Battery cell, positive electrode sheet, preparation method therefor, secondary battery, battery apparatus, and electric apparatus

Abstract

The present application discloses a battery cell, a positive electrode sheet, a preparation method therefor, a secondary battery, a battery apparatus, and an electric apparatus. A battery cell, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a current collector and a film layer having active particles, the current collector and the film layer are arranged in a stacked configuration, the film layer comprises a first surface and a second surface which are opposite each other, a first region and a second region which are located between the first surface and the second surface, and the first surface is distributed facing away from the current collector; a porosity of the first region is greater than a porosity of the second region; and a Dv50 of active particles in the first region is less than a Dv50 of active particles in the second region. The embodiments of the present application balance high-rate charge-discharge performance and cycling performance of battery cells.

Description

Battery cells, positive electrode sheets and their preparation methods, secondary batteries, battery devices and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510027371.7, filed on January 8, 2025, entitled “Battery cell, positive electrode sheet and method for preparation thereof, secondary battery, battery device and power consumption device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to secondary batteries, and more particularly to a battery cell, a positive electrode sheet and its preparation method, a secondary battery, a battery device and an electrical device. Background Technology

[0004] Because battery cells can convert chemical energy into electrical energy, they have become one of the important energy sources for human production and life, and are therefore widely used in many fields such as power tools, electric vehicles, and electronic devices to provide them with power.

[0005] With the widespread application of battery cells in various fields, the requirements for their performance are becoming increasingly stringent. Among these, the charge-discharge performance and cycle performance of battery cells have become key areas of focus. Therefore, improving the charge-discharge performance and cycle performance of battery cells is one of the most pressing technical problems that needs to be solved. Summary of the Invention

[0006] This application provides a battery cell, a positive electrode sheet and its preparation method, a secondary battery, a battery device, and an electrical device, which can take into account both the high-rate charge-discharge performance and cycle performance of the battery cell.

[0007] In a first aspect, embodiments of this application provide a battery cell including a positive electrode sheet, the positive electrode sheet including a current collector and a film layer having active particles stacked together, the film layer including a first surface, a second surface, a first region and a second region located between the first surface and the second surface, the first surface being distributed away from the current collector; wherein, the porosity of the first region is greater than the porosity of the second region; the Dv50 of the active particles in the first region is less than the Dv50 of the active particles in the second region.

[0008] This application embodiment improves the overall wettability of the membrane layer and reduces the ion insertion / extraction path by gradient setting the porosity and Dv50 of active particles in different regions of the membrane layer, so that the porosity far from the current collector membrane layer is greater than that near the current collector membrane layer, and the Dv50 of active particles in the first region is less than that of active particles in the second region. This can simultaneously improve the high-rate charge / discharge performance and cycle performance of the battery cell.

[0009] In any embodiment of this application, the porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

[0010] The porosity range of the embodiments of this application can better improve the overall wettability of the membrane layer, and at the same time, it can better reduce the content of trace water / organic solvents in the membrane layer.

[0011] In any embodiment of this application, the mass percentage of active particles in the first region is 30% to 70%.

[0012] The active particle mass ratio in the embodiments of this application can better balance power performance and cycle life.

[0013] In any embodiment of this application, the mass percentage of active particles in the first region is 40% to 60%.

[0014] In any embodiment of this application, the specific surface area of ​​the active particles in the first region is greater than that of the active particles in the second region.

[0015] The embodiments of this application specifically design the specific surface area of ​​active particles in different regions, which can improve the wettability of electrolyte in active particles, so that ions in electrolyte can be inserted and extracted in active particles more quickly, thereby reducing the ion insertion and extraction path and improving power efficiency, thereby improving charge and discharge performance at high rates.

[0016] In any embodiment of this application, the difference in specific surface area between the active particles in the first region and the active particles in the second region is 0.1 to 10 m². 2 / g.

[0017] The specific surface area range of the embodiments of this application can better reduce the ion insertion / extraction path and improve power efficiency.

[0018] In any embodiment of this application, the active particles comprise lithium iron phosphate, wherein the specific surface areas of the lithium iron phosphate in the first region and the lithium iron phosphate in the second region are independently selected from 10 to 30 m². 2 / g.

[0019] The specific surface area range of the embodiments of this application can better reduce the ion insertion / extraction path and improve power efficiency.

[0020] In any embodiment of this application, the lithium iron phosphate in the film layer has a Dv10 of 0.2 to 1.0 μm, a Dv50 of 0.3 to 5.0 μm, and a Dv90 of 1 to 20 μm.

[0021] The particle size distribution of the embodiments of this application can take into account both the high-rate charge-discharge performance and cycle performance of individual battery cells.

[0022] In any embodiment of this application, the lithium iron phosphate in the first region has a Dv10 of 0.2–0.8 μm, a Dv50 of 0.3–1.0 μm, and a Dv90 of 1–10 μm; the lithium iron phosphate in the second region has a Dv10 of 0.3–1.0 μm, a Dv50 of 0.5–5.0 μm, and a Dv90 of 5–20 μm.

[0023] The particle size distribution of the embodiments of this application can take into account both the high-rate charge-discharge performance and cycle performance of individual battery cells.

[0024] In any embodiment of this application, the compaction density of the first region is 2.2–2.4 g / cm³. 3 The compaction density of the second region is 2.4–2.7 g / cm³. 3 .

[0025] The compaction density range of the embodiments of this application can improve the energy density of a single battery cell.

[0026] In any embodiment of this application, the mass of the membrane layer is greater than or equal to 200 mg.

[0027] The film quality of the embodiments of this application can better improve the energy density of the battery cell.

[0028] In any embodiment of this application, the thickness ratio of the first region to the second region is 3:7 to 7:3.

[0029] In any embodiment of this application, the film layer further includes an adhesive and a conductive agent.

[0030] The film layer in the embodiments of this application can improve the conductivity and cycle life of the battery cell.

[0031] In any embodiment of this application, in the first region, the total mass of the binder and conductive agent accounts for the percentage of the mass of the active particles as W1; in the second region, the total mass of the binder and conductive agent accounts for the percentage of the mass of the active particles as W2; wherein, W1 is less than W2.

[0032] The embodiments of this application, through the gradient design of binder and conductive agent content in different regions, can increase the content of active particles in the first region, so as to better leverage the advantages of active particles in the first region, and thus better balance charge-discharge performance and cycle performance at high rates.

[0033] In any embodiment of this application, an auxiliary coating is further provided between the film layer and the current collector; the auxiliary coating includes one or more of a binder, a conductive agent, and a dispersant.

[0034] The functional coating configuration of this application reduces the content of binder and conductive agent in the film layer, so as to better utilize the positional advantage of the first region of the film layer. It can maximize the content ratio of active particles in the first and second regions, thereby balancing the conductivity brought by the functional material and the cycle performance brought by the film layer.

[0035] In any embodiment of this application, the coating weight of the functional coating is ≤10mg / 1540.25mm. 2 .

