Battery cell, battery device, and electric device

Abstract

The present disclosure provides a battery cell, comprising a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer comprises a first negative electrode film layer. The negative electrode sheet extends in a first direction. The length of the negative electrode sheet in the first direction being greater than the length in a second direction. The second direction is perpendicular to the first direction. The first negative electrode film layer comprises a first region, a second region and a third region which are sequentially arranged in the second direction of the negative electrode sheet, wherein the first region and the third region comprise a first active substance, and the second region comprises a second active substance; and the electronic conductivity and / or ionic conductivity of the second region is less than the electronic conductivity and / or ionic conductivity of the first region and the third region.

Description

Battery cells, battery packs, and electrical devices

[0001] Cross-references to related applications

[0002] This disclosure is based on and claims priority to Chinese patent applications No. 202411754765.4, filed on December 2, 2024, entitled "Battery Cell, Battery Device and Electrical Device", and No. 202510329280.9, filed on March 19, 2025, entitled "Battery Cell, Battery Device and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of lithium battery technology, and in particular to a battery cell, a battery device, and an electrical device. Background Technology

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

[0005] However, during the charging and discharging process of the battery, lithium plating is prone to occur in the central region of the electrode, which affects the battery's rate performance and cycle performance. Therefore, improvements are needed to address this issue. Summary of the Invention

[0006] This disclosure is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery device and an electrical device. The battery cell prepared by this disclosure can effectively alleviate the problem of lithium plating in the middle and improve the cycle life of the battery cell.

[0007] To achieve the above objectives, a first aspect of this disclosure provides 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 surface of the negative current collector, the negative electrode film layer including a first negative electrode film layer, the negative electrode sheet extending along a first direction, the length of the negative electrode sheet in the first direction being greater than the length in a second direction, the second direction being perpendicular to the first direction, the first negative electrode film layer including a first region, a second region and a third region sequentially disposed along the second direction of the negative electrode sheet, wherein the first region and the third region include a first active material, and the second region includes a second active material; wherein the electronic conductivity and / or ionic conductivity of the second region is less than the electronic conductivity and / or ionic conductivity of the first region and the third region.

[0008] Therefore, by setting three regions along the second direction in the negative electrode film layer, and setting the electronic conductivity and / or ionic conductivity of the second region (i.e., the middle region) to be lower than that of the first and third regions (i.e., the edge / side regions), ions preferentially embed into the edge / side regions with higher electronic conductivity and / or ionic conductivity, thereby adjusting the distribution of active ions, reducing the problem of high SOC in the middle region, balancing the stress distribution inside the electrode, and making the overall polarization of the electrode tend to be consistent, thus effectively alleviating the problem of lithium plating in the middle of the electrode, and improving the rate performance and cycle performance of the battery.

[0009] In some embodiments, the negative electrode film layer further includes a second negative electrode film layer located on the side of the first negative electrode film layer facing or away from the negative electrode current collector. This design facilitates the creation of a gradient distribution of the characteristics (e.g., capacity) of each layer along the thickness direction of the electrode, thereby further improving battery performance.

[0010] In some embodiments, the first active material includes first silicon-carbon particles, and the second active material includes second silicon-carbon particles, wherein the average particle size of the first silicon-carbon particles is smaller than the average particle size of the second silicon-carbon particles. By adjusting the average particle size of silicon-carbon particles in different regions, the ionic conductivity of the first and third regions is made better than that of the second region, thereby effectively alleviating the problem of lithium plating in the center of the electrode and improving the rate performance and cycle performance of the battery.

[0011] In some embodiments, the average particle size of the first silicon-carbon particles is 0.1 to 0.9 times the average particle size of the second silicon-carbon particles. By providing first and second silicon-carbon particles with the aforementioned difference in average particle size, effective and moderate ion shunting is achieved during full charging, thereby effectively mitigating the problem of intermediate lithium plating on the electrode and improving the rate and cycle performance of the battery.

[0012] In some embodiments, the average particle size of the second silicon-carbon particles is 5 μm to 15 μm. In some embodiments, the average particle size of the first silicon-carbon particles is 2 μm to 10 μm. Thus, by setting the first and second silicon-carbon particles with average particle sizes within the above ranges, the ionic conductivity of both is within a suitable range, which is beneficial for ion insertion and extraction, thereby improving battery performance.

[0013] In some embodiments, the first active material comprises first graphite particles, the second active material comprises second graphite particles, and the average particle size of the first graphite particles is smaller than the average particle size of the second graphite particles. By making the average particle size of the graphite particles in the first and third regions smaller than that in the second region, the ionic conductivity of the first and third regions is superior to that of the second region. This promotes preferential dispersion of ions in the first and third regions during ion intercalation, thereby reducing lithium plating problems in the second region and improving the rate performance and cycle performance of the battery.

[0014] In some embodiments, the average particle size of the first graphite particles is 0.1 to 0.9 times the average particle size of the second graphite particles. Therefore, by providing first and second graphite particles with the aforementioned difference in average particle size, effective and moderate ion shunting is achieved during full charging, thereby effectively mitigating intermediate lithium plating and improving the battery's rate capability and cycle performance.

[0015] In some embodiments, the average particle size of the second graphite particles is 7 μm to 17 μm. In some embodiments, the average particle size of the first graphite particles is 3 μm to 13 μm. By setting the first and second graphite particles with average particle sizes within the above ranges, the ionic conductivity of the second and first graphite particles is within a suitable range, which is beneficial for ion insertion and extraction, thereby improving battery performance.

[0016] In some embodiments, the first active material includes first graphite particles, and the second active material includes second graphite particles, wherein the powder OI value of the first graphite particles is lower than that of the second graphite particles. Therefore, by setting a difference in the powder OI values ​​between the first and second graphite particles, the first and third regions more readily receive ions from the positive electrode, thereby generating effective current shunting. This effectively alleviates the intermediate lithium plating problem and improves the rate performance and cycle performance of the battery.

[0017] In some embodiments, the OI value of the first graphite particle is 0.1 to 0.9 times that of the second graphite particle. Therefore, by setting the first and second graphite particles with OI values ​​within the aforementioned range, the intermediate lithium plating problem can be effectively mitigated, and the rate capability and cycle performance of the battery can be improved.

[0018] In some embodiments, the powder OI value of the first graphite particles is 2 to 10. In some embodiments, the powder OI value of the second graphite particles is 6 to 14. Thus, the ionic conductivity of the first and third regions is within a suitable range, which is conducive to ion insertion and extraction, thereby improving battery performance.

[0019] In some embodiments, the first and third regions include a first dispersant, and the second region includes a second dispersant; and the ionic conductivity of the first dispersant is greater than that of the second dispersant. This establishes a difference in ionic conductivity within the negative electrode film, generating effective current shunting, thereby effectively mitigating the lithium plating problem in the second region and improving the rate performance and cycle performance of the battery.

[0020] In some embodiments, the contents of the first dispersant and the second dispersant are the same, ranging from 0.1% to 1%. This establishes a difference in ionic conductivity within the negative electrode film, resulting in effective current shunting. Furthermore, the use of the aforementioned dispersant content effectively reduces graphite particle agglomeration and improves the dispersion of graphite particles.

[0021] In some embodiments, the first dispersant comprises CMC-Li, and the second dispersant comprises CMC. Thus, by using a carboxymethyl cellulose salt capable of conducting Li / Na ions in the first and third regions, an ionic conductivity difference is created between the second region and the first and third regions, resulting in effective current splitting.

[0022] The resistivity of the first active material powder is lower than that of the second active material powder. This creates a difference in conductivity within the film, resulting in effective current shunting, which effectively alleviates the lithium plating problem in the second region and improves the battery's rate performance and cycle performance.

[0023] In some embodiments, the first active material comprises silicon-carbon particles with a powder resistivity of 4 Ω·m to 10 Ω·m at 16 MPa, and the second active material comprises silicon-carbon particles with a powder resistivity of 10 Ω·m to 17 Ω·m at 16 MPa. This establishes a conductivity difference within the film layer, generating effective current shunting, thereby effectively mitigating the lithium plating problem in the second region and improving the rate performance and cycle performance of the battery.

[0024] The first and / or second active materials comprise artificial graphite with an OI value of 2 to 14 and a graphitization degree of 91% to 93%. This gives the negative electrode film a suitable ion diffusion rate, thereby improving the rate performance of the battery.

[0025] In some implementations, the weight percentage of the first active material is lower than that of the second active material per unit area of ​​the negative electrode film. Consequently, the film resistance of the first and third regions is lower than that of the second region, and the second region has more active sites, thereby mitigating the lithium plating problem in the second region and improving the rate performance and cycle performance of the battery.

[0026] In some embodiments, the first active material is the same as the second active material. This is beneficial to the battery's processing performance.

