A secondary battery and an electronic device

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises an electrode assembly, the electrode assembly is in a winding structure, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, a first separator and a second separator, the negative electrode sheet is located between the first separator and the second separator, the first separator comprises a first base film and a first adhesive layer, the second separator comprises a second base film and a second adhesive layer, the first adhesive layer comprises a first adhesive, and the second adhesive layer comprises a second adhesive. The first base film is a non-woven fabric film, the first adhesive comprises at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The second base film is a microporous film, and the second adhesive comprises at least one of polyimide, polyvinyl alcohol or sodium carboxymethyl cellulose. Through the above arrangement, the adhesion between the separator and the positive electrode sheet and the adhesion between the separator and the negative electrode sheet can be improved, the cycle performance and high-temperature hot box performance of the secondary battery are improved, and the secondary battery also has a high energy density.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness, and are widely used in aviation, aerospace, marine, and electric vehicle industries. The performance of the separator in a lithium-ion battery determines its interface structure and internal resistance, directly affecting its capacity, cycle life, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of lithium-ion batteries.

[0003] The separator consists of a base membrane and an adhesive layer. Commonly used base membranes include polyolefin microporous membranes or nonwoven membranes. Polyolefin microporous membranes include polypropylene (PP) microporous membranes or polyethylene (PE) microporous membranes. Nonwoven membranes are thicker than polyolefin microporous membranes, which reduces the energy density of lithium-ion batteries. The adhesive layer includes polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyimide (PI), polyvinyl alcohol (PVA), or sodium carboxymethyl cellulose (CMC-Na). PVDF and PVDF-HFP have good compatibility with the electrolyte and good adhesion to the electrode, but they have low melting points, ranging from 115°C to 170°C. They melt at higher temperatures, resulting in ineffective adhesion of active material particles to the electrode. PI, PVA, and CMC-Na have high melting points, exceeding 200°C, which can improve the thermal stability of the separator at high temperatures. However, they cannot produce effective swelling, thus failing to effectively improve adhesion and ionic conductivity, which reduces the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device that can improve the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, thereby improving the cycle performance and high-temperature thermal performance of the secondary battery, while also giving the secondary battery a higher energy density. The specific technical solution is as follows:

[0005] A first aspect of this application provides a secondary battery comprising an electrode assembly having a wound structure. The electrode assembly includes a positive electrode, a negative electrode, a first separator, and a second separator. The negative electrode is located between the first separator and the second separator, and the first separator is located between the positive electrode and the negative electrode. The first separator includes a first base film and a first adhesive layer. The second separator includes a second base film and a second adhesive layer. The first adhesive layer includes a first adhesive, and the second adhesive layer includes a second adhesive. The first base film is a non-woven fabric film, and the material of the first base film includes at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone. The first adhesive includes at least one selected from polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The second base membrane is a microporous membrane, and the material of the second base membrane includes a polyolefin, wherein the polymer monomer of the polyolefin includes at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. The second binder includes at least one selected from polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose.

[0006] This application utilizes a nonwoven fabric membrane with high mechanical strength, high glass transition temperature, and high porosity, combined with a first adhesive layer with high ionic conductivity and low melting point to form a first separator. The nonwoven fabric membrane can store a large amount of electrolyte, and the high ionic conductivity of the first adhesive layer improves the cycle performance of the secondary battery. Simultaneously, due to the high mechanical strength and high glass transition temperature of the nonwoven fabric membrane, it shrinks less at high temperatures, compensating for the lower melting point of the first adhesive layer, which cannot effectively prevent the shrinkage of the separator base membrane at high temperatures, thus improving the high-temperature thermal performance of the secondary battery. A second separator is formed by combining a microporous membrane with a lower glass transition temperature, thinner thickness, and higher chemical stability with a second adhesive layer with a higher melting point. This compensates for the energy density loss caused by the larger thickness of the first separator. Furthermore, the second adhesive layer, which maintains good adhesion at high temperatures, reduces the possibility of shrinkage of the lower-melting-point microporous membrane, resulting in good high-temperature thermal performance of the secondary battery. Because the first separator is thicker and the non-woven membrane has higher strength, placing the first separator between the positive and negative electrodes can better reduce the possibility of short circuits caused by separator shrinkage at high temperatures, and also reduce the possibility of large positive electrode active material particles puncturing the separator and causing short circuits. The secondary battery of this application, by using different types of first and second separators, can improve the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, thereby improving the cycle performance and high-temperature thermal performance of the secondary battery, while also giving it a higher energy density.

[0007] In one embodiment of this application, the material of the first base film comprises polyethylene terephthalate, and the first binder comprises polyvinylidene fluoride-hexafluoropropylene copolymer. The material of the second base film comprises a polyolefin, wherein the polymerizing monomer of the polyolefin comprises at least one of ethylene or propylene, and the second binder comprises polyimide. By selecting the materials and first adhesives of the first base membrane and the second base membrane, respectively, a first separator is formed by combining a nonwoven fabric membrane with high mechanical strength, high glass transition temperature, and high porosity with a first adhesive layer with high ionic conductivity and low melting point. The nonwoven fabric membrane can store more electrolyte, and combined with the high ionic conductivity of the first adhesive layer, it can further improve the cycle performance of the secondary battery. At the same time, due to the high mechanical strength and high glass transition temperature of the nonwoven fabric membrane, it shrinks less at high temperatures, which can compensate for the problem that the first adhesive layer has a low melting point and cannot effectively prevent the separator base membrane from shrinking at high temperatures, thus further improving the high-temperature thermal performance of the secondary battery. A second separator is formed by combining a microporous membrane with a low glass transition temperature, thinner thickness, and higher chemical stability with a second adhesive layer with a higher melting point, which can compensate for the energy density loss caused by the large thickness of the first separator. At the same time, the second adhesive layer, which still has good adhesion at high temperatures, can reduce the possibility of shrinkage of the microporous membrane with a lower melting point at high temperatures, further improving the high-temperature thermal performance of the secondary battery.

[0008] In one embodiment of this application, the negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the negative current collector. Along the winding direction of the electrode assembly, the length of the first negative electrode material layer is greater than the length of the second negative electrode material layer. The first separator is located on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is located on one side of the second negative electrode material layer of the negative electrode sheet. With this configuration, the first base film has a larger porosity and the first binder has greater swelling, which is beneficial for the first separator to store more electrolyte. When the first separator is located on one side of the first negative electrode material layer of the negative electrode sheet, it is beneficial to adsorb more electrolyte at the A-side of the negative electrode sheet of the secondary battery, reducing the risk of lithium plating at the interface between the electrolyte and the negative electrode sheet due to electrolyte bridging in the later stages of the secondary battery cycle. Simultaneously, by setting the above structure in the secondary battery, while maintaining energy density, it is beneficial to improve the high-temperature thermal performance and cycle performance of the secondary battery.

[0009] In one embodiment of this application, the average particle size of the first binder is 4 μm to 15 μm, and the average particle size of the second binder is 10 μm to 20 μm. By adjusting the average particle size of the first binder and the second binder within the scope of this application, the first binder and the second binder have suitable average particle sizes, enabling the first binder slurry in the preparation process of the first binder layer to have suitable viscosity, and the second binder slurry in the preparation process of the second binder layer to have suitable viscosity. This results in the first binder layer and the second binder layer having high adhesion, which can further improve the adhesion between the separator and the positive electrode sheet, and between the separator and the negative electrode sheet, which is beneficial to the transport of lithium ions, thereby further improving the cycle performance of the secondary battery. At the same time, the secondary battery also has good high-temperature thermal performance.

[0010] In one embodiment of this application, the coating weight of the first adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 The coating weight of the second adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 By adjusting the coating weight of the first adhesive layer and the coating weight of the second adhesive layer within the scope of this application, a high bonding force is achieved between the first separator and the positive electrode and / or negative electrode, and between the second separator and the positive electrode and / or negative electrode. This strengthens the interface between the first separator and the positive electrode and / or negative electrode, and between the second separator and the positive electrode and / or negative electrode, which is beneficial for lithium-ion transport and can further improve the cycle performance of the secondary battery.

