Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer which is located on at least one surface of the negative electrode current collector and comprises a negative electrode active material, the negative electrode active material comprises a first carbon-based material and a second carbon-based material, the first carbon-based material has a pore structure, ID / IG of the first carbon-based material is less than or equal to 0.280, ID represents D peak intensity at 1350 + / -50 cm <-1 > in a Raman spectrum, IG represents G peak intensity at 1580 + / -50 cm <-1 > in the Raman spectrum, and the second carbon-based material is an amorphous carbon material. The secondary battery of the present application has high energy density, and has excellent cycle performance and dynamic performance.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, 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 many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the application range of secondary batteries becomes wider and wider, higher requirements are put forward for their performance.

[0003] Therefore, how to enable secondary batteries to have high energy density while having excellent cycling performance and kinetic performance 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, in which the secondary battery has high energy density while taking into account excellent cycling performance and kinetic performance.

[0005] In a first aspect of the present application, a secondary battery is provided, including a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material. Among them, the negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material has a pore structure, and the I D / I G is less than or equal to 0.280. Among them, I D represents the intensity of the D peak at 1350±50 cm -1 in the Raman spectrum, and I G represents the intensity of the G peak at 1580±50 cm -1 in the Raman spectrum. The second carbon-based material is an amorphous carbon material.

[0006] By making the negative electrode active material in the negative electrode film layer include both the first carbon-based material and the second carbon-based material, the first carbon-based material has a pore structure, the I D / I G is less than or equal to 0.280, and the second carbon-based material is an amorphous carbon material. Thus, the negative electrode plate can have a high tap density, low volume change performance, and high active ion transport speed, so that the secondary battery using the negative electrode plate can have high energy density while taking into account excellent cycling performance and kinetic performance.

[0007] In some embodiments, the I D / I Gis 0.155 - 0.220; thus, it is more conducive to the battery to balance excellent energy density, cycle performance, and kinetic performance.

[0008] In some embodiments, the I of the second carbon-based material D / I G is less than or equal to 0.250. Optionally, the I of the second carbon-based material D / I G is less than or equal to 0.230. Thus, it is more conducive to the battery to balance excellent cycle performance and higher energy density.

[0009] In some embodiments, the Dv50 of the first carbon-based material is greater than the Dv50 of the second carbon-based material. Thus, it is more conducive to improving the energy density and kinetic performance of the battery.

[0010] In some embodiments, the X-ray powder diffraction pattern of the first carbon-based material has diffraction peaks at 2θ diffraction angles of 26.5° ± 0.2°, 44.5° ± 0.2°, and 54.6° ± 0.2°, and there are no obvious diffraction peaks in the X-ray powder diffraction pattern of the second carbon-based material. Thus, by making the first carbon-based material contain graphite and the second carbon-based material be amorphous carbon, the secondary battery can have high energy density while balancing excellent cycle performance and kinetic performance.

[0011] In some embodiments, the first carbon-based material has lattice fringes in HR-TEM, and the second carbon-based material has no lattice fringes in HR-TEM. Thus, by making the first carbon-based material contain graphite and the second carbon-based material be amorphous carbon, the secondary battery can have high energy density while balancing excellent cycle performance and kinetic performance.

[0012] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20000N is greater than the powder compaction density of the second carbon-based material under a pressure of 20000N. Thus, it is beneficial for the secondary battery to balance high energy density and good kinetic performance.

[0013] In some embodiments, the true density of the first carbon-based material is greater than the true density of the second carbon-based material. The larger true density of the first carbon-based material is beneficial for increasing the compaction density of the negative electrode film layer and improving the energy density of the secondary battery. The smaller true density of the second carbon-based material promotes the insertion and extraction of active ions, thereby improving the kinetic performance of the secondary battery. Therefore, by adjusting the true density of the first carbon-based material to be greater than the true density of the second carbon-based material, it is beneficial for the secondary battery to balance high energy density and good kinetic performance.

[0014] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 - 2.27 g / cm 3 , and may be 2.23 g / cm 3 - 2.26 g / cm 3 . By making the true density of the first carbon-based material within the above range and greater than that of the second carbon-based material, it is beneficial to improve the energy density of the secondary battery.

[0015] In some embodiments, the first carbon-based material includes one or more pore structures with an area greater than or equal to 0.15 μm 2 , and optionally includes one or more pore structures with an area of 0.15 μm 2 - 2.0 μm 2 . By making the first carbon-based material and / or the second carbon-based material include the pore structures with the above pore areas, the pore structures can reserve sufficient and stable expansion space for the volume change of the first carbon-based material and / or the second carbon-based material particles, reduce the risk of fragmentation of the first carbon-based material and / or the second carbon-based material particles, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0016] In some embodiments, 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. In the cross-sectional view of the first carbon-based material, the total pore area of the outer region is denoted as S 1 , the total pore area of the inner region is denoted as S2, and S2 > S1. Optionally, 2.6 ≤ S2 / S1 ≤ 450.7. The pore area S1 of the outer region of the first carbon-based material is smaller than the pore area S2 of the inner region, indicating that the structure of the outer region of this carbon-based material is denser than that of the inner region. Thus, the secondary battery can better balance high energy density and good cycle performance.

[0017] In some embodiments, the area of the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , and may be less than or equal to 0.13 μm 2 , and / or, the inner region of the first carbon-based material includes one or more pore structures with an area greater than or equal to 0.15 μm 2 , and optionally includes one or more pore structures with an area of 0.15 μm 2 - 2.0 μm 2By controlling the area of ​​the pore structure in the outer region of the first carbon-based material within the above range, the outer region of the first carbon-based material can have a dense structure, thereby effectively improving the structural stability of the first carbon-based material, avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, and thus effectively improving the cycle performance of the secondary battery. By making the inner region of the first carbon-based material include a pore structure of the above size, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, reducing the risk of breakage of the first carbon-based material particles and reducing the occurrence of side reactions. On the other hand, it can also improve the compaction density of the negative electrode film layer and buffer the volume change of the negative electrode film layer.

[0018] In some embodiments, the first carbon-based material has a powder compaction density of 1.65 g / cm2 at a pressure of 20,000 N. 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 , which is beneficial to improve the energy density of secondary batteries.

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

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

[0021] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, and can be selected as 0.90-1.50. By making the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material within the above range, its particle stacking performance is good, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also conducive to adjusting the pore distribution of the negative electrode film layer, improving the active ion and electron transport performance, and improving the infiltration and retention characteristics of the negative electrode film layer to the electrolyte, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0022] In some embodiments, the tap density of the first carbon-based material is 0.85 g / cm 3 -1.30g / cm 3, optionally 0.90 g / cm 3 -1.25 g / cm 3 . By making the tap density of the first carbon-based material within the above range, it is beneficial to improve the processing performance; it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the transport performance of active ions and electrons, improve the wetting and retention characteristics of the negative electrode film layer for the electrolyte, and thus improve the kinetic performance and cycling performance of the secondary battery.

[0023] In some embodiments, the graphitization degree of the first carbon-based material is greater than or equal to 95.5%, optionally 95.5% - 98.0%. By making the graphitization degree of the first carbon-based material within the above range, the secondary battery can have a high energy density.

[0024] In some embodiments, 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%, and the proportion of the number 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 a high structural stability and reduce the occurrence of side reactions, thereby improving the cycling performance of the secondary battery.

[0025] In some embodiments, 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 . By making the true density of the second carbon-based material within the above range and less than that of the first carbon-based material, it is beneficial to improve the kinetic performance of the secondary battery.

