A secondary battery and an electric device

Abstract

A secondary battery and a power utilization device, the secondary battery comprising an electrode assembly, the electrode assembly comprising a positive electrode tab, a negative electrode tab and a separator, the separator being arranged between the positive electrode tab and the negative electrode tab; the positive electrode tab comprising a positive electrode lug, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, along a first direction, the positive electrode tab comprising a second region and a first region connected in sequence, the positive electrode lug being integrally arranged with the positive electrode current collector in the first region, the first molecular sieve coating being arranged on at least one surface of the positive electrode current collector in the first region, the positive electrode active material layer being arranged on at least one surface of the positive electrode current collector in the second region, the first direction being an extension direction of the positive electrode lug in an unfolded state; the first molecular sieve coating comprising a molecular sieve and a first binder, the mass percentage content of the molecular sieve being 10% to 90% and the mass percentage content of the first binder being 10% to 90% based on the mass of the first molecular sieve coating. The secondary battery has good cycle performance and drop safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to a secondary battery and a power utilization device. BACKGROUND

[0002] With the development of society, smart phones and notebooks play an important role in our life, and the market scale of wearable devices, smart home, electric vehicles and electric bicycles is gradually increasing. The secondary battery represented by lithium ion batteries and sodium ion batteries is widely applied to the above fields due to its high energy density and environmental protection, and therefore the market demand for the secondary battery is rapidly increasing.

[0003] In the existing secondary battery, the electrolyte is prone to accumulate at the head of the electrode assembly (the side where the tab of the electrode assembly protrudes), resulting in weak binding force between the layers of the electrode sheet, and the edge of the electrode sheet becomes a weak area that cannot be ignored, which affects the cycle performance and drop safety of the secondary battery. SUMMARY

[0004] The purpose of the present application is to provide a secondary battery and a power utilization device to improve the cycle performance and drop safety performance of the secondary battery.

[0005] It should be noted that in the application content, the lithium ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium ion battery. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a positive electrode tab, a negative electrode tab and a separator, the separator being arranged between the positive electrode tab and the negative electrode tab; the positive electrode tab comprising a positive electrode tab, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, along a first direction, the positive electrode tab comprising a second region and a first region connected in sequence, the positive electrode tab being integrally arranged with the positive electrode current collector in the first region, the first molecular sieve coating being arranged on at least one surface of the positive electrode current collector in the first region, the positive electrode active material layer being arranged on at least one surface of the positive electrode current collector in the second region, the first direction being the extension direction of the positive electrode tab in the unfolded state; the first molecular sieve coating comprises a molecular sieve and a first binder, the mass percentage of the molecular sieve is 10% to 90% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 10% to 90%. By arranging the first molecular sieve coating on at least one surface of the positive electrode current collector in the first region, on the one hand, the first molecular sieve coating can prevent the positive electrode current collector from piercing the separator to cause short circuit, and prevent the positive electrode active material layer from exceeding the positive electrode active material layer in the width direction, so that the positive electrode current collector directly contacts the negative electrode active material to cause dangerous short circuit, so that 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 controlled within the above range, so that the first molecular sieve coating has good adhesion, can enhance the adhesion between the positive electrode tab and the separator at the head of the electrode assembly, reduce the risk of weak adhesion between the tab layers caused by electrolyte accumulation at the head of the electrode assembly, and reduce the risk of weak adhesion between the positive electrode active material layer and the separator, so that the positive electrode tab and the separator at the head of the electrode assembly have good adhesion effect, thereby the positive electrode tab and the separator have good interface contact effect, the lithium precipitation on the negative electrode tab is less, and the cycle performance of the secondary battery is improved. Moreover, the positive electrode tab and the separator have good adhesion effect, the probability of the separator folding is reduced, thereby the drop safety performance of the secondary battery is improved. In addition, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, which can reduce the risk of gas swelling of the secondary battery, thereby improving the storage performance and high temperature safety performance of the secondary battery.

[0007] In an embodiment of the present application, the mass percentage of the molecular sieve is 20% to 80% based on the mass of the first molecular sieve coating, and the mass percentage of the first binder is 20% to 80%. Controlling the mass percentage of the molecular sieve and the first binder in the first molecular sieve coating within the above range can make the first molecular sieve layer have better short circuit prevention effect and better adhesion effect.

[0008] In an embodiment of the present application, 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. Controlling the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating within the above ranges can better balance the effects of preventing short circuit and improving adhesion of the first molecular sieve layer.

[0009] In an embodiment of the present application, the width of the first molecular sieve coating is 0.5 mm to 10 mm in the first direction, and the length of the first molecular sieve coating is greater than or equal to the length of the positive active material layer and less than or equal to the length of the positive electrode sheet in the direction perpendicular to the first direction. Setting the width of the first molecular sieve coating to 0.5 mm to 10 mm can better prevent the positive current collector and the negative active material from directly contacting each other to cause short circuit, while taking into account the energy density of the secondary battery, and at the same time, the first molecular sieve coating has good adhesion to the separator. The length of the first molecular sieve coating being greater than or equal to the length of the positive active material layer and less than or equal to the length of the positive electrode sheet can more effectively achieve the above effects in the length direction.

[0010] In an embodiment of the present application, the width of the first molecular sieve coating is 1 mm to 3 mm in the first direction. Setting the width of the first molecular sieve coating to 1 mm to 3 mm can further improve the adhesion of the first molecular sieve coating to the separator, thereby further improving the drop safety performance of the secondary battery, while better preventing the positive current collector and the negative active material from directly contacting each other to cause short circuit and taking into account the energy density of the secondary battery.

[0011] In an embodiment of the present application, the thickness of the first molecular sieve coating is less than the thickness of the positive active material layer, and the thickness of the first molecular sieve coating is 0.5 μm to 40 μm. Controlling the thickness of the first molecular sieve coating within the above range can make the first molecular sieve coating better prevent short circuit and improve adhesion to the separator, and also take into account the energy density of the secondary battery.

[0012] In an embodiment of the present application, the thickness of the first molecular sieve coating is 5 μm to 20 μm. Controlling the thickness of the first molecular sieve coating within the above range is conducive to further improving the short circuit prevention performance, cycle performance, drop safety performance and storage performance of the secondary battery.

[0013] In an embodiment of the present application, the second molecular sieve coating layer is arranged on the surface of the separator opposite to the first region; the second molecular sieve coating layer comprises a molecular sieve, and the mass percentage of the molecular sieve in the second molecular sieve coating layer is 20% to 80% based on the mass of the second molecular sieve coating layer. Arranging the second molecular sieve coating layer on the surface of the separator opposite to the first region and controlling the content of the molecular sieve in the second molecular sieve coating layer within the above range is beneficial to further improving the short circuit prevention performance, cycle performance, drop safety performance and storage performance of the secondary battery. Meanwhile, the second molecular sieve coating layer on the separator can also reduce the possibility of shrinkage of the separator substrate layer and improve the high temperature resistance of the secondary battery.

[0014] In an embodiment of the present application, the thickness of the second molecular sieve coating layer is 0.5 μm to 10 μm. Controlling the thickness of the second molecular sieve coating layer within the above range is beneficial to making the secondary battery have good short circuit prevention performance, cycle performance, drop safety performance and storage performance.

[0015] In an embodiment of the present application, the porosities of the first molecular sieve coating layer and the second molecular sieve coating layer are each independently 30% to 60%. Controlling the porosities of the first molecular sieve coating layer and the second molecular sieve coating layer within the above range can make the first molecular sieve coating layer and the second molecular sieve coating layer have good insulation and structural strength so that the first molecular sieve coating layer and the second molecular sieve coating layer can play their effects of preventing short circuit and can also play the effects of improving the adhesion of the first molecular sieve coating layer and the second molecular sieve coating layer.

[0016] In an embodiment of the present application, the specific surface area of the molecular sieve is 200 m 2 / g to 2000 m 2 / g, and the pore size of the molecular sieve is 0.3 nm to 45 nm. Controlling the specific surface area and the pore size of the molecular sieve within the above range can better play the role of the molecular sieve in improving the adhesion and further improve the cycle performance, drop safety performance and storage performance of the secondary battery.

[0017] In an embodiment of the present application, the molecular sieve comprises at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 13X molecular sieve, ZSM-22 molecular sieve, ZSM-5 molecular sieve, MOR molecular sieve, ITQ molecular sieve, Y molecular sieve, SAPO type molecular sieve or ALPO type molecular sieve. Selecting the above types of molecular sieve is beneficial to making the secondary battery have good cycle performance, drop safety performance and storage performance.

[0018] In an 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, polyacryl alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

[0019] In an embodiment of the present application, the positive electrode tab further comprises an electrically conductive layer, the electrically conductive layer is arranged on the surface of the first molecular sieve coating away from the positive electrode current collector; the electrically conductive layer comprises an electrically conductive agent, the mass percentage of the electrically conductive agent is 5% to 70% based on the mass of the electrically conductive layer. Arranging the electrically conductive layer on the surface of the first molecular sieve coating away from the positive electrode current collector in the positive electrode tab can further reduce the possibility of lithium precipitation in the secondary battery, thereby further improving the cycle performance, while having good drop safety performance and storage performance.

