Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises a negative pole piece, the negative pole piece comprises a negative pole current collector and a negative pole film layer located on at least one surface of the negative pole current collector, the negative pole film layer is provided with a first surface far away from the negative pole current collector and a second surface opposite to the first surface, the thickness of the negative electrode film layer is marked as H, the area from the second surface of the negative electrode film layer to the thickness range of 0.3 H is marked as the first area of the negative electrode film layer, the area from the first surface of the negative electrode film layer to the thickness range of 0.3 H is marked as the second area of the negative electrode film layer, the first area comprises a first active material, and the second area comprises a second active material; the first active material comprises a first carbon-based material, the second active material comprises a second carbon-based material, the first carbon-based material has a pore structure, and the second carbon-based material comprises an amorphous carbon material. The secondary battery provided by the invention has excellent cycle performance and dynamic performance while having high energy density.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the application scope of secondary batteries becomes wider and wider, higher requirements are put forward for their performance.

[0003] Therefore, how to enable secondary batteries to have excellent cycle performance and kinetic performance while having a high energy density has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a secondary battery and an electrical device, the secondary battery having a high energy density while taking into account excellent cycle performance and kinetic performance.

[0005] A first aspect of the present application provides a secondary battery, including a negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface disposed opposite to the first surface. The thickness of the negative electrode film layer is denoted as H. The region within a thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as the first region of the negative electrode film layer, and the region within a thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as the second region of the negative electrode film layer. The first region includes a first active material, and 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. The outer region refers to the region formed by extending a distance of 2.5 μm from the particle surface of the first carbon-based material into the particle interior. In the 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, and S2 > S1. The second carbon-based material includes an amorphous carbon material.

[0006] By making the first region of the negative electrode film layer include the above-mentioned first carbon-based material and the second region of the negative electrode film layer include an amorphous carbon material, the synergistic advantage between the first carbon-based material and the second carbon-based material can be fully exerted. Thus, the negative electrode sheet provided by the present application can have a good pore structure, and at the same time has a high tap density and a low volume change, enabling the secondary battery to have good kinetic performance and cycling performance on the premise of having a high energy density.

[0007] 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 plane of the 3R phase of the first carbon-based material in the X-ray diffraction pattern, and I 2H(004) is the diffraction peak intensity of the 004 plane of the 2H phase of the first carbon-based material in the X-ray diffraction pattern. Thus, the surface stability of the carbon-based material particles is relatively high, which can effectively reduce surface side reactions, reduce the consumption of active ions, and is beneficial for the secondary battery to obtain better cycling performance.

[0008] In some embodiments, the true density of the second carbon-based material is less than that of the first carbon-based material. Thus, it is beneficial for the first region and the second region of the negative electrode film layer to have a suitable pore distribution, so as to improve the wetting and retention characteristics of the negative electrode film layer for the electrolyte, thereby improving the kinetic performance and / or cycling performance of the secondary battery.

[0009] In some embodiments, the powder tap density of the second carbon-based material under a pressure of 20000N is less than the powder tap density of the first carbon-based material under a pressure of 20000N. By adjusting the powder tap density of the second carbon-based material to be less than that 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 for the first region and the second region of the negative electrode film layer to have a suitable pore distribution, thereby improving the wetting and retention characteristics of the negative electrode film layer for the electrolyte, and thus improving the kinetic performance and / or cycling performance of the secondary battery.

[0010] In some embodiments, the first carbon-based material and / or the second carbon-based material includes one or more pore structures with an area greater than or equal to 0.15μm 2 optionally includes one or more pore structures with an area of 0.15μm 2 -2.0μm 2The pore structure. By making the first carbon-based material and / or the second carbon-based material include the pore structure with the above pore area, the pore structure can reserve sufficient and stable expansion space for the volume change of the particles, reduce the risk of particle breakage, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0011] In some embodiments, 2.1 ≤ S2 / S1 ≤ 478.9, optionally, 2.5 ≤ S2 / S1 ≤ 418.6. Thus, the secondary battery can better balance high energy density and good cycle performance.

[0012] In some embodiments, 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. Thus, it is beneficial to improve the kinetic performance of the secondary battery.

[0013] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27 g / cm 3 , optionally 2.23 g / cm 3 -2.26 g / cm 3 . The first carbon-based material has a relatively large true density, which is beneficial to improving the energy density of the secondary battery.

[0014] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20000 N is 1.65 g / cm 3 -2.0 g / cm 3 , optionally 1.68 g / cm 3 -1.98 g / cm 3 . By making the first carbon-based material have a relatively large powder compaction density, the compaction density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved; it is also beneficial to form a reasonable pore structure between the negative electrode film layers, improve the active ion and electron transport performance, and improve the infiltration and retention characteristics of the negative electrode film layer for the electrolyte, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0015] In some embodiments of the present application, the specific surface area of the first carbon-based material is ≤ 2.8 m 2 / g, optionally 1.1 m 2 / g - 2.7 m 2 / g. 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 the formation of the SEI film, so that the secondary battery can balance high first Coulomb efficiency and good cycle performance.

[0016] In some embodiments, the volume-based particle size distribution Dv50 of the first carbon-based material is 8.0 μm - 25.0 μm, and may be optionally 10.0 μm - 22.0 μm. In some embodiments, the volume-based particle size distribution Dv90 of the first carbon-based material is 16.0 μm - 45.0 μm, and may be optionally 16.5 μm - 42.0 μm.

[0017] By making the volume-based particle size distribution Dv50 and / or Dv90 of the first carbon-based material within the above ranges, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. Additionally, it can 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.

[0018] 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 may be optionally 0.90 - 1.40. By making the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material within the above ranges, its particle packing performance is better, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; additionally, it is also beneficial to adjust the pore distribution of the negative electrode film layer, improve the transport performance of active ions and electrons, and improve the wetting and retention characteristics of the negative electrode film layer to the electrolyte, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0019] In some embodiments, the specific capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and may be optionally 355 mAh / g - 370 mAh / g. When the specific capacity of the first carbon-based material is within the above ranges, it is beneficial to improve the energy density of the secondary battery.

[0020] In some embodiments, the second carbon-based material is at least one of soft carbon and hard carbon.

[0021] In some embodiments, the true density of the second carbon-based material is 1.95 g / cm 3 - 2.22 g / cm 3 and may be optionally 1.97 g / cm 3 - 2.21 g / 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.

[0022] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 20000 N is 0.85 g / cm 3 - 1.35 g / cm 3 and may be optionally 0.90 g / cm 3 - 1.30 g / cm3 . 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 kinetic performance of the secondary battery.

[0023] In some embodiments, the specific surface area of the second carbon-based material is greater than or equal to 1.5 m 2 / g, and can be optionally 1.9 m 2 / g - 7.5 m 2 / g; when the specific surface area of the second carbon-based material is within the above range, the higher reaction activity is beneficial to improving the power performance of the secondary battery.

[0024] 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, the cycle performance of the secondary battery can be improved, and in addition, it is also beneficial to improving the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery.

[0025] 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 good, which is beneficial 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 beneficial to the negative electrode film layer having a suitable pore distribution, thereby improving the kinetic performance of the secondary battery.

[0026] In some embodiments, the tapped density of the second carbon-based material is 0.80 g / cm 3 -1.20 g / cm 3 , and can be optionally 0.83 g / cm 3 -1.15 g / cm 3 . By making the tapped density of the second carbon-based material within the above range, a reasonable pore structure can be formed between the particles of the negative electrode film layer, the transport performance of active ions and electrons can be improved, the infiltration and retention characteristics of the negative electrode film layer for the electrolyte can be improved, and further, the kinetic performance and cycle performance of the secondary battery can be improved.

[0027] In some embodiments, the specific capacity of the second carbon-based material is 330 mAh / g - 480 mAh / g, and can be optionally 340 mAh / g - 470 mAh / g. By adjusting the specific capacity of the second carbon-based material within the above range, the energy density of the secondary battery can be improved.

