WO2023040862A1

WO2023040862A1 - Electrode assembly and application thereof

Info

Publication number: WO2023040862A1
Application number: PCT/CN2022/118591
Authority: WO
Inventors: 崔宏玉; 贺飞; 李素丽; 李俊义; 徐延铭
Original assignee: 珠海冠宇电池股份有限公司
Priority date: 2021-09-15
Filing date: 2022-09-14
Publication date: 2023-03-23
Also published as: CN113809475A

Abstract

The present application provides an electrode assembly and an application thereof. The electrode assembly of the present application comprises a positive electrode plate, a negative electrode plate, and a diaphragm. The diaphragm is disposed between the positive electrode plate and the negative electrode plate. The ratio of the elongation of the diaphragm in the length direction to the thickness of the positive electrode plate is (0.9-3.7): 1; and the ratio of the elongation of the diaphragm in the width direction to the thickness of the positive electrode plate is (0.9-3.7): 1. According to the electrode assembly of the present application, by matching the elongation of the diaphragm in the electrode assembly with the thickness of the positive electrode plate, when the electrode assembly is subjected to mechanical abuse, the contact between a positive electrode current collector and a negative electrode active layer can be reduced, and the generation of short circuit points is reduced, such that the probability of thermal runaway occurrence is reduced, and a lithium-ion battery may have relatively high safety performance.

Description

A kind of electrode assembly and its application

This application claims the priority of the Chinese patent application with the application number 202111081831.2 and the application title "An Electrode Assembly and Its Application" submitted to the China Patent Office on September 15, 2021, the entire contents of which are incorporated by reference in this application .

technical field

The application belongs to the technical field of lithium ion batteries, and in particular relates to an electrode assembly and its application.

Background technique

Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, aerospace and other fields due to their high volume specific energy, mass specific energy and cycle performance. With the continuous development of lithium-ion batteries, not only the demand for high energy density and high rate performance of lithium-ion batteries is increasing, but also the demand for safety performance of lithium-ion batteries is also increasing.

The existing lithium-ion battery is composed of a positive electrode, a negative electrode, and a polyolefin porous separator arranged between the positive electrode and the negative electrode. When the existing lithium-ion battery is tested by mechanical abuse (such as puncture), a short circuit will occur between the positive and negative electrodes. , leading to thermal runaway and safety issues.

application content

The present application provides an electrode assembly, and a lithium ion battery including the electrode assembly has high safety performance.

The present application provides a lithium ion battery, which has high safety performance.

The present application provides an electrode assembly, including a positive electrode sheet, a negative electrode sheet, and a separator, and the separator is arranged between the positive electrode sheet and the negative electrode sheet;

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

The ratio of the elongation 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 thickness of the positive electrode sheet is 60-120 mm; and/or,

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

The elongation of the separator in the width direction is 60-220%.

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

The ratio of the extensibility 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 of the separator in the length direction is 100-220%;

The elongation of the separator in the width direction is 100-220%.

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

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

The above electrode assembly, wherein the porosity of the polyolefin porous separator substrate is 20-60%.

The above-mentioned electrode assembly, wherein the air permeability of the polyolefin porous separator substrate is 30-250sec/100cc.

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

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

The present application provides an electrochemical device, comprising the above-mentioned electrode assembly.

The electrode assembly of the present application starts with the diaphragm and the positive electrode sheet, and makes the ratio of the elongation of the diaphragm in the electrode assembly to the thickness of the positive electrode sheet more appropriate, thereby improving the safety performance of the lithium-ion battery. Specifically, when the electrode assembly is mechanically abused, the contact between the positive electrode current collector and the negative electrode active layer can be reduced, and the generation of short circuit points can be reduced, thereby reducing the probability of thermal runaway and making the lithium-ion battery have higher safety performance.

The lithium-ion battery of the present application has high safety performance because it includes the above-mentioned electrode assembly.

Description of drawings

Fig. 1 is the top view of diaphragm in the present application;

FIG. 2 is a schematic structural view of an electrode assembly in some embodiments of the present application;

Fig. 3 is a schematic diagram of a lithium-ion battery acupuncture test.

