Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material; the negative electrode active material comprises a first carbon-based material and a second carbon-based material; the first carbon-based material comprises artificial graphite of secondary particles; the second carbon-based material comprises an outer region and an inner region located on the inner side of the outer region; the outer region refers to a region extending from the particle surface of the second carbon-based material to the interior of the particle by a distance of 2.5 μm; and in the 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 is greater than S1.

Description

Secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311643117.7, application date November 30, 2023, and invention name “Secondary Battery and Electrical Device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. As the scope of secondary battery applications expands, people are placing higher demands on their performance, especially their cycle performance.

[0005] Therefore, how to improve the cycle performance of secondary batteries has become an urgent problem to be solved in this field.

[0006] Summary of the Invention

[0007] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a secondary battery and an electric device, wherein the secondary battery has excellent cycle performance.

[0008] A first aspect of the present disclosure provides a secondary battery, comprising a negative electrode pole piece, the negative electrode pole piece comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material, wherein the negative electrode active material comprises a first carbon-based material and a second carbon-based material, the first carbon-based material comprises artificial graphite of secondary particles, the second carbon-based material comprises an external region and an internal region located inside the external region, the external region refers to a region extending from the particle surface of the second carbon-based material to the interior of the particle by a distance of 2.5 μm, and in a cross-sectional view of the second carbon-based material, the total pore area of ​​the external region is recorded as S1, the total pore area of ​​the internal region is recorded as S2, and S2>S1.

[0009] In the present disclosure, the negative electrode active material includes the above-mentioned first carbon-based material and the second carbon-based material. The first carbon-based material is artificial graphite secondary particles. The secondary particles have high isotropy, expand less during the cycle, and have a more stable electrode structure, which is conducive to reducing side reactions during the cycle and helping to improve the cycle performance of the battery cell. In addition, S2>S1 of the above-mentioned second carbon-based material indicates that the structure of the outer region of the carbon-based material is denser than that of the inner region. The dense surface structure is conducive to reducing active lithium consumption, thereby improving the cycle performance of the secondary battery.

[0010] In some embodiments, the Occhio roughness of the second carbon-based material is less than the Occhio roughness of the first carbon-based material. The Occhio roughness of the artificial graphite of the secondary particles is larger, the surface has more edges and corners, and the particle size is larger. In addition, the Occhio roughness of the second carbon-based material is smaller, indicating that the surface is rounder and the particle size is smaller. In the present disclosure, by combining the first carbon-based material and the second carbon-based material, graphite particles of different particle sizes and different roughness are mixed together, and the prepared negative electrode plate can form a better particle stacking effect during cold pressing, thereby increasing the contact area between the particles, improving the bonding force, and making the negative electrode plate have a higher cohesive force, thereby suppressing the expansion of the plate during the graphite ring process, and can further improve the cycle performance of the secondary battery.

[0011] In some embodiments, the first carbon-based material has an Occhio roughness greater than or equal to 0.20, optionally ranging from 0.25 to 0.40; and / or the second carbon-based material has an Occhio roughness less than or equal to 0.28, optionally ranging from 0.08 to 0.25. By ensuring that the Occhio roughness of the first and second carbon-based materials are within the above ranges, the first carbon-based material particles have more angular shapes 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 negative electrode active material has a higher cohesive force, thereby suppressing electrode expansion.

[0012] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.1 m 2 / g-2.5m 2 / g, optional 1.2m 2 / g-2.0m 2 / g; and / or, the specific surface area of ​​the second carbon-based material is 1.0m 2 / g-2.1m 2 / g, optional 1.3m 2 / g-1.9m 2 By setting the specific surface area of ​​the first carbon-based material and the specific surface area of ​​the second carbon-based material within the above range, the consumption of active ions by SEI film formation can be reduced, thereby facilitating improved cycle performance of the secondary battery.

[0013] In some embodiments, the gram capacity of the first carbon-based material is less than the gram capacity of the second carbon-based material. In some embodiments, the gram capacity of the first carbon-based material is 340 mAh / g-360 mAh / g, optionally 345 mAh / g-358 mAh / g; and / or the gram 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 gram capacities of the first and second carbon-based materials are within the above ranges, the secondary battery can have a higher volumetric energy density.

[0014] In some embodiments, the artificial graphite secondary particles comprise greater than or equal to 60% of the first carbon-based material, and may be 70% to 85%. By increasing the proportion of artificial graphite secondary particles in the first carbon-based material, the isotropy is increased, effectively suppressing electrode expansion during cycling and improving battery cycling performance.

[0015] 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 enabling the negative electrode to have a higher gram capacity and powder compaction density.

[0016] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8 μm-18.0 μm, optionally 10 μm-16 μm; and / or the volume distribution particle size Dv50 of the second carbon-based material is 10.0 μm-20.0 μm, optionally 12.0 μm-18.0 μm. As a result, the specific surface area of ​​the carbon-based material is lower, which is conducive to the battery having a higher first coulombic efficiency.

[0017] 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 , can be selected to be less than or equal to 0.13μm 2 ; and / or, the inner region of the second carbon-based material includes one or more areas 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 2By forming a structure with a dense exterior and porous interior, the initial coulombic efficiency can be improved while mitigating the expansion of the electrode during the cycle and improving the stability during the cycle.

[0018] In some embodiments, 1.5≤S2 / S1≤500, and 2≤S2 / S1≤450. This can further improve the cycle performance of the secondary battery.

[0019] In some embodiments, the second carbon-based material includes primary particles. Optionally, the primary particles account for 80% or more of the second carbon-based material. This can provide a higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0020] 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 / cm 3 , optional 1.88g / cm 3 -2.00g / cm 3 ; (2) the tap density of the first carbon-based material is 0.8 g / cm 3 -1.1g / cm 3 , optional 0.85g / cm 3 -1.05g / cm 3 (3) [(Dv90) - (Dv10)] / (Dv50)] of the first carbon-based material is 0.8-1.5, and can be optionally 0.9-1.4; (4) The adsorption capacity of linseed oil per 100g of the first carbon-based material is 50ml-70ml, and can be optionally 55ml-65ml. Ensuring that the first carbon-based material satisfies at least one of the above conditions is more conducive to improving the energy density, charging capacity, and cycle performance of the secondary battery.

