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, wherein the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite the first surface; the thickness of the negative electrode film layer is denoted as H; a region within a thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as a first region of the negative electrode film layer, and a region within a thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as a second region of the negative electrode film layer; the first region comprises a first active material, and the second region comprises a second active material; the first active material comprises a first carbon-based material, and the second active material comprises a second carbon-based material; the first carbon-based material comprises an external region and an internal region located on an inner side of the external region, and the external region is a region extending a distance of 2.5 μm from the surface to the interior of particles of the first carbon-based material; in the cross-sectional view of the first 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 is greater than S1; and the second carbon-based material includes an amorphous carbon material.

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 202311641361.X, 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, military equipment, aerospace, and other fields. As the application range of secondary batteries becomes wider and wider, people are also placing higher demands on their performance.

[0005] Therefore, how to make secondary batteries have high energy density while having excellent cycle performance and kinetic performance 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 its object is to provide a secondary battery and an electric device, wherein the secondary battery has high energy density while achieving excellent cycle performance and dynamic performance.

[0008] A first aspect of the present disclosure provides 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, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within a thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, the area within a thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, the first area includes The first active material includes a first carbon-based material, the second active material includes a second carbon-based material, the first 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 first carbon-based material to the interior of the particle, in the cross-sectional view of the first 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, and the second carbon-based material includes an amorphous carbon material.

[0009] By including the first carbon-based material in the first region of the negative electrode film layer and the amorphous carbon material in the second region of the negative electrode film layer, the synergistic effect between the first carbon-based material and the second carbon-based material can be fully utilized. As a result, the negative electrode sheet provided by the present disclosure can have a good pore structure, high compaction density, and low volume change, enabling the secondary battery to achieve both good dynamic performance and cycle performance while maintaining high energy density.

[0010] In some embodiments, the first carbon-based material satisfies: I 3R(101) / I 2H(004) ≤0.1, optionally, 0.008≤I 3R(101) / I 2H(004) ≤0.065; I 3R(101) is the diffraction peak intensity of the 101 crystal plane of the 3R phase of the first carbon-based material in the X-ray diffraction pattern, I 2H(004) The X-ray diffraction spectrum shows the diffraction peak intensity of the 004 crystal plane of the 2H phase of the first carbon-based material. Thus, the carbon-based material particles have high surface stability, which can effectively reduce surface side reactions and active ion consumption, thereby achieving better cycle performance for the secondary battery.

[0011] In some embodiments, the second carbon-based material has a lower true density than the first carbon-based material. This facilitates a suitable pore distribution between the first and second regions of the negative electrode film layer, thereby improving the negative electrode film layer's ability to wet and retain the electrolyte, thereby improving the kinetic performance and / or cycle performance of the secondary battery.

[0012] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 20,000 N is less than the powder compaction density of the first carbon-based material under a pressure of 20,000 N. By adjusting the powder compaction density of the second carbon-based material to be less than the compaction density of the first carbon-based material, on the one hand, it is beneficial to improve the energy density of the secondary battery, and on the other hand, it is beneficial to have a suitable pore distribution in the first region and the second region of the negative electrode film layer, thereby improving the wetting and retention characteristics of the negative electrode film layer for the electrolyte, thereby improving the dynamic performance and / or cycle performance of the secondary battery.

[0013] In some embodiments, the first carbon-based material and / or the second carbon-based material comprises at least one carbon-based material having an area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 By making the first carbon-based material and / or 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 particle volume changes, reduce the risk of particle breakage, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0014] In some embodiments, 2.1≤S2 / S1≤478.9, and optionally, 2.5≤S2 / S1≤418.6. Thus, the secondary battery can better achieve both high energy density and good cycle performance.

[0015] In some embodiments, at least a portion of the surface of the first carbon-based material has a coating layer. Optionally, the coating layer comprises a carbon coating layer. This is beneficial for improving the dynamic performance of the secondary battery.

[0016] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 The first carbon-based material has a larger true density, which is beneficial to improving the energy density of secondary batteries.

[0017] In some embodiments, the first carbon-based material has a powder compaction density of 1.65 g / cm3 under a pressure of 20,000 N. 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3By making the first carbon-based material have a larger powder compaction density, the compaction density of the negative electrode film layer can be increased, thereby improving the energy density of the secondary battery. It is also conducive to forming a reasonable pore structure between the negative electrode film layers, improving the active ion and electron transport performance, and improving the negative electrode film layer's electrolyte infiltration and retention characteristics, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0018] In some embodiments of the present disclosure, the specific surface area of ​​the first carbon-based material is ≤2.8m 2 / g, optional 1.1m 2 / g-2.7m 2 When the specific surface area of ​​the first carbon-based material is within the above range, it is beneficial to reduce the occurrence of side reactions and reduce the consumption of active ions by SEI film formation, thereby enabling the secondary battery to have both high initial coulombic efficiency and good cycle performance.

[0019] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, optionally 10.0 μm-22.0 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, optionally 16.5 μm-42.0 μm.

[0020] By ensuring that the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above-mentioned range, it is beneficial to improve the transmission performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0021] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, and can be optionally 0.90-1.40. By ensuring that the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is within the above range, its particle packing performance is better, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also conducive to adjusting the pore distribution of the negative electrode film layer, improving the active ion and electron transport performance, and improving the electrolyte infiltration and retention characteristics of the negative electrode film layer, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0022] In some embodiments, the gram capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and can be 355 mAh / g-370 mAh / g. When the gram capacity of the first carbon-based material is within the above range, it is beneficial to improve the energy density of the secondary battery.

[0023] In some embodiments, the second carbon-based material is at least one of soft carbon and hard carbon.

[0024] In some embodiments, the true density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 By making the second carbon-based material have a smaller true density, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, thereby improving the kinetic performance of the secondary battery.

[0025] In some embodiments, the second carbon-based material has a powder compaction density of 0.85 g / cm2 under a pressure of 20,000 N. 3 -1.35g / cm 3 , optional 0.90g / cm 3 -1.30g / cm 3 By making the second carbon-based material have a smaller powder compaction density, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, thereby improving the dynamic performance of the secondary battery.

[0026] In some embodiments, the specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 / g; when the specific surface area of ​​the second carbon-based material is within the above range, the higher the reaction activity, the better the power performance of the secondary battery.

[0027] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, and can be optionally 5.0 μm-15.0 μm; by making the volume distribution particle size Dv50 of the second carbon-based material within the above range, the specific surface area of ​​the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the cycle performance of the secondary battery can be improved. In addition, it is also beneficial to improve the transmission performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery.

[0028] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and can be optionally 1.1-1.75. When the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is within the above range, its particle packing performance is better, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also conducive to the negative electrode film layer having a suitable pore distribution, thereby improving the dynamic performance of the secondary battery.

[0029] In some embodiments, the tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 By ensuring that the tap density of the second carbon-based material is within the above range, a reasonable pore structure can be formed between the particles of the negative electrode film layer, the active ion and electron transport performance can be improved, and the infiltration and retention characteristics of the negative electrode film layer for the electrolyte can be improved, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0030] In some embodiments, the gram capacity of the second carbon-based material is 330 mAh / g-480 mAh / g, optionally 340 mAh / g-470 mAh / g. By adjusting the gram capacity of the second carbon-based material within the above range, the energy density of the secondary battery can be increased.

