Secondary battery and electric device

Abstract

The application provides a secondary battery and an electric device, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a first carbon-based material and a second carbon-based material, the first carbon-based material comprising artificial graphite secondary particles, the second carbon-based material comprising an outer region and an inner region inside the outer region, the outer region being a region extending from the surface of the particles of the second carbon-based material to the interior of the particles by a distance of 2.5 μm, in a cross-sectional view of the second carbon-based material, the total pore area of the outer region being denoted as S1, the total pore area of the inner region being denoted as S2, and S2>S1. The application can improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. As the application scope of rechargeable batteries becomes increasingly widespread, people are placing higher demands on their performance, especially their cycle performance.

[0003] Therefore, improving the cycle performance of secondary batteries has become an urgent problem to be solved in this field. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device, the secondary battery having excellent cycle performance.

[0005] This application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector and including a negative electrode active material, wherein the negative electrode active material includes a first carbon-based material and a second carbon-based material, the first carbon-based material including artificial graphite of secondary particles, the second carbon-based material including an outer region and an inner region located inside the outer region, the outer region being a region extending 2.5 μm from the particle surface to the particle interior of the second carbon-based material, in a cross-sectional view of the second carbon-based material, the total pore area of ​​the outer region is denoted as S1, the total pore area of ​​the inner region is denoted as S2, and S2>S1.

[0006] In this application, the negative electrode active material includes the aforementioned first carbon-based material and second carbon-based material. The first carbon-based material is artificial graphite secondary particles. Secondary particles have high isotropy, exhibit minimal expansion during cycling, and result in a more stable electrode structure, which is beneficial for reducing side reactions during cycling and improving the cycle performance of the battery cell. Furthermore, the second carbon-based material has a S2 > S1 ratio, indicating that the structure of the outer region of this carbon-based material is more dense than that of the inner region. This dense surface structure helps reduce active lithium consumption, thereby improving the cycle performance of the secondary battery.

[0007] In some embodiments, the octogenetic roughness of the second carbon-based material is less than that of the first carbon-based material. The artificial graphite of the secondary particles has a larger octogenetic roughness, with more sharp edges and a larger particle size. Conversely, the second carbon-based material has a smaller octogenetic roughness, indicating a more rounded surface and a smaller particle size. In this application, by combining the first and second carbon-based materials, graphite particles of different sizes and roughnesses are mixed together. The resulting negative electrode sheet exhibits better particle stacking during cold pressing, thereby increasing the contact area between particles, improving adhesion, and giving the negative electrode sheet higher cohesion. This suppresses electrode sheet expansion during graphite ring formation, further improving the cycle performance of the secondary battery.

[0008] In some embodiments, the octogen roughness of the first carbon-based material is greater than or equal to 0.20, optionally 0.25-0.40; and / or, the octogen roughness of the second carbon-based material is less than or equal to 0.28, optionally 0.08-0.25. By ensuring that the octogen roughness of the first and second carbon-based materials are respectively within the above-mentioned ranges, the first carbon-based material has more angular particles and a larger particle size, while the second carbon-based material has a more rounded surface and a smaller particle size. When used in combination, the two are more conducive to the negative electrode active material having higher cohesion, thereby suppressing electrode expansion.

[0009] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.1 m². 2 / g-2.5m 2 / g, can be selected as 1.2m 2 / g-2.0m 2 / g; and / or, the specific surface area of ​​the second carbon-based material is 1.0m². 2 / g-2.1m 2 / g, can be selected as 1.3m 2 / g-1.9m 2 / g. By ensuring that the specific surface area of ​​the first carbon-based material and the specific surface area of ​​the second carbon-based material are within the above-mentioned range, the consumption of active ions during SEI film formation can be reduced, thereby improving the cycle performance of the secondary battery.

[0010] In some embodiments, the specific capacity of the first carbon-based material is less than that of the second carbon-based material. In some embodiments, the specific capacity of the first carbon-based material is 340 mAh / g-360 mAh / g, optionally 345 mAh / g-358 mAh / g; and / or, the specific capacity of the second carbon-based material is 358 mAh / g-372 mAh / g, optionally 365 mAh / g-372 mAh / g. By ensuring that the specific capacities of the first and second carbon-based materials are within the above ranges, the secondary battery can achieve a higher volumetric energy density.

[0011] In some embodiments, the proportion of the secondary particles of artificial graphite in the first carbon-based material is greater than or equal to 60%, and can be selected as 70%-85%. By making the proportion of secondary particles of artificial graphite in the first carbon-based material large, the isotropy is high, which can effectively suppress electrode expansion during cycling and improve battery cycle performance.

[0012] In some embodiments, the degree of graphitization of the first carbon-based material is less than that of the second carbon-based material. The degree of graphitization of the first carbon-based material is 90.0%-95.0%, optionally 92.0%-94.0%; and / or, the degree of graphitization of the second carbon-based material is 95.0%-98.0%, optionally 95.5%-97.5%, thereby resulting in a higher specific capacity and powder compaction density of the negative electrode.

[0013] In some embodiments, the volumetric particle size distribution Dv50 of the first carbon-based material is smaller than that of the second carbon-based material. In some embodiments, the volumetric particle size distribution Dv50 of the first carbon-based material is 8 μm-18.0 μm, optionally 10 μm-16 μm; and / or, the volumetric particle size distribution Dv50 of the second carbon-based material is 10.0 μm-20.0 μm, optionally 12.0 μm-18.0 μm. This results in a lower specific surface area of ​​the carbon-based material, which is beneficial for the battery to have a higher initial coulombic efficiency.

[0014] In some embodiments, the area of ​​the pore structure in the outer region of the second carbon-based material is less than or equal to 0.15 μm. 2 The option is less than or equal to 0.13μm. 2 ; and / or, the internal region of the second carbon-based material includes one or more particles with an area greater than or equal to 0.15 μm. 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm. 2 -2.0μm 2 The porous structure, with a dense exterior and porous interior, can improve the initial coulombic efficiency while mitigating electrode expansion during cycling and enhancing stability during cycling.

[0015] In some implementations, 1.5 ≤ S2 / S1 ≤ 500, and 2 ≤ S2 / S1 ≤ 450. This allows for further improvement in the cycle performance of the secondary battery.

[0016] In some embodiments, the second carbon-based material comprises primary particles. Optionally, the primary particles account for more than or equal to 80% of the second carbon-based material. This enables it to have higher structural stability and reduces the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0017] In some embodiments, the first carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the first carbon-based material under a pressure of 50,000 N is greater than or equal to 1.85 g / cm³. 3 The option is 1.88g / cm³. 3 -2.00g / cm 3 (2) The tap density of the first carbon-based material is 0.8 g / cm³. 3 -1.1g / cm 3 0.85g / cm³ is an optional value. 3 -1.05g / cm 3 (3) The [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is 0.8-1.5, and can be selected as 0.9-1.4; (4) The adsorption capacity of 100g of the first carbon-based material for linseed oil is 50ml-70ml, and can be selected as 55ml-65ml. By ensuring that the first carbon-based material meets at least one of the above conditions, it is more beneficial to improve the energy density, charging capacity, and cycle performance of the secondary battery.