[0021] 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 / cm 3 -2.10g / cm 3 , optional 1.85 g / cm 3 -2.08g / cm 3 ; (2) The tap density of the second carbon-based material is 0.95 g / cm 3 -1.30g / cm 3 , optional 1.00g / cm 3 -1.25g / cm 3(3) [(Dv90)-(Dv10)] / (Dv50)] of the second carbon-based material is 0.70-1.10, and can be optionally 0.75-1.05; (4) The volume particle size Dv90 of the second carbon-based material is 13.0 μm-30.0 μm, and can be optionally 16.0 μm-25.0 μm; (5) The adsorption capacity of linseed oil by 100 g of the second carbon-based material is 40 mL-60 mL, and can be optionally 40 mL-55 mL. By making the second carbon-based material meet at least one of the above conditions, it is more conducive to improving the energy density, charging capacity, and cycle performance of the secondary battery.

[0022] In some embodiments, the content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%, optionally 40wt%-60wt%. By making the content of the second carbon-based material within the above range, it is more conducive to improving the cycle performance of the secondary battery.

[0023] In some embodiments, the negative electrode active material further comprises a silicon-based material. Optionally, in the negative electrode active material, the content of the silicon-based material is greater than or equal to 5 wt %, and more optionally 10 wt % to 30 wt %.

[0024] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0025] Effects of the Invention

[0026] The secondary battery of the present disclosure has excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0028] FIG1 is a schematic diagram of a cross-sectional image of particles of a second carbon-based material according to the present disclosure.

[0029] FIG2 is a scanning electron microscope (SEM) image of one embodiment of the first carbon-based material disclosed herein.

[0030] FIG3 is an ion polishing cross-sectional (CP) diagram of an embodiment of the second carbon-based material disclosed herein.

[0031] FIG. 4 is a schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0032] FIG. 5 is an exploded schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0033] FIG. 6 is a schematic diagram of an embodiment of a battery module according to the present disclosure.

[0034] FIG. 7 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0035] FIG8 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG7 .

[0036] FIG. 9 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present disclosure as a power source.

[0037] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 100 second carbon-based material, 101 external region, 102 internal region. DETAILED DESCRIPTION

[0038] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0039] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0043] Currently, secondary batteries are increasingly being used in a wide range of applications, leading to higher demands on their performance. In particular, the cycling performance of secondary batteries is increasingly failing to meet these demands. Therefore, improving the cycling performance of secondary batteries has become a pressing issue in the field.

[0044] In view of this, a first aspect of an embodiment of the present disclosure provides a secondary battery.

[0045] The present disclosure has no particular restrictions on the types of secondary batteries. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present disclosure has no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes can also include an isolation membrane, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0046] [Negative electrode]

[0047] In the secondary battery disclosed herein, the negative electrode plate 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, 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 external region and an internal region located inside the external region, the external region refers to a region extending 2.5 μm from the particle surface of the second carbon-based material to the interior of the particle, in a cross-sectional view of the second carbon-based material, the total pore area of ​​the external region is recorded as S1, the total pore area of ​​the internal region is recorded as S2, and S2>S1. In the present disclosure, "internal region" refers to the region in the material particle other than the external region.

[0048] In the present disclosure, artificial graphite generally refers to crystalline carbon obtained by high-temperature graphitization treatment, which usually does not have a pore structure inside, or does not have a pore structure that can be directly observed from a cross-sectional image (such as a scanning electron microscope image with a magnification of 1000 times).

[0049] In the present disclosure, the first carbon-based material comprises artificial graphite of secondary particles, the secondary particles have high isotropy, small expansion during the cycle, and a more stable electrode structure, which is conducive to reducing side reactions during the cycle and helping to improve the cycle performance of the battery cell. On the other hand, S2>S1 of the second carbon-based material, that is, the number of pores in the internal region is large and / or the pore size is large, while the number of pores in the external region is small and / or the pore size is small, indicating that the structure of the external region of the carbon-based material is denser than the internal region, and the pore structure in the internal region can reserve the required expansion space for the volume change of the particles, thereby reducing the risk of particle breakage to produce new interfaces, reducing the rebound rate of the thickness of the negative electrode film layer, and thus reducing the occurrence of side reactions; the number of pores in the external region is small and / or the pore size is small, thereby making the second carbon-based material particles have a stable structure and avoiding the electrolyte from penetrating into the pore structure inside the second carbon-based material particles as much as possible, thereby further reducing the occurrence of side reactions and reducing the consumption of active ions by the SEI film formation inside the particles. Therefore, by combining the artificial graphite of secondary particles with the second carbon-based material with S2>S1, the cycle performance of the secondary battery can be improved.

[0050] In some embodiments, the Occhio roughness of the second carbon-based material is less than the Occhio roughness of the first carbon-based material. The Occhio roughness of the artificial graphite of the secondary particles is large, and the surface has more edges and corners. In addition, the Occhio roughness of the second carbon-based material is small, indicating that the surface is rounder. In the present disclosure, by combining the first carbon-based material and the second carbon-based material, graphite particles of different particle sizes and different roughness are mixed together, and the prepared negative electrode plate can form a better particle stacking effect during cold pressing, thereby increasing the contact area between the particles, improving the bonding force, and making the negative electrode plate have a higher cohesive force, thereby suppressing the expansion of the plate during the graphite ring process, and can further improve the cycle performance of the secondary battery.

[0051] In some embodiments, the Ochio roughness of the first carbon-based material is greater than or equal to 0.20, for example, 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 range therebetween, preferably 0.25-0.40. The second carbon-based material has an Occhio roughness of less than or equal to 0.28, for example, 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 range therebetween, preferably 0.08-0.25. By setting the Occhio roughness of the first and second carbon-based materials within the above range, the first carbon-based material particles have 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 the two are used in combination, it is more conducive to the negative electrode active material having a higher cohesive force, thereby inhibiting expansion, thereby improving the cycle performance of the secondary battery.

