Negative electrode active material and preparation method thereof, negative electrode sheet, battery and electrical device

Abstract

This application discloses a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery, and an electrical device. The negative electrode active material comprises a carbon core; a porous carbon skeleton layer having an internal accommodation space within which the carbon core is located; a carbon coating layer that covers at least a portion of the outer surface of the porous carbon skeleton layer; and an absorbing material and silicon-based particles, each independently distributed within the region containing the carbon core and the porous carbon skeleton layer. This negative electrode active material can improve battery cycle performance and energy density.

Description

Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to negative electrode active materials and preparation methods thereof, negative electrode sheets, batteries and electrical devices. Background Art

[0002] Lithium-ion batteries are environmentally friendly, high-energy, and low-carbon. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. With the development of today's society, people's demands for lithium-ion batteries are becoming increasingly higher, such as high energy density. The anode is a key component of lithium-ion batteries. Selecting a high-capacity anode active material can help improve the battery's energy density. For example, silicon-based anode active materials can improve the battery's energy density. Summary of the Invention

[0003] In view of the technical problems existing in the background technology, the present application provides a negative electrode active material, aiming to improve the energy density and cycle performance of the battery.

[0004] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a negative electrode active material, including: a carbon core; a porous carbon skeleton layer, the porous carbon skeleton layer has an accommodation space inside, and the carbon core is located in the accommodation space; a carbon coating layer, the carbon coating layer is coated on at least a portion of the outer surface of the porous carbon skeleton layer; an absorbing material and silicon-based particles, the absorbing material and the silicon-based particles are independently distributed in the area where the carbon core and the porous carbon skeleton layer are located.

[0005] Compared with the prior art, the negative electrode active material of the present application has at least the following beneficial effects: 1. The negative electrode active material has both the high conductivity and stability of carbon materials and the high capacity of silicon materials. Using it in the negative electrode sheet is beneficial to improving the negative electrode capacity and conductivity, and improving the energy density and electrical performance of the battery; 2. The silicon-based particles are distributed in the carbon core and the porous carbon skeleton layer, that is, the silicon-based particles are distributed in the outermost carbon coating layer. The porous structure of the porous carbon skeleton layer and the carbon coating layer located in the outermost layer can be used to effectively limit the volume expansion of silicon during the charge and discharge cycle, thereby improving the structural stability of the negative electrode active material, thereby effectively improving the volume expansion that may occur during the cycle of the negative electrode sheet and the battery, and improving the cycle performance of the battery; 3. The preparation process is controllable, and absorbing materials can be used to achieve the directional distribution of silicon-based particles in the area where the carbon core and the porous carbon skeleton layer are located.

[0006] In some embodiments of the present application, the absorbing material content distributed within the porous carbon skeleton layer is no less than 90 wt%, and the absorbing material content distributed within the region where the carbon core resides is no greater than 10 wt%, based on the total mass of the absorbing material. Maintaining the absorbing material distribution within this range further promotes the deposition of more silicon deep within the pores of the porous carbon skeleton layer. The porous carbon skeleton's pore structure, combined with the carbon coating, effectively limits the volume expansion of the silicon-based particles, thereby improving cycling performance.

[0007] In some embodiments of the present application, the absorbing material content is 0.5 wt% to 15 wt% based on the mass of the porous carbon skeleton layer. Controlling the amount of absorbing material within this range facilitates deposition of silicon within the porous carbon skeleton layer and the carbon core, while simultaneously minimizing the space occupied by the negative electrode active material. This facilitates high silicon deposition and balances the gram capacity and kinetic performance of the negative electrode active material.

[0008] In some embodiments of the present application, the content of the absorbing material is no greater than 10 wt %, and may be 3 wt % to 8 wt %, based on the mass of the negative electrode active material. Controlling the amount of the absorbing material within this range facilitates deposition of silicon within the porous carbon skeleton layer and the carbon core, while simultaneously minimizing the space occupied by the negative electrode active material. This facilitates high silicon deposition and balances the gram capacity and kinetic performance of the negative electrode active material.

[0009] In some embodiments of the present application, the absorbing material meets at least one of the following conditions: an absorption range of 5.2 GHz to 15.9 GHz, an absorption bandwidth of 8.4 GHz to 10.7 GHz, and a particle size of 20 nm to 500 nm. Controlling the particle size of the absorbing material within this range further facilitates uniform distribution of the absorbing material and silicon-based particles within the negative electrode active material, increases the amount of silicon deposited within the negative electrode active material, and improves the specific capacity and kinetic performance of the negative electrode active material.

[0010] In some embodiments of the present application, the absorbing material includes one or more of a single metal, an alloy, a metal oxide, a composite metal oxide, a carbide, and a sulfide. Optionally, the absorbing material includes one or more of single iron, an iron-containing alloy, and an iron-containing oxide. Selecting a given range of absorbing materials facilitates precise heating at specific locations, promoting uniform and directional deposition of more silicon within the negative electrode active material, particularly within the pores of the multilayer carbon skeleton layer.

[0011] In some embodiments of the present application, the silicon-based particles include one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. Silicon-based particles within the given range have a higher capacity and can increase the overall gram capacity of the negative electrode active material.

[0012] In some embodiments of the present application, the content of the silicon-based particles is 30 wt% to 70 wt% (or optionally 30 wt% to 50 wt%), based on the mass of the negative electrode active material. Controlling the content of the silicon-based particles within the given range can balance the gram capacity and cycle stability of the negative electrode active material.

[0013] In some embodiments of the present application, the porosity of the porous carbon skeleton layer is 40% to 70%. Controlling the porosity of the porous carbon skeleton layer within the given range can not only take into account the overall strength of the negative electrode active material, but also improve the specific capacity and cycle stability of the negative electrode active material.

[0014] In some embodiments of the present application, the pore size of the porous carbon skeleton layer is 1 nm to 50 nm. Controlling the pore size of the porous carbon skeleton layer within the given range can further improve the specific capacity and cycle structural stability of the negative electrode active material.

[0015] In some embodiments of the present application, the negative electrode active material satisfies at least one of the following conditions: the particle size of the carbon core is 1 μm to 5 μm; the thickness of the carbon coating layer is not greater than 1 μm, optionally not greater than 0.2 μm, further optionally not greater than 0.1 μm, and further optionally 0.05 μm to 0.08 μm; the Dv50 particle size of the negative electrode active material is not greater than 10 μm, and the Dv90 particle size is not greater than 20 μm.

[0016] In some embodiments of the present application, the carbon core includes one or more of graphite, porous carbon, and mesocarbon microbeads. Optionally, the porous carbon includes hard carbon.

[0017] In some embodiments of the present application, the carbon precursor materials used to form the porous carbon skeleton layer and the carbon coating layer independently include one or more of asphalt, resin, soluble starch, sucrose, glucose, and polyacrylate.

[0018] In some embodiments of the present application, the negative electrode active material further includes a carbon core coating layer, the carbon core coating layer coating at least a portion of the outer surface of the carbon core and located within the accommodation space, and an absorbing material distributed within the carbon core coating layer. Meeting these conditions can further promote silicon deposition throughout the negative electrode active material, reduce silicon content on the surface of the negative electrode active material, and improve the negative electrode active material's ability to limit the volume expansion of silicon-based particles during charge and discharge cycles.

[0019] In some embodiments of the present application, the mass proportion of the absorbing material in the carbon core coating layer is greater than the mass proportion of the absorbing material in the porous carbon skeleton layer. Meeting this condition can further facilitate the deposition of more silicon within the porous carbon skeleton layer, resulting in a greater amount of silicon deposited on the side of the porous carbon skeleton layer closer to the carbon core than on the side closer to the carbon coating layer.

[0020] In some embodiments of the present application, the thickness of the carbon core coating layer is no greater than 1 μm, and may be 0.3 μm to 1 μm, or further 0.3 μm to 0.5 μm. Controlling the thickness of the carbon core coating layer within the given range can promote the deposition of more silicon within the entire negative electrode active material, thereby improving cycle performance while further balancing the overall gram capacity of the negative electrode active material.

[0021] In some embodiments of the present application, the resistivity of the negative electrode active material at room temperature and a pressure of 4 MPa is between 100 mΩ·cm and 10,000 mΩ·cm, and may be between 100 mΩ·cm and 300 mΩ·cm. Controlling the resistivity of the negative electrode active material within this range can improve its volume effect and cycle performance while also taking into account kinetic performance.

[0022] The second aspect of the present application provides a method for preparing the negative electrode active material of the first aspect of the present application, comprising: mixing a carbon core material, a pore-forming agent, a carbon skeleton precursor material and a solvent to obtain a first mixed liquid; mixing an absorbing material with the first mixed liquid to obtain a second mixed liquid; spray-forming and fluidized drying the second mixed liquid to obtain composite particles; carbonizing and activating the composite particles to obtain skeleton particles with a porous carbon skeleton layer covering a carbon core; microwave heating the skeleton particles and introducing a gaseous silicon source to deposit silicon to obtain precursor particles; coating at least a portion of the outer surface of the precursor particles with a carbon coating layer to obtain a negative electrode active material.

[0023] Compared with the prior art, the method of preparing negative electrode active materials in the present application has at least the following beneficial effects: not only is the preparation process controllable, but also absorbing materials and microwave heating can be used for precise heating to achieve directional distribution of silicon and obtain negative electrode active materials with the expected structure. It is also beneficial to reduce the heating temperature and heating time in the preparation process, improve production efficiency, and reduce costs. At the same time, the negative electrode active material prepared can effectively limit the volume expansion of silicon and improve its structural stability during the cycle.

