Carbon material, method for manufacturing the same, and secondary battery and electric device containing the same

Abstract

The present application provides a kind of carbon material and its preparation method, and the secondary battery and electric device containing it, the carbon material includes external area and internal area located in the external area, the external area refers to the region formed by the distance of 0.25L from the particle surface of the carbon material to the inside of particle, L refers to the short axis length of the carbon material particle, the total pore area of the external area is recorded as S1, the total pore area of the internal area is recorded as S2, open and S2>S1.The carbon material provided by the present application can make the secondary battery have high initial coulomb efficiency, high energy density and good cycle performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a carbon material and its preparation method, as well as a secondary battery and electrical device containing the same. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. The negative electrode active material is a crucial component of secondary batteries, significantly impacting their performance and cost. Currently, graphite is the primary negative electrode active material, with natural graphite receiving considerable attention due to its relatively low cost. However, natural graphite suffers from numerous defects, including high porosity and poor compatibility with electrolytes, leading to poor cycle performance in secondary batteries. Therefore, improving the performance of natural graphite has become a key research focus. Summary of the Invention

[0003] The purpose of this application is to provide a carbon material and its preparation method, as well as a secondary battery and power device containing the same, which enables the secondary battery to achieve high initial coulombic efficiency, high energy density and good cycle performance.

[0004] The first aspect of this application provides a carbon material, the carbon material including an outer region and an inner region located inside the outer region, the outer region being a region extending 0.25L from the particle surface of the carbon material into the particle interior, where L is the minor axis length of the carbon material particle, the total pore area of ​​the outer region being denoted as S1, the total pore area of ​​the inner region being denoted as S2, and S2 > S1.

[0005] The carbon material provided in this application satisfies S2 > S1. In this case, the carbon material particles may have the following characteristics: a large number of pores and / or large pore size in the internal region, and a small number of pores and / or small pore size in the external region. The large number of pores and / or large pore size in the internal region of the carbon material particles allows for expansion space required for volume changes, thereby reducing the risk of particle breakage and the formation of new interfaces, thus reducing side reactions, decreasing irreversible capacity loss in the secondary battery, and improving the cycle performance of the secondary battery. The small number of pores and / or small pore size in the external region of the carbon material particles allows for a more stable structure and minimizes electrolyte penetration into the internal pore structure, thereby reducing side reactions, decreasing the consumption of active ions by the SEI film formation inside the particles, improving the initial coulombic efficiency of the carbon material, and further improving the cycle performance of the secondary battery.

[0006] Therefore, the carbon material provided in this application can effectively reduce the irreversible capacity loss of secondary batteries, improve the capacity utilization characteristics of secondary batteries, and enable secondary batteries to achieve high initial coulombic efficiency, high energy density, and good cycle performance.

[0007] In any embodiment of this application, 1.5 ≤ S2 / S1 ≤ 500, and optionally, 2.5 ≤ S2 / S1 ≤ 120. When S2 / S1 is also within the above range, the secondary battery can better balance high initial coulombic efficiency, high energy density, and good cycle performance.

[0008] In any embodiment of this application, 0.01 μm 2 ≤S1≤10.0μm 2 Optionally, 0.1μm 2 ≤S1≤4.5μm 2 When the total pore area of ​​the external region of the carbon material is within the above range, on the one hand, the carbon material particles can have a more stable structure, and the electrolyte can be prevented from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by the formation of the SEI film inside the carbon material particles. On the other hand, it will not affect the transport performance of active ions and electrons.

[0009] In any embodiment of this application, 1.8 μm 2 ≤S2≤25.0μm 2 Optionally, 2.1μm 2 ≤S2≤20.0μm 2 When the total pore area of ​​the internal region of a carbon material is within the above-mentioned range, on the one hand, sufficient and stable expansion space can be reserved for changes in the volume of carbon material particles, reducing the risk of carbon material particles breaking and generating new interfaces, reducing the occurrence of side reactions on the surface of new interfaces, and reducing the consumption of active ions by the formation of SEI film on the surface of new interfaces. On the other hand, it can also improve the capacity and first coulombic efficiency of carbon materials.

[0010] In any embodiment of this application, L ≥ 5 μm, and optionally, 6 μm ≤ L ≤ 20 μm.

[0011] In any embodiment of this application, the area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm. 2 The option is less than or equal to 0.10 μm. 2 By controlling the area of ​​the pore structure in the outer region of the carbon material within the aforementioned range, the outer region of the carbon material can have a dense structure, thereby effectively improving the structural stability of the carbon material and minimizing the penetration of electrolyte into the pore structure inside the carbon material particles, thus effectively improving the cycle performance of the secondary battery.

[0012] In any embodiment of this application, the internal region of the carbon material includes one or more particles with an area greater than or equal to 0.15 μm. 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm. 2 -2.0μm 2 The porous structure. By incorporating the aforementioned pore size into the internal region of the carbon material, sufficient and stable expansion space can be reserved for changes in the volume of the carbon material particles, reducing the risk of particle breakage. Furthermore, the compaction density of the carbon material can be increased.

[0013] In any embodiment of this application, the interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1≥d2, and optionally, d1>d2.

[0014] The larger interlayer spacing in the outer region of carbon materials is more conducive to the rapid insertion and extraction of active ions, thereby further improving the kinetic performance of secondary batteries; the smaller interlayer spacing in the inner region of carbon materials is conducive to improving the specific capacity and compaction density of carbon materials, thereby further improving the energy density of secondary batteries.

[0015] In any embodiment of this application, d1 is 0.33565nm-0.33615nm.

[0016] In any embodiment of this application, d2 is 0.33557nm-0.33595nm.

[0017] In any embodiment of this application, the specific surface area of ​​the carbon material is ≤2.1m². 2 / g, optional 0.7m 2 / g-1.8m 2 / g. The carbon material of this application has a low specific surface area and low surface activity, which can reduce the consumption of active ions during SEI film formation and improve the first coulombic efficiency of the carbon material.

[0018] In any embodiment of this application, the volume distribution particle size Dv50 of the carbon material is 8.0 μm-25.0 μm, and can be optionally 9.0 μm-22.0 μm.

[0019] In any embodiment of this application, the volume distribution particle size Dv90 of the carbon material is 16.0 μm-35.0 μm, and can be optionally 17.0 μm-34.0 μm.

[0020] When the volume distribution particle size Dv50 and / or Dv90 of carbon materials are within the above range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the cycle performance and / or rate performance of secondary batteries.

[0021] In any embodiment of this application, the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.5-1.5, and optionally 0.7-1.3. This is beneficial for increasing the compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0022] In any embodiment of this application, the morphology of the carbon material includes one or more of blocky, spherical, and near-spherical shapes. This is beneficial for increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0023] In any embodiment of this application, the degree of graphitization of the carbon material is 91.5%-98%, optionally 92%-98%. When the degree of graphitization of the carbon material is within the above range, it is beneficial for the secondary battery to achieve both high energy density and good cycle performance, storage performance and / or rate performance.

[0024] In any embodiment of this application, the powder resistivity of the carbon material at 8 MPa pressure is 0.009 Ω·cm to 0.052 Ω·cm, optionally 0.01 Ω·cm to 0.04 Ω·cm. When the powder resistivity of the carbon material is within the above range, it is beneficial to improve electron transport performance, thereby further improving the cycle performance and rate performance of the secondary battery.

[0025] In any embodiment of this application, the tap density of the carbon material is 0.80 g / cm³. 3 -1.50g / cm 3 0.85g / cm³ is an optional value. 3 -1.45g / cm 3 When the tap density of carbon materials is within the above range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery; it is also beneficial to improve the active ion and electron transport performance, and improve the cycle performance and kinetic performance of the secondary battery.

