阅读说明：本技术 一种复合膨胀膜及其制备方法和应用 (Composite expansion membrane and preparation method and application thereof ) 是由 梁玉典 刘荣江 黄德怀 黄彬彬 祝媛 刘金成 刘建华 于 2020-12-17 设计创作，主要内容包括：本发明提供一种复合膨胀膜及其制备方法和应用,所述复合膨胀膜包括依次设置的基层、第一粘合层、耐温层和第二粘合层；所述基层的材料包括聚苯乙烯,所述耐温层的材料为热膨胀系数不大于6×10～(-6)/K的材料；所述复合膨胀膜通过设置具有较好膨胀效果的材料作为基层,并搭配具有热膨胀系数较小的材料作为耐温层,使得所述复合膨胀膜在具有优异膨胀性能的同时还具有很好的耐温效果,可以保证所述复合膨胀膜在90℃高温烘烤时膜宽不会变化,进而避免了因膜宽收缩引起的金属集流体暴露的问题,降低了使用风险。(The invention provides a composite expansion film and a preparation method and application thereof, wherein the composite expansion film comprises a base layer, a first bonding layer, a temperature-resistant layer and a second bonding layer which are sequentially arranged; the material of the base layer comprises polystyrene, and the material of the temperature-resistant layer has a thermal expansion coefficient not greater than 6 x 10 ‑6 A material of/K; the composite expansion film is characterized in that a material with a good expansion effect is arranged as a base layer, and a material with a small thermal expansion coefficient is matched as a temperature-resistant layer, so that the composite expansion film has a good temperature-resistant effect while having excellent expansion performance, and can ensure that the composite expansion film has a good temperature-resistant effectThe film width of the composite expansion film can not change when the composite expansion film is baked at the high temperature of 90 ℃, so that the problem of exposure of a metal current collector caused by film width shrinkage is avoided, and the use risk is reduced.)

1. The composite expansion film is characterized by comprising a base layer, a first bonding layer, a temperature-resistant layer and a second bonding layer which are sequentially arranged;

the material of the base layerThe material comprises polystyrene, and the material of the temperature resistant layer has a thermal expansion coefficient not greater than 6 x 10^-6The material of/K.

2. The composite intumescent film of claim 1, wherein said base layer has a thickness of 35 to 70 μm.

3. The composite intumescent film of claim 1 or 2, wherein the thickness of said first and second adhesive layers is each independently 2 to 6 μ ι η;

preferably, the materials of the first adhesive layer and the second adhesive layer are polyacrylate slurry independently;

preferably, the polyacrylate syrup comprises a combination of polyacrylate and a curing agent;

preferably, the mass ratio of the curing agent to the polyacrylate is 1 (46-98);

preferably, the polyacrylate paste further comprises a color paste;

preferably, the mass ratio of the color paste to the polyacrylate is 1 (97-200).

4. The composite intumescent film of any of claims 1 to 3, wherein said temperature resistant layer has a thickness of 6 to 12 μm;

preferably, the material of the temperature-resistant layer comprises polyethylene terephthalate and/or polyimide.

5. A method for preparing the composite expanded membrane according to any one of claims 1 to 4, comprising the steps of:

(1) respectively coating the material of the first bonding layer and the material of the second bonding layer on two surfaces of the temperature-resistant layer, drying and rolling to obtain bonding expansion films;

(2) and (2) attaching a base layer to the first bonding layer of the bonding expansion film obtained in the step (1), and rolling to obtain the composite expansion film.

6. The method according to claim 5, wherein the drying temperature in step (1) is 80 to 90 ℃ independently;

preferably, the drying time in the step (1) is 0.5-2 min independently.

7. The manufacturing method according to claim 5 or 6, wherein the temperature of the rolling in the step (2) is 20 to 30 ℃;

preferably, the rolling pressure of the step (1) and the rolling pressure of the step (2) are respectively and independently 0.2-1.2 MPa;

preferably, the rolling in step (1) and step (2) is carried out under the condition of protecting release paper, and the release paper is pulled out after the rolling is finished.

8. The production method according to any one of claims 5 to 7, characterized by further comprising a step of aging treatment after the rolling in step (2);

preferably, the temperature of the aging treatment is 20-30 ℃;

preferably, the aging treatment time is 12-96 h.

