Package film, electrochemical device, and electronic device

Abstract

The present invention provides a packaging film, an electrochemical device, and an electronic device. This packaging film includes an inner layer containing a thermoplastic resin, an outer layer containing a thermosetting resin, and a metal layer located between the inner layer and the outer layer. The metal layer includes at least one of stainless steel, titanium alloy, and nickel alloy. The thickness of the metal layer is 10 μm to 60 μm, the tensile strength of the metal layer is 300 MPa to 2000 MPa, and the ratio of the thickness of the inner layer to the thickness of the metal layer is 0.6 to 3. By using a metal layer containing at least one of stainless steel, titanium alloy, and nickel alloy, with the tensile strength of the metal layer being 300 MPa to 2000 MPa and the ratio of the thickness of the inner layer to the thickness of the metal layer being 0.6 to 3, even when the thickness of the packaging film is relatively thin, a relatively high puncture resistance strength can be achieved, further improving the puncture resistance strength of the electrochemical device and reducing the adverse effect on the energy density of the electrochemical device.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and specifically to a packaging film, an electrochemical device, and an electronic device.

Background Art

[0002] With the wide application of electrochemical devices (such as lithium-ion batteries) to various electronic products, the requirements for the energy density and thinning of electrochemical devices are also increasing. The packaging pack made of a packaging film is an essential and important assembly of a lithium-ion battery, playing an important role in blocking air and moisture and protecting the internal electrode assembly from damage. Aluminum-plastic film is currently the most common and technically mature packaging pack, and is widely applied because it has relatively good packaging characteristics.

[0003] However, in order to ensure the safety of the electrode assembly and improve the ability to resist puncture by external forces, generally, the aluminum-plastic film increases the puncture resistance by using a relatively thick metal layer and nylon layer. Such a design achieves a relatively high puncture resistance and results in a loss of the volume energy density of the lithium-ion battery. Therefore, it is expected to further improve this problem.

Summary of the Invention

[0004] Embodiments of the present invention provide a packaging film, which includes an inner layer containing a thermoplastic resin, an outer layer containing a thermosetting resin, and a metal layer located between the inner layer and the outer layer. The metal layer includes at least one of stainless steel, titanium alloy, and nickel alloy. The thickness of the metal layer is 10 μm to 60 μm, the tensile strength of the metal layer is 300 MPa to 2000 MPa, and the ratio of the thickness of the inner layer to the thickness of the metal layer is 0.6 to 3.

[0005] In some embodiments, the thickness of the metal layer is 30 μm to 40 μm. In some embodiments, the ratio of the thickness of the inner layer to the thickness of the metal layer is 0.6 to 2. In some embodiments, the thickness of the outer layer is 1 μm to 10 μm. In some embodiments, the elongation at break of the metal layer is 10% to 45%. In some embodiments, the thermoplastic resin includes at least one of polyethylene, polyvinyl chloride, polypropylene, and polystyrene. In some embodiments, the thermosetting resin includes at least one of polyurethane and polyacrylate. In some embodiments, the package film further includes an adhesive layer, and the adhesive layer is located between the inner layer and the metal layer. In some embodiments, the adhesive layer includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, polydifluoroethylene, aqueous acrylic resin, and polyvinyl formal. In some embodiments, the thickness of the package film is 20 μm to 130 μm, and the puncture resistance of the package film is 30 N to 70 N.

[0006] Embodiments of the present invention further provide an electrochemical device including the package film.

[0007] Embodiments of the present invention further provide an electronic device including the electrochemical device.

[0008] The present invention uses a metal layer including at least one of stainless steel, titanium alloy, and nickel alloy, with the tensile strength of the metal layer being 300 MPa to 2000 Mpa and the ratio of the thickness of the inner layer to the thickness of the metal layer being 0.6 to 3. Thus, even when the thickness of the package film is relatively thin, a relatively high puncture resistance can be achieved, further improving the puncture resistance of the electrochemical device and reducing the adverse effect on the energy density of the electrochemical device.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0010] According to the following embodiments, those skilled in the art can understand the present invention more comprehensively, but it does not limit the present application in any way.

