WO2024244232A1 - Composite conductive agent, and negative electrode composition, negative electrode sheet, battery and electric device comprising same - Google Patents

Abstract

Provided in the present application are a composite conductive agent, and a negative electrode composition, a negative electrode sheet, a battery and an electric device comprising same. The composite conductive agent comprises a conductive base material and an organic film-forming additive, wherein the organic film-forming additive comprises a halogen atom and is attached to a surface of the conductive base material.

Description

Composite conductive agent, negative electrode composition containing the same, negative electrode sheet, battery and electrical device

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese patent application 202310611703.7 filed on May 26, 2023, entitled “Composite conductive agent, negative electrode composition containing the same, negative electrode sheet, battery and electrical device”, the entire contents of which are incorporated herein by reference.

Technical Field

The present application relates to the field of battery technology, and in particular to a composite conductive agent, a negative electrode composition containing the composite conductive agent, a negative electrode sheet, a battery and an electrical device.

Background Art

Secondary batteries rely on active ions to be reciprocated between the positive and negative electrodes for charging and discharging. Secondary batteries represented by lithium-ion batteries have outstanding features such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy source, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy. As a result, higher requirements are also placed on the cycle performance of secondary batteries.

Summary of the invention

In order to achieve the above-mentioned purpose, the present application provides a composite conductive agent, which can improve the cycle performance of a battery containing the composite conductive agent; the present application also provides a negative electrode composition, a negative electrode sheet, a battery and an electrical device containing the composite conductive agent.

A first aspect of an embodiment of the present application provides a composite conductive agent, which includes a conductive substrate and an organic film-forming additive, wherein the organic film-forming additive includes halogen atoms, and the organic film-forming additive is attached to the surface of the conductive substrate.

Without intending to be limited by any theory or explanation, the composite guide tube of the present application embodiment The organic film-forming additive contained in the electrolyte contains halogen atoms in its molecules, which can interact with the electrolyte to form a solid electrolyte interface (SEI film) in situ. In the related art, when preparing the negative electrode slurry, the organic film-forming additive is mixed with other ingredients as an independent component, and the resulting negative electrode slurry is coated and dried to form a negative electrode film layer; however, during the drying process of the negative electrode slurry, the organic film-forming additive will migrate to the surface of the formed negative electrode film layer and precipitate, which on the one hand causes the SEI film subsequently formed on the surface of the negative electrode film layer to be unstable, and on the other hand, it may also occupy the position of the binder, resulting in the risk of the negative electrode film layer falling off from the surface of the current collector. Compared with the related art, in the embodiment of the present application, the organic film-forming additive is attached to the surface of the conductive substrate, which can allow the organic film-forming additive to be uniformly dispersed in the negative electrode slurry along with the conductive substrate, and then uniformly dispersed in the negative electrode slurry coating. Therefore, on the one hand, the probability of precipitation of organic film-forming additives during the drying process of the negative electrode sheet can be significantly reduced, thereby reducing the risk of the negative electrode film layer falling off from the current collector surface caused by the precipitation of organic film-forming additives; on the other hand, the organic film-forming additives can be evenly distributed in the negative electrode film layer. The appropriate amount of organic film-forming additives evenly distributed in the negative electrode film layer is conducive to the in-situ formation of a dense, uniform and stable SEI film on the surface of the negative electrode film layer, thereby effectively inhibiting the capacity decay of the battery and improving the stability of the negative electrode environment.

Therefore, the composite conductive agent of the embodiment of the present application is applied to a secondary battery, which can effectively improve the cycle performance of the battery.

In any embodiment of the present application, the organic film-forming additive is attached to the surface of the conductive substrate through chemical bonds.

When the organic film-forming additive is attached to the surface of the conductive substrate through chemical bonds, the organic film-forming additive and the conductive substrate can be more firmly combined together, thereby reducing the risk of the organic film-forming additive falling off the surface of the conductive substrate during the preparation and processing of the negative electrode plate. This is conducive to further improving the uniformity and stability of the SEI film, thereby improving the cycle performance of the battery.

In any embodiment of the present application, the conductive substrate includes a carbon material, and the carbon material includes unsaturated carbon-carbon double bonds and/or carbon-carbon triple bonds.

The organic film-forming additives include fluorine-containing film-forming additives, which contain fluorine-substituted carbon chains and electrophilic groups pendant from the carbon chains.

The fluorine-containing film-forming additive is attached to the surface of the conductive substrate through a covalent bond formed by the reaction of an electrophilic group with a carbon-carbon double bond and/or a carbon-carbon triple bond.

When the organic film-forming additive includes a fluorine-containing film-forming additive, it is beneficial to further improve the density of the SEI film, thereby further improving the stability of the negative electrode environment during the charge and discharge cycle, thereby improving the cycle performance of the battery.

In any embodiment of the present application, the molecular chain of the fluorine-containing film-forming additive comprises a structural unit of of the copolymer chain segment.

Here, R ₁ and R ₂ each independently represent a hydrogen atom or a C1-C6 alkyl group.

Therefore, the composite conductive agent of the embodiment of the present application is applied to the negative electrode sheet of the secondary battery, and can form a uniform, dense and stable SEI film on the surface of the negative electrode sheet, thereby improving the cycle performance of the battery.

In any embodiment of the present application, in the fluorine-containing film-forming additive, and The average molar ratio of is 0.5 to 5. Therefore, the composite conductive agent of the embodiment of the present application has a suitable content of conductive substrate and fluorine-containing film-forming additive, and is applied to the negative electrode sheet to enable the battery to maintain good rate performance and improve the cycle performance of the battery.

In any embodiment of the present application, the weight average molecular weight Mw of the fluorine-containing film-forming additive is 3000 to 800000. This can not only improve the film-forming performance of the composite conductive agent, but also make the composite conductive agent evenly dispersed in the negative electrode film layer and entangled with each other, so that the composite conductive agent has certain bonding properties.

In any embodiment of the present application, the fluorine-containing film-forming additive includes one or more of the compounds shown in Formula 1.

Here, R ₁₁ to R ₁₄ each independently represent a hydrogen atom or a C1 to C6 alkyl group.

m is selected from integers of 0 to 3000, n is selected from integers of 30 to 3000, p is selected from integers of 0 to 3000, and m+p＞0.

