Secondary battery and electric apparatus

Abstract

A secondary battery and an electric apparatus. The secondary battery comprises an electrode assembly, which comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode tab, a positive-electrode current collector, a first molecular sieve coating and a positive-electrode active material layer, and in a first direction, the positive electrode sheet comprises a second region and a first region which are connected in sequence, wherein the positive electrode tab and the positive-electrode current collector in the first region are integrally arranged, the first molecular sieve coating is arranged on at least one surface of the positive-electrode current collector in the first region, the positive-electrode active material layer is arranged on at least one surface of the positive-electrode current collector in the second region, and the first direction is the extension direction of the positive electrode tab in an unfolded state; and the first molecular sieve coating comprises a molecular sieve and a first binder, and on the basis of the mass of the first molecular sieve coating, the mass percentage of the molecular sieve ranges from 10% to 90%, and the mass percentage of the first binder also ranges from 10% to 90%. The secondary battery has a good cycling performance and a good drop safety performance.

Description

Secondary battery and power-consuming device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] With the development of society, smartphones and laptops have become increasingly important in our lives. The market for wearable devices, smart homes, electric vehicles, and electric bicycles is also expanding. Secondary batteries, such as lithium-ion and sodium-ion batteries, are widely used in these areas due to their high energy density and environmental friendliness. Consequently, market demand for these batteries is also rapidly growing.

[0003] In existing secondary batteries, electrolyte tends to accumulate at the head of the electrode assembly (the side where the tab extends from the electrode assembly), resulting in weak binding force between the electrode layers. The edge of the electrode becomes a weak area that cannot be ignored, affecting the cycle performance and drop safety of the secondary battery.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electrical device to improve the cycle performance and drop safety performance of the secondary battery.

[0006] It should be noted that in the application content, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including a positive electrode plate, a negative electrode plate and a separator, the separator is arranged between the positive electrode plate and the negative electrode plate; the positive electrode plate includes a positive electrode tab, a positive electrode collector, a first molecular sieve coating and a positive electrode active material layer, along a first direction, the positive electrode plate includes a second region and a first region connected in sequence, the positive electrode tab and the positive electrode collector in the first region are integrally arranged, the first molecular sieve coating is provided on at least one surface of the positive electrode collector in the first region, and the positive electrode active material layer is provided on at least one surface of the positive electrode collector in the second region, and the first direction is the extension direction of the positive electrode tab in an unfolded state; the first molecular sieve coating includes a molecular sieve and a first binder, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10% to 90%, and the mass percentage of the first binder is 10% to 90%. In the present application, a first molecular sieve coating is provided on at least one surface of the positive electrode current collector in the first region. On the one hand, the conventional ceramic coatings such as alumina and boehmite can be applied here to prevent the positive electrode current collector burrs from piercing the separator and causing a short circuit, and to prevent the positive electrode current collector from directly contacting the negative electrode active material and causing a dangerous short circuit when the negative electrode active material layer exceeds the positive electrode active material layer in the width direction, thereby making the secondary battery have good anti-short circuit performance. On the other hand, the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is controlled within the above-mentioned range, so that the first molecular sieve coating has good bonding effect, can enhance the bonding effect between the positive electrode plate and the separator at the head of the electrode assembly, reduce the risk of weak bonding between the electrode plate layers due to electrolyte accumulation at the head of the electrode assembly, and reduce the risk of weak bonding between the positive electrode active material layer and the separator, so that the positive electrode plate and the separator at the head of the electrode assembly have good bonding effect. As a result, there is good interface contact between the positive electrode plate and the separator, less lithium plating occurs on the negative electrode plate, and the cycle performance of the secondary battery is improved. Furthermore, the first region of the positive electrode sheet and the separator have good adhesion, reducing the probability of the separator folding, thereby improving the drop safety of the secondary battery. Furthermore, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, reducing the risk of flatulence in the secondary battery, thereby improving the storage performance and high-temperature safety of the secondary battery.

[0008] In one embodiment of the present application, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 20% to 80%, and the mass percentage of the first binder is 20% to 80%. By regulating the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating within the above ranges, the first molecular sieve layer can have a better short-circuit protection function and a better bonding effect.

[0009] In one embodiment of the present application, based on the mass of the first molecular sieve coating, the molecular sieve content is 30% to 70% by mass, and the first binder content is 30% to 70% by mass. By regulating the molecular sieve and first binder content in the first molecular sieve coating within the above ranges, the first molecular sieve layer can better balance the short-circuit protection function and the bonding effect.

[0010] In one embodiment of the present application, along the first direction, the width of the first molecular sieve coating is 0.5mm to 10mm; along the direction perpendicular to the first direction, the length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet. The width of the first molecular sieve coating is set at 0.5mm to 10mm, which can better prevent the positive electrode current collector and the negative electrode active material from directly contacting and causing a short circuit, while taking into account the energy density of the secondary battery, so that the first molecular sieve coating has good adhesion to the diaphragm. The length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet, which can more effectively achieve the above-mentioned effect in the length direction.

[0011] In one embodiment of the present application, the width of the first molecular sieve coating layer is 1 mm to 3 mm along the first direction. Setting the width of the first molecular sieve coating layer to 1 mm to 3 mm can better prevent the positive electrode current collector and the negative electrode active material from directly contacting each other and causing a short circuit, while also taking into account the energy density of the secondary battery. At the same time, it can further improve the adhesion of the first molecular sieve coating layer to the separator, thereby further improving the drop safety performance of the secondary battery.

[0012] In one embodiment of the present application, the thickness of the first molecular sieve coating layer is less than that of the positive electrode active material layer, and the thickness of the first molecular sieve coating layer is 0.5 μm to 40 μm. Controlling the thickness of the first molecular sieve coating layer within the above range allows the first molecular sieve coating layer to better prevent short circuits and improve adhesion to the separator, while also ensuring the energy density of the secondary battery.

[0013] In one embodiment of the present application, the thickness of the first molecular sieve coating is 5 μm to 20 μm. Adjusting the thickness of the first molecular sieve coating within the above range is beneficial to further improve the short circuit resistance, cycle performance, drop safety performance and storage performance of the secondary battery.

[0014] In one embodiment of the present application, a second molecular sieve coating is provided on the surface of the diaphragm opposite to the first region; the second molecular sieve coating includes a molecular sieve, and the mass percentage of the molecular sieve is 20% to 80% based on the mass of the second molecular sieve coating. The second molecular sieve coating is provided on the surface of the diaphragm opposite to the first region, and the content of the molecular sieve in the second molecular sieve coating is regulated within the above range, which is conducive to further improving the short-circuit resistance, cycle performance, drop safety performance and storage performance of the secondary battery. At the same time, the second molecular sieve coating on the diaphragm can also reduce the possibility of shrinkage of the diaphragm substrate layer and improve the high temperature resistance of the secondary battery.

[0015] In one embodiment of the present application, the thickness of the second molecular sieve coating is 0.5 μm to 10 μm. Adjusting the thickness of the second molecular sieve coating within the above range is beneficial for the secondary battery to have good short circuit resistance, cycle performance, drop safety performance and storage performance.

[0016] In one embodiment of the present application, the porosity of the first molecular sieve coating and the second molecular sieve coating is independently 30% to 60%. By regulating the porosity of the first molecular sieve coating and the second molecular sieve coating within the above range, the first molecular sieve coating and the second molecular sieve coating can have good insulation and structural strength, thereby enabling the first molecular sieve coating and the second molecular sieve coating to exert their short circuit prevention effect and also to enhance the bonding effect of the first molecular sieve coating and the second molecular sieve coating.

[0017] In one embodiment of the present application, the specific surface area of ​​the molecular sieve is 200m 2 / g to 2000m 2 / g, and the pore size of the molecular sieve is 0.3nm to 45nm. By regulating the specific surface area and pore size of the molecular sieve within the above range, the molecular sieve can better play its role in improving the bonding force, further improving the cycle performance, drop safety performance and storage performance of the secondary battery.

[0018] In one embodiment of the present application, the molecular sieve includes at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 13X molecular sieve, ZSM-22 molecular sieve, ZSM-5 molecular sieve, MOR molecular sieve, ITQ molecular sieve, Y molecular sieve, SAPO molecular sieve, or ALPO molecular sieve. The selection of the above molecular sieves is conducive to the secondary battery having good cycle performance, drop safety performance, and storage performance.

[0019] In one embodiment of the present application, the first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polypropylene alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

[0020] In one embodiment of the present application, the positive electrode plate further comprises a conductive layer disposed on a surface of the first molecular sieve coating layer facing away from the positive electrode current collector; the conductive layer comprises a conductive agent, the weight percentage of the conductive agent being 5% to 70% based on the weight of the conductive layer. Providing the conductive layer on the surface of the first molecular sieve coating layer facing away from the positive electrode current collector in the positive electrode plate can further reduce the likelihood of lithium plating while maintaining good drop safety and storage performance, thereby further improving cycling performance of the secondary battery.

[0021] In one embodiment of the present application, the sum of the thickness of the first molecular sieve coating and the thickness of the conductive layer is less than or equal to the thickness of the positive electrode active material layer; the thickness of the conductive layer is 0.5 μm to 30 μm. The sum of the thickness of the first molecular sieve coating and the thickness of the conductive layer is less than or equal to the thickness of the positive electrode active material layer, which can reduce the possibility of a gap between the second region of the positive electrode plate and the separator due to excessive thickness of the first molecular sieve coating and the conductive layer, so that the second region of the positive electrode plate is in full contact with the separator to ensure the interface performance between the positive electrode plate and the separator. At the same time, by regulating the thickness of the first molecular sieve coating within the above range, it can adapt to the production requirements of most secondary batteries on the market.

[0022] In one embodiment of the present application, the conductive agent includes at least one of acetylene black, Ketjen black, conductive graphite, graphene, and carbon nanotubes.

