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

Abstract

The application provides a carbon material and a preparation method thereof, and a secondary battery and an electric device containing the carbon material, the carbon material comprising a pore structure, wherein in a thermal gravimetric analysis test under an air atmosphere, a weight loss rate of the carbon material between 35 DEG C and 790 DEG C is less than or equal to 60%. The carbon material provided by the application can make the secondary battery have high initial coulomb efficiency and good storage performance.

Description

Technical Field

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

[0002] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasingly widespread application of rechargeable batteries, significant challenges have been placed on their performance, such as balancing energy density and lifespan. The negative electrode active material is a crucial component of rechargeable batteries, influencing their performance. Currently, graphite is the primary negative electrode active material; however, existing technologies face the problem that high-capacity graphite struggles to achieve high initial coulombic efficiency, and also leads to rapid capacity decay during battery storage. Summary of the Invention

[0003] The purpose of this application is to provide a carbon material and a method for preparing the same, as well as a secondary battery and an electrical device containing the same, which enables the secondary battery to achieve both high initial coulombic efficiency and good storage performance.

[0004] The first aspect of this application provides a carbon material comprising a porous structure, wherein in a thermogravimetric analysis test of the carbon material in an air atmosphere, the carbon material has a weight loss rate of ≤60% between 35°C and 790°C.

[0005] The weight loss rate of carbon materials between 35℃ and 790℃ reflects their chemical stability. The carbon material of this application exhibits a low weight loss rate between 35℃ and 790℃, thus possessing fewer surface and / or bulk defects. This reduces the consumption of active ions during SEI film formation and the consumption of active ions during secondary battery storage. The carbon material provided in this application includes a porous structure, which provides the necessary expansion space for changes in carbon particle volume. This reduces the risk of carbon particle breakage and the formation of new interfaces, thereby reducing side reactions and the consumption of active ions. Therefore, the carbon material provided in this application enables secondary batteries using it to achieve both high initial coulombic efficiency and good storage performance.

[0006] In any embodiment of this application, the carbon material experiences a weight loss rate of 5%-55% between 35°C and 790°C, optionally 15%-45%. In this case, the secondary battery using the carbon material can have a higher initial coulombic efficiency and better storage performance.

[0007] In any embodiment of this application, in the thermogravimetric analysis test of the carbon material in an air atmosphere, the maximum weight loss rate of the carbon material is ≤5.5% / min, optionally 0.5% / min-5% / min. The lower maximum weight loss rate of the carbon material during sintering in an air atmosphere results in fewer surface and / or bulk defects, further reducing the consumption of active ions. Consequently, secondary batteries using the carbon material can achieve higher initial coulombic efficiency and better storage performance.

[0008] In any embodiment of this application, in the thermogravimetric analysis test of the carbon material in an air atmosphere, the temperature corresponding to the maximum weight loss rate of the carbon material is denoted as T. max Then T max The temperature range is 790℃-910℃, with an optional range of 800℃-850℃. Therefore, secondary batteries using the aforementioned carbon material can achieve higher initial coulombic efficiency and better storage performance.

[0009] In any embodiment of this application, in the thermogravimetric analysis test of the carbon material in an air atmosphere, the initial weight loss temperature of the carbon material is denoted as T0, which is 725℃-900℃, and can be selected as 728℃-785℃. This can improve the initial coulombic efficiency and storage performance of the secondary battery.

[0010] In any embodiment of this application, the carbon material includes one or more pores with an area greater than or equal to 0.1 μm. 2 The pore structure may optionally include one or more pores with an area of ​​0.12 μm. 2 -1.5μm 2 The porous structure. When the carbon material includes a porous structure with the above-mentioned pore area, the porous structure can reserve the necessary expansion space for changes in the volume of the carbon material particles, thereby further reducing the risk of carbon material particles breaking and generating new interfaces, which in turn can reduce the occurrence of side reactions, reduce irreversible capacity loss of the secondary battery, and improve the storage performance and cycle performance of the secondary battery.

[0011] In any embodiment of this application, the carbon material includes an outer region and an inner region located inside the outer region. The outer region refers to the region formed by extending 0.25L from the surface of the carbon material particles into the particle interior, where L refers to the minor axis length of the carbon material particles. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1.

[0012] In any embodiment of this application, 1.5 ≤ S2 / S1 ≤ 400, and optionally, 2 ≤ S2 / S1 ≤ 200.

[0013] This can effectively reduce irreversible capacity loss in secondary batteries, improve capacity utilization characteristics, and enable secondary batteries to better balance high initial coulombic efficiency with good storage and cycle performance.

[0014] In any embodiment of this application, 0.01 μm 2 ≤S1≤5.5μm 2 Optionally, 0.06μm 2 ≤S1≤4.5μm 2 When the total pore area of ​​the external region of the carbon material is within the above range, on the one hand, the carbon material particles can have a more stable structure, and the electrolyte can be prevented from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by the formation of the SEI film inside the carbon material particles. On the other hand, it will not affect the transport performance of active ions and electrons.

[0015] In any embodiment of this application, 2.5 μm 2 ≤S2≤25.0μm 2 Optionally, 4.0μm 2 ≤S2≤15.0μm 2 When the total pore area of ​​the internal region of a carbon material is within the above-mentioned range, on the one hand, sufficient and stable expansion space can be reserved for changes in the volume of carbon material particles, reducing the risk of carbon material particles breaking and generating new interfaces, reducing the occurrence of side reactions on the surface of new interfaces, and reducing the consumption of active ions by the formation of SEI film on the surface of new interfaces. On the other hand, it can also improve the capacity and first coulombic efficiency of carbon materials.

[0016] In any embodiment of this application, L ≥ 7 μm, and optionally, 7 μm ≤ L ≤ 18 μm.

[0017] In any embodiment of this application, the area of ​​the pore structure in the outer region of the carbon material is less than 0.2 μm. 2 The option is less than or equal to 0.12μm. 2 By controlling the area of ​​the pore structure in the outer region of the carbon material within the aforementioned range, the outer region of the carbon material particles can have a dense structure, thereby effectively improving the structural stability of the carbon material and minimizing the penetration of electrolyte into the pore structure inside the carbon material particles. This, in turn, can effectively improve the initial coulombic efficiency, storage performance, and cycle performance of the secondary battery.

[0018] In any embodiment of this application, the internal region of the carbon material includes one or more particles with an area greater than or equal to 0.12 μm. 2 The pore structure optionally includes one or more pores with an area of ​​0.12 μm. 2 -2.5μm 2The porous structure. By incorporating the aforementioned pore size into the internal region of the carbon material, sufficient and stable expansion space can be reserved for changes in the volume of the carbon material particles, reducing the risk of particle breakage. On the other hand, the compaction density of the carbon material can be increased, thereby improving the energy density of the secondary battery.

[0019] In any embodiment of this application, the interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1≥d2, and optionally, d1>d2.

[0020] The larger interlayer spacing in the outer region of carbon materials is more conducive to the rapid insertion and extraction of active ions, thereby further improving the kinetic performance of secondary batteries; the smaller interlayer spacing in the inner region of carbon materials is conducive to improving the specific capacity and compaction density of carbon materials, thereby further improving the energy density of secondary batteries.

[0021] In any embodiment of this application, d1 is 0.33565nm-0.33620nm.

[0022] In any embodiment of this application, d2 is 0.33557nm-0.33589nm.

[0023] In any embodiment of this application, the specific surface area of ​​the carbon material is 0.7 m². 2 / g-1.6m 2 / g, optional 0.8m 2 / g-1.4m 2 / g. The carbon material of this application has a low specific surface area and low surface activity, which can reduce the consumption of active ions during SEI film formation and improve the first coulombic efficiency of the carbon material and the storage performance of the secondary battery.

[0024] In any embodiment of this application, the volume distribution particle size Dv50 of the carbon material is 10.0 μm-20.0 μm, and can be optionally 12.0-18.0 μm.

[0025] In any embodiment of this application, the volume distribution particle size Dv10 of the carbon material is 4.0 μm-13.0 μm, and can be optionally 6.0 μm-11.0 μm.

[0026] In any embodiment of this application, the volume distribution particle size Dv90 of the carbon material is 25.0 μm-35.0 μm, and can be optionally 27.0 μm-32.0 μm.

[0027] When the volume distribution particle size of carbon materials is within the above range (Dv10, Dv50, and / or Dv90), it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the cycle performance and kinetic performance of secondary batteries.

[0028] In any embodiment of this application, the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.90-1.10, and optionally 0.95-1.05. This is beneficial for increasing the compaction density of the carbon material, thereby further improving the energy density of the secondary battery.

[0029] In any embodiment of this application, the morphology of the carbon material includes one or more of blocky, spherical, and near-spherical shapes. This is beneficial for increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0030] In any embodiment of this application, the tap density of the carbon material is 1.0 g / cm³. 3 -1.5g / cm 3 The option is 1.1g / cm³. 3 -1.4g / cm 3 When the tap density of carbon materials is within the above range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery; it is also beneficial to improve the active ion and electron transport performance, and improve the cycle performance and kinetic performance of the secondary battery.

