Bipolar plate and preparation method thereof

Abstract

The invention discloses a bipolar plate and a preparation method thereof, and belongs to the technical field of vanadium battery, the preparation method of the bipolar plate comprises the following steps: modifying maleic anhydride grafted polyolefin through a silane coupling agent KH550 to obtain modified maleic anhydride grafted polyolefin; mixing the modified maleic anhydride grafted polyolefin with expanded graphite powder, and reacting to obtain a modified maleic anhydride grafted polyolefin-expanded graphite blend; the modified maleic anhydride grafted polyolefin-expanded graphite blend is mixed with nano silicon resin, and a modified maleic anhydride grafted polyolefin-expanded graphite-nano silicon resin mixture is obtained; and carrying out compression molding on the modified maleic anhydride grafted polyolefin-expanded graphite-nano silicon resin mixture, and curing to obtain the bipolar plate. The binding force of the graphite material and the high polymer material is enhanced through chemical bonding, and meanwhile, the hydrophobicity of the surface of the bipolar plate material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vanadium batteries, and more specifically, to a bipolar plate and a preparation method thereof. Background Art

[0002] With the development of the energy field, energy storage systems are playing an increasingly crucial role. On the one hand, it can coordinate intermittent renewable energy with the power grid; on the other hand, it can also make the utilization of electricity more efficient and economical. In energy storage systems, all-vanadium redox flow batteries are considered a promising energy storage system due to their excellent characteristics, such as a long cycle life of up to 20,000 cycles (or more than 20 years), independently scalable energy and power, explosion-free and safe operation, and deep discharge reversibility. Generally, an all-vanadium flow battery stack is composed of bipolar plates, electrodes, proton exchange membranes, electrode frames, etc. As a key component in the all-vanadium flow battery system, the main function of the bipolar plate is to collect and conduct the current generated during the charge and discharge process of the battery, provide effective mechanical support for the membrane and electrodes, connect multiple single cells, prevent the mixing of positive and negative electrolyte solutions and the direct contact of electrodes, and have a significant impact on the energy efficiency of the stack.

[0003] Existing flow bipolar plates are mainly divided into three categories, namely isostatic graphite bipolar plates, flexible graphite impregnated bipolar plates, and carbon-plastic composite graphite bipolar plates. Isostatic graphite bipolar plates are brittle and prone to fracture, usually requiring a thickness of 3 - 5 mm, with a large cost, and there are certain pores on the graphite surface, which are prone to liquid leakage; flexible graphite impregnated bipolar plates seal the pores through polymer impregnation. Due to their porous structure, they are easily affected by vanadium ion penetration, and the currently used impregnating glue (acrylic polymer) is usually applicable in fuel cell systems and is easily decomposed in the strong acid and strong oxidation electrolyte environment of vanadium batteries; carbon-plastic composite graphite bipolar plates have excellent mechanical strength, good electrical conductivity and sealing performance, low cost, and are easy to process, so they have been widely studied.

[0004] However, the existing high-conductivity carbon-plastic composite graphite bipolar plates have the following problems:

[0005] (1) Currently, it is widely adopted to heat and melt a thermoplastic polymer and then carry out kneading and mixing with graphite materials. However, the compatibility between graphite materials and thermoplastic polymer materials is poor. The bipolar plates prepared by pressing have problems such as poor bonding force, low density, and easy detachment, and large amounts of dust and harmful gases are easily generated during the kneading process, causing pollution;

[0006] (2) The surface of the bipolar plate is not treated at all, and its hydrophobicity is poor. Water molecules or vanadium ions are easily adsorbed on the surface of the bipolar plate and penetrate into the material during use. After long-term operation, it will cause oxidative corrosion of the carbon material and generate CO, CO 2Swelling caused by gases such as

[0007] In view of this, the present invention provides a new solution to solve the above problems. Summary of the Invention