[0023] The second aspect of the present application provides an electric device, wherein the electric device comprises the secondary battery described in any of the aforementioned embodiments. Therefore, the electric device has good performance.

[0024] Beneficial effects of this application:

[0025] The present application provides a secondary battery and an electrical device. The secondary battery has a first molecular sieve coating disposed on both surfaces of the positive electrode current collector in the first region. The coating can replace traditional ceramic coatings such as alumina and boehmite and play the same role in preventing short circuits. The mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is controlled within the above-mentioned range, so that the first molecular sieve coating has a good bonding effect, which can enhance the bonding effect between the positive electrode plate and the separator at the head of the electrode assembly, reduce the risk of weak bonding between the electrode plate layers due to electrolyte accumulation at the head of the electrode assembly, and reduce the risk of weak bonding between the positive electrode active material layer and the separator, so that the positive electrode plate and the separator at the head of the electrode assembly have a good bonding effect. As a result, there is a good interface contact effect between the positive electrode plate and the separator, less lithium plating occurs on the negative electrode plate, and the cycle performance of the secondary battery is improved. In addition, there is a good bonding effect between the first region of the positive electrode plate and the separator, and the probability of the separator flipping is reduced, thereby improving the drop safety performance of the secondary battery. In addition, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, which can reduce the risk of flatulence in the secondary battery, thereby improving the storage performance and high-temperature safety performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0027] FIG1 is a schematic diagram of a cross-sectional structure of a secondary battery according to an embodiment of the present application at a positive electrode tab along its own thickness direction and a first direction;

[0028] FIG2 is a schematic diagram of the cross-sectional structure of the electrode assembly in FIG1 along its own thickness direction and the first direction when the positive electrode tab is unfolded;

[0029] FIG3 is a top view of a positive electrode sheet in an unfolded state according to an embodiment of the present application;

[0030] FIG4 is a schematic diagram of the cross-sectional structure of a positive electrode sheet in an unfolded state at the positive electrode tab along its own thickness direction and the first direction according to one embodiment of the present application;

[0031] FIG5 is a schematic diagram of the cross-sectional structure of a positive electrode sheet in an unfolded state at a non-positive electrode tab along its own thickness direction and a direction perpendicular to the first direction according to another embodiment of the present application;

[0032] FIG6 is a schematic diagram of the cross-sectional structure of a secondary battery according to another embodiment of the present application at a positive electrode tab along its own thickness direction and a first direction;

[0033] FIG7 is a schematic diagram of a cross-sectional structure of a diaphragm along its thickness direction according to some embodiments of the present application;

[0034] FIG8 is a schematic diagram of a cross-sectional structure of a diaphragm along its thickness direction according to other embodiments of the present application;

[0035] FIG9 is a schematic diagram of the cross-sectional structure of a positive electrode sheet along its thickness direction according to another embodiment of the present application. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the examples described in this specification are only some examples of this application, not all of them. All other examples obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0037] It should be noted that in the specific embodiments, lithium-ion batteries are used as an example of secondary batteries to explain this application. However, the secondary batteries of this application are not limited to lithium-ion batteries, but are also applicable to sodium-ion batteries and other common batteries in the field that can use the relevant technology of this application. The specific technical solution is as follows:

[0038] A first aspect of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the separator is arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode tab, a positive electrode collector, a first molecular sieve coating and a positive electrode active material layer, along a first direction, the positive electrode sheet includes a second region and a first region connected in sequence, the positive electrode tab and the positive electrode collector in the first region are integrally arranged, the first molecular sieve coating is provided on at least one surface of the positive electrode collector in the first region, and the positive electrode active material layer is provided on at least one surface of the positive electrode collector in the second region, the first direction is the extension direction of the positive electrode tab in an unfolded state, that is, the width direction of the positive electrode sheet. It can be understood that the above-mentioned “a first molecular sieve coating is provided on at least one surface of the positive electrode current collector in the first region” means that, in some embodiments, a first molecular sieve coating is provided on one surface of the positive electrode current collector in the first region, and in other embodiments, a first molecular sieve coating is provided on both surfaces of the positive electrode current collector in the first region, wherein the “surface” can be the entire surface of the positive electrode current collector in the first region, or a portion of the surface of the positive electrode current collector in the first region; the above-mentioned “a positive electrode active material layer is provided on at least one surface of the positive electrode current collector in the second region” means that, in some embodiments, a positive electrode active material layer is provided on one surface of the positive electrode current collector in the second region, and in other embodiments, a positive electrode active material layer is provided on both surfaces of the positive electrode current collector in the second region. The “surface” can be the entire surface of the positive electrode current collector in the second region, or a portion of the surface of the positive electrode current collector in the second region.

[0039] In this application, for ease of understanding, the first direction is defined as X, the direction perpendicular to the first direction is defined as Y, and the thickness direction of the positive electrode sheet is defined as Z. It is understood that the thickness direction of the negative electrode sheet and the separator is the same as the thickness direction of the positive electrode sheet. It should be noted that the above-mentioned "direction perpendicular to the first direction" can be understood as the perpendicular relationship on the plane formed by the length and width directions of the positive electrode sheet. As shown in Figures 1 to 4, the secondary battery includes an electrode assembly 100 and a packaging bag 200. The electrode assembly 100 is contained in the packaging bag 200. The electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The separator 30 is arranged between the positive electrode sheet 10 and the negative electrode sheet 20; the positive electrode sheet 10 includes a positive electrode tab 11, a positive electrode collector 12, a first molecular sieve coating 13 and a positive electrode active material layer 14. Along a first direction X, the positive electrode sheet 10 includes a second region 102 and a first region 101 connected in sequence. The positive electrode tab 11 is integrally arranged with the positive electrode collector 12 in the first region 101. The first molecular sieve coating 13 is provided on both surfaces of the positive electrode collector 12 in the first region 101, and the positive electrode active material layer 14 is provided on at least one surface of the positive electrode collector 12 in the second region 102. The first direction X is the extension direction of the positive electrode tab 11 in the unfolded state (as shown in Figure 2). It is understandable that the positive electrode tab is integrally arranged with the positive electrode current collector in the first region, and when the positive electrode tab is not folded, the extension direction of the positive electrode tab is parallel to the positive electrode current collector. During the preparation process of the secondary battery, considering the actual production process, the portion of the positive electrode tab extending outside the positive electrode current collector may be folded. In this way, the portion of the positive electrode tab extending outside the positive electrode current collector will bend (as shown in Figure 1), and the extension direction of the positive electrode tab in a tortuous state is no longer parallel to the positive electrode current collector. It should be noted that the above-mentioned "parallel" refers to parallelism under ideal conditions. In actual production, due to the influence of manual or operational factors during the preparation process, it may be approximately parallel. The first molecular sieve coating includes a molecular sieve and a first binder. Based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10% to 90%, and the mass percentage of the first binder is 10% to 90%. For example, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any value between any two of the above numerical ranges. For example, based on the mass of the first molecular sieve coating, the mass percentage of the first binder is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any value between any two of the above numerical ranges.

[0040] Based on the first molecular sieve coating, when the mass percentage of the molecular sieve is less than 10% or the mass percentage of the first binder is greater than 90%, the content of the molecular sieve in the first molecular sieve coating is too small, and the density of the first molecular sieve coating is poor, which will affect the insulation protection effect of the first molecular sieve coating on the positive electrode current collector adjacent to it; when the mass percentage of the molecular sieve is greater than 90% or the mass percentage of the first binder is less than 10%, the content of the first binder in the first molecular sieve coating is too small, the bonding force of the formed first molecular sieve coating is poor, and the interface bonding between the positive electrode plate and the diaphragm and the negative electrode plate is poor, which will affect the cycle performance of the secondary battery, and when the secondary battery falls or hits, the diaphragm is prone to fold, affecting the drop safety performance of the secondary battery.

[0041] In the present application, a first molecular sieve coating is provided on at least one surface of the positive electrode current collector in the first region. On the one hand, the conventional ceramic coating such as alumina or boehmite can be applied thereto to prevent the positive electrode current collector burrs from piercing the separator and causing a short circuit, and to prevent the positive electrode current collector from directly contacting the negative electrode active material and causing a dangerous short circuit when the negative electrode active material layer exceeds the positive electrode active material layer in the width direction, thereby providing the secondary battery with good anti-short circuit performance. On the other hand, the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating are controlled within the above-mentioned ranges. The molecular sieve and the first binder cooperate with each other, so that the first molecular sieve coating has good bonding effect, which can enhance the bonding effect between the positive electrode sheet and the separator at the head of the electrode assembly, reduce the risk of weak bonding between the electrode sheet layers due to electrolyte accumulation at the head of the electrode assembly, and reduce the risk of weak bonding between the positive electrode active material layer and the separator, thereby providing good bonding effect between the positive electrode sheet and the separator at the head of the electrode assembly. As a result, there is good interfacial contact between the positive electrode sheet and the separator, less lithium plating occurs on the negative electrode sheet, and the cycle performance of the secondary battery is improved. Furthermore, the first region of the positive electrode sheet and the separator have good adhesion, reducing the probability of the separator folding, thereby improving the drop safety of the secondary battery. Furthermore, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, reducing the risk of flatulence in the secondary battery and thus improving the storage performance of the secondary battery.

