Silicon-carbon negative electrode material, preparation method therefor, negative electrode piece, electrode, and electric device

Abstract

The present application relates to the field of batteries and provides a silicon-carbon negative electrode material, a preparation method therefor, a negative electrode piece, an electrode, and an electric device. The silicon-carbon negative electrode material comprises porous carbon and silicon particles attached to the pore walls of the porous carbon, a crystal phase being present in the silicon particles, crystallinity being at least 90%, and the average crystal grain size of the silicon particles being less than 4 nm. The silicon-carbon negative electrode material can allow batteries to obtain better cycle stability and high initial Coulombic efficiency.

Description

Silicon-carbon negative electrode material and preparation method thereof, negative electrode sheet, electrode and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311523761.0 filed on November 15, 2023, entitled “Silicon-carbon negative electrode material and preparation method thereof, negative electrode sheet, electrode and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of batteries, and more specifically, to a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode sheet, an electrode, and an electrical device. Background Art

[0004] Silicon is a high-capacity material suitable for use as anode material, with a theoretical capacity over 10 times that of the currently mainstream graphite anode. Silicon also boasts high safety, abundant resources, and low production costs. Carbon, on the other hand, offers high electrical conductivity, a relatively stable structure, minimal volume expansion during cycling (typically less than 10%), and excellent flexibility and lubricity. Combining the advantages of both silicon-carbon anode materials could significantly enhance the performance of secondary batteries.

[0005] However, although the capacity of the current gas-phase synthesized silicon-carbon materials has been improved compared to traditional technologies, the first coulombic efficiency is low. In order to improve the first coulombic efficiency of the silicon-carbon negative electrode materials, there is a defect of sacrificing cycle stability. That is, after the existing silicon-carbon negative electrode materials are used in batteries, it is impossible to achieve both better cycle stability and high first coulombic efficiency.

[0006] Summary of the Invention

[0007] In view of the above problems, the present application proposes a silicon-carbon negative electrode material and its preparation method, a negative electrode plate, an electrode and an electrical device, which can improve the technical problem that the battery cannot achieve both good cycle stability and high first coulombic efficiency.

[0008] In a first aspect, an embodiment of the present application provides a silicon-carbon negative electrode material, which includes porous carbon and silicon particles attached to the pore walls of the porous carbon, wherein a crystalline phase exists in the silicon particles and the crystallinity is at least 90%, and the average grain size of the silicon particles is less than 4 nm.

[0009] In the silicon-carbon negative electrode material provided by the present application, since there is a crystalline phase (that is, crystalline silicon) in the silicon particles and the crystallinity is at least 90%, the first coulombic efficiency of the battery can be effectively improved compared to amorphous silicon. The silicon particles are attached to the pore walls of the porous carbon and the average grain size of the silicon particles is less than 4nm. On the one hand, the average grain size of the silicon particles is limited to alleviate and reduce the difference in expansion force of crystalline silicon in all directions, which is beneficial to alleviate and improve the cycle stability of the battery. On the other hand, a part of the space can be reserved in the pores to buffer the volume expansion caused by the silicon particles, which can further improve the cycle performance of the battery using this negative electrode material.

[0010] That is, the silicon-carbon negative electrode material provided in this application can enable the battery to obtain both better cycle stability and high first coulombic efficiency.

[0011] In some embodiments, the average grain size of the silicon particles is less than 2 nm. Within the above range, it is beneficial to reduce the difference in expansion force of the crystalline silicon in various directions, which is beneficial to further improve the cycle performance of the battery.

[0012] In some embodiments, the average pore size of the porous carbon is ≤4 nm, and can be ≤2 nm, which is beneficial for improving the cycle performance of batteries using such negative electrode materials.

[0013] In some embodiments, the porous carbon satisfies at least one of the following characteristics:

[0014] (a1) The porous carbon has micropores, mesopores, and macropores, with the volume proportion of micropores being ≥75%;

[0015] (a2) The specific surface area of ​​porous carbon is ≥1700m 2 / g;

[0016] (a3) The pore volume of porous carbon is ≥ 0.75 m 3 / g;

[0017] Optionally, the porous carbon satisfies at least one of the following characteristics:

[0018] (b1) Porous carbon has micropores, mesopores, and macropores, with the volume proportion of micropores being ≥85%;

[0019] (b2) The specific surface area of ​​porous carbon is ≥1800m 2 / g;

[0020] (b3) The pore volume of porous carbon is ≥0.8m 3 / g.

[0021] Within the above range, the battery using this negative electrode material can achieve better capacity, coulombic efficiency and cycle performance.

[0022] In some embodiments, porous carbon and silicon particles serve as the main body, and the silicon-carbon negative electrode material further includes a carbon coating layer coated on the main body. The carbon coating layer, wrapped around the surface of the main body, not only seals the pores, making them closed-pore, thereby preventing external electrolyte from entering the internal pores, but also reduces the specific surface area, thereby minimizing the loss of active lithium during the formation of the SEI film on the surface of the silicon-carbon negative electrode material. Furthermore, it prevents problems such as capacity loss caused by oxidation of silicon on the material surface, which can lead to a decrease in the battery's initial coulombic efficiency.

[0023] In some embodiments, the carbon coating layer is discontinuous, and the thickness of the carbon coating layer is 1 to 40 nm.

[0024] In some embodiments, the silicon-carbon anode material satisfies at least one of the following characteristics:

[0025] (c1) The mass content of silicon particles in the silicon-carbon negative electrode material is 35% to 55%;

[0026] (c2) The porosity of the silicon-carbon negative electrode material is 40% to 60%;

[0027] (c3) The specific surface area of ​​silicon-carbon negative electrode material is ≤6m 2 / g;

[0028] (c4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 4 μm to 15 μm.

