Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, which is located on at least one surface of the negative electrode current collector and comprises a negative electrode active material. The negative electrode active material comprises a first carbon-based material and a second carbon-based material, wherein the first carbon-based material comprises an external region and an internal region, which is located inside the external region. The external region refers to a region formed by extending a distance of 2.5 μm from the surface of a particle of the first carbon-based material to the interior of the particle. In a sectional view of the first carbon-based material, the total pore area of the external region is recorded as S1, the total pore area of the internal region is recorded as S2, S2＞S1, and the graphitization degree of the first carbon-based material is greater than that of the second carbon-based 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 202311641330.4, 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] According to a first aspect of the present disclosure, a secondary battery is provided, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector 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 comprising an outer region and an inner region located inside the outer region, the outer region being a region extending 2.5 μm from a particle surface of the first carbon-based material toward an 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, and the first carbon-based material has a greater degree of graphitization than the second carbon-based material.

[0009] By making the negative electrode active material in the negative electrode film layer include a first carbon-based material and a second carbon-based material at the same time, wherein S2>S1 of the first carbon-based material, it means that the structure of the outer region of the carbon-based material is denser than that of the inner region, and the degree of graphitization of the first carbon-based material is greater than that of the second carbon-based material. Thus, the negative electrode plate can 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 degree of graphitization of the first carbon-based material is greater than or equal to 95.5%, and may be 95.5%-98.0%; the degree of graphitization of the second carbon-based material is 85%-90.5%, and may be 85.5%-90%. By ensuring that the degree of graphitization of the first carbon-based material is within the above range, the negative electrode active material has a high compaction density, and by ensuring that the degree of graphitization of the second carbon-based material is within the above range, the active ion transport performance of the negative electrode film layer is improved, thereby enabling the secondary battery to achieve both high energy density and good kinetic performance.

[0011] In some embodiments, the gram capacity of the second carbon-based material is less than the gram capacity of the first carbon-based material. By combining the first carbon-based material with a high capacity and the second carbon-based material with a low degree of graphitization, the secondary battery can achieve both high energy density and good kinetic performance.

[0012] In some embodiments, the interlayer spacing of the 002 crystal plane of the second carbon-based material is greater than the interlayer spacing of the 002 crystal plane of the first carbon-based material. The larger interlayer spacing of the second carbon-based material is conducive to the rapid deintercalation of active ions, while the smaller interlayer spacing of the first carbon-based material leads to a higher specific capacity. Therefore, by adjusting the interlayer spacing of the 002 crystal plane of the second carbon-based material to be greater than the interlayer spacing of the 002 crystal plane of the first carbon-based material, it is beneficial for the secondary battery to have both high energy density and good kinetic performance.

[0013] In some embodiments, the second carbon-based material D / I G Greater than the I of the first carbon-based material D / I G , I D The Raman spectrum of carbon-based materials is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of carbon-based materials is 1580±50cm -1 G peak intensity at, optionally, the I of the first carbon-based material D / I G Denoted as A, the I of the second carbon-based material D / IG By adjusting the I of the second carbon-based material D / I G Greater than the I of the first carbon-based material D / I G On the one hand, it is beneficial to improve the overall surface stability of the negative electrode active material, reduce the occurrence of side reactions, and improve the cycle performance; on the other hand, it is also beneficial for the secondary battery to have good kinetic performance.

[0014] In some embodiments, the first carbon-based material and / or the second carbon-based material include primary particles. Optionally, the primary particles in the first carbon-based material account for greater than or equal to 80%, and the primary particles in the second carbon-based material account for greater than or equal to 80%. By ensuring that the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, the material can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery. In addition, the compaction density of the negative electrode film layer can be increased, thereby improving the energy density of the secondary battery.

[0015] In some embodiments, 1.8≤S2 / S1≤199.8, and 2.3≤S2 / S1≤148.7. This allows the secondary battery to better balance dynamic performance and cycle performance.

[0016] 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 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 preventing 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.

[0017] In some embodiments, the inner region of the first carbon-based material includes one or more areas 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 μm2-2.0 μm 2 By ensuring that the internal region of the first carbon-based material includes a pore structure of the aforementioned size, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, thereby 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 change of the negative electrode film layer.

[0018] In some embodiments, at least a portion of the surface of the first carbon-based material has a coating layer. Optionally, the coating layer comprises a carbon coating layer. This is beneficial for improving the dynamic performance of the secondary battery.

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

[0020] 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 true density of the first carbon-based material is within the above range, it is beneficial to increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[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 By making the compaction density of the powder of the first carbon-based material within the above range, the compaction density of the negative electrode film layer can be increased, thereby increasing the energy density of the secondary battery.

[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 making the tap density of the first carbon-based material within the above range, the carbon material has better processing performance, which can increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0026] In some embodiments, the first carbon-based material D / I G Less than or equal to 0.280, and optionally 0.155-0.220. This can effectively reduce active lithium consumption, further improve cycle performance, and take into account kinetic performance.

[0027] In some embodiments, the amount of linseed oil adsorbed by the first carbon-based material per 100 g is 30 mL to 47 mL. When the amount of linseed oil adsorbed by the carbon material is within this range, the first carbon-based material exhibits better processability and lower surface side reaction activity of the particles, thereby reducing the consumption of active ions during SEI film formation.

