阅读说明：本技术 一种电极组件及其应用 (Electrode assembly and application thereof ) 是由 崔宏玉 贺飞 李素丽 李俊义 徐延铭 于 2021-09-15 设计创作，主要内容包括：本发明提供一种电极组件及其应用。本发明的电极组件,包括正极片、负极片和隔膜,所述隔膜设置于所述正极片和所述负极片之间；所述隔膜在长度方向上的延展率与所述正极片的厚度之比为(0.9-3.7)：1；所述隔膜在宽度方向上的延展率与所述正极片的厚度之比为(0.9-3.7)：1。本发明的电极组件,通过匹配电极组件中隔膜的延展率与正极片的厚度,当电极组件受到机械滥用时,可以减少正极集流体与负极活性层的接触,减少短路点的产生,从而减少热失控发生的概率,可以使锂离子电池具有较高的安全性能。(The invention provides an electrode assembly and application thereof. The electrode assembly comprises a positive plate, a negative plate and a diaphragm, wherein the diaphragm is arranged between the positive plate and the negative plate; the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet is (0.9-3.7): 1; the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (0.9-3.7): 1. according to the electrode assembly, by matching the extension rate of the diaphragm in the electrode assembly with the thickness of the positive plate, when the electrode assembly is abused mechanically, the contact between the positive current collector and the negative active layer can be reduced, and the generation of short-circuit points is reduced, so that the probability of thermal runaway is reduced, and the lithium ion battery has higher safety performance.)

1. An electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet;

the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet is (0.9-3.7): 1;

the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (0.9-3.7): 1.

2. the electrode assembly according to claim 1, wherein the positive electrode tab has a thickness of 60 to 120 mm; and/or the presence of a gas in the gas,

the elongation of the diaphragm in the length direction is 60-220%;

the extension rate of the separator in the width direction is 60 to 220%.

3. The electrode assembly according to claim 1 or 2, wherein the ratio of the elongation rate of the separator in the length direction to the thickness of the positive electrode sheet is (1.2-3.7): 1;

the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (1.2-3.7): 1.

4. the electrode assembly as claimed in claim 3, wherein the expansion rate of the separator in the length direction is 100-220%;

the extension rate of the separator in the width direction is 100-220%.

5. The electrode assembly according to any one of claims 1 to 4, wherein the separator comprises a polyolefin porous separator substrate and a coating layer disposed on at least one functional surface of the polyolefin porous separator substrate.

6. The electrode assembly according to claim 5, wherein the polyolefin porous separator substrate has a thickness of 1 to 20 μm; and/or the presence of a gas in the gas,

the porosity of the polyolefin porous diaphragm base material is 20-60%.

7. The electrode assembly of any of claims 5-6, wherein the polyolefin porous separator substrate has a gas permeability value of 30-250sec/100 cc.

8. The electrode assembly of any of claims 5-7, wherein the coating layer has a thickness of 0.5-12 μm.

9. The electrode assembly of any of claims 5-8, wherein the coating layer comprises at least one of inorganic particles and a polymer.

10. A lithium ion battery comprising the electrode assembly of any one of claims 1-9.

Technical Field

The invention relates to the technical field of batteries, in particular to an electrode assembly and application thereof.

Background

The lithium ion battery has high volumetric specific energy, mass specific energy and cycle performance, so that the lithium ion battery is widely applied to the fields of portable electronic equipment, electric automobiles, aerospace and the like. With the continuous development of lithium ion batteries, people not only have an increasing demand on the high energy density, high rate and other performances of the lithium ion batteries, but also have an increasing demand on the safety performance of the lithium ion batteries.

The conventional lithium ion battery consists of a positive electrode, a negative electrode and a polyolefin porous diaphragm arranged between the positive electrode and the negative electrode, and when the conventional lithium ion battery is tested by mechanical abuse (such as puncture), short circuit can be generated between the positive electrode and the negative electrode, so that thermal runaway is caused, and the safety problem is caused.

Disclosure of Invention

The invention provides an electrode assembly, and a lithium ion battery comprising the electrode assembly has higher safety performance.

The invention provides a lithium ion battery which has higher safety performance.