[0036] The coating weight of the embodiments of this application can better balance the conductivity and cycle life brought by the functional materials with the overall weight of the positive electrode sheet.

[0037] In any embodiment of this application, lithium iron phosphate includes lithium iron phosphate with a carbon material coated on its surface; based on the total mass of lithium iron phosphate, the mass percentage of carbon elements coated on the surface of lithium iron phosphate is 0.5% to 2.5%.

[0038] The active particles in this application embodiment can balance the electronic conductivity and energy density of the active particles, thereby improving the charge and discharge performance at high rates.

[0039] In any embodiment of this application, the mass of carbon elements coated on the surface of lithium iron phosphate in the first region is greater than the mass of carbon elements coated on the surface of lithium iron phosphate in the second region.

[0040] The carbon content settings in different regions of this application can better leverage the locational advantages of the first region, thereby further improving the electronic conductivity of the first region while taking into account both the electronic conductivity and energy density of the active particles.

[0041] Secondly, embodiments of this application provide a positive electrode sheet, which includes a current collector stacked on top of each other and a film layer having active particles. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface, with the first surface facing away from the current collector. The porosity of the first region is greater than that of the second region, and the Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0042] This application embodiment improves the overall wettability of the membrane layer and reduces the ion insertion / extraction path by gradient setting the porosity and Dv50 of active particles in different regions of the membrane layer, so that the porosity far from the current collector membrane layer is greater than that near the current collector membrane layer, and the Dv50 of active particles in the first region is less than that of active particles in the second region. This can simultaneously improve the high-rate charge / discharge performance and cycle performance of the battery cell.

[0043] In any embodiment of this application, the porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

[0044] The porosity range of the embodiments of this application can better improve the overall wettability of the membrane layer, and at the same time, it can better reduce the content of trace water / organic solvents in the membrane layer.

[0045] Thirdly, embodiments of this application provide a method for preparing a positive electrode sheet, wherein a second slurry and a first slurry are coated on the same side of a current collector, and after drying and cold pressing, a first region film layer containing the first slurry and a second region film layer containing the second slurry are obtained, and then the positive electrode sheet is obtained after slitting; wherein the porosity of the first region is greater than that of the second region; and the Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0046] The embodiments of this application can form film layers with different regions by using different coating equipment and coating processes.

[0047] Fourthly, embodiments of this application provide a secondary battery, including a positive electrode sheet. The positive electrode sheet includes a current collector and a film layer having active particles stacked on top of each other. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface. The first surface is distributed away from the current collector. The porosity of the first region is greater than that of the second region. The Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0048] Fifthly, embodiments of this application provide a battery device including a battery cell as described in the first aspect. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 shows a schematic diagram of a battery cell provided in some embodiments of this application.

[0051] Figure 2 shows a schematic diagram of an electrical device provided in some embodiments of this application.

[0052] Figure 3 shows a schematic diagram of the positive electrode sheet provided in some embodiments of this application.

[0053] The accompanying drawings are not necessarily drawn to scale.

[0054] The reference numerals in the attached figures are explained as follows: 7, film layer; 71, first region; 72, second region; 73, first surface; 74, second surface. Detailed Implementation

[0055] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0056] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0057] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, positive electrode sheet, preparation method thereof, secondary battery, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions 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.

[0058] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0060] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0061] 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.

[0062] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0063] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0064] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0065] Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C.

[0066] The battery cells mentioned in the embodiments of this application are capable of charging and discharging independently. The battery cells may be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited in this respect. Figure 1 shows an example of a cuboid battery cell.

[0067] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0068] The battery cell provided in the embodiments of this application includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the negative electrode and the positive electrode. During the charging and discharging process of the battery cell, active ions (e.g., lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, serves to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. The electrode assembly can be a wound structure or a stacked structure; the embodiments of this application are not limited in this regard.

[0069] The battery cell also includes an outer packaging, which encapsulates the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0070] The battery cells provided in the embodiments of this application can be lithium-ion battery cells, sodium-ion battery cells, sodium-lithium-ion battery cells, lithium metal battery cells, sodium metal battery cells, lithium-sulfur battery cells, magnesium-ion battery cells, nickel-metal hydride battery cells, nickel-cadmium battery cells, lead-acid battery cells, etc., and the embodiments of this application are not limited to these.

[0071] The method for preparing the battery cell of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained.

[0072] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0073] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0074] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0075] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0076] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0077] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0078] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0079] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0080] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0081] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery cells or battery devices, such as, but not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains (subways, trains, bullet trains, high-speed trains, etc.), ships and satellites, energy storage systems, etc. Battery cells and battery devices are used to store or provide electrical energy.

[0082] Figure 2 is a schematic diagram of an example electrical device. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0083] With the continuous deepening of battery cell research and the continuous improvement of market demand, especially the widespread application of electric vehicles (EVs) and hybrid electric vehicles (HEVs) in recent years, not only are high energy density, sufficient reliability and ultra-long cycle life required for battery cells, but the demand for high-rate charging and discharging of battery cells is also increasing.

[0084] However, currently, improving the high-rate charge and discharge performance of individual battery cells inevitably reduces their cycle performance.

[0085] In view of this, the embodiments of this application provide a battery cell, a positive electrode sheet and its preparation method, a secondary battery, a battery device and an electrical device, which can take into account both the high-rate charge-discharge performance and cycle performance of the battery cell.

[0086] battery cell

[0087] This application provides a battery cell including a positive electrode sheet. The positive electrode sheet includes a current collector 6 and a film layer 7 stacked together. The film layer 7 includes a first surface 73 and a second surface 74 opposite to each other, a first region 71 and a second region 72 located between the first surface 73 and the second surface 74. The first surface 73 is distributed away from the current collector 6. The porosity of the first region 71 is greater than that of the second region 72. The Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0088] In the embodiments of this application, the first region and the second region can be adjacent and non-overlapping. As an example, the thickness of the film layer 7 is denoted as H. The region from the first surface 73 of the film layer 7 to a thickness of 0.3H is the first region 71 of the film layer 7, and the region from the second surface 74 of the film layer 7 to a thickness of 0.7H is the second region 72 of the film layer 7. That is to say, the sum of the thicknesses of the first region 71 and the second region 72 is always H.

[0089] This application embodiment achieves this by gradient porosity in different regions of the membrane layer, such that the porosity further away from the current collector membrane layer (first region) is greater than that closer to the current collector membrane layer (second region), thereby forming an outwardly expanding pore channel. On one hand, the electrolyte directly on the membrane surface can better penetrate into the first region and reach the second region through the outwardly expanding pore channel, thereby improving the overall wettability of the membrane layer, enhancing ion transport performance, and thus improving the charge-discharge performance of the battery cell at high rates. On the other hand, when removing trace water / organic solvents from the positive electrode, the outwardly expanding pore channel allows trace water / organic solvents deep within the membrane to diffuse out better, thereby reducing the content of trace water / organic solvents in the membrane layer, improving the stability of the battery cell, and thus improving the cycle performance of the battery cell.