[0031] In any embodiment of this application, the specific capacity of the carbon material is 350 mAh / g-372 mAh / g, optionally 353 mAh / g-371 mAh / g. When the specific capacity of the carbon material is within the above range, the energy density of the secondary battery can be improved.

[0032] In any embodiment of this application, the degree of graphitization of the carbon material is 91.5%-98.5%, optionally 92.5%-98.0%. When the degree of graphitization of the carbon material is within the above range, it is beneficial for the secondary battery to achieve both high energy density and good cycle performance, storage performance and / or kinetic performance.

[0033] The second aspect of this application provides a method for preparing a carbon material, comprising the following steps: Step 1, providing a raw material having a plurality of pore structures; Step 2, mixing the raw material and a filler material uniformly in a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes a pore structure, and in a thermogravimetric analysis test of the carbon material in an air atmosphere, the weight loss rate of the carbon material between 35℃ and 790℃ is ≤60%.

[0034] In any embodiment of this application, the raw material includes natural graphite, and optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite.

[0035] In any embodiment of this application, the volume distribution particle size Dv50 of the raw material is 10.0 μm-20.0 μm, and can be selected as 12.0-18.0 μm.

[0036] In any embodiment of this application, the carbon content of the raw material is ≥90.0 wt%, and optionally ≥95.0 wt%.

[0037] In any embodiment of this application, the volume distribution particle size Dv50 of the filling material is less than or equal to 6 μm, and can be selected as 2 μm-5 μm.

[0038] In any embodiment of this application, the softening point temperature of the filler material is 80℃-150℃, and optionally 90℃-140℃.

[0039] In any embodiment of this application, the coking value of the filler material is 15%-40%, optionally 15%-35%.

[0040] In any embodiment of this application, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds and resins, and optionally includes petroleum pitch.

[0041] In any embodiment of this application, the mass ratio of the filler material to the raw material is (10-35):100, and can be optionally (15-32):100.

[0042] By adjusting one or more parameters such as the type of filler material, softening point, coking value, and amount added to be within the above-mentioned range, it is beneficial to adjust the weight loss rate of carbon materials within a suitable range. It is also beneficial to adjust the pore size and / or number of pores in the external and internal regions of carbon materials within a suitable range. In addition, after the filler material is heated and melted, its viscosity is not high, it maintains good fluidity, and it is not easy to stick to the raw material particles. This can reduce the agglomeration of particles in subsequent preparation processes. This can reduce problems such as increased surface defects and increased surface side reaction active sites of carbon material particles due to the need to add deagglomeration process, which can further help to reduce the weight loss rate of carbon materials.

[0043] In any embodiment of this application, the heating process of mixing the raw material and the filler material evenly in a predetermined ratio and then heating them to a first temperature T1 is a staged heating process, which may optionally include a first heating process and a second heating process.

[0044] In any embodiment of this application, the first heating process is to heat to 200℃-250℃ and hold at that temperature for 1h-3h.

[0045] In any embodiment of this application, the second heating process is to heat to the first temperature T1 and hold at that temperature for a first time t1.

[0046] In any embodiment of this application, the heating rate of the first heating process is 1℃ / min-10℃ / min, and can be selected as 1.5℃ / min-8℃ / min.

[0047] In any embodiment of this application, the heating rate of the second heating process is 2℃ / min-10℃ / min, and can be selected as 2.5℃ / min-8℃ / min.

[0048] In any embodiment of this application, the first temperature T1 is 700℃-1200℃, and can be selected as 800℃-1100℃.

[0049] In any embodiment of this application, the first time t1 is 1h-5h, and can be selected as 2h-4h.

[0050] By adjusting one or more of the heating rate, the first temperature, the first time, and the heating process within the above range, it is beneficial to adjust the weight loss rate, the maximum weight loss rate, the initial weight loss temperature T0, and / or the temperature T corresponding to the maximum weight loss rate of the carbon material. max Within a suitable range, it is also beneficial to adjust the pore size and / or number of pores in the outer and inner regions of carbon materials to a suitable range.

[0051] In any embodiment of this application, the second temperature T2 is 2000℃-2700℃, and can be selected as 2100℃-2600℃.

[0052] In any embodiment of this application, the second time t2 is 1.5h-6h, and can be selected as 2h-5h.

[0053] By adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the weight loss rate, maximum weight loss rate, initial weight loss temperature T0, and / or the temperature T corresponding to the maximum weight loss rate of the carbon material. max Within a suitable range.

[0054] A third aspect of this application provides a secondary battery comprising a negative electrode, wherein the negative electrode comprises the carbon material of the first aspect of this application or the carbon material prepared by the method of the second aspect of this application.

[0055] The fourth aspect of this application provides an electrical device that includes the secondary battery of the third aspect of this application.

[0056] The carbon material provided in this application enables secondary batteries using it to achieve both high initial coulombic efficiency and good storage performance. The electrical devices of this application include the secondary battery provided in this application, and therefore possess at least the same advantages as the aforementioned secondary battery. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0058] Figure 1 This is a schematic diagram of a cross-sectional image of a carbon material particle of this application.

[0059] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0060] Figure 3 This is an exploded view of one embodiment of the secondary battery of this application.

[0061] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0062] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0063] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown.

[0064] Figure 7 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0065] Figure 8 These are the thermogravimetric curves and thermogravimetric differential curves of the carbon material prepared in Example 2.

[0066] Figure 9 These are the thermogravimetric curves and thermogravimetric differential curves of the carbon material prepared in Comparative Example 2.

[0067] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 100 Carbon material, 101 External area, 102 Internal area. Detailed Implementation

[0068] The carbon material of this application, its preparation method, and embodiments of secondary batteries and power-consuming devices containing it are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0069] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0071] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0072] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0074] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0076] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0077] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a battery, including but not limited to lithium ions.

[0078] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0079] Based on different manufacturing processes or sources, graphite can be divided into artificial graphite and natural graphite. The preparation of artificial graphite generally requires a high-temperature graphitization process, which is energy-intensive and costly, resulting in a higher overall cost. Natural graphite, derived from nature, has the advantage of relatively low cost. Furthermore, natural graphite also boasts high volumetric strength and high compaction density.

[0080] Natural graphite mainly includes flake graphite, natural spherical graphite, and microcrystalline graphite. Unlike artificial graphite, natural graphite particles have numerous pores and defects both internally and externally. During the first charge of a secondary battery, the electrolyte reacts extensively with the pores on the particle surface and inside the particles, leading to high initial irreversible capacity loss, low initial coulombic efficiency, and poor storage performance. In particular, flake graphite and natural spherical graphite have high crystallinity and graphitization, and their microstructure is predominantly layered. This structure results in significant volume changes during the extraction and insertion of active ions, making the layered structure prone to breakage and particle fragmentation. After particle fragmentation, the exposed fresh surfaces continue to react with the electrolyte, further increasing the irreversible capacity loss of the secondary battery.

[0081] Currently, the properties of natural graphite are mainly improved through particle surface coating treatment and / or particle internal filling treatment.

[0082] Surface coating of natural graphite particles mainly involves mixing natural graphite with a coating agent (such as asphalt, polymer compounds, etc.) and then heat-treating the mixture to coat the surface of the natural graphite particles with an amorphous carbon layer, thus slightly repairing surface defects. However, the inventors of this application discovered during their research that the surface-coated amorphous carbon layer leads to a decrease in the specific capacity and / or compaction density of natural graphite, affecting the energy density of the secondary battery. Furthermore, the surface-coated amorphous carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles, thus resulting in limited improvement on the initial coulombic efficiency and storage performance of the secondary battery.

[0083] The internal filling treatment of natural graphite particles mainly involves mixing natural graphite with fillers (such as asphalt, polymer compounds, etc.) and filling the pores inside the particles with the filler through methods such as preset pressure, vacuuming, and heating, to obtain natural graphite particles without internal pores. However, the inventors of this application discovered during their research that the large amount of carbon, especially soft carbon, filling the particles reduces both the specific capacity and compaction density of natural graphite, affecting the energy density of the secondary battery. Simultaneously, because the pores inside the natural graphite particles are completely filled with carbon, the volume change during the extraction and insertion of active ions is significant, making the particles more prone to breakage. This leads to repeated damage and reconstruction of the SEI film on the particle surface, further increasing the irreversible consumption of active ions, increasing the irreversible capacity loss of the secondary battery, and shortening its lifespan. Existing technologies further coat the surface of the natural graphite particles without internal pores with an amorphous carbon layer, which further reduces the specific capacity and / or compaction density of the natural graphite. Furthermore, the particle surface still has many defects, thus failing to effectively improve the lifespan of the secondary battery.

[0084] Therefore, although the above-mentioned particle surface coating treatment and / or particle internal filling treatment can modify natural graphite, it can reduce the irreversible capacity loss of secondary batteries to a certain extent and improve the first coulombic efficiency of secondary batteries. However, its effect on improving the first coulombic efficiency and storage performance of secondary batteries is limited.

