CN118613947A

CN118613947A - Electrochemical device and electronic device

Info

Publication number: CN118613947A
Application number: CN202280090543.XA
Authority: CN
Inventors: 侯天昊
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-03-31
Filing date: 2022-03-31
Publication date: 2024-09-06
Also published as: WO2023184363A1

Abstract

An electrochemical device is provided, which includes an electrode assembly and an encapsulation film for encapsulating the electrode assembly, the encapsulation film including a first layer and a second layer, each of the first layer and the second layer being in a closed state, wherein a water vapor permeation rate WVTR of the encapsulation film is less than or equal to 0.001 g/(m ². Day). The volume of the packaging film for packaging the electrode assembly in the electrochemical device is small in proportion, the water vapor permeation rate of the packaging film is low, and the packaging reliability can be ensured while the volume energy density of the electrochemical device is improved. An electronic device including the electrochemical device is also provided.

Description

Electrochemical device and electronic device

Technical Field

The application relates to the field of energy storage, in particular to an electrochemical device and an electronic device.

Background

Secondary batteries have a wide range of applications in the consumer electronics field, and in recent years their end market has presented a demand for miniaturization, high energy density. Currently, there are two main current packaging forms of secondary batteries, soft packs and metal cases. However, these two conventional mainstream packaging processes have problems of relatively low space utilization and large battery energy density loss. The soft pack secondary battery generally has a top seal and a side seal, and the seal has no active material but occupies a certain volume, thus reducing the energy density of the battery, and the smaller the capacity of the electrode assembly, the more the energy density is reduced. In the prior art, although the energy density loss can be reduced by using a side seal flanging process, the leakage risk exists at the top seal position due to the fact that the electrode lug hot-melt layer and the packaging bag hot-melt layer are connected. In order to avoid short circuit between the electrode assembly and the shell, plastic gaskets or gummed paper are added for insulating treatment, and the parts do not contribute to stored energy but occupy the volume of the electrode assembly, so that the energy density of the secondary battery is reduced.

Disclosure of Invention

In view of the above problems of the prior art, the present application provides an electrochemical device and an electronic device including the same. The volume of the packaging film for packaging the electrode assembly in the electrochemical device is small in proportion, the water vapor permeation rate of the packaging film is low, and the packaging reliability can be ensured while the volume energy density of the electrochemical device is improved.

In a first aspect, the present application provides an electrochemical device comprising an electrode assembly and an encapsulation film for encapsulating the electrode assembly, the encapsulation film comprising a first layer and a second layer, each of the first layer and the second layer being in a closed configuration, wherein the water vapor permeation rate WVTR of the encapsulation film is less than or equal to 0.001 g/(m ² -day). The sealing film has the advantages that each layer in the sealing film is in a closed form, and structures such as sealing edges which do not contribute to energy storage are not arranged, so that the space utilization rate of an electrochemical device can be greatly improved, and the volume energy density of the electrochemical device is further improved. Meanwhile, the water vapor permeation rate of the packaging film is low, so that water vapor and oxygen molecules in the air can be effectively isolated from entering the electrochemical device, and solvent molecules in the electrolyte are isolated from escaping the electrochemical device, and the packaging reliability is ensured.

According to some embodiments of the application, the mass content of each metal element in the first layer and the second layer is less than 80%.

In some embodiments, the first layer is obtained by applying a first layer of raw material to the surface of the electrode assembly. According to the application, the first layer is integrally formed on the surface of the electrode assembly in a coating and packaging mode, and operations such as heat sealing or welding are not needed, so that structures such as sealing edges which do not contribute to stored energy are not needed, the space utilization rate of the electrochemical device can be greatly improved, and the volume energy density of the electrochemical device can be improved. In addition, the coating and packaging mode can better meet the packaging of the special-shaped electrochemical device.

According to some embodiments of the application, the second layer comprises an inorganic layer and optionally an organic polymer layer. The second layer of the application can isolate water vapor and oxygen molecules in the air from entering the electrochemical device, and isolate solvent molecules in the electrolyte from escaping the electrochemical device, so that the packaging reliability can be greatly ensured.

According to some embodiments of the application, the second layer comprises alternating inorganic layers and organic polymer layers.

According to some embodiments of the application, the inorganic layer has a thickness of 1nm or more. In some embodiments, the thickness of the organic polymer layer is greater than or equal to 1 μm.