[0090] This application embodiment features a specific design for the particle size of active particles in different regions. Specifically, the Dv50 of the active particles in the first region is smaller than that in the second region. The active particles in the first region are located in the film layer away from the current collector, and therefore closer to the separator, thus receiving ions transmitted from the other electrode side through the separator first. The smaller particle size of the active particles in the first region reduces the path for ions to be inserted into or extracted from the active material, thereby improving power efficiency and consequently enhancing charge-discharge performance at high rates.

[0091] Therefore, by designing the porosity and particle size of active particles in different regions, this application embodiment can improve the overall wettability of the film layer and reduce the ion insertion / extraction path, thereby improving the high-rate charge / discharge performance of the battery cell. Furthermore, by designing the porosity of different regions, the content of trace water / organic solvents in the film layer can be reduced, thereby improving the stability of the battery cell and thus improving its cycle performance.

[0092] The embodiments of this application further maximize the contribution of the porosity and active particle Dv50 gradient settings in different regions to improving the high-rate charge-discharge performance and cycle performance of battery cells by setting the thickness of different regions.

[0093] Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50% for a material, and can be determined using instruments and methods known in the art. For example, by performing ion polishing cross-sectional morphology analysis (CP) on a disassembled positive electrode sheet, and then combining this with software analysis to calculate the particle size of a specific region.

[0094] In other embodiments, the first region and the second region can be divided into two or more layers. The first region can be divided into two or more layers according to the aforementioned thickness ratio, and the second region can also be divided into two or more layers according to the aforementioned thickness ratio. Furthermore, the porosity of the first / second region after layering is also a gradient decrease or increase. For example, in the first region, the thickness of the film layer 7 is denoted as H. The regions from the first surface of the film layer to the thickness range of 0.3H, 0.4H, 0.5H, 0.6H, and 0.7H are respectively denoted as the first-first region, the first-second region, the first-third region, the first-fourth region, and the first-fifth region of the film layer, and the porosity of the first-first region, the first-second region, the first-third region, the first-fourth region, and the first-fifth region decreases sequentially. Similarly, the porosity of different regions can be refined in the second region. For example, the regions from the second surface of the film to the thickness range of 0.7H, 0.6H, 0.5H, 0.4H, and 0.3H are respectively designated as the second-first region, the second-second region, the second-third region, the second-fourth region, and the second-fifth region of the film, and the porosity of the second-first region, the second-second region, the second-third region, the second-fourth region, and the second-fifth region decreases sequentially.

[0095] In this application, the porosity of different regions of the membrane layer has a meaning known in the art, referring to the ratio of the pore volume of different regions within the membrane layer to the total volume of the membrane layer, and can be measured using instruments and methods known in the art. For example, by performing ion polishing cross-sectional morphology analysis (CP) on the disassembled positive electrode sheet, and then combining this with software analysis and calculation of the proportion of pore volume in a specific region.

[0096] In some embodiments, the thickness ratio of the first region to the second region is 3:7 to 7:3.

[0097] Optionally, the thickness ratio of the first region to the second region is independently selected from 3.0:7.0, 3.1:6.9, 3.2:6.8, 3.3:6.7, 3.4:6.6, 3.5:6.5, 3.6:6.4, 3.7:6.3, 3.8:6.2, 3.9:6.1, 4.0:6.0, 4.1:5.9, 4.2:5.8, 4.3:5.7, 4.4:5.6, 4.5:5.5, 4.6:5.4, 4.7:5.3, 4.8:5.2, 4.9:5.1, 5 .0: 5.0, 5.1: 4.9, 5.2: 4.8, 5.3: 4.7, 5.4: 4.6, 5.5: 4.5, 5.6: 4.4, 5.7: 4.3, 5.8: 4.2, 5.9: 4.1, 6.0: 4.0, 6.1: 3.9, 6.2: 3.8, 6.3: 3.7, 6.4: 3.6, 6.5: 3.5, 6.6: 3.4, 6.7: 3.3, 6.8: 3.2, 6.9: 3.1, 7.0: 3.0, or any value in the range of any two.

[0098] In some embodiments, in order to better improve the overall wettability of the membrane layer and also better reduce the content of trace water / organic solvents in the membrane layer, the porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

[0099] Optionally, the porosity of the first region is independently selected from any value of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range between any two.

[0100] Optionally, the porosity of the second region is independently selected from any value of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range between any two.

[0101] In some embodiments, the specific surface area of ​​the active particles in the first region is greater than that of the active particles in the second region.

[0102] This application embodiment features a specific design for the specific surface area of ​​active particles in different regions. Specifically, the specific surface area of ​​the active particles in the first region is greater than that in the second region. The active particles in the first region are located in the membrane layer away from the current collector, and therefore closer to the separator, where they will first receive ions transmitted from the other electrode side through the separator. The presence of active particles with a large specific surface area in the first region improves the wettability of the electrolyte within the active particles, allowing ions in the electrolyte to be more quickly intercalated and deintercalated within the active particles. This reduces the ion intercalation / deintercalation path, thereby improving power efficiency and ultimately enhancing charge / discharge performance at high rates.

[0103] In some embodiments, to better reduce the ion insertion / extraction pathway and improve power efficiency, the active particles comprise lithium iron phosphate, wherein the specific surface areas of lithium iron phosphate in the first region and lithium iron phosphate in the second region are independently selected from 10 to 30 m². 2 / g.

[0104] In some embodiments, to better reduce the ion insertion / extraction pathway and improve power efficiency, the specific surface area difference between the active particles in the first region and the active particles in the second region is 0.1–10 m². 2 / g.

[0105] The specific surface area of ​​the active particles in different regions of this application embodiment has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a NOVA 2000e specific surface area and pore size analyzer from Quanta Computer Corporation, USA. As a specific example, the test method is as follows: Ion cross-sectional polishing morphology analysis (CP) is performed on the electrode sheet, and the thickness of the active material coating in the first region and the second region is measured respectively. Based on the measured thickness, active material particles are scraped from different locations, and then the active particles in the first region and the second region are measured respectively according to the BET standard test method. As a specific example, the BET standard test method is as follows: Take 8.000g to 15.000g of active material from a weighed empty sample tube, stir the active material evenly and weigh it. Place the sample tube in a NOVA 2000e degassing station for degassing. Weigh the total mass of the degassed active material and the sample tube. Subtract the mass of the empty sample tube from the total mass to calculate the mass G of the degassed active material. Place the sample tube in a NOVA 2000e and measure the amount of nitrogen adsorbed on the surface of the active material under different relative pressures. Based on the Brownnor-Etter-Teller multilayer adsorption theory and its formula, calculate the monolayer adsorption amount, and then calculate the total surface area A of the active material. Calculate the specific surface area of ​​the active material by A / G.