[0024] In some embodiments of the present application, before preparing the first mixed liquid, the method further includes: coating a carbon core coating layer on at least a portion of the outer surface of the carbon core material.

[0025] In some embodiments of the present application, the pore-forming agent includes one or more of sodium chloride, potassium chloride, zinc chloride, sodium carbonate, potassium carbonate, zinc carbonate, zinc acetate, and ammonium acetate.

[0026] In some embodiments of the present application, the total mass proportion of the pore-forming agent and the carbon skeleton precursor material in the first mixed solution is 10 wt % to 70 wt %.

[0027] In some embodiments of the present application, the mass ratio of the pore-forming agent to the carbon skeleton precursor material is (10-1): (1-100), optionally (10-1): (2-10), and further optionally (10-1): (2-5). By controlling the amount of the pore-forming agent within the given range, it is further advantageous to obtain a porous carbon skeleton layer with a desired porosity and micro-mesoporous structure.

[0028] The third aspect of the present application provides a negative electrode sheet, which includes: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application.

[0029] The fourth aspect of the present application provides a battery, which includes: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application, and / or the negative electrode sheet of the third aspect of the present application.

[0030] The fifth aspect of the present application provides an electrical device, which includes: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application, and / or the negative electrode sheet of the third aspect of the present application, and / or the battery of the fourth aspect of the present application.

[0031] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0033] Figure 1 Schematic diagram of the cross-sectional structure of the negative electrode active material according to one embodiment of the present application.

[0034] Figure 2 Schematic diagram of the cross-sectional structure of a negative electrode active material according to another embodiment of the present application.

[0035] Figure 3Schematic diagram of an implementation of an electrical device used as a power source according to an embodiment of the present application.

[0036] Figure 4 This is the XRD pattern of the negative electrode active material prepared according to Example 1 of the present application.

[0037] Figure 5 This is the XRD pattern of the negative electrode active material prepared according to Comparative Example 1 of the present application.

[0038] Reference numerals:

[0039] 10-carbon core; 11-carbon core coating layer; 20-porous carbon skeleton layer; 30-carbon coating layer. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0041] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0042] The "ranges" disclosed herein are defined in terms of lower and / or upper limits. A given range is defined by selecting a lower limit and / or an upper limit, and the selected lower limit and / or upper limit define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, i.e., any lower limit may be combined with any upper limit to form an unspecified range, and any lower limit may be combined with any other lower limit to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range. For example, if a range of not more than 20 is listed for a particular parameter, it is understood that ranges of 2 to 18 and 5 to 15, etc., that meet the range of not more than 20 are also contemplated. Furthermore, if the minimum range values ​​listed are 1 and 5, and if the maximum range values ​​listed are 10 and 30, then the following ranges are all contemplated: 1 to 10, 1 to 30, 5 to 10, and 5 to 30. In this application, unless otherwise specified, a numerical range such as "30-100" is an abbreviation for any combination of real numbers between 30 and 100, where 30 and 100 are real numbers. For example, the numerical range "1-30" means that all real numbers between "1-30" are listed herein, and "1-30" is merely an abbreviation for these numerical combinations.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0045] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed sequentially, or may include steps S2 and S1 performed sequentially. For example, the method may further include step S3, which means that step S3 may be added to the method in any order, for example, the method may include steps S1, S2, and S3, or may include steps S1, S3, and S2, or may include steps S3, S1, and S2, etc.

[0046] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or comprised, or may mean that only the listed components are included or comprised. Furthermore, as used in this application, the terms "plurality" and "multiple" refer to two or more components.

[0047] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0048] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned description of the drawings and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0049] At present, as the demand for power batteries gradually expands, the demand for the energy density of power batteries is also getting higher and higher. However, silicon-based materials with higher energy density have a dramatic volume expansion during the cycle process, especially when silicon nanoparticles are deeply embedded with lithium batteries, the volume expansion can reach 300%. Usually, the expansion effect of silicon can be effectively limited by compounding carbon materials with different structures and dimensions, but there will be a large amount of silicon free outside the carbon structure. For example, there is a process of adding silicon dispersion dropwise to a vigorously stirred metal oxide-graphene dispersion, obtaining a metal oxide-graphene-silicon composite material by filtration, and then combining acid etching and carbon thermal reaction to obtain a porous graphene silicon negative electrode material. This process not only has high raw material costs, but also makes it difficult to sink silicon into the interior of the active material. This silicon distributed on the outer surface directly increases the conduction resistance of electrons between particles, and during the cycle, the expansion caused by silicon exposed on the surface of the material will also affect the cycle life.

[0050] In view of this, the first aspect of the present application provides a negative electrode active material, referring to Figure 1It is understood that the negative electrode active material includes: a carbon core 10, a porous carbon skeleton layer 20, a carbon coating layer 30, and an absorbing material (not shown) and silicon-based particles (not shown). The porous carbon skeleton layer 20 has an accommodating space (not shown) that can accommodate the carbon core 10, and the carbon core 10 is located in the accommodating space; the carbon coating layer 30 is coated on at least a portion of the outer surface of the porous carbon skeleton layer 20; the absorbing material and the silicon-based particles are independently distributed in the area where the carbon core 10 and the porous carbon skeleton layer 20 are located, for example, the two can be independently distributed partially or completely in the skeleton pores of the porous carbon skeleton layer 20.

[0051] According to the embodiments of the present application, by compounding carbon material and silicon-based particles and controlling the above structure, on the one hand, the negative electrode active material can have both the high conductivity and stability of carbon material and the high capacity of silicon material, and its use in the negative electrode sheet is beneficial to improving the negative electrode capacity and conductivity, and improving the energy density and electrical performance of the battery; on the other hand, in the negative electrode active material, the silicon-based particles are distributed in the carbon core and the porous carbon skeleton layer, that is, the silicon-based particles are distributed in the outermost carbon coating layer, and the porous structure of the porous carbon skeleton layer and the carbon coating layer located in the outermost layer can be used to effectively limit the volume expansion of silicon during the charge and discharge cycle, thereby improving the structural stability of the negative electrode active material, thereby effectively improving the volume expansion that may occur during the cycle of the negative electrode sheet and the battery, and improving the cycle performance of the battery; on the other hand, the preparation process of the negative electrode active material is controllable, and the absorbing material can be used to achieve the directional distribution of silicon-based particles in the area where the carbon core and the porous carbon skeleton layer are located.

[0052] Furthermore, after in-depth research, the inventors have discovered that, in addition to satisfying the aforementioned conditions, the negative electrode active material of the first aspect of this application can further improve the performance of the negative electrode active material, including but not limited to capacity, conductivity, and cycle stability, by controlling the distribution location, addition amount, and absorption range of the absorbing material, as well as the selection and dosage of the silicon-based particles, the porous carbon skeleton layer structure, and the carbon core. That is, in addition to satisfying the aforementioned conditions, one or more of the following conditions may also be optionally satisfied.

[0053] In some embodiments of the present application, the content of the absorbing material distributed in the porous carbon skeleton layer 20 is greater than the content of the absorbing material distributed in the area where the carbon core 10 is located. The reasons why a large amount of silicon is free outside the carbon structure or exposed on the surface of the silicon-carbon composite negative electrode active material include: the traditional heat treatment method for silicon-carbon composite materials requires high temperatures, long sintering times, consumes a lot of energy, and cannot accurately control the temperature of different regions of the material. Under this traditional heat treatment process mode, it is difficult to control the finished state of the silicon-carbon composite material. Not only does it consume a lot of energy, but the silicon in it has difficulty entering the interior of the carbon skeleton, resulting in many silicon grains on the surface of the material. This can easily cause serious expansion problems during battery cycling, directly affecting the stability of the silicon-carbon composite material structure and ultimately affecting the cycling performance. In order to address the negative impact of conventional heat treatment on silicon-carbon composite materials, by introducing absorbing materials into the silicon-carbon composite material, the wavelength of the absorbing material can be coupled with the basic microstructure of the material to generate heat to accurately heat specific locations of the material, while having the advantages of fast heating speed, high energy utilization, high heating efficiency, safety, hygiene and pollution-free. In the embodiments of the present application, by distributing more of the absorbing material in the porous carbon skeleton layer, during the preparation process of the negative electrode active material, its own heat generation and gradient-free overall heating method, as well as the rapid heating rate, can be utilized to promote the deposition of more silicon into the deep pores of the porous carbon skeleton layer, that is, to promote silicon to enter the interior of the negative electrode active material, significantly reducing its content on the surface of the negative electrode active material, thereby effectively limiting the volume expansion of silicon, which is beneficial to maintaining the structural stability of the silicon-based particles during long-term circulation; at the same time, the carbon coating layer can also be used to further limit the volume expansion of the internal silicon-based particles and improve the cycle performance.