[0008] The object of the present invention is to provide a bipolar plate and a preparation method thereof, which can enhance the bonding force between graphite material and polymer material through chemical bonding, and at the same time improve the hydrophobicity of the surface of the bipolar plate material.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A preparation method of a bipolar plate, comprising the following steps:

[0011] Modify maleic anhydride grafted polyolefin with silane coupling agent KH550 to obtain modified maleic anhydride grafted polyolefin;

[0012] Mix the modified maleic anhydride grafted polyolefin with expanded graphite powder, and react to obtain a modified maleic anhydride grafted polyolefin-expanded graphite blend;

[0013] Mix the modified maleic anhydride grafted polyolefin with expanded graphite powder and add it to a reaction solvent for reaction, and obtain a modified maleic anhydride grafted polyolefin-expanded graphite blend through heating and curing;

[0014] Perform compression molding and curing on the modified maleic anhydride grafted polyolefin-expanded graphite-nano silicone resin mixture to obtain a bipolar plate.

[0015] Further preferably: The maleic anhydride grafted polyolefin is maleic anhydride grafted PP or maleic anhydride grafted PE.

[0016] Further preferably: The nano silicone resin is a hydrophobic alkyl nano silicone resin.

[0017] Further preferably: The nano silicone resin is dimethyl silicone oxide nano resin or diethyl silicone oxide nano resin.

[0018] Further preferably: In the bipolar plate, the mass ratio of the nano silicone resin is 0.5-2%.

[0019] Further preferably: In the bipolar plate, the mass ratio of the nano silicone resin is 2%.

[0020] Further preferably: In the bipolar plate, the mass ratio of the modified maleic anhydride grafted polyolefin is 10-20%.

[0021] More preferably, the nano-silicone resin is added in a spraying manner, and the modified maleic anhydride grafted polyolefin-expanded graphite blend is baked after being mixed with the nano-silicone resin;

[0022] The mixing time is 10 - 60 min;

[0023] The baking time is 0.5 - 2 h;

[0024] The baking temperature is 40 - 60 °C.

[0025] More preferably, the compression molding includes a hot molding stage, the temperature of the hot molding is 150 °C, the pressure is 20 - 60 MPa, and the time is 20 min;

[0026] The curing temperature is 150 - 180 °C, and the time is 30 - 60 min.

[0027] A bipolar plate is obtained by the preparation method of the bipolar plate.

[0028] In summary, the present invention has the following beneficial effects:

[0029] (1) Maleic anhydride grafted polyolefin is a thermoplastic polymer material. In the present invention, the functional group anhydride on the molecular chain of maleic anhydride grafted polyolefin reacts with the amino group at one end of the molecular chain of silane coupling agent KH550, and the two are tightly combined by chemical bonds to obtain the modified maleic anhydride grafted polyolefin, and the three ethoxy groups at the other end of KH550 are reserved as the next functional groups;

[0030] (2) When the modified maleic anhydride grafted polyolefin and expanded graphite are mixed in a solvent, the three ethoxy groups in KH550 are hydrolyzed to form an oligomeric siloxane molecular chain with 3 Si-OH. In the subsequent heating and curing process, one Si-OH in the oligomeric siloxane molecular chain with 3 Si-OH reacts with the -OH on the surface of expanded graphite to form a -Si-O bond. Thus, maleic anhydride grafted polyolefin and expanded graphite are combined by chemical bonds through the KH550 molecular chain, enhancing their binding force. The remaining two Si-OH in KH550 are in a free state and are reserved as important functional groups for the next hydrophobic treatment;

[0031] (3) In the curing stage, the 2 free Si-OH in the modified maleic anhydride grafted PP-expanded graphite blend react with the Si-OH in the nano-silicone resin to form a -Si-O bond. The two methyl functional hydrophobic groups contained in the side chain of the nano-silicone resin molecule are arranged towards the air direction, playing a surface hydrophobic role.

