Battery diaphragm, thermal composite battery cell, preparation method of thermal composite battery cell and secondary battery

Abstract

The invention discloses a battery diaphragm, a thermal composite battery cell, a preparation method of the thermal composite battery cell and a secondary battery, and belongs to the technical field of batteries. The battery diaphragm provided by the invention comprises a base membrane, a first matrix type adhesive layer and a second matrix type adhesive layer, wherein the first matrix type adhesive layer and the second matrix type adhesive layer are respectively stacked on the surfaces of the two sides of the base membrane; the first matrix type adhesive layer is used for bonding a positive pole piece and comprises a plurality of raised first adhesive points which are distributed in a matrix manner; the second matrix type adhesive layer is used for bonding a negative pole piece and comprises a plurality of raised second adhesive points which are distributed in a matrix manner; the first glue point comprises a first polymer, the second glue point comprises a second polymer, and the glass transition temperature of the first polymer is higher than that of the second polymer. Based on the structure, the battery diaphragm can improve the bonding strength between the battery diaphragm and the positive and negative pole pieces.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery separator, a thermal composite cell and its preparation method, and a secondary battery. Background Technology

[0002] The separator plays a crucial role in lithium-ion batteries, including transporting lithium ions, isolating the positive and negative electrodes, and preventing short circuits. Currently, in the fabrication of lithium-ion batteries, the positive and negative electrode sheets are typically assembled in a wound or stacked manner, with the separator wound simultaneously between the positive and negative electrodes.

[0003] For wound batteries, when the bond strength between the separator and the positive and negative electrodes is low, separator wrinkles or misalignments are prone to occur during electrode winding, resulting in defective products. For stacked batteries, the separator is typically wound in a Z-shape between the positive and negative electrodes. When the bond strength between the separator and the electrodes is low, voids can easily form between the electrodes and the separator, affecting electrolyte distribution, increasing internal resistance, and impacting cycle life and rate performance. Therefore, it is necessary to improve the bond strength between the separator and the electrodes. Summary of the Invention

[0004] This application provides a battery separator, a thermally composite battery cell, a method for preparing the same, and a secondary battery, which can improve the bonding strength between the battery separator and the positive and negative electrode sheets. The technical solution is as follows:

[0005] On one hand, this application provides a battery separator, the battery separator comprising: a base film, a first matrix adhesive layer and a second matrix adhesive layer, wherein the first matrix adhesive layer and the second matrix adhesive layer are respectively stacked on both sides of the base film;

[0006] The first matrix adhesive layer is used to bond the positive electrode sheet and includes a plurality of first adhesive dots that are distributed in a matrix and raised.

[0007] The second matrix adhesive layer is used to bond the negative electrode sheet and includes multiple raised second adhesive dots arranged in a matrix.

[0008] The first adhesive dot includes a first polymer, the second adhesive dot includes a second polymer, and the glass transition temperature of the first polymer is greater than that of the second polymer.

[0009] In one possible implementation, the glass transition temperature of the first polymer is 90°C to 270°C, and the glass transition temperature of the second polymer is -80°C to 45°C.

[0010] In another possible implementation, the primary particles of the first polymer have a particle size of 50 nm to 500 nm, and the primary particles of the second polymer have a particle size of 50 nm to 500 nm.

[0011] In another possible implementation, the diameter of the first adhesive dot is 250 μm to 500 μm, the center distance between any two adjacent first adhesive dots is 600 μm to 800 μm, and the coverage of the first adhesive dot is 8.0% to 30%.

[0012] The diameter of the second adhesive dot is 500μm to 1200μm, the center distance between any two adjacent second adhesive dots is 800μm to 1500μm, and the coverage of the second adhesive dot is 30% to 50%.

[0013] In another possible implementation, the first polymer is selected from at least one of polymethyl methacrylate, polyacrylonitrile, and polyimide;

[0014] The second polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinyl acetate, polyethylene-co-vinyl acetate, and polyethylene oxide.

[0015] In another possible implementation, the first adhesive dot further includes: a first adhesive and a first additive;

[0016] Wherein, the mass fraction of the first polymer is 50% to 55%, the mass fraction of the first binder is 40% to 45%, and the mass fraction of the first additive is less than or equal to 5%.

[0017] In another possible implementation, the second adhesive dot further includes: a second adhesive and a second additive;

[0018] The second polymer has a mass fraction of 50% to 60%, the second binder has a mass fraction of 35% to 45%, and the second additive has a mass fraction of less than or equal to 5%.

[0019] In another possible implementation, the first adhesive and the second adhesive each independently contain at least one of the following polar groups: hydroxyl, carboxyl, imide, nitrile, or ester.

[0020] In another possible implementation, the first adhesive and the second adhesive are each independently selected from at least one of polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

[0021] In another possible implementation, the thickness of the base film is 1 μm to 30 μm, the height of the first adhesive dot is 0.5 μm to 10 μm, and the height of the second adhesive dot is 0.5 μm to 10 μm.

[0022] On the other hand, this application provides a thermal composite battery cell, which includes a plurality of positive electrode plates, a plurality of negative electrode plates, and a battery separator as described in any of the above.

[0023] The negative electrode and the positive electrode are stacked alternately, and adjacent negative electrode and positive electrode are separated by the battery separator. The battery separator is bonded to the positive electrode by the first matrix adhesive layer and to the negative electrode by the second matrix adhesive layer.

[0024] In one possible implementation, the number of negative electrode plates is one more than the number of positive electrode plates, and the thermal composite cell includes a plurality of first electrode plate units and a second electrode plate unit arranged in sequence.

[0025] The first electrode unit includes a battery separator, a negative electrode, a battery separator, and a positive electrode arranged in sequence. The second electrode unit includes a battery separator, a negative electrode, and a battery separator arranged in sequence.

[0026] In another possible implementation, the negative electrode sheet has a thickness of 50 μm to 200 μm, a porosity of 20% to 40%, and a compaction density of 1.30 g / cm³. 3 ~1.80g / cm 3 ;

[0027] The positive electrode sheet has a thickness of 50 μm to 300 μm, a porosity of 10% to 30%, and a compaction density of 2.10 g / cm³. 3 ~3.10g / cm 3 .

[0028] In another possible implementation, the negative electrode includes a first active material having a median particle size of 0.5 μm to 2.0 μm and a specific surface area of ​​10 m². 2 / g~15m 2 / g;

[0029] The positive electrode sheet includes a second active material, the second active material having a median particle size of 10.0 μm to 15.0 μm and a specific surface area of ​​1.0 m². 2 / g~2.5m 2 / g.

[0030] On the other hand, this application provides a method for preparing a thermally composite battery cell, wherein the thermally composite battery cell is as described in any of the above claims, and the preparation method includes:

[0031] A stacking assembly is provided, the stacking assembly including a plurality of positive electrode sheets, a plurality of negative electrode sheets, and two layers of battery separator, wherein the plurality of positive electrode sheets are stacked on one side surface of one of the battery separator layers, and the plurality of negative electrode sheets are stacked between the two layers of battery separator.

[0032] The laminated assembly is subjected to thermal bonding treatment to form a hot-pressed laminated assembly;

[0033] The hot-pressed lamination assembly is laminated to obtain the thermal composite cell.

[0034] In another possible implementation, the stacked assembly includes a plurality of first electrode units and a second electrode unit;

[0035] The process of thermally bonding the laminated assembly to form a hot-pressed laminated assembly includes:

[0036] Multiple first electrode units and second electrode units are thermally composited to form a hot-pressed laminated assembly;

[0037] The thermal composite process corresponding to the first electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~2.0t, and time of 1s~80s.

[0038] The thermal composite process corresponding to the second electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~3.0t, and time of 1s~180s.

[0039] On the other hand, this application provides a secondary battery, the secondary battery comprising: a casing, an electrolyte contained inside the casing, and a thermally composite battery cell, the thermally composite battery cell being as described in any of the preceding claims.

