Electrode and method of making same, electrochemical device, and electronic device

Abstract

The application provides an electrode and a manufacturing method thereof, an electrochemical device and an electronic device. The electrode comprises a current collector and an active material layer on one side or both sides of the current collector; the active material layer is subjected to thermogravimetric analysis under an inert atmosphere at a temperature increasing rate of 10 DEG C / min; and the result of the thermogravimetric analysis shows that the mass change of the active material layer is 0% to 0.2% at 200 DEG C to 800 DEG C, which indicates that the electrode provided in the application has good conductivity of the active material layer, and is beneficial to increasing the thickness of the active material layer while not deteriorating the performance, thereby being beneficial to improving the energy density of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to electrodes and their fabrication methods, electrochemical devices, and electronic devices. Background Technology

[0002] Electrochemical devices, such as lithium-ion batteries, possess advantages such as high energy density, high power, and long cycle life, and are widely used in various fields. With technological advancements, the requirements for the energy density of electrochemical devices are becoming increasingly stringent. To improve the energy density of electrochemical devices, some technologies increase the capacity or voltage of active materials, while others increase the content of active materials per unit volume and reduce the content of inactive materials. Reducing the thickness of current collectors or separators, decreasing the proportion of inactive materials in the formulation, and fabricating thicker electrodes can all reduce the proportion of inactive substances. However, in practical applications, the thickness of current collectors and separators has been reduced to near its limit, thus necessitating an increase in electrode thickness. However, excessively increasing electrode thickness may negatively impact the performance of the electrochemical device, making a significant increase in electrode thickness impractical. Therefore, how to improve the energy density of electrochemical devices while ensuring their performance remains a pressing issue. Summary of the Invention

[0003] Some embodiments of this application provide an electrode and its preparation method, an electrochemical device, and an electronic device. In this method, thermogravimetric analysis is performed on the active material layer of the electrode at a heating rate of 10°C / min under an inert atmosphere. The results of the thermogravimetric analysis show that the mass change of the active material layer is 0% to 0.2% between 200°C and 800°C, which can improve the conductivity of the active material layer and thus help to improve the energy density of the electrochemical device.

[0004] In some embodiments of this application, an electrode is proposed. The electrode includes a current collector and an active material layer located on one or both sides of the current collector. Thermogravimetric analysis (TGA) of the active material layer is performed under an inert atmosphere at a heating rate of 10 °C / min. The results show that the mass change of the active material layer from 200 °C to 800 °C is 0% to 0.2%. The active material layer in this application exhibits good conductivity, which is beneficial to the performance of the electrochemical device and helps to improve energy density.

[0005] In some embodiments of this application, thermogravimetric analysis results show that the number of weight loss peaks in the active material layer between 200°C and 800°C is 0. This indicates that the content of polymeric compounds in the active material layer in this application is zero or extremely low, which is beneficial for improving ion and electron conduction in the active material layer.

[0006] In some embodiments of this application, the electrode is either a positive or negative electrode. In some embodiments, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, the current collector is a negative electrode current collector, and the compaction density ρ1 of the negative electrode active material layer is ≥0.6 g / cm³. 3 Higher compaction density is beneficial for increasing the energy that an electrochemical device can store per unit volume. In some embodiments, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector is ≥10 μm, and a thicker layer is beneficial for increasing the energy density of the electrochemical device. In some embodiments, the porosity n1 of the negative electrode active material layer satisfies: 35% ≥ n1 ≥ 25%. By setting an appropriate porosity, the wetting and conductivity of the electrolyte can be guaranteed while ensuring energy density. In some embodiments, the resistivity of the negative electrode active material layer is from 0.01 Ω*cm to 50 Ω*cm, indicating that the negative electrode active material layer of this application has good conductivity, which is beneficial for the charge and discharge performance of the electrochemical device. In some embodiments, the negative electrode active material layer includes a negative electrode material, which includes at least one of lithium titanate, silicon-based materials, tin-based materials, lithium metal materials, or carbon materials.

[0007] In some embodiments of this application, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, the current collector is a negative electrode current collector, and the compaction density ρ1 of the negative electrode active material layer satisfies: 1.85 g / cm³. 3 ≥ρ1≥0.65 g / cm 3 This is beneficial for improving the energy density of the electrochemical device. In some embodiments, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies: 1500μm≥h1≥15μm, which helps to improve the energy density of the electrochemical device while preventing the active material layer from falling off.

[0008] In some embodiments of this application, the compaction density ρ1 of the negative electrode active material layer satisfies: 1.83 g / cm³ 3 ≥ρ1≥1.0 g / cm 3 In some embodiments of this application, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies: 150μm≥h1≥30μm.

[0009] In some embodiments of this application, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the compaction density ρ2 of the positive electrode active material layer is ≥2 g / cm³. 3This is beneficial for improving the energy density of the electrochemical device. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector is ≥20 μm, which is beneficial for improving the energy density of the electrochemical device. In some embodiments, the porosity n2 of the positive electrode active material layer satisfies: 20% ≥ n2 ≥ 15%, thus ensuring electrolyte wetting and conductivity without significantly affecting the energy density. In some embodiments, the resistivity of the positive electrode active material layer is 0.1 Ω*cm to 500 Ω*cm, thus providing good conductivity. In some embodiments, the positive electrode active material layer includes a positive electrode material, which includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide.

[0010] In some embodiments of this application, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the compaction density ρ2 of the positive electrode active material layer satisfies: 4.25 g / cm³. 3 ≥ρ2≥2.3 g / cm 3 This improves energy density while preventing the positive electrode active material layer from detaching or breaking. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies: 1500μm ≥ h2 ≥ 25μm, thereby improving the energy density of the electrochemical device while avoiding increasing the requirements for the adhesion between the positive electrode active material layer and the positive electrode current collector. In some embodiments of this application, the compaction density ρ2 of the positive electrode active material layer satisfies: 4.23 g / cm³. 3 ≥ρ2≥4.0 g / cm 3 In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies: 130μm≥h2≥26μm.