Explanation of reference signs:

1: negative active layer;

2: Positive current collector;

3: Diaphragm:

4: Negative electrode collector;

5: positive electrode active layer.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the application with reference to the drawings in the embodiments of the application. Apparently, the described embodiments are only some of the embodiments of the application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

Figure 1 is a top view of the diaphragm in the application. As shown in FIG. 1 , all definitions of "length" and "width" below refer to the "length L direction" and "width W direction" of the separator. Taking the functional surface (the functional surface refers to the two largest and opposite surfaces) as a rectangle as an example, the length L direction of the diaphragm refers to the direction where the largest side length of the functional surface of the diaphragm is located, and the width W direction of the diaphragm refers to the direction of the functional surface of the diaphragm. The direction in which the minimum edge length lies.

Fig. 2 is a schematic structural view of an electrode assembly in some embodiments of the present application. As shown in Figure 2, the first aspect of the present application provides an electrode assembly, including a positive electrode sheet, a negative electrode sheet and a separator 3, and the separator 3 is arranged between the positive electrode sheet and the negative electrode sheet;

The ratio of the elongation rate of the diaphragm 3 in the length direction to the thickness of the positive electrode sheet is (0.9-3.7): 1;

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

It can be understood that in the present application, the electrode assembly of the present application can be formed by sequentially stacking the positive electrode sheet, the separator 3 and the negative electrode sheet; the winding arrangement of the positive electrode sheet, the separator 3 and the negative electrode sheet can also form the electrode assembly of the present application. .

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

The present application does not specifically limit the negative electrode current collector 4 and the negative electrode active layer 1 , which may be selected from the negative electrode current collector 4 and the negative electrode active layer 1 commonly used in the field.

In this application, the elongation rate of the diaphragm 3 in the longitudinal direction refers to the ratio of the increase of the specified distance of the diaphragm 3 in the longitudinal direction to the specified distance when the diaphragm 3 breaks under a certain tensile force, expressed in percentage. The elongation rate of the diaphragm 3 in the width direction refers to the ratio of the increase in the specified distance of the diaphragm 3 in the width direction to the width of the specified distance when the diaphragm 3 breaks under a certain tensile force, expressed as a percentage.

In this application, the designated distance of the diaphragm 3 in the length direction is: the distance between any two points A and B in the extension direction of the length of the diaphragm 3; the designated distance of the diaphragm 3 in the width direction is: the extension of the width of the diaphragm 3 The distance between any two points in the direction A' and B'.

In this application, the elongation rate of the diaphragm 3 in the length direction and the elongation rate of the diaphragm 3 in the width direction can be tested respectively by the following methods:

The diaphragm 3 is cut into a rectangular spline, and the extension direction of the long side of the spline is consistent with the length direction of the diaphragm 3, so that the edge of the spline is smooth without gaps (to prevent defects from affecting the test results). Clamp the above-mentioned spline between the upper and lower fixtures of the universal tensile machine, the long axis of the spline (the central axis in the direction of the length of the spline) coincides with the center line of the fixture, and at a tensile test speed of 100mm/min, along the spline Stretch the spline in the length direction until the diaphragm 3 breaks, obtain the increment of the specified distance of the diaphragm 3 in the length direction, and calculate the elongation rate of the diaphragm 3 in the length direction.

The elongation test method of the diaphragm 3 in the width direction is basically the same as the elongation test method in the length direction, the only difference is that the extension direction of the long side of the spline is consistent with the width direction of the diaphragm 3 .

The positive electrode sheet of the present application includes a positive electrode collector 2 and a positive electrode active layer 5 disposed on at least one functional surface of the positive electrode collector 2 . In the present application, 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 .

In this application, the ratio of the elongation rate of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet is (0.9-3.7):1, and the unit is %/mm. In this application, the ratio of the elongation rate of the separator 3 in the width direction to the thickness of the positive electrode sheet is (0.9-3.7):1, and the unit is %/mm.

In the present application, the ratio of the elongation rate of the separator 3 in the longitudinal direction to the thickness of the positive electrode sheet and the ratio of the elongation rate of the separator 3 in the width direction to the thickness of the positive electrode sheet can be the same or different, as long as they are within the above range within.

