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

Abstract

The application discloses a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery and electrical equipment, and relates to the field of batteries. The negative electrode active material includes: a silicon core, a silicon nitride layer covering the surface of the silicon core, and a carbon layer covering the surface of the silicon nitride layer, and the particle size of the negative electrode active material is nanoscale. The negative electrode active material utilizes the combination of structure, material and particle size to alleviate the current situation of poor rate performance and low lifespan of existing silicon-based negative electrode active materials, and has excellent cycle stability and rate performance.

Description

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

technical field

The present application relates to the field of batteries, in particular, to a negative electrode active material, a preparation method thereof, a negative electrode sheet, a battery and electrical equipment.

Background technique

As the main energy storage device, batteries have been widely used in portable electronic products, electric vehicles and grid storage systems. In recent years, with the market demand for batteries with high energy density, high rate performance and long cycle life, the research and development of negative electrode materials is particularly important. Silicon has become a competitive anode material due to its high specific capacity and moderate lithium intercalation potential. However, when silicon-based anode active materials are actually applied to batteries, there are problems of poor rate performance and low life.

Contents of the invention

The purpose of the embodiments of the present application is to provide a negative electrode active material and its preparation method, negative electrode sheet, battery and electrical equipment, which can improve the technical problems of poor rate performance and low lifespan of silicon-based negative electrode active materials.

In the first aspect, the embodiment of the present application provides a negative electrode active material, which includes: a silicon core, a silicon nitride layer covering the surface of the silicon core, and a carbon layer covering the surface of the silicon nitride layer, the negative electrode active material The particle size of the material is nanoscale.

In the technical solution of the embodiment of the present application, a silicon nitride layer is used to coat the surface of the silicon core to suppress the volume expansion of silicon during the intercalation/delithiation process and improve its cycle life. Due to the poor conductivity of silicon and silicon nitride , so the electrical conductivity of the negative electrode active material is significantly improved through the outermost coating of the carbon layer, so that the electrochemical performance of the negative electrode active material can be fully exerted, and its rate performance can be improved, and the particle size of the negative electrode active material is nanoscale, which is relatively Compared with micron-scale negative electrode active materials, the lithium ion diffusion distance is shorter, the specific surface area is larger, and the lithium intercalation sites are more, so its electrochemical performance is better. In summary, the anode active material utilizes the combination of structure, material, and particle size to alleviate the current situation of poor rate performance and low lifespan of existing silicon-based anode active materials, and has excellent cycle stability and rate performance.

In some embodiments, the particle size of the negative electrode active material is 30nm-90nm. The negative electrode active material within the above particle size range has the advantages of large specific surface area and many lithium intercalation sites, which can increase the discharge specific capacity of the negative electrode active material and improve its rate performance.

In some embodiments, the thickness of the silicon nitride layer is 6nm-8nm. The thickness of silicon nitride within the above range is reasonable, which can improve the conductivity of lithium ions in the process of lithium intercalation of silicon nitride. If the silicon nitride layer is too thin, it will not have a good effect on the volume expansion limit when the silicon core deintercalates lithium. , reducing its cycle life, too thick will affect the lithium insertion capacity of the negative active material.

Optionally, based on the total weight of the silicon core and the silicon nitride layer as 100%, the mass fraction of the silicon core is 65%-85%. Reasonable silicon core content within the above range makes the negative electrode active material not only have a high specific capacity, but also helps the silicon nitride layer to suppress its expansion and improve its cycle stability.

In some embodiments, based on the total weight of the negative active material as 100%, the mass fraction of the carbon layer is 15%-20%. The proportion of the carbon layer within the above range is reasonable, which can effectively improve the conductivity of the negative electrode active material, improve the rate performance of the negative electrode active material and enhance its cycle life.

Optionally, the carbon layer contains graphitic carbon.

Optionally, the carbon layer contains graphene. The arrangement of the carbon layer containing graphene can further improve the conductivity of the negative electrode active material.

In a second aspect, the present application 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, and the negative electrode active material layer includes the negative electrode active material in the above embodiment.

In a third aspect, the present application provides a battery, which includes the negative electrode sheet in the above embodiment.

In a fourth aspect, the present application provides an electric device, which includes the battery in the above embodiment.

In a fifth aspect, the present application provides a method for preparing a negative electrode active material, which includes: in a direct current arc reaction chamber having a cathode and an anode, using a silicon block as the anode and under a reactive gas atmosphere, making the anode and the cathode A DC arc discharge occurs to generate negative active materials; wherein, the reaction gas can be transformed into nitrogen atoms, hydrogen atoms, and carbon atoms in a plasma state through the high temperature generated by the DC arc discharge.

In the technical solution of the embodiment of the present application, a negative electrode active material with a particle size of nanometer and a structure of silicon core/silicon nitride layer/carbon layer is prepared in one step by using a direct current arc method. The preparation method is simple to operate and has high preparation efficiency. The structure of each layer of the negative electrode active material prepared by the arc method is dense, the silicon nitride layer is formed in situ and uniformly covers the silicon core, and the carbon layer is formed in situ and uniformly covers the silicon nitride layer, so the granularity of the negative electrode active material formed is The diameter is relatively uniform, and each layer is stably connected together, further improving the long-term stability of the electrochemical performance of the negative electrode active material, so that it has a better cycle life.

In some embodiments, the discharge current of the DC arc is 10A-200A, and the voltage is 5V-30V. The reasonable selection of the discharge current and voltage enables it to generate a stable DC arc, and improves the yield under the premise of ensuring the safety of preparing negative electrode active materials. If the discharge current and voltage are too high, it will cause potential safety hazards, and if the discharge current and voltage are too small, the yield of the negative electrode active material will decrease.

