A battery and an electric device

Abstract

The application provides a battery and a power consumption device, and belongs to the technical field of secondary battery manufacturing. The battery comprises a negative electrode sheet, a positive electrode sheet, a diaphragm and an electrolyte. The negative electrode sheet comprises a composite current collector, a negative electrode active layer located on at least one side of the composite current collector, and a negative electrode protection layer located on the side of the negative electrode active layer away from the composite current collector; the composite current collector comprises a PET base film and metal layers located on both sides of the PET base film, the thickness of the negative electrode protection layer is nanoscale and the negative electrode protection layer can conduct ions; the diaphragm is located between the negative electrode sheet and the positive electrode sheet; the electrolyte contains an organic solvent and an additive, and the additive can react on the surface of the negative electrode active layer to form an SEI film of inorganic salt components in preference to the organic solvent, and the battery can effectively improve the chemical stability of the PET base composite current collector when applied to the end of the battery cell while maintaining the inherent properties of the PET base film.

Description

Technical Field

[0001] This application relates to the field of secondary battery manufacturing technology, and more specifically, to a battery and an electrical device. Background Technology

[0002] With the rapid development of new energy technologies, lithium-ion batteries have been widely used in portable electronic devices and electric vehicles due to their advantages such as high energy density, long cycle life, and environmental friendliness. However, traditional current collector materials for lithium-ion batteries (such as copper foil and aluminum foil) have some limitations, such as occupying a large proportion of the battery's internal space, which seriously affects the battery's energy density.

[0003] To address the aforementioned issues, composite current collectors have garnered significant attention in recent years due to their lightweight, thinness, and low cost. In particular, composite current collectors based on polyethylene terephthalate (PET) have attracted considerable interest in the lithium-ion battery field due to their superior mechanical and electrical properties. However, insufficient understanding of PET-based composite current collectors has led to insufficient chemical stability in their application at the battery cell level, consequently affecting the electrical performance of the corresponding batteries.

[0004] Currently, to address the insufficient chemical stability of PET-based composite current collectors, current methods typically focus on the composite current collector level. For example, patent CN118791770A discloses adding various auxiliary agents during the preparation of the PET base film to obtain a PET-based composite current collector with good resistance to electrolyte corrosion and mechanical properties. Another example is patent CN118721913A, which discloses setting multiple protective layers on both sides of the PET base film to improve its resistance to electrolyte corrosion and high-temperature performance. However, these modification methods sacrifice the inherent properties of the PET base film to some extent and have limited improvement on its chemical stability, resulting in the PET-based composite current collector batteries still exhibiting poor electrical performance. Summary of the Invention

[0005] The purpose of this application is to provide a battery and an electrical device that can effectively improve the chemical stability of PET-based composite current collectors when used in battery cells while maintaining the inherent properties of PET-based films.

[0006] The embodiments of this application are implemented as follows: In a first aspect, embodiments of this application provide a battery comprising a composite current collector, a negative electrode active layer located on at least one side of the composite current collector, and a negative electrode protective layer located on the side of the negative electrode active layer opposite to the composite current collector; the composite current collector comprises a PET base film and metal layers located on both sides of the PET base film, the negative electrode protective layer having a thickness on the nanometer scale and being capable of conducting ions; a separator located between the negative electrode sheet and the positive electrode sheet; the electrolyte contains an organic solvent and an additive, and the additive is able to react preferentially on the surface of the negative electrode active layer to form an SEI film of inorganic salt components.