[0054] In some embodiments of the present application, based on the total mass of the absorbing material, the content of the absorbing material distributed in the porous carbon skeleton layer 20 may be no less than 90 wt% (for example, it may be 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%, etc., or it may be a range consisting of any of the above values), and the content of the absorbing material distributed in the region where the carbon core 10 is located may be no more than 10 wt% (for example, it may be 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, etc., or it may be a range consisting of any of the above values). The presence of absorbing material can be determined by combining the intensity signal of the negative electrode active material in an electromagnetic wave environment. For example, for silicon-containing negative electrode active materials, the silicon can be etched away before determining whether the absorbing material is present. XRD testing can be combined to determine the crystal form or type of the absorbing material. Energy dispersive spectroscopy (EDS) can be used to analyze the types and contents of the micro-region components within the cross-sectional area of ​​the negative electrode active material to determine the distribution of the absorbing material in different regions and analyze the mass proportion of the absorbing material in different regions. In the embodiments of the present application, by ensuring that the distribution of the absorbing material meets the above-mentioned conditions, more silicon can be further deposited deep into the pores of the porous carbon skeleton layer. The pore structure of the porous carbon skeleton, in combination with the carbon coating layer, effectively limits the volume expansion of the silicon-based particles, thereby improving the cycling performance.

[0055] In some embodiments of the present application, the content of the absorbing material can be 0.5 wt% to 15 wt% based on the mass of the porous carbon skeleton layer 20, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, etc., or can be any range consisting of the above values. The content of the absorbing material in the porous carbon skeleton layer can be obtained by analyzing the types and contents of the component elements in the porous carbon skeleton layer region in the cross section of the negative electrode active material in combination with XRD testing and energy dispersive spectroscopy (EDS). Among them, if the content of the absorbing material is too high, it is easy to agglomerate into large particles in the porous carbon skeleton layer, reducing the dispersion uniformity of the absorbing material and causing the absorbing effect to be significantly weakened. The inventors of this application unexpectedly discovered that covering a small amount of absorbing material inside the structure of the negative electrode active material can achieve the effect of precise heating and controlling silicon deposition, and by controlling the amount of added absorbing material within a given range, it is beneficial to deposit more silicon in the area where the porous carbon skeleton layer and the carbon core are located, while not occupying too much space inside the negative electrode active material, which is beneficial to obtaining a higher silicon deposition amount and taking into account the gram capacity and kinetic performance of the negative electrode active material.

[0056] In some embodiments of the present application, based on the mass of the negative electrode active material, the content of the absorbing material may be no more than 10wt%, for example, it may be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, etc., or it may be a range consisting of any of the above values. Controlling the amount of the absorbing material added within the given range is beneficial for depositing more silicon in the porous carbon skeleton layer and the area where the carbon core is located, while not occupying too much space inside the negative electrode active material, which is beneficial for obtaining a higher silicon deposition amount and taking into account the gram capacity and kinetic performance of the negative electrode active material. Optionally, based on the mass of the negative electrode active material, the content of the absorbing material may be 3wt% to 8wt%. Controlling the amount of the absorbing material added within the given range can, on the basis of obtaining a higher silicon deposition amount, further avoid the absorbing material occupying too much space inside the negative electrode active material, thereby improving the gram capacity and kinetic performance of the negative electrode active material.

[0057] In some embodiments of the present application, the absorption range of the absorbing material can be 5.2 GHz to 15.9 GHz, for example, 6 GHz, 7 GHz, 8 GHz, 9 GHz, 10 GHz, 11 GHz, 12 GHz, 13 GHz, 14 GHz, 15 GHz, etc., or a range composed of any of the above values. The negative electrode active material (when silicon is deposited, it can also be desiliconized first) can be placed in a specific variable frequency electromagnetic wave environment to collect electromagnetic wave intensity signals to test the absorption frequency band range of the absorbing material. Optionally, the absorption range of the absorbing material can be 6 GHz to 10 GHz. Selecting the absorption range within the given range is beneficial to improving the heating efficiency and effect of the absorbing material within a specific band, improving production efficiency, and reducing production costs.

[0058] In some embodiments of the present application, the absorption bandwidth of the absorbing material can be 8.4 GHz to 10.7 GHz, for example, 8.5 GHz, 9 GHz, 9.5 GHz, 10 GHz, 10.5 GHz, or any range thereof. The absorption bandwidth is the frequency bandwidth, i.e., the frequency difference between the maximum and minimum absorption wavelengths.

[0059] In some embodiments of the present application, the particle size of the absorbing material can be between 20 nm and 500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 500 nm, or any range thereof. The particle size of the absorbing material can be measured using a transmission electron microscope. For example, using an Fe-based absorbing material as an example, the absorbing material is in the form of solid particles. Its particle size can be observed using a high-magnification transmission electron microscope. Dark particles appear in the field of view, and the average particle size of the particles in the field of view can be calculated. In actual operation, multiple measurements can be performed to obtain an average value. If the particle size of the absorbing material is too large, it is not conducive to its uniform dispersion in the porous carbon skeleton layer, and it is easy to affect the uniform distribution of silicon-based particles and the deposition amount inside the negative electrode active material. The use of small-particle absorbing materials is not only beneficial to increasing the number of absorbing material particles and increasing the surface activity of the absorbing material, but also conducive to the uniform dispersion of the absorbing material. Under the radiation of the microwave field, it can promote the conversion of electromagnetic energy into thermal energy, achieve precise heating at specific locations, and thus promote more silicon in the negative electrode active material, especially in the pores of the multi-layer carbon skeleton layer. By controlling the particle size of the absorbing material within a given range, it can further facilitate the uniform distribution of the absorbing material and silicon-based particles inside the negative electrode active material, increase the deposition amount of silicon inside the negative electrode active material, and improve the specific capacity and kinetic performance of the negative electrode active material.

[0060] In some embodiments of the present application, the absorbing material may include one or more of a metal element, an alloy, a metal oxide, a composite metal oxide, a carbide, and a sulfide. For example, it may include but is not limited to silicon carbide, iron, copper, zinc, calcium, titanium, chromium, and related derivatives (such as alloys, metal oxides such as FeO, Fe3O4, Fe2O3, ZnO, or composite metal oxides such as LaFeO3, LaSrFeO3, etc.), as well as oxides such as MoO2, NiO, TiO2, Co3O4, WO3, etc. Optionally, the absorbing material may include one or more of elemental iron, an iron-containing alloy, and an iron-containing oxide, for example, one or more of Fe, FeO, Fe3O4, and Fe2O3. The manufacturing process of the iron-containing absorbing material within the given range is to convert metal ions into metal oxides by heating in situ. The particles have a small particle size (the average particle size is generally not greater than 100 nm, and can be optionally 20 nm to 50 nm) and are dispersed within the porous carbon skeleton layer (partially nanoscale particles). In the composite structure, both the absorbing material and the porous carbon material have absorbing properties. Electromagnetic synergy can be used to improve the impedance matching of the composite of the absorbing material and the carbon material, thereby enhancing the electromagnetic wave absorption performance. At the same time, the iron-containing absorbing material within the given range has a small particle size and a large number of surface atoms, which not only increases the surface activity of the material but also has good magnetic permeability. Under the radiation of the microwave field, the movement of atoms and electrons is intensified, which can promote magnetization to convert electrical energy into thermal energy, and in turn increase the ability of the overall composite material to absorb, attenuate, and convert electromagnetic waves. This can further facilitate the precise heating of specific locations, promote the uniform and directional deposition of more silicon inside the negative electrode active material, especially in the pores of the multi-layer carbon skeleton layer, and improve the specific capacity and kinetic performance of the negative electrode active material.

[0061] In some embodiments of the present application, silicon-based particles include, but are not limited to, one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. Silicon-based particles within the given range have a relatively high capacity, which can increase the overall gram capacity of the negative electrode active material and improve the energy density of the battery.

[0062] In some embodiments of the present application, based on the mass of the negative electrode active material, the content of the silicon-based particles can be 30 wt% to 70 wt%, for example, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, etc., or can be a range consisting of any of the above values. The content of the silicon-based particles in the negative electrode active material can be obtained in combination with ICP testing, and can be specifically determined with reference to EPA 6010D-2014 standard. For example, ICP-OES (elemental analysis-inductively coupled plasma optical emission spectrometry) testing can be used. First, the solid to be tested is dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. Further, the gaseous atoms to be tested are ionized and excited in a strong magnetic field, and then return to the ground state from the excited state; in the above process, energy is released and recorded as different characteristic spectral lines for quantitative analysis of trace elements. If the content of silicon-based particles is too low, it is difficult to significantly increase the overall gram capacity of the negative electrode active material. However, if the content of silicon-based particles is too high, it is easy to cause the overall expansion of the negative electrode active material during the charge and discharge cycle to exceed the adjustment limit of the core-shell composite structure of the negative electrode active material, affecting the cycle performance. By controlling the content of silicon-based particles in the negative electrode active material within a given range, the gram capacity and cycle stability of the negative electrode active material can be taken into account at the same time, thereby improving the energy density and cycle performance of the battery. Optionally, the content of silicon-based particles can be 30wt% to 50wt% based on the mass of the negative electrode active material. Controlling this condition can further take into account the gram capacity and cycle stability of the negative electrode active material, thereby improving the energy density and cycle performance of the battery.

[0063] In some embodiments of the present application, the porosity of the porous carbon skeleton layer 20 can be 40% to 70%, for example, 43%, 46%, 49%, 52%, 55%, 58%, 61%, 64%, 67%, etc., or can be a range composed of any of the above values. If the porosity of the porous carbon skeleton layer is too small, on the one hand, it is not conducive to improving the uniformity of dispersion of silicon-based particles in the porous carbon skeleton layer. On the other hand, the porous carbon skeleton layer has limited capacity for silicon-based particles, which not only easily reduces the amount of silicon deposited into the negative electrode active material, but also affects the restrictive effect of the porous carbon skeleton layer on the expansion of silicon-based particles. If the porosity of the porous carbon skeleton layer is too large, it will affect the overall strength of the negative electrode active material, and there is a risk of the overall structure collapsing. By controlling the porosity of the porous carbon skeleton layer within the given range, it is possible to take into account the overall strength of the negative electrode active material while improving the gram capacity and cycle stability of the negative electrode active material, thereby improving the energy density and cycle performance of the battery.

