Battery cell and electric device containing the same

Abstract

The application discloses a battery monomer and an electric device containing the same, the battery monomer comprising an electrode assembly, the electrode assembly comprising a positive electrode sheet and a separator film, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material being 2-6.5 mu m; the separator film comprising a porous base material and a porous coating layer arranged on at least one surface of the porous base material, and the porous coating layer comprising a fibrous material and a particulate filler. The application can make the battery have high energy density and good low-temperature power performance and cycle performance.

Description

[0001] This application is a divisional application based on the invention with application number 202311475935.0, application date November 8, 2023, applicant CATL, and invention title "Battery cell and electrical device containing the same". Technical Field

[0002] This application relates to a battery cell and an electrical device containing the same. Background Technology

[0003] In recent years, batteries have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. As the application scope of batteries expands, the demands on them are also increasing. For example, batteries are required to have high thermal stability to prevent fires and explosions, high energy density, and good power performance even at low temperatures. However, to improve thermal stability and reduce internal short circuits, a thicker separator is usually needed. Increasing the separator thickness often reduces the battery's energy density and affects its low-temperature power performance. Therefore, achieving good overall battery performance remains a challenge in current battery development. Summary of the Invention

[0004] This application provides a battery cell and an electrical device containing the same, which enables the battery to have high energy density, good low-temperature power performance, and good cycle performance.

[0005] The first aspect of this application provides a battery cell comprising an electrode assembly, the electrode assembly comprising a positive electrode sheet and a separator, the positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material being 2μm-6.5μm; the separator comprising a porous substrate and a porous coating disposed on at least one surface of the porous substrate, and the porous coating comprising a fibrous material and particulate filler.

[0006] This application enables the battery to have high energy density, good low-temperature power performance, and good cycle performance by adjusting the type and volume distribution of the positive electrode active material, particle size Dv50, and the composition of the porous coating of the separator.

[0007] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material is 2μm-6μm, and can be selected as 2μm-5.3μm.

[0008] By further adjusting the volume distribution particle size Dv50 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened, enabling the positive electrode active material to rapidly consume lithium ions in the electrolyte. This can further increase the lithium ion concentration difference between the negative and positive sides of the separator, increase the driving force for lithium ion transport from the negative to the positive electrode, and thus further improve the low-temperature power performance of the battery. It can also reduce battery side reactions, reduce the battery capacity decay rate, and thus help improve the battery cycle life. Furthermore, it can give the positive electrode sheet a higher compaction density, which is also beneficial to improving the battery energy density.

[0009] In some embodiments, the volume distribution particle size Dv90 of the positive electrode active material is less than or equal to 14.3 μm, and can be selected as 4.4 μm-13.5 μm.

[0010] By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened. This can further increase the lithium ion concentration difference between the negative and positive sides of the separator, increase the driving force for lithium ions to be transported from the negative to the positive electrode, and thus further improve the low-temperature power performance of the battery. It can also reduce battery side reactions, reduce the battery capacity decay rate, and thus help improve the battery cycle life. Furthermore, it can give the positive electrode sheet a higher compaction density, which is also beneficial to improving the energy density of the battery.

[0011] In some embodiments, the volume distribution particle size Dv10 of the positive electrode active material is less than or equal to 3 μm, and can be selected as 1 μm-2 μm.

[0012] By further adjusting the volume distribution particle size Dv10 of the positive electrode active material, battery side reactions can be reduced, the battery capacity decay rate can be decreased, which is beneficial to improving the cycle life of the battery. It can also make the positive electrode sheet have a higher compaction density, which is also beneficial to improving the energy density of the battery.

[0013] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material is 0.8-2.5, and can be optionally 1.3-2.3.

[0014] By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the above range, the compaction density of the positive electrode sheet can be increased, the space utilization of the positive electrode active material can be improved, and thus the energy density of the battery can be improved. It can also reduce the contact resistance between the positive electrode active material particles, reduce the impedance of the battery, and thus help improve the low-temperature power performance of the battery.

[0015] In some embodiments, the positive electrode active material comprises a single-crystal layered lithium-containing transition metal oxide.

[0016] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 5 μm, and can be selected as 2 μm-4 μm.

[0017] In some embodiments, the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 10 μm, and can be selected as 4.4 μm-8 μm.

[0018] In some embodiments, the volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 3 μm, and can be selected as 1 μm-2 μm.

[0019] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide is 0.8-2.5, and can be optionally 1.3-1.5.

[0020] By adjusting the volume distribution, particle size, and particle size distribution of the single-crystal layered lithium-containing transition metal oxide within the above-mentioned range, it is beneficial for the battery to have both good low-temperature power performance and good cycle performance.

[0021] In some embodiments, the positive electrode active material includes single-crystal layered lithium-containing transition metal oxides and polycrystalline layered lithium-containing transition metal oxides.

[0022] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 7 μm-12 μm, and optionally 8 μm-10 μm.

[0023] In some embodiments, the volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide is 12 μm-20 μm, and optionally 13 μm-18 μm.

[0024] In some embodiments, the volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide is 2μm-6μm, and can be optionally 3μm-5μm.

[0025] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 1.1-1.5, and optionally 1.2-1.4.

[0026] In some embodiments, the polycrystalline layered lithium-containing transition metal oxide accounts for 20 wt% to 80 wt% of the weight of the positive electrode active material. By adjusting the weight percentage of the polycrystalline layered lithium-containing transition metal oxide within the above range, the battery can possess high energy density, good low-temperature power performance, and good cycle performance.

[0027] In some embodiments, the aspect ratio of the fiber material is 5-60, optionally 10-30. Adjusting the aspect ratio of the fiber material within the above range helps to form a three-dimensional skeleton structure, and also facilitates the integration of the formed three-dimensional skeleton structure with the particulate filler, thereby improving the heat resistance of the separator and its wetting and retention properties with the electrolyte, thus contributing to improved battery thermal stability and cycle performance.

[0028] In some embodiments, the average length of the fiber material is 100nm-600nm, optionally 200nm-450nm. Adjusting the average length of the fiber material within this range helps it form a three-dimensional skeleton structure, and also facilitates the integration of the formed three-dimensional skeleton structure with the particulate filler, thereby further improving the heat resistance and ion transport characteristics of the separator, thus contributing to enhanced battery thermal stability.

[0029] In some embodiments, the average diameter of the fiber material is 11 nm-40 nm, optionally 12 nm-34 nm. Adjusting the average diameter of the fiber material within this range helps it form a three-dimensional skeleton structure, and also facilitates the integration of the formed three-dimensional skeleton structure with the particulate filler, thereby further improving the ion transport characteristics of the separator and thus contributing to improved battery cycle performance.

[0030] In some embodiments, the fibrous material in the porous coating has a weight content of less than or equal to 40 wt%, optionally 10 wt% to 30 wt%.

[0031] In some embodiments, the particulate filler in the porous coating contains a weight content of 60 wt% or more, optionally 68 wt%-88 wt%.

[0032] The weight content of fiber materials and particulate fillers within the above range is beneficial for the porous coating slurry to have a suitable viscosity, which is conducive to coating. In addition, it is also beneficial for the three-dimensional skeleton structure formed by the fiber materials to overlap with the particulate fillers to form an integrated effect. This enables the porous coating to have a more stable spatial network structure, which can further improve the heat resistance, ion transport characteristics, electrolyte wetting and retention characteristics, and voltage breakdown resistance of the separator, thereby helping to improve the thermal stability and cycle performance of the battery.

[0033] In some embodiments, the fibrous material comprises one or more of organic and inorganic materials. Optionally, the organic material comprises one or more of cellulose nanofibers, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the inorganic material comprises one or more of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0034] In some embodiments, the fibrous material includes nanocellulose, the nanocellulose including modifying groups, the modifying groups including one or more of amino groups, carboxyl groups, aldehyde groups, sulfonic acid groups, boric acid groups and phosphate groups, optionally including one or more of sulfonic acid groups, boric acid groups and phosphate groups.

[0035] In some embodiments, the particulate filler includes one or more of organic particles, inorganic particles, and organic-inorganic framework materials.

[0036] In some embodiments, the particulate filler comprises a first component with a secondary particle morphology and a second component with a primary particle morphology.

[0037] In some embodiments, the average particle size of the first component of the secondary particle morphology is smaller than the average particle size of the second component of the primary particle morphology. This facilitates better utilization of the roles of the first component of the secondary particle morphology and the second component of the primary particle morphology.

[0038] In some embodiments, the average particle size of the first component of the secondary particle morphology is less than 200 nm.

[0039] The average particle size of the first component with secondary particle morphology is within the above range, which can give it a higher specific surface area and better match and overlap with the three-dimensional skeleton structure formed by the fiber material to form an integrated effect. This can increase the heat resistance of the separator and the wetting and retention characteristics of the separator to the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery.

[0040] In some embodiments, the average particle size of the second component of the primary particle morphology is 200 nm to 800 nm.

[0041] When the average particle size of the second component with the primary particle morphology is within the above range, the supporting role of the second component with the primary particle morphology can be better utilized, enabling the porous coating to maintain a stable pore structure during long-term charge and discharge. This is beneficial for reducing the moisture content of the separator and promoting ion transport, while also improving the heat resistance of the separator.

[0042] In some embodiments, the particle size of the primary particles in the first component constituting the secondary particle morphology is 8nm-30nm, and can be selected as 10nm-20nm.

[0043] If the particle size of the primary particles in the first component constituting the secondary particle morphology is within the above range, the first component can have a good secondary particle morphology, which is conducive to the better integration of the first component with the three-dimensional skeleton structure formed by the fiber material to form an integrated effect.

[0044] In some embodiments, the weight content of the first component with secondary particle morphology in the porous coating is greater than the weight content of the second component with primary particle morphology in the porous coating. This facilitates better utilization of the roles of the first component with secondary particle morphology and the second component with primary particle morphology.

[0045] In some embodiments, the weight content of the first component of the secondary particle morphology in the porous coating is 20wt%-85wt%.

[0046] The weight content of the first component with secondary particle morphology within the above range is beneficial for the porous coating slurry to have a suitable viscosity, which is more conducive to coating. In addition, it is also beneficial for the three-dimensional skeleton structure formed with the fiber material to form an integrated effect, thereby enabling the porous coating to have a more stable spatial network structure, which can further improve the tensile strength, puncture resistance and external extrusion resistance of the separator.

