CN115832212A - Negative pole piece and secondary battery, battery module, battery pack and electric device comprising same - Google Patents

Abstract

The application provides a single-layer coated negative electrode sheet, which satisfies a certain relationship by limiting the mass fraction of carbon microtubes and conductive agents in the negative electrode film layer, thereby improving the diffusion capacity of lithium ions in the negative electrode film layer and improving the performance of the battery. Charging performance. The present application also provides a double-coated negative electrode sheet, by including carbon microtubes in at least one of the first film layer and the second film layer, so as to achieve the purpose of improving the charging performance of the battery. In addition, the present application also relates to a secondary battery, a battery module, a battery pack, and an electrical device comprising the above-mentioned single-layer coated and double-layer coated negative electrode sheets.

Description

Negative electrode sheet and secondary battery containing it, battery module, battery pack, electrical device

technical field

The present application relates to the technical field of lithium batteries, in particular to a single-layer coated negative electrode sheet and a double-layer coated negative electrode sheet, as well as secondary batteries, battery modules, battery packs and electrical devices containing them.

Background technique

In recent years, as the application range of secondary batteries has become more and more extensive, secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power plants, as well as electric tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields.

However, when the secondary battery has an electrode with a thick coating weight (for example, at least 9mg/cm ² ), the fast charging performance of the battery is low; the internal polarization of the battery increases, the life of the battery deteriorates, and lithium precipitation occurs. Factors that cause safety hazards. Therefore, the electrochemical performance of secondary batteries with thick coatings still needs to be improved, especially to improve their fast charging performance.

Contents of the invention

The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode sheet capable of improving the chargeability of a secondary battery, and to provide a secondary battery, a battery module, a battery pack, and a battery for use including the negative electrode sheet of the present application. electric device.

In order to achieve the above object, the first aspect of the present application provides a single-layer coated negative electrode sheet, which includes a current collector and a negative electrode film layer arranged on at least one surface of the current collector, the negative electrode film layer contains negative active The substance and carbon microtubes optionally contain a conductive agent; wherein, the mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer meet: when 0.2%≤W1≤2%, then W1+W2≤2%; when W1>2%, then 0≤W2≤0.5%, based on the total weight of the negative film layer.

This application adds carbon microtubes to the negative electrode film layer, and limits the mass fraction of carbon microtubes and conductive agent in the negative electrode film layer to meet a certain relationship, so as to improve the liquid retention capacity of the negative electrode film layer and promote lithium ion in the negative electrode film. The diffusion ability of the layer, thereby improving the charging performance of the secondary battery.

In any embodiment, in the single-layer coated negative electrode sheet, the mass fraction W1 of carbon microtubes in the negative electrode film layer is 0.2% to 5%. In this way, the components of the negative electrode film layer are further optimized to improve the charging performance of the secondary battery.

In any embodiment, in the single-layer coated negative electrode sheet, the inner diameter of the carbon microtube is 0.2 μm to 12 μm, optionally 2 μm to 10 μm; optionally, the aspect ratio is 2-20; further optionally , the wall thickness of carbon microtubes is 0.01 μm to 1 μm. By limiting the specifications of the carbon microtubes, the carbon microtubes can fully play the role of liquid storage and liquid retention in the negative electrode film layer, improve the liquid phase diffusion ability, and thus make full use of the active material of the negative electrode film layer to improve the charging performance of the battery .

In any embodiment, in the single-layer coated negative electrode sheet, the negative active material includes at least one of artificial graphite, natural graphite, and silicon-based materials; optionally, the conductive agent includes conductive agent sp, KS-6 , conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF at least one.

The second aspect of the present application provides a double-coated negative electrode sheet, which includes a current collector, a first film layer, and a second film layer; wherein the first film layer is disposed on at least one surface of the current collector, The second film layer is arranged on the outer surface of the first film layer; the first film layer is located between the current collector and the second film layer; and, the first film layer contains the first negative electrode active material, and the second film layer contains the second film layer negative electrode active material; at least one layer of the first film layer and the second film layer contains carbon microtubes; one of them is different.

This application introduces carbon microtubes into the film layer of the double-coated negative electrode sheet, which improves the liquid storage capacity of the film layer, ensures the diffusion of lithium ions in the entire film layer, and makes full use of the active materials in the film layer. The purpose of improving the electrochemical performance of the secondary battery, especially the charging performance.

In any embodiment, in the double-coated negative electrode sheet, the first film layer does not contain carbon microtubes, and the second film layer contains carbon microtubes. Thus, by further limiting the distribution of carbon microtubes, the second film layer (upper layer) has sufficient electrolyte solution, thereby promoting the diffusion of lithium ions to the first film layer (lower layer) to make full use of the negative electrode active material.

In any embodiment, in the double-coated negative electrode sheet, both the first film layer and the second film layer contain carbon microtubes. As a result, the liquid retention capacity of the two layers of film is increased, and the lithium ion channel runs through the entire film layer to further improve the diffusion capacity of lithium ions.

In any embodiment, in the double-coated negative electrode sheet, in the first film layer and the second film layer, the total mass fraction W3 of the carbon microtubes is 0.2% to 5%, based on the first The total weight of the film layer and the second film layer. Thus, the mass fraction of carbon microtubes in the double film layer is further limited to optimize the electrochemical performance of the negative electrode sheet, thereby improving the charging capacity of the battery.

In any embodiment, in the double-coated negative electrode sheet, the first film layer and the second film layer optionally also contain a conductive agent, and the total mass fraction W3 of the carbon microtubes is related to the conductive material. The total mass fraction W4 of the agent satisfies: when 0.2%≤W3≤2%, then W3+W4≤2%; when W3>2%, then 0≤W4≤0.5%, based on the first film layer and the second The total mass of the two film layers. When the total mass fraction of carbon microtubes and conductive agent satisfies a specific relationship, the balance between the amount of load (carbon microtubes and conductive agent), energy density and charging performance can be achieved, and the fast charging ability can be improved.

In any embodiment, in the double-coated negative electrode sheet, the mass of the carbon microtubes in the second film layer is 50-100% relative to the total mass of the carbon microtubes. All or most of the carbon microtubes exist in the second film layer, which is conducive to the diffusion of more lithium-ion-containing electrolytes to the upper layer, so as to provide sufficient lithium ions to reach the interface between the upper layer and the lower layer, and the lower layer and the collector. At the fluid interface, the purpose of making full use of the active material in the lower layer is achieved.

In any embodiment, in the double-coated negative electrode sheet, the diameter of the carbon microtube is 0.2 μm to 12 μm, optionally 2 μm to 10 μm; the aspect ratio is 2-20; the tube wall of the carbon microtube The thickness is 0.01 μm to 1 μm. By limiting the carbon microtubes with appropriate specifications, the uniformity of pore size distribution is realized, the liquid storage and liquid retention capacity of the membrane layer are enhanced, and the lithium ion diffusion capacity is improved.