[0028] In some embodiments, the first carbon-based material and / or the second carbon-based material includes primary particles. Optionally, the proportion of the primary particles in the first carbon-based material is greater than or equal to 80%, and the proportion of the primary particles in the second carbon-based material is greater than or equal to 80%. By making the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, it can have high structural stability and reduce the occurrence of side reactions, thereby improving the cycling performance of the secondary battery; in addition, it can also improve the compaction density of the negative electrode film layer, thereby improving the energy density of the secondary battery.

[0029] In some embodiments, the mass proportion of the first carbon-based material in the first region is greater than or equal to 80%, optionally 90% - 98.5%; and / or, the mass proportion of the second carbon-based material in the second region is greater than or equal to 80%, optionally 90% - 98.5%. When the contents of the first carbon-based material and the second carbon-based material are respectively within the above ranges, the secondary battery has good kinetic performance and cycling performance while having a high energy density.

[0030] In some embodiments, the first region and / or the second region further includes a silicon-based material. The higher lithium intercalation potential of the silicon-based material is beneficial to improving the kinetic performance of the secondary battery; at the same time, it can also improve the negative electrode capacity, thereby further improving the energy density of the secondary battery. In some embodiments, both the first region and the second region include a silicon-based material, 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 cycling performance and / or kinetic performance of the secondary battery.

[0031] In some embodiments, the intermediate region between the first region and the second region includes the first active material and / or the second active material.

[0032] In some embodiments, the compaction density of the negative electrode film layer is 1.20 g / cm 3 - 1.70 g / cm 3 , optionally 1.25 g / cm 3 - 1.65 g / cm 3 . This is beneficial for the negative electrode film layer to balance high capacity, high active ion and electron transport performance, and thus beneficial for the secondary battery to balance high energy density and good cycling performance and kinetic performance.

[0033] In some embodiments, the areal density of the negative electrode film layer is 5.0 mg / cm 2 - 25.0 mg / cm2 , optionally 5.5 mg / cm 2 -22.5 mg / cm 2 . This is conducive to the negative electrode film layer taking into account high capacity, high active ion and electron transport performance, and further conducive to the secondary battery taking into account high energy density as well as good cycle performance and kinetic performance.

[0034] In some embodiments, the thickness of the negative electrode film layer is 40 μm - 120 μm, optionally 45 μm - 100 μm.

[0035] The second aspect of the present application provides an electrical device, which includes the secondary battery of the first aspect of the present application.

[0036] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the drawings.

[0038] Figure 1 is a schematic diagram of an embodiment of the negative electrode plate of the present application.

[0039] Figure 2 is a schematic diagram of another embodiment of the negative electrode plate of the present application.

[0040] Figure 3 is a schematic diagram of yet another embodiment of the negative electrode plate of the present application.

[0041] Figure 4 is a scanning electron microscope (SEM) image of an embodiment of the negative electrode plate of the present application.

[0042] Figure 5 is a schematic diagram of a cross-sectional image of particles of the first carbon-based material of the present application.

[0043] Figure 6 is a schematic diagram of an embodiment of the secondary battery of the present application.

[0044] Figure 7 is an exploded schematic diagram of an embodiment of the secondary battery of the present application.

[0045] Figure 8 is a schematic diagram of an embodiment of the battery module of the present application.

[0046] Figure 9It is a schematic diagram of an embodiment of the battery pack of the present application.

[0047] Figure 10 is Figure 9 An exploded schematic diagram of the shown embodiment of the battery pack.

[0048] Figure 11 It is a schematic diagram of an embodiment of an electrical device using the secondary battery of the present application as a power source.

[0049] In the drawings, the drawings are not necessarily drawn to actual scale. The reference numerals are explained as follows: 1 battery pack, 2 upper box body, 3 lower box body, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 10 negative electrode tab, 101 negative 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 external region, 202 internal region. Detailed Description of Specific Embodiments

[0050] Hereinafter, embodiments of the secondary battery and the electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily long 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 application and are not intended to limit the subject matter recited in the claims.

[0051] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] If there is no special instruction, all embodiments and alternative embodiments of this application can be combined with each other to form new technical solutions.

[0053] If there is no special instruction, all technical features and alternative technical features of this application can be combined with each other to form new technical solutions.

[0054] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0055] If there is no special instruction, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0056] If there is no special instruction, the numerical values of the various parameters mentioned in this application can be measured using various common testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0057] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0058] In this application, the terms "a plurality of" and "a variety of" mean two or more.

[0059] The inventors have found that the key to improving the kinetic performance of a secondary battery, especially the fast charging performance, lies in improving the kinetic performance of the negative electrode. At present, most methods for improving the kinetic performance of the negative electrode are to reduce the areal density or the compaction density of the negative electrode film layer. However, a large number of studies have shown that the above methods for improving the kinetics of the negative electrode only improve the kinetic performance at the initial stage of battery charging to a certain extent, and have no obvious effect on improving the kinetic performance at the end stage of battery charging, resulting in the ineffective improvement of the kinetic performance of the secondary battery, and even making it impossible to actually perform high-rate charging on the secondary battery. In addition, the energy density of the secondary battery will also be significantly reduced.

[0060] When improving the energy density of a secondary battery by, for example, increasing the compaction density of the negative electrode film layer, it often leads to the deterioration of the kinetic performance and the cycling performance of the secondary battery.

[0061] Therefore, it is difficult for current secondary batteries to balance high energy density, good cycling performance and kinetic performance.

[0062] In view of the above situation, a first aspect of this application provides a secondary battery.

[0063] This application does not particularly limit the type of secondary battery. For example, the secondary battery can be a lithium-ion battery, etc. Generally, the 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 intercalate and deintercalate 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. This application does not particularly limit the type of the electrolyte, which 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 solution). In a secondary battery using an electrolyte solution and some secondary batteries using a solid electrolyte, a separator can also be included, and the separator is disposed between the positive electrode plate and the negative electrode plate to play a role in isolation.

[0064] [Negative electrode plate]

[0065] Figures 1 to 3 is a schematic diagram of an embodiment of the negative electrode plate of this application. As Figures 1 to 3As shown, the negative electrode plate 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 far from the negative electrode current collector 101 and a second surface 102b oppositely arranged with respect to the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H. The region within the thickness range from the second surface 102b of the negative electrode film layer to 0.3H is denoted as the first region 1021 of the negative electrode film layer. The region within the thickness range from the first surface 102a of the negative electrode film layer to 0.3H is denoted as the second region 1022 of the negative electrode film layer. The first region 1021 includes a first active material, the first active material includes a first 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 the region formed by extending 2.5 μm from the particle surface of the first carbon-based material towards the particle interior. In the cross-sectional view of the first carbon-based material, the total pore area of the external region is denoted as S1, and the total pore area of the internal region is denoted as S2, and S2 > S1. The second region 1022 includes a second active material, the second active material includes a second carbon-based material, and the second carbon-based material contains an amorphous carbon material. The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer on one side of the negative electrode current collector.

[0066] In this application, the "internal region" refers to the region in the material particles other than the external region.

[0067] In this application, 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 external region of the first carbon-based material is denser than that of the internal region), and making the second region of the negative electrode film layer include an amorphous carbon material, the synergistic effect advantage between the first carbon-based material and the second carbon-based material can be fully exerted. Thus, the negative electrode plate provided by this application can have a good pore structure, and at the same time has a high tap density and low volume change, enabling the secondary battery to take into account good kinetic performance and cycling performance on the premise of having a high energy density.

[0068] The inventors found in in-depth research that for amorphous carbon materials, their layer spacing is relatively large, which is conducive to the rapid insertion and extraction of active ions, and has a higher lithium potential, which is beneficial to improving the kinetic performance of the battery. However, the particles of amorphous carbon materials are harder and have more edges and corners, with a low tap density, poor bonding ability with the current collector, and are prone to film peeling. Usually, more binder is required to reduce the risk of film peeling, but at the same time, it also reduces the mass ratio of the active material. Moreover, the compaction density of amorphous carbon is also relatively low, resulting in a low energy density of the battery.

[0069] In the present application, the negative electrode film layer is set in 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 far 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 proportion 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 application 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 internal region is large and / or the pore size is large, while the number of pores in the external region is small and / or the pore size is small. 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 change, 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 the formation of the SEI film 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 respectively located in the first area and the second area, which can achieve a good pore structure distribution and is also beneficial to improving the charging performance of the battery.