[0026] In some embodiments, the specific surface area of the second carbon-based material is greater than or equal to 1.5 m 2 / g, optionally 1.9 m 2 / g - 7.5 m 2 / g. By making the specific surface area of the second carbon-based material within the above range, it is beneficial to the rapid insertion and extraction of active ions, and thus can further improve the kinetic performance of the secondary battery.

[0027] In some embodiments, the 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 occurrence of side reactions is reduced, the cycling performance of the secondary battery is improved. In addition, it is also beneficial to improve the transport performance of active ions and electrons, and thus can further improve the kinetic performance of the secondary battery.

[0028] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and may be optionally 1.1 - 1.75. When the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is within the above range, its particle packing performance is better, which is beneficial to improving the compaction density of the negative electrode film layer and the energy density of the secondary battery; in addition, it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the transport performance of active ions and electrons in the negative electrode film layer, and thus improve the kinetic performance of the secondary battery.

[0029] In some embodiments, the powder compaction density of the second carbon-based material under a pressure of 20000N is 0.85g / cm 3 -1.35g / cm 3 and may be optionally 0.90g / cm 3 -1.30g / cm 3 . The powder compaction density of the second carbon-based material is lower than that of the first carbon-based material. By making the powder compaction density of the second carbon-based material within the above range, it is beneficial to improve the transport performance of active ions in the negative electrode film layer, and thus improve the kinetic performance of the secondary battery.

[0030] In some embodiments, the tapped density of the second carbon-based material is 0.80g / cm 3 -1.20g / cm 3 and may be optionally 0.83g / cm 3 -1.15g / cm 3 . By making the tapped density of the second carbon-based material within the above range, it is beneficial to have a suitable pore distribution in the negative electrode film layer, improve the transport performance of active ions, improve the wetting characteristics of the negative electrode film layer with the electrolyte, and thus improve the kinetic performance and cycle performance of the secondary battery.

[0031] In some embodiments, the specific capacity of the second carbon-based material is 330mAh / g - 480mAh / g, and may be optionally 340mAh / g - 470mAh / g. By making the specific capacity of the second carbon-based material within the above range, the energy density of the secondary battery can be improved.

[0032] In some embodiments, at least part of the surface of the first carbon-based material and / or the second carbon-based material has a carbon coating layer. Optionally, the coating layer includes a carbon coating layer. Thereby, it is beneficial to improve the speed of active ion insertion into the negative electrode film layer, improve the transport performance of active ions in the negative electrode film layer, and thus improve the kinetic performance of the secondary battery.

[0033] In some embodiments, the content of the first carbon-based material in the negative electrode active material is greater than or equal to 40wt%, optionally 50wt%-80wt%. When the content of the first carbon-based material is within the above range, the secondary battery has high energy density while having good processing performance, dynamic performance and cycle performance.

[0034] In some embodiments, the negative electrode active material further comprises a silicon-based material, and optionally, in the negative electrode active material, the content of the silicon-based material is 3wt%-30wt%. The silicon-based material has a higher lithium insertion potential, which 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.

[0035] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.70g / cm 3 , optional 1.45g / cm 3 -1.67g / cm 3 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

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

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

[0038] A second aspect of the present application provides an electrical device, which includes the secondary battery of the first aspect of the present application.

[0039] Effects of the Invention

[0040] The secondary battery of the present application has high energy density and excellent cycle performance and kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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 be obtained based on the drawings.

[0042] Figure 1 It is a schematic diagram of a cross-sectional image of the particles of the first carbon-based material of the present application.

[0043] Figure 2 It is an SEM image of an embodiment of the negative electrode sheet of the present application.

[0044] Figure 3 It is a schematic diagram of an embodiment of the secondary battery of the present application.

[0045] Figure 4 It is an exploded schematic diagram of an embodiment of the secondary battery of the present application.

[0046] Figure 5 It is a schematic diagram of an embodiment of the battery module of the present application.

[0047] Figure 6 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0048] Figure 7 is Figure 6 An exploded schematic diagram of the embodiment of the battery pack shown.

[0049] Figure 8 It is a schematic diagram of an embodiment of an electrical device including the secondary battery of the present application as a power source.

[0050] 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, 100 first carbon-based material, 101 external region, 102 internal region. Specific Embodiments

[0051] Hereinafter, the 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 detailed descriptions 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 avoid 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.

[0052] 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 the end values or not include 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 stated, 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.

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

[0054] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0055] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which 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.

[0056] Currently, when improving the kinetic performance of secondary batteries, especially the fast charging performance, most often the kinetic performance of the negative electrode is improved by reducing 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 moreover, the above methods often result in a significant reduction in the energy density of secondary batteries.

[0057] Therefore, it is currently difficult for secondary batteries to achieve both high energy density and good kinetic and cycling performance.

[0058] In view of this, a first aspect of an embodiment of the present application provides a secondary battery.

[0059] The present application places no particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion battery or the like. Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, etc. During the charging and discharging process of the secondary battery, active ions are intercalated and deintercalated back and forth between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting the active ions between the positive electrode sheet and the negative electrode sheet. The present application places no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution). In a secondary battery using an electrolytic solution, and some secondary batteries using a solid electrolyte, a separator can also be included, and the separator is disposed between the positive electrode sheet and the negative electrode sheet to play a role of isolation.

[0060] [Negative electrode sheet]

[0061] In the secondary battery of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material. Among them, the negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material has a pore structure, and the I D / I G is 0.152 - 0.280. Among them, I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 50 cm -1 , and the second carbon-based material is an amorphous carbon material.

[0062] In the present application, "the first carbon-based material has a pore structure" means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (such as a scanning electron microscope image with a magnification of 1000 times), that is, the pore structure in the main structure for preparing the first carbon-based material is not completely filled.

[0063] For amorphous carbon materials, their interlayer spacing is relatively large, which is beneficial to the rapid insertion and extraction of active ions. Moreover, they have a higher lithium potential, which is conducive to improving the kinetic performance of the battery. However, amorphous carbon materials have a relatively high surface activity and are prone to side reactions with the electrolyte. During the first charge, a large amount of active lithium ions are consumed, resulting in a reduction in the active ions of the secondary battery, a decrease in the capacity of the secondary battery, and a reduction in the energy density of the secondary battery. Therefore, the application of amorphous carbon materials in batteries is limited.

[0064] The negative electrode active material of this application simultaneously includes a first carbon-based material and amorphous carbon as the second carbon-based material. The first carbon-based material has a pore structure, which is equivalent to reserving a certain space inside the material, effectively improving the compaction density of the electrode sheet during the preparation of the electrode sheet, thereby enhancing the energy density of the battery. And the I D / I G of the first carbon-based material is within a specific range, and there is less disordered carbon on the surface of the carbon-based material, making the material have higher chemical stability, capable of reducing the occurrence of side reactions. During the first charge, the consumption of active ions can be effectively reduced, and the energy density and cycle performance of the battery can be further improved. Thus, the battery can have better kinetics while taking into account higher energy density and cycle performance.

[0065] In some embodiments, the I D / I G of the above-mentioned first carbon-based material is 0.155 - 0.220; thus, excellent energy density, cycle performance, and kinetic performance can be obtained with better balance.

[0066] In some embodiments, the I D / I G of the above-mentioned second carbon-based material is less than or equal to 0.250. Optionally, the I D / I G of the above-mentioned second carbon-based material is less than or equal to -0.230. Thus, the cycle performance and energy density of the battery can be further improved. In some embodiments, the X-ray powder diffraction pattern of the above-mentioned first carbon-based material has diffraction peaks at 2θ diffraction angles of 26.5° ± 0.2°, 44.5° ± 0.2°, and 54.6° ± 0.2°. There are no obvious diffraction peaks in the X-ray powder diffraction pattern of the above-mentioned second carbon-based material.