[0028] In some embodiments, the gram capacity of the second carbon-based material is 280 mAh / g-340 mAh / g, optionally 300 mAh / g-338 mAh / g. By adjusting the gram capacity of the second carbon-based material within the above range, the dynamic performance of the secondary battery can be improved.

[0029] In some embodiments, the interlayer spacing of the 002 crystal plane of the second carbon-based material is 0.33622nm-0.33669nm, and optionally 0.33626nm-0.33665nm. By adjusting the interlayer spacing of the second carbon-based material within the above range, it is beneficial to facilitate the rapid deintercalation and deintercalation of active ions, thereby improving the active ion transport performance of the negative electrode film layer, and enabling the secondary battery to have good dynamic performance.

[0030] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 10 μm-18 μm, optionally 12 μm-17 μm. By setting the volume distribution particle size Dv50 of the second carbon-based material within the above range, the specific surface area of ​​the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the cycle performance of the secondary battery can be improved.

[0031] In some embodiments, the tap density of the second carbon-based material is 0.95 g / cm 3 -1.35g / cm 3 , optional 1.00g / cm 3 -1.30g / cm 3 By making the tap density of the second carbon-based material within the above range, the second carbon-based material has better processability.

[0032] In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is 25.0 μm-45.0 μm, and optionally 26.5 μm-42.0 μm. The second carbon-based material has good processability and is conducive to having a suitable pore distribution in the negative electrode film layer, thereby improving the dynamic performance of the secondary battery.

[0033] In some embodiments, the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.90, and can be selected from 0.90 to 1.85. This is beneficial for increasing the compaction density of the negative electrode film layer and improving the energy density of the secondary battery. Furthermore, 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.

[0034] In some embodiments, the amount of linseed oil adsorbed by the second carbon-based material per 100 g is 38 mL to 50 mL. When the amount of linseed oil adsorbed by the carbon material is within this range, the second carbon-based material particles have better processability and lower surface side reaction activity, thereby reducing the consumption of active ions during SEI film formation.

[0035] In some embodiments, the second carbon-based material is artificial graphite. Artificial graphite has a stable structure, thereby improving the cycle performance of the secondary battery.

[0036] In some embodiments, the second carbon-based material D / I G The value is 0.20-0.40, and can be optionally 0.25-0.35. This can further improve the dynamic performance.

[0037] In some embodiments, the content of the first carbon-based material in the negative electrode active material is greater than or equal to 30 wt %, and can be 50 wt % to 80 wt %. When the content of the first carbon-based material is within the above range, the secondary battery has high energy density while having good kinetic performance and cycle performance.

[0038] In some embodiments, the negative electrode active material further comprises a silicon-based material. Optionally, the silicon-based material is present in an amount of 0.5 wt% to 30 wt% of the negative electrode active material. The higher lithium insertion potential of the silicon-based material helps improve the kinetic performance of the secondary battery and also increases the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0039] In some embodiments, the compaction density of the negative electrode film layer is 1.45 g / cm 3 -1.90g / cm 3 , optional 1.50g / cm 3 -1.85g / 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.

[0040] 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.

[0041] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, optionally 45 μm-100 μm.

[0042] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0043] Effects of the Invention

[0044] The secondary battery of the present disclosure has high energy density and excellent cycle performance and kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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.

[0046] FIG1 is a schematic diagram of a cross-sectional image of a particle of a first carbon-based material according to the present disclosure.

[0047] FIG. 2 is a schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0048] FIG3 is an exploded schematic diagram of an embodiment of a secondary battery of the present disclosure.

[0049] FIG. 4 is a schematic diagram of an embodiment of a battery module according to the present disclosure.

[0050] FIG5 is a schematic diagram of an embodiment of a battery pack according to the present disclosure.

[0051] FIG. 6 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 5 .

[0052] FIG. 7 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, carbon-based materials are commonly used as negative electrode active materials in secondary batteries. To improve the performance of these materials, these carbon-based material particles are typically treated with surface coatings. However, these treatments reduce both the specific capacity and compacted density, impacting the energy density of the secondary battery. The surface coatings, typically made of soft or hard carbon materials, are highly active and prone to side reactions, which can affect the battery's cycling performance.

[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 plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and including a negative electrode active material. The negative electrode active material includes a first carbon-based material and a second carbon-based material, the first carbon-based material including an outer region and an inner region located inside the outer region, the outer region being a region extending 2.5 μm from the surface of a particle 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. Furthermore, the degree of graphitization of the first carbon-based material is greater than the degree of graphitization of the second carbon-based material.

[0065] In this disclosure, "inner region" refers to a region other than the outer region in a particle of a material.

[0066] By making the first carbon-based material satisfy S2>S1, the first carbon-based material has the following characteristics: the number of pores in the internal region is large and / or the pore size is large, while the number of pores in the external region is small and / or the pore size is small, indicating that the structure of the external region of the carbon-based material is denser than the internal region. The pore structure in the internal 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 number of pores in the external region of the first carbon-based material is small and / or the pore size is small, 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, by including the above-mentioned first carbon-based material, the cycle performance of the secondary battery can be improved.

