CN117581399B

CN117581399B - Secondary battery and electricity utilization device

Info

Publication number: CN117581399B
Application number: CN202380012652.4A
Authority: CN
Inventors: 黄永强; 刘凯; 李佳原
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2023-08-31
Filing date: 2023-08-31
Publication date: 2025-12-19
Anticipated expiration: 2043-08-31
Also published as: CN117581399A; WO2025043614A1

Abstract

The secondary battery comprises an electrode assembly, the electrode assembly comprises a positive electrode plate, a negative electrode plate and a diaphragm, the diaphragm is arranged between the positive electrode plate and the negative electrode plate, the positive electrode plate comprises a positive electrode lug, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, the positive electrode plate comprises a second area and a first area which are sequentially connected along a first direction, the positive electrode lug and the positive electrode current collector in the first area are integrally arranged, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first area, the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector in the second area, the first direction is the extending direction of the positive electrode lug in an unfolded state, the first molecular sieve coating comprises a molecular sieve and a first binder, the mass percentage of the molecular sieve is 10-90% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 10-90%. The secondary battery has good cycle performance and drop safety performance.

Description

Secondary battery and electricity utilization device

Technical Field

The application relates to the technical field of electrochemistry, in particular to a secondary battery and an electric device.

Background

Along with the development of society, smart phones and notebooks play an important role in our lives, and the market scale of wearable devices, smart home, electric vehicles and electric bicycles is gradually increasing. Secondary batteries represented by lithium ion batteries and sodium ion batteries are widely used in the above fields due to their high energy density, environmental protection, etc., and thus the market demand for secondary batteries is also rapidly growing.

In the existing secondary battery, electrolyte is easy to accumulate at the head part of the electrode assembly (one side of the electrode assembly, extending out of the lug), so that weak binding force between the electrode sheet layers is caused, the edge of the electrode sheet becomes a weak area which cannot be ignored, and the cycle performance and drop safety of the secondary battery are affected.

Disclosure of Invention

The application aims to provide a secondary battery and an electric device, which are used for improving the cycle performance and drop safety performance of the secondary battery.

In the present application, the present application is explained using a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery. The specific technical scheme is as follows:

The first aspect of the application provides a secondary battery, which comprises an electrode assembly, wherein the electrode assembly comprises a positive electrode plate, a negative electrode plate and a diaphragm, the diaphragm is arranged between the positive electrode plate and the negative electrode plate, the positive electrode plate comprises a positive electrode lug, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, the positive electrode plate comprises a second area and a first area which are sequentially connected along a first direction, the positive electrode lug and the positive electrode current collector in the first area are integrally arranged, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first area, the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector in the second area, the first direction is the extending direction of the positive electrode lug in an unfolded state, the first molecular sieve coating comprises a molecular sieve and a first binder, the mass percentage of the molecular sieve is 10-90% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 10-90%. According to the application, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first area, so that on one hand, the effects of preventing the short circuit caused by the penetration of burrs of the positive electrode current collector through the diaphragm and preventing the dangerous short circuit caused by the direct contact of the positive electrode current collector and the negative electrode active material when the negative electrode active material layer exceeds the positive electrode active material layer in the width direction are achieved by coating the traditional alumina, boehmite and other ceramic coatings, and the secondary battery has good short circuit prevention performance, on the other hand, the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating has good bonding effect, the bonding effect between the positive electrode plate and the diaphragm of the head of the electrode assembly can be enhanced, the risk of weak bonding between the plate layer and the diaphragm caused by the accumulation of electrolyte at the head of the electrode assembly is reduced, and the risk of weak bonding between the positive electrode plate and the diaphragm is reduced, and the positive electrode plate and the diaphragm of the head of the electrode assembly have good bonding effect, and therefore the positive electrode plate and the diaphragm have good interface contact effect, and the lithium precipitation cycle performance of the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved. In addition, the molecular sieve in the first molecular sieve coating has the capability of absorbing gas, so that the risk of gas expansion of the secondary battery can be reduced, and the storage performance and the high-temperature safety performance of the secondary battery are improved.

In one embodiment of the present application, the molecular sieve is 20 to 80% by mass and the first binder is 20 to 80% by mass based on the mass of the first molecular sieve coating. The mass percentage of the molecular sieve and the first binder in the first molecular sieve coating are regulated and controlled within the range, so that the first molecular sieve layer has a good bonding effect under the condition of good short circuit prevention effect.

In one embodiment of the present application, the molecular sieve is 30 to 70% by mass and the first binder is 30 to 70% by mass based on the mass of the first molecular sieve coating. The mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is regulated and controlled within the range, so that the short circuit prevention effect of the first molecular sieve layer and the bonding improvement effect can be better considered.

In one embodiment of the present application, the first molecular sieve coating has a width of 0.5mm to 10mm in the first direction, and the first molecular sieve coating has a length 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 tab in a direction perpendicular to the first direction. The width of the first molecular sieve coating is set to be 0.5mm to 10mm, so that the first molecular sieve coating has good binding force on the diaphragm while the effect of preventing short circuit caused by direct contact between the positive electrode current collector and the negative electrode active material is better achieved and the energy density of the secondary battery is considered. 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, so that the effect can be more effectively achieved in the length direction.

In one embodiment of the application, the first molecular sieve coating has a width in the first direction of from 1mm to 3mm. The width of the first molecular sieve coating is set to be 1-3 mm, so that the effect of preventing the positive electrode current collector from being in direct contact with the negative electrode active material to cause short circuit can be better achieved, the energy density of the secondary battery is considered, and meanwhile, the binding force of the first molecular sieve coating to the diaphragm is further improved, and the falling safety performance of the secondary battery is further improved.

In one embodiment of the present application, the thickness of the first molecular sieve coating layer is less than the thickness of the positive electrode active material layer, and the thickness of the first molecular sieve coating layer is 0.5 μm to 40 μm. The thickness of the first molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating can better play the effects of preventing short circuit and improving the bonding force with the diaphragm, and the energy density of the secondary battery can be considered.

In one embodiment of the application, the first molecular sieve coating has a thickness of 5 μm to 20 μm. The thickness of the first molecular sieve coating is regulated and controlled within the range, so that the short-circuit prevention performance, the cycle performance, the drop safety performance and the storage performance of the secondary battery are further improved.

In one embodiment of the application, a second molecular sieve coating is disposed on the surface of the membrane opposite the first region, the second molecular sieve coating comprising a molecular sieve in an amount of 20 to 80 mass percent based on the mass of the second molecular sieve coating. And a second molecular sieve coating is arranged on the surface of the diaphragm opposite to the first area, and the content of the molecular sieve in the second molecular sieve coating is regulated and controlled within the range, so that the short circuit prevention performance, the circulation performance, the drop safety performance and the storage performance of the secondary battery are further improved. Meanwhile, 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.

In one embodiment of the application, the second molecular sieve coating has a thickness of 0.5 μm to 10 μm. The thickness of the second molecular sieve coating is regulated and controlled within the range, so that the secondary battery has good short-circuit prevention performance, circulation performance, drop safety performance and storage performance.

In one embodiment of the application, the first molecular sieve coating and the second molecular sieve coating each independently have a porosity of 30% to 60%. The porosity of the first molecular sieve coating and the second molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating and the second molecular sieve coating have good insulativity and structural strength, the first molecular sieve coating and the second molecular sieve coating exert the effect of preventing short circuits, and the first molecular sieve coating and the second molecular sieve coating also exert the effect of improving cohesive force.

In one embodiment of the application, the molecular sieve has a specific surface area of 200m ²/g to 2000m ²/g and a pore size of 0.3nm to 45nm. The specific surface area and the pore diameter of the molecular sieve are regulated and controlled within the above range, so that the effect of improving the adhesion force of the molecular sieve can be better exerted, and the cycle performance, the falling safety performance and the storage performance of the secondary battery are further improved.

In one embodiment of the present application, the molecular sieve comprises at least one of a 3A molecular sieve, a 4A molecular sieve, a 5A molecular sieve, a 13X molecular sieve, a ZSM-22 molecular sieve, a ZSM-5 molecular sieve, a MOR molecular sieve, an ITQ molecular sieve, a Y molecular sieve, a SAPO molecular sieve, or an ALPO molecular sieve. The molecular sieve of the above kind is selected to be favorable for the secondary battery to have good cycle performance, drop safety performance and storage performance.

In one embodiment of the present application, the first binder comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber, or styrene butadiene rubber.

In one embodiment of the application, the positive electrode plate further comprises a conductive layer, wherein the conductive layer is arranged on the surface of the first molecular sieve coating, which faces away from the positive electrode current collector, and comprises a conductive agent, and the mass percentage of the conductive agent is 5-70% based on the mass of the conductive layer. The surface of the first molecular sieve coating, which is far away from the positive current collector, in the positive electrode plate is provided with the conducting layer, and the possibility of lithium precipitation can be further reduced under the condition that the secondary battery has good falling safety performance and storage performance, so that the cycle performance is further improved.

