Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises an adhesive tape, a positive electrode sheet, a negative electrode sheet, and a separator provided between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode tab; the adhesive tape is located between the separator and the positive electrode tab, and comprises a porous substrate and an adhesive layer provided on at least one surface of the substrate; the adhesive layer comprises inert substances including a first inert substance and a second inert substance; the particle size of the first inert substance is d1nm, the particle size of the second inert substance is d2nm, 300<d1≤900, and 50≤d2≤300; the average particle size of the first inert substance is D1nm, the average particle size of the second inert substance is D2nm, 400≤D1≤800, and 100≤D2≤200; and in any region on the surface of the adhesive layer, the ratio of the number of particles of the first inert substance to the number of particles of the second inert substance is 3:7-7:3. By means of the described configuration, the secondary battery has good dynamic performance.

Description

Secondary battery and electronic device

[0001] The present application claims priority to the Chinese patent application No. 202510216132.6 filed on February 26, 2025, and entitled "Secondary battery and electronic device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, and in particular, to a secondary battery and an electronic device. BACKGROUND

[0003] Secondary batteries (such as lithium ion batteries) have the advantages of high energy density, long cycle life, low self-discharge rate, environmental protection and no pollution, and have been widely used in the fields of aviation, aerospace, navigation, electric vehicles, consumer electronics, etc. A lithium ion battery is composed of a positive electrode sheet, a negative electrode sheet, a separator, a glue paper and other components. The ion-conducting glue paper in the existing lithium ion battery is produced by a micro-gravure process. The glue layer is a mixed slurry (including boehmite, glue layer material and solvent) coated on the substrate. After the solvent is volatilized, the place originally occupied by the solvent becomes a pore. The boehmite in the glue layer is prone to agglomeration, resulting in excessive local impedance, which affects the kinetic performance of the lithium ion battery. SUMMARY

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to improve the kinetic performance of the secondary battery.

[0005] It should be noted that the lithium ion battery is taken as an example to explain the present application in the summary of 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 this application provides a secondary battery, which includes adhesive tape, a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The positive electrode includes a positive electrode tab, and the adhesive tape is located between the separator and the positive electrode tab. The adhesive tape includes a porous substrate and an adhesive layer disposed on at least one surface of the substrate. The adhesive layer includes an inert material, which includes a first inert material and a second inert material. The particle size of the first inert material is d1 nm, and the particle size of the second inert material is d2 nm, and 300 < d1 ≤ 900, 50 ≤ d2 ≤ 300. The average particle size of the first inert material is D1 nm, and the average particle size of the second inert material is D2 nm, and 400 ≤ D1 ≤ 800, 100 ≤ D2 ≤ 200. In any region on the surface of the adhesive layer, the ratio of the number of particles of the first inert material to the number of particles of the second inert material is 3:7 to 7:3. The secondary battery provided in the first aspect of this application incorporates both a larger first inert material and a smaller second inert material into the adhesive layer. The average particle size and the ratio of the number of particles of the first and second inert materials are controlled within the range specified in this application. This allows the larger first inert material particles and the smaller second inert material particles to work together. The larger first inert material particles can support and create pores on the porous substrate surface, improving the permeability of the porous substrate and consequently the permeability of the adhesive tape. This reduces the probability of lithium plating in the adhesive tape area. The smaller second inert material particles create smaller pores, increasing the adhesion of the adhesive layer and reducing the probability of the adhesive layer falling off during winding. This improves both the kinetic and processing performance of the secondary battery. Furthermore, the adhesive tape of this application has high permeability, allowing lithium ions to move freely within the adhesive tape area. Therefore, the capacity of the adhesive tape area can still be utilized, thereby increasing the energy density of the secondary battery.

[0007] In some embodiments of this application, 1 / 7 ≤ D2 / D1 ≤ 1 / 3. By controlling the ratio D2 / D1 between the average particle size of the second inert material and the average particle size of the first inert material within the above range, the probability of lithium plating occurring in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle can be reduced, thus ensuring good kinetic performance of the secondary battery. It also reduces the probability of the adhesive layer falling off during the winding process. Furthermore, lithium ions can freely move within the area where the adhesive tape is applied, so the capacity of the adhesive tape area can still be utilized, thereby improving the energy density of the secondary battery.

[0008] In some embodiments of this application, the average pore size of the porous substrate is P nm; D2 and P satisfy the following relationship: 0.5 ≤ P / D2 ≤ 1. By controlling the ratio P / D2 between the average pore size of the porous substrate and the average particle size of the second inert material within the above range, the probability of the adhesive layer falling off during the winding process is low, and the probability of lithium plating occurring in the adhesive-coated area during the later stages of the secondary battery charge-discharge cycle is also low, thus giving the secondary battery good kinetic performance. Lithium ions can freely shuttle in the area where the adhesive is applied, so the capacity of the adhesive-coated area can still be utilized, thereby improving the energy density of the secondary battery.

[0009] In some embodiments of this application, 50 ≤ P ≤ 200. Controlling the average pore size of the porous substrate within the above range allows the porous substrate to have a suitable average pore size, which is beneficial for achieving better adhesion between the adhesive layer and the porous substrate, and for the adhesive paper to have higher air permeability.

[0010] In some embodiments of this application, the adhesive layer includes an adhesive binder, and the mass ratio of the inert material to the adhesive binder is 3:7 to 7:3. By controlling the mass ratio of the inert material to the adhesive binder within this range, the probability of the adhesive layer falling off during winding is low, and the probability of lithium plating occurring in the adhesive-coated area during the later stages of the secondary battery charge-discharge cycle is also low, thus giving the secondary battery good kinetic performance. Lithium ions can freely move within the area where the adhesive tape is located, therefore the capacity of the adhesive-coated area can still be utilized, thereby improving the energy density of the secondary battery.

[0011] In some embodiments of this application, the air permeability of the adhesive tape is between 180 s / 100 mL and 600 s / 100 mL, indicating that the adhesive tape has good air permeability.

[0012] In some embodiments of this application, the porosity of the porous substrate is 25% to 55%. By controlling the porosity of the porous substrate within the above range, the probability of interface lithium plating during charge-discharge cycles is reduced, and the secondary battery exhibits good kinetic performance.

[0013] In some embodiments of this application, the thickness of the porous substrate is between 9 μm and 24 μm. Controlling the thickness of the porous substrate within this range can reduce the probability of increased local impedance, decrease the occurrence of lithium plating at the interface during charge-discharge cycles of the secondary battery, and improve the kinetic performance of the secondary battery. It can also reduce energy density loss due to excessive porous substrate thickness, resulting in a secondary battery with higher energy density.

[0014] In some embodiments of this application, the thickness of the adhesive layer is 2 μm to 6 μm. By controlling the thickness of the adhesive layer within the above range, the probability of the adhesive layer falling off during the winding process is reduced, which also helps to reduce the energy density loss of the secondary battery caused by excessive adhesive layer thickness, thereby enabling the secondary battery to have a higher energy density.

[0015] In some embodiments of this application, the secondary battery satisfies at least one of the following characteristics: (1) the particle number ratio of the first inert material to the second inert material is 1:1 to 7:3; (2) 1 / 5 ≤ D2 / D1 ≤ 1 / 3; (3) the mass ratio of the inert material to the adhesive layer is 1:2 to 7:3; (4) the thickness of the porous substrate is 12 μm to 16 μm; (5) the thickness of the adhesive layer is 3 μm to 5 μm. This is beneficial for the secondary battery to have good kinetic and safety performance, and high energy density.

[0016] In some embodiments of this application, the inert material includes at least one of boehmite, diaspore, halloysite, or silica sand. Using such inert materials improves the air permeability and strength of the adhesive paper.

[0017] In some embodiments of this application, the adhesive layer includes at least one selected from polymethyl methacrylate, polyacrylic acid, ethylene-acrylic acid copolymer, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyurethane, or epoxy resin. Selecting the above-mentioned types of adhesive layer materials is beneficial for achieving better adhesion of the adhesive layer and improving the bonding properties of the adhesive tape.