[0027] In some embodiments, the first and third regions include a first conductive agent, and the second region includes a second conductive agent; and the conductivity of the first conductive agent is greater than that of the second conductive agent. This establishes a conductivity difference within the film layer, thereby adjusting the stress distribution in the negative electrode film layer, alleviating the lithium plating problem in the second region, and further improving the rate performance and cycle performance of the battery.

[0028] In some embodiments, the first and third regions include a first conductive agent, and the second region includes a second conductive agent; and based on the unit area weight of the negative electrode film, the content of the first conductive agent is greater than the content of the second conductive agent. This results in the first and third regions having better conductivity per unit area weight than the second region, thereby mitigating the lithium plating problem in the second region and improving the rate performance and cycle performance of the battery.

[0029] In some implementations, the sum of the lengths of the first region and the third region in the second direction is greater than 0 and less than or equal to 0.8, relative to the length of the negative electrode sheet in the second direction. This creates a conductivity difference in the second direction of the electrode sheet, reducing lithium plating issues in the second region and thus improving the rate performance and cycle performance of the battery.

[0030] In some implementations, the widths of the first and third regions may be the same or different. This allows for applicability to various application scenarios.

[0031] In some embodiments, the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector. This facilitates the creation of a gradient distribution of the characteristics (e.g., capacity) of each layer along the thickness direction of the electrode, thereby further improving the performance of the battery.

[0032] In some embodiments, the silicon content M1 in the first negative electrode film layer and the silicon content M2 in the second negative electrode film layer satisfy the following relationship: 2.5% ≤ M1 - M2 ≤ 68%. By making the silicon content M1 in the first negative electrode film layer greater than the silicon content M2 in the second negative electrode film layer, it is possible to construct a film layer with high upper capacity and low lower capacity, which is beneficial to improving the energy density and dynamic performance of the battery.

[0033] In some embodiments, the first negative electrode film layer comprises silicon-carbon particles and graphite particles, wherein M1 is 2.5% to 68%, and the second negative electrode film layer comprises graphite, wherein M2 is 0% to 40%. By ensuring that the silicon content in the first and second negative electrode film layers is within the above-mentioned ranges, both the energy density and kinetic performance of the battery cell can be balanced.

[0034] In some implementations, M1 is 5.5% to 48%, and / or M2 is 0% to 20%. This allows for a further balance between the energy density and kinetic performance of the battery cells.

[0035] In some embodiments, 5.5% ≤ M1-M2 ≤ 48%. In other embodiments, 10% ≤ M1-M2 ≤ 40%. This allows for the construction of a film layer with high upper capacity and low lower capacity, further improving the energy density and kinetic performance of the battery.

[0036] In some embodiments, the thickness of the first negative electrode film is 0.1 to 0.9 times the total thickness of the negative electrode film. This balances the overall conductivity and current shunting capability of the electrode, thereby further improving lithium plating in the second region while maintaining battery performance.

[0037] In some embodiments, the thickness of the first negative electrode film layer accounts for 0.12 to 0.8% of the total thickness of the negative electrode film layer. This further balances the overall conductivity and current shunting capability of the electrode, thereby improving lithium plating in the second region while maintaining battery performance.

[0038] In some embodiments, the total areal density of the negative electrode film is 0.1 g / 1540.25 mm². 2 Up to 0.2g / 1540.25mm 2 The areal density of the first negative electrode film is 0.01 g / 1540.25 mm. 2 Up to 0.1g / 1540.25mm 2 Therefore, it is possible to improve battery performance and energy density while taking into account the supporting capacity of the electrode sheets.

[0039] In some embodiments, the areal density of the first negative electrode film layer is 0.01 g / 1540.25 mm. 2 Up to 0.05g / 1540.25mm 2 This allows the first negative electrode film layer to maintain high capacity and good support capability.

[0040] In some embodiments, the silicon-carbon particles satisfy one or more of the following characteristics: (1) the silicon-carbon particles comprise porous carbon and silicon-containing material dispersed in the pores of the porous carbon; (2) the silicon-carbon particles further comprise a carbon-containing coating layer located on the surface of the porous carbon and / or the silicon-containing material; (3) the silicon content in the silicon-carbon particles is 30% to 70% by mass; (4) the BET specific surface area of ​​the silicon-carbon particles is 1.0 m². 2 / g to 6.7m 2 / g; (5) The mass content of carbon and other trace doping elements in the silicon-carbon particles is 40% to 70%. The above-mentioned silicon-carbon particles can provide suitable capacity, maintain the stability of the material structure and suitable conductivity.

[0041] In some embodiments, the ionic impedance and / or film resistance of the second region is 1.2 to 10 times that of the first and third regions. This allows for the creation of regions with different conductivity in the second direction of the electrode, thereby generating effective current shunting during ion insertion / extraction and electron transport. This reduces lithium plating in the second region, thereby improving the rate performance and cycle performance of the battery.

[0042] A second aspect of this disclosure provides a battery device, which includes the battery cell of the first aspect.

[0043] A third aspect of this disclosure provides an electrical device, which includes a battery cell from the first aspect. Attached Figure Description

[0044] Figure 1 shows a schematic diagram of the cross-section of the negative electrode film layer according to an embodiment of the present disclosure.

[0045] Figure 2 shows a schematic diagram of the cross-section of the negative electrode film layer according to another embodiment of the present disclosure.

[0046] Figure 3 shows a schematic diagram of the cross-section of the negative electrode film layer according to another embodiment of the present disclosure.

[0047] Figure 4 is a schematic diagram of a battery cell according to one embodiment of the present disclosure.

[0048] Figure 5 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 4.

[0049] Figure 6 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0050] Figure 7 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0051] Figure 8 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 7.

[0052] Figure 9 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0053] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 10 Negative electrode sheet; 101 Negative current collector; 102 Negative electrode film; S1 First region; S2 Second region; S3 Third region; 102a: First negative electrode film; 102b: Second negative electrode film. Detailed Implementation

[0054] 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 disclosure. 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 disclosure and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the 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 expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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 disclosure, 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.

[0056] It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or parts, these elements, components, areas, layers, and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or part from another element, component, area, layer, or part. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or part discussed below may be referred to as a second element, component, area, layer, or part. And the discussion of a second element, component, area, layer, or part does not imply that the first element, component, area, layer, or part necessarily exists in this disclosure.

[0057] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0059] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0060] Unless otherwise specified, all steps of this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means 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.

[0061] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0062] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0063] During the charging and discharging process of a battery, the electrochemical changes and stress distribution inside the electrode are uneven, with the stress distribution in the middle region being more concentrated, making the reaction more intense. As a result, the SOC (State of Charge) in the middle region of the electrode is higher, leading to the problem of lithium plating in the middle region.

[0064] To address these issues, high-viscosity separators are currently widely used to tightly bind the positive and negative electrode interfaces together, reducing the formation of gaps between the electrodes. However, the change in SoH (State of Health) is an intrinsic process; even with strong external forces to reduce the gaps, the problem of lithium plating in the middle of the cell cannot be fundamentally changed.

[0065] In view of this, the present invention proposes a battery cell, a battery device, and an electrical device.

[0066] battery cell

[0067] A first aspect of this disclosure provides a battery cell.

[0068] In this embodiment of the disclosure, 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.

[0069] The battery cell can be a lithium-ion battery, a sodium-ion battery, a sodium-lithium-ion battery, a lithium metal battery, or a sodium metal battery, but this disclosure does not limit the types of batteries.

[0070] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0071] [Negative electrode plate]

[0072] The battery cell includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode sheet extends along a first direction, and its length in the first direction is greater than its length in a second direction. The second direction is perpendicular to the first direction. The first negative electrode film layer includes a first region, a second region, and a third region sequentially disposed along the second direction of the negative electrode sheet. The first and third regions include a first active material, and the second region includes a second active material. The electronic conductivity and / or ionic conductivity of the second region is less than that of the first and third regions.

[0073] As mentioned above, the lithium plating phenomenon in the middle region is due to the higher stress concentration and more intense reaction in the middle region. Therefore, in this disclosure, the negative electrode film layer is divided into three regions along the second direction of the negative electrode sheet, and the electronic conductivity and / or ionic conductivity of the second region (i.e., the middle region) is lower than that of the first and third regions (i.e., the edge / side regions). This fundamentally reduces the electronic conductivity and / or ionic conductivity of the middle region. Thus, when faced with a large number of ion insertions and / or electron transports, it can promote the dispersion of ions and / or electrons to the side regions of the electrode sheet, thereby adjusting the distribution of active ions such as Li ions during full charge, reducing the problem of high SOC in the middle region, balancing the stress distribution inside the electrode sheet, and thus balancing the degree of chemical reaction inside the electrode sheet, making the overall polarization of the electrode sheet more uniform. This can effectively alleviate the lithium plating phenomenon in the middle of the electrode sheet, thereby improving the rate performance and cycle performance of the battery.

[0074] In some embodiments, as shown in FIG1, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 located on one side surface of the negative electrode current collector. The negative electrode film layer 102 includes a first region S1, a second region S2 and a third region S3.