[0070] In the present application, 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 sheet. As an example, the test method can be: cutting the negative electrode plate into a sample to be tested of a certain size (for example, 2cm×2cm), fixing the negative electrode plate 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 produced by Japan's JEOL company) and performing vacuuming (for example, 10-4Pa), setting the argon gas flow rate (for example, 0.15MPa) and voltage (for example, 8KV) and polishing time (for example, 2h), 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 plate 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 4It is a scanning electron microscope (SEM) image of an embodiment of the negative electrode sheet of the present application. As can be seen from the figure, in the first region of the negative electrode film layer, the first carbon-based material with obvious pore structure inside the particles and no sharp corners; in the second region of the negative electrode film layer, the second carbon-based material is amorphous carbon with more sharp corners.

[0071] 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, and 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 coexist with 3R-phase crystalline carbon and 2H-phase crystalline carbon and satisfying I 3R(101) / I 2H(004) ≤0.1, there can be more active sites on the surface of the carbon-based material particles, which can accelerate the transport of active ions; at the same time, the surface stability of the carbon-based material particles is relatively high, thereby effectively reducing surface side reactions, reducing the consumption of active ions, and being beneficial to improving the kinetic performance and cycling performance of the secondary battery.

[0072] In some embodiments, the true density of the second carbon-based material is less than that of the first carbon-based material. This is beneficial to having 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, and thus improving the kinetic performance and / or cycling performance of the secondary battery.

[0073] 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 larger powder compaction density of the first carbon-based material is beneficial to improving the compaction density of the negative electrode film layer and the energy density of the secondary battery. The smaller powder compaction density of the second carbon-based material is beneficial to increasing the porosity of the electrode sheet and the insertion / extraction of active ions, and thus 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 that of the second carbon-based material, it is beneficial for the secondary battery to have both high energy density and good kinetic performance.

[0074] In some embodiments, the first carbon-based material and / or the second carbon-based material includes one or more pore structures with a pore area greater than or equal to 0.15 μm 2 optionally including one or more pore areas of 0.15 μm 2 -2.0 μm 2The pore structure. 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 change in its particle volume, thereby further reducing the risk of new interfaces generated by particle fragmentation, further reducing the occurrence of side reactions, and improving the cycle performance of the secondary battery.

[0075] 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, 3.0 ≤ S2 / S1 ≤ 100. The inventors further found in the study that when S2 / S1 also satisfies the above range, the secondary battery can better balance high energy density and good cycle performance.

[0076] In the present application, 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 the cross-sectional image of the first carbon-based material.

[0077] Figure 5 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 200 of the present application. As Figure 5 shown, the region formed by extending a distance of 2.5 μm from the particle surface of the first carbon-based material 200 towards the particle interior is the outer region 201, and the region inside the outer region 201 is the inner region 202.

[0078] In this application, for the pore area, S1, and S2 values of the first carbon-based material, a cross-section of the first carbon-based material can be obtained using a cross-section polishing instrument (such as the IB-09010CP type argon ion cross-section polishing instrument from JEOL, Japan); then, referring to JY / T 010-1996, the cross-section of the first carbon-based material is scanned using a scanning electron microscope (such as the Sigma300 type scanning electron microscope from ZEISS, Germany); finally, through an image processing software (such as AVIZO), the pore area of any one pore in the first carbon-based material, the total pore area S2 of the internal region, and the total pore area S1 of the external region are obtained respectively, and the value of S2 / S1 is thereby obtained. Exemplarily, samples can be obtained from different regions 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 samples to obtain cross-sections using a cross-section polishing instrument, and at least 10 particles (such as 10, 20, 50, or even more particles) of cross-sections are randomly selected from the images of the scanning electron microscope of each cross-section. According to the above definitions, the total pore area S2' of the internal region and the total pore area S1' of the external region of each particle cross-section are obtained using image processing software, and the value of S2' / S1' of each particle cross-section is thereby obtained. Calculate the arithmetic mean of S2' / S1' of all measured particle cross-sections as the S2 / S1 value of the first carbon-based material.

[0079] In some embodiments, the area of the pore structure in the external region of the first carbon-based material is less than or equal to 0.15 μm 2 , and can be optionally less than or equal to 0.10 μm 2 . The inventors also found in further research that by controlling the area of the pore structure in the external region of the first carbon-based material within the above range, the external 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 as much as possible avoiding the penetration of the electrolyte into the pore structure inside the first carbon-based material particles, and further effectively improving the cycle performance and kinetic performance of the secondary battery. Of course, this application does not intend to limit that the area of all pore structures in the external region of the first carbon-based material is less than or equal to 0.15 μm 2 , for example, the area of more than 95%, and optionally more than 99% of the pore structures can be controlled to be less than or equal to 0.15 μm 2 .

[0080] In some embodiments, the internal region of the first carbon-based material includes more than one pore structure with an area greater than or equal to 0.15 μm 2 , and optionally includes more than one pore structure with an area of 0.15 μm 2 - 2.0 μm 2The pore structure. The inventors further found in their research that by making the internal region of the first carbon-based material include the pore structure of the above size, on the one hand, the rolling pressure of the negative electrode sheet can be effectively reduced, particle damage can be effectively reduced, and sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, reducing the risk of particle breakage of the first carbon-based material. On the other hand, 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.

[0081] The inventors further found in their research that when the first carbon-based material meets the above design and further meets one or more of the following conditions, the performance of the secondary battery can be further improved, such as improving at least one of the energy density, kinetic performance, and cycle performance of the secondary battery.

[0082] In some embodiments, 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. Thus, it is beneficial to improve the kinetic performance of the secondary battery.

[0083] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27 g / cm 3 , optionally 2.23 g / cm 3 -2.26 g / cm 3 . When the true density of the first carbon-based material is within the above range, the energy density of the secondary battery can be further improved.

[0084] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20,000 N is 1.65 g / cm 3 -2.0 g / cm 3 , optionally 1.68 g / cm 3 -1.98 g / cm 3 . By making the first carbon-based material have a large 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 beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance, improving the wetting and retention characteristics of the negative electrode film layer for the electrolyte, and further improving the kinetic performance and cycle performance of the secondary battery.

[0085] In some embodiments, the specific surface area of the first carbon-based material is ≤2.8 m 2 / g, optionally 1.1 m 2 / g - 2.7 m 2 / g. 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, reduce the consumption of active ions by SEI film formation, and further enable the secondary battery to balance high first Coulomb efficiency and good cycle performance.

[0086] In some embodiments, the volume-based particle size distribution Dv50 of the first carbon-based material is 8.0 μm - 25.0 μm, and may be optionally 10.0 μm - 22.0 μm. In some embodiments, the volume-based particle size distribution Dv90 of the first carbon-based material is 16.0 μm - 45.0 μm, and may be optionally 16.5 μm - 42.0 μm.

[0087] By making the volume-based particle size distribution Dv50 and / or Dv90 of the first carbon-based material within the above ranges, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. Additionally, it can 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.

[0088] 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 may be optionally 0.90 - 1.40. By making the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material within the above ranges, its particle packing performance is good, which is beneficial to improve the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; additionally, it is beneficial to adjust the pore distribution of the negative electrode film layer, improve the transport performance of active ions and electrons, and improve the wetting and retention characteristics of the negative electrode film layer to the electrolyte, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0089] In some embodiments, the specific capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and may be optionally 355 mAh / g - 370 mAh / g. When the specific capacity of the first carbon-based material is within the above ranges, the energy density of the secondary battery is further improved.

[0090] In some embodiments, the second carbon-based material is at least one of soft carbon and hard carbon.

[0091] In some embodiments, the true density of the second carbon-based material is 1.95 g / cm 3 - 2.22 g / cm 3 and may be optionally 1.97 g / cm 3 - 2.21 g / cm 3 ; by making the second carbon-based material have a smaller true density, it is possible to make the electrode sheet have a suitable pore structure, improve the transport performance of active ions, and further improve the kinetics and cycle performance of the secondary battery.