Optionally, the distance between the cathode and the anode is 10mm-25mm. Within the above distance range, a stable DC arc can be generated. If the distance is too large, the DC arc will be broken and a stable DC arc cannot be formed. If the distance is too small, the anode and cathode will be bonded and short circuited, which will easily damage the equipment and cause safety hazards.

Optionally, the material of the cathode is tungsten or graphite. The above two materials are not only resistant to high temperature, but also do not react with plasma gas to avoid the introduction of impurities.

In some embodiments, the molar ratio of carbon atoms to nitrogen atoms is (1.5:1)-(4.5:1), and the ratio of the above-mentioned carbon atoms to nitrogen atoms is reasonable, which is conducive to controlling the formation of carbon layers and silicon nitride layers thickness and content.

In some embodiments, the reaction gas is a mixture of methane, nitrogen and hydrogen. The raw materials of the above-mentioned reaction gases are not only easy to ionize under the high temperature generated by the direct current arc, but also easy to obtain and low in cost, which can reduce the preparation of negative electrode active materials. cost.

Optionally, before the DC arc discharge, the total pressure of the reaction gas is 38kpa-53kpa, and the partial pressure ratio of methane, nitrogen and hydrogen is 25:(3-18):10, optionally 25:(10-15) :10. Since the volume of the DC arc reaction chamber is limited, and the DC arc discharge reaction is to feed the reaction gas in advance, no additional reaction gas is introduced during the reaction process, so within the above total pressure range, not only the DC arc reaction chamber has enough reaction gas, And it is beneficial to improve the safety of DC arc discharge reaction. Under the partial pressure ratio under this total pressure condition, the ionization rate of methane and nitrogen can reach 1:1 during DC arc discharge, which is beneficial to control the molar ratio of ionized carbon atoms and nitrogen atoms, Therefore, the thickness and content of the formed carbon layer and silicon nitride layer are controlled, and the hydrogen content is reasonable, which is beneficial to promote the ionization of methane and nitrogen.

In some embodiments, the preparation method further includes: after the DC arc discharge reaction is completed, after cooling for 3h-5h, passing passivation gas for passivation treatment, and collecting the negative electrode active material attached to the inner wall of the DC arc reaction chamber. The passivation treatment is used to passivate the surface energy of the negative electrode active material, so as to facilitate safe collection of the negative electrode active material.

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

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the application. Also, the same reference numerals are used to denote the same components throughout the drawings. In the attached picture:

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

Fig. 2 is a schematic diagram of an exploded structure of a battery in some embodiments of the present application;

3 is a schematic diagram of an exploded structure of a battery cell in some embodiments of the present application;

Fig. 4 is the TEM figure of the composite material that the embodiment 1 of the present application makes;

Fig. 5 is the XRD spectrum of the composite material that the application embodiment 1 makes;

Fig. 6 is the cycle performance figure of the negative electrode electrode of the composite material that the embodiment 1 of the present application makes;

Fig. 7 is the coulombic efficiency diagram of the negative electrode using the composite material that embodiment 1 makes;

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

The reference numerals in the specific embodiment are as follows:

1000 - vehicle;

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

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

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

Detailed ways

Embodiments of the technical solutions of the present application will be described in detail below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solution of the present application more clearly, and therefore are only examples, rather than limiting the protection scope of the present application.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the application; the terms used herein are only for the purpose of describing specific embodiments, and are not intended to To limit this application; the terms "comprising" and "having" and any variations thereof in the specification and claims of this application and the description of the above drawings are intended to cover a non-exclusive inclusion.

In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and should not be understood as indicating or implying relative importance or implicitly indicating the number, specificity, or specificity of the indicated technical features. Sequence or primary-secondary relationship. In the description of the embodiments of the present application, "plurality" means two or more, unless otherwise specifically defined.

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 present application. The occurrences of this 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 understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments.

In the description of the embodiment of the present application, the term "and/or" is only a kind of association relationship describing associated objects, which means that there may be three kinds of relationships, such as A and/or B, which may mean: A exists alone, and A exists at the same time and B, there are three cases of B alone. In addition, the character "/" in this article generally indicates that the contextual objects are an "or" relationship.

In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), similarly, "multiple groups" refers to more than two groups (including two), and "multiple pieces" refers to More than two pieces (including two pieces).

In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical" "Horizontal", "Top", "Bottom", "Inner", "Outer", "Clockwise", "Counterclockwise", "Axial", "Radial", "Circumferential", etc. indicate the orientation or positional relationship based on the drawings Orientation or positional relationship is only for the convenience of describing the embodiment of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as an implementation of the present application. Example limitations.

In the description of the embodiments of this application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection" and "fixation" should be interpreted in a broad sense, for example, it can be a fixed connection or a fixed connection. Disassembled connection, or integration; it can also be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediary, and it can be the internal communication of two components or the interaction relationship between two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the embodiments of the present application according to specific situations.

At present, batteries are not only used in energy storage power systems such as water power, fire power, wind power and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric vehicles, as well as military equipment and aerospace. field. With the continuous expansion of battery application fields, its market demand is also constantly expanding.

The inventors have noticed that the existing negative electrode using silicon as the negative active material has the problems of low coulombic efficiency and low cycle life. The main reason is that silicon is accompanied by a 300% The volume change and the formation of unstable solid electrolyte interfacial film greatly reduce its rate performance and cycle life.

