Positive pole piece and battery monomer
By employing a double-layer coating design on the positive electrode of the battery cell and using a hybrid structure of polycrystalline particles and a high proportion of monocrystalline particles, the problem of gas generation in the battery cell is solved, thereby improving the battery's fast charging performance and cycle stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-13
AI Technical Summary
Existing battery cells have gas generation issues, which affect cycle stability and safety performance. Current improvement methods sacrifice the fast charging performance of the battery cells.
The positive electrode adopts a double-coated design. The first positive electrode active material layer is a polycrystalline particle, and the second positive electrode active material layer is a functional layer with a high proportion of single crystal particles. By adjusting the thickness and particle ratio, the contact between the polycrystalline particles and the electrolyte is reduced, thereby reducing polarization and lithium-ion diffusion resistance.
It improves the gas generation problem of individual battery cells, while enhancing fast charging performance and cycle stability, and ensuring the energy density and dynamic performance of individual battery cells.
Smart Images
Figure CN121662730A_ABST
Abstract
Description
Technical Field
[0001] Embodiments of this application relate to positive electrode sheets and battery cells. Background Technology
[0002] In the new energy field, to meet the demand for long driving range in electric vehicles, improving the performance of battery cells has become a trend in modern power battery technology development. However, existing battery cells suffer from gas production issues, which affect their cycle stability and safety performance. Therefore, it is necessary to improve gas production in battery cells. Summary of the Invention
[0003] This application aims to solve the gas generation problem caused by the positive electrode sheet. Some embodiments of this application provide a positive electrode sheet, including: a positive current collector and a positive active material layer located on at least one side of the positive current collector, wherein the positive active material layer includes a first positive active material layer disposed on the positive current collector, and a second positive active material layer disposed on the surface of the first positive active material layer on the side away from the positive current collector. The first positive active material layer includes a first positive active material, and the second positive active material layer includes a second positive active material. The first positive active material is a first polycrystalline particle, and the second positive active material includes a single crystal particle and a second polycrystalline particle. Based on the total mass of the second positive active material, the mass percentage of the single crystal particle is 50%-90%.
[0004] In this application, the first positive electrode active material layer is a pure polycrystalline layer. Compared with a single crystal layer, the polycrystalline layer has a higher energy density and better conductivity. The polycrystalline layer is formed by the agglomeration of primary particles. The primary particles have a smaller particle size than the single crystal, resulting in a smaller lithium-ion diffusion path. The polycrystalline surface has more active sites, which can reduce polarization. Furthermore, the second positive electrode active material layer is a functional layer that uses a high proportion of single crystal particles (mass percentage of 50%-90%). This can reduce the contact between the polycrystalline particles of the first positive electrode active material layer and the electrolyte. While ensuring that the first positive electrode active material layer of the positive electrode sheet can achieve its energy density, it further improves the gas generation problem of the battery cell.
[0005] In some embodiments, the first positive electrode active material layer has a first thickness and the second positive electrode active material layer has a second thickness, the first thickness being denoted as t1 μm and the second thickness being denoted as t2 μm, satisfying:
[0006] In some embodiments, the mass percentage of the second polycrystalline particles is 10%-50% based on the total mass of the second positive electrode active material.
[0007] In some embodiments, the single-crystal particles have a particle size of 4μm-6μm. In some embodiments, the first polycrystalline particle and the second polycrystalline particle are formed by the agglomeration of primary particles, wherein the particle size of the primary particles is 100nm-500nm.
[0008] In some embodiments, the single-crystal particle, the first polycrystalline particle, and the second polycrystalline particle are all lithium-containing nickel-cobalt-manganese composite metal oxide particles. In some embodiments, the chemical formula of the lithium-containing nickel-cobalt-manganese composite metal oxide is Li. a Ni b Co c Mn d O e A 2-e Where 0.8≤a≤1.2, 0.6≤b<1, 0<c<1, 0<d<1, 0<e≤2, b+c+d=1, and A is selected from one or more of N, F, S and Cl.
[0009] In some embodiments, the first polycrystalline particle and the second polycrystalline particle have the same chemical composition and / or particle size.
[0010] In some embodiments, the mass content of the binder in the first positive electrode active material layer is greater than the mass content of the binder in the second positive electrode active material layer.
[0011] Other embodiments of this application provide a battery cell including the above-described positive electrode sheet. Attached Figure Description
[0012] Various aspects of the invention will be best understood from the following detailed description when read in conjunction with the accompanying drawings.
[0013] Figure 1 This is a schematic diagram of an electronic device according to an embodiment of this application.
[0014] Figure 2 A schematic diagram of the overall structure of a battery cell according to an embodiment of this application is shown.
[0015] Figure 3 A cross-sectional schematic diagram of a battery cell according to an embodiment of this application is shown.
[0016] Figure 4 A schematic diagram of the electrode assembly of a battery cell according to an embodiment of this application is shown.
[0017] Figure 5 A schematic diagram of the positive electrode sheet according to an embodiment of this application is shown.
[0018] Figure 6A The SOH retention rates of the positive electrode sheets of Example 1 and Comparative Example 1 at 25°C are shown. Figure 6BThe storage volume expansion rate of the pouch cells of Example 1 and Comparative Example 1 at 60°C is shown.
