CN112563452B

CN112563452B - Pole piece, battery cell and electronic equipment

Info

Publication number: CN112563452B
Application number: CN202011405642.1A
Authority: CN
Inventors: 史骁
Original assignee: Dongguan Poweramp Technology Ltd
Current assignee: Dongguan Poweramp Technology Ltd
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2022-07-05
Anticipated expiration: 2040-12-02
Also published as: CN112563452A

Abstract

The application relates to the technical field of electrochemical devices, in particular to a pole piece, a battery cell and electronic equipment. The pole piece includes: the current collector, the first material layer and the second material layer. The current collector has a first surface and a second surface opposite the first surface. The first material layer is arranged on the first surface. The second material layer is arranged on the second surface. The expansion coefficient of the first material layer is a, the expansion coefficient of the second material layer is b, and b/a is more than 1.02 and less than or equal to 1.5. When the pole piece is applied to the battery cell, the situation that the overall performance of the battery cell is reduced due to the fact that the first material layer and the second material layer are made of materials with high expansion coefficients can be avoided. The pole piece is applied to the battery cell, and the problem that the overall performance of the battery cell is poor due to the fact that the first material layer and the second material layer are made of lithium titanate or hard carbon and the like with low expansion coefficients can be avoided.

Description

Pole piece, battery cell and electronic equipment

Technical Field

The embodiment of the application relates to the technical field of electrochemical devices, in particular to a pole piece, a battery cell and electronic equipment.

Background

The electrochemical device is often accompanied by volume change during charging, which may cause volume change of the whole cell in the electrochemical device or extrusion of the internal space of the cell, resulting in a series of problems. For example, in the case of a cell of a wound structure, expansion or contraction of the cell will cause the interface between the components of the cell to be poor, impedance to be increased, and the space at the corners of the wound cell to be small when the cell is expanded, which may cause insufficient supply of electrolyte and lithium deposition to occur.

However, in the process of implementing the embodiments of the present application, the inventors of the present application found that: the expansion coefficients of the two material layers of the pole piece of the battery core are the same, when the two material layers are made of materials with high expansion coefficients, the problems are caused, and when the two material layers are made of materials with low expansion coefficients, the problems of low first effect, relatively poor circulation and low energy density can occur.

Disclosure of Invention

In view of the above problems, embodiments of the present application provide a pole piece, a battery cell, and an electronic device, which overcome or at least partially solve the above problems.

According to an aspect of an embodiment of the present application, there is provided a pole piece including a current collector having a first surface and a second surface opposite to the first surface; the first material layer is arranged on the first surface; the second material layer is arranged on the second surface; the expansion coefficient of the first material layer is a, the expansion coefficient of the second material layer is b, and b/a is more than 1.02 and less than or equal to 1.5.

In an alternative mode, 1.04. ltoreq. b/a. ltoreq.1.4.

In an alternative mode, 1.05. ltoreq. b/a. ltoreq.1.3.

In an alternative form, the expansion coefficient a is in the range of 1 to 1.5 and the expansion coefficient b is in the range of 1 to 1.5.

In an alternative mode, the first material layer and the second material layer each include an active material, a binder, and a conductive agent, wherein the first material layer and the second material layer have different compositions of the active material and/or different content ratios of the active material.

In an optional mode, the content of the active material is between 80% and 100%, the content of the binder is U, and 0% < U < 10%, and the content of the conductive agent is W, and 0% < W < 10%.

According to an aspect of the embodiments of the present application, an electrical core is provided, which is formed by winding or stacking a first pole piece, an isolation film, and a second pole piece, which are sequentially disposed, where the first pole piece or the second pole piece adopts the above-mentioned pole piece.

In an alternative mode, the battery cell is formed by winding, the first pole piece is the pole piece according to any one of claims 1 to 6, the expansion coefficient a of a first material layer in the first pole piece is smaller than the expansion coefficient b of a second material layer, and the first material layer in the first pole piece is arranged towards the winding center of the battery cell.

