Battery cell and preparation method therefor, positive electrode sheet, and electric device

Abstract

A battery cell and a preparation method therefor, a positive electrode sheet, and an electric device. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a current collector, a first positive electrode active material layer arranged on at least one side of the surface of the current collector, and a second positive electrode active material layer arranged on the side of the surface of the first positive electrode active material layer facing away from the current collector. The volume distribution particle size Dv99 of a first positive electrode active material in the first positive electrode active material layer is less than or equal to 3 μm. When the state of charge (SOC) of the battery cell is 0%, the compacted density of the positive electrode sheet is 3.55-3.80 g / cm3. The material of the current collector comprises an aluminum foil, wherein the aluminum foil comprises aluminum, silicon, and iron, and the mass ratio of aluminum, silicon, and iron in the aluminum foil is limited within a certain range. The present application improves energy density of a battery while ensuring a long service life of the battery.

Description

Battery cells and their preparation methods, positive electrode plates and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202510307421.7, filed on March 14, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a battery cell and its preparation method, a positive electrode sheet, and an electrical device. Background Technology

[0004] In recent years, with the increasingly wide range of applications, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0005] With the application and promotion of batteries, higher requirements have been placed on battery energy density and lifespan. Summary of the Invention

[0006] This application addresses the aforementioned issues and aims to provide a battery cell, its preparation method, a positive electrode, and an electrical device thereof. The goal is to improve the energy density of the battery while maintaining a long battery life.

[0007] To achieve the above objectives, in a first aspect, this application provides a battery cell, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a current collector, a first positive active material layer disposed on at least one side of the current collector surface, and a second positive active material layer disposed on the side of the first positive active material layer opposite to the current collector; the volume distribution particle size Dv99 of the first positive active material in the first positive active material layer is ≤3μm; and the compaction density of the positive electrode is 3.55~3.80g / cm³ when the state of charge (SOC) of the battery cell is 0%. 3 The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The mass percentage of aluminum in the aluminum foil is greater than or equal to 99.3%, the mass percentage of silicon in the aluminum foil is 0.05% to 0.20%, and the mass percentage of iron in the aluminum foil is 0.20% to 0.40%.

[0008] Therefore, the high positive electrode compaction density in this application's technical solution is beneficial for improving the battery's energy density. Furthermore, by controlling the aluminum, silicon, and iron content in the aluminum foil within the aforementioned range, the elongation at break of the electrode is improved, reducing damage to the current collector under high compaction density, thereby extending the battery cell's lifespan. Simultaneously, the presence of a first positive electrode active material layer helps reduce electrolyte corrosion of the current collector, further extending the battery cell's lifespan. By controlling the volume distribution particle size Dv99 of the first positive electrode active material, the larger particle size is kept small, preventing damage to the current collector from larger particles under high compaction density, further extending the battery cell's lifespan.

[0009] In any embodiment, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) the first positive electrode active material includes lithium phosphate; (3) the mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%. Therefore, setting a suitable mass percentage of lithium phosphate in the first positive electrode active material layer is beneficial to improving the energy density of the battery.

[0010] In any embodiment, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) the lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.2 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr. Therefore, the volume distribution particle size of the first positive electrode active material is within the aforementioned suitable range, which helps to avoid damage such as scratching to the current collector during the coating process of the first positive electrode active material layer. Using the aforementioned lithium-containing phosphate is beneficial for improving the energy density of the battery.

[0011] In any embodiment, the lithium-containing phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.1, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr. Using the above-mentioned lithium-containing phosphate is beneficial for improving the energy density of the battery.

[0012] In any embodiment, the first positive electrode active material layer further includes a conductive agent. The addition of the conductive agent helps to improve the conductivity of the first positive electrode active material layer and promotes the uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0013] In any embodiment, the conductive agent satisfies at least one of the following conditions: (1) the conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) the average length of the conductive agent is 1-15 μm; (3) the average diameter of the conductive agent is 30-60 nm; and (4) the mass percentage of the conductive agent in the first positive electrode active material layer is 15%-20%. Using conductive agents with a large aspect ratio, such as carbon nanotubes and carbon nanofibers, is beneficial for promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer, reducing the aggregation of the first positive electrode active material, and improving the uniformity of the coating of the first positive electrode active material layer. The average length, average diameter, and mass percentage of the aforementioned suitable conductive agent are all conducive to forming an interwoven network, further promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0014] In any embodiment, the thickness of the first positive electrode active material layer is 0.5–3.5 μm. The thickness of the first positive electrode active material layer within this suitable range helps reduce electrolyte corrosion of the current collector, extending the lifespan of the battery cell while maintaining a high energy density.

[0015] In any embodiment, the tensile strength of the current collector is 250–330 MPa; and / or, the elongation at break of the positive electrode sheet is 2%–2.4%. The tensile strength of the current collector within this suitable range is beneficial for reducing deformation and breakage of the current collector under high pressure density conditions of the positive electrode film. The elongation at break of the positive electrode sheet within this suitable range is beneficial for extending the battery's lifespan.

[0016] In any embodiment, the second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide. This material has a high specific capacity and can improve the energy density of the battery cell.

[0017] In any embodiment, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R eThe material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.2. This material has a high specific capacity and a relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0018] In any embodiment, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The materials, M, include at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.2. These materials possess high specific capacity and relatively stable crystal structure, which is beneficial for increasing the compaction density of the positive electrode film, thereby improving the energy density and lifespan of the battery cell.

[0019] Secondly, this application provides a method for preparing a battery cell, including a positive electrode preparation step, wherein the positive electrode preparation step includes:

[0020] Provide current collectors;

[0021] A first positive electrode active material layer is formed on at least one side of the current collector surface; the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm.

[0022] A second positive electrode active material layer is formed on the side of the first positive electrode active material layer facing away from the current collector.

[0023] The compaction density of the positive electrode sheet ranges from 3.55 to 3.80 g / cm³. 3 ;

[0024] The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

[0025] The preparation method is simple and conducive to industrial application.