[0092] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 20000 N is 0.85 g / cm 3 - 1.35 g / cm 3, optionally 0.90 g / cm 3 -1.30 g / cm 3 . By making the second carbon-based material have a smaller powder compaction density, the electrode sheet can have a suitable pore structure, improve the transport performance of active ions, and further improve the kinetics and cycling performance of the secondary battery.

[0093] In some embodiments, the specific surface area of the second carbon-based material is greater than or equal to 1.5 m 2 / g, optionally 1.9 m 2 / g - 7.5 m 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.

[0094] 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 transport performance of active ions and electrons can be further improved, thereby further improving the kinetic performance of the secondary battery.

[0095] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, 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 kinetic performance of the secondary battery.

[0096] In some embodiments, the tapped density of the second carbon-based material is 0.80 g / cm 3 -1.20 g / cm 3 , optionally 0.83 g / cm 3 -1.15 g / cm 3 . By making the tapped density of the second carbon-based material within the above range, a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the transport performance of active ions and electrons, and improving the infiltration and retention characteristics of the negative electrode film layer for the electrolyte, thereby improving the kinetic performance and cycling performance of the secondary battery.

[0097] In some embodiments, the specific capacity of the second carbon-based material is 330 mAh / g - 480 mAh / g, optionally 340 mAh / g - 470 mAh / g. By adjusting the discharge specific capacity of the second carbon-based material within the above range, the energy density of the secondary battery can be further improved.

[0098] In some embodiments, the first carbon-based material and / or the second carbon-based material includes primary particles. Optionally, the proportion 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 proportion 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 high structural stability, reduce the occurrence of side reactions, and further improve the cycling performance of the secondary battery.

[0099] 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 optionally 90% to 98.5%, for example, it can be 81%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98%; the mass proportion of the second carbon-based material in the second region is greater than or equal to 80%, and can be optionally 90% to 98.5%, for example, it can be 81%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98%. When the contents of the first carbon-based material and the second carbon-based material are respectively within the above ranges, the secondary battery has good kinetic performance and cycling performance while having a high energy density.

[0100] As Figures 1 to 3 shown, the negative electrode film layer 102 further includes an intermediate 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).

[0101] In some embodiments, the intermediate region includes the first active material and / or the second active material. For example, as Figure 2 shown, the intermediate region 1023 may have the same composition as the first region 1021. Thus, the distribution region of the first active material in the thickness direction of the negative electrode film layer 102 is within the thickness range from the second surface 102b of the negative electrode film layer to 0.7H; or, as Figure 3 shown, the intermediate region 1023 may have the same composition as the second region 1022. Thus, the distribution region of the second active material in the thickness direction of the negative electrode film layer 102 is within the thickness range from the first surface 102a of the negative electrode film layer to 0.7H; or, as Figure 1As shown, the intermediate region 1023 includes both the first active material and the second active material. At this time, the intermediate region 1023 includes both a layer structure with the first active material and a layer structure with the second active material. The above two layer structures may also have a layer interface (the layer interface can be confirmed by using a cross-section polishing instrument to distinguish the first carbon-based material and the second carbon-based material).

[0102] 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 above-mentioned first carbon-based material. For example, it may further include a silicon-based material. The silicon-based material can play a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and retention of the electrolyte, and enhancing the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further enhancing 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 material.

[0103] In some embodiments, when the first region of the negative electrode film layer further includes a silicon-based material, the mass ratio of the silicon-based material in the first region of the negative electrode film layer may be ≤ 30%, for example, it may be 1% - 8%, 2% - 6%, or 13% - 17%. Thereby, while enhancing the kinetic performance and energy density of the secondary battery, the secondary battery can also have good cycle performance.

[0104] 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 above-mentioned second carbon-based material. For example, it may further include a silicon-based material. The relatively high lithium intercalation potential of the silicon-based material is beneficial to enhancing the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further enhancing 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 material.

[0105] In some embodiments, when the second region of the negative electrode film layer further includes a silicon-based material, the mass ratio of the silicon-based material in the second region of the negative electrode film layer may be ≤ 30%, for example, it may be 1% - 8%, 2% - 6%, or 13% - 17%. Thereby, while enhancing the kinetic performance and energy density of the secondary battery, the secondary battery can also have good cycle performance.

[0106] In some embodiments, both the first region and the second region include a silicon-based material, and the mass ratio of the silicon-based material in the first region is less than or equal to the mass ratio 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 intercalation potential, which is beneficial to improving the kinetic performance of the secondary battery. Additionally, 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.

[0107] In some embodiments, the intermediate region of the negative electrode film layer further includes a silicon-based material.

[0108] In some embodiments, the first region, the second region, and the intermediate region of the negative electrode film layer may further optionally include a negative electrode conductive agent and / or a negative electrode binder.

[0109] The present application does not particularly limit 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.

[0110] The present application does not particularly limit 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, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0111] In some embodiments, the first region, the second region, and the intermediate region of the negative electrode film layer may further optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0112] In some embodiments, the tap density of the negative electrode film layer is 1.20 g / cm 3 -1.70 g / cm 3 , and may be optionally 1.25 g / cm 3 -1.65 g / cm 3 . This is beneficial for the negative electrode film layer to balance high capacity, good active ion and electron transport performance, and thus beneficial for the secondary battery to balance high energy density, good cycle performance, and kinetic performance.

[0113] In some embodiments, the areal density of the negative electrode film layer is 5.0 mg / cm 2 -25.0 mg / cm 2 , and may be optionally 5.5 mg / cm2 -22.5 mg / cm 2 This is conducive to the negative electrode film layer taking into account high capacity, good active ion and electron transport performance, and further conducive to the secondary battery taking into account high energy density as well as good cycle performance and kinetic performance.

[0114] In some embodiments, the thickness of the negative electrode film layer is 40 μm - 120 μm, and optionally 45 μm - 100 μm.

[0115] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, copper foil can be used. The composite current collector can 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 can 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 can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0116] The negative electrode plate does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application further includes a conductive bottom coating (for example, 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 application further includes a protective layer covering the surface of the negative electrode film layer.

[0117] The negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector. It should be noted that each parameter of the negative electrode film layer given in the present application (such as compaction density, areal density, porosity, OI value, thickness, etc.) refers to the parameter of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, the parameter of the negative electrode film layer on any one side satisfies the present application, and it is considered to fall within the protection scope of the present application.

[0118] In the present application, whether there is a carbon coating layer on the surface of a material (such as the first carbon-based material, the second carbon-based material, etc.) can be judged by a transmission electron microscope.

[0119] In the present application, I 3R(101) / I 2H(004) can be tested by X-ray diffraction analysis, and the specific test method can be referred to in the examples.

[0120] In this application, the specific surface area of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T 19587-2017, and the nitrogen adsorption specific surface area analysis test method can be used for testing, and the BET (Brunauer Emmett Teller) method can be used for calculation. The test instrument can be the Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Corporation, USA.

[0121] In this application, the volume distribution particle sizes Dv10, Dv50, and Dv90 of the material (such as the first carbon-based material, the second carbon-based material, etc.) have the meaning well-known in the art, which respectively represent the particle sizes corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T19077-2016, and a laser particle size analyzer can be used for measurement. The test instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Limited, UK.

[0122] In this application, the true density of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be measured by instruments and methods known in the art. Referring to the reference standard GB / T24586-2009, the exemplary test method is as follows: Place a clean and dry sample cup on the balance and zero it. Add the powder sample into the sample cup, about occupying 1 / 2 of the volume of the sample cup, and record the sample mass. Place the sample cup with the sample in the true density tester, seal the test system, introduce helium gas according to the procedure, detect the pressures of the gases in the sample chamber and the expansion chamber, and then calculate the true volume according to Boyle's law (PV = nRT), so as to calculate the true density. The volume of the test sample cup: 3.5 cm 3 , and the analysis gas: helium. In this application, the bulk density of the powder of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T24533-2009, and it can be measured by an electronic pressure testing machine (such as the UTM7305 type electronic pressure testing machine). The exemplary test method is as follows: Weigh 1 g of the sample powder, add it into a mold with a bottom area of 1.327 cm2, apply pressure up to 2000 kg, keep the pressure for 30 s, then release the pressure, keep it for 10 s, and then record and calculate to obtain the bulk density of the powder of the material under a pressure of 20000 N.