[0020] In an embodiment of the present application, the sum of the thickness of the first molecular sieve coating and the thickness of the electrically conductive layer is less than or equal to the thickness of the positive electrode active material layer; the thickness of the electrically 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 electrically conductive layer being less than or equal to the thickness of the positive electrode active material layer can reduce the possibility of a gap being generated between the second region of the positive electrode tab and the separator due to the first molecular sieve coating and the electrically conductive layer being too thick, so that the second region of the positive electrode tab is in sufficient contact with the separator to ensure the interface performance between the positive electrode tab and the separator, while the thickness of the first molecular sieve coating being regulated within the above range can meet the production requirements of most secondary batteries on the market.

[0021] In an embodiment of the present application, the electrically conductive agent comprises at least one of acetylene black, ketjen black, conductive graphite, graphene, carbon nanotube.

[0022] The second aspect of the present application provides a power-using device, wherein the power-using device comprises the secondary battery according to any one of the preceding embodiments. Therefore, the power-using device has good use performance.

[0023] The beneficial effects of the present application are as follows:

[0024] This application provides a secondary battery and an electrical device. The secondary battery has a first molecular sieve coating disposed on both surfaces of the positive electrode current collector in the first region. This coating can replace traditional ceramic coatings such as alumina and boehmite and provide the same short-circuit protection. By controlling the mass percentage of molecular sieve and first binder in the first molecular sieve coating within the aforementioned range, the coating exhibits excellent adhesion, enhancing the adhesion between the positive electrode and the separator at the electrode assembly head. This reduces the risk of weak adhesion between electrode layers due to electrolyte accumulation at the electrode assembly head, and also reduces the risk of weak adhesion between the positive electrode active material layer and the separator. This results in excellent adhesion between the positive electrode and the separator at the electrode assembly head, leading to good interfacial contact between the positive electrode and the separator, less lithium plating on the negative electrode, and improved cycle performance of the secondary battery. Furthermore, the good adhesion between the first region of the positive electrode and the separator reduces the probability of separator folding, thereby improving the drop safety performance of the secondary battery. In addition, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, which can reduce the risk of gas swelling in the secondary battery, thereby improving the storage performance and high-temperature safety performance of the secondary battery. Attached Figure Description

[0025] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0026] Figure 1 This is a schematic cross-sectional view of a secondary battery according to one embodiment of this application, showing its thickness direction and a first direction at the positive electrode tab.

[0027] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of the electrode assembly in the unfolded state of the positive electrode tab along its own thickness direction and the first direction;

[0028] Figure 3 This is a top view of the positive electrode sheet in its unfolded state according to one embodiment of this application;

[0029] Figure 4 This is a schematic cross-sectional view of the positive electrode sheet in its unfolded state at the positive electrode tab along its own thickness direction and a first direction, according to one embodiment of this application.

[0030] Figure 5 This is a schematic cross-sectional view of the positive electrode sheet in its unfolded state, at the non-positive electrode tab, along its own thickness direction and in the direction perpendicular to the first direction, representing another embodiment of this application.

[0031] Figure 6A cross-sectional structure of a secondary battery according to another embodiment of the present application along the thickness direction of the positive electrode tab and the first direction;

[0032] Figure 7 A cross-sectional structure of a separator according to some embodiments of the present application along the thickness direction of the separator;

[0033] Figure 8 A cross-sectional structure of a separator according to some other embodiments of the present application along the thickness direction of the separator;

[0034] Figure 9 A cross-sectional structure of a positive electrode tab according to another embodiment of the present application along the thickness direction of the positive electrode tab. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions, and advantages of the present application clearer, the present application will be further described in detail with reference to the accompanying drawings and embodiments. Obviously, the embodiments described in the present application are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application shall fall within the scope of the present application.

[0036] It should be noted that in the specific embodiments, the lithium ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium ion battery, and is also applicable to the sodium ion battery and other common batteries that can use the related technology of the present application. The specific technical solutions are as follows:

[0037] The first aspect of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a positive electrode tab, a negative electrode tab and a separator, the separator being arranged between the positive electrode tab and the negative electrode tab; the positive electrode tab comprising a positive electrode lug, a positive electrode current collector, a first molecular sieve coating and a positive electrode active material layer, along a first direction, the positive electrode tab comprises a second region and a first region connected in sequence, the positive electrode lug is integrally arranged with the positive electrode current collector in the first region, the first molecular sieve coating is arranged on at least one surface of the positive electrode current collector in the first region, and the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector in the second region, the first direction being the extension direction of the positive electrode lug in the unfolded state, i.e. the width direction of the positive electrode tab. It can be understood that the above "the first molecular sieve coating is arranged 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 arranged on one surface of the positive electrode current collector in the first region, and in other embodiments, the first molecular sieve coating is arranged on two surfaces of the positive electrode current collector in the first region, wherein the "surface" can be all surfaces of the positive electrode current collector in the first region, or can be part of the surfaces of the positive electrode current collector in the first region; the above "the positive electrode active material layer is arranged 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 arranged on one surface of the positive electrode current collector in the second region, and in other embodiments, the positive electrode active material layer is arranged on two surfaces of the positive electrode current collector in the second region. Wherein, the "surface" can be all surfaces of the positive electrode current collector in the second region, or can be part of the surfaces of the positive electrode current collector in the second region.

[0038] In the present application, in order to facilitate understanding, the first direction is defined as X, the direction perpendicular to the first direction is Y, and the thickness direction of the positive electrode tab is Z. It can be understood that the thickness direction of the negative electrode tab and the separator is the same as the thickness direction of the positive electrode tab. It should be noted that the above "direction perpendicular to the first direction" can be understood as the perpendicular relationship in the plane formed by the length direction and the width direction of the positive electrode tab. For example, Figures 1 to 4As shown, the secondary battery includes an electrode assembly 100 and a packaging bag 200. The electrode assembly 100 is housed within the packaging bag 200. The electrode assembly 100 includes a positive electrode 10, a negative electrode 20, and a separator 30, with the separator 30 disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10 includes a positive electrode tab 11, a positive current collector 12, a first molecular sieve coating 13, and a positive active material layer 14. Along the first direction X, the positive electrode 10 includes a second region 102 and a first region 101 connected in sequence. The positive electrode tab 11 is integrally formed with the positive current collector 12 in the first region 101. The first molecular sieve coating 13 is disposed on two surfaces of the positive current collector 12 in the first region 101, and the positive active material layer 14 is disposed on at least one surface of the positive current collector 12 in the second region 102. The first direction X is the state where the positive electrode tab 11 is folded (e.g., ...). Figure 2 The extension direction is shown in the diagram. It is understood that when the positive electrode tab is integrally formed with the positive current collector in the first region and the positive electrode tab is not folded, its extension direction is parallel to the positive current collector. During the manufacturing process of the secondary battery, considering actual production technology, the portion of the positive electrode tab extending beyond the positive current collector may fold. Thus, the portion of the positive electrode tab extending beyond the positive current collector will bend (e.g., ...). Figure 1 As shown), the extension direction of the tortuous positive electrode tab is no longer parallel to the positive electrode current collector. It should be noted that the "parallelism" mentioned above refers to ideal parallelism; in actual production, due to human intervention or operational factors during the preparation process, it may be approximately parallel. The first molecular sieve coating includes a molecular sieve and a first binder. Based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10% to 90%, and the mass percentage of the first binder is 10% to 90%. For example, based on the mass of the first molecular sieve coating, the mass percentage of the molecular sieve is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any value between any two of the above ranges. For example, based on the mass of the first molecular sieve coating, the mass percentage of the first binder is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any value between any two of the above ranges.

[0039] When the mass percentage of the molecular sieve is less than 10% or the mass percentage of the first binder is greater than 90% based on the first molecular sieve coating, the content of the molecular sieve in the first molecular sieve coating is too low, and the compactness of the first molecular sieve coating is poor, which will affect the insulation protection effect of the first molecular sieve coating on the positive current collector adjacent thereto; when the mass percentage of the molecular sieve is greater than 90% or the mass percentage of the first binder is less than 10%, the content of the first binder in the first molecular sieve coating is too low, and the adhesion of the first molecular sieve coating formed is poor, and the interfacial adhesion between the positive electrode plate and the separator and the negative electrode plate is poor, which will affect the cycle performance of the secondary battery, and when the secondary battery falls or is impacted, the separator is prone to folding, which affects the drop safety performance of the secondary battery.

[0040] The present application sets the first molecular sieve coating on at least one surface of the positive current collector in the first region, which can play the following roles: on the one hand, the first molecular sieve coating can prevent the positive current collector from piercing the separator to cause short circuit and prevent the positive current collector from directly contacting the negative active material to cause dangerous short circuit in the case that the negative active material layer exceeds the positive active material layer in the width direction, so that the secondary battery has good short circuit prevention performance; on the other hand, the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating are controlled within the above range, and the molecular sieve and the first binder cooperate with each other, so that the first molecular sieve coating has good adhesion, which can enhance the adhesion between the positive electrode plate and the separator at the head of the electrode assembly, reduce the risk of weak adhesion between the positive active material layer and the separator, and improve the cycle performance of the secondary battery. The adhesion between the positive electrode plate and the separator at the head of the electrode assembly is good, the interface contact effect between the positive electrode plate and the separator is good, the amount of lithium precipitation on the negative electrode plate is small, and the cycle performance of the secondary battery is improved. Moreover, the adhesion between the first region of the positive electrode plate and the separator is good, and the probability of folding of the separator is reduced, so that the drop safety performance of the secondary battery is improved. In addition, the molecular sieve in the first molecular sieve coating has the ability to absorb gas, which can reduce the risk of swelling of the secondary battery, thereby improving the storage performance of the secondary battery.

