Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer is internally provided with a negative electrode active material, and the negative electrode active material comprises graphite; the negative electrode film layer comprises a first region, a second region and a third region, and the first region, the second region and the third region are sequentially arranged in the first direction; the negative pole piece meets at least one of the following conditions: the graphitization degree of graphite in the first region and the third region is greater than the graphitization degree of graphite in the second region; the graphite volume particle size distribution Dv50 in the first area and the third area is greater than the graphite Dv50 in the second area; the OI value of graphite in the first area and the third area is greater than the OI value of graphite in the second area; when the secondary battery is assembled by taking the first direction as the width direction of the negative pole piece disclosed by the invention, lithium precipitation in the middle of the negative pole piece in the use process of the secondary battery can be relieved, and the cycle performance of the secondary battery is improved.

Description

[0001] Related applications

[0002] This application is a divisional application of the invention patent application filed on June 30, 2023, with application number 202310797696.4 and invention title "Negative electrode sheet, secondary battery and power-consuming device". Technical Field

[0003] This application relates to the field of secondary battery technology, and more particularly to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0004] In recent years, as the application scope of secondary batteries has become increasingly wide, 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 and electric vehicles.

[0005] Due to the significant advancements in rechargeable batteries, higher demands have been placed on their cycle performance. Batteries with excellent cycle performance require high-quality negative electrode plates. Currently, rechargeable batteries are prone to lithium plating on the negative electrode plates during use. If the deposited lithium continuously accumulates on the negative electrode plate, it can easily puncture the separator, affecting the cycle performance of the rechargeable battery.

[0006] Therefore, seeking secondary batteries with better cycle performance is one of the key areas of focus for those skilled in the art. Summary of the Invention

[0007] This application is made in view of the above-mentioned problems, and one of its objectives is to provide a negative electrode sheet that can alleviate lithium plating on the negative electrode sheet during the use of a secondary battery, thereby improving the cycle performance of the secondary battery.

[0008] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a negative electrode active material, the negative electrode active material comprising graphite; the negative electrode film layer comprises a first region, a second region and a third region, the first region, the second region and the third region being sequentially disposed in a first direction;

[0009] Wherein, the negative electrode sheet satisfies at least one of the following:

[0010] (1) The graphitization degree of the graphite in the first region and the third region is greater than that of the graphite in the second region.

[0011] (2) The volumetric particle size distribution Dv50 of the graphite in the first region and the third region is greater than that of the graphite in the second region.

[0012] (3) The OI value of the graphite in the first region and the third region is greater than the OI value of the graphite in the second region.

[0013] This application divides the negative electrode film layer into multiple regions along a first direction, and sets the graphitization degree of the negative electrode active material graphite in the first and third regions located at both ends to be greater than that of the graphite in the second region located in the middle, and / or the volume particle size distribution Dv50 of the graphite in the first and third regions to be greater than that of the graphite in the second region, and / or the OI value of the graphite in the first and third regions to be greater than that of the graphite in the second region; when the first direction is used as the width direction of the negative electrode sheet to assemble the battery, the phenomenon of lithium deposition in the middle of the negative electrode sheet can be prevented during the cycle of the secondary battery, thereby effectively alleviating the problem of easy lithium deposition in the middle of the negative electrode sheet and improving the cycle performance of the secondary battery.

[0014] In any embodiment, the degree of graphitization of the graphite in the first region is a1, the degree of graphitization of the graphite in the third region is a2, and the degree of graphitization of the graphite in the second region is b, where 0 < a1 - b < 40% and 0 < a2 - b < 40%. This further improves the cycle performance of the secondary battery.

[0015] In any implementation, 5% < a1-b < 20%; 5% < a2-b < 20%. This can further improve the cycle performance of the secondary battery.

[0016] In any embodiment, the graphitization degree of the graphite in the first region and the third region is independently 65%~100%; the graphitization degree of the graphite in the second region is 60%~90%. This effectively improves the cycle performance of the secondary battery.

[0017] In any embodiment, the volumetric particle size distribution Dv50 of the graphite in the first region is c1, the volumetric particle size distribution Dv50 of the graphite in the third region is c2, and the volumetric particle size distribution Dv50 of the graphite in the second region is d, where 0 < c1 - d < 10.0 μm and 0 < c2 - d < 10.0 μm. This can better improve the problem of lithium plating in the center of the negative electrode sheet and further improve the cycle performance of the secondary battery.

[0018] In any implementation, 2 μm < c1-d < 8.0 μm, and 2 μm < c2-d < 8.0 μm. This further improves the cycle performance of the secondary battery.

[0019] In any embodiment, the volumetric particle size distribution Dv50 of the graphite in the first region and the third region is independently 7 μm to 15 μm; the volumetric particle size distribution Dv50 of the graphite in the second region is 6 μm to 14.5 μm. This effectively improves the cycle performance of the secondary battery.

[0020] In any embodiment, the OI value of the graphite in the first region is e1, the OI value of the graphite in the third region is e2, and the OI value of the graphite in the second region is f, where 0 < e1 - f < 9 and 0 < e2 - f < 9. This further improves the cycle performance of the secondary battery.

[0021] In any implementation, 1.5 < e1-f < 3.0, and 1.5 < e2-f < 3.0. This further improves the cycle performance of the secondary battery.

[0022] In any embodiment, the OI value of the graphite in the first region and the third region is independently 5.0 to 10.0; the OI value of the graphite in the second region is 2.5 to 4.5. This effectively improves the cycle performance of the secondary battery.

