solvent is injected; then, the carbon nanotubes are placed in another container, the remaining amount of NMP is added and stirred evenly, and then the mixture is also transferred to the stirring tank of the vacuum mixer; finally, the mixer is used to stir at a speed of 500-700RPM for 30-60 minutes, then stirred at a speed of 100-300RPM for 30-60 minutes under vacuum state, and finally stirred at a speed of 200-400RPM for 5-10 hours.

[0070] Step 2: Prepare the bipolar plate for coating and mark the coating areas on both sides. Place the bipolar plate on a glass plate and apply a certain amount of the prepared conductive slurry to the marked areas. Adjust the coating blade to a thickness of 0.15-0.28mm and apply the slurry from left to right. Next, place the prepared carbon felt, which will serve as the first electrode, on top of the coating and gently press.

[0071] Step 3: Flip the bipolar plate over and coat the second side, attaching the carbon felt that serves as the second electrode. Once completed, place one side down and press at a pressure of 0.5-2 kPa for 13-16 minutes. Then, flip the plate over and press at a pressure of 0.5-2 kPa for another 13-16 minutes.

[0072] Step 4: Place the composite electrode in a vacuum drying oven and vacuum dry it at 110-130° C. (preferably 120° C.) for 10-12 hours; continue drying it in a blast drying oven for 7-10 hours to obtain a composite electrode.

[0073] The sources of materials used in the examples and comparative examples of this application are as follows:

[0074] Conductive carbon black comes from Hefei Kejing;

[0075] Carbon nanotubes (CNTs) come from Harbin Jinna Technology;

[0076] Polyvinylidene fluoride (PVDF) was from Hefei Kejing;

[0077] NMP comes from Kain Industries;

[0078] The carbon felt comes from Jiangyou Runsheng;

[0079] The bipolar plates come from Ningbo Xinyuan;

[0080] The positive and negative electrolytes come from Aladdin reagent;

[0081] Styrene-butadiene latex comes from Dongguan Donglin Polymer Materials;

[0082] Sodium carboxymethyl cellulose was sourced from Shandong Weifang Lite.

[0083] Example 1

[0084] This embodiment provides a conductive paste, which is made of conductive carbon black, carbon nanotubes, polyvinylidene fluoride and N-methylpyrrolidone, wherein the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L.

[0085] The conductive paste of this embodiment is prepared by the following method:

[0086] Conductive carbon black, polyvinylidene fluoride and carbon nanotubes are weighed according to a mass ratio of 1.08: 1: 0.9, and N-Methyl pyrrolidone is measured in a ratio of 0.17 kg / L to conductive carbon black, carbon nanotubes and polyvinylidene fluoride as solids and N-Methyl pyrrolidone as a solvent. Conductive carbon black and polyvinylidene fluoride are placed in a mortar and ground until there are no obvious white particles in the powder, and the mixture is then transferred to the stirring tank of a vacuum stirrer, and half of the amount of N-Methyl pyrrolidone solvent is injected. Then, carbon nanotubes are placed in another container, the remaining amount of N-Methyl pyrrolidone is added and stirred, and then transferred to the stirring tank of the same vacuum stirrer. Using a stirrer, a stirring speed of 600 RPM is performed for 40 min, followed by a stirring speed of 200 RPM for 50 min under a vacuum state, and finally stirred for 6.5 h at a speed of 300 RPM to obtain a conductive paste.

[0087] Example 2

[0088] The only difference between this embodiment and embodiment 1 is that the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1:1:0.84.

[0089] Example 3

[0090] The only difference between this embodiment and embodiment 1 is that the mass ratio of the conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.1:1:0.93.

[0091] Example 4

[0092] The only difference between this embodiment and embodiment 1 is that the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to the N-methylpyrrolidone as a solvent is 0.1 kg / L.

[0093] Example 5

[0094] The only difference between this embodiment and embodiment 1 is that the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to the N-methylpyrrolidone as a solvent is 0.2 kg / L.

[0095] Comparative Example 1

[0096] The only difference between this comparative example and Example 1 is that the mass ratio of conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 1.3:1.5:1.2.

[0097] Comparative Example 2

[0098] The only difference between this comparative example and Example 1 is that the mass ratio of conductive carbon black, polyvinylidene fluoride and carbon nanotubes is 0.8:0.9:0.7.

[0099] Comparative Example 3

[0100] The only difference between this comparative example and Example 1 is that the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to the N-methylpyrrolidone as a solvent is 0.08 kg / L.

[0101] Comparative Example 4

[0102] The only difference between this comparative example and Example 1 is that the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.21 kg / L.

[0103] Comparative Example 5

[0104] This comparative example provides a conductive paste, which is made of conductive carbon black, polyvinylidene fluoride and N-methylpyrrolidone, wherein the mass ratio of the conductive carbon black to the polyvinylidene fluoride is 1:0.84, and the ratio of the conductive carbon black and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L.

