A negative electrode, an electrochemical device, and an electronic device.

Abstract

A negative electrode sheet includes a current collector and a negative electrode active material layer, the negative electrode active material layer including a first region and a second region, wherein the porosity of the first region is less than that of the second region, and the ratio of the active material particle Dv50 of the first region to the active material particle Dv50 of the second region is 0.3 to 0.9; an electrochemical device includes a negative electrode sheet.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a negative electrode, an electrochemical device, and an electronic device. Background Technology

[0002] The market continues to have a strong demand for improved lithium battery energy density; however, conventional methods for increasing energy density each have their own problems. One method is to increase the coating weight of the active material on the electrode, but this leads to deterioration of kinetics, especially severe concentration polarization in the negative electrode material, resulting in increased temperature at high charge / discharge rates and low-temperature lithium plating. Another method is to increase the compaction density, but this also leads to deterioration of kinetics, and excessively high compaction density can cause insufficient liquid retention, easily leading to cycle capacity decay. Summary of the Invention

[0003] In view of the problems existing in the prior art, the purpose of this application is to provide a negative electrode, an electrochemical device and an electronic device, which can not only improve the energy density of the electrochemical device, but also enable the electrochemical device to maintain good cycle performance.

[0004] In a first aspect, this application provides a negative electrode sheet, which includes a current collector and a negative electrode active material layer. The negative electrode active material layer includes a first region and a second region, wherein the porosity of the first region is less than that of the second region, and the ratio of active material particles Dv50 in the first region to active material particles Dv50 in the second region is 0.3 to 0.9.

[0005] In this application, the negative electrode includes a first region and a second region. The first region includes at least one dense region composed of small particles, and the second region includes at least one non-dense region composed of large particles. The first region not only improves the energy density of the electrochemical device, but also has strong adhesion to the electrode, making it less prone to demolding, thereby effectively improving the stability of the electrode and preventing deformation. The second region has larger particles and higher porosity, which is beneficial for electrolyte storage and provides a rapid diffusion channel for the electrolyte within the electrode, facilitating rapid electrolyte diffusion and retention. Working in conjunction with the surrounding dense region, it reduces the electrolyte transport path in the first region and improves kinetics.

[0006] According to some embodiments of this application, the Dv50 of the active material particles in the first region is 5 μm to 20 μm. According to some embodiments of this application, the Dv50 of the active material particles in the second region is 20 μm to 50 μm. The Dv50 of the active material particles in the first and second regions meets the above ranges. This allows the negative electrode active material layer to maintain appropriate electrode reactivity while ensuring its overall wettability in the electrolyte, reducing side reactions caused by unreasonable particle size distribution, lowering production difficulty, and improving the yield rate in the electrode production process.

[0007] According to some embodiments of this application, the porosity of the first region is 15% to 30%. According to some embodiments of this application, the porosity of the second region is 30% to 45%. The porosity of the first region and the porosity of the second region satisfy the above ranges, and the negative electrode active material layer can reduce the concentration polarization of the electrochemical device, reduce the internal resistance, and significantly improve the energy density of the electrode while ensuring electrolyte wettability and diffusion ability.

[0008] According to some embodiments of this application, the thickness of the negative electrode active material layer is 50 μm to 300 μm. A thickness within this range allows for optimization of the energy density of the electrochemical device while further improving the electrolyte wettability and diffusion capacity of the electrode in the thickness direction. According to some embodiments of this application, the thickness of the negative electrode active material layer is 100 μm to 250 μm.

[0009] According to some embodiments of this application, the active material particles in the first region and / or the second region are arranged in an array or not in an array.

[0010] According to some embodiments of this application, the active material particles in the first region and / or the second region are arranged in an array, and the aspect ratio of the active material particles is 1.1 to 5. The active material particles in both the first and second regions are arranged in an array, which facilitates rapid lithium-ion insertion and extraction.

