CN115843395A

CN115843395A - Electrochemical device and electronic device

Info

Publication number: CN115843395A
Application number: CN202280005101.0A
Authority: CN
Inventors: 刘明举
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-03-08
Filing date: 2022-03-08
Publication date: 2023-03-24
Also published as: WO2023168584A1

Abstract

In some embodiments of the present application, an electrochemical device and an electronic apparatus are provided. An electrochemical device includes an electrode including an active material layer, the electrode having a bending radius of 0.5mm to 1.5mm and an elongation at break of 2% to 8%. The electrode has good flexibility and deformation adaptability, and can meet the requirement on a flexible electrochemical device.

Description

Electrochemical device and electronic device

Technical Field

Embodiments of the present disclosure relate to the field of electrochemical technologies, and in particular, to an electrochemical device and an electronic device.

Background

Electrochemical devices, such as lithium ion batteries, have the advantages of high energy density, high power, long cycle life, etc., are widely used in various fields, and along with the development of technologies, the requirements for deformation adaptability of the electrochemical devices are provided, and the electrochemical devices are required to have good flexibility.

Disclosure of Invention

In some embodiments of the present application, an electrochemical device and an electronic apparatus are provided.

In some embodiments, an electrochemical device is provided, which includes an electrode including an active material layer, the electrode having a bending radius of 0.5mm to 1.5mm, and an elongation at break of 2% to 8%. This indicates that the electrode has good flexibility and deformation adaptability, and can meet the requirements for flexible electrochemical devices.

In some embodiments, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material including at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium cobalt oxide, or a lithium rich material. In some embodiments, the thickness of the positive electrode active material layer is 40 μm to 2500 μm, thereby satisfying the requirements of capacity and flexibility. In some embodiments, the positive electrode active material layer has a compacted density of 2.2g/cm ³ To 4.3g/cm ³ . In some embodiments, the porosity of the positive electrode active material layer is 20% to 30%, thereby securing energy density and kinetic properties.

In some embodiments, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and the thickness of the positive electrode active material layer is 40 μm to 320 μm. In some embodiments, the positive electrode active material layer has a compacted density of 2.2g/cm ³ To 4.23g/cm ³ 。

In some embodiments, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material including at least one of lithium titanate, a silicon-based material, silicon oxide, silicon carbon, graphite, or hard carbon. In some embodiments, the thickness of the anode active material layer is 30 μm to 3000 μm, thereby securing capacity and flexibility. In some embodiments, the anode active material layer has a compacted density of 0.6g/cm ³ To 1.85g/cm ³ . In some embodiments, the porosity of the negative electrode active material layer is 30% to 40%, thereby securing energy density and kinetic properties.

In some embodiments, the electrode is an anode, the active material layer is an anode active material layer, and the thickness of the anode active material layer is 50 μm to 400 μm. In some embodiments, the compacted density of the anode active material layer is 1.3g/cm ³ To 1.8g/cm ³ 。

In some embodiments, the active material layer includes an active material and a conductive agent, and the conductive agent includes a first conductive agent including carbon nanotubes, thereby improving long-range conductivity and structural strength of the active material layer. In some embodiments, the conductive agent further comprises a second conductive agent comprising at least one of conductive carbon black, graphene, conductive graphite, or carbon fiber, thereby increasing short-range conductivity.

In some embodiments, the active material is present in an amount of 50 to 99% by mass of the active material layer and the conductive agent is present in an amount of 1 to 50% by mass of the active material layer, based on the total mass of the active material layer; the second conductive agent accounts for 1 to 50 mass percent of the conductive agent based on the total mass of the conductive agent. In some embodiments, every 2 to 1000 carbon nanotubes are arranged to form a bundle-like carbon nanotube aggregate, the carbon nanotube aggregate is wound with a second conductive agent to form a three-dimensional network structure, and at least part of the particles of the active material are located in the three-dimensional network structure, thereby improving the structural strength of the whole active material layer and ensuring the kinetic performance. In some embodiments, the carbon nanotubes have a tube diameter of 0.5nm to 10nm and a length of 1 μm to 100 μm, thereby ensuring structural strength of the three-dimensional network structure.