[0018] In some embodiments, the second carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the second carbon-based material under a pressure of 50,000 N is 1.80 g / cm³. 3 -2.10g / cm 3 The option is 1.85g / cm³. 3 -2.08g / cm 3 (2) The tap density of the second carbon-based material is 0.95 g / cm³. 3 -1.30g / cm 3 1.00 g / cm³ is an optional value. 3 -1.25g / cm 3(3) The [(Dv90)-(Dv10)] / (Dv50)] of the second carbon-based material is 0.70-1.10, and can be selected as 0.75-1.05; (4) The volumetric particle size Dv90 of the second carbon-based material is 13.0μm-30.0μm, and can be selected as 16.0μm-25.0μm; (5) The adsorption capacity of 100g of the second carbon-based material for linseed oil is 40mL-60mL, and can be selected as 40mL-55mL. By ensuring that the second carbon-based material meets at least one of the above conditions, it is more beneficial to improve the energy density, charging capacity, and cycle performance of the secondary battery.

[0019] In some embodiments, the content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%, optionally 40wt%-60wt%. By keeping the content of the second carbon-based material within the above range, it is more beneficial to improve the cycle performance of the secondary battery.

[0020] In some embodiments, the negative electrode active material further includes a silicon-based material. Optionally, the content of the silicon-based material in the negative electrode active material is greater than or equal to 5 wt%, and more preferably 10 wt% to 30 wt%.

[0021] A second aspect of this application provides an electrical device that includes the secondary battery of the first aspect of this application.

[0022] Invention Effects

[0023] The secondary battery of this application has excellent cycle performance. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a cross-sectional image of the particles of the second carbon-based material of this application.

[0026] Figure 2 This is a scanning electron microscope (SEM) image of one embodiment of the first carbon-based material of this application.

[0027] Figure 3 This is an ion-polished cross-section (CP) diagram of one embodiment of the second carbon-based material of this application.

[0028] Figure 4 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0029] Figure 5 This is an exploded view of one embodiment of the secondary battery of this application.

[0030] Figure 6 This is a schematic diagram of one embodiment of the battery module of this application.

[0031] Figure 7 This is a schematic diagram of one embodiment of the battery pack of this application.

[0032] Figure 8 yes Figure 7 An exploded view of an embodiment of the battery pack shown.

[0033] Figure 9 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0034] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 100 Second carbon-based material, 101 External area, 102 Internal area. Detailed Implementation

[0035] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed 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 making the following description unnecessarily lengthy 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.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0039] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Currently, the applications of rechargeable batteries are becoming increasingly widespread, and people are placing higher demands on their performance. In particular, the cycle performance of rechargeable batteries is increasingly failing to meet these requirements. Therefore, how to improve the cycle performance of rechargeable batteries has become an urgent problem to be solved in this field.

[0041] In view of this, the first aspect of the embodiments of this application provides a secondary battery.

[0042] This application does not impose any particular limitation on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions repeatedly insert and extract between the positive and negative electrode, and the electrolyte acts as a conductor for these active ions. This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). Secondary batteries using electrolyte solutions, and some secondary batteries using solid electrolytes, may also include a separator membrane disposed between the positive and negative electrode to provide isolation.

[0043] [Negative electrode plate]

[0044] In the secondary battery of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material. The negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material includes artificial graphite with secondary particles. The second carbon-based material includes an outer region and an inner region located inside the outer region. The outer region refers to the area extending 2.5 μm from the particle surface to the particle interior of the second carbon-based material. In a cross-sectional view of the second carbon-based material, the total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1. In this application, "inner region" refers to the region in the material particles other than the outer region.

[0045] In this application, artificial graphite generally refers to crystalline carbon obtained by graphitization at high temperature, which usually does not have a porous structure or a porous structure that can be directly observed from cross-sectional images (e.g., scanning electron microscope images with a magnification of 1000x).

[0046] In this application, the first carbon-based material comprises artificial graphite with secondary particles. These secondary particles exhibit high isotropy, resulting in minimal expansion during cycling and a more stable electrode structure. This is beneficial for reducing side reactions during cycling and improving the cycle performance of the battery cell. On the other hand, the second carbon-based material exhibits a S2>S1 ratio, meaning that the internal region has a higher number and / or larger pore size than the external region. This indicates that the external region of the carbon-based material has a denser structure than the internal region. The pore structure in the internal region allows for expansion space to accommodate particle volume changes, thereby reducing the risk of particle breakage and the formation of new interfaces, lowering the negative electrode film thickness rebound rate, and thus reducing the occurrence of side reactions. The smaller number and / or smaller pore size in the external region ensures a stable structure for the second carbon-based material particles and minimizes electrolyte penetration into the pore structure within the particles, further reducing side reactions and minimizing the consumption of active ions by the SEI film formation within the particles. Therefore, by combining artificial graphite with secondary particles and the second carbon-based material with an S2>S1 ratio, the cycle performance of the secondary battery can be improved.

[0047] In some embodiments, the octogenetic roughness of the second carbon-based material is less than that of the first carbon-based material. The artificial graphite with secondary particles has a larger octogenetic roughness and more sharp edges on its surface. Conversely, the second carbon-based material has a smaller octogenetic roughness, indicating a more rounded surface. In this application, by combining the first and second carbon-based materials, graphite particles of different sizes and roughnesses are mixed together. The resulting negative electrode sheet exhibits better particle stacking during cold pressing, thereby increasing the contact area between particles, improving adhesion, and giving the negative electrode sheet higher cohesion. This suppresses electrode sheet expansion during graphite ring formation, further improving the cycle performance of the secondary battery.

[0048] In some embodiments, the octogen roughness of the first carbon-based material is greater than or equal to 0.20, for example, it can be 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, or any value range between two of these. Preferably, it is 0.25-0.40. The octanoic roughness of the second carbon-based material is less than or equal to 0.28, for example, it can be 0.06, 0.07, 0.08, 0.09, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.27 or any value between two of these, preferably 0.08-0.25. By ensuring that the octanoic roughness of the first and second carbon-based materials are within the above range, the first carbon-based material has more angular surfaces and a larger particle size, while the second carbon-based material has a more rounded surface and a smaller particle size. When used in combination, the two materials are more conducive to the negative electrode active material having higher cohesion, thereby suppressing expansion and improving the cycle performance of the secondary battery.

[0049] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.1 m². 2 / g-2.5m 2 / g, for example, can be 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, etc., preferably 1.2m 2 / g-2.0m 2 / g; the specific surface area of ​​the above-mentioned second carbon-based material is 1.0m². 2 / g-2.1m 2 / g, for example, can be 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g、2.1m 2 / g, etc., preferably 1.3m 2 / g-1.9m 2 / g. By ensuring that the specific surface areas of the first carbon-based material and the second carbon-based material are within the above-mentioned range, it is possible to reduce the consumption of active ions during SEI film formation, which is beneficial to improving the cycle performance of the battery.

[0050] In some embodiments, the specific capacity of the first carbon-based material is less than that of the second carbon-based material.