In one embodiment of the present application, 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, and 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 smaller than or equal to the thickness of the positive electrode active material layer, so that the possibility of generating a gap between the second region of the positive electrode plate and the diaphragm caused by the excessive thickness of the first molecular sieve coating and the conductive layer can be reduced, the second region of the positive electrode plate is fully contacted with the diaphragm to ensure the interface performance between the positive electrode plate and the diaphragm, and meanwhile, the thickness of the first molecular sieve coating is regulated and controlled within the range, so that the production requirements of most secondary batteries on the market can be met.

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.

A second aspect of the present application provides an electric device, wherein the electric device comprises the secondary battery according to any one of the foregoing embodiments. Therefore, the electric device has good service performance.

The application has the beneficial effects that:

The application provides a secondary battery and an electricity utilization device, wherein a first molecular sieve coating is arranged on two surfaces of a positive electrode current collector in a first area of the secondary battery, the secondary battery can replace traditional ceramic coatings such as alumina, boehmite and the like and has the same short-circuit prevention effect, the mass percent of a molecular sieve and a first binder in the first molecular sieve coating are regulated and controlled within the range, so that the first molecular sieve coating has good bonding effect, the bonding effect between a positive electrode plate and a diaphragm of the head of an electrode assembly can be enhanced, the risk of weak bonding between a plate layer and a layer caused by electrolyte accumulation of the head of the electrode assembly and the risk of weak bonding between a positive electrode active material layer and the diaphragm are reduced, the positive electrode plate and the diaphragm of the head of the electrode assembly have good bonding effect, therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on a negative electrode plate is less, and the cycle performance of the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved. In addition, the molecular sieve in the first molecular sieve coating has the capability of absorbing gas, so that the risk of gas expansion of the secondary battery can be reduced, and the storage performance and the high-temperature safety performance of the secondary battery are improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application.

Fig. 1 is a schematic cross-sectional structure of a secondary battery according to an embodiment of the present application at a positive electrode tab in a self-thickness direction and a first direction;

Fig. 2 is a schematic cross-sectional structure of the electrode assembly of fig. 1 in a thickness direction and a first direction thereof in an unfolded state of a positive electrode tab;

FIG. 3 is a top view of a positive electrode sheet in an expanded state according to one embodiment of the present application;

FIG. 4 is a schematic cross-sectional view of a positive electrode tab in a first direction and a thickness direction of the positive electrode tab in an expanded state according to an embodiment of the present application;

FIG. 5 is a schematic cross-sectional view of a positive electrode tab in a non-positive electrode tab in a direction perpendicular to the first direction and in a thickness direction of the positive electrode tab in an expanded state according to another embodiment of the present application;

fig. 6 is a schematic cross-sectional structure of a secondary battery according to another embodiment of the present application at a positive electrode tab in a self-thickness direction and a first direction;

FIG. 7 is a schematic cross-sectional view of a separator according to some embodiments of the present application along its thickness direction;

FIG. 8 is a schematic cross-sectional view of a separator according to other embodiments of the present application along its thickness direction;

Fig. 9 is a schematic cross-sectional structure of a positive electrode sheet according to still another embodiment of the present application in the thickness direction thereof.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail below by referring to the accompanying drawings and examples. It should be apparent that the embodiments described in the specification of the present application are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by the person skilled in the art based on the present application fall within the scope of protection of the present application.

In the embodiment, the present application is explained using a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery, and is applicable to a battery that is common in the art such as a sodium ion battery and that can use the related art of the present application. The specific technical scheme is as follows:

The first aspect of the application provides a secondary battery, which comprises an electrode assembly, wherein the electrode assembly comprises a positive electrode plate, a negative electrode plate and a diaphragm, the diaphragm is arranged between the positive electrode plate and the negative electrode plate, the positive electrode plate comprises a positive electrode lug, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, the positive electrode plate comprises a second area and a first area which are sequentially connected along a first direction, the positive electrode lug and the positive electrode current collector in the first area are integrally arranged, at least one surface of the positive electrode current collector in the first area is provided with the first molecular sieve coating, at least one surface of the positive electrode current collector in the second area is provided with the positive electrode active material layer, and the first direction is the extending direction of the positive electrode lug in an unfolded state, namely the width direction of the positive electrode plate. It will be appreciated that the above-mentioned "the first molecular sieve coating is disposed on at least one surface of the positive electrode current collector in the first region" means that in some embodiments, the first molecular sieve coating is disposed on one surface of the positive electrode current collector in the first region, in other embodiments, the first molecular sieve coating is disposed on two surfaces of the positive electrode current collector in the first region, where the "surface" may be the entire surface of the positive electrode current collector in the first region or may be a partial surface of the positive electrode current collector in the first region, and the above-mentioned "the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector in the second region" means that in some embodiments, the positive electrode active material layer is disposed on one surface of the positive electrode current collector in the second region, and in other embodiments, the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector in the second region. The "surface" may be the entire surface of the positive electrode current collector in the second region, or may be a part of the surface of the positive electrode current collector in the second region.

In the present 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 being understood that the thickness directions of the negative electrode sheet and the separator are the same as the thickness direction of the positive electrode sheet. The "direction perpendicular to the first direction" is understood to be a perpendicular relationship on a plane formed by the length direction and the width direction of the positive electrode sheet. As shown in fig. 1 to 4, the secondary battery includes an electrode assembly 100 and a packing bag 200, the electrode assembly 100 is accommodated in the packing bag 200, the electrode assembly 100 includes a positive electrode tab 10, a negative electrode tab 20 and a separator 30, the separator 30 is disposed between the positive electrode tab 10 and the negative electrode tab 20, the positive electrode tab 10 includes a positive electrode tab 11, a positive electrode current collector 12, a first molecular sieve coating 13 and a positive electrode active material layer 14, the positive electrode tab 10 includes a second region 102 and a first region 101 connected in sequence in a first direction X, the positive electrode tab 11 is integrally disposed with the positive electrode current collector 12 in the first region 101, the first molecular sieve coating 13 is disposed on both surfaces of the positive electrode current collector 12 in the first region 101, the positive electrode active material layer 14 is disposed on at least one surface of the positive electrode current collector 12 in the second region 102, and the first direction X is an extending direction in an unfolded state (as shown in fig. 2) of the positive electrode tab 11. It can be appreciated that the positive electrode tab is integrally disposed with the positive electrode current collector in the first region, and when the positive electrode tab is not folded, the extending direction of the positive electrode tab is parallel to the positive electrode current collector. In the process of manufacturing the secondary battery, from the practical production process, the portion of the positive electrode tab extending beyond the positive electrode current collector may be folded, so that the portion of the positive electrode tab extending beyond the positive electrode current collector may be bent (as shown in fig. 1), and the extending direction of the positive electrode tab in a meandering state is no longer parallel to the positive electrode current collector. It should be noted that "parallel" refers to parallel in an ideal state, and may be approximately parallel in an actual production process due to the influence of manpower or operation in the preparation process. The first molecular sieve coating comprises a molecular sieve and a first binder, wherein the mass percentage of the molecular sieve is 10-90% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 10-90%. For example, the molecular sieve is present in a mass percent of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any value in a range between any two of the foregoing values, based on the mass of the first molecular sieve coating. For example, the first binder may be present in an amount of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any value in the range of any two values based on the mass of the first molecular sieve coating.

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 more than 90%, the content of the molecular sieve in the first molecular sieve coating is too small, the compactness of the first molecular sieve coating is poor, the insulating protection effect of the first molecular sieve coating on the adjacent positive electrode current collector is affected, and when the mass percentage of the molecular sieve is more 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 cohesive force of the formed first molecular sieve coating is poor, the interface bonding effect between the positive electrode plate and the diaphragm is poor, the cycle performance of the secondary battery is affected, and when the secondary battery falls or collides, the diaphragm is easy to turn over, and the falling safety performance of the secondary battery is affected.

According to the application, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first area, so that on one hand, the effects of preventing the short circuit caused by the penetration of the membrane by the burrs of the positive electrode current collector and preventing the dangerous short circuit caused by the direct contact of the positive electrode current collector and the negative electrode active material when the negative electrode active material layer exceeds the positive electrode active material layer in the width direction are achieved, and the secondary battery has good short circuit prevention performance, on the other hand, the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating are regulated and controlled within the range, the molecular sieve and the first binder are mutually matched, so that the first molecular sieve coating has good bonding effect, the bonding effect between the positive electrode plate and the membrane of the head of the electrode assembly can be enhanced, the risk of weak bonding between the plate layer and the membrane caused by the accumulation of electrolyte at the head of the electrode assembly is reduced, and the risk of weak bonding between the positive electrode plate and the membrane is reduced, and the positive electrode plate of the head of the electrode assembly has good bonding effect when the positive electrode plate and the membrane are in good interface, and the lithium precipitation performance on the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved. In addition, the molecular sieve in the first molecular sieve coating has the capability of absorbing gas, so that the risk of the secondary battery generating gas expansion can be reduced, and the storage performance of the secondary battery is improved.