According to some embodiments of the application, the inorganic layer comprises at least one of a metal, an inorganic oxide, or a nitride. According to some embodiments of the application, the organic polymer layer comprises a resin.

According to some embodiments of the application, the encapsulation film further includes a third layer, the first layer being in contact with the electrode assembly, the second layer being disposed between the third layer and the first layer.

According to some embodiments of the application, the first layer comprises a resin. In some embodiments, the third layer comprises fibers and a resin.

In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect.

Compared with the prior art, the application adopts a coating and packaging mode, greatly reduces the volume ratio of the packaging film and improves the energy density of the electrochemical device. Meanwhile, the packaging film has low water vapor permeation rate, can effectively isolate water vapor and oxygen molecules in air from entering the electrochemical device and isolate solvent molecules in electrolyte from escaping the electrochemical device, and ensures the packaging reliability.

Drawings

Fig. 1 is a schematic view of an encapsulation film in an electrochemical device according to some embodiments of the present application.

Fig. 2 is a schematic view illustrating the structure of an electrode assembly and a packaging film in an electrochemical device according to some embodiments of the present application.

Fig. 3 is a schematic view illustrating the structure of an electrode assembly and a packaging film in an electrochemical device according to some embodiments of the present application.

Fig. 4 is a schematic view of a barrier layer of the encapsulation film of fig. 3.

Fig. 5 is an X-ray CT diagram of a conventional aluminum plastic film-encapsulated electrochemical device, in which the outer encapsulation film of the electrode assembly is discontinuous and there is a significant trace of fusion encapsulation within the CT cross-sectional view range excluding the tab or post.

Fig. 6 is an X-ray CT view of a conventional metal-can-encapsulated electrochemical device, in which the outer encapsulation of the electrode assembly is discontinuous and there is a significant trace of fusion welding within the scope of the CT cross-sectional view excluding the tab or post.

Fig. 7 is an X-ray CT view of an electrochemical device according to some embodiments of the present application, in which the electrode assembly outer packaging film is continuous, free of obvious welding and packaging marks, and exhibits a continuous closure characteristic within a CT sectional view range excluding tabs or posts.

The reference numerals are explained as follows: 100-packaging film; 10-a closing layer; 20-a barrier layer; 200-electrode assembly; 1-an inorganic layer; 2-an organic polymer layer.

Detailed Description

The application is further described below in conjunction with the detailed description. It should be understood that the detailed description is intended by way of illustration only and is not intended to limit the scope of the application.

1. Electrochemical device

The "closed morphology" in the present application is that the morphology of each layer is uniform throughout, there is no structure formed by heat sealing or welding, for example, when the electrochemical device is observed by X-ray CT, no obvious welding or heat sealing trace exists in each layer in any CT sectional view range not including the tab or the post, and the closed characteristic is exhibited. More clearly, the cross-section can be observed by optical microscopy, as well as any other microscopic imaging means.

The "electrode assembly" in the present application refers to a portion of an electrochemical device composed of a positive electrode, a negative electrode, and a separator.

According to some embodiments of the application, the water vapor permeation rate WVTR of the encapsulating film is in the range of 0.0001 g/(m ² -day), 0.0002 g/(m ² -day), 0.0003 g/(m ² -day), 0.0004 g/(m ² -day), 0.0005 g/(m ² -day), 0.0006 g/(m ² -day), 0.0007 g/(m ² -day), 0.0008 g/(m ² -day), 0.0009 g/(m ² -day), or any two of these values.

According to some embodiments of the application, the mass content of the respective metallic element in the first and second layers is less than 80%, for example less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, less than 50%, less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 5% or less than 1%.

In some embodiments, the first layer is obtained by applying a first layer of raw material to the surface of the electrode assembly. According to the application, the first layer is integrally formed on the surface of the electrode assembly in a coating and packaging mode, and operations such as heat sealing or welding are not needed, so that structures such as sealing edges which do not contribute to stored energy are not needed, the space utilization rate of the electrochemical device can be greatly improved, and the volume energy density of the electrochemical device can be improved. In addition, the coating and packaging mode can better meet the packaging of the special-shaped electrochemical device. In some embodiments, coating comprises at least one of spraying, knife coating, dip coating, or brush coating.

In some embodiments, the first layer is a sealing layer, which is used to seal the electrode assembly on the one hand, ensure sealing fluid-tightness, and serves as a substrate for the second layer on the other hand, to increase adhesion with the second layer.