[0029] Within the above range, it is beneficial for batteries using this negative electrode material to have better capacity, coulombic efficiency and cycle performance. In some embodiments, the silicon-carbon negative electrode material meets at least one of the following characteristics:

[0030] (d1) The mass content of silicon particles in the silicon-carbon negative electrode material is 40% to 50%;

[0031] (d2) The porosity of the silicon-carbon negative electrode material is 45% to 55%;

[0032] (d3) The specific surface area of ​​silicon-carbon negative electrode material is ≤4m 2 / g;

[0033] (d4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 5 μm to 10 μm.

[0034] Within the above range, the battery using this negative electrode material can achieve better capacity, coulombic efficiency and cycle performance.

[0035] In a second aspect, the present application provides a method for preparing the silicon-carbon negative electrode material in the above embodiment, which comprises: depositing silicon particles on porous carbon by chemical vapor deposition; wherein the average pore size of the porous carbon is ≤4 nm.

[0036] In the technical solution of the embodiment of the present application, silicon particles are deposited on porous carbon by chemical vapor deposition. The silicon particles are deposited in the pores of the porous carbon. Therefore, the maximum grain size of the silicon particles is less than the pore size of the porous carbon, and the average grain size of the silicon particles is less than the average pore size of the porous carbon. Therefore, the average pore size of the porous carbon is ≤4nm, so that the average grain size of the silicon particles can be controlled to be less than 4nm, so that after the prepared silicon-carbon negative electrode material is applied to the battery, the battery has both better cycle stability and high first coulombic efficiency.

[0037] In some embodiments, the method of depositing silicon particles on porous carbon using chemical vapor deposition includes:

[0038] The porous carbon is placed in a reaction atmosphere and kept warm at 400°C to 550°C for at least 8 hours, wherein the reaction atmosphere is a mixed atmosphere of protective gas and silicon source gas, the gas flow ratio of the protective gas to the silicon source gas is 90:10 to 70:30, and the protective gas includes at least one of an inert gas and hydrogen; by adjusting the temperature, gas ratio and holding time within the above range to control the decomposition efficiency and deposition rate of the silicon source gas, on the one hand, it is beneficial to uniformly distribute the silicon particles in the pores of the porous carbon, and on the other hand, it is beneficial to generate crystalline silicon and to suppress the generation of capacity-less silicon carbide or excessive amorphous silicon.

[0039] Optionally, the temperature of the heat preservation reaction is 430°C to 530°C.

[0040] Optionally, the gas flow ratio of the protective gas to the silicon source gas is 85:15 to 75:25.

[0041] Optionally, the insulation reaction time is 8 hours to 16 hours, and optionally 10 hours to 16 hours.

[0042] In some embodiments, the preparation method further comprises: the preparation method further comprises: using a product obtained by depositing silicon particles on porous carbon as a body, placing the body in a mixed atmosphere of a carbon source and an inert gas, and pyrolyzing the carbon source to form a carbon coating layer covering the body;

[0043] The carbon source includes one or more of alkanes, alkynes and alkenes.

[0044] The above arrangement can form a uniformly distributed carbon coating layer on the surface of the body, thereby improving the stability of the material interface and reducing the specific surface area, which is beneficial for the battery to have both better first coulombic efficiency and better cycle performance.

[0045] Optionally, the temperature of the pyrolysis carbon source is 400° C. to 800° C., and the pyrolysis time is 0.2 h to 2 h;

[0046] Optionally, the gas flow ratio of the inert gas to the carbon source is 1:(1.5-5).

[0047] In a third aspect, the present application provides a negative electrode plate, which includes the silicon-carbon negative electrode material in the above embodiment.

[0048] In a fourth aspect, the present application provides a battery comprising the battery cell in the above embodiment.

[0049] In a fifth aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0050] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0052] FIG1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

[0053] FIG2 is a schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0054] FIG3 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0055] FIG4 is a schematic structural diagram of a negative electrode sheet in some embodiments of the present application;

[0056] FIG5 is an XRD pattern of the silicon-carbon negative electrode material provided in Example 1;

[0057] FIG6 is an XRD pattern of the silicon-carbon negative electrode material provided in Comparative Example 1;

[0058] FIG7 is an XRD diagram of the silicon-carbon negative electrode material provided in Comparative Example 2.

[0059] The figure numbers in the specific implementation manner are as follows: 1000-vehicle; 100-battery; 200-controller; 300-motor; 10-housing; 11-first part; 12-second part; 20-battery cell; 21-housing; 22-electrode assembly; 23-electrode terminal; 24-pressure relief structure; 211-housing; 212-cover; 221-negative electrode sheet; 2211-negative electrode current collector; 2212-negative electrode tab; 2213-negative electrode active material layer. DETAILED DESCRIPTION

[0060] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0062] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0063] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0064] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0065] 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 groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0066] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do 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 a limitation on the embodiments of the present application.

[0067] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0068] In order to alleviate the problem that batteries using existing silicon-carbon negative electrode materials cannot achieve both good cycle stability and high first coulombic efficiency, the present application designs a silicon-carbon negative electrode material, which includes porous carbon and silicon particles attached to the pore walls of the porous carbon. There is a crystalline phase in the silicon particles and the crystallinity is at least 90%, and the average grain size of the silicon particles is less than 4nm.

[0069] In such a silicon-carbon negative electrode material, since there is a crystalline phase (that is, crystalline silicon) in the silicon particles and the crystallinity is at least 90%, the first coulombic efficiency of the battery can be effectively improved compared to amorphous silicon. The average grain size of the silicon particles is less than 4nm, which can effectively improve the cycle stability of the battery. In addition, the silicon particles are attached to the pore walls of the porous carbon so that a part of the space can be reserved in the pores to buffer the volume expansion caused by the silicon particles, which can further improve the cycle performance of the battery.

[0070] The batteries disclosed in the embodiments of this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power supply system comprising the batteries disclosed in this application can be used to alleviate and improve the initial coulombic efficiency and cycle performance of the battery.