The electrode assembly of the present application can be obtained by stacking or winding the positive electrode sheet, separator 3 and negative electrode sheet according to the conventional assembly method, wherein the elongation of the separator 3 in length and width is the same as that of the positive electrode sheet The thickness ratio satisfies the above requirements. For example, the electrode assembly can be prepared by selecting a separator 3 with a suitable elongation rate that matches the above-mentioned ratio according to the thickness of the positive electrode sheet on the basis of the positive electrode sheet; A positive electrode sheet with a suitable thickness is used to prepare an electrode assembly.

The present application does not limit the preparation methods of the positive electrode sheet and the negative electrode sheet. In one embodiment, the positive electrode active material, the conductive agent, and the binder are added to the stirring tank according to a certain mass ratio, a certain proportion of NMP solution is added, and the positive electrode active slurry with a certain solid content is obtained by stirring, and the positive electrode active slurry is The material is coated on at least one functional surface of the positive electrode current collector 2, and then dried to remove the solvent in the positive electrode active slurry, and finally the rolling, cutting, and sheet-making processes are sequentially performed to obtain the positive electrode sheet.

In one embodiment, the negative electrode active material, conductive agent, and binder are added into the stirring tank according to a certain mass ratio, a certain proportion of deionized water is added, and the negative electrode active slurry with a certain solid content is obtained by stirring. The slurry is coated on at least one functional surface of the negative electrode current collector 4, and then dried to remove the moisture in the negative electrode active slurry, and finally the rolling, cutting, and sheet-making processes are sequentially performed to obtain the negative electrode sheet.

The electrode assembly of the present application takes the diaphragm 3 and the positive electrode sheet as objects, by making the elongation of the diaphragm 3 in the electrode assembly more match the thickness of the positive electrode sheet, that is, making the elongation of the diaphragm 3 in the longitudinal direction consistent with the thickness of the positive electrode sheet The thickness ratio is (0.9-3.7):1; the ratio of the elongation rate of the diaphragm in the width direction to the thickness of the positive electrode sheet is (0.9-3.7):1, so as to improve the safety performance of the lithium-ion battery. During the application of the lithium ion battery comprising the electrode assembly of the present application, when the electrode assembly is subject 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 can be reduced, and the probability of thermal runaway can be reduced , can make the lithium ion battery containing the electrode assembly of the present application have higher safety performance.

In some embodiments of the present application, in order to better improve the safety performance of lithium-ion batteries, the thickness of the positive electrode sheet is 60-120mm; and/or,

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

The elongation of the separator 3 in the width direction is 60-220%.

Further, when the ratio of the elongation rate of the diaphragm 3 in the length direction to the thickness of the positive electrode sheet is (1.2-3.7): 1; the ratio of the elongation rate of the diaphragm 3 in the width direction to the thickness of the positive electrode sheet is (1.2-3.7 ): 1. Lithium-ion batteries have higher safety performance.

In some embodiments of the present application, the elongation rate of the membrane 3 in the length direction is 100-220%; the elongation rate of the membrane 3 in the width direction is 100-220%.

In some embodiments of the present application, 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 can be understood that the diaphragm 3 of the present application can be obtained by providing a coating layer on any functional surface of the polyolefin porous diaphragm substrate, or by providing a coating layer on both functional surfaces of the polyolefin porous diaphragm substrate. get. Wherein, the elongation rate of the diaphragm 3 is mainly related to the elongation rate of the polyolefin porous diaphragm substrate.

In some embodiments of the present application, the polyolefin porous membrane substrate has a thickness of 1-20 μm.

In this application, if the thickness of the polyolefin porous diaphragm substrate is too thick, the excessively thick polyolefin porous diaphragm substrate will make the electrode assembly too thick, which is not conducive to the optimization of the energy density of lithium-ion batteries. If the polyolefin porous diaphragm substrate The thickness is too thin, and the polyolefin porous separator base material that is too thin is prone to damage during the long-term operation of the lithium-ion battery, which shortens the service life of the lithium-ion battery. In the present application, the thickness of the polyolefin porous separator substrate is 1-20 μm, and within this range, the lithium-ion battery can have good energy density and long service life.

