Electrodes, electrochemical devices and electronic devices

Abstract

This application provides an electrode, an electrochemical device, and an electronic device. The electrode includes: a current collector; a first coating disposed on the current collector, the first coating comprising an active material, and the first coating sequentially including a first edge portion, a middle portion, and a second edge portion in the width direction of the current collector; a second coating including a first portion and a second portion respectively disposed on the first edge portion and the second edge portion; wherein the surface of the first portion away from the first edge portion has a first adhesive force, the surface of the second portion away from the second edge portion has a second adhesive force, and the surface of the middle portion away from the current collector has a third adhesive force, and both the first adhesive force and the second adhesive force are greater than the third adhesive force. The embodiments of this application improve the electrical performance and safety performance of the electrochemical device while minimizing the impact on the volumetric energy density of the electrochemical device.

Description

[0001] This application is a divisional application of the invention patent filed on August 31, 2020, with application number 202080010007.5 (international application number: PCT / CN2020 / 112469), entitled "Electrode, Electrochemical Device and Electronic Device". Technical Field

[0002] This application relates to the field of electronic technology, and more particularly to electrodes, electrochemical devices, and electronic devices. Background Technology

[0003] Currently, to ensure the processing and safety performance of the electrodes, high-adhesion coatings can be applied to cover the entire active material layer or current collector. However, this results in a loss of volumetric energy density in the electrochemical device (e.g., lithium-ion battery). How to improve the electrical performance of the electrochemical device while maintaining its volumetric energy density remains a problem to be solved. Summary of the Invention

[0004] The embodiments of this application provide a high-adhesion coating in specific areas, which improves the electrical performance and safety performance of the electrochemical device while minimizing the impact on the volumetric energy density of the electrochemical device.

[0005] An embodiment of this application provides an electrode sheet, comprising: a current collector; a first coating disposed on the current collector, the first coating comprising an active material, and the first coating sequentially comprising a first edge portion, a middle portion, and a second edge portion in the width direction of the current collector; a second coating comprising a first portion and a second portion respectively disposed on the first edge portion and the second edge portion; wherein the surface of the first portion away from the first edge portion has a first adhesive force, the surface of the second portion away from the second edge portion has a second adhesive force, and the surface of the middle portion away from the current collector has a third adhesive force, wherein both the first adhesive force and the second adhesive force are greater than the third adhesive force.

[0006] In some embodiments, the first portion has a width d1, the second portion has a width d2, the first coating has a width D, and wherein 1% ≤ d1 / D ≤ 10%, 1% ≤ d2 / D ≤ 10%.

[0007] In some embodiments, the first adhesive force and the second adhesive force are both 2 to 10 times the third adhesive force; and / or the first adhesive force and the second adhesive force are both greater than 5 N / m.

[0008] In some embodiments, the thickness of the second coating is h, the thickness of the middle portion is H, 0.5 μm < h < 8 μm, 20 μm < H < 200 μm.

[0009] In some embodiments, the first coating includes a first adhesive, the content of which is 0.5% to 6%, and the first adhesive includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber or polyvinyl alcohol.

[0010] In some embodiments, the second coating includes a second adhesive, the content of which is 30% to 80%, and the second adhesive includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber or polyvinyl alcohol.

[0011] In some embodiments, in the length direction of the first coating, the first portion and / or the second portion are discontinuously coated, and the ratio of the total coating length of the first portion to the length of the first coating is greater than 80%, and the ratio of the total coating length of the second portion to the length of the first coating is greater than 80%.

[0012] In some embodiments, at least a portion of the current collector is etched.

[0013] In some embodiments, the regions corresponding to the current collector and the first edge portion and the second edge portion are etched, and the roughness of the regions corresponding to the current collector and the first edge portion and the second edge portion is 2 to 4 times that of the roughness of the regions corresponding to the current collector and the middle portion.

[0014] Another embodiment of this application provides an electrochemical device, including: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode; wherein the positive electrode and / or the negative electrode is any of the above-mentioned electrodes.

