WO2024092500A1

WO2024092500A1 - Negative electrode sheet and preparation method therefor, electrochemical device, and electronic device

Info

Publication number: WO2024092500A1
Application number: PCT/CN2022/128962
Authority: WO
Inventors: 雷廷玲
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-11-01
Filing date: 2022-11-01
Publication date: 2024-05-10
Also published as: CN117157776A

Abstract

The present application relates to a negative electrode sheet and a preparation method therefor, an electrochemical device, and an electronic device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer comprises a first active material layer and a second active material layer, wherein the first active material layer is disposed on the surface of the negative electrode current collector, and the first active material layer comprises a plurality of first through holes which penetrate through the first active material layer along the thickness direction of the negative electrode current collector and are disposed at intervals; the second active material layer is at least disposed on the surface of the negative electrode current collector; the first active material layer is disposed between the second active material layer and the negative electrode current collector; the first active material layer comprises silicon-based particles; and the second active material layer comprises carbon-based particles.

Description

Negative electrode sheet and preparation method thereof, electrochemical device and electronic device

Technical Field

The present application relates to the field of energy storage technology, and more specifically, to a negative electrode plate and a preparation method thereof, an electrochemical device and an electronic device.

Background technique

Electrochemical devices have the characteristics of high energy density, high operating voltage, and light weight, so they are widely used in electronic products such as mobile phones, laptops, and cameras. While improving the electrochemical performance of electrochemical devices, other performances cannot be ignored. With the improvement of the performance requirements of electronic products, the performance requirements of electrochemical devices are also gradually increasing.

However, due to the limitation of negative electrode active materials, the energy density of electrochemical devices is generally low. Therefore, the energy density of existing electrochemical devices still needs to be improved.

Summary of the invention

The present application provides a negative electrode plate and a preparation method thereof, an electrochemical device and an electronic device, which can improve the energy density of the electrochemical device.

In the first aspect, the present application proposes a negative electrode sheet, comprising a negative current collector and a negative active material layer. The negative active material layer comprises a first active material layer and a second active material layer, the first active material layer is arranged on the surface of the negative current collector, and the first active material layer comprises a plurality of first through holes arranged at intervals and penetrating the first active material layer along the thickness direction of the negative current collector, the second active material layer is arranged on the surface of the first active material layer, and at least partially passes through the first through hole to contact the surface of the negative current collector. The first active material layer comprises silicon-based particles; the second active material layer comprises carbon-based particles.

In some embodiments of the present application, the negative electrode current collector includes two surfaces opposite to each other along its own thickness direction; and the negative electrode active material layers are disposed on the two surfaces of the negative electrode current collector.

In some embodiments of the present application, the second active material layer includes a base layer and an extension portion connected to the base layer and protruding relative to the base layer, the base layer is arranged on the surface of the first active material layer facing away from the negative electrode current collector, and the extension portion is arranged in the first through hole and extends to the surface of the negative electrode current collector.

In some embodiments of the present application, the negative electrode current collector includes a plurality of second through holes arranged at intervals and penetrating the negative electrode current collector along the thickness direction of the negative electrode current collector, the second through holes are connected to the first through holes, and the extension portion extends into the second through holes.

In some embodiments of the present application, the opening shapes of each of the first through hole and the second through hole are independently selected from rectangle, square, circle, ellipse, diamond, cone, bar or triangle.

In some embodiments of the present application, the area _S1 of the negative electrode current collector covered by the first active material layer and the area _S0 of the negative electrode current collector satisfy 60% _≤S1 / _S0≤90 %.

In some embodiments of the present application, the area _S1 of the negative electrode current collector covered by the first active material layer and the area _S0 of the negative electrode current collector satisfy 70% _≤S1 / _S0≤80 %.

In some embodiments of the present application, based on the total mass of the silicon-containing particles in the first active material layer, the silicon-containing particles account for 50% to 98% of the total mass of the first active material layer, and optionally 60% to 95%.

In some embodiments of the present application, the silicon-based particles are selected from one or more of elemental silicon, silicon alloys, silicon-carbon composite materials, and silicon oxide materials.

In some embodiments of the present application, the carbon-based particles are selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon and mesophase carbon microbeads.

In some embodiments of the present application, the negative electrode sheet satisfies one or more of the following (1) to (4):

(1) The first active material layer further comprises a first binder, the first binder is selected from one or more of polypropylene, polyacrylate, acrylonitrile multipolymer and carboxymethyl cellulose salt, and optionally the first binder is selected from one or more of the monomer polymers of acrylic acid nitrile, acrylic acid salt, acrylamide and acrylic acid ester;

(2) The thickness of the first active material layer is 3 μm to 12 μm, preferably 3 μm to 6 μm;

(3) The bonding force between the first active material layer and the negative electrode current collector is greater than or equal to 150 N/m;

(4) The capacity ratio per unit area of the first active material layer to that of the second active material layer is 1:(1 to 4).

In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

Providing a first active slurry containing at least silicon-based particles, and forming a first active material layer on a negative electrode current collector from the first active slurry to obtain a composite body, wherein the first active material layer includes a plurality of first through holes arranged at intervals and penetrating the first active material layer along a thickness direction of the negative electrode current collector;

A second active slurry containing at least carbon-based particles is provided, and a second active material layer is formed on the composite body by the second active slurry to obtain a negative electrode sheet, wherein the second active material layer is at least arranged on the surface of the negative electrode collector.

In some embodiments of the present application, the negative electrode current collector is provided with a plurality of second through holes arranged at intervals, and the preparation method of the second through holes includes:

The negative electrode current collector is pore-formed to obtain a negative electrode current collector having second through holes.

The composite is pore-formed to obtain a negative electrode current collector having second through holes, and first through holes are formed on the first active material layer.

In a third aspect, an embodiment of the present application provides an electrochemical device, comprising the negative electrode sheet in any embodiment of the first aspect or the negative electrode sheet prepared by the preparation method in any embodiment of the second aspect.

In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the electrochemical device in any embodiment of the third aspect above.

The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a first active material layer and a second active material layer, wherein the first active material layer includes silicon-based particles. Since the theoretical gram capacity of the silicon-based particles is relatively high, the reversible gram capacity of the negative electrode sheet is relatively high, and when the negative electrode sheet of the present application is used as an electrochemical device, the electrochemical device has a relatively high energy density. Moreover, the first active material layer of the present application is arranged between the second active material layer and the negative electrode current collector, the first active material layer is provided with a first through hole, and a part of the second active material layer penetrates the first through hole and contacts with the negative electrode current collector. The negative electrode active material layer of the present application is a novel double-layer structure formed by the second active material layer located on the outside and the first active material layer located on the inside that does not completely cover the negative electrode current collector. The second active material layer contacts the surface of the negative electrode current collector through the first through hole, providing an additional current channel for the second active material layer, thereby reducing the impedance of the electrochemical device. Moreover, the rate and cycle performance of the second active material layer containing carbon-based particles are better than those of the first active material layer containing silicon-based particles. The second active material layer is in direct contact with the negative electrode current collector through the first through hole, which can effectively exert the advantages of the rate and cycle performance of the second active material layer, thereby alleviating the defect of the first active material layer with a high content of the first binder added and with high adhesion, which leads to reduced electrical performance. In addition, the new double-layer structure eliminates the poor electrical properties of the first active material layer to a certain extent, and reduces the impact on the charge, discharge and cycle performance of the second active material layer and the electrochemical device. The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will briefly describe the drawings necessary for describing the embodiments of the present application or the prior art to facilitate the description of the embodiments of the present application. Obviously, the drawings described below are only some of the embodiments in the present application. For those skilled in the art, without the need for creative work, drawings of other embodiments can still be obtained based on the structures illustrated in these drawings.

