Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises a first carbon-based material and a second carbon-based material, the first carbon-based material has a pore structure, and the total pore area S2 of an internal region of the first carbon-based material is larger than the total pore area S1 of an external region of the first carbon-based material; and the second carbon-based material meets ID / IG≤0.140.

Description

Secondary battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311643835.4, application date November 30, 2023, and invention name “A secondary battery and electrical device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

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

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. As the scope of secondary battery applications expands, so too does the demand for their performance. For example, the development of various green energy sources requires secondary batteries to have higher storage performance and energy density.

[0005] Summary of the Invention

[0006] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a secondary battery and an electric device, wherein the secondary battery has improved storage performance and energy density.

[0007] The first aspect of the present disclosure provides a secondary battery. The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, wherein the negative electrode active material includes a first carbon-based material and a second carbon-based material, the first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending from the surface of the first carbon-based material to the inside by a distance of 2.5 μm, in a cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure, the total pore area of ​​the external region of the first carbon-based material is recorded as S1, and the total pore area of ​​the internal region of the first carbon-based material is recorded as S2, then the first carbon-based material satisfies: S2>S1; the second carbon-based material satisfies I D / I G ≤0.140, where I D The Raman spectrum of the second carbon-based material is 1350 ± 50 cm -1 The D peak intensity at I G The Raman spectrum of the second carbon-based material is 1580 ± 50 cm-1 The G peak intensity at .

[0008] The total pore area S1 of the outer region of the first carbon-based material is smaller than the total pore area S2 of the inner region. This means that the structure of the outer region of the first carbon-based material is denser than that of the inner region. Compared with traditional natural graphite materials, the stability of the material is improved and the gram capacity is increased, but its storage performance is still not ideal. The second carbon-based material satisfies I D / I G ≤0.140, reflecting fewer surface defects, reduced side reactions, and less active lithium consumption, resulting in a better initial coulombic efficiency and improved battery storage performance. Thus, the negative electrode active material obtained by combining the first carbon-based material and the second carbon-based material in this disclosure can fully leverage the advantages of both to improve the storage performance and energy density of secondary batteries.

[0009] In some embodiments, the second carbon-based material satisfies 0.10≤I D / I G ≤0.14, optionally, 0.11≤I D / I G ≤0.13. When the second carbon-based material satisfies the above I D / I G range, it is beneficial to the improvement of the initial coulombic efficiency and storage performance of the secondary battery.

[0010] In some embodiments, the first carbon-based material D / I G Greater than the I of the second carbon-based material D / I G .

[0011] In some embodiments, the first carbon-based material satisfies I D / I G ≤0.30, optionally, 0.15≤I D / I G ≤0.28.

[0012] By adjusting the I D / I G The value can reduce the reactivity of the negative electrode active material, reduce the side reaction between the negative electrode active material and the electrolyte, and is beneficial to improving the storage performance of the secondary battery.

[0013] In some embodiments, the second carbon-based material is artificial graphite. Artificial graphite has a relatively dense structure with substantially no pores in the particles, resulting in fewer side reactions and good storage and cycle performance.

[0014] In some embodiments, the interlayer spacing of the 002 crystal plane of the first carbon-based material is smaller than the interlayer spacing of the 002 crystal plane of the second carbon-based material. Optionally, the interlayer spacing of the 002 crystal plane of the first carbon-based material is ≤0.33569nm, optionally 0.33557-0.33569nm. Optionally, the interlayer spacing of the 002 crystal plane of the second carbon-based material is ≤0.336088nm, optionally 0.335744-0.336088nm. The interlayer spacing of the 002 crystal plane of the first carbon-based material is within the above range, reflecting a higher degree of graphitization and a higher gram capacity, and thus can effectively improve the energy density of the battery. The second carbon-based material, the smaller interlayer spacing of the 002 crystal plane reflects the high degree of graphitization of the second carbon-based material, and the higher degree of graphitization can enable the second carbon-based material to have a high gram capacity and powder compaction density, which is beneficial to improving the energy density of the secondary battery.

[0015] In any embodiment, the first carbon-based material comprises at least one pore with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15-2.0 μm 2 By making the internal region of the first carbon-based material include a pore structure of the aforementioned size, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles. On the other hand, the compaction density of the negative electrode film layer can be increased, thereby improving the energy density of the secondary battery.

[0016] In some embodiments, the first carbon-based material satisfies the following ratio: 1.5 ≤ S2 / S1 ≤ 450, optionally 2 ≤ S2 / S1 ≤ 400. When the S2 / S1 ratio of the first carbon-based material is within the above range, the material has balanced gram capacity and stability, and can improve its storage performance, resulting in a secondary battery with better energy density and cycle performance.

[0017] In some embodiments, the first carbon-based material includes primary particles. Optionally, the number of primary particles in the first carbon-based material accounts for ≥80%. The first carbon-based material is mainly in the form of primary particles, which is beneficial to maintaining its low side reaction activity and reducing the occurrence of side reactions, thereby further improving the storage performance of the secondary battery. Optionally, the surface of the first carbon-based material does not have a coating layer. The lack of a carbon coating layer on the surface of the first carbon-based material can reduce surface reaction activity, which is beneficial to the storage performance of the secondary battery.

[0018] In some embodiments, the second carbon-based material includes primary particles. Optionally, the number of primary particles in the second carbon-based material accounts for ≥80%. Optionally, the surface of the second carbon-based material does not have a coating layer. Similarly, the second carbon-based material is mainly in the form of primary particles, and further has no carbon coating layer on its surface, which is conducive to maintaining low side reaction activity on the particle surface and reducing the occurrence of side reactions, thereby further improving the storage performance of the secondary battery and reducing the impact on energy density.

[0019] In some embodiments, the first carbon-based material has a higher degree of graphitization than the second carbon-based material. When the two are combined, the higher degree of graphitization of the first carbon-based material can increase the specific capacity of the negative electrode active material, which is beneficial to improving the energy density of the secondary battery.

[0020] In some embodiments, the first carbon-based material has a degree of graphitization of 96% or greater, optionally 96.5% to 98.5%; and / or the second carbon-based material has a degree of graphitization of 91% to 96.5%, optionally 92% to 96%. The graphitization degrees of the first and second carbon-based materials within the above ranges enable the secondary battery to have a higher energy density.

[0021] In some embodiments, the specific surface area of ​​the first carbon-based material is greater than that of the second carbon-based material. By adjusting the specific surface areas of the first and second carbon-based materials, the occurrence of side reactions can be reduced, and the consumption of active ions by SEI film formation can be reduced, thereby improving cycling performance and storage performance while achieving a high initial coulombic efficiency.

[0022] In some embodiments, the specific surface area of ​​the first carbon-based material is less than or equal to 2.1 m 2 / g, optionally 1.3m 2 / g-2.1m 2 / g; the specific surface area of ​​the second carbon-based material is less than or equal to 1.3m 2 / g, optional 0.8m 2 / g-1.2m 2 When the specific surface areas of the first carbon-based material and the second carbon-based material are respectively within the above ranges, the secondary battery has improved storage performance while also taking into account cycle performance.

[0023] In any embodiment, the volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material.

[0024] In some embodiments, the negative electrode active material satisfies at least one of the following:

[0025] (1) The volume distribution particle size Dv50 of the negative electrode active material is ≥10 μm, and can be selected from 10 μm to 23 μm.

[0026] (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤ 40 μm, and can be selected from 23 μm to 40 μm.

[0027] (3) The particle size distribution of the negative electrode active material [(Dv90)-(Dv10)] / (Dv50)] is ≤1.20, and can be optionally 0.9-1.20.

[0028] (4) The gram capacity of the negative electrode active material is ≥358 mAh / g, and can be optionally 358 mAh / g-370 mAh / g.

[0029] (5) The negative electrode active material satisfies I D / I G ≤0.2, optionally 0.13-0.20, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0030] By combining the first carbon-based material and the second carbon-based material having the above-mentioned properties, a negative electrode active material having any one of the properties (1)-(5) above can be obtained, thereby improving the overall storage performance and gram capacity of the negative electrode active material, thereby enabling the secondary battery to have improved storage performance and energy density while taking into account the cycle performance.