[0015] Embodiments of this application also provide an electronic device including the electrochemical device described above.

[0016] The embodiments of this application, by providing a coating with different adhesion strength on the edge region of the active material layer, such that the adhesion strength between the coating and the separator is greater than the adhesion strength between the active material layer and the separator, can reduce the impact of the slitting blade on the electrode during electrode slitting (e.g., the generation of burrs or debris). Furthermore, because the coating is provided on the edge region of the active material, the adhesion strength between the edge region of the electrode and the separator can be improved, thereby reducing the impact of electrode delamination on the electrode assembly at the electrode assembly level, and thus improving the electrical and safety performance of the electrochemical device. Simultaneously, since the coating is only provided on the edge region of the active material layer, the impact on the volumetric energy density of the electrochemical device can be minimized. Attached Figure Description

[0017] Figure 1 A front view of an electrode sheet according to an embodiment of this application is shown.

[0018] Figure 2 A top view of a first coating (continuous) and a current collector according to an embodiment of this application is shown.

[0019] Figure 3 A top view of a first coating (discontinuous) and a current collector according to another embodiment of this application is shown.

[0020] Figure 4 A front view of the electrode assembly of an electrochemical device according to an embodiment of this application is shown. Detailed Implementation

[0021] 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.

[0022] like Figure 1 The diagram shows a front view (cross-sectional view) of an electrode sheet according to an embodiment of this application. The electrode sheet may include a current collector 1 and a first coating 2 disposed on the current collector 1. In some embodiments, the first coating 2 includes an active material. In some embodiments, the first coating 2 sequentially includes a first edge portion 4, a middle portion 6, and a second edge portion 5 in the width direction of the current collector 1, wherein the middle portion 6 is located between the first edge portion 4 and the second edge portion 5. It should be understood that, although Figure 1 The first edge portion 4, the second edge portion 5, and the central region 6 are distinguished by dashed lines, but in reality, the boundary at the dashed lines may not actually exist. In some embodiments, the electrode further includes a second coating 3, which may include a first portion 7 and a second portion 8 respectively disposed on the first edge portion 4 and the second edge portion 5. In some embodiments, the material, width, and thickness of the first portion 7 and the second portion 8 may be the same or different.

[0023] In some embodiments, the first portion 7, located away from the first edge portion, may have a first adhesive force, i.e., the first portion 7 may have a first adhesive force with the separator; the surface of the second portion 8, located away from the second edge portion, may have a second adhesive force, i.e., the second portion 8 may have a second adhesive force with the separator; the surface of the middle portion 6, located away from the current collector, may have a third adhesive force, i.e., the middle portion 6 may have a third adhesive force with the separator, wherein both the first and second adhesive forces are greater than the third adhesive force. In embodiments of this application, by respectively providing the first portion 7 and the second portion 8 of the second coating 3 on the first edge portion 4 and the second edge portion 5 of the first coating 2, the influence of the cutting blade on the electrode sheet during electrode slitting (e.g., generating burrs or debris) can be reduced. Furthermore, since both the first and second adhesive forces are greater than the third adhesive force, the adhesion between the edge region of the electrode sheet and the separator can be improved, thereby reducing the impact of electrode sheet delamination on the electrode assembly at the electrode assembly level, and thus improving the electrical performance and safety performance of the electrochemical device. Simultaneously, since the second coating 3 is only provided on the edge portion of the first coating 2, the impact on the volumetric energy density of the electrochemical device can be minimized.

[0024] In some embodiments, the first portion 7 has a width d1, the second portion 8 has a width d2, and the first coating 2 has a width D, where 1% ≤ d1 / D ≤ 10% and 1% ≤ d2 / D ≤ 10%. If the width of the first portion 7 or the second portion 8 is too small, for example, less than 1% of the width of the first coating 2, the effect of the second coating 3 in improving the adhesion between the second coating 3 and the separator is limited. If the width of the first portion 7 or the second portion 8 is too large, for example, greater than 10% of the width of the first coating 2, it will adversely affect the volumetric energy density of the electrochemical device.