[0067] There are lattice fringes in the HR-TEM pattern of the above-mentioned first carbon-based material, indicating that this carbon material has a crystal structure.

[0068] There are no obvious lattice fringes in the HR-TEM pattern of the above-mentioned second carbon-based material, indicating that this carbon material does not have a crystal structure. Usually, this type of material is called amorphous carbon.

[0069] In some embodiments, the second carbon-based material may be soft carbon or hard carbon.

[0070] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20,000 N is greater than that of the second 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, improving the insertion and 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.

[0071] In some embodiments, the true density of the first carbon-based material is greater than that of the second carbon-based material. This is beneficial for the secondary battery to have both high energy density and good kinetic performance.

[0072] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 - 2.27 g / cm 3 , and may be 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.

[0073] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is greater than that of the second carbon-based material. Thereby, the energy density of the battery can be further improved, and it is also helpful for improving the kinetic performance.

[0074] In some embodiments, the tapped density of the first carbon-based material is greater than that of the second carbon-based material. Thereby, the processing performance of the battery can be further improved.

[0075] In some embodiments, the first carbon-based material includes one or more pore structures with an area greater than or equal to 0.15 μm 2 , and optionally includes one or more pore structures with an area of 0.15 μm 2 - 2.0 μm 2 . By making the first carbon-based material and / or the second carbon-based material include pore structures with the above pore areas, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles and / or the second carbon-based material, reducing the risk of particle breakage of the first carbon-based material and / or the second carbon-based material, reducing the occurrence of side reactions, improving the cycle performance of the secondary battery. In addition, it can also increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0076] In some embodiments, the first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region extending 2.5 μm from the particle surface of the first carbon-based material to the inside of the particle, and in the cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is denoted as S. 1 The total pore area of ​​the internal region is recorded as S2, and S2>S1. In this application, "internal region" refers to the region in the material particle other than the external region.

[0077] When the first carbon-based material satisfies S2>S1, it means that the structure of the outer region of the carbon-based material is denser than that of the inner region, and the first carbon-based material further has the following characteristics: the inner region has a large number of pores and / or a large pore size, while the outer region has a small number of pores and / or a small pore size. The pore structure of the inner region of the first carbon-based material can reserve the required expansion space for the volume change of the particles, thereby reducing the risk of particle breakage to produce a new interface, reducing the rebound rate of the thickness of the negative electrode film layer, and thus reducing the occurrence of side reactions; the outer region of the first carbon-based material has a small number of pores and / or a small pore size, thereby making the first carbon-based material particles have a stable structure and avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby further reducing the occurrence of side reactions and reducing the consumption of active ions by the SEI film formation inside the particles. Therefore, when the first carbon-based material satisfies S2>S1, the first coulomb efficiency of the secondary battery can be improved, and the cycle performance of the secondary battery can be further improved.

[0078] Preferably, 2.6≤S2 / S1≤450.7, for example, 3≤S2 / S1≤430, 4≤S2 / S1≤400, 5≤S2 / S1≤350, 6≤S2 / S1≤300, 7≤S2 / S1≤250, 8≤S2 / S1≤200. The inventors found in further research that when S2 / S1 is also within the above range, the secondary battery can better balance high energy density and good cycle performance.

[0079] In the present application, the total pore area S of the outer region of the first carbon-based material is 1 The total pore area S2 of the internal region can be obtained by testing the cross-sectional image of the first carbon-based material.

[0080] Figure 1 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 100 of the present application. Figure 1 As shown, the region extending 2.5 μm from the particle surface of the first carbon-based material 100 to the inside of the particle is the outer region 101 , and the region inside the outer region 101 is the inner region 102 .

[0081] In the present 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 polisher (such as the IB-09010CP type argon ion cross-section polisher from JEOL Ltd., 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, 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 through an image processing software (such as AVIZO), and the value of S2 / S1 is obtained therefrom. 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 polisher, and cross-sections of at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross-section. According to the above definition, 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 the image processing software, and the value of S2' / S1' of each particle cross-section is obtained therefrom. The arithmetic mean of S2' / S1' of all measured particle cross-sections is calculated as the S2 / S1 value of the first carbon-based material.

[0082] In some embodiments, the area of the pore structure in the external region of the above-mentioned first carbon-based material is less than or equal to 0.15 μm 2 , and can be optionally less than or equal to 0.13 μm 2 . The inventors further found in the 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 infiltration of the electrolyte into the pore structure inside the first carbon-based material particles, and further effectively improving the cycle performance of the secondary battery. Of course, the present 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%, optionally more than 99% of the pore structures can be controlled to be less than or equal to 0.15 μm 2 .

[0083] In some embodiments, the internal region of the above-mentioned 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 a pore structure of the above size, on the one hand, it can reserve sufficient and stable expansion space for the volume change of the first carbon-based material particles, reduce the risk of fragmentation of the first carbon-based material particles, and reduce the occurrence of side reactions. On the other hand, it can also improve the compaction density of the negative electrode film layer and buffer the volume change of the negative electrode film layer.

[0084] In some embodiments, the powder compaction density of the above-mentioned first carbon-based material under a pressure of 20,000 N is 1.65 g / cm 3 - 2.0 g / cm 3 , and may be optionally 1.68 g / cm 3 - 1.98 g / cm 3 . When the powder compaction density of the first carbon-based material is within the above range, the battery can better balance the energy density and kinetic performance.

[0085] In some embodiments, the volume distribution particle size Dv50 of the above-mentioned 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 distribution particle size Dv90 of the above-mentioned first carbon-based material is 16.0 μm - 45.0 μm, and may be optionally 16.5 μm - 42.0 μm.

[0086] When the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the occurrence of side reactions and improve the cycle performance of the secondary battery.

[0087] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the above-mentioned first carbon-based material is less than or equal to 1.55, and may be optionally 0.90 - 1.50. When the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is within the above range, its particle packing performance is better, which is 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 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.

[0088] In some embodiments, the tapped density of the above-mentioned first carbon-based material is 0.85 g / cm 3 - 1.30 g / cm 3 , and may be optionally 0.90 g / cm 3 - 1.25 g / cm 3 . When the tapped density of the first carbon-based material is within the above range, it is beneficial to improve the processing performance.

[0089] In some embodiments, the graphitization degree of the first carbon-based material is greater than or equal to 95.5%, and may be optionally 95.5% - 98.0%. By adjusting the graphitization degree of the first carbon-based material within the above range, the secondary battery can have a higher energy density. In addition, the particles of the amorphous carbon material are usually hard and have many edges and corners, with poor processability and poor adhesion to the current collector. A greater cold pressing pressure is required during the processing of the electrode sheet, which is likely to cause damage to the current collector. When used in combination with the first carbon-based material with a higher graphitization degree, the cold pressing pressure during the processing of the electrode sheet can be reduced, thereby reducing the damage to the current collector and the risk of current collector cracking during the battery cycle, and further improving the safety performance of the battery.

[0090] In some embodiments, the above-mentioned first carbon-based material and / or the above-mentioned 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%, and may be, for example, 80% - 100%, 85% - 90%, 80% - 90%, 80% - 100%, 85% - 90%, 80% - 100%, 90% - 100%, or 95% - 100%. The proportion of the number of the primary particles in the second carbon-based material is greater than or equal to 80%, and may be, for example, 80% - 100%, 85% - 90%, 80% - 90%, 80% - 100%, 85% - 90%, 80% - 100%, 90% - 100%, or 95% - 100%. The first carbon-based material and / or the second carbon-based material containing an appropriate proportion of primary particles can make it have higher structural stability and also reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0091] In some embodiments, the true density of the above-mentioned 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 true density of the second carbon-based material within the above range and less than that of the first carbon-based material, it is beneficial to maintain the porosity of the negative electrode sheet of the secondary battery, and further improve the kinetic performance of the secondary battery.