[0031] In some embodiments, the first carbon-based material satisfies at least one of the following:

[0032] (1) The volume distribution particle size Dv50 of the first carbon-based material is ≥13 μm, optionally 15 μm-25 μm.

[0033] (2) The volume distribution particle size Dv90 of the first carbon-based material is ≤40 μm, and can be optionally 28 μm-40 μm.

[0034] The particles of the first carbon-based material have a relatively large particle size. When the volume distribution particle size Dv50 and / or Dv90 thereof is within the above range, it is beneficial to reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0035] (3) The particle size distribution of the first carbon-based material is [(Dv90) - (Dv10)] / (Dv50)] ≤ 1.55, optionally 0.90-1.50. When the particle size distribution of the first carbon-based material is within the above range, its particle packing performance is good, which is beneficial to increasing the compaction density of the negative electrode film layer and improving the energy density of the secondary battery.

[0036] (4) The gram capacity of the first carbon-based material is ≥360 mAh / g, optionally 365 mAh / g-372 mAh / g. When the gram capacity of the first carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0037] When the first carbon-based material further has any one of the properties (1) to (5) above, it is beneficial to at least one of the storage performance and energy density cycle performance of the secondary battery.

[0038] In some embodiments, the second carbon-based material satisfies at least one of the following:

[0039] (1) The volume distribution particle size Dv50 of the second carbon-based material is ≤ 18 μm, and can optionally be 13 μm-18 μm. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, the specific surface area of ​​the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0040] (2) The particle size distribution of the second carbon-based material [(Dv90) - (Dv10)] / (Dv50)] is ≤ 1.35, and optionally 1.0-1.30. When the particle size distribution of the second carbon-based material is within the above range, its particle packing performance is good, which is conducive to increasing the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0041] (3) The gram capacity of the second carbon-based material is ≥357 mAh / g, and can be 357 mAh / g-363 mAh / g. When the gram capacity of the second carbon-based material is within the above range, the energy density of the secondary battery can be improved.

[0042] When the second carbon-based material further has any one of the properties (1) to (3) above, it is possible to improve at least one of the storage performance, energy density, and cycle performance of the secondary battery.

[0043] In some embodiments, the first carbon-based material accounts for ≥30 wt% of the negative electrode active material, and optionally 50 wt% to 80 wt%. When the first carbon-based material accounts for a mass fraction of the negative electrode active material within the above range, the first carbon-based material and the second carbon-based material can jointly leverage their respective advantages to achieve improved storage performance while also achieving good energy density.

[0044] In some embodiments, the negative electrode active material further comprises a silicon-based material. Silicon-based materials can improve the pore structure in the negative electrode film, facilitating electrolyte infiltration and retention, thereby enhancing the dynamic performance of the secondary battery. They can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0045] In some embodiments, the negative electrode film layer satisfies at least one of the following:

[0046] (1) The compaction density of the negative electrode film is ≥1.40 g / cm 3 , optionally 1.45 g / cm 3 -1.90g / cm 3 .

[0047] (2) The surface density of the negative electrode film layer is ≥6.0 g / cm 2 , optionally 7.0 g / cm 2 -15g / cm 2 .

[0048] (3) The porosity of the negative electrode film layer is 18.0%-36.7%, optionally 19.0%-34.0%.

[0049] (4) The thickness of the negative electrode film layer is ≥70 μm, and can be optionally 90 μm-130 μm.

[0050] When the negative electrode film layer has any one of the properties (1) to (4) above, it is beneficial to at least one of the storage performance and energy density of the secondary battery.

[0051] A second aspect of the present disclosure further provides an electrical device, comprising the secondary battery according to any of the embodiments of the first aspect of the present disclosure.

[0052] The electric device disclosed in the present invention includes any one of the secondary batteries of the various embodiments of the first aspect, and thus has at least the same advantages as the secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG1 is a schematic diagram of a cross-sectional image of a particle of a first carbon-based material of the present disclosure.

[0054] FIG2 is an ion polishing cross-sectional (CP) diagram of an embodiment of the first carbon-based material disclosed herein.

[0055] FIG. 3 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0056] FIG. 4 is an exploded view of the battery cell shown in FIG. 3 according to an embodiment of the present disclosure.

[0057] FIG5 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0058] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0059] FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present disclosure.

[0060] FIG8 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0061] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0062] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0063] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0066] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0067] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0068] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0069] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0070] When improving the storage performance of secondary batteries, it is desirable to use carbon materials with stable surfaces and few internal defects, such as artificial graphite. However, such materials often have unsatisfactory specific capacity, resulting in a low energy density of the secondary battery. Natural graphite has a high degree of graphitization and a high specific capacity, and natural graphite has a large number of pores inside, which makes it easy to obtain a high compaction density and improve the capacity density of the secondary battery. However, natural graphite has many surface defects and a porous structure that leads to more side reactions, low initial coulombic efficiency, which reduces the storage performance of the secondary battery. In addition, during the charge and discharge process, the material is prone to expansion, resulting in an unsatisfactory cycle life of the secondary battery. Carbon coating of natural graphite particles can inhibit their expansion to a certain extent. However, the carbon coating layer often forms amorphous carbon with high reaction activity, which is not conducive to the storage performance of the secondary battery. In addition, when the energy density of the secondary battery is increased by, for example, increasing the compaction density of the negative electrode film layer, the electrolyte wetting characteristics of the negative electrode film layer deteriorate at high compaction density, and the risk of negative electrode active material particles breaking increases, thereby increasing side reactions inside the battery, which in turn affects the storage performance of the secondary battery.

[0071] Therefore, current secondary batteries often find it difficult to achieve both high energy density, good storage performance, and cycle life.

[0072] In view of this, a first aspect of an embodiment of the present disclosure provides a secondary battery.

[0073] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0074] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0075] [Negative electrode]

[0076] The secondary battery disclosed in the present invention includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material. The negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm from the surface of the first carbon-based material to the inside. In the cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure, the total pore area of ​​the external region of the first carbon-based material is recorded as S1, and the total pore area of ​​the internal region of the first carbon-based material is recorded as S2. Then the first carbon-based material satisfies: S2>S1; the second carbon-based material satisfies I D / I G ≤0.140, where I D The Raman spectrum of the second carbon-based material is 1350 ± 50 cm -1 The D peak intensity at I G The Raman spectrum of the second carbon-based material is 1580 ± 50 cm -1 The G peak intensity at .

[0077] In the present disclosure, the total pore area S1 of the outer region of the first carbon-based material is smaller than the total pore area S2 of the inner region. This means that the structure of the outer region of the first carbon-based material is denser than that of the inner region. In addition, the first carbon-based material in the present disclosure satisfies "S1>S2", which means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (for example, a scanning electron microscope image with a magnification of 1000 times). That is, the area of ​​the pores in the main structure of the first carbon-based material, especially the pores in the outer region, is significantly smaller than the area of ​​the pores in the inner region.

[0078] Referring to Figure 1 , a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 100 of the present disclosure is shown, and the cross-sectional image passes through the center of the particle of the first carbon-based material 100. As shown in Figure 1 , the region extending 2.5 μm from the particle surface of the first carbon-based material 100 toward the interior of the particle is denoted as the outer region 101, and the region inside the outer region 101 is denoted as the inner region 102.

[0079] The pore structure in the first carbon-based material can be observed by a cross-sectional polisher, for example, by performing an ion polishing cross-sectional morphology (CP) test on the negative electrode sheet. Specifically, the negative electrode sheet is cut into a sample to be tested of a certain size (e.g., 2 cm×2 cm), and the negative electrode sheet is fixed on a sample stage using paraffin wax; the sample stage is placed in a sample holder and locked and fixed, the argon ion cross-sectional polisher (e.g., IB-09010CP argon ion cross-sectional polisher from JEOL, Japan) is powered on and vacuumed (e.g., 10-4 Pa), the argon flow rate (e.g., 0.15 MPa) and voltage (e.g., 8 KV) and polishing time (e.g., 2 h) are set, and the sample stage is adjusted to a rocking mode to start polishing; a certain area in the first area 1021 is randomly selected from the sample to be tested for scanning testing (e.g., referring to JY / T010-1996, scanning is performed using a scanning electron microscope), and an ion polishing cross-sectional morphology (CP) image of the negative electrode sheet is obtained at a certain magnification (e.g., 1000 times). As shown in FIG. 2 , it can be seen that the first carbon-based material has a certain number of pores in the inner region near the center of the particle, while the outer region near the surface of the particle has a denser structure.