[0041] In an embodiment of the present application, 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. For example, the mass percentage of the molecular sieve is 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value within any two of the above-mentioned numerical ranges based on the mass of the first molecular sieve coating. For example, the mass percentage of the first binder is 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value within any two of the above-mentioned numerical ranges based on the mass of the first molecular sieve coating. Controlling the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating within the above-mentioned ranges can further enhance the adhesion between the positive electrode sheet and the separator at the head of the electrode assembly, reduce the risk of weak adhesion between the layers of the positive electrode sheet caused by electrolyte accumulation at the head of the electrode assembly, and further reduce the risk of weak adhesion between the layers of the positive electrode sheet and the separator, so that the positive electrode sheet and the separator at the head of the electrode assembly have good adhesion, the positive electrode sheet and the separator have good interface contact, lithium precipitation on the negative electrode sheet is less, and the cycle performance of the secondary battery is further improved. Moreover, the first region of the positive electrode sheet and the separator have good adhesion, the probability of the separator folding is reduced, and the drop safety performance of the secondary battery is further improved.

[0042] In an embodiment of the present application, 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. For example, the mass percentage of the molecular sieve is 30%, 40%, 50%, 60%, 70% or any value within any two of the above-mentioned numerical ranges based on the mass of the first molecular sieve coating. For example, the mass percentage of the first binder is 30%, 40%, 50%, 60%, 70% or any value within any two of the above-mentioned numerical ranges based on the mass of the first molecular sieve coating. Controlling the mass percentages of the molecular sieve and the first binder in the first molecular sieve coating within the above-mentioned ranges can further enhance the adhesion between the positive electrode sheet and the separator at the head of the electrode assembly, reduce the risk of weak adhesion between the layers of the positive electrode sheet caused by electrolyte accumulation at the head of the electrode assembly, and further reduce the risk of weak adhesion between the layers of the positive electrode sheet and the separator, so that the positive electrode sheet and the separator at the head of the electrode assembly have good adhesion, the positive electrode sheet and the separator have good interface contact, lithium precipitation on the negative electrode sheet is less, and the cycle performance of the secondary battery is further improved. Moreover, the first region of the positive electrode sheet and the separator have good adhesion, the probability of the separator folding is reduced, and the drop safety performance of the secondary battery is further improved.

[0043] In one embodiment of this application, such as Figure 3 and Figure 4 As shown, along the first direction X, the width W of the first molecular sieve coating 13 is... 13 The width of the first molecular sieve coating is between 0.5 mm and 10 mm. For example, the width of the first molecular sieve coating can be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any value within any two of the above ranges. Setting the width of the first molecular sieve coating to between 0.5 mm and 10 mm can better prevent short circuits caused by direct contact between the positive electrode current collector and the negative electrode active material, while also ensuring the energy density of the secondary battery, and giving the first molecular sieve coating good adhesion to the separator. The length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet, which can more effectively achieve the above effects in the length direction. As a result, there is a good interfacial contact effect between the positive electrode sheet and the separator, less lithium plating occurs on the negative electrode sheet, the cycle performance of the secondary battery is improved, and the secondary battery has a higher energy density and safety performance. In addition, there is a good adhesion effect between the first region of the positive electrode sheet and the separator, the probability of separator folding is reduced, thereby improving the drop safety performance of the secondary battery.

[0044] In one embodiment of this application, such as Figure 3 and Figure 4 As shown, along the first direction X, the width W of the first molecular sieve coating 13 is... 13 The width is 1mm to 3mm. For example, the width of the first molecular sieve coating is 1mm, 2mm, 3mm, or any value between any two of the above ranges. Setting the width of the first molecular sieve coating to 1mm to 3mm can better prevent short circuits caused by direct contact between the positive electrode current collector and the negative electrode active material, while also taking into account the energy density of the secondary battery, and further improve the adhesion of the first molecular sieve coating to the separator, thereby further improving the drop safety performance of the secondary battery.

[0045] In one embodiment of this application, along a direction perpendicular to the first direction, the length of the first molecular sieve coating is greater than or equal to the length of the positive electrode active material layer and less than or equal to the length of the positive electrode sheet. Exemplarily, in some embodiments, such as... Figure 3 As shown, along the direction Y perpendicular to the first direction X, the length L of the first molecular sieve coating 13 is... 13 The length L of the positive electrode active material layer 14 is equal to 14 And equal to the length L of the positive electrode plate 10 10In some 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 sheet along 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 electrode active material layer and equal to the length of the positive electrode sheet along 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 sheet along a direction perpendicular to the first direction. This application does not impose any particular limitations on the length of the first molecular sieve coating, the length of the positive electrode active material layer, and the length of the positive electrode sheet. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. By adjusting the length of the first molecular sieve coating within the above range, the area of ​​the positive electrode sheet where the positive electrode active material layer is disposed is provided with the first molecular sieve coating. The first molecular sieve coating can be set according to the original structure of the positive electrode sheet. With the enhanced adhesion of each layer of the wound electrode assembly and the stacked electrode assembly, the space of the secondary battery can also be fully utilized. Furthermore, while better preventing short circuits caused by direct contact between the positive electrode current collector and the negative electrode active material, and maintaining the energy density of the secondary battery, the first molecular sieve coating also ensures good adhesion to the separator. This results in excellent interfacial contact between the positive electrode and the separator, reducing lithium plating on the negative electrode, improving the cycle performance of the secondary battery, and enhancing its energy density and safety. In addition, the good adhesion between the first region of the positive electrode and the separator reduces the probability of separator folding, thereby improving the drop safety of the secondary battery.

[0046] In one embodiment of this application, such as Figure 4 As shown, the thickness H of the first molecular sieve coating 13 13 The thickness H is less than that of the positive electrode active material layer 14 14 The thickness H of the first molecular sieve coating 13 13 The thickness ranges from 0.5 μm to 40 μm. For example, the thickness of the first molecular sieve coating can be 0.5 μm, 5 μm, 20 μm, 40 μm, or any value between any two of the above ranges. By controlling the thickness of the first molecular sieve coating within the above range, the coating can effectively cover the positive electrode current collector without increasing the volume of the secondary battery. This allows the coating to better prevent short circuits and improve adhesion to the separator, while also maintaining the energy density of the secondary battery. Consequently, there is good interfacial contact between the positive electrode and the separator, less lithium plating occurs on the negative electrode, the cycle performance of the secondary battery is improved, and the battery exhibits high energy density and good short-circuit protection. Furthermore, the first region of the positive electrode has good adhesion to the separator, reducing the probability of separator folding and thus improving the drop safety performance of the secondary battery.

[0047] This application does not impose any particular limitation on the thickness of the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode active material layer can be from 30 μm to 200 μm.

[0048] In one embodiment of this application, the thickness of the first molecular sieve coating is from 5 μm to 20 μm. For example, the thickness of the first molecular sieve coating is 5 μm, 7 μm, 10 μm, 15 μm, 18 μm, 20 μm, or any value between any two of the above ranges. Controlling the thickness of the first molecular sieve coating within the above range is beneficial for further improving the short-circuit protection, cycle performance, drop safety, and storage performance of the secondary battery.

[0049] In one embodiment of this application, such as Figure 5 As shown, along the thickness direction Z of the positive electrode 10, the first molecular sieve coating 13 and the positive electrode active material layer 14 have an overlapping region 40. In the overlapping region 40, the positive electrode active material layer 14 is located between the first molecular sieve coating 13 and the positive electrode current collector 12. It should be noted that, for ease of understanding, Figure 5 The portion marked with an elliptical frame 50 has been magnified. In reality, after the positive electrode sheet is rolled during the manufacturing process, the surface is approximately flat, and the portion marked with an elliptical frame 50 is not as flat as depicted in the image. Figure 5 The protrusion shown is not flush with the surface of the positive electrode active material layer 14, which does not have an overlapping region 40. Along the first direction X, the width W of the overlapping region 40... 40 The width of the overlapping area is 0 mm to 0.5 mm. For example, the width of the overlapping area is 0 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any value between any two of the above ranges. The positive electrode active material layer and the first molecular sieve coating have an overlapping area, and controlling the width of the overlapping area within the above range can reduce the risk of direct exposure of the positive electrode current collector, which is beneficial to reducing the safety risks of the secondary battery. Furthermore, by minimizing the contact area between the positive electrode active material layer and the first molecular sieve coating, the first molecular sieve coating can exert its good adhesion effect. Therefore, there is a good interfacial contact effect between the positive electrode sheet and the separator, less lithium plating occurs on the negative electrode sheet, and the cycle performance of the secondary battery is improved. Moreover, the first region of the positive electrode sheet has a good adhesion effect with the separator, reducing the probability of separator folding, thereby improving the drop safety performance of the secondary battery.