9. The method according to any one of claims 5 to 8, characterized by comprising the steps of:

(1) respectively coating the material of the first bonding layer and the material of the second bonding layer on two surfaces of the temperature-resistant layer, drying at 85-90 ℃ for 0.5-2 min, rolling under the pressure of 0.2-1.2 MPa and under the protection of release paper, and removing the release paper to obtain an adhesive expansion film;

(2) and (2) attaching an expansion layer to the first bonding layer of the bonding expansion film obtained in the step (1), rolling under the pressure of 0.2-1.2 MPa and under the protection of release paper, taking out the release paper, and carrying out aging treatment at the temperature of 20-30 ℃ for 12-96 hours to obtain the composite expansion film.

10. Use of a composite intumescent film as claimed in any of claims 1 to 4 in a lithium ion battery;

preferably, the lithium ion battery is a cylindrical steel shell type lithium ion battery.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite expansion membrane and a preparation method and application thereof.

Background

The cylindrical steel shell type lithium ion battery is often assembled in various different devices, and the phenomenon of frequent and repeated vibration and shaking exists when an end user operates the device; because the lithium battery bears active materials, has a certain dead weight, and is connected with the shell in a welding way through the metal conductive lead fluid to conduct electricity, in the using process, the metal conductive lead fluid is broken along with the increase of the vibration shaking times, and the battery fails, thereby further causing great potential safety hazard.

In order to solve the problems, a series of organic material base films are usually adhered to the surface of a winding core, and the organic base films can be expanded to 150-180% of the original thickness after being soaked in electrolyte containing organic solvents such as lipids and the like, so that gaps between the winding core and a steel shell can be filled, the effect of resisting vibration and shaking of the cylindrical steel shell lithium ion battery is enhanced, and a lot of reports are provided on the organic base films with expandable thicknesses. CN207330823U discloses an acrylic ester inflation sticky tape, including three layer construction, be antiseized layer, substrate layer and glue film in proper order, antiseized layer surface frosting is handled, the substrate layer is the polystyrene substrate, the glue film is glued for acrylic ester, provides a expansibility height, and is corrosion-resistant, and viscidity is strong, can not take place the acrylic ester inflation sticky tape that reacts with electrolyte, fixed battery that can be better. CN107746682A discloses a method for manufacturing an acrylate expansion adhesive tape, which comprises the following steps: treating a base material layer: the base material layer is a polystyrene base material, and one surface of the polystyrene base material is subjected to frosting treatment; glue line treatment: the adhesive layer adopts acrylic ester glue, the acrylic ester glue is coated on the double-sided release film, and then the double-sided release film is dried at high temperature; gluing the glue layer with the substrate layer: and (3) attaching the dried acrylate glue to the other surface of the polystyrene substrate, and rewinding to tear the double-sided release film. CN109294463A discloses a fire-retardant inflation double-sided tape, from top to bottom include first compound acrylic acid glue film in proper order, fire-retardant polystyrene synthetic resin layer, second compound acrylic acid glue film and two-sided release rete, the fire-retardant inflation double-sided tape who obtains has the viscidity height, the strong characteristics of fixity, consequently can be fixed electric core and shell firmly, the sticky tape has electrolyte-resistant characteristic simultaneously can not influence electrolyte composition and can not influence battery performance, and the sticky tape inflation multiple exceeds 3 times, can be better fill the equipment clearance, reach the possibility that reduces the vibration displacement, consequently, good security has.

The expansion films obtained in the patent have good expansion effect, the risk of fracture of the metal drainage body can be reduced, but the base films with good expansion effect can be subjected to shrinkage deformation after being baked at 45-60 ℃; therefore, when the expansion film is applied to the lithium ion battery, the winding core pasted with the expansion film is baked at the high temperature of 80-90 ℃, the film width of the expansion film is reduced due to shrinkage, electrolyte in the winding core of the lithium ion battery flows outwards, and the problem that products are unqualified is caused, and even potential safety hazards are caused.

Therefore, the development of the composite expansion film with high temperature resistance and high expansion performance has important significance.

Disclosure of Invention

In view of the disadvantages of the prior art, the present invention provides a composite expansion film, a method for preparing the same and application thereof, wherein the composite expansion film is prepared by arranging a base layer made of a high expansion rate material and has a thermal expansion coefficient not greater than 6 x 10^-6The temperature-resistant layer made of the material of/K ensures that the width of the composite expansion membrane is not affected after the composite expansion membrane resists high temperature, has excellent expansion performance, can be applied to a lithium ion battery, solves the problems of easy breakage of a metal drainage body of the lithium ion battery and outflow of electrolyte, and has important significance.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a composite intumescent film comprising a base layer, a first adhesive layer, a temperature resistant layer, and a second adhesive layer, which are sequentially disposed;

the material of the base layer comprises polystyrene, and the material of the temperature-resistant layer has a thermal expansion coefficient not greater than 6 x 10^-6Materials with a/K coefficient of thermal expansion of, for example, 5X 10^-6/K、4×10^-6/K、3×10^-6/K、2×10^-6Or 1X 10^-6K, and the specific values between the aforementioned values, are limited by space and for the sake of brevity and are not intended to be an exhaustive list of the specific values included in the stated ranges.