[0026] In any embodiment, the step of forming a first positive electrode active material layer on at least one side of the current collector surface includes: coating a first positive electrode active material layer slurry onto at least one side of the current collector surface to form the first positive electrode active material layer; wherein the solid content of the first positive electrode active material layer slurry is 12% to 20%; and / or, the viscosity of the first positive electrode active material layer slurry is 1500 to 3000 mPa·s. This suitable solid content and suitable slurry viscosity range are beneficial for reducing damage to the current collector during the coating process of the first positive electrode active material layer and also for ensuring uniform coating.

[0027] Thirdly, this application provides a positive electrode sheet, comprising a current collector, a first positive electrode active material layer disposed on at least one side of the surface of the current collector, and a second positive electrode active material layer disposed on the surface of the first positive electrode active material layer facing away from the current collector; the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm; and the compaction density of the positive electrode sheet is 3.55~3.80g / cm³ when the state of charge (SOC) of the battery cell is 0%. 3 The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

[0028] Therefore, the high positive electrode compaction density in this application's technical solution is beneficial for improving the battery's energy density. Furthermore, by controlling the aluminum, silicon, and iron content in the aluminum foil within the aforementioned range, the elongation at break of the electrode is improved, reducing damage to the current collector under high compaction density, thereby extending the battery cell's lifespan. Simultaneously, the presence of a first positive electrode active material layer helps reduce electrolyte corrosion of the current collector, further extending the battery cell's lifespan. By controlling the volume distribution particle size Dv99 of the first positive electrode active material, the larger particle size is minimized, preventing damage to the current collector from larger particles under high compaction density, further extending the battery cell's lifespan.

[0029] In any embodiment, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) the first positive electrode active material includes lithium phosphate; (3) the mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%. Therefore, setting a suitable mass percentage of lithium phosphate in the first positive electrode active material layer is beneficial to improving the energy density of the battery.

[0030] In any embodiment, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) the lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.2 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr. Therefore, the volume distribution particle size of the first positive electrode active material is within the aforementioned suitable range, which helps to avoid damage such as scratching to the current collector during the coating process of the first positive electrode active material layer. Using the aforementioned lithium-containing phosphate is beneficial for improving the energy density of the battery.

[0031] In any embodiment, the lithium-containing phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr. Using the above-mentioned lithium-containing phosphate is beneficial for improving the energy density of the battery.

[0032] In any embodiment, the first positive electrode active material layer further includes a conductive agent. The addition of the conductive agent helps to improve the conductivity of the first positive electrode active material layer and promotes the uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0033] In any embodiment, the conductive agent satisfies at least one of the following conditions: (1) the conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) the average length of the conductive agent is 1-15 μm; (3) the average diameter of the conductive agent is 30-60 nm; and (4) the mass percentage of the conductive agent in the first positive electrode active material layer is 15%-20%. Using conductive agents with a large aspect ratio, such as carbon nanotubes and carbon nanofibers, is beneficial for promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer, reducing the aggregation of the first positive electrode active material, and improving the uniformity of the coating of the first positive electrode active material layer. The appropriate length, diameter, and mass percentage of the conductive agent described above are all conducive to forming an interwoven network, further promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0034] In any embodiment, the thickness of the first positive electrode active material layer is 0.5–3.5 μm. The thickness of the first positive electrode active material layer within this suitable range helps reduce electrolyte corrosion of the current collector, extending the lifespan of the battery cell while maintaining a high energy density.

[0035] In any embodiment, the tensile strength of the current collector is 250–330 MPa; and / or, the elongation at break of the positive electrode sheet is 2%–2.4%. The tensile strength of the current collector within this suitable range is beneficial for reducing deformation and breakage of the current collector under high pressure density conditions of the positive electrode film. The elongation at break of the positive electrode sheet within this suitable range is beneficial for extending the battery's lifespan.

[0036] In any embodiment, the second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide. This material has a high specific capacity and can improve the energy density of the battery cell.

[0037] In any embodiment, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material, M, includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8<m<1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.2. This material has a high specific capacity and a relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0038] In any embodiment, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R eThe materials, M, include at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.2. These materials possess high specific capacity and relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0039] Fourthly, this application proposes an electrical device comprising a battery cell according to the first aspect of this application. Attached Figure Description

[0040] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0041] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0042] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0043] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0044] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0045] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0046] Figure 7 is a cross-sectional view of the positive electrode sheet in Embodiment 1 of this application.

[0047] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0048] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its preparation method, positive electrode, and electrical device of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0049] 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.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0052] 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.

[0053] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0054] 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.

[0055] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. When there are multiple battery cells, they are connected in series, parallel, or mixed through a busbar. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0056] In some embodiments, the battery can be a battery module; when there are multiple battery cells, the multiple battery cells 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 in 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 a part of the vehicle's floor, or a portion of the housing can be at least a part of the vehicle's crossbeams and longitudinal beams.

[0057] In some implementations, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0058] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0059] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0060] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0061] In some embodiments, the aforementioned battery cells and battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0062] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0063] In one embodiment of this application, a battery cell is provided.

[0064] A single battery cell includes electrode components and an electrolyte.

[0065] The electrode assembly includes a positive electrode and a negative electrode. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting.

[0066] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0067] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0068] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0069] In a first aspect, embodiments of this application provide a battery cell, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a current collector, a first positive active material layer disposed on at least one side of the current collector surface, and a second positive active material layer disposed on the side of the first positive active material layer opposite to the current collector. The volume distribution particle size Dv99 of the first positive active material in the first positive active material layer is ≤3 μm. Under the condition that the state of charge (SOC) of the battery cell is 0%, the compaction density of the positive electrode is 3.55–3.80 g / cm³. 3The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The mass percentage of aluminum in the aluminum foil is greater than or equal to 99.3%, the mass percentage of silicon in the aluminum foil is 0.05% to 0.20%, and the mass percentage of iron in the aluminum foil is 0.20% to 0.40%.

