CN115832212A

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

Info

Publication number: CN115832212A
Application number: CN202210538481.6A
Authority: CN
Inventors: 王育文; 叶永煌; 吴益扬; 武宝珍
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-05-18
Filing date: 2022-05-18
Publication date: 2023-03-21

Abstract

The application provides a negative pole piece of individual layer coating, satisfies certain relation through the mass fraction of injecing carbon micron pipe and conductive agent in the negative pole rete to improve the diffusibility of lithium ion at the negative pole rete, improve the charging performance of battery. The application also provides a double-layer coated negative pole piece, and the purpose of improving the charging performance of the battery is achieved by that at least one layer in the first film layer and the second film layer contains the carbon micron tube. In addition, the present application also relates to a secondary battery, a battery module, a battery pack, and an electric device, which include the above-described single-layer coated and double-layer coated negative electrode sheet.

Description

Negative pole piece and secondary battery, battery module, battery pack and electric device comprising same

Technical Field

The application relates to the technical field of lithium batteries, in particular to a single-layer coated negative pole piece, a double-layer coated negative pole piece, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, with the wider application range of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power, and solar power stations, and in various fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, and aerospace.

However, the coating weight in the secondary battery is thick (e.g., at least 9 mg/cm) ² ) When the electrode is used, the quick charging performance of the battery is lower; the polarization inside the battery cell is increased, the service life of the battery cell is deteriorated, and factors causing potential safety hazards such as lithium precipitation appear. Therefore, the electrochemical performance of the secondary battery having a thick coating still remains to be improved, especially, the rapid charging performance thereof is improved.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a negative electrode tab capable of improving the charging ability of a secondary battery, and to provide a secondary battery, a battery module, a battery pack, and an electric device including the negative electrode tab of the present invention.

In order to achieve the above object, a first aspect of the present application provides a single-layer coated negative electrode sheet comprising a current collector and a negative electrode film layer disposed on at least one surface of the current collector, the negative electrode film layer comprising a negative electrode active material and carbon nanotubes, optionally comprising a conductive agent; wherein, 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.

The carbon micron tube is added into the negative electrode film layer, and the mass fraction of the carbon micron tube and the conductive agent in the negative electrode film layer is limited to meet a certain relation, so that the liquid retention capacity of the negative electrode film layer is improved, the diffusion capacity of lithium ions in the negative electrode film layer is promoted, and the charging performance of the secondary battery is improved.

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

In any embodiment, in the single-layer coated negative electrode sheet, the carbon nanotubes have an inner diameter of 0.2 μm to 12 μm, optionally 2 μm to 10 μm; alternatively, the aspect ratio is from 2 to 20; further optionally, the carbon nanotubes have a wall thickness of 0.01 μm to 1 μm. By limiting the specification of the carbon micron tube, the carbon micron tube can fully play the roles of liquid storage and liquid retention in the negative electrode film layer, and the liquid phase diffusion capacity is improved, so that the active substances of the negative electrode film layer are fully utilized, and the charging performance of the battery is improved.

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 a 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.

A 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, and the second film layer is disposed on an outer surface of the first film layer; the first film layer is positioned between the current collector and the second film layer; and the first membrane layer comprises a first negative active material and the second membrane layer comprises a second negative active material; at least one of the first and second film layers comprises carbon nanotubes; the first film layer and the second film layer are different from each other at least in one of the negative electrode active material and the presence/absence of the carbon nanotube.

This application has promoted the stock solution ability of rete through introducing carbon micron pipe in the rete of the negative pole piece of double-deck coating, has guaranteed the diffusion of lithium ion in whole rete, reaches active material's in the make full use of rete purpose to improve secondary cell's electrochemical performance, especially charging performance.

In any embodiment, in the double coated negative electrode sheet, the first film layer does not comprise carbon nanotubes and the second film layer comprises carbon nanotubes. Thus, by further limiting the distribution of the carbon nanotubes, the second film layer (upper layer) is provided with a sufficient amount of electrolyte, and diffusion of lithium ions into the first film layer (lower layer) is promoted, thereby making full use of the negative electrode active material.

In any embodiment, in the double coated negative electrode sheet, the first film layer and the second film layer each comprise carbon nanotubes. Therefore, the liquid retention capacity of the two film layers is increased, and the lithium ion channel penetrates through the whole film layer so as to further improve the diffusion capacity of lithium ions.

In any embodiment, in the double-coated negative electrode sheet, 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. Therefore, the mass fraction of the carbon micron tube in the double-film layer is further limited so as to optimize the electrochemical performance of the negative pole piece, and the charging capacity of the battery is improved.

In any embodiment, in the double-layer coated negative electrode sheet, the first film layer and the second film layer optionally further comprise a conductive agent, and 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. When the total mass fraction of the carbon micro-tube and the conductive agent satisfies a specific relationship, the balance among the amount of the load (the carbon micro-tube and the conductive agent), the energy density and the charging performance can be realized, and the rapid charging capability is improved.

In any embodiment, in the double-coated negative electrode sheet, the mass of the carbon nanotubes in the second film layer is 50 to 100% relative to the total mass of the carbon nanotubes. The carbon microtubes are completely or mostly arranged in the second film layer, so that more electrolyte containing lithium ions can be favorably diffused to the upper layer, sufficient lithium ions can be provided to reach the interface between the upper layer and the lower layer and the interface between the lower layer and the current collector, and the aim of fully utilizing the active substances of the lower layer is fulfilled.