[0092] In some embodiments, the specific surface area of the above-mentioned 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. By making the specific surface area of the second carbon-based material within the above range, it is beneficial to the rapid insertion and extraction of active ions, and thus can further improve the kinetic performance of the secondary battery.

[0093] In some embodiments, the Dv50 of the above-mentioned second carbon-based material is 4.0 μm - 15.0 μm, and 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, it is beneficial to improve the transport performance of active ions, thereby further improving the kinetic performance of the secondary battery.

[0094] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the above-mentioned second carbon-based material is less than or equal to 1.75, and optionally 1.1 - 1.75. When the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is within the above range, its particle packing performance is better, which is beneficial to improving the compaction density of the negative electrode film layer and the energy density of the secondary battery; in addition, it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the transport performance of active ions and electrons in the negative electrode film layer, and further improve the kinetic performance of the secondary battery.

[0095] 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 optionally 0.90 g / cm 3 -1.30 g / cm 3 . The powder compaction density of the second carbon-based material is lower than that of the first carbon-based material. By making the powder compaction density of the second carbon-based material within the above range, it is beneficial to improve the porosity of the negative electrode plate and the transport performance of active ions in the negative electrode film layer, and further improve the kinetic performance of the secondary battery.

[0096] In some embodiments, the tapped density of the above-mentioned second carbon-based material is 0.80 g / cm 3 -1.20 g / cm 3 and optionally 0.83 g / cm 3 -1.15 g / cm 3 This can better balance the processing performance and kinetic 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, and optionally 340 mAh / g - 470 mAh / g. By making the 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, at least part of the surface of the above-mentioned first carbon-based material and / or second carbon-based material has a carbon coating layer. Optionally, the above-mentioned coating layer includes a carbon coating layer. Optionally, more than 80% of the surface of the above-mentioned first carbon-based material and / or second carbon-based material is covered with a carbon coating layer. Further, 90%-100% of the surface is covered with a carbon coating layer. Thereby, it is beneficial to improve the speed of active ion embedding into the negative electrode film layer, improve the active ion transport performance of the negative electrode film layer, and further improve the kinetic performance of the secondary battery.

[0099] In some embodiments, the coating layer of the above-mentioned first carbon-based material can be prepared as follows: Mix the first carbon-based material with an organic carbon source and then perform carbonization treatment to form a carbon coating layer on at least part of the surface of the particles. Optionally, the above-mentioned organic carbon source can adopt carbon-containing materials known in the art suitable for coating. For example, it can include one or more of coal tar pitch, petroleum pitch, epoxy resin, phenolic resin, polymer, etc. Optionally, the above-mentioned carbonization temperature is 900°C - 1300°C. In addition, the coating layer of the above-mentioned second carbon-based material can be prepared by the following method: Method 1: Use chemical vapor deposition to deposit carbon material on the surface of the second carbon-based material at a temperature of 1200 - 1600°C, and the gas is one of methane, ethylene, and acetylene; Method 2: Mix the second carbon-based material with a coating agent and perform heat treatment at a temperature of 1600 - 2600°C, and the coating agent is one or more of asphalt or polymer. Thereby, it is beneficial to adjust the I D / I G , and further improve the cycle performance of the secondary battery.

[0100] In some embodiments, the content of the above-mentioned first carbon-based material in the above-mentioned negative electrode active material is greater than or equal to 40 wt%, optionally 50 wt% - 80 wt%, for example 55 wt% - 75 wt%, 60 wt% - 70 wt%. When the content of the first carbon-based material is within the above range, the secondary battery can take into account high energy density, good kinetic performance, and cycle performance. In addition, the content of the above-mentioned second carbon-based material in the above-mentioned negative electrode active material can be 20 wt% - 50 wt%, optionally 25 wt% - 45 wt%, 30 wt% - 40 wt%.

[0101] In some embodiments, the above-mentioned negative electrode active material may further include other negative electrode active materials known in the art in addition to the above-mentioned first carbon-based material and second silicon-based material. For example, the above-mentioned negative electrode active material may further include a silicon-based material, and the silicon-based material has a relatively high lithium insertion potential. It is beneficial to improve the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery. Optionally, the above-mentioned silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0102] In some embodiments, when the negative electrode active material in the above-mentioned negative electrode film layer further includes a silicon-based material, the content of the silicon-based material is 3 wt% - 30 wt%. For example, it can be 4 wt% - 25 wt% or 5 wt% - 20 wt%. Thereby, while improving the kinetic performance and energy density of the secondary battery, the secondary battery can also have good cycle performance and rate performance.

[0103] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. 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.

[0104] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. 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, aqueous acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0105] In some embodiments, 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.

[0106] In some embodiments, the tap density of the negative electrode film layer is 1.40 g / cm 3 - 1.70 g / cm 3 , and may be optionally 1.45 g / cm 3 - 1.67 g / cm 3 . Thereby, it is beneficial for the negative electrode film layer to have both high capacity, high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0107] 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 / cm 2 - 22.5 mg / cm 2 . Thereby, it is beneficial for the negative electrode film layer to have both high capacity, high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0108] In some embodiments, the thickness of the above-mentioned negative electrode film layer is 40 μm - 120 μm, and optionally 45 μm - 100 μm.

[0109] In some embodiments, the above-mentioned 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 above-mentioned composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the above-mentioned polymer material base layer. As an example, the above-mentioned 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 above-mentioned polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0110] The negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector. It should be noted that the parameters of each negative electrode film layer given in this application (such as compaction density, areal density, thickness, etc.) refer to the parameters of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of this application, and it is considered to fall within the protection scope of this application.

[0111] In this application, the above-mentioned negative electrode tab can further include other additional functional layers in addition to the above-mentioned negative electrode film layer. For example, in some embodiments, the negative electrode tab further includes a conductive bottom coating (such as composed of a conductive agent and a binder) sandwiched between the above-mentioned negative electrode current collector and the above-mentioned negative electrode film layer and disposed on the surface of the above-mentioned negative electrode current collector; in some embodiments, the negative electrode tab further includes a protective layer covering the surface of the above-mentioned negative electrode film layer.

[0112] In this application, the I D / I G of materials (such as the first carbon-based material, the second carbon-based material, etc.) can be tested using a Raman spectrometer. I D represents the intensity of the D peak of the Raman spectrum of the material at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum of the material at 1580 ± 50 cm -1 . The test conditions are as follows: the excitation wavelength is 532 nm, the grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the accumulation times is 3 times, and area scanning is performed to obtain the intensities of the D peak and G peak at 100 points, and calculate the I D / I G of the 100 points. Remove the 30 highest and 30 lowest I D / I G , and the average value of the remaining 40 points is the I of the material.D / I G The testing instrument can adopt Horiba LabRAM HR800 Raman spectrometer.

[0113] In this application, for the X-ray diffraction analysis test of materials (such as the first carbon-based material, the second carbon-based material, etc.), a copper target can be used as the anode target, with CuKα ray as the radiation source, and the ray wavelength The scanning range of 2θ angle is 20° - 80°, and the scanning rate is 4° / min.