The schematic cross-sectional structure of the composite expansion membrane provided by the invention is shown in fig. 1, wherein 1 represents a base layer, the material of the base layer 1 comprises polystyrene, the thickness of the polystyrene material after being soaked in electrolyte can be increased to 300-400 times of that before being soaked, the polystyrene material has good expansion performance, but the composite expansion membrane is not high-temperature resistant, and is easy to shrink at high temperature; 2 represents a first adhesive layer, 3 represents a temperature resistant layer, the temperature resistant layer 3 and the base layer 1 are connected together by the first adhesive layer 2, and the material selection thermal expansion coefficient of the temperature resistant layer 3 is less than 6 multiplied by 10^-6The material is almost free from any deformation after being baked at a high temperature of 80-90 ℃, so that the high-temperature resistance of the composite expansion film is ensured; through the arrangement of the base layer 1 and the temperature-resistant layer 3, the composite expansion film has excellent temperature resistance and higher expansibility, so that the conditions that a metal drainage body is broken and a battery fails when the composite expansion film is applied to a lithium ion battery along with the increase of vibration and shaking times are reduced, and the electrolyte in a lithium ion battery roll core flows out due to film shrinkage at high temperature can not be caused; 4 represents a second adhesive layer, the second adhesive layer 4 mayAnd the composite expansion film is well bonded on the outer side of the lithium ion battery roll core.

Preferably, the thickness of the base layer is 35 to 70 μm, such as 37 μm, 41 μm, 45 μm, 48 μm, 52 μm, 56 μm, 59 μm, 63 μm, 65 μm or 69 μm, and the specific values therebetween are not exhaustive, and are not included in the scope of the present invention for brevity and conciseness.

Preferably, the thickness of the first adhesive layer and the second adhesive layer is 2 to 6 μm, such as 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or 5.5 μm, and the specific values therebetween are not exhaustive, and the invention is not limited to the specific values included in the range for brevity and conciseness.

Preferably, the material of the first adhesive layer and the second adhesive layer is polyacrylate paste independently.

Preferably, the polyacrylate syrup comprises a combination of polyacrylate and curing agent.

Preferably, the mass ratio of the curing agent to the polyacrylate is 1 (46-98), such as 1:49, 1:53, 1:59, 1:62, 1:66, 1:70, 1:75, 1:80, or 1: 85.

Preferably, the polyacrylate paste further comprises a color paste.

Preferably, the mass ratio of the color paste to the acrylate is 1 (97-200), such as 1:100, 1:110, 1:130, 1:140, 1:150, 1:160, 1:170, 1:180, 1:190, 1:192, 1:196, 1:197, or 1:199, etc.

Preferably, the thickness of the temperature-resistant layer is 6 to 12 μm, such as 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm or 11 μm, and the specific values therebetween are limited by space and for the sake of brevity, and the present invention is not exhaustive of the specific values included in the range.

Preferably, the material of the temperature-resistant layer comprises polyethylene terephthalate and/or polyimide.

In a second aspect, the present invention provides a method for preparing a composite expanded membrane according to the first aspect, the method comprising the steps of:

(1) respectively coating the material of the first bonding layer and the material of the second bonding layer on two surfaces of the temperature-resistant layer, drying and rolling to obtain bonding expansion films;

(2) and (2) attaching a base layer to the first bonding layer of the bonding expansion film obtained in the step (1), and rolling to obtain the composite expansion film.

Preferably, the drying temperature in step (1) is 80-90 ℃, such as 80 ℃, 81 ℃, 82 ℃, 83 ℃, 84 ℃, 85 ℃, 86 ℃, 87 ℃, 88 ℃ or 89 ℃, and the specific values therebetween are not exhaustive for the sake of brevity and simplicity.

Preferably, the drying time in step (1) is 0.5-2 min, such as 0.6min, 0.7min, 0.8min, 0.9min, 1min, 1.2min, 1.4min, 1.6min or 1.8min, and the specific values therebetween are not exhaustive, and for brevity and clarity, the invention is not exhaustive. Preferably, the rolling temperature in step (2) is 20-30 ℃, for example, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃ or 29 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive of the specific values included in the range.

