Preparation method and application of composite bipolar plate

Abstract

The present invention discloses a method for preparing and applying a composite bipolar plate, belonging to the field of liquid flow battery technology. This method first modifies carbon nanotubes, overcoming their inherent tendency to aggregate, enhancing conductivity and improving compatibility with resin substrates. Secondly, a fluidized bed reactor is utilized for the reaction, saving reaction time. Finally, the composition is preheated and mixed in an airflow dryer, ensuring a more uniform mixture and improving bipolar plate formability. This preparation method is simple, characterized by a short reaction time and high reaction efficiency. The formed bipolar plates can be laser welded for assembly in liquid flow battery stacks, exhibiting excellent conductivity and mechanical strength, and are readily adaptable to industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow batteries, and in particular relates to a preparation method and application of a composite bipolar plate. Background Art

[0002] Flow batteries are a new type of high-capacity energy storage battery that has emerged in recent years. Composed of a stack unit, electrolyte, electrolyte storage and supply unit, and management and control unit, they utilize separate, circulating positive and negative electrolytes. With the increasing construction and adoption of photovoltaic and wind power stations, flow battery energy storage systems are gaining traction due to their high capacity, high safety, and long service life. Bipolar plates, a key material in flow battery stacks, support the electrodes and channel current.

[0003] At present, the industry generally adopts the method of stacking single-piece battery cells to assemble liquid flow battery stacks. The single-piece batteries are sealed by sealing rings, hot melt adhesive films, self-sealing and other methods to achieve the overall sealing of the stack. However, this assembly method has high cost and poor reliability. The rubber is prone to electrolyte leakage after aging, and the sealing ring is also prone to aging and cracking in the pressed state after long-term use, causing electrolyte leakage. The bipolar plate substrate used in the above-mentioned traditional sealing method is usually a thermosetting resin, which plays the role of filling the pores of the carbon material. Due to the small amount of thermosetting resin added, long-term use in the liquid flow battery electrolyte will cause the bipolar plate to swell, and then cause the positive and negative electrolytes to mix, affecting the normal operation of the liquid flow battery. The emerging stack sealing method is laser welding, that is, using a thermoplastic resin-based bipolar plate and an electrode frame to achieve the overall sealing of the stack by laser welding, thereby avoiding the use of seals, saving costs, and slowing down the corrosion of the electrolyte. However, ordinary conductive carbon materials have poor compatibility with resin substrates, resulting in uneven mixing of the composition. The conductivity of the pressed bipolar plates is uneven and poor, which inevitably requires increasing the amount of conductive carbon material added. However, excessive addition of conductive carbon material will reduce the reliability of welding and cannot simultaneously meet the needs of high conductivity and weldability.

[0004] Chinese patent document with publication number CN118996487A discloses a method for preparing nitrogen-doped multi-walled carbon nanotube-loaded metal Cr electrocatalytic material, in which carbon nanotubes are calcined at high temperature to achieve nitrogen doping, but the nitrogen doping process time of this method is too long and the efficiency is low; Chinese patent document with publication number CN114497614A discloses a liquid flow battery composite bipolar plate and a preparation method thereof, in which the bipolar plate is prepared by partitioning, the middle area is highly conductive, and the edge area is weldable, but due to the poor compatibility of ordinary conductive carbon materials with resin substrates, the connectivity between the conductive area and the transition area and the insulating area is poor, and the mechanical properties of the connecting part are poor, making it unsuitable for industrial production. Summary of the Invention

[0005] The present invention provides a preparation method and application of a composite bipolar plate. The preparation method provided by the present invention is simple, has a short reaction time, and a high reaction efficiency. The formed bipolar plate can be used for the assembly of liquid flow battery stacks by laser welding. It has excellent electrical conductivity and mechanical strength and is easy to industrialize.