[0050] In one embodiment of this application, such as Figure 6As shown, the second molecular sieve coating 23 is provided on the surface of the separator 20 opposite to the first region 101. It can be understood that the "surface" can be one surface of the separator or both surfaces of the separator. The "opposite" means that the separator at least overlaps with the first region in the thickness direction of the separator. Exemplarily, in some embodiments of the present application, as shown in Figure 7 As shown, the second molecular sieve coating 23 is provided on both surfaces of the separator 20 opposite to the first region 101. In some other embodiments of the present application, as shown in Figure 8 As shown, the second molecular sieve coating 23 is provided on the first surface 20a of the separator 20 opposite to the first region 101. It is to be noted that the second molecular sieve coating 23 can also be provided on the second surface 20b of the separator 20 opposite to the first region 101. The mass percentage of the molecular sieve in the second molecular sieve coating is 20% to 80% based on the mass of the second molecular sieve coating. For example, the mass percentage of the molecular sieve in the second molecular sieve coating is 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value within the range between any two of the above values based on the mass of the second molecular sieve coating. The second molecular sieve coating is provided on the surface of the separator opposite to the first region, and the content of the molecular sieve in the second molecular sieve coating is controlled within the above range. The second molecular sieve coating is bonded with the first molecular sieve coating and the negative electrode tab, and can play a good bonding role to further bond the separator with the positive electrode tab and the negative electrode tab, so that the bonding effect of the separator with the positive electrode tab and the negative electrode tab is further improved. In this way, the interface contact effect between the positive electrode tab, the separator and the negative electrode tab is further strengthened, and the cycle performance of the secondary battery is further improved. Moreover, the provision of the second molecular sieve coating can further reduce the risk of the positive current collector burr piercing the separator to cause the direct contact between the positive current collector and the negative active material to trigger a short circuit, and further improve the short circuit prevention performance of the secondary battery. The provision of the second molecular sieve coating on the separator can also reduce the possibility of shrinkage of the base material layer in the separator and improve the high temperature resistance of the secondary battery. In addition, the probability of folding of the separator is further reduced, so that the drop safety performance of the secondary battery can be further improved.

[0051] In an embodiment of the present application, the second molecular sieve coating further comprises a first binder, and the mass percentage of the first binder is 20% to 80% based on the mass of the second molecular sieve coating. For example, the mass percentage of the first binder is 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value within the range between any two of the above values based on the mass of the second molecular sieve coating.

[0052] In an embodiment of the present application, as shown in Figure 7 and Figure 8 As shown, the thickness H of the second molecular sieve coating 23 is 0.1 to 10 microns. 23The thickness of the second molecular sieve coating layer is 0.5 pm to 10 pm. For example, the thickness of the second molecular sieve coating layer is 0.5 pm, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, or any value within any two of the above-mentioned numerical ranges. By adjusting the thickness of the second molecular sieve coating layer within the above-mentioned range, the second molecular sieve coating layer can have a good covering effect on the separator without increasing the size of the secondary battery, and the second molecular sieve coating layer can better prevent short circuit and improve the adhesion to the separator. In this way, the interface contact effect between the positive electrode sheet, the separator, and the negative electrode sheet is further enhanced, the lithium precipitation on the negative electrode sheet is further reduced, the cycle performance of the secondary battery is further improved, and the secondary battery has high energy density and good short circuit prevention performance. Moreover, the probability of the separator being folded is further reduced, thereby further improving the drop safety performance of the secondary battery.

[0053] The width and length of the second molecular sieve coating layer are not particularly limited in the present application, and those skilled in the art can adjust them according to the width and length of the first molecular sieve coating layer, as long as the purpose of the present application can be achieved. For example, along the first direction X, the width of the second molecular sieve coating layer is 0.5 mm to 15 mm. Along the direction Y perpendicular to the first direction X, the length of the second molecular sieve coating layer is less than or equal to the length of the separator.

[0054] Those skilled in the art can understand that in the secondary battery, the thickness direction, the width direction, and the length direction of the positive electrode sheet, the negative electrode sheet, and the separator are all the same. Therefore, the first direction X and the direction Y perpendicular to the first direction X are the same direction in the positive electrode sheet and the separator.

[0055] In an embodiment of the present application, the porosity of the first molecular sieve coating layer is 30% to 60%. For example, the porosity of the first molecular sieve coating layer is 30%, 40%, 50%, 60%, or any value within any two of the above-mentioned numerical ranges. By adjusting the porosity of the first molecular sieve coating layer within the above-mentioned range, the first molecular sieve coating layer can have good insulation and structural strength to prevent short circuit and improve adhesion. In this way, the positive electrode sheet and the separator have good interface contact effect, the lithium precipitation on the negative electrode sheet is less, the cycle performance of the secondary battery is improved, and the secondary battery also has good short circuit prevention performance. Moreover, the first region of the positive electrode sheet and the separator have good adhesion, and the probability of the separator being folded is reduced, thereby improving the drop safety performance of the secondary battery.

[0056] In an embodiment of the present application, the porosity of the second molecular sieve coating is 30% to 60%. For example, the porosity of the second molecular sieve coating is 30%, 40%, 50%, 60%, or any value within any two of the above-mentioned numerical ranges. By adjusting the porosity of the second molecular sieve coating within the above-mentioned range, the second molecular sieve coating can have good insulation and structural strength so that the second molecular sieve coating can play its effect of preventing short circuit and can also play the effect of the second molecular sieve coating of improving the adhesion. In this way, the separator has good interface contact effect with the positive electrode sheet and the negative electrode sheet, the lithium precipitation on the negative electrode sheet 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 base material layer of the separator and improve the high temperature resistance of the secondary battery. In addition, the probability of the folding of the separator is further reduced, thereby further improving the drop safety performance of the secondary battery.

[0057] The present application does not have a particular limitation on the adjustment method of the porosity of the first molecular sieve coating and the second molecular sieve coating, as long as the purpose of the present application can be achieved. For example, the adjustment can be achieved by adjusting the type of molecular sieve, the content ratio of the molecular sieve and the first binder, and the pore size of the molecular sieve in the first molecular sieve coating and the second molecular sieve coating.

[0058] In an embodiment of the present application, the specific surface area of the molecular sieve is 200 m 2 / g to 2000 m 2 / g. For example, the specific surface area of the molecular sieve is 200 m 2 / g, 400 m 2 / g, 600 m 2 / g, 800 m 2 / g, 1000 m 2 / g, 1200 m 2 / g, 1400 m 2 / g, 1600 m 2 / g, 1800 m 2 / g, 2000 m 2nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or any value within a range between any two of the aforementioned values. In an embodiment of the present application, the pore size of the molecular sieve is 0.3 nm to 45 nm. For example, the pore size of the molecular sieve is 0.3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or any value within a range between any two of the aforementioned values. By adjusting the specific surface area of the molecular sieve and / or the pore size of the molecular sieve within the aforementioned range, the molecular sieve has a higher specific surface area, and / or the molecular sieve has a larger pore size, the bonding area of the molecular sieve is increased when the molecular sieve is applied to the first molecular sieve coating and / or the second molecular sieve coating, the mechanical embedding effect is enhanced, the molecular sieve has a large cohesion after being combined with the first binder, and the binding force is strong. In this way, the first molecular sieve coating and the second molecular sieve coating are highly dispersed after being fully swollen at high temperature and form a good bonding force. As a result, the positive electrode sheet and the separator, or the positive electrode sheet, the separator, and the negative electrode sheet have a good interface contact effect, and the cycle performance of the secondary battery is improved. Moreover, the probability of the separator being folded is reduced, and the drop safety performance of the secondary battery is improved. In addition, the molecular sieve has the ability to absorb gas, which can reduce the risk of the secondary battery swelling and improve the problem of the secondary battery swelling and bulging under special working conditions (such as high-temperature storage, over-discharge, storage after over-discharge, charge-discharge after over-discharge, overcharge, thermal runaway, etc.), thereby improving the storage performance of the secondary battery. In the present application, "high temperature" refers to a temperature of 40°C to 90°C.

[0059] The average volume particle size of the molecular sieve is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the average volume particle size of the molecular sieve is 0.5 μm to 20 μm. In the present application, the average volume particle size Dv50 represents the particle size at which 50% of the volume is accumulated from the small particle size side in the particle size distribution on a volume basis.

[0060] In an embodiment of the present application, the molecular sieve includes at least one of 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 13X molecular sieve, ZSM-22 molecular sieve, ZSM-5 molecular sieve, MOR molecular sieve, ITQ molecular sieve, Y molecular sieve, SAPO molecular sieve or ALPO molecular sieve. Further, the ITQ molecular sieve includes at least one of ITQ-24, ITQ-40 or ITQ-55; the Y molecular sieve includes at least one of NaY, HY, USY or RY; the SAPO molecular sieve includes at least one of SAPO-11, SAPO-20 or SAPO-34; and the ALPO molecular sieve includes at least one of ALPO-4, ALPO-15 or ALPO-18. The above-mentioned molecular sieves have a large specific surface area and pore size, and when applied to the first molecular sieve coating and / or the second molecular sieve coating, the bonding area of the molecular sieve can be increased, the mechanical embedding effect can be enhanced, the cohesion of the molecular sieve after being combined with the binder is large, and the bonding force is strong. In this way, the first molecular sieve coating and the second molecular sieve coating can be fully swollen and dispersed at high temperature, and a good bonding force can be formed. As a result, the positive electrode sheet and the separator, or the positive electrode sheet, the separator and the negative electrode sheet have a good interface contact effect, and the cycle performance of the secondary battery is improved. In addition, the probability of the separator being folded is reduced, and the drop safety performance of the secondary battery can be improved. In addition, the molecular sieve has the ability to absorb gas, which can reduce the risk of the secondary battery swelling, improve the problem of the secondary battery swelling and bulging under special working conditions, and thus improve the storage performance of the secondary battery.

