WO2023184364A1

WO2023184364A1 - Electrochemical device and electronic device

Info

Publication number: WO2023184364A1
Application number: PCT/CN2022/084461
Authority: WO
Inventors: 侯天昊; 胡乔舒
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-31
Filing date: 2022-03-31
Publication date: 2023-10-05

Abstract

Provided is an electrochemical device, which comprises a packaging body and an electrode assembly located inside the packaging body, wherein the packaging body has a multi-layer structure, and each layer of the multi-layer structure is in a closed state. Each layer of the packaging body of the present application is in a closed state, and there are no structures such as seal edges which do not contribute to energy storage, so that the space utilization rate of the electrochemical device can be greatly increased, thereby improving the volumetric energy density of the electrochemical device. Also provided is an electronic device comprising the electrochemical device.

Description

Electrochemical devices and electronic devices

Technical field

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

Background technique

Secondary batteries are widely used in the field of consumer electronics, and in recent years, their end markets have shown demands for miniaturization and high energy density. Currently, there are two mainstream packaging forms for secondary batteries, soft pack and metal shell packaging. However, these two traditional mainstream packaging processes have problems such as relatively low space utilization and large loss of battery energy density. Soft-pack secondary batteries commonly have top seals and side-sealing edges. The seal edges have no active material but occupy a certain volume, thus reducing the energy density of soft-pack batteries. And the smaller the battery capacity, the more the energy density decreases. Although the side sealing and folding process can be used in the prior art to reduce energy density loss, there is a risk of liquid leakage at the top seal due to the hot melt layer connecting the tab and the hot melt layer of the packaging bag. Metal shell batteries generally have sealed flange edges, or in order to avoid short circuiting between the electrode assembly and the case, plastic gaskets or tapes need to be added for insulation. This part also does not contribute to energy storage but occupies the volume of the electrode assembly, thus reducing secondary Energy density of secondary battery.

Contents of the invention

In view of the above problems existing in the prior art, the present application provides an electrochemical device and an electronic device including the electrochemical device, so as to improve the space utilization of the electrochemical device and thereby increase its energy density.

In a first aspect, the present application provides an electrochemical device, which includes a package body and an electrode assembly located inside the package body. The package body has a multi-layer structure, wherein each layer in the multi-layer structure is in a closed form. Each layer of the package of the present application is in a closed form, and there are no edge sealing and other structures that do not contribute to energy storage, which can greatly improve the space utilization of the electrochemical device and thereby increase its volumetric energy density.

According to some embodiments of the present application, the mass content of metal elements in each layer of the multi-layer structure is less than 80%.

According to some embodiments of the present application, the volume of the electrochemical device is V1, and the volume of the electrode assembly is V2, where 1.01≤V1/V2≤2. When the volume ratio of the electrochemical device and the electrode assembly in the present application is within the above range, the volume ratio of the package is correspondingly reduced, and the space utilization rate of the electrochemical device is high, which can effectively increase its volumetric capacity density.

According to some embodiments of the present application, the maximum vertical distance between the electrode assembly and the package is g, 0.1 mm ≤ g ≤ 15 mm. If g is too small, the cycle capacity retention rate of the electrochemical device will be low. When g is too large, the energy density of the electrochemical device is low.

According to some embodiments of the present application, the thickness of the package is h, 70 μm≤h≤2000 μm. If the thickness is too small, the packaging reliability of the package will be low, which will further reduce the electrochemical cycle capacity retention rate. When the thickness is too large, the volume ratio of the package increases and the space utilization of the electrochemical device decreases, which in turn reduces its energy density.

According to some embodiments of the present application, the package body includes a first layer, a second layer and a third layer arranged in a stack, and the first layer is in contact with the electrode assembly.

According to some embodiments of the present application, the first layer is obtained by coating the first layer of raw material on the surface of the electrode assembly. In this application, the coating and encapsulation method is used to integrate the first layer on the surface of the electrode assembly, eliminating the need for operations such as heat sealing or welding. Furthermore, there is no edge sealing or other structures that do not contribute to energy storage, which can be extremely effective. Greatly improve the space utilization of electrochemical devices and increase their volumetric energy density. In addition, the coating and packaging method of the present application can also better meet the packaging requirements of special-shaped electrochemical devices.

