Electrochemical devices and electronic devices

Abstract

Provided in some embodiments of the present application are an electrochemical device and an electronic device. The electrochemical device comprises an electrode, the electrode comprising an active material layer, the electrode having a bending radius of 0.5 mm to 1.5 mm, and the electrode having an elongation at break of 2% to 8%. The electrode has good flexibility and deformation adaptability, and can meet the requirements of a flexible electrochemical device.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to the field of electrochemistry, and in particular, to an electrochemical device and an electronic device. BACKGROUND

[0002] An electrochemical device, such as a lithium ion battery, has the advantages of high energy density, high power, long cycle life, etc., and is widely used in various fields. With the development of technology, the electrochemical device is required to have deformation adaptability, and needs to have good flexibility. SUMMARY

[0003] In some embodiments of the present application, an electrochemical device and an electronic device are provided.

[0004] In some embodiments, an electrochemical device is provided, including an electrode, the electrode including an active material layer, the electrode having a bending radius of 0.5 mm to 1.5 mm, and the electrode having a breaking elongation of 2% to 8%. This indicates that the electrode has good flexibility and deformation adaptability, and can meet the requirements of a flexible electrochemical device.

[0005] In some embodiments, the electrode is a positive electrode, the active material layer is a positive active material layer, and the positive active material layer includes a positive active material, the positive active material including at least one of lithium iron phosphate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium manganese acid, lithium cobalt acid, or a lithium-rich material. In some embodiments, the thickness of the positive active material layer is 40 μm to 2500 μm, thereby meeting the requirements of capacity and flexibility. In some embodiments, the positive active material layer has a compaction density of 2.2 g / cm 3 to 4.3 g / cm 3 In some embodiments, the positive active material layer has a porosity of 20% to 30%, thereby ensuring energy density and kinetic performance.

[0006] In some embodiments, the electrode is a positive electrode, the active material layer is a positive active material layer, and the thickness of the positive active material layer is 40 μm to 320 μm. In some embodiments, the positive active material layer has a compaction density of 2.2 g / cm 3 to 4.23 g / cm 3 .

[0007] In some embodiments, the electrode is a negative electrode, the active material layer is a negative active material layer, and the negative active material layer includes a negative active material, the negative active material including at least one of lithium titanate, a silicon-based material, silicon monoxide, silicon, silicon carbon, graphite, or hard carbon. In some embodiments, the thickness of the negative active material layer is 30 μm to 3000 μm, thereby ensuring capacity and flexibility. In some embodiments, the negative active material layer has a compaction density of 0.6 g / cm 3Up to 1.85 g / cm 3 In some embodiments, the porosity of the negative electrode active material layer is 30% to 40%, thereby ensuring energy density and kinetic performance.

[0008] In some embodiments, the electrode is a negative electrode, and the active material layer is a negative electrode active material layer with a thickness of 50 μm to 400 μm. In some embodiments, the compaction density of the negative electrode active material layer is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 .

[0009] In some embodiments, the active material layer includes an active material and a conductive agent, the conductive agent including a first conductive agent comprising carbon nanotubes, thereby improving long-range conductivity and structural strength of the active material layer. In some embodiments, the conductive agent further includes a second conductive agent, the second conductive agent including at least one of conductive carbon black, graphene, conductive graphite, or carbon fiber, thereby improving short-range conductivity.

[0010] In some embodiments, based on the total mass of the active material layer, the active material accounts for 50% to 99% of the mass percentage of the active material layer, and the conductive agent accounts for 1% to 50% of the mass percentage of the active material layer; based on the total mass of the conductive agent, the second conductive agent accounts for 1% to 50% of the mass percentage of the conductive agent. In some embodiments, every 2 to 1000 carbon nanotubes are arranged to form bundled carbon nanotube aggregates, and the carbon nanotube aggregates are entangled with the second conductive agent to form a three-dimensional network structure, with at least some of the active material particles located within the three-dimensional network structure, thereby improving the overall structural strength of the active material layer and ensuring kinetic performance. In some embodiments, the diameter of the carbon nanotubes is 0.5 nm to 10 nm, and the length of the carbon nanotubes is 1 μm to 100 μm, thereby ensuring the structural strength of the three-dimensional network structure.

