CN115832237A

CN115832237A - Negative active material, preparation method thereof, negative pole piece, battery and electric equipment

Info

Publication number: CN115832237A
Application number: CN202210504950.2A
Authority: CN
Inventors: 梁静爽; 滕国鹏
Original assignee: Jiangsu Contemporary Amperex Technology Ltd
Current assignee: Jiangsu Contemporary Amperex Technology Ltd
Priority date: 2022-05-10
Filing date: 2022-05-10
Publication date: 2023-03-21

Abstract

The application discloses a negative active material, a preparation method thereof, a negative pole piece, a battery and electric equipment, and relates to the field of batteries. The negative active material includes: the cathode active material comprises a silicon core, a silicon nitride layer coated on the surface of the silicon core and a carbon layer coated on the surface of the silicon nitride layer, wherein the particle size of the cathode active material is nano-scale. The cathode active material utilizes the matching of the structure, the material and the particle size, alleviates the current situations of poor rate capability and short service life of the existing silicon-based cathode active material, and has excellent cycle stability and rate capability.

Description

Negative active material, preparation method thereof, negative pole piece, battery and electric equipment

Technical Field

The application relates to the field of batteries, in particular to a negative active material, a preparation method thereof, a negative pole piece, a battery and electric equipment.

Background

Batteries have been widely used as the primary energy storage device in portable electronic products, electric vehicles, and grid storage systems. In recent years, research and development of negative electrode materials have become important in response to market demands for batteries having high energy density, high rate performance, and long cycle life. Silicon becomes a negative electrode material with certain competitiveness due to high specific capacity and moderate lithium intercalation potential, but the silicon-based negative electrode active material has the problems of poor rate capability and short service life when being practically applied to a battery.

Disclosure of Invention

An object of the embodiments of the present application is to provide a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery, and an electric device, which can solve the technical problems of poor rate performance and short service life of a silicon-based negative electrode active material.

In a first aspect, embodiments of the present application provide an anode active material, including: the silicon core, the silicon nitride layer coated on the surface of the silicon core and the carbon layer coated on the surface of the silicon nitride layer, wherein the particle size of the negative electrode active material is in a nanometer level.

According to the technical scheme of the embodiment of the application, the silicon nitride layer is coated on the surface of the silicon core, the volume expansion of silicon in the lithium insertion/removal process is inhibited, the cycle life of the silicon core is prolonged, and the conductivity of the silicon and the silicon nitride is poor, so that the conductivity of the cathode active material is remarkably improved through the outermost coated carbon layer, the electrochemical performance of the cathode active material is fully exerted, the rate performance of the cathode active material is improved, the particle size of the cathode active material is nanoscale, and compared with a micron-sized cathode active material, the lithium ion diffusion distance of the cathode active material is shorter, the specific surface area is larger, the lithium insertion sites are more, and the electrochemical performance of the cathode active material is better. In conclusion, the negative active material utilizes the matching of the structure, the material and the particle size, relieves the current situations of poor rate capability and short service life of the existing silicon-based negative active material, and has excellent cycle stability and rate capability.

In some embodiments, the particle size of the negative active material is 30nm to 90nm. The negative active material in the particle size range has the advantages of large specific surface area and more lithium insertion sites, and can improve the discharge specific capacity and the rate capability of the negative active material.

In some embodiments, the silicon nitride layer has a thickness of 6nm to 8nm. The thickness of the silicon nitride within the range is reasonable, the conductivity of lithium ions in the lithium intercalation process of the silicon nitride can be improved, if the silicon nitride layer is too thin, the limiting effect on the volume expansion of the silicon core during lithium intercalation is not good, the cycle life of the silicon core is shortened, and if the silicon nitride layer is too thick, the lithium intercalation capacity of the negative active material is influenced.

Optionally, the mass fraction of the silicon core is 65% to 85% based on 100% of the total weight of the silicon core and the silicon nitride layer. The content of silicon core in the range is reasonable, so that the negative active material has high specific capacity, and the silicon nitride layer is favorable for inhibiting the expansion of the negative active material and improving the cycle stability of the negative active material.

In some embodiments, the carbon layer is 15% to 20% by mass based on 100% by total weight of the anode active material. The carbon layer has reasonable proportion in the range, can effectively improve the conductivity of the negative active material, improve the rate capability of the negative active material and prolong the cycle life of the negative active material.

Optionally, the carbon layer comprises graphitic carbon.

Optionally, the carbon layer comprises graphene. The provision of the carbon layer containing graphene can further improve the conductivity of the anode active material.

In a second aspect, the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material in the above embodiments.

In a third aspect, the present application provides a battery comprising the negative electrode tab of the above embodiments.

In a fourth aspect, the present application provides a powered device comprising the battery of the above embodiments.

In a fifth aspect, the present application provides a method of preparing an anode active material, including: generating a direct current arc discharge between an anode and a cathode in a direct current arc reaction chamber having the cathode and the anode, with a silicon block as the anode, in an atmosphere of a reaction gas to generate a negative electrode active material; wherein the reaction gas can be converted into nitrogen atoms, hydrogen atoms and carbon atoms in a plasma state through high temperature generated by direct current arc discharge.

According to the technical scheme of the embodiment of the application, the direct current arc method is utilized to prepare the cathode active material with the nanoscale particle size and the silicon core/silicon nitride layer/carbon layer structure in one step, the preparation method is simple to operate and high in preparation efficiency, each layer of the cathode active material prepared by the direct current arc method is compact in structure, the silicon nitride layer is formed in situ and evenly covers the silicon core, and the carbon layer is formed in situ and evenly covers the silicon nitride layer, so that the formed cathode active material is uniform in particle size, and all the layers are stably connected together, the long-acting stability of the electrochemical performance of the cathode active material is further improved, and the cathode active material has a better cycle life.

In some embodiments, the discharge current of the DC arc is 10A-200A and the voltage is 5V-30V. By utilizing reasonable selection of discharge current and voltage, the method can generate stable direct current arc, and improves the yield on the premise of ensuring the safety of preparing the cathode active material. If the discharge current and voltage are too large, a safety hazard may be caused, and if the discharge current and voltage are too small, the yield of the negative electrode active material may be reduced.