[0085] In view of this, the inventors of this application, after extensive research, have proposed a novel carbon material that enables secondary batteries to achieve both high initial coulombic efficiency and good storage performance.

[0086] carbon materials

[0087] A first aspect of this application provides a carbon material having a porous structure, wherein in a thermogravimetric analysis (TG test) of the carbon material in an air atmosphere, the carbon material has a weight loss rate of ≤60% between 35°C and 790°C.

[0088] During their research, the inventors discovered that the weight loss rate of carbon materials between 35℃ and 790℃ reflects their chemical stability. The carbon material of this application exhibits a low weight loss rate between 35℃ and 790℃, thus possessing fewer surface and / or bulk defects. This reduces the consumption of active ions during SEI film formation and the consumption of active ions during secondary battery storage.

[0089] The carbon materials provided in this application include a porous structure. In this application, "carbon materials including a porous structure" means that the carbon material has a porous structure that can be directly identified from cross-sectional images (e.g., scanning electron microscope images at 1000x magnification), indicating that the porous structure in the raw materials used to prepare the carbon material is not completely filled. Therefore, the porous structure in the carbon material can reserve the necessary expansion space for changes in the volume of the carbon material particles, thereby reducing the risk of carbon material particles breaking and generating new interfaces, thus reducing the occurrence of side reactions and the consumption of active ions.

[0090] Therefore, the carbon material provided in this application enables secondary batteries using it to achieve both high initial coulombic efficiency and good storage performance.

[0091] When the weight loss rate of carbon materials is greater than 60% between 35℃ and 790℃, there are more surface defects and / or bulk defects in the carbon material particles. Consequently, the formation of the SEI film consumes more active ions, and the consumption of active ions during the storage of the secondary battery is also greater. Therefore, it is difficult for the secondary battery to achieve both high initial coulombic efficiency and good storage performance.

[0092] In some embodiments, the weight loss rate of the carbon material between 35°C and 790°C is ≤55%, optionally 5%-55%, 10%-50%, 15%-45%, or 18%-45%. Further research by the inventors revealed that when the weight loss rate of the carbon material between 35°C and 790°C is within the above range, the secondary battery using the carbon material can exhibit higher initial coulombic efficiency and better storage performance.

[0093] In some embodiments, during the thermogravimetric analysis of the carbon material in an air atmosphere, the maximum weight loss rate of the carbon material is ≤5.5% / min, optionally 0.5% / min-5% / min, 0.8% / min-4% / min, 1% / min-4% / min, or 1.2% / min-3.5% / min. A lower maximum weight loss rate during sintering of the carbon material in an air atmosphere indicates that the carbon material may have fewer surface and / or bulk defects, thereby further reducing the consumption of active ions. Consequently, secondary batteries using the carbon material can achieve higher initial coulombic efficiency and better storage performance.

[0094] In some embodiments, in the thermogravimetric analysis test of the carbon material in an air atmosphere, the temperature corresponding to the maximum weight loss rate of the carbon material is denoted as T. max Then T max ≥790℃, optionally 790℃-910℃, 800℃-880℃, 800℃-850℃, or 810℃-850℃. The carbon material of this application exhibits a high temperature T corresponding to the maximum weight loss rate. max This indicates that carbon materials possess good thermal stability and low reactivity. Therefore, the carbon material of this application can have fewer surface and / or bulk defects, thereby reducing the consumption of active ions during SEI film formation and the consumption of active ions during secondary battery storage. Consequently, secondary batteries using the aforementioned carbon material can achieve higher initial coulombic efficiency and better storage performance.

[0095] In some embodiments, in the thermogravimetric analysis test of the carbon material in an air atmosphere, the initial weight loss temperature of the carbon material is denoted as T0, where T0 ≥ 725℃, and can be selected as 725℃-900℃, 726℃-850℃, 727℃-800℃, 728℃-785℃, or 730℃-785℃. The carbon material of this application has a high initial weight loss temperature T0, which indicates good thermal stability and low reactivity. Therefore, the carbon material of this application can have fewer surface defects and / or bulk defects, such as a smaller number of active functional groups on the particle surface. This reduces the consumption of active ions by the active functional groups during film formation and storage, thereby improving the initial coulombic efficiency and storage performance of the secondary battery.

[0096] Thermogravimetric analysis of carbon materials can be performed according to JY / T 014-1996. This application can also be performed under the following conditions: sample weight 10±0.05 mg, purge gas is air at a flow rate of 60 mL / min, heating rate is 5℃ / min, and test temperature range is 35℃-950℃. The testing instrument can be a NETZSCH STA449F3 simultaneous thermal analyzer from NETZSCH Instruments GmbH, Germany.

[0097] In this application, the initial weight loss temperature T0 of the carbon material is the temperature corresponding to the intersection of the tangent line at the horizontal level before the step of the thermogravimetric curve of the carbon material and the tangent line at the maximum weight loss rate.

[0098] In this application, the temperature T corresponding to the maximum weight loss rate of the carbon material is... max is the peak temperature of the thermogravimetric differential curve of the carbon material.

[0099] In some embodiments, the carbon material includes one or more pores with an area greater than or equal to 0.1 μm. 2 The pore structure may optionally include one or more pores with an area of ​​0.12 μm. 2 -1.5μm 2 The inventors further discovered that when carbon materials include a pore structure with the aforementioned pore area, the pore structure can reserve the necessary expansion space for changes in the volume of carbon material particles. This can further reduce the risk of carbon material particles breaking and generating new interfaces, thereby reducing the occurrence of side reactions, reducing irreversible capacity loss in secondary batteries, and improving the storage and cycle performance of secondary batteries.

[0100] In some embodiments, the carbon material includes an outer region and an inner region located inside the outer region. The outer region is defined as the region extending 0.25L from the surface of the carbon material particles into the particle interior, where L is the minor axis length of the carbon material particles. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1.

[0101] Further research by the inventors revealed that when the carbon material further satisfies S2 > S1, the carbon material particles can possess the following characteristics: a large number and / or large pore size in the internal region, and a small number and / or small pore size in the external region. The large number and / or large pore size in the internal region of the carbon material allows for expansion space to accommodate volume changes, thereby reducing the risk of particle breakage and the formation of new interfaces, thus reducing side reactions, decreasing irreversible capacity loss in the secondary battery, and improving storage and cycle performance. The small number and / or small pore size in the external region of the carbon material results in a more stable structure and minimizes electrolyte penetration into the internal pore structure, further reducing side reactions, decreasing the consumption of active ions by the SEI film formation within the particles, and ultimately improving the initial coulombic efficiency of the carbon material, further enhancing the storage and cycle performance of the secondary battery.

[0102] Therefore, when carbon materials further satisfy S2 > S1, the irreversible capacity loss of secondary batteries can be effectively reduced, the capacity utilization characteristics of secondary batteries can be improved, and secondary batteries can better balance high initial coulombic efficiency with good storage performance and cycle performance.

[0103] In some embodiments, 1.5 ≤ S2 / S1 ≤ 400, 1.6 ≤ S2 / S1 ≤ 350, 1.8 ≤ S2 / S1 ≤ 300, 2 ≤ S2 / S1 ≤ 200, 3 ≤ S2 / S1 ≤ 180, and 3.5 ≤ S2 / S1 ≤ 150. Further research by the inventors revealed that when S2 / S1 also falls within the aforementioned ranges, the secondary battery can better balance high initial coulombic efficiency and good storage performance.

[0104] In some embodiments, 0.01 μm 2 ≤S1≤5.5μm 2 Optionally, 0.01μm 2 ≤S1≤5.0μm 2 0.06μm 2 ≤S1≤4.5μm 2 0.08μm 2 ≤S1≤4.0μm 2 0.09μm 2 ≤S1≤3.5μm 2 When the total pore area of ​​the external region of the carbon material is within the above range, on the one hand, the carbon material particles can have a more stable structure, and the electrolyte can be prevented from penetrating into the pore structure inside the carbon material particles as much as possible, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by the formation of the SEI film inside the carbon material particles. On the other hand, it will not affect the transport performance of active ions and electrons.

[0105] In some embodiments, 2.5μm 2 ≤S2≤25.0μm 2 Optionally, 3.0μm 2 ≤S2≤22.5μm 2 4.0μm 2 ≤S2≤15.0μm 2 When the total pore area of ​​the internal region of a carbon material is within the above-mentioned range, on the one hand, sufficient and stable expansion space can be reserved for changes in the volume of carbon material particles, reducing the risk of carbon material particles breaking and generating new interfaces, reducing the occurrence of side reactions on the surface of new interfaces, and reducing the consumption of active ions by the formation of SEI film on the surface of new interfaces. On the other hand, it can also improve the capacity and first coulombic efficiency of carbon materials.

[0106] In this application, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material can be obtained by testing the cross-sectional image of the carbon material.