[0123] In this application, the tapped density of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be measured by the instruments and methods known in the art. For example, reference can be made to GB / T 5162-2006 and a powder tapped density tester can be used for measurement. The test instrument can be BT-301 of Dandong BETTER, and the test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration times 5000 times, measuring cylinder 25 mL.

[0124] In this application, the specific capacity of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be tested by the methods known in the art. An exemplary test method is as follows: Mix the sample powder with conductive agent carbon black (Super P) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 with solvent N-methylpyrrolidone (NMP) to make a slurry; coat the prepared slurry on the surface of the negative electrode current collector copper foil, dry it in an oven and set aside; Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve LiPF 6 in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then use a lithium metal sheet as the counter electrode, a polyethylene (PE) film as the separator, and assemble it with the above electrolyte into a CR2430 type button cell in a glove box under argon protection; After the obtained button cell is left standing for 12 h, at 25 °C, it is discharged at a constant current of 0.05 C to 0.005 V, left standing for 10 minutes, discharged at a constant current of 50 μA to 0.005 V, left standing for 10 minutes, and discharged at a constant current of 10 μA to 0.005 V; Then it is charged at a constant current of 0.1 C to 2 V, and the charging capacity is recorded. The ratio of the charging capacity to the sample mass is the specific capacity of the corresponding material.

[0125] In this application, the primary particle has the meaning well-known in the art. A primary particle refers to a non-agglomerated particle. An agglomerated particle formed by the aggregation of two or more primary particles is a secondary particle. The primary particles and secondary particles can be distinguished by using a scanning electron microscope (SEM) image.

[0126] In this application, the areal density of the negative electrode film layer has the meaning well-known in the art and can be tested by the methods known in the art. For example, a single-sided coated and cold-pressed negative electrode sheet (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first) can be taken, punched into small round pieces with an area of S1, weighed, and recorded as M1. Then wipe off the negative electrode film layer of the above weighed negative electrode sheet and weigh the weight of the negative electrode current collector, recorded as M0. The areal density of the negative electrode sheet = (M1 - M0) / S1.

[0127] In this application, the tap density of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art. The tap density of the negative electrode film layer = the areal density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100 type with an accuracy of 0.1 μm).

[0128] It should be noted that for the various parameter tests of the first active material, the second active material or the negative electrode film layer, samples can be taken from the prepared secondary battery for testing according to the following steps.

[0129] Discharge the secondary battery (for safety reasons, generally make the secondary battery in a fully discharged state); disassemble the secondary battery and take out the negative electrode plate, soak the negative electrode plate in dimethyl carbonate for a certain period of time (e.g., 2 h - 10 h); then take out the negative electrode plate and dry it at a certain temperature and for a certain time (e.g., 60 °C, for more than 4 h), and take out the negative electrode plate after drying. At this time, samples can be taken from the dried negative electrode plate to test the above-mentioned parameters related to the negative electrode film layer, such as the areal density, tap density, thickness, etc. of the negative electrode film layer.

[0130] Bake the dried negative electrode plate at a certain temperature and for a certain time (e.g., 400 °C, for more than 2 h), select an area at random in the baked negative electrode plate, first take a sample of the second active material (blade scraping for powder sampling can be used), and the sampling position is the second area of the negative electrode film layer; then take a sample of the first active material in the same way, and the sampling position is the first area of the negative electrode film layer; sieve the collected first active material and second active material respectively (e.g., sieve with a 200-mesh sieve), and finally obtain samples of the first active material and the second active material that can be used to test the above-mentioned material parameters of this application.

[0131] [Preparation method of negative electrode plate]

[0132] This application also provides a method for preparing the negative electrode plate of this application. The method includes the following steps: providing a first slurry containing a first active material and a second slurry containing a second active material; coating the first slurry on the negative electrode current collector, coating the second slurry on the first slurry, and obtaining the negative electrode plate after drying and cold pressing.

[0133] In some embodiments, the first active material and optional conductive agent, optional binder and other optional additives can be dispersed in a solvent (e.g., deionized water) to form the first slurry.

[0134] In some embodiments, the second active material and optional conductive agent, optional binder and other optional additives can be dispersed in a solvent (e.g., deionized water) to form the second slurry.

[0135] In some embodiments, the first active material includes a first carbon-based material.

[0136] In some embodiments, the second active material includes a second carbon-based material.

[0137] In some embodiments, the first slurry and / or the second slurry further includes a silicon-based material.

[0138] The first slurry and the second slurry can be coated simultaneously at one time, or can be coated in two times. In some embodiments, the first slurry and the second slurry are coated simultaneously at one time. Coating simultaneously at one time can reduce the resistance of the negative electrode film layer, thereby further improving the kinetic performance and cycling performance of the secondary battery.

[0139] The coating weights of the first slurry and the second slurry can be adjusted according to the actual situation.

[0140] In the present application, the above-mentioned first active material, second active material, etc. can be obtained by commercial purchase, or can be obtained by the method as follows in the present application.

[0141] In some embodiments, the preparation method of the first carbon-based material includes: Step 1, providing a raw material with a plurality of pore structures; Step 2, mixing the raw material and a filling material evenly according to a predetermined ratio, then keeping warm at a first temperature T1 for a first time t1, and cooling to room temperature after completion to obtain an intermediate; Step 3, keeping the obtained intermediate warm at a second temperature T2 for a second time t2, and obtaining the first carbon-based material after completion.

[0142] In some embodiments, in Step 1, the raw material for preparing the first carbon-based material includes natural graphite. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0143] "Natural spherical graphite" refers to natural graphite having 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 the required particle size and morphology can be obtained by pretreating flake graphite. Optionally, the pretreatment includes processes such as crushing, classification, spheroidization, and purification.

[0144] In some embodiments, in Step 1, the morphology of the raw material includes one or more of spherical or quasi-spherical.

[0145] 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 beneficial for preparing the first carbon-based material with the desired volume distribution particle size.

[0146] In some embodiments, in step 1, the specific surface area of the raw material may be ≥ 2.5 m 2 / g, and may be optionally 2.5 m 2 / g - 10.0 m 2 / g. When the specific surface area of the raw material is within the above range, it is beneficial for subsequent filling treatment and obtaining the first carbon-based material with the desired specific surface area. It is also beneficial for the first carbon-based material to have both high capacity and high initial Coulomb efficiency. In addition, it is beneficial for the first carbon-based material to have better kinetic performance.

[0147] By adjusting the particle size of the raw material (such as volume distribution particle size Dv50 and / or specific surface area) within the above range, it is also possible to minimize the agglomeration of the raw material during subsequent preparation, thereby minimizing problems such as an increase in surface defects and an increase in surface active sites caused by particle breakage.

[0148] 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) Within a suitable range, the lower the softening point temperature, the larger I 3R(101) / I 2H(004) ; it is also beneficial to adjust the pore size and / or pore number in the external and internal regions of the carbon material within a suitable range.

[0149] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filling material is less than or equal to 6 μm, and may be optionally 1 μm - 6 μm, 1 μm - 5 μm, 2 μm - 5 μm, 3 μm - 5 μm. This is beneficial for the filling material to melt and fill into the pore structure of the raw material after heating, and is also beneficial for improving the dispersion uniformity of the filling material and the raw material.

[0150] In some embodiments, in step 2, the coking value of the filling material is 19% - 47%, and may be optionally 22% - 40%. When the coking value of the filling material is within the above range, it is beneficial to adjust I 3R(101) / I 2H(004)Within a suitable range, the smaller the coking value, the larger the I 3R(101) / I 2H(004) is. 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. In this application, the coking value of the filling material has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, it can be measured with reference to GB / T 8727-2008.

[0151] In some embodiments, in step 2, the filling material includes one or more of coal tar pitch, petroleum pitch, high molecular compounds, and resins, and may be optionally one or more of coal tar pitch and petroleum pitch.

[0152] In some embodiments, in step 2, the mass ratio of the filling material to the raw material is (10-32):100, and may be optionally (12-30):100, (14-28):100, (15-25):100. (10-40):100, and may be 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) Within a suitable range, the larger the mass ratio of the filling material, the larger the I 3R(101) / I 2H(004) is. 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.