[0051] In some embodiments, the specific capacity of the first carbon-based material is 340 mAh / g-360 mAh / g, for example, it can be 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 354 mAh / g, 356 mAh / g, 358 mAh / g, etc., preferably 345 mAh / g-358 mAh / g. The specific capacity of the second carbon-based material is 358 mAh / g-372 mAh / g, for example, it can be 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 364 mAh / g, 366 mAh / g, 368 mAh / g, 370 mAh / g, 372 mAh / g, etc., preferably 365 mAh / g-370 mAh / g. By ensuring that the specific capacity of the first carbon-based material and the second carbon-based material is within the aforementioned range, it is possible to achieve a higher energy density in the secondary battery.

[0052] In some embodiments, the proportion of the artificial graphite in the secondary particles in the first carbon-based material is greater than or equal to 60%, for example, it can be 62%, 65%, 68%, 70%, 72%, 74%, 76%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, etc., preferably 70%-85%. By making the proportion of artificial graphite in the secondary particles high, the isotropy is higher, which can effectively suppress electrode expansion during cycling and improve battery cycle performance.

[0053] In some embodiments, the degree of graphitization of the first carbon-based material is lower than that of the second carbon-based material. The degree of graphitization of the first carbon-based material is 90.0%-95.0%, for example, it can be 90.5%, 91.0%, 91.5%, 92.0%, 92.5%, 93.0%, 93.5%, 94.0%, 95.0%, etc., preferably 92.0%-94.0%. The degree of graphitization of the second carbon-based material is 95.0%-98.0%, for example, it can be 95.5%, 96%, 96.5%, 97%, 97.5%, etc., preferably 95.5%-97.5%. This results in the anode material having a higher specific capacity and powder compaction density.

[0054] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is smaller than that of the second carbon-based material. After thorough mixing of the smaller-diameter first carbon-based material and the larger-diameter second carbon-based material, a denser stacking effect is achieved, enhancing particle adhesion after cold pressing and reducing electrode expansion. Simultaneously, the particle size of the second carbon-based material within the aforementioned range results in a lower specific surface area, which is beneficial for improving the initial coulombic efficiency of the battery. The volume distribution particle size Dv50 of the first carbon-based material is 8 μm-18.0 μm, for example, it can be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm, preferably 10 μm-16 μm. In addition, the volumetric particle size Dv50 of the second carbon-based material is 10.0 μm-20.0 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, preferably 12.0 μm-18.0 μm.

[0055] In some embodiments, the second carbon-based material comprises one or more particles with an area greater than or equal to 0.25 μm. 2 The pore structure. By incorporating the aforementioned pore area into the second carbon-based material, the pore structure can reserve sufficient and stable expansion space for changes in the volume of the second carbon-based material particles, reducing the risk of particle breakage, minimizing side reactions, and improving the cycle performance of the secondary battery.

[0056] In some embodiments, preferably, 1.5 ≤ S2 / S1 ≤ 500, 2 ≤ S2 / S1 ≤ 450, 2.2 ≤ S2 / S1 ≤ 400, 2.4 ≤ S2 / S1 ≤ 300, 2.5 ≤ S2 / S1 ≤ 250, 2.6 ≤ S2 / S1 ≤ 200, 2.8 ≤ S2 / S1 ≤ 150, and 3.0 ≤ S2 / S1 ≤ 100. Further research by the inventors revealed that when S2 / S1 also falls within the above ranges, the secondary battery can better balance high energy density and good cycle performance.

[0057] In this application, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the second carbon-based material can be obtained by testing a cross-sectional image of the second carbon-based material. Figure 1 This is a schematic diagram of a cross-sectional image of particles of the second carbon-based material 100 of this application. Figure 1 As shown, the region extending 2.5 μm from the surface of the second carbon-based material 100 particles into the particle interior is the outer region 101, and the region inside the outer region 101 is the inner region 102.

[0058] In this application, the pore area, S1, and S2 values ​​of the second carbon-based material can be obtained by using a cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL Corporation, Japan) to obtain the cross-section of the second carbon-based material; then, referring to JY / T010-1996, the cross-section of the second carbon-based material is scanned using a scanning electron microscope (e.g., the Sigma300 scanning electron microscope from ZEISS Corporation, Germany); finally, the pore area of ​​any pore in the second carbon-based material is obtained by image processing software (e.g., AVIZO); as well as the total pore area S2 of the internal region and the total pore area S1 of the external region, and the value of S2 / S1 is obtained from this. For example, samples can be obtained from different regions of the negative electrode in a secondary battery. At least five locations (e.g., 5, 10, 15, or more) are randomly selected from the samples, and cross-sections are obtained using a cross-section polishing instrument. From the scanning electron microscope images of each cross-section, at least ten particles (e.g., 10, 20, 50, or more particles) are randomly selected for their cross-sections. Using image processing software, the total pore area S2' of the internal region and the total pore area S1' of the external region of each particle's cross-section are obtained according to the above definition, thus obtaining the S2' / S1' value for each particle's cross-section. The arithmetic mean of S2' / S1' for all tested particle cross-sections is calculated as the S2 / S1 value of the second carbon-based material.

[0059] In some embodiments, the area of ​​the pore structure in the outer region of the second carbon-based material is less than or equal to 0.15 μm. 2 The option is less than or equal to 0.13μm. 2 Further research by the inventors revealed that by controlling the area of ​​the pore structure in the outer region of the second carbon-based material within the aforementioned range, the outer region of the second carbon-based material can possess a dense structure. This effectively improves the structural stability of the second carbon-based material, minimizes the penetration of electrolyte into the pore structure inside the particles, and thus effectively enhances the cycle performance of the secondary battery. Of course, this application does not intend to limit the area of ​​all pore structures in the outer region of the second carbon-based material to less than or equal to 0.15 μm. 2For example, more than 95%, and optionally more than 99%, of the pore structure area can be controlled to be less than or equal to 0.15 μm. 2 .

[0060] In some embodiments, the internal region of the second carbon-based material includes one or more particles with an area greater than or equal to 0.25 μm. 2 The inventors further discovered that by including the aforementioned pore structure in the internal region of the second carbon-based material, sufficient and stable expansion space can be reserved for changes in the volume of the second carbon-based material particles, reducing the occurrence of side reactions. On the other hand, the compaction density of the negative electrode film can be increased, buffering the volume changes of the negative electrode film.

[0061] In some embodiments, the compacted density of the powder of the first carbon-based material under a pressure of 50,000 N is greater than or equal to 1.85 g / cm³. 3 The option is 1.88g / cm³. 3 -2.00g / cm 3 Therefore, a higher powder compaction density is beneficial for the electrode to have a higher energy density.

[0062] In some embodiments, the tap density of the first carbon-based material is 0.8 g / cm³. 3 -1.1g / cm 3 0.85g / cm³ is an optional value. 3 -1.05g / cm 3 Therefore, mixing it with a second carbon-based material can improve the stacking effect.

[0063] In some embodiments, the [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is 0.8-1.5, and optionally 0.9-1.4. Thus, a narrower [(Dv90)-(Dv10)] / (Dv50)] indicates that the proportion of large and small particles in the first carbon-based material is relatively small, which is beneficial to the stability of electrical properties.

[0064] In some embodiments, 100g of the first carbon-based material adsorbs 50ml-70ml of linseed oil, optionally 55ml-65ml. Thus, by combining it with the second carbon-based material, the fluidity of the slurry is improved.