[0047] In some embodiments, the second component of the primary particle morphology has a weight content of 5wt%-60wt% in the porous coating.

[0048] When the weight content of the second component with the primary particle morphology is within the above range, the supporting role of the second component with the primary particle morphology can be better utilized, so that the porous coating can maintain a stable pore structure during long-term charge and discharge. This is beneficial to reduce the moisture content of the separator and promote ion transport, while also improving the heat resistance of the separator.

[0049] In some embodiments, the thickness of the porous substrate is less than or equal to 5.5 μm, optionally 3 μm-5 μm. This helps to improve the energy density of the battery.

[0050] In some embodiments, the thickness of the porous coating is less than or equal to 3 μm, optionally between 0.5 μm and 2 μm. This helps to improve the energy density of the battery.

[0051] In some embodiments, the layered lithium-containing transition metal oxide includes Ni, wherein the molar amount of Ni accounts for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; optionally, the molar amount of Ni accounts for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide. This allows the battery to have a high energy density.

[0052] In some embodiments, the upper limit cutoff voltage for charging of the battery cell is greater than or equal to 4.25V, and can be selected as 4.30V-4.45V. This allows the battery to have a high energy density.

[0053] A second aspect of this application provides an electrical device that includes a battery cell from the first aspect of this application.

[0054] The electrical device of this application includes the battery cell provided in this application, and therefore has at least the same advantages as the battery cell. Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0056] Figure 1 The diagram shows a schematic of a battery cell provided in some embodiments of this application.

[0057] Figure 2 This document shows schematic diagrams of battery modules provided in some embodiments of this application.

[0058] Figure 3 This illustration shows a schematic diagram of a battery pack provided in some embodiments of this application.

[0059] Figure 4 yes Figure 3 The diagram shown is an exploded view of the battery pack.

[0060] Figure 5 An exploded view of a battery cell provided in some embodiments of this application is shown.

[0061] Figure 6 A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0062] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell and the electrical device comprising it. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0064] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0067] 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.

[0068] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0069] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0070] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0071] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0072] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0073] In this application, the terms "single-crystal layered lithium-containing transition metal oxide" and "polycrystalline layered lithium-containing transition metal oxide" have meanings known in the art.

[0074] "Layered lithium-containing transition metal oxides with single-crystal morphology" also includes layered lithium-containing transition metal oxides with quasi-single-crystal (also known as near-single-crystal) morphology. Quasi-single-crystal (near-single-crystal) is a well-known term in the art, typically referring to particles formed by the aggregation of a small number (e.g., 2-5) of primary particles. Layered lithium-containing transition metal oxides with polycrystalline morphology refer to layered lithium-containing transition metal oxides with a secondary particle morphology formed by the aggregation of multiple primary particles.

[0075] "Layered lithium-containing transition metal oxides with single-crystal morphology" and "layered lithium-containing transition metal oxides with polycrystalline morphology" can be distinguished by scanning electron microscopy.

[0076] It should be noted that the various parameter tests for separators, positive electrode plates, negative electrode plates, etc. in this application embodiment can be performed either during the battery manufacturing process or after disassembling each component from the manufactured battery.

[0077] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0078] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0079] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0080] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0081] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 2 This is a schematic diagram of battery module 4 as an example. Figure 2 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0082] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0083] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0084] Figure 3 and Figure 4 This is a schematic diagram of battery pack 1 as an example. Figure 3 and Figure 4 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0085] The battery cell provided in this application includes an electrode assembly and an electrolyte. The battery cell provided in this application may include a secondary battery cell, such as a lithium-ion secondary battery cell.

[0086] The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0087] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). In some embodiments, such as... Figure 5 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0088] The electrode assembly includes a positive electrode, a negative electrode, and a separator.

[0089] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material is less than or equal to 6.5 μm.

[0090] The separator includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate, wherein the porous coating includes fibrous material and particulate filler.

[0091] In this application, fiber material refers to material with an aspect ratio of 5 or higher.

[0092] The separator is located between the positive and negative electrodes, and its main function is to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass freely to form a circuit.

[0093] With the application and promotion of rechargeable batteries, people have increasingly higher requirements for battery energy density. Thinning the separator is an effective measure to improve battery energy density. Currently, commercially available rechargeable batteries typically use polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, with melting points between 130℃ and 160℃. Therefore, when the thickness is reduced, the heat resistance of the separator deteriorates, and a significant thermal shrinkage effect occurs when heated, causing direct contact between the positive and negative electrodes inside the battery, leading to internal short circuits and reducing the battery's thermal stability.

[0094] The separator provided in this application embodiment has a porous coating comprising fibrous material and particulate filler on at least one surface of a porous substrate. The fibrous material has advantages such as light weight, high temperature resistance, and small volume change after heating. This reduces the thermal shrinkage of the separator, improves its heat resistance, and thus enables batteries using this separator to have high thermal stability. Furthermore, using fibrous material in the porous coating allows for a thinner design, thereby reducing the overall thickness of the separator and enabling the battery to have a higher energy density.

[0095] However, when a porous coating includes both fibrous materials and particulate fillers, the porosity of the separator will decrease, which will affect ion diffusion and consequently affect the low-temperature power performance of the battery.

[0096] At low temperatures, battery impedance increases, the discharge voltage plateau decreases, and the battery terminal voltage drops rapidly, resulting in a faster decline in the battery's usable capacity and power. Taking batteries for electric vehicles as an example, the acceleration and hill-climbing characteristics of electric vehicles deteriorate rapidly at low temperatures.

[0097] The positive electrode provided in this application uses a positive electrode active material with a volume distribution particle size Dv50 of less than or equal to 6.5 μm, and the positive electrode active material includes layered lithium-containing transition metal oxides. This shortens the diffusion path of lithium ions in the positive electrode active material, thereby rapidly consuming lithium ions transported from the negative electrode to the positive electrode via the separator. At this time, the lithium ion concentration difference between the negative and positive sides of the separator increases, and the driving force for lithium ions to transport from the negative electrode to the positive electrode increases, thereby improving the low-temperature power performance and cycle performance of the battery.

[0098] Therefore, by adjusting the type and volume distribution of the positive electrode active material, the particle size Dv50, and the composition of the porous coating of the separator, the battery can have high energy density, good low-temperature power performance, and good cycle performance.

[0099] In some embodiments, the volumetric particle size Dv50 of the positive electrode active material can be less than or equal to 6 μm, for example, it can be 2 μm, 2.3 μm, 2.6 μm, 3 μm, 3.5 μm, 4 μm, 4.6 μm, 5.3 μm, 6 μm, or any range of the above values. Optionally, the volumetric particle size Dv50 of the positive electrode active material can be 2 μm-6 μm, 2 μm-5.3 μm, 2.3 μm-5.3 μm, 2.6 μm-5.3 μm, or 2.6 μm-4.6 μm.

[0100] By further adjusting the volume distribution particle size Dv50 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened, allowing the positive electrode active material to rapidly consume lithium ions in the electrolyte. This further increases the lithium ion concentration difference between the negative and positive sides of the separator, increasing the driving force for lithium ion transport from the negative to the positive electrode, and thus further improving the low-temperature power performance of the battery. Further adjusting the volume distribution particle size Dv50 of the positive electrode active material can also reduce battery side reactions and decrease the battery capacity decay rate, thereby improving the battery's cycle life. Furthermore, further adjusting the volume distribution particle size Dv50 of the positive electrode active material can also give the positive electrode sheet a higher compaction density, which is also beneficial for improving the battery's energy density.

[0101] In some embodiments, the volumetric particle size Dv90 of the positive electrode active material can be less than or equal to 14.3 μm, for example, it can be 4.4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 13.5 μm, 13.8 μm, 14.3 μm, or any range of the above values. Optionally, the volumetric particle size Dv90 of the positive electrode active material can be 4.4 μm-13.5 μm, 4.4 μm-11 μm, or 4.4 μm-9.0 μm.

[0102] By further adjusting the volume distribution particle size Dv90 of the positive electrode active material, the diffusion path of lithium ions in the positive electrode active material can be further shortened. This can further increase the lithium ion concentration difference between the negative and positive sides of the separator, increasing the driving force for lithium ion transport from the negative to the positive electrode, and thus further improving the low-temperature power performance of the battery. Further adjusting the volume distribution particle size Dv90 of the positive electrode active material can also reduce battery side reactions and decrease the battery capacity decay rate, thereby improving the battery's cycle life. Furthermore, further adjusting the volume distribution particle size Dv90 of the positive electrode active material can also give the positive electrode sheet a higher compaction density, which is also beneficial for improving the battery's energy density.

[0103] In some embodiments, the volumetric particle size Dv10 of the positive electrode active material can be less than or equal to 3 μm, for example, it can be 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, or any range of the above values. Optionally, the volumetric particle size Dv10 of the positive electrode active material can be 1 μm-2 μm or 1.4 μm-2 μm.

[0104] By further adjusting the volume distribution particle size Dv10 of the positive electrode active material, battery side reactions can be reduced, the battery capacity decay rate can be decreased, which is beneficial to improving the cycle life of the battery. It can also make the positive electrode sheet have a higher compaction density, which is also beneficial to improving the energy density of the battery.

[0105] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material can be 0.8-2.5, for example, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.43, 1.52, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or any range of the above values, and can be selected as 1.3-2.3, 1.3-2.1, or 1.3-2.0.

[0106] By further adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the aforementioned range, the compaction density of the positive electrode sheet can be increased, improving the space utilization of the positive electrode active material and thus contributing to the improvement of the battery's energy density. Furthermore, by adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material within the aforementioned range, the contact resistance between the positive electrode active material particles can also be reduced, lowering the battery's impedance and further contributing to improved low-temperature power performance of the battery.

[0107] In some embodiments, the positive electrode active material may include a single-crystal layered lithium-containing transition metal oxide.

[0108] Layered lithium-containing transition metal oxides with a single-crystal morphology typically have a small specific surface area and good interfacial and thermal stability, which can reduce battery side reactions. They also maintain good particle integrity during long-term charge-discharge cycles, thereby reducing the battery capacity decay rate. Therefore, including layered lithium-containing transition metal oxides with a single-crystal morphology in the cathode active material is beneficial for improving battery cycle performance. However, the lithium-ion diffusion coefficient of layered lithium-containing transition metal oxides with a single-crystal morphology is usually low, which can reduce the battery's low-temperature power performance.