[0019] Figure 7A The SOH retention rates of the positive electrode sheets of Example 1 and Comparative Example 2 at 25°C are shown. Figure 7B The storage volume expansion rate of the pouch cells of Example 1 and Comparative Example 1 at 60°C is shown. Detailed Implementation
[0020] In the field of new energy batteries, the positive electrode sheet is a layer containing positive active material. The positive active material can be either polycrystalline or monocrystalline. Compared to monocrystalline materials, polycrystalline materials offer higher energy density and better conductivity. Polycrystalline materials are formed by the agglomeration of primary particles, which have smaller particle sizes than monocrystalline materials, resulting in a narrower lithium-ion diffusion path, less polarization, and more surface active sites. This can also reduce polarization and enhance the kinetics and rate performance of the battery cell. However, it introduces the problem of gas generation. As mentioned above, the positive electrode sheet in a battery cell can generate a large amount of gas, affecting the cycle stability and safety performance of the battery cell. Changing the electrolyte system is one of the most common methods to improve the gas generation problem in lithium-ion battery cells. However, a more stable solvent system often reduces the kinetics of the battery cell, affecting its fast-charging performance. Regarding improvements to the positive electrode material, some researchers have proposed a double-layer coated electrode material where monocrystalline particles coat polycrystalline particles. This reduces the contact between the polycrystalline particles and the electrolyte, significantly reducing side reactions and gas generation. However, pure single-crystal particles have obvious problems of large polarization and insufficient kinetics on the electrode surface, which seriously affects the fast charging performance of the battery cell.
[0021] The applicant discovered that by introducing a functional layer (second positive electrode active material layer) that mixes single-crystal and polycrystalline particles, the polycrystalline particles of the underlying first positive electrode active material layer can be effectively protected, reducing side reactions with the electrolyte. Furthermore, by incorporating a small amount of polycrystalline particles into the single-crystal particle layer, the kinetics can be improved, reducing the thickness of the functional layer to 1 / 10-1 / 5 of the thickness of the underlying layer. This not only gives the polycrystalline material of the first positive electrode active material layer (first positive electrode active material) a higher energy density, but also, due to the presence of a thinner second positive electrode active material layer, reduces lithium-ion diffusion resistance, reduces the risk of peeling between the first and second positive electrode active material layers, and further improves the fast-charging performance and cycle stability of the battery cell.
[0022] Based on the above, this application provides a positive electrode sheet, a battery cell, and an electronic device. The positive electrode sheet provided by this application can solve the gas generation problem caused by the positive electrode sheet. Furthermore, it can correspondingly ensure the fast-charging performance and cycle stability of the battery cell. The following detailed description of the above-mentioned positive electrode sheet, battery cell, and electronic device is provided in conjunction with specific embodiments.
[0023] refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of an electronic device in an embodiment of the present invention. The electronic device 1000 in this embodiment can be, for example, a vehicle, which may include a body 1100 and a battery pack. The battery pack may include one or more individual battery cells 1200. The battery pack is disposed inside the body 1100 to supply power to the vehicle and ensure its normal operation. In practical applications, the vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.
[0024] In other embodiments, the electronic device 1000 may be, for example, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and a power tool, etc. This embodiment does not limit the type of the electronic device 1000.
[0025] refer to Figures 2 to 4 In this embodiment, the battery cell 1200 may include a housing 1210, a top cover 1220, and an electrode assembly 1230. The top cover 1220 has an adapter piece 1221 on the side facing the housing 1210. The housing 1210 has an internal accommodating space, and one end of the housing 1210 has an opening. The electrode assembly 1230 can be accommodated in the internal accommodating space of the housing 1210. The top cover 1220 can close onto the opening of the housing 1210 and is fixedly connected to the housing 1210, so that the interior of the housing 1210 is relatively sealed.
[0026] like Figure 4 As shown, the electrode assembly 1230 may include a positive electrode 100a, a negative electrode 100b, and a separator 200. The separator 200 is located between the positive electrode 100a and the negative electrode 100b to isolate them and prevent them from contacting each other, thus avoiding a short circuit. The positive electrode 100a, the separator 200, and the negative electrode 100b are simultaneously wound to form the electrode assembly 1230 in a wound state.
[0027] Figure 5 A schematic diagram of the positive electrode 100a is shown. Figure 5As can be seen from the image, the positive electrode 100a includes: a positive current collector 101 and a positive active material layer 100H located on at least one side of the positive current collector 101. The positive active material layer 100H includes a first positive active material layer 102 disposed on the positive current collector 101 and a second positive active material layer 103 disposed on the surface of the first positive active material layer 102 on the side away from the positive current collector 101. The first positive active material layer 102 includes a first positive active material, and the second positive active material layer 103 includes a second positive active material. The first positive active material is a first polycrystalline particle, and the second positive active material includes a single crystal particle and a second polycrystalline particle. Based on the total mass of the second positive active material, the mass ratio of the single crystal particle is 50%-90%. Clearly, the first positive electrode active material layer 102 is a pure polycrystalline layer. Compared to a monocrystalline layer, a polycrystalline layer has a higher energy density and better conductivity. Polycrystalline layers are formed by the agglomeration of primary particles, which have smaller particle sizes than monocrystalline layers, resulting in a shorter lithium-ion diffusion path, less polarization, and more active sites on the polycrystalline surface. This also reduces polarization and enhances the kinetics and rate performance of the corresponding battery cell. Furthermore, the second positive electrode active material layer 103 is a functional layer using a high proportion of monocrystalline particles (50%-90% by mass). This reduces the contact between the polycrystalline particles of the first positive electrode active material layer 102 and the electrolyte, ensuring the first positive electrode active material layer 102 achieves its energy density while further improving the gas generation problem of the battery cell. In some embodiments, based on the total mass of the second positive electrode active material, the mass percentage of the second polycrystalline particles is 10%-50%. In other words, under these circumstances, when the total mass fraction of single-crystal particles and second polycrystalline particles in the second positive electrode active material is 10 parts, the mass ratio of single-crystal particles to second polycrystalline particles is 5:5-9:1. Adding a small proportion of second polycrystalline particles (10%-50% by mass) to the second positive electrode active material layer 103 with a high proportion of single-crystal particles can improve gas generation while enhancing the kinetics of the second positive electrode active material layer 103, further improving the cycle performance of the battery cell.