[0011] In some package films, a three-layer structure of a polyester layer, a metal layer, and a hot-melt resin layer is used to reduce the use of an intermediate binder, thereby thinning the total thickness of the package film and reducing the loss of the energy density of the lithium-ion battery. However, in order to ensure that the package film has a relatively high puncture resistance strength, the thickness of the metal layer is required to be 30 μm or more, and the total thickness of the package film is required to be 140 μm or less. Therefore, it still does not have a good improvement effect on the loss of the energy density of the lithium-ion battery. In some other package films, a three-layer structure of a polyamide layer, a metal layer, and a hot-melt resin layer is used, in which the thickness of the polyamide layer is 10 μm or more, the thickness of the metal layer is 36 μm or more, and the total thickness of the package film is required to be 83 μm or more. The total thickness of the package film designed in this way is still relatively large, and in order to ensure that it has a relatively high puncture resistance strength, the requirements for the thickness of the metal layer are also stricter, and it still does not have a good improvement effect on the loss of the energy density of the lithium-ion battery.

[0012] Embodiments of the present invention provide a packaging film for use in an electrochemical device. FIG. 1 is a schematic cross-sectional view showing the packaging film of some embodiments of the present invention. This packaging film includes an inner layer 101, a metal layer 102, and an outer layer 103, and the metal layer 102 is located between the inner layer 101 and the outer layer 103. In some embodiments, the inner layer 101, the metal layer 102, and the outer layer 103 can be bonded by lamination, but this is merely exemplary and does not limit the present invention.

[0013] In some embodiments, the inner layer 101 includes a thermoplastic resin. In some embodiments, the outer layer 103 includes a thermosetting resin, and thus, the outer layer 103 is used to suppress deformation due to the expansion of the internal electrode assembly. In some embodiments, the metal layer 102 includes at least one of stainless steel, titanium alloy, and nickel alloy. Since the strength of these materials is relatively high, it is advantageous for reducing the use thickness of the metal layer 102. In some embodiments, the thickness of the metal layer 102 is 10 μm to 60 μm. If the thickness of the metal layer 102 is too small, the puncture resistance of the packaging film becomes relatively small. If the thickness of the metal layer 102 is too large, it is disadvantageous for improving the energy density of the electrochemical device. In some embodiments, the thickness of the metal layer 102 is 30 μm to 40 μm. In some embodiments, the thickness of the metal layer 102 may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or other appropriate values.

[0014] In some embodiments, the tensile strength of the metal layer 102 is from 300 MPa to 2000 MPa. If the tensile strength of the metal layer 102 is too small, the strength of the metal layer 102 will be relatively low, and the puncture resistance of the package film will be insufficient. If the tensile strength of the metal layer 102 is too large, the ductility of the metal layer 102 will be relatively poor, showing a certain brittleness, and similarly, it will cause a decrease in the puncture resistance of the package film. In some embodiments, the tensile strength of the metal layer 102 may be 300 MPa, 500 MPa, 800 MPa, 1000 MPa, 1200 MPa, 1500 MPa, 1800 MPa, 2000 MPa or other appropriate values.

[0015] In some embodiments, the ratio of the thickness of the inner layer 101 to the thickness of the metal layer 102 is from 0.6 to 3. In some embodiments, the ratio of the thickness of the inner layer 101 to the thickness of the metal layer 102 is from 0.6 to 2. If the ratio of the thickness of the inner layer 101 to the thickness of the metal layer 102 is too small, the thickness of the thermoplastic resin layer will be too thin, and since the inner layer 101 also provides part of the mechanical strength, the puncture resistance of the entire package film will be insufficient. If the ratio of the thickness of the inner layer 101 to the thickness of the metal layer 102 is too large, the thickness of the thermoplastic resin layer will be relatively large, so the thickness of the entire package film will be relatively large. Therefore, the puncture resistance is relatively high, but it will have an adverse effect on the energy density of the electrochemical device. In some embodiments, the ratio of the thickness of the inner layer 101 to the thickness of the metal layer 102 may be 0.6, 1, 1.2, 1.5, 2, 2.5, 3 or other appropriate values.