[0011] This application also proposes an electronic device, including any of the electrochemical devices proposed in this application.

[0012] The electrode of the electrochemical device in this application has a bending radius of 0.5 mm to 1.5 mm and a fracture elongation of 2% to 8%, which indicates that the electrode has good flexibility and deformation adaptability, and can meet the requirements for flexible electrochemical devices. Attached Figure Description

[0013] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the originals and elements are not necessarily drawn to scale.

[0014] Figure 1 This is a schematic diagram of electrodes in some embodiments of this application. Detailed Implementation

[0015] The following embodiments are intended to enable those skilled in the art to fully understand this application, but do not limit this application in any way.

[0016] Electrochemical devices, such as lithium-ion batteries, are widely used in various fields. With technological advancements, there are increasing demands on the deformation adaptability of these devices. They require highly flexible devices that can maintain structural and functional integrity after repeated deformations, while also meeting energy density requirements. The key to flexible electrochemical devices lies in flexible electrodes. In related technologies, electrodes often exhibit poor flexibility and weak bendability, and the presence of binders and current collectors further reduces energy density.

[0017] An electrochemical device is proposed in some embodiments of this application. In some embodiments, the electrochemical device includes an electrode comprising an active material layer, a bending radius of 0.5 mm to 1.5 mm, and an elongation at break of 2% to 8%.

[0018] In some embodiments, the electrochemical device can be a lithium-ion battery, and the electrode can be the positive or negative electrode of the electrochemical device. In some embodiments, the bending radius of the electrode is measured as follows: the electrode is pressed onto a stainless steel rod of a certain radius, bent around the rod, held for 2 to 3 seconds after bending, the sample is removed, and the electrode surface is observed with a 4x magnifying glass for phenomena such as meshing, cracks, or peeling of the active material layer, indicating electrode damage. The smallest rod radius that allows the electrode to bend on rods of different radii without causing electrode damage is taken as the bending radius of the electrode, thereby characterizing the flexibility of the electrode. In this application, the bending radius of the electrode is 0.5 mm to 1.5 mm, and the elongation at break is 2% to 8%, indicating that the electrode has good flexibility and deformation adaptability, which can meet the requirements for flexible electrochemical devices. In some embodiments of this application, the electrode may be without a current collector, which can improve energy density. Since there is no current collector, the use of binder is avoided, and the electrode may not contain binder. In addition to improving energy density, this can also improve the overall kinetic performance of the active material layer, improve conductivity, and thus help improve rate performance and cycle performance.

[0019] In some embodiments of this 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, which includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium cobalt oxide, or lithium-rich materials. In some embodiments, the positive electrode active material in the positive electrode active material layer affects the capacity of the electrochemical device. The aforementioned positive electrode active material has a high specific capacity, which is beneficial to ensuring the energy density of the electrochemical device.

[0020] In some embodiments of this application, the thickness of the positive electrode active material layer is from 40 μm to 2500 μm. In some embodiments, a thicker positive electrode active material layer results in a greater mass of positive electrode active material, which is more beneficial for improving the capacity of the positive electrode and thus the overall capacity of the electrochemical device. However, when the positive electrode active material layer is too thick, the overall flexibility of the positive electrode active material layer will be affected. When the thickness of the positive electrode active material layer is within the above range, it can simultaneously possess good flexibility and capacity. In some embodiments, the thickness of the positive electrode active material layer is from 40 μm to 320 μm, thereby further improving flexibility and capacity. In some embodiments, the thickness of the positive electrode active material layer is from 100 μm to 200 μm.