[0018] In some embodiments of this application, the positive electrode includes a positive active material layer and a positive current collector. The positive current collector includes a first surface and a second surface opposite to each other. The positive active material layer is disposed at least on the first surface of the positive current collector. A first groove is provided in the positive active material layer to expose the positive current collector. A positive electrode tab is disposed in the first groove and connected to the positive current collector. The second surface includes a first empty foil area opposite to the first groove. Adhesive tape is pasted on at least one of the following: the surface of the positive electrode tab, the first empty foil area, the surface of the negative electrode adjacent to the first groove, the surface of the negative electrode adjacent to the first empty foil area, or the end area of ​​the positive electrode. Pasting the adhesive tape at the above-mentioned different locations allows lithium ions in the area covered by the adhesive tape to freely shuttle and exert the capacity of the active material. It also reduces the risk of short circuit caused by positive and negative electrode contact and the probability of lithium plating, thereby giving the secondary battery higher energy density and better safety and kinetic performance.

[0019] In some embodiments of this application, the negative electrode sheet includes a negative current collector, a negative active material layer, and a negative electrode tab. The negative current collector includes a third surface and a fourth surface opposite to each other. The negative active material layer is disposed on at least the third surface of the negative current collector. A second groove is provided in the negative active material layer to expose the negative current collector. The negative electrode tab is disposed in the second groove and connected to the negative current collector. The fourth surface includes a second empty foil area opposite to the second groove. Adhesive tape is pasted on at least one part of the negative electrode tab surface or the second empty foil area. Pasting adhesive tape on the negative electrode tab surface and the second empty foil area enables lithium ions to be intercalated into the negative active material layer covered by the adhesive tape, increasing the lithium ion intercalation sites and increasing the capacity of the negative active material layer, thereby giving the secondary battery a higher energy density.

[0020] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device exhibits good performance.

[0021] The beneficial effects of this application are:

[0022] This application provides a secondary battery and an electronic device. The secondary battery includes adhesive tape, a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The positive electrode includes a positive electrode tab. The adhesive tape is located between the separator and the positive electrode tab. The adhesive tape includes a porous substrate and an adhesive layer disposed on at least one surface of the porous substrate. The adhesive layer includes an inert material, which includes a first inert material and a second inert material. The particle size of the first inert material is d1 nm, and the particle size of the second inert material is d2 nm, and 300 < d1 ≤ 900, 50 ≤ d2 ≤ 300. The average particle size of the first inert material is D1 nm, and the average particle size of the second inert material is D2 nm, and 400 ≤ D1 ≤ 800, 100 ≤ D2 ≤ 200. In any region on the surface of the adhesive layer, the ratio of the number of particles of the first inert material to the number of particles of the second inert material is 3:7 to 7:3. The adhesive tape incorporates a first inert material with larger particles and a second inert material with smaller particles in the adhesive layer. The ratio of the first to second inert material particles is controlled within a specified range. This allows the larger particles to work together, creating pores on the porous substrate surface, thus increasing the substrate's permeability and consequently the adhesive tape's permeability. This reduces the probability of lithium plating in the adhesive tape area. The smaller particles of the second inert material create smaller pores, improving the adhesive layer's bonding strength and reducing the likelihood of the adhesive layer falling off during winding. This improves both the kinetic and processing performance of the secondary battery. Furthermore, the high permeability of the adhesive tape allows lithium ions to move freely within the tape-covered area, ensuring the capacity of the tape-covered area remains utilized and ultimately increasing the secondary battery's energy density.

[0023] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0025] Figure 1 is a schematic cross-sectional view of the adhesive tape along its thickness direction and longitudinal direction in some embodiments of this application;

[0026] Figure 2 is a schematic diagram of the adhesive tape for attaching the positive electrode tab in some embodiments of this application;

[0027] Figure 3 is a schematic diagram showing the position of the adhesive tape in some embodiments of this application;

[0028] Figure 4 is a schematic diagram showing the position of the adhesive tape in some other embodiments of this application.

[0029] 10-Positive electrode sheet; 11-Positive current collector; 12-Positive active material layer; 13-Positive electrode tab; 11a-First surface; 11b-Second surface; 15-First groove; 16-First empty foil area; 20-Negative electrode sheet; 21-Negative current collector; 22-Negative active material layer; 23-Negative electrode tab; 25-Second groove; 26-Second empty foil area; 21c-Third surface; 21d-Fourth surface; 30-Separator; 40-Adhesive paper; 41-Porous substrate; 42-Adhesive layer; 50-Non-ion-conducting adhesive paper. Detailed Implementation

[0030] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0031] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0032] The first aspect of this application provides a secondary battery, comprising adhesive tape, a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode includes a positive electrode tab, and the adhesive tape is located between the separator and the positive electrode tab. The adhesive tape includes a porous substrate and an adhesive layer disposed on at least one surface of the porous substrate. The adhesive layer includes an inert material, comprising a first inert material and a second inert material. The first inert material has a particle size of d1 nm, and the second inert material has a particle size of d2 nm, wherein 300 < d1 ≤ 900, and 50 ≤ d2 ≤ 300. The average particle size of the first inert material is D1 nm, and the average particle size of the second inert material is D2 nm, wherein 400 ≤ D1 ≤ 800, and 100 ≤ D2 ≤ 200. In any region on the surface of the adhesive layer, the ratio of the number of particles of the first inert material to the number of particles of the second inert material is 3:7 to 7:3.

[0033] The aforementioned "adhesive layer disposed on at least one surface of a porous substrate" means that the adhesive layer can be disposed on one surface of the porous substrate or on two surfaces of the porous substrate. For ease of understanding, the longitudinal direction of the adhesive tape is defined as X, its transverse direction as Y, and its thickness as Z. It should be understood that the above definitions of direction are for the purpose of describing this application, and the directions defined in this application can be understood based on the relative positions of the accompanying drawings and actual product elements. As shown in Figures 1 and 2, when the adhesive tape 40 is attached to the positive electrode 10, the longitudinal direction X of the adhesive tape 40 is parallel to the extension direction of the positive electrode tab 13, the transverse direction Y of the adhesive tape 40 is perpendicular to the extension direction of the positive electrode tab 13, and the thickness direction Z of the adhesive tape 40 is perpendicular to both the transverse direction Y and the longitudinal direction X of the adhesive tape 40. In some embodiments, as shown in Figure 1, the adhesive tape 40 includes a porous substrate 41 and an adhesive layer 42, with the adhesive layer 42 disposed on one surface of the porous substrate 41. It is understood that in other embodiments, the adhesive layer 42 may also be disposed on the other surface of the porous substrate 41. In some embodiments, the adhesive layer 42 may also be disposed on two surfaces of the porous substrate 41 respectively.

[0034] For example, d1 is 301, 320, 350, 370, 410, 430, 450, 470, 500, 533, 550, 570, 590, 610, 650, 700, 720, 750, 770, 790, 800, 810, 840, 870, 900, or any value between any two of the above ranges. For example, d2 is 50, 71, 90, 105, 110, 130, 150, 173, 200, 220, 245, 260, 300, or any value between any two of the above ranges. In this application, a first inert material with a particle size d1 satisfying 300 < d1 ≤ 900 is defined as a large-particle inert material; a second inert material with a particle size d2 satisfying 50 ≤ d2 ≤ 300 is defined as a small-particle inert material. When the particle size d2 is less than 50, the particle size of the inert material is too small. The inert material is prone to clogging the pores of the porous substrate, which will reduce the air permeability of the porous substrate. In addition, the probability of the inert material itself agglomerating or agglomerating with the adhesive layer will increase, which will make the probability of lithium plating interface problems in the later stage of charge and discharge cycle of the secondary battery too high. When the particle size d1 is greater than 900, the particle size of the inert material is too large, which will reduce the adhesion of the adhesive layer. The inert material is also easy to be filtered out during the slurry filtration process due to its large particle size, which will affect the composition content of the adhesive layer, increase the difficulty of the preparation process, and affect the ion conduction and adhesion of the adhesive paper.