[0052] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.1 m 2 / g-2.5m 2 / g, for example, it 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, 2.2m2 / 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 second carbon-based material is 1.0m 2 / g-2.1m 2 / g, for example, it can be 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g, 2.1m 2 / g, etc., preferably 1.3m 2 / g-1.9m 2 By setting the specific surface areas of the first carbon-based material and the second carbon-based material within the above range, the consumption of active ions in SEI film formation can be reduced, which is beneficial to improving the cycle performance of the battery.

[0053] In some embodiments, the gram capacity of the first carbon-based material is less than the gram capacity of the second carbon-based material.

[0054] In some embodiments, the gram capacity of the first carbon-based material is 340 mAh / g-360 mAh / g, for example, 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 gram capacity of the second carbon-based material is 358 mAh / g-372 mAh / g, for example, 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 setting the gram capacity of the first carbon-based material and the second carbon-based material to be within the above range, the secondary battery can have a higher energy density.

[0055] In some embodiments, the artificial graphite in the secondary particles accounts for 60% or more of the first carbon-based material, for example, 62%, 65%, 68%, 70%, 72%, 74%, 76%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, etc., preferably 70%-85%. By increasing the proportion of artificial graphite in the secondary particles, the isotropy is increased, which can effectively suppress electrode expansion during cycling and improve battery cycling performance.

[0056] In some embodiments, the degree of graphitization of the first carbon-based material is less than the degree of graphitization 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%. As a result, the negative electrode material has a higher gram capacity and powder compaction density.

[0057] In some embodiments, the volume distribution particle size Dv50 of the above-mentioned first carbon-based material is smaller than the volume distribution particle size Dv50 of the above-mentioned second carbon-based material. After the first carbon-based material with small particle size and the second carbon-based material with large particle size are fully mixed, they can have a denser stacking effect, strengthen the particle bonding effect after cold pressing, and reduce the expansion of the pole piece. At the same time, the particle size of the second carbon-based material is within the above-mentioned range, which can make the specific surface area lower, thereby helping to improve the first coulombic efficiency of the battery. The volume distribution particle size Dv50 of the above-mentioned first carbon-based material is 8μm-18.0μm, for example, it can be 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, preferably 10μm-16μm. In addition, the volume particle size Dv50 of the above-mentioned second carbon-based material is 10.0μm-20.0μm, for example, it can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, preferably 12.0μm-18.0μm.

[0058] In some embodiments, the second carbon-based material includes at least one carbon-based material having an area greater than or equal to 0.25 μm 2 By making the second carbon-based material include a pore structure with the above-mentioned pore area, the pore structure can reserve sufficient and stable expansion space for the volume change of the second carbon-based material particles, reduce the risk of second carbon-based material particles breaking, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0059] 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. The inventors found in further research that when S2 / S1 is also within the above range, the secondary battery can better balance high energy density and good cycle performance.

[0060] In the present disclosure, 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. FIG1 is a schematic diagram of a cross-sectional image of a particle of the second carbon-based material 100 of the present disclosure. As shown in FIG1 , the area extending 2.5 μm from the particle surface of the second carbon-based material 100 to the interior of the particle is the outer region 101, and the area inside the outer region 101 is the inner region 102.

[0061] In the present disclosure, the pore area, S1, and S2 values ​​of the second carbon-based material can be obtained by using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL of Japan) to obtain the cross-section of the second carbon-based material; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope from ZEISS of Germany) is used to scan the cross-section of the second carbon-based material; finally, the pore area of ​​any one hole in the second carbon-based material is obtained respectively through image processing software (such as AVIZO); and the total pore area S2 of the internal area and the total pore area S1 of the external area, and thereby the value of S2 / S1 is obtained. For example, samples can be obtained from different areas of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross section. The total pore area S2' and the total pore area S1' of the inner region of each particle cross section are obtained using image processing software according to the above definition, and the S2' / S1' value of each particle cross section is obtained. The arithmetic average of the S2' / S1' of all the measured particle cross sections is calculated as the S2 / S1 value of the second carbon-based material.

[0062] 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 , can be selected to be less than or equal to 0.13μm 2In further research, the inventors also found that by controlling the area of ​​the pore structure in the outer region of the second carbon-based material within the above range, the outer region of the second carbon-based material can have a dense structure, thereby effectively improving the structural stability of the second carbon-based material and avoiding the electrolyte from penetrating into the pore structure inside the second carbon-based material particles as much as possible, thereby effectively improving the cycle performance of the secondary battery. Of course, the present disclosure does not intend to limit the area of ​​all pore structures in the outer region of the second carbon-based material to be less than or equal to 0.15 μm. 2 For example, the area of ​​the pore structure can be controlled to be less than or equal to 0.15 μm by more than 95%, or more than 99%. 2 .

[0063] In some embodiments, the inner region of the second carbon-based material includes at least one area greater than or equal to 0.25 μm 2 The inventors further discovered that by including the aforementioned pore structure in the interior of the second carbon-based material, sufficient and stable expansion space can be reserved for the volume changes of the second carbon-based material particles, reducing the occurrence of side reactions. Furthermore, the compaction density of the negative electrode film can be increased, thereby buffering the volume changes of the negative electrode film.

[0064] In some embodiments, 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 / cm 3 , optional 1.88g / cm 3 -2.00g / cm 3 Therefore, a larger powder compaction density is conducive to a higher energy density of the electrode.

[0065] In some embodiments, the tap density of the first carbon-based material is 0.8 g / cm 3 -1.1g / cm 3 , optional 0.85g / cm 3 -1.05g / cm 3 Thus, mixing with the second carbon-based material can enhance the stacking effect.

[0066] In some embodiments, the ratio [(Dv90) - (Dv10)] / (Dv50)] of the first carbon-based material is 0.8-1.5, and optionally 0.9-1.4. Thus, a narrower ratio [(Dv90) - (Dv10)] / (Dv50)] indicates that the first carbon-based material has a smaller ratio of large particles to small particles, which is beneficial to the stability of electrical properties.