[0026] In any embodiment of this application, the specific capacity of the carbon material is 350 mAh / g-372 mAh / g, optionally 353 mAh / g-371 mAh / g. When the specific capacity of the carbon material is within the above range, the energy density of the secondary battery can be improved.

[0027] The first aspect of this application provides a method for preparing a carbon material, comprising the following steps: Step 1, providing a raw material having a plurality of pore structures; Step 2, mixing the raw material and a filler material uniformly in a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes an outer region and an inner region located inside the outer region, the outer region being a region extending 0.25L from the surface of the carbon material particles into the particle interior, where L is the minor axis length of the carbon material particles, 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.

[0028] In any embodiment of this application, the raw material includes natural graphite, and optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite.

[0029] In any embodiment of this application, the volume distribution particle size Dv50 of the raw material is 8.0 μm-25.0 μm, and can be optionally 9.0 μm-22.0 μm.

[0030] In any embodiment of this application, the pore volume of the raw material is ≥6.0 mm. 3 / g, optional 6mm 3 / g-100mm 3 / g.

[0031] By adjusting the particle size and / or pore volume of the raw materials within the above range, the agglomeration of the raw materials during subsequent preparation can be minimized. This reduces problems such as increased surface defects and increased surface side reaction active sites in carbon material particles due to the need for deagglomeration processes.

[0032] In any embodiment of this application, the softening point temperature of the filler material is 90℃-150℃, optionally 100℃-140℃. When the softening point temperature of the filler material is within the above range, it is beneficial to adjust the pore size and / or number of pores in the outer and inner regions of the carbon material to a suitable range.

[0033] In any embodiment of this application, the volumetric particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected as 2 μm-5 μm. This is beneficial for the filler material to fill into the pore structure of the raw material after being heated and melted, and also helps to improve the dispersion uniformity of the filler material and the raw material.

[0034] In any embodiment of this application, the coking value of the filler material is 15%-40%, optionally 20%-34%. When the coking value of the filler material is within the above range, it is beneficial to adjust the pore size and / or number of pores in the outer and inner regions of the carbon material to a suitable range.

[0035] In any embodiment of this application, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds and resins, and may optionally include one or more of coal tar pitch and petroleum pitch.

[0036] In any embodiment of this application, the mass ratio of the filler material to the raw material is (15-30):100, optionally (18-28):100. This facilitates adjusting the pore size and / or number of pores in the outer and inner regions of the carbon material within a suitable range.

[0037] In any embodiment of this application, the heating process of mixing the raw material and the filler material evenly in a predetermined ratio and then heating them to a first temperature T1 is a staged heating process, which may optionally include a first heating process and a second heating process.

[0038] In any embodiment of this application, the first heating process is to heat to 200℃-250℃ and hold at that temperature for 1h-3h.

[0039] In any embodiment of this application, the second heating process is to heat to the first temperature T1 and hold at that temperature for a first time t1.

[0040] In any embodiment of this application, the temperature is increased to the first temperature T1 at a rate of 1℃ / min-10℃ / min, optionally 1.5℃ / min-8℃ / min.

[0041] In any embodiment of this application, the first temperature T1 is 700℃-1150℃, and can be selected as 850℃-1100℃.

[0042] In any embodiment of this application, the first time t1 is 1h-5h, and can be selected as 2h-4h.

[0043] By adjusting one or more of the heating rate, first temperature, first time, and heating process within the above range, it is beneficial to prepare carbon materials with the desired structure.

[0044] In any embodiment of this application, the second temperature T2 is 1600℃-2620℃, and can be selected as 1800℃-2450℃.

[0045] In any embodiment of this application, the second time t2 is 1.5h-6h, and can be selected as 2h-5h.

[0046] By adjusting one or more of the second temperature and the second time within the above-mentioned range, it is beneficial to adjust the content of disordered carbon in the carbon material within a suitable range, and it is also beneficial to prepare carbon materials with the desired structure and properties.

[0047] A third aspect of this application provides a secondary battery comprising a negative electrode, wherein the negative electrode comprises the carbon material of the first aspect of this application or the carbon material prepared by the method of the second aspect of this application.

[0048] The fourth aspect of this application provides an electrical device that includes the secondary battery of the third aspect of this application.

[0049] The carbon material provided in this application can effectively reduce irreversible capacity loss in secondary batteries, improve the capacity utilization characteristics of secondary batteries, and enable secondary batteries to achieve high initial coulombic efficiency, high energy density, and good cycle performance. The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0051] Figure 1 This is a schematic diagram of a cross-sectional image of a carbon material particle of this application.

[0052] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0053] Figure 3 This is an exploded view of one embodiment of the secondary battery of this application.

[0054] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0055] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0056] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown.

[0057] Figure 7This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0058] Figure 8 This is a scanning electron microscope image of the carbon material prepared in Example 4.

[0059] Figure 9 This is a scanning electron microscope image of the carbon material prepared in Comparative Example 1.

[0060] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 100 Carbon material, 101 External area, 102 Internal area. Detailed Implementation

[0061] The carbon material of this application, its preparation method, and embodiments of secondary batteries and power-consuming devices containing it are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0062] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0065] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0067] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0068] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0069] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0070] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0071] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0072] Based on different manufacturing processes or sources, graphite can be divided into artificial graphite and natural graphite. The preparation of artificial graphite generally requires a high-temperature graphitization process, which is energy-intensive and costly, resulting in a higher overall cost. Natural graphite, derived from nature, has the advantage of relatively low cost. Furthermore, natural graphite also boasts high volumetric strength and high compaction density.

[0073] Natural graphite mainly includes flake graphite, natural spherical graphite, and microcrystalline graphite. Unlike artificial graphite, natural graphite particles have numerous pores and defects both internally and externally. During the initial charging of a secondary battery, the electrolyte reacts extensively with the pores on the particle surface and within the particles, leading to high initial irreversible capacity loss, low initial coulombic efficiency, and poor cycle and storage performance. In particular, flake graphite and natural spherical graphite exhibit high crystallinity and graphitization, with a predominantly layered microstructure. This structure results in significant volume changes during the extraction and insertion of active ions, making the layered structure prone to breakage and particle fragmentation. After particle fragmentation, the exposed fresh surfaces continue to react with the electrolyte, further increasing the irreversible capacity loss of the secondary battery.

[0074] Currently, the properties of natural graphite are mainly improved through particle surface coating treatment and / or particle internal filling treatment.

[0075] Surface coating of natural graphite particles mainly involves mixing natural graphite with a coating agent (such as asphalt, polymer compounds, etc.) and then heat-treating the mixture to coat the surface of the natural graphite particles with an amorphous carbon layer, thus slightly repairing surface defects. However, the inventors of this application discovered during their research that the surface-coated amorphous carbon layer leads to a decrease in the specific capacity and / or compaction density of natural graphite, affecting the energy density of the secondary battery. Furthermore, the surface-coated amorphous carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles, resulting in limited improvement on the initial coulombic efficiency, cycle performance, and / or storage performance of the secondary battery.

