Composite bipolar plate and preparation method thereof, and bipolar battery stack

Abstract

The present invention relates to the technical field of bipolar plate structure, and discloses a composite bipolar plate and a preparation method thereof, and a bipolar stack, comprising a conductive part and an insulating part, wherein the conductive part comprises a plurality of groups, wherein the plurality of groups of conductive part arrays are arranged in the insulating part, wherein the plurality of groups of conductive parts are not mutually conductive, and wherein the ratio of the normal direction resistance to the horizontal direction resistance of the composite bipolar plate is less than 10 ‑8 The present invention provides a composite bipolar plate structure with anisotropic resistance. When an internal short circuit occurs in a battery stack prepared by the composite bipolar plate, most of the internal current can still maintain the original vertical flow, avoiding a large amount of current from gathering at the short circuit point, thereby reducing the heat generation of the battery and improving the safety of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of bipolar plate structures, and in particular to a composite bipolar plate and a preparation method thereof, and a bipolar battery stack. Background Art

[0002] Internal short circuit failures in batteries are one of the main causes of fire accidents in new energy vehicles. There are many reasons for internal short circuits in power batteries, such as dendrite precipitation during high-rate charging, battery deformation caused by car collisions, and the introduction of impurities during battery preparation, which can trigger internal short circuits in batteries. Since the battery cell is a parallel structure of multiple battery cells, if an internal short circuit occurs in one of the cells, part of the current of the cell and its neighboring cells will be concentrated at the short circuit point, and in severe cases, a transient "surge" phenomenon will occur. Once this phenomenon occurs, it cannot be stopped, causing the temperature at the short circuit location to rise rapidly, and then causing thermal runaway of the battery.

[0003] The current collectors of the same polarity inside the battery are in a parallel conduction structure, so after the short circuit in the battery is triggered, the current collector acts as a "bridge" for current collection. In order to improve this problem, the structure of the current collector can be optimized, for example: the composite current collector proposed in patent number CN201710022284.8, which includes an insulating layer and a conductive layer, and the short-circuit resistance is increased by reducing the thickness of the conductive layer. However, this method does not improve the parallel structure inside the battery, so the battery still has the risk of short circuit and will also affect the rate performance of the battery.

[0004] Existing bipolar batteries are achieved by coating positive and negative active materials on both sides of the bipolar plates, stacking them in a sequence of relative placement of different polarities, thereby achieving an internal series structure of the battery cells. Compared with traditional power batteries, the battery cells of bipolar batteries are independent of each other, and the bipolar plates are not connected to each other. When an internal short circuit occurs, there will be no current convergence in adjacent cells. Therefore, bipolar batteries can improve battery safety to a certain extent. However, after an internal short circuit occurs in a bipolar battery, current convergence will still occur in the battery cell where the internal short circuit point is located. Summary of the invention

[0005] In order to solve the problem that the internal parallel structure of the battery in the prior art cannot avoid the drastic temperature rise after the internal short circuit, the present invention provides a composite bipolar plate and a preparation method thereof, and a bipolar battery stack, which improves the battery safety by improving the bipolar plate structure.

[0006] The technical contents of the present invention are as follows:

[0007] The present invention provides a composite bipolar plate, comprising a conductive part and an insulating part, wherein the conductive part comprises a plurality of groups, wherein the plurality of groups of conductive part arrays are arranged in the insulating part, wherein the plurality of groups of conductive parts are not connected to each other, wherein the insulating part comprises two groups of insulating films of the same size, wherein the insulating films are each provided with a plurality of holes, wherein the holes on the two groups of insulating films are arranged in a one-to-one correspondence, wherein the conductive part comprises a conductive sheet and an adhesive sheet, wherein the size of the conductive sheet is the same as the plurality of holes arranged on the insulating part, wherein the conductive part is fixed to any one group of insulating films through an adhesive sheet, wherein the two groups of insulating films are arranged on both sides of the conductive sheet, wherein the conductive sheet is arranged in the insulating part in correspondence with the holes, and wherein the ratio of the normal direction resistance to the horizontal direction resistance of the composite bipolar plate is lower than 10 -8 .