[0067] In some embodiments, the amount of linseed oil adsorbed by 100g of the first carbon-based material is 50ml-70ml, optionally 55ml-65ml. Thus, by combining with the second carbon-based material, the fluidity of the slurry is improved.

[0068] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 50,000 N is 1.80 g / cm 3 -2.10g / cm 3 , optional 1.85g / cm 3 -2.08g / cm 3 Therefore, a larger powder compaction density is conducive to the electrode having a higher energy density.

[0069] In some embodiments, the tap density of the second carbon-based material is 0.95 g / cm 3 -1.30g / cc g / cm 3 , optional 1.00g / cm 3 -1.25g / cc g / cm 3 ,Thus, a higher tap density can improve the stacking ,effect of the particles.

[0070] In some embodiments, [(Dv90) - (Dv10)] / (Dv50)] of the second carbon-based material is 0.70-1.10, and optionally 0.75-1.05. This indicates that the ratio of large particles to small particles in the second carbon-based material is relatively small, ensuring the stability of electrical properties.

[0071] In some embodiments, the volume particle size Dv90 of the second carbon-based material is 13.0 μm-30.0 μm, and optionally 16.0 μm-23.0 μm. Thus, the proportion of large particles is relatively small, ensuring the stability of electrical properties.

[0072] In some embodiments, the adsorption capacity of linseed oil by 100 g of the second carbon-based material is 40 mL-60 mL, optionally 40 mL-55 mL. Therefore, the lower linseed oil adsorption capacity indicates that the second carbon-based material has better fluidity after being made into slurry.

[0073] In some embodiments, at least part of the surface of the above-mentioned second carbon-based material has a coating layer. Optionally, the above-mentioned coating layer includes carbon. Optionally, more than 80% of the surface of the above-mentioned second carbon-based material is covered with a carbon coating layer, and further, 90%-100% of the surface of the above-mentioned second carbon-based material is covered with a carbon coating layer. In some embodiments, the above-mentioned carbon in the above-mentioned coating layer includes amorphous carbon and / or crystalline carbon with a degree of graphitization between 68% and 90%. Thus, by having a coating layer on at least part of the surface of the second carbon-based material, the dynamic performance of the secondary battery can be further improved.

[0074] In some embodiments, the second carbon-based material includes primary particles. Optionally, the number 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 making the second carbon-based material contain primary particles in the above ratio, it can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0075] In some embodiments, the content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%, optionally 40wt%-60wt%; by making the content of the second carbon-based material within the above range, the secondary battery can obtain excellent cycle performance.

[0076] 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 5wt%, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, etc., preferably 10wt% to 30wt%. This can improve the kinetic performance and energy density of the secondary battery while also ensuring good cycle performance.

[0077] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. For 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.

[0078] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present disclosure does not particularly limit the type of the negative electrode binder. For example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0079] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0080] 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 polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0081] The negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, thickness, etc.) given in this disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of this disclosure and are considered to fall within the scope of protection of this disclosure.

[0082] In the present disclosure, 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 further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0083] In the present disclosure, the Occhio roughness of a material (such as a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be tested using methods known in the art, for example, it can be obtained by measuring and calculating using Occhio Callisto 3D software. An exemplary test method is as follows: After dispersing the graphite particles to be tested, photographing them using Occhio Callisto 3D software obtains a high-contrast, high-definition picture to delineate the specific morphology and boundaries of the graphite particles, determining the particle projection area, and defining a smooth reference by examining the maximum inscribed circle of the original contour pixel contained in the contour of the corresponding pixel. Wherein, an inscribed circle with a radius of 80% of the smooth reference radius is continuously inscribed within the particle projection area, and the total area of ​​the inscribed circle is defined as 80% of the 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 measured particle is to smoothness. Taking 80% of the maximum inscribed circle radius as the reference radius can better define and quantify the final Occhio roughness value. The Occhio roughness disclosed in the present invention refers to 1-(the ratio of an 80% smooth reference to the projected area of ​​the particle), which can indicate the sphericity parameter (surface roughness) of the particle material. The larger the Occhio roughness value, the higher the surface roughness of the material.

[0084] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, a negative electrode film layer, etc.) has a meaning well known in the art and can be tested using methods known in the art. An exemplary test method is as follows: the sample powder is mixed evenly with the conductive agent carbon black (Super P), the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is applied to the surface of the negative electrode current collector copper foil, dried in an oven and set aside; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to a concentration of 1 mol / L The electrolyte was then added. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. The cells were assembled into CR2430 button cells in an argon-protected glove box with the electrolyte. After standing for 12 hours, the cells were discharged at 0.05C to 0.005V at 25°C. The cells were then allowed to stand for 10 minutes, and then discharged again at 50μA to 0.005V. The cells were allowed to stand for 10 minutes, and then discharged again at 10μA to 0.005V. The cells were then charged at 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0085] In the present disclosure, the specific surface area of ​​a material (e.g., a first carbon-based material, a second carbon-based material) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.

[0086] In the present disclosure, the volume distribution particle size D10, Dv50, and Dv90 of the material (e.g., the first carbon-based material, the second carbon-based material, etc.) are well-known in the art, and respectively represent the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer with reference to GB / T19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0087] In the present disclosure, the degree of graphitization of a material (e.g., the first carbon-based material, the second carbon-based material, etc.) is a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) plane in the crystal structure of the material. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0088] In the present disclosure, the powder compaction density of a material (e.g., the first carbon-based material, the second carbon-based material) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured by an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine) with reference to GB / T24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and added to a bottom area of ​​1.327 cm 2 In the mold, pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the powder compaction density of the material under 50000N pressure.

[0089] In the present disclosure, the tap density of a material (such as a first carbon-based material and a second carbon-based material) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, GB / T 5162-2006 can be referred to and a powder tap density tester can be used for measurement. The test instrument can be Dandong Baxter BT-301, and the test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration number 5000 times, and graduated cylinder 25 mL.