In some embodiments of the present application, the porosity of the polyolefin porous separator substrate is 20-60%. Specifically, the polyolefin porous separator substrate meeting the above porosity can not only meet the electrical properties of the lithium-ion battery, but also help to improve the mechanical properties of the polyolefin porous separator substrate and prolong the service life of the lithium-ion battery.

In some embodiments of the present application, the air permeability of the polyolefin porous membrane substrate is 30-250 sec/100 cc.

In this application, the air permeability value of the polyolefin porous membrane substrate refers to the time required for 100 cc of air to pass through the polyolefin porous membrane 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, and the self-discharge of the lithium-ion battery is large. When the air permeability value of the polyolefin porous diaphragm substrate is too large, it is easy to make The internal resistance of the lithium-ion battery is too large, which affects the electrical performance of the lithium-ion battery. In the present application, when the air permeability of the polyolefin porous separator substrate is 30-250 sec/100 cc, the lithium-ion battery can have both good electrical performance and low self-discharge performance.

In some embodiments of the present application, 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 0.5-12 μm.

In some embodiments of the present application, the coating layer includes at least one of inorganic particles and polymers.

The inorganic particles of the present application can be selected from inorganic particles commonly used in the art, for example, can be selected from alumina, silicon dioxide, boehmite, zinc oxide, magnesium oxide, zirconium dioxide, titanium oxide, barium oxide, calcium oxide, At least one of aluminum nitride, titanium nitride, silicon nitride, boron nitride, aluminum hydroxide, magnesium hydroxide and barium sulfate.

The polymer of the present application can be selected from commonly used polymers in this field, for example, can be selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethyl cellulose, polyacrylate, polyacrylonitrile , polyvinyl alcohol, styrene-butadiene rubber, polyurethane, ethylene-acrylic acid copolymer, polymethyl methacrylate, polyimide, aramid, polystyrene and polyester.

In this application, if the coating layer only includes inorganic particles, it is called an inorganic coating layer; if the polymer only includes polymers, it is called an organic coating layer; if the coating layer includes both organic particles and polymers, it is called a composite coating layer. coating layer. The diaphragm of the present application can be obtained by setting 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 diaphragm substrate, or by The two functional surfaces of the material are provided with at least one of an inorganic coating layer, an organic coating layer and a composite coating layer.

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, the inorganic coating layer, the organic coating layer and the composite coating layer At least two of them can be stacked, and at least two of the inorganic coating layer, the organic coating layer and the composite coating layer can also be arranged side by side on the functional surface of the polyolefin porous membrane substrate. In addition, the present application does not specifically limit the order of stacked arrangements, nor does it specifically limit the order of parallel arrangements.

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

A second aspect of the present application provides a lithium ion battery, comprising the above-mentioned electrode assembly.

Put the above-mentioned electrode assembly in the outer packaging, after the top sealing and side sealing of the outer packaging, bake the water, inject the electrolyte into the outer packaging, and then go through the processes of vacuum packaging, standing, chemical formation and shaping in order to obtain lithium ion Battery.

The lithium-ion battery of the present application has more excellent safety performance because it includes the above-mentioned electrode assembly.

Hereinafter, the technical solutions of the present application will be described in conjunction with specific embodiments.

Example 1

The lithium-ion battery of this embodiment is prepared through the following steps:

1. Preparation of diaphragm

One functional surface of the polyolefin porous diaphragm substrate adopts gravure coating to set the alumina ceramic layer, and then adopts gravure coating to set the polyvinylidene fluoride (PVDF) glue layer on the other functional surface of the polyolefin porous diaphragm substrate, in The functional surface of the alumina ceramic layer away from the polyolefin porous diaphragm substrate is coated with a PVDF adhesive layer by gravure coating to obtain a diaphragm;

Among them, the thickness of the polyolefin porous diaphragm substrate is 5 μm, the porosity of the polyolefin porous diaphragm substrate is 32%, the air permeability value of the polyolefin porous diaphragm substrate is 145sec/100cc, the thickness of the alumina ceramic layer is 2 μm, PVDF The thickness of the adhesive layer is 1 μm, the elongation rate of the separator in the longitudinal direction is 180%, and the elongation rate of the separator in the width direction is 165%.

