Negative electrode sheet, method for manufacturing the same, battery cell, battery device, and electric device

Abstract

The application discloses a negative electrode sheet, a preparation method thereof, a battery monomer, a battery device and a power utilization device. The battery monomer comprises the negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and a lithium supplement layer is arranged on the side of the negative electrode film layer away from the negative electrode current collector; the negative electrode film layer comprises: a first region located at both ends of the negative electrode current collector along a first direction, wherein the first direction is perpendicular to the thickness direction of the negative electrode sheet; and a second region continuously arranged with the first region along the first direction and sandwiched between the first regions; wherein the porosity of the negative electrode film layer in the first region is phi 1, the porosity of the negative electrode film layer in the second region is phi 2, and phi 1 < phi 2. The battery monomer provided by the application has improved cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode sheet and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0002] Batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric car toys, electric toy ships, electric toy airplanes, and power tools.

[0003] In the development of battery cells, improving the cycle performance of battery cells is one of the urgent problems to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a negative electrode sheet and its preparation method, a battery cell, a battery device, and an electrical device.

[0005] In a first aspect, embodiments of this application provide a battery cell, the battery cell including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer having a lithium replenishment layer disposed on the side away from the negative current collector; the negative electrode film layer including: a first region located at both ends of the negative current collector along a first direction, the first direction being perpendicular to the thickness direction of the negative electrode sheet; a second region continuously disposed along the first direction with the first region, and the second region being sandwiched between the first regions; wherein, the porosity of the negative electrode film layer located in the first region is The porosity of the negative electrode film layer located in the second region is

[0006] This application embodiment differentiates the porosity of the negative electrode film layer, such that when the porosity of the negative electrode film layer in the first region and the negative electrode film layer in the second region meet the above-mentioned range, the negative electrode film layer located in the middle of the negative electrode sheet has a higher porosity. The electrolyte wets faster in the middle of the negative electrode sheet, thereby improving the electrolyte wetting ability in the middle of the negative electrode sheet, accelerating the electrolyte wetting speed in the middle of the negative electrode sheet, and shortening the time difference between the electrolyte reaching the end and middle of the negative electrode sheet. This allows the middle of the negative electrode sheet to receive sufficient film-forming additives, thereby improving the film uniformity of the negative electrode sheet and improving the cycle performance of the battery cell.

[0007] In some embodiments, This can further improve the film uniformity of the negative electrode sheet, thereby improving the cycle performance of the battery cell.

[0008] In some embodiments, This allows the end of the negative electrode to have a suitable electrolyte wetting rate, while the negative electrode can have a high compaction density, which is beneficial to improving the energy density of the battery cell.

[0009] In some embodiments, This allows the middle part of the negative electrode to have a higher electrolyte wetting rate, improving the film formation consistency of the negative electrode. At the same time, the negative electrode can have extremely high compaction density, enabling the battery cell to have improved cycle performance and high energy density.

[0010] In some embodiments, along the first direction, the second region accounts for 25%-50% of the total size of the negative electrode sheet. This allows the central region of the negative electrode sheet to have higher porosity and better electrolyte wettability, thereby further improving the film uniformity of the negative electrode sheet and thus improving the cycle performance of the battery cell.

[0011] In some embodiments, the dimension of the negative electrode sheet along the first direction is smaller than the dimension of the negative electrode sheet along the second direction, and the first direction, the second direction, and the thickness direction are perpendicular to each other. This can further improve the electrolyte wettability in the central region of the negative electrode sheet and improve the cycle performance of the battery cell.

[0012] In some embodiments, the range of impedance values ​​of the negative electrode film, measured based on AC impedance spectroscopy, is less than or equal to 1. This results in high film formation consistency across different regions of the negative electrode film, thereby further improving the cycle performance of the battery cell.

[0013] In some embodiments, the range of impedance values ​​of the negative electrode film determined based on AC impedance spectroscopy is 0.3-1.0.

[0014] In some embodiments, the lithium replenishment layer includes a lithium replenishment material, which includes one or more of lithium metal or lithium alloy.

[0015] In some embodiments, the thickness of the lithium replenishment layer is 2μm-6μm.

[0016] Secondly, embodiments of this application provide a battery device, including a single battery cell from the first aspect of this application.

[0017] Thirdly, embodiments of this application provide an electrical device, including a battery cell from the first aspect of this application or a battery device from the second aspect of this application.