FIG1 is a schematic diagram of a partial structure of a negative electrode sheet provided in some embodiments of the present application;

FIG2 is a front view of a first active material layer of a negative electrode sheet provided in some embodiments of the present application;

FIG3 is a partial front view of a negative electrode sheet provided in some embodiments of the present application;

FIG4 is a schematic diagram of a partial cross-sectional structure of a negative electrode sheet provided in some embodiments of the present application;

FIG5 is a schematic structural diagram of a-a of the negative electrode sheet of FIG4 ;

FIG6 is a schematic structural diagram of the negative electrode sheet b-b of FIG4 ;

7 is a schematic diagram of the structure of a negative electrode current collector and a first active material layer of a negative electrode sheet provided in some embodiments of the present application;

8 is a schematic diagram of the structure of a negative electrode current collector and a first active material layer of a negative electrode sheet provided in some other embodiments of the present application;

9 is a schematic diagram of the structure of a negative electrode current collector and a first active material layer of a negative electrode sheet provided in some further embodiments of the present application;

FIG10 is a schematic diagram of the structure of a negative electrode current collector and a first active material layer of a negative electrode sheet provided in some other embodiments of the present application;

11 is a schematic diagram of the structure of a negative electrode current collector and a first active material layer of a negative electrode sheet provided in some other embodiments of the present application;

FIG. 12 is a schematic diagram of a partial structure of a negative electrode plate including a second through hole provided in some embodiments of the present application.

The drawings are not drawn to scale.

Among them, the reference numerals in the figure are:

100. Negative electrode;

10. negative electrode current collector; 11. second through hole;

20. Negative electrode active material layer; 21. First active material layer; 211. First through hole; 22. Second active material layer; 221. Base layer; 222. Extension portion.

Detailed ways

The embodiments of the present application will be described in detail below. In the entire text of the present application specification, the same or similar components and components with the same or similar functions are represented by similar reference numerals. The embodiments of the accompanying drawings described herein are illustrative and graphical and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

In addition, sometimes amounts, ratios and other numerical values are presented in range format herein. It should be understood that such range format is for convenience and brevity, and should be flexibly understood to include not only the numerical values explicitly specified as range limits, but also all individual numerical values or sub-ranges encompassed within the range, as if each numerical value and sub-range were explicitly specified.

In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "one or more of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

The grouping of alternative elements or embodiments disclosed herein should not be construed as limiting. Each group member may be adopted and claimed individually, or may be adopted and claimed in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in or deleted from the group for convenience and/or patentability reasons.

It is obvious to those skilled in the art that various modifications and changes can be made in this application without departing from the scope of protection of this application. Therefore, this application is intended to cover modifications and changes of this application that fall within the scope of the corresponding claims (scopes for protection) and their equivalents. It should be noted that the implementation methods provided in the embodiments of this application can be combined with each other without contradiction.

Before explaining the scope of protection provided by the embodiments of the present application, in order to facilitate the understanding of the embodiments of the present application, the present application first specifically describes the problems existing in the related technology.

Batteries are widely used in electronic products such as mobile phones, tablets, and drones. People have higher and higher requirements for the battery capacity of electronic products. In order to increase the battery capacity in a limited space, higher requirements are placed on the energy density of the battery. The theoretical gram capacity of graphite currently used is only 372mAh/g, which cannot meet the demand for higher energy density; while the maximum theoretical gram capacity of silicon material reaches 4200mAh/g, which is 10 times higher than that of graphite. The use of silicon material can greatly improve the energy density of the battery and is hailed as the negative electrode material of the next generation of batteries. However, in lithium-ion batteries, the volume of silicon materials expands significantly (>300%) during the high lithium insertion process. After the expansion of the negative electrode sheet, the negative electrode is pulverized and the material falls off. The adhesion between the negative electrode materials deteriorates, the SEI on the negative electrode surface is repeatedly destroyed and grown, a large amount of electrolyte is consumed, and more and more side reactions are generated, which eventually leads to a decrease in cycle performance. The large volume expansion of silicon materials during the battery cycle limits its development. Therefore, it is necessary to improve the expansion problem of silicon materials during the cycle process.

Therefore, the inventors tried to use nano-scale silicon materials, such as nano-sized SiO and SiC. Nano-scale silicon materials have the characteristics of large specific surface area, short ion diffusion path, strong creeping and high plasticity, and small volume change during charge and discharge, which can alleviate the volume effect to a certain extent. However, the inventors further found that the theoretical gram capacity of silicon composite materials such as SiO and SiC is lower than that of single substance Si, and the actual reversible gram capacity is lower. For example, the gram capacity of SiO is about 2400mAh/g, and the actual reversible gram capacity is about 1500mAh/g. Moreover, the first charging efficiency of silicon composite materials is low, generally less than 80%. The inventors also tried to use Sn-based composite materials. Sn is similar to Si and has a high lithium storage capacity. However, due to its own high cost, it is difficult to coat it uniformly, which does not have an advantage over silicon materials.

In view of this, the inventor uses an adhesive with strong bonding ability to restrain the expansion of silicon. However, with the addition of an adhesive with strong bonding ability, the internal resistance of the battery will increase, thereby weakening the electrical performance of the battery. Therefore, from the perspective of improving the structure of the negative electrode sheet, the present application is based on the first active material layer being arranged between the second active material layer and the negative electrode current collector, the first active material layer being provided with a first through hole, and a portion of the second active material layer being passed through the first through hole and in contact with the negative electrode current collector, providing an additional current channel for the second active material layer, reducing the impedance of the electrochemical device, thereby reducing the internal resistance of the electrochemical device. At the same time, the second active material layer is in direct contact with the negative electrode current collector through the first through hole, which can effectively give play to the advantages of the rate and cycle performance of the second active material layer, thereby alleviating the defect of the low electrical performance of the first active material layer. Next, the technical solution of the present application is described in detail.

In the present application, an electrochemical device includes any device that generates an electrochemical reaction, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. Exemplarily, the electrochemical device is a lithium secondary battery, which may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

Negative electrode

The present application proposes a negative electrode sheet, as shown in FIG. 1 to FIG. 3, the negative electrode sheet 100 includes a negative electrode current collector 10 and a negative electrode active material layer 20. The negative electrode active material layer 20 includes a first active material layer 21 and a second active material layer 22, the first active material layer 21 is arranged on the surface of the negative electrode current collector 10, and the first active material layer 21 includes a plurality of first through holes 211 arranged at intervals and penetrating the first active material layer 21 along the thickness direction of the negative electrode current collector 10, the second active material layer 22 is at least arranged on the surface of the negative electrode current collector 10, and the first active material layer 21 is arranged between the second active material layer 22 and the negative electrode current collector 10. Among them, the first active material layer 21 includes silicon-based particles; the second active material layer 22 includes carbon-based particles.

A negative electrode active material layer is disposed on the negative electrode current collector 10, and the negative electrode current collector 10 can collect and output the current generated by the negative electrode active material layer 20, and can input the current into the negative electrode active material layer. The negative electrode current collector 10 can be a metal foil or a porous metal plate, such as a foil or a porous plate of a metal such as copper, nickel, titanium, iron, or an alloy thereof. The negative electrode current collector 10 includes two surfaces opposite to each other along its own thickness direction, and the negative electrode active material layer can be disposed on both surfaces, or of course, the negative electrode active material layer can be disposed on only one of the two surfaces.

In some embodiments of the present application, the negative electrode current collector 10 is a copper foil with a thickness of 4 μm to 15 μm.