[0042] In one embodiment of the present application, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 20% to 80%, and the mass percentage of the first binder is 20% to 80%. For example, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value between any two of the above numerical ranges. For example, based on the mass of the first molecular sieve coating, the mass percentage of the first binder is 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value between any two of the above numerical ranges. By regulating the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating within the above range, while ensuring that the first molecular sieve coating is short-circuit-proof, the bonding effect between the positive electrode plate and the diaphragm at the head of the electrode assembly can be further enhanced, reducing the risk of weak bonding between the electrode plate layers due to electrolyte accumulation at the head of the electrode assembly, and further reducing the risk of weak bonding between the positive electrode active material layer and the diaphragm, so that the positive electrode plate and the diaphragm at the head of the electrode assembly have a good bonding effect. As a result, there is a good interface contact effect between the positive electrode plate and the diaphragm, less lithium deposition occurs on the negative electrode plate, and the cycle performance of the secondary battery is further improved. In addition, there is a good bonding effect between the first region of the positive electrode plate and the diaphragm, and the probability of the diaphragm folding is reduced, thereby further improving the drop safety performance of the secondary battery.

[0043] In one embodiment of the present application, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 30% to 70%, and the mass percentage of the first binder is 30% to 70%. For example, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 30%, 40%, 50%, 60%, 70%, or any value between any two of the above numerical ranges. For example, based on the mass of the first molecular sieve coating, the mass percentage of the first binder is 30%, 40%, 50%, 60%, 70%, or any value between any two of the above numerical ranges. By regulating the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating within the above range, the bonding between the positive electrode plate and the diaphragm at the head of the electrode assembly can be further enhanced, the risk of weak bonding between the electrode plate layers due to electrolyte accumulation at the head of the electrode assembly can be reduced, and the risk of weak bonding between the positive electrode active material layer and the diaphragm can be further reduced, so that the positive electrode plate and the diaphragm at the head of the electrode assembly have good bonding effect. As a result, there is good interface contact between the positive electrode plate and the diaphragm, less lithium deposition occurs on the negative electrode plate, and the cycle performance of the secondary battery is further improved. In addition, there is good bonding effect between the first region of the positive electrode plate and the diaphragm, and the probability of the diaphragm folding is reduced, thereby further improving the drop safety performance of the secondary battery.

[0044] In one embodiment of the present application, as shown in FIG3 and FIG4 , along the first direction X, the width W of the first molecular sieve coating 13 is 13 0.5mm to 10mm. For example, the width of the first molecular sieve coating is 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or any value between any two of the above numerical ranges. Setting the width of the first molecular sieve coating to 0.5mm to 10mm can better prevent the positive electrode current collector and the negative electrode active material from directly contacting and causing a short circuit, while taking into account the energy density of the secondary battery, so that the first molecular sieve coating has good adhesion to the diaphragm. The length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet, which can more effectively achieve the above effect in the length direction. As a result, there is a good interface contact effect between the positive electrode sheet and the diaphragm, less lithium plating occurs on the negative electrode sheet, the cycle performance of the secondary battery is improved, and the secondary battery has higher energy density and safety performance. In addition, there is a good bonding effect between the first region of the positive electrode sheet and the diaphragm, and the probability of the diaphragm flipping is reduced, thereby improving the drop safety performance of the secondary battery.

[0045] In one embodiment of the present application, as shown in FIG3 and FIG4 , along the first direction X, the width W of the first molecular sieve coating 13 is 13 The width of the first molecular sieve coating is 1 mm to 3 mm. For example, the width of the first molecular sieve coating is 1 mm, 2 mm, 3 mm, or any value between any two of the above numerical ranges. Setting the width of the first molecular sieve coating to 1 mm to 3 mm can better prevent the positive electrode current collector and the negative electrode active material from directly contacting each other and causing a short circuit, while taking into account the energy density of the secondary battery, further improve the adhesion of the first molecular sieve coating to the separator, thereby further improving the drop safety performance of the secondary battery.

[0046] In one embodiment of the present application, along the direction perpendicular to the first direction, the length of the first molecular sieve coating layer is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet. For example, in some embodiments, as shown in FIG3 , along the direction Y perpendicular to the first direction X, the length L of the first molecular sieve coating layer 13 is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet. 13 Equal to the length L of the positive electrode active material layer 14 14 and is equal to the length L of the positive electrode plate 10 10. In other embodiments, along the direction perpendicular to the first direction, the length of the first molecular sieve coating is greater than the length of the positive electrode active material layer and is equal to the length of the positive electrode sheet. In some further embodiments, along the direction perpendicular to the first direction, the length of the first molecular sieve coating is equal to the length of the positive electrode active material layer and is equal to the length of the positive electrode sheet. In some further embodiments, along the direction perpendicular to the first direction, the length of the first molecular sieve coating is greater than the length of the positive electrode active material layer and is less than the length of the positive electrode sheet. The present application has no particular restrictions on the length of the first molecular sieve coating, the length of the positive electrode active material layer and the length of the positive electrode sheet. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. The length of the first molecular sieve coating is regulated within the above range, so that the area of ​​the positive electrode sheet where the positive electrode active material layer is provided is provided with the first molecular sieve coating, and the first molecular sieve coating can be set according to the original structure of the positive electrode sheet. When the adhesion of each layer of the wound electrode assembly and the laminated electrode assembly is enhanced, the space of the secondary battery can also be fully utilized. Furthermore, the first molecular sieve coating can better prevent the positive electrode current collector and the negative electrode active material from directly contacting each other, thereby causing a short circuit, while also taking into account the energy density of the secondary battery. This results in good interfacial contact between the positive electrode sheet and the separator, less lithium deposition on the negative electrode sheet, improved cycle performance of the secondary battery, and a higher energy density and safety performance. Furthermore, the first region of the positive electrode sheet has good adhesion to the separator, reducing the probability of the separator folding, thereby improving the drop safety performance of the secondary battery.

[0047] In one embodiment of the present application, as shown in FIG4 , the thickness H of the first molecular sieve coating 13 is 13 smaller than the thickness H of the positive electrode active material layer 14 14 The thickness H of the first molecular sieve coating 13 is 13 It is 0.5μm to 40μm. For example, the thickness of the first molecular sieve coating is 0.5μm, 5μm, 20μm, 40μm or any value between any two of the above numerical ranges. By regulating the thickness of the first molecular sieve coating within the above range, the first molecular sieve coating can have a good covering effect on the positive electrode current collector without increasing the volume of the secondary battery, so that the first molecular sieve coating can better prevent short circuits and improve the adhesion with the diaphragm, and can also take into account the energy density of the secondary battery. In this way, there is a good interface contact effect between the positive electrode sheet and the diaphragm, less lithium plating occurs on the negative electrode sheet, the cycle performance of the secondary battery is improved, and the secondary battery has a higher energy density and good anti-short circuit performance. In addition, there is a good bonding effect between the first area of ​​the positive electrode sheet and the diaphragm, and the probability of the diaphragm flipping is reduced, thereby improving the drop safety performance of the secondary battery.

[0048] The thickness of the positive electrode active material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 200 μm.

[0049] In one embodiment of the present application, the thickness of the first molecular sieve coating is 5 μm to 20 μm. For example, the thickness of the first molecular sieve coating is 5 μm, 7 μm, 10 μm, 15 μm, 18 μm, 20 μm, or any value between any two of the above ranges. Controlling the thickness of the first molecular sieve coating within the above ranges is beneficial for further improving the short-circuit resistance, cycle performance, drop safety, and storage performance of the secondary battery.

[0050] In one embodiment of the present application, as shown in FIG5 , along the thickness direction Z of the positive electrode sheet 10, the first molecular sieve coating 13 and the positive electrode active material layer 14 have an overlapping area 40. In the overlapping area 40, the positive electrode active material layer 14 is located between the first molecular sieve coating 13 and the positive electrode current collector 12. It should be noted that for ease of understanding, the portion marked with an elliptical frame 50 in FIG5 is magnified. In actual circumstances, the surface of the positive electrode sheet is approximately flat after rolling during the preparation process. The portion marked with an elliptical frame 50 is not a protrusion as shown in FIG5 , but is substantially flush with the surface of the positive electrode active material layer 14 that does not have the overlapping area 40. Along the first direction X, the width W of the overlapping area 40 is 40 It is 0mm to 0.5mm. For example, the width of the overlapping area is 0mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm or any value between any two of the above numerical ranges. The positive electrode active material layer and the first molecular sieve coating have an overlapping area, and the width of the overlapping area is regulated within the above range, which can reduce the risk of direct exposure of the positive electrode current collector, which is beneficial to reducing the safety risk of the secondary battery. And when the contact area between the positive electrode active material layer and the first molecular sieve coating is as small as possible, the first molecular sieve coating exerts its good bonding effect. As a result, there is a good interface contact effect between the positive electrode plate and the diaphragm, less lithium plating occurs on the negative electrode plate, and the cycle performance of the secondary battery is improved. In addition, there is a good bonding effect between the first area of ​​the positive electrode plate and the diaphragm, and the probability of the diaphragm folding is reduced, thereby improving the drop safety performance of the secondary battery.

[0051] In one embodiment of the present application, as shown in FIG6 , a second molecular sieve coating 23 is provided on the surface of the diaphragm 20 opposite to the first region 101. It will be understood that the above-mentioned “surface” can be one surface of the diaphragm or two surfaces of the diaphragm. The above-mentioned “relative” refers to the portion of the diaphragm at least overlapping with the first region when projected along the thickness direction of the diaphragm. For example, in some embodiments of the present application, as shown in FIG7 , a second molecular sieve coating 23 is provided on the two surfaces of the diaphragm 20 opposite to the first region 101. In other embodiments of the present application, as shown in FIG8 , a second molecular sieve coating 23 is provided on the first surface 20a of the diaphragm 20 opposite to the first region 101. It should be noted that the second molecular sieve coating 23 can also be provided on the second surface 20b of the diaphragm 20 opposite to the first region 101. Based on the mass of the second molecular sieve coating, the mass percentage of molecular sieve is 20% to 80%. For example, based on the mass of the second molecular sieve coating, the mass percentage of the molecular sieve is 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value between any two of the above numerical ranges. A second molecular sieve coating is provided on the surface of the diaphragm opposite to the first region, and the content of the molecular sieve in the second molecular sieve coating is regulated within the above range. The second molecular sieve coating is bonded to the first molecular sieve coating and the negative electrode sheet, and can exert its good bonding effect, further bonding the diaphragm to the positive electrode sheet and the negative electrode sheet, so that the bonding effect of the diaphragm to the positive electrode sheet and the negative electrode sheet is further improved. In this way, the interface contact effect between the positive electrode sheet, the diaphragm and the negative electrode sheet is further strengthened, and the cycle performance of the secondary battery is further improved. In addition, the provision of the second molecular sieve coating can further reduce the risk of the positive current collector burr piercing the diaphragm, causing the positive current collector to directly contact with the negative electrode active material and cause a short circuit, thereby further improving the anti-short circuit performance of the secondary battery. The second molecular sieve coating on the separator can also reduce the possibility of shrinkage of the separator substrate layer, improving the high-temperature resistance of the secondary battery. In addition, the probability of the separator folding is further reduced, further improving the drop safety performance of the secondary battery.