[0107] In this application, the cross-sectional image of the carbon material includes a cross-sectional image passing through the center of the carbon material particle. The "particle center" refers to the range within a radius of 0.1 μm extending from the geometric center of the particle towards the particle surface.

[0108] In this application, the minor axis length of a particle refers to the minimum value when the line connecting two points on the particle surface passes through the geometric center of the particle.

[0109] Figure 1 This is a schematic diagram of a cross-sectional image of a particle of carbon material 100 according to this application, and the cross-sectional image passes through the center of the particle of carbon material 100. Figure 1 As shown, L represents the short axis length of the carbon material 100 particles. The region formed by extending 0.25L from the surface of the carbon material 100 particles into the particle interior is the outer region 101, and the region inside the outer region 101 is the inner region 102.

[0110] The cross-section of the carbon material can be prepared using a cross-section polisher (e.g., the IB-09010CP argon ion cross-section polisher from JEOL, Japan); then, referring to JY / T010-1996, the cross-section of the carbon material can be scanned using a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany); finally, the total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material can be calculated using image processing software (e.g., AVIZO).

[0111] In some embodiments, L ≥ 7 μm, and optionally, 7 μm ≤ L ≤ 18 μm, 8 μm ≤ L ≤ 18 μm, or 8 μm ≤ L ≤ 16 μm.

[0112] In some embodiments, the area of ​​the pore structure in the outer region of the carbon material is less than 0.2 μm. 2 The option is less than or equal to 0.12μm. 2 Further research by the inventors revealed that by controlling the area of ​​the pore structure in the outer region of the carbon material within the aforementioned range, the outer region of the carbon material particles can possess a dense structure. This effectively improves the structural stability of the carbon material, minimizes electrolyte penetration into the pore structure inside the carbon material particles, and consequently enhances the initial coulombic efficiency, storage performance, and cycle performance of the secondary battery. Of course, this application does not intend to limit the area of ​​all pore structures in the outer region of the carbon material to less than or equal to 0.2 μm. 2 For example, more than 95%, and optionally more than 99%, of the pore structures have an area of ​​less than or equal to 0.2 μm. 2 The option is less than or equal to 0.12μm. 2 .

[0113] In some embodiments, the internal region of the carbon material includes one or more particles with an area greater than or equal to 0.12 μm. 2 The pore structure optionally includes one or more pores with an area of ​​0.12 μm. 2 -2.5μm 2 The inventors further discovered in their research that by including the aforementioned pore size in the internal region of the carbon material, sufficient and stable expansion space can be reserved for changes in the volume of the carbon material particles, reducing the risk of particle breakage. Furthermore, the compaction density of the carbon material can be increased, thereby improving the energy density of the secondary battery.

[0114] In some embodiments, the interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1≥d2, and optionally, d1>d2.

[0115] The larger interlayer spacing in the outer region of carbon materials is more conducive to the rapid insertion and extraction of active ions, thereby further improving the kinetic performance of secondary batteries; the smaller interlayer spacing in the inner region of carbon materials is conducive to improving the specific capacity and compaction density of carbon materials, thereby further improving the energy density of secondary batteries.

[0116] In some embodiments, d1 is 0.33565nm-0.33620nm.

[0117] In some embodiments, d2 is 0.33557nm-0.33589nm.

[0118] The interlayer spacing in different regions of carbon material particles can be measured using instruments and methods known in the art. For example, a high-resolution transmission electron microscope (HRTEM) can be used. The instrument used can be the Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0119] In some embodiments, the morphology of the carbon material includes one or more of blocky, spherical, and near-spherical shapes. This is beneficial for increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0120] In some embodiments, the carbon material comprises primary particles. Optionally, the proportion of primary particles in the carbon material is ≥50%, for example, it can be 55%-95%, 60%-100%, 65%-90%, 65%-80%, 70%-100%, 75%-90%, 80%-100%, 90%-100%, or 95%-100%. The inclusion of an appropriate proportion of primary particles in the carbon material enables it to have higher structural stability and reduces the occurrence of side reactions; in addition, it can increase the compaction density of the negative electrode sheet, thereby improving the energy density of the secondary battery.

[0121] In some embodiments, the carbon material may consist entirely of primary particles, meaning that the primary particles constitute 100% of the carbon material.

[0122] Primary particles and secondary particles are both well-known terms in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0123] In this application, the proportion of primary particles in the carbon material can be tested as follows: a test sample is randomly selected in the negative electrode film layer, and multiple test areas are randomly selected in the test sample. Images of multiple test areas are obtained using a scanning electron microscope. The proportion of the number of carbon material particles with primary particle morphology in each image is counted to the total number of carbon material particles. The average of multiple statistical results is the proportion of primary particles in the carbon material.

[0124] In some embodiments, the degree of graphitization of the carbon material is 91.5%-98.5%, optionally 92.5%-98.0%, 93.5%-98.0%, or 94.0%-98.0%. When the degree of graphitization of the carbon material is within the above range, it is beneficial for the secondary battery to achieve both high energy density and good cycle performance, storage performance, and / or kinetic performance.

[0125] The degree of graphitization of carbon materials is a well-known concept in the art and can be tested using instruments and methods known in the field. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be referenced in JIS K0131-1996 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 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the (002) crystal plane in the crystal structure of carbon materials, expressed in nanometers (nm).

[0126] In some embodiments, the specific surface area of ​​the carbon material is 0.7 m². 2 / g-1.6m 2 / g, optional 0.8m 2 / g-1.4m 2 / g. The carbon material of this application has a low specific surface area and low surface activity, which can reduce the consumption of active ions during SEI film formation and improve the first coulombic efficiency of the carbon material and the storage performance of the secondary battery.

[0127] The specific surface area of ​​carbon materials is a well-known concept in the art and can be determined using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0128] In some embodiments, the volume distribution particle size Dv50 of the carbon material is 10.0 μm-20.0 μm, and optionally 12.0-18.0 μm.

[0129] In some embodiments, the volume distribution particle size Dv10 of the carbon material is 4.0 μm-13.0 μm, and optionally 6.0 μm-11.0 μm.

[0130] In some embodiments, the volume distribution particle size Dv90 of the carbon material is 25.0 μm-35.0 μm, and optionally 27.0 μm-32.0 μm.

[0131] When the volume distribution particle size of carbon materials is within the above range (Dv10, Dv50, and / or Dv90), it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the cycle performance and kinetic performance of secondary batteries.

[0132] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.90-1.10, and optionally 0.95-1.05. 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.

[0133] The volumetric distribution particle sizes Dv10, Dv50, and Dv90 of carbon materials are well-known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0134] In some embodiments, the tap density of the carbon material is 1.0 g / cm³. 3 -1.5g / cm 3 The option is 1.1g / cm³. 3 -1.4g / cm 3 When the tap density of carbon materials is within the above range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery; it is also beneficial to improve the active ion and electron transport performance, and improve the cycle performance and kinetic performance of the secondary battery.

[0135] The tap density of carbon materials is a well-known concept in the art and can be determined using instruments and methods known in the field. For example, it can be determined using a powder tap density tester, referring to GB / T 5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0136] In some embodiments, the specific capacity of the carbon material is 350 mAh / g-372 mAh / g, optionally 353 mAh / g-371 mAh / g. When the specific capacity of the carbon material is within the above range, the energy density of the secondary battery can be improved.

[0137] The specific capacity of carbon materials has a meaning known in the art and can be determined using instruments and methods known in the art. An exemplary test method is as follows: A carbon material sample is thoroughly mixed with a binder styrene-butadiene rubber (SBR), a thickener sodium carboxymethyl cellulose (CMC), and a conductive agent carbon black in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry; the negative electrode slurry is uniformly coated onto the surface of a copper foil current collector and dried in an oven for later use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then, a CR2430 coin cell is assembled in an argon-protected glove box using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator. At 25°C, the prepared coin cell was first discharged at a constant current of 0.15 mA to 0.005 V, allowed to stand for 5 min, and then discharged at a constant current of 10 μA to 0.005 V. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.3 mA to 2.0 V, and the charging capacity of the coin cell was recorded. The ratio of the charging capacity of the coin cell to the mass of the carbon material sample is the specific capacity of the carbon material.

[0138] Preparation method

[0139] The second aspect of this application provides a method for preparing a carbon material, which can prepare the carbon material of the first aspect of this application.

[0140] The preparation method of the carbon material includes the following steps: Step 1, providing a raw material with multiple pore structures; Step 2, mixing the raw material and a filler material uniformly according to a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein the carbon material includes a pore structure, and in the thermogravimetric analysis test of the carbon material in an air atmosphere, the weight loss rate of the carbon material between 35℃ and 790℃ is ≤60%.

[0141] In some embodiments, the raw material used to prepare the carbon material includes natural graphite. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0142] "Natural spherical graphite" refers to natural graphite with a spherical or near-spherical shape, but not all natural graphite particles are controlled to be ideally spherical. In some embodiments, natural spherical graphite with the desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes processes such as crushing, grading, spheroidizing, and purification.

