Electrode assembly and battery therefor
By employing a composite system of monocrystalline and polycrystalline cathode materials in ternary lithium-ion batteries, combined with reasonable compaction density and separator safety range design, the problems of high-rate performance and thermal stability of ternary lithium-ion batteries have been solved, achieving improvements in high energy density and safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU RELIANCE ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-03-04
- Publication Date
- 2026-06-12
AI Technical Summary
Existing ternary lithium-ion batteries are prone to increased polarization and capacity decay during high-rate charging and discharging, and have poor thermal stability, especially under extreme conditions where they are prone to thermal runaway.
A composite system of single-crystal and polycrystalline positive electrode active materials is adopted, combined with a reasonable positive electrode sheet compaction density and a separator safety range. The particle size ratio is designed through packing theory to optimize ion transport and thermal safety performance.
It achieves a balance between high-rate performance and thermal stability, ensuring that the battery has excellent ion and electron transport capabilities while maintaining high volumetric energy density, thereby improving battery safety and lifespan.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and more specifically, to an electrode assembly and a battery. Background Technology
[0002] Ternary lithium-ion batteries, due to their high energy density and excellent charge-discharge efficiency, have been widely used in new energy vehicles, energy storage systems, and other fields. As application scenarios continue to place higher demands on battery performance, the synergistic optimization of rate performance and thermal safety performance has become a core technological bottleneck: on the one hand, the ion transport rate inside the battery needs to match the electron migration efficiency during high-rate charge and discharge, otherwise problems such as intensified polarization and capacity decay are likely to occur; on the other hand, ternary materials have relatively poor thermal stability, and thermal runaway is likely to occur under extreme conditions such as overcharging and short circuits.
[0003] Therefore, designing and fabricating a ternary lithium-ion battery that can balance high-rate performance and thermal stability, addressing the existing technical problems of ternary lithium-ion batteries, has significant research value and application significance. Summary of the Invention
[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides an electrode assembly and a battery that, when using ternary materials as the positive electrode active material, can achieve both high rate performance and thermal stability.
[0005] To solve the above-mentioned technical problems, this application is implemented as follows: According to one aspect of this application, an embodiment of this application provides an electrode assembly, the electrode assembly including a positive electrode sheet, a separator and a negative electrode sheet arranged sequentially, the positive electrode sheet including a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer including a positive active material, the positive active material including a monocrystalline positive active material and a polycrystalline positive active material; The compaction density of the positive electrode sheet is denoted as ρ, and the unit is g / cm³. 3 The safe range of the diaphragm is denoted as ΔT, with the unit being °C, where 44.9 ≤ ΔT × ρ ≤ 80.5.
[0006] In some of these implementations, ρ and ΔT satisfy: 50.5 ≤ ΔT × ρ ≤ 75.9.
[0007] In some embodiments, the mass ratio of the monocrystalline positive electrode active material to the polycrystalline positive electrode active material is 2~5:5~8.
[0008] In some embodiments, the compaction density ρ of the positive electrode sheet satisfies 3.4 g / cm³. 3 ~3.8g / cm 3 .
[0009] In some of these embodiments, the closed pore temperature T1 of the separator is ≥140 °C, the puncture temperature T2 of the separator is ≥152 °C, and ΔT = T2 - T1 ≥ 12 °C.
[0010] In some of these embodiments, the chemical general formula of the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O2, where 0.6 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z < 1, and M is selected from at least one of Al, Mg, Zr, Ti, W, Sr, Y, and Nb.
[0011] In some of these embodiments, the Dv50 of the polycrystalline positive electrode active material is 10 μm to 15 μm.
[0012] In some of these embodiments, the Dv50 of the single crystal positive electrode active material is 2.5 μm to 4.5 μm.
[0013] In some of these embodiments, the specific surface area of the positive electrode active material is 0.5 m 2 / g to 0.9 m 2 / g.
[0014] In some of these embodiments, the positive electrode active layer further includes a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent, and the binder is 95 to 96.5:2 to 3:2 to 3.
[0015] In some of these embodiments, the separator includes a base film and a functional coating located on at least one surface of the base film.
[0016] In some of these embodiments, the base film includes at least one of polyethylene PE, polypropylene PP, and a multilayer composite base film PP / PE / PP.
[0017] In some of these embodiments, the functional coating includes at least one of an inorganic ceramic material, a polymer, and a composite synergistic material.