Optionally, the spacing between the cathode and the anode is between 10mm and 25mm. Within the above distance range, a stable direct current arc can be generated, if the distance is too large, the direct current arc can be broken, the stable direct current arc cannot be formed, if the distance is too small, the cathode and the anode are adhered and short-circuited, equipment is easily damaged, and potential safety hazards are caused.

Optionally, the cathode is made of tungsten or graphite. The two materials are high temperature resistant, do not react with plasma gas, and avoid introducing impurities.

In some embodiments, the molar ratio of the carbon atoms to the nitrogen atoms is (1.5.

In some embodiments, the reaction gas is a mixture of methane, nitrogen and hydrogen, and the raw materials of the reaction gas are not only easy to ionize at high temperature generated by direct current arc, but also easy to obtain and low in cost, so that the preparation cost of the negative active material can be reduced.

Optionally, before the dc arc discharge, the total pressure of the reaction gas is 38kpa to 53kpa, and the partial pressure ratio of methane, nitrogen and hydrogen is 25: (3-18) 10, optionally 25: (10-15):10. Because the volume of the direct current arc reaction chamber is limited, the direct current arc discharge reaction is to introduce the reaction gas in advance, and the reaction gas is not additionally introduced in the reaction process, the direct current arc reaction chamber has enough reaction gas in the total pressure range, and the safety of the direct current arc discharge reaction is improved. Under the condition of partial pressure ratio under the total pressure condition, the ionization rate of methane and nitrogen during direct current arc discharge can reach 1, so that the method is favorable for controlling and obtaining the molar ratio of carbon atoms to nitrogen atoms after ionization, and controlling the thickness and the content of a formed carbon layer and a formed silicon nitride layer, and the hydrogen content is reasonable, and the method is favorable for promoting the ionization of methane and nitrogen.

In some embodiments, the method of making further comprises: after the direct current arc discharge reaction is finished, cooling for 3-5 h, introducing passivation gas for passivation treatment, and collecting the negative electrode active material attached to the inner wall of the direct current arc reaction chamber. The passivation treatment is used for passivating the surface energy of the negative active material, so that the negative active material can be collected safely.

Optionally, the passivation gas is air or oxygen with the pressure of 1kPa-2kPa, and the time of the passivation treatment is 6h-10h. The passivation treatment is easy to operate and low in cost.

Drawings

Various additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Moreover, like reference numerals are used to refer to like elements throughout. In the drawings:

FIG. 1 is a schematic structural view of a vehicle according to some embodiments of the present application;

FIG. 2 is an exploded view of a battery according to some embodiments of the present application;

fig. 3 is an exploded view of a battery cell according to some embodiments of the present disclosure;

FIG. 4 is a TEM image of a composite material obtained in example 1 of the present application;

FIG. 5 is an XRD pattern of a composite material prepared according to example 1 of the present application;

FIG. 6 is a graph showing cycle characteristics of a negative electrode of the composite material obtained in example 1 of the present application;

fig. 7 is a graph of coulombic efficiency of a negative electrode using the composite material prepared in example 1;

fig. 8 is a graph of rate performance of a negative electrode using the composite material prepared in example 1.

The reference numbers in the detailed description are as follows:

1000-a vehicle;

100-a battery; 200-a controller; 300-a motor;

10-a box body; 11-a first part; 12-a second part;

20-a battery cell; 21-end cap; 21 a-electrode terminal; 22-a housing; 23-an electrode assembly; 23 a-tab.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only used to illustrate the technical solutions of the present application more clearly, and therefore are only used as examples, and the protection scope of the present application is not limited thereby.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "including" and "having," and any variations thereof, in the description and claims of this application and the description of the above figures are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first", "second", and the like are used only for distinguishing different objects, and are not to be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary-secondary relationship of the technical features indicated. In the description of the embodiments of the present application, "a plurality" means two or more unless specifically defined otherwise.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is only one kind of association relationship describing an associated object, and means that three relationships may exist, for example, a and/or B, and may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.

In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two), and similarly, "plural sets" refers to two or more (including two), and "plural pieces" refers to two or more (including two).

In the description of the embodiments of the present application, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like, indicate the directions or positional relationships indicated in the drawings, and are only for convenience of description of the embodiments of the present application and for simplicity of description, but do not indicate or imply that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and thus, should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless otherwise explicitly stated or limited, the terms "mounted," "connected," "fixed," and the like are used in a broad sense, and for example, may be fixedly connected, detachably connected, or integrated; mechanical connection or electrical connection is also possible; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the embodiments of the present application can be understood by those of ordinary skill in the art according to specific situations.

At present, batteries are not only applied to energy storage power supply systems such as hydraulic power, fire power, wind power and solar power stations, but also widely applied to electric vehicles such as electric bicycles, electric motorcycles, electric automobiles and the like, and a plurality of fields such as military equipment and aerospace. As the field of application of batteries is continuously expanded, the market demand thereof is also continuously expanded.

The present inventors have noticed that the conventional negative electrode using silicon as a negative electrode active material has problems of low coulombic efficiency and low cycle life, mainly due to the fact that silicon is accompanied by volume change of up to 300% and unstable formation of a solid electrolyte interface film during the lithium intercalation/deintercalation process, thereby greatly reducing rate performance and cycle life thereof.

In order to solve the above problems, the inventors tried to coat silicon to form a core-shell structure, wherein silicon nitride is a high-performance structural ceramic with high temperature resistance and oxidation resistance, and can be used as an excellent semiconductor material in the fields of normal temperature and high temperature, so that silicon nitride is coated on silicon, silicon nitride is used to inhibit the expansion of silicon, and an unstable solid electrolyte interface film generated by directly exposing silicon outside is avoided, but both silicon and silicon nitride are semiconductor materials, so that the conductivity of the composite material is poor, and thus silicon nitride is further coated by a carbon layer to improve the conductivity of the negative active material, fully exert the electrochemical performance, improve the coulombic efficiency and prolong the cycle life.