[0007] In the above technical solution, on the one hand, a nanometer-thick negative electrode protective layer capable of conducting ions is set on the surface of the negative electrode active layer. Since a negative electrode protective layer (i.e., a SEI film is set in advance) is set on the surface of the negative electrode active layer in advance, the intensity of the electrolyte reaction at the surface of the negative electrode active layer can be reduced during the formation stage, which helps to reduce the generation of alkoxy lithium at the surface of the negative electrode active layer. In addition, setting a nanometer-thick negative electrode protective layer on the surface of the negative electrode active layer can also reduce the contact area between the electrolyte and the surface of the negative electrode active layer during battery charging and discharging without affecting the electrolyte wetting of the negative electrode active layer. This also helps to reduce the generation of alkoxy lithium at the surface of the negative electrode active layer. The reduction in the generation of alkoxy lithium can also reduce the amount of alkoxy lithium that penetrates to the surface of the internal PET base film (the PET base film will be corroded by side reactions when in contact with alkoxy lithium), thereby improving the chemical stability of the PET base film during the application process at the cell end. On the other hand, the electrolyte also contains additives, which preferentially react with organic solvents on the surface of the negative electrode active layer to form an inorganic salt SEI film. This effectively improves the incompleteness and low density of local defects in the negative electrode protective layer, thus better assisting the negative electrode protective layer in reducing the formation of alkoxy lithium on the surface of the negative electrode active layer. Through the combined effect of these two aspects, the chemical stability of the PET-based composite current collector can be effectively improved when used in battery cells while maintaining the inherent properties of the PET-based film.

[0008] In some alternative implementations, the material of the negative electrode protective layer is selected from at least one of LiF, Li3N, AlF3, SiO2, TiC and Li2CO3.

[0009] In the above technical solution, the material of the negative electrode protective layer is selected from the above types so that the negative electrode protective layer has excellent stability, density and ion conduction ability, thereby effectively reducing the generation of alkoxy lithium on the surface of the negative electrode active layer; at the same time, there are many types of materials that can be used for the negative electrode protective layer, which can provide more feasible solutions, thereby facilitating the promotion and application of the technical solution provided in the embodiments of this application.

[0010] In some alternative implementations, the material of the negative electrode protective layer is selected from LiF.

[0011] In the above technical solution, the negative electrode protective layer is made of LiF, so that the negative electrode protective layer has better stability, density and ion conduction ability, thereby more effectively reducing the generation of alkoxy lithium on the surface of the negative electrode active layer.

[0012] In some alternative implementations, the thickness of the single-sided negative electrode protective layer is 10 nm to 100 nm.

[0013] In the above technical solution, limiting the thickness of the single-sided negative electrode protective layer within the above range can effectively reduce the generation of alkoxy lithium on the surface of the negative electrode active layer, while also enabling the negative electrode protective layer to have a lower impedance.

[0014] In some alternative embodiments, the additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, LiNO3, and 1,3-propanesulfonate lactone.

[0015] In the above technical solutions, the selection of the above-mentioned additives results in an inorganic salt component SEI film that is relatively stable and dense, which can effectively reduce the generation of alkoxy lithium on the surface of the negative electrode active layer. At the same time, the additives can be made of a variety of materials, providing more feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0016] In some optional implementations, the additive accounts for 0.1% to 20% of the total mass.

[0017] In the above technical solution, limiting the mass ratio of the additive in the electrolyte to the above range can form a relatively stable and dense SEI film. At the same time, it can also ensure that the other components in the electrolyte have a suitable amount and can better exert their respective effects.

[0018] In some alternative embodiments, the positive electrode includes a positive current collector, a positive active layer located on at least one side of the positive current collector, and a positive protective layer located on the side of the positive active layer opposite to the positive current collector, the positive protective layer having a thickness on the nanometer scale and being capable of conducting ions.

[0019] In the above technical solution, a nanometer-thick protective layer capable of conducting ions is provided on the surface of the positive electrode active layer. This can effectively reduce side reactions of the electrolyte at the interface of the positive electrode active layer, thereby reducing the metal ions generated on the positive electrode side due to side reactions. At the same time, the nanometer-thick protective layer on the surface of the positive electrode active layer also helps to improve the stability of the positive electrode active layer during charge-discharge cycles, and also helps to reduce the metal ions dissolved on the positive electrode side. This reduces the risk of metal ions depositing on the negative electrode side and damaging the negative electrode protective layer or SEI film, thereby indirectly reducing the alkoxy lithium generated at the interface of the negative electrode active layer.

[0020] In some alternative embodiments, the material of the positive electrode protective layer is selected from at least one of Al2O3, MgO, TiO2, ZnO, ZrO2, Nb2O5, La2O3, AlF3, Li3N and Li3PO4.