[0106] Optionally, the specific surface area of ​​lithium iron phosphate in the first region is independently selected from 10 m². 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g、30m 2 Any value in / g or any range between the two.

[0107] Optionally, the specific surface area of ​​lithium iron phosphate in the second region is independently selected from 10 m². 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g、30m 2 Any value in / g or any range between the two.

[0108] Optionally, the difference in specific surface area between the active particles in the first region and the active particles in the second region is independently selected from 0.1 m. 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m2 / g、2.6m 2 / g、2.7m 2 / g、2.8m 2 / g、2.9m 2 / g、3.0m 2 / g、3.1m 2 / g、3.2m 2 / g、3.3m 2 / g、3.4m 2 / g、3.5m 2 / g、3.6m 2 / g、3.7m 2 / g、3.8m 2 / g、3.9m 2 / g、4.0m 2 / g、4.1m 2 / g、4.2m 2 / g、4.3m 2 / g、4.4m 2 / g、4.5m 2 / g、4.6m 2 / g、4.7m 2 / g、4.8m 2 / g、4.9m 2 / g、5.0m 2 / g、5.1m 2 / g、5.2m 2 / g、5.3m 2 / g、5.4m 2 / g、5.5m 2 / g、5.6m 2 / g、5.7m 2 / g、5.8m 2 / g、5.9m 2 / g、6.0m 2 / g、6.1m 2 / g、6.2m 2 / g、6.3m 2 / g、6.4m 2 / g、6.5m 2 / g、6.6m 2 / g、6.7m 2 / g、6.8m 2 / g、6.9m 2 / g、7.0m 2 / g、7.1m 2 / g、7.2m 2 / g、7.3m 2 / g、7.4m 2 / g、7.5m2 / g, 7.6m 2 / g, 7.7m 2 / g, 7.8m 2 / g, 7.9m 2 / g, 8.0m 2 / g、8.1m 2 / g、8.2m 2 / g、8.3m 2 / g, 8.4m 2 / g, 8.5m 2 / g, 8.6m 2 / g, 8.7m 2 / g, 8.8m 2 / g, 8.9m 2 / g, 9.0m 2 / g, 9.1m 2 / g, 9.2m 2 / g, 9.3m 2 / g, 9.4m 2 / g, 9.5m 2 / g, 9.6m 2 / g, 9.7m 2 / g, 9.8m 2 / g, 9.9m 2 / g, 10.0m 2 Any value in / g or any range between the two.

[0109] In some embodiments, the lithium iron phosphate in the film has a Dv10 of 0.2–1.0 μm, a Dv50 of 0.3–5.0 μm, and a Dv90 of 1–20 μm.

[0110] In some embodiments, the lithium iron phosphate in the first region has a Dv10 of 0.2–0.8 μm, a Dv50 of 0.3–1.0 μm, and a Dv90 of 1–10 μm; the lithium iron phosphate in the second region has a Dv10 of 0.3–1.0 μm, a Dv50 of 0.5–5.0 μm, and a Dv90 of 5–20 μm.

[0111] The embodiments of this application can obtain suitable porosity and specific surface area in the first / second region by adjusting the particle size distribution of the active particles in the first / second region, thereby balancing the high-rate charge-discharge performance and cycle performance of the battery cell.

[0112] Dv10 represents the particle size corresponding to a cumulative volumetric distribution percentage of 10%, Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50%, and Dv90 represents the particle size corresponding to a cumulative volumetric distribution percentage of 90%. These measurements can be performed using instruments and methods known in the art. For example, ion-polished cross-sectional morphology analysis (CP) can be performed on the disassembled electrode sheets, followed by software analysis and calculation of the particle size in specific regions.

[0113] In some embodiments, to improve the energy density of a single battery cell, the compaction density of the first region is 2.2–2.4 g / cm³. 3 The compaction density of the second region is 2.4–2.7 g / cm³. 3 .

[0114] In this application, the compaction density of different regions of the film layer has a meaning known in the art and can be measured using instruments and methods known in the art. For example, by performing ion polishing cross-sectional morphology analysis (CP) on the disassembled electrode sheet, and then combining it with software analysis to calculate the compaction density of a specific region.

[0115] Optionally, the compaction density of the first region is independently selected from 2.20 g / cm³. 3 2.21 g / cm 3 2.22 g / cm 3 2.23 g / cm 3 2.24 g / cm 3 2.25g / cm 3 2.26 g / cm 3 2.27 g / cm 3 2.28g / cm 3 2.29 g / cm 3 2.30g / cm 3 2.31 g / cm 3 2.32 g / cm 3 2.33 g / cm 3 2.34 g / cm 3 2.35g / cm 3 2.36 g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.39 g / cm 3 2.40 g / cm 3 Any value in the range or any value between the two.

[0116] In some embodiments, in order to better balance power performance and cycle life, the mass percentage of active particles in the first region is 30% to 70%.

[0117] In some embodiments, in order to better balance power performance and cycle life, the mass percentage of active particles in the first region is 40% to 60%.

[0118] The mass percentage of active particles in the embodiments of this application has a meaning known in the art and can be determined using instruments and methods known in the art. For example, ion section polishing morphology analysis (CP) can be performed on the disassembled electrode, and the thickness of the active material coating in the first region and the active material coating in the second region can be measured respectively. Based on the measured thickness, active material particles from different locations can be scraped, weighed, and calculated to obtain the mass percentage.

[0119] Optionally, the mass percentage of active particles in the first region is independently selected from any value or a range between 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, and 70%.

[0120] In some embodiments, in order to better improve the energy density of the battery cell, the mass of the film layer is greater than or equal to 200 mg.

[0121] In some embodiments, in order to improve the conductivity and cycle life of the battery cells, the film layer also includes a binder and a conductive agent.

[0122] In some embodiments, in the first region, the total mass of the binder and conductive agent accounts for the percentage of the mass of the active particles as W1; in the second region, the total mass of the binder and conductive agent accounts for the percentage of the mass of the active particles as W2; wherein, W1 is less than W2.

[0123] This application embodiment increases the content of active particles in the first region by using a gradient design of binder and conductive agent content in different areas. The first region, located far from the current collector and closer to the separator, receives ions transported from the other electrode side through the separator first, thus possessing a positional advantage. While maintaining the same membrane quality, to balance conductivity and cycle life provided by the binder and conductive agent, a higher proportion of active particles is placed in the first region. This improves the wettability of the electrolyte in the active particles, allowing ions in the electrolyte to be more quickly intercalated and deintercalated within the active particles, thereby reducing the ion intercalation / deintercalation path and improving power efficiency. This achieves a balance between charge / discharge performance at high rates and cycle performance.

[0124] In some embodiments, in order to further improve the conductivity of the first region, the specific surface area of ​​the conductive agent in the first region is higher than that of the conductive agent in the second region.

[0125] In some embodiments, the specific surface area of ​​the conductive agent in the first and second regions is independently selected from 30 to 1000 m². 2 / g.

