Aluminum laminate film and lithium ion secondary battery comprising the same

Abstract

This application relates to the field of battery materials and discloses an aluminum-plastic film and a lithium-ion secondary battery comprising the same. The aluminum-plastic film provided in this application includes a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together. The substrate layer includes a nylon layer and a thermally conductive layer, with the thermally conductive layer disposed between the aluminum foil layer and the nylon layer. By adding a thermally conductive layer between the nylon layer and the aluminum foil layer of the aluminum-plastic film, and utilizing the excellent thermal conductivity of the thermally conductive layer, the heat generated by the battery can be quickly conducted from the interior of the aluminum-plastic film to the exterior for heat dissipation, significantly improving the thermal safety of the battery. The lithium-ion secondary battery of this application has the advantages of good electrical performance and high thermal safety.

Description

Technical Field

[0001] This application relates to the field of battery materials, specifically to an aluminum-plastic film and a lithium-ion secondary battery containing the same. Background Technology

[0002] Currently, lithium-ion rechargeable batteries may experience thermal runaway during thermal and electrical abuse. Related technical reports suggest that the thermal safety performance of lithium-ion rechargeable batteries can be improved by doping and coating the cathode material, reducing the thermal shrinkage rate of the separator, increasing the separator thickness, or optimizing the electrolyte composition. However, these improvements result in a loss of energy density, leading to a deterioration in electrical performance. Therefore, how to improve the thermal safety performance of batteries without compromising electrical performance is a pressing technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0003] This application provides an aluminum-plastic film, which aims to address, to some extent, the problem that existing lithium-ion secondary batteries cannot simultaneously achieve both electrical performance and thermal safety.

[0004] This application also provides a lithium-ion secondary battery comprising the aforementioned aluminum-plastic film.

[0005] In a first aspect, this application provides an aluminum-plastic film, comprising a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together, wherein the substrate layer comprises a nylon layer and a thermally conductive layer, and the thermally conductive layer is disposed between the aluminum foil layer and the nylon layer.

[0006] In one alternative embodiment, the thickness L of the thermally conductive layer S With respect to the thickness L of the nylon layer NL The following condition must be met: 18 ≥ L NL / L S >1, where L S The range is 3μm-20μm, L NL The range is 4μm-55μm.

[0007] In one optional embodiment, the adhesion force F between the thermally conductive layer and the nylon layer is 80 N / m to 150 N / m.

[0008] In one optional embodiment, the thermally conductive layer comprises a thermally conductive material with a particle size Dv50. S With L S Satisfy: 300≥Ls / Dv50 S ≥3, where Dv50 S The range is 0.1μm-5μm.

[0009] In one optional embodiment, the particle size of the thermally conductive material is Dv50. S With L SSatisfy: 30≥Ls / Dv50 S ≥5.

[0010] In one optional embodiment, the particle size Dv99 of the thermally conductive material is 3μm-15μm.

[0011] In one optional embodiment, the thermally conductive material includes at least one of alumina, magnesium oxide, graphite, carbon black, graphene, silver particles, and copper particles.

[0012] In one alternative embodiment, the thickness L of the substrate layer J With respect to the thickness L of the aluminum foil layer Al The thickness L of the heat-sealing layer PP and the total thickness L of the aluminum-plastic film 总 The following relationship is satisfied between them: 0.75*L 总 ≥L J ≥0.5*(L Al +L PP ), where L 总 80μm-120μm, L J 5μm-60μm, L Al The range is 20μm-80μm, L PP The range is 5μm-40μm.

[0013] In one optional embodiment, the tensile strength TS of the aluminum-plastic film is 45MPa-200MPa.

[0014] In one optional embodiment, the tensile strength TS of the aluminum-plastic film is 80MPa-160MPa.

[0015] In one optional embodiment, the elongation E of the aluminum-plastic film is 35%-100%.

[0016] In one optional embodiment, the elongation E of the aluminum-plastic film is 60%-85%.

[0017] In one optional embodiment, the thermal conductivity K of the aluminum-plastic film is 0.5 W·m. -1 ·K -1 -5W·m -1 ·K -1 .

[0018] In one optional embodiment, the thermal conductivity K of the aluminum-plastic film is 1 W·m. -1 ·K -1 -4W·m -1 ·K -1 .

[0019] Secondly, this application provides a lithium-ion secondary battery, including a battery cell and an aluminum-plastic film, wherein the aluminum-plastic film is wrapped around the outside of the battery cell; the aluminum-plastic film is the aluminum-plastic film described in the first aspect of this application, and the substrate layer in the aluminum-plastic film is disposed away from the battery cell.

[0020] In one optional embodiment, the battery further includes an electrolyte comprising a carboxylic acid ester solvent; the mass percentage of the carboxylic acid ester solvent is M% based on the weight of the electrolyte, wherein the value of M satisfies: 1.5 ≥ M / L NL ≥0.01, and / or, 20 ≥ M / L S ≥0.05; L NL L represents the thickness of the nylon layer, in μm. S The thickness of the thermally conductive layer is expressed in μm.

[0021] In one alternative implementation, M takes the value 0.1-40.

[0022] In one optional embodiment, the carboxylic acid ester solvent includes at least one of methyl formate, ethyl acetate, ethyl propionate, methyl acetate, methyl butyrate, methyl propyl carbonate, propyl propionate, ethyl butyrate, methyl fluoroformate, ethyl difluoroacetate, ethyl 2-fluoropropionate, methyl fluoroacetate, methyl 4-fluorobutyrate, propyl 2-fluoropropionate, and ethyl 4-fluorobutyrate.

[0023] In one optional embodiment, the battery cell includes a negative electrode, the negative electrode including a negative electrode active material layer, the negative electrode active material layer including graphite, the graphite having a particle size Dv50. G The relationship between the specific surface area BET of the graphite and the graphite satisfies: 100 ≥ Dv50 G / BET≥1.2.

[0024] In one alternative implementation, Dv50 G The range is 3μm-20μm, and the BET value is 0.2m. 2 / g-2.0m 2 / g.

[0025] In one alternative implementation, 800≥TS / BET≥40, where TS is the tensile strength of the aluminum-plastic film in MPa.

[0026] In one alternative embodiment, the battery cell includes a negative electrode, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a silicon-based material, and the silicon-based material has a mass percentage content of more than 5% based on the weight of the negative electrode active material layer.

[0027] In one optional embodiment, the battery cell further includes a metal strip and tabs, the tab adhesive being sleeved on at least a portion of the surface of the metal strip, the tab adhesive being connected to a heat-sealing layer in the aluminum-plastic film; the tensile force P between the tab adhesive and the aluminum-plastic film is 7N-30N.

[0028] In one optional embodiment, the tensile force P between the tab adhesive and the aluminum-plastic film is 10N-25N.

[0029] In one alternative embodiment, the tab adhesive comprises an adhesive layer with a melting point of less than 120°C.

[0030] The technical solution of this application has the following advantages:

[0031] The aluminum-plastic film provided in this application includes a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together. The substrate layer includes a nylon layer and a thermally conductive layer, with the thermally conductive layer disposed between the aluminum foil layer and the nylon layer. By adding a thermally conductive layer between the nylon layer and the aluminum foil layer of the aluminum-plastic film, and utilizing the excellent thermal conductivity of the thermally conductive layer, the heat generated by the battery can be quickly conducted from the interior of the aluminum-plastic film to the exterior for heat dissipation, significantly improving the thermal safety of the battery.