[0076] The internal filling treatment of natural graphite particles mainly involves mixing natural graphite with fillers (such as asphalt, polymer compounds, etc.) and filling the pores inside the particles with the filler through methods such as preset pressure, vacuuming, and heating, to obtain natural graphite particles without internal pores. However, the inventors of this application discovered during their research that the large amount of carbon filling inside the particles reduces both the specific capacity and compaction density of the natural graphite, affecting the energy density of the secondary battery. Simultaneously, because all the pores inside the natural graphite particles are filled with carbon, the volume change during the extraction and insertion of active ions is significant, making the particles more prone to breakage. This leads to repeated damage and reconstruction of the SEI film on the particle surface, further increasing the irreversible consumption of active ions, increasing the irreversible capacity loss of the secondary battery, and shortening its lifespan. Existing technologies further coat the surface of the natural graphite particles without internal pores with an amorphous carbon layer, which further reduces the specific capacity and / or compaction density of the natural graphite. Furthermore, the particle surface still has many defects, thus failing to effectively improve the lifespan of the secondary battery.

[0077] Therefore, although the above-mentioned surface coating treatment and / or internal filling treatment of natural graphite can reduce the irreversible capacity loss of secondary batteries and improve the first coulombic efficiency of secondary batteries to a certain extent, its improvement effect on the first coulombic efficiency of secondary batteries is limited, and it will also reduce the energy density of secondary batteries. In addition, the capacity performance characteristics of secondary batteries during long-term use are still poor.

[0078] In view of this, the inventors of this application, after extensive research, have proposed a novel carbon material that combines high specific capacity, high initial coulombic efficiency, and small volume change, and enables secondary batteries to achieve high initial coulombic efficiency, high energy density, and good cycle performance.

[0079] carbon materials

[0080] A first aspect of this application provides a carbon material, the carbon material including an outer region and an inner region located inside the outer region, the outer region being a region extending 0.25L from the particle surface of the carbon material into the particle interior, where L is the minor axis length of the carbon material particle, the total pore area of ​​the outer region being denoted as S1, the total pore area of ​​the inner region being denoted as S2, and S2 > S1.

[0081] The carbon material provided in this application satisfies S2 > S1. In this case, the carbon material particles may have the following characteristics: a large number of pores and / or large pore size in the internal region, and a small number of pores and / or small pore size in the external region. The large number of pores and / or large pore size in the internal region of the carbon material particles allows for expansion space required for volume changes, thereby reducing the risk of particle breakage and the formation of new interfaces, thus reducing side reactions, decreasing irreversible capacity loss in the secondary battery, and improving the cycle performance of the secondary battery. The small number of pores and / or small pore size in the external region of the carbon material particles allows for a more stable structure and minimizes electrolyte penetration into the internal pore structure, thereby reducing side reactions, decreasing the consumption of active ions by the SEI film formation inside the particles, improving the initial coulombic efficiency of the carbon material, and further improving the cycle performance of the secondary battery.

[0082] Therefore, the carbon material provided in this application can effectively reduce the irreversible capacity loss of secondary batteries, improve the capacity utilization characteristics of secondary batteries, and enable secondary batteries to achieve high initial coulombic efficiency, high energy density, and good cycle performance.

[0083] In some embodiments, 1.5 ≤ S2 / S1 ≤ 500; optionally, 1.8 ≤ S2 / S1 ≤ 250, 2 ≤ S2 / S1 ≤ 200, 2.2 ≤ S2 / S1 ≤ 150, 2.5 ≤ S2 / S1 ≤ 120, 4 ≤ S2 / S1 ≤ 120, 5 ≤ S2 / S1 ≤ 120, and 6 ≤ S2 / S1 ≤ 120. Further research by the inventors revealed that when S2 / S1 is also within the above ranges, the secondary battery can better balance high initial coulombic efficiency, high energy density, and good cycle performance.

[0084] In some embodiments, 0.01 μm 2 ≤S1≤10.0μm 2 Optionally, 0.02μm 2 ≤S1≤8.0μm 2 0.03μm 2 ≤S1≤7.0μm 2 0.04μm 2 ≤S1≤6.0μm 2 0.05μm 2 ≤S1≤5.0μm 2 0.06μm 2 ≤S1≤4.5μm 2 0.07μm 2 ≤S1≤4.5μm 2 0.09μm 2 ≤S1≤4.5μm 2 0.1μm2 ≤S1≤4.5μm 2 0.1μm 2 ≤S1≤4.0μm 2 0.1μm 2 ≤S1≤3.5μm 2 When the total pore area of ​​the external region of the carbon material is within the above range, on the one hand, the carbon material particles can have a more stable structure, and the electrolyte can be prevented from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by the formation of the SEI film inside the carbon material particles. On the other hand, it will not affect the transport performance of active ions and electrons.

[0085] In some embodiments, 1.8 μm 2 ≤S2≤25.0μm 2 Optionally, 2.0μm 2 ≤S2≤22.5μm 2 2.1μm 2 ≤S2≤20.0μm 2 2.2μm 2 ≤S2≤17.5μm 2 3.0μm 2 ≤S2≤15.0μm 2 When the total pore area of ​​the internal region of a carbon material is within the above-mentioned range, on the one hand, sufficient and stable expansion space can be reserved for changes in the volume of carbon material particles, reducing the risk of carbon material particles breaking and generating new interfaces, reducing the occurrence of side reactions on the surface of new interfaces, and reducing the consumption of active ions by the formation of SEI film on the surface of new interfaces. On the other hand, it can also improve the capacity and first coulombic efficiency of carbon materials.

[0086] In this application, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material can be obtained by testing the cross-sectional image of the carbon material.

[0087] In this application, the cross-sectional image of the carbon material includes a cross-sectional image passing through the center of the carbon material particle. The "particle center" refers to the range within a radius of 0.1 μm extending from the geometric center of the particle towards the particle surface.

[0088] In this application, the minor axis length of a particle refers to the minimum value when the line connecting two points on the particle surface passes through the geometric center of the particle.

[0089] Figure 1 This is a schematic diagram of a cross-sectional image of a particle of carbon material 100 according to this application, and the cross-sectional image passes through the center of the particle of carbon material 100. Figure 1As shown, L represents the short axis length of the carbon material 100 particles. The region formed by extending 0.25L from the surface of the carbon material 100 particles into the particle interior is the outer region 101, and the region inside the outer region 101 is the inner region 102.

[0090] The cross-section of the carbon material can be prepared using a cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL, Japan); then, referring to JY / T010-1996, the cross-section of the carbon material can be scanned using a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany); finally, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material can be calculated using image processing software (e.g., AVIZO).

[0091] In some embodiments, L ≥ 5 μm, and optionally, 5 μm ≤ L ≤ 20 μm, 6 μm ≤ L ≤ 20 μm, 8 μm ≤ L ≤ 20 μm, and 8 μm ≤ L ≤ 18 μm.

[0092] In some embodiments, the area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm. 2 The option is less than or equal to 0.10 μm. 2 Further research by the inventors revealed that by controlling the area of ​​the pore structure in the outer region of the carbon material within the aforementioned range, the outer region of the carbon material can possess a dense structure. This effectively improves the structural stability of the carbon material, minimizes the penetration of electrolyte into the pore structure inside the carbon material particles, and thus effectively improves the cycle performance of the secondary battery. Of course, this application does not intend to limit the area of ​​all pore structures in the outer region of the carbon material to less than or equal to 0.15 μm. 2 For example, more than 95%, and optionally more than 99%, of the pore structure area can be controlled to be less than or equal to 0.15 μm. 2 The option is less than or equal to 0.10 μm. 2 .

[0093] In some embodiments, the internal region of the carbon material includes one or more particles with an area greater than or equal to 0.15 μm. 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm. 2 -2.0μm 2 The inventors further discovered in their research that by including the aforementioned pore size in the internal region of the carbon material, sufficient and stable expansion space can be reserved for changes in the volume of the carbon material particles, reducing the risk of particle breakage. Furthermore, the compaction density of the carbon material can also be increased.