[0052] In one embodiment of the present application, the second molecular sieve coating further comprises a first binder, and the weight percentage of the first binder is 20% to 80% based on the weight of the second molecular sieve coating. For example, the weight percentage of the first binder is 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value between any two of the above ranges, based on the weight of the second molecular sieve coating.

[0053] In one embodiment of the present application, as shown in FIG7 and FIG8 , the thickness H of the second molecular sieve coating 23 is 23It is 0.5μm to 10μm. For example, the thickness of the second molecular sieve coating is 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any value between any two of the above numerical ranges. By regulating the thickness of the second molecular sieve coating within the above range, the second molecular sieve coating can have a good covering effect on the diaphragm without increasing the volume of the secondary battery, so that the second molecular sieve coating can better prevent short circuits and improve the adhesion with the diaphragm, and can also take into account the energy density of the secondary battery. In this way, the interface contact effect between the positive electrode, the diaphragm and the negative electrode is further enhanced, the lithium plating on the negative electrode is further reduced, the cycle performance of the secondary battery is further improved, and the secondary battery has a higher energy density and good anti-short circuit performance. In addition, the probability of the diaphragm flipping is further reduced, thereby further improving the drop safety performance of the secondary battery.

[0054] The width and length of the second molecular sieve coating are not particularly limited in this application. Those skilled in the art can adjust the width and length of the first molecular sieve coating according to the width and length of the first molecular sieve coating, as long as the purpose of this application can be achieved. For example, along the first direction X, the width of the second molecular sieve coating is 0.5 mm to 15 mm. Along the direction Y perpendicular to the first direction X, the length of the second molecular sieve coating is less than or equal to the length of the diaphragm.

[0055] Those skilled in the art will understand that in a secondary battery, the positive electrode sheet, negative electrode sheet, and separator are all the same in thickness, width, and length. Therefore, the first direction X and the direction Y perpendicular to the first direction X refer to the same direction in both the positive electrode sheet and the separator.

[0056] In one embodiment of the present application, the porosity of the first molecular sieve coating is 30% to 60%. For example, the porosity of the first molecular sieve coating is 30%, 40%, 50%, 60% or any value between any two of the above numerical ranges. By regulating the porosity of the first molecular sieve coating within the above range, the first molecular sieve coating can have good insulation and structural strength so that the first molecular sieve coating can play its anti-short circuit effect, and can also play the effect of the first molecular sieve coating to improve the adhesion. In this way, there is a good interface contact effect between the positive electrode sheet and the diaphragm, less lithium deposition occurs on the negative electrode sheet, the cycle performance of the secondary battery is improved, and the secondary battery also has good anti-short circuit performance. In addition, there is a good bonding effect between the first area of ​​the positive electrode sheet and the diaphragm, and the probability of the diaphragm flipping is reduced, thereby improving the drop safety performance of the secondary battery.

[0057] In one embodiment of the present application, the porosity of the second molecular sieve coating is 30% to 60%. For example, the porosity of the second molecular sieve coating is 30%, 40%, 50%, 60% or any value between any two of the above numerical ranges. By regulating the porosity of the second molecular sieve coating within the above range, the second molecular sieve coating can have good insulation and structural strength so that the second molecular sieve coating can play its anti-short circuit effect, and can also play the effect of the second molecular sieve coating to improve the adhesion. In this way, there is a good interface contact effect between the diaphragm and the positive electrode sheet and the negative electrode sheet, and lithium plating on the negative electrode sheet is less, the cycle performance of the secondary battery is improved, and the secondary battery also has good anti-short circuit performance. The second molecular sieve coating can also reduce the possibility of shrinkage of the substrate layer in the diaphragm and improve the high temperature resistance of the secondary battery. In addition, the probability of the diaphragm flipping is further reduced, thereby further improving the drop safety performance of the secondary battery.

[0058] The present application does not particularly limit the method for controlling the porosity of the first molecular sieve coating and the second molecular sieve coating, as long as the purpose of the present application can be achieved. For example, this can be achieved by controlling the type of molecular sieve in the first molecular sieve coating and the second molecular sieve coating, the ratio of the molecular sieve to the first binder, the pore size of the molecular sieve, etc.

[0059] In one embodiment of the present application, the specific surface area of ​​the molecular sieve is 200m 2 / g to 2000m 2 / g. For example, the specific surface area of ​​molecular sieve is 200m 2 / g, 400m 2 / g、600m 2 / g、800m 2 / g、1000m 2 / g、1200m 2 / g、1400m 2 / g、1600m 2 / g、1800m 2 / g、2000m 2 / g or any value between any two numerical ranges mentioned above. In one embodiment of the present application, the pore size of the molecular sieve is 0.3nm to 45nm. For example, the pore size of the molecular sieve is 0.3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or any value between any two numerical ranges mentioned above. The specific surface area of ​​the molecular sieve and / or the pore size of the molecular sieve are regulated within the above range, the molecular sieve has a higher specific surface area, and / or the molecular sieve has a larger pore size. When the molecular sieve is applied to the first molecular sieve coating and / or the second molecular sieve coating, the bonding area of ​​the molecular sieve can be increased, the mechanical intercalation effect is enhanced, and the molecular sieve has a large cohesive force after being combined with the first binder, and the bonding force is strong. In this way, the first molecular sieve coating and the second molecular sieve coating are highly dispersed after being fully swollen at high temperature, and form good bonding force. Thus, there is a good interface contact effect between the positive electrode sheet and the diaphragm, or the positive electrode sheet, the diaphragm and the negative electrode sheet, and the cycle performance of the secondary battery is improved. Furthermore, the probability of the diaphragm folding is reduced, which can improve the drop safety performance of the secondary battery. In addition, the molecular sieve has the ability to absorb gas, which can reduce the risk of secondary battery flatulence and improve the problem of secondary battery flatulence and bulging under special working conditions (such as high temperature storage, over-discharge, storage after over-discharge, charge and discharge after over-discharge, overcharge, thermal runaway, etc.), thereby improving the storage performance of the secondary battery. In this application, "high temperature" refers to a temperature of 40°C to 90°C.

[0060] The present application does not particularly limit the average volume particle size of the molecular sieve, as long as it can achieve the purpose of this application. For example, the average volume particle size of the molecular sieve is 0.5 μm to 20 μm. In this application, the average volume particle size Dv50 represents the particle size at which the volume of the molecular sieve particles reaches 50% of the cumulative volume, starting from the smallest particle size side, in the volume-based particle size distribution.

[0061] In one embodiment of the present application, the molecular sieve comprises at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 13X molecular sieve, ZSM-22 molecular sieve, ZSM-5 molecular sieve, MOR molecular sieve, ITQ molecular sieve, Y molecular sieve, SAPO molecular sieve, or ALPO molecular sieve. Furthermore, the ITQ molecular sieve comprises at least one of ITQ-24, ITQ-40, or ITQ-55; the Y molecular sieve comprises at least one of NaY, HY, USY, or RY; the SAPO molecular sieve comprises at least one of SAPO-11, SAPO-20, or SAPO-34; and the ALPO molecular sieve comprises at least one of ALPO-4, ALPO-15, or ALPO-18. For interfacial bonding, the molecular sieve of the above type has a larger specific surface area and pore size. When applied to the first molecular sieve coating and / or the second molecular sieve coating, the bonding area of ​​the molecular sieve can be increased, the mechanical intercalation effect is enhanced, and the molecular sieve has a large cohesive force after being combined with the binder, and the bonding force is strong. In this way, the first molecular sieve coating and the second molecular sieve coating are highly dispersed after being fully swollen at high temperature, and form a good bonding force. Thus, there is a good interface contact effect between the positive electrode sheet and the diaphragm, or between the positive electrode sheet, the diaphragm and the negative electrode sheet, and the cycle performance of the secondary battery is improved. Moreover, the probability of the diaphragm being turned over decreases, which can improve the drop safety performance of the secondary battery. In addition, the molecular sieve has the ability to absorb gas, which can reduce the risk of flatulence in the secondary battery, improve the problem of flatulence and bulging of the secondary battery in special working conditions, thereby improving the storage performance of the secondary battery.