[0008] Furthermore, the insulating part can also be an insulating material with a plurality of conductive particles arranged inside, and the conductive particles in the insulating part do not overlap with each other. The conductive part can also be composed of two groups of conductive sheets, and the two groups of conductive sheets are relatively arranged on both sides of the insulating part, and the conductive particles located between the two groups of conductive sheets can overlap with each other. The conductive sheets form a conductive path through the conductive particles that can overlap with each other.

[0009] The present invention also provides a method for preparing a composite bipolar plate, comprising the following steps:

[0010] Selecting two sets of insulating films of the same size, and opening a plurality of holes of the same size as the conductive sheet on the insulating films;

[0011] Lay any of the insulating films flat, align the conductive sheet with the holes on the insulating film, fix it to the insulating film through the adhesive part, and then cover it with another set of insulating films;

[0012] The two sets of insulating films and the conductive sheets are compounded by high-temperature hot pressing to form a composite bipolar plate with anisotropic resistance.

[0013] The present invention also provides a method for preparing a composite bipolar plate, comprising the following steps:

[0014] The conductive particles with a volume percentage of 30-80% are uniformly mixed with the insulating part in a flowing state, and then prepared into a film semi-finished product;

[0015] Arranging two groups of the conductive sheets opposite to each other on both sides of the film semi-finished product, and applying pressure to the conductive sheets toward the inner side of the film semi-finished product to obtain a film, so that a conductive path is formed between the conductive sheets and the conductive particles;

[0016] After solidification, the film forms a composite bipolar plate with anisotropic resistance.

[0017] The present invention also provides a bipolar battery stack, comprising the composite bipolar plate described in any one of the above items, the bipolar battery stack also comprising: a current collector, a positive electrode active layer, a separator, a negative electrode active layer and a sealing component, the positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate are stacked in sequence to form a battery cell, the current collector comprises two groups, the two groups of current collectors are arranged at the upper and lower ends of the battery cell, the sealing component is wrapped around the battery cell, and the two groups of current collectors and the sealing component encapsulate the positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate.

[0018] Furthermore, the positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate all include multiple groups.

[0019] The beneficial effects of the present invention include at least: the present invention provides a composite bipolar plate structure with anisotropic resistance. When an internal short circuit occurs in a battery stack prepared by the composite bipolar plate, most of the internal current can still maintain the original vertical flow, avoiding a large amount of current from gathering at the short circuit point, thereby reducing the heat generation of the battery and improving the safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of a composite bipolar plate provided by the present invention.

[0021] Figure 2 This is a schematic diagram of the cross-sectional structure of a composite bipolar plate provided in Example 1 of the present invention.

[0022] Figure 3 This is a schematic diagram of the cross-sectional structure of a composite bipolar plate provided in Example 2 of the present invention.

[0023] Figure 4 A schematic cross-sectional structure diagram of a bipolar fuel cell stack provided in Example 3 of the present invention.

[0024] Figure 5 Schematic diagram of the temperature rise after the two battery models provided by the present invention simulate the internal short circuit.

[0025] in:

[0026] 1- Composite bipolar plate;

[0027] 101-conductive part; 102-insulating part;

[0028] 2-positive electrode active layer;

[0029] 3- diaphragm;

[0030] 4- negative electrode active layer;

[0031] 5- Sealing components;

[0032] 6-Current collector. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] Combination Figure 1-2 As shown, this embodiment provides a composite bipolar plate, including a conductive part 101 and an insulating part 102, the conductive part 101 includes a plurality of groups, and the plurality of groups of conductive parts 101 are arrayed on the insulating part 102, and the plurality of groups of conductive parts 101 are not conductive to each other, the insulating part 102 includes two groups of insulating films of the same size, and the insulating films are each provided with a plurality of holes, and the holes on the two groups of insulating films are arranged one by one, the conductive part 101 includes a conductive sheet and an adhesive sheet, the adhesive sheet is arranged on both sides of the conductive sheet, and the conductive sheet is bonded and fixed to the insulating film through the adhesive sheets on both sides, the size of the conductive sheet is the same as the plurality of holes arranged on the insulating part, the conductive part is fixed to any one group of insulating films through the adhesive sheet, the two groups of insulating films are arranged on both sides of the conductive sheet, and the conductive sheet and the holes are arranged correspondingly when the conductive part is arranged on the insulating part, and the ratio of the normal direction resistance to the horizontal direction resistance of the composite bipolar plate is lower than 10 -8 Holes in Figure 2 The top is covered by a conductive sheet.