[0032] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is the surface morphology of the thermally conductive layer obtained in embodiment C1 of this application;

[0035] Figure 2 This is a schematic diagram of the structure of the aluminum-plastic film prepared in Embodiment C1 of this application.

[0036] The reference numerals in the attached figures are explained as follows:

[0037] 1. Heat-sealing layer; 21. First adhesive layer; 22. Second adhesive layer; 23. Third adhesive layer; 3. Aluminum foil layer; 4. Thermally conductive layer; 5. Nylon layer. Detailed Implementation

[0038] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0039] In the description of this application, it should be noted that the terms "inner," "outer," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0042] This application provides an aluminum-plastic film and a lithium-ion secondary battery, which can significantly improve the thermal safety of the battery without compromising its electrical performance. The technical solution adopted in this application is described below.

[0043] In a first aspect, the aluminum-plastic film provided in this application includes a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together. The substrate layer includes a nylon layer and a thermally conductive layer, with the thermally conductive layer disposed between the aluminum foil layer and the nylon layer.

[0044] Those skilled in the art will understand that lithium-ion secondary batteries generate a large amount of heat during thermal and electrical abuse processes such as hot box testing. This heat is difficult to dissipate and accumulates, pushing up the temperature of the electrode components and inducing a chain reaction. This chain reaction further promotes heat generation, and if the heat generation is difficult to control, it will lead to thermal runaway of the battery. To solve the problem of battery thermal runaway, the aluminum-plastic film provided in this application adds a thermally conductive layer between the nylon layer and the aluminum foil layer. Utilizing the excellent thermal conductivity of the thermally conductive layer, the heat generated by the battery can be quickly conducted from the inside of the aluminum-plastic film to the outside for heat dissipation, significantly improving the thermal safety of the battery.

[0045] In one alternative embodiment, the thickness L of the thermally conductive layer S With respect to the thickness L of the nylon layer NL The following condition must be met: 18 ≥ LNL / L S >1, where L S The range is 3μm-20μm, L NL The thickness is 4μm-55μm. As a functional coating, the thermally conductive layer should not be too thick, otherwise it will occupy too much thickness space, thus reducing the energy density of the battery; however, the thickness of the thermally conductive layer should not be too thin either, otherwise it will not be conducive to achieving a good heat dissipation effect. Therefore, this application controls the ratio of the thickness of the nylon layer to the thermally conductive layer within the above-mentioned range, which can significantly improve the thermal safety of the battery without sacrificing the battery's electrical performance. As an example, the thickness L of the nylon layer is... NL With thermal conductive layer thickness L S The ratio can be 1.3, 3, 5, 7, 10, 13, 15, 18 or within any two of the above values.

[0046] The applicant's research found that the thickness L of the thermally conductive layer S Within the range of 3μm-20μm, it is possible to ensure good thermal safety of the battery while maintaining its energy density. As an example, the thickness L of the thermally conductive layer... S It can be 3μm, 5μm, 7μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or within any two of the above values.

[0047] It should be noted that the nylon layer itself has high tensile strength. Increasing the thickness of the nylon layer can further improve the tensile strength of the aluminum-plastic film. This results in a smaller expansion space for the aluminum-plastic film during the hot box test, allowing the gas and heat generated by the battery cell to be quickly compressed and expelled from the aluminum-plastic film, achieving better heat dissipation. As an example, the thickness L of the nylon layer... NL For example, 4μm, 7μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, or within the range of any two of the above values.

[0048] In one optional embodiment, the adhesion force F between the thermally conductive layer and the nylon layer is 80 N / m to 150 N / m. Increased adhesion between the two layers helps to further improve the thermal conductivity of the aluminum-plastic film from the inside out, thereby enhancing the thermal safety of the battery. As an example, the adhesion force F between the thermally conductive layer and the nylon layer can be 80 N / m, 90 N / m, 100 N / m, 110 N / m, 120 N / m, 130 N / m, 140 N / m, 150 N / m, or within any two of these values.

[0049] In one optional embodiment, the thermally conductive layer comprises a thermally conductive material with a particle size Dv50.S With respect to the thickness L of the thermally conductive layer S Satisfy: 300≥Ls / Dv50 S ≥3. The applicant's research found that when the thickness of the thermal conductive layer Ls is related to the particle size Dv50 of the thermal conductive material... S When the ratio is too large, the heat-conducting layer may lose energy density due to its excessive thickness, or the heat-conducting material in the heat-conducting layer may be too densely packed, making it difficult to achieve good heat conduction and dissipation effects; conversely, if the ratio of the heat-conducting layer thickness Ls to the heat-conducting material particle size Dv50 is too large, the heat-conducting layer thickness Ls may be too large, or the heat-conducting material particle size Dv50 may be too small. S If the ratio is too small, it indicates that the thermal conductive layer is too thin and cannot achieve good heat conduction and dissipation. As an example, the thickness L of the thermal conductive layer... S With the particle size Dv50 of the thermally conductive material S The ratio can be 3, 5, 10, 20, 30, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, or within any range of two of the above values. In some embodiments, the particle size Dv50 of the thermally conductive material is... S The particle size is 0.1μm-5μm. The applicant's research found that when the thermally conductive material particle size Dv50... S If the particle size is too large, it can easily lead to an excessively thick heat-conducting layer, resulting in a loss of energy density. However, when the particle size of the heat-conducting material is Dv50... S If the particle size is too small, the material packing is too dense, making it difficult to achieve good thermal conductivity and heat dissipation. For example, the particle size of the thermally conductive material is Dv50. S It can be 0.1μm, 1μm, 2μm, 3μm, 4μm, 5μm, or within any two of the above values.

[0050] In one optional embodiment, the particle size Dv99 of the thermally conductive material is 3μm-15μm. The Dv99 particle size of the thermally conductive material determines the thickness of the thermally conductive layer to a certain extent. The thickness of the thermally conductive layer should not be too large, otherwise it will occupy too much thickness space, thus reducing the energy density of the battery. At the same time, the thickness of the thermally conductive layer should not be too small, otherwise it will not be conducive to achieving a good heat dissipation effect. This application improves thermal safety without sacrificing the battery energy density by controlling the particle size Dv99 of the thermally conductive material within the above range. As an example, the particle size Dv99 of the thermally conductive material can be 3μm, 6μm, 8μm, 10μm, 12μm, 15μm, or within any two of the above values.

[0051] It is understandable that Dv50 represents the particle size when the cumulative volume distribution value is 50%, and Dv99 represents the particle size when the cumulative volume distribution value is 99%.

[0052] In one optional embodiment, the thermally conductive material includes at least one selected from aluminum oxide, magnesium oxide, graphite, carbon black, graphene, silver particles, and copper particles. It is understood that these materials all possess excellent thermal conductivity, and using them to prepare the thermally conductive layer ensures its superior thermal conductivity. In particular, the use of metal oxides such as aluminum oxide and magnesium oxide further enhances the tensile strength of the aluminum-plastic film, thereby improving the thermal safety of the battery.

[0053] The thermally conductive layer in this application is formed by mixing thermally conductive material with adhesive and curing agent in a mass ratio of 50-80:10-30:2-20. It is understood that the adhesive can be at least one of epoxy resin, polyimide resin, phenolic resin, polyurethane or acrylic resin, and the curing agent can be at least one of common aliphatic polyamines (e.g. ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenediamine, polyethylene polyamine, etc.), alicyclic polyamines (e.g. isophorone diamine), low molecular weight polyamides (e.g., number average molecular weight in the range of 1000-1500), tertiary amines, dicyandiamide or ethanolamine.