In one embodiment of the present application, the molecular sieve is 20 to 80% by mass and the first binder is 20 to 80% by mass based on the mass of the first molecular sieve coating. For example, the molecular sieve is present in a mass percent of 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value in a range between any two of the foregoing values, based on the mass of the first molecular sieve coating. For example, the first binder may be present in an amount of 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value in the range of any two of the foregoing, based on the mass of the first molecular sieve coating. The mass percentage of the molecular sieve and the first binder in the first molecular sieve coating are regulated and controlled within the range, so that the bonding effect between the positive pole piece and the diaphragm of the head of the electrode assembly can be further enhanced on the premise of ensuring that the first molecular sieve coating is short-circuited, the risk of weak bonding between the pole piece layer and the layer caused by stacking of electrolyte at the head of the electrode assembly is reduced, the risk of weak bonding between the positive active material layer and the diaphragm is further reduced, and the positive pole piece and the diaphragm of the head of the electrode assembly have good bonding effect, therefore, the positive pole piece and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative pole piece is less, and the cycle performance of the secondary battery is further improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be further improved.

In one embodiment of the present application, the molecular sieve is 30 to 70% by mass and the first binder is 30 to 70% by mass based on the mass of the first molecular sieve coating. For example, the molecular sieve may be present in an amount of 30%, 40%, 50%, 60%, 70% or any value in the range of any two values based on the mass of the first molecular sieve coating. For example, the first binder may be present in an amount of 30%, 40%, 50%, 60%, 70% or any value in the range of any two values based on the mass of the first molecular sieve coating. The mass percentage of the molecular sieve and the first binder in the first molecular sieve coating is regulated and controlled within the range, so that the bonding effect between the positive pole piece and the diaphragm of the head of the electrode assembly can be further enhanced, the risk of weak bonding between the pole piece layers caused by stacking of electrolyte on the head of the electrode assembly is reduced, and the risk of weak bonding between the positive active material layer and the diaphragm is further reduced, so that the positive pole piece and the diaphragm of the head of the electrode assembly have good bonding effect, therefore, the positive pole piece and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative pole piece is less, and the cycle performance of the secondary battery is further improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be further improved.

In one embodiment of the present application, as shown in fig. 3 and 4, the width W ₁₃ of the first molecular sieve coating 13 is 0.5mm to 10mm in the first direction X. 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 in the range of any two of the foregoing values. The width of the first molecular sieve coating is set to be 0.5-10 mm, so that the first molecular sieve coating has good binding force on the diaphragm while the effect of preventing short circuit caused by direct contact of the positive electrode current collector and the negative electrode active material is better achieved and the energy density of the secondary battery is considered. 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, so that the effect can be more effectively achieved in the length direction. Therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative electrode plate is less, the cycle performance of the secondary battery is improved, and the secondary battery has higher energy density and safety performance. In addition, the first area of the positive pole piece and the diaphragm have good bonding effect, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

In one embodiment of the present application, as shown in fig. 3 and 4, the width W ₁₃ of the first molecular sieve coating 13 is 1mm to 3mm in the first direction X. For example, the width of the first molecular sieve coating is 1mm, 2mm, 3mm, or any value between any two of the foregoing ranges. The width of the first molecular sieve coating is set to be 1-3 mm, so that the effect of preventing the positive electrode current collector from being in direct contact with the negative electrode active material to cause short circuit can be better achieved, the energy density of the secondary battery is considered, and meanwhile, the binding force of the first molecular sieve coating to the diaphragm is further improved, and the falling safety performance of the secondary battery is further improved.

In one embodiment of the present application, 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 tab in a direction perpendicular to the first direction. Illustratively, in some embodiments, as shown in fig. 3, the length L ₁₃ of the first molecular sieve coating 13 is equal to the length L ₁₄ of the positive electrode active material layer 14 and equal to the length L ₁₀ of the positive electrode tab 10 along the direction Y perpendicular to the first direction X. In other embodiments, the length of the first molecular sieve coating is greater than the length of the positive electrode active material layer and equal to the length of the positive electrode tab in a direction perpendicular to the first direction. In still other embodiments, the length of the first molecular sieve coating is equal to the length of the positive active material layer and equal to the length of the positive electrode tab in a direction perpendicular to the first direction. In still other embodiments, the length of the first molecular sieve coating is greater than the length of the positive electrode active material layer and less than the length of the positive electrode tab in a direction perpendicular to the first direction. 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 are not particularly limited, and can be selected according to actual needs by a person skilled in the art as long as the purpose of the application can be achieved. The length of the first molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating is arranged in the area of the positive electrode plate, where the positive electrode active material layer is arranged, and the first molecular sieve coating can be set according to the original structure of the positive electrode plate, and under the condition that the bonding force of each layer of the winding electrode assembly and the lamination electrode assembly is enhanced, the space of the secondary battery can be fully utilized. And the first molecular sieve coating has good binding force to the diaphragm while better preventing the short circuit caused by direct contact of the positive electrode current collector and the negative electrode active material and considering the energy density of the secondary battery. Therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative electrode plate is less, the cycle performance of the secondary battery is improved, and the secondary battery has higher energy density and safety performance. In addition, the first area of the positive pole piece and the diaphragm have good bonding effect, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved. .

In one embodiment of the present application, as shown in fig. 4, the thickness H ₁₃ of the first molecular sieve coating layer 13 is smaller than the thickness H ₁₄ of the positive electrode active material layer 14, and the thickness H ₁₃ of the first molecular sieve coating layer 13 is 0.5 μm to 40 μm. For example, the first molecular sieve coating has a thickness of 0.5 μm, 5 μm, 20 μm, 40 μm, or any value in the range between any two of the foregoing values. The thickness of the first molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating has good covering effect on the anode current collector under the condition of not increasing the volume of the secondary battery, the first molecular sieve coating can better exert the effects of preventing short circuit and improving the binding force with the diaphragm, and the energy density of the secondary battery can be considered. Therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative electrode plate is less, the cycle performance of the secondary battery is improved, and the secondary battery has higher energy density and good short circuit prevention performance. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

The thickness of the positive electrode active material layer is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 200 μm.

In one embodiment of the application, the first molecular sieve coating has a thickness of 5 μm to 20 μm. For example, the first molecular sieve coating has a thickness of 5 μm, 7 μm, 10 μm, 15 μm, 18 μm, 20 μm, or any value in the range of any two values. The thickness of the first molecular sieve coating is regulated and controlled within the range, so that the short-circuit prevention performance, the cycle performance, the drop safety performance and the storage performance of the secondary battery are further improved.

In one embodiment of the present application, as shown in fig. 5, the first molecular sieve coating layer 13 and the positive electrode active material layer 14 have an overlap region 40 along the thickness direction Z of the positive electrode sheet 10, and in the overlap region 40, the positive electrode active material layer 14 is located between the first molecular sieve coating layer 13 and the positive electrode current collector 12. It should be noted that, for ease of understanding, the portion marked with an oval frame 50 in fig. 5 is subjected to enlargement treatment, in fact, the surface of the positive electrode sheet is approximately flat after being rolled during the manufacturing process, and the portion marked with the oval frame 50 is not raised as shown in fig. 5 but is substantially flush with the surface of the positive electrode active material layer 14 without the overlap region 40. The width W ₄₀ of the overlap region 40 is 0mm to 0.5mm in the first direction X. For example, the width of the overlap region is 0mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, or any value between any two of the above. The positive electrode active material layer and the first molecular sieve coating layer have an overlapping area, and the width of the overlapping area is regulated and controlled within the range, so that the risk of direct exposure of the positive electrode current collector can be reduced, and the safety risk of the secondary battery can be reduced. And the first molecular sieve coating layer exerts its good adhesive effect with the contact area between the positive electrode active material layer and the first molecular sieve coating layer as small as possible. Therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative electrode plate is less, and the cycle performance of the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

In one embodiment of the present application, as shown in fig. 6, a second molecular sieve coating 23 is provided on the surface of membrane 20 opposite first region 101. It will be appreciated that the "surface" may be one surface of the diaphragm or both surfaces of the diaphragm. The term "opposed" as used herein means a portion of the diaphragm overlapping at least the first region, as projected in the thickness direction of the diaphragm. Illustratively, in some embodiments of the application, as shown in FIG. 7, a second molecular sieve coating 23 is disposed on the two surfaces of the membrane 20 opposite the first region 101. In other embodiments of the present application, as shown in fig. 8, the second molecular sieve coating 23 is disposed on the first surface 20a of the membrane 20 opposite to the first region 101, and it should be noted that the second molecular sieve coating 23 may also be disposed on the second surface 20b of the membrane 20 opposite to the first region 101. The mass percent of the molecular sieve is 20 to 80 percent based on the mass of the second molecular sieve coating. For example, the molecular sieve is present in a mass percent of 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value in a range between any two of the foregoing values, based on the mass of the second molecular sieve coating. The second molecular sieve coating is arranged on the surface of the diaphragm opposite to the first area, the content of the molecular sieve in the second molecular sieve coating is regulated and controlled in the range, the second molecular sieve coating is bonded with the first molecular sieve coating and the negative electrode plate, so that good bonding effect can be exerted, the diaphragm is further bonded with the positive electrode plate and the negative electrode plate, the bonding effect of the diaphragm and the positive electrode plate and the negative electrode plate is further improved, and therefore, the interface contact effect among the positive electrode plate, the diaphragm and the negative electrode plate is further enhanced, and the cycle performance of the secondary battery is further improved. And the arrangement of the second molecular sieve coating can further reduce the risk of short circuit caused by direct contact between the positive current collector and the negative active material due to the fact that the burrs of the positive current collector pierce the diaphragm, and further improve the short circuit prevention performance of the secondary battery. The second molecular sieve coating is arranged on the diaphragm, so that the possibility of shrinkage of a substrate layer in the diaphragm can be reduced, and the high temperature resistance of the secondary battery is improved. In addition, the probability of the membrane turning over is further reduced, so that the falling safety performance of the secondary battery can be further improved.