[0011] In some embodiments of this application, the active material layer includes a first conductive agent and a second conductive agent; the first conductive agent includes carbon nanotubes, and the second conductive agent includes at least one of carbon fiber, acetylene black, graphene, Ketjen black, or conductive carbon black. The long-range conductivity of carbon nanotubes is beneficial for improving the conductivity of the active material layer and for maintaining the structural stability of the active material layer. In some embodiments, the active material layer includes an active material, comprising the following components by mass: 0 to 2 parts of the first conductive agent (excluding 0 parts), 0 to 1 part of the second conductive agent, and 97 to 100 parts of the active material, thereby ensuring both conductivity and energy density. In some embodiments, the carbon nanotubes have a diameter of 0.5 nm to 10 nm and a length of 1 μm to 100 μm, with 2 to 1000 carbon nanotubes forming an aggregate, the aggregate having a diameter of 1 nm to 500 nm and a length of 1 μm to 100 μm, thereby contributing to the structural stability of the active material layer.

[0012] In some embodiments of this application, a method for preparing an electrode is proposed, which can be used to manufacture any electrode of this application, comprising: coating an active material layer slurry onto at least one surface of a current collector, drying, and cold pressing to obtain an initial electrode; and processing the initial electrode to obtain an electrode; wherein, processing the initial electrode includes: plasma treatment of the initial electrode in a vacuum environment, wherein the plasma power is 0.5kW to 5kW, the gas source includes at least one of nitrogen, argon, or carbon tetrafluoride, the gas flow rate is 3000sccm to 5000sccm, the temperature is 20°C to 60°C, and the processing time is 1min to 60min; or, heat treatment of the initial electrode in a vacuum or inert gas environment, wherein the heat treatment temperature is greater than 200°C, and the heat treatment time is not less than 5min; or, laser bombardment of the initial electrode in a vacuum or inert gas environment, wherein the laser intensity is 30W to 100W, the processing time is 1s to 600s, and the distance between the laser and the initial electrode is 3cm to 10cm.

[0013] This application proposes an electrochemical device, including an electrode: the electrode is any of the electrodes in this application, or the electrode is an electrode prepared using the electrode preparation method proposed in this application.

[0014] This application discloses an electronic device, including the electrochemical device disclosed herein.

[0015] An electrode is proposed in the embodiments of this application; the electrode includes a current collector and an active material layer located on one or both sides of the current collector; thermogravimetric analysis is performed on the active material layer under an inert atmosphere at a heating rate of 10°C / min. The thermogravimetric analysis results show that the mass change of the active material layer from 200°C to 800°C is 0% to 0.2%, which indicates that the active material layer in the electrode proposed in the embodiments of this application has good conductivity, which is beneficial to increasing the thickness of the active material layer without deteriorating the performance, thereby improving the energy density of the electrochemical device using this electrode. Attached Figure Description

[0016] 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 elements are not necessarily drawn to scale.

[0017] Figure 1 This is a schematic diagram of an electrode according to an embodiment of the present disclosure. Detailed Implementation

[0018] 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.

[0019] To improve the energy density of electrochemical devices, some technologies increase the thickness of the active material layer in the electrode. However, increasing the thickness of the active material layer may deteriorate its conductivity due to excessive thickness. To further improve conductivity, some technologies employ multi-layer active material structures. However, the composite cold-pressing process of multiple monolayers is complex and cannot avoid changes in the original compaction density and porosity of each monolayer during subsequent cold pressing. Furthermore, weak bonding between layers can lead to delamination, affecting electron and ion conduction and worsening cycle performance. Other technologies use lasers to drill holes in the active material layer; however, laser drilling is inefficient, costly, and prone to energy density loss during the drilling process. Still other technologies apply a pore-forming agent solution to the electrode surface, but this cannot prevent electrode surface dissolution, and the pore depth formed by the pore-forming agent is limited, offering limited improvement to the near-current collector side. The above technologies have solved the problem of ion transport from the electrolyte to the surface of the active material through different methods, but the ion transport from the surface of the active material to the interior of the active material layer remains unchanged. The obstacles to ion transport and long-range electron transport still exist, and the improvement effect is not good.

[0020] Some embodiments of this application provide an electrode that improves the conductivity of the active material layer and reduces ion transport resistance, thereby improving the energy density of the electrochemical device employing the electrode. In some embodiments, the electrode may be an electrode sheet; the electrode includes a current collector and an active material layer located on one or both sides of the current collector; thermogravimetric analysis (TGA) of the active material layer is performed under an inert atmosphere at a heating rate of 10°C / min, and the results show that the mass change of the active material layer from 200°C to 800°C is 0% to 0.2%. In some embodiments, the detection accuracy of the TGA device is 0.2%. In this embodiment, the mass change of the active material layer is not greater than the detection accuracy, indicating that the content of polymeric compounds in the active material layer in this application is zero or extremely low. This is beneficial for improving ion and electron conduction in the active material layer, thereby improving the electrical performance of the electrochemical device.

[0021] In some embodiments of this application, thermogravimetric analysis results show that the number of weight loss peaks in the active material layer between 200°C and 800°C is 0. In some embodiments, if the active material layer contains polymeric compounds, such as polymeric binders, weight loss peaks will be generated due to thermal decomposition during thermogravimetric analysis in the range of 200°C to 800°C. However, in this application, the active material layer does not exhibit any weight loss peaks in the range of 200°C to 800°C. This indicates that the active material layer in the embodiments of this application does not contain polymeric compounds. This avoids the influence of organic matter in the active material layer on the electronic and ionic conduction of the active material layer, thereby improving the ionic and electronic conduction performance of the active material layer. Thus, when the thickness of the active material layer is increased to improve the energy density of the electrochemical device, the good conductivity of the active material layer prevents the electrochemical performance of the device from deteriorating due to the increased thickness. Therefore, the electrode proposed in the embodiments of this application, due to the good conductivity of the active material layer, is beneficial to improving the performance of the electrochemical device using the electrode and to increasing the energy density.

[0022] In some embodiments of this application, the electrode is either a positive or negative electrode, such as the positive or negative electrode of an electrochemical device. In some embodiments, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector. The negative electrode current collector can be copper foil, aluminum foil, steel foil, etc., and is not limited thereto. In some embodiments, the compaction density ρ1 of the negative electrode active material layer is ≥0.6 g / cm³. 3 A higher compaction density indicates that the electrode carries a greater mass of active material per unit volume. A larger mass of active material per unit volume increases the energy that the electrochemical device can store per unit volume, thus improving the energy density. In some embodiments, the compaction density ρ1 of the negative electrode active material layer satisfies: 1.85 g / cm³. 3 ≥ρ1≥0.65 g / cm 3 Optional, 1.83g / cm 3 ≥ρ1≥1.0 g / cm 3 This is beneficial for improving the energy density of the electrochemical device. In some embodiments, the compaction density of the negative electrode active material layer is limited to not less than 1.0 g / cm³. 3 This further ensures the energy density of the electrochemical device, while limiting the compaction density of the negative electrode active material layer to no more than 1.83 g / cm³. 3 It can prevent the particles in the active material layer from breaking due to excessive compaction density, which would increase electrolyte consumption and deteriorate cycle performance.