The invention provides an electrode assembly, which comprises a positive plate, a negative plate and a diaphragm, wherein the diaphragm is arranged between the positive plate and the negative plate;

the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet is (0.9-3.7): 1;

the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (0.9-3.7): 1.

the electrode assembly as described above, wherein the positive electrode tab has a thickness of 60 to 120 mm; and/or the presence of a gas in the gas,

the elongation of the diaphragm in the length direction is 60-220%;

the extension rate of the separator in the width direction is 60 to 220%.

The electrode assembly as described above, wherein the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet is (1.2-3.7): 1;

the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (1.2-3.7): 1.

the electrode assembly as described above, wherein the elongation rate of the separator in the length direction is 100-220%;

the extension rate of the separator in the width direction is 100-220%.

The electrode assembly as described above, wherein the separator includes a polyolefin porous separator substrate and a coating layer disposed on at least one functional surface of the polyolefin porous separator substrate.

The electrode assembly as described above, wherein the polyolefin porous separator substrate has a thickness of 1 to 20 μm.

The electrode assembly as described above, wherein the polyolefin porous separator substrate has a porosity of 20 to 60%.

The electrode assembly as described above, wherein the polyolefin porous separator substrate has a gas permeation value of 30-250sec/100 cc.

The electrode assembly as described above, wherein the coating layer has a thickness of 0.5 to 12 μm.

The electrode assembly as described above, wherein the coating layer includes at least one of inorganic particles and a polymer.

The present invention provides an electrochemical device comprising an electrode assembly as described above.

The electrode assembly takes the diaphragm and the positive plate as starting points, so that the ratio of the extension rate of the diaphragm to the thickness of the positive plate in the electrode assembly is more suitable, and the safety performance of the lithium ion battery is improved. Particularly, when the electrode assembly is subjected to mechanical abuse, the contact between the positive electrode current collector and the negative electrode active layer can be reduced, and the generation of short-circuit points is reduced, so that the probability of thermal runaway is reduced, and the lithium ion battery has higher safety performance.

The lithium ion battery of the invention has higher safety performance because of comprising the electrode assembly.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the related art, the drawings used in the description of the embodiments of the present invention or the related art are briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

FIG. 1 is a top view of a septum of the present invention;

FIG. 2 is a schematic structural view of an electrode assembly according to some embodiments of the present invention;

fig. 3 is a schematic diagram of a lithium ion battery needling test.

Description of reference numerals:

1: a negative electrode active layer;

2: a positive current collector;

3: a diaphragm:

4: a negative current collector;

5: and a positive electrode active layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Figure 1 is a top view of a septum of the invention. As shown in fig. 1, all definitions of "length" and "width" are hereinafter referred to with reference to the "length L direction" and the "width W direction" of the separator. Taking the functional surfaces (the functional surfaces are the two largest and opposing surfaces) as a rectangle for example, the length L direction of the separator is the direction in which the largest sides of the functional surfaces of the separator are located, and the width W direction of the separator is the direction in which the smallest sides of the functional surfaces of the separator are located.

Fig. 2 is a schematic view of the structure of an electrode assembly according to some embodiments of the present invention. As shown in fig. 2, a first aspect of the present invention provides an electrode assembly comprising a positive electrode tab, a negative electrode tab, and a separator 3, the separator 3 being disposed between the positive electrode tab and the negative electrode tab;

the ratio of the elongation of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet is (0.9 to 3.7): 1;

the ratio of the extension rate of the separator 3 in the width direction to the thickness of the positive electrode sheet is (0.9-3.7): 1.

it is understood that, in the present invention, the electrode assembly of the present invention may be formed by sequentially stacking the positive electrode sheet, the separator 3, and the negative electrode sheet; the electrode assembly of the present invention may also be formed by winding the positive electrode sheet, separator 3, and negative electrode sheet.

The negative electrode sheet of the present invention includes a negative electrode current collector 4 and a negative electrode active layer 1 disposed on at least one functional surface of the negative electrode current collector 4.

The negative electrode current collector 4 and the negative electrode active layer 1 are not particularly limited in the present invention, and may be selected from the negative electrode current collectors 4 and the negative electrode active layers 1 commonly used in the art.

In the present invention, the elongation of the membrane 3 in the longitudinal direction refers to a ratio of an increase of a specified distance of the membrane 3 in the longitudinal direction to the specified distance when the membrane 3 is broken under a certain tensile force, and is expressed as a percentage. The elongation of the separator 3 in the width direction is a ratio of an increase in a specified distance of the separator 3 in the width direction to a width of the specified distance when the separator 3 is broken by a certain tensile force, and is expressed as a percentage.