In any embodiment, in the double-coated negative electrode sheet, under the condition that only the first film layer contains carbon microtubes, the first film layer and the second film layer optionally also contain conductive agent; the mass fraction of the carbon microtubes in the second film layer is 0.4% to 10%, and the mass fraction of the conductive agent is 0% to 4%, optionally 0% to 1.6%, based on The weight of the second film layer; the mass fraction of the conductive agent in the first film layer is 0% to 4%, optionally 0% to 2%, based on the weight of the first film layer.

In any embodiment, in the double-coated negative electrode sheet, under the condition that the first and second film layers both contain carbon microtubes, the first film layer and the second film layer optionally further contain conductive agent; the mass fraction of the carbon microtubes in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on the weight of each film layer.

By further limiting the mass content of carbon microtubes and conductive agents in each film layer, the composition and structure of the negative electrode film layer are optimized, so as to achieve the best fast charging capability.

In any embodiment, in the double-coated negative electrode sheet, under the condition that both the first and the second film layers contain carbon microtubes, the carbon microtubes in the second film layer and in the first film layer The mass fraction ratio in 10:3 to 1:1.

In any embodiment, in the double-coated negative electrode sheet, the weight ratio of the second film layer to the first film layer is 1:4 to 4:1. As a result, the diffusion performance of the upper layer and the lower layer reaches an optimal ratio, further improving the fast charging capability of the battery.

In any embodiment, in the double-coated negative electrode sheet, the first and second negative electrode active materials may be the same or different, including at least one of artificial graphite, natural graphite, and silicon-based materials.

In any embodiment, in the double-coated negative electrode sheet, the conductive agent can be the same or different in the first film layer and the second film layer, including conductive agent sp, KS-6, conductive graphite, carbon At least one of nanotubes, graphene, carbon fiber VGCF.

The third aspect of the present application provides a secondary battery, which includes the single-layer coated negative electrode sheet described in the first aspect of the present application and the double-layer coated negative electrode sheet described in the second aspect of the present application.

A fourth aspect of the present application provides a battery module, which includes the secondary battery described in the third aspect of the present application.

A fifth aspect of the present application provides a battery pack, which includes the battery module described in the fourth aspect of the present application.

The sixth aspect of the present application provides an electric device, which includes the secondary battery described in the third aspect of the present application, the battery module described in the fourth aspect of the present application, or the battery pack described in the fifth aspect of the present application. at least one.

This application uses carbon microtubes in the negative electrode sheet of the secondary battery, and at the same time limits the mass fraction of the carbon microtubes and the conductive agent to satisfy a certain relationship, so that the fast charging capability of the secondary battery is improved. Correspondingly, the battery pack, battery module and electric device provided by the present application have improved fast charging capability.

Description of drawings

FIG. 1 is a schematic diagram of a single-layer coated negative electrode sheet according to an embodiment of the present application.

Figure 2 is a schematic diagram of a double-coated negative electrode sheet according to an embodiment of the present application

FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 4 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 3 .

FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 7 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 6 .

FIG. 8 is a schematic diagram of a secondary battery used as a power consumption device according to an embodiment of the present application.

Explanation of reference signs:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 6 current collector; film layer; 9 second film layer.

Detailed ways

Hereinafter, embodiments of the negative electrode sheet and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of the present application will be disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known items and repeated descriptions of substantially the same configurations may be 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.

A "range" disclosed herein is defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-6. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all steps in 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 in sequence, and may also include steps (b) and (a) performed in sequence. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.

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

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by either of the following: 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).

With the rapid development of new energy sources, the requirements for lithium-ion batteries are getting higher and higher. While pursuing energy density, in order to alleviate users' mileage anxiety, it is necessary to improve the charging capacity of lithium-ion batteries at the same time. For the current system, liquid phase diffusion is the bottleneck of fast charging, so a substantial increase in liquid phase diffusion is crucial to improve the charging capability.

Existing methods to improve fast charging capacity include drilling and hole-making technology, and carbon nanotube technology, but there are problems such as large energy density loss, small liquid storage and liquid retention, large specific surface area, and many side reactions. .

The inventors found that by introducing carbon microtubes into the negative electrode film, the liquid storage and liquid retention functions can be fully exerted, thereby improving the liquid phase diffusion ability, and realizing lithium ions running through the entire negative electrode film layer, so as to make full use of the negative electrode active material, especially It is a negative electrode active material close to the current collector to achieve the purpose of improving the charging capacity of the battery.

[Negative pole piece]

The first aspect of the present application provides a single-layer coated negative electrode sheet, which includes a current collector and a negative electrode film layer arranged on at least one surface of the current collector, and the negative electrode film layer includes a negative electrode active material and Carbon microtubes, optionally including a conductive agent; wherein, the mass fraction W1 of the carbon microtubes in the negative electrode film layer and the mass fraction W2 of the conductive agent in the negative electrode film layer meet: when 0.2%≤W1≤2%, then W1+ W2≤2%; when W1>2%, optional 2%<W1<5.8%, then 0≤W2≤0.5%, based on the total weight of the negative film layer.

By adding carbon microtubes in the negative electrode film layer of the present application, the liquid retention capacity of the negative electrode film layer can be improved, the liquid phase diffusion can be promoted, and the active material can be fully utilized; at the same time, carbon microtubes and conductive agents are limited in the negative electrode film layer The ratio of the mass fraction of the battery makes the battery have a good energy density, and the charging capacity of the battery is improved. The single-layer coated negative electrode sheet of the present application is shown in FIG. 1 .

In some embodiments, the mass fraction W1 of carbon microtubes in the negative electrode film layer is 0.2-5%. By further limiting the mass fraction of carbon microtubes in the negative electrode film layer, the components of the negative electrode film layer are optimized to improve the fast charging capability of the battery.

In some embodiments, the inner diameter of the carbon nanotube (i.e. the diameter of the hollow cavity) is 0.2 μm to 12 μm, optionally 2 μm to 10 μm; optionally, the aspect ratio (i.e. the ratio of the length of the carbon nanotube to the inner diameter) is 2-20; further optionally, the wall thickness of the carbon microtubes is 0.01 μm to 1 μm. Wherein, the inner diameter of the carbon microtubes may also be 1 μm to 12 μm, or 2 μm to 4 μm.

The carbon microtubes of the above specifications are similar to through-holes, and their advantages are that they can fully play the role of liquid storage and liquid retention, improve the liquid phase diffusion capacity, thereby making full use of the active material of the negative electrode film layer, and improving the fast charging capacity of the battery; and , compared with the pore-forming and punching technology used in the prior art (the inner diameter is tens of microns), the inner diameter of the carbon microtubes of the present application is smaller, even several microns, and its advantage is that the carbon microtubes The distance is small and the distribution is uniform, which can improve the consistency of the pore size distribution, make the polarization distribution inside the battery uniform, avoid the phenomenon of local lithium precipitation, and also effectively play the role of liquid retention, improve the charging capacity as a whole, reduce the Small energy density loss. Compared with the carbon nanotube technology used in the prior art, the inner diameter of the carbon nanotube of the present application is smaller, which can play the role of liquid storage and retention, and improve the diffusion capacity of lithium ions.