[0018] Fourthly, embodiments of this application provide a negative electrode sheet, including a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein a lithium replenishment layer is disposed on the side of the negative electrode film layer away from the negative electrode current collector; the negative electrode film layer includes: a first region located at both ends of the negative electrode current collector along a first direction, the first direction being perpendicular to the thickness direction of the negative electrode sheet; a second region continuously disposed along the first direction with the first region, and the second region being sandwiched between the first regions; wherein the porosity of the negative electrode film layer located in the first region is The porosity of the negative electrode film layer located in the second region is

[0019] Fifthly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising the following steps:

[0020] Provide negative electrode slurry;

[0021] The negative electrode slurry is coated on at least one side surface of the negative electrode current collector to form a negative electrode film layer. The negative electrode film layer includes a first region and a second region. The first region is located at both ends of the negative electrode current collector along a first direction, which is perpendicular to the thickness direction of the negative electrode sheet. The second region is continuously disposed with respect to the first region along the first direction, and the second region is sandwiched between the first regions.

[0022] The first region is baked at a first temperature, and the second region is baked at a second temperature, wherein the first temperature is lower than the second temperature;

[0023] A lithium replenishment layer is formed on the surface of the negative electrode film.

[0024] According to embodiments of this application, by baking the negative electrode sheet at different temperatures in the first and second regions, the negative electrode film layer exhibits greater rebound in the high-temperature baking region, thus achieving higher porosity in this region, while the negative electrode film layer in the low-temperature baking region achieves lower porosity. By employing different baking temperatures at different locations on the negative electrode sheet, the central portion of the negative electrode sheet (i.e., the second region) can achieve higher porosity, thereby improving the electrolyte wettability in the central portion of the negative electrode sheet. This shortens the time difference between electrolyte wetting the ends and the center of the negative electrode sheet, enhances the film formation consistency on the surface of the negative electrode sheet, and ultimately improves the cycle performance of the battery cell.

[0025] Therefore, the method for preparing the negative electrode sheet provided in the fifth aspect embodiment of this application can be used to prepare the negative electrode sheet in the four aspects embodiment of this application.

[0026] In some embodiments, the first temperature is 90°C-180°C.

[0027] In some embodiments, the second temperature is 150°C-220°C.

[0028] In some embodiments, the step of baking the first region at a first temperature and baking the second region at a second temperature includes: baking the first region and the second region at the first temperature, and then baking the second region at the second temperature. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0030] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0031] Figure 2 This is an exploded schematic diagram of a battery provided for some embodiments of this application.

[0032] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0033] Figure 4 This is a cross-sectional schematic diagram of the negative electrode sheet provided in some embodiments of this application.

[0034] Figure 5 for Figure 1 The diagram shows a schematic of the negative electrode film layer on the negative electrode plate.

[0035] The accompanying drawings are not necessarily drawn to scale.

[0036] The reference numerals in the attached drawings are explained as follows: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Receiving space; 6. Battery module; 7. Battery cell; 8. Negative electrode sheet; 81. Negative electrode current collector; 82. Negative electrode film; 821. First region; 822. Second region; 83. Lithium replenishment layer. Detailed Implementation

[0037] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0038] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0044] 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.

[0045] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0046] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0047] The battery device mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0048] A single battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. When there are multiple battery cells, they are connected in series, parallel, or mixed connections through a busbar.

[0049] In some embodiments, the battery device may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0050] In some embodiments, the battery device may be a battery pack, which includes a housing and individual battery cells, with the individual battery cells or battery modules housed within the housing.

[0051] 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.

[0052] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0053] The technical solutions described in the embodiments of this application are applicable to battery devices and electrical devices that use battery devices.

[0054] Battery devices can be used as the power source for electrical devices or as energy storage units for electrical devices. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0055] Electrical devices can choose the type of battery device according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0056] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0057] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0058] like Figure 1 As shown, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0059] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0060] In some embodiments, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0061] Figure 2 This is a schematic diagram of a battery explosion provided for some embodiments of this application. For example... Figure 2 As shown, the battery device 2 includes a housing 5 and battery cells (not shown), with the battery cells housed within the housing 5.

[0062] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0063] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0064] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0065] In battery device 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells are connected in both series and parallel configurations. Multiple battery cells can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells is housed in housing 5. Alternatively, multiple battery cells can first be connected in series, in parallel, or in a mixed configuration to form battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a mixed configuration to form a whole assembly, which is then housed in housing 5.

[0066] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0067] like Figure 3 As shown, in some embodiments, there are multiple battery cells 7, which are first connected in series, parallel, or mixed to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or mixed to form a whole and housed in a casing.

[0068] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6.

[0069] The battery cells mentioned in the embodiments of this application may include lithium-ion battery cells or sodium-ion battery cells.