[0032] In summary, the present invention specifically provides a method for preparing an anti-swelling flow-through bipolar plate. The bipolar plate prepared by this method has a low swelling rate, good hydrophobicity, and stable performance output during the cyclic operation of a vanadium battery stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the process flow chart of the preparation of the bipolar plate in this embodiment;

[0034] Figure 2 is the result graph of the swelling rate test of the bipolar plate;

[0035] Figure 3 is the result graph of the contact angle test of the bipolar plate;

[0036] Figure 4 is the result graph of the cyclic stability test of the bipolar plate stack;

[0037] Figure 5 is the result graph of the change in the O / C ratio on the surface of the bipolar plate material before and after the stack test. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described in detail below with reference to the accompanying drawings.

[0039] Unless otherwise defined, all terms used hereinafter shall be construed in accordance with the ordinary meaning understood by those skilled in the art. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0040] Unless otherwise specified, all raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or prepared by existing methods.

[0041] The present invention specifically provides an anti-swelling flow-through bipolar plate and a method for preparing the same. The bipolar plate prepared by this method has the advantages of low swelling rate, good hydrophobicity, and stable performance output during the cyclic operation of a vanadium battery stack.

[0042] The method for preparing the bipolar plate, as Figure 1 shown, includes the following steps:

[0043] (1) Modify maleic anhydride grafted polyolefin with silane coupling agent KH550 (γ-aminopropyltriethoxysilane) to obtain modified maleic anhydride grafted polyolefin.

[0044] Among them, the maleic anhydride grafted polyolefin is in powder form.

[0045] Preferably, the maleic anhydride grafted polyolefin is maleic anhydride grafted PP (maleic anhydride grafted polypropylene) or maleic anhydride grafted PE (maleic anhydride grafted polyethylene). Specifically, the maleic anhydride grafted polyolefin is maleic anhydride grafted PP.

[0046] In the above steps, under the action of the amino molecules at one end of KH550, the anhydride ring molecular chain of maleic anhydride grafted PP breaks, and ammonia molecules are incorporated to form water. This reaction connects maleic anhydride grafted PP and KH550 together through chemical bonds. In the present invention, by using maleic anhydride grafted PP, since it contains anhydride groups, it can react with the silane coupling agent KH550 containing active group amino to undergo chemical bonding, making the two closely combined. The key to achieving this step is to add maleic anhydride grafted PP powder into the silane coupling agent KH550. Under the action of ultrasonic dispersion and a shearing machine, each maleic anhydride grafted PP particle can be covered with the coupling agent on its surface. In addition, to allow the amino group and the anhydride to undergo chemical bonding, it needs to be completed at a certain temperature. Therefore, after maleic anhydride grafted PP and the coupling agent KH550 are well dispersed, condensation to form amide chemical bonds needs to occur at a temperature not lower than 150 °C. For ordinary PP (polypropylene), the silane coupling agent KH550 can only form simple physical entanglement with PP molecules, relying on intermolecular forces, and the bonding strength is weak. Therefore, the present invention utilizes the reaction between maleic anhydride grafted PP and KH550.

[0047] (2) Mix the modified maleic anhydride grafted polyolefin with expanded graphite powder and then add them to a reaction solvent for reaction. After heating and curing, a modified maleic anhydride grafted polyolefin-expanded graphite blend is obtained.

[0048] Preferably, the reaction solvent is a water / ethanol mixture.

[0049] Specifically, add the modified maleic anhydride grafted PP powder and expanded graphite powder into a water / ethanol (mass ratio 1:9) mixture. After shear dispersion, place the mixture in an oven at 120 °C for curing to obtain a chemically bonded modified maleic anhydride grafted PP-expanded graphite blend.

[0050] In the above steps, the three ethoxy groups at the other end of the KH550 molecular chain in the modified maleic anhydride grafted PP undergo hydrolysis in the water / ethanol mixture to form three Si-OH oligomeric siloxane molecular chains. One Si-OH in the oligomeric siloxane chain undergoes dehydration with the -OH on the surface of the expanded graphite material during the heating and curing process to form a covalent bond connection, and the remaining two Si-OH are in a free state.