The negative electrode active material layer 20 includes a first active material layer 21 and a second active material layer 22, wherein the first active material layer 21 includes a first through hole 211 penetrating the first active material layer 21 along the thickness direction of the negative electrode current collector 10, and the first active material layer 21 includes silicon-based particles. The silicon-based particles contain silicon elements, and the silicon-based particles may also contain carbon elements, oxygen elements, nitrogen elements, phosphorus elements, sulfur elements, etc. The second active material layer 22 is at least arranged on the surface of the negative electrode current collector 10, and the first active material layer 21 is arranged between the second active material layer 22 and the negative electrode current collector 10. It can be understood that a part of the second active material layer 22 is arranged on the side of the first active material layer 21 away from the negative electrode current collector 10, and the other part is arranged in the first through hole 211 and contacts with the negative electrode current collector 10. The carbon-based material contains carbon elements, and the silicon-based particles may also contain nitrogen, oxygen and other elements.

In the embodiment of the present application, there are a plurality of first through holes 211 in the first active material layer 21 , and the plurality of first through holes 211 are arranged at intervals on the first active material layer 21 .

The negative electrode active material layer 20 of the negative electrode sheet of the present application includes a first active material layer 21 and a second active material layer 22, wherein the first active material layer 21 includes silicon-based particles. Since the theoretical gram capacity of the silicon-based particles is high, the reversible gram capacity of the negative electrode sheet is high, and when the negative electrode sheet of the present application is used as an electrochemical device, the electrochemical device has a high energy density. Moreover, the first active material layer 21 of the present application is arranged between the second active material layer 22 and the negative electrode collector 10, the first active material layer 21 is provided with a first through hole 211, and a part of the second active material layer 22 is arranged in the first through hole 211 and contacts the negative electrode collector 10. The negative electrode active material layer 20 of the present application is a new double-layer structure formed by the second active material layer 22 located on the outside and the first active material layer 21 located on the inside and not completely covering the negative electrode collector 10. The second active material layer 22 contacts the surface of the negative electrode collector 10 through the first through hole 211, providing an additional current channel for the second active material layer 22, thereby reducing the impedance of the electrochemical device. Moreover, the rate and cycle performance of the second active material layer 22 containing carbon-based particles are better than those of the first active material layer 21 containing silicon-based particles. The second active material layer 22 is in direct contact with the negative electrode current collector 10 through the first through hole 211, which can effectively exert the advantages of the rate and cycle performance of the second active material layer 22, thereby alleviating the defect of low electrical performance caused by the first active material layer 21 with a high content of the first binder having high adhesion. In addition, the new double-layer structure can eliminate the poor electrical performance of the first active material layer 21 to a certain extent, and reduce the influence of the second active material layer 22 and the charge, discharge and cycle performance of the electrochemical device.

In some embodiments of the present application, the negative electrode current collector 10 includes two surfaces opposite to each other along its own thickness direction. The negative electrode active material layer 20 is arranged on both surfaces of the negative electrode current collector 10. The negative electrode active material layer 20 includes a first active material layer 21 and a second active material layer 22. The negative electrode active material layer 20 is arranged on both surfaces of the negative electrode current collector 10. It can be understood that along the thickness direction of the negative electrode current collector 10, it includes the second active material layer 22, the first active material layer 21, the negative electrode current collector 10, the first active material layer 21 and the second active material layer 22 in sequence, wherein a portion of the second active material layer 22 on both sides of the negative electrode current collector 10 is in contact with the negative electrode current collector 10 through the first active material layer 21 respectively. With such a configuration, the effect of improving the energy density is more significant.

Referring to FIGS. 4 to 6 , FIG. 4 is a schematic diagram of a partial cross-sectional structure of a negative electrode sheet provided in some embodiments of the present application; FIG. 5 is a schematic diagram of a cross-sectional view of the negative electrode sheet taken along line a-a of FIG. 4 ; and FIG. 6 is a schematic diagram of a cross-sectional view of the negative electrode sheet taken along line b-b of FIG. 4 ;

In some embodiments of the present application, as shown in FIGS. 4 to 6 , the second active material layer 22 includes a base layer 221 and an extension portion 222 connected to the base layer 221 and protruding relative to the base layer 221. The base layer 221 is disposed on the surface of the first active material layer 21 away from the negative electrode current collector 10, and the extension portion 222 is disposed in the first through hole 211 and extends to the surface of the negative electrode current collector 10. The second active material layer 22 includes a base layer 221 and an extension portion 222. The first active material layer 21 is provided with a first through hole 211 for accommodating the extension portion 222. The base layer 221 is stacked on the first active material layer 21, and the extension portion 222 is connected to the hole wall of the first through hole 211 and contacts the negative electrode current collector 10. The extension portion 222 in the second active material layer 2 is in direct contact with the negative electrode current collector 10 through the first through hole 211, which can effectively give play to the advantages of the rate and cycle performance of the second active material layer 22.

In some embodiments, the extension 222 fills the gap of the first through hole 211 and contacts the negative electrode current collector 10. In this way, the second active material layer 2 directly contacts the negative electrode current collector 10 through the first through hole 211, which can effectively exert the advantages of the rate and cycle performance of the second active material layer 22.

In some embodiments, the first through hole 211 located on one side of the negative electrode current collector 10 is disposed opposite to the first through hole 211 located on the other side of the negative electrode current collector 10 .

In some other embodiments, the first through hole 211 located on one side of the negative electrode current collector 10 is staggered with the first through hole 211 located on the other side of the negative electrode current collector 10 .

In some embodiments of the present application, the first active material layer 21 includes a plurality of first through holes 211, and the plurality of first through holes 211 are arranged at intervals. The plurality of first through holes 211 are arranged on the first active material layer 21, which can increase the contact area between the first active material layer 21 and the second active material layer 22, and further increase the connection stability between the two. Moreover, the first through holes 211 arranged at intervals make the extension part 222 distributed in more areas, and the rate and cycle performance of the second active material layer 22 are better than those of the first active material layer 21. The second active material layer 22 is in direct contact with the negative electrode current collector 10 through the first through holes 211 not coated with the first active material layer 21, which more effectively exerts the advantages of the second active material layer 22 in rate and cycle performance, and does not significantly reduce the deterioration of the electrical performance of the first active material layer 21. In addition, the extension part 222 is inserted into the first through hole 211, which can absorb and buffer the stress generated by the volume expansion of the first active material layer 21 to a certain extent, and improve the connection stability of the first active material layer 21.

For example, the plurality of first through holes 211 are arranged at equal intervals, so that the first through holes 211 are more evenly dispersed, the connection stability between the first active material layer 21 and the second active material layer 22 is improved, and the advantages of the second active material layer 22 in rate and cycle performance are more advantageous.

Exemplarily, the opening areas of the plurality of first through holes 211 are equal. With such a configuration, the excellent activity of the first active material layer 21 can be utilized to maintain the activity of the entire battery cell, and the high energy density of the second active material layer 22 can be utilized to make the overall energy density uniform. In addition, the binding force of each extension 222 on the first active material layer 21 is similar, thereby ensuring that the first active material layer 21 has a uniform volume expansion rate as a whole, reducing the local volume expansion difference to a certain extent, and the phenomenon of powder falling.

In some embodiments of the present application, the opening shape of each first through hole 211 is selected from rectangle, square, circle, ellipse, diamond, cone, strip or triangle. The above opening shapes are conventional structures, which are easy to produce and process.

Exemplarily, the opening shapes of the plurality of first through holes 211 are the same, for example, the opening shape is circular, which can improve production efficiency and processing performance.