[0006] To solve the above technical problems, the present invention includes the following steps:

[0007] (1) Add carbon nanotubes to concentrated nitric acid 5 to 10 times the mass of the carbon nanotubes, treat at 70 to 90 °C for 1 to 3 hours, pour into ice water for quenching, filter, wash with water until neutral, and vacuum dry to obtain carbon nanotube powder;

[0008] (2) The carbon nanotube powder obtained in step (1) is charged into a fluidized bed reactor, nitrogen is introduced, the temperature is raised to 700-800°C, ammonia is introduced, and the pressure in the reactor is maintained to react for 8-10 minutes to obtain nitrogen-doped carbon nanotube powder;

[0009] (3) preheating and premixing the nitrogen-doped carbon nanotube powder obtained in step (2) with a zero-dimensional conductive filler, a two-dimensional conductive filler, and a thermoplastic plastic in an air flow dryer to obtain a premixed composition, wherein the premixed composition is the nitrogen-doped carbon nanotube;

[0010] (4) The premixed composition obtained in step (3) is compression molded to obtain a composite bipolar plate.

[0011] Preferably, the ammonia flow rate in step (2) is 3~4m 3 / min, and the pressure inside the reactor is 2~4MPa.

[0012] Preferably, in step (3), the zero-dimensional conductive filler is acetylene black or Ketjen black; the two-dimensional conductive filler is graphene or flake graphite; and the thermoplastic is one of high-density polyethylene, polypropylene, or polyvinylidene fluoride. The ratio of the added amount of the zero-dimensional conductive filler, nitrogen-doped carbon nanotube powder, and two-dimensional conductive filler is 1:1.5-4:0.5-2; and the mass ratio of the sum of the mass of the zero-dimensional conductive filler and the two-dimensional conductive filler to the thermoplastic is 1:0.4-0.7.

[0013] Preferably, in step (3), the operating temperature of the air flow dryer is 100-170° C., and the operating time is 15-30 seconds.

[0014] Another technical solution provided by the present invention is to use the prepared composite bipolar plate in a liquid flow battery.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The technical solution of the composite bipolar plate preparation method provided by the present invention is to nitrogen-dope carbon nanotubes under high temperature and high pressure conditions by using a fluidized bed reactor. Compared with the traditional tubular furnace reaction, the materials in the fluidized bed reactor are in a suspended fluidized state. During the process of introducing ammonia gas, the contact area between the two can be increased, the doping reaction is more rapid, and the reaction efficiency is higher;

[0017] (2) The technical solution of the composite bipolar plate preparation method provided by the present invention is to nitrogen-dope the carbon nanotubes. The nitrogen doping temperature is controlled at a high temperature of 700-800°C, so that the unstable groups on the surface of the carbon nanotubes are freed and stable -NH2 is introduced, so that the obtained bipolar plate has higher conductivity and better mechanical properties. The presence of the surface groups also enhances the dispersion performance of the carbon nanotubes, thereby improving their interfacial compatibility with the polymer resin, making the conductivity of the obtained bipolar plate more uniform.

[0018] (3) The present invention uses nitrogen-doped carbon nanotubes as one-dimensional conductive fillers, and then adds zero-dimensional and two-dimensional conductive fillers respectively, so that the three conductive fillers cooperate with each other to form a conductive network, thereby improving conductivity;

[0019] (4) The present invention utilizes an airflow dryer to simultaneously preheat and premix the composition, completing the process in a short period of time. The composition can be fully mixed and quickly preheated in an airflow environment. Compared with traditional bipolar plate preparation methods, this method saves material mixing time. The airflow dryer can also remove a small amount of water contained in the premixed composition in a relatively short period of time, which helps reduce defects in the bipolar plate and improve mechanical properties.

