CN118299608B

CN118299608B - Preparation method of composite bipolar plate

Info

Publication number: CN118299608B
Application number: CN202410729593.9A
Authority: CN
Inventors: 秦妍; 张琦; 刘利娜; 朱荣振; 钟玉雪; 袁玉慧; 王淑坤; 张天舒; 刘桂杉; 李守明
Original assignee: Shandong Haihua Co ltd; Shandong Haihua Group Co Ltd
Current assignee: Shandong Haihua Co ltd; Shandong Haihua Group Co Ltd
Priority date: 2024-06-06
Filing date: 2024-06-06
Publication date: 2024-09-24
Anticipated expiration: 2044-06-06
Also published as: CN118299608A

Abstract

The invention relates to the technical field of electrochemistry, in particular to a preparation method of a composite bipolar plate, the method is to prepare a composite bipolar plate by reducing graphene oxide by using rosmarinic acid, which is a natural green reducing agent, and taking the obtained reduced graphene oxide as a raw material. The rosmarinic acid is used as the reducing agent, the dispersion degree of the rosmarinic acid in the blend can be improved through pi-pi interaction between the rosmarinic acid and the reduced graphene oxide, the conductive performance of the composite bipolar plate is improved, and the addition amount of the reduced graphene oxide is effectively reduced. Meanwhile, after the composite bipolar plate is prepared, the bipolar plate is slowly cooled in a cooling control mode, and the conductivity of the bipolar plate is greatly improved. In addition, the bipolar plate prepared by the method has thinner plate thickness, greatly reduces the manufacturing cost and achieves the purposes of cost reduction and efficiency enhancement.

Description

Preparation method of composite bipolar plate

Technical Field

The invention relates to the technical field of electrochemistry, in particular to a preparation method of a composite bipolar plate.

Background

Bipolar plates have been widely focused and studied in recent years as a new energy storage technology has evolved as one of the key components of flow batteries and fuel cell stacks. A number of materials, such as graphite, metals, polymer matrix composites, and the like, are used in the manufacture of bipolar plates. Among them, carbon-plastic composite bipolar plates are widely used because of their low cost, light weight, good mechanical properties, corrosion resistance and other advantages. In order to obtain a composite bipolar plate having high conductivity, a large amount of conductive filler is generally introduced during the compounding process, but when the addition amount of the conductive filler is too high, the mechanical properties of the bipolar plate are significantly reduced. In addition, the operation difficulty of injection molding is high due to the increase of the viscosity of the high filler system, and compression molding becomes a main processing mode of high filler system molding. However, during the hot press forming process, the elevated temperature and pressure cause the polymers within the bipolar plate to tend to aggregate toward the surface, resulting in an increase in interfacial contact resistance and a dramatic decrease in conductivity of the bipolar plate.

To solve this problem, some of the efforts currently have focused on modifying the surface of bipolar plates to reduce their surface resistance and improve the cell performance. In chinese patent CN114566666a, two conductive paper layers with low resistivity are compounded on both sides of the thermoplastic conductive plastic by means of electric heating and melting, so as to solve the problems of high resistivity and low toughness of the existing flow battery plate. In another chinese patent CN115447215A, a carbon plastic conductive sheet is used as an intermediate layer, a graphite felt, a carbon fiber cloth or a carbon paper is used as a high conductive layer, and the intermediate layer and the high conductive layer are hot pressed to obtain a conductive sheet, and the conductive sheet can be used for a bipolar plate of a flow battery. In chinese patent CN111370718a, the upper and lower surfaces of the bipolar plate are coated with conductive paste, and the bipolar plate is obtained after heating, shaping by shaping roller, traction and winding. The method introduces conductive materials on the surface of the bipolar plate, and reduces the interface contact resistance of the bipolar plate, but also increases the manufacturing cost and the complexity of the process of the bipolar plate, and restricts the large-scale application of the carbon-plastic composite bipolar plate.