The present application also provides an electronic device comprising the electrochemical device of any one of the applications.

The bending radius of the electrode of the electrochemical device is 0.5mm to 1.5mm, and the fracture elongation of the electrode is 2% to 8%, which indicates that the electrode has good flexibility and deformation adaptability, and can meet the requirements for the flexible electrochemical device.

Drawings

The above and other features, advantages and aspects of various embodiments of the present disclosure will become more apparent by referring to the following detailed description when taken in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numbers refer to the same or similar elements. It should be understood that the drawings are schematic and that elements and features are not necessarily drawn to scale.

FIG. 1 is a schematic illustration of an electrode according to some embodiments of the present application.

Detailed Description

The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.

Electrochemical devices, such as lithium ion batteries, are widely used in various fields, and with the development of technology, there is a demand for deformation adaptability of electrochemical devices, and electrochemical devices with good flexibility are required, which can maintain structural and functional integrity after multiple deformations, and require energy density to meet the demand. The key of the flexible electrochemical device is the flexible electrode, and in the related art, the electrode has poor flexibility and weak bendability, and the energy density is reduced due to the existence of the binder and the current collector.

In some embodiments of the present application, an electrochemical device is provided. Among them, an electrochemical device is provided in some embodiments, which includes an electrode including an active material layer, a bending radius of the electrode is 0.5mm to 1.5mm, and a fracture elongation of the electrode is 2% to 8%.

In some embodiments, the electrochemical device can be a lithium ion battery, the electrode can be a positive or negative electrode of the electrochemical device, and in some embodiments, the bend radius of the electrode is measured as follows: pressing an electrode on a stainless steel shaft rod with a certain shaft rod radius, bending the stainless steel shaft rod around the shaft rod, keeping the stainless steel shaft rod for 2 to 3 seconds after bending, taking down a sample, observing whether the surface of the electrode has phenomena of electrode damage such as reticulate patterns, cracks or active substance layer peeling and the like by using a 4-time magnifier, and taking the minimum shaft rod radius of the electrode which is bent on shaft rods with different shaft rod radii and does not cause electrode damage as the bending radius of the electrode so as to represent the flexibility of the electrode. The bending radius of the electrode in the application is 0.5mm to 1.5mm, and the fracture elongation of the electrode is 2% to 8%, which shows that the electrode has good flexibility and deformation adaptability, and can meet the requirements for flexible electrochemical devices. In some embodiments of the present application, the electrode may not have a current collector, which may improve energy density, and because there is no current collector, the use of a binder is avoided, and the electrode may not have a binder, which may not only improve energy density, but also improve the overall dynamic performance of the active material layer, improve conductivity, and further facilitate the improvement of rate capability and cycle performance.

In some embodiments of the present application, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material including at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium cobalt oxide, or a lithium rich material. In some embodiments, the positive electrode active material in the positive electrode active material layer affects the capacity of the electrochemical device, and the positive electrode active material has a higher gram capacity, which is advantageous for ensuring the energy density of the electrochemical device.

In some embodiments of the present application, the thickness of the positive electrode active material layer is 40 μm to 2500 μm. In some embodiments, the thicker the positive electrode active material layer is, the more the positive electrode active material is, the more the capacity of the positive electrode is advantageously increased, and thus the capacity of the entire electrochemical device is increased, but when the positive electrode active material layer is too thick, the flexibility of the entire positive electrode active material layer may be affected, and when the thickness of the positive electrode active material layer is within the above range, the better the flexibility and capacity may be achieved at the same time, and in some embodiments, the thickness of the positive electrode active material layer is 40 μm to 320 μm, thereby further improving the flexibility and capacity, and in some embodiments, the thickness of the positive electrode active material layer is 100 μm to 200 μm.