The fluorine-containing film-forming additive is attached to the surface of the conductive substrate through a covalent bond formed by the reaction of an azide group with a carbon-carbon double bond and/or a carbon-carbon triple bond.

The compound shown in Formula 1 has a specific structural unit, which can improve the conductivity and film-forming properties of the composite conductive agent. Therefore, the composite conductive agent is applied to the negative electrode of the secondary battery to improve the density, uniformity and stability of the SEI film, thereby improving the cycle performance of the battery.

In any embodiment of the present application, R ₁₁ to R ₁₄ each independently represent a hydrogen atom or a C1 to C3 alkyl group.

In any embodiment of the present application, m is selected from an integer of 300 to 3000, n is selected from an integer of 30 to 3000, and p is selected from an integer of 300 to 3000.

When at least one of R ₁₁ to R ₁₄ , m, n, and p satisfies the above conditions, the conductivity and film-forming properties of the composite conductive agent can be further improved. Thus, the composite conductive agent is applied to the negative electrode of the secondary battery to further improve the compactness, uniformity and stability of the SEI film, thereby improving the cycle performance of the battery.

In any embodiment of the present application,

In any embodiment of the present application,

When m, n, and p in Formula 1 satisfy the above conditions, the fluorine-containing film-forming additive molecular chain can contain an appropriate amount of azide groups, so that the fluorine-containing film-forming additive molecular chain is connected to an appropriate amount of conductive substrate. In this way, the conductive performance of the composite conductive agent can be improved. In addition, when m, n, and p in Formula 1 satisfy the above conditions, the fluorine-containing film-forming additive molecular chain can also be connected to an appropriate amount of conductive substrate. The membrane additive has a suitable fluorine content, thereby improving the density and stability of the SEI membrane. Therefore, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can further improve the cycle performance of the battery.

In any embodiment of the present application, 0.5≤m/p≤1.5.

In any embodiment of the present application, 0.8≤m/p≤1.2.

When the ratio of m to p in the compound shown in Formula 1 is within the above range, it can be considered that the molecular chain of the fluorine-containing film-forming additive has a higher symmetry. In other words, when the ratio of m to p is within the above range, the fluorine atoms can be more evenly distributed in the molecular chain of the fluorine-containing film-forming additive. Thus, the uniformity of the SEI film formed in situ by the composite conductive agent can be further improved. Therefore, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can further improve the cycle performance of the battery.

In any embodiment of the present application, the conductive substrate includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

The surface of the conductive substrate selected from the above types may include an appropriate amount of active oxygen-containing groups, so that it can be easily modified to introduce unsaturated carbon-carbon double bonds and/or carbon-carbon triple bonds, thereby allowing the conductive substrate to be firmly combined with the organic film-forming additive. As a result, the composite conductive agent of the embodiment of the present application can form a more uniform SEI film in situ in the negative electrode film layer, thereby improving the cycle performance of the battery.

In any embodiment of the present application, based on the total mass of the composite conductive agent, the mass percentage of the conductive substrate is 8% to 95%. By adjusting the mass percentage of the conductive substrate in the composite conductive agent, the conductive properties and film-forming properties of the composite conductive agent can be regulated. When the mass percentage of the conductive substrate meets the given range, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can improve the cycle stability of the battery and extend the cycle life of the battery.

A second aspect of an embodiment of the present application provides a negative electrode composition, which includes a negative electrode active material and the composite conductive agent of the first aspect.

The negative electrode composition of the second aspect of the embodiment of the present application includes the composite conductive agent of the first aspect, and is applied to the negative electrode plate of the secondary battery, and can form a dense, uniform and stable SEI film in situ on the surface of the negative electrode film layer, thereby effectively inhibiting the capacity decay of the battery and improving the battery life. Improve the stability of the negative electrode environment. Thus, the cycle performance of the battery can be effectively improved.

In any embodiment of the present application, based on the total mass of the negative electrode composition, the mass percentage of the composite conductive agent is 0.2% to 3.0%, and can be optionally 0.5% to 2.0%.

When the mass percentage of the composite conductive agent is within the above-mentioned appropriate range, the negative electrode film layer can contain an appropriate amount of fluorine-containing film-forming additive, thereby improving the density and uniformity of the SEI film, thereby improving the cycle stability of the battery.

A third aspect of an embodiment of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises the negative electrode composition of the second aspect.

The negative electrode sheet of the third aspect of the embodiment of the present application includes the negative electrode composition of the second aspect, and is applied to the negative electrode sheet of a secondary battery, which can form a dense, uniform and stable SEI film in situ on the surface of the negative electrode film layer, thereby effectively suppressing the capacity decay of the battery and improving the stability of the negative electrode environment. Thus, the cycle performance of the battery can be effectively improved.

In any embodiment of the present application, the infrared absorption spectrum of the negative electrode plate may have a characteristic peak located at 1180 cm ^-1 to 1185 cm ^-1 . The above characteristic peak is a characteristic peak for characterizing -CF ₂ -. When the infrared absorption spectrum of the negative electrode plate has the above characteristic peak, it is beneficial to further improve the density of the SEI film. Therefore, it is beneficial to further improve the stability of the negative electrode environment during the charge and discharge cycle, thereby improving the cycle performance of the battery.

A fourth aspect of an embodiment of the present application provides a battery, comprising the negative electrode plate of the third aspect.

A fifth aspect of an embodiment of the present application provides an electrical device, comprising the battery of the fourth aspect.

The electric device of the embodiment of the present application comprises the battery of the fourth aspect, and thus has at least the same advantages as the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a battery cell of the present application.

FIG. 2 is an exploded view of the embodiment of the battery cell of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.

FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.

FIG. 5 is an exploded view of the battery pack of the present application shown in FIG. 4 .

FIG6 is a schematic diagram of an embodiment of an electric device of the present application. The electric device may include a battery pack or a battery module according to an embodiment of the present application as a power source.

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate.

DETAILED DESCRIPTION

Hereinafter, the embodiments of the composite conductive agent, the negative electrode composition containing the composite conductive agent, the negative electrode sheet, the battery and the electric device of the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

"Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

In this article, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain structures and branched structures. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl (such as n-propyl, isopropyl), butyl (such as n-butyl, isobutyl, sec-butyl, tert-butyl), pentyl (such as n-pentyl, isopentyl, neopentyl). In various embodiments, C1-C6 alkyl, i.e., alkyl, may contain 1 to 6 carbon atoms.