[0109] By adjusting the volume distribution particle size Dv50 of the positive electrode active material to be less than or equal to 6.5 μm, the low-temperature power performance of the battery can be improved, while also fully leveraging the effect of the single-crystal morphology of layered lithium-containing transition metal oxides on improving the battery cycle performance.

[0110] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide can be less than or equal to 5 μm, for example, it can be 2 μm, 2.3 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.6 μm, 5 μm, or any combination of the above values, preferably 2 μm-4 μm, and more preferably 2.3 μm-3.5 μm.

[0111] In some embodiments, the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide can be less than or equal to 10 μm, for example, it can be 4.4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination of the above values, and can be selected as 4.4 μm-8 μm, or more preferably 4.4 μm-7 μm.

[0112] In some embodiments, the volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide can be less than or equal to 3 μm, for example, it can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, or any combination of the above values. It can be selected as 1 μm-2 μm, and more preferably 1.4 μm-2 μm.

[0113] The reduced particle size of layered lithium-containing transition metal oxides with single-crystal morphology can further shorten the diffusion path of lithium ions in the positive electrode active material, enabling the positive electrode active material to rapidly consume lithium ions in the electrolyte. This can further increase the lithium ion concentration difference between the negative and positive sides of the separator, increase the driving force for lithium ions to be transported from the negative to the positive electrode, and thus further improve the low-temperature power performance of the battery. However, the cycle performance of the battery will decrease to some extent.

[0114] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the single-crystal morphology of layered lithium-containing transition metal oxides within the above range, it is beneficial for the battery to have both good low-temperature power performance and good cycle performance.

[0115] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide can be 0.8-2.5, for example, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.43, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or any combination of the above values, and can be selected as 1.1-1.8, 1.2-1.6, 1.3-1.5, 1.3-1.43.

[0116] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide within the above range, the compaction density of the positive electrode sheet can be increased, the space utilization of the positive electrode active material can be improved, and thus the energy density of the battery can be improved. It can also reduce the contact resistance between the positive electrode active material particles, reduce the battery impedance, and thus help improve the low-temperature power performance of the battery.

[0117] In some embodiments, the positive electrode active material may include a single-crystal layered lithium-containing transition metal oxide, wherein the weight percentage of the single-crystal layered lithium-containing transition metal oxide in the positive electrode active material may be 95 wt% or more; the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 5 μm, optionally 2 μm-4 μm, and more preferably 2.3 μm-3.5 μm; the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide may be less than... The particle size distribution (Dv10) of the single-crystal layered lithium-containing transition metal oxide can be less than or equal to 3 μm, with a selectable range of 1 μm to 2 μm, and more preferably 1.4 μm to 2 μm. The particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide can be 0.8-2.5, with a selectable range of 1.3-1.5, and more preferably 1.3-1.43. This allows the battery to possess high energy density, good low-temperature power performance, and good cycle performance.

[0118] In some embodiments, the positive electrode active material may simultaneously include the single-crystal layered lithium-containing transition metal oxide and the polycrystalline layered lithium-containing transition metal oxide described above.

[0119] Polycrystalline layered lithium-containing transition metal oxides exhibit higher lithium-ion diffusion coefficients, better electrolyte wettability, and shorter lithium-ion diffusion paths. Therefore, when the cathode active material includes both single-crystal and polycrystalline layered lithium-containing transition metal oxides, the low-temperature power performance of the battery can be further improved.

[0120] Furthermore, compared to single-crystal layered lithium-containing transition metal oxides, when the cathode active material simultaneously comprises both single-crystal and polycrystalline layered lithium-containing transition metal oxides, the cathode electrode can achieve a higher compaction density. Therefore, when the cathode active material simultaneously comprises both single-crystal and polycrystalline layered lithium-containing transition metal oxides, it is also beneficial to improve the energy density of the battery.

[0121] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide can be 7μm-12μm, for example, it can be 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or any combination of the above values, and can be selected as 8μm-10μm.

[0122] In some embodiments, the volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide can be 12μm-20μm, for example, it can be 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or any combination of the above values, and can be selected as 13μm-18μm.

[0123] In some embodiments, the volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide can be 2μm-6μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, or any combination of the above values, and can be selected as 3μm-5μm.

[0124] The reduced particle size of polycrystalline layered lithium-containing transition metal oxides is beneficial for improving the low-temperature power performance of batteries; however, the energy density of the batteries will also decrease to some extent, and the manufacturing cost of the batteries will increase significantly.

[0125] By adjusting the volume distribution particle size Dv50, Dv90 and / or Dv10 of the polycrystalline layered lithium-containing transition metal oxide within the above range, it is beneficial for the battery to have high energy density, good low-temperature power performance, good cycle performance and low manufacturing cost.

[0126] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide can be 1.1-1.5, for example, it can be 1.1, 1.2, 1.3, 1.43, 1.5, or any of the above values, and can be selected as 1.2-1.4.

[0127] By adjusting the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide within the above range, the compaction density of the positive electrode sheet can be increased, the space utilization of the positive electrode active material can be improved, and thus the energy density of the battery can be improved. It can also reduce the contact resistance between the positive electrode active material particles, reduce the battery impedance, and thus help improve the low-temperature power performance of the battery.

[0128] In some embodiments, the weight percentage of the polycrystalline layered lithium-containing transition metal oxide in the positive electrode active material can be 20wt%-80wt%, for example, it can be 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, or any of the above values.

[0129] Increasing the content of polycrystalline layered lithium-containing transition metal oxides is beneficial to improving the low-temperature power performance of batteries; however, the cycle performance of batteries will decrease to some extent.

[0130] By adjusting the weight percentage of polycrystalline layered lithium-containing transition metal oxides within the above range, batteries can possess high energy density, good low-temperature power performance, and good cycle performance.

[0131] In some embodiments, the positive electrode active material may simultaneously include both the single-crystal layered lithium-containing transition metal oxide and the polycrystalline layered lithium-containing transition metal oxide; the weight percentage of the polycrystalline layered lithium-containing transition metal oxide in the positive electrode active material may be 20wt%-80wt%; the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 5μm, optionally 2μm-4μm, and more preferably 2.3μm-3.5μm; the volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 10μm, optionally 4.4μm-8μm, and more preferably 4.4μm-7μm; the volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 3μm, optionally 1μm-2μm, and more preferably 1.4μm- The particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide can be 0.8-2.5, optionally 1.3-1.5, and more preferably 1.3-1.43; the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide can be 7μm-12μm, optionally 8μm-10μm; the volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide can be 12μm-20μm, optionally 13μm-18μm; the volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide can be 2μm-6μm, optionally 3μm-5μm; the particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide can be 1.1-1.5, optionally 1.2-1.4. This allows batteries to have low manufacturing costs, high energy density, good low-temperature power performance, and good cycle performance.

[0132] In some embodiments, the layered lithium-containing transition metal oxide may include Ni. The molar amount of Ni may account for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; optionally, the molar amount of Ni may account for more than 80% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; more preferably, the molar amount of Ni may account for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide. This can further improve the energy density of the battery.

[0133] In some embodiments, layered lithium-containing transition metal oxides may include Li a Ni b Coc M d O e A f Wherein, 0 < a ≤ 1.2; 0.8 ≤ b < 1, optionally, 0.9 ≤ b < 1; 0 < c < 1; 0 < d < 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; A includes, but is not limited to, one or more of N, F, S, and Cl. This can further improve the energy density of the battery.

[0134] In some embodiments, as an example, layered lithium-containing transition metal oxides may include, but are not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.06 Mn 0.04 O2, LiNi 0.92 Co 0.06 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 One or more of O2.

[0135] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0136] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0137] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. An example of a metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymeric material substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0138] The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0139] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode binders, and positive electrode conductive agents in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0140] The Dv10, Dv50, and Dv90 values ​​of positive electrode active materials, single-crystal layered lithium-containing transition metal oxides, and polycrystalline layered lithium-containing transition metal oxides are all well-known in the art and can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer (such as the Malvern Mastersizer 3000) according to GB / T 19077-2016. The physical definition of Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90%; the physical definition of Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50%; and the physical definition of Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10%.

[0141] [Isolation membrane]

[0142] The separator includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate, wherein the porous coating includes fibrous material and particulate filler.

[0143] In some embodiments, the fibrous material may include one or more of organic and inorganic materials.

[0144] Optionally, in some embodiments, the organic material may include one or more of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers.

[0145] Optionally, in some embodiments, the inorganic material may include one or more of halloysite nanotubes, nanorod alumina, nanorod boehmite, nanorod silica, and glass fiber.

[0146] In some embodiments, the fibrous material may include nanocellulose.

[0147] Nanocellulose refers to cellulose with any dimension within the nanometer range (e.g., within 100 nm), possessing both the characteristics of cellulose and those of nanoparticles. Nanocellulose can be a high-molecular-weight nanomaterial extracted from natural sources such as wood and cotton through one or more chemical, physical, or biological methods. It boasts advantages such as wide availability, low cost, biodegradability, high modulus, and high specific surface area, making it an excellent alternative to traditional petrochemical resources and effectively alleviating environmental pollution and petrochemical resource shortages. Nanocellulose also exhibits good high-temperature resistance and minimal volume change upon heating, thereby improving the heat resistance of separators. Furthermore, its low density reduces battery weight and increases gravimetric energy density.

[0148] In addition, the structure formed by combining nanocellulose with particulate fillers can have tiny nanopores, which can reduce current leakage and enable the separator to have both good electrolyte wetting and retention properties as well as good voltage breakdown resistance.

[0149] Optionally, nanocellulose may include cellulose nanofibers, which have the advantage of high crystallinity, thereby better improving the heat resistance of the separator and enhancing the thermal stability of the battery.

[0150] In some embodiments, nanocellulose may include hydroxyl groups and modified groups.

[0151] In some embodiments, the modifying groups of nanocellulose may include one or more of amino, carboxyl, aldehyde, sulfonic acid, boric acid, and phosphate groups. Optionally, the modifying groups of nanocellulose may include one or more of sulfonic acid, boric acid, and phosphate groups.

