Composition for making bipolar plates, composite material for bipolar plates and method for making same, bipolar plates and flow battery

Abstract

This invention relates to the field of flow battery technology, specifically to a composition for preparing a bipolar plate, a composite material for a bipolar plate and a method for preparing the same, a bipolar plate, and a flow battery. The composition contains a resin matrix, a conductive agent, a modifier, and a curing agent; based on the total weight of the composition, the content of the resin matrix is ​​10-40 wt%, the content of the conductive agent is 35-70 wt%, the content of the modifier is 3-20 wt%, and the content of the curing agent is 1-6 wt%; the modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The composite material prepared from the composition provided by the present invention has high flexural strength and low vanadium ion permeability; at the same time, when the composite material is used in a bipolar plate, the efficiency of the flow battery assembled from the bipolar plate is improved by enhancing the high mechanical strength and low vanadium ion permeability of the bipolar plate.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically to a composition for preparing a bipolar plate, a composite material for a bipolar plate, a method for preparing a composite material for a bipolar plate, a bipolar plate, and a flow battery. Background Technology

[0002] Currently developed flow batteries include vanadium redox flow batteries, iron-chromium flow batteries, and zinc-bromine flow batteries. Flow batteries have independent energy units and power units. Energy units generally refer to the positive and negative electrolytes of the battery. The concentration and volume of active materials in the electrolyte determine the upper limit of the flow battery's energy. Power units generally refer to a single cell or a battery stack. The electrolyte flows through the electrodes within the battery stack, and the active materials react on the electrode surfaces, thereby converting chemical energy into electrical energy, or vice versa.

[0003] The stack of a flow battery mainly consists of electrodes, a separator, bipolar plates, and current collectors. Among these, the bipolar plates are a key component, serving to connect the positive and negative electrodes of different individual cells, conduct electricity within the battery's internal circuitry, block electrolytes from both sides, and support the positive and negative electrodes. They should possess good conductivity, mechanical strength, and resistance to chemical oxidation and electrochemical corrosion. Composite bipolar plates combine the high conductivity and corrosion resistance of graphite with the high toughness of polymer materials, and have been widely used. Furthermore, optimization of the surface and structure of the bipolar plates is also significant for the performance of flow batteries.

[0004] CN110192299A discloses a design for providing a bipolar plate, a unit frame, a unit group, and a redox flow battery, thereby achieving good electrolyte diffusion and improving battery reaction performance. In this design, the roughness of the bipolar plate is between 0.1-25 μm. The structure adopts a direct liquid injection method, which may cause bipolar plate displacement during assembly, resulting in electrolyte leakage.

[0005] How to maintain the mechanical strength of the bipolar plate while blocking the penetration of vanadium ions, and how to optimize the bipolar plate design to improve the efficiency of flow batteries, is a problem that urgently needs to be solved to achieve further large-scale production of this technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing bipolar plates being unable to simultaneously possess high mechanical strength and vanadium ion penetration barrier properties, how to optimize bipolar plate design, and how to improve the efficiency of flow batteries. This invention provides a composition for preparing a bipolar plate, a composite material for a bipolar plate, a method for preparing the composite material for a bipolar plate, a bipolar plate, and a flow battery. The composite material obtained from this composition has high mechanical strength and low vanadium ion permeability. Using this composite material in a bipolar plate, combined with a specific structural configuration of the bipolar plate, results in a flow battery assembled from this bipolar plate exhibiting excellent electrochemical performance. Furthermore, this method has advantages such as simple preparation process, low cost, and environmental friendliness.

[0007] To achieve the above objectives, a first aspect of the present invention provides a composition for preparing a bipolar plate, the composition comprising a resin matrix, a conductive agent, a modifier, and a curing agent;

[0008] Wherein, based on the total weight of the combination, the content of the resin matrix is ​​10-40 wt%, the content of the conductive agent is 35-70 wt%, the content of the modifier is 3-20 wt%, and the content of the curing agent is 1-6 wt%.

[0009] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0010] A second aspect of the present invention provides a composite material for bipolar plates, which is obtained by hot pressing the composition provided in the first aspect.

[0011] A third aspect of the present invention provides a method for preparing a composite material for a bipolar plate, the method comprising the following steps:

[0012] (1) The resin matrix, conductive agent, modifier and curing agent are mixed and ground in sequence to obtain solid powder;

[0013] (2) The solid powder is hot-pressed to obtain a composite material;

[0014] The weight ratio of the resin matrix, conductive agent, modifier, and curing agent is 10-40:35-70:3-20:1-6.

[0015] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0016] A fourth aspect of the present invention provides a bipolar plate comprising the composite material provided in the second aspect, or the composite material prepared by the method provided in the third aspect.

[0017] The fifth aspect of the present invention provides a flow battery comprising the bipolar plate provided in the fourth aspect.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The composition for preparing bipolar plates provided by the present invention has a carbon atom number C 22 -C 24 A mixture of polycyclic aromatic hydrocarbons is used as a modifier, combined with a resin matrix, conductive agent and curing agent. Through the synergistic effect and content ratio between the components, the composite material made from this composition has high flexural strength and low vanadium ion permeability.

[0020] (2) The composite material provided by the present invention is used in bipolar plates to improve the mechanical strength of the bipolar plates and reduce the permeability of vanadium ions, thereby improving the efficiency of the flow battery assembled by the bipolar plates; in particular, the electrochemical performance of the flow battery can be further improved by combining the specific roughness Ra of the bipolar plates and the specific structure of the electrolyte inlet and electrolyte outlet.