Throughout this specification, the substituents of compounds are disclosed in groups or ranges. It is expressly intended that this description includes each individual subcombination of the members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 alkyl" discloses C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5 and C5-C6 alkyl individually.

With the application of secondary batteries in various electronic products and new energy vehicles and other industries The promotion and application of secondary batteries have put forward higher requirements on the cycle performance of secondary batteries.

During the first charging process of a secondary battery, a solid electrolyte interface (SEI) film is formed on the surface of the negative electrode active material. The SEI film is insoluble in organic solvents and can exist stably in organic electrolyte solutions. The SEI film allows active lithium ions to pass through, but does not allow solvent molecules to pass through, thereby effectively inhibiting the co-embedding of solvent molecules and reducing the damage of solvent molecules to the negative electrode active materials. However, during the charge and discharge cycle, the SEI film may rupture due to reasons such as the expansion of the negative electrode active material, and active lithium ions need to be continuously consumed to form a new SEI film. The instability of the SEI film will not only aggravate the capacity decay of the battery, but also be detrimental to maintaining the stability of the negative electrode environment, thereby deteriorating the battery's cycle performance. Since the formation mechanism and composition of the SEI film are not very clear at present, how to generate a stable SEI film is still a very challenging technical task.

In view of this, an embodiment of the present application provides a composite conductive agent, which can improve the cycle performance of a battery containing the composite conductive agent; the present application also provides a negative electrode composition, a negative electrode sheet, a battery and an electrical device containing the composite conductive agent.

Composite conductive agent

A first aspect of an embodiment of the present application proposes a composite conductive agent, which includes a conductive substrate and an organic film-forming additive. The organic film-forming additive includes halogen atoms, and the organic film-forming additive is attached to the surface of the conductive substrate.

In the present application, "the organic film-forming additive is attached to the surface of the conductive substrate" means that the molecules of the organic film-forming additive are anchored on the surface of the conductive substrate by interacting with the surface of the conductive substrate. For example, the organic film-forming additive can be attached to the surface of the conductive substrate by chemical bonds or strong hydrogen bonds. As an example, those skilled in the art can modify the organic film-forming additive and/or the conductive substrate so that the organic film-forming additive interacts with the conductive substrate (for example, forming chemical bonds or hydrogen bonds), so that the organic film-forming additive is attached to the surface of the conductive substrate.

Without intending to be limited by any theory or explanation, the organic film-forming additive contained in the composite conductive agent of the embodiment of the present application contains halogen atoms in the organic film-forming additive molecules, which can interact with the electrolyte to form an SEI film in situ. In the related art, when preparing the negative electrode slurry, the organic film-forming additive is mixed with other ingredients as an independent component. The obtained negative electrode slurry is coated and dried into a negative electrode film layer; however, during the drying process of the negative electrode slurry, the organic film-forming additive will migrate to the surface of the formed negative electrode film layer and precipitate, which, on the one hand, causes the SEI film subsequently formed on the surface of the negative electrode film layer to be unstable, and on the other hand, it may also occupy the position of the binder, resulting in the risk of the negative electrode film layer falling off from the surface of the current collector. Compared with the related art, in the embodiment of the present application, the organic film-forming additive is attached to the surface of the conductive substrate, which allows the organic film-forming additive to be uniformly dispersed in the negative electrode slurry along with the conductive substrate, and then uniformly dispersed in the negative electrode slurry coating. As a result, on the one hand, the probability of precipitation of the organic film-forming additive during the drying process of the negative electrode pole piece can be significantly reduced, thereby reducing the risk of the negative electrode film layer falling off from the surface of the current collector caused by the precipitation of the organic film-forming additive; on the other hand, the organic film-forming additive can be uniformly distributed in the negative electrode film layer. An appropriate amount of organic film-forming additive is uniformly distributed in the negative electrode film layer, which is conducive to the in-situ formation of a dense, uniform and stable SEI film on the surface of the negative electrode film layer, thereby effectively inhibiting the capacity decay of the battery and improving the stability of the negative electrode environment.

Therefore, the composite conductive agent of the embodiment of the present application is applied to a secondary battery, which can effectively improve the cycle performance of the battery.

Examples of conductive substrates may include one or more conductive materials known in the art. Examples of organic film-forming additives may include fluorine-containing film-forming additives and/or chlorine-containing film-forming additives known in the art. Those skilled in the art may select suitable conductive substrates and organic film-forming additives according to the needs of practical applications, provided that the organic film-forming additives can adhere to the surface of the conductive substrate, and this is not limited here.

In some embodiments, the organic film-forming additive is attached to the surface of the conductive substrate via chemical bonds.

Without intending to be bound by any theory or explanation, when the organic film-forming additive is attached to the surface of the conductive substrate through chemical bonds, the organic film-forming additive and the conductive substrate can be more firmly combined together, thereby reducing the risk of the organic film-forming additive falling off the surface of the conductive substrate during the preparation and processing of the negative electrode plate. This is conducive to further improving the uniformity of the distribution of the organic film-forming additive in the negative electrode film layer, thereby improving the uniformity and stability of the SEI film, and further improving the cycle performance of the battery.

In some embodiments, the conductive substrate includes a carbon material, and the carbon material may include unsaturated carbon-carbon double bonds and/or carbon-carbon triple bonds. The organic film-forming additive may include a fluorine-containing film-forming The additive, the fluorine-containing film-forming additive may include a fluorine-substituted carbon chain and an electrophilic group suspended from the carbon chain, wherein the fluorine-containing film-forming additive is attached to the surface of the conductive substrate by a covalent bond formed by the reaction of the electrophilic group with a carbon-carbon double bond and/or a carbon-carbon triple bond.

Without intending to be limited by any theory or explanation, when the organic film-forming additive includes a fluorine-containing film-forming additive, it is beneficial to further improve the density of the SEI film, thereby further improving the stability of the negative electrode environment during the charge and discharge cycle, thereby improving the cycle performance of the battery.

In some embodiments, the molecular chain of the fluorine-containing film-forming additive comprises a structural unit of wherein R ₁ and R ₂ may each independently represent a hydrogen atom or a C1-C6 alkyl group.