[0070] The compaction density of the electrode is a well-known concept in the art and can be tested using methods known in the art. With the state of charge (SOC) of the battery cell at 0%, the electrode is removed from the battery, and a certain area of ​​the electrode is taken. The mass and thickness of the electrode and the current collector after removing the film layer are measured respectively. The compaction density of the electrode is calculated according to the following formula: Compaction density of the electrode = (Electrode mass - Current collector mass) / [(Electrode thickness - Current collector thickness) × Electrode area]. In this application, the film layer of the positive electrode includes a first positive electrode active material layer and a second positive electrode active material layer.

[0071] In this application, the material of the current collector, and the content of aluminum, silicon, and iron in the aluminum foil, can be tested using instruments and methods known in the art. For example, the aluminum foil can be placed in an appropriate amount of concentrated nitric acid solvent for digestion and digested using the plate digestion method. Finally, the solvent is dissolved and extracted with hydrochloric acid, and the resulting solution is then brought to an appropriate volume and quantitatively tested using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0072] For example, under the condition that the state of charge (SOC) of a single battery cell is 0%, the compaction density of the positive electrode sheet can be 3.55 g / cm³. 3 3.6g / cm 3 3.65g / cm 3 3.7g / cm 3 3.75g / cm 3 3.80g / cm 3 Or a range of values ​​consisting of any two of the above values.

[0073] For example, the mass percentage of silicon in the aluminum foil can be any two values ​​within the range of 0.05%, 0.1%, 0.15%, 0.2%, or higher. The mass percentage of iron in the aluminum foil can be any two values ​​within the range of 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or higher. The mass percentage of aluminum in the aluminum foil can be any two values ​​within the range of 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, or higher. The aluminum foil typically also includes unavoidable impurity elements, and the sum of the mass percentages of all elements and the impurity elements is 100%.

[0074] Using a high positive electrode compaction density is beneficial for improving the energy density of the battery. However, high compaction density can easily damage the current collector. Therefore, in this embodiment, by controlling the content of aluminum, silicon, and iron in the aluminum foil within the aforementioned range, it is beneficial to improve the elongation at break of the current collector electrode, reduce damage to the current collector under high compaction density, and thus extend the service life of the battery cell. However, considering that a high iron content in the aluminum foil may lead to electrolyte corrosion of the current collector, the first positive electrode active material layer in this embodiment serves as a protective layer, which helps to reduce electrolyte corrosion of the current collector, thereby further extending the service life of the battery cell while maintaining high energy density. Furthermore, controlling the volume distribution particle size Dv99 of the first positive electrode active material results in a smaller particle size of the larger particles, avoiding damage to the current collector from larger particles under high compaction density, and further extending the service life of the battery cell. Thus, this embodiment improves the energy density of the battery while also ensuring a long battery life.

[0075] In some embodiments, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) the first positive electrode active material includes lithium phosphate; (3) the mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%. Therefore, setting a suitable mass percentage of lithium phosphate in the first positive electrode active material layer is beneficial to improving the energy density of the battery.

[0076] For example, the mass percentage of the first positive electrode active material in the first positive electrode active material layer can be any two values ​​of 3%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, 5%, or more.

[0077] In some embodiments, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) the lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α)The PO4 material has the following properties: 0.2 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr. Therefore, the volume distribution particle size of the first positive electrode active material is within the aforementioned suitable range, which helps to avoid damage such as scratching to the current collector during the coating process of the first positive electrode active material layer. Using the aforementioned lithium-containing phosphate is beneficial for improving the energy density of the battery.

[0078] In this application, the volumetric distribution particle size Dv99 represents the particle size corresponding to a cumulative volumetric distribution percentage of 99%, and the volumetric distribution particle size Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50%. Both can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0079] For example, the volume distribution particle size Dv99 of the first positive electrode active material can be any range of two values, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 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, 2.1 μm, 2.2 μm. The volume distribution particle size Dv50 of the first positive electrode active material can be any range of two values, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm.

[0080] In this application, the first positive electrode active material layer and the second positive electrode active material layer can be distinguished by measurement based on the cross-sectional SEM image of the positive electrode sheet. In this application, the microscopic morphology of the cross-section of the positive electrode sheet can be observed. The boundary between the first and second positive electrode active material layers can be observed. "Cross-section of the positive electrode sheet" refers to a section perpendicular to the thickness direction of the positive electrode sheet. Furthermore, the microscopic morphology of the cross-section of the positive electrode sheet can be observed and combined with compositional analysis (such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analysis, etc.) to identify elemental types and confirm the composition of different layers. Exemplarily, the cross-section of the positive electrode sheet can be obtained using instruments or equipment including but not limited to a focused electron beam (FIB) microscope (such as the FEI Scios 2HiVac device), an ion cross-section polisher (such as the IB-09010CP argon ion cross-section polisher and IB-19500CP ion cross-section polisher from JEOL Corporation, Japan). Microscopic morphology observation methods can employ instruments or equipment including, but not limited to, scanning electron microscopy (SEM). For example, a high-resolution field emission scanning electron microscope (FEM) can be used. Non-limiting examples of SEM instruments include the Sigma 300 scanning electron microscope and the Apreo 2 SEM field emission scanning electron microscope from ZEISS GmbH, Germany. In the SEM microscopic morphology image of the cross-section of the positive electrode sheet, the boundaries between different layers and the thickness of each layer can be identified based on the obvious discontinuous changes in the microscopic morphology.

[0081] After confirming the boundary and thickness of the first and second positive electrode active material layers, the positive electrode active material layer can be removed using an ion cross-section polisher (such as the IB-09010CP argon ion cross-section polisher or IB-19500CP ion cross-section polisher from JEOL Corporation of Japan), retaining the first positive electrode active material layer. The chemical formula of the lithium phosphate in the first positive electrode active material layer can be confirmed using any method and testing equipment in this field. Take the positive electrode sheet with the positive electrode active material layer removed, peel the first positive electrode active material layer from the current collector, dissolve the peeled first positive electrode active material layer in N-methylpyrrolidone solvent, and after the binder and other components in the first positive electrode active material layer dissolve in the solvent, filter and dry to obtain the sample to be tested. Digest with HF, add it to an ICP-OES instrument to detect the content of elements such as Li, Fe, and P, obtain the specific elemental molar ratio, and obtain the specific chemical composition.