[0023] In some embodiments, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector is ≥ 10 μm. In some embodiments, a thicker negative electrode active material layer is beneficial to increasing the proportion of the active material layer in the electrochemical device, thereby increasing the energy density of the electrochemical device. In some embodiments of this application, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies: 1500 μm ≥ h1 ≥ 15 μm, optionally, 150 μm ≥ h1 ≥ 30 μm. By limiting the thickness of the negative electrode active material layer to not less than 30 μm, a relatively thick negative electrode active material layer can be ensured, thereby increasing the overall energy density of the electrochemical device. By limiting the thickness of the negative electrode active material layer to not more than 150 μm, the excessive thickness of the negative electrode active material layer is prevented. When the negative electrode active material layer is too thick, the problem of detachment between the negative electrode active material layer and the current collector may occur.

[0024] In some embodiments, the porosity n1 of the negative electrode active material layer satisfies: 35% ≥ n1 ≥ 25%. In some embodiments, the porosity of the negative electrode active material layer is not less than 25%, which can ensure that the negative electrode active material layer and the electrolyte can be fully wetted and can provide sufficient transport channels for the transport of ions and electrons. The porosity of the negative electrode active material layer is not greater than 35%, which can prevent the energy density from being affected by excessive porosity. By setting an appropriate porosity, the wetting of the electrolyte and the conductivity can be ensured while ensuring the energy density.

[0025] In some embodiments, the resistivity of the negative electrode active material layer is from 0.01 Ω*cm to 50 Ω*cm, indicating that the negative electrode active material layer of this application has good conductivity, which is beneficial to the electrical performance of the electrochemical device. In some embodiments, the negative electrode active material layer includes a negative electrode material, which includes at least one of lithium titanate, silicon suboxide, silicon, graphite, and hard carbon, for example, a combination of at least two of the above materials.

[0026] In some embodiments of this application, the electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the compaction density ρ2 of the positive electrode active material layer is ≥2 g / cm³. 3 A higher compaction density is beneficial for increasing the energy density of electrochemical devices. In some embodiments of this application, the compaction density ρ2 of the positive electrode active material layer satisfies: 4.25 g / cm³. 3 ≥ρ2≥2.3 g / cm 3 Optional, 4.23g / cm 3 ≥ρ2≥4.0 g / cm 3 This improves energy density while preventing the positive electrode active material layer from detaching from the positive electrode current collector and preventing particle breakage.

[0027] In some embodiments of this application, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector is ≥ 20 μm. A thicker positive electrode active material layer can store more energy, which is beneficial to improving the energy density of the electrochemical device. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies: 1500 μm ≥ h2 ≥ 25 μm, optionally, 130 μm ≥ h2 ≥ 26 μm, thereby improving the energy density of the electrochemical device while avoiding the positive electrode active material layer from detaching from the positive electrode current collector due to excessive thickness.

[0028] In some embodiments of this application, the porosity n2 of the positive electrode active material layer satisfies: 20% ≥ n2 ≥ 15%, thereby ensuring electrolyte wetting and conductivity without significantly affecting energy density.

[0029] In some embodiments of this application, the resistivity of the positive electrode active material layer is from 0.1 Ω*cm to 500 Ω*cm, indicating that the positive electrode active material layer has good conductivity, which is beneficial to improving the electrical performance of the electrochemical device. In some embodiments, the positive electrode active material layer includes a positive electrode material, which includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide.

[0030] In some embodiments of this application, the active material layer includes a first conductive agent and a second conductive agent; the first conductive agent includes carbon nanotubes, which may include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; the second conductive agent includes at least one of carbon fiber, acetylene black, graphene, Ketjen black, or conductive carbon black. The long-range conductivity of carbon nanotubes is beneficial for improving the conductivity of the active material layer and for maintaining the structural stability of the active material layer.

[0031] In some embodiments, the active material layer includes an active material comprising the following components by mass: 0 to 2 parts of a first conductive agent (excluding 0 parts), 0 to 1 part of a second conductive agent, and 97 to 100 parts of the active material, thereby ensuring both conductivity and energy density. In some embodiments, the second conductive agent can be 0 parts by mass, but the first conductive agent cannot be 0 parts, meaning the active material layer must contain carbon nanotubes. This is because the active material layer in this embodiment does not contain polymeric compounds, and therefore does not contain polymeric binders. Thus, carbon nanotubes can be used to improve conductivity while stabilizing the structure of the active material layer.

[0032] In some embodiments of this disclosure, the carbon nanotubes have a diameter of 0.5 nm to 10 nm and a length of 1 μm to 100 μm. Two to 1000 carbon nanotubes form an aggregate with a diameter of 1 nm to 500 nm and a length of 1 μm to 100 μm, thereby contributing to the structural stability of the active material layer. For some embodiments, please refer to... Figure 1 , Figure 1 The diagram schematically illustrates the composition of an electrode in one embodiment, including a current collector 10 and an active material layer. The active material layer includes an active material 20 and a conductive agent 30. The conductive agent may include zero-dimensional conductive agents, one-dimensional conductive agents, and two-dimensional conductive agents. Zero-dimensional conductive agents may include particulate conductive agents such as conductive carbon black, one-dimensional conductive agents may include carbon nanotubes, and two-dimensional conductive agents may include graphene. In this embodiment, the aggregates can further enhance the structural stability of the active material layer, and the multi-dimensional conductive agents from zero-dimensional to two-dimensional can better fill the gaps between the active materials 20, further improving the conductivity of the active material layer.

[0033] In some embodiments of this application, a method for preparing an electrode is proposed, which can be used to manufacture the electrode of any electrochemical device of this application, comprising: coating a slurry of an active material layer onto at least one surface of a current collector, drying, and cold pressing to obtain an initial electrode; and processing the initial electrode to obtain an electrode.