In the present application, in order to observe the morphological characteristics of the first active material layer 21, the second active material layer 22 can be peeled off from the first active material layer 21 by a peeling method, such as a tape bonding method, to peel the second active material layer 22 from the first active material layer 21, thereby exposing the first active material layer 21.

In the present application, the tape stripping method specifically includes: (1) cutting the negative electrode sheet coated with the first active material layer 21 and the second active material layer 22 into strips with a length of 120 mm and a width of 20 mm; (2) sticking a double-sided tape with a length of about 100 mm and a width of 25 mm on a flat plate; (3) sticking the cut negative electrode sheet coated with the first active material layer 21 and the second active material layer 22 on the double-sided tape, leaving a suitable length at one end of the negative electrode sheet not in contact with the double-sided tape to facilitate stripping of the film, and appropriately pressing the negative electrode sheet so that the negative electrode sheet is in contact with the double-sided tape and the double-sided tape is in contact with the flat plate; (4) pulling up the negative electrode sheet from the end of the negative electrode sheet that is not in contact with the double-sided tape and stripping it off For the negative electrode sheet, since the bonding force between the second active material layer 22 and the first active material layer 21 and between the second active material layer 22 and the negative electrode current collector 10 is much weaker than the bonding force between the first active material layer 21 and the negative electrode current collector 10, the second active material layer 22 will be peeled off and remain on the tape, while the first active material layer 21 will remain on the negative electrode current collector 10, exposing the morphology of the first active material layer 21; in particular, if the bonding of the second active material layer 22 itself is too weak, resulting in the peeling of the tape from between the second active material layers 22, the peeled negative electrode sheet can be repeated with steps (3) and (4) until the first active material layer 21 and the current collector not coated with the first active material layer 21 are exposed.

In the present application, the cross section of the negative electrode sheet is obtained by electron beam cutting or circular knife slitting. Observed under a scanning electron microscope, as shown in Figures 5 and 6, the first active material layer 21 containing silicon-based particles has relatively small particles, and the second active material layer 22 containing carbon-based particles has relatively large particles. Further referring to Figure 5, the first through holes 211 are spaced apart on the first active material layer 21, and the extension 222 of the second active material layer 22 contacts the negative electrode current collector 10 through the first through holes 211, and the second active material layer 22 completely covers the first active material layer 21. Further referring to Figure 6, the first active material layer 21 is continuously arranged on the negative electrode current collector 10, and the second active material layer 22 completely covers the first active material layer 21.

In the present application, as shown in FIGS. 7 to 11 , a plurality of first through holes 211 form pattern effects such as an island pattern, a mesh pattern, and a sheet pattern.

Please refer to FIG. 12 , which is a schematic diagram of a partial structure of a negative electrode plate including a second through hole provided in some embodiments of the present application.

In some embodiments of the present application, as shown in FIG. 12 , the negative electrode current collector 10 includes a plurality of second through holes 11 spaced apart and extending through the negative electrode current collector 10 along the thickness direction of the negative electrode current collector 10 , the second through holes 11 are connected to the first through holes 211 , and the extension portion 222 extends into the second through holes 11 .

The negative electrode current collector 10 is penetrated by a second through hole 11, the second through hole 11 is connected to the first through hole 211, the extension part 222 extends into the second through hole 11, and the second active material layer 22 located on both sides of the negative electrode current collector 10 is connected through the second through hole 11 and the first through hole 211, providing an additional current channel for the second active material layer 22 on the outside, and compared with the negative electrode sheet including the first active material layer 21 and the second active material layer 22 without a through hole, the impedance of the electrochemical device is reduced, and the influence of the poor electrical performance of the first active material layer 21 on the charge, discharge and cycle performance of the second active material layer 22 and the overall electrochemical device is eliminated. In addition, compared with the negative electrode sheet including the first active material layer 21 and the second active material layer 22 without a through hole, the current collector layer including the second through hole 11 not only reduces the weight of the current collector, but also provides an additional attachment space for the negative active material layer 20, further improving the energy density of the electrochemical device. The plurality of second through holes 11 are arranged at intervals, and the second active material layers 22 on both sides are connected through the second through holes 11 of the negative electrode current collector 10 to connect the second active material layers 22 on both sides to form an integral structure, further enhancing the overall structural stability of the second active material layers 22 .

In some embodiments, the second through hole 11 is connected to the first through hole 211 , and in the thickness direction, the opening area of the first through hole 211 may be equal to or different from the opening area of the second through hole 11 .

Optionally, the opening area of the first through hole 211 is equal to the opening area of the second through hole 11, so as to facilitate the integration of the two and improve the processing efficiency.

In some embodiments of the present application, the opening shape of each second through hole 11 is selected from rectangle, square, circle, ellipse, diamond, cone, bar or triangle. The opening shape of the second through hole 11 can be the same as the opening shape of the first through hole 211.

Optionally, the opening shape of each second through hole 11 is circular. In this way, compared with other shapes, the second through holes 11 of other shapes may have sharp corners, and there are weak positions, and the sharp corners are easy to break, so that the strength of the negative electrode current collector 10 is reduced, and the circular second through holes 11 are easier to process and manufacture.

In some embodiments of the present application, the area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 and the area _S0 of the negative electrode current collector 10 satisfy 60% _≤S1 / _S0≤90 %. In order to balance the gram capacity of the negative electrode sheet and the internal resistance of the electrochemical device, _S1 / _S0 should not be less than 60%. When it is less than 60%, the gram capacity of the negative electrode sheet is relatively low, which may cause undesirable phenomena such as lithium precipitation during the cycle of the electrochemical device. When _S1 / _S0 is greater than 90%, the impedance of the electrochemical device is high, resulting in a longer full charge time, and it is difficult to meet the needs of fast charging. The area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 is within a suitable range to ensure the proportion of the first active material layer 21, thereby ensuring the energy density of the electrochemical device. And the area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 is suitable to reserve the current collector 10 and the second active material layer 22 for conduction, reduce the impedance of the electrochemical device, and improve the electrochemical performance of the electrochemical device. Therefore, the area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 and the area S0 of the negative electrode current collector ₁₀ satisfy 60% _≤S1 / _S0≤90 %, which can take into account both the cycle performance and the energy density of the electrochemical device.

In some embodiments, the area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 and the area S0 of the negative electrode current collector ₁₀ satisfy 60% _≤S1 / _S0≤90 %, and the area S1 of the negative electrode current collector 10 covered by the first active material layer ₂₁ and the area _S0 of the negative electrode current collector 10 satisfy 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90% or in other ranges formed by any two of the above endpoints.

Optionally, the area _S1 of the negative electrode current collector 10 covered by the first active material layer 21 and the area S0 of the negative electrode current collector ₁₀ satisfy 70%≤S ₁ /S ₀ ≤80%.

In some embodiments of the present application, the silicon-containing particles account for 50% to 98% of the total mass of the first active material layer 21 based on the total mass of the first active material layer 21. The appropriate proportion of silicon-containing particles enables the electrochemical device formed by the first active material layer 21 to have a higher energy density.

Optionally, the silicon-containing particles account for 60% to 95% of the total mass of the first active material layer 21 .

In some embodiments of the present application, the first active material layer 21 further includes a first binder, and the first binder is selected from one or more of polypropylene, polyacrylate, acrylonitrile multipolymer and carboxymethyl cellulose salt.