[0021] In the above technical solution, the positive electrode protective layer is selected from the above types of materials so that the positive electrode protective layer has excellent stability, density and ion conduction ability, thereby effectively reducing the metal ions dissolved on the positive electrode side; at the same time, there are many types of materials that can be used for the positive electrode protective layer, which can provide more feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0022] In some alternative implementations, the thickness of the single-sided positive electrode protective layer is 1 nm to 10 nm.

[0023] In the above technical solution, limiting the thickness of the positive electrode protective layer on one side to the above range can effectively reduce the metal ions dissolved on the positive electrode side, and at the same time, it can also make the positive electrode protective layer have a low impedance.

[0024] Secondly, embodiments of this application provide an electrical device, including the battery provided in the first aspect embodiment. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of a battery provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of this application; Figure 3This is a schematic diagram of the structure of a positive electrode sheet provided in an embodiment of this application; Figure 4 This is a disassembled physical image of the PET base film provided in Embodiment 1 of this application; Figure 5 This is a disassembled physical image of the PET base film provided in Embodiment 2 of this application; Figure 6 This is a disassembled physical image of the PET base film provided in Comparative Example 1 of this application; Figure 7 This is a disassembled physical image of the PET base film provided in Comparative Example 2 of this application; Figure 8 This is a disassembled physical image of the PET base film provided in Comparative Example 3 of this application.

[0027] Icons: 10-Battery; 100-Negative electrode; 110-Composite current collector; 111-PET base film; 112-Metal layer; 120-Negative active layer; 130-Negative protective layer; 200-Positive electrode; 210-Positive current collector; 220-Positive active layer; 230-Positive protective layer; 300-Separator. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] The inventors discovered that PET-based composite current collectors suffer from poor stability during battery cell applications. The core reason for this is that during battery formation and charging / discharging, the electrolyte reacts on the surface of the negative electrode (i.e., at the interface between the negative electrode active layer and the electrolyte) to generate organic substances such as lithium alkoxy groups. These substances can penetrate from the surface of the negative electrode active layer to the surface of the internal PET base film through defects such as grain boundaries (even with protective layers added to both sides of the PET base film, it is impossible to effectively prevent the penetration of lithium alkoxy groups). Because the PET base film contains a large number of carbonyl groups, coupled with the nucleophilicity of lithium alkoxy groups, PET is prone to side reactions with lithium alkoxy groups and is corroded, which leads to poor stability of PET-based composite current collectors during battery cell applications.

[0032] It should be noted that organic compounds such as lithium alkoxy groups are mainly generated on the surface of the negative electrode rather than within the pores. The main reason is that this reaction is an interfacial reaction, which requires electrons, lithium ions, solvents, and a suitable potential to proceed. Lithium ions cross the membrane from the positive electrode, and the first place they reach is the surface of the negative electrode. Since there are no electrons in the pores, electrons are transferred to the graphite through the negative electrode current collector. Therefore, the reaction of the electrolyte and the generation of organic compounds such as lithium alkoxy groups mainly occur on the surface of the negative electrode. Thus, the amount of organic compounds such as lithium alkoxy groups generated is reduced by focusing on the surface of the negative electrode.

[0033] Based on this, the inventors innovatively proposed adding a nanometer-thick negative electrode protective layer to the surface of the negative electrode active layer, which is capable of conducting ions. They also added an additive to the electrolyte that can preferentially react on the surface of the negative electrode active layer to form an inorganic salt film, which is more likely to react than organic solvents. They found that this can effectively reduce the generation of alkoxy lithium at the battery level, thereby effectively improving the chemical stability of PET-based composite current collectors when used in battery cells while maintaining the inherent properties of the PET-based film.

[0034] The following is a detailed description of a battery 10 and an electrical device according to an embodiment of this application.

[0035] See Figure 1 and Figure 2 In a first aspect, embodiments of this application provide a battery 10, including a composite current collector 110, a negative electrode active layer 120 located on at least one side of the composite current collector 110, and a negative electrode protective layer 130 located on the side of the negative electrode active layer 120 opposite to the composite current collector 110; the composite current collector 110 includes a PET base film 111 and metal layers 112 located on both sides of the PET base film 111, the negative electrode protective layer 130 has a thickness of nanometer scale and is capable of conducting ions; a separator 300 is located between a negative electrode sheet 100 and a positive electrode sheet 200; the electrolyte contains an organic solvent and additives, and the additives can react preferentially on the surface of the negative electrode active layer 120 of the negative electrode sheet 100 to form an inorganic salt component SEI film.