[0023] In any embodiment, the dimensions of the first region, the second region, and the third region in the first direction are g, h, and i, respectively, and the dimension of the negative electrode sheet in the first direction is j, where 0.1 ≤ h / j ≤ 0.75, 0.125 ≤ g / j ≤ 0.45, and 0.125 ≤ i / j ≤ 0.45. This allows for a more rational distribution of the rapid lithium intercalation capability of the negative electrode active material in the negative electrode film layer along the first direction, further improving the cycle performance of the secondary battery.

[0024] In any embodiment, the thickness of the negative electrode sheet is 50 μm to 400 μm.

[0025] A second aspect of this application provides a secondary battery, including the negative electrode sheet of the first aspect of this application. The secondary battery is a wound battery, and the secondary battery is wound with the first direction being the width direction of the negative electrode sheet. The secondary battery has good cycle performance.

[0026] In any embodiment, the negative electrode sheet has a first overhang region and a second overhang region at its two ends in the first direction, respectively; the range of the first region covers the first overhang region; and the range of the third region covers the second overhang region.

[0027] In any implementation, the size of the first region in the first direction is greater than the size of the first overhang region in the first direction.

[0028] In any implementation, the size of the third region in the first direction is greater than the size of the second overhang region in the first direction.

[0029] A third aspect of this application provides an electrical device, including a secondary battery as described in the second aspect of this application.

[0030] The negative electrode sheet of this application divides the negative electrode film layer into multiple regions along a first direction, and makes the graphitization degree of the negative electrode active material graphite in the first and third regions on both sides greater than that of the graphite in the second region in the middle, and / or the volume particle size distribution Dv50 of the graphite in the first and third regions greater than that of the graphite in the second region, and / or the OI value of the graphite in the first and third regions greater than that of the graphite in the second region; when the first direction is used as the width direction of the negative electrode sheet to assemble a secondary battery, the phenomenon of lithium plating in the middle of the negative electrode sheet is less likely to occur during the cycle of the secondary battery, thereby improving the cycle performance of the secondary battery. Attached Figure Description

[0031] Figure 1 This is a plan view of the negative electrode sheet according to one embodiment of this application;

[0032] Figure 2 This is a cross-sectional view of the negative electrode sheet along the thickness direction according to an embodiment of this application;

[0033] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0034] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0035] Figure 5 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1. Negative electrode sheet; 11. Negative current collector; 12. Negative electrode film; 121. First region; 122. Second region; 123. Third region; 124. First overhang region; 125. Second overhang region; 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0038] Hereinafter, some embodiments of the separator, secondary battery, and electrical device of this application are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" have been listed in this article; "0~5" is just a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0042] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the 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 the method may also include step (c), it means that step (c) can 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.

[0043] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0044] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0045] The weights described in the embodiments of this application may be weight units known in the chemical industry, such as μg, mg, g, and kg.

[0046] Currently, lithium plating easily occurs on the negative electrode of secondary batteries during use. If the deposited lithium accumulates continuously on the negative electrode, it can easily puncture the separator, posing a significant safety hazard and affecting the cycle performance of the secondary battery. To address this, this application proposes a negative electrode that effectively improves the lithium plating phenomenon on the negative electrode during the use of secondary batteries, thereby enhancing the safety and cycle performance of the secondary battery.

[0047] Please see Figure 1 and Figure 2 One embodiment of this application provides a negative electrode sheet 1, which includes a negative electrode current collector 11 and a negative electrode film layer 12 disposed on at least one surface of the negative electrode current collector 11. The negative electrode film layer 12 has a negative electrode active material, including graphite. The negative electrode film layer 12 includes a first region 121, a second region 122, and a third region 123. The first region 121, the second region 122, and the third region 123 are sequentially arranged in a first direction. The degree of graphitization of the graphite active material in the first region 121 and the third region 123 is greater than that of the graphite in the second region 122. And / or the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 is greater than that of the graphite in the second region 122. And / or the OI value of the graphite in the first region 121 and the third region 123 is greater than that of the graphite in the second region 122.

[0048] During the cycling process of a secondary battery, the uneven temperature and expansion force at different locations on the negative electrode 1 lead to uneven polarization distribution along its width. Specifically, in the wound negative electrode 1, due to heat dissipation, the temperature in the middle of the negative electrode 1 is generally higher, the expansion force is greater, and the polarization is smaller; while the two ends of the negative electrode 1 along the width direction have lower temperatures, smaller expansion forces, and greater polarization. Affected by this uneven polarization distribution, during the cycling process of the secondary battery, lithium ions tend to diffuse and intercalate towards the middle of the negative electrode 1, resulting in a lower lithium intercalation amount at the two ends along the width direction compared to the middle. This makes the middle of the negative electrode 1 more prone to lithium plating, affecting the cycle performance of the secondary battery.

[0049] The negative electrode film layer 12 of the negative electrode sheet 1 described above in this application includes a first region 121, a second region 122, and a third region 123; the first region 121, the second region 122, and the third region 123 are arranged sequentially in a first direction, such that the graphitization degree of the negative electrode active material graphite in the first region 121 and the third region 123 is greater than the graphitization degree of the graphite in the second region 122; and / or the volume particle size distribution Dv50 of the graphite in the first region 121 and the third region 123 is greater than the volume particle size distribution Dv50 of the graphite in the second region 122; and / or the OI value of the graphite in the first region 121 and the third region 123 is greater than the OI value of the graphite in the second region 122. Thus, when the first direction is used as the width direction of the negative electrode 1 to assemble a secondary battery, the rapid lithium intercalation capability in the second region in the middle of the negative electrode 1 can be improved. This makes it less likely for lithium to be deposited in the middle of the negative electrode 1 during the cycle of the secondary battery, thereby effectively alleviating the problem of easy lithium deposition in the middle of the negative electrode 1 and improving the cycle performance of the secondary battery.