[0034] The initial electrode treatment includes: plasma treatment in a vacuum environment, with a plasma power of 0.5kW to 5kW, a gas source including at least one of nitrogen, argon, or carbon tetrafluoride, a gas flow rate of 3000sccm to 5000sccm, a temperature of 20°C to 60°C, and a treatment time of 1min to 60min; or heat treatment in a vacuum or inert gas environment, with a heat treatment temperature greater than 200°C and a heat treatment time of not less than 5min, and in some embodiments, the heat treatment temperature can be 200°C to 800°C and the heat treatment time can be 5min to 600min; or laser bombardment in a vacuum or inert gas environment, with a laser intensity of 30W to 100W and a treatment time of 1s to 600s, wherein the distance between the laser and the initial electrode during laser bombardment can be 3cm to 10cm.

[0035] The electrode preparation method proposed in this application removes polymer compounds from the active material layer by treating the electrode, thereby improving the conductivity of the electrochemical device and consequently increasing the energy density. In some embodiments of this disclosure, the active material layer of the electrode includes active materials and conductive agents, but does not contain polymer compounds (such as polymeric binders and thickeners), thus avoiding the obstruction of electron and ion transport by polymer compounds.

[0036] In some embodiments of this application, the electrochemical device includes an electrode. The electrode can be any of the electrodes described in any of the embodiments of this application, or it can be an electrode prepared using the electrode preparation method proposed in this application. In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, and a separating membrane disposed between the positive and negative electrodes. In some embodiments, the positive or negative electrode can be any of the electrodes described above. In some embodiments, the current collector for the positive electrode can be an Al foil; of course, other current collectors commonly used in the art can also be used.

[0037] In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene comprises 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0050] Example 1

[0051] Preparation of the positive electrode sheet: Lithium cobalt oxide (CPF), polyvinylidene fluoride (PVDF), carbon nanotubes (the first conductive agent), and conductive carbon black (Super P) (the second conductive agent) are mixed in a mass ratio of 97.5:1.0:1.0:0.5. N-methylpyrrolidone (NMP) is used as a solvent to prepare a slurry, which is then stirred until homogeneous to form the positive electrode active material layer. The slurry is uniformly coated onto the positive electrode current collector aluminum foil and dried at 90°C to obtain the positive electrode sheet.

[0052] Preparation of negative electrode sheet: Graphite, conductive agent (carbon nanotubes and conductive carbon black (Super P) in a mass ratio of 2:1), and lithium carboxymethyl cellulose in a mass ratio of 97.5:1.5:1.0 are mixed with deionized water as solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector. The negative electrode active material layer slurry is coated onto the negative electrode current collector and dried at 90℃. The dried electrode sheet is then heat-treated at 350℃ for 10 minutes to obtain the negative electrode sheet.

[0053] Preparation of the separator: The separator is made of polyethylene (PE) with a thickness of 8 μm.

[0054] 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.

[0055] Preparation of lithium-ion batteries: Positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to form an 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, a lithium-ion battery is obtained.

[0056] The relevant parameters for Example 1 are as follows: the negative electrode material is graphite; the mass percentage of the negative electrode material in the negative electrode active material layer is 98.5%; the conductive agent in the negative electrode active material layer is carbon nanotubes (CNTs) and conductive carbon black, with a mass ratio of carbon nanotubes to conductive carbon black of 2:1; the mass percentage of the conductive agent in the negative electrode active material layer is 1.5%; the thermogravimetric mass change of the negative electrode active material layer from 200℃ to 800℃ is 0%, the number of weight loss peaks is 0; the resistivity of the negative electrode active material layer is 0.1 Ω*cm; the single-layer thickness of the negative electrode active material layer is 75 μm; and the compaction density of the negative electrode active material layer is 1.78 g / cm³. 3 .

[0057] Examples 2 to 6, 13 to 22, and 34 to 43 are based on the steps of Example 1 with parameter changes. The specific parameters changed are shown in the table below.

[0058] Example 7

[0059] Preparation of the positive electrode sheet: Lithium cobalt oxide, polyvinylidene fluoride, and conductive agents (carbon nanotubes and conductive carbon black (Super P), in a mass ratio of 2:1) are mixed at a mass ratio of 97.5:1:1.5. N-methylpyrrolidone (NMP) is used as a solvent to prepare a slurry, which is then stirred until homogeneous to form the positive electrode active material layer. The slurry is uniformly coated onto the positive electrode current collector aluminum foil, dried at 90°C, and then heat-treated at 500°C for 10 minutes. The resulting positive electrode sheet is obtained after heat treatment.

[0060] Preparation of negative electrode sheet: Graphite, styrene acrylate and lithium carboxymethyl cellulose are mixed in a mass ratio of 98:1:1 with deionized water as solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector. The negative electrode active material layer slurry is coated on the negative electrode current collector and dried at 90°C to obtain the negative electrode sheet.

[0061] The remaining preparation steps of Example 7 are the same as those of Example 1.

[0062] Examples 8 to 11 and 23 to 33 are based on the steps of Example 7 with parameter changes. The specific parameters changed are shown in the table below.

[0063] Example 12

[0064] Preparation of the positive electrode sheet: Lithium cobalt oxide, polyvinylidene fluoride, and conductive agents (carbon nanotubes and conductive carbon black (Super P), in a mass ratio of 2:1) are mixed at a mass ratio of 97.5:1:1.5. N-methylpyrrolidone (NMP) is used as a solvent to prepare a slurry, which is then stirred until homogeneous to form the positive electrode active material layer. The slurry is uniformly coated onto the positive electrode current collector aluminum foil. The dried electrode sheet is then heat-treated at 500℃ for 10 minutes to obtain the positive electrode sheet.

[0065] Preparation of negative electrode sheet: Graphite, carbon nanotubes, and sodium carboxymethyl cellulose, the negative electrode material, are mixed in a mass ratio of 97.5:1.5:1.0 with deionized water as solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector. The negative electrode active material layer slurry is coated on the negative electrode current collector and dried at 90°C. The dried electrode sheet is then heat-treated at 350°C for 10 minutes to obtain the negative electrode sheet.

[0066] The remaining preparation steps of Example 12 are the same as those of Example 1.

[0067] Examples 13 to 43 are based on the steps of Example 1 with parameter changes. The specific parameters changed are shown in the table below.

[0068] Comparative Example 1

[0069] Preparation of negative electrode sheet: The negative electrode material graphite and the binder (styrene acrylate and sodium carboxymethyl cellulose in a mass ratio of 2:1.5) are mixed in a mass ratio of 96.5:3.5. Deionized water is used as a solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector. The negative electrode active material layer slurry is coated on the negative electrode current collector and dried at 90°C to obtain the negative electrode sheet.