[0040] This application provides a battery separator comprising a base film, a first matrix adhesive layer, and a second matrix adhesive layer. The first matrix adhesive layer includes multiple first adhesive dots for bonding a positive electrode sheet; the second matrix adhesive layer includes multiple second adhesive dots for bonding a negative electrode sheet. The glass transition temperature of the first polymer in the first adhesive dots is higher than the glass transition temperature of the second polymer in the second adhesive dots. On one hand, the matrix adhesive layer design can significantly increase the contact area between the battery separator and the electrode sheet, thereby improving the bonding strength between the battery separator and the positive and negative electrode sheets. On the other hand, matrix adhesive layers with different compositions are designed on both sides of the base film. The lower the glass transition temperature of the polymer, the higher the flexibility of the polymer, the larger the contact area with the electrode sheet, and the higher the bonding strength. Therefore, this application specifically designs matrix adhesive layers and polymers with different glass transition temperatures to match the matrix adhesive layers according to the different characteristics of the positive and negative electrode sheets, thereby improving the bonding strength between the battery separator and the positive and negative electrode sheets. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a thermally composited battery cell after lamination processing, provided in an embodiment of this application.

[0042] Figure 2 This is a schematic diagram of a thermally composited battery cell before lamination processing, provided in an embodiment of this application. Detailed Implementation

[0043] To make the technical solution and advantages of this application clearer, the embodiments of this application will be described in further detail below.

[0044] On one hand, embodiments of this application provide a battery separator, which includes: a base film, a first matrix adhesive layer and a second matrix adhesive layer, wherein the first matrix adhesive layer and the second matrix adhesive layer are respectively stacked on both sides of the base film.

[0045] The first matrix adhesive layer is used to bond the positive electrode sheet and includes multiple first adhesive dots that are distributed in a matrix and are raised; the second matrix adhesive layer is used to bond the negative electrode sheet and includes multiple second adhesive dots that are distributed in a matrix and are raised.

[0046] The first adhesive dot includes a first polymer, the second adhesive dot includes a second polymer, and the glass transition temperature of the first polymer is greater than that of the second polymer.

[0047] This application provides a battery separator comprising a base film, a first matrix adhesive layer, and a second matrix adhesive layer. The first matrix adhesive layer includes multiple first adhesive dots for bonding a positive electrode sheet; the second matrix adhesive layer includes multiple second adhesive dots for bonding a negative electrode sheet. The glass transition temperature of the first polymer in the first adhesive dots is higher than the glass transition temperature of the second polymer in the second adhesive dots. On one hand, the matrix adhesive layer design can significantly increase the contact area between the battery separator and the electrode sheet, thereby improving the bonding strength between the battery separator and the positive and negative electrode sheets. On the other hand, matrix adhesive layers with different compositions are designed on both sides of the base film. The lower the glass transition temperature of the polymer, the higher the flexibility of the polymer, the larger the contact area with the electrode sheet, and the higher the bonding strength. Therefore, this application specifically designs matrix adhesive layers and polymers with different glass transition temperatures to match the matrix adhesive layers according to the different characteristics of the positive and negative electrode sheets, thereby improving the bonding strength between the battery separator and the positive and negative electrode sheets.

[0048] In the embodiments of this application, the first adhesive dots can be distributed in a square matrix, a rectangular matrix, a hexagonal honeycomb matrix, an alternating row and column matrix, or other matrix distribution patterns, without specific limitation. The second adhesive dots can also be distributed in a square matrix, a rectangular matrix, a hexagonal honeycomb matrix, an alternating row and column matrix, or other matrix distribution patterns, without specific limitation. Furthermore, the matrix distribution patterns of the first adhesive dots and the second adhesive dots can be the same or different. For example, both the first and second adhesive dots can be distributed in a square matrix, or both can be distributed in a hexagonal honeycomb matrix, or the first adhesive dots can be distributed in a square matrix, and the second adhesive dots can be distributed in a hexagonal honeycomb matrix.

[0049] The following explanation uses the first adhesive dot as an example to illustrate the above-mentioned matrix distributions. For instance, if multiple first adhesive dots are distributed in a square matrix, they can be arranged in an equally spaced square grid, with each dot located at a grid intersection. This matrix distribution method exhibits strong regularity and is easy to process and control. Similarly, if the first adhesive dots are distributed in a rectangular matrix, the distance between any two adjacent first adhesive dots in the same row is equal. This matrix distribution method also exhibits strong regularity and is easy to process and control. Furthermore, if multiple first adhesive dots are distributed in a hexagonal honeycomb matrix, they are arranged in a hexagonal stack, similar to a honeycomb structure. This matrix distribution method provides high coverage density. Finally, if the first adhesive dots are distributed in an alternating row-column matrix, the rows and columns are staggered. For example, compared to even rows, odd rows are shifted a certain distance to the right, which is half the distance between two adjacent first adhesive dots in even rows. This distribution method can disperse stress concentration points and reduce the risk of adhesive layer cracking during charging and discharging.

[0050] In one possible implementation, the glass transition temperature of the first polymer is 90°C to 270°C, and the glass transition temperature of the second polymer is -80°C to 45°C.

[0051] For example, the glass transition temperature of the first polymer can be 90℃, 95℃, 100℃, 150℃, 200℃, 250℃, 270℃, etc. The glass transition temperature of the second polymer can be -80℃, -70℃, -65℃, -60℃, -50℃, -45℃, -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, 20℃, 30℃, 40℃, 45℃, etc.

[0052] In the embodiments of this application, the lower the glass transition temperature, the higher the flexibility of the adhesive, the larger the contact area with the electrode during hot pressing, and the higher the bonding strength. Therefore, based on the strong polarity and high specific surface area of ​​the positive electrode, a first polymer with a relatively high glass transition temperature (90℃~270℃) is matched, and based on the weak polarity and low specific surface area of ​​the negative electrode, a second polymer with a relatively low glass transition temperature (-80℃~45℃) is matched, thereby improving the bonding strength between the battery separator and the positive and negative electrode, thereby improving the thickness uniformity of the electrode unit, and ultimately improving the thickness uniformity of the thermally composite cell.

[0053] In one possible implementation, the primary particles of the first polymer have a particle size of 50 nm to 500 nm, and the primary particles of the second polymer have a particle size of 50 nm to 500 nm.

[0054] For example, the particle size of the primary particles of the first polymer can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc. The particle size of the primary particles of the second polymer can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc.

[0055] In addition, the particle size of the primary particles of the first polymer can be the same as or different from that of the primary particles of the second polymer, and no specific limitation is made in this regard.

[0056] In the embodiments of this application, the particle size of the primary particles of the first polymer and the second polymer is in the range of 50nm to 500nm, which can form a micro-rough surface, enhance the mechanical interlocking effect between the battery separator and the positive and negative electrode sheets, thereby improving the bonding strength between the battery separator and the positive and negative electrode sheets.

[0057] In one possible implementation, the diameter of the first adhesive dot is 250 μm to 500 μm, the center distance between any two adjacent first adhesive dots is 600 μm to 800 μm, and the coverage of the first adhesive dot is 8.0% to 30%.

[0058] The diameter of the second adhesive dot is 500μm to 1200μm, the center distance between any two adjacent second adhesive dots is 800μm to 1500μm, and the coverage of the second adhesive dot is 30% to 50%.

[0059] For example, the diameter of the first adhesive dot can be 250μm, 280μm, 300μm, 320μm, 350μm, 380μm, 400μm, 420μm, 450μm, 480μm, 500μm, etc., and the center-to-center distance between any two adjacent first adhesive dots can be 600μm, 620μm, 650μm, 680μm, 700μm, 720μm, 750μm, 780μm, 800μm, etc., and the coverage of the first adhesive dot can be 8.0%, 9.0%, 10.0%, 12%, 15%, 20%, 22%, 25%, 28%, 30%, etc. Further, the coverage of the first adhesive dot can be 20% to 30%.