[0126] In some embodiments, the conductive agent includes carbon nanotubes (CNTs), wherein the mass percentage of carbon nanotubes is 0.1% to 2%.

[0127] Optionally, the mass percentage of carbon nanotubes is independently selected from any value or a range between 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%.

[0128] The special type of conductive agent in the embodiments of this application can significantly suppress the volume expansion of the positive electrode sheet in the later stage of cycling after the thick coating layer is applied, thereby improving the cycling performance.

[0129] In other embodiments, an additive coating is further provided between the film layer and the current collector; the additive coating includes one or more of a binder, a conductive agent, and a dispersant.

[0130] In order to better leverage the positional advantage of the first region of the membrane, the proportion of active particles in the first and second regions can be increased as much as possible in this embodiment. In order to balance the conductivity and cycle life brought by the functional materials, an auxiliary coating can be separately set between the membrane and the current collector.

[0131] In some embodiments, to better balance the conductivity and cycle life provided by the functional materials with the overall weight of the positive electrode, the coating weight of the functional coating is ≤10mg / 1540.25mm. 2 .

[0132] In some embodiments, in order to balance the electronic conductivity and energy density of the active particles, lithium iron phosphate includes lithium iron phosphate with a carbon coating on its surface; based on the total mass of lithium iron phosphate, the mass percentage of carbon elements coating the surface of lithium iron phosphate is 0.5% to 2.5%.

[0133] The carbon content and its amount on the surface of lithium iron phosphate in this application embodiment can be determined using instruments and methods known in the art. For example, lithium iron phosphate is extracted and tested using infrared absorption. The test sample is burned in an oxygen stream to generate CO2. Under a certain pressure, the energy absorbed by CO2 in infrared light is proportional to its concentration. Therefore, the carbon content can be calculated based on the measured energy change of CO2 gas before and after passing through the infrared absorber.

[0134] In some embodiments, the mass of carbon elements coated on the surface of lithium iron phosphate in the first region is greater than the mass of carbon elements coated on the surface of lithium iron phosphate in the second region.

[0135] In this embodiment, the first region of the film layer is far from the current collector. By designing a gradient of carbon elements coated on the surface of lithium iron phosphate in different regions, the mass of carbon elements coated on the surface of lithium iron phosphate in the first region is greater than that in the second region. This can further improve the electronic conductivity of the first region while taking into account both the electronic conductivity and energy density of the active particles.

[0136] The mass content of carbon in the first or second region of this application embodiment has a meaning known in the art and can be detected using equipment and methods known in the art. For example, ion section polishing (CP) morphology analysis can be performed on the electrode, and the thickness of the active material coating in the first and second regions can be measured respectively. Based on the measured thickness, active material particles from different locations can be scraped off, and an appropriate amount of active material particles can be collected for testing using infrared absorption. The test sample is burned in an oxygen stream to generate CO2. Under a certain pressure, the energy of CO2 absorbing infrared radiation is proportional to its concentration. Therefore, the carbon content can be calculated based on the measured energy change of CO2 gas before and after passing through the infrared absorber.

[0137] Optionally, based on the total mass of lithium iron phosphate, the mass percentage of carbon elements coated on the surface of lithium iron phosphate is independently selected from any value or a range between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, and 2.5%.

[0138] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly consists of a positive electrode, a negative electrode, and a separator. The battery cell primarily functions by the movement of metal ions between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector, and the uncoated positive current collector protrudes beyond the coated positive current collector, serving as the positive electrode tab.

[0139] In addition, the battery cell also includes a housing for housing the electrode assembly and electrolyte, wherein the electrolyte can play a role in transferring electrons between the positive and negative electrode plates.

[0140] [Positive electrode plate]

[0141] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0142] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium.

[0143] As examples, positive electrode active materials may include, but are not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium titanium oxides, and their respective modified compounds. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon composites, and their respective modified compounds.

[0144] In some embodiments, to further improve the energy density of a single battery cell, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e D f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include, but is not limited to, one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include, but is not limited to, one or more of N, F, S and Cl.

[0145] In some embodiments, the positive electrode active material may simultaneously comprise lithium transition metal oxide and lithium phosphate. This is advantageous for obtaining battery cells that balance high capacity and high reliability.

[0146] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, and LiNi 1 / 2 Mn 1 / 2 O2, LiMn2O4, Li 4 / 3 Ti 5 / 3 O4, LiNi 1 / 2 Mn1 / 2 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0147] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting sodium. For example, the positive electrode active material may include, but is not limited to, one or more of layered transition metal oxides (including but not limited to P2 type, O3 type, etc.), polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian materials.

[0148] In some embodiments, as an example, the positive electrode active material may include, but is not limited to, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na 0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, and Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, and Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, and one or more of their respective modified compounds.

[0149] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0150] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0151] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0152] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0153] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0154] [Negative electrode plate]

[0155] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0156] The negative electrode active material may be any material known in the art that can be used in battery cells. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxide, and tin alloys.

[0157] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0159] In some embodiments, the negative electrode film layer may also include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0160] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0161] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0162] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.

[0163] In some embodiments, the negative electrode sheet can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0164] [Electrolytes]

[0165] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0166] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0167] Taking a lithium battery cell as an example, the electrolyte salt may include, but is not limited to, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0168] Taking sodium battery cells as an example, the electrolyte salt may include, but is not limited to, one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonyl imide (NaFSI), sodium difluoromethanesulfonyl imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0169] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0170] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature power performance of the battery cell.

[0171] [Isolation membrane]

[0172] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes, while allowing metal ions to pass through. 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.

[0173] In some embodiments, the isolation membrane includes a porous base membrane and a coating located on at least one side of the porous base membrane.

[0174] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0175] In some embodiments, the coating includes a heat-resistant layer and an adhesive layer, the heat-resistant layer being disposed between the base film and the adhesive layer, the heat-resistant layer including heat-resistant particles, and the adhesive layer including organic particles.

[0176] In some embodiments, the heat-resistant particles include one or more of inorganic particles or organic particles.

[0177] In some embodiments, inorganic particles may include one or more of the following: inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, or inorganic particles capable of undergoing electrochemical reactions.

[0178] In some embodiments, inorganic particles having a dielectric constant of 5 or higher may include boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxides, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, aluminum hydroxide, barium oxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, calcium fluoride, barium fluoride, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb (Mg3Nb) 2 / 3 The inorganic particles can be selected from one or more of PbTiO3 (PMN-PT) and their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification.

[0179] In some embodiments, inorganic particles that are ion-conductive but do not store ions may include Li3PO4, lithium titanium phosphate (Li3PO4), etc. x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 One or more of the following are given: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can improve the ion conductivity of the separator.

[0180] In some embodiments, the inorganic particles capable of undergoing electrochemical reactions may include one or more of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0181] In some embodiments, the organic particles may include at least one of a thermoplastic resin polymer, a thermosetting resin polymer, or a crosslinked polymer.