[0075] In some embodiments, the electronic conductivity of the second region is less than that of the first and third regions. In some embodiments, the ionic conductivity of the second region is less than that of the first and third regions. In some embodiments, the electronic conductivity of the second region is less than that of the first and third regions, and the ionic conductivity of the second region is also less than that of the first and third regions.

[0076] In this disclosure, the term "electronic conductivity" refers to the ability of a material to conduct current as charge carriers, and is inversely related to resistivity. Typically, electronic conductivity can be tested using equipment and methods known in the art. Exemplarily, a battery is disassembled to obtain the negative electrode, which can then be measured using the four-probe method according to GB / T 30835-2014. The testing instrument can be a Crystallography ST2263 dual-electrical-measurement digital four-probe tester.

[0077] In this disclosure, the term "ionic conductivity" is a measure used to describe the tendency of ions to conduct in a substance. In some embodiments, the ionic conductivity is lithium-ion conductivity. In some embodiments, the ionic conductivity is sodium-ion conductivity. Typically, ionic conductivity can be tested using equipment and methods known in the art. Exemplarily, a coating is applied to the surface of a blank aluminum foil, cut into small discs with a diameter of 20 mm, and a coin cell is assembled in the following order: positive electrode shell, small disc (coated side up), gasket, spring, small disc (coated side down), and negative electrode shell. The electrochemical impedance spectroscopy (EIS) method is used to test the Nyquist plot using a Solartron 1470E CellTest multichannel electrochemical workstation. The Nyquist plot is then analyzed using the equivalent circuit curve fitting method. The difference in the abscissa of the intersection point of the extended curves in the low-frequency and high-frequency regions of the Nyquist plot with the horizontal axis reflects the ionic impedance R of the coating. The test voltage can be 10 mV, and the test frequency can be 0.1 Hz to 100 kHz. Alternatively, the battery can be disassembled to obtain the negative electrode sheet, which can then be cut to obtain, for example, the electrode sheet in the first region. This electrode sheet can then be assembled with a lithium metal sheet to form a coin cell. The coin cell can be subjected to electrochemical impedance spectroscopy, and the electrode ion impedance Rion can be obtained by fitting the impedance.

[0078] In this disclosure, the first direction is the extension direction of the negative electrode sheet, representing the length direction of the electrode sheet. The second direction is perpendicular to the first direction, representing the width direction of the electrode sheet.

[0079] In some embodiments, the negative electrode film layer further includes a second negative electrode film layer. In some embodiments, the second negative electrode film layer is located on the side of the first negative electrode film layer facing the negative electrode current collector, that is, the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector. In some embodiments, the second negative electrode film layer is located on the side of the first negative electrode film layer away from the negative electrode current collector. In this disclosure, by providing a second negative electrode film layer above or below the first negative electrode film layer along the thickness direction of the electrode sheet, it is beneficial to construct a gradient distribution of the characteristics (e.g., capacity) of each layer in the thickness direction of the electrode sheet, thereby further improving the performance of the battery.

[0080] In some embodiments, as shown in FIG2, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer located on one side surface of the negative electrode current collector, wherein the negative electrode film layer includes a first negative electrode film layer 102a and a second negative electrode film layer 102b, the first negative electrode film layer 102a including a first region S1, a second region S2 and a third region S3.

[0081] In some embodiments, as shown in FIG3, the negative electrode sheet 10 includes a negative current collector 101 and a negative electrode film layer located on one side surface of the negative current collector, wherein the negative electrode film layer includes a first negative electrode film layer 102a and a second negative electrode film layer 102b, the first negative electrode film layer 102a including a first region S1, a second region S2 and a third region S3.

[0082] In some embodiments, the first active material comprises first silicon-carbon particles, the second active material comprises second silicon-carbon particles, and the average particle size of the first silicon-carbon particles is smaller than the average particle size of the second silicon-carbon particles. A smaller average particle size indicates a shorter ion diffusion distance and superior ionic conductivity. By making the average particle size of the silicon-carbon particles in the first and third regions smaller than that in the second region, the ionic conductivity of the first and third regions is superior to that of the second region. This promotes ion dispersion in the first and third regions during ion intercalation, thereby reducing lithium plating in the second region and improving the rate performance and cycle performance of the battery.

[0083] In this disclosure, the "average particle size" can be tested using equipment and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used, referring to JY / T010-1996, to obtain a scanning electron microscope (SEM) image of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample with a length × width of 50 mm × 100 mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 1000x when measuring silicon carbide particles), read the particle size of each silicon carbide particle in each test area (i.e., take the distance between the two farthest points on the silicon carbide particle as the particle size). Count the number and particle size values ​​of silicon carbide particles in each test area, and take the arithmetic mean of the silicon carbide particles in each test area, which is the average particle size of the silicon carbide particles in the test sample. To ensure the accuracy of the test results, the above test can be repeated with multiple test samples (e.g., 10 samples), and the average value of each test sample can be taken as the final test result.

[0084] In some embodiments, the average particle size of the first silicon-carbon particles is 0.1 to 0.9 times the average particle size of the second silicon-carbon particles, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 times, or any combination thereof. By setting the first and second silicon-carbon particles with the aforementioned difference in average particle size, the difference in ionic conductivity between them can induce effective and moderate ion shunting during full charging, thereby effectively alleviating the problem of intermediate lithium plating on the electrode and improving the rate and cycle performance of the battery.

[0085] In some embodiments, the average particle size of the second silicon-carbon particles is from 5 μm to 15 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any combination thereof. In some embodiments, the average particle size of the first silicon-carbon particles is from 2 μm to 10 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination thereof. Therefore, by further limiting the difference in average particle size between the first and second silicon-carbon particles, lithium plating in the center of the negative electrode can be further mitigated, thereby further improving the cycle life of the secondary battery. Thus, by setting the first and second silicon-carbon particles with average particle sizes within the above-mentioned ranges, their ionic conductivity is within a suitable range, which is beneficial for ion insertion and extraction, thereby improving battery performance.

[0086] In some embodiments, the first active material comprises first graphite particles, the second active material comprises second graphite particles, and the average particle size of the first graphite particles is smaller than the average particle size of the second graphite particles. As mentioned above, a smaller average particle size indicates a shorter ion diffusion distance and better ionic conductivity. By making the average particle size of the graphite particles in the first and third regions smaller than that in the second region, the ionic conductivity of the first and third regions is superior to that of the second region. This promotes preferential dispersion of ions in the first and third regions during ion intercalation, thereby reducing lithium plating problems in the second region and improving the rate performance and cycle performance of the battery.

[0087] In some embodiments, the average particle size of the first graphite particles is 0.1 to 0.9 times the average particle size of the second graphite particles, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 times, or any combination thereof. As described above, by setting the first and second graphite particles with the aforementioned difference in average particle size, the difference in ionic conductivity between them can cause effective and moderate current shunting during full charge, thereby effectively mitigating intermediate lithium plating and improving the battery's rate and cycle performance.

[0088] In some embodiments, the average particle size of the second graphite particles is 7 μm to 17 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or any combination thereof. In some embodiments, the average particle size of the first graphite particles is 3-13 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, or any combination thereof. Therefore, by setting the first and second graphite particles with average particle sizes within the above ranges, their ionic conductivity is within a suitable range, which facilitates ion insertion and extraction, thereby improving battery performance.

[0089] In some embodiments, the OI value of the first graphite particles is lower than that of the second graphite particles. A smaller OI value indicates better isotropy of the material, which is more conducive to the material receiving ions from the positive electrode and to ion diffusion within the material. Therefore, by setting the OI value of the first graphite particles to be lower than that of the second graphite particles, the first and third regions more easily receive ions from the positive electrode, thereby creating a difference in ionic conductivity and generating effective current shunting. This effectively alleviates the intermediate lithium plating problem and improves the rate performance and cycle performance of the battery.

[0090] In this disclosure, the term "powder OI value" has a meaning known in the art and can be tested using instruments and methods known in the art. For example, an X-ray powder diffractometer (X'pert PRO) can be used for testing, and the test can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction pattern of the powder sample. The powder OI value of the sample is calculated according to OI value = I004 / I110. Wherein, I004 is the integrated area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I110 is the integrated area of ​​the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of this disclosure, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, the ray wavelength scanning 2θ angle range is 20° to 80°, and the scanning rate is 4° / min.

[0091] In some embodiments, the powder OI value of the first graphite particle is 0.1 to 0.9 times that of the powder OI value of the second graphite particle, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 times, or any combination thereof. By setting the powder OI values ​​of the first and second graphite particles as described above, the difference in ionic conductivity between them can induce effective and moderate current shunting during full charging, thereby effectively mitigating intermediate lithium plating and improving the battery's rate capability and cycle performance.

