Secondary battery and electrical apparatus

Abstract

Provided are a secondary battery and an electrical apparatus. The secondary battery comprises a negative electrode plate; the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material; the negative electrode active material comprises a first carbon-based material and a second carbon-based material; the first carbon-based material has a hole structure, ID / IG of the first carbon-based material being less than or equal to 0.280, ID representing the D peak intensity at 1350±50 cm-1 in the Raman spectrum, and IG representing the G peak intensity at 1580±50 cm-1 in the Raman spectrum; and the second carbon-based material is an amorphous carbon material.

Description

Secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311641312.6, application date November 30, 2023, and invention name “Secondary Battery and Electrical Device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this disclosure as a reference. Technical Field

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

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

[0005] Therefore, how to make secondary batteries have high energy density while having excellent cycle performance and kinetic performance has become an urgent problem to be solved in this field.

[0006] Summary of the Invention

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

[0008] The present disclosure provides a secondary battery in a first aspect, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material, wherein the negative electrode active material comprises a first carbon-based material and a second carbon-based material, wherein the first carbon-based material has a pore structure, and the I of the first carbon-based material is D / I G Less than or equal to 0.280, where 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 , the second carbon-based material is an amorphous carbon material.

[0009] By making the negative electrode active material in the negative electrode film layer include the first carbon-based material and the second carbon-based material, the first carbon-based material has a pore structure, and the I of the first carbon-based material D / I G Less than or equal to 0.280, the second carbon-based material is an amorphous carbon material, thereby enabling the negative electrode plate to have a high compaction density, low volume change performance and high active ion transmission speed, so that the secondary battery using the negative electrode plate can have high energy density while taking into account excellent cycle performance and kinetic performance.

[0010] In some embodiments, the first carbon-based material D / I G It is 0.155-0.220; thus, it is more conducive to the battery to have excellent energy density, cycle performance and kinetic performance.

[0011] In some embodiments, the second carbon-based material D / I G Less than or equal to 0.250, optionally, the I of the second carbon-based material D / I G Less than or equal to 0.230. This is more conducive to the battery having both excellent cycle performance and higher energy density.

[0012] In some embodiments, the Dv50 of the first carbon-based material is greater than the Dv50 of the second carbon-based material, thereby being more conducive to improving the energy density and dynamic performance of the battery.

[0013] In some embodiments, the X-ray powder diffraction pattern of the first carbon-based material has diffraction peaks at 2θ diffraction angles of 26.5°±0.2°, 44.5°±0.2°, and 54.6°±0.2°, while the X-ray powder diffraction pattern of the second carbon-based material does not have obvious diffraction peaks. Thus, by containing graphite in the first carbon-based material and amorphous carbon in the second carbon-based material, the secondary battery can have high energy density while also having excellent cycle performance and kinetic performance.

[0014] In some embodiments, the first carbon-based material exhibits lattice fringes in HR-TEM, while the second carbon-based material exhibits no lattice fringes in HR-TEM. Thus, by including graphite in the first carbon-based material and amorphous carbon in the second carbon-based material, a secondary battery can have both high energy density and excellent cycling and kinetic performance.

[0015] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20,000 N is greater than the powder compaction density of the second carbon-based material under a pressure of 20,000 N. This helps ensure that the secondary battery has both high energy density and good dynamic performance.

[0016] In some embodiments, the true density of the first carbon-based material is greater than the true density of the second carbon-based material. The greater true density of the first carbon-based material is beneficial for increasing the compaction density of the negative electrode film layer and improving the energy density of the secondary battery. The lower true density of the second carbon-based material improves the intercalation and deintercalation of active ions, thereby improving the kinetic performance of the secondary battery. Therefore, by adjusting the true density of the first carbon-based material to be greater than the true density of the second carbon-based material, it is beneficial to achieve a secondary battery with both high energy density and good kinetic performance.

[0017] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 By ensuring that the true density of the first carbon-based material is within the above range and greater than that of the second carbon-based material, the energy density of the secondary battery is improved.

[0018] In some embodiments, the first carbon-based material includes one or more carbon-based materials with an area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 By making the first carbon-based material and / or the second carbon-based material include a pore structure with the above-mentioned pore area, the pore structure can reserve sufficient and stable expansion space for the volume change of the first carbon-based material and / or the second carbon-based material particles, thereby reducing the risk of breakage of the first carbon-based material and / or the second carbon-based material particles, reducing the occurrence of side reactions, and improving the cycle performance of the secondary battery.

[0019] In some embodiments, the first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region extending 2.5 μm from the surface of the particles of the first carbon-based material to the interior of the particles. In a cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is recorded as S1, the total pore area of ​​the inner region is recorded as S2, and S2>S1, optionally, 2.6≤S2 / S1≤450.7. The pore area S1 of the outer region of the first carbon-based material is smaller than the pore area S2 of the inner region, indicating that the structure of the outer region of the carbon-based material is denser than that of the inner region, thereby enabling the secondary battery to better balance high energy density and good cycle performance.

[0020] In some embodiments, the area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm2, and optionally less than or equal to 0.13 μm2. 2, and / or, the inner region of the first carbon-based material includes one or more pore structures with an area greater than or equal to 0.15 μm2, and optionally includes one or more pore structures with an area of ​​0.15 μm2 2 -2.0μm 2 By controlling the area of ​​the pore structure in the outer region of the first carbon-based material to be within the above range, the outer region of the first carbon-based material can have a dense structure, thereby effectively improving the structural stability of the first carbon-based material, and avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby effectively improving the cycle performance of the secondary battery. By making the inner region of the first carbon-based material include a pore structure of the above size, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, reducing the risk of breakage of the first carbon-based material particles and reducing the occurrence of side reactions. On the other hand, it can also improve the compaction density of the negative electrode film layer and buffer the volume change of the negative electrode film layer.

[0021] In some embodiments, the first carbon-based material has a powder compaction density of 1.65 g / cm3 under a pressure of 20,000 N. 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 , which is beneficial to improving the energy density of secondary batteries.

[0022] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, optionally 10.0 μm-22.0 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, optionally 16.5 μm-42.0 μm.

