WO2023184246A1

WO2023184246A1 - Negative electrode sheet, electrochemical apparatus, and electronic apparatus

Info

Publication number: WO2023184246A1
Application number: PCT/CN2022/084118
Authority: WO
Inventors: 李铎
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2023-10-05
Also published as: CN116097465A

Abstract

A negative electrode sheet, comprising a current collector and a negative electrode active material layer. The negative electrode active material layer comprises a first region and a second region, the porosity of the first region being lower than that of the second region, and the ratio of active material particles Dv50 of the first region to active material particles Dv50 of the second region being 0.3-0.9. An electrochemical apparatus, comprising a negative electrode sheet.

Description

Negative electrode plate, electrochemical device and electronic device

Technical field

The present application relates to the field of energy storage, and specifically relates to a negative electrode plate, an electrochemical device and an electronic device.

Background technique

The market still maintains a strong demand for increasing the energy density of lithium batteries. However, conventional means of increasing energy density have their own problems. One way to increase the energy density is to increase the coating weight of the active material of the pole piece. However, this will cause deterioration of the kinetics. In particular, the negative electrode material will have severe concentration polarization, resulting in high temperature at high charge and discharge rates. Increase, low temperature lithium precipitation and other issues. Another way to increase energy density is to increase compaction density, but this will also lead to deterioration of dynamics, and excessive compaction density will result in insufficient liquid retention and prone to circulation capacity attenuation.

Contents of the invention

In view of the problems existing in the prior art, the purpose of this application is to provide a negative electrode plate, an electrochemical device and an electronic device. The negative electrode plate can not only increase the energy density of the electrochemical device, but also keep the electrochemical device in good condition. cycle performance.

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

In this application, the negative electrode plate includes a first region and a second region. The first region includes at least one dense region composed of small particles, and the above-mentioned second region includes at least one non-dense region composed of large particles. The first area can not only increase the energy density of the electrochemical device, but also has strong adhesion to the pole piece and is difficult to demould, thereby effectively improving the stability of the pole piece and avoiding pole piece deformation. The particle size of the second area is relatively large and the porosity is large, which is conducive to the storage of electrolyte, and provides a rapid diffusion channel for the electrolyte inside the pole piece, which is conducive to the rapid diffusion and retention of electrolyte, and works in conjunction with the surrounding dense areas , reducing the electrolyte transport path in the first area and improving dynamics.

According to some embodiments of the present application, the Dv50 of the active material particles in the first region is 5 μm to 20 μm. According to some embodiments of the present 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 region and the second region meets the above range. The negative active material layer can maintain appropriate electrode plate reactivity and reduce unreasonable particle size while ensuring its overall wettability in the electrolyte. Side reactions caused by distribution, reduce production difficulty, and improve the yield rate during the pole piece production process.

According to some embodiments of the present application, the first region has a porosity of 15% to 30%. According to some embodiments of the present application, the second region has a porosity of 30% to 45%. The porosity of the first region and the porosity of the second region meet the above range. The negative active material layer can reduce the concentration polarization of the electrochemical device and reduce the internal resistance while ensuring the wettability and diffusion ability of the electrolyte. Significantly improve the energy density of the pole piece.

According to some embodiments of the present application, the thickness of the negative active material layer is 50 μm to 300 μm. The thickness of the negative active material layer is within the above range, which can further improve the electrolyte wettability and diffusion ability of the electrode piece in the thickness direction while optimizing the energy density of the electrochemical device. According to some embodiments of the present application, the thickness of the negative active material layer is 100 μm to 250 μm.

According to some embodiments of the present application, the active material particles in the first region and/or the second region are arranged in an array or in a non-array arrangement.

According to some embodiments of the present 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 the first region and the second region are arranged in an array, which is conducive to the rapid insertion and extraction of lithium ions.

According to some embodiments of the present application, an angle between the active material particles in the first region and/or the second region and the current collector along the long diameter direction 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, which is beneficial to improving dynamics.

According to some embodiments of the present application, along the thickness direction of the pole piece, based on the projected area of the active material layer, the projected area of the second region accounts for 5% to 50%. In this range, the electrolyte diffusion efficiency can be improved , which is beneficial to improving dynamics.