[0105] The conductive paste of this comparative example was prepared by the following method:

[0106] Conductive carbon black and polyvinylidene fluoride were ground in a mortar at a mass ratio of 1:0.84 for 30 minutes, until no white particles remained. The mixture was then transferred to the mixing tank of a vacuum mixer and NMP was added at a ratio of 0.17 kg / L of conductive carbon black and polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent. The mixture was stirred at 600 RPM for 40 minutes, then at 200 RPM under vacuum for 50 minutes, and finally at 300 RPM for 6.5 hours to obtain a conductive paste.

[0107] Comparative Example 6

[0108] The only difference between this comparative example and Example 1 is that ethanol is used as the solvent.

[0109] Comparative Example 7

[0110] The only difference between this comparative example and Example 1 is that tetrahydrofuran was used as the solvent.

[0111] Comparative Example 8

[0112] The only difference between this comparative example and Example 1 is that n-butyl acetate is used as the solvent.

[0113] Comparative Example 9

[0114] The slurry of Comparative Example 9 was prepared by blending conductive carbon black with styrene-butadiene latex and sodium carboxymethyl cellulose in a weight ratio of 1:0.9:0.84, using water as a solvent, wherein water was added at a ratio of 0.2 kg / L of conductive carbon black as solids to styrene-butadiene latex and sodium carboxymethyl cellulose to water as a solvent.

[0115] The preparation method of the aqueous slurry is as follows: placing a styrene-butadiene latex emulsion in a container, adding deionized water to dilute it, and then magnetically stirring it under vacuum for 30 minutes; then, placing conductive carbon black and sodium carboxymethyl cellulose in a mortar and grinding them until there are no obvious white particles in the powder, adding deionized water, and then transferring it to a stirring tank containing the styrene-butadiene latex emulsion, and finally magnetically stirring it at 300RPM under vacuum for 12 hours.

[0116] Performance Testing

[0117] The composite electrode is prepared from the conductive slurry of Example 1 as follows: prepare a cut bipolar plate with a size of 28*22cm, and mark the coating area on both sides (25*15cm). Place the bipolar plate on a glass plate, take 18g of the prepared conductive slurry of Example 1 and place it in the marked area, adjust the coating blade to a thickness of 0.21mm, and apply it from left to right. Then, cover the prepared carbon felt with a size of 25*15cm on the coating and press it lightly. Turn the bipolar plate over, coat the second side, and paste the second piece of carbon felt of the same size, as shown in Figure 1. After completion, place one side down, apply a force of 37.5N to press for 15 minutes, then turn it over, and press with a force of 37.5N for 15 minutes. Finally, place the composite electrode in a vacuum drying oven, vacuum dry it at 120°C for 10.5h, and continue drying it in a blast drying oven for 8h to obtain a composite electrode. To verify the repeatability of the preparation process, two batches of composite electrodes were prepared, designated Sample 1 and Sample 2. A loop resistance meter was used to measure the resistance of the composite electrodes before and after application of the conductive slurry. The results are shown in Figure 2. As shown in Figure 2, the resistance of the composite electrodes decreased by approximately 15%, indicating a stable resistance reduction effect.

[0118] The performance test of the flow battery using the composite electrode is as follows: the prepared composite electrode is used to assemble the battery, and charge and discharge cycles are performed at different currents. The initial vanadium electrolyte valence of the positive and negative electrode electrolytes is 3.5, and the amount of positive and negative electrode electrolytes is 0.5L each. First, a smaller current of 37.5A is used for constant current charge and discharge, and 30 cycle tests are performed. Then the charge and discharge current is increased to 56A, and 20 to 30 cycles of charge and discharge tests are performed. Finally, the current is reduced back to 37.5A and another 20 cycles of charge and discharge tests are performed. The change curves of the battery voltage at different charge and discharge currents are compared, as shown in Figure 3. It can be found that: at a smaller current of 37.5A, the battery polarization effect is small, and the discharge voltage range is maintained at 2.78-2.46V. When the current is increased to 56A, the battery polarization is more obvious, and the discharge voltage range is reduced to 2.71-2.37V. However, this change in polarization phenomenon is reversible. When the charge and discharge current is switched from 56A back to 37.5A, the battery voltage change curve can completely return to the previous level, indicating that the composite electrode is stable under long-term multi-cycle charge and discharge conditions. Comparing the charge and discharge performance of the battery assembled with the composite electrodes prepared twice, as shown in Figure 4, its voltage efficiency can reach 90% under a smaller current test. After the current is increased, the voltage efficiency decreases slightly, but it is still not less than 86%. After resuming the use of a smaller current, its efficiency can be restored to its initial state. The charge and discharge test shows that the composite electrode is stable during the battery charge and discharge operation, and the prepared composite electrode effect is reproducible.

[0119] Similarly, the performance of composite electrodes prepared from the conductive pastes of Examples 2-5 and Comparative Examples 1-9 and flow batteries using the composite electrodes were tested, and the results are shown in Table 1 and Figures 5-7 below.

[0120] Table 1

[0121] The greater the resistance change before and after compounding, the better the formulation. The results in Table 1 show that compared to Comparative Examples 1-9, the composite electrodes prepared using the conductive pastes of Examples 1-4 of the present invention exhibit a greater resistance change before and after compounding, indicating that the conductive pastes of Examples 1-4 of the present invention exhibit better performance.