[0031] In some embodiments, the first carbon-based material and / or the second carbon-based material include primary particles. Optionally, the primary particles in the first carbon-based material account for greater than or equal to 80%, and the primary particles in the second carbon-based material account for greater than or equal to 80%. By ensuring that the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, the material can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery. In addition, the compaction density of the negative electrode film layer can be increased, thereby improving the energy density of the secondary battery.

[0032] In some embodiments, the first carbon-based material accounts for greater than or equal to 80% by mass, and optionally ranges from 90% to 98.5% in the first region; and / or the second carbon-based material accounts for greater than or equal to 80% by mass, and optionally ranges from 90% to 98.5% in the second region. By ensuring that the contents of the first carbon-based material and the second carbon-based material are within the aforementioned ranges, the secondary battery exhibits both high energy density and good kinetic and cycling performance.

[0033] In some embodiments, the first region and / or the second region further include silicon-based materials. The higher lithium insertion potential of silicon-based materials is beneficial to improving the kinetic performance of secondary batteries; at the same time, it can also improve the capacity of the negative electrode, thereby further improving the energy density of the secondary battery. In some embodiments, both the first region and the second region include silicon-based materials, and the mass proportion of the silicon-based material in the first region is less than or equal to the mass proportion of the silicon-based material in the second region. This is beneficial to improving the wetting characteristics of the negative electrode film layer to the electrolyte, improving the transport performance of active ions, and improving the cycle performance and / or kinetic performance of the secondary battery.

[0034] In some embodiments, an intermediate region between the first region and the second region includes the first active material and / or the second active material.

[0035] In some embodiments, the compaction density of the negative electrode film layer is 1.20 g / cm 3 -1.70g / cm 3 , optional 1.25g / cm 3 -1.65g / cm 3 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0036] In some embodiments, the surface density of the negative electrode film layer is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0037] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, optionally 45 μm-100 μm.

[0038] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0039] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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.

[0041] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present disclosure.

[0042] FIG2 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0043] FIG3 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0044] FIG. 4 is a scanning electron microscope (SEM) image of an embodiment of a negative electrode sheet of the present disclosure.

[0045] FIG5 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material of the present disclosure.

[0046] FIG. 6 is a schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0047] FIG. 7 is an exploded schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0048] FIG8 is a schematic diagram of an embodiment of a battery module according to the present disclosure.

[0049] FIG. 9 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0050] FIG. 10 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 9 .

[0051] FIG. 11 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present disclosure as a power source.

[0052] 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, 10 negative electrode sheet, 101 negative electrode current collector, 102 negative electrode film layer, 102a first surface, 102b second surface, 1021 first region, 1022 second region, 1023 intermediate region, 200 first carbon-based material, 201 outer region, 202 inner region. DETAILED DESCRIPTION

[0053] 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.

[0054] " 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 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0057] 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.

[0058] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0059] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0060] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0061] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0062] The inventors have discovered that the key to improving the kinetic performance of secondary batteries, especially their fast charging performance, lies in improving the kinetic performance of the negative electrode. Currently, most approaches to improving the kinetic performance of the negative electrode are by reducing the surface density of the negative electrode film or reducing the compaction density of the negative electrode film. However, numerous studies have shown that these methods of improving the kinetics of the negative electrode only improve the kinetic performance of the battery in the early stages of charging to a certain extent, and have no significant effect on improving the kinetic performance of the battery in the final stages of charging. This results in the secondary battery's kinetic performance failing to be effectively improved, and even makes it impossible to actually charge the secondary battery at a high rate. In addition, the energy density of the secondary battery will also be significantly reduced.

[0063] When the energy density of a secondary battery is increased by, for example, increasing the compaction density of the negative electrode film layer, the kinetic performance and cycle performance of the secondary battery are often deteriorated.

[0064] Therefore, it is difficult for current secondary batteries to achieve both high energy density and good cycle performance and kinetic performance.

[0065] In view of the above circumstances, a first aspect of the present disclosure provides a secondary battery.

[0066] 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.

[0067] [Negative electrode]

[0068] Figures 1 to 3 are schematic diagrams of an embodiment of the negative electrode sheet of the present disclosure. As shown in Figures 1 to 3, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b disposed opposite the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H. The area within the thickness range of 0.3H from the second surface 102b of the negative electrode film layer is denoted as the first region 1021 of the negative electrode film layer. The area within the thickness range of 0.3H from the first surface 102a of the negative electrode film layer is denoted as the second region 1022 of the negative electrode film layer. Domain 1021 includes a first active material, which includes a first carbon-based material. The first carbon-based material includes an outer region and an inner region located within the outer region. The outer region refers to the region extending 2.5 μm from the surface of the first carbon-based material particle to the interior of the particle. In a cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, with S2 > S1. Second region 1022 includes a second active material, which includes a second carbon-based material, which includes an amorphous carbon material. The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer located on a single side of the negative electrode current collector.

[0069] In the present disclosure, "inner region is" refers to a region other than the outer region in a particle of a material.

[0070] In the present disclosure, by making the first region of the negative electrode film layer include a first carbon-based material with S2>S1 (S2>S1 indicates that the structure of the outer region of the first carbon-based material is denser than the inner region), and making the second region of the negative electrode film layer include an amorphous carbon material, the synergistic effect between the first carbon-based material and the second carbon-based material can be fully utilized. As a result, the negative electrode plate provided by the present disclosure can have a good pore structure, a high compaction density, and a low volume change, enabling the secondary battery to have good dynamic performance and cycle performance while having a high energy density.

[0071] Through in-depth research, the inventors discovered that amorphous carbon materials have a larger interlayer spacing, which facilitates the rapid deintercalation of active ions and has a higher potential for lithium, which is beneficial for improving the battery's kinetic performance. However, amorphous carbon materials have hard and angular particles, low tap density, poor adhesion to the current collector, and are easy to demold. More binder is usually required to reduce the risk of demolding, but this also reduces the mass proportion of active material. Furthermore, the compacted density of amorphous carbon is also low, resulting in a lower energy density of the battery.

[0072] In the present disclosure, the negative electrode film layer is provided with multiple regions, and an amorphous carbon material is included in the second region away from the current collector side. The above-mentioned characteristics of the amorphous carbon material are used to improve the dynamic performance of the battery. Moreover, because the second region is away from the current collector, there is no need to use a large amount of adhesive to achieve bonding with the current collector, which increases the mass ratio of the active material and also helps to improve the dynamic performance and energy density of the battery. In addition, the first carbon-based material is included in the first region close to the current collector, thereby avoiding the problem of bonding between amorphous carbon and the current collector. Good bonding between the negative electrode film layer and the current collector can be achieved with less adhesive, which is beneficial to improve the mass ratio of the active material. At the same time, the first carbon-based material has a pore structure and has a higher compaction ability, which also enables the negative electrode plate of the present disclosure to achieve a higher plate compaction density and achieve high energy density. Moreover, S2 of the first carbon-based material is greater than S1, and has the following characteristics: the number of pores in the inner region is large and / or the pore size is large, while the number of pores in the outer region is small and / or the pore size is small. The pore structure in the internal area of ​​the first carbon-based material can effectively reduce the rolling pressure of the negative electrode plate, effectively reduce particle damage, and reserve the required expansion space for particle volume changes, effectively reducing the expansion of the plate. At the same time, the number of pores in the external area of ​​the first carbon-based material is small and / or the pore size is small, which can maintain a stable structure when the external area is embedded with lithium, and avoid the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by SEI film formation inside the particles. Therefore, the cycle performance of the secondary battery can be improved. In addition, the first carbon-based material and the second carbon-based material are located in the first area and the second area, respectively, which can achieve a good pore structure distribution, which is also beneficial to improving the charging performance of the battery.