[0060] The diameter of the second adhesive dot can be 500μm, 550μm, 600μm, 700μm, 800μm, 900μm, 1000μm, 1100μm, 1200μm, etc., and the center-to-center distance between any two adjacent second adhesive dots can be 800μm, 850μm, 900μm, 1000μm, 1100μm, 1200μm, 1300μm, 1400μm, 1500μm, etc., and the coverage of the second adhesive dots can be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, etc. Further, the coverage of the second adhesive dots can be 40%–50%.

[0061] In the embodiments of this application, the first adhesive dot and the second adhesive dot are set in such a way that the diaphragm and the electrode have a large contact area, and the adhesive dots are avoided from overlapping or excessively accumulating, thereby improving the adhesion of the diaphragm. At the same time, the diaphragm also has a high liquid absorption and liquid retention capacity.

[0062] In one possible implementation, the first polymer is selected from at least one of polymethyl methacrylate, polyacrylonitrile, and polyimide; and the second polymer is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl acetate, polyethylene-co-vinyl acetate, and polyethylene oxide.

[0063] In the embodiments of this application, the above-mentioned materials are polar or contain polar groups. When the first polymer is selected from the above-mentioned materials, it can form a directional bond with the polar groups of the active material in the positive electrode sheet based on its polarity or through the corresponding polar groups, thereby improving the bonding strength between the battery separator and the positive electrode sheet. When the second polymer is selected from the above-mentioned materials, it can form a directional bond with the polar groups of the active material in the negative electrode sheet based on its polarity or through the corresponding polar groups, thereby improving the bonding strength between the battery separator and the negative electrode sheet.

[0064] In one possible implementation, the first adhesive point further includes: a first adhesive and a first auxiliary agent; wherein the mass fraction of the first polymer is 50% to 55%, the mass fraction of the first adhesive is 40% to 45%, and the mass fraction of the first auxiliary agent is less than or equal to 5%.

[0065] For example, the mass fraction of the first polymer can be 50%, 51%, 52%, 53%, 54%, 55%, etc. The mass fraction of the first binder can be 40%, 41%, 42%, 43%, 45%, etc. The mass fraction of the first additive can be 0%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0066] In this embodiment, the first polymer has a mass fraction of 50% to 55%, and is the main component of the first matrix adhesive layer. A high proportion of the first polymer ensures stable adhesion between the positive electrode and the battery separator. The first binder has a mass fraction of 40% to 45%, and a higher content of the first binder enhances the adhesion strength between the first matrix adhesive layer and the base film. A small amount (≤5%) of the first additive can improve the uniformity and surface smoothness of the first matrix adhesive layer, reduce the interfacial tension of the first matrix adhesive layer, and ensure the wettability of the first matrix adhesive layer with the base film and the positive electrode, which is beneficial for improving the adhesion of the battery separator.

[0067] In one possible implementation, the second adhesive point further includes: a second binder and a second additive; wherein the mass fraction of the second polymer is 50% to 60%, the mass fraction of the second binder is 35% to 45%, and the mass fraction of the second additive is less than or equal to 5%.

[0068] For example, the mass fraction of the second polymer can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc. Further, the mass fraction of the second polymer can be 55% to 60%.

[0069] The mass fraction of the second adhesive can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 45%, etc. Further, the mass fraction of the second adhesive can be 40%–45%. The mass fraction of the second auxiliary agent can be 0%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0070] In this embodiment, the second polymer has a mass fraction of 50%–60%, and is the main component of the second matrix adhesive layer. A high proportion of the second polymer ensures stable adhesion between the negative electrode sheet and the battery separator. The second binder has a mass fraction of 35%–45%, and a higher content of the second binder enhances the adhesion strength between the second matrix adhesive layer and the base film. A small amount (≤5%) of the second additive can improve the uniformity and surface smoothness of the second matrix adhesive layer, reduce the interfacial tension of the second matrix adhesive layer, and ensure the wettability of the second matrix adhesive layer with the base film and the negative electrode sheet, which is beneficial for improving the adhesion of the battery separator.

[0071] In the embodiments of this application, the first adjuvant and the second adjuvant may be the same or different, and there is no specific limitation on this. Here, we will only describe the case where the first adjuvant and the second adjuvant are the same, and take the first adjuvant as an example.

[0072] The first additive includes at least one of a thickener, a dispersant, and a wetting agent. The thickener is mainly used to change the viscosity and thixotropy of the adhesive slurry, allowing it to maintain fluidity while quickly setting during coating. The dispersant is mainly used to ensure uniform dispersion of the polymer and binder, improving the uniformity of the matrix adhesive layer. The wetting agent is mainly used to reduce the interfacial tension of the matrix adhesive layer, ensuring wettability between the matrix adhesive layer and the base film and the negative electrode sheet, which is beneficial for improving the adhesion of the battery separator.

[0073] The thickener may be selected from at least one of sodium carboxymethyl cellulose, sodium carboxymethyl cellulose, and xanthan gum. The dispersant may be selected from at least one of polyvinylpyrrolidone, sodium polyacrylate, polyethylene glycol, and polyvinyl alcohol. The wetting agent may be selected from at least one of sodium dodecyl sulfate, polysorbate, and fluorocarbon wetting agents.

[0074] In one possible implementation, the glass transition temperature of the first adhesive is -70℃ to 270℃, and the glass transition temperature of the second adhesive is -70℃ to 270℃.

[0075] For example, the glass transition temperature of the first adhesive can be -70℃, -60℃, -50℃, -30℃, 0℃, 10℃, 20℃, 50℃, 100℃, 150℃, 200℃, 250℃, 270℃, etc. The glass transition temperature of the second adhesive can be -70℃, -60℃, -50℃, -30℃, 0℃, 10℃, 20℃, 50℃, 100℃, 150℃, 200℃, 250℃, 270℃, etc.

[0076] In this embodiment, the first adhesive has a wide glass transition temperature range (-70℃ to 270℃), which not only improves the bonding strength between the first matrix adhesive layer and the base film at room temperature, but also prevents brittle cracking at low temperatures, ensuring the structural integrity of the battery separator in cold environments. Similarly, the second adhesive has a wide glass transition temperature range (-70℃ to 270℃), which not only improves the bonding strength between the second matrix adhesive layer and the base film at room temperature, but also prevents brittle cracking at low temperatures, ensuring the structural integrity of the battery separator in cold environments.

[0077] The first and second adhesives mentioned above each independently contain at least one of the following polar groups: hydroxyl (-OH), carboxyl (-COOH), imide (-CONH-), nitrile (R-CN), or ester (-COO-).

[0078] In the embodiments of this application, the hydroxyl (-OH), carboxyl (-COOH), imide (-CONH-), nitrile (R-CN), and ester (-COO-) groups are all polar groups. These polar groups can form directional bonds with the polar groups in the first polymer or the second polymer through hydrogen bonds, van der Waals forces, or dipole interactions, thereby improving the adhesion strength between the matrix adhesive layer formed by the first polymer or the second polymer and the base film.

[0079] In one possible implementation, the first adhesive and the second adhesive are each independently selected from at least one of polymethyl methacrylate (PMMA), polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

[0080] In this implementation, the first adhesive and the second adhesive can be the same or different, and there is no specific limitation on this.

[0081] Polymethyl methacrylate, polyvinyl acetate, and polyethylene-co-vinyl acetate contain ester groups, polyacrylonitrile contains nitrile groups, polyimide contains imide groups, and polyethylene oxide contains hydroxyl groups. Therefore, when the first adhesive and the second adhesive are each independently selected from the above materials, they can form directional bonds with the polar groups in the first polymer or the second polymer through the corresponding polar groups, thereby improving the bonding strength between the matrix adhesive layer formed by the first polymer or the second polymer and the base film.

[0082] In one possible implementation, at ≤110℃, the air permeability increment of the battery separator before and after coating with the first matrix adhesive layer and the second matrix adhesive layer is ≤35s / 100mL, that is, the air permeability increment of the battery separator before and after coating with the double-sided matrix adhesive layer is ≤35s / 100mL.