In some embodiments, the negative electrode active material contained in the negative electrode film layer includes at least one of artificial graphite, natural graphite, and silicon-based materials, optionally selected from artificial graphite; the conductive agent includes conductive agent sp, KS-6, conductive At least one of graphite, carbon nanotubes, graphene, carbon fiber VGCF, optional conductive agent sp.

In the single-layer coated negative electrode sheet of the present application, further optionally, the negative electrode film layer includes carbon microtubes with an inner diameter of 2 μm to 4 μm, and the mass fraction W1 of the carbon microtubes in the negative electrode film layer is equal to the The mass fraction W2 of the conductive agent in the negative electrode film layer satisfies: when 1.5%≤W1≤2%, then 1.6%≤W1+W2≤2%; when 2.5%≤W1≤3%, then 0≤W2 ≤0.5%, based on the total weight of the negative film layer.

The second aspect of the present application provides a double-coated negative electrode sheet, which includes a current collector, a first film layer, and a second film layer, wherein the first film layer is disposed on at least one surface of the current collector, The second film layer is arranged on the outer surface of the first film layer; the first film layer is located between the current collector and the second film layer; and the first film layer contains the first negative active material; the second film The layer comprises the second negative electrode active material; at least one layer in the first film layer and the second film layer comprises carbon microtubes; , one of the two is different.

In this application, optionally, an intermediate coating is further included between the current collector and the first film layer. The intermediate coating is used to enhance the binding force between the negative electrode active material and the current collector, enhance electron transport, and reduce polarization. The thickness of the intermediate coating is not more than 6 μm, including conductive agent and binder. Wherein, the conductive agent includes at least one of conductive agent sp, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, and the binder includes styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, At least one of nitrile rubber and polybutylene fluoride (PVDF).

In this application, a double-layer coating process is used to form a negative electrode film layer with a double-layer structure of a first film layer and a second film layer, as shown in FIG. 2 . The total thickness of the negative film layer is 25-110 μm.

It should be noted that the "first film layer", "first film layer" and "lower layer" used in this application have the same meaning, and refer to the layer containing the active material near the current collector; "the second film Layer", "second film layer" and "upper layer" have the same meaning, and refer to the layer that contains the active material away from the current collector; "double film layer" refers to the first film layer and the second film layer ; "total mass" refers to the total mass of a substance in the first film layer and the second film layer.

In the present application, in the double-layer coated negative electrode sheet, especially in the negative electrode sheet with a thick coating weight (at least 9mg/cm ² ), it is beneficial to improve the rapidity of the secondary battery by adding carbon microtubes. charging capacity.

In some embodiments, in the double-coated negative electrode sheet, the first film layer does not contain carbon microtubes, and the second film layer contains carbon microtubes. This is conducive to enhancing the liquid storage capacity of the electrolyte in the second film layer, so that the second film layer (upper layer) has sufficient electrolyte solution to improve the diffusion ability of lithium ions to the first film layer (lower layer) and promote the diffusion of lithium ions To the film layer on the surface of the current collector, the purpose of making full use of the negative electrode active material is achieved, and the charging capacity of the battery is improved.

In some embodiments, in the double-layer coated negative electrode sheet, both the first film layer and the second film layer contain carbon microtubes. As a result, a smooth lithium ion channel is formed in the double-layer film of the negative electrode sheet, which ensures the lithium ion diffusion path from the upper layer/electrolyte interface to the lower layer/current collector interface, and further improves the flow rate of lithium ions from the upper layer to the lower layer. Diffusion depth and diffusion speed, so as to make full use of the negative electrode active material and improve the charging capacity of the battery.

In some embodiments, in the double-layer coated negative electrode sheet, in the double-layer film layer composed of the first film layer and the second film layer, the total mass fraction W3 of carbon microtubes is 0.2% to 5%, Optionally 1.5% to 3%, further optional 1.8% to 2.6%, based on the total weight of the first film layer and the second film layer. As a result, the charging capability of the double-layer coated negative electrode sheet is further improved.

In some embodiments, in the double-layer coated negative electrode sheet, the first film layer and the second film layer optionally further comprise a conductive agent; Among them, the total mass fraction W3 of carbon microtubes and the total mass fraction W4 of the conductive agent satisfy: when 0.2%≤W3≤2%, then W3+W4≤2%; when W3>2%, then 0≤ W4≤0.5%, based on the total mass of the first film layer and the second film layer.

By limiting the total mass fraction of the carbon microtubes and the conductive agent in the double-layer film layer to satisfy a specific relationship, the secondary battery can improve the fast charging capability without compromising the energy density. That is, a balance between the amount of loads (carbon microtubes and conductive agent), energy density, and charging performance is achieved.

In some embodiments, in the double-coated negative electrode sheet, the mass of the carbon microtubes in the second film layer is 50-100% relative to the total mass of the carbon microtubes. As a result, the carbon microtubes can all or mostly exist in the second film layer, which is conducive to the diffusion of more lithium-ion-containing electrolytes to the upper layer, and then to the lower layer, so as to improve the lithium ion diffusion capacity of the lower layer and realize The purpose of making full use of the active substances in the lower layer.

In some embodiments, in the double-layer coated negative electrode sheet, the carbon microtubes have an inner diameter of 0.2 μm to 12 μm, or 1 μm to 12 μm, optionally 2 μm to 10 μm, and further optionally 2 μm to 4 μm; the aspect ratio is 2-20, and the tube wall thickness is 0.01μm to 1μm.

By selecting carbon microtubes of specific specifications, the liquid storage and liquid retention functions of carbon microtubes are further optimized, and the diffusion of electrolyte is promoted, so that the negative electrode active material can be more fully utilized, and the deintercalation of lithium ions can be accelerated to further improve the performance of the battery. The purpose of fast charging capability. In particular, the inner diameter of the carbon microtubes is limited to 0.2 μm to 12 μm, so that the distance between the carbon microtubes is small and evenly distributed, thereby ensuring uniform pore size distribution, uniform polarization distribution inside the battery cell, and avoiding localized lithium deposition. The phenomenon, and the loss of energy density is small, and the charging capacity can be further improved.

In some embodiments, in the double-layer coated negative electrode sheet, under the condition that only the second film layer contains carbon microtubes, and optionally also includes a conductive agent in the first film layer and the second film layer, The mass fraction of carbon microtubes in the second film layer is 0.4% to 10%, and the mass fraction of the conductive agent is 0% to 4%, optionally 0% to 1.6%, based on the weight of the second film layer; The mass fraction of the conductive agent in the first film layer is 0% to 4%, optionally 0% to 2%, and optionally 0.4% to 2%, based on the weight of the first film layer.

In some embodiments, in the double-layer coated negative electrode sheet, carbon microtubes are included in both the first film layer and the second film layer, and optionally also include carbon microtubes in the first film layer and the second film layer Under the condition of the conductive agent, the mass fraction of the carbon microtubes in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on each film layer weight gauge. Thus, the composition and structure of the negative pole piece are optimized, and the fast charging capability of the secondary battery is optimized.