[0036] In this application, on the one hand, a nanometer-thick negative electrode protective layer 130 capable of conducting ions is provided on the surface of the negative electrode active layer 120. Since the negative electrode protective layer 130 (i.e., the SEI film is provided in advance) is provided on the surface of the negative electrode active layer 120 beforehand, the intensity of the electrolyte reaction at the interface of the negative electrode active layer 120 can be reduced during the formation stage, which helps to reduce the generation of alkoxy lithium on the surface of the negative electrode active layer 120. In addition, the nanometer-thick negative electrode protective layer 130 capable of conducting ions is provided on the surface of the negative electrode active layer 120. During the charging and discharging process of battery 10, the contact area between the electrolyte and the surface of the negative electrode active layer 120 can be reduced without affecting the wetting of the negative electrode active layer 120 by the electrolyte. This also helps to reduce the generation of alkoxy lithium on the surface of the negative electrode active layer 120. The reduction in the generation of alkoxy lithium reduces the amount of alkoxy lithium that penetrates to the surface of the PET base film 111 (the PET base film 111 will undergo side reactions and be corroded when in contact with alkoxy lithium), thereby improving the chemical stability of the PET base film 111 in the cell application process. On the other hand, the electrolyte also contains additives, which can preferentially react on the surface of the negative electrode active layer 120 to form an inorganic salt SEI film, which can effectively improve the incomplete and low-density local defects of the negative electrode protective layer 130, thereby better assisting the negative electrode protective layer 130 in reducing the generation of alkoxy lithium on the surface of the negative electrode active layer 120. Through the combined effect of these two aspects, the chemical stability of the PET-based composite current collector 110 in the cell application can be effectively improved while maintaining the inherent properties of the PET base film 111.

[0037] As an example, the material of the negative electrode protective layer 130 is selected from at least one of LiF, Li3N, AlF3, SiO2, TiC and Li2CO3.

[0038] In this embodiment, the material of the negative electrode protective layer 130 is selected from the above-mentioned types so that the negative electrode protective layer 130 has excellent stability, density and ion conduction ability, thereby effectively reducing the alkoxy lithium generated on the surface of the negative electrode active layer 120; at the same time, a variety of materials can be used for the negative electrode active layer 120 and the negative electrode protective layer 130, which can provide a variety of feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0039] As an example, the negative electrode protective layer 130 is made of LiF.

[0040] In this embodiment, the negative electrode protective layer 130 is made of LiF, so that the negative electrode protective layer 130 has better stability, density and ion conduction ability, thereby more effectively reducing the generation of alkoxy lithium on the surface of the negative electrode active layer 120.

[0041] As an example, the thickness of the single-sided negative electrode protective layer 130 is 10 nm to 100 nm, for example, but not limited to any one of the following thicknesses: 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm and 100 nm, or any range between two of them.

[0042] In this embodiment, limiting the thickness of the single-sided negative electrode protective layer 130 to the above-mentioned range can effectively reduce the generation of alkoxy lithium at the interface of the negative electrode active layer 120, while also enabling the negative electrode protective layer 130 to have a lower impedance.

[0043] As an example, the thickness of the PET base film 111 is 3 μm to 10 μm, for example, but not limited to any one of the thicknesses of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm or any range between two of them.

[0044] As an example, the material of the metal layer 112 is selected from copper foil, and the thickness of a single metal layer 112 is 0.1 μm to 3 μm, for example, but not limited to any one of the thicknesses of 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm and 3 μm or any range between two of them.

[0045] As an example, the active material in the negative electrode active layer 120 includes at least one of graphite and silicon.

[0046] As an example, the thickness of a single negative electrode active layer 120 is 50 μm to 300 μm, for example, but not limited to any one of the thicknesses of 50 μm, 100 μm, 150 μm, 200 μm, 250 μm and 300 μm or any range between two.

[0047] As an example, the additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, LiNO3, and 1,3-propanesulfonic acid lactone.