[0082] In some implementations, α can be a range of values ​​consisting of any two values ​​from 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or above.

[0083] In some implementations, β can be a range of values ​​consisting of any two values, such as 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, or more.

[0084] In some embodiments, the lithium-containing phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr. As an example, the first positive electrode active material can be LiFePO4 or LiMn. 0.2 Fe 0.8 PO4 and LiFe 0.5 Mn 0.5 One or more of PO4 and its doped or coated compounds. Using the above-mentioned lithium-containing phosphates is beneficial for improving the energy density of the battery.

[0085] In some embodiments, the first positive electrode active material layer further includes a conductive agent. The addition of the conductive agent helps to improve the conductivity of the first positive electrode active material layer and promotes the uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0086] In some embodiments, the conductive agent satisfies at least one of the following conditions: (1) the conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) the average length of the conductive agent is 1-15 μm; (3) the average diameter of the conductive agent is 30-60 nm; and (4) the mass percentage of the conductive agent in the first positive electrode active material layer is 15%-20%. Using conductive agents with a large aspect ratio, such as carbon nanotubes and carbon nanofibers, is beneficial for promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer, reducing the aggregation of the first positive electrode active material, and improving the uniformity of the coating of the first positive electrode active material layer. The average length, average diameter, and mass percentage of the aforementioned suitable conductive agent are all conducive to forming an interwoven network, further promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0087] The average length and average diameter of the conductive agent can be determined using instruments and methods known in the art. For example, SEM can be used to observe the microstructure of the cross-section of the positive electrode sheet, and then a ruler or CCD (inductively coupled plasma) can be used to measure the length and diameter of multiple conductive agents, and the average value of these multiple conductive agents' length and diameter can be taken.

[0088] For example, the average length of the conductive agent can be any two values ​​within the range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or more. The average diameter of the conductive agent can be any two values ​​within the range of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, or more. The mass percentage of the conductive agent in the first positive electrode active material layer can be any two values ​​within the range of 15%, 16%, 17%, 18%, 19%, 20%, or more.

[0089] In some embodiments, the thickness of the first positive electrode active material layer is 0.5–3.5 μm. This suitable range of thickness helps reduce electrolyte corrosion of the current collector, extending the lifespan of the battery cell while maintaining a high energy density. For example, the thickness of the first positive electrode active material layer can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or any two of these values ​​within a range.

[0090] In some embodiments, the tensile strength of the current collector is 250–330 MPa. The elongation at break of the positive electrode sheet is 2%–2.4%. A tensile strength within this suitable range is beneficial for reducing deformation and breakage of the current collector under high pressure density conditions of the positive electrode film. An elongation at break within this suitable range is beneficial for extending the battery's lifespan. For example, the tensile strength of the current collector can be 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 310 MPa, 320 MPa, 330 MPa, or any two of these values ​​within a range. Generally, a higher elongation at break indicates better ductility of the material, allowing it to undergo plastic deformation under external forces, thereby reducing stress concentration and extending the battery's lifespan. For example, the elongation at break of the positive electrode can be a range of values ​​consisting of any two of the following: 2%, 2.1%, 2.15%, 2.2%, 2.25%, 2.3%, 2.35%, 2.4%, or more.

[0091] In this application, tensile strength refers to the maximum stress value that a material can withstand before breaking. The tensile strength of the current collector in the embodiments of this application can be tested using instruments and methods known in the art. The specific conditions and requirements for the tensile test can be performed in accordance with relevant standards, such as the relevant provisions and requirements in the Chinese National Standard GB / T 228.1—2021 "Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature". As an example, the following method can be used for testing: Lay the current collector flat on a horizontal table and cut it into sections, each section being approximately 15 cm in length; turn on the tensile testing machine, pass the current collector through the upper and lower clamps, step on the air valve to clamp the upper clamp first, maintaining a weak connection, and then clamp the lower clamp. The test is performed by pulling both clamps outward until the current collector breaks in the middle. The test is completed, and the stress at which the positive current collector breaks is output as the tensile strength, with a tensile rate of 5 mm / min.

[0092] In this application, the elongation at break is the ratio of the increase in length of the material before fracture to the original length. The specific test method for the elongation at break is as follows: take a tensile specimen with an original length of L0, stretch the tensile specimen on a tensile testing machine until fracture, and the length of the tensile specimen before fracture is Lh. Then the elongation at break of the tensile specimen is Δh=(Lh-L0) / L0×100%. The specific conditions and requirements for the tensile test can be carried out with reference to relevant standards, such as the relevant provisions and requirements in the Chinese National Standard GB / T 228.1—2021 "Metallic materials, tensile testing—Part 1: Test method at room temperature".

[0093] In some embodiments, the second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide. This material has a high specific capacity and can improve the energy density of the battery cell.

[0094] In some embodiments, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.2. This material has a high specific capacity and a relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0095] After confirming the boundary and thickness of the first and second positive electrode active material layers, a portion of the second positive electrode active material layer can be obtained by scraping. The chemical formula of the lithium transition metal oxide in the second positive electrode active material layer can be confirmed using any method and testing equipment in the art. Take the scraped portion of the second positive electrode active material layer, dissolve it in N-methylpyrrolidone solvent, and after the binder, dispersant, etc., in the positive electrode active material layer have dissolved in the solvent, filter and dry to obtain the sample to be tested. Digest it with HF, and add it to an ICP-OES instrument to detect the content of elements such as Li, Ni, Co, and Mn, obtaining the specific elemental molar ratio and the specific chemical composition.

[0096] In some implementations, m can be a range of values ​​consisting of any two values ​​from 0.8, 0.9, 1.0, 1.1, 1.2, or higher.

[0097] In some implementations, 'a' can be a range of values ​​consisting of any two values ​​from 0.51, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 0.99, or above.

[0098] In some implementations, b can be a range of values ​​consisting of any two values, such as 0, 0.1, 0.2, 0.3, 0.4, or higher.

[0099] In some implementations, c can be a range of values ​​consisting of any two values ​​from 0, 0.1, 0.2, 0.3, 0.4, or higher.