In the present invention, the specified distance of the separator 3 in the longitudinal direction is: the distance between the point A and the point B at any two points in the extension direction of the length of the diaphragm 3; the specified distance of the separator 3 in the width direction is: the distance between the points a 'and B' at any two points in the extending direction of the width of the diaphragm 3.

In the present invention, the elongation of the separator 3 in the length direction and the elongation of the separator 3 in the width direction can be separately tested by the following methods:

the membrane 3 is cut into rectangular sample strips, and the extending direction of the long edges of the sample strips is consistent with the length direction of the membrane 3, so that the edges of the sample strips are smooth and have no gaps (the defects are prevented from influencing the test result). And clamping the sample strip between an upper clamp and a lower clamp of a universal tensile machine, enabling the long axis of the sample strip (the central axis in the length direction of the sample strip) to coincide with the central line of the clamps, stretching the sample strip along the length direction of the sample strip at a tensile test speed of 100mm/min until the diaphragm 3 is broken, obtaining the increment of the specified distance of the diaphragm 3 in the length direction, and calculating the elongation of the diaphragm 3 in the length direction.

The test method of the elongation of the separator 3 in the width direction is substantially the same as the test method of the elongation in the length direction, except that the extending direction of the long side of the spline coincides with the width direction of the separator 3.

The positive plate of the present invention includes a positive electrode current collector 2 and a positive electrode active layer 5 disposed on at least one functional surface of the positive electrode current collector 2. In the present invention, the thickness of the positive electrode sheet refers to the sum of the thickness of the positive electrode active layer 5 and the thickness of the positive electrode current collector 2.

The ratio of the elongation of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet in the present invention is (0.9 to 3.7): 1 in%/mm. The ratio of the extension rate of the separator 3 in the width direction to the thickness of the positive electrode sheet in the present invention is (0.9 to 3.7): 1 in%/mm.

In the present invention, the ratio of the elongation of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet and the ratio of the elongation of the separator 3 in the width direction to the thickness of the positive electrode sheet may be the same or different, and may be within the above range.

The electrode assembly of the present invention is obtained by performing lamination-type assembly or winding-type assembly of the positive electrode sheet, the separator 3, and the negative electrode sheet in a conventional assembly manner, wherein the ratio of the elongation of the separator 3 in the length and width to the thickness of the positive electrode sheet satisfies the above requirements. For example, an electrode assembly may be prepared by selecting a separator 3 having an appropriate elongation rate matching the above ratio according to the thickness of the positive electrode sheet, based on the positive electrode sheet; an electrode assembly may also be prepared by selecting a positive electrode sheet having an appropriate thickness matching the above ratio according to the elongation of the separator 3 based on the separator 3.

The invention does not limit the preparation method of the positive plate and the negative plate. In one embodiment, the positive electrode active material, the conductive agent and the adhesive are added into a stirring tank according to a certain mass ratio, a certain proportion of NMP solution is added, positive electrode active slurry with a certain solid content is obtained through stirring, the positive electrode active slurry is coated on at least one functional surface of the positive electrode current collector 2, then drying is carried out to remove the solvent in the positive electrode active slurry, and finally, rolling, slitting and sheet making are carried out in sequence to obtain the positive electrode sheet.

In one embodiment, the negative electrode active material, the conductive agent and the adhesive are added into a stirring tank according to a certain mass ratio, deionized water is added according to a certain ratio, negative electrode active slurry with a certain solid content is obtained through stirring, the negative electrode active slurry is coated on at least one functional surface of a negative electrode current collector 4, then drying is carried out to remove water in the negative electrode active slurry, and finally rolling, slitting and sheet making processes are sequentially carried out, so that the negative electrode sheet is obtained.

The electrode assembly of the present invention is directed to a separator 3 and a positive electrode sheet, and the ratio of the elongation of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet is set to (0.9 to 3.7): 1; the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (0.9-3.7): 1, the improvement of the safety performance of the lithium ion battery is realized. In the application process of the lithium ion battery containing the electrode assembly, when the electrode assembly is subjected to mechanical abuse, the contact between the positive electrode current collector 2 and the negative electrode active layer 1 can be reduced, the generation of short-circuit points is reduced, the probability of thermal runaway is reduced, and the lithium ion battery containing the electrode assembly has higher safety performance.