In some embodiments of the present application, the positive electrode active material layer has a compacted density of 2.2g/cm ³ To 4.3g/cm ³ . In some embodiments, the compaction density of the positive electrode active material layer is correlated with flexibility, where too high a compaction density may result in greater internal stress in the positive electrode active material layer, which is detrimental to flexibility, and too low a compaction density may result in lower energy density in the positive electrode active material layer. In some embodiments, the positive electrode active material layer has a compacted density of 2.2g/cm ³ To 4.23g/cm ³ Thereby further achieving better flexibility and energy density.

In some embodiments of the present application, the porosity of the positive electrode active material layer is 20% to 30%. In some embodiments, the porosity of the positive active material layer has an influence on the wetting of the electrolyte and ion transport, when the porosity of the positive active material layer is too small, the contact between the positive active material layer and the electrolyte is influenced, the ion transport channel is reduced, the dynamic performance is influenced, the rate performance is not favorable, when the porosity of the positive active material layer is too large, the energy density is influenced, and the cycle performance is influenced.

In some embodiments of the present disclosure, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of lithium titanate, a silicon-based material, silicon oxide, silicon carbon, graphite, or hard carbon. In some embodiments, the negative electrode active material may be a mixture of the above active materials, and the particle diameters of the particles of the different negative electrode active materials may be different.

In some embodiments of the present application, the thickness of the anode active material layer is 30 μm to 3000 μm. The thickness on negative pole active material layer can influence the pliability and the energy density of negative pole, and when the thickness on negative pole active material layer was too big, probably resulted in the pliability to reduce, when the thickness undersize on negative pole active material layer, can be unfavorable for energy density, guarantees energy density when can keep better pliability with the thickness on negative pole active material layer in above-mentioned scope. In some embodiments, the thickness of the anode active material layer is 50 μm to 400 μm, and in some embodiments, the thickness of the anode active material layer is 100 μm to 200 μm.

In some embodiments of the present application, the anode active material layer has a compacted density of 0.6g/cm ³ To 1.85g/cm ³ . The compacted density of the negative electrode active material layer also affects the flexibility and energy density of the negative electrode, and when the compacted density is too large, the flexibility is not favorable and the particles of the negative electrode active material are easily broken, and when the compacted density is too small, the energy density is affected. In some embodiments, the compacted density of the anode active material layer is 1.3g/cm ³ To 1.8g/cm ³ Thereby ensuring both the flexibility and the energy density of the negative electrode.

In some embodiments, the porosity of the negative electrode active material layer is 30% to 40%, and in some embodiments, the porosity of the negative electrode active material layer has an influence on wetting of the electrolyte and ion transport, and when the porosity of the negative electrode active material layer is too small, contact of the negative electrode active material layer with the electrolyte is influenced, an ion transport channel is reduced, kinetic performance is influenced, rate performance is not facilitated, and when the porosity of the negative electrode active material layer is too large, energy density is influenced, and cycle performance is influenced.

In some embodiments, referring to fig. 1, the active material layer includes an active material 10 and a conductive agent 20, the conductive agent 20 includes a first conductive agent 201, and the first conductive agent 201 includes carbon nanotubes. In some embodiments, the carbon nanotubes can improve the long-range conductivity of the active material layer, stabilize the structure of the active material layer, and ensure the flexibility, and the linear structure of the carbon nanotubes can enable ions to be transmitted in a longer distance, and connect the active material layers at different positions, thereby preventing the active material from being broken during the bending process and improving the breaking elongation. In some embodiments, the conductive agent 20 further includes a second conductive agent including at least one of conductive carbon black, graphene, conductive graphite, or carbon fibers, which may include a zero-dimensional conductive agent 202 and a two-dimensional conductive agent 203. In some embodiments, the active material layer may only include the active material 10 and the conductive agent 20, the active material of the positive electrode is a positive active material, the active material of the negative electrode is a negative active material, because the active material layer only includes the active material 10 and the conductive agent 20 and does not include a polymer binder, the barrier of the polymer binder to electron and ion transmission is avoided, the proportion of an inactive material is reduced, the energy density is improved, the flexibility and the long-range conductivity of the electrode are increased by the addition of the linear carbon nanotube, the deformation adaptability is improved, and the effect of stabilizing the structure of the active material layer is achieved, the short-range conductivity of the active material layer is increased by the second conductive agent, and through the first conductive agent and the second conductive agent, the long-range conductivity and the short-range conductivity of the active material layer are improved while the flexibility and the structural stability are ensured.