In any embodiment, in the double coated negative electrode sheet, the carbon nanotubes have a diameter of 0.2 μm to 12 μm, optionally 2 μm to 10 μm; the length-diameter ratio is 2-20; the carbon micron tube has a tube wall thickness of 0.01 to 1 μm. By limiting the carbon micron tube with proper specification, the uniformity of pore size distribution is realized, the liquid storage and retention capacity of the film layer is 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 comprises the carbon nanotube, a conductive agent is optionally further included in the first film layer and the second film layer; 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.

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

The composition and the structure of the negative electrode film layer are optimized by further limiting the mass content of the carbon micron tube and the conductive agent in each film layer, so that the optimal quick charging capability is achieved.

In any embodiment, in the double-coated negative electrode sheet, under the condition that the first and second film layers both comprise carbon nanotubes, the mass fraction ratio of the carbon nanotubes in the second film layer to the first film layer is 10 to 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. Therefore, the diffusion performance of the upper layer and the lower layer reaches the optimal proportion, and the quick charging capacity of the battery is further improved.

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

In any embodiment, in the double-layer coated negative electrode sheet, 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 fibers VGCF.

A third aspect of the present application provides a secondary battery comprising a single-layer coated negative electrode sheet according to the first aspect of the present application and a double-layer coated negative electrode sheet according to the second aspect of the present application.

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

A fifth aspect of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.

A sixth aspect of the present application provides an electric device including at least one of the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, or the battery pack according to the fifth aspect of the present application.

This application is through using the carbon micron pipe in secondary cell's negative pole piece, and the mass fraction of injecing carbon micron pipe and conducting agent simultaneously satisfies certain relation, makes secondary cell's quick charge ability promote. Correspondingly, the battery pack, the battery module and the electric device have improved quick charging capacity.

Drawings

Fig. 1 is a schematic view of a single-layer coated negative electrode tab according to an embodiment of the present disclosure.

FIG. 2 is a schematic view of a double-coated negative electrode sheet according to an embodiment of the present disclosure

Fig. 3 is a schematic view of a secondary battery according to an embodiment of the present application.

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

Fig. 5 is a schematic view 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 the embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic diagram of a secondary battery according to an embodiment of the present application as an electric device.

Description of reference numerals:

1, a battery pack; 2, putting the box body on the box body; 3, a lower box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 a top cover assembly; 6, collecting a current body; 7 a single-layer negative electrode film layer; 8 a first film layer; 9 a second film layer.

Detailed Description

Hereinafter, embodiments of the negative electrode sheet and the method for manufacturing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., 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 also contemplated. Furthermore, 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 contemplated: 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 a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

With the rapid development of new energy, the demand on the lithium ion battery is higher and higher, and the charging capability of the lithium ion battery needs to be improved simultaneously in order to relieve the mileage anxiety of a user while pursuing energy density. For the current system, liquid phase diffusion is a bottleneck of fast charging, so that the great improvement of liquid phase diffusion is crucial to the improvement of charging capability.

The existing methods for improving the quick charging capacity comprise a punching and pore-forming technology and a carbon nano tube technology, but have the problems of large energy density loss, small liquid storage and retention effects, large specific surface area, more side reactions and the like.

The inventor finds that the carbon micron tube is introduced into the negative electrode film layer, so that the liquid storage and retention effects can be fully exerted, the liquid phase diffusion capacity is improved, lithium ions penetrate through the whole negative electrode film layer, the negative electrode active material, particularly the negative electrode active material close to the current collector, is fully utilized, and the purpose of improving the charging capacity of the battery is achieved.

[ negative electrode sheet ]

A first aspect of the present application provides a single-layer coated negative electrode sheet comprising a current collector and a negative electrode film layer disposed on at least one surface of the current collector, the negative electrode film layer comprising a negative electrode active material and a carbon nanotube, optionally comprising a conductive agent; wherein, 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 percent, 2 percent is more than 2 percent, W1 is less than 5.8 percent, then W2 is more than or equal to 0 and less than or equal to 0.5 percent, based on the total weight of the negative electrode film layer.

By adding the carbon micron tube into the negative electrode film layer, the liquid retention capacity of the negative electrode film layer can be improved, liquid phase diffusion is promoted, and active substances are fully utilized; meanwhile, the proportion of the mass fractions of the carbon micron tube and the conductive agent in the negative electrode film layer is limited, so that the battery has 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 the carbon nanotubes in the negative electrode film layer is 0.2 to 5%. The mass fraction of the carbon micron tube in the negative electrode film layer is further limited to optimize the components of the negative electrode film layer and improve the quick charging capacity of the battery.

In some embodiments, the carbon nanotubes have an inner diameter (i.e., the diameter of the hollow lumen) of 0.2 μm to 12 μm, optionally 2 μm to 10 μm; alternatively, the aspect ratio (i.e., the ratio of the length to the inner diameter of the carbon nanotubes) is from 2 to 20; further optionally, the carbon nanotubes have a wall thickness of 0.01 μm to 1 μm. Wherein, the inner diameter of the carbon micron tube can be 1 μm to 12 μm or 2 μm to 4 μm.

The carbon micron tube with the specification is similar to a straight-through hole, and has the advantages that the carbon micron tube can fully play the roles of liquid storage and liquid retention and improve the liquid phase diffusion capacity, so that the active substances of the negative electrode membrane layer are fully utilized, and the quick charging capacity of the battery is improved; moreover, compare with the pore-creating that uses among the prior art and the technique of punching (the internal diameter is tens of microns), the internal diameter of the carbon micron pipe of this application is littleer, several microns even, its advantage lies in, the distance between the carbon micron pipe is less and distribute evenly, can improve the uniformity of aperture distribution for the inside polarization distribution of electric core is even, avoids appearing the phenomenon of local lithium of separating out, also plays the effect of guarantor effectively simultaneously, wholly promotes the charge capacity, reduces energy density loss. Compared with the carbon nanotube technology used in the prior art, the carbon nanotube has smaller inner diameter, can play the roles of storing liquid and preserving liquid, and improves the diffusion capacity of lithium ions.