Disclosure of Invention

The invention aims to provide a preparation method of a composite bipolar plate. According to the method, the natural green reducing agent, namely rosmarinic acid, is used for reducing the graphene oxide, so that the problem of excessive accumulation of the graphene oxide due to strong van der Waals force between the sheets in the reduction and blending processes can be effectively avoided. In addition, by controlling the cooling rate and the forming thickness, the manufacturing cost of the bipolar plate is greatly reduced, and the bipolar plate has higher conductivity and achieves the purposes of cost reduction and efficiency enhancement.

To achieve the purpose, the technical scheme of the invention is as follows:

A preparation method of a composite bipolar plate comprises the following steps:

(1) Regulating the pH value of the graphene oxide aqueous solution to 11-13 by using an alkaline solution, adding rosmarinic acid, refluxing for 5-8 hours at 90-100 ℃ under the nitrogen atmosphere, filtering and drying the obtained mixed solution to obtain reduced graphene oxide powder;

(2) Mixing the reduced graphene oxide powder with a thermoplastic polymer and a conductive carbon material at 20000-28000 rpm for 15-100 s to obtain a blend;

(3) And (3) placing the blend into a forming die, carrying out hot pressing treatment for 5-12 min at the temperature of 200-260 ℃ and the pressure of 10-20 MPa, maintaining the hot pressing pressure after the hot pressing is finished, and slowly cooling to room temperature by controlling the cooling rate to obtain the composite bipolar plate.

Preferably, the alkaline solution is one of ammonia water, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

Preferably, the concentration of the graphene oxide aqueous solution is 0.5-2 mg/mL, and the mass ratio of the graphene oxide to the rosemary is 1:10-20.

Preferably, the thermoplastic polymer is one of polyethylene terephthalate, polystyrene and polyamide, and the conductive carbon material is a combination of two of graphite powder, carbon black, expanded graphite, carbon fiber and carbon nanotube.

Preferably, the thermoplastic polymer accounts for 30-50% of the mass fraction of the blend, the reduced graphene oxide powder accounts for 3-8% of the mass fraction of the blend, and the conductive carbon material accounts for 42-67% of the mass fraction of the blend.

Preferably, in the step (3), the cooling rate is controlled to be 0.5-2 ℃/min.

Preferably, the thickness of the composite bipolar plate is 0.3-0.7 mm.

Compared with the prior art, the invention has the following beneficial effects:

(1) The invention adopts rosmarinic acid, which is a green and natural reducing agent, to reduce graphene oxide. In the reduction process, excessive accumulation between the reduced graphene oxide sheets is avoided through pi-pi interaction between benzene ring molecules in rosmarinic acid and the graphene oxide sheets, so that the dispersion performance of the reduced graphene oxide is improved;

(2) According to the invention, the cooling mode of the bipolar plate is controlled so as to influence the crystallization process of the polymer, so that the conductive carbon material is gathered in a smaller amorphous area, a communicated conductive network is formed in the bipolar plate, and the conductivity of the bipolar plate is improved;

(3) Compared with the existing composite bipolar plate, the bipolar plate prepared by the method has the advantages that the conductivity of the bipolar plate is effectively improved under the condition of avoiding the use of a conductive paper layer and conductive slurry by adopting a lower cooling rate, and the thickness of the prepared bipolar plate is thinner, so that the manufacturing cost is greatly saved.

Drawings

Fig. 1 is a diagram of an internal mechanism of a bipolar plate prepared by treating the bipolar plate through slow cooling, wherein in the diagram, 1 is a forming die, 2 is a polymer spherulite, 3 is graphene oxide reduced by rosmarinic acid, and 4 is a conductive carbon material.

Fig. 2 is a diagram showing an internal mechanism of a bipolar plate prepared when the cooling rate of the comparative example is high, wherein 1 is a forming die, 2 is a polymer spherulite, 3 is graphene oxide reduced by rosmarinic acid, and 4 is a conductive carbon material.

FIG. 3 is an X-ray photoelectron spectrum of graphene oxide before and after rosmarinic acid reduction in the present invention. Wherein a is an X-ray photoelectron spectrum of graphene oxide, and B is an X-ray photoelectron spectrum of reduced graphene oxide obtained by reduction of rosmarinic acid in example 3.