[0064] In some embodiments of the present application, the pore size of the porous carbon skeleton layer 20 can be 1 nm to 50 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, etc., or can be a range composed of any of the above values. If the pore size of the porous carbon skeleton layer is too small, it will not only increase the difficulty of silicon deposition inside the negative electrode active material, especially in the pores of the porous carbon skeleton layer, but also affect the restrictive effect of the porous carbon skeleton layer on the expansion of silicon-based particles; and if the pore size of the porous carbon skeleton layer is too large, it will affect the dispersion uniformity of silicon-based particles in the porous carbon skeleton layer. By controlling the pore size of the porous carbon skeleton layer within the given range, it can further help improve the gram capacity and cycle structural stability of the negative electrode active material, and improve the energy density and cycle performance of the battery.

[0065] In some embodiments of the present application, the Dv50 particle size of the negative electrode active material may be no greater than 10 μm (for example, no greater than 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, etc., or may be a range consisting of any of the above values); the Dv90 particle size of the negative electrode active material may be no greater than 20 μm (for example, no greater than 18 μm, 17 μm, 15 μm, 14 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm, 8 μm, 5 μm, etc., or may be a range consisting of any of the above values). The Dv50 particle size and Dv90 particle size of the negative electrode active material can be measured using a laser particle size analyzer (such as the Malvern Master Size 3000) in accordance with standard GB / T 19077.1-2016. If the particle size of the negative electrode active material is too large, it can easily hinder the transmission of active ions such as lithium ions, thereby affecting battery performance. By controlling the Dv50 and Dv90 particle sizes of the negative electrode active material within the given ranges, the conductivity of the negative electrode sheet can be improved, thereby enhancing the improvement in battery performance. Furthermore, the Dv50 particle size of the negative electrode active material can be no less than 1 μm, and the Dv90 particle size can be no less than 3 μm. Controlling the particle size of the negative electrode active material to meet the given conditions can help avoid excessive side reactions with the electrolyte caused by excessively small negative electrode active material particles, which can affect the improvement in battery performance.

[0066] In some embodiments of the present application, the thickness of the carbon coating layer 30 may be no greater than 1 μm, for example, it may be 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc., or it may be a range consisting of any of the above values. Regarding the thickness of the carbon coating layer, you can refer to JY / T010-1996, first polish the cross section of the negative electrode active material particles, observe their cross-sectional structure and confirm the regional components, and further obtain the coating thickness data. Specifically, you can observe the layered boundaries of the particle cross section through the polished cross-sectional morphology (CP morphology) of the negative electrode active material particles, and further use transmission electron microscopy to observe the thickness of the outermost coating layer of the particles. Select different positions of the particles in the center of the field of view to record the values ​​and calculate the average value. By setting a carbon coating layer, on the one hand, the volume expansion of silicon-based particles during the charge and discharge cycle can be further limited, and on the other hand, the conductivity of the negative electrode active material can be improved. If the thickness of the carbon coating layer is too large, on the one hand, it will affect the overall gram capacity of the negative electrode active material, and on the other hand, it will make the carbon coating layer play a greater role in embedding deions, which may easily lead to a faster capacity decay of the negative electrode active material, but will not be effective in improving the cycle stability of the negative electrode active material, affecting the power performance and cycle performance of the battery. If the thickness of the carbon coating layer is too small, it will affect the conductivity of the negative electrode active material and the effect of limiting the volume expansion of silicon-based particles during the charge and discharge cycle. By controlling the thickness of the carbon coating layer within a given range, the gram capacity of the negative electrode active material can be improved while improving the conductivity of the negative electrode active material and the volume expansion generated during the charge and discharge cycle. Optionally, the thickness of the carbon coating layer 30 can be no more than 0.2 μm, further no more than 0.1 μm, and further 0.05 μm to 0.08 μm. Further controlling the thickness of the carbon coating layer within the given range can further take into account the gram capacity of the negative electrode active material and its volume stability, conductivity and cycle life during the charge and discharge process.

[0067] In some embodiments of the present application, the particle size of the carbon core 10 can be 1 μm to 5 μm, for example, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, etc., or can be a range composed of any of the above values. The particle size of the carbon core can be obtained by observing the cross-sectional morphology of the particles, recording the particle size values ​​in the field of view, counting and calculating the average value. Based on the particle size of the negative electrode active material and the thickness of the carbon coating layer, controlling the particle size of the carbon core within the given range can further take into account the overall structural stability and gram capacity of the negative electrode active material, improve the conductivity of the negative electrode active material and the volume expansion generated during the charge and discharge cycle.

[0068] In some embodiments of the present application, the carbon core may include one or more of graphite, porous carbon, and mesophase carbon microbeads (MCMB). Selecting graphite, porous carbon, and mesophase carbon microbeads as carbon core materials is more conducive to the embedding and extraction of active ions (such as lithium ions), which is beneficial to improving cycle performance and fast charging capability. Among them, graphite may include artificial graphite and / or natural graphite, and artificial graphite may be selected. Porous carbon may include but is not limited to hard carbon, and hard carbon may include but is not limited to carbon black, pyrolytic carbon obtained by using resin (such as phenolic resin, etc.) and / or other organic polymers as precursors. Optionally, porous carbon may include hard carbon, which has a relatively high specific capacity compared to graphite and mesophase carbon microbeads. Using hard carbon as the carbon core is beneficial to further increase the gram capacity of the negative electrode active material and improve the battery energy density.

[0069] In some embodiments of the present application, it can be understood that the carbon precursor materials used to form the porous carbon skeleton layer and the carbon coating layer are not particularly limited, and those skilled in the art can flexibly select them according to actual needs. For example, the carbon precursor materials used to form the porous carbon skeleton layer and the carbon coating layer can independently include one or more of asphalt, resin, soluble starch, sucrose, glucose, and polyacrylate.

[0070] In some embodiments of the present application, reference is made to Figure 2 It is understood that the negative electrode active material may further include: a carbon core coating layer 11, which coats at least a portion of the outer surface of the carbon core 10 and is located within the accommodation space. The carbon core coating layer 11 may be distributed with an absorbing material. This arrangement can form a central thermal field on the surface of the carbon core during the preparation process, thereby enhancing the absorbing effect within the entire negative electrode active material. This can further promote the deposition of silicon within the entire negative electrode active material, reduce the silicon content on the surface of the negative electrode active material, and improve the negative electrode active material's ability to limit the volume expansion of silicon-based particles during charge and discharge cycles.

[0071] In some embodiments of the present application, the mass proportion of the absorbing material in the carbon core coating layer 11 can be greater than the mass proportion of the absorbing material in the porous carbon skeleton layer 20. In the preparation process of the negative electrode active material, the use of this structure helps the interior to be heated first, forming a state where the internal temperature is higher than the external temperature, which is conducive to the internal deposition of silicon first and gradually extending to the outside, and the silicon content forms a distribution that decreases from the inside to the outside. This can further allow more silicon to be deposited inside the porous carbon skeleton layer, so that the silicon deposition amount of the porous carbon skeleton layer on the side close to the carbon core is greater than the silicon deposition amount on the side close to the carbon coating layer. On the one hand, it is beneficial to further reduce the silicon content on the surface of the negative electrode active material, and on the other hand, it can further improve the improvement effect of the porous carbon skeleton layer and the carbon coating layer on the volume effect of silicon-based particles. Both are beneficial to improving the structural stability of the negative electrode active material during the cycle and improving the energy density and cycle performance of the battery.

[0072] In some embodiments of the present application, the thickness of the carbon core coating layer 11 may be no greater than 1 μm, for example, it may be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc., or it may be a range composed of any of the above values. The thickness of the carbon core coating layer can be obtained by vacuum cutting the material by an Ar ion beam, directly observing the cross-sectional morphology, identifying the layered material on the surface of the carbon core, testing the thickness of multiple points of the selected particles, and taking the average value. Controlling the thickness of the carbon core coating layer within the given range can promote the deposition of more silicon into the entire negative electrode active material, improve the cycle performance, and further take into account the overall gram capacity of the negative electrode active material. Optionally, the thickness of the carbon core coating layer 11 can be 0.3 μm to 1 μm, and can be further selected as 0.3 μm to 0.5 μm.

[0073] In some embodiments of the present application, the resistivity of the negative electrode active material at room temperature and 4Mpa pressure can be 100mΩ·cm to 10000mΩ·cm, for example, 100mΩ·cm, 120mΩ·cm, 150mΩ·cm, 200mΩ·cm, 250mΩ·cm, 300mΩ·cm, 350mΩ·cm, 400mΩ·cm, etc., or can be a range composed of any of the above values. The resistivity of the negative electrode active material can be measured using a powder resistivity & compaction density meter (such as the model PRCD2100, Yuanneng Technology). The specific operations may include: weighing a certain mass of sample at room temperature, adjusting the depth of the feeding chamber, adding the sample to the feeding chamber, applying pressure, manually collecting data, and recording the resistivity test results of the sample powder at different pressure points. In the embodiments of the present application, the resistivity of the sample powder under 4Mpa can be recorded and examined. Improving the ionic conductivity of the negative electrode active material can further improve the kinetic properties of the negative electrode active material. Optionally, the resistivity of the negative electrode active material at room temperature and 4 MPa pressure may be 100 mΩ·cm to 300 mΩ·cm. Controlling the resistivity of the negative electrode active material within the given range may further improve the kinetic performance on the basis of improving its volume effect and cycle performance.