In some embodiments, the negative electrode film layer comprises a negative electrode active material comprising at least one of artificial graphite, natural graphite, silicon-based materials, optionally selected from artificial graphite; the conductive agent comprises at least one of conductive agents sp, KS-6, conductive graphite, carbon nanotubes, graphene and carbon fibers VGCF, and the conductive agent sp can be selected.

In the single-layer coated negative electrode sheet of the present application, further optionally, the negative electrode film layer comprises a carbon nanotube with an inner diameter of 2 μm to 4 μm, and a mass fraction W1 of the carbon nanotube in the negative electrode film layer and a mass fraction W2 of the conductive agent in the negative electrode film layer satisfy: when W1 is more than or equal to 1.5 percent and less than or equal to 2 percent, then W1+ W2 is more than or equal to 1.6 percent and less than or equal to 2 percent; when W1 is more than or equal to 2.5% and less than or equal to 3%, then W2 is more than or equal to 0 and less than or equal to 0.5%, based on the total weight of the negative electrode film layer.

A second aspect of the present application provides a double-coated negative electrode sheet, comprising 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, and the second film layer is disposed on an outer surface of the first film layer; a first membrane layer is positioned between the current collector and the second membrane layer; also, the first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; at least one of the first and second film layers comprises carbon nanotubes; and whether the first film layer and the second film layer include the carbon nanotube or not at least in the negative electrode active material, either of which is different.

In the present application, an intermediate coating layer is optionally further included between the current collector and the first film layer. The intermediate coating layer is used for enhancing the binding force between the negative electrode active material and the current collector, enhancing the transmission of electrons and reducing polarization. The intermediate coating has a thickness of not more than 6 μm and includes a conductive agent and a binder. The conductive agent comprises at least one of conductive agents sp and KS-6, conductive graphite, a carbon nano tube, graphene and carbon fiber VGCF, and the binder comprises at least one of Styrene Butadiene Rubber (SBR), polyacrylate, ethylene propylene rubber, nitrile butadiene rubber and polyvinylidene fluoride (PVDF).

In the present application, a double-layer coating process is used to form a negative electrode film layer having 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 electrode film layer is 25-110 μm.

As used herein, "first film layer", and "lower layer" have the same meaning and refer to the layer containing the active material that is adjacent to the current collector; the terms "second film layer", "second film layer" and "upper layer" have the same meaning and refer to the layer containing the active material away from the current collector; "double-layer film layer" means a first film layer and a second film layer; "Total mass" refers to the total mass of a substance in a first film layer and a second film layer.

In the present application, in the double-coated negative electrode sheet, in particular, the negative electrode sheet has a thick coating weight (at least 9 mg/cm) ² ) The carbon micron tube is added into the negative pole piece, so that the quick charging capability of the secondary battery is improved.

In some embodiments, in the double-coated negative electrode sheet, the first film layer does not comprise carbon nanotubes and the second film layer comprises carbon nanotubes. The method is favorable for enhancing the liquid storage capacity of the electrolyte on the second film layer, so that the second film layer (upper layer) has sufficient electrolyte, the diffusion capacity of lithium ions to the first film layer (lower layer) is improved, the lithium ions are promoted to diffuse to the film layer on the surface of the current collector, the purpose of fully utilizing the negative active material is achieved, and the charging capacity of the battery is improved.

In some embodiments, in the double coated negative electrode sheet, both the first film layer and the second film layer comprise carbon nanotubes. Therefore, a smooth lithium ion channel is formed in the double-layer film layer of the negative pole piece, a lithium ion diffusion path from the upper layer/electrolyte interface to the lower layer/current collector interface is ensured, the diffusion depth and diffusion speed of lithium ions from the upper layer to the lower layer are further improved, and therefore the negative pole active materials are fully utilized, and the charging capacity of the battery is improved.

In some embodiments, in the double-layer coated negative electrode sheet, the total mass fraction W3 of the carbon nanotubes in the double-layer film layer composed of the first film layer and the second film layer is 0.2% to 5%, optionally 1.5% to 3%, further optionally 1.8% to 2.6%, based on the total weight of the first film layer and the second film layer. Thereby, the charging capability of the double-layer coated negative electrode pole piece is further improved.

In some embodiments, in the double-coated negative electrode sheet, the first and second film layers optionally further comprise a conductive agent; in the double-layer film layer formed by the first film layer and the second film layer, the total mass fraction W3 of the carbon micron tube and the total mass fraction W4 of the conductive agent meet the following conditions: 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 > 2%, then 0. Ltoreq. W4. Ltoreq.0.5%, based on the total mass of the first and second film layers.

The total mass fraction of the carbon nanotubes and the conductive agent in the double-layer film layer satisfies a specific relationship, so that the secondary battery can improve the rapid charging capability without damaging the energy density. That is, a balance between the amount of the load (carbon nanotube and conductive agent), the energy density, and the charging performance is achieved.

In some embodiments, the mass of the carbon nanotubes in the second film layer in the double coated negative electrode sheet is 50 to 100% relative to the total mass of the carbon nanotubes. Therefore, the carbon microtubes can be completely or mostly arranged in the second film layer, which is beneficial to more electrolyte containing lithium ions to diffuse to the upper layer, and further the lower layer is achieved, so that the lithium ion diffusion capacity of the lower layer is improved, and the purpose of fully utilizing the active material of the lower layer is realized.