[0054] In one alternative embodiment, the thickness L of the substrate layer J With respect to the thickness L of the aluminum foil layer Al The thickness L of the heat-sealing layer PP and the total thickness L of the aluminum-plastic film 总 The following relationship is satisfied between them: 0.75*L 总 ≥L J ≥0.5*(L Al +L PP ), where L 总 80μm-120μm, L J 5μm-60μm, L Al The range is 20μm-80μm, L PP The thickness is 5μm-40μm. The aluminum-plastic film provided in this application, while maintaining a total thickness of 80μm-120μm, increases the thickness of the substrate layer to be greater than or equal to half the sum of the aluminum foil layer and the heat-sealing layer thickness and less than or equal to 75% of the total thickness of the aluminum-plastic film. On the one hand, the newly added thermally conductive layer in the substrate layer can quickly conduct the heat generated by the battery from the inside of the aluminum-plastic film to the outside for heat dissipation, improving the battery's thermal safety. On the other hand, the substrate layer is mainly a nylon layer. Utilizing the high tensile strength of nylon, the aluminum-plastic film of this application has a small expansion space within the aluminum-plastic film cavity after a tear at the tab during the hot box test. The gas and heat generated by the battery cell can be quickly compressed and expelled from the aluminum-plastic film, achieving better heat dissipation. Therefore, it significantly improves the battery's thermal safety without sacrificing electrical performance. As an example, the thickness L of the substrate layer... JIt can be the thickness L of the aluminum foil layer Al With heat seal layer thickness L PP The sum of the values ​​is 0.5 times, 0.6 times, 0.8 times, 1.0 times, 1.5 times, 2.0 times, 2.5 times, 3 times, or falls within the range of any two of the above values, where the total thickness L of the aluminum-plastic film is... 总 For example, the thickness L of the substrate layer can be 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, or within any two of the above values. J For example, the thickness L of the aluminum foil layer can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, or within any two of the above values. Al For example, the thickness L of the heat-sealing layer is 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, or within any two of the above values. PP For example, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, or within the range of any two of the above values.

[0055] Those skilled in the art will understand that the total thickness L of the aluminum-plastic film in this application 总 This refers to the sum of the thicknesses of the various functional layers, including the heat-sealing layer, aluminum foil layer, nylon layer, and thermally conductive layer, as well as the adhesive layers between them, i.e., L. 总 =L PP +L Al +L NL +2*L NH Or L 总 =L PP +L Al +L NL +L S +3*L NH Similarly, L J =L NL Or L J =L NL +L S +L NH Among them, L NH This represents the thickness of each adhesive layer, typically ranging from 1μm to 3μm. For example, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, or any combination of these values. It is understood that when comparing the thicknesses of different functional layers in an aluminum-plastic film, the same unit of thickness, such as micrometers (μm), must be used.

[0056] In one optional embodiment, the tensile strength TS of the aluminum-plastic film is 45MPa-200MPa. The applicant's research has found that aluminum-plastic films with higher tensile strength can reduce the expandable space after battery thermal chamber testing, thereby compressing the gas inside the aluminum-plastic film cavity and allowing it to be quickly expelled, resulting in excellent heat dissipation. This ensures good thermal safety of the battery while maintaining its energy density. As an example, the tensile strength TS of the aluminum-plastic film can be 45MPa, 60MPa, 80MPa, 100MPa, 120MPa, 140MPa, 160MPa, 180MPa, 200MPa, or within any two of these values.

[0057] In one optional embodiment, the elongation E of the aluminum-plastic film is 35%-100%. The applicant has found that aluminum-plastic films with a higher elongation can ensure good thermal safety of the battery while maintaining its energy density. As an example, the elongation E of the aluminum-plastic film can be, for example, 35%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 100%, or within any two of these values.

[0058] In one optional embodiment, the thermal conductivity K of the aluminum-plastic film is 0.5 W·m. -1 ·K -1 -5W·m -1 ·K -1 The applicant's research found that aluminum-plastic films with high thermal conductivity can ensure good thermal safety of the battery while maintaining its energy density. For example, the thermal conductivity K of the aluminum-plastic film can be 0.5 W·m. -1 ·K -1 1.0 W·m -1 ·K -1 1.5W·m -1 ·K -1 2.0 W·m -1 ·K -1 2.5W·m -1 ·K -1 3.0 W·m -1 ·K -1 3.5W·m -1 ·K -1 4.0 W·m -1 ·K -1 4.5 W·m -1 ·K -1 5.0 W·m -1 ·K -1 Or it falls within the range formed by any two of the above values.

[0059] Secondly, this application provides a lithium-ion secondary battery, including a battery cell and an aluminum-plastic film, wherein the aluminum-plastic film is wrapped around the outside of the battery cell; the aluminum-plastic film is the aluminum-plastic film described in the first aspect of this application, and the substrate layer in the aluminum-plastic film is disposed away from the battery cell. The lithium-ion secondary battery with the aluminum-plastic film of this application can overcome the problem that existing batteries cannot simultaneously achieve both electrical performance and thermal safety.

[0060] In one optional embodiment, the battery further includes an electrolyte comprising a carboxylic acid ester solvent; the mass percentage of the carboxylic acid ester solvent is M% based on the weight of the electrolyte, wherein the value of M satisfies: 1.5 ≥ M / L NL ≥0.01, and / or, 20 ≥ M / L S ≥0.05; L NL L represents the thickness of the nylon layer, in μm. S The thickness of the thermally conductive layer is expressed in μm. Adding carboxylic acid ester solvents to the electrolyte ensures the battery's low-temperature performance. The amount of carboxylic acid ester solvent added should not be too small, otherwise it will not have the desired effect; however, the amount should also not be too large, because carboxylic acid ester solvents typically have low boiling points, and excessive amounts can significantly worsen the thermal stability of the battery cell. Therefore, in some embodiments, the mass percentage of carboxylic acid ester solvent in the electrolyte is 0.1%-40%. As an example, the mass percentage of carboxylic acid ester solvent in the electrolyte can be 0.1%, 1%, 5%, 10%, 20%, 30%, 40%, or within any two of these values. The applicant's research found that when the mass percentage M% of carboxylic acid ester solvent in the electrolyte is related to the nylon layer thickness L... NL The ratio is in the range of 0.01-1.5, and / or, the value of M is related to the thickness of the thermally conductive layer L. S The ratio is in the range of 0.05-20, which can ensure good heat dissipation without sacrificing battery energy density. As an example, the value of M is related to the nylon layer thickness L. NL The ratio can be 0.01, 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, or within any two of the above values; the value of M is related to the thickness of the thermally conductive layer L. S The ratio can be 0.05, 0.5, 1, 3, 5, 7, 9, 12, 15, 18, 20 or within any two of the above values.

[0061] Those skilled in the art will understand that the carboxylic acid ester solvent can be at least one of methyl formate (MF), ethyl acetate (EA), ethyl propionate (EP), methyl acetate (MA), methyl butyrate (MB), methyl propyl carbonate (MP), propyl propionate (PP), ethyl butyrate (EB), or their fluorinated derivatives, wherein the fluorinated carboxylic acid ester can be, for example, methyl fluoroformate, ethyl difluoroacetate, ethyl 2-fluoropropionate, methyl fluoroacetate, methyl 4-fluorobutyrate, propyl 2-fluoropropionate, or ethyl 4-fluorobutyrate.