[0011] In one embodiment of this application, the thickness of the first base film is 10 μm to 15 μm, and the thickness of the second base film is 3 μm to 9 μm. By adjusting the thickness of the first and second base films within the scope of this application, it is beneficial to reduce the risk of lithium dendrites piercing the second base film and causing a short circuit in the secondary battery during cycling. The first and second base films have good mechanical strength and thermal stability, and are not easily shrunk at high temperatures, which can further improve the high-temperature thermal performance of the secondary battery. At the same time, it makes the lithium ion transport distance during the cycling process moderate, which can further improve the cycling performance of the secondary battery. In addition, the total thickness of the first and second base films is small, so the secondary battery has a high energy density.

[0012] In one embodiment of this application, the porosity of the first base membrane is 40% to 70%, and the porosity of the second base membrane is 5% to 50%. By adjusting the porosity of the first and second base membranes within the scope of this application, the first and second separators have higher mechanical strength and better thermal stability, which can further improve the high-temperature thermal performance of the secondary battery; at the same time, the first and second separators have stronger liquid absorption and retention capabilities, which is beneficial to the transport of lithium ions, thereby further improving the cycle performance of the secondary battery.

[0013] In one embodiment of this application, the first separator further includes a first ceramic coating located between the first base film and the first adhesive layer, and / or the second separator further includes a second ceramic coating located between the second base film and the second adhesive layer. The first ceramic coating includes first ceramic particles, and the second ceramic coating includes second ceramic particles. The first ceramic particles and the second ceramic particles are each independently selected from at least one of alumina, boehmite (γ-AlOOH), silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. The first separator further includes the first ceramic coating, and / or the second separator further includes the second ceramic coating. The types of first ceramic particles in the first ceramic coating and the types of second ceramic particles in the second ceramic coating, within the scope of this application, can further improve the thermal stability and mechanical strength of the first and second separators, effectively slowing down the shrinkage of the first and second separators at high temperatures, thereby further improving the high-temperature thermal performance of the secondary battery.

[0014] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0015] The beneficial effects of this application are:

[0016] This application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly with a wound structure. The electrode assembly includes a positive electrode, a negative electrode, a first separator, and a second separator. The negative electrode is located between the first separator and the second separator. The first separator includes a first base film and a first adhesive layer. The second separator includes a second base film and a second adhesive layer. The first adhesive layer includes a first adhesive, and the second adhesive layer includes a second adhesive. The first base film is a non-woven fabric film, and the material of the first base film includes at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenylene oxide), polyarylether sulfone ketone, aramid, or aramid sulfone. The first adhesive includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The second base membrane is a microporous membrane, and its material includes polyolefins. The polymer monomers of the polyolefin include at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. The second binder includes at least one selected from polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. By using different types of first and second separators in combination, the secondary battery of this application can improve the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, thereby improving the cycle performance and high-temperature thermal performance of the secondary battery, while also giving the secondary battery a higher energy density.

[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0019] Figure 1 This is a schematic diagram of the structure of an electrode assembly according to one embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the electrode assembly according to another embodiment of this application;

[0021] Figure 3 This is a schematic diagram of the electrode assembly according to another embodiment of this application;

[0022] Figure 4 This is a schematic diagram of the electrode assembly according to another embodiment of this application;

[0023] Figure 5This is a schematic diagram of the electrode assembly according to another embodiment of this application.

[0024] Figure label:

[0025] Electrode assembly 100; first separator 10; first base film 11; first adhesive layer 12; first ceramic coating 13; second separator 20; second base film 21; second adhesive layer 22; second ceramic coating 23; negative electrode 30; negative current collector 31; negative electrode material layer 32; first negative electrode material layer 33; second negative electrode material layer 34; positive electrode 40; positive current collector 41; positive electrode material layer 42. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0028] This application provides a secondary battery, which includes an electrode assembly. The electrode assembly has a wound structure, and the winding direction of the electrode assembly is defined as the W direction. The electrode assembly includes a positive electrode, a negative electrode, a first separator, and a second separator. Those skilled in the art should understand that the winding directions of the positive electrode, negative electrode, first separator, and second separator are the same as the winding direction of the electrode assembly. To facilitate understanding of the positional relationship of the positive electrode, negative electrode, first separator, and second separator in the electrode assembly, Figure 1 A partial structural schematic diagram of the electrode assembly after it has been unwound along the winding direction W is shown. Figure 1 As shown, the electrode assembly 100 includes a first separator 10, a second separator 20, a negative electrode 30, and a positive electrode 40. The negative electrode 30 is located between the first separator 10 and the second separator 20. The first separator 10 is located between the positive electrode 40 and the negative electrode 30. The first separator 10 includes a first base film 11 and a first adhesive layer 12, with the first adhesive layer 12 disposed on both sides of the first base film 11. The second separator 20 includes a second base film 21 and a second adhesive layer 22, with the second adhesive layer 22 disposed on both sides of the second base film 21. The negative electrode 30 includes a negative current collector 31 and negative electrode material layers 32 disposed on both surfaces of the negative current collector 31. The positive electrode 40 includes a positive current collector 41 and positive electrode material layers 42 disposed on both surfaces of the positive current collector 41.

[0029] The first adhesive layer includes a first adhesive, and the second adhesive layer includes a second adhesive. The first base membrane is a non-woven membrane, and the material of the first base membrane includes at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate (PET), poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone. The first adhesive includes at least one selected from polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The second base membrane is a microporous membrane, and the material of the second base membrane includes a polyolefin, and the polymerizing monomer of the polyolefin includes at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. The second adhesive includes at least one selected from polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose.

[0030] Currently, commonly used base membranes in separators include microporous membranes or nonwoven membranes. Microporous membranes are made of polyolefins, such as polypropylene (PP) microporous membranes or polyethylene (PE) microporous membranes. Nonwoven membranes have a more uniform pore size distribution and higher porosity, exhibiting good thermal and dimensional stability. When applied to secondary batteries, they offer advantages such as higher mechanical strength and stronger liquid absorption and retention capabilities, resulting in better charge-discharge performance and safety. However, nonwoven membranes are thicker than polyolefin microporous membranes, leading to thickness loss and thus reducing the energy density of the secondary battery. The binders in the separator's adhesive layer include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyimide (PI), polyvinyl alcohol (PVA), or sodium carboxymethyl cellulose (CMC-Na). PVDF and PVDF-HFP have low crystallinity and glass transition temperature, resulting in good compatibility with electrolytes and adhesion to electrodes. However, they have low melting points, ranging from 115°C to 170°C. When the ambient temperature approaches the melting point of these binders, they melt, preventing effective adhesion to the positive or negative electrode and hindering further prevention of membrane shrinkage. PI, PVA, and CMC-Na have higher melting points, exceeding 200°C, allowing for effective adhesion to the positive or negative electrode at higher temperatures and improving the thermal stability of the separator at high temperatures. However, these binders cannot effectively swell in the electrolyte, failing to effectively improve adhesion and ionic conductivity, thus reducing the electrochemical performance of the secondary battery. In this application, high temperature refers to a temperature above 180°C.

[0031] This application utilizes a nonwoven fabric membrane with high mechanical strength, high glass transition temperature, and high porosity, combined with a first adhesive layer with high ionic conductivity and low melting point to form a first separator. The nonwoven fabric membrane can store a large amount of electrolyte, and the high ionic conductivity of the first adhesive layer improves the cycle performance of the secondary battery. Simultaneously, due to the high mechanical strength and high glass transition temperature of the nonwoven fabric membrane, it shrinks less at high temperatures, compensating for the lower melting point of the first adhesive layer, which cannot effectively prevent the shrinkage of the separator base membrane at high temperatures, thus improving the high-temperature thermal performance of the secondary battery. A second separator is formed by combining a microporous membrane with a lower glass transition temperature, thinner thickness, and higher chemical stability with a second adhesive layer with a higher melting point. This compensates for the energy density loss caused by the larger thickness of the first separator. Furthermore, the second adhesive layer, which maintains good adhesion at high temperatures, reduces the possibility of shrinkage of the lower-melting-point microporous membrane, resulting in good high-temperature thermal performance of the secondary battery. Because the first separator is thicker and the non-woven membrane has higher strength, placing the first separator between the positive and negative electrodes can better reduce the possibility of short circuits caused by separator shrinkage at high temperatures, and also reduce the possibility of large positive electrode active material particles puncturing the separator and causing short circuits. The secondary battery of this application, by using different types of first and second separators, can improve the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, thereby improving the cycle performance and high-temperature thermal performance of the secondary battery, while also giving it a higher energy density.