[0016] Therefore, by using a metal layer containing at least one of stainless steel, titanium alloy, and nickel alloy, with the tensile strength of the metal layer being 300 MPa to 2000 MPa, the thickness of the metal layer being 10 μm to 60 μm, and the ratio of the thickness of the inner layer to the thickness of the metal layer being 0.6 to 3, even when the thickness of the package film is relatively thin, a relatively high puncture resistance can be achieved, further improving the puncture resistance of the electrochemical device and reducing the adverse effect on the energy density of the electrochemical device. When the design of other layers remains unchanged, the overall thickness of the package film of the present invention can be significantly reduced, and the puncture resistance can be maintained and even improved compared to a thicker aluminum-plastic film, thereby improving the volume energy density and safety of the entire lithium-ion battery.

[0017] In some embodiments, the thickness of the outer layer 103 is 1 μm to 10 μm. The outer layer 103 can play a role in protecting the metal layer 102 and relatively well improving the insulation with the outside. If the thickness of the outer layer 103 is too small, the outer layer 103 is likely to be damaged, so that the metal layer 102 is likely to be exposed, and further the external insulation becomes poor. If the thickness of the outer layer 103 is too large, it will affect the volume energy density of the entire fabricated electrochemical device. In some embodiments, the thickness of the outer layer 103 may be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm or other appropriate values.

[0018] In some embodiments, the elongation at break of the metal layer 102 is 10% to 45%. If the elongation at break of the metal layer 102 is too small, the ductility of the metal layer 102 becomes relatively poor. If the elongation at break of the metal layer 102 is too large, the structural stability of the package film becomes poor. In some embodiments, the elongation at break of the metal layer 102 may be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or other appropriate values.

[0019] In some embodiments, the thermoplastic resin includes at least one of polyethylene, polyvinyl chloride, polypropylene, and polystyrene. By using these thermoplastic resin materials, the inner layer 101 can be fused by heat sealing and exhibit a relatively good sealing effect. Note that the inner layer 101 may be made of any suitable material commonly used for the inner layer of packaging films in the art. When the packaging film is used as a packaging pack to accommodate the electrode assembly, since the inner layer 101 is close to the electrode assembly, it is called the inner layer, while the outer layer 103 is far from the electrode assembly, so it is called the outer layer. In some embodiments, the thermosetting resin includes at least one of polyurethane and polyacrylate. In the present invention, a thinner polyurethane layer is used instead of the polyester or polyamide insulating layer, which is the outer layer of the conventionally technically mature aluminum-plastic film, to ensure good external insulation.

[0020] Figure 2 is a schematic cross-sectional view showing a packaging film according to some other embodiments of the present invention. In some embodiments, as shown in Figure 2, the packaging film further includes an adhesive layer 104, and the adhesive layer 104 is located between the inner layer 101 and the metal layer 102. In some embodiments, the adhesive layer 104 serves as an adhesive between the inner layer 101 and the metal layer 102. In some embodiments, the adhesive layer 104 includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamide-imide, polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene, aqueous acrylic resin, and polyvinyl formal.

[0021] In some embodiments, the thickness of the package film is from 20 μm to 130 μm. By using a package film with a thickness in such a range, the requirement for the puncture resistance strength of the package film can be met, and the adverse effect on the energy density of the electrochemical device can be reduced. In some embodiments, the thickness of the package film may be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm or other appropriate values. In some embodiments, the puncture resistance strength of the package film is from 30 N to 70 N. In this way, the requirement for the puncture resistance strength of the package film can be met, and an unnecessary increase in the thickness of the package film can be avoided.

[0022] In some embodiments, as described above, the electrode assembly is sealed by a package pack formed of a package film, that is, the electrode assembly is provided in a housing cavity formed of the package film. In some embodiments, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator provided between the positive electrode sheet and the negative electrode sheet.