[0021] (3) The method for preparing composite materials provided by the present invention is mild, simplifies the process flow, has low cost, and is easy to design for industrial production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a bipolar plate for a flow battery according to a specific embodiment of the present invention;

[0023] Figure 2 This is a specific embodiment of the present invention, a cross-sectional schematic diagram of the electrolyte inlet along the flow direction of the electrolyte, wherein the arrow points to indicate the flow direction of the electrolyte;

[0024] Figure 3 This is a specific embodiment of the present invention, a cross-sectional schematic diagram of the electrolyte outlet along the flow direction of the electrolyte, wherein the arrow points to indicate the flow direction of the electrolyte.

[0025] Explanation of reference numerals in the attached figures

[0026] 6-1. Electrolyte inlet section; 6-11. First straight section; 6-12. Diameter expansion section

[0027] 6-2, Electrolyte outlet section; 6-21, Diameter reduction section; 6-22, Second straight section Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first mixture" and "second mixture," "first" and "second" are only used to distinguish that these are not the same mixture.

[0030] The first aspect of the present invention provides a composition for preparing bipolar plates, the composition comprising a resin matrix, a conductive agent, a modifier, and a curing agent;

[0031] Wherein, based on the total weight of the combination, the content of the resin matrix is ​​10-40 wt%, the content of the conductive agent is 35-70 wt%, the content of the modifier is 3-20 wt%, and the content of the curing agent is 1-6 wt%.

[0032] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0033] The inventors of this invention have discovered that, with a carbon atom number of C... 22 -C 24 A mixture of polycyclic aromatic hydrocarbons is used as a modifier, combined with a resin matrix, conductive agent, and curing agent, resulting in a composite material with both high flexural strength and low vanadium ion permeability. Specifically, the modifier in the composition can improve the reduction in mechanical strength caused by the conductive agent. Combined with the synergistic effect between the resin matrix, modifier, conductive agent, and curing agent, and a specific content ratio, the performance of the composite material can be further optimized, resulting in flow batteries assembled with bipolar plates containing this composite material exhibiting excellent electrochemical performance.

[0034] In some embodiments of the present invention, preferably, based on the total weight of the combination, the content of the resin matrix is ​​preferably 20-40 wt%, the content of the conductive agent is 40-65 wt%, the content of the modifier is 3-15 wt%, and the content of the curing agent is 2-6 wt%. Using these preferred conditions is more conducive to improving the performance of the composite material obtained from this composition, namely, making the composite material have high flexural strength and low vanadium ion permeability.

[0035] In some embodiments of the present invention, preferably, the resin matrix is ​​selected from phenolic resin, and the viscosity of the phenolic resin is ≥0.125 Pa·S / (20°C, 50% alcohol).

[0036] In some embodiments of the present invention, preferably, the conductive agent is selected from at least one of expanded graphite, carbon fiber, and carbon nanotubes.

[0037] In some embodiments of the present invention, preferably, the curing agent is an amine curing agent, including but not limited to hexamethylenetetramine curing agents.

[0038] In a preferred embodiment of the present invention, preferably, the polycyclic aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted, and more preferably, has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

[0039] In this invention, the source of the polycyclic aromatic hydrocarbon mixture has a wide range of choices. It can be obtained by purchase or by preparation. For details, please refer to "Pyrolysis Characteristics and Properties of Thermal Conversion Products of Toluene-Soluble Components in Medium-Temperature Asphalt", Zhu Yaming, Zhao Xuefei, Cheng Junxia, ​​Liu Wei, Lü Jun, Wang Ying; Materials Reports B: Research Article; June 2017 (B) Vol. 31 No. 6, pp. 109-125.

[0040] In one specific embodiment of the present invention, the polycyclic aromatic hydrocarbon mixture is prepared by the following method: asphalt and toluene are first mixed, the first mixture is extracted, and the resulting extract is distilled to obtain the polycyclic aromatic hydrocarbon mixture.

[0041] In some embodiments of the present invention, preferably, the weight ratio of the asphalt to toluene is 1:1-15, for example, 1:1, 1:2, 1:5, 1:6, 1:8, 1:10, 1:15, and any value within the range of any two values, preferably 1:5-10.

[0042] In this invention, the first mixing is intended to uniformly mix the asphalt and toluene. Preferably, the conditions for the first mixing include: a temperature of 80-100°C, more preferably 85-95°C; and a rotation speed of 100-1000 rpm, more preferably 300-700 rpm.

[0043] In some embodiments of the present invention, preferably, the extraction conditions include: a temperature of 80-100°C, more preferably 85-95°C; and a time of 1-10 hours, more preferably 1-5 hours.

[0044] In this invention, the extract is filtered before distillation, the resulting extract is distilled, and the residue is recovered or discharged.

[0045] In this invention, the distillation aims to remove toluene from the extract to obtain the polycyclic aromatic hydrocarbon mixture. Preferably, the distillation conditions include: a temperature of 60-80°C, more preferably 65-75°C; and a pressure of 0.01-0.1 MPa, more preferably 0.05-0.1 MPa.

[0046] In this invention, unless otherwise specified, all pressures refer to gauge pressure.

[0047] In some embodiments of the present invention, preferably, the asphalt is selected from at least one of petroleum asphalt, coal tar pitch, direct coal liquefaction pitch, indirect coal liquefaction pitch, and mesophase pitch.

[0048] A second aspect of the present invention provides a composite material for bipolar plates, which is obtained by hot pressing the composition provided in the first aspect.

[0049] In this invention, unless otherwise specified, the hot pressing is performed in a hot press.

[0050] In this invention, segmented pressing can fully promote the penetration and wetting of resin, conductive agent, and modifier, thereby improving the mechanical strength of the bipolar plate and effectively blocking the penetration of vanadium ions. Preferably, the hot pressing includes a first hot pressing and a second hot pressing.

