Liquid flow battery graphite bipolar plate and its preparation method and application

Abstract

The present invention discloses a flow battery graphite bipolar plate and a preparation method and application thereof. The bipolar plate is composed of the following components by mass: 50 to 70 parts of expanded graphite; 5 to 10 parts of flake graphite; 15 to 20 parts of fully reduced polyaniline; 12 to 16 parts of polyetheretherketone; and 3 to 4 parts of ethylene-vinyl acetate copolymer. The present invention adopts expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer to prepare polymer-graphite composite bipolar plate, so that EVA with toughening effect and PEEK with soft ether bond are filled between LB and graphite, which can alleviate thermal shock and prevent cracks from appearing, improve the physical and mechanical properties of the material, and reasonably proportion graphite and polymer, reduce resistance and improve conductivity, so that the graphite bipolar plate material can take into account both mechanical properties and electrical properties.

Description

Technical Field

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

[0002] Bipolar plate is one of the key components of all-vanadium liquid flow battery. It plays the role of connecting the positive and negative electrodes of different single cells and conducting the internal circuit of the battery. It is required to have good conductivity, mechanical strength, chemical oxidation resistance and electrochemical corrosion resistance. The available materials mainly include metal bipolar plates, pure graphite bipolar plates and polymer-carbon composite bipolar plates.

[0003] At present, metal bipolar plates have disadvantages in price and corrosion resistance and are rarely studied and used; pure graphite bipolar plates have excellent conductivity, but they are easy to break during processing and installation, which limits their large-scale industrial applications; polymer-carbon composite bipolar plates have good mechanical properties, but their resistivity is relatively high. Summary of the invention

[0004] The present invention provides a graphite bipolar plate for a flow battery having excellent mechanical properties and electrical conductivity, and a preparation method and application thereof.

[0005] In order to solve the above technical problems, in a first aspect, the present invention provides a graphite bipolar plate for a flow battery, which is composed of the following components in parts by mass:

[0006] 50 to 70 parts of expanded graphite;

[0007] 5-10 parts of flake graphite;

[0008] 15 to 20 parts of fully reduced polyaniline;

[0009] 12 to 16 parts of polyetheretherketone;

[0010] 3 to 4 parts of ethylene-vinyl acetate copolymer.

[0011] The expanded graphite involved in this embodiment is a loose and porous worm-like substance obtained by intercalation, washing, drying and high-temperature expansion of natural graphite flakes. When the expanded graphite is exposed to high temperature, the volume can be instantly expanded by 150 to 300 times, and the flake shape changes into a worm shape, so that the structure is loose, porous and curved, the surface area is enlarged, the surface energy is improved, the adsorption force of flake graphite is enhanced, and the worm-like graphite can be self-interlocked, which enhances the softness, resilience and plasticity of the device.

[0012] The flake graphite involved in this embodiment is natural phaneritic graphite, which is a natural solid lubricant. It is shaped like fish scales, belongs to the hexagonal crystal system, has a layered structure, and has good high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity and acid and alkali resistance.

[0013] The fully reduced polyaniline (LB) involved in this embodiment is a polyaniline material obtained by further dedoping and reducing the intrinsic polyaniline (EB) obtained by dedoping the doped polyaniline (ES) with ammonia water. Compared with ES and EB, LB has a higher capacity utilization rate and can take into account both reversible specific capacity and cycle stability.

[0014] The polyetheretherketone (PEEK) involved in this embodiment is a polymer composed of repeating units containing one ketone bond and two ether bonds in the main chain structure. It is a special polymer material with physical and chemical properties such as high temperature resistance and chemical corrosion resistance. It is a type of semi-crystalline polymer material that can be used as a high temperature resistant structural material and electrical insulating material, and can be composited with glass fiber or carbon fiber to prepare reinforced materials.

[0015] The ethylene-vinyl acetate copolymer (EVA) involved in this embodiment has good low-temperature resistance and a low thermal decomposition temperature of about 230°C. As the molecular weight increases, the softening point of EVA increases, and the processability and surface gloss of the plastic part decrease, but the strength increases, and the impact toughness and environmental stress cracking resistance are improved. It is used as a toughening agent in the preparation process of the bipolar plate.

[0016] Furthermore, the chemical composition of the fully reduced polyaniline is C 6 H 5 N·0.10H 2 O, the oxidation degree is 0. Preferably, the fully reduced polyaniline prepared in the "AEM: Complete Utilization and Stable Cycle of Polyaniline Cathode Materials" jointly conducted by Professor Song Zhiping of Wuhan University and Professor Wang Yonggang of Fudan University.

[0017] Furthermore, the expanded graphite is prepared by sulfur-free intercalation of natural graphite and high-temperature expansion, and its sulfur content is less than 500 PPM and its iron content is less than 10 PPM.

