CN114311911A

CN114311911A - Packaging film, electrochemical device comprising same and electronic device

Info

Publication number: CN114311911A
Application number: CN202011050068.2A
Authority: CN
Inventors: 林乐乐
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2022-04-12

Abstract

The application provides a packaging film, electrochemical device and electron device who contains this packaging film, wherein packaging film includes substrate layer, metal foil layer and sealing layer, and the metal foil layer sets up between substrate layer and sealing layer, and wherein, the sealing layer contains the copolymer, and the monomer that forms the copolymer includes first monomer and second monomer, and first monomer is propylene, and the second monomer includes at least one in ethylene, vinylidene fluoride, chloroethylene, butadiene, isoprene, styrene, acrylonitrile, ethylene oxide, epoxypropane, acrylate, vinyl acetate or caprolactone. The electrochemical device has the advantages that the relative displacement between the electrode assembly and the packaging film under the abuse condition of the electrochemical device is avoided, and the safety performance of the electrochemical device is improved.

Description

Packaging film, electrochemical device comprising same and electronic device

Technical Field

The present disclosure relates to the field of electrochemical technologies, and more particularly, to a packaging film, an electrochemical device including the packaging film, and an electronic device including the packaging film.

Background

The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and is widely applied to various fields of electric energy storage, portable electronic equipment, electric automobile power supply and the like. With the continuous expansion of the application range of the lithium ion battery, the market puts higher requirements on the lithium ion battery, and on one hand, the lithium ion battery is required to have higher mass energy density and volume energy density, and meanwhile, the lithium ion battery is also required to have better safety. For example, in the use process of the consumer electronic lithium ion battery, the problems of falling, collision and the like inevitably occur, and it is very important to improve the safety of the lithium ion battery under the abuse conditions of falling, collision and the like.

However, the packaging film of the lithium ion battery and the electrode assembly are usually not adhered, so that the electrode assembly and the packaging film are easy to generate relative displacement under abuse conditions of dropping, impact and the like of the lithium ion battery, and potential safety hazards exist. Therefore, a new technical solution is needed to prevent the lithium ion battery from generating relative displacement between the electrode assembly and the packaging film under the condition of abuse, so as to improve the safety performance of the lithium ion battery.

Disclosure of Invention

An object of the present application is to provide a packaging film, an electrochemical device and an electronic device including the packaging film, so as to improve the safety performance of a lithium ion battery. The specific technical scheme is as follows:

a first aspect of the present application provides a packaging film comprising a substrate layer, a metal foil layer, and a sealant layer, the metal foil layer being disposed between the substrate layer and the sealant layer,

wherein the sealing layer comprises a copolymer, the copolymer-forming monomers comprising a first monomer and a second monomer;

the first monomer is propylene;

the second monomer includes at least one of ethylene, vinylidene fluoride, vinyl chloride, butadiene, isoprene, styrene, acrylonitrile, ethylene oxide, propylene oxide, an acrylate, vinyl acetate, or caprolactone.

The sealing layer herein comprises a copolymer, the monomers forming the copolymer comprising at least two monomers, wherein the first monomer is propylene and the first monomer comprises 30 to 95 mol% of the total monomer amount. Preferably, the first monomer is present in an amount of from 50 mol% to 90 mol%, more preferably from 60 mol% to 80 mol%, based on the total amount of monomers. By controlling the first monomer in the proportion, the sealing layer has good bonding performance, the packaging film is well bonded with the electrode assembly, relative displacement between the electrode assembly and the packaging film under abuse conditions of the lithium ion battery is effectively avoided, and safety performance of the lithium ion battery is improved.

The second monomer comprises at least one of ethylene, vinylidene fluoride, vinyl chloride, butadiene, isoprene, styrene, acrylonitrile, ethylene oxide, propylene oxide, acrylate, vinyl acetate or caprolactone, and accounts for 5 mol% to 70 mol%, preferably 10 mol% to 50 mol%, more preferably 20 mol% to 40 mol% of the total monomer amount. By controlling the second monomer in the proportion, the sealing layer has good bonding performance and electrolyte swelling performance, so that the safety performance of the lithium ion battery is improved. The second monomer may be selected from a combination of one or more of the foregoing monomers. When a combination of a plurality of monomers is selected to provide the second monomer, the ratio between the monomers is not particularly limited and may be any ratio as long as the requirements of the present application are satisfied.

In one embodiment of the present application, the copolymer further includes at least one of a hydroxyl group, an amino group, a carboxyl group, or a carbonyl group, and the above-mentioned polar functional group can further improve the adhesion property of the sealing layer, thereby securing the adhesion between the sealing layer and the electrode assembly.

In one embodiment of the present application, the copolymer has an infrared spectrum test spectrum having peaks in at least one of the following wavenumber ranges:

a)3500cm^-1to 3700cm^-1；

b)3200cm^-1To 3500cm^-1；

c)1600cm^-1To 1800cm^-1。

When the infrared spectrum test spectrum of the copolymer has peaks in the wave number range, the copolymer is proved to have polar functional groups, so that the adhesive property of the sealing layer is further improved.