[0094] In some embodiments, the interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1≥d2, and optionally, d1>d2.

[0095] The larger interlayer spacing in the outer region of carbon materials is more conducive to the rapid insertion and extraction of active ions, thereby further improving the kinetic performance of secondary batteries; the smaller interlayer spacing in the inner region of carbon materials is conducive to improving the specific capacity and compaction density of carbon materials, thereby further improving the energy density of secondary batteries.

[0096] In some embodiments, d1 is 0.33565nm-0.33615nm.

[0097] In some embodiments, d2 is 0.33557nm-0.33595nm.

[0098] The interlayer spacing in different regions of carbon material particles can be measured using instruments and methods known in the art. For example, a high-resolution transmission electron microscope (HRTEM) can be used. The instrument used can be the Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0099] In some embodiments, the degree of graphitization of the carbon material is 91.5%-98%, optionally 92%-98%, 93%-98%, or 94%-97.5%. When the degree of graphitization of the carbon material is within the above range, it is beneficial for the secondary battery to achieve both high energy density and good cycle performance, storage performance, and / or rate performance.

[0100] The degree of graphitization of carbon materials is a well-known concept in the art and can be tested using instruments and methods known in the field. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be referenced in JISK0131-1996 and JB / T4220-2011 to obtain the average interlayer spacing d of the (002) crystal plane in the carbon material crystal structure. 002 Then, according to the Mering-Maire formula, g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the (002) crystal plane in the crystal structure of carbon materials, expressed in nanometers (nm).

[0101] In some embodiments, the morphology of the carbon material includes one or more of blocky, spherical, and near-spherical shapes. This is beneficial for increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0102] In some embodiments, the carbon material comprises primary particles. Optionally, the proportion of primary particles in the carbon material is ≥50%, for example, it can be 55%-95%, 60%-100%, 65%-90%, 65%-80%, 70%-100%, 75%-90%, 80%-100%, 90%-100%, or 95%-100%. The inclusion of an appropriate proportion of primary particles in the carbon material enables it to have higher structural stability and reduces the occurrence of side reactions; in addition, it can increase the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0103] In some embodiments, the carbon material may consist entirely of primary particles, meaning that the primary particles constitute 100% of the carbon material.

[0104] Primary particles and secondary particles are both well-known terms in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0105] In this application, the proportion of primary particles in the carbon material can be tested as follows: a test sample is randomly selected in the negative electrode film layer, and multiple test areas are randomly selected in the test sample. Images of multiple test areas are obtained using a scanning electron microscope. The proportion of the number of carbon material particles with primary particle morphology in each image is counted to the total number of carbon material particles. The average of multiple statistical results is the proportion of primary particles in the carbon material.

[0106] In some embodiments, the specific surface area of ​​the carbon material is ≤2.1 m². 2 / g, optional 0.7m 2 / g-1.8m 2 / g. The carbon material of this application has a low specific surface area and low surface activity, which can reduce the consumption of active ions during SEI film formation and improve the first coulombic efficiency of the carbon material.

[0107] The specific surface area of ​​carbon materials is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0108] In some embodiments, the volume distribution particle size Dv50 of the carbon material is 8.0 μm-25.0 μm, and optionally 9.0 μm-22.0 μm.

[0109] In some embodiments, the volume distribution particle size Dv90 of the carbon material is 16.0 μm-35.0 μm, and optionally 17.0 μm-34.0 μm.

[0110] When the volume distribution particle size Dv50 and / or Dv90 of carbon materials are within the above range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the cycle performance and / or rate performance of secondary batteries.

[0111] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.5-1.5, optionally 0.7-1.3. When the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is within the above range, it is beneficial to increase the compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0112] The volumetric distribution particle sizes Dv10, Dv50, and Dv90 of carbon materials are well-known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0113] In some embodiments, the powder resistivity of the carbon material at 8 MPa pressure is 0.009 Ω·cm to 0.052 Ω·cm, optionally 0.01 Ω·cm to 0.04 Ω·cm. When the powder resistivity of the carbon material is within the above range, it is beneficial to improve electron transport performance, thereby further improving the cycle performance and rate performance of the secondary battery.

[0114] The resistivity of carbon powder is a well-known concept in the art and can be measured using instruments and methods known in the field. For example, it can be measured using a powder resistivity tester (e.g., Suzhou Jinglü ST2722, Sansi Zongheng UTM7305) employing the four-probe method, referring to GB / T 30835-2014. An exemplary test method is as follows: a certain amount of the sample powder to be tested is weighed and placed in a special mold, and the test pressure is set to obtain the powder resistivity under different pressures. In this application, the test pressure can be set to 8 MPa.

[0115] In some embodiments, the tap density of the carbon material is 0.80 g / cm³. 3 -1.50g / cm 3 0.85g / cm³ is an optional value. 3 -1.45g / cm 3 When the tap density of carbon materials is within the above range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery; it is also beneficial to improve the active ion and electron transport performance, and improve the cycle performance and kinetic performance of the secondary battery.

[0116] The tap density of carbon materials is a well-known concept in the art and can be determined using instruments and methods known in the field. For example, it can be determined using a powder tap density tester, referring to GB / T 5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0117] In some embodiments, the specific capacity of the carbon material is 350 mAh / g-372 mAh / g, optionally 353 mAh / g-371 mAh / g. When the specific capacity of the carbon material is within the above range, the energy density of the secondary battery can be improved.

[0118] The specific capacity of carbon materials is a concept known in the art and can be tested using methods known in the art. An exemplary test method is as follows: A carbon material sample is thoroughly mixed with a binder styrene-butadiene rubber (SBR), a thickener sodium carboxymethyl cellulose (CMC), and a conductive agent carbon black in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry; the negative electrode slurry is uniformly coated onto the surface of a copper foil current collector and dried in an oven for later use; 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; then, a CR2430 coin cell is assembled in an argon-protected glove box using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator. At 25°C, the prepared coin cell was first discharged at a constant current of 0.15 mA to 0.005 V, allowed to stand for 5 min, and then discharged at a constant current of 10 μA to 0.005 V. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.3 mA to 2.0 V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the carbon material sample is the specific capacity of the carbon material.

[0119] Preparation method

[0120] The second aspect of this application provides a method for preparing a carbon material, which can prepare the carbon material of the first aspect of this application.

[0121] The method for preparing the carbon material includes the following steps: Step 1, providing a raw material with multiple pore structures; Step 2, mixing the raw material and a filler material uniformly according to a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes an outer region and an inner region located inside the outer region, the outer region being the region extending 0.25L from the particle surface of the carbon material into the particle interior, where L is the minor axis length of the carbon material particle, 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.

[0122] In some embodiments, the raw material used to prepare the carbon material includes natural graphite. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0123] "Natural spherical graphite" refers to natural graphite with a spherical or near-spherical shape, but not all natural graphite particles are controlled to be ideally spherical. In some embodiments, natural spherical graphite with the desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes processes such as crushing, grading, spheroidizing, and purification.

[0124] In some embodiments, the morphology of the raw material includes one or more of spherical and near-spherical shapes.

[0125] In some embodiments, the volumetric particle size Dv50 of the raw material is 8.0 μm-25.0 μm, optionally 9.0 μm-22.0 μm. When the volumetric particle size of the raw material is within the above range, it is beneficial for subsequent filling processes.