According to some embodiments of the present application, the thickness of the first layer is H1, and the thickness of the third layer is H3, where 0.5≤H3/H1≤5. The ratio of H3/H1 will affect the energy density and cycle performance of the electrochemical device. If H3/H1 is too small, the packaging reliability of the package will be low, which will in turn reduce the electrochemical cycle capacity retention rate. When H3/H1 is too large, the space utilization of the electrochemical device is reduced, which in turn reduces its energy density.

According to some embodiments of the present application, 5μm≤H1≤1000μm. In some embodiments, the thickness of the second layer is H2, 1 nm≤H2≤500 μm. In some embodiments, 5 μm ≤ H3 ≤ 1900 μm.

According to some embodiments of the present application, the material of the first layer includes resin. In some embodiments, the material of the second layer includes at least one selected from metal elements, non-metal oxides or metal oxides and optional resin. In some embodiments, the material of the third layer includes fiber and resin.

According to some embodiments of the present application, the bonding force between the second layer and the third layer is ≥1 N/m. When the bonding force between the second layer and the third layer is less than 1 N/m, the package is prone to delamination, which in turn affects the cycle capacity retention rate of the electrochemical device.

In a second aspect, the present application provides an electronic device including the electrochemical device described in the first aspect.

Compared with the existing technology, this application uses coating and encapsulation, which greatly reduces the volume ratio of the package, improves the energy density of the electrochemical device, and can also better meet the packaging requirements of special-shaped electrochemical devices.

Description of drawings

Figure 1 is a perspective view of an electrochemical device according to some embodiments of the present application.

Figure 2 is a top view and A-A' cross-sectional view of the electrochemical device shown in Figure 1.

Fig. 3 is a front view and a B-B' cross-sectional view of the electrochemical device shown in Fig. 1.

Figure 4 is a front view and a B-B' cross-sectional view of the electrochemical device shown in Figure 1.

Figure 5 is an X-ray CT image of the traditional aluminum-plastic film-encapsulated electrochemical device in Comparative Example 1-1.

Figure 6 is an X-ray CT image of the traditional metal shell packaged electrochemical device in Comparative Example 1-2.

Figure 7 is an X-ray CT image of the electrochemical device of Example 1-2.

Figure 8 is an electrochemical device in the form of temples according to some embodiments of the present application.

Figure 9 is a schematic diagram of the maximum vertical distance from the surface of the electrode assembly to the outer surface of the package of the electrochemical device according to some embodiments of the present application.

The reference numbers are as follows: 100-electrochemical device; 10-pole lug; 20-package body; 1-electrode assembly; 2-pole post; 3-sealing layer; 4-barrier layer; 5-protective layer; 201, 202 , 203-The vertical distance from the surface of the electrode assembly to the outer surface of the package.

Detailed ways

The present application will be further elaborated below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

1. Electrochemical device

The "closed form" in this application means that the morphology of each layer is uniform throughout, and there is no structure formed by heat sealing or welding. For example, when observing the electrochemical device through X-ray CT, it does not contain tabs or poles. Within the scope of any CT cross-section of the column, there are no obvious traces of welding and heat sealing in each layer, showing closed characteristics. More clearly, the above-mentioned cross-section can be observed through an optical microscope and any other microscopic imaging method.

According to some embodiments of the present application, the mass content of metal elements in each layer of the multi-layer structure accounts for less than 80%, such as 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%.

According to some embodiments of the present application, the volume of the electrochemical device is V1, and the volume of the electrode assembly is V2, where 1.01≤V1/V2≤2. In some embodiments, V1/V2 is a range consisting of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or any two of these values. When the volume ratio of the electrochemical device and the electrode assembly in the present application is within the above range, the volume ratio of the package is correspondingly reduced, and the space utilization rate of the electrochemical device is high, which can effectively increase its volumetric capacity density.

"Electrode assembly" in this application refers to the part of an electrochemical device consisting of a positive electrode, a negative electrode and a separator.

In this application, the "volume of the electrochemical device" includes the product of the projected area of the electrochemical device of the package and the thickness of the electrochemical device. The projected area of the electrochemical device is the most stable form of the electrochemical device. The projected area of the bottom surface of the electrochemical device when placed on a flat plate.