[0152] Nanocellulose has the aforementioned specific modifying groups, which can effectively improve the heat resistance of the separator and enhance the thermal stability of the battery; on the other hand, it can also improve the bonding strength between the porous coating and the porous substrate.

[0153] Nanocellulose possesses the aforementioned specific modifying groups, which also facilitate the integration of nanocellulose with granular fillers to form an integrated effect. This enables the porous coating to have a stable spatial network structure, thereby helping to improve the wetting and retention characteristics of the separator with electrolyte, enhance the ion transport characteristics and voltage breakdown resistance of the separator, and also facilitate the matching of high-voltage positive electrode active materials, further improving the energy density of the battery.

[0154] In addition, the presence of modified groups can reduce the proportion of hydroxyl groups, which is beneficial for the porous coating slurry to have a suitable viscosity, making it more conducive to coating, thereby improving the production efficiency of the separator and the uniformity of the porous coating.

[0155] In some embodiments, the molar ratio of the modified group to the hydroxyl group can be from 1:4 to 4:1, and optionally from 2:3 to 7:3. A molar ratio of the modified group to the hydroxyl group within the above range can further improve the heat resistance, ion transport characteristics, and electrolyte wetting and retention properties of the separator, thereby contributing to improved battery thermal stability and cycle performance.

[0156] The types of modifying groups in nanocellulose can be determined using infrared spectroscopy. For example, the infrared spectrum of the material can be tested to identify its characteristic peaks, thereby determining the types of modifying groups. Specifically, the material can be analyzed using infrared spectroscopy with instruments and methods known in the art, such as an infrared spectrometer (e.g., the Nicolet IS10 Fourier transform infrared spectrometer) according to the General Rules for Infrared Spectroscopic Analysis in GB / T 6040-2019.

[0157] In some embodiments, the aspect ratio of the fiber material can be 5-60, preferably 10-30. Adjusting the aspect ratio of the fiber material within the above range helps the fiber material form a three-dimensional skeleton structure, and also facilitates the integration of the formed three-dimensional skeleton structure with the particulate filler to achieve an integrated effect. This can improve the heat resistance of the separator and the wetting and retention characteristics of the separator to the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery.

[0158] In some embodiments, the average length of the fiber material can be 100nm-600nm, optionally 200nm-450nm. By adjusting the average length of the fiber material within the above range, it is helpful for the fiber material to form a three-dimensional skeleton structure, and it is also beneficial for the formed three-dimensional skeleton structure to overlap with the particulate filler to form an integrated effect, thereby further improving the heat resistance and ion transport characteristics of the separator, thus helping to improve the thermal stability of the battery.

[0159] In some embodiments, the average diameter of the fiber material can be 11 nm-40 nm, optionally 12 nm-34 nm. By adjusting the average diameter of the fiber material within the above range, it is helpful for the fiber material to form a three-dimensional skeleton structure, and it is also beneficial for the formed three-dimensional skeleton structure to overlap with the particulate filler to form an integrated effect, thereby further improving the ion transport characteristics of the separator and thus helping to improve the cycle performance of the battery.

[0160] The average length and average diameter of the fiber material can be determined by the following method: A 3.6 mm × 3.6 mm sample is cut from any region of the separator. The microstructure of the porous coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300). A high vacuum mode is selected, with a working voltage of 3 kV and a magnification of 30,000x to obtain a SEM image. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for length statistics. Each test region has a size of 0.5 μm × 0.5 μm. The average length of the fiber material obtained from each test region is then taken as the average length of the fiber material. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for diameter statistics using Nano Measurer particle size distribution statistical software. Each test region has a size of 0.5 μm × 0.5 μm. The average diameter of the fiber material obtained from each test region is then taken as the average diameter of the fiber material.

[0161] In some embodiments, the weight content of the fibrous material in the porous coating may be less than or equal to 40 wt%, and optionally 10 wt% to 30 wt%.

[0162] In some embodiments, the particulate filler content in the porous coating may be greater than or equal to 60 wt%, optionally 68 wt%-88 wt%.

[0163] The weight content of fiber materials and particulate fillers within the above range is beneficial for the porous coating slurry to have a suitable viscosity, which is conducive to coating. In addition, it is also beneficial for the three-dimensional skeleton structure formed by the fiber materials to overlap with the particulate fillers to form an integrated effect. This enables the porous coating to have a more stable spatial network structure, which can further improve the heat resistance, ion transport characteristics, electrolyte wetting and retention characteristics, and voltage breakdown resistance of the separator, thereby helping to improve the thermal stability and cycle performance of the battery.

[0164] In some embodiments, nanocellulose can be obtained by the following method: providing cellulose powder with a whiteness ≥80%; mixing and reacting the obtained cellulose powder with a modified solution, followed by washing to remove impurities, to obtain cellulose nanowhiskers; adjusting the pH of the obtained cellulose nanowhiskers to neutral, and then grinding and cutting them to obtain nanocellulose.

[0165] Optionally, the cellulose powder with a whiteness ≥80% can be obtained commercially or by chemical methods (e.g., acid hydrolysis, alkali treatment, Tempo catalytic oxidation), biological methods (e.g., enzymatic treatment), or mechanical methods (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization). The fiber raw materials used to prepare the cellulose powder with a whiteness ≥80% may include one or more of the following: cotton fiber (e.g., cotton fibers, kapok fibers), hemp fiber (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, abaca fiber, etc.), palm fiber, wood fiber, bamboo fiber, and grass fiber.

[0166] In some embodiments, the cellulose powder with a whiteness of ≥80% can also be prepared by the following method: after the fiber raw material is opened and slag is removed, it is cooked with an alkaline solution (e.g., an aqueous solution of NaOH, the concentration of which can be 4wt% to 20wt%, optionally 5wt% to 15wt%), and then sequentially subjected to water washing to remove impurities (e.g., water washing 3 to 6 times), bleaching (e.g., sodium hypochlorite and / or hydrogen peroxide can be used), acid washing to remove impurities, water washing to remove impurities, water removal, and air drying to obtain cellulose powder.

[0167] In some embodiments, the modified solution may be an acid solution (e.g., aqueous sulfuric acid solution, aqueous boric acid solution, aqueous phosphoric acid solution, aqueous acetic acid solution) or an alkaline solution (e.g., urea organic solvent solution). Optionally, the modified solution is an acid solution.

[0168] Optionally, the concentration of the acid solution can be from 5 wt% to 80 wt%. When the modifying solution is an aqueous sulfuric acid solution, the concentration of the acid solution can be from 40 wt% to 80 wt%, thereby obtaining cellulose powder with sulfonic acid groups. When the modifying solution is an aqueous boric acid solution, the concentration of the acid solution can be from 5 wt% to 10 wt%, thereby obtaining cellulose powder with boric acid groups. When the modifying solution is an aqueous phosphoric acid solution, the concentration of the acid solution can be from 45 wt% to 75 wt%, thereby obtaining cellulose powder with phosphoric acid groups. When the modifying solution is an aqueous acetic acid solution, the concentration of the acid solution can be from 40 wt% to 80 wt%, thereby obtaining cellulose powder with carboxylic acid groups.

[0169] Optionally, the urea organic solvent solution is a urea xylene solution, thereby obtaining cellulose powder with amine groups.

[0170] In some embodiments, the weight ratio of cellulose powder to modified solution may be from 1:2.5 to 1:50, and optionally from 1:5 to 1:30.

[0171] When sulfuric acid aqueous solution is used as the modifying solution, the weight ratio of cellulose powder to acid solution can be 1:5 to 1:30. When boric acid aqueous solution is used as the modifying solution, the weight ratio of cellulose powder to acid solution can be 1:20 to 1:50. When phosphoric acid aqueous solution is used as the modifying solution, the weight ratio of cellulose powder to acid solution can be 1:5 to 1:30. When acetic acid aqueous solution is used as the modifying solution, the weight ratio of cellulose powder to acid solution can be 1:5 to 1:30. When urea organic solvent solution is used as the modifying solution, the weight ratio of cellulose powder to urea organic solvent solution can be 1:4 to 1:40.

[0172] In some embodiments, when the modified solution is an acidic solution, the reaction can be carried out at a temperature not exceeding 80°C, preferably at a temperature between 30°C and 60°C, and the reaction time between the cellulose powder and the modified solution can be 0.5 h to 4 h, preferably 1 h to 3 h.

[0173] In some embodiments, when the modified solution is an alkaline solution, the reaction can be carried out at 100°C to 145°C, and the reaction time between the cellulose powder and the modified solution can be 1 h to 5 h.

[0174] In some embodiments, grinding can be performed using a grinding machine, and cutting can be performed using a high-pressure homogenizer. By adjusting the grinding parameters of the grinding machine (e.g., grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose with different average diameters and / or different average lengths can be obtained.

[0175] In some embodiments, the particulate filler may include one or more of organic particles, inorganic particles, and organic-inorganic framework materials.

[0176] In some embodiments, the particulate filler may include a first component with a secondary particle morphology and a second component with a primary particle morphology.

[0177] The first component with secondary particle morphology can better integrate with the three-dimensional skeleton structure formed by the fiber material to achieve a unified effect. This enables the porous coating to have a more stable spatial network structure, thereby further improving the heat resistance of the separator and enhancing the thermal stability of the battery.

[0178] The second component with primary particle morphology helps reduce the moisture content of the porous coating and improves the ion transport characteristics of the porous coating, thereby helping to improve the cycle performance of the battery.

[0179] In some embodiments, the average particle size of the first component with secondary particle morphology is smaller than the average particle size of the second component with primary particle morphology. This is beneficial for better utilizing the roles of the first component with secondary particle morphology and the second component with primary particle morphology.

[0180] In some embodiments, the average particle size of the first component with secondary particle morphology is less than 200 nm, and can be selected as 50 nm-200 nm. Having an average particle size within this range allows the first component to have a higher specific surface area and better match and overlap with the three-dimensional skeleton structure formed by the fiber material to form an integrated effect. This increases the heat resistance of the separator and its wetting and retention properties with the electrolyte, thereby helping to improve the thermal stability and cycle performance of the battery.

[0181] In some embodiments, the particle size of the primary particles in the first component constituting the secondary particle morphology can be 8nm-30nm, and optionally 10nm-20nm. Having the particle size of the primary particles in the first component constituting the secondary particle morphology within the above range allows the first component to have a good secondary particle morphology, which is beneficial for better integration of the first component with the three-dimensional skeleton structure formed by the fiber material to achieve a unified effect.