[0153] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, addition amount, etc. of the filling material within the above range, it is beneficial to adjust the pore number and / or pore size in the outer region and the inner region of the first carbon-based material within a suitable range, and it is beneficial to adjust S2 / S1 and I 3R(101) / I 2H(004) within a suitable range.

[0154] By adjusting the parameters such as the type, softening point, coking value, addition amount, etc. of the filling material within the above range, after the filling material is heated and melted, the viscosity is not high, it maintains good fluidity, and at the same time it is not easy to bond the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process. Thus, it can also reduce problems such as an increase in surface defects and an increase in surface active sites of the first carbon-based material particles due to the need to increase the depolymerization process.

[0155] In some embodiments, in step 2, the heating process of heating the raw material and the filling material to the first temperature T1 after mixing them evenly in a predetermined ratio is a staged heating process.

[0156] In some embodiments, the stepwise heating process includes a first heating process, a second heating process, and a third heating process.

[0157] In some embodiments, the first heating process is to heat to 200°C - 250°C and hold at this temperature for 0.5 h - 3 h.

[0158] In some embodiments, the second heating process is to heat to 450°C - 550°C and hold at this temperature for 0 h - 2 h. When the holding time is 0 h, it means that when heating to the range of 450°C - 550°C, no heat preservation treatment is carried out, but continue to heat to the first temperature T1.

[0159] In some embodiments, the third heating process is to heat to the first temperature T1 and hold at this temperature for the first time t1.

[0160] During the stepwise heating process, first heat to 200°C - 250°C. Since the heating temperature is higher than the softening point temperature of the filling material, at this time, the filling material is heated and melted and softened. Holding for 0.5 h - 3 h can make it flow and fill into the pore structure of the raw material; then heat to 450°C - 550°C. At this time, the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state, becoming a viscous liquid or solid, thereby preventing the filling material from entering all the pore structures of the raw material; finally heat to the first temperature. At this time, the filling material undergoes a carbonization reaction, thereby enabling the pore structures occupied by the filling material to be effectively filled.

[0161] In some embodiments, in step 2, heat 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 composed of the above values. Optionally, 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

[0162] In some embodiments, the heating rate of the first heating process can 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, 2°C / min - 5°C / min.

[0163] In some embodiments, the heating rate of the second heating process can be 1°C / min - 10°C / min, optionally 2°C / min - 8°C / min.

[0164] 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.

[0165] In some embodiments, in step 2, the first temperature T1 is 700 °C - 1200 °C. For example, the first temperature T1 may be 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1200 °C or any range composed of the above values. Optionally, the first temperature T1 is 750 °C - 1100 °C, 800 °C - 1100 °C, 850 °C - 1000 °C.

[0166] In some embodiments, in step 2, the first time t1 is 1 h - 5 h. For example, the first time t1 may be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h or any range composed of the above values. Optionally, the first time t1 is 2 h - 4 h.

[0167] In some embodiments, in step 2, the heat treatment can be carried out in equipment capable of programmed heating such as intermediate frequency furnaces, roller kilns, rotary kilns, pusher kilns, vertical granulation kettles, horizontal granulation kettles, vertical reaction kettles, horizontal reaction kettles or drum furnaces.

[0168] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0169] 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 ranges, it is beneficial to adjust the number and / or size of pores in the outer and inner regions of the first carbon-based material within a suitable range, and it is beneficial to adjust S2 / S1 of the first carbon-based material within a suitable range.

[0170] 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.

[0171] In some embodiments, in step 3, the second time t2 is 1.5 h - 6 h. For example, the second time t1 can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h or any range composed of the above values. Optionally, the second time t2 is 2 h - 5 h.

[0172] In some embodiments, in step 3, the heat treatment can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace or an internal series graphitization furnace.

[0173] In some embodiments, in step 3, the atmosphere of the intermediate frequency furnace and the continuous graphitization heat treatment can be a protective gas atmosphere. The protective gas can include one or more of nitrogen, argon, and helium.

[0174] In step 3, by adjusting one or more of the second temperature and the second time within the above ranges, it is beneficial to adjust the content of disordered carbon in the first carbon-based material within a suitable range, and it is beneficial for the first carbon-based material to have a suitable graphitization degree, interlayer spacing, etc.

[0175] In the above method for preparing the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above ranges, it is beneficial to adjust S2 / S1, I 3R(101) / I 2H(004) , specific capacity, specific surface area, particle size, true density, powder compacted density, tapped density and other parameters of the first carbon-based material.

[0176] [Positive electrode plate]

[0177] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0178] The positive electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil can be used. The composite current collector can 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 can 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 can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0179] The positive electrode film layer generally includes a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually 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 can 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 fluorinated 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.

[0180] The positive electrode active material can be a positive electrode active material for secondary batteries known in the art.

[0181] When the secondary battery of the present application 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, 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.

[0182] 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.

[0183] In some embodiments, as an example, the positive electrode active material for the lithium-ion battery may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 and LiMnPO 4 One or more of the above.

[0184] In this application, the modified compound of each of the above cathode active materials may be doping modification and / or surface coating modification of the cathode active material.

[0185] [Electrolyte]

[0186] In some embodiments, the electrolyte uses an electrolytic solution, and the electrolytic solution includes an electrolyte salt and a solvent.

[0187] The type of the electrolyte salt is not specifically limited and can be selected according to actual needs.

[0188] When the secondary battery of this application is a lithium-ion battery, by way of example, the electrolyte salt may include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP) one or more of them.

[0189] The type of the solvent is not particularly limited and can be selected according to actual needs. In some embodiments, by way of example, the solvent may include one or more of 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).

[0190] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives that can improve certain performance of the secondary battery, such as additives for improving the overcharge performance of the secondary battery, additives for improving the high-temperature performance of the secondary battery, additives for improving the low-temperature power performance of the secondary battery, and the like.

[0191] [Separator membrane]

[0192] This application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0193] In some embodiments, the material of the separator membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane may be a single-layer thin film or a multi-layer composite thin film. When the separator membrane is a multi-layer composite thin film, the materials of each layer may be the same or different.

[0194] In some embodiments, the positive electrode sheet, the separator membrane, and the negative electrode sheet may be made into an electrode assembly by a winding process or a stacking process.

[0195] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0196] In some embodiments, the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0197] The shape of the secondary battery in this application is not particularly limited, and it can be cylindrical, square, or any other shape. For example, Figure 6 is a secondary battery 5 with a square structure as an example.

[0198] In some embodiments, for example, Figure 7 as shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, which can be adjusted according to requirements.

[0199] The preparation method of the secondary battery in this application is well-known. In some embodiments, the positive electrode plate, the separator, the negative electrode plate, and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode plate, the separator, and the negative electrode plate can be formed into an electrode assembly through a winding process or a stacking process, the electrode assembly is placed in the outer package, dried and then injected with the electrolyte, and after processes such as vacuum packaging, standing, forming, and shaping, a secondary battery is obtained.

[0200] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0201] Figure 8 is a schematic diagram of a battery module 4 as an example. For example, Figure 8 as shown, in the battery module 4, multiple secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the multiple secondary batteries 5 can be fixed by fasteners.

[0202] Optionally, the battery module 4 may further include a housing with a receiving space, and the multiple secondary batteries 5 are accommodated in the receiving space.

[0203] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0204] Figure 9 and Figure 10 are schematic diagrams of a battery pack 1 as an example. For example, Figure 9 and Figure 10As shown in the figure, a battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0205] The present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, tablet computer, laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0206] The electrical device can select a secondary battery, battery module, or battery pack according to its usage requirements.

[0207] Figure 11 It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for high power and high energy density, a battery pack or battery module can be used.

[0208] Another example of an electrical device can be a mobile phone, tablet computer, laptop computer, etc. This electrical device usually requires being thin and light, and a secondary battery can be used as the power source.

[0209] Embodiment

[0210] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the embodiments are commercially available.