[0090] In the present disclosure, the oil absorption value of a material (eg, the first carbon-based material, the second carbon-based material) has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, referring to GB / T 3780.2-2017, 20g of the dried test sample is weighed and placed in the mixing chamber of the oil absorptometer at a temperature of 23°C with the lid closed; the oil delivery pipe of the constant-rate burette is aligned with the hole above the mixing chamber cover; the oil absorptometer is started, the instrument starts running and linseed oil is added dropwise. As the amount of oil absorbed by the sample increases, the mixed material changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continues to increase. The viscosity is transmitted to the torque sensor system of the oil absorptometer. When the added oil causes the semi-plastic agglomerate to reach a preset torque level, the oil absorptometer and the constant-rate burette are automatically closed; the value corresponding to 70% of the maximum torque of the fitting curve is read, and the adsorption amount A of linseed oil by 100g of carbon material is calculated using the formula A=(V / m)×100, where 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.

[0091] In this disclosure, primary particles and secondary particles have meanings well known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to agglomerated 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.

[0092] In the present disclosure, the quantitative ratio of secondary particles of artificial graphite in the first carbon-based material refers to: randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the ratio of the number of secondary particles of artificial graphite in each image to the total number of particles of the first carbon-based material. The average value of the multiple statistical results is the quantitative ratio of secondary particles of artificial graphite in the first carbon-based material.

[0093] In the present disclosure, the quantitative proportion of primary particles in the second carbon-based material refers to: randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the percentage of the number of second carbon-based materials with primary particle morphology in each image to the total number of particles of the second carbon-based material. The average value of the multiple statistical results is the quantitative proportion of primary particles in the second carbon-based material.

[0094] It should be noted that the various parameter tests on the negative electrode active material or the negative electrode film layer can be performed by sampling and testing the prepared secondary battery according to the following steps.

[0095] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged). Disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2-10 hours). Then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours). After drying, remove the negative electrode. Samples can now be taken from the dried negative electrode to test the aforementioned parameters related to the negative electrode film, such as the density, gram capacity, and specific surface area of ​​the negative electrode film.

[0096] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2 hours), and a sample of the negative electrode active material is taken from any area of ​​the baked negative electrode sheet (a blade can be used for scraping powder sampling); the collected negative electrode active material is sieved (for example, sieved with 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.

[0097] The first carbon-based material and the second carbon-based material can be distinguished by scanning electron microscopy (SEM) or ion polishing cross-section (CP) images. The first carbon-based material and the second carbon-based material can be distinguished from the images. Figure 2 is an SEM image of the first carbon-based material of the present disclosure. It can be seen from the figure that the first carbon-based material has a secondary particle morphology. Figure 3 is an ion polishing cross-section (CP) image of the second carbon-based material of the present disclosure. It can be seen from the figure that the outer region of the second carbon-based material has a dense structure, and the inner region has a relatively large porous structure.

[0098] In the present disclosure, the first carbon-based material mentioned above can be obtained commercially.

[0099] In some embodiments, the preparation method of the above-mentioned second carbon-based material includes: step 1, providing a raw material with a plurality of pore structures; step 2, mixing the above-mentioned raw material and the filling material uniformly in a predetermined proportion, and then keeping it warm at a first temperature T1 for a first time t1, and cooling to room temperature after the end to obtain an intermediate; step 3, keeping the obtained intermediate warm at a second temperature T2 for a second time t2, and obtaining the second carbon-based material after the end.

[0100] In some embodiments, in step 1, the raw material for preparing the second carbon-based material includes natural graphite. Natural graphite generally refers to graphite naturally formed in nature, which does not require graphitization, and the interior of natural graphite particles generally has a relatively large number of closed-pore structures. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more optionally includes natural spherical graphite.

[0101] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with a desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes crushing, classification, spheroidization, purification, and other processes.

[0102] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 10.5.0 μm-19.5 μm.

[0103] In some embodiments, in step 1, the specific surface area of ​​the raw material may be greater than or equal to 2.5m 2 / g, optional 2.5m 2 / g-10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to carry out subsequent filling processing and obtain the second carbon-based material with the required specific surface area, and it is also beneficial for the second carbon-based material to have both high capacity and high first coulombic efficiency. In addition, it is also beneficial for the second carbon-based material to have better kinetic properties.

[0104] In some embodiments, in step 2, the softening point temperature of the filling material is 100° C.-150° C. Optionally, the softening point temperature of the filling material is 100° C.-146° C., 100° C.-142° C., 100° C.-138° C., 100° C.-134° C., 100° C.-130° C., 104° C.-146° C., 104° C.-142° C., 104° C.-138° C., 104° C.-134° C., 104° C.-130° C.

[0105] 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 from 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, and 3 μm-5 μm. This facilitates the filler material to melt upon heating and fill into the pore structure of the raw material, and also helps improve the uniformity of the dispersion of the filler material and the raw material.

[0106] In some embodiments, in step 2, the coking value of the filler material is 15%-40%, and optionally 18%-34%. In this disclosure, the coking value of the filler material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured in accordance with GB / T 8727-2008.

[0107] In some embodiments, in step 2, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and may optionally include one or more of coal tar and petroleum asphalt.

[0108] In some embodiments, in step 2, the mass ratio of the above-mentioned filling material to the above-mentioned raw material is (11-34):100, and can be optionally (12-33):100, (12-30):100, (12-28):100, (14-25):100.

[0109] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filling material within the above-mentioned range, it is beneficial to adjust the number of pores and / or pore size in the outer and inner areas of the first carbon-based material within a suitable range, which is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0110] By adjusting the type, softening point, coking value, addition amount and other parameters of the filling material within the above range, the viscosity of the filling material is not high after being heated and melted, and it maintains good fluidity. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process. This can also reduce the problems of increased surface defects of the first carbon-based material particles and increased surface active sites due to the need to add a depolymerization process.

[0111] In some embodiments, in step 2, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 may be a staged heating process.

[0112] In some embodiments, the staged temperature increasing process includes a first temperature increasing process, a second temperature increasing process, and a third temperature increasing process.

[0113] In some embodiments, the first temperature raising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 0.5 h-3 h.