[0083] In this embodiment, the air permeability increment of the battery separator before and after coating with the first matrix adhesive layer and the second matrix adhesive layer refers to the difference between the air permeability value of the battery separator obtained after coating the base membrane with the first matrix adhesive layer and the second matrix adhesive layer and the air permeability value of the base membrane. The formulation of the first matrix adhesive layer and the second matrix adhesive layer, as well as the structure of the first polymer and the second polymer, ensure that the air permeability increment of the battery separator before and after coating with the first matrix adhesive layer and the second matrix adhesive layer is ≤35s / 100mL, indicating that the battery separator has good stability and can avoid sudden changes in ion transport resistance caused by pore collapse or shrinkage.

[0084] In one possible implementation, the thickness of the base film is 1 μm to 30 μm, the height of the first adhesive dot is 0.5 μm to 10 μm, and the height of the second adhesive dot is 0.5 μm to 10 μm.

[0085] For example, the thickness of the base film can be 1μm, 2μm, 3μm, 5μm, 7μm, 9μm, 10μm, 12μm, 15μm, 17μm, 19μm, 20μm, 22μm, 25μm, 28μm, 30μm, etc. The height of the first adhesive dot can be 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc. The height of the second adhesive dot can be 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0086] In this embodiment, when the base film thickness is small, for example, between 1 μm and 10 μm, the total thickness of the battery separator can be effectively reduced, providing space for increasing battery energy density. When the base film thickness is large, for example, between 10 μm and 30 μm, the puncture strength of the battery separator can be effectively improved, and the thermal shrinkage rate is controllable at high temperatures, ensuring that the battery separator maintains structural integrity in high-temperature environments and avoiding direct contact between the positive and negative electrodes due to excessive shrinkage, thereby improving battery safety. The height of the first adhesive dot and the height of the second adhesive dot are between 0.5 μm and 10 μm, allowing the first adhesive dot to protrude from the base film. The protruding first and second adhesive dots support the positive and negative electrode sheets, creating a gap (GAP), thereby improving the cell's liquid retention rate.

[0087] In one possible implementation, the base film is selected from at least one of polyethylene (PE) and polypropylene (PP).

[0088] PE exhibits excellent chemical stability. When PE is used as the base film, the battery separator has good wettability to the electrolyte, ensuring efficient ion conduction. Furthermore, PE is resistant to low temperatures and highly flexible, making it suitable for low-temperature applications. PP possesses good high-temperature resistance, maintaining structural stability under high-temperature conditions and reducing the risk of thermal runaway. Additionally, PP has high mechanical strength, allowing the battery separator to withstand volume changes and mechanical stresses during battery charging and discharging.

[0089] In one possible implementation, the molecular weight of the base film is 30 w (ten thousand) g / mol to 300 w (ten thousand) g / mol.

[0090] For example, the molecular weight of the base film can be 30 w g / mol, 40 w g / mol, 50 w g / mol, 80 w g / mol, 100 w g / mol, 120 w g / mol, 150 w g / mol, 180 w g / mol, 200 w g / mol, 220 w g / mol, 250 w g / mol, 280 w g / mol, 300 w g / mol, etc.

[0091] When the base film is PE, the molecular weight of PE can be 30w g / mol to 300w g / mol; when the base film is PP, the molecular weight of PP is ≤100w g / mol.

[0092] In the embodiments of this application, when the molecular weight of the base film is between 30 w g / mol and 300 w g / mol, the base film can have high mechanical strength, structural stability and thermal stability.

[0093] In one possible implementation, the air permeability of the base membrane is 50 s / 100 mL to 500 s / 100 mL.

[0094] For example, the air permeability of the base membrane can be 50s / 100mL, 100s / 100mL, 150s / 100mL, 200s / 100mL, 250s / 100mL, 300s / 100mL, 350s / 100mL, 400s / 100mL, 450s / 100mL, 500s / 100mL, etc.

[0095] In the embodiments of this application, the air permeability of the base membrane is between 50s / 100mL and 500s / 100mL. This can ensure rapid ion migration and improve battery power density under high porosity, while also limiting excessively large pore size to avoid excessive electrolyte permeation, which could lead to electron leakage current between the positive and negative electrodes and maintain battery voltage consistency.

[0096] On the other hand, embodiments of this application provide a thermal composite battery cell, which includes a plurality of positive electrode plates, a plurality of negative electrode plates, and the battery separator described above.

[0097] Negative and positive electrode sheets are stacked alternately, and adjacent negative and positive electrode sheets are separated by a battery separator. The battery separator is bonded to the corresponding electrode sheet by an adhesive layer.

[0098] See Figure 1 , Figure 1 This is a schematic diagram of a thermally composite battery cell obtained after lamination processing. Figure 1 As can be seen, the negative electrode 10 and the positive electrode 11 are stacked alternately, and adjacent negative electrode 10 and positive electrode 11 are separated by the battery separator 12.

[0099] In the embodiments of this application, according to the different characteristics of the positive and negative electrode sheets, the battery separator is bonded to the corresponding electrode sheets through different adhesive layers, which can improve the bonding strength between the battery separator and the positive and negative electrode sheets.

[0100] In one possible implementation, the number of negative electrode plates is one more than the number of positive electrode plates, and the thermal composite cell includes multiple first electrode plate units and a second electrode plate unit arranged in sequence.

[0101] The first electrode unit includes a battery separator, a negative electrode, a battery separator, and a positive electrode arranged in sequence. The second electrode unit includes a battery separator, a negative electrode, and a battery separator arranged in sequence.

[0102] In this design, both sides of the negative electrode are bonded to the second adhesive layer of the battery separator, meaning the negative electrode is located between two battery separator layers. One side of the positive electrode is bonded to the first adhesive layer of the battery separator. This first side of the positive electrode can be bonded to either the first adhesive layer of the upper or lower battery separator.

[0103] In this embodiment, the battery separator is a continuous membrane material. The battery separator includes multiple main bodies and multiple bending portions arranged alternately and continuously. The multiple main bodies are stacked along the thickness direction of the negative electrode sheet, and adjacent main bodies are connected by bending portions.

[0104] Negative and positive electrode sheets are stacked alternately, with each positive electrode sheet located between two negative electrode sheets. Adjacent negative and positive electrode sheets are separated by the main body of the battery separator. The projections of the positive and negative electrode sheets along the thickness direction of the negative electrode sheet fall entirely within the planar area of ​​the main body between them, ensuring that the main body completely separates the negative and positive electrode sheets and prevents short circuits caused by contact between the positive and negative electrode sheets.

[0105] See Figure 2 Before the lamination process, the thermal composite cell includes multiple adjacent first electrode units 20 and a second electrode unit 21. The first electrode unit 20 includes a battery separator 201, a negative electrode 202, a battery separator 203, and a positive electrode 204 arranged in sequence. The second electrode unit 21 includes a battery separator 201, a negative electrode 202, and a battery separator 203 arranged in sequence.

[0106] In this embodiment, positive and negative electrode sheets and battery separator are formed into electrode units, and then stacked and assembled. This eliminates the separator winding process and avoids the situation where only a single electrode sheet and separator can be combined at a time in Z-shaped stacking assembly, thus greatly improving the production efficiency of electrode assembly.

[0107] In one possible implementation, the number of first electrode units is 1 to 200.

[0108] For example, the number of first electrode units can be 1, 5, 10, 20, 30, 50, 80, 90, 100, 120, 150, 160, 180, 190, 200, etc.

[0109] In the embodiments of this application, the number of first electrode units can be flexibly set according to different capacity requirements to prepare batteries with different capacities.

[0110] In one possible implementation, the thickness of the negative electrode sheet is 50 μm to 200 μm, the porosity is 20% to 40%, and the compaction density is 1.30 g / cm³. 3 ~1.80g / cm 3 ;

[0111] The thickness of the positive electrode sheet is 50μm to 300μm, the porosity is 10% to 30%, and the compacted density is 2.10 g / cm³. 3 ~3.10g / cm3 .