[0048] In this embodiment, the additives selected are of the above types, and the resulting inorganic salt component SEI film has the advantages of being relatively stable and dense, which can effectively reduce the generation of alkoxy lithium on the surface of the negative electrode active layer 120. At the same time, there are many types of materials that can be used for the additives, which can provide more feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0049] As an example, the additive may be present in the range of 0.1% to 20% by mass, for example, but not limited to any one of the following mass percentages or a range between any two: 0.1%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, and 20%.

[0050] In this embodiment, limiting the mass ratio of the additive in the electrolyte to the above-mentioned range enables the formation of a relatively stable and dense SEI film. At the same time, it also allows the other components in the electrolyte to have a suitable amount and perform their respective functions well.

[0051] As an example, the lithium salt in the electrolyte is selected from lithium hexafluorophosphate.

[0052] As an example, the organic solvent is selected from at least two of ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0053] See Figure 3 As an example, the positive electrode 200 includes a positive current collector 210, a positive active layer 220 located on at least one side of the positive current collector 210, and a positive protective layer 230 located on the side of the positive active layer 220 opposite to the positive current collector 210. The thickness of the positive protective layer 230 is on the nanometer scale and it is capable of conducting ions.

[0054] In this embodiment, a positive electrode protective layer 230 with a thickness of nanometers and capable of conducting ions is provided on the surface of the positive electrode active layer 220. This can effectively reduce the side reactions of the electrolyte on the surface of the positive electrode active layer 220, thereby reducing the metal ions generated on the positive electrode side due to the side reactions. At the same time, the positive electrode protective layer 230 with a thickness of nanometers and capable of conducting ions is provided on the surface of the positive electrode active layer 220, which also helps to improve the stability of the positive electrode active layer 220 during charge and discharge cycles. It also helps to reduce the metal ions dissolved on the positive electrode side, thereby reducing the risk of metal ions depositing on the negative electrode side and damaging the negative electrode protective layer 130 or the SEI film, thereby indirectly reducing the alkoxy lithium generated on the surface of the negative electrode active layer 120.

[0055] As an example, the material of the positive electrode protective layer 230 is selected from at least one of Al2O3, MgO, TiO2, ZnO, ZrO2, Nb2O5, La2O3, AlF3, Li3N and Li3PO4.

[0056] In this embodiment, the positive electrode protective layer 230 is made of the aforementioned materials so that the positive electrode protective layer 230 has both excellent stability, density and ion conduction ability, thereby effectively reducing the metal ions dissolved from the positive electrode side; at the same time, the positive electrode protective layer 230 can be made of a variety of materials, which can provide more feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0057] As an example, the thickness of the single-sided positive electrode protective layer 230 is 1 nm to 10 nm, for example, but not limited to any one of the thicknesses of 1 nm, 2 nm, 4 nm, 6 nm, 8 nm and 10 nm or any range between two.

[0058] In this embodiment, limiting the thickness of the single-sided positive electrode protective layer 230 to the above range can effectively reduce the metal ions dissolved on the positive electrode side, while also enabling the positive electrode protective layer 230 to have a lower impedance.

[0059] As an example, the positive current collector 210 is selected from aluminum foil, and the thickness of the positive current collector 210 is 8 μm to 20 μm, for example, but not limited to any one of the thicknesses of 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm and 20 μm or any range between two of them.

[0060] As an example, the active material in the positive electrode active layer 220 includes at least one of ternary high-nickel positive electrode materials and lithium iron phosphate.

[0061] As an example, the thickness of a single positive electrode active layer 220 is 50 μm to 300 μm, for example, but not limited to any one of the thicknesses of 50 μm, 100 μm, 150 μm, 200 μm, 250 μm and 300 μm or any range between two.

[0062] As an example, the diaphragm 300 is selected from polypropylene-coated ceramic diaphragm 300 and has a thickness of 10 μm to 20 μm, such as, but not limited to, any point value or range between any two of the thicknesses of 10 μm, 12 μm, 14 μm, 16 μm, 18 μm and 20 μm.

[0063] It should be noted that structural or functional units in the battery that are not specifically described or limited can be set in accordance with conventional choices in the field.