[0023] By ensuring that the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above range, it is beneficial to improve the transmission performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the occurrence of side reactions and improve the cycle performance of the secondary battery.

[0024] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, and can be optionally 0.90-1.50. By ensuring that the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is within the above range, its particle packing performance is better, which is conducive to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also conducive to adjusting the pore distribution of the negative electrode film layer, improving the active ion and electron transport performance, and improving the electrolyte infiltration and retention characteristics of the negative electrode film layer, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0025] In some embodiments, the tap density of the first carbon-based material is 0.85 g / cm 3 -1.30g / cm 3 , optional 0.90g / cm 3 -1.25g / cm 3 By ensuring that the tap density of the first carbon-based material is within the above range, processing performance is improved. This also facilitates the formation of a reasonable pore structure between the particles of the negative electrode film layer, thereby enhancing the active ion and electron transport properties, and improving the negative electrode film layer's electrolyte infiltration and retention properties, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0026] In some embodiments, the graphitization degree of the first carbon-based material is greater than or equal to 95.5%, and can be 95.5%-98.0%. By making the graphitization degree of the first carbon-based material within the above range, the secondary battery can have a high energy density.

[0027] In some embodiments, the first carbon-based material and / or the second carbon-based material include primary particles. Optionally, the primary particles in the first carbon-based material account for greater than or equal to 80%, and the primary particles in the second carbon-based material account for greater than or equal to 80%. By ensuring that the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, the material can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0028] In some embodiments, the true density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 By ensuring that the true density of the second carbon-based material is within the above range and is less than that of the first carbon-based material, the kinetic performance of the secondary battery is improved.

[0029] In some embodiments, the specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 By making the specific surface area of ​​the second carbon-based material within the above range, it is beneficial to the rapid insertion and extraction of active ions, thereby further improving the dynamic performance of the secondary battery.

[0030] In some embodiments, the Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, optionally 5.0 μm-15.0 μm. By ensuring that the volume distribution particle size Dv50 of the second carbon-based material is within the above range, the occurrence of side reactions is reduced, the cycle performance of the secondary battery is improved, and the transport performance of active ions and electrons is improved, thereby further improving the kinetic performance of the secondary battery.

[0031] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and can be optionally 1.1-1.75. When the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is within the above range, its particle packing performance is good, which is beneficial to improving the compaction density of the negative electrode film layer and the energy density of the secondary battery. In addition, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance in the negative electrode film layer, and thus improving the kinetic performance of the secondary battery.

[0032] In some embodiments, the second carbon-based material has a powder compaction density of 0.85 g / cm2 under a pressure of 20,000 N. 3 -1.35g / cm 3 , optional 0.90g / cm 3 -1.30g / cm 3 The powder compaction density of the second carbon-based material is lower than that of the first carbon-based material. By making the powder compaction density of the second carbon-based material within the above range, it is beneficial to improve the active ion transport performance in the negative electrode film layer, thereby improving the kinetic performance of the secondary battery.

[0033] In some embodiments, the tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 By making the tap density of the second carbon-based material within the above range, it is beneficial to have a suitable pore distribution in the negative electrode film layer, improve the active ion transport performance, improve the electrolyte infiltration characteristics of the negative electrode film layer, and thus improve the kinetic performance and cycle performance of the secondary battery.

[0034] In some embodiments, the gram capacity of the second carbon-based material is 330 mAh / g-480 mAh / g, optionally 340 mAh / g-470 mAh / g. By making the gram capacity of the second carbon-based material within the above range, the energy density of the secondary battery can be improved.

[0035] In some embodiments, at least a portion of the surface of the first carbon-based material and / or the second carbon-based material comprises a carbon coating. Optionally, the coating comprises a carbon coating. This facilitates increasing the rate at which active ions are embedded into the negative electrode film, improving the active ion transport performance of the negative electrode film, and thereby improving the kinetic performance of the secondary battery.

[0036] In some embodiments, the content of the first carbon-based material in the negative electrode active material is greater than or equal to 40wt%, optionally 50wt%-80wt%. When the content of the first carbon-based material is within the above range, the secondary battery has high energy density while having good processing performance, dynamic performance, and cycle performance.

[0037] In some embodiments, the negative electrode active material further comprises a silicon-based material. Optionally, the silicon-based material comprises 3 wt% to 30 wt% of the negative electrode active material. Silicon-based materials have a higher lithium insertion potential, which is beneficial for improving the kinetic performance of the secondary battery. They also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0038] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.70g / cm 3 , optional 1.45g / cm 3 -1.67g / cm 3 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0039] In some embodiments, the surface density of the negative electrode film layer is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0040] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, optionally 45 μm-100 μm.

[0041] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0042] Effects of the Invention

[0043] The secondary battery of the present disclosure has high energy density and excellent cycle performance and kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0045] FIG1 is a schematic diagram of a cross-sectional image of a particle of a first carbon-based material according to the present disclosure.

[0046] FIG2 is a SEM image of an embodiment of a negative electrode sheet disclosed herein.

[0047] FIG. 3 is a schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0048] FIG. 4 is an exploded schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0049] FIG5 is a schematic diagram of an embodiment of a battery module according to the present disclosure.

[0050] FIG6 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0051] FIG. 7 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 6 .

[0052] FIG8 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present disclosure as a power source.

[0053] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 100 first carbon-based material, 101 outer region, 102 inner region. DETAILED DESCRIPTION

[0054] 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.

[0055] " 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.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0058] 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.

[0059] Currently, efforts to improve the kinetic performance of secondary batteries, particularly their fast-charging performance, often involve reducing the areal density or compaction density of the negative electrode film. However, numerous studies have shown that these methods only improve the kinetic performance of the battery during the initial charging phase and often result in a significant reduction in the energy density of the secondary battery.

[0060] Therefore, it is difficult for current secondary batteries to achieve both high energy density and good kinetic and cycle performance.

[0061] In view of this, a first aspect of an embodiment of the present disclosure provides a secondary battery.