[0073] In the present disclosure, the first carbon-based material and the second carbon-based material can be distinguished by a cross-section polisher. For example, the first carbon-based material and the second carbon-based material can be distinguished by performing an ion polishing cross-section morphology (CP) test on the negative electrode. As an example, the test method may be: cutting the negative electrode piece into a sample to be tested of a certain size (for example, 2 cm × 2 cm), fixing the negative electrode piece on the sample stage with paraffin; placing the sample stage into the sample holder and locking it, turning on the power of the argon ion cross-section polisher (for example, the IB-09010CP argon ion cross-section polisher from Japan's JEOL company) and performing vacuuming (for example, 10-4 Pa), setting the argon flow rate (for example, 0.15 MPa) and voltage (for example, 8 KV) and polishing time (for example, 2 h), adjusting the sample stage to a rocking mode and starting polishing; randomly selecting an area in the sample to be tested for scanning testing (for example, referring to JY / T010-1996, scanning using a scanning electron microscope), and obtaining an ion polishing cross-sectional morphology (CP) image of the negative electrode piece at a certain magnification (for example, 1000 times), from which the first carbon-based material and the second carbon-based material can be distinguished. Figure 4 is a scanning electron microscope (SEM) image of one embodiment of the negative electrode plate disclosed in the present invention. It can be seen from the figure that in the first area of ​​the negative electrode film layer, the particles with obvious pore structure and no sharp edges are the first carbon-based material, and in the second area of ​​the negative electrode film layer, the particles with more sharp edges are the second carbon-based material amorphous carbon.

[0074] In some embodiments, the first carbon-based material satisfies: I 3R(101) / I 2H(004) ≤0.1, optionally, 0.008≤I 3R(101) / I 2H(004) ≤0.065; I 3R(101) is the diffraction peak intensity of the 101 crystal plane of the 3R phase of the first carbon-based material in the X-ray diffraction pattern, I 2H(004) is the diffraction peak intensity of the 004 crystal plane of the 2H phase of the first carbon-based material in the X-ray diffraction pattern. By making the carbon-based material contain both 3R phase crystalline carbon and 2H phase crystalline carbon, and satisfying I 3R(101) / I 2H(004) ≤0.1, which can enable more active sites to exist on the surface of carbon-based material particles and accelerate the transmission of active ions; at the same time, the surface stability of carbon-based material particles is also relatively high, thereby effectively reducing surface side reactions and reducing active ion consumption, which is beneficial to improving the kinetic performance and cycle performance of secondary batteries.

[0075] In some embodiments, the second carbon-based material has a lower true density than the first carbon-based material. This facilitates a suitable pore distribution in the first and second regions of the negative electrode film layer, thereby improving the negative electrode film layer's ability to wet and retain the electrolyte, thereby improving the kinetic performance and / or cycle performance of the secondary battery.

[0076] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 20,000 N is less than the powder compaction density of the first carbon-based material under a pressure of 20,000 N. The powder compaction density of the first carbon-based material is relatively large, which is beneficial to improving the compaction density of the negative electrode film layer and improving the energy density of the secondary battery. The powder compaction density of the second carbon-based material is relatively small, which is beneficial to improving the porosity of the electrode and improving the deintercalation of active ions, thereby improving the kinetic performance of the secondary battery. Therefore, by adjusting the powder compaction density of the first carbon-based material to be greater than the powder compaction density of the second carbon-based material, it is beneficial to make the secondary battery have both high energy density and good kinetic performance.

[0077] In some embodiments, the first carbon-based material and / or the second carbon-based material comprises at least one pore with an 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 When the first carbon-based material and / or the second carbon-based material includes a pore structure having the above-mentioned pore area, the pore structure can reserve the required expansion space for the volume change of its particles, thereby further reducing the risk of particle breakage and generation of new interfaces, thereby reducing the occurrence of side reactions and improving the cycle performance of the secondary battery.

[0078] In some embodiments, 2.1≤S2 / S1≤478.9, 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 have further discovered that when S2 / S1 is also within the above range, the secondary battery can better balance high energy density and good cycle performance.

[0079] 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 first carbon-based material can be obtained by testing a cross-sectional image of the first carbon-based material.

[0080] FIG5 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 200 of the present disclosure. As shown in FIG5 , the region extending 2.5 μm from the surface of the particle of the first carbon-based material 200 toward the interior of the particle is the outer region 201, and the region inside the outer region 201 is the inner region 202.

[0081] In the present disclosure, the pore area, S1, and S2 values ​​of the first 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 first 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 first carbon-based material; finally, the pore area of ​​any one hole in the first 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 first carbon-based material.

[0082] In some embodiments, the area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.10μm 2 In further research, the inventors also found that by controlling the area of ​​the pore structure in the outer region of the first carbon-based material within the above range, the outer region of the first carbon-based material can have a dense structure, thereby effectively improving the structural stability of the first carbon-based material and avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby effectively improving the cycle performance and dynamic 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 first 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 .

[0083] In some embodiments, the inner region of the first carbon-based material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2The inventors further discovered that by including the aforementioned pore structure in the interior of the first carbon-based material, the rolling pressure of the negative electrode sheet can be effectively reduced, effectively reducing particle damage, and reserving sufficient and stable expansion space for the volume change of the first carbon-based material particles, thereby reducing the risk of first carbon-based material particle breakage. Furthermore, the compaction density of the negative electrode film layer can be increased, and the volume change of the negative electrode film layer can be buffered.

[0084] The inventors further discovered that when the first carbon-based material satisfies one or more of the following conditions in addition to the above-mentioned design, the performance of the secondary battery can be further improved, such as enhancing at least one of the energy density, kinetic performance, and cycle performance of the secondary battery.

[0085] In some embodiments, at least a portion of the surface of the first carbon-based material has a coating layer. Optionally, the coating layer comprises a carbon coating layer. This is beneficial for improving the dynamic performance of the secondary battery.

[0086] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 When the actual density of the first carbon-based material is within the above range, the energy density of the secondary battery can be further improved.

[0087] In some embodiments, the first carbon-based material has a powder compaction density of 1.65 g / cm3 under a pressure of 20,000 N. 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 By making the first carbon-based material have a larger powder compaction density, the compaction density of the negative electrode film layer can be increased, further improving the energy density of the secondary battery. It is also conducive to forming a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance, and improving the negative electrode film layer's electrolyte infiltration and retention characteristics, further improving the kinetic performance and cycle performance of the secondary battery.

[0088] In some embodiments, the specific surface area of ​​the first carbon-based material is ≤2.8 m 2 / g, optional 1.1m 2 / g-2.7m 2 When the specific surface area of ​​the first carbon-based material is within the above range, it is beneficial to reduce the occurrence of side reactions and the consumption of active ions by SEI film formation, thereby further enabling the secondary battery to achieve both high initial coulombic efficiency and good cycle performance.

[0089] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, optionally 10.0 μm-22.0 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, optionally 16.5 μm-42.0 μm.

[0090] By ensuring that the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above-mentioned range, it is beneficial to improve the transmission performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and further improve the cycle performance of the secondary battery.