Fig. 4 is a transmission electron microscope image of graphene oxide reduced by rosmarinic acid in example 5 of the present invention.

Detailed Description

The invention is further illustrated, but not limited, by the following figures and examples.

Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, are commercially available products.

Example 1

(1) Regulating the pH value of 800mL of graphene oxide aqueous solution with the concentration of 0.5mg/mL to be 11 by using an ammonia water solution, adding 8g of rosmarinic acid, filling nitrogen, refluxing for 6 hours at 95 ℃, filtering the obtained mixed solution after the reaction is finished, and drying the obtained solid at 80 ℃ for 6 hours to obtain reduced graphene oxide powder;

(2) 2.5g of polystyrene, 1.7g of graphite powder, 0.55g of carbon fiber and 0.25g of reduced graphene oxide powder are poured into a high-speed homogenizing mixer and mixed for 60s at 22000rpm to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 220 ℃, setting the pressure to be 15MPa, and carrying out hot pressing treatment for 12min. And after the hot pressing is finished, maintaining the hot pressing temperature and pressure, and setting the cooling rate of the vulcanizing press to be 2 ℃/min to obtain the composite bipolar plate for the flow battery with the thickness of 0.5 mm.

Example 2

(1) Regulating the pH value of 600mL of graphene oxide aqueous solution with the concentration of 2mg/mL to be 13 by using a sodium hydroxide aqueous solution with the mass concentration of 1%, adding 18g of rosmarinic acid, filling nitrogen, refluxing for 8 hours at the temperature of 100 ℃, centrifuging the obtained mixed solution after the reaction is finished, washing and centrifuging for many times, and drying the obtained solid at the temperature of 80 ℃ for 12 hours to obtain reduced graphene oxide powder;

(2) 12g of polyethylene terephthalate, 13.4g of carbon black, 3.7g of carbon nanotubes and 0.9g of reduced graphene oxide powder are poured into a multifunctional pulverizer and mixed for 15s at 28000rpm to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 250 ℃, setting the pressure to be 20MPa, and carrying out hot pressing treatment for 10min. And after the hot pressing is finished, maintaining the hot pressing temperature and pressure, and setting the cooling rate of the vulcanizing press to be 1 ℃/min to obtain the composite bipolar plate for the flow battery with the thickness of 0.3 mm.

Example 3

(1) Regulating the pH value of 800mL of graphene oxide aqueous solution with the concentration of 1mg/mL to be 12 by using a potassium hydroxide aqueous solution with the mass concentration of 0.5%, adding 11g of rosmarinic acid, filling nitrogen, refluxing for 5 hours at 100 ℃, filtering the obtained mixed solution after the reaction is finished, and drying the obtained solid at 80 ℃ for 10 hours to obtain reduced graphene oxide powder;

(2) 2.5g of polyamide PA6, 2.1g of graphite powder, 1.15g of carbon nano tube and 0.5g of reduced graphene oxide powder are poured into a high-speed stirrer and stirred at 26000rpm for 30s to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 200 ℃, setting the pressure to be 18MPa, and carrying out hot pressing treatment for 5min. And after the hot pressing is finished, maintaining the hot pressing temperature and pressure, and setting the cooling rate of the vulcanizing press to be 1 ℃/min to obtain the composite bipolar plate for the flow battery with the thickness of 0.4 mm.

Example 4

(1) Adjusting the pH value of 2000mL of graphene oxide aqueous solution with the concentration of 1.5mg/mL to be 11 by using a sodium hydroxide aqueous solution with the mass concentration of 0.8%, adding 30g of rosmarinic acid, filling nitrogen, refluxing for 7 hours at 90 ℃, filtering the obtained mixed solution after the reaction is finished, and drying the obtained solid at 80 ℃ for 20 hours to obtain reduced graphene oxide powder;

(2) 22g of polystyrene, 32.5g of carbon black, 16.6g of carbon fiber and 2.2g of reduced graphene oxide powder are poured into a universal pulverizer, and mixed for 90s at 20000rpm to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 230 ℃, setting the pressure to be 10MPa, and carrying out hot pressing treatment for 8min. And after the hot pressing is finished, maintaining the hot pressing temperature and pressure, and setting the cooling rate of the vulcanizing press to be 1.5 ℃/min to obtain the composite bipolar plate for the flow battery with the thickness of 0.7 mm.