[0051] In some embodiments of the present invention, preferably, the conditions for the first hot pressing include: a pressure of 10-30 MPa, preferably 15-25 MPa; a temperature of 120-170°C, preferably 120-150°C; and a time of 1-10 min, preferably 3-8 min.

[0052] In some embodiments of the present invention, preferably, the conditions for the second hot pressing include: a pressure of 70-120 MPa, preferably 80-110 MPa; a temperature of 180-240°C, preferably 180-220°C; and a time of 1-20 min, preferably 5-15 min.

[0053] According to the present invention, preferably, the flexural strength of the composite material is ≥40 MPa, more preferably 45-70 MPa; the vanadium ion concentration on the deionized water side is ≤1.4×10⁻⁶. -3 mol / L, preferably 1×10 -3 -1.35×10 -3 mol / L.

[0054] In this invention, unless otherwise specified, the bending strength parameter is directly measured using an electronic universal testing machine; the vanadium ion permeability is determined using a spectrophotometer.

[0055] Vanadium ion permeability test method: A bipolar plate is sandwiched between two chambers. Deionized water and 1 mol / L vanadium electrolyte are added to both sides of the chambers, while maintaining a pressure difference of 0.02 MPa between the two sides of the electrolyte. This condition is maintained for 30 days. Afterward, a small sample is taken from the deionized water side, and the vanadium ion concentration is determined by spectrophotometer. It should be noted that the lower the measured vanadium ion concentration, the less vanadium ions permeate, and the better the vanadium blocking performance.

[0056] A third aspect of the present invention provides a method for preparing a composite material for a bipolar plate, the method comprising the following steps:

[0057] (1) The resin matrix, conductive agent, modifier and curing agent are mixed and ground in sequence to obtain solid powder;

[0058] (2) The solid powder is hot-pressed to obtain a composite material;

[0059] The weight ratio of the resin matrix, conductive agent, modifier, and curing agent is 10-40:35-70:3-20:1-6.

[0060] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0061] In this invention, unless otherwise specified, the types and limitations of the resin matrix, conductive agent, modifier and curing agent in step (1) are all in accordance with the above limitations, and this invention will not elaborate on them.

[0062] In a preferred embodiment of the present invention, preferably, the weight ratio of the resin matrix, conductive agent, modifier and curing agent is 20-40:40-65:3-15:2-6.

[0063] In this invention, the method and conditions for the second mixing in step (1) have a wide range of options. As long as the resin matrix, conductive agent, modifier and additive are mixed evenly in a certain weight ratio, this invention will not elaborate on this.

[0064] In some embodiments of the present invention, preferably, in step (1), the grinding conditions include: a rotational speed of 100-1000 rpm, preferably 300-500 rpm; and a time of 0.1-10 h, preferably 2-5 h. In the present invention, unless otherwise specified, the grinding is performed in a ball mill.

[0065] In some embodiments of the present invention, preferably, in step (2), the hot pressing includes a first hot pressing and a second hot pressing; more preferably, the conditions for the first hot pressing include: a pressure of 10-30 MPa, preferably 15-25 MPa; a temperature of 120-170°C, preferably 120-150°C; and a time of 1-10 min, preferably 3-8 min; more preferably, the conditions for the second hot pressing include: a pressure of 70-120 MPa, preferably 80-110 MPa; a temperature of 180-240°C, preferably 180-220°C; and a time of 1-20 min, preferably 5-15 min. Segmented pressing can fully promote the penetration and wetting of the resin, conductive agent, and modifier, thereby improving the mechanical strength of the bipolar plate and effectively blocking the penetration of vanadium ions.

[0066] A fourth aspect of the present invention provides a bipolar plate comprising the composite material provided in the second aspect, or the composite material prepared by the method provided in the third aspect.

[0067] In some embodiments of the present invention, preferably, the roughness Ra of the bipolar plate is 0.05-12.5 μm, and the bipolar plate is only provided with an electrolyte inlet and an electrolyte outlet; wherein, along the flow direction of the electrolyte, the electrolyte inlet is sequentially divided into a first straight section and an expanding section; the electrolyte outlet is sequentially divided into a narrowing section and a second straight section.

[0068] In this invention, unless otherwise specified, the bipolar plate only has an electrolyte inlet and an electrolyte outlet. That is, the bipolar plate provided by this invention does not have an electrolyte flow channel, only an electrolyte inlet and an electrolyte outlet. In other words, the bipolar plate provided by this invention does not require a flow field structure, resulting in a simpler process, lower cost, and improved efficiency of the flow battery assembled from this bipolar plate. In contrast, existing bipolar plates without a flow field structure have rough surfaces, with a surface roughness Ra typically greater than 12.5 μm.

[0069] According to a preferred embodiment of the present invention, the surface roughness Ra of the bipolar plate is 0.05-9 μm, for example, 0.05 μm, 1 μm, 3.2 μm, 5 μm, 6.3 μm, 9 μm, and any value within the range of any two values, further selected as 0.063-7 μm. In the present invention, if the surface roughness Ra is too high, a gap exists between the electrode and the bipolar plate, which is not conducive to the diffusion of electrolyte on the electrode; if the surface roughness Ra is too low, it may lead to misalignment of the electrode and the bipolar plate.

[0070] In this invention, the surface roughness Ra parameter is measured using a probe contact profilometer. It should be noted that, in this invention, the surface of the bipolar plate refers to the effective surface in contact with the electrolyte.

[0071] According to the present invention, preferably, the thickness of the bipolar plate is 2-6 mm, for example, 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, and any value within the range of any two values, and more preferably 2.5-5 mm.

