Carbon material and preparation method thereof, and secondary battery and electric device containing carbon material

Abstract

The invention provides a carbon material and a preparation method thereof, and a secondary battery and an electric device containing the carbon material, the carbon material comprises an outer region and an inner region located at the inner side of the outer region, the outer region is a region formed by extending 0.25 L from the particle surface of the carbon material to the interior of the particle, and the inner region is a region formed by extending 0.25 L from the particle surface of the carbon material to the interior of the particle. L refers to the short axis length of the carbon material particles, the total pore area of the outer region is recorded as S1, the total pore area of the inner region is recorded as S2, and S2 is larger than S1. According to the carbon material provided by the invention, the secondary battery can give consideration to high initial coulombic efficiency, high energy density and good cycle performance.

Description

Carbon material and preparation method thereof, as well as secondary battery and electric device containing the same Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a carbon material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same. Background Art

[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 stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. The negative electrode active material is an important component of the secondary battery, which affects the performance and cost of the secondary battery. At present, the negative electrode active material mainly includes graphite, and natural graphite has received widespread attention due to its relatively low cost. However, natural graphite has defects such as many pores, many defects, and poor compatibility with the electrolyte, which leads to poor cycle performance of secondary batteries. Therefore, how to improve the performance of natural graphite has become the current research focus.

[0003] Summary of the Invention

[0004] The purpose of the present application is to provide a carbon material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same, which can enable the secondary battery to have high first coulombic efficiency, high energy density and good cycle performance.

[0005] In a first aspect, the present application provides a carbon material, comprising an external region and an internal region located inside the external region, wherein the external region refers to a region extending a distance of 0.25L from the particle surface of the carbon material to the interior of the particle, L refers to the minor axis length of the carbon material particle, the total pore area of ​​the external region is denoted as S1, the total pore area of ​​the internal region is denoted as S2, and S2>S1.

[0006] The carbon material provided in the present application satisfies S2>S1. In this case, the carbon material particles may have the following characteristics: the number of pores in the inner region is large and / or the pore size is large, while the number of pores in the outer region is small and / or the pore size is small. The number of pores in the inner region of the carbon material particles is large and / or the pore size is large, so that the pore structure can reserve the required expansion space for the volume change of the carbon material particles, thereby reducing the risk of carbon material particles breaking and producing new interfaces, thereby reducing the occurrence of side reactions, reducing the irreversible capacity loss of the secondary battery, and improving the cycle performance of the secondary battery; the number of pores in the outer region of the carbon material particles is small and / or the pore size is small, thereby making the carbon material particles have a more stable structure and avoiding the electrolyte from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions, reducing the consumption of active ions by the SEI film formation inside the particles, thereby improving the first coulomb efficiency of the carbon material, and further improving the cycle performance of the secondary battery.

[0007] Therefore, the carbon material provided in this application can effectively reduce the irreversible capacity loss of the secondary battery, improve the capacity utilization characteristics of the secondary battery, and enable the secondary battery to have high first coulombic efficiency, high energy density and good cycle performance.

[0008] In any embodiment of the present application, 1.5≤S2 / S1≤500, optionally, 2.5≤S2 / S1≤120. When S2 / S1 is also within the above range, the secondary battery can better achieve high initial coulombic efficiency, high energy density and good cycle performance.

[0009] In any embodiment of the present application, 0.01 μm 2 ≤S1≤10.0μm 2 , optionally, 0.1 μm 2 ≤S1≤4.5μm 2 When the total pore area of ​​the outer 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 transmission performance of active ions and electrons.

[0010] In any embodiment of the present application, 1.8 μm 2 ≤S2≤25.0μm 2 , optionally, 2.1 μm 2 ≤S2≤20.0μm 2When the total pore area of ​​the internal region of the carbon material is within the above range, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the carbon material particles, reducing the risk of carbon material particles breaking to produce new interfaces, reducing the occurrence of side reactions on the new interface surface, and reducing the consumption of active ions by the formation of the SEI film on the new interface surface. On the other hand, it can also improve the capacity and first coulombic efficiency of the carbon material.

[0011] In any embodiment of the present application, L≥5 μm, optionally, 6 μm≤L≤20 μm.

[0012] In any embodiment of the present application, the area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm 2 , can be selected to be less than or equal to 0.10μm 2 By controlling the area of ​​the pore structure in the outer region of the carbon material within the above range, the outer region of the carbon material can have a dense structure, thereby effectively improving the structural stability of the carbon material and preventing the electrolyte from penetrating into the pore structure inside the carbon material particles as much as possible, thereby effectively improving the cycle performance of the secondary battery.

[0013] In any embodiment of the present application, the inner region of the carbon material includes one or more areas greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 By making the internal area of ​​the carbon material include the pore structure of the above size, on the one hand, sufficient and stable expansion space is reserved for the volume change of the carbon material particles, reducing the risk of carbon material particle breakage, and on the other hand, the compaction density of the carbon material can be increased.

[0014] In any embodiment of the present application, the interlayer spacing of the outer region of the carbon material is recorded as d1, the interlayer spacing of the inner region of the carbon material is recorded as d2, and the carbon material satisfies d1≥d2, optionally, d1>d2.

[0015] The interlayer spacing in the outer region of the carbon material is larger, which is more conducive to the rapid embedding and extraction of active ions, thereby further improving the kinetic performance of the secondary battery; the interlayer spacing in the inner region of the carbon material is smaller, which is conducive to improving the gram capacity and compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0016] In any embodiment of the present application, d1 is 0.33565 nm-0.33615 nm.

[0017] In any embodiment of the present application, d2 is 0.33557 nm-0.33595 nm.

[0018] In any embodiment of the present application, the specific surface area of ​​the carbon material is ≤2.1m 2 / g, optional 0.7m 2 / g-1.8m 2 The carbon material of the present application has a low specific surface area and low surface activity, thereby reducing the consumption of active ions in the formation of the SEI film and improving the first coulombic efficiency of the carbon material.

[0019] In any embodiment of the present 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.

[0020] In any embodiment of the present 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.

[0021] When the volume distribution particle size Dv50 and / or Dv90 of the carbon material is 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 the secondary battery.

[0022] In any embodiment of the present application, the particle size distribution of the carbon material (Dv90-Dv10) / Dv50 is 0.5-1.5, and optionally 0.7-1.3, which is beneficial to improving the compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0023] In any embodiment of the present application, the morphology of the carbon material includes one or more of block, spherical, and quasi-spherical, which is beneficial to improving the compaction density of the negative electrode sheet and thus improving the energy density of the secondary battery.

[0024] In any embodiment of the present 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 have both high energy density and good cycle performance, storage performance and / or rate performance.