[0074] The second aspect of the present application provides a method for preparing the negative electrode active material of the first aspect of the present application, comprising: mixing a carbon core material, a pore-forming agent, a carbon skeleton precursor material and a solvent to obtain a first mixed liquid; mixing an absorbing material with the first mixed liquid to obtain a second mixed liquid; spray-forming and fluidized drying the second mixed liquid to obtain composite particles; carbonizing and activating the composite particles to obtain skeleton particles with a porous carbon skeleton layer covering a carbon core; microwave heating the skeleton particles and introducing a gaseous silicon source to deposit silicon to obtain precursor particles; coating at least a portion of the outer surface of the precursor particles with a carbon coating layer to obtain a negative electrode active material.

[0075] Compared with the problem in the traditional heat treatment process mode of negative electrode active materials that "it is difficult to control the finished product state of silicon-carbon composite materials. Not only is the required temperature high and the sintering time long, and a large amount of energy is consumed, but the silicon therein is difficult to enter the interior of the carbon skeleton, resulting in the presence of many silicon grains on the surface of the material, causing serious expansion problems during the battery cycle, directly affecting the stability of the silicon-based material structure, and ultimately affecting the cycle performance." In the embodiments of the present application, by adding absorbing materials during the preparation process, the wave band of the absorbing material can be coupled with the basic fine structure of the material to generate heat to accurately heat a specific position of the material, and at the same time has the advantages of fast heating speed, high energy utilization, high heating efficiency, safety, hygiene and pollution-free. Moreover, compared with the heat transfer process from the outside to the inside in the traditional heating process, the use of the absorbing material's own heat and gradient-free overall heating method, as well as the rapid heating rate, can also effectively reduce the heating temperature and heating time, improve productivity, reduce costs, and improve product quality. More importantly, silicon can be deposited more deeply into the pores of the porous carbon skeleton layer, which can effectively limit the volume expansion of silicon and maintain the structural stability of silicon-based particles during long-term cycling. Furthermore, by further forming a carbon coating layer to obtain a composite core-shell structure, the layers of structure can interact with each other, further limiting the expansion of internal silicon-based particles and improving the cycle performance of the battery. In summary, the method for preparing negative electrode active materials in this application has at least the following beneficial effects: not only is the preparation process controllable, but also absorbing materials and microwave heating can be used for precise heating to achieve directional distribution of silicon and obtain negative electrode active materials of the expected structure. It is also beneficial to reduce the heating temperature and heating time during the preparation process, improve production efficiency, and reduce costs. At the same time, the prepared negative electrode active material can effectively limit the volume expansion of silicon and improve its structural stability during the cycle.

[0076] In some embodiments of the present application, a carbon core material (such as a hard carbon material, etc.) is mixed with a pore-forming agent, a carbon skeleton precursor material (such as a phenolic resin, etc.) and a solvent (such as a volatile solvent) to obtain a first mixed liquid. In this process, the carbon skeleton precursor material is mixed with the carbon core material, which is conducive to the formation of a porous carbon skeleton layer on the surface of the carbon core material in the later stage; optionally, the carbon skeleton precursor material and the pore-forming agent can be fully dissolved in the solvent, which is more conducive to the formation of a porous carbon skeleton layer on the surface of the carbon core material. The addition of the pore-forming agent can form a porous structure in the carbon skeleton layer formed later, which is conducive to the deposition of silicon in the later stage. It is understandable that there is no particular restriction on the specific types of pore-forming agents and solvents, as long as the relevant effects can be achieved. Those skilled in the art can flexibly select according to actual needs. For example, the pore-forming agent may include one or more of sodium chloride, potassium chloride, zinc chloride, sodium carbonate, potassium carbonate, zinc carbonate, zinc acetate, and ammonium acetate; the solvent includes but is not limited to water and / or alcohol. For example, the solvent may be a mixture of water and alcohol, that is, an alcohol solution, and the alcohol includes but is not limited to methanol, ethanol, ethylene glycol, polyethylene glycol, glycerol, isopropanol or a polyol. As some specific examples, the hard carbon material, phenolic resin, zinc chloride and ethanol aqueous solution can be fully mixed to obtain a first mixed solution. In addition, the relative amounts of the carbon core material and the carbon skeleton precursor material can be flexibly selected according to the actual conditions such as the core-shell structure size of the negative electrode active material to be obtained and the type of core-shell material, and are not particularly limited here. The relevant characteristics such as the type, particle size and type of carbon skeleton precursor material of the carbon core material have been explained in the previous section and will not be repeated here.

[0077] In some embodiments of the present application, the mass ratio of the pore-forming agent to the carbon skeleton precursor material can be (10-1): (1-100), for example, it can be 5 / 1, 3 / 1, 2 / 1, 1.5 / 1, 5 / 4, 1 / 1, 0.5 / 1, 2 / 5, 1 / 3, 1 / 2, 1 / 5, 1 / 10, 1 / 15, 1 / 20, 1 / 30, 1 / 40, 1 / 50, 1 / 60, 1 / 70, 1 / 80, 1 / 90, etc., or it can be a range composed of any of the above values. The amount of the pore-forming agent has a certain degree of influence on the porosity and pore size of the porous carbon skeleton layer finally formed. By controlling the amount of the pore-forming agent within the given range, it can be further beneficial to obtain a porous carbon skeleton layer with the expected porosity and micro-mesoporous structure. Optionally, the mass ratio of the pore-forming agent to the carbon skeleton precursor material can be (10-1): (2-10), such as 1: (2-10), and can further be (10-1): (2-5), such as 1: (2-5), which can further help improve the porosity and pore size of the carbon skeleton layer, optimize the distribution and deposition amount of silicon inside the negative electrode active material, and the overall structure of the negative electrode active material. The limiting effect of the expansion of silicon-based particles, improve the specific capacity and cycle performance of the negative electrode active material.

[0078] In some embodiments of the present application, the sum of the mass proportions of the pore-forming agent and the carbon skeleton precursor material in the first mixed solution can be 10 wt% to 70 wt%, for example, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, etc., or can be a range composed of any of the above values. In the actual preparation process, based on the structure of the negative electrode active material, the amount of the carbon core material is less than that of the carbon skeleton precursor material, and in order to facilitate the formation of the porous carbon skeleton layer, it is expected that the pore-forming agent and the carbon skeleton precursor material can be completely dissolved in the solvent. On this basis, by controlling the mass proportion of the pore-forming agent and the carbon skeleton precursor material in the first mixed solution to meet the given range, it is further beneficial to form a porous carbon skeleton layer on the surface of the carbon core. At the same time, the thickness of the porous carbon skeleton layer can be flexibly controlled by adjusting the mass proportion of the pore-forming agent and the carbon skeleton precursor material in the first mixed solution, thereby facilitating the preparation of a negative electrode active material with a desired structural size.

[0079] In some embodiments of the present application, during the process of mixing the absorbing material with the first mixed liquid to form the second mixed liquid, the particle size of the absorbing material can be controlled to be nanometer-sized. For example, Fe3O4 nanoparticles can be mixed with the first mixed liquid. For micrometer-sized carbon core materials, selecting a nanometer-sized absorbing material not only facilitates greater distribution of the absorbing material within the later-formed carbon skeleton layer but also improves its uniformity within the carbon skeleton layer. Furthermore, due to the small particle size of the nanoparticles, the surface activity of the absorbing material can be increased, thereby improving absorbing performance. It should be noted that the amount and type of the absorbing material have been described in connection with the negative electrode active material of the first aspect of the present application and will not be further elaborated here.

[0080] In some embodiments of the present application, before preparing the first mixed liquid, the following may be included: coating a carbon core coating layer on at least a portion of the outer surface of the carbon core material, wherein an absorbing material is distributed in the carbon core coating layer, such as by using a liquid phase method to attach an absorbing material or an absorbing material precursor material to the surface of the carbon core material, and combining it with relevant post-processing processes. For example, taking Fe3O4 as the absorbing material of the carbon core coating layer as an example, the carbon core material, a soluble alkali salt and water can be mixed to obtain an alkaline dispersion, which is then mixed with a soluble iron salt for hydrothermal reaction and heat treatment, so as to form a carbon core coating layer similar to a porous carbon skeleton layer structure on the surface of the carbon core material. Among them, after mixing the alkaline dispersion and the absorbing material or the absorbing material precursor material, post-processing can be performed according to actual conditions to obtain a carbon core coating layer similar to a porous carbon skeleton layer structure.