[0062] In one optional embodiment, the battery cell includes a negative electrode, the negative electrode including a negative electrode active material layer, the negative electrode active material layer including graphite, the graphite having a particle size Dv50. G The relationship between the specific surface area BET of the graphite and the graphite satisfies: 100 ≥ Dv50 G / BET≥1.2. As an example, the particle size of graphite is Dv50. G The ratio of its specific surface area (BET) to the total surface area (BET) can be 1.2, 5, 10, 30, 50, 70, 90, 100, or within any range of two of these values. In some embodiments, the graphite particle size Dv50 G The graphite has a surface area of ​​3μm-20μm and a specific surface area (BET) of 0.2m². 2 / g-2.0m 2 / g; as an example, the particle size of graphite is Dv50 G The specific surface area (BET) of graphite can be 3μm, 6μm, 9μm, 12μm, 15μm, 18μm, 20μm, or within any two of these values. For example, the specific surface area (BET) of graphite is 0.2m². 2 / g, 0.5m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g or within the range of any two of the above values. Anodes made of graphite materials with small particle size and large specific surface area are prone to lithium metal deposition and thermal runaway under fast-charging conditions in liquid electrolyte systems due to drastic structural changes and significant polarization effects, leading to battery cycle performance degradation and safety accidents. To address this, the combination of the aluminum-plastic film provided in this application and the aforementioned graphite anode results in a lithium-ion secondary battery with better thermal safety, suitable for fast-charging applications.

[0063] In some embodiments, 800 ≥ TS / BET ≥ 40, where TS is the tensile strength of the aluminum-plastic film in MPa. It is understood that the main challenge in achieving fast charging of lithium-ion secondary batteries is the fast charging of graphite anodes, which suffer from poor thermal safety. Therefore, this application combines this type of graphite anode with the aluminum-plastic film provided herein, ensuring that the ratio of the tensile strength TS of the aluminum-plastic film to the specific surface area BET of the graphite is within the range of 40-800, thus significantly improving the thermal safety of lithium-ion secondary batteries during fast charging. As an example, the ratio of the tensile strength TS of the aluminum-plastic film to the specific surface area BET of the graphite can be 40, 100, 300, 500, 600, 700, 800, or within any two of these values.

[0064] In some embodiments, the battery cell includes a negative electrode, which includes a negative electrode active material layer comprising a silicon-based material. The silicon-based material comprises at least 5% by weight of the negative electrode active material layer. Currently, the reversible specific capacity of graphite negative electrodes is close to the theoretical specific capacity. To improve the energy density of lithium-ion secondary batteries, related technologies have chosen to dope graphite materials with silicon-based materials to create silicon-based negative electrodes. The lithium-ion secondary battery formed by combining the silicon-based negative electrode with the aluminum-plastic film provided in this application has better thermal safety and higher energy density. As an example, the silicon-based material can be at least one of elemental silicon, silicon alloy, silicon-carbon, and silicon-oxygen. The doping amount of the silicon-based material can be, for example, 5%, 6%, 7%, 8%, 9%, 10%, or within any two of these values.

[0065] In one optional embodiment, the battery cell further includes a tab, which comprises a metal strip and tab adhesive. The tab adhesive is fitted onto at least a portion of the surface of the metal strip and is connected to a heat-sealing layer in the aluminum-plastic film. The tensile force P between the tab adhesive and the aluminum-plastic film is 7N-30N. To ensure manufacturing reliability and that the tab can open smoothly during the hot box test, the tensile force P between the tab adhesive and the aluminum-plastic film should not be too small or too large. If the value of P is too large, the bonding point between the tab and the aluminum-plastic film cannot open smoothly during the hot box test, resulting in the inability to dissipate gas and heat. If the value of P is too small, manufacturing reliability cannot be guaranteed, and there is a risk of leakage during the manufacturing process. As an example, the tensile force P between the tab adhesive and the aluminum-plastic film can be, for example, 7N, 8N, 10N, 12N, 15N, 17N, 20N, 23N, 25N, 28N, 30N, or within any two of the above values.

[0066] In one optional embodiment, the tab adhesive includes an adhesive layer with a melting point less than 120°C. This helps reduce the tension between the tab adhesive and the aluminum-plastic film during hot box testing, allowing the bonding joint between the tab and the aluminum-plastic film to open smoothly, dissipate heat promptly, and further improve the thermal safety of the battery. As an example, the low-melting-point adhesive layer in the tab adhesive can be at least one of polyethylene, polypropylene, and polyethylene terephthalate.

[0067] In one optional embodiment, the expansion rate of the cell under hot-box testing conditions is 0.5%-6%, and the hot-box testing is conducted according to the method specified in GB / T 8897.4-2008. The applicant has found that lithium-ion secondary batteries with smaller expansion space can quickly compress and expel the generated gas and heat during hot-box testing, achieving timely heat dissipation and ensuring good thermal safety of the cell. As an example, the expansion rate of the cell under hot-box testing conditions is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or within any two of the above values.

[0068] Those skilled in the art will understand that a lithium-ion secondary battery includes a cell, an electrolyte, and an aluminum-plastic film. The cell includes a cell body, a positive electrode tab, and a negative electrode tab. One end of the positive electrode tab and one end of the negative electrode tab are respectively connected to the cell body. The cell body is sealed within the cell body accommodating area of ​​an encapsulation formed by the aluminum-plastic film. The cell body includes a positive electrode plate, a negative electrode plate, and a separator. During the charging and discharging process of the battery, lithium ions are inserted and extracted back and forth between the positive and negative electrode plates. The electrolyte plays a role in conducting ions between the positive and negative electrode plates. The separator is disposed between the positive and negative electrode plates, mainly to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through.

[0069] As an example, the positive electrode sheet includes a positive current collector and a positive active material layer. The positive current collector has two opposing surfaces in its own thickness direction, and the positive active material layer is disposed on either or both of the opposing surfaces of the positive current collector. The materials, composition, and manufacturing methods of the positive electrode sheet used in the lithium-ion secondary battery of this application may include any techniques disclosed in the prior art.

[0070] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the opposing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the lithium-ion secondary battery of this application may include any techniques disclosed in the prior art.

[0071] The material and shape of the separator used in the lithium-ion secondary battery of this application are not particularly limited, and may include any technology disclosed in the prior art.

[0072] The electrolyte used in the lithium-ion secondary battery of this application may include any technology disclosed in the prior art.

[0073] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in this application. In all embodiments and comparative examples of this application, the unit wt% represents the mass percentage content.

[0074] Example C1

[0075] The method for preparing the aluminum-plastic film provided in this embodiment includes the following steps:

[0076] (1) Preparation of thermal conductive layer

[0077] Alumina (particle size distribution as follows: Dv50 = 0.5 μm, Dv99 = 3.0 μm) was selected as the thermally conductive material and added to N-methylpyrrolidone to prepare a dispersion with a concentration of 20 wt%. This dispersion (based on the mass of alumina) was then mixed with hexamethylenediamine curing agent and epoxy resin binder at a mass ratio of 70:20:10 to form a slurry. This slurry was coated into a film, and after drying, a thermally conductive layer was obtained, with the surface morphology as shown below. Figure 1 As shown, from Figure 1 It can be seen that the thermally conductive layer particles are evenly dispersed, which is beneficial to improving the thermal conductivity.