[0011] According to some embodiments of this application, the angle between the active material particles in the first region and / or the second region and the current collector along the long axis is 45° to 135°. The active material particles are arranged with the current collector within this angle range, which shortens the diffusion path of lithium ions and improves kinetics.

[0012] According to some embodiments of this application, along the electrode thickness direction, based on the projected area of ​​the active material layer, the projected area of ​​the second region accounts for 5% to 50%, which can improve the electrolyte diffusion efficiency and is beneficial to improving kinetics.

[0013] According to some embodiments of this application, the second region is distributed in a strip shape or an island shape.

[0014] According to some embodiments of this application, the second region is disposed through the width of the negative electrode sheet.

[0015] According to some embodiments of this application, the adhesion strength of the negative electrode sheet is 5 N / m to 15 N / m. The active material particles in the second region have a smaller particle size and a larger specific surface area, resulting in a stronger interaction force with the binder. The larger the contact area between the second region and the current collector, the stronger the adhesion, and the greater the self-adhesion. Strong adhesion can prevent the electrode sheet from demolding during processing, use of electrode assemblies, or misuse.

[0016] According to some embodiments of this application, the ratio of the width of the first region to the width of the second region is 1 to 20, and the second region is distributed in a strip shape or an island shape. According to some embodiments of this application, the ratio of the width of the first region to the width of the second region is 1 to 10. In this application, the width of the first region and the width of the second region refer to the width of the first region and the width of the second region on the surface of the negative electrode sheet.

[0017] According to some embodiments of this application, the width of the first region is 1 mm to 50 mm. According to some embodiments of this application, the second region is distributed in an island-like pattern, and each island is square or rectangular in shape.

[0018] According to some embodiments of this application, the ratio of the thickness of the first region to the thickness of the second region is 1 to 2. A ratio within this range can improve electrolyte diffusion efficiency and enhance kinetics.

[0019] According to some embodiments of this application, a primer layer is further provided between the current collector and the negative electrode active material layer. The primer layer can increase the adhesion between the negative electrode active material and the current collector, effectively reducing demolding, deformation, and other phenomena caused by the differentiated design of different areas of the negative electrode sheet.

[0020] According to some embodiments of this application, the base coating includes a conductive material, a binder, and a dispersant.

[0021] According to some embodiments of this application, the conductive material in the base coating includes at least one of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes, and graphene.

[0022] According to some embodiments of this application, the adhesive includes styrene-butadiene rubber.

[0023] According to some embodiments of this application, the dispersant includes sodium carboxymethyl cellulose.

[0024] According to some embodiments of this application, the active material particles in the first and / or second regions are arranged in a non-array configuration, and the thickness of the base coating is 0.5 μm to 1.5 μm. According to other embodiments of this application, the active material particles in the first and / or second regions are arranged in an array configuration, and the thickness of the base coating is 1.5 μm to 3.0 μm. This is because the adhesion between the active material particles and the current collector deteriorates after the active material particles are arranged in an array, and increasing the thickness of the base coating can improve adhesion and prevent demolding.

[0025] In a second aspect, this application provides an electrochemical device comprising a negative electrode as described in the first aspect of this application.

[0026] In a third aspect, this application provides an electronic device, including the electrochemical device as described in the second aspect of this application.

[0027] The negative electrode provided in this application can not only improve the energy density of the electrochemical device, but also enable the electrochemical device to maintain good cycle performance. Attached Figure Description

[0028] Figure 1 This is a cross-sectional schematic diagram along the length of a negative electrode sheet according to some embodiments of this application, wherein 1 is a copper current collector, 2 is a base coating, 3 is a small particle dense region, and 4 is a large particle non-dense region.

[0029] Figure 2 This is a cross-sectional schematic diagram along the length of the negative electrode sheet according to some other embodiments of this application, wherein 1 is a copper current collector, 2 is a base coating, 3 is a small particle dense region, and 4 is a large particle non-dense region.

[0030] Figure 3 This is a top view schematic diagram of a negative electrode sheet according to some embodiments of this application, wherein the second region is a strip distribution.