[0061] In an embodiment of the present application, the first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

[0062] In an embodiment of the present application, as Figure 9As shown, the positive electrode tab 10 further comprises an electrically conductive layer 15 disposed on the surface 13a of the first molecular sieve coating layer 13 facing away from the positive electrode current collector 12; the electrically conductive layer comprises an electrically conductive agent, the mass percentage content of the electrically conductive agent being 5% to 70% based on the mass of the electrically conductive layer. For example, the mass percentage content of the electrically conductive layer is 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or any value within any two of the above-mentioned numerical ranges based on the mass of the electrically conductive layer. The electrically conductive layer further comprises a second binder, the mass percentage content of the second binder being 30% to 95% based on the mass of the electrically conductive layer. For example, the mass percentage content of the second binder is 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or any value within any two of the above-mentioned numerical ranges based on the mass of the electrically conductive layer. The positive electrode tab edge resistance is often greater than the main body, and the positive electrode tab has a large current density, thus, lithium precipitation is prone to occur in the overhang region of the negative electrode tab in the electrode assembly. The electrically conductive layer is disposed on the surface of the first molecular sieve coating layer in the positive electrode tab facing away from the positive electrode current collector, the electrically conductive layer can induce a polarization electric field, the polarization electric field can balance the electric field intensity on the electrode surface, and the Li + / Li concentration of the negative electrode tab edge negative electrode plays a uniformity role, thereby improving lithium precipitation caused by uneven electric field, and achieving the purpose of prolonging the cycle life of the secondary battery. By adjusting the mass percentage content of the electrically conductive agent and the second binder in the electrically conductive layer within the above-mentioned range, the electrically conductive layer has good adhesion effect in the case of inducing a polarization electric field, so that the positive electrode tab has good adhesion effect with the separator and the negative electrode tab, thereby the positive electrode tab has good interface contact effect with the separator, and the cycle performance of the secondary battery is improved. Moreover, the first region of the positive electrode tab has good adhesion effect with the separator, the probability of the separator being folded is reduced, thereby the drop safety performance of the secondary battery can be improved.

[0063] The second binder is not particularly limited in the present application, as long as the purpose 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, polyacrylic alcohol, sodium polyacrylate, polyurethane, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, fluorinated rubber or styrene-butadiene rubber.

[0064] In an embodiment of the present application, as shown in Figure 9 the thickness H 13 of the first molecular sieve coating layer 13 is less than the thickness H 15 of the electrically conductive layer 15. 14The 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 thickness of the first molecular sieve coating layer is 0.5 μm, 20 μm, 40 μm, or any value within a range between any two of the above 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 within a range between any two of the above values. Controlling the sum of the thickness of the first molecular sieve coating layer and the thickness of the conductive layer to be within the above range relative to the thickness of the positive active material layer can reduce the possibility of a gap between the second region of the positive electrode plate and the separator due to the first molecular sieve coating layer and the conductive layer being too thick, so that the second region of the positive electrode plate and the separator are in sufficient contact, and the positive electrode plate and the separator have good interface properties. Controlling the thickness of the first molecular sieve coating layer and the thickness of the conductive layer to be within the above range is conducive to improving lithium precipitation caused by uneven electric field without increasing the size of the secondary battery, so as to prolong the cycle life of the secondary battery. Furthermore, the positive electrode plate, the separator, and the negative electrode plate have good interface contact, and the cycle performance of the secondary battery is improved. Furthermore, the first region of the positive electrode plate and the separator have good adhesion, and the probability of the separator being folded is reduced, so as to improve the drop safety performance of the secondary battery.

[0065] In an 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 types of conductive agents have good conductivity.

[0066] The structure of the electrode assembly is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the structure of the electrode assembly is a jelly-roll structure or a stacked structure. The type of the positive current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the positive current collector includes an aluminum foil, an aluminum alloy foil, or the like.

[0067] In an embodiment of the present application, the positive electrode active material layer comprises a positive electrode active material. The kind of the positive electrode active material is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the positive electrode active material can comprise at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate, etc. Optionally, the positive electrode active material layer further comprises a positive electrode conductive agent, a positive electrode binder. The kind of the positive electrode conductive agent and the positive electrode binder in the positive 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 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 in the present application, which can be selected by those skilled in the art according to actual needs as long as the object 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).

[0068] In an embodiment of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be disposed on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or can be part of the area of the negative electrode current collector, which is not particularly limited in the present application as long as the object of the present application can be achieved. The negative electrode current collector is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the negative electrode current collector can comprise a copper foil, a copper alloy foil, a nickel foil, a titanium foil, a nickel foam, or a copper foam, etc. The negative electrode active material layer comprises a negative electrode active material. The kind of the negative electrode active material is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the negative electrode active material can comprise at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, tin-based material, silicon-based material, lithium titanate, or transition metal nitride, etc. Optionally, the negative electrode active material layer further comprises at least one of a negative electrode conductive agent, a thickening agent, and a negative electrode binder. The kind of the negative electrode conductive agent, the thickening agent, 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 negative electrode active material, the negative electrode conductive agent, the thickening agent, 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. For example, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the thickening agent, and the negative electrode binder in the negative electrode active material layer is (96-98):(0-1.5):(0.5-1.5):(1.0-1.9).

[0069] The thickness of the negative current collector and the negative active material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the negative current collector is 5 to 20 pm, and the thickness of the negative active material layer is 30 to 120 pm.

[0070] The separator is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaced film.

[0071] The secondary battery of the present application further includes an electrolyte, and the electrolyte and the electrode assembly are contained in a packaging bag. The packaging bag and the electrolyte are not particularly limited in the present application, and those skilled in the art can select the packaging bag and the electrolyte known in the art as needed, as long as the purpose of the present application can be achieved.

[0072] The preparation method of the positive electrode tab is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0073] For example, in some embodiments of the present application, the positive electrode tab includes a positive electrode tab, a positive current collector, a first molecular sieve coating layer, and a positive active material layer, and the preparation method of the positive electrode tab includes, but is not limited to, the following steps: (1) preparing a positive electrode slurry and a first molecular sieve coating layer slurry; (2) coating the positive electrode slurry and the first molecular sieve coating layer slurry on one surface of the positive current collector, and after drying, obtaining a positive electrode tab coated with a single-side positive active material layer and a first molecular sieve coating layer; coating the positive electrode slurry and the first molecular sieve coating layer slurry on the other surface of the positive current collector, and after drying, obtaining a positive electrode tab coated with a double-side positive active material layer and a first molecular sieve coating layer; wherein the first molecular sieve coating layer is arranged in a first region of the positive electrode tab, and the positive active material layer is arranged in a second region of the positive electrode tab; (3) cold pressing and cutting. The preparation method of the positive electrode slurry and the first molecular sieve coating layer slurry in the above step (1) is not particularly limited in the present application, as long as the content of the molecular sieve and the first binder in the first molecular sieve coating layer is within the scope of the present application, and the purpose of the present application can be achieved. The temperature and time of drying in the above step (2) are not particularly limited in the present application, and those skilled in the art can select as needed, as long as the purpose of the present application can be achieved. The process parameters of cold pressing and cutting in the above step (3) are not particularly limited in the present application, and those skilled in the art can select as needed, as long as the purpose of the present application can be achieved.

[0074] For example, in some embodiments of the present application, the positive electrode tab 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 tab comprises but is not limited to the following steps: (1) preparing a positive electrode slurry, a first molecular sieve coating slurry and a conductive layer slurry; (2) coating the positive electrode slurry and the first molecular sieve coating slurry on one surface of the positive electrode current collector, and after drying, obtaining a positive electrode tab coated with a single surface of a positive electrode active material layer and a first molecular sieve coating, and coating the conductive layer slurry on the surface of the first molecular sieve coating away from the positive electrode current collector, and after drying, obtaining a positive electrode tab coated with a single surface of a positive electrode active material layer, a first molecular sieve coating and a conductive layer; repeating the above steps to obtain a positive electrode tab coated with a double surface of a positive electrode active material layer, a first molecular sieve coating and a conductive layer; wherein the first molecular sieve coating and the conductive layer are arranged in the first region of the positive electrode tab, and the positive electrode active material layer is arranged in the second region of the positive electrode tab; (3) cold pressing and cutting. The present application does not particularly limit the preparation method of the positive electrode slurry, the first molecular sieve coating slurry and the conductive layer slurry in the above step (1), as long as the content of the molecular sieve and the first binder in the first molecular sieve coating and the content of the conductive agent and the second binder in the conductive layer are within the scope of the present application, and the purpose of the present application can be achieved. The present application does not particularly limit the temperature and time of drying in the above step (2), and the person skilled in the art can choose according to the actual needs, as long as the purpose of the present application can be achieved. The present application does not particularly limit the process parameters of cold pressing and cutting in the above step (3), and the person skilled in the art can choose according to the actual needs, as long as the purpose of the present application can be achieved.

[0075] The present application does not particularly limit the preparation method of the second molecular sieve coating, as long as the purpose of the present application can be achieved. For example, the preparation method of the second molecular sieve coating comprises but is not limited to the following steps: (1) preparing a second molecular sieve coating slurry; (2) coating the second molecular sieve coating slurry on one surface of the separator opposite to the first region of the positive electrode tab, and drying to obtain a separator coated with a single surface of a second molecular sieve coating. Then, repeat the above steps on the other surface of the separator opposite to the first region of the positive electrode tab to obtain a separator coated with a double surface of a second molecular sieve coating. The present application does not particularly limit the preparation method of the second molecular sieve coating slurry in the above step (1), as long as the content of the molecular sieve and the first binder in the second molecular sieve coating is within the scope of the present application, and the purpose of the present application can be achieved. The present application does not particularly limit the temperature and time of drying in the above step (2), and the person skilled in the art can choose according to the actual needs, as long as the purpose of the present application can be achieved.