In the above-mentioned embodiment, the fluorine-containing film-forming additive can be used to form a structural unit Monomers and structural units The monomers are formed by alternating copolymerization, random copolymerization or block copolymerization, which is not limited here.

Without intending to be bound by any theory or explanation, the structural unit It has a high F atom content, which can interact with the electrolyte to form a dense and stable SEI film in situ; structural unit The fluorine-containing film-forming additive can be grafted onto the surface of the conductive substrate by the reaction of the azide group with the carbon-carbon double bond and/or carbon-carbon triple bond contained in the conductive substrate, so that the fluorine-containing film-forming additive is attached to the surface of the conductive substrate by the covalent bond formed by the reaction of the azide group with the carbon-carbon double bond and/or carbon-carbon triple bond. Thus, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, and a uniform conductive film can be formed on the surface of the negative electrode. A uniform, dense and stable SEI film can be formed, thereby improving the cycle performance of the battery.

In some embodiments, in the fluorine-containing film-forming additive, and The average molar ratio can be 0.5-5, for example, 0.5, 0.7, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, or a range consisting of any two of the above values.

Without intending to be bound by any theory or explanation, when the fluorinated film-forming additive contains and When the average molar ratio of satisfies the above range, the composite conductive agent can have both good conductivity and good film-forming properties, so that the secondary battery can have both good rate performance and cycle performance. Specifically, the structural unit and The average molar ratio of is within the above-mentioned suitable range, which allows the fluorine-containing film-forming additive to be combined with an appropriate amount of conductive substrate to obtain a composite conductive agent. The composite conductive agent has a suitable conductive substrate content, and when applied to the negative electrode sheet, it can form a conductive network inside the negative electrode film layer, thereby reducing polarization and allowing the battery to maintain good rate performance. The composite conductive agent also has a suitable fluorine-containing film-forming additive content, and when applied to the negative electrode sheet, it can form a dense and stable SEI film on the surface of the negative electrode sheet, thereby improving the cycle performance of the battery.

In some embodiments, the weight average molecular weight Mw of the fluorine-containing film-forming additive may be 3000 to 800000, for example, 3000, 5000, 8000, 10000, 50000, 100000, 300000, 500000, 800000, or a range consisting of any two of the above values.

Without intending to be limited by any theory or explanation, when the weight average molecular weight Mw of the fluorine-containing film-forming additive satisfies the given range, the fluorine-containing film-forming additive can have a suitable molecular chain length and fluorine atom content. The fluorine-containing film-forming additive has a suitable molecular chain length and fluorine atom content, which can not only improve the film-forming performance of the composite conductive agent, but also make the composite conductive agent uniformly dispersed in the negative electrode film layer and entangled with each other, so that the composite conductive agent has a certain bonding performance. As a result, the negative electrode film layer can be allowed to have a lower binder content, thereby allowing the battery to have a higher energy density.

The weight average molecular weight has a well-known meaning in the art, and can represent the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights. The weight average molecular weight can be measured using equipment and methods known in the art. For example, it can be measured using a high temperature GPC (differential refractive index detector).

In some embodiments, the fluorine-containing film-forming additive may include one or more of the compounds shown in Formula 1.

In Formula 1, R ₁₁ to R ₁₄ each independently represent a hydrogen atom or a C1 to C6 alkyl group.

m is selected from integers of 0 to 3000, n is selected from integers of 30 to 3000, p is selected from integers of 0 to 3000, and m+p>0. Optionally, m+p≥300.

The fluorine-containing film-forming additive is attached to the surface of the conductive substrate through a covalent bond formed by the reaction of an azide group with a carbon-carbon double bond and/or a carbon-carbon triple bond.

The compound shown in Formula 1 has a specific structural unit, which can improve the conductivity and film-forming properties of the composite conductive agent. Therefore, the composite conductive agent is applied to the negative electrode of the secondary battery to improve the density, uniformity and stability of the SEI film, thereby improving Battery cycle performance.

In the compound shown in Formula 1, the respective values of m, n, and p can be measured by equipment and methods known in the art. For example, the nuclear magnetic resonance hydrogen spectrum of the fluorine-containing film-forming additive can be measured by a nuclear magnetic resonance instrument, and the respective values of m, n, and p can be measured using the nuclear magnetic resonance hydrogen spectrum.

In some embodiments, R ₁₁ to R ₁₄ may each independently represent a hydrogen atom or a C1 to C3 alkyl group.

Alternatively, in some embodiments, at least one of R ₁₁ to R ₁₄ represents a hydrogen atom. As an example, R ₁₁ to R ₁₄ may all represent a hydrogen atom.

In some embodiments, m is selected from an integer ranging from 300 to 3000, n is selected from an integer ranging from 30 to 3000, and p is selected from an integer ranging from 300 to 3000.

Optionally, in some embodiments, m is selected from an integer of 1000-2000, n is selected from an integer of 100-2000, and p is selected from an integer of 1000-2000.

Without intending to be limited by any theory or explanation, when at least one of R ₁₁ to R ₁₄ , m, n, and p satisfies the above conditions, the conductivity and film-forming properties of the composite conductive agent can be further improved. Therefore, the composite conductive agent is applied to the negative electrode of the secondary battery to further improve the compactness, uniformity and stability of the SEI film, thereby improving the cycle performance of the battery.

In some embodiments, Formula 1 may satisfy: For example, It can be 0.05, 0.10, 0.12, 0.15, 0.19, 0.21, 0.23, 0.27, 0.30, 0.32, 0.35, or a range consisting of any two of the above values.

In some embodiments, Formula 1 may also satisfy: etc.

Without intending to be limited by any theory or explanation, when m, n, and p in Formula 1 satisfy the above conditions, the fluorine-containing film-forming additive molecular chain can contain an appropriate amount of azide groups, thereby connecting the fluorine-containing film-forming additive molecular chain to an appropriate amount of conductive substrate. In this way, the conductivity of the composite conductive agent can be improved. In addition, when m, n, and p in Formula 1 meet the above conditions, the fluorine-containing film-forming additive can also have a suitable fluorine content, thereby improving the density and stability of the SEI film. Therefore, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can further improve the cycle performance of the battery.

In some embodiments, Formula 1 may satisfy: 0.5≤m/p≤1.5. For example, m/p may be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of the above values.