[0025] In some embodiments, the first adhesive force and the second adhesive force are both 2 to 10 times the third adhesive force. In some embodiments, both the first adhesive force and the second adhesive force are greater than 5 N / m. This ensures a strong adhesion between the second coating 3 and the release liner.

[0026] In some embodiments, the thickness of the second coating 3 is h, and the thickness of the middle portion of the first coating 2 is H, where 0.5 μm < h < 8 μm, and 20 μm < H < 200 μm. In some embodiments, the thickness H of the middle portion of the second coating can be equal to the sum of the thicknesses of the first edge portion 4 and the first portion 7, or it can be equal to the sum of the thicknesses of the second edge portion 5 and the second portion 8. If the thickness of the second coating 3 is too small, for example, less than 0.5 μm, a sufficiently strong adhesion between the second coating 3 and the separator cannot be ensured. If the thickness of the second coating is too large, it will adversely affect the volumetric energy density of the electrochemical device. If the thickness of the first coating 2 is too small, the amount of active material per unit area will be too small, affecting the volumetric energy density of the electrochemical device. If the thickness of the first coating 2 is too large, the lithium ion insertion and extraction migration path near the current collector of the first coating 2 will be too long, affecting the lithium ion insertion and extraction efficiency.

[0027] In some embodiments, the first coating 2 further includes a first adhesive. In some embodiments, the first adhesive includes at least one selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol. In some embodiments, the content of the first adhesive in the first coating 2 is 0.5% to 6%. If the content of the first adhesive is too low, it will not provide sufficient adhesion to the material of the first coating 2, and will also be detrimental to the adhesion between the first coating 2 and the current collector or between the first coating 2 and the separator. If the content of the first adhesive is too high, it will adversely affect the volumetric energy density of the electrochemical device.

[0028] In some embodiments, the second coating 3 includes a second adhesive. In some embodiments, the second adhesive includes at least one selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol. In some embodiments, the mass content of the second adhesive in the second coating 3 is 30% to 80%. If the mass content of the second adhesive is too small, sufficient adhesion between the second coating 2 and the release liner cannot be adequately ensured. If the mass content of the second adhesive is too large, the conductivity of the second coating 3 will be too low.

[0029] In some embodiments, the second coating 3 further includes a conductive agent. In some embodiments, the conductive agent in the second coating 3 may include at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, or carbon nanofibers. In some embodiments, the mass content of the conductive agent in the second coating 3 is 20% to 70%. If the mass content of the conductive agent in the second coating 3 is too low, it will adversely affect the conductivity of the second coating 3. If the mass content of the conductive agent in the second coating 3 is too high, it will result in too low a mass content of the second binder, affecting the adhesion performance of the second coating 3. In some embodiments, the second coating 3 further includes ceramic particles.

[0030] It should be understood that, although Figure 1 The diagram shows a first coating 2 and a second coating 3 formed on both sides of the current collector 1, but this is only an example, and the first coating 2 and the second coating 3 may also be formed only on one side of the current collector 1.

[0031] like Figure 2 The diagram shows a top view of a second (continuous) coating and a first coating according to an embodiment of this application. For simplicity, only the middle portion 6 of the first coating 2 and the first portion 7 and the second portion 8 of the second coating 3 are shown. Figure 2 The dashed lines indicate the slitting positions of the electrode sheet. By applying the second coating 3 to the edge portion of the first coating 2, the effects of stress during slitting and the generation of burrs in the current collector during slitting can be reduced. Additionally, the adhesion between the electrode sheet and the separator can be improved. In some embodiments, the first portion 7 and / or the second portion 8 may be continuously coated along the length of the first coating 2.

[0032] like Figure 3 As shown, in some embodiments, the first portion 7 and / or the second portion 8 can be discontinuously coated along the length of the first coating 2, and the ratio of the total coating length of the first portion 7 to the length of the first coating 2 is greater than 80%, and the ratio of the total coating length of the second portion 8 to the length of the first coating 2 is also greater than 80%. By employing a discontinuous coating method, the impact on the volumetric energy density of the electrochemical device is further reduced. Furthermore, if the coating length of the first portion 7 and / or the second portion 8 is too short, it will affect the full utilization of the adhesion properties of the second coating 3.