In some embodiments of the invention, in order to better improve the safety performance of the lithium ion battery, the thickness of the positive plate is 60-120 mm; and/or the presence of a gas in the gas,

the elongation of the membrane 3 in the length direction is 60-220%;

the extension ratio of the separator 3 in the width direction is 60 to 220%.

Further, when the ratio of the elongation of the separator 3 in the length direction to the thickness of the positive electrode sheet is (1.2 to 3.7): 1; the ratio of the extension rate of the separator 3 in the width direction to the thickness of the positive electrode sheet is (1.2-3.7): 1, the lithium ion battery has higher safety performance.

In some embodiments of the invention, the elongation of the membrane 3 in the length direction is 100-220%; the expansion ratio of the separator 3 in the width direction was 100-220%.

In some embodiments of the present invention, in order to better improve the safety performance of the lithium ion battery, the separator 3 includes a polyolefin porous separator substrate and a coating layer disposed on at least one functional surface of the polyolefin porous separator substrate.

It is understood that the separator 3 of the present invention may be obtained by providing a coating layer on either functional surface of the polyolefin porous separator substrate, or may be obtained by providing a coating layer on both functional surfaces of the polyolefin porous separator substrate. Among them, the elongation of the separator 3 is mainly related to the elongation of the polyolefin porous separator substrate.

In some embodiments of the present invention, the polyolefin porous separator substrate has a thickness of 1 to 20 μm.

In the invention, if the thickness of the polyolefin porous diaphragm base material is too thick, the too thick polyolefin porous diaphragm base material can cause the electrode assembly to be too thick, which is not beneficial to the optimization of the energy density of the lithium ion battery, and if the thickness of the polyolefin porous diaphragm base material is too thin, the too thin polyolefin porous diaphragm base material is easy to damage in the long-term operation of the lithium ion battery, thereby shortening the service life of the lithium ion battery. In the invention, the thickness of the polyolefin porous diaphragm substrate is 1-20 μm, and the lithium ion battery has good energy density and long service life in the range.

In some embodiments of the present invention, the polyolefin porous separator substrate has a porosity of 20 to 60%. In particular, the polyolefin porous diaphragm base material meeting the porosity can not only meet the electrical property of the lithium ion battery, but also be beneficial to improving the mechanical property of the polyolefin porous diaphragm base material and prolonging the service life of the lithium ion battery,

in some embodiments of the invention, the polyolefin porous separator substrate has a permeability value of 30 to 250sec/100 cc.

In the present invention, the air permeability value of the polyolefin porous separator substrate means the time required for 100cc of air to pass through the polyolefin porous separator substrate under a pressure of 0.25 MPa. When the air permeability value of the polyolefin porous diaphragm substrate is too small, the polyolefin porous diaphragm substrate is easy to permeate other substances, the self-discharge of the lithium ion battery is large, and when the air permeability value of the polyolefin porous diaphragm substrate is too large, the internal resistance of the lithium ion battery is easy to be too large, so that the electrical property of the lithium ion battery is influenced. In the invention, when the air permeability value of the polyolefin porous diaphragm substrate is 30-250sec/100cc, the lithium ion battery can have good electrical property and smaller self-discharge property.

In some embodiments of the present invention, in order to further improve the safety performance of the lithium ion battery without affecting the energy density of the lithium ion battery, the thickness of the coating layer is 0.5 to 12 μm.

In some embodiments of the invention, the coating layer comprises at least one of inorganic particles and a polymer.

The inorganic particles of the present invention may be selected from inorganic particles commonly used in the art, and for example, may be selected from at least one of alumina, silica, boehmite, zinc oxide, magnesium oxide, zirconia, titania, barium oxide, calcium oxide, aluminum nitride, titanium nitride, silicon nitride, boron nitride, aluminum hydroxide, magnesium hydroxide, and barium sulfate.

The polymer of the present invention may be selected from polymers commonly used in the art, for example, may be selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethylcellulose, polyacrylate, polyacrylonitrile, polyvinyl alcohol, styrene-butadiene rubber, polyurethane, ethylene-acrylic acid copolymer, polymethyl methacrylate, polyimide, aramid, polystyrene, and polyester.