[0021] In some embodiments of this application, the compaction density of the positive electrode active material layer is 2.2 g / cm³. 3 Up to 4.3 g / cm 3 In some embodiments, the compaction density of the positive electrode active material layer is related to its flexibility. Excessive compaction density leads to higher internal stress in the positive electrode active material layer, which is detrimental to flexibility; conversely, insufficient compaction density results in lower energy density. In some embodiments, the compaction density of the positive electrode active material layer is 2.2 g / cm³. 3 Up to 4.23 g / cm 3 This allows for further improvement in flexibility and energy density.

[0022] In some embodiments of this application, the porosity of the positive electrode active material layer is 20% to 30%. In some embodiments, the porosity of the positive electrode active material layer affects the wetting of the electrolyte and ion transport. When the porosity of the positive electrode active material layer is too small, it affects the contact between the positive electrode active material layer and the electrolyte, reduces the ion transport channels, affects the kinetic performance, and is detrimental to the rate performance. When the porosity of the positive electrode active material layer is too large, it affects the energy density and also affects the cycle performance.

[0023] In some embodiments of this application, the electrode is a negative electrode, and the active material layer is a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, which includes at least one of lithium titanate, silicon-based materials, silicon suboxide, silicon, silicon carbide, graphite, or hard carbon. In some embodiments, the negative electrode active material can be a mixture of the above-mentioned active materials, and the particle size of different negative electrode active materials can be different.

[0024] In some embodiments of this application, the thickness of the negative electrode active material layer is from 30 μm to 3000 μm. The thickness of the negative electrode active material layer affects the flexibility and energy density of the negative electrode. When the thickness of the negative electrode active material layer is too large, it may lead to a decrease in flexibility; when the thickness of the negative electrode active material layer is too small, it will be detrimental to the energy density. Keeping the thickness of the negative electrode active material layer within the above range can maintain good flexibility while ensuring energy density. In some embodiments, the thickness of the negative electrode active material layer is from 50 μm to 400 μm; in some embodiments, the thickness of the negative electrode active material layer is from 100 μm to 200 μm.

[0025] In some embodiments of this application, the compaction density of the negative electrode active material layer is 0.6 g / cm³. 3 Up to 1.85 g / cm 3 The compaction density of the negative electrode active material layer also affects the flexibility and energy density of the negative electrode. Excessive compaction density hinders flexibility and easily leads to particle breakage of the negative electrode active material; conversely, insufficient compaction density affects energy density. In some embodiments, the compaction density of the negative electrode active material layer is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 This ensures both the flexibility and energy density of the negative electrode.

[0026] In some embodiments, the porosity of the negative electrode active material layer is 30% to 40%. In some embodiments, the porosity of the negative electrode active material layer affects the wetting of the electrolyte and ion transport. When the porosity of the negative electrode active material layer is too small, it affects the contact between the negative electrode active material layer and the electrolyte, reduces the ion transport channels, affects the kinetic performance, and is detrimental to the rate performance. When the porosity of the negative electrode active material layer is too large, it will affect the energy density and also affect the cycle performance.

[0027] In some embodiments, please refer to Figure 1The active material layer includes an active material 10 and a conductive agent 20. The conductive agent 20 includes a first conductive agent 201, which includes carbon nanotubes. In some embodiments, carbon nanotubes can improve the long-range conductivity of the active material layer, stabilize the structure of the active material layer, and ensure flexibility. The linear structure of the carbon nanotubes enables ions to transport over long distances and connects the active material layers at different locations, preventing breakage during bending and improving the elongation at break. In some embodiments, the conductive agent 20 further includes a second conductive agent, which includes at least one of conductive carbon black, graphene, conductive graphite, or carbon fiber. The second conductive agent may include a zero-dimensional conductive agent 202 and a two-dimensional conductive agent 203. In some embodiments, the active material layer may contain only active material 10 and conductive agent 20. The active material of the positive electrode is the positive active material, and the active material of the negative electrode is the negative active material. Because the active material layer contains only active material 10 and conductive agent 20 and does not contain polymer binder, the obstruction of electron and ion transport by polymer binder is avoided, the proportion of inactive material is reduced, and the energy density is increased. The addition of linear carbon nanotubes increases the flexibility and long-range conductivity of the electrode, improves deformation adaptability, and plays a role in stabilizing the structure of the active material layer. The second conductive agent increases the short-range conductivity of the active material layer. Through the first and second conductive agents, the long-range conductivity and short-range conductivity of the active material layer are improved while ensuring flexibility and structural stability.