[0071] The present invention provides an electric device that uses a battery as a power source. The electric device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0072] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0073] Please refer to Figure 1, which is a schematic structural diagram of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000. For example, the battery 100 can serve as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0074] In some embodiments of the present application, the battery 100 can serve not only as an operating power source for the vehicle 1000, but also as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0075] In this application, the battery 100 refers to a single physical module that includes one or more battery cells 20 to provide a certain voltage and capacity. It can be in the form of a battery pack, a battery module, etc. The battery 100 may also include a box 10 for encapsulating one or more battery cells 20. The box 10 can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0076] Please refer to Figure 2, which is an exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a storage space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 can include a first portion 11 and a second portion 12, which overlap each other and together define a storage space for the battery cell 20. The second portion 12 can be a hollow structure with one end open. The first portion 11 can be a plate-like structure, with the first portion 11 overlapping the open side of the second portion 12, so that the first portion 11 and the second portion 12 together define a storage space. Alternatively, the first portion 11 and the second portion 12 can each be a hollow structure with one end open, with the open side of the first portion 11 overlapping the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0077] 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 a hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. The multiple battery cells 20 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 20 may be housed within the housing 10. Alternatively, the battery 100 may be constructed by first connecting multiple battery cells 20 in series, in parallel, or in a hybrid connection to form a battery module, which is then connected in series, in parallel, or in a hybrid connection to form a complete battery module, and then housed within the housing 10. The battery 100 may also include other structures, such as a busbar assembly for electrically connecting the multiple battery cells 20.

[0078] The battery cell 20 refers to the smallest unit constituting the battery 100. The battery cell 20 may be a lithium-ion battery.

[0079] Please refer to Figure 3, which is a schematic diagram of the exploded structure of a battery cell 20 provided in some embodiments of the present application. Referring to Figure 3, the battery cell 20 may include a housing 21, an electrode assembly 22, and an electrolyte, wherein the electrode assembly 22 and the electrolyte are both contained within the housing 21.

[0080] The outer shell 21 may include a shell 211 and a cover 212. The shell 211 is a component used to cooperate with the cover 212 to form an internal sealed space of the battery cell 20, wherein the formed sealed space can be used to accommodate the electrode assembly 22, electrolyte and other components. The cover 212 refers to a component that covers the opening of the shell 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the shell 211 to cooperate with the shell 211. Functional components such as electrode terminals 23 and pressure relief structures 24 can also be provided on the cover 212. A sealing ring can be configured between the opening of the shell 211 and the cover 212 to achieve sealing between the shell 211 and the cover 212.

[0081] The shell 211 and the cover 212 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shapes of the shell 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell 211 and the cover 212 can be various, such as but not limited to metals such as copper, iron, aluminum, stainless steel, and aluminum alloy. The material of the sealing ring can be various, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate) and other materials that are resistant to electrolyte corrosion, high toughness and fatigue resistance. A coating can be formed on the outer surface of the shell 211, and the material of the coating can be various, such as but not limited to corrosion-resistant materials such as Ni and Cr.

[0082] The battery cell 20 may also be in the form of a soft pack, such as a pouch-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0083] The electrode assembly 22 includes a negative electrode sheet, a separator, and a positive electrode sheet. The battery cell 20 primarily operates by the movement of metal ions between the positive and negative electrode sheets. During the charge and discharge process, active ions are embedded in and released from the positive and negative electrode sheets. The separator, located between the positive and negative electrode sheets, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The electrode assembly 22 can be a wound or laminated structure, but the embodiments of the present application are not limited thereto.

[0084] The positive electrode sheet includes a positive electrode collector, a positive electrode tab and a positive electrode active material layer. The positive electrode active material layer is arranged on at least one side of the positive electrode collector, and a primer layer may also be arranged between the positive electrode active material layer and the positive electrode collector; the positive electrode tab protrudes from the positive electrode collector, and the positive electrode tab is located at one end or two opposite ends of the positive electrode collector, for example.

[0085] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector and the positive electrode tab may be made of aluminum. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0087] In some embodiments, the positive electrode active material layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] The isolation membrane is located between the positive electrode sheet and the negative electrode sheet and serves as an isolation membrane. The embodiment of the present application has no particular restriction on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0089] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0090] As shown in Figure 4, the negative electrode sheet 221 includes a negative electrode current collector 2211, a negative electrode tab 2212 and a negative electrode active material layer 2213. The negative electrode active material layer 2213 is arranged on at least one side of the negative electrode current collector 2211, and a primer layer or the like can be further arranged between the negative electrode current collector 2211 and the negative electrode active material layer 2213; the negative electrode tab 2212 protrudes from the negative electrode current collector 2211, and the negative electrode tab 2212 is located at one end or two opposite ends of the negative electrode current collector 2211, for example.

[0091] Among them, the negative electrode current collector 2211 can be made of metal foil or a composite current collector. For example, the material of the negative electrode current collector 2211 and the negative electrode tab 2212 can be copper. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] The negative electrode active material in the negative electrode active material layer 2213 includes a silicon-carbon negative electrode material.

[0093] In some embodiments, the negative electrode active material layer 2213 may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0094] In some embodiments, the negative electrode active material layer 2213 may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In some embodiments, the negative electrode active material layer 2213 may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0096] The silicon-carbon negative electrode material and its preparation method proposed in the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0097] According to some embodiments of the present application, the silicon-carbon negative electrode material includes porous carbon and silicon particles attached to the pore walls of the porous carbon. The silicon particles contain a crystalline phase and have a crystallinity of at least 90%. The average grain size of the silicon particles is less than 4 nm.

[0098] Porous carbon includes but is not limited to graphite, soft carbon, hard carbon and other porous carbons.