2. Preparation of positive electrode sheet

Add the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and the binder PVDF into the stirring tank according to the mass ratio of 97.2:1.5:1.3, then add the NMP solution, and fully stir to obtain the positive electrode active slurry. The slurry is respectively coated on the two functional surfaces of the aluminum foil of the positive electrode current collector, then dried to remove the solvent, and finally the positive electrode sheet is obtained by rolling, cutting and sheeting in sequence;

Wherein, the thickness of the positive electrode sheet is 90mm.

3. Preparation of negative electrode sheet

Add the negative electrode active material graphite, the conductive agent acetylene black, and the binder carboxymethylcellulose sodium into the stirring tank according to the mass ratio of 97:1.5:1.5, then add deionized water, and obtain the negative electrode active slurry after thorough stirring. The negative electrode active slurry is respectively coated on the two functional surfaces of the copper foil of the negative electrode current collector, then dried to remove water, and finally the rolling, cutting and sheet-making processes are sequentially carried out to obtain the negative electrode sheet.

4. Preparation of electrode assembly

The separator obtained in step 1, the positive electrode sheet obtained in step 2, and the negative electrode sheet obtained in step 3 are stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain an electrode assembly;

Among them, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 2:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.83:1.

5. Preparation of Li-ion battery

Place the electrode assembly obtained in step 4 in the aluminum-plastic film of the outer packaging. After the aluminum-plastic film is top-sealed and side-sealed, the moisture is removed by baking, and the electrolyte is injected into the outer packaging. Formation and shaping to obtain lithium-ion batteries;

Among them, the electrolyte solution is prepared by the following steps: in a glove box filled with argon (H ₂ O<0.1ppm, O ₂ <0.1ppm), ethylene carbonate (EC), propylene carbonate (PC), dicarbonate Mix ethyl ester (DEC) and n-propyl propionate evenly, then add 1.2mol/L fully dry lithium hexafluorophosphate (LiPF ₆ ) to it, dissolve in non-aqueous organic solvent, stir evenly, and pass the test of moisture and free acid After that, the basic electrolyte is obtained.

In step 1 of this embodiment, the elongation rate of the diaphragm in the length direction and the elongation rate of the diaphragm in the width direction are obtained by a method test comprising the following steps:

Cut the diaphragm into a rectangular spline with a width of 1.5 cm and a length greater than 5 cm. The extension direction of the long side of the spline is consistent with the length direction of the diaphragm 3, so that the edge of the spline is smooth without gaps (to prevent defects from affecting the test results). Clamp the above-mentioned spline between the upper and lower clamps of the universal tensile machine. The long axis of the spline coincides with the center line of the clamp. The distance between the upper and lower clamps of the tensile machine is the specified distance of the diaphragm, and the specified distance in the direction of the diaphragm length is 5cm. Under the tensile test speed of 100mm/min, stretch the spline along the length direction of the spline until the diaphragm ruptures, obtain the increase of the specified distance of the diaphragm in the length direction, and calculate the elongation rate of the diaphragm in the length direction.

The test method for the elongation of the diaphragm in the width direction is basically the same as the test method for the elongation in the length direction, the only difference is that the extension direction of the long side of the spline is consistent with the width direction of the diaphragm 3 .

Example 2

The difference between the preparation steps of the lithium-ion battery of this embodiment and the preparation steps of the lithium-ion battery of Example 1 is:

In step 1, the two functional surfaces of the polyolefin porous diaphragm substrate are provided with an alumina ceramic layer by gravure coating, and the PVDF adhesive layer is respectively arranged on the functional surface of the alumina ceramic layer far away from the polyolefin porous diaphragm substrate by gravure coating , to obtain the diaphragm.

In this embodiment, the elongation rate of the separator in the longitudinal direction, the elongation rate of the separator in the width direction, and the thickness of the positive electrode sheet are the same as those in Embodiment 1.

In step 1 of this embodiment, the test methods for the elongation rate of the membrane in the length direction and the elongation rate of the membrane in the width direction are the same as those in Example 1.

Example 3

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

Wherein, the thickness of the coating layer is 4 μm, and the mass ratio of alumina to PVDF is 9:1.

Example 4

In step 1, a polyolefin porous diaphragm base material different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 105%, and the elongation rate of the diaphragm in the width direction is 95%;

In step 2, the thickness of the positive electrode sheet is 75 mm.