[0076] The preparation method of the secondary battery is not particularly limited in the present application, and a preparation method known in the art can be used as long as the object of the present application can be achieved. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, then fixing the four corners of the entire stack structure to obtain an electrode assembly of the stack structure, placing the electrode assembly into a packaging bag, welding the positive electrode tab and the negative electrode tab to the metal sheet through the adapter welding respectively and leading out of the packaging bag, injecting the electrolyte into the packaging bag and sealing, to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly of a wound structure, the electrode assembly is placed into a packaging bag, the positive electrode tab and the negative electrode tab are welded to the metal sheet through the adapter welding respectively and led out of the packaging bag, the electrolyte is injected into the packaging bag and sealed, to obtain the secondary battery. The type of the above-mentioned metal sheet is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the metal sheet for welding the positive electrode tab can be an aluminum sheet, and the metal sheet for welding the negative electrode tab can be a copper sheet, a nickel sheet, or a copper-nickel plated sheet.

[0077] The secondary battery of the present application is not particularly limited, and it can include a device that generates an electrochemical reaction. For example, the secondary battery can 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.

[0078] The second aspect of the present application provides an electric device, wherein the electric device includes the secondary battery according to any one of the above-mentioned embodiments. Therefore, the electric device has good use performance.

[0079] The electric device of the present application is not particularly limited, and it can be an electric device known in the art. For example, the electric device can include, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, a lithium ion capacitor.

[0080] Examples

[0081] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods.

[0082] Test methods and equipment:

[0083] Lithium precipitation test:

[0084] The lithium ion battery of each example and the comparative example was charged to full at 25°C (the charging system was constant current charging to 4.48 V at 4C rate, and then constant voltage charging to 0.05C), rested for 5 min, and then discharged to 3.0 V at 1 / 3C. The above steps were repeated 900 times on the same lithium ion battery.

[0085] The lithium ion battery after 300 cycles, 500 cycles, 700 cycles, and 900 cycles was charged to full at room temperature according to the standard charging method (0.5C charging to 4.48 V, and constant voltage charging to 0.02C at 4.48 V), and then disassembled. The lithium ion battery was disassembled, and the distribution of lithium precipitation on the surface of the negative electrode sheet was checked.

[0086] Adhesion test:

[0087] The lithium ion battery to be disassembled was taken out, the edges of the packaging bag were cut off, and then the packaging bag was opened and the electrode assembly was unfolded. The positive electrode sheet, the separator, and the negative electrode sheet were separated, and the positive electrode sheet and the separator were retained. The positive electrode sheet and the separator were taken from approximately the same position in the first region of the positive electrode sheet and the same surface. The positive electrode sheet and the separator were cut into a sample of 10 mm x 50 mm with a blade. Double-sided tape (manufacturer: Nitto, product model: 5000NS) was attached to a steel plate, and the cut sample was attached to the aforementioned double-sided tape with the test surface facing up, i.e., from bottom to top in the order of steel plate, double-sided tape, positive electrode sheet, and separator. A paper tape with a width equal to that of the sample and a length > 50 mm was attached to the surface of the separator, and was fixed with a corrugated adhesive. The peel angle was 180°, and the peel force data obtained by the tensile testing machine were the adhesion data of the positive electrode sheet and the separator.

[0088] Drop test:

[0089] The lithium ion batteries of each example and the comparative example were charged to full according to the standard charging method (0.5C charging to 4.48 V, and constant voltage charging to 0.02C at 4.48 V), and then dropped from a height of 1 m along 6 faces and 4 corners in a marble drop floor at a test environment of 20±5°C, for a total of 5 rounds of testing. The pass criteria for the test were: no fire, no explosion, no smoke, no liquid leakage, and a voltage drop <100 mV.

[0090] The number of lithium ion batteries that passed the test was counted for each example and the comparative example, and the drop safety performance was represented by the proportion of the number of passed batteries. The higher the number of passed batteries, the better the drop safety performance of the lithium ion battery. The proportion of the number of passed batteries = number of passed batteries / 5.

[0091] Storage performance test:

[0092] The lithium ion batteries of each example and comparative example were fully charged at 25°C according to a standard charging mode (0.5C charging to a voltage of 4.48V, constant voltage charging at 4.48V to 0.02C), and were placed in a constant temperature oven at 80°C for 48h. The thicknesses of the lithium ion batteries before and after storage were tested, and the expansion rates were obtained: expansion rate (%) = (thickness after testing - thickness before testing) / thickness before testing x 100%.

[0093] The storage performance of the lithium ion battery was characterized by the expansion rate, and the lower the expansion rate, the better the storage performance of the lithium ion battery.

[0094] Test of porosity:

[0095] Test by a true density tester.

[0096] The lithium ion batteries in each example and comparative example were disassembled after full discharge (0.5C constant current discharge to 3.0V), and the positive electrode sheets and separators obtained by disassembly were cleaned in n-butanol and then dried. The first molecular sieve coating in the positive electrode sheet was peeled off using a scraper, the second molecular sieve coating in the separator was peeled off, and both were ground into powders.

[0097] The powder obtained by grinding the first molecular sieve coating was compacted and punched into a sample with a regular shape of 10mm x 10mm, and was placed on a true density tester (AccuPyc II1340) for testing to obtain the true volume of the first molecular sieve coating. The length, width and height of the sample were measured with a ruler, and the apparent volume of the first molecular sieve coating was calculated as length x width x height. The porosity of the first molecular sieve coating (%) = (apparent volume of the first molecular sieve coating - true volume of the first molecular sieve coating) / apparent volume of the first molecular sieve coating x 100%.

[0098] The powder obtained by grinding the second molecular sieve coating was compacted and punched into a sample with a regular shape of 10mm x 10mm, and was placed on a true density tester (AccuPyc II1340) for testing to obtain the true volume of the second molecular sieve coating. The length, width and height of the sample were measured with a ruler, and the apparent volume of the second molecular sieve coating was calculated as length x width x height. The porosity of the second molecular sieve coating (%) = (apparent volume of the second molecular sieve coating - true volume of the second molecular sieve coating) / apparent volume of the second molecular sieve coating x 100%.

[0099] Test of specific surface area and pore size of molecular sieve:

[0100] The lithium ion batteries in each example and comparative example were disassembled after full discharge (0.5C constant current discharge to 3.0V), and the positive electrode sheets and separators obtained by disassembly were cleaned in n-butanol and then dried. The first molecular sieve coating in the positive electrode sheet was peeled off using a scraper, the second molecular sieve coating in the separator was peeled off, and both were ground into powders, and the following tests were performed respectively:

[0101] 1 g of powder was placed in a sample tube, the sample tube was heated to 150°C, and it was subjected to an evacuation degassing treatment for 2 h. The treated sample was introduced into a test system (instrument model: Mic3 Flex, USA), and it was saturated with adsorption by continuously introducing nitrogen into the sample for 1 h using a Topley pump that quantitatively transferred the gas. When the adsorption reached equilibrium, the pressure value was measured by a pressure sensor, the adsorption amount was calculated according to the pressure value, and the adsorption-desorption isotherm was obtained. The specific surface area was calculated using the BET equation. The pore size was calculated using the density functional theory (DFT).

[0102] Example 1-1

[0103] Preparation of the positive electrode tab

[0104] ①The positive electrode conductive agent and the positive electrode active material lithium cobaltate were placed in a blender, the entire positive electrode binder and 2 / 3 of the formula weight of the dispersion medium were added to the blender, and high-speed stirring was performed for 20 minutes. After stirring, the bubbles were removed for 10 minutes.

[0105] ②The remaining 1 / 3 of the formula weight of the dispersion medium was added to the material prepared in ①, high-speed stirring was performed for 30 minutes, and after stirring, the bubbles were removed for 5 minutes to obtain the positive electrode slurry. The dispersion medium was N-methyl pyrrolidone (NMP), the positive electrode conductive agent was conductive carbon black and carbon nanotubes, the positive electrode binder was polyvinylidene fluoride (PVDF), and the solid content of the positive electrode slurry was 75 wt%. The mass ratio of lithium cobaltate, acetylene carbon black, multi-walled carbon nanotubes, and polyvinylidene fluoride was 96.5:1.5:0.5:1.5.

[0106] The molecular sieve MOR molecular sieve (manufacturer: Shanghai Yuan Ye Biological Technology Co., Ltd., model: 12445-20-4) and the first binder polymethyl methacrylate (weight average molecular weight 75000) were mixed in a mass ratio of 90:10, N-methyl pyrrolidone (NMP) was added as a solvent, and the first molecular sieve coating slurry was stirred under the action of a vacuum blender until the solid content was 72 wt% and the system was uniform. The specific surface area of the molecular sieve was 350 m 2 / g, the pore size of the molecular sieve was 0.6 nm, and the average volume particle size Dv50 of the molecular sieve was 1 μm.

[0107] The positive electrode slurry and the first molecular sieve coating slurry were uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and were dried at 100°C to obtain a positive electrode tab coated with a single layer of positive electrode active material and a first molecular sieve coating. Subsequently, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode tab coated with a double layer of positive electrode active material and a first molecular sieve coating (as shown in FIG. 1). Figure 4The first molecular sieve coating is provided on the first region of the positive electrode sheet, and the positive electrode active material layer is provided on the second region of the positive electrode sheet. After cold pressing, the positive electrode sheet with a size of 74 mm x 1183 mm is obtained.