In some embodiments, the active material is present in an amount of 50 to 99% by mass of the active material layer and the conductive agent is present in an amount of 1 to 50% by mass of the active material layer, based on the total mass of the active material layer; the second conductive agent accounts for 1 to 50 mass percent of the conductive agent based on the total mass of the conductive agent.

In some embodiments, every 2 to 1000 carbon nanotubes are aligned to form a bundle-like carbon nanotube aggregate, the carbon nanotube aggregate is entangled with a second conductive agent to form a three-dimensional network structure, and at least a part of the particles of the active material are located within the three-dimensional network structure. In some embodiments, the carbon nanotube aggregates formed by the carbon nanotubes can improve the structural strength of the whole carbon nanotubes, and the three-dimensional grid structure formed by the carbon nanotube aggregates can provide sites for the active material, so that the active material layer can be well gathered together through the three-dimensional network structure, the structural strength of the whole active material layer is improved, the flexibility is ensured, and the three-dimensional network structure can enable ions to be better conducted in multiple directions.

In some embodiments, the diameter of the carbon nanotube is 0.5nm to 10nm, the diameter of the carbon nanotube is 1 μm to 100 μm, and too small a length of the carbon nanotube is not favorable for stabilizing the structure of the active material layer, and the carbon nanotube may be easily broken if too long a length.

In some embodiments of this application, the electrochemical device that provides has good flexible shape to need not the mass flow body and can self-supporting, reduced inactive material's such as binder and account for than, can not only guarantee that the pliability improves the deformation adaptability, can also promote energy density.

In some embodiments, an electrochemical device includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 50 μm.

In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder ₂ O ₃ ) Silicon oxide (SiO) ₂ ) Magnesium oxide (MgO), titanium oxide (TiO) ₂ ) Hafnium oxide (HfO) ₂ ) Tin oxide (SnO) ₂ ) Cerium oxide (CeO) ₂ ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) ₂ ) Yttrium oxide (Y) ₂ O ₃ ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film 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 polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.

In some embodiments of the present application, the electrochemical device may be of a roll-to-roll type or a stack type. In some embodiments, the positive electrode and/or the negative electrode of the electrochemical device may be a multilayer structure formed by winding or stacking, or may be a single-layer structure in which a single-layer positive electrode, a single-layer negative electrode, and a separator are stacked.

In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. 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 including a lithium salt and a non-aqueous solvent. The lithium salt is selected from LiPF ₆ 、LiBF ₄ 、LiAsF ₆ 、LiClO ₄ 、LiB(C ₆ H ₅ ) ₄ 、LiCH ₃ SO ₃ 、LiCF ₃ SO ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、LiSiF ₆ One or more of LiBOB or lithium difluoroborate. For example, the lithium salt is LiPF ₆ Because it has high ionic conductivity and can improve cycle characteristics.

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

Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound 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, trifluoromethylethylene carbonate, or a combination thereof.

Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.

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

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

In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode, a separator, and a negative electrode are sequentially wound or stacked to form an electrode member, and then the electrode member is placed in, for example, an aluminum plastic film for packaging, and an electrolyte is injected into the electrode member for formation and packaging, so as to form the lithium ion battery. And then, performing performance test on the prepared lithium ion battery.

Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.