[0050] In some embodiments, the graphitization degree of graphite in the first region 121 and the third region 123 is greater than that in the second region 122. The graphitization degree of graphite in the negative electrode active material has a significant impact on the rapid lithium intercalation capability of graphite. After graphitization, carbon materials form an ordered layered structure, allowing lithium ions to intercalate between graphite layers when used as a negative electrode active material. Generally, the lower the graphitization degree of graphite, the higher the disorder between material layers, and the better its fast-charging performance. By setting the graphitization degree of graphite in the first region 121 and the third region 123 of the negative electrode sheet 1 to be greater than that in the second region 122, the fast-charging performance of graphite in the second region 122 can be made greater than that of graphite in the first region 121 and the third region 123, thereby improving the lithium plating problem in the middle of the negative electrode sheet 1 and improving the cycle performance of the secondary battery.

[0051] In some embodiments, the graphitization degree of graphite in the first region 121 is a1, the graphitization degree of graphite in the third region 123 is a2, and the graphitization degree of graphite in the second region 122 is b, where 0 < a1 - b < 40% and 0 < a2 - b < 40%. This can further improve the lithium plating problem in the center of the negative electrode 1 and further improve the cycle performance of the secondary battery.

[0052] In some embodiments, 5% < a1-b < 20%; 5% < a2-b < 20%. This can further improve the lithium plating problem in the middle of the negative electrode 1 and further enhance the cycle performance of the secondary battery.

[0053] In some embodiments, the graphitization degree of graphite in the first region 121 and the third region 123 is independently 65% ​​to 100%; the graphitization degree of graphite in the second region 122 is 60% to 90%. The graphitization degree of graphite in the first region 121, the second region 122, and the third region 123 being within the above range can further improve the lithium plating problem in the center of the negative electrode 1 and further improve the cycle performance of the secondary battery.

[0054] In some embodiments, the volumetric particle size distribution Dv50 of graphite in the first region 121 and the third region 123 is greater than that of graphite in the second region 122. The particle size of graphite, the negative electrode active material, has a significant impact on its rapid lithium intercalation capability. Within a certain particle size range, the smaller the volumetric particle size distribution Dv50 of graphite, the greater its rapid lithium intercalation capability. By setting the volumetric particle size distribution Dv50 of graphite in the first region 121 and the third region 123 of the negative electrode sheet 1 to be greater than that of graphite in the second region 122, the rapid lithium intercalation capability of graphite in the second region 122 can be made greater than that of graphite in the first and third regions, thereby improving the lithium plating problem in the middle of the negative electrode sheet 1 and improving the safety and cycle performance of the secondary battery.

[0055] It should be noted that the volumetric particle size distribution Dv50 refers to the particle size that reaches 50% of the total volumetric particle size in the particle size distribution of a material on a volumetric basis, starting from the smallest particle size.

[0056] In some embodiments, the graphite volumetric particle size distribution Dv50 in the first region 121 of the negative electrode 1 is c1, the graphite volumetric particle size distribution Dv50 in the third region 123 is c2, and the graphite volumetric particle size distribution Dv50 in the second region 122 is d, where 0 < c1 - d < 10.0 μm and 0 < c2 - d < 10.0 μm. The relative sizes of the graphite volumetric particle size distribution Dv50 in the first region 121, second region 122, and third region 123 of the negative electrode 1 are within the above range, which can better improve the lithium plating problem in the center of the negative electrode 1 and further improve the cycle performance of the secondary battery.

[0057] In some embodiments, 2 μm < c1-d < 8.0 μm and 2 μm < c2-d < 8.0 μm. This further improves the lithium plating problem in the center of the negative electrode 1, and further enhances the cycle performance of the secondary battery.

[0058] In some embodiments, the graphite volumetric particle size distribution Dv50 in the first region 121 and the third region 123 is independently 7 μm to 15 μm; the graphite volumetric particle size distribution Dv50 in the second region 122 is 6 μm to 14.5 μm. The graphite volumetric particle size distribution Dv50 in the first region 121, the second region 122, and the third region 123 being within the above range can further improve the lithium plating problem in the center of the negative electrode 1 and further improve the cycle performance of the secondary battery.

[0059] In some embodiments, the OI value of the graphite in the first region 121 and the third region 122 is greater than the OI value of the graphite in the second region 122. Generally, the smaller the OI value of the graphite material, the more favorable it is for lithium-ion diffusion and intercalation; the larger the OI value, the less favorable it is for lithium-ion diffusion and intercalation. By setting the OI values ​​of the graphite in the first region 121 and the third region 122 to be greater than the OI value of the graphite in the second region 122, this application enables the active material in the second region located in the middle of the electrode to have better lithium-ion diffusion and rapid lithium intercalation capabilities compared to the two sides in the first direction. This improves the lithium plating problem in the middle of the negative electrode 1 and enhances the safety and cycle performance of the secondary battery.

[0060] It should be noted that the OI value of graphite refers to the graphite orientation index, which represents the ratio of the peak intensity of the 004 peak to the 110 peak in graphite material (i.e., I0). 004 / I 110 ), among which, I 004 I represents the peak intensity of the (004) crystal plane of graphite material during X-ray diffraction. 110 This represents the peak intensity of the (110) crystal plane of the graphite material during X-ray diffraction.

[0061] In some embodiments, the OI value of graphite in the first region 121 is e1, the OI value of graphite in the third region 123 is e2, and the OI value of graphite in the second region 122 is f, where 0 < e1 - f < 9 and 0 < e2 - f < 9. This further improves the problem of lithium plating in the center of the negative electrode 1 and further enhances the cycle performance of the secondary battery.