[0025] In any embodiment of the present application, the powder resistivity of the carbon material at a pressure of 8 MPa is 0.009 Ω.cm-0.052 Ω.cm, and optionally 0.01 Ω.cm-0.04 Ω.cm. When the powder resistivity of the carbon material is within the above range, it is beneficial to improve the electron transport performance, thereby further improving the cycle performance and rate performance of the secondary battery.

[0026] In any embodiment of the present application, the tap density of the carbon material is 0.80 g / cm 3 -1.50g / cm3 , optional 0.85g / cm 3 -1.45g / cm 3 When the tap density of the carbon material is within the above range, it can increase the compaction density of the negative electrode sheet, thereby increasing 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.

[0027] In any embodiment of the present application, the gram capacity of the carbon material is 350 mAh / g-372 mAh / g, and optionally 353 mAh / g-371 mAh / g. When the gram capacity of the carbon material is within the above range, the energy density of the secondary battery can be improved.

[0028] The second aspect of the present 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, uniformly mixing the raw material and the filler material in a predetermined proportion, and then keeping the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; step 3, keeping the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes an external region and an internal region located inside the external region, the external region refers to a region extending from the particle surface of the carbon material to the interior of the particle by a distance of 0.25L, L refers to the short axis length of the carbon material particle, the total pore area of ​​the external region is denoted as S1, the total pore area of ​​the internal region is denoted as S2, and S2>S1.

[0029] In any embodiment of the present application, the raw material includes natural graphite. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite and microcrystalline graphite.

[0030] In any embodiment of the present 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.

[0031] In any embodiment of the present application, the pore volume of the raw material is ≥6.0mm 3 / g, optional 6mm 3 / g-100mm 3 / g.

[0032] By adjusting the particle size and / or pore volume of the raw materials within the above range, the agglomeration of the raw materials in the subsequent preparation process can be minimized, thereby reducing problems such as increased surface defects of carbon material particles and increased surface side reaction active sites due to the need for a depolymerization process.

[0033] In any embodiment of the present application, the softening point temperature of the filler material is 90° C.-150° C., optionally 100° C.-140° C. When the softening point temperature of the filler material is within the above range, it is beneficial to adjust the pore size and / or pore number in the outer region and the inner region of the carbon material to be within a suitable range.

[0034] In any embodiment of the present application, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be optionally 2 μm-5 μm. This facilitates the filler material to be filled 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.

[0035] In any embodiment of the present 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 pore number in the outer region and the inner region of the carbon material to be within a suitable range.

[0036] In any embodiment of the present application, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and can optionally include one or more of coal tar and petroleum asphalt.

[0037] In any embodiment of the present application, the mass ratio of the filler material to the raw material is (15-30):100, and can be optionally (18-28):100. This facilitates adjusting the pore size and / or pore number in the outer region and the inner region of the carbon material to be within a suitable range.

[0038] In any embodiment of the present application, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 is a staged heating process, which may optionally include a first heating process and a second heating process.

[0039] In any embodiment of the present application, the first temperature raising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 1 hour-3 hours.

[0040] In any embodiment of the present application, the second temperature raising process is to raise the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0041] In any embodiment of the present application, the temperature is increased to the first temperature T1 at a rate of 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min.

[0042] In any embodiment of the present application, the first temperature T1 is 700°C-1150°C, and can be optionally 850°C-1100°C.

[0043] In any embodiment of the present application, the first time t1 is 1 hour to 5 hours, and can be optionally 2 hours to 4 hours.

[0044] By adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above range, it is beneficial to prepare a carbon material with a desired structure.

[0045] In any embodiment of the present application, the second temperature T2 is 1600°C-2620°C, and can be optionally 1800°C-2450°C.

[0046] In any embodiment of the present application, the second time t2 is 1.5 hours to 6 hours, and can be optionally 2 hours to 5 hours.

[0047] By adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the carbon material within a suitable range, and is also beneficial to prepare a carbon material with desired structure and performance.

[0048] A third aspect of the present application provides a secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises the carbon material of the first aspect of the present application or the carbon material prepared by the method of the second aspect of the present application.

[0049] A fourth aspect of the present application provides an electrical device comprising the secondary battery of the third aspect of the present application.

[0050] The carbon materials provided herein 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. The electrical device of the present application includes the secondary battery provided herein, and thus has at least the same advantages as the aforementioned secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0052] FIG1 is a schematic diagram of a cross-sectional image of a particle of the carbon material of the present application.

[0053] FIG. 2 is a schematic diagram of an embodiment of a secondary battery of the present application.

[0054] FIG3 is an exploded schematic diagram of an embodiment of a secondary battery of the present application.

[0055] FIG4 is a schematic diagram of an embodiment of a battery module of the present application.

[0056] FIG5 is a schematic diagram of an embodiment of a battery pack of the present application.

[0057] FIG. 6 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 5 .

[0058] FIG. 7 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.

[0059] FIG8 is a scanning electron microscope image of the carbon material prepared in Example 4.

[0060] FIG9 is a scanning electron microscope image of the carbon material prepared in Comparative Example 1.

[0061] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 100 carbon material, 101 external region, 102 internal region. DETAILED DESCRIPTION

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

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

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

[0065] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

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

[0067] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0068] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0069] Unless otherwise specified, the terms used in this application have the common meanings generally understood by those skilled in the art.

[0070] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in this application.

[0071] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0072] In this application, the terms "plurality" and "multiple" refer to two or more.

[0073] Graphite can be divided into artificial graphite and natural graphite based on its preparation process or source. Artificial graphite generally undergoes a high-temperature graphitization process, which is energy-intensive and costly, resulting in a higher cost. Natural graphite, derived from nature, offers the advantage of being relatively inexpensive. Furthermore, natural graphite has the advantages of high capacity and compaction density.

[0074] Natural graphite mainly includes flake graphite, natural spherical graphite and microcrystalline graphite. Unlike artificial graphite, natural graphite has a large number of pores and defects inside and outside the particles. During the first charging process of a secondary battery, the electrolyte produces many side reactions with the pores on the surface and inside the particles, resulting in a high first irreversible capacity loss of the secondary battery, a low first coulombic efficiency, and poor cycle performance and storage performance. In particular, flake graphite and natural spherical graphite have high crystallinity and high graphitization degree, and their microstructure is mostly layered. This structure causes the volume of natural graphite to change significantly during the extraction and insertion of active ions, which easily leads to the breakage of the graphite layered structure and the breakage of particles. After the particles are broken, the exposed fresh surface will continue to react with the electrolyte, thereby further increasing the irreversible capacity loss of the secondary battery.

[0075] Currently, the properties of natural graphite are mainly improved by surface coating treatment of particles and / or internal filling treatment of particles.