In the present invention, if the coating layer includes only inorganic particles, it is referred to as an inorganic coating layer; if the polymer comprises only polymer, it is referred to as an organic coating layer; if the coating layer includes both organic particles and polymers, it is referred to as a composite coating layer. The membrane of the invention can be obtained by arranging at least one of an inorganic coating layer, an organic coating layer and a composite coating layer on any functional surface of a polyolefin porous membrane substrate, or can be obtained by arranging at least one of an inorganic coating layer, an organic coating layer and a composite coating layer on two functional surfaces of a polyolefin porous membrane substrate.

When at least two of the inorganic coating layer, the organic coating layer and the composite coating layer are arranged on a certain functional surface of the polyolefin porous diaphragm substrate, at least two of the inorganic coating layer, the organic coating layer and the composite coating layer can be arranged in a stacked manner, and at least two of the inorganic coating layer, the organic coating layer and the composite coating layer can also be arranged in parallel on the functional surface of the polyolefin porous diaphragm substrate. In the present invention, the order of stacking is not particularly limited, and the order of arranging the layers in parallel is not particularly limited.

In some embodiments, the inorganic coating layer is disposed on a functional surface of the polyolefin porous separator substrate, and the organic coating layer and/or the composite coating layer is disposed on the functional surface of the inorganic coating layer away from the polyolefin porous separator substrate.

A second aspect of the invention provides a lithium ion battery comprising the electrode assembly described above.

And placing the electrode assembly in an outer package, carrying out top sealing and side sealing on the outer package, baking moisture, injecting electrolyte into the outer package, and then sequentially carrying out vacuum packaging, standing, formation and shaping procedures to obtain the lithium ion battery.

The lithium ion battery of the present invention has more excellent safety performance because it includes the electrode assembly.

Hereinafter, the technical solution of the present invention will be described with reference to specific examples.

Example 1

The lithium ion battery of the present example was prepared by the following steps:

1. preparation of the separator

Arranging an aluminum oxide ceramic layer on one functional surface of the polyolefin porous diaphragm substrate by adopting gravure coating, arranging a polyvinylidene fluoride (PVDF) adhesive layer on the other functional surface of the polyolefin porous diaphragm substrate by adopting gravure coating, and arranging a PVDF adhesive layer on the functional surface of the aluminum oxide ceramic layer, which is far away from the polyolefin porous diaphragm substrate, by adopting gravure coating to obtain a diaphragm;

wherein the thickness of the polyolefin porous membrane substrate is 5 μm, the porosity of the polyolefin porous membrane substrate is 32%, the air permeability value of the polyolefin porous membrane substrate is 145sec/100cc, the thickness of the alumina ceramic layer is 2 μm, the thickness of the PVDF glue layer is 1 μm, the extensibility of the membrane in the length direction is 180%, and the extensibility of the membrane in the width direction is 165%.

2. Preparation of positive plate

Mixing a positive electrode active material lithium cobaltate, a conductive agent conductive carbon black and a binder PVDF according to the weight ratio of 97.2: 1.5: adding the mixture into a stirring tank according to the mass ratio of 1.3, adding an NMP solution, fully stirring to obtain positive active slurry, respectively coating the positive active slurry on two functional surfaces of an aluminum foil of a positive current collector, drying to remove a solvent, and finally sequentially performing rolling, slitting and sheet making to obtain a positive plate;

wherein, the thickness of the positive plate is 90 mm.

3. Preparation of negative plate

Mixing a negative electrode active material graphite, a conductive agent acetylene black and a binder sodium carboxymethyl cellulose according to a ratio of 97: 1.5: adding the mixture into a stirring tank according to the mass ratio of 1.5, adding deionized water, fully stirring to obtain negative active slurry, respectively coating the negative active slurry on two functional surfaces of a copper foil of a negative current collector, drying to remove water, and finally sequentially performing rolling, slitting and sheet making procedures to obtain a negative sheet.

4. Preparation of electrode assemblies

Laminating the diaphragm obtained in the step 1, the positive plate obtained in the step 2 and the negative plate obtained in the step 3 according to the order of the positive plate, the diaphragm and the negative plate, and then winding to obtain an electrode assembly;

wherein, the ratio of the elongation of the diaphragm in the length direction to the thickness of the positive plate is 2: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet is 1.83: 1.