According to some embodiments of the present application, the second area is distributed in a stripe shape or an island shape.

According to some embodiments of the present application, the second region is disposed through the negative electrode plate in the width direction.

According to some embodiments of the present application, the bonding force of the negative electrode piece is 5 N/m to 15 N/m. The particle size of the active material particles in the second region is smaller, the specific surface area is larger, and the interaction force with the binder is stronger. The larger the contact area between the second region and the current collector, the stronger the bonding force, and the greater its own bonding force; The strong bonding force can prevent the pole piece from being demolded during processing and use or abuse of the electrode assembly.

According to some embodiments of the present application, the ratio of the width of the first area to the width of the second area is 1 to 20, and the second area is distributed in a stripe shape or an island shape. According to some embodiments of the present application, the ratio of the first area width to the second area width is 1 to 10. In this application, the first area width and the second area width refer to the first area width and the second area width of the negative electrode plate surface layer.

According to some embodiments of the present application, the first area width is 1 mm to 50 mm. According to some embodiments of the present application, the second area is distributed in an island shape and the shape of each island is a square or a rectangle.

According to some embodiments of the present application, the ratio of the thickness of the first region to the thickness of the second region is 1 to 2. The 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 to improving dynamics.

According to some embodiments of the present application, a primer layer is further provided between the current collector and the negative active material layer. The setting of the undercoat can increase the adhesion between the negative active material and the current collector, and effectively reduce demoulding, deformation and other phenomena caused by the differentiated design of different areas of the negative electrode piece.

According to some embodiments of the present application, the base coating includes conductive materials, binders, and dispersants.

According to some embodiments of the present application, the conductive material in the undercoat layer includes at least one of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes and graphene.

According to some embodiments of the present application, the adhesive includes styrene-butadiene rubber.

According to some embodiments of the present application, the dispersant includes sodium carboxymethylcellulose.

According to some embodiments of the present application, the active material particles in the first region and/or the second region are arranged in a non-array arrangement, and the thickness of the undercoat layer is 0.5 μm to 1.5 μm. According to other embodiments of the present application, the active material particles in the first region and/or the second region are arranged in an array, and the thickness of the undercoat layer is 1.5 μm to 3.0 μm. This is because after the active material particles are arranged in an array, The adhesion ability to the current collector becomes poor. Increasing the thickness of the primer layer can improve the adhesion and prevent demolding.

In a second aspect, the present application provides an electrochemical device, which includes the negative electrode piece as described in the first aspect of the present application.

In a third aspect, the present application provides an electronic device, including the electrochemical device according to the second aspect of the present application.

The negative electrode sheet provided by this application can not only increase the energy density of the electrochemical device, but also maintain good cycle performance of the electrochemical device.

Description of drawings

Figure 1 is a schematic cross-sectional view of a negative electrode sheet in the length direction according to some embodiments of the present application, where 1 is a copper current collector, 2 is an undercoat layer, 3 is a small particle dense area, and 4 is a large particle non-dense area.

Figure 2 is a schematic cross-sectional view of the negative electrode sheet in the length direction according to other embodiments of the present application, in which 1 is a copper current collector, 2 is an undercoat layer, 3 is a small particle dense area, and 4 is a large particle non-dense area. .

FIG. 3 is a schematic top view of a negative electrode plate according to some embodiments of the present application, in which the second area is distributed in a strip shape.

FIG. 4 is a schematic top view of a negative electrode sheet according to other embodiments of the present application, in which the second area is distributed in a strip shape.

FIG. 5 is a schematic top view of a negative electrode piece according to other embodiments of the present application, in which the second area is distributed in an island shape.

Detailed ways

The present application will be further elaborated below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application.

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are part of the embodiments of the present application, not All examples. The related embodiments described herein are illustrative in nature and are intended to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limitations of the present application. For the sake of simplicity, only certain numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

Unless otherwise stated, terms used in this application have their commonly understood meanings as generally understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the 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.