[0114] In this application, the HR-TEM of materials (such as the first carbon-based material, the second carbon-based material, etc.) can be tested by methods known in the art. For example, referring to the standard JBT9352-1999, use a focused ion beam FIB to slice the powder, with a slice thickness of ~100 nm, and test it under a transmission electron microscope.

[0115] In this application, the true density of materials (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 methods known in the art. Referring to the standard GB / T24586-2009, an exemplary testing 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, which accounts for about 1 / 2 of the volume of the sample cup, and record the sample mass. Place the sample cup containing the sample in a true density tester, seal the testing 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 tested sample cup: 3.5 cm 3 , Analyzing gas: Helium.

[0116] In this application, whether there is a coating layer on the surface of materials (such as the first carbon-based material, the second carbon-based material, etc.) can be judged by a high-resolution transmission electron microscope (HR-TEM).

[0117] In this application, the specific capacity has the meaning well-known in the art and can be tested by methods known in the art. An exemplary testing method is as follows: Mix the sample powder with conductive agent carbon black (Super P), 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 current collector copper foil, dry it in an oven and reserve it; 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 LiPF 6Dissolve it in the above-mentioned organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then use a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, and assemble it with the above-mentioned electrolyte into a CR2430 type button cell in a glove box under argon protection; after standing the obtained button cell for 12 h, at 25 °C, discharge it at a constant current of 0.05 C to 0.005 V, stand for 10 minutes, then discharge it at a constant current of 50 μA to 0.005 V, stand for 10 minutes, and then discharge it at a constant current of 10 μA to 0.005 V; then charge it at a constant current of 0.1 C to 2 V and record the charge capacity. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material.

[0118] 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 the instruments and methods known in the art. For example, it can be measured by referring to GB / T 19587-2017 using the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. The test instrument can be the Tri-Star 3020 type specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0119] 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 the instruments and methods known in the art. For example, it can be measured by referring to GB / T19077-2016 using a laser particle size analyzer. The test instrument can be the Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited in the UK.

[0120] In this application, the powder compaction 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, it can be measured by referring to GB / T 24533-2009 using 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 sample powder and add it to a mold with a bottom area of 1.327 cm 2 Press it to 2000 kg, keep the pressure for 30 s, then release the pressure, keep it for 10 s, and then record and calculate the powder compaction density of the material under a pressure of 20000 N.

[0121] 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 from 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.

[0122] In this application, the graphitization degree 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 instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average layer spacing d of the C(002) crystal plane in the crystal structure of the material. 002 , and then the graphitization degree can be calculated according to the formula g=(0.344-d 002 ) / (0.344 - 0.3354)×100%. In the above formula, d 002 is the average layer spacing of the C(002) crystal plane in the crystal structure of the material expressed in nanometers (nm).

[0123] In this application, the primary particle has the meaning well-known in the art. A primary particle refers to a non-agglomerated particle. A particle formed by the aggregation of two or more primary particles is an agglomerated particle, which is a secondary particle. Primary particles can be distinguished by using a scanning electron microscope (SEM) image.

[0124] In this application, the proportion of the number of primary particles in the first carbon-based material and / or the second carbon-based material means that: in a test sample randomly taken from the negative electrode film layer, multiple test areas are randomly taken in this test sample, and images of multiple test areas are obtained by using a scanning electron microscope. The proportion of the number of the first carbon-based materials with the morphology of primary particles in each image to the total number of carbon-based material particles is statistically calculated, and the average value of multiple statistical results is the proportion of the number of primary particles in the first carbon-based material.

[0125] 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 negative electrode plate after single-sided coating and cold pressing can be taken (if it is a double-sided coated negative electrode plate, the negative electrode film layer on one side can be wiped off first), and it is punched into small round pieces with an area of S 1 , and its weight is weighed and recorded as M 1 . Then the negative electrode film layer of the above-mentioned weighed negative electrode plate is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M 0 . The areal density of the negative electrode plate=(M1 -M 0 ) / S 1 。

[0126] In the present 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, for example, using a micrometer (such as Mitutoyo 293-100 type with an accuracy of 0.1 μm).

[0127] It should be noted that the various parameter tests for the negative electrode active material or the negative electrode film layer can be sampled and tested from the prepared secondary battery according to the following steps.

[0128] Discharge the secondary battery (for safety reasons, generally make the secondary battery in a fully discharged state); after disassembling the secondary battery, take out the negative electrode plate, soak the negative electrode plate with dimethyl carbonate for a certain time (such as 2h - 10h); then take out the negative electrode plate and dry it at a certain temperature and time (such as 60°C, for more than 4h), 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.

[0129] Bake the above-mentioned dried negative electrode plate at a certain temperature and time (such as 400°C, for more than 2h), select an area at random in the baked negative electrode plate, and sample the negative electrode active material (blade scraping for powder sampling can be used); sieve the collected negative electrode active material (such as sieving with a 200-mesh sieve), and finally obtain a sample that can be used to test the above-mentioned parameters of the negative electrode active material.

[0130] The first carbon-based material and the second carbon-based material can be distinguished by SEM. Figure 2 It is an SEM image of an embodiment of the negative electrode plate of the present application. It can be seen from the figure that the particle cross-section with an obvious pore structure is the first carbon-based material, and the particle cross-section without a pore structure is the second carbon-based material.

[0131] In the present application, the above-mentioned second carbon-based material can be obtained by commercial purchase or prepared according to methods well-known in the art. In addition, the above-mentioned first carbon-based material can be prepared and obtained by the following method.

[0132] In some embodiments, the preparation method of the above-mentioned first carbon-based material includes: Step 1, providing a raw material with a plurality of pore structures; Step 2, mixing the above-mentioned raw material and the filling material evenly according to a predetermined ratio, and then keeping it warm at the first temperature T 1 for the first time t 1, after completion, cool to room temperature to obtain an intermediate; Step 3, keep the obtained intermediate at a second temperature T 2 for a second time t 2 , and obtain a first carbon-based material after completion.

[0133] In some embodiments, in Step 1, the raw materials for preparing the above-mentioned first carbon-based material include natural graphite. Natural graphite generally refers to graphite naturally formed in nature, without the need for graphitization, and there are usually many closed pore structures inside natural graphite particles. Optionally, the above-mentioned natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0134] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with the desired particle size and morphology can be obtained by pretreating flake graphite. Optionally, the above-mentioned pretreatment includes processes such as crushing, classification, spheroidization, and purification.

[0135] In some embodiments, in Step 1, the volume distribution particle size Dv50 of the above-mentioned raw materials can be 6.0 μm - 25.0 μm.

[0136] In some embodiments, in Step 1, the specific surface area of the above-mentioned raw materials can be greater than or equal to 2.5 m 2 / g, and can be optionally 2.5 m 2 / g - 10.0 m 2 / g. When the specific surface area of the raw materials is within the above range, it is beneficial for subsequent filling treatment and obtaining a 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 first Coulomb efficiency. In addition, it is beneficial for the first carbon-based material to have better kinetic performance.

[0137] In some embodiments, in Step 2, the softening point temperature of the above-mentioned filling material is 90°C - 150°C. Optionally, the softening point temperature of the above-mentioned filling material is 94°C - 146°C, 94°C - 142°C, 94°C - 138°C, 94°C - 134°C, 94°C - 130°C, 104°C - 146°C, 104°C - 142°C, 104°C - 138°C, 104°C - 134°C, 104°C - 130°C.

[0138] In some embodiments, in Step 2, the volume distribution particle size Dv50 of the above-mentioned filling material is less than or equal to 6 μm, and can 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 materials after heating, and is also beneficial for improving the dispersion uniformity of the filling material and the raw materials.