[0018] Furthermore, the mass ratio of graphite to polymer is (6-7):(3-4), the graphite includes the expanded graphite and flake graphite, and the polymer includes conductive polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer.

[0019] Further preferably, the mass ratio of the graphite to the polymer is 7:3.

[0020] Furthermore, the mass ratio of the fully reduced polyaniline to polyetheretherketone is (1-1.8):1.

[0021] Further preferably, the mass ratio of the fully reduced polyaniline to polyetheretherketone is 1.25:1.

[0022] In a second aspect, the present invention further provides a method for preparing a graphite bipolar plate for a flow battery as described in the first aspect, comprising the following steps:

[0023] Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used to mix for about 10 minutes to 15 minutes and the material is discharged, the torque rheometer speed is 60r / min to 90r / min, and the temperature is 160°C to 180°C; a flat plate vulcanizer is used for compression molding, the pressure is 7MPa to 10MPa, and the temperature is 140°C to 200°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

[0024] In a third aspect, the present invention further provides a use of the graphite bipolar plate for a flow battery as described in the first aspect in preparing a flow battery.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The present invention adopts expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer to prepare polymer-graphite composite bipolar plates. A hydrogen bond is formed between the carbonyl group of polyetheretherketone and the fully reduced polyaniline to enhance the bonding force between PEEK and LB. Meanwhile, EVA with a toughening effect and PEEK with a soft ether bond are filled between LB and graphite to alleviate thermal shock and prevent cracks from appearing, thereby improving the physical and mechanical properties of the material. Expanded graphite, flake graphite, fully reduced polyaniline and other materials with excellent electrical properties are adopted as main bipolar plate materials, and graphite and polymer are reasonably proportioned to reduce resistance and improve electrical conductivity, so that the graphite bipolar plate material can take into account both mechanical properties and electrical properties. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0028] As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0029] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0030] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention have no restrictions on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the number is obviously intended to be in the singular form.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0032] Example 1

[0033] A graphite bipolar plate for a liquid flow battery, comprising the following components in parts by mass:

[0034] Expanded graphite 50 parts;

[0035] Flake graphite 5;

[0036] 15 parts of fully reduced polyaniline;

[0037] 12 parts of polyetheretherketone;

[0038] 3 parts of ethylene-vinyl acetate copolymer.

[0039] A method for preparing a graphite bipolar plate for a flow battery comprises the following steps:

[0040] Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used for mixing for about 10 minutes to discharge the material, the speed of the torque rheometer is 90r / min, and the temperature is 160°C; a flat plate vulcanizer is used for compression molding, the pressure is 7MPa, and the temperature is 140°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

[0041] Example 2

[0042] A graphite bipolar plate for a liquid flow battery, comprising the following components in parts by mass:

[0043] Expanded graphite 70 parts;

[0044] 10 parts of flake graphite;

[0045] 20 parts of fully reduced polyaniline;

[0046] 16 parts of polyetheretherketone;

[0047] 4 parts of ethylene-vinyl acetate copolymer.

[0048] A method for preparing a graphite bipolar plate for a flow battery comprises the following steps:

[0049] Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used to mix for about 15 minutes to discharge the material, the torque rheometer speed is 60r / min, and the temperature is 160°C; a flat plate vulcanizer is used for compression molding, the pressure is 10MPa, and the temperature is 200°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

[0050] Example 3

[0051] A graphite bipolar plate for a liquid flow battery, comprising the following components in parts by mass:

[0052] Expanded graphite 65 parts;

[0053] 5 parts of flake graphite;

[0054] 15 parts of fully reduced polyaniline;

[0055] 12 parts of polyetheretherketone;

[0056] 3 parts of ethylene-vinyl acetate copolymer.

[0057] A method for preparing a graphite bipolar plate for a flow battery comprises the following steps:

[0058] Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used to mix for about 15 minutes to discharge the material, the torque rheometer speed is 60r / min, and the temperature is 160°C; a flat plate vulcanizer is used for compression molding, the pressure is 7MPa, and the temperature is 200°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

[0059] Example 4

[0060] A graphite bipolar plate for a liquid flow battery, comprising the following components in parts by mass:

[0061] Expanded graphite 55 parts;

[0062] 10 parts of flake graphite;

[0063] 20 parts of fully reduced polyaniline;

[0064] 12 parts of polyetheretherketone;

[0065] 3 parts of ethylene-vinyl acetate copolymer.

[0066] A method for preparing a graphite bipolar plate for a flow battery comprises the following steps:

[0067] Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used to mix for about 15 minutes to discharge the material, the torque rheometer speed is 60r / min, and the temperature is 160°C; a flat plate vulcanizer is used for compression molding, the pressure is 7MPa, and the temperature is 200°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

[0068] Comparative Example 1

[0069] Carbon black is used instead of expanded graphite and flake graphite, and the rest is the same as in Example 3.