In this application, the "volume of the electrode assembly" is the product of the projected area of the electrode assembly and the thickness of the electrode assembly in a state that does not include the package and does not contain the electrolyte. The projected area of the electrode assembly is The projected area of the bottom surface of the electrode assembly when it is placed on a flat plate in its most stable state.

According to some embodiments of the present application, the maximum vertical distance between the electrode assembly and the package is g, 0.1 mm ≤ g ≤ 15 mm. In some embodiments, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm , 4.0mm, 4.5mm, 5.0mm, 5.5mm, 6.0mm, 6.5mm, 7.0mm, 7.5mm, 8.0mm, 8.5mm, 9.0mm, 9.5mm, 10mm, 10.5mm, 11mm, 11.5mm, 12mm, 12.5 mm, 13mm, 13.5mm, 14mm, 14.5mm or a range consisting of any two of these values. If g is too small, the cycle capacity retention rate of the electrochemical device will be low. When g is too large, the energy density of the electrochemical device is low.

According to some embodiments of the present application, the thickness of the package is h, 70 μm≤h≤2000 μm. In some embodiments, h is 70 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm , 1800μm, 1900μm or these values A range consisting of any two of them. If the thickness is too small, the packaging reliability of the package will be low, which will further reduce the electrochemical cycle capacity retention rate. When the thickness is too large, the volume ratio of the package increases and the space utilization of the electrochemical device decreases, which in turn reduces its energy density.

According to some embodiments of the present application, the package body includes a first layer, a second layer and a third layer arranged in a stack, and the first layer is in contact with the electrode assembly. In some embodiments, the first layer is a sealing layer, used to seal the electrode assembly to ensure that the sealing is liquid-tight. In some embodiments, the second layer is a barrier layer used to block water vapor and oxygen molecules in the air from entering the electrochemical device and to block solvent molecules in the electrolyte from escaping from the electrochemical device. In some embodiments, the third layer is a protective layer used to protect the electrode assembly and provide high mechanical strength to inhibit expansion of the electrode assembly.

According to some embodiments of the present application, the first layer is obtained by coating the first layer of raw material on the surface of the electrode assembly. In this application, the coating and encapsulation method is used to integrate the first layer on the surface of the electrode assembly, eliminating the need for operations such as heat sealing or welding. Furthermore, there is no edge sealing or other structures that do not contribute to energy storage, which can be extremely effective. Greatly improve the space utilization of electrochemical devices and increase their volumetric energy density. In addition, the coating and packaging method of the present application can also better meet the packaging requirements of special-shaped electrochemical devices. In some embodiments, coating includes at least one of spraying, blade coating, dipping or brushing.

As shown in Figures 1 to 4, some embodiments of the present application provide an electrochemical device 100. The electrochemical device is wrapped by a package 20, and the positive electrode tab or the negative electrode tab is exposed to the outside for communication with the outside. Circuit item connections. Among them, in Figure 2, the innermost side of the AA' cross-section is the electrode assembly 1, and the cross-section does not include the tab 10. The shaded part is an integrated continuous packaging shell with no traces of welding or hot-melt packaging. To the outside are the sealing layer 3, the barrier layer 4 and the protective layer 5. In Figure 3, the innermost side of the B-B' cross-section is the electrode assembly 1, and the cross-section does not include the tab 10. The shaded part is the integrated continuous packaging shell, with no traces of welding or hot-melt packaging, from the inside to the outside. In order, there are sealing layer 3, barrier layer 4 and protective layer 5. In Figure 4, the innermost side of the C-C' cross-sectional view is the electrode assembly 1, but it contains the tab 10 or the pole 2. The shaded part is the integrated continuous packaging shell, but it is discontinuous at the tab or pole. , from the inside to the outside are the sealing layer 3, the barrier layer 4 and the protective layer 5.

According to some embodiments of the present application, 5μm≤H1≤1000μm. In some embodiments, H1 is a range consisting of 10 μm, 50 μm, 70 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or any two of these values.

According to some embodiments of the present application, the thickness of the second layer is H2, 1 nm≤H2≤500 μm. In some embodiments, H2 is 50 nm, 100 nm, 500 nm, 700 nm, 1 μm, 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 any of these values The range composed of both.

According to some embodiments of the present application, 5μm≤H3≤1900μm. In some embodiments, H3 is 10 μm, 50 μm, 70 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 16 00μm, 1700μm, 1800μm or A range consisting of any two of these values.