Negative pole piece

In this application, the negative electrode piece has two regions, a first region composed of small particles and a second region composed of large particles. The first area mainly contributes to the energy density of the electrochemical device; the second area has a relatively large particle size and a large porosity, which is conducive to storing electrolyte and providing a fast channel for the electrolyte to diffuse into the interior of the pole piece, which is conducive to the rapid development of electrolyte. Diffusion and liquid retention simultaneously bring electrolyte supply to the surrounding first area, reduce the electrolyte transport path in the first area, and improve dynamics.

According to some embodiments of the present application, the Dv50 of the active material particles in the first region is 5 μm to 20 μm. In some embodiments, the Dv50 of the active material particles in the first region is in a range of 5 μm, 8 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any two thereof. According to some embodiments of the present application, the Dv50 of the active material particles in the second region is 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 two thereof. The Dv50 of the active material particles in the first region and the second region meets the above range. The negative active material layer can maintain appropriate electrode plate reactivity and reduce unreasonable particle size while ensuring its overall wettability in the electrolyte. Side reactions caused by distribution, reduce production difficulty, and improve the yield rate during the pole piece production process.

According to some embodiments of the present application, the first region has a porosity of 15% to 30%. In some embodiments, the porosity of the first region ranges from 15%, 18%, 20%, 25%, 28%, 30%, or any two thereof. According to some embodiments of the present application, the second region has a porosity of 30% to 45%. In some embodiments, the porosity of the second region ranges from 30%, 35%, 40%, 45%, or any two thereof. The porosity of the first region and the porosity of the second region meet the above range. The negative active material layer can significantly increase the energy density of the pole piece while ensuring the electrolyte wettability and diffusion ability of the first region.

According to some embodiments of the present application, the thickness of the negative active material layer is 50 μm to 300 μm. In some embodiments, the thickness of the negative active material layer is 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 two thereof. scope. The thickness of the negative active material layer is within the above range, which can ensure the wettability and diffusion ability of the electrolyte and significantly increase the energy density of the electrode piece. According to some embodiments of the present application, the thickness of the negative active material layer is 100 μm to 250 μm.

According to some embodiments of the present application, the active material particles in the first region and/or the second region are arranged in an array or in a non-array arrangement. According to some embodiments of the present 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 the first region and the second region are arranged in an array, which is conducive to the rapid insertion and extraction of lithium ions. According to some embodiments of the present application, the active material particles have an aspect ratio of 1.5 to 5. According to some embodiments of the present application, the active material particles have an aspect ratio of 2 to 5.

According to some embodiments of the present application, an angle between the active material particles in the first region and/or the second region and the current collector along the long diameter direction 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 diameter direction is 45° to 135°, such as 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135° or a range consisting of any two of them. In some embodiments, the angle between the active material particles in the second region and the current collector along the long diameter direction is 45° to 135°, such as 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135° or a range consisting of any two of them. The active material particles are arranged with the current collector within this angle range, which shortens the diffusion path of lithium ions, which is beneficial to improving dynamics.

According to some embodiments of the present application, along the thickness direction of the pole piece, based on the projected area of the active material layer, the projected area of the second region accounts for 5% to 50%. In this range, the electrolyte diffusion efficiency can be improved , which is beneficial to improving dynamics. In some embodiments, along the thickness direction of the pole piece, based on the projected area of the active material layer, the projected area ratio of the second region is 5%, 10%, 15%, 20%, 25%, 30% , 35%, 40%, 45%, 50% or a range consisting of any two of them. In some embodiments, along the thickness direction of the pole piece, based on the projected area of the active material layer, the projected area of the second region accounts for 15% to 30%.

According to some embodiments of the present application, the second area is distributed in a strip shape or in an island shape.

According to some embodiments of the present application, the bonding force of the negative electrode piece is 5 N/m to 15 N/m. In some embodiments, the bonding force of the negative electrode piece is 5N/m, 6N/m, 7N/m, 8N/m, 9N/m, 10N/m, 11N/m, 12N/m, 13N/m, 14N/m, 15N/m or a range consisting of any two of them. The particle size of the active material particles in the second region is smaller, the specific surface area is larger, and the interaction force with the binder is stronger. The larger the contact area between the second region and the current collector, the stronger the bonding force, and the greater its own bonding force; The strong bonding force can prevent the pole piece from being demolded during processing and use or abuse of the electrode assembly.