In one embodiment of the application, the second molecular sieve coating further comprises a first binder, the first binder being present in an amount of 20 to 80% by mass based on the mass of the second molecular sieve coating. For example, the first binder may be present in an amount of 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value in the range of any two of the foregoing, based on the mass of the second molecular sieve coating.

In one embodiment of the present application, as shown in fig. 7 and 8, the second molecular sieve coating 23 has a thickness H ₂₃ of 0.5 μm to 10 μm. For example, the second molecular sieve coating has a thickness of 0.5 μm,1 μm, 2 μm, 3 μm,4 μm,5 μm,6 μm, 7 μm, 8 μm, 9 μm,10 μm, or any value in the range of any two of the foregoing values. The thickness of the second molecular sieve coating is regulated and controlled within the range, so that the second molecular sieve coating has good covering effect on the diaphragm under the condition of not increasing the volume of the secondary battery, the second molecular sieve coating can better play the effects of preventing short circuit and improving the bonding force with the diaphragm, and the energy density of the secondary battery can also be considered. Therefore, the interface contact effect among the positive electrode plate, the diaphragm and the negative electrode plate is further enhanced, the lithium precipitation condition on the negative electrode plate is further reduced, the cycle performance of the secondary battery is further improved, and the secondary battery has higher energy density and good short-circuit prevention performance. Further, the probability of the separator turning over is further reduced, and thus the falling safety performance of the secondary battery can be further improved.

The width and length of the second molecular sieve coating are not particularly limited in the present application, and those skilled in the art can control according to the width and length of the first molecular sieve coating as long as the object of the present application can be achieved. For example, the width of the second molecular sieve coating in the first direction X is 0.5mm to 15mm. The second molecular sieve coating has a length in a direction Y perpendicular to the first direction X that is less than or equal to the length of the separator.

It will be understood by those skilled in the art that the thickness direction, the width direction, and the length direction of the positive electrode tab, the negative electrode tab, and the separator themselves are the same in the secondary battery. Therefore, the first direction X and the direction Y perpendicular to the first direction X are the same direction in both the positive electrode sheet and the separator.

In one embodiment of the application, the first molecular sieve coating has a porosity of 30% to 60%. For example, the first molecular sieve coating has a porosity of 30%, 40%, 50%, 60%, or any value in the range between any two of the foregoing values. The porosity of the first molecular sieve coating is regulated and controlled within the range, so that the first molecular sieve coating has good insulativity and structural strength, the first molecular sieve coating can exert the effect of preventing short circuits, and the effect of improving the adhesion of the first molecular sieve coating can also be exerted. Therefore, the positive electrode plate and the diaphragm have good interface contact effect, the lithium precipitation condition on the negative electrode plate is less, the cycle performance of the secondary battery is improved, and the secondary battery also has good short-circuit prevention performance. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

In one embodiment of the application, the second molecular sieve coating has a porosity of 30% to 60%. For example, the second molecular sieve coating has a porosity of 30%, 40%, 50%, 60%, or any value in the range between any two of the values recited above. The porosity of the second molecular sieve coating is regulated and controlled within the range, so that the second molecular sieve coating has good insulativity and structural strength, the second molecular sieve coating can exert the effect of preventing short circuit, and the effect of improving the adhesive force of the second molecular sieve coating can also be exerted. Therefore, the separator has good interface contact effect with the positive electrode plate and the negative electrode plate, the lithium precipitation condition on the negative electrode plate is less, the cycle performance of the secondary battery is improved, and the secondary battery also has good short circuit prevention 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 membrane turning over is further reduced, so that the falling safety performance of the secondary battery can be further improved.

The mode of controlling the porosity of the first molecular sieve coating and the second molecular sieve coating is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the molecular sieve coating can be realized by regulating the molecular sieve types in the first molecular sieve coating and the second molecular sieve coating, the content ratio of the molecular sieve to the first binder, the pore diameter of the molecular sieve and the like.

In one embodiment of the application, the molecular sieve has a specific surface area of 200m ²/g to 2000m ²/g. For example, the molecular sieve has a specific surface area of 200m²/g、400m²/g、600m²/g、800m²/g、1000m²/g、1200m²/g、1400m²/g、1600m²/g、1800m²/g、2000m²/g or any value between any two of the above ranges. In one embodiment of the application, the molecular sieve has a pore size of 0.3nm to 45nm. For example, the molecular sieve has a pore size of 0.3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or any value between any two of the foregoing. The specific surface area of the molecular sieve and/or the pore diameter of the molecular sieve are/is regulated and controlled in the range, the molecular sieve has higher specific surface area, and/or the molecular sieve has larger pore diameter, so that 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 embedding effect is enhanced, the cohesive force after the molecular sieve is combined with the first binder is large, the binding force is strong, and thus, the first molecular sieve coating and the second molecular sieve coating can be fully swelled at high temperature and are highly dispersed, and good binding force is formed. Therefore, the positive electrode plate and the diaphragm or the positive electrode plate, the diaphragm and the negative electrode plate have good interface contact effect, and the cycle performance of the secondary battery is improved. In addition, the probability of the membrane turning over is reduced, and the falling safety performance of the secondary battery can be improved. In addition, the molecular sieve has the capability of absorbing gas, can reduce the risk of the secondary battery generating gas expansion, and improve the problem of the gas expansion of the secondary battery under special working conditions (such as high-temperature storage, overdischarge, storage after overdischarge, charge and discharge after overdischarge, overcharge, thermal runaway and the like), thereby improving the storage performance of the secondary battery. In the present application, "high temperature" means a temperature of 40 ℃ to 90 ℃.

The average volume particle diameter of the molecular sieve is not particularly limited as long as the object of the present application can be achieved. For example, molecular sieves have an average volume particle size of 0.5 μm to 20 μm. In the present application, the average volume particle diameter Dv50 means a particle diameter at which 50% by volume of molecular sieve particles are accumulated from the small particle diameter side in the particle size distribution on a volume basis.

In one embodiment of the present application, the molecular sieve comprises at least one of a 3A molecular sieve, a 4A molecular sieve, a 5A molecular sieve, a 13X molecular sieve, a ZSM-22 molecular sieve, a ZSM-5 molecular sieve, a MOR molecular sieve, an ITQ molecular sieve, a Y molecular sieve, a SAPO molecular sieve, or an ALPO molecular sieve. Further, 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 adhesion, the molecular sieve of the type has larger specific surface area and aperture, when the molecular sieve is applied to the first molecular sieve coating and/or the second molecular sieve coating, the adhesion area of the molecular sieve can be increased, the mechanical jogging effect is enhanced, the cohesive force after the molecular sieve is combined with the binder is large, and the binding force is strong, so that the first molecular sieve coating and the second molecular sieve coating can be fully swelled at high temperature and then are highly dispersed, and good binding force is formed. Therefore, the positive electrode plate and the diaphragm or the positive electrode plate, the diaphragm and the negative electrode plate have good interface contact effect, and the cycle performance of the secondary battery is improved. In addition, the probability of the membrane turning over is reduced, and the falling safety performance of the secondary battery can be improved. In addition, the molecular sieve has the capability of absorbing gas, so that the risk of the secondary battery generating gas expansion can be reduced, the problem of the gas expansion and swelling of the secondary battery under special working conditions can be solved, and the storage performance of the secondary battery can be improved.

In one embodiment of the present application, as shown in fig. 9, the positive electrode tab 10 further includes a conductive layer 15, the conductive layer 15 being disposed on a surface 13a of the first molecular sieve coating 13 facing away from the positive electrode current collector 12, the conductive layer including a conductive agent in a mass percentage of 5% to 70% based on the mass of the conductive layer. For example, the conductive layer may comprise 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or any value between any two of the foregoing values by mass percent based on the mass of the conductive layer. The conductive layer further includes a second binder, the second binder being 30 to 95% by mass based on the mass of the conductive layer. For example, the second binder may be present in an amount of 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or any value in the range of any two values based on the mass of the conductive layer. The edge impedance of the positive electrode sheet tends to be larger than that of the main body, and the current density of the positive electrode sheet is larger, so that lithium is likely to be separated out in the region (overhang) of the negative electrode sheet exceeding the positive electrode sheet in the electrode assembly. The conductive layer is arranged on the surface of the first molecular sieve coating, which is away from the positive current collector, in the positive pole piece, and can induce a polarized electric field, the polarized electric field can balance the electric field intensity on the surface of the electrode, and the uniformity effect is achieved on the Li ⁺/Li concentration of the negative electrode at the edge of the negative pole piece, so that lithium precipitation caused by nonuniform electric field is improved, and the purpose of prolonging the cycle life of the secondary battery is achieved. The mass percentage of the conductive agent and the second binder in the conductive layer is controlled within the range, the conductive layer has good bonding effect under the condition of inducing a polarized electric field, and the positive electrode plate, the diaphragm and the negative electrode plate have good bonding effect, so that the positive electrode plate and the diaphragm have good interface contact effect, and the cycle performance of the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

The second binder is not particularly limited as long as the object of the present application can be achieved. For example, the second binder includes, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber, or styrene-butadiene rubber.