[0092] In some embodiments, the powder OI value of the first graphite particles is 2 to 10, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, or any combination thereof. In some embodiments, the powder OI value of the second graphite particles is 6 to 14, such as 6, 7, 8, 9, 10, 11, 12, 13, 14, or any combination thereof. By setting the first graphite particles with powder OI values ​​within the above ranges, the ionic conductivity of the first and third regions is within a suitable range, which facilitates ion insertion and extraction, thereby improving battery performance.

[0093] In some embodiments, the first and third regions include a first dispersant, and the second region includes a second dispersant; and the ionic conductivity of the first dispersant is greater than that of the second dispersant. Similarly, by providing a dispersant with relatively high ionic conductivity in the first and third regions and a dispersant with relatively low ionic conductivity in the second region, an ionic conductivity difference can be established in the film layer, thereby effectively shunting the flow and effectively mitigating lithium plating in the second region, thus improving the rate performance and cycle performance of the battery.

[0094] In some embodiments, the contents of the first and second dispersants are the same, ranging from 0.1% to 1%, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or any combination thereof, based on the total weight of the negative electrode film. By setting the first and second dispersants within this range, the difference in ionic conductivity between the first and third regions and the second region can be effectively established, thereby enabling effective current shunting. Simultaneously, it can effectively reduce the agglomeration of graphite particles and improve their dispersion, thus benefiting the rate performance and cycle performance of the battery.

[0095] In some embodiments, the first dispersant comprises lithium carboxymethyl cellulose (CMC-Li), and the second dispersant comprises sodium carboxymethyl cellulose (CMC). Thus, by using a carboxymethyl cellulose salt capable of conducting Li / Na ions in the first and third regions, an ionic conductivity difference is created between the second region and the first and third regions, resulting in effective current splitting.

[0096] In some embodiments, the resistivity of the first active material powder is lower than that of the second active material powder. Lower powder resistivity indicates better conductivity of the material. By setting the powder resistivity of the first active material to be lower than that of the second active material powder, a difference in conductivity between the first and third regions and the second region can be created, thereby generating effective current shunting and effectively mitigating lithium plating in the second region, thus improving the rate performance and cycle performance of the battery.

[0097] In this disclosure, the term "powder resistivity" is a parameter used to characterize the electrical conductivity of a material, and it can typically be tested using instruments and methods known in the art. For example, the active material can be pressed into cylindrical sheets of the same size and then tested using a four-probe or two-probe method.

[0098] In some embodiments, the first active material comprises silicon-carbon particles with a powder resistivity of 4 Ω·m to 10 Ω·m at 16 MPa, and the second active material comprises silicon-carbon particles with a powder resistivity of 10 Ω·m to 17 Ω·m at 16 MPa. Exemplarily, the silicon-carbon particles in the first active material have a powder resistivity of 4 Ω·m, 5 Ω·m, 6 Ω·m, 7 Ω·m, 8 Ω·m, 9 Ω·m, 10 Ω·m, or any combination thereof at 16 MPa, and the silicon-carbon particles in the second active material have a powder resistivity of 10 Ω·m, 11 Ω·m, 12 Ω·m, 13 Ω·m, 14 Ω·m, 15 Ω·m, 16 Ω·m, 17 Ω·m, or any combination thereof at 16 MPa. By employing highly conductive silicon-carbon particles in the first and third regions, and ordinary silicon-carbon particles in the second region, different conductivity levels can be achieved in different regions of the membrane. This facilitates electron transport in the first and third regions, thereby adjusting the consistency of charge and discharge of the negative electrode film and mitigating lithium plating in the second region. Consequently, the rate performance and cycle performance of the secondary battery are further improved. In this disclosure, a resistivity meter (Suzhou Jinglü Electronics ST2722) is used. A 1g powder sample is placed between the electrodes of the meter and subjected to a constant pressure of 16MPa using an electronic press for 15-25s. The sample height h (m), voltage U, current I, and resistance R (Ω) are recorded. The area S after powder pressing is 1cm². 2 The resistivity of the powder is calculated using the formula δ=S*R*1000 / h, with the unit being Ω·m.

[0099] In some embodiments, the first active material and / or the second active material comprises artificial graphite with a powder OI value of 2 to 14 and a graphitization degree of 91% to 93%. Exemplarily, the first active material and / or the second active material comprises artificial graphite with an OI value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or any combination thereof, and a graphitization degree of 91%, 91.5%, 92%, 92.5%, 93%, or any combination thereof. This enables the first negative electrode film layer (upper layer) to have a suitable ion diffusion rate, further improving the charging capability of the first negative electrode film layer.

[0100] In this disclosure, the term "graphitization degree" has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the test can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011. The average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure is obtained, and then calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. Here, d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure, expressed in nanometers (nm).

[0101] In some implementations, the weight percentage of the first active material is lower than that of the second active material per unit area of ​​the negative electrode film. By making the weight percentage of the active material per unit area in the first and third regions lower than that in the second region, less active material results in lower film resistance in the first and third regions compared to the second region. Furthermore, more active sites are provided in the second region, thereby mitigating lithium plating in the second region and improving the rate performance and cycle performance of the battery.

[0102] In some embodiments, the first active material and the second active material are the same. "The same" means that the first active material and the second active material are made of the same material. This is beneficial to the battery's processing performance.

[0103] In some embodiments, the first and third regions include a first conductive agent, and the second region includes a second conductive agent; and the conductivity of the first conductive agent is greater than that of the second conductive agent. By using a first conductive agent with higher conductivity in the first and third regions, electrons can be transported more quickly in the first and third regions under the same conditions, adjusting the consistency of the overall polarization of the electrode, thereby adjusting the stress distribution in the negative electrode film layer, which can alleviate lithium plating in the second region and further improve the rate performance and cycle performance of the battery.

[0104] For example, carbon nanotubes and graphene may be used as conductive agents in the first and third regions, and conductive carbon may be used as a conductive agent in the second region.

[0105] In some implementations, the content of the first conductive agent is greater than the content of the second conductive agent per unit area weight of the negative electrode film. By using more of the first conductive agent in the first and third regions, the conductivity of the first and third regions per unit area weight of the film is superior to that of the second region, thereby alleviating the lithium plating problem in the second region and improving the rate performance and cycle performance of the battery.

[0106] In some embodiments, the content of the first conductive agent and / or the second conductive agent is 0.05% to 2% based on the unit area weight of the negative electrode film, such as 0.05%, 0.1%, 0.15%, 0.2%, or any combination thereof.

[0107] In some embodiments, the sum of the lengths of the first and third regions in the second direction, relative to the length of the negative electrode sheet, is greater than 0 and less than or equal to 0.8, such as a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any combination thereof. By providing the first and third regions with higher electronic / ionic conductivity in the second direction compared to the second region, a region with a difference in conductivity can be created in the second direction of the electrode sheet, thereby generating effective current shunting when faced with ion insertion / extraction. This reduces lithium plating problems in the second region, thereby improving the rate performance and cycle performance of the battery.

[0108] In some implementations, the widths of the first and third regions may be the same or different. This allows for applicability to various application scenarios.

[0109] In some embodiments, the second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector. By providing the second negative electrode film layer between the first negative electrode film layer and the negative electrode current collector along the thickness direction of the electrode, it is beneficial to create a gradient distribution of the characteristics (e.g., capacity) of each layer in the thickness direction of the electrode, thereby further improving the performance of the battery. In some embodiments, the second negative electrode film layer comprises natural graphite particles with an average particle size of 6 μm to 25 μm, a graphitization degree of 90% to 96%, and a powder OI value of 4 to 10.

[0110] In some embodiments, the silicon content M1 in the first negative electrode film and the silicon content M2 in the second negative electrode film satisfy the following relationship: 2.5% < M1 - M2 ≤ 68%. The theoretical specific capacity of silicon is much greater than that of carbon; therefore, a higher silicon content indicates a higher capacity. By making the silicon content M1 in the first negative electrode film greater than the silicon content M2 in the second negative electrode film, it is possible to construct a film layer with a high upper capacity and a low lower capacity, which is beneficial for improving the energy density and kinetic performance of the battery.

[0111] In some embodiments, the first negative electrode film layer comprises silicon-carbon particles and graphite, with M1 being 2.5% to 68%; and the second negative electrode film layer comprises graphite, with M2 being 0% to 40%. This allows the silicon content M1 in the first negative electrode film layer to be greater than the silicon content M2 in the second negative electrode film layer, enabling the construction of a film layer with high upper capacity and low lower capacity, thereby improving the energy density and kinetic performance of the battery.

[0112] In some embodiments, M1 ranges from 5.5% to 48%, and exemplaryly, M1 is a range of 5.5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, or any combination thereof. This allows for a capacity gradient distribution while simultaneously enhancing the support capacity of the first negative electrode film layer, ensuring the stability of the electrode structure during high-concentration ion diffusion intercalation.

[0113] In some implementations, M2 is between 0 and 20%. Exemplarily, M2 is a range of 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any combination thereof. This allows for a suitable capacity gradient distribution, improving the battery's energy density.