[0099] Silicon particles attached to the pore walls of porous carbon refer to the situation where the silicon particles are attached to the pore walls of the porous carbon and the pore spaces are not completely filled with silicon particles. In other words, the porous carbon with silicon particles attached to the pore walls still has some porosity.

[0100] The presence of a crystalline phase in the silicon particles and a crystallinity of at least 90% means that: the silicon particles are entirely crystalline, in which case the silicon particles are entirely crystalline silicon, or the silicon particles are a mixture of crystalline and amorphous phases, in which the crystalline phase accounts for at least 90% by mass. The crystallinity can be calculated based on the characteristic peaks of silicon in the Raman spectrum of the silicon-carbon anode material. Specifically, the crystallinity can be calculated by dividing the area of ​​the Raman peak representing the crystalline silicon in the silicon particles by the area of ​​the Raman peak representing the total silicon, including the crystalline and amorphous phases in the silicon particles.

[0101] Illustratively, the crystallinity is any value among 90%, 92%, 93%, 95%, 96%, 97%, 98%, 99%, 100%, or between any two values.

[0102] The average grain size of the silicon particles here refers to the average size of the crystalline silicon in the silicon particles. Since there is a crystalline phase in the silicon particles and the crystallinity is at least 90%, that is, most of them are crystalline silicon, crystalline silicon is anisotropic when it expands. Therefore, the average grain size of the silicon particles is less than 4nm to alleviate the anisotropy of the crystalline silicon during expansion.

[0103] The average grain size of silicon particles can be calculated by measuring the XRD pattern of a sample according to the JIS / K0131-1996 test standard. The half-height width β and diffraction angle θ of the Si(111) crystal plane diffraction peak are taken from the XRD pattern of the sample and substituted into the Debye-Scherrer formula to obtain the average grain size of the silicon particles. The Debye-Scherrer formula is: Dhkl = kλ / βcosθ, where Dhkl is the average grain size of the silicon particles, in nm; k is the Scherrer constant, 0.89; λ is the wavelength of the incident X-ray, 0.15406 nm; β is the half-height width of the diffraction peak, in rad; and θ is the diffraction angle, in degrees.

[0104] Illustratively, the average grain size of the silicon particles includes, but is not limited to, any value of 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 3.9 nm, and the like.

[0105] In the silicon-carbon negative electrode material provided by the present application, since there is a crystalline phase (that is, crystalline silicon) in the silicon particles and the crystallinity is at least 90%, the first coulombic efficiency of the battery can be effectively improved compared to amorphous silicon. The silicon particles are attached to the pore walls of the porous carbon and the average grain size of the silicon particles is less than 4nm. On the one hand, the average size limitation is utilized to alleviate and reduce the difference in expansion force of crystalline silicon in various directions, which is beneficial to alleviate and improve the cycle stability of the battery. On the other hand, a part of the space can be reserved in the pores to buffer the volume expansion caused by the silicon particles, which can further improve the cycle performance of the battery.

[0106] That is, the silicon-carbon negative electrode material provided in this application can enable the battery to obtain both better cycle stability and high first coulombic efficiency.

[0107] In some embodiments, the average grain size of the silicon particles is <2 nm.

[0108] Within the above range, it is beneficial to further reduce the difference in expansion force of crystalline silicon in various directions, which is beneficial to improving the cycle performance of the battery.

[0109] In some embodiments, the porous carbon has an average pore size of ≤ 4 nm.

[0110] Porous carbon can be divided into crack pores, conical pores, cylindrical pores, spherical pores, etc. according to the pore shape, and some pores are irregular. Therefore, the pore diameter here is defined as the distance between the two farthest points on the pore wall.

[0111] It can be understood that the arrangement of silicon particles attached to the pore walls of porous carbon, that is, the pore size of porous carbon is used to limit the size of silicon grains. The maximum grain size of silicon particles is bound to be smaller than the pore size of porous carbon, and the average grain size of silicon particles is also smaller than the average pore size of porous carbon, thereby leaving a certain space after deposition to alleviate expansion.

[0112] Therefore, the average pore size of porous carbon is ≤4nm. On the one hand, it can effectively limit the average grain size of silicon particles to <4nm, which is beneficial to improving the cycle performance. On the other hand, under the same volume, the larger the pore size, the lower the porosity, resulting in concentrated distribution of pores. Therefore, when the average pore size of porous carbon is ≤4nm, the pores on the porous carbon are basically evenly distributed, which is beneficial to the uniform distribution of silicon particles in the silicon-carbon negative electrode material, thereby improving the cycle performance of the battery.

[0113] Optionally, the average pore size of the porous carbon is ≤2 nm.

[0114] Within the above range, the average grain size of silicon particles can be effectively limited to less than 2 nm, and it is beneficial to the uniform distribution of silicon particles in the silicon-carbon negative electrode material, thereby improving the cycle performance of the battery.

[0115] In some embodiments, the porous carbon satisfies at least one of the following characteristics:

[0116] (a1) The porous carbon has micropores, mesopores and macropores, and the volume proportion of micropores is ≥75%.

[0117] Micropores, mesopores and macropores are distinguished according to the pore size. Among them, pores with a diameter less than 2nm are called micropores; pores with a diameter greater than 50nm are called macropores; and pores with a diameter between 2 and 50nm are called mesopores (or mesopores).

[0118] The more pores there are, the larger the corresponding pore volume. Therefore, the volume ratio is used to reflect the number of micropores, that is, the micropore ratio is based on the size of the average pore diameter, which further limits the number of micropores. From the description of the pore size distribution, it can be seen that micropores can better limit the size of silicon particles and promote the uniform distribution of silicon within the material. Therefore, using a micropore volume ratio of ≥75% is beneficial to further improve expansion and enhance the cycle performance of the battery.

[0119] Illustratively, the volume fraction of the micropores includes but is not limited to any value of 75%, 80%, 85%, 90%, 95%, etc.