[0062] The present disclosure has no particular restrictions on the types of secondary batteries. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present disclosure has no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes can also include an isolation membrane, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0063] [Negative electrode]

[0064] In the secondary battery disclosed herein, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material, wherein the negative electrode active material includes a first carbon-based material and a second carbon-based material, the first carbon-based material has a pore structure, and the I of the first carbon-based material is D / I G is 0.152-0.280, among which I D Indicates that the Raman spectrum is at 1350 ± 50 cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at , the second carbon-based material is an amorphous carbon material.

[0065] In the present disclosure, "the first carbon-based material has a pore structure" means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (for example, a scanning electron microscope image with a magnification of 1000 times), that is, the pore structure in the main structure used to prepare the first carbon-based material is not completely filled.

[0066] Amorphous carbon materials have a large interlayer spacing, which facilitates the rapid intercalation and deintercalation of active ions. They also have a higher potential for lithium, which improves the battery's kinetic performance. However, amorphous carbon materials have a high surface activity and are prone to side reactions with the electrolyte. During the initial charge, they consume a large amount of active lithium ions, reducing the active ions in the secondary battery, lowering the secondary battery capacity and energy density. Therefore, the application of amorphous carbon materials in batteries is limited.

[0067] The negative electrode active material disclosed in the present invention includes a first carbon-based material and a second carbon-based material amorphous carbon. The first carbon-based material has a pore structure, which is equivalent to reserving a certain space inside the material, so that the compaction density of the pole piece is effectively improved during the pole piece preparation process, thereby improving the energy density of the battery. D / I G Within a specific range, the carbon-based material has less disordered carbon on its surface, which makes the material more chemically stable, reduces the occurrence of side reactions, and effectively reduces the consumption of active ions during the first charge, which can further improve the battery's energy density and cycle performance. As a result, the battery can achieve both high energy density and cycle performance while maintaining good kinetics.

[0068] In some embodiments, the first carbon-based material D / I G It is 0.155-0.220; thus, excellent energy density, cycle performance and kinetic performance can be obtained in a better balance.

[0069] In some embodiments, the second carbon-based material D / I G Less than or equal to 0.250, optionally, the I of the second carbon-based material D / I G Less than or equal to -0.230. As a result, the cycle performance and energy density of the battery can be further improved. In some embodiments, the X-ray powder diffraction pattern of the first carbon-based material has diffraction peaks at 2θ diffraction angles of 26.5°±0.2°, 44.5°±0.2°, and 54.6°±0.2°. There is no obvious diffraction peak in the X-ray powder diffraction pattern of the second carbon-based material.

[0070] The HR-TEM spectrum of the first carbon-based material shows lattice fringes, indicating that the carbon material has a crystalline structure.

[0071] There are no obvious lattice fringes in the HR-TEM spectrum of the second carbon-based material, which means that the carbon material does not have a crystal structure. Usually, such materials are called amorphous carbon.

[0072] In some embodiments, the second carbon-based material may be soft carbon or hard carbon.

[0073] In some embodiments, the powder compaction density of the above-mentioned first carbon-based material under a pressure of 20,000 N is greater than the powder compaction density of the above-mentioned second carbon-based material under a pressure of 20,000 N. The powder compaction density of the first carbon-based material is relatively large, which is beneficial to improving the compaction density of the negative electrode film layer and improving the energy density of the secondary battery. The powder compaction density of the second carbon-based material is relatively small, which is beneficial to improving the porosity of the electrode and improving the deintercalation of active ions, thereby improving the kinetic performance of the secondary battery. Therefore, by adjusting the powder compaction density of the first carbon-based material to be greater than the powder compaction density of the second carbon-based material, it is beneficial to make the secondary battery have both high energy density and good kinetic performance.

[0074] In some embodiments, the true density of the first carbon-based material is greater than the true density of the second carbon-based material, which is beneficial for achieving both high energy density and good kinetic performance in the secondary battery.

[0075] In some embodiments, the true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 When the actual density of the first carbon-based material is within the above range, the energy density of the secondary battery can be further improved.

[0076] 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. This can further improve the energy density of the battery and also contribute to the improvement of dynamic performance.

[0077] In some embodiments, the tap density of the first carbon-based material is greater than the tap density of the second carbon-based material, thereby further improving the processing performance of the battery.

[0078] In some embodiments, the first carbon-based material includes at least one carbon-based material having an area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 By making the first carbon-based material and / or the second carbon-based material include a pore structure with the above-mentioned pore area, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles and / or the second carbon-based material, thereby reducing the risk of breakage of the first carbon-based material and / or the second carbon-based material particles, reducing the occurrence of side reactions, and improving the cycle performance of the secondary battery. In addition, the compaction density of the negative electrode film layer can also be increased, thereby increasing the energy density of the secondary battery.

[0079] In some embodiments, the first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region extending 2.5 μm from the particle surface of the first carbon-based material to the interior of the particle. In a cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is denoted as S1, the total pore area of ​​the inner region is denoted as S2, and S2>S1. In this disclosure, the "inner region" refers to the region in the material particle other than the outer region.

[0080] When the first carbon-based material satisfies S2>S1, it means that the structure of the outer region of the carbon-based material is denser than that of the inner region, and the first carbon-based material further has the following characteristics: the inner region has a large number of pores and / or a large pore size, while the outer region has a small number of pores and / or a small pore size. The pore structure of the inner region of the first carbon-based material can reserve the required expansion space for the volume change of the particles, thereby reducing the risk of particles breaking to produce new interfaces, reducing the rebound rate of the thickness of the negative electrode film layer, and thus reducing the occurrence of side reactions; the outer region of the first carbon-based material has a small number of pores and / or a small pore size, thereby making the first carbon-based material particles have a stable structure and avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby further reducing the occurrence of side reactions and reducing the consumption of active ions by the SEI film formation inside the particles. Therefore, when the first carbon-based material satisfies S2>S1, the first coulomb efficiency of the secondary battery can be improved, and the cycle performance of the secondary battery can be further improved.

[0081] Preferably, 2.6≤S2 / S1≤450.7, for example, 3≤S2 / S1≤430, 4≤S2 / S1≤400, 5≤S2 / S1≤350, 6≤S2 / S1≤300, 7≤S2 / S1≤250, and 8≤S2 / S1≤200. The inventors found in further research that when S2 / S1 also satisfies the above range, the secondary battery can better achieve both high energy density and good cycle performance.