[0023] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. In some embodiments, the positive electrode active material layer is provided on one or both sides of the positive electrode current collector. In some embodiments, the positive electrode active material layer contains a positive electrode active material. In some embodiments, the positive electrode active material contains at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium manganate. In some embodiments, the positive electrode active material layer may further contain a conductive agent. In some embodiments, the conductive agent in the positive electrode active material layer may contain at least one of conductive carbon black, Ketjen black, flaky graphite, graphene, carbon nanotubes, and carbon fibers. In some embodiments, the positive electrode active material layer may further contain a binder. The binder in the positive electrode active material layer may contain at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer may be (80-99):(0.1-10):(0.1-10). In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 200 μm. It should be understood that the above description is merely an example, and any other suitable materials, thicknesses, and mass ratios can be used for the positive electrode active material layer of the positive electrode.

[0024] In some embodiments, the positive electrode current collector may be made of Al foil, and of course, other current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 100 μm. In some embodiments, the positive electrode active material layer may be coated only on a part of the region of the positive electrode current collector.

[0025] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. In some embodiments, the negative electrode active material layer is provided on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode active material layer contains a negative electrode active material. The negative electrode active material may include at least one of graphite, hard carbon, silicon, silicon monoxide, and silicone. In some embodiments, the negative electrode active material layer may further include a conductive agent and a binder. In some embodiments, the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, flaky graphite, graphene, carbon nanotubes, and carbon fibers. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material layer may be (80-98):(0.1-10):(0.1-10). It should be understood that the above description is merely an example, and any other suitable materials and mass ratios can be used. In some embodiments, the negative electrode current collector may be made of at least one of copper foil, nickel foil, and carbon-based current collectors.

[0026] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene play a good role in preventing short circuits and can improve the stability of the battery by the shutdown effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 50 μm.

[0027] In some embodiments, the surface of the separator may further include a porous layer. The porous layer is provided on at least one surface of the separator substrate. The porous layer includes inorganic particles and a binder. The inorganic particles are at least one selected from the group consisting of alumina (Al2O3), silica (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In some embodiments, the pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from the group consisting of polyvinylidene fluoride, a copolymer of vinylidene fluoride - hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The porous layer on the surface of the separator can improve the heat resistance, oxidation resistance, and electrolyte wettability of the separator, and enhance the adhesiveness between the separator and the electrode tab.

[0028] In some embodiments of the present invention, the electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly, or a folded electrode assembly. In some embodiments, the positive electrode tab and / or negative electrode tab of the electrochemical device may have a multilayer structure formed in a wound or stacked type, or may have a single-layer structure in which a single-layer positive electrode tab, a separator, and a single-layer negative electrode tab are stacked.

[0029] In some embodiments, the electrochemical device includes a lithium-ion battery, but the present invention is not limited thereto. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution. The electrolytic solution includes a lithium salt and a non-aqueous solvent. The lithium salt is one or more selected from the group consisting of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, as the lithium salt, LiPF6 is selected because it has high ionic conductivity and can improve cycle characteristics.

[0030] The non-aqueous solvent may be a carbonic ester compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0031] The carbonic ester compound may be a linear carbonic ester compound, a cyclic carbonic ester compound, a fluorinated carbonic ester compound, or a combination thereof.

[0032] Examples of the chain carbonate ester compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), or combinations thereof. Examples of the cyclic carbonate ester compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of the fluoro carbonate ester compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or combinations thereof.

[0033] Examples of the carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, methyl formate, or combinations thereof.

[0034] Examples of the ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0035] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate esters, or combinations thereof.

[0036] In some embodiments of the present invention, taking a lithium-ion battery as an example, after winding or laminating a positive electrode, a separator, and a negative electrode in this order to form an electrode assembly, it is, for example, placed in an aluminum plastic film for packaging, an electrolytic solution is injected, and through formation and packaging, a lithium-ion battery is manufactured. Next, a characteristic test is performed on the prepared lithium-ion battery.

[0037] Those skilled in the art should understand that the preparation method of the electrochemical device (for example, a lithium-ion battery) described above is only an example. Other methods commonly used in the art can be adopted without departing from the content disclosed in the present invention.