[0070] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0071] Electrode assemblies generally include a positive electrode, a negative electrode, and a separator.

[0072] Lithium replenishment technology using lithium metal and other lithium sources as negative electrode sources can significantly improve the lifespan of individual battery cells. However, in practical applications, it has been found that because the electrolyte wets the negative electrode from both sides towards the center, a solid electrolyte interface (SEI) film simultaneously forms on the surface of the negative electrode during the electrolyte wetting process. This consumes film-forming additives in the electrolyte, and gas is generated during film formation. The formation of the SEI film and gas generation on the negative electrode hinder the electrolyte wetting rate, resulting in poorer electrolyte wettability in the center of the negative electrode. The central part of the negative electrode is wetted later than the sides, leading to a reduced amount of film-forming additives received, poor film quality, and ultimately uneven film formation, affecting the cycle performance of the individual battery cells.

[0073] In view of this, the embodiments of this application target battery cells with lithium replenishment on the negative electrode sheet. By adjusting the structural design of the negative electrode sheet, the difference in electrolyte wettability between the middle position and both sides of the negative electrode sheet with the lithium replenishment layer is reduced, thereby improving the film formation consistency of the negative electrode sheet and thus improving the cycle performance of the battery cell.

[0074] [Negative electrode plate]

[0075] like Figure 4 and Figure 5 As shown, the negative electrode sheet 8 includes a negative current collector 81 and a negative electrode film layer 82 located on at least one side of the negative current collector 81. A lithium replenishment layer 83 is disposed on the side of the negative electrode film layer 82 away from the negative current collector 81. The negative electrode film layer 82 includes a first region 821 and a second region 822. The first region 821 is located at both ends of the negative current collector 81 along a first direction X, and the first direction X is perpendicular to the thickness direction of the negative electrode sheet 8. The second region 822 is continuously disposed with the first region 821 along the first direction X, and the second region 822 is sandwiched between the first regions 821. The porosity of the negative electrode film layer located in the first region 821 is... The porosity of the negative electrode film layer located in the second region 822 is

[0076] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the current collector.

[0077] This application embodiment differentiates the porosity of the negative electrode film layer, such that when the porosity of the negative electrode film layer in the first region and the negative electrode film layer in the second region meet the above-mentioned range, the negative electrode film layer located in the middle of the negative electrode sheet has a higher porosity. The electrolyte wets faster in the middle of the negative electrode sheet, thereby improving the electrolyte wetting ability in the middle of the negative electrode sheet, accelerating the electrolyte wetting speed in the middle of the negative electrode sheet, and shortening the time difference between the electrolyte reaching the end and middle of the negative electrode sheet. This allows the middle of the negative electrode sheet to receive sufficient film-forming additives, thereby improving the film uniformity of the negative electrode sheet and improving the cycle performance of the battery cell.

[0078] In some embodiments, the porosity of the negative electrode film layer located in the first region and the porosity of the negative electrode film layer located in the second region It can satisfy: As an example, The value can be 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, or a range of any of the above values. Optionally,

[0079] According to the embodiments of this application, by ensuring that the porosity of the negative electrode film layer in the first region and the porosity of the negative electrode film layer in the second region meet the above-mentioned range, the difference in electrolyte wettability between the end and middle of the negative electrode sheet can be further reduced, the time difference of electrolyte reaching the end and middle of the negative electrode sheet can be shortened, the film uniformity of the negative electrode sheet can be further improved, and the cycle performance of the battery cell can be improved.

[0080] In some embodiments, the porosity of the negative electrode film layer located in the first region It can satisfy: As an example, It can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range of any of the above values. Optionally,

[0081] According to the embodiments of this application, by making the porosity of the negative electrode film layer located in the first region meet the above-mentioned range, the end of the negative electrode sheet can have a suitable electrolyte wetting speed, and the negative electrode sheet can have extremely high compaction density, which is beneficial to improving the energy density of the battery cell.

[0082] In some embodiments, the porosity of the negative electrode film layer located in the first region It can satisfy: As an example, It can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, or any range of the above values. Optionally,

[0083] According to the embodiments of this application, by making the porosity of the negative electrode film layer located in the second region meet the above-mentioned range, the middle part of the negative electrode sheet can have a higher electrolyte wetting speed, improve the film formation consistency of the negative electrode, and at the same time, the negative electrode sheet can have extremely high compaction density, so that the battery cell has improved cycle performance and high energy density.