[0091] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, and can be optionally 0.90-1.40. By ensuring that the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is within the above range, its particle packing performance is better, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also conducive to adjusting the pore distribution of the negative electrode film layer, improving the active ion and electron transport performance, and improving the electrolyte infiltration and retention characteristics of the negative electrode film layer, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0092] In some embodiments, the gram capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and can be 355 mAh / g-370 mAh / g. When the gram capacity of the first carbon-based material is within the above range, the energy density of the secondary battery is further improved.

[0093] In some embodiments, the second carbon-based material is at least one of soft carbon and hard carbon.

[0094] In some embodiments, the true density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 By making the second carbon-based material have a smaller true density, the electrode can have a suitable pore structure, improve the transmission performance of active ions, and further improve the dynamics and cycle performance of the secondary battery.

[0095] In some embodiments, the second carbon-based material has a powder compaction density of 0.85 g / cm3 under a pressure of 20,000 N. 3 -1.35g / cm 3, optional 0.90g / cm 3 -1.30g / cm 3 By making the second carbon-based material have a smaller powder compaction density, the electrode can have a suitable pore structure, improve the transmission performance of active ions, and further improve the dynamics and cycle performance of the secondary battery.

[0096] In some embodiments, the specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 / g; when the specific surface area of ​​the second carbon-based material is within the above range, it is beneficial to improve the power performance of the secondary battery.

[0097] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, optionally 5.0 μm-15.0 μm; by making the volume distribution particle size Dv50 of the second carbon-based material within the above range, the transmission performance of active ions and electrons is further improved, thereby further improving the kinetic performance of the secondary battery.

[0098] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and can be optionally 1.1-1.75. When the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is within the above range, it is beneficial for the negative electrode film layer to have a suitable pore distribution, thereby improving the dynamic performance of the secondary battery.

[0099] In some embodiments, the tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 By ensuring that the tap density of the second carbon-based material is within the above range, a reasonable pore structure can be formed between the particles of the negative electrode film layer, the active ion and electron transport performance can be improved, and the infiltration and retention characteristics of the negative electrode film layer for the electrolyte can be improved, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0100] In some embodiments, the gram capacity of the second carbon-based material is 330 mAh / g-480 mAh / g, optionally 340 mAh / g-470 mAh / g. By adjusting the gram capacity of the second carbon-based material within the above range, the energy density of the secondary battery is further improved.

[0101] In some embodiments, the first carbon-based material and / or the second carbon-based material include primary particles. Optionally, the amount of the primary particles in the first carbon-based material is greater than or equal to 80%, for example, it can be 80%-100%, 85%-90%, 80%-100%, 90%-100%, or 95%-100%. The amount of the primary particles in the second carbon-based material is greater than or equal to 80%, for example, it can be 80%-100%, 85%-90%, 80%-100%, 90%-100%, or 95%-100%. By making the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, it can have a higher structural stability, reduce the occurrence of side reactions, and further improve the cycle performance of the secondary battery.

[0102] In some embodiments, the mass proportion of the first carbon-based material in the first region is greater than or equal to 80%, and can be 90% to 98.5%, for example, 81%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, or 98%; the mass proportion of the second carbon-based material in the second region is greater than or equal to 80%, and can be 90% to 98.5%, for example, 81%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, or 98%. By making the contents of the first carbon-based material and the second carbon-based material respectively within the above ranges, the secondary battery has high energy density while having good kinetic performance and cycle performance.

[0103] As shown in FIG. 1 to FIG. 3 , the negative electrode film layer 102 further includes a middle region 1023 located between the first region 1021 and the second region 1022 of the negative electrode film layer and having a thickness of 0.4H (H represents the thickness of the negative electrode film layer 102 ).

[0104] In some embodiments, the intermediate region includes the first active material and / or the second active material. For example, as shown in FIG2 , the intermediate region 1023 may be the same in composition as the first region 1021, whereby the first active material is distributed in the thickness direction of the negative electrode film layer 102 within the range from the second surface 102b of the negative electrode film layer to a thickness of 0.7H; or, as shown in FIG3 , the intermediate region 1023 may be the same in composition as the second region 1022, whereby the second active material is distributed in the thickness direction of the negative electrode film layer 102 within the range from the first surface 102a of the negative electrode film layer to a thickness of 0.7H; or, as shown in FIG1 , the intermediate region 1023 includes both the first active material and the second active material. In this case, the intermediate region 1023 includes both a layer structure having the first active material and a layer structure having the second active material, and the two-layer structure may further have a layer interface (the layer interface can be confirmed by using a cross-section polisher to distinguish between the first carbon-based material and the second carbon-based material).

[0105] In some embodiments, the first region of the negative electrode film layer may further include other negative electrode active materials known in the art in addition to the first carbon-based material described above. For example, it may also include a silicon-based material. The silicon-based material can improve the pore structure in the negative electrode film layer, facilitate electrolyte infiltration and retention, and enhance the dynamic performance of the secondary battery. It can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery. Optionally, the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0106] In some embodiments, when the first region of the negative electrode film layer further comprises a silicon-based material, the mass proportion of the silicon-based material in the first region of the negative electrode film layer may be ≤30%, for example, 1%-8%, 2%-6%, or 13%-17%. This improves the kinetic performance and energy density of the secondary battery while also ensuring good cycle performance.

[0107] In some embodiments, the second region of the negative electrode film layer may further include other negative electrode active materials known in the art in addition to the aforementioned second carbon-based material. For example, it may also include a silicon-based material. The higher lithium insertion potential of silicon-based materials is beneficial for improving the kinetic performance of the secondary battery; it can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery. Optionally, the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0108] In some embodiments, when the second region of the negative electrode film layer further comprises a silicon-based material, the mass proportion of the silicon-based material in the second region of the negative electrode film layer may be ≤30%, for example, 1%-8%, 2%-6%, or 13%-17%. This improves the kinetic performance and energy density of the secondary battery while also ensuring good cycle performance.

[0109] In some embodiments, both the first region and the second region comprise a silicon-based material, and the mass fraction of the silicon-based material in the first region is less than or equal to the mass fraction of the silicon-based material in the second region. During the charge and discharge process of the secondary battery, the silicon-based material has a higher lithium insertion potential, which is beneficial for improving the dynamic performance of the secondary battery. In addition, due to the higher porosity of the second region of the negative electrode film layer, the active ion transport performance of the first region of the negative electrode film layer can also be improved.

[0110] In some embodiments, the middle region of the negative electrode film layer further comprises a silicon-based material.

[0111] In some embodiments, the first region, the second region, and the middle region of the negative electrode film layer may optionally further include a negative electrode conductor and / or a negative electrode binder.

[0112] The present disclosure has no particular limitation on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] The present disclosure has no particular limitation on the type of the negative electrode binder. As an 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).

[0114] In some embodiments, the first region, the second region, and the middle region of the negative electrode film layer may further optionally 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.

[0115] In some embodiments, the compaction density of the negative electrode film layer is 1.20 g / cm 3 -1.70g / cm 3 , optional 1.25g / cm 3 -1.65g / cm 3This is beneficial for the negative electrode film layer to have both high capacity and good active ion and electron transport properties, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0116] In some embodiments, the surface density of the negative electrode film layer is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 This is beneficial for the negative electrode film layer to have both high capacity and good active ion and electron transport properties, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0117] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, optionally 45 μm-100 μm.

[0118] 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).

[0119] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present disclosure further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present disclosure further includes a protective layer covering the surface of the negative electrode film layer.

[0120] 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, porosity, OI value, 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.