In order to solve the above problems, the inventors tried to coat silicon to form a core-shell structure, in which 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 field of room temperature and high temperature. Therefore, Use silicon nitride to cover silicon, use silicon nitride to suppress the expansion of silicon, and avoid the unstable solid electrolyte interfacial film caused by direct exposure of silicon, but both silicon and silicon nitride are semiconductor materials, making the composite material poor in conductivity. Therefore, a carbon layer is further used to coat silicon nitride to improve the conductivity of the negative electrode active material, so that its electrochemical performance can be fully exerted, and the low Coulombic efficiency and cycle life can be improved.

However, the inventors found that the existing preparation method for preparing the negative electrode active material with the above-mentioned structure improvement is usually a two-step method: first forming a silicon nitride layer covering the surface of the silicon core, and then forming a silicon nitride layer covering the surface of the silicon core. The preparation steps of the carbon layer on the surface of the silicon layer are cumbersome, and the preparation of silicon nitride is difficult, and the particle size of the prepared negative electrode active material is micron, which limits its electrochemical performance.

Therefore, the inventors further tried to adopt the direct current arc method to prepare negative electrode active materials with a nanoscale particle size and a structure of silicon core/silicon nitride layer/carbon layer in one step. This preparation method is simple to operate and has high preparation efficiency, and the direct current arc method is adopted The layers of the prepared negative electrode active material are densely and stably connected together, which improves the long-term stability of the electrochemical performance of the negative electrode active material, and the particle size of the formed negative electrode active material is relatively uniform and nanoscale, which improves the stability of the negative electrode active material. Cycling stability and rate performance.

The batteries disclosed in the embodiments of the present application can be used, but not limited to, in electric devices such as vehicles, ships or aircrafts. The battery disclosed in this application can be used to form the power supply system of the electric device, which is beneficial to improve the stability of battery performance and battery life.

The embodiment of the present application provides an electric device using a battery as a power source. The electric device can be, but not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric boat toys, electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, spaceships, etc.

In the following embodiments, for the convenience of description, a vehicle 1000 as an electric device according to an embodiment of the present application is taken as an example for description.

Please refer to FIG. 1 , which is a schematic structural diagram of a vehicle 1000 provided by some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle. The interior of the vehicle 1000 is provided with a battery 100 , and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000 . The battery 100 can be used for power supply of the vehicle 1000 , for example, the battery 100 can be used as an operating power source of the vehicle 1000 . The vehicle 1000 may further include a controller 200 and a motor 300 , the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, for starting, navigating and running the vehicle 1000 .

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

Please refer to FIG. 2 , which is an exploded view of a battery 100 provided by some embodiments of the present application. The battery 100 includes a case 10 and battery cells 20 housed in the case 10 . Wherein, the box body 10 is used to provide accommodating space for the battery cells 20 , and the box body 10 may adopt various structures. In some embodiments, the box body 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 cover each other, the first part 11 and the second part 12 jointly define a of accommodation space. The second part 12 can be a hollow structure with one end open, the first part 11 can be a plate-like structure, and the first part 11 covers the opening side of the second part 12, so that the first part 11 and the second part 12 jointly define an accommodation space ; The first part 11 and the second part 12 can also be hollow structures with one side opening, and the opening side of the first part 11 is covered by the opening side of the second part 12 . Of course, the box body 10 formed by the first part 11 and the second part 12 can be in various shapes, such as a cylinder, a cuboid and the like.

In the battery 100 , there may be multiple battery cells 20 , and the multiple battery cells 20 may be connected in series, in parallel or in parallel. The mixed connection means that the multiple battery cells 20 are connected in series and in parallel. A plurality of battery cells 20 can be directly connected in series, in parallel or mixed together, and then the whole composed of a plurality of battery cells 20 is housed in the box 10; of course, the battery 100 can also be a plurality of battery cells 20 The battery modules are firstly connected in series or parallel or in combination, and then multiple battery modules are connected in series or in parallel or in combination to form a whole, which is accommodated in the case 10 . The battery 100 may also include other structures, for example, the battery 100 may also include a bus component for realizing electrical connection between multiple battery cells 20 .

Wherein, each battery cell 20 can 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 in the form of a cylinder, a flat body, a cuboid or other shapes.

Please refer to FIG. 3 , which is a schematic diagram of an exploded structure of a battery cell 20 provided in some embodiments of the present application. The battery cell 20 refers to the smallest unit constituting a battery. As shown in FIG. 3 , the battery cell 20 includes an end cover 21 , a casing 22 , an electrode assembly 23 and other functional components.

The end cap 21 refers to a component that covers the opening of the casing 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the housing 22 to fit the housing 22 . Optionally, the end cap 21 can be made of a material (such as aluminum alloy) with a certain hardness and strength, so that the end cap 21 is not easy to deform when being squeezed and collided, so that the battery cell 20 can have a higher Structural strength and safety performance can also be improved. Functional components such as electrode terminals 21 a may be provided on the end cap 21 . The electrode terminal 21 a can be used to be electrically connected with the electrode assembly 23 for outputting or inputting electric energy of the battery cell 20 . In some embodiments, the end cover 21 may also be provided with a pressure relief mechanism for releasing 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 can also be various, for example, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not particularly limited in this embodiment of the present application. In some embodiments, an insulator can be provided inside the end cover 21 , and the insulator can be used to isolate the electrical connection components in the housing 22 from the end cover 21 to reduce the risk of short circuit. Exemplarily, the insulating member may be plastic, rubber or the like.