[0020] (5) Compared with traditional production processes, the present invention has a shorter reaction time. The prepared bipolar plates are not only weldable but also have excellent electrical conductivity and mechanical strength, making them easy to industrialize. The electrical conductivity of the composite bipolar plates can reach 150-185 S / cm, the tensile strength can reach 20.9-28.3 MPa, and the flexural strength can reach 40.2-55.7 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the X-ray photoelectron spectroscopy (XPS) spectrum of nitrogen-doped carbon nanotubes; wherein, a is the full XPS spectrum of nitrogen-doped carbon nanotubes, b is the N1s spectrum of nitrogen-doped carbon nanotubes;

[0022] Figure 2 The following are scanning electron microscope (SEM) and scanning electron microscope energy dispersive spectrum (EDS) images of Example 1. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to specific examples, but is not limited thereto. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available products unless otherwise specified. In the following examples of the present invention, the fluidized bed reactor used is a gas-solid phase fluidized bed reactor, and the airflow dryer used is a cyclonic airflow dryer, both of which are within the scope of the prior art. Example 1

[0024] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 80 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 1 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder.

[0025] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 700°C, ammonia was introduced at an ammonia flow rate of 4 m³ / min, the pressure in the reactor was maintained at 3 MPa, and after reacting for 10 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0026] (3) Weigh 2.412 g of nitrogen-doped carbon nanotube powder obtained in step (2), 1.608 g of acetylene black, 1.608 g of graphene, and 2.412 g of polypropylene, respectively. Preheat and premix the four fillers in an air flow dryer at a temperature of 170° C. for 15 s. After preheating and premixing, 8.04 g of a premixed composition is obtained.

[0027] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 200°C for molding. The mold was pressed at a pressure of 20 MPa for 10 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0028] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 30 W and a laser operating speed of 200 mm / min. Example 2

[0029] (1) Add 1000 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 70 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 2 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 95.1 g of carbon nanotube powder.

[0030] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 750°C, ammonia was introduced at an ammonia flow rate of 3 m³ / min, the pressure in the reactor was maintained at 4 MPa, and after reacting for 8 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0031] (3) 4.272 g of nitrogen-doped carbon nanotube powder, 1.068 g of Ketjen black, 1.068 g of flake graphite, and 4.272 g of polyvinylidene fluoride obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 150° C. for 30 s. After the preheating and premixing, 10.68 g of the premixed composition was obtained.

[0032] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 180°C for molding. The mold was pressed at a pressure of 15 MPa for 12 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0033] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 35 W and a laser operating speed of 100 mm / min. Example 3

[0034] (1) Add 1000 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 90 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 3 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 95.1 g of carbon nanotube powder.

[0035] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 800°C, ammonia was introduced at an ammonia flow rate of 3.5 m³ / min, the pressure in the reactor was maintained at 2 MPa, and after reacting for 9 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0036] (3) 3.204 g of nitrogen-doped carbon nanotube powder, 2.136 g of acetylene black, 1.602 g of flake graphite, and 3.738 g of polyvinylidene fluoride obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 150° C. for 20 s. After the preheating and premixing, 10.68 g of a premixed composition was obtained.

[0037] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 180°C for molding. The mold was pressed at a pressure of 17 MPa for 15 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0038] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 33 W and a laser operating speed of 150 mm / min. Example 4

[0039] (1) Add 750 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 80 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 2 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 96.7 g of carbon nanotube powder.

[0040] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 800°C, ammonia was introduced at an ammonia flow rate of 4 m³ / min, the pressure in the reactor was maintained at 4 MPa, and after reacting for 9 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0041] (3) 2.814 g of nitrogen-doped carbon nanotube powder, 1.206 g of Ketjen black, 1.608 g of graphene, and 2.412 g of high-density polyethylene obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 100° C. for 30 seconds. After the preheating and premixing were completed, 8.04 g of the premixed composition was obtained.

[0042] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 160°C for molding. The mold was pressed at a pressure of 17 MPa for 10 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0043] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 30 W and a laser operating speed of 100 mm / min. Example 5

[0044] (1) Add 750 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 90 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 1 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 96.7 g of carbon nanotube powder.