[0051] (3) Mix the modified maleic anhydride grafted PP-expanded graphite blend with nano-silicon resin to obtain a modified maleic anhydride grafted PP-expanded graphite-nano-silicon resin mixture.

[0052] Preferably, the nano-silicon resin is a hydrophobic alkyl nano-silicon resin, specifically dimethylsiloxane nano-resin or diethylsiloxane nano-resin. More specifically, the nano-silicon resin is dimethylsiloxane nano-resin.

[0053] Preferably, the modified maleic anhydride grafted PP-expanded graphite blend and nano-silicone resin are stirred and mixed in a certain proportion. After mixing, the powder is placed in an oven for heating and drying to remove the solvent in the nano-silicone resin, obtaining a modified maleic anhydride grafted PP-expanded graphite-nano-silicone resin mixture (mixed resin powder). The addition amount of the nano-silicone resin is controlled at 0.5-2%, preferably 2%. The mixing time of the materials is 10-60 min, preferably 60 min. The drying time is 0.5-2 h, preferably 2 h, and the temperature is 40-60 °C, preferably 40 °C.

[0054] Specifically, the modified maleic anhydride grafted PP-expanded graphite blend is placed in a closed mixer, and the stirring is started. The mixer is externally connected with a liquid spraying nozzle, and the nano-silicone resin solution is evenly sprayed into the modified maleic anhydride grafted PP-expanded graphite blend at a fixed time and fixed quantity through gas-liquid spraying. In this spraying method, the liquid nano-silicone resin can be atomized into fine particles and quickly cover the surface of the powder. After stirring evenly, the material is taken out and placed in an oven, and heated to 40 °C to remove the solvent in the silicone resin.

[0055] (4) The modified maleic anhydride grafted PP-expanded graphite-nano-silicone resin mixture is subjected to compression molding and curing to obtain a swelling-resistant liquid flow bipolar plate.

[0056] Specifically, the modified maleic anhydride grafted PP-expanded graphite-nano-silicone resin mixture is successively cold-pressed and hot-pressed through a powder compression molding device to obtain a primary bipolar plate. The hot-pressing temperature is controlled at 150-180 °C, the pressure is 20-60 MPa, and the time is 20 min. By heating and pressurizing, the modified maleic anhydride grafted PP-expanded graphite-nano-silicone resin mixture can quickly increase its bulk density. In the subsequent curing process, the two free Si-OH in the modified maleic anhydride grafted PP-expanded graphite blend and the Si-OH in the nano-silicone resin (dimethyl silicone nano-resin) undergo dehydration condensation under the action of heating. The two methyl functional hydrophobic groups contained in the side chain of the nano-silicone resin molecule are arranged towards the air direction, thus playing a role in surface hydrophobicity. The curing temperature is 150-180 °C, and the time is 30-60 min.

[0057] The present invention will be further elaborated in detail below with reference to the accompanying drawings and specific embodiments.

[0058] Example 1:

[0059] The preparation method of the bipolar plate includes the following steps:

[0060] (1) Preparation of PP-expanded graphite mixture: Expandable graphite powder and PP (polypropylene) powder are mixed at a mass ratio of 17:3 at a high speed to obtain a powder for standby;

[0061] (2) Powder mixing process: Rotor speed is 50 r / min, mixing time is 2 h;

[0062] (3) Process for preparing bipolar plates by molding: Place the powder in the mold of a cold pressing and molding machine, and use the upper mold to pre-press it to obtain a bipolar plate with a certain thickness and strength. The molding pressure in this process is 50 MPa, and the molding time is 5 min; Secondly, place the pre-pressed bipolar plate in a hot pressing and molding machine, heat it, and perform secondary molding to obtain the required bipolar plate. In this hot pressing process, the molding temperature is 150 °C, the molding time is 20 min. After the molding is completed, start the cooling function to cool down the mold. When the temperature of the bipolar plate reaches 100 °C, demold it, and the preparation of the bipolar plate is completed.