[0031] Figure 4 This is a top view schematic diagram of a negative electrode sheet according to some other embodiments of this application, wherein the second region is a strip distribution.

[0032] Figure 5 This is a top view schematic diagram of a negative electrode sheet according to some other embodiments of this application, wherein the second region is distributed in an island shape. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are only for illustrating the present application.

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application. For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower limit or upper limit and be combined with any other point or single value or with other lower limits or upper limits to form a range not explicitly stated.

[0035] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0036] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0037] Negative electrode sheet

[0038] In a first aspect, this application provides a negative electrode sheet, which includes a current collector and a negative electrode active material layer. The negative electrode active material layer includes a first region and a second region, wherein the porosity of the first region is less than that of the second region, and the ratio of active material particles Dv50 in the first region to active material particles Dv50 in the second region is 0.3 to 0.9.

[0039] In this application, the negative electrode has two regions: a first region composed of small particles and a second region composed of large particles. The first region mainly contributes to the energy density of the electrochemical device; the second region has larger particles and higher porosity, which is beneficial for storing electrolyte and providing a fast channel for electrolyte diffusion into the electrode interior, facilitating rapid electrolyte diffusion and retention. At the same time, it provides electrolyte supply to the surrounding first region, reduces the electrolyte transport path in the first region, and improves kinetics.

[0040] According to some embodiments of this application, the Dv50 of the active material particles in the first region is from 5 μm to 20 μm. In some embodiments, the Dv50 of the active material particles in the first region is a range of 5 μm, 8 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any combination thereof. According to some embodiments of this application, the Dv50 of the active material particles in the second region is from 20 μm to 50 μm. In some embodiments, the Dv50 of the active material particles in the second region is a range of 20 μm, 25 μm, 28 μm, 32 μm, 35 μm, 42 μm, 45 μm, 50 μm, or any combination thereof. The Dv50 of the active material particles in the first and second regions satisfies the above ranges, enabling the negative electrode active material layer to maintain appropriate electrode reactivity while ensuring its overall wettability in the electrolyte, reducing side reactions caused by unreasonable particle size distribution, lowering production difficulty, and improving the yield rate in the electrode production process.

[0041] According to some embodiments of this application, the porosity of the first region is 15% to 30%. In some embodiments, the porosity of the first region is a range of 15%, 18%, 20%, 25%, 28%, 30%, or any combination thereof. According to some embodiments of this application, the porosity of the second region is 30% to 45%. In some embodiments, the porosity of the second region is a range of 30%, 35%, 40%, 45%, or any combination thereof. When the porosity of the first region and the porosity of the second region satisfy the above ranges, the negative electrode active material layer can significantly improve the energy density of the electrode while ensuring the electrolyte wettability and diffusion capacity of the first region.

[0042] According to some embodiments of this application, the thickness of the negative electrode active material layer is from 50 μm to 300 μm. In some embodiments, the thickness of the negative electrode active material layer is within the range of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, or any combination thereof. A thickness of the negative electrode active material layer within the above range can significantly improve the energy density of the electrode while ensuring electrolyte wettability and diffusion capacity. According to some embodiments of this application, the thickness of the negative electrode active material layer is from 100 μm to 250 μm.

[0043] According to some embodiments of this application, the active material particles in the first and / or second regions are arranged in an array or not. According to some embodiments of this application, the active material particles in the first and / or second regions are arranged in an array, and the aspect ratio of the active material particles is 1.1 to 5. The active material particles in both the first and second regions are arranged in an array, which facilitates rapid lithium-ion insertion and extraction. According to some embodiments of this application, the aspect ratio of the active material particles is 1.5 to 5. According to some embodiments of this application, the aspect ratio of the active material particles is 2 to 5.