5. preparation of lithium ion battery

Placing the electrode assembly obtained in the step (4) in an outer packaging aluminum-plastic film, carrying out top sealing and side sealing on the aluminum-plastic film, baking to remove moisture, injecting electrolyte into the outer packaging, and carrying out positive air packaging, standing, formation and shaping to obtain a lithium ion battery;

the electrolyte is prepared by the following steps: in a glove box filled with argon (H)₂O＜0.1ppm，O₂< 0.1ppm), Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), n-propyl propionate were mixed well, and then 1.2mol/L of well-dried lithium hexafluorophosphate (LiPF) was added thereto₆) Dissolving the electrolyte in a non-aqueous organic solvent, uniformly stirring, and obtaining the basic electrolyte after the water and free acid are detected to be qualified.

The elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example were obtained by testing a method including the following steps:

the diaphragm is cut into rectangular sample strips with the width of 1.5cm and the length of more than 5cm, and the extending direction of the long edges of the sample strips is consistent with the length direction of the diaphragm 3, so that the edges of the sample strips are smooth and have no gaps (the defect is prevented from influencing the test result). And clamping the sample strip between an upper clamp and a lower clamp of a universal tensile machine, wherein the long axis of the sample strip is superposed with the central line of the clamps, the distance between the upper clamp and the lower clamp of the tensile machine is the specified distance of the diaphragm, the specified distance in the length direction of the diaphragm is 5cm, and the sample strip is stretched in the length direction of the sample strip at the tensile test speed of 100mm/min until the diaphragm is broken, so that the increase of the specified distance of the diaphragm in the length direction is obtained, and the elongation of the diaphragm in the length direction is calculated.

The test method of the elongation of the separator in the width direction is substantially the same as the test method of the elongation in the length direction, except that the extending direction of the long sides of the splines coincides with the width direction of the separator 3.

Example 2

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, an alumina ceramic layer is coated on two functional surfaces of the polyolefin porous diaphragm substrate by adopting a gravure mode, and a PVDF glue layer is coated on the functional surface, far away from the polyolefin porous diaphragm substrate, of the alumina ceramic layer by adopting the gravure mode respectively, so that the diaphragm is obtained.

In this example, the elongation of the separator in the longitudinal direction, the elongation of the separator in the width direction, and the thickness of the positive electrode sheet were the same as those in example 1.

The method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 3

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

step 1, mixing aluminum oxide and PVDF to obtain mixed slurry, and respectively coating the mixed slurry on two functional surfaces of a polyolefin porous diaphragm substrate by adopting a gravure coating mode to obtain a coating layer and a diaphragm;

wherein the thickness of the coating layer is 4 μm, and the mass ratio of the aluminum oxide to the PVDF is 9: 1.

in this example, the elongation of the separator in the longitudinal direction, the elongation of the separator in the width direction, and the thickness of the positive electrode sheet were the same as those in example 1.

The method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 4

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in step 1, a polyolefin porous separator substrate different from that in example 1 was used, so that the elongation of the separator in the length direction was 105% and the elongation of the separator in the width direction was 95%;

in step 2, the thickness of the positive plate is 75 mm.

In the present example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 1.4: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet is 1.27: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 5

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 2 in that:

in step 1, a polyolefin porous separator substrate different from that of example 2 was used, wherein the polyolefin porous separator substrate had a thickness of 7 μm and an elongation of the separator in the width direction of 175%.

In this example, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet was 1.94: 1.

in this example, the elongation of the separator in the longitudinal direction and the thickness of the positive electrode sheet were the same as in example 2.

The test method of the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 2.

Example 6

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in step 1, a polyolefin porous membrane substrate having a porosity and a gas permeability different from those of example 1 was used, wherein the polyolefin porous membrane substrate had a porosity of 39% and the polyolefin porous membrane substrate had a gas permeability of 105sec/100 cc.

In this example, the elongation of the separator in the longitudinal direction and the thickness of the positive electrode sheet were the same as in example 1.

The test method of the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 2.

Example 7

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 180%, and the extension rate of the diaphragm in the width direction is 180%;

in step 2, the thickness of the positive plate is 60 mm.

In this example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 3: 1, the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is 3: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 8

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 110%, and the extension rate of the diaphragm in the width direction is 110%;

in the present example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 1.2: 1, the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.2: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 9

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 81%, and the extension rate of the diaphragm in the width direction is 81%;

in this example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 0.9: 1, the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is 0.9: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 10

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 220%, and the extension rate of the diaphragm in the width direction is 220%;

in the present example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 3.7: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet was 3.67: 1.