[0035] For example, D1 is 400, 415, 447, 472, 500, 530, 556, 581, 600, 610, 630, 653, 671, 700, 720, 740, 762, 788, 800, or any value between any two of the above ranges. If D1 is less than 400, the average particle size of the first inert material is too small, and the overall particle size of the first inert material is too small. When used in combination with the second inert material, the overall particle size of the inert material is too small, resulting in fewer inert material particles used to support pore formation, or the pores formed by the inert material are too small, making it difficult to improve the air permeability of the porous substrate. This reduces the probability of lithium plating in the adhesive tape area. If D1 is greater than 800, the average particle size of the first inert material is too large, and the overall particle size of the first inert material is too large. This will reduce the adhesion of the adhesive layer, and the inert material is easily filtered out during the slurry filtration process due to its large particle size. This will affect the composition content of the adhesive layer, increase the difficulty of the preparation process, and affect the ion conductivity and adhesion of the adhesive tape.

[0036] For example, D2 can be 100, 107, 115, 130, 140, 150, 162, 175, 180, 190, 200, or any value within any two of the above ranges. If D2 is less than 100, the average particle size of the second inert material is too small, and the overall particle size of the second inert material is too small. The second inert material is more likely to block the pores of the porous substrate, reducing the permeability of the porous substrate. Furthermore, the probability of the second inert material itself agglomerating or agglomerating with the adhesive layer will increase, thus increasing the probability of lithium plating interface problems in the later stages of charge-discharge cycles of the secondary battery. If D2 is greater than 200, the average particle size of the second inert material is too large, and the overall particle size of the second inert material is too large. This will affect the adhesion of the second inert material to the adhesive layer, thereby increasing the probability of the adhesive layer falling off during the winding process.

[0037] For example, the particle ratio of the first inert material to the second inert material can be 3:7, 4:7, 5:7, 6:7, 1:1, 7:6, 7:5, 7:4, 7:3, or any ratio within any two of the above ranges. If the particle ratio of the first inert material to the second inert material is less than 3:7, the number of particles of the first inert material is too small, resulting in insufficient large particles of inert material to support the pores and poor air permeability of the adhesive tape. If the number of particles of the second inert material is too large, the extra small particles of inert material, in addition to improving the adhesion of the adhesive layer, can easily block the pores of the porous substrate, reducing the air permeability of the adhesive tape. Furthermore, the small particles of inert material are difficult to disperse and prone to agglomeration, increasing the probability of point-like lithium plating interface problems during charge-discharge cycles of the secondary battery. If the ratio of the number of particles of the two inert materials is greater than 7:3, and the number of particles of the second inert material is too small, the adhesive layer will have poor adhesion, and the adhesive layer will be too likely to fall off during the winding process. If the number of particles of the first inert material is too large, the large particles will have a small specific surface area, which will reduce the adhesion to porous substrates, resulting in poor adhesion between the porous substrate and the adhesive layer. This will also lead to a high probability of the adhesive layer falling off during the winding process or a high probability of local lithium plating at the interface during the charge and discharge cycle of the secondary battery.

[0038] Overall, the adhesive tape in this application's secondary battery, by simultaneously incorporating larger particles of a first inert material and smaller particles of a second inert material into the adhesive layer, and controlling the average particle size and particle number ratio of the first and second inert materials within the range of this application, allows the larger particles of the first inert material and the smaller particles of the second inert material to work together. The larger particles of the first inert material can support and create pores on the porous substrate surface, thereby increasing the air permeability of the porous substrate and thus increasing the air permeability of the adhesive tape. This reduces the probability of lithium plating in the adhesive tape area. The smaller particles of the second inert material create smaller pores, which improves the adhesion of the adhesive layer, reducing the probability of the adhesive layer falling off during winding. Therefore, the kinetic performance and processing performance of the secondary battery can be improved. Furthermore, the adhesive tape of this application has high air permeability, allowing lithium ions to move freely in the area where the adhesive tape is located. Therefore, the capacity of the adhesive tape area can still be utilized, thereby increasing the energy density of the secondary battery.

[0039] In this application, particle size refers to the single particle size of an individual particle, which can also be understood as equivalent particle size. Average particle size refers to the average particle size obtained by measuring the particle size of inert material particles in several arbitrary regions selected on the surface of the adhesive layer. The aforementioned "several regions" can be one or more. This application does not impose any particular limitation on the size of the aforementioned "any arbitrary region," and those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved.

[0040] This application does not impose any particular restrictions on the method for controlling the particle size of the inert material, as long as the purpose of this application can be achieved. For example, it can be achieved through crushing or sieving. This application also does not impose any particular restrictions on the method for controlling the average particle size of the inert material, as long as the purpose of this application can be achieved. For example, after preparing a film using the process described in this application, its average particle size can be measured using scanning electron microscopy, and inert material particles of the desired size can be selected. When testing the average particle size, the average diameter of the largest circumscribed circle of 50 particles is selected as the average particle size.

[0041] It is understood that the particle size of the inert material defined in this application refers to the main particle size. Within the allowable error range, the proportion of particles with a diameter greater than 900 nm and less than 50 nm in the total number of inert material particles does not exceed 5%.

[0042] In some embodiments of this application, the particle number ratio of the first inert material to the second inert material is from 1:1 to 7:3. For example, the particle number ratio of the first inert material to the second inert material is 1:1, 7:6, 7:5, 7:4, 7:3, or any ratio within any two of the above ranges. By controlling the particle number ratio of the first inert material to the second inert material within the above range, the first and second inert materials work together to support the pores on the porous substrate surface, improving the air permeability of the adhesive tape. This also allows the inert material to have high adhesion to the porous substrate surface, improving the bonding force between the porous substrate and the adhesive layer. This reduces the probability of lithium plating in the adhesive tape area during the later stages of the secondary battery's charge-discharge cycle, resulting in good kinetic performance of the secondary battery. It also reduces the probability of the adhesive layer falling off during the winding process. Furthermore, lithium ions can freely move within the area where the adhesive tape is present, so the capacity of the adhesive tape area can still be utilized, thereby increasing the energy density of the secondary battery.

[0043] This application does not impose any particular restrictions on the method of controlling the particle number ratio of the first inert material to the second inert material, as long as the purpose of this application can be achieved. For example, the first inert material and the second inert material can be obtained separately by crushing and screening, and then the first inert material and the second inert material with corresponding particle number ratios can be mixed according to actual needs.

[0044] In some embodiments of this application, 1 / 7 ≤ D2 / D1 ≤ 1 / 3. For example, the value of D1 / D2 is 1 / 7, 1 / 6, 1 / 5, 1 / 4, 1 / 3.7, 1 / 3.5, 1 / 3.2, 1 / 3, or any value between any two of the above ranges. By controlling the ratio of the average particle size of the second inert material to the average particle size of the first inert material, D2 / D1, within the above range, the matching of large and small inert material particles is beneficial for supporting the porous substrate surface, improving the permeability of the adhesive tape, and also improving the adhesion of the inert material to the porous substrate surface, thus increasing the bonding force between the porous substrate and the adhesive layer. This reduces the probability of lithium plating in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle, resulting in good kinetic performance of the secondary battery, and also reduces the probability of the adhesive layer falling off during winding. Furthermore, lithium ions can freely move within the area where the adhesive tape is applied, so the capacity of the adhesive tape area can still be utilized, thereby increasing the energy density of the secondary battery.

[0045] In some embodiments of this application, 1 / 5 ≤ D2 / D1 ≤ 1 / 3. For example, the value of D1 / D2 is 1 / 5, 1 / 4.5, 1 / 4, 1 / 3.7, 1 / 3.5, 1 / 3.2, 1 / 3, or any value between any two of the above ranges. By controlling the value of the ratio D2 / D1 between the average particle size of the second inert material and the average particle size of the first inert material within the above range, the large and small particles of inert material are matched, which is more conducive to supporting the porous substrate surface and improving the air permeability of the adhesive tape. It is also more conducive to improving the adhesion of the inert material to the porous substrate surface, thereby improving the bonding force between the porous substrate and the adhesive layer. In this way, the probability of lithium plating in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle can be reduced, so that the secondary battery has good kinetic performance. It also reduces the probability of the adhesive layer falling off during the winding process. In addition, lithium ions can move freely in the area where the adhesive tape is set, so the capacity of the adhesive tape area can still be utilized, thereby improving the energy density of the secondary battery.