[0120] (a2) The specific surface area of ​​porous carbon is ≥1700m 2 / g.

[0121] The above specific surface area range is conducive to the deposition of silicon particles in the pores of the porous carbon, thereby improving the initial discharge capacity and cycle performance of the battery.

[0122] (a4) The pore volume of porous carbon is ≥ 0.75 m 3 / g.

[0123] The pore volume refers to the total volume of pores per unit mass of porous carbon, and the pore volume of porous carbon corresponds to the deposition amount of silicon particles.

[0124] By limiting the pore volume of porous carbon to >0.75m 3 / g, it is beneficial to deposit a target amount of silicon in the porous carbon to increase the capacity of the silicon-carbon negative electrode material, and after the silicon is deposited to the target amount, the porous carbon still has sufficient pores to buffer the volume expansion caused by the silicon particles, thereby improving the first discharge capacity and cycle performance of the battery.

[0125] In some embodiments, the porous carbon satisfies at least one of the following characteristics:

[0126] (b1) Porous carbon has micropores, mesopores, and macropores, with the volume proportion of micropores being >85%;

[0127] The volume proportion of micropores is greater than 85%, which is conducive to the uniform distribution of silicon within the material, thereby improving expansion and enhancing cycle performance.

[0128] (b2) Specific surface area of ​​porous carbon>1800m 2 / g;

[0129] The above-mentioned specific surface area range is conducive to the deposition of silicon particles in the pores of porous carbon, further improving the capacity and cycle performance of the battery.

[0130] (b3) The pore volume of porous carbon is >0.8m 3 / g.

[0131] Within the above range, it is beneficial to further improve the capacity and cycle performance of the battery.

[0132] In some embodiments, porous carbon and silicon particles are used as the main body, and the silicon-carbon negative electrode material further includes a carbon coating layer coated on the main body.

[0133] Since silicon particles are highly active, a carbon coating layer is used to wrap the surface of the body. On the one hand, the pores are sealed to make them closed-pores, so that the external electrolyte cannot enter the internal pores, and the specific surface area is reduced, thereby reducing the loss of active lithium when the SEI film is formed on the surface of the silicon-carbon negative electrode material. On the other hand, it can prevent the capacity loss caused by the oxidation of silicon on the surface of the material, which leads to a decrease in the first coulombic efficiency of the battery.

[0134] In some embodiments, the carbon coating layer is discontinuous, and the thickness of the carbon coating layer is 1 to 40 nm.

[0135] Exemplarily, the thickness of the carbon layer is tested by embedding and curing the negative electrode active material with epoxy resin, and then using ultrathin sectioning to cut the material into sizes of 50nm to 70nm, and prepare the sample. A high-power transmission electron microscope is used to select a cross-section of the particle sample for observation, and the pore area and the disordered carbon layer area are observed. The pore area and the disordered carbon layer area are the body, and the outermost disordered part of the entire body is the carbon shell. The material is photographed and observed by TEM, and then the image analysis software Image J is used to randomly select 10 negative electrode material particles from the photo to obtain the thickness of the outermost disordered part (carbon coating layer) of these negative electrode material particles, and then the average thickness of the 10 negative electrode material particles is taken as the thickness of the carbon coating layer.

[0136] Within the above thickness range, lithium can diffuse through the carbon coating layer and effectively coat the body.

[0137] In some embodiments, the silicon-carbon negative electrode material satisfies at least one of the following characteristics:

[0138] (c1) The mass content of silicon particles in the silicon-carbon negative electrode material is 35-55%;

[0139] The silicon content determines the capacity of the material. Too low a silicon content will result in low material capacity, but too high a silicon content will also result in low residual porosity of the material, which will not be able to control the expansion of the silicon-carbon negative electrode material well.

[0140] Therefore, the silicon-carbon negative electrode material uses a silicon particle content of 35-55% by mass, which can improve the battery's initial discharge capacity, cycle performance, and initial coulombic efficiency.

[0141] Illustratively, the mass content of silicon particles in the silicon-carbon negative electrode material is any value among 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, or between any two values.

[0142] (c2) The porosity of the silicon-carbon negative electrode material is 40% to 60%;

[0143] Using porous carbon with the same parameters, if the porosity is too low, the expansion cannot be effectively controlled, thus affecting the material's cycling performance. If the porosity is too high, on the one hand, the silicon-carbon anode material's capacity will be low due to the small amount of silicon deposited, and on the other hand, it will become structurally unstable and there is a risk of cracking during cold pressing. Therefore, using a silicon-carbon anode material with a porosity of 40% to 60% can achieve a battery with better capacity, cycling performance, and high initial coulombic efficiency.

[0144] For example, the porosity of the silicon-carbon negative electrode material is any one of 40%, 43%, 45%, 47%, 50%, 53%, 55%, 57%, 60%, or between any two values. (c3) The specific surface area of ​​the silicon-carbon negative electrode material is ≤ 6m 2 / g;

[0145] By controlling the specific surface area of ​​silicon-carbon negative electrode materials to ≤6m 2 / g, to avoid excessive loss of active lithium when SEI film is formed on the surface of silicon-carbon negative electrode material due to excessive specific surface area, resulting in low initial coulombic efficiency of the battery and deterioration of cycle performance.

[0146] For example, the specific surface area of ​​the silicon-carbon negative electrode material includes but is not limited to 6m 2 / g、5m 2 / g、4m 2 / g、3m 2 / g, 2m 2 / g、1m 2 / g or 0.5m 2 / g, etc.

[0147] (c4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 4 μm to 15 μm.

[0148] The volume particle size distribution Dv50 refers to a particle size distribution parameter determined by a particle size distribution measurement value. For example, the volume particle size distribution Dv50 is determined using a particle size analyzer-laser diffraction method. Specifically, the standard GB / T 19077-2016 can be referred to and the laser diffraction scattering particle size analyzer can be used for measurement.