According to some embodiments of the application, the second layer comprises an inorganic layer and optionally an organic polymer layer. In some embodiments, the second layer is a barrier layer. The second layer of the application can isolate water vapor and oxygen molecules in the air from entering the electrochemical device, and isolate solvent molecules in the electrolyte from escaping the electrochemical device, so that the packaging reliability can be greatly ensured. In some embodiments, the second layer is vapor deposited on the surface of the first layer. In some embodiments, vapor deposition includes at least one of chemical vapor deposition, physical vapor deposition, or atomic layer deposition.

According to some embodiments of the application, the second layer comprises an inorganic layer and an organic polymer layer. In some embodiments, the second layer comprises alternating inorganic layers and organic polymer layers. In some embodiments, the second layer includes an inorganic layer, an organic polymer layer, and an inorganic layer stacked in that order. In some embodiments, the inorganic layer is formed by coating an organic polymer precursor on the surface of the first layer, and then evaporating an inorganic substance on the organic polymer layer using vapor deposition. In some embodiments, an inorganic layer is formed on the surface of the first layer by vapor deposition of an inorganic substance, and then an organic polymer precursor is coated on the surface of the inorganic layer, resulting in an organic polymer layer.

According to some embodiments of the application, the thickness of the inorganic layer is ≡1nm, for example in the range 5nm、10nm、30nm、50nm、70nm、90nm、100nm、110nm、130nm、150nm、170nm、190nm、200nm、230nm、250nm、270nm、300nm、350nm、400nm、450nm、500nm or any two of these values.

According to some embodiments of the application, the thickness of the organic polymer layer is ≡1 μm, for example 5 μm, 7 μm, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm or a range of any two of these values.

According to some embodiments of the application, the inorganic layer comprises at least one of a metal, an inorganic oxide, or a nitride. In some embodiments, the metal comprises at least one of a noble metal or a transition metal. In some embodiments, the metal comprises at least one of aluminum, iron, copper, silver, gold, nickel, manganese, zinc, tin, zirconium, titanium, or vanadium. In some embodiments, the inorganic oxide comprises at least one of titanium oxide, aluminum oxide, hafnium oxide, iron oxide, copper oxide, silver oxide, nickel oxide, manganese oxide, zinc oxide, tin oxide, zirconium titanium oxide, or vanadium oxide. In some embodiments, the nitride comprises at least one of silicon nitride, silicon oxynitride, boron nitride, titanium nitride, or aluminum nitride.

According to some embodiments of the application, the organic polymer layer comprises a resin. In some embodiments, the organic polymer layer includes at least one of an acrylic, an epoxy, or a polyurethane.

According to some embodiments of the application, the encapsulation film further includes a third layer, the first layer being in contact with the electrode assembly, the second layer being disposed between the third layer and the first layer. In some embodiments, the third layer is a protective layer for protecting the electrode assembly and providing high mechanical strength to inhibit expansion of the electrode assembly.

In some embodiments, the resin comprises at least one of a thermosetting resin or a thermoplastic resin.

"Thermosetting resin" in the present application may refer to a resin having thermosetting properties. Thermosetting means a property of being not dissolved even when the resin composition is heated to a temperature equal to or higher than the glass transition temperature Tg or the melting point Tm after being subjected to chemical change after heating and gradually hardened and molded. According to the test standard of the standard GB/T3682.1-2018, the melt index should be less than 1g/10min. In some embodiments, the thermosetting resin includes, but is not limited to, phenolic resins, epoxy resins, melamine resins, polyimide resins, polyester resins, acrylic resins, silicone resins, crosslinked polyolefin resins, and mixtures thereof.

The "thermoplastic resin" in the present application may refer to a resin having thermoplasticity. Thermoplastic refers to the property of repeatedly softening by heat, cooling and solidifying without chemical reaction. According to the standard GB/T3682.1-2018, the melt index should be greater than 1g/10min. In some embodiments, the thermoplastic resin includes, but is not limited to, polypropylene, polyethylene, polyvinylchloride, polystyrene, polyoxymethylene, polycarbonate, polyphenylene oxide, polysulfone, polyethylene terephthalate, and mixtures thereof.

According to some embodiments of the present application, an electrode assembly includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.

According to some embodiments of the application, a positive electrode includes a positive electrode active material layer and a positive electrode current collector.