In some embodiments, the double coated negative electrode sheet has an inner diameter of the carbon nanotubes of 0.2 μm to 12 μm, alternatively 1 μm to 12 μm, alternatively 2 μm to 10 μm, further alternatively 2 μm to 4 μm; the length-diameter ratio is 2-20, and the thickness of the tube wall is 0.01-1 μm.

By selecting the carbon micron tube with a specific specification, the liquid storage and retention effects of the carbon micron tube are further optimized, and the diffusion of electrolyte is promoted, so that the cathode active material is more fully utilized, the deintercalation of lithium ions is accelerated, and the purpose of further improving the quick charging capacity of the battery is achieved. Especially, the inner diameter of the carbon micro-tubes is limited to be 0.2-12 mu m, so that the distances among the carbon micro-tubes are small and the carbon micro-tubes are uniformly distributed, the uniformity of pore size distribution is ensured, the polarization distribution in the battery core is uniform, the phenomenon of local lithium precipitation is avoided, the energy density loss is small, and the charging capacity is further improved.

In some embodiments, in a double-coated negative electrode sheet, with only the second film layer comprising carbon nanotubes and optionally further comprising a conductive agent in the first and second film layers, the mass fraction of 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%, alternatively 0% to 2%, and yet alternatively 0.4% to 2%, based on the weight of the first film layer.

In some embodiments, in the double-coated negative electrode sheet, the carbon nanotube is included in each of the first film layer and the second film layer, and 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, with the proviso that the conductive agent is optionally further included in each of the first film layer and the second film layer. Therefore, the composition and the structure of the negative pole piece are optimized, and the quick charging capacity of the secondary battery is optimized.

Optionally, the mass fraction ratio of the carbon nanotube in the negative electrode plate in the second film layer to the first film layer is 10 to 1. By further limiting the mass fraction ratio of the carbon micron tube in the two film layers, the diffusion depth of the electrolyte in the direction towards the current collector is increased, and the liquid retention function is effectively exerted, so that the purpose of fully utilizing the negative active material is achieved, and the quick charging capacity of the battery is improved.

Optionally, the weight ratio of the second film layer to the first film layer in the negative electrode sheet is 1. The weight ratio is the ratio of the coating weight of the second film layer to the coating weight of the first film layer. Therefore, the structure of the negative pole piece is further optimized, the coating process is simple and easy to operate, and the quick charging capacity of the battery is improved.

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

In some embodiments, the conductive agent may be the same or different, including at least one of conductive agents sp, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, with the optional inclusion of a conductive agent in the first and second film layers.

In the present application, the current collector is not particularly limited, and a metal foil or a composite current collector may be used. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (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 further optionally include a binder. The binder comprises at least one of Styrene Butadiene Rubber (SBR), polyacrylate, ethylene propylene rubber, nitrile rubber and polyvinylidene fluoride (PVDF), and can be selected from styrene butadiene rubber. This is advantageous for obtaining better adhesion properties.

In the present application, the anode film layer, the first film layer and the second film layer further optionally include a dispersant. The dispersing agent comprises at least one of sodium carboxymethylcellulose (CMC-Na), methylcellulose and ethylcellulose; alternatively, sodium carboxymethylcellulose. This is advantageous for obtaining better dispersion properties.

Preparation method

In the present application, the carbon nanotube is prepared as follows:

carrying out electrostatic spinning on a precursor solution containing polystyrene to obtain nano-fiber filaments, uniformly dispersing the nano-fiber filaments into a hydrochloric acid solution containing pyrrole and the like, wherein the mass ratio of pyrrole to nano-fiber filaments is 0.8.

The carbon nanotubes with different inner diameters can be obtained by adopting tetrahydrofuran and the nano-fiber filaments with different mass ratios.

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

The single-layer coated negative pole piece is prepared by a conventional single-layer coating process, and the specific method comprises the following steps:

s1: adding raw material components of the negative electrode film layer, such as a negative electrode active material, a conductive agent, a binder, a dispersing agent and/or a carbon micron tube, into a solvent (such as water or deionized water) according to a certain proportion, mixing, and stirring uniformly to form negative electrode slurry;

s2: and coating the negative electrode slurry on at least one surface of the negative electrode current collector, and drying and compacting to obtain the single-layer coated negative electrode piece.

The layer formed by the negative electrode slurry is referred to as a negative electrode film layer.

Optionally, an intermediate coating layer may be further included between the negative electrode current collector and the negative electrode film layer, the intermediate coating layer being formed before step S2, and the intermediate coating layer is obtained by mixing a conductive agent (Sp, KS-6 or carbon nanotubes) with a binder (styrene butadiene rubber (SBR), polyacrylate, ethylene propylene rubber, nitrile butadiene rubber or polyvinylidene fluoride (PVDF)) in a certain ratio to prepare a slurry and then coating the slurry onto at least one surface of the current collector, and has a thickness of not more than 6 μm.

In the application, the double-layer coated negative electrode plate is prepared by a conventional double-layer coating process, and the specific method comprises the following steps:

p1: raw material components for preparing the first film layer, such as a first negative electrode active material, a conductive agent, a binder, a dispersing agent and/or a carbon micron tube, are added into a solvent (water or deionized water) according to a certain proportion and mixed, and after uniform stirring, slurry of the first film layer, also called lower layer slurry, is formed;

p2: adding raw material components for preparing a second film layer, such as a negative electrode active material, a conductive agent, a binder, a dispersing agent and/or a carbon micron tube, into a solvent (water or deionized water) according to a certain proportion, mixing, and stirring uniformly to form slurry of the second film layer, which is also called upper layer slurry;

p3: the lower layer slurry prepared by the above P1 was coated on at least one surface of the negative electrode current collector to prepare a first film layer (lower layer). And then coating the upper layer slurry prepared by the P2 on the surface of the first film layer, and drying and compacting to obtain a second film layer (upper layer). From this, prepare the double-coated negative pole piece of this application.