[0080] The second carbon-based material of the present disclosure satisfies I D / I G ≤0.140. I D / I G The value reflects, to a certain extent, the carbon disorder on the material surface. The lower the value, the fewer surface defects the material has, the lower the carbon disorder, the lower the reaction activity, the fewer side reactions with the electrolyte, the less consumption of active ions, and the higher the initial coulombic efficiency, which is beneficial to improving the storage performance of the secondary battery.

[0081] According to the above definition, when the particles of the first carbon-based material satisfy S2>S1, it is beneficial to the stability of the material, reduces the expansion during the charge and discharge cycle, and has an increased gram capacity, which is beneficial to improving the energy density of the secondary battery and having improved cycle performance. However, the storage performance of the first carbon-based material is still insufficient. By meeting I D / I G The mixed use of the second carbon-based material with a carbon content of ≤0.140 can make up for the insufficient storage performance of the first carbon-based material, thereby obtaining a secondary battery with improved energy density and storage performance.

[0082] In some embodiments, the second carbon-based material satisfies 0.10≤I D / I G ≤0.14, optionally, 0.11≤I D / I G ≤0.13. When the second carbon-based material satisfies the above I D / I G range, the surface stability is high, the side reaction with the electrolyte is small, the consumption of active ions is small, and the first coulombic efficiency of the negative electrode can be improved, which is beneficial to the storage performance of the secondary battery, including the improvement of high-temperature storage performance.

[0083] In some embodiments, the first carbon-based material D / I G Greater than the I of the second carbon-based material D / I G .

[0084] In some embodiments, the first carbon-based material satisfies I D / I G ≤0.30, optionally, 0.15≤I D / I G ≤0.28.

[0085] First carbon-based material I D / I G When the value is within the above range, the surface properties of the material are relatively stable, which can reduce the overall reaction activity of the negative electrode active material and reduce the side reaction between the negative electrode active material and the electrolyte, which is conducive to further improving the storage performance of the secondary battery.

[0086] In some embodiments, the second carbon-based material is artificial graphite. Artificial graphite has a relatively dense structure with substantially no pores in the particles, thereby reducing side reactions and having good storage performance.

[0087] In this disclosure, artificial graphite generally refers to crystalline carbon obtained through a high-temperature graphitization process. The particles generally lack a pore structure, or lack a pore structure that can be directly observed from a cross-sectional image (e.g., a scanning electron microscope image at a magnification of 1000x). Therefore, by obtaining a cross-section of the negative electrode sheet using a cross-section polisher and observing it under a microscope, it can be distinguished from the first carbon-based material.

[0088] Mixing the second carbon material of artificial graphite with excellent storage performance and cycle performance with the first carbon material with high gram capacity and improved cycle performance can make the secondary battery have higher energy density and storage performance while taking into account better cycle performance.

[0089] In some embodiments, the interlayer spacing of the 002 crystal plane of the first carbon-based material is smaller than the interlayer spacing of the 002 crystal plane of the second carbon-based material. The present disclosure combines first and second carbon-based materials, each having good storage performance and gram capacity, to obtain a negative electrode active material by adjusting the interlayer spacing of the 002 crystal planes of the two carbon-based materials. The smaller interlayer spacing of the 002 crystal plane of the first carbon-based material contributes to a greater gram capacity.

[0090] According to some embodiments, the interlayer spacing of the 002 crystal plane of the first carbon-based material is ≤0.33569nm, optionally 0.33557-0.33569nm. According to some embodiments, the interlayer spacing of the 002 crystal plane of the second carbon-based material is ≤0.336088nm, optionally 0.335744-0.336088nm. The smaller interlayer spacing of the 002 crystal plane of the first carbon-based material reflects that the material has a higher degree of graphitization, and thus has a higher gram capacity, and thus can effectively improve the energy density of the secondary battery. The second carbon-based material, the smaller interlayer spacing of the 002 crystal plane reflects that the second carbon-based material also has a higher degree of graphitization. The higher degree of graphitization can enable the second carbon-based material to have a high gram capacity and powder compaction, which is beneficial to improving the energy density of the battery cell.

[0091] In some embodiments, the first carbon-based material comprises one or more pores with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15-2.0 μm 2 pore structure.

[0092] In the present disclosure, "a pore structure within an interior region of a material (e.g., the first carbon-based material)" means that the material has a pore structure that can be directly observed from a cross-sectional image (e.g., a scanning electron microscope image at a magnification of 1000x), i.e., the first carbon-based material has a pore structure within its main structure. More specifically, the main structure has a pore structure at least within its interior.

[0093] By making the inner region of the first carbon-based material include a pore structure of the above size, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, thereby facilitating the cycle life of the secondary battery.

[0094] In some embodiments, the first carbon-based material satisfies: 1.5≤S2 / S1≤450, optionally, 2≤S2 / S1≤400. Exemplarily, the first carbon-based material satisfies: 2.0≤S2 / S1≤400, 2.4≤S2 / S1≤300, 2.5≤S2 / S1≤250, 2.6≤S2 / S1≤200, 2.8≤S2 / S1≤150, or 3.0≤S2 / S1≤100. When the S2 / S1 of the first carbon-based material is within the above range, it reflects that the pore structure of the outer region of the particle is smaller and has a relatively dense structure, thereby improving the stability of the material while helping to reduce the side reaction between the first carbon-based material and the electrolyte, and reducing the formation of the SEI film inside the particle, reducing the loss of active substances. Therefore, the first carbon-based material has a balanced gram capacity and stability, and can improve its storage performance, so that the secondary battery has better energy density and cycle performance.

[0095] In some embodiments, the first carbon-based material includes primary particles. Optionally, the number of primary particles in the first carbon-based material accounts for greater than or equal to 80%. For example, the number of primary particles in the first carbon-based material accounts for greater than or equal to 80%, 85%, 90%, 95%, or even all of them are primary particles. The first carbon-based material is advantageously mainly composed of primary particles. Primary particles are conducive to maintaining the stability of their surface, thereby reducing side reactions, which is beneficial to the storage performance and high energy density of the secondary battery.

[0096] In some embodiments, the primary particles of the first carbon-based material do not have a coating on their surfaces. Conventional carbon coatings on carbon-based materials are soft carbon, which has low specific capacity and high active ion consumption, resulting in poor storage performance. Therefore, the absence of a coating on the first carbon-based material helps maintain low side reaction activity, reducing the occurrence of side reactions, thereby maintaining the storage performance of the secondary battery; furthermore, it does not adversely affect the capacity density of the secondary battery.

[0097] In some embodiments, the second carbon-based material includes primary particles. Optionally, the primary particles in the second carbon-based material account for greater than or equal to 80%. For example, the primary particles in the second carbon-based material account for greater than or equal to 80%, 85%, 90%, 95%, or even all of them are primary particles. Similarly, the second carbon-based material is advantageously mainly primary particles. Primary particles help maintain the stability of their surface, thereby reducing side reactions and improving the storage performance of the secondary battery.

[0098] In some embodiments, the primary particles of the second carbon-based material do not have a coating layer on their surfaces. Similarly, the primary particles of the second carbon-based material without a coating layer are advantageously used to maintain low side reaction activity and reduce the occurrence of side reactions, thereby further improving the storage performance of the secondary battery; and do not adversely affect the capacity density of the secondary battery.

[0099] In some embodiments, the first carbon-based material has a greater degree of graphitization than the second carbon-based material. Adjusting the degree of graphitization of the first and second carbon-based materials can increase the specific capacity of the negative electrode active material, thereby improving the energy density of the secondary battery.