[0062] In one embodiment of the present application, the first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polypropylene alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

[0063] In one embodiment of the present application, as shown in FIG9 , the positive electrode sheet 10 further includes a conductive layer 15 , which is disposed on a surface 13 a of the first molecular sieve coating 13 facing away from the positive electrode current collector 12 ; the conductive layer includes a conductive agent, and the weight percentage of the conductive agent is 5% to 70% based on the weight of the conductive layer. For example, the weight percentage of the conductive layer is 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any value between any two of the above numerical ranges based on the weight of the conductive layer. The conductive layer further includes a second binder, and the weight percentage of the second binder is 30% to 95% based on the weight of the conductive layer. For example, the weight percentage of the second binder is 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or any value between any two of the above numerical ranges based on the weight of the conductive layer. The edge impedance of the positive electrode is often greater than that of the main body, and the current density of the positive electrode is relatively high. Therefore, lithium deposition is more likely to occur in the overhang area of ​​the negative electrode in the electrode assembly. A conductive layer is provided on the surface of the first molecular sieve coating in the positive electrode facing away from the positive electrode current collector. The conductive layer can induce a polarization electric field, which can balance the electric field strength on the electrode surface and exert a certain influence on the lithium ion battery at the edge of the negative electrode. + / Li concentration plays a role in uniformity, thereby improving lithium precipitation caused by uneven electric field and achieving the purpose of extending the cycle life of the secondary battery. The mass percentage of the conductive agent and the second binder in the conductive layer is controlled within the above range. When the conductive layer induces a polarization electric field, it has a good bonding effect, so that the positive electrode sheet and the diaphragm and the negative electrode sheet have a good bonding effect. As a result, there is a good interface contact effect between the positive electrode sheet and the diaphragm, and the cycle performance of the secondary battery is improved. In addition, there is a good bonding effect between the first area of ​​the positive electrode sheet and the diaphragm, and the probability of the diaphragm folding is reduced, thereby improving the drop safety performance of the secondary battery.

[0064] The present application has no particular restrictions on the second binder, as long as it can achieve the purpose of the present application. For example, the second binder includes, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polypropylene alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber, or styrene-butadiene rubber.

[0065] In one embodiment of the present application, as shown in FIG9 , the thickness H of the first molecular sieve coating 13 is 13 The thickness H of the conductive layer 15 15 The sum is less than the thickness H of the positive electrode active material layer 14 14; The thickness of the first molecular sieve coating is 0.5μm to 40μm, and the thickness of the conductive layer is 0.5μm to 30μm. For example, the thickness of the first molecular sieve coating is 0.5μm, 20μm, 40μm, or any value between any two of the above numerical ranges. For example, the thickness of the conductive layer is 0.5μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, or any value between any two of the above numerical ranges. By regulating the relationship between the sum of the thickness of the first molecular sieve coating and the thickness of the conductive layer and the thickness of the positive electrode active material layer within the above range, the possibility of a gap between the second region of the positive electrode sheet and the diaphragm due to excessive thickness of the first molecular sieve coating and the conductive layer can be reduced, so that the second region of the positive electrode sheet is in full contact with the diaphragm, and good interface performance is achieved between the positive electrode sheet and the diaphragm. Regulating the thickness of the first molecular sieve coating and the thickness of the conductive layer within the above range is beneficial to improving lithium plating caused by uneven electric field without increasing the volume of the secondary battery, thereby achieving the purpose of extending the cycle life of the secondary battery. Furthermore, the positive electrode sheet, separator, and negative electrode sheet have good interfacial contact, improving the cycle performance of the secondary battery. Furthermore, the first region of the positive electrode sheet and the separator have good adhesion, reducing the probability of the separator folding, thereby improving the drop safety performance of the secondary battery.

[0066] In one embodiment of the present application, the conductive agent includes at least one of acetylene black, Ketjen black, conductive graphite, graphene, single-walled carbon nanotubes, or multi-walled carbon nanotubes. The above conductive agents have good electrical conductivity.

[0067] This application does not specifically limit the structure of the electrode assembly, as long as it can achieve the objectives of this application. For example, the electrode assembly can be a wound structure or a laminated structure. This application does not specifically limit the type of positive electrode current collector, as long as it can achieve the objectives of this application. For example, the positive electrode current collector includes aluminum foil, aluminum alloy foil, etc.

[0068] In one embodiment of the present application, the positive electrode active material layer includes a positive electrode active material. The present application does not particularly limit the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. Optionally, the positive electrode active material layer also includes a positive electrode conductive agent and a positive electrode binder. The present application does not particularly limit the types of positive electrode conductive agent and positive electrode binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the positive electrode active material, positive electrode conductive agent and positive electrode binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of the positive electrode active material, positive electrode conductive agent and positive electrode binder in the positive electrode active material layer is (96.5~97.9):(0.9~2.0):(1.0~2.0).

[0069] In one embodiment of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along the thickness direction of itself, or can be disposed on two surfaces of the negative electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, titanium foil, foam nickel or foam copper, etc. The negative electrode active material layer includes a negative electrode active material. This application has no special restrictions on the type of negative electrode active material, as long as the purpose of this application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microbeads, tin-based materials, silicon-based materials, lithium titanate or transition metal nitrides. Optionally, the negative electrode active material layer also includes at least one of a negative electrode conductor, a thickener, and a negative electrode binder. The present application does not particularly limit the types of negative electrode conductors, thickeners, and negative electrode binders in the negative electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the negative electrode active material, negative electrode conductor, thickener, and negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, negative electrode conductor, thickener, and negative electrode binder in the negative electrode active material layer is (96-98):(0-1.5):(0.5-1.5):(1.0-1.9).

[0070] The thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 5 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

[0071] The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0072] The secondary battery of the present application also includes an electrolyte, and the electrolyte and electrode assembly are contained in a packaging bag. The present application does not particularly limit the packaging bag and electrolyte. Those skilled in the art can select packaging bags and electrolytes known in the art as needed, as long as they can achieve the purpose of the present application.

[0073] The present application has no particular restrictions on the preparation method of the positive electrode sheet, as long as it can achieve the purpose of the present application.

[0074] For example, in some embodiments of the present application, the positive electrode sheet includes a positive electrode tab, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, and the preparation method of the positive electrode sheet includes but is not limited to the following steps: (1) preparing a positive electrode slurry and a first molecular sieve coating slurry; (2) coating the positive electrode slurry and the first molecular sieve coating slurry on one surface of the positive electrode current collector, and drying to obtain a positive electrode sheet coated with a positive electrode active material layer and a first molecular sieve coating on one side; coating the positive electrode slurry and the first molecular sieve coating slurry on the other surface of the positive electrode current collector, and drying to obtain a positive electrode sheet coated with a positive electrode active material layer and a first molecular sieve coating on both sides; wherein the first molecular sieve coating is arranged in a first area of ​​the positive electrode sheet, and the positive electrode active material layer is arranged in a second area of ​​the positive electrode sheet; (3) cold pressing and cutting. The present application has no special restrictions on the preparation method of the positive electrode slurry and the first molecular sieve coating slurry in the above step (1), as long as the content of the molecular sieve and the first binder in the first molecular sieve coating is within the scope of the present application and the purpose of the present application can be achieved. The present application does not impose any particular restrictions on the drying temperature and time in step (2). Those skilled in the art can select the temperature and time according to actual needs, as long as the purpose of the present application can be achieved. The present application does not impose any particular restrictions on the process parameters for cold pressing and cutting in step (3). Those skilled in the art can select the temperature and time according to actual needs, as long as the purpose of the present application can be achieved.

[0075] For example, in some other embodiments of the present application, the positive electrode sheet includes a positive electrode tab, a positive electrode current collector, a first molecular sieve coating, a conductive layer and a positive electrode active material layer, and the preparation method of the positive electrode sheet includes but is not limited to the following steps: (1) preparing a positive electrode slurry, a first molecular sieve coating slurry and a conductive layer slurry; (2) coating the positive electrode slurry and the first molecular sieve coating slurry on one surface of the positive electrode current collector, and after drying, obtaining a positive electrode sheet with a single-side coating of the positive electrode active material layer and the first molecular sieve coating, coating the conductive layer slurry on the surface of the first molecular sieve coating away from the positive electrode current collector, and after drying, obtaining a positive electrode sheet with a single-side coating of the positive electrode active material layer, the first molecular sieve coating and the conductive layer; repeating the above steps to obtain a positive electrode sheet with a double-side coating of the positive electrode active material layer, the first molecular sieve coating and the conductive layer; wherein the first molecular sieve coating and the conductive layer are arranged in the first area of ​​the positive electrode sheet, and the positive electrode active material layer is arranged in the second area of ​​the positive electrode sheet; (3) cold pressing and cutting. The present application has no special restrictions on the preparation methods of the positive electrode slurry, the first molecular sieve coating slurry and the conductive layer slurry in the above step (1). As long as the contents of the molecular sieve and the first binder in the first molecular sieve coating are within the scope of the present application, and the contents of the conductive agent and the second binder in the conductive layer are within the scope of the present application, the purpose of the present application can be achieved. The present application has no special restrictions on the temperature and time of the drying in the above step (2). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the process parameters of cold pressing and cutting in the above step (3). Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0076] The present application has no particular restrictions on the preparation method of the second molecular sieve coating, as long as the purpose of the present application can be achieved. For example, the preparation method of the second molecular sieve coating includes but is not limited to the following steps: (1) preparing a second molecular sieve coating slurry; (2) coating the second molecular sieve coating slurry on one surface of the diaphragm opposite to the first area of ​​the positive electrode plate, drying, and obtaining a diaphragm coated with the second molecular sieve coating on one side. Afterwards, repeat the above steps on the other surface of the diaphragm opposite to the first area of ​​the positive electrode plate to obtain a diaphragm coated with the second molecular sieve coating on both sides. The present application has no particular restrictions on the preparation method of the second molecular sieve coating slurry in the above step (1), as long as the content of the molecular sieve and the first binder in the second molecular sieve coating is within the scope of the present application, the purpose of the present application can be achieved. The present application has no particular restrictions on the temperature and time of drying in the above step (2), and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0077] The present application does not impose any particular restrictions on the preparation method of the secondary battery, and any preparation method known in the art may be selected, as long as the purpose of the present application can be achieved. For example, the preparation method of the secondary battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, then fixing the four corners of the entire laminate structure to obtain an electrode assembly of the laminate structure, placing the electrode assembly in a packaging bag, welding the positive electrode tab and the negative electrode tab to the metal sheet by transfer welding and leading them out of the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. Alternatively, stacking and winding the positive electrode sheet, the separator and the negative electrode sheet in order to obtain an electrode assembly of the wound structure, placing the electrode assembly in a packaging bag, welding the positive electrode tab and the negative electrode tab to the metal sheet by transfer welding and leading them out of the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. The present application does not impose any particular restrictions on the type of the above-mentioned metal sheet, as long as the purpose of the present application can be achieved. For example, the metal sheet welded to the positive electrode tab may be an aluminum sheet, and the metal sheet welded to the negative electrode tab may be a copper sheet, a nickel sheet, or a copper-plated nickel sheet.