[0044] According to some embodiments of this application, the angle between the active material particles in the first region and / or the second region and the current collector along the long axis is 45° to 135°. In some embodiments, the angle between the active material particles in the first region and the current collector along the long axis is 45° to 135°, for example, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135° or any combination thereof. In some embodiments, the angle between the active material particles in the second region and the current collector along the long axis is 45° to 135°, for example, a range of 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, or any combination thereof. The active material particles are arranged with the current collector within this angular range, which shortens the diffusion path of lithium ions and improves kinetics.

[0045] According to some embodiments of this application, along the electrode thickness direction, based on the projected area of ​​the active material layer, the projected area of ​​the second region accounts for 5% to 50%, which can improve electrolyte diffusion efficiency and is beneficial for enhancing kinetics. In some embodiments, along the electrode thickness direction, based on the projected area of ​​the active material layer, the projected area of ​​the second region accounts for 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination thereof. In some embodiments, along the electrode thickness direction, based on the projected area of ​​the active material layer, the projected area of ​​the second region accounts for 15% to 30%.

[0046] According to some embodiments of this application, the second region is distributed in a strip shape or an island shape.

[0047] According to some embodiments of this application, the second region is disposed through the width of the negative electrode sheet.

[0048] According to some embodiments of this application, the bonding force of the negative electrode sheet is from 5 N / m to 15 N / m. In some embodiments, the bonding force of the negative electrode sheet is within the range of 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, or any combination thereof. The active material particles in the second region have a smaller particle size and a larger specific surface area, resulting in a stronger interaction force with the binder. The larger the contact area between the second region and the current collector, the stronger the bonding force, and the greater the self-bonding force. Strong bonding force can prevent the electrode sheet from demolding during processing, use of the electrode assembly, or misuse.

[0049] According to some embodiments of this application, the ratio of the width of the first region to the width of the second region is 1 to 20, and the second region is a strip-shaped distribution or an island-shaped distribution. In some embodiments, the ratio of the width of the first region to the width of the second region is a range of 1, 3, 5, 7, 10, 12, 15, 18, 20, or any combination thereof. According to some embodiments of this application, the ratio of the width of the first region to the width of the second region is 1 to 10. In this application, the width of the first region and the width of the second region refer to the width of the first region and the width of the second region on the surface of the negative electrode sheet.

[0050] According to some embodiments of this application, the width of the first region is from 1 mm to 50 mm, for example, 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm or any combination thereof.

[0051] According to some embodiments of this application, the second region is distributed in an island-like pattern, and each island is square or rectangular in shape.

[0052] According to some embodiments of this application, the ratio of the thickness of the first region to the thickness of the second region is 1 to 2. In some embodiments, the ratio of the thickness of the first region to the thickness of the second region is a range of 1, 1.2, 1.4, 1.6, 1.8, 2, or any combination thereof. A ratio of the thickness of the first region to the thickness of the second region within this range can improve the electrolyte diffusion efficiency and is beneficial for enhancing kinetics.

[0053] According to some embodiments of this application, a primer layer is further provided between the current collector and the negative electrode active material layer. The primer layer can increase the adhesion between the negative electrode active material and the current collector, effectively reducing demolding, deformation, and other phenomena caused by the differentiated design of different areas of the negative electrode sheet.

[0054] According to some embodiments of this application, the conductive material in the base coating includes at least one of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes, and graphene.

[0055] According to some embodiments of this application, the adhesive includes styrene-butadiene rubber.

[0056] According to some embodiments of this application, the dispersant includes sodium carboxymethyl cellulose.

[0057] According to some embodiments of this application, the active material particles in the first and / or second regions are arranged in a non-array configuration, and the thickness of the base coating is 0.5 μm to 1.5 μm. According to other embodiments of this application, the active material particles in the first and / or second regions are arranged in an array configuration, and the thickness of the base coating is 1.5 μm to 3.0 μm. This is because the adhesion between the active material particles and the current collector deteriorates after the active material particles are arranged in an array, and increasing the thickness of the base coating can improve adhesion and prevent demolding.

[0058] According to some embodiments of this application, the active material in the negative electrode active material layer is graphite. In this application, the negative electrode also includes a current collector, which may include: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal according to some embodiments of this application, or any combination thereof.