[0084] In this application, the porosity of the negative electrode film layer has a well-known meaning in the art and can be measured using methods and instruments known in the art. For example, a negative electrode sheet coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the composite positive electrode film layer on one side can be wiped off first) can be cut into small circular samples of a certain area, and the apparent volume V1 of the negative electrode sheet can be calculated. Referring to GB / T24586-2009, an inert gas (such as helium or nitrogen) is used as the medium, and the gas replacement method is adopted to measure the true volume V2 of the negative electrode sheet using a true density meter. The porosity of the negative electrode film layer = (V1-V2) / V1×100%. Multiple negative electrode sheet samples (such as 30 sheets) with good appearance and no powder shedding at the edges can be tested, and the average value of the results is taken, which can improve the accuracy of the test results. The testing instrument can be a Micromeritics AccuPyc II 1340 true density meter. In this application, the porosity values ​​of the negative electrode film layer in the first region and the negative electrode film layer in the second region can be obtained by sampling in the first region and the second region respectively.

[0085] In some embodiments, along the first direction, the size percentage of the second region, based on the total size of the negative electrode sheet, can be 25%-50%. As an example, based on the total size of the negative electrode sheet, the size percentage of the second region can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 2%, 33%, 34%, 5%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 3%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range of the above values. Optionally, based on the total size of the negative electrode sheet, the size percentage of the second region can be 30%-45%.

[0086] It can be understood that, along the first direction, the first region is respectively provided at both ends of the negative electrode current collector, and the widths of the two first regions in the first direction can be the same or different. When the widths of the first regions at both ends are the same, the second region is located at the center of the negative electrode current collector; when the widths of the first regions at both ends are different, the second region is located in the middle of the negative electrode current collector, biased towards the first region with the smaller width.

[0087] According to the embodiments of this application, by making the size ratio of the second region in the first direction within the above-mentioned range, the central region of the negative electrode sheet can have a higher porosity and the central part of the negative electrode sheet has better electrolyte wettability, thereby further improving the film uniformity of the negative electrode sheet and thus improving the cycle performance of the battery cell.

[0088] In some embodiments, the range of impedance values ​​of the negative electrode film determined based on AC impedance spectroscopy can be less than or equal to 1. As an example, the range of impedance values ​​of the negative electrode film determined based on AC impedance spectroscopy can be 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or any range of the above values. Optionally, the range of impedance values ​​of the negative electrode film determined based on AC impedance spectroscopy can be 0.3-1.0.

[0089] In this application, the impedance value of the negative electrode film can be determined using electrochemical impedance spectroscopy (EIS). The range of impedance values ​​can be obtained by measuring the impedance values ​​of different regions of the negative electrode film (for example, measuring the impedance values ​​of 10 regions spaced apart along the first direction on the negative electrode film), obtaining the impedance values ​​of different regions of the negative electrode film, and then calculating the range of all measured impedance values.

[0090] According to the embodiments of this application, by making the impedance difference of the negative electrode film layer meet the above range, the negative electrode film layer has high film formation consistency in different regions, thereby further improving the cycle performance of the battery cell.

[0091] In this embodiment, the first direction can be parallel to the length or width direction of the negative electrode sheet.

[0092] Optionally, the first aspect is parallel to the width direction of the negative electrode sheet. In this case, the dimension of the negative electrode sheet along the first direction is smaller than the dimension of the negative electrode sheet along the second direction. The first direction, the second direction, and the thickness direction are perpendicular to each other, that is, the first direction is parallel to the width direction of the negative electrode sheet, and the second direction is parallel to the length direction of the negative electrode sheet.

[0093] In some embodiments, the lithium replenishment layer includes a lithium replenishment material, which may include one or more of lithium metal or lithium alloy.

[0094] As an example, lithium alloys may include one or more of the following: lithium silicon alloys, lithium aluminum alloys, lithium magnesium alloys, and lithium tin alloys.

[0095] In some embodiments, the lithium replenishment material may include one or more of lithium foil, lithium strip, lithium powder, and pre-lithiation reagent.

[0096] In some embodiments, the thickness of the lithium replenishment layer can be 2μm-6μm. As an example, the thickness of the lithium replenishment layer can be 2μm, 3μm, 4μm, 5μm, 6μm, or any range of the above values.

[0097] In some embodiments, the negative electrode film may include a negative electrode active material.

[0098] As an example, the negative electrode active material may include one or more of the following: artificial graphite, natural graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, and silicon-carbon composites.

[0099] Silicon-based composite materials can be prepared by methods known in the art. For example, they can be prepared by vapor deposition using graphite and silicon materials as raw materials.

[0100] In some embodiments, the negative electrode active material may further include one or more of Li, Sn, Zn and their alloys.

[0101] 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.