The casing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20 , wherein the formed internal environment can be used to accommodate the electrode assembly 23 , electrolyte and other components. The housing 22 and the end cover 21 can be independent components, and an opening can be provided on the housing 22 , and the internal environment of the battery cell 20 can be formed by making the end cover 21 cover the opening at the opening. Without limitation, the end cover 21 and the housing 22 can also be integrated. Specifically, the end cover 21 and the housing 22 can form a common connection surface before other components are inserted into the housing. When the inside of the housing 22 needs to be encapsulated , then make the end cover 21 cover the housing 22. The housing 22 can be in various shapes and sizes, such as cuboid, cylinder, hexagonal prism and so on. Specifically, the shape of the casing 22 can be determined according to the specific shape and size of the electrode assembly 23 . The housing 22 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not particularly limited in this embodiment of the present application.

The electrode assembly 23 is a part where the electrochemical reaction occurs 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 positive electrode sheets and negative electrode sheets, and a separator is usually provided between the positive electrode sheets and the negative electrode sheets. The part of the positive electrode sheet and the negative electrode sheet with the active material constitutes the main body of the electrode assembly, and the parts of the positive electrode sheet and the negative electrode sheet without the active material respectively constitute the tab 23a. The positive pole tab and the negative pole tab can be located at one end of the main body together or at two ends of the main body respectively. During the charging and discharging process of the battery, the positive electrode active material and the negative electrode active material react with the electrolyte, and the tabs 23a are connected to the electrode terminals to form a current loop.

According to some embodiments of the present application, the present application provides a negative electrode active material, which includes: a silicon core, a silicon nitride layer covering the surface of the silicon core, and a carbon layer covering the surface of the silicon nitride layer , the particle size of the negative electrode active material is nanoscale.

That is to say, the negative electrode active material has a core-shell structure, wherein silicon core/silicon nitride layer/carbon layer are sequentially arranged from the inside to the outside.

Wherein, the silicon core refers to a particle whose material is pure silicon, or whose material is mainly silicon but contains dopant elements, wherein the silicon core means that the content of silicon in the silicon core is greater than that of the dopant element.

The silicon nitride layer refers to the cladding layer whose material is pure silicon nitride, or the material is mainly silicon nitride but contains doping elements, where silicon nitride is the main body refers to the content of silicon nitride in the silicon nitride layer greater than the content of doping elements.

The carbon layer refers to a cladding layer whose material is pure carbon, or whose material is mainly carbon but contains doping elements, where carbon is the main body means that the content of carbon in the carbon layer is greater than the content of doping elements.

The particle size of the negative electrode active material is nanoscale means that the particle size of the negative electrode active material is ≤100nm.

In the technical solution of the embodiment of the present application, a silicon nitride layer is used to coat the surface of the silicon core to suppress the volume expansion of silicon during the intercalation/delithiation process and improve its electrochemical cycle life. Due to the conductive properties of silicon and silicon nitride Poor, so through the carbon layer coated on the outermost layer, the conductivity of the negative electrode active material is significantly improved, so that the electrochemical performance of the negative electrode active material can be fully exerted, and the particle size of the negative electrode active material is nanometer, compared to micron The negative electrode active material of the grade has a shorter lithium ion diffusion distance, a larger specific surface area, and more lithium intercalation sites, so its electrochemical performance is better. To sum up, the negative electrode active material utilizes the combination of structure, material and particle size to alleviate the current situation of poor rate performance and short cycle life of existing silicon-based negative electrode active materials.

According to some embodiments of the present application, optionally, the particle diameter of the negative electrode active material is 30nm-90nm.

The negative electrode active material within the above particle size range has the advantages of large specific surface area and many lithium intercalation sites, so its electrochemical performance is good, and the Coulombic efficiency and cycle life of the negative electrode active material can be improved.

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

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

Since the negative electrode active material is granular, 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 silicon nitride within the above range is reasonable, which can improve the conductivity of lithium ions in the process of lithium intercalation of silicon nitride. If the silicon nitride layer is too thin, it will not have a good effect on the volume expansion limit when the silicon core deintercalates lithium. , reduce its electrochemical cycle life, and if it is too thick, it will affect the lithium intercalation capacity of the negative electrode active material.

As an example, the thickness of the silicon nitride layer includes, but is not limited to, any value among 6nm, 6.5nm, 7nm, 7.2nm, 7.5nm and 8nm, or a range between any two values.

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

A reasonable silicon core content within the above range enables the negative electrode active material to have a better specific capacity, and is also beneficial to suppress the expansion of the silicon nitride layer.

As an example, based on the total weight of the silicon core and the silicon nitride layer as 100%, the mass fraction of the silicon core includes, but is not limited to, 65%, 70%, 75%, 80%, 85%, 90%, Any one of 95% and 100% or a range between any two values.

According to some embodiments of the present application, optionally, based on the total weight of the negative electrode active material being 100%, the mass fraction of the carbon layer is 15%-20%.

The proportion of the carbon layer within the above range is reasonable, which can effectively improve the conductivity of the negative electrode active material, improve the rate performance of the negative electrode active material, and enhance its Coulombic efficiency.

As an example, based on the total weight of the negative electrode active material as 100%, the mass fraction of the carbon layer includes, but is not limited to, any value in 15%, 16%, 17%, 18%, 19% and 20% etc. Or a range between any two values.

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

The arrangement of the carbon layer containing graphene can further improve the conductivity of the negative electrode active material.

According to some embodiments of the present application, the present application also 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, and the negative electrode active material layer includes the negative electrode active material of any of the above schemes .

According to some embodiments of the present application, the present application also provides a battery, which includes the negative electrode sheet of any one of the above schemes.