[0112] For example, the thickness of the negative electrode sheet can be 50μm, 60μm, 80μm, 100μm, 120μm, 150μm, 180μm, 200μm, etc., the porosity can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc., and the compaction density can be 1.30g / cm³. 3 1.40g / cm 3 1.50g / cm 3 1.60g / cm 3 1.70g / cm 3 1.80g / cm 3 wait.

[0113] The thickness of the positive electrode sheet can be 50μm, 60μm, 80μm, 100μm, 120μm, 150μm, 180μm, 200μm, 220μm, 250μm, 280μm, 300μm, etc., and the porosity can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, etc., with a compaction density of 2.10 g / cm³. 3 2.20g / cm 3 2.30g / cm 3 2.40 g / cm 3 2.50g / cm 3 2.60g / cm 3 2.70 g / cm 3 2.80g / cm 3 2.90g / cm 3 3.0g / cm 3 3.10 g / cm 3 wait.

[0114] In this embodiment, the negative electrode sheet with a thickness of 50μm to 200μm is adapted to the expansion requirements of silicon-based negative electrodes, and mechanical buffering reduces the probability of electrode delamination. The positive electrode sheet with a thickness of 50μm to 300μm can effectively disperse charging and discharging stress, reducing the risk of coating cracking. The negative electrode sheet with a porosity of 20% to 40% can improve electrolyte storage capacity, promote uniform lithium ion insertion / extraction, and suppress interface degradation caused by the volume expansion of silicon-based negative electrodes. The positive electrode sheet with a porosity of 10% to 30% can reduce the amount of electrolyte retained at the positive electrode interface, reducing the risk of side reaction gas generation. The compaction density is 1.30 g / cm³. 3 ~1.80g / cm 3 The negative electrode sheet is adapted to the expansion characteristics of silicon-based negative electrodes, avoiding excessive compaction that could lead to particle breakage and interface failure. The compaction density is 2.10 g / cm³.3 ~3.10g / cm 3 The positive electrode sheet can increase the proportion of active material, thereby increasing the energy density.

[0115] In one possible implementation, the negative electrode includes a first active material with a median particle size of 0.5 μm to 2.0 μm and a specific surface area of ​​10 m². 2 / g~15m 2 / g;

[0116] The positive electrode includes a second active material, which has a median particle size of 10.0 μm to 15.0 μm and a specific surface area of ​​1.0 m². 2 / g~2.5m 2 / g.

[0117] For example, the median particle size of the first active material can be 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, etc., and the specific surface area can be 10 m². 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g etc.

[0118] The median particle size of the second active material can be 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, etc., and the specific surface area can be 1.0 m². 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.2m 2 / g, 2.5m 2 / g etc.

[0119] The first active material can be one or a combination of silicon-based materials, graphite materials, and lithium metal, and the second active material can be one or a combination of ternary materials such as lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and lithium nickel cobalt aluminum oxide (NCA), without specific limitations.

[0120] In this embodiment, the median particle size of the first active material in the negative electrode is relatively small, ranging from 0.5 μm to 2.0 μm. This shortens the lithium-ion diffusion path, increases the lithium insertion / extraction rate, and the small particle size of the first active material can buffer the expansion stress of the silicon-based negative electrode, improving cycle performance. The median particle size of the second active material in the positive electrode is relatively large, ranging from 10.0 μm to 15.0 μm. This reduces the risk of breakage of fine particles and extends cycle life. The specific surface area of ​​the first active material in the negative electrode is relatively large, at 10 m² / m³. 2 / g~15m 2 / g provides sufficient lithium-ion reaction sites while avoiding excessive electrolyte decomposition due to excessive specific surface area. The specific surface area of ​​the second active material in the positive electrode is relatively small, at 1.0m². 2 / g~2.5m 2 / g can reduce the contact area between the positive electrode and the electrolyte, thereby reducing the risk of metal dissolution under high voltage.

[0121] On the other hand, embodiments of this application also provide a method for preparing a battery separator, the method comprising:

[0122] (1) Provide a first matrix adhesive layer slurry and a second matrix adhesive layer slurry.

[0123] The first matrix adhesive slurry comprises the following components by mass fraction: 50%–60% first polymer, 30%–45% first binder, and ≤5% first additive. The first polymer, first binder, first additive, and solvent are mixed uniformly to obtain the first matrix adhesive slurry. The solid content of the first matrix adhesive slurry is 5%–35%.

[0124] For example, the solid content of the first matrix adhesive layer slurry can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, etc. Further, the solid content of the first matrix adhesive layer slurry can be 5% to 25%.

[0125] The second matrix adhesive slurry comprises the following components by mass fraction: 50%–55% second polymer, 40%–45% second binder, and ≤5% second additive. The second polymer, second binder, second additive, and solvent are mixed uniformly to obtain the second matrix adhesive slurry. The solid content of the second matrix adhesive slurry is 5%–35%.

[0126] For example, the solid content of the second matrix adhesive slurry can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, etc. Further, the solid content of the second matrix adhesive slurry can be 5% to 25%.

[0127] (2) A first matrix adhesive layer slurry and a second matrix adhesive layer slurry are coated on both sides of the base film by a matrix coating process, and the battery separator is obtained after drying.

[0128] The first matrix adhesive layer slurry and the second matrix adhesive layer slurry can be coated in one step, that is, the first matrix adhesive layer slurry and the second matrix adhesive layer slurry are coated on both sides of the base film simultaneously. Alternatively, the first matrix adhesive layer slurry and the second matrix adhesive layer slurry can be coated in two steps, that is, one type of matrix adhesive layer slurry is first coated on one side of the base film, and then the other type of matrix adhesive layer slurry is coated on the other side of the base film.

[0129] Matrix coating processes can be extrusion coating, screen printing coating, slot coating, transfer coating, or other coating processes, without specific limitations. For example, in a transfer coating process, a first matrix adhesive layer slurry and a second matrix adhesive layer slurry are coated onto the surface of a base film using a rubber roller, and the battery separator is obtained after drying.

[0130] The material of the rubber roller can be set and changed as needed. For example, the material of the rubber roller can be EPDM rubber, styrene-butadiene rubber, butyl rubber, etc.

[0131] The rubber roller has a grid of dots, each dot being raised. The arrangement of these dots can be set and modified based on the morphology and distribution of the first and second adhesive dots. Based on the morphology and distribution of the first adhesive dots, the height of each grid dot can be 0.5 μm to 10 μm, the diameter 250 μm to 500 μm, and the center-to-center distance between any two adjacent first adhesive dots 600 μm to 800 μm. Similarly, based on the morphology and distribution of the second adhesive dots, the height of each grid dot can be 0.5 μm to 10 μm, the diameter 500 μm to 1200 μm, and the center-to-center distance between any two adjacent second adhesive dots 800 μm to 1500 μm.

[0132] In the embodiments of this application, polymers with different glass transition temperatures can be selected and mixed with binders, additives, etc. to form a slurry based on the structural characteristics (thickness, porosity, and compaction density, etc.) of the positive and negative electrode sheets and the characteristics (particle size and specific surface area, etc.) of the active material. Then, a matrix coating process is used to coat the slurry onto the surface of the base film to obtain a matrix coated diaphragm with high adhesion and low air permeability.

[0133] On the other hand, embodiments of this application also provide a method for preparing a thermally composite battery cell, which is as described above. The preparation method includes:

[0134] Step 1: Provide the stacked assembly.

[0135] The stacked assembly includes multiple positive electrode sheets, multiple negative electrode sheets, and two battery separators. The multiple positive electrode sheets are stacked on one side of one of the battery separators, and the multiple negative electrode sheets are stacked between the two battery separators. The number of negative electrode sheets is one more than the number of positive electrode sheets.

[0136] In the embodiments of this application, the positive electrode sheet and the negative electrode sheet can be cut by a feeding system to obtain the positive electrode sheet and the negative electrode sheet of the required size.

[0137] In one possible implementation, the stacked assembly includes multiple first electrode units and one second electrode unit.