[0102] 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-Na), PTC thermistor materials, etc.

[0103] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one side of the polymeric material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymeric material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0104] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer sandwiched between the negative electrode current collector and the negative electrode film layer and located on the surface of the negative electrode current collector, which may be composed of a conductive agent and a binder; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0105] [Preparation method of negative electrode sheet]

[0106] Another embodiment of this application provides a method for preparing a negative electrode sheet, which may include the following steps S10 to S40:

[0107] S10 provides negative electrode slurry;

[0108] S20, a negative electrode slurry is coated on at least one side surface of the negative electrode current collector to form a negative electrode film layer. The negative electrode film layer includes a first region and a second region. The first region is located at both ends of the negative electrode current collector along a first direction, and the first direction is perpendicular to the thickness direction of the negative electrode sheet. The second region is continuously disposed with the first region along the first direction, and the second region is sandwiched between the first regions.

[0109] S30, the first region is baked at a first temperature, and the second region is baked at a second temperature, wherein the first temperature is lower than the second temperature;

[0110] S40 forms a lithium replenishment layer on the surface of the negative electrode film.

[0111] According to embodiments of this application, by baking the negative electrode sheet at different temperatures in the first and second regions, the negative electrode film layer exhibits greater rebound in the high-temperature baking region, thus achieving higher porosity in this region, while the negative electrode film layer in the low-temperature baking region achieves lower porosity. By applying different baking temperatures to different locations on the negative electrode sheet, the central location (i.e., the second region) of the negative electrode sheet can achieve higher porosity, thereby improving the electrolyte wettability in the central location of the negative electrode sheet. This shortens the time difference between electrolyte wetting the ends and the center of the negative electrode sheet, enhances the film formation consistency on the surface of the negative electrode sheet, and ultimately improves the cycle performance of the battery cell. Therefore, the method for preparing the negative electrode sheet provided in this application embodiment can be used to prepare the negative electrode sheet of this application embodiment.

[0112] In some embodiments, the first temperature can be 90℃-180℃. As examples, the first temperature can be 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, or 180℃. Optionally, the first temperature can be 110℃-170℃.

[0113] In some embodiments, the second temperature can be 150°C-220°C. As an example, the second temperature can be 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, or any range of the above values.

[0114] In some embodiments, step S30 may include: baking the first region and the second region at a first temperature, and then baking the second region at a second temperature.

[0115] According to the embodiments of this application, when baking the negative electrode sheet, the entire negative electrode film layer can be baked at a first temperature first, and then the second region can be baked at a second temperature. The high-temperature baking makes the second region of the negative electrode film layer have a greater rebound and thus have a high porosity.

[0116] In this embodiment, the baking process for the negative electrode sheet can be carried out using methods known in the art, such as laser heating.

[0117] In this application, the thickness of each layer in the negative electrode sheet can be measured and analyzed using SEM (scanning electron microscope) of the cross-section of the negative electrode sheet, or it can be measured using a laser thickness gauge. In this application, the microscopic morphology of the cross-section of the negative electrode sheet can be observed, allowing for the observation of the interface between the current collector and the negative electrode film layer, thereby determining the thickness of each layer. In this application, the cross-section of the electrode sheet refers to the cross-section formed by slicing along the thickness direction of the electrode sheet. The microscopic morphology of the cross-section of the negative electrode sheet can be observed and combined with compositional analysis, such as EDS and X-ray diffraction (XRD) analysis, to determine the elemental composition of each layer of the negative electrode sheet. Additionally, instruments such as focused electron beam (FIB) microscopes (e.g., FEI Scios2HiVa equipment) and ion cross-section polishers (e.g., JEOL's IB-09010CP argon ion cross-section polisher) can be used to polish the cross-section to obtain a clear cross-section.

[0118] [Positive electrode plate]

[0119] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the current collector, the positive electrode film layer including a positive active material.

[0120] As an example, the current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the current collector.

[0121] In some embodiments, the positive electrode active material may include one or more of lithium phosphate, layered lithium transition metal oxide, Prussian blue compounds, polyanionic compounds, and sodium transition metal oxide.

[0122] If the positive electrode active material is one or more of lithium phosphate and layered lithium transition metal oxide, then the positive electrode active material can be used in lithium-ion battery cells; if the positive electrode active material is one or more of Prussian blue compounds, polyanionic compounds, and sodium transition metal oxide, then the positive electrode material can be used in sodium-ion battery cells.

[0123] Lithium-containing phosphates may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their respective modified compounds.

[0124] Examples of layered lithium-containing transition metal oxides may include 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, and their respective modified compounds.