[0100] In some embodiments, the degree of graphitization of the first carbon-based material is greater than or equal to 96.0%, optionally 96.5%-98.5%. For example, the degree of graphitization of the first carbon-based material may be 96.0%, 96.5%, 97.0%, 97.5%, 98.0%, 98.5%, or a value between any two values. By adjusting the degree of graphitization of the first carbon-based material within the above range, it is beneficial for the negative electrode active material to have a high gram capacity, thereby allowing the secondary battery to have an improved energy density.

[0101] In some embodiments, the degree of graphitization of the second carbon-based material is 91%-96.5%, optionally 92%-96%. For example, the degree of graphitization of the first carbon-based material may be 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, or any value between two values. Selecting a relatively high degree of graphitization of the second carbon-based material is beneficial to the energy density of the secondary battery while providing good storage performance.

[0102] In some embodiments, the BET specific surface area of ​​the first carbon-based material is greater than the BET specific surface area of ​​the second carbon-based material.

[0103] In some embodiments, the specific surface area of ​​the first carbon-based material is BET ≤ 2.1 m 2 / g, optionally 1.3m 2 / g-2.1m 2 / g. For example, the surface area of ​​the first carbon-based material may be 1.3m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 1.9m 2 / g, 2.1m 2 / g, or a value between any two values. Since the internal region of the first carbon-based material has a porous structure, the specific surface area is larger than that of the second carbon material including the artificial graphite with a dense overall structure. The specific surface area of ​​the first carbon-based material is controlled to be less than or equal to 2.1m 2 / g can reduce the reactivity of the first carbon-based material, which is beneficial to the storage performance of the secondary battery.

[0104] In some embodiments, the specific surface area of ​​the second carbon-based material is less than or equal to 1.3 m 2 / g, optional 0.8m 2 / g-1.2m 2 For example, the surface area of ​​the second carbon-based material may be 0.8 m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, or any value between two values.

[0105] By adjusting the first and second carbon-based materials to have a smaller specific surface area, the reaction activity of the material can be reduced, the occurrence of side reactions can be reduced, and the consumption of active ions in SEI film formation can be reduced, thereby having a higher first coulombic efficiency, which is beneficial to the cycle performance and storage performance.

[0106] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material.

[0107] In some embodiments, the tap density of the first carbon-based material is greater than the tap density of the second carbon-based material.

[0108] When the first carbon-based material and the second carbon-based material meeting the above design are combined as negative electrode active materials, the negative electrode active materials meet one or more of the following characteristics, so that the secondary battery has good energy density and storage performance while taking into account cycle life.

[0109] The volume distribution particle size Dv50 of the negative electrode active material is ≥10 μm, and can be selected from 10 μm to 23 μm.

[0110] The volume distribution particle size Dv90 of the negative electrode active material is ≤40 μm, and can be optionally 23 μm-40 μm.

[0111] The particle size distribution of the negative electrode active material [(Dv90)-(Dv10)] / (Dv50)] is ≤1.20, and can be optionally 0.9-1.20.

[0112] The gram capacity of the negative electrode active material is ≥358 mAh / g, and can be optionally 358 mAh / g-370 mAh / g.

[0113] The negative electrode active material satisfies I D / I G ≤0.2, optionally 0.13-0.2, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0114] By combining the first carbon-based material and the second carbon-based material having the above-mentioned properties, a negative electrode active material having any of the above-mentioned properties can be obtained, thereby improving the overall storage performance and capacity of the negative electrode active material, thereby enabling the secondary battery to have improved storage performance and energy density while taking into account cycle performance.

[0115] In some embodiments, when the first carbon-based material further satisfies one or more of the following conditions on the basis of satisfying the above-mentioned design, it can further reduce the adverse effects on the reaction performance of the material surface, increase the gram capacity, and further improve the performance of the secondary battery, for example, further improve at least one of the energy density, storage performance, and cycle performance of the secondary battery.

[0116] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is ≥13 μm, optionally 15 μm-25 μm. For example, the volume distribution particle size Dv50 of the first carbon-based material is 15 μm, 17 μm, 20 μm, 23 μm, 25 μm, etc., or a value between any two values, but is not limited thereto.

[0117] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is ≤40 μm, optionally 28 μm-40 μm. For example, the volume distribution particle size Dv90 of the first carbon-based material is 28 μm, 30 μm, 33 μm, 35 μm, 37 μm, 40 μm, or a range between any two values, but is not limited thereto.

[0118] The particles of the first carbon-based material have a relatively large particle size. When the volume distribution particle size Dv50 and / or Dv90 thereof is within the above range, it is beneficial to reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0119] In some embodiments, the particle size distribution of the first carbon-based material [(Dv90)-(Dv10)] / (Dv50)] ≤ 1.55, optionally 0.90-1.50. For example, the particle size distribution of the first carbon-based material [(Dv90)-(Dv10)] / (Dv50)] is 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, 1.55, etc., or a value between the ranges consisting of any two values, but not limited thereto. When the particle size distribution of the first carbon-based material is within the above range, its particle stacking performance is better, which is beneficial to improve the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0120] In some embodiments, the gram capacity of the first carbon-based material is ≥360 mAh / g, optionally 365 mAh / g-372 mAh / g. When the gram capacity of the first carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0121] In some embodiments, when the second carbon-based material further satisfies one or more of the following conditions on the basis of satisfying the above-mentioned design, while having good cycle performance, it can further reduce the reactivity of the negative electrode active material, increase the gram capacity of the negative electrode active material, and increase the compaction density of the negative electrode film layer, thereby further improving the performance of the secondary battery, for example, further improving at least one of the energy density, storage performance, and cycle performance of the secondary battery.

[0122] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is ≤18 μm, optionally 13 μm-18 μm. Exemplarily, the volume distribution particle size Dv50 of the second carbon-based material is 13 μm, 14 μm, 15 μm, 15.5 μm, 16 μm, 17 μm, 18 μm, etc., or a value between any two values. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, the specific surface area of ​​the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0123] In some embodiments, the particle size distribution of the second carbon-based material [(Dv90)-(Dv10)] / (Dv50)] is ≤1.35, optionally 1.0-1.35. Exemplarily, the particle size distribution of the second carbon-based material [(Dv90)-(Dv10)] / (Dv50)] is 1.0, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, etc., or a value between any two values. When the particle size distribution of the second carbon-based material is within the above range, its particle stacking performance is better, which is beneficial to improve the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0124] In some embodiments, the gram capacity of the second carbon-based material is greater than or equal to 357 mAh / g, and can be 357 mAh / g-363 mAh / g. Exemplarily, the gram capacity of the second carbon-based material is 357 mAh / g, 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, or the like, or a value between any two values. When the gram capacity of the second carbon-based material is within the above range, on the one hand, the energy density of the secondary battery can be improved.

[0125] In some embodiments, in the negative electrode active material, the mass proportion of the first carbon-based material is ≥30 wt %, optionally 50 wt %-80 wt %. Exemplarily, in the negative electrode active material, the mass proportion of the first carbon-based material is 50 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, or a value or range formed between any two values.

[0126] When the mass proportion of the first carbon-based material in the negative electrode active material is within the above range, it can work together with the second carbon-based material to exert their respective advantages to obtain improved storage performance while having good cycle performance and energy density.

[0127] In some embodiments, the mass proportion of the second carbon-based material in the negative electrode active material is ≤70wt%, optionally 20-50wt%. Exemplarily, the mass proportion of the second carbon-based material in the negative electrode active material is 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, etc., or a value or range formed between any two values.

[0128] In some embodiments, the negative electrode active material is composed of the first carbon-based material and the second carbon-based material.

[0129] In other embodiments, the negative electrode active material may also include other negative electrode active materials known in the art, such as silicon-based materials. Silicon-based materials can improve the pore structure in the negative electrode film, facilitating electrolyte infiltration and retention, thereby enhancing the dynamic performance of the secondary battery. They can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0130] The silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys.

[0131] In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material is less than or equal to 10%, and optionally 3%-10%. This can improve the secondary battery's performance and energy density while ensuring good cycle performance and storage performance.

[0132] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0134] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0135] Further research has found that when the negative electrode film layer meets one or more of the following conditions, the performance of the secondary battery can be further improved, for example, at least one of the energy density, storage performance, and cycle performance of the secondary battery can be further improved.