[0038] Embodiments of the present invention further provide an electronic device including the electrochemical device. The electronic device of the embodiments of the present invention is not particularly limited and may be any known electronic device used in the prior 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 e-book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an auxiliary bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household storage battery, and a lithium-ion capacitor, etc.

[0039] The following provides several specific examples and comparative examples for a more detailed description of the present invention. Here, a lithium-ion battery is used as an example.

[0040] Comparative Example 1 Preparation of the positive electrode sheet: An aluminum layer was used as the positive electrode current collector. Lithium cobaltate as the positive electrode active material, conductive carbon black as the conductive agent, and polyvinylidene fluoride as the binder were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 96:2.2:1.2 to form a positive electrode active material layer slurry. The positive electrode active material layer slurry was coated on the positive electrode current collector with a coating thickness of 80 μm to obtain a positive electrode active material layer. Then, after drying, cold pressing, and cutting, a positive electrode was obtained. The compression density of the positive electrode active material layer was 4.1 g / cm 3 was obtained.

[0041] Preparation of the negative electrode sheet: Artificial graphite, acetylene black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber as the binder were dissolved in deionized water at a weight ratio of 96:1:1.5:1.5 to form a negative electrode slurry. A copper foil with a thickness of 10 μm was used as the negative electrode current collector. The negative electrode slurry was coated on the negative electrode current collector with a coating thickness of 120 μm, dried, and cut to obtain a negative electrode sheet.

[0042] Preparation of the separator: The separator substrate was polyethylene (PE) with a thickness of 8 μm. Alumina ceramic layers with a thickness of 2 μm were coated on both sides of the separator substrate. Finally, polyvinylidene fluoride (PVDF) as a binder with a weight of 2.5 mg / cm 2 was coated on both sides where the ceramic layers were applied and then dried.

[0043] Preparation of the electrolyte: In an environment with a water content of less than 10 ppm, LiPF6 was added to a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20:30:20:28:2, by weight ratio), and the concentration of LiPF6 was set to 1.15 mol / L and uniformly mixed to obtain an electrolyte.

[0044] Preparation of Lithium-Ion Battery: The separator was interposed between the positive electrode plate and the negative electrode plate to play a role of isolation. The positive electrode plate, the separator, and the negative electrode plate were laminated in this order and wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film, and after removing moisture at 80°C, the electrolyte was injected and packaged. Through process flows such as formation, degassing, and trimming, a lithium-ion battery was obtained. The thickness of the aluminum plastic film was 145 μm, which was a polypropylene layer, a highly ductile aluminum foil layer, and a nylon layer in order from the inside to the outside. The thickness of the aluminum foil layer was 50 μm, the thickness of the nylon layer was 20 μm, and the thickness of the polypropylene layer was 75 μm. The capacity of the lithium-ion battery was about 3 Ah. It was charged at a constant current up to 4.43 V with a charging current of 1 C, and then charged at a constant voltage up to 0.05 C. Next, it was left standing for 5 min and discharged at 0.7 C down to 3.0 V. It was charged and discharged 600 times at room temperature so as to repeat the charge and discharge process.

[0045] Example 1 Compared with Comparative Example 1, the difference was that the packaging film was a polypropylene layer, stainless steel, and a polyurethane layer in order from the inside to the outside. The thickness of the stainless steel was 30 μm, the tensile strength was 800 Mpa, the elongation at break was 20%, the thickness of the polyurethane layer was 5 μm, and the thickness of the polypropylene layer was 45 μm. The capacity of the lithium-ion battery and the charge and discharge method were the same as those in Comparative Example 1. In Examples 2 to 15 and Comparative Examples 2 to 7, the difference from Example 1 was only in the packaging film, and the details are shown in the following table. The capacity of the lithium-ion battery and the charge and discharge method were the same as those in Example 1.