[0018] In some of these embodiments, the thickness of the functional coating is 2 μm to 8 μm.
[0019] In some of these embodiments, the porosity of the functional coating is 50% to 70%.
[0020] In some of these embodiments, the inorganic ceramic material includes at least one of alumina, silica, boehmite, barium sulfate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate oxide, and phyllosilicate minerals.
[0021] In some embodiments, the polymer includes at least one selected from polyvinylidene fluoride (PVDF), polyacrylonitrile, polyimide, poly(p-phenylene terephthalamide), and modified nanocellulose.
[0022] In some of these embodiments, the composite synergistic material includes at least one of the following: alumina / poly(methyl methacrylate-butyl acrylate), alumina / polyvinylidene fluoride (PVDF), alumina / polyamide-amine (PAMAM), silica / polymethyl methacrylate (PMMA), silica / polyvinylidene fluoride (PVDF), boehmite / polyvinylidene fluoride (PVDF), silica / poly(p-phenylene terephthalamide), boron nitride / poly(p-phenylene terephthalamide), titanium dioxide / polyacrylonitrile, silica / polyacrylonitrile, lithium lanthanum zirconium oxide / polyvinylidene fluoride (PVDF), and silica / polymethyl methacrylate (PMMA).
[0023] In some embodiments, the thickness of the base film is 9 μm to 15 μm, and the air permeability of the base film is 100 s / 100 mL to 150 s / 100 mL.
[0024] According to another aspect of this application, embodiments of this application provide a battery including the aforementioned electrode assembly.
[0025] Implementing the technical solution of the present invention has at least the following beneficial effects: In this embodiment, polycrystalline cathode materials are used in combination with monocrystalline cathode materials, enabling the battery to achieve high volumetric energy density while ensuring excellent ion and electron transport capabilities. Furthermore, by coupling the "safety range (ΔTs)" with the "density of state (ρ)," the product of which satisfies the aforementioned relationship, ensuring that the battery possesses both high rate performance and high safety performance.
[0026] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation
[0027] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.
[0028] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges or individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0029] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.
[0030] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.
[0031] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.
[0032] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.
[0033] In existing technologies, improving rate performance often involves increasing the cathode compaction density to increase the loading of active materials. However, excessively high compaction density can reduce electrode porosity, hindering electrolyte wetting and lithium-ion transport, thus worsening rate performance. Improving thermal safety is often achieved through separator coating modification, but single separator modification struggles to balance thermal stability and ion conductivity, and it doesn't consider the synergistic effect with cathode structural parameters. Furthermore, it neglects the difference between the separator's pore-closing temperature and its rupture temperature (i.e., the "safe range")—this difference directly determines the buffer time before battery thermal runaway. Existing technologies rarely optimize this difference in relation to cathode compaction density. Simultaneously, existing technologies often limit cathode material selection to single-crystal or polycrystalline systems. Even when using composite systems, particle size design doesn't follow packing theory—polycrystalline materials should form the framework with large particles, while single-crystal materials fill the voids to maximize packing density and ion transport channels.
[0034] Therefore, it is urgent to develop a design scheme based on the packing theory that combines the compaction density of single-crystal and polycrystalline composite cathodes with the safety range of the separator. By constructing mathematical models and reasonable value ranges for both, the rate performance and thermal safety performance can be improved simultaneously.
[0035] In view of this, embodiments of this application provide an electrode assembly, the electrode assembly including a positive electrode sheet, a separator and a negative electrode sheet arranged sequentially, the positive electrode sheet including a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer including a positive active material, the positive active material including a monocrystalline positive active material and a polycrystalline positive active material; The compaction density of the positive electrode sheet is denoted as ρ, and the unit is g / cm³. 3 The safe range of the diaphragm is denoted as ΔT, with the unit being °C, where 44.9 ≤ ΔT × ρ ≤ 80.5.
[0036] The positive electrode active material of this invention includes monocrystalline and polycrystalline positive electrode active materials. The polycrystalline positive electrode active material is composed of numerous nano- or submicron-sized primary particles aggregated together, with grain boundaries between the grains. This shortens the lithium-ion transport path and improves the material's rate performance. Furthermore, the presence of grain boundaries in the polycrystalline positive electrode active material provides additional lithium-ion diffusion paths, significantly improving ion transport kinetics and thus enhancing the battery's rate performance. The monocrystalline positive electrode active material consists of complete single crystals without internal grain boundaries, exhibiting good structural stability and effectively suppressing particle breakage, thus improving cycle stability. Simultaneously, it prevents the formation of microcracks in the positive electrode under high voltage, reducing side reactions and resulting in better thermal stability of the battery. Additionally, when graded with polycrystalline materials, it can fill the voids between large polycrystalline particles, thereby increasing the compaction density.