In an alternative mode, the battery cell is formed by winding, the first pole piece is the pole piece according to any one of claims 1 to 6, the expansion coefficient a of a first material layer in the first pole piece is smaller than the expansion coefficient b of a second material layer in the first pole piece, and the second material layer in the first pole piece is arranged towards the winding center of the battery cell.

According to an aspect of the embodiments of the present application, there is provided an electronic device, including a casing and a battery cell disposed in the casing, where the battery cell includes the battery cell described above.

The beneficial effects of the embodiment of the application are that: when the pole piece is applied to a battery cell or electronic equipment, because the expansion coefficient a of the first material layer of the pole piece is different from the expansion coefficient b of the second material layer, the problems that the battery cell expands to extrude the inner space of the battery cell due to the fact that the first material layer and the second material layer are made of materials with high expansion coefficients, and then the interface generated by the battery cell in the circulating process is poor, or the impedance is increased and lithium is separated out from corners due to insufficient space can be avoided. In addition, the problems that the energy density of the battery cell is low due to the fact that the first material layer and the second material layer are made of materials with low expansion coefficients (such as lithium titanate) or the first efficiency of the battery cell is low due to the fact that the materials with low expansion coefficients (such as hard carbon) are made of materials with low expansion coefficients can be solved.

Drawings

One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.

Fig. 1 is a schematic diagram of a pole piece provided in an embodiment of the present application;

fig. 2 illustrates a first material layer and a current collector in a full-charge state of a cell provided in an embodiment of the present application;

fig. 3 illustrates a first material layer and a current collector in a full discharge state of a cell provided in an embodiment of the present application;

fig. 4 is a schematic diagram of a battery cell provided in an embodiment of the present application.

Detailed Description

In order to facilitate an understanding of the present application, the present application is described in more detail below with reference to the accompanying drawings and specific embodiments. It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may be present. The terms "vertical," "horizontal," "left," "right," "inner," "outer," and the like as used herein are for descriptive purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1, a pole piece 100 includes a current collector 101, a first material layer 102, and a second material layer 103. The current collector 101 has a first surface and a second surface opposite the first surface. The first material layer 102 is disposed on the first surface. The second material layer 103 is disposed on the second surface. The coefficient of expansion a of the first material layer 102 is different from the coefficient of expansion b of the second material layer 103. The pole piece 100 is applied to the battery core, and the expansion coefficient a of the first material layer 102 of the pole piece 100 is different from the expansion coefficient b of the second material layer 103, so that the problem that the battery core expands to extrude the internal space of the battery core due to the fact that the first material layer 102 and the second material layer 103 are made of materials with high expansion coefficients can be solved, and then the interface of the battery core generated in the circulation process is poor, or the problems that the impedance is increased and lithium is separated out at corners due to insufficient space are solved. The pole piece 100 is applied to the battery cell, the expansion coefficient a of the first material layer 102 of the pole piece 100 is different from the expansion coefficient b of the second material layer 103, wherein b/a is more than 1.02 and less than or equal to 1.5, so that the problems that the energy density of the battery cell is low because the first material layer 102 and the second material layer 103 both adopt lithium titanate with low expansion coefficients, or the first effect of the battery cell is low because hard carbon with low expansion coefficients is both adopted can be avoided.

It should be noted that the pole piece 100 may be used as a positive electrode of a battery cell, and may also be used as a negative electrode of the battery cell. In practical applications, the volume change of the battery cell generally comes from the negative electrode, so the pole piece 100 is preferably applied to the negative electrode of the battery cell.

With respect to the first material layer 102 and the second material layer 103 described above, in some embodiments, 1.04. ltoreq. b/a. ltoreq.1.4.