[0121] In the present disclosure, whether a carbon coating layer exists on the surface of a material (eg, the first carbon-based material, the second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0122] In this disclosure, I 3R(101) / I 2H(004) X-ray diffraction analysis can be used for testing, and the specific testing method can be found in the examples.

[0123] In the present disclosure, the specific surface area of ​​a material (e.g., a first carbon-based material, a second carbon-based material, etc.) 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.

[0124] In the present disclosure, the volume distribution particle size Dv10, 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 / T 19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0125] In the present disclosure, the true density of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be measured using instruments and methods known in the art. Referring to the standard GB / T 24586-2009, an exemplary test method is as follows: Take a clean and dry sample cup and place it on a balance, reset it to zero, add the powder sample to the sample cup, occupying about 1 / 2 of the volume of the sample cup, and record the mass of the sample. Place the sample cup containing the sample in a true density tester, a closed test system, and introduce helium according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the true volume is calculated according to Bohr's law (PV=nRT), thereby calculating the true density. Test sample cup volume: 3.5cm 3, analysis gas: helium. In the present disclosure, the powder compaction density of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known 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 (such as a UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: weigh 1 g of sample powder, add it to a mold with a bottom area of ​​1.327 cm2, pressurize it to 2000 kg, maintain the pressure for 30 seconds, then release the pressure, maintain for 10 seconds, and then record and calculate the powder compaction density of the material under a pressure of 20,000 N.

[0126] In the present disclosure, the tap density 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 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.

[0127] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, 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.

[0128] In this disclosure, primary particles have a meaning well known in the art. Primary particles refer to non-agglomerated particles. Agglomerated particles formed by the aggregation of two or more primary particles are secondary particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0129] In the present disclosure, the areal density of the negative electrode film layer has a meaning well known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold pressed can be taken (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), punched into small discs with an area of ​​S1, weighed, and recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode sheet = (M1-M0) / S1.

[0130] In this disclosure, the compacted density of the negative electrode film layer is well known in the art and can be measured using methods known in the art. The compacted density of the negative electrode film layer = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0131] It should be noted that the various parameter tests on the first active material, the second active material or the negative electrode film layer can be performed by sampling and testing the prepared secondary battery according to the following steps.

[0132] 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 surface density, compacted density, and thickness of the negative electrode film.

[0133] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2 hours), and a region of the baked negative electrode sheet is selected to sample the second active material (a blade can be used for scraping powder for sampling), and the sampling position is the second region of the negative electrode film layer; then the first active material is sampled in the same manner, and the sampling position is the first region of the negative electrode film layer; the collected first active material and second active material are sieved separately (for example, sieved with a 200-mesh sieve), and finally the first active material and second active material samples that can be used to test the various material parameters mentioned above in the present disclosure are obtained.

[0134] [Method for preparing negative electrode sheet]

[0135] The present disclosure also provides a method for preparing the negative electrode sheet of the present disclosure. The method comprises the following steps: providing a first slurry containing a first active material and a second slurry containing a second active material; applying the first slurry to the negative electrode current collector, applying the second slurry to the first slurry, and drying and cold pressing to obtain the negative electrode sheet.

[0136] In some embodiments, the first active material, an optional conductive agent, an optional binder, and other optional auxiliary agents may be dispersed in a solvent (eg, deionized water) to form a first slurry.

[0137] In some embodiments, the second active material, an optional conductive agent, an optional binder, and other optional auxiliary agents may be dispersed in a solvent (eg, deionized water) to form a second slurry.

[0138] In some embodiments, the first active material includes a first carbon-based material.

[0139] In some embodiments, the second active material comprises a second carbon-based material.

[0140] In some embodiments, the first slurry and / or the second slurry further comprises a silicon-based material.

[0141] The first slurry and the second slurry can be applied simultaneously at one time or in two separate applications. In some embodiments, the first slurry and the second slurry are applied simultaneously at one time. Applying them simultaneously at one time can reduce the negative electrode film resistance, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0142] The coating weight of the first slurry and the second slurry can be adjusted according to actual conditions.

[0143] In the present disclosure, the first active material, the second active material, etc. mentioned above can be obtained through commercial purchase, or prepared by the following method of the present disclosure.

[0144] In some embodiments, the preparation method of the first carbon-based material includes: step 1, providing a raw material having a plurality of pore structures; step 2, uniformly mixing the raw material and the filler material in a predetermined proportion, then keeping the mixture at a first temperature T1 for a first time t1, and cooling to room temperature to obtain an intermediate; step 3, keeping the obtained intermediate at a second temperature T2 for a second time t2, and obtaining the first carbon-based material.

[0145] In some embodiments, in step 1, the raw material for preparing the first carbon-based material includes natural graphite. Alternatively, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0146] "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.

[0147] In some embodiments, in step 1, the morphology of the raw material includes one or more of spherical or spherical-like shapes.

[0148] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 7.0 μm-25.0 μm, and may be optionally 10.0 μm-20.0 μm, which is conducive to preparing the first carbon-based material with a desired volume distribution particle size.

[0149] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥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 first carbon-based material with the required specific surface area. It is also beneficial for the first carbon-based material to have both high capacity and high first coulombic efficiency. In addition, it is also beneficial for the first carbon-based material to have better kinetic properties.

[0150] By adjusting the particle size of the raw materials (such as volume distribution particle size Dv50 and / or specific surface area) within the above range, the agglomeration of the raw materials during the subsequent preparation process can be minimized, thereby minimizing problems such as increased surface defects and increased surface active sites caused by particle breakage.

[0151] In some embodiments, in step 2, the softening point temperature of the filling material is 102°C-175°C. Optionally, the softening point temperature of the filling material is 106°C-162°C, 106°C-156°C, 106°C-150°C, 106°C-146°C, 106°C-142°C, 110°C-162°C, 110°C-156°C, 110°C-150°C, 110°C-146°C, 110°C-142°C. When the softening point temperature of the filling material is within the above range, it is beneficial to adjust I 3R(101) / I 2H(004) In the appropriate range, the lower the softening point temperature, the 3R(101) / I2H(004) It is also beneficial to adjust the pore size and / or pore number in the outer region and the inner region of the carbon material within a suitable range.

[0152] 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 be melted by heat and filled into the pore structure of the raw material, and also helps to improve the dispersion uniformity of the filler material and the raw material.

[0153] In some embodiments, in step 2, the coking value of the filler material is 19%-47%, and optionally 22%-40%. When the coking value of the filler material is within the above range, it is beneficial to adjust I 3R(101) / I 2H(004) In the appropriate range, the smaller the coking value, the higher the 3R(101) / I 2H(004) The larger the carbon material, the better. It is also beneficial to adjust the pore size and / or pore number in the outer region and the inner region of the carbon material within an appropriate range. In this disclosure, the coking value of the filler material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured with reference to GB / T 8727-2008.

[0154] 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.

[0155] In some embodiments, in step 2, the mass ratio of the filler material to the raw material is (10-32):100, optionally (12-30):100, (14-28):100, (15-25):100. (10-40):100, optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (12-20):100, (14-28):100, (15-25):100. Thus, it is beneficial to adjust I 3R(101) / I 2H(004) In the appropriate range, the larger the filler material mass ratio, the 3R(101) / I 2H(004) It is also beneficial to adjust the pore size and / or pore number in the outer region and the inner region of the carbon material within a suitable range.

[0156] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filler material within the above range, it is beneficial to adjust the number and / or pore size of the pores in the outer region and the inner region of the first carbon-based material within a suitable range, which is beneficial to adjust the S2 / S1 and I 3R(101) / I 2H(004) In a suitable range.