[0037] Furthermore, the compaction density of the positive electrode is denoted as ρ, with units of g / cm³. 3 The safe range of the separator is denoted as ΔT, in °C, where 44.9 ≤ ΔT × ρ ≤ 80.5. When the product of ρ and ΔT satisfies the above range, the battery can have excellent thermal stability and rate performance. If the product of the two is too high, the thermal safety risk is extremely high; if the product of the two is too low, lithium-ion transport is hindered, and the rate performance is reduced.
[0038] Based on the above, this invention combines polycrystalline cathode materials with monocrystalline cathode materials, enabling the battery to achieve high volumetric energy density while ensuring excellent ion and electron transport capabilities. Furthermore, by coupling the "safety range (ΔTs)" with the "density of state (ρ)," the product of which satisfies the aforementioned relationship, ensuring that the battery possesses both high rate performance and high safety performance.
[0039] It should be noted that "ΔT×ρ" is a numerical calculation only and does not include units.
[0040] In one specific embodiment, ρ and ΔT satisfy: 50.5≤ΔT×ρ≤75.9, for example, 50.5, 55, 60, 66, 70, 75.9 or within the range of any two of the above values.
[0041] In one specific embodiment, the mass ratio of the monocrystalline positive electrode active material to the polycrystalline positive electrode active material is 2~5:5~8, for example, 2:5, 2:8, 5:5, 5:8, or other ratios within the above range. When the mass ratio of the monocrystalline positive electrode active material to the polycrystalline positive electrode active material is within the above range, efficient lithium-ion transport channels can be simultaneously constructed within the positive electrode sheet, laying the kinetic foundation for high-rate discharge of the battery, and giving the positive electrode sheet excellent structural and thermal stability, ensuring a longer battery life and superior thermal safety performance. Furthermore, if the mass ratio of the monocrystalline positive electrode active material to the polycrystalline positive electrode active material is too low, the positive electrode sheet is prone to microcracks under high voltage, increasing the occurrence of side reactions and reducing the thermal stability of the battery; if the mass ratio of the monocrystalline positive electrode active material to the polycrystalline active material is too high, there is a lack of additional lithium-ion diffusion paths, thus affecting the rate performance of the battery.
[0042] In one specific embodiment, the compaction density ρ of the positive electrode sheet satisfies 3.4 g / cm³. 3 ~3.8g / cm 3 For example, 3.4 g / cm³. 3 3.45g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 Or it may fall within the range of any two of the above values. The compaction density ρ of the positive electrode is within the above range, which, while pursuing high volumetric energy density, avoids the obstruction of ion migration caused by excessive compaction.
[0043] In a specific embodiment, the closing temperature T1 of the separator is ≥ 140 °C, the puncturing temperature T2 of the separator is ≥ 152 °C, and ΔT = T2 - T1 ≥ 12 °C. Defining the ranges of the closing temperature and the puncturing temperature of the separator establishes a dual thermal protection mechanism for the battery. The first layer is timely shut-off (closing of pores), and the second layer is tenacious resistance (anti-tearing). Moreover, the safety interval (ΔTs) is not less than 12 °C, which wins crucial response time for the battery under abusive conditions. Based on the limitation of the above parameters, at least 120 seconds of crucial buffer time is obtained for the battery management system (BMS) to identify thermal risks and initiate measures such as cooling or power-off, thereby achieving a 100% passing rate in the 10V severe overcharge test and greatly enhancing the absolute safety of the battery.
[0044] In a specific embodiment, the chemical general formula of the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O2, where 0.6 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z < 1, and M is selected from at least one of Al, Mg, Zr, Ti, W, Sr, Y, and Nb.
[0045] In a specific embodiment, the Dv50 of the polycrystalline positive electrode active material is 10 μm to 15 μm. For example, it is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or within the range composed of any two of the above values.
[0046] In a specific embodiment, the Dv50 of the single crystal positive electrode active material is 2.5 μm to 4.5 μm. For example, it is 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or within the range composed of any two of the above values.