[0082] In the present disclosure, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the first carbon-based material can be obtained by testing a cross-sectional image of the first carbon-based material.

[0083] FIG1 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 100 of the present disclosure. As shown in FIG1 , the region extending 2.5 μm from the surface of the particle of the first carbon-based material 100 toward the interior of the particle is defined as the outer region 101, and the region within the outer region 101 is defined as the inner region 102.

[0084] In the present disclosure, the pore area, S1, and S2 values ​​of the first carbon-based material can be obtained by using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL of Japan) to obtain the cross-section of the first carbon-based material; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope from ZEISS of Germany) is used to scan the cross-section of the first carbon-based material; finally, the pore area of ​​any one hole in the first carbon-based material is obtained respectively through image processing software (such as AVIZO); and the total pore area S2 of the internal area and the total pore area S1 of the external area, and thereby the value of S2 / S1 is obtained. For example, samples can be obtained from different areas of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross section. The total pore area S2' and the total pore area S1' of the inner region of each particle cross section are obtained using image processing software according to the above definition, and the S2' / S1' value of each particle cross section is obtained. The arithmetic average of the S2' / S1' of all the measured particle cross sections is calculated as the S2 / S1 value of the first carbon-based material.

[0085] In some embodiments, the area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 In further research, the inventors also found that by controlling the area of ​​the pore structure in the outer region of the first carbon-based material within the above range, the outer region of the first carbon-based material can have a dense structure, thereby effectively improving the structural stability of the first carbon-based material and avoiding the electrolyte from penetrating into the pore structure inside the first carbon-based material particles as much as possible, thereby effectively improving the cycle performance of the secondary battery. Of course, the present disclosure does not intend to limit the area of ​​all pore structures in the outer region of the first carbon-based material to be less than or equal to 0.15 μm 2 For example, the area of ​​the pore structure can be controlled to be less than or equal to 0.15 μm by more than 95%, or more than 99%. 2 .

[0086] In some embodiments, the inner region of the first carbon-based material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2The inventors further discovered that by including the aforementioned pore structure in the interior of the first carbon-based material, sufficient and stable expansion space can be reserved for volume changes in the first carbon-based material particles, reducing the risk of first carbon-based material particle breakage and the occurrence of side reactions. Furthermore, the compaction density of the negative electrode film layer can be increased, thereby buffering the volume changes of the negative electrode film layer.

[0087] In some embodiments, the powder compaction density of the first carbon-based material under a pressure of 20,000 N is 1.65 g / cm 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 When the powder compaction density of the first carbon-based material is within the above range, the battery can better balance energy density and dynamic performance.

[0088] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, optionally 10.0 μm-22.0 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, optionally 16.5 μm-42.0 μm.

[0089] When the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above range, it is beneficial to improve the transmission performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the occurrence of side reactions and improve the cycle performance of the secondary battery.

[0090] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is less than or equal to 1.55, and can be optionally 0.90-1.50. When the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is within the above range, its particle packing performance is good, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery; in addition, it is also beneficial to adjust the pore distribution of the negative electrode film layer, improve the active ion and electron transport performance, and improve the electrolyte infiltration and retention characteristics of the negative electrode film layer, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0091] In some embodiments, the tap density of the first carbon-based material is 0.85 g / cm 3 -1.30g / cm 3 , optional 0.90g / cm 3 -1.25g / cm 3 When the tap density of the first carbon-based material is within the above range, it is beneficial to improve processing performance.

[0092] In some embodiments, the degree of graphitization of the first carbon-based material is greater than or equal to 95.5%, and can be optionally 95.5%-98.0%. By adjusting the degree of graphitization of the first carbon-based material within the above range, the secondary battery can have a higher energy density. In addition, the particles of amorphous carbon materials are usually harder and have more edges and corners, poor processing performance, poor adhesion to the current collector, and require greater cold pressing pressure during pole piece processing, which can easily cause damage to the current collector. When used in combination with a first carbon-based material with a higher degree of graphitization, the cold pressing pressure during pole piece processing can be reduced, thereby reducing damage to the current collector, reducing the risk of current collector cracking during battery cycling, and further improving the safety performance of the battery.

[0093] In some embodiments, the first carbon-based material and / or the second carbon-based material include primary particles. Optionally, the amount of the primary particles in the first carbon-based material is greater than or equal to 80%, for example, it can be 80%-100%, 85%-90%, 80%-90%, 80%-100%, 85%-90%, 80%-100%, 90%-100%, or 95%-100%. The amount of the primary particles in the second carbon-based material is greater than or equal to 80%, for example, it can be 80%-100%, 85%-90%, 80%-90%, 80%-100%, 85%-90%, 80%-100%, 90%-100%, or 95%-100%. The first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, which can give it higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery.

[0094] In some embodiments, the actual density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 By ensuring that the true density of the second carbon-based material is within the above range and is less than that of the first carbon-based material, it is beneficial to maintain the porosity of the negative electrode sheet of the secondary battery, thereby improving the dynamic performance of the secondary battery.

[0095] In some embodiments, the specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 By making the specific surface area of ​​the second carbon-based material within the above range, it is beneficial to the rapid insertion and extraction of active ions, thereby further improving the dynamic performance of the secondary battery.

[0096] In some embodiments, the Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, and optionally 5.0 μm-15.0 μm. By ensuring that the volume distribution particle size Dv50 of the second carbon-based material is within the above range, the transport performance of active ions is improved, thereby further improving the dynamic performance of the secondary battery.

[0097] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is less than or equal to 1.75, and can be optionally 1.1-1.75. When the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is within the above range, its particle packing performance is good, which is beneficial for improving the compaction density of the negative electrode film layer and the energy density of the secondary battery. In addition, it is beneficial for forming a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance in the negative electrode film layer, and thus improving the kinetic performance of the secondary battery.