[0078] (2) Preparation of aluminum-plastic film

[0079] Prepare the heat-sealing layer, aluminum foil layer, thermally conductive layer, nylon layer, and epoxy resin adhesive;

[0080] The nylon layer is bonded to the thermally conductive layer using an adhesive to form the first composite layer;

[0081] An adhesive is applied to the thermally conductive surface of the first composite layer, and then an aluminum foil layer is applied to bond and form the second composite layer.

[0082] An adhesive is coated onto the surface of the aluminum foil in the second composite layer, followed by a heat-sealing layer. The mixture is then bonded, dried, and rolled to produce an aluminum-plastic film, as shown in the schematic diagram below. Figure 2 As shown, from the inside out, it includes a heat-sealing layer 1, a first adhesive layer 21, an aluminum foil layer 3, a second adhesive layer 22, a thermally conductive layer 4, a third adhesive layer 23, and a nylon layer 5, which are stacked together.

[0083] The preparation method of the aluminum-plastic film in Example C2 is basically the same as that in Example C1, except that the thickness of each functional layer (see Table 1) and the use of phenolic resin as a binder to prepare the first composite layer are different.

[0084] The preparation method of the aluminum-plastic film in Example C3 is basically the same as that in Example C1, except that the thickness of each functional layer (see Table 1) and the use of polyurethane as an adhesive to prepare the first composite layer are different.

[0085] The preparation method of the aluminum-plastic film in Example C4 is basically the same as that in Example C1, except for the thickness of each functional layer (see Table 1) and the use of polyimide resin as a binder to prepare the first composite layer.

[0086] The preparation method of the aluminum-plastic film in Example C5 is basically the same as that in Example C1, except that the thickness of each functional layer (see Table 1) and the use of acrylic resin as an adhesive to prepare the first composite layer are different.

[0087] Example C6

[0088] The method for preparing the aluminum-plastic film provided in this embodiment includes the following steps:

[0089] (1) Preparation of thermal conductive layer

[0090] Magnesium oxide (particle size distribution as follows: Dv50 is 5μm, Dv99 is 12μm) was selected as the thermal conductive material and added to deionized water to prepare a dispersion with a concentration of 40wt%. The dispersion (based on the mass of magnesium oxide) was mixed with ethanolamine curing agent and phenolic resin binder at a mass ratio of 75:10:15 to form a mixed slurry. The mixed slurry was coated into a film and dried to obtain a thermal conductive layer.

[0091] (2) Preparation of aluminum-plastic film

[0092] Prepare the heat-sealing layer, aluminum foil layer, thermally conductive layer, nylon layer, and epoxy resin adhesive;

[0093] The nylon layer is bonded to the thermally conductive layer using an adhesive to form the first composite layer;

[0094] An adhesive is applied to the thermally conductive surface of the first composite layer, and then an aluminum foil layer is applied to bond and form the second composite layer.

[0095] An adhesive is applied to the surface of the aluminum foil in the second composite layer, followed by a heat-sealing layer. The film is then bonded, dried, and rolled to obtain an aluminum-plastic film.

[0096] The preparation method of the aluminum-plastic film in Example C7 is basically the same as that in Example C6, except that the thickness of each functional layer is different (see Table 1 for details).

[0097] The preparation method of the aluminum-plastic film in Example C8 is basically the same as that in Example C6, except that the thickness of each functional layer (see Table 1) and the use of phenolic resin as a binder to prepare the first composite layer are different.

[0098] The preparation method of the aluminum-plastic film in Example C9 is basically the same as that in Example C6, except that the thickness of each functional layer (see Table 1) and the use of polyurethane as an adhesive to prepare the first composite layer are different.

[0099] The preparation method of the aluminum-plastic film in Example C10 is basically the same as that in Example C6, except that the thickness of each functional layer (see Table 1) and the use of polyimide as a binder to prepare the first composite layer are different.

[0100] The preparation method of the aluminum-plastic film in Example C11 is basically the same as that in Example C6, except that the thickness of each functional layer (see Table 1) and the use of acrylic resin as an adhesive to prepare the first composite layer are different.

[0101] Example C12

[0102] The method for preparing the aluminum-plastic film provided in this embodiment includes the following steps:

[0103] (1) Preparation of thermal conductive layer

[0104] Silver particles (with particle size distribution as follows: Dv50 is 1μm, Dv99 is 4μm) were selected as the thermal conductive material and added to nitric acid to prepare a dispersion with a concentration of 15wt%. The dispersion (based on the mass of silver) was mixed with dicyandiamide curing agent and polyurethane binder at a mass ratio of 70:20:10 to form a mixed slurry. The mixed slurry was coated into a film and dried to obtain a thermal conductive layer.

[0105] (2) Preparation of aluminum-plastic film

[0106] Prepare the heat-sealing layer, aluminum foil layer, thermally conductive layer, nylon layer, and epoxy resin adhesive;

[0107] The nylon layer is bonded to the thermally conductive layer using an adhesive to form the first composite layer;

[0108] An adhesive is applied to the thermally conductive surface of the first composite layer, and then an aluminum foil layer is applied to bond and form the second composite layer.

[0109] An adhesive is applied to the surface of the aluminum foil in the second composite layer, followed by a heat-sealing layer. The film is then bonded, dried, and rolled to obtain an aluminum-plastic film.

[0110] The preparation method of the aluminum-plastic film in Example C13 is basically the same as that in Example C12, except that the thickness of each functional layer is different, as detailed in Table 1.

[0111] The preparation method of the aluminum-plastic film in Example C14 is basically the same as that in Example C12, except that the thickness of each functional layer is different, as detailed in Table 1.

[0112] The preparation method of the aluminum-plastic film in Example C15 is basically the same as that in Example C12, except for the thickness of each functional layer, as detailed in Table 1.

[0113] The preparation method of the aluminum-plastic film in Example C16 is basically the same as that in Example C12, except that the thickness of each functional layer is different, as detailed in Table 1.

[0114] The preparation method of the aluminum-plastic film in Example C17 is basically the same as that in Example C12, except for the thickness of each functional layer, as detailed in Table 1.

[0115] The preparation method of the aluminum-plastic film in Example C18 is basically the same as that in Example C12, except that the thickness of each functional layer is different, as detailed in Table 1.

[0116] Example C19

[0117] The method for preparing the aluminum-plastic film provided in this embodiment includes the following steps:

[0118] (1) Preparation of thermal conductive layer

[0119] Copper particles (with particle size distribution as follows: Dv50 is 0.1μm and Dv99 is 1μm) were selected as the thermal conductive material and added to nitric acid to prepare a dispersion with a concentration of 30wt%. The dispersion (based on the mass of copper) was mixed with dicyandiamide curing agent and polyurethane binder at a mass ratio of 60:20:20 to form a mixed slurry. The mixed slurry was coated into a film and dried to obtain a thermal conductive layer.

[0120] (2) Preparation of aluminum-plastic film

[0121] Prepare the heat-sealing layer, aluminum foil layer, thermally conductive layer, nylon layer, and epoxy resin adhesive;

[0122] The nylon layer is bonded to the thermally conductive layer using an adhesive to form the first composite layer;

[0123] An adhesive is applied to the thermally conductive surface of the first composite layer, and then an aluminum foil layer is applied to bond and form the second composite layer.