[0036] The conductive part 101 is one or more of stainless steel, copper, aluminum, copper-aluminum composite material, and conductive graphite.

[0037] The conductive part 101 is a sheet structure of one or more of stainless steel, copper, aluminum, copper-aluminum composite material, and conductive graphite.

[0038] The conductivity of the conductive part ranges from 1×10 5 -6.25×10 7 S / m.

[0039] The insulating part is one or more of polyvinyl chloride, polyethylene, polypropylene, polystyrene, polytetrafluoroethylene, polyethylene terephthalate, polyamide, polyimide, polyether nitrile, polymethyl acrylate, polyvinylidene fluoride, polyurethane, polyacrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose, and modified polyolefin.

[0040] The electrical conductivity of the insulation is less than 1S / m.

[0041] The composite bipolar plate provided in this embodiment has a thickness ranging from 30 to 5000 μm.

[0042] The composite bipolar plate of this embodiment is prepared by a composite bipolar plate preparation method, comprising the following steps:

[0043] Selecting two sets of insulating films of the same size, and opening a plurality of holes of the same size as the conductive sheet on the insulating films;

[0044] Lay any of the insulating films flat, align the conductive sheet with the holes on the insulating film, fix it to the insulating film through the adhesive part, and then cover it with another set of insulating films;

[0045] The two sets of insulating films and the conductive sheets are compounded by high-temperature hot pressing to form a composite bipolar plate with anisotropic resistance.

[0046] Example 2

[0047] Combination Figure 1 , Figure 3 As shown, this embodiment provides a composite bipolar plate, including a conductive part 101 and an insulating part 102, wherein the conductive part 101 includes a plurality of groups, wherein the plurality of groups of the conductive parts 101 are arranged in an array on the insulating part 102, wherein the plurality of groups of the conductive parts 101 are not connected to each other, wherein a plurality of conductive particles are arranged inside the insulating part 102, wherein the conductive particles in the insulating part 102 are not overlapped with each other, wherein the conductive part 101 includes two groups of conductive sheets, wherein the two groups of the conductive sheets are arranged on both sides of the insulating part 102 in a relative manner, wherein the conductive particles between the two groups of the conductive sheets can overlap with each other, and wherein the conductive sheets form a conductive path through the conductive particles that can overlap with each other. The conductive particles in the insulating part 102 form conductive particles that can overlap with each other due to the conductive sheets arranged on both sides in a relative manner, so that the conductive part 101 forms a conductive path in the insulating part 102, and the ratio of the normal direction resistance to the horizontal direction resistance of the composite bipolar plate is lower than 10 -8 .

[0048] The conductive part 101 of this embodiment is one or more of stainless steel, copper, aluminum, copper-aluminum composite material, and conductive graphite.

[0049] The conductive part 101 is a particle structure of one or more of stainless steel, copper, aluminum, copper-aluminum composite material, and conductive graphite, or a conductive sheet.

[0050] The composite bipolar plate of this embodiment is prepared by a composite bipolar plate preparation method, comprising the following steps:

[0051] The conductive particles with a volume percentage of 30-80% are uniformly mixed with the insulating part in a flowing state, and then prepared into a film semi-finished product;

[0052] Arranging two groups of the conductive sheets opposite to each other on both sides of the film semi-finished product, and applying pressure to the conductive sheets toward the inner side of the film semi-finished product to obtain a film, so that a conductive path is formed between the conductive sheets and the conductive particles;

[0053] After solidification, the film forms a composite bipolar plate with anisotropic resistance.

[0054] The requirements for the conductivity of the conductive part, the conductivity of the insulating part, the material selection of the insulating part and the thickness range of the prepared composite bipolar plate in this embodiment are the same as those in Example 1, so they are not elaborated one by one in this embodiment.