[0098] In some embodiments, the second carbon-based material has a powder compaction density of 0.85 g / cm3 under a pressure of 20,000 N. 3 -1.35g / cm 3 , optional 0.90g / cm 3 -1.30g / cm 3 The powder compaction density of the second carbon-based material is lower than the powder compaction density of the first carbon-based material. By making the powder compaction density of the second carbon-based material within the above range, it is beneficial to improve the porosity of the negative electrode sheet, improve the active ion transport performance in the negative electrode film layer, and thus improve the kinetic performance of the secondary battery.

[0099] In some embodiments, the tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 . It can make the secondary battery better balance the processing performance and dynamic performance.

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

[0101] In some embodiments, at least part of the surface of the first carbon-based material and / or the second carbon-based material has a carbon coating layer. Optionally, the coating layer includes a carbon coating layer. Optionally, more than 80% of the surface of the first carbon-based material and / or the second carbon substrate is covered with a carbon coating layer, and further, 90%-100% of the surface is covered with a carbon coating layer. This is conducive to improving the speed at which active ions are embedded in the negative electrode film layer, improving the active ion transport performance of the negative electrode film layer, and thus improving the kinetic performance of the secondary battery.

[0102] In some embodiments, the coating layer of the first carbon-based material can be prepared as follows: the first carbon-based material is mixed with an organic carbon source and then carbonized to form a carbon coating layer on at least part of the surface of the particle. Optionally, the organic carbon source can be a carbon-containing material known in the art suitable for coating, for example, it can include one or more of coal tar, petroleum asphalt, epoxy resin, phenolic resin, high molecular polymer, etc. Optionally, the carbonization temperature is 900°C-1300°C. In addition, the coating layer of the second carbon-based material can be prepared by the following method: Method 1: using chemical vapor deposition to deposit carbon material on the surface of the second carbon-based material at a temperature of 1200-1600°C, the gas is one of methane, ethylene, and acetylene; Method 2: mixing the second carbon-based material with a coating agent and heat treating it at a temperature of 1600-2600°C, the coating agent is one or more of asphalt or polymer. Thus, it is beneficial to adjust the I of the second carbon-based material. D / I G , thereby further improving the cycle performance of secondary batteries.

[0103] In some embodiments, the content of the first carbon-based material in the negative electrode active material is greater than or equal to 40wt%, optionally 50wt%-80wt%, for example, 55wt%-75wt%, 60wt%-70wt%. When the content of the first carbon-based material is within the above range, the secondary battery can take into account high energy density, good kinetic performance and cycle performance. In addition, the content of the second carbon-based material in the negative electrode active material can be 20wt%-50wt%, optionally 25wt%-45wt%, 30wt%-40wt%.

[0104] In some embodiments, the negative electrode active material may further include other negative electrode active materials known in the art in addition to the first carbon-based material and the second silicon-based material. For example, the negative electrode active material may also include a silicon-based material, which has a high lithium insertion potential. This is beneficial for improving the kinetic performance of the secondary battery and also increases the negative electrode capacity, thereby further improving the energy density of the secondary battery. Optionally, the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0105] In some embodiments, when the negative electrode active material in the negative electrode film layer further includes a silicon-based material, the content of the silicon-based material is 3 wt%-30 wt%, for example, 4 wt%-25 wt% or 5 wt%-20 wt%. This improves the kinetic performance and energy density of the secondary battery while also ensuring good cycle performance and cycling performance.

[0106] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present disclosure does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present disclosure does not particularly limit the type of the negative electrode binder. For example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0109] In some embodiments, the compaction density of the negative electrode film is 1.40 g / cm 3 -1.70g / cm 3 , optional 1.45g / cm 3 -1.67g / cm 3 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0110] In some embodiments, the surface density of the negative electrode film is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 This is beneficial for the negative electrode film layer to have both high capacity and high active ion and electron transport performance, and further beneficial for the secondary battery to have both high energy density and good cycle performance and kinetic performance.

[0111] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, and optionally 45 μm-100 μm.

[0112] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0113] The negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, thickness, etc.) given in this disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of this disclosure and are considered to fall within the scope of protection of this disclosure.

[0114] In the present disclosure, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0115] In the present disclosure, the I of a material (eg, a first carbon-based material, a second carbon-based material, etc.) D / I G Raman spectrometer can be used for testing. 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 30 I D / I G The average value of the remaining 40 points is the ID / I G The testing instrument may be a Horiba LabRAM HR800 Raman spectrometer.

[0116] In the present disclosure, the X-ray diffraction analysis test of the material (such as the first carbon-based material, the second carbon-based material, etc.) can use a copper target as the anode target and CuKα rays as the radiation source with a ray wavelength of The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0117] In the present disclosure, HR-TEM of materials (e.g., the first carbon-based material, the second carbon-based material, etc.) can be measured using methods known in the art. For example, referring to standard JBT9352-1999, powders are sliced ​​using a focused ion beam (FIB) with a thickness of ∼100 nm and then measured under a transmission electron microscope.

[0118] In the present disclosure, the true density of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be tested using methods known in the art. Referring to the standard GB / T 24586-2009, an exemplary test method is as follows: Take a clean and dry sample cup and place it on a balance, reset it to zero, add the powder sample to the sample cup, occupying about 1 / 2 of the volume of the sample cup, and record the mass of the sample. Place the sample cup containing the sample in a true density tester, a closed test system, and introduce helium according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the true volume is calculated according to Bohr's law (PV=nRT), thereby calculating the true density. Test sample cup volume: 3.5cm 3 , analysis gas: helium.

[0119] 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 high-resolution transmission electron microscopy (HR-TEM).

[0120] In the present disclosure, gram capacity has a meaning well known in the art and can be tested by 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 on 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.

[0121] 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.

[0122] 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.

[0123] 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 2000kg, maintain pressure for 30s, then release the pressure, maintain for 10s, and then record and calculate the powder compaction density of the material under a pressure of 20000N.

[0124] In the present disclosure, the tap density of a material (such as a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, GB / T 5162-2006 can be referred to and a powder tap density tester can be used for measurement. The test instrument can be Dandong Baxter BT-301, and the test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration number 5000 times, and graduated cylinder 25 mL.

[0125] In the present disclosure, the degree of graphitization of a material (e.g., the first carbon-based material, the second carbon-based material, etc.) is a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) plane in the crystal structure of the material. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0126] In this disclosure, primary particles have a meaning well known in the art. Primary particles refer to non-agglomerated particles. Agglomerated particles formed by the aggregation of two or more primary particles are secondary particles. Primary particles can be distinguished using scanning electron microscopy (SEM) images.