[0064] It should be noted that the battery assembly process is not limited and can be carried out according to conventional processes in this field.

[0065] Secondly, embodiments of this application provide an electrical device, including the battery provided in the first aspect embodiment.

[0066] It should be noted that there are no restrictions on the type of electrical equipment; for example, it can be a mobile phone, a car, an airplane, a ship, etc.

[0067] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0068] Example 1 This application provides a battery assembly process, including the following steps: Positive electrode preparation: A copper foil with a thickness of 12 μm was selected as the positive electrode current collector. Then, the positive electrode slurry was coated on both sides of the positive electrode current collector and dried. The positive electrode slurry included NCM811 positive electrode active material, conductive carbon and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5 to form a single-layer positive electrode active layer with a thickness of 100 μm. Then, a single-layer aluminum layer with a thickness of 2 nm was formed on the surface of the positive electrode active layer by magnetron sputtering and annealed at 80°C to form an Al2O3 positive electrode protective layer.

[0069] Negative electrode preparation: PET with a thickness of 4.5 μm was selected as the base film. Then, a copper layer with a thickness of 1 μm was formed on both sides of the PET base film using magnetron sputtering. The negative electrode slurry was then coated on the surface of the metal layer and dried. The negative electrode slurry consisted of graphite negative electrode active material, conductive carbon, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2 to form a single-layer negative electrode active layer with a thickness of 180 μm. Then, a single-layer LiF negative electrode protective layer with a thickness of 20 nm was formed on the surface of the negative electrode active layer using magnetron sputtering and annealed at 80 °C.

[0070] Electrolyte preparation: EC, DMC and EMC are mixed in a volume ratio of 1:1:1 to form an organic solvent. Then lithium hexafluorophosphate and additives are added to it. The mass percentage of lithium salt in the electrolyte is 15%, and the mass percentage of additives is 8% (composed of 2% vinylene carbonate-VC, 5% fluoroethylene carbonate-FEC, and 1% lithium difluorooxalate borate-LiDFOB).

[0071] Then, the negative electrode, separator (a 15 μm thick ceramic separator coated with polypropylene) and positive electrode are assembled using a stacking process to obtain a bare cell. The bare cell is then placed in a casing and the electrolyte is injected into the dried battery. After encapsulation, settling, formation, shaping and capacity testing, the battery is assembled.

[0072] Example 2 This application provides a battery assembly process, including the following steps: Positive electrode preparation: A copper foil with a thickness of 12 μm is selected as the positive electrode current collector. Then, the positive electrode slurry is coated on both sides of the positive electrode current collector and dried. The positive electrode slurry includes NCM811 positive electrode active material, conductive carbon and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5 to form a single positive electrode active layer with a thickness of 100 μm.

[0073] Negative electrode preparation: PET with a thickness of 4.5 μm was selected as the base film. Then, a copper layer with a thickness of 1 μm was formed on both sides of the PET base film using magnetron sputtering. The negative electrode slurry was then coated on the surface of the metal layer and dried. The negative electrode slurry consisted of graphite negative electrode active material, conductive carbon, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2 to form a single-layer negative electrode active layer with a thickness of 180 μm. Then, a single-layer LiF negative electrode protective layer with a thickness of 20 nm was formed on the surface of the negative electrode active layer using magnetron sputtering and annealed at 80 °C.

[0074] Electrolyte preparation: EC, DMC and EMC are mixed in a volume ratio of 1:1:1 to form an organic solvent. Then lithium hexafluorophosphate and additives are added to it. The mass percentage of lithium salt in the electrolyte is 15%, and the mass percentage of additives is 8% (composed of 2% vinylene carbonate-VC, 5% fluoroethylene carbonate-FEC, and 1% lithium difluorooxalate borate-LiDFOB).

[0075] Then, the negative electrode, separator (a 15 μm thick ceramic separator coated with polypropylene) and positive electrode are assembled using a stacking process to obtain a bare cell. The bare cell is then placed in a casing and the electrolyte is injected into the dried battery. After encapsulation, settling, formation, shaping and capacity testing, the battery is assembled.