[0124] An adhesive is applied to the surface of the aluminum foil in the second composite layer, followed by a heat-sealing layer. The film is then bonded, dried, and rolled to obtain an aluminum-plastic film.

[0125] The preparation method of the aluminum-plastic film in Example C20 is basically the same as that in Example C19, except that the thickness of each functional layer is as detailed in Table 1.

[0126] The preparation method of the aluminum-plastic film in Example C21 is basically the same as that in Example C19, except that the thickness of each functional layer is as detailed in Table 1.

[0127] The preparation method of the aluminum-plastic film in Example C22 is basically the same as that in Example C19, except that the thickness of each functional layer is as detailed in Table 1.

[0128] The preparation method of the aluminum-plastic film in Example C23 is basically the same as that in Example C19, except that the thickness of each functional layer is as detailed in Table 1.

[0129] The preparation method of the aluminum-plastic film in Example C24 is basically the same as that in Example C19, except that the thickness of each functional layer is as detailed in Table 1.

[0130] Comparative Example C1

[0131] The aluminum-plastic film in this comparative example includes a heat-sealing layer, an aluminum foil layer, and a nylon layer stacked together. The preparation method of the aluminum-plastic film includes the following steps:

[0132] Prepare the heat-sealing layer, aluminum foil layer, nylon layer, and epoxy resin adhesive using the same method as in Example C1;

[0133] The nylon layer and the aluminum foil layer are bonded together using an adhesive to form a composite layer;

[0134] An adhesive is coated onto the aluminum foil surface of the composite layer, followed by a heat-sealing layer, bonding, drying, and rolling to obtain an aluminum-plastic film.

[0135] Comparative Example C2

[0136] The aluminum-plastic film in this comparative example includes a heat-sealing layer, an aluminum foil layer, a nylon layer, and a thermally conductive layer stacked together. The preparation method of the aluminum-plastic film includes the following steps:

[0137] The thermally conductive layer was prepared using the same method as in Example C1, and the heat-sealing layer, aluminum foil layer, nylon layer, and epoxy resin adhesive were prepared.

[0138] The thermally conductive layer is bonded to the nylon layer using an adhesive to form the first composite layer;

[0139] An adhesive is applied to the nylon surface of the first composite layer, and then an aluminum foil layer is applied to bond and form the second composite layer.

[0140] An adhesive is applied to the surface of the aluminum foil in the second composite layer, followed by a heat-sealing layer. The film is then bonded, dried, and rolled to obtain an aluminum-plastic film.

[0141] Comparative Example C3

[0142] The aluminum-plastic film in this comparative example includes a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together. The preparation method of the aluminum-plastic film includes the following steps:

[0143] (1) Preparation of substrate layer

[0144] Alumina (particle size distribution as follows: Dv50 is 0.5μm, Dv99 is 3.0μm) was selected as the thermal conductive material and added to N-methylpyrrolidone to prepare a dispersion with a concentration of 20wt%. The dispersion (based on the mass of alumina) was mixed with nylon particles, hexamethylenediamine curing agent, and epoxy resin binder at a mass ratio of 35:20:10 to form a mixed slurry. The mixed slurry was coated into a film and dried to obtain the substrate layer.

[0145] (2) Preparation of aluminum-plastic film

[0146] The heat-sealing layer, aluminum foil layer, and epoxy resin adhesive were prepared using the same method as in Example C1;

[0147] An adhesive is used to bond the aluminum foil layer to the substrate layer obtained in step (1) to form a composite layer;

[0148] An adhesive is coated onto the aluminum foil surface of the composite layer, followed by a heat-sealing layer, bonding, drying, and rolling to obtain an aluminum-plastic film.

[0149] Example E1

[0150] The lithium-ion secondary battery provided in this embodiment is prepared using the following method:

[0151] Step 1: Preparing the positive electrode sheet

[0152] Conductive carbon black and carbon nanotubes were added to a polyvinylidene fluoride (PVDF) adhesive solution and stirred until homogeneous. Then, lithium cobalt oxide was added and stirred until homogeneous again to prepare a positive electrode active material slurry. This slurry was coated onto the surface of a positive electrode protective layer, and after baking and rolling, a positive electrode sheet was obtained. The positive electrode active material layer contained 97.6% lithium cobalt oxide, 1.05% PVDF, and 1.35% conductive carbon black and carbon nanotubes (with a carbon black to carbon nanotube mass ratio of 1:1).

[0153] Step 2: Preparation of the negative electrode sheet

[0154] Graphite with a mass fraction of 97.3% (with a particle size Dv50) G It has a diameter of 12 μm and a specific surface area (BET) of 2 m². 2 / g, Dv50 G A negative electrode active material slurry is prepared by mixing 0.5% conductive carbon black, 1.3% binder and 0.9% dispersant evenly, and then adding an appropriate amount of deionized water to disperse evenly. The negative electrode active material slurry is coated on carbon-coated copper foil, and after baking and rolling, a negative electrode sheet is obtained.

[0155] Step 3: Prepare the electrolyte

[0156] Add ethyl propionate to a commercially available electrolyte (in which the lithium salt is LiFP6) and stir until homogeneous, so that ethyl propionate accounts for 5% of the mass of the electrolyte.

[0157] Step 4: After the positive and negative electrode sheets are slit and formed, they are wound with a separator to obtain a core. The core is then encapsulated with the aluminum-plastic film provided in Embodiment C1 of this application, followed by baking, electrolyte injection, formation, secondary sealing, sorting, and open-circuit voltage testing (OCV) to obtain a lithium-ion secondary battery. The tab protection layer uses polypropylene tab adhesive, and the tab adhesive and the aluminum-plastic film (whose structure is as follows) Figure 2 As shown in the figure, the two opposite ends of the heat-sealing layer are connected, and the tension P between the tab adhesive and the aluminum-plastic film is shown in Table 2.

[0158] The preparation methods of lithium-ion secondary batteries in Examples E2-E24 are similar to those in Example E1, except that the core is encapsulated with the aluminum-plastic film prepared in Examples C2-C24 of this application.

[0159] The preparation methods of lithium-ion secondary batteries in Examples E25-E28 are similar to those in Example E1, except for the types and mass percentages of carboxylic acid esters in the electrolyte, as detailed in Table 2.

[0160] The preparation methods of lithium-ion secondary batteries in Examples E29-E33 are similar to those in Example E1, except that the tension P between the tab adhesive and the aluminum-plastic film is detailed in Table 2.

[0161] The preparation method of the lithium-ion secondary battery in Example E34 is similar to that in Example E1, except that the negative electrode active material is a silicon-carbon-graphite composite material (where the silicon-carbon doping content is 5 wt% and the graphite content is 95 wt%).

[0162] The preparation method of the lithium-ion secondary battery in Example E35 is similar to that in Example E1, except that the negative electrode active material is a silicon-oxygen-graphite composite material (where the silicon-oxygen doping amount is 10wt% and the graphite content is 90wt%).

[0163] The preparation method of the lithium-ion secondary battery in Example E36 is similar to that in Example E1, except that the negative electrode active material is a silicon-aluminum alloy-graphite composite material (where the silicon-aluminum alloy doping amount is 8wt% and the graphite content is 92wt%).