[0028] In some embodiments, based on the total mass of the active material layer, the active material accounts for 50% to 99% of the mass percentage of the active material layer, and the conductive agent accounts for 1% to 50% of the mass percentage of the active material layer; based on the total mass of the conductive agent, the second conductive agent accounts for 1% to 50% of the mass percentage of the conductive agent.

[0029] In some embodiments, 2 to 1000 carbon nanotubes are arranged to form bundled carbon nanotube aggregates. These aggregates are entangled with a second conductive agent to form a three-dimensional network structure, with at least some of the active material particles located within this network. In some embodiments, the bundled carbon nanotube aggregates enhance the overall structural strength of the carbon nanotubes. The resulting three-dimensional network structure provides sites for the active material, allowing the active material layer to aggregate effectively through the network structure. This improves the overall structural strength of the active material layer, ensures flexibility, and enables better ion conduction in multiple directions.

[0030] In some embodiments, the diameter of the carbon nanotube is 0.5 nm to 10 nm, and the length of the carbon nanotube is 1 μm to 100 μm. If the length of the carbon nanotube is too small, it will be detrimental to the stable structure of the active material layer, and if the length of the carbon nanotube is too long, it may be easy to break.

[0031] In some embodiments of this application, the provided electrochemical device has good flexibility and can be self-supported without the need for a current collector, reducing the proportion of inactive substances such as binders. This not only ensures flexibility and improves deformation adaptability, but also increases energy density.

[0032] In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, are effective in preventing short circuits and can improve battery stability through a turn-off effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 50 μm.

[0033] 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 comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina (Al₂O₃), silicon oxide (SiO₂), magnesium oxide (MgO), titanium oxide (TiO₂), hafnium dioxide (HfO₂), tin oxide (SnO₂), cerium dioxide (CeO₂), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The binder for the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the separator's heat resistance, oxidation resistance, and electrolyte wetting properties, and enhance the adhesion between the separator and the electrode.

[0034] In some embodiments of this application, the electrochemical device may be of a wound or stacked type. In some embodiments, the positive and / or negative electrodes of the electrochemical device may be multilayer structures formed by winding or stacking, or they may be single-layer structures consisting of a single-layer positive electrode, a separator, and a single-layer negative electrode.

[0035] In some embodiments, the electrochemical device includes a lithium-ion battery, but this application is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, wherein the electrolyte solution includes a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, LiPF6 is selected as the lithium salt because it has high ionic conductivity and can improve cycle characteristics.

[0036] The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

[0037] Examples of chain carbonate compounds 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 cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0038] Examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, methyl formate, or combinations thereof.

[0039] Examples of ether compounds are dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0040] Examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

[0041] In some embodiments of this application, taking a lithium-ion battery as an example, the positive electrode, separator, and negative electrode are sequentially wound or stacked into electrode components, then encapsulated in, for example, an aluminum-plastic film, and then injected with electrolyte. Formation and encapsulation are then performed to manufacture a lithium-ion battery. The prepared lithium-ion battery is then subjected to performance testing.

[0042] Those skilled in the art will understand that the methods for preparing the electrochemical devices (e.g., lithium-ion batteries) described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0043] This application discloses an electronic device, including an electrochemical device; the electrochemical device is any of the electrochemical devices described in this application. The electronic device in the embodiments of this application is not particularly limited, and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, drones, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, or large household batteries, etc.