According to some embodiments of the present application, the present application also provides an electric device, including the battery of any one of the above schemes, and the battery is used to provide electric energy for the electric device.

The electric device may be any of the aforementioned devices or systems using batteries.

According to some embodiments of the present application, the present application provides a method for preparing a negative electrode active material, which includes: using a silicon block as an anode in a DC arc reaction chamber having a cathode and an anode, and making the anode A DC arc discharge occurs between the cathode and the cathode to generate negative electrode active materials; wherein, the reaction gas can be transformed into nitrogen atoms, hydrogen atoms and carbon atoms in the plasma state through the high temperature generated by the DC arc discharge.

Among them, the DC arc reaction is carried out in a DC arc reactor, and the DC arc reactor has a cooling system, which is used to reduce the temperature of the inner wall of the reaction chamber during the DC arc reaction, to avoid safety accidents, and to facilitate the adhesion of the prepared negative active material Regarding the inner wall of the DC arc reaction chamber, the DC arc reactor can be directly purchased in the market, and there is no limitation here. The DC arc reaction chamber refers to the cavity where the DC arc reactor performs DC arc discharge.

Silicon block refers to a solid material made of silicon, which has a certain shape and is obtained in a non-accumulated form. The shape of silicon block can be regular or irregular cake, sheet, block, rod, etc. Those skilled in the art can according to The actual demand selection is not specifically limited here.

Arcing refers to the phenomenon that the cathode and anode are kept electrically conductive by gaseous charged particles, such as electrons or ions, under a certain voltage.

It can be understood that the silicon block is used as the anode, so in actual use, the silicon block is placed on a conductive metal seat (such as a copper seat) that is energized in the DC arc reaction chamber, and a circuit can be formed between the conductive metal seat and the cathode through an arc. , so that the silicon block can be used as the anode.

The DC arc discharge reaction refers to: the arc flame of the DC arc generated between the cathode and the anode generates a high temperature of thousands of degrees Celsius, and the arc flame of the DC arc is used as a heat source for the high-energy state growth material, with the arc flame as the center of the heat source, There is a certain temperature gradient from the inside to the outside of the heat source, and the temperature gradually decreases from the inside to the outside of the heat source, and the growth process of the negative electrode active material is completed in this heat source area. Specifically, first, the silicon block is evaporated into gaseous silicon atoms inside the arc flame, and the reaction gas can be converted into plasma nitrogen atoms, hydrogen atoms, and carbon atoms through the high temperature generated by DC arc discharge, and the nucleation temperature of silicon > nitrogen The nucleation temperature of silicon oxide is greater than the nucleation temperature of carbon, so when the temperature of the heat source is lowered to the melting point of silicon (about 1414°C), silicon nanoparticles begin to nucleate and grow spontaneously, and the temperature of the heat source decreases to a lower level with the flow of silicon vapor, etc. Nitriding temperature (about 1200°C), at this time, silicon nitride begins to undergo heterogeneous nucleation on the surface of silicon nanoparticles, grows into a layer of silicon nitride coating, continues to flow to the flame core area away from the arc flame, and the temperature continues Lower the nucleation temperature of carbon atoms, so that carbon atoms start to grow into carbon layers on the surface of silicon nitride, and finally form a negative electrode active material with a three-layer core-shell structure of silicon core/silicon nitride layer/carbon layer and a nanoscale size.

Among them, the hydrogen atoms are used to promote the ionization of the reactive gas into nitrogen atoms and carbon atoms in plasma state.

Plasma refers to an ionized gaseous substance composed of positive and negative ions produced by ionized atoms and atomic groups after some electrons have been deprived.

In the technical solution of the embodiment of the present application, a negative electrode active material with a particle size of nanoscale and a structure of silicon core/silicon nitride layer/carbon layer is prepared in one step by using a direct current arc method. The preparation method is simple to operate and has high preparation efficiency. Each layer of the negative electrode active material prepared by the direct current arc method has a compact structure, high particle size sphericity and uniform particle size distribution.

The silicon nitride layer can buffer the stress generated by the volume expansion of the silicon core during the cycle. It reacts with the electrolyte to produce a lithium nitride phase, which exists in the solid electrolyte interface film and can promote the transfer of lithium ions. The carbon coating layer can further Improve the stability of the overall structure of the composite material and the high-current charge-discharge capability of the electrode. Using the in-situ introduction of the silicon nitride layer and the carbon layer, the layers can be stably connected together, and the coating is more uniform and the particle size is smaller. For uniformity, the long-term stability of the electrochemical performance of the negative electrode active material can be further improved, so that it has a better cycle life.

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

Exemplarily, carbon atoms and hydrogen atoms can be provided by at least one of alkanes, alkynes and alkenes. For cost considerations and to facilitate ionization, carbon atoms and hydrogen atoms can be provided by C _1-4 alkanes, C _1-4 alkynes And at least one of C _1-4 alkene provides, alternatively, carbon atoms and hydrogen atoms can be provided by at least one of C _1-4 alkane, C _1-2 alkyne. Hydrogen atoms can also be provided by hydrogen gas. Nitrogen atoms may be provided by at least one of nitrogen gas and ammonia gas.

It should be noted that when the hydrogen atoms are at least partly provided by hydrogen gas, since the hydrogen gas is active, the hydrogen gas is first introduced into the DC arc reaction chamber, and then other gases are introduced.

Optionally, in order to avoid interference from impurities, the raw material purity of the reaction gas is >99.9%.