However, the inventors found that the conventional method for preparing the anode active material with the improved structure is generally a two-step method: the preparation steps are complicated, the preparation difficulty of the silicon nitride is high, and the particle size of the prepared cathode active material is in the micron order, so that the electrochemical performance of the cathode active material is limited.

Therefore, the inventor further tries to prepare the cathode active material with the nano-scale particle size and the silicon core/silicon nitride layer/carbon layer structure by a direct current arc method in one step, the preparation method is simple to operate and high in preparation efficiency, and the cathode active material prepared by the direct current arc method is compactly and stably connected with each layer of structure, so that the long-term stability of the electrochemical performance of the cathode active material is improved, the particle size of the formed cathode active material is uniform and nano-scale, and the cycle stability and the rate capability of the cathode active material are improved.

The battery disclosed in the embodiment of the present application can be used in electric devices such as vehicles, ships or aircrafts, but not limited thereto. The power supply system with the battery and the like disclosed by the application can be used, so that the stability of the performance of the battery is favorably improved, and the service life of the battery is prolonged.

The embodiment of the application provides an electric device using a battery as a power supply, wherein the electric device can be but is not limited to a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, a battery car, an electric automobile, a ship, a spacecraft and the like. The electric toy may include a stationary or mobile electric toy, such as a game machine, an electric car toy, an electric ship toy, an electric airplane toy, and the like, and the spacecraft may include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

For convenience of description, the following embodiments take an example in which a power consuming apparatus according to an embodiment of the present application is a vehicle 1000.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a vehicle 1000 according to some embodiments of the present disclosure. The vehicle 1000 may be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile may be a pure electric automobile, a hybrid electric automobile, or a range-extended automobile, etc. The battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom or the head or the tail of the vehicle 1000. The battery 100 may be used for power supply of the vehicle 1000, for example, the battery 100 may serve as an operation power source of the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300, the controller 200 being configured to control the battery 100 to supply power to the motor 300, for example, for starting, navigation, and operational power requirements while the vehicle 1000 is traveling.

In some embodiments of the present application, the battery 100 may be used not only as an operating power source of the vehicle 1000, but also as a driving power source of the vehicle 1000, instead of or in part of fuel or natural gas, to provide driving power for the vehicle 1000.

Referring to fig. 2, fig. 2 is an exploded view of a battery 100 according to some embodiments of the present disclosure. The battery 100 includes a case 10 and a battery cell 20, and the battery cell 20 is accommodated in the case 10. The case 10 is used to provide a receiving space for the battery cells 20, and the case 10 may have various structures. In some embodiments, the case 10 may include a first portion 11 and a second portion 12, the first portion 11 and the second portion 12 cover each other, and the first portion 11 and the second portion 12 together define a receiving space for receiving the battery cell 20. The second part 12 may be a hollow structure with one open end, the first part 11 may be a plate-shaped structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a containing space; the first portion 11 and the second portion 12 may be both hollow structures with one side open, and the open side of the first portion 11 may cover the open side of the second portion 12. Of course, the box 10 formed by the first and second portions 11 and 12 may have various shapes, such as a cylinder, a rectangular parallelepiped, and the like.

In the battery 100, the number of the battery cells 20 may be multiple, and the multiple battery cells 20 may be connected in series or in parallel or in series-parallel, where in series-parallel refers to both series connection and parallel connection among the multiple battery cells 20. The plurality of battery cells 20 can be directly connected in series or in parallel or in series-parallel, and the whole formed by the plurality of battery cells 20 is accommodated in the box body 10; of course, the battery 100 may also be formed by connecting a plurality of battery cells 20 in series, in parallel, or in series-parallel to form a battery module, and then connecting a plurality of battery modules in series, in parallel, or in series-parallel to form a whole, and accommodating the whole in the case 10. The battery 100 may further include other structures, for example, the battery 100 may further include a bus member for achieving electrical connection between the plurality of battery cells 20.

Each of the battery cells 20 may be a primary battery or a secondary battery. In particular, the battery cell 20 is a lithium secondary battery including, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The battery cell 20 may be cylindrical, flat, rectangular parallelepiped, or other shape.

Referring to fig. 3, fig. 3 is an exploded schematic view of a battery cell 20 according to some embodiments of the present disclosure. The battery cell 20 refers to the smallest unit constituting the battery. As shown in fig. 3, the battery cell 20 includes an end cap 21, a case 22, an electrode assembly 23, and other functional components.

The end cap 21 refers to a member that covers an opening of the case 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 may be adapted to the shape of the housing 22 to fit the housing 22. Alternatively, the end cap 21 may be made of a material (e.g., an aluminum alloy) having a certain hardness and strength, so that the end cap 21 is not easily deformed when being impacted, and the battery cell 20 may have a higher structural strength and improved safety. The end cap 21 may be provided with functional components such as the electrode terminals 21 a. The electrode terminal 21a may be used to electrically connect with the electrode assembly 23 for outputting or inputting electric energy of the battery cell 20. In some embodiments, the end cap 21 may further include a pressure relief mechanism for relieving the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold value. The material of the end cap 21 may also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited in this embodiment. In some embodiments, insulation may also be provided on the inside of the end cap 21, which may be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. Illustratively, the insulator may be plastic, rubber, or the like.

The case 22 is an assembly for mating with the end cap 21 to form an internal environment of the battery cell 20, wherein the formed internal environment may be used to house the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 may be separate components, and an opening may be provided in the housing 22, and the opening may be covered by the end cap 21 to form the internal environment of the battery cell 20. Without limitation, the end cap 21 and the housing 22 may be integrated, and specifically, the end cap 21 and the housing 22 may form a common connecting surface before other components are inserted into the housing, and when it is necessary to enclose the inside of the housing 22, the end cap 21 covers the housing 22. The housing 22 may be a variety of shapes and sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the case 22 may be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 may be various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present invention is not limited thereto.

The electrode assembly 23 is a part in which electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 may be contained within the case 22. The electrode assembly 23 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is generally provided between the positive electrode sheet and the negative electrode sheet. The portions of the positive and negative electrode tabs having the active material constitute the body portions of the electrode assembly, and the portions of the positive and negative electrode tabs having no active material each constitute a tab 23a. The positive electrode tab and the negative electrode tab may be located at one end of the main body portion together or at both ends of the main body portion, respectively. During the charge and discharge of the battery, the positive and negative active materials react with the electrolyte, and the tab 23a is connected to the electrode terminal to form a current loop.