[0063] The bipolar plate prepared in this example is a PP-expanded graphite composite bipolar plate, and the mass ratio of PP is 15%.

[0064] Example 2:

[0065] The preparation method of the bipolar plate includes the following steps:

[0066] (1) Preparation of modified maleic anhydride grafted PP: Graft maleic anhydride onto PP powder and KH550 silane coupling agent in a mass ratio of 1:5, shear and ultrasonically disperse and mix them, take out, and cure at 150 °C to obtain modified maleic anhydride grafted PP;

[0067] (2) Preparation of modified maleic anhydride grafted PP-expanded graphite mixture: Mix expanded graphite powder and modified maleic anhydride grafted PP powder at a high speed in a mass ratio of 17:3 to obtain the powder for standby;

[0068] (3) Powder mixing process: Rotor speed is 50 r / min, mixing time is 2 h;

[0069] (4) Process for preparing bipolar plates by molding: Place the powder in the mold of a cold pressing and molding machine, and use the upper mold to pre-press it to obtain a bipolar plate with a certain thickness and strength. The molding pressure in this process is 50 MPa, and the molding time is 5 min; Secondly, place the pre-pressed bipolar plate in a hot pressing and molding machine, heat it, and perform secondary molding to obtain the required bipolar plate. In this hot pressing process, the molding temperature is 150 °C, the molding time is 20 min. After the molding is completed, start the cooling function to cool down the mold. When the temperature of the bipolar plate reaches 100 °C, demold it, and the preparation of the bipolar plate is completed.

[0070] The bipolar plate prepared in this example is a modified maleic anhydride grafted PP-expanded graphite composite bipolar plate, and the mass ratio of modified maleic anhydride grafted PP is 15%.

[0071] Example 3:

[0072] The preparation method of the bipolar plate includes the following steps:

[0073] (1) Preparation of modified maleic anhydride grafted PP: Maleic anhydride grafted PP powder and silane coupling agent KH550 are shear ultrasonically dispersed and mixed at a mass ratio of 1:5, taken out, and cured at 150 °C to obtain mixture A;

[0074] (2) Preparation of modified maleic anhydride grafted PP - expanded graphite mixture: Mixture A, expanded graphite powder, and water / ethanol mixture (mass ratio of 1:9) are mixed at a mass ratio of 13:86.5:398 for shear dispersion. The shear speed is 1000 r / min, and the shear time is 30 min. After mixing, it is taken out and placed in an oven, and cured at 120 °C to obtain mixture B;

[0075] (3) Place mixture B in a closed mixer, start stirring. The mixer is externally connected to a liquid spraying nozzle, and the nano - silicone resin solution is sprayed into the mixer at a fixed time and quantity through a gas - liquid spraying device. The spraying pressure is controlled at 0.3 MPa, the spraying amount is 10 g / min, and the time interval for each spraying is 10 min. After the nano - silicone resin spraying is completed, the whole material continues to be stirred for 60 min and then taken out, and dried at 40 °C to remove the solvent in the silicone resin to obtain mixture C. In mixture C, the proportion of mixture B is 99.5%, and the proportion of nano - silicone resin is 0.5%;

[0076] (4) Process for preparing bipolar plates by compression molding: Place powder C in the mold of a cold - press molding machine, and use the upper mold to pre - press it to obtain a bipolar plate sheet with a certain thickness and strength. The molding pressure in this process is 50 MPa, and the molding time is 5 min; Secondly, place the pre - pressed bipolar plate in a hot - press molding machine, heat it, and perform secondary molding to obtain the required bipolar plate. In this hot - press process, the molding temperature is 150 °C, the molding time is 20 min. After the molding is completed, start the cooling function to cool the mold. When the temperature of the bipolar plate reaches 100 °C, demold it, and the preparation of the bipolar plate is completed.