[0078] The secondary battery of the present application is not particularly limited and may include a device that generates an electrochemical reaction. For example, the secondary battery may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a sodium ion secondary battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, and a sodium ion battery.

[0079] The second aspect of the present application provides an electric device, wherein the electric device comprises the secondary battery described in any of the aforementioned embodiments. Therefore, the electric device has good performance.

[0080] The electrical devices of the present application are not particularly limited and may be any electrical devices known in the art. For example, the electrical devices may include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0081] Example

[0082] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0083] Test methods and equipment:

[0084] Lithium deposition test:

[0085] At 25°C, the lithium-ion batteries of each embodiment and comparative example were charged to full charge (charging system was constant current charging at a rate of 4C to 4.48V, and then constant voltage charging to a current of 0.05C), left for 5 minutes, and then discharged at 1 / 3C to 3.0V. The above steps were repeated 900 times for the same lithium-ion battery.

[0086] After completing 300, 500, 700, and 900 cycle tests, the lithium-ion batteries were fully charged at room temperature using the standard charging method (0.5C charging to 4.48V, 4.48V constant voltage charging to 0.02C). The lithium-ion batteries were disassembled to check the distribution of lithium deposition on the surface of the negative electrode.

[0087] Adhesion test:

[0088] Take out the lithium-ion battery to be disassembled, cut off the edge of the packaging bag, then open the packaging bag and unfold the electrode assembly. Separate the positive electrode sheet, diaphragm, and negative electrode sheet, retain the positive electrode sheet and diaphragm, and take approximately the same position and the same surface in the first area of ​​the positive electrode sheet for different lithium-ion batteries. Take the positive electrode sheet and diaphragm, and use a blade to cut into 10mm×50mm samples. Stick double-sided tape (manufacturer: Nitto, product model: 5000NS) on the steel plate, and stick the cut sample on the aforementioned double-sided tape with the test surface facing up, that is, from bottom to top, the order is steel plate, double-sided tape, positive electrode sheet, and diaphragm. Stick a paper tape with a width equal to the sample and a length greater than 50mm to the diaphragm surface and fix it with wrinkle glue. Use a tensile tester to separate, with a peeling angle of 180°. The peeling force data tested is the adhesion data of the positive electrode sheet and diaphragm.

[0089] Drop test:

[0090] The lithium-ion batteries from each example and comparative example were fully charged using a standard charging method (0.5C charging to 4.48V, then constant voltage charging at 4.48V to 0.02C). The batteries were then dropped from a height of 1m onto a marble floor in a test environment at 20±5°C, with each drop occurring once along each of the six sides and once at each of the four corners, for a total of five cycles. Pass criteria included: no fire, no explosion, no smoke, no leakage, and a voltage drop of <100mV.

[0091] Five lithium-ion batteries were tested in each embodiment and comparative example, and the drop safety performance was characterized by the ratio of the number of batteries that passed the test. The higher the number of batteries that passed the test, the better the drop safety performance of the lithium-ion battery; the ratio of the number of batteries that passed the test = the number of batteries that passed / 5.

[0092] Storage performance test:

[0093] The lithium-ion batteries of the embodiments and comparative examples were fully charged at 25°C using a standard charging method (0.5C charging to a voltage of 4.48V, constant voltage charging at 4.48V to 0.02C), and stored in an 80°C constant temperature oven for 48 hours. The thickness of the lithium-ion batteries before and after storage was measured to obtain the expansion ratio: Expansion ratio (%) = (thickness after test - thickness before test) / thickness before test × 100%.

[0094] The storage performance of lithium-ion batteries is characterized by the expansion rate. The lower the expansion rate, the better the storage performance of the lithium-ion battery.

[0095] Porosity test:

[0096] Tested by true density tester.

[0097] The lithium-ion batteries in each example and comparative example were fully discharged (discharged to 3.0V at a constant current of 0.5C) and then disassembled. The resulting positive electrode sheets and separators were cleaned in n-butanol and then air-dried. The first molecular sieve coating on the positive electrode sheet and the second molecular sieve coating on the separator were peeled off using a scraper and then ground into powder.

[0098] The powder obtained by grinding the first molecular sieve coating was compacted and punched into a 10 mm x 10 mm sample. The sample was placed on a true density meter (AccuPyc II 1340) to determine the true volume of the first molecular sieve coating. The length, width, and height of the sample were measured with a ruler, and the apparent volume of the first molecular sieve coating was calculated as follows: length × width × height. The porosity (%) of the first molecular sieve coating was calculated as follows: (apparent volume of the first molecular sieve coating - true volume of the first molecular sieve coating) / apparent volume of the first molecular sieve coating × 100%.

[0099] The powder obtained by grinding the second molecular sieve coating was compacted and punched into a 10 mm x 10 mm sample. The sample was placed on a true density tester (AccuPyc II 1340) to determine the true volume of the second molecular sieve coating. The length, width, and height of the sample were measured with a ruler, and the apparent volume of the second molecular sieve coating was calculated as follows: length × width × height. The porosity (%) of the second molecular sieve coating was calculated as follows: (apparent volume of the second molecular sieve coating - true volume of the second molecular sieve coating) / apparent volume of the second molecular sieve coating × 100%.

[0100] Test of molecular sieve specific surface area and pore size:

[0101] The lithium-ion batteries in each example and comparative example were fully discharged (discharged to 3.0V at a constant current of 0.5C) and then disassembled. The resulting positive electrode sheets and separators were washed in n-butanol and then air-dried. The first molecular sieve coating on the positive electrode sheet and the second molecular sieve coating on the separator were peeled off using a scraper. After grinding each into powder, the following tests were performed:

[0102] A 1g weight of powder was placed in a sample tube, which was heated to 150°C and evacuated for 2 hours. The treated sample was connected to a test system (instrument model: American Micron 3Flex), and nitrogen was continuously introduced into the sample for 1 hour using a Toepler pump that can quantitatively transfer gas to saturate it with adsorption. When the adsorption reached equilibrium, the pressure value was measured by a pressure sensor. The adsorption amount was calculated based on the pressure value, and the isothermal adsorption-desorption line was obtained. The specific surface area was calculated using the BET equation. The pore size was calculated using density functional theory (DFT).

[0103] Example 1-1

[0104] <Preparation of positive electrode sheet>

[0105] ①Put the positive electrode conductive agent and the positive electrode active material lithium cobalt oxide into a blender, add all the positive electrode binder according to the formula weight and 2 / 3 of the dispersion medium according to the formula weight into the blender, stir at high speed for 20 minutes, and remove bubbles for 10 minutes after stirring;

[0106] ② Add the remaining 1 / 3 of the weight of the dispersion medium to the material prepared in ①. Stir at high speed for 30 minutes. Degas for 5 minutes to obtain a positive electrode slurry. The dispersion medium is N-methylpyrrolidone (NMP), the positive electrode conductive agents are conductive carbon black and carbon nanotubes, and the positive electrode binder is polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry is 75 wt%. The mass ratio of lithium cobalt oxide, acetylene black, multi-walled carbon nanotubes, and polyvinylidene fluoride is 96.5:1.5:0.5:1.5.

[0107] The molecular sieve MOR molecular sieve (manufacturer: Shanghai Yuanye Biotechnology Co., Ltd., model: 12445-20-4) and the first binder polymethyl methacrylate (weight average molecular weight 75000) were mixed in a mass ratio of 90:10, N-methylpyrrolidone (NMP) was added as a solvent, and stirred in a vacuum mixer until the solid content was 72wt% and the system was uniform to form the first molecular sieve coating slurry. The specific surface area of ​​the molecular sieve was 350m 2 / g, the pore size of the molecular sieve is 0.6nm, and the average volume particle size of the molecular sieve Dv50 is 1μm.

[0108] The positive electrode slurry and the first molecular sieve coating slurry are respectively and evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 100 ° C to obtain a positive electrode sheet coated with a positive electrode active material layer and a first molecular sieve coating on one side. Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer and a first molecular sieve coating on both sides (as shown in Figure 4). The first molecular sieve coating is arranged in the first area of ​​the positive electrode sheet, and the positive electrode active material layer is arranged in the second area of ​​the positive electrode sheet. Cold pressing and then cutting are performed to obtain a positive electrode sheet with a specification of 74mm×1183mm for standby use.

[0109] Among them, the width W of the first molecular sieve coating is 13 =1mm, thickness H 13 =10 μm. The thickness of the positive electrode active material layer is 40 μm, the width is 73 mm, the length of the positive electrode active material layer is 1183 mm, and the length of the first molecular sieve coating layer is 1183 mm.

[0110] <Preparation of negative electrode sheet>

[0111] The negative electrode active material artificial graphite, the negative electrode conductive agent acetylene black, the thickener carboxymethyl cellulose (CMC), the negative electrode binder styrene butadiene rubber (abbreviated as SBR, with a weight average molecular weight of 50×10 5 ) were mixed in a mass ratio of 96:1:1.5:1.5, then deionized water was added as a solvent and stirred in a vacuum mixer until a solid content of 54 wt% and a uniform negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 85°C to obtain a negative electrode sheet coated on one side with a negative electrode active material layer (45 μm thick). The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer. The sheet was then cold pressed and cut into pieces with a size of 76 mm x 1186 mm for later use.