[0062] In some embodiments, 1.5 < e1-f < 3.0, and 1.5 < e2-f < 3.0. This further improves the problem of lithium plating in the middle of the negative electrode 1, and further enhances the cycle performance of the secondary battery.

[0063] In some embodiments, the OI value of graphite in the first region 121 and the third region 123 is independently 5.0 to 10.0; the OI value of graphite in the second region 122 is 2.5 to 4.5. The graphite OI values ​​in the first region 121, the second region 122, and the third region 123 are within the above range, which can further improve the lithium plating problem in the center of the negative electrode 1 and further improve the cycle performance of the secondary battery.

[0064] In some embodiments, the dimension of the first region 121 along the first direction is g, the dimension of the second region 122 along the first direction is h, the dimension of the third region 123 along the first direction is i, and the dimension of the negative electrode 1 along the first direction is j, where 0.1 ≤ h / j ≤ 0.75, 0.125 ≤ g / j ≤ 0.45, and 0.125 ≤ i / j ≤ 0.45. The ratio of the dimensions of the first region 121, the second region 122, and the third region 123 along the first direction to the dimension of the negative electrode 1 along the first direction is within the aforementioned range. This allows for a more reasonable distribution of the rapid lithium intercalation capability of the negative electrode active material in the negative electrode film layer 12 along the first direction, further improving the problem of lithium plating in the middle of the negative electrode 1 and further enhancing the cycle performance of the secondary battery.

[0065] In some embodiments, the thickness of the negative electrode 1 is 50 μm to 400 μm. It is understood that the thickness of the negative electrode 1 includes the sum of the thickness of the negative current collector 11 and the thickness of the negative electrode film layer 12 on the upper and lower surfaces of the negative current collector 11. The thickness of the negative electrode 1 can be, but is not limited to, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm, 360 μm, 380 μm, and 400 μm.

[0066] A second aspect of this application also provides a secondary battery, which includes the negative electrode 1 of the first aspect of this application. This secondary battery is a wound battery, and the secondary battery is wound with the width direction of the negative electrode 1 as the first direction. Therefore, the secondary battery has better safety and cycle performance.

[0067] Please see Figure 1 In some embodiments, the negative electrode 1 has a first overhang region 124 and a second overhang region 125 at its two ends along the first direction; the range of the first region 121 covers the first overhang region 124, and the range of the third region 123 covers the second overhang region 125.

[0068] Furthermore, in some embodiments, the size of the first region 121 along the first direction is greater than the size of the first overhang region 124 along the first direction; the size of the third region 123 along the first direction is greater than the size of the second overhang region 125 along the first direction.

[0069] In other words, in the secondary battery of this application, the first region 121 of the negative electrode 1 includes the first overhang region 124 and a portion of the non-overhang region; similarly, the third region 123 includes the second overhang region 125 and a portion of the non-overhang region; while the second region 122 is within the non-overhang region.

[0070] It should be noted that the overhang area refers to the area on the negative electrode 1 that does not overlap with the positive electrode after the negative electrode 1 and the positive electrode 1 are wound together, while the non-overhang area refers to the area on the negative electrode 1 that overlaps with the positive electrode after the negative electrode 1 and the positive electrode 1 are wound together.

[0071] A third aspect of this application also provides an electrical device that includes a secondary battery as described in the second aspect of this application.

[0072] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0073] Unless otherwise specified, the battery components, material types or contents mentioned apply to both lithium-ion and sodium-ion secondary batteries.

[0074] In one embodiment of this application, a secondary battery is provided.

[0075] Typically, a secondary battery consists of 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 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.

[0076] Positive electrode sheet

[0077] 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.

[0078] 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.

[0079] In some embodiments, the positive electrode 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 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 on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may be (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the positive electrode active material may comprise a positive electrode active material known in the art for use in batteries.

[0081] As an example, the positive electrode active material of a lithium-ion secondary battery 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 application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries 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 may 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 LiNi 0.5 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 0.15 Al 0.05At 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.

[0082] As an example, the positive electrode active material of a sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0083] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0084] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0085] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0086] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n-The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0087] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0088] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0089] The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0090] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder accounts for 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0091] 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. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0092] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40wt%~80wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s~25000 mPa·s. The positive electrode slurry is then coated onto the surface of the positive current collector, dried, and cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 150 mg / m². 2 ~350 mg / m 2 The compaction density of the positive electrode sheet is 3.0 g / cm³. 3 ~3.6 g / cm 3 The option is 3.3 g / cm³. 3 ~3.5 g / cm 3 .

[0093] The formula for calculating the compaction density is:

[0094] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0095] The mass M of the positive electrode active material per unit area of ​​the positive electrode membrane can be obtained by weighing using a standard balance.

[0096] The thickness T of the positive electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film mentioned in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for battery assembly after cold pressing and compaction.

[0097] Negative electrode sheet

[0098] The negative electrode in the secondary battery of this application adopts the negative electrode of the first aspect of this application.

[0099] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0100] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0101] 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 on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0102] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0103] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0 to 20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0104] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight percentage of the other additives in the negative electrode film is 0-15% by weight, based on the total weight of the negative electrode film.

[0105] 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, wherein the solid content of the negative electrode slurry is 30wt%~70wt%, and the viscosity at room temperature is adjusted to 2000 mPa·s~10000 mPa·s; the obtained negative electrode slurry is coated onto a negative electrode current collector, and after a drying process, cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coating is 75 mg / m². 2 ~220 mg / m 2 The compaction density of the negative electrode sheet is 1.2 g / m³. 3 ~2.0 g / m 3 .

[0106] The mass M of the negative electrode active material per unit area of ​​the negative electrode membrane can be obtained by weighing using a standard balance.