[0046] Hereinafter, the measurement methods of each parameter of the present invention will be described. Measurement of the force reaching the limit by piercing with a blunt nail: The lithium-ion battery was fully charged, and the fully charged lithium-ion battery was placed on a flat iron plate. A blunt nail with a hemispherical tip, a diameter of φ6 ± 0.1 mm, and a length of 6.7 cm was used. The hemispherical tip was made perpendicular to the geometric center of the sample, and a hydraulic device was used to apply a pressing force to the blunt nail at a speed of 300 N / min, acting on the surface of the lithium-ion battery. The pressing force and the pressing displacement were recorded. The point at which the pressing displacement changed rapidly was recorded as the point where the sample was crushed and penetrated, and the maximum force corresponding to this time was recorded as the force reaching the limit.

[0047] Measurement of elongation at break: The sample for measurement was punched into a 15 mm × 70 mm sample with a punching machine, the sample was fixed to the measuring jig of a tensile testing machine made by Gotech, and the tensile strength of the sample was measured. The tensile speed was set at 5 mm / min, and the reference distance S0 between the two jigs of the tensile testing machine was set at 30 mm. The amount of tensile displacement was recorded, and when the sample broke, the amount of displacement by which the sample was stretched was taken as the maximum elongation amount S1 of the measurement sample. The calculation formula for the elongation rate of the measurement sample was S = S1 / S0 × 100%.

[0048] Measurement of puncture resistance: The sample for measurement was punched into a sample which was a round sheet with a circular diameter of 50 mm with a punching machine, and the sample was fixed to the test bench. Regarding the size of the puncturing steel nail used, the diameter of the body of the nail was 1 mm, and the tip of the nail was a hemisphere with a radius of 0.5 mm. The sample was punctured at a pressing speed of 50 mm / min. The maximum puncturing resistance applied to the steel nail during puncturing was taken as the puncture resistance of the sample.

[0049] Measurement of tensile strength: After manually peeling off the thermoplastic resin layer in the sample for measurement, it was immersed in N,N-dimethylformamide (NMF) for 3 h in an inert atmosphere at room temperature and without moisture. After the adhesion between the outer polymer insulation layer and the metal layer became weak and then dissolved and peeled off, it was wiped clean, the metal layer was separated and taken out for measurement. The sample for measurement was punched into a 15 mm×70 mm sample with a punching machine, the sample was fixed to the measuring jig of a tensile machine made by Gotech, and the tensile strength of the sample was measured. The tensile speed was set at 5 mm / min and the initial distance between the two jigs of the tensile machine was set at 30 mm. The strength and displacement during tension were recorded, and the maximum tensile strength when the sample broke was taken as the tensile strength of the sample.

[0050] Measurement of volume energy density: The lithium-ion battery was charged at a constant current to 4.45 V at a rate of 0.2 C and then charged at a constant voltage to 0.025 C to fully charge the lithium-ion battery. Next, it was discharged at a constant current to a voltage of 3.0 V at a rate of 0.2 C, and the total capacity discharged during discharge was recorded as C. The actual thickness H of the lithium-ion battery was measured, and the actual volume V of the lithium-ion battery was calculated. The energy density satisfies the energy density = C / V. Table 1 shows the respective parameters and evaluation results of Examples 1 to 15 and Comparative Examples 1 to 7.

[0051]

Table 1

[0052] As can be seen from the comparison between Examples 1 to 15 and Comparative Example 1, when using the high-strength metal package film of the present invention, the puncture resistance of the package film is greater than that of a normal aluminum plastic film with a greater thickness. The force required to reach the limit when the lithium-ion battery using the high-strength metal package film is punctured by a blunt nail is much greater than the force required to reach the limit when the lithium-ion battery using a normal aluminum plastic film with a greater thickness is punctured by a blunt nail. Moreover, since the thickness of the package film is reduced, the energy density of the lithium-ion battery is also significantly improved.

[0053] As can be seen from the comparison between Examples 1 to 5 and Comparative Examples 2 and 3, when the thickness of the metal layer in the high-strength metal package film is 10 μm to 60 μm, the package film exhibits an optimal improvement effect. When the thickness of the metal layer exceeds 60 μm, the thickness of the package film becomes relatively large, so the puncture resistance increases, but it has a significant adverse effect on the volume energy density of the lithium-ion battery. When the thickness of the metal layer is less than 10 μm, the thickness of the package film is relatively thin and the puncture resistance is small, so it is insufficient to improve the ability of the lithium-ion battery to resist breakage by external force.