In one embodiment of the present application, as shown in fig. 9, the sum of the thickness H ₁₃ of the first molecular sieve coating layer 13 and the thickness H ₁₅ of the conductive layer 15 is smaller than the thickness H ₁₄ of the positive electrode active material layer 14, the thickness of the first molecular sieve coating layer is 0.5 μm to 40 μm, and the thickness of the conductive layer is 0.5 μm to 30 μm. For example, the first molecular sieve coating has a thickness of 0.5 μm, 20 μm, 40 μm, or any value in the range between any two of the foregoing values. For example, the thickness of the conductive layer is 0.5 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value between any two of the above ranges. 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 is regulated and controlled within the above range, so that the possibility of generating a gap between the second region of the positive electrode sheet and the diaphragm due to the excessive thickness of the first molecular sieve coating and the conductive layer can be reduced, the second region of the positive electrode sheet is fully contacted with the diaphragm, and good interface performance is achieved between the positive electrode sheet and the diaphragm. The thickness of the first molecular sieve coating and the thickness of the conducting layer are regulated and controlled within the above range, so that lithium precipitation caused by nonuniform electric field is improved under the condition of not increasing the volume of the secondary battery, and the purpose of prolonging the cycle life of the secondary battery is achieved. And the positive electrode plate, the diaphragm and the negative electrode plate have good interface contact effect, and the cycle performance of the secondary battery is improved. And moreover, a good bonding effect is provided between the first area of the positive electrode plate and the diaphragm, and the probability of the diaphragm turning over is reduced, so that the falling safety performance of the secondary battery can be improved.

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-mentioned kind of conductive agent has good conductivity.

The structure of the electrode assembly is not particularly limited as long as the object of the present application can be achieved. For example, the electrode assembly is constructed in a wound structure or a lamination structure. The kind of the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode current collector includes aluminum foil, aluminum alloy foil, and the like.

In one embodiment of the present application, the positive electrode active material layer includes a positive electrode active material. The kind of the positive electrode active material is not particularly limited as long as the object 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 aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, lithium titanate, or the like. Optionally, the positive electrode active material layer further includes a positive electrode conductive agent, a positive electrode binder. The types of the positive electrode conductive agent and the positive electrode binder in the positive electrode active material layer are not particularly limited as long as the object of the present application can be achieved. The mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder in the positive electrode active material layer is not particularly limited, and can be selected by a person skilled in the art 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, the positive electrode conductive agent and the positive electrode binder in the positive electrode active material layer is (96.5-97.9): (0.9-2.0): (1.0-2.0).

In one embodiment of the present application, a negative electrode tab 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 "anode active material layer disposed on at least one surface of the anode current collector" means that the anode active material layer may be disposed on one surface of the anode current collector in the thickness direction thereof, or may be disposed on both surfaces of the anode current collector in the thickness direction thereof. The "surface" here may be the entire region of the negative electrode current collector or may be a partial region of the negative electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved. The negative electrode current collector is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, foam nickel, foam copper, or the like. The anode active material layer includes an anode active material. The kind of the negative electrode active material is not particularly limited as long as the object of the present application can be achieved. For example, the anode active material may contain at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, tin-based material, silicon-based material, lithium titanate, transition metal nitride, or the like. Optionally, the anode active material layer further includes at least one of an anode conductive agent, a thickener, and an anode binder. The kind of the negative electrode conductive agent, the thickener and the negative electrode binder in the negative electrode active material layer is not particularly limited in the present application as long as the object of the present application can be achieved. The mass ratio of the anode active material, the anode conductive agent, the thickener, and the anode binder in the anode active material layer is not particularly limited as long as the object of the present application can be achieved. For example, the mass ratio of the anode active material, the anode conductive agent, the thickener and the anode binder in the anode active material layer is (96-98): 0-1.5): 0.5-1.5): 1.0-1.9.

The thicknesses of the anode current collector and the anode active material layer are not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the anode current collector is 5 μm to 20 μm, and the thickness of the anode active material layer is 30 μm to 120 μm.

The separator is not particularly limited as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of Polyethylene (PE), polypropylene (PP) -based Polyolefin (PO), polyester (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 film, a nonwoven film, a microporous film, a composite film, a rolled film, or a spun film.

The secondary battery of the present application further includes an electrolyte, and the electrolyte and the electrode assembly are contained in the pouch. The present application is not particularly limited as to the package bag and the electrolyte, and those skilled in the art can select the package bag and the electrolyte known in the art as required as long as the object of the present application can be achieved.

The method for preparing the positive electrode sheet is not particularly limited as long as the object of the present application can be achieved.

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, steps of (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, drying to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer and the first molecular sieve coating, 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 with a double-sided coated positive electrode active material layer and the first molecular sieve coating, wherein the first molecular sieve coating is disposed on a first region of the positive electrode sheet, and the positive electrode active material layer is disposed on a second region of the positive electrode sheet, (3) cold pressing and cutting. The method for preparing the cathode slurry and the first molecular sieve coating slurry in the step (1) is not particularly limited, so 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 object of the present application can be achieved. The temperature and time of the drying in the step (2) are not particularly limited, and may be selected according to actual needs by those skilled in the art as long as the object of the present application can be achieved. The process parameters of cold pressing and cutting in the step (3) are not particularly limited, and can be selected by a person skilled in the art according to actual needs, so long as the purpose of the application can be achieved.

For example, in other embodiments of the present application, the positive electrode sheet comprises 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 comprises, but is not limited to, the steps of (1) preparing positive electrode slurry, first molecular sieve coating slurry and 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, drying to obtain a positive electrode sheet with a single-sided 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 facing away from the positive electrode current collector, drying to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material layer, the first molecular sieve coating and the conductive layer, and repeating the steps to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material layer, the first molecular sieve coating and the conductive layer, wherein the first molecular sieve coating is arranged on a first area of the positive electrode sheet, and the positive electrode active material layer is arranged on a second area of the positive electrode sheet, and (3) cold-pressing the sheet. The method for preparing the cathode slurry, the first molecular sieve coating slurry and the conductive layer slurry in the step (1) is not particularly limited, and the purpose of the present application can be achieved as long as the contents of the molecular sieve and the first binder in the first molecular sieve coating layer 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 temperature and time of the drying in the step (2) are not particularly limited, and may be selected according to actual needs by those skilled in the art as long as the object of the present application can be achieved. The process parameters of cold pressing and cutting in the step (3) are not particularly limited, and can be selected by a person skilled in the art according to actual needs, so long as the purpose of the application can be achieved.

The method for preparing the second molecular sieve coating is not particularly limited as long as the object of the present application can be achieved. For example, the method of preparing the second molecular sieve coating includes, but is not limited to, the steps of (1) preparing a second molecular sieve coating slurry, and (2) coating the second molecular sieve coating slurry on a surface of the separator opposite to the first region of the positive electrode sheet, and drying to obtain a separator with a single-sided coating of the second molecular sieve coating. And repeating the steps on the other surface of the diaphragm opposite to the first area of the positive pole piece to obtain the diaphragm coated with the second molecular sieve coating on both sides. The method for preparing the second molecular sieve coating slurry in the step (1) is not particularly limited, as long as the contents of the molecular sieve and the first binder in the second molecular sieve coating layer are within the scope of the present application, and the object of the present application can be achieved. The temperature and time of the drying in the step (2) are not particularly limited, and may be selected according to actual needs by those skilled in the art as long as the object of the present application can be achieved.

The method of manufacturing the secondary battery according to the present application is not particularly limited, and a manufacturing method known in the art may be selected as long as the object of the present application can be achieved. For example, the method for manufacturing the secondary battery includes, but is not limited to, stacking a positive electrode tab, a separator and a negative electrode tab in order, fixing four corners of the entire lamination structure to obtain an electrode assembly of the lamination structure, putting the electrode assembly into a packing bag, respectively welding a positive electrode tab and a negative electrode tab on a metal sheet through transfer welding and leading out of the packing bag, injecting an electrolyte into the packing bag, and sealing to obtain the secondary battery. Or sequentially stacking and winding the positive electrode plate, the diaphragm and the negative electrode plate to obtain an electrode assembly with a winding structure, putting the electrode assembly into a packaging bag, respectively welding the positive electrode tab and the negative electrode tab on a metal sheet through transfer welding and leading out the packaging bag, injecting electrolyte into the packaging bag, and sealing to obtain the secondary battery. The kind of the metal sheet is not particularly limited as long as the object of the present application can be achieved. For example, the metal sheet welded by the positive electrode tab may be an aluminum sheet, and the metal sheet welded by the negative electrode tab may be a copper sheet, a nickel sheet or a copper nickel plated sheet.