According to some embodiments of the present application, the ratio of the width of the first area to the width of the second area is 1 to 20, and the second area is distributed in a stripe shape or an island shape. 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 two of them. According to some embodiments of the present application, the ratio of the first area width to the second area width is 1 to 10. In this application, the first area width and the second area width refer to the first area width and the second area width of the negative electrode plate surface layer.

According to some embodiments of the present application, the width of the first area is 1 mm to 50 mm, such as a range of 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm or any two of them.

According to some embodiments of the present application, the second area is distributed in an island shape and the shape of each island is a square or a rectangle.

According to some embodiments of the present 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 consisting of 1, 1.2, 1.4, 1.6, 1.8, 2, or any two of them. The 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 to improving dynamics.

According to some embodiments of the present application, the active material in the negative 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, coated with conductive material. According to some embodiments of the present application, the negative active material layer is metal. Polymer base or any combination thereof.

The negative active material layer may further include a conductive agent and/or a binder. In some embodiments, the conductive agent includes at least one of 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% by mass of the active material layer. In some embodiments, the binder includes polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic ester, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose , at least one of polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene, polyhexafluoropropylene or styrene-butadiene rubber. In some embodiments, the binder accounts for 0.5% to 10% by mass of the active material layer.

electrochemical device

The electrochemical device of the present application includes any device that generates electrochemical reactions, and specific examples thereof include all types of primary batteries and secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device of the present application includes a positive electrode, a negative electrode, a separator and an electrolyte.

1. Negative pole

The negative electrode in the electrochemical device of the present application includes the negative electrode piece of the first aspect.

2. Positive electrode

The materials, composition and manufacturing methods of the positive electrode that can be used in the embodiments of the present application include any technology disclosed in the prior art.

According to some embodiments of the present application, the positive electrode includes a current collector and a positive active material layer located on the current collector. According to some embodiments of the present application, the cathode active material includes, but is not limited to: lithium cobalt oxide (LiCoO ₂ ), lithium nickel cobalt manganate (NCM), lithium nickel cobalt aluminate, lithium iron phosphate (LiFePO ₄ ) or manganese Lithium oxide (LiMn ₂ O ₄ ).

According to some embodiments of the present application, the positive active material layer further includes a binder and optionally a conductive material. The binder improves the binding of the positive active material particles to each other and also improves the binding of the positive active material to the current collector. In some embodiments, the binder 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, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

According to some embodiments of the present application, conductive materials include, but are 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 fiber, carbon nanotubes, or any combination thereof. In some embodiments, the metal-based material is selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

According to some embodiments of the present application, the current collector may include, but is not limited to: aluminum.

3. Electrolyte

The electrolyte solution that can be used in the embodiments of the present application may be an electrolyte solution known in the art.

In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and additives. The organic solvent of the electrolyte solution according to the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte solution. The electrolyte used in the electrolyte solution according to the present application is not limited, and it can be any electrolyte known in the prior art. The additives of the electrolyte according to the present application may be any additives known in the art that can be used as electrolyte additives.

In some embodiments, organic solvents include, but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) ), propylene carbonate or ethyl propionate.

In some embodiments, lithium salts include, but are not limited to: lithium hexafluorophosphate LiPF ₆ , lithium tetrafluoroborate LiBF ₄ , lithium difluorophosphate LiPO ₂ F ₂ , lithium bistrifluoromethanesulfonimide LiN (CF ₃ SO ₂ ) ₂ (abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ ) (abbreviated as LiFSI), lithium bisoxalatoborate LiB(C ₂ O ₄ ) ₂ (abbreviated as LiBOB) or Lithium difluorooxalate borate LiBF ₂ (C ₂ O ₄ ) (abbreviated as LiDFOB).

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.

4. Isolation film

The material and shape of the isolation membrane used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes polymers or inorganic substances formed of materials that are stable to the electrolyte of the present application.

For example, the isolation film may include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, film or composite film with a porous structure. The base material layer is made of at least one material selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane can be used.

A surface treatment layer is provided on at least one surface of the base layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic layer.

The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, At least one of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy , at least one of polymethylmethacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

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

electronic device

The present application further provides an electronic device, which includes the electrochemical device of the second aspect of the present application.