[0028] In some embodiments, the first positive electrode active material layer 102 has a first thickness t1 μm and the second positive electrode active material layer 103 has a second thickness t2 μm, wherein the first thickness t1 μm and the second thickness t2 μm satisfy: It is clearly understandable that the first thickness t1μm and the second thickness t2μm can be as follows: Figure 5 The measurement is taken in the direction V1 or V2 away from the positive electrode current collector. In this application, the second thickness t2 μm of the second positive electrode active material layer 103 and the first thickness t1 μm of the first positive electrode active material layer 102 are defined as follows: While effectively protecting the first positive electrode active material layer 102, the thinner second positive electrode active material layer (a thin-film functional layer) can reduce lithium-ion diffusion resistance and the risk of layer peeling during battery cell cycling, further improving the fast-charging performance and cycle stability of the battery cell. The upper and lower layers are as follows: Figure 5 The first positive electrode active material layer 102 shown is the lower layer, and the second positive electrode active material layer 103 is the upper layer. In some embodiments, the first thickness t1μm can be in the range of 30μm-120μm, and the second thickness t2μm can be in the range of 3μm-30μm. This can be set according to requirements, or it can be any other suitable value.
[0029] In some embodiments, the single-crystal particles in the second positive electrode active material have a particle size of 4 μm-6 μm. The first and second polycrystalline particles are formed by the agglomeration of primary particles, and the particle size of the primary particles is 100 nm-500 nm. In this application, the first and second polycrystalline particles are formed by the agglomeration of primary particles. Since the particle size of the primary particles (approximately 100 nm-500 nm) is generally smaller than that of the single-crystal particles (approximately 4 μm-6 μm), the polycrystalline particles tend to have smaller lithium-ion diffusion paths, resulting in smaller diffusion polarization. Furthermore, the surface of the polycrystalline particles can expose more active sites, resulting in better reactivity compared to single-crystal particles. In this application, "approximately" represents values within ±10% of the described values.
[0030] In some embodiments, the single-crystal particles, the first polycrystalline particles, and the second polycrystalline particles are all lithium-containing nickel-cobalt-manganese composite metal oxide particles, the chemical formula of which is Li. a Ni b Co c Mn d O e A 2-e Wherein, 0.8≤a≤1.2, 0.6≤b<1, 0<c<1, 0<d<1, 0<e≤2, b+c+d=1, and A is selected from one or more of N, F, S, and Cl. The high-nickel positive electrode sheet formed in lithium-containing nickel-cobalt-manganese composite metal oxide particles with a high nickel content of 0.6≤b<1 can effectively improve the energy density of a single battery cell. Therefore, using the positive electrode sheet provided in this application can improve the gas generation problem of a single battery cell while increasing energy density.
[0031] In some embodiments, the first polycrystalline particle and the second polycrystalline particle have the same chemical composition and / or particle size. In this application, having the same particle size for the first and second polycrystalline particles can avoid uneven volume expansion caused by particle size differences, reduce polarization differences, and enhance the cycle stability of the corresponding battery cell.
[0032] In some embodiments, the mass content of the binder in the first positive electrode active material layer 102 is greater than the mass content of the binder in the second positive electrode active material layer 103. In this application, increasing the mass content of the binder in the first positive electrode active material layer 102 can make the first polycrystalline particles bond more tightly, suppress microcracks and new grain boundaries caused by volume expansion during lithium insertion / extraction, and reduce side reaction gas generation; maintaining a low binder content in the second positive electrode active material layer 103 can reduce the obstruction to the lithium-ion transport path and further increase the kinetics of the upper layer; by adjusting the ratio of the binder in the second positive electrode active material layer 103 and the first positive electrode active material layer 102, not only can the adhesion of the electrode be increased, but it can also synergize with the material system to further improve the gas generation of the battery cell and optimize the kinetics.
[0033] In summary, the positive electrode provided in this application is a double-layer coated hybrid positive electrode. By introducing a functional layer (second positive electrode active material layer 103) with a high proportion of single-crystal particles onto the surface of the polycrystalline layer (first positive electrode active material layer 102), the gas generation problem of the battery cell can be improved. In addition, the doping of a small number of polycrystalline particles in the second positive electrode active material layer 103 can enhance the kinetics of the second positive electrode active material layer, thereby optimizing the kinetics and stability of the battery cell.
[0034] Other embodiments of this application provide a battery cell including the aforementioned positive electrode. Furthermore, the battery cell can be a lithium-ion battery cell, a sodium-ion battery cell, a sodium-lithium-ion battery cell, etc., and this application is not limited thereto. In some embodiments, the battery cell is a lithium-ion battery cell, which includes the aforementioned positive electrode, negative electrode, separator, and electrolyte.
[0035] Positive electrode sheet
[0036] In some implementations, the corresponding positive electrode active material, conductive agent and binder are mixed in a mass ratio of 90-99:0.5-8:0.5-2, a solvent (such as N-methylpyrrolidone, NMP) is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on the corresponding area of the corresponding positive electrode active material layer on the positive electrode current collector, air-dried at room temperature, transferred to an oven for further drying, and then cold-pressed, slit and cut to obtain the positive electrode sheet.
[0037] As described above, the positive electrode active material may include the aforementioned materials. In some embodiments, the positive electrode active material may be a positive electrode active material conventionally used in the field for the positive electrode of pouch cells, and the positive electrode active material may be a ternary positive electrode active material (NCM).