[0046] In some embodiments of this application, the average pore size of the porous substrate is P nm; D2 and P satisfy the following relationship: 0.5 ≤ P / D2 ≤ 1. For example, the value of P / D2 is 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value between any two of the above ranges. By controlling the value of P / D2, the ratio between the average pore size of the porous substrate and the average particle size of the second inert material, within the above range, the second inert material can have a higher adhesion to the porous substrate, and the probability of small particles of inert material falling into the pores of the porous substrate is also reduced, thereby resulting in better adhesion between the adhesive layer and the porous substrate, and higher air permeability of the adhesive tape. In this way, the probability of the adhesive layer falling off during the winding process is low, and the probability of lithium plating occurring in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle is low, thus giving the secondary battery good kinetic performance. Lithium ions can freely shuttle in the area where the adhesive tape is provided, so the capacity of the adhesive tape area can still be utilized, thereby improving the energy density of the secondary battery.

[0047] In some embodiments of this application, 50 ≤ P ≤ 200. For example, P is 50, 60, 80, 100, 120, 130, 140, 150, 162, 170, 180, 190, 200, or any value between any two of the above ranges. Controlling the average pore size of the porous substrate within the above range, the porous substrate has a suitable average pore size, which is beneficial for good adhesion between the adhesive layer and the porous substrate, and for the adhesive tape to have high air permeability. This reduces the probability of the adhesive layer falling off during winding, and reduces the probability of lithium plating in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle, thus giving the secondary battery good kinetic performance. Lithium ions can freely move in the area where the adhesive tape is placed, so the capacity of the adhesive tape area can still be utilized, thereby improving the energy density of the secondary battery.

[0048] This application does not impose any particular restrictions on the method of controlling the average pore size of the porous substrate, as long as the purpose of this application can be achieved. For example, it can be achieved by controlling the bidirectional (transverse and longitudinal) stretching ratio during the preparation of the porous substrate.

[0049] In some embodiments of this application, the adhesive layer includes an adhesive binder, and the mass ratio of the inert material to the adhesive binder is 3:7 to 7:3. For example, the mass ratio of the inert material to the adhesive binder is 3:7, 4:7, 5:7, 6:7, 1:1, 7:6, 7:5, 7:4, 7:3, or any ratio within any two of the above ranges. Controlling the mass ratio of the inert material to the adhesive binder within the above range is beneficial for the adhesive paper to have higher air permeability and adhesion. This reduces the probability of the adhesive layer falling off during winding and lowers the probability of lithium plating in the adhesive-coated area during the later stages of the secondary battery charge-discharge cycle, thus giving the secondary battery good kinetic performance. Lithium ions can freely move within the area where the adhesive paper is located, so the capacity of the adhesive-coated area can still be utilized, thereby improving the energy density of the secondary battery.

[0050] In some embodiments of this application, the mass ratio of the inert material to the adhesive layer is from 1:2 to 7:3. For example, the mass ratio of the inert material to the adhesive layer is 1:2, 1:1, 7:6, 7:5, 7:4, 7:3, or any ratio within any two of the above ranges. Controlling the mass ratio of the inert material to the adhesive layer within the above range is beneficial for further improving the air permeability and adhesion of the adhesive tape. This further reduces the probability of the adhesive layer falling off during the winding process and also further reduces the probability of lithium plating occurring in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle, thus giving the secondary battery better kinetic performance.

[0051] In some embodiments of this application, the air permeability of the adhesive tape is from 180 s / 100 mL to 600 s / 100 mL. For example, the air permeability of the adhesive tape is 180 s / 100 mL, 200 s / 100 mL, 220 s / 100 mL, 240 s / 100 mL, 260 s / 100 mL, 280 s / 100 mL, 3200 s / 100 mL, 380 s / 100 mL, 400 s / 100 mL, 420 s / 100 mL, 452 s / 100 mL, 480 s / 100 mL, 512 s / 100 mL, 530 s / 100 mL, 550 s / 100 mL, 573 s / 100 mL, 600 s / 100 mL, or any value between any two of the above ranges. Controlling the air permeability of the adhesive tape within the above range helps reduce the probability of lithium plating occurring in the adhesive tape area during the later stages of the secondary battery charge-discharge cycle, thus enabling the secondary battery to have good kinetic performance.

[0052] This application does not impose any particular limitation on the method of controlling the air permeability of the adhesive tape, as long as it achieves the purpose of this application. For example, it can be achieved by controlling at least one of the following: the mass ratio of inert material to adhesive layer binder, the porosity of the porous substrate, or the average pore size of the porous substrate. Generally speaking, the higher the content of inert material in the adhesive layer, the better the air permeability of the adhesive tape (the lower the air permeability value); the lower the content of inert material in the adhesive layer, the worse the air permeability of the adhesive tape (the higher the air permeability value). The higher the porosity of the porous substrate, the better the air permeability of the adhesive tape; the lower the porosity of the porous substrate, the worse the air permeability of the adhesive tape. The larger the average pore size of the porous substrate, the better the air permeability of the adhesive tape; the smaller the average pore size of the porous substrate, the worse the air permeability of the adhesive tape.

[0053] In some embodiments of this application, the porosity of the porous substrate is between 25% and 55%. For example, the porosity of the porous substrate is 25%, 30%, 34%, 40%, 45%, 50%, 55%, or any value between any two of the above ranges. Controlling the porosity of the porous substrate within the above range is beneficial for achieving good air permeability while maintaining high strength. Consequently, the adhesive paper also exhibits good air permeability, reducing the probability of interface lithium plating during charge-discharge cycles in the secondary battery, and resulting in good kinetic performance of the secondary battery.

[0054] This application does not impose any particular restrictions on the method of controlling the porosity of porous substrates, as long as the purpose of this application can be achieved. For example, it can be achieved by controlling the biaxial stretching ratio during the preparation process of the porous substrate.

[0055] In some embodiments of this application, the thickness of the porous substrate is from 9 μm to 24 μm. For example, the thickness of the porous substrate is 9 μm, 12 μm, 14 μm, 17 μm, 20 μm, 21 μm, 22 μm, 24 μm, or any value between any two of the above ranges. As shown in FIG1, the thickness of the porous substrate 41 is expressed as T 41 As shown. By controlling the thickness of the porous substrate within the aforementioned range, the porous substrate possesses sufficient tensile strength. When the adhesive slurry is coated onto the surface of the porous substrate, the flow of the adhesive slurry can be slowed down, reducing the probability of adhesive agglomeration and resulting in uneven adhesive layer. This reduces the probability of increased local impedance, decreases the occurrence of lithium plating at the interface during charge-discharge cycles of the secondary battery, and improves the kinetic performance of the secondary battery. It also reduces the energy density loss caused by excessive thickness of the porous substrate, resulting in a higher energy density for the secondary battery.

[0056] In some embodiments of this application, the thickness of the porous substrate is from 12 μm to 16 μm. For example, the thickness of the porous substrate is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or any value between any two of the above ranges. As shown in FIG1, the thickness of the porous substrate 41 is expressed as T 41 As shown, controlling the thickness of the porous substrate within the aforementioned range helps to further reduce the probability of adhesive layer agglomeration leading to uneven adhesive layer, and also helps to further reduce the energy density loss of the secondary battery caused by excessive porous substrate thickness. This results in the secondary battery having good kinetic performance and high energy density.

[0057] This application does not impose any particular limitation on the material of the porous substrate, as long as it can achieve the purpose of this application. For example, the materials of the porous substrate include, but are not limited to, at least one of polypropylene, low-density polyethylene, polyethylene terephthalate, polytetrafluoroethylene, microporous polyolefin, cellulose membrane or nonwoven fabric.

[0058] In some embodiments of this application, the thickness of the adhesive layer is from 2 μm to 6 μm. For example, the thickness of the adhesive layer is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or any value between any two of the above ranges. As shown in Figure 1, the thickness of the adhesive layer 42 is expressed as T 42 As shown. Controlling the thickness of the adhesive layer within the above range is beneficial for the adhesive paper to have good adhesion, reduces the probability of the adhesive layer falling off during the winding process, and also helps to reduce the energy density loss of the secondary battery caused by excessive adhesive layer thickness, thereby enabling the secondary battery to have a higher energy density.