[0072] According to a specific embodiment of the present invention, such as Figure 1 As shown, the bipolar plate is provided with an electrolyte inlet 6-1 (e.g., Figure 1 (as shown in the lower left corner) and electrolyte outlet 6-2 (e.g.) Figure 1 (As shown in the upper right corner). The present invention does not have a particular limitation on the location of the electrolyte inlet and electrolyte outlet. In order to reduce electrolyte dead zones, preferably, the electrolyte inlet and electrolyte outlet are arranged diagonally on the bipolar plate.

[0073] In this invention, unless otherwise specified, the electrolyte inlet consists of a first cylindrical section and an expanding section; the electrolyte outlet consists of a narrowing section and a second cylindrical section.

[0074] In some embodiments of the present invention, preferably, the cross-sections of the first straight cylindrical section and the second straight cylindrical section are each independently regular in shape along the flow direction of the electrolyte, preferably rectangular or square.

[0075] In some embodiments of the present invention, preferably, the cross-sections of the expanding section and the contracting section along the flow direction of the electrolyte are each independently a regular shape or an irregular shape, preferably a regular shape, and more preferably a rectangle, square, or trapezoid. This preferred approach not only helps reduce processing difficulty but can also reduce the dead zone of the electrolyte.

[0076] In this invention, unless otherwise specified, the cross-sections of the first straight section, the second straight section, the expanded section, and the reduced section refer to planes parallel to the thickness of the bipolar plate.

[0077] In this invention, unless otherwise specified, the regular shapes include, but are not limited to, rectangles, squares, and trapezoids.

[0078] In some embodiments of the present invention, preferably, along the flow direction of the electrolyte, the included angle α of the expanding section is ≥90°, preferably 100-150°, for example, α includes but is not limited to 90°, 100°, 120°, 135°, 150°; the included angle β of the narrowing section is ≤90°, preferably 30-80°, for example, β includes but is not limited to 30°, 45°, 60°, 80°, 90°.

[0079] In some embodiments of the present invention, preferably, the ratio of the inner diameter m of the expanded section to the inner diameter n of the first straight section is 1.1-15:1, more preferably 2-10:1; preferably, the ratio of the inner diameter p of the reduced section to the inner diameter q of the second straight section is 1.1-15:1, more preferably 2-10:1.

[0080] In one specific embodiment of the present invention, the inner diameter m of the expanding section and the inner diameter p of the contracting section are each independently 0.5-5 mm, preferably 1-4.5 mm, more preferably 1.5-4.5 mm; further preferably, the inner diameter n of the first straight section and the inner diameter q of the second straight section are each independently 0.5-2.5 mm, preferably 0.5-1.5 mm.

[0081] In some embodiments of the present invention, preferably, the lengths of the electrolyte inlet and the electrolyte outlet are each independently the same as the thickness of the bipolar plate.

[0082] In one specific embodiment of the present invention, the lengths of the electrolyte inlet and the electrolyte outlet are each independently 2-6 mm, preferably 2.5-5 mm.

[0083] In some embodiments of the present invention, preferably, in the electrolyte inlet section, the ratio of the length a of the expanding section to the length b of the first straight section is 3-1:1; in the electrolyte outlet section, the ratio of the length c of the narrowing section to the length d of the second straight section is 3-1:1.

[0084] In this invention, unless otherwise specified, the inner diameter and length of the first straight section, the second straight section, the expanding section, and the contracting section refer to the width perpendicular to the electrolyte flow direction and the depth parallel to the electrolyte flow direction, respectively.

[0085] In some embodiments of the present invention, such as Figure 2-3As shown, along the flow direction of the electrolyte, the electrolyte inlet 6-1 is sequentially divided into a first cylindrical section 6-11 and an expanding section 6-12, and the electrolyte outlet 6-2 is sequentially divided into a narrowing section 6-21 and a second cylindrical section 6-22; wherein, along the flow direction of the electrolyte, the cross-sections of the first cylindrical section 6-11 and the second cylindrical section 6-22 are both rectangular or square, and the cross-sections of the expanding section 6-12 and the narrowing section 6-21 are both trapezoidal, rectangular, or square; wherein Along the flow direction of the electrolyte, the included angle α of the expanding section 6-12 is ≥90°; the included angle β of the narrowing section 6-21 is ≤90°; the lengths of the electrolyte inlet 6-1 and the electrolyte outlet 6-2 are each independently the same as the thickness of the bipolar plate; the ratio of the inner diameter m of the expanding section 6-12 to the inner diameter n of the first straight section 6-11 is 1.1-15:1; the ratio of the inner diameter p of the narrowing section 6-21 to the inner diameter q of the second straight section 6-22 is 1.1-15:1; in the electrolyte inlet 6-1, the ratio of the length a of the expanding section 6-12 to the length b of the first straight section 6-11 is 3-1:1; in the electrolyte outlet 6-2, the ratio of the length c of the narrowing section 6-21 to the length d of the second straight section 6-22 is 3-1:1. This preferred implementation method is more conducive to enhancing mass transfer, reducing the concentration polarization resistance of the battery, and making it less likely for the bipolar plates to shift during battery assembly, thereby suppressing electrolyte leakage.

[0086] According to a particularly preferred embodiment of the present invention, a bipolar plate is provided, wherein the material of the bipolar plate is a composite material obtained by hot pressing a composition for preparing the bipolar plate.

[0087] Wherein, based on the total weight of the combination, the content of the phenolic resin is 20-40 wt%, the content of the conductive agent is 40-65 wt%, the content of the modifier is 3-15 wt%, and the content of the curing agent is 2-6 wt%.

[0088] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The curing agent is hexamethylenetetramine curing agent;

[0089] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The fused-ring aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted;

[0090] The surface roughness Ra of the bipolar plate is 0.05-12.5μm, and no electrolyte flow channel is provided on the bipolar plate;

[0091] Along the flow direction of the electrolyte, the electrolyte inlet is divided into a first straight section and an expanding section; the electrolyte outlet is divided into a narrowing section and a second straight section.