[0138] Specifically, two layers of battery separator, negative electrode sheet, and positive electrode sheet can be stacked in the order of battery separator, negative electrode sheet, battery separator, and positive electrode sheet to obtain the first electrode unit; two layers of battery separator and negative electrode sheet can be stacked in the order of battery separator, negative electrode sheet, and battery separator to obtain the second electrode unit.

[0139] Step 2: Perform thermal bonding treatment on the laminated assembly to form a hot-pressed laminated assembly.

[0140] Multiple first electrode units and one second electrode unit are thermally combined to form a hot-pressed laminated assembly.

[0141] The thermal composite process corresponding to the first electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~2.0t, and time of 1s~80s.

[0142] For example, the temperature can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., the pressure can be 0.2t, 0.3t, 0.5t, 0.8t, 1.0t, 1.2t, 1.5t, 1.8t, 2.0t, etc., and the time can be 1s, 2s, 5s, 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, etc.

[0143] In this embodiment, by controlling the thermal bonding temperature corresponding to the first electrode unit, the viscosity of the binder in the battery separator can be activated, promoting the diffusion and fusion of molecular chains at the interface between the positive electrode, negative electrode, and battery separator, thereby improving the bonding strength. By controlling the thermal bonding pressure and thermal bonding time corresponding to the first electrode unit, the interface between the positive electrode, negative electrode, and battery separator can be compacted, while avoiding damage to the pore structure of the negative electrode due to excessive pressure and time.

[0144] The peel force between the negative electrode and the first and second battery separators in the first electrode unit obtained by the above thermal bonding process is ≥2.5N, and the peel force between the positive electrode and the first battery separator is ≥4N. The greater the peel force, the higher the bonding strength. It can be seen that the bonding strength between the positive and negative electrode sheets and the battery separator is relatively high.

[0145] The thermal composite process corresponding to the second electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~3.0t, and time of 1s~180s.

[0146] For example, the temperature can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., the pressure can be 0.2t, 0.3t, 0.5t, 0.8t, 1.0t, 1.2t, 1.5t, 1.8t, 2.0t, 2.5t, 3.0t, etc., and the time can be 1s, 2s, 5s, 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 100s, 120s, 150s, 180s, etc.

[0147] In this embodiment, by controlling the thermal bonding temperature corresponding to the second electrode unit, the adhesiveness of the binder in the battery separator can be activated, promoting the diffusion and fusion of molecular chains at the interface between the negative electrode and the battery separator, thereby improving the bonding strength. By controlling the thermal bonding pressure and thermal bonding time corresponding to the second electrode unit, the interface between the negative electrode and the battery separator can be compacted, while avoiding damage to the pore structure of the negative electrode due to excessive pressure and time.

[0148] The peel force between the negative electrode and the first and second battery separators in the second electrode unit obtained by the above thermal bonding process is ≥2.5N. The greater the peel force, the higher the bonding strength. It can be seen that the bonding strength between the negative electrode and the battery separator is relatively high.

[0149] Step 3: Perform lamination processing on the hot-pressed lamination assembly to obtain a thermal composite cell.

[0150] A thermocomposite battery cell is obtained by stacking hot-pressed lamination assemblies sequentially along the thickness direction of the negative electrode sheet using a lamination device.

[0151] In this embodiment, the positive electrode sheet, negative electrode sheet, and battery separator are thermally bonded together using a thermal bonding process. This improves the adhesion strength between the positive and negative electrode sheets and the battery separator, thereby enhancing the bonding degree of the positive and negative electrode sheets. Simultaneously, it eliminates problems such as powder shedding and delamination during electrode unit transport, increasing the yield rate of electrode units and thus improving the production efficiency of stacked assembly. Furthermore, the thermally bonded battery cell prepared in this embodiment exhibits good liquid retention, good thickness consistency, and high safety and cycle life.

[0152] On the other hand, embodiments of this application also provide a secondary battery, which includes: a casing, an electrolyte contained inside the casing, and a thermally composite battery cell, wherein the thermally composite battery cell is as described above.

[0153] The secondary battery provided in this application embodiment has all the advantages of thermally composite cells. Furthermore, this secondary battery can be a lithium-ion battery or other types of batteries, such as sodium-ion batteries, etc., without specific limitation.

[0154] The technical solution of this application will be described in detail below through specific embodiments.

[0155] In the following specific embodiments, unless otherwise specified, all operations shall be performed under normal conditions or conditions recommended by the manufacturer.

[0156] Example 1

[0157] Example 1 provides a battery separator and a thermally composite battery cell based on the battery separator. The battery separator includes a PE base film, a first matrix adhesive layer, and a second matrix adhesive layer, which are respectively stacked on both sides of the base film. The PE base film has a thickness of 5 μm, the height of the first adhesive dot in the first matrix adhesive layer is 1 μm, and the height of the second adhesive dot in the second matrix adhesive layer is 1 μm.

[0158] The first adhesive point comprises the following components by mass percentage: 55% first polymer, 41% first binder, and 4% first additive. The first polymer is selected from polyacrylonitrile, with a molecular weight of 3wg / mol to 4wg / mol and a glass transition temperature of 90℃ to 100℃. The first binder is selected from polyacrylonitrile, and the first additive is selected from sodium carboxymethyl cellulose.

[0159] The second adhesive point comprises the following components by weight percentage: 55% second polymer, 41% second binder, and 4% second additive. The second polymer is selected from PVDF-HFP with a molecular weight of 50w g / mol to 80w g / mol and a glass transition temperature of -40℃ to -30℃. The second binder is selected from polyacrylonitrile, and the second additive is selected from sodium carboxymethyl cellulose.

[0160] The battery separator was prepared by the following method:

[0161] The first polymer, the first binder, the first additive, and water are mixed evenly to obtain a first matrix adhesive slurry with a solid content of 20%.

[0162] The second polymer, the second binder, the second additive, and water are mixed evenly to obtain the second matrix adhesive slurry, which has a solid content of 20%.

[0163] A transfer coating process is used to coat the first matrix adhesive layer slurry and the second matrix adhesive layer slurry onto the surface of the base film using an EPDM rubber roller. After drying, the battery separator is obtained.

[0164] The thermally composite battery cell based on this battery separator includes 99 first electrode units and 1 second electrode unit arranged in sequence, wherein the number of positive electrode units is 99 and the number of negative electrode units is 100. Each first electrode unit includes a battery separator, a negative electrode, a battery separator, and a positive electrode arranged in sequence. The second electrode unit includes a battery separator, a negative electrode, and a battery separator arranged in sequence. Both surfaces of the negative electrode are bonded to a second matrix adhesive layer of the battery separator, and one surface of the positive electrode is bonded to a first matrix adhesive layer of the battery separator.

[0165] This thermal composite battery cell was prepared by the following method:

[0166] (1) Stack two layers of battery separator, 99 negative electrode plates and 99 positive electrode plates in the order of battery separator, negative electrode plate, battery separator and positive electrode plate to obtain 99 first electrode plate units. Stack two layers of battery separator and 1 negative electrode plate in the order of battery separator, negative electrode plate and battery separator to obtain 1 second electrode plate unit.

[0167] (2) 99 first electrode units and 1 second electrode unit are thermally bonded to form a hot-pressed laminated assembly. The thermal bonding process for the first electrode unit meets the following process parameters: temperature 50℃, pressure 1t, and time 40s. The thermal bonding process for the second electrode unit meets the following process parameters: temperature 50℃, pressure 1.5t, and time 90s.

[0168] (3) The hot-pressed lamination assembly is laminated to obtain a thermal composite cell.

[0169] Example 2

[0170] Example 2 provides a battery separator and a thermally composite battery cell based on the battery separator. The structure of the battery separator is the same as that in Example 1, except that the thickness of the PE base film is 7μm, the height of the first adhesive dot is 3μm, and the height of the second adhesive dot is 3μm.

[0171] The first adhesive point comprises the following components by weight percentage: 55% first polymer, 41% first binder, and 4% first additive. The first polymer is selected from polyimide with a molecular weight of 2w g / mol to 3w g / mol and a glass transition temperature of 250℃ to 270℃. The first binder is selected from polyvinyl acetate, and the first additive is selected from sodium carboxymethyl cellulose.