[0038] The binder can be a component that facilitates the bonding between the active material and the conductive agent, and also facilitates the bonding between the active material and the current collector. It can typically be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers. In some embodiments, polyvinylidene fluoride (PVDF) can be used as the binder.
[0039] Conductive agents are reagents used to ensure that electrodes have good charge and discharge performance. They can be selected from graphite-based materials such as natural graphite, carbon nanotubes (CNTs), single-walled carbon nanotubes (SWCNTs), and artificial graphite; conductive carbon black (SP); conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide. In some embodiments, one of conductive carbon black (SP), carbon nanotubes (CNTs), and single-walled carbon nanotubes (SWCNTs) can be used as the conductive agent.
[0040] For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without restriction. Commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. Positive electrode current collectors can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.
[0041] Negative electrode sheet
[0042] The negative electrode sheet can be prepared using conventional methods in the art. For example, the following method can be used: after mixing the negative electrode active material, binder, conductive agent and optionally thickener in a certain weight ratio, a solvent is added and mixed evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated onto the negative electrode current collector; after drying at room temperature, it is transferred to an oven for further drying, and then cold-pressed, slit and cut to obtain the negative electrode sheet.
[0043] The negative electrode active material can be any negative electrode active material conventionally used in the art to prepare negative electrode sheets, and can be selected from one or more of graphite and silicon-based materials, specifically at least one of graphene, artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide, and silicon carbide; the binder plays a role in improving the adhesion between the negative electrode active materials and the adhesion between the negative electrode active materials and the negative electrode current collector, and its type is not particularly limited. Specific examples of binders may include polyacrylic acid (PAA), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene copolymer (PVDFcoHFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used.
[0044] There are no particular limitations on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery cells. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc. In addition, a thickener such as carboxymethyl cellulose (CMC) can be used, but there are no specific limitations.
[0045] For the negative electrode current collector, the negative electrode current collector can be a current collector conventionally used for negative electrodes in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can be made of a non-chemically reactive and conductive material without limitation. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum-cadmium alloys can be used, or copper, stainless steel, or aluminum-cadmium alloys surface-treated with carbon, nickel, titanium, or silver. Furthermore, to enhance the adhesion of the negative electrode active material, micro-embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a membrane, sheet, foil, mesh, or porous body.
[0046] Separating membrane
[0047] The separator placed between the positive and negative electrodes uses an insulating film with high ion permeability and high mechanical strength. The separator typically has a thickness of 9 μm-18 μm; a pore size of 5 μm-300 μm; an air permeability of 180 s / 100 mL-380 s / 100 mL; and a porosity of 30% to 50%. As a separator, it is chemically resistant and hydrophobic, and is usually made of sheets or nonwoven fabrics made of olefin polymers such as polypropylene or polyethylene films; glass fibers; or, further, using the aforementioned sheets or nonwoven fabrics as a base film, coated with a coating.
[0048] electrolyte
[0049] In this application, the electrolyte can be a conventional electrolyte used in lithium-ion battery cells, generally including non-aqueous solvents, lithium salts, and additives.
[0050] In some embodiments, the non-aqueous solvent may be a conventional non-aqueous solvent in the art, preferably an ester solvent, and more preferably a carbonate solvent. The carbonate solvent may be one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).
[0051] In some embodiments, the additive may be one or more selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), vinylene sulfate, 1,3-propane sulfonyl lactone (PS), propylene sulfonate lactone, and 1,4-butane sulfonate lactone. The conventional amount of the additive in the electrolyte is 1%-4% of the electrolyte, for example, 2%.
[0052] In some embodiments, the lithium salt may be a conventional lithium salt in the art, such as at least one selected from LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), LiBF2(C2O4) (abbreviated as LiDFOB), LiN(SO2RF)2, and LiN(SO2F)(SO2RF). The concentration of the lithium salt may be conventional in the art, and the lithium salt is preferably present in the electrolyte at a concentration of 5%-20%, typically 1 mol / L-2 mol / L.
[0053] In this application, the preparation method of the electrolyte can be conventional in the art, generally involving mixing a non-aqueous solvent, lithium salt, and additives.
[0054] Battery cell (taking pouch cell as an example)
[0055] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a soft-pack cell is obtained.
[0056] Electronic devices
[0057] In this application, the electronic device includes the aforementioned battery cell, and the electronic device can be the vehicle described above, or it can be a mobile phone, portable device, laptop, ship, spacecraft, electric toy, power tool, etc. The vehicle can be a gasoline-powered car, a natural gas-powered car, or a new energy vehicle; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. It can also be an energy storage electronic device that stores energy and then discharges it externally. This application does not impose any special limitations on the aforementioned electronic devices.
[0058] The present application is further illustrated below by way of embodiments, but these embodiments are not intended to limit the scope of the present application. Experimental methods not specifically described in the following embodiments are performed according to conventional methods and conditions in the art, or as selected according to the product specification.
[0059] The pouch cells, positive and negative electrode sheets, and electrolytes of the battery cells in Examples 1-10 and Comparative Examples 1-2 were all prepared using the following methods.
[0060] Example 1
[0061] Preparation of positive electrode sheet
[0062] First positive electrode slurry: The first positive electrode active material LiNi... 0.6 Co 0.2 Mn 0.2 O2 first polycrystalline particles (lithium nickel cobalt manganese oxide polycrystalline particles), conductive agent conductive carbon black (SP), and binder PVDF are mixed in a mass ratio of 93:4:3. NMP solvent is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain the first positive electrode slurry. The solid content of the first positive electrode slurry is 75%. The first polycrystalline particles are formed by the agglomeration of primary particles, and the particle size of the primary particles is 100nm-500nm.