[0044] In some embodiments of this application, a method for preparing an electrode is also proposed. The electrodes in the embodiments of this application can be prepared using this method, which includes the following steps:

[0045] Carbon nanotubes, the first conductive agent, and a dispersant are added to a dispersion medium, which can be N-methylpyrrolidone (NMP) or water. A uniform dispersion of the first conductive agent is formed by methods such as ultrasound, stirring, and sand milling. An active material, a second conductive agent, and a pore-forming agent are added to the dispersion of the first conductive agent and stirred evenly to form a slurry. The slurry is coated on the surface of a substrate and dried at 80°C to 120°C. The electrode automatically peels off from the substrate to form a self-supporting electrode. In some embodiments, the dispersant includes one or more of sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (SDBS), hexadecyltrimethylammonium bromide (C16 TMAB), polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), and lithium carboxymethyl cellulose (CMC-Li). In some embodiments, the pore-forming agent includes one or more of oxalic acid solution (0.2 mol / L to 12 mol / L), ammonium carbonate solution (0.2 mol / L to 12 mol / L), ammonium bicarbonate solution (0.2 mol / L to 12 mol / L), azodicarbonamide solution (0.2 mol / L to 12 mol / L), lithium carbonate, and lithium hydroxide. In some embodiments, the substrate is polyethylene terephthalate (PET) with a release film, the release film thickness is 0 μm to 25 μm, and the release film can be one of silicone oil coating, polyurethane coating, and acrylic coating.

[0046] In some embodiments of this application, the active material layer of the electrode contains only active material and conductive agent, without polymer binder. This avoids the binder's obstruction of electron and ion transport, reduces the proportion of inactive material, and increases energy density. The addition of pore-forming agent during the preparation process increases the porosity of the electrode, reduces the lithium ion transport distance, and improves rate performance. Furthermore, the addition of long-range linear conductive carbon material increases the flexibility of the electrode and improves deformation adaptability.

[0047] The following specific embodiments and comparative examples are provided to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0048] Example 1

[0049] Preparation of the positive electrode:

[0050] Carbon nanotubes (a first conductive agent) and a dispersant are added to a dispersion medium, N-methylpyrrolidone (NMP), and a uniform dispersion of the first conductive agent is formed by methods such as ultrasonication, stirring, and sand milling. Lithium cobalt oxide (a positive electrode active material), graphene (a second conductive agent), and a pore-forming agent are added to the dispersion of the first conductive agent and stirred evenly to form a slurry. The slurry is coated onto the surface of polyethylene terephthalate (PET) substrate with a release film and dried at 90°C. The positive electrode active material layer automatically peels off from the substrate to form the positive electrode.

[0051] Preparation of the negative electrode: The negative electrode active materials graphite, styrene acrylate and lithium carboxymethyl cellulose are mixed in a mass ratio of 98:1:1, and deionized water is used as a solvent to form a slurry of negative electrode active material layer. Copper foil is used as the negative electrode current collector, and the slurry of negative electrode active material layer is coated on the negative electrode current collector. The mixture is dried at 90°C to obtain the negative electrode.

[0052] Preparation of the separator: The separator is made of 8μm thick polyethylene (PE).

[0053] Preparation of electrolyte: Under an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC) = 20:30:20:28:2, by weight) were mixed at a weight ratio of 8:92 to form an electrolyte.

[0054] Lithium-ion battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film package, and after dehydration at 80°C, the electrolyte is injected and the battery is sealed. Following formation, degassing, and edge trimming processes, the lithium-ion battery is obtained.

[0055] Examples 2 to 13 are based on the steps of Example 1 with parameter changes. The specific parameters changed are shown in the table below.