[0059] In some embodiments of this application, the thickness of the adhesive layer is from 3 μm to 5 μm. For example, the thickness of the adhesive layer is 3 μm, 4 μm, 5 μm, or any value between any two of the above ranges. As shown in Figure 1, the thickness of the adhesive layer 42 is expressed as T42 As shown. Controlling the thickness of the adhesive layer within the above range is beneficial for the adhesive paper to have good adhesion, reduces the probability of the adhesive layer falling off during the winding process, and also helps to reduce the energy density loss of the secondary battery caused by excessive adhesive layer thickness, thereby enabling the secondary battery to have a higher energy density.

[0060] This application does not impose any particular limitation on the thickness of the adhesive tape, as long as it achieves the purpose of this application. For example, the thickness of the adhesive tape can be from 11 μm to 36 μm.

[0061] In some embodiments of this application, the inert material includes at least one of boehmite, gibbsite, halloysite, or silica sand. In some embodiments, the first and second inert materials each independently include at least one of boehmite, gibbsite, halloysite, or silica sand. In some embodiments, the first and second inert materials are the same type. In other embodiments, the first and second inert materials are different types. Using the above-mentioned types of inert materials is beneficial for giving the adhesive tape better air permeability and higher strength. This reduces the probability of interface lithium plating during charge-discharge cycles, thus giving the secondary battery good kinetic performance. The probability of the adhesive tape being punctured by particles or burrs on the surface of the positive or negative electrode is also lower, thus giving the secondary battery good safety performance.

[0062] In some embodiments of this application, the adhesive layer includes at least one selected from polymethyl methacrylate, polyacrylic acid (PAA), ethylene-acrylic acid copolymer (EAA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyimide (PI), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), polyurethane, or epoxy resin. Selecting the above-mentioned types of adhesive layer materials is beneficial for achieving better adhesion of the adhesive layer and improving the bonding properties of the adhesive tape.

[0063] This application does not impose any particular limitation on the weight-average molecular weight of the above-mentioned adhesive layer, as long as the purpose of this application can be achieved.

[0064] For ease of understanding, it is defined that, in the unfolded state of the positive electrode sheet, the length direction of the positive electrode sheet is the same as the transverse direction (Y) of the adhesive paper, the width direction of the positive electrode sheet is the same as the longitudinal direction (X) of the adhesive paper, and the thickness direction of the positive electrode sheet is the same as the thickness direction (Z) of the adhesive paper. It can be understood that, in the unfolded state of the positive electrode sheet, negative electrode sheet, and separator, the length, width, and thickness directions of the positive current collector, positive active material layer, negative electrode sheet, and separator are the same as those of the positive electrode sheet.

[0065] In some embodiments of this application, the positive electrode includes a positive active material layer and a positive current collector. The positive current collector includes a first surface and a second surface opposite to each other. The positive active material layer is at least disposed on the first surface of the positive current collector. A first groove is provided in the positive active material layer to expose the positive current collector. A positive electrode tab is disposed in the first groove and connected to the positive current collector. The second surface includes a first empty foil area opposite to the first groove. Adhesive tape is pasted on at least one of the following: the surface of the positive electrode tab, the first empty foil area, the surface of the negative electrode adjacent to the first groove, the surface of the negative electrode adjacent to the first empty foil area, or the end area of ​​the positive electrode. The phrase "the positive active material layer is at least disposed on the first surface of the positive current collector" means that in some embodiments, the positive active material layer is disposed on the first surface of the positive current collector; in other embodiments, the positive active material layer is disposed on both the first and second surfaces of the positive current collector. The "first surface" and the "second surface" can be part or all of the surfaces of the positive current collector. It should be noted that the negative electrode in the "negative electrode surface adjacent to the first groove" and the negative electrode in the "negative electrode surface adjacent to the first empty foil area" are not the same layer of negative electrode. They are two layers of negative electrode adjacent to the positive electrode respectively. The above-mentioned "two layers of negative electrode" can be two negative electrode or two layers formed by winding one negative electrode. As shown in Figure 3, the separator 30 is located between the positive electrode 10 and the negative electrode 20. The positive electrode 10 includes a positive current collector 11, a positive active material layer 12, and a positive electrode tab 13. The positive current collector 11 includes a first surface 11a and a second surface 11b opposite to each other along its thickness direction Z. The positive active material layer 12 is disposed on the first surface 11a of the positive current collector 11 and also on the second surface 11b of the positive current collector 11. The positive active material layer 12 disposed on the first surface 11a has a first groove 15 exposing the positive current collector 11. The positive electrode tab 13 is disposed in the first groove 15 and connected to the positive current collector 11. The second surface 11b includes a first empty foil area 16 opposite to the first groove 15. Adhesive tape 40 is respectively attached to the surface of the positive electrode tab 13, the first empty foil area 16, the surface of the negative electrode 20 adjacent to the first groove 15, the surface of the negative electrode 20 adjacent to the first empty foil area 16, and the ending area of ​​the positive electrode 10. Normally, along the length Y of the positive electrode 10, the length of the adhesive tape 40 attached to the surface of the positive electrode tab 13 and the first empty foil area 16 is greater than the length of the adhesive tape 40 attached to the surface of the negative electrode 20 adjacent to the first groove 15 and the surface of the negative electrode 20 adjacent to the first empty foil area 16.Applying adhesive tape to the surface of the positive electrode tab and the surface of the negative electrode sheet adjacent to the first groove can reduce the probability of burrs on the positive electrode tab penetrating the negative electrode active material layer and contacting the negative electrode current collector, thus causing a short circuit. In the area of ​​the positive electrode active material layer covered by the adhesive tape on the surface of the positive electrode tab, lithium ions can be normally extracted and then normally embedded in the corresponding negative electrode active material layer, thereby reducing capacity waste and the probability of lithium plating. Applying adhesive tape to the first empty foil area and the surface of the negative electrode sheet adjacent to the first empty foil area can reduce the probability of burrs in the first empty foil area penetrating the negative electrode active material layer and contacting the negative electrode current collector, thus causing a short circuit. In the area of ​​the first empty foil area covered by the adhesive tape on the positive electrode active material layer, lithium ions can be normally extracted and then normally embedded in the corresponding negative electrode active material layer, thereby reducing capacity waste and the probability of lithium plating. Applying adhesive tape to the end area of ​​the positive electrode sheet can reduce the probability of the positive electrode current collector contacting the negative electrode sheet. Therefore, by attaching adhesive tape to the above-mentioned different locations, lithium ions in the area covered by the adhesive tape can freely move around to exert the capacity of the active material. It can also reduce the risk of short circuit caused by positive and negative electrode contact and the probability of lithium plating, thereby giving the secondary battery high energy density and good safety and kinetic performance.

[0066] In some embodiments of this application, the negative electrode sheet includes a negative current collector, a negative active material layer, and a negative electrode tab. The negative current collector includes a third surface and a fourth surface opposite to each other. The negative active material layer is disposed at least on the third surface of the negative current collector. A second groove is provided in the negative active material layer to expose the negative current collector. The negative electrode tab is disposed in the second groove and connected to the negative current collector. The fourth surface includes a second empty foil area opposite to the second groove. Adhesive tape is pasted on at least one part of the negative electrode tab surface or the second empty foil area. The above-mentioned "the negative active material layer is disposed at least on the third surface of the negative current collector" means that in some embodiments, the negative active material layer is disposed on the third surface of the negative current collector, and in other embodiments, the negative active material layer is disposed on both the third and fourth surfaces of the negative current collector. As shown in Figure 4, the separator 30 is located between the positive electrode 10 and the negative electrode 20. The negative electrode 20 includes a negative current collector 21, a negative active material layer 22, and a negative electrode tab 23. The negative current collector 21 includes a third surface 21c and a fourth surface 21d opposite each other along its thickness direction Z. The negative active material layer 22 is disposed on the third surface 21c and the fourth surface 21d of the negative current collector 21. A second groove 25 is provided in the negative active material layer 22 located on the third surface 21c, exposing the negative current collector 21. The negative electrode tab 23 is disposed in the second groove 25 and connected to the negative current collector 21. The fourth surface 21d includes a second empty foil area 26 opposite to the second groove 25. Adhesive tape 40 is pasted on the surface of the negative electrode tab 23 and the second empty foil area 26. Non-ion-conducting adhesive tape 50 is pasted on the surface of the positive electrode 10 adjacent to the second groove 25 and the surface of the positive electrode 10 adjacent to the second empty foil area 26. Applying adhesive tape to the surface of the negative electrode tab and the second empty foil area allows lithium ions to be embedded in the negative electrode active material layer covered by the adhesive tape, increasing the lithium ion embedding sites and the capacity of the negative electrode active material layer, thereby giving the secondary battery a higher energy density.