Example 5

(1) Regulating the pH value of 5000mL of graphene oxide aqueous solution with the concentration of 2mg/mL to be 12 by ammonia water, adding 150g of rosmarinic acid, filling nitrogen, refluxing for 8 hours at 95 ℃, filtering the obtained mixed solution after the reaction is finished, and drying the obtained solid at 80 ℃ for 38 hours to obtain reduced graphene oxide powder;

(2) 50g of polyethylene terephthalate, 24.7g of graphite powder, 17.3g of expanded graphite and 8g of reduced graphene oxide powder are poured into a high-speed pulverizer, mixed for 120s at 25000rpm, extruded and granulated to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 260 ℃, setting the pressure to be 13MPa, and carrying out hot pressing treatment for 8min. And after the hot pressing is finished, maintaining the hot pressing temperature and pressure, and setting the cooling rate of the vulcanizing press to be 0.5 ℃/min to obtain the composite bipolar plate for the flow battery with the thickness of 0.4 mm.

Comparative example

(1) 40ML of hydrazine hydrate is dripped into 1500mL of graphene oxide aqueous solution with the concentration of 2mg/mL, the mixed solution is poured into a three-neck flask, and reflux reaction is carried out for 24h at 98 ℃. Centrifuging the obtained mixed solution after the reaction is finished, and drying the obtained solid for 20 hours at 80 ℃ after washing and centrifuging for a plurality of times to obtain reduced graphene oxide powder;

(2) 32g of polyethylene terephthalate, 31.6g of carbon black, 13.2g of carbon nanotubes and 3.2g of reduced graphene oxide powder were poured into a high-speed pulverizer, and mixed at 24000rpm for 30s to obtain a blend;

(3) Placing the blend into a forming die, placing the die into a flat vulcanizing machine, setting the temperature of the flat vulcanizing machine to be 250 ℃, setting the pressure to be 20MPa, and carrying out hot pressing treatment for 10min. And after the hot pressing is finished, maintaining the pressure of the vulcanizing press, and controlling the cooling rate to be 40 ℃/min by using tap water to obtain the composite bipolar plate for the flow battery with the thickness of 1mm.

As can be seen from table 1, the composite bipolar plates prepared in examples 1 to 5 exhibited higher conductivity than the comparative examples, which is mainly due to the fact that the crystallinity of the inside of the polymer increases after the slow cooling of the bipolar plates is achieved by controlling the cooling rate, and the crystallization process of the polymer is affected due to the fact that the conductive carbon material inside the bipolar plates blocks the migration of the polymer molecular chains, so that the conductive particles are aggregated in the amorphous region, as shown in fig. 1. It can be seen that the crystallinity of the polymer can be increased by slowly cooling, and coarse spherulites are more easily generated, so that the graphene oxide sheets reduced by rosemary and the conductive carbon material are promoted to gather in a relatively small amorphous region, a communicated conductive network structure is facilitated to be formed in the bipolar plate, and the conductivity of the bipolar plate is further improved.