Preferably, the rolling pressure of step (1) and step (2) is 0.2 to 1.2MPa, such as 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1MPa or 1.1MPa, and specific values therebetween are not exhaustive, and for the sake of brevity, the invention is not intended to be exhaustive of the specific values included in the ranges.

Preferably, the rolling in step (1) and step (2) is carried out under the condition of protecting release paper, and the release paper is pulled out after the rolling is finished.

Preferably, the method further comprises a step of aging treatment after the rolling in the step (3) is finished.

Preferably, the temperature of the aging treatment is 20 to 30 ℃, for example, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃ or 29 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive of the specific values included in the range. Preferably, the aging time is 12-96 h, such as 20h, 30h, 40h, 50h, 60h, 70h, 80h or 85h, and the specific values therebetween are limited by space and for brevity, and the invention is not exhaustive of the specific values included in the range.

As a preferred technical scheme, the preparation method comprises the following steps:

(1) respectively coating the material of the first bonding layer and the material of the second bonding layer on two surfaces of the temperature-resistant layer, drying at 85-90 ℃ for 0.5-2 min, rolling under the pressure of 0.2-1.2 MPa and under the protection of release paper, and removing the release paper to obtain an adhesive expansion film;

(2) and (2) attaching an expansion layer to the first bonding layer of the bonding expansion film obtained in the step (1), rolling under the pressure of 0.2-1.2 MPa and under the protection of release paper, taking out the release paper, and carrying out aging treatment at the temperature of 20-30 ℃ for 12-96 hours to obtain the composite expansion film.

In a third aspect, the present invention provides a use of the composite expanded membrane according to the first aspect in a lithium ion battery.

Preferably, the lithium ion battery is a cylindrical steel shell type lithium ion battery.

Compared with the prior art, the invention has the following beneficial effects:

according to the composite expansion film provided by the invention, the material with a good expansion effect is used as the base layer, and the material with a small thermal expansion coefficient is matched as the temperature-resistant layer, so that the composite expansion film has excellent expansion performance, the thickness change before and after the electrolyte is soaked is 87.5-137.5, and therefore, the gap between the battery core and the shell can be filled after the expansion, and the anti-vibration and shaking stability of the battery can be improved through a severe roller test.

The composite expansion film also has a good temperature-resistant effect, does not shrink at high temperature of 90 ℃, and hardly changes in width, so that the composite expansion film can be ensured that the film width does not change when being baked at high temperature, and therefore when the composite expansion film is applied to a lithium ion battery, the risk of exposure of a metal current collector caused by film width shrinkage is avoided, and the use risk is reduced.

Drawings

Fig. 1 is a schematic cross-sectional structure diagram of the composite intumescent film provided by the invention, wherein 1 is a base layer, 2 is a first adhesive layer, 3 is a temperature-resistant layer, and 4 is a second adhesive layer.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

A composite expansion film comprising a base layer (polystyrene (OPS of 45 μm, DuPont Hongkun film Co., Ltd.) having a thickness of 45 μm), a first adhesive layer (polyacrylate paste obtained by mixing a color paste (Rido electric Co., Ltd., Phthalocyanine blue) having a thickness of 3 μm, a curing agent (BR-20 SE, Taiwan Changchun chemical Co., Ltd.) and an acrylic ester (acrylic adhesive for Rido electric Co., Ltd., adhesive tape)) having a mass ratio of 1:2:4, a temperature-resistant layer (polyethylene terephthalate (PET of 8 μm, DuPont Hongkun film Co., Ltd., PET of 8 μm) having a thickness of 8 μm, and a thermal expansion coefficient of 6X 10^-6K) and a second adhesive layer having a thickness of 3 μm (a polyacrylate paste obtained by mixing a color paste (zeto electrical corporation, phthalocyanine blue) having a mass ratio of 1:2:4, a curing agent (taiwan vinpocetine chemical limited, BR-20SE), and an acrylate (zeto electrical corporation, acryl glue for tape);

the preparation method comprises the following steps:

(1) respectively coating polymethyl acrylate slurry on two surfaces of a temperature-resistant layer, drying at 85 ℃ for 1min, rolling under the pressure of 1MPa and under the protection of release paper (Sichuan feather seal new material Co., Ltd., 20 mu m monocrystalline silicon PET film), and removing the release paper to obtain an adhesive expansion film;

(2) and (2) attaching an expansion layer to the first bonding layer of the bonding expansion film obtained in the step (1), rolling under the pressure of 1MPa and under the protection of release paper, taking out the release paper, and carrying out aging treatment at 25 ℃ for 24 hours to obtain the composite expansion film.