[0067] This application does not impose any particular restrictions on the type of non-ion-conducting adhesive paper. Any non-ion-conducting adhesive paper known in the art can be selected as needed, as long as it can achieve the purpose of this application.

[0068] This application does not impose any particular restriction on the material of the positive electrode tab, as long as it achieves the purpose of this application. For example, the material of the positive electrode tab includes at least one of aluminum (Al) or aluminum alloy. This application does not impose any particular restriction on the material of the negative electrode tab, as long as it achieves the purpose of this application. For example, the material of the negative electrode tab includes at least one of nickel (Ni), copper (Cu), or copper plated with nickel (Ni-Cu).

[0069] This application does not impose any particular limitation on the type of positive electrode current collector, as long as it achieves the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, etc. This application does not impose any particular limitation on the positive electrode active material layer, as long as it achieves the purpose of this application. In one embodiment of this application, the positive electrode active material layer includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. Optionally, the positive electrode active material layer may also include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode conductive agent and positive electrode binder in the positive electrode active material layer, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the mass ratio of positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode active material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the positive electrode active material layer can be 30 μm to 120 μm.

[0070] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam, etc. This application does not impose any particular limitation on the negative electrode active material layer, as long as it can achieve the purpose of this application. In one embodiment of this application, the negative electrode active material layer includes a negative electrode active material. This application does not impose any particular limitation on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, tin-based materials, silicon-based materials, lithium titanate, transition metal nitrides, or natural flake graphite, etc. Optionally, the negative electrode active material layer may also include at least one of a negative electrode conductive agent, a thickener, and a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents, thickeners, and negative electrode binders in the negative electrode active material layer, as long as they can achieve the purpose of this application. This application does not impose any particular limitation on the mass ratio of negative electrode active material, negative electrode conductive agent, thickener, and negative electrode binder in the negative electrode active material layer, as long as the purpose of this application is achieved. This application also does not impose any particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the negative electrode current collector can be 5 μm to 20 μm, and the thickness of the negative electrode active material layer can be 30 μm to 120 μm.

[0071] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may 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 diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0072] The secondary battery of this application also includes a packaging bag and an electrolyte. The adhesive layer, positive electrode, negative electrode, separator, and electrolyte are contained in the packaging bag. This application does not impose any particular restrictions on the packaging bag and electrolyte; any packaging bag and electrolyte known in this application may be selected according to actual needs, as long as the purpose of this application can be achieved.

[0073] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0074] This application does not impose any particular limitation on the preparation method of the adhesive layer, as long as it can achieve the purpose of this application. For example, the preparation method of the adhesive layer includes, but is not limited to, the following steps: (1) mixing an inert substance and an adhesive layer binder, adding a solvent, and stirring evenly to obtain an adhesive layer slurry; (2) coating the adhesive layer slurry onto the surface of a release film using a micro-grooved roller, during which the slurry forms a film and shrinks, finally forming a porous adhesive layer, after which the adhesive layer is laminated with a porous substrate, a release agent is placed on the surface of the porous substrate away from the adhesive layer, and after drying, the adhesive layer is obtained, wound up, slit, and ready for use. This application does not impose any particular limitation on the solid content of the adhesive layer slurry, as long as it can achieve the purpose of this application. For example, the solid content of the adhesive layer slurry is 10wt% to 30wt%. This application does not impose any particular limitation on the type of "solvent" mentioned above, as long as it can achieve the purpose of this application. This application does not impose any particular limitation on the drying and drying temperature in step (2) above, as long as it can achieve the purpose of this application. This application does not impose any particular restrictions on the release film and release agent mentioned above. Those skilled in the art can select any known release film and release agent according to the actual situation, as long as the purpose of this application can be achieved.

[0075] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the separator, positive electrode, separator and negative electrode in sequence, and then attaching adhesive tape, and then winding, folding or other operations as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery; or, stacking the separator, positive electrode, separator and negative electrode in sequence, and then attaching adhesive tape, fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0076] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device exhibits good performance.

[0077] There are no particular limitations on the electronic devices covered by this application, which may include, but are not limited to, the following: laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0078] Example

[0079] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0080] Test methods and equipment:

[0081] Method for extracting porous substrates from lithium-ion batteries:

[0082] The lithium-ion battery was disassembled in an environment with room temperature and humidity less than 20%. After separating the positive electrode, separator, and negative electrode, the adhesive tape was peeled off with tweezers. If the adhesive tape was located between the negative electrode and the separator, it was peeled off and then placed in a mixed solvent of toluene and ethyl acetate (mass ratio of toluene to ethyl acetate 7:3) and water, respectively. After stirring at 50°C for 20 minutes, it was removed and dried at 100°C for 2 hours until no solution remained, thus obtaining a porous substrate. If the adhesive tape was located on the positive electrode and between the separator, it was peeled off and placed in N-methylpyrrolidone (NMP). After stirring at 50°C for 20 minutes, it was removed and dried at 100°C for 2 hours until no solution remained, thus obtaining a porous substrate.

[0083] Thickness testing:

[0084] (1) Adhesive tape thickness T 40 The test:

[0085] Remove the positive and negative electrode plates from the lithium-ion battery and measure the thickness T of the adhesive tape at the electrode plate using a micrometer. 总 Thickness T of the area without adhesive tape 极片 Adhesive tape thickness T 40 =T 总 -T 极片 .

[0086] (2) Thickness T of porous substrate 41 The test:

[0087] The thickness of the porous substrate sample was randomly measured at 6 locations using a micrometer screw gauge, and the average value was calculated to obtain the thickness T of the porous substrate. 41 .

[0088] (3) Adhesive layer thickness T 42 The test:

[0089] Based on the aforementioned adhesive tape thickness T 40 and the thickness T of the porous substrate 41 The thickness T of the adhesive layer was calculated. 42 :T 42 =T 40 -T 41 .

[0090] Testing the average pore size of porous substrates:

[0091] A porous substrate sample was taken, and scanning electron microscope (SEM) images were captured at an accelerating voltage (EHT) of 3 kV and a magnification of 10,000. Using imageJ software, five different regions of 10 μm × 10 μm were randomly selected, and the pore size was measured. The average value was taken as the median pore size, which is the average pore size.

[0092] Tests of particle size, average particle size, and the ratio of inert particles:

[0093] Take a sample of adhesive tape and take a SEM image of the adhesive layer at EHT=3kV and magnification of 10000x. Using ImageJ software, randomly select five different regions of 10μm×10μm size and count the number of particles of different sizes to obtain the ratio of the number of particles of the first inert material and the second inert material. At the same time, select 50 large inert material particles and 50 small inert material particles respectively, measure the maximum circumscribed circle diameter of their outer contours, and take the average value as the average particle size.

[0094] Test of the air permeability of adhesive tape:

[0095] Cut the adhesive paper sample to a size of 50mm×50mm, place it on the air permeability tester, press the start button, and the test will be completed after five seconds, automatically displaying the air permeability value; perform 5 repeated experiments for each sample, and take the average value as the air permeability of the adhesive paper of this application.

[0096] Testing the porosity of porous substrates:

[0097] The porosity φ of the porous substrate is calculated using the following formula: φ = [1 - m(s × h × ρ)] × 100%. Where m is the mass of the porous substrate sample, s is the area of ​​the porous substrate sample, h is the thickness of the porous substrate sample, and ρ is the density of the porous substrate material.