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

In some embodiments of the present application, a method for preparing an electrode is also provided, and the electrode in the embodiments of the present application can be prepared by the method, including the following steps:

adding a first conductive agent carbon nano tube and a dispersing agent into a dispersing medium, wherein the dispersing medium can be N-methyl pyrrolidone (NMP) or water, and forming uniform first conductive agent dispersion liquid by methods of ultrasound, stirring, sanding and the like; adding an active substance, a second conductive agent and a pore-forming agent into the first conductive agent dispersion liquid, and uniformly stirring to form slurry; coating the slurry on the surface of a substrate, drying at 80-120 ℃, and automatically stripping the electrode from the substrate to form the self-supporting electrode. In some embodiments, the dispersant comprises one or more of Sodium Dodecyl Sulfate (SDS), sodium dodecyl sulfate (SDBS), cetyl trimethyl ammonium bromide (C16 TMAB), polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), and lithium carboxymethyl cellulose (CMC-Li); in some embodiments, the pore-forming agent is one or more of oxalic acid solution of 0.2mol/L to 12mol/L, ammonium carbonate solution of 0.2mol/L to 12mol/L, ammonium bicarbonate solution of 0.2mol/L to 12mol/L, azodicarbonamide solution of 0.2mol/L to 12mol/L, lithium carbonate and lithium hydroxide. In some embodiments, the substrate is polyethylene terephthalate (PET) with a release film having a thickness of 0 μm to 25 μm, and the release film may be one of a silicone oil coating, a polyurethane coating, and an acrylate coating.

The active material layer of the electrode prepared in some embodiments of the application only contains active materials and conductive agents, does not contain a high-molecular binder, avoids the obstruction of the binder to electron and ion transmission, reduces the proportion of inactive materials, improves the energy density, increases the porosity of the electrode by adding the pore-forming agent in the preparation process, reduces the transmission distance of lithium ions, improves the multiplying power performance, increases the flexibility of the electrode by adding the long-range linear conductive carbon material, and improves the deformation adaptability.

In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.

Example 1

Preparation of the positive electrode:

adding a first conductive agent carbon nano tube and a dispersing agent into a dispersion medium N-methyl pyrrolidone (NMP), and forming uniform first conductive agent dispersion liquid by methods of ultrasound, stirring, sanding and the like; adding a positive electrode active material lithium cobaltate, a second conductive agent graphene and a pore-forming agent into the first conductive agent dispersion liquid, and uniformly stirring to form slurry; and coating the slurry on the surface of polyethylene glycol terephthalate with a release film on a substrate, drying at 90 ℃, and automatically stripping the active substance layer of the positive electrode from the substrate to form the positive electrode.

Preparation of a negative electrode: mixing negative active materials graphite, styrene acrylate and carboxymethyl cellulose lithium according to a mass ratio of 98:1:1, mixing, taking deionized water as a solvent to form slurry of a negative active material layer, taking copper foil as a negative current collector, coating the slurry of the negative active material layer on the negative current collector, and drying at 90 ℃ to obtain the negative electrode.

Preparing an isolating membrane: the release film was 8 μm thick Polyethylene (PE).

Preparing an electrolyte: in an environment with a water content of less than 10ppm, mixing lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene Carbonate (PC): propyl Propionate (PP): vinylene Carbonate (VC) = 20) in a weight ratio of 8:92 are formulated to form an electrolyte.

Preparing a lithium ion battery: and sequentially stacking the anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.

In examples 2 to 13, parameters were changed in addition to the procedure of example 1, and specific changed parameters are shown in the following table.

Example 14

Preparation of the positive electrode: mixing a positive electrode active material lithium cobaltate, polyvinylidene fluoride (PVDF), conductive carbon black (Super P, SP) and a Carbon Nano Tube (CNT) according to a mass ratio of 97.2:1.5:0.8:0.5, mixing the above components, preparing a slurry using N-methylpyrrolidone (NMP) as a solvent, and stirring the slurry uniformly to form a slurry of the positive electrode active material layer. And uniformly coating the slurry on an aluminum foil of a positive current collector, and drying at 90 ℃ to obtain the positive electrode.