[0182] In some embodiments, the average particle size of the second component with the primary particle morphology is 200 nm-800 nm, optionally 200 nm-400 nm. When the average particle size of the second component with the primary particle morphology is within the above range, its supporting role can be better utilized, enabling the porous coating to maintain a stable pore structure during long-term charge-discharge processes. This, in turn, helps reduce the moisture content of the separator and promotes ion transport, while also improving the heat resistance of the separator.

[0183] The average particle size of the first component of the secondary particle morphology and the second component of the primary particle morphology can be tested using equipment and methods known in the art. For example, the microstructure of the porous coating in the sample can be mapped using a scanning electron microscope (e.g., ZEISS Sigma 300). Referring to JY / T 0584-2020, scanning electron microscope (SEM) images of the porous coating of the isolation membrane can be obtained. The longest diagonal length of the particles can be measured from the SEM images, and then the average value can be taken. The number of selected particles can be more than 100.

[0184] In some embodiments, the weight content of the first component with secondary particle morphology in the porous coating can be greater than the weight content of the second component with primary particle morphology in the porous coating. This is beneficial for better utilizing the roles of the first component with secondary particle morphology and the second component with primary particle morphology.

[0185] In some embodiments, the weight content of the first component with secondary particle morphology in the porous coating can be 20wt%-85wt%. A weight content of the first component with secondary particle morphology within this range is beneficial for the porous coating slurry to have a suitable viscosity, which is more conducive to coating. Furthermore, it facilitates the integration with the three-dimensional skeleton structure formed by the fibrous material, thereby enabling the porous coating to have a more stable spatial network structure, which further improves the tensile strength, puncture resistance, and resistance to external extrusion of the separator.

[0186] In some embodiments, the weight content of the second component with primary particle morphology in the porous coating can be 5wt%-60wt%. Within this range, the weight content of the second component with primary particle morphology can better leverage its supporting role, enabling the porous coating to maintain a stable pore structure during long-term charge-discharge processes. This, in turn, helps reduce the moisture content of the separator and promotes ion transport, while also improving the heat resistance of the separator.

[0187] In some embodiments, the first component of the secondary particle morphology may include one or more of inorganic particles and organic particles.

[0188] Optionally, the inorganic particles include boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), and silicon oxides (SiO2). x One or more of the following: (0 < x ≤ 2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium dioxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2). More preferably, the inorganic particles include boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), and silicon oxide (SiO2). x (0<x≤2), one or more of titanium oxide (TiO2), zinc oxide (ZnO), cerium oxide (CeO2) and barium titanate (BaTiO3).

[0189] Alternatively, the organic particles may include one or more of polystyrene and polyacrylic wax.

[0190] In some embodiments, the first component with secondary particle morphology may include inorganic particles with secondary particle morphology, and the crystal form of the inorganic particles with secondary particle morphology includes at least two of α-crystal form, θ-crystal form, γ-crystal form, and η-crystal form. Optionally, the crystal form of the inorganic particles with secondary particle morphology includes at least two of α-crystal form, θ-crystal form, and γ-crystal form.

[0191] The inorganic particles with the α-crystal form and secondary particle morphology exhibit diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the weight content of the inorganic particles with the α-crystal form and secondary particle morphology in the secondary particle morphology may be ≥1.2 wt%, optionally from 1.2 wt% to 10 wt%, and more preferably from 1.2 wt% to 5 wt%, based on the total weight of the inorganic particles with the secondary particle morphology.

[0192] The inorganic particles with a secondary particle morphology of θ crystal form exhibit diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the weight content of the inorganic particles with a secondary particle morphology of θ crystal form in the total weight of the inorganic particles with a secondary particle morphology may be ≥50 wt%, optionally from 60 wt% to 85 wt%, and more preferably from 60 wt% to 82.5 wt%, based on the total weight of the inorganic particles with a secondary particle morphology.

[0193] The γ-crystalline secondary particle morphology inorganic particles exhibit diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the weight content of the γ-crystalline secondary particle morphology inorganic particles in the secondary particle morphology inorganic particles may be ≥10 wt%, optionally from 15 wt% to 60 wt%, and more preferably from 15 wt% to 35 wt%, based on the total weight of the secondary particle morphology inorganic particles.

[0194] The inorganic particles with an η-crystal secondary morphology exhibit diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the weight content of the η-crystal secondary morphology inorganic particles in the total weight of the secondary morphology inorganic particles may be ≤5wt%, optionally ≤2wt%, and more preferably ≤1wt%, based on the total weight of the secondary morphology inorganic particles.

[0195] Inorganic particles with α-crystal secondary particle morphology have advantages such as high hardness, good heat resistance, low dielectric constant, high safety and high true density; inorganic particles with θ-crystal secondary particle morphology have moderate specific surface area and hardness, which can better improve the heat resistance and ion transport characteristics of the separator at the same time; inorganic particles with γ-crystal and η-crystal secondary particle morphology have the advantage of large specific surface area.

[0196] Therefore, selecting inorganic particles with different crystalline secondary particle morphologies can help improve at least one of the following properties of the separator: heat resistance, adhesion strength, and wetting and retention properties of the electrolyte.

[0197] In some embodiments, the first component with secondary particle morphology may include inorganic particles with secondary particle morphology, and the crystal forms of the inorganic particles with secondary particle morphology include α-crystal form, θ-crystal form, γ-crystal form, and η-crystal form. The weight content of the inorganic particles with secondary particle morphology of α-crystal form in the inorganic particles with secondary particle morphology may be 1.2 wt% to 5 wt%, the weight content of the inorganic particles with secondary particle morphology of θ-crystal form in the inorganic particles with secondary particle morphology may be 60 wt% to 82.5 wt%, the weight content of the inorganic particles with secondary particle morphology of γ-crystal form in the inorganic particles with secondary particle morphology may be 15 wt% to 35 wt%, and the weight content of the inorganic particles with secondary particle morphology of η-crystal form in the inorganic particles with secondary particle morphology may be ≤1 wt%, all based on the total weight of the inorganic particles with secondary particle morphology.

[0198] The X-ray diffraction pattern of inorganic particles with secondary particle morphology can be obtained by the following method: After drying the inorganic particles with secondary particle morphology, grind them in a mortar (such as an agate mortar) for 30 minutes, and then use an X-ray diffractometer (such as a Miniflex 600-C) to obtain the X-ray diffraction pattern. During the test, a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scanning range of 5°–80° can be used.

[0199] In some embodiments, the first component with a secondary particle morphology may include inorganic particles with a secondary particle morphology. These inorganic particles can be prepared by: subjecting a precursor solution of inorganic particles to an oxidation reaction via high-pressure sputtering, followed by heating at 600°C to 900°C (e.g., 1 hour to 3 hours) to form small particles, and then drying and shaping at 150°C to 250°C (e.g., 30 minutes to 60 minutes) to obtain the inorganic particles with a secondary particle morphology. The average particle size of the inorganic particles with a secondary particle morphology can be adjusted by regulating sputtering parameters, such as temperature and time.

[0200] In some embodiments, the shape of the first component of the secondary particle morphology may include one or more of the following: string-like, chain-like, amorphous, spherical, quasi-spherical, and pyramidal.

[0201] In some embodiments, the second component with a primary particle morphology comprises inorganic particles with a primary particle morphology.

[0202] Optionally, the inorganic particles with a primary particle morphology may include one or more of the following: inorganic particles with a dielectric constant of 5 or higher, inorganic particles with ionic conductivity but without ion storage, and inorganic particles capable of undergoing electrochemical reactions.

[0203] Optionally, inorganic particles having a dielectric constant of 5 or higher include one or more of the following: boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb (Mg3Nb) 2 / 3 PMN-PT (PbTiO3) and its modified inorganic particles are used. Optionally, the inorganic particles can be modified chemically and / or physically. Chemical modification methods include coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the porous coating to have a more stable and uniform spatial network structure. Furthermore, by selecting coupling agents, surfactants, or polymers with specific functional groups to modify the inorganic particles, it is also helpful to improve the wetting and retention properties of the porous coating in the electrolyte and enhance the adhesion of the porous coating to the porous substrate.

[0204] Optionally, the inorganic particles that are ion-conductive but do not store ions include one or more of the following: Li3PO4, lithium titanium phosphate (Li... x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Lix7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 The following equations are given: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can further improve the ion transport characteristics of the separator.

[0205] Optionally, the inorganic particles capable of undergoing electrochemical reactions include one or more of the following: lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0206] In some embodiments, the second component of the primary particle morphology includes inorganic particles with a primary particle morphology. The crystal form of the inorganic particles with the primary particle morphology may include one or more of α-crystal form and γ-crystal form, optionally including α-crystal form. Inorganic particles with an α-crystal form of the primary particle morphology have advantages such as high hardness, good heat resistance, low dielectric constant, high safety and high true density, thereby further improving the heat resistance of porous coatings.

[0207] In some embodiments, the crystal form of the inorganic particles with primary particle morphology includes α crystal form, and the weight content of the inorganic particles with primary particle morphology of α crystal form in the inorganic particles with primary particle morphology can be ≥90wt%, optionally from 95wt% to 100wt%, based on the total weight of the inorganic particles with primary particle morphology.

[0208] In some embodiments, the shape of the second component of the primary particle morphology may include at least one of spherical, dumbbell-shaped, and polygonal shapes.

[0209] In some embodiments, the porous coating may further include a non-particulate binder. This application does not impose any particular limitation on the type of non-particulate binder; any known material with good adhesion can be selected. Optionally, the non-particulate binder includes aqueous solution-based binders, which have the advantages of good thermodynamic stability and environmental friendliness, thereby facilitating the preparation and application of the porous coating slurry. As an example, aqueous solution-based binders may include, but are not limited to, one or more of aqueous solution-based acrylic resins (e.g., acrylic acid, methacrylic acid, sodium acrylate monomer homopolymers or copolymers with other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymers, and polyacrylamide.

[0210] Optionally, the content of non-particulate binder in the porous coating can be less than or equal to 3 wt%, based on the total weight of the porous coating. The porous coating can have a stable spatial network structure, thereby enabling the release membrane to maintain high adhesion while reducing the amount of binder used.