[0032] In one embodiment of this application, the first base film is made of polyethylene terephthalate, and the first binder is made of polyvinylidene fluoride-hexafluoropropylene copolymer. The second base film is made of polyolefin, wherein the polymerizing monomer of the polyolefin includes at least one of ethylene or propylene, and the second binder includes polyimide. By selecting the materials and first adhesives of the first base membrane and the second base membrane, respectively, a first separator is formed by combining a nonwoven fabric membrane with high mechanical strength, high glass transition temperature, and high porosity with a first adhesive layer with high ionic conductivity and low melting point. The nonwoven fabric membrane can store more electrolyte, and combined with the high ionic conductivity of the first adhesive layer, it can further improve the cycle performance of the secondary battery. At the same time, due to the high mechanical strength and high glass transition temperature of the nonwoven fabric membrane, it shrinks less at high temperatures, which can compensate for the problem that the first adhesive layer has a low melting point and cannot effectively prevent the separator base membrane from shrinking at high temperatures, thus further improving the high-temperature thermal performance of the secondary battery. A second separator is formed by combining a microporous membrane with a low glass transition temperature, thinner thickness, and higher chemical stability with a second adhesive layer with a higher melting point, which can compensate for the energy density loss caused by the large thickness of the first separator. At the same time, the second adhesive layer, which still has good adhesion at high temperatures, can reduce the possibility of shrinkage of the microporous membrane with a lower melting point at high temperatures, further improving the high-temperature thermal performance of the secondary battery.

[0033] In one embodiment of this application, such as Figure 2 As shown, the negative electrode 30 includes a negative current collector 31 and a first negative electrode material layer 33 and a second negative electrode material layer 34 located on both sides of the negative current collector 31. Along the winding direction of the electrode assembly, i.e., the W direction, one end of the first negative electrode material layer 33 and the second negative electrode material layer 34 are flush, and the length of the other end of the first negative electrode material layer 33 is greater than the length of the other end of the second negative electrode layer 34. The first separator 10 is located on one side of the first negative electrode material layer 33 of the negative electrode 30, and the second separator 20 is located on one side of the second negative electrode material layer 34 of the negative electrode 30. With the above arrangement, the porosity of the first base film is large and the swelling of the first binder is large, which is beneficial for the first separator to store more electrolyte. When the first separator is located on one side of the first negative electrode material layer of the negative electrode, it is beneficial to adsorb more electrolyte at the A side of the negative electrode of the secondary battery, reducing the risk of lithium deposition at the interface between the electrolyte and the negative electrode due to electrolyte bridging in the later stages of the secondary battery cycle. Meanwhile, by incorporating the aforementioned structure into the secondary battery, the high-temperature thermal performance and cycle performance of the secondary battery can be improved while maintaining energy density. In this application, the A-side of the negative electrode sheet refers to one side of the negative electrode sheet that includes the first negative electrode material layer, i.e., the side of the negative electrode sheet with the longer negative electrode material layer.

[0034] In one embodiment of this application, the negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the negative current collector. Along the winding direction of the electrode assembly, i.e., the W direction, the lengths at both ends of the first negative electrode material layer are greater than the lengths at both ends of the second negative electrode material layer. A first separator is located on one side of the first negative electrode material layer of the negative electrode sheet, and a second separator is located on one side of the second negative electrode material layer of the negative electrode sheet. With this configuration, the porosity of the first base film is relatively large, and the swelling of the first binder is relatively large, which is beneficial for the first separator to store more electrolyte. When the first separator is located on one side of the first negative electrode material layer of the negative electrode sheet, it is beneficial to adsorb more electrolyte at the A-side of the negative electrode sheet of the secondary battery, reducing the risk of lithium plating at the interface between the electrolyte and the negative electrode sheet due to electrolyte bridging in the later stages of the secondary battery cycle. Simultaneously, by setting the above structure in the secondary battery, while maintaining energy density, it is beneficial to improve the high-temperature thermal performance and cycle performance of the secondary battery.

[0035] In one embodiment of this application, the average particle size D1 of the first adhesive is from 4 μm to 15 μm. Exemplarily, the average particle size D1 of the first adhesive can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range consisting of any two of the above values. The average particle size D2 of the second adhesive is from 10 μm to 20 μm. Exemplarily, the average particle size D2 of the second adhesive can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or a range consisting of any two of the above values. Within the scope of this application, by adjusting the average particle size D1 of the first binder and the average particle size D2 of the second binder, the first binder and the second binder have suitable average particle sizes, which enables the first binder slurry in the preparation process of the first binder layer to have suitable viscosity and the second binder slurry in the preparation process of the second binder layer to have suitable viscosity. This results in the first binder layer and the second binder layer having high adhesion, which can further improve the adhesion between the separator and the positive electrode sheet and between the separator and the negative electrode sheet, which is beneficial to the transport of lithium ions, thereby further improving the cycle performance of the secondary battery. At the same time, the secondary battery also has good high-temperature thermal performance.

[0036] In one embodiment of this application, the coating weight CW1 of the first adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 For example, the coating weight CW1 of the first adhesive layer can be 0.0004 mg / mm². 2 0.0006 mg / mm 2 0.0008 mg / mm 2 0.001 mg / mm 2 0.0012 mg / mm 2 0.0014 mg / mm 2 0.0016 mg / mm 2 0.0018 mg / mm 2 0.002 mg / mm 2 Or it can be a range consisting of any two of the above values. The coating weight CW2 of the second adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 For example, the coating weight CW2 of the second adhesive layer can be 0.0004 mg / mm². 2 0.0006 mg / mm 2 0.0008 mg / mm 2 0.001 mg / mm 2 0.0012 mg / mm2 0.0014 mg / mm 2 0.0016 mg / mm 2 0.0018 mg / mm 2 0.002 mg / mm 2 Or it can be a range consisting of any two of the above values. By adjusting the coating weight CW1 of the first adhesive layer and the coating weight CW2 of the second adhesive layer within the scope of this application, the first separator and the positive electrode and / or negative electrode, and the second separator and the positive electrode and / or negative electrode have a high adhesion force, which can strengthen the interface between the first separator and the positive electrode and / or negative electrode, and between the second separator and the positive electrode and / or negative electrode, which is beneficial to the transport of lithium ions and can further improve the cycle performance of the secondary battery.

[0037] In one embodiment of this application, the thickness H1 of the first base film is 10 μm to 15 μm. Exemplarily, the thickness H1 of the first base film can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range consisting of any two of the above values. The thickness H2 of the second base film is 3 μm to 9 μm. Exemplarily, the thickness H2 of the second base film can be 3 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or a range consisting of any two of the above values. By adjusting the thickness H1 of the first base film and the thickness H2 of the second base film within the scope of this application, it is beneficial to reduce the risk of lithium dendrites piercing the second base film and causing a short circuit in the secondary battery during the cycling process. The first and second base films have good mechanical strength and thermal stability, and are not easily shrunk at high temperatures, which can further improve the high-temperature thermal performance of the secondary battery. At the same time, it makes the lithium ion transport distance during the cycling process moderate, which can further improve the cycling performance of the secondary battery. In addition, the total thickness of the first and second base films is small, so the secondary battery has a high energy density.

[0038] In one embodiment of this application, the porosity P1 of the first base membrane is 40% to 70%. Exemplarily, the porosity P1 of the first base membrane can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, or a range consisting of any two of the above values. The porosity P2 of the second base membrane is 5% to 50%. Exemplarily, the porosity P2 of the second base membrane can be 5%, 7%, 9%, 10%, 13%, 15%, 17%, 20%, 23%, 25%, 27%, 30%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, 50%, or a range consisting of any two of the above values. Within the scope of this application, by adjusting the porosity P1 of the first base membrane and the porosity P2 of the second base membrane, the first and second separators have higher mechanical strength and better thermal stability, which can further improve the high-temperature thermal performance of the secondary battery; at the same time, the first and second separators have stronger liquid absorption and retention capabilities, which is beneficial to the transport of lithium ions, thereby further improving the cycle performance of the secondary battery.