In some embodiments, Formula 1 may also satisfy: 0.8≤m/p≤1.2. For example, m/p may be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, or a range formed by any two of the above values.

Without intending to be limited by any theory or explanation, when the ratio of m to p in the compound shown in Formula 1 is within the above range, it can be considered that the molecular chain of the fluorine-containing film-forming additive has a higher symmetry. In other words, when the ratio of m to p is within the above range, the fluorine atoms can be more evenly distributed in the molecular chain of the fluorine-containing film-forming additive. Thus, the uniformity of the SEI film formed in situ by the composite conductive agent can be further improved. Therefore, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can further improve the cycle performance of the battery.

In some embodiments, the conductive substrate may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

The surface of the conductive substrate selected from the above types may include an appropriate amount of active oxygen-containing groups, so that it can be easily modified to introduce unsaturated carbon-carbon double bonds and/or carbon-carbon triple bonds, thereby allowing the conductive substrate to be firmly combined with the organic film-forming additive. As a result, the composite conductive agent of the embodiment of the present application can form a more uniform SEI film in situ in the negative electrode film layer, thereby improving the cycle performance of the battery.

In some embodiments, based on the total mass of the composite conductive agent, the mass percentage of the conductive substrate can be 8% to 95%, for example, 8%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any two of the above values. range.

It is not intended to be limited by any theory or explanation. Adjusting the mass percentage of the conductive substrate in the composite conductive agent can regulate the conductive properties and film-forming properties of the composite conductive agent. When the mass percentage of the conductive substrate meets the given range, the composite conductive agent of the embodiment of the present application is applied to the negative electrode of the secondary battery, which can not only improve the conductive properties of the negative electrode, inhibit the growth of the internal resistance of the battery during the cycle, but also form a dense SEI film in situ on the surface of the negative electrode, thereby enhancing the stabilizer of the negative electrode environment and inhibiting the capacity decay of the battery. In this way, the cycle stability of the battery can be improved and the cycle life of the battery can be extended.

The composite conductive agent of the embodiment of the present application can be obtained in various ways. As an example, the composite conductive agent can be obtained through the following steps S10 to S30.

S10, providing a conductive material modified with a carbon-carbon double bond and/or a carbon-carbon triple bond.

Step S10 can be implemented by methods known in the art. In some embodiments, the conductive material may include a conductive carbon material, for example, conductive carbon black Super P. Providing a conductive material modified with a carbon-carbon double bond and/or a carbon-carbon triple bond may specifically include: uniformly mixing conductive carbon black and propargyl alcohol, a catalytic amount of N,N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), so that groups such as carboxyl groups on the surface of the conductive carbon black react with propargyl alcohol under the catalysis of DCC and DMAP, thereby obtaining a conductive carbon black modified with a carbon-carbon double bond. The molar ratio of the conductive carbon black to the propargyl alcohol may be (1:0.8) to (1:1.2).

S20, providing an organic film-forming additive containing an electrophilic group, wherein the organic film-forming additive includes a halogen atom.

Step S20 can be achieved by methods known in the art. The organic film-forming additive containing halogen atoms can be modified, or the organic film-forming additive containing both electrophilic groups and halogen atoms can be directly synthesized, which is not limited here.

S30, mixing the conductive material modified by carbon-carbon double bonds and/or carbon-carbon triple bonds and the organic film-forming additive containing electrophilic groups in a suitable amount of solvent, evacuating the mixture (to prevent free radicals from being oxidized), and then adding a catalytic amount of CuCl in an inert atmosphere to react the conductive material modified by carbon-carbon double bonds and/or carbon-carbon triple bonds and the organic film-forming additive containing electrophilic groups in a suitable amount of solvent at a reaction temperature, and pouring the resulting crude product into a 0°C The composite conductive agent can be obtained by settling in icy ether.

In step S30, the inert atmosphere may include a nitrogen atmosphere and/or a rare gas atmosphere. The reaction temperature may be 23°C to 27°C, for example, room temperature (25°C).

In some embodiments, providing an organic film-forming additive containing an electrophilic group may include the following steps S21 to S24 .

S21, acryloyl chloride, ethyl azido and a catalytic amount of triethylamine are uniformly mixed in an appropriate amount of solvent tetrahydrofuran (THF) to allow acryloyl chloride and ethyl azido to react to obtain an intermediate product A

In step S21, the inert atmosphere may include a nitrogen atmosphere and/or a rare gas atmosphere. The reaction temperature may be -5°C to 5°C, for example, 0°C.

S22, dissolving vinylidene fluoride in an appropriate amount of THF solvent, evacuating the mixture (to avoid oxidation of free radicals), adding an initiator under an inert atmosphere to allow the vinylidene fluoride to undergo polymerization at the reaction temperature, pouring the crude product into 0°C ice ether for precipitation, and separating and obtaining the intermediate product B.

In step S22, the inert atmosphere may include a nitrogen atmosphere and/or a rare gas atmosphere. The initiator may include, but is not limited to, one or more of a peroxide initiator, an azo initiator, and a redox initiator, for example, azobisisobutyronitrile (AIBN). The reaction temperature may be 65°C to 75°C, for example, 70°C.

S23, dissolving the intermediate product A and the intermediate product B in an appropriate amount of solvent THF, evacuating the mixture (to avoid oxidation of free radicals), adding an initiator under an inert atmosphere, causing the intermediate product A and the intermediate product B to undergo polymerization reaction at the reaction temperature, pouring the crude product into 0°C ice ether for precipitation, and separating to obtain the intermediate product C.

In step S23, the inert atmosphere may include a nitrogen atmosphere and/or a rare gas atmosphere. The initiator may include, but is not limited to, one or more of a peroxide compound initiator, an azo initiator, and a redox initiator, such as azobisisobutyronitrile (AIBN). The reaction temperature may be 65°C to 75°C, such as 70°C.

S24, dissolving the intermediate product C and vinylidene fluoride in an appropriate amount of solvent THF After evacuating the mixture (to avoid oxidation of free radicals), an initiator is added under an inert atmosphere to allow the intermediate product C and vinylidene fluoride to undergo polymerization reaction at the reaction temperature. The crude product is poured into ice ether at 0°C for precipitation, and an organic film-forming additive containing an electrophilic group is separated.