According to some embodiments of the present application, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent. In some embodiments, the positive electrode active material may include at least one of lithium cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganate, spinel type lithium nickel manganate, and lithium titanate. In some embodiments, the binder may include various binder polymers, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, any conductive material may be used as the conductive agent as long as it does not cause a chemical change. Examples of the conductive agent include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like; metal-based materials such as metal powders or metal fibers including copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives and the like; or mixtures thereof.

According to some embodiments of the application, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, or the like) on a polymer substrate.

According to some embodiments of the application, a negative electrode includes a negative electrode active material layer and a negative electrode current collector.

According to some embodiments of the application, the anode active material layer includes an anode active material, a binder, and a conductive agent. In some embodiments, the anode active material may include a material that reversibly intercalates/deintercalates lithium ions, lithium metal alloy, or transition metal oxide. In some embodiments, the negative electrode active material includes at least one of a carbon material including at least one of graphite, hard carbon, or a silicon material including at least one of silicon, a silicon oxygen compound, a silicon carbon compound, or a silicon alloy. In some embodiments, the binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, aqueous acrylic resin, polyvinyl formal, or styrene-acrylic copolymer resin. In some embodiments, any conductive material may be used as the conductive material as long as it does not cause chemical changes. In some embodiments, the conductive material comprises at least one of conductive carbon black, acetylene black, carbon nanotubes, ketjen black, conductive graphite, or graphene.

According to some embodiments of the present application, the negative electrode current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

The material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic, etc., formed from a material that is stable to the electrolyte of the present application. For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

The surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer includes inorganic particles and a binder, the inorganic particles being at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is at least one selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The polymer layer contains a polymer, and the material of the polymer is at least one selected from polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).

The electrochemical device of the present application further includes an electrolyte. The electrolyte that can be used in the present application may be an electrolyte known in the art.

In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and optionally an additive. The organic solvent of the electrolyte according to the present application may be any organic solvent known in the art as a solvent of the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and may be any electrolyte known in the art. The additive of the electrolyte according to the present application may be any additive known in the art as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent comprises an ether-type solvent, for example, comprising at least one of 1, 3-Dioxapentacyclic (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the electrolyte salt may be a lithium salt, a sodium salt, or the like. In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium difluorophosphate (LiPO ₂F ₂), lithium bis (trifluoromethanesulfonyl) imide LiN (CF ₃SO ₂) ₂ (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO ₂F) ₂) (LiFSI), lithium bis (oxalato) borate LiB (C ₂O ₄) ₂ (LiBOB) or lithium difluorooxalato borate LiBF ₂(C ₂O ₄) (lidaob).

In some embodiments, the electrochemical device of the present application includes, but is not limited to: primary batteries, secondary batteries, or capacitors of all kinds. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries. In some embodiments, the electrochemical device is a sodium ion battery.

2. Electronic device

The present application further provides an electronic device comprising an electrochemical device according to the first aspect of the application.

The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-compact discs, transceivers, electronic notepads, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, gaming machines, watches, power tools, flashlights, cameras, home-use large storage batteries, lithium ion capacitors, and the like.

In the following examples and comparative examples, reagents, materials and instruments used, unless otherwise specified, were commercially available.

Examples and comparative examples

1. Preparation of negative electrode plate

Mixing negative electrode active material Graphite (Graphite), conductive carbon black (Super P) and Styrene Butadiene Rubber (SBR) according to a weight ratio of 96:1.5:2.5, adding deionized water (H ₂ O) as a solvent, preparing into slurry with solid content of 0.7, and uniformly stirring. The slurry is uniformly coated on a negative current collector copper foil, and the weight of an effective substance on a pole piece is 95g/m ². And drying at 110 ℃ to obtain the negative electrode plate. After the steps are finished, the single-sided coating of the negative electrode plate is finished. And then, completing the steps on the back of the pole piece by a completely consistent method, and obtaining the double-sided coated negative pole piece. After coating, cold pressing the negative electrode plate to a compaction density of 1.7g/cm ³, and thus completing all preparation processes of the negative electrode plate.

2. Preparation of positive electrode plate

The positive electrode active material lithium cobaltate (LiCoO ₂), conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 97.5:1.0:1.5, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is prepared into slurry with the solid content of 0.75, and the slurry is uniformly stirred. The slurry is uniformly coated on an aluminum foil of the positive current collector, and the weight of the active substances on the pole piece is 180g/m ². And drying at 90 ℃ to obtain the positive electrode plate. After the steps are finished, the single-sided coating of the positive electrode plate is finished. And then, completing the steps on the back of the pole piece by a completely consistent method, and obtaining the positive pole piece with the double-sided coating. After coating, cold pressing the positive pole piece to a compaction density of 4.1g/cm ³, and thus completing all preparation processes of the positive pole piece.