[0039] In one embodiment of this application, the first diaphragm further includes a first ceramic coating located between the first base film and the first adhesive layer, and / or the second diaphragm further includes a second ceramic coating located between the second base film and the second adhesive layer. The first ceramic coating includes first ceramic particles, and the second ceramic coating includes second ceramic particles. The first ceramic particles and the second ceramic particles are each independently selected from at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0040] In one embodiment of this application, such as Figure 3 As shown, the first separator 10 further includes a first ceramic coating 13 located between the first base membrane 11 and the first adhesive layer 12. The first ceramic coating 13 includes first ceramic particles selected from at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. The first separator further includes the first ceramic coating, and the type of first ceramic particles in the first ceramic coating is within the scope of this application, which can further improve the thermal stability and mechanical strength of the first separator, effectively slow down the shrinkage of the first separator at high temperatures, thereby further improving the high-temperature thermal performance of the secondary battery.

[0041] In one embodiment of this application, such as Figure 4As shown, the second separator 20 further includes a second ceramic coating 23 located between the second base membrane 21 and the second adhesive layer 22. The second ceramic coating 23 includes second ceramic particles selected from at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. The second separator further includes a second ceramic coating, and the type of second ceramic particles in the second ceramic coating is within the scope of this application, which can further improve the thermal stability and mechanical strength of the second separator, effectively slow down the shrinkage of the second separator at high temperatures, thereby further improving the high-temperature thermal performance of the secondary battery.

[0042] In one embodiment of this application, such as Figure 5 As shown, the first separator 10 further includes a first ceramic coating 13 located between the first base membrane 11 and the first adhesive layer 12, and the second separator 20 further includes a second ceramic coating 23 located between the second base membrane 21 and the second adhesive layer 22. The first ceramic coating 13 includes first ceramic particles, and the second ceramic coating 23 includes second ceramic particles. The first ceramic particles and the second ceramic particles are each independently selected from at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. The first separator further includes the first ceramic coating, and the second separator further includes the second ceramic coating. The types of first ceramic particles in the first ceramic coating and the types of second ceramic particles in the second ceramic coating are within the scope of this application, which can further improve the thermal stability and mechanical strength of the first separator and the second separator, and can effectively slow down the shrinkage of the first separator and the second separator at high temperatures, thereby further improving the high-temperature thermal performance of the secondary battery.

[0043] In one embodiment of this application, the first ceramic coating further includes a third adhesive, and the second ceramic coating further includes a fourth adhesive. This application does not impose any particular limitation on the types of the third and fourth adhesives, as long as they achieve the purpose of this application. For example, the third and fourth adhesives are each independently selected from at least one of styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, or polyacrylonitrile. This application does not impose any particular limitation on the content of the first ceramic particles and the third adhesive in the first ceramic coating, or the content of the second ceramic particles and the fourth adhesive in the second ceramic coating. Those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the coating weight of the first and second ceramic coatings. Those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0044] This application does not impose any particular limitation on the weight-average molecular weight of the material of the first base film, as long as it can achieve the purpose of this application. For example, the weight-average molecular weight of the material of the first base film can be 2 × 10⁻⁶. 5 Up to 1.5×10 6 This application does not impose any particular limitation on the weight-average molecular weight of the material of the second base film, as long as it can achieve the purpose of this application. For example, the weight-average molecular weight of the material of the second base film can be 2 × 10⁻⁶. 5 Up to 1.5×10 6 This application does not impose any particular limitation on the preparation method of the microporous membrane, as long as it achieves the purpose of this application. For example, the microporous membrane can be prepared from materials within the scope of this application by a wet or dry process using uniaxial or biaxial stretching, or by a thermally induced phase separation method. This application does not impose any particular limitation on the preparation method of the nonwoven membrane, as long as it achieves the purpose of this application. For example, the nonwoven membrane can be prepared from materials within the scope of this application by at least one of meltblowing, spunbonding, wet papermaking, hydroentangling, needle punching, or hot rolling. In this application, it is understood that the material of the first base membrane is the same as the material of the nonwoven membrane, and the material of the second base membrane is the same as the material of the microporous membrane. Alternatively, commercially available nonwoven membranes and microporous membranes of different materials can be selected, and the first and second base membranes can be selected from the desired materials. This application has no particular limitations, as long as it achieves the purpose of this application.

[0045] This application does not impose any particular limitation on the weight-average molecular weight (Mw) of the first adhesive, as long as it achieves the purpose of this application. For example, the weight-average molecular weight of the first adhesive can be 6 × 10⁻⁶. 5 Up to 9×10 6 This application does not impose any particular limitation on the weight-average molecular weight of the second adhesive, as long as it achieves the purpose of this application. For example, the weight-average molecular weight of the second adhesive can be 5 × 10⁻⁶. 5 Up to 7×10 6 .

[0046] In one embodiment of this application, the first adhesive layer may further include a first thickener, and the second adhesive layer may further include a second thickener. Applying the first thickener to the first adhesive layer and the second thickener to the second adhesive layer helps to increase the stability of the first and second adhesive layer slurries and prevents the sedimentation of the components in the first and second adhesive layer slurries. This application does not particularly limit the types of the first and second thickeners, as long as they can achieve the purpose of this application. For example, the first and second thickeners are each independently selected from at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide, or sodium alginate. This application does not particularly limit the content of the first thickener in the first adhesive layer and the content of the second thickener in the second adhesive layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, based on the mass of the first adhesive layer, the mass percentage of the first thickener is 0.3% to 6%; based on the mass of the second adhesive layer, the mass percentage of the second thickener is 0.3% to 6%. This application does not impose any particular restrictions on the content of the first adhesive in the first adhesive layer and the content of the second adhesive in the second adhesive layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, based on the mass of the first adhesive layer, the mass percentage content of the first adhesive is 94% to 99.7%; based on the mass of the second adhesive layer, the mass percentage content of the second adhesive is 94% to 99.7%.

[0047] This application does not impose any particular limitation on the preparation method of the first diaphragm, as long as it can achieve the purpose of this application. For example, the preparation method of the first diaphragm includes, but is not limited to, the following steps: (1) mixing the first adhesive and the first thickener evenly to obtain a first adhesive layer slurry; (2) coating the first adhesive layer slurry on one surface of the first base film, and drying it to obtain a first diaphragm with the first adhesive layer coated on one side; (3) repeating the above steps on the other surface of the first base film to obtain the first diaphragm.

[0048] In another embodiment of this application, the preparation method of the first diaphragm may include, but is not limited to, the following steps: (1) mixing the first binder and the first thickener evenly to obtain a first adhesive layer slurry; (2) mixing the first ceramic particles and the third binder evenly to obtain a first ceramic coating slurry; (3) coating the first adhesive layer slurry on one surface of the first base film, and after drying, forming a first adhesive layer on one surface of the first base film; coating the first ceramic coating slurry on the other surface of the first base film, and after drying, forming a first ceramic coating on the other surface of the first base film; then coating the first adhesive layer slurry on the surface of the first ceramic coating away from the first base film, and after drying, forming another first adhesive layer on the surface of the first ceramic coating away from the first base film, thus obtaining the first diaphragm.

[0049] This application does not impose any particular limitation on the preparation method of the second diaphragm, as long as it can achieve the purpose of this application. For example, the preparation method of the second diaphragm includes, but is not limited to, the following steps: (1) mixing the second binder and the second thickener evenly to obtain a second adhesive layer slurry; (2) coating the second adhesive layer slurry on one surface of the second base film, and drying it to obtain a second diaphragm with a second adhesive layer coated on one side; (3) repeating the above steps on the other surface of the second base film to obtain the second diaphragm.

[0050] In another embodiment of this application, the preparation method of the second diaphragm may include, but is not limited to, the following steps: (1) mixing the second binder and the second thickener evenly to obtain a second adhesive layer slurry; (2) mixing the second ceramic particles and the fourth binder evenly to obtain a second ceramic coating slurry; (3) coating the second adhesive layer slurry on one surface of the second base film, and after drying, forming a second adhesive layer on one surface of the second base film; first coating the second ceramic coating slurry on the other surface of the second base film, and after drying, forming a second ceramic coating on the other surface of the second base film; then coating the second adhesive layer slurry on the surface of the second ceramic coating away from the second base film, and after drying, forming another second adhesive layer on the surface of the second ceramic coating away from the second base film, thus obtaining the second diaphragm.