Referring to fig. 2 and 3, fig. 2 shows the first material layer 102 and the current collector 101 in a cell full charge state, and fig. 3 shows the first material layer 102 and the current collector 101 in a cell full discharge state. The expansion coefficient a is the ratio of the thickness of the first material layer 102 in the fully charged state to the thickness in the fully discharged state, i.e.:

a=H1/H2

wherein H1 is the thickness of the first material layer 102 in the fully charged state, and H2 is the thickness of the first material layer 102 in the fully discharged state.

It should be noted that, the expansion coefficient b of the second material layer 103 can be calculated by referring to the expansion coefficient a, which is not described herein again.

In some embodiments, the first material layer 102 has a coefficient of expansion a in the range of 1 to 1.5 and the second material layer 103 has a coefficient of expansion b in the range of 1 to 1.5. For the first material layer 102 or the second material layer 103 with the expansion coefficient larger than 1.5, if the first material layer or the second material layer is applied to the battery core, the expansion coefficient is too large, so that the first material layer or the second material layer is not practical.

In some embodiments, the expansion coefficient a and the expansion coefficient b satisfy: b/a is more than or equal to 1.05 and less than or equal to 1.3.

It is worth noting that the first material layer 102 and the second material layer 103 both include an active material, a binder, and a conductive agent, wherein the first material layer 102 and the second material layer 103 have different compositions of the active material and/or different content ratios of the active material, so that the expansion coefficient a of the first material layer 102 is different from the expansion coefficient b of the second material layer 103.

In some embodiments, the active material is present in an amount between 80% and 100%, the binder is present in an amount between 0% and 10%, and the conductive agent is present in an amount between 0% and 10%.

In some embodiments, the active material comprises at least one of artificial graphite, natural graphite, mesophase carbon spheres, silicon oxide, hard carbon, and lithium titanate.

In general, the magnitude of the expansion coefficient of the active material satisfies: silicon, silicon oxide, natural graphite, artificial graphite, intermediate phase carbon spheres, hard carbon and lithium titanate. For example, in the first material layer 102 composed of silicon/graphite, the expansion coefficient a is between 1.05 and 1.5 according to the addition amount of silicon; the first material layer 102 made of pure graphite has an expansion coefficient a of 1.01-1.2; the expansion coefficient a of the first material layer 102 composed of hard carbon is between 1.01 and 1.1; the expansion coefficient of the first material layer 102 composed of lithium titanate is between 1.01 and 1.08.

In some embodiments, the binder comprises at least one of hydroxymethyl cellulose, styrene butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, and polyamide.

In some embodiments, the conductive agent comprises at least one of conductive carbon black, acetylene black, carbon nanotubes, and carbon nanofibers.

In this embodiment of the application, when the pole piece 100 is applied to a battery cell, it may be avoided that the first material layer 102 and the second material layer 103 are made of materials with high expansion coefficients, so that the battery cell expands to cause overall performance degradation of the battery cell. In addition, the problem that the overall performance of the battery core is poor due to the fact that the first material layer 102 and the second material layer 103 are made of lithium titanate or hard carbon with low expansion coefficients can be avoided.

The embodiment of the application further provides an embodiment of a battery cell 200, in which the battery cell 200 is formed by winding or stacking a first pole piece 100n, a separation film 201, and a second pole piece 100p, which are sequentially arranged. The above-mentioned pole piece 100 is adopted as the first pole piece 100n or the second pole piece 100p, and for the specific structure and function of the first pole piece 100n or the second pole piece 100p, reference may be made to the above-mentioned embodiments, and details are not repeated here.

The first pole piece 100n and the second pole piece 100p correspond to a positive electrode or a negative electrode of the battery cell 200, and the first pole piece 100n serves as the negative electrode of the battery cell 200, and then the second pole piece 100p serves as the positive electrode of the battery cell 200, or the first pole piece 100n serves as the positive electrode of the battery cell 200 and the second pole piece 100p serves as the negative electrode of the battery cell 200.

Note that, in practical applications, since the volume change of the battery cell 200 is generally caused by a negative electrode, it is preferable to apply the pole piece 100 to the negative electrode of the battery cell 200.