[0076] The particle surface coating treatment mainly involves mixing natural graphite with a coating agent (such as asphalt, polymer compounds, etc.) and then heat-treating it to coat the surface of the natural graphite particles with an amorphous carbon layer, slightly repairing the surface defects of the particles. However, during the research process, the inventors of this application found that the surface-coated amorphous carbon layer can cause the specific capacity and / or compaction density of natural graphite to decrease, affecting the energy density of the secondary battery. At the same time, the surface-coated amorphous carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles, resulting in limited improvement in the initial coulombic efficiency, cycle performance and / or storage performance of the secondary battery.

[0077] The particle internal filling process mainly involves mixing natural graphite with a filler (such as asphalt, a polymer compound, etc.), and filling the filler into the particle internal pores by means of preset pressure, vacuuming, and heating, so as to obtain natural graphite without pores in the particle interior. However, the inventors of the present application have found in the course of research that a large amount of carbon filled in the particle interior causes the gram capacity and compacted density of natural graphite to decrease, affecting the energy density of the secondary battery. Simultaneously, since the pores in the natural graphite particles are all filled with carbon, the volume change of natural graphite produced during the active ion escape and embedding process is large, and the particles are more easily broken, thereby causing the SEI film on the particle surface to be repeatedly destroyed and reconstructed, further increasing the irreversible consumption of active ions, increasing the irreversible capacity loss of the secondary battery, and shortening the service life of the secondary battery. The prior art also continues to coat a layer of amorphous carbon layer on the natural graphite surface without pores in the above-mentioned particles interior, which causes the gram capacity and / or compacted density of natural graphite to further decrease, and at this time, the particle surface defects are still more, thus the service life of the secondary battery can not be effectively improved.

[0078] Therefore, after modifying natural graphite through the above-mentioned particle surface coating treatment and / or particle internal filling treatment, although the irreversible capacity loss of the secondary battery can be reduced to a certain extent and the first coulombic efficiency of the secondary battery can be improved, its improvement effect on the first coulombic efficiency of the secondary battery is limited, and the energy density of the secondary battery will also be lost. In addition, the capacity utilization characteristics of the secondary battery during long-term use are still poor.

[0079] In view of this, the inventors of this application have proposed a new type of carbon material after extensive research, which has a higher gram capacity, a higher first coulombic efficiency and a smaller volume change, and can also enable secondary batteries to have high first coulombic efficiency, high energy density and good cycle performance.

[0080] carbon materials

[0081] The first aspect of an embodiment of the present application provides a carbon material, which includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending from the particle surface of the carbon material to the interior of the particle by a distance of 0.25L, L refers to the short axis length of the carbon material particle, the total pore area of ​​the external region is recorded as S1, the total pore area of ​​the internal region is recorded as S2, and S2>S1.

[0082] The carbon material provided in the present application satisfies S2>S1. In this case, the carbon material particles may have the following characteristics: the number of pores in the inner region is large and / or the pore size is large, while the number of pores in the outer region is small and / or the pore size is small. The number of pores in the inner region of the carbon material particles is large and / or the pore size is large, so that the pore structure can reserve the required expansion space for the volume change of the carbon material particles, thereby reducing the risk of carbon material particles breaking and producing new interfaces, thereby reducing the occurrence of side reactions, reducing the irreversible capacity loss of the secondary battery, and improving the cycle performance of the secondary battery; the number of pores in the outer region of the carbon material particles is small and / or the pore size is small, thereby making the carbon material particles have a more stable structure and avoiding the electrolyte from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions, reducing the consumption of active ions by the SEI film formation inside the particles, thereby improving the first coulomb efficiency of the carbon material, and further improving the cycle performance of the secondary battery.

[0083] Therefore, the carbon material provided in this application can effectively reduce the irreversible capacity loss of the secondary battery, improve the capacity utilization characteristics of the secondary battery, and enable the secondary battery to have high first coulombic efficiency, high energy density and good cycle performance.

[0084] 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. The inventors found in further research that when S2 / S1 is also within the above range, the secondary battery can better balance high first coulombic efficiency, high energy density, and good cycle performance.

[0085] In some embodiments, 0.01 μm 2 ≤S1≤10.0μm 2 , optionally, 0.02 μm 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 , 0.1μm 2 ≤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 outer 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 transmission performance of active ions and electrons.

[0086] In some embodiments, 1.8 μm 2 ≤S2≤25.0μm 2 , optionally, 2.0 μm 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 the carbon material is within the above range, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the carbon material particles, reducing the risk of carbon material particles breaking to produce new interfaces, reducing the occurrence of side reactions on the new interface surface, and reducing the consumption of active ions by the formation of the SEI film on the new interface surface. On the other hand, it can also improve the capacity and first coulombic efficiency of the carbon material.

[0087] In the present 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 a cross-sectional image of the carbon material.

[0088] In the present application, the cross-sectional image of the carbon material includes a cross-sectional image passing through the center of the carbon material particle. "Particle center" refers to the range within a radius of 0.1 μm extending from the geometric center of the particle to the particle surface.

[0089] In this application, the minor axis length of a particle refers to the minimum value when a line connecting two points on the particle surface passes through the geometric center of the particle.

[0090] FIG1 is a schematic diagram of a cross-sectional image of a particle of carbon material 100 of the present application, and the cross-sectional image passes through the center of the particle of carbon material 100. As shown in FIG1 , L represents the minor axis length of the particle of carbon material 100, and the region extending 0.25L from the particle surface of carbon material 100 toward the interior of the particle is the outer region 101, and the region inside outer region 101 is the inner region 102.

[0091] 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, a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany) is used to scan the cross-section of the carbon material; finally, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material are calculated using image processing software (e.g., AVIZO).

[0092] In some embodiments, L≥5 μm, optionally, 5 μm≤L≤20 μm, 6 μm≤L≤20 μm, 8 μm≤L≤20 μm, 8 μm≤L≤18 μm.

[0093] In some embodiments, the area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm 2 , can be selected to be less than or equal to 0.10μm 2 The inventors also found in further research that by controlling the area of ​​the pore structure in the outer region of the carbon material within the above range, the outer region of the carbon material can have a dense structure, thereby effectively improving the structural stability of the carbon material and preventing the electrolyte from penetrating into the pore structure inside the carbon material particles as much as possible, thereby effectively improving 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 be less than or equal to 0.15 μm 2 For example, the area of ​​the pore structure can be controlled to be less than or equal to 0.15 μm by more than 95%, or more than 99%. 2 , can be selected to be less than or equal to 0.10μm 2 .

[0094] In some embodiments, the inner region of the carbon material includes one or more carbon atoms 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 2The inventors further discovered that by including the aforementioned pore structure in the internal region of the carbon material, sufficient and stable expansion space can be reserved for the volume changes of the carbon material particles, thereby reducing the risk of carbon material particle breakage. Furthermore, the compaction density of the carbon material can be increased.

[0095] In some embodiments, the interlayer distance of the outer region of the carbon material is denoted as d1, and the interlayer distance of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1≥d2, and optionally, d1>d2.