According to some embodiments of the present application, the material of the first layer includes resin. According to some embodiments of the present application, the material of the second layer includes at least one selected from metal elements, non-metal oxides or metal oxides and optional resin. According to some embodiments of the present application, the material of the third layer includes fiber and resin.

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

"Thermosetting resin" in this application may refer to a resin with thermosetting properties. Thermoset refers to the property that chemical changes occur after heating and gradually harden into shape. After hardening into shape, it cannot dissolve even when heated to above the glass transition temperature Tg or melting point Tm. According to the test standards of the standard "GB/T 3682.1-2018", the melt index should be <1g/10min. In some embodiments, thermoset resins include, but are not limited to, phenolic resins, epoxy resins, melamine resins, polyimide resins, polyester resins, acrylic resins, silicone resins, cross-linked polyolefin resins, and mixtures thereof.

"Thermoplastic resin" in this application may refer to a resin with thermoplasticity. Thermoplasticity refers to the property of repeatedly softening when heated and solidifying when cooled without chemical reaction. According to the standard "GB/T 3682.1-2018", the melt index should be greater than 1g/10min. In some embodiments, thermoplastic resins include, but are not limited to, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyphenylene ether, polysulfone, polyethylene terephthalate, and its mixture.

In some embodiments, the metal element includes at least one of aluminum, copper, silver, gold, titanium or nickel. In some embodiments, the non-metal oxide includes at least one of silicon oxide, silicon nitride, or silicon oxynitride. In some embodiments, the metal oxide includes at least one of titanium oxide, aluminum oxide, or hafnium dioxide.

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

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

According to some embodiments of the present application, the positive active material layer includes a positive active material, a binder, and a conductive agent. In some embodiments, the cathode active material may include lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron manganese phosphate, silicic acid At least one of lithium iron, 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 polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethylcellulose, lithium carboxymethylcellulose, modified At least one of polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, any conductive material can be used as the conductive agent as long as it does not cause chemical changes. Examples of conductive agents include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials, such as metal powder or metal fibers including copper, nickel, aluminum, silver, etc. ; Conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof.

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

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

According to some embodiments of the present application, the negative active material layer includes a negative active material, a binder, and a conductive agent. In some embodiments, the negative active material may include a material that reversibly intercalates/deintercalates lithium ions, lithium metal, lithium metal alloy, or transition metal oxide. In some embodiments, the negative active material includes at least one of carbon material or silicon material, the carbon material includes at least one of graphite and hard carbon, and the silicon material includes silicon, silicon oxy compound, silicon carbon compound or silicon alloy. of at least one. In some embodiments, the binder includes styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, water-based acrylic resin , at least one of polyvinyl formal or styrene-acrylic acid copolymer resin. In some embodiments, any conductive material can be used as the conductive material as long as it does not cause chemical changes. In some embodiments, the conductive material includes 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 copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with conductive metal, or a combination thereof.

The material and shape of the isolation membrane used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes polymers or inorganic substances formed of materials that are stable to the electrolyte of the present application. For example, the isolation film may include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, film or composite film with a porous structure. The base material layer is made of at least one material selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane can be used.

A surface treatment layer is provided on at least one surface of the base layer. 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 layer.

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

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

The electrochemical device of the present application also includes an electrolyte. Electrolytes useful in this application may be electrolytes known in the art.

In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent of the electrolyte solution according to the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte solution. The electrolyte used in the electrolyte solution according to the present application is not limited, and it can be any electrolyte known in the prior art. The additives of the electrolyte according to the present application may be any additives known in the art that can be used as electrolyte additives. In some embodiments, organic solvents include, but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) ), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes ether solvents, such as at least one of 1,3-dioxane (DOL) and ethylene glycol dimethyl ether (DME). 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 ₂ F ₂ ), lithium bistrifluoromethanesulfonimide LiN (CF ₃ SO ₂ ) ₂ (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), lithium bisoxalatoborate LiB(C ₂ O ₄ ) ₂ (LiBOB) or Lithium difluorooxalate borate LiBF ₂ (C ₂ O ₄ ) (LiDFOB).

