Electrochemical device and separator therefor

Abstract

The application discloses an electrochemical device and a diaphragm thereof. The diaphragm of the electrochemical device comprises a base film and a coating layer formed on two side surfaces of the base film. The coating layer comprises a ceramic coating layer and a thermal bonding coating layer. The ceramic coating layer and the thermal bonding coating layer formed on the same side of the base film do not coincide with each other. The thermal bonding coating layer formed on one side of the base film does not coincide with the projection of the thermal bonding coating layer formed on the other side of the base film on the base film. After the diaphragm is hot-pressed with an electrode sheet, the electrode can be effectively fixed, so that the production efficiency of a laminated sheet preparation battery cell process is improved. Meanwhile, the diaphragm also has the advantages of low air permeability, high conductivity, simple production process and the like.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and more specifically, to a diaphragm for an electrochemical device and an electrochemical device having the diaphragm. Background Technology

[0002] Lithium-ion batteries are composed of materials such as an anode, cathode, electrolyte, and separator. The separator is an important component, allowing electrolyte ions to pass freely and separating the anode and cathode to prevent direct contact between them and avoid internal short circuits. Its performance determines the battery interface structure and internal resistance.

[0003] Currently, power batteries on the market are manufactured using either winding or stacking processes. With technological advancements and market demands, wound batteries no longer meet requirements in many aspects. This is because wound cells have higher internal resistance, making it difficult to achieve high-current charging and discharging, resulting in poor rate performance. Conversely, stacked cells have lower internal resistance, are easier to charge and discharge with high current, and offer better rate performance. Furthermore, stacking better meets the demands of pure electric vehicle applications for large modules, large batteries, and ultra-long lifespans. Therefore, stacking is gradually becoming the primary process for manufacturing power battery cells.

[0004] Currently, there are several drawbacks to the lamination process for battery cells. First, precise alignment between the anode and cathode electrodes is extremely difficult during lamination, leading to misalignment. This is particularly problematic in high-capacity battery production, where electrode alignment adjustments are time-consuming, severely impacting production efficiency. Second, cells manufactured using this process are susceptible to electrode and separator misalignment during impacts, drops, or vibrations, resulting in direct contact between the positive and negative electrodes, potentially causing short circuits and posing safety risks. Third, the connection between the separator and the upper and lower electrodes in lamination-manufactured cells is relatively loose, making cell assembly into the casing more challenging.

[0005] In conclusion, existing membranes used in electrochemical devices still need improvement. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide an electrochemical device and its diaphragm. This diaphragm, after being hot-pressed with electrode sheets, can effectively fix the electrodes, thereby improving the production efficiency of the stacked battery cell manufacturing process. Simultaneously, this diaphragm also has advantages such as low air permeability, high conductivity, and simple manufacturing process.

[0007] In one aspect of the invention, a diaphragm for an electrochemical device is provided. According to an embodiment of the invention, the diaphragm comprises: a base membrane; and coatings formed on both sides of the base membrane; the coatings include a ceramic coating and a thermally bonded coating, wherein the ceramic coating and the thermally bonded coating formed on the same side of the base membrane do not overlap, and the projections of the thermally bonded coating formed on one side of the base membrane and the thermally bonded coating formed on the other side of the base membrane onto the base membrane do not overlap.

[0008] According to an embodiment of the electrochemical device of the present invention, the separator has coatings formed on both sides of its base membrane. The ceramic coating significantly enhances the thermal stability of the separator and reduces its thermal shrinkage rate; while the thermal bonding coating enables good adhesion between the separator and the electrode sheet during hot pressing. On one side surface of the base membrane, the ceramic coating and the thermal bonding coating do not overlap, thereby effectively avoiding the problems of uneven coating thickness and poor adhesion between the separator and the electrode sheet caused by partial overlap (or overlap) of the ceramic coating and the thermal bonding coating. Furthermore, by ensuring that the projections of the thermal bonding coating formed on one side of the base membrane and the thermal bonding coating formed on the other side of the base membrane do not overlap, i.e., ensuring that the two sides of the same part of the base membrane are not simultaneously thermal bonding coatings, the separator can have a lower thermal shrinkage rate, avoiding the risk of short circuits after battery assembly due to excessive thermal shrinkage of the separator.