[0149] Within the above range, the battery is beneficial to having better cycle performance, first coulombic efficiency and fast charging performance.

[0150] Exemplarily, the volume particle size distribution Dv50 of the silicon-carbon negative electrode material is any value of 4 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 13 μm, 15 μm, or between any two values.

[0151] In some embodiments, the silicon-carbon negative electrode material satisfies at least one of the following characteristics:

[0152] (d1) The mass content of silicon particles in the silicon-carbon negative electrode material is 40% to 50%;

[0153] (d2) The porosity of the silicon-carbon negative electrode material is 45% to 55%;

[0154] (d3) The specific surface area of ​​silicon-carbon negative electrode material is less than 4m 2 / g;

[0155] (d4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 5 μm to 10 μm.

[0156] By limiting the above parameters, it is beneficial to improve the battery capacity, cycle performance and first coulombic efficiency.

[0157] In some embodiments, the present application also provides a method for preparing the above-mentioned silicon-carbon negative electrode material, which comprises: depositing silicon particles on porous carbon by chemical vapor deposition;

[0158] The average pore size of the porous carbon is ≤4 nm.

[0159] In the above preparation method, silicon particles are deposited on porous carbon by chemical vapor deposition. The silicon particles are deposited in the pores of the porous carbon. Therefore, the maximum grain size of the silicon particles is less than the pore size of the porous carbon, and the average grain size of the silicon particles is less than the average pore size of the porous carbon. Therefore, by using the average pore size of the porous carbon ≤4nm, the average grain size of the silicon particles can be controlled to be less than 4nm, so that after the prepared silicon-carbon negative electrode material is applied to the battery, the battery has both better cycle stability and high first coulombic efficiency.

[0160] In some embodiments, the method of depositing silicon particles on porous carbon using chemical vapor deposition includes:

[0161] The porous carbon is placed in a reaction atmosphere and kept warm at 400°C to 550°C for at least 8 hours, wherein the reaction atmosphere is a mixed atmosphere of protective gas and silicon source gas, the gas flow ratio of the protective gas to the silicon source gas is 90:10 to 70:30, and the protective gas includes at least one of an inert gas and hydrogen.

[0162] Inert gases include but are not limited to nitrogen, argon, etc.

[0163] The silicon source gas includes but is not limited to one or more silane-containing hydrocarbons such as silane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0164] It can be understood that the method of depositing silicon particles on porous carbon by chemical vapor deposition can be carried out in the heating chamber of the vapor deposition furnace. The porous carbon can be placed in the heating chamber of the vapor deposition furnace first, and then the heating chamber is evacuated by a vacuum pump, and then an inert gas is introduced into the heating chamber to avoid interference from impurities. After the inert gas fills the heating chamber, a mixed gas is introduced at a gas flow ratio of 90:10 to 70:30 between the protective gas and the silicon source gas. While introducing the mixed gas, the temperature of the heating chamber of the vapor deposition furnace is raised to 400°C to 550°C, so that the silicon source gas decomposes silicon and is deposited in the pores of the porous carbon. The mixed gas is continuously introduced into the heating chamber of the vapor deposition furnace, and the pressure in the heating chamber of the vapor deposition furnace is maintained at normal pressure for at least 8 hours of insulation reaction.

[0165] Among them, if the proportion of silicon source gas in the mixed gas is too high, the silicon deposition rate will be too fast, the nano-silicon particles will easily agglomerate, and the agglomerated silicon particles will easily clog the pores, resulting in less silicon deposition in the center of the porous carbon, thereby affecting the uneven distribution of internal silicon particles, resulting in large local expansion of the silicon-carbon negative electrode material during the cycle, easy to crack and break, affecting the structural stability of the silicon-carbon negative electrode material, and if the proportion of silicon source gas in the mixed gas is too low, the deposition rate will be too slow and the process efficiency will be too low. Therefore, the gas flow ratio of the protective gas to the silicon source gas is 90:10 to 70:30. Exemplarily, the gas flow ratio of the protective gas to the silicon source gas is any value among 90:10, 89:11, 85:15, 83:17, 80:20, 77:23, 75:25, 73:27, 71:29, 70:30, or between any two values.

[0166] The holding temperature affects the decomposition of the silicon source gas and the components obtained. 400°C is the temperature at which the silicon source gas begins to decompose into amorphous silicon. If the temperature is too low, silane cannot be decomposed and the silicon deposition process cannot be carried out. If the temperature is too high, on the one hand, the decomposition rate is too fast, which can easily cause pore blockage and uneven distribution of silicon within the material. On the other hand, if the temperature is too high, it is easy for nano-silicon and carbon substrates to react to produce silicon carbide, which cannot provide capacity, resulting in material capacity loss. Therefore, the holding temperature is 400°C to 550°C. Exemplarily, the temperature of the holding reaction is any value of 400°C, 430°C, 450°C, 460°C, 470°C, 500°C, 530°C, 550°C, or between any two values.

[0167] Since the silicon-carbon negative electrode material mainly relies on silicon particles to provide capacity, if the holding time is too short, the amount of deposited silicon particles will be small, the capacity of the silicon-carbon negative electrode material will be low, and too short a holding time is not conducive to the formation of crystalline silicon; if the holding time is too long, too many silicon particles will be deposited, which will lead to a low residual porosity of the silicon-carbon negative electrode material and fail to meet the requirement of reserved pores to reduce expansion. On the other hand, when the pores are full of nano-silicon particles, silicon will be deposited on the surface of the material to form a silicon-rich layer. The silicon on the surface is not within the limit of the porous carbon substrate framework, and its expansion is not restricted. Therefore, it expands greatly during the cycle, and the surface of the material is prone to cracking to form a thicker by-product layer. Once the by-product layer is too thick, the silicon-carbon negative electrode material will lose its activity and no longer participate in the cycle process, thereby affecting the cycle performance. Therefore, the holding time is at least 8 hours.