[0092] The fifth aspect of the present invention provides a flow battery comprising the bipolar plate provided in the fourth aspect.

[0093] The present invention will be described in detail below through embodiments.

[0094] Bending strength parameters were obtained directly using an electronic universal testing machine;

[0095] Vanadium ion permeability was measured using a spectrophotometer;

[0096] Vanadium ion permeability test method: A bipolar plate is sandwiched between two chambers. Deionized water and 1 mol / L vanadium electrolyte are added to both sides of the chambers, while maintaining a pressure difference of 0.02 MPa between the two sides of the electrolyte. This condition is maintained for 30 days. Afterward, a small sample is taken from the deionized water side, and the vanadium ion concentration is determined by spectrophotometer. It should be noted that the lower the measured vanadium ion concentration, the less vanadium ions permeate, and the better the vanadium blocking performance.

[0097] Preparation Example

[0098] 500g of asphalt and 2500g of toluene were mixed evenly and extracted in a constant-temperature water bath at 90℃ and 500rpm for 5 hours. The extracted product was then filtered, and the resulting liquid mixture was distilled at 0.09MPa and 70℃ to obtain a mixture of polycyclic aromatic hydrocarbons (PAHs). The total carbon number of the PAHs in the mixture was C. 22 -C 24 Furthermore, fused-ring aromatic hydrocarbons have a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

[0099] Example I-1

[0100] (1) The resin matrix (phenolic resin, viscosity ≥ 0.125 Pa·S / (20℃, 50% alcohol)), conductive agent (expanded graphite), modifier (mixture of polycyclic aromatic hydrocarbons) and curing agent (hexamethylenetetramine curing agent) are mixed in a weight ratio of 30:58:10:2 and then ground in a ball mill (speed 500 rpm, time 3h) to obtain solid powder;

[0101] (2) The powder is subjected to segmented hot pressing in a hot press. The conditions for the first hot pressing are: pressure of 25 MPa, temperature of 150°C, and time of 5 min. The conditions for the second hot pressing are: pressure of 100 MPa, temperature of 200°C, and time of 10 min, to obtain composite material S1.

[0102] The physical properties of composite material S1 are listed in Table 1.

[0103] Example I-2

[0104] (1) The resin matrix (phenolic resin, viscosity ≥ 0.125 Pa·S / (20℃, 50% alcohol)), conductive agent (carbon fiber), modifier (polycyclic aromatic hydrocarbon mixture) and curing agent (hexamethylenetetramine curing agent) are mixed in a weight ratio of 21:63:13:3 and then ground in a ball mill (500 rpm for 3 h) to obtain solid powder;

[0105] (2) The powder is subjected to segmented hot pressing in a hot press. The conditions for the first hot pressing are: pressure of 20 MPa, temperature of 140°C, and time of 8 min. The conditions for the second hot pressing are: pressure of 90 MPa, temperature of 190°C, and time of 15 min. Composite material S2 is obtained.

[0106] The physical properties of composite material S2 are listed in Table 1.

[0107] Example I-3

[0108] (1) The resin matrix (phenolic resin, viscosity ≥ 0.125 Pa·S / (20℃, 50% alcohol)), conductive agent (carbon nanotubes), modifier (mixture of polycyclic aromatic hydrocarbons) and curing agent (hexamethylenetetramine curing agent) are mixed in a weight ratio of 40:49:6:5 and then ground in a ball mill (300 rpm for 5 h) to obtain a solid powder;

[0109] (2) The powder is subjected to segmented hot pressing in a hot press. The conditions for the first hot pressing are: pressure of 15 MPa, temperature of 150°C, and time of 3 min. The conditions for the second hot pressing are: pressure of 110 MPa, temperature of 220°C, and time of 5 min. Composite material S3 is obtained.

[0110] The physical properties of composite material S3 are listed in Table 1.

[0111] Example I-4

[0112] The method of Example I-1 is different except that in step (1), the weight ratio of the resin matrix (phenolic resin, viscosity ≥ 0.125 Pa·S / (20℃, 50% alcohol)), conductive agent (expanded graphite), modifier (polycyclic aromatic hydrocarbon mixture) and curing agent (hexamethylenetetramine curing agent) is replaced with 10:70:19:1, and the other conditions are the same, to obtain composite material S4.

[0113] The physical properties of composite material S4 are listed in Table 1.

[0114] Example I-5

[0115] The method of Example I-1 is different in that, in step (2), the conditions of the first hot pressing are replaced with a pressure of 30 MPa, a temperature of 170°C, and a time of 1 min; the conditions of the second hot pressing are replaced with a pressure of 70 MPa, a temperature of 230°C, and a time of 20 min, and the other conditions are the same, so as to obtain composite material S5.

[0116] The physical properties of composite material S5 are listed in Table 1.

[0117] Example I-6

[0118] The method of Example I-1 is different except that in step (2), the above solid powder is hot-pressed. The hot-pressing conditions include: pressure of 50 MPa, temperature of 200 °C, time of 15 min, and other conditions are the same, to obtain composite material S6.

[0119] The physical properties of composite material S6 are listed in Table 1.

[0120] Comparative Example I-1

[0121] The method of Example I-1 is different except that in step (1), the weight ratio of the resin matrix (phenolic resin, viscosity ≥ 0.125 Pa·S / (20℃, 50% alcohol)), conductive agent (expanded graphite), modifier (polycyclic aromatic hydrocarbon mixture) and curing agent (hexamethylenetetramine curing agent) is replaced with 47:20:25:8, while the other conditions are the same, and the composite material DS1 is obtained.

[0122] The physical properties of the composite material DS1 are listed in Table 1.