[0065] In some embodiments, the compacted density of the second carbon-based material under a pressure of 50,000 N is 1.80 g / cm³. 3 -2.10g / cm 3 The option is 1.85g / cm³. 3 -2.08g / cm 3 Therefore, a higher powder compaction density is beneficial for the electrode to have a higher energy density.

[0066] In some embodiments, the tap density of the second carbon-based material is 0.95 g / cm³. 3 -1.30g / cc g / cm 3 1.00 g / cm³ is an optional value. 3 -1.25g / cc g / cm 3 Therefore, a higher tap density can improve the stacking effect of particles.

[0067] In some embodiments, the ratio of [(Dv90)-(Dv10)] / (Dv50)] of the second carbon-based material is 0.70-1.10, and optionally 0.75-1.05. This indicates that the proportion of large and small particles in the second carbon-based material is relatively low, ensuring the stability of its electrical properties.

[0068] In some embodiments, the volumetric particle size Dv90 of the second carbon-based material is 13.0 μm-30.0 μm, and optionally 16.0 μm-23.0 μm. This results in a lower proportion of large particles, ensuring the stability of the electrical properties.

[0069] In some embodiments, the adsorption capacity of 100g of the second carbon-based material for linseed oil is 40mL-60mL, optionally 40mL-55mL. Thus, the lower adsorption capacity of linseed oil indicates that the second carbon-based material has good fluidity after being made into a slurry.

[0070] In some embodiments, at least a portion of the surface of the second carbon-based material has a coating layer. Optionally, the coating layer comprises carbon. Optionally, more than 80% of the surface of the second carbon-based material is covered with a carbon coating layer, and further, 90%-100% of the surface of the second carbon-based material is covered with a carbon coating layer. In some embodiments, the carbon in the coating layer comprises amorphous carbon and / or crystalline carbon with a graphitization degree between 68% and 90%. Thus, by having a coating layer on at least a portion of the surface of the second carbon-based material, the kinetic performance of the secondary battery can be further improved.

[0071] In some embodiments, the second carbon-based material comprises primary particles. Optionally, the proportion of primary particles in the second carbon-based material is greater than or equal to 80%. For example, it can be 80%-100%, 90%-100%, or 95%-100%. By including the above proportion of primary particles in the second carbon-based material, it can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0072] In some embodiments, the content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%, optionally 40wt%-60wt%; by keeping the content of the second carbon-based material within the above range, the secondary battery can obtain excellent cycle performance.

[0073] In some embodiments, when the negative electrode active material in the negative electrode film layer further includes a silicon-based material, the content of the silicon-based material is greater than or equal to 5 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, etc., preferably 10 wt% to 30 wt%. This allows the secondary battery to achieve good cycle performance while improving its kinetic performance and energy density.

[0074] In some embodiments, the aforementioned negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the aforementioned negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0076] In some embodiments, the negative electrode film layer may optionally include other additives. For example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0077] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0078] The negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of these opposing surfaces. It should be noted that the negative electrode film layer parameters (e.g., compacted density, areal density, thickness, etc.) given in this application refer to the parameters of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, if the parameters of the negative electrode film layer on either side satisfy those of this application, it is considered to fall within the protection scope of this application.

[0079] In this application, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0080] In this application, the Occhio roughness of the material (e.g., the first carbon-based material, the second carbon-based material, etc.) has a well-known meaning in the art and can be tested using methods known in the art, such as calculation using Occhio Callisto 3D software. An exemplary testing method is as follows: After dispersing the graphite particles to be tested, high-contrast, high-resolution images are obtained using Occhio Callisto 3D software to delineate the specific shape and boundaries of the graphite particles, determine the particle projection area, and define a smooth reference by checking the largest inscribed circle of the original contour pixels contained in the contour of the corresponding pixels. Specifically, an inscribed circle with a radius equal to 80% of the smooth reference radius continuously inscribed within the particle projection area, and the total area of ​​this inscribed circle is defined as the 80% reference. The ratio of the 80% smooth reference to the particle projection area is between 0 and 1; the larger the ratio, the closer the surface morphology of the tested particle is to smoothness. Taking 80% of the radius of the largest inscribed circle as the reference radius better defines and quantifies the final Occhio roughness value. The Ochio roughness in this application refers to 1-(the ratio of the 80% smooth reference to the projected area of ​​the particle), which can indicate the sphericity parameter (surface roughness) of the particulate material. The larger the Ochio roughness value, the higher the surface roughness of the material.

[0081] In this application, the specific capacity of materials (e.g., first carbon-based material, second carbon-based material, negative electrode film layer, etc.) has a meaning known in the art and can be tested using methods known in the art. An exemplary test method is as follows: Sample powder is mixed uniformly with conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) at a mass ratio of 91.6:1.8:6.6 and solvent N-methylpyrrolidone (NMP) to prepare a slurry; the prepared slurry is coated onto the surface of the negative electrode current collector copper foil and dried in an oven for later use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare a solution with a concentration of 1 mol / L. The electrolyte was prepared; then, using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, the CR2430 coin cell was assembled with the electrolyte in an argon-protected glove box. After the coin cell was left to stand for 12 hours, it was discharged at 25°C with a constant current of 0.05C to 0.005V, left to stand for 10 minutes, and then discharged again with a constant current of 50μA to 0.005V. After standing for 10 minutes, it was discharged again with a constant current of 10μA to 0.005V. Then, it was charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the sample mass is the specific capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0082] In this application, the specific surface area of ​​the materials (e.g., the first carbon-based material, the second carbon-based material) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0083] In this application, the volumetric particle sizes D10, Dv50, and Dv90 of the materials (e.g., the first carbon-based material, the second carbon-based material, etc.) have meanings known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0084] In this application, the degree of graphitization of materials (e.g., first carbon-based materials, second carbon-based materials, etc.) has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) crystal plane in the material's crystal structure. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the C(002) crystal plane in the material crystal structure, expressed in nanometers (nm).

[0085] In this application, the powder compaction density of the materials (e.g., the first carbon-based material, the second carbon-based material) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined by referring to GB / T 24533-2009 using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine). An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 50,000 N, held for 30 seconds, then the pressure is released and held for 10 seconds. The compaction density of the powder under 50,000 N pressure is then recorded and calculated.

[0086] In this application, the tap density of materials (e.g., the first carbon-based material, the second carbon-based material) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T5162-2006. The testing instrument can be Dandong Baite BT-301, with the following testing parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a measuring cylinder of 25mL.

[0087] In this application, the oil absorption value of the material (e.g., the first carbon-based material, the second carbon-based material) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, referring to GB / T3780.2-2017, weigh 20g of dried test sample and place it in the mixing chamber of the oil absorption meter. The mixing chamber temperature is 23℃, and the lid is closed. Align the oil delivery port of the constant speed burette with the opening above the mixing chamber lid. Start the oil absorption meter, and the instrument will begin to run and add linseed oil. As the amount of oil absorbed by the sample increases, the mixture changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continuously increases. This viscosity is transmitted to the torque sensor system of the oil absorption meter. When the added oil causes the semi-plastic agglomerate to reach the preset torque level, the oil absorption meter and the constant speed burette automatically shut off. Read the value corresponding to 70% of the maximum torque of the fitted curve, and use the formula A=(V / m)×100 to calculate the adsorption amount A of 100g of carbon material on linseed oil. V represents the volume of linseed oil consumed by the sample at 70% of the maximum torque, in ml; m is the mass of the added sample, in g.