[0172] The second adhesive point comprises the following components by weight percentage: 55% second polymer, 41% second binder, and 4% second additive. The second polymer is selected from PVDF with a molecular weight of 50 wt g / mol to 80 wt g / mol and a glass transition temperature of -40°C to -30°C. The second binder is selected from polyethylene-co-vinyl acetate, and the second additive is selected from sodium carboxymethyl cellulose.

[0173] The preparation process of the battery separator can be found in Example 1, and will not be repeated here.

[0174] The structure and preparation process of the thermal composite cell based on this battery separator are the same as those of the thermal composite cell in Example 1, and will not be repeated here.

[0175] Example 3

[0176] Example 3 provides a battery separator and a thermally composite battery cell based on the battery separator. The structure of the battery separator is the same as that in Example 1, except that the base film is a PP base film with a thickness of 9 μm, the height of the first adhesive dot is 5 μm, and the height of the second adhesive dot is 5 μm.

[0177] The first adhesive point comprises the following components in the following mass percentages: 55% first polymer and 45% first binder. The first polymer is selected from polymethyl methacrylate with a molecular weight of 2.5 wg / mol to 3.5 wg / mol and a glass transition temperature of 100℃ to 110℃. The first binder is selected from polyvinyl acetate.

[0178] The second adhesive point comprises the following components by mass percentage: 58% second polymer and 42% second binder. The second polymer is selected from polyethylene oxide with a molecular weight of 2000 g / mol to 5000 g / mol and a glass transition temperature of -70℃ to -60℃. The second binder is selected from polyethylene-co-vinyl acetate.

[0179] The preparation process of the battery separator can be found in Example 1, and will not be repeated here.

[0180] The structure of the thermal composite cell based on the battery separator can be found in Example 1, except that the number of positive electrode plates is 149 and the number of negative electrode plates is 150.

[0181] The fabrication process of this thermally composite battery cell can be found in Example 1, except that the thermal composite process for the first electrode unit meets the following process parameters: temperature 80℃, pressure 1.5t, and time 60s. The thermal composite process for the second electrode unit meets the following process parameters: temperature 80℃, pressure 2t, and time 130s.

[0182] Example 4

[0183] Example 4 provides a battery separator and a thermally composite battery cell based on the battery separator. The structure of the battery separator is the same as that in Example 1, except that the base film is a PP base film with a thickness of 9 μm, the height of the first adhesive dot is 7 μm, and the height of the second adhesive dot is 7 μm.

[0184] The first adhesive point comprises the following components in the following mass percentages: 52% first polymer, 43% first binder, and 5% first additive. The first polymer is selected from polymethyl methacrylate with a molecular weight of 2.5 wg / mol to 3.5 wg / mol and a glass transition temperature of 100℃ to 110℃. The first binder is selected from polyimide, and the first additive is selected from sodium carboxymethyl cellulose.

[0185] The second adhesive point comprises the following components by weight percentage: 50% second polymer, 45% second binder, and 5% first additive. The second polymer is selected from polyethylene-co-vinyl acetate with a molecular weight of 2w g / mol to 3w g / mol and a glass transition temperature of -40℃ to -20℃. The second binder is selected from polyethylene oxide, and the second additive is selected from sodium carboxymethyl cellulose.

[0186] The base film is selected from PP.

[0187] The preparation process of the battery separator can be found in Example 1, and will not be repeated here.

[0188] The structure of the thermal composite cell based on the battery separator can be found in Example 1, except that the number of positive electrode plates is 189 and the number of negative electrode plates is 190.

[0189] The fabrication process of this thermally composite battery cell can be found in Example 1, except that the thermal composite process for the first electrode unit meets the following process parameters: temperature 90℃, pressure 2.0t, and time 80s. The thermal composite process for the second electrode unit meets the following process parameters: temperature 90℃, pressure 3.0t, and time 150s.

[0190] Comparative Example 1

[0191] Comparative Example 1 provides a battery separator and a thermally composite battery cell based on the battery separator. The composition of the battery separator is the same as that in Example 1, except that the battery separator includes a base film, a first adhesive layer and a second adhesive layer, which are respectively stacked on both sides of the base film.

[0192] The battery separator is prepared by spray coating, and the specific preparation method is as follows:

[0193] The first polymer, the first binder, and the first additive are mixed evenly to obtain the first adhesive layer slurry.

[0194] The second polymer, the second binder, and the second additive are mixed evenly to obtain the second adhesive slurry.

[0195] The first and second adhesive layers are sprayed onto the surface of the base film using a rotary spraying device, and the battery separator is obtained after drying.

[0196] The structure and preparation process of the thermal composite cell based on this battery separator are the same as those of the thermal composite cell in Example 1, and will not be repeated here.

[0197] This application tested the air permeability, thermal shrinkage rate, and liquid retention rate of the battery separators prepared in Examples 1-4 and Comparative Example 1, and tested the adhesion strength of the thermal composite cells prepared in Examples 1-4 and Comparative Example 1. The relevant test items are shown below:

[0198] Test method for heat shrinkage rate:

[0199] The core steps include: sampling → initial measurement → high-temperature treatment → cooling measurement → calculation of thermal shrinkage rate.

[0200] Sampling: Specifically, cut uniform rectangular battery separator samples with a size of 100mm×100mm from the separator roll material, and cut 3 sheets as a set of parallel samples; draw number axes (XY axes) on the surface of these 3 battery separator samples as the reference for measurement, and determine a mark line L on the reference.

[0201] Initial measurement: Specifically, the coordinates of the marker line L were measured using a laser micrometer (accuracy of 0.01); the measurements were taken twice in the X and Y directions respectively, and the average value was taken to finally determine the coordinates of the marker line as (X0, Y0).

[0202] High-temperature treatment: Specifically, the target temperature of the hot air circulating oven (oven temperature deviation ≤ ±2℃) is set to 110℃. 6mm thick glass plates are pressed on the top and bottom surfaces of each battery separator in this group to fix the position of the battery separator, and then placed in the oven for 1 hour of baking.

[0203] Cooling measurement: Specifically, after the oven is powered off, the diaphragm group is moved into the dryer and cooled to room temperature for 30 minutes. Then, the coordinates of the mark line L are measured using a laser micrometer (accuracy of 0.01). The measurements are taken twice in the X and Y directions respectively, and the average value is taken. Finally, the coordinates of the mark line are determined to be (X1, Y1).

[0204] The lateral thermal shrinkage rate is the change in length of the battery separator in the X direction, calculated using the following formula:

[0205] The longitudinal thermal shrinkage rate is the change in length of the battery separator in the Y direction, calculated using the following formula:

[0206] Methods for testing breathability:

[0207] The air permeability test method follows GB / T36363-2018. The air permeability of the base membrane and the diaphragm at room temperature (25℃) are measured separately. Three diaphragm pieces are cut longitudinally from the membrane roll at 150mm intervals. If the diaphragm width is ≥100mm, the sample size is 100mm × 100mm; if the diaphragm width is <100mm, the sample size is 100mm × diaphragm width. The diaphragm is placed in the test head of the air permeability meter, ensuring a good seal and preventing damage. The initial air pressure is set (usually 1.21 kPa), the air permeability meter is started, and the time required for 100mL of test gas to pass through the diaphragm is recorded. The test is repeated multiple times, and the average value is taken as the air permeability value of the diaphragm. The unit of air permeability value is s / 100mL.

[0208] The testing process for the base membrane is the same as that for the diaphragm, and will not be repeated here.

[0209] Test method for liquid retention rate:

[0210] The battery separator sample was completely immersed in the electrolyte (1M LiPF6 electrolyte of ethylene carbonate (EC) and dimethyl carbonate (DMC) (v / v = 1:1)) and allowed to stand until saturation adsorption. After removal, the surface liquid was drained, and the total mass after liquid absorption was weighed to calculate the liquid absorption volume. Wherein, liquid absorption volume = total mass of battery separator after immersion - initial mass of battery separator.