[0081] As some specific embodiments, when forming a carbon core coating, the carbon core material (such as hard carbon) can be ultrasonically dispersed in deionized water, and NaOH is added to adjust the mixture to a weak alkaline state, such as to a pH of about 9, or preferably 9±1. A trivalent iron salt and / or its hydrate (such as FeCl3·6H2O) is then added and ultrasonically dispersed at low temperature. After uniform dispersion, a reducing agent (such as hydrazine hydrate) is added for a hydrothermal reaction. The reaction product is then cooled, cleaned, and dried, and sintered under a nitrogen atmosphere to obtain a carbon core having a porous coating layer, wherein the porous coating layer includes the absorbing material Fe3O4. Sintering under a nitrogen atmosphere can effectively avoid or suppress the problem of the carbon core material being sensitive to oxygen at high temperatures and prone to oxidative ablation. In addition, compared to Fe3O4, using a soluble iron salt as a precursor to form the absorbing material Fe3O4 can further improve the uniformity of the absorbing material's dispersion on the carbon core surface and facilitate the production of nanoparticles of the absorbing material. It should be noted that the specific operating process and process parameters for controlling the formation of the carbon core coating layer on the surface of the carbon core material can be flexibly selected according to actual needs such as the type of absorbing material selected, and no special restrictions are imposed here; in addition, other relevant characteristics and effects of forming the carbon core coating layer including the absorbing material on the surface of the carbon core material have been described in the previous section and will not be repeated here.

[0082] In some embodiments of the present application, when a carbon core coating layer is formed on the surface of the carbon core material, the mass ratio of the absorbing material to the carbon core material can be 1:(5-20), for example, 1 / 6, 1 / 7, 1 / 8, 1 / 9, 1 / 10, 1 / 11, 1 / 12, 1 / 13, 1 / 14, 1 / 15, 1 / 16, 1 / 17, 1 / 18, 1 / 19, etc., or can be a range composed of any of the above values. Controlling the amount of the absorbing material in the carbon core coating layer within the given range can, on the one hand, ensure that there is sufficient absorbing material in the carbon core coating layer on the surface of the carbon core material, thereby promoting more silicon to deposit deep into the pores of the porous carbon skeleton layer. On the other hand, it is also beneficial to avoid the absorbing material from agglomerating into large molecules on the surface of the carbon core material when the amount is too much, thereby affecting the dispersion uniformity and absorbing effect of the absorbing material on the surface of the carbon core material, further promoting the uniform and directional deposition of silicon, and improving the cycle performance of the negative electrode active material.

[0083] In some embodiments of the present application, during the spray forming and fluidized drying of the second mixed liquid and the carbonization and activation of the obtained composite particles, the specific process conditions for spray forming, fluidized drying, carbonization and activation can be flexibly selected according to actual needs and are not particularly limited in the embodiments of the present application. For example, the second mixed liquid can be atomized and solidified into spherical particles under conditions not lower than 100°C, and then enter the fluidized drying step to stabilize the resin surface and reduce adhesion between the particles; the collected spherical particles are then sintered and carbonized, and then superheated steam is introduced to activate the sintered and carbonized products. Optionally, the temperature of the carbonization treatment can be 700°C to 1600°C; the temperature of the activation treatment can be 700°C to 1200°C, and the time can be selected from 0.5h to 10h. Controlling the carbonization and activation treatment conditions within the given range can further promote the formation of a porous carbon skeleton layer-coated carbon core composite structure.

[0084] In some embodiments of the present application, when the skeleton particles are subjected to microwave heating and a vapor-phase silicon source is introduced to deposit silicon, the frequency setting range and heating time of the microwave treatment can be flexibly selected according to the type of absorbing material. For example, the microwave frequency range can be set to 8.0GHz to 12.4GHz to achieve fixed-point heating, and its absorption rate range is 12dB to 16dB. The absorbing material absorbs wavelengths within this frequency band and converts them into heat energy, and the heating time is adjusted based on the amount of silicon deposited. Furthermore, the specific type of vapor-phase silicon source is not particularly limited here and can be flexibly selected according to actual needs, such as vapor-phase silane, etc.; in addition, the microwave heating time and the flow rate of the vapor-phase silicon source per unit time can be flexibly adjusted based on the expected amount of silicon deposited inside the negative electrode active material.

[0085] In some embodiments of the present application, when a carbon coating is formed on the surface of precursor particles obtained by microwave heating and depositing silicon, the precursor particles can be mixed with a carbon coating layer precursor material (such as asphalt, etc.) and heat-treated to obtain a negative electrode active material having a carbon coating layer coated on at least a portion of the outer surface of the precursor particles. Optionally, when forming the carbon coating layer, the heat treatment temperature can be 800°C to 1150°C and the time can be 1 hour to 5 hours. It should be noted that when the precursor particles are mixed with the carbon coating layer precursor material, the coating used can be asphalt, resin, or vapor-phase CVD coating, etc. The relative amounts of the precursor particles and the carbon coating layer precursor material can be flexibly selected based on the actual situation such as the structural size of the desired negative electrode active material, and are not particularly limited here.

[0086] The third aspect of the present application provides a negative electrode sheet, comprising: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application. It should be noted that the features and effects described in the negative electrode active material of the first aspect of the present application and the method for preparing the negative electrode active material of the second aspect of the present application are also applicable to the negative electrode sheet and will not be repeated here. In general, the negative electrode sheet has better structural stability during the charge and discharge cycle, which helps reduce safety risks such as battery bulging.

[0087] In some embodiments of the present application, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer provided on at least one layer of the negative electrode current collector. The active material in the negative electrode active material layer may be partially or entirely the negative electrode active material of the first aspect of the present application. In addition, in addition to the active material, the negative electrode active material layer may also include a conductive agent and a binder. The relative amounts of the active material, the conductive agent and the binder, and the content of the negative electrode active material of the first aspect of the present application in the active material, the specific types of the conductive agent and the binder, the material of the negative electrode current collector, the thickness of the negative electrode active material layer, the compaction density or the surface density, etc. can be flexibly selected according to actual conditions and are not particularly limited here.

[0088] A fourth aspect of the present application provides a battery comprising: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared using the method for preparing a negative electrode active material of the second aspect of the present application, and / or the negative electrode sheet of the third aspect of the present application. Optionally, the battery may be a secondary battery. Further optionally, the battery may be a lithium-ion battery.

[0089] Compared to conventional batteries, the negative electrode active material of the first aspect of this application, or the negative electrode active material prepared using the method for preparing a negative electrode active material of the second aspect of this application, or the negative electrode sheet of the third aspect of this application, can improve the battery's cycle performance and energy density. Furthermore, it is understood that the features and effects described for the negative electrode active material of the first aspect of this application, the method for preparing a negative electrode active material of the second aspect of this application, and the negative electrode sheet of the third aspect of this application are also applicable to the battery of the fourth aspect of this application and will not be further elaborated here.

[0090] In addition, in addition to the negative electrode sheet, the battery generally includes a positive electrode sheet, a diaphragm, an electrolyte and a shell assembly, and the electrode sheet, diaphragm and electrolyte are located in the accommodating cavity formed by the shell assembly. According to the type of battery, the shell assembly can be an aluminum-plastic film or a metal shell assembly, etc., and the metal shell assembly can include a square shell assembly and a cylindrical shell assembly. Regardless of the type of battery, as long as it includes the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application, and / or the negative electrode sheet of the third aspect of the present application, it can be understood as being included in the technical scope of the battery of the fourth aspect of the present application. The characteristics of the negative electrode sheet have been explained in the previous section and will not be repeated here; the structure and composition of the positive electrode sheet, the specific material or type of the diaphragm can be selected according to the general selection in the field, and the composition of the electrolyte can also be selected according to the general composition in the field. Those skilled in the art can flexibly select according to actual needs.

[0091] In some embodiments of the present application, the battery can be either a laminated battery or a wound battery, and the wound battery can be either a prismatic battery or a cylindrical battery. Depending on the battery type, the positive electrode sheet, the negative electrode sheet, and the separator can be stacked to form a laminate unit, or can be stacked and then wound to form a wound body.

[0092] In some embodiments of the present application, the battery may be a single cell or a battery module assembled from cells. A battery module may include multiple cells, the specific number of which may be adjusted based on the application and capacity of the battery module. Furthermore, the battery module may also include a packaging assembly having a storage space, which may include a bottom plate, side plates, and a cover plate.

[0093] In some embodiments of the present application, the above-mentioned battery modules may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0094] In addition, the present application also provides an electrical device, which includes: the negative electrode active material of the first aspect of the present application, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material of the second aspect of the present application, and / or the negative electrode sheet of the third aspect of the present application, and / or the battery of the fourth aspect of the present application.

[0095] The battery, such as a cell, a module or a pack, can be used as both a power source and an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), 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, satellites, and energy storage systems. Figure 3 It is understood that, as a specific example, the electrical device may be a vehicle.

[0096] The electrical device can select the specific type of battery according to its usage requirements, such as battery cells, battery modules or battery packs.

[0097] As an example, the electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of the battery, a battery pack or battery module may be used.

[0098] As another example, the electrical device may be a mobile phone, a tablet computer, or a laptop computer. The electrical device is generally required to be lightweight and thin, and may use a battery cell as a power source.

[0099] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0100] Example 1

[0101] (1) Preparation of positive electrode

[0102] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, and the solvent N-methylpyrrolidone (NMP) was added. The mixture was stirred under the action of a vacuum mixer until the system became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12 μm, dried at 115°C for 15 min, and cold pressed to obtain a single-side positive electrode active material layer with a thickness of 84 μm. The positive electrode sheet with a length of 605 mm and a film width of 88 mm was cut and the single-side coating weight was 20 mg / cm 2 The compaction density of the positive electrode active material layer is 2.4g / cm 3 .

[0103] (2) Preparation of negative electrode active materials and negative electrode sheets

[0104] (i) Synthesis of negative electrode active materials:

[0105] (a) 50 g of hard carbon with a particle size Dv50 of 3 μm was weighed and dispersed in 1000 g of anhydrous ethanol. 500 g of phenolic resin and 500 g of anhydrous zinc chloride (Aladdin) were then added and stirred until a uniform composite resin dilute solution was formed.