[0157] 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.

[0158] 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 is a staged heating process.

[0159] 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.

[0160] 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.

[0161] In some embodiments, the second temperature raising process is to raise the temperature to 450°C-550°C and keep the temperature at this temperature for 0-2 hours. When the holding time is 0 hours, it means that when the temperature is raised to the range of 450°C-550°C, no holding treatment is performed, but the temperature is continued to rise to the first temperature T1.

[0162] In some embodiments, the third temperature raising process is to raise the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0163] In the staged heating process, the temperature is first raised to 200℃-250℃. 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 0.5h-3h allows it to flow and fill into the pore structure of the raw material; then the temperature is raised to 450℃-550℃. 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.

[0164] 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, 2°C / min-5°C / min

[0165] 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.

[0166] In some embodiments, the heating rate of the second heating process may be 1° C. / min-10° C. / min, and may be optionally 2° C. / min-8° C. / min.

[0167] In some embodiments, the heating rate of the third heating process may be 1° C. / min-10° C. / min, and may be optionally 2° C. / min-8° C. / min.

[0168] In some embodiments, in step 2, the first temperature T1 is 700° C.-1200° C. For example, the first temperature T1 can be 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., 1100° C., 1200° C., or any range thereof. Alternatively, the first temperature T1 is 750° C.-1100° C., 800° C.-1100° C., or 850° C.-1000° C.

[0169] 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. Optionally, the first time t1 is 2 hours to 4 hours.

[0170] 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.

[0171] 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.

[0172] 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 first carbon-based material within a suitable range, and it is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0173] In some embodiments, in step 3, the second temperature T2 is 1960° C.-2640° C. Optionally, the second temperature T2 is 2025° C.-2525° C., 2025° C.-2475° C., 2025° C.-2425° C., 2025° C.-2375° C., 2075° C.-2525° C., 2075° C.-2475° C., 2075° C.-2425° C., 2075° C.-2375° C.

[0174] 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. Optionally, the second time t2 is 2 hours to 5 hours.

[0175] 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 inner-string graphitization furnace.

[0176] 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 nitrogen, argon, and helium.

[0177] 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 first carbon-based material within a suitable range, which is beneficial for the first carbon-based material to have a suitable degree of graphitization, interlayer spacing, etc.

[0178] In the preparation method of the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filler material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above range, it is beneficial to adjust the S2 / S1, I 3R(101) / I 2H(004) , gram capacity, specific surface area, particle size, true density, powder compaction density, tap density and other parameters.

[0179] [Positive electrode]

[0180] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0181] 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).

[0182] The positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. 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.

[0183] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0184] When the secondary battery of the present disclosure is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0185] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include one or more of lithium transition metal oxides represented by the general formula LiaNibCocMdOeAf and their 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.

[0186] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O'2 (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.

[0187] In the present disclosure, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active material.

[0188] [Electrolyte]

[0189] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0190] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0191] When the secondary battery of the present disclosure is a lithium ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium 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).

[0192] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, for example, the solvent 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.

[0193] In some embodiments, the electrolyte may further optionally 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.

[0194] [Isolation film]

[0195] The present disclosure has no particular limitation on the type of the isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0196] 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.

[0197] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.

[0198] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0199] 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).

[0200] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG6 shows a secondary battery 5 with a square structure as an example.

[0201] In some embodiments, as shown in FIG7 , the outer packaging may include a shell 51 and a cover plate 53 . The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates together form a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and can be adjusted according to demand.

[0202] 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.

[0203] 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.

[0204] Figure 8 is a schematic diagram of an exemplary battery module 4. As shown in Figure 8 , 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 together using fasteners.

[0205] 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.

[0206] 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.

[0207] Figures 9 and 10 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 9 and 10, 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.

[0208] 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.

[0209] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0210] Figure 11 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.

[0211] 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.

[0212] Example

[0213] 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.

[0214] Preparation of the first carbon-based material

[0215] Materials 1-1

[0216] Step 1: Mechanically crush, classify, spheroidize and purify the flake graphite to obtain natural spherical graphite. Step 2: Mix the obtained natural spherical graphite with the filler petroleum asphalt in a ratio of 100:20. The softening point of the petroleum asphalt is 115°C and the coking value is 35%. The mixed material is then placed in a programmable temperature raising device, heated to 200°C and kept warm for 1 hour (the first heating process), and then continuously heated to 700°C and kept warm for 2 hours. After the end, it is cooled to room temperature to obtain an intermediate. Step 3: Place the obtained intermediate in a graphitization furnace and perform a heat treatment at 2450°C. After the end, demagnetize and screen to obtain the first carbon-based material (material 1-1). The S2 / S1 of material 1-1 is 1.5, I 3R(101) / I 2H(004) The compacted density of the powder under a pressure of 20000N is 1.88g / cm 3 , the true density is 2.25g / cm 3 .

[0217] The S2 / S1 of the first carbon-based material is obtained by testing using the following method.

[0218] A sample preparation binder and the first carbon-based material powder are mixed evenly and then applied to a copper foil. The mixture is then dried at 60°C for 30 minutes before use. Five samples to be tested are cut into 6 mm x 6 mm pieces at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples are then cut using a plasma beam to obtain cross-sections of each sample. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from Japan's JEOL.

[0219] Each sample cross section of the first carbon-based material was scanned using a scanning electron microscope, and a scanned image was obtained from an arbitrarily selected region within each sample cross section. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from ZEISS, Germany.

[0220] Randomly select cross sections of 20 particles of the first carbon-based material from the scanned image. The area formed by extending 0.25 μm from the particle surface of the first 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 first 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 first carbon-based material. The image processing software can be AVIZO.

[0221] Materials 1-2 to 1-7

[0222] The preparation methods of materials 1-2 to 1-7 are similar to those of material 1-1, except that the softening point temperature, coking value, and mixing ratio of natural spherical graphite and filler petroleum asphalt of the filler material are adjusted as shown in Table 1, and the third heating process is adjusted so that the S2 / S1 of the first carbon-based material is the value shown in Table 1.

[0223] Table 1

[0224] Materials 1'-1

[0225] The preparation method of material 1'-1 is similar to that of material 1-1, except that the material 1'-1 is adjusted as shown in Table 2 so that the S2 / S1 of the first carbon-based material is the value shown in Table 2.

[0226] Table 2

[0227] Materials 1-8 to 1-12

[0228] The preparation methods of materials 1-8 to 1-12 are similar to those of material 1-1, except that the softening point temperature, coking value, and mixing ratio of natural spherical graphite and filler petroleum asphalt of the filler are adjusted as shown in Table 3, and the heat treatment temperature is adjusted to make I 3R(101) / I 2H(004 The values ​​are shown in Table 3.

[0229] Table 3

[0230] Preparation of the second carbon substrate

[0231] Coconut shells were used as raw materials, heat treated at 600°C, crushed, alkaline-soaked to remove impurities, and then heat treated at 1000°C to obtain amorphous carbon materials (hard carbon) with a true density of 2.1g / cm 3 The compacted density of the powder under a pressure of 20000N is 1.05g / cm 3 .