[0211] After absorbing the electrolyte, the battery separator sample was laid flat on a glass plate, and the surface electrolyte was wiped off with lint-free paper. This process was repeated three times, and the sample was weighed to calculate the electrolyte retention rate. The electrolyte retention rate is calculated as follows: (mass of the battery separator after electrolyte absorption - initial mass of the battery separator) / amount of electrolyte absorbed * 100%.

[0212] Test method for bonding strength of thermally bonded battery cells:

[0213] The thermally bonded area between the electrode and the battery separator in the thermally bonded cell is cut into samples with a length (a) of 100 mm and a width (b) of 20 mm to ensure the integrity of the bonded interface. The free end of the sample is folded 180° and clamped in the upper and lower fixtures of a tensile testing machine. Peeling is performed at a constant rate (e.g., 50 mm / min), and the maximum force value during the peeling process is recorded.

[0214] For the positive electrode, record the maximum force F1 when the positive electrode peels off from the battery separator. Based on the sample width b and the maximum force F1, calculate the adhesion strength σ1 between the positive electrode and the battery separator according to the formula σ=F / b, and take the average value after multiple measurements.

[0215] For the negative electrode sheet, record the maximum force F2 when the negative electrode sheet peels off from the battery separator. Based on the sample width b and the maximum force F2, calculate the adhesion strength σ2 between the negative electrode sheet and the battery separator according to the formula σ=F / b, and take the average value after multiple measurements.

[0216] The test results of Examples 1-4 and Comparative Example 1 are shown in Table 1.

[0217] Table 1

[0218]

[0219] As can be seen from Table 1, compared with Comparative Example 1, the bonding strength between the battery separators of Examples 1-4 and the positive and negative electrode sheets is significantly higher than that of Comparative Example 1, and the liquid retention rate of the battery separators is higher, while the lateral thermal shrinkage rate and longitudinal thermal shrinkage rate are also lower. This demonstrates that the battery separators provided in this application can indeed improve the bonding strength between them and the positive and negative electrode sheets.

[0220] The above description is only for the purpose of enabling those skilled in the art to understand the technical solution of this application, and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A battery separator, characterized in that, The battery separator includes: a base film, a first matrix adhesive layer and a second matrix adhesive layer, wherein the first matrix adhesive layer and the second matrix adhesive layer are respectively stacked on both sides of the base film; The first matrix adhesive layer is used to bond the positive electrode sheet and includes a plurality of first adhesive dots that are distributed in a matrix and raised. The second matrix adhesive layer is used to bond the negative electrode sheet and includes multiple raised second adhesive dots arranged in a matrix. The first adhesive dot includes a first polymer, the second adhesive dot includes a second polymer, and the glass transition temperature of the first polymer is greater than that of the second polymer.

2. The battery separator according to claim 1, characterized in that, The glass transition temperature of the first polymer is 90℃~270℃, and the glass transition temperature of the second polymer is -80℃~45℃.

3. The battery separator according to claim 1, characterized in that, The primary particle size of the first polymer is 50 nm to 500 nm, and the primary particle size of the second polymer is 50 nm to 500 nm.

4. The battery separator according to claim 1, characterized in that, The diameter of the first adhesive dot is 250μm to 500μm, the center distance between any two adjacent first adhesive dots is 600μm to 800μm, and the coverage of the first adhesive dot is 8.0% to 30%. The diameter of the second adhesive dot is 500μm to 1200μm, the center distance between any two adjacent second adhesive dots is 800μm to 1500μm, and the coverage of the second adhesive dot is 30% to 50%.

5. The battery separator according to any one of claims 1 to 4, characterized in that, The first polymer is selected from at least one of polymethyl methacrylate, polyacrylonitrile, and polyimide; The second polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinyl acetate, polyethylene-co-vinyl acetate, and polyethylene oxide.

6. The battery separator according to claim 1, characterized in that, The first adhesive point further includes: a first adhesive and a first additive; Wherein, the mass fraction of the first polymer is 50% to 55%, the mass fraction of the first binder is 40% to 45%, and the mass fraction of the first additive is less than or equal to 5%.

7. The battery separator according to claim 6, characterized in that, The second adhesive point also includes: a second adhesive and a second additive; The second polymer has a mass fraction of 50% to 60%, the second binder has a mass fraction of 35% to 45%, and the second additive has a mass fraction of less than or equal to 5%.

8. The battery separator according to claim 7, characterized in that, The first adhesive and the second adhesive each independently contain at least one of the following polar groups: hydroxyl, carboxyl, imide, nitrile, or ester.

9. The battery separator according to claim 8, characterized in that, The first adhesive and the second adhesive are each independently selected from at least one of polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide and polyethylene oxide.

10. The battery separator according to claim 1, characterized in that, The thickness of the base film is 1μm to 30μm, the height of the first adhesive dot is 0.5μm to 10μm, and the height of the second adhesive dot is 0.5μm to 10μm.

11. A thermally composite battery cell, characterized in that, The thermal composite cell includes multiple positive electrode plates, multiple negative electrode plates, and a battery separator as described in any one of claims 1 to 10; The negative electrode and the positive electrode are stacked alternately, and adjacent negative electrode and positive electrode are separated by the battery separator. The battery separator is bonded to the positive electrode by the first matrix adhesive layer and to the negative electrode by the second matrix adhesive layer.

12. The thermally composite battery cell according to claim 11, characterized in that, The number of negative electrode plates is one more than the number of positive electrode plates, and the thermal composite cell includes a plurality of first electrode plate units and a second electrode plate unit arranged in sequence. The first electrode unit includes a battery separator, a negative electrode, a battery separator, and a positive electrode arranged in sequence. The second electrode unit includes a battery separator, a negative electrode, and a battery separator arranged in sequence.

13. The thermally composite battery cell according to claim 11, characterized in that, The negative electrode sheet has a thickness of 50 μm to 200 μm, a porosity of 20% to 40%, and a compaction density of 1.30 g / cm³. 3 ~1.80g / cm 3 ; The positive electrode sheet has a thickness of 50 μm to 300 μm, a porosity of 10% to 30%, and a compaction density of 2.10 g / cm³. 3 ~3.10g / cm 3 .

14. The thermally composite battery cell according to claim 11, characterized in that, The negative electrode sheet includes a first active material, the median particle size of which is 0.5 μm to 2.0 μm, and the specific surface area is 10 m². 2 / g~15m 2 / g; The positive electrode sheet includes a second active material, the second active material having a median particle size of 10.0 μm to 15.0 μm and a specific surface area of ​​1.0 m². 2 / g~2.5m 2 / g.

15. A method for preparing a thermally composite battery cell, characterized in that, The thermal composite battery cell is as described in any one of claims 11 to 14, and the preparation method includes: A stacking assembly is provided, the stacking assembly including a plurality of positive electrode sheets, a plurality of negative electrode sheets, and two layers of battery separator, wherein the plurality of positive electrode sheets are stacked on one side surface of one of the battery separator layers, and the plurality of negative electrode sheets are stacked between the two layers of battery separator. The laminated assembly is subjected to thermal bonding treatment to form a hot-pressed laminated assembly; The hot-pressed lamination assembly is laminated to obtain the thermal composite cell.

16. The preparation method according to claim 15, characterized in that, The stacked assembly includes multiple first electrode units and one second electrode unit; The process of thermally bonding the laminated assembly to form a hot-pressed laminated assembly includes: Multiple first electrode units and second electrode units are thermally composited to form a hot-pressed laminated assembly; The thermal composite process corresponding to the first electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~2.0t, and time of 1s~80s. The thermal composite process corresponding to the second electrode unit satisfies at least one of the following process parameters: temperature of 30℃~90℃, pressure of 0.2t~3.0t, and time of 1s~180s.

17. A secondary battery, characterized in that, The secondary battery includes: a casing, an electrolyte contained inside the casing, and a thermally composite battery cell, wherein the thermally composite battery cell is as described in any one of claims 11 to 14.

Images