[0070] The remaining preparation steps of Comparative Example 1 are the same as those of Example 1. The differences in parameters between Comparative Example 1 and Example 1 are shown in the table below.

[0071] Comparative Examples 2 and 3 are based on the steps of Comparative Example 1 with parameter changes. The specific parameters that were changed are shown in the table below.

[0072] Comparative Example 4

[0073] Preparation of the positive electrode sheet: Lithium cobalt oxide, polyvinylidene fluoride, and conductive carbon black (Super P) were mixed in a mass ratio of 95:3.5:1.5, 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 sheet.

[0074] The remaining preparation steps of Comparative Example 4 are the same as those of Example 7, with specific parameter changes shown in the table below.

[0075] Comparative Examples 5 and 6 are based on the steps of Comparative Example 4, with parameter changes. The specific parameters that were changed are shown in the table below.

[0076] The testing methods for this application are described below.

[0077] 1. Thermogravimetric test

[0078] Thermogravimetric analysis (TGA) was used to determine the positive and negative active material layers of the prepared lithium-ion battery. The mass change and the number of weight loss peaks during the TGA process were measured. The test range was 200℃ to 800℃, the heating rate was 10℃ / min, and the test atmosphere was inert atmosphere.

[0079] 2. Resistivity test

[0080] The resistivity of the positive and negative active material layers was tested using a resistance meter. The electrode was directly measured using a controllable pressure probe with upper and lower planes. An alternating current was applied to the positive or negative electrode, and a certain pressure (0.35T) was applied to the active material layer. The overall resistance in the thickness direction of the electrode was obtained. The area (A) and thickness (l) of the electrode under test were collected. The resistivity of the electrode under test was derived according to the resistivity calculation formula (ρ=R*A / l).

[0081] 3. AC resistance test

[0082] A small AC current of 1kHz is applied to the positive and negative terminals of the battery, and the AC resistance value of the battery is obtained by measuring its voltage response.

[0083] 4. DC resistance (DCR) test at 25℃

[0084] 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).

[0085] 5. Ratio performance testing

[0086] In an environment of 25 ℃, the battery was discharged at a constant current to 3V for the first charge and discharge cycle. Constant current charging was performed at a charging current of 0.7C until the upper limit voltage reached 4.48V, followed by constant voltage charging to 0.05C. Then, constant current discharge was performed at a discharge 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 charging current of 0.7C until the upper limit voltage reached 4.48V, followed by constant voltage charging to 0.05C. Then, the discharge rate was set to 3C for constant current discharge until the final voltage reached 3V. The discharge capacity at 3C was recorded.

[0087] 3C discharge capacity retention rate = (3C discharge capacity / discharge capacity at 0.2C) × 100%

[0088] Table 1

[0089] Negative electrode material content (%) in the negative electrode active material layer Types of negative electrode conductive agents Mass ratio of negative electrode conductive agent Types of negative electrode binders Adhesive mass fraction Change in thermogravimetric mass of negative electrode (%) Resistivity of the negative electrode active material layer (Ω*cm) Number of negative electrode thermogravimetric loss peaks AC resistance (mΩ) DC resistance (mΩ) 3C discharge capacity retention rate (%) Example 1 98.5 CNT: Conductive Carbon Black = 2:1 1.50% Lithium carboxymethyl cellulose 1.0% 0 0.1 0 20.5 35 76 Example 2 98.5 CNT: Conductive Carbon Black = 2:1 1.50% Sodium carboxymethyl cellulose 1.0% 0.1 0.1 0 20 35.2 75 Example 3 98.5 CNT: Conductive Carbon Black = 2:1 1.50% Styrene acrylate: lithium carboxymethyl cellulose = 1:1 1.0% 0.2 0.1 0 21 35.3 74.7 Example 4 98.5 CNT 1.50% Sodium carboxymethyl cellulose 1.0% 0.1 0.05 0 18 33 80 Example 5 97 CNT:Graphene = 2:1 3.00% Sodium carboxymethyl cellulose 1.0% 0.1 0.03 0 15 30 83 Example 6 99.5 CNT 0.50% Sodium carboxymethyl cellulose 1.0% 0.1 0.15 0 25 39 70 Example 12 98.5 CNT 1.50% Sodium carboxymethyl cellulose 1.0% 0.1 0.05 0 13 28 90 Comparative Example 1 95 none 0% Styrene acrylate: Sodium carboxymethyl cellulose = 2:1.5 3.50% 3 1.2 2 40 55 47 Comparative Example 2 97 none 0% Styrene-butadiene rubber: Sodium carboxymethyl cellulose = 2:1 3% 2.6 1.2 2 35 50 49 Comparative Example 3 98 none 0% Styrene acrylate: lithium carboxymethyl cellulose = 1:1 2% 1.6 1.2 2 30 45 55

[0090] Table 1 shows the preparation parameters and performance test results of Examples 1 to 6, 12 and Comparative Examples 1 to 3. The differences between Examples 1 to 6 and Comparative Examples 1 to 3 are only in the parameters shown in Table 1. In Examples 1 to 6, the negative electrode was heat-treated. In Example 12, both the negative electrode and the positive electrode were heat-treated. In Comparative Examples 1 to 3, neither the positive nor the negative electrode was heat-treated.

[0091] Please refer to Table 1. In Examples 1 to 6 and 12, the thermogravimetric mass change of the negative electrode active material layer between 200°C and 800°C is less than 0.2%, and the number of weight loss peaks is 0. In Comparative Examples 1 to 3, the thermogravimetric mass change of the negative electrode active material layer between 200°C and 800°C is greater than 0.2%, and the number of weight loss peaks is not 0. As can be seen from Table 1, the AC resistance and DC resistance of the lithium-ion batteries in Examples 1 to 6 and 12 are significantly lower than those in Comparative Examples 1 to 3, which is consistent with the resistivity data. The capacity retention rate after 3C rate discharge in Examples 1 to 6 and 12 is significantly higher than that in Comparative Examples 1 to 3. The above data shows that when the mass change of the weight loss peaks is less than 0.2% after thermogravimetric analysis of the negative electrode active material layer between 200°C and 800°C, the conductivity of the negative electrode active material layer can be improved, thereby reducing the resistance of the electrochemical device and improving rate performance.