In one embodiment of the present application, the copolymer has an isotacticity of 30 to 85%, preferably 35 to 60%, and the copolymer has an isotacticity in the above range, and a sealant layer having an appropriate softening temperature and good adhesion can be obtained.

In one embodiment of the present application, the copolymer has a weight average molecular weight of from 500g/mol to 1000000g/mol, preferably from 1000g/mol to 100000 g/mol. By controlling the weight average molecular weight of the present application within the above range, a copolymer having good adhesion can be obtained, so that the sealing layer and the electrode assembly are more firmly bonded, thereby improving the safety performance of the lithium ion battery.

In one embodiment of the present application, the crystallinity of the copolymer is from 10% to 40%. Without being limited to any theory, when the crystallinity of the copolymer is too high, the softening temperature of the material is too high, which is not beneficial to improving the bonding performance of the sealing layer; when the crystallinity of the copolymer is too low, the swelling property and the adhesion property of the electrolyte of the sealing layer are affected. By controlling the crystallinity of the copolymer of the present invention within the above range, a sealant layer having an appropriate softening temperature and good adhesion can be obtained.

In one embodiment herein, the copolymer has a softening temperature of 70 ℃ to 90 ℃. Without being limited to any theory, when the softening temperature of the copolymer is too high, the processing and the improvement of the bonding performance of the sealing layer are not facilitated; when the softening temperature of the copolymer is too low, the copolymer is soft, which is also not beneficial to improving the bonding performance of the sealing layer. By controlling the softening temperature of the copolymer of the present application within the above range, the copolymer of the present application can have better adhesive properties. In particular, when the copolymer is contained in the sealing layer of the present application, the adhesion between the packaging film and the electrode assembly can be improved, and the relative displacement between the electrode assembly and the packaging film under the abuse condition of the lithium ion battery can be avoided, so that the safety performance of the lithium ion battery can be improved.

In a lithium ion battery, the swelling degree of the copolymer in the sealing layer in the electrolyte used in the lithium ion battery affects the performance of the lithium ion battery. The swelling degree of the copolymer in the electrolyte used by the lithium ion battery refers to the property that the copolymer absorbs the electrolyte or a solvent in the electrolyte to swell after being dried, and the excessive swelling degree of the copolymer can cause the bonding failure of the sealing layer and the electrode assembly, so that the relative displacement is generated between the electrode assembly and a packaging film under the abuse condition of the lithium ion battery, and the safety of the lithium ion battery is influenced.

In one embodiment of the present application, the swelling degree of the copolymer is less than 40%, so that when the sealing layer contacts with the electrolyte, the copolymer in the sealing layer has a low swelling degree, and does not chemically react with components such as a solvent and a lithium salt in the electrolyte, the bonding property of the copolymer cannot be damaged by the electrolyte, good bonding between the packaging film and the electrode assembly can be ensured, and relative displacement between the electrode assembly and the packaging film under abuse conditions of the lithium ion battery can be avoided.

In one embodiment of the present application, the sealing layer has a thickness of 10 μm to 50 μm. Without being limited to any theory, when the thickness of the sealing layer is too low, the bonding force is poor, and the improvement of the anti-falling performance of the lithium ion battery is not facilitated; when the thickness of the sealing layer is too high, the energy density of the lithium ion battery is not promoted. By controlling the thickness of the sealing layer in the range, the whole packaging film has lower thickness and excellent adhesive property, so that the energy density and the safety performance of the lithium ion battery are improved.

The substrate layer and the metal foil layer are not particularly limited as long as the requirements of the present application can be met, and for example, the substrate layer may include at least one of nylon (PA) or polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or polyethylene naphthalate (PEN). The thickness of the substrate layer is in the range of 15-30 μm, so that the appearance of the packaging film is ensured, and air permeation is prevented; the metal foil layer may include at least one of an aluminum foil, a stainless alloy steel foil, a nickel foil, or a nickel alloy foil. The thickness of the metal foil layer is in the range of 25 μm to 45 μm, and functions to prevent water from permeating, maintain the internal environment of the lithium ion battery, and prevent external damage to the lithium ion battery.

In an embodiment of the application, a first adhesive layer is further disposed between the substrate layer and the metal foil layer, a second adhesive layer is further disposed between the metal foil layer and the sealing layer, and the first adhesive layer and the second adhesive layer respectively and independently include at least one of isocyanate, polyester polyurethane, polyether polyurethane resin, vinyl acetate, or acrylic resin.

The material of the first adhesive layer is not particularly limited, and the first adhesive layer may be composed of any material known as an adhesive as long as the object of the present application is achieved, and for example, the material of the first adhesive layer may include at least one of isocyanate, polyester urethane, polyether urethane resin, vinyl acetate, or acrylic resin. The thickness of the first adhesive layer is not particularly limited in the present application as long as the object of the present application is achieved, and for example, the thickness of the first adhesive layer is more than 0.4 μm and less than 4 μm.