Optionally, an intermediate coating layer may be further included between the negative electrode current collector and the first film layer, the intermediate coating layer being formed in advance before step P3, the intermediate coating layer being obtained by mixing a conductive agent (Sp, KS-6 or carbon nanotubes) with a binder (styrene butadiene rubber (SBR), polyacrylate, ethylene propylene rubber, nitrile butadiene rubber or polyvinylidene fluoride (PVDF)) in a certain ratio to prepare a slurry, and then coating the slurry onto at least one surface of the current collector, and having a thickness of not more than 6 μm.

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

Secondary battery

The secondary battery, the battery module, the battery pack, and the electric device according to the present application will be described below.

Secondary battery

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

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

[ Positive electrode sheet ]

The positive pole piece includes the anodal mass flow body and sets up the positive pole rete on anodal mass flow body at least one surface, positive pole rete includes anodal active material.

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

In some embodiments, the positive electrode current collector may employ 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 may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive active material may employ a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates of olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g., liNiO) ₂ ) Lithium manganese oxide (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) ₄ ) Complex of lithium manganese phosphate and carbonAt 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 further optionally includes 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 fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes 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 may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of the electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution).

In some embodiments, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte 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 ) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium dioxaoxalato borate (LiBOB), lithium difluorophosphates (LiPO) ₂ F ₂ )、One or more of lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

In some embodiments, the solvent may be selected from one or more of 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), fluoro Ethylene Carbonate (FEC), methyl Formate (MF), methyl Acetate (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), dimethylsulfone (MSM), methylethylsulfone (EMS), and diethylsulfone (ESE).

In some embodiments, the electrolyte may optionally further comprise an additive. For example, the additive can comprise a negative electrode film forming additive, can also comprise a positive electrode film forming additive, and can also comprise an additive capable of improving certain performances of the battery, such as an additive capable of improving the overcharge performance of the battery, an additive capable of improving the high-temperature performance of the battery, an additive capable of improving the low-temperature performance of the battery, and the like.

[ isolation film ]

In some embodiments, a separator is further included in the secondary battery. The isolating film is arranged between the positive pole piece and the negative pole piece to play an isolating role. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

[ outer Package ]

In some embodiments, the secondary battery may include an overwrap for encapsulating the positive electrode tab, the negative electrode tab, and the electrolyte. As one example, the positive electrode sheet, the negative electrode sheet, and the separator may be laminated or wound to form a laminated structure cell or a wound structure cell, the cell being enclosed within an outer package; the electrolyte can adopt electrolyte, and the electrolyte is soaked in the battery core. The number of the battery cells in the secondary battery can be one or more, and can be adjusted according to requirements.

In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process. The overwrap may be used to encapsulate the electrode assembly and electrolyte described above.

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

Method for manufacturing secondary battery

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

The preparation of the secondary battery may further include a 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 plate, the separator, and the negative electrode plate may be sequentially wound or laminated, so that the separator is located between the positive electrode plate and the negative electrode plate to perform an isolation function, thereby obtaining the battery cell. And (4) placing the battery core in an outer package, injecting electrolyte and sealing 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, a positive electrode active material, a conductive agent, and a binder may be dispersed in a solvent (e.g., N-methylpyrrolidone, NMP for short) to form a uniform positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

In some embodiments, the preparation of the secondary battery comprises the step of preparing a negative electrode sheet according to the methods described herein.

Electric device, battery module, or battery pack

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 3 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to fig. 4, the overpack may include a shell 51 and a lid 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodation chamber, and a cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may 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 series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

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

Fig. 6 and 7 are a battery pack 1 as an example. Referring to fig. 6 and 7, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides a power consumption device, power consumption device includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

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

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

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or apparatus used are conventional products commonly used in the art and commercially available, and are not indicated by the manufacturer. The contents of the components in the examples of the present application are, unless otherwise specified, based on the mass not containing crystal water.

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

In the present application, the coating weights are all dry weights.

The raw material sources related to the embodiment of the application are as follows:

nickel cobalt manganese ternary material (LiMO) ₂ M is a Ni-Co-Mn solid solution, and the specific proportions thereof are shown in examples

Artificial graphite a (guangdong kaiki new energy science and technology ltd, DV50=22 μm);

artificial graphite b (guangdong kaiki new energy science and technology ltd, DV50=12 μm);

n-methylpyrrolidone (NMP, CAS:872-50-4, shanghai Michelin Biotech Co., ltd.)

Polyvinylidene fluoride (CAS: 24937-79-9, shanghai McLin Biotech Co., ltd.)

Acetylene black (Guangdong Kaikin new energy science and technology Co., ltd.)

Acrylic ester (CAS: 25067-02-1, shanghai Maxlin Biotech Co., ltd.)

Dimethyl carbonate (DMC, CAS:616-38-6, shanghai Michelin Biotech Co., ltd.)

The carbon micron tube is prepared according to the following method:

carrying out electrostatic spinning (with voltage of 20Kv and flow rate of 50 mL/min) on a nanofiber silk precursor solution (with N-methyl pyrrolidone as a solvent) containing 15% (mass percent) of polystyrene to obtain nanofiber silk; uniformly dispersing the nano-fiber filaments into a 1M hydrochloric acid solution containing 15% (mass percentage) of pyrrole, wherein the mass ratio of the pyrrole to the nano-fiber filaments is 1:1; then adding ammonium persulfate to carry out polymerization reaction, wherein the mass of the ammonium persulfate is 1.2 times that of the nanofiber to obtain the nanofiber with the polymer coated on the surface, and then adding tetrahydrofuran into the polymer nanofiber with the polymer coated on the surface, wherein the mass of the tetrahydrofuran is 16 times that of the nanofiber; fully stirring for 6 hours at 25 ℃, dissolving polystyrene to obtain a hollow polymer tube, pre-sintering for 2 hours at 300 ℃ and carbonizing for 4 hours at 1200 ℃, and cooling to obtain a micron-sized carbon tube;

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

Repeating the implementation process, and changing the mass ratio of the tetrahydrofuran to the nanofiber filaments to be 20, 19, 17, 14, 13, 12 and 10 respectively to obtain the carbon microtubes with the inner diameters of 0.2, 1, 2, 4, 6, 10 and 12 micrometers respectively.