[0114] In some embodiments, the second heating process is to heat the material to 450°C-550°C and hold the temperature at that temperature for 0-2 hours. When the holding time is 0 hours, it means that when the temperature is within the range of 450°C-550°C, no holding treatment is performed, but the temperature is continued to the first temperature T1.

[0115] In some embodiments, the third temperature increasing process is to increase the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0116] In the staged heating process, the temperature is first raised to 200°C. Since the heating temperature is higher than the softening point of the filling material, the filling material is melted and softened by the heat. Keeping it warm for 1 hour allows it to flow and fill into the pore structure of the raw material; then the temperature is raised to 500°C. At this time, the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state and turning into a viscous liquid or solid, thereby preventing the filling material from entering the entire pore structure of the raw material; finally, the temperature is raised to the first temperature. At this time, the filling material undergoes a carbonization reaction, thereby enabling the pore structure occupied by the filling material to be effectively filled.

[0117] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min-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 thereof. Alternatively, the heating rate is 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, 2°C / min-6°C / min, or 2°C / min-5°C / min.

[0118] In some embodiments, the heating rate of the first heating process may be 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, 2°C / min-6°C / min, or 2°C / min-5°C / min. In some embodiments, the heating rate of the second heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min. In some embodiments, the heating rate of the third heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min.

[0119] In some embodiments, in step 2, the first temperature T1 is 1100° C.-1400° C. For example, the first temperature T1 can be 1100° C., 1150° C., 1200° C., 1250° C., 1300° C., 1350° C., 1400° C., or any range thereof. Alternatively, the first temperature T1 is 1100° C.-1400° C., 1100° C.-1350° C., 1100° C.-1350° C., 1100° C.-1300° C., 1100° C.-1250° C., or 1100° C.-1200° C.

[0120] In some embodiments, in step 2, the first time t1 is 1 hour to 5 hours. For example, the first time t1 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range thereof. Alternatively, the first time t1 is 2 hours to 4 hours.

[0121] In some embodiments, in step 2, the heat treatment can be carried out in a device capable of programmed temperature increase, such as a medium frequency furnace, a roller kiln, a rotary kiln, a push plate kiln, a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor or a drum furnace.

[0122] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere, which may include one or more of nitrogen, argon, and helium.

[0123] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above-mentioned range, it is beneficial to adjust the number of pores and / or the pore size in the outer area and the inner area of ​​the second carbon-based material within a suitable range, and thus it is beneficial to adjust the S2 / S1 of the second carbon-based material within a suitable range.

[0124] In some embodiments, in step 3, the second temperature T2 is 1600° C.-3000° C. Optionally, the second temperature T2 is 1600° C.-2800° C., 1650° C.-2750° C., 1650° C.-2700° C., 1700° C.-2650° C., 1750° C.-2600° C., 1850° C.-2550° C., 1950° C.-2550° C., or 1950° C.-2500° C.

[0125] In some embodiments, in step 3, the second time t2 is 1.5 hours to 6 hours. For example, the second time t1 can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range thereof. Alternatively, the second time t2 is 2 hours to 5 hours.

[0126] In some embodiments, in step 3, the heat treatment may be performed in a medium frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace, or an internal string graphitization furnace.

[0127] 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.

[0128] In step 3, by adjusting one or more of the second temperature and the second time within the above-mentioned range, it is beneficial to adjust the content of disordered carbon in the second carbon-based material within a suitable range, which is beneficial for the second carbon-based material to have a suitable degree of graphitization, interlayer spacing, etc.

[0129] In the preparation method of the above-mentioned second carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above-mentioned range, it is beneficial to adjust the S2 / S1, graphitization degree, gram capacity, particle size, specific surface area, Ochio roughness and other parameters of the second carbon-based material.

[0130] [Positive electrode]

[0131] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0132] The positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0133] The above-mentioned positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The above-mentioned positive electrode film layer is generally formed by coating the positive electrode slurry on the above-mentioned positive electrode current collector, drying and cold pressing. The above-mentioned positive electrode slurry is generally formed by dispersing the positive electrode active material, the optional conductive agent, the optional binder and any other components in a solvent and stirring them evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0134] The above-mentioned positive electrode active material can adopt the positive electrode active material for secondary batteries well-known in the art.

[0135] When the secondary battery of the present disclosure is a lithium-ion battery, the above-mentioned positive electrode active material can 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 can 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 can 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.

[0136] 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 can 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.

[0137] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery can 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.

[0138] In the present disclosure, the modified compound of each positive electrode active material may be a compound obtained by doping and / or surface coating the positive electrode active material.

[0139] [Electrolytes]

[0140] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0141] The types of the above electrolyte salts are not particularly limited and can be selected according to actual needs.

[0142] When the secondary battery of the present disclosure is a lithium ion battery, as an example, the above-mentioned electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0143] The types of the above-mentioned solvents are not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the above-mentioned solvents may include 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), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

[0144] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain properties 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.

[0145] [Isolation film]

[0146] The present disclosure has no particular limitation on the type of the above-mentioned isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0147] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0148] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process or a lamination process.

[0149] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0150] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0151] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG4 shows a secondary battery 5 with a square structure as an example.

[0152] In some embodiments, as shown in FIG5 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the above-mentioned opening to close the above-mentioned receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the above-mentioned receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0153] The preparation method of the secondary battery disclosed herein is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped to obtain the secondary battery.

[0154] In some embodiments of the present disclosure, the secondary batteries according to the present disclosure may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0155] Figure 6 is a schematic diagram of an exemplary battery module 4. As shown in Figure 6 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0156] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0157] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0158] Figures 7 and 8 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0159] The present disclosure also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack of the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0160] The above-mentioned electrical devices can select secondary batteries, battery modules or battery packs according to their usage requirements.