Optionally, the mass fraction ratio of carbon microtubes in the second film layer to that in the first film layer in the negative electrode sheet is 10:3 to 1:1. By further limiting the mass fraction ratio of carbon microtubes in the two layers of film, the depth of diffusion of the electrolyte in the direction of the current collector is increased, and at the same time, the liquid retention effect is effectively exerted, so as to achieve the purpose of making full use of the negative electrode active material , to improve the fast charging capability of the battery.

Optionally, the weight ratio of the second film layer to the first film layer in the negative electrode sheet is 1:4 to 4:1. The weight ratio refers to the ratio of the coating weight of the second film layer to that of the first film layer. In this way, the structure of the negative electrode sheet is further optimized, the coating process is simple and easy to operate, and the fast charging capacity of the battery is improved at the same time.

In some embodiments, in the first film layer and the second film layer, the first and second negative electrode active materials can be the same or different, including at least one of artificial graphite, natural graphite, and silicon-based materials; Optionally, the first negative electrode active material in the first film layer can be artificial graphite a, with a median particle size DV50 of 20-25 μm, and the second negative electrode active material in the second film layer can be artificial graphite b, with a median particle diameter The diameter DV50 is 10-14μm.

In some embodiments, under the condition that the conductive agent is optionally included in the first film layer and the second film layer, the conductive agent can be the same or different, including conductive agent sp, KS-6, conductive graphite, carbon At least one of nanotubes, graphene, carbon fiber VGCF.

In this application, the current collector is not particularly limited, and a metal foil or a composite current collector can be used. For example, copper foil can be used as the metal foil. The composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material. Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the present application, the negative electrode film layer, the first film layer and the second film layer may also optionally include a binder. The binder includes at least one of styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber, and polybutylene fluoride (PVDF), and styrene-butadiene rubber is optional. This facilitates better bonding properties.

In the present application, the negative electrode film layer, the first film layer and the second film layer may also optionally include a dispersant. The dispersant includes at least one of carboxymethylcellulose sodium (CMC-Na), methylcellulose, and ethylcellulose; optionally, sodium carboxymethylcellulose. This facilitates better dispersion properties.

Preparation

In this application, the preparation method of carbon microtubes is as follows:

The precursor solution containing polystyrene is electrospun to obtain nanofibers, and the nanofibers are evenly dispersed in a hydrochloric acid solution containing pyrrole, etc., and the mass ratio of pyrrole to nanofibers is 0.8:1 to 1.2:1, Adding ammonium persulfate to carry out polymerization reaction, the quality of ammonium persulfate is 1.1-1.3 times of the nanofiber silk, obtains the nanofiber silk of surface coating polymer, then adds tetrahydrofuran to the polymer nanofiber silk of above-mentioned surface coating, The quality of tetrahydrofuran is 8-22 times that of nanofibers. Stir thoroughly to dissolve polystyrene to obtain a hollow polymer tube. After pre-sintering at 280-320°C for 1-3h and carbonization at 1100-1300°C for 3-5h, cool After that, micron-sized carbon tubes are obtained.

Wherein, the carbon microtubes with different inner diameters described in this application can be obtained by using different mass ratios of tetrahydrofuran and nanofiber filaments.

In this application, single-layer coated and double-coated negative electrode sheets are prepared according to conventional methods in the art.

The single-layer coated negative electrode sheet is prepared by a conventional single-layer coating process, and the specific method is as follows:

S1: Add the raw material components of the negative electrode film layer, such as negative electrode active materials, conductive agents, binders, dispersants and/or carbon microtubes, into a solvent (such as water or deionized water) in a certain proportion, mix, and stir Negative electrode slurry is formed after uniformity;

S2: Coating the negative electrode slurry on at least one surface of the negative electrode current collector, drying and compacting to obtain the single-layer coated negative electrode sheet of the present application.

Wherein, the layer formed by the above-mentioned negative electrode slurry is called the negative electrode film layer.

Optionally, an intermediate coating may also be included between the above-mentioned negative electrode current collector and the negative electrode film layer, and the intermediate coating is formed before step S2 by combining a conductive agent (Sp, KS-6 or carbon nanotubes) with Agent (styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber or polyvinylidene fluoride (PVDF)) is mixed according to a certain proportion to make a slurry, and then coated on at least one surface of the current collector The above-mentioned intermediate coating is obtained, the thickness of which is not more than 6 μm.

In this application, the double-layer coated negative electrode sheet is prepared by a conventional double-layer coating process, and the specific method is as follows:

P1: The raw material components for preparing the first film layer, such as the first negative electrode active material, conductive agent, binder, dispersant and/or carbon microtubes, are added to the solvent (water or deionized water) in a certain proportion Mix, and form the slurry of the first film layer after stirring evenly, also known as the lower layer slurry;

P2: The raw material components for preparing the second film layer, such as negative electrode active material, conductive agent, binder, dispersant and/or carbon microtubes, are mixed in a solvent (water or deionized water) according to a certain proportion, After stirring evenly, the slurry forming the second film layer is also called the upper layer slurry;

P3: Coating the lower layer slurry prepared in the above P1 on at least one surface of the negative electrode current collector to form the first film layer (lower layer). Then apply the upper layer slurry prepared in P2 above to the surface of the first film layer, and after drying and compacting, the second film layer (upper layer) is obtained. Thus, the double-coated negative electrode sheet of the present application was prepared.

Optionally, an intermediate coating may also be included between the above-mentioned negative electrode current collector and the first film layer, which is formed before step P3 by mixing a conductive agent (Sp, KS-6 or carbon nanotubes) with The binder (styrene-butadiene rubber (SBR), polyacrylate, ethylene-propylene rubber, nitrile rubber or polyvinylidene fluoride (PVDF)) is mixed in a certain proportion to make a slurry, and then coated on at least one of the current collectors The above-mentioned intermediate coating is obtained on the surface, the thickness of which is not more than 6 μm.

It should be understood that the negative electrode sheet of the present application can be used not only for secondary batteries, but also for any other batteries, battery modules, battery packs or electrical devices that need to improve the fast charging capability.

secondary battery

The secondary battery, battery module, battery pack and electric device of the present application are described below.

secondary battery

In one embodiment of the present application, a secondary battery is provided, which includes the negative electrode sheet of the present application.

Typically, a secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode. The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, and the positive electrode film layer includes a positive electrode active material.

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

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

In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for batteries. As an example, the positive active material may include at least one of the following materials: olivine-structured lithium-containing phosphate, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (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 abbreviated as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also abbreviated as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also abbreviated as NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 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 its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also may be abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon At least one of a composite material, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

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

In some embodiments, the positive electrode film layer may also optionally include a conductive agent. 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 above-mentioned components used to prepare the positive electrode sheet, such as positive electrode active material, conductive agent, 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Electrolyte]

The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The present application has no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte may be selected from at least one of solid electrolytes and liquid electrolytes (ie, electrolytic solutions).

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

In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), difluorosulfonyl Lithium amide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate borate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

In some embodiments, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB) , ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) kind.

In some embodiments, additives are optionally included in the electrolyte. For example, additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance. Additives etc.