Example 2

A composite expansion film comprising a base layer (polystyrene (OPS of 45 μm, DuPont Hongkun film Co., Ltd.) having a thickness of 35 μm, a first adhesive layer (polyacrylate paste obtained by mixing a color paste (Rido electric Co., Ltd., Phthalocyanine blue) having a mass ratio of 1:3: 6), a curing agent (BR-20 SE, Taiwan Changchun chemical Co., Ltd.) and an acrylic ester (acrylic adhesive for tape Co., Ltd.), a temperature-resistant layer (polyimide (PI film of 12 μm, DuPont Hongkun film Co., Ltd.) having a thickness of 6 μm), and a thermal expansion coefficient of 3X 10^-6K) and a second adhesive layer having a thickness of 2 μm (polyacrylate paste obtained by mixing a color paste (zeto electrical corporation, phthalocyanine blue) having a mass ratio of 1:3:6, a curing agent (taiwan vinpocetine chemical limited, BR-20SE), and an acrylate (zeto electrical corporation, acryl glue for tape);

the preparation method is the same as that of example 1.

Example 3

A composite expansion film comprising a base layer (polystyrene (OPS 55 μm, DuPont Corp.) of 55 μm thickness) of 55 μm, a first adhesive layer (polyacrylate paste obtained by mixing a color paste (Nindon electric Co., Ltd., Phthalocyanine blue) of 1:2:4, a curing agent (BR-20 SE, Taiwan Changchun chemical Co., Ltd.) and an acrylic ester (acrylic adhesive for adhesive tape, Nindon electric Co., Ltd.) of 6: 2:4 by mass), a temperature-resistant layer (polyethylene terephthalate (Nindon electric Co., Ltd., acrylic adhesive for adhesive tape) of 12 μm thickness, and a thermal expansion coefficient of 6 × 10^-6K) and a second adhesive layer having a thickness of 6 μm (polyacrylate paste obtained by mixing a color paste (zeto electrical corporation, phthalocyanine blue) having a mass ratio of 1:2:4, a curing agent (taiwan vinpocetine chemical limited, BR-20SE), and an acrylate (zeto electrical corporation, acryl glue for tape);

the preparation method is the same as that of example 1.

Comparative example 1

An expanded film which is different in structure from example 1 in that a temperature-resistant layer and a second adhesive layer are not included, and the other structure and material are the same as those of example 1;

the preparation method comprises the following steps: coating polymethyl acrylate slurry on the surface of a base layer, drying at 45 ℃ for 2h, rolling under the pressure of 1MPa and the protection condition of release paper (Sichuan feather seal new material Co., Ltd., 20 mu m monocrystalline silicon PET film), and extracting the release paper to obtain the expansion film.

Comparative example 2

A temperature-resistant film whose structure differs from that of example 1 in that a base layer and a first adhesive layer are not included, and the other structure and material are the same as those of example 1;

the preparation method comprises the following steps: coating the polymethyl acrylate slurry on the surface of a temperature-resistant layer, drying at 85 ℃ for 1min, rolling under the pressure of 1MPa and the protection condition of release paper (Sichuan feather seal new material Co., Ltd., 20 mu m monocrystalline silicon PET release film), and drawing away the release paper to obtain the temperature-resistant film.

Application examples 1 to 3

A cylindrical lithium ion battery with a steel case comprising the composite expansion film obtained in examples 1 to 3 and a roll core (Huizhou Yi latitude lithium energy Co., Ltd., 18650)

The preparation method comprises the following steps:

(1) the positive electrode coating area is coated with a positive electrode active material, and the positive electrode blank spot welding area is coated with a positive electrode active material; the negative pole piece is provided with a negative pole coating area coated with a negative pole active material and a negative pole blank spot welding area, and a positive pole lug is welded and connected with the positive pole blank spot welding area; the positive pole piece and the negative pole piece are separated by a diaphragm and are wound to form a wound body in a winding mode, a positive blank spot welding area is located at the end portion, close to the center of the wound body, of the positive pole piece, a negative blank spot welding area is located at the tail end portion, close to the outer surrounding ring of the wound body, of the negative pole piece, positive lugs and negative lugs are respectively arranged at two ends of the wound body, and most of cylindrical winding needles of the wound body are arranged;