[0182] In some embodiments, the thermoplastic resin polymer may include one or more of the following: polycarbonate organic particles, polymethyl methacrylate organic particles, polyoxymethylene organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyether ether ketone organic particles, polyimide organic particles, polysulfone organic particles, polyether sulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamide-imide organic particles, and polyethyleneimine organic particles.

[0183] In some embodiments, the thermosetting resin polymer may include one or more of the following: phenolic resin organic particles, polymer particles containing triazine ring structural units, epoxy resin organic particles, unsaturated polyester resin organic particles, urea-formaldehyde resin organic particles, and furan resin organic particles.

[0184] In some embodiments, the crosslinking polymer may include one or more of crosslinked styrene organic particles and silicon-containing organic crosslinked resin particles.

[0185] In some embodiments, the coating includes an adhesive, which may include, but is not limited to, one or more of polyacrylate adhesives, nitrile rubber adhesives, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0186] In some embodiments, the coating may further include a dispersant, such as one or more of alkylphenol polyoxyethylene ethers, polyacrylic acid dispersants, and cellulose dispersants, including but not limited to. For example, the dispersant may include one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0187] Positive electrode sheet

[0188] This application provides a positive electrode sheet, which includes a current collector and a film layer with active particles stacked on top of each other. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface, and the first surface is distributed away from the current collector. The porosity of the first region is greater than that of the second region. The Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0189] This application embodiment sets the porosity in different regions of the membrane layer in a gradient manner, so that the porosity of the membrane layer farther away from the current collector (first region) is greater than that of the membrane layer closer to the current collector (first region), thereby forming an outwardly expanding pore channel. On the one hand, the electrolyte directly on the membrane surface can better penetrate into the first region and reach the second region through the outwardly expanding pore channel, thereby improving the overall wettability of the membrane layer, improving ion transport performance, and thus improving the charge and discharge performance of the battery cell at high rates. On the other hand, when removing trace water / organic solvents from the positive electrode, the outwardly expanding pore channel allows trace water / organic solvents deep in the membrane to diffuse out better, thereby reducing the content of trace water / organic solvents in the membrane layer, improving the stability of the battery cell, and thus improving the cycle performance of the battery cell.

[0190] This application embodiment features a specific design for the particle size of active particles in different regions. Specifically, the Dv50 of the active particles in the first region is smaller than that in the second region. The active particles in the first region are located in the film layer away from the current collector, and therefore closer to the separator, thus receiving ions transmitted from the other electrode side through the separator first. The smaller particle size of the active particles in the first region reduces the path for ions to be inserted into or extracted from the active material, thereby improving power efficiency and consequently enhancing charge-discharge performance at high rates.

[0191] Therefore, by designing the porosity and particle size of active particles in different regions, this application embodiment can improve the overall wettability of the film layer and reduce the ion insertion / extraction path, thereby improving the high-rate charge / discharge performance of the battery cell. Furthermore, by designing the porosity of different regions, the content of trace water / organic solvents in the film layer can be reduced, thereby improving the stability of the battery cell and thus improving its cycle performance.

[0192] The embodiments of this application further maximize the contribution of the porosity and active particle Dv50 gradient settings in different regions to improving the high-rate charge-discharge performance and cycle performance of battery cells by setting the thickness of different regions.

[0193] In other embodiments, the first region and the second region can be divided into two or more layers. The first region can be divided into two or more layers according to the aforementioned thickness ratio, and the second region can also be divided into two or more layers according to the aforementioned thickness ratio. Furthermore, the porosity of the first / second region after layering is also a gradient decrease or increase. For example, in the first region, the regions within the thickness range of 0.3H, 0.4H, 0.5H, 0.6H, and 0.7H from the first surface of the film are respectively denoted as the first-first region, the first-second region, the first-third region, the first-fourth region, and the first-fifth region of the film, and the porosity of the first-first region, the first-second region, the first-third region, the first-fourth region, and the first-fifth region decreases sequentially. Similarly, the porosity of different regions can be refined in the second region. For example, the regions from the second surface of the film to the thickness range of 0.7H, 0.6H, 0.5H, 0.4H, and 0.3H are respectively designated as the second-first region, the second-second region, the second-third region, the second-fourth region, and the second-fifth region of the film, and the porosity of the second-first region, the second-second region, the second-third region, the second-fourth region, and the second-fifth region decreases sequentially.

[0194] In this application, the porosity of different regions of the membrane layer has a meaning known in the art, referring to the ratio of the pore volume of different regions within the membrane layer to the total volume of the membrane layer, and can be measured using instruments and methods known in the art. For example, by performing ion polishing cross-sectional morphology analysis (CP) on the disassembled positive electrode sheet, and then combining this with software analysis and calculation of the proportion of pore volume in a specific region.

[0195] In some embodiments, in order to better improve the overall wettability of the membrane layer and also better reduce the content of trace water / organic solvents in the membrane layer, the porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

[0196] Optionally, the porosity of the first region is independently selected from any value of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range between any two.

[0197] Optionally, the porosity of the second region is independently selected from any value of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range between any two.

[0198] Preparation method

[0199] This application provides a method for preparing a positive electrode sheet, wherein a second slurry and a first slurry are coated on the same side of a current collector, and after drying and cold pressing, a first region film layer containing the first slurry and a second region film layer containing the second slurry are obtained, and then the positive electrode sheet is obtained after slitting; wherein the porosity of the first region is greater than that of the second region; and the Dv50 of the active particles in the first region is less than that of the active particles in the second region.

[0200] The embodiments of this application can utilize a double-layer extrusion coating apparatus or a single-layer coating apparatus to form a first region film layer containing a first slurry and a second region film layer containing a second slurry. For example, a double-layer extrusion coating apparatus can be used to simultaneously coat the second slurry and the first slurry onto the current collector to form a first region film layer containing the first slurry and a second region film layer containing the second slurry; alternatively, a single-layer extrusion coating apparatus can be used to sequentially coat the second slurry and the first slurry onto the current collector to form a first region film layer containing the first slurry and a second region film layer containing the second slurry.

[0201] In other embodiments, in order to separate the first region and the second region into layers, one or more layers of the first-first region, the first-second region, the first-third region, the first-fourth region and the first-fifth region of a preset thickness can be coated sequentially according to the coating method described above; similarly, one or more layers of the second-first region, the second-second region, the second-third region, the second-fourth region and the second-fifth region of a preset thickness can be coated sequentially.

[0202] In other embodiments, in order to obtain membranes with different porosities, membranes with preset porosities can be obtained by setting slurries with active particles of different particle size distributions and setting condition parameters in cold pressing.

[0203] In other embodiments, in order to obtain a first region film layer and a second region film layer with different Dv50, the Dv50 of the first slurry and the second slurry can be set to obtain a first region film layer and a second region film layer with different Dv50.