[Isolation film]

In some embodiments, a separator is further included in the secondary battery. The separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation. The present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

[outer packaging]

In some embodiments, the secondary battery may include an outer package for encapsulating the positive electrode tab, the negative electrode tab, and the electrolyte. As an example, the positive pole piece, the negative pole piece and the separator can be laminated or wound to form a laminated structure cell or a wound structure cell, and the cell is packaged in the outer package; the electrolyte can be electrolyte, and the electrolyte can be infiltrated in the cell. The number of cells in the secondary battery can be one or several, and can be adjusted according to requirements.

In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer package of the secondary battery may be a soft bag, such as a pouch-type soft bag. The material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. can be included. In some embodiments, the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.

Preparation method of secondary battery

In one embodiment, the present application provides a method for preparing a secondary battery, wherein the negative electrode sheet described in the first aspect and/or the second aspect of the present application is used.

The preparation of the secondary battery may also include the step of assembling the negative electrode sheet, the positive electrode sheet and the electrolyte of the present application to form a secondary battery. In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be sequentially wound or laminated, so that the separator is placed between the positive electrode sheet and the negative electrode sheet for isolation, and a battery cell is obtained. Put the battery cell in the outer package, inject the electrolyte and seal it to obtain the secondary battery.

In some embodiments, the preparation of the secondary battery may further include the step of preparing a positive electrode sheet. As an example, the positive electrode active material, conductive agent and binder can be dispersed in a solvent (such as N-methylpyrrolidone, referred to as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, After drying, cold pressing and other processes, the positive electrode sheet is obtained.

In some embodiments, the preparation of the secondary battery includes the step of preparing a negative electrode sheet according to the method described in this application.

Electrical device, battery module or battery pack

The present application has no special limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG. 3 shows a square-shaped secondary battery 5 as an example.

In some embodiments, referring to FIG. 4 , the outer package may include a housing 51 and a cover 53 . Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity. The positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 5 is a battery module 4 as an example. Referring to FIG. 5 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

6 and 7 show the battery pack 1 as an example. Referring to FIGS. 6 and 7 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric devices may include mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, etc.) , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited thereto.

As the electric device, a secondary battery, a battery module or a battery pack can be selected according to its use requirements.

FIG. 8 is an example of an electrical device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module may be used.

As another example, a device may be a cell phone, tablet, laptop, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used, those whose manufacturers are not indicated, are conventional products commonly used in this field and available commercially. The content of each component in the examples of the present application is based on the mass without water of crystallization, unless otherwise specified.

The following descriptive terms: "the negative electrode sheet of embodiment A1" refers to the negative electrode sheet used in the lithium ion battery preparation process of embodiment A1; "the positive electrode sheet of embodiment A1" refers to the lithium ion battery of embodiment A1 The positive electrode sheet used in the preparation process; "the electrolyte of embodiment A1" refers to the electrolyte used in the lithium ion battery preparation process of embodiment A1; "the separator of embodiment A1" refers to the electrolyte of embodiment A1 The separator used in the preparation process of the lithium-ion battery; "the lithium-ion battery of Example A1" refers to the lithium-ion battery prepared from the positive electrode, separator, negative electrode, and electrolyte of Example A1.

In this application, coat weights are all dry weights.

The sources of raw materials involved in the embodiments of the present application are as follows:

Nickel-cobalt-manganese ternary material (LiMO ₂ , M is a Ni-Co-Mn solid solution, see the specific ratios in each embodiment)

Artificial graphite a (Guangdong Kaijin New Energy Technology Co., Ltd., DV50=22μm);

Artificial graphite b (Guangdong Kaijin New Energy Technology Co., Ltd., DV50=12 μm);

N-Methylpyrrolidone (NMP, CAS: 872-50-4, Shanghai McLean Biotechnology Co., Ltd.)

Polyvinylidene fluoride (CAS: 24937-79-9, Shanghai McLean Biotechnology Co., Ltd.)

Acetylene black (Guangdong Kaijin New Energy Technology Co., Ltd.)

Acrylate (CAS: 25067-02-1, Shanghai McLean Biotechnology Co., Ltd.)

Dimethyl carbonate (DMC, CAS: 616-38-6, Shanghai McLean Biotechnology Co., Ltd.)

Carbon microtubes were prepared as follows:

Carry out electrospinning (voltage 20Kv, flow velocity 50mL/min) with the nanofiber silk precursor solution (N methylpyrrolidone as solvent) that contains the polystyrene of 15% (mass percentage), obtain nanofiber silk; Disperse in 1M hydrochloric acid solution containing 15% (mass percentage) pyrrole, the mass ratio of pyrrole and nanofiber silk is 1:1; then add ammonium persulfate to carry out polymerization reaction, the quality of ammonium persulfate is 1.2 times of nanofiber silk , to obtain nanofibers coated with polymers on the surface, and then add tetrahydrofuran to the above-mentioned polymer nanofibers coated on the surface, the quality of tetrahydrofuran is 16 times that of nanofibers; at 25 ° C, fully stir for 6 hours, dissolve the polymer Styrene, that is, to obtain hollow polymer tubes, after pre-sintering at 300°C for 2 hours and carbonization at 1200°C for 4 hours, micron-sized carbon tubes are obtained after cooling;

The carbon microtubes thus obtained had an inner diameter of 2.5 μm, a wall thickness of 0.05 μm, and a length of 15 μm.

Repeat the above implementation process, change the mass ratio of tetrahydrofuran to nanofibers to 20, 19, 17, 14, 13, 12, and 10, respectively, and obtain carbon micrometers with inner diameters of 0.2, 1, 2, 4, 6, 10, and 12 μm, respectively. Tube.

Example A1

【Preparation of Negative Electrode Slurry】

Each component of raw material: Negative electrode active material artificial graphite b (median particle diameter DV50=12 μ m), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose CMC, conductive agent sp, carbon microtube according to mass fraction 95%: 1.8%: 1.2%: 0.2%: 1.8% (based on the total weight of the raw material) mixes, adds deionized water, and obtains a negative electrode slurry whose solid component mass fraction is 50% under the action of a vacuum mixer; used The inner diameter of the carbon microtube is 2.5 μm, the wall thickness is 0.05 μm, and the length is 15 μm.

[Preparation of negative electrode sheet]

The negative electrode slurry prepared above was uniformly coated on the negative electrode current collector copper foil with a thickness of 8 μm at a coating weight of 9 mg/cm ² (dry weight); then the copper foil was dried at room temperature and then transferred to a 120 ° C oven for drying 1h, and then cold-pressed and cut to obtain the negative electrode sheet.

【Preparation of Positive Electrode】

Mix the positive electrode active material nickel-cobalt-manganese ternary material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ), the binder polyvinylidene fluoride, and the conductive agent acetylene black according to the mass ratio of 8:1:1, add the solvent NMP, and vacuum The positive electrode slurry is obtained under the action of the mixer; the positive electrode slurry is evenly coated on the On a positive electrode current collector aluminum foil with a thickness of 13 μm; after drying the aluminum foil at room temperature, transfer it to an oven at 120°C for 1 hour, and then cold press and cut to obtain the positive electrode sheet.