[0100] In some implementations, d can be a range of values ​​consisting of any two values, such as 0, 0.05, 0.1, 0.15, or higher.

[0101] In some implementations, e can be a range of values ​​consisting of any two values, such as 0, 0.05, 0.1, 0.15, or higher.

[0102] In some embodiments, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.2. As an example, LiNi could be used.0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2 and at least one of its doped or coated modified compounds. These materials have high specific capacity and relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0103] In some embodiments, the first positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0104] In some embodiments, the second positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0105] In some embodiments, the second positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] The negative electrode sheet includes 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.

[0107] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0108] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0110] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0111] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0113] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0114] In some embodiments, the electrolyte comprises an electrolyte salt and a solvent.

[0115] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0116] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0117] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0118] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0119] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0120] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0121] Secondly, embodiments of this application provide a method for preparing a battery cell, including a positive electrode preparation step, wherein the positive electrode preparation step includes:

[0122] Provide current collectors;

[0123] A first positive electrode active material layer is formed on at least one side of the current collector surface; the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm.

[0124] A positive electrode active material layer is formed on the surface of the first positive electrode active material layer on the side opposite to the current collector.

[0125] The compaction density of the positive electrode sheet ranges from 3.55 to 3.80 g / cm³. 3 ;

[0126] The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

[0127] The preparation method is simple and conducive to industrial application.

[0128] In some embodiments, the step of forming a first positive electrode active material layer on at least one side of the current collector surface includes: coating a first positive electrode active material layer slurry onto at least one side of the current collector surface to form the first positive electrode active material layer; wherein the solid content of the first positive electrode active material layer slurry is 12% to 20%; and the viscosity of the first positive electrode active material layer slurry is 1500 to 3000 mPa·s. Within this suitable solid content and suitable slurry viscosity range, it is beneficial to reduce damage to the current collector during the coating process of the first positive electrode active material layer, and also beneficial to the uniformity of the coating. Exemplarily, coating the first positive electrode active material layer slurry onto at least one side of the current collector surface to form the first positive electrode active material layer can be performed using a microgravure coating machine.

[0129] For example, the solid content of the first positive electrode active material layer slurry can be any two values ​​of 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or more. The viscosity of the first positive electrode active material layer slurry can be any two values ​​of 1500 mPa·s, 1800 mPa·s, 2000 mPa·s, 2200 mPa·s, 2400 mPa·s, 2600 mPa·s, 2800 mPa·s, 3000 mPa·s, or more.

[0130] Thirdly, embodiments of this application provide a positive electrode sheet, comprising a current collector, a first positive electrode active material layer disposed on at least one side of the surface of the current collector, and a second positive electrode active material layer disposed on the surface of the first positive electrode active material layer facing away from the current collector; the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm; and the compaction density of the positive electrode sheet is 3.55~3.80g / cm³ when the state of charge (SOC) of the battery cell is 0%. 3 The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

[0131] Using a high positive electrode compaction density is beneficial for improving the energy density of the battery. However, high compaction density can easily damage the current collector. Therefore, in this embodiment, by controlling the content of aluminum, silicon, and iron in the aluminum foil within the aforementioned range, it is beneficial to improve the elongation at break of the current collector electrode, reduce damage to the current collector under high compaction density, and thus extend the service life of the battery cell. However, considering that a high iron content in the aluminum foil may lead to electrolyte corrosion of the current collector, the first positive electrode active material layer in this embodiment helps to reduce electrolyte corrosion of the current collector, thereby further extending the service life of the battery cell while maintaining high energy density. Furthermore, controlling the volume distribution particle size Dv99 of the first positive electrode active material results in a smaller particle size of the larger particles, avoiding damage to the current collector from larger particles under high compaction density, and further extending the service life of the battery cell. Thus, this embodiment improves the energy density of the battery while also ensuring a long battery life.

[0132] For example, under the condition that the state of charge (SOC) of a single battery cell is 0%, the compaction density of the positive electrode sheet can be 3.55 g / cm³. 3 3.6g / cm 3 3.65g / cm 3 3.7g / cm 3 3.75g / cm 3 3.80g / cm 3 Or a range of values ​​consisting of any two of the above values.

[0133] For example, the mass percentage of silicon in the aluminum foil can be any two values ​​within the range of 0.05%, 0.1%, 0.15%, 0.2%, or higher. The mass percentage of iron in the aluminum foil can be any two values ​​within the range of 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or higher. The mass percentage of aluminum in the aluminum foil can be any two values ​​within the range of 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, or higher. The aluminum foil typically also includes unavoidable impurity elements, and the sum of the mass percentages of all elements and the impurity elements is 100%.

[0134] In some embodiments, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) the first positive electrode active material includes lithium phosphate; (3) the mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%. Therefore, setting a suitable mass percentage of lithium phosphate in the aforementioned first positive electrode active material layer is beneficial for improving the energy density of the battery. For example, the mass percentage of the first positive electrode active material in the first positive electrode active material layer can be any two of the following values: 3%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, 5%, or a range of values.

[0135] In some embodiments, the first positive electrode active material satisfies at least one of the following conditions: (1) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) the volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) the lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.2 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr. Therefore, the volume distribution particle size of the first positive electrode active material is within the aforementioned suitable range, which helps to avoid damage such as scratching to the current collector during the coating process of the first positive electrode active material layer. Using the aforementioned lithium-containing phosphate is beneficial for improving the energy density of the battery. For example, the volume distribution particle size Dv99 of the first positive electrode active material can be any range of two values, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 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, 2.1 μm, 2.2 μm. The volume distribution particle size Dv50 of the first positive electrode active material can be any range of two values, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm.

[0136] In some implementations, α can be a range of values ​​consisting of any two values ​​from 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or above.

[0137] In some implementations, β can be a range of values ​​consisting of any two values, such as 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, or more.