[0067] In the present disclosure, the second carbon-based material has a lower degree of graphitization than the first carbon-based material, and has a larger interlayer spacing, which is conducive to the rapid deintercalation of active ions and has good kinetic performance. However, the second carbon-based material has a lower gram capacity and compaction density, which has an adverse effect on the energy density of the negative electrode film layer and even the secondary battery. The first carbon-based material has a high gram capacity and a porous structure, and its compaction density is relatively high. Therefore, it can improve the energy density of the negative electrode film layer and even the secondary battery.

[0068] In the present disclosure, by making the negative electrode active material in the negative electrode film layer include the above-mentioned first carbon-based material and the second carbon-based material at the same time, the high capacity and high compaction density characteristics of the first carbon-based material and the excellent kinetic characteristics of the second carbon-based material can be fully utilized, so that the secondary battery has high energy density and excellent kinetic performance. In addition, as mentioned above, the internal pore structure of the first carbon-based material can buffer the expansion of particles when lithium is inserted, while the second carbon-based material has a low degree of graphitization and a large interlayer spacing, and the volume change of the particles is small when lithium ions are inserted, and the expansion is low. That is, both the first carbon-based material and the second carbon-based material can reduce expansion, thereby effectively avoiding SEI damage caused by expansion, significantly reducing active lithium consumption, and greatly improving the cycle performance of the battery.

[0069] 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, it is beneficial for the negative electrode active material to have a high compaction density and gram capacity. The degree of graphitization of the second carbon-based material is 85%-90.5%, and can be optionally 85.5%-90%. By making the degree of graphitization of the second carbon-based material within the above range, at this time, the interlayer spacing of the second carbon-based material is larger, thereby improving the active ion transport performance of the negative electrode film layer. Therefore, by simultaneously containing the first carbon-based material and the second carbon-based material, the secondary battery can take into account both high energy density and good kinetic performance. In some embodiments, the gram capacity of the second carbon-based material is less than the gram capacity of the first carbon-based material. Optionally, the gram capacity of the first carbon-based material is greater than or equal to 355mAh / g, and can be optionally 355mAh / g-370mAh / g. When the gram capacity of the first carbon-based material is within the above range, it is beneficial to improve the energy density of the secondary battery. Optionally, the gram capacity of the second carbon-based material is 280 mAh / g-340 mAh / g, and optionally 300 mAh / g-338 mAh / g. Thus, by combining a first carbon-based material having a high capacity with a second carbon-based material having a low degree of graphitization, it is beneficial for the secondary battery to have both high energy density and good kinetic performance.

[0070] In some embodiments, the interlayer spacing of the 002 crystal plane of the second carbon-based material is greater than the interlayer spacing of the 002 crystal plane of the first carbon-based material. The larger interlayer spacing of the second carbon-based material is conducive to the rapid deintercalation of active ions, while the smaller interlayer spacing of the first carbon-based material leads to a higher specific capacity. Therefore, by adjusting the interlayer spacing of the 002 crystal plane of the second carbon-based material to be greater than the interlayer spacing of the 002 crystal plane of the first carbon-based material, the secondary battery can be further improved to achieve both high energy density and good kinetic performance.

[0071] In some embodiments, the second carbon-based material D / I G Greater than the I of the first carbon-based material D / I G , I D The Raman spectrum of carbon-based materials is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of carbon-based materials is 1580±50cm -1 Optionally, the I of the first carbon-based material D / I G Denoted as A, I of the second carbon-based material D / I GDenoted as B, the range of A / B is 0.45-0.85. For example, it can be 0.46, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.8, 0.85. By adjusting the I D / I G Greater than the I of the first carbon-based material D / I G On the one hand, it is beneficial to improve the overall surface stability of the negative electrode active material, reduce the occurrence of side reactions, and improve the cycle performance; on the other hand, it is also beneficial for the secondary battery to have good kinetic performance.

[0072] 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%, 90%-100%, 95%-100%, or 85%-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%, 90%-100%, 95%-100%, or 85%-100%. By making the first carbon-based material and / or the second carbon-based material contain an appropriate proportion of primary particles, it can have higher structural stability and reduce the occurrence of side reactions, thereby improving the cycle performance of the secondary battery; in addition, it can also increase the compaction density of the negative electrode film layer, further improving the energy density of the secondary battery.

[0073] In some embodiments, preferably 1.8≤S2 / S1≤199.8, for example, 2≤S2 / S1≤199.8, 2≤S2 / S1≤190, 2.3≤S2 / S1≤180, 2.3≤S2 / S1≤170, and more preferably 2.3≤S2 / S1≤148.7, for example, 3.0≤S2 / S1≤140, 4.0≤S2 / S1≤100. The inventors found in further research that when S2 / S1 is also within the above range, the secondary battery can better balance good kinetic performance and good cycle performance.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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 .

[0078] 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.