Preparation of a negative electrode: adding a first conductive agent carbon nano tube and a dispersing agent carboxymethyl cellulose lithium into dispersion medium deionized water, and forming uniform first conductive agent dispersion liquid by methods of ultrasound, stirring, sanding and the like; adding a negative active material graphite, a second conductive agent graphene and a pore-forming agent oxalic acid solution of 1mol/L into the first conductive agent dispersion liquid, and uniformly stirring to form slurry; and coating the slurry on the surface of polyethylene glycol terephthalate with a release film on a substrate, drying at 90 ℃, and automatically stripping the negative electrode active substance layer from the substrate to form the negative electrode.

Example 14 the remaining preparation steps were the same as in example 1. Examples 15 to 22 were carried out by changing parameters in addition to the procedure of example 14, and the parameters specifically changed were as shown in the following tables

Comparative example 1

Preparation of the positive electrode: mixing a positive electrode active material lithium cobaltate, polyvinylidene fluoride (PVDF), conductive carbon black (Super P, SP) and a Carbon Nano Tube (CNT) according to a mass ratio of 97.2:1.5:0.8:0.5, mixing the mixture, preparing slurry by using N-methyl pyrrolidone (NMP) as a solvent, and uniformly stirring the slurry to form the slurry of the positive electrode active material layer. And (3) uniformly coating the slurry on an aluminum foil of a positive current collector, and drying at 90 ℃ to obtain the positive electrode.

Preparation of a negative electrode: mixing a negative active material graphite, a binder styrene butadiene rubber and a dispersant carboxymethyl cellulose lithium according to a mass ratio of 95:3.5: and 1.5, mixing, taking deionized water as a solvent to form slurry of the negative active material layer, taking copper foil as a negative current collector, coating the slurry of the negative active material layer on the negative current collector, and drying at 90 ℃ to obtain the negative electrode.

The remaining preparation steps of comparative example 1 were the same as in example 1. Comparative examples 2 and 3 were modified based on the procedure of comparative example 1, and the parameters specifically modified are shown in the following table.

The test method of the present application is described below.

1. DCR test of 25 ℃ direct current resistance

Charging the lithium ion battery to 3.95V at a constant current of 0.5C and then to 0.05C at a constant voltage at 25 ℃; standing for 30min; discharging at 0.1C for 10s (taking point once at 0.1 s), and recording corresponding voltage value U ₁ ) Put at 1CElectricity 360s (0.1 s taking point once, recording corresponding voltage value U ₂ ). The charging and discharging steps were repeated 5 times. Here, "1C" is a current value at which the battery capacity is completely discharged within 1 hour. The DCR of the battery is calculated according to the following formula: DCR = (U) ₂ -U ₁ )/(1C-0.1C)。

2. Test of Rate Properties

In an environment of 25 ℃, discharging the battery to 3V at a constant current, carrying out first charging and discharging, carrying out constant current charging under a charging current of 0.7C until the upper limit voltage is 4.48V, then carrying out constant voltage charging to 0.05C, then carrying out constant current discharging under a discharging current of 0.2C until the final voltage is 3V, recording the discharging capacity of 0.2C, then repeatedly carrying out charging under a charging current of 0.7C until the upper limit voltage is 4.48V, then carrying out constant voltage charging to 0.05C, then setting the discharging rate to 3C, carrying out constant current discharging until the final voltage is 3V, and recording the discharging capacity of 3C.

Retention ratio of 3C discharge capacity = (discharge capacity at 3C discharge capacity/0.2C) × 100%

3. And (3) testing the cycle performance:

the lithium ion battery is placed in a thermostat with the temperature of 45 +/-2 ℃ for standing for 2 hours, and is charged to 4.48V at the rate of 1C, and then is charged to 0.05C at the constant voltage of 4.48V. And then discharging to 3.0V at a rate of 1C for cycle performance test, carrying out cycle charging and discharging for 800 circles, and taking the ratio of the discharge capacity of the 800 th circle to the discharge capacity of the 1 st circle as the cycle capacity retention rate of the 800 th circle.