[0127] In the present disclosure, the proportion of primary particles in the first carbon-based material and / or the second carbon-based material refers to: randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the proportion of the number of first carbon-based materials with primary particle morphology in each image to the total number of first carbon-based material particles. The average value of multiple statistical results is the proportion of primary particles in the first carbon-based material.

[0128] 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.

[0129] 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).

[0130] 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.

[0131] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged). Disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2-10 hours). Then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours). After drying, remove the negative electrode. Samples can now be taken from the dried negative electrode to test the aforementioned parameters related to the negative electrode film, such as the surface density, compacted density, and thickness of the negative electrode film.

[0132] 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.

[0133] The first carbon-based material and the second carbon-based material can be distinguished by SEM. Figure 2 is an SEM image of an embodiment of the negative electrode sheet disclosed herein. As can be seen from the figure, particles with obvious pores in the cross section are the first carbon-based material, while particles with no pores in the cross section are the second carbon-based material.

[0134] In the present disclosure, the second carbon-based material mentioned above can be obtained commercially or prepared according to methods known in the art. In addition, the first carbon-based material mentioned above can be prepared by the following method.

[0135] In some embodiments, the preparation method of the above-mentioned first carbon-based material includes: step 1, providing a raw material with a plurality of pore structures; step 2, mixing the above-mentioned raw material and the filling material evenly in a predetermined proportion, and 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.

[0136] In some embodiments, in step 1, the raw material used to prepare 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 more preferably includes natural spherical graphite.

[0137] "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.

[0138] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 6.0 μm-25.0 μm.

[0139] In some embodiments, in step 1, the specific surface area of ​​the raw material may be greater than or equal to 2.5m 2 / g, optional 2.5m 2 / g-10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to carry out subsequent filling processing and obtain the first carbon-based material with the required specific surface area. It is also beneficial for the first carbon-based material to have both high capacity and high first coulombic efficiency. In addition, it is also beneficial for the first carbon-based material to have better kinetic properties.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] In some embodiments, in step 2, the mass ratio of the filler material to the raw material is (10-40):100, optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, (15-25):100. Generally, when other process conditions remain unchanged, the more the filler material is added, the higher the I of the first carbon-based material. D / I G The larger the mass ratio, the greater the yield. Those skilled in the art can adjust the mass ratio within the above-mentioned range according to their needs to obtain the desired I D / I G Numeric value.

[0145] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filling material within the above-mentioned range, it is beneficial to adjust the number of pores and / or pore size in the outer and inner areas of the first carbon-based material within a suitable range, which is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] In some embodiments, in step 3, the medium frequency furnace and the continuous graphitization heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of argon and helium.

[0164] 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 In general, when other process conditions remain unchanged, the higher the second temperature, the higher the I of the first carbon material. D / I G The smaller the temperature, the better. Those skilled in the art can adjust the temperature within the above-mentioned temperature range according to their needs to obtain the desired I D / I G Numeric value.

[0165] In the preparation method of the above-mentioned first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above-mentioned range, it is beneficial to adjust the parameters of the first carbon-based material such as S2 / S1, graphitization degree, gram capacity, particle size, powder compaction density, tap density, and adsorption amount of linseed oil.

[0166] In some embodiments, the first carbon-based material obtained above is mixed with an organic carbon source and then carbonized to form a carbon coating on at least a portion of the surface of the particles. Alternatively, the organic carbon source may be a carbon-containing material known in the art suitable for coating, such as one or more of coal tar, petroleum asphalt, phenolic resin, coconut shell, and the like. Optionally, the carbonization temperature is 900°C to 1300°C.

[0167] In some embodiments, the second carbon-based material is purchased through commercial channels.

[0168] [Positive electrode]

[0169] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0170] The positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0171] The above-mentioned positive electrode film layer usually contains a positive electrode active material, an optional binder, and an optional conductive agent. The above-mentioned positive electrode film layer is usually formed by coating a positive electrode slurry on the above-mentioned positive electrode current collector and then drying and cold pressing. The above-mentioned positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder used for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent used for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0172] The above-mentioned positive electrode active material can adopt the positive electrode active material for secondary batteries well-known in the art.

[0173] When the secondary battery of the present disclosure is a lithium-ion battery, the above-mentioned positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the above-mentioned lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the above-mentioned lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0174] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0175] In some embodiments, as examples, the positive electrode active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0176] In the present disclosure, the modified compound of each positive electrode active material may be a compound obtained by doping and / or surface coating the positive electrode active material.

[0177] [Electrolytes]

[0178] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0179] The types of the above electrolyte salts are not particularly limited and can be selected according to actual needs.

[0180] When the secondary battery of the present disclosure is a lithium ion battery, as an example, the above-mentioned electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0181] The types of the above-mentioned solvents are not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the above-mentioned solvents may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

[0182] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0183] [Isolation film]

[0184] The present disclosure has no particular limitation on the type of the above-mentioned isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0185] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0186] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process or a lamination process.

[0187] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0188] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0189] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG3 shows a secondary battery 5 with a square structure as an example.

[0190] In some embodiments, as shown in FIG4 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the above-mentioned opening to close the above-mentioned receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the above-mentioned receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0191] The preparation method of the secondary battery disclosed herein is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped to obtain the secondary battery.

[0192] In some embodiments of the present disclosure, the secondary batteries according to the present disclosure may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0193] Figure 5 is a schematic diagram of an exemplary battery module 4. As shown in Figure 5 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0194] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0195] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0196] Figures 6 and 7 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0197] The present disclosure also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack of the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0198] The above-mentioned electrical devices can select secondary batteries, battery modules or battery packs according to their usage requirements.

[0199] Figure 8 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0200] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0201] Example

[0202] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. All instruments used in the examples are commercially available.