[0079] In some embodiments, at least part of the surface of the above-mentioned first carbon-based material has a coating layer. Optionally, the above-mentioned coating layer includes a carbon coating layer. Optionally, more than 80% of the surface of the above-mentioned first carbon-based material is covered with a carbon coating layer, and further, 90%-100% of the surface of the above-mentioned first carbon-based material is covered with a carbon coating layer. In some embodiments, the above-mentioned carbon in the above-mentioned coating layer includes amorphous carbon and / or crystalline carbon with a degree of graphitization between 68% and 90%. Thus, by having a coating layer on at least part of the surface of the first carbon-based material, the dynamic performance of the secondary battery can be further improved.

[0080] In some embodiments, the gram capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and can be selected from 355 mAh / g to 370 mAh / g, thereby further improving the energy density of the secondary battery.

[0081] 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 true density of the first carbon-based material is within the above range, it is beneficial to increase the compaction density of the negative electrode film layer and further increase the energy density of the secondary battery.

[0082] 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, it can increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery. It is also conducive to forming a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance, and improving the negative electrode film layer's electrolyte infiltration and retention characteristics, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0083] In some embodiments, the volume distribution particle size Dv50 of the above-mentioned first carbon-based material is 8.0μm-25.0μm, and can be optionally 10.0μm-22.0μm. In some embodiments, the volume distribution particle size Dv90 of the above-mentioned first carbon-based material is 16.0μm-45.0μm, and can be optionally 16.5μm-42.0μm. When the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above-mentioned range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, it can also reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery.

[0084] 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.

[0085] 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 has good processing performance, can also increase the compaction density of the negative electrode film layer, and improve the energy density of the secondary battery.

[0086] In some embodiments, the amount of linseed oil adsorbed by 100g of the first carbon-based material is 30mL-47mL. When the amount of linseed oil adsorbed by the carbon material is within this range, the first carbon-based material has good processability and low surface side reaction activity of the particles, thereby reducing the consumption of active ions during SEI film formation.

[0087] In some embodiments, the first carbon-based material D / I G Less than or equal to 0.280, and optionally 0.155-0.220. This can effectively reduce active lithium consumption, further improve cycle performance, and take into account kinetic performance.

[0088] In some embodiments, the gram capacity of the above-mentioned second carbon-based material is 280mAh / g-340mAh / g, and can be optionally 300mAh / g-338mAh / g. Thus, it is beneficial to improve the kinetic performance of the secondary battery. In some embodiments, the interlayer spacing of the 002 crystal plane of the above-mentioned second carbon-based material is 0.33622nm-0.33669nm, and can be optionally 0.33626nm-0.33665nm. By adjusting the interlayer spacing of the second carbon-based material within the above-mentioned range, it is beneficial to the rapid deintercalation of active ions, thereby improving the active ion transport performance of the negative electrode film layer, thereby further improving the kinetic performance of the secondary battery.

[0089] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 10 μm-18 μm, and optionally 12 μm-17 μm. By setting the volume distribution particle size Dv50 of the second carbon-based material within the above range, the specific surface area of ​​the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the cycle performance of the secondary battery can be improved.

[0090] In some embodiments, the tap density of the second carbon-based material is 0.95 g / cm 3 -1.35g / cm 3 , optional 1.00g / cm 3 -1.30g / cm 3 By making the tap density of the second carbon-based material within the above range, the second carbon-based material has better processing performance, and at the same time, the compaction density of the negative electrode film layer can be increased, thereby increasing the energy density of the secondary battery.

[0091] In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is 25.0 μm-45.0 μm, and optionally 26.5 μm-42.0 μm. The second carbon-based material has good processability and is conducive to having a suitable pore distribution in the negative electrode film layer, thereby improving the dynamic performance of the secondary battery.

[0092] In some embodiments, the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.90, and may be 0.90-1.85. This is beneficial for increasing the compaction density of the negative electrode film and the energy density of the secondary battery. Furthermore, it is beneficial for forming a reasonable pore structure between the particles of the negative electrode film, improving the transport performance of active ions and electrons in the negative electrode film, and thus improving the kinetic performance of the secondary battery.

[0093] In some embodiments, the amount of linseed oil adsorbed by 100g of the second carbon-based material is 38mL-50mL. When the amount of linseed oil adsorbed by the carbon material is within this range, the second carbon-based material particles have better processability and lower surface side reaction activity, thereby reducing the consumption of active ions during SEI film formation.

[0094] In some embodiments, the content of the first carbon-based material in the negative electrode active material is greater than or equal to 30%, and can be optionally 50wt%-80wt%, for example, 55wt%-75wt%, 60wt%-70wt%. The content of the second carbon-based material in the negative electrode active material is less than or equal to 70%, for example, 20wt%-50wt%, optionally 25wt%-45wt%, 30wt%-40wt%. When the contents of the first carbon-based material and the second carbon-based material are respectively within the above ranges, the secondary battery can have high energy density, good kinetic performance and cycle performance.

[0095] Optionally, the above-mentioned second carbon-based material includes artificial graphite, which generally refers to crystalline carbon obtained by high-temperature graphitization treatment, and usually does not have a pore structure inside, or does not have a pore structure that can be directly observed from a cross-sectional image (such as a scanning electron microscope image with a magnification of 1000 times).