[0092] Table 2

[0093] Content of positive electrode material in the positive electrode active material layer (%) Types of positive electrode conductive agents Mass percentage of positive conductive agent Types of positive electrode binders positive electrode binder mass fraction Change in thermogravimetric mass of positive electrode (%) Resistivity of the positive electrode active material layer (Ω*cm) Positive electrode compaction density (g / cm³) Number of positive electrode thermogravimetric loss peaks AC resistance (mΩ) DC resistance (mΩ) 3C discharge capacity retention rate (%) Example 7 98.5 CNT: Conductive Carbon Black = 2:1 1.50% PVDF 1.0% 0 1.0 4.15 0 24 39 70 Example 8 98.5 CNT: Conductive Carbon Black = 2:1 1.50% PVDF:PVP = 1:1 1.0% 0.1 1.0 4.15 0 23 38 70.8 Example 9 98.5 CNT: Conductive Carbon Black = 2:1 1.50% PVP 1.0% 0.2 1.0 4.15 0 23.3 38.5 70.7 Example 10 97 CNT:Graphene = 2:1 3.00% PVDF:PVP = 1:1 1.0% 0.1 0.8 4.15 0 20 36 73 Example 11 99.5 CNT 0.50% PVDF:PVP = 1:1 1.0% 0.1 3.0 4.15 0 28 41 68 Example 12 98.5 CNT: Conductive Carbon Black = 2:1 1.50% PVDF 1.0% 0 0.1 4.15 0 13 28 90 Comparative Example 4 95 Conductive carbon black 1.50% PVDF 3.50% 2.8 70 4.15 1 50 65 37 Comparative Example 5 96 CNT: Conductive Carbon Black = 2:1 1.50% PVDF 2.5% 2 50 4.15 1 40 55 46 Comparative Example 6 97.5 CNT: Conductive Carbon Black = 2:1 1.50% PVDF 1.0% 0.8 50 4.15 1 30 45 55

[0094] Table 2 shows the preparation parameters and performance test results of Examples 7 to 12 and Comparative Examples 4 to 6. The differences between Examples 7 to 11 and Comparative Examples 4 to 6 are only in the parameters shown in Table 2. In Examples 7 to 11, the positive electrode was heat-treated. In Example 12, both the negative electrode and the positive electrode were heat-treated. In Comparative Examples 4 to 6, neither the positive nor the negative electrode was heat-treated.

[0095] Please refer to Table 2. In Examples 7 to 12, the thermogravimetric mass change of the positive electrode active material layer between 200°C and 800°C is less than 0.2%, and the number of weight loss peaks is 0. In Comparative Examples 4 to 6, the thermogravimetric mass change of the positive electrode active material layer between 200°C and 800°C is greater than 0.2%, and the number of weight loss peaks is not 0. As can be seen from Table 2, the AC resistance and DC resistance of the lithium-ion batteries in Examples 7 to 12 are significantly lower than those in Comparative Examples 4 to 6, which is consistent with the resistivity data. The capacity retention rate after 3C discharge in Examples 7 to 12 is significantly higher than that in Comparative Examples 4 to 6. The above data shows that when the mass change of the weight loss peaks is less than 0.2% after thermogravimetric analysis of the positive electrode active material layer between 200°C and 800°C, the conductivity of the positive electrode active material layer can be improved, thereby reducing the resistance of the electrochemical device and improving rate performance.

[0096] Tables 1 and 2 also show that the lithium-ion battery in Example 12 has the lowest DC resistance and AC resistance, the highest 3C discharge capacity retention rate, and the best overall performance. This is because in Example 12, not only the negative electrode was heat-treated, but also the positive electrode. The thermogravimetric mass change of both the positive and negative electrode active materials layers was less than 0.2% from 200°C to 800°C. Neither the positive nor the negative electrode contains polymer compounds, thus achieving the best kinetic performance.

[0097] Table 3

[0098] Example Anode material Compacted density of negative electrode active material layer (g / cm³) Thickness of the active material layer on one side of the negative electrode (μm) Change in thermogravimetric mass of the negative electrode active material layer (%) Number of weight loss peaks in the negative electrode active material layer Porosity of the negative electrode active material layer (%) Resistivity of the negative electrode active material layer (Ω*cm) AC resistance (mΩ) DC resistance (mΩ) 3C discharge capacity retention rate (%) 13 graphite 0.60 75 0.1 0 35 0.3 30 45 85 14 graphite 1.00 75 0.1 0 34 0.25 27 43 82 2 graphite 1.78 75 0.1 0 30 0.1 20 35.2 75 15 graphite 1.83 75 0.1 0 25 0.08 18 33 73 16 graphite 1.78 30 0.1 0 30 0.1 10 25 92 2 graphite 1.78 75 0.1 0 30 0.1 20 35.2 75 17 graphite 1.78 150 0.1 0 30 0.1 25 40 70 18 graphite 1.78 1500 0.1 0 30 0.1 60 79 42 19 silicon dioxide 1.60 24 0.1 0 33 0.2 31 45 64 20 Lithium titanate 1.75 160 0.1 0 25 0.16 28.5 42 67 2 graphite 1.78 75 0.1 0 30 0.1 20 35.2 75 21 silicon 1.60 12 0.1 0 32 0.15 27.5 41 65 22 Hard carbon 1.30 63 0.1 0 35 0.05 13 27 87

[0099] Table 3 shows the preparation parameters and performance test results of Examples 2, 13 to 22. The only difference between Examples 13 to 22 and Example 2 is the parameters shown in Table 3; the other parameters are the same.

[0100] As shown in Examples 2, 13 to 15, with the increase of the compaction density of the negative electrode active material layer, the porosity of the negative electrode active material layer decreases, the resistivity of the negative electrode active material layer decreases, the AC resistance of the lithium-ion battery gradually decreases, the DC resistance also gradually decreases, and the 3C discharge capacity retention rate gradually decreases. It can be seen that when the compaction density of the negative electrode active material layer is too low, it is not conducive to AC resistance and DC resistance, that is, it is not conducive to kinetic performance, and the volumetric energy density is low. Appropriately increasing the compaction density of the negative electrode active material layer can reduce the resistance of the lithium-ion battery, but excessive compaction density is not conducive to rate performance. This may be because excessive compaction density is not conducive to electrolyte wetting.