[0107] The thickness T of the negative electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the negative electrode film mentioned in this application refers to the thickness of the negative electrode film in the negative electrode sheet used for battery assembly after cold pressing and compaction.

[0108] electrolytes

[0109] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0110] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0111] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0112] The electrolyte salt for sodium-ion secondary batteries can be selected from one or more of the following: sodium hexafluorophosphate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0113] The concentration of the electrolyte salt is typically 0.1 mol / L to 5 mol / L.

[0114] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0115] 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.

[0116] Separating membrane

[0117] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0118] 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.

[0119] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

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

[0121] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0122] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0123] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0124] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or 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.

[0125] In some embodiments, the secondary battery 5 can be assembled into a battery module, and the number of secondary batteries 5 contained in the battery module 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 module.

[0126] In the battery module, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be secured with fasteners.

[0127] Optionally, the battery module may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0128] 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.

[0129] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0130] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is 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.

[0131] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0132] Figure 5 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0133] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0134] The following are some examples.

[0135] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0136] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0137] I. Battery Example

[0138] Example 1:

[0139] 1) Preparation of negative electrode sheet

[0140] Artificial graphite (specific capacity of 340 mAh / g, volumetric particle size distribution Dv50=15.0 μm), conductive agent acetylene black, binder SBR (styrene-butadiene latex), and binder CMC (carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity of 340 mAh / g, volumetric particle size distribution Dv50=14.3 μm), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0141] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0142] 2) Preparation of positive electrode sheet

[0143] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (polyvinylidene fluoride) (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0144] 3) Electrolyte preparation

[0145] In an argon-atmosphere glove box with a water content of <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC (ethylene carbonate), DTD (ethylene sulfate), and PS (propylene sulfite) were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0146] 4) Separating membrane

[0147] Polyethylene porous membrane is used as the separation membrane.

[0148] 5) Battery assembly

[0149] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0150] Example 2:

[0151] This embodiment is basically the same as Embodiment 1, except that the volumetric particle size distribution Dv50 of the graphite active material in the second region of the negative electrode film is different. In this embodiment, the volumetric particle size distribution Dv50 of the graphite active material in the second region is 12.5 μm.

[0152] Example 3:

[0153] This embodiment is basically the same as Embodiment 1, except that the volumetric particle size distribution Dv50 of the graphite active material in the second region of the negative electrode film is different. In this embodiment, the volumetric particle size distribution Dv50 of the graphite active material in the second region is 11.7 μm.

[0154] Example 4:

[0155] This embodiment is basically the same as Embodiment 1, except that the volumetric particle size distribution Dv50 of the graphite active material in the second region of the negative electrode film is different. In this embodiment, the volumetric particle size distribution Dv50 of the graphite active material in the second region is 10.3 μm.

[0156] Example 5:

[0157] This embodiment is basically the same as Embodiment 1, except that the volumetric particle size distribution Dv50 of the graphite active material in the second region of the negative electrode film is different. In this embodiment, the volumetric particle size distribution Dv50 of the graphite active material in the second region is 8.6 μm.

[0158] Example 6:

[0159] This embodiment is basically the same as Embodiment 1, except that the volumetric particle size distribution Dv50 of the graphite active material in the second region of the negative electrode film is different. In this embodiment, the volumetric particle size distribution Dv50 of the graphite active material in the second region is 6.8 μm.

[0160] Example 7:

[0161] 1) Preparation of negative electrode sheet

[0162] Artificial graphite (specific capacity 340 mAh / g, graphitization degree = 90%), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity 340 mAh / g, graphitization degree = 86%), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0163] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0164] 2) Preparation of positive electrode sheet

[0165] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as a solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0166] 3) Electrolyte preparation

[0167] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0168] 4) Separating membrane

[0169] Polyethylene porous membrane is used as the separation membrane.

[0170] 5) Battery assembly

[0171] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0172] Example 8:

[0173] This embodiment is basically the same as Embodiment 7, except that the degree of graphitization of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the degree of graphitization of the negative electrode active material graphite in the second region is 81%.

[0174] Example 9:

[0175] This embodiment is basically the same as Embodiment 7, except that the degree of graphitization of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the degree of graphitization of the negative electrode active material graphite in the second region is 78%.

[0176] Example 10:

[0177] This embodiment is basically the same as Embodiment 7, except that the degree of graphitization of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the degree of graphitization of the negative electrode active material graphite in the second region is 76%.

[0178] Example 11:

[0179] This embodiment is basically the same as Embodiment 7, except that the degree of graphitization of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the degree of graphitization of the negative electrode active material graphite in the second region is 72%.

[0180] Example 12:

[0181] This embodiment is basically the same as Embodiment 7, except that the degree of graphitization of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the degree of graphitization of the negative electrode active material graphite in the second region is 65%.

[0182] Example 13:

[0183] 1) Preparation of negative electrode sheet

[0184] Artificial graphite (specific capacity 340 mAh / g, OI=5.22), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity 340 mAh / g, OI=4.36), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0185] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0186] 2) Preparation of positive electrode sheet

[0187] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as a solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0188] 3) Electrolyte preparation

[0189] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0190] 4) Separating membrane

[0191] Polyethylene porous membrane is used as the separation membrane.

[0192] 5) Battery assembly

[0193] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0194] Example 14:

[0195] This embodiment is basically the same as Embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.89.

[0196] Example 15:

[0197] This embodiment is basically the same as Embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.45.

[0198] Example 16:

[0199] This embodiment is basically the same as Embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 3.21.

[0200] Example 17:

[0201] This embodiment is basically the same as Embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 2.99.

[0202] Example 18:

[0203] This embodiment is basically the same as Embodiment 13, except that the OI value of the negative electrode active material graphite in the second region of the negative electrode film is different. In this embodiment, the OI value of the negative electrode active material graphite in the second region is 2.12.