[0033] In some embodiments, at least a portion or all of the current collector 1 is etched. Etching the current collector 1 increases its roughness, thereby increasing the adhesion between the current collector 1 and the first coating 2. In some embodiments, the regions of the current collector 1 corresponding to the first edge portion 4 and the second edge portion 5 are etched, and the roughness of these regions is 2 to 4 times that of the region corresponding to the middle portion 6. Etching the first edge portion 4 and the second edge portion 5 further enhances the adhesion between the current collector 1 and the first coating 2, and also enhances the adhesion between the edge regions of the overall electrode and the separator. In some embodiments, etching is primarily performed using browning or blackening methods; however, other suitable etching methods can also be used. In some embodiments, the roughness of the etched region of the current collector 1 is 2 to 4 times that of the unetched region. In some embodiments, the roughness of the unetched region is less than 2 μm.

[0034] It should be understood that the electrode in this application can be either a positive electrode or a negative electrode. For example... Figure 4 As shown, embodiments of this application also provide an electrochemical device, which includes a separator 11, a positive electrode 12, and a negative electrode 13. The separator 11 is disposed between the positive electrode 12 and the negative electrode 13, wherein the positive electrode 12 and / or the negative electrode 13 are electrodes with the structure described above.

[0035] In some embodiments, the positive current collector of the positive electrode 12 can be aluminum (Al) foil, or other positive current collectors commonly used in the art can be used. In some embodiments, the thickness of the positive current collector can be 1 μm to 200 μm.

[0036] In some embodiments, when the electrode is a positive electrode 12, the active material of the first coating 2 may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide. In some embodiments, the first coating 2 further includes a conductive agent. In some embodiments, the conductive agent in the first coating 2 may include at least one of conductive carbon black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the first coating 2 may be 91–99:0.5–3:0.5–6. It should be understood that the above description is merely an example, and the positive electrode active material layer may use any other suitable material, thickness, and mass ratio.

[0037] In some embodiments, the negative current collector of the negative electrode 13 may be at least one of copper foil, nickel foil, or carbon-based current collector; of course, other negative current collectors commonly used in the art may also be used. In some embodiments, the thickness of the negative current collector may be 1 μm to 200 μm.

[0038] In some embodiments, when the electrode is a negative electrode 13, the active material of the first coating 2 may include at least one of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, silicon alloy, tin alloy, or pure silicon. In some embodiments, the first coating 2 may also include a conductive agent. The conductive agent in the first coating 2 may include at least one of conductive carbon black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. It should be understood that the materials disclosed above are merely exemplary, and the first coating 2, as the negative electrode active material layer, may use any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, conductive agent, and binder in the first coating 2 may be 91–99:0–3:1–6. It should be understood that the above description is merely an example, and any other suitable mass ratio may be used.

[0039] In some embodiments, the separator 11 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 20 μm.

[0040] 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.

[0041] In some embodiments of this application, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.

[0042] 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 chosen as the lithium salt because it provides high ionic conductivity and improves cycle characteristics.

[0043] The non-aqueous solvent may be selected from carbonate compounds, carboxylic acid ester compounds, ether compounds, other organic solvents, or combinations thereof.

[0044] The carbonate compound may be selected from chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.

[0045] The chain carbonate compound may be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. The cyclic carbonate compound may be selected from ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. The fluorinated carbonate compound may be selected from 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.

[0046] The carboxylic acid ester compound may be selected from methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, methyl formate, or combinations thereof.

[0047] The ether compound may be selected from dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0048] Other organic solvents may be selected from 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.

[0049] 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 an electrode assembly, then encapsulated in, for example, an aluminum-plastic film, and injected with electrolyte. The assembly is then formed and encapsulated to produce a lithium-ion battery. The prepared lithium-ion battery is then subjected to performance testing.