[0123] Comparative Example I-2

[0124] The method of Example I-1 is followed, except that in step (1), no modifier (mixture of polycyclic aromatic hydrocarbons) is added, and the other conditions are the same, to obtain composite material DS2.

[0125] The physical properties of the composite material DS2 are listed in Table 1.

[0126] Comparative Example 3

[0127] The method of Example I-1 is followed, except that in step (1), the modifier (mixture of polycyclic aromatic hydrocarbons) is replaced with a modifier (naphthalene), and the other conditions are the same, to obtain the composite material DS3.

[0128] The physical properties of the composite material DS3 are listed in Table 1.

[0129] Comparative Example 4

[0130] The method of Example 1 is followed, except that in step (1), the modifier (mixture of polycyclic aromatic hydrocarbons) is replaced with the modifier (anthracene), and the other conditions are the same, to obtain the composite material DS4.

[0131] The physical properties of the composite material DS4 are listed in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] Note: * refers to the weight ratio of resin matrix, conductive agent, modifier and curing agent in the composite material.

[0136] As can be seen from the results in Table 1, compared with Comparative Examples I-1 to I-4, the composite materials prepared in Examples I-1 to I-6 have higher flexural strength parameters and lower vanadium ion concentration parameters on the deionized water side. That is, the composite materials provided by the present invention have higher mechanical strength and lower vanadium ion permeability.

[0137] Comparing Examples I-1 and I-4, it can be seen that by limiting the weight ratio of resin matrix, conductive agent, modifier and curing agent to a preferred range, the resulting composite material has a higher flexural strength parameter and a lower vanadium ion concentration parameter on the deionized water side.

[0138] Comparing Examples I-1 and I-5, it can be seen that by limiting the conditions of the first hot pressing and the second hot pressing to a preferred range, the resulting composite material has a higher flexural strength parameter and a lower vanadium ion concentration parameter on the deionized water side.

[0139] Comparing Examples I-1 and I-6, it can be seen that by limiting the hot pressing within a preferred range, the resulting composite material has a higher flexural strength parameter and a lower vanadium ion concentration parameter on the deionized water side.

[0140] Example II-1

[0141] (1) Bipolar plate

[0142] like Figure 1-2 As shown, the bipolar plate has a flat plate structure with dimensions of 80 mm in length, 60 mm in width, and 3 mm in thickness. Its surface roughness Ra is 5 μm. The material of the bipolar plate is the composite material S1 obtained in Example I-1.

[0143] An electrolyte inlet is provided on the bipolar plate. Figure 1 (bottom left corner) and electrolyte outlet ( Figure 1 (Top right corner) The lengths of the electrolyte inlet and electrolyte outlet are both 3mm; the ratio of the length a of the expansion section to the length b of the first straight section is 2:1; the ratio of the length c of the reduction section to the length d of the second straight section is 2:1.

[0144] Along the flow direction of the electrolyte, the electrolyte inlet is divided into a first straight section and an expanding section, and the electrolyte outlet is divided into a narrowing section and a second straight section. Along the flow direction of the electrolyte, the cross-sections of the first and second straight sections are both rectangular, while the cross-sections of the expanding and narrowing sections are both trapezoidal.

[0145] Along the flow direction of the electrolyte, the included angle α of the expanding section is 135°, and the included angle β of the narrowing section is 45°.

[0146] Along the flow direction of the electrolyte, the inner diameter m of the expanding section increases from 0.5 mm to 4.5 mm; the inner diameter p of the narrowing section decreases from 4.5 mm to 0.5 mm; the inner diameter n of the first straight section and the inner diameter q of the second straight section are both 0.5 mm, that is, the ratio of the inner diameter m of the expanding section to the inner diameter n of the first straight section is 9:1; the ratio of the inner diameter p of the narrowing section to the inner diameter q of the second straight section is 9:1.

[0147] Assemble a flow battery:

[0148] The flow battery includes a separator (perfluorosulfonic acid separator, commercially available from Chemours Chemical Company, product name Nafion 115), a positive electrode disposed on one side of the separator and a negative electrode disposed on the other side, wherein the positive electrode and the negative electrode are both porous carbon fiber felt, commercially available from SGL Chemical Company, product name GFD4.6EA, with dimensions of 50mm × 40mm × 4.6mm.

[0149] The flow battery further includes a first bipolar plate adjacent to the positive electrode and a second bipolar plate adjacent to the negative electrode; both the first and second bipolar plates are the aforementioned bipolar plates; a current collector (made of copper plate) and an end plate (made of aluminum alloy) are provided on the outer sides of both the first and second bipolar plates, and the above components are fastened with bolts through pre-set holes; a sealing element is provided between the first bipolar plate and the positive electrode, and between the second bipolar plate and the negative electrode, to prevent electrolyte leakage; wherein, the positive electrode electrolyte is 0.8 mol / L. -1 V(IV) + 0.8 mol L -1 V(V) + 3mol L -1 The H2SO4 solution, with a negative electrode electrolyte of 0.8 mol / L... -1 V(II) + 0.8 mol L -1 V(III) + 3mol L -1A solution of H2SO4 was prepared; the electrolyte was delivered to the battery stack using a peristaltic pump to obtain a vanadium redox flow battery P1.

[0150] The output performance of the vanadium redox flow battery P1 was measured using a potentiostat, and the coulombic efficiency, voltage efficiency, and energy efficiency were calculated using the charge-discharge curves. The test results are listed in Table 2.

[0151] Examples II-2 to II-6

[0152] The flow batteries were assembled according to Example II-1, except that the material of the bipolar plates was replaced with the composite materials (S1-S6) of Examples I-2 to I-6, while the other conditions remained the same, resulting in all-vanadium redox flow batteries P2-P6. The test results are listed in Table 2.