[0126] In some embodiments, the pore volume of the raw material is ≥6.0 mm. 3 / g, optional 6mm 3 / g-100mm 3 / g, 7mm 3 / g-80mm 3 / g, 8mm 3 / g-60mm 3 / g, 8mm 3 / g-40mm 3 / g. When the pore volume of the raw material is within the above range, it is beneficial for subsequent filling processing.

[0127] By adjusting the particle size and / or pore volume of the raw materials within the above range, it is possible to minimize the agglomeration of the raw materials during subsequent preparation processes. This can reduce problems such as increased surface defects and increased surface side reaction active sites in carbon material particles due to the need for deagglomeration processes.

[0128] In some embodiments, the softening point temperature of the filler material is 90℃-150℃. For example, the softening point temperature of the filler material can be a range of 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, or any of the above values. Optionally, the softening point temperature of the filler material is 95℃-145℃, 95℃-140℃, 95℃-135℃, 100℃-145℃, 100℃-140℃, 100℃-135℃, 105℃-145℃, 105℃-140℃, 105℃-135℃, 110℃-145℃, 110℃-140℃, or 110℃-135℃.

[0129] During their research, the inventors discovered that when the softening point temperature of the filling material is within the aforementioned range, it is beneficial to adjust the pore size and / or number of pores in the outer and inner regions of the carbon material to a suitable range. It can effectively avoid the following situations: When the softening point temperature of the filler material is too high, the filler material is not easy to flow and fill into the pore structure of the raw material after being heated and melted. Therefore, it cannot effectively modify the internal defects of the particles, nor can it effectively prevent the electrolyte from penetrating into the pore structure of the obtained carbon material particles, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery; When the softening point temperature of the filler material is too low, the filler material contains a lot of small molecules. These small molecules are easily volatilized when heated. Therefore, although the filler material is easy to flow and fill into the pore structure of the raw material after being heated and melted, the small molecules in the filler material volatilize during the heat treatment in step 2 and / or step 3. This results in the actual residual carbon in the filling area not being able to effectively fill the pore structure of the raw material, failing to achieve an effective filling effect, or the actual residual carbon in the filling area having a large number of pores. Therefore, it cannot reduce the consumption of active ions by the SEI film formation and reduce the irreversible capacity loss of the secondary battery. At the same time, it will also affect the cycle performance and / or storage performance of the secondary battery.

[0130] In some embodiments, the volumetric particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected as 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, or 3 μm-5 μm. This facilitates the filler material to fill the pore structure of the raw material after being heated and melted, and also helps to improve the dispersion uniformity of the filler material and the raw material.

[0131] In some embodiments, the coking value of the filler material is 15%-40%, optionally 16%-38%, 16%-35%, 18-35%, or 20%-34%. The inventors discovered during their research that when the coking value of the filler material is within the above range, it is beneficial to adjust the pore size and / or number of pores in the outer and inner regions of the carbon material to a suitable range.

[0132] In this application, the coking value of the filler material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined with reference to GB / T 8727-2008.

[0133] In some embodiments, the softening point temperature of the filler material is 100°C-140°C, and the coking value is 20%-34%. This facilitates the adjustment of the pore size and / or number of pores in the outer and inner regions of the carbon material within a suitable range.

[0134] In some embodiments, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds, and resins, and may optionally include one or more of coal tar pitch and petroleum pitch.

[0135] In some embodiments, the mass ratio of the filler material to the raw material is (15-30):100, optionally (18-28):100. This facilitates adjusting the pore size and / or number of pores in the outer and inner regions of the carbon material within a suitable range. It can effectively avoid the following situations: When the mass ratio of filler material to raw material is too small, the dispersion uniformity of filler material and raw material may deteriorate. In this case, after the filler material is heated and melted, it is not easy to flow and fill the pore structure of the raw material. As a result, it cannot effectively modify the internal defects of the particles, nor can it effectively prevent the electrolyte from penetrating into the pore structure of the obtained carbon material particles, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery. When the mass ratio of filler material to raw material is too large, it is easy to completely fill the pore structure of the raw material. In this case, the volume change of the obtained carbon material is large, the particles are more easily broken, the consumption of active ions in SEI film formation increases, and the irreversible capacity loss of the secondary battery increases. In addition, when the mass ratio of filler material to raw material is too large, a large amount of filler material will remain on the particle surface. In this case, the particles are more likely to agglomerate, which not only increases the deagglomeration process, but also reduces the specific capacity and compaction density of the obtained carbon material.

[0136] By adjusting parameters such as the type of filler material, softening point, coking value, and amount added to be within the above range, the filler material has low viscosity after being heated and melted, maintaining good fluidity. At the same time, it is not easy to stick to the raw material particles, which can reduce the agglomeration of raw material particles in subsequent preparation processes. This can reduce problems such as increased surface defects and increased surface side reaction active sites of carbon material particles due to the need to add a deagglomeration process.

[0137] In some embodiments, the heating process in step 2, which involves uniformly mixing the raw material and the filler material in a predetermined ratio and then heating them to a first temperature T1, is a staged heating process, which may optionally include a first heating process and a second heating process.

[0138] In some embodiments, the first heating process involves heating to 200°C-250°C and holding at that temperature for 1-3 hours.

[0139] In some embodiments, the second heating process involves heating to the first temperature T1 and holding at that temperature for a first time t1.

[0140] During the phased heating process, the temperature is first raised to 200℃-250℃. Since the heating temperature is higher than the softening point of the filler material, the filler material melts and softens when heated. Holding the temperature for 1-3 hours allows it to flow and fill the pore structure of the raw material. Then, the temperature is raised to the first temperature T1. At this time, the melted and softened filler material undergoes a carbonization reaction, which enables the pore structure occupied by the filler material to be effectively filled.

[0141] In some embodiments, in step 2, the first temperature T1 is 700℃-1150℃. For example, the first temperature T1 can be a range consisting of 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, or any value above. Optionally, the first temperature T1 is 850℃-1100℃.

[0142] During their research, the inventors discovered that when the first temperature is within the aforementioned range, it is beneficial to adjust the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situations: if the first temperature is too low, the filling material may not be completely converted into carbon material, and will continue to decompose into small molecules during the subsequent heat treatment step 3. This results in the filling region having a large number of pores, failing to effectively modify the internal defects of the particles, and also failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery; if the first temperature is too high, the energy consumption during the carbon material preparation process increases.

[0143] In some embodiments, the first time t1 is 1h-5h. For example, the first time t1 can be a range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any of the above values. Optionally, the first time t1 is 2h-4h.

[0144] During their research, the inventors discovered that keeping the initial time within the aforementioned range is beneficial for adjusting the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situations: if the initial time is too short, the filling material may not be completely converted into carbon material, and will continue to decompose into small molecules during the subsequent heat treatment step 3. This results in the filling region having a large number of pores, failing to effectively modify the internal defects of the particles, and also failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery; if the initial time is too long, the energy consumption during the carbon material preparation process increases.

[0145] In some embodiments, in step 2, the temperature is increased to the first temperature T1 at a rate of 1°C / min to 10°C / min. For example, the heating rate can be 1.5°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 of the above values. Optionally, the heating rate can be 1.5°C / min to 8°C / min, 1.5°C / min to 6°C / min, or 1.5°C / min to 5°C / min.

[0146] During their research, the inventors discovered that when the heating rate is within the aforementioned range, it is beneficial to adjust the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situations: If the heating rate is too high, the filler material may carbonize on the surface of the raw material particles, making it difficult for the filler material to flow and fill the pore structure of the raw material after melting. This fails to effectively modify internal particle defects and prevents electrolyte penetration into the pore structure of the obtained carbon material particles, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery. If the heating rate is too low, the filler material easily flows and fills all the pore structures of the raw material after melting, resulting in larger volume changes during the extraction and insertion of active ions. The particles are more prone to breakage, increasing the consumption of active ions during SEI film formation, increasing irreversible capacity loss in the secondary battery, and also affecting the cycle performance, storage performance, and / or rate performance of the secondary battery.