In some embodiments of the present application, a first binder with a high relative content and high adhesion is added to the first active material layer 21 to suppress the expansion of the first binder, but a first binder with a high relative content and high adhesion will cause a large internal resistance of the battery, thereby weakening the electrical performance. Therefore, a first through hole 211 is reserved in the first active material layer 21, and a second active material layer 22 containing carbon-based particles is formed on the first active material layer 21. The rate and cycle performance of the second active material layer 22 are better than the first active material layer 21 containing silicon-based particles. The second active material layer 22 is in direct contact with the negative electrode current collector 10 through the first through hole 211, which can effectively play the advantages of the rate and cycle performance of the second active material layer 22, thereby alleviating the defect of reducing the electrical performance caused by adding a first active material layer 21 with a high relative content and high adhesion. In addition, compared with a mixed single layer such as graphite, silicon or silicon alloy, the first active material layer 21 uses a first binder with stronger adhesion, and the first binder can restrain the expansion of the silicon-based particles of the first active material layer 21 during the cycle process. The adhesive of the first active material layer 21 uses highly adhesive polypropylene, polyacrylate, acrylonitrile copolymer and carboxymethyl cellulose salt, etc., which has small swelling in the electrolyte, can maintain a high bonding force, and effectively inhibit the volume expansion of silicon-based particles during charging and lithium insertion.

Optionally, the first binder is selected from one or more monomer polymers of acrylic nitrile, acrylic acid salt, acrylamide and acrylic ester.

In some embodiments of the present application, the first active material layer 21 further includes a first conductive agent, and the first conductive agent is selected from one or more of conductive carbon black (Super P), carbon fiber, graphene, or carbon nanotubes (CNT). In the case where the first active material layer 21 includes silicon-containing particles, a first binder, and a first conductive agent, the mass ratio of the silicon-containing particles, the first binder, and the first conductive agent is (85% to 97%): (2% to 10%): (1% to 5%).

In some embodiments of the present application, the thickness of the first active material layer 21 is 3 μm to 12 μm. The first active material layer 21 has a suitable thickness to ensure that the first active material layer 21 has a high electron migration rate. Moreover, the thickness of the first active material layer 21 is suitable, so that the silicon-containing particles have a high total mass, thereby achieving a high energy density.

In some embodiments, the thickness of the first active material layer 21 is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm or in other ranges formed by any two endpoints thereof.

Optionally, the thickness of the first active material layer 21 is 3 μm to 10 μm.

In some embodiments of the present application, the bonding force between the first active material layer 21 and the negative electrode current collector 10 is greater than or equal to 150N/m. When the content of the first binder in the first active material layer 21 is high, the bonding force of the first active material layer 21 is good, so that the first active material layer 21 can be stably attached to the negative electrode current collector 10. Therefore, the appropriate first binder content can ensure that the bonding force of the first active material layer 21 is greater than or equal to 150N/m. However, it is necessary to further control the content of the first binder to reduce the diffusion of lithium ions and reduce the performance of the negative electrode sheet when the content of the first binder is too high.

Optionally, the bonding force between the first active material layer 21 and the negative electrode current collector 10 is greater than or equal to 150 N/m.

More optionally, the bonding force between the first active material layer 21 and the negative electrode current collector 10 is greater than or equal to 300 N/m.

In some embodiments of the present application, the second active material layer 22 further includes a second binder, and the second binder is selected from one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and (polyacrylic acid) PAA.

In some embodiments of the present application, the second active material layer 22 also includes a second conductive agent, one or more of conductive carbon black Super P, carbon fiber, carbon nanotube CNT, acetylene black, conductive graphite, and graphene.

In some embodiments of the present application, the second active material layer 22 further includes other additives, such as: leveling agent, dispersant, thickener, surfactant, etc. In the case where the second active material layer 22 includes carbon-based particles, a second binder, a second conductive agent, and other additives, the mass ratio of the carbon-based particles, the second binder, the second conductive agent, and the other additives is (92% to 98%): (1% to 3%): (1% to 3%): (0% to 2%).

In some embodiments of the present application, the thickness of the negative electrode active material layer is 20 μm to 60 μm. The negative electrode active material layer has a suitable thickness to ensure the charging capacity of the entire chemical system.

Optionally, the thickness of the second active material layer 22 is greater than or equal to the thickness of the first active material layer 21 .

In some embodiments of the present application, the single-side unit area capacity ratio of the first active material layer 21 to the second active material layer 22 is 1: (1-4). An appropriate single-side unit area capacity ratio of the first active material layer 21 to the second active material layer 22 effectively reduces the risk of a large proportion of the first active material layer 21 with relatively poor kinetics, resulting in a deterioration of the overall kinetics.

Method for preparing negative electrode sheet

The present application provides a method for preparing a negative electrode sheet, comprising:

S1, providing a first active slurry containing at least silicon-based particles, and forming a first active material layer 21 on the negative electrode current collector 10 from the first active slurry to obtain a composite, wherein the first active material layer 21 includes a plurality of first through holes 211 arranged at intervals and penetrating the first active material layer 21 along the thickness direction of the negative electrode current collector 10;

S2. Provide a second active slurry containing at least carbon-based particles, and form a second active material layer 22 on the composite from the second active slurry to obtain a negative electrode sheet, wherein the second active material layer 22 is at least disposed on the surface of the negative electrode collector 10 .

According to an embodiment of the negative electrode sheet preparation method of the present application, a first active slurry is first prepared to form a composite having a first active material layer 21 on the negative electrode current collector 10, and then a second active slurry is prepared to form a second active material layer 22 on the composite. Such an arrangement is conducive to forming a first through hole 211 in the first active material layer 21, and is also conducive to adjusting the first active material layer 21 and the second active material layer 22 respectively, and has high flexibility in production and manufacturing.

In some embodiments of the present application, after the first active slurry is coated, it is dried to directly form the first active material layer 21 having the first through hole 211; or, after the first active slurry is coated, it is dried to form a base film, and then the base film is opened to form the first active material layer 21 having the first through hole 211. The coating method of the first active material layer 21 is selected from one of gravure, micro-gravure, screen printing, roller printing, electrospraying, transfer coating or extrusion coating.

Exemplarily, the coating method of the first active material layer 21 is gravure coating. By designing parameters such as the area ratio and shape of the recessed area and the non-recessed area in the gravure roller, the first active material layer 21 with a certain coating structure design can be coated. When a non-recessed area of a certain shape is designed on the gravure roller, a through-hole area of a corresponding shape will be left in the first active material layer 21; when a recessed area of a certain shape is designed on the gravure roller, a coating area of a corresponding shape will be left in the first active material layer 21.

Optionally, the drying temperature of the first active slurry is 80°C to 150°C.

In some embodiments of the present application, the second active slurry is coated on the surface of the first active material layer 21, and the second active slurry can penetrate into the first through hole 211 and contact the negative electrode current collector 10. The coating method of the second active slurry is selected from extrusion coating, micro gravure, transfer coating, gravure printing, etc.

Exemplarily, the coating method of the second active material layer 22 is extrusion coating, and the second active slurry is attached to the first active material layer 21 and the negative electrode current collector 10 by extrusion coating, and then dried to form the second active material layer 22 .

Optionally, the drying temperature of the second active slurry is 80°C to 150°C.

In some embodiments of the present application, the negative electrode current collector 10 is provided with a plurality of second through holes 11 arranged at intervals, and the method for preparing the second through holes 11 includes: forming holes in the negative electrode current collector 10 to obtain the negative electrode current collector 10 having the second through holes 11. The second through holes 11 are firstly opened on the negative electrode current collector 10, and then the first active slurry is coated on the negative electrode current collector 10, and the second through holes 11 correspond to the non-coated area of the first active slurry, so as to form the first through holes 211 in the first active material layer 21.