In order to avoid impurity interference, before the reaction gas is introduced into the DC arc reaction chamber, the DC arc reaction chamber can be evacuated, for example, to a vacuum degree of 10 ^-2 -10 ^-5 Pa.

Wherein, the cathode and the anode can be arranged horizontally in the DC arc reaction chamber. For the convenience of placing the silicon block, optionally, the cathode and the anode are vertically arranged in the DC arc reaction chamber, and the cathode is located above the anode.

In order to stabilize the arc, 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.

The reasonable selection of the discharge current and voltage enables it to generate a stable DC arc, and improves the yield under the premise of ensuring the safety of preparing negative electrode active materials. If the discharge current and voltage are too high, it will cause potential safety hazards, and if the discharge current and voltage are too small, the yield of the negative electrode active material will decrease.

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

As an example, the voltage of the DC arc includes, but is not limited to, any one of 5V, 7V, 10V, 15V, 20V, 25V, and 30V, or a range between any two values.

In some embodiments, optionally, the distance 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 tapered surface, the distance between the cathode and the anode refers to the distance between the tip of the cathode and the anode facing the tip. The distance between one end face.

Within the above distance range, a stable DC arc can be generated. If the distance is too large, the DC arc will be broken and a stable DC arc cannot be formed. If the distance is too small, the anode and cathode will be bonded and short circuited, which will easily damage the equipment and cause safety hazards.

It can be understood that, in actual use, the distance between the cathode and the anode can be adjusted, so that an appropriate distance can be selected for DC arc discharge reaction.

As an example, the distance between the cathode and the anode includes, but is not limited to, any one of 10mm, 12mm, 15mm, 18mm, 20mm, 23mm and 25mm, or a range between any two values.

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

The above two materials are not only resistant to high temperature, but also do not react with plasma gas to avoid the introduction of impurities.

In some embodiments, optionally, the molar ratio of carbon atoms to nitrogen atoms is (1.5:1)-(4.5:1).

The carbon atoms and nitrogen atoms here refer to the nitrogen atoms and carbon atoms that the reaction gas is transformed into plasma state by the high temperature generated by DC arc discharge.

The above-mentioned ratio of carbon atoms and nitrogen atoms is reasonable, which is beneficial to control the thickness and content of the formed carbon layer and silicon nitride layer. Since the role of the hydrogen atoms is to promote the ionization of the reaction gas, the content thereof is not limited here.

As an example, the molar ratio of carbon atoms to nitrogen atoms includes, but is not limited to, any one of 1.5:1, 2:1, 2.5:1, 3:1, 4:1, and 4.5:1, or any two of them. range between values.

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

The raw materials of the above-mentioned reaction gases are not only easy to ionize under the high temperature generated by the direct current arc, but also easy to obtain and low in cost, which can reduce the preparation cost of the negative electrode active material.

In some embodiments, optionally, before DC arc discharge, the total pressure of the reaction gas is 38kPa-53kPa, and the partial pressure ratios of methane, nitrogen and hydrogen are 25:(3-18):10 in sequence.

The partial pressure ratio refers to the pressure formed by a certain component of a gas mixture when it occupies the same volume of the gas mixture at the same temperature.

Since the volume of the DC arc reaction chamber is limited, and the DC arc discharge reaction is to feed the reaction gas in advance, no additional reaction gas is introduced during the reaction process, so within the above total pressure range, not only the DC arc reaction chamber has enough reaction gas, And it is beneficial to improve the safety of DC arc discharge reaction. Under the partial pressure ratio under this total pressure condition, the ionization rate of methane and nitrogen can reach 1:1 during DC arc discharge, which is beneficial to control the molar ratio of ionized carbon atoms and nitrogen atoms, In this way, the thickness and content of the formed carbon layer and silicon nitride layer are controlled, and the hydrogen content is reasonable, which is conducive to promoting the ionization of methane and nitrogen. As an example, before DC arc discharge, the partial pressure ratios of methane, nitrogen and hydrogen include but are not limited to 25:3:10, 25:5:10, 25:10:10, 25:12:10, 25 Any one of :13:10, 25:15:10, 25:16:10, 25:17:10, and 25:18:10, or the range between any two values.

Optionally, before DC arc discharge, the partial pressure ratios of methane, nitrogen and hydrogen are 25:(10-15):10 in sequence.

As an example, before DC arc discharge, the total pressure of the reaction gas includes, but is not limited to, any one of 38kPa, 40kPa, 43kPa, 45kPa, 47kPa, 49kPa, 50kPa, and 53kPa, or a range between any two values.

In some embodiments, optionally, the preparation method further includes: after the DC arc discharge reaction is finished, after cooling for 3h-5h, pass passivation gas to perform passivation treatment, and collect the negative electrode attached to the inner wall of the DC arc reaction chamber active material.

The passivation treatment is used to passivate the surface energy of the negative electrode active material, so as to facilitate safe collection of the negative electrode active material.

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

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

The above-mentioned passivation treatment is easy to operate and low in cost, and the passivation time is too short, and the surface energy of the negative electrode active material is still relatively large, posing potential safety hazards.

As an example, the pressure of the passivation gas includes, but is not limited to, any one value among 1 kPa, 1.2 kPa, 1.5 kPa, 1.7 kPa, and 2 kPa, or a range between any two values.

As an example, the passivation treatment time includes but is not limited to any one of 6h, 8h, 9h and 10h or a range between any two values.

Optionally, after the passivation treatment, the negative electrode active material can be sieved according to actual needs, so as to obtain the negative electrode active material with a specific particle size.