[0143] In some embodiments, the morphology of the raw material includes one or more of spherical and near-spherical shapes.

[0144] In some embodiments, the volumetric particle size Dv50 of the raw material is 10.0 μm-20.0 μm, optionally 12.0-18.0 μm. When the volumetric particle size of the raw material is within the above range, it is beneficial for subsequent filling processes.

[0145] In some embodiments, the carbon content of the raw material is ≥90.0 wt%, optionally ≥95.0 wt%, ≥98.0 wt%, or ≥99.0 wt%. This results in a carbon material with a low heteroatom content, thereby reducing the consumption of active ions by heteroatoms, which helps improve the initial coulombic efficiency and storage performance of the secondary battery.

[0146] In some embodiments, the volumetric particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected as 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, or 3 μm-5 μm. This facilitates the filler material's entry into the pore structure of the raw material and also improves the uniformity of dispersion between the filler material and the raw material.

[0147] In some embodiments, the softening point temperature of the filler material is 80℃-150℃, and can be selected as 90℃-145℃, 95℃-145℃, 100℃-145℃, 105℃-145℃, 90℃-140℃, 95℃-140℃, 100℃-140℃, 105℃-140℃, 105℃-135℃, 110℃-140℃, or 110℃-135℃.

[0148] During their research, the inventors discovered that when the softening point temperature of the filler material is within the aforementioned range, it is beneficial to adjust the weight loss rate of the carbon material within a suitable range. It also helps to adjust the pore size and / or number of pores in the external and internal regions of the carbon material within a suitable range. Furthermore, it effectively avoids the following situation: when the softening point temperature of the filler material is too high, the filler material does not flow easily to fill the pore structure of the raw material, thus failing to effectively modify the internal structural defects of the particles, thereby increasing the weight loss rate of the carbon material and lowering its initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. maxFurthermore, it cannot effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thus affecting the initial coulombic efficiency, storage performance, and / or cycle performance of the secondary battery. When the softening point temperature of the filler material is too low, the filler material contains a large number of small molecules, which are easily volatilized by heat. Therefore, although the filler material can easily flow and fill into the pore structure of the raw material, the small molecules in the filler material volatilize during the heat treatment in steps 2 and / or 3. This results in the actual residual carbon not being able to fill the pore structure of the raw material, failing to achieve an effective filling effect, or the actual residual carbon having a large number of pores, resulting in more defects in the carbon material, increasing the weight loss rate of the carbon material, and also reducing its initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. max It cannot effectively reduce the consumption of active ions during SEI film formation and reduce the irreversible capacity loss of secondary batteries, and it will also affect the cycle performance and / or storage performance of secondary batteries.

[0149] In some embodiments, the coking value of the filler material is 15%-40%, optionally 15%-35%. The inventors discovered during their research that when the coking value of the filler material is within the above range, it is beneficial to adjust the weight loss rate of the carbon material within a suitable range, and also beneficial to adjust the pore size and / or number of pores in the outer and inner regions of the carbon material within a suitable range.

[0150] In this application, the coking value of the filler material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined with reference to GB / T 8727-2008.

[0151] In some embodiments, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds, and resins, and optionally includes petroleum pitch.

[0152] In some embodiments, the mass ratio of the filler material to the raw material is (10-35):100, optionally (15-32):100, or (18-30):100. This is beneficial for adjusting the weight loss rate of the carbon material within a suitable range, and also for adjusting the pore size and / or number of pores in the external and internal regions of the carbon material within a suitable range. It effectively avoids the following situation: when the mass ratio of the filler material to the raw material is too small, the dispersion uniformity of the filler material and the raw material may deteriorate. In this case, the filler material cannot effectively modify the internal structural defects of the particles, thereby increasing the weight loss rate of the carbon material and reducing its initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. maxFurthermore, it cannot effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thus affecting the initial coulombic efficiency and storage performance of the secondary battery. When the mass ratio of filler material to raw material is too high, the pore structure inside the raw material is easily completely filled. At this time, the volume change of the obtained carbon material is large, the particles are more easily broken, the consumption of active ions by SEI film formation increases, and the irreversible capacity loss of the secondary battery increases. When the mass ratio of filler material to raw material is too high, a large amount of filler material will remain on the particle surface. At this time, the particles are more likely to agglomerate. In the subsequent deagglomeration process, the particle structure will be broken, forming new defects and side reaction active sites, reducing the thermal stability of the carbon material, thereby increasing the weight loss rate of the carbon material, and also reducing its initial weight loss temperature T0 and / or the temperature corresponding to the maximum weight loss rate T. max .

[0153] By adjusting one or more parameters such as the type of filler material, softening point, coking value, and amount added to be within the above-mentioned range, it is beneficial to adjust the weight loss rate of carbon materials within a suitable range. It is also beneficial to adjust the pore size and / or number of pores in the external and internal regions of carbon materials within a suitable range. In addition, after the filler material is heated and melted, its viscosity is not high, it maintains good fluidity, and it is not easy to stick to the raw material particles. This can reduce the agglomeration of particles in subsequent preparation processes. This can reduce problems such as increased surface defects and increased surface side reaction active sites of carbon material particles due to the need to add deagglomeration process, which can further help to reduce the weight loss rate of carbon materials.

[0154] In some embodiments, the heating process in step 2, which involves uniformly mixing the raw material and the filler material in a predetermined ratio and then heating them to a first temperature T1, is a staged heating process, which may optionally include a first heating process and a second heating process.

[0155] In some embodiments, the first heating process involves heating to 200℃-250℃ and holding at that temperature for 1-3 hours. During their research, the inventors discovered that holding time within this range is beneficial for adjusting the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situations: when the holding time is too short, the filler material, after melting upon heating, does not easily flow and fill the pore structure of the raw material, thus failing to effectively modify surface and bulk defects of the particles, and also failing to effectively prevent electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency, storage performance, and / or cycle performance of the secondary battery; when the holding time is too long, the filler material easily flows and fills into all the pore structures of the raw material, resulting in a larger volume change in the carbon material during the extraction and insertion of active ions, making the particles more prone to breakage, thereby increasing the consumption of active ions during SEI film formation, increasing the irreversible capacity loss of the secondary battery, and also affecting the cycle performance, storage performance, and / or kinetic performance of the secondary battery.

[0156] In some embodiments, the second heating process involves heating to the first temperature T1 and holding at that temperature for a first time t1.

[0157] During the phased heating process, the temperature is first raised to 200℃-250℃. Since the heating temperature is higher than the softening point of the filler material, the filler material melts and softens when heated. Holding the temperature for 1-3 hours allows it to flow and fill the pore structure of the raw material. Then, the temperature is raised to the first temperature, at which point the filler material undergoes a carbonization reaction, thereby effectively filling the pore structure occupied by the filler material.

[0158] In some embodiments, the first temperature T1 is 700℃-1200℃, and can be selected as 750℃-1100℃, 800℃-1100℃, 850℃-1100℃, or 900℃-1100℃.

[0159] During their research, the inventors discovered that a first temperature within the aforementioned range is beneficial for adjusting the weight loss rate of the carbon material to a suitable range, and also for adjusting the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. Furthermore, it effectively avoids the following situation: if 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 step 3. This results in a large number of residual pores, failing to effectively modify the internal structural defects of the particles, thereby increasing the weight loss rate of the carbon material and lowering its initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. maxFurthermore, it cannot effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and storage performance of the secondary battery; when the initial temperature is too high, the energy consumption during the carbon material preparation process increases.

[0160] In some embodiments, the first time t1 is 1h-5h. For example, the first time t1 can be a range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any of the above values. Optionally, the first time t1 is 2h-4h.

[0161] During their research, the inventors discovered that having the initial time within the aforementioned range is beneficial for adjusting the weight loss rate of the carbon material to a suitable range, and also for adjusting the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situation: if the initial time is too short, the filler material may not be completely converted into carbon material, and will continue to decompose into small molecules during the subsequent heat treatment step 3. This results in the actual residual carbon having a large number of pores, failing to effectively modify the internal structural defects of the particles, thereby increasing the weight loss rate of the carbon material and lowering its initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. max Furthermore, it cannot effectively prevent the electrolyte from penetrating into the pore structure inside the obtained carbon material particles, thereby affecting the initial coulombic efficiency and storage performance of the secondary battery; when the initial time is too long, the energy consumption in the carbon material preparation process increases.

[0162] In some embodiments, the heating rate of the first heating process can be 1℃ / min-10℃ / min, and can be selected as 1.5℃ / min-8℃ / min or 1.5℃ / min-5℃ / min.