[0096] In some embodiments, the second carbon-based material D / I G The value is 0.20-0.40, and can be optionally 0.25-0.35. This can further improve the dynamic performance.

[0097] 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 carbon-based material. For example, the negative electrode active material may also include a silicon-based material. The higher lithium insertion potential of the silicon-based material helps improve the kinetic performance of the secondary battery; it can also increase the negative electrode capacity, thereby further increasing 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.

[0098] 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 0.5 wt%-30 wt%, for example, 0.8%-25%, 1%-20%, 1%-15%, 1%-10%, 1.5%-8%, 2%-6%, or 3%-7%. This improves the kinetic performance and energy density of the secondary battery while also ensuring good cycle performance and cycling performance.

[0099] 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.

[0100] 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).

[0101] 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.

[0102] In some embodiments, the compaction density of the negative electrode film is 1.45 g / cm 3 -1.90g / cm 3 , optional 1.50g / cm 3 -1.85g / 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.

[0103] 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.

[0104] In some embodiments, the thickness of the negative electrode film layer is 40 μm-120 μm, and optionally 45 μm-100 μm.

[0105] 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).

[0106] 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.

[0107] 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.

[0108] 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).

[0109] In the present disclosure, the interlayer spacing of the 002 crystal plane of a material (e.g., the first carbon-based material, the second carbon-based material) has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., a Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the interlayer spacing of the C(002) crystal plane in the material's crystal structure.

[0110] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be tested using methods known in the art. An exemplary test method is as follows: the sample powder is mixed evenly with the conductive agent carbon black (Super P), the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is applied to the surface of the negative electrode current collector copper foil, dried in an oven and set aside; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to a concentration of 1 mol / L The electrolyte was then added. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. The cells were assembled into CR2430 button cells in an argon-protected glove box with the electrolyte. After standing for 12 hours, the cells were discharged at 0.05C to 0.005V at 25°C. The cells were then allowed to stand for 10 minutes, and then discharged again at 50μA to 0.005V. The cells were allowed to stand for 10 minutes, and then discharged again at 10μA to 0.005V. The cells were then charged at 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0111] In the present disclosure, the first carbon-based material and the second carbon-based material 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 GThe average value of the remaining 40 points is the I D / I G The testing instrument may be a Horiba LabRAM HR800 Raman spectrometer.

[0112] In the present disclosure, whether there is a coating layer on the surface of a material (eg, the first carbon-based material, the second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In the present disclosure, the adsorption capacity of linseed oil by 100g of the first carbon-based material can be tested according to the following method: referring to GB / T3780.2-2017, a certain mass (e.g. 20g) of the dried test sample is weighed and placed in the mixing chamber of the oil absorptometer, the temperature of the mixing chamber is 22°C-23°C, and the lid is closed; the oil delivery pipe of the constant-rate burette is aligned with the top of the hole of the mixing chamber cover; the oil absorptometer is started, the instrument starts running and linseed oil is added dropwise, and as the oil absorption of the sample increases, the mixed material changes from a free-flowing state to a The semi-plastic agglomerates and the viscosity of the mixture continue to increase, and the viscosity is transmitted to the torque sensor system of the oil absorptometer. When the added oil causes the semi-plastic agglomerates to reach the preset torque level, the oil absorptometer and the constant-rate burette are automatically closed; the value corresponding to 70% of the maximum torque of the fitting curve is read, and the formula A=(V / m)×100 is used to calculate the adsorption amount A of linseed oil by 100g of carbon material, where V represents the volume of linseed oil consumed by the sample corresponding to 70% of the maximum torque, in ml; m is the mass of the added sample, in g.

[0118] In this disclosure, primary particles have a meaning well known in the art. Primary particles refer to non-agglomerated particles, and particles aggregated from primary particles are secondary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0119] 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.

[0120] 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.

[0121] 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).

[0122] It should be noted that the above-mentioned various parameter tests on the negative electrode active material or the negative electrode film layer can be conducted by sampling and testing the prepared secondary battery according to the following steps.

[0123] 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.

[0124] 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.

[0125] The first carbon-based material and the second carbon-based material can be distinguished by a cross-section polisher. For example, the types of the first carbon-based material and the second carbon-based material can be distinguished by performing an ion polishing cross-section morphology (CP) test on the negative electrode. As an example, the test method can be: cutting the negative electrode into a sample to be tested of a certain size (for example, 2cm×2cm), and fixing the negative electrode on the sample stage with paraffin wax; placing the sample stage into the sample holder and locking it, turning on the power of the argon ion cross-section polisher (for example, the IB-09010CP argon ion cross-section polisher of Japan's JEOL company) and evacuating the sample (for example, 10-4 Pa), set the argon flow rate (e.g., 0.15 MPa) and voltage (e.g., 8 KV) and polishing time (e.g., 2 h), adjust the sample stage to the rocking mode and start polishing; randomly select an area in the sample to be tested for scanning testing (e.g., refer to JY / T010-1996, use a scanning electron microscope for scanning), and obtain an ion polishing cross-sectional morphology (CP) image of the negative electrode piece at a certain magnification (e.g., 1000 times), from which the first carbon-based material and the second carbon-based material can be distinguished.