[0088] In this application, primary particles and secondary particles have meanings known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0089] In this application, the proportion of artificial graphite in secondary particles in the first carbon-based material refers to: taking a test sample randomly in the negative electrode film layer, taking multiple test areas randomly in the test sample, acquiring images of multiple test areas using a scanning electron microscope, and counting the proportion of the number of artificial graphite in secondary particles in each image to the total number of particles in the first carbon-based material. The average of multiple statistical results is the proportion of artificial graphite in secondary particles in the first carbon-based material.

[0090] In this application, the proportion of primary particles in the second carbon-based material refers to: taking a test sample randomly in the negative electrode film layer, taking multiple test areas randomly in the test sample, acquiring images of multiple test areas using a scanning electron microscope, and statistically analyzing the proportion of the number of primary particles in the second carbon-based material to the total number of particles in the second carbon-based material in each image. The average of the multiple statistical results is the proportion of primary particles in the second carbon-based material.

[0091] It should be noted that the above-mentioned tests on various parameters of the negative electrode active material or negative electrode film can be performed by sampling and testing from the prepared secondary battery according to the following steps.

[0092] The secondary battery is discharged (for safety, it is generally left fully discharged); after disassembling the secondary battery, the negative electrode is removed and soaked in dimethyl carbonate for a certain period of time (e.g., 2-10 hours); then the negative electrode is removed and dried at a certain temperature and time (e.g., 60°C for more than 4 hours), and then the negative electrode is removed. At this point, samples can be taken from the dried negative electrode to test the parameters related to the negative electrode film, such as the density, specific capacity, and specific surface area of ​​the negative electrode film.

[0093] The dried negative electrode sheet is baked at a certain temperature and time (e.g., 400℃ for more than 2 hours). A sample of the negative electrode active material is taken from a random area of ​​the baked negative electrode sheet (a blade can be used to scrape the powder for sampling). The collected negative electrode active material is sieved (e.g., sieved through a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the above-mentioned negative electrode active materials.

[0094] The first carbon-based material and the second carbon-based material can be distinguished by scanning electron microscopy (SEM) or ion-polished cross-section (CP) images. The first carbon-based material and the second carbon-based material can be distinguished from the images. Figure 2 This is a SEM image of the first carbon-based material of this application. As can be seen from the image, the first carbon-based material has a secondary particle morphology. Figure 3 This is an ion-polished cross-section (CP) of the second carbon-based material of this application. As can be seen from the figure, the outer region of the second carbon-based material has a dense structure, while the inner region has a large number of pores.

[0095] In this application, the first carbon-based material mentioned above can be obtained commercially.

[0096] In some embodiments, the preparation method of the second carbon-based material includes: step 1, providing a raw material having a plurality of pore structures; step 2, mixing the raw material and a filler material uniformly in a predetermined ratio, then holding the mixture at a first temperature T1 for a first time t1, and then cooling it to room temperature to obtain an intermediate; step 3, holding the obtained intermediate at a second temperature T2 for a second time t2, and then obtaining the second carbon-based material.

[0097] In some embodiments, in step 1, the raw material used to prepare the second carbon-based material includes natural graphite. Natural graphite generally refers to graphite formed naturally in nature, which does not require graphitization, and natural graphite particles typically have a large number of closed-cell structures. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0098] "Natural spherical graphite" refers to natural graphite with a spherical or near-spherical shape, but not all natural graphite particles are controlled to be ideally spherical. In some embodiments, natural spherical graphite with the desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes processes such as crushing, grading, spheroidizing, and purification.

[0099] In some embodiments, in step 1, the volume distribution particle size Dv50 of the above-mentioned raw material can be 10.5.0 μm-19.5 μm.

[0100] In some embodiments, in step 1, the specific surface area of ​​the raw material can be greater than or equal to 2.5 m². 2 / g, optional 2.5m 2 / g-10.0m 2 / g. When the specific surface area of ​​the raw material is within the above range, it is beneficial for subsequent filling processing and obtaining the second carbon-based material with the required specific surface area. It is also beneficial for the second carbon-based material to have both high capacity and high initial coulombic efficiency. In addition, it is also beneficial for the second carbon-based material to have better kinetic performance.

[0101] In some embodiments, in step 2, the softening point temperature of the filler material is 100℃-150℃. Optionally, the softening point temperature of the filler material is 100℃-146℃, 100℃-142℃, 100℃-138℃, 100℃-134℃, 100℃-130℃, 104℃-146℃, 104℃-142℃, 104℃-138℃, 104℃-134℃, or 104℃-130℃.

[0102] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected as 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, or 3 μm-5 μm. This is beneficial for the filler material to fill into the pore structure of the raw material after being heated and melted, and also helps to improve the dispersion uniformity of the filler material and the raw material.

[0103] In some embodiments, in step 2, the coking value of the filler material is 15%-40%, optionally 18%-34%. In this application, the coking value of the filler material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined with reference to GB / T 8727-2008.

[0104] In some embodiments, in step 2, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds and resins, and may optionally include one or more of coal tar pitch and petroleum pitch.

[0105] In some embodiments, in step 2, the mass ratio of the filler material to the raw material is (11-34):100, which can be (12-33):100, (12-30):100, (12-28):100, or (14-25):100.

[0106] In step 2, by adjusting one or more parameters such as the type of filler material, softening point, coking value, and amount added to be within the above range, it is beneficial to adjust the number and / or size of pores in the outer and inner regions of the first carbon-based material to be within a suitable range, and to adjust the S2 / S1 ratio of the first carbon-based material to be within a suitable range.

[0107] By adjusting parameters such as the type of filler material, softening point, coking value, and amount added to be within the above range, the filler material has low viscosity after being heated and melted, maintaining good fluidity. At the same time, it is not easy to stick to the raw material particles, which can reduce the agglomeration of raw material particles in subsequent preparation processes. This can also reduce problems such as increased surface defects and increased surface active sites of the first carbon-based material particles due to the need to add a deagglomeration process.

[0108] In some embodiments, the heating process in step 2, which involves uniformly mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1, can be a staged heating process.

[0109] In some embodiments, the above-mentioned staged heating process includes a first heating process, a second heating process, and a third heating process.

[0110] In some embodiments, the first heating process described above involves heating to 200°C-250°C and holding at that temperature for 0.5h-3h.

[0111] In some embodiments, the second heating process described above involves heating to 450℃-550℃ and holding at that temperature for 0h-2h. When the holding time is 0h, it means that when the temperature is raised to the range of 450℃-550℃, no holding process is performed, but the temperature is raised to the first temperature T1.

[0112] In some embodiments, the third heating process described above involves heating to the first temperature T1 and holding at that temperature for a first time t1.

[0113] In the staged heating process, the temperature is first raised to 200℃. Since the heating temperature is higher than the softening point of the filler material, the filler material melts and softens when heated. Holding at this temperature for 1 hour allows it to flow and fill the pore structure of the raw material. Then, the temperature is raised to 500℃. At this point, the melted and softened filler material undergoes a carbonization reaction, gradually forming a semi-coke state, becoming a viscous liquid or solid. This prevents the filler material from entering all the pore structures of the raw material. Finally, the temperature is raised to the first temperature. At this point, the filler material undergoes a carbonization reaction, which allows the pore structure occupied by the filler material to be effectively filled.