The electronic equipment or device of the present application is not particularly limited. In some embodiments, electronic devices of the present application include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, and stereo headsets. , VCR, LCD TV, portable cleaner, portable CD player, mini disc, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, drone, motor, car, motorcycle, Power bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

The present application will be further described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

Examples and Comparative Examples

Test Methods

DC internal resistance test: Charge the lithium-ion battery to 50% SOC at 0.2C, let it sit for 30 minutes, then discharge it at 0.1C for 1s, and then discharge it at 1C for 1s. Calculate the ratio of the voltage difference to the current difference at the end of the two discharge points. Get the DC internal resistance.

Rate discharge test: charge to 4.4V at a constant voltage of 0.2C, then charge to a constant voltage of 0.02C, let it sit for 30 minutes, discharge it to 3.0V at 0.2C to get the actual capacity of the lithium-ion battery, and then fully charge it in the same way and let it stand. After 30 minutes, 3C was discharged to 3.0V to obtain the lithium-ion battery capacity, and compared with the actual capacity, the capacity retention rate was calculated.

Pole piece bonding force measurement method

Cut the pole piece into a rectangular piece of size 20mm×10cm. Use a 20mm wide double-sided tape to stick it on a clean steel plate with a width of 20mm. After manually peeling off 20mm, use a tensile machine to fix the peeled part of the steel plate and pole piece respectively to make the peeling easier. Keep the surface consistent with the force line of the testing machine, test the peeling force of the electrode piece at 180°, and the tensile machine stretching speed is 50mm/min. From the peeling force curve obtained, take the average value of the plateau section as the peeling force F ₀ , then the negative electrode piece is tested The bonding force is: F＝F ₀ /0.02 ＝50F ₀ .

Example 1-1

Preparation of the positive electrode: Use 12 μm aluminum foil as the current collector of the positive electrode, mix the positive active material lithium cobalt oxide, conductive agent conductive carbon black, and polyvinylidene fluoride in a weight ratio of 97.5:1.5:1.0, and use electrostatic spraying to spray the powder onto the aluminum current collector, and then undergo cold pressing and cutting to obtain the positive electrode piece with the required thickness and size.

Undercoating: Mix conductive carbon:PVDF=97:3 in water and apply it on the 6μm Cu current collector by transfer coating. The thickness of the undercoat is 1μm.

Preparation of non-array negative electrode: Mix graphite with a Dv50 of 15 μm, sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber in a weight ratio of 97.7:1.3:1 to obtain the first powder, which is then electrostatically sprayed. The first powder is sprayed onto a copper current collector with a thickness of 6 μm to prepare the first area; then graphite with a Dv50 of 30 μm, sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber are used in a weight ratio of 97.7:1.3: 1 is mixed to obtain a second powder, and electrostatic spraying is used to spray the second powder onto the corresponding second area on the copper current collector. Then, the negative electrode piece is obtained through cold pressing and cutting.

Preparation of isolation film: The base material of the isolation film is 8 μm thick polyethylene (PE). A 2 μm alumina ceramic layer is coated on both sides of the isolation film base material. Finally, 2.5 μm alumina ceramic layer is coated on both sides of the ceramic layer. mg/cm ² binder polyvinylidene fluoride (PVDF), dried.

Preparation of electrolyte: In an environment with a water content of less than 10 ppm, add LiPF ₆ to a non-aqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) and dimethyl carbonate ( DMC) = 1:1:1:1, weight ratio), the concentration of LiPF ₆ is 1 mol/L, mix evenly to obtain an electrolyte.

Preparation of lithium-ion battery: Stack the positive electrode sheet, isolation film, and negative electrode sheet in order, so that the isolation film is between the positive electrode sheet and the negative electrode sheet for isolation, and wind it to obtain the electrode assembly. The electrode assembly is placed in the outer packaging aluminum plastic film, and after the moisture is removed at 80°C, the above-mentioned electrolyte is injected and packaged. After formation, degassing, trimming and other processes, a lithium-ion battery is obtained.