[0126] In the present disclosure, the second carbon-based material can be obtained commercially and can be prepared by a known method. In addition, the first carbon-based material can be prepared by the following method of the present disclosure.

[0127] 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.

[0128] 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 and does not require graphitization. Alternatively, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0129] "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.

[0130] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 6.0 μm-25.0 μm.

[0131] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥2.5m 2 / g, optional 2.5m 2 / g-10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to carry out subsequent filling processing and obtain the first carbon-based material with the required specific surface area. It is also beneficial for the first carbon-based material to have both high capacity and high first coulombic efficiency. In addition, it is also beneficial for the first carbon-based material to have better kinetic properties.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] In some embodiments, the first temperature raising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 0.5 h-3 h.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] In some embodiments, in step 3, the medium frequency furnace and the continuous graphitization heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] In some embodiments, the preparation method of the above-mentioned second carbon-based material includes: step 11, providing raw materials; step 12, crushing and shaping the raw materials to obtain a first intermediate; step 13, graphitizing the first intermediate to obtain the second carbon-based material.

[0160] In some embodiments, in step 11, the feedstock may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.

[0161] In some embodiments, in step 12, a mechanical mill or a roller mill can be used to crush the raw material. In addition, a shaping machine can be used for shaping.

[0162] In some embodiments, in step 13, the graphitization temperature is 2700°C-3200°C.

[0163] By adjusting the graphitization temperature and / or graphitization time, the second carbon-based material can have a suitable degree of graphitization. In the above-mentioned method for preparing the second carbon-based material, by adjusting one or more parameters of the raw material parameters (such as particle size, particle size distribution, gram capacity, etc.), it is beneficial to adjust the graphitization degree, interlayer spacing, gram capacity, particle size, tap density and other parameters of the second carbon-based material.

[0164] [Positive electrode]

[0165] 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.

[0166] 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).

[0167] The above-mentioned positive electrode film layer generally comprises a positive electrode active material, an optional binder and an optional conductive agent. The above-mentioned positive electrode film layer is generally formed by coating the positive electrode slurry on the above-mentioned positive electrode current collector, drying and cold pressing. The above-mentioned positive electrode slurry is generally formed by dispersing the positive electrode active material, the optional conductive agent, the optional binder and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0168] The positive electrode active material may be a positive electrode active material for a secondary battery known in the art.

[0169] 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, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0170] 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 general formula of Li a Ni b Coc M d O e A f One or more of lithium transition metal oxides and their modified compounds thereof. 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.

[0171] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 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 O2, LiFePO4, and LiMnPO4.

[0172] In the present disclosure, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the above positive electrode active materials.

[0173] [Electrolyte]

[0174] In some embodiments, the above electrolyte uses an electrolytic solution, and the above electrolytic solution includes an electrolyte salt and a solvent.

[0175] The types of the above electrolyte salts are not specifically limited and can be selected according to actual needs.

[0176] 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).

[0177] 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.

[0178] 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.

[0179] [Isolation film]

[0180] 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.

[0181] 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.

[0182] 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.

[0183] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0184] 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).

[0185] The present disclosure has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG2 shows a secondary battery 5 with a square structure as an example.

[0186] In some embodiments, as shown in FIG3 , 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.

[0187] 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.

[0188] 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.

[0189] Figure 4 is a schematic diagram of an exemplary battery module 4. As shown in Figure 4 , 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.

[0190] 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.

[0191] 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.

[0192] Figures 5 and 6 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 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.

[0193] 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.

[0194] The above-mentioned electrical devices can select secondary batteries, battery modules or battery packs according to their usage requirements.

[0195] Figure 7 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.

[0196] 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.

[0197] Example

[0198] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0199] Preparation of the first carbon-based material:

[0200] Materials 1-1

[0201] Step 1, mechanically crush, classify, spheroidize and purify the flake graphite to obtain natural spherical graphite. Step 2, mix the obtained natural spherical graphite with the filler petroleum asphalt in a mass ratio of 100:23, 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 (first heating process), and then continue to heat it to 700°C and keep it warm for 2 hours (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 2250°C. After the end, demagnetize and sieve to obtain the first carbon-based material (material 1-1). The obtained material 1-1 meets the following requirements: S2 / S1 is 11.6, the degree of graphitization is 94.9%, I D / I G It is 0.175, and the number of primary particles accounts for 80%.

[0202] The S2 / S1 of the first carbon-based material is obtained by testing using the following method.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] Materials 1-2 to 1-4

[0207] The preparation methods of materials 1-2 to 1-4 are similar to those of material 1-1, except that the amounts of spherical graphite and filler and the heat treatment temperature are adjusted as shown in Table 1, so that the graphitization degrees of materials 1-2 to 1-4 are the values ​​shown in Table 1. The details are as follows:

[0208] Table 1.

[0209] Materials 1-5 to 1-9

[0210] The preparation methods of materials 1-5 to 1-9 are similar to those of material 1-1, except that the softening point temperature, coking value, and mixing ratio of natural spherical graphite and filler petroleum asphalt of the filler material are adjusted as shown in Table 2, and then the third heating process is adjusted so that the S2 / S1 of the first carbon-based material is the value shown in Table 2.