[0112] <Preparation of Separator>

[0113] A polyethylene film with a thickness of 7 μm was used (manufacturer: Hunan Zhongli New Materials Co., Ltd.).

[0114] <Preparation of Electrolyte>

[0115] Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:7 to obtain an organic solvent, and then lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to obtain a basic electrolyte. Based on the mass of the above basic electrolyte, 2 wt% of fluoroethylene carbonate (FEC) is additionally added to prepare an electrolyte.

[0116] <Preparation of lithium-ion batteries>

[0117] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and the positive and negative electrode tabs are transfer welded to the aluminum and copper sheets, respectively, and then led out of the packaging bag. The electrode assembly is dried and then injected with electrolyte. The lithium-ion battery is produced through vacuum packaging, static standing, formation, degassing, and trimming.

[0118] Example 1-2 to Example 1-19

[0119] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0120] Among them, in Example 1-8 to Example 1-10, as the width of the first molecular sieve coating layer changes, the width of the positive electrode active material layer is 73.5 mm, 71 mm, and 64 mm, respectively.

[0121] Example 2-1

[0122] <Preparation of Separator>

[0123] A polyethylene film with a thickness of 7 μm was used (manufacturer: Hunan Zhongli New Materials Co., Ltd.).

[0124] The molecular sieve MOR molecular sieve (manufacturer: Shanghai Yuanye Biotechnology Co., Ltd., model: 12445-20-4) and the first binder polymethyl methacrylate (weight average molecular weight 75000) were mixed in a mass ratio of 80:20, N-methylpyrrolidone (NMP) was added as a solvent, and stirred under the action of a vacuum mixer until the solid content was 72wt% and the system was uniform to form a second molecular sieve coating slurry. Among them, the specific surface area of ​​the molecular sieve is 350m 2 / g, the pore size of the molecular sieve is 0.6nm, and the average volume particle size of the molecular sieve Dv50 is 1μm.

[0125] The second molecular sieve coating slurry was applied to the surface of the polyethylene film opposite the first region of the positive electrode plate and dried at 100°C to obtain a separator coated with the second molecular sieve coating on one side. The above steps were then repeated on the other surface of the polyethylene film opposite the first region of the positive electrode plate to obtain a separator coated with the second molecular sieve coating on both sides (as shown in Figure 7).

[0126] Wherein, the thickness of the second molecular sieve coating H 23 =10μm.

[0127] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those in Example 1-1.

[0128] Example 2-2 to Example 2-7

[0129] Except for adjusting the preparation parameters according to Table 3, the rest is the same as Example 2-1.

[0130] Example 3-1

[0131] <Preparation of positive electrode sheet>

[0132] The conductive agent acetylene black (manufacturer: Jiaozuo Hexing Chemical Industry Co., Ltd.) and the second binder PVDF (weight-average molecular weight 755,000) were mixed in a mass ratio of 30:70, deionized water was added as a solvent, and stirred in a vacuum mixer until a conductive layer slurry with a solid content of 45 wt% and a uniform system was obtained.

[0133] The positive electrode slurry and the first molecular sieve coating slurry are respectively and evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 100°C to obtain a positive electrode sheet coated with a positive electrode active material layer and a first molecular sieve coating on one side. The conductive layer slurry is coated on the surface of the first molecular sieve coating away from the positive electrode current collector, and dried at 100°C to obtain a positive electrode sheet coated with a positive electrode active material layer, a first molecular sieve coating and a conductive layer on one side. Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer, a first molecular sieve coating and a conductive layer on both sides (as shown in FIG9 ). The first molecular sieve coating and the conductive layer are arranged in the first area of ​​the positive electrode sheet, and the positive electrode active material layer is arranged in the second area of ​​the positive electrode sheet. Cold pressing and then cutting are performed to obtain a positive electrode sheet with a specification of 74 mm × 1183 mm for standby use.

[0134] Among them, the width W of the first molecular sieve coating is 13 =1mm, thickness H 13 =10μm. Thickness of the conductive layer H 15 =20μm, width 1mm. The thickness H of the positive electrode active material layer 14 =90μm.

[0135] <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those in Example 1-1.

[0136] Example 3-2 to Example 3-6

[0137] Except for adjusting the preparation parameters according to Table 4, the rest is the same as Example 3-1.

[0138] Wherein, based on the mass of the conductive layer, when the mass percentage of the conductive agent changes, the mass percentage of the second binder changes accordingly, and the sum of the mass percentages of the conductive agent and the second binder is 100%.

[0139] Examples 3-7

[0140] <Preparation of positive electrode sheet> is the same as that of Example 3-1, and <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those of Example 2-1.

[0141] Comparative Example 1

[0142] <Preparation of positive electrode sheet>

[0143] Ceramic boehmite particles and polyvinylidene fluoride (PVDF, weight-average molecular weight 755,000) as a ceramic layer binder were mixed in a mass ratio of 95:5. Deionized water was added as a solvent and stirred in a vacuum mixer until a uniform ceramic coating slurry with a solids content of 40 wt% was obtained. The boehmite had an average volume particle size (Dv50) of 0.6 μm.

[0144] The positive electrode slurry and ceramic coating slurry were evenly coated on one surface of a 10μm thick positive electrode current collector aluminum foil, and then dried at 100°C to obtain a positive electrode sheet coated on one side with a positive electrode active material layer and a ceramic coating. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer and a ceramic coating. The ceramic coating was applied to the first region of the positive electrode sheet, and the positive electrode active material layer was applied to the second region of the positive electrode sheet. After drying at 100°C, the sheet was cold pressed and then cut into pieces, resulting in a 74mm x 1183mm positive electrode sheet ready for use.

[0145] The width of the ceramic coating is 1 mm, the thickness is 10 μm, the length of the positive electrode active material layer is 1183 mm, and the length of the ceramic coating is 1183 mm.

[0146] <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those in Example 1-1.

[0147] Comparative Example 2

[0148] The process is the same as that of Comparative Example 1 except that the ceramic layer binder is replaced by the first binder polymethyl methacrylate (weight average molecular weight 75,000).

[0149] Comparative Example 3 and Comparative Example 4

[0150] Except for adjusting the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0151] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0152] Table 1

[0153] Note: “\” in Table 1 means no corresponding parameter; “W f1 " represents the mass percentage of the molecular sieve based on the mass of the first molecular sieve coating; "Wz1" in Table 1 represents the mass percentage of the first binder based on the mass of the first molecular sieve coating; the difference between Comparative Example 1 and Comparative Example 2 is that the binder in the ceramic coating of Comparative Example 1 is PVDF, and the binder in the ceramic coating of Comparative Example 2 is polymethyl methacrylate.

[0154] Table 2

[0155] From Examples 1-1 to 1-19 and Comparative Examples 1 to 4, it can be seen that the embodiments of the present application use a positive electrode sheet having a first molecular sieve coating provided on both surfaces of the positive electrode current collector in the first region, and the content of the molecular sieve and the first binder in the first molecular sieve coating being within the scope of the present application, which has a high adhesion force, indicating that the positive electrode sheet and the separator have a high adhesion force. The above-mentioned positive electrode sheet is applied to a secondary battery. Compared with Comparative Examples 1 and 2, the secondary batteries of Examples 1-1 to 1-19 have a higher proportion of the number of cells that pass the drop test and less lithium plating, indicating that the cycle performance and drop safety performance of the secondary battery are improved; at the same time, it has a lower expansion rate, indicating that the risk of flatulence in the secondary battery is lower and its storage performance is improved. In Comparative Examples 1 and 2, however, the positive electrode sheets without the first molecular sieve coating were used, which exhibited extremely low adhesion. The secondary batteries using these positive electrode sheets had a low percentage of cells passing the drop test and exhibited severe lithium deposition, indicating poor cycling performance and drop safety. Furthermore, the secondary batteries in Comparative Examples 1 and 2 exhibited high expansion rates, indicating a high risk of flatulence and failure to improve storage performance. In Comparative Example 3, the molecular sieve content is too high and the binder content is too low, which cannot fully bond the positive electrode sheet and the separator, resulting in too low bonding force between the two, which easily causes failure when dropped. At the same time, the interface performance of the positive electrode sheet and the separator is poor during the cycle, resulting in lithium precipitation; in Comparative Example 4, the binder content is too high and the molecular sieve content is too low. The molecular sieve cannot fully physically block the burrs, wrinkles, etc. on the positive electrode current collector from puncturing the separator and contacting the negative electrode active material when dropped, so a short circuit is likely to occur. At the same time, due to the low molecular sieve content, the battery cannot fully absorb the generated gas when stored at high temperature, causing the battery to swell too much and have poor storage performance.

[0156] The mass percentage of molecular sieve and the first binder in the first molecular sieve coating usually affects the cycle performance, drop safety performance and storage performance of the secondary battery. From Examples 1-1 to 1-7, Comparative Examples 3 and 4, it can be seen that the secondary battery in which the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is within the scope of this application has a higher ratio of the number of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance. Among them, the molecular sieve content of Example 1-1 is higher, which can absorb more gas to inhibit battery expansion, but the binder content is lower, the bonding force is smaller, and the drop test performance is not as good as that of Examples 1-2 to 1-6; the binder content of Example 1-7 is higher, and the bonding force is greater than that of Example 1-1, but because the molecular sieve is smaller, the binder cannot be fully swollen, resulting in its bonding force being inferior to that of Examples 1-2 to 1-6, and at the same time, it cannot absorb more gas, resulting in a larger expansion rate of the battery; the comprehensive performance of the batteries of Examples 1-2 to 1-6 is significantly better than that of Examples 1-1 and 1-7. In Examples 1-3 to 1-5, due to the appropriate ratio of molecular sieve and binder, the molecular sieve coating has better adhesion, which makes the interface performance between the diaphragm and the active material layer better. At the same time, the ability of the molecular sieve to absorb gas can be fully utilized, and the battery's anti-drop performance, anti-expansion performance, and ability to prevent lithium precipitation are better overall.