[0009] In addition, the diaphragm of the electrochemical device according to the above embodiments of the present invention may also have the following additional technical features:

[0010] In some embodiments of the present invention, on one side surface of the base film, the percentage of the area covered by the ceramic coating on one side surface of the base film is S1, and the percentage of the area covered by the thermal bonding coating on one side surface of the base film is S2, wherein S1 and S2 satisfy S1+S2=100%.

[0011] In some embodiments of the present invention, S1 and S2 satisfy S1:S2 = 1 to 10.

[0012] In some embodiments of the present invention, the thickness of the ceramic coating is 2 to 4 μm.

[0013] In some embodiments of the present invention, the ratio of the thickness of the thermally bonded coating to the thickness of the ceramic coating is 1.2 to 1.5.

[0014] In some embodiments of the present invention, the base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene / polyethylene / polypropylene composite base film, polyimide base film, polyvinylidene fluoride film, polyethylene nonwoven base film, PET nonwoven base film, polypropylene nonwoven base film, polyimide nonwoven base film, and polyvinylidene fluoride film.

[0015] In some embodiments of the present invention, the ceramic coating comprises at least one selected from Al2O3, AlOOH, SiO2, TiO2, ZrO2, CeO2, BaSO4, MgO, and Mg(OH)2.

[0016] In some embodiments of the present invention, the thermally bonded coating comprises at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene mixture (PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene mixture (PVDF-CTFE), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyethylene oxide (PEO), and polydopamine.

[0017] In some embodiments of the present invention, the coating is formed by at least one of the following methods: microgravure roller coating, anilox roller coating, overcoating, and screen printing.

[0018] In another aspect of the invention, an electrochemical device is provided. According to an embodiment of the invention, the electrochemical device includes the diaphragm described above. Thus, the electrochemical device possesses all the features and advantages described for the diaphragm of the electrochemical device above, which will not be repeated here. In summary, the electrochemical device has advantages such as high safety, excellent cycle performance, and high rate performance.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0021] Figure 1 This is a schematic diagram of the membrane structure of an electrochemical device according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the membrane structure of an electrochemical device according to another embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the membrane structure of an electrochemical device according to yet another embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the membrane structure of an electrochemical device according to another embodiment of the present invention. Detailed Implementation

[0025] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0028] In one aspect of the invention, a diaphragm for an electrochemical device is provided. According to an embodiment of the invention, reference is made to... Figures 1-4 The diaphragm includes a base membrane 100 and a coating 200. The coating 200 is formed on both sides of the base membrane 100. The coating 200 includes a ceramic coating 210 and a thermally bonded coating 220. The ceramic coating 210 and the thermally bonded coating 220 formed on the same side of the base membrane 100 do not overlap. The projections of the thermally bonded coating 220 formed on one side of the base membrane 100 and the thermally bonded coating 220 formed on the other side of the base membrane 100 do not overlap on the base membrane 100.

[0029] According to an embodiment of the electrochemical device of the present invention, the separator has coatings formed on both sides of its base membrane. The ceramic coating significantly enhances the thermal stability of the separator and reduces its thermal shrinkage rate; while the thermal bonding coating enables good adhesion between the separator and the electrode sheet during hot pressing. On one side surface of the base membrane, the ceramic coating and the thermal bonding coating do not overlap, thereby effectively avoiding the problems of uneven coating thickness and poor adhesion between the separator and the electrode sheet caused by partial overlap (or overlap) of the ceramic coating and the thermal bonding coating. Furthermore, by ensuring that the projections of the thermal bonding coating formed on one side of the base membrane and the thermal bonding coating formed on the other side of the base membrane do not overlap, i.e., ensuring that the two sides of the same part of the base membrane are not simultaneously thermal bonding coatings, the separator can have a lower thermal shrinkage rate, avoiding the risk of short circuits after battery assembly due to excessive thermal shrinkage of the separator.