[0051] This application does not impose any particular restrictions on the method of controlling the average particle size of the first adhesive and the average particle size of the second adhesive, as long as the purpose of this application can be achieved. For example, commercially available first and second adhesives with different average particle sizes can be selected, and the average particle sizes of the first and second adhesives can be tested using the test method of "average particle size test of first and second adhesives" in this application, and the first and second adhesives with the desired average particle size can be selected.

[0052] In this application, the coating weight of the first adhesive layer and the coating weight of the second adhesive layer can be controlled by means known to those skilled in the art. For example, when coating the first adhesive layer slurry onto the surface of the first base film, the coating amount of the first adhesive layer slurry can be increased to increase the coating weight of the first adhesive layer, based on a certain solid content of the first adhesive layer slurry; when coating the second adhesive layer slurry onto the surface of the second base film, the coating amount of the second adhesive layer slurry can be increased to increase the coating weight of the second adhesive layer, based on a certain solid content of the second adhesive layer slurry. This application does not impose any particular restrictions, as long as the purpose of this application can be achieved.

[0053] This application does not impose any particular restrictions on the method of controlling the thickness of the first base film and the second base film, as long as the purpose of this application can be achieved. For example, commercially available first and second base films with different thicknesses can be selected, and the thicknesses of the first and second base films can be tested using the test method for "thickness test of the first and second base films" in this application, and the desired thickness of the first and second base films can be selected.

[0054] This application does not impose any particular restrictions on the method of controlling the porosity of the first base membrane and the second base membrane, as long as the purpose of this application can be achieved. For example, commercially available nonwoven membranes and microporous membranes with different porosities can be selected, and the porosity of the first base membrane and the second base membrane can be tested using the test method of "porosity test of the first base membrane and the second base membrane" in this application, and the first base membrane and the second base membrane with the desired porosity can be selected.

[0055] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0056] The negative electrode material layer, the first negative electrode material layer, and the second negative electrode material layer of this application include a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12The negative electrode material layer, the first negative electrode material layer, and the second negative electrode material layer of this application also include a negative electrode binder. This application does not have any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, the negative electrode binder may include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, carboxymethyl cellulose, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. The negative electrode material layer, the first negative electrode material layer, and the second negative electrode material layer of this application may also include a negative electrode conductive agent. This application does not have any particular limitation on the negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, acetylene black and / or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in each of the negative electrode material layers, the first negative electrode material layer, and the second negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0057] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector can be 4 μm to 15 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, the first negative electrode material layer, and the second negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be 30 μm to 130 μm, the thickness of the single-sided first negative electrode material layer can be 30 μm to 130 μm, and the thickness of the single-sided second negative electrode material layer can be 30 μm to 130 μm.

[0058] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned negative electrode conductive agents and negative electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0059] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved. For example, as shown... Figures 1 to 5 As shown, the positive electrode 40 includes a positive current collector 41 and a positive electrode material layer 42 disposed on both surfaces of the positive current collector 41. This application does not impose any particular limitation on the positive current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0060] The positive electrode material layer of this application includes a positive electrode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in a multilayer positive electrode material layer can contain the same or different positive electrode active materials. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the positive electrode conductive agent and positive electrode binder in the positive electrode material layer, as long as they can achieve the purpose of this application. For example, the positive electrode conductive agent can include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder can include at least one of the above-mentioned negative electrode binders. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0061] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be 9 μm to 15 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be 30 μm to 120 μm.

[0062] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned positive electrode conductive agents and positive electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0063] In this application, the secondary battery also includes an electrolyte. The electrolyte includes lithium salts. This application does not particularly limit the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte includes non-aqueous organic solvents. This application does not particularly limit the non-aqueous organic solvents, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0064] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0065] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0066] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, the first separator, the negative electrode, and the second separator in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0067] A second aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. The secondary battery of this application exhibits good cycle performance, high-temperature thermal performance, and high energy density; therefore, the electronic device of this application has excellent performance characteristics.

[0068] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0069] Example

[0070] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0071] Test methods and equipment:

[0072] Sampling methods for the first and second septa:

[0073] The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the first and second separators were removed. The separators were soaked in dimethyl carbonate (DMC) for 20 minutes to remove electrolyte residue. Then, the first and second separators were placed in an oven and dried at 60°C for 12 hours to obtain the first and second separator samples. The first and second separators were sampled using the above method for the following tests on the average particle size of the first and second binders, and the thickness of the first and second base films.

[0074] Average particle size test of the first and second binders:

[0075] The average particle size of the first and second binders can be obtained by observing the surfaces of the first and second separators perpendicular to their thickness directions using a scanning electron microscope (SEM). The average particle size D1 of the first binder is obtained by randomly selecting 10 particles of the first binder in the first adhesive layer, and the average particle size D2 of the second binder is obtained by randomly selecting 10 particles of the second binder in the second adhesive layer. It is worth noting that because the particles of the first and second binders deform under the pressure of cold pressing and hot pressing during the lithium-ion battery manufacturing process, the diameter of the particles differs along the separator thickness direction and perpendicular to the separator thickness direction. Therefore, the average particle size of the first and second binders in this application is the diameter measured on the surface perpendicular to the separator thickness direction. Thus, the average particle size of the first and second binders is not limited by the thickness of the first and second adhesive layers.

[0076] Thickness testing of the first and second base films:

[0077] Argon ion polishing was performed on the first diaphragm to obtain the cross section of the first diaphragm. The morphology of the cross section of the first diaphragm along the thickness direction was observed and scanned electron micrographs were taken using a field emission scanning electron microscope (Philips, XL-30). The thickness H1 of the first base film was measured by scanning electron microscopy.

[0078] The second diaphragm was argon-ion polished to obtain its cross-section. The morphology of the cross-section along the thickness direction of the second diaphragm was observed and scanned electron micrographs were taken using a field emission scanning electron microscope (Philips XL-30). The thickness H2 of the second base film was measured by scanning electron microscopy.

[0079] Porosity testing of the first and second base films:

[0080] The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the first and second separators were removed. The separators were soaked in dimethyl carbonate (DMC) for 20 minutes to remove electrolyte residue. Then, the first and second separators were placed in an oven and dried at 60°C for 12 hours to obtain the first and second separator samples. The first and second separator samples obtained after cleaning and drying with DMC were placed in a container, and an appropriate amount of N-methylpyrrolidone (NMP) was added. The container was then placed in an ultrasonic instrument with heating function and ultrasonicated at 45°C for 3 hours. When the first and second separators became completely transparent, they were removed to obtain the first and second base film samples.

[0081] The gas displacement method is used for testing. The first and second base film samples are prepared by punching with a mold (those skilled in the art can select molds of common sizes and shapes in the art according to the size, shape, and testing equipment requirements of the test samples). The true volume V0 of the sample is measured by a true density tester. The apparent volume V of the sample can be calculated from the area and thickness of the sample. Then, the percentage of the sample pore volume to the total area P = (V-V0) / V×100%, which is the porosity of the first or second base film.

[0082] Lithium-ion battery thickness testing:

[0083] Adjust the test pressure to 600g by adding or removing weights; place a 3mm gauge block on the platform, press the white buttons on both sides, and the panel pressure gap battery thickness gauge (PPG battery thickness gauge) will automatically feed the gauge block in and test it. Test any 9 points sequentially, and verify the tolerance to ±0.02mm. Only gauge blocks within specifications can be used. Hold the lithium-ion battery with one hand, barcode side up, on the platform. First scan the barcode, then press the white buttons on both sides. The instrument will automatically feed the lithium-ion battery in and test it. Record the test result, which is the lithium-ion battery thickness THK. In this application, the smaller the thickness of the lithium-ion battery, the smaller its volume, and the higher its energy density.

[0084] Cyclic performance test:

[0085] At 25°C, the lithium-ion battery was charged at a constant current of 2C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.02C. After resting for 5 minutes, it was discharged at a constant current of 0.7C to 3.0V. This was the first cycle, and the discharge capacity was recorded. The lithium-ion battery was subjected to charge-discharge cycles according to the above process. The test was stopped after 1000 cycles (cls), and the capacity retention rate was calculated as an indicator to evaluate the cycle performance of the lithium-ion battery.