According to some embodiments of the present application, there is provided an anode active material including: the cathode material comprises a silicon core, a silicon nitride layer coated on the surface of the silicon core, and a carbon layer coated on the surface of the silicon nitride layer, wherein the particle size of the cathode active material is in a nanometer level.

Namely, the cathode active material is of a core-shell structure, wherein a silicon core/a silicon nitride layer/a carbon layer are sequentially arranged from inside to outside.

The silicon nucleus refers to pure silicon or particles which take silicon as a main body and contain doping elements, wherein the silicon as the main body refers to the fact that the content of silicon in the silicon nucleus is larger than that of the doping elements.

The silicon nitride layer is pure silicon nitride or a coating layer which takes silicon nitride as a main body and contains doping elements, wherein the silicon nitride as the main body means that the content of the silicon nitride in the silicon nitride layer is greater than that of the doping elements.

The carbon layer is pure carbon or a coating layer which takes carbon as a main body and contains doping elements, wherein the carbon as the main body means that the content of the carbon in the carbon layer is greater than that of the doping elements.

The nano-scale particle size of the negative electrode active material means that the particle size of the negative electrode active material is less than or equal to 100nm.

According to the technical scheme of the embodiment of the application, the silicon nitride layer is coated on the surface of the silicon core, the volume expansion of silicon in the lithium insertion/removal process is inhibited, the electrochemical cycle life of the silicon core is prolonged, and the conductivity of the negative active material is remarkably improved through the carbon layer coated on the outermost layer due to the poor conductivity of the silicon and the silicon nitride, so that the electrochemical performance of the negative active material is fully exerted, and the particle size of the negative active material is in a nanometer level. In conclusion, the negative electrode active material utilizes the matching of the structure, the material and the particle size, and alleviates the current situations of poor rate capability and short cycle life of the conventional silicon-based negative electrode active material.

According to some embodiments of the present application, optionally, the negative active material has a particle size of 30nm to 90nm.

The negative active material in the particle size range has the advantages of large specific surface area and more lithium insertion sites, so that the electrochemical performance is good, and the coulomb efficiency and the cycle life of the negative active material can be improved.

As an example, the particle diameter of the anode active material includes, for example, but is not limited to, any one value or a range between any two values of 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, and the like.

According to some embodiments of the application, the silicon nitride layer is optionally 6nm to 8nm thick.

Since the negative electrode active material is in the form of particles, the thickness of the silicon nitride layer refers to the thickness of the silicon nitride layer in the radial direction of the negative electrode active material.

The thickness of the silicon nitride within the range is reasonable, the conductivity of lithium ions in the lithium intercalation process of the silicon nitride can be improved, if the silicon nitride layer is too thin, the limiting effect on the volume expansion of silicon nuclei during lithium intercalation is not good, the electrochemical cycle life of the silicon nuclei is reduced, and if the silicon nitride layer is too thick, the lithium intercalation capacity of the negative active material is influenced.

By way of example, the thickness of the silicon nitride layer includes, but is not limited to, any one of 6nm, 6.5nm, 7nm, 7.2nm, 7.5nm, 8nm, and the like, or a range between any two values, for example.

According to some embodiments of the present application, the mass fraction of the silicon nuclei is optionally 65% to 85% based on 100% by weight of the total of the silicon nuclei and the silicon nitride layer.

The silicon core content in the range is reasonable, so that the negative active material has better specific capacity, and the silicon nitride layer is favorable for inhibiting the expansion of the negative active material.

By way of example, the mass fraction of silicon nuclei is, for example, any one value or a range between any two values including, but not limited to, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and 100%, etc., based on 100% of the total weight of the silicon nuclei and the silicon nitride layer.

According to some embodiments of the present application, optionally, the carbon layer has a mass fraction of 15% to 20% based on 100% of the total weight of the anode active material.

The carbon layer is reasonable in proportion in the range, the conductivity of the negative active material can be effectively improved, the rate capability of the negative active material is improved, and the coulomb efficiency of the negative active material is enhanced.

As an example, the mass fraction of the carbon layer includes, for example, but is not limited to, any one value or a range between any two values of 15%, 16%, 17%, 18%, 19%, 20%, and the like, based on 100% by weight of the total anode active material.

According to some embodiments of the present application, optionally, the carbon layer comprises graphitic carbon, further optionally, the carbon layer comprises graphene.

The provision of the carbon layer containing graphene can further improve the conductivity of the anode active material.

According to some embodiments of the present application, the present application further provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material according to any of the above aspects.

According to some embodiments of the present application, there is also provided a battery comprising the negative electrode tab of any of the above aspects.

According to some embodiments of the present application, there is also provided an electric device, including the battery of any of the above aspects, and the battery is used for providing electric energy for the electric device.

The powered device may be any of the aforementioned battery-powered devices or systems.

According to some embodiments of the present application, there is provided a method of preparing an anode active material, including: generating a direct current arc discharge between an anode and a cathode in a direct current arc reaction chamber having the cathode and the anode, with a silicon block as the anode, in an atmosphere of a reaction gas to generate a negative electrode active material; wherein the reaction gas can be converted into nitrogen atoms, hydrogen atoms and carbon atoms in a plasma state through high temperature generated by direct current arc discharge.

The direct current arc reaction is carried out in a direct current arc reactor, the direct current arc reactor is provided with a cooling system and used for reducing the temperature of the inner wall of the reaction chamber during the direct current arc reaction, safety accidents are avoided, the prepared cathode active material is convenient to attach to the inner wall of the direct current arc reaction chamber, the direct current arc reactor can be directly purchased from the market, and limitation is not made herein, and the direct current arc reaction chamber refers to a cavity for carrying out direct current arc discharge by the direct current arc reactor.

The silicon block is a solid which is made of silicon and has a certain shape and is obtained in a non-stacking form, the shape of the silicon block can be regular or irregular cake, sheet, block, rod and the like, and the silicon block can be selected by a person skilled in the art according to actual needs and is not specifically limited herein.