【Preparation of Electrolyte】

In an argon atmosphere glove box with a water content <10ppm, in a beaker, mix EC and EMC at a mass ratio of 3:7, add LiPF ₆ to form an electrolyte, and in the electrolyte, the mass content of LiPF ₆ is 12.5 %.

【Isolation film】

The isolation film was purchased from Cellgard, and the model was cellgard2400.

【Preparation of lithium ion battery】

Stack the positive electrode, separator, and negative electrode in order, so that the separator is between the positive and negative electrodes for isolation, and then wind the bare cell; the bare cell with a capacity of 4.3Ah Put it in the outer packaging foil, inject 8.6g of the above-mentioned prepared electrolyte into the dried battery, and go through processes such as vacuum packaging, standing, forming, and shaping to obtain a lithium-ion battery. The outer package is 33mm (width)×220mm (length)×97mm (height), the thickness of the casing is 0.6mm; the margin of the battery group is 90%.

Examples A2-A5 and A15-A16

The preparation process of the lithium-ion battery is generally referred to in Example A1, the difference is that in the preparation of the negative electrode slurry, the inner diameter of the carbon microtubes is changed, and the specific values are shown in Table 1.

Examples A6-A12

The preparation process of the lithium-ion battery is generally referred to in Example A1, the difference is that in the preparation of the negative electrode slurry, the mass fractions of the conductive agent sp and carbon microtubes in the raw materials are changed, as shown in Table 1.

Comparative example 1

The preparation process of the lithium-ion battery refers to Example A1 as a whole. The difference is that in the preparation of the negative electrode slurry, the mass fractions of carbon microtubes and conductive agent sp in the raw materials are changed to 1.8% and 2%, respectively, as shown in Table 1. .

Comparative example 2

The preparation process of the lithium-ion battery is generally referred to in Example A1, the difference is that no conductive agent is added in the preparation of the negative electrode slurry, and the mass fraction of carbon microtubes is 6%, as shown in Table 1.

Comparative example 3

The preparation process of the lithium-ion battery is generally referred to in Example A1, the difference is that no carbon microtubes are added in the preparation of the negative electrode sheet, as shown in Table 1.

In embodiment A2-A16 and comparative example 1-3, the massfraction of carbon microtube and conductive agent used in preparing slurry in the raw material is the carbon microtube and conductive agent in the negative film layer shown in table 1. Mass fraction; for the remaining components used in the preparation of the slurry, the negative electrode active material artificial graphite, the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose are added in a mass ratio of 95:1.8:1.2.

Example B1

The preparation process of the lithium-ion battery refers to Example A1 as a whole, the difference lies in the preparation process of the negative electrode:

[Preparation of slurry for the first film layer]

Raw material components: the first negative electrode active material artificial graphite a (median particle diameter Dv50=22), conductive agent sp, binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose according to mass fraction 96%: 1% : 1.8%: 1.2% (based on the total weight of the raw material) mixes, adds deionized water, and obtains the negative electrode slurry that the solid component mass fraction is 50% under the effect of vacuum mixer; It is used to prepare the lower layer of the negative electrode film layer, namely The layer next to the current collector.

[Preparation of slurry for the second film layer]

Raw material components: second negative electrode active material artificial graphite b (median particle diameter Dv50=12), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose CMC, carbon microtube according to mass fraction 94%: 1.8 %: 1.2%: 3% (based on the total weight of the raw materials) mixed, adding deionized water, under the action of a vacuum mixer to obtain a negative electrode slurry with a solid component mass fraction of 50%; for preparing the upper layer of the negative electrode film layer, That is, the layer away from the current collector, which does not contain carbon microtubes.

[Preparation of negative electrode sheet]

The slurry of the first film layer prepared above was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm at a coating weight of 7 mg/cm ² (dry weight), and dried to obtain the first film used in this embodiment. A film layer (i.e. the lower layer of the negative electrode film layer); on the first film layer, the slurry of the second film layer prepared above is evenly coated with a coating weight of 7mg/cm ² (dry weight); then the copper foil is placed on the After drying at room temperature, it was transferred to an oven at 120° C. for 1 hour, and then subjected to cold pressing and slitting to obtain negative electrode sheets.

Wherein, the inner diameter of the carbon microtubes used is 2.5 μm, the wall thickness is 0.05 μm, and the length is 15 μm. The coating weight ratio of the first film layer to the second film layer is 1:1, which is the weight ratio of the first film layer to the second film layer.

Examples B2-B5 and B15-B16

The preparation process of the lithium-ion battery is generally referred to in Example B1, the difference is that in the slurry preparation of the first and second film layers, the inner diameter of the carbon microtubes is changed, and the specific values are shown in Table 2.

Examples B6 and B17-B18

The preparation process of the lithium-ion battery refers to Example B1 as a whole, the difference is that in the slurry preparation of the first film layer, the mass fraction of the conductive agent sp of the raw material is shown in Table 2, and the remaining components are the first negative active material Artificial graphite a (median particle diameter Dv50=22), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose add according to mass ratio 96:1.8:1.2;

In the slurry preparation of the second film layer, the raw material also includes conductive agent sp, the mass fractions of carbon microtubes and conductive agent sp in the raw material are shown in Table 2 respectively, and the second negative electrode active material artificial graphite b (middle) of the remaining components Value particle size Dv50=12), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose are added according to the mass ratio of 94:1.8:1.2.

Examples B7-B12

The preparation process of the lithium-ion battery refers to Example B1 as a whole, the difference is that in the slurry preparation of the first film layer, the mass fraction of the conductive agent sp of the raw material is shown in Table 2, and the remaining components are the first negative active material Artificial graphite a (median particle diameter Dv50=22), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose add according to mass ratio 96:1.8:1.2;

In the slurry preparation of the second film layer, change the mass fraction of carbon microtubes in the raw material as shown in Table 2 respectively; The second negative electrode active material artificial graphite b (median particle diameter Dv50=12) of the remaining components, bonding The agent styrene-butadiene rubber and the dispersant sodium carboxymethylcellulose are added according to the mass ratio of 94:1.8:1.2.

Examples B13-B14

The preparation process of the lithium-ion battery refers to Example B1 as a whole, the difference is that in the slurry preparation of the first film layer, the mass fraction of the conductive agent sp of the raw material is shown in Table 2, and the remaining components are the first negative active material Artificial graphite a (median particle diameter Dv50=22), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose add according to mass ratio 96:1.8:1.2;

In the preparation of the negative electrode sheet, the coating ratio of the first film layer and the second film layer was changed, as shown in Table 2.

Examples B19-B20

The preparation process of the lithium-ion battery refers to Example B1 as a whole, the difference is that in the slurry preparation of the first film layer, the mass fraction of the conductive agent sp of the raw material is shown in Table 2, and the remaining components are the first negative active material Artificial graphite a (median particle diameter Dv50=22), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose add according to mass ratio 96:1.8:1.2;

In the slurry preparation of the second film layer, the raw material of Example B20 also contains conductive agent sp, the mass fractions of carbon microtubes and conductive agent sp in the raw material are shown in Table 2, and the remaining components of the second negative electrode active material are artificial Graphite b (median particle size Dv50=12), binder styrene-butadiene rubber, and dispersant sodium carboxymethylcellulose are added in a mass ratio of 94:1.8:1.2.