In step S24, the inert atmosphere may include a nitrogen atmosphere and/or a rare gas atmosphere. The initiator may include, but is not limited to, one or more of a peroxide initiator, an azo initiator, and a redox initiator, such as azobisisobutyronitrile (AIBN). The reaction temperature may be 65°C to 75°C, such as 70°C.

Negative electrode composition

A second aspect of an embodiment of the present application provides a negative electrode composition, which includes a negative electrode active material and the composite conductive agent of the first aspect.

The negative electrode composition of the second aspect of the embodiment of the present application includes the composite conductive agent of the first aspect, and is applied to the negative electrode plate of the secondary battery, and can form a dense, uniform and stable SEI film in situ on the surface of the negative electrode film layer, thereby effectively suppressing the capacity decay of the battery and improving the stability of the negative electrode environment. Thus, the cycle performance of the battery can be effectively improved.

In some embodiments, based on the total mass of the negative electrode composition, the mass percentage of the composite conductive agent may be 0.2% to 3.0%, and optionally 0.5% to 2.0%.

Without intending to be limited by any theory or explanation, the mass percentage of the composite conductive agent within the above-mentioned appropriate range can allow the negative electrode film layer to contain an appropriate amount of fluorine-containing film-forming additives, thereby improving the density and uniformity of the SEI film, thereby improving the cycle stability of the battery.

In the negative electrode composition of the embodiment of the present application, the negative electrode active material may adopt the negative electrode active material for secondary batteries known in the art. As an example, the negative electrode active material may include one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials. The embodiments of the present application are not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode active material may include a silicon-based material. The negative electrode composition of the embodiment includes a composite conductive agent, which can improve the density and uniformity of the SEI film, thereby improving the stability and capacity of the silicon-based material during the cycle process, thereby allowing the battery to have a high energy density.

In some embodiments, the negative electrode composition may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode composition may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

Negative electrode

A third aspect of an embodiment of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and the negative electrode film layer includes the negative electrode composition of the second aspect.

The negative electrode sheet of the third aspect of the embodiment of the present application includes the negative electrode composition of the second aspect, and is applied to the negative electrode sheet of a secondary battery, which can form a dense, uniform and stable SEI film in situ on the surface of the negative electrode film layer, thereby effectively suppressing the capacity decay of the battery and improving the stability of the negative electrode environment. Thus, the cycle performance of the battery can be effectively improved.

In some embodiments, the infrared absorption spectrum of the negative electrode sheet may have a characteristic peak located at 1180 cm ^-1 to 1185 cm ^-1 .

The above characteristic peak is a characteristic peak for characterizing -CF ₂ -. When the infrared absorption spectrum of the negative electrode has the above characteristic peak, it is beneficial to further improve the density of the SEI film. Therefore, it is beneficial to further improve the stability of the negative electrode environment during the charge and discharge cycle, thereby improving the cycle performance of the battery.

The infrared absorption spectrum of the negative electrode sheet can be measured by equipment and methods known in the art. As an example, the negative electrode film layer can be scraped to obtain the negative electrode film layer powder, the negative electrode film layer powder is mixed with a solvent (such as N-methylpyrrolidone), filtered after being fully dissolved, and the filter residue is taken for infrared spectrum testing to obtain the infrared absorption spectrum of the negative electrode sheet.

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. The negative electrode current collector has two opposite surfaces in the thickness direction, and the negative electrode film layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil or aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode sheet can be prepared by the following method: dispersing the above-mentioned negative electrode composition, such as the negative electrode active material, the composite conductive agent, the binder and any other components in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on one or two surfaces of the negative electrode collector; after drying, cold pressing and other processes, the negative electrode sheet of the present application can be obtained.

In addition, the negative electrode plate of the embodiment of the present application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the embodiment of the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode plate of the embodiment of the present application also includes a protective layer covering the surface of the negative electrode film layer.

Battery

The fourth aspect of the embodiments of the present application provides a battery. The battery mentioned in the embodiments of the present application may include one or more battery cells to provide a single physical module with higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar.

The battery cell may be a secondary battery, which is also called a rechargeable battery or storage battery, and refers to a battery cell that can be recharged to activate the active material after the battery cell is discharged and continue to be used. The present application embodiment has no particular limitation on the type of secondary battery, for example, the secondary battery may be a lithium ion battery, a lithium metal battery, etc., and in particular, the secondary battery may be a lithium ion battery.

Typically, a battery cell includes an electrode assembly and an electrolyte. Including positive electrode sheet, negative electrode sheet and isolation membrane.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[Positive electrode]

The positive electrode plate included in the battery of the embodiment of the present application includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In the positive electrode sheet of the embodiment of the present application, the positive electrode active material may be a positive electrode active material for a secondary battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the embodiment of the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for lithium-ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O 2 (also referred to as NCM _{622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 )} , and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include A polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent and an optional dispersant. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative electrode]

The negative electrode sheet included in the battery of the embodiment of the present application includes the negative electrode sheet of the third aspect of the embodiment of the present application. The embodiment of the negative electrode sheet has been described and illustrated in detail above, and will not be repeated here. It can be understood that the battery of the embodiment of the present application can achieve the beneficial effects of any of the above embodiments of the negative electrode sheet of the embodiment of the present application.

[Isolation film]

The separator is disposed between the positive electrode sheet and the negative electrode sheet to play a role of isolation. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, The materials of each layer may be the same or different, without particular limitation.

[Electrolytes]

The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application embodiment has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid or gel.

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

In some embodiments, the battery cell further includes a housing for accommodating the electrode assembly and the electrolyte. The housing of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The housing of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The embodiment of the present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. For example, FIG1 is a battery cell 5 of a square structure as an example.

In some embodiments, referring to FIG. 2 , the housing may include a housing 51 and a cover plate. 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

The preparation method of the battery cell of the embodiment of the present application is well known. In some embodiments, the electrode assembly can be placed in a housing, and after drying, an electrolyte can be injected, and the battery cell can be obtained through vacuum packaging, standing, forming, shaping and other processes.