Arcing refers to the phenomenon in which the cathode and anode are maintained in electrical conduction by gaseous charged particles, such as electrons or ions, at a certain voltage.

It can be understood that the silicon block is used as the anode, and therefore in practical use, the silicon block is placed on a conductive metal seat (for example, a copper seat) electrified in the direct current arc reaction chamber, and a loop can be formed between the conductive metal seat and the cathode through an arc, so that the silicon block is used as the anode.

The direct current arc discharge reaction refers to: the arc flame of the direct current arc generated between the cathode and the anode generates high temperature reaching thousands of degrees centigrade, the arc flame of the direct current arc is used as a heat source for supplying high-energy growth substances, the arc flame is used as the center of the heat source, the heat source has a certain temperature gradient from inside to outside, the heat source gradually reduces from inside to outside, and the growth process of the cathode active material is completed in the heat source region. Specifically, firstly, the silicon block is evaporated into gaseous silicon atoms inside the arc flame, the reaction gas can be converted into nitrogen atoms, hydrogen atoms and carbon atoms in a plasma state through high temperature generated by direct current arc discharge, and the nucleation temperature of silicon is greater than the nucleation temperature of silicon nitride and greater than the nucleation temperature of carbon, so that when the temperature of a heat source is reduced to the melting point of silicon (about 1414 ℃), silicon nanoparticles begin to grow by spontaneous nucleation and flow to the heat source temperature along with silicon vapor and the like to be reduced to a lower nitridation temperature (about 1200 ℃), at the moment, silicon nitride begins to carry out heterogeneous nucleation on the surfaces of the silicon nanoparticles to grow into a silicon nitride coating layer, and continues to flow to a flame core region far away from the arc flame, the temperature continues to be reduced to the nucleation temperature of the carbon atoms, so that the carbon atoms begin to grow into a carbon layer on the surface of the silicon nitride, and finally, the negative electrode active material with a silicon core-shell structure/silicon nitride layer/silicon layer/carbon layer core-shell structure and a nano-size is formed.

Among them, hydrogen atoms are nitrogen atoms and carbon atoms for promoting the reaction gas to be ionized into a plasma state.

The plasma refers to: and ionized gaseous matter comprising positive and negative ions produced by ionizing atoms and radicals with some electrons being deprived.

According to the technical scheme of the embodiment of the application, the direct current arc method is utilized to prepare the cathode active material with the nano-scale particle size and the silicon core/silicon nitride layer/carbon layer structure in one step, the preparation method is simple to operate and high in preparation efficiency, and each layer of the cathode active material prepared by the direct current arc method is compact in structure, high in particle size sphericity and uniform in particle size distribution.

The silicon nitride layer can buffer the stress generated by volume expansion of the silicon core in the circulation process, the stress reacts with electrolyte to generate a lithium nitride phase, the lithium nitride phase exists in a solid electrolyte interface film and can promote the transmission of lithium ions, the carbon coating layer can further improve the stability of the integral structure of the composite material and the large-current charging and discharging capacity of an electrode, and the layers can be stably connected together by utilizing the in-situ introduction of the silicon nitride layer and the carbon layer, the coating is more uniform, the particle size is more uniform, so the long-acting stability of the electrochemical performance of the cathode active material can be further improved, and the cathode active material has better cycle life.

It is understood that the reaction gas is a gaseous organic compound or mixture of carbon, hydrogen and nitrogen, optionally a gaseous organic compound or mixture of carbon, hydrogen and nitrogen only, in order to avoid introducing impurities.

Illustratively, the carbon atoms and hydrogen atoms may be provided by at least one of alkanes, alkynes, and alkenes, and for cost and ease of ionization, the carbon atoms and hydrogen atoms may be provided by C _1-4 Alkane, C _1-4 Alkyne and C _1-4 At least one of the olefins providing, optionally, carbon and hydrogen atoms, may be represented by C _1-4 Alkane, C _1-2 At least one of the alkynes. The hydrogen atoms may also be provided by hydrogen gas. The nitrogen atom may be provided by at least one of nitrogen gas and ammonia gas.

It should be noted that, when hydrogen atoms are at least partially provided by hydrogen, the hydrogen is firstly introduced and then other gases are introduced in the process of introducing the reaction gas into the direct current arc reaction chamber because the hydrogen is active.

Alternatively, the starting purity of the reaction gas is > 99.9% in order to avoid impurity interference.

To avoid impurity interference, the reaction gas may be aligned before being introduced into the DC arc reaction chamberThe flow-arc reaction chamber is evacuated, e.g. to a vacuum of 10 ^-2 -10 ^-5 pa。

Wherein, the cathode and the anode can be transversely arranged in the direct current arc reaction chamber, and in order to facilitate the placement of the silicon block, optionally, the cathode and the anode are vertically arranged in the direct current arc reaction chamber, and the cathode is positioned above the anode.

For arc stabilization, optionally, the end of the cathode facing the anode is tapered.

In some embodiments, optionally, the discharge current of the DC arc is 10A-200A and the voltage is 5V-30V.

By utilizing reasonable selection of discharge current and voltage, the method can generate stable direct current arc, and improves the yield on the premise of ensuring the safety of preparing the cathode active material. If the discharge current and voltage are too large, a safety hazard may be caused, and if the discharge current and voltage are too small, the yield of the negative electrode active material may be reduced.

By way of example, the discharge current of the dc arc includes, but is not limited to, any one or a range between any two of 10A, 30A, 50A, 75A, 100A, 125A, 150A, 175A, and 200A, etc.

By way of example, the voltage of the dc arc includes, but is not limited to, any one value or a range between any two values of 5V, 7V, 10V, 15V, 20V, 25V, 30V, and the like.

In some embodiments, optionally, the spacing between the cathode and the anode is 10mm-25mm.

The distance between the cathode and the anode refers to the shortest distance between the cathode and the anode, that is, when the end of the cathode facing the anode is a conical surface, the distance between the cathode and the anode refers to the distance between the tip of the cathode and the end face of the anode facing the tip.