[0086] Capacity retention rate (%) = (Discharge capacity after 1000 cls of cycling / Discharge capacity of the first cycle) × 100%.

[0087] High-temperature hot chamber test:

[0088] Under conditions of 25℃, lithium-ion batteries that have been charged at a constant current of 2C to 4.5V and then at a constant voltage of 4.5V to a current of 0.02C are placed in a test chamber with circulating air convection, a temperature of 25℃, and a humidity of 80%. After standing for 5 minutes, the test chamber is heated to 130℃ at a rate of 5℃ / min and maintained at 130℃ for 10 minutes. The test is then stopped, and the lithium-ion batteries are checked for fire or explosion. A battery that does not fire or explode is considered to have passed the test. The pass rate for the 130℃ hot chamber test is calculated as: (Number of batteries passing the 130℃ hot chamber test) / (Total number of batteries tested at 130℃) (10 batteries).

[0089] Under conditions of 25℃, lithium-ion batteries that have been charged at a constant current of 2C to 4.5V and then at a constant voltage of 4.5V to a current of 0.02C are placed in a test chamber with circulating air convection, a temperature of 25℃, and a humidity of 80%. After standing for 5 minutes, the test chamber is heated to 132℃ at a rate of 5℃ / min and maintained at 132℃ for 10 minutes. The test is then stopped, and the lithium-ion batteries are checked for fire or explosion. A battery that does not fire or explode is considered to have passed the test. The pass rate for the 132℃ hot chamber test is calculated as: (Number of batteries passing the 132℃ hot chamber test) / (Total number of batteries tested at 132℃) (10 batteries).

[0090] Test of the adhesion between the diaphragm and the electrode:

[0091] The dry-press adhesion between the separator and the electrode was measured using a 180° peel test standard. The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the positive electrode, negative electrode, first separator, and second separator were peeled off.

[0092] The electrode and separator to be tested were soaked in dimethyl ether for 20 minutes to remove the electrolyte. Then, the separator and electrode were laminated together using a hot press at 85℃, 1MPa, and 85s. The laminated sample was cut into 15mm × 54.2mm strips to obtain test strips for testing the adhesion between the separator and the electrode. A 15mm × 55mm double-sided adhesive tape (NITTO.NO5000NS) was attached to a steel plate, and the test strips were then attached to the tape with the test side facing down. A 15mm × 70mm paper tape was connected to one end of the test strip using the double-sided adhesive tape. A 2kg roller was manually pushed across the test strip 8 times to obtain the test sample. A tensile testing machine was used for testing. The test sample is fixed on the test stage, the paper tape is folded upwards 180° and secured with clamps, and then the tensile testing machine starts pulling the paper tape at a speed of 50 mm / min until the test diaphragm and the test electrode on the double-sided adhesive surface separate, ending the test and saving the test data. The adhesion force F between the test diaphragm and the test electrode is calculated based on the tensile force and displacement during separation, in N / m. The adhesion force F1 between the first diaphragm and the positive electrode is calculated in N / m; the adhesion force F2 between the first diaphragm and the negative electrode is calculated in N / m; and the adhesion force F3 between the second diaphragm and the negative electrode is calculated in N / m.

[0093] Example 1-1

[0094] <Preparation of the first diaphragm>

[0095] A nonwoven fabric membrane with a thickness H1 of 12 μm was used as the first base membrane. The material of the nonwoven fabric membrane was polyethylene terephthalate, and the porosity P1 of the first base membrane was 55%. (Manufacturer: DuPont, grade: FR543).

[0096] The first adhesive is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Mw = 8.5 × 10⁻⁶). 6 ) and the first thickener sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a first adhesive layer slurry with a solid content of 75wt%.

[0097] A first adhesive layer slurry is coated on one surface of the first base film and dried at 60°C to obtain a first diaphragm with the first adhesive layer coated on one side. Then, the above steps are repeated on the other surface of the first base film to obtain the first diaphragm. The average particle size D1 of the first adhesive is 8 μm, and the coating weight CW1 of the first adhesive layer is 0.001 mg / mm². 2 .

[0098] <Preparation of the Second Diaphragm>

[0099] A microporous membrane with a thickness H2 of 7 μm was used as the second base membrane. The microporous membrane was made of polypropylene and polyethylene, with a mass ratio of polypropylene to polyethylene of 1:1. The porosity P2 of the second base membrane was 18%. (Manufacturer: Celgard, grade: 2325).

[0100] The second adhesive, polyimide (PI, Mw = 6 × 10), is used. 5 ) and the second thickener, sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a second adhesive layer slurry with a solid content of 75wt%.

[0101] A second adhesive layer slurry is coated on one surface of the second base membrane and dried at 60°C to obtain a second diaphragm with a single-sided coating of the second adhesive layer. The above steps are then repeated on the other surface of the second base membrane to obtain the second diaphragm. The average particle size D2 of the second adhesive is 15 μm, and the coating weight CW2 of the second adhesive layer is 0.0005 mg / mm². 2 .

[0102] <Preparation of Negative Electrode Sheets>

[0103] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.6:1.1:1.3, and deionized water was added as a solvent. After stirring evenly, a first negative electrode slurry with a solid content of 70 wt% was obtained. This first negative electrode slurry was also used as a second negative electrode slurry. The first negative electrode slurry was coated onto one surface of a 6 μm thick copper foil current collector and dried at 90°C to obtain a negative electrode sheet with a first negative electrode material layer coating thickness of 50 μm. The second negative electrode slurry was coated onto the other surface of the copper foil current collector and dried, resulting in a second negative electrode material layer coating thickness of 50 μm, thus obtaining a negative electrode sheet with a total thickness of 106 μm. The coated negative electrode sheet was cold-pressed and then cut into 74 mm × 824 mm dimensions for later use. The compaction density of the first negative electrode material layer was 1.735 g / cm³. 3 The length is 720mm, and the compaction density of the second negative electrode material layer is 1.735g / cm³. 3 It is 680mm long.

[0104] <Preparation of the positive electrode>

[0105] Lithium cobalt oxide (CCO), conductive carbon black (CCO), and polyvinylidene fluoride (PVDF) (PVDF binder) were mixed in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was thoroughly stirred to form a positive electrode slurry with a solid content of 75 wt%. This slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 90°C to obtain a positive electrode sheet with a single-sided coating thickness of 55 μm. The positive electrode slurry was then coated onto the other surface of the aluminum foil current collector and dried, resulting in a 55 μm thick positive electrode layer on that surface, thus obtaining a double-sided coated positive electrode sheet with a total thickness of 120 μm. The coated positive electrode sheets were then cold-pressed and cut into 70 mm × 800 mm dimensions for later use. The compaction density of the positive electrode layer was 4.23 g / cm³. 3 .

[0106] <Preparation of Electrolyte>

[0107] In a glove box filled with a dry argon atmosphere, propylene carbonate (PC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent, dissolved, and thoroughly mixed to obtain the electrolyte. The mass percentage of LiPF6 in the electrolyte was 12%, with the remainder being the base solvent.

[0108] <Preparation of Lithium-ion Batteries>

[0109] The prepared positive electrode sheet, first separator, negative electrode sheet, and second separator are stacked sequentially and then wound to obtain an electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The first negative electrode material layer is close to the first separator, and the second negative electrode material layer is close to the second separator. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Then, the prepared electrolyte is injected, followed by vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes to obtain a lithium-ion battery.

[0110] Examples 1-2 to Examples 1-10

[0111] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0112] Examples 1-11

[0113] Except for the preparation of lithium-ion batteries according to the following steps, the rest is the same as in Example 1-1.

[0114] <Preparation of Lithium-ion Batteries>

[0115] The prepared positive electrode sheet, first separator, negative electrode sheet, and second separator are stacked sequentially and then wound to obtain the electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The first negative electrode material layer is close to the second separator, and the second negative electrode material layer is close to the first separator. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Then, the prepared electrolyte is injected. After vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes, a lithium-ion battery is obtained.