[0106] (b) 16 g of nano-Fe 3 O 4 powder (average particle size of 20 nm) was further added to the above solution, and a uniform dispersion was obtained after ultrasonic treatment for 30 min.

[0107] (c) The dispersion is further atomized and solidified into spherical resin particles at 150° C. through a spray forming process; and then fluidized drying is performed.

[0108] (d) The stabilized spherical resin particles were collected and carbonized at a temperature of 1000°C at a heating rate of 2°C / min for 2 h. The carbonized material was then activated by introducing superheated steam at 800°C at a water flow rate of 2 L / min for 2 h.

[0109] (e) The carbon material obtained by the activation treatment is heated by microwave heating. The microwave treatment frequency range is set to 8 GHz to 12.4 GHz. When the system temperature reaches 500°C, silane gas is introduced for thermal decomposition and silicon deposition treatment.

[0110] (f) The above-obtained material is further mixed with asphalt, wherein the amount of asphalt is 5 wt % of the mass of the material obtained in step (e), and heat-treated at 1150° C. for 1 h to obtain a silicon-carbon composite negative electrode active material comprising, from the inside to the outside, a carbon core, a porous carbon skeleton layer, and a carbon coating layer, wherein absorbing materials and silicon-based particles are distributed in the pores of the porous carbon skeleton layer.

[0111] (ii) Preparation of negative electrode sheet:

[0112] The negative electrode active material (25 wt% of the silicon-carbon composite negative electrode active material prepared in step (i) above + 75 wt% of artificial graphite), conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber latex (SBR) were fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry; the negative electrode slurry was coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8 μm, and after drying and other processes, a single-side negative electrode active material layer with a thickness of 50 μm and a single-side density of 8 mg / cm 2 The negative electrode sheet has a compaction density of 1.6 g / cm 3 .

[0113] (3) Preparation of electrolyte:

[0114] 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 fully dried lithium salt LiPF6 is dissolved in the above organic solvent. The concentration of the lithium salt is 1 mol / L, and the mixture is evenly mixed to obtain an electrolyte.

[0115] (4) Preparation of diaphragm

[0116] A polyethylene film with a thickness of 12 μm was selected as the separator.

[0117] (5) Preparation of secondary batteries

[0118] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator being placed between the positive and negative electrode sheets to serve as an isolation. Lithium foil is placed on the surface of the non-reactive area, and then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte at an injection coefficient of 4.2g / Ah. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery with a capacity of about 3Ah is obtained.

[0119] Example 2

[0120] The difference from Example 1 is that when performing (i) synthesis of the negative electrode active material, step (a) includes:

[0121] (a-1) 50 g of hard carbon with a particle size of 3 μm was ultrasonically dispersed in deionized water, and NaOH was added to adjust the pH to 9;

[0122] (a-2) Weigh 15 g of FeCl3·6H2O and pour it into the dispersion obtained in (a-1), and continue low-temperature ultrasonic dispersion.

[0123] (a-3) Pour 5 ml of hydrazine hydrate into the mixed solution obtained in (a-2), stir rapidly until uniform, pour into a hydrothermal reactor, and heat at 140°C for 8 h in a homogeneous reactor;

[0124] (a-4) Cooling to room temperature, the product in the kettle was washed with ethanol and deionized water, filtered, and then dried; the product was placed in a tubular furnace, and heated to 400°C at a rate of 10°C / min under a nitrogen atmosphere for 1 hour to obtain hard carbon coated with a wave-absorbing material layer.

[0125] (a-5) Weigh 50 g of the hard carbon obtained in step (a-4) and disperse it in 1000 g of anhydrous ethanol. Then, add 500 g of phenolic resin and 500 g of anhydrous zinc chloride (Aladdin) and stir until a uniform dilute composite resin solution is formed.

[0126] Comparative Example 1

[0127] The difference from Example 1 is that when (i) synthesizing the negative electrode active material, step (b) is not included, that is, the absorbing material Fe3O4 is not added when preparing the negative electrode active material.

[0128] Examples 3 to 8

[0129] The difference from Example 1 is that during the synthesis of the negative electrode active material (i), the amount of Fe3O4 powder added in step (b) is different. The Fe3O4 content of the absorbing material varies based on the mass of the resulting negative electrode active material, as detailed in Table 1.

[0130] Examples 9 to 11

[0131] The difference from Example 1 is that when performing (i) synthesis of the negative electrode active material, the average particle size of the absorbing material Fe3O4 used is different, see Table 1 for details.

[0132] Examples 12 to 14

[0133] The difference from Example 2 is that when performing (i) synthesis of the negative electrode active material, in step (a-2), the amount of FeCl3·6H2O used is different, and the thickness of the formed carbon core coating layer is different, see Table 1 for details.

[0134] Examples 15 to 19

[0135] The difference from Example 1 is that when (i) synthesizing the negative electrode active material, the type of absorbing material is different, see Table 1 for details.

[0136] Examples 20 to 23

[0137] The difference from Example 1 is that when performing (i) synthesis of the negative electrode active material, the amount of asphalt used to form the carbon coating layer is different, and the thickness of the formed carbon coating layer is different, see Table 1 for details.

[0138] Examples 24 to 27

[0139] The difference from Example 1 is that when performing (i) synthesis of the negative electrode active material, the amount of the pore-forming agent in step (a) is different. That is, in step (a), the amount of phenolic resin is controlled to be the same as in Example 1, and the amount of the pore-forming agent is changed to change the mass ratio of the two, as shown in Table 1.

[0140] Performance test of secondary batteries:

[0141] The secondary batteries prepared in the above embodiments and comparative examples were subjected to rate charging performance tests and cycle performance tests. The testing methods include:

[0142] 1. Cycle performance test of secondary batteries

[0143] Perform the following steps at 25°C: let stand for 5 minutes; discharge at 0.33C to 2.5V; let stand for 5 minutes; charge at 0.33C to 3.65V, charge at 3.65V to 0.05C; let stand for 5 minutes; discharge at 0.33C to 2.5V, and record the capacity at this time as C0'. After the secondary battery has been allowed to stand for 5 minutes, transfer it to a 45°C environment and perform a charge and discharge cycle according to the following steps: let stand for 20 minutes, charge at 1C to 3.65V, charge at 3.65V to 0.05C; let stand for 5 minutes; discharge at 1C to 2.5V; let stand for 5 minutes. Record the discharge capacity C of each cycle. m , m represents the number of cycles, until C m / C0'×100%=80%, record the value of m at this time as the cycle life of the secondary battery.

[0144] 2. Negative electrode thickness growth rate test

[0145] Take the prepared negative electrode sheet and test the thickness of the negative electrode sheet before winding. Measure at multiple points (with the help of a polymer film), take the average value, and record it as d0. After the secondary battery is assembled, let it stand at 25°C to allow the secondary battery to reach a constant temperature. Charge it to 3.65V at a constant current of 0.33C, and charge it at a constant voltage of 3.65V until the current is 0.05C. Then discharge it to 2.5V at 0.33C. After repeating this step for m cycles, charge it to 3.65V at a constant current of 0.33C, and charge it at a constant voltage of 3.65V until the current is 0.05C. Disassemble the battery, take out the negative electrode sheet, and after the surface of the negative electrode is dry, determine the point position of the negative electrode sheet before winding (with the help of a polymer film) and measure the thickness of the negative electrode sheet again at multiple points, take the average value, and record it as d m , the thickness growth rate of the negative electrode sheet after m cycles is (d m -d0) / d0×100%.

[0146] 3. Test of the thickness of the carbon coating layer and core coating layer in the negative electrode active material:

[0147] Refer to JY / T010-1996, including: 1. Sample preparation, including: a) Mixing sample preparation glue (PVDF dispersed in NMP, PVDF content 8 wt%) and negative electrode active material powder in a mass ratio of 1:5, then applying to copper foil, drying at 60°C for 30 minutes, and setting aside; b) Cutting the sample into 6mm x 6mm pieces with scissors and attaching it to the CP sample stage, with the sample protruding no more than 1mm from the stage; c) Cutting: Voltage: 7.5kV (efficiency and mass balance point), Time: 30 minutes; d) Gold plating of the sample, depending on the conductivity: Precursor: Approximately 60 seconds. 2. Parameter Settings: Mode: In-lens, Voltage: 10kV, Aperture: 30µm, Working Distance: 4.5mm. 3. Testing Procedure: Focusing on the interior of medium or large particles, with three shots at 50K, 30K, 10K, 5K, 3K, 1K, and 500K. 4. In the high-magnification image, select three particles in the central area of ​​the test area, select 5 reading sites for each particle, and then calculate the average value.

[0148] 4. XRD test: carried out in accordance with JIS K 0131-1996 (General rules for X-ray diffractometer measurement and analysis).

[0149] The negative electrode active materials and secondary batteries prepared in Examples 1 to 27 and Comparative Example 1 were tested under the same conditions. The test results are shown in Table 1. The negative electrode active materials prepared in Example 1 and Comparative Example 1 were tested by XRD. The results are shown in Table 1. Figures 4-5 .