TABLE 1

TABLE 2

Tables 1 and 2 show the differences in the production parameters and the results of the performance tests for examples 1 to 5, with the production parameters not shown being otherwise identical.

In examples 1 to 5, the positive electrode using the electrode proposed in this application can be seen to have a bending radius of 0.5mm to 1.5mm and a breaking elongation of 2% to 8%, which indicates that the positive electrode has good flexibility, and it can be seen that the direct current resistance is small and the test results of rate capability and cycle performance are good in examples 1 to 5, which may be because the positive electrode in examples 1 to 5 of this application does not have a polymer binder, thereby avoiding the influence of the polymer binder on the kinetic performance.

TABLE 3

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TABLE 4

The production parameters and performance test results of examples 6 to 13 are shown in tables 3 and 4, and the production parameters not shown are the same as in example 1.

In examples 6 to 13, the positive electrode of the electrochemical device employs the electrode sheet proposed in the present application, and it can be seen from examples 6 to 9 that the kind of the second conductive agent in the positive electrode active material layer has an influence on the performance of the electrochemical device, and it can be seen that the second conductive agent is carbon fiber, conductive carbon black, carbon nanotube or conductive graphite, which all have better performance, wherein when the second conductive agent is carbon nanotube, the direct current resistance is the smallest, and the rate capability and cycle performance are the best. And when the second conductive agent is carbon fiber or carbon nanotube, the elongation at break of the positive electrode is the longest, which is probably because the one-dimensional structure of the carbon fiber and the carbon nanotube can play a role of stabilizing the structure.

As can be seen from examples 10 to 13, as the compaction density of the positive electrode active material layer changes, the porosity of the positive electrode active material layer changes, and the bending radius and the fracture elongation of the positive electrode are affected, in the illustrated range, the larger the compaction density of the positive electrode active material layer is, the smaller the porosity is, the smaller the bending radius is, the larger the fracture elongation is, the dc resistance decreases and then increases, and the rate capability and the cycle capability increase and then decreases, which may be because the increase in the compaction density increases the contact and connection strength between the positive electrode active materials, thereby facilitating the decrease in the dc resistance, but an excessively large compaction density may cause the decrease in the passage of ion transport, and conversely, adversely affect the kinetic performance.

TABLE 5

TABLE 6

The production parameters and performance test results of examples 14 to 22 are shown in tables 5 and 6, and the production parameters not shown are the same as in example 1.

In examples 14 to 22, the negative electrode of the electrochemical device employs the electrode sheet proposed in the present application, and it can be seen from examples 14 to 18 that when the mass percentage content of the negative electrode active material in the negative electrode active material layer, the mass percentage content of the conductive agent, the composition of the conductive agent, the number of carbon nanotubes in the carbon nanotube aggregate, the tube diameter of the carbon nanotubes, the length of the carbon nanotubes, the thickness of the negative electrode active material layer, and the porosity of the negative electrode active material layer are controlled within the ranges shown in examples 14 to 18, the requirements of the bending radius and the fracture elongation of the negative electrode can be satisfied, and a lower direct current resistance, a better rate performance, and a cycle performance can be obtained.

As can be seen from examples 19 to 22, changing the thickness of the negative electrode active material and the negative electrode active material layer affects the bending radius and elongation at break of the negative electrode, and affects the direct current resistance, rate capability and cycle performance, and better performance is obtained when the negative electrode active material is silica, lithium titanate, silicon or silicon carbon, of which rate capability and cycle performance are the best when the negative electrode active material is lithium titanate.

TABLE 7

TABLE 8

"/" indicates absence, the production parameters and performance test results of comparative examples 1 to 3 are shown in tables 7 and 8, and the remaining production parameters not shown are the same as in comparative example 1.