[0139] In some embodiments, in step 2, the coking value of the above-mentioned filling material is 15%-40%, optionally 18%-34%. In the present 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.

[0140] In some embodiments, in step 2, the above-mentioned filling material includes one or more of coal tar pitch, petroleum pitch, high molecular compounds and resins, and is optionally one or more of coal tar pitch and petroleum pitch.

[0141] In some embodiments, in step 2, the mass ratio of the above-mentioned filling material to the above-mentioned raw material is (10-40):100, optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, (15-25):100. Generally, when other process conditions remain unchanged, the more the amount of the filling material added, the larger the I D / I G is. Those skilled in the art can adjust within the above-mentioned mass ratio range according to requirements to obtain the desired I D / I G value.

[0142] 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 number of pores 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 of the first carbon-based material within a suitable range.

[0143] By adjusting 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 adhere to the raw material particles, which can reduce the agglomeration of raw material particles in the subsequent preparation process. Therefore, 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.

[0144] In some embodiments, in step 2, after mixing the above-mentioned raw material and the above-mentioned filling material evenly in a predetermined ratio, the temperature is raised to the first temperature T 1 The temperature-raising process can be a staged temperature-raising process.

[0145] In some embodiments, the above-mentioned staged temperature-raising process includes a first temperature-raising process, a second temperature-raising process and a third temperature-raising process.

[0146] In some embodiments, the above-mentioned first heating process is to heat up to 200°C - 250°C and hold the temperature for 0.5 h - 3 h.

[0147] In some embodiments, the above-mentioned second heating process is to heat up to 450°C - 550°C and hold the temperature for 0 h - 2 h. When the holding time is 0 h, it means that when heating up to the range of 450°C - 550°C, no heat preservation treatment is carried out, but continue to heat up to the first temperature T 1 。

[0148] In some embodiments, the above-mentioned third heating process is to heat up to the above-mentioned first temperature T 1 and hold the temperature for the first time t 1 。

[0149] During the staged heating process, first heat up 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 the temperature for 0.5 h - 3 h can make it flow and fill into the pore structure of the raw material; then heat up to 450°C - 550°C. At this time, the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state and becoming a viscous liquid or solid, thereby preventing the filling material from entering all the pore structures of the raw material; finally heat up to the first temperature, at which time the filling material undergoes a carbonization reaction, thereby enabling the pore structures occupied by the filling material to be effectively filled.

[0150] In some embodiments, in step 2, heat up to the above-mentioned first temperature T at a rate of 1°C / min - 10°C / min 1 。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.

[0151] In some embodiments, the heating rate of the above-mentioned 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. In some embodiments, the heating rate of the above-mentioned second heating process can be 1°C / min - 10°C / min, optionally 2°C / min - 8°C / min. In some embodiments, the heating rate of the above-mentioned third heating process can be 1°C / min - 10°C / min, optionally 2°C / min - 8°C / min.

[0152] In some embodiments, in step 2, the above-mentioned first temperature T 1 is 700°C - 1200°C. For example, the first temperature T 1 can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1200°C or any range composed of the above values. Optionally, the above-mentioned first temperature T 1 is 750°C - 1100°C, 800°C - 1100°C, 850°C - 1100°C, 900°C - 1100°C, 850°C - 1000°C.

[0153] In some embodiments, in step 2, the above-mentioned first time t 1 is 1h - 5h. For example, the first time t 1 can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any range composed of the above values. Optionally, the above-mentioned first time t 1 is 2h - 4h.

[0154] 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.

[0155] In some embodiments, in step 2, the heat treatment atmosphere can be a protective gas atmosphere. The above-mentioned protective gas can include one or more of nitrogen, argon, and helium.

[0156] 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 range, it is beneficial to adjust the number and / or size of pores in the outer region and the inner region of the first carbon-based material within a suitable range, and further beneficial to adjust S2 / S1 of the first carbon-based material within a suitable range.

[0157] In some embodiments, in step 3, the above-mentioned second temperature T 2 is 2070°C - 2700°C. Optionally, the above-mentioned second temperature T 2 is 2070°C - 2570°C, 2070°C - 2510°C, 2070°C - 2450°C, 2070°C - 2360°C, 2140°C - 2570°C, 2140°C - 2510°C, 2140°C - 2450°C, 2140°C - 2360°C.

[0158] In some embodiments, in step 3, the above-mentioned second time t 2 is 1.5h - 6h. For example, the second time t 1It can be in the range composed of any value such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h or above. Optionally, the above-mentioned second time t 2 is 2h - 5h.

[0159] In some embodiments, in step 3, the above 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.

[0160] In some embodiments, in step 3, the heat treatment atmosphere of the intermediate frequency furnace and the continuous graphitization can be a protective gas atmosphere. The above protective gas can include one or more of argon and helium.

[0161] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the first carbon-based material within a suitable range, which is beneficial for the first carbon-based material to have a suitable graphitization degree, interlayer spacing and I D / I G etc. Generally, when other process conditions remain unchanged, the higher the second temperature, the smaller the I D / I G of the first carbon material. Those skilled in the art can adjust within the above-given temperature range according to requirements to obtain the desired I D / I G value.

[0162] 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 range, it is beneficial to adjust parameters such as S2 / S1, graphitization degree, specific capacity, particle size, powder compacted density, tapped density, and adsorption amount of linseed oil of the first carbon-based material.

[0163] In some embodiments, the obtained first carbon-based material is mixed with an organic carbon source and then carbonized to form a carbon coating layer on at least part of the surface of the particles. Optionally, the above organic carbon source can adopt a carbon-containing material suitable for coating known in the art. For example, it can include one or more of coal tar pitch, petroleum pitch, phenolic resin, coconut shell, etc. Optionally, the carbonization temperature is 900°C - 1300°C.

[0164] In some embodiments, the above second carbon-based material is purchased through commercial channels.

[0165] [Positive electrode plate]

[0166] In some embodiments, the above-mentioned positive electrode tab 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 either or both of the two opposite surfaces of the positive electrode current collector.

[0167] 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 may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0168] 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 generally formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent 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.

[0169] The positive electrode active material can be a positive electrode active material for secondary batteries known in the art.

[0170] When the secondary battery of the present application is a lithium-ion battery, the above-mentioned positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the above-mentioned lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the above-mentioned lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0171] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having a general formula of Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0172] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , 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 Al0.05 O 2 、 LiFePO 4 and LiMnPO 4 or one or more of them.

[0173] In this application, the modified compounds of the above-mentioned cathode active materials can be doping modification and / or surface coating modification of the above-mentioned cathode active materials.

[0174] [Electrolyte]

[0175] In some embodiments, the above-mentioned electrolyte uses an electrolytic solution, and the above-mentioned electrolytic solution includes an electrolyte salt and a solvent.

[0176] The type of the above-mentioned electrolyte salt is not specifically limited and can be selected according to actual needs.

[0177] When the secondary battery of this application is a lithium-ion battery, by way of example, the above-mentioned 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(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP) or one or more of them.

[0178] The type of the above-mentioned solvent is not specifically limited and can be selected according to actual needs. In some embodiments, by way of example, the above-mentioned solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE) or one or more of them.

[0179] In some embodiments, the above electrolyte may further optionally include additives. For example, the above additives may include negative electrode film-forming additives, may also include positive electrode film-forming additives, and may further include additives capable of improving 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.

[0180] [Separator film]

[0181] The present application does not particularly limit the type of the above separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0182] In some embodiments, the material of the above separator film may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The above separator film may be a single-layer film or a multi-layer composite film. When the above separator film is a multi-layer composite film, the materials of each layer may be the same or different.