The material of the second adhesive layer is not particularly limited, and the second adhesive layer may be composed of any material known as an adhesive as long as the object of the present application is achieved, and for example, the material of the second adhesive layer may include at least one of isocyanate, polyester urethane, polyether urethane resin, vinyl acetate, or acrylic resin. The thickness of the second adhesive layer is not particularly limited in the present application as long as the object of the present application is achieved, and for example, the thickness of the second adhesive layer is more than 0.4 μm and less than 4 μm.

The method for producing the copolymer is not particularly limited, and a production method known to those skilled in the art may be used, and is selected depending on the kind of the monomer used, for example, a solution method, a slurry method, a gas phase method, and the like.

For example, when the second monomer is selected from ethylene, the following method may be employed:

respectively dissolving a main catalyst and an auxiliary catalyst in hexane to obtain a hexane solution of the main catalyst and a hexane solution of the auxiliary catalyst, adding hexane into a reaction kettle, adding the hexane solution of the main catalyst and the hexane solution of the auxiliary catalyst into the reaction kettle under the protection of nitrogen, introducing propylene and ethylene, heating to 50-60 ℃, maintaining the pressure in the reaction kettle to be 0.3-0.5 MPa in the reaction process, stopping the reaction by using acidified ethanol after reacting for 0.5-2 hours, washing the obtained product for 3-5 times by using absolute ethanol, filtering, and drying in a vacuum drying oven at 50-70 ℃ for 3-5 hours.

The procatalyst and the cocatalyst are not particularly limited as long as the object of the present invention can be achieved, and for example, a metallocene catalyst system is used, wherein the procatalyst includes a metallocene complex (e.g., ferrocene or its derivatives), and the cocatalyst includes methylaluminoxane; the amounts of the main catalyst and the cocatalyst are not particularly limited in the present application as long as the object of the present invention can be achieved. In addition, the reaction kettle can be firstly vacuumized and drained before reaction, and then nitrogen is used for replacing the reaction kettle for 3 to 5 times, so that the reaction kettle is clean.

When the second monomer is selected from butadiene, the same as the above-mentioned propylene-ethylene copolymer production method is used except that ethylene in the above-mentioned propylene-ethylene copolymer production method is replaced with butadiene.

When the second monomer is selected from acrylates, the difference from the above-mentioned propylene-ethylene copolymer production method is: replacing ethylene in the preparation method of the propylene-ethylene copolymer with acrylic ester, adding hexane, hexane solution of a main catalyst and hexane solution of a cocatalyst into a reaction kettle under the protection of nitrogen, then adding acrylic ester, and then introducing propylene, wherein the rest is the same as the preparation method of the propylene-ethylene copolymer.

The acrylate monomer may be any one selected from methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, isooctyl acrylate, and hydroxyethyl acrylate.

For the copolymerization of other monomers, none of them are listed in the present application, and the preparation methods known in the art can be used.

The structure of the electrochemical device is not particularly limited as long as the object of the present application can be achieved, and may include, for example, at least one of a wound structure or a laminated structure. And the electrode assembly in the electrochemical device comprises a positive pole piece, a negative pole piece and an isolating membrane, wherein the isolating membrane is positioned between the positive pole piece and the negative pole piece.

The positive electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode tab generally includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is not particularly limited, and may be any positive electrode current collector known in the art, such as an aluminum foil, an aluminum alloy foil, or a composite current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited, and any positive electrode active material known in the art may be used, and for example, may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, a lithium rich manganese-based material, lithium cobalt oxide, lithium manganese iron phosphate, or lithium titanate.

The negative electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode tab generally includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector is not particularly limited, and any negative electrode current collector known in the art, such as copper foil, aluminum alloy foil, and composite current collector, may be used. The anode active material layer includes an anode active material, and the anode active material is not particularly limited, and any anode active material known in the art may be used. For example, at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon, lithium titanate, and the like may be included.

The separator of the present application includes, but is not limited to, at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.

The surface of the separation film may further include a porous layer disposed on at least one surface of the separation film, the porous layer including inorganic particles selected from alumina (Al) and a binder, and the inorganic particles₂O₃) Silicon oxide (SiO)₂) Magnesium oxide (MgO), titanium oxide (TiO)₂) Hafnium oxide (HfO)₂) Tin oxide (SnO)₂) Cerium oxide (CeO)₂) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)₂) Yttrium oxide (Y)₂O₃) Silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The adhesive is selected from one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The porous layer can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the bonding performance between the isolating membrane and the anode or the cathode.

The lithium ion battery of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte including a lithium salt and a non-aqueous solvent.

In some embodiments herein, the lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.

Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

A second aspect of the present application provides an electrochemical device comprising a case and an electrode assembly, wherein the case comprises the packaging film as described in the first aspect, and a sealing layer bonds the case and the electrode assembly, thereby preventing the electrochemical device from being displaced relative to each other under abuse conditions, and improving safety of the electrochemical device.