[0047] In a specific embodiment, the specific surface area of the positive electrode active material is 0.5 m 2 / g to 0.9 m 2 / g. For example, it is 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g or within the range composed of any two of the above values.
[0048] In a specific embodiment, the positive electrode active layer further includes a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent, and the binder is 95 - 96.5:2 - 3:2 - 3. For example, it is 95:2:3, 96:2.5:2, 96.5:3:3 or other ratios within the above range.
[0049] In one specific embodiment, the conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, or graphene.
[0050] The conductive carbon blacks mentioned above include acetylene black, Ketjen black, etc. The conductive carbon fibers mentioned above include vapor-grown carbon fibers.
[0051] In one specific embodiment, the adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, or polyacrylic acid.
[0052] In one specific embodiment, the thickness of the positive electrode active layer is 70~140μm, and the positive electrode current collector includes aluminum foil.
[0053] In one specific embodiment, the diaphragm includes a base membrane and a functional coating located on at least one side of the surface of the base membrane.
[0054] As an example, the base film has two surfaces opposite each other in its own thickness direction, and the functional coating is present on both opposite surfaces of the base film. It will be understood that in other embodiments, the functional coating may be disposed on either of the two surfaces of the base film.
[0055] In one specific embodiment, the base film includes at least one of polyethylene (PE), polypropylene (PP), and a multilayer composite base film PP / PE / PP. For example, it can be polyethylene (PE), polypropylene (PP), or a multilayer composite base film PP / PE / PP.
[0056] In one specific embodiment, the functional coating comprises at least one of inorganic ceramic materials, polymers, and composite synergistic materials. For example, it may include inorganic ceramic materials, polymers, or composite synergistic materials.
[0057] In one specific embodiment, the thickness of the functional coating is 2μm to 8μm. For example, it is 2μm, 4μm, 6μm, 8μm, or within any two of the above values.
[0058] In one specific embodiment, the porosity of the functional coating is 50% to 70%. For example, it is 50%, 60%, 70%, or within any two of the above values.
[0059] In one specific embodiment, the inorganic ceramic material includes at least one of alumina, silicon dioxide, boehmite, barium sulfate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphorus oxide, and layered silicate minerals. For example, the inorganic ceramic material can be alumina, silicon dioxide, or boehmite.
[0060] In one specific embodiment, when the composite membrane functional coating contains inorganic ceramic materials, the functional coating is composed of 90%~98% inorganic ceramic materials, 2%~10% binder (polyvinylidene fluoride PVDF or styrene-butadiene rubber SBR), and 0%~2% dispersant (ammonium polyacrylate PAA-NH4).
[0061] In one specific embodiment, the polymer includes at least one selected from polyvinylidene fluoride (PVDF), polyacrylonitrile, polyimide, poly(p-phenylene terephthalamide), and modified nanocellulose. For example, the polymer can be polyvinylidene fluoride, polyacrylonitrile, or polyimide.
[0062] In one specific embodiment, when the composite membrane functional coating contains a polymer, the functional coating is composed of 95%~100% organic polymer and 0%~5% additives (one of the following: acetylenol 104, polyether modified polysiloxane BYK-3455, polydimethylsiloxane BYK-011, hydrophobic fumed silica Aerosil 200, polyethylene glycol PEG, triphenyl phosphate TPP, ammonium polyphosphate APP, etc.).
[0063] In one specific embodiment, the composite synergistic material includes at least one of the following: alumina / poly(methyl methacrylate-butyl acrylate), alumina / polyvinylidene fluoride (PVDF), alumina / polyamide-amine (PAMAM), silica / polymethyl methacrylate (PMMA), silica / polyvinylidene fluoride (PVDF), boehmite / polyvinylidene fluoride (PVDF), silica / poly(p-phenylene terephthalamide), boron nitride / poly(p-phenylene terephthalamide), titanium dioxide / polyacrylonitrile, silica / polyacrylonitrile, lithium lanthanum zirconium oxide / polyvinylidene fluoride (PVDF), and silica / polymethyl methacrylate (PMMA). For example, the composite synergistic material can be alumina / poly(methyl methacrylate-butyl acrylate), alumina / polyvinylidene fluoride, or silica / polyvinylidene fluoride.