[0116] Examples 1-12

[0117] Except for the steps of preparing the first separator and in the <Preparation of Lithium-ion Battery>, where only the side of the first separator coated with the first adhesive layer is close to the negative electrode, the rest is the same as in Example 1-1.

[0118] <Preparation of the first diaphragm>

[0119] A nonwoven fabric membrane with a thickness H1 of 12 μm was used as the first base membrane. The material of the nonwoven fabric membrane was polyethylene terephthalate, and the porosity P1 of the first base membrane was 55%. (Manufacturer: DuPont, grade: FR543).

[0120] The first adhesive is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Mw = 8.5 × 10⁻⁶). 6 ) and the first thickener sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a first adhesive layer slurry with a solid content of 75wt%.

[0121] The first ceramic particle is alumina (Al2O3), and the third binder is styrene-butadiene rubber (Mw = 7 × 10⁻⁶). 6 Solvent and deionized water are mixed in a mass ratio of 35:10:55 to obtain the first ceramic coating slurry.

[0122] A first adhesive layer slurry is coated on one surface of a first base film and dried at 60°C to form a first adhesive layer on that surface. A first ceramic coating slurry is first coated on the other surface of the first base film and dried at 60°C to form a first ceramic coating on that surface. Then, the first adhesive layer slurry is coated on the surface of the first ceramic coating away from the first base film, and after drying, another first adhesive layer is formed on the surface of the first ceramic coating away from the first base film, thus obtaining the first diaphragm. The average particle size D1 of the first adhesive is 8 μm, and the coating weight CW1 of the first adhesive layer is 0.001 mg / mm². 2 The coating weight of the first ceramic coating is 0.09 mg / mm². 2 .

[0123] Examples 1-13

[0124] Except for the steps of preparing the second separator and in the <Preparation of Lithium-ion Battery>, where only the side of the second separator coated with the second adhesive layer is close to the negative electrode, the rest is the same as in Example 1-1.

[0125] <Preparation of the Second Diaphragm>

[0126] A microporous membrane with a thickness H2 of 7 μm was used as the second base membrane. The microporous membrane was made of polypropylene and polyethylene, with a mass ratio of polypropylene to polyethylene of 1:1. The porosity P2 of the second base membrane was 18%. (Manufacturer: Celgard, grade: 2325).

[0127] The second adhesive, polyimide (PI, Mw = 6 × 10), is used. 5 ) and the second thickener, sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a second adhesive layer slurry with a solid content of 75wt%.

[0128] The second ceramic particle, alumina (Al2O3), and the fourth binder, styrene-butadiene rubber (Mw = 7 × 10⁻⁶), are combined. 6 The solvent and deionized water were mixed at a mass ratio of 35:10:55 to obtain the second ceramic coating slurry.

[0129] A second adhesive layer slurry is coated on one surface of the second base membrane and dried at 60°C to form a second adhesive layer on that surface. A second ceramic coating slurry is first coated on the other surface of the second base membrane and dried at 60°C to form a second ceramic coating. Then, a second adhesive layer slurry is coated on the surface of the second ceramic coating away from the second base membrane, and after drying, another second adhesive layer is formed on the surface of the second ceramic coating away from the second base membrane, thus obtaining the second diaphragm. The average particle size D2 of the second adhesive is 15 μm, and the coating weight CW2 of the second adhesive layer is 0.0005 mg / mm². 2 The coating weight of the second ceramic coating is 0.09 mg / mm². 2 .

[0130] Examples 1-14

[0131] Except for using the first separator from Examples 1-12, the second separator from Examples 1-13, and preparing the lithium-ion battery according to the following steps, everything else is the same as in Examples 1-1.

[0132] <Preparation of Lithium-ion Batteries>

[0133] The prepared positive electrode, first separator, negative electrode, and second separator are stacked sequentially and then wound to obtain the electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. Specifically, the side of the first separator coated with only the first adhesive layer is close to the negative electrode, and the side of the second separator coated with only the second adhesive layer is close to the negative electrode. The first negative electrode material layer is close to the first separator, and the second negative electrode material layer is close to the second separator. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Then, the prepared electrolyte is injected. After vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes, a lithium-ion battery is obtained.

[0134] Examples 2-1 to 2-4

[0135] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0136] Examples 2-5 to Examples 2-8

[0137] Except for adjusting the amount of the first adhesive layer slurry to achieve the coating weight of the first adhesive layer as shown in Table 2, and adjusting the amount of the second adhesive layer slurry to achieve the coating weight of the second adhesive layer as shown in Table 2, the rest is the same as in Example 1-1.

[0138] Examples 3-1 to 3-8

[0139] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0140] Comparative Examples 1 to 6

[0141] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0142] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0143] Table 1

[0144]

[0145]

[0146]

[0147] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0148] As can be seen from Examples 1-1 to 1-14 and Comparative Examples 1 to 6, the electrode assembly of the secondary battery is a wound structure, using a first separator and a second separator. The first base film is a non-woven fabric film, and the second base film is a microporous membrane. By controlling the types of the first and second binders within the scope of this application, the adhesion between the first separator and the positive electrode sheet, and between the second separator and the negative electrode sheet, is relatively high. The capacity retention rate of the lithium-ion battery after 1000 cycles is relatively high, the pass rate of the hot box test at 130°C and 132°C is relatively high, and the thickness of the lithium-ion battery is relatively small. This indicates that in the lithium-ion battery of this application, the adhesion between the separator and the positive electrode sheet, and between the separator and the negative electrode sheet is relatively high. At the same time, the lithium-ion battery has good cycle performance and high temperature hot box performance, as well as high energy density. Compared to Examples 1-1, Comparative Example 1 uses a microporous membrane as the first base film. The thickness of the microporous membrane is relatively small, resulting in a thinner lithium-ion battery. However, the microporous membrane has low porosity, storing less electrolyte, which is detrimental to the cycle performance of the lithium-ion battery. Furthermore, the microporous membrane has relatively low mechanical strength and shrinks significantly at high temperatures, thus Comparative Example 1 also exhibits poor high-temperature thermal performance. Compared to Examples 1-1, Comparative Example 2 uses a non-woven fabric membrane as the second base film. The thickness of the non-woven fabric membrane is relatively large, resulting in a thicker lithium-ion battery and lower energy density. Simultaneously, the lithium-ion transport path is longer, leading to even worse cycle performance. Compared to Examples 1-1, Comparative Example 3 shows lower adhesion of the first separator to the positive electrode due to the low swelling and bonding strength of PI at room temperature. The low ionic conductivity of PI also contributes to poor cycle performance of the lithium-ion battery. Compared to Examples 1-1, Comparative Example 4 uses PVDF-HFP with a lower melting point and poorer thermal stability at high temperatures, resulting in poorer high-temperature thermal performance of the lithium-ion battery. Compared to Examples 1-1, Comparative Example 5 has a thicker lithium-ion battery and a lower energy density; simultaneously, the lithium-ion transport path is longer, resulting in poorer cycle performance. Compared to Examples 1-1, Comparative Example 6 has a relatively thinner microporous membrane and a smaller lithium-ion battery; however, the microporous membrane has lower porosity, and the ionic conductivity of the PI is also lower. Using a combination of a microporous membrane and PI as the first separator cannot effectively improve the cycle performance of the lithium-ion battery. Furthermore, due to the relatively low mechanical strength of the microporous membrane and its significant shrinkage at high temperatures, the high-temperature thermal performance of Comparative Example 6 is also poor.

[0149] The structure of the electrode assembly typically affects the safety performance, high-temperature thermal performance, cycle performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 1-11, when the electrode assembly structure is within the scope of this application, the lithium-ion battery exhibits a high capacity retention rate after 1000 cycles, indicating that the lithium-ion battery of this application has good cycle performance.

[0150] The first separator also includes a first ceramic coating, which comprises first ceramic particles. The type of the first ceramic particles typically affects the high-temperature thermal performance of the lithium-ion battery. As can be seen from Examples 1-1 and 1-12, when the first separator also includes a first ceramic coating, which comprises first ceramic particles, and the type of the first ceramic particles is within the scope of this application, the lithium-ion battery is thicker, the capacity retention rate after 1000 cycles is higher, and the pass rate of thermal tests at 130°C and 132°C is higher. This indicates that the lithium-ion battery of this application has good high-temperature thermal performance and good cycle performance. Furthermore, the adhesion between the first separator and the positive electrode, and between the second separator and the negative electrode, is higher.