[0163] During their research, the inventors discovered that when the heating rate is within the aforementioned range, it is beneficial to adjust the pore size and / or number of pores in the external and internal regions of the carbon material to a suitable range. This effectively avoids the following situations: When the heating rate is too high, the filler material may carbonize on the surface of the raw material particles, making it difficult for the filler material to fill into the pore structure of the raw material. This fails to effectively modify internal structural defects in the particles and cannot effectively prevent electrolyte penetration into the pore structure inside the obtained carbon material particles, thus affecting the initial coulombic efficiency, storage performance, and cycle performance of the secondary battery. Conversely, when the heating rate is too low, the time required for carbon material preparation and equipment energy consumption increase. Furthermore, the filler material easily flows and fills into all the pore structures of the raw material, resulting in larger volume changes during the extraction and insertion of active ions. The particles are more prone to breakage, which increases the consumption of active ions during SEI film formation, increases irreversible capacity loss in the secondary battery, and also affects the storage performance, cycle performance, and kinetic performance of the secondary battery.

[0164] In some embodiments, the heating rate of the second heating process is 2℃ / min-10℃ / min, and can be selected as 2.5℃ / min-8℃ / min.

[0165] In some embodiments, in step 2, the heat treatment can be carried out in a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor, or a rotary kiln.

[0166] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0167] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, and the heating process within the above range, it is beneficial to adjust the weight loss rate, the maximum weight loss rate, the initial weight loss temperature T0, and / or the temperature T corresponding to the maximum weight loss rate of the carbon material. max Within a suitable range, it is also beneficial to adjust the pore size and / or number of pores in the outer and inner regions of carbon materials to a suitable range.

[0168] In some embodiments, the second temperature T2 is 2000℃-2700℃, and can be selected as 2050℃-2600℃, 2100℃-2600℃, 2150℃-2600℃, 2200℃-2600℃, 2250℃-2600℃, 2100℃-2500℃, 2150℃-2500℃, 2200℃-2500℃, 2250℃-2500℃, 2100℃-2400℃, 2150℃-2400℃, or 2200℃-2400℃.

[0169] During their research, the inventors discovered that when the second temperature is within the aforementioned range, it is beneficial for carbon materials to have fewer surface and bulk defects, thereby reducing the weight loss rate of the carbon materials. Furthermore, it effectively avoids the following situation: when the second temperature is too low, the obtained carbon materials have more surface and / or bulk defects, thus increasing the weight loss rate of the carbon materials and lowering the initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. max This increases the consumption of active ions, affecting the initial coulombic efficiency and storage performance of the secondary battery. When the second temperature is too high, the crystallinity and graphitization of the obtained carbon material are very high, which is not conducive to the rapid extraction and insertion of active ions. At the same time, the high second temperature will also reduce the volume of residual carbon in the filling area, resulting in an increase in the total pore area of ​​the outer region of the carbon material. As a result, the surface defects of the carbon material may increase, affecting the storage performance of the secondary battery. In addition, the energy consumption required for the carbon material preparation process will also increase.

[0170] In some embodiments, the second time t2 is 1.5h-6h. For example, the second time t1 can be a range of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any of the above values. Optionally, the second time t2 is 2h-5h.

[0171] During their research, the inventors discovered that when the second time is within the aforementioned range, it is beneficial for carbon materials to have fewer surface and bulk defects, thereby reducing the weight loss rate of the carbon materials. Furthermore, it effectively avoids the following situation: when the second time is too short, the obtained carbon materials have more surface and / or bulk defects, thus increasing the weight loss rate of the carbon materials and lowering the initial weight loss temperature T0 and / or the temperature T corresponding to the maximum weight loss rate. max This increases the consumption of active ions, affecting the initial coulombic efficiency and storage performance of the secondary battery. When the second time is too long, the crystallinity and graphitization of the obtained carbon material are very high, which is not conducive to the rapid extraction and insertion of active ions. At the same time, an excessively long second time will also lead to a reduction in the volume of residual carbon in the filling area, resulting in an increase in the total pore area of ​​the carbon material's external region. As a result, the surface defects of the carbon material may increase, affecting the storage performance of the secondary battery. In addition, the energy consumption required for the carbon material preparation process will also increase.

[0172] In some embodiments, in step 3, the heat treatment can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Atchison graphitization furnace, a continuous graphitization furnace, or an internal series graphitization furnace.

[0173] 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.

[0174] By adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the weight loss rate, maximum weight loss rate, initial weight loss temperature T0, and / or the temperature T corresponding to the maximum weight loss rate of the carbon material. max Within a suitable range.

[0175] The carbon material preparation method of this application is simple and safe, requiring no pre-pressurization or vacuum treatment, and eliminating the need for an additional depolymerization step during heat treatment. The carbon material prepared in this application has fewer surface and bulk defects, and can simultaneously possess high specific capacity, high initial coulombic efficiency, and small volume change. Furthermore, it enables secondary batteries to achieve both high initial coulombic efficiency and good storage performance.

[0176] The preparation method described in this application is low-cost, highly practical, and suitable for large-scale production.

[0177] Secondary batteries

[0178] The third aspect of this application provides a secondary battery.

[0179] This application does not impose any particular limitation on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions repeatedly insert and extract between the positive and negative electrode, and the electrolyte acts as a conductor for these active ions. This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). Secondary batteries using electrolyte solutions, and some secondary batteries using solid electrolytes, may also include a separator membrane disposed between the positive and negative electrode to provide isolation.

[0180] [Negative electrode plate]

[0181] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0182] In some embodiments, the negative electrode film layer comprises the carbon material of the first aspect of this application or the carbon material prepared by the method of the second aspect of this application. This enables the secondary battery to achieve both high initial coulombic efficiency and good storage performance.

[0183] In some embodiments, the negative electrode film layer may further comprise other negative electrode active materials besides the carbon materials described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0184] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0186] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0187] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0188] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0189] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0190] [Positive electrode plate]

[0191] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0192] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0193] The positive electrode film typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder used for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. As an example, the conductive agent used for the positive electrode film includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0194] The positive electrode active material may be a positive electrode active material known in the art for use in secondary batteries.

[0195] When the secondary battery of this application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0196] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Nib Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0197] In some embodiments, as an example, the positive electrode active material for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0198] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0199] [Electrolytes]

[0200] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0201] The type of electrolyte salt is not specifically limited and can be selected according to actual needs.

[0202] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0203] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0204] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0205] [Isolation membrane]

[0206] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0207] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0208] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0209] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0210] In some embodiments, the outer packaging may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging may also be a flexible package, such as a pouch. The material of the flexible package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0211] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0212] In some embodiments, such as Figure 3 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0213] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0214] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0215] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0216] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0217] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0218] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0219] Electrical appliances

[0220] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0221] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0222] Figure 7 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0223] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0224] Example

[0225] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0226] Example 1

[0227] (1) Preparation of carbon materials

[0228] 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 15μm and a carbon content of 99.0%.

[0229] Step 2: The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 114℃, volume distribution particle size Dv50 of 4.5μm, coking value of 29%) are mixed in a VC mixer at a mass ratio of 100:25 for 30 min. Then, the mixed material is placed in a drum furnace and heated to 225℃ at a rate of 5℃ / min and held for 1.5 h (first heating process). Then, the temperature is increased to 1000℃ at a rate of 5℃ / min and held for 3 h (second heating process). After the process is completed, the mixture is cooled to room temperature to obtain an intermediate.

[0230] Step 3: Place the obtained intermediate in an Atchison graphitization furnace, heat it to 2380℃ and hold it for 5 hours. After the process, demagnetize and sieve to obtain carbon material.

[0231] (2) Preparation of button cell (half-cell)

[0232] The carbon material prepared above was mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CMC) as a thickener, and carbon black as a conductive agent in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil current collector and dried in an oven for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. A CR2430 coin cell was then assembled in an argon-protected glove box using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator.

[0233] (3) Preparation of secondary batteries (full batteries)

[0234] The carbon material prepared above, conductive carbon black (Super P), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly 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, and after drying and cold pressing, a negative electrode sheet was obtained.

[0235] LiFePO4, conductive carbon black, and polyvinylidene fluoride were mixed in a weight ratio of 96:2.5:1.5, and an appropriate amount of NMP solvent was added. The mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0236] A 12μm thick polypropylene film is used as a separator. It is placed in sequence with the positive and negative electrode sheets prepared above, so that the separator is in the middle of the positive and negative electrode sheets to play a role in isolation. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with the same electrolyte as the button cell prepared above. After vacuum sealing, standing, formation, capacity testing and other processes, a secondary battery is obtained.

[0237] Comparative Example 1

[0238] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0239] 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 carbon content of 99.0%.

[0240] Comparative Example 2

[0241] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0242] 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 carbon content of 99.0%.

[0243] The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 114℃, volume distribution particle size Dv50 of 4.5μm, and coking value of 29%) were mixed in a VC mixer at a mass ratio of 100:25 for 30 min. The mixed material was then graphitized at 3200℃ for 10 h. After the treatment, the mixture was cooled to room temperature to obtain carbon material.

[0244] Comparative Example 3

[0245] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0246] 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 carbon content of 99.0%.

[0247] The obtained natural spherical graphite and petroleum asphalt (softening point temperature of 114℃, volume distribution particle size Dv50 of 4.5μm, and coking value of 29%) were mixed in a VC mixer at a mass ratio of 100:25 for 30 min. The mixed material was then carbonized at 1200℃ for 2 h. After the carbonization was completed, the mixture was cooled to room temperature to obtain carbon material.