[0211] In some embodiments, the thickness of the porous coating can be less than or equal to 3 μm, optionally between 0.5 μm and 2 μm. This helps to improve the energy density of the battery. In this application, the thickness of the porous coating refers to the thickness of the porous coating located on one side of the porous substrate.

[0212] In some embodiments, the separator may further include an adhesive layer. The adhesive layer may be disposed on at least a portion of the surface of the porous coating and / or on at least a portion of the surface of the porous substrate where the porous coating is not disposed. The adhesive layer not only prevents the porous coating from detaching, improving battery reliability, but also improves the interface between the separator and the electrode, enhancing the battery's cycle performance.

[0213] Alternatively, the adhesive layer may include a granular adhesive.

[0214] Optionally, the binder includes one or more of the following: acrylate monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorinated olefin monomer homopolymers or copolymers. The comonomer includes, but is not limited to, one or more of the following: acrylate monomers, acrylic monomers, olefin monomers, halogenated olefin monomers, fluoroether monomers, etc.

[0215] Optionally, the binder comprises vinylidene fluoride polymers, such as homopolymers of vinylidene fluoride monomer (VDF) and / or copolymers of vinylidene fluoride monomer and comonomers. The comonomer may be one or more of olefin monomers, fluorinated olefin monomers, chlorinated olefin monomers, acrylate monomers, acrylic monomers, and fluoroether monomers. Optionally, the comonomer may include one or more of the following: trifluoroethylene (VF3), trifluorochloroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-m-dioxacyclopentene), and perfluoro(2,2-dimethyl-1,3-m-dioxacyclopentene) (PDD).

[0216] This application does not impose any particular limitation on the material of the porous substrate; any known substrate with good chemical and mechanical stability can be selected. For example, the porous substrate may include one or more of porous polyolefin-based resin membranes (e.g., polyethylene, polypropylene, polyvinylidene fluoride, etc.), porous glass fibers, and porous nonwoven fabrics. The porous substrate can be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0217] In some embodiments, the thickness of the porous substrate can be less than or equal to 5.5 μm, and can be selected as 3 μm-5 μm. The porous coating provided in this application embodiment helps to improve the heat resistance of the separator, thereby allowing for the use of a thinner porous substrate, which in turn helps to improve the energy density of the battery.

[0218] In some embodiments, the longitudinal thermal shrinkage rate of the separator at 150°C for 0.5 h may be less than or equal to 5%, and may be selected as 0.5% to 3%.

[0219] In some embodiments, the transverse thermal shrinkage rate of the separator at 150°C for 0.5 h may be less than or equal to 5%, and may be selected as 0.5% to 3%.

[0220] The separator exhibits low thermal shrinkage in both the lateral and longitudinal directions at a high temperature of 150℃, thereby improving the thermal stability and reliability of the battery.

[0221] The heat shrinkage rate of the release liner can be tested as follows: The release liner is punched into samples with a width of 50mm and a length of 100mm using a punching machine. These samples are then placed on A4 paper and fixed. The A4 paper containing the samples is then placed on corrugated paper with a thickness of 1mm to 5mm. The temperature of the forced-air drying oven is set to 150℃. After the temperature reaches the set temperature and stabilizes for 30 minutes, the A4 paper placed on the corrugated paper is placed in the oven and the timer is started. After the set time (0.5h in this application), the width a1 and length a2 of the release liner are measured. The transverse heat shrinkage rate of the release liner at 150℃ for 0.5h is calculated as [(50-a1) / 50]×100%, and the longitudinal heat shrinkage rate of the release liner at 150℃ for 0.5h is calculated as [(100-a2) / 100]×100%.

[0222] In some embodiments, the air permeability of the separator membrane may be less than or equal to 300 s / 100 mL, and may be selected from 100 s / 100 mL to 250 s / 100 mL.

[0223] The air permeability of the separator membrane can be tested as follows: at 25°C, measure the time required for 100 mL of air to pass through the separator membrane. The testing instrument can be a Kumagai KRK air permeability meter.

[0224] In some embodiments, the porosity of the separator can be 30%-35%, optionally 30%-33%.

[0225] The porosity of the separator can be tested according to GB / T 24586-2009. The test method may include the following steps: cut the separator into circular pieces of a certain area, measure the thickness, and calculate the apparent volume V1 of the separator according to the formula for the volume of a cylinder; referring to GB / T 24586-2009, using inert nitrogen gas as the medium, employ the gas displacement method and a true density meter to measure the true volume V2 of the separator. The porosity of the separator = (V1-V2) / V1×100%. The testing instrument can be the AccuPyc II 1340 fully automatic true density meter from Micromeritics, USA.

[0226] It should be noted that the porous coating parameters of the above-mentioned separator are all the porous coating parameters of one side of the porous substrate. When the porous coating is disposed on both sides of the porous substrate, if the porous coating parameters of either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0227] [Negative electrode plate]

[0228] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0229] The negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0230] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymer substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0231] The negative electrode active material may be any negative electrode active material known in the art for use in batteries. In some embodiments, as an example, the negative electrode active material may be one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0232] As an example, silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. In some embodiments, silicon-based materials may include silicon and one or more of alkali metals and alkaline earth metals. Optionally, the alkali metal element includes Li. Optionally, the alkaline earth metal element includes Mg. As an example, the silicon-based material may be a silicon-based material pre-intercalated with alkali metals and / or alkaline earth metals, such as a silicon-based material pre-intercalated with Li and / or Mg.

[0233] As an example, tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxides, and tin alloys.

[0234] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0235] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0236] In some embodiments, the negative electrode film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0237] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0238] The negative electrode sheet can be prepared by dispersing the negative electrode active material, optional negative electrode binder, optional negative electrode conductive agent, and optional other additives in a solvent and stirring evenly to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing drying, cold pressing, and other processes to form the negative electrode sheet. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0239] [Electrolytes]

[0240] A single battery cell includes an electrolyte.

[0241] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more of solid electrolytes, gel electrolytes, and liquid electrolytes (i.e., electrolyte solutions).

[0242] In some embodiments, the electrolyte may be an electrolyte solution, which may include an electrolyte salt and a solvent.

[0243] In some embodiments, the electrolyte salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0244] In some embodiments, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0245] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0246] In some embodiments, the upper limit cutoff voltage for charging a single battery cell can be greater than or equal to 4.25V, optionally between 4.30V and 4.45V. This allows the battery to have a high energy density.

[0247] Methods for preparing battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the aforementioned electrolyte. After vacuum sealing, settling, and formation processes, a battery cell is obtained. Multiple battery cells can further be connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0248] This application also provides an electrical device, which includes the battery provided in this application embodiment. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0249] Electrical devices can choose the type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0250] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0251] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0252] Example

[0253] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0254] Preparation of nanocellulose

[0255] After the cotton linters are opened and the slag is removed by a cotton opener, they are cooked at 150°C for 2 hours using a 5wt% NaOH aqueous solution. Then, the cotton cellulose powder with a whiteness of ≥85% is obtained by sequentially washing and removing impurities (washing 3 times), bleaching with sodium hypochlorite, washing and removing impurities with dilute hydrochloric acid, washing and removing impurities (washing 1 time), water removal, and air drying.

[0256] 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt% sulfuric acid aqueous solution and reacted at 55℃ to 60℃ for 1 h to 1.5 h. After the reaction was completed, the mixture was then sequentially washed with water (washed 3 times), filtered, and deacidified to obtain cellulose nanofibers with sulfonic acid groups.

[0257] The pH of cellulose nanofibers with sulfonic acid groups was first adjusted to neutral using a 10wt% NaOH aqueous solution. Then, the nanofibers were ground using a grinder and then cut into nanoscale pieces using a high-pressure homogenizer to obtain cellulose nanofibers with sulfonic acid modified groups, and the molar ratio of sulfonic acid groups to hydroxyl groups was 5:3.

[0258] During the preparation process, nanocellulose with different average diameters and / or different average lengths can be obtained by adjusting the processing parameters of the grinding mill and the cutting parameters of the high-pressure homogenizer.

[0259] The molar ratio of modified groups to surface hydroxyl groups in nanocellulose can be determined by the following method: The hydroxyl values ​​(equivalent to milligrams of potassium hydroxide per gram of sample) of the raw cellulose and nanocellulose are tested according to the phthalic anhydride method in GB / T12008.3-2009. The resulting values ​​are in mg KOH / g, which are then converted to mmol / g as the hydroxyl content. The content of modified groups (i.e., the content of modified hydroxyl groups) is obtained by subtracting the hydroxyl content of nanocellulose from the hydroxyl content of the raw cellulose. The molar ratio of modified groups to hydroxyl groups can then be calculated.

[0260] Example 1

[0261] Preparation of positive electrode sheet

[0262] LiNi, the positive electrode active material 0.9 Co 0.06 Mn 0.04 O2, conductive agent Super P, and binder polyvinylidene fluoride are mixed in a weight ratio of 96.5:1.5:2, and an appropriate amount of solvent NMP is added. The mixture is stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry is coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0263] Positive electrode active material LiNi 0.9 Co 0.06 Mn0.04 The O2 has a single crystal morphology, and the volume distribution of the positive electrode active material has particle sizes of Dv50 of 2.3 μm, Dv90 of 4.4 μm, Dv10 of 1.4 μm, and (Dv90-Dv10) / Dv50 of 1.30.

[0264] Preparation of negative electrode sheet

[0265] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (bestowed in a weight ratio of 96.4:0.7:1.8:1.1) are mixed evenly in an appropriate amount of deionized water to obtain a cathode slurry. The cathode slurry is then coated onto a copper foil (cathode current collector), and the cathode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0266] Preparation of the separating membrane

[0267] Provides a porous PE substrate with a thickness of 5μm.

[0268] Preparation of porous coating slurry: Nanocellulose, alumina (first component), alumina (second component), and polyacrylic acid binder are mixed evenly in an appropriate amount of deionized water at a weight ratio of 20:55:23:2 to obtain porous coating slurry.

[0269] The average length of the nanocellulose is 420 nm, the average diameter is 24 nm, and the aspect ratio is 17.5.

[0270] The first component alumina has a secondary particle morphology with an average particle size of 150 nm. The contents of α-crystal, θ-crystal, γ-crystal and η-crystal forms in the first component alumina are 1.5 wt%, 74.7 wt%, 23.3 wt% and 0.5 wt%, respectively, based on the total weight of the first component alumina.