(2) the barrel-shaped opening hard shell is made of SU305 steel, copper alloy, copper nickel plating, steel nickel plating and the like, and the combination cap is assembled by a sealing ring, a PTC, an explosion-proof sheet and a top cover. And (3) placing the insulating ring with the round hole, bending the negative pole lug, fixing the insulating ring, placing the negative pole lug end of the winding body into the steel shell, inserting a welding needle made of tungsten steel, copper and the like into the center of the winding body, and welding and conducting the negative pole lug and the bottom of the hard shell by using a welding machine through resistance welding equipment. And (3) punching a groove at the opening end of the hard shell, penetrating the positive lug into an insulating ring with a plurality of small holes and a positive lug hole, welding the conduction of the positive lug and the combined cap by using laser welding, resistance welding, ultrasonic welding and other modes, placing the combined cap into a groove position of the shell after welding, punching an opening of the hard shell by using a die, and closing up the edge inwards to fix the combined cap to obtain the cylindrical steel shell lithium ion battery.

Comparative application example 1

A cylindrical steel-shell lithium ion battery comprising the expanded film obtained in comparative example 1 and a winding core (promo lithium energy corporation, 18650); the preparation method is the same as in application example 1.

Comparative application example 2

A cylindrical steel-shell lithium ion battery comprising the temperature-resistant film obtained in comparative example 2 and a winding core (promo li latitude li energy corporation, 18650); the preparation method is the same as in application example 1.

And (3) performance testing:

(1) thickness variation: the obtained high-temperature-resistant composite expanded film was immersed in an electrolyte (containing ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a mass ratio of 1:1:1, and 1mol/L of lithium hexafluorophosphate) at 45 ℃ for 12 hours, and the change in the thickness direction was measured to obtain the expansion ratio.

(2) Width variation at 90 ℃: the obtained high temperature resistant composite expanded film was left at 90 ℃ for 16 hours, and the change in width thereof was tested.

(3) Failure times are as follows: and testing the 8m drop internal resistance value of the cylindrical steel shell lithium ion battery by using a resistance tester (HIOKI, BT35627), disassembling and analyzing whether the current collector is broken when the internal resistance is greater than 20%, judging that the current collector is failed when the current collector is broken, and counting the drop test times corresponding to 2% failure.

Testing the composite expansion film provided in examples 1-3, the expansion film provided in comparative example 1 and the temperature-resistant film provided in comparative example 2 according to the above test methods (1) and (2); the lithium ion batteries provided by application examples 1-3 and comparative application examples 1 and 2 are tested according to the test method (3), and the test results are shown in table 1:

TABLE 1

As can be seen from the data in table 1: the composite expansion film provided by the invention has excellent expansion rate and high-temperature resistance stability.

Specifically, the thickness of the composite expansion film provided in examples 1 to 3 before and after the electrolyte immersion was changed to 87.5 to 137.5, and the width of the composite expansion film was almost unchanged after the composite expansion film was placed at 90 ℃ for 16 hours; whereas the expanded film provided in comparative example 1 was reduced in width shrinkage by 60% after being left at 90 ℃ for 16 hours, the temperature-resistant film provided in comparative example 2 hardly suffered any expansion.

The cylindrical steel shell lithium ion batteries provided by application examples 1-3 and comparative application examples 1-2 are tested according to the test method (3), and test results are shown in table 2:

TABLE 2

	Medicine for treating chronic hepatitis BEffect of (1)2% ofFalling downFall offNext timeNumber (times) )
		Applications ofExample (b) 1	190
Applications ofExample (b) 2	145
		Applications ofExample (b) 3	210
Comparison ofApplications ofExample (b) 1	Harvesting machineAfter shrinking it cannotEquipment andnote thatLiquid for treating urinary tract infection
		Comparison ofApplications ofExample (b) 2	25

According to data in table 2, it can be seen that the cylindrical steel shell lithium ion battery provided in application examples 1 to 3 has a 2% failure drop frequency of 145 to 210 times, and compared with the cylindrical steel shell lithium ion battery obtained by applying the temperature-resistant film provided in comparative example 2 (compare with application example 2), the 2% failure drop frequency is improved by 480 to 740%, and the cylindrical steel shell lithium ion battery prepared by applying the expansion film obtained in application example 2 cannot be equipped and injected with liquid after being contracted.

The applicant states that the present invention is illustrated by the above examples to describe a composite expanded membrane and the process for its preparation and use, but the present invention is not limited to the above process steps, i.e. it does not mean that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.