[0248] Comparative Example 4

[0249] The preparation methods for half-cells and full-cells are similar to those in Example 1, except for the preparation process of carbon materials.

[0250] 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 carbon content of 99.0%.

[0251] The obtained natural spherical graphite was mixed with petroleum asphalt (softening point temperature 114℃, volumetric particle size Dv50 4.5μm, coking value 29%) in a VC mixer for 30 min. The mixture was then added to a reactor, which was heated gradually at a rate of 2℃ / min while maintaining constant stirring. The temperature was raised to 190℃, and the reactor was evacuated to a pressure of -0.1 MPa, then held for 2 h. After this holding period, the reactor was heated to 650℃ and held for 2 h. The reactor was then cooled to approximately 160℃, and petroleum asphalt was slowly added to the reactor at a ratio of 1:1 to the previous addition. The reactor was then heated again to 190℃, and the reactor was evacuated to a pressure of -0.1 MPa, then held for 2 h. After this holding period, the reactor was heated to 650℃ and held for 2 h. Finally, the reactor was cooled using a condensation cooling method. Finally, the material processed in the above process is heat-treated at 1200℃ for 2 hours. The heat-treated sample is then crushed and sieved to obtain carbon material without internal pores.

[0252] Example 2-23

[0253] The preparation methods for half-cells and full-cells are similar to those in Example 1, except that the preparation process parameters of the carbon material are adjusted, as detailed in Table 1.

[0254] Performance testing

[0255] (1) Thermogravimetric analysis of carbon materials

[0256] Referring to JY / T 014-1996, a certain amount of carbon material was weighed and placed in a flat-bottomed crucible, shaken evenly, and left open. Air was used as the purging gas at a flow rate of 60 mL / min, and the heating rate was 5℃ / min. Thermogravimetric analysis was performed within the range of 35℃-950℃ to obtain the thermogravimetric (TG) curve and thermogravimetric differential (DTG) curve of the carbon material. The testing instrument can be a NETZSCH STA 449F3 simultaneous thermal analyzer from NETZSCH Instruments, Germany.

[0257] The initial weight loss temperature T0 of carbon material is the temperature corresponding to the intersection of the tangent line at the horizontal level before the step in the thermogravimetric curve of carbon material and the tangent line at the maximum weight loss rate.

[0258] Temperature T corresponding to the maximum weight loss rate of carbon materials max is the peak temperature of the thermogravimetric differential curve of the carbon material.

[0259] (2) Total pore area test of the external and internal regions of carbon materials

[0260] The sample preparation binder is mixed evenly with the carbon material powder and then coated onto copper foil. It is then dried at 60℃ for 30 minutes. The sample is cut into 6mm × 6mm pieces and pasted onto the sample stage of a CP-type argon ion section polisher. The sample is then cut using a plasma beam to obtain the cross-section of the carbon material, with the cross-section passing through the center of the carbon material particles. The testing instrument can be the IB-09010CP argon ion section polisher from JEOL Corporation of Japan.

[0261] The cross-section of the carbon material was scanned using a scanning electron microscope. The testing procedure can be referenced in JY / T010-1996. The testing instrument can be a ZEISS Sigma 300 scanning electron microscope (Germany).

[0262] The region extending 0.25L from the surface of a carbon particle into its interior is denoted as the outer region, and the region beyond the outer region is denoted as the inner region. L represents the minor axis length of the carbon particle. The total pore area S1 of the outer region and the total pore area S2 of the inner region of the carbon material are calculated using image processing software, such as AVIZO.

[0263] (3) First coulombic efficiency test of carbon materials

[0264] At 25°C, the prepared coin cell was first discharged at a constant current of 0.15 mA to 0.005 V, allowed to stand for 5 minutes, and then discharged at a constant current of 10 μA to 0.005 V. The first discharge capacity of the coin cell was recorded. Subsequently, it was charged at a constant current of 0.3 mA to 2.0 V, and the first charge capacity of the coin cell was recorded. The initial coulombic efficiency (%) of the carbon material = (first charge capacity of the coin cell / first discharge capacity of the coin cell) × 100%.

[0265] (4) Storage performance test of secondary batteries

[0266] At 25°C, the prepared secondary battery was charged at a constant current of 1C to the upper limit cutoff voltage (corresponding to 100% SOC), and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to the lower limit cutoff voltage (corresponding to 0% SOC). The discharge capacity at this time was recorded, which is the discharge capacity before storage.

[0267] At 25°C, the prepared secondary battery was charged at a constant current of 1C to the upper limit cutoff voltage (corresponding to 100% SOC), and then charged at a constant voltage until the current was 0.05C. The secondary battery was then stored in a 60°C constant temperature chamber until its discharge capacity decreased to 90% of its initial discharge capacity. The test was then stopped, and the number of days the secondary battery was stored was recorded.

[0268] Figure 8 These are the thermogravimetric curves and thermogravimetric differential curves of the carbon material prepared in Example 2. Figure 9 The thermogravimetric curves and thermogravimetric differential curves of the carbon material prepared in Comparative Example 2 are shown. As can be seen from the figures, the carbon material prepared in this application exhibits a low weight loss rate, a low maximum weight loss rate, and a high maximum weight loss rate at temperature T between 35℃ and 790℃. max And the initial weightlessness temperature T0.

[0269] The test results in Table 2 show that when the weight loss rate of the carbon material is ≤60% between 35℃ and 790℃, the battery can achieve both high initial coulombic efficiency and good storage performance. Furthermore, when the weight loss rate of the carbon material between 35℃ and 790℃ is further reduced to 5%-55%, or optionally 15%-45%, the battery can achieve even higher initial coulombic efficiency and better storage performance.

[0270] The test results in Table 2 also show that when T max At ≥790℃, with options for 790℃-910℃, and even 800℃-850℃, the battery can achieve higher initial coulombic efficiency and better storage performance.

[0271] The test results in Table 2 also show that when T0 ≥ 725℃, the temperature can be selected from 725℃ to 900℃, or even from 728℃ to 785℃, which can further enable the battery to have higher initial coulombic efficiency and better storage performance.

[0272] The carbon materials prepared in Comparative Examples 1-4 all had a weight loss rate greater than 60% between 35℃ and 790℃, and none of them could achieve both high initial coulombic efficiency and good storage performance in the battery.

[0273] The carbon materials prepared in Comparative Examples 2-3 consist of a carbon layer coating formed on the surface of natural spherical graphite. However, this carbon layer only exists on the surface of natural spherical graphite and fails to achieve an effective filling effect. It cannot effectively modify the internal defects of natural spherical graphite, and the carbon layer cannot effectively prevent the electrolyte from penetrating into the pore structure inside the particles. Consequently, the improvement effect on the first coulombic efficiency and storage performance of the battery is limited.

[0274] In Comparative Example 4, when preparing the carbon material, the filler material was injected into all the pores of the natural spherical graphite particles using a vacuum method. However, the actual residual carbon in the filled areas was soft carbon, which did not result in a carbon material with low reactivity, thus limiting its improvement on the battery's initial coulombic efficiency and storage performance. Furthermore, the volume change of the carbon material during the extraction and insertion of active ions was still significant, making the particles more prone to breakage. This increased the occurrence of side reactions and the consumption of active ions.

[0275] The test results in Table 2 also show that when the carbon material further satisfies S2 > S1, and optionally 1.5 ≤ S2 / S1 ≤ 400, 2 ≤ S2 / S1 ≤ 200, the carbon material can further improve the initial coulombic efficiency and storage performance of the battery. In this case, the carbon material particles further have the following characteristics: a large number of pores and / or large pore size in the internal region, and a small number of pores and / or small pore size in the external region. The pore structure in the internal region of the carbon material can reserve the necessary expansion space for volume changes in the carbon material particles, thereby reducing the risk of carbon material particle breakage and the generation of new interfaces, thus reducing the occurrence of side reactions and reducing irreversible capacity loss in the secondary battery; the small number of pores and / or small pore size in the external region of the carbon material can give the carbon material particles a more stable structure and minimize the penetration of electrolyte into the pore structure inside the carbon material particles, thereby reducing the occurrence of side reactions and reducing the consumption of active ions by the formation of the SEI film inside the particles. Therefore, the carbon material can further improve the initial coulombic efficiency and storage performance of the battery.

[0276] The specific surface area, volume distribution, particle size, particle size distribution, degree of graphitization, tap density, and other parameters of the carbon materials prepared in Examples 1-23 are all within the range described in this application specification.

[0277] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0278]

[0279] Table 2

[0280]

Claims

1. A carbon material, wherein, The carbon material includes a porous structure. In the thermogravimetric analysis test of the carbon material in an air atmosphere, the weight loss rate of the carbon material between 35℃ and 790℃ is ≤ 60%. In the thermogravimetric analysis test of the carbon material in an air atmosphere, the initial weight loss temperature of the carbon material is denoted as T0, and T0 is 725℃-900℃.