[0101] As shown in Examples 2, 16 to 18, as the thickness of the negative electrode active material layer on one side of the negative electrode current collector increases, the AC resistance and DC resistance of the lithium-ion battery increase, and the 3C discharge capacity retention rate decreases. This may be because the increased thickness of the negative electrode active material layer leads to an increased path for ion and electron transport, which is detrimental to conductivity. However, if the thickness of the negative electrode active material layer is too small, it will lead to a decrease in the capacity that the negative electrode can store, which is detrimental to energy density. Therefore, it is necessary to balance the performance and capacity density of the lithium-ion battery.

[0102] As shown in Examples 2, 19 to 22, the effects of different anode materials are demonstrated. When the anode material is silicon oxide, lithium titanate, graphite, silicon, or hard carbon, it has good overall performance. However, different anode materials will affect resistivity, compaction density, etc. Overall, when the anode material is graphite, the overall performance is better.

[0103] Table 4

[0104] Example cathode materials Compacted density of the positive electrode active material layer (g / cm³) Thickness of the active material layer on one side of the positive electrode (μm) Porosity of the positive electrode active material layer (%) Resistivity of the positive electrode active material layer (Ω*cm) Change in thermogravimetric mass of the positive electrode active material layer (%) Number of weight loss peaks in the positive electrode active material layer AC resistance (mΩ) DC resistance (mΩ) 3C discharge capacity retention rate (%) 23 Lithium cobalt oxide 2 63 25 5 0.1 0 29 45 80 24 Lithium cobalt oxide 4 63 20 3 0.1 0 25 40 75 8 Lithium cobalt oxide 4.15 63 17 1.0 0.1 0 23 38 70.8 25 Lithium cobalt oxide 4.25 63 15 0.9 0.1 0 20 35 73 26 Lithium cobalt oxide 4.15 25 17 1.0 0.1 0 15 30 80 27 Lithium cobalt oxide 4.15 26 17 1.0 0.1 0 16 31 79 8 Lithium cobalt oxide 4.15 63 17 1.0 0.1 0 23 38 70.8 28 Lithium cobalt oxide 4.15 130 17 1.0 0.1 0 25 42 66 29 Lithium cobalt oxide 4.15 1500 17 1.0 0.1 0 39 55 56 30 Lithium iron phosphate 2.3 63 25 3.0 0.1 0 42 53 58 31 Lithium nickel cobalt manganese oxide 3.5 63 23 1.2 0.1 0 24 40 69 8 Lithium cobalt oxide 4.15 63 17 1.0 0.1 0 23 38 70.8 32 Lithium manganese oxide 3.1 63 20 1.5 0.1 0 26 42 67 33 Lithium nickel cobalt aluminum oxide 3.5 63 23 2.0 0.1 0 33 47 63

[0105] Table 4 shows the preparation parameters and performance test results of Examples 8, 23 to 33. The only difference between Examples 23 to 33 and Example 8 is the parameters shown in Table 4; the other parameters are the same.

[0106] As shown in Examples 8, 23 to 25, with the increase of the compaction density of the positive electrode active material layer, the porosity of the positive electrode active material layer decreases, the resistivity of the positive electrode active material layer decreases, the AC resistance of the lithium-ion battery gradually decreases, and the DC resistance also gradually decreases. The 3C discharge capacity remains unchanged, decreasing first and then increasing. It can be seen that when the compaction density of the positive electrode active material layer is too low, it is not conducive to AC resistance and DC resistance, that is, it is not conducive to kinetic performance, and it will also affect the volumetric energy density. Appropriately increasing the compaction density of the negative electrode active material layer can reduce the resistance of the lithium-ion battery, but excessive compaction density is not conducive to rate performance.

[0107] As shown in Examples 8, 26 to 29, as the thickness of the positive electrode active material layer on one side of the positive electrode current collector increases, the AC resistance and DC resistance of the lithium-ion battery increase, and the 3C discharge capacity retention rate decreases. This may be because the increased thickness of the positive electrode active material layer leads to an increase in the ion and electron transport path, which is detrimental to conductivity. However, if the thickness of the positive electrode active material layer is too small, it will lead to a decrease in the capacity that the negative electrode can store, which is detrimental to energy density. Therefore, it is necessary to balance the performance and capacity density of the lithium-ion battery.

[0108] As shown in Examples 8, 30 to 33, the effects of different cathode materials are demonstrated. When the cathode material is lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, or lithium nickel cobalt aluminum oxide, it has good overall performance. However, different cathode materials will affect resistivity, compaction density, etc. Overall, when the cathode material is lithium cobalt oxide, the overall performance is better.

[0109] Table 5

[0110] Example CNT tube diameter (nm) CNT length (μm) The number of CNTs (roots) contained in the aggregate. Aggregate diameter (nm) Aggregate length (μm) Change in thermogravimetric mass of the negative electrode active material layer (%) Number of weight loss peaks in the negative electrode active material layer Resistivity of the negative electrode active material layer (Ω*cm) AC resistance (mΩ) DC resistance (mΩ) 3C discharge capacity retention rate (%) 2 0.5 10 25 12.5 10 0.1 0 0.05 20 35.2 75 34 2 10 25 50 10 0.1 0 0.1 23 38 73 35 10 10 25 250 10 0.1 0 0.15 26 40 68 36 0.5 1 25 12.5 1 0.1 0 0.16 27 41 66 2 0.5 10 25 12.5 10 0.1 0 0.05 20 35.2 75 37 0.5 100 25 12.5 100 0.1 0 0.03 16 31.4 79.5 38 0.5 10 2 1 10 0.1 0 0.04 19 34 76 2 0.5 10 25 12.5 10 0.1 0 0.05 20 35.2 75 39 0.5 10 1000 500 10 0.1 0 0.08 24 38 69

[0111] The parameters of Examples 34 to 39 differ from those of Example 2 only in the data shown in Table 5; the other parameters, which are not shown, are the same as those in Example 2. In Table 5, CNTs refer to carbon nanotubes in the positive and negative electrodes.

[0112] As shown in Examples 2, 34 and 35, when the diameter of the carbon nanotube is in the range of 0.5 nm to 10 nm, the overall performance of the lithium-ion battery is better. When the diameter of the carbon nanotube is too long, it may be detrimental to conductivity and rate performance.

[0113] As shown in Examples 2, 36 and 37, as the length of CNT increases, the DC resistance and AC resistance decrease, and the 3C discharge capacity retention rate increases. This is because the increase in the length of carbon nanotubes improves long-range conductivity and is beneficial to stabilizing the structure of the active material layer.