[0063] Second cathode slurry: The second cathode active material is LiNi. 0.6 Co 0.2 Mn 0.2 O2 second polycrystalline particles (lithium nickel cobalt manganese oxide polycrystalline particles) and LiNi 0.6 Co 0.2 Mn 0.2 O2 single-crystal particles (lithium nickel cobalt manganese oxide single-crystal particles), wherein the mass ratio of single-crystal particles to second polycrystalline particles is 9:1, that is, based on the total mass of the second positive electrode active material, the mass proportion of single-crystal particles is 90%, and the mass proportion of second polycrystalline particles is 10%. The second positive electrode active material, conductive carbon black (SP) as a conductive agent, and PVDF as a binder are mixed at a mass ratio of 93:4:3, and NMP solvent is added. The mixture is stirred under vacuum until the system is homogeneous to obtain the first positive electrode slurry. The solid content of the second positive electrode slurry is 75%, and the particle size of the single-crystal particles is 4μm-6μm. The second polycrystalline particles are formed by the agglomeration of primary particles, and the particle size of the primary particles is 100nm-500nm.
[0064] The first positive electrode slurry and the second positive electrode slurry are simultaneously coated using a dual-die coating machine to obtain a first positive electrode active material layer and a second positive electrode active material layer. The relationship between the first thickness t1μm of the first positive electrode active material layer and the second thickness t2μm of the second positive electrode active material layer satisfies: That is, the second thickness of the second positive electrode active material layer is 1 / 5 of the first thickness of the first positive electrode active material layer. Specifically, the first thickness t1μm is 100μm and the second thickness t2μm is 20μm. Afterwards, it is dried at 120℃ for 1 hour, and then rolled and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 3.5g / cm³. 3 .
[0065] Preparation of negative electrode sheet
[0066] The negative electrode active material graphite, conductive agent carbon nanotubes and binder PAA are mixed evenly in a ratio of 94:3:3 and dispersed in deionized water to obtain a black slurry. The evenly stirred slurry is coated evenly on both sides of copper foil, and after baking, rolling and cutting, the negative electrode sheet is obtained.
[0067] Preparation of electrolyte
[0068] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Finally, 2% VC was added as a film-forming additive.
[0069] Preparation of the separating membrane
[0070] A polyethylene film with a thickness of 12μm was selected as the separator.
[0071] Lithium-ion battery cell (taking pouch cell as an example)
[0072] The roll-cut positive and negative electrode sheets are stacked in the order of positive electrode sheet, separator, and negative electrode sheet. The stacked bare cells are then packaged, baked, injected with electrolyte, formed, heat-sealed, and capacity tested to obtain soft-pack cells.
[0073] Performance testing of pouch cells.
[0074] (1) The test method for capacity retention is as follows:
[0075] Under a constant temperature environment of 25℃, the cell is charged at 1C to 4.25V, then charged at 4.25V at a constant voltage until the current is ≤0.05mA. After resting for 5 minutes, it is discharged at 1C to 2.5V to obtain the capacity D1. Repeat the above process for 100 cycles and record the capacity D100 of the soft-pack cell. The capacity retention rate after 100 cycles is D100 / D1.
[0076] Cyclic performance test: At 25°C, the soft-pack cells prepared in the examples and comparative examples were fully charged at 1C to the corresponding cutoff voltage of 4.25V, left to stand for 30 minutes, and then discharged at a constant current of 1C to the corresponding cutoff voltage, left to stand for 30 minutes. This is one charge-discharge cycle. The discharge capacity of the first cycle was recorded. The charge-discharge cycle was repeated in this way until the capacity of the soft-pack cell decayed to 80% of the initial capacity. The number of cycles was recorded.
[0077] (2) The gas generation test method for pouch cells is as follows:
[0078] The pouch cells were charged to 4.19V at 0.33C and then stored in a 60℃ incubator. They were taken out and cooled to room temperature on days 1, 3, 6, 9, 12, 15, 20, 25 and 30 respectively. The volume of the pouch cells was measured using a volume measuring instrument. The amount of gas produced was characterized by the volume expansion rate of the pouch cells.
[0079] (3) Particle size testing method:
[0080] Disassemble the aforementioned soft-pack battery cell, remove the positive electrode sheet, clean and dry it with NMP solvent, scrape off the positive electrode active material powder, place it in anhydrous ethanol, and ultrasonically disperse it for 15-20 minutes to ensure that the particles do not agglomerate. Use a field emission scanning electron microscope (e.g., Hitachi SU8020) to obtain secondary electron (SE) and backscattered electron (BSE) images of the dispersed positive electrode material. The secondary electron image is used to observe the morphology and boundaries, and the backscattered electron image is used to help distinguish between single crystal / primary particles and additives. As an example, the following method can be used for testing: randomly select multiple test areas (e.g., 6, with a planar area of 3mm × 3mm), where the planar area represents the area in the direction parallel to the current collector plane, and at a certain magnification (e.g., 10,000x for observing single crystal particles and 50,000x for primary particles), distinguish single crystal / primary particles, additives, and agglomerates based on image features. Specifically, single crystals / primary particles appear as spherical or cubic shapes in SE images, with complete outlines, clear edges, and dense surfaces without flocculent deposits; they appear bright white in BSE images. By differentiating through morphology and BSE multi-dimensional analysis, additives and agglomerates can be more accurately excluded. Fifteen suspected particles were randomly selected for EDS (Energy Dispersive Spectroscopy) point scanning: if characteristic cathode elements such as Ni, Co, and Mn were detected, and the C element content was <5wt% (no obvious additive residue), they were determined to be valid single crystals / primary particles; if only C was detected, they were determined to be additives and excluded. The secondary electron images were opened using ImageJ software (image processing software), and the outlines of valid single crystals / primary particles were manually delineated using the "Particle Analysis" function. The number of particles in each region was cumulatively counted, with a total count of no less than 50. The software automatically calculated the equivalent circular diameter of each particle (4 × particle area / particle perimeter) and output the particle size data (unit: μm) for all particles. The arithmetic mean of the single crystal / primary particle size in the test area is taken as the average particle size of the single crystal / primary particle in the test sample. To ensure the accuracy of the test results, the above test can be repeated multiple times, and the average value is taken as the final test result.