[0098] Lithium plating test:

[0099] The lithium-ion battery was charged at a low temperature (12℃) at a rate of 1.5C to the set voltage of 4.45V, and then discharged at 1.5C to 3V. After 10 cycles, the lithium-ion battery was disassembled and the surface of the electrode at the adhesive tape position on the positive electrode tab was observed to see if silvery-white lithium metal appeared. Based on the total area of ​​the adhesive tape, the lithium plating area was less than 1% and considered no lithium plating, 1% to 5% and considered slight lithium plating, 5% to 10% and considered moderate lithium plating, and more than 10% and considered severe lithium plating.

[0100] The degree of lithium plating is used to characterize the kinetic performance of lithium-ion batteries. The more severe the lithium plating (i.e., the larger the lithium plating area), the worse the kinetic performance of the lithium-ion battery; the less severe the lithium plating (i.e., the smaller the lithium plating area), the better the kinetic performance of the lithium-ion battery.

[0101] Energy density (ED) testing:

[0102] Taking the labeling on the outer packaging of lithium-ion batteries as an example, when the voltage range marked on the outer packaging of the battery is 3.0V to 4.45V, the charging cut-off voltage is 4.45V and the discharging cut-off voltage is 3.0V.

[0103] In both the comparative and example cases at 25°C, the voltage was directly charged to 4.45V at 0.2C, then charged at a constant voltage of 4.45V to a full charge of 0.025C, and finally discharged to 3.0V at a current of 0.2C. This process was repeated three times, and the average capacity was taken as the actual capacity.

[0104] ED = Actual capacity × Discharge plateau / (volume of lithium-ion battery).

[0105] Adhesion strength test:

[0106] The adhesion between the adhesive tape and the negative electrode sheet was tested using a 180° peel test. Adhesive tape and a negative electrode sheet of 100mm to 300mm in length were taken and cut into samples measuring 54.2mm × 72.5mm. The cut adhesive tape and negative electrode sheet were neatly stacked, and the stacked samples were placed in a flatbed press with a pressure of 2kg to bond the adhesive tape and negative electrode sheet together. Using a die and a punch, the samples were cut into strips of 72.5mm × 15mm to separate the adhesive tape and negative electrode sheet. A 15mm wide A4 sheet was used to attach the samples, and wrinkle adhesive was applied to both sides of the joint to complete the sample preparation. The high-speed rail tensile testing machine was turned on and set sequentially as follows: adhesion test, speed 50mm / min, initial clamp spacing 40mm. "Start" was clicked to perform a pre-stretch of ~5mm. After the pre-stretch, the force and displacement were reset to zero, and the test began. At least 5 samples were measured in each group. The average value is taken as the final adhesive force value.

[0107] Adhesive strength is used to characterize the probability of the adhesive layer falling off during the winding process of the adhesive tape. The greater the adhesive strength, the lower the probability of the adhesive layer falling off during the winding process; the lower the adhesive strength, the higher the probability of the adhesive layer falling off during the winding process.

[0108] Example 1-1

[0109] <Preparation of Adhesive Tape>

[0110] Inert boehmite and polymethyl methacrylate (Mw = 86W), a binder for the adhesive layer, were mixed, and ethyl acetate was added as a solvent. The mixture was stirred until homogeneous to obtain an adhesive layer slurry with a solid content of 20 wt%. The mass ratio of the inert material to the binder was 1:1. The inert material consisted of a first inert material with a particle size d1 satisfying 300 < d1 ≤ 900 nm and a second inert material with a particle size d2 satisfying 50 ≤ d2 ≤ 300 nm. The average particle size of the first inert material was D1 = 600 nm, and the average particle size of the second inert material was D2 = 140 nm. The particle size ratio of the first inert material to the second inert material was 3:2.

[0111] The above-mentioned adhesive slurry was applied to the surface of a polyethylene terephthalate (PET) release film with a release force of 10g using a micro-grooving roller. After drying at 110°C, a film with a thickness of T was formed.42 =3μm adhesive layer, and then at the winding point, the adhesive layer is bonded to the porous substrate (thickness T) 41 =14μm, 45% porosity biaxially oriented polypropylene (BOPP film) (manufacturer: Dalian Yike Energy Technology Co., Ltd., model: ECO-9) is laminated, the adhesive layer is transferred to the surface of the porous substrate, and the product is wound up to obtain an intermediate product with release film and porous substrate; the porous substrate side (opposite side of adhesive layer) of the intermediate product is coated with silicone release agent (manufacturer: Dow Corning) using a micro-grooving roller, and after drying, the release film is removed while the porous substrate is wound up to obtain a thickness T 40 =17μm adhesive tape.

[0112] <Preparation of the positive electrode>

[0113] Lithium cobalt oxide (CCO), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) (a binder) were mixed in a mass ratio of 95.5:2.5:2.0. NMP was added as a solvent, and the mixture was stirred under vacuum until a homogeneous CCO slurry with a solid content of 72 wt% was obtained. The CCO slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 85°C to obtain a single-sided CCO electrode sheet with a 50 μm thick active material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided CCO electrode sheet. After cold pressing, cutting, and welding of CCO tabs, a 70 mm × 1400 mm CCO electrode sheet was obtained for later use.

[0114] <Preparation of Negative Electrode Sheets>

[0115] Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (negative electrode thickener), and styrene-butadiene rubber (negative electrode binder) were mixed in a mass ratio of 98.2:0.8:1.0. Deionized water was then added as a solvent, and the mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 42 wt% was obtained. The negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer (60 μm thick). The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After cold pressing, cutting, and welding of negative electrode tabs (nickel tabs), a negative electrode sheet with dimensions of 74 mm × 1408 mm was obtained for later use.

[0116] <Preparation of the diaphragm>

[0117] The diaphragm base membrane is 8μm thick polyethylene (PE). A 2μm thick alumina ceramic layer is coated on each of the two surfaces of the base membrane along its thickness direction. Finally, a 2.5mg / cm² coating is applied to each of the two surfaces of the ceramic layer along its thickness direction.2 The PVDF binder is dried to obtain the diaphragm.

[0118] <Preparation of Electrolyte>

[0119] In an environment with a water content of less than 10 ppm, a basic electrolyte was prepared by mixing non-aqueous organic solvents propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:0.5:1. Lithium hexafluorophosphate (LiPF6) was then added and mixed evenly to obtain the electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0120] <Preparation of Lithium-ion Batteries>

[0121] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to obtain a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.

[0122] As shown in Figure 3, adhesive tape 40 is attached to the surface of the positive electrode tab 13, the first empty foil area 16, the surface of the negative electrode 20 adjacent to the first groove 15, the surface of the negative electrode 20 adjacent to the first empty foil area 16, and the tail area of ​​the positive electrode 10; as shown in Figure 4, adhesive tape 40 is attached to the surface of the negative electrode tab 23 and the second empty foil area 26, and non-ion-conducting adhesive tape 50 (manufacturer: Top Chemical (Shanghai) Co., Ltd., model: T4116BR) is attached to the surface of the positive electrode tab 23 and the second empty foil area 26.

[0123] Examples 1-2 to Examples 1-16

[0124] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0125] Examples 2-1 to 2-11

[0126] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0127] Examples 3-1 to 3-16

[0128] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0129] Comparative Examples 1 to 8

[0130] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0131] The preparation parameters and performance data of each embodiment and comparative example are shown in Tables 1 to 3.

[0132] Table 1

[0133] Note: "\" in Table 1 indicates no corresponding parameter; "A" in Table 1 indicates the ratio of the number of particles of the first inert substance and the second inert substance.