[0147] In some embodiments, the heating rate of the first heating process can be 1℃ / min-10℃ / min, and can be selected as 1.5℃ / min-8℃ / min, 1.5℃ / min-6℃ / min, or 1.5℃ / min-5℃ / min.

[0148] In some embodiments, the heating rate of the second heating process can be 1℃ / min-10℃ / min, or optionally 1.5℃ / min-8℃ / min, 1.5℃ / min-6℃ / min, or 1.5℃ / min-5℃ / min.

[0149] In some embodiments, in step 2, the heat treatment can be carried out in a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor, or a rotary kiln.

[0150] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0151] In step 2, by adjusting one or more of the heating rate, first temperature, first time, and heating process within the above range, it is beneficial to prepare carbon materials with the desired structure.

[0152] In some embodiments, the second temperature T2 is 1600℃-2620℃. For example, the second temperature can be a range of 1600℃, 1700℃, 1800℃, 1900℃, 2000℃, 2100℃, 2200℃, 2300℃, 2400℃, 2500℃, 2600℃, or any of the above values. Optionally, the second temperature T2 is 1800℃-2500℃, 1800℃-2450℃, 2000℃-2450℃, 2050℃-2450℃, or 2100℃-2450℃.

[0153] During their research, the inventors discovered that a second temperature within the aforementioned range is beneficial for the carbon material to have a stable structure, minimizing particle breakage. This effectively avoids the following situations: when the second temperature is too low, the obtained carbon material contains a high amount of disordered carbon, resulting in a high defect content and affecting the initial coulombic efficiency, cycle performance, and storage performance; when the second temperature is too high, the obtained carbon material contains too little disordered carbon, resulting in high crystallinity and graphitization, which is not conducive to the rapid extraction and insertion of active ions. Furthermore, the large volume change of the carbon material during charge and discharge increases the risk of particle breakage, thus affecting the cycle performance of the secondary battery; additionally, when the second temperature is too high, the energy consumption and cost of the carbon material preparation process also increase.

[0154] In some embodiments, the second time t2 is 1.5h-6h. For example, the second time t1 can be a range of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any of the above values. Optionally, the second time t2 is 2h-5h.

[0155] During their research, the inventors discovered that when the second time is within the aforementioned range, it is beneficial for regulating the disorder of carbon materials and for ensuring a stable structure, thus minimizing particle breakage. Furthermore, it effectively avoids the following situations: If the second time is too short, the resulting carbon material contains a high content of disordered carbon, leading to a high defect content and affecting the specific capacity and initial coulombic efficiency; if the second time is too long, the resulting carbon material contains too little disordered carbon, resulting in high crystallinity and graphitization, which is not conducive to the rapid extraction and insertion of active ions. Simultaneously, the large volume change of the carbon material during charge and discharge increases the risk of particle breakage, thus affecting the cycle performance and storage performance of the secondary battery; in addition, when the second time is too long, the energy consumption and cost of the carbon material preparation process increase.

[0156] In some embodiments, in step 3, the heat treatment can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Atchison graphitization furnace, a continuous graphitization furnace, or an internal series graphitization furnace.

[0157] 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.

[0158] By adjusting one or more of the second temperature and the second time within the above-mentioned range, it is beneficial to adjust the content of disordered carbon in the carbon material within a suitable range, and it is also beneficial to prepare carbon materials with the desired structure and properties.

[0159] The carbon material preparation method of this application is simple and safe, requiring no pre-pressurization or vacuum treatment, and eliminating the need for an additional depolymerization step during heat treatment. The carbon material prepared by this application exhibits small volume expansion, high structural stability, and low surface activity, thus achieving a balance between high specific capacity, high initial coulombic efficiency, and small volume change. Furthermore, it enables secondary batteries to achieve high initial coulombic efficiency, high energy density, and good cycle performance.

[0160] The preparation method described in this application is low-cost, highly practical, and suitable for large-scale production.

[0161] Secondary batteries

[0162] The third aspect of this application provides a secondary battery.

[0163] This application does not impose any particular limitation on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions repeatedly insert and extract between the positive and negative electrode, and the electrolyte acts as a conductor for these active ions. This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). Secondary batteries using electrolyte solutions, and some secondary batteries using solid electrolytes, may also include a separator membrane disposed between the positive and negative electrode to provide isolation.

[0164] [Negative electrode plate]

[0165] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0166] In some embodiments, the negative electrode film layer comprises the carbon material of the first aspect of this application or the carbon material prepared by the method described in the first aspect of this application. This enables the secondary battery to achieve high initial coulombic efficiency, high energy density, and good cycle performance.

[0167] In some embodiments, the negative electrode film layer may further comprise other negative electrode active materials besides the carbon materials described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0168] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0169] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0170] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0171] 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0172] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0173] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0174] [Positive electrode plate]

[0175] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0176] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. 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).

[0177] The positive electrode film typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder used for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. As an example, the conductive agent used for the positive electrode film includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0178] The positive electrode active material may be a positive electrode active material known in the art for use in secondary batteries.

[0179] When the secondary battery of this application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0180] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0181] In some embodiments, as an example, the positive electrode active material for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0182] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0183] [Electrolytes]

[0184] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0185] The type of electrolyte salt is not specifically limited and can be selected according to actual needs.

[0186] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0187] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: 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), butyl ester 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics 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.

[0189] [Isolation membrane]

[0190] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0191] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0192] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0193] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0194] In some embodiments, the outer packaging may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging may also be a flexible package, such as a pouch. The material of the flexible package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0195] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0196] In some embodiments, such as Figure 3 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0197] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0198] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0199] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0200] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0201] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0202] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0203] Electrical appliances

[0204] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0205] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0206] Figure 7 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0207] Another example of an electrical device could be a mobile phone, a desktop computer, or a laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0208] Example

[0209] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0210] Example 1

[0211] (1) Preparation of carbon materials

[0212] Step 1: Mechanically crush, classify, spheroidize, and purify 100-mesh flake graphite to obtain natural spherical graphite with a volume distribution particle size Dv50 of 15 μm and a pore volume of 18 mm. 3 / g.

[0213] Step 2: The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 120℃, volume distribution particle size Dv50 of 5μm, coking value of 30%) are mixed in a VC mixer at a mass ratio of 100:20 for 30 min. Then, the mixed material is placed in a roller kiln and heated to 225℃ at a rate of 5℃ / min and held for 1 h (first heating process). Then, the temperature is increased to 900℃ at a rate of 5℃ / min and held for 2 h (second heating process). After the process, the mixture is cooled to room temperature to obtain an intermediate.

[0214] Step 3: Place the obtained intermediate in an Atchison graphitization furnace, heat it to 1900℃ and hold it for 3 hours. After the process, demagnetize and sieve to obtain carbon material.

[0215] (2) Preparation of button cell (half-cell)

[0216] The carbon material prepared above was mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CMC) as a thickener, and carbon black as a conductive agent in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil current collector and dried in an oven for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. A CR2430 coin cell was then assembled in an argon-protected glove box using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator.

[0217] (3) Preparation of secondary batteries (full batteries)

[0218] The carbon material, conductive agent carbon black (Super P), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96:1:1:2 to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet was obtained.