[0096] The interlayer spacing in the outer region of the carbon material is larger, which is more conducive to the rapid embedding and extraction of active ions, thereby further improving the kinetic performance of the secondary battery; the interlayer spacing in the inner region of the carbon material is smaller, which is conducive to improving the gram capacity and compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0097] In some embodiments, d1 is 0.33565 nm-0.33615 nm.

[0098] In some embodiments, d2 is 0.33557 nm - 0.33595 nm.

[0099] The interlayer spacing between different regions of the 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 for testing. The testing instrument can be a Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0100] In some embodiments, the carbon material has a degree of graphitization of 91.5% to 98%, optionally 92% to 98%, 93% to 98%, or 94% to 97.5%. When the degree of graphitization of the carbon material is within the above range, it is beneficial for the secondary battery to have both high energy density and good cycle performance, storage performance, and / or rate performance.

[0101] The degree of graphitization of carbon materials is well known in the art and can be measured using instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average 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) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer distance between (002) planes in the carbon material crystal structure expressed in nanometers (nm).

[0102] In some embodiments, the carbon material has a morphology of one or more of block, spherical, and quasi-spherical, which is beneficial for increasing the compaction density of the negative electrode sheet and thus improving the energy density of the secondary battery.

[0103] In some embodiments, the carbon material includes primary particles. Optionally, the primary particles in the carbon material account for ≥50%, for example, 55%-95%, 60%-100%, 65%-90%, 65%-80%, 70%-100%, 75%-90%, 80%-100%, 90%-100%, or 95%-100%. The carbon material containing an appropriate proportion of primary particles can provide it with higher structural stability and reduce the occurrence of side reactions. In addition, it can also increase the compaction density of the negative electrode sheet, thereby increasing the energy density of the secondary battery.

[0104] In some embodiments, the carbon materials may all be primary particles, that is, the number of the primary particles in the carbon materials accounts for 100%.

[0105] Primary particles and secondary particles are both well-known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0106] In the present application, the number ratio of primary particles in the carbon material can be tested according to the following method: randomly select a test sample in the negative electrode film layer, randomly select multiple test areas in the test sample, use a scanning electron microscope to obtain images of the multiple test areas, and count the ratio of the number of carbon material particles with primary particle morphology in each image to the total number of carbon material particles. The average value of multiple statistical results is the number ratio of primary particles in the carbon material.

[0107] In some embodiments, the specific surface area of ​​the carbon material is ≤2.1 m 2 / g, optional 0.7m 2 / g-1.8m 2 The carbon material of the present application has a low specific surface area and low surface activity, thereby reducing the consumption of active ions in the formation of the SEI film and improving the first coulombic efficiency of the carbon material.

[0108] The specific surface area of ​​a carbon material is well known in the art and can be measured using instruments and methods known in the art. For example, the specific surface area can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0109] In some embodiments, the volume distribution particle size Dv50 of the carbon material is 8.0 μm-25.0 μm, optionally 9.0 μm-22.0 μm.

[0110] In some embodiments, the volume distribution particle size Dv90 of the carbon material is 16.0 μm-35.0 μm, optionally 17.0 μm-34.0 μm.

[0111] When the volume distribution particle size Dv50 and / or Dv90 of the carbon material is 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 the secondary battery.

[0112] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.5-1.5, and 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.

[0113] The volume distribution particle sizes Dv10, Dv50, and Dv90 of carbon materials are well known in the art and represent the particle sizes corresponding to the 10%, 50%, and 90% cumulative volume distribution percentages of the material, respectively. These can be measured using instruments and methods known in the art. For example, they can be conveniently measured using a laser particle size analyzer, as described in GB / T 19077-2016: Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0114] In some embodiments, the powder resistivity of the carbon material at a pressure of 8 MPa is 0.009 Ω.cm-0.052 Ω.cm, and optionally 0.01 Ω.cm-0.04 Ω.cm. When the powder resistivity of the carbon material is within the above range, it is beneficial to improve the electron transport performance, thereby further improving the cycle performance and rate performance of the secondary battery.

[0115] The powder resistivity of carbon materials is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder resistivity tester (e.g., Suzhou Jingge ST2722, Sansi Zongheng UTM7305) using the four-probe method, with reference to GB / T 30835-2014. An exemplary test method is as follows: a certain amount of sample powder to be tested is weighed and placed in a dedicated mold. A test pressure is set to obtain the powder resistivity at different pressures. In this application, the test pressure can be set to 8 MPa.

[0116] In some embodiments, the tap density of the carbon material is 0.80 g / cm 3 -1.50g / cm 3 , optional 0.85g / cm 3 -1.45g / cm 3 When the tap density of the carbon material is within the above range, it can increase the compaction density of the negative electrode sheet, thereby increasing 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.

[0117] The tap density of carbon materials is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. A suitable tester is the Dandong Better BT-301.

[0118] In some embodiments, the gram capacity of the carbon material is 350 mAh / g-372 mAh / g, optionally 353 mAh / g-371 mAh / g. When the gram capacity of the carbon material is within the above range, the energy density of the secondary battery can be increased.

[0119] The gram capacity of carbon materials is a well-known meaning 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 stirred and mixed with a binder of styrene-butadiene rubber (SBR), a thickener of sodium carboxymethyl cellulose (CMC), and a conductive agent of carbon black in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of solvent deionized water to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil 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; a metal lithium sheet is then used as a counter electrode and a polyethylene (PE) film is used as an isolation membrane to assemble a CR2430 button cell in an argon-protected glove box. At 25°C, the prepared button 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-cycle discharge capacity of the button cell was recorded. The cell was then charged at a constant current of 0.3 mA to 2.0 V, and the charge capacity of the button cell was recorded. The ratio of the charge capacity of the button cell to the mass of the carbon material sample is the gram capacity of the carbon material.

[0120] Preparation method

[0121] A second aspect of the embodiments of the present application provides a method for preparing a carbon material, which can prepare the carbon material of the first aspect of the embodiments of the present application.

[0122] The preparation method of the carbon material includes the following steps: step 1, providing a raw material with multiple pore structures; step 2, uniformly mixing the raw material and the filling material in a predetermined proportion, and then keeping the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; step 3, keeping the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes an external region and an internal region located inside the external region, the external region refers to a region extending from the particle surface of the carbon material to the interior of the particle by a distance of 0.25L, L refers to the short axis length of the carbon material particle, the total pore area of ​​the external region is recorded as S1, the total pore area of ​​the internal region is recorded as S2, and S2>S1.

[0123] In some embodiments, the raw material for preparing 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.

[0124] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with a desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes crushing, classification, spheroidization, purification, and other processes.

[0125] In some embodiments, the morphology of the raw material includes one or more of spherical and spheroidal shapes.

[0126] In some embodiments, the volume distribution particle size Dv50 of the raw material is 8.0 μm-25.0 μm, optionally 9.0 μm-22.0 μm. When the volume distribution particle size of the raw material is within the above range, it is beneficial to the subsequent filling process.