[0136] In some embodiments, the compaction density of the negative electrode film layer is ≤1.40 g / cm 3 , optionally 1.45 g / cm 3 -1.90g / cm 3 For example, the compaction density of the negative electrode film layer is 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, or any range of two values, but is not limited thereto. A compaction density of the negative electrode film layer within the above range is beneficial for achieving both high capacity and, in turn, high storage performance and high energy density in the secondary battery.

[0137] In some embodiments, the surface density of the negative electrode film layer is ≥6.0 g / cm 2 , optionally 7.0 g / cm 2 -15g / cm 2 For example, the compaction density of the negative electrode film is 6.0 g / cm 2 , 7.0g / cm 2 , 8.0g / cm 2 , 9.0g / cm 2 、10.0g / cm 2 、11.0g / cm 2、12.0g / cm 2 、13.0g / cm 2 、14.0g / cm 2 、15.0g / cm 2 etc., or a value between any two values ​​in a range.

[0138] The area density of the negative electrode film layer being within the above range is beneficial for the negative electrode film layer to have both high capacity and high energy density, thereby being beneficial for the secondary battery to have both high energy density and good storage performance.

[0139] In some embodiments, the porosity of the negative electrode film layer is 18.0%-36.7%, optionally 19.0%-34.0%. For example, the compacted density of the negative electrode film layer is 18.0%, 20.0%, 22.0%, 24.0%, 26.0%, 28.0%, 30.0%, 32.0%, 34.0%, or a range between any two values. This helps the negative electrode film layer achieve both high capacity and high energy density, which in turn helps the secondary battery achieve both high energy density and good storage performance.

[0140] In any embodiment, the thickness of the negative electrode film layer is ≥70 μm, and optionally 90 μm-130 μm. For example, the thickness of the negative electrode film layer is 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, etc., or a value between any two values.

[0141] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0142] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material including the first carbon-based material and the second carbon-based material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0143] The above embodiments are described only by taking the composition of the negative electrode film layer on the surface of one side of the negative electrode current collector as an example. It should be understood that the negative electrode current collector has two surfaces opposite to each other in the direction of its thickness, and the negative electrode film layer described in the above embodiments is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, porosity, thickness, etc.) given in the present disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is arranged on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of the present disclosure and are considered to fall within the scope of protection of the present disclosure.

[0144] In the present disclosure, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0145] In the present disclosure, the total pore area S1 of the outer region and the total pore area S2 of the inner region of a material (e.g., a first carbon-based material) can be obtained by using a cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL, Japan) to obtain the cross-section of the carbon material; then, referring to JY / T010-1996, a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany) is used to scan the cross-section of the carbon material; finally, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material are obtained respectively through image processing software (e.g., AVIZO), and the value of S2 / S1 can be obtained thereby. For example, samples can be obtained from different areas of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross section. The total pore area S2' and the total pore area S1' of the inner region of each particle cross section are obtained using image processing software according to the above definition, and the S2' / S1' value of each particle cross section is obtained. The arithmetic average of the S2' / S1' of all the measured particle cross sections is calculated as the S2 / S1 value of the first carbon-based material.

[0146] In the present disclosure, the I of a material (eg, a first carbon-based material, a second carbon-based material, etc.) D / I G The value can be tested using Raman spectrometer, I D The Raman spectrum of the material is 1350±50cm-1 The D peak intensity at I G The Raman spectrum of the material is 1580±50cm -1 The test conditions are: excitation wavelength 532nm, grating 600 lines, objective lens 50 times, integration time 10s, accumulation times 3 times, surface scanning, obtain the D peak and G peak intensity of 100 points, calculate the I of 100 points D / I G , remove the largest and smallest 25 I D / I G The average value of the remaining 50 points is the I D / I G The testing instrument may be a Horiba LabRAM HR800 Raman spectrometer.

[0147] In the present disclosure, the interlayer spacing of the 002 crystal plane of a material (e.g., the first carbon-based material, the second carbon-based material) has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., a 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 interlayer spacing of the C(002) crystal plane in the material's crystal structure.

[0148] In the present disclosure, the degree of graphitization of a material (e.g., the first carbon-based material, the second carbon-based material) has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) plane in the crystal structure of the material. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0149] In this disclosure, primary particles and secondary particles have meanings well known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0150] In the present disclosure, the proportion of primary particles in the first carbon-based material and / or the second carbon-based material, taking the first carbon-based material as an example, refers to: randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the proportion of the number of first carbon-based materials with primary particle morphology in each image to the total number of particles of the first carbon-based material. The average value of multiple statistical results is the proportion of primary particles in the first carbon-based material.

[0151] In the present disclosure, whether there is a coating layer on the surface of a material (eg, the first carbon-based material, the second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0152] In the present disclosure, the specific surface area of ​​a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.

[0153] In the present disclosure, the volume distribution particle size Dv10, Dv50, and Dv90 of the material (e.g., the first carbon-based material, the second carbon-based material, etc.) are well-known in the art, and respectively represent the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer with reference to GB / T 19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0154] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be tested using methods known in the art. An exemplary test method is as follows: the sample powder is mixed evenly with the conductive agent carbon black (Super P), the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is applied to the surface of the negative electrode current collector copper foil, dried in an oven and set aside; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to a concentration of 1 mol / L The electrolyte was then added. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. The cells were assembled into CR2430 button cells in an argon-protected glove box with the electrolyte. After standing for 12 hours, the cells were discharged at 0.05C to 0.005V at 25°C. The cells were then allowed to stand for 10 minutes, and then discharged again at 50μA to 0.005V. The cells were allowed to stand for 10 minutes, and then discharged again at 10μA to 0.005V. The cells were then charged at 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0155] In the present disclosure, the powder compaction density of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and added to a container with a bottom area of ​​1.327 cm 2 In the mold, pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the powder compaction density of the material under 50000N pressure.

[0156] In the present disclosure, the areal density of the negative electrode film layer has a meaning well known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold pressed can be taken (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), punched into small discs with an area of ​​S1, weighed, and recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode sheet = (M1-M0) / S1.

[0157] In this disclosure, the compacted density of the negative electrode film layer is well known in the art and can be measured using methods known in the art. The compacted density of the negative electrode film layer = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0158] In the present disclosure, the thickness of the negative electrode film layer has a well-known meaning in the art and can be measured by methods known in the art, such as using a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0159] In the X-ray diffraction analysis test disclosed herein, a copper target can be used as an anode target, and CuKα rays can be used as a radiation source. The wavelength of the rays is The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0160] It should be noted that the various parameter tests on the negative electrode active material or the negative electrode film layer can be performed by sampling and testing the prepared secondary battery according to the following steps.

[0161] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged). Disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2-10 hours). Then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours). After drying, remove the negative electrode. Samples can now be taken from the dried negative electrode to test the aforementioned parameters related to the negative electrode film, such as the surface density, compacted density, porosity, OI value, thickness, etc.

[0162] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2 hours), and a sample of the negative electrode active material is taken from any area of ​​the baked negative electrode sheet (a blade can be used for scraping powder sampling); the collected negative electrode active material is sieved (for example, sieved with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the above-mentioned negative electrode active materials.

[0163] In the present disclosure, the first carbon-based material and the second carbon-based material mentioned above can be obtained commercially, or can also be prepared by the following method of the present disclosure.

[0164] In some embodiments, the preparation method of the first carbon-based material includes: step 1, providing a raw material having multiple pore structures; step 2, mixing the above raw material and the filling material evenly in a predetermined proportion, then keeping it warm at a first temperature T1 for a first time t1, and cooling it to room temperature to obtain an intermediate; step 3, keeping the obtained intermediate warm at a second temperature T2 for a second time t2, and obtaining the first carbon-based material after the end, wherein the first carbon-based material has a pore structure, the total pore area of ​​the external region of the first carbon-based material is recorded as S1, and the total pore area of ​​the internal region of the first carbon-based material is recorded as S2, then the first carbon-based material satisfies: S2>S1.