[0153] Example II-7

[0154] The flow battery was assembled according to Example II-1, except that the surface roughness of the bipolar plates was replaced with 12.5 μm, while all other conditions remained the same, resulting in a vanadium redox flow battery P7. The test results are listed in Table 2.

[0155] Example II-8

[0156] The flow battery was assembled according to Example II-1, except that the surface roughness of the bipolar plates was replaced with 25 μm, while all other conditions remained the same, resulting in a vanadium redox flow battery P8. The test results are listed in Table 2.

[0157] Example II-9

[0158] Assemble a flow battery according to Example II-1, except that, along the flow direction of the electrolyte, the electrolyte inlet and the electrolyte outlet are respectively a first straight section and a second straight section, and the cross-sections of the first straight section and the second straight section are both rectangular.

[0159] The inner diameters of both the electrolyte inlet and outlet are 1.5 mm, and all other conditions are the same, resulting in a vanadium redox flow battery P9. The test results are listed in Table 2.

[0160] Example II-10

[0161] Assemble a flow battery according to Example II-1, except that, along the electrolyte flow direction, the inner diameter m of the expanding section is increased from 0.5 mm to 6 mm; the inner diameter p of the contracting section is decreased from 6 mm to 0.5 mm; the inner diameter n of the first straight section and the inner diameter q of the second straight section are both 0.5 mm; that is, the ratio of the inner diameter m of the expanding section to the inner diameter n of the first straight section is 12:1; the ratio of the inner diameter p of the contracting section to the inner diameter q of the second straight section is 12:1, and the other conditions are the same, to obtain bipolar plate P10.

[0162] Comparative Examples II-1 to II-4

[0163] The flow batteries were assembled according to Example II-1, except that the material of the bipolar plates was replaced with the composite materials of Comparative Examples I-1 to I-4 (DS1-DS4), while the other conditions remained the same, resulting in all-vanadium redox flow batteries DP1-DP4. The test results are listed in Table 2.

[0164] Table 2

[0165] Coulomb efficiency, % Voltage efficiency, % Energy efficiency, % Example II-1 92.8 91.4 84.8 Example II-2 92.0 91.3 84.0 Example II-3 90.9 90.0 81.8 Example II-4 89.4 87.3 78.0 Example II-5 87.2 86.7 75.6 Example II-6 85.8 86.0 73.8 Example II-7 87.3 85.6 74.7 Example II-8 84.7 85.1 72.1 Example II-9 84.3 85.0 71.7 Example II-10 84.6 85.2 72.1 Comparative Example II-1 84.0 84.8 71.2 Comparative Example II-2 80.0 81.3 65.0 Comparative Example II-3 82.1 84.3 69.2 Comparative Example II-4 81.7 82.6 67.5

[0166] As can be seen from the results in Table 2, compared with Comparative Examples II-1 to II-4, the flow batteries assembled from bipolar plates prepared in Examples II-1 to II-10 have higher coulombic efficiency, voltage efficiency and energy efficiency. That is, the flow batteries provided by the present invention have higher efficiency and excellent electrochemical performance.

[0167] Comparing Examples II-1 and Examples II-2 to II-6, it can be seen that the present invention controls the efficiency parameters of the flow battery by adjusting the performance of the composite material (flexural strength parameter and vanadium ion concentration parameter on the deionized water side).

[0168] Comparing Examples II-1 and II-7, or comparing Examples II-1 and II-8, it can be seen that the present invention, by limiting the surface roughness of the bipolar plate to meet the preferred protection range, results in a flow battery with high efficiency parameters.

[0169] Comparing Examples II-1 and II-9, or comparing Examples II-1 and II-10, it can be seen that the present invention, by limiting the structural configuration of the electrolyte inlet and electrolyte outlet to meet the preferred protection range, obtains a flow battery with high efficiency parameters.

[0170] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for preparing bipolar plates for flow batteries, characterized in that, The composition contains a resin matrix, a conductive agent, a modifier, and a curing agent; Wherein, based on the total weight of the composition, the content of the resin matrix is ​​10-40 wt%, the content of the conductive agent is 35-70 wt%, the content of the modifier is 3-20 wt%, and the content of the curing agent is 1-6 wt%; The modifier is a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The fused-ring aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted. The resin matrix is ​​selected from phenolic resin, and the viscosity of the phenolic resin is ≥0.125 Pa·S / 20℃, 50% alcohol.

2. The composition according to claim 1, wherein, Based on the total weight of the composition, the content of the resin matrix is ​​20-40 wt%, the content of the conductive agent is 40-65 wt%, the content of the modifier is 3-15 wt%, and the content of the curing agent is 2-6 wt%.

3. The composition according to claim 1, wherein, The conductive agent is selected from at least one of expanded graphite, carbon fiber, and carbon nanotubes.

4. The composition according to claim 1, wherein, The curing agent is an amine-based curing agent.

5. The composition according to claim 4, wherein, The curing agent is hexamethylenetetramine curing agent.

6. The composition according to claim 1, wherein, The fused-ring aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

7. The composition according to claim 1, wherein, The polycyclic aromatic hydrocarbon mixture is prepared by the following method: asphalt and toluene are first mixed, the first mixture is extracted, and the resulting extract is distilled to obtain the polycyclic aromatic hydrocarbon mixture.

8. The composition according to claim 7, wherein, The asphalt is selected from at least one of petroleum asphalt, coal tar pitch, direct coal liquefaction pitch, indirect coal liquefaction pitch, and mesophase pitch.

9. A composite material for bipolar plates, characterized in that, The composite material is obtained by hot pressing the composition according to any one of claims 1-8.

10. The composite material according to claim 9, wherein, The hot pressing includes a first hot pressing and a second hot pressing.