Taking the above-mentioned pole piece 100 as the first pole piece 100n, and the first pole piece 100n is a negative electrode of the battery cell 200 as an example, please refer to fig. 4, where fig. 4 is a schematic diagram of a direction of the winding structure of the battery cell 200. In fig. 4, the first pole piece 100n serves as a negative electrode of the battery cell 200, and the second pole piece 100p serves as a positive electrode of the battery cell 200.

Referring to fig. 4, for the first pole piece 100n, the expansion coefficient a of the first material layer 102 in the first pole piece 100n is smaller than the expansion coefficient b of the second material layer 103, and the first material layer 102 in the first pole piece 100n is disposed toward the winding center of the battery cell 200. By arranging the first material layer 102 with a small expansion coefficient near the winding center of the battery cell 200, that is, arranging the first material layer 102 with a small expansion coefficient in the inner ring of the battery cell 200, the space of the inner ring is relatively small, and when the battery cell 200 expands, the expansion of the inner ring is small, so that the overall performance of the battery cell 200 is not easily affected.

It is understood that the second material layer in the first pole piece may also be disposed toward the winding center of the cell (not shown).

For convenience of a reader to intuitively understand the performance and the effect of the pole piece, 12 different pole pieces in the application and 6 pole pieces in the prior art are selected as comparative examples to carry out a comparison experiment.

The pole piece in the comparative example comprises a current collector, a first material layer and a second material layer, wherein the first material layer and the second material layer in the comparative example are made of the same material, and the expansion coefficient of the first material layer is the same as that of the second material layer.

Comparative example 1, the first material layer and the second material layer each include: 5% silicon oxide, 90.8% graphite (active material); 1% conductive carbon black, 0.5% carbon nanotubes (conductive agent); 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber (adhesive). The first material layer and the second material layer each had an expansion coefficient of 1.1.

Comparative example 2, the first material layer and the second material layer each include: 10% silicon oxide, 85% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.5 percent of hydroxymethyl cellulose and 2 percent of styrene butadiene rubber. The first material layer and the second material layer each had a coefficient of expansion of 1.15.

Comparative example 3, the first material layer and the second material layer each include: 90% silicon oxide; 2% of conductive carbon black, 3% of carbon nanotubes; 2% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer and the second material layer each have an expansion coefficient of 1.4.

Comparative example 4, the first material layer and the second material layer each include: 90% silicon; 2% of conductive carbon black, 3% of carbon nanotubes; 2% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer and the second material layer each have an expansion coefficient of 1.5.

Comparative example 5, the first material layer and the second material layer each include: 2% silicon, 93.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose, 1 percent of styrene butadiene rubber and 0.5 percent of polyacrylic acid. The first material layer and the second material layer each had an expansion coefficient of 1.1.

Comparative example 6, the first material layer and the second material layer each include: 50% silicon oxide, 43% graphite; 2% of conductive carbon black, 1% of carbon nano tube; 1.5% hydroxymethyl cellulose, 2.5% polyacrylic acid. The first material layer and the second material layer each have an expansion coefficient of 1.2.

And (3) respectively taking the pole pieces in the 6 th comparative example and the 13 different pole pieces in the application as negative poles to prepare a battery cell, and measuring the expansion rate of the battery cell. The expansion rate of the battery cell is the ratio of the thickness of the battery cell when fully charged to the thickness of the battery cell when fully discharged.

The experimental data of the expansion ratio of 12 different pole pieces and each pole piece relative to the battery cell with a certain proportion are as follows:

pole piece 1, the second material layer includes: 5% silicon oxide, 90.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose and 1.5 percent of styrene butadiene rubber. The first material layer includes: 96.8% graphite; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.1 and the first material layer had a coefficient of expansion of 1.05. Compared with comparative example 1, the cell expansion rate was improved from 2.5% to 1.8%.