Examples 1-1 to 1-11, Comparative Examples 1-3 and 1-4 all adopt the stripe morphology in the width direction of the pole piece (as shown in Figure 3). See Table 1 for the differences. Comparative Example 1-1 only uses graphite with a Dv50 of 15 μm, that is, it only has the first region. In Comparative Example 1-2, a 5:1 mixture of graphite with Dv50 of 155 μm and Dv50 of 305 μm was used, that is, it did not have the first region and the second region.

It can be seen from Example 1-1 to Example 1-11, Comparative Example 1-3 and Comparative Example 1-4 in Table 1: the appropriate distribution of the first region and the second region in the negative active material layer, specifically , the thickness ratio, width ratio, area ratio, particle size and porosity of the first region and the second region are within the scope of the present application. The DC internal resistance of the lithium-ion battery is significantly reduced, thereby achieving a relatively high rate of discharge at a high rate. High capacity retention rate. Neither Comparative Example 1-1 nor Comparative Example 1-2 has the first region and the second region of the present application. Comparative Example 1-1 only has small particles of graphite. The mixture of two kinds of graphite particles in Comparative Example 1-2 will cause As a result, the gaps between large particles are filled with small particles, and the ion diffusion path becomes longer or blocked, causing the DC internal resistance of the lithium-ion battery to increase, making it impossible to achieve a higher capacity retention rate under high-rate discharge.

Examples 2-1 to 2-8 all adopt the stripe morphology in the length direction of the pole piece (as shown in Figure 4), as detailed in Table 2 below.

It can be seen from the examples in Table 2 that for the stripe morphology in the length direction of the pole piece, the thickness ratio, width ratio, area ratio, particle size and porosity of the first region and the second region are all within the scope of the present application. It is beneficial to improve the electrolyte diffusion efficiency, and the DC internal resistance of the lithium-ion battery is significantly reduced, thereby achieving a higher capacity retention rate under high-rate discharge, which is beneficial to improving the dynamic performance of the electrochemical device.

Examples 3-1 to 3-7 all adopt island-like distribution morphology (as shown in Figure 5), as detailed in Table 3 below.

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

In addition, in the embodiments of Tables 1 to 3, the active material particles in the first region and the second region are arranged in a non-array, according to Embodiments 1-1 to 1-8, Embodiments 2-1 to 2-8 and Comparison of Examples 3-1 to 3-8 found that in the technical solution in which the second region is provided along the width direction of the pole piece, the DC internal resistance and discharge capacity retention rate of the electrochemical device are better than that in which the second region is provided along the length direction. This may be due to the fact that when the electrode assembly is wound along the length direction, the electrolyte can be infiltrated from both ends of the wound electrode assembly, and the second area arranged through the width direction of the pole piece is helpful for electrolysis. The regional diffusion of the liquid improves the DC internal resistance of the electrochemical device and maintains a better capacity retention rate in higher rate discharges. For the island-like distribution morphology, the proportion of the second region is small, so the DC internal resistance is relatively large, and the 3C discharge rate capacity retention rate is low, but the increased proportion of the first region can increase the energy density.

Example 4-1

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

Undercoating: Mix conductive carbon:PVDF=97:3 in water and apply it on the 6μm Cu current collector by transfer coating. The thickness of the undercoat is 2.5μm.

Preparation of array negative electrode: Dissolve small particle size graphite, sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber in deionized water at a weight ratio of 97.7:1.3:1 to form a small particle negative electrode slurry. The solid content is 70%; the preparation of large-particle anode slurry is the same as that of small particles; 3D printing technology is used to extrude the small-particle anode slurry perpendicularly to the current collector onto a 6μm Cu current collector, and a thermal light source is used to volatilize water at the same time, and the printed The slurry is cured in a short time to form the required morphology; then 3D printing is used to print the large particle slurry to the corresponding position, and then cold pressed and cut to obtain the array negative electrode piece, in which the aspect ratio of the active material particle raw material is 2 to 5.

Examples 4-1 to 4-8, Comparative Examples 4-3 and 4-4 all adopt the stripe morphology in the width direction of the pole piece. The differences are detailed in Table 4 below. Comparative Example 4-1 only uses graphite with a Dv50 of 15 μm, that is, it only has the first region. In Comparative Example 4-2, a 5:1 mixture of graphite with Dv50 of 155 μm and Dv50 of 305 μm was used, that is, it did not have the first region and the second region.