11. The composite material according to claim 10, wherein, The conditions for the first hot pressing include: pressure of 10-30 MPa; temperature of 120-170 °C; and time of 1-10 min.

12. The composite material according to claim 11, wherein, The conditions for the first hot pressing include: pressure of 15-25 MPa; temperature of 120-150℃; and time of 3-8 min.

13. The composite material according to claim 10, wherein, The conditions for the second hot pressing include: pressure of 70-120 MPa; temperature of 180-240 °C; and time of 1-20 min.

14. The composite material according to claim 13, wherein, The conditions for the second hot pressing include: pressure of 80-110 MPa; temperature of 180-220℃; and time of 5-15 min.

15. The composite material according to claim 9, wherein, The composite material has a flexural strength ≥ 40 MPa; the vanadium ion concentration on the deionized water side is ≤ 1.4 × 10⁻⁶. -3 mol / L.

16. The composite material according to claim 15, wherein, The composite material has a flexural strength of 45-70 MPa; the vanadium ion concentration on the deionized water side is 1×10⁻⁶. -3 -1.35×10 -3 mol / L.

17. A method for preparing a composite material for a bipolar plate in a flow battery, characterized in that, The method includes the following steps: (1) The resin matrix, conductive agent, modifier and curing agent are mixed and ground in sequence to obtain solid powder; (2) The solid powder is hot-pressed to obtain a composite material; The weight ratio of the resin matrix, conductive agent, modifier and curing agent is 10-40:35-70:3-20:1-6. The modifier is a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The fused-ring aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted. The resin matrix is ​​selected from phenolic resin, and the viscosity of the phenolic resin is ≥0.125 Pa·S / 20℃, 50% alcohol.

18. The method according to claim 17, wherein, In step (1), the weight ratio of the resin matrix, conductive agent, modifier and curing agent is 20-40:40-65:3-15:2-6.

19. The method of claim 17, wherein, The grinding conditions include: a rotation speed of 100-1000 rpm and a grinding time of 0.1-10 h.

20. The method according to claim 19, wherein, The grinding conditions include: a rotation speed of 300-500 rpm and a grinding time of 2-5 hours.

21. The method according to claim 17, wherein, In step (2), the hot pressing includes: first hot pressing and second hot pressing.

22. The method according to claim 21, wherein, The conditions for the first hot pressing include: pressure of 10-30 MPa; temperature of 120-170 °C; and time of 1-10 min.

23. The method according to claim 22, wherein, The conditions for the first hot pressing include: pressure of 15-25 MPa; temperature of 120-150℃; and time of 3-8 min.

24. The method according to claim 21, wherein, The conditions for the second hot pressing include: pressure of 70-120 MPa; temperature of 180-240 °C; and time of 1-20 min.

25. The method according to claim 24, wherein, The conditions for the second hot pressing include: pressure of 80-110 MPa; temperature of 180-220℃; and time of 5-15 min.

26. A bipolar plate, characterized in that, The bipolar plate is made of the composite material described in any one of claims 9-16, or the composite material prepared by the method described in any one of claims 17-25.

27. The bipolar plate according to claim 26, wherein, The bipolar plate has a roughness Ra of 0.05-12.5 μm, and the bipolar plate is only provided with an electrolyte inlet and an electrolyte outlet; wherein, along the electrolyte flow direction, the electrolyte inlet is sequentially divided into a first straight section and an expanding section; the electrolyte outlet is sequentially divided into a narrowing section and a second straight section.

28. The bipolar plate according to claim 27, wherein, Along the flow direction of the electrolyte, the cross-sections of the first and second straight cylindrical sections are each independently a regular shape.

29. The bipolar plate according to claim 28, wherein, Along the flow direction of the electrolyte, the cross-sections of the first and second straight cylindrical sections are each independently rectangular or square.

30. The bipolar plate according to claim 27, wherein, Along the flow direction of the electrolyte, the cross-sections of the expanding section and the contracting section are each independently a regular shape or an irregular shape.

31. The bipolar plate according to claim 30, wherein, Along the flow direction of the electrolyte, the cross-sections of the expanding section and the contracting section are each independently rectangular, square, or trapezoidal.

32. The bipolar plate according to claim 27, wherein, Along the flow direction of the electrolyte, the included angle α of the expanding section is ≥90°; the included angle β of the narrowing section is ≤90°.

33. The bipolar plate according to claim 32, wherein, Along the flow direction of the electrolyte, the included angle α of the expanding section is 100-150°; the included angle β of the narrowing section is 30-80°.

34. The bipolar plate according to claim 27, wherein, The ratio of the inner diameter m of the expanded section to the inner diameter n of the first straight section is 1.1-15:

1.

35. The bipolar plate according to claim 34, wherein, The ratio of the inner diameter m of the expanded section to the inner diameter n of the first straight section is 2-10:

1.

36. The bipolar plate according to claim 27, wherein, The ratio of the inner diameter p of the reduced diameter section to the inner diameter q of the second straight section is 1.1-15:

1.

37. The bipolar plate according to claim 36, wherein, The ratio of the inner diameter p of the reduced diameter section to the inner diameter q of the second straight section is 2-10:

1.

38. The bipolar plate according to claim 27, wherein, The lengths of the electrolyte inlet and electrolyte outlet are each independently the same as the thickness of the bipolar plate.

39. The bipolar plate according to claim 27, wherein, In the electrolyte inlet, the ratio of the length a of the expanding section to the length b of the first straight section is 3-1:1; in the electrolyte outlet, the ratio of the length c of the narrowing section to the length d of the second straight section is 3-1:

1.

40. A flow battery, characterized in that, The flow battery contains the bipolar plate as described in any one of claims 26-39.

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