Pole piece 2, the second material layer comprises: 10% silicon oxide, 85% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.5 percent of hydroxymethyl cellulose and 2 percent of styrene butadiene rubber. The first material layer includes: 96.8% graphite; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.15 and the first material layer had a coefficient of expansion of 1.05. Compared with comparative example 2, the cell expansion rate was improved from 3.5% to 2.3%.

Pole piece 3, the second material layer comprises: 10% silicon oxide, 85% graphite; conductive agent 1% conductive carbon black, 0.5% carbon nano tube; 1.5 percent of hydroxymethyl cellulose and 2 percent of styrene butadiene rubber. The first material layer includes: 5% silicon oxide, 90.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose and 1.5 percent of styrene butadiene rubber. The second material layer has an expansion coefficient of 1.15 and the first material layer has an expansion coefficient of 1.1. Compared with comparative example 2, the cell expansion rate was improved from 3.5% to 2.8%.

Pole piece 4, the second material layer includes: 2% silicon, 93.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose, 1 percent of styrene butadiene rubber and 0.5 percent of polyacrylic acid. The first material layer includes: 96.8% graphite; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.1 and the first material layer had a coefficient of expansion of 1.05. Compared with comparative example 5, the cell expansion rate was improved from 2.5% to 1.8%.

Pole piece 5, the second material layer includes: 5% silicon oxide, 90.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose and 1.5 percent of styrene butadiene rubber. The first material layer includes: 96.8% hard carbon; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.1 and the first material layer had a coefficient of expansion of 1.02. Compared with comparative example 1, the cell expansion rate was improved from 2.5% to 1.2%.

The pole piece 6, the second material layer includes: 90% silicon; 3% of conductive carbon black, 3% of carbon nanotubes; 1% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer includes: 96.8% graphite; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer has an expansion coefficient of 1.5 and the first material layer has an expansion coefficient of 1.05. Compared with comparative example 4, the expansion rate of the cell was improved from 18% to 10%.

Pole piece 7, the second material layer comprises: 90% silicon oxide; 2% of conductive carbon black, 3% of carbon nanotubes; 2% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer includes: 96.8% graphite; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.4 and the first material layer had a coefficient of expansion of 1.05. Compared with comparative example 3, the cell expansion rate was improved from 15% to 9%.

Pole piece 8, the second material layer comprises: 90% silicon; 2% of conductive carbon black, 3% of carbon nanotubes; 2% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer includes: 96.8% hard carbon; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.5 and the first material layer had a coefficient of expansion of 1.02. Compared with comparative example 4, the expansion rate of the cell was improved from 18% to 10%.

Pole piece 9, the second material layer comprises: 90% silicon oxide; 2% of conductive carbon black, 3% of carbon nanotubes; 2% of hydroxymethyl cellulose and 3% of polyacrylic acid. The first material layer includes: 96.8% hard carbon; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.4 and the first material layer had a coefficient of expansion of 1.02. Compared with comparative example 3, the expansion rate of the cell was improved from 15% to 8%.

Pole piece 10, the second material layer comprises: 50% silicon oxide, 43% graphite; 2% of conductive carbon black, 1% of carbon nano tube; 1.5% hydroxymethyl cellulose, 2.5% polyacrylic acid. The first material layer includes: 96.8% hard carbon; the conductive agent is 0.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.2 and the first material layer had a coefficient of expansion of 1.02. Compared with comparative example 6, the cell expansion rate was improved from 10% to 5%.

The pole piece 11, the second material layer includes: 5% silicon oxide, 90.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose and 1.5 percent of styrene butadiene rubber. The first material layer includes: 95.8% lithium titanate; the conductive agent is 1.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.1 and the first material layer had a coefficient of expansion of 1.01. Compared with comparative example 1, the cell expansion rate was improved from 2.5% to 1%.