[0157] The width W of the first molecular sieve coating layer 13 It usually affects the cycle performance, drop safety performance and storage performance of the secondary battery. From Examples 1-2, 1-8 to 1-10, it can be seen that the width W of the first molecular sieve coating is selected. 13 Secondary batteries within the scope of this application have a high percentage of cells passing the drop test, less lithium deposition, and a low expansion rate, indicating good cycling performance, drop safety, and storage performance. Examples 1-2, 1-9, and 1-10 have a wider first molecular sieve coating, and their overall performance is significantly better than that of Example 1-8. However, the wider molecular sieve coating of Example 1-10 results in a decrease in battery energy density, and therefore is not a preferred solution.

[0158] The thickness of the first molecular sieve coating H 13 It usually affects the cycle performance, drop safety performance and storage performance of the secondary battery. From Examples 1-2, 1-11 to 1-15, it can be seen that the thickness H of the first molecular sieve coating is selected. 13The secondary batteries within the scope of this application have a high percentage of cells passing the drop test, less lithium plating, and a low expansion rate, indicating that the secondary batteries have good cycling performance, drop safety, and storage performance. Among them, the first molecular sieve coating thickness of Examples 1-2, 1-12, and 1-15 is thicker, and the overall performance is significantly better than that of Example 1-11. However, the thicker molecular sieve coatings of Examples 1-14 and 1-15 will result in a decrease in battery energy density without further improving performance, and therefore are not preferred.

[0159] The type, specific surface area, and pore size of the molecular sieve, as well as the porosity of the first molecular sieve coating, generally affect the cycling performance, drop safety performance, and storage performance of the secondary battery. As can be seen from Examples 1-2, 1-16, and 1-19, secondary batteries whose molecular sieve type, specific surface area, and pore size, as well as the porosity of the first molecular sieve coating, fall within the ranges of this application have a higher percentage of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary batteries have good cycling performance, drop safety performance, and storage performance.

[0160] Table 3

[0161] Note: “\” in Table 3 means no corresponding parameter; “W f2 " " in Table 3 represents the mass percentage of the molecular sieve based on the mass of the second molecular sieve coating; "Wz2" in Table 3 represents the mass percentage of the first binder based on the mass of the second molecular sieve coating.

[0162] As can be seen from Examples 1-2 and 2-1 to 2-7, by providing a second molecular sieve coating on the surface of the separator opposite the first region, the adhesion between the positive electrode plate and the separator can be further enhanced. When the separator is used in a secondary battery, the secondary battery has a higher percentage of cells passing the drop test and less lithium deposition, indicating that the secondary battery's cycle performance and drop safety performance are further improved. It also has a lower expansion rate, indicating a lower risk of flatulence in the secondary battery and further improved storage performance.

[0163] The mass percentage of molecular sieve in the second molecular sieve coating generally affects the cycling performance, drop safety, and storage performance of a secondary battery. As can be seen from Examples 2-1 and 2-3, secondary batteries using molecular sieves with a mass percentage in the second molecular sieve coating within the range of this application have a higher percentage of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary batteries have good cycling performance, drop safety, and storage performance.

[0164] The thickness of the second molecular sieve coating H 23 It usually affects the cycle performance, drop safety performance and storage performance of the secondary battery. From Examples 2-1, 2-4 and 2-5, it can be seen that the thickness H of the second molecular sieve coating is selected. 23 The secondary batteries within the scope of this application have a higher ratio of the number of batteries that pass the drop test, less lithium plating, and a lower expansion rate, indicating that the secondary batteries have good cycle performance, drop safety performance, and storage performance.

[0165] The porosity of the second molecular sieve coating typically affects the cycling performance, drop safety, and storage performance of secondary batteries. As can be seen from Examples 2-1, 2-6, and 2-7, secondary batteries using a second molecular sieve coating with a porosity within the range of this application have a higher percentage of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary batteries have good cycling performance, drop safety, and storage performance.

[0166] Table 4

[0167] Note: “\” in Table 4 means no corresponding parameter; “W d " represents the mass percentage of the conductive agent based on the mass of the conductive layer; "W z3 " represents the mass percentage of the second binder based on the mass of the conductive layer; the difference between Example 3-1 and Example 3-7 is that the diaphragm of Example 3-1 is not provided with a second molecular sieve coating, while the diaphragm of Example 3-7 is provided with a second molecular sieve coating.

[0168] It can be seen from Examples 1-2 and Implementation 3-1 to Example 3-6, Example 2-1 and Example 3-7 that a conductive layer in which a conductive agent and a second binder are provided on the surface of the first molecular sieve coating facing away from the positive electrode current collector can further reduce lithium plating while the secondary battery has a higher proportion of cells passing the drop test and a lower expansion rate, indicating that the secondary battery has further improved its cycle performance while having good drop safety performance and storage performance.

[0169] The mass percentages of the conductive agent and the second binder in the conductive layer generally affect the cycling performance, drop safety, and storage performance of a secondary battery. As can be seen from Examples 1-2 and 3-1 to 3-3, secondary batteries with the mass percentages of the conductive agent and the second binder in the conductive layer within the ranges of this application exhibit a higher percentage of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary batteries have good cycling performance, drop safety, and storage performance.

[0170] Thickness of the conductive layer H 15 It usually affects the cycle performance, drop safety performance and storage performance of the secondary battery. From Examples 1-2, 3-1, 3-4 and 3-5, it can be seen that the thickness H of the conductive layer is selected. 15 The secondary batteries within the scope of this application have a higher ratio of the number of batteries that pass the drop test, less lithium plating, and a lower expansion rate, indicating that the secondary batteries have good cycle performance, drop safety performance, and storage performance.

[0171] The type of conductive agent generally affects the cycling performance, drop safety, and storage performance of secondary batteries. As can be seen from Examples 3-1 and 3-6, secondary batteries using conductive agents within the scope of this application have a higher percentage of cells passing the drop test, less lithium deposition, and a lower expansion rate, indicating that the secondary batteries have good cycling performance, drop safety, and storage performance.

[0172] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0173] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0174] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet; The positive electrode sheet comprises a positive electrode tab, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer. Along a first direction, the positive electrode sheet comprises a second region and a first region connected in sequence. The positive electrode tab is integrally arranged with the positive electrode current collector in the first region. The first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first region. The positive electrode active material layer is arranged on at least one surface of the positive electrode current collector in the second region. The first direction is the extension direction of the positive electrode tab in an unfolded state. The first molecular sieve coating comprises a molecular sieve and a first binder. Based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10% to 90%, and the mass percentage of the first binder is 10% to 90%.

2. The secondary battery according to claim 1, wherein Based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 20% to 80%, and the mass percentage of the first binder is 20% to 80%.

3. The secondary battery according to claim 1, wherein Based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 30% to 70%, and the mass percentage of the first binder is 30% to 70%.

4. The secondary battery according to claim 1, wherein Along the first direction, the width of the first molecular sieve coating is 0.5 mm to 10 mm; along the direction perpendicular to the first direction, the length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode plate.

5. The secondary battery according to claim 4, wherein Along the first direction, the width of the first molecular sieve coating layer is 1 mm to 3 mm.

6. The secondary battery according to claim 1, wherein The thickness of the first molecular sieve coating layer is smaller than that of the positive electrode active material layer, and the thickness of the first molecular sieve coating layer is 0.5 μm to 40 μm.

7. The secondary battery according to claim 6, wherein The thickness of the first molecular sieve coating layer is 5 μm to 20 μm.

8. The secondary battery according to claim 1, wherein A second molecular sieve coating is disposed on the surface of the diaphragm opposite to the first region; The second molecular sieve coating layer comprises the molecular sieve, and based on the mass of the second molecular sieve coating layer, the mass percentage of the molecular sieve is 20% to 80%.

9. The secondary battery according to claim 8, wherein The thickness of the second molecular sieve coating layer is 0.5 μm to 10 μm.

10. The secondary battery according to claim 8, wherein The porosity of the first molecular sieve coating layer and the second molecular sieve coating layer is independently 30% to 60%.

11. The secondary battery according to claim 8, wherein The specific surface area of ​​the molecular sieve is 200m 2 / g to 2000m 2 / g, and the pore size of the molecular sieve is 0.3nm to 45nm.

12. The secondary battery according to any one of claims 1 to 11, wherein The molecular sieve includes at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 13X molecular sieve, ZSM-22 molecular sieve, ZSM-5 molecular sieve, MOR molecular sieve, ITQ molecular sieve, Y molecular sieve, SAPO molecular sieve or ALPO molecular sieve; The first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

13. The secondary battery according to claim 1, wherein The positive electrode plate further comprises a conductive layer, and the conductive layer is disposed on a surface of the first molecular sieve coating layer facing away from the positive electrode current collector; The conductive layer includes a conductive agent, and based on the mass of the conductive layer, the mass percentage of the conductive agent is 5% to 70%.

14. The secondary battery according to claim 13, wherein The sum of the thickness of the first molecular sieve coating layer and the thickness of the conductive layer is less than or equal to the thickness of the positive electrode active material layer; The thickness of the conductive layer is 0.5 μm to 30 μm.

15. The secondary battery according to claim 13, wherein The conductive agent includes at least one of acetylene black, Ketjen black, conductive graphite, graphene, and carbon nanotubes.

16. An electrical device, wherein: The electric device includes the secondary battery according to any one of claims 1 to 15.

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