[0271] The second component alumina has a primary particle morphology with an average particle size of 350 nm. The crystal form of the second component alumina is mainly α crystal, with the α crystal accounting for more than 99 wt% of the total weight of the second component alumina.

[0272] Preparation of adhesive layer slurry: Mix polyvinylidene fluoride monomer (VDF) homopolymer particles, polymethyl methacrylate, dispersant sodium carboxymethyl cellulose (CMC) and surfactant in an appropriate amount of deionized water at a weight ratio of 87:8:3:2 to obtain adhesive layer slurry.

[0273] Coating: The prepared porous coating slurry is coated onto one surface of the PE porous substrate using a coating machine. An adhesive layer slurry is then coated onto both the porous coating surface and the uncoated surface of the PE porous substrate. After drying and slitting, a release film is obtained. The porous coating has a thickness of 0.8 μm, and the total thickness of the release film is 8 μm.

[0274] Preparation of electrolyte

[0275] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 30:70 to obtain an organic solvent. Fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0276] Battery manufacturing

[0277] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the porous coating of the separator facing the positive electrode. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery is obtained. The battery dimensions are 50mm × 194mm × 110mm.

[0278] Comparative Example 1

[0279] The battery was prepared using a method similar to that in Example 1, except that the preparation process of the separator was different.

[0280] Provides a porous PE substrate with a thickness of 7μm.

[0281] Preparation of porous coating slurry: Alumina and binder polyacrylic acid are mixed evenly in an appropriate amount of deionized water at a weight ratio of 94:6 to obtain a porous coating slurry. The alumina has a primary particle morphology with a volume distribution particle size Dv50 of 800 nm, and the alumina crystal form is mainly α crystal, accounting for more than 99 wt% of the total weight of alumina.

[0282] Preparation of adhesive layer slurry: Mix polyvinylidene fluoride monomer (VDF) homopolymer particles, polymethyl methacrylate, dispersant sodium carboxymethyl cellulose (CMC) and surfactant in an appropriate amount of deionized water at a weight ratio of 87:8:3:2 to obtain adhesive layer slurry.

[0283] Coating: The prepared porous coating slurry is coated onto both surfaces of the PE porous substrate using a coating machine. The adhesive layer slurry is then coated onto the porous coating. After drying and slitting, a release film is obtained. The thickness of each porous coating is 1.5 μm, and the total thickness of the release film is 12 μm.

[0284] Performance testing of the separator

[0285] The porosity of the separator was tested according to GB / T 24586-2009. The test method is as follows: the separator was cut into circular pieces of a certain area, the thickness was measured, and the apparent volume V1 of the separator was calculated according to the formula for the volume of a cylinder; referring to GB / T24586-2009, inert gas nitrogen was used as the medium, and the true volume V2 of the separator was measured using a true density meter by the gas displacement method. The porosity of the separator is calculated as (V1-V2) / V1×100%. The testing instrument was an AccuPyc II 1340 fully automatic true density meter from Micromeritics, USA. For accuracy, the average value of five parallel samples was taken as the test result.

[0286] The air permeability of the separator membrane was tested as follows: at 25°C, the time required for 100 mL of air to pass through the separator membrane was measured. The testing instrument used was a Kumagai KRK air permeability meter. For accuracy, the average value of five parallel samples was taken as the test result.

[0287] The ionic conductivity of the separator was obtained by AC impedance spectroscopy. The test method is as follows: the separator was cut into circular pieces of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it was sealed to form a coin cell. AC impedance spectroscopy was performed using an electrochemical workstation to obtain the ionic conductivity of the separator. The electrochemical workstation used was a Shanghai Chenhua CHI 660C electrochemical workstation with an AC signal frequency range of 0.01Hz to 1MHz and a sinusoidal potential amplitude of 5mV. For accuracy, the average value of five parallel samples was taken as the test result.

[0288] The heat shrinkage rate of the release liner was tested as follows: The release liner was punched into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on A4 paper and fixed. The A4 paper containing the samples was then placed on corrugated paper with a thickness of 1 mm to 5 mm. The temperature of the forced-air drying oven was set to 150℃. After the temperature reached the set temperature and stabilized for 30 minutes, the A4 paper placed on the corrugated paper was placed in and the timer was started. After the set time (0.5 h in this application) was reached, the width a1 and length a2 of the release liner were measured. The transverse heat shrinkage rate of the release liner at 150℃ and 0.5 h was calculated as [(50-a1) / 50]×100%, and the longitudinal heat shrinkage rate of the release liner at 150℃ and 0.5 h was calculated as [(100-a2) / 100]×100%. For accuracy, the average value of the five parallel samples was taken as the test result.

[0289] Battery volumetric energy density test

[0290] At 25°C, the battery prepared above was charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After standing for 5 minutes, the battery was discharged at 0.33C to 2.8V, and the discharge energy Q was obtained. The volumetric energy density of the battery (Wh / L) = discharge energy Q / battery volume V.

[0291] Table 1 shows the performance test results of the separator in Example 1 and Comparative Example 1, and the volumetric energy density test results of the battery.

[0292] Table 1

[0293]

[0294] As can be seen from the test results in Table 1, the porous coating of the separator provided in this application embodiment includes nanocellulose and particulate filler, which can make the separator have both low thickness and low thermal shrinkage rate, thereby improving the space utilization of the battery and thus helping the battery to have high volumetric energy density and high thermal stability.

[0295] Example 2

[0296] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 The O2 has a single crystal morphology, and the volume distribution of the positive electrode active material has particle sizes of Dv50 of 3.5 μm, Dv90 of 7 μm, Dv10 of 2 μm, and (Dv90-Dv10) / Dv50 of 1.43.

[0297] Example 3

[0298] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 O2 includes single-crystal and polycrystalline morphologies. The weight percentage of single-crystal particles is 80 wt%, and the weight percentage of polycrystalline particles is 20 wt%. The volume distribution particle sizes of the positive electrode active material are Dv50 4.6 μm, Dv90 9.0 μm, Dv10 2.0 μm, and (Dv90-Dv10) / Dv50 1.52.

[0299] The volume distribution of the positive electrode active material with single crystal morphology has particle sizes of Dv50 of 2.3 μm, Dv90 of 4.4 μm, Dv10 of 1.4 μm, and (Dv90-Dv10) / Dv50 of 1.30.

[0300] The volume distribution of the positive electrode active material with polycrystalline morphology has particle sizes of Dv50 of 8.5 μm, Dv90 of 14.5 μm, Dv10 of 4 μm, and (Dv90-Dv10) / Dv50 of 1.24.

[0301] Example 4

[0302] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 O2 includes single-crystal and polycrystalline morphologies. The weight percentage of single-crystal particles is 40 wt%, and the weight percentage of polycrystalline particles is 60 wt%. The volume distribution particle sizes of the positive electrode active material are Dv50 5.3 μm, Dv90 13.5 μm, Dv10 1.5 μm, and (Dv90-Dv10) / Dv50 2.26.

[0303] The volume distribution of the positive electrode active material with single crystal morphology is as follows: particle size Dv50 is 3.5 μm, Dv90 is 7 μm, Dv10 is 2 μm, and (Dv90-Dv10) / Dv50 is 1.43.

[0304] The volume distribution of the positive electrode active material with polycrystalline morphology has particle sizes of Dv50 of 8.5 μm, Dv90 of 14.5 μm, Dv10 of 4 μm, and (Dv90-Dv10) / Dv50 of 1.24.

[0305] Example 5

[0306] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 O2 includes single-crystal and polycrystalline morphologies. The weight percentage of single-crystal particles is 30 wt%, and the weight percentage of polycrystalline particles is 70 wt%. The volume distribution particle sizes of the positive electrode active material are Dv50 6.0 μm, Dv90 13.8 μm, Dv10 1.6 μm, and (Dv90-Dv10) / Dv50 2.03.

[0307] The volume distribution of the positive electrode active material with single crystal morphology is as follows: particle size Dv50 is 3.5 μm, Dv90 is 7 μm, Dv10 is 2 μm, and (Dv90-Dv10) / Dv50 is 1.43.

[0308] The volume distribution of the positive electrode active material with polycrystalline morphology has particle sizes of Dv50 of 8.5 μm, Dv90 of 14.5 μm, Dv10 of 4 μm, and (Dv90-Dv10) / Dv50 of 1.24.

[0309] Example 6

[0310] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 O2 includes single-crystal and polycrystalline morphologies. The weight percentage of single-crystal particles is 20 wt%, and the weight percentage of polycrystalline particles is 80 wt%. The volume distribution particle sizes of the positive electrode active material are Dv50 6.5 μm, Dv90 14.3 μm, Dv10 1.9 μm, and (Dv90-Dv10) / Dv50 1.91.

[0311] The volume distribution of the positive electrode active material with single crystal morphology is as follows: particle size Dv50 is 3.5 μm, Dv90 is 7 μm, Dv10 is 2 μm, and (Dv90-Dv10) / Dv50 is 1.43.

[0312] The volume distribution of the positive electrode active material with polycrystalline morphology has particle sizes of Dv50 of 8.5 μm, Dv90 of 14.5 μm, Dv10 of 4 μm, and (Dv90-Dv10) / Dv50 of 1.24.

[0313] Example 7

[0314] The battery was prepared using a method similar to that in Example 1, except that the average length of the nanocellulose in the preparation of the separator was 210 nm and the average diameter was 12 nm.

[0315] Example 8

[0316] The battery was prepared using a method similar to that in Example 1, except that the average length of the nanocellulose in the preparation of the separator was 595 nm and the average diameter was 34 nm.

[0317] Example 9

[0318] The battery was prepared using a method similar to that in Example 1, except that the average length of the nanocellulose in the preparation of the separator was 175 nm and the average diameter was 10 nm.

[0319] Example 10

[0320] The battery was prepared using a method similar to that in Example 1, except that the average length of the nanocellulose in the preparation of the separator was 770 nm and the average diameter was 44 nm.

[0321] Example 11

[0322] The battery was prepared using a method similar to that in Example 1, except that the average particle size of the first component aluminum oxide in the preparation of the separator was 250 nm, and the average particle size of the second component aluminum oxide was 200 nm.

[0323] Example 12

[0324] The battery was prepared using a method similar to that in Example 1, except that the weight ratio of nanocellulose, first component alumina, second component alumina, and binder polyacrylic acid in the preparation of the separator was 20:35:43:2.