[0138] In some embodiments, the lithium-containing phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3 ≤ α ≤ 1, 0.8 ≤ β ≤ 1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr. As an example, the first positive electrode active material can be LiFePO4 or LiMn. 0.2 Fe 0.8 PO4 and LiFe 0.5 Mn 0.5 One or more of PO4 and its doped or coated compounds. Using the above-mentioned lithium-containing phosphates is beneficial for improving the energy density of the battery.

[0139] In some embodiments, the first positive electrode active material layer further includes a conductive agent. The addition of the conductive agent helps to improve the conductivity of the first positive electrode active material layer and promotes the uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0140] In some embodiments, the conductive agent satisfies at least one of the following conditions: (1) the conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) the average length of the conductive agent is 1-15 μm; (3) the average diameter of the conductive agent is 30-60 nm; and (4) the mass percentage of the conductive agent in the first positive electrode active material layer is 15%-20%. Using conductive agents with a large aspect ratio, such as carbon nanotubes and carbon nanofibers, is beneficial for promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer, reducing the aggregation of the first positive electrode active material, and improving the uniformity of the coating of the first positive electrode active material layer. The average length, average diameter, and mass percentage of the aforementioned suitable conductive agent are all conducive to forming an interwoven network, further promoting uniform dispersion of the first positive electrode active material in the first positive electrode active material layer.

[0141] For example, the average length of the conductive agent can be any two values ​​within the range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or more. The average diameter of the conductive agent can be any two values ​​within the range of 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, or more. The mass percentage of the conductive agent in the first positive electrode active material layer can be any two values ​​within the range of 15%, 16%, 17%, 18%, 19%, 20%, or more.

[0142] In some embodiments, the thickness of the first positive electrode active material layer is 0.5–3.5 μm. This suitable range of thickness helps reduce electrolyte corrosion of the current collector, extending the lifespan of the battery cell while maintaining a high energy density. For example, the thickness of the first positive electrode active material layer can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or any two of these values ​​within a range.

[0143] In some embodiments, the tensile strength of the current collector is 250–330 MPa. The elongation at break of the positive electrode sheet is 2%–2.4%. The tensile strength of the current collector within this suitable range is beneficial for reducing deformation and breakage of the current collector under high pressure density conditions of the positive electrode film. The elongation at break of the positive electrode sheet within this suitable range is beneficial for extending the battery's lifespan. Exemplarily, the tensile strength of the current collector can be any two values ​​from 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 310 MPa, 320 MPa, 330 MPa, or any range of two values ​​above. The elongation at break of the positive electrode sheet can be any two values ​​from 2%, 2.1%, 2.15%, 2.2%, 2.25%, 2.3%, 2.35%, 2.4%, or any range of two values ​​above.

[0144] In some embodiments, the second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide. This material has a high specific capacity and can improve the energy density of the battery cell.

[0145] In some embodiments, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R eThe material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.2. This material has a high specific capacity and a relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0146] In some implementations, m can be a range of values ​​consisting of any two values, such as 0.8, 0.9, 1.0, 1.1, 1.2, or higher.

[0147] In some implementations, 'a' can be a range of values ​​consisting of any two values ​​from 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 0.99, or above.

[0148] In some implementations, b can be a range of values ​​consisting of any two values, such as 0, 0.1, 0.2, 0.3, 0.4, or higher.

[0149] In some implementations, c can be a range of values ​​consisting of any two values ​​from 0, 0.1, 0.2, 0.3, 0.4, or higher.

[0150] In some implementations, d can be a range of values ​​consisting of any two values, such as 0, 0.05, 0.1, 0.15, or higher.

[0151] In some implementations, e can be a range of values ​​consisting of any two values, such as 0, 0.05, 0.1, 0.15, or higher.

[0152] In some embodiments, the lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.2. As an example, LiNi could be used. 0.6 Co 0.2 Mn0.2 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2 and at least one of its doped or coated modified compounds. These materials have high specific capacity and relatively stable crystal structure, which is beneficial for improving the compaction density of the positive electrode film, thereby increasing the energy density and lifespan of the battery cell.

[0153] Fourthly, embodiments of this application provide an electrical device including a battery cell from the first aspect of embodiments of this application.

[0154] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0155] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0156] Another example 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.

[0157] Example

[0158] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0159] 1. Preparation of positive electrode sheet

[0160] Referring to Figure 7, the positive electrode sheet includes a positive current collector, a first positive active material layer, and a second positive active material layer. The first positive active material layer is disposed on both sides of the positive current collector, and the second positive active material layer is disposed on the surface of the first positive active material layer. The positive current collector is aluminum foil, which contains aluminum, silicon, iron, and trace elements. The mass percentage of aluminum in the aluminum foil is 99.5%, silicon is 0.1%, iron is 0.30%, and the trace elements include 0.012% Cu, 0.01% Ti, and 0.01% V by mass, with the remainder being unavoidable impurities. The tensile strength of the aluminum foil is 265 MPa.

[0161] The first positive electrode active material layer is formed by uniformly coating a first positive electrode active material layer slurry (solvent being N-methylpyrrolidone, NMP) onto the surface of the positive electrode current collector. The solid content of the first positive electrode active material layer slurry is 18%, and the viscosity is 2500 mPa·s. The first positive electrode active material layer comprises a first positive electrode active material, a conductive agent, and a binder, polyvinylidene fluoride (PVDF), in a mass ratio of 3:18:79. The first positive electrode active material is LiFe. 0.5 Mn 0.5 The first positive electrode active material, PO4, has a volumetric particle size distribution of 0.8 μm (Dv99) and 0.28 μm (Dv50). The conductive agent is carbon nanotubes with an average length of 10 μm and an average diameter of 50 nm. The thickness of the first positive electrode active material layer is 2.61 μm.

[0162] The second positive electrode active material layer comprises a film layer formed by uniformly coating a second positive electrode active material layer slurry (solvent being N-methylpyrrolidone NMP) onto the surface of the first positive electrode active material layer, followed by drying and cold pressing. The second positive electrode active material layer comprises a second positive electrode active material in a weight ratio of 90:5:5, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black.

[0163] The second positive electrode active material is LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0164] Under the condition that the state of charge (SOC) of the battery cell is 0%, the compaction density of the positive electrode sheet is 3.7 g / cm³. 3 .