Within the above distance range, a stable direct current arc can be generated, if the distance is too large, the direct current arc can be broken, the stable direct current arc cannot be formed, if the distance is too small, the cathode and the anode are adhered and short-circuited, equipment is easily damaged, and potential safety hazards are caused.

It can be understood that, in practical use, the distance between the cathode and the anode is adjustable, so that a proper distance is selected for the direct current arc discharge reaction.

By way of example, the spacing between the cathode and anode includes, but is not limited to, any one or a range of any two of 10mm, 12mm, 15mm, 18mm, 20mm, 23mm, 25mm, and the like.

In some embodiments, the cathode is made of tungsten or graphite.

The two materials are high temperature resistant, do not react with plasma gas, and avoid introducing impurities.

In some embodiments, optionally, the molar ratio of carbon atoms to nitrogen atoms is (1.5.

The carbon atoms and the nitrogen atoms are nitrogen atoms and carbon atoms which are converted into a plasma state by a high temperature generated by the direct current arc discharge of the reaction gas.

The carbon atoms and the nitrogen atoms are reasonable in proportion, and the thickness and the content of the formed carbon layer and the silicon nitride layer are favorably controlled. Since the hydrogen atom functions to promote ionization of the reaction gas, the content thereof is not limited herein.

By way of example, the molar ratio of carbon atoms to nitrogen atoms includes, but is not limited to, any one or a range between any two of 1.5.

In some embodiments, optionally, the reaction gas is a mixture of methane, nitrogen, and hydrogen.

The raw materials of the reaction gas are easy to ionize at high temperature generated by direct current arc, are easy to obtain and low in cost, and the preparation cost of the cathode active material can be reduced.

In some embodiments, optionally, the total pressure of the reaction gas before the dc arc discharge is 38kpa to 53kpa, and the partial pressure ratio of methane, nitrogen, and hydrogen is 25: (3-18):10.

The partial pressure ratio refers to the pressure that a component in a gas mixture develops when the component occupies the same volume of the gas mixture at the same temperature.

Because the volume of the direct current arc reaction chamber is limited, the direct current arc discharge reaction is to introduce the reaction gas in advance, and the reaction gas is not additionally introduced in the reaction process, the direct current arc reaction chamber has enough reaction gas in the total pressure range, and the safety of the direct current arc discharge reaction is improved. Under the partial pressure ratio condition under the total pressure condition, the ionization rate of methane and nitrogen during direct current arc discharge can reach 1, so that the molar ratio of carbon atoms to nitrogen atoms after ionization can be controlled, the thickness and the content of a formed carbon layer and a formed silicon nitride layer can be controlled, and meanwhile, the hydrogen content is reasonable, and the ionization of methane and nitrogen can be promoted. By way of example, the partial pressure ratio of methane, nitrogen and hydrogen before the dc arc discharge includes, but is not limited to, in order of 25.

Optionally, before the dc arc discharge, the partial pressure ratio of methane, nitrogen and hydrogen is 25: (10-15):10.

By way of example, the total pressure of the reactant gases prior to the DC arc discharge may include, but is not limited to, any one or a range of any two values of 38kPa, 40kPa, 43kPa, 45kPa, 47kPa, 49kPa, 50kPa, 53kPa, and the like.

In some embodiments, optionally, the preparation method further comprises: after the direct current arc discharge reaction is finished, cooling for 3-5 h, introducing passivation gas for passivation treatment, and collecting the negative electrode active material attached to the inner wall of the direct current arc reaction chamber.

The passivation treatment is used for passivating the surface energy of the negative active material, so that the negative active material can be collected safely.

It should be noted that the water cooling system is turned on during the cooling process to lower the temperature and activity of the product obtained after the dc arc discharge reaction.

In some embodiments, optionally, the passivation gas is air or oxygen at 1kPa to 2kPa, and the time of the passivation treatment is 6h to 10h.

The passivation treatment is easy to operate, low in cost and short in passivation time, the surface energy of the negative active material is still large, and potential safety hazards exist.

By way of example, the pressure of the passivation gas includes, but is not limited to, any one of, or a range between any two of, 1kPa, 1.2kPa, 1.5kPa, 1.7kPa, 2kPa, and the like.

By way of example, the time of the passivation process includes, but is not limited to, any one of 6h, 8h, 9h, 10h, etc., or a range between any two values.

Alternatively, after the passivation treatment, the anode active material may be sieved according to actual requirements to obtain an anode active material with a specific particle size.

Some specific examples are listed below to better illustrate the present application.

In the following examples and comparative examples, the DC arc reactor was model NP-450 from North space vacuum technology, inc., shenyang, liaoning.

Examples and comparative examples

1) Placing a silicon block with the purity of more than 99.9 percent on an anode copper seat of a direct current arc reactor to be used as an anode, wherein a cathode is positioned above the anode, one end of the cathode facing the anode is conical, and the distance between the anode and the cathode is adjusted as shown in table 1.

2) The reaction chamber was evacuated to about 10 deg.f ^-2 Pa, the reaction gas shown in Table 1 was introduced.

3) And (3) starting a cooling system of the direct current arc reactor, switching on a power supply, starting an arc, adjusting the current and the distance between two electrodes corresponding to each embodiment according to data shown in table 1, and stabilizing the arc, so that the generated cathode active material is deposited on the inner wall of the direct current arc reactor.

4) Filling passivation gas into the direct current arc reaction chamber, and performing passivation treatment to collect powder to obtain the silicon core/silicon nitride layer/carbon layer composite material with the core-shell structure.

And (3) performance testing:

(1) The composite materials prepared in each example and comparative example were dispersed in ethanol as a dispersant, and after 30 minutes of ultrasonic treatment, the samples were put into a laser particle size (witness Bettersize 2600) apparatus to test the D50 particle size of the negative active material.

(2) The composite materials prepared in each example and comparative example are respectively dispersed in ethanol serving as a dispersing agent, a dilute suspension is formed after ultrasonic treatment for 40 minutes, a small amount of suspension is dropped on a copper micro-grid attached with a carbon film by using a capillary, the copper micro-grid is dried for 2 hours at room temperature and then placed in a sample rod of a transmission electron microscope (Tecnai G2F 30S-TWIN) for observation, TEM images of each example and the composite material prepared in the comparative example are obtained, and the thickness of a silicon nitride layer is measured according to the TEM images.