[0077] The bipolar plate prepared in this example is a modified maleic anhydride - nano - silicone resin - expanded graphite composite bipolar plate, and the mass proportion of modified maleic anhydride grafted PP is 13%, and the mass proportion of nano - silicone resin is 0.5%.

[0078] Example 4:

[0079] The preparation method of the bipolar plate includes the following steps:

[0080] (1) Preparation of modified maleic anhydride grafted PP: Maleic anhydride grafted PP powder and silane coupling agent KH550 are shear ultrasonically dispersed and mixed at a mass ratio of 1:5, taken out, and cured at 150 °C to obtain mixture A;

[0081] (2) Preparation of modified maleic anhydride grafted PP-expanded graphite mixture: Mixture A, expanded graphite powder, and water / ethanol mixture (mass ratio 1:9) are mixed in a mass ratio of 13:85.5:398 for shear dispersion. The shear speed is 1000 r / min and the shear time is 30 min. After mixing, it is taken out and placed in an oven to be cured at 120 °C to obtain mixture B;

[0082] (3) Place mixture B in a closed mixer, start stirring. The mixer is externally connected to a liquid spraying nozzle, and the nano-silicone resin solution is sprayed into the mixer at a fixed time and quantity through a gas-liquid spraying device. The spraying pressure is controlled at 0.3 MPa, the spraying amount is 10 g / min, and the time interval for each spraying is 10 min. After the nano-silicone resin spraying is completed, the whole material continues to be stirred for 60 min and then taken out, and dried at 40 °C to remove the solvent in the silicone resin to obtain mixture C. In mixture C, the proportion of mixture B is 98.5%, and the proportion of nano-silicone resin is 1.5%;

[0083] (4) Process for preparing bipolar plates by compression molding: Place powder C in the mold of a cold compression molding press, and use the upper mold to pre-press it to obtain a bipolar plate sheet with a certain thickness and strength. The compression molding pressure in this process is 50 MPa and the compression molding time is 5 min; Secondly, place the pre-pressed bipolar plate in a hot compression molding press, heat it, and perform secondary molding to obtain the required bipolar plate. In this hot compression process, the compression molding temperature is 150 °C, the compression molding time is 20 min. After the compression molding is completed, start the cooling function to cool down the mold. When the temperature of the bipolar plate reaches 100 °C, demold it, and the preparation of the bipolar plate is completed.

[0084] The bipolar plate prepared in this example is a modified maleic anhydride-nano-silicone resin-expanded graphite composite bipolar plate, and the mass proportion of modified maleic anhydride grafted PP is 13%, and the mass proportion of nano-silicone resin is 1.5%.

[0085] Example 5:

[0086] The preparation method of the bipolar plate includes the following steps:

[0087] (1) Preparation of modified maleic anhydride grafted PP: Maleic anhydride grafted PP powder and silane coupling agent KH550 are mixed by shear ultrasonic dispersion in a mass ratio of 1:5, taken out, and cured at 150 °C to obtain mixture A;

[0088] (2) Preparation of modified maleic anhydride grafted PP-expanded graphite mixture: Mixture A, expanded graphite powder, and water / ethanol mixture (mass ratio 1:9) are mixed in a mass ratio of 13:85:398 for shear dispersion. The shear speed is 1000 r / min and the shear time is 30 min. After mixing, it is taken out and placed in an oven to be cured at 120 °C to obtain mixture B;

[0089] (3) Place mixture B in a closed mixer, start stirring, and connect a liquid spraying nozzle to the mixer. The nano-silicone resin solution is sprayed into the mixer at a fixed time and quantity through a gas-liquid spraying device. The spraying pressure is controlled at 0.3 MPa, the spraying quantity is 10 g / min, and the time interval for each spraying is 10 min. After the spraying of the nano-silicone resin ends, the whole material continues to be stirred for 60 min and then taken out, and dried at 40 °C to remove the solvent in the silicone resin to obtain mixture C. In mixture C, the proportion of mixture B is 98%, and the proportion of nano-silicone resin is 2%.