[0150] Table 1 Differences and test results of Examples 1 to 27 and Comparative Example 1

[0151]

[0152] Results and Conclusions:

[0153] in, Figure 4 and Figure 5 The XRD patterns of the negative electrode active materials prepared in Example 1 and Comparative Example 1 are shown, respectively. The strong diffraction peaks shown in the figures are all signals of silicon. As can be seen from the figures, the silicon peak is more pronounced in the negative electrode active material prepared in Comparative Example 1. This is attributed to the presence of an absorber in the structure of the negative electrode active material prepared in Example 1, which facilitates the distribution of silicon within the carbon bulk, resulting in the silicon diffraction peak being covered by the carbon. In Comparative Example 1, silicon is not synthesized within the bulk phase and is exposed on the carbon surface, resulting in a more pronounced silicon peak.

[0154] Combining the test results of Examples 1 to 27, Comparative Example 1, and Table 1, it can be seen that the negative electrode active material prepared by the method of the above-mentioned embodiment of the present application has a good improvement effect on the negative electrode expansion and cycle performance; further, compared with forming only a carbon coating layer outside the porous carbon skeleton layer, forming a carbon core coating layer containing an absorbing material outside the carbon core is conducive to further improving the negative electrode expansion and cycle performance. On this basis, it is possible to further optimize the type, addition amount, and particle size of the absorbing material introduced into the negative electrode active material, as well as the thickness of the carbon coating layer outside the porous carbon skeleton layer, the thickness of the core coating layer, the relative amount of the pore-forming agent and the carbon skeleton precursor, etc., to further obtain better cycle stability and cycle life. Among them, from the overall point of view, as the mass proportion of the absorbing material in the negative electrode active material increases, its effect of improving the cycle stability and cycle life of the negative electrode active material first increases and then decreases. Considering the comprehensive cost, energy density and other aspects, the mass proportion of the absorbing material in the negative electrode active material can be selected to be no more than 10wt%; in addition, as the thickness of the carbon coating layer increases, although the volume expansion of the negative electrode active material can be significantly improved, the problem of decreased cycle life may occur. The reason for this is that an excessively thick carbon coating layer may cause the ion migration path to be too long, causing too many ions to be embedded and deintercalated only in the carbon coating layer, thereby causing the cycle life to decay rapidly. The thickness of the carbon coating layer can be selected to be no more than 1μm, and then no more than 0.1μm; in addition, when preparing the negative electrode active material, the relative amount of the pore former and the carbon skeleton precursor will also affect the improvement effect on the volume expansion and cycle life of the negative electrode active material to a certain extent. The reason for this may be that the relative amount of the two will affect the porosity of the porous carbon skeleton layer, thereby affecting the proportion of the absorbing material in the negative electrode active material and the cycle performance of the negative electrode active material.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode active material, characterized in that include: carbon core; A porous carbon skeleton layer, wherein the porous carbon skeleton layer has an accommodation space therein, and the carbon core is located in the accommodation space; a carbon coating layer, wherein the carbon coating layer is coated on at least a portion of the outer surface of the porous carbon skeleton layer; Wave-absorbing materials and silicon-based particles, the wave-absorbing materials and the silicon-based particles are independently distributed in the regions where the carbon core and the porous carbon skeleton layer are located; Based on the total mass of the absorbing material, the content of the absorbing material distributed in the porous carbon skeleton layer is not less than 90 wt %, and the content of the absorbing material distributed in the region where the carbon core is located is not more than 10 wt %.

2. The negative electrode active material according to claim 1, characterized in that Based on the mass of the porous carbon skeleton layer, the content of the absorbing material is 0.5wt% to 15wt%; and / or, Based on the mass of the negative electrode active material, the content of the absorbing material is no more than 10 wt %.

3. The negative electrode active material according to claim 2, characterized in that Based on the mass of the negative electrode active material, the content of the absorbing material is 3wt% to 8wt%.

4. The negative electrode active material according to claim 1, characterized in that The absorbing material meets at least one of the following conditions: an absorbing range of 5.2 GHz to 15.9 GHz, an absorbing bandwidth of 8.4 GHz to 10.7 GHz, and a particle size of 20 nm to 500 nm.

5. The negative electrode active material according to claim 1, characterized in that The absorbing material includes one or more of a metal element, an alloy, a metal oxide, a composite metal oxide, a carbide and a sulfide; and / or, The silicon-based particles include one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

6. The negative electrode active material according to claim 5, characterized in that The absorbing material includes one or more of iron, iron-containing alloys, and iron-containing oxides.

7. The negative electrode active material according to claim 1 or 5, characterized in that Based on the mass of the negative electrode active material, the content of the silicon-based particles is 30 wt% to 70 wt%.

8. The negative electrode active material according to claim 7, characterized in that Based on the mass of the negative electrode active material, the content of the silicon-based particles is 30 wt% to 50 wt%.

9. The negative electrode active material according to claim 1, characterized in that The porosity of the porous carbon skeleton layer is 40% to 70%; and / or the pore size of the porous carbon skeleton layer is 1 nm to 50 nm.

10. The negative electrode active material according to claim 1 or 9, characterized in that: At least one of the following conditions is met: The particle size of the carbon core is 1 μm to 5 μm; The thickness of the carbon coating layer is not greater than 1 μm; The Dv50 particle size of the negative electrode active material is not greater than 10 μm, and the Dv90 particle size is not greater than 20 μm.

11. The negative electrode active material according to claim 10, characterized in that The thickness of the carbon coating layer is no more than 0.2 μm.

12. The negative electrode active material according to claim 11, characterized in that The thickness of the carbon coating layer is no more than 0.1 μm.

13. The negative electrode active material according to claim 12, characterized in that The thickness of the carbon coating layer is 0.05 μm to 0.08 μm.

14. The negative electrode active material according to claim 1, characterized in that The carbon core comprises one or more of graphite, porous carbon, and mesophase carbon microspheres; and / or, The carbon precursor materials used to form the porous carbon skeleton layer and the carbon coating layer independently include one or more of pitch, resin, soluble starch, sucrose, glucose, and polyacrylate.

15. The negative electrode active material according to claim 14, characterized in that The porous carbon includes hard carbon.

16. The negative electrode active material according to claim 1, characterized in that Also includes: A carbon core coating layer is coated on at least a portion of the outer surface of the carbon core and is located in the accommodation space, and a wave absorbing material is distributed in the carbon core coating layer.

17. The negative electrode active material according to claim 16, characterized in that The mass proportion of the absorbing material in the carbon core coating layer is greater than the mass proportion of the absorbing material in the porous carbon skeleton layer.

18. The negative electrode active material according to claim 16 or 17, characterized in that The thickness of the carbon core coating layer is no more than 1 μm.

19. The negative electrode active material according to claim 18, characterized in that The thickness of the carbon core coating layer is 0.3 μm to 1 μm.

20. The negative electrode active material according to claim 19, characterized in that The thickness of the carbon core coating layer is 0.3 μm to 0.5 μm.

21. The negative electrode active material according to claim 1 or 17, characterized in that The resistivity of the negative electrode active material at room temperature and a pressure of 4 MPa is 100 mΩ·cm to 10000 mΩ·cm.

22. The negative electrode active material according to claim 21, characterized in that The resistivity of the negative electrode active material at room temperature and a pressure of 4 MPa is 100 mΩ·cm to 300 mΩ·cm.

23. A method for preparing the negative electrode active material according to any one of claims 1 to 22, characterized in that: include: Mixing a carbon core material, a pore-forming agent, a carbon skeleton precursor material, and a solvent to obtain a first mixed solution; mixing the absorbing material with the first mixed liquid to obtain a second mixed liquid; performing spray forming and fluidized bed drying on the second mixed liquid to obtain composite particles; Carrying out carbonization and activation treatment on the composite particles to obtain skeleton particles with a porous carbon skeleton layer covering a carbon core; heating the skeleton particles with microwaves and introducing a gaseous silicon source to deposit silicon to obtain precursor particles; A carbon coating layer is coated on at least a portion of the outer surface of the precursor particles to obtain a negative electrode active material.

24. The method according to claim 23, wherein Before preparing the first mixed liquid, the method further includes: coating a carbon core coating layer on at least a portion of the outer surface of the carbon core material.

25. The method according to claim 23 or 24, characterized in that At least one of the following conditions is met: The pore-forming agent includes one or more of sodium chloride, potassium chloride, zinc chloride, sodium carbonate, potassium carbonate, zinc carbonate, zinc acetate, and ammonium acetate; The total weight proportion of the pore-forming agent and the carbon skeleton precursor material in the first mixed solution is 10 wt% to 70 wt%; The mass ratio of the pore-forming agent to the carbon skeleton precursor material is (10-1): (1-100).

26. The method according to claim 25, characterized in that The mass ratio of the pore-forming agent to the carbon skeleton precursor material is (10-1): (2-10).

27. The method according to claim 26, characterized in that The mass ratio of the pore-forming agent to the carbon skeleton precursor material is (10-1): (2-5).

28. A negative electrode sheet, characterized in that: The negative electrode active material comprises the negative electrode active material according to any one of claims 1 to 22, and / or the negative electrode active material prepared by the method according to any one of claims 23 to 27.

29. A battery, characterized in that: The invention comprises the negative electrode active material according to any one of claims 1 to 22, and / or the negative electrode active material prepared by the method according to any one of claims 23 to 27, and / or the negative electrode sheet according to claim 28.

30. An electrical device, characterized in that: The invention comprises the negative electrode active material according to any one of claims 1 to 22, and / or the negative electrode active material prepared by the method according to any one of claims 23 to 27, and / or the negative electrode sheet according to claim 28, and / or the battery according to claim 29.

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