[0204] Example 19:

[0205] 1) Preparation of negative electrode sheet

[0206] Artificial graphite (specific capacity 340 mAh / g, volumetric particle size distribution Dv50=15.0 μm, graphitization degree=90%, OI value=5.22), conductive agent acetylene black, binder SBR (styrene-butadiene latex), and binder CMC (carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity 340 mAh / g, volumetric particle size distribution Dv50=10.3 μm, graphitization degree=76%, OI value=3.21), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0207] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the second region / width of the negative electrode sheet h / j = 0.05, the thickness of the negative current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative current collector is equal.

[0208] 2) Preparation of positive electrode sheet

[0209] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (polyvinylidene fluoride) (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0210] 3) Electrolyte preparation

[0211] In an argon-atmosphere glove box with a water content of <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC (ethylene carbonate), DTD (ethylene sulfate), and PS (propylene sulfite) were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0212] 4) Separating membrane

[0213] Polyethylene porous membrane is used as the separation membrane.

[0214] 5) Battery assembly

[0215] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0216] Example 20:

[0217] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode sheet h / j = 0.1.

[0218] Example 21:

[0219] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film to the negative electrode film region is different. In this embodiment, the width of the second region / width of the negative electrode sheet h / j = 0.25.

[0220] Example 22:

[0221] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode sheet h / j = 0.5.

[0222] Example 23:

[0223] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film to the negative electrode film region is different. In this embodiment, the width of the second region / the width of the negative electrode sheet, h / j = 0.75.

[0224] Example 24:

[0225] This embodiment is basically the same as Embodiment 19, except that the ratio of the second region of the negative electrode film to the negative electrode film region is different. In this embodiment, the width of the second region / width of the negative electrode sheet h / j = 0.85.

[0226] II. Battery Comparison

[0227] Comparative Example 1:

[0228] 1) Preparation of negative electrode sheet

[0229] Artificial graphite (specific capacity of 340 mAh / g, volumetric particle size distribution Dv50=15.0 μm, degree of graphitization=90%, OI=5.22), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4, and deionized water was added as solvent. The mixture was stirred thoroughly to obtain a negative electrode slurry.

[0230] The aforementioned negative electrode slurry was coated onto the entire upper and lower surfaces of the negative electrode current collector copper foil; after drying and cold pressing, the negative electrode sheet was obtained. The coating weight of the negative electrode film was 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on both the upper and lower sides of the negative electrode current collector is equal.

[0231] 2) Preparation of positive electrode sheet

[0232] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as a solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0233] 3) Electrolyte preparation

[0234] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0235] 4) Separating membrane

[0236] Polyethylene porous membrane is used as the separation membrane.

[0237] 5) Battery assembly

[0238] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0239] Comparative Example 2:

[0240] This comparative example is basically the same as Comparative Example 1, except that the volumetric particle size distribution Dv50, degree of graphitization, and OI value of the artificial graphite active material in the negative electrode slurry are different. In this comparative example, the volumetric particle size distribution Dv50 of the artificial graphite is 12.5 μm, the degree of graphitization is 86%, and the OI value is 4.36.

[0241] Comparative Example 3:

[0242] This comparative example is basically the same as Comparative Example 1, except that the volumetric particle size distribution Dv50, degree of graphitization, and OI value of the artificial graphite active material in the negative electrode slurry are different. In this comparative example, the volumetric particle size distribution Dv50 of the artificial graphite is 10.3 μm, the degree of graphitization is 81%, and the OI value is 2.99.

[0243] Comparative Example 4:

[0244] 1) Preparation of negative electrode sheet

[0245] Artificial graphite (specific capacity of 340 mAh / g, volumetric particle size distribution Dv50=14.3 μm), conductive agent acetylene black, binder SBR (styrene-butadiene latex), and binder CMC (carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity of 340 mAh / g, volumetric particle size distribution Dv50=15 μm), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0246] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0247] 2) Preparation of positive electrode sheet

[0248] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (polyvinylidene fluoride) (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0249] 3) Electrolyte preparation

[0250] In an argon-atmosphere glove box with a water content of <10 ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC (ethylene carbonate), DTD (ethylene sulfate), and PS (propylene sulfite) were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0251] 4) Separating membrane

[0252] Polyethylene porous membrane is used as the separation membrane.

[0253] 5) Battery assembly

[0254] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0255] Comparative Example 5:

[0256] This comparative example is basically the same as Comparative Example 4, except that the volumetric particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is different. In this example, the volumetric particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is 12.5 μm.

[0257] Comparative Example 6:

[0258] This comparative example is basically the same as Comparative Example 4, except that the volumetric particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is different. In this example, the volumetric particle size distribution Dv50 of the active material graphite in the negative electrode slurry 1 is 10.3 μm.

[0259] Comparative Example 7:

[0260] 1) Preparation of negative electrode sheet

[0261] Artificial graphite (specific capacity 340 mAh / g, graphitization degree = 86%), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity 340 mAh / g, graphitization degree = 90%), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0262] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0263] 2) Preparation of positive electrode sheet

[0264] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as a solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0265] 3) Electrolyte preparation

[0266] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0267] 4) Separating membrane

[0268] Polyethylene porous membrane is used as the separation membrane.

[0269] 5) Battery assembly

[0270] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0271] Comparative Example 8:

[0272] This comparative example is basically the same as Comparative Example 7, except that the degree of graphitization of the active material graphite in the negative electrode slurry 1 is different. In this example, the degree of graphitization of the active material graphite in the negative electrode slurry 1 is 81%.