In some embodiments, the battery mentioned in the embodiments of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the embodiments of the present application can be a battery module or a battery pack. The battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

In some embodiments, there may be multiple battery cells in the battery, and the multiple battery cells may be connected in series, in parallel, or in a hybrid connection. A hybrid connection means that the multiple battery cells are both connected in series and in parallel. The multiple battery cells may be directly connected in series, in parallel, or in a hybrid connection, and then the whole formed by the multiple battery cells is accommodated in the box; of course, multiple battery cells may be first connected in series, in parallel, or in a hybrid connection to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a hybrid connection to form a whole, and then accommodated in the box.

FIG3 is a schematic diagram of a battery module 4 as an example. As shown in FIG3 , there are multiple battery cells 5, and the multiple battery cells 5 are first connected in series, in parallel, or in mixed connection to form a battery module 4. The multiple battery cells 5 in the battery module 4 can be electrically connected through a busbar component to realize the series connection, parallel connection, or mixed connection of the multiple battery cells 5 in the battery module 4. In the battery module 4, the multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the multiple battery cells 5 can be fixed by fasteners.

In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

FIG4 and FIG5 are schematic diagrams of a battery pack 1 as an example. As shown in FIG4 and FIG5, the battery pack 1 may include a case and a plurality of battery modules 4 disposed in the case. The plurality of battery modules 4 in the battery pack 1 may be electrically connected through a busbar component to achieve series connection, parallel connection, or mixed connection of the plurality of battery modules 4 in the battery pack 1. The case includes an upper case 2 and a lower case 3, and the upper case 2 is used to cover the lower case 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

Electrical devices

The embodiment of the present application also provides an electric device, the electric device includes a battery cell provided in the embodiment of the present application, and the battery cell is used to provide electrical energy. The battery cell can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

As the electrical device, a battery cell, a battery module including a plurality of battery cells, or a battery pack may be selected according to its usage requirements.

Fig. 6 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

As another example, the power-consuming device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a battery cell may be used as a power source.

Example

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

Example 1

Preparation of composite conductive agent

Step (1): At 25°C, 1.1 mol of propargyl alcohol and 1 mol of conductive carbon black are reacted under the catalysis of 0.1 mol N,N'-dicyclohexylcarbodiimide (DCC) and 0.1 mol of 4-dimethylaminopyridine (DMAP) for 8 hours to obtain modified conductive carbon black containing a carbon-carbon triple bond.

Step (2): under 0°C, add 1.1 mol of acryloyl chloride and 1 mol of ethyl azide in the presence of 1 mL of triethylamine and react for 4 h to obtain intermediate A.

Step (3): Weigh 1 mol of vinylidene fluoride, dissolve it in 200 mL of tetrahydrofuran, evacuate the flask (to avoid oxidation of free radicals), continue to introduce N ₂ into the three-necked flask, add 0.05 g of azobisisobutyronitrile initiator, heat to 70°C, stir and react for 12 hours, and then pour the obtained crude product into 0°C ice ether to precipitate, thereby obtaining intermediate product B.

Step (4): Weigh 0.1 mol of intermediate product B, add 1 mol of intermediate product A, dissolve in 200 mL of tetrahydrofuran (THF), evacuate (to avoid oxidation of free radicals), continue to introduce N ₂ into a three-necked flask, add 0.01 g of azobisisobutyronitrile initiator, heat to 70°C, stir to react for 12 h, and then pour the obtained crude product into 0°C ice ether to precipitate, to obtain intermediate product C.

Step (5): Weigh 0.1 mol of intermediate product C, add 1 mol of vinylidene fluoride, dissolve in 200 mL of tetrahydrofuran, evacuate (to avoid oxidation of free radicals), continue to introduce N ₂ into a three-necked flask, add 0.05 g of azobisisobutyronitrile initiator, heat to 70°C, stir to react for 12 hours, and then pour the obtained crude product into 0°C ice ether to precipitate, to obtain intermediate product D.

Step (6): Weigh 1 mol of the intermediate product D, dissolve it in 200 mL of tetrahydrofuran, add 1 mol of modified conductive carbon black, evacuate the flask (to prevent free radicals from being oxidized), continue to introduce N ₂ into the three-necked flask, add 0.1 mol of CuCl, stir and react at room temperature for 12 h, pour the obtained crude product into 0°C ice ether for precipitation, separate and dry to obtain a composite conductive agent.

Preparation of positive electrode

The positive electrode active material lithium iron phosphate, the positive electrode binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a mass ratio of 96:2.5:1.5, N-methylpyrrolidone (NMP) is added as a solvent, the solid content is adjusted to 70%-80%, and the positive electrode slurry is obtained by stirring evenly; the positive electrode slurry is coated on an aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

Preparation of negative electrode

The negative electrode active material artificial graphite, composite conductive agent, binder SBR, and sodium carboxymethyl cellulose (CMC-Na) are mixed in a mass ratio of 96:1.5:1.5:1, dispersed in deionized water, and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode collector copper foil, dried, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

Isolation film

Polypropylene film is used as the isolation film.

Preparation of electrolyte

LiPF ₆ was dissolved in a solvent prepared by mixing ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 to obtain an electrolyte solution with a LiPF ₆ concentration of 1 mol/L.

Preparation of secondary batteries

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order to obtain an electrode assembly; the electrode assembly is placed in a packaging shell, and after drying, liquid injection, vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

Embodiments 2 to 11

Based on the preparation process of the composite conductive agent in Example 1, the amounts of the intermediate product D and the modified conductive carbon in step (6), and the amounts of azobisisobutyronitrile in steps (3) to (5) were adjusted from m ₁ to m ₃ as shown in Table 1 to prepare the composite conductive agents of Examples 2 to 11. The preparation of the positive electrode sheet, negative electrode sheet, separator, electrolyte and secondary battery of Examples 2 to 11 is the same as that of Example 1.

Comparative Example 1

Based on the preparation process of the positive electrode sheet, the negative electrode sheet, the separator, the electrolyte and the secondary battery of Example 1, the secondary battery of Comparative Example 1 was prepared by replacing the composite conductive agent with an equal mass of conductive carbon black.

Comparative Example 2

Based on the preparation process of the composite conductive agent in Example 1, an intermediate product D was prepared; 1 mol of the intermediate product D was weighed and mixed evenly with 1 mol of unmodified conductive carbon black to obtain a mixed conductive agent.