In some embodiments, electrochemical devices of the present application include, but are not limited to: all types of primary batteries, secondary batteries, or capacitors. 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 devices

The present application further provides an electronic device, which includes the electrochemical device described in the first aspect of the present application.

The electronic equipment or device of the present application is not particularly limited. In some embodiments, electronic devices of the present application include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, and stereo headsets. , VCR, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, power-assisted bicycle, bicycle , lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

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

Examples and Comparative Examples

1. Preparation of negative electrode pieces

Mix the negative active materials graphite (Graphite), conductive carbon black (Super P), and styrene-butadiene rubber (SBR) at a weight ratio of 96:1.5:2.5, add deionized water (H ₂ O) as the solvent, and prepare to a solid content 0.7 slurry and stir evenly. The slurry is evenly coated on the negative electrode current collector copper foil, and the weight of the effective substance on the electrode piece is 95g/m ² . Dry at 110°C to obtain the negative electrode piece. After the above steps are completed, the single-sided coating of the negative electrode piece has been completed. After that, these steps are also completed on the back of the electrode piece in a completely consistent method, that is, a double-sided coated negative electrode piece is obtained. After the coating is completed, the negative electrode sheet is cold-pressed to a compacted density of 1.7g/ ^cm3 , which completes the entire preparation process of the negative electrode sheet.

2. Preparation of positive electrode pieces

Mix the cathode active materials lithium cobalt oxide (LiCoO ₂ ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) at a weight ratio of 97.5:1.0:1.5, and add N-methylpyrrolidone (NMP) as a solvent , prepare into a slurry with a solid content of 0.75, and stir evenly. The slurry is evenly coated on the positive electrode current collector aluminum foil, and the weight of the effective substance on the electrode piece is 180g/m ² . Dry at 90°C to obtain the positive electrode piece. After the above steps are completed, the single-sided coating of the positive electrode sheet has been completed. After that, these steps are also completed on the back of the electrode piece in a completely consistent manner, that is, a double-sided coated positive electrode piece is obtained. After the coating is completed, the positive electrode sheet is cold-pressed to a compacted density of 4.1g/ ^cm3 , which completes the entire preparation process of the positive electrode sheet.

3. Preparation of electrolyte

In a dry argon atmosphere, first mix the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a mass ratio of EC:EMC:DEC=30:50:20, and then Add the lithium salt lithium hexafluorophosphate (LiPF ₆ ) to the organic solvent, dissolve it and mix it evenly to obtain an electrolyte solution with a lithium salt concentration of 1.15M.

4. Battery preparation

Use polyethylene (PE) with a thickness of 15 μm as the isolation film, stack the positive electrode piece, isolation film, and negative electrode piece in order, so that the isolation film is between the positive and negative electrodes to play the role of isolation, and then fold the stacked The pole piece and isolation film are rolled into an electrode assembly, and the electrode assembly is packaged. Specifically, a polyolefin solution was dissolved in cyclohexane to prepare a solution with a mass fraction of 15%, and was sprayed (spraying pressure was 0.2MPa) on the surface of the electrode assembly. After solidification, a sealing layer was obtained. Then, aluminum oxide is deposited on the surface of the sealing layer using chemical vapor deposition to form a barrier layer. Finally, the glass fiber is pre-wound on the surface of the electrode assembly, and then sprayed with epoxy paint (spraying pressure is 0.2MPa) to form a protective layer on the surface of the barrier layer to complete the packaging of the electrode assembly (the sealing layer, barrier layer and protective layer For thicknesses H1, H2 and H3, please refer to specific examples or comparative examples). The encapsulated electrode assembly is subjected to a liquid injection operation, and after formation (0.02C constant current charging to 3.3V, and then 0.1C constant current charging to 3.6V) and other operations, a soft-packed lithium-ion battery is obtained.

Test Methods

1. EDS test

The battery is completely embedded in epoxy resin, and then the embedded battery is placed in a liquid nitrogen atmosphere, and the battery is subjected to brittle fracture treatment (the outermost part of the brittle fracture position of the battery does not contain tabs, and cryo-ultrathin sectioning technology is used to The effect will be better if the cross section is smoothed), and transfer the sample from the packaging film area to the scanning electron microscope (SEM) cavity to obtain the sample for scanning electron microscopy analysis.

Observe the sample under SEM, and use X-ray energy spectroscopy (EDS) at an appropriate magnification to collect data to obtain the element content in the packaging film area. Collect at least 3 different locations and take the average.