[0183] In some embodiments, the above positive electrode sheet, the above separator film, and the above negative electrode sheet may be made into an electrode assembly by a winding process or a stacking process.

[0184] In some embodiments, the above secondary battery may include an outer package. The outer package may be used to encapsulate the above electrode assembly and electrolyte.

[0185] 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 above soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0186] The present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, square, or any other arbitrary shape. As Figure 3 is a secondary battery 5 with a square structure as an example.

[0187] In some embodiments, as Figure 4 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 a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the above opening to close the above receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the above receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or several, which can be adjusted according to requirements.

[0188] The preparation method of the secondary battery of the present application is well-known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a stacking process, the electrode assembly is placed in an outer package, dried, and then the electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0189] In some embodiments of the present application, the secondary battery according to the present application can be assembled into a battery module. The number of secondary batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0190] Figure 5 is a schematic diagram of a battery module 4 as an example. As Figure 5 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.

[0191] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple secondary batteries 5 are accommodated in the accommodation space.

[0192] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0193] Figure 6 and Figure 7 are schematic diagrams of a battery pack 1 as an example. As Figure 6 and Figure 7 shown, the battery pack 1 can include a battery box and multiple battery modules 4 arranged 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 multiple battery modules 4 can be arranged in the battery box in any way.

[0194] The present application also provides an electrical device, and the above electrical device includes at least one of the secondary battery, the battery module, or the battery pack of the present application. The above secondary battery, battery module, or battery pack can be used as the power source of the above electrical device or as the energy storage unit of the above electrical device. The above electrical device can be but is not limited to mobile devices (such as mobile phones, tablet computers, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0195] The above-mentioned electrical device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.

[0196] Figure 8 It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a 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 a battery module can be adopted.

[0197] Another example of an electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires thin and light, and a secondary battery can be adopted as the power source.

[0198] Embodiment

[0199] 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 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.

[0200]

[0201] Material 1-1

[0202] 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 100:25. The softening point of the petroleum pitch is 120°C and the coking value is 36%. Then, place the mixed material in a programmable temperature-raising device, raise the temperature to 200°C and keep it warm for 1 h (the first temperature-raising process), and then continuously raise the temperature to 700°C and keep it warm for 2 h (the third temperature-raising process). After that, cool it to room temperature to obtain an intermediate. Step 3: Place the obtained intermediate in a graphitization furnace and perform heat treatment at 2580°C. After that, demagnetize and screen to obtain the first carbon-based material. The I D / I G value is 0.152, S2 / S1 is 14.7, and DV50 is 18.3 μm.

[0203] The S2 / S1 of the first carbon-based material is obtained by the following method.

[0204] Mix the binder for sample preparation with the first carbon-based material powder evenly, then coat it on the copper foil and dry it at 60 °C for 30 min for standby; Cut it into 5 test samples of 6 mm × 6 mm at 5 different positions and paste them on the sample stage of the CP type argon ion cross-section polishing instrument respectively; Use the plasma beam to cut the samples to obtain the cross-sections of each sample. The test instrument can be the IB-09010CP type argon ion cross-section polishing instrument of JEOL Company, Japan.

[0205] 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 the Sigma 300 type scanning electron microscope of ZEISS Company, Germany.

[0206] Randomly select the cross-sections of 20 particles of the first carbon-based material from the scanning images. 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, and calculate the value of S2' / S1'; And calculate the arithmetic mean of S2' / S1' of all 20 particles as the value of S2 / S1 of the first carbon-based material. The image processing software can be AVIZO.

[0207] Materials 1-2 to 1-5

[0208] The preparation methods of Materials 1-2 to 1-5 are similar to the preparation method of the above-mentioned Material 1-1, the difference is: Adjust the mixing ratio of natural spherical graphite and filler petroleum pitch and the heat treatment temperature, so that the I D / I G value is the value shown in Table 1.

[0209] Table 1

[0210]

[0211] Materials 1-6 to 1-10

[0212] The preparation methods of Materials 1-6 to 1-10 are similar to the preparation method of the above-mentioned Material 1-1, the difference is: As shown in Table 2, adjust the softening point temperature, coking value of the filler material, the mixing ratio of natural spherical graphite and filler petroleum pitch, and adjust the third heating process, so that the S2 / S1 of the first carbon-based material is the value shown in Table 2.

[0213] Table 2

[0214]

[0215]

[0216] Material 1-11

[0217] The preparation method of Materials 1-11 is similar to that of the above-mentioned Materials 1-3, with the difference that: after the flake graphite is mechanically crushed, classified, and spheroidized, the particle size distribution Dv50 is adjusted to 10.2 μm.

[0218]

[0219] Material 2-1

[0220] Using coconut shell as raw material, through heat treatment at 600 °C, crushing, alkali pickling for impurity removal, and heat treatment at 1000 °C, an amorphous carbon material is obtained. Then, the amorphous carbon is coated and heat-treated. The amorphous carbon and the coating agent are mixed at a mass ratio of 100:10 and heat-treated at a temperature of 2450 °C. The coating agent is pitch. After demagnetization and screening, a second carbon-based material is obtained. The I D / I G value is 0.17 and the Dv50 is 10.2 μm.

[0221] Materials 2-2 to 2-4

[0222] Similar to the preparation method of the above-mentioned Material 2-1, with the difference that: as shown in Table 3, the dosage of the coating agent and the heat treatment temperature are adjusted to obtain a second carbon-based material with the I D / I G shown in Table 3.

[0223] Table 3

[0224]

[0225] Material 2-5

[0226] Similar to the preparation method of the above-mentioned Material 2-1, with the difference that: the particle size distribution Dv50 after crushing is adjusted to 14.5 μm.

[0227] Example 1

[0228] Preparation of secondary battery

[0229] 1. Negative electrode sheet: The negative electrode active material (a mixture obtained by mixing the above-mentioned Material 1-1 (the first carbon-based material) and Material 2-1 (the second carbon-based material) in a mass ratio of 70:30), 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 a solvent in a weight ratio of 96.4:1:1.2:1.4 to form a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.

[0230] 2. Positive electrode sheet: LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), conductive agent carbon black (Super P), and binder polyvinylidene fluoride are mixed in a weight ratio of 96:2:2, and an appropriate amount of solvent NMP is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0231] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF 6 is dissolved in the above-mentioned organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0232] 4. Separator: A polypropylene membrane is used.

[0233] 5. Preparation of secondary battery: The positive electrode sheet and negative electrode sheet prepared above are placed in order, and the separator is placed in the middle of the positive electrode sheet and negative electrode sheet to play a role in isolation, 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, a secondary battery is obtained.

[0234] Example 2-8

[0235] The battery preparation method of Example 2-8 is similar to that of Example 1, the difference is that: the first carbon-based material or the second carbon-based material selects I D / I G different materials, for details, see Table 4.

[0236] Comparative Example 1

[0237] A secondary battery is assembled in a similar manner to the preparation method of Example 1, the difference is that: the negative electrode active material only contains the second carbon-based material 2-1 used in Example 1.

[0238] Comparative Example 2

[0239] A secondary battery was assembled in a similar preparation method as in Example 1, except that: the negative electrode active material only contained the first carbon-based material 1-3.

[0240] Performance test

[0241] (1) Energy density

[0242] At 25 °C, the secondary battery was charged at a constant current of 1 / 3C to 4.3V, then charged at a constant voltage of 4.3V until the current reached 0.05C, left standing for 5 min, and then discharged at a constant current of 1 / 3C to 2.8V. 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 4.