[0064] In one specific embodiment, when the composite membrane functional coating contains composite synergistic materials, the functional coating is composed of 70%~90% inorganic particles, 10%~30% organic polymers, and 0%~5% dispersant (ammonium polycarboxylate salts such as Disperbyk-190, Tego Dispers 755 W, EFKA-4580; nonionic polymers such as Disperbyk-2015, Tego Dispers 750 W; and polymeric block / graft copolymer superdispersants such as BYK-110 / 111, BYK-180, Tego Dispers 610 / 650, EFKA-4010 / 4050, etc.); when the functional coating is an inorganic-organic composite material and is mainly composed of organic materials, it consists of 15%~40% inorganic particles, 60%~85% organic polymers, and 0%~5% dispersant (ammonium polycarboxylate salts such as Disperbyk-190, Tego Dispers 755 W, etc.). The composition includes W, EFKA-4580, nonionic polymers such as Disperbyk-2015 and Tego Dispers 750 W, and high molecular weight block / graft copolymer superdispersants such as BYK-110 / 111, BYK-180, Tego Dispers 610 / 650, and EFKA-4010 / 4050. It should be noted that the inorganic particles and organic polymers mentioned correspond to the inorganic materials and organic polymers in the aforementioned composite synergistic material.
[0065] In one specific embodiment, the thickness of the base film is 9 μm to 15 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or within any two of the above values. The air permeability of the base film is 100 s / 100 mL to 150 s / 100 mL, for example, 100 s / 100 mL, 110 s / 100 mL, 120 s / 100 mL, 130 s / 100 mL, 140 s / 100 mL, 150 s / 100 mL, or within any two of the above values.
[0066] It should be noted that when the composite separator meets the above characteristics, it can satisfy the following: the pore-closing temperature of the separator is ≥140℃, the pore-breaking temperature of the separator is ≥152℃, and the safety range (ΔT) is not lower than 12℃, thereby achieving the effect of improving the battery safety performance.
[0067] In this embodiment, the materials and structures of the negative electrode current collector, the conductive agent and the binder in the negative electrode active material layer are not limited, and negative electrode structures and components known in the art that can be used in secondary batteries can be selected.
[0068] Based on the same inventive concept, embodiments of this application provide a battery including the aforementioned electrode assembly.
[0069] Because this battery includes the electrode assembly provided in this embodiment, it has excellent rate performance and safety performance.
[0070] It should also be noted that the battery in this application does not limit the specific material or type of electrolyte. Any components and types known in the art that can be used in secondary batteries can be selected, as long as the purpose of this application can be achieved.
[0071] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.
[0072] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.
[0073] Example 1 Preparation of positive electrode sheet 96 parts by weight of the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2 (containing 30% monocrystalline and 70% polycrystalline), 2 parts by weight of polyvinylidene fluoride (PVDF) binder, and 2 parts by weight of conductive agent SP are added to solvent NMP and stirred to obtain a positive electrode slurry with a solid content of 68%. This slurry is then coated on both sides of an aluminum foil and dried to obtain a positive electrode sheet. The aluminum foil thickness is 15 μm, and the coating thickness on one side is 68 μm.
[0074] Preparation of negative electrode sheet A negative electrode slurry with a solid content of 40% was prepared by adding 96 parts by weight of artificial graphite and silicon carbide, 1 part by weight of conductive agent SP, 1 part by weight of thickener CMC, and 2 parts by weight of binder polyvinylidene fluoride (PVDF) to deionized water. This slurry was then coated onto both sides of a copper foil and dried to obtain the negative electrode sheet. The copper foil thickness was 8 μm, the single-sided coating thickness was 43 μm, and the mass ratio of artificial graphite to silicon carbide was 8:2.
[0075] Preparation of diaphragm (1) The composite synergistic material (Al2O3 and PVDF in a mass ratio of 1:9) and organic solvent are mixed and stirred evenly to obtain a slurry with a solid content of 20%; (2) The slurry is coated on both sides of the base film PE to obtain the coated diaphragm, and the porosity of the diaphragm functional coating is 60%.
[0076] Preparation of electrolyte Lithium salt (LiPF6 1.0M) was dissolved in an organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) in a volume ratio of 3.5:5.5:1, and finally the solution was prepared as an electrolyte.
[0077] Battery assembly After the positive and negative electrode sheets are slit and die-cut using a winding machine, they are wound together with the separator to form a core. The core is then cut and stacked with positive and negative electrode tabs. The positive and negative busbars are then welded to the core, and the negative busbar is welded to the steel shell. An insulating sheet is placed on top of the positive busbar, and the positive busbar is welded to the cap. Next, grooving, electrolyte injection, and sealing are completed. Finally, the experimental cylindrical battery is obtained through a formation process.