In the preparation of the negative electrode sheet, the weight ratio of the first film layer to the second film layer was changed, as shown in Table 2.

Comparative example 4

The preparation process of the lithium-ion battery refers to Example B1 as a whole, the difference is that in the preparation of the second film layer, the slurry of the second film layer does not contain carbon microtubes, but contains a conductive agent with a mass fraction of 3%, As shown in table 2.

Example C1

The preparation process of the lithium-ion battery refers to Example A1 as a whole, the difference lies in the following preparation process:

[Preparation of slurry for the first film layer]

Raw material components: the first negative electrode active material artificial graphite a (median particle diameter Dv50=22), conductive agent sp, binding agent styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, carbon microtubes according to the mass fraction of 95.3%: 0.8%: 1.5%: 1.2%: 1.2% (based on the total weight of raw materials) mixed, adding deionized water, under the action of a vacuum mixer to obtain a negative electrode slurry with a solid component mass fraction of 50%; for Prepare the lower layer of the negative electrode film layer, that is, the layer close to the current collector.

[Preparation of slurry for the second film layer]:

The raw material components: the second negative electrode active material artificial graphite b (median particle diameter Dv50=12), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, carbon microtubes are 93.3% according to the mass fraction: 1.5 %: 1.2%: 4% (based on the total weight of the raw materials) mixed, adding deionized water, under the action of a vacuum mixer to obtain a negative electrode slurry with a solid component mass fraction of 50%; for preparing the upper layer of the negative electrode film layer, That is, the layer away from the current collector.

[Preparation of negative electrode sheet]

The slurry of the first film layer prepared above was evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm at a coating weight of 6 mg/cm ² (dry weight), and dried to obtain the first film used in this embodiment. One film layer (i.e. the lower layer of the negative electrode film layer); on the first film layer, the slurry of the second film layer prepared above is evenly coated with a coating weight of 6mg/cm ² (dry weight); then the copper foil is placed on the After drying at room temperature, it was transferred to an oven at 120° C. for 1 hour, and then subjected to cold pressing and slitting to obtain negative electrode sheets.

Wherein, the inner diameter of the carbon microtubes used is 2.5 μm, the wall thickness is 0.05 μm, and the length is 15 μm. The coating weight ratio of the first film layer to the second film layer is 1:1, which is the weight ratio of the first film layer to the second film layer.

Examples C2-C5 and C15-C16

The preparation process of the lithium-ion battery is generally referred to in Example C1, the difference is that in the slurry preparation of the first and second film layers, the inner diameter of the carbon microtubes is changed, and the specific values are shown in Table 3.

Examples C6-C12 and C17-C18

The preparation process of the lithium-ion battery refers to Example C1 as a whole, the difference is:

In the slurry preparation of the first film layer, the conductive agent sp is optionally included in the raw material, and the mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 3, and the remaining components are the first negative electrode active material artificial graphite a (median particle size Dv50=22), binder styrene-butadiene rubber, and dispersant sodium carboxymethylcellulose are added according to the mass ratio of 95.3:1.5:1.2;

In the slurry preparation of the second film layer, the raw material optionally includes a conductive agent sp, the mass fractions of the carbon microtubes and the conductive agent sp in the raw material are shown in Table 3, and the remaining components are the second negative active material artificial graphite b (median particle size Dv50=12), binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are added in a mass ratio of 93.3:1.5:1.2.

C13-C14 and C19-C20

The preparation process of the lithium-ion battery refers to Example C1 as a whole, the difference is:

In the slurry preparation of the first membrane layer, the massfraction of carbon microtubes and conductive agent sp in the raw material is shown in table 3 respectively, and the first negative electrode active material artificial graphite a (median particle diameter Dv50=22) of all the other components , Binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose are added according to the mass ratio of 95.3:1.5:1.2;

In the slurry preparation of the second film layer, the raw material also includes conductive agent sp, the mass fractions of carbon microtubes and conductive agent sp in the raw material are shown in Table 3 respectively, and the second negative electrode active material artificial graphite b (middle) of the remaining components Value particle size Dv50=12), binder styrene-butadiene rubber, dispersant sodium carboxymethylcellulose are added according to the mass ratio of 93.3:1.5:1.2;

In the preparation of the negative electrode sheet, the weight ratio of the first film layer to the second film layer was changed, as shown in Table 3.

Comparative example 5

The preparation process of the lithium-ion battery refers to Example C1 as a whole. The difference is that in the preparation of the negative electrode sheet, the slurry of the first and second film layers does not contain carbon microtubes, and the mass fraction of the conductive agent in the raw materials is the same. is 1%, as shown in Table 3;

The remaining components in the slurry prepared by the first film layer are the first negative electrode active material artificial graphite a (median particle diameter Dv50=22), binding agent styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose according to mass ratio 96.3 : 1.5: 1.2 added; the remaining components in the slurry prepared by the second film layer, the first negative electrode active material artificial graphite b (median particle size Dv50=12), binder styrene-butadiene rubber, dispersant carboxymethyl fiber Vegetarian sodium is added according to the mass ratio of 96.3:1.5:1.2.

【Related parameters and battery performance test】

1. Determination of carbon microtubes

In this application, the length, inner diameter and wall thickness of carbon microtubes can be tested by using a scanning electron microscope (ZEISSSigma 300). The sample preparation is as follows: Cut the pole piece into a sample with a size of 8mm×3mm, place it on the sample stage, and test it at a magnification of 10K through a scanning electron microscope (ZEISS Sigma 300). Measurement of tube length, inside diameter and wall thickness.

2. Determination of the structure of the negative electrode film layer

In this application, the structure of the negative electrode film layer can be tested under a magnification of 10K by using a scanning electron microscope (ZEISS Sigma 300). The sample preparation is as follows: firstly, the negative pole piece is cut into a sample to be tested with a size of 2cm×2cm, and the negative pole piece is fixed on the sample stage by paraffin. Then put the sample stage into the sample rack and lock it, turn on the power of the argon ion cross-section polisher (IB-19500CP), vacuumize (10 ^-4 Pa), and set the argon gas flow (0.15MPa) and voltage (8KV) at the same time As well as the polishing time (2 hours), adjust the sample stage to swing mode and start polishing. The sample test is carried out with reference to JY/T010-1996.

3. Battery fast charging capability test

At 25°C, the batteries of the above-mentioned examples and comparative examples were charged and discharged for the first time with a current of 1C (that is, the current value at which the theoretical capacity is completely released within 1h), specifically including: charging the battery with a constant current at a rate of 1C to a voltage of 4.25V, then charged at a constant voltage to a current of ≤0.05C, let it stand for 5 minutes, and then discharged at a rate of 0.33C to a voltage of 2.8V, and recorded its actual capacity as C0.