The secondary battery of the present application is not particularly limited, and may include a device in which an electrochemical reaction occurs. 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, a sodium ion battery.

The electric device of the present application is not particularly limited, and may be one used in a known electric device in the prior art. For example, the powered device may include, but is not limited to, a notebook computer, a pen-type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a hand-held cleaner, a portable CD, a mini-compact disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flash, a camera, a household large-sized battery, a lithium ion capacitor.

Examples

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. The various tests and evaluations were carried out according to the following methods.

Test method and apparatus:

Lithium precipitation test:

The lithium ion batteries of each example and comparative example were charged to full charge (charging regime was constant current charging to 4.48V at 4C rate, then constant voltage charging to current 0.05C), left for 5min, and then discharged to 3.0V at 1/3C, and the above steps were repeated 900 times for the same lithium ion battery.

And (3) fully charging the lithium ion batteries subjected to the cycle tests of 300 times, 500 times, 700 times and 900 times respectively at normal temperature according to a standard charging mode (0.5C is charged to 4.48V, and 4.48V is charged to 0.02C at a constant voltage), disassembling the lithium ion batteries, and checking the lithium precipitation distribution condition on the surface of the negative electrode plate.

And (3) adhesive force test:

And taking out the lithium ion battery to be disassembled, cutting off the edge of the packaging bag, opening the packaging bag, and unfolding the electrode assembly. The positive pole piece, the diaphragm and the negative pole piece are separated, the positive pole piece and the diaphragm are reserved, and different lithium ion batteries take approximately the same position and the same surface in the first area of the positive pole piece. The positive electrode sheet and the separator were taken and cut into 10mm×50mm samples with a blade. And (3) attaching double faced adhesive tape (manufacturer: nitto, product model: 5000 NS) to the steel plate, attaching the intercepted sample to the double faced adhesive tape, and arranging the steel plate, the double faced adhesive tape, the positive electrode plate and the diaphragm in sequence from bottom to top with the test surface facing upwards. A paper tape with the same width as the sample and a length of >50mm was attached to the diaphragm surface and fixed with a crepe adhesive. And (3) separating by using a pulling machine, wherein the stripping angle is 180 degrees, and the tested stripping force data is the bonding force data of the positive pole piece and the diaphragm.

Drop test:

The lithium ion batteries of each example and comparative example were fully charged in a standard charging manner (0.5C to 4.48V and constant voltage to 0.02C at 4.48V), and then dropped 1 time along 6 sides from a 1m drop height with a marble drop floor in a 20±5 ℃ test environment, and dropped 1 time at 4 corners, for a total of 5 rounds of testing. The standard of passing the test is no fire, no explosion, no smoke, no liquid leakage and voltage drop <100mV.

Each example and comparative example tested 5 lithium ion batteries to characterize drop safety performance by the number ratio tested, the higher the number of pass tests, the better the drop safety performance of lithium ion batteries, the number ratio of pass tests = pass number/5.

Storage performance test:

The lithium ion batteries of each example and comparative example were fully charged in a standard charging manner (0.5C to a voltage of 4.48V and constant voltage charged to 0.02C at a voltage of 4.48V) at 25 ℃, placed in an 80 ℃ incubator for 48 hours, and the thickness of the lithium ion batteries before and after storage was measured to obtain an expansion ratio = (thickness after measurement-thickness before measurement)/thickness before measurement x 100%.

The storage performance of the lithium ion battery is characterized by the expansion rate, and the lower the expansion rate is, the better the storage performance of the lithium ion battery is.

Porosity test:

Tested by a true density tester.

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, and the positive electrode sheet and separator obtained by disassembly were washed in n-butanol and then dried. And stripping the first molecular sieve coating in the positive electrode plate by using a scraper, stripping the second molecular sieve coating in the diaphragm, and respectively grinding into powder.

The powder obtained by grinding the first molecular sieve coating was compacted and die cut into 10mm x 10mm regular shaped samples, which were placed on a true density tester (AccuPyc II 1340) for testing, resulting in a 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=length×width×height of the first molecular sieve coating was calculated. Porosity (%) = (apparent volume of first molecular sieve coating-true volume of first molecular sieve coating)/apparent volume of first molecular sieve coating x 100%.

The powder obtained by grinding the second molecular sieve coating was compacted and die cut into 10mm x 10mm regular shaped samples, which were placed on a true density tester (AccuPyc II 1340) for testing, resulting in a 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=length×width×height of the second molecular sieve coating was calculated. Porosity (%) = (apparent volume of second molecular sieve coating-true volume of second molecular sieve coating)/apparent volume of second molecular sieve coating x 100%.

Molecular sieve specific surface area and pore size testing:

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, and the positive electrode sheet and separator obtained by disassembly were washed in n-butanol and then dried. Stripping the first molecular sieve coating in the positive electrode plate by using a scraper, stripping the second molecular sieve coating in the diaphragm, respectively grinding into powder, and respectively performing the following tests:

A1 g weight of the powder was placed in a sample tube, the sample tube was heated to 150℃and subjected to evacuation and degassing for 2 hours. The treated sample was connected to a test system (instrument model: U.S. microphone 3 Flex), and nitrogen was continuously introduced into the sample by means of a Topler pump capable of quantitatively transferring a gas for 1 hour to allow saturated adsorption. When the adsorption reaches equilibrium, the pressure sensor measures the pressure value, the adsorption quantity can be calculated according to the pressure value, and an isothermal adsorption and desorption line is obtained. The specific surface area was calculated by taking the point using the BET equation. Pore size was calculated using Density Functional Theory (DFT).

Example 1-1

< Preparation of Positive electrode sheet >

① Putting a positive electrode conductive agent and a positive electrode active material lithium cobaltate into a stirrer, adding all positive electrode binder according to the formula weight ratio and a dispersion medium according to the formula weight ratio of 2/3 into the stirrer, stirring at a high speed for 20 minutes, and removing bubbles after stirring for 10 minutes;

② Adding the rest dispersing medium with the weight ratio of 1/3 to the material prepared by ①, stirring at high speed for 30 minutes, and removing bubbles for 5 minutes after stirring to obtain the anode slurry. The dispersion medium is N-methyl pyrrolidone (NMP), the positive electrode conductive agent is conductive carbon black and carbon nano tubes, the positive electrode binder is polyvinylidene fluoride (PVDF), and the solid content of the positive electrode slurry is 75wt%. Wherein the mass ratio of the lithium cobaltate to the acetylene black to the multi-walled carbon nano tube to the polyvinylidene fluoride is 96.5:1.5:0.5:1.5.

Molecular sieve MOR molecular sieve (manufacturer: shanghai source leaf Biotechnology Co., ltd., model: 12445-20-4) and first binder polymethyl methacrylate (weight average molecular weight 75000) are mixed according to a mass ratio of 90:10, N-methylpyrrolidone (NMP) is added as solvent, and the mixture is stirred under the action of a vacuum stirrer until the solid content is 72wt% and the system is uniform. Wherein the specific surface area of the molecular sieve is 350m ²/g, the pore diameter of the molecular sieve is 0.6nm, and the average volume particle diameter Dv50=1μm of the molecular sieve.

And respectively and uniformly coating the anode slurry and the first molecular sieve coating slurry on one surface of an anode current collector aluminum foil with the thickness of 10 mu m, and drying at 100 ℃ to obtain an anode sheet with a single-sided coated anode active material layer and a first molecular sieve coating. And repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the double-sided coating positive electrode active material layer and the first molecular sieve coating (shown in fig. 4). The first molecular sieve coating is arranged in a first area of the positive electrode plate, and the positive electrode active material layer is arranged in a second area of the positive electrode plate. Cold pressing, and cutting to obtain the positive pole piece with the specification of 74mm multiplied by 1183mm for standby.

Wherein the first molecular sieve coating has a width W ₁₃ = 1mm and a thickness H ₁₃ = 10 μm. The thickness of the positive electrode active material layer was 40 μm, the width was 73mm, the length of the positive electrode active material layer was 1183mm, and the length of the first molecular sieve coating layer was 1183mm.

< Preparation of negative electrode sheet >

Mixing negative electrode active material artificial graphite, negative electrode conductive agent acetylene black, thickener carboxymethyl cellulose (CMC) and negative electrode binder styrene-butadiene rubber (abbreviated as SBR, weight average molecular weight is 50 multiplied by 10 ⁵) according to the mass ratio of 96:1:1.5:1.5, then adding deionized water as solvent, and stirring under the action of a vacuum stirrer until the solid content is 54wt% and the system is uniform. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil having a thickness of 8 μm, and dried at 85 ℃ to obtain a negative electrode tab having a single-sided coated negative electrode active material layer (thickness 45 μm). And repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode active material layer. Cold pressing, and cutting to obtain the negative electrode plate with the specification of 76mm multiplied by 1186mm for standby.

< Preparation of separator >

Polyethylene film (manufacturer: lithium New Material Co., ltd. In lake south) having a thickness of 7 μm was used.