[0070] Comparative Example 2

[0071] Doped polyaniline is used instead of fully reduced polyaniline, and the rest is the same as in Example 3.

[0072] Comparative Example 3

[0073] Polyimide is used instead of fully reduced polyaniline, and the rest is the same as in Example 3.

[0074] Comparative Example 4

[0075] No polyetheretherketone was added, and the rest was the same as in Example 3.

[0076] Performance Testing

[0077] Conductivity test: Scanning electron microscopy was used to observe the distribution of graphite and resin in the composite graphite bipolar plate, and the sampling position was the middle of the bipolar plate sample. A four-probe resistance meter (ST2258C) was used to test the in-plane conductivity of the bipolar plate, and the test results are shown in Table 1.

[0078] Bending strength test: The bending strength of the sample was determined by a three-point bending test using a mechanical testing machine (instron3369), and the bending strength of the composite bipolar plate was measured at a loading speed of 0.5 mm / min. The size of the sample was 40 mm x 10 mm, and the span was 20 mm. Five samples were tested in each group, and the average value was taken. The test results are shown in Table 1.

[0079] Contact resistance test: The bipolar plate contact resistance test adopts the national standard GBT200426-2011, and the test results are shown in Table 1.

[0080] Table 1 Bipolar plate performance test results

[0081] product Conductivity / S / cm Bending strength / MPa <![CDATA[Contact resistance / mΩ·cm 2 > Example 1 487.4 42.72 4.54 Example 2 501.9 37.98 5.47 Example 3 525.3 43.56 3.13 Example 4 477.5 41.67 7.42 Comparative Example 1 273.8 28.12 18.13 Comparative Example 2 404.3 42.88 12.75 Comparative Example 3 111.4 49.74 27.48 Comparative Example 4 550.9 16.21 2.96

[0082] According to Table 1, the mechanical and electrical properties of the graphite bipolar plate for flow batteries prepared by using expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are the best, with a mass ratio of graphite to polymer of 7:3, a mass ratio of conductive polyaniline to polyetheretherketone of 1.25:1, and a conductivity of 525.3S / cm, a flexural strength of 43.56 / MPa, and a contact resistance of 3.13mΩ·cm. 2 Compared with Comparative Examples 1-4, Example 3 uses expanded graphite, flake graphite, fully reduced polyaniline and polyetheretherketone as raw materials for preparing bipolar plates, which can improve the conductivity and bending strength of the bipolar plates and reduce the contact resistance.

[0083] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A graphite bipolar plate for a flow battery, characterized in that: It is composed of the following components in parts by mass: 50 to 70 parts of expanded graphite; 5-10 parts of flake graphite; 15 to 20 parts of fully reduced polyaniline; 12 to 16 parts of polyetheretherketone; 3 to 4 parts of ethylene-vinyl acetate copolymer.

2. The graphite bipolar plate for a liquid flow battery according to claim 1, characterized in that: The chemical composition of the fully reduced polyaniline is C6H5N·0.10H2O, and the oxidation degree is 0.

3. The graphite bipolar plate for a liquid flow battery according to claim 1, characterized in that: The sulfur content of the expanded graphite is less than 500 PPM, and the iron content is less than 10 PPM.

4. The graphite bipolar plate for a liquid flow battery according to claim 1, characterized in that: The mass ratio of graphite to polymer is (6-7):(3-4), the graphite includes expanded graphite and flake graphite, and the polymer includes fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer.

5. The graphite bipolar plate for a liquid flow battery according to claim 4, characterized in that: The mass ratio of the graphite to the polymer is 7:

3.

6. The graphite bipolar plate for a liquid flow battery according to claim 1, characterized in that: The mass ratio of the fully reduced polyaniline to polyetheretherketone is 1.25:

1.

7. A method for preparing a graphite bipolar plate for a flow battery according to any one of claims 1 to 6, characterized in that: The following steps are involved: Expanded graphite, flake graphite, fully reduced polyaniline, polyetheretherketone and ethylene-vinyl acetate copolymer are weighed according to their mass fractions and mixed in a crusher; a torque rheometer is used to mix for 10 to 15 minutes and the material is discharged, the torque rheometer speed is 60 r / min to 90 r / min, and the temperature is 160°C to 180°C; a flat plate vulcanizer is used for compression molding, the pressure is 7MPa to 10MPa, and the temperature is 140°C to 200°C; and the liquid flow battery graphite bipolar plate is obtained by natural cooling.

8. Use of the graphite bipolar plate for a liquid flow battery as claimed in any one of claims 1 to 6 in the preparation of a liquid flow battery.