[0125] In some embodiments, the layered lithium-containing transition metal oxide may include Ni. The molar amount of Ni may account for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; optionally, the molar amount of Ni may account for more than 80% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; more preferably, the molar amount of Ni may account for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

[0126] The higher the Ni content in layered lithium-containing transition metal oxides, the higher the energy density of the battery cell.

[0127] In some embodiments, layered lithium-containing transition metal oxides may include Li a Ni b Co c M d O e A f Wherein, 0 < a ≤ 1.2; 0.8 ≤ b < 1; 0 < c < 1; 0 < d < 1; b + c + d = 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; A includes, but is not limited to, one or more of N, F, S, and Cl. This can further improve the energy density of individual battery cells.

[0128] In some embodiments, as an example, layered lithium-containing transition metal oxides may include, but are not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.06 Mn 0.04 O2, LiNi 0.92 Co 0.06 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2N 0.02 One or more of them.

[0129] During the charging and discharging process of a battery cell, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar Li content may change when the positive electrode active material is applied to the battery cell.

[0130] In some embodiments, as an example, sodium transition metal oxides may include, but are not limited to:

[0131] Na 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0132] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 It is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0133] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,

[0134] 0.67 <d+e<0.8,b+c+d+e=1。

[0135] In some embodiments, as an example, the polyanionic compound may include, but is not limited to:

[0136] A 1 f M 3 g (PO4) i O j X 1 3-j, wherein A is one or more selected from H, Li, Na, K and NH4, and M 3 is one or more selected from Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, and X 1 is one or more selected from F, Cl and Br, 0<f≤4, 0<g≤2, 1≤i≤3, 0≤j≤2;

[0137] Na n M 4 PO4X 2 , wherein M 4 is one or more selected from Mn, Fe, Co, Ni, Cu and Zn, and X 2 is one or more selected from F, Cl and Br, 0<n≤2;

[0138] Na p M 5 q (SO4)3, wherein M 5 is one or more selected from Mn, Fe, Co, Ni, Cu and Zn, 0<p≤2, 0<q≤2;

[0139] Na s Mn t Fe 3-t (PO4)2(P2O7), wherein 0<s≤4, 0≤t≤3, for example, t is 0, 1, 1.5, 2 or 3.

[0140] In some embodiments, by way of example, Prussian blue analog compounds may include but are not limited to:

[0141] A u M 6 v [M 7 (CN)6] w ·xH2O, wherein A is H + , NH4 + , one or more of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, 0<u≤2, 0<v≤1, 0<w≤1, 0<x<6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr2+ Ba 2+ and Ra 2+ One or more of them, M 6 and M 7 Each is an independently selected cation of one or more transition metal elements chosen from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W. Optionally, A is Li. + Na + and K + One or more of them, M 6 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni, and Cu, M 7 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni and Cu.

[0142] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0143] 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.

[0144] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0145] In some implementations, the weight percentage of the binder in the positive electrode film layer is greater than or equal to 0.5%, which is beneficial for obtaining good adhesion performance.

[0146] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In some embodiments, the current collector serving as the positive electrode may also be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be made by forming a metal material, such as aluminum, aluminum alloy, copper, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, on the polymer material substrate. The polymer material substrate may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and other substrates.

[0148] In some embodiments, the thickness of the positive current collector is from 4 μm to 20 μm. It is optionally from 6 μm to 18 μm, and more preferably from 8 μm to 16 μm.

[0149] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0150] In some embodiments, the electrode sheet provided in this application can be a negative electrode sheet.

[0151] [Electrolytes]

[0152] A single battery cell includes an electrolyte.

[0153] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0154] In some embodiments, the electrolyte includes anion, which may include bis(fluorosulfonyl)imide anion (FSI). - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), dioxaborate anion (BOB) - ), difluorooxalate borate anion (DFOB) - ), difluorodioxanol phosphate anion (DFOP) - ), tetrafluorooxalate phosphate anion (TFOP) - ), difluorophosphate anion (PO2F2) - ), hexafluorophosphate anion (PF6) - ), tetrafluoroborate anion (BF4) - ), hexafluoroarsenate anion (AsF6) - ), trifluoromethanesulfonate anion (CF3SO3) - One or more of the following.

[0155] In some embodiments, the electrolyte includes cations, which may include one or more of lithium ions and sodium ions.

[0156] In some embodiments, the concentration of the electrolyte salt may be 0.3 mol / L or higher, optionally 0.7 mol / L or higher, and further optionally 4 mol / L or lower, optionally 2.5 mol / L or lower, or 1.7 mol / L or lower. When the concentration of the electrolyte salt is within the above range, the electrolyte can have a suitable ionic conductivity.