In some other embodiments of the present application, the negative electrode current collector 10 is provided with a plurality of second through holes 11 arranged at intervals, and the preparation method of the second through holes 11 includes:

The composite body is pore-formed to obtain the negative electrode current collector 10 having the second through hole 11, and the first through hole 211 is formed on the first active material layer 21. The first active slurry is firstly coated on the negative electrode current collector 10 to form a composite body having the first through hole 211, and the negative electrode current collector 10 is pore-formed through the first through hole 211 to obtain the second through hole 11.

Positive electrode

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.

It is understandable that the positive electrode sheet may be provided with a positive electrode active material layer on one surface of the positive electrode current collector, or may be provided with a positive electrode active material layer on both surfaces of the positive electrode current collector, and the embodiments of the present application do not specifically limit this.

The positive electrode current collector may be a metal foil or a porous metal plate, such as a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, iron, or an alloy thereof. In some embodiments of the present application, the positive electrode current collector is aluminum foil.

In some embodiments of the present application, the positive electrode active material can be selected from at least one of olivine structure materials such as lithium iron manganese phosphate, lithium iron phosphate, lithium manganese phosphate, ternary structure materials such as NCM811, NCM622, NCM523, NCM333, lithium cobalt oxide materials, lithium manganese oxide materials, and other metal oxides capable of deintercalating and releasing lithium.

In some embodiments of the present application, the positive electrode active material layer further includes a binder, which improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector. Exemplarily, the binder can be selected from at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon.

In some embodiments of the present application, the positive electrode active material layer further includes a conductive agent, which is selected from at least one of a carbon-based material, a metal-based material, a conductive polymer, and a mixture thereof. Exemplarily, the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, or any combination thereof. The metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. The conductive polymer is a polyphenylene derivative.

The positive electrode sheet in the present application can be prepared according to conventional methods in the art. For example, the active material, the conductive material and the binder are dispersed and mixed in N-methylpyrrolidone (NMP) to form a uniform positive electrode slurry, the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying, cold pressing, cutting, slitting and re-drying.

Isolation film

The electrochemical device of the embodiment of the present application may further include a separator, which is disposed between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet and the negative electrode sheet to reduce the risk of direct contact between the negative electrode and the positive electrode. The negative electrode, the separator and the positive electrode have a variety of structural forms, for example, the negative electrode, the separator and the positive electrode are sequentially stacked to form a laminated structure, or the negative electrode, the separator and the positive electrode are wound to form a wound structure.

The separator is a separator known in the art that can be used in electrochemical devices, such as but not limited to a polyolefin microporous membrane. In some embodiments, the separator comprises at least one of polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer.

In some embodiments, the isolation film is a single-layer isolation film or a multi-layer isolation film.

In some embodiments, the isolation film is coated with a coating. In some embodiments, the coating comprises at least one of an organic coating and an inorganic coating, wherein the organic coating is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, acrylic acid-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, and sodium carboxymethyl cellulose, and the inorganic coating is selected from at least one of SiO ₂ , Al ₂ O ₃ , CaO, TiO ₂ , ZnO ₂ , MgO, ZrO ₂ , and SnO ₂ .

The present application has no particular limitation on the shape and thickness of the isolation membrane. The method for preparing the isolation membrane is a method for preparing an isolation membrane that can be used in an electrochemical device and is well known in the art.

Electrolyte

The electrochemical device of the embodiment of the present application may also include an electrolyte. The electrolyte of the present application contains an electrolyte salt. The electrolyte salt is an electrolyte salt suitable for electrochemical devices that is well known in the art. For different electrochemical devices, a suitable electrolyte salt can be selected. For example, for lithium-ion batteries, the electrolyte salt is generally a lithium salt.

In some embodiments, the lithium salt includes or is selected from at least one of an organic lithium salt and an inorganic lithium salt.

In some embodiments, the lithium salt includes or is selected from at least one of lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoroantimonate (LiSbF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perfluorobutylsulfonate (LiC ₄ F ₉ SO ₃ ), lithium perchlorate (LiClO ₄ ), lithium aluminate (LiAlO ₂ ), lithium tetrachloroaluminate (LiAlCl ₄ ), lithium bis(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), wherein x and y are natural numbers), lithium chloride (LiCl) or lithium fluoride (LiF). In some embodiments, the mass percentage of the lithium salt in the electrolyte of the present application is 10 wt % to 15 wt %, for example, 10%, 11%, 12%, 13%, 14%, 15% or any range therebetween.

The electrolyte of the present application may also contain a non-aqueous organic solvent. In some embodiments, the non-aqueous organic solvent includes at least one of carbonate, carboxylate, ether compound, sulfone compound or other aprotic solvent. In some embodiments, the mass percentage of the non-aqueous organic solvent is 21% to 90%, for example, 21%, 30%, 40%, 50%, 60%, 70%, 80%, 90 or any range therebetween.

In some embodiments, the carbonate solvent comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

In some embodiments, the carboxylate solvent comprises at least one of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, valerolactone, and butyrolactone.

In some embodiments, the ether compound solvent comprises at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, bis(2,2,2-trifluoroethyl) ether, 1,3-dioxane, and 1,4-dioxane.

In some embodiments, the sulfone compound comprises at least one of ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, and sulfolane.

The non-aqueous organic solvent in the electrolyte may be a single non-aqueous organic solvent or a mixture of multiple non-aqueous organic solvents. When a mixed solvent is used, the mixing ratio can be controlled according to the desired performance of the electrochemical device.

The electrolyte of the present application may also contain functional additives, such as film-forming additives and positive electrode film-forming additives. The film-forming additives may form an interface film on the surface of the negative electrode sheet and/or the positive electrode sheet, thereby protecting the negative electrode sheet and/or the positive electrode sheet. In some embodiments, the film-forming additive may be a polynitrile additive, a sulfonate additive, and the like.

case

The positive electrode sheet, the separator and the negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet, and then the electrode assembly is obtained by winding. The electrode assembly is placed in a shell, and then the electrolyte is injected. After vacuum packaging, standing, formation, vacuum forming and other processes, an electrochemical device can be obtained.

The housing may be a hard shell or a flexible shell. For example, the hard shell may be made of metal. The flexible shell may be made of metal plastic film, such as aluminum plastic film, steel plastic film, etc.

Electronic Devices

The second aspect of the present application provides an electronic device, which includes the electrochemical device provided in the first aspect of the present application. The electrochemical device provided in the present application not only has good high-temperature storage performance and high-temperature cycle performance and high energy density, but also has good high-temperature storage performance and high-temperature cycle performance and high energy density.

The embodiments of the present application do not particularly limit the electronic device, which can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

Example

The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations will be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

For the convenience of description, the following embodiments take the electrochemical device as a lithium ion secondary battery as an example to describe the electrochemical device and its manufacturing method in detail.

Examples 1 to 17, Comparative Examples 1 to 3

Example 1

Preparation of lithium-ion batteries

(1) Preparation of negative electrode

a) Silicon: acrylic nitrile: electrocarbon black (Super P) is mixed in a mass percentage of 94%: 4%: 2%, and the solvent is water. The mixture is dispersed by a planetary mixer to prepare a first active slurry. The first active slurry is applied to both surfaces of the negative electrode current collector by using a patterned gravure roller without recesses in some parts. The first active slurry is scraped off at the position without recesses on the gravure roller after being scraped by a scraper, and the first active slurry is not coated on the corresponding negative electrode current collector, that is, the position of the first through hole. The first active slurry is retained after being scraped by a scraper at the position with recesses, and is transferred to the surface of the negative electrode current collector, corresponding to the position where the first active slurry is coated on the negative electrode current collector. After being dried in an oven at 100° C. and cold pressed, a first active material layer is formed to obtain a composite, wherein the first active material layer includes a first through hole penetrating the first active material layer along the thickness direction of the negative electrode current collector, and the area S ₁ of the negative electrode current collector covered by the first active material layer and the area S ₀ of the negative electrode current collector satisfy S ₁ /S ₀ is 70%, the thickness of the first active material layer is 3 μm, and the bonding force between the first active material layer and the negative electrode current collector is greater than 300 N/m;

b) Graphite: styrene-butadiene rubber (SBR): carbon nanotubes (CNT) are mixed in a mass percentage of 94%: 4%: 2%, and the solvent is water. The mixture is dispersed by a planetary mixer to prepare a second active slurry. The second active slurry is coated on the surface of the first active material layer by extrusion coating, and the second active slurry penetrates into the first through hole to contact the negative electrode current collector. The second active material layer is formed by drying in an oven at 100° C. The thickness of the negative electrode active material layer is 47.5 μm, and a negative electrode sheet is obtained.