[0114] In some embodiments, in step 2, the temperature is increased to the first temperature T1 at a rate of 1°C / min to 10°C / min. For example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any range of the above values. Optionally, the heating rate can be 1.5°C / min to 8°C / min, 1.5°C / min to 6°C / min, 2°C / min to 6°C / min, or 2°C / min to 5°C / min.

[0115] In some embodiments, the heating rate of the first heating process can be 1℃ / min-10℃ / min, and can be selected as 1.5℃ / min-8℃ / min, 1.5℃ / min-6℃ / min, 2℃ / min-6℃ / min, or 2℃ / min-5℃ / min. In some embodiments, the heating rate of the second heating process can be 1℃ / min-10℃ / min, and can be selected as 2℃ / min-8℃ / min. In some embodiments, the heating rate of the third heating process can be 1℃ / min-10℃ / min, and can be selected as 2℃ / min-8℃ / min.

[0116] In some embodiments, in step 2, the first temperature T1 is 1100℃-1400℃. For example, the first temperature T1 can be a range of 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, or any of the above values. Optionally, the first temperature T1 is 1100℃-1400℃, 1100℃-1350℃, 1100℃-1350℃, 1100℃-1300℃, 1100℃-1250℃, or 1100℃-1200℃.

[0117] In some embodiments, in step 2, the first time t1 is 1h-5h. For example, the first time t1 can be a range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any of the above values. Optionally, the first time t1 is 2h-4h.

[0118] In some embodiments, in step 2, the heat treatment can be carried out in equipment capable of programmed temperature rise, such as an induction furnace, roller kiln, rotary kiln, pusher kiln, vertical granulation kettle, horizontal granulation kettle, vertical reactor, horizontal reactor, or drum furnace.

[0119] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0120] In step 2, by adjusting one or more of the heating rate, first temperature, first time, heating process, etc., within the above range, it is beneficial to adjust the number and / or size of pores in the outer and inner regions of the second carbon-based material within a suitable range, thereby facilitating the adjustment of S2 / S1 of the second carbon-based material within a suitable range.

[0121] In some embodiments, in step 3, the second temperature T2 is 1600℃-3000℃. Optionally, the second temperature T2 is 1600℃-2800℃, 1650℃-2750℃, 1650℃-2700℃, 1700℃-2650℃, 1750℃-2600℃, 1850℃-2550℃, 1950℃-2550℃, or 1950℃-2500℃.

[0122] In some embodiments, in step 3, the second time t2 is 1.5h-6h. For example, the second time t1 can be a range of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any of the above values. Optionally, the second time t2 is 2h-5h.

[0123] In some embodiments, in step 3, the heat treatment described above can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Atchison graphitization furnace, a continuous graphitization furnace, or an internal series graphitization furnace.

[0124] In some embodiments, in step 3, the medium-frequency furnace and the continuous graphitization heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of argon and helium.

[0125] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the second carbon-based material within a suitable range, and to ensure that the second carbon-based material has a suitable degree of graphitization, interlayer spacing, etc.

[0126] In the above-mentioned method for preparing the second carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filler material, the heating rate, the first temperature, the first time, the heating process, the second temperature, and the second time within the above-mentioned range, it is beneficial to adjust the parameters of the second carbon-based material such as S2 / S1, degree of graphitization, specific capacity, particle size, specific surface area, and roughness.

[0127] [Positive electrode plate]

[0128] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0129] The aforementioned positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The aforementioned composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the aforementioned polymer material base layer. As an example, the aforementioned metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the aforementioned polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0130] The aforementioned positive electrode film typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The aforementioned positive electrode film is typically formed by coating a positive electrode slurry onto the aforementioned positive electrode current collector, followed by drying and cold pressing. The aforementioned positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to it. As an example, the binder used for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. As an example, the conductive agent used for the positive electrode film includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] The aforementioned positive electrode active material can be any positive electrode active material known in the art for use in secondary batteries.

[0132] When the secondary battery of the present application is a lithium-ion battery, the above-mentioned positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the above-mentioned lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the above-mentioned lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0133] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0134] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4.

[0135] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the above-mentioned positive electrode active materials.

[0136] [Electrolytes]

[0137] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0138] The types of electrolyte salts mentioned above are not specifically limited and can be selected according to actual needs.

[0139] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include 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).

[0140] The types of solvents mentioned above are not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvents mentioned above may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0141] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0142] [Isolation membrane]

[0143] This application does not impose any particular restrictions on the type of the aforementioned separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0144] In some embodiments, the material of the aforementioned separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0145] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be manufactured into an electrode assembly by a winding process or a stacking process.

[0146] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte.

[0147] In some embodiments, the outer packaging can be a rigid shell, such as a rigid plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a flexible package, such as a pouch. The material of the aforementioned flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0148] 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. Figure 4 This is an example of a square-structured secondary battery 5.

[0149] In some embodiments, such as Figure 5 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, which can be adjusted according to needs.

[0150] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0151] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0152] Figure 6 This is a schematic diagram of battery module 4 as an example. Figure 6 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0153] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0154] 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 adjusted according to the application and capacity of the battery pack.

[0155] Figure 7 and Figure 8 This is a schematic diagram of battery pack 1 as an example. Figure 7 and Figure 8 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0156] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described 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 can be, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0157] The aforementioned electrical devices can be equipped with secondary batteries, battery modules, or battery packs according to their usage requirements.

[0158] Figure 9 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0159] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0160] Example

[0161] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0162] Preparation of the first carbon-based material

[0163] Material 1-1

[0164] Needle coke raw material is coarsely crushed, broken, and shaped. The main frequency of the crushing and shaping machine is 55Hz, resulting in intermediate 1 with a particle size of 10μm. Intermediate 1 is mixed with asphalt (softening point 250℃) at a ratio of 100:15 and granulated in a heating device to obtain intermediate 2 with a particle size of 15μm. Intermediate 2 is placed in a graphitization furnace and subjected to graphitization heat treatment at 3000℃. After the treatment, it is demagnetized and sieved to obtain artificial graphite with secondary particles.

[0165] The properties of the obtained secondary particles of artificial graphite are as follows: volume distribution particle size Dv50 = 15.0 μm, Occio roughness = 0.30, and graphitization degree 94%.

[0166] Materials 1-2 to 1-5

[0167] The preparation methods of materials 1-2 to 1-5 are similar to those of material 1-1, except that the main frequency of the crushing and shaping machine is adjusted to obtain materials 1-2 to 1-5.

[0168] Table 1

[0169] Serial Number Host frequency (Hz) Oucchio roughness Materials 1-2 67 0.19 Materials 1-3 65 0.20 Materials 1-4 60 0.25 Materials 1-5 20 0.45

[0170] Preparation of second carbon-based materials

[0171] Material 2-1

[0172] Flake graphite was mechanically crushed and spheroidized, with 20 spheroidizing machines used in the process. The spheroidized particles had a diameter of 18 μm and were then purified to obtain natural spherical graphite. The obtained natural spherical graphite was mixed with petroleum asphalt (softening point 110℃) at a ratio of 100:22. The mixture was then placed in a continuously heated equipment, heated to 200℃ and held for 1 hour, then continuously heated to 700℃ and held for 1 hour. After cooling to room temperature, an intermediate was obtained. The intermediate was placed in a graphitization furnace and subjected to graphitization heat treatment at 2500℃. After demagnetization and sieving, a second carbon-based material was obtained.