[0204] Example

[0205] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0206] Examples 1-5 and Comparative Examples 1-2

[0207] 1. Preparation of current collectors modified with functional coatings:

[0208] The binder PVDF, conductive agent SuperP and surfactant lauryl acetate were mixed in a mass ratio of 49.3:50.2:0.5, and a certain amount of solvent NMP was added. The mixture was stirred to form a uniform slurry. The slurry of a predetermined mass was applied to the positive electrode current collector aluminum foil using a coating device. After drying, a current collector with a functional coating was obtained.

[0209] 2. Preparation of the positive electrode sheet:

[0210] 2.1 The active material particles of lithium iron phosphate (Dv50 = 0.5~5.0μm, BET (specific surface area) = 10~30m²) are prepared. 2 / g, carbon content of 0.5% to 2.5%), binder PVDF, conductive agent CNT (BET = 80m 2 After mixing (g) at a mass ratio of 97.1:2.1:0.8, a certain amount of solvent NMP is added, and the mixture is stirred to prepare a uniform second slurry;

[0211] 2.2 The active material particles of lithium iron phosphate (Dv50 = 0.3~1.0μm, BET = 10~30μm) are... 2 / g, carbon content 0.5%~2.5%, binder PVDF, conductive agent CNT (BET=100m 2 Mix the ingredients in a mass ratio of 97.6:1.8:0.6 (or 97.1:2.1:0.8) and add a certain amount of solvent NMP. Stir to prepare a uniform first slurry.

[0212] 2.3 Using a double-layer extrusion coating equipment, a second slurry and a first slurry of a predetermined mass are simultaneously and uniformly coated on the current collector modified with a functional base coating; then, after drying, cold pressing, and slitting, a positive electrode sheet is prepared.

[0213] 3. Preparation of the negative electrode sheet:

[0214] The negative electrode active material graphite, the negative electrode binder styrene-butadiene rubber (SBR), the negative electrode thickener carboxymethyl cellulose sodium (CMC-Na), and the negative electrode conductive agent acetylene black are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96:1.5:0.5:2 to form a uniform negative electrode slurry.

[0215] The negative electrode slurry is coated onto the surface of the negative electrode current collector copper foil, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0216] 4. Separating membrane:

[0217] Porous polyethylene (PE) membrane is used as the separator.

[0218] 5. Electrolyte:

[0219] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a non-aqueous solvent. Then, the electrolyte salt LiPF6 and the electrolyte additives FEC (fluoroethylene carbonate) and VC (ethylene carbonate) were dissolved in the above non-aqueous solvent. The concentration of the electrolyte salt in the mixed solvent was 1 mol / L, and the mass ratios of the additives FEC and VC in the electrolyte were 1 wt% and 3 wt%, respectively.

[0220] 6. Assembly of individual battery cells:

[0221] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, and then wound to obtain the bare cell.

[0222] The bare battery cell is placed in the outer packaging, injected with the prepared electrolyte, and then sealed, injected, formed, and vented to obtain a battery cell.

[0223] Data Analysis:

[0224] 1. Particle size test of positive electrode active material (Dv50):

[0225] After disassembling the battery, cut the positive electrode sheet into 6mm*6mm pieces using ceramic scissors. Place the sample on a sample stage coated with paraffin, ensuring the sample protrudes slightly (<1mm) from the edge of the sample stage. Set appropriate polishing time and voltage to polish the end face of the positive electrode sheet (ion cross-section polishing).

[0226] The samples prepared above were tested using a scanning electron microscope and energy dispersive spectroscopy (equipment model Sigma300), and the testing was carried out in accordance with JY / T010-1996. Active material particles at different positions of the positive electrode were selected for analysis using Avizo image processing (which can analyze the particle size and distribution at different positions).

[0227] 2. BET test

[0228] Ion cross-sectional polishing morphology analysis (CP) was performed on the positive electrode sheet. The thickness of the active material coating in the first region and the active material coating in the second region were measured respectively. Based on the measured thickness, active material particles were scraped from different positions. An appropriate amount of active material particles were collected and tested according to the BET standard test method. The BET standard test method refers to the standard GB / T19587-2004 "Determination of specific surface area of ​​solid materials by gas adsorption BET method".

[0229] 3. Carbon content test of cathode material

[0230] Ion-cut surface polishing (CP) morphology analysis was performed on the positive electrode sheet. The thickness of the active material coating in the first and second regions was measured. Based on the measured thickness, active material particles were scraped from different locations. A suitable amount of active material particles were collected and tested using infrared absorption spectroscopy: the test sample was burned in an oxygen stream to generate CO2. Under a certain pressure, the energy of CO2 absorbing infrared radiation is proportional to its concentration. Therefore, the carbon content can be calculated based on the measured energy change of CO2 gas before and after passing through the infrared absorber.

[0231] 4. Cathode material compaction density test:

[0232] Ion cross-sectional polishing morphology analysis (CP) was performed on the positive electrode sheet. The thickness of the active material coating in the first region and the active material coating in the second region were measured respectively. Based on the measured thickness, active material particles were scraped from different positions. After collecting an appropriate amount of active material particles, the following test was performed: A certain amount of active material particles were placed in a compaction mold, and then the mold was placed on a compaction density instrument. Different pressures were set, and the thickness of the powder under different pressures could be read on the instrument. The compaction density was calculated by using ρ = m / v.

[0233] 5. Positive electrode adhesion test:

[0234] Referring to GB-T2790-1995 national standard "Test Method for 180° Peel Strength of Adhesives", the adhesion test process of the embodiments and comparative examples in this application is as follows: A sample with a width of 30mm and a length of 100-160mm is cut with a blade. Special double-sided adhesive tape is applied to a steel plate, with a tape width of 20mm and a length of 90-150mm. The positive electrode film layer of the previously cut positive electrode sample is then applied to the double-sided adhesive tape, followed by three rolls in the same direction using a 2kg pressure roller. A paper strip with a width equal to the positive electrode and a length of 250mm is fixed to the current collector of the positive electrode and secured with wrinkle adhesive. The power of the Sansi tensile testing machine (sensitivity 1N) is turned on; the indicator light illuminates. The limit block is adjusted to a suitable position, and the end of the steel plate not covered with the positive electrode is secured with the lower clamp. The paper strip is folded upwards and secured with the upper clamp. The position of the upper clamp is adjusted using the "up" and "down" buttons on the manual controller attached to the tensile testing machine. Then, tests were conducted and values ​​were recorded. The force when the positive electrode sheet was in equilibrium was divided by the width of the tape to obtain the adhesive force per unit length of the positive electrode sheet, which characterizes the bonding strength between the positive electrode film and the current collector.

[0235] 6. Energy density test:

[0236] Under a constant temperature environment of 25℃, the battery of the device was left to stand for 10 minutes, then discharged at a constant current of 0.33C to the lower limit of the battery's operating voltage. After standing for 10 minutes, it was charged at a constant current of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage to a current of 0.05C, and left to stand for 10 minutes. After that, it was discharged at a constant current of 0.33C to the lower limit voltage of 2.0V. The cell capacity was calculated, and the energy density was calculated as energy / cell weight.