[0081] Example 2
[0082] The difference from Example 1 is that in Example 2, the mass ratio of single crystal particles to second polycrystalline particles in the second positive electrode active material layer is 8:2. That is, based on the total mass of the second positive electrode active material, the mass ratio of single crystal particles is 80% and the mass ratio of second polycrystalline particles is 20%. The remaining preparation methods and parameters are the same as in Example 1.
[0083] Example 3
[0084] The difference from Example 1 is that in Example 3, the mass ratio of single crystal particles to second polycrystalline particles in the second positive electrode active material layer is 6:4. That is, based on the total mass of the second positive electrode active material, the mass ratio of single crystal particles is 60% and the mass ratio of second polycrystalline particles is 40%. The remaining preparation methods and parameters are the same as in Example 1.
[0085] Example 4
[0086] The difference from Example 1 is that in Example 4, the mass ratio of single crystal particles to second polycrystalline particles in the second positive electrode active material layer is 5:5. That is, based on the total mass of the second positive electrode active material, the mass ratio of single crystal particles is 50% and the mass ratio of second polycrystalline particles is 50%. The rest of the preparation methods and parameters are the same as those in Example 1.
[0087] Example 5
[0088] The difference from Example 1 is that in Example 5, the relationship between the first thickness t1μm of the first positive electrode active material layer and the second thickness t2μm of the second positive electrode active material layer satisfies: That is, the second thickness of the second positive electrode active material layer is 1 / 10 of the first thickness of the first positive electrode active material layer. Specifically, the first thickness t1μm is 100μm and the second thickness t2μm is 10μm. The remaining preparation methods and parameters are consistent with those in Example 1.
[0089] Example 6
[0090] The difference from Example 1 is that in Example 6, the relationship between the first thickness t1μm of the first positive electrode active material layer and the second thickness t2μm of the second positive electrode active material layer satisfies: That is, the second thickness of the second positive electrode active material layer is 1 / 6 of the first thickness of the first positive electrode active material layer. Specifically, the first thickness t1μm is 100μm and the second thickness t2μm is 16.7μm. The remaining preparation methods and parameters are consistent with those in Example 1.
[0091] Example 7
[0092] The difference from Example 1 is that in Example 7, the first thickness t1μm of the first positive electrode active material layer is equal to the second thickness t2μm of the second positive electrode active material layer. Specifically, the first thickness t1μm and the second thickness t2μm are both 60μm, and the rest of the preparation methods and parameters are the same as in Example 1.
[0093] Example 8
[0094] The difference from Example 1 is that in Example 8, the first positive electrode active material is LiNi. 0.8 Co0.1 Mn 0.1 The first polycrystalline O2 particle, and the second positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 second polycrystalline particles and LiNi 0.8 Co 0.1 Mn 0.1 O2 single crystal particles, the rest of the preparation methods and parameters are consistent with those in Example 1.
[0095] Example 9
[0096] The difference from Example 1 is that in Example 9, the first positive electrode active material is LiNi. 0.6 Co 0.2 Mn 0.2 The first polycrystalline O2 particle, and the second positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 second polycrystalline particles and LiNi 0.8 Co 0.1 Mn 0.1 O2 single crystal particles, the rest of the preparation methods and parameters are consistent with those in Example 1.
[0097] Example 10
[0098] The difference from Example 1 is that in Example 10, the mass ratio of the first positive electrode active material, conductive carbon black (SP) and binder PVDF in the first positive electrode slurry is 92:4:4, and the mass ratio of the second positive electrode active material, conductive carbon black (SP) and binder PVDF in the second positive electrode slurry is 93:4:3. The mass content of binder in the prepared first positive electrode active material layer is greater than the mass content of binder in the second positive electrode active material layer. The remaining preparation methods and parameters are consistent with those in Example 1.
[0099] Comparative Example 1
[0100] The difference from Example 1 is that, in Comparative Example 1, the first positive electrode active material in the first positive electrode active material layer is LiNi. 0.6 Co 0.2 Mn 0.2 O2 first polycrystalline particles (lithium nickel cobalt manganese oxide polycrystalline particles) and LiNi 0.6 Co 0.2 Mn 0.2O2 single-crystal particles (lithium nickel cobalt manganese oxide single-crystal particles), wherein the mass ratio of single-crystal particles to the first polycrystalline particles is 1:9, that is, based on the total mass of the first positive electrode active material, the mass proportion of the first polycrystalline particles is 90%, and the mass proportion of the single-crystal particles is 10%, with a particle size of 4μm-6μm. Furthermore, the second positive electrode active material in the second positive electrode active material layer is the same as in Example 1, and the remaining preparation methods and parameters are consistent with Example 1.
[0101] Comparative Example 2
[0102] The difference from Example 1 is that in Comparative Example 2, the positive electrode active material layer of the positive electrode sheet is a single-layer polycrystalline layer, and both the first and second positive electrode active materials are made of lithium nickel cobalt manganese oxide polycrystalline particles, thereby forming the corresponding polycrystalline single layer. The other preparation methods and parameters are consistent with those of Example 1.