[0045] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 700°C, ammonia was introduced at a flow rate of 3.5 m³ / min, the pressure in the reactor was maintained at 2 MPa, and after reacting for 10 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0046] (3) 3.216 g of nitrogen-doped carbon nanotube powder, 0.804 g of acetylene black, 1.206 g of flake graphite, and 2.814 g of polypropylene obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 170°C for 20 seconds. After the preheating and premixing were completed, 8.04 g of the premixed composition was obtained.

[0047] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 200°C for molding. The mold was pressed at a pressure of 15 MPa for 15 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0048] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 33 W and a laser operating speed of 150 mm / min. Example 6

[0049] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir, heat in a water bath to 80 ° C, add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 3 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder;

[0050] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 750°C, ammonia was introduced at an ammonia flow rate of 3 m³ / min, the pressure in the reactor was maintained at 3 MPa, and after reacting for 8 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0051] (3) 3.216 g of nitrogen-doped carbon nanotube powder, 1.608 g of Ketjen black, 0.804 g of graphene, and 3.216 g of high-density polyethylene obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 100° C. for 15 seconds. After the preheating and premixing were completed, 8.04 g of the premixed composition was obtained.

[0052] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 160°C for molding. The mold was pressed at a pressure of 20 MPa for 12 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0053] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 35 W and a laser operating speed of 200 mm / min. Comparative Example 1

[0054] (1) 2.412 g of carbon nanotubes, 1.608 g of acetylene black, 1.608 g of graphene, and 2.412 g of polypropylene were weighed separately and premixed in a high-speed blender for 15 seconds to obtain 8.04 g of a premixed composition.

[0055] (2) The premixed composition obtained in step (1) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 190°C for molding. The mold was pressed at a pressure of 20 MPa for 10 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0056] (3) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 30 W and a laser operating speed of 200 mm / min. Comparative Example 2

[0057] (1) Weigh 2.412 g of carbon nanotubes, 1.608 g of acetylene black, 1.608 g of graphene, and 2.412 g of polypropylene, respectively. Preheat and premix the four fillers in an air flow dryer at a temperature of 170°C for 15 seconds. After preheating and premixing, 8.04 g of the premixed composition is obtained.

[0058] (2) The premixed composition obtained in step (1) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 190°C for molding. The mold was pressed at a pressure of 20 MPa for 10 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0059] (3) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 30 W and a laser operating speed of 200 mm / min. Comparative Example 3

[0060] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir. Heat in a water bath to 80 ° C. Add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 2 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder.

[0061] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 750°C, ammonia was introduced at an ammonia flow rate of 3 m³ / min, the pressure in the reactor was maintained at 4 MPa, and after reacting for 8 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0062] (3) 4.272 g of the nitrogen-doped carbon nanotube powder obtained in step (2), 1.068 g of Ketjen black, 1.068 g of flake graphite, and 4.272 g of polyvinylidene fluoride were weighed separately. The above four fillers were premixed in a high-speed blender for 30 seconds to obtain 10.68 g of a premixed composition.

[0063] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 200°C for molding. The mold was pressed at a pressure of 15 MPa for 12 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0064] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 35 W and a laser operating speed of 100 mm / min. Comparative Example 4

[0065] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir, heat in a water bath to 90 ° C, add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 3 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder;

[0066] (2) The carbon nanotube powder obtained in (1) was charged into a tubular furnace, nitrogen was continuously introduced, the temperature of the tubular furnace was raised to 800°C, ammonia was introduced at an ammonia flow rate of 3.5 m³ / min, and after reacting for 9 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0067] (3) 3.204 g of nitrogen-doped carbon nanotube powder, 2.136 g of acetylene black, 1.602 g of flake graphite, and 3.738 g of polyvinylidene fluoride obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 150° C. for 20 s. After the preheating and premixing, 10.68 g of a premixed composition was obtained.