[0127] 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 When the pore volume of the raw material is within the above range, it is beneficial for subsequent filling treatment.

[0128] By adjusting the particle size and / or pore volume of the raw materials within the above range, the agglomeration of the raw materials in the subsequent preparation process can be minimized, thereby reducing problems such as increased surface defects of carbon material particles and increased surface side reaction active sites due to the need for a depolymerization process.

[0129] In some embodiments, the softening point temperature of the filler material is 90°C-150°C. For example, the softening point temperature of the filler material can be 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C or any range thereof. Optionally, the softening point temperature of the filler material is 95°C-145°C, 95°C-140°C, 95°C-135°C, 100°C-145°C, 100°C-140°C, 100°C-135°C, 105°C-145°C, 105°C-140°C, 105°C-135°C, 110°C-145°C, 110°C-140°C, 110°C-135°C.

[0130] During the research process, the inventors found that when the softening point temperature of the filling material is within the above range, it is beneficial to adjust the pore size and / or pore number in the outer region and the inner region of the carbon material to be within an appropriate range. And it can effectively avoid the following situations: when the softening point temperature of the filling material is too high, the filling material is not easy to flow and fill into the pore structure of the raw material after being heated and melted, thereby failing to effectively modify the internal defects of the particles, and failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and cycle performance of the secondary battery; when the softening point temperature of the filling material is too low, the filling material contains more small molecules, which are easily volatilized when heated. Therefore, although the filling material is easy to flow and fill into the pore structure of the raw material after being heated and melted, when step 2 and / or step 3 are heat treated, the small molecules in the filling material volatilize, thereby resulting in the actual residual carbon in the filling area failing 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 has more pore structures, thereby failing to reduce the consumption of active ions by SEI film formation and reduce the irreversible capacity loss of the secondary battery, and at the same time affecting the cycle performance and / or storage performance of the secondary battery.

[0131] In some embodiments, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected from 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, and 3 μm-5 μm. This facilitates the filler material to be melted and filled into the pore structure of the raw material after heating, and also helps to improve the uniformity of the dispersion of the filler material and the raw material.

[0132] 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 have found during 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 pore number in the outer region and the inner region of the carbon material to be within a suitable range.

[0133] In this application, the coking value of the filler material has a well-known meaning in the art and can be measured using instruments and methods known in the art, for example, according to GB / T 8727-2008.

[0134] In some embodiments, the filler material has a softening point temperature of 100° C.-140° C. and a coking value of 20%-34%. This facilitates adjusting the pore size and / or pore number in the outer and inner regions of the carbon material within a suitable range.

[0135] In some embodiments, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and may optionally include one or more of coal tar and petroleum asphalt.

[0136] In some embodiments, 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 pore number in the outer region and the inner region of the carbon material to be within a suitable range. It can also effectively avoid the following situations: when the mass ratio of the filling material to the raw material is too small, the dispersion uniformity of the filling material and the raw material may deteriorate. At this time, the filling material is not easy to flow and fill into the pore structure of the raw material after being heated and melted, thereby failing to effectively modify the internal defects of the particles, nor effectively preventing the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the first coulombic efficiency and cycle performance of the secondary battery; when the mass ratio of the filling material to the raw material is too large, it is easy to cause the internal pore structure of the raw material to be completely filled. At this time, the volume of the obtained carbon material changes greatly, the particles are more easily broken, the consumption of active ions for SEI film formation increases, and the irreversible capacity loss of the secondary battery increases; in addition, when the mass ratio of the filling material to the raw material is too large, a large amount of filling material will remain on the surface of the particles. At this time, the particles are more likely to agglomerate, which not only increases the depolymerization process, but also reduces the gram capacity and compaction density of the obtained carbon material.

[0137] By adjusting the type, softening point, coking value, addition amount and other parameters of the filling material within the above range, the viscosity of the filling material is not high after being heated and melted, and good fluidity is maintained. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process, thereby reducing the problems of increased surface defects of carbon material particles and increased surface side reaction active sites due to the need to add a depolymerization process.

[0138] In some embodiments, in step 2, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the temperature to the first temperature T1 is a staged heating process, which may optionally include a first heating process and a second heating process.

[0139] In some embodiments, the first temperature raising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 1 hour-3 hours.

[0140] In some embodiments, the second temperature raising process is to raise the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0141] In the staged heating process, the temperature is first raised to 200°C-250°C. Since the heating temperature is higher than the softening point of the filling material, the filling material is melted and softened by the heat. Keeping it warm for 1h-3h allows it to flow and fill into the pore structure of the raw material; then the temperature is raised to the first temperature T1, at which time the melted and softened filling material undergoes a carbonization reaction, thereby effectively filling the pore structure occupied by the filling material.

[0142] In some embodiments, in step 2, the first temperature T1 is 700° C.-1150° C. For example, the first temperature T1 can be 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., 1100° C., or any range thereof. Optionally, the first temperature T1 is 850° C.-1100° C.

[0143] During their research, the inventors discovered that when the first temperature is within the above-mentioned range, it is beneficial to adjust the pore size and / or pore number in the outer and inner regions of the carbon material to within an appropriate range. This can also effectively avoid the following situations: when the first temperature is too low, the filler material may not be completely converted into carbon material, and will continue to decompose into small molecules during the subsequent heat treatment in step 3. This will result in the filler region having a large porous structure, failing to effectively modify the internal defects of the particles and failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and cycle performance of the secondary battery; when the first temperature is too high, the energy consumption during the carbon material preparation process increases.

[0144] In some embodiments, the first time t1 is 1 hour to 5 hours. For example, the first time t1 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range thereof. Alternatively, the first time t1 is 2 hours to 4 hours.

[0145] During the research process, the inventors found that when the first time is within the above range, it is beneficial to adjust the pore size and / or pore number in the outer region and inner region of the carbon material to an appropriate range. It can also effectively avoid the following situations: when the first 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 in step 3, resulting in a large number of pores in the filling area, failing to effectively modify the internal defects of the particles, and failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and cycle performance of the secondary battery; when the first time is too long, the energy consumption in the carbon material preparation process increases.

[0146] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min-10°C / min. For example, the heating rate can be 1.5°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 thereof. Alternatively, the heating rate is 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, or 1.5°C / min-5°C / min.

[0147] During the research process, the inventors found that when the heating rate is within the above range, it is beneficial to adjust the pore size and / or pore number in the outer region and inner region of the carbon material within an appropriate range. It can also effectively avoid the following situations: when the heating rate is too high, the filler material may be carbonized on the surface of the raw material particles, resulting in the filler material being difficult to flow and fill into the pore structure of the raw material after being heated and melted, thereby failing to effectively modify the internal defects of the particles and failing to effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and cycle performance of the secondary battery; when the heating rate is too low, the filler material is easy to flow and fill into the entire pore structure of the raw material after being heated and melted, resulting in a large volume change of the carbon material during the process of active ion extraction and embedding, and the particles are more easily broken, thereby increasing the consumption of active ions by the SEI film formation, increasing the irreversible capacity loss of the secondary battery, and also affecting the cycle performance, storage performance and / or rate performance of the secondary battery.