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

By comparing the examples in Table 1 and Table 4, for example, by comparing Examples 1-7 with Example 4-1 or by comparing Examples 1-8 with Examples 4-5, it can be seen that since the negative electrode adopts an array arrangement , the kinetic performance of the electrochemical device can be further improved, so the thickness of the pole piece can be further increased. The thickness of array-arranged graphite can be 120 μm to reach the kinetic level of 100 μm for non-array-arranged graphite.

Examples 5-1 to 5-7 all adopt the stripe morphology in the length direction of the pole piece, as detailed in Table 5 below.

It can be seen from the examples in Table 5 that for the stripe morphology in the length direction of the pole piece, the thickness ratio, width ratio, area ratio, particle size and porosity of the first region and the second region are all within the scope of the present application. It is beneficial to improve the electrolyte diffusion efficiency, and the DC internal resistance of the lithium-ion battery is significantly reduced, thereby achieving a higher capacity retention rate under high-rate discharge, which is beneficial to improving the dynamic performance of the electrochemical device.

By comparing the examples in Table 2 and Table 5, for example, by comparing Example 2-7 with Example 5-1 or by comparing Example 2-8 with Example 5-5, it can be seen that since the negative electrode adopts an array arrangement , the kinetic performance of the electrochemical device can be further improved.

Examples 6-1 to 6-7 all adopt island morphology, as shown in Table 6 below.

It can be seen from the examples in Table 6 that for the island-shaped morphology, the thickness ratio, width ratio, area ratio, particle size and porosity of the first region and the second region are within the scope of this application, which is beneficial to improving The electrolyte diffusion efficiency and the DC internal resistance of lithium-ion batteries are significantly reduced, thereby achieving a higher capacity retention rate under high-rate discharge, which is beneficial to improving the kinetic performance of the electrochemical device. .

By comparing the examples in Table 3 and Table 6, for example, by comparing Example 3-7 with Example 6-1, it can be seen that since the negative electrode is arranged in an array, the kinetic performance of the electrochemical device can be further improved.

In addition, it can be seen from Table 4 to Table 6 that the performance rules of the strip morphology and island morphology of the array arrangement are the same as those of the non-array arrangement, that is, the second area arranged throughout the width direction of the pole piece is compared with If it is arranged through the length direction or in an island shape, the DC internal resistance and discharge capacity retention rate of the electrochemical device are better.

The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still implement the foregoing implementations. The technical solutions described in the examples are modified, or some or all of the technical features are equivalently replaced; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solution of this application.

Claims

A negative electrode plate includes a current collector and a negative active material layer. The negative active material layer includes a first region and a second region, wherein the porosity of the first region is smaller than the porosity of the second region, so The ratio of Dv50 of the active material particles in the first region to the Dv50 of the active material particles in the second region is 0.3 to 0.9.
The negative electrode plate according to claim 1, wherein at least one of the following conditions is 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 second region has a porosity of 30% to 45%.
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.
The negative electrode sheet according to any one of claims 1 to 3, wherein an angle between the active material particles in the first region and/or the second region and the current collector along the long diameter direction is 45°. to 135°.
The negative electrode piece according to any one of claims 1 to 3, wherein along the thickness direction of the electrode piece, based on the projected area of the active material layer, the projected area ratio of the second region is 5% to 50%. %.
The negative electrode piece according to any one of claims 1-3, wherein at least one of the following conditions is met:

(e) The second area is a strip distribution or an island distribution,

(f) the second region is provided through the negative electrode piece in the width direction,

(g) The bonding force of the negative electrode piece is 5N/m to 15N/m.
The negative electrode piece according to any one of claims 1 to 3, wherein the ratio of the thickness of the first region to the thickness of the second region is 1 to 2; and/or the thickness of the first region is The ratio of the width to the width of the second area is 1 to 20.
The negative electrode sheet according to any one of claims 1 to 3, wherein an undercoat layer is further provided between the current collector and the negative active material layer, and the thickness of the undercoat layer is 0.5 μm. to 3.0μm.
An electrochemical device comprising the negative electrode piece according to any one of claims 1-8.
An electronic device comprising the electrochemical device according to claim 9.