[0114] In some embodiments, 10% ≤ M1-M2 ≤ 40%. Exemplarily, M1-M2 = 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any combination thereof. This allows for the construction of a film layer with a high upper capacity and a low lower capacity, improving the energy density and kinetic performance of the battery.

[0115] In some embodiments, the thickness of the first negative electrode film is 0.1-0.9% of the total thickness of the negative electrode film, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9% or any combination thereof. This balances the overall conductivity and current shunting capability of the electrode, thereby significantly improving lithium plating in the second region while maintaining battery performance.

[0116] In this disclosure, the thicknesses of the negative electrode sheet, the first negative electrode film layer, and the second negative electrode film layer in the cross-section of the negative electrode sheet in the second direction can be observed and measured in the following manner: Specifically, the battery is disassembled to obtain the negative electrode sheet, which is then fixed on a sample stage; the sample stage is installed in a sample holder and locked in place; the power of an argon ion cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL Corporation of Japan) is turned on and a vacuum is applied (e.g., 10⁻⁷ Pa); the argon flow rate is set (e.g., 0.12 MPa) and the polishing time is set (e.g., 90 min); the sample stage is adjusted to the swing mode to begin polishing. After polishing, the cross-section is subjected to cross-sectional morphology and elemental analysis tests to distinguish the first negative electrode film layer and the second negative electrode film layer, thereby obtaining the thicknesses of the negative electrode sheet, the first negative electrode film layer, and the second negative electrode film layer.

[0117] In some embodiments, the thickness of the first negative electrode film layer accounts for 0.12 to 0.8% of the total thickness of the negative electrode film layer, such as 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any combination thereof. This allows for a further balance between the overall conductivity and current shunting capability of the electrode, thereby significantly improving lithium plating in the second region while maintaining battery performance.

[0118] In some embodiments, the total areal density of the negative electrode film is 0.1-0.2 g / 1540.25 mm. 2 For example, the areal density of the first negative electrode film is 0.1 g / 1540.25 mm². 20.11g / 1540.25mm 2 0.12g / 1540.25mm 2 0.13g / 1540.25mm 2 0.14g / 1540.25mm 2 0.15g / 1540.25mm 2 0.16g / 1540.25mm 2 0.17g / 1540.25mm 2 0.18g / 1540.25mm 2 0.19g / 1540.25mm 2 0.2g / 1540.25mm 2 Or a range consisting of any two of them. This ensures the support capacity of the electrode sheets, maintaining battery performance and appropriate energy density.

[0119] The term "area density" refers to an area of ​​1540.25 mm². 2 The quality of the upper negative electrode film layer. This can typically be determined using instruments and methods known in the art. For example, an electrode of a specified area can be taken at room temperature, and a circular hole with an area of ​​1540.25 mm² can be punched into the electrode using a punching machine. 2 Then, its mass m1 (in g) is measured using an electronic balance. Next, the blank current collector (blank foil) is flushed in the same manner, and its mass m2 (in g) is measured using the same electronic balance. Finally, the areal density (in g / 1540.25 mm²) is obtained using the formula (m1-m2) / 1540.25. 2 ).

[0120] In some embodiments, the areal density of the first negative electrode film layer is 0.01-0.1 g / 1540.25 mm. 2 For example, the areal density of the first negative electrode film is 0.01 g / 1540.25 mm². 2 0.02g / 1540.25mm 2 0.03g / 1540.25mm 2 0.04g / 1540.25mm 2 0.05g / 1540.25mm 2 0.06g / 1540.25mm 2 0.07g / 1540.25mm 2 0.08g / 1540.25mm 2 0.09g / 1540.25mm 2 0.1g / 1540.25mm 2Optionally, in some embodiments, the areal density of the first negative electrode film layer is 0.01-0.05 g / 1540.25 mm. 2 This ensures the high capacity and good support of the first negative electrode film layer.

[0121] In this disclosure, "silicon-carbon particles" refers to silicon-carbon composite particles, including porous carbon material and silicon material located in the pores of the porous carbon material. The hard silicon-carbon material has an angular shape and strong support, allowing it to form a top-to-bottom through-structure in the electrode, ensuring the stability of the electrode structure when high-concentration ions are injected from the upper layer. The silicon-carbon composite can be prepared using conventional silicon-carbon composites or conventional preparation methods, such as depositing nano-silicon material on porous carbon via chemical vapor deposition, followed by carbon coating, such as amorphous carbon coating.

[0122] In some embodiments, the silicon-carbon composite satisfies one or more of the following characteristics:

[0123] (1) The silicon-carbon composite includes porous carbon and silicon-containing materials dispersed in the pores of the porous carbon; optionally, the porous carbon is hard carbon;

[0124] (2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of porous carbon and / or silicon-containing materials;

[0125] (3) The silicon content in the silicon-carbon composite is 30% to 70% by mass;

[0126] (4) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g to 6.7m 2 / g.

[0127] In some embodiments, the silicon-carbon composite includes a core comprising porous carbon and silicon-containing material dispersed in the pores of the porous carbon. The porous carbon, acting as a carrier for the silicon-containing material, provides support for the nanoscale silicon-containing material and, simultaneously, provides expansion space for the expansion of the silicon nanoparticles, effectively mitigating the stress compression caused by expansion during charging. Especially when the silicon-containing particles are in the nanometer range, the specific capacity is higher and dispersion in the pores of the porous carbon is facilitated. Furthermore, the buffering effect of the porous carbon's pores on expansion can be more fully utilized. When this silicon-carbon composite is applied in a wound electrode assembly, it can significantly alleviate the stretching of the outer negative electrode sheet caused by silicon expansion.

[0128] In some embodiments, the porous carbon may optionally be hard carbon. When the porous carbon is hard carbon, it has stronger support, a more stable pore structure, and is harder, thus providing better porosity for the negative electrode active layer, providing a smoother path for active ion transport, and improving the charging capability of the battery cell.

[0129] In some embodiments, the silicon-containing material includes at least one of elemental silicon, silicon oxides, silicon nitrides, and silicon alloys. In some embodiments, the silicon-containing material includes crystalline silicon, thereby further improving the structural stability of the silicon-containing material and the energy density of the battery cell.

[0130] In some embodiments, the silicon-carbon composite further includes a carbon-containing coating layer that coats the surface of the core. This can improve the conductivity of the silicon-carbon composite and reduce the internal impedance of the battery cell, while also effectively reducing the probability of direct contact between the silicon-containing material in the porous carbon channels and the external environment, thereby improving the chemical stability of the silicon-carbon composite.

[0131] In some embodiments, the silicon content in the silicon-carbon composite is 30% to 70% by mass. This approach, while maximizing the specific capacity of the negative electrode active material by utilizing silicon, also facilitates the full dispersion of silicon in the carbon-containing porous material and helps control the expansion of silicon during charging.

[0132] In this disclosure, the method for testing the silicon content in the silicon-carbon composite can be any method known in the art. As an example, the following method can be used: a certain amount of silicon-carbon composite is taken, and the mass of silicon in the silicon-carbon composite is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). The mass percentage of silicon in the silicon-carbon composite can then be calculated.

[0133] In addition to providing structural support and buffering for the expansion of silicon materials, the pores in the silicon-carbon composite also form between the particles. To further improve the flow of lithium ions through the intraparticle and interparticle pores, in some embodiments, the average particle size of the silicon-carbon composite is 2 μm to 15 μm. Optionally, the average particle size of the silicon-carbon composite is 7 μm to 11 μm, or 5 μm to 10 μm. This creates a particle size distribution between the average particle size of the silicon-carbon composite and the average particle size of the graphite material, which is more conducive to increasing the compaction of the negative electrode active layer by utilizing the interparticle gaps, thereby further improving the energy density of the battery cell.

[0134] The average particle size of the aforementioned silicon-carbon composite can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) (e.g., ZEISS Sigma 300) can be used, referring to JY / T010-1996, to obtain SEM images of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample of length × width = 50 mm × 100 mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 1000x when measuring silicon-carbon composites), read the particle size of each silicon-carbon composite particle in each test area (i.e., take the distance between the two farthest points on the silicon-carbon composite particle as the particle size). Count the number and particle size values ​​of silicon-carbon composite particles in each test area, and take the arithmetic mean of the silicon-carbon composite particles in each test area, which is the average particle size of the silicon-carbon composite particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be used to repeat the above test, and the average value of each test sample can be taken as the final test result.

[0135] In some embodiments, the BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g~6.7m 2 / g. For example, the specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 6.7m 2 / g or a range between the values ​​of either / g or any two of them.

[0136] In this disclosure, the method for testing the BET specific surface area of ​​silicon-carbon composites can employ methods known in the art. As an example, referring to GB / T 19587-2017, a nitrogen adsorption specific surface area analysis method can be used. The sample tube containing the first graphite material sample is immersed in liquid nitrogen at -196°C, and the amount of nitrogen adsorbed on the surface of the solid sample at different pressures of 0.05–0.30 is measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount of the sample is obtained, and thus the BET specific surface area is calculated. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0137] In some embodiments, the silicon content in the silicon-carbon particles is 30% to 60% by mass. Exemplarily, the silicon content in the silicon-carbon composite material is a value within the range of 30%, 40%, 50%, 60%, or any combination thereof. This allows for the provision of suitable capacity while maintaining the stability of the material structure and appropriate conductivity.