[0203] Preparation of the first carbon-based material

[0204] Materials 1-1

[0205] Step 1: Mechanically crush, classify, spheroidize and purify the flake graphite to obtain natural spherical graphite. Step 2: Mix the obtained natural spherical graphite with filler petroleum asphalt in a ratio of 100:25. The softening point of petroleum asphalt is 120°C and the coking value is 36%. Then, place the mixed material in a programmable temperature rising device, heat it to 200°C and keep it warm for 1 hour (the first heating process), then continue to heat it to 700°C and keep it warm for 2 hours (the third heating process), and then cool it to room temperature to obtain an intermediate. Step 3: Place the obtained intermediate in a graphitization furnace and perform a heat treatment at 2580°C. After the end, demagnetize and sieve to obtain the first carbon-based material. The obtained first carbon-based material I D / I G The value is 0.152, S2 / S1 is 14.7, and DV50 is 18.3μm.

[0206] The S2 / S1 of the first carbon-based material is obtained by testing using the following method.

[0207] A sample preparation binder and the first carbon-based material powder are mixed evenly and then applied to a copper foil. The mixture is then dried at 60°C for 30 minutes before use. Five samples to be tested are cut into 6 mm x 6 mm pieces at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples are then cut using a plasma beam to obtain cross-sections of each sample. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from Japan's JEOL.

[0208] 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.

[0209] 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.

[0210] Materials 1-2 to 1-5

[0211] The preparation methods of materials 1-2 to 1-5 are similar to the preparation method of material 1-1, except that the mixing ratio of natural spherical graphite and filler petroleum asphalt and the heat treatment temperature are adjusted so that the first carbon-based material I D / I G The values ​​are as shown in Table 1.

[0212] Table 1

[0213] Materials 1-6 to 1-10

[0214] The preparation methods of materials 1-6 to 1-10 are similar to the preparation method of the above-mentioned material 1-1, except that the softening point temperature, coking value, and mixing ratio of natural spherical graphite and filler petroleum asphalt of the filler material are adjusted as shown in Table 2, and the third heating process is adjusted so that the S2 / S1 of the first carbon-based material is the value shown in Table 2.

[0215] Table 2

[0216] Materials 1-11

[0217] The preparation method of material 1-11 is similar to the preparation method of the above-mentioned material 1-3, except that the particle size distribution Dv50 of the flake graphite after mechanical crushing, classification, and spheroidization is adjusted to 10.2 μm.

[0218] Preparation of the second carbon-based material (amorphous carbon):

[0219] Materials 2-1

[0220] Coconut shells were used as raw materials, heat treated at 600°C, crushed, alkaline-impregnated, and heat treated at 1000°C to obtain an amorphous carbon material. The amorphous carbon was then coated and heat treated by mixing the amorphous carbon with a coating agent in a mass ratio of 100:10 and heat treated at 2450°C. The coating agent was asphalt. After demagnetization and screening, a second carbon-based material was obtained. D / I G The value is 0.17 and Dv50 is 10.2μm.

[0221] Materials 2-2 to 2-4

[0222] The preparation method is similar to the above-mentioned material 2-1, except that the amount of coating agent and the heat treatment temperature are adjusted as shown in Table 3 to obtain the I shown in Table 3. D / I G The second carbon-based material.

[0223] Table 3

[0224] Materials 2-5

[0225] The preparation method is similar to the above-mentioned material 2-1, except that the particle size distribution Dv50 after crushing is adjusted to 14.5 μm.

[0226] Example 1

[0227] Preparation of secondary batteries

[0228] 1. Negative Electrode: Thoroughly stir and mix the negative electrode active material (a mixture of the aforementioned material 1-1 (first carbon-based material) and material 2-1 (second carbon-based material) in a weight ratio of 70:30), conductive carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in a weight ratio of 96.4:1:1.2:1.4 in an appropriate amount of deionized water 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.

[0229] 2. Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) is mixed with carbon black (Super P), a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 96:2:2. An appropriate amount of NMP solvent is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is then coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet is obtained.

[0230] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0231] 4. Diaphragm: Polypropylene film.

[0232] 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.

[0233] Examples 2-8

[0234] The battery preparation methods of Examples 2-8 are similar to those of Example 1, except that the first carbon-based material or the second carbon-based material is selected from D / I G For details of different materials, please see Table 4.

[0235] Comparative Example 1

[0236] A secondary battery was assembled similarly to the preparation method of Example 1, except that the negative electrode active material only contained the second carbon-based material 2-1 used in Example 1.

[0237] Comparative Example 2

[0238] A secondary battery was assembled similarly to the preparation method of Example 1, except that the negative electrode active material only contained the first carbon-based material 1-3.

[0239] Performance Testing

[0240] (1) Energy density

[0241] At 25°C, the secondary battery was charged at a constant current of 1 / 3C to 4.3V. Then, it was charged at a constant voltage of 0.05C at 4.3V. After resting for 5 minutes, it was discharged at a constant current of 1 / 3C to 2.8V. The discharge energy of the battery was recorded. The battery discharge energy divided by the battery weight is the battery's gravimetric energy density, expressed in Wh / kg. The measurement data is shown in Table 4.

[0242] (2) Fast charging performance test of secondary batteries

[0243] At 25°C, the secondary battery was charged to 4.3V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.8V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0244] Then the secondary battery is charged with constant current at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 in sequence to a negative electrode cutoff potential of 4.3V or 0V (whichever is reached first). After each charge, it is discharged to 2.8V at 1C0. The SOC (State of Charge) at different charge rates is recorded. The charge rate-negative electrode potential curve under different SOC states was drawn, and the charge rate corresponding to the negative electrode potential of 0 V under different SOC states was obtained after linear fitting. The charge rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, respectively. The charging time T of the secondary battery from 10% SOC to 80% SOC (assuming that the secondary battery does not undergo lithium deposition) is calculated according to the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, and the unit is min.

[0245] The shorter the charging time, the better the dynamic performance of the secondary battery.

[0246] (3) Cycle performance test of secondary batteries

[0247] At 45°C, the prepared secondary battery was charged at a constant current of 1C to an upper cutoff voltage of 4.3V (corresponding to 100% SOC), then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to a lower cutoff voltage of 2.8V (corresponding to 0% SOC). The discharge capacity at this point was recorded as the discharge capacity in the first cycle. The secondary battery was subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0248] Capacity retention rate (%) of the secondary battery after 1000 cycles at 45° C. = discharge capacity after 1000 cycles / discharge capacity at the first cycle×100%.