[0076] Comparative Example 1 This application provides a comparative example of a battery assembly process, including the following steps: Positive electrode preparation: A copper foil with a thickness of 12 μm is selected as the positive electrode current collector. Then, the positive electrode slurry is coated on both sides of the positive electrode current collector and dried. The positive electrode slurry includes NCM811 positive electrode active material, conductive carbon and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5 to form a single positive electrode active layer with a thickness of 100 μm.

[0077] Negative electrode preparation: PET with a thickness of 4.5 μm is selected as the base film. Then, a copper layer with a thickness of 1 μm is formed on both sides of the PET base film using magnetron sputtering coating technology. Then, the negative electrode slurry is coated on the surface of the metal layer and dried. The negative electrode slurry includes graphite negative electrode active material, conductive carbon, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2 to form a single-layer negative electrode active layer with a thickness of 180 μm.

[0078] Electrolyte preparation: Mix EC, DMC and EMC in a volume ratio of 1:1:1 to form an organic solvent, and then add lithium hexafluorophosphate to it. The mass percentage of lithium salt in the electrolyte is 15%.

[0079] Then, the negative electrode, separator (a 15 μm thick ceramic separator coated with polypropylene) and positive electrode are assembled using a stacking process to obtain a bare cell. The bare cell is then placed in a casing and the electrolyte is injected into the dried battery. After encapsulation, settling, formation, shaping and capacity testing, the battery is assembled.

[0080] Comparative Example 2 This application provides a comparative example of a battery assembly process, including the following steps: Positive electrode preparation: A copper foil with a thickness of 12 μm is selected as the positive electrode current collector. Then, the positive electrode slurry is coated on both sides of the positive electrode current collector and dried. The positive electrode slurry includes NCM811 positive electrode active material, conductive carbon and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5 to form a single positive electrode active layer with a thickness of 100 μm.

[0081] Negative electrode preparation: PET with a thickness of 4.5 μm was selected as the base film. Then, a copper layer with a thickness of 1 μm was formed on both sides of the PET base film using magnetron sputtering. The negative electrode slurry was then coated on the surface of the metal layer and dried. The negative electrode slurry consisted of graphite negative electrode active material, conductive carbon, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2 to form a single-layer negative electrode active layer with a thickness of 180 μm. Then, a single-layer LiF negative electrode protective layer with a thickness of 20 nm was formed on the surface of the negative electrode active layer using magnetron sputtering and annealed at 80 °C.

[0082] Electrolyte preparation: Mix EC, DMC and EMC in a volume ratio of 1:1:1 to form an organic solvent, and then add lithium hexafluorophosphate to it. The mass percentage of lithium salt in the electrolyte is 15%.

[0083] Then, the negative electrode, separator (a 15 μm thick ceramic separator coated with polypropylene) and positive electrode are assembled using a stacking process to obtain a bare cell. The bare cell is then placed in a casing and the electrolyte is injected into the dried battery. After encapsulation, settling, formation, shaping and capacity testing, the battery is assembled.

[0084] Comparative Example 3 This application provides a comparative example of a battery assembly process, including the following steps: Positive electrode preparation: A copper foil with a thickness of 12 μm is selected as the positive electrode current collector. Then, the positive electrode slurry is coated on both sides of the positive electrode current collector and dried. The positive electrode slurry includes NCM811 positive electrode active material, conductive carbon and polyvinylidene fluoride in a mass ratio of 95:2.5:2.5 to form a single positive electrode active layer with a thickness of 100 μm.

[0085] Negative electrode preparation: PET with a thickness of 4.5 μm is selected as the base film. Then, a copper layer with a thickness of 1 μm is formed on both sides of the PET base film using magnetron sputtering coating technology. Then, the negative electrode slurry is coated on the surface of the metal layer and dried. The negative electrode slurry includes graphite negative electrode active material, conductive carbon, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2 to form a single-layer negative electrode active layer with a thickness of 180 μm.

[0086] Electrolyte preparation: EC, DMC and EMC are mixed in a volume ratio of 1:1:1 to form an organic solvent. Then lithium hexafluorophosphate and additives are added to it. The mass percentage of lithium salt in the electrolyte is 15%, and the mass percentage of additives is 8% (composed of 2% vinylene carbonate-VC, 5% fluoroethylene carbonate-FEC, and 1% lithium difluorooxalate borate-LiDFOB).