A third aspect of the present application provides an electronic device comprising the electrochemical device according to the second aspect described above, having good safety performance.

The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

The process for preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, a lithium ion battery can be manufactured by the following process: and overlapping the positive pole piece and the negative pole piece through an isolating film, winding, folding and the like according to needs, putting the overlapped positive pole piece and the negative pole piece into a packaging film, injecting electrolyte into the packaging film, sealing the packaging film, and performing hot-pressing shaping to obtain the lithium ion battery. In the hot-pressing shaping process, the sealing layer on the inner surface of the packaging film is softened to generate the adhesive property, and the packaging film and the electrode assembly are adhered and fixed, so that the relative displacement between the electrode assembly and the packaging film is prevented under the abuse condition of the lithium ion battery. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as necessary to prevent a pressure rise or overcharge/discharge inside the lithium ion battery.

In the embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.

The application provides a packaging film, electrochemical device and electronic device who contains this packaging film, wherein, packaging film includes the substrate layer, metal foil layer and sealing layer, metal foil layer sets up between substrate layer and sealing layer, because the sealing layer contains the copolymer, the monomer that forms this copolymer includes first monomer and second monomer, make this sealing layer have good adhesion properties, thereby make packaging film pass through the sealing layer and bond with electrode assembly, avoid lithium ion battery to produce relative displacement between electrode assembly and the packaging film under the abuse condition, thereby promote lithium ion battery's security performance.

Drawings

In order to illustrate the technical solutions of the present application and the prior art more clearly, the following briefly introduces examples and figures that need to be used in the prior art, it being obvious that the figures in the following description are only some examples of the present application.

FIG. 1 is a schematic structural view of a packaging film according to an embodiment of the present application;

fig. 2 is a schematic structural view of a packaging film according to another embodiment of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments.

In some embodiments, the relative displacement between the electrode assembly and the packaging film can also be reduced by disposing a double-sided tape between the electrode assembly and the packaging film, but this method requires an additional step of disposing the double-sided tape, thereby increasing the manufacturing complexity of the lithium ion battery, and the thickness of the double-sided tape is usually in the millimeter level, which increases the overall thickness of the lithium ion battery, so that the volumetric energy density of the lithium ion battery is lost, and the stability of the double-sided tape in the electrolyte for a long time is subject to many uncertainties, so that it is difficult to ensure the safety of the lithium ion battery in the long-term use process.

In view of the above, the present application provides a packaging film, as shown in fig. 1, comprising a substrate layer 101, a metal foil layer 102 and a sealant layer 103, the metal foil layer being disposed between the substrate layer and the sealant layer,

the first monomer is propylene;

In an embodiment of the present application, as shown in fig. 2, a first adhesive layer 104 is further disposed between the substrate layer 101 and the metal foil layer 102, and the first adhesive layer improves the adhesion property between the substrate layer and the metal foil layer; a second adhesive layer 105 is further disposed between the metal foil layer 102 and the sealing layer 103, and the second adhesive layer improves the adhesion between the metal foil layer and the sealing layer.

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.

The test method and the test equipment are as follows:

copolymer infrared spectrum test:

the infrared spectrum test is carried out on the copolymer by adopting the national standard GB/T21186-2007 Fourier transform infrared spectrometer.

Copolymer isotacticity test:

the isotacticity of the copolymers was tested according to the FTIR (Fourier transform Infrared Spectroscopy) method, which uses the national standard GB/T21186-2007 Fourier transform Infrared Spectroscopy.

Measurement of crystallinity of copolymer:

a certain amount of a copolymer sample (for example, 5mg) is heated to 180 ℃ at a certain rate (for example, 5 ℃/min) using a general-purpose Differential Scanning Calorimeter (DSC), the temperature is maintained for 2min, and then the temperature is reduced to 80 ℃ at a certain rate (for example, 5 ℃/min), and the crystallinity obtained by the DSC method is determined by the following formula:

degree of crystallinity Δ H_m/ΔH_m ⁰

In the formula,. DELTA.H_m、ΔH_m ⁰The heat of fusion of the sample and the heat of fusion of the fully crystallized sample, respectively.

Testing of the softening temperature of the copolymer:

by DSC method: a5 mg sample of the copolymer was taken, the temperature was raised to 150 ℃ at a rate of 5 ℃/min, a DSC curve was taken, and the softening temperature of the copolymer was determined from the obtained DSC curve.