(3) And (3) electrochemical performance testing:

respectively taking the silicon/silicon nitride layer/carbon layer composite materials prepared in the embodiments and the comparative examples as negative active materials, mixing the negative active materials with a conductive agent Super P and a binder CMC + SBR according to a mass ratio of 8; and then drying the negative electrode diaphragm obtained by tabletting in a constant-temperature drying oven at 110 ℃ for 24h, then carrying out vacuum drying at 80 ℃ for 12h, punching into a pole piece with the diameter of 14mm by using a punch, and transferring into a vacuum glove box for later use.

The assembly of the CR2025 type button lithium ion battery takes a metal lithium sheet as a positive electrode, takes (LiPF 6/EC + DEC) as electrolyte, takes the pole piece with the diameter of 14mm as a negative electrode piece, adopts a microporous polypropylene film (PP) as a diaphragm, and all operations are carried out in a glove box; it is referred to as a button-type lithium ion battery.

2) Electrochemical performance tests were performed on button type lithium ion batteries manufactured in examples and comparative examples using a wuhan blue electricity (lance 2001A) electrochemical performance tester, with a voltage range of 0.01 to 2.00V (vs. Li/Li +), a current density of 0.1C to 2C (1C: 1000 mA/g).

The specific discharge capacity after 200 cycles of charge and discharge under the charge and discharge conditions of 0.1C and the coulombic efficiency after 200 cycles were measured.

And (3) measuring the discharge specific capacity of the manufactured button lithium ion battery under 2C (1C.

The results are shown in Table 2.

TABLE 1 EXAMPLES 1-20 AND COMPARATIVE EXAMPLES 1-9 test parameters

TABLE 2 test results

Taking the total weight of the silicon core and the silicon nitride layer as M, the mass fraction of the silicon core in Table 2 refers to the mass fraction of the silicon core in M. The mass fraction of the carbon layer refers to the mass fraction of the carbon layer in the composite material.

Comparative examples 1 to 2 and examples 1 to 3 are different only in that the distance between the cathode and the anode is changed, and it can be seen from comparative examples 1 to 2 and examples 1 to 3 that the distance has no influence on the D50 particle diameter of the composite material and the thickness of the silicon nitride layer. The distance between the cathode and the anode in the embodiments 1 to 3 is 10mm to 25mm, the distance in the comparative example 1 is less than 10mm, and the cathode and the anode are easy to adhere in the powder preparation process; the distance in the comparative example 2 is more than 25mm, and the cathode and the anode are easy to break the arc in the powder preparation process. It can be seen from comparison between examples 1 to 3 and comparative examples 1 to 2 that the cycle performance and rate performance of the composite materials of examples 1 to 3 are superior to those of comparative examples 1 to 2 under the condition that the D50 particle diameter and the thickness of the silicon nitride layer of the composite materials prepared in examples 1 to 3 and comparative examples 1 to 2 are the same.

Comparative examples 3 to 4 and examples 1 and 4 to 6 differ only in the change in discharge current. It can be seen from comparative examples 3 to 4 and examples 1 and 4 to 6 that the discharge current had no effect on the D50 particle diameter of the composite material and the thickness of the silicon nitride layer. The discharge current in examples 1, 4-6 was 10A-200A, the discharge current in comparative example 3 was less than 10A, the current was too low, and the arc was unstable; the discharge current in comparative example 4 is more than 200A, and the current is too large, which affects safety. As can be seen from comparison of examples 1, 4 to 6 and comparative examples 3 to 4, the cycle performance and rate capability of the composite materials of examples 1 and 4 to 6 are better than those of comparative examples 3 to 4 under the condition that the D50 particle diameter and the thickness of the silicon nitride layer of the composite materials prepared in examples 1, 4 to 6 and comparative examples 3 to 4 are the same.

Comparative examples 5 to 6 and examples 1 and 7 to 9 differ only in the change in voltage. It can be seen from comparative examples 5 to 6 and examples 1 and 7 to 9 that the voltage has no influence on the D50 particle diameter of the composite material and the thickness of the silicon nitride layer. The voltage in examples 1, 7-9 is 5V-30V, the voltage in comparative example 5 is less than 5V, the voltage is too small, and the arc is unstable; the voltage in comparative example 6 is more than 30V, and the voltage is too large, which affects safety. As can be seen from comparison of examples 1, 7 to 9 and comparative examples 5 to 6, the cycle performance and rate capability of the composites of examples 1 and 7 to 9 were superior to those of comparative examples 5 to 6 under the condition that the D50 particle diameter and the thickness of the silicon nitride layer of the composites prepared in examples 1, 7 to 9 and comparative examples 5 to 6 were the same.

Comparative examples 7 to 8 and examples 1 and 10 to 14 differ only in the amounts of nitrogen, methane and hydrogen added. The total addition amount of the reaction gases (nitrogen, methane and hydrogen) in examples 1, 10-14 was 38kpa-53kpa, and the total addition amount of the reaction gases in comparative example 7 and comparative example 8 was within the above range, however, the ratio of the addition amounts (partial pressure ratio) of methane and nitrogen in examples 1, 10-14 was 25 (3-18), resulting in a theoretical carbon atom to nitrogen atom molar ratio of (1.5. In comparative example 8, the ratio of the addition amounts (partial pressure ratio) of methane and nitrogen is 25.5, so that the theoretical molar ratio of carbon atoms to nitrogen atoms is greater than 4.5 during ionization, the thickness of the silicon nitride layer is too small, the silicon nucleus expansion inhibition effect is poor, the cycle performance and rate performance of the negative electrode active material are significantly affected, and the electrochemical performance of the negative electrode active material is inferior to that of examples 1 and 10 to 14.

According to examples 1 and 10 to 14, it can be seen that when the ratio of the addition amounts (partial pressure ratio) of methane and nitrogen is 25 (10 to 15), the cycle performance and rate performance of the negative electrode active material are better, and the content of nitrogen atoms affects the particle size.