[0068] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 180°C for molding. The mold was pressed at a pressure of 17 MPa for 15 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0069] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 33 W and a laser operating speed of 150 mm / min. Comparative Example 5

[0070] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir, heat in a water bath to 90 ° C, add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 3 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder;

[0071] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 600°C, ammonia was introduced at an ammonia flow rate of 3.5 m³ / min, the pressure in the reactor was maintained at 2 MPa, and after reacting for 9 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0072] (3) 3.204 g of nitrogen-doped carbon nanotube powder, 2.136 g of acetylene black, 1.602 g of flake graphite, and 3.738 g of polyvinylidene fluoride obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 150° C. for 20 s. After the preheating and premixing, 10.68 g of a premixed composition was obtained.

[0073] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 180°C for molding. The mold was pressed at a pressure of 17 MPa for 15 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0074] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 33 W and a laser operating speed of 150 mm / min. Comparative Example 6

[0075] (1) Add 500 g of concentrated nitric acid to a 3 L three-necked flask and stir, heat in a water bath to 90 ° C, add 100 g of carbon nanotubes to the concentrated nitric acid and stir for 3 h. After the reaction is completed, pour the reactant into ice water to quench, filter with a Buchner funnel, wash with water until neutral, recover the mother liquor, and dry the filter cake in a vacuum oven at 120 ° C to obtain 98.3 g of carbon nanotube powder;

[0076] (2) The carbon nanotube powder obtained in (1) was charged into a fluidized bed reactor, nitrogen was continuously introduced, the temperature of the fluidized bed reactor was raised to 1000°C, ammonia was introduced at a flow rate of 3.5 m³ / min, the pressure in the reactor was maintained at 2 MPa, and after reacting for 9 minutes, nitrogen-doped carbon nanotube powder was obtained;

[0077] (3) 3.204 g of nitrogen-doped carbon nanotube powder, 2.136 g of acetylene black, 1.602 g of flake graphite, and 3.738 g of polyvinylidene fluoride obtained in step (2) were weighed separately. The four fillers were preheated and premixed in an air flow dryer at a temperature of 150° C. for 20 s. After the preheating and premixing, 10.68 g of a premixed composition was obtained.

[0078] (4) The premixed composition obtained in step (3) was filled into a mold with a size of 10 cm × 10 cm × 0.5 mm, and then the mold was placed in a hydraulic press preheated to 180°C for molding. The mold was pressed at a pressure of 17 MPa for 15 minutes. After the pressing was completed, the mold was cooled in a water bath to obtain a composite bipolar plate.

[0079] (5) The composite bipolar plate obtained in step (4) was laser welded to the electrode frame at a laser power of 33 W and a laser operating speed of 150 mm / min.

[0080]

[0081] Table 1 is the experimental analysis data of the embodiments and comparative examples of this patent. By comparing Comparative Examples 1 and 2 with Example 1, it can be seen that the bipolar plates prepared by nitrogen-doped carbon nanotubes have greatly improved conductivity and mechanical properties, and the mechanical properties and conductivity are higher. This is because the nitrogen-doped carbon nanotubes have better compatibility with thermoplastics, which makes the connection between carbon and resin tighter and closer; and because the nitrogen-doped carbon nanotubes introduce nitrogen atoms, not only the carbon nanotubes are better dispersed, forming an effective conductive network with conductive fillers of different latitudes, but also the electron transfer of the carbon nanotubes is accelerated, and the conductivity is better, so that the obtained bipolar plates have better conductivity and greatly improved conductivity.

[0082] By comparing Comparative Example 3 with Example 2, it can be seen that the use of an air flow dryer can also improve the conductivity and mechanical properties of the prepared bipolar plates. This is because the air flow dryer preheats and premixes the composition in a dispersed state, and can quickly and efficiently remove moisture from the composition. As a result, the pressed bipolar plates have fewer defects, higher mechanical properties, faster electron transfer rate, and higher conductivity.

[0083] From the comparison between Comparative Example 4 and Example 3, it can be seen that the traditional tube furnace high-temperature calcination cannot make the carbon nanotubes have a high nitrogen doping degree in a short time, so the bipolar plate prepared in this way has poor conductivity and mechanical properties.