3. Preparation of electrolyte

In a dry argon atmosphere, the organic solvents of Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) are firstly mixed according to the mass ratio EC: EMC: dec=30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF ₆) is added into the organic solvent for dissolution and uniform mixing, so that an electrolyte with the concentration of lithium salt of 1.15M is obtained.

4. Preparation of lithium ion batteries

Polyethylene (PE) with the thickness of 15 mu m is selected as an isolating film, a positive pole piece, the isolating film and a negative pole piece are sequentially stacked, the isolating film is positioned between the positive pole piece and the negative pole piece to play a role of isolation, then the stacked pole pieces and the isolating film are rolled into an electrode assembly, then the electrode assembly is injected with liquid, and the electrode assembly with the injected liquid is packaged. Specifically, the resin precursor (specific type see table below) is preferably coated, a resin layer (i.e., a sealing layer) is formed after curing, then the inorganic substance (specific type see table below) is evaporated on the surface of the resin layer by using a vapor deposition method, and the resin precursor (specific type see table below) is optionally coated on the surface of the layer formed by the inorganic substance, so as to form a barrier layer. And (3) performing operations such as formation (0.02C constant current charging to 3.3V and then 0.1C constant current charging to 3.6V) on the packaged electrode assembly to obtain the soft-package lithium ion battery.

Test method

1. Water vapor permeation rate test

The finished battery is carefully disassembled with ceramic scissors, the electrode assembly and the packaging film are peeled off, and the packaging film with a size of at least 1 square centimeter is removed. Meanwhile, an aluminum plastic film with the diameter of 10cm is prepared, and the aluminum plastic film has at least 4 hole breaking defects of 0.5 square centimeter. And (3) sticking the packaging film of the finished battery to the hole breaking area of the aluminum plastic film by using double faced adhesive tape, and then testing by referring to national standard GB/T21529-2008.

2、X-ray CT

The battery was transferred into an X-Ray computerized tomography (X-Ray CT, model: GE Phoenix m 300) equipped cavity and scanned. And then, using software matched with the equipment to calculate and synthesize the scanned image of the battery. The processed image can be cut off to any section of the battery, and a synthesized X-ray CT section image is obtained.

Note that during the process of selecting the cross-sectional image, the region including the tab at the outermost side of the battery in the taken image is avoided. The resulting image is truncated to adjust brightness until the outline of the package can be distinguished.

3. Optical microscope for observing package outline

And (3) completely embedding the battery by using epoxy resin, then placing the embedded battery in a liquid nitrogen atmosphere, carrying out brittle fracture treatment (the outermost side of the brittle fracture position of the battery does not contain a lug), and carrying out leveling treatment on the fracture of the fracture section by using a frozen ultrathin section technology to obtain a sample suitable for observation by an optical microscope.

And placing the sample under an optical microscope (model: olympus BX 53M), adjusting the focal length to a clear position of the packaging body, selecting a microscope lens with proper magnification, and obtaining a complete section optical microscopic image by using the image stitching function.

4、EDS

And (3) completely embedding the battery by using epoxy resin, then placing the embedded battery in a liquid nitrogen atmosphere, carrying out brittle fracture treatment on the battery (the outermost side of the brittle fracture position of the battery core does not contain a lug, and using a frozen ultrathin section technology to make a section have a better leveling treatment effect), and transferring a sample of the packaging film area into a Scanning Electron Microscope (SEM) cavity to obtain a sample for scanning electron microscope analysis.

The sample is observed under SEM, and data acquisition is carried out by utilizing X-ray energy spectrum analysis (EDS) under proper magnification, so that the element content of the packaging film region is obtained. At least 3 different positions are collected and averaged.

5. Energy density of battery

Standing the battery for not less than 30 minutes at room temperature (25 ℃ plus or minus 2 ℃); charging to a specified cutoff condition (charging time is not longer than 8 h) according to a specified charging mode of shipment; standing for not less than 30 minutes, and measuring discharge energy E (in terms of Wh); measuring the maximum value of the length, width and height directions of the lithium ion battery by using a micrometer or a vernier caliper, and measuring the volume V (in L); volumetric energy density of battery discharge VED (Wh/L) =e/V.