Measurement of the degree of swelling of the copolymer:

the copolymer slurry was coated on a Teflon plate to prepare a copolymer film sample having a thickness of 6 μm, and the empty weighing flask was weighed using a balance, and then the prepared copolymer film sample was put into the weighing flask and weighed again to determine the mass of the sample. The weighed sample was placed in a test tube, electrolyte was added to 1/3 of the test tube (the composition and concentration of the electrolyte were the same as in a lithium ion battery), the test tube was capped, and then the test tube was placed in a thermostatic water bath at 25 ℃ for swelling. Then, measuring the mass of the sample at intervals, slightly taking out a swelling body for each measurement, quickly sucking the solvent attached to the surface of the sample by using filter paper, immediately putting the sample into a weighing bottle, covering the bottle stopper tightly, weighing, then putting the sample into a test tube with electrolyte for continuous swelling until the mass difference obtained by two times of weighing is not more than 0.01g, namely, considering that the swelling process is balanced, and calculating the swelling degree of the sample according to the following formula:

degree of swelling (w1-w0)/w0

Where w0 represents the mass of the sample before soaking and w1 represents the mass of the sample at equilibrium after swelling.

Impact test of the lithium ion battery:

the lithium ion battery is placed on a plane, a steel column with the diameter of 15.8mm +/-0.2 mm is placed in the center of the lithium ion battery, the longitudinal axis of the steel column is parallel to the plane, a weight with the mass of 9.1kg +/-0.1 kg freely falls onto the steel column above the center of the lithium ion battery from the height of 610mm +/-25 mm, and the test is finished and the observation is carried out for 6 hours. The lithium ion battery is tested to pass the test without explosion or fire.

Drop impact test of the lithium ion battery:

fully charging the lithium ion battery, then freely falling to the surface of the smooth marble from a position with a height of 1.5 meters, wherein the falling sequence is as follows: the method comprises the steps of testing the front surface, the back surface, the lower surface, the upper surface, the left surface, the right surface, the upper left corner, the upper right corner, the lower left corner and the lower right corner of the lithium ion battery, continuously performing 1 drop test on each surface or corner, and falling for one round, measuring the voltage of the lithium ion battery after each round of test is finished, checking the appearance of the lithium ion battery, wherein each lithium ion battery falls for 10 rounds. After the lithium ion battery falls for 10 rounds, the lithium ion battery passes the test with no burning, no fire, no explosion, no liquid leakage, no smoke and pressure drop less than 30 mV.

Example 1

<1-1. preparation of copolymer >

In a 1L stainless steel reaction kettle, adding 77 parts (volume fraction) of hexane solvent, 19 parts (volume fraction) of hexane solution (ferrocene content 70mg/L) of main catalyst ferrocene and 4 parts (volume fraction) of hexane solution (methylaluminoxane content 10mg/L) of cocatalyst methylaluminoxane under the protection of nitrogen, then adding vinylidene fluoride (PVDF), then introducing propylene, heating to 50 ℃, controlling the pressure of the reaction kettle to be 0.4MPa, and adjusting the adding amount of the propylene/vinylidene fluoride to enable the molar ratio between the first monomer and the second monomer to be 60: 40, after reacting for 1h, terminating the reaction by using acidified ethanol to obtain a propylene-vinylidene fluoride copolymer (relevant parameters are shown in table 1), washing the obtained product for 3 times by using absolute ethanol, filtering, and drying in a vacuum drying oven at 60 ℃ for 4 h.

<1-2. preparation of Positive electrode sheet >

Mixing the positive active material lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 94: 3, adding N-methylpyrrolidone (NMP) as a solvent, preparing slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on one surface of an aluminum foil with the thickness of 12 mu m, drying at 90 ℃, obtaining a positive pole piece with the thickness of a positive active material layer of 100 mu m after cold pressing, and then repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on the two surfaces. Cutting the positive pole piece into the specification of 74mm multiplied by 867mm, and welding the pole lugs for later use.

<1-3. preparation of negative electrode sheet >

Mixing the negative active material artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethylcellulose according to the mass ratio of 96: 1: 1.5, adding deionized water as a solvent, preparing slurry with the solid content of 70%, and uniformly stirring. And uniformly coating the slurry on one surface of a copper foil with the thickness of 8 mu m, drying at 110 ℃, obtaining a negative pole piece with the negative active material layer coated on one surface and the thickness of the negative active material layer of 150 mu m after cold pressing, and then repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the negative active material layer coated on the two surfaces. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.

<1-4. preparation of separator >

Alumina and polyacrylate were mixed in a mass ratio of 90: 10 and dissolved in deionized water to form a ceramic slurry with 50% solids. The ceramic slurry was then uniformly coated on one side of a porous substrate (polyethylene, thickness 7 μm, average pore diameter 0.073 μm, porosity 26%) by a gravure coating method, and dried to obtain a two-layer structure of a ceramic coating layer and the porous substrate, the ceramic coating layer having a thickness of 50 μm.

Polyvinylidene fluoride was mixed with polyacrylate in a mass ratio of 96: 4 and dissolved in deionized water to form a polymer syrup having a solids content of 50%. And then uniformly coating the polymer slurry on two surfaces of the ceramic coating and porous substrate double-layer structure by adopting a dimple coating method, and drying to obtain the isolating membrane, wherein the thickness of a single-layer coating formed by the polymer slurry is 2 mu m.