[0273] Comparative Example 9:

[0274] This comparative example is basically the same as Comparative Example 7, except that the degree of graphitization of the active material graphite in the negative electrode slurry 1 is different. In this example, the degree of graphitization of the active material graphite in the negative electrode slurry 1 is 76%.

[0275] Comparative Example 10:

[0276] 1) Preparation of negative electrode sheet

[0277] Artificial graphite (specific capacity 340 mAh / g, OI=4.36), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 1. Artificial graphite (specific capacity 340 mAh / g, OI=5.22), conductive agent acetylene black, binder SBR, and binder CMC were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain negative electrode slurry 2.

[0278] The aforementioned negative electrode slurry 1 is coated onto the two ends of the copper foil in the width direction of the negative electrode current collector, and negative electrode slurry 2 is coated onto the middle position of the copper foil in the width direction of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The areas coated with negative electrode slurry 1 in the negative electrode film layer of the negative electrode sheet are designated as the first and third regions, and the area coated with negative electrode slurry 2 is designated as the second region. The coating weight of the negative electrode film layer is 0.108 g / 1540.25 mm. 2 (Based on weight excluding solvent). The width of the first region is 60 mm, the width of the second region is 60 mm, the width of the third region is 60 mm, the thickness of the negative electrode current collector is 6 μm, the total thickness of the negative electrode sheet is 110 μm, and the thickness of the negative electrode film layer on the upper and lower sides of the negative electrode current collector is equal.

[0279] 2) Preparation of positive electrode sheet

[0280] Lithium iron phosphate (specific capacity 139 mAh / g), acetylene black (conductive agent), and PVDF (binder) were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone (N-methylpyrrolidone) was added as a solvent, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto a positive electrode current collector aluminum foil. The coating weight of the negative electrode slurry was 0.224 g / 1540.25 mm. 2(Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0281] 3) Electrolyte preparation

[0282] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC, DTD, and PS were added to the mixed organic solvent and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0283] 4) Separating membrane

[0284] Polyethylene porous membrane is used as the separation membrane.

[0285] 5) Battery assembly

[0286] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the prepared electrolyte, and sealed for formation to obtain a lithium-ion secondary battery.

[0287] Comparative Example 11:

[0288] This comparative example is basically the same as Comparative Example 7, except that the OI value of the active material graphite in the negative electrode slurry 1 is different. In this example, the OI value of the negative electrode active material graphite in the negative electrode slurry 1 is 3.89.

[0289] Comparative Example 12:

[0290] This comparative example is basically the same as Comparative Example 7, except that the degree of graphitization of the active material graphite in the negative electrode slurry 1 is different. In this example, the degree of graphitization of the active material graphite in the negative electrode slurry 1 is 3.45.

[0291] III. Testing Methods

[0292] 1) Volumetric particle size distribution Dv50 test

[0293] Unless otherwise specified, the particle size distribution parameter Dv50 of the negative electrode active material determined by particle size distribution measurement in this application is determined by particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, use a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions.

[0294] 2) Graphitization degree test

[0295] Crystal cell parameters were calculated using X-ray polycrystalline diffraction. The centroid method was used to locate the peaks of C004 and Si311 in two parallel samples. These peaks were then substituted into the interplanar spacing formula to calculate the graphite interlayer spacing d002. The obtained d002 was then substituted into the Mering-Maire formula: g = [(3.440 - d002) / (3.440 - 3.354)] * 100% to obtain the degree of graphitization g. The degree of graphitization g of the negative electrode active material can be determined using XRD diffraction based on the lattice parameters of the carbon crystal, referring to standards JB / T4220-2011 and JISK0131-1996.

[0296] 3) OI value test

[0297] According to the embodiments of this application, the OI value GOI of the negative electrode active material powder can be determined by XRD testing with reference to JISK0131-1996. Specifically, according to the embodiments of this application, the OI value of the active material powder can be calculated according to the formula GOI=C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of the negative electrode, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the negative electrode.

[0298] 4) Battery room temperature cycle performance test

[0299] At 25 °C, the lithium-ion secondary battery was first charged at a constant current of 1 C (the current value required to completely discharge the theoretical capacity within 1 hour) to a voltage of 3.65 V, then charged at a constant voltage of 3.65 V to a current of 0.05 C. After resting for 5 minutes, the lithium-ion secondary battery was discharged at a constant current of 1 C to a voltage of 2.5 V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to multiple charge-discharge cycles using the above method until the discharge capacity of the lithium-ion secondary battery decreased to 80%, and the number of cycles was recorded.

[0300] 5) Battery high-temperature cycle performance test

[0301] At 60 °C, the lithium-ion secondary battery was first charged at a constant current of 1 C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) to a voltage of 3.65 V, then charged at a constant voltage of 3.65 V to a current of 0.05 C. After resting for 5 minutes, the lithium-ion secondary battery was discharged at a constant current of 1 C to a voltage of 2.5 V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to multiple charge-discharge cycles using the above method, and the discharge capacity of the 500th cycle was measured.

[0302] The capacity retention rate of a lithium-ion secondary battery after 500 cycles at 60 °C is calculated as (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0303] The parameters and performance test data of the various embodiments and comparative examples of this application are shown in Tables 1, 2 and 3.

[0304] Table 1

[0305]

[0306]

[0307] Table 2

[0308]

[0309]

[0310] Table 3

[0311]

[0312]

[0313] As shown in Examples 1 to 6 and Comparative Examples 1 to 6, by controlling the volumetric particle size distribution Dv50 of graphite in the central region (i.e., the second region) of the negative electrode sheet to be smaller than that in the outer region (i.e., the first and third regions), the fast-charging capability of graphite in the central region can be greater than that in the outer region. Simultaneously, keeping the difference in volumetric particle size distribution Dv50 within a suitable range is beneficial for improving the consistency of polarization performance between the central and outer regions. However, when c1-d ≥ 8 μm or c2-d ≥ 8 μm, the graphite kinetics in the outer region are too slow, which increases the probability of lithium plating in the outer region.