[0164] The preparation method of the lithium-ion secondary battery in Example E37 is similar to that in Example E1, except that a particle size of Dv50 is used. G Its thickness is 3μm and its specific surface area (BET) is 1.2m². 2 / g(Dv50 G Anode sheets were prepared using graphite with a ratio of / BET=2.5.

[0165] The preparation method of the lithium-ion secondary battery in Example E38 is similar to that in Example E1, except that a particle size of Dv50 is used. G Its diameter is 20 μm and its specific surface area (BET) is 0.2 m². 2 / g(Dv50 G Anode sheets were prepared using graphite with a / BET=100 ratio.

[0166] The preparation method of the lithium-ion secondary battery in Comparative Example E1 is similar to that in Example E1, except that the core is encapsulated with the aluminum-plastic film prepared in Comparative Example C1 of this application.

[0167] The preparation method of the lithium-ion secondary battery in Comparative Example E2 is similar to that in Example E1, except that the core is encapsulated with the aluminum-plastic film prepared in Comparative Example C2 of this application.

[0168] The preparation method of the lithium-ion secondary battery in Comparative Example E3 is similar to that in Example E1, except that the core is encapsulated with the aluminum-plastic film prepared in Comparative Example C3 of this application.

[0169] Test case

[0170] 1. Hot box test

[0171] First, charge the battery at 0.2C to the cutoff voltage of 0.02C and test the initial state of the battery, including voltage, internal resistance, thickness, etc. Then, put the battery in an oven and heat it at an initial temperature of 25±3℃, with a heating rate of 5±2℃ to reach the target temperature of ±2℃. Hold the temperature for 60 minutes and the test will end.

[0172] 2. Low-temperature cycling test

[0173] The battery was placed in a constant temperature room at 10℃ for 4 hours and then discharged at 1C to its lower limit voltage (3.0V). The battery was then charged at 1.5C to its upper limit voltage (4.5V), and then discharged again at 1C to its lower limit voltage. This charge-discharge cycle constitutes one test cycle. This cycle was repeated 800 times to calculate the battery's discharge capacity retention rate. The initial discharge capacity is Q1, and the discharge capacity after 800 cycles is Q2. Therefore, the discharge capacity retention rate = (Q2 / Q1) * 100%.

[0174] 3. Low-temperature discharge test

[0175] The capacity of a fully charged battery discharged at 0.2C at room temperature is C1. After being left to stand at -20℃ for 4 hours, the capacity discharged at 0.2C is C2. The low-temperature discharge capacity retention rate = C2 / C1*100%.

[0176] 4. Expansion rate S after hot box test

[0177] After the hot box test in Test Example 1, the volume V1 of the battery was measured by the water displacement method, and the volume V of the cell in the fully charged state (before the test) was also measured. S = (V1-V) / V*100%.

[0178] 5. Tensile strength and elongation test

[0179] In this application, the tensile strength and the elongation at break can be obtained by testing as follows: Take a negative electrode current collector with a width of 15 mm and a length of 200 mm (this is the initial length L0), use a tensile tester, and the tensile speed is 50 mm / min. After the tensile tester breaks, the tensile strength output by the tensile tester is the tensile strength. Measure the length of the negative electrode current collector after it breaks and record it as L1. Then, the elongation at break = (L1-L0) / L0.

[0180] 6. Thermal conductivity test

[0181] The thermal conductivity was measured by a thermal conductivity meter.

[0182] 7. Adhesion test between thermally conductive layer and nylon layer

[0183] The adhesive force is measured by stretching the thermally conductive layer at one end and the nylon layer at the other end using a tensile testing machine.

[0184] 8. Tensile test between tab adhesive and aluminum-plastic film

[0185] The tensile strength between the two is measured by stretching the tab adhesive at one end of a tensile testing machine and the aluminum-plastic film at the other end.

[0186] 9. Particle size testing

[0187] Particle size was measured using a laser particle size analyzer.

[0188] 10. Battery Energy Density Test

[0189] The battery was charged at a constant current rate of 0.2C to 4.5V, and then charged at a constant voltage rate to 0.025C to complete the full charge. Next, it was discharged at a constant current rate of 0.2C until the battery voltage dropped to 3V. The total capacity discharged during the discharge process was recorded as C, and the actual battery volume V was calculated.

[0190] Energy density (ED) = discharge capacity C * voltage plateau / cell volume V; where the plateau voltage of the 4.5V system is usually 3.9V.

[0191] Energy density loss rate = (ED of each example battery - ED of Comparative Example 1 battery) / ED of Comparative Example 1 battery * 100%.

[0192] Please see Tables 1-4 for the test results.

[0193] Table 1. Structural and performance parameters of aluminum-plastic film

[0194]

[0195]

[0196] In Table 1, the thickness of the adhesive layer between each functional layer is 2 μm, and " / " indicates that it does not exist.

[0197] As shown in Table 1, compared to Comparative Examples C1-C3, the aluminum-plastic films prepared in Examples C1-C24 exhibit higher tensile strength, greater elongation, and higher thermal conductivity, particularly in Examples C1-C5 and C16-C18. This indicates that, compared to aluminum-plastic films without a thermally conductive layer, with the thermally conductive layer located outside the nylon layer, or with the thermally conductive material incorporated into the nylon layer, this application significantly improves the thermal conductivity of the aluminum-plastic film by setting a thermally conductive layer between the aluminum foil layer and the nylon layer. This allows for rapid heat dissipation from the inside of the aluminum-plastic film to the outside, enhancing the thermal safety of the battery. Furthermore, since Examples C1-C24 use metal or metal oxide as the thermally conductive material, the tensile strength and elongation of the aluminum-plastic film are also simultaneously improved. This results in a smaller expansion space for the aluminum-plastic film during the hot box test, allowing the gas and heat generated by the battery cell to be quickly compressed and expelled from the aluminum-plastic film, achieving better heat dissipation.

[0198] Table 2 Structural parameters of lithium-ion secondary batteries

[0199]

[0200]

[0201]

[0202] In Table 2, " / " indicates that it does not exist.

[0203] Table 3 Electrical performance and thermal safety of lithium-ion secondary batteries

[0204]

[0205]

[0206] In Table 3, “—” indicates the baseline value of energy density.

[0207] As can be seen from Tables 2-3, compared with Comparative Examples E1-E3, the lithium-ion secondary batteries prepared in Examples E1-E24 have a smaller expansion rate, higher thermal safety, and virtually no energy density loss. In particular, the performance of Examples E1-E5 and Examples E16-E18 is especially outstanding. This demonstrates that, compared to aluminum-plastic films without a thermally conductive layer, or with the thermally conductive layer located outside the nylon layer, or with the thermally conductive material incorporated into the nylon layer, this application significantly improves the thermal conductivity of the aluminum-plastic film by setting a thermally conductive layer between the aluminum foil layer and the nylon layer. This allows for rapid heat dissipation from the inside of the aluminum-plastic film to the outside, enhancing the battery's thermal safety. Furthermore, since Examples E1-E24 use metal or metal oxide as the thermally conductive material, the tensile strength and elongation of the aluminum-plastic film are also improved simultaneously. This results in a smaller expansion space for the aluminum-plastic film during the hot box test, allowing the gas and heat generated by the battery cell to be quickly compressed and expelled from the aluminum-plastic film, achieving better heat dissipation. At the same time, compared to Comparative Examples E1-E3, the total thickness of the aluminum-plastic film in this application is not increased, thus avoiding any loss in battery energy density. In fact, the energy density of some batteries is even slightly improved, especially for batteries using silicon-based anodes, where the introduction of silicon-based materials significantly enhances the battery's energy density.