[0050] 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.

[0051] Embodiments of this application also provide electronic devices including the aforementioned electrochemical apparatus. The electronic devices in these embodiments are 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, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0052] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0053] Example 1

[0054] Preparation of the positive electrode sheet: Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 97.6:1.1:1.3 to form a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated onto the current collector to a thickness of 50 μm. After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0055] Preparation of the negative electrode sheet: The negative electrode active material, artificial graphite, and the binder, styrene-butadiene rubber, were dissolved in deionized water at a weight ratio of 98:2 to form a first coating slurry. A copper foil with a thickness of 10 μm and a width of 80 mm was used as the negative electrode current collector. The first coating slurry was coated onto the negative electrode current collector to a thickness of 60 μm, and then dried to obtain the first coating.

[0056] The first binder, polyvinylidene fluoride, and the first conductive agent, conductive carbon black, were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 60:40 to form a second coating slurry. The second coating slurry was then applied to the two edge portions of the first coating, with a coating width of 5 mm and a thickness of 2 μm on each edge portion. After drying, cold pressing, and slitting, the negative electrode sheet was obtained.

[0057] Preparation of the separator membrane: The separator membrane substrate is 8μm thick polyethylene (PE). A 2μm thick alumina ceramic layer is coated on each side of the separator membrane substrate. Finally, 2.5mg of polyvinylidene fluoride (PVDF) binder is coated on each side of the ceramic layer and then dried.

[0058] Electrolyte preparation: Under an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (ethylene carbonate (EC): dimethyl carbonate (DMC) = 40:60, weight ratio) were mixed at a weight ratio of 8:92 to form an electrolyte.

[0059] 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.

[0060] Other embodiments and comparative examples are based on the steps of Example 1 with parameter changes. In Comparative Example 1, a bottom coating is first applied to the negative electrode current collector. The thickness of the bottom coating is 2 μm, and the material of the bottom coating consists of polyvinylidene fluoride and conductive carbon black in a weight ratio of 60:40. The specific parameters changed are shown in the table below.

[0061] The test methods for each parameter of this application are described below.

[0062] Methods for testing volumetric energy density:

[0063] Place the lithium-ion battery in a 25°C constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge the battery at a constant current of 0.5C to a voltage of 4.4V, then charge it at a constant voltage of 4.4V to a current of 0.05C, and finally discharge it at 0.5C to a voltage of 3.0V. Record the discharge energy.

[0064] Volumetric energy density = Discharge energy / (Length * Width * Thickness of lithium-ion battery).

[0065] Cyclic expansion rate test:

[0066] The thickness of the lithium-ion battery plates after formation was measured. After the lithium-ion batteries were placed in a constant temperature chamber at 45℃±2℃ for 2 hours, they were charged at a 1C rate to 4.4V, and then charged at a constant voltage of 4.4V to 0.05C. Subsequently, they were discharged at a 1C rate to 3.0V, and this process was repeated as one cycle. The thickness of the lithium-ion battery plates was measured after 500 cycles. Four lithium-ion batteries were taken from each group, and the average value was calculated to determine the cycle expansion rate.

[0067] Cyclic expansion rate = (thickness of lithium-ion battery after 500 cycles / thickness of lithium-ion battery after formation - 1) × 100%.

[0068] Table 1 shows the parameters and evaluation results for the embodiments and comparative examples.

[0069] Table 1

[0070]

[0071]

[0072] Comparing Example 1 and Comparative Example 1, it can be seen that, compared to the lithium-ion battery with a bottom coating on the negative electrode sheet in Comparative Example 1, the volumetric energy density is increased by 1.2% in Example 1 by eliminating the bottom coating. Simultaneously, the application of a high-viscosity coating on the electrode sheet not only reduces the impact of the cutting blade on the electrode sheet edge thickness during slitting but also achieves good adhesion with the separator, suppressing the electrode sheet expansion process and reducing the cycle expansion rate by 1%. In Examples 2-4, slight control of the electrode sheet expansion rate and volumetric energy density can be achieved by adjusting the width of the applied high-viscosity coating. Furthermore, as the width of the second coating (i.e., the high-viscosity coating) increases, the increase in volumetric energy density tends to decrease.