The method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 11

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 2, the thickness of the positive plate is 120 mm;

in the present embodiment, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 1.5: 1, the ratio of the elongation of the separator in the width direction to the thickness of the positive electrode sheet is 1.375: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 12

The lithium ion battery of this example was prepared using the following steps as compared to the lithium ion battery of example 7:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 7 is adopted, so that the extension rate of the diaphragm in the length direction is 60%, and the extension rate of the diaphragm in the width direction is 60%;

in this example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 1: 1, the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is 1: 1.

the test method of the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example were the same as in example 7.

Example 13

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 220%, and the extension rate of the diaphragm in the width direction is 220%;

in the present example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 2.44: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet was 2.44: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Example 14

The preparation procedure of the lithium ion battery of the present example differs from that of the lithium ion battery of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate with a different extension rate from that of the polyolefin porous diaphragm substrate in the example 1 is adopted, so that the extension rate of the diaphragm in the length direction is 100%, and the extension rate of the diaphragm in the width direction is 100%;

in the step 2, the thickness of the positive plate is 80 mm;

in the present example, the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet was 1.25: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet is 1.25: 1.

the method of testing the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this example was the same as in example 1.

Comparative example 1

The lithium ion battery of this comparative example was prepared in steps different from those of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate different from that of the embodiment 1 is adopted, so that the extension rate of the diaphragm in the length direction is 58%, and the extension rate of the diaphragm in the width direction is 62%;

in the present comparative example, the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet was 0.64: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet was 0.69: 1.

in this comparative example, the thickness of the positive electrode sheet was the same as in example 1.

The test method of the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this comparative example were the same as in example 1.

Comparative example 2

The lithium ion battery of this comparative example was prepared in steps different from those of example 1 in that:

in the step 1, a polyolefin porous diaphragm substrate different from that of the embodiment 1 is adopted, so that the extension rate of the diaphragm in the length direction is 92%, and the extension rate of the diaphragm in the width direction is 89%;

the thickness of the positive plate in the step 2 is 120 mm.

In the present comparative example, the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet was 0.77: 1, the ratio of the extension ratio of the separator in the width direction to the thickness of the positive electrode sheet was 0.74: 1.

the test method of the elongation of the separator in the length direction and the elongation of the separator in the width direction in step 1 of this comparative example were the same as in example 1.

Test of needling Performance

The lithium ion batteries in the examples and comparative examples were charged in a standard charge-discharge mode, and after full charge, the lithium ion batteries were subjected to a needle punch test, using a steel needle with a diameter of 3mm, placing the lithium ion batteries on a horizontal plane, the steel needle passing through the center of the lithium ion batteries at a speed of 150mm/s and remaining in the lithium ion batteries for 10min, and if the lithium ion batteries did not ignite and explode, the lithium ion batteries were considered to pass the test. Each lithium ion battery of each example and comparative example was tested 100 times, and the puncture passing rate was calculated and the test results are shown in table 1.

Fig. 3 is a schematic diagram of a lithium ion battery needling test. As shown in fig. 3, when the lithium ion battery is subjected to the needling test, the steel needle passes through the negative electrode active layer 1, the negative electrode current collector 4, the negative electrode active layer 1, the diaphragm 3, the positive electrode active layer 5 and the positive electrode current collector 2 in sequence, if the lithium ion battery is short-circuited, the internal current temperature of the ion battery rises, and then the lithium ion battery is ignited, which indicates that the needling test result of the lithium ion battery does not pass.

TABLE 1

As can be seen from table 1, the electrode assembly of the present invention is used in a lithium ion battery, and can improve the safety performance of the lithium ion battery. The result proves that by matching the extension rate of the diaphragm in the electrode assembly with the thickness of the positive plate, the short circuit points of the positive electrode and the negative electrode can be reduced during the acupuncture test, and the heat generated by short circuit is effectively reduced, so that the safety performance of the battery is improved.

Further, as can be seen from examples 1 to 8, 10 to 11, and 13 to 14, when the ratio of the elongation of the separator in the length direction to the thickness of the positive electrode sheet is (1.2 to 3.7): 1; the ratio of the extension rate of the separator in the width direction to the thickness of the positive electrode sheet is (1.2-3.7): 1, the lithium ion battery has better safety performance, and the needling passage rate is more than or equal to 83 percent.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.