2. X-ray CT

Transfer the battery to a cavity equipped with X-ray electronic computed tomography (X-Ray CT, model: GE Phoenix m300) to scan the battery. The scanned battery images are then calculated and synthesized using the software provided by the device. The processed image can be used to cut any cross-section of the battery to obtain a synthesized X-ray CT cross-sectional image.

Please note that when selecting cross-sectional images, avoid the area containing the tabs on the outermost side of the battery in the captured image. The brightness of the captured image should be adjusted until the outline of the package can be distinguished.

3. Observe the package outline with an optical microscope

Use epoxy resin to completely embed the battery, and then place the embedded battery in a liquid nitrogen atmosphere to conduct brittle fracture treatment (the outermost part of the brittle fracture position of the battery does not contain tabs), and then use frozen ultra-thin sections Using technology to smooth the cross section, a sample suitable for optical microscope observation can be obtained.

Place the above sample under an optical microscope (model: Olympus BX53M), adjust the focal length to a clear position of the package, select a microscope lens with an appropriate magnification, and use the image stitching function to obtain a complete cross-sectional optical microscopic image.

4. Battery capacity and energy density

At room temperature (25℃±2℃), let the battery sit for no less than 30 minutes; charge it according to the charging method specified in the shipment to the cut-off conditions specified in the shipment (charging time is no more than 8 hours); let it sit for no less than 30 minutes. Measure the discharge energy E (in Wh); use a micrometer or vernier caliper to measure the maximum length, width and height of the lithium-ion battery, and measure the volume V (in L); the volumetric energy density of battery discharge VED (Wh/L) = E /V.

5. Battery cycle capacity retention rate

Let the battery stand for 30 minutes at 25±3℃, connect the external circuit, charge to 4.4V with a constant current of 0.5C, then charge to a current of 0.05C with a constant voltage of 4.4V, and then discharge to 3.0V with a current of 0.2C. Record the discharge capacity as Q1. Repeat the above steps 500 times and record the discharge capacity as Q500. Then the capacity retention rate after 500 cycles at 25°C:

η(%)＝Q500/Q1×100%

6. Adhesion force F between protective layer and barrier layer

Using the same preparation process as the battery package, prepare the barrier layer and protective layer on the PET film, then cut it into pieces (width 20mm × length 60mm), and attach them to a steel plate with double-sided tape (double-sided tape The size is smaller than the packaging film, 20mm×50mm), and the lower ends of the protective layer/barrier layer/double-sided tape/steel plate are flush. Cut a paper strip of a certain size (20mm×60mm), and use wrinkle glue to bond one end of the paper strip to the upper end of the protective layer (facing the double-sided tape side) to complete the sample preparation. Place the sample after the above preparation in the tensile machine, that is, the upper end of the steel plate is fixed between the lower end of the tensile machine, the paper strip is turned 180°, and one end of the paper strip that is not connected to the protective layer is fixed between the upper end of the tensile machine. Open the tensile machine testing software, set the parameters and perform the test to obtain the curve of the tensile force changing with the moving distance. After the tensile force value stabilizes, read the corresponding value f (N). The bonding force between the protective layer and the barrier layer surface F = f/0.02(N/m).

Test Results

Table 1

The comparison between the comparative examples and the examples in Table 1 shows that the battery energy using coating packaging has a higher energy density. The comparative example is the traditional aluminum plastic film and steel shell packaging technology, both of which use pure metal as packaging material or as packaging material. Among the main packaging materials of a certain layer, the proportion of metal in the shell cross-section measured by EDS is greater than 40%, so the proportion of non-metallic elements is less than 60%. In the embodiment, it is a laminated structure coated with polymer or metal oxide. Metal is not used as the main packaging material, so the proportion of non-metallic elements is >60%.

Figure 5 shows the X-Ray CT of the aluminum-plastic film-encapsulated battery in Comparative Example 1-1. Within the CT cross-sectional view that does not include the tabs or poles, the outer packaging film of the electrode assembly is discontinuous and there is obvious melting. Traces of encapsulation.

Figure 6 shows the X-Ray CT of the battery packaged in the stainless steel shell of Comparative Example 1-2. Within the CT cross-sectional view that does not include the tabs or poles, the outer packaging of the electrode assembly is discontinuous and there are obvious traces of molten welding. .