[0030] The diaphragm of the electrochemical device according to an embodiment of the present invention will be described in further detail below.

[0031] According to some embodiments of the present invention, the term "electrochemical device" as used herein refers to a lithium-ion battery.

[0032] According to some embodiments of the present invention, on one side of the base membrane, the percentage of the ceramic coating covering one side of the base membrane is S1, and the percentage of the thermal bonding coating covering one side of the base membrane is S2, where S1 and S2 satisfy S1+S2=100%. That is, on one side of the base membrane, the ceramic coating and the thermal bonding coating completely cover one side of the base membrane. This further improves the thermal stability and adhesion performance of the separator. The inventors found in their research that if S1+S2>100%, the ceramic coating and the thermal bonding coating partially overlap, leading to uneven coating thickness and poor adhesion between the separator and the electrode sheet; if S1+S2<100%, there are areas on the separator surface where no coating has been formed, leading to an increased thermal shrinkage rate of the separator and a possibility of short circuits after battery assembly.

[0033] According to some embodiments of the present invention, S1 and S2 satisfy S1:S2 = 1 to 10. That is, the ratio of the area percentage of the ceramic coating covering the surface of the base film to the area percentage of the thermal bonding coating covering the surface of the base film is 1 to 10, and this ratio can be, for example, 1, 3, 5, 8, 10, etc. If S1:S2 < 1, the area of ​​the ceramic coating on one side is smaller than that of the thermal bonding coating, which will lead to an increase in the thermal shrinkage rate of the separator, and there is a possibility of short circuit after the battery is assembled. If S1:S2 > 10, the area of ​​the thermal bonding coating on one side is too small, the adhesion performance between the electrode sheet and the separator is poor, and the separator cannot effectively fix the electrode during the hot pressing process.

[0034] According to some embodiments of the present invention, the thickness of the ceramic coating can be 2–4 μm, such as 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, etc. If the thickness of the ceramic coating is less than 2 μm, it will lead to an increase in the thermal shrinkage rate of the separator, which may cause a short circuit after the battery is assembled, posing a safety hazard; if the thickness of the ceramic coating is greater than 4 μm, it will lead to excessive air permeability and an increase in the ion resistance of the separator.

[0035] According to some embodiments of the present invention, the ratio of the thickness of the thermally bonded coating to the thickness of the ceramic coating is 1.2 to 1.5, and this ratio can be, for example, 1.2, 1.3, 1.4, 1.5, etc. The inventors discovered in their research that during the hot pressing process of the lamination process, the thermal shrinkage rate of the thermally bonded coating in the thickness direction is greater than that of the ceramic coating in the thickness direction. When the ratio of the thermally bonded coating thickness to the ceramic coating thickness is less than 1.2, it leads to poor adhesion between the electrode sheet and the diaphragm, and the diaphragm cannot effectively fix the electrode during the hot pressing process. When the ratio of the thermally bonded coating thickness to the ceramic coating thickness is greater than 1.5, it leads to excessive air permeability and increased ionic resistance of the diaphragm.

[0036] Additionally, it should be noted that the specific shape or distribution of the ceramic coating 210 and the thermally bonded coating 220 formed on both sides of the base film 100 can be selected by those skilled in the art according to actual needs, provided that the foregoing conditions are met. For example, Figures 1-4 These are schematic diagrams of diaphragm structures according to several different specific embodiments of the present invention, wherein a is a top view of the front of the diaphragm, b is a top view of the back of the diaphragm, and c is a cross-sectional view of the diaphragm.

[0037] The specific type of the base membrane is not particularly limited, and those skilled in the art can choose flexibly according to actual needs. For example, commercially available diaphragms suitable for electrochemical devices can be used. According to some embodiments of the present invention, the base membrane can be at least one selected from polyethylene base membrane, polypropylene base membrane, polypropylene / polyethylene / polypropylene composite base membrane, polyimide base membrane, polyvinylidene fluoride membrane, polyethylene nonwoven base membrane, PET nonwoven base membrane, polypropylene nonwoven base membrane, polyimide nonwoven base membrane, and polyvinylidene fluoride membrane.