[0148] In some embodiments, the heating rate of the first heating process may be 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, or 1.5°C / min-5°C / min.

[0149] In some embodiments, the heating rate of the second heating process may be 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, or 1.5°C / min-5°C / min.

[0150] In some embodiments, in step 2, the heat treatment can be performed in a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor, or a drum furnace.

[0151] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere, which may include one or more of nitrogen, argon, and helium.

[0152] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above range, it is beneficial to prepare a carbon material with a desired structure.

[0153] In some embodiments, the second temperature T2 is 1600° C.-2620° C. For example, the second temperature may be 1600° C., 1700° C., 1800° C., 1900° C., 2000° C., 2100° C., 2200° C., 2300° C., 2400° C., 2500° C., 2600° C., or any range thereof. Alternatively, the second temperature T2 is 1800° C.-2500° C., 1800° C.-2450° C., 2000° C.-2450° C., 2050° C.-2450° C., or 2100° C.-2450° C.

[0154] During their research, the inventors discovered that when the second temperature is within the above range, the carbon material has a stable structure and can minimize particle breakage. This can effectively avoid the following situations: when the second temperature is too low, the resulting carbon material contains a high content of disordered carbon, which results in a high defect content in the carbon material, affecting the initial coulombic efficiency, cycle performance, and storage performance of the carbon material; when the second temperature is too high, the resulting carbon material contains too little disordered carbon, resulting in high crystallinity and graphitization, which is not conducive to the rapid extraction and embedding of active ions. Furthermore, the volume change of the carbon material during charge and discharge is significant, increasing the risk of carbon material particle breakage and thus affecting the cycle performance of the secondary battery; and, when the second temperature is too high, the energy consumption and cost of the carbon material preparation process increase.

[0155] In some embodiments, the second time t2 is 1.5 hours to 6 hours. For example, the second time t1 can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range thereof. Alternatively, the second time t2 is 2 hours to 5 hours.

[0156] During the research process, the inventors found that when the second time is within the above range, it is beneficial to adjust the disorder of the carbon material, and it is also beneficial for the carbon material to have a stable structure and avoid particle breakage as much as possible. It can also effectively avoid the following situations: when the second time is too short, the content of disordered carbon in the obtained carbon material is relatively high, thereby resulting in a high defect content in the carbon material, affecting the gram capacity and initial coulombic efficiency of the carbon material; when the second time is too long, the content of disordered carbon in the obtained carbon material is too low, and the crystallinity and graphitization degree of the carbon material are both very high, which is not conducive to the rapid extraction and embedding of active ions. At the same time, the volume change of the carbon material during the charge and discharge process is also large, thereby increasing the risk of carbon material particle breakage, thereby 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.

[0157] In some embodiments, in step 3, the heat treatment may be performed in a medium frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace, or an inner-string graphitization furnace.

[0158] 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.

[0159] By adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the carbon material within a suitable range, and is also beneficial to prepare a carbon material with desired structure and performance.

[0160] The carbon material preparation method of the present application is simple and highly safe, does not require a preset pressure or vacuum treatment, and does not require an additional depolymerization step during the heat treatment process. The carbon material prepared in the present application has low volume expansion, high structural stability, and low surface activity, thereby achieving a high gram capacity, a high first coulombic efficiency, and a small volume change. It also enables secondary batteries to have high first coulombic efficiency, high energy density, and good cycle performance.

[0161] The preparation method of the present application is low-cost, highly practical, and suitable for large-scale production.

[0162] secondary batteries

[0163] A third aspect of the embodiments of the present application provides a secondary battery.

[0164] The present application has no particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion battery, etc. In general, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte, etc. During the charge and discharge process of the secondary battery, active ions are embedded and released back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present application has no particular restrictions on the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). Secondary batteries using electrolytes and some secondary batteries using solid electrolytes can also include an isolation membrane, which is arranged between the positive electrode plate and the negative electrode plate to play an isolation role.

[0165] [Negative electrode]

[0166] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0167] In some embodiments, the negative electrode film layer comprises the carbon material of the first aspect of the embodiment of the present application or the carbon material prepared by the method described in the second aspect of the embodiment of the present application, thereby enabling the secondary battery to have high initial coulombic efficiency, high energy density, and good cycle performance.

[0168] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned carbon materials. 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 composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0169] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As examples, 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.

[0170] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0171] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0172] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0173] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until uniformly mixed. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0174] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0175] [Positive electrode]

[0176] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0177] The positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0178] The positive electrode film layer generally includes a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0179] The positive electrode active material can adopt the positive electrode active materials for secondary batteries well-known in the art.

[0180] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0181] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0182] In some embodiments, as examples, the positive electrode active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0183] In the present application, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification on the positive electrode active materials.

[0184] [Electrolytes]

[0185] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0186] The type of the electrolyte salt is not particularly limited and can be selected according to actual needs.

[0187] When the secondary battery of the present 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 bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0188] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, for example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). One or more.

[0189] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0190] [Isolation film]

[0191] The present application has no particular limitation on the type of the isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0192] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0193] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.

[0194] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0195] In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0196] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG2 shows a secondary battery 5 with a square structure as an example.

[0197] In some embodiments, as shown in FIG3 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0198] The preparation method of the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped.

[0199] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0200] Figure 4 is a schematic diagram of an exemplary battery module 4. As shown in Figure 4 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0201] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0202] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0203] Figures 5 and 6 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0204] Electrical devices

[0205] The present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0206] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0207] Figure 7 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0208] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0209] Example

[0210] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0211] Example 1

[0212] (1) Preparation of carbon materials

[0213] 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.

[0214] Step 2: The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 120 ° C, volume distribution particle size Dv50 of 5 μm, coking value of 30%) are mixed in a VC mixer at a mass ratio of 100:20 for 30 minutes, and then the mixed material is placed in a roller kiln, heated to 225 ° C at a rate of 5 ° C / min and kept warm for 1 hour (first heating process), and then heated to 900 ° C at a rate of 5 ° C / min and kept warm for 2 hours (second heating process), and then cooled to room temperature to obtain an intermediate.

[0215] Step 3: Place the obtained intermediate in an Acheson graphitization furnace, heat it to 1900°C and keep it warm for 3 hours. After the graphitization is completed, demagnetize and sieve to obtain the carbon material.