[0232] Example 1

[0233] Preparation of secondary batteries

[0234] 1. Negative Electrode: Thoroughly stir and mix the first carbon-based material (Material 1-1) as the first active material, carbon black (Super P) as the conductive agent, sodium carboxymethyl cellulose as the thickener, and styrene-butadiene rubber (SBR) as the binder in an appropriate amount of deionized water at a weight ratio of 96.4:1:1.2:1.4 to form a first slurry. Thoroughly stir and mix the second carbon-based material (see Table 1) as the second active material, carbon black (Super P) as the conductive agent, sodium carboxymethyl cellulose as the thickener, and styrene-butadiene rubber (SBR) as the binder in an appropriate amount of deionized water at a weight ratio of 96.4:1:1.2:1.4 to form a second slurry. The first and second slurries are extruded simultaneously using a dual-chamber coating apparatus. The first slurry is applied to the negative electrode current collector copper foil, and the second slurry is applied over the first slurry. After drying and cold pressing, the negative electrode is obtained. The coating weights of the first and second slurries are the same. The compacted density of the negative electrode film is 1.55 g / cc.

[0235] 2. Positive Electrode: Mix lithium iron phosphate with carbon black (Super P), a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 96:2:2. Add an appropriate amount of NMP solvent and stir evenly to obtain a positive electrode slurry. Apply the positive electrode slurry to both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0236] 3. Electrolyte: 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.

[0237] 4. Isolation film: polyethylene film.

[0238] 5. Preparation of secondary batteries: Place the positive electrode and negative electrode sheets prepared above in order, with the separator placed between the positive and negative electrode sheets to act as an isolate, and then wind them to obtain an electrode assembly; place the electrode assembly in an outer package, inject the electrolyte after drying, and obtain a secondary battery through vacuum packaging, standing, formation, shaping and other processes.

[0239] Examples 2-8

[0240] The battery preparation methods of Examples 2-8 are similar to those of Example 1, except that the first carbon-based material is a material having different S2 / S1 characteristics, or the second carbon-based material is a soft carbon. See Table 4 for details.

[0241] Comparative Example 1

[0242] The first carbon-based material (see Table 1 for details) as the first active material, carbon black (Super P) as a conductive agent, sodium carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent at a weight ratio of 96.4:1:1.2:1.4 to form a first slurry. The first slurry was applied to the negative electrode current collector copper foil in the same amount as the first slurry in Example 1. After drying and cold pressing, a negative electrode sheet was obtained (no second carbon-based material was used, no second region was present). Otherwise, the preparation was identical to that of Example 5 to obtain a secondary battery.

[0243] Comparative Example 2

[0244] A secondary battery was prepared in a similar manner to the preparation method of Example 5, except that the first carbon-based material used was Material 1′-1.

[0245] Comparative Example 3

[0246] The coating positions of the first and second slurries were changed. The second slurry (the second carbon-based material (see Table 5 for details), conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber, mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 95.2:1:1.4:2.4) was applied to the negative electrode current collector copper foil. The first slurry was applied to the second slurry prepared in the example. After drying and cold pressing, the negative electrode sheet was obtained. Otherwise, the preparation was identical to the example to obtain a secondary battery.

[0247] The following tests were performed on the secondary batteries of the above examples and comparative examples, and the results are shown in Tables 4 and 5 below.

[0248] Performance Testing

[0249] (1) X-ray diffraction analysis test

[0250] X-ray diffractometer testing was performed according to JIS K 0131-1996 to obtain an X-ray diffraction pattern of the carbon material. The test conditions were as follows: the carbon material was prepared using a flat plate method, CuKα radiation was used as the radiation source, a copper target was used as the anode target, a voltage of 40 kV, a current of 40 mA, a 1 mm anti-scatter slit, a scanning range of 20°-80°, a step size of 0.01671°, a step duration of 0.24 s per step, and a scan rate of 4° / min. The test instrument can be a Bruker D8 Discover X-ray diffractometer.

[0251] The 2θ diffraction peak for the 3R phase 101 crystal plane is within the range of 43°-44°, the 2θ diffraction peak for the 2H phase 004 crystal plane is within the range of 53°-55°, and the 2θ diffraction peak for the 3R phase 012 crystal plane is within the range of 46°-47°. The peak intensities of the diffraction peaks for the 3R phase 101 crystal plane and the 2H phase 004 crystal plane are expressed as the integrated areas of the corresponding diffraction peaks.

[0252] (2) Energy density

[0253] At 25°C, the secondary battery was charged at a constant current of 1 / 3C to 3.65V. Then, it was charged at a constant voltage at 3.65V to a current of 0.05C. After resting for 5 minutes, it was discharged at a constant current of 1 / 3C to 2.0V. The discharge energy of the battery was recorded. The battery discharge energy divided by the battery weight is the battery's gravimetric energy density, expressed in Wh / kg. The measurement data is shown in Table 1.

[0254] (3) Fast charging performance test of secondary batteries

[0255] At 25°C, the secondary battery was charged to 3.65V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.5V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0256] Then the secondary battery is charged with constant current in sequence at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 to 3.65V or 0V negative electrode cut-off potential (whichever is reached first). After each charge, it is discharged to 2.5V at 1C0. Record the state of charge (SOC) at different charge rates to 10%, 20%, 30%, ..., 80%. The charge rate-negative electrode potential curve under different SOC states was drawn, and the charge rate corresponding to the negative electrode potential of 0 V under different SOC states was obtained after linear fitting. The charge rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, respectively. The charging time T of the secondary battery from 10% SOC to 80% SOC (assuming that the secondary battery does not undergo lithium deposition) is calculated according to the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, and the unit is min. The shorter the charging time, the better the dynamic performance of the secondary battery.

[0257] (4) Cycle performance test of secondary batteries

[0258] At 45°C, the prepared secondary battery was charged at a constant current of 1C to an upper cutoff voltage of 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 a lower cutoff voltage of 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.

[0259] 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%.

[0260] Table 4

[0261] Table 5

[0262] It can be seen from Tables 4 and 5 that in the embodiment, by making the first region of the negative electrode film layer include the first carbon-based material with S2 greater than S1, and making the second region of the negative electrode film layer include the second carbon material amorphous carbon, the interaction advantage between the first carbon-based material and the second carbon-based material can be fully utilized, and the negative electrode plate can have a high compaction density. At the same time, the negative electrode film layer can also have a reasonable pore distribution, which is conducive to the transmission of active ions. As a result, the battery can have high energy density while taking into account excellent kinetic performance and cycle performance.

[0263] In Comparative Example 1, the negative electrode film layer contained only the first carbon-based material, which failed to achieve both high energy density and balanced kinetic and cycling performance. In particular, the kinetic performance was poor. In Comparative Examples 2 and 3, the S2 / S1 ratio of the first carbon-based material was 0.93, and the first carbon-based material's external pore structure was not repaired or filled, resulting in poor structural stability and poor cycling performance.

[0264] In Comparative Example 3, the first region comprises amorphous carbon and the second region comprises the first carbon-based material. To bond the amorphous carbon to the current collector, the binder content in the slurry is increased, which reduces the mass ratio of the active material, resulting in a lower energy density of the battery and worsening the kinetic performance.

[0265] Examples 9-13

[0266] A secondary battery was prepared using the same method as in Example 5, except that materials 1-8 to 1-12 were used as the first carbon-based material. It should be noted that for ease of comparison, the data from Example 5 are also shown in Table 6.

[0267] Table 6

[0268] The results of Table 6 above show that by making the first carbon-based material 3R(101) / I 2H(004) ≤0.1, the secondary battery has excellent kinetic performance and the cycle performance is further improved. In addition, by making 0.008≤I 3R(101) / I 2H(004) ≤0.065, the cycle performance is further improved.