<1-5 > preparation of electrolyte solution >

Mixing non-aqueous organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP) and Vinylene Carbonate (VC) according to a mass ratio of 20: 30: 20: 28: 2 in an environment with water content less than 10ppm, and then adding lithium hexafluorophosphate (LiPF) to the non-aqueous organic solvent₆) Dissolving and mixing uniformly to obtain electrolyte, wherein the LiPF is₆The mass ratio of the organic solvent to the non-aqueous organic solvent is 8: 92.

<1-6. production of packaging film >

A first adhesive layer with a thickness of 2 μm was formed by coating a nylon substrate layer with a thickness of 25 μm with isocyanate, and then a second adhesive layer with a thickness of 2 μm was formed by coating an aluminum metal foil layer with a thickness of 30 μm and then a layer of isocyanate on the surface of the aluminum metal foil layer, and then a sealant layer with a thickness of 30 μm was formed by coating a copolymer prepared in this example.

<1-7. preparation of lithium ion Battery >

And (3) stacking the prepared positive pole piece, the prepared isolating membrane and the prepared negative pole piece in sequence to enable the isolating membrane to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into the prepared packaging film, dehydrating at 80 ℃, injecting the prepared electrolyte, softening a sealing layer on the inner surface of the packaging film to generate adhesive property through the processes of vacuum packaging, standing, formation, hot-pressing and shaping and the like, and bonding the packaging film and the electrode assembly to obtain the lithium ion battery.

Example 2

Propylene-vinylidene fluoride copolymers, whose crystallinity, weight average molecular weight, softening temperature and swelling degree are shown in Table 1, were prepared in a similar manner to the preparation of the (1-1) copolymer in example 1.

Example 3

Example 4

Example 5

Example 6

Example 7

Using a method similar to the preparation of the (1-1) copolymer in example 1, propylene-vinylidene fluoride copolymers were prepared, the crystallinity, weight average molecular weight, softening temperature, isotacticity, and degree of swelling of which are shown in Table 2.

Example 8

Example 9

Example 10

Example 11

Example 12

Example 13

Using a method similar to the preparation of the (1-1) copolymer in example 1, a propylene-vinylidene fluoride copolymer was prepared, the crystallinity, weight average molecular weight, softening temperature, isotacticity, and degree of swelling of which are shown in Table 3; in a manner similar to the production of the (1-6) packaging film in example 1, sealant layers were produced, the thickness of which is shown in Table 3.

Example 14

Example 15

Example 16

In a similar manner to the preparation of the (1-1) copolymer in example 1, the molar ratio of the propylene monomer to the vinylidene fluoride monomer was changed to 30: 70, propylene-vinylidene fluoride copolymers were prepared, the crystallinity, weight average molecular weight, softening temperature, isotacticity, and swelling degree of which are shown in Table 4.

Example 17

In a similar manner to that in the preparation of the (1-1) copolymer in example 1, the molar ratio of the propylene monomer to the vinylidene fluoride monomer was changed to 95: 5, propylene-vinylidene fluoride copolymers were prepared, and the crystallinity, weight average molecular weight, softening temperature, isotacticity, and degree of swelling were as shown in Table 4.

Example 18

The procedure was as in example 1 except that the preparation of the copolymer was different from that of example 1.

<2-1. preparation of copolymer >

Adding 77 parts (volume fraction) of hexane solvent, 19 parts (volume fraction) of hexane solution (ferrocene content 70mg/L) of main catalyst ferrocene and 4 parts (volume fraction) of hexane solution (methylaluminoxane content 10mg/L) of cocatalyst methylaluminoxane into a 1L stainless steel reaction kettle under the protection of nitrogen, introducing propylene/ethylene mixed gas, heating to 50 ℃, controlling the pressure of the reaction kettle to be 0.4MPa, and adjusting the adding amount of propylene/ethylene to ensure that the molar ratio between a first monomer and a second monomer is 60: 40, after reacting for 1h, terminating the reaction by using acidified ethanol to obtain a propylene-ethylene copolymer, washing the obtained product by using absolute ethanol for 3 times, filtering, and drying in a vacuum drying oven at 60 ℃ for 4 h. The crystallinity, weight average molecular weight, softening temperature, isotacticity and degree of swelling of the copolymer are shown in Table 4.

Example 19

<3-1. preparation of copolymer >

Adding 77 parts (volume fraction) of hexane solvent, 19 parts (volume fraction) of hexane solution (ferrocene content 70mg/L) of main catalyst ferrocene and 4 parts (volume fraction) of hexane solution (methylaluminoxane content 10mg/L) of cocatalyst methylaluminoxane into a 1L stainless steel reaction kettle under the protection of nitrogen, introducing propylene/butadiene mixed gas, heating to 50 ℃, controlling the pressure of the reaction kettle to be 0.4MPa, and adjusting the adding amount of propylene/butadiene to ensure that the molar ratio between a first monomer and a second monomer is 60: 40, after reacting for 1h, terminating the reaction by using acidified ethanol to obtain a propylene-butadiene copolymer, washing the obtained product by using absolute ethanol for 3 times, filtering, and drying in a vacuum drying oven at 60 ℃ for 4 h. The crystallinity, weight average molecular weight, softening temperature, isotacticity and degree of swelling of the copolymer are shown in Table 4.