Because the elevated temperature and pressure during hot pressing tend to cause polymer aggregation at the surface of the bipolar plate, and the faster cooling rate is adopted in the comparative example, the surface polymer molecular chains of the composite bipolar plate are frozen during molding, so that the inside of the bipolar plate presents a phenomenon that conductive carbon materials aggregate and surface polymers aggregate, as shown in fig. 2. It can be seen that with a faster cooling rate, the polymer molecular chains on the bipolar plate surface are frozen, causing the conductive carbon material to migrate from the surface layer into the bipolar plate. At the same time, the faster cooling rate also reduces the crystallinity of the polymer inside the bipolar plate. In addition, due to the shorter crystallization time, the polymer spherulites become smaller in size, and these small and small polymer spherulites are difficult to promote the conductive carbon material to form a connected conductive network inside the bipolar plate, thereby making the surface of the bipolar plate exhibit higher contact resistance. In addition, as the traditional reducing agent hydrazine hydrate has stronger reducing capability, when the graphene oxide is reduced, the reduced graphene oxide sheets are aggregated due to Van der Waals force, so that the dispersibility of the reduced graphene oxide in the blend is affected, and the reduced graphene oxide has lower conductivity.

The graphene oxide before and after reduction with rosmarinic acid in example 3 was characterized by X-ray photoelectron spectroscopy (XPS). Fig. 3A is an XPS spectrum of graphene oxide prior to reduction. By peaking C1s, it can be seen that graphene oxide before reduction contains abundant C-0, C-OH and O-c=o bonds. After rosmarinic acid reduction, the content of C-O bonds is obviously reduced, as shown in figure 3B, which proves that rosmarinic acid has stronger reducing capability on graphene oxide. After rosmarinic acid is reduced, the oxygen content of the reduced graphene oxide is reduced, the conjugated structure is partially recovered, and the conductivity is improved.

In addition, as the rosmarinic acid contains two benzene ring structures in the molecule, the rosmarinic acid can be used as a reducing agent of graphene oxide, and can also be used as an intercalating agent to prevent adjacent reduced graphene oxide sheets from stacking or agglomerating through pi-pi conjugation interaction. The morphology of the reduced graphene oxide sheets is characterized by a scanning electron microscope, and the stacking degree of the reduced graphene oxide is reflected by the color and the folds of the scanning electron microscope image, as shown in fig. 4. It can be seen that obvious wrinkles exist on the reduced graphene oxide sheets after rosmarinic acid reduction, and the image color is lighter, which proves that the stacking between the reduced graphene oxide sheets is greatly reduced after rosmarinic acid reduction, so that the dispersion performance of the reduced graphene oxide in the blend is improved, and the conductivity of the bipolar plate is improved. Meanwhile, after reduction, the reduced graphene oxide presents a large lamellar structure with lamellar size of about 30 mu m, and the large lamellar structure is beneficial to being easier to contact with other conductive carbon materials in the subsequent blending process, and is mutually built to form a communicated conductive network, so that the conductivity of the bipolar plate is improved.

Claims

1. The preparation method of the composite bipolar plate is characterized by comprising the following steps of:

(3) Placing the blend into a forming die, carrying out hot pressing treatment for 5-12 min at 200-260 ℃ and 10-20 MPa, maintaining the hot pressing pressure after the hot pressing is finished, and slowly cooling to room temperature by controlling the cooling rate to obtain a composite bipolar plate; the cooling rate is 0.5-2 ℃/min.

2. The method of manufacturing a composite bipolar plate according to claim 1, wherein the alkaline solution is one of aqueous ammonia or aqueous sodium hydroxide or aqueous potassium hydroxide.

3. The method for preparing the composite bipolar plate according to claim 1, wherein the concentration of the graphene oxide aqueous solution is 0.5-2 mg/mL, and the mass ratio of graphene oxide to rosemary is 1:10-20.

4. The method of claim 1, wherein the thermoplastic compound is one of polyethylene terephthalate, polystyrene, and polyamide, and the conductive carbon material is a combination of two of graphite powder, carbon black, expanded graphite, carbon fiber, and carbon nanotube.

5. The method for preparing the composite bipolar plate according to claim 1, wherein the thermoplastic polymer accounts for 30-50% of the mass fraction of the blend, the reduced graphene oxide powder accounts for 3-8% of the mass fraction of the blend, and the conductive carbon material accounts for 42-67% of the mass fraction of the blend.

6. The method of manufacturing a composite bipolar plate according to claim 1, wherein the thickness of the composite bipolar plate is 0.3-0.7 mm.