[0114] As shown in Examples 2, 38 to 29, as the number of carbon nanotubes contained in the aggregate increases, the conductivity and 3C discharge capacity retention of the lithium-ion battery decrease slightly. When the number of carbon nanotubes contained in the aggregate is in the range of 2 to 1000, the overall performance of the lithium-ion battery is good.

[0115] As shown in Examples 2, 38 to 39, as the diameter of the aggregate increases, the AC resistance and DC resistance of the lithium-ion battery increase, and the 3C discharge capacity retention rate decreases. Therefore, in some examples, the aggregate diameter is limited to 1 nm to 500 nm to avoid the impact on the performance of the lithium-ion battery when the aggregate diameter is too large. If the diameter of the aggregate is too small, it may not be able to stabilize the structure of the active material layer well.

[0116] As shown in Examples 2, 42 to 43, as the length of the aggregate increases, the AC resistance and DC resistance of the lithium-ion battery decrease, and the 3C discharge capacity retention rate increases. This may be because a longer aggregate improves the stability of the overall structure of the active material layer and enhances long-range conductivity.

[0117] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application 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 any combination of the above-described technical features or their equivalents. For example, technical solutions formed by substituting the above-described features with technical features having similar functions disclosed in this application.

Claims

1. An electrode, characterized in that, The electrode includes a current collector and an active material layer located on one or both sides of the current collector; the active material layer is subjected to thermogravimetric analysis at a heating rate of 10°C / min under an inert atmosphere, and the results of the thermogravimetric analysis show that the mass change of the active material layer from 200°C to 800°C is 0% to 0.2%, and the active material layer does not contain polymeric compounds. The active material layer includes a first conductive agent, which includes carbon nanotubes with a diameter of 0.5 nm to 10 nm and a length of 1 μm to 100 μm. Every 2 to 1000 carbon nanotubes form an aggregate with a diameter of 1 nm to 500 nm and a length of 1 μm to 100 μm.

2. The electrode according to claim 1, characterized in that, The thermogravimetric analysis results showed that the number of weight loss peaks in the active material layer between 200°C and 800°C was 0.

3. The electrode 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 the current collector is a negative electrode current collector.

4. The electrode according to claim 3, characterized in that, The electrode satisfies at least one of the following conditions: (a) The compaction density ρ1 of the negative electrode active material layer is ≥ 0.6 g / cm³. 3 ; (b) The thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector is ≥10μm; (c) The porosity n1 of the negative electrode active material layer satisfies: 35% ≥ n1 ≥ 25%; (d) The resistivity of the negative electrode active material layer is from 0.01 Ω*cm to 50 Ω*cm; (e) The negative electrode active material layer includes a negative electrode material, which includes at least one of lithium titanate, silicon suboxide, graphite, silicon, and hard carbon.

5. The electrode according to claim 3, characterized in that, The electrode satisfies at least one of the following conditions: (f) The compaction density ρ1 of the negative electrode active material layer satisfies: 1.85 g / cm³ 3 ≥ρ1≥0.65g / cm 3 ; (g) The thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies: 1500μm≥h1≥15μm.

6. The electrode according to claim 3, characterized in that, The electrode satisfies at least one of the following conditions: (h) The compaction density ρ1 of the negative electrode active material layer satisfies: 1.83 g / cm³ 3 ≥ρ1≥1.0g / cm 3 ; (i) The thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies: 150μm≥h1≥30μm.

7. The electrode according to claim 1, characterized in that, The electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the electrode satisfies at least one of the following conditions: (j) The compaction density ρ2 of the positive electrode active material layer is ≥ 2 g / cm³ 3 ; (k) The thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector is ≥20μm; (l) The porosity n2 of the positive electrode active material layer satisfies: 20% ≥ n2 ≥ 15%; (m) The resistivity of the positive electrode active material layer is from 0.1 Ω*cm to 500 Ω*cm; (n) The positive electrode active material layer includes a positive electrode material, which includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide.

8. The electrode according to claim 1, characterized in that, The electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the electrode satisfies at least one of the following conditions: (o) The compaction density ρ2 of the positive electrode active material layer satisfies: 4.25 g / cm³ 3 ≥ρ2≥2.3g / cm 3 ; (p) The thickness h2 of the positive active material layer on one side of the positive current collector satisfies: 1500μm≥h2≥25μm.

9. The electrode according to claim 1, characterized in that, The electrode is a positive electrode, the active material layer is a positive electrode active material layer, the current collector is a positive electrode current collector, and the electrode satisfies at least one of the following conditions: (q) The compaction density ρ2 of the positive electrode active material layer satisfies: 4.23 g / cm³ 3 ≥ρ2≥4.0g / cm 3 ; (r) The thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies: 130μm≥h2≥26μm.

10. The electrode according to claim 1, characterized in that, The active material layer includes a second conductive agent; The second conductive agent includes at least one of carbon fiber, acetylene black, graphene, Ketjen black, or conductive carbon black.

11. The electrode according to claim 10, characterized in that, The active material layer includes an active material, and the active material layer comprises the following components by mass: 0 to 2 parts of the first conductive agent and 0 parts of the second conductive agent, and 97 to 100 parts of the active material.

12. A method for preparing an electrode as described in any one of claims 1 to 11, characterized in that, include: The active material layer slurry is coated onto at least one surface of the current collector, dried, and cold-pressed to obtain the initial electrode; The initial electrode is treated to remove polymeric compounds from the active material layer, thereby obtaining the electrode; The processing of the initial electrode includes: The initial electrode is subjected to plasma treatment in a vacuum environment, with a plasma power of 0.5kW to 5kW, a gas source including at least one of nitrogen, argon or carbon tetrafluoride, a gas flow rate of 3000sccm to 5000sccm, a temperature of 20°C to 60°C, and a treatment time of 1min to 60min. or, The initial electrode is subjected to heat treatment in a vacuum or inert gas environment at a temperature greater than 200°C for a time of not less than 5 minutes. or, The initial electrode is subjected to laser bombardment in a vacuum or inert gas environment, with a laser intensity of 30W to 100W and a processing time of 1s to 600s.

13. An electrochemical device, characterized in that, Including electrodes: The electrode is the electrode according to any one of claims 1 to 11, or, The electrode is prepared using the preparation method described in claim 12.

14. An electronic device, characterized in that, Includes the electrochemical device as described in claim 13.

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