[0211]

[0212] Material 1-1

[0213] Step 1, mechanically crush, classify, spheroidize, and purify flake graphite to obtain natural spherical graphite. Step 2, mix the obtained natural spherical graphite with the filler petroleum pitch in a ratio range of 100:20. The softening point of the petroleum pitch is 115 °C and the coking value is 35%. Then, place the mixed material in a programmable temperature-raising device, heat it to 200 °C and keep it warm for 1 h (the first temperature-raising process), then continuously heat it to 700 °C, keep it warm for 2 h, and after cooling to room temperature, obtain an intermediate. Step 3, place the obtained intermediate in a graphitization furnace, perform heat treatment at 2450 °C, and after demagnetization and screening, 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) is 0.025, and the powder compaction density under a pressure of 20000 N is 1.88 g / cm 3 , and the true density is 2.25 g / cm 3 .

[0214] The S2 / S1 of the first carbon-based material is obtained by the following test method.

[0215] Mix the sample preparation binder with the first carbon-based material powder evenly, coat it on the copper foil, dry it at 60 °C for 30 min for standby; cut it into 5 test samples of 6 mm × 6 mm in size at 5 different positions, and paste them on the sample stage of a CP type argon ion cross-section polishing instrument respectively; use a plasma beam to cut the samples to obtain the cross-sections of each sample. The test instrument can be an IB-09010CP type argon ion cross-section polishing instrument of JEOL Company, Japan.

[0216] Use a scanning electron microscope to scan the cross-sections of each sample of the first carbon-based material, and obtain a scanning image by randomly selecting an area in each sample cross-section. The test can refer to JY / T010-1996. The test instrument can be a Sigma 300 type scanning electron microscope of ZEISS Company, Germany.

[0217] Randomly select the cross-sections of 20 particles of the first carbon-based material from the scanning image. The area formed by extending 0.25 μm from the surface of the particles of the first carbon-based material into the particles is denoted as the external area, and the area inside the external area is denoted 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, calculate the value of S2' / S1'; and calculate the arithmetic mean of S2' / S1' of all 20 particles as the S2 / S1 value of the first carbon-based material. The image processing software can be AVIZO.

[0218] Materials 1-2 to 1-7

[0219] The preparation methods of Materials 1-2 to 1-7 are similar to that of Material 1-1, except that the softening point temperature, coking value of the filler material, and the mixing ratio of natural spherical graphite and filler petroleum asphalt are adjusted as shown in Table 1, and the third heating process is adjusted to make the S2 / S1 of the first carbon-based material the value shown in Table 1.

[0220] Table 1

[0221]

[0222] Material 1'-1

[0223] The preparation method of Material 1'-1 is similar to that of Material 1-1, except that it is adjusted as shown in Table 2 to make the S2 / S1 of the first carbon-based material the value shown in Table 2.

[0224] Table 2

[0225]

[0226] Materials 1-8 to 1-12

[0227] The preparation methods of Materials 1-8 to 1-12 are similar to that of Material 1-1, except that the softening point temperature, coking value of the filler material, and the mixing ratio of natural spherical graphite and filler petroleum asphalt are adjusted as shown in Table 3, and the heat treatment temperature is adjusted to make I 3R(101) / I 2H(004 the value shown in Table 3,

[0228] Table 3

[0229]

[0230]

[0231] Using coconut shell as raw material, heat-treating at 600 °C, crushing, pickling with alkali for impurity removal, and then heat-treating at 1000 °C to obtain an amorphous carbon material (hard carbon), whose true density is 2.1 g / cm 3 , and the powder compaction density under 20000 N pressure is 1.05 g / cm 3 .

[0232] Example 1

[0233] Preparation of secondary battery

[0234] 1. Anode electrode sheet: The first carbon-based material (Material 1-1) as the first active material, conductive agent carbon black (SuperP), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are fully stirred and mixed in an appropriate amount of deionized water solvent according to a weight ratio of 96.4:1:1.2:1.4 to form a first slurry. The second carbon-based material as the second active material (see Table 1 for details), conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are fully stirred and mixed in an appropriate amount of deionized water solvent according to a weight ratio of 96.4:1:1.2:1.4 to form a second slurry. Through a double-chamber coating device, the first slurry and the second slurry are simultaneously extruded. The first slurry is coated on the anode current collector copper foil, and the second slurry is coated on the first slurry; after drying and cold pressing, the anode electrode sheet is obtained. The coating weights of the first slurry and the second slurry are the same. The compaction density of the anode film layer is 1.55 g / cc.

[0235] 2. Cathode electrode sheet: Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride are mixed according to a weight ratio of 96:2:2, and an appropriate amount of solvent NMP is added and stirred evenly to obtain a cathode slurry. The cathode slurry is coated on both surfaces of the cathode current collector aluminum foil, and after drying and cold pressing, the cathode electrode sheet is obtained.

[0236] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to 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. Separator: A polyethylene film is used.

[0238] 5. Preparation of secondary battery: The prepared cathode electrode sheet and anode electrode sheet are placed in order, and the separator is placed in the middle of the cathode electrode sheet and the anode electrode sheet to play a separating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, the secondary battery is obtained.

[0239] Examples 2-8

[0240] The battery preparation methods of Examples 2-8 are similar to those of Example 1, and the differences are that: for the first carbon-based material, materials with different S2 / S1 are selected, or for the second carbon-based material, soft carbon is selected. See Table 4 for details.

[0241] Comparative Example 1

[0242] The first carbon-based material as the first active material (see Table 1 for details), conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are fully stirred and mixed in deionized water as the solvent in a weight ratio of 96.4:1:1.2:1.4 to form a first slurry. The first slurry is coated on the negative electrode current collector copper foil, and the coating amount is the same as that of the first slurry in Example 1. After drying and cold pressing, a negative electrode sheet is obtained (the second carbon-based material is not used and there is no second region). Except for this, it is prepared in the same manner as in Example 5 to obtain a secondary battery.

[0243] Comparative Example 2

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

[0245] Comparative Example 3

[0246] Change the coating positions of the first slurry and the second slurry. Coat the second slurry (the second carbon-based material (see Table 5 for details), conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are fully stirred and mixed in deionized water as the solvent in a weight ratio of 95.2:1:1.4:2.4) on the negative electrode current collector copper foil, and coat the first slurry on the second slurry prepared in the example; after drying and cold pressing, a negative electrode sheet is obtained. Except for this, it is prepared in the same manner as in the example to obtain a secondary battery.

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

[0248] Performance Test

[0249] (1) X-ray Diffraction Analysis Test

[0250] The test is carried out using an X-ray diffractometer with reference to JIS K 0131-1996 to obtain the X-ray diffraction pattern of the carbon material. The test conditions are as follows: The carbon material is sampled by the flat sample preparation method, using CuKα ray as the radiation source, a copper target as the anode target, a voltage of 40 KV, a current of 40 mA, an anti-scattering slit of 1 mm, a scanning 2θ angle range of 20°-80°, a step size of 0.01671°, a time of 0.24 s for each step, and a scanning rate of 4° / min. The test instrument can use a Bruker D8 Discover X-ray diffractometer.

[0251] The 2θ of the diffraction peak of the 3R phase 101 crystal plane is in the range of 43° - 44°, the 2θ of the diffraction peak of the 2H phase 004 crystal plane is in the range of 53° - 55°, and the 2θ of the diffraction peak of the 3R phase 012 crystal plane is in the range of 46° - 47°. The peak intensity of the diffraction peak of the 3R phase 101 crystal plane and the peak intensity of the diffraction peak of the 2H phase 004 crystal plane are represented by the integral area of the corresponding diffraction peak.

[0252] (2) Energy density

[0253] At 25°C, the secondary battery is charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V until the current is 0.05C, left standing for 5 minutes, and then discharged at a constant current of 1 / 3C to 2.0V. Record the battery discharge energy at this time. The battery discharge energy divided by the weight of the battery is the weight energy density of the battery, with the unit of Wh / kg. The measurement data are shown in Table 1.