Pole piece 12, the second material layer comprising: 5% silicon oxide, 90.8% graphite; 1% of conductive carbon black, 0.5% of carbon nano tube; 1.2 percent of hydroxymethyl cellulose and 1.5 percent of styrene butadiene rubber. The first material layer includes: 95.8% mesophase carbon spheres; the conductive agent is 1.5 percent of conductive carbon black; the adhesive is 1.2% of hydroxymethyl cellulose and 1.5% of styrene butadiene rubber. The second material layer had a coefficient of expansion of 1.1 and the first material layer had a coefficient of expansion of 1.04. Compared with comparative example 1, the cell expansion rate was improved from 2.5% to 1.7%.

Through the pole pieces 1-12 and the comparative examples 1-6, the expansion coefficients of the first material layers of the pole pieces 1-12 are smaller than that of the second material layers, and compared with one of the comparative examples, the expansion rates of the battery cell are reduced by comparing the pole pieces 1-12, so that the cycle performance of the battery cell can be improved.

In the above-mentioned pole pieces 1 to 12, the first material layer is preferably made of graphite or hard carbon.

The embodiment of the application further provides an embodiment of an electronic device, where the electronic device includes a casing and a battery cell disposed in the casing, and reference may be made to the above embodiment for specific structure and function of the battery cell, which is not described herein any more.

It should be noted that the description of the present application and the accompanying drawings set forth preferred embodiments of the present application, however, the present application may be embodied in many different forms and is not limited to the embodiments described in the present application, which are not intended as additional limitations to the present application, but are provided for the purpose of providing a more thorough understanding of the present disclosure. Moreover, the above-mentioned technical features are combined with each other to form various embodiments which are not listed above, and all the embodiments are regarded as the scope described in the present specification; further, modifications and variations may occur to those skilled in the art in light of the foregoing description, and it is intended to cover all such modifications and variations as fall within the scope of the appended claims.

Claims

1. A pole piece, comprising:

a current collector having a first surface and a second surface opposite the first surface;

the first material layer is arranged on the first surface;

the second material layer is arranged on the second surface;

the material is characterized in that the first material layer and the second material layer respectively comprise an active material, a binder and a conductive agent, the expansion coefficient of the first material layer is a, the expansion coefficient of the second material layer is b, and b/a is more than 1.02 and less than or equal to 1.5.

2. The pole piece of claim 1, wherein b/a is 1.04. ltoreq. b/a.ltoreq.1.4.

3. The pole piece of claim 1, wherein b/a is greater than or equal to 1.05 and less than or equal to 1.3.

4. The pole piece of claim 1 wherein the coefficient of expansion a is in the range of 1 to 1.5 and the coefficient of expansion b is in the range of 1 to 1.5.

5. The pole piece of claim 1, wherein the first material layer and the second material layer have different compositions of the active materials and/or different content ratios of the active materials.

6. The pole piece according to claim 5, wherein the content of the active material is between 80% and 100%, the content of the binder is U, and 0% < U ≦ 10%, and the content of the conductive agent is W, and 0% < W ≦ 10%.

7. An electric core is formed by winding or stacking a first pole piece, a separation film and a second pole piece which are sequentially arranged, and is characterized in that the first pole piece or the second pole piece adopts the pole piece of any one of claims 1 to 6.

8. The battery cell of claim 7, wherein the battery cell is formed by winding, the first pole piece is the pole piece of any one of claims 1 to 6, the expansion coefficient a of the first material layer in the first pole piece is smaller than the expansion coefficient b of the second material layer, and the first material layer in the first pole piece is disposed toward the winding center of the battery cell.

9. The battery cell of claim 7, wherein the battery cell is formed by winding, the first pole piece is the pole piece of any one of claims 1 to 6, and a coefficient of expansion a of a first material layer in the first pole piece is smaller than a coefficient of expansion b of a second material layer in the first pole piece, and the second material layer in the first pole piece is disposed toward a winding center of the battery cell.

10. An electronic device comprising a housing and a cell disposed within the housing, wherein the cell comprises the cell of any of claims 7-9.