[0173] The properties of the obtained second carbon-based material are as follows: S2 / S1 = 15, volume distribution particle size Dv50 = 18.0 μm, Occio roughness = 0.10, and graphitization degree 96%.

[0174] The S2 / S1 ratio of the second carbon-based material was obtained by testing using the following method.

[0175] The sample preparation adhesive was mixed evenly with the second carbon-based material powder and then coated onto copper foil. The mixture was dried at 60°C for 30 minutes. Five samples, each 6mm x 6mm in size, were cut at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples were then cut using a plasma beam to obtain the cross-sections of each sample. The testing instrument can be the IB-09010CP argon ion cross-section polisher from JEOL Corporation of Japan.

[0176] The cross-sections of each sample of the second carbon-based material were scanned using a scanning electron microscope (SEM). Scanned images were obtained by arbitrarily selecting a region within each sample cross-section. The testing procedure is based on JY / T010-1996. The testing instrument can be a ZEISS Sigma 300 scanning electron microscope (Germany).

[0177] Cross-sections of 20 particles of the second carbon-based material were randomly selected from the scanned images. The region extending 0.25 μm from the particle surface into the particle's interior was designated as the outer region, and the region inside the outer region was designated as the inner region. Image processing software was used to obtain the total pore area S1' of the outer region and the pore area S2' of the inner region of each particle cross-section, and the value of S2' / S1' was calculated. The arithmetic mean of S2' / S1' for all 20 particles was then calculated as the S2 / S1 value of the second carbon-based material. AVIZO could be used as the image processing software.

[0178] Materials 2-2 to 2-5

[0179] The preparation methods of materials 2-2 to 2-5 are similar to those of material 2-1, except that the number of machines connected to the shaping machine during spheroidization is adjusted to obtain materials 2-2 to 2-5.

[0180] Table 2

[0181] Serial Number Number of spheroidizing and shaping machines Occio roughness Material 2-2 22 units 0.08 Materials 2-3 15 units 0.25 Materials 2-4 13 units 0.28 Materials 2-5 10 units 0.33

[0182] Material 3:

[0183] Needle coke raw material is coarsely crushed, broken, and shaped to obtain intermediate 1 with a particle size of 15 μm. Intermediate 1 is placed in a graphitization furnace and subjected to graphitization heat treatment at 3000℃. After the treatment, it is demagnetized and sieved to obtain artificial graphite with primary particles.

[0184] The properties of the obtained primary particles of artificial graphite are as follows: volume distribution particle size Dv50 = 15.0 μm, graphitization degree 94.2%.

[0185] Example 1

[0186] Preparation of secondary batteries

[0187] The negative electrode active material (material 1-1 and material 2-1 mixed at a mass ratio of 1:1), conductive agent carbon black (SuperP), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.4:1:1.2:1.4 to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet was obtained.

[0188] Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride were mixed in a weight ratio of 96:2:2, and an appropriate amount of solvent NMP was added. The mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0189] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0190] A polyethylene film is used as a separator and is placed in sequence with the positive and negative electrode sheets prepared above, so that the separator is placed between the positive and negative electrode sheets to play a separating role. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, a secondary battery is obtained.

[0191] Comparative Example 1

[0192] The preparation method of Comparative Example 1 is similar to that of Example 1, except that the negative electrode active material is a mixture of material 3 and material 2-1 in a mass ratio of 1:1.

[0193] Performance testing

[0194] (1) Electrode expansion rate

[0195] Samples were taken from the negative electrode sheets prepared in the above embodiments and comparative examples, and the thickness of the negative electrode film was measured using a micrometer along the cut surface. This thickness was recorded as the initial thickness of the negative electrode film. The secondary batteries prepared in the above embodiments and comparative examples were charged to 3.65V at a constant current of 1 / 3C, and then charged to 0.05C at a constant voltage. After disassembly, the thickness of the negative electrode film was measured again and recorded as the full-charge thickness of the negative electrode film. The full-charge expansion rate of the electrode sheet is then calculated as (full-charge thickness of the negative electrode film - initial thickness of the negative electrode film) / cold-pressed thickness of the electrode sheet × 100%.

[0196] (2) Cycle performance test of secondary batteries

[0197] At 45°C, the prepared secondary battery was charged at a constant current of 1C to 3.65V (corresponding to 100% SOC), then charged at a constant voltage to a current of 0.05C. After resting for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.5V (corresponding to 0% SOC), and the discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0198] The capacity retention rate (%) of a secondary battery after 1000 cycles at 45℃ = discharge capacity after 1000 cycles / discharge capacity of the first cycle × 100%.

[0199] Table 3

[0200]

[0201] As shown in Table 1, this application achieves excellent cycle performance by simultaneously including a first carbon-based material (artificial graphite with secondary particles) and a second carbon-based material in the negative electrode active material of the negative electrode film layer. This results in a low electrode expansion rate. In contrast, in Comparative Example 1, when artificial graphite primary particles are combined with the second carbon-based material, the high anisotropy of the primary particles leads to greater electrode expansion, which in turn causes SEI breakage and the formation of fresh interfaces during cycling, resulting in poor cycle performance.

[0202] Examples 2-5

[0203] As shown in Table 4, the type of the first carbon-based material was changed, but the secondary battery was prepared using the same method as in Example 1. Specific parameters and test results are shown in Table 4.

[0204] It should be noted that, for ease of comparison, the results of Example 1 are also shown in Table 4.

[0205] Table 4

[0206]

[0207] As shown in Table 4, the cycle performance can be further improved by making the eutectic roughness of the second carbon-based material smaller than that of the first carbon-based material, and the eutectic roughness of the first carbon-based material greater than or equal to 0.20.

[0208] Examples 6-9

[0209] As shown in Table 5, the type of the second carbon-based material was changed, but the secondary battery was prepared using the same method as in Example 1. Specific parameters and test results are shown in Table 5.

[0210] It should be noted that, for ease of comparison, the results of Example 1 are also shown in Table 5.

[0211] Table 5

[0212]

[0213] As shown in Table 5, compared with Examples 1 and 6-8, Example 9 can further improve cycle performance by making the eutectic roughness of the second carbon-based material smaller than that of the first carbon-based material. Furthermore, making the eutectic roughness of the second carbon-based material less than or equal to 0.28 is beneficial to improving cycle performance.

[0214] 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 secondary battery comprising a negative electrode sheet including a negative electrode current collector and a negative electrode film layer including a negative electrode active material on at least one surface of the negative electrode current collector, wherein the negative electrode active material includes a first carbon-based material and a second carbon-based material; the first carbon-based material includes artificial graphite of secondary particles; the second carbon-based material includes an outer region and an inner region inside the outer region, the outer region refers to a region constituted by a distance of 2.5 pm extending from a particle surface of the second carbon-based material to the inside of the particle, in a cross-sectional view of the second carbon-based material, a total pore area of the outer region is denoted as S1, a total pore area of the inner region is denoted as S2, and S2 > S1; and a roughness of the second carbon-based material is smaller than a roughness of the first carbon-based material.