[0325] Comparative Example 2

[0326] The battery was prepared using a method similar to that in Example 1, the difference being the positive electrode active material LiNi. 0.9 Co 0.06 Mn 0.04 O2 includes single-crystal and polycrystalline morphologies. The weight percentage of single-crystal particles is 20 wt%, and the weight percentage of polycrystalline particles is 80 wt%. The volume distribution particle sizes of the positive electrode active material are Dv50 8.5 μm, Dv90 14.5 μm, Dv10 4 μm, and (Dv90-Dv10) / Dv50 1.24.

[0327] The volume distribution of the positive electrode active material with single crystal morphology has particle sizes of Dv50 of 4.6 μm, Dv90 of 9.0 μm, Dv10 of 2.0 μm, and (Dv90-Dv10) / Dv50 of 1.52.

[0328] The volume distribution of the positive electrode active material with polycrystalline morphology has particle sizes of Dv50 of 10 μm, Dv90 of 16.5 μm, Dv10 of 4.5 μm, and (Dv90-Dv10) / Dv50 of 1.2.

[0329] Low-temperature power performance testing of batteries

[0330] At 25°C, the battery prepared above was charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After standing for 5 minutes, the battery was discharged at 0.33C to 2.8V, and the discharge capacity A and discharge energy B were recorded. At 25°C, the battery prepared above was charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After standing for 30 minutes, the battery was discharged at 0.33C for 90 minutes, the SOC was adjusted to 50%, and the voltage U1 before discharge was recorded. Then the temperature was adjusted to -25°C, and the battery was left to stand for 2 hours until the battery temperature stabilized. Then it was discharged at a constant current of 1C for 10 seconds, and the voltage U2 after discharge was recorded.

[0331] The battery power W = lower cutoff voltage × (U1 - lower cutoff voltage) / (U1 - U2) / 1C.

[0332] Power density P = battery power W / battery discharge energy B, unit W / Wh. Lower cutoff voltage is 2.8V.

[0333] For accuracy, the average of five parallel samples was taken as the test result.

[0334] Battery cycle performance test

[0335] At 25°C, the battery prepared above was charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage until the current was ≤0.05C. After standing for 30 minutes, the battery was discharged at 0.5C to 2.8V. The battery was subjected to a cyclic charge-discharge test according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the battery decreased to 80% of the discharge capacity of the first cycle. The number of cycles at this point was taken as the cycle life of the battery.

[0336] For accuracy, the average of two parallel samples is taken as the test result.

[0337] Table 2 presents the low-temperature power performance and cycle performance test results of the batteries of Examples 1 to 12 and Comparative Example 2.

[0338] Table 2

[0339]

[0340] As shown in Table 2, the battery using the separator of Example 1 also meets the requirement that the positive electrode active material of the positive electrode sheet includes layered lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material is less than or equal to 6.5 μm. In this case, the battery can also have good low-temperature power performance and good cycle performance.

[0341] The test results in Table 2 also show that the battery performance can be further improved by further adjusting the composition of the porous coating of the separator.

[0342] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, comprising an electrode assembly, the electrode assembly comprising a positive electrode and a separator, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which is a mixture of single-crystal layered lithium-containing transition metal oxide and polycrystalline layered lithium-containing transition metal oxide. The polycrystalline layered lithium-containing transition metal oxide accounts for 60wt%-80wt% of the weight of the positive electrode active material. The volume distribution particle size Dv50 of the positive electrode active material is 2μm-6.5μm, the volume distribution particle size Dv90 of the positive electrode active material is less than or equal to 14.3μm, and the volume distribution particle size Dv10 of the positive electrode active material is less than or equal to 3μm. The separator includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate. The porous coating includes fibrous material and particulate filler.

2. The battery cell according to claim 1, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 2μm-6μm.

3. The battery cell according to claim 2, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 2μm-5.3μm.

4. The battery cell according to any one of claims 1-3, characterized in that, The particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material is 0.8-2.

5.

5. The battery cell according to any one of claims 1-4, characterized in that, The positive electrode active material also satisfies one or more of the following conditions (1) to (3): (1) The volume distribution particle size Dv90 of the positive electrode active material is 4.4 μm-13.5 μm; (2) The volume distribution particle size Dv10 of the positive electrode active material is 1μm-2μm; (3) The particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material is 1.3-2.

3.

6. The battery cell according to claim 1, characterized in that, The volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 5 μm.

7. The battery cell according to claim 6, characterized in that, The volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide is 2μm-4μm.

8. The battery cell according to any one of claims 6-7, characterized in that, The single-crystal layered lithium-containing transition metal oxide also satisfies one or more of the following conditions (1) to (3): (1) The volume distribution particle size Dv90 of the single-crystal morphology of the layered lithium-containing transition metal oxide is less than or equal to 10 μm; (2) The volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide is less than or equal to 3 μm; (3) The particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide is 0.8-2.

5.

9. The battery cell according to any one of claims 6-8, characterized in that, The single-crystal layered lithium-containing transition metal oxide also satisfies one or more of the following conditions (1) to (3): (1) The volume distribution particle size Dv90 of the single-crystal layered lithium-containing transition metal oxide is 4.4 μm-8 μm; (2) The volume distribution particle size Dv10 of the single-crystal layered lithium-containing transition metal oxide is 1μm-2μm; (3) The particle size distribution (Dv90-Dv10) / Dv50 of the single-crystal layered lithium-containing transition metal oxide is 1.3-1.

5.

10. The battery cell according to claim 1, characterized in that, The polycrystalline layered lithium-containing transition metal oxide satisfies one or more of the following conditions (1) to (4): (1) The volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 7μm-12μm; (2) The volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide is 12μm-20μm; (3) The volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide is 2μm-6μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 1.1-1.

5.

11. The battery cell according to claim 10, characterized in that, The polycrystalline layered lithium-containing transition metal oxide satisfies one or more of the following conditions (1) to (4): (1) The volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 8μm-10μm; (2) The volume distribution particle size Dv90 of the polycrystalline layered lithium-containing transition metal oxide is 13μm-18μm; (3) The volume distribution particle size Dv10 of the polycrystalline layered lithium-containing transition metal oxide is 3μm-5μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the polycrystalline layered lithium-containing transition metal oxide is 1.2-1.

4.

12. The battery cell according to any one of claims 1-11, characterized in that, The aspect ratio of the fiber material is 5-60; and / or, The average length of the fiber material is 100nm-600nm; and / or, The average diameter of the fiber material is 11nm-40nm.

13. The battery cell according to any one of claims 1-12, characterized in that, The aspect ratio of the fiber material is 10-30; and / or, The average length of the fiber material is 200nm-450nm; and / or, The average diameter of the fiber material is 12nm-34nm.

14. The battery cell according to any one of claims 1-13, characterized in that, The fibrous material in the porous coating contains less than or equal to 40 wt% by weight; and / or, The particulate filler in the porous coating has a weight content of greater than or equal to 60 wt%.

15. The battery cell according to claim 14, characterized in that, The fibrous material in the porous coating has a weight content of 10wt%-30wt%; and / or, The particulate filler in the porous coating has a weight content of 68wt%-88wt%.

16. The battery cell according to any one of claims 1-14, characterized in that, The fiber material includes one or more of organic and inorganic materials.

17. The battery cell according to claim 16, characterized in that, The organic material includes one or more of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers; and / or, The inorganic material includes one or more of halloysite nanotubes, nanorod alumina, nanorod boehmite, nanorod silica, and glass fiber.

18. The battery cell according to any one of claims 1-17, characterized in that, The fiber material includes nanocellulose, which includes modifying groups, including one or more of amino, carboxyl, aldehyde, sulfonic acid, boric acid, and phosphate groups.

19. The battery cell according to claim 18, characterized in that, The modified groups include one or more of sulfonic acid groups, boric acid groups, and phosphate groups.

20. The battery cell according to any one of claims 1-19, characterized in that, The particulate filler includes one or more of organic particles, inorganic particles, and organic-inorganic framework materials.

21. The battery cell according to claim 20, characterized in that, The particulate filler comprises a first component with a secondary particle morphology and a second component with a primary particle morphology.

22. The battery cell according to claim 21, characterized in that, The average particle size of the first component of the secondary particle morphology is smaller than the average particle size of the second component of the primary particle morphology.

23. The battery cell according to claim 21 or 22, characterized in that, The average particle size of the first component with the secondary particle morphology is less than 200 nm; and / or, The average particle size of the second component with the primary particle morphology is 200 nm to 800 nm.

24. The battery cell according to any one of claims 21-22, characterized in that, The primary particles in the first component constituting the secondary particle morphology have a particle size of 8nm-30nm.

25. The battery cell according to claim 24, characterized in that, The primary particles in the first component constituting the secondary particle morphology have a particle size of 10nm-20nm.

26. The battery cell according to any one of claims 21-25, characterized in that, The weight content of the first component of the secondary particle morphology in the porous coating is greater than the weight content of the second component of the primary particle morphology in the porous coating.

27. The battery cell according to any one of claims 21-26, characterized in that, The first component of the secondary particle morphology has a weight content of 20wt%-85wt% in the porous coating; and / or, the second component of the primary particle morphology has a weight content of 5wt%-60wt% in the porous coating.

28. The battery cell according to any one of claims 1-27, characterized in that, The thickness of the porous substrate is less than or equal to 5.5 μm; and / or, The thickness of the porous coating is less than or equal to 3 μm.

29. The battery cell according to claim 28, characterized in that, The thickness of the porous substrate is 3μm-5μm; and / or, The thickness of the porous coating is 0.5μm-2μm.

30. The battery cell according to any one of claims 1-29, characterized in that, The layered lithium-containing transition metal oxide includes Ni element, and the molar amount of Ni element accounts for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

31. The battery cell according to claim 30, characterized in that, The molar amount of Ni accounts for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

32. The battery cell according to any one of claims 1-31, characterized in that, The upper limit cutoff voltage for charging of the battery cell is greater than or equal to 4.25V.

33. The battery cell according to claim 32, characterized in that, The upper limit cutoff voltage for charging the battery cell is 4.30V-4.45V.

34. An electrical appliance, characterized in that, Includes the battery cell described in any one of claims 1-33.

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