In comparative examples 1 to 3, the positive electrode and the negative electrode of the electrochemical device did not adopt the electrode sheet proposed in the present application, and as can be seen from comparative examples 1 to 3, the bending radius of the negative electrode was not less than 3mm and the elongation at break of the negative electrode was not more than 1.9%, which indicates that the flexibility of the negative electrode was poor, and the direct current resistance was large, the 3C rate performance was poor and the cycle performance was poor in comparative examples 1 to 3. This is probably because the binders were added in all of comparative examples 1 to 3, deteriorating the kinetic properties, resulting in a decrease in rate capability and cycle performance.

The foregoing description is only exemplary of the preferred embodiments of the disclosure and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention in the embodiments of the present disclosure is not limited to the specific combination of the above-mentioned features, but also encompasses other embodiments in which any combination of the above-mentioned features or their equivalents is made without departing from the inventive concept as defined above. For example, the above features and (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure are mutually replaced to form the technical solution.

Claims

1. An electrochemical device comprising an electrode including an active material layer, characterized in that the electrode has a bending radius of 0.5mm to 1.5mm and an elongation at break of 2% to 8%.

2. The electrochemical device according to claim 1, wherein the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and at least one of the following is satisfied:

(a) The positive active material layer comprises a positive active material, and the positive active material comprises at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium cobalt oxide or a lithium-rich material;

(b) The thickness of the positive electrode active material layer is 40 to 2500 [ mu ] m;

(c) The compacted density of the positive electrode active material layer is 2.2g/cm ³ To 4.3g/cm ³ ；

(d) The positive electrode active material layer has a porosity of 20% to 30%.

3. The electrochemical device according to claim 1, wherein the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and at least one of the following is satisfied:

(e) The thickness of the positive electrode active material layer is 40 to 320 [ mu ] m;

(f) The compacted density of the positive electrode active material layer is 2.2g/cm ³ To 4.23g/cm ³ 。

4. The electrochemical device according to claim 1, wherein the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and at least one of the following is satisfied:

(g) The negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of lithium titanate, a silicon-based material, silicon oxide, silicon carbon, graphite or hard carbon;

(h) The thickness of the negative electrode active material layer is 30 to 3000 [ mu ] m;

(i) The compacted density of the negative electrode active material layer was 0.6g/cm ³ To 1.85g/cm ³ ；

(j) The negative electrode active material layer has a porosity of 30% to 40%.

5. The electrochemical device according to claim 1, wherein the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and at least one of the following is satisfied:

(k) The negative electrode active material layer has a thickness of 50 to 400 [ mu ] m;

(l) The compacted density of the negative electrode active material layer was 1.3g/cm ³ To 1.8g/cm ³ 。

6. The electrochemical device according to claim 1, wherein the active material layer includes an active material and a conductive agent, the conductive agent includes a first conductive agent, and the first conductive agent includes carbon nanotubes.

7. The electrochemical device according to claim 6,

the conductive agent further includes a second conductive agent including at least one of conductive carbon black, graphene, conductive graphite, or carbon fiber.

8. The electrochemical device of claim 7, wherein at least one of the following is satisfied:

(m) the active material accounts for 50 to 99% by mass of the active material layer, and the conductive agent accounts for 1 to 50% by mass of the active material layer, based on the total mass of the active material layer; the second conductive agent accounts for 1 to 50 percent of the total mass of the conductive agent;

(n) arranging every 2 to 1000 of the carbon nanotubes to form a bundle-shaped carbon nanotube aggregate, the carbon nanotube aggregate being wound with a second conductive agent to form a three-dimensional network structure, at least a part of the particles of the active material being located within the three-dimensional network structure.

9. The electrochemical device according to claim 6,

the tube diameter of the carbon nano tube is 0.5nm to 10nm, and the length of the carbon nano tube is 1 mu m to 100 mu m.

10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.