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 1.4:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.27:1.

Example 5

The difference between the preparation steps of the lithium ion battery of this embodiment and the preparation steps of the lithium ion battery of embodiment 2 is:

In step 1, a polyolefin porous membrane substrate different from that in Example 2 was used, wherein the thickness of the polyolefin porous membrane substrate was 7 μm, and the elongation of the membrane in the width direction was 175%.

In this embodiment, the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.94:1.

In this embodiment, the elongation rate of the separator in the longitudinal direction and the thickness of the positive electrode sheet are the same as those in Embodiment 2.

In step 1 of this embodiment, the test methods for the elongation rate of the diaphragm in the length direction and the elongation rate of the diaphragm in the width direction are the same as those in embodiment 2.

Example 6

In step 1, the porosity and gas permeability value of the polyolefin porous diaphragm substrate different from that in Example 1 are used, wherein the porosity of the polyolefin porous diaphragm substrate is 39%, and the gas permeability value of the polyolefin porous diaphragm substrate is 105sec/100cc.

In this embodiment, the elongation rate of the separator in the longitudinal direction and the thickness of the positive electrode sheet are the same as those in Embodiment 1.

Example 7

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 180%, and the elongation rate of the diaphragm in the width direction is 180%;

In step 2, the thickness of the positive electrode sheet is 60 mm.

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

Example 8

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 110%, and the elongation rate of the diaphragm in the width direction is 110%;

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 1.2:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.2:1.

Example 9

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 81%, and the elongation rate of the diaphragm in the width direction is 81%;

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 0.9:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 0.9:1.

Example 10

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 220%, and the elongation rate of the diaphragm in the width direction is 220%;

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 3.7:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 3.67:1.

Example 11

In step 2, the thickness of the positive electrode sheet is 120mm;

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

Example 12

The difference between the preparation steps of the lithium-ion battery of this embodiment and the preparation steps of the lithium-ion battery of Example 7 is:

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 7 is used, so that the elongation rate of the diaphragm in the length direction is 60%, and the elongation rate of the diaphragm in the width direction is 60%;

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 1:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1:1.

In step 1 of this embodiment, the test methods for the elongation rate of the diaphragm in the length direction and the elongation rate of the diaphragm in the width direction are the same as those in embodiment 7.

Example 13

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 2.44:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 2.44:1.

Example 14

The difference between the preparation steps of the lithium ion battery of the present embodiment and the preparation steps of the lithium ion battery of embodiment 1 is:

In step 1, the polyolefin porous diaphragm base material whose elongation rate is different from that in Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 100%, and the elongation rate of the diaphragm in the width direction is 100%;

In step 2, the thickness of the positive electrode sheet is 80mm;

In this embodiment, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 1.25:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 1.25:1.

Comparative example 1

The difference between the preparation steps of the lithium-ion battery of this comparative example and the preparation steps of the lithium-ion battery of Example 1 is:

In step 1, a polyolefin porous diaphragm base material different from that of Example 1 is used, so that the elongation of the diaphragm in the length direction is 58%, and the elongation of the diaphragm in the width direction is 62%;

In this comparative example, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 0.64:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 0.69:1.

In this comparative example, the thickness of the positive electrode sheet is the same as that of Example 1.

In step 1 of this comparative example, the test methods for the elongation rate of the diaphragm in the length direction and the elongation rate of the diaphragm in the width direction are the same as those in Example 1.

Comparative example 2

In step 1, a polyolefin porous diaphragm base material different from that of Example 1 is used, so that the elongation rate of the diaphragm in the length direction is 92%, and the elongation rate of the diaphragm in the width direction is 89%;

The thickness of the positive electrode sheet in step 2 is 120mm.

In this comparative example, the ratio of the elongation rate of the separator in the longitudinal direction to the thickness of the positive electrode sheet is 0.77:1, and the ratio of the elongation rate of the separator in the width direction to the thickness of the positive electrode sheet is 0.74:1.