< Preparation of electrolyte >

Mixing Ethylene Carbonate (EC) and diethyl carbonate (DEC) according to a volume ratio of 3:7 to obtain an organic solvent, dissolving lithium salt LiPF ₆ in the mixed organic solvent according to a mol/L ratio to obtain a basic electrolyte, and finally adding 2wt% of fluoroethylene carbonate (FEC) based on the mass of the basic electrolyte to prepare the electrolyte.

< Preparation of lithium ion Battery >

And stacking and winding the prepared negative electrode plate, the prepared diaphragm and the prepared positive electrode plate in sequence to obtain the electrode assembly with a winding structure. And placing the electrode assembly in an aluminum plastic film packaging bag, respectively welding the positive electrode tab and the negative electrode tab on an aluminum sheet and a copper sheet in a transfer way, leading out the packaging bag, drying the electrode assembly, injecting electrolyte, and carrying out the procedures of vacuum packaging, standing, formation, degassing, trimming and the like to obtain the lithium ion battery.

Examples 1-2 to 1-19

The procedure of example 1-1 was repeated except that the preparation parameters were adjusted in accordance with Table 1.

Wherein, in examples 1-8 to 1-10, the widths of the positive electrode active material layers were 73.5mm, 71mm, and 64mm, respectively, as the widths of the first molecular sieve coating layers were varied.

Example 2-1

< Preparation of separator >

Molecular sieve MOR molecular sieve (manufacturer: shanghai Source leaf biology Co., ltd., model: 12445-20-4) and first binder polymethyl methacrylate (weight average molecular weight 75000) were mixed according to a mass ratio of 80:20, N-methylpyrrolidone (NMP) was added as a solvent, and stirred under a vacuum stirrer to a second molecular sieve coating slurry having a solid content of 72wt% and a uniform system. Wherein the specific surface area of the molecular sieve is 350m ²/g, the pore diameter of the molecular sieve is 0.6nm, and the average volume particle diameter Dv50=1μm of the molecular sieve.

And coating a second molecular sieve coating slurry on one surface of the polyethylene film opposite to the first area of the positive pole piece, and drying at 100 ℃ to obtain the diaphragm with the single-sided coating of the second molecular sieve coating. Then, repeating the above steps on the other surface of the polyethylene film opposite to the first region of the positive electrode sheet to obtain a membrane with the double-sided coating of the second molecular sieve (as shown in fig. 7).

Wherein the second molecular sieve coating has a thickness H ₂₃ = 10 μm.

< Preparation of positive electrode sheet >, < preparation of negative electrode sheet >, < preparation of electrolyte >, < preparation of lithium ion battery > are the same as in example 1-1.

Examples 2-2 to 2-7

The procedure of example 2-1 was repeated except that the preparation parameters were adjusted as shown in Table 3.

Example 3-1

< Preparation of Positive electrode sheet >

The conductive agent acetylene black (manufacturer: joker and Xingxiong chemical industry Co., ltd.) and a second binder PVDF (weight average molecular weight 755000) are mixed according to a mass ratio of 30:70, deionized water is added as a solvent, and the mixture is stirred under the action of a vacuum stirrer until the solid content is 45wt% and the system is uniform.

The method comprises the steps of uniformly coating anode slurry and first molecular sieve coating slurry on one surface of an anode current collector aluminum foil with the thickness of 10 mu m respectively, drying at 100 ℃ to obtain an anode plate with a single-sided coated anode active material layer and a first molecular sieve coating, coating conductive layer slurry on the surface of the first molecular sieve coating, which is far away from the anode current collector, and drying at 100 ℃ to obtain an anode plate with the single-sided coated anode active material layer, the first molecular sieve coating and the conductive layer. And repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the positive electrode active material layer, the first molecular sieve coating and the conductive layer coated on both sides (as shown in fig. 9). The first molecular sieve coating and the conducting layer are arranged in a first area of the positive electrode plate, and the positive electrode active material layer is arranged in a second area of the positive electrode plate. Cold pressing, and cutting to obtain the positive pole piece with the specification of 74mm multiplied by 1183mm for standby.

Wherein the first molecular sieve coating has a width W ₁₃ = 1mm and a thickness H ₁₃ = 10 μm. The thickness H ₁₅ = 20 μm and the width of the conductive layer was 1mm. The thickness H ₁₄ =90 μm of the positive electrode active material layer.

< Preparation of negative electrode sheet >, < preparation of separator >, < preparation of electrolyte >, < preparation of lithium ion battery > are the same as in example 1-1.

Examples 3-2 to 3-6

The procedure of example 3-1 was repeated except that the preparation parameters were adjusted as shown in Table 4.

Wherein, when the mass percentage of the conductive agent is changed based on the mass of the conductive layer, the mass percentage of the second binder is changed, and the sum of the mass percentages of the conductive agent and the second binder is 100%.

Examples 3 to 7

< Preparation of positive electrode sheet > was the same as in example 3-1, < preparation of negative electrode sheet >, < preparation of separator >, < preparation of electrolyte >, < preparation of lithium ion battery > was the same as in example 2-1.

Comparative example 1

< Preparation of Positive electrode sheet >

Mixing ceramic particle boehmite and polyvinylidene fluoride (PVDF, weight average molecular weight 755000) serving as a ceramic layer binder according to a mass ratio of 95:5, adding deionized water serving as a solvent, and stirring under the action of a vacuum stirrer to obtain ceramic coating slurry with a solid content of 40wt% and a uniform system. Wherein the average volume particle diameter dv50=0.6 μm of boehmite.

And respectively and uniformly coating the anode slurry and the ceramic coating slurry on one surface of an anode current collector aluminum foil with the thickness of 10 mu m, and drying at 100 ℃ to obtain an anode sheet with a single-sided coated anode active material layer and a ceramic coating. And repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the double-sided coating positive electrode active material layer and the ceramic coating. Wherein, ceramic coating sets up in the first region of positive pole piece, and positive electrode active material layer sets up in the second region of positive pole piece. And (3) drying at 100 ℃, cold pressing, and cutting to obtain the positive pole piece with the specification of 74mm multiplied by 1183mm for later use.

Wherein the width of the ceramic coating is 1mm and the thickness is 10 mu m. The length of the positive electrode active material layer was 1183mm, and the length of the ceramic coating layer was 1183mm.

Comparative example 2

The procedure of comparative example 1 was repeated except that the ceramic layer binder was replaced with the first binder polymethyl methacrylate (weight average molecular weight 75000).

Comparative example 3 and comparative example 4

The preparation parameters and performance parameters of each example and comparative example are shown in tables 1 to 4.

TABLE 1

Note that "\" in table 1 indicates that there is no corresponding parameter, "W _f1" in table 1 indicates the mass percent of molecular sieve based on the mass of the first molecular sieve coating, "Wz ₁" in table 1 indicates the mass percent of the first binder based on the mass of the first molecular sieve coating, and 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.

TABLE 2

As can be seen from examples 1-1 to 1-19 and comparative examples 1 to 4, the examples of the present application select the positive electrode sheet having the first molecular sieve coating layer provided on both surfaces of the positive electrode current collector in the first region, and the content of the intermediate molecular sieve and the first binder of the first molecular sieve coating layer being within the scope of the present application, which has a higher adhesive force, indicate a higher adhesive force between the positive electrode sheet and the separator. The positive electrode sheet was applied to a secondary battery, and the secondary batteries of examples 1-1 to 1-19 had a higher number ratio of drop-through tests, had fewer lithium-out conditions, indicating that the cycle performance and drop safety performance of the secondary battery were improved, and at the same time, had a lower expansion ratio, indicating that the risk of occurrence of gassing of the secondary battery was lower, and the storage performance thereof was improved, as compared with comparative examples 1 and 2. In comparative examples 1 and 2, the positive electrode sheet without the first molecular sieve coating was selected, which had extremely low adhesion, and the secondary battery using the positive electrode sheet had a low number ratio of drop passing tests and a severe lithium precipitation, indicating that the secondary battery had poor cycle performance and drop safety. Also, the secondary batteries of comparative examples 1 and 2 have a higher expansion ratio, indicating that the secondary batteries have a higher risk of gassing, and the storage performance thereof has not been improved. In comparative example 3, the content of the molecular sieve is too high, the content of the binder is low, the bonding force between the positive electrode plate and the diaphragm cannot be sufficiently caused, the bonding force between the positive electrode plate and the diaphragm is too low, failure is easy to occur when the battery falls, meanwhile, the interface performance between the positive electrode plate and the isolating diaphragm is poor in the circulation process, lithium precipitation is caused, in comparative example 4, the content of the binder is too high, the content of the molecular sieve is too low, burrs, folds and the like on the positive electrode current collector cannot be sufficiently blocked by the molecular sieve to be in contact with the negative electrode active material when the battery falls, short circuit is easy to occur, meanwhile, the generated gas cannot be sufficiently absorbed when the battery is stored at a high temperature due to the fact that the molecular sieve content is too low, the expansion of the battery is too large, and the storage performance is poor.