[0269] Example 14

[0270] Except for using the first carbon-based material and the second carbon-based material prepared as follows, a secondary battery was prepared and performance tested in the same manner as in Example 5. It should be noted that the data of Example 5 are also shown in Table 7 for comparison purposes.

[0271] Preparation of the first carbon-based material: Step 1, mechanically crush, grade, spheroidize and purify the flake graphite to obtain natural spherical graphite. Step 2, mix the obtained natural spherical graphite with the filler petroleum asphalt in a ratio of 100:40, the softening point of the petroleum asphalt is 150°C, and the coking value is 40%. Then, place the mixed material in a programmable temperature rising device, heat it to 200°C and keep it warm for 1 hour (the first heating process), and then continue to heat it to 700°C and keep it warm for 2 hours. After the end, cool it to room temperature to obtain an intermediate. Step 3, place the obtained intermediate in a graphitization furnace and perform a heat treatment at 1960°C. After the end, demagnetize and sieve to obtain the first carbon-based material, and its powder compaction density is 1.30g / cm 3 .

[0272] Preparation of the second carbon-based material: Coconut shell was used as raw material, heat treated at 600°C, crushed, alkaline-soaked to remove impurities, and then heat treated at 1400°C to obtain an amorphous carbon material (hard carbon). The compacted density of the powder was 1.35g / cm 3 .

[0273] Table 7

[0274] It can be seen from Table 7 that the powder compaction density of the second carbon-based material under a pressure of 20,000 N is less than the powder compaction density of the first carbon-based material under a pressure of 20,000 N, which can further improve the performance of the secondary battery, and the energy density, cycle performance and kinetic performance are all better improved.

[0275] 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. Industrial Applicability

[0276] The present disclosure provides a secondary battery and an electrical device, the secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface remote from the negative electrode current collector and a second surface disposed opposite the first surface, the thickness of the negative electrode film layer being denoted as H, the region from the second surface of the negative electrode film layer to a thickness range of 0.3 H being denoted as the first region of the negative electrode film layer, the region from the first surface of the negative electrode film layer to a thickness range of 0.3 H being denoted as the second region of the negative electrode film layer, the first region comprising a first active material, the second region comprising a second active material, the first active material comprising a first carbon-based material, the second active material comprising a second carbon-based material, the first carbon-based material having a pore structure, and the second carbon-based material comprising an amorphous carbon material. The secondary battery disclosed herein has high energy density while exhibiting excellent cycle performance and kinetic performance.

Claims

1. A secondary battery comprising a negative electrode sheet, The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface. The thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer. The first region includes a first active material, the second region includes a second active material, the first active material includes a first carbon-based material, and the second active material includes a second carbon-based material, The first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region extending 2.5 μm from the particle surface of the first carbon-based material to the inside of the particle, and in the cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is recorded as S1, the total pore area of ​​the inner region is recorded as S2, and S2>S1, The second carbon-based material includes an amorphous carbon material.

2. The secondary battery according to claim 1, wherein The first carbon-based material satisfies: I 3R(101) / I 2H(004) ≤0.1, optionally, 0.008≤I 3R(101) / I 2H(004) ≤0.065; I 3R(101) is the diffraction peak intensity of the 101 crystal plane of the 3R phase of the first carbon-based material in the X-ray diffraction spectrum, I 2H(004) is the diffraction peak intensity of the 004 crystal plane of the 2H phase of the first carbon-based material in the X-ray diffraction pattern.

3. The secondary battery according to claim 1 or 2, wherein: The true density of the second carbon-based material is less than the true density of the first carbon-based material.

4. The secondary battery according to any one of claims 1 to 3, wherein The powder compaction density of the second carbon-based material under a pressure of 20,000 N is less than the powder compaction density of the first carbon-based material under a pressure of 20,000 N.

5. The secondary battery according to any one of claims 1 to 4, wherein The first carbon-based material and / or the second carbon-based material comprises at least one pore with an 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 -2.0μm2 pore structure.

6. The secondary battery according to any one of claims 1 to 5, wherein 2.1≤S2 / S1≤478.9, optionally, 2.5≤S2 / S1≤418.

6.

7. The secondary battery according to any one of claims 1 to 6, wherein At least part of the surface of the first carbon-based material has a coating layer; optionally, the coating layer includes a carbon coating layer.

8. The secondary battery according to any one of claims 1 to 7, wherein The first carbon-based material satisfies at least one of the following conditions: (1) The true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 ; (2) The powder compaction density of the first carbon-based material under a pressure of 20000N is 1.65g / cm 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 ; (3) The specific surface area of ​​the first carbon-based material is less than or equal to 2.8 m 2 / g, optional 1.1m 2 / g-2.7m 2 / g; (4) The volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, and can be optionally 10.0 μm-22.0 μm; (5) The volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, and can be optionally 16.5 μm-42.0 μm; (6) the particle size distribution of the first carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.55, and can be selected from 0.90 to 1.40; (7) The gram capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and can be optionally 355 mAh / g-370 mAh / g.

9. The secondary battery according to any one of claims 1 to 8, wherein The second carbon-based material is at least one of soft carbon and hard carbon.

10. The secondary battery according to any one of claims 1 to 9, wherein The second carbon-based material satisfies at least one of the following conditions: (1) The true density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 ; (2) The powder compaction density of the second carbon-based material under a pressure of 20000N is 0.85g / cm 3 -1.35g / cm 3 , optional 0.90g / cm 3 -1.30g / cm 3 ; (3) The specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 / g; (4) Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, and can be 5.0 μm-15.0 μm; (5) the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.75, and can be 1.1-1.75; (6) The tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 ; (7) The gram capacity of the second carbon-based material is 330 mAh / g-480 mAh / g, and can be optionally 340 mAh / g-470 mAh / g.

11. The secondary battery according to any one of claims 1 to 10, wherein The first carbon-based material and / or the second carbon-based material comprises primary particles; Optionally, the amount of the primary particles in the first carbon-based material accounts for greater than or equal to 80%; Optionally, the number of the primary particles in the second carbon-based material accounts for greater than or equal to 80%.

12. The secondary battery according to any one of claims 1 to 11, wherein In the first region, the mass proportion of the first carbon-based material is greater than or equal to 80%, and may be 90% to 98.5%; and / or, In the second region, the mass proportion of the second carbon-based material is greater than or equal to 80%, and can be optionally 90% to 98.5%.

13. The secondary battery according to any one of claims 1 to 12, wherein The first region and / or the second region further comprises a silicon-based material; Optionally, both the first region and the second region include silicon-based materials, and a mass proportion of the silicon-based material in the first region is less than or equal to a mass proportion of the silicon-based material in the second region.

14. The secondary battery according to any one of claims 1 to 13, wherein An intermediate region between the first region and the second region includes the first active material and / or the second active material.

15. The secondary battery according to any one of claims 1 to 14, wherein The negative electrode film layer satisfies at least one of the following (1)-(3): (1) The compaction density of the negative electrode film layer is 1.20 g / cm 3 -1.70g / cm 3 , optional 1.25g / cm 3 -1.65g / cm 3 ; (2) The surface density of the negative electrode film layer is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 ; (3) The thickness of the negative electrode film layer is 40 μm-120 μm, and can be optionally 45 μm-100 μm.

16. An electrical device comprising the secondary battery according to any one of claims 1 to 15.

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