[0211] Table 2

[0212] Materials 1'-1

[0213] The preparation method of material 1'-1 is similar to that of material 1-1, except that the material 1'-1 is adjusted as shown in Table 3 so that the S2 / S1 of the first carbon-based material is the value shown in Table 3.

[0214] Table 3

[0215] Materials 1-10 to 1-12

[0216] The preparation methods of materials 1-10 to 1-12 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 as shown in Table 4, so that the I of the first carbon-based material is D / I G The values ​​are as shown in Table 4.

[0217] Table 4

[0218] In the following examples and comparative examples, the second carbon-based material was commercially obtained (from Shanghai Shanshan Technology Co., Ltd. and Jiangxi Zichen Technology Co., Ltd.).

[0219] Example 1

[0220] Preparation of secondary batteries

[0221] 1. Negative Electrode: Thoroughly stir and mix the negative electrode active material (material 1-1 (first carbon-based material) and the 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.

[0222] 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.

[0223] 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.

[0224] 4. Isolation film: Polypropylene film is used as the isolation film.

[0225] 5. Secondary battery: Place the positive electrode sheet and negative electrode sheet prepared above in order, with the separator between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wind to obtain an electrode assembly; place the electrode assembly in an outer package, inject electrolyte after drying, and obtain a secondary battery after vacuum packaging, standing, formation, shaping and other processes.

[0226] Examples 2 to 10

[0227] The battery preparation methods of Examples 2-10 are similar to those of Example 1, except that the first carbon-based material or the second carbon-based material is a material with a different degree of graphitization, as shown in Table 5 for details.

[0228] Comparative Example 1

[0229] The same preparation as in Example 1 was performed except that Material 1-4 was used as the first carbon-based material and the second carbon-based material was not used.

[0230] Comparative Example 2

[0231] The same preparation as in Example 1 was performed except that the first carbon-based material was not used.

[0232] Comparative Example 3

[0233] The same preparation as in Example 1 was performed except that Material 1-4 was used as the first carbon-based material and the second carbon-based material had a higher degree of graphitization than the first carbon-based material.

[0234] Comparative Example 4

[0235] The same preparation as in Example 1 was performed except that Material 1'-1 was used as the first carbon-based material.

[0236] Performance Testing

[0237] (1) Energy density

[0238] 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 at 4.3V to a current of 0.05C. After standing 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 5.

[0239] (2) 1200cycle pole piece expansion rate

[0240] The thickness of the negative electrode after cold pressing is recorded as H0. The cold-pressed negative electrode sheet is made into a secondary battery with the positive electrode sheet, isolation membrane, and electrolyte. At 25°C, the secondary battery is subjected to a 1C / 1C cycle of 100% DOD (100% depth of discharge, that is, full charge and then full discharge) in a Xinwei charger and discharger. The discharge capacity of the first cycle (i.e., the initial capacity) is recorded as 100%, and the cycle stops when the cycle reaches 1200 cycles. The secondary battery is then charged to 100% SOC (State of Charge), the secondary battery is disassembled and the thickness of the corresponding negative electrode sheet is tested, which is recorded as H1.

[0241] The cycle expansion rate of the negative electrode plate after 1200 cycles is: (H1 / H0-1)×100%.

[0242] (3) Cycle performance test of secondary batteries

[0243] At 45°C, the prepared secondary battery was charged at a constant current of 1C to the upper cutoff voltage (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 the lower cutoff voltage (corresponding to 0% SOC). The discharge capacity at this point was recorded as the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0244] 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%.

[0245] (4) Fast charging performance test of secondary batteries

[0246] 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.

[0247] 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.

[0248] The shorter the charging time, the better the dynamic performance of the secondary battery.

[0249] Table 5

[0250] It can be seen from the results in Table 5 that in Examples 1 to 10, by making the negative electrode active material in the negative electrode film layer include a first carbon-based material with S2 greater than S1 and a second carbon-based material with a graphitization degree less than that of the first carbon-based material, the expansion of the electrode can be effectively suppressed, and the secondary battery has excellent cycle performance and kinetic performance, and excellent energy density.

[0251] Comparative Example 1 only contains the first carbon-based material. Although the cyclability is good, the charging time is very long and the kinetic performance is poor. Comparative Example 2 only includes the second carbon-based material, with a low degree of graphitization and low energy density; the content of the amorphous carbon component is high. Although the expansion rate is low, due to the high activity of amorphous carbon, it is easy to react with the electrolyte, so the cyclability is poor. In Comparative Example 3, although the first carbon-based material and the second carbon-based material are included, since the degree of graphitization of the second carbon-based material is higher than that of the first carbon-based material, the electrode expansion rate is high and the cyclability is poor. In addition, the degree of graphitization is high and the interlayer spacing is small, resulting in a long charging time and poor kinetic performance. In Comparative Example 4, when S2 / S1 of the first carbon-based material is equal to 0.92, the cyclability is poor.

[0252] Examples 11-16

[0253] A battery was prepared in the same manner as in Example 4 except that the S2 / S1 of the first carbon-based material was set to the values ​​shown in Table 6. The specific results are shown in Table 5.