[0168] In the chemical vapor deposition method provided in the present application, since the pore size of the porous carbon used is relatively small, it is necessary to control the decomposition efficiency and deposition rate of the silicon source gas by adjusting the temperature, gas ratio and holding time within the above range. On the one hand, it is beneficial to the uniform distribution of silicon particles in the pores of the porous carbon, and on the other hand, it is beneficial to the generation of crystalline silicon while suppressing the generation of capacity-less silicon carbide or excessive amorphous silicon.

[0169] In some embodiments, the temperature of the insulation reaction is 430°C to 530°C.

[0170] The above range is conducive to the formation of crystalline silicon, which is beneficial to improving the capacity and first coulombic efficiency of the battery.

[0171] In some embodiments, the gas flow ratio of the shielding gas to the silicon source gas is 85:15 to 75:25.

[0172] The above range is beneficial to improving the battery cycle performance.

[0173] In some embodiments, the insulation reaction time is 8 hours to 16 hours.

[0174] Optionally, the insulation reaction time is 10 to 16 hours.

[0175] The above range is conducive to the battery having high capacity, better cycle stability and high first coulombic efficiency.

[0176] In some embodiments, the preparation method further includes: using the product obtained by depositing silicon particles on porous carbon as the body, placing the body in a mixed atmosphere of a carbon source and an inert gas, and pyrolyzing the carbon source to form a carbon coating layer coated on the body, wherein the carbon source includes one or more of alkanes, alkynes, and alkenes.

[0177] Inert gases include, but are not limited to, nitrogen or argon.

[0178] Alkanes include but are not limited to methane, alkenes include but are not limited to ethylene, and alkynes include but are not limited to acetylene.

[0179] Through the above-mentioned setting method, a carbon coating layer can be formed on the surface of the main body. The setting of the carbon coating layer is used to reduce the specific surface area to improve the interface stability of the material, and can alleviate the problem of the first coulomb efficiency loss caused by the oxidation of silicon dioxide on the surface of the material.

[0180] If the temperature of the pyrolysis carbon source is too low, the carbon source cannot be decomposed and effectively coated on the surface of the body. If the temperature is too high, the deposited silicon particles and porous carbon will easily react to form silicon carbide, resulting in material capacity loss. If the pyrolysis carbon source is too short, the carbon coating amount is too small, and it cannot completely cover the body surface to achieve the purpose of reducing the specific surface area. To ensure the coating effect, the carbon coating temperature is kept at a relatively high level. At this temperature, there is a risk of silicon carbide forming. Therefore, if the coating time is too long, it is easy to promote the formation of silicon carbide, resulting in capacity loss.

[0181] In some embodiments, the temperature for pyrolyzing the carbon source is 400° C. to 800° C., and the pyrolysis time is 0.2 h to 2 h.

[0182] By controlling the temperature of the pyrolysis carbon source and the pyrolysis time, the carbon coating layer can completely cover the surface of the body to reduce the specific surface area and alleviate the formation of silicon carbide, thereby effectively improving the capacity and cycle performance of the battery.

[0183] Illustratively, the temperature of the pyrolyzed carbon source is any one of 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or between any two values.

[0184] Illustratively, the pyrolysis time is any one of 0.2 h, 0.5 h, 0.7 h, 1 h, 1.2 h, 1.5 h, 1.7 h, 2 h, or between any two values.

[0185] In some embodiments, the gas flow ratio of the inert gas to the carbon source is 1:(1.5-5).

[0186] By controlling the gas flow ratio of inert gas to carbon source within the above range, on the one hand, the coating efficiency is effectively improved, and on the other hand, it is convenient to control the decomposition rate of the carbon source, alleviate its local enrichment, and facilitate obtaining a coating layer with uniform thickness, which is beneficial to improving the battery's cycle performance and first coulomb rate.

[0187] According to some embodiments of the present application, the present application also provides a negative electrode plate, comprising the silicon-carbon negative electrode material of any of the above schemes.

[0188] According to some embodiments of the present application, the present application also provides a battery comprising the negative electrode sheet of any of the above schemes.

[0189] According to some embodiments of the present application, the present application further provides an electrical device, which includes a battery according to any of the above solutions, and the battery is used to provide electrical energy.

[0190] Some specific embodiments are listed below to better illustrate the present application.

[0191] In the following examples and comparative examples, the relevant parameters of the porous carbon were determined as follows:

[0192] Average pore size, pore volume and micropore ratio of porous carbon

[0193] The pore size is tested by gas adsorption method according to the test standards GB / T19587-2017 & GB / T21650.2-2008. Specifically, porous carbon is taken as a sample, and the sample tube is immersed in liquid nitrogen at -196°C. Nitrogen is adsorbed on the material to be tested at a relative pressure of 0 to 1. The pore size distribution and pore volume of the porous material are characterized based on the relationship between the volume of each pore size and the corresponding partial pressure.

[0194] The micropore fraction can be calculated based on the pore size distribution of the porous material.

[0195] [Specific surface area of ​​porous carbon]

[0196] The specific surface area is tested by the gas adsorption method according to the GB / T19587-2017 test standard, as follows: porous carbon is taken as a sample, the sample tube is immersed in liquid nitrogen at -196°C, and the adsorption amount of nitrogen on the solid surface at different pressures is measured at a relative pressure of 0.05 to 0.30. The monolayer adsorption amount of the sample is obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area of ​​the solid.

[0197] BET formula:

[0198] n a - amount of adsorbed gas, in mol / g; P / P0-relative pressure; n m -Monolayer adsorption capacity.

[0199] Example 1

[0200]

Silicon-carbon anode material

[0201] (1) The porous carbon shown in Table 1 is placed in a heating chamber of a vapor deposition furnace, and the heating chamber is evacuated using a vacuum pump.