[0208] Compared to Example E1, Examples E25-E27, by adjusting the type and amount of carboxylic acid ester solvent in the electrolyte, also produced lithium-ion secondary batteries exhibiting a smaller expansion rate and higher thermal safety. This indicates that the aluminum-plastic film of this application can be used in combination with an electrolyte containing carboxylic acid ester to solve the problem of poor thermal safety of this type of battery.

[0209] Compared to Example E1, Examples E29-E33, by adjusting the tension between the tab adhesive and the aluminum-plastic film, also produced lithium-ion secondary batteries with a smaller expansion rate and higher thermal safety. This indicates that the adhesion between the aluminum-plastic film and the tab adhesive in this application can balance the manufacturing reliability and thermal safety of the battery within a suitable range.

[0210] Compared to Example E1, Examples E34-E36, by adjusting the type and amount of silicon-based material in the negative electrode, resulted in lithium-ion secondary batteries that not only exhibited a smaller expansion rate and higher thermal safety, but also improved energy density. This demonstrates that the aluminum-plastic film of this application can be used in combination with different types of silicon-based negative electrodes to obtain lithium-ion secondary batteries with good thermal safety and high energy density.

[0211] Compared to Example E1, Examples E37-E38, by adjusting the particle size and specific surface area of ​​the graphite anode material, also produced lithium-ion secondary batteries exhibiting a smaller expansion rate and higher thermal safety. This indicates that the aluminum-plastic film of this application can be used in combination with fast-charging graphite anodes to solve the thermal safety problem of batteries in fast-charging applications.

[0212] Table 4 Low-temperature performance of lithium-ion secondary batteries

[0213] Example E1 90.90 85.63 Example E2 89.81 85.19 Example E3 90.18 84.98 Example E4 90.85 85.33 Example E5 90.75 85.49 Comparative Example E1 89.63 83.90

[0214] This application further tested the low-temperature performance of some lithium-ion secondary batteries, and the results are shown in Table 4. As can be seen from Table 4, the capacity retention rates of Examples E1-E5 under low-temperature cycling and low-temperature discharge conditions are comparable to those of Comparative Example E1. This indicates that the lithium-ion secondary batteries of this application also possess good low-temperature performance and are suitable for cold environments.

[0215] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A lithium-ion secondary battery, comprising a battery cell and an aluminum-plastic film, wherein the aluminum-plastic film is wrapped around the outside of the battery cell; characterized in that, The aluminum-plastic film includes a heat-sealing layer, an aluminum foil layer, and a substrate layer stacked together. The substrate layer includes a nylon layer and a thermally conductive layer, with the thermally conductive layer disposed between the aluminum foil layer and the nylon layer. The total thickness L of the aluminum-plastic film is... 总 The thickness is 80μm-120μm, and the substrate layer in the aluminum-plastic film is disposed away from the battery cell; The lithium-ion secondary battery also includes an electrolyte, which includes a carboxylic acid ester solvent. The mass percentage of the carboxylic acid ester solvent is M% based on the weight of the electrolyte, where M is 0.1-40%. Where M takes the value that satisfies: 1.5 ≥ M / L NL ≥0.01, 20≥M / L S ≥0.05; L NL L represents the thickness of the nylon layer, in μm. S L represents the thickness of the thermally conductive layer, in μm. S 3μm-20μm, L NL The range is 4μm-55μm.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The carboxylic acid ester solvents include at least one of methyl formate, ethyl acetate, ethyl propionate, methyl acetate, methyl butyrate, propyl propionate, ethyl butyrate, methyl fluoroformate, ethyl difluoroacetate, ethyl 2-fluoropropionate, methyl fluoroacetate, methyl 4-fluorobutyrate, propyl 2-fluoropropionate, and ethyl 4-fluorobutyrate.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The thickness L of the heat-conducting layer S With respect to the thickness L of the nylon layer NL The following condition must be met: 18 ≥ L NL / L S >1; And / or, the adhesion force F between the thermally conductive layer and the nylon layer is 80 N / m-150 N / m.

4. The lithium-ion secondary battery according to claim 1, characterized in that, The thermally conductive layer comprises a thermally conductive material and satisfies at least one of the following conditions: (1) The particle size Dv50 of the thermally conductive material S With L S Satisfy: 300≥Ls / Dv50 S ≥3, where Dv50 S The range is 0.1μm-5μm; (2) The particle size Dv99 of the thermally conductive material is 3μm-15μm; (3) The thermally conductive material includes at least one of alumina, magnesium oxide, graphite, carbon black, graphene, silver particles, and copper particles.

5. The lithium-ion secondary battery according to claim 4, characterized in that, 30≥Ls / Dv50 S ≥5.

6. The lithium-ion secondary battery according to claim 1, characterized in that, The thickness L of the substrate layer J With respect to the thickness L of the aluminum foil layer Al The thickness L of the heat-sealing layer PP and the total thickness L of the aluminum-plastic film 总 The following relationship is satisfied between them: 0.75 × L 总 ≥L J ≥0.5×(L Al +L PP ), L J 5μm-60μm, L Al The range is 20μm-80μm, L PP The range is 5μm-40μm.

7. The lithium-ion secondary battery according to any one of claims 1-6, characterized in that, At least one of the following conditions must be met: (1) The tensile strength TS of the aluminum-plastic film is 45MPa-200MPa; (2) The elongation E of the aluminum-plastic film is 35%-100%; (3) The thermal conductivity K of the aluminum-plastic film is 0.5 W·m. -1 ·K -1 -5W·m -1 ·K -1 .

8. The lithium-ion secondary battery according to claim 7, characterized in that, At least one of the following conditions must be met: (1) The tensile strength TS of the aluminum-plastic film is 80MPa-160MPa; (2) The elongation E of the aluminum-plastic film is 60%-85%; (3) The thermal conductivity K of the aluminum-plastic film is 1 W·m. -1 ·K -1 -4W·m -1 ·K -1 .

9. The lithium-ion secondary battery according to claim 1 or 8, characterized in that, The battery cell includes a negative electrode, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes graphite, and the graphite has a particle size of Dv50. G The relationship between the specific surface area BET of the graphite and the graphite satisfies: 100 ≥ Dv50 G / BET≥1.2, Dv50 G The range is 3μm-20μm, and the BET value is 0.2m. 2 / g-2.0m 2 / g.

10. The lithium-ion secondary battery according to claim 9, characterized in that, 800≥TS / BET≥40, where TS is the tensile strength of the aluminum-plastic film in MPa.

11. The lithium-ion secondary battery according to claim 1, characterized in that, The battery cell includes a negative electrode, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a silicon-based material, and the silicon-based material has a mass percentage content of more than 5% based on the weight of the negative electrode active material layer.

12. The lithium-ion secondary battery according to claim 1, characterized in that, The battery cell includes a tab, the tab includes a metal strip and tab adhesive, the tab adhesive is sleeved on at least a portion of the surface of the metal strip, and the tab adhesive is connected to the heat-sealing layer in the aluminum-plastic film; The adhesion force P between the tab adhesive and the aluminum-plastic film is 7N / m-30N / m.

13. The lithium-ion secondary battery according to claim 12, characterized in that, P is 10N / m-25N / m; And / or, the tab adhesive includes an adhesive layer with a melting point of less than 120°C.

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