[0314] As shown in Examples 7 to 12 and Comparative Examples 1 to 3 and 7 to 9, by controlling the graphitization degree of graphite in the middle region of the negative electrode sheet to be less than that in the outer region, the fast-charging capability of the graphite in the middle region is greater than that in the outer region. Simultaneously, keeping the graphitization degree difference within a suitable range is beneficial for improving the consistency of polarization performance between the middle and outer regions. However, when a1-b ≥ 20% or a2-b ≥ 20%, the graphite kinetics in the outer region are too slow, which increases the probability of lithium plating in the outer region.

[0315] As shown in Examples 13 to 18 and Comparative Examples 1 to 3 and 10 to 12, by controlling the OI value of the graphite in the middle region of the negative electrode sheet to be lower than that in the outer region, the fast-charging capability of the graphite in the middle region is greater than that in the outer region. Simultaneously, keeping the OI value difference within a suitable range is beneficial for improving the consistency of polarization performance between the middle and outer regions. However, when e1-f ≥ 3.0 or e2-f ≥ 3.0, the graphite kinetics in the outer region are too slow, which increases the probability of lithium plating in the outer region.

[0316] As can be seen from Examples 19 to 24 and Comparative Examples 1 to 3, the ratio of the width of the central region to the width of the negative electrode sheet affects the improvement of lithium plating in the central region. When h / j is less than 1 / 10, the central region is too narrow and there is still local lithium plating. When h / j is greater than 3 / 4, the central region is too wide and there is also local lithium plating.

[0317] In summary, addressing the issues of high temperature, large expansion force, and small positive polarization in the middle of the electrode during cell cycling, and low temperature, small expansion force, and large positive polarization at the head and bottom of the electrode, this application proposes a novel differentiated design for the negative electrode. By adjusting the graphite fast-charging capability of the middle region (second region) of the negative electrode to be greater than that of the outer regions (first and third regions), the rapid lithium intercalation capability of the graphite in the middle region is improved, thereby alleviating the problem of positive and negative electrode mismatch during cell cycling and improving the lithium plating in the middle of the cell.

[0318] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer contains a negative electrode active material, including graphite. The negative electrode film layer includes a first region, a second region, and a third region, which are sequentially disposed in a first direction. The first direction is the width direction of the negative electrode sheet. Wherein, the negative electrode sheet satisfies at least one of the following: (1) The graphitization degree of the graphite in the first region and the third region is greater than that of the graphite in the second region. (2) The volumetric particle size distribution Dv50 of the graphite in the first region and the third region is greater than that of the graphite in the second region. (3) The OI value of the graphite in the first region and the third region is greater than the OI value of the graphite in the second region.

2. The negative electrode sheet according to claim 1, characterized in that, The graphite degree of the graphite in the first region is a1, the graphite degree of the graphite in the third region is a2, and the graphite degree of the graphite in the second region is b, where 0 < a1 - b < 40% and 0 < a2 - b < 40%.

3. The negative electrode sheet according to claim 2, characterized in that, If 5% < a1-b < 40%, the option is 5% < a1-b < 20%; if 5% < a2-b < 40%, the option is 5% < a2-b < 20%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The graphitization degree of the graphite in the first region and the third region is independently 65%~100%; the graphitization degree of the graphite in the second region is 60%~90%.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The volumetric particle size distribution Dv50 of the graphite in the first region is c1, the volumetric particle size distribution Dv50 of the graphite in the third region is c2, and the volumetric particle size distribution Dv50 of the graphite in the second region is d, where 0 < c1 - d < 10.0 μm and 0 < c2 - d < 10.0 μm.

6. The negative electrode sheet according to claim 5, characterized in that, 2 μm<c1-d<8.0 μm, 2 μm<c2-d<8.0 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that, The volumetric particle size distribution Dv50 of the graphite in the first region and the third region is independently 7 μm to 15 μm; the volumetric particle size distribution Dv50 of the graphite in the second region is 6 μm to 14.5 μm.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that, The OI value of the graphite in the first region is e1, the OI value of the graphite in the third region is e2, and the OI value of the graphite in the second region is f, where 0 < e1 - f < 9 and 0 < e2 - f < 9.

9. The negative electrode sheet according to claim 8, characterized in that, 1.33≤e1-f<9, can be selected as 1.5<e1-f<3.0; 1.33≤e2-f<9, can be selected as 1.5<e2-f<3.

0.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The OI value of the graphite in the first region and the third region is independently 5.0~10.0; the OI value of the graphite in the second region is 2.5~4.

5.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that, The dimensions of the first region, the second region, and the third region in the first direction are g, h, and i, respectively, and the dimension of the negative electrode sheet in the first direction is j, where 0.1≤h / j≤0.75, 0.125≤g / j≤0.45, and 0.125≤i / j≤0.

45.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that, The thickness of the negative electrode sheet is 50 μm to 400 μm.

13. A secondary battery, characterized in that, It includes the negative electrode sheet according to any one of claims 1 to 12; optionally, the secondary battery is a wound battery.

14. The secondary battery according to claim 13, characterized in that, The negative electrode sheet has a first overhang region and a second overhang region at its two ends in the first direction; the range of the first region covers the first overhang region; the range of the third region covers the second overhang region. Optionally, the size of the first region in the first direction is larger than the size of the first overhang region in the first direction; Optionally, the size of the third region in the first direction is greater than the size of the second overhang region in the first direction.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 13 or 14.

Images