[0056] Example 14

[0057] Preparation of the positive electrode: Lithium cobalt oxide, polyvinylidene fluoride (PVDF), conductive carbon black (Super P, SP), and carbon nanotubes (CNTs) were mixed in a mass ratio of 97.2:1.5:0.8:0.5, using N-methylpyrrolidone (NMP) as a solvent to form a slurry. The slurry was stirred evenly to form the positive electrode active material layer. The slurry was uniformly coated onto the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode.

[0058] Preparation of the negative electrode: Carbon nanotubes (the first conductive agent) and lithium carboxymethyl cellulose (the dispersant) are added to deionized water as a dispersion medium. A uniform dispersion of the first conductive agent is formed by ultrasonication, stirring, and sand milling. Graphite (the negative electrode active material), graphene (the second conductive agent), and a 1 mol / L oxalic acid solution (the pore-forming agent) are added to the dispersion of the first conductive agent and stirred until homogeneous to form a slurry. The slurry is coated onto the surface of polyethylene terephthalate (PET) substrate with a release film and dried at 90°C. The negative electrode active material layer automatically peels off from the substrate to form the negative electrode.

[0059] The remaining preparation steps in Example 14 are the same as in Example 1. Examples 15 to 22 are based on the steps of Example 14 with parameter changes, as shown in the table below.

[0060] Comparative Example 1

[0061] Preparation of the positive electrode: Lithium cobalt oxide, polyvinylidene fluoride (PVDF), conductive carbon black (Super P, SP), and carbon nanotubes (CNTs) were mixed in a mass ratio of 97.2:1.5:0.8:0.5, using N-methylpyrrolidone (NMP) as a solvent to form a slurry. The slurry was stirred evenly to form the positive electrode active material layer. The slurry was uniformly coated onto the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode.

[0062] Preparation of the negative electrode: The negative electrode active material graphite, the binder styrene-butadiene rubber and the dispersant lithium carboxymethyl cellulose are mixed in a mass ratio of 95:3.5:1.5. Deionized water is used as a solvent to form a slurry of negative electrode active material layer. Copper foil is used as the negative electrode current collector. The slurry of negative electrode active material layer is coated on the negative electrode current collector and dried at 90°C to obtain the negative electrode.

[0063] The remaining preparation steps of Comparative Example 1 were the same as those of Example 1. Comparative Examples 2 and 3 were based on the steps of Comparative Example 1 with parameter changes, the specific parameters of which are shown in the table below.

[0064] The testing methods for this application are described below.

[0065] 1. DC resistance (DCR) test at 25℃

[0066] At 25℃, the lithium-ion battery was charged at a constant current of 0.5C to 3.95V, then charged at a constant voltage of 0.05C; allowed to stand for 30 minutes; then discharged at 0.1C for 10 seconds (taking a point every 0.1 seconds and recording the corresponding voltage value U1), and discharged at 1C for 360 seconds (taking a point every 0.1 seconds and recording the corresponding voltage value U2). This charge-discharge cycle was repeated 5 times. Here, "1C" is the current value required to completely discharge the battery within 1 hour. The battery's DCR was calculated using the following formula: DCR = (U2 - U1) / (1C - 0.1C).

[0067] 2. Ratio performance testing

[0068] In an environment of 25℃, the battery was discharged at a constant current to 3V for the first charge and discharge cycle. The battery was charged at a constant current of 0.7C until the upper limit voltage reached 4.48V, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 0.2C until the final voltage reached 3V. The discharge capacity at 0.2C was recorded. The battery was then charged at a constant current of 0.7C until the upper limit voltage reached 4.48V, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 3C until the final voltage reached 3V. The discharge capacity at 3C was recorded.