[0161] Figure 9 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0162] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0163] Example

[0164] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0165] Preparation of the first carbon-based material

[0166] Materials 1-1

[0167] The needle coke raw material was coarsely crushed, pulverized, and shaped, with the main frequency of the crusher and shaper being 55 Hz, to obtain an intermediate 1 with a particle size of 10 μm. Intermediate 1 was then mixed with pitch (softening point 250°C) in a ratio of 100:15 and granulated in a heating device to obtain an intermediate 2 with a particle size of 15 μm. Intermediate 2 was placed in a graphitization furnace and subjected to a graphitization heat treatment at 3000°C. After completion, it was demagnetized and sieved to obtain secondary particles of artificial graphite.

[0168] The properties of the obtained artificial graphite of secondary particles are as follows: volume distribution particle size Dv50=15.0 μm, Ochio roughness=0.30, and graphitization degree 94%.

[0169] Materials 1-2 to 1-5

[0170] 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.

[0171] Table 1

[0172] Preparation of the second carbon-based material

[0173] Materials 2-1

[0174] The flake graphite is mechanically crushed and spheroidized, wherein the number of shaping machines in the spheroidization process is 20, and the particle size after spheroidization is 18μm. After purification, natural spherical graphite is obtained. The obtained natural spherical graphite is mixed with filler petroleum asphalt (softening point is 110℃) in a ratio of 100:22. The mixed material is then placed in a continuous heating device, heated to 200℃ and kept warm for 1h, then continuously heated to 700℃ and kept warm for 1h. After the end, it is cooled to room temperature to obtain an intermediate. The obtained intermediate is placed in a graphitization furnace and subjected to graphitization heat treatment at 2500℃. After the end, it is demagnetized and sieved to obtain the second carbon-based material.

[0175] The properties of the obtained second carbon-based material are as follows: S2 / S1=15, volume distribution particle size Dv50=18.0 μm, Ochio roughness=0.10, and graphitization degree 96%.

[0176] The S2 / S1 of the second carbon-based material is obtained by testing using the following method.

[0177] Mix the sample preparation binder and the second carbon-based material powder evenly, then apply the mixture to a copper foil and dry at 60°C for 30 minutes. Cut five test samples, each measuring 6 mm x 6 mm, at five different locations and attach them to the sample stage of a CP-type argon ion cross-section polisher. Use a plasma beam to cut the samples to obtain a cross section. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from JEOL, Japan.

[0178] Each cross-section of the second carbon-based material sample was scanned using a scanning electron microscope, and a scanned image was obtained from an arbitrarily selected region within each cross-section of the sample. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from ZEISS, Germany.

[0179] Randomly select cross sections of 20 particles of the second carbon-based material from the scanned image. The area formed by extending 0.25 μm from the particle surface of the second carbon-based material to the interior of the particle is recorded as the external area, and the area inside the external area is recorded as the internal area. Use image processing software to obtain the total pore area S1' of the external area of ​​each particle cross section and the pore area S2' of the internal area of ​​the second carbon-based material, and calculate the value of S2' / S1'; and calculate the arithmetic average of S2' / S1' of all 20 particles as the value of S2 / S1 of the second carbon-based material. The image processing software can be AVIZO.

[0180] Materials 2-2 to 2-5

[0181] The preparation methods of materials 2-2 to 2-5 are similar to those of material 2-1, except that the number of shaping machines connected during spheroidization is adjusted to obtain materials 2-2 to 2-5.

[0182] Table 2

[0183] Ingredients 3:

[0184] The needle coke raw material is coarsely crushed, broken, and shaped to obtain an intermediate 1 with a particle size of 15 μm. The intermediate 1 is placed in a graphitization furnace and subjected to graphitization heat treatment at 3000° C. After completion, it is demagnetized and sieved to obtain primary particles of artificial graphite.

[0185] The properties of the obtained primary particles of artificial graphite are as follows: volume distribution particle size Dv50=15.0 μm, and degree of graphitization 94.2%.

[0186] Example 1

[0187] Preparation of secondary batteries

[0188] The negative electrode active material (Material 1-1 and Material 2-1 were mixed in a 1:1 weight ratio), conductive carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber (SBR) were thoroughly stirred in an appropriate amount of deionized water to form a negative electrode slurry. The negative electrode slurry was applied to both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained.

[0189] Lithium iron phosphate was mixed with carbon black (Super P), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a weight ratio of 96:2:2. An appropriate amount of NMP solvent was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was then coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained.

[0190] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0191] A polyethylene film is used as an isolation film and is placed in order with the positive electrode sheet and the negative electrode sheet prepared above, so that the isolation film is located between the positive electrode sheet and the negative electrode sheet to play an isolation role. The electrode assembly is then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0192] Comparative Example 1

[0193] 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.

[0194] Performance Testing

[0195] (1) Pole expansion rate

[0196] Samples of the negative electrode sheets prepared in the above examples and comparative examples were taken and the thickness of the negative electrode membrane was measured along the cut surface using a micrometer. This was recorded as the initial thickness of the negative electrode membrane. The secondary batteries prepared in the above examples and comparative examples were charged to 3.65V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage, and then disassembled. The thickness of the negative electrode membrane was again measured and recorded as the full-charge thickness of the negative electrode membrane. The full-charge expansion ratio of the negative electrode membrane = (full-charge thickness of the negative electrode membrane - initial thickness of the negative electrode membrane) / cold-pressed thickness of the negative electrode membrane × 100%.

[0197] (2) Cycle performance test of secondary batteries

[0198] 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 standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.5V (corresponding to 0% SOC). The discharge capacity at this point was recorded as the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0199] Capacity retention rate (%) of the secondary battery after 1000 cycles at 45° C. = discharge capacity after 1000 cycles / discharge capacity at the first cycle×100%.

[0200] Table 3

[0201] As shown in Table 1, the present disclosure achieves excellent cycling performance by including both a first carbon-based material (artificial graphite secondary particles) and a second carbon-based material in the negative electrode active material layer. This results in a low electrode expansion rate and excellent cycling performance for the secondary battery. In contrast, in Comparative Example 1, where artificial graphite primary particles are combined with a second carbon-based material, the high anisotropy of the primary particles leads to significant electrode expansion. This can cause SEI fragmentation and the formation of fresh interfaces during cycling, resulting in poor cycling performance.