[0237] 7. Room temperature cycling performance test:

[0238] Under a constant temperature environment of 25℃, the prepared battery cells were charged at a constant current of 0.5C to the upper limit voltage of 3.8V, then charged at a constant voltage of 3.8V until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to the lower limit voltage of 2.0V. This constitutes one cycle of charge and discharge. The discharge capacity at this point is recorded as the discharge capacity of the first cycle. The battery cells were subjected to cycle charge and discharge tests using the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the battery cell decreased to 80% of the discharge capacity of the first cycle. The cycle number at this point is used to characterize the cycle performance of the battery cell. The higher the cycle number of the battery cell, the better the cycle performance.

[0239] 8. 50% SOC pulse discharge test (25℃):

[0240] Under a constant temperature environment of 25℃, the device's battery was left to stand for 10 minutes, then discharged at a constant current of 0.33C to the lower limit of the voltage used by the individual battery cells, 2.0V. After standing for 10 minutes, it was charged at a constant current of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage to a current of 0.05C. After standing for 10 minutes, it was discharged at a constant current of 0.33C to the lower limit voltage of 2.0V, and the discharge capacity C0 at this time was recorded. Then it was left to stand for 10 minutes, then charged at a constant current of 0.33C to 0.5C0, left to stand for 10 minutes, then discharged at 4C0 for 30 seconds, and left to stand for 10 minutes.

[0241] The test results are shown in Tables 1 and 2.

[0242] Table 1. Condition parameters in Examples 1-5 and Comparative Examples 1-2

[0243] Table 2

[0244] As shown in Tables 1 and 2, by adjusting the pore distribution in the first and second regions, the high-rate charge-discharge performance and cycle performance of the battery cell can be improved simultaneously. Furthermore, by adjusting the particle size and specific surface area of ​​the first and second regions, the energy density of the battery cell can be increased. Moreover, the additional functional undercoating significantly improves the adhesion between the active material coating and the current collector, while also improving discharge power and cycle performance (preventing the active material coating from losing adhesion to the current collector and thus losing electrical bonding in the later stages of cycling).

[0245] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A battery cell, comprising a positive electrode sheet, characterized in that, The positive electrode includes a current collector stacked in layers and a film layer with active particles. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface, and the first surface is distributed away from the current collector. Wherein, the porosity of the first region is greater than that of the second region; The Dv50 of the active particles in the first region is smaller than that of the active particles in the second region.

2. The battery cell according to claim 1, characterized in that, The porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

3. The battery cell according to claim 1 or 2, characterized in that, Based on the mass of the active particles in the membrane layer, the mass percentage of active particles in the first region is 30% to 70%. Optionally, the active particles in the first region account for 40% to 60% of the total mass.

4. The battery cell according to any one of claims 1-3, characterized in that, The specific surface area of ​​the active particles in the first region is greater than that of the active particles in the second region.

5. The battery cell according to claim 4, characterized in that, The difference in specific surface area between the active particles in the first region and the active particles in the second region is 0.1–10 m². 2 / g.

6. The battery cell according to any one of claims 1-5, characterized in that, The active particles comprise lithium iron phosphate, wherein the specific surface areas of the lithium iron phosphate in the first region and the lithium iron phosphate in the second region are independently selected from 10 to 30 m². 2 / g.

7. The battery cell according to claim 6, characterized in that, The lithium iron phosphate in the membrane has a Dv10 of 0.2–1.0 μm, a Dv50 of 0.3–5.0 μm, and a Dv90 of 1–20 μm.

8. The battery cell according to claim 7, characterized in that, The lithium iron phosphate in the first region has a Dv10 of 0.2–0.8 μm, a Dv50 of 0.3–1.0 μm, and a Dv90 of 1–10 μm; the lithium iron phosphate in the second region has a Dv10 of 0.3–1.0 μm, a Dv50 of 0.5–5.0 μm, and a Dv90 of 5–20 μm.

9. The battery cell according to any one of claims 6-8, characterized in that, The lithium iron phosphate includes lithium iron phosphate with a carbon material coated on its surface; Based on the total mass of the lithium iron phosphate, the mass percentage of carbon elements coated on the surface of the lithium iron phosphate is 0.5% to 2.5%.

10. The battery cell according to claim 9, characterized in that, The mass of carbon elements coated on the surface of lithium iron phosphate in the first region is greater than the mass of carbon elements coated on the surface of lithium iron phosphate in the second region.

11. The battery cell according to any one of claims 6-10, characterized in that, The compaction density of the first region is 2.2–2.4 g / cm³. 3 The compaction density of the second region is 2.4–2.7 g / cm³. 3 .

12. The battery cell according to any one of claims 1-11, characterized in that, The mass of the membrane layer is greater than or equal to 200 mg.

13. The battery cell according to any one of claims 1-12, characterized in that, The thickness ratio of the first region to the second region is 3:7 to 7:

3.

14. The battery cell according to any one of claims 1-13, characterized in that, The film layer also includes an adhesive and a conductive agent.

15. The battery cell according to claim 14, characterized in that, In the first region, the total mass of the binder and the conductive agent accounts for W1% of the mass of the active particles; in the second region, the total mass of the binder and the conductive agent accounts for W2% of the mass of the active particles; wherein, W1 is less than W2.

16. The battery cell according to any one of claims 1-15, characterized in that, An additive coating is further provided between the membrane layer and the current collector; The additive coating includes one or more of binders, conductive agents, and dispersants.

17. The battery cell according to claim 16, characterized in that, The coating weight of the additive is ≤10mg / 1540.25mm. 2 .

18. A positive electrode plate, characterized in that, The positive electrode includes a current collector stacked in layers and a film layer with active particles. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface, and the first surface is distributed away from the current collector. Wherein, the porosity of the first region is greater than that of the second region; The Dv50 of the active particles in the first region is smaller than that of the active particles in the second region.

19. The positive electrode sheet according to claim 18, characterized in that, The porosity of the first region and the porosity of the second region are independently selected from 15% to 30%.

20. A method for preparing a positive electrode sheet, characterized in that, The second slurry and the first slurry are coated on the same side of the current collector. After drying and cold pressing, a first region film containing the first slurry and a second region film containing the second slurry are obtained. After slitting, a positive electrode sheet is obtained. Wherein, the porosity of the first region is greater than that of the second region; The Dv50 of the active particles in the first region is smaller than that of the active particles in the second region.

21. A secondary battery, comprising a positive electrode, characterized in that, The positive electrode includes a current collector stacked in layers and a film layer with active particles. The film layer includes a first surface, a second surface, a first region and a second region located between the first surface and the second surface, and the first surface is distributed away from the current collector. Wherein, the porosity of the first region is greater than that of the second region; The Dv50 of the active particles in the first region is smaller than that of the active particles in the second region.

22. A battery device, characterized in that, It includes the battery cells according to any one of claims 1-17.

23. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1-17 or the battery device according to claim 22.

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