[0151] The second separator also includes a second ceramic coating, which comprises second ceramic particles. The type of the second ceramic particles typically affects the high-temperature thermal performance of the lithium-ion battery. As can be seen from Examples 1-1 and 1-13, when the second separator also includes a second ceramic coating, which comprises second ceramic particles, and the type of the second ceramic particles is within the scope of this application, the lithium-ion battery is thicker, the capacity retention rate after 1000 cycles is higher, and the pass rate of thermal tests at 130°C and 132°C is higher. This indicates that the lithium-ion battery of this application has good high-temperature thermal performance and good cycle performance. Furthermore, the adhesion between the first separator and the positive electrode, and between the second separator and the negative electrode, is higher.

[0152] The first separator also includes a first ceramic coating, which comprises first ceramic particles, the type of which is specified. The second separator also includes a second ceramic coating, which comprises second ceramic particles, the type of which typically affects the high-temperature thermal performance of the lithium-ion battery. As can be seen from Examples 1-1 and 1-14, when the first separator also includes a first ceramic coating, which comprises first ceramic particles, the type of which is specified, and the second separator also includes a second ceramic coating, which comprises second ceramic particles, the type of which is specified within the scope of this application, the lithium-ion battery is thicker, has a higher capacity retention rate after 1000 cycles, and a higher pass rate in thermal tests at 130℃ and 132℃. This indicates that the lithium-ion battery of this application has better high-temperature thermal performance and better cycle performance. Furthermore, the adhesion between the first separator and the positive electrode, and between the second separator and the negative electrode, is higher.

[0153] Table 2

[0154]

[0155]

[0156] The average particle size D1 of the first binder and the average particle size D2 of the second binder typically affect the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, as well as the cycle performance and high-temperature thermal performance of the lithium-ion battery. As can be seen from Examples 1-1, 2-1 to 2-4, an increase in the average particle size of the first binder reduces the contact area between the first binder and the positive electrode active material particles, thus reducing the adhesion of the first separator to the positive electrode. Similarly, an increase in the average particle size of the second binder reduces the contact area between the second binder and the negative electrode active material particles, thus reducing the adhesion of the second separator to the negative electrode. When the average particle size D1 of the first binder and the average particle size D2 of the second binder are within the range of this application, the lithium-ion battery exhibits high capacity retention after 1000 cycles, high pass rates in thermal tests at 130℃ and 132℃, and a relatively small thickness, indicating that the lithium-ion battery of this application has good cycle performance and high-temperature thermal performance, and also possesses high energy density.

[0157] The coating weights CW1 of the first adhesive layer and CW2 of the second adhesive layer typically affect the adhesion between the separator and the positive electrode, and between the separator and the negative electrode, thus impacting the cycle performance of the lithium-ion battery. As seen in Examples 1-1, 2-5 to 2-8, increasing the coating weight of the first adhesive layer increases the content of the first binder per unit area, thus increasing the adhesion of the first separator to the positive electrode; similarly, increasing the coating weight of the second adhesive layer increases the content of the second binder per unit area, thus increasing the adhesion of the second separator to the positive electrode. When the coating weights CW1 and CW2 of the first adhesive layer are within the range specified in this application, the lithium-ion battery exhibits high capacity retention after 1000 cycles, high pass rates in hot box tests at 130°C and 132°C, and a relatively small thickness, indicating that the lithium-ion battery of this application possesses good cycle performance, as well as good high-temperature hot box performance and high energy density.

[0158] Table 3

[0159]

[0160]

[0161] The thickness H1 of the first base film and the thickness H2 of the second base film typically affect the high-temperature thermal performance, cycle performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-4, when the thickness H1 of the first base film and the thickness H2 of the second base film are within the range of this application, the adhesion between the first separator and the positive electrode, and between the second separator and the negative electrode, is high. This results in a high capacity retention rate after 1000 cycles and a high pass rate in thermal tests at 130℃ and 132℃, indicating that the lithium-ion battery of this application has good high-temperature thermal performance and cycle performance, and the adhesion between the first separator and the positive electrode, and between the second separator and the negative electrode, is also high. In Example 3-3, the thickness of the first base film and the thickness of the second base film are relatively small, resulting in a relatively small amount of stored lithium ions and relatively poor cycle performance. Furthermore, the smaller thickness of the base film leads to lower mechanical strength and easier shrinkage at high temperatures, resulting in poor high-temperature thermal performance of the lithium-ion battery. In Examples 3-4, the thickness of the first base film and the thickness of the second base film are relatively large, resulting in a larger thickness of the lithium-ion battery and a lower energy density.

[0162] The porosity P1 of the first base film and the porosity P2 of the second base film typically affect the high-temperature thermal performance and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-5 to 3-8, when the porosity P1 of the first base film and the porosity P2 of the second base film are within the range of this application, the lithium-ion battery exhibits high capacity retention after 1000 cycles, high pass rates in thermal tests at 130℃ and 132℃, and a smaller battery thickness. This indicates that the lithium-ion battery of this application has good high-temperature thermal performance and cycle performance, as well as high energy density. In Examples 3-7, the porosity of the first and second base films is relatively small, resulting in relatively less electrolyte stored in the first and second separators, which is detrimental to lithium-ion transport and leads to poor cycle performance of the lithium-ion battery. In Examples 3-8, the porosity of the first base membrane and the porosity of the second base membrane are relatively large. The first and second separators store relatively more electrolyte, which is beneficial to the transport of lithium ions and the cycle performance of the lithium-ion battery is good. However, excessive porosity will lead to poor mechanical strength of the separator, large shrinkage at high temperature, and poor high-temperature thermal performance of the lithium-ion battery.

[0163] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0164] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0165] The above description is only a preferred embodiment 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 scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly having a wound structure, the electrode assembly comprising a positive electrode, a negative electrode, a first separator, and a second separator, the negative electrode being located between the first separator and the second separator, the first separator being located between the positive electrode and the negative electrode, the first separator comprising a first base film and a first adhesive layer, the second separator comprising a second base film and a second adhesive layer, the first adhesive layer comprising a first adhesive, and the second adhesive layer comprising a second adhesive; The first base film is a non-woven fabric film, and the material of the first base film includes at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone. The first adhesive includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; The second base membrane is a microporous membrane, and the material of the second base membrane includes polyolefin, wherein the polymer monomer of the polyolefin includes at least one of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene or cyclohexene; The second adhesive includes at least one of polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose.

2. The secondary battery according to claim 1, wherein, The material of the first base film includes polyethylene terephthalate, and the first binder includes polyvinylidene fluoride-hexafluoropropylene copolymer; The material of the second base film includes a polyolefin, wherein the polymer monomer of the polyolefin includes at least one of ethylene or propylene, and the second binder includes a polyimide.

3. The secondary battery according to claim 1, wherein, The negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the negative current collector. Along the winding direction of the electrode assembly, the length of the first negative electrode material layer is greater than the length of the second negative electrode material layer. The first separator is located on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is located on one side of the second negative electrode material layer of the negative electrode sheet.

4. The secondary battery according to any one of claims 1 to 3, wherein, The first adhesive has an average particle size of 4 μm to 15 μm, and the second adhesive has an average particle size of 10 μm to 20 μm.

5. The secondary battery according to any one of claims 1 to 3, wherein, The coating weight of the first adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 The coating weight of the second adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 .

6. The secondary battery according to any one of claims 1 to 3, wherein, The thickness of the first base film is 10 μm to 15 μm, and the thickness of the second base film is 3 μm to 9 μm.

7. The secondary battery according to any one of claims 1 to 3, wherein, The porosity of the first base film is 40% to 70%, and the porosity of the second base film is 5% to 50%.

8. The secondary battery according to any one of claims 1 to 3, wherein, The first diaphragm further includes a first ceramic coating located between the first base film and the first adhesive layer, and / or the second diaphragm further includes a second ceramic coating located between the second base film and the second adhesive layer. The first ceramic coating includes first ceramic particles, and the second ceramic coating includes second ceramic particles. The first ceramic particles and the second ceramic particles are each independently selected from at least one of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

9. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 8.

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