[0103] The relevant parameters and test results of Examples 1-10 and Comparative Examples 1-2 are shown in Table 1 below.
[0104] Table 1. Relevant parameters and test results for Examples 1-10 and Comparative Examples 1-2
[0105]
[0106] As can be seen from Examples 1 to 4 in Table 1 above, the positive electrode sheet provided in this application adopts a double-layer coating process. The first positive electrode active material layer includes a first positive electrode active material, which is a first polycrystalline particle. The second positive electrode active material layer includes a second positive electrode active material, which includes single-crystal particles and second polycrystalline particles. Based on the total mass of the second positive electrode active material, the mass ratio of single-crystal particles is 50%-90%. In this application, the first positive electrode active material layer is a pure polycrystalline layer. Compared with the single-crystal layer, the polycrystalline layer has a higher energy density and better conductivity. It is formed by the agglomeration of primary particles. The primary particles have a smaller particle size than the single crystal, resulting in a smaller lithium-ion diffusion path and more surface active sites. This can reduce polarization and enhance kinetics and rate performance. At the same time, the second positive electrode active material layer is a functional layer with a high proportion of single-crystal particles. This can reduce the contact between the polycrystalline particles of the first positive electrode active material layer and the electrolyte. While ensuring that the first positive electrode active material layer of the positive electrode sheet can exert its energy density, it can improve the gas generation problem of the soft-pack battery cell.
[0107] Furthermore, the mass percentage of the second polycrystalline particles is 10%-50%, meaning that when the total mass percentage of single-crystal particles and second polycrystalline particles is 10 parts by mass, the mass ratio of single-crystal particles to second polycrystalline particles in the second positive electrode active material is 5:5-9:1. In this case, the doping of a small amount of polycrystalline particles in the second positive electrode active material layer can improve the kinetics of this second positive electrode active material layer (functional layer). In addition, as shown in Table 1 above, when the ratio of single-crystal particles to polycrystalline particles in the second positive electrode active material layer is 8:2 (80% single-crystal particles and 20% polycrystalline particles), the kinetics of the material can be further improved without deteriorating gas generation, thus enhancing the cycle stability of the pouch cell.
[0108] Figure 6A The SOH retention rates of the positive electrode sheets of Example 1 and Comparative Example 1 at 25°C at 0.33C / 0.33C are shown, and... Figure 6B The storage volume expansion rate of the pouch cells of Example 1 and Comparative Example 1 at 60°C is shown. (Combined with...) Figures 6A to 6B Based on the data in Table 1 above, comparing Example 1 with Comparative Example 1, it can be seen that, compared with the first positive electrode active material layer in Comparative Example 1 which is a mixture of single-crystal particles and polycrystalline particles, the positive electrode in Example 1 uses a pure polycrystalline layer as the first positive electrode active material layer, which can significantly reduce the polarization of the positive electrode, improve the kinetics and cycle stability of the battery cell, and does not deteriorate gas production.
[0109] Figure 7A The SOH retention rates of the positive electrode sheets of Example 1 and Comparative Example 2 at 25°C at 0.33C / 0.33C are shown, and... Figure 7B The storage volume expansion rate of the pouch cells of Example 1 and Comparative Example 1 at 60°C is shown. (Combined with...) Figures 7A to 7B Based on the data in Table 1 above, comparing Example 1 with Comparative Example 2 shows that, compared to the pure polycrystalline layer positive electrode sheet of Comparative Example 2, covering the polycrystalline layer with a functional layer (a second positive electrode active material layer with single-crystal particles) can significantly improve gas generation. Therefore, the positive electrode sheet provided in this application, by covering the surface of the first positive electrode active material layer with a second positive electrode active material layer (a high proportion of single-crystal functional layer), wherein, based on the total mass of the second positive electrode active material in the second positive electrode active material layer, the mass ratio of single-crystal particles is 50%-90%, and the mass ratio of second polycrystalline particles is 10%-50%, can effectively reduce the contact between the electrolyte and the lower polycrystalline particles, thereby reducing side reactions and gas generation. Incorporating a small proportion of second polycrystalline particles (mass ratio of 10%-50%) into the single-crystal functional layer (second positive electrode active material layer) can improve gas generation while enhancing the kinetics of the upper layer, further improving the cycle performance of the pouch cell.
[0110] Based on the data in Table 1 above, it can be seen from Examples 1, 5 to 6 that the first thickness t1 μm of the first positive electrode active material layer and the second thickness t2 μm of the second positive electrode active material layer satisfy the following: This is because during cycling, the second positive electrode active material layer often experiences greater stress concentration and strain. Limiting the thickness of the second positive electrode active material layer to 1 / 5 to 1 / 10 of the first positive electrode active material layer (lower layer) can reduce the delamination problem caused by the difference in volumetric strain between the upper and lower layers during cycling. Simultaneously, it can enhance the uniformity of the conductive network and binder distribution between the upper and lower layers during coating, avoiding the risk of positive electrode peeling. In other words, it can effectively protect the first positive electrode active material layer while reducing lithium-ion diffusion resistance and the risk of peeling between the first and second positive electrode active material layers during cycling. Furthermore, as can be seen from Examples 1, 5, and 6, when the thickness of the second positive electrode active material layer (upper functional layer) is 1 / 6 of the first positive electrode active material layer (lower layer), the material kinetics can be further improved without worsening gas generation, thus enhancing the cycling stability of the pouch cell.