[0216] (2) Preparation of button cells (half-cells)

[0217] The carbon material prepared above was thoroughly stirred and mixed with the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC), and the conductive agent carbon black in an appropriate amount of deionized water at a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry was evenly coated on the surface of the negative electrode current collector copper foil and dried in an oven for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and LiPF6 was dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. A metal lithium sheet was then used as the counter electrode and a polyethylene (PE) film as the separator to assemble a CR2430 button cell in an argon-protected glove box.

[0218] (3) Preparation of secondary batteries (full batteries)

[0219] The carbon material prepared above, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed 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, dried, and cold pressed to obtain a negative electrode sheet.

[0220] LiFePO4 was mixed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 96:2.5:1.5. An appropriate amount of NMP solvent was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained.

[0221] A polypropylene film with a thickness of 12 μm is used as an isolation membrane, and is placed in order with the positive electrode sheet and the negative electrode sheet prepared above, so that the isolation membrane is located between the positive electrode sheet and the negative electrode sheet to play an isolation role, and then the electrode assembly is obtained by winding; the electrode assembly is placed in an outer package, dried, and then injected with the same electrolyte as the button battery prepared above, and after vacuum packaging, standing, formation, capacity and other processes, a secondary battery is obtained.

[0222] Comparative Example 1

[0223] The preparation methods of half cells and full cells are similar to those in Example 1, except for the preparation process of the carbon material.

[0224] The 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 half-cells and full cells were prepared using the obtained natural spherical graphite as carbon material.

[0225] Comparative Example 2

[0226] The preparation methods of half cells and full cells are similar to those in Example 1, except for the preparation process of the carbon material.

[0227] The 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 The obtained natural spherical graphite and petroleum pitch (softening point temperature of 120°C, volume distribution particle size Dv50 of 5μm, and coking value of 30%) were mixed in a VC mixer at a mass ratio of 100:20 for 30 minutes. The mixed material was then graphitized at 3200°C for 10 hours and then cooled to room temperature to obtain a carbon material.

[0228] Comparative Example 3

[0229] The preparation methods of half cells and full cells are similar to those in Example 1, except for the preparation process of the carbon material.

[0230] The 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 The obtained natural spherical graphite and petroleum pitch (softening point temperature of 120°C, volume distribution particle size Dv50 of 5 μm, and coking value of 30%) were mixed in a VC mixer at a mass ratio of 100:20 for 30 minutes. The mixed material was then carbonized at 1300°C for 2 hours and then cooled to room temperature to obtain a carbon material.

[0231] Comparative Example 4

[0232] The preparation methods of half cells and full cells are similar to those in Example 1, except for the preparation process of the carbon material.

[0233] The 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 ° C, volume distribution particle size Dv50 of 5 μm, coking value of 30%) were mixed in a VC mixer for 30 minutes. The mixed materials were then put into a reactor, and the reactor was gradually heated at a heating rate of 2 ° C / min. While heating, the reactor was kept in a uniform stirring state, and the temperature was raised to 190 ° C. The reactor was evacuated to a pressure of -0.1 MPa and then kept warm for 2 hours. After the insulation was completed, the reactor was heated to 650 ° C and kept warm for 2 hours. After that, the reactor was cooled to about 160 ° C, and then petroleum asphalt was slowly added to the reactor. The mass ratio of the amount of petroleum asphalt added this time to the previous petroleum asphalt was 1:1. After that, the reactor was heated to 190 ° C again, the reactor was evacuated to a pressure of -0.1 MPa, and then kept warm for 2 hours. After that, the reactor was heated to 650 ° C and kept warm for 2 hours. After that, the temperature was cooled by condensation cooling. Finally, the material processed by the above process was heat-treated at 1300°C for 2 hours, and the heat-treated sample was crushed and sieved to obtain a carbon material with no pores inside.

[0234] Example 2-28

[0235] The preparation methods of half cells and full cells are similar to those in Example 1, except that the preparation process parameters of the carbon material are adjusted. See Table 1 for details.

[0236]

[0237] Performance Testing

[0238] (1) Total pore area test in the outer and inner regions of carbon materials

[0239] Mix the sample preparation binder and carbon material powder evenly, then apply the mixture to copper foil and dry at 60°C for 30 minutes. Cut the sample into 6mm x 6mm pieces and affix them to the sample stage of a CP-type argon ion cross-section polisher. Use a plasma beam to cut the sample to obtain a cross section of the carbon material, with the cross section passing through the center of the carbon material particle. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from JEOL, Japan.

[0240] The cross section of the carbon material was scanned using a scanning electron microscope. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from the German ZEISS company.

[0241] The area extending 0.25L from the particle surface of the carbon material to the interior of the particle is recorded as the outer area, and the area inside the outer area is recorded as the inner area, where L represents the minor axis length of the carbon material particle. The total pore area S1 of the outer area of ​​the carbon material and the total pore area S2 of the inner area of ​​the carbon material are calculated using image processing software. The image processing software can be AVIZO.

[0242] (2) The first coulombic efficiency test of carbon materials

[0243] At 25°C, the prepared button 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-cycle discharge capacity of the button cell was recorded. The cell was then charged at a constant current of 0.3 mA to 2.0 V, and the first-cycle charge capacity was recorded. First-cycle coulombic efficiency (%) of the carbon material = first-cycle charge capacity of the button cell / first-cycle discharge capacity of the button cell × 100%.

[0244] (3) Cycle performance test of secondary batteries

[0245] 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 standing for 5 minutes, the secondary battery was discharged at a constant current of 0.5C to the lower cutoff voltage (corresponding to 0% SOC). The discharge capacity at this point was recorded as the initial discharge capacity. The secondary battery was subjected to a cyclic charge and discharge test according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decayed to 80% of the initial discharge capacity. The number of cycles at this point was recorded.

[0246] Table 2

[0247]

[0248]

[0249] Figure 8 is a scanning electron micrograph of the carbon material prepared in Example 4. Figure 9 is a scanning electron micrograph of the carbon material prepared in Comparative Example 1. As can be seen from the figure, Comparative Example 1 uses untreated natural spherical graphite as the carbon material, and its particles have a large number of pores. Combined with the test results in Table 2, it can be seen that the battery prepared in this manner has a low initial coulombic efficiency and a short cycle life.

[0250] In the present application, after natural spherical graphite is mixed with filling materials such as petroleum asphalt and heat-treated, the filling material can be filled in the pore structure of the natural spherical graphite to form a carbon material in which the outer region is dense and the inner region still retains a small part of the pore structure, and the carbon materials all satisfy S2>S1. The pore structure in the inner region can reserve the required expansion space for the volume change of the carbon material particles, thereby reducing the risk of the carbon material particles breaking to produce new interfaces, thereby reducing the occurrence of side reactions and reducing the irreversible capacity loss of the battery. The outer region has a dense structure, which can avoid the electrolyte from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions. Therefore, the carbon material provided by the present application has small volume expansion, high structural stability and low surface activity, and can enable the battery to take into account high gram capacity, high first coulomb efficiency and long cycle life.