The mass percent of the molecular sieve and the first binder in the first molecular sieve coating typically affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 1-1 to 1-7, comparative examples 3 and 4, the secondary batteries having a higher number proportion of falling passing tests, less lithium evolution, lower expansion ratio, indicating good cycle performance, falling safety performance and storage performance, were selected using the molecular sieves and the first binder in the first molecular sieve coating layer in mass percentage within the scope of the present application. The molecular sieve of example 1-1 has higher content, can absorb more gas to inhibit the expansion of the battery, but has lower content of binder, smaller binding force and lower drop test performance than those of examples 1-2 to 1-6, the binder of example 1-7 has higher content, and higher binding force than that of example 1-1, but the binder cannot be fully swelled due to smaller molecular sieve, so that the binding force is not as high as that of examples 1-2 to 1-6, and the expansion rate of the battery is higher due to the fact that more gas cannot be absorbed, and the overall performance of the batteries of examples 1-2 to 1-6 is obviously better than that of examples 1-1 and 1-7. Examples 1-3 to 1-5, the molecular sieve coating has better adhesion due to the proper proportion of the molecular sieve and the binder, so that the interface performance between the diaphragm and the active material layer is better, the gas absorption capacity of the molecular sieve can be fully exerted, and the anti-dropping performance, the anti-expansion performance and the lithium precipitation prevention capacity of the battery are better.

The width W ₁₃ of the first molecular sieve coating generally affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 1-2, examples 1-8 to examples 1-10, the secondary battery having a width W ₁₃ of the first molecular sieve coating layer within the scope of the present application, which has a higher number proportion of falling passing tests, has less lithium precipitation, and a lower expansion rate, shows that the secondary battery has good cycle performance, falling safety performance, and storage performance. The first molecular sieve coatings of examples 1-2, examples 1-9 and examples 1-10 are wider in width and have significantly better overall performance than examples 1-8, but the larger width of the molecular sieve coatings of examples 1-10 results in a decrease in battery energy density and is therefore not a preferred option.

The thickness H ₁₃ of the first molecular sieve coating generally affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 1-2, examples 1-11 to examples 1-15, the secondary battery having a thickness H ₁₃ of the first molecular sieve coating layer within the scope of the present application, which has a higher number proportion of falling passing tests, has less lithium precipitation, has a lower expansion rate, indicates that the secondary battery has good cycle performance, falling safety performance and storage performance. The first molecular sieve coating layers of examples 1-2 and examples 1-12 to 1-15 have a larger thickness, and the overall performance is significantly better than that of examples 1-11, but the thicker molecular sieve coatings of examples 1-14 and examples 1-15 result in a decrease in the energy density of the battery without further improvement in performance, and are therefore not preferred.

The type, specific surface area and pore size of the molecular sieve, and the porosity of the first molecular sieve coating layer generally affect the cycle performance, drop safety performance and storage performance of the secondary battery. As can be seen from examples 1-2, examples 1-16 to examples 1-19, the secondary battery having a higher number proportion of falling passing tests, less lithium evolution, lower expansion ratio, showing good cycle performance, falling safety performance and storage performance, was selected from the molecular sieves, the specific surface area and pore diameter, and the porosity of the first molecular sieve coating layer.

TABLE 3 Table 3

Note that "\" in table 3 indicates no corresponding parameter, "W _f2" in table 3 indicates the mass percent of molecular sieve based on the mass of the second molecular sieve coating, and "Wz ₂" in table 3 indicates the mass percent of the first binder based on the mass of the second molecular sieve coating.

As can be seen from examples 1-2, 2-1 to 2-7, by providing the second molecular sieve coating layer on the surface of the separator opposite to the first region, the adhesion between the positive electrode sheet and the separator can be further increased, and the separator can be applied to a secondary battery, which has a higher number ratio of falling passing tests, has fewer lithium precipitation cases, and shows that the cycle performance and the falling safety performance of the secondary battery are further improved. It has a lower expansion ratio, indicating that the secondary battery is less at risk of generating flatulence, and its storage performance is further improved.

The mass percent of the molecular sieve in the second molecular sieve coating typically affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 2-1 to 2-3, the secondary battery having a higher number proportion of falling passing tests, less lithium evolution condition, lower expansion rate, showing good cycle performance, falling safety performance and storage performance, was selected as the molecular sieve in the second molecular sieve coating layer.

The thickness H ₂₃ of the second molecular sieve coating layer generally affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 2-1, 2-4 and 2-5, the secondary battery having a thickness H ₂₃ of the second molecular sieve coating layer within the scope of the present application, which has a higher number ratio of drop passing tests, has less lithium precipitation, and a lower expansion rate, shows that the secondary battery has good cycle performance, drop safety performance and storage performance.

The porosity of the second molecular sieve coating generally affects the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 2-1, 2-6 to 2-7, the secondary battery having the porosity of the second molecular sieve coating layer within the range of the present application, which has a higher number ratio of drop passing tests, has less lithium precipitation, and a lower expansion rate, shows that the secondary battery has good cycle performance, drop safety performance, and storage performance.

TABLE 4 Table 4

Note that "\" in table 4 indicates no corresponding parameter, "W _d" in table 4 indicates the mass percent of the conductive agent based on the mass of the conductive layer, "W _z3" in table 4 indicates the mass percent of the second binder based on the mass of the conductive layer, and the difference between examples 3-1 and 3-7 is that the separator of example 3-1 is not provided with the second molecular sieve coating and the separator of example 3-7 is provided with the second molecular sieve coating.

It can be seen from examples 1-2 and 3-1 to 3-6, 2-1 and 3-7 that providing the conductive layer with the conductive agent and the second binder on the surface of the first molecular sieve coating layer facing away from the positive electrode current collector, which is within the scope of the present application, can further reduce the lithium precipitation condition of the secondary battery with a higher number proportion of falling passing tests and a lower expansion rate, indicating that the secondary battery further improves the cycle performance with good falling safety performance and storage performance.

The mass percentage of the conductive agent and the second binder in the conductive layer generally affects the cycle performance, the drop safety performance, and the storage performance of the secondary battery. As can be seen from examples 1-2, 3-1 to 3-3, the secondary battery having a higher number ratio of drop passing tests, less lithium evolution, lower expansion ratio, showing good cycle performance, drop safety performance and storage performance, was selected as the conductive layer.

The thickness H ₁₅ of the conductive layer generally affects the cycle performance, the drop safety performance, and the storage performance of the secondary battery. As can be seen from examples 1-2, 3-1, 3-4 and 3-5, the secondary battery having a thickness H ₁₅ of the conductive layer within the scope of the present application, which has a higher number ratio of drop passing tests, less lithium evolution, lower expansion rate, shows that the secondary battery has good cycle performance, drop safety performance and storage performance.

The kind of the conductive agent generally affects the cycle performance, the drop safety performance, and the storage performance of the secondary battery. As can be seen from examples 3-1 and 3-6, the secondary battery with the conductivity agent type within the scope of the present application has a higher number ratio for falling through test, less lithium precipitation, lower expansion rate, indicating that the secondary battery has good cycle performance, falling safety performance and storage performance.

It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

In this specification, each embodiment is described in a related manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments.

The foregoing description of the preferred embodiments of the application is not intended to limit the application to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the application are intended to be included within the scope of the application.

Claims

1. The secondary battery comprises an electrode assembly, wherein the electrode assembly comprises a positive electrode plate, a negative electrode plate and a diaphragm, and the diaphragm is arranged between the positive electrode plate and the negative electrode plate;

The positive electrode plate comprises a positive electrode tab, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, wherein the positive electrode tab comprises a second area and a first area which are sequentially connected, the positive electrode tab and the positive electrode current collector in the first area are integrally arranged, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first area, the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector in the second area, and the first direction is the extending direction of the positive electrode tab in an unfolded state;

the first molecular sieve coating comprises a molecular sieve and a first binder, wherein the mass percentage of the molecular sieve is 10-90% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 10-90%.

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

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

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

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

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

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

8. The secondary battery according to claim 1, wherein a second molecular sieve coating is provided on a surface of the separator opposite the first region;

the second molecular sieve coating includes the molecular sieve, the molecular sieve having a mass percent content of 20% to 80% based on the mass of the second molecular sieve coating.

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

10. The secondary battery of claim 8, wherein the first molecular sieve coating and the second molecular sieve coating each independently have a porosity of 30% to 60%.

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

12. The secondary battery according to any one of claims 1 to 11, wherein the molecular sieve comprises at least one of a 3A molecular sieve, a 4A molecular sieve, a 5A molecular sieve, a 13X molecular sieve, a ZSM-22 molecular sieve, a ZSM-5 molecular sieve, a MOR molecular sieve, an ITQ molecular sieve, a Y molecular sieve, a SAPO-type molecular sieve, or an ALPO-type molecular sieve;

the first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber, or styrene-butadiene rubber.

13. The secondary battery of claim 1, wherein the positive electrode sheet further comprises a conductive layer disposed on a surface of the first molecular sieve coating facing away from the positive electrode current collector;

The conductive layer includes a conductive agent, and the conductive agent is 5 to 70% by mass based on the mass of the conductive layer.

14. The secondary battery according to claim 13, wherein a sum of a thickness of the first molecular sieve coating layer and a thickness of the conductive layer is less than or equal to a 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 comprises at least one of acetylene black, ketjen black, conductive graphite, graphene, carbon nanotubes.

16. An electric device, wherein the electric device comprises the secondary battery according to any one of claims 1 to 15.