[0111] Furthermore, based on the data in Table 1 above, it can be seen from Examples 1 and 7 that when the first thickness t1μm of the first positive electrode active material layer is equal to the second thickness t2μm of the second positive electrode active material layer, the improvement effect on the corresponding positive electrode sheet is limited. Therefore, reducing the thickness of the second positive electrode active material layer can significantly increase the cycle stability of the pouch cell.
[0112] As can be seen from Examples 1, 8, and 9, the single-crystal particles, the first polycrystalline particles, and the second polycrystalline particles are all lithium-containing nickel-cobalt-manganese composite metal oxide particles, and the chemical formula of these lithium-containing nickel-cobalt-manganese composite metal oxide particles is Li. a Ni b Co c Mn d O e A 2-e Wherein, 0.8≤a≤1.2, 0.6≤b<1, 0<c<1, 0<d<1, 0<e≤2, b+c+d=1, and A is selected from one or more of N, F, S, and Cl. In lithium-containing nickel-cobalt-manganese composite metal oxide particles with a high nickel content of 0.6≤b<1, the resulting high-nickel positive electrode sheet can effectively improve the energy density of the corresponding pouch cell. Therefore, using the positive electrode sheet provided in this application can improve the gas generation problem of pouch cells while increasing energy density. Furthermore, Example 9 further illustrates the case where the first polycrystalline particle has a different chemical composition than the single-crystal particle and the second polycrystalline particle. It can be seen that when the first polycrystalline particle has a different chemical composition than the single-crystal particle and the second polycrystalline particle, it also has a certain improvement effect on the gas generation of the pouch cell.
[0113] As can be seen from Examples 1 to 9, the polycrystalline particles in the first and second positive electrode active material layers are formed by the agglomeration of primary particles. Since the particle size of the primary particles (approximately 100 nm-500 nm) is usually smaller than that of the single-crystal particles in the second positive electrode active material layer (approximately 4 μm-6 μm), the polycrystalline particles often have smaller lithium-ion diffusion paths, resulting in less diffusion polarization. Furthermore, the surface of the polycrystalline particles can expose more active sites, exhibiting better reactivity compared to single-crystal particles. Therefore, using pure polycrystalline particles as the active material in the first positive electrode active material layer (lower layer) can significantly reduce material polarization and enhance kinetic and rate performance.
[0114] As can be seen from Examples 1 and 10, when the mass content of the binder in the first positive electrode active material layer is greater than that in the second positive electrode active material layer, increasing the binder content in the first positive electrode active material layer can make the first polycrystalline particles bond more tightly, suppress the microcracks and new grain boundaries caused by volume expansion during lithium insertion / extraction, and reduce gas generation from side reactions. Maintaining a lower binder content in the second positive electrode active material layer can reduce the obstruction to the lithium-ion transport path and further increase the kinetics of the upper layer. By adjusting the ratio of binders in the second positive electrode active material layer and the first positive electrode active material layer, not only can the adhesion of the electrode be increased, but it can also work synergistically with the material system to further improve gas generation and optimize kinetics of the battery cell.
[0115] The foregoing outlines features of several embodiments to enable those skilled in the art to better understand aspects of the invention. Those skilled in the art should understand that they can readily use this invention as a basis to design or modify other processes and structures for implementing the same purposes and / or achieving the same advantages as the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the invention, and that various changes, substitutions, and modifications can be made to them herein without departing from the spirit and scope of the invention.
Claims
1. A positive electrode plate, characterized in that, include: A positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive electrode active material layer includes a first positive electrode active material layer disposed on the positive electrode current collector, and a second positive electrode active material layer disposed on the surface of the first positive electrode active material layer away from the positive electrode current collector. The first positive electrode active material layer includes a first positive electrode active material, and the second positive electrode active material layer includes a second positive electrode active material. The first positive electrode active material is a first polycrystalline particle, and the second positive electrode active material includes single crystal particles and second polycrystalline particles. Based on the total mass of the second positive electrode active material, the mass ratio of the single crystal particles is 50%-90%.
2. The positive electrode sheet according to claim 1, characterized in that, The first positive electrode active material layer has a first thickness, and the second positive electrode active material layer has a second thickness, where the first thickness is denoted as t1μm and the second thickness is denoted as t2μm, satisfying the following:
3. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the second positive electrode active material, the mass percentage of the second polycrystalline particles is 10%-50%.
4. The positive electrode sheet according to claim 1, characterized in that, The particle size of the single crystal particles is 4μm-6μm.
5. The positive electrode sheet according to claim 1, characterized in that, The first polycrystalline particle and the second polycrystalline particle are formed by primary particle agglomeration. The particle size of the primary particles is 100nm-500nm.
6. The positive electrode sheet according to claim 1, characterized in that, The single crystal particles, the first polycrystalline particles, and the second polycrystalline particles are all lithium-containing nickel-cobalt-manganese composite metal oxide particles.
7. The positive electrode sheet according to claim 6, characterized in that, The chemical formula of the lithium-containing nickel-cobalt-manganese composite metal oxide is Li a Ni b Co c Mn d O e A 2-e Where 0.8≤a≤1.2, 0.6≤b<1, 0<c<1, 0<d<1, 0<e≤2, b+c+d=1, and A is selected from one or more of N, F, S and Cl.
8. The positive electrode sheet according to claim 1, characterized in that, The first polycrystalline particle and the second polycrystalline particle have the same chemical composition and / or particle size.
9. The positive electrode sheet according to claim 1, characterized in that, The mass content of the binder in the first positive electrode active material layer is greater than the mass content of the binder in the second positive electrode active material layer.
10. A single battery cell, characterized in that, Includes the positive electrode sheet according to any one of claims 1-9.