[0055] Example 3

[0056] According to Examples 1-2 and Figure 4 As shown, this embodiment provides a bipolar stack, including the composite bipolar plate 1 in any of the above embodiments.

[0057] The bipolar battery stack also includes: a current collector 6, a positive electrode active layer 2, a separator 3, a negative electrode active layer 4 and a sealing component 5. The positive electrode active layer 2, the separator 3, the negative electrode active layer 4 and the composite bipolar plate 1 are stacked in sequence to form a battery cell. The current collector 6 includes two groups, and the two groups of current collectors 6 are arranged at the upper and lower ends of the battery cell. The sealing component 5 is wrapped around the battery cell. The two groups of current collectors 6 and the sealing component 5 encapsulate the positive electrode active layer 2, the separator 3, the negative electrode active layer 4 and the composite bipolar plate 1.

[0058] Furthermore, the positive electrode active layer 2 , the separator 3 , the negative electrode active layer 4 and the composite bipolar plate 1 each include multiple groups.

[0059] The resistance value of the composite bipolar plate is related to the resistance value, volume fraction, structure and current direction of each phase material. If the current passes through the composite bipolar plate vertically, then the components are in parallel; if the current passes through the composite bipolar plate horizontally, then the components are in series. The calculation formulas for series and parallel resistance values ​​are:

[0060] R=R 1 +R 2 (1);

[0061]

[0062] Among them, the series resistance is greater than each of the partial resistances, and the parallel resistance is smaller than each of the partial resistances. Therefore, the resistance of the current passing vertically through the bipolar plate is much smaller than the resistance passing horizontally through the bipolar plate, that is, the vertical resistance of the composite bipolar plate is smaller than the horizontal resistance. Although bipolar plates composed of a single material also have this feature due to their small thickness, the effect of the composite bipolar plate is to maximize the anisotropy of this resistance and try to keep the current flowing in the composite bipolar plate in the vertical direction.

[0063] For example, the conductive part is aluminum, the insulating part is pp material, and the detailed parameters are shown in Table 1. Then, according to the resistance calculation formula, R = ρl / S, the monomer resistance of each material in a fixed direction can be calculated, and then the resistance of the composite material in different directions can be calculated by the series-parallel formula. The results of each embodiment and comparative example are shown in Table 2. The resistance of the composite bipolar plate in the normal direction is in the range of 10 -10 Ω, while the horizontal resistance is on the order of 10 21 Ω, so the resistance anisotropy of the composite bipolar plate is very obvious. In addition, although the horizontal resistance in Example 2 is the lowest, the preparation method of Example 1 is more difficult, while the preparation method of Example 2 is the simplest, so the preparation method of the composite bipolar plate should preferably be the method in Example 2.

[0064] Table 1

[0065] Material Resistivity Ω·m aluminum <![CDATA[2.85×10 -8 ]]> pp <![CDATA[1×10 17 ]]>

[0066] Table 2

[0067]

[0068] The bipolar battery stack proposed in this embodiment is composed of the composite bipolar plates provided in the above embodiments, with positive and negative active materials coated on both sides of the bipolar plates respectively, and then stacked in the order of relative placement of active materials of different polarities. A separator is also arranged between the positive and negative active materials, and a sealing component is arranged at the edge of the active material, so that each battery unit can be independent of each other during installation.

[0069] The bipolar stack provided in this embodiment is composed of 4 composite bipolar plates, and the two sides of the composite bipolar plates are coated with positive and negative active materials respectively. When the composite bipolar plates are stacked, the active materials of different polarities are stacked relatively, and a diaphragm is arranged between the active materials of different polarities. Then, a sealing component is arranged on the outer edge of the composite bipolar plates after stacking, and two groups of current collectors are arranged relatively on the other two sides of the stacked composite bipolar plates. The current collectors can use appropriate conductive materials according to the properties of the coated active material layers, and pole ears are arranged. The composite bipolar plate provided in this embodiment can effectively prevent the short-circuit current from flowing into the short-circuit through the bipolar plates when an internal short circuit occurs, without affecting the vertical conduction of the bipolar stack current, thereby greatly improving the safety of the bipolar stack.