[0254] Table 6

[0255] From the results in Table 6, it can be seen that by setting 1.8≤S2 / S1≤199.8, the cycle performance and kinetic performance of the secondary battery are further improved, and by setting 2.3≤S2 / S1≤148.7, the cycle performance and kinetic performance of the secondary battery are further improved.

[0256] Examples 16-21

[0257] In addition to making the first carbon-based material and the second carbon-based material D / I G A secondary battery was prepared in the same manner as in Example 4 except that the values ​​shown in Table 7 were the same. Specific parameters and test results are shown in Table 7.

[0258] Table 7

[0259] From the results in Table 7, it can be seen that compared with Example 21, the I of the second carbon-based material in Examples 16-20 is D / I G Greater than the I of the first carbon-based material D / I G , the cycle performance and kinetic performance of the secondary battery are further improved. In Examples 17-19, by making A / B within the range of 0.45-0.85, the cycle performance and kinetic performance of the secondary battery can be further improved.

[0260] 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, The negative electrode active material includes a first carbon-based material and a second carbon-based material, The first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm from the particle surface of the first carbon-based material to the inside of the particle, and in a 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, and the degree of graphitization of the first carbon-based material is greater than that of the second carbon-based material.

2. The secondary battery according to claim 1, wherein The graphitization degree of the first carbon-based material is greater than or equal to 95.5%, and may be 95.5%-98.0%; and / or the graphitization degree of the second carbon-based material is 85%-90.5%, and may be 85.5%-90%.

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

4. The secondary battery according to any one of claims 1 to 3, wherein The interlayer spacing of the 002 crystal plane of the second carbon-based material is greater than the interlayer spacing of the 002 crystal plane of the first carbon-based material.

5. The secondary battery according to any one of claims 1 to 4, wherein The second carbon-based material I D / I G Greater than the I of the first carbon-based material D / I G , I D The Raman spectrum of carbon-based materials is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of carbon-based materials is 1580±50cm -1 The G peak intensity at Optionally, the first carbon-based material I D / I G Denoted as A, I of the second carbon-based material D / I G Let it be B, then the range of A / B is 0.45-0.

85.

6. The secondary battery according to any one of claims 1 to 5, 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%.

7. The secondary battery according to any one of claims 1 to 6, wherein 1.8≤S2 / S1≤199.8, optionally, 2.3≤S2 / S1≤148.

7.

8. The secondary battery according to claim 7, 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.

9. The secondary battery according to any one of claims 1 to 8, wherein At least part of the surface of the first carbon-based material has a coating layer; optionally, the coating layer includes a carbon coating layer.

10. The secondary battery according to any one of claims 1 to 9, wherein The first carbon-based material satisfies at least one of the following conditions: (1) The gram capacity of the first carbon-based material is greater than or equal to 355 mAh / g, and can be 355 mAh / g-370 mAh / g; (2) 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 ; (3) 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 ; (4) The volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-25.0 μm, and can be optionally 10.0 μm-22.0 μm; (5) The volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm-45.0 μm, and can be optionally 16.5 μm-42.0 μm; (6) the particle size distribution of the first carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.55, and can be selected as 0.90-1.50; (7) 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 ; (8) The adsorption amount of linseed oil by 100g of the first carbon-based material is 30mL-47mL; (9) I of the first carbon-based material D / I G Less than or equal to 0.280, optional: 0.155-0.

220.

11. The secondary battery according to any one of claims 1 to 10, wherein The second carbon-based material satisfies at least one of the following conditions: (1) The gram capacity of the second carbon-based material is 280 mAh / g-340 mAh / g, and can be 300 mAh / g-338 mAh / g; (2) The interlayer spacing of the 002 crystal plane of the second carbon-based material is 0.33622nm-0.33669nm, and can be optionally 0.33626nm-0.33665nm; (3) the volume distribution particle size Dv50 of the second carbon-based material is 10 μm-18 μm, and can be optionally 12 μm-17 μm; (4) The tap density of the second carbon-based material is 0.95 g / cm 3 -1.35g / cm 3 , optional 1.00g / cm 3 -1.30g / cm 3 ; (5) The volume distribution particle size Dv90 of the second carbon-based material is 25.0 μm-45.0 μm, and can be optionally 26.5 μm-42.0 μm; (6) the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is less than or equal to 1.90, and can be selected from 0.90 to 1.85; (7) The adsorption amount of linseed oil by 100g of the second carbon-based material is 38mL-50mL; (8) The second carbon-based material is artificial graphite; (9) I of the second carbon-based material D / I G It is 0.20-0.40, and can be optionally 0.25-0.

35.

12. The secondary battery according to any one of claims 1 to 11, wherein In the negative electrode active material, the content of the first carbon-based material is greater than or equal to 30 wt %, and can be optionally 50 wt %-80 wt %.

13. The secondary battery according to any one of claims 1 to 12, 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 0.5wt%-30wt%.

14. The secondary battery according to any one of claims 1 to 13, 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 1.45 g / cm 3 -1.90g / cm 3 , optional 1.50g / cm 3 -1.85g / 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.

15. An electrical device comprising the secondary battery according to any one of claims 1 to 14.

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