[0073] By comparing Examples 5-7 and Comparative Example 1, it can be seen that for electrodes with active material coatings of different thicknesses, the energy density and electrode expansion rate can be improved by applying a high-viscosity coating on the active material layer. Furthermore, as the thickness of the first coating (i.e., the active material layer) increases, the volumetric energy density improvement rate tends to decrease, while the rate of decrease in cycle expansion rate tends to increase.

[0074] By comparing Examples 8, 9, 10 and Comparative Example 1, it was found that the thickness of the high-viscosity coating on the active material layer can be controlled, and improvements in energy density and electrode expansion rate can be achieved at different coating thicknesses. However, when the coating thickness is too thin, good adhesion between the electrode and the separator cannot be guaranteed, and the control effect on electrode expansion rate is slightly limited, but the effect on improving energy density is more significant, reaching 1.3%.

[0075] By comparing Examples 11-12 and Comparative Example 1, the adhesive strength was controlled by adjusting the binder content of the high-viscosity coating. The binder content had no effect on the improvement of volumetric energy density, and all could reach 1.2%. However, different binder contents would affect the expansion rate of the electrode.

[0076] By comparing Example 13 and Comparative Example 1, a high-viscosity coating was applied using an intermittent coating method. This method not only further improves the volumetric energy density of the battery by up to 1.4%, but also achieves a 1% improvement in the electrode expansion rate because it also has a limiting effect on the entire electrode.

[0077] 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 sheet, characterized in that, include: current collector; A first coating is disposed on the current collector, the first coating comprising an active material, and the first coating comprising, in sequence along the width direction of the current collector, a first edge portion, a middle portion and a second edge portion; The second coating includes a first portion and a second portion respectively disposed on the first edge portion and the second edge portion; Wherein, the surface of the first portion away from the first edge portion has a first adhesive force, the surface of the second portion away from the second edge portion has a second adhesive force, and the surface of the middle portion away from the current collector has a third adhesive force. The first adhesive force and the second adhesive force are both greater than the third adhesive force. The first coating includes a first adhesive with a mass content of 0.5% to 6%. The second coating includes a second adhesive with a mass content of 30% to 80%.

2. The electrode according to claim 1, wherein, The first portion has a width d1, the second portion has a width d2, the first coating has a width D, and wherein 1% ≤ d1 / D ≤ 10%, 1% ≤ d2 / D ≤ 10%.

3. The electrode according to claim 1, wherein, The first adhesive force and the second adhesive force are both 2 to 10 times the third adhesive force; and / or the first adhesive force and the second adhesive force are both greater than 5 N / m.

4. The electrode according to claim 1, wherein, The thickness of the second coating is h, and the thickness of the middle portion is H, where 0.5μm < h < 8μm and 20μm < H < 200μm.

5. The electrode according to claim 1, wherein, The first adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol; the second adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefins, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol.

6. The electrode according to claim 1, wherein, Along the length of the first coating, the first portion and / or the second portion are discontinuous coatings, and the ratio of the total coating length of the first portion to the length of the first coating is greater than 80%, and the ratio of the total coating length of the second portion to the length of the first coating is greater than 80%.

7. The electrode according to claim 1, wherein, At least a portion of the current collector is etched.

8. The electrode according to claim 7, wherein, The area corresponding to the current collector and the first edge portion and the second edge portion is etched, and the roughness of the area corresponding to the current collector and the first edge portion and the second edge portion is 2 to 4 times that of the roughness of the area corresponding to the current collector and the middle portion.

9. An electrochemical device, characterized in that, include: Positive electrode sheet; Negative electrode sheet; as well as A separator is disposed between the positive electrode and the negative electrode; Wherein, the positive electrode and / or the negative electrode are electrodes according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device according to claim 9.

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