[0108] The width W of the first molecular sieve coating is 1 mm, and the thickness H of the first molecular sieve coating is 10 μm. 13 The width W of the first molecular sieve coating is 1 mm, and the thickness H of the first molecular sieve coating is 10 μm. 13 The thickness of the positive electrode active material layer is 40 μm, and the width of the positive electrode active material layer is 73 mm. The length of the positive electrode active material layer is 1183 mm, and the length of the first molecular sieve coating is 1183 mm.

[0109] <Preparation of a negative electrode sheet>

[0110] The negative electrode active material artificial graphite, the negative electrode conductive agent acetylene black, the thickening agent carboxymethyl cellulose (CMC), and the negative electrode binder styrene butadiene rubber (abbreviated as SBR, with a weight average molecular weight of 50 x 10 5 ) are mixed in a mass ratio of 96:1:1.5:1.5, and then deionized water is added as a solvent. The negative electrode slurry is stirred in a vacuum stirrer until the solid content is 54 wt% and the system is uniform. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, and is dried at 85°C to obtain a single-side coated negative electrode active material layer (with a thickness of 45 μm). Then, the above steps are repeated on the other surface of the copper foil to obtain a double-side coated negative electrode active material layer. After cold pressing, the negative electrode sheet with a size of 76 mm x 1186 mm is obtained.

[0111] <Preparation of a separator>

[0112] A polyethylene film with a thickness of 7 μm (manufacturer: Hunan Zhongli New Material Co., Ltd.) is used.

[0113] <Preparation of an electrolyte>

[0114] Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:7 to obtain an organic solvent. Then, lithium salt LiPF6 is dissolved in the mixed organic solvent at a proportion of 1 mol / L to obtain a basic electrolyte. Finally, 2 wt% of fluoroethylene carbonate (FEC) is additionally added based on the mass of the basic electrolyte to prepare the electrolyte.

[0115] <Preparation of a lithium ion battery>

[0116] The prepared negative electrode sheet, the separator and the positive electrode sheet are stacked and wound in sequence to obtain an electrode assembly with a winding structure. The electrode assembly is placed in an aluminum plastic film packaging bag, the positive and negative electrode tabs are respectively welded on the aluminum sheet and the copper sheet by butt welding and led out of the packaging bag, the electrode assembly is dried and then injected with electrolyte, and then the lithium ion battery is obtained through the processes of vacuum packaging, standing, formation, degassing and edge cutting.

[0117] Examples 1-2 to 1-19

[0118] The rest is the same as Example 1-1 except that the preparation parameters are adjusted according to Table 1.

[0119] Among them, in Example 1-8 to Example 1-10, the width of the positive active material layer is 73.5 mm, 71 mm and 64 mm respectively as the width of the first molecular sieve coating changes.

[0120] Example 2-1

[0121] <Preparation of the separator>

[0122] A polyethylene film with a thickness of 7 μm (manufacturer: Hunan Zhongli New Material Co., Ltd.) is used.

[0123] The molecular sieve MOR molecular sieve (manufacturer: Shanghai Yuan Ye Biological Co., Ltd., model: 12445-20-4) and the first binder polymethyl methacrylate (weight average molecular weight 75000) are mixed in a mass ratio of 80:20, N-methyl pyrrolidone (NMP) is added as a solvent, and the second molecular sieve coating slurry is stirred in a vacuum stirrer until the solid content is 72wt% and the system is uniform. Among them, the specific surface area of the molecular sieve is 350 m 2 / g, the pore size of the molecular sieve is 0.6 nm, and the average volume particle size Dv50 of the molecular sieve is 1 μm.

[0124] The second molecular sieve coating slurry is coated on the surface of the polyethylene film opposite to the first area of the positive electrode sheet, and dried at 100°C to obtain a separator coated with a second molecular sieve coating on one side. Then, the above steps are repeated on the other surface of the polyethylene film opposite to the first area of the positive electrode sheet to obtain a separator coated with a second molecular sieve coating on both sides (as shown in Figure 7 ).

[0125] Among them, the thickness H 23 of the second molecular sieve coating is 10 μm.

[0126] The preparation of the positive electrode sheet, the preparation of the negative electrode sheet, the preparation of the electrolyte and the preparation of the lithium ion battery are the same as Example 1-1.

[0127] Examples 2-2 to 2-7

[0128] The rest was the same as Example 2-1, except that the preparation parameters were adjusted according to Table 3.

[0129] Example 3-1

[0130] Preparation of the positive electrode tab

[0131] The conductive agent acetylene black (manufacturer: Jiaozuo Hexing Chemical Industry Co., Ltd.) and the second binder PVDF (weight average molecular weight 755000) were mixed in a mass ratio of 30:70, deionized water was added as a solvent, and the conductive layer slurry was stirred in a vacuum stirrer until the solid content was 45wt% and the system was uniform.

[0132] The positive electrode slurry and the first molecular sieve coating slurry were uniformly coated on one surface of the positive current collector aluminum foil with a thickness of 10 μm, respectively, and dried at 100°C to obtain a positive electrode tab coated with a single-sided positive active material layer and a first molecular sieve coating. The conductive layer slurry was coated on the surface of the first molecular sieve coating away from the positive current collector, and dried at 100°C to obtain a positive electrode tab coated with a single-sided positive active material layer, a first molecular sieve coating and a conductive layer. Then, the above steps were repeated on the other surface of the aluminum foil, i.e. a positive electrode tab coated with a double-sided positive active material layer, a first molecular sieve coating and a conductive layer was obtained (as shown in Figure 9 The first molecular sieve coating and the conductive layer were arranged in the first region of the positive electrode tab, and the positive active material layer was arranged in the second region of the positive electrode tab. Cold pressing, and then cutting, to obtain a positive electrode tab with a specification of 74 mm x 1183 mm for use.

[0133] The width W 13 of the first molecular sieve coating was 1 mm, and the thickness H 13 was 10 μm. The thickness H 15 of the conductive layer was 20 μm, and the width was 1 mm. The thickness H 14 of the positive active material layer was 90 μm.

[0134] Preparation of the negative electrode tab, Preparation of the separator, Preparation of the electrolyte, and Preparation of the lithium ion battery were the same as Example 1-1.

[0135] Examples 3-2 to 3-6

[0136] The rest was the same as Example 3-1, except that the preparation parameters were adjusted according to Table 4.

[0137] The mass percentage content of the second binder changed with the mass percentage content of the conductive agent, and the sum of the mass percentage contents of the conductive agent and the second binder was 100%, based on the mass of the conductive layer.

[0138] Example 3-7

[0139] <Preparation of positive electrode sheet> was the same as Example 3-1, <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium ion battery> were the same as Example 2-1.

[0140] Comparative Example 1

[0141] <Preparation of positive electrode sheet>

[0142] Ceramic particles boehmite and ceramic layer binder polyvinylidene fluoride (PVDF, weight average molecular weight 755000) were mixed in a mass ratio of 95:5, deionized water was added as a solvent, and the system was stirred under the action of a vacuum stirrer until the ceramic coating slurry had a solid content of 40wt% and was uniform. Among them, the average volume particle size Dv50 of boehmite is 0.6μm.

[0143] The positive electrode slurry and the ceramic coating slurry were uniformly coated on one surface of the positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 100℃ to obtain a positive electrode sheet coated with a single layer of positive electrode active material and a ceramic coating. Then, repeat the above steps on the other surface of the aluminum foil, i.e. obtain a positive electrode sheet coated with a double layer of positive electrode active material and ceramic coating. Among them, the ceramic coating is arranged in the first region of the positive electrode sheet, and the positive electrode active material layer is arranged in the second region of the positive electrode sheet. After drying at 100℃, cold pressing, and then cutting, a positive electrode sheet with a specification of 74mm×1183mm is obtained for use.

[0144] Among them, the width of the ceramic coating is 1mm, and the thickness is 10μm. The length of the positive electrode active material layer is 1183mm, and the length of the ceramic coating is 1183mm.

[0145] <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of electrolyte>, and <Preparation of lithium ion battery> were the same as Example 1-1.

[0146] Comparative Example 2

[0147] Except that the ceramic layer binder is replaced by the first binder polymethyl methacrylate (weight average molecular weight 75000), the rest is the same as Comparative Example 1.

[0148] Comparative Example 3 and Comparative Example 4

[0149] Except that the preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0150] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 4.

[0151] Table 1

[0152]

[0153]

[0154] Note: In Table 1, "\" indicates no corresponding parameter; in Table 1, "W" indicates no corresponding parameter. f1 "" indicates the mass percentage of the molecular sieve based on the mass of the first molecular sieve coating; "Wz1" in Table 1 indicates the mass percentage of the first binder based on the mass of the first molecular sieve coating; the difference between Comparative Example 1 and Comparative Example 2 is that the binder in the ceramic coating of Comparative Example 1 is PVDF, and the binder in the ceramic coating of Comparative Example 2 is polymethyl methacrylate.