Example A1

[ preparation of negative electrode slurry ]

The method comprises the following steps: the negative electrode active material artificial graphite b (median diameter DV50=12 μm), binder styrene butadiene rubber, dispersant carboxymethyl cellulose sodium CMC, conductive agent sp and carbon micron tube are 95% by mass: 1.8%:1.2%:0.2%:1.8 percent (based on the total weight of the raw materials) and adding deionized water, and obtaining cathode slurry with the solid component mass fraction of 50 percent under the action of a vacuum stirrer; the carbon nanotubes used had an internal diameter of 2.5 μm, a wall thickness of 0.05 μm and a length of 15 μm.

[ PREPARATION OF NEGATIVE ELECTRODE PIECE ]

The negative electrode slurry prepared above was stirred at 9mg/cm ² The coating weight (dry weight) was uniformly coated on a negative current collector copper foil having a thickness of 8 μm; and then, airing the copper foil at room temperature, transferring the copper foil to a 120 ℃ oven for drying for 1h, and then carrying out cold pressing and slitting to obtain the negative pole piece.

[ PREPARATION OF POSITIVE ELECTRODE PIECE ]

Preparing a positive active material nickel-cobalt-manganese ternary material (LiNi) _0.8 Co _0.1 Mn _0.1 O ₂ ) The adhesive polyvinylidene fluoride and the conductive agent acetylene black are mixed according to the mass ratio of 8:1:1, mixing, adding a solvent NMP, and obtaining anode slurry under the action of a vacuum stirrer; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil with the thickness of 13 mu m according to a certain coating weight (according to N/P =1.05, N/P refers to the ratio of the negative electrode surface capacity per unit area to the positive electrode surface capacity per unit area); and (3) airing the aluminum foil at room temperature, transferring the aluminum foil to a 120 ℃ oven for drying for 1h, and then performing cold pressing and slitting to obtain the positive pole piece.

[ preparation of electrolyte ]

At water content<In a 10ppm argon atmosphere glove box, in a beaker, EC and EMC were measured as 3:7, adding LiPF ₆ Forming an electrolyte in which LiPF is present ₆ The mass content is 12.5%.

[ isolating film ]

The separator was purchased from Cellgard corporation, model number Cellgard2400.

[ preparation of lithium ion batteries ]

Stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and then winding to obtain a bare cell; and (3) placing the bare cell with the capacity of 4.3Ah in an outer packaging foil, injecting the prepared 8.6g of electrolyte into the dried battery, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery. The external package is 33mm (width) × 220mm (length) × 97mm (height), and the thickness of the shell is 0.6mm; the battery pack margin was 90%.

Examples A2 to A5 and A15 to A16

The lithium ion battery was prepared in the entirety according to example A1, except that the inner diameter of the carbon nanotube was changed in the preparation of the negative electrode slurry, and the specific values are shown in table 1.

Examples A6 to A12

The lithium ion battery was prepared in the entirety with reference to example A1, except that in the preparation of the negative electrode slurry, the mass fractions of the conductive agent sp and the carbon microtubes in the raw materials were changed as shown in table 1.

Comparative example 1

The lithium ion battery was manufactured as a whole with reference to example A1 except that the mass fractions of the carbon microtubes and the conductive agent sp in the raw materials were changed to 1.8% and 2%, respectively, in the manufacture of the negative electrode slurry, as shown in table 1.

Comparative example 2

The lithium ion battery was prepared as a whole with reference to example A1, except that in the preparation of the negative electrode slurry, no conductive agent was added, and the mass fraction of the carbon nanotubes was 6%, as shown in table 1.

Comparative example 3

The lithium ion battery was prepared as a whole with reference to example A1, except that no carbon microtubes were added to the preparation of the negative electrode sheet, as shown in table 1.

In examples A2 to a16 and comparative examples 1 to 3, the mass fractions of the carbon nanotubes and the conductive agent used for preparing the slurry in the raw materials were the mass fractions of the carbon nanotubes and the conductive agent in the negative electrode film layer shown in table 1; for the rest components used for preparing the slurry, adding the artificial graphite serving as a negative electrode active material, styrene butadiene rubber serving as a binder and sodium carboxymethyl cellulose serving as a dispersing agent according to a mass ratio of 95.8.

Example B1

The lithium ion battery was prepared in a manner generally referred to in example A1, except that the negative electrode was prepared in a manner that:

[ preparation of slurry for first film layer ]

The raw material components are as follows: the first negative electrode active material artificial graphite a (median diameter Dv50= 22), the conductive agent sp, the binder styrene butadiene rubber, and the dispersant carboxymethylcellulose sodium are 96% by mass: 1%:1.8%:1.2 percent (based on the total weight of the raw materials) and adding deionized water, obtaining cathode slurry with the solid component mass fraction of 50 percent under the action of a vacuum stirrer; the lower layer for preparing the negative electrode film layer, namely the layer close to the current collector.