[0054] As can be seen from the comparison between Examples 1, 6, and 7 and Comparative Examples 4 and 5, when the tensile strength of the metal layer in the high-strength metal package film is 300 MPa to 2000 MPa, the package film exhibits an optimal improvement effect. When the tensile strength of the metal layer exceeds 2000 MPa, due to the very high strength of the metal layer, the elongation rate deteriorates significantly and it shows a certain brittleness, so the puncture resistance decreases and it cannot meet the requirements. When the tensile strength of the metal layer is less than 300 MPa, due to the very low strength of the metal layer, its strength is insufficient to improve the ability to resist breakage by external force, so the puncture resistance is insufficient.

[0055] As can be seen from the comparison between Example 1, Examples 8 to 11 and Comparative Examples 6 and 7, when the ratio of the thickness of the thermoplastic resin layer (i.e., the inner layer) to the thickness of the metal layer is 0.6 to 3, the packaging film exhibits an optimal improvement effect. When this ratio exceeds 3, since the thickness of the inner layer becomes relatively large, the thickness of the entire packaging film becomes relatively large, so the puncture resistance strength becomes relatively high, but the volume energy density of the lithium-ion battery deteriorates. When this ratio is less than 0.6, the thickness of the inner layer is too thin, and since the inner layer also provides part of the mechanical strength, the puncture resistance strength of the entire packaging film is insufficient.

[0056] As can be seen from the comparison between Example 1, Example 12, and Example 13, by using a titanium alloy or a nickel alloy as the metal layer, an improvement effect similar to that of stainless steel can be achieved.

[0057] As can be seen from the comparison between Example 1, Example 14, and Example 15, as the thickness of the outer layer increases, the puncture resistance strength and the force reaching the limit when punctured by a blunt nail can be improved to a certain extent, but the volume energy density decreases.

[0058] The above description is only an explanation of the preferred embodiments of the present invention and the technical principles used. Those skilled in the art should understand that the scope disclosed in the present invention is not limited to the technical solutions formed by the specific combination of the above technical features, and should also include other technical solutions formed by arbitrarily combining the above technical features or their equivalent features. For example, a technical solution formed by replacing the above features with technical features having similar functions disclosed in the present invention can be cited.

Claims

1. A package film, comprising: an inner layer containing a thermoplastic resin; an outer layer containing a thermosetting resin; and a metal layer located between the inner layer and the outer layer, wherein the metal layer contains at least one of stainless steel, titanium alloy, and nickel alloy; the thickness of the metal layer is 10 μm to 60 μm; the tensile strength of the metal layer is 300 MPa to 2000 MPa; the ratio of the thickness of the inner layer to the thickness of the metal layer is 0.6 to 3. The package film.

2. The package film according to claim 1, wherein the thickness of the metal layer is 30 μm to 40 μm.

3. The package film according to claim 1, wherein the ratio of the thickness of the inner layer to the thickness of the metal layer is 0.6 to 2.

4. The package film according to claim 1, wherein the thickness of the outer layer is 1 μm to 10 μm.

5. The package film according to claim 1, wherein the elongation at break of the metal layer is 10% to 45%.

6. The package film according to claim 1, wherein the thermoplastic resin contains at least one of polyethylene, polyvinyl chloride, polypropylene, and polystyrene.

7. The package film according to claim 1, wherein the thermosetting resin contains at least one of polyurethane and polyacrylate.

8. The package film further comprises an adhesive layer, wherein the adhesive layer is located between the inner layer and the metal layer. The package film according to claim 1.

9. The package film according to claim 8, wherein the adhesive layer contains at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, polydifluoroethylene, aqueous acrylic resin, and polyvinyl formal.

10. The thickness of the package film is 20 μm to 130 μm, and the puncture resistance of the package film is 30 N to 70 N. The package film according to claim 1.

11. An electrochemical device comprising the package film according to any one of claims 1 to 10.

12. An electronic device comprising the electrochemical device according to claim 11.

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