[0059] The negative electrode active material layer may further include a conductive agent and / or a binder. In some embodiments, the conductive agent includes at least one selected from conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, or graphene. In some embodiments, the conductive agent accounts for 0.5% to 10% of the active material layer by mass. In some embodiments, the binder includes at least one selected from polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene-butadiene rubber. In some embodiments, the binder accounts for 0.5% to 10% of the active material layer by mass.

[0060] Electrochemical device

[0061] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all types of primary and secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries. In some embodiments, the electrochemical device of this application includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0062] 1. Negative electrode

[0063] The negative electrode in the electrochemical device of this application includes the negative electrode sheet of the first aspect.

[0064] 2. Positive electrode

[0065] The materials, composition, and manufacturing methods of the positive electrode that can be used in the embodiments of this application include any techniques disclosed in the prior art.

[0066] According to some embodiments of this application, the positive electrode includes a current collector and a layer of positive electrode active material located on the current collector. According to some embodiments of this application, the positive electrode active material includes, but is not limited to: lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide, lithium iron phosphate (LiFePO4), or lithium manganese oxide (LiMn2O4).

[0067] According to some embodiments of this application, the positive electrode active material layer further includes an adhesive and optionally a conductive material. The adhesive improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector. In some embodiments, the adhesive includes: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0068] According to some embodiments of this application, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanotubes, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0069] According to some embodiments of this application, the current collector may include, but is not limited to, aluminum.

[0070] 3. Electrolyte

[0071] The electrolyte that can be used in the embodiments of this application can be an electrolyte known in the prior art.

[0072] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and additives. The organic solvent of the electrolyte according to this application may be any organic solvent known in the prior art that can be used as a solvent for an electrolyte. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art. The additives of the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives.

[0073] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0074] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium difluorophosphate LiPO2F2, lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (abbreviated as LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (abbreviated as LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (abbreviated as LiDFOB).

[0075] In some embodiments, the concentration of lithium salt in the electrolyte is 0.5 mol / L to 3 mol / L, 0.5 mol / L to 2 mol / L, or 0.8 mol / L to 1.5 mol / L.

[0076] 4. Separating membrane

[0077] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0078] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0079] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0080] The inorganic layer comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0081] The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0082] Electronic devices

[0083] This application further provides an electronic device that includes the electrochemical device of the second aspect of this application.

[0084] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are not limited to, laptops, pen input 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, drones, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0085] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0086] Examples and Comparative Examples

[0087] Test methods

[0088] DC internal resistance test: Charge the lithium-ion battery to 50% SOC at 0.2C, let it stand for 30 minutes, then discharge it at 0.1C for 1 second, and then discharge it at 1C for 1 second. Calculate the ratio of the voltage difference to the current difference at the two discharge points to obtain the DC internal resistance.

[0089] Rate discharge test: Charge at 0.2C constant voltage to 4.4V, then charge at 0.02C constant voltage, let stand for 30 minutes, and then discharge at 0.2C to 3.0V to obtain the actual capacity of the lithium-ion battery. Then charge fully in the same way, let stand for 30 minutes, and then discharge at 3C to 3.0V to obtain the capacity of the lithium-ion battery. Compare with the actual capacity and calculate the capacity retention rate.

[0090] Electrode adhesion force measurement method

[0091] Cut the electrode sheet into rectangular pieces measuring 20mm × 10cm. Adhere these pieces to a clean steel plate with a width of 20mm using 20mm wide double-sided tape. Manually peel off 20mm of the electrode sheet. Then, use a tensile testing machine to fix the steel plate and the peeled portion of the electrode sheet, ensuring the peeled surface is aligned with the machine's force line. Test the peel force at 180°. The tensile testing machine's stretching speed is 50mm / min. Take the average value of the stable segment of the obtained peel force curve as the peel force F0. Therefore, the adhesive force of the tested negative electrode sheet is: F = F0 / 0.02 = 50F0.