Figure 7 shows the X-Ray CT of the battery of Example 1-2. Within the scope of the CT cross-sectional view that does not include the tabs or poles, the outer packaging film of the electrode assembly is continuous, with no obvious traces of welding and packaging, and appears continuous. closed features.

Table 2

The examples in Table 2 use lithium-ion batteries with two capacity specifications. The 0.284Ah positive electrode material is lithium cobalt oxide, and the 12Ah positive electrode material is lithium iron phosphate. The maximum vertical distance g from the surface of the electrode assembly to the outer surface of the package affects the energy density and cycle performance. When making a 0.284Ah lithium-ion battery, if g is too small, it will affect the cycle capacity retention rate, as in Example 2-1. When the lithium-ion battery capacity is 12 Ah, if g is too large, the energy density of the lithium-ion battery will be affected, as shown in Example 2-2.

table 3

The embodiment in Table 3 uses lithium-ion batteries with two capacity specifications. The total thickness of the packaging case affects the energy density and cycle performance. When making a 0.284Ah lithium-ion battery, the thickness is too small, which affects the packaging reliability and thus the cycle capacity. Retention rate, as in Example 3-1. When the lithium-ion battery capacity is 12Ah, if the thickness is too large, the energy density of the lithium-ion battery will be affected, as in Example 3-2.

Table 4

The embodiment in Table 4 uses lithium-ion batteries with two capacity specifications. The value of H3/H1 affects the energy density and cycle performance. When making a 0.284Ah lithium-ion battery, H3/H1 is too small, which affects the packaging reliability and thus the packaging reliability. Cycle capacity retention rate, as in Example 4-1. When the lithium-ion battery capacity is 12Ah, if H3/H1 is too large, the energy density of the lithium-ion battery will be affected, as in Example 4-2.

table 5

The examples in Table 5 compare the impact of the bonding force between the barrier layer and the protective layer. The bonding force between the barrier layer and the protective layer mainly affects the packaging reliability, and then affects the cycle performance. When the bonding force is less than 1N/m, it will This leads to delamination of the package and affects the cycle retention rate, as shown in Example 5-1.

Although illustrative embodiments have been shown and described, those skilled in the art will understand that the above-described embodiments are not to be construed as limitations of the present application, and that changes may be made in the embodiments without departing from the spirit, principles and scope of the present application. , substitutions and modifications.

Claims

An electrochemical device includes a package body and an electrode assembly located inside the package body. The package body has a multi-layer structure, wherein each layer in the multi-layer structure is in a closed form.
The electrochemical device according to claim 1, wherein the mass content of metal elements in each layer of the multi-layer structure is less than 80%.
The electrochemical device according to claim 1, wherein the volume of the electrochemical device is V1 and the volume of the electrode assembly is V2, wherein 1.01≤V1/V2≤2; and/or

The maximum vertical distance between the electrode assembly and the package is g, 0.1mm≤g≤15mm.
The electrochemical device according to claim 1, wherein the thickness of the package is h, 70 μm≤h≤2000 μm.
The electrochemical device according to claim 1, wherein the package body includes a first layer, a second layer and a third layer arranged in a stack, the first layer being in contact with the electrode assembly.
The electrochemical device according to claim 5, wherein the first layer is obtained by coating a first layer of raw material on the surface of the electrode assembly.
The electrochemical device according to claim 5, wherein the thickness of the first layer is H1 and the thickness of the third layer is H3, where 0.5≤H3/H1≤5.
The electrochemical device according to claim 5, wherein the electrochemical device satisfies at least one of the following conditions (a) to (c):

(a)5μm≤H1≤1000μm;

(b) The thickness of the second layer is H2, 1nm≤H2≤500μm;

(c)5μm≤H3≤1900μm.
The electrochemical device according to claim 5, wherein the electrochemical device satisfies at least one of the following conditions (d) to (g):

(d) The material of the first layer includes resin;

(e) The material of the second layer includes at least one of metal, non-metal oxide or metal oxide and optional resin;

(f) The material of the third layer includes fiber and resin;

(g) The bonding force between the second layer and the third layer is ≥1 N/m.
An electronic device including the electrochemical device according to any one of claims 1 to 9.