[0078] Examples 2-5 The differences between Examples 2-5 and Example 1 are shown in Table 1. Any content not covered in Table 1 is the same as that in Example 1.
[0079] Comparative Examples 1-4 The differences between Comparative Examples 1-4 and Example 1 are shown in Table 1. All contents not covered in Table 1 are the same as those in Example 1.
[0080] Table 1 Table 2 As can be seen from Table 2, the types of materials and the thickness of the functional coating in the composite separator ensure that the ΔT=T2-T1≥12℃ of the separator is within a reasonable range required by this invention, thereby ensuring that 44.9≤ΔT×ρ≤80.5, which is good for the high-temperature performance of the battery.
[0081] Test case 5C Capacity Retention Test The batteries prepared in the examples and comparative examples were placed in a constant temperature chamber at 25°C for more than 4 hours, with a voltage window of 2.5V~4V, and tested according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 10 minutes; (2) Charge the battery at a constant current of 0.1C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.01C, and let it stand for 10 minutes. (3) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 10 minutes. Then read the capacity value C0 at this time. (4) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (5) Discharge the battery at a constant current of 0.5C until it reaches 2.5V cutoff, and let it stand for 10 minutes; (6) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (7) Discharge the battery at a constant current of 1C until it is cut off at 2.5V, and let it stand for 10 minutes; (8) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (9) Discharge the battery under constant current at 2C until it is cut off at 2.5V, and let it stand for 10 minutes; (10) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (11) Discharge the battery under constant current at 3C until it is cut off at 2.5V, and let it stand for 10 minutes; (12) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (13) Discharge the battery under constant current at 4C until it is cut off at 2.5V, and let it stand for 10 minutes; (14) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (15) Discharge the battery under constant current at 5C until it is cut off at 2.5V, let it stand for 10 minutes, and record it as C5; (16) 5C capacity retention rate = C5 / C0 × 100%.
[0082] Overcharge test Place the sample in a 25℃ constant temperature chamber for more than 4 hours, and perform the test according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 5 minutes; (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.05C, and let it stand for 5 minutes. (3) Discharge the battery at a constant current of 0.2C until it is cut off at 2.5V, and let it stand for 5 minutes; (4) Temperature sensing wires are attached to the head, middle and bottom of the battery cell to collect temperature signals; (5) Charge to 10.0V using 3C constant current, then switch to constant voltage charging for 1 hour, with a sampling interval of 1 second; (6) Let stand for 30 minutes; (7) A cell that does not catch fire or explode and whose maximum temperature does not exceed 150°C is considered to have passed. The pass rate is calculated after parallel testing of 10 cells.
[0083] The test results of each embodiment and comparative example are shown in Table 3.
[0084] Table 3 As shown in Table 3, the batteries prepared in this application all exhibit excellent high-rate discharge performance and high-temperature stability. The examples demonstrate that this design enables the battery to maintain a capacity retention rate of over 90% under 5C ultra-high-rate discharge, overcoming the bottleneck of poor rate performance of traditional high-density electrodes. Furthermore, a wide-window, dual-insurance active thermal safety defense line is established: by employing a composite separator with a pore-closing temperature ≥140℃, a membrane rupture temperature ≥152℃, and a safety range ΔTs ≥12℃, a dual thermal protection mechanism is established for the battery. The first layer is timely shutdown (pore closure), and the second layer is robust resistance (tear resistance). This provides the Battery Management System (BMS) with at least 120 seconds of critical buffer time to identify thermal risks and initiate cooling or power-off measures, thereby achieving a 100% pass rate in the stringent 10V overcharge test and greatly improving the absolute safety of the battery. Furthermore, by limiting the range of ΔT×ρ to 44.9~80.5, the optimal balance between the high rate performance of the positive electrode and the high safety redundancy of the separator is achieved.