Acupuncture performance test

The lithium-ion batteries in the examples and comparative examples are charged according to the standard charge-discharge mode. After fully charged, the lithium-ion batteries are subjected to acupuncture testing. Use a steel needle with a diameter of 3mm to place the lithium-ion battery on a horizontal plane. The speed of /s passes through the center of the lithium-ion battery and remains in the lithium-ion battery for 10 minutes. If the lithium-ion battery does not catch fire or explode, it is considered to pass the test. 100 lithium-ion batteries of each example and comparative example were tested, and the pass rate of acupuncture was calculated. The test results are shown in Table 1.

Fig. 3 is a schematic diagram of a lithium-ion battery acupuncture test. As shown in Figure 3, when performing acupuncture tests on lithium-ion batteries, steel needles pass through negative electrode active layer 1, negative electrode current collector 4, negative electrode active layer 1, separator 3, positive electrode active layer 5, and positive electrode current collector 2 in sequence. When a short circuit occurs in the ion battery, the internal current temperature of the ion battery will rise, which will cause the lithium ion battery to catch fire, indicating that the acupuncture test result of the lithium ion battery is not passed.

Table 1

项目project	针刺通过率/％Acupuncture pass rate/%
实施例1Example 1	95/10095/100
实施例2Example 2	99/10099/100
实施例3Example 3	91/10091/100
实施例4Example 4	87/10087/100
实施例5Example 5	100/100100/100
实施例6Example 6	94/10094/100
实施例7Example 7	100/100100/100
实施例8Example 8	83/10083/100
实施例9Example 9	69/10069/100
实施例10Example 10	100/100100/100
实施例11Example 11	89/10089/100
实施例12Example 12	75/10075/100
实施例13Example 13	100/100100/100
实施例14Example 14	85/10085/100

对比例1Comparative example 1	19/10019/100
对比例2Comparative example 2	27/10027/100

It can be seen from Table 1 that the electrode assembly of the present application is used in lithium ion batteries, which can improve the safety performance of lithium ion batteries. It is proved that by matching the elongation rate of the separator in the electrode assembly and the thickness of the positive sheet, the generation of short circuit points between the positive and negative electrodes can be reduced during the acupuncture test, and the heat generated by the short circuit can be effectively reduced, thereby improving the safety performance of the battery.

Further, it can be seen from Examples 1-8, 10-11, and 13-14 that when 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 separator in the width direction The ratio of the elongation rate on the surface to the thickness of the positive electrode sheet is (1.2-3.7): 1. The lithium-ion battery has better safety performance, and the acupuncture pass rate is greater than or equal to 83%.

Each embodiment in this specification is described in a related manner, the same and similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments. The above are only preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application are included within the protection scope of this application.

Claims

An electrode assembly, including a positive electrode sheet, a negative electrode sheet, and a separator, and the separator is arranged between the positive electrode sheet and the negative electrode sheet;

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

The ratio of the elongation 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 according to claim 1, wherein the thickness of the positive electrode sheet is 60-120 mm; and/or,

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

The elongation of the separator in the width direction is 60-220%.
The electrode assembly according to claim 1 or 2, wherein the ratio of the elongation of the separator in the longitudinal direction to the thickness of the positive electrode sheet is (1.2-3.7): 1;

The ratio of the extensibility of the separator in the width direction to the thickness of the positive electrode sheet is (1.2-3.7):1.
The electrode assembly according to claim 3, wherein the elongation of the separator in the length direction is 100-220%;

The elongation of the separator in the width direction is 100-220%.
The electrode assembly according to any one of claims 1-4, wherein the separator comprises a polyolefin porous membrane substrate and a coating layer provided on at least one functional surface of the polyolefin porous membrane substrate.
The electrode assembly according to claim 5, wherein the thickness of the polyolefin porous separator substrate is 1-20 μm; and/or,

The porosity of the polyolefin porous diaphragm substrate is 20-60%.
The electrode assembly according to any one of claims 5-6, wherein the gas permeability of the polyolefin porous separator substrate is 30-250sec/100cc.
The electrode assembly according to any one of claims 5-7, wherein the coating layer has a thickness of 0.5-12 μm.
The electrode assembly according to any one of claims 5-8, wherein the coating layer comprises at least one of inorganic particles and polymers.
A lithium ion battery, wherein, comprising the electrode assembly described in any one of claims 1-9.