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

In the following examples and comparative examples, the DC arc reactor is the NP-450 model produced by Liaoning Shenyang Beiyu Vacuum Technology Co., Ltd.

Examples and comparative examples

1) Take a silicon block with a purity greater than 99.9% and place it on the anode copper seat of the DC arc reactor as the anode, the cathode is located above the anode, and the end of the cathode facing the anode is tapered, and the distance between the anode and the cathode is adjusted as shown in the table 1.

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

3) Turn on the cooling system of the DC arc reactor, turn on the power and start the arc, adjust the current and the distance between the poles corresponding to each embodiment according to the data shown in Table 1 and stabilize the arc, so that the generated negative electrode active material is deposited in the DC arc reaction chamber on the inner wall.

4) Fill the DC arc reaction chamber with a passivation gas, collect the powder after passivation treatment, and obtain a silicon core/silicon nitride layer/carbon layer composite material with a core-shell structure.

Performance Testing:

(1) The composite materials prepared in each embodiment and comparative example were respectively dispersed in the dispersant ethanol, and after ultrasonication for 30 minutes, the sample was added to the laser particle size (Zhoudong Bettersize 2600) instrument, and the D50 of the negative electrode active material was tested particle size.

(2) The composite material that each embodiment and comparative example make are respectively dispersed in the dispersant ethanol, form dilute suspension after ultrasonic 40 minutes, get a small amount of suspension and drip on the copper microgrid that is attached with carbon film with capillary, room temperature After drying for 2 hours, put it into a transmission electron microscope (Tecnai G2 F30 S-TWIN) sample rod for observation, obtain TEM images of the composite materials prepared in each example and comparative example, and measure the thickness of the silicon nitride layer according to the TEM images.

(3) Electrochemical performance test:

The silicon/silicon nitride layer/carbon layer composite materials prepared in each embodiment and comparative example were respectively used as the negative electrode active material, and were mixed with the conductive agent Super P and the binder CMC+SBR in sequence according to the mass ratio of 8:1:1 to form The slurry was coated on the copper foil to prepare the negative electrode, and dried in vacuum at 80°C for 12h; then the negative electrode membrane obtained by pressing was dried in a constant temperature drying oven at 110°C for 24h, and then vacuum-dried at 80°C for 12h, and washed with a punch Head-punched into pole pieces with a diameter of 14 mm and transferred to a vacuum glove box for later use.

The assembly of the CR2025 button-type lithium-ion battery is to use metal lithium as the positive electrode, use (LiPF6/EC+DEC) as the electrolyte, use the above-mentioned pole piece with a diameter of 14mm as the negative pole piece, and use a microporous polypropylene film ( PP), all operations were carried out in a glove box; recorded as a button-type lithium-ion battery.

2) The electrochemical performance test was carried out on the button-type lithium-ion batteries prepared in the examples and comparative examples by using the Wuhan Landian (LAND 2001A) electrochemical performance tester, and the voltage range was 0.01-2.00V (vs.Li/Li+) , the current density is 0.1C-2C (1C: 1000mA/g).

The discharge specific capacity and the Coulombic efficiency after 200 cycles of charging and discharging under the condition of 0.1C charging and discharging were measured.

The discharge specific capacity of the fabricated button lithium ion battery at 2C (1C: 1000mA/g) was measured.

The results are shown in Table 2.

Table 1 embodiment 1-20 and comparative example 1-9 test parameter

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.

The difference between comparative example 1-2 and embodiment 1-3 is only that the spacing between the cathode and the anode changes. According to comparative example 1-2 and embodiment 1-3, it can be seen that the spacing has a great influence on the D50 particle size and nitriding of the composite material. The thickness of the silicon layer has no effect. The distance between the cathode and the anode in Examples 1-3 is 10mm-25mm, the distance in Comparative Example 1 is less than 10mm, and the cathode and anode are easy to stick during the powder preparation process; the distance in Comparative Example 2 is greater than 25mm, and the powder preparation During the process, the cathode and anode are easy to break the arc. Through the comparison of Example 1-3 and Comparative Example 1-2, it can be seen that under the same conditions of the D50 particle diameter and the thickness of the silicon nitride layer of the composite material prepared by Example 1-3 and Comparative Example 1-2, the results of Example 1-3 The cycle performance and rate performance of the composite material of 3 are better than those of Comparative Examples 1-2.

The only difference between Comparative Examples 3-4 and Examples 1 and 4-6 lies in the change of the discharge current. According to Comparative Examples 3-4 and Examples 1 and 4-6, it can be seen that the discharge current has no effect on the D50 particle size of the composite material and the thickness of the silicon nitride layer. The discharge current in Examples 1 and 4-6 is 10A-200A, the discharge current in Comparative Example 3 is less than 10A, the current is too small, and the arc is unstable; the discharge current in Comparative Example 4 is greater than 200A, and the current is too large, which affects safety . Through the comparison of Example 1, 4-6 and Comparative Example 3-4, it can be seen that under the same conditions of the D50 particle diameter and the thickness of the silicon nitride layer of the composite material prepared by Example 1, 4-6 and Comparative Example 3-4, The cycle performance and rate performance of the composite materials of Examples 1 and 4-6 are better than those of Comparative Examples 3-4.

The difference between Comparative Examples 5-6 and Examples 1 and 7-9 is only the change of voltage. According to Comparative Examples 5-6 and Examples 1 and 7-9, it can be seen that the voltage has no effect on the D50 particle size of the composite material and the thickness of the silicon nitride layer. The voltage in Examples 1 and 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 greater than 30V, the voltage is too large, which affects safety. Through the comparison of Examples 1, 7-9 and Comparative Examples 5-6, it can be seen that under the same conditions of the D50 particle diameter and the thickness of the silicon nitride layer of the composite material prepared by Example 1, 7-9 and Comparative Examples 5-6, The cycle performance and rate performance of the composite materials of Examples 1 and 7-9 are better than those of Comparative Examples 5-6.