Comparative example 9 and example 10 differ only in the total addition amount of the reaction gas, which was 38kpa in example 10 and 19kpa in comparative example 9, and it can be seen that the silicon nitride layer of the anode active material was small in thickness because the concentration thereof was low due to the small addition amount of the reaction gas in the comparative example.

As can be seen from example 15 and example 1, since acetylene has a smaller ionization rate than methane, it is sufficient to add more acetylene to match the ionization rate of nitrogen gas. From example 16 and example 1, it can be seen that, when the specific raw material of the nitrogen source is changed, it is only necessary to adjust the amount of the specific raw material in accordance with the rate at which nitrogen atoms are produced by ionization thereof.

Comparing example 16 with example 17, it can be seen that the content of carbon atoms affects the particle size.

From example 17, it is understood that the hydrogen atom can be obtained by decomposing only methane.

As is clear from example 18 and example 1, the change in the cathode material affects the cycle performance and rate performance of the negative electrode active material to some extent.

Example 19 is different from example 1 in that the passivation gas is different, and it can be seen from example 1 and example 19 that the difference in particle size and silicon nitride thickness are not affected by the difference in passivation gas and the difference in passivation time, and the cycle performance and rate performance of the negative active material are only slightly affected because the passivation gas affects the surface energy of the negative active material.

The example 20 is different from the example 1 in the passivation time, and it is understood from the example 1 and the example 20 that the difference in the passivation time does not affect the particle diameter and the silicon nitride thickness, but the passivation affects the surface energy of the negative electrode active material, and therefore only slightly affects the cycle performance and rate performance of the negative electrode active material.

Fig. 4 is a TEM image of the composite material obtained in example 1, and from fig. 4 it can be seen that the composite material is three layers, the silicon nitride layer having a thickness of about 7nm.

Fig. 5 is an XRD spectrum of the composite material prepared in example 1. The XRD measurement mode is as follows: an X-ray diffractometer (XRD-6000) of Shimadzu corporation, japan, was used, a copper target was used as a radiation light source (λ =0.15416 nm), a voltage was 40kV, a current was 30mA, a scanning speed was 4 °/min, and a scanning angle was in a range of 20 ° -80 °.

As can be seen from fig. 5, the characteristic peaks of the silicon phase, the silicon nitride phase, and the carbon phase are present at the same time, and the XRD pattern shows that the carbon contains graphitic carbon, which can be seen by comparing with the XRD pattern of the conventional graphene.

FIG. 6 is a graph of the cycling performance of the negative electrode of the composite material prepared in example 1 at a current density of 100 mA/g. FIG. 7 is a graph of coulombic efficiency at a current density of 100mA/g for the negative electrode of the composite material prepared in example 1. According to the fig. 6 and 7, after 200 cycles of the negative electrode of the composite material prepared in the example 1 under the current density of 100mA/g, the specific capacity can be maintained at 1413mAh/g, and the coulombic efficiency is as high as 99.58%.

Fig. 8 is a rate performance graph of the negative electrode of the composite material prepared in example 1, and the cycle performance graphs of the assembled CR2025 button lithium ion battery at different rates of 0.1C, 0.5C, 1C, 1.5C, 2C (1c. As can be seen from FIG. 8, the composite material is stable under various current density tests, and the composite material has good rate capability, and when the current density is 2A/g, the specific discharge capacity is high at 893mAh/g.

In summary, the negative active material, the preparation method thereof, the negative electrode plate, the battery and the electric device provided by the application can solve the technical problems of poor rate performance and short service life of the silicon-based negative active material.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An anode active material, comprising: the cathode comprises a silicon core, a silicon nitride layer and a carbon layer, wherein the silicon nitride layer wraps the surface of the silicon core, the carbon layer wraps the surface of the silicon nitride layer, and the particle size of the cathode active material is in a nanometer level.

2. The negative electrode active material according to claim 1, wherein the particle diameter of the negative electrode active material is 30nm to 90nm.

3. The negative active material according to claim 1 or 2, wherein the silicon nitride layer has a thickness of 6nm to 8nm;

optionally, the mass fraction of the silicon core is 65% to 85% based on 100% of the total weight of the silicon core and the silicon nitride layer.

4. The anode active material according to claim 1 or 2, wherein the carbon layer is 15% to 20% by mass based on 100% by weight of the anode active material;

optionally, the carbon layer comprises graphitic carbon;

optionally, the carbon layer comprises graphene.

5. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 4.

6. A battery comprising the negative electrode tab of claim 5.

7. An electric device comprising the battery of claim 6.

8. A method for preparing an anode active material, comprising:

generating a direct current arc discharge between a cathode and an anode in a direct current arc reaction chamber having the cathode and the anode, with a silicon block as the anode, under an atmosphere of a reaction gas to generate a negative electrode active material;

wherein the reaction gas can be converted into nitrogen atoms, hydrogen atoms and carbon atoms in a plasma state through the high temperature generated by the direct current arc discharge.

9. The method according to claim 8, wherein the discharge current of the dc arc is 10A to 200A, and the voltage is 5V to 30V;

optionally, the distance between the cathode and the anode is 10mm-25mm, optionally 15mm-25mm;

optionally, the cathode is made of tungsten or graphite.

10. The production method according to claim 8, characterized in that the molar ratio of the carbon atom to the nitrogen atom is (1.5.

11. The production method according to claim 10, wherein the reaction gas is a mixture of methane, nitrogen, and hydrogen;

optionally, before the dc arc discharge, the total pressure of the reaction gas is 38kpa to 53kpa, and the partial pressure ratio of the methane, the nitrogen, and the hydrogen is 25: (3-18) 10, optionally 25: (10-15):10.

12. The method of any one of claims 8-11, further comprising: after the direct current arc discharge reaction is finished, cooling for 3-5 h, introducing passivation gas for passivation treatment, and collecting the negative electrode active material attached to the inner wall of the direct current arc reaction chamber;

optionally, the passivation gas is air or oxygen with the pressure of 1kPa-2kPa, and the time of the passivation treatment is 6h-10h.