[0092] Example 1-1

[0093] Preparation of the positive electrode: 12μm aluminum foil is used as the current collector of the positive electrode. The positive electrode active material lithium cobalt oxide, conductive agent conductive carbon black and polyvinylidene fluoride are mixed in a weight ratio of 97.5:1.5:1.0. The powder is sprayed onto the aluminum current collector by electrostatic spraying. After cold pressing and cutting, the positive electrode sheet with the required thickness and size is obtained.

[0094] Base coating: Conductive carbon and PVDF are mixed in water at a ratio of 97:3 and applied to a 6μm Cu current collector by transfer coating. The thickness of the base coating is 1μm.

[0095] Preparation of the non-array negative electrode: Graphite with a Dv50 of 15 μm, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder were mixed at a weight ratio of 97.7:1.3:1 to obtain a first powder. This first powder was then electrostatically sprayed onto a copper current collector with a thickness of 6 μm to prepare the first region. Next, graphite with a Dv50 of 30 μm, sodium carboxymethyl cellulose (CMC), and SBR binder were mixed at a weight ratio of 97.7:1.3:1 to obtain a second powder. This second powder was then electrostatically sprayed onto the corresponding second region of the copper current collector. Finally, the negative electrode sheet was obtained through cold pressing and cutting.

[0096] 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, a 2.5mg / cm² alumina ceramic layer is coated on each side of the ceramic layer. 2 The binder, polyvinylidene fluoride (PVDF), is dried.

[0097] Preparation of electrolyte: Under an environment with a water content of less than 10 ppm, LiPF6 was added to a non-aqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) and dimethyl carbonate (DMC) = 1:1:1:1, by weight), with a LiPF6 concentration of 1 mol / L. The mixture was stirred evenly to obtain the electrolyte.

[0098] 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.

[0099] Examples 1-1 to 1-11, Comparative Examples 1-3 and 1-4 all employ a stripe morphology in the width direction of the electrode sheet (e.g. Figure 3(As shown), the differences are shown in Table 1. Comparative Example 1-1 uses only graphite with a Dv50 of 15 μm, that is, it only has the first region. Comparative Example 1-2 uses a 5:1 mixture of graphite with a Dv50 of 155 μm and a Dv50 of 305 μm, that is, it does not have the first region and the second region.

[0100] As can be seen from Examples 1-1 to 1-11, Comparative Examples 1-3 and 1-4 in Table 1, the appropriate distribution of the first and second regions in the negative electrode active material layer, specifically the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions within the scope of this application, significantly reduces the DC internal resistance of the lithium-ion battery, thereby achieving a high capacity retention rate under high-rate discharge conditions. Comparative Examples 1-1 and 1-2 do not have the first and second regions of this application. Comparative Example 1-1 only contains small-particle graphite, while the mixing of the two types of graphite particles in Comparative Example 1-2 results in the small particles filling the gaps between large particles, lengthening or obstructing the ion diffusion path, leading to an increase in the DC internal resistance of the lithium-ion battery and making it impossible to achieve a high capacity retention rate under high-rate discharge conditions.

[0101] Examples 2-1 to 2-8 all employ a stripe morphology along the length of the electrode (e.g., Figure 4 As shown in Table 2 below.

[0102] As can be seen from the examples in Table 2, for the stripe morphology along the length of the electrode, the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions are all beneficial to improving the electrolyte diffusion efficiency and significantly reducing the DC internal resistance of the lithium-ion battery. This results in a higher capacity retention rate under high-rate discharge conditions, which is beneficial to improving the kinetic performance of the electrochemical device.

[0103] Examples 3-1 to 3-7 all employ an island-like distribution morphology (e.g. Figure 5 As shown in Table 3 below.