[0122] As shown in (a) of Figure 6, the composite electrode formed with the conductive paste of Example 1 containing carbon nanotubes exhibits the largest oxidation and reduction currents compared to the composite electrode formed with the conductive paste of Comparative Example 5 that does not contain carbon nanotubes. Therefore, the conductive paste formulation of the embodiment of the present application has excellent electrocatalytic activity for the electrolyte of the flow battery.

[0123] As shown in Figure 6(b), when the mass ratio of conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is between 1.08:1:0.23 and 1.08:1:0.92, both the oxidation and reduction currents in the test results continue to increase. However, when the mass ratio of conductive carbon black, polyvinylidene fluoride, and carbon nanotubes exceeds 1.08:1:0.91, the oxidation and reduction currents decrease slightly, and the dispersion of the carbon nanotubes begins to deteriorate when the slurry is prepared with this sample.

[0124] The coating method for the conductive paste of Comparative Example 9 was consistent with that of Example 1. Compared with the conductive paste of Example 1, the aqueous slurry of Comparative Example 9 was easily oxidized and had poor stability. A high-potential continuous oxidation reaction was performed on the bipolar plate coated with the conductive paste of Comparative Example 9 using an electrochemical workstation. The electrolyte was a 3.5-valent vanadium electrolyte diluted to 0.1 M. The applied potential was 1 V, corresponding to the electrode potential of the vanadium electrolyte positive electrode reaction.

[0125] As shown in Figure 5, the sample using the oil-based conductive paste in Example 1 experienced only a slight decrease in current within 6 hours after the test current stabilized, remaining stable at approximately 1.2 mA. However, the current of the aqueous slurry sample in Comparative Example 9 continued to decrease within the first 0.5 hours as oxidation continued under high potential, ultimately stabilizing at 0.3 mA, a mere 25% of the current of the sample using the oil-based conductive paste in Example 1. This result demonstrates that aqueous conductive pastes exhibit poor stability in oxidizing environments and cannot meet the operating conditions required for flow batteries.

[0126] In addition, the charge and discharge performance of a battery using a composite electrode containing the conductive paste of Example 1 of the present application was compared with that of a battery using an uncombined electrode. The three efficiency values ​​obtained by charge and discharge at a current of 37.5A are shown in Figure 7. This comparison shows that: the coulombic efficiency of the two batteries is similar, but the voltage efficiency of the electrode increases from 85.6% to 90% after the composite electrode, so the energy efficiency of the composite electrode battery also increases from 83% before the composite electrode to 87.8%.

[0127] Although the embodiments disclosed in this application are as described above, the contents described are merely embodiments adopted to facilitate understanding of this application and are not intended to limit this application. Any person skilled in the art to which this application belongs may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in this application. However, the scope of patent protection of this application shall still be based on the scope defined by the attached claims.

Claims

1. A conductive paste, characterized in that, The conductive paste is made of conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone.

2. The conductive paste according to claim 1, wherein, The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1:1:0.84 - 1.1:1:0.

93.

3. The conductive paste according to any one of claims 1-2, wherein, The ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 - 0.2 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.2 kg / L.

4. A method for preparing the conductive paste according to any one of claims 1 to 3, characterized in that, The method includes the following steps: 1) Place the conductive carbon black and polyvinylidene fluoride in a mortar and grind until there are no obvious white particles in the powder, then transfer the mixture to the mixing tank of a vacuum mixer and inject half of the required amount of N-methylpyrrolidone solvent; 2) Place the carbon nanotubes in another container, add the remaining amount of N-methylpyrrolidone and stir evenly, then transfer to the same mixing tank of the vacuum mixer; 3) Use the mixer to stir at a speed of 500 - 700 RPM for 30 - 60 min, then stir at a speed of 100 - 300 RPM for 30 - 60 min under a vacuum state, and finally stir at a speed of 200 - 400 RPM for 5 - 10 h to obtain the conductive paste.

5. The method according to claim 4, wherein, The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1:1:0.84 - 1.1:1:0.

93.

6. The method according to claim 4, wherein, The ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 - 0.2 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1:1:0.84, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.1:1:0.93, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.17 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.1 kg / L; or The mass ratio of the conductive carbon black, polyvinylidene fluoride, and carbon nanotubes is 1.08:1:0.9, and the ratio of the conductive carbon black, the carbon nanotubes, and the polyvinylidene fluoride as solids to N-methylpyrrolidone as a solvent is 0.2 kg / L.

7. A composite electrode, characterized in that, The composite electrode includes a first electrode, a bipolar plate, a second electrode, and the conductive paste according to any one of claims 1 to 3 or the conductive paste prepared by the method according to any one of claims 4 to 6, wherein the conductive paste is disposed between the first electrode and the bipolar plate and between the second electrode and the bipolar plate.

8. The composite electrode according to claim 7, wherein, The first electrode and the second electrode are carbon felts.

9. The composite electrode according to claim 7, wherein, The material of the bipolar plate is flexible carbon.

10. A flow battery, characterized in that, The flow battery includes the composite electrode according to any one of claims 7-9.

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