[0165] In some embodiments, in step 1, the raw material for preparing the first carbon-based material includes natural graphite. Natural graphite generally refers to graphite naturally formed in nature, which does not require graphitization, and the interior of natural graphite particles generally has a relatively large number of closed-pore structures. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and particularly includes natural spherical graphite.

[0166] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with a desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes crushing, classification, spheroidization, purification, and other processes.

[0167] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 6.0 μm-25.0 μm.

[0168] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥2.5m 2 / g, optional 2.5m 2 / g-10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to perform subsequent filling treatment and obtain the first carbon-based material with a desired specific surface area.

[0169] In some embodiments, in step 2, the softening point temperature of the filling material is 90° C.-150° C. Optionally, the softening point temperature of the 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.

[0170] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected from 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, and 3 μm-5 μm. This facilitates the filler material to be melted by heat and filled into the pore structure of the raw material, and also helps to improve the uniformity of the dispersion of the filler material and the raw material.

[0171] In some embodiments, in step 2, the coking value of the filler material is 15%-40%, and optionally 18%-34%. In this disclosure, the coking value of the filler material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured in accordance with GB / T 8727-2008.

[0172] In some embodiments, in step 2, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and may optionally include one or more of coal tar and petroleum asphalt.

[0173] 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, and can be optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, (15-25):100.

[0174] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filling material within the above-mentioned range, the number of pores and / or pore size in the outer and inner regions of the first carbon-based material can be adjusted within a suitable range, thereby making the S2 / S1 of the first carbon-based material within a suitable range.

[0175] By adjusting the type, softening point, coking value, addition amount and other parameters of the filling material within the above range, the viscosity of the filling material is not high after being heated and melted, and it maintains good fluidity. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process. This can also reduce the problems of increased surface defects of the first carbon-based material particles and increased surface active sites due to the need to add a depolymerization process.

[0176] In some embodiments, in step 2, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 may be a staged heating process.

[0177] In some embodiments, the staged temperature increasing process includes a first temperature increasing process, a second temperature increasing process, and a third temperature increasing process.

[0178] In some embodiments, the first temperature rising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 0.5 h-3 h.

[0179] In some embodiments, the second heating process is to heat the material to 450°C-550°C and hold the temperature at that temperature for 0-2 hours. When the holding time is 0 hours, it means that when the temperature is within the range of 450°C-550°C, no holding treatment is performed, but the temperature is continued to the first temperature T1.

[0180] In some embodiments, the third temperature increasing process is to increase the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0181] In the staged heating process, the temperature is first raised to 200℃-250℃. Since the heating temperature is higher than the softening point of the filling material, the filling material is melted and softened by the heat. Keeping it warm for 0.5h-3h allows it to flow and fill into the pore structure of the raw material; then the temperature is raised to 450℃-550℃. At this time, the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state and turning into a viscous liquid or solid, thereby preventing the filling material from entering the entire pore structure of the raw material; finally, the temperature is raised to the first temperature. At this time, the filling material undergoes a carbonization reaction, thereby enabling the pore structure occupied by the filling material to be effectively filled.

[0182] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min-10°C / min. For example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any range thereof. Alternatively, the heating rate is 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, 2°C / min-6°C / min, or 2°C / min-5°C / min.

[0183] In some embodiments, the heating rate of the first heating process may be 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, 2°C / min-6°C / min, or 2°C / min-5°C / min. In some embodiments, the heating rate of the second heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min. In some embodiments, the heating rate of the third heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min.

[0184] In some embodiments, in step 2, the first temperature T1 is 700° C.-1200° C. For example, the first temperature T1 can be 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., 1100° C., 1200° C., or any range thereof. Alternatively, the first temperature T1 is 750° C.-1100° C., 800° C.-1100° C., 850° C.-1100° C., 900° C.-1100° C., or 850° C.-1000° C.

[0185] In some embodiments, in step 2, the first time t1 is 1 hour to 5 hours. For example, the first time t1 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range thereof. Alternatively, the first time t1 is 2 hours to 4 hours.

[0186] In some embodiments, in step 2, the heat treatment can be carried out in a device capable of programmed temperature increase, such as a medium frequency furnace, a roller kiln, a rotary kiln, a push plate kiln, a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor or a drum furnace.

[0187] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere, which may include one or more of nitrogen, argon, and helium.

[0188] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above-mentioned range, it is beneficial to adjust the number of pores and / or the pore size in the outer area and the inner area of ​​the first carbon-based material within a suitable range, and thus it is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0189] In some embodiments, in step 3, the second temperature T2 is 2070° C.-2700° C. Optionally, the second temperature T2 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., or 2140° C.-2360° C.

[0190] In some embodiments, in step 3, the second time t2 is 1.5 hours to 6 hours. For example, the second time t1 can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range thereof. Alternatively, the second time t2 is 2 hours to 5 hours.

[0191] In some embodiments, in step 3, the heat treatment may be performed in a medium frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace, or an internal string graphitization furnace.

[0192] When the second temperature T2 and the second time t2 are within the above range, it is beneficial to adjust the I D / I G , which is also beneficial for the first carbon-based material to have a stable structure. Generally, the higher the second temperature and / or the longer the second time, the greater the stability of the first carbon-based material. D / I G The smaller.

[0193] In some embodiments, in step 3, the medium frequency furnace and the continuous graphitization heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0194] 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 to be 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 wait.

[0195] In the preparation method of the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filler material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above range, it is beneficial to adjust the S2 / S1, I D / I G , graphitization degree, gram capacity, specific surface area, particle size, interlayer spacing of 002 crystal plane, powder compaction density, tap density and other parameters.

[0196] In some embodiments, the preparation method of the artificial graphite in the second carbon-based material includes: step 11, providing raw materials; step 12, crushing and shaping the raw materials to obtain a first intermediate; step 13, graphitizing the first intermediate to obtain a second carbon-based material after the graphitization is completed, and the second carbon-based material meets I D / I G ≤0.140.

[0197] In some embodiments, in step 11, the feedstock may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.

[0198] In some embodiments, in step 12, a mechanical mill or a roller mill can be used to crush the raw material. In addition, a shaping machine can be used for shaping.

[0199] In some embodiments, in step 13, the graphitization temperature is 2800°C-3200°C.

[0200] By adjusting the graphitization temperature and / or graphitization time, the second carbon-based material can have a suitable I D / I G value and degree of graphitization.

[0201] In the preparation method of the second carbon-based material, by adjusting the parameters of each device (such as a mechanical mill or roller mill, a shaping machine, a granulator, etc.), the parameters of the raw materials, the amount of the organic carbon source added, the amount of the binder added, the graphitization temperature, the graphitization time, the carbonization temperature, the carbonization time, etc., it is beneficial to adjust the 002 crystal plane interlayer spacing, I D / I G , graphitization degree, gram capacity, volume distribution particle size, specific surface area, powder compaction density, tap density and other parameters.

[0202] [Positive electrode]

[0203] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material according to the first aspect of the present disclosure.

[0204] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0205] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0206] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0207] For other active ion batteries, such as sodium ion batteries, the positive electrode active material may include conventionally known positive electrode active materials for sodium ion batteries. For example, the positive electrode active material includes at least one of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound.

[0208] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the material's initial state, i.e., before addition. When a positive electrode active material is used in a battery system, its molar Li content will change over the course of charge and discharge cycles.

[0209] The molar oxygen content in the positive electrode active materials listed in this disclosure is only a theoretical value. Lattice oxygen release can cause the molar oxygen content to change, and the actual molar oxygen content will fluctuate. The molar content of other elements may also change after battery manufacturing and during use. Therefore, the molar ratios of the elements in the molecular formulas of the positive electrode active materials above are the molar ratios at the time of preparation.

[0210] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0211] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0212] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0213] [Electrolytes]

[0214] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0215] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0216] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0217] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0218] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0219] [Isolation film]

[0220] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0221] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0222] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0223] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0224] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0225] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 having a square structure as an example.

[0226] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0227] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0228] FIG5 shows an example battery module 4. Referring to FIG5 , in the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0229] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0230] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0231] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0232] In addition, the second aspect of the present disclosure further provides an electric device, which includes the secondary battery provided by each of the above embodiments. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, 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 and satellites, energy storage systems, etc., but is not limited thereto.