[0104] As can be seen from the examples in Table 3, for island-shaped distribution morphology, the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions are all beneficial to improving electrolyte diffusion efficiency within the scope of this application, significantly reducing the DC internal resistance of the lithium-ion battery, thereby achieving a higher capacity retention rate under high-rate discharge conditions, which is beneficial to improving the kinetic performance of the electrochemical device.

[0105] Furthermore, in the embodiments listed in Tables 1 to 3, the active material particles in the first and second regions are not arranged in an array. A comparison of Examples 1-1 to 1-8, 2-1 to 2-8, and 3-1 to 3-8 reveals that the second region, which extends through the electrode width, exhibits better DC internal resistance and discharge capacity retention than when the second region extends through the length or is arranged in an island configuration. This is likely because when the electrode assembly is wound along its length, the electrolyte can wet both ends of the wound electrode assembly. The second region extending through the electrode width facilitates regional diffusion of the electrolyte, thereby improving the DC internal resistance of the electrochemical device and maintaining a better capacity retention rate at higher discharge rates. For island-shaped distributions, the proportion of the second region is smaller, resulting in a higher DC internal resistance and a lower 3C discharge rate capacity retention rate. However, increasing the proportion of the first region can improve the energy density.

[0106] [Table 1]

[0107]

[0108]

[0109]

[0110] [Table 2]

[0111]

[0112]

[0113] [Table 3]

[0114]

[0115]

[0116] Example 4-1

[0117] The preparation methods for the positive electrode sheet, separator, electrolyte, and lithium-ion battery are the same as in Example 1;

[0118] Base coating: Conductive carbon and PVDF are mixed in water at a ratio of 97:3 and applied to a 6μm Cu current collector by transfer coating. The thickness of the base coating is 2.5μm.

[0119] Preparation of the array negative electrode: Small-particle graphite, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber binder are dissolved in deionized water at a weight ratio of 97.7:1.3:1 to form a small-particle negative electrode slurry with a solid content of 70%. The preparation of the large-particle negative electrode slurry is the same as that of the small particles. Using 3D printing technology, the small-particle negative electrode slurry is extruded perpendicularly to the current collector onto a 6μm Cu current collector. At the same time, a thermal light source is used to evaporate the water and solidify the printed slurry in a short time to form the desired morphology. Then, the large-particle slurry is printed into the corresponding positions using 3D printing. After cold pressing and cutting, the array negative electrode sheet is obtained. The aspect ratio of the active material particles is 2 to 5.

[0120] Examples 4-1 to 4-8, Comparative Examples 4-3 and 4-4 all employ a stripe morphology along the electrode width, with specific differences shown in Table 4 below. Comparative Example 4-1 uses only graphite with a Dv50 of 15 μm, i.e., it only has the first region. Comparative Example 4-2 uses a 5:1 mixture of graphite with a Dv50 of 155 μm and a Dv50 of 305 μm, i.e., it does not have the first and second regions.

[0121] As can be seen from the examples and comparative examples in Table 4, the appropriate distribution of the first and second regions in the negative electrode active material layer, specifically the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions within the scope of this application, significantly reduces the DC internal resistance of the lithium-ion battery, thereby achieving a higher capacity retention rate under high-rate discharge conditions.

[0122] By comparing the embodiments in Tables 1 and 4, for example, by comparing Examples 1-7 with Example 4-1 or by comparing Examples 1-8 with Example 4-5, it can be seen that: because the negative electrode is arranged in an array, the kinetic performance of the electrochemical device can be further improved. Therefore, the thickness of the electrode can be further increased. The thickness of the array-arranged graphite is 120 μm, which can achieve the kinetic level of the non-array-arranged graphite of 100 μm.

[0123] Examples 5-1 to 5-7 all employ stripe morphology along the length of the electrode sheet, as detailed in Table 5 below.

[0124] As can be seen from the examples in Table 5, for the stripe morphology along the length of the electrode, the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions are all beneficial to improving the electrolyte diffusion efficiency and significantly reducing the DC internal resistance of the lithium-ion battery. This results in a higher capacity retention rate under high-rate discharge conditions, which is beneficial to improving the kinetic performance of the electrochemical device.