[0038] The specific type of ceramic coating is not particularly limited, and those skilled in the art can choose flexibly according to actual needs. For example, commercially available coatings formed by inorganic ceramic ions suitable for electrochemical devices can be used. According to some embodiments of the present invention, the ceramic coating may include at least one selected from Al2O3, AlOOH, SiO2, TiO2, ZrO2, CeO2, BaSO4, MgO, and Mg(OH)2.

[0039] The specific type of the aforementioned thermally bonded coating is not particularly limited, and those skilled in the art can flexibly select it according to actual needs. For example, a coating formed from a commercially available thermally bonded polymer suitable for electrochemical devices can be used. According to some embodiments of the present invention, the aforementioned thermally bonded coating may include at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene mixture (PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene mixture (PVDF-CTFE), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyethylene oxide (PEO), and polydopamine.

[0040] According to some embodiments of the present invention, the coating is formed by at least one method selected from microgravure roller coating, anilox roller coating, overprinting, and screen printing. Therefore, the coating formation method is mature and simple.

[0041] As described above, the electrochemical membrane proposed in this invention has at least one of the following advantages:

[0042] (1) After the diaphragm and electrode are hot-pressed together, the diaphragm of the present invention has a strong adhesion to the electrode sheet, which can effectively fix the electrode and improve the production efficiency of the stacking process.

[0043] (2) After the separator and electrodes of the present invention are hot-pressed, the battery cell is easier to insert into the casing during the battery assembly process. At the same time, it avoids misalignment of the electrodes and separator during battery collisions, drops or vibrations, reduces the occurrence of short circuits, and improves the safety of battery use;

[0044] (3) The diaphragm of the present invention has excellent thermal stability, low air permeability, high membrane conductivity, and simple production process.

[0045] In summary, the separator of the electrochemical device of the present invention can improve the production efficiency of the cell stacking process, has a low air permeability value, a simple production process, improve battery safety, and extend battery cycle life.

[0046] In another aspect of the invention, an electrochemical device is provided. According to an embodiment of the invention, the electrochemical device includes the diaphragm described above. Thus, the electrochemical device possesses all the features and advantages described for the diaphragm of the electrochemical device above, which will not be repeated here. In summary, the electrochemical device has advantages such as high safety, excellent cycle performance, and high rate performance.

[0047] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0048] Examples 1-4, Comparative Examples 1-3

[0049] The diaphragm was prepared according to the parameters and materials in Table 1.

[0050] Table 1. Diaphragm parameters and materials

[0051]

[0052] (In Table 1, S1 is the percentage of the area of ​​the ceramic coating covering one side of the base film, S2 is the percentage of the area of ​​the thermal bonding coating covering one side of the base film, H1 is the thickness of the ceramic coating on one side of the base film, and H2 is the thickness of the thermal bonding coating on one side of the base film, in μm.)

[0053] Test case

[0054] 1. Diaphragm heat shrinkage rate test

[0055] The thermal shrinkage rate was used to characterize the high-temperature resistance of ceramic coating samples. The test method followed GB / T12027-2004. Specifically, five samples with dimensions greater than or equal to 100 mm × 100 mm were taken along the MD and TD directions of the film. The actual dimensions (LM0, LT0) of the samples were measured along the MD and TD directions of the film, respectively. The samples were then sandwiched between two sheets of A4 paper. After the oven temperature stabilized, the samples were placed in the oven and heated at 130°C for 1 hour. After heating, the dimensions (LM1, LT1) were measured. The thermal shrinkage rates in the MD and TD directions were calculated using the following formulas:

[0056] (ηM, ηT): ηi=(L) i0 -L i1 ) / L i0 ×100%, where i = M, T.

[0057] 2. Diaphragm-electrode peel force test

[0058] Select the flat part of the diaphragm, cut each test sample into 25mm×500mm samples, and hot press the diaphragm sample with the positive and negative electrodes at 1MPa and 90℃ for 1min, and then test the peel force at 180°.