The preparation methods of Examples 2 to 12 and Comparative Examples 1 to 3 are similar to the preparation method of Example 1, except that the first active material layer covers at least one of the area _S1 of the negative electrode collector and the area _S0 of the negative electrode collector and the thickness of the first active material layer.

The relevant parameters of Examples 1 to 12 and Comparative Examples 1 to 3 are shown in Table 1.

Examples 13 to 17

The preparation method is similar to that of Example 1, except that a second through hole is provided on the negative electrode current collector, and the negative electrode current collector is punched to obtain a plurality of second through holes, and each second through hole is arranged corresponding to each first through hole, as shown in Table 2.

(2) Preparation of positive electrode

The positive electrode active material lithium cobalt oxide ( _LiCoO2 ), the conductive agent carbon nanotube (CNT), and the binder polyvinylidene fluoride are added to the N-methylpyrrolidone (NMP) solvent in a weight ratio of 95:2:3, and stirred under the action of a vacuum mixer to form a uniform positive electrode slurry, and then the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil; after drying at 85°C, it is cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

(3) Preparation of electrolyte

In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a mass ratio of 1:3:6, and then additives were added, dissolved and fully stirred, and then lithium salt LiPF ₆ was added and mixed to obtain an electrolyte. The concentration of LiPF ₆ was 1.20 mol/L.

(4) Preparation of isolation membrane

Boehmite and polyacrylate are mixed and dissolved in deionized water to form a coating slurry. The coating slurry is then uniformly coated on both surfaces of a porous substrate using a micro-concave coating method, and dried to obtain a desired isolation film.

(5) Preparation of lithium-ion batteries

The positive electrode, the separator, and the negative electrode are stacked in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role, and then they are wound, and the tabs are welded to obtain a bare cell, and the bare cell is placed in an outer packaging foil aluminum-plastic film, and the prepared electrolyte is injected, and after vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft-pack lithium-ion battery is obtained.

Performance Testing:

(1) Measurement of the thickness of the first active material layer

Under the environment of (25±5)℃, take the negative electrode current collector and the negative electrode current collector having only the first active material layer; use a micrometer to measure the thickness of at least 10 different points of the coated negative electrode current collector, and record the average thickness of all test points as T ₀ ; use a micrometer to measure the thickness of at least 10 different points of the negative electrode current collector having the first active material layer, and record the average thickness of all test points as T ₁ ; in particular, the micrometer measuring head must avoid falling into the area of the first through hole; the thickness of the first active material layer is: T ₁ -T ₀ .

(2) Measurement of the thickness of the negative electrode active material layer

Under the environment of (25±5)℃, take the negative electrode current collector having only the first active material layer and the second active material layer and the single negative electrode current collector; use a micrometer to measure the thickness of at least 10 different points of the coated negative electrode current collector, and record the average thickness of all test points as T ₀ ; use a micrometer to measure the thickness of at least 10 different points of the negative electrode current collector having the first active material layer and the second active material layer, and record the average thickness of all test points as T ₂ ; the total thickness of the active material layer is: T ₂ -T ₀ .

(3) Adhesion

The bonding force between the first active material layer and the negative electrode current collector was tested using a high-speed rail tensile machine and a 90° angle method:

Preparation of test negative electrode sheets: avoid double-sided tape adhering to the negative electrode current collector not coated with the first active material layer, which would affect the adhesion test; use a wire rod coater to prepare a negative electrode sheet with a single-sided first active material layer completely covering the current collector, with a thickness of 4 μm for adhesion test; make the negative electrode sheet coated with the first active material layer into strips, and adhere a part of the negative electrode sheet to a steel plate from one end of the negative electrode sheet along the length direction through double-sided tape; fix the steel plate at the corresponding position of the high-speed rail tensile testing machine, pull up the negative electrode sheet that is not adhered to the steel plate, and clamp the negative electrode sheet in the chuck through a connector or directly, and start testing with the high-speed rail tensile testing machine when the tension at the chuck is greater than 0 kgf and less than 0.02 kgf; the average tension in the stable area is finally measured and recorded as the adhesion between the first active material layer and the current collector.

(4) The area _S1 of the first active material layer covering the negative electrode current collector accounts for the area _S0 of the negative electrode current collector.

Take a negative electrode current collector of a certain area coated with a first active material layer; place the negative electrode current collector under a CCD lens and take an image of the current collector, wherein the dark color in the image is the first active material layer, and the light color is an empty negative electrode current collector; the dark color area in the field of view of the image is counted by the software as S ₁ , that is, the area of the first active material layer coated area in the field of view; calculate the total area S ₀ of the field of view (including the area of the dark area), that is, the area of the negative electrode current collector in the field of view; the area S ₁ of the negative electrode current collector covered by the first active material layer accounts for the area S ₀ of the negative electrode current collector: S ₁ /S ₀ .

(5) Theoretical gram capacity of the negative electrode active material layer

A negative electrode sheet coated with only the first active material layer or the first active material layer is prepared and cut into discs, the disc areas are s ₁ and s ₂ respectively, and the coating weights are m ₁ and m ₂ respectively; a lithium ion secondary battery is assembled, and the lithium ion secondary battery is subjected to charge and discharge tests, and the capacity C ₁ of the lithium ion secondary battery of the first active material layer and the capacity C ₂ of the lithium ion secondary battery of the second active material layer are measured respectively; the coating weights of the first active material layer and the second active material layer in the area of S are M ₁ and M ₂ ; the theoretical gram capacity per unit area of the negative electrode active material layer including the first active material layer and the second active material layer is shown as follows:

(6) Cycle life test of lithium-ion batteries

Place the lithium-ion battery in an environment with a temperature of 25±3℃; charge it at a constant current of 1C to a voltage of 4.45V, and continue to charge it at a constant voltage of 4.45V until the current is ≤0.025C, then stop charging, and then discharge it at a constant current of 0.5C until the voltage is ≤2.75V; this is recorded as one charge and discharge cycle; repeat the above steps until the capacity of the lithium-ion battery is less than 80%; the number of cycles at this time is the cycle life of the lithium-ion battery.

(7) Lithium ion internal resistance test

Place the lithium-ion battery in an environment with a temperature of 25±3℃; connect a rated AC power supply (sinusoidal, 1000Hz frequency wave, current I is 10mA) and a voltmeter at both ends of the battery; use the voltmeter to measure the voltage U across the battery, then the AC internal resistance of the battery Rcell≈Rtest=U/I.