Example 20

<4-1. preparation of copolymer >

In a 1L stainless steel reaction kettle, adding 77 parts (volume fraction) of hexane solvent, 19 parts (volume fraction) of hexane solution (ferrocene content 70mg/L) of main catalyst ferrocene and 4 parts (volume fraction) of hexane solution (methylaluminoxane content 10mg/L) of cocatalyst methylaluminoxane under the protection of nitrogen, then adding ethyl acrylate, then introducing propylene, raising the temperature to 50 ℃, controlling the pressure of the reaction kettle to be 0.4MPa, and adjusting the adding amount of the propylene/ethyl acrylate to ensure that the molar ratio between the first monomer and the second monomer is 60: 40, after reacting for 1h, terminating the reaction by using acidified ethanol to obtain a propylene-ethyl acrylate copolymer, washing the obtained product by using absolute ethanol for 3 times, filtering, and drying in a vacuum drying oven at 60 ℃ for 4 h. The crystallinity, weight average molecular weight, softening temperature, isotacticity and degree of swelling of the copolymer are shown in Table 4. The infrared spectrum test spectrum of the obtained copolymer is 1600cm^-1To 1800cm^-1Peaks in the wavenumber range indicate the presence of carbonyl groups in the copolymer.

Example 21

<5-1. preparation of copolymer >

Adding 77 parts (volume fraction) of hexane solvent, 19 parts (volume fraction) of hexane solution (ferrocene content 70mg/L) of main catalyst ferrocene and 4 parts (volume fraction) of hexane solution (methylaluminoxane content 10mg/L) of cocatalyst methylaluminoxane into a 1L stainless steel reaction kettle under the protection of nitrogen, then adding ethyl acrylate, then introducing propylene and ethylene, heating to 50 ℃, controlling the pressure of the reaction kettle to be 0.4MPa, and adjusting the adding amount of the propylene/ethylene/ethyl acrylate to ensure that the first and the second catalysts are the sameThe molar ratio of the two monomers is 60: 40 (wherein the ethylene monomer and the ethyl acrylate monomer are in equal molar ratio), reacting for 1h, terminating the reaction by using acidified ethanol to obtain a propylene-ethylene-ethyl acrylate copolymer, washing the obtained product by using absolute ethanol for 3 times, filtering, and drying in a vacuum drying oven at 60 ℃ for 4 h. The crystallinity, weight average molecular weight, softening temperature, isotacticity and degree of swelling of the copolymer are shown in Table 4. The infrared spectrum test spectrum of the obtained copolymer is 1600cm^-1To 1800cm^-1Peaks in the wavenumber range indicate the presence of carbonyl groups in the copolymer.

Comparative example 1

<6-1. preparation of Positive electrode sheet >

The preparation method is the same as that of the positive pole piece in the embodiment 1.

<6-2. preparation of negative electrode sheet >

<6-3. preparation of separator >

<6-4. preparation of electrolyte solution >

<6-5. production of packaging film >

A first adhesive layer with a thickness of 2 μm is formed by coating a layer of isocyanate on the surface of a nylon base material layer with a thickness of 25 μm, and then a second adhesive layer with a thickness of 2 μm is formed by coating a layer of aluminum metal foil with a thickness of 30 μm and then a layer of isocyanate on the surface of the aluminum metal foil, and then a polypropylene (PP) film sealing layer with a thickness of 30 μm is applied.

<6-6. preparation of lithium ion Battery >

And (3) stacking the prepared positive pole piece, the prepared isolating membrane and the prepared negative pole piece in sequence to enable the isolating membrane to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into the prepared packaging film, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery, wherein the PP sealing layer is not softened, and the packaging film is not bonded with the electrode assembly.

Comparative example 2

Except that < preparation of lithium ion battery > was different from comparative example 1, the rest was the same as comparative example 1.

< preparation of lithium ion Battery >

And stacking the prepared positive pole piece, the prepared isolating membrane and the prepared negative pole piece in sequence, enabling the isolating membrane to be positioned between the positive pole piece and the negative pole piece to play an isolating role, winding to obtain an electrode assembly, sticking a double-sided adhesive tape on the electrode assembly, putting the electrode assembly into the prepared packaging membrane, enabling the packaging membrane to be bonded with the electrode assembly through the double-sided adhesive tape, dehydrating at 80 ℃, injecting prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

Comparative example 3

Using a method similar to the preparation of the (1-1) copolymer in example 1, a propylene-vinylidene fluoride copolymer was prepared, the crystallinity, weight-average molecular weight, softening temperature, and swelling degree of which are shown in Table 1; in a manner similar to the production of the (1-6) packaging film in example 1, sealant layers were produced, the thickness of which is shown in Table 1.