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

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

[0256] Then the secondary battery is charged at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 to 3.65V or the 0V negative electrode cut-off potential (whichever comes first). After each charge is completed, it needs to be discharged at 1C0 to 2.5V. Record the negative electrode potential corresponding to 10%, 20%, 30%, ……, 80% SOC (State of Charge) at different charging rates, and plot the charging rate - negative electrode potential curve at different SOC states. After linear fitting, obtain the charging rate corresponding to the negative electrode potential of 0V at different SOC states. This charging rate is the charging window at this SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC respectively. 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%, calculate the charging time T of the secondary battery from 10% SOC to 80% SOC (on the premise that the secondary battery does not lithium plate out), with the unit of min. The shorter this charging time is, the better the kinetic performance of the secondary battery is.

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

[0258] At 45 °C, the secondary battery prepared above was charged at a constant current of 1C to the upper cut-off voltage of 3.65V (corresponding to 100% SOC), then charged at a constant voltage until the current was 0.05C. After standing for 5 min, the secondary battery was discharged at a constant current of 1C to the lower cut-off voltage of 2.5V (corresponding to 0% SOC), and the discharge capacity at this time was recorded, which was 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 of the first cycle × 100%.

[0260] Table 4

[0261]

[0262] Table 5

[0263]

[0264] As can be seen from Tables 4 and 5, in the examples, by making the first region of the negative electrode film layer include a first carbon-based material with S2 greater than S1, and making the second region of the negative electrode film layer include a second carbon material, amorphous carbon, the advantageous effects between the first carbon-based material and the second carbon-based material can be fully exerted, enabling the negative electrode sheet to have both a high tap density, and at the same time, the negative electrode film layer can also have a reasonable pore distribution, which is beneficial to the transport of active ions. Therefore, the battery can have high energy density while taking into account excellent kinetic performance and cycle performance.

[0265] In Comparative Example 1, the negative electrode film layer only contains the first carbon-based material, and it is impossible to make the battery take into account kinetic performance and cycle performance while having high energy density. In particular, the kinetic performance is poor. In Comparative Examples 2 and 3, S2 / S1 of the first carbon-based material is 0.93, and the external pore structure of the first carbon-based material is not repaired and filled, resulting in poor structural stability and poor cycle performance.

[0266] In addition, in Comparative Example 3, the first region contains amorphous carbon and the second region contains the first carbon-based material. In order to bond the amorphous carbon to the current collector, the content of the binder in the slurry is increased, reducing the mass ratio of the active material, resulting in a decrease in the energy density of the battery and deterioration of the kinetic performance.

[0267] Examples 9 - 13

[0268] Secondary batteries were prepared using the same method as in Example 5, except that Materials 1-8 to Materials 1-12 were used as the first carbon-based material. It should be noted that for the convenience of comparison, the data of Example 5 are also shown in Table 6.

[0269] Table 6

[0270]

[0271] The results in Table 6 above show that by making I of the first carbon-based material 3R(101) / I 2H(004) ≤ 0.1, while the secondary battery has excellent kinetic performance, 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.

[0272] Example 14

[0273] A secondary battery was prepared and performance tested in the same manner as in Example 5, except that the first carbon-based material and the second carbon-based material prepared as follows were used. It should be noted that for the convenience of comparison, the data of Example 5 are also shown in Table 7.

[0274] Preparation of the first carbon-based material: Step 1, the flake graphite was mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite. Step 2, the obtained natural spherical graphite was mixed with the filler petroleum pitch in a ratio range of 100:40. The softening point of the petroleum pitch was 150 °C and the coking value was 40%. Then, the mixed material was placed in a programmable temperature-raising device, heated to 200 °C and held for 1 h (the first temperature-raising process), and then continuously heated to 700 °C and held for 2 h. After cooling to room temperature, an intermediate was obtained. Step 3, the obtained intermediate was placed in a graphitization furnace and heat-treated at 1960 °C. After demagnetization and screening, the first carbon-based material was obtained, and its powder compaction density was 1.30 g / cm 3 .

[0275] Preparation of the second carbon-based material: Using coconut shell as the raw material, it was heat-treated at 600 °C, crushed, and pickled with alkali to remove impurities, and then heat-treated at 1400 °C to obtain an amorphous carbon material (hard carbon), and its powder compaction density was 1.35 g / cm 3 .

[0276] Table 7

[0277]

[0278] As can be seen from Table 7, by making the powder compaction density of the second carbon-based material under a pressure of 20000 N less than that of the first carbon-based material under a pressure of 20000 N, the performance of the secondary battery can be further improved, and the energy density, cycle performance, and kinetic performance are all better improved.

[0279] It should be noted that this application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having the same constitution in essence as the technical idea and achieving the same effects within the scope of the technical solution of this application are all included within the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, as well as other ways constructed by combining some of the constituent elements in the embodiments, are also included within the scope of this application.

Claims

1. A secondary battery, comprising a negative electrode plate, wherein, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface facing away from the negative electrode current collector and a second surface disposed opposite to the first surface, the thickness of the negative electrode film layer is denoted as H, and the region within a thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as the first region of the negative electrode film layer, and the region within a thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as the second region 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, the outer region refers to the region formed by extending a distance of 2.5 μm from the particle surface of the first carbon-based material into the particle interior, in the cross-sectional view of the first carbon-based material, the total pore area of the outer region is denoted as S1, the total pore area of the inner region is denoted as S2, and S2 > S1, the second carbon-based material contains 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 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.

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 20000 N is less than the powder compaction density of the first carbon-based material under a pressure of 20000 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 includes one or more pore structures with a pore area of 0.15 μm or more 2 Optionally, it includes one or more pore structures with a pore area of 0.15 μm 2 -2.0 μm 2 or more.

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 a 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 -2.27 g / cm 3 , optionally 2.23 g / cm 3 -2.26 g / cm 3 ; (2) The powder compaction density of the first carbon-based material under a pressure of 20,000 N is 1.65 g / cm 3 - 2.0 g / cm 3 , and can be optionally 1.68 g / cm 3 - 1.98 g / cm 3 ; (3) The specific surface area of the first carbon-based material is less than or equal to 2.8 m 2 / g, and may be optionally 1.1 m 2 / g - 2.7 m 2 / g; (4) 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; (5) 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; (6) The particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, optionally 0.90 - 1.40; (7) The specific capacity of the first carbon-based material is greater than or equal to 355 mAh / g, 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 - 2.22 g / cm 3 , optionally 1.97 g / cm 3 - 2.21 g / cm 3 ; (2) The powder compaction density of the second carbon-based material under a pressure of 20,000 N is 0.85 g / cm 3 -1.35 g / cm 3 , and can be optionally 0.90 g / cm 3 -1.30 g / cm 3 ; (3) The specific surface area of the second carbon-based material is greater than or equal to 1.5 m 2 / g, and may be optionally 1.9 m 2 / g - 7.5 m 2 / g; (4) The Dv50 of the second carbon-based material is 4.0 μm - 15.0 μm, optionally 5.0 μm - 15.0 μm; (5) The particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, optionally 1.1 - 1.75; (6) The tap density of the second carbon-based material is 0.80 g / cm 3 -1.20 g / cm 3 , and can be optionally 0.83 g / cm 3 -1.15 g / cm 3 ; (7) The specific capacity of the second carbon-based material is 330 mAh / g - 480 mAh / g, 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 includes primary particles; Optionally, the proportion of the number of the primary particles in the first carbon-based material is greater than or equal to 80%; Optionally, the proportion of the number of the primary particles in the second carbon-based material is 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%, optionally 90% - 98.5%; and / or, in the second region, the mass proportion of the second carbon-based material is greater than or equal to 80%, optionally 90% - 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 includes a silicon-based material; Optionally, both the first region and the second region include a silicon-based material, 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.

14. The secondary battery according to any one of claims 1 to 13, wherein, the 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 - 1.70 g / cm 3 , and can be optionally 1.25 g / cm 3 - 1.65 g / cm 3 ; (2) The areal density of the negative electrode film layer is 5.0 mg / cm 2 - 25.0 mg / cm 2 , and can be optionally 5.5 mg / cm 2 - 22.5 mg / cm 2 ; (3) The thickness of the negative electrode film layer is 40 μm - 120 μm, optionally 45 μm - 100 μm.

16. An electrical device, characterized in that, it includes the secondary battery according to any one of claims 1 - 15.

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