[0243] (2) Fast charging performance test of the secondary battery

[0244] At 25 °C, the secondary battery was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage until the current reached 0.05C. After standing for 5 min, the secondary battery was discharged at a constant current of 0.33C to 2.8V, and record its actual capacity as C0.

[0245] Then the secondary battery was successively charged at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 to 4.3V or the 0V negative electrode cut-off potential (whichever is reached first). After each charge was completed, it was discharged at 1C0 to 2.8V. 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 deposit lithium), with the unit of min.

[0246] The shorter this charging time is, the better the kinetic performance of the secondary battery.

[0247] (3) Cycle performance test of the secondary battery

[0248] At 45 °C, the secondary battery prepared above was charged at a constant current of 1C to the upper cut-off voltage of 4.3V (corresponding to 100% SOC), then charged at a constant voltage until the current was 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to the lower cut-off voltage of 2.8V (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.

[0249] Retention rate of capacity (%) of the secondary battery after 1000 cycles at 45 °C = Discharge capacity after 1000 cycles / Discharge capacity of the first cycle × 100%.

[0250] Table 4

[0251]

[0252]

[0253] From the results in Table 4, it can be seen that in the examples, by making the negative active material in the negative electrode film layer include both the first carbon-based material and the second carbon-based material of the present application, it is possible to have both a high energy density and excellent cycle performance and kinetic performance. In addition, by making the I D / I G of the first carbon-based material within the range of 0.155 - 0.220, a secondary battery with better balance of energy density, cycle performance and kinetic performance can be obtained.

[0254] In addition, compared with the examples, in Comparative Example 1 and Comparative Example 2, since only the first carbon-based material or the second carbon-based material is included, the technical effects of the present application cannot be obtained.

[0255] Examples 9 - 13

[0256] The battery preparation methods of Examples 9 - 13 are similar to those of Example 1, the difference being that: for the first carbon-based material, materials with different S2 / S1 were selected, and materials 1 - 6 to materials 1 - 10 were respectively selected. For details, see Table 5.

[0257] It should be noted that, for the convenience of comparison, the data of Example 3 were also included in Table 5.

[0258] Table 5

[0259]

[0260] As can be seen from Table 5, by making the S2 / S1 of the first carbon-based material within the range of 2.5 - 460, the capacity retention rate of the secondary battery is further improved, and better cycle performance is obtained.

[0261] Example 14

[0262] The battery preparation method of Example 14 is similar to that of Example 1, except that the first carbon-based material and the second carbon-based material are made of materials with different DV50 values, as shown in Table 6 for details.

[0263] It should be noted that, for the convenience of comparison, the data of Example 3 are also listed in Table 6.

[0264] Table 6

[0265]

[0266] It can be seen from Table 6 that by making the DV50 of the first carbon-based material greater than the DV50 of the second carbon-based material, the energy density of the secondary battery is further improved, the charging time is shortened, and the battery kinetics is more excellent.

[0267] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material, wherein, the negative electrode active material includes a first carbon-based material and a second carbon-based material; The first carbon-based material has a pore structure, and the I D / I G is less than or equal to 0.280, where I D represents the intensity of the D peak at 1350 ± 50 cm -1 in the Raman spectrum, and I G represents the intensity of the G peak at 1580 ± 50 cm -1 in the Raman spectrum; the second carbon-based material is an amorphous carbon material.

2. The secondary battery according to claim 1, wherein, The I of the first carbon-based material D / I G is 0.155 - 0.

220.

3. The secondary battery according to claim 1 or 2, wherein, The I of the second carbon-based material D / I G is less than or equal to 0.

250. Optionally, the I of the second carbon-based material D / I G is less than or equal to 0.

230.

4. The secondary battery according to any one of claims 1 to 3, wherein, the Dv50 of the first carbon-based material is greater than the Dv50 of the second carbon-based material.

5. The secondary battery according to any one of claims 1 to 4, wherein, the X-ray powder diffraction pattern of the first carbon-based material has diffraction peaks at diffraction angles 2θ of 26.5° ± 0.2°, 44.5° ± 0.2°, and 54.6° ± 0.2°, and there are no diffraction peaks in the X-ray powder diffraction pattern of the second carbon-based material.

6. The secondary battery according to any one of claims 1 to 5, wherein, the first carbon-based material has lattice fringes in HR-TEM, and the second carbon-based material has no lattice fringes in HR-TEM.

7. The secondary battery according to any one of claims 1 to 6, wherein, the powder compaction density of the first carbon-based material under a pressure of 20000 N is greater than the powder compaction density of the second carbon-based material under a pressure of 20000 N.

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

9. The secondary battery according to any one of claims 1 to 8, wherein, 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 .

10. The secondary battery according to any one of claims 1 to 9, wherein, The first carbon-based material includes one or more pore structures with a pore area of 0.15 μm or more, and optionally includes one or more pore structures with a pore area of 0.15 μm 2 -2.0 μm 2 -2.0 μm 2 .

11. The secondary battery according to any one of claims 1 to 10, wherein, 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 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. Optionally, 2.6 ≤ S2 / S1 ≤ 450.

7.

12. The secondary battery according to claim 11, wherein, The area of the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , optionally less than or equal to 0.13 μm 2 ; and / or, The internal region of the first carbon-based material includes one or more pore structures with an area greater than or equal to 0.15 μm 2 , and optionally includes one or more pore structures with an area of 0.15 μm 2 -2.0 μm 2 .

13. The secondary battery according to any one of claims 1 to 12, wherein, the first carbon-based material satisfies at least one of the following conditions: (1) The powder compaction density of the first carbon-based material under a pressure of 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 ; (2) 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; (3) 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; (4) The particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, optionally 0.90 - 1.50; (5) The tap density of the first carbon-based material is 0.85 g / cm 3 -1.30 g / cm 3 , and may be optionally 0.90 g / cm 3 -1.25 g / cm 3 ; (6) The graphitization degree of the first carbon-based material is greater than or equal to 95.5%, and may be optionally 95.5% - 98.0%.

14. The secondary battery according to any one of claims 1 to 13, 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%.

15. The secondary battery according to any one of claims 1 to 14, 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 , and it can be optionally 1.97 g / cm 3 -2.21 g / cm 3 (2) 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; (3) The Dv50 of the second carbon-based material is 4.0 μm - 15.0 μm, and may be optionally 5.0 μm - 15.0 μm; (4) The particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and may be optionally 1.1 - 1.75; (5) 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 ; (6) The tap density of the second carbon-based material is 0.80 g / cm 3 -1.20 g / cm 3 , and may 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, and may be optionally 340 mAh / g - 470 mAh / g.

16. The secondary battery according to any one of claims 1 to 15, wherein, at least a part of the surface of the first carbon-based material and / or the second carbon-based material has a coating layer; optionally, the coating layer includes a carbon coating layer.

17. The secondary battery according to any one of claims 1 to 16, wherein, in the negative electrode active material, the content of the first carbon-based material is greater than or equal to 40 wt%, and may be optionally 50 wt% - 80 wt%.

18. The secondary battery according to any one of claims 1 to 17, wherein, the negative electrode active material further includes a silicon-based material; optionally, in the negative electrode active material, the content of the silicon-based material is 3 wt% - 30 wt%.

19. The secondary battery according to any one of claims 1 to 18, 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 1.40 g / cm 3 -1.70 g / cm 3 , and can be optionally 1.45 g / cm 3 -1.67 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 it 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, and may be optionally 45 μm - 100 μm.

20. An electrical device, characterized in that, it includes the secondary battery according to any one of claims 1 - 19.

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