[0155] Table 2

[0156]

[0157]

[0158] As can be seen from Examples 1-1 to 1-19, Comparative Examples 1 to 4, the positive electrode plate of the present application has two surfaces of the positive current collector in the first region provided with a first molecular sieve coating, and the content of the intermediate molecular sieve and the first binder of the first molecular sieve coating is within the range of the present application, which has a higher adhesive force, indicating that the positive electrode plate and the separator have a higher adhesive force. The above-mentioned positive electrode plate is applied to a secondary battery, compared with Comparative Examples 1 and 2, the secondary batteries of Examples 1-1 to 1-19 have a higher proportion of passing the drop test, have less lithium precipitation, indicating that the cycle performance and drop safety performance of the secondary battery are improved; at the same time, it has a lower expansion rate, indicating that the risk of gas generation of the secondary battery is lower, and its storage performance is improved. In Comparative Examples 1 and 2, the positive electrode plate without the first molecular sieve coating has a very low adhesive force, and the secondary battery using the positive electrode plate has a lower proportion of passing the drop test and a more serious lithium precipitation, indicating that the cycle performance and drop safety performance of the secondary battery are poor. Moreover, the secondary batteries in Comparative Examples 1 and 2 have a higher expansion rate, indicating that the secondary battery has a higher risk of gas generation, and its storage performance has not been improved. In Comparative Example 3, the content of the molecular sieve is too high, and the content of the binder is too low, which cannot fully bond the positive electrode plate and the separator, resulting in a too low adhesive force between them, which is easy to cause failure during dropping, and the interface performance between the positive electrode plate and the separator is poor during the cycle process, resulting in lithium precipitation; in Comparative Example 4, the content of the binder is too high, and the content of the molecular sieve is too low, so the molecular sieve cannot fully physically block the contact between the positive current collector and the negative active material caused by the burrs, wrinkles and the like of the positive current collector during dropping, so short circuit is easy to occur, and at the same time, due to the too low content of the molecular sieve, the battery cannot fully absorb the generated gas during storage at high temperature, resulting in too large expansion of the battery and poor storage performance.

[0159] The mass percentage of molecular sieve and first binder in the first molecular sieve coating typically affects the cycle performance, drop safety, and storage performance of secondary batteries. As can be seen from Examples 1-1 to 1-7, Comparative Examples 3 and 4, secondary batteries using molecular sieve and first binder within the mass percentage range of this application in the first molecular sieve coating exhibit a higher drop test pass rate, less lithium plating, and a lower expansion rate, indicating good cycle performance, drop safety, and storage performance. Specifically, Example 1-1 has a higher molecular sieve content, which can absorb more gas and suppress battery expansion, but the binder content is lower, resulting in weaker adhesion and drop test performance inferior to Examples 1-2 to 1-6. Example 1-7 has a higher binder content and stronger adhesion than Example 1-1, but due to the smaller molecular sieve size, it cannot fully swell the binder, leading to weaker adhesion than Examples 1-2 to 1-6. Furthermore, it cannot absorb as much gas, resulting in a higher battery expansion rate. The overall performance of the batteries in Examples 1-2 to 1-6 is significantly better than that of Examples 1-1 and 1-7. In Examples 1-3 to 1-5, due to the appropriate ratio of molecular sieve and binder, the adhesion of the molecular sieve coating is better, resulting in better interfacial performance between the separator and the active material layer. At the same time, the ability of the molecular sieve to absorb gas can be fully utilized, and the battery's overall performance in terms of drop resistance, expansion resistance, and lithium plating prevention is better.

[0160] The width W of the first molecular sieve coating 13 This typically affects the cycle performance, drop safety, and storage performance of secondary batteries. As can be seen from Examples 1-2, 1-8 to 1-10, the width W of the selected first molecular sieve coating... 13 The secondary batteries within the scope of this application exhibit a high rate of passing drop tests, minimal lithium plating, and low expansion rates, indicating good cycle performance, drop safety, and storage performance. Among these, Examples 1-2, 1-9, and 1-10 have wider first molecular sieve coatings, resulting in significantly better overall performance than Examples 1-8. However, the larger molecular sieve coating width in Examples 1-10 leads to a decrease in battery energy density, therefore it is not a preferred solution.

[0161] The thickness H of the first molecular sieve coating 13 This typically affects the cycle performance, drop safety, and storage performance of secondary batteries. As can be seen from Examples 1-2, 1-11 to 1-15, the thickness H of the first molecular sieve coating is... 13The secondary battery within the scope of the present application has a higher proportion of the number of drop-through tests, less lithium precipitation, and a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance, and storage performance. The first molecular sieve coating thickness of examples 1-2, 1-12 to 1-15 is larger, and the comprehensive performance is obviously better than that of example 1-11, but the thicker molecular sieve coating of examples 1-14 and 1-15 will cause the battery energy density to decrease, and does not bring further performance improvement, so it is not a preferred solution.

[0162] The type, specific surface area, and pore size of the molecular sieve, and the porosity of the first molecular sieve coating generally affect the cycle performance, drop safety performance, and storage performance of the secondary battery. As can be seen from examples 1-2, 1-16 to 1-19, the secondary battery within the scope of the present application has a higher proportion of the number of drop-through tests, less lithium precipitation, and a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance, and storage performance.

[0163] Table 3

[0164]

[0165] Note: “\” in Table 3 indicates no corresponding parameter; “W f2 ” in Table 3 indicates the mass percentage content of the molecular sieve based on the mass of the second molecular sieve coating; and “Wz2” in Table 3 indicates the mass percentage content of the first binder based on the mass of the second molecular sieve coating.

[0166] As can be seen from examples 1-2, 2-1 to 2-7, by providing a second molecular sieve coating on the surface of the separator opposite the first region, the adhesion between the positive electrode sheet and the separator can be further increased. When the separator is applied to a secondary battery, the secondary battery has a higher proportion of the number of drop-through tests, less lithium precipitation, indicating that the cycle performance and drop safety performance of the secondary battery are further improved. It has a lower expansion rate, indicating that the risk of gas swelling of the secondary battery is lower, and its storage performance is further improved.

[0167] The mass percentage content of the molecular sieve in 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 to 2-3, the secondary battery within the scope of the present application has a higher proportion of the number of drop-through tests, less lithium precipitation, and a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance, and storage performance.

[0168] The thickness H of the second molecular sieve coating 23 Generally affect the cycle performance, drop safety performance and storage performance of the secondary battery. As can be seen from Example 2-1, Example 2-4 and Example 2-5, the secondary battery with the thickness H of the second molecular sieve coating within the scope of the present application has a higher number ratio of passing the drop test, has less lithium precipitation and lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance. 23

[0169] 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 Example 2-1, Example 2-6 to Example 2-7, the secondary battery with the porosity of the second molecular sieve coating within the scope of the present application has a higher number ratio of passing the drop test, has less lithium precipitation and lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance.

[0170] Table 4

[0171]

[0172] Note: “\” in Table 4 means no corresponding parameter; “W d ” in Table 4 means the mass percentage content of the conductive agent based on the mass of the conductive layer; “W z3 ” in Table 4 means the mass percentage content of the second binder based on the mass of the conductive layer; the difference between Example 3-1 and Example 3-7 is that the 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.

[0173] As can be seen from Example 1-2 and Example 3-1 to Example 3-6, Example 2-1 and Example 3-7, the conductive layer with the conductive agent and the second binder on the surface of the first molecular sieve coating away from the positive current collector within the scope of the present application can further reduce the lithium precipitation of the secondary battery under the condition of having a higher number ratio of passing the drop test and a lower expansion rate, indicating that the secondary battery further improves the cycle performance under the condition of having good drop safety performance and storage performance.

[0174] ​The mass percentage of the conductive agent and the second binder in the conductive layer generally affects the cycle performance, drop safety performance and storage performance of the secondary battery. As can be seen from Example 1-2, Example 3-1 to Example 3-3, the secondary battery selected with the mass percentage of the conductive agent and the second binder in the conductive layer within the range of the present application has a higher proportion of the number of drop passing tests, has less lithium precipitation, and has a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance.

[0175] The thickness H of the conductive layer 15 Generally affects the cycle performance, drop safety performance and storage performance of the secondary battery. As can be seen from Example 1-2, Example 3-1, Example 3-4 and Example 3-5, the secondary battery selected with the thickness H of the conductive layer within the range of the present application has a higher proportion of the number of drop passing tests, has less lithium precipitation, and has a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance. 15

[0176] The type of the conductive agent generally affects the cycle performance, drop safety performance and storage performance of the secondary battery. As can be seen from Example 3-1, Example 3-6, the secondary battery selected with the type of the conductive agent within the range of the present application has a higher proportion of the number of drop passing tests, has less lithium precipitation, and has a lower expansion rate, indicating that the secondary battery has good cycle performance, drop safety performance and storage performance.

[0177] It should be noted that the relational terms herein such as first and second and the like are used only to differentiate one entity or operation from another, and do not necessarily require or imply that any such actual relationship or order exists between or among the entities or operations. Also, the terms "comprising", "containing", or any other similar term are intended to encompass non-exclusive inclusion, such that a process, method, article or apparatus that comprises a list of elements does not necessarily include only those elements, but can include other elements not expressly listed or inherent to such process, method, article or apparatus.

[0178] Each of the embodiments in the specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0179] The above is only the preferred embodiment of the present application, and does not limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

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

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

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

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

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

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

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

8. The secondary battery according to claim 1, wherein, A second molecular sieve coating is provided on the surface of the diaphragm opposite to the first region; The second molecular sieve coating includes the molecular sieve, and the molecular sieve has a mass percentage 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 thickness of the second molecular sieve coating is 0.5 μm to 10 μm.

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

11. The secondary battery according to claim 8, wherein, The specific surface area of ​​the molecular sieve is 200 m². 2 / g to 2000m 2 / g, wherein the pore size of the molecular sieve is from 0.3nm to 45nm.

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

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

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

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

16. An electrical appliance, wherein, The electrical device includes the secondary battery as described in any one of claims 1 to 15.

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