[0125] By comparing the embodiments in Tables 2 and 5, for example by comparing Examples 2-7 with Example 5-1 or by comparing Examples 2-8 with Example 5-5, it can be seen that the kinetic performance of the electrochemical device can be further improved due to the array arrangement of the negative electrode.

[0126] Examples 6-1 to 6-7 all adopt an island-shaped morphology, as detailed in Table 6 below.

[0127] As can be seen from the examples in Table 6, for island-shaped morphology, the thickness ratio, width ratio, area ratio, particle size, and porosity of the first and second regions are all beneficial to improving electrolyte diffusion efficiency and significantly reducing the DC internal resistance of lithium-ion batteries, thereby achieving a higher capacity retention rate under high-rate discharge conditions, which is beneficial to improving the kinetic performance of electrochemical devices.

[0128] By comparing the embodiments in Tables 3 and 6, for example, by comparing Examples 3-7 with Example 6-1, it can be seen that the kinetic performance of the electrochemical device can be further improved due to the array arrangement of the negative electrode.

[0129] Furthermore, as can be seen from Tables 4 to 6, the performance characteristics of the strip-shaped and island-shaped array arrangements are the same as those of the non-array arrangement. That is, the second region, which is set through the width of the electrode, has better DC internal resistance and discharge capacity retention than the second region, which is set through the length or island-shaped.

[0130] [Table 4]

[0131]

[0132]

[0133]

[0134] [Table 5]

[0135]

[0136]

[0137] [Table 6]

[0138]

[0139]

[0140] Electrochemical testing:

[0141] The discharge specific capacity and capacity retention of the materials from Examples 1-3 and Comparative Example 1 were measured after cycling at 0.5C for 100 cycles, at 3C for 100 cycles, and at 1C for 500 cycles, respectively. The specific values ​​are shown in Table 1.

[0142] [Table 1]

[0143]

[0144] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A negative electrode sheet, comprising a current collector and a negative electrode active material layer, the negative electrode active material layer comprising a first region and a second region, wherein the porosity of the first region is less than that of the second region, the ratio of the active material particle Dv50 of the first region to the active material particle Dv50 of the second region is 0.3 to 0.9; the ratio of the thickness of the first region to the thickness of the second region is 1 to 2; the second region is disposed through the width direction of the negative electrode sheet, the ratio of the width of the first region to the width of the second region is 1 to 5, and the width of the first region is 1 mm to 5 mm.

2. The negative electrode sheet according to claim 1, wherein, At least one of the following conditions must be met: (a) The Dv50 of the active material particles in the first region is 5 μm to 20 μm. (b) The Dv50 of the active material particles in the second region is 20 μm to 50 μm. (c) The porosity of the first region is 15% to 30%. (d) The porosity of the second region is 30% to 45%.

3. The negative electrode sheet according to claim 1, wherein, The active material particles in the first region and / or the second region are arranged in an array, and the aspect ratio of the active material particles is 1.1 to 5.

4. The negative electrode sheet according to any one of claims 1-3, wherein, The angle between the active material particles in the first region and / or the second region and the current collector along the long axis is 45° to 135°.

5. The negative electrode sheet according to any one of claims 1-3, wherein, Along the thickness direction of the electrode, based on the projected area of ​​the active material layer, the projected area of ​​the second region accounts for 5% to 50%.

6. The negative electrode sheet according to any one of claims 1-3, wherein, At least one of the following conditions must be met: (e) The second region is a strip-shaped or island-shaped distribution. (g) The bonding force of the negative electrode sheet is 5 N / m to 15 N / m.

7. The negative electrode sheet according to any one of claims 1-3, wherein, An undercoating layer with a thickness of 0.5 μm to 3.0 μm is also provided between the current collector and the negative electrode active material layer.

8. An electrochemical device comprising a negative electrode sheet according to any one of claims 1-7.

9. An electronic device comprising the electrochemical device of claim 8.

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