[0233] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0234] Figure 8 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0235] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0236] Example

[0237] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0238] In the following examples and comparative examples, the first carbon-based material used can be prepared by the following method disclosed in the present invention.

[0239] Preparation of material 1-1:

[0240] The flake graphite is mechanically crushed, classified, spheroidized and purified to obtain natural spherical graphite, wherein the volume distribution particle size of the natural spherical graphite is Dv50=16.7μm. The obtained natural spherical graphite is mixed with the filler petroleum asphalt in a mass ratio of 100:20, and the softening point of the petroleum asphalt is 135°C. The mixed material is then placed in a programmable temperature raising device, heated to 680°C (first treatment temperature), kept warm for 2.5h, and then cooled to room temperature to obtain an intermediate. The obtained intermediate is placed in a graphitization furnace and heat treated at 2450°C (second treatment temperature). After the end, it is demagnetized and sieved to obtain material 1-1. Material 1-1 meets the following requirements: S2 / S1=7.9, ID / I G =0.17, volume distribution particle size Dv50=17.0 μm and degree of graphitization is 97%.

[0241] Preparation of materials 1-2 to 1-3:

[0242] The preparation methods of materials 1-2 to 1-3 are similar to those of material 1, except that the ratio of natural spherical graphite to filler and the first treatment temperature are adjusted to obtain materials 1-2 to 1-3. The details are as follows:

[0243] Table 1

[0244] Preparation of materials 1-4:

[0245] Provide natural spherical graphite, mix the natural spherical graphite and petroleum asphalt in a mass ratio of 100:6, the softening point of the petroleum asphalt is 250°C, and perform low-temperature heat treatment at 1100°C for 2 hours to obtain natural graphite with a carbon coating layer, namely material 1-4. Wherein, material 1-4 satisfies: S2 / S1=0.8, I D / I G =0.36, volume distribution particle size Dv50=17.8μm and degree of graphitization is 97%.

[0246] Preparation of Material 2-1:

[0247] The needle coke raw material is crushed by a roller mill and shaped by a shaping machine to obtain a first intermediate. The first intermediate is graphitized in a graphitization furnace at a temperature of 3050°C for 6 hours to obtain material 2-1. Material 2-1 satisfies the following conditions: D / I G =0.12, volume distribution particle size Dv50 = 16.0 μm, specific surface area BET = 1.05 m 2 / g, and the degree of graphitization is 95.0%.

[0248] Preparation of materials 2-2 to 2-4:

[0249] The preparation method of materials 2-2 to 2-4 is similar to that of material 1, except that the graphitization temperature is adjusted to adjust the I D / I G The details are as follows:

[0250] Table 2

[0251] Example 1

[0252] Preparation of secondary batteries:

[0253] 1. Negative Electrode Sheet: Thoroughly stir and mix the negative electrode active material (70 wt% Material 1-1 and 30 wt% Material 2-1), conductive carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in an appropriate amount of deionized water at a weight ratio of 96.4:1:1.2:1.4 to form a negative electrode slurry. Apply the negative electrode slurry to both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0254] 2. Positive Electrode: LiFePO4, carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96:2:2. An appropriate amount of NMP solvent is added and stirred to obtain a positive electrode slurry. The positive electrode slurry is applied to both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0255] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to prepare an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Vinylene carbonate (VC) is then added to an amount of 1% by weight of the total electrolyte.

[0256] 4. Isolation film: polypropylene film.

[0257] 5. Preparation of secondary batteries: Place the positive electrode and negative electrode sheets prepared above in order, with the separator placed between the positive and negative electrode sheets to act as an isolate, and then wind them to obtain an electrode assembly; place the electrode assembly in an outer package, inject the electrolyte after drying, and obtain a secondary battery through vacuum packaging, standing, formation, shaping and other processes.

[0258] Examples 2-3

[0259] The battery preparation methods of Examples 2 to 3 are similar to those of Example 1, except that the first carbon-based materials are selected from materials 1-2 to 1-3, respectively. See Table 1 for details.

[0260] Comparative Example 1

[0261] The preparation method is similar to that of Example 1, except that the first carbon-based material is selected from materials 1-4, as shown in Table 1 for details.

[0262] Comparative Example 2

[0263] The preparation method is similar to that of Example 1, except that the negative electrode active material only contains the first carbon-based material used in Example 1 (the material 1-1 prepared above), and the secondary battery is assembled according to the above method.

[0264] Comparative Example 3

[0265] The preparation method is similar to that of Example 1, except that the negative electrode active material only contains the second carbon-based material used in Example 1 (the material 2-1 prepared above), and the secondary battery is assembled according to the above method.

[0266] Performance Testing

[0267] 1. Material testing

[0268] The S1 / S of the first carbon-based material is obtained by testing using the following method.

[0269] A sample preparation binder and the first carbon-based material powder are mixed evenly and then applied to a copper foil. The mixture is then dried at 60°C for 30 minutes before use. Five samples to be tested, each measuring 6 mm x 6 mm, are cut at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples are then cut using a plasma beam to obtain cross-sections of each sample. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from JEOL, Japan.

[0270] Each sample cross section of the first carbon-based material was scanned using a scanning electron microscope, and a scanned image was obtained from an arbitrarily selected region within each sample cross section. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from ZEISS, Germany.

[0271] Randomly select cross sections of 20 particles of the first carbon-based material from the scanned image. The area formed by extending 0.25 μm from the particle surface of the first carbon-based material to the interior of the particle is recorded as the external area, and the area inside the external area is recorded as the internal area. Use image processing software to obtain the total pore area S1' of the external area of ​​each particle cross section and the pore area S2' of the internal area of ​​the first carbon-based material, and calculate the value of S2' / S1'; and calculate the arithmetic average of S2' / S1' of all 20 particles as the value of S2 / S1 of the first carbon-based material. The image processing software can be AVIZO.

[0272] 2. Battery performance test

[0273] (1) Storage performance test of secondary batteries

[0274] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 3.65V, then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.5V. The discharge capacity at this time was recorded, which was the discharge capacity before storage.

[0275] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 3.65V, and then charged at a constant voltage to a current of 0.05C. The secondary battery was then stored in a thermostat at 60°C for 240 days. Capacity retention (%) of the secondary battery after 240 days of storage at 60°C = discharge capacity after storage / discharge capacity before storage × 100%.

[0276] (3) Energy density of secondary batteries

[0277] At 25°C, the secondary battery was charged at a constant current of 1 / 3C to 3.65V. Then, it was charged at a constant voltage at 3.65V to a current of 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1 / 3C to 2.5V. The discharge energy at this point was recorded. The volumetric energy density of the battery is calculated by dividing the discharge energy by the battery volume, expressed in Wh / L. The measurement data is shown in Table 1.

[0278] (3) Initial Coulombic efficiency of the negative electrode

[0279] At 45°C, the secondary battery prepared above was first charged to 20% SOC at a constant current of 0.02C, and the charging capacity was recorded as C0; the temperature was lowered to 25°C, allowed to stand for 30 minutes, and then discharged to 2.5V at a constant current of 0.2C, and the discharge capacity was recorded as D0. After standing for 5 minutes, the battery was charged to 3.65V at a constant current of 1 / 3C and then charged to 0.05C at a constant voltage, and the charging capacity was recorded as C1. After standing for 5 minutes, the battery was discharged to 2.5V at a constant current of 1 / 3C, and the discharge capacity was recorded as D1.

[0280] First coulombic efficiency of secondary battery (%) = D1 / (C0+C1-D1)×100%

[0281] The batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 3.

[0282] Table 3

[0283] As can be seen from Table 1 above, according to Comparative Examples 2 and 3, which respectively use only the first carbon-based material and the second carbon-based material, the first carbon-based material can provide a good energy density for the secondary battery, but the high-temperature storage performance is relatively low; the second carbon-based material has a good first coulombic efficiency, which brings high high-temperature storage performance to the secondary battery, but the energy density is relatively low. The present invention combines the first carbon-based material and the second carbon-based material as the negative electrode active material, so that the secondary battery has both good energy density and high-temperature storage performance.