[0202] Examples 2-5

[0203] The type of the first carbon-based material was changed as shown in Table 4. Otherwise, a secondary battery was prepared according to the same preparation method as in Example 1. Specific parameters and test results are shown in Table 4.

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

[0205] Table 4

[0206] From the results in Table 4, it can be seen that the cycle performance can be further improved by making the Occhio roughness of the second carbon-based material smaller than that of the first carbon-based material and the Occhio roughness of the first carbon-based material greater than or equal to 0.20.

[0207] Examples 6-9

[0208] As shown in Table 5, except for changing the type of the second carbon-based material, a secondary battery was prepared according to the same preparation method as in Example 1. Specific parameters and test results are shown in Table 5.

[0209] It should be noted that, for the sake of comparison, the results of Example 1 are also shown in Table 5.

[0210] Table 5

[0211] The results in Table 5 show that, compared with Examples 1 and 6-8, Example 9 can further improve the cycle performance by making the Occhio roughness of the second carbon-based material smaller than that of the first carbon-based material. Furthermore, making the Occhio roughness of the second carbon-based material less than or equal to 0.28 is conducive to improving the cycle performance.

[0212] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising 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 secondary particles of artificial graphite; The second carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm from the particle surface of the second carbon-based material to the inside of the particle, and in the cross-sectional view of the second carbon-based material, the total pore area of ​​the external region is denoted as S1, the total pore area of ​​the internal region is denoted as S2, and S2>S1.

2. The secondary battery according to claim 1, wherein The Occhio roughness of the second carbon-based material is smaller than the Occhio roughness of the first carbon-based material.

3. The secondary battery according to claim 1 or 2, wherein: The Ochio roughness of the first carbon-based material is greater than or equal to 0.20, and can be optionally 0.25-0.4; and / or, The Ochio roughness of the second carbon-based material is less than or equal to 0.28, and can be optionally 0.08-0.

25.

4. The secondary battery according to any one of claims 1 to 3, wherein The specific surface area of ​​the first carbon-based material is 1.1 m 2 / g-2.5m 2 / g, optional 1.2m 2 / g-2.0m 2 / g; and / or, the specific surface area of ​​the second carbon-based material is 1.0m 2 / g-2.1m 2 / g, optional 1.3m 2 / g-1.9m 2 / g.

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

6. The secondary battery according to any one of claims 1 to 5, wherein The gram capacity of the first carbon-based material is 340 mAh / g-360 mAh / g, and can be 345 mAh / g-358 mAh / g; and / or, The gram capacity of the second carbon-based material is 358 mAh / g-372 mAh / g, and can be optionally 365 mAh / g-370 mAh / g.

7. The secondary battery according to any one of claims 1 to 6, wherein The amount of the artificial graphite of the secondary particles in the first carbon-based material accounts for greater than or equal to 60%, and can be optionally 70%-85%.

8. The secondary battery according to any one of claims 1 to 7, wherein The graphitization degree of the first carbon-based material is lower than the graphitization degree of the second carbon-based material.

9. The secondary battery according to any one of claims 1 to 8, wherein The graphitization degree of the first carbon-based material is 90.0%-95.0%, and optionally 92.0%-94.0%; and / or, The graphitization degree of the second carbon-based material is 95.0%-98.0%, and can be optionally 95.5%-97.5%.

10. The secondary battery according to any one of claims 1 to 9, wherein The volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material.

11. The secondary battery according to any one of claims 1 to 10, wherein The volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-18.0 μm, and can be 10.0 μm-16.0 μm; and / or, The volume particle size Dv50 of the second carbon-based material is 10.0 μm-20.0 μm, and can be optionally 12.0 μm-18.0 μm.

12. The secondary battery according to any one of claims 1 to 11, 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 μm 2 , can be selected to be less than or equal to 0.13μm 2 and / or, The inner region of the second carbon-based material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 The pore structure.

13. The secondary battery according to any one of claims 1 to 12, wherein 1.5≤S2 / S1≤500, optionally, 2≤S2 / S1≤450.

14. The secondary battery according to any one of claims 1 to 13, wherein The second carbon-based material includes primary particles; optionally, the primary particles account for greater than or equal to 80% of the second carbon-based material.

15. The secondary battery according to any one of claims 1 to 14, 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 50,000 N is greater than or equal to 1.85 g / cm 3 , optional 1.88g / cm 3 -2.00g / cm 3 ; (2) The tap density of the first carbon-based material is 0.8 g / cm 3 -1.1g / cm 3 , optional 0.85g / cm 3 -1.05g / cm 3 ; (3) [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is 0.8-1.5, and can be 0.9-1.4; (4) The adsorption amount of linseed oil by 100g of the first carbon-based material is 50ml-70ml, and can be optionally 55ml-65ml.

16. The secondary battery according to any one of claims 1 to 15, 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 50000N is 1.80g / cm 3 -2.10g / cm 3 , optional 1.85g / cm 3 -2.08g / cm 3 ; (2) The tap density of the second carbon-based material is 0.95 g / cm 3 -1.30g / cm 3 , optional 1.00g / cm 3 -1.25g / cm 3 ; (3) [(Dv90)-(Dv10)] / (Dv50)] of the second carbon-based material is 0.70-1.10, and can be 0.75-1.05; (4) The volume particle size Dv90 of the second carbon-based material is 13.0 μm-30.0 μm, and can be optionally 16.0 μm-25.0 μm; (5) The adsorption amount of linseed oil by 100g of the second carbon-based material is 40mL-60mL, and can be optionally 40mL-55mL.

17. The secondary battery according to any one of claims 1 to 16, wherein The mass content of the second carbon-based material in the negative electrode active material is 20wt%-80wt%, and can be optionally 40wt%-60wt%.

18. The secondary battery according to any one of claims 1 to 17, wherein The negative electrode active material further comprises a silicon-based material; optionally, in the negative electrode active material, the content of the silicon-based material is greater than or equal to 5wt%, and more optionally 10wt% to 30wt%.

19. An electrical device comprising the secondary battery according to any one of claims 1 to 18.

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