[0249] Table 4

[0250] From the results in Table 4, it can be seen that in the embodiment, by making the negative electrode active material in the negative electrode film layer include the first carbon-based material and the second carbon-based material disclosed in the present invention, it is possible to have high energy density while taking into account excellent cycle performance and kinetic performance. D / I GIn the range of 0.155-0.220, a secondary battery with better balance among energy density, cycle performance and kinetic performance can be obtained.

[0251] In addition, compared with the embodiment, in Comparative Examples 1 and 2, since only the first carbon-based material or the second carbon-based material is included, the technical effect of the present disclosure cannot be obtained.

[0252] Examples 9-13

[0253] The battery preparation methods of Examples 9-13 are similar to those of Example 1, except that different materials S2 / S1 are selected as the first carbon-based material, and materials 1-6 to 1-10 are selected respectively. See Table 5 for details.

[0254] It should be noted that, for the convenience of comparison, the data of Example 3 are also listed in Table 5.

[0255] Table 5

[0256] It can be seen from Table 5 that by making the S2 / S1 of the first carbon-based material within the range of 2.5 to 460, the capacity retention rate of the secondary battery is further improved, and better cycle performance is obtained.

[0257] Example 14

[0258] The battery preparation method of Example 14 is similar to that of Example 1, except that different materials of DV50 are selected for the first carbon-based material and the second carbon-based material, as shown in Table 6 for details.

[0259] It should be noted that, for the convenience of comparison, the data of Example 3 are also listed in Table 6.

[0260] Table 6

[0261] It can be seen from Table 6 that by making the DV50 of the first carbon-based material greater than the DV50 of the second carbon-based material, the energy density of the secondary battery is further improved, the charging time is shortened, and the battery kinetics is more excellent.

[0262] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material, wherein: The negative electrode active material includes a first carbon-based material and a second carbon-based material; The first carbon-based material has a pore structure, and the I D / I G Less than or equal to 0.280, where 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 The second carbon-based material is an amorphous carbon material.

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

220.

3. The secondary battery according to claim 1 or 2, wherein: The second carbon-based material I D / I G less than or equal to 0.250, optionally, the I of the second carbon-based material D / I G Less than or equal to 0.

230.

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

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

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

7. The secondary battery according to any one of claims 1 to 6, wherein The powder compaction density of the first carbon-based material under a pressure of 20,000 N is greater than the powder compaction density of the second carbon-based material under a pressure of 20,000 N.

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

9. The secondary battery according to any one of claims 1 to 8, wherein The true density of the first carbon-based material is 2.22 g / cm 3 -2.27g / cm 3 , optional 2.23g / cm 3 -2.26g / cm 3 .

10. The secondary battery according to any one of claims 1 to 9, 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 μm 2 -2.0μm 2 The pore structure.

11. The secondary battery according to any one of claims 1 to 10, wherein 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 particle surface of the first carbon-based material to the interior of the particle, and in the cross-sectional view of the first carbon-based material, the total pore area of ​​the external region is denoted as S1, the total pore area of ​​the internal region is denoted as S2, and S2>S1, optionally, 2.6≤S2 / S1≤450.

7.

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

13. The secondary battery according to any one of claims 1 to 12, wherein The first carbon-based material satisfies at least one of the following conditions: (1) The powder compaction density of the first carbon-based material under a pressure of 20000N is 1.65g / cm 3 -2.0g / cm 3 , optional 1.68g / cm 3 -1.98g / cm 3 ; (2) the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, and can be optionally 10.0 μm-22.0 μm; (3) The volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, and can be optionally 16.5 μm-42.0 μm; (4) the particle size distribution of the first carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.55, and can be selected as 0.90-1.50; (5) The tap density of the first carbon-based material is 0.85 g / cm 3 -1.30g / cm 3 , optional 0.90g / cm 3 -1.25g / cm 3 ; (6) The graphitization degree of the first carbon-based material is greater than or equal to 95.5%, and can be optionally 95.5%-98.0%.

14. The secondary battery according to any one of claims 1 to 13, wherein The first carbon-based material and / or the second carbon-based material comprises primary particles; Optionally, the amount of the primary particles in the first carbon-based material accounts for greater than or equal to 80%; Optionally, the number of the primary particles in the second carbon-based material accounts for greater than or equal to 80%.

15. The secondary battery according to any one of claims 1 to 14, wherein The second carbon-based material satisfies at least one of the following conditions: (1) The true density of the second carbon-based material is 1.95 g / cm 3 -2.22g / cm 3 , optional 1.97g / cm 3 -2.21g / cm 3 (2) The specific surface area of ​​the second carbon-based material is greater than or equal to 1.5 m 2 / g, optional 1.9m 2 / g-7.5m 2 / g; (3) Dv50 of the second carbon-based material is 4.0 μm-15.0 μm, and can be 5.0 μm-15.0 μm; (4) the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.75, and can be 1.1-1.75; (5) The powder compaction density of the second carbon-based material under a pressure of 20000N is 0.85g / cm 3 -1.35g / cm 3 , optional 0.90g / cm 3 -1.30g / cm 3 ; (6) The tap density of the second carbon-based material is 0.80 g / cm 3 -1.20g / cm 3 , optional 0.83g / cm 3 -1.15g / cm 3 ; (7) The gram capacity of the second carbon-based material is 330 mAh / g-480 mAh / g, and can be optionally 340 mAh / g-470 mAh / g.

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

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

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

19. The secondary battery according to any one of claims 1 to 18, wherein The negative electrode film layer satisfies at least one of the following (1)-(3): (1) The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.70g / cm 3 , optional 1.45g / cm 3 -1.67g / cm 3 ; (2) The surface density of the negative electrode film layer is 5.0 mg / cm 2 -25.0mg / cm 2 , optional 5.5mg / cm 2 -22.5mg / cm 2 ; (3) The thickness of the negative electrode film layer is 40 μm-120 μm, and can be optionally 45 μm-100 μm.

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

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