[0069] 3C discharge capacity retention rate = (3C discharge capacity / discharge capacity at 0.2C) × 100%

[0070] 3. Cyclic performance test:

[0071] The lithium-ion battery was placed in a constant temperature chamber at 45℃±2℃ for 2 hours, charged at a 1C rate to 4.48V, and then charged at a constant voltage of 4.48V to 0.05C. Subsequently, it was discharged at a 1C rate to 3.0V for cycle performance testing, and 800 charge-discharge cycles were performed. The ratio of the discharge capacity on the 800th cycle to the discharge capacity on the 1st cycle was used as the 800-cycle capacity retention rate.

[0072] Table 1

[0073]

[0074] Table 2

[0075]

[0076] Tables 1 and 2 show the differences in preparation parameters and performance test results for Examples 1 to 5. The other preparation parameters, not shown, are the same.

[0077] In Examples 1 to 5, the positive electrode used is the electrode proposed in this application. It can be seen that the bending radius of the positive electrode is 0.5 mm to 1.5 mm and the elongation at break is 2% to 8%, which indicates that the positive electrode has good flexibility. It can be seen that the DC resistance in Examples 1 to 5 is small, and the test results of rate performance and cycle performance are also good. This may be because there is no polymer binder in the positive electrode in Examples 1 to 5 of this application, thus avoiding the influence of polymer binder on kinetic performance.

[0078] Table 3

[0079]

[0080]

[0081] Table 4

[0082]

[0083] Tables 3 and 4 show the preparation parameters and performance test results for Examples 6 to 13. The remaining preparation parameters, which are not shown, are the same as those for Example 1.

[0084] In Examples 6 to 13, the positive electrode of the electrochemical device uses the electrode sheet proposed in this application. Examples 6 to 9 show the influence of the type of the second conductive agent in the positive electrode active material layer on the performance of the electrochemical device. It can be seen that when the second conductive agent is carbon fiber, conductive carbon black, carbon nanotubes, or conductive graphite, all exhibit good performance. Among these, when the second conductive agent is carbon nanotubes, the DC resistance is the lowest, and the rate performance and cycle performance are the best. Furthermore, when the second conductive agent is carbon fiber or carbon nanotubes, the elongation at break of the positive electrode is the longest, which may be because the one-dimensional structure of carbon fiber and carbon nanotubes can play a role in stabilizing the structure.

[0085] 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 also changes, and it affects the bending radius and elongation at break of the positive electrode. Within the range shown, the greater the compaction density of the positive electrode active material layer, the smaller the porosity, the smaller the bending radius, and the greater the elongation at break. The DC resistance first decreases and then increases, while the rate performance and cycle performance first increase and then decrease. This may be because the increase in compaction density improves the contact and connection strength between the positive electrode active materials, which is beneficial to reducing the DC resistance. However, excessive compaction density will reduce the ion transport channels, which is detrimental to the kinetic performance.

[0086] Table 5

[0087]

[0088] Table 6

[0089]

[0090] Tables 5 and 6 show the preparation parameters and performance test results for Examples 14 to 22. The remaining preparation parameters, which are not shown, are the same as those for Example 1.

[0091] In Examples 14 to 22, the negative electrode of the electrochemical device adopts the electrode sheet proposed in this application. As can be seen from Examples 14 to 18, when the mass percentage of the negative electrode active material, the mass percentage of the conductive agent, the composition of the conductive agent, the number of carbon nanotubes in the carbon nanotube aggregate, the 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 for the bending radius and elongation at break of the negative electrode can be met, and lower DC resistance, better rate performance, and cycle performance can be obtained.

[0092] 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 will affect the bending radius and elongation at break of the negative electrode, and will also affect the DC resistance, rate performance and cycle performance. When the negative electrode active material is silicon suboxide, lithium titanate, silicon or silicon carbide, good performance can be obtained. Among them, the rate performance and cycle performance are the best when the negative electrode active material is lithium titanate.

[0093] Table 7

[0094]

[0095] Table 8

[0096]

[0097] " / " indicates that it does not exist. Tables 7 and 8 show the preparation parameters and performance test results of Comparative Examples 1 to 3. The remaining preparation parameters, which are not shown, are the same as those of Comparative Example 1.