Then charge the battery at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, constant current to the full battery charge cut-off voltage of 4.25V or 0V negative cut-off potential (whichever comes first) After each charge, it needs to be discharged at 1C0 to the full battery discharge cut-off voltage of 2.8V, and recorded at different charge rates to 10%, 20%, 30%, ..., 80% Electric state) corresponding to the negative electrode potential, draw the charge rate-negative electrode potential curves under different SOC states, and after linear fitting, the corresponding charge rate when the negative electrode potential is 0V under different SOC states is obtained, the charge rate is The charging window under the SOC state is recorded as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC, according to the formula (60/C20% SOC+60/C30%SOC+60/C40%SOC+60/C50%SOC+60/C60%SOC+60/C70%SOC+60/C80%SOC)×10% Calculate the battery is charged from 10%SOC Charging time T to 80% SOC, unit is min. The shorter the time, the better the fast charging performance of the battery. Initial discharge DCR (DC resistance, Directive Current Resistance) test

According to the above process, the lithium-ion batteries of the embodiment and the comparative example were respectively tested, and the specific values are shown in Table 1-Table 3.

Table 1: Effects of parameters related to the preparation of single-layer coated negative electrode sheets on battery performance

Compared with the comparative examples in the examples of the present application, it can be seen from Table 1 that when the mass fraction of the carbon microtubes and the conductive agent in the negative electrode film layer coated with a single layer satisfies a specific relational expression, the fast charging capacity of the battery can be significantly improved ; As can be seen from Table 2-3, when the double-coated negative pole sheet contains carbon microtubes, the charging capacity of the battery is significantly improved.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same effects are included in the technical scope of the present application. In addition, without departing from the scope of the present application, various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

Claims (21)

1. A single-layer coated negative pole piece is characterized in that,

the single-layer coated negative electrode sheet comprises a current collector and a negative electrode film layer arranged on at least one surface of the current collector, wherein the negative electrode film layer comprises a negative electrode active material and a carbon micron tube, and optionally comprises a conductive agent;

the mass fraction W1 of the carbon micron tube on the negative electrode film layer and the mass fraction W2 of the conductive agent on the negative electrode film layer meet the following requirements: when W1 is more than or equal to 0.2% and less than or equal to 2%, then W1+ W2 is less than or equal to 2%; when W1 is more than 2%, then 0. Ltoreq. W2. Ltoreq.0.5%, based on the total weight of the negative electrode film layer.

2. The single-layer coated negative electrode sheet according to claim 1, wherein the mass fraction W1 of the carbon nanotube in the negative electrode film layer is 0.2% to 5%.

3. The single coated negative electrode sheet of claim 1 or 2, wherein the carbon nanotubes have an internal diameter of 0.2 to 12 μ ι η, optionally 2 to 10 μ ι η; alternatively, the aspect ratio is from 2 to 20; further optionally, the carbon nanotube has a tube wall thickness of 0.01 μm to 1 μm.

4. The single-layer coated negative electrode sheet according to any one of claims 1 to 3, wherein the negative active material comprises at least one of artificial graphite, natural graphite, and silicon-based material; optionally, the conductive agent comprises at least one of conductive agents sp, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fibers VGCF.

5. A double-layer coated negative pole piece is characterized in that,

the double-layer coated negative pole piece comprises a current collector, a first film layer and a second film layer, wherein the first film layer is arranged on at least one surface of the current collector, and the second film layer is arranged on the outer surface of the first film layer; the first membrane layer is positioned between the current collector and the second membrane layer;

wherein the first film layer comprises a first negative electrode active material; the second film layer includes a second negative active material; at least one of the first and second membrane layers comprises carbon nanotubes; the first film layer and the second film layer are different from each other at least in one of a negative electrode active material and whether or not the negative electrode active material includes a carbon nanotube.

6. The double-coated negative electrode sheet of claim 5, wherein the first film layer does not comprise carbon nanotubes and the second film layer comprises carbon nanotubes.

7. The double-coated negative electrode sheet of claim 5, wherein the first and second film layers each comprise carbon nanotubes.

8. The double-coated negative electrode sheet according to any one of claims 5 to 7, wherein the total mass fraction W3 of the carbon nanotubes in the first and second film layers is 0.2 to 5% based on the total weight of the first and second film layers.

9. The double-coated negative electrode sheet according to any one of claims 5 to 8, wherein in the first and second film layers, optionally further comprising a conductive agent, the total mass fraction W3 of the carbon nanotubes and the total mass fraction W4 of the conductive agent satisfy: when W3 is more than or equal to 0.2% and less than or equal to 2%, then W3+ W4 is less than or equal to 2%; when W3 is greater than 2%, then 0. Ltoreq. W4. Ltoreq.0.5%, based on the total mass of the first and second film layers.

10. The double-coated negative electrode sheet according to any one of claims 5 to 9, wherein the mass of the carbon nanotubes in the second film layer is 50 to 100% with respect to the total mass of the carbon nanotubes.

11. The double-coated negative electrode sheet according to any of claims 5 to 10, wherein the carbon nanotubes have an internal diameter of 0.2 to 12 μm, optionally 2 to 10 μm; alternatively, the aspect ratio is from 2 to 20; further optionally, the carbon nanotube has a tube wall thickness of 0.01 μm to 1 μm.

12. The double-coated negative electrode sheet according to claim 6, wherein in the first and second film layers, a conductive agent is optionally further contained; the mass fraction of the carbon nanotubes in the second film layer is from 0.4% to 10%, and the mass fraction of the conductive agent is from 0% to 4%, optionally from 0% to 1.6%, based on the weight of the second film layer; the mass fraction of the conductive agent in the first film layer is 0% to 4%, optionally 0% to 2%, based on the weight of the first film layer.

13. The double-coated negative electrode sheet according to claim 7, wherein in the first and second film layers, a conductive agent is optionally further contained; when the first and second film layers each contain the carbon nanotube, the mass fraction of the carbon nanotube in each film layer is 0.2% to 5%, and the mass fraction of the conductive agent in each film layer is 0% to 2%, based on the weight of each film layer.

14. The double-coated negative electrode sheet according to claim 13, wherein the mass fraction ratio of the carbon nanotube in the second film layer to the first film layer is 10 to 1.

15. The double-coated negative electrode sheet according to any one of claims 5 to 14, wherein the weight ratio of the second film layer to the first film layer is 1.

16. The double-coated negative electrode tab according to any one of claims 5 to 15, wherein the first and second negative active materials may be the same or different and comprise at least one of artificial graphite, natural graphite, silicon-based materials.

17. The bilayer coated negative electrode sheet of any one of claims 9 to 16, wherein the conductive agent may be the same or different in the first and second film layers, including at least one of conductive agents sp, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fibres VGCF.

18. A secondary battery comprising the single-layer coated negative electrode sheet of any one of claims 1 to 4, or the double-layer coated negative electrode sheet of any one of claims 5 to 17.

19. A battery module characterized by comprising the secondary battery according to claim 18.

20. A battery pack comprising the battery module according to claim 19.

21. An electric device comprising at least one selected from the secondary battery according to claim 18, the battery module according to claim 19, and the battery pack according to claim 20.

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