Performance test results:

Table 1 Components and related parameters and properties of Examples 1 to 12 and Comparative Examples 1 to 3

Table 2 Components and related parameters and properties of Examples 2, 1/3 to 17, and Comparative Example 1

As shown in Table 1 and Table 2, the gram capacity, full charge time and cycle life of the negative electrode sheets in Examples 1 to 17 are all good. The negative electrode active material layer of the negative electrode sheet of the present application includes a first active material layer and a second active material layer, wherein the first active material layer includes silicon-based particles. Since the theoretical gram capacity of the silicon-based particles is relatively high, the reversible gram capacity of the negative electrode sheet is relatively high, and the rate and cycle performance of the second active material layer containing carbon-based particles are better than those of the first active material layer containing silicon-based particles. The second active material layer is in direct contact with the negative electrode collector through the first through hole, which can effectively exert the advantages of the rate and cycle performance of the second active material layer, thereby alleviating the defect of reducing the electrical performance of the first active material layer due to the addition of a first binder with a relatively high content and high adhesion.

The performance test results in Table 1 show that compared with Comparative Example 2, when the thickness of the first active layer material layer remains unchanged, the negative electrode plate adopts a pure silicon system, and although the gram capacity is higher, the cycle life is significantly reduced and the internal resistance becomes larger. As the coverage area of the first active material layer silicon on the negative electrode current collector decreases, that is, the contact area between the second active material layer silicon and the negative electrode current collector increases, the internal resistance of the battery gradually decreases, that is, the impedance of the electrochemical device is effectively reduced, thereby increasing the cycle life of the electrochemical device; compared with Comparative Example 3, Examples 2, 8 to 11, the silicon-containing system has an advantage in gram capacity. Therefore, the lithium-ion battery made of the negative electrode plate of the present application can maintain a balance between cycle life and gram capacity.

Compared with Example 2 and Comparative Example 1, Comparative Example 1 does not have the first through hole, and the lithium-ion battery prepared by using the negative electrode plate of the application has a higher cycle life and a lower internal resistance.

Compared with Example 12, Example 2 improves the adhesion between the first active material layer and the negative electrode current collector, and the cycle life of the lithium-ion battery is longer. The higher the adhesion of the first active material layer, the more conducive it is to restrain the expansion of silicon during the charge and discharge process. However, after the first active material layer expands, the negative electrode is pulverized and the material falls off. The adhesion between the first active material layer and the negative electrode current collector deteriorates, and the SEI on the negative electrode surface is repeatedly destroyed and grown, consuming a large amount of electrolyte, generating more and more side reactions, and finally causing the cycle performance to plummet.

Further referring to Examples 1 to 7, it can be seen that by controlling the thickness of the first active material layer and reserving a certain uncoated area (i.e., the first through hole) to coat the second active material layer, the thicker the first active material layer, the greater the internal resistance of the electrochemical device, and the battery cycle performance will gradually decrease. In order to balance the cycle performance and the gram capacity of the negative electrode active layer, the thickness of the first active material layer is controlled within a certain range under the condition that the coverage of the first active material layer silicon on the negative electrode current collector is certain, and the gram capacity and cycle performance of the negative electrode active material layer can be taken into account, preferably 3 to 5 μm. Referring to Comparative Example 1, Examples 2 and 13 to 17, the negative electrode current collector is provided with a second through hole, and the second through hole provides an additional current channel for the second active material layer on the outside. Compared with Comparative Example 1, the internal resistance of the electrochemical device is smaller, the impedance of the electrochemical device is reduced, and the poor electrical performance of the first active material layer is eliminated. Compared with Example 1, Example 2 and Example 13, due to the second through hole, the impedance of the electrochemical device is further reduced, and the impedance and cycle performance of the second active material layer and the overall electrochemical device can be adjusted to a certain extent.

Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

A negative electrode sheet, comprising:

A negative electrode current collector; and

A negative electrode active material layer, the negative electrode active material layer comprising a first active material layer and a second active material layer, the first active material layer being arranged on the surface of the negative electrode current collector, and the first active material layer comprising a plurality of first through holes arranged at intervals and penetrating the first active material layer along the thickness direction of the negative electrode current collector, the second active material layer being arranged on the surface of the first active material layer, and at least partially passing through the first through holes to contact with the surface of the negative electrode current collector, wherein:

The first active material layer includes silicon-based particles;

The second active material layer includes carbon-based particles.
The negative electrode sheet according to claim 1, wherein:

The second active material layer includes a base layer and an extension portion connected to the base layer and protruding relative to the base layer, the base layer is arranged on the surface of the first active material layer away from the negative electrode collector, and the extension portion is arranged in the first through hole and extends to the surface of the negative electrode collector.
The negative electrode sheet according to claim 2, wherein:

The negative electrode current collector includes a plurality of second through holes arranged at intervals and penetrating the negative electrode current collector along a thickness direction of the negative electrode current collector, the second through holes are communicated with the first through holes, and the extension portion extends into the second through holes.
The negative electrode sheet according to claim 1 or 3, wherein:

The opening shapes of each of the first through hole and the second through hole are independently selected from rectangle, square, circle, ellipse, diamond, cone, strip or triangle.
The negative electrode sheet according to claim 1, wherein:

An area S1 of the negative electrode current collector covered by the first active material layer and an area S0 of the negative electrode current collector satisfy 60% ≤S1 / S0≤90 %.
The negative electrode sheet according to claim 5, wherein:

An area S1 of the negative electrode current collector covered by the first active material layer and an area S0 of the negative electrode current collector satisfy 70% ≤S1 / S0≤80 %.
The negative electrode sheet according to claim 1, wherein:

The silicon-based particles are selected from one or more of elemental silicon, silicon alloys, silicon-carbon composite materials and silicon oxide materials.
The negative electrode sheet according to claim 1, wherein:

The carbon-based particles are selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon and mesophase carbon microspheres.
The negative electrode sheet according to claim 1, wherein:

The negative electrode plate satisfies one or more of the following (1) to (4):

(1) The first active material layer further includes a first binder, which is selected from one or more of polypropylene, polyacrylate, acrylonitrile multipolymer and carboxymethyl cellulose salt. Optionally, the first binder is selected from one or more of the monomers of acrylic acid nitrile, acrylic acid salt, acrylamide and acrylic acid ester;

(2) The thickness of the first active material layer is 3 μm to 12 μm;

(3) The bonding force between the first active material layer and the negative electrode current collector is greater than or equal to 300 N/m;

(4) The capacity ratio per unit area of the first active material layer to the second active material layer is 1:(1 to 4).
The negative electrode sheet according to claim 1, wherein the thickness of the first active material layer is 3 μm to 6 μm.
A method for preparing a negative electrode sheet, comprising:

Providing a first active slurry containing at least silicon-based particles, and forming a first active material layer on a negative electrode current collector from the first active slurry to obtain a composite body, wherein the first active material layer includes a plurality of first through holes arranged at intervals and penetrating the first active material layer along a thickness direction of the negative electrode current collector;

A second active slurry containing at least carbon-based particles is provided, and a second active material layer is formed on the composite by the second active slurry to obtain a negative electrode sheet, wherein the second active material layer is at least arranged on the surface of the negative electrode collector.
The method for preparing a negative electrode sheet according to claim 11, wherein:

The negative electrode current collector is provided with a plurality of second through holes arranged at intervals, and the preparation method of the second through holes comprises:

The negative electrode current collector is pore-formed to obtain the negative electrode current collector having the second through holes.
The method for preparing a negative electrode sheet according to claim 11, wherein:

The negative electrode current collector is provided with a plurality of second through holes arranged at intervals, and the preparation method of the second through holes comprises:

The composite is pore-formed to obtain the negative electrode current collector having the second through holes, and the first through holes are formed on the first active material layer.
An electrochemical device, comprising the negative electrode sheet according to any one of claims 1 to 10 or the negative electrode sheet prepared by the preparation method according to any one of claims 11 to 13.
An electrical device comprising the electrochemical device according to claim 14.