[0157] Organic solvents may include, but are not limited to, one or more of esters, ethers, sulfones, and nitriles. Esters may include, but are not limited to, one or more of carbonates, phosphate esters, carboxylic esters, sulfate esters, and sulfonates. Carbonates may include cyclic carbonates and / or chain carbonates; optionally, carbonates may include both cyclic and chain carbonates. Chain carbonates may include low-viscosity polar chain carbonates, aliphatic branched carbonates, etc.

[0158] As an example, organic solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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), diethyl sulfone (ESE), dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of the following: decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecylfluorohexyl methyl ether, 5-trifluoromethyl dodecylfluorohexyl ethyl ether, 5-trifluoromethyl dodecylfluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexadecylfluorooctyl methyl ether, 7-trifluoromethyl hexadecylfluorooctyl ethyl ether, and 7-trifluoromethyl hexadecylfluorooctyl propyl ether.

[0159] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0160] [Isolation Component]

[0161] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0162] In some embodiments, the isolation chamber includes an isolation membrane. This application does not impose any particular limitation on the type of isolation membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0163] 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, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation. The separator may be a single component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be applied to the surface of the separator.

[0164] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0165] Example

[0166] 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.

[0167] Example 1

[0168] Positive electrode sheet

[0169] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 80:10:10 and then added to the solvent N-methylpyrrolidone (NMP) to uniformly disperse and obtain a positive electrode slurry. The solid content of the positive electrode slurry is controlled to be 60%. The positive electrode slurry is coated onto the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0170] Negative electrode sheet

[0171] A negative electrode slurry is prepared by uniformly mixing graphite, conductive carbon, and sodium polyacrylate in deionized water at a mass ratio of 95:2:3. The negative electrode slurry is then uniformly coated on the surface of copper foil, a negative electrode current collector, and dried to form a negative electrode film. After cold pressing and slitting, the negative electrode sheet is obtained.

[0172] The negative electrode film layer includes a first region and a second region. The first region is located at both ends of the negative electrode current collector along a first direction, which is perpendicular to the thickness direction of the negative electrode sheet and parallel to the width direction of the negative electrode sheet. The second region is continuously disposed with the first region along the first direction and sandwiched between the first regions. Based on the total width of the negative electrode sheet, the width of the first region accounts for 40%. The negative electrode sheet is unwound and baked, wherein the first region is baked at 150°C and the second region is baked at 200°C, and the unwound baking rate is 15 m / min.

[0173] After baking, a 5μm lithium foil is coated onto the surface of the negative electrode film using a cold press to form a lithium replenishment layer.

[0174] Separating membrane

[0175] A polyethylene (PE) film with a thickness of 12μm was selected.

[0176] electrolyte

[0177] The electrolyte solvent is a mixture of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1. The electrolyte salt is LiPF6, and the concentration of the electrolyte salt is 1 mol / L.

[0178] battery cell

[0179] The positive electrode, negative electrode, and separator are stacked in sequence and wound to form a wound electrode assembly. The electrode assembly is placed into the housing and injected with electrolyte to obtain a single battery cell.

[0180] Examples 2-9

[0181] The preparation method of the battery cell is similar to that in Example 1, except that the parameters of the negative electrode are different. For details of the parameter adjustments, please refer to Table 1.

[0182] Comparative Examples 1-2

[0183] The preparation method of the battery cell is similar to that in Example 1, except that the negative electrode sheet is not unwound and baked. For specific parameter adjustments, please refer to Table 1.

[0184] Comparative Example 3

[0185] The preparation method of the battery cell is similar to that in Example 1, except that the temperature for unwinding and baking the negative electrode sheet is different. For details of the parameter adjustments, please refer to Table 1.

[0186] Table 1

[0187]

[0188]

[0189] Test section

[0190] 1. Electrolyte wetting height of negative electrode plate

[0191] Disassemble the battery cell to obtain the negative electrode sheet. Immerse one end of the negative electrode sheet in the electrolyte to a depth of 10 mm below the electrolyte surface. Let it stand for 10 minutes and record the height of the electrolyte wetting the upper part of the negative electrode sheet.

[0192] 2. Range of negative electrode film impedance values

[0193] The negative electrode sheet is obtained by disassembling the battery cell. The impedance value of the negative electrode film is measured at 10 locations (covering the first and second regions) in the width direction using AC impedance spectroscopy. Then the range of impedance values ​​is calculated.