[0284] It can be seen from Examples 1-3 and Comparative Example 1 that changing the S2 / S1 value of the first carbon-based material mainly affects the first coulombic efficiency of the negative electrode and the storage performance of the secondary battery. The larger the value of S2 / S1, the better the high-temperature storage performance. On the contrary, when S2 is less than S1 (i.e., the pore area in the inner region of the particle is low, while the pore area in the outer region of the particle is high), the first coulombic efficiency of the storage performance decreases.

[0285] Examples 4-5

[0286] The battery preparation methods of Examples 4 to 5 are similar to those of Example 1, wherein the first carbon-based material is material 1-1, and the second carbon-based material is selected from materials 2-2 to 2-3 respectively.

[0287] Comparative Example 4

[0288] The battery preparation method of Comparative Example 4 is similar to that of Example 1, except that the second carbon-based material is selected from Material 2-4.

[0289] The batteries prepared in Examples 4 to 5 and Comparative Example 4 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 4.

[0290] Table 4

[0291] As can be seen from Table 4 above, changing the I D / I G value, which can affect its surface activity, I D / I G The larger the value, the higher the surface activity, which leads to a decrease in the first coulombic efficiency of the negative electrode and affects the high-temperature storage performance of the secondary battery, but has little effect on the energy density.

[0292] Examples 6 and 7

[0293] The battery preparation methods of Examples 6 and 7 are similar to those of Example 1, except that the amounts of the first carbon-based material and the second carbon-based material are changed. For details, see Table 5.

[0294] The batteries prepared in Examples 6 and 7 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 5.

[0295] Table 5

[0296] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a first carbon-based material and a second carbon-based material, The first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region extending from the surface of the first carbon-based material to the inside by a distance of 2.5 μm. In a cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure, the total pore area of ​​the outer region of the first carbon-based material is recorded as S1, and the total pore area of ​​the inner region of the first carbon-based material is recorded as S2, then the first carbon-based material satisfies: S2>S1; The second carbon-based material satisfies I D / I G ≤0.14, where I D The Raman spectrum of the second carbon-based material is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of the second carbon-based material is 1580±50cm -1 The G peak intensity at .

2. The secondary battery according to claim 1, wherein The second carbon-based material satisfies 0.10≤I D / I G ≤0.14, optionally, 0.11≤I D / I G ≤0.

13.

3. The secondary battery according to claim 1 or 2, wherein: The first carbon-based material D / I G Greater than the I of the second carbon-based material D / I G .

4. The secondary battery according to any one of claims 1 to 3, wherein: The first carbon-based material satisfies I D / I G ≤0.30, optionally, 0.15≤I D / I G ≤0.28; where I D The Raman spectrum of the first carbon-based material is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of the first carbon-based material is 1580±50cm -1 The G peak intensity at .

5. The secondary battery according to any one of claims 1 to 4, wherein: The second carbon-based material is artificial graphite.

6. The secondary battery according to any one of claims 1 to 5, wherein: The interlayer spacing of the 002 crystal plane of the first carbon-based material is smaller than the interlayer spacing of the 002 crystal plane of the second carbon-based material; Optionally, the interlayer spacing of the 002 crystal plane of the first carbon-based material is ≤0.33569 nm, and may be 0.33557-0.33569 nm; Optionally, the interlayer spacing of the 002 crystal plane of the second carbon-based material is ≤0.336088 nm, and can be optionally 0.335744-0.336088 nm.

7. The secondary battery according to any one of claims 1 to 6, wherein: The first carbon-based material includes at least one pore area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15-2.0 μm 2 The pore structure.

8. The secondary battery according to claim 1, wherein: The first carbon-based material satisfies: 1.5≤S2 / S1≤450; optionally, 2≤S2 / S1≤400.

9. The secondary battery according to any one of claims 1 to 8, wherein: The first carbon-based material includes primary particles; Optionally, the amount of the primary particles in the first carbon-based material accounts for ≥80%; Optionally, the surface of the first carbon-based material has no coating layer.

10. The secondary battery according to any one of claims 1 to 9, wherein: The second carbon-based material includes primary particles; Optionally, the amount of the primary particles in the second carbon-based material accounts for ≥80%; Optionally, the surface of the second carbon-based material has no coating layer.

11. The secondary battery according to any one of claims 1 to 10, wherein: The graphitization degree of the first carbon-based material is greater than the graphitization degree of the second carbon-based material.

12. The secondary battery according to any one of claims 1 to 11, wherein: The graphitization degree of the first carbon-based material is ≥ 96%, optionally 96.5%-98.5%; The graphitization degree of the second carbon-based material is 91%-96.5%, and optionally 92%-96%.

13. The secondary battery according to any one of claims 1 to 12, wherein: The specific surface area of ​​the first carbon-based material is greater than the specific surface area of ​​the second carbon-based material.

14. The secondary battery according to any one of claims 1 to 13, wherein: The specific surface area of ​​the first carbon-based material is less than or equal to 2.1 m 2 / g, optionally 1.3-2.0m 2 / g; The specific surface area of ​​the second carbon-based material is less than or equal to 1.3 m 2 / g, optional 0.8-1.2m 2 / g.

15. The secondary battery according to any one of claims 1 to 14, wherein: The volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material.

16. The secondary battery according to any one of claims 1 to 15, wherein: The negative electrode active material satisfies at least one of the following: (1) The volume distribution particle size Dv50 of the negative electrode active material is ≥10 μm, which can be 10 μm-23 μm; (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤40 μm, which can be 23 μm-40 μm; (3) The particle size distribution of the negative electrode active material [(Dv90)-(Dv10)] / (Dv50)] is ≤ 1.20, and can be 0.9-1.20; (4) The gram capacity of the negative electrode active material is ≥358 mAh / g, which can be 358 mAh / g-370 mAh / g; (5) The negative electrode active material satisfies I D / I G ≤0.2, optionally 0.13-0.20, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

17. The secondary battery according to any one of claims 1 to 16, wherein: The first carbon-based material satisfies at least one of the following: (1) The volume distribution particle size Dv50 of the first carbon-based material is ≥13 μm, optionally 15 μm-20 μm; (2) the volume distribution particle size Dv90 of the first carbon-based material is ≤40 μm, optionally 28 μm-40 μm; (3) the particle size distribution of the first carbon-based material [(Dv90)-(Dv10)] / (Dv50)]≤1.55, optionally 0.90-1.50; (4) The gram capacity of the first carbon-based material is ≥360 mAh / g, optionally 365 mAh / g-372 mAh / g.

18. The secondary battery according to any one of claims 1 to 17, wherein: The second carbon-based material satisfies at least one of the following: (1) The volume distribution particle size Dv50 of the second carbon-based material is ≤18 μm, optionally 13 μm-18 μm; (2) the particle size distribution of the second carbon-based material [(Dv90)-(Dv10)] / (Dv50)] is ≤1.35, optionally 1.0-1.30; (3) The gram capacity of the second carbon-based material is ≥357 mAh / g, and can be optionally 357 mAh / g-363 mAh / g.

19. The secondary battery according to any one of claims 1 to 18, wherein: The mass proportion of the first carbon-based material in the negative electrode active material is ≥30wt%, and optionally 50wt%-80wt%.

20. The secondary battery according to any one of claims 1 to 19, wherein: The negative electrode active material also includes a silicon-based material.

21. The secondary battery according to any one of claims 1 to 20, wherein: The negative electrode film layer satisfies at least one of the following: (1) The compaction density of the negative electrode film layer is ≥1.40 g / cm 3 , optionally 1.45 g / cm 3 -1.90g / cm 3 ; (2) The surface density of the negative electrode film layer is ≥6.0 mg / cm 2 , optionally 7.0 mg / cm 2 -15.0mg / cm 2 ; (3) The porosity of the negative electrode film layer is 18.0%-36.7%, optionally 19.0%-34.0%; (4) The thickness of the negative electrode film layer is ≥70 μm, and can be optionally 90 μm-130 μm.

22. An electrical device comprising the secondary battery according to any one of claims 1 to 21.

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