[0138] In some embodiments, the mass content of carbon and other trace doping elements in the silicon-carbon particles is 40% to 70%. Exemplarily, the mass percentage of silicon in the silicon-carbon composite material is a value within the range of 40%, 50%, 60%, 70%, or any combination thereof. This allows for the provision of suitable capacity while maintaining the stability of the material structure and appropriate conductivity.

[0139] In this disclosure, the mass content of silicon in the negative electrode film, the first negative electrode film, the second negative electrode film, and the silicon-carbon particles can be determined by inductively coupled plasma emission spectrometry (ICP-OES).

[0140] In this disclosure, the ionic impedance and / or film resistance of the second region is 1.2 to 10 times that of the ionic impedance and / or film resistance of the first and third regions, exemplarily values ​​within a range of 1.2, 2, 3, 4, 5, 6, 7, 8, 9, 10 times, or any combination thereof. This allows for the creation of a region with a conductivity difference in the second direction of the electrode, thereby generating effective current shunting when faced with ion insertion / extraction. This reduces lithium plating problems in the second region, thereby improving the rate performance and cycle performance of the battery.

[0141] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0142] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0143] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0144] [Positive electrode plate]

[0145] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0146] As an example, the positive 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 positive current collector.

[0147] In some embodiments, the positive current collector may 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0148] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0149] During the charging and discharging process of a battery, 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 disclosure, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0150] In the examples of positive electrode active materials in this disclosure, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0151] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0152] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] 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 the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0154] [Electrolytes]

[0155] The electrolyte acts as a conductor of ions between the positive and negative electrodes. In this disclosure, the electrolyte is a liquid electrolyte, and its specific composition can be selected according to requirements.

[0156] Electrolytes consist of electrolyte salts and solvents.

[0157] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0158] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

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

[0160] [Isolation membrane]

[0161] In some embodiments, the battery cell also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0162] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0163] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process.

[0164] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0165] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0166] This disclosure does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 shows a square battery cell 5 as an example.

[0167] In some embodiments, referring to FIG5, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0168] Battery device

[0169] This disclosure also provides a battery device, including the aforementioned battery cell, or a battery cell obtained by the aforementioned preparation method. The battery device may be a battery module or a battery pack, etc.

[0170] The battery apparatus mentioned in the embodiments of this disclosure may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0171] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0176] 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.

[0177] 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.

[0178] In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least a part of the vehicle's floor, or a portion of the housing can be at least a part of the vehicle's crossbeams and longitudinal beams. The technical solutions described in the embodiments of this disclosure are applicable to various electrical devices using individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft, etc. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0179] Figure 6 shows a battery module 4 as an example. Referring to Figure 6, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0180] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0181] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0182] Figures 7 and 8 show a battery pack 1 as an example. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0183] Electrical appliances

[0184] This disclosure also provides an electrical device, which will be described below with appropriate reference to the accompanying drawings.

[0185] The electrical devices mentioned in the embodiments of this disclosure include battery cells provided in this disclosure, battery cells obtained by the preparation method provided in this disclosure, or battery devices of this disclosure. The battery cells can be used as the power source of the electrical device or as the energy storage unit of the electrical device. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, 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, ships and satellites, energy storage systems, etc.

[0186] As an electrical device, you can choose individual battery cells or battery packs, such as battery modules or battery packs, according to your usage requirements.

[0187] Figure 9 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0188] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0189] Example

[0190] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0191] Example 1

[0192] Preparation of battery cells

[0193] (1) Preparation of positive electrode sheet

[0194] The positive electrode active material, ternary material nickel-cobalt-manganese (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed evenly at a mass ratio of 97:2:1 and added to the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 85°C, cold-pressed, and then die-cut and slit to obtain the positive electrode sheet.

[0195] (2) Preparation of negative electrode sheet

[0196] a. Preparation of the first negative electrode slurry: The first negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the first negative electrode slurry. The first negative electrode active material, based on the total weight of the negative electrode active material, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbide particles with an average particle size of 4 μm (powder resistivity of 4.5 Ω·m at 16 MPa).

[0197] b. Preparation of the second negative electrode slurry: The second negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the second negative electrode slurry. The first negative electrode active material, based on the total weight of the negative electrode active material, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbide particles with an average particle size of 12 μm (the powder resistivity at 16 MPa is 13 Ω·m).

[0198] c. Three regions with a width ratio of 4:2:4 are defined on the copper foil of the negative electrode current collector: a first region, a second region, and a third region. Using a three-extrusion head extrusion coating machine, the first and second negative electrode slurries are simultaneously extruded. The first negative electrode slurry is coated on the first and third regions, and the second negative electrode slurry is coated on the second region. After drying at 85°C, the coating is cold-pressed to obtain the negative electrode sheet. The coating weight of the first, second, and third regions is consistent at 105 mg / 1540.25 mm². 2

[0199] (3) Preparation of the separating membrane

[0200] Using polyethylene microporous film as the porous separator substrate, inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent were mixed evenly in a weight ratio of 3:1.5:5.5 to form a slurry, which was then coated on one side of the substrate and dried to obtain a separator with a thickness of 7μm.

[0201] (4) Preparation of electrolyte

[0202] Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:2:1) to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0203] The negative electrode, separator, and positive electrode are arranged in sequence, with the separator positioned between the negative and positive electrodes to provide insulation. The electrodes are then bent and wound to form an electrode assembly. The electrode assembly is placed in outer packaging, dried, and then injected with the prepared electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell is obtained. The battery's N / P (initial negative electrode capacity / initial positive electrode capacity) is 1, and the designed rated capacity is 100 Ah.

[0204] Example 2

[0205] The battery cells were prepared using the same method as in Example 1, except that the negative electrode sheet was prepared using the following method.

[0206] Preparation of negative electrode sheet

[0207] a. Preparation of the first negative electrode slurry: The first negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the first negative electrode slurry. The first negative electrode active material, based on the total weight of the negative electrode active material, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbon particles with an average particle size of 4 μm.

[0208] b. Preparation of the second negative electrode slurry: The second negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the second negative electrode slurry. The second negative electrode active material, based on its total weight, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbon particles with an average particle size of 12 μm.

[0209] c. Preparation of the third negative electrode slurry: The third negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the third negative electrode slurry. The third negative electrode active material is natural graphite particles with an average particle size of 13μm.

[0210] d. Three regions with a width ratio of 4:2:4 are defined on the negative electrode current collector copper foil as a first region, a second region, and a third region. Using an extrusion coating machine, the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode material are simultaneously extruded. The third negative electrode slurry is coated onto the negative electrode current collector copper foil, and the first and second negative electrode slurries are coated onto the third negative electrode slurry. The first negative electrode slurry is coated on both the first and third regions, and the second negative electrode slurry is coated on the second region. After drying at 85°C, the material is cold-pressed to obtain a negative electrode sheet. The total coating weight of the electrode sheet is 105 mg / 1540.25 mm. 2 .

[0211] Example 3

[0212] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with an average particle size of 12 μm and artificial graphite particles with an average particle size of 10 μm were used when preparing the first negative electrode slurry; and silicon-carbon particles with an average particle size of 12 μm and artificial graphite particles with an average particle size of 17 μm were used when preparing the second negative electrode slurry.

[0213] Example 4

[0214] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with a powder resistivity of 6 Ω·m at 16 MPa were used when preparing the first negative electrode slurry, and silicon-carbon particles with a powder resistivity of 12 Ω·m at 16 MPa were used when preparing the second negative electrode slurry.

[0215] Example 5

[0216] Battery cells were prepared using the same method as in Example 2, except that the negative electrode sheet was prepared using the following method.

[0217] Preparation of negative electrode sheet

[0218] a. Preparation of the first negative electrode slurry: The first negative electrode active material, conductive agent carbon nanotubes (CNT), acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:1:1:1:1 and mixed evenly to form the first negative electrode slurry. The first negative electrode active material, based on the total weight of the negative electrode active material, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbon particles with an average particle size of 12 μm.

[0219] b. Preparation of the second negative electrode slurry: The second negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the second negative electrode slurry. The second negative electrode active material, based on its total weight, includes 60 wt% artificial graphite particles with an average particle size of 13 μm and 40 wt% silicon carbon particles with an average particle size of 12 μm.

[0220] c. Preparation of the third negative electrode slurry: The third negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the third negative electrode slurry. The third negative electrode active material is natural graphite particles with an average particle size of 13μm.