The difference between Comparative Examples 7-8 and Embodiments 1 and 10-14 is only that the amounts of nitrogen, methane and hydrogen added are different. The total addition amount of reaction gas (nitrogen, methane and hydrogen) in embodiment 1,10-14 is 38kpa-53kpa, the total addition amount of reaction gas in comparative example 7 and comparative example 8 is within the above range, but, embodiment 1 , 10-14, the ratio of the addition amount (partial pressure ratio) of methane and nitrogen is 25:(3-18), resulting in the theoretical carbon atom and nitrogen atom molar ratio being (1.5:1)-(4.5: 1), the ratio of the addition amount (partial pressure ratio) of methane and nitrogen in Comparative Example 7 is 25:20, thus causing the molar ratio of carbon atoms to nitrogen atoms in theory to be less than 1.5:1 during ionization, resulting in the thickness of the silicon nitride layer Too large, so that its cycle performance and rate performance are inferior to the electrochemical performance of Example 1. The ratio of the addition amount (partial pressure ratio) of methane and nitrogen in Comparative Example 8 is 25:2.5, thus causing the theoretical molar ratio of carbon atoms to nitrogen atoms to be greater than 4.5:1 during ionization, resulting in too small thickness of the silicon nitride layer, The effect of inhibiting the expansion of the silicon core is not good, which significantly affects the cycle performance and rate performance of the negative electrode active material, resulting in its electrochemical performance being inferior to that of Examples 1 and 10-14.

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

The difference between comparative example 9 and embodiment 10 is only that the total addition amount of reaction gas is different, the total addition amount of reaction gas is 38kpa among the embodiment 10, and the total addition amount of reaction gas is 19kpa among the comparative example 9, it can be seen that due to the In the proportion, the addition amount of the reaction gas is small, resulting in a low concentration thereof, so the thickness of the silicon nitride layer of the negative electrode active material is small.

According to Example 15 and Example 1, since the ionization rate of acetylene is lower than that of methane, it is sufficient to add more acetylene to match the ionization rate of nitrogen gas. According to Example 16 and Example 1, when the specific raw material of the nitrogen source is changed, it is only necessary to adjust the amount of the specific raw material according to the rate at which nitrogen atoms are generated by its ionization.

Comparing Example 16 and Example 17, it can be seen that the content of carbon atoms will affect the particle size.

According to Example 17, hydrogen atoms can be obtained only by decomposing methane.

According to Example 18 and Example 1, it can be seen that the change of the cathode material will affect the cycle performance and rate performance of the negative electrode active material to a certain extent.

The difference between Example 19 and Example 1 is that the passivation gas is different. According to Example 1 and Example 19, the difference in passivation gas and passivation time will not affect the particle size and silicon nitride thickness. The gas affects the surface energy of the negative electrode active material, so it only slightly affects the cycle performance and rate performance of the negative electrode active material.

The difference between Example 20 and Example 1 is that the passivation time is different. According to Example 1 and Example 20, the difference in passivation time will not affect the particle size and silicon nitride thickness, but the passivation will affect the thickness of the negative electrode active material. Therefore, the surface energy 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 prepared in Example 1. It can be seen from FIG. 4 that the composite material has three layers, and the thickness of the silicon nitride layer is about 7 nm.

Figure 5 is the XRD spectrum of the composite material prepared in Example 1. The XRD measurement method is: adopt X-ray diffractometer (XRD-6000) of Shimadzu Corporation, use copper target as radiation source (λ=0.15416nm), voltage 40kV, current 30mA, scan speed 4°/min, scan angle Range 20°-80°.

According to Figure 5, it can be seen that there are characteristic peaks of silicon phase, silicon nitride phase and carbon phase at the same time, and according to the characteristic peaks of the XRD spectrum at about 25°, it shows that carbon contains graphitic carbon, which can be further combined with existing graphene Comparison of the XRD patterns shows that the graphitic carbon should be graphene at this time.

FIG. 6 is a cycle performance diagram of the negative electrode of the composite material prepared in Example 1 at a current density of 100 mA/g. FIG. 7 is a Coulombic efficiency diagram of the negative electrode of the composite material prepared in Example 1 at a current density of 100 mA/g. According to Figure 6 and Figure 7, the negative electrode of the composite material prepared in Example 1 can maintain a specific capacity of 1413mAh/g after 200 cycles at a current density of 100mA/g, and the Coulombic efficiency is as high as 99.58%.

Fig. 8 is the rate performance diagram of the negative electrode electrode of the composite material that embodiment 1 makes, use Wuhan blue electricity (LAND 2001A) electrochemical performance tester at 0.1-2C (1C: 1000mA/g), and obtain its cycle performance diagrams at different rates of 0.1C, 0.5C, 1C, 1.5C, and 2C (1C: 1000mA/g). It can be seen from Figure 8 that the composite material is stable in cycling under various current density tests, and the composite material has good rate performance. When the current density is 2A/g, the discharge specific capacity is 893mAh/g higher.

In summary, the negative electrode active material and its preparation method, negative electrode sheet, battery and electrical equipment provided by the present application can improve the technical problems of poor rate performance and low lifespan of silicon-based negative electrode active materials.

The above are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, there may be various modifications and changes in the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Claims (12)

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.

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