2. The secondary battery according to claim 1, wherein the roughness of the first carbon-based material is equal to or greater than 0.20; and / or the roughness of the second carbon-based material is equal to or smaller than 0.

28.

3. The secondary battery according to claim 2, wherein the roughness of the first carbon-based material is 0.25-0.4; and / or the roughness of the second carbon-based material is 0.08-0.

25.

4. The secondary battery according to any one of claims 1-3, wherein 5. The secondary battery according to claim 4, wherein a gram capacity of the first carbon-based material is smaller than a gram capacity of the second carbon-based material.

7. The secondary battery according to any one of claims 1-3, wherein the gram capacity of the first carbon-based material is 340 mAh / g-360 mAh / g; and / or the gram capacity of the second carbon-based material is 358 mAh / g-372 mAh / g.

8. The secondary battery according to claim 7, wherein the gram capacity of the first carbon-based material is 345 mAh / g-358 mAh / g; and / or the gram capacity of the second carbon-based material is 365 mAh / g-370 mAh / g.

9. The secondary battery according to any one of claims 1-3, wherein a proportion of the artificial graphite of secondary particles in the first carbon-based material is equal to or greater than 60%.

10. The secondary battery according to claim 9, wherein the proportion of the artificial graphite of secondary particles in the first carbon-based material is 70%-85%.

11. The secondary battery according to any one of claims 1-3, wherein a graphitization degree of the first carbon-based material is smaller than a graphitization degree of the second carbon-based material.

12. The secondary battery according to claim 11, wherein the graphitization degree of the first carbon-based material is 90.0%-95.0%; and / or the graphitization degree of the second carbon-based material is 95.0%-98.0%.

13. The secondary battery according to claim 12, wherein the graphitization degree of the first carbon-based material is 92.0%-94.0%; and / or the graphitization degree of the second carbon-based material is 95.5%-97.5%. said first carbon-based material has a specific surface area comprised between 1.1 m 2 / g and 2.5 m 2 / g; and / or, said second carbon-based material has a specific surface area comprised between 1.0 m 2 / g and 2.1 m 2 / g. ​ The specific surface area of the first carbon-based material is 1.2 m 2 / g-2.0 m 2 / g; and / or, The specific surface area of the second carbon-based material is 1.3 m 2 / g-1.9 m 2 / g.

6. The secondary battery according to any one of claims 1 to 3, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 11. The secondary battery according to any one of claims 1-3, wherein, ​ ​ ​ ​ ​ ​ ​ 14. The secondary battery according to any one of claims 1-3, wherein, The volume distribution particle size Dv50 of the first carbon-based material is less than the volume distribution particle size Dv50 of the second carbon-based material.

15. The secondary battery according to claim 14, wherein, The volume distribution particle size Dv50 of the first carbon-based material is 8.0 pm to 18.0 pm; and / or, The volume distribution particle size Dv50 of the second carbon-based material is 10.0 pm to 20.0 pm.

16. The secondary battery according to claim 15, wherein, The volume distribution particle size Dv50 of the first carbon-based material is 10.0 pm to 16.0 pm; and / or, The volume distribution particle size Dv50 of the second carbon-based material is 12.0 pm to 18.0 pm.

17. The secondary battery according to any one of claims 1 to 3, wherein, The area of the pore structure in the outer region of the second carbon-based material is less than or equal to 0.15 pm2; and / or, The inner region of the second carbon-based material includes one or more pore structures having an area of 0.15 pm2to 2.0 pm2.

18. The secondary battery according to claim 17, wherein, The area of the pore structure in the outer region of the second carbon-based material is less than or equal to 0.13 pm2; and / or, The inner region of the second carbon-based material includes one or more pore structures having an area of 0.15 pm2to 2.0 pm2.

19. The secondary battery according to any one of claims 1-3, wherein, 1.5 ≤ S2 / S1 ≤ 500.

20. The secondary battery according to claim 19, wherein 2 ≤ S2 / S1 ≤ 450.

21. The secondary battery according to any one of claims 1-3, wherein, The second carbon-based material includes primary particles.

22. The secondary battery of claim 21, wherein, The number of the primary particles in the second carbon-based material is greater than or equal to 80%.

23. The secondary battery according to any one of claims 1 to 3, wherein The first carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the first carbon-based material under a pressure of 50000 N is greater than or equal to 1.85 g / cm3 3 ; (2) the tap density of the first carbon-based material is 0.8 g / cm 3 -1.1 g / cm 3 ; (3) The [(Dv90) - (Dv10)] / (Dv50)] of the first carbon-based material is 0.8 to 1.5; (4) The adsorption amount of 100 g of the first carbon-based material for linseed oil is 50 ml to 70 ml.

24. The secondary battery according to claim 23, wherein The first carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the first carbon-based material under a pressure of 50000 N is 1.88 g / cm 3 -2.00 g / cm 3 ; (2) the tap density of the first carbon-based material is 0.85 g / cm 3 -1.05 g / cm 3 ; (3) The [(Dv90) - (Dv10)] / (Dv50)] of the first carbon-based material is 0.9 to 1.4; (4) The adsorption amount of 100 g of the first carbon-based material for linseed oil is 55 ml to 65 ml.

25. The secondary battery according to any one of claims 1-3, wherein, The second carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the second carbon-based material under a pressure of 50000 N is 1.80 g / cm 3 -2.10 g / cm 3 ; (2) the tap density of the second carbon-based material is 0.95 g / cm 3 -1.30 g / cm 3 ; (3) The [(Dv90) - (Dv10)] / (Dv50)] of the second carbon-based material is 0.70 to 1.10; (4) The volume particle size Dv90 of the second carbon-based material is 13.0 pm to 30.0 pm; (5) The adsorption amount of 100 g of the second carbon-based material for linseed oil is 40 mL to 60 mL.

26. The secondary battery of claim 25, wherein, The second carbon-based material satisfies at least one of the following conditions: (1) the powder compaction density of the second carbon-based material under a pressure of 50000 N is 1.85 g / cm 3 -2.08 g / cm 3 ; (2) the tap density of the second carbon-based material is 1.00 g / cm 3 -1.25 g / cm 3 ; (3) The [(Dv90) - (Dv10)] / (Dv50)] of the second carbon-based material is 0.75 to 1.05; (4) The volume particle size Dv90 of the second carbon-based material is 16.0 pm to 25.0 pm; (5) The adsorption amount of 100 g of the second carbon-based material for linseed oil is 40 mL to 55 mL.

27. The secondary battery according to any one of claims 1-3, wherein, The mass content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%.

28. The secondary battery of claim 27, wherein, The mass content of the second carbon-based material in the negative electrode active material is 40wt%-60wt%.

29. The secondary battery according to any one of claims 1-3, wherein, The negative electrode active material further comprises a silicon-based material.

30. The secondary battery of claim 29, wherein, In the negative electrode active material, the content of the silicon-based material is greater than or equal to 5wt %.

31. The secondary battery of claim 30, wherein, In the negative electrode active material, the content of the silicon-based material is 10wt%-30wt%.

32. An electrical device, comprising: The secondary battery according to any one of claims 1-31.

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