[0194] 3. Ear temperature rise

[0195] A temperature sensing wire is placed in the battery cell during manufacturing. The temperature sensing wire is located between the two tabs of the battery cell. Then, liquid is injected into the battery cell, and the highest temperature measured by the temperature sensing wire is recorded. This highest temperature is the tab temperature rise.

[0196] 4. Cyclic performance

[0197] At 25°C, the battery cell was charged to 3.65V at a constant current of 0.33C, allowed to stand for 30 minutes, and then discharged to 2.5C at a constant current of 0.33C. The discharge capacity C0 was recorded. The battery cell was then subjected to charge-discharge cycles using the above method, and the discharge capacity C on the nth cycle was recorded. n Cyclic capacity retention rate (%) = C n / C0×100%.

[0198] The test results are detailed in Table 2.

[0199] Table 2

[0200]

[0201]

[0202] Based on the data in Table 2, the battery cell provided in this application embodiment, by baking with gradient temperature, makes the first and second regions of the negative electrode sheet have different porosities, which can improve the electrolyte wettability of the negative electrode sheet and thus improve the cycle performance of the battery cell.

[0203] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The negative electrode includes a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein a lithium replenishment layer is disposed on the side of the negative electrode film layer away from the negative electrode current collector; the negative electrode film layer comprises: The first region is located at both ends of the negative electrode current collector along a first direction, which is perpendicular to the thickness direction of the negative electrode sheet. The second region is continuously disposed along the first region in a first direction, and the second region is sandwiched between the first regions; wherein, The porosity of the negative electrode film layer located in the first region is φ1, and the porosity of the negative electrode film layer located in the second region is φ2, where φ1 < φ2.

2. The battery cell according to claim 1, characterized in that, 0.66≤φ1 / φ2≤0.

85.

3. The battery cell according to claim 2, characterized in that, 25% ≤ φ1 ≤ 35%; and / or 30% ≤ φ2 ≤ 45%.

4. The battery cell according to any one of claims 1-3, characterized in that, Along the first direction, based on the total size of the negative electrode sheet, the size ratio of the second region is 25%-50%.

5. The battery cell according to any one of claims 1-4, characterized in that, The dimension of the negative electrode sheet along the first direction is smaller than the dimension of the negative electrode sheet along the second direction, and the first direction, the second direction and the thickness direction are perpendicular to each other.

6. The battery cell according to any one of claims 1-5, characterized in that, The range of impedance values ​​of the negative electrode film determined by AC impedance spectroscopy is less than or equal to 1.

7. The battery cell according to claim 6, characterized in that, The impedance range of the negative electrode film, as determined by AC impedance spectroscopy, is 0.3–1.

0.

8. The battery cell according to any one of claims 1-7, characterized in that, The lithium replenishment layer includes a lithium replenishment material, which includes one or more of lithium metal or lithium alloy.

9. The battery cell according to any one of claims 1-8, characterized in that, The thickness of the lithium replenishment layer is 2μm-6μm.

10. A battery device, characterized in that, Includes the battery cell according to any one of claims 1-9.

11. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1-9 or the battery device according to claim 10.

12. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein a lithium replenishment layer is disposed on the side of the negative electrode film layer away from the negative electrode current collector; the negative electrode film layer includes: The first region is located at both ends of the negative electrode current collector along a first direction, which is perpendicular to the thickness direction of the negative electrode sheet. The second region is continuously disposed along the first region in a first direction, and the second region is sandwiched between the first regions; wherein, The porosity of the negative electrode film layer located in the first region is φ1, and the porosity of the negative electrode film layer located in the second region is φ2, where φ1 < φ2.

13. A method for preparing a negative electrode sheet, characterized in that, Includes the following steps: Provide negative electrode slurry; The negative electrode slurry is coated on at least one side surface of the negative electrode current collector to form a negative electrode film layer. The negative electrode film layer includes a first region and a second region. The first region is located at both ends of the negative electrode current collector along a first direction, which is perpendicular to the thickness direction of the negative electrode sheet. The second region is continuously disposed with the first region along the first direction and sandwiched between the first regions. The first region is baked at a first temperature, and the second region is baked at a second temperature, wherein the first temperature is lower than the second temperature; A lithium replenishment layer is formed on the surface of the negative electrode film.

14. The preparation method according to claim 13, characterized in that, The first temperature is 90℃-180℃; and / or The second temperature is 150℃-220℃.

15. The preparation method according to claim 13 or 14, characterized in that, The steps of baking the first region at a first temperature and baking the second region at a second temperature include: The first region and the second region are baked at a first temperature, and then the second region is baked at a second temperature.

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