[0134] As can be seen from Examples 1-1 to 1-13 and Comparative Examples 1 to 8, the secondary battery of this application, by selecting adhesive paper in which both larger particles of the first inert material and smaller particles of the second inert material are added to the adhesive layer, and by controlling the average particle size of the first inert material and the ratio of the number of particles of the first inert material and the second inert material within the range of this application, results in a less severe lithium plating at the interface of the secondary battery, a higher energy density, and greater adhesive strength of the adhesive paper. This indicates that the secondary battery of this application can achieve both high kinetic performance, high energy density, and a low probability of delamination during winding. In contrast, the comparative secondary battery only contains larger particles of the first inert material or smaller particles of the second inert material in the adhesive layer. At least one of the average particle size of the first inert material, the average particle size of the second inert material, or the ratio of the number of particles of the first inert material and the second inert material is not within the scope of this application. The comparative secondary battery has more severe interfacial lithium plating, or the adhesive paper has lower adhesion, or the secondary battery has lower energy density. This indicates that the comparative secondary battery cannot simultaneously achieve high kinetic performance, energy density, and low probability of delamination during winding.

[0135] The average particle size D1 of the first inert material, the average particle size D2 of the second inert material, and their ratio D2 / D1 typically affect the kinetic performance, energy density, and roll-off probability of a secondary battery. As can be seen from Examples 1-1 to 1-10 and Comparative Examples 1 to 4, secondary batteries using average particle sizes D1 of the first inert material, D2 of the second inert material, and their ratio D2 / D1 within the range of this application exhibit less interface lithium plating, higher energy density, and stronger adhesive strength, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0136] The ratio of the number of particles of the first inert material to the number of particles of the second inert material typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. As can be seen from Examples 1-1, 1-11 to 1-13, Comparative Example 5, and Comparative Example 6, secondary batteries using a particle ratio of the first inert material to the second inert material within the range of this application exhibit less interface lithium plating, higher energy density, and stronger adhesive strength, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0137] The average pore size P of the porous substrate and the ratio P / D2 between the average pore size of the porous substrate and the average particle size of the second inert material typically affect the kinetic performance, energy density, and roll-off probability of the secondary battery. As can be seen from Examples 1-1, 1-5 to 1-7, and 1-14 to 1-16, selecting a secondary battery with an average pore size P of the porous substrate and a ratio P / D2 between the average pore size of the porous substrate and the average particle size of the second inert material within the range of this application is beneficial for controlling the specific surface area of ​​the porous substrate within a suitable range, increasing the adhesion ability of particles to the porous substrate, improving the bonding effect between the porous substrate and the adhesive layer, resulting in less interfacial lithium plating, higher energy density, and higher adhesive strength of the adhesive tape. This indicates that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0138] Table 2

[0139] The mass ratio of inert material to adhesive layer typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. As can be seen from Examples 1-1, 2-1 to 2-6, secondary batteries using inert material and adhesive layer masses within the range of this application exhibit less interfacial lithium plating, higher energy density, and stronger adhesive adhesion, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0140] The type of inert material typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. Examples 1-1, 2-7, and 2-8 demonstrate that secondary batteries using inert materials within the scope of this application exhibit less interface lithium plating, higher energy density, and stronger adhesive strength, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0141] The type of adhesive layer typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. Examples 1-1, 2-9 to 2-11 show that secondary batteries using adhesive layers within the scope of this application exhibit less interface lithium plating, higher energy density, and stronger adhesive adhesion, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0142] Table 3

[0143] The porosity of porous substrates typically affects the kinetic performance, energy density, and roll-off probability of secondary batteries. As can be seen from Examples 1-1, 3-1 to 3-4, secondary batteries using porous substrates with porosity within the range of this application are beneficial for maintaining the air permeability of the adhesive tape within a suitable range, reducing the likelihood of interface problems, exhibiting less lithium plating at the interface, higher energy density, and stronger adhesive tape adhesion. This indicates that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0144] The thickness of the porous substrate typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. Examples 1-1, 3-5 to 3-10 show that secondary batteries with porous substrate thicknesses within the range of this application exhibit less interface lithium plating, higher energy density, and stronger adhesive strength, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0145] The thickness of the adhesive layer typically affects the kinetic performance, energy density, and roll-off probability of a secondary battery. As can be seen from Examples 1-1, 3-11 to 3-16, selecting a secondary battery with an adhesive layer thickness within the range of this application is beneficial for maintaining the air permeability of the adhesive paper within a suitable range, while also maintaining good bonding strength. This results in less interfacial lithium plating, higher energy density, and higher adhesive adhesion, indicating that the secondary battery can achieve a balance between good kinetic performance, high energy density, and low roll-off probability.

[0146] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0147] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0148] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising adhesive tape, a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive electrode tab, the adhesive tape is located between the separator and the positive electrode tab, and the adhesive tape includes a porous substrate and an adhesive layer disposed on at least one surface of the porous substrate; wherein, The adhesive layer includes an inert material, which includes a first inert material and a second inert material. The particle size of the first inert material is d1 nm, and the particle size of the second inert material is d2 nm, and 300 < d1 ≤ 900, 50 ≤ d2 ≤ 300. The average particle size of the first inert material is D1 nm, the average particle size of the second inert material is D2 nm, and 400≤D1≤800, 100≤D2≤200; In any region of the adhesive layer surface, the ratio of the number of particles of the first inert material to the number of particles of the second inert material is 3:7 to 7:

3.

2. The secondary battery according to claim 1, wherein, 1 / 7≤D2 / D1≤1 / 3.

3. The secondary battery according to claim 1, wherein, The average pore size of the porous substrate is P nm; D2 and P satisfy the following relationship: 0.5≤P / D2≤1.

4. The secondary battery according to claim 3, wherein, 50≤P≤200。 5. The secondary battery according to claim 1, wherein, The adhesive layer includes an adhesive layer binder, wherein the mass ratio of the inert substance to the adhesive layer binder is 3:7 to 7:

3.

6. The secondary battery according to claim 5, wherein, The air permeability of the adhesive paper is from 180s / 100mL to 600s / 100mL.

7. The secondary battery according to any one of claims 1 to 6, wherein, The porosity of the porous substrate is 25% to 55%.

8. The secondary battery according to claim 5, wherein, The thickness of the porous substrate is 9 μm to 24 μm.

9. The secondary battery according to claim 8, wherein, The thickness of the adhesive layer is 2 μm to 6 μm.

10. The secondary battery according to claim 9, wherein, The secondary battery satisfies at least one of the following characteristics: (1) The ratio of the number of particles of the first inert material to the number of particles of the second inert material is 1:1 to 7:3; (2) 1 / 5 ≤ D2 / D1 ≤ 1 / 3; (3) The mass ratio of the inert substance to the adhesive layer is 1:2 to 7:3; (4) The thickness of the porous substrate is 12 μm to 16 μm; (5) The thickness of the adhesive layer is 3 μm to 5 μm.

11. The secondary battery according to any one of claims 1 to 6, wherein, The inert material includes at least one of boehmite, diaspore, halloysite, or quartz sand.

12. The secondary battery according to any one of claims 1 to 6, wherein, The adhesive layer comprises at least one of polymethyl acrylate, polyacrylic acid, ethylene-acrylic acid copolymer, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyurethane, or epoxy resin.

13. The secondary battery according to any one of claims 1 to 6, wherein, The positive electrode sheet includes a positive active material layer and a positive current collector. The positive current collector includes a first surface and a second surface opposite to each other. The positive active material layer is at least disposed on the first surface of the positive current collector. A first groove is disposed in the positive active material layer to expose the positive current collector. The positive electrode tab is disposed in the first groove and connected to the positive current collector. The second surface includes a first empty foil area opposite to the first groove. The adhesive tape is pasted on at least one of the following: the surface of the positive electrode tab, the first empty foil area, the surface of the negative electrode adjacent to the first groove, the surface of the negative electrode adjacent to the first empty foil area, or the end area of ​​the positive electrode.

14. The secondary battery according to any one of claims 1 to 6, wherein, The negative electrode sheet includes a negative electrode current collector, a negative electrode active material layer, and a negative electrode tab. The negative electrode current collector includes a third surface and a fourth surface opposite to each other. The negative electrode active material layer is at least disposed on the third surface of the negative electrode current collector. A second groove is disposed in the negative electrode active material layer that exposes the negative electrode current collector. The negative electrode tab is disposed in the second groove and connected to the negative electrode current collector. The fourth surface includes a second empty foil area opposite to the second groove. The adhesive tape is affixed to at least one location on the surface of the negative electrode tab or in the second empty foil area.

15. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 14.

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