[0221] d. Three regions with a width ratio of 4:2:4 are defined on the negative electrode current collector copper foil as a first region, a second region, and a third region. Using an extrusion coating machine, the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode material are simultaneously extruded. The third negative electrode slurry is coated onto the negative electrode current collector copper foil, and the first and second negative electrode slurries are coated onto the third negative electrode slurry. The first negative electrode slurry is coated on both the first and third regions, and the second negative electrode slurry is coated on the second region. After drying at 85°C, the material is cold-pressed to obtain a negative electrode sheet. The total coating weight of the electrode sheet is 105 mg / 1540.25 mm. 2 .

[0222] Comparative Example 1

[0223] The battery cells were prepared using the same method as in Example 1, except that the negative electrode sheet was prepared using the following method.

[0224] Preparation of negative electrode sheet

[0225] a. Preparation of the first negative electrode slurry: The first negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the first negative electrode slurry. The first negative electrode active material, based on its total weight, includes 60 wt% artificial graphite particles with an average particle size of 13 μm, 20 wt% silicon-carbon particles with an average particle size of 4 μm, and 20 wt% silicon-carbon particles with an average particle size of 12 μm.

[0226] Using a coating extrusion head, the aforementioned first negative electrode slurry is coated onto the negative electrode current collector copper foil. After drying and cold pressing, a negative electrode film layer is formed, resulting in a negative electrode sheet. The total coating weight of the electrode sheet is 105 mg / 1540.25 mm. 2 .

[0227] Comparative Example 2

[0228] The battery cells were prepared using the same method as in Example 2, except that the negative electrode sheet was prepared using the following method.

[0229] Preparation of negative electrode sheet

[0230] a. Preparation of the first negative electrode slurry: The first negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to deionized water in a mass ratio of 96:2:1:1 and mixed evenly to form the first negative electrode slurry. The first negative electrode active material, based on its total weight, includes 60 wt% artificial graphite particles with an average particle size of 13 μm, 20 wt% silicon-carbon particles with an average particle size of 4 μm, and 20 wt% silicon-carbon particles with an average particle size of 12 μm.

[0231] b. Preparation of the third negative electrode slurry: The third negative electrode active material, conductive agent acetylene black, dispersant sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to the solvent deionized water at a mass ratio of 96:2:1:1 and mixed evenly to form the third negative electrode slurry. The third negative electrode active material is natural graphite particles with an average particle size of 13μm.

[0232] A double-layer coating extrusion head is used to simultaneously extrude the first and third negative electrode slurries. The third electrode slurry is coated onto the copper foil of the negative electrode current collector, and the first negative electrode slurry is coated onto the third negative electrode slurry. After drying and cold pressing, a negative electrode film is formed, resulting in a negative electrode sheet. The total coating weight of the electrode sheet is 105 mg / 1540.25 mm. 2 .

[0233] Parameter testing

[0234] (1) Ionic conductivity test

[0235] A symmetrical cell with one negative electrode and one negative electrode was fabricated. The ionic impedance spectroscopy (IIS) method was used to test the IIS on a Solartron 1470E CellTest multichannel electrochemical workstation. The Nyquist plot obtained from the test was analyzed using the equivalent circuit curve fitting method. The difference in the abscissa of the intersection points of the extended curves in the low-frequency and high-frequency regions of the Nyquist plot with the horizontal axis reflects the ionic impedance R of the film. The ionic impedance is used to reflect the ionic conductivity of the film in the electrode. The results are shown in Table 1 below.

[0236] (2) Electron conductivity test

[0237] The negative electrode sheet was cut into three sections—A at both ends, the middle section, and B at both ends—according to the composition of the upper slurry. The film resistance of each section was tested using a Crystallography ST2263 dual-electrical-measurement digital four-probe tester with the four-probe method. The test area was 154.02 mm². 2 The film resistance is used to reflect the electronic conductivity of the film layer in the electrode.

[0238] (3) Element content test

[0239] After discharging the secondary battery to 3V with a constant current of 1C, disassemble it, remove the negative electrode plate, scrape off the negative electrode film, weigh 0.2g of the negative electrode film into a 100mL beaker, add 10mL of 10% w / w nitric acid solution, heat and digest at 120℃ for 0.5 hours, then dilute to volume with a 100mL volumetric flask, and then use a pipette to transfer 1mL to a 100mL volumetric flask and dilute to volume to obtain the solution to be tested.

[0240] The mass percentage of silicon in the negative electrode film and silicon-carbon composite material was measured using an inductively coupled plasma optical emission spectrometer (EXPEC 6000). The ICP test results showed that the mass percentage of silicon in the silicon-carbon composite material was 47% in the above examples and comparative examples. The results of the silicon content in the film are shown in Table 1 below.

[0241] Battery cell performance testing

[0242] (1) Battery capacity

[0243] At 25℃, the battery cells were charged at a constant current rate of 0.33C to 4.25V, then charged at a constant voltage rate to a current of 0.05C. After standing for 5 minutes, they were discharged at a constant current rate of 0.33C to 2.5V. The discharge capacity at this point was recorded, which is the 0.33C discharge capacity. The results are recorded in Table 2 below.

[0244] (2) Ratio Performance Test

[0245] At 25℃, charge the battery cell at a constant current rate of 0.1C to 4.25V, then charge at a constant voltage rate to a current of 0.05C, let it stand for 5 minutes, and then discharge it at a constant current rate of 0.1C to 2.5V. Record the discharge capacity at this point, which is the 0.1C discharge capacity. Let it stand for 30 minutes, then charge the battery cell at a constant current rate of 0.5C to 4.25V, then charge it at a constant voltage rate to a current of 0.05C, let it stand for 5 minutes, and then discharge it at a constant current rate of 0.5C to 2.5V. Record the discharge capacity at this point, which is the 0.5C discharge capacity. Repeat this process for testing at rates from 0.1C to 1.5C.

[0246] The rate performance of a battery is calculated as 1C / 0.1C (%) = 1C discharge capacity / 0.1C discharge capacity × 100%. The results are recorded in Table 2 below.

[0247] (3) Cyclic performance test

[0248] At 25°C, the battery cell is charged to 4.25V with a constant current of 1C, then charged at a constant voltage of 4.25V until the current drops to 0.05C, and then discharged to 2.5V with a constant current of 1C. The discharge specific capacity of the first cycle (Cd1) is obtained. This charging and discharging is repeated until the 400th cycle, and the discharge specific capacity after 400 cycles is denoted as Cdn.

[0249] Capacity retention (%) = Discharge specific capacity after 400 cycles (Cdn) / Discharge specific capacity in the first cycle (Cd1) × 100%. The results are recorded in Table 2 below.

[0250] (4) Lithium plating window test and fast charging performance test

[0251] The maximum test rate (lithium plating window) of a battery at different SOCs was measured using a three-electrode cell with the same positive and negative electrode coating mass areal density. The base mass areal density of the negative electrode coating was 105 mg / 1540.25 mm². 2 The cathode was a conventional ternary cathode. Based on the lithium plating window calculated according to the 15-minute fast charging requirement at 35℃, fast charging cycles were tested on different cells at 100% DoD (Depth of Discharge), a voltage range of 2.5-4.25V, using 8-80% SOC fast charging / 0.5C discharging and a 2-hour charging rest period. The number of cycles for each cell when the capacity retention rate dropped to 80% was recorded. The results are recorded in Table 2 below.

[0252] Table 1

[0253] Table 2

[0254] As can be seen from Table 1 above, reducing the average particle size of silicon-carbon / graphite particles can improve the ionic conductivity of the electrode, while reducing the powder resistivity of silicon-carbon particles or using a conductive agent with excellent conductivity can improve the electronic conductivity of the electrode.

[0255] As can be seen from Table 2 above, setting an upper and lower layer structure can improve battery capacity and capacity retention. Setting a difference in the conductivity of electrons / ions along the second direction in the first negative electrode film layer can improve the lithium plating fast charging cycle life, indicating that the battery of this disclosure suppresses the lithium plating problem in the middle of the electrode to a certain extent.

[0256] Example 6

[0257] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with an average particle size of 5 μm and artificial graphite particles with an average particle size of 12 μm were used when preparing the first negative electrode slurry; and silicon-carbon particles with an average particle size of 7.5 μm and artificial graphite particles with an average particle size of 12 μm were used when preparing the second negative electrode slurry.

[0258] Example 7

[0259] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with an average particle size of 4 μm and artificial graphite particles with an average particle size of 12 μm were used when preparing the first negative electrode slurry; and silicon-carbon particles with an average particle size of 13 μm and artificial graphite particles with an average particle size of 17 μm were used when preparing the second negative electrode slurry.

[0260] Example 8

[0261] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with an average particle size of 2 μm and artificial graphite particles with an average particle size of 13 μm were used when preparing the first negative electrode slurry; and silicon-carbon particles with an average particle size of 12 μm and artificial graphite particles with an average particle size of 15 μm were used when preparing the second negative electrode slurry.