[ preparation of slurry for second film layer ]

The raw material components are as follows: the second negative electrode active material artificial graphite b (median diameter Dv50= 12), binder styrene-butadiene rubber, dispersant carboxymethylcellulose sodium CMC, carbon micron tube, according to the mass fraction of 94%:1.8%:1.2%:3 percent (based on the total weight of the raw materials) are mixed, deionized water is added, and negative pole slurry with the solid component mass fraction of 50 percent is obtained under the action of a vacuum stirrer; the upper layer for preparing the negative electrode film layer, i.e. the layer far away from the current collector, does not contain carbon nanotubes.

[ PREPARATION OF NEGATIVE ELECTRODE PIECE ]

After the slurry of the first film layer prepared above was applied at a rate of 7mg/cm ² The coating weight (dry weight) was uniformly coated on a negative current collector copper foil having a thickness of 8 μm, and dried to obtain a first film layer (i.e., a lower layer of the negative film layer) used in this example; on the first film layer at 7mg/cm ² Coating weight (dry weight) of the slurry uniformly coating the second film layer prepared above; and then, airing the copper foil at room temperature, transferring the copper foil to a 120 ℃ oven for drying for 1h, and then performing cold pressing and slitting to obtain the negative pole piece.

Wherein the carbon nanotube has an inner diameter of 2.5 μm, a wall thickness of 0.05 μm, and a length of 15 μm. The coating weight ratio of the first film layer to the second film layer is 1.

Examples B2 to B5 and B15 to B16

The lithium ion battery was prepared in the entirety with reference to example B1, except that the inner diameter of the carbon nanotube was changed in the slurry preparation of the first and second film layers, and the specific values are shown in table 2.

Examples B6 and B17 to B18

The lithium ion battery is prepared by referring to example B1 as a whole, except that in the preparation of the slurry for the first film layer, the mass fractions of the conductive agent sp of the raw materials are shown in table 2, and the rest of the components, namely, the first negative electrode active material artificial graphite a (median particle diameter Dv50= 22), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium are added in a mass ratio of 96;

in the preparation of the slurry for the second film layer, the raw material further contains a conductive agent sp, the mass fractions of the carbon nanotube and the conductive agent sp in the raw material are respectively shown in table 2, and the rest of the components, namely, the second negative electrode active material artificial graphite b (median particle diameter Dv50= 12), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium, are added in a mass ratio of 94.

Examples B7 to B12

in the preparation of the slurry of the second film layer, the mass fractions of the carbon nanotubes in the raw materials were changed and are respectively shown in table 2; the balance of components, namely a second negative electrode active material, namely artificial graphite b (with a median particle diameter Dv50= 12), binder styrene butadiene rubber and a dispersant, namely sodium carboxymethyl cellulose, are added according to a mass ratio of 94.

Examples B13 to B14

in the preparation of the negative electrode plate, the coating ratio of the first film layer to the second film layer was changed as shown in table 2.

Examples B19 to B20

in the preparation of the slurry for the second film layer, the raw material of example B20 further contains a conductive agent sp, the mass fractions of the carbon nanotube and the conductive agent sp in the raw material are respectively shown in table 2, and the remaining components of the second negative electrode active material artificial graphite B (median particle diameter Dv50= 12), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium are added in a mass ratio of 94.

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

Comparative example 4

The lithium ion battery was fabricated as a whole with reference to example B1, except that the second film layer was fabricated in such a manner that the slurry of the second film layer did not include carbon nanotubes, but included a conductive agent in a mass fraction of 3%, as shown in table 2.

Example C1

The lithium ion battery was prepared in the entirety with reference to example A1, with the following differences:

[ preparation of slurry for first film layer ]

The raw material components are as follows: the composite material comprises a first negative electrode active material artificial graphite a (median particle diameter Dv50= 22), a conductive agent sp, a binder styrene-butadiene rubber, a dispersing agent sodium carboxymethyl cellulose and a carbon micron tube, wherein the mass fraction is 95.3%:0.8%:1.5%:1.2%:1.2 percent (based on the total weight of the raw materials) and adding deionized water, and obtaining cathode slurry with the solid component mass fraction of 50 percent under the action of a vacuum stirrer; the lower layer for preparing the negative electrode film layer, namely the layer close to the current collector.

[ preparation of slurry for second film layer ]:

the raw material components are as follows: the second negative electrode active material artificial graphite b (median diameter Dv50= 12), binder styrene-butadiene rubber, dispersant carboxymethylcellulose sodium, and carbon micron tube are 93.3% by mass: 1.5%:1.2%:4 percent (based on the total weight of the raw materials) are mixed, deionized water is added, and negative pole slurry with the solid component mass fraction of 50 percent is obtained under the action of a vacuum stirrer; the upper layer for preparing the negative electrode film layer, namely the layer far away from the current collector.

[ PREPARATION OF NEGATIVE ELECTRODE PIECE ]

The slurry of the first film layer prepared above was mixed at 6mg/cm ² The coating weight (dry weight) was uniformly coated on a negative current collector copper foil having a thickness of 8 μm, and dried to obtain a first film layer (i.e., a lower layer of the negative film layer) used in this example; on the first film layer at 6mg/cm ² Coating weight (dry weight) of the slurry uniformly coating the second film layer prepared above; and then, airing the copper foil at room temperature, transferring the copper foil to a 120 ℃ oven for drying for 1h, and then performing cold pressing and slitting to obtain the negative pole piece.

Examples C2 to C5 and C15 to C16

The lithium ion battery was prepared in the entirety according to example C1, except that the inner diameter of the carbon nanotube was changed in the slurry preparation of the first and second film layers, and the specific values are shown in table 3.