[0090] (4) Process for preparing bipolar plates by molding: Place powder C in the mold of a cold pressing mold press, and use the upper mold to pre-press it to obtain a bipolar plate with a certain thickness and strength. The molding pressure in this process is 50 MPa, and the molding time is 5 min; then place the pre-pressed bipolar plate in a hot pressing mold press, heat it, and perform secondary molding to obtain the required bipolar plate. In this hot pressing process, the molding temperature is 150 °C, the molding time is 20 min. After the molding is completed, start the cooling function to cool the mold. When the temperature of the bipolar plate reaches 100 °C, demold it, and the preparation of the bipolar plate is completed.

[0091] The bipolar plate prepared in this example is a modified maleic anhydride-nano-silicone resin-expanded graphite composite bipolar plate, and the mass proportion of the modified maleic anhydride grafted PP is 13%, and the mass proportion of nano-silicone resin is 2%.

[0092] Performance test:

[0093] (1) The swelling rate tests were respectively carried out on the bipolar plates prepared in Examples 1, 2, and 5, and the test results are as Figure 2 shown.

[0094] As Figure 2 can be seen, after the bipolar plates prepared in Examples 1, 2, and 5 were immersed in 3 mol / L sulfuric acid and 1.7 mol / L vanadium electrolyte solution for 90 days, the swelling rate of the bipolar plate prepared in Example 5 was only 0.0026%, while the swelling rate of the bipolar plate prepared in Example 1 was 1.10%, and the swelling rate of the bipolar plate prepared in Example 2 was 0.24%. It can be seen that the swelling rate of the bipolar plate prepared in Example 5 is significantly lower than that of the bipolar plates prepared in Examples 1 and 2, that is, the graphite composite bipolar plate prepared from maleic anhydride grafted PP modified by silane coupling agent KH550 and added with nano-silicone resin has the smallest swelling rate in the electrolyte.

[0095] (2) The contact angle tests were respectively carried out on the bipolar plates prepared in Examples 1-5, and the test results are as Figure 3 shown.

[0096] As Figure 3It can be seen that when the addition amount of nano-silicone resin is controlled at 0.5%, the contact angle is about 93°, which is significantly larger than that of the bipolar plates without adding nano-silicone resin series, namely the ordinary PP-expanded graphite composite bipolar plate (contact angle 41°) and the modified maleic anhydride grafted PP-expanded graphite composite bipolar plate (contact angle 41°). With the increase of the addition amount of nano-silicone resin, the contact angle between the bipolar plate and water also gradually increases. When the addition amount is 2%, the contact angle reaches 141°, which indicates that the number of hydrophobic groups on the surface of the graphite composite bipolar plate increases significantly, and the hydrophobic effect is further strengthened. Thus, it can be seen that neither ordinary PP nor modified maleic anhydride grafted PP has an effect on the surface hydrophobicity of the bipolar plate material. However, after the maleic anhydride grafted PP is modified and nano-silicone resin is added, the hydrophobicity is significantly improved, and it shows an increasing trend with the increase of the addition amount of silicone resin.

[0097] (3) The performance of the bipolar plate prepared in Example 5 was tested in an electric stack, and the test results are as Figure 4 shown.

[0098] It can be Figure 4 seen that under the current density of 160 mA / cm 2 of the bipolar plate prepared in Example 5, after 665 cycles, the energy efficiency output decreased from 81% to 80.9%, and the energy efficiency decay per cycle was only 0.00015%, and the output of the electric stack was stable. Thus, it can be seen that the bipolar plate prepared by the 13% modified maleic anhydride + 2% nano-silicone resin + expanded graphite system has very stable energy efficiency of the electric stack during 800 h of operation of the electric stack, without obvious decay.