[0251] The carbon materials prepared in Comparative Examples 1-4 do not satisfy S2>S1, and cannot enable the battery to have high gram capacity, high first coulombic efficiency and long cycle life.

[0252] The carbon material prepared in Comparative Examples 2-3 forms a carbon layer coating on the surface of natural spherical graphite, but the carbon layer only exists on the surface of natural spherical graphite, failing to achieve an effective filling effect, and the carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles, which leads to limited improvement in the battery's first coulombic efficiency and cycle performance.

[0253] When preparing the carbon material in Comparative Example 4, the filling material is filled into all the pore structures inside the natural spherical graphite particles by vacuum extraction. As a result, the volume change of the carbon material during the extraction and embedding of active ions is large, and the particles are more easily broken, which in turn leads to limited improvement in the cycle performance of the battery.

[0254] The parameters such as specific surface area, volume distribution particle size, particle size distribution, degree of graphitization, powder resistivity, and tap density of the carbon materials prepared in Examples 1-28 are all within the ranges described in the specification of this application.

[0255] 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 satisfies 2.5≤S2 / S1≤120, the first coulombic efficiency and / or cycle performance of the battery can be further improved.

[0256] 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 properties can be obtained by the preparation method of the present application.

[0257] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A carbon material, wherein The carbon material includes an external region and an internal region located inside the external region. The external region refers to the region extending from the particle surface of the carbon material to the interior of the particle by a distance of 0.25L, and L refers to the short axis length of the carbon material particle. The total pore area of ​​the external region is recorded as S1, and the total pore area of ​​the internal region is recorded as S2, and S2>S1.

2. The carbon material according to claim 1, wherein 1.5≤S2 / S1≤500, optionally, 2.5≤S2 / S1≤120.

3. The carbon material according to claim 1 or 2, wherein 0.01μm 2 ≤S1≤10.0μm 2 , optionally, 0.1 μm 2 ≤S1≤4.5μm 2 and / or, 1.8μm 2 ≤S2≤25.0μm 2 , optionally, 2.1 μm 2 ≤S2≤20.0μm 2 .

4. The carbon material according to any one of claims 1 to 3, wherein L≥5μm, optionally, 6μm≤L≤20μm.

5. The carbon material according to any one of claims 1 to 4, wherein The area of ​​the pore structure in the outer region of the carbon material is less than 0.15 μm 2 , can be selected to be less than or equal to 0.10μm 2 .

6. The carbon material according to any one of claims 1 to 5, wherein The inner region of the carbon material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may optionally include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 pore structure.

7. The carbon material according to any one of claims 1 to 6, wherein The interlayer spacing of the outer region of the carbon material is recorded as d1, and the interlayer spacing of the inner region of the carbon material is recorded as d2, and the carbon material satisfies d1≥d2; Optionally, d1>d2.

8. The carbon material according to claim 7, wherein d1 is 0.33565nm-0.33615nm; and / or, d2 is 0.33557nm-0.33595nm.

9. The carbon material according to any one of claims 1 to 8, wherein The carbon material satisfies at least one of the following: (1) The specific surface area of ​​the carbon material is ≤2.1m 2 / g, optional 0.7m 2 / g-1.8m 2 / g; (2) 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; (3) 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; (4) The particle size distribution of the carbon material (Dv90-Dv10) / Dv50 is 0.5-1.5, and can be optionally 0.7-1.3; (5) The morphology of the carbon material includes one or more of block, spherical and quasi-spherical shapes.

10. The carbon material according to any one of claims 1 to 9, wherein The carbon material satisfies at least one of the following: (1) The graphitization degree of the carbon material is 91.5%-98%, and can be optionally 92%-98%; (2) The powder resistivity of the carbon material under a pressure of 8 MPa is 0.009 Ω.cm-0.052 Ω.cm, and can be optionally 0.01 Ω.cm-0.04 Ω.cm; (3) The tap density of the carbon material is 0.80 g / cm 3 -1.50g / cm 3 , optional 0.85g / cm 3 -1.45g / cm 3 ; (4) The gram capacity of the carbon material is 350 mAh / g-372 mAh / g, and can be optionally 353 mAh / g-371 mAh / g.

11. 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, uniformly mixing the raw material and a filler material in a predetermined ratio, and then maintaining the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; step 3, maintaining the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein: The carbon material includes an external region and an internal region located inside the external region. The external region refers to the region extending from the particle surface of the carbon material to the interior of the particle by a distance of 0.25L, and L refers to the short axis length of the carbon material particle. The total pore area of ​​the external region is recorded as S1, and the total pore area of ​​the internal region is recorded as S2, and S2>S1.

12. The method according to claim 11, wherein The raw materials satisfy at least one of the following: (1) The raw material includes natural graphite, and optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite and microcrystalline graphite; (2) 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; (3) The pore volume of the raw material is ≥6.0mm 3 / g, optional 6mm 3 / g-100mm 3 / g.

13. The method according to claim 11 or 12, wherein: The filling material satisfies at least one of the following: (1) The softening point temperature of the filling material is 90°C-150°C, and can be optionally 100°C-140°C; (2) The coking value of the filler material is 15%-40%, and can be optionally 20%-34%; (3) The volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be optionally 2 μm-5 μm.

14. The method according to claim 13, wherein: The filling material includes one or more of coal tar, petroleum tar, polymer compound and resin, and can be selected to include one or more of coal tar and petroleum tar.

15. The method according to any one of claims 11 to 14, wherein: The mass ratio of the filling material to the raw material is (15-30):100, and can be optionally (18-28):

100.

16. The method according to any one of claims 11 to 15, wherein: The heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 is a staged heating process, which may optionally include a first heating process and a second heating process.

17. The method according to claim 16, wherein The first heating process is heating to 200-250°C and keeping the temperature at this temperature for 1-3 hours; and / or, The second temperature raising process is to raise the temperature to the first temperature T1 and keep the temperature at the first time t1.

18. The method according to any one of claims 11 to 17, wherein: The temperature is raised to the first temperature T1 at a rate of 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min.

19. The method according to any one of claims 11 to 18, wherein: The first temperature T1 is 700° C.-1150° C., optionally 850° C.-1100° C.; and / or, The first time t1 is 1 hour to 5 hours, and can be optionally 2 hours to 4 hours.

20. The method according to any one of claims 11 to 19, wherein: The second temperature T2 is 1600° C.-2620° C., optionally 1800° C.-2450° C.; and / or, The second time t2 is 1.5 hours to 6 hours, and can be optionally 2 hours to 5 hours.

21. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises the carbon material according to any one of claims 1 to 10 or the carbon material prepared by the method according to any one of claims 11 to 20.

22. An electric device comprising the secondary battery according to claim 21.

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