[0070] In order to verify the mitigation effect of the composite bipolar plate on internal short circuit, a thermoelectric coupling model of a bipolar stack with 5 units in series was established, in which the ratio of the normal to horizontal resistance of the composite bipolar plate was 10 -10 At the same time, a traditional lithium battery model with 5 units of the same capacity connected in parallel was established. An internal short-circuit point was set at the center of the third unit. Assuming that both models were in an adiabatic state, the temperature rise results of the two groups of batteries were obtained. Figure 5 It can be seen that the bipolar battery stack composed of anisotropic composite bipolar plates has a significantly lower temperature rise than a traditional lithium battery if a short circuit occurs during discharge, and can maintain a temperature below 100°C for 100 seconds. This proves that the composite bipolar plate and bipolar battery stack provided by the present invention have a significant effect in alleviating internal short circuit heat generation.

[0071] The present invention provides a composite bipolar plate structure with anisotropic resistance, and uses the composite bipolar plate to prepare a bipolar battery stack. When an internal short circuit occurs in a battery cell, most of the current in the cell can still maintain the original vertical flow, avoiding a large amount of current from converging to the short circuit point, thereby reducing the heat generation effect after the short circuit in the battery and improving the safety of the battery.

[0072] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A composite bipolar plate, characterized in that: The invention comprises a conductive part and an insulating part, wherein the conductive part comprises a plurality of groups, wherein the array of the plurality of conductive parts is arranged in the insulating part, wherein the plurality of conductive parts are not connected to each other, wherein the insulating part comprises two groups of insulating films of the same size, wherein the insulating films are provided with a plurality of holes, wherein the holes on the two groups of insulating films are arranged in a one-to-one correspondence, wherein the conductive part comprises a conductive sheet and an adhesive sheet, wherein the size of the conductive sheet is the same as the plurality of holes arranged on the insulating part, wherein the conductive part is fixed to any one group of insulating films through an adhesive sheet, wherein the two groups of insulating films are arranged on both sides of the conductive sheet, wherein the conductive sheet is arranged in the insulating part in correspondence with the holes, and wherein the ratio of the normal direction resistance to the horizontal direction resistance of the composite bipolar plate is lower than 10 -8 ; The conductive part is a sheet structure of one or more of stainless steel, copper, aluminum, copper-aluminum composite material, and conductive graphite; The conductivity of the conductive part ranges from 1×10 5 -6.25×10 7 S / m; The insulating part is one or more of polyvinyl chloride, polyethylene, polypropylene, polystyrene, polytetrafluoroethylene, polyethylene terephthalate, polyamide, polyimide, polyether nitrile, polymethyl acrylate, polyvinylidene fluoride, polyurethane, polyacrylonitrile, styrene-butadiene rubber, and sodium carboxymethyl cellulose; The electrical conductivity of the insulation is less than 1 S / m; The thickness of the composite bipolar plate ranges from 30 μm.

2. The method for preparing a composite bipolar plate according to claim 1, characterized in that: The following steps are involved: Selecting two sets of insulating films of the same size, and opening a plurality of holes of the same size as the conductive sheet on the insulating films; Lay any of the insulating films flat, align the conductive sheet with the holes on the insulating film, fix it to the insulating film through the adhesive part, and then cover it with another set of insulating films; The two sets of insulating films and the conductive sheets are compounded by high-temperature hot pressing to form a composite bipolar plate with anisotropic resistance.

3. A bipolar stack, comprising the composite bipolar plate according to claim 1, characterized in that: The bipolar battery stack also includes: a current collector, a positive electrode active layer, a separator, a negative electrode active layer and a sealing component. The positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate are stacked in sequence to form a battery cell. The current collector includes two groups, and the two groups of current collectors are arranged at the upper and lower ends of the battery cell. The sealing component is wrapped around the battery cell. The two groups of current collectors and the sealing component encapsulate the positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate.

4. The bipolar fuel cell stack according to claim 3, characterized in that: The positive electrode active layer, the separator, the negative electrode active layer and the composite bipolar plate all include multiple groups.

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