6. Cycle capacity retention rate of battery

The battery was left to stand at 25.+ -. 3 ℃ for 30 minutes, an external circuit was turned on, charged to 4.4V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.4V, then discharged to 3.0V at a current of 0.2C, and the discharge capacity was recorded as Q1. Repeating the above steps 500 times, recording the capacity retention rate of 500 circles at 25 ℃ when the discharge capacity is Q500:

η(％)＝Q500/Q1×100％

Test results

TABLE 1

The effect of different encapsulation on volumetric energy density is presented in table 1, comparative example 1 and comparative example 2 being conventional soft-or metal-shell encapsulation, example 1 being a coated encapsulation. Compared with the traditional packaging mode, the energy density of the lithium ion battery is improved by more than 15%.

TABLE 2

Table 2 shows the effect of different barrier layer compositions on cell cycle performance. The material selected in comparative example 3 contained no inorganic barrier layer and had a water vapor permeability of 0.10015 g/(m ². Day), so that the cycle capacity decayed faster. Examples 2 and 3 employed a barrier process of atomic layer deposition of single or double layer alumina, with lower moisture permeability and cycle life improved by more than 30% compared to comparative example 3.

TABLE 3 Table 3

Note that: the battery preparation of examples 3-1 to 3-5 and the remaining parameters were identical to example 1, except for the barrier layer material.

The impact of different inorganic barrier materials on cell cycle performance is shown in table 3, examples 3-1 and 3-2 are pure metals, examples 3-3 and 3-4 are inorganic oxides, and examples 3-5 are composite structures of metal + inorganic oxides. Wherein, the composite structure of metal and inorganic oxide has remarkable improvement on the cycle performance of the battery.

TABLE 4 Table 4

Note that: the battery preparation of examples 4-1 to 4-2 and the remaining parameters were identical to example 3, except for the barrier layer material and structure.

Table 4 shows the effect of different barrier layer structures on the cycle performance of the battery, examples 4-1 and 4-2 are laminated structures of inorganic layer and organic layer, and example 4-3 is a 3-composite laminated structure of inorganic layer and organic layer and inorganic layer, and compared with the single-layer inorganic barrier layer, the cycle performance is improved by more than 5%.

TABLE 5

Note that: the battery preparation of examples 5-1 to 5-3 and the remaining parameters were identical to example 3, except for the barrier layer material, structure and thickness.

Table 5 shows the effect of different barrier layer thicknesses on cell cycling performance, with example 5-1 using a thinner inorganic barrier layer, the energy density is relatively high, and cycling performance is affected somewhat relative to thicker examples 5-2 and 5-3 for thicker barrier layers. Therefore, the thickness of the inorganic layer is preferably 10nm or more.

Although illustrative embodiments have been shown and described, it will be understood by those skilled in the art that the foregoing embodiments are not to be construed as limiting the application, and that changes, substitutions and alterations may be made therein without departing from the spirit, principles and scope of the application.

Claims

An electrochemical device comprising an electrode assembly and an encapsulation film for encapsulating the electrode assembly, the encapsulation film comprising a first layer and a second layer, each of the first layer and the second layer being in a closed configuration, wherein the water vapor permeation rate WVTR of the encapsulation film is less than or equal to 0.001 g/(m ² -day).
The electrochemical device according to claim 1, wherein the mass content of each metal element in the first layer and the second layer is less than 80%.
The electrochemical device according to claim 1, wherein the first layer is obtained by coating a first layer raw material on the surface of the electrode assembly.
The electrochemical device of claim 1, wherein the second layer comprises an inorganic layer and an optional organic polymer layer.
The electrochemical device of claim 1, wherein the second layer comprises alternating inorganic and organic polymer layers.
The electrochemical device according to claim 4 or 5, wherein the inorganic layer has a thickness of 1nm or more and the organic polymer layer has a thickness of 1 μm or more.
The electrochemical device of claim 4 or 5, wherein the inorganic layer comprises at least one of a metal, an inorganic oxide, or a nitride; and/or

The organic polymer layer includes a resin.
The electrochemical device of claim 1, wherein the encapsulation film further comprises a third layer, the first layer being in contact with the electrode assembly, the second layer being disposed between the third layer and the first layer.
The electrochemical device of claim 8, wherein the first layer comprises a resin and/or the third layer comprises fibers and a resin.
An electronic device comprising the electrochemical device of any one of claims 1 to 9.