[0087] Then, the negative electrode, separator (a 15 μm thick ceramic separator coated with polypropylene) and positive electrode are assembled using a stacking process to obtain a bare cell. The bare cell is then placed in a casing and the electrolyte is injected into the dried battery. After encapsulation, settling, formation, shaping and capacity testing, the battery is assembled.

[0088] Test case The batteries prepared in Examples 1-2 and Comparative Examples 1-3 were used as test samples. Each sample was fully charged and placed in a 45°C constant temperature explosion-proof cabinet for 7 days. Each sample was then removed and its capacity was tested again to calculate the capacity retention rate of each sample. The test results are summarized in Table 1. After each battery was discharged, the negative electrode sheet in the middle position was removed, the negative electrode slurry was removed in water, and the copper layer was removed in water using ultrasound. The surface morphology of the PET base film was observed using an optical microscope.

[0089] Table 1

[0090] See Table 1 and Figure 4~Figure 8 As can be seen from the test results of Examples 1-2 and Comparative Examples 1-3, adding a nanometer-thick negative electrode protective layer that can conduct ions to the surface of the negative electrode active layer, and adding an additive to the electrolyte that can preferentially react with organic solvents at the interface of the negative electrode active layer to form an inorganic salt film, can effectively alleviate the problem of corrosion of PET base film. This can effectively improve the chemical stability of PET base composite current collector when used in the cell without affecting the inherent performance of PET base film, thereby making the corresponding battery have a better capacity retention rate.

[0091] The test results of Examples 1 and 2 show that by adding a nanometer-thick negative electrode protective layer to the surface of the negative electrode active layer and enabling it to conduct ions, and by adding an additive to the electrolyte that can preferentially react with organic solvents at the interface of the negative electrode active layer to form an inorganic salt film, further adding a nanometer-thick negative electrode protective layer to the surface of the negative electrode active layer can further alleviate the problem of corrosion of the PET base film. This can more effectively improve the chemical stability of the PET base composite current collector when it is used in the cell without affecting the inherent performance of the PET base film, thereby making the corresponding battery have a better capacity retention rate.

[0092] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A battery, characterized in that, include: A negative electrode sheet, comprising a composite current collector, a negative electrode active layer located on at least one side of the composite current collector, and a negative electrode protective layer located on the side of the negative electrode active layer opposite to the composite current collector; the composite current collector comprises a PET base film and metal layers located on both sides of the PET base film, and the negative electrode protective layer has a thickness on the nanometer scale and is capable of conducting ions; A positive electrode and a separator, wherein the separator is located between the negative electrode and the positive electrode; An electrolyte containing an organic solvent and an additive, wherein the additive is able to react preferentially over the organic solvent on the surface of the negative electrode active layer to form an SEI film of inorganic salt components.

2. The battery according to claim 1, characterized in that, The material of the negative electrode protective layer is selected from at least one of LiF, Li3N, AlF3, SiO2, TiC and Li2CO3.

3. The battery according to claim 2, characterized in that, The negative electrode protective layer is made of LiF.

4. The battery according to claim 1, characterized in that, The thickness of the negative electrode protective layer on one side is 10 nm to 100 nm.

5. The battery according to any one of claims 1 to 4, characterized in that, The additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, LiNO3, and 1,3-propanesulfonic acid lactone.

6. The battery according to claim 5, characterized in that, In the electrolyte, the additive accounts for 0.1% to 20% by mass.

7. The battery according to any one of claims 1 to 4, characterized in that, The positive electrode includes a positive current collector, a positive active layer located on at least one side of the positive current collector, and a positive protective layer located on the side of the positive active layer opposite to the positive current collector. The thickness of the positive protective layer is on the nanometer scale and it is capable of conducting ions.

8. The battery according to claim 7, characterized in that, The material of the positive electrode protective layer is selected from at least one of Al2O3, MgO, TiO2, ZnO, ZrO2, Nb2O5, La2O3, AlF3, Li3N and Li3PO4.

9. The battery according to claim 8, characterized in that, The thickness of the positive electrode protective layer on one side is 1 nm to 10 nm.

10. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 1 to 9.

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