[0165] The elongation at break of the positive electrode is 2.2%.

[0166] 2. Preparation of negative electrode sheet

[0167] The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on both sides of the negative current collector, and the negative current collector is copper foil.

[0168] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 90:8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0169] 3. Preparation of electrolyte:

[0170] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 were mixed, and then 5% fluoroethylene carbonate (FEC) was added to obtain an organic solvent. LiPF6 lithium salt was added and dissolved in the organic solvent, and the mixture was stirred evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0171] 4. Preparation of lithium-ion batteries:

[0172] The positive electrode, polypropylene separator, and negative electrode are stacked in sequence, with the polypropylene separator acting as a separator between the positive and negative electrodes. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0173] The parameters of Examples 1-11 and Comparative Examples 1-3 of this application are as specified in Table 1.

[0174] Performance testing:

[0175] The batteries from Examples 1 to 11 and Comparative Examples 1 to 3 were subjected to the following tests:

[0176] (1) Test of elongation at break of positive electrode sheet:

[0177] A positive electrode sheet tensile specimen with an initial length of L0 is taken. The preload force of the tensile testing machine is 1N, and the tensile rate is 5mm / min. The tensile specimen is stretched on the tensile testing machine until it breaks. The length of the tensile specimen before fracture is Lh. Then the elongation at break of the tensile specimen is Δh=(Lh-L0) / L0×100%.

[0178] (2) Energy density test:

[0179] At 25℃, the battery is charged at a constant current and constant voltage of 0.33C to the designed upper limit voltage of 4.17V, with a cutoff current of 0.05C. After standing for 30 minutes, it is discharged at 0.33C to the designed lower limit voltage of 2.8V. The discharge energy P (Wh) and the cell weight m (kg) are recorded. Then the energy density (Wh / kg) = P / m.

[0180] (3) Cyclic performance test:

[0181] At 25°C, charge the battery cells at a constant current of 1C to the charging cutoff voltage of 4.17V, then charge at a constant voltage of 4.17V until the charging current is less than or equal to 0.05C, and let stand for 30 minutes; then discharge at a constant current of 1C to 2.8V, and let stand for 30 minutes. This constitutes one charge-discharge cycle. Repeat the above charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0×100%) is 80%, and record the number of cycles.

[0182] (4) LSV test:

[0183] The electrochemical workstation is constructed using the following method: 1. Working electrode (WE): The positive electrode to be tested is fixed with conductive adhesive or clamps to ensure an effective exposed area (e.g., 1 cm²). 2 2. Reference electrode (RE): Saturated calomel electrode (SCE), placed near the working electrode in the electrolyte. 3. Counter electrode (CE): Platinum sheet, placed symmetrically to the working electrode. 4. Electrolytic cell: Pour in the electrolyte (the electrolyte used in Example 1), ensuring all three electrodes are completely submerged, with an electrode spacing of 1–2 cm.

[0184] Allow the sample to stand for 10–30 minutes, recording the potential change over time until it stabilizes (fluctuation < ±2 mV / min). Obtain the stable potential of the positive electrode in the electrolyte, which is taken as the open circuit potential (OCP). Starting from approximately 0.2 V below the OCP, scan towards the positive potential until a significant anodic current is observed (e.g., -1.5 V → 0 V vs. SCE). Scan rate: 3 mV / s; data acquisition frequency: 1 Hz. Obtain the current response curves (LSV curves) at different potentials. By analyzing the LSV curves, the corrosion potential can be determined.

[0185] The corrosion potential is the potential corresponding to the intersection of the anodic polarization curve and the cathodic polarization curve.

[0186] Table 2 Battery performance parameters of Examples 1 to 11 and Comparative Examples 1 to 3 (Table 2)

[0187] As shown in Table 1-2, the product of specific capacity and positive electrode compaction density is positively correlated with battery energy density. In Comparative Example 1, aluminum foil with a relatively lower iron content was used as the current collector. Although the battery energy density remained at a high level with a compaction density of 3.7%, the battery cycle performance was significantly reduced due to the decreased tensile strength of the current collector and the low elongation at break of the electrode. In Comparative Example 2, aluminum foil with a relatively high iron content was used as the current collector. Although the tensile strength of the current collector and the elongation at break of the electrode were higher, the lack of a first positive electrode active material layer resulted in a high corrosion current and poorer corrosion resistance, leading to poor cycle performance. In Comparative Example 3, a first positive electrode active material with a relatively higher Dv99 was used. The larger particle size of the larger particles reduced the elongation at break of the electrode, also resulting in poor cycle performance.

[0188] In embodiments 1-11 of this application, a first positive electrode active material layer and a second positive electrode active material layer are sequentially stacked on the surface of the current collector, and the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm. Furthermore, the aluminum, silicon, and iron content in the current collector is controlled within appropriate ranges. This approach improves the battery's energy density while also ensuring good cycle performance, i.e., a long battery life.

[0189] As can be seen from Examples 1-3, with the increase of iron content in aluminum foil, the elongation at break of the positive electrode increases and the corrosion current increases, but good cycle performance is still maintained.

[0190] As can be seen from Examples 4-5, the battery energy density increases with increasing compaction. Although the elongation at break of the positive electrode decreases, it still maintains good cycle performance.

[0191] As can be seen from Examples 1 and 6-8, as the Dv99 of the first positive electrode active material in the first positive electrode active material layer decreases, the corrosion current decreases.

[0192] As can be seen from Examples 1 and 9-11, by adjusting the thickness of the first positive electrode active material layer and the type of conductive agent, the corrosion current can be further reduced and the cycle performance of the battery can be improved.

[0193] 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, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a current collector, a first positive active material layer disposed on at least one side of the surface of the current collector, and a second positive active material layer disposed on the surface of the first positive active material layer opposite to the current collector. The volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm; When the state of charge (SOC) of the battery cell is 0%, the compaction density of the positive electrode sheet is 3.55–3.80 g / cm³. 3 ; The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

2. The battery cell according to claim 1, characterized in that, The first positive electrode active material satisfies at least one of the following conditions: (1) The volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) The first positive electrode active material includes lithium phosphate; (3) The mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%.