The preparation parameters and test results of the examples and comparative examples are shown in the following tables 1 to 4:

as can be seen from examples 1-6 of table 1, as the crystallinity of the copolymer in the sealant layer increases, the softening temperature of the copolymer increases and the degree of swelling generally decreases.

As can be seen from table 2, examples 1, 7-12, both the drop and impact pass rates increased significantly as the copolymer isotacticity in the seal layer decreased. It can be seen that the lithium ion batteries of the present application can be made to have high drop through ratios and impact through ratios as long as the isotacticity of the copolymer is within the range of the present application.

As can be seen from table 3, examples 1, 13 to 15, the drop-through ratio and the impact-through ratio of the lithium ion battery tended to increase as the thickness of the sealing layer increased. It can be seen that the lithium ion battery of the present application can have a high drop-through ratio and impact-through ratio as long as the sealing layer thickness is within the range of the present application.

The crystallinity of a copolymer generally affects the degree of regularity of its molecular structure; the weight average molecular weight of the copolymer generally affects its adhesion and electrolyte resistance properties; the softening temperature of the copolymer generally affects its adhesive properties; the isotacticity of the copolymer generally affects its adhesive properties. As can be seen from examples 16 to 21 in table 4, the object of the present invention can be achieved by making the lithium ion battery of the present application have a high drop-through ratio and impact-through ratio by making the sealing layer excellent in electrolyte resistance and adhesion performance as long as the crystallinity, weight average molecular weight, softening temperature, and isotacticity of the copolymer fall within the ranges of the present application.

Overall, it can be seen from examples 1 to 21 and comparative examples 1 to 2 that the drop passage ratio and the impact passage ratio of the lithium ion battery having the sealing layer of the present application are both significantly improved, indicating that the lithium ion battery of the present application has excellent safety performance.

As can be seen from examples 1 to 21 and comparative example 3, when the thickness of the sealing layer was within the range of the present application, both the drop passage ratio and the impact passage ratio of the lithium ion battery were significantly increased, indicating that the lithium ion battery of the present application had excellent safety performance.

In summary, the lithium ion battery with the sealing layer can enable the packaging film to be well bonded with the electrode assembly through the sealing layer, and avoids relative displacement between the electrode assembly and the packaging film under the abuse condition of the lithium ion battery, so that the safety performance of the lithium ion battery is improved.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A packaging film comprises a substrate layer, a metal foil layer and a sealing layer, wherein the metal foil layer is arranged between the substrate layer and the sealing layer,

wherein the sealing layer comprises a copolymer, the monomers forming the copolymer comprising a first monomer and a second monomer;

the first monomer is propylene;

the second monomer comprises at least one of ethylene, vinylidene fluoride, vinyl chloride, butadiene, isoprene, styrene, acrylonitrile, ethylene oxide, propylene oxide, acrylate, vinyl acetate, or caprolactone.

2. The packaging film of claim 1, wherein the first monomer comprises 30 to 95 mol% of the total monomer amount of the copolymer, the second monomer comprises 5 to 70 mol% of the total monomer amount of the copolymer, and the copolymer further comprises at least one of a hydroxyl group, an amino group, a carboxyl group, or a carbonyl group.

3. The packaging film of claim 1, wherein the copolymer has an infrared spectrum test spectrum having peaks in at least one of the following wavenumber ranges:

a)3500cm^-1to 3700cm^-1；

b)3200cm^-1To 3500cm^-1；

c)1600cm^-1To 1800cm^-1。

4. The packaging film of claim 1, wherein the copolymer has at least one of the following characteristics:

a) the copolymer has an isotacticity of 30 to 85%;

b) the copolymer has a weight average molecular weight of 500g/mol to 1000000 g/mol;

c) the crystallinity of the copolymer is from 10% to 40%;

d) the softening temperature of the copolymer is 70 ℃ to 90 ℃;

e) the copolymer has a swelling degree of less than 40%.

5. The packaging film of claim 4, wherein the copolymer has at least one of the following characteristics:

a) the copolymer has an isotacticity of 35 to 60%;

b) the weight average molecular weight of the copolymer is 1000g/mol to 100000 g/mol.

6. The packaging film of claim 1, wherein the sealing layer has a thickness of 10 to 50 μ ι η.

7. The packaging film of claim 1, wherein the substrate layer comprises at least one of nylon, polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate; the metal foil layer comprises at least one of aluminum foil, stainless steel alloy foil, steel foil, nickel foil or nickel alloy foil.

8. The packaging film of claim 1, wherein a first adhesive layer is further disposed between the substrate layer and the metal foil layer, and a second adhesive layer is further disposed between the metal foil layer and the sealant layer, and the first adhesive layer and the second adhesive layer each independently comprise at least one of isocyanate, polyester urethane, polyether urethane resin, vinyl acetate, or acrylic resin.

9. An electrochemical device comprising a case and an electrode assembly, the case comprising the packaging film according to any one of claims 1 to 8, and the sealing layer bonding the case and the electrode assembly.

10. An electronic device comprising the electrochemical device of claim 9.