[0084] By comparing Comparative Examples 5 and 6 with Example 3, it can be seen that if the temperature of the fluidized bed reactor is too low or too high, the conductivity and mechanical properties of the bipolar plate will be affected. This is because if the temperature is too low, the nitrogen doping degree of the carbon nanotubes will be low, while if the temperature is too high, the nitrogen-containing groups on the carbon nanotubes will be free and fall off, thereby reducing the conductivity and mechanical properties of the bipolar plate.

[0085] The elemental composition of the nitrogen-doped carbon nanotubes prepared in Example 1 was characterized by X-ray photoelectron spectroscopy (XPS). Figure 1 shown. Figure 1 a is the full XPS spectrum of nitrogen-doped carbon nanotubes, where the peaks at 284 eV, 399 eV, and 531 eV represent the carbon peak, nitrogen peak, and oxygen peak of nitrogen-doped carbon nanotubes, respectively. Figure 1 b) N1s spectrum of nitrogen-doped carbon nanotubes. Peak analysis of the N1s peak shows that the peaks at 398.8 eV, 399.5 eV, and 401.2 eV are attributed to pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen, respectively. This indicates that nitrogen atoms are doped into the carbon nanotube lattice. The doped nitrogen atoms alter the electronic structure of the carbon material at the nitrogen-doped sites, facilitating electron transport and effectively improving the electrical properties of the nitrogen-doped carbon nanotubes.

[0086] The surface morphology and element distribution of the composite bipolar plate prepared in Example 1 were analyzed using scanning electron microscopy (SEM) and scanning electron microscopy energy dispersive spectroscopy (EDS). Figure 2 As shown, the composite bipolar plate surface is relatively uniform overall, with no significant distribution of carbon material observed. EDS surface scanning of the composite bipolar plate also revealed a uniform distribution of C and F elements, demonstrating that the preheating and premixing in the airflow dryer resulted in a relatively uniform dispersion of the mixture, with no significant agglomeration of the carbon material and polymer. EDS surface scanning reveals a distinct distribution of C on the composite bipolar plate surface, demonstrating the presence of a connected conductive network on the composite bipolar plate surface, resulting in high electrical conductivity.

Claims

1. A method for preparing a composite bipolar plate, characterized in that: The following steps are involved: (1) Add carbon nanotubes to concentrated nitric acid 5 to 10 times the mass of the carbon nanotubes, treat at 70 to 90 °C for 1 to 3 hours, pour into ice water for quenching, filter, wash with water until neutral, and vacuum dry to obtain carbon nanotube powder; (2) The carbon nanotube powder obtained in step (1) is charged into a fluidized bed reactor, nitrogen is introduced, the temperature is raised to 700-800°C, ammonia is introduced, and the pressure in the reactor is maintained to react for 8-10 minutes to obtain nitrogen-doped carbon nanotube powder; Ammonia flow rate is 3~4m 3 / min, the pressure in the reactor is 2~4MPa; (3) preheating and premixing the nitrogen-doped carbon nanotubes obtained in step (2) with a zero-dimensional conductive filler, a two-dimensional conductive filler, and a thermoplastic plastic in an air flow dryer to obtain a premixed composition, wherein the operating temperature of the air flow dryer is 100-170° C. and the operating time is 15-30 seconds; (4) compression molding the premixed composition obtained in step (3) to obtain a composite bipolar plate; In step (3), the zero-dimensional conductive filler is acetylene black or Ketjen black; the two-dimensional conductive filler is graphene or flake graphite; the thermoplastic plastic is one of high-density polyethylene, polypropylene or polyvinylidene fluoride; the mass ratio of the zero-dimensional conductive filler, nitrogen-doped carbon nanotubes and two-dimensional conductive filler is 1:1.5~4:0.5~2; The mass ratio of the sum of the mass of the zero-dimensional conductive filler and the two-dimensional conductive filler to the mass of the thermoplastic plastic is 1:0.4~0.

7.

2. Application of the composite bipolar plate prepared by the method according to claim 1, characterized in that: The composite bipolar plate is used in a liquid flow battery.

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