2. The carbon material according to claim 1, wherein, The weight loss rate of the carbon material is 5%-55% between 35℃ and 790℃.

3. The carbon material according to claim 2, wherein, The weight loss rate of the carbon material is 15%-45% between 35℃ and 790℃.

4. The carbon material according to any one of claims 1-3, wherein, In the thermogravimetric analysis test of the carbon material in an air atmosphere, the maximum weight loss rate of the carbon material was ≤ 5.5% / min.

5. The carbon material according to claim 4, wherein, In the thermogravimetric analysis test of the carbon material in an air atmosphere, the maximum weight loss rate of the carbon material was 0.5% / min-5% / min.

6. The carbon material according to any one of claims 1-5, wherein, In the thermogravimetric analysis test of the carbon material in an air atmosphere, the temperature corresponding to the maximum weight loss rate of the carbon material is denoted as T. max Then T max The temperature range is 790℃-910℃.

7. The carbon material according to claim 6, wherein, T max The temperature range is 800℃-850℃.

8. The carbon material according to any one of claims 1-7, wherein, T0 is 728℃-785℃.

9. The carbon material according to any one of claims 1-8, wherein, The carbon material includes one or more pore structures with a pore area greater than or equal to 0.1 μm².

10. The carbon material according to claim 9, wherein, The carbon material comprises one or more pore structures with a pore area of ​​0.12 μm² to 1.5 μm².

11. The carbon material according to any one of claims 1-10, wherein, The carbon material includes an outer region and an inner region located inside the outer region. The outer region refers to the area formed by extending 0.25 L from the surface of the carbon material particles into the particle interior, where L refers to the minor axis length of the carbon material particles. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted as S2, where S2 > S1.

12. The carbon material according to claim 11, wherein, 1.5 ≤ S2 / S1 ≤ 400.

13. The carbon material according to claim 11, wherein, 2 ≤ S2 / S1 ≤ 200.

14. The carbon material according to any one of claims 11-13, wherein, 0.01μm² ≤ S1 ≤ 5.5μm²; and / or, 2.5μm² ≤ S² ≤ 25.0μm²; and / or, L ≥ 7μm.

15. The carbon material according to claim 14, wherein, 0.06μm² ≤ S1 ≤ 4.5μm²; and / or, 4.0 μm² ≤ S² ≤ 15.0 μm²; and / or, 7μm ≤ L ≤ 18μm.

16. The carbon material according to any one of claims 11-15, wherein, The area of ​​the pore structure in the outer region of the carbon material is less than 0.2 μm²; and / or, The internal region of the carbon material includes one or more pore structures with an area greater than or equal to 0.12 μm².

17. The carbon material according to claim 16, wherein, The area of ​​the pore structure in the outer region of the carbon material is less than or equal to 0.12 μm²; and / or, The internal region of the carbon material includes one or more pore structures with an area of ​​0.12 μm² to 2.5 μm².

18. The carbon material according to any one of claims 11-17, wherein, The interlayer spacing of the outer region of the carbon material is denoted as d1, and the interlayer spacing of the inner region of the carbon material is denoted as d2. The carbon material satisfies d1 ≥ d2.

19. The carbon material according to claim 18, wherein, d1 > d2.

20. The carbon material according to claim 18 or 19, wherein, d1 is 0.33565nm-0.33620nm; and / or, d2 is 0.33557nm-0.33589nm.

21. The carbon material according to any one of claims 1-20, wherein, The carbon material satisfies at least one of the following: (1) The specific surface area of ​​the carbon material is 0.7 m². 2 / g-1.6m 2 / g; (2) The volume distribution particle size Dv50 of the carbon material is 10.0 μm-20.0 μm; (3) The volume distribution particle size Dv10 of the carbon material is 4.0 μm-13.0 μm; (4) The volume distribution particle size Dv90 of the carbon material is 25.0 μm-35.0 μm; (5) The particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.90-1.10; (6) The morphology of the carbon material includes one or more of the following: blocky, spherical and quasi-spherical.

22. The carbon material according to claim 21, wherein, The carbon material satisfies at least one of the following: (1) The specific surface area of ​​the carbon material is 0.8 m². 2 / g-1.4m 2 / g; (2) The volume distribution particle size Dv50 of the carbon material is 12.0-18.0 μm; (3) The volume distribution particle size Dv10 of the carbon material is 6.0 μm-11.0 μm; (4) The volume distribution particle size Dv90 of the carbon material is 27.0 μm-32.0 μm; (5) The particle size distribution (Dv90-Dv10) / Dv50 of the carbon material is 0.95-1.

05.

23. The carbon material according to any one of claims 1-22, wherein, The carbon material satisfies at least one of the following: (1) The tap density of the carbon material is 1.0 g / cm³. 3 -1.5g / cm 3 ; (2) The specific capacity of the carbon material is 350mAh / g-372mAh / g; (3) The degree of graphitization of the carbon material is 91.5%-98.5%.

24. The carbon material according to claim 23, wherein, The carbon material satisfies at least one of the following: (1) The tap density of the carbon material is 1.1 g / cm³. 3 -1.4g / cm 3 ; (2) The specific capacity of the carbon material is 353mAh / g-371mAh / g; (3) The degree of graphitization of the carbon material is 92.5%-98.0%.

25. A method for preparing a carbon material, comprising the following steps: Step 1, providing a raw material having a plurality of pore structures; Step 2, mixing the raw material and a filler material uniformly according to a predetermined ratio, and then holding the mixture at a first temperature T1 for a first time t1 to obtain an intermediate; Step 3, holding the obtained intermediate at a second temperature T2 for a second time t2 to obtain a carbon material, wherein... The carbon material includes a porous structure. In the thermogravimetric analysis test of the carbon material in an air atmosphere, the weight loss rate of the carbon material between 35℃ and 790℃ is ≤ 60%. In the thermogravimetric analysis test of the carbon material in an air atmosphere, the initial weight loss temperature of the carbon material is denoted as T0, and T0 is 725℃-900℃.

26. The method of claim 25, wherein, The raw materials satisfy at least one of the following: (1) The raw materials include natural graphite; (2) The volume distribution particle size Dv50 of the raw material is 10.0μm-20.0μm; (3) The carbon content of the raw material is ≥ 90.0 wt%.

27. The method according to claim 26, wherein, The raw materials satisfy at least one of the following: (1) 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 12.0-18.0 μm; (3) The carbon content of the raw material is ≥ 95.0 wt%.

28. The method according to any one of claims 25-27, wherein, The filler material satisfies at least one of the following: (1) The softening point temperature of the filler material is 80℃-150℃; (2) The coking value of the filler material is 15%-40%; (3) The volume distribution particle size Dv50 of the filling material is less than or equal to 6 μm; (4) The filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds and resins.

29. The method according to claim 28, wherein, The filler material satisfies at least one of the following: (1) The softening point temperature of the filler material is 90℃-140℃; (2) The coking value of the filler material is 15%-35%; (3) The volume distribution particle size Dv50 of the filler material is 2μm-5μm; (4) The filler material includes petroleum asphalt.

30. The method according to any one of claims 25-29, wherein, The mass ratio of the filler material to the raw material is (10-35):

100.

31. The method according to claim 30, wherein, The mass ratio of the filler material to the raw material is (15-32):

100.

32. The method according to any one of claims 25-29, wherein, The heating process of mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1 is a staged heating process.

33. The method according to claim 32, wherein, The heating process, which involves uniformly mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1, includes a first heating process and a second heating process.

34. The method according to claim 33, wherein, The first heating process involves heating to 200℃-250℃ and holding at that temperature for 1-3 hours; and / or, The second heating process involves heating to the first temperature T1 and holding at that temperature for a first time t1.

35. The method according to any one of claim 33 or 34, wherein, The heating rate of the first heating process is 1℃ / min-10℃ / min; and / or, The heating rate of the second heating process is 2℃ / min-10℃ / min.

36. The method according to claim 35, wherein, The heating rate of the first heating process is 1.5℃ / min-8℃ / min; and / or, The heating rate of the second heating process is 2.5℃ / min-8℃ / min.

37. The method according to any one of claims 25-36, wherein, The first temperature T1 is 700℃-1200℃; and / or, The first time t1 is 1h-5h.

38. The method according to claim 37, wherein, The first temperature T1 is 800℃-1100℃; and / or, The first time t1 is 2h-4h.

39. The method according to any one of claims 25-38, wherein, The second temperature T2 is 2000℃-2700℃; and / or, The second time t2 is 1.5h-6h.

40. The method according to claim 39, wherein, The second temperature T2 is 2100℃-2600℃; and / or, The second time t2 is 2h-5h.

41. A secondary battery, comprising a negative electrode, said negative electrode comprising the carbon material according to any one of claims 1-24 or the carbon material prepared by the method according to any one of claims 25-40.

42. An electrical device comprising the secondary battery of claim 41.

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