3. The battery cell according to claim 1, characterized in that, The first positive electrode active material satisfies at least one of the following conditions: (1) The volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) The volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) The lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The material of PO4, wherein 0.2≤α≤1, 0.8≤β≤1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3≤α≤1, 0.8≤β≤1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr.

5. The battery cell according to any one of claims 1 to 3, characterized in that, The first positive electrode active material layer also includes a conductive agent.

6. The battery cell according to claim 5, characterized in that, The conductive agent satisfies at least one of the following conditions: (1) The conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) The average length of the conductive agent is 1-15 μm; (3) The average diameter of the conductive agent is 30-60 nm; (4) The conductive agent accounts for 15% to 20% of the mass of the first positive electrode active material layer.

7. The battery cell according to any one of claims 1 to 3, characterized in that, The thickness of the first positive electrode active material layer is 0.5–3.5 μm.

8. The battery cell according to any one of claims 1 to 3, characterized in that, The tensile strength of the current collector is 250–330 MPa; and / or, The elongation at break of the positive electrode sheet is 2% to 2.4%.

9. The battery cell according to any one of claims 1 to 3, characterized in that, The second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide.

10. The battery cell according to claim 9, characterized in that, The lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.

2.

11. The battery cell according to claim 9, characterized in that, The lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.

2.

12. A method for preparing a single battery cell, characterized in that, The process includes the preparation steps of a positive electrode sheet, wherein the preparation steps of the positive electrode sheet include: Provide current collectors; A first positive electrode active material layer is formed on at least one side of the current collector surface; the volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm. A second positive electrode active material layer is formed on the side of the first positive electrode active material layer facing away from the current collector. The compaction density of the positive electrode sheet ranges from 3.55 to 3.80 g / cm³. 3 ; The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

13. The preparation method according to claim 12, characterized in that, The step of forming a first positive electrode active material layer on at least one side of the current collector surface includes: A first positive electrode active material layer slurry is coated on at least one side of the current collector surface to form a first positive electrode active material layer; wherein the solid content of the first positive electrode active material layer slurry is 12% to 20%; and / or the viscosity of the first positive electrode active material layer slurry is 1500 to 3000 mPa·s.

14. A positive electrode plate, characterized in that, It includes a current collector, a first positive electrode active material layer disposed on at least one side of the surface of the current collector, and a second positive electrode active material layer disposed on the side of the surface of the first positive electrode active material layer opposite to the current collector; The volume distribution particle size Dv99 of the first positive electrode active material in the first positive electrode active material layer is ≤3μm; When the state of charge (SOC) of the battery cell is 0%, the compaction density of the positive electrode sheet is 3.55–3.80 g / cm³. 3 ; The current collector is made of aluminum foil, which contains aluminum, silicon and iron. The aluminum content in the aluminum foil is greater than or equal to 99.3% by mass, the silicon content in the aluminum foil is 0.05% to 0.20% by mass, and the iron content in the aluminum foil is 0.20% to 0.40% by mass.

15. The positive electrode sheet according to claim 14, characterized in that, The first positive electrode active material satisfies at least one of the following conditions: (1) The volume distribution particle size of the first positive electrode active material satisfies Dv50≤0.8μm; (2) The first positive electrode active material includes lithium phosphate; (3) The mass percentage of the first positive electrode active material in the first positive electrode active material layer is 3% to 5%.

16. The positive electrode sheet according to claim 14, characterized in that, The first positive electrode active material satisfies at least one of the following conditions: (1) The volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv99≤2.2μm; (2) The volume distribution particle size of the first positive electrode active material satisfies 0.2≤Dv50≤0.8μm; (3) The lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The material of PO4, wherein 0.2≤α≤1, 0.8≤β≤1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr.

17. The positive electrode sheet according to any one of claims 14 to 16, characterized in that, The lithium phosphate in the first positive electrode active material includes Li β Fe α M (1-α) The PO4 material has the following properties: 0.3≤α≤1, 0.8≤β≤1.2, and M includes at least one of Ti, V, Mg, Cu, Mn, Zn, Co, Ni, and Sr.

18. The positive electrode sheet according to any one of claims 14 to 16, characterized in that, The first positive electrode active material layer also includes a conductive agent.

19. The positive electrode sheet according to claim 18, characterized in that, The conductive agent satisfies at least one of the following conditions: (1) The conductive agent includes at least one of carbon nanotubes and carbon nanofibers; (2) The average length of the conductive agent is 1-15 μm; (3) The average diameter of the conductive agent is 30-60 nm; (4) The conductive agent accounts for 15% to 20% of the mass of the first positive electrode active material layer.

20. The positive electrode sheet according to any one of claims 14 to 18, characterized in that, The thickness of the first positive electrode active material layer is 0.5–3.5 μm.

21. The positive electrode sheet according to any one of claims 14 to 18, characterized in that, The tensile strength of the current collector is 250–330 MPa; and / or, The elongation at break of the positive electrode sheet is 2% to 2.4%.

22. The positive electrode sheet according to any one of claims 14 to 18, characterized in that, The second positive electrode active material in the second positive electrode active material layer includes a lithium-containing transition metal oxide.

23. The positive electrode sheet according to claim 22, characterized in that, The lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, V, Ga, Sn, Ge, B, Ta, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, Cl, Br, and P, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.5<a<1, 0≤b<0.5, 0≤c<0.5, 0≤d<0.2, and 0≤e<0.

2.

24. The positive electrode sheet according to claim 22, characterized in that, The lithium-containing transition metal oxide includes Li m Ni a Co b Mn c M d O 2-e R e The material M includes at least one of Zr, Al, Cu, Mg, Zn, Ti, Sn, B, Mo, W, Nb, Sb, Sr, and La; R includes at least one of F, S, and Cl, wherein a+b+c+d=1, 0.8≤m≤1.2, 0.7≤a≤0.95, 0<b≤0.3, 0<c≤0.3, 0≤d≤0.2, and 0≤e≤0.

2.

25. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1 to 11.

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