[0085] The failures of Comparative Example 1 (pure monocrystalline) and Comparative Example 3 (pure polycrystalline) directly demonstrate the indispensability of gradation: pure monocrystalline, lacking the support and rapid internal diffusion path of polycrystalline, suffers a sharp drop in rate performance; while pure polycrystalline, with microcracks generated at high voltage, exacerbates side reactions, leading to a collapse in thermal stability, which manifests as complete failure (0% pass rate) in overcharge testing. Comparative Example 5 (pure PVDF separator) reveals the fundamental significance of the separator's basic thermal performance: its excessively low pore-closing and membrane-breaking temperatures render the first line of defense for thermal safety ineffective, causing the battery to rapidly lose control under thermal abuse. Particularly crucial is Comparative Example 2, which shows that even if other parameters are acceptable, an excessively narrow thermal safety range leads to a severe deficiency in system buffer capacity, resulting in poor thermal stability.
[0086] The parts of this invention not described in detail are techniques known to those skilled in the art.
[0087] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.
[0088] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.
[0089] In the detailed description and claims, 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, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.
[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. An electrode assembly, characterized in that, The electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet arranged sequentially. The positive electrode sheet includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector. The positive active layer includes a positive active material, which includes a monocrystalline positive active material and a polycrystalline positive active material. The compaction density of the positive electrode sheet is denoted as ρ, and the unit is g / cm³. 3 The safe range of the diaphragm is denoted as ΔT, with the unit being °C, where 44.9 ≤ ΔT × ρ ≤ 80.
5.
2. The electrode assembly according to claim 1, characterized in that, The ρ and ΔT satisfy: 50.5≤ΔT×ρ≤75.
9.
3. The electrode assembly according to any one of claims 1 to 2, characterized in that, The mass ratio of the monocrystalline positive electrode active material to the polycrystalline positive electrode active material is 2~5:5~8; and / or, The compaction density ρ of the positive electrode sheet satisfies 3.4 g / cm³. 3 ~3.8g / cm 3 ; and / or, The pore-closing temperature T1 of the diaphragm is ≥140℃, the pore-breaking temperature T2 of the diaphragm is ≥152℃, and ΔT = T2 - T1 is ≥12℃.
4. The electrode assembly according to claim 1, characterized in that, The chemical general formula of the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O2, where 0.6 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z < 1, and M is selected from at least one of Al, Mg, Zr, Ti, W, Sr, Y, and Nb.
5. The electrode assembly according to claim 1, characterized in that, The Dv50 of the polycrystalline positive electrode active material is 10μm~15μm; and / or, The Dv50 of the single-crystal positive electrode active material is 2.5μm~4.5μm.
6. The electrode assembly according to claim 1 or 4, characterized in that, The specific surface area of the positive electrode active material is 0.5 m². 2 / g~0.9m 2 / g; and / or, The positive electrode active layer further includes a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent, and the binder is 95~96.5:2~3:2~3.
7. The electrode assembly according to claim 1, characterized in that, The diaphragm includes a base membrane and a functional coating located on at least one side surface of the base membrane; The base film includes at least one of polyethylene (PE), polypropylene (PP), and multilayer composite base film PP / PE / PP; The functional coating includes at least one of inorganic ceramic materials, polymers, and composite synergistic materials.
8. The electrode assembly according to claim 7, characterized in that, The functional coating satisfies at least one of the following features (1) to (5): (1) The thickness of the functional coating is 2μm~8μm; (2) The porosity of the functional coating is 50%~70%; (3) The inorganic ceramic material includes at least one of alumina, silicon dioxide, boehmite, barium sulfate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphorus oxide, and layered silicate minerals; (4) The polymer includes at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile, polyimide, poly(p-phenylene terephthalamide), and modified nanocellulose; (5) The composite synergistic material includes at least one of the following: alumina / poly(methyl methacrylate-butyl acrylate), alumina / polyvinylidene fluoride (PVDF), alumina / polyamide-amine (PAMAM), silica / polymethyl methacrylate (PMMA), silica / polyvinylidene fluoride (PVDF), boehmite / polyvinylidene fluoride (PVDF), silica / poly(p-phenylene terephthalamide), boron nitride / poly(p-phenylene terephthalamide), titanium dioxide / polyacrylonitrile, silica / polyacrylonitrile, lithium lanthanum zirconium oxide / polyvinylidene fluoride (PVDF), and silica / polymethyl methacrylate (PMMA).
9. The electrode assembly according to claim 7, characterized in that, The thickness of the base membrane is 9μm to 15μm, and the air permeability of the base membrane is 100s / 100mL to 150s / 100mL.
10. A battery, characterized in that, Includes the electrode assembly as described in any one of claims 1 to 9.