Based on the positive electrode sheet, negative electrode sheet, separator, electrolyte and In the preparation process of the secondary battery, the composite conductive agent is replaced with a mixed conductive agent of equal mass to prepare the secondary battery of Comparative Example 2.

The following tests were performed on Examples 1 to 11 and Comparative Examples 1 to 2. The test results are shown in Table 2.

(1) Battery DC resistance (DCR) test

At 25°C, the secondary battery was allowed to stand for 30 minutes, and then charged at a constant current of 0.33C to 3.65V; then charged at a constant voltage of 3.65V to a cut-off current of 0.05C; after standing for 5 minutes, the battery was discharged at a constant current of 0.33C for 90 minutes to a cut-off current of 0.5C, and the voltage at this time was recorded as U ₀ ; after standing for 1 hour, the battery was discharged at a rate of 2C for 30 seconds, the discharge current was recorded as I, and the voltage at the 10th second of discharge was recorded as U ₁ ; after standing for 5 minutes, the test was terminated.

The DCR of the battery = (U ₁ ‐U ₀ )/I.

(2) Normal temperature cycle performance test

At 25°C, let the secondary battery stand for 30 minutes, then discharge it at 0.33C to 2.5V. After standing for 30 minutes, charge it at 0.33C constant current to 3.65V, then charge it at 3.65V constant voltage to a cut-off current of 0.05C; let it stand for 30 minutes; discharge it at 0.33C to 2.5V; let it stand for 30 minutes. Repeat the above steps for the same battery, and record the discharge capacity _C1 of the first cycle and the discharge capacity _C1000 of the 1000th cycle.

The cycle capacity retention rate of the secondary battery is P ₁₀₀₀ =(C ₁₀₀₀ /C ₁ )*100%.

Table 1

Table 2

It can be seen from Table 1 and Table 2 that the composite conductive agent provided in the embodiments of the present application is applied to the negative electrode plate of a secondary battery, which can effectively reduce the internal resistance of the battery and improve the cycle performance of the battery.

Based on the test results of Examples 1-5, it can be seen that by adjusting the relative content of the conductive substrate and the film-forming additive in the composite conductive agent, the conductive properties and film-forming properties of the composite conductive agent can be adjusted, thereby adjusting the internal resistance and cycle performance of the battery. Based on the test results of Examples 1, 6-11, it can be seen that by adjusting the content of the electrophilic group in the film-forming additive, the content of the conductive substrate in the composite conductive agent can be adjusted, thereby adjusting the conductive properties and film-forming properties of the composite conductive agent, thereby adjusting the internal resistance and cycle performance of the battery.

In contrast, the conventional conductive agent used in Comparative Example 1 has unsatisfactory internal resistance and cycle performance of the battery. In the mixed conductive agent of Comparative Example 2, the film-forming additive is not attached to the surface of the conductive substrate, which not only fails to improve the cycle performance of the battery, but also deteriorates the internal resistance and cycle performance of the battery.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (19)

A composite conductive agent, comprising: a conductive substrate; and The organic film-forming additive comprises halogen atoms and is attached to the surface of the conductive substrate. The composite conductive agent according to claim 1, wherein The organic film-forming additive is attached to the surface of the conductive substrate through chemical bonds. The composite conductive agent according to claim 1 or 2, wherein the conductive substrate comprises a carbon material, and the carbon material comprises an unsaturated carbon-carbon double bond and/or a carbon-carbon triple bond; The organic film-forming additive comprises a fluorine-containing film-forming additive, wherein the fluorine-containing film-forming additive comprises a fluorine-substituted carbon chain and an electrophilic group suspended from the carbon chain. The fluorine-containing film-forming additive is attached to the surface of the conductive substrate through a covalent bond formed by the reaction of the electrophilic group with the carbon-carbon double bond and/or carbon-carbon triple bond. The composite conductive agent according to claim 3, wherein the molecular chain of the fluorine-containing film-forming additive comprises a structural unit of The copolymer chain segment Here, R ₁ and R ₂ each independently represent a hydrogen atom or a C1-C6 alkyl group. The composite conductive agent according to claim 3 or 4, wherein In the fluorine-containing film-forming additive, and The average molar ratio is 0.5-5. The composite conductive agent according to any one of claims 3 to 5, wherein The weight average molecular weight Mw of the fluorine-containing film-forming additive is 3,000 to 800,000. The composite conductive agent according to any one of claims 3 to 6, wherein The fluorine-containing film-forming additive includes one or more of the compounds shown in Formula 1,
wherein R ₁₁ to R ₁₄ each independently represent a hydrogen atom or a C1 to C6 alkyl group; m is selected from an integer of 0 to 3000, n is selected from an integer of 30 to 3000, p is selected from an integer of 0 to 3000, and m+p＞0; The fluorine-containing film-forming additive is attached to the surface of the conductive substrate via a covalent bond formed by the reaction of an azide group with the carbon-carbon double bond and/or carbon-carbon triple bond. The composite conductive agent according to claim 7, wherein R ₁₁ to R ₁₄ each independently represent a hydrogen atom, a C1 to C3 alkyl group; and/or m is selected from integers ranging from 300 to 3000, n is selected from integers ranging from 300 to 3000, and p is selected from integers ranging from 300 to 3000; and/or
The composite conductive agent according to claim 7 or 8, wherein The composite conductive agent according to claim 7 or 8, wherein 0.5≤m/p≤1.5. The composite conductive agent according to claim 7 or 8, wherein 0.8≤m/p≤1.2. The composite conductive agent according to any one of claims 1 to 11, wherein The conductive substrate includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The composite conductive agent according to any one of claims 1 to 12, wherein Based on the total mass of the composite conductive agent, the mass percentage of the conductive substrate is 8% to 95%. A negative electrode composition comprises a negative electrode active material and the composite conductive agent according to any one of claims 1 to 13. The negative electrode composition according to claim 14, wherein Based on the total mass of the negative electrode composition, the mass percentage of the composite conductive agent is 0.2%～3.0%. A negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises the negative electrode composition according to any one of claims 14 or 15. The negative electrode plate according to claim 16, wherein the infrared absorption spectrum of the negative electrode plate has a characteristic peak located at 1180 cm ^-1 to 1185 cm ^-1 . A battery comprising the negative electrode sheet as claimed in claim 16 or 17. An electrical device comprising the battery as claimed in claim 18.