[0219] LiFePO4, conductive carbon black, and polyvinylidene fluoride were mixed in a weight ratio of 96:2.5:1.5, and an appropriate amount of NMP solvent was added. The mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0220] A 12μm thick polypropylene film is used as a separator. It is placed in sequence with the positive and negative electrode sheets prepared above, so that the separator is in the middle of the positive and negative electrode sheets to play a role in isolation. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with the same electrolyte as the button cell prepared above. After vacuum sealing, standing, formation, capacity testing and other processes, a secondary battery is obtained.

[0221] Comparative Example 1

[0222] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0223] 100-mesh flake graphite was mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite with a volume distribution particle size Dv50 of 15 μm and a pore volume of 18 mm. 3 / g, and then used the obtained natural spherical graphite as carbon material to prepare half-cells and full-cells.

[0224] Comparative Example 2

[0225] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0226] 100-mesh flake graphite was mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite with a volume distribution particle size Dv50 of 15 μm and a pore volume of 18 mm. 3 / g. The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 120℃, volume distribution particle size Dv50 of 5μm, coking value of 30%) were mixed in a VC mixer at a mass ratio of 100:20 for 30 min. The mixed material was then graphitized at 3200℃ for 10 h. After the treatment, the mixture was cooled to room temperature to obtain carbon material.

[0227] Comparative Example 3

[0228] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0229] 100-mesh flake graphite was mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite with a volume distribution particle size Dv50 of 15 μm and a pore volume of 18 mm. 3 / g. The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 120℃, volume distribution particle size Dv50 of 5μm, coking value of 30%) were mixed in a VC mixer at a mass ratio of 100:20 for 30 min. The mixed material was then carbonized at 1300℃ for 2 h. After the treatment, it was cooled to room temperature to obtain carbon material.

[0230] Comparative Example 4

[0231] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0232] 100-mesh flake graphite was mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite with a volume distribution particle size Dv50 of 15 μm and a pore volume of 18 mm. 3 / g. The obtained natural spherical graphite and petroleum asphalt (softening point temperature 120℃, volume distribution particle size Dv50 5μm, coking value 30%) were mixed in a VC mixer for 30 min. The mixture was then added to a reactor, which was heated gradually at a rate of 2℃ / min while maintaining uniform stirring. The temperature was raised to 190℃, and the reactor was evacuated to a pressure of -0.1 MPa, then held for 2 h. After this holding period, the reactor was heated to 650℃ and held for 2 h. The reactor was then cooled to approximately 160℃, and petroleum asphalt was slowly added to the reactor at a ratio of 1:1 to the previous addition. The reactor was then heated again to 190℃, and the reactor was evacuated to a pressure of -0.1 MPa, then held for 2 h. After this holding period, the reactor was heated to 650℃ and held for 2 h. Finally, the reactor was cooled by condensation. Finally, the material processed in the above process is heat-treated at 1300℃ for 2 hours. The heat-treated sample is then crushed and sieved to obtain carbon material without internal pores.

[0233] Example 2-28

[0234] The preparation methods for half-cells and full-cells are similar to those in Example 1, except that the preparation process parameters of the carbon material are adjusted, as detailed in Table 1.

[0235]

[0236] Performance testing

[0237] (1) Measurement of total pore area in the external and internal regions of carbon materials

[0238] The sample preparation binder is mixed evenly with carbon material powder and then coated onto copper foil. It is then dried at 60℃ for 30 minutes. The sample is cut into 6mm × 6mm pieces and pasted onto the sample stage of a CP-type argon ion section polisher. The sample is then cut using a plasma beam to obtain the cross-section of the carbon material, with the cross-section passing through the center of the carbon material particles. The testing instrument can be the JEOL IB-09010 CP-type argon ion section polisher from Japan.

[0239] The cross-section of the carbon material was scanned using a scanning electron microscope. The testing procedure can be referenced in JY / T010-1996. The testing instrument can be a ZEISS Sigma 300 scanning electron microscope (Germany).

[0240] The region extending 0.25L from the surface of a carbon particle into its interior is denoted as the outer region, and the region beyond the outer region is denoted as the inner region. L represents the minor axis length of the carbon particle. The total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material are calculated using image processing software, such as AVIZO.

[0241] (2) First coulombic efficiency test of carbon materials

[0242] At 25°C, the prepared coin cell was first discharged at a constant current of 0.15 mA to 0.005 V, allowed to stand for 5 minutes, and then discharged at a constant current of 10 μA to 0.005 V. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.3 mA to 2.0 V, and the first charge capacity of the coin cell was recorded. The initial coulombic efficiency (%) of the carbon material = (first charge capacity of the coin cell / first discharge capacity of the coin cell) × 100%.

[0243] (3) Cyclic performance test of secondary batteries

[0244] At 25°C, the prepared secondary battery was charged at a constant current of 0.5C to the upper cutoff voltage (corresponding to 100% SOC), then charged at a constant voltage to a current of 0.05C. After resting for 5 minutes, the secondary battery was discharged at a constant current of 0.5C to the lower cutoff voltage (corresponding to 0% SOC), and the discharge capacity at this point was recorded as the initial discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the initial discharge capacity, and the number of cycles at this point was recorded.

[0245] Table 2

[0246]

[0247]

[0248] Figure 8 This is a scanning electron microscope image of the carbon material prepared in Example 4. Figure 9 The image shows a scanning electron microscope (SEM) image of the carbon material prepared in Comparative Example 1. As can be seen from the image, Comparative Example 1 uses untreated natural spherical graphite as the carbon material, and its particles have numerous pores. Combined with the test results in Table 2, it can be seen that the battery prepared in this way has low initial coulombic efficiency and short cycle life.

[0249] This application involves mixing natural spherical graphite with fillers such as petroleum asphalt and then heat-treating the mixture. The filler material fills the porous structure of the natural spherical graphite, forming a carbon material with a dense outer region and a partially porous inner region, where the carbon material satisfies S2 > S1. The porous structure of the inner region provides the necessary expansion space for changes in the volume of the carbon material particles, thereby reducing the risk of particle breakage and the formation of new interfaces, thus reducing side reactions and irreversible capacity loss in the battery. The dense structure of the outer region minimizes electrolyte penetration into the porous structure of the carbon material particles, further reducing side reactions. Therefore, the carbon material provided in this application exhibits low volume expansion, high structural stability, and low surface activity, enabling the battery to achieve high specific capacity, high initial coulombic efficiency, and long cycle life.

[0250] The carbon materials prepared in Comparative Examples 1-4 do not satisfy the condition S2 > S1, and none of them can enable the battery to achieve high specific capacity, high initial coulombic efficiency, and long cycle life.

[0251] The carbon materials prepared in Comparative Examples 2-3 consist of a carbon layer coating formed on the surface of natural spherical graphite. However, this carbon layer only exists on the surface of natural spherical graphite and fails to achieve an effective filling effect. Furthermore, the carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles, thus resulting in limited improvement on the first coulombic efficiency and cycle performance of the battery.

[0252] In Comparative Example 4, when preparing carbon materials, the filler material was filled into all the pores inside the natural spherical graphite particles by vacuuming. This resulted in a large volume change of the carbon material during the extraction and insertion of active ions, making the particles more prone to breakage, and thus limiting the improvement of the battery's cycle performance.

[0253] The specific surface area, volume distribution, particle size, particle size distribution, degree of graphitization, powder resistivity, tap density, and other parameters of the carbon materials prepared in Examples 1-28 are all within the range described in this application specification.