Examples C6 to C12 and C17 to C18

The lithium ion battery was prepared as a whole with reference to example C1, with the difference that:

in the preparation of the slurry for the first film layer, a conductive agent sp is optionally contained in the raw material, the mass fractions of the carbon nanotube and the conductive agent sp in the raw material are respectively shown in table 3, and the rest of the components, namely, the first negative electrode active material artificial graphite a (median particle diameter Dv50= 22), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium are mixed in a mass ratio of 95.3:1.5:1.2 adding;

in the preparation of the slurry for the second film layer, the raw material optionally contains a conductive agent sp, the mass fractions of the carbon nanotube and the conductive agent sp in the raw material are respectively shown in table 3, and the rest of the components, namely, the second negative electrode active material artificial graphite b (median particle diameter Dv50= 12), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium are mixed in a mass ratio of 93.3:1.5:1.2 addition.

C13-C14 and C19-C20

in the preparation of the slurry of the first film layer, the mass fractions of the carbon nanotube and the conductive agent sp in the raw materials are respectively shown in table 3, and the remaining components, namely the first negative electrode active material artificial graphite a (median particle diameter Dv50= 22), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium, are as follows by mass ratio of 95.3:1.5:1.2 adding;

in the preparation of the slurry for the second film layer, the raw material further includes a conductive agent sp, the mass fractions of the carbon micron tube and the conductive agent sp in the raw material are respectively shown in table 3, and the remaining components are the second negative electrode active material artificial graphite b (median particle diameter Dv50= 12), the binder styrene-butadiene rubber, and the dispersant carboxymethylcellulose sodium in a mass ratio of 93.3:1.5:1.2 adding;

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

Referring to example C1, the lithium ion battery was prepared in the same manner as in example C1, except that in the preparation of the negative electrode sheet, the slurries of the first and second film layers did not contain carbon nanotubes, and the mass fractions of the conductive agents in the raw materials were 1%, as shown in table 3;

the remaining components of the slurry prepared from the first film layer, namely, the first negative electrode active material artificial graphite a (median particle diameter Dv50= 22), the binder styrene-butadiene rubber, and the dispersant sodium carboxymethyl cellulose, are mixed according to a mass ratio of 96.3:1.5:1.2 adding; the remaining components of the slurry prepared from the second film layer, namely the first negative electrode active material artificial graphite b (median particle diameter Dv50= 12), the binder styrene-butadiene rubber and the dispersant sodium carboxymethyl cellulose, are mixed according to the mass ratio of 96.3:1.5:1.2 addition.

[ test of related parameters and Battery Performance ]

1. Method for measuring carbon micron tube

In the present application, the length, inner diameter and wall thickness of the carbon nanotubes can be measured by using a scanning electron microscope (ZEISS Sigma 300). Samples were prepared as follows: the pole piece is cut into samples with the size of 8mm multiplied by 3mm, the samples are placed on a sample table, a scanning electron microscope (ZEISS Sigma 300) is used for testing under the magnification of 10K times, the carbon micron tube can be observed, and the length, the inner diameter and the wall thickness of the carbon micron tube are measured.

2. Method for measuring structure of negative electrode film layer

In the present application, the structure of the negative electrode film layer can be tested by using a scanning electron microscope (ZEISS Sigma 300) at a magnification of 10K. Samples were prepared as follows: firstly, cutting the negative pole piece into a sample to be detected with the size of 2cm multiplied by 2cm, and fixing the negative pole piece on a sample table through paraffin. Then the sample stage is loaded into a sample holder, locked and fixed, and the power supply of an argon ion cross section polisher (IB-19500 CP) is turned on and vacuumized (10) ^-4 Pa), setting argon flow (0.15 MPa), voltage (8 KV) and polishing time (2 hours), and adjusting the sample table to be in a swing mode to start polishing. Sample testing was performed with reference to JY/T010-1996.

3. Rapid chargeability testing of batteries

The batteries of the above examples and comparative examples were first charged and discharged at 25 ℃ with a current of 1C (i.e., a current value at which the theoretical capacity was completely discharged within 1 h), specifically including: charging the battery to a voltage of 4.25V at a constant current of 1C multiplying power, then charging at a constant voltage until the current is less than or equal to 0.05C, standing for 5min, then discharging at a constant current of 0.33C multiplying power until the voltage is 2.8V, and recording the actual capacity as C0.

Then charging the battery with 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 and constant current to full battery charging cut-off voltage of 4.25V or 0V negative electrode cut-off potential (based on the condition that the constant current is reached first), after charging is completed every time, discharging with 1C0 to full battery discharging cut-off voltage of 2.8V, recording charging rates of 10%, 20%, 30%, 8230, 80% SOC (State of Charge), drawing charging rate-negative electrode potential curves under different SOC states, after linear fitting, obtaining the corresponding charging multiplying factor when the cathode potential is 0V under different SOC states, wherein the charging multiplying factor is the charging window under the SOC State and is respectively marked as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC and C80% SOC, and calculating the charging time T of the battery from 10% SOC to 80% 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). Times.10%, wherein the unit is min. The shorter the time, the more excellent the quick-charging performance of the battery. Initial discharge DCR (direct Current Resistance) test

The lithium ion batteries of examples and comparative examples were respectively tested according to the above procedure, and specific values are shown in tables 1 to 3.

Table 1: influence of relevant parameters for preparing single-layer coated negative pole piece on battery performance

Compared with the comparative example, as can be seen from table 1, when the mass fractions of the carbon nanotube and the conductive agent in the single-layer coated negative electrode film layer satisfy a specific relational expression, the rapid charging capability of the battery can be remarkably improved; as can be seen from tables 2-3, the charging ability of the battery was significantly improved when the double-coated negative electrode sheet included the carbon nanotube.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

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.