[0099] (4) The O / C ratio of the material of the bipolar plate prepared in Example 5 was tested after 800 cycles of the bipolar plate electric stack, and the test results are as Figure 5 shown.

[0100] It can be Figure 5 seen that for the bipolar plate prepared by the 13% modified maleic anhydride + 2% nano-silicone resin + expanded graphite system during 800 h of operation of the electric stack, there is no obvious change in O / C on the surface of the bipolar plate material before and after operation, indicating that the material is not corroded by the electrolyte, that is, no gases such as CO, CO 2 are generated, and the anti-swelling ability of the bipolar plate is significantly enhanced.

[0101] The present invention compares the hydrophobic effects of the ordinary PP-expanded graphite composite bipolar plate, the modified maleic anhydride grafted PP-expanded graphite composite bipolar plate, and the modified maleic anhydride-nano-silicone resin-expanded graphite, and simultaneously investigates the influence of the addition amount of nano-silicone resin on the hydrophobic degree of the graphite composite bipolar plate.

[0102] It can be known from the tests of the swelling rate, contact angle, performance of the stack, and the O / C ratio of the material after 800 cycles of the bipolar plate stack that the bipolar plate prepared by this preparation method has the advantages of low swelling rate and good hydrophobicity, and the performance output is relatively stable during the cyclic operation of the vanadium battery stack.

[0103] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a bipolar plate, characterized in that: The following steps are involved: The maleic anhydride grafted polyolefin is modified by using a silane coupling agent KH550 to obtain a modified maleic anhydride grafted polyolefin; The modified maleic anhydride grafted polyolefin and expanded graphite powder are mixed and added into a reaction solvent for reaction, and then heated and cured to obtain a modified maleic anhydride grafted polyolefin-expanded graphite blend; The modified maleic anhydride grafted polyolefin-expanded graphite blend is mixed with nano silicone resin to obtain a modified maleic anhydride grafted polyolefin-expanded graphite-nano silicone resin mixture; The modified maleic anhydride grafted polyolefin-expanded graphite-nano silicone resin mixture is compression molded and cured to obtain a bipolar plate.

2. The method for preparing a bipolar plate according to claim 1, characterized in that: The maleic anhydride grafted polyolefin is maleic anhydride grafted PP or maleic anhydride grafted PE.

3. The method for preparing a bipolar plate according to claim 1, characterized in that: The nano silicone resin is a hydrophobic alkyl nano silicone resin.

4. The method for preparing a bipolar plate according to claim 3, characterized in that: The nano-silicon resin is dimethylsiloxane nano-resin or diethylsiloxane nano-resin.

5. The method for preparing a bipolar plate according to claim 1, characterized in that: In the bipolar plate, the mass proportion of the nano-silicon resin is 0.5-2%.

6. The method for preparing a bipolar plate according to claim 5, characterized in that: In the bipolar plate, the nano-silicon resin accounts for 2% by mass.

7. The method for preparing a bipolar plate according to claim 1, characterized in that: In the bipolar plate, the modified maleic anhydride grafted polyolefin accounts for 10-20% by mass.

8. The method for preparing a bipolar plate according to claim 1, characterized in that: The nano-silicone resin is added in a spraying manner, and the modified maleic anhydride grafted polyolefin-expanded graphite blend is mixed with the nano-silicone resin and then baked; The mixing time is 10-60min; The baking time is 0.5-2h; The temperature of the baking material is 40-60°C.

9. The method for preparing a bipolar plate according to claim 1, characterized in that: The compression molding includes a hot molding stage, wherein the hot molding temperature is 150°C, the pressure is 20-60MPa, and the time is 20min; The curing temperature is 150-180° C. and the curing time is 30-60 minutes.

10. A bipolar plate, characterized in that: The bipolar plate is prepared by the method for preparing the bipolar plate according to any one of claims 1 to 9.

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