[0254] Based on the test results of Examples 1-28, it can be seen that when the carbon material further satisfies 1.5≤S2 / S1≤500, and optionally 2.5≤S2 / S1≤120, the initial coulombic efficiency and / or cycle performance of the battery can be further improved.

[0255] Based on the test results of Examples 4 and 25-28, it can be seen that when the raw materials have different volume distribution particle sizes Dv50 and / or pore volumes, carbon materials with excellent electrochemical performance can be obtained by the preparation method of this application.

[0256] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A carbon material, wherein, The carbon material includes an outer region and an inner region located inside the outer region. The outer region refers to the area formed by extending 0.25 L from the surface of the carbon material particles into the particle interior, where L refers to the minor axis length of the carbon material particles. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1.

2. The carbon material according to claim 1, wherein, 1.5 ≤ S2 / S1 ≤ 500.

3. The carbon material according to claim 2, wherein, 2.5 ≤ S2 / S1 ≤ 120.

4. The carbon material according to any one of claims 1-3, wherein, 0.01μm² ≤ S1 ≤ 10.0μm²; and / or, 1.8μm² ≤ S2 ≤ 25.0μm².

5. The carbon material according to claim 4, wherein, 0.1μm² ≤ S1 ≤ 4.5μm²; and / or, 2.1μm² ≤ S2 ≤ 20.0μm².

6. The carbon material according to any one of claims 1-5, wherein, L ≥ 5μm.

7. The carbon material according to claim 6, wherein, 6μm ≤ L ≤ 20μm.

8. The carbon material according to any one of claims 1-7, wherein, The area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm².

9. The carbon material according to claim 8, wherein, The area of ​​the pore structure in the outer region of the carbon material is less than or equal to 0.10 μm².

10. The carbon material according to any one of claims 1-9, wherein, The internal region of the carbon material includes one or more pore structures with an area greater than or equal to 0.15 μm².

11. The carbon material according to claim 10, wherein, The internal region of the carbon material includes one or more pore structures with an area of ​​0.15 μm² to 2.0 μm².

12. The carbon material according to any one of claims 1-11, wherein, The interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1 ≥ d2.

13. The carbon material according to claim 12, wherein, d1 > d2.

14. The carbon material according to claim 12 or 13, wherein, d1 is 0.33565nm-0.33615nm; and / or, d2 is 0.33557nm-0.33595nm.

15. The carbon material according to any one of claims 1-14, wherein, The carbon material satisfies at least one of the following: (1) The specific surface area of ​​the carbon material is ≤ 2.1m². 2 / g; (2) The volume distribution particle size Dv50 of the carbon material is 8.0 μm-25.0 μm; (3) The volume distribution particle size Dv90 of the carbon material is 16.0 μm-35.0 μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.5-1.5; (5) The morphology of the carbon material includes one or more of the following: blocky, spherical and quasi-spherical.

16. The carbon material according to claim 15, wherein, The carbon material satisfies at least one of the following: (1) The specific surface area of ​​the carbon material is 0.7 m². 2 / g-1.8m 2 / g; (2) The volume distribution particle size Dv50 of the carbon material is 9.0 μm-22.0 μm; (3) The volume distribution particle size Dv90 of the carbon material is 17.0 μm-34.0 μm; (4) The particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.7-1.

3.

17. The carbon material according to any one of claims 1-16, wherein, The carbon material satisfies at least one of the following: (1) The degree of graphitization of the carbon material is 91.5%-98%; (2) The resistivity of the carbon material powder under 8 MPa pressure is 0.009 Ω·cm - 0.052 Ω·cm; (3) The tap density of the carbon material is 0.80 g / cm³. 3 -1.50g / cm 3 ; (4) The specific capacity of the carbon material is 350mAh / g-372mAh / g.

18. The carbon material according to claim 17, wherein, The carbon material satisfies at least one of the following: (1) The degree of graphitization of the carbon material is 92%-98%; (2) The resistivity of the carbon material powder under 8 MPa pressure is 0.01 Ω·cm - 0.04 Ω·cm; (3) The tap density of the carbon material is 0.85 g / cm³. 3 -1.45g / cm 3 ; (4) The specific capacity of the carbon material is 353mAh / g-371mAh / g.

19. A method for preparing a carbon material, comprising the following steps: Step 1, providing a raw material having a plurality of pore structures; Step 2, mixing the raw material and a filler material uniformly according to a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein... The carbon material includes an outer region and an inner region located inside the outer region. The outer region refers to the area formed by extending 0.25 L from the surface of the carbon material particles into the particle interior, where L refers to the minor axis length of the carbon material particles. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1.

20. The method according to claim 19, wherein, The raw materials satisfy at least one of the following: (1) The raw materials include natural graphite; (2) The volume distribution particle size Dv50 of the raw material is 8.0μm-25.0μm; (3) The pore volume of the raw material is ≥ 6.0 mm. 3 / g.

21. The method according to claim 20, wherein, The natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite.

22. The method according to claim 20, wherein, The volumetric particle size Dv50 of the raw material is 9.0 μm-22.0 μm.

23. The method of claim 20, wherein, The pore volume of the raw material is 6mm. 3 / g-100mm 3 / g.

24. The method according to any one of claims 19-23, wherein, The filler material satisfies at least one of the following: (1) The softening point temperature of the filler material is 90℃-150℃; (2) The coking value of the filler material is 15%-40%; (3) The volume distribution particle size Dv50 of the filling material is less than or equal to 6 μm.

25. The method according to claim 24, wherein, The filler material satisfies at least one of the following: (1) The softening point temperature of the filler material is 100℃-140℃; (2) The coking value of the filler material is 20%-34%; (3) The volume distribution particle size Dv50 of the filling material is 2μm-5μm.

26. The method according to claim 24 or 25, wherein, The filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds, and resins.

27. The method according to claim 26, wherein, The filler material includes one or more of coal tar pitch and petroleum pitch.

28. The method according to any one of claims 19-27, wherein, The mass ratio of the filler material to the raw material is (15-30):

100.

29. The method according to claim 28, wherein, The mass ratio of the filler material to the raw material is (18-28):

100.

30. The method according to any one of claims 19-29, wherein, The heating process of mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1 is a staged heating process.

31. The method according to claim 30, wherein, The heating process, which involves uniformly mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1, includes a first heating process and a second heating process.

32. The method according to claim 31, wherein, The first heating process involves heating to 200℃-250℃ and holding at that temperature for 1-3 hours; and / or, The second heating process involves heating to the first temperature T1 and holding at that temperature for a first time t1.

33. The method according to any one of claims 19-32, wherein, The temperature is increased to the first temperature T1 at a rate of 1℃ / min-10℃ / min.

34. The method according to claim 33, wherein, The temperature is increased to the first temperature T1 at a rate of 1.5℃ / min to 8℃ / min.

35. The method according to any one of claims 19-34, wherein, The first temperature T1 is 700℃-1150℃; and / or, The first time t1 is 1h-5h.

36. The method according to claim 35, wherein, The first temperature T1 is 850℃-1100℃; and / or, The first time t1 is 2h-4h.

37. The method according to any one of claims 19-36, wherein, The second temperature T2 is 1600℃-2620℃; and / or, The second time t2 is 1.5h-6h.

38. The method according to claim 37, wherein, The second temperature T2 is 1800℃-2450℃; and / or, The second time t2 is 2h-5h.

39. A secondary battery, comprising a negative electrode, said negative electrode comprising the carbon material according to any one of claims 1-18 or the carbon material prepared by the method according to any one of claims 19-38.

40. An electrical device comprising the secondary battery of claim 39.

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