[0262] Example 9

[0263] Battery cells were prepared using the same method as in Example 5, except that silicon-carbon particles with an average particle size of 9 μm and artificial graphite particles with an average particle size of 12 μm were used when preparing the first negative electrode slurry; and silicon-carbon particles with an average particle size of 9 μm and artificial graphite particles with an average particle size of 12 μm were used when preparing the second negative electrode slurry.

[0264] Example 10

[0265] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with a powder resistivity of 5 Ω·m at 16 MPa were used when preparing the first negative electrode slurry, and silicon-carbon particles with a powder resistivity of 16 Ω·m at 16 MPa were used when preparing the second negative electrode slurry.

[0266] Example 11

[0267] Battery cells were prepared using the same method as in Example 2, except that silicon-carbon particles with a powder resistivity of 4 Ω·m at 16 MPa were used when preparing the first negative electrode slurry, and silicon-carbon particles with a powder resistivity of 16 Ω·m at 16 MPa were used when preparing the second negative electrode slurry.

[0268] Examples 6 to 11 were tested using the same testing method described above. The test results are shown in Table 3 below.

[0269] Table 3

[0270] As can be seen from Table 3 above, when the ion impedance or film resistance of the second region is about 1.2 to 10 times that of the first and third regions, the lithium plating fast-charging cycle life of the battery cell can be improved, and the lithium plating problem in the middle of the electrode can be suppressed to a certain extent.

[0271] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. 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, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A battery cell, the battery cell comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer comprising a first negative electrode film layer, The negative electrode plate extends along a first direction, and the length of the negative electrode plate in the first direction is greater than its length in the second direction, wherein the second direction is perpendicular to the first direction. The first negative electrode film layer includes a first region, a second region, and a third region sequentially disposed along the second direction of the negative electrode sheet, wherein the first region and the third region include a first active material, and the second region includes a second active material; in, The electronic conductivity and / or ionic conductivity of the second region is less than that of the first region and the third region.

2. The battery cell according to claim 1, wherein, The negative electrode film layer further includes a second negative electrode film layer, which is located on the side of the first negative electrode film layer facing or away from the negative electrode current collector.

3. The battery cell according to claim 1 or 2, wherein, The first active material comprises first silicon-carbon particles, and the second active material comprises second silicon-carbon particles. The average particle size of the first silicon-carbon particle is smaller than the average particle size of the second silicon-carbon particle.

4. The battery cell according to claim 3, wherein, The average particle size of the first silicon-carbon particle is 0.1 to 0.9 times the average particle size of the second silicon-carbon particle.

5. The battery cell according to claim 3 or 4, wherein, The average particle size of the second silicon-carbon particles is 5 μm to 15 μm; and / or The average particle size of the first silicon-carbon particles is 2 μm to 10 μm.

6. The battery cell according to any one of claims 1 to 5, wherein, The first active material comprises first graphite particles, and the second active material comprises second graphite particles. The average particle size of the first graphite particle is smaller than the average particle size of the second graphite particle.

7. The battery cell according to claim 6, wherein, The average particle size of the first graphite particle is 0.1 to 0.9 times the average particle size of the second graphite particle.

8. The battery cell according to claim 6 or 7, wherein, The average particle size of the second graphite particles is 7 μm to 17 μm; and / or The average particle size of the first graphite particles is 3 μm to 13 μm.

9. The battery cell according to any one of claims 1 to 8, wherein, The first active material comprises first graphite particles, and the second active material comprises second graphite particles. The powder OI value of the first graphite particle is less than that of the second graphite particle.

10. The battery cell according to claim 9, wherein, The powder OI value of the first graphite particle is 0.1 to 0.9 times that of the powder OI value of the second graphite particle.

11. The battery cell according to claim 9 or 10, wherein, The second graphite particle has a powder OI value of 6 to 14; and / or The powder OI value of the first graphite particle is 2 to 10.

12. The battery cell according to any one of claims 1 to 11, wherein, The first region and the third region include a first dispersant, and the second region includes a second dispersant; The ionic conductivity of the first dispersant is greater than that of the second dispersant.

13. The battery cell according to claim 12, wherein, Based on the total weight of the negative electrode film, the contents of the first dispersant and the second dispersant are the same, ranging from 0.1% to 1%.

14. The battery cell according to claim 12 or 13, wherein, The first dispersant comprises CMC-Li, and the second dispersant comprises CMC.

15. The battery cell according to any one of claims 1 to 14, wherein, The resistivity of the powder of the first active material is lower than that of the powder of the second active material.

16. The battery cell according to claim 15, wherein, The first active material comprises silicon-carbon particles with a powder resistivity of 4 Ω·m to 10 Ω·m at 16 MPa; and The second active material comprises silicon-carbon particles with a powder resistivity of 10 Ω·m to 17 Ω·m at 16 MPa.

17. The battery cell according to claim 16, wherein, The first active material and / or the second active material include artificial graphite with a powder OI value of 2 to 14 and a graphitization degree of 91% to 93%.

18. The battery cell according to any one of claims 1 to 17, wherein, Based on the unit area weight of the negative electrode film, the weight percentage of the first active material is lower than that of the second active material.

19. The battery cell according to claim 18, wherein, The first active substance is the same as the second active substance.

20. The battery cell according to any one of claims 1 to 19, wherein, The first region and the third region include a first conductive agent, and the second region includes a second conductive agent; The conductivity of the first conductive agent is greater than that of the second conductive agent.

21. The battery cell according to any one of claims 1 to 20, wherein, The first region and the third region include a first conductive agent, and the second region includes a second conductive agent; Among them, based on the unit area weight of the negative electrode film, the content of the first conductive agent is greater than the content of the second conductive agent.

22. The battery cell according to any one of claims 1 to 21, wherein, The sum of the lengths of the first region and the third region in the second direction is greater than 0 and less than or equal to 0.8, relative to the length of the negative electrode sheet in the second direction.

23. The battery cell according to claim 22, wherein, The widths of the first region and the third region may be the same or different.

24. The battery cell according to any one of claims 1 to 23, wherein, The second negative electrode film layer is located between the first negative electrode film layer and the negative electrode current collector.

25. The battery cell according to claim 24, wherein, The silicon content M1 in the first negative electrode film layer and the silicon content M2 in the second negative electrode film layer satisfy the following relationship: 2.5% ≤ M1 - M2 ≤ 68%.

26. The battery cell according to claim 25, wherein, The first negative electrode film layer comprises silicon-carbon particles and graphite particles, wherein M1 is 2.5% to 68%, and The second negative electrode film layer comprises graphite particles, wherein M2 is 0 to 40%.

27. The battery cell according to claim 25 or 26, wherein, M1 is 5.5% to 48%, and / or M2 ranges from 0% to 20%.

28. The battery cell according to any one of claims 25 to 27, wherein, 5.5% ≤ M1 - M2 ≤ 48%.

29. The battery cell according to any one of claims 25 to 28, wherein, 10% ≤ M1 - M2 ≤ 40%.

30. The battery cell according to any one of claims 2 to 29, wherein, The thickness of the first negative electrode film layer accounts for 0.1 to 0.9 of the total thickness of the negative electrode film layer.

31. The battery cell according to claim 30, wherein, The thickness of the first negative electrode film layer accounts for 0.12 to 0.8 of the total thickness of the negative electrode film layer.

32. The battery cell according to any one of claims 1 to 31, wherein, The total areal density of the negative electrode film is 0.1 g / 1540.25 mm. 2 Up to 0.2g / 1540.25mm 2 The areal density of the first negative electrode film layer is 0.01 g / 1540.25 mm. 2 Up to 0.1g / 1540.25mm 2 .

33. The battery cell according to claim 32, wherein, The areal density of the first negative electrode film is 0.01 g / 1540.25 mm. 2 Up to 0.05g / 1540.25mm 2 .

34. The battery cell according to any one of claims 3 to 5, 16, and 26, wherein, The silicon-carbon particles satisfy one or more of the following characteristics: (1) The silicon-carbon particles include porous carbon and silicon-containing materials dispersed in the pores of the porous carbon; (2) The silicon-carbon particles further include a carbon-containing coating layer, which is located on the surface of the porous carbon and / or the silicon-containing material; (3) The silicon content in the silicon-carbon particles is 30% to 70% by mass; (4) The BET specific surface area of ​​the silicon-carbon particles is 1.0 m². 2 / g to 6.7m 2 / g; (5) The mass content of carbon and other trace doping elements in the silicon-carbon particles is 40% to 70%.

35. The battery cell according to any one of claims 1 to 34, wherein, The ionic impedance and / or membrane resistance of the second region is 1.2 to 10 times that of the ionic impedance and / or membrane resistance of the first region and the third region.

36. The battery cell according to any one of claims 1 to 35, wherein, The battery cell also includes a positive electrode sheet and a separator, wherein the positive electrode sheet, the separator, and the negative electrode sheet are wound together to form an electrode assembly.

37. A battery device comprising a battery cell according to any one of claims 1 to 36.

38. An electrical device comprising a battery cell according to any one of claims 1 to 36.

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