[0059] 3. Diaphragm air permeability test

[0060] Select a flat section of the diaphragm and cut each test sample into three 100mm × 100mm pieces. Use a Gurley-4100 air permeability meter to test the air permeability value. At an ambient temperature of 25℃, the air permeability of the ceramic diaphragm is determined by the time T it takes for 100mL of air to pass through a specific area of ​​the diaphragm under a certain pressure. The increase in diaphragm air permeability, ΔT, characterizes the air permeability performance of the coated diaphragm and is calculated using the following formula:

[0061] ΔT = T1 - T0. Where T1 is the air permeability value of the membrane after coating, and T2 is the air permeability value of the base membrane.

[0062] 4. Diaphragm conductivity test

[0063] A CR2032 battery was assembled by sandwiching a separator between two stainless steel sheets, injecting electrolyte, and then assembling it. The separator resistance was measured using AC impedance spectroscopy at room temperature (25°C) via an electrochemical workstation, employing the formula: σ = L / SR. b Where L is the thickness of the diaphragm, S is the area of ​​the stainless steel sheet, and R... b The resistance of the diaphragm was measured.

[0064] The test results are shown in Table 2.

[0065] Table 2 Performance Comparison of Examples and Comparative Examples

[0066]

[0067]

[0068] Test results show that the separator according to the embodiments of the present invention has better performance than the comparative examples. As can be seen from Comparative Example 1, the area of ​​the single-sided ceramic coating is smaller than that of the thermal bonding coating, which leads to an increased thermal shrinkage rate of the separator, potentially causing a short circuit after battery assembly. As can be seen from Comparative Example 2, the area of ​​the single-sided thermal bonding coating is too small, resulting in poor adhesion between the electrode sheets and the separator, and the separator cannot effectively fix the electrodes during hot pressing. As can be seen from Comparative Example 3, when the ratio of the thermal bonding coating thickness to the ceramic coating thickness is too large, it leads to excessive air permeability and increased ion resistance of the separator.

[0069] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0070] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A diaphragm for an electrochemical device, characterized in that, include: Base film; A coating is formed on both sides of the base film; the coating includes a ceramic coating and a thermally bonded coating, wherein the ceramic coating and the thermally bonded coating formed on the same side of the base film do not overlap, and the projections of the thermally bonded coating formed on one side of the base film and the thermally bonded coating formed on the other side of the base film on the base film do not overlap. On one side surface of the base film, the percentage of area covered by the ceramic coating on that side surface is S1, and the percentage of area covered by the thermally bonded coating on that side surface is S2, where S1 and S2 satisfy S1 + S2 = 100%. S1 and S2 satisfy S1 : S2 = 1~10, The thickness of the ceramic coating is 2~4 μm.

2. The diaphragm according to claim 1, characterized in that, The ratio of the thickness of the thermally bonded coating to the thickness of the ceramic coating is 1.2 to 1.

5.

3. The diaphragm according to claim 1, characterized in that, The base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene / polyethylene / polypropylene composite base film, polyimide base film, polyvinylidene fluoride film, polyethylene nonwoven base film, PET nonwoven base film, polypropylene nonwoven base film, polyimide nonwoven base film, and polyvinylidene fluoride film.

4. The diaphragm according to claim 1, characterized in that, The ceramic coating includes at least one selected from Al2O3, AlOOH, SiO2, TiO2, ZrO2, CeO2, BaSO4, MgO, and Mg(OH)2.

5. The diaphragm according to claim 1, characterized in that, The thermally bonded coating comprises at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene mixture, polyvinylidene fluoride-chlorotrifluoroethylene mixture, polytetrafluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, and polydopamine.

6. The diaphragm according to claim 1, characterized in that, The coating is formed by at least one of the following methods: gravure roller coating, anilox roller coating, overcoating, and screen printing.

7. An electrochemical device, characterized in that, Includes the diaphragm as described in any one of claims 1 to 6.

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