[0098] In Comparative Examples 1 to 3, the positive and negative electrodes of the electrochemical devices did not use the electrodes proposed in this application. As can be seen from Comparative Examples 1 to 3, the bending radius of the negative electrode is not less than 3 mm, and the elongation at break of the negative electrode is not greater than 1.9%, indicating poor flexibility of the negative electrode. Furthermore, Comparative Examples 1 to 3 exhibit higher DC resistance, poorer 3C rate performance, and poorer cycle performance. This may be because binders were added in Comparative Examples 1 to 3, which worsened the kinetic performance, thus leading to reduced rate and cycle performance.

[0099] The above description is merely a selection of preferred embodiments of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. An electrochemical device comprising an electrode, said electrode including an active material layer, characterized in that, The electrode has a bending radius of 0.5 mm to 1.5 mm and a breaking elongation of 2% to 8%. The active material layer comprises an active material and a conductive agent. The conductive agent includes a first conductive agent comprising carbon nanotubes and a second conductive agent. Two to 1000 carbon nanotubes are arranged to form bundles of carbon nanotubes. These carbon nanotube aggregates are intertwined with the second conductive agent to form a three-dimensional mesh structure. At least a portion of the active material particles are located within this three-dimensional mesh structure. The conductive agent accounts for 1% to 50% of the mass percentage of the active material layer. Based on the total mass of the conductive agent, the second conductive agent accounts for 1% to 50% of the mass percentage of the conductive agent. The electrode does not have a binder. Wherein, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and the porosity of the positive electrode active material layer is 21% to 30%; or, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the porosity of the negative electrode active material layer is 30% to 40%.

2. The electrochemical device according to claim 1, characterized in that, The electrode is a positive electrode, the active material layer is a positive electrode active material layer, and satisfies at least one of the following: (a) The positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium cobalt oxide, or lithium-rich materials. (b) The thickness of the positive electrode active material layer is from 40 μm to 2500 μm; (c) The compaction density of the positive electrode active material layer is 2.2 g / cm³ to 4.3 g / cm³.

3. The electrochemical device according to claim 1, characterized in that, The electrode is a positive electrode, the active material layer is a positive electrode active material layer, and satisfies at least one of the following: (e) The thickness of the positive electrode active material layer is 40 μm to 320 μm; (f) The compaction density of the positive electrode active material layer is from 2.2 g / cm³ to 4.23 g / cm³.

4. The electrochemical device according to claim 1, characterized in that, The electrode is a negative electrode, the active material layer is a negative electrode active material layer, and satisfies at least one of the following: (g) The negative electrode active material layer includes a negative electrode active material, which includes at least one of lithium titanate, silicon-based material, graphite or hard carbon. (h) The thickness of the negative electrode active material layer is from 30 μm to 3000 μm; (i) The compaction density of the negative electrode active material layer is from 0.6 g / cm³ to 1.85 g / cm³.

5. The electrochemical device according to claim 1, characterized in that, The electrode is a negative electrode, the active material layer is a negative electrode active material layer, and satisfies at least one of the following: (k) The thickness of the negative electrode active material layer is 50 μm to 400 μm; (l) The compaction density of the negative electrode active material layer is 1.3 g / cm³ to 1.8 g / cm³.

6. The electrochemical device according to claim 1, characterized in that, The second conductive agent includes at least one of conductive carbon black, graphene, conductive graphite, or carbon fiber.

7. The electrochemical device according to claim 6, characterized in that, The following conditions must be met: Based on the total mass of the active material layer, the active material accounts for 50% to 99% of the mass of the active material layer.

8. The electrochemical device according to claim 1, characterized in that, The carbon nanotubes have a diameter of 0.5 nm to 10 nm and a length of 1 μm to 100 μm.

9. An electronic device, characterized in that, Includes the electrochemical device according to any one of claims 1 to 8.

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