[0202] (2) Nitrogen is introduced into the heating chamber. After the protective gas fills the heating chamber, a mixed gas is introduced at a nitrogen:silane gas flow ratio of 85:15. While introducing the mixed gas, the heating chamber is heated to 460°C to decompose silane into silicon, which is deposited in the pores of the porous carbon. The mixed gas is continuously introduced into the heating chamber, and the pressure in the heating chamber is maintained at normal pressure. The heating chamber is kept at this temperature for 12 hours to obtain the body.

[0203] (3) Under a nitrogen atmosphere, the heating chamber is first heated to 660°C, and then acetylene gas is used as a carbon source. A nitrogen:acetylene gas mixture is introduced at a flow rate ratio of 1:2. The heating chamber is kept at this temperature for 0.5 h. The surface of the body is carbon-coated to obtain a silicon-carbon negative electrode material. The synthesis process of the silicon-carbon negative electrode material is shown in Table 1.

[0204]

Performance test

[0205] (1) Silicon particle crystallinity

[0206] The crystallinity is calculated by dividing the area of ​​the Raman peak representing the crystalline silicon in the silicon particle by the area of ​​the Raman peak representing the entire silicon including the crystalline phase and the amorphous phase in the silicon particle.

[0207] (2) XRD test and average grain size calculation

[0208] The XRD pattern of the sample was tested according to the JIS / K0131-1996 test standard. Based on the XRD pattern of the sample, the half-height width β and diffraction angle θ of the Si(111) crystal plane diffraction peak were taken and substituted into the Debye-Scherrer formula to calculate the particle size of the nano-silicon grains. The Debye-Scherrer formula is: Dhkl = kλ / βcosθ, where Dhkl is the particle size of the nano-silicon grains in nm; k is the Scherrer constant, 0.89; λ is the wavelength of the incident X-ray, 0.15406 nm; β is the half-height width of the diffraction peak, in rad; and θ is the diffraction angle in degrees.

[0209] (3) Silicon content test

[0210] The silicon content was determined by inductively coupled plasma (ICP) emission spectroscopy, specifically as follows: a carbon-silicon composite was taken as a sample, the sample was digested with aqua regia and hydrofluoric acid HF, and the silicon content of the solution after digestion was measured.

[0211] (4) Porosity test of silicon-carbon negative electrode materials

[0212] Tested according to GB / T24586 test standard, porosity P = (V2-V1) / V2*100%, apparent volume V2 = S*H*A, where: S-area, cm 2; H-thickness, cm; A-sample number, EA; V1-sample true volume, cm 3 ; V2-apparent volume of sample, cm 3 .

[0213] (5) Battery preparation and related performance testing

[0214]

Preparation of positive electrode sheet

[0215] The 811 type high nickel ternary material (Li(Ni 0.8 Co 0.1 Mn 0.1 )O2), acetylene black (a conductive agent), and PVDF (polyvinylidene fluoride) (a binder) were mixed in a weight ratio of 94:4:2. N-methylpyrrolidone (a solvent) was added and thoroughly stirred to obtain a positive electrode slurry. The positive electrode slurry was applied to both surfaces of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0216]

Preparation of negative electrode sheet

[0217] The silicon-carbon negative electrode material prepared in each example and comparative example, along with the conductive agent acetylene black, the binder SBR (styrene-butadiene rubber), and the thickener CMC-Na (sodium carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent and thoroughly stirred to obtain a negative electrode slurry. The negative electrode slurry was applied to both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0218]

Preparation of electrolyte

[0219] 0.6122 g of sodium perchlorate was weighed and added to 10 ml of propylene carbonate solvent, and the mixture was stirred until the sodium perchlorate was completely dissolved. Then, 3% by mass of fluoroethylene carbonate was added as an additive, and the mixture was thoroughly stirred to prepare the electrolyte.

[0220]

Provide isolation film

[0221] A polyethylene porous membrane was used as the separator.

[0222]

Assembly button battery

[0223] The negative electrode sheet, separator, and lithium metal sheet as the positive electrode prepared above are stacked in order, so that the separator is placed between the negative electrode sheet and the lithium metal sheet to play an isolating role. The separator is soaked with the electrolyte prepared above, and then compacted to obtain a button battery.

[0224]

Assembling a full battery

[0225] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. After winding, they are placed in an outer package, injected with the prepared electrolyte, and packaged, injected, formed, and vented to obtain a lithium-ion battery.

[0226] Those skilled in the art will understand that, in the above methods of the specific embodiments and comparative examples, the writing order of the steps does not mean a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of the steps should be determined by their functions and possible internal logic.

[0227]

First coulombic efficiency test of button cell

[0228] Test procedure: At room temperature, the battery was left to rest for 3 hours, then discharged at a constant current of 0.05C to a voltage of 0.005V. Further discharged at a constant current of 50μA to a voltage of 0.005V, recording the capacity at this point as the lithium insertion capacity. After resting for 5 minutes, the battery was then charged at a rate of 0.1C to a voltage of 2V, recording the capacity at this point as the lithium removal capacity.

[0229] The first coulombic efficiency of silicon-carbon negative electrode material (%) = (lithium removal capacity / lithium insertion capacity) * 100%.

[0230]

Full battery cycle performance and first discharge capacity test

[0231] Normal temperature cycle performance test:

[0232] Test conditions: At room temperature, the battery was left to rest for 30 minutes, then charged at a rate of 0.5C to a voltage of 4.2V. Further, it was charged at a constant voltage of 4.2V to a current of 0.05C, left to rest for 5 minutes, and then discharged at a rate of 0.5C to a voltage of 2.8V. This constituted one charge-discharge cycle. The discharge capacity was recorded at each cycle. The capacity retention rate after n cycles (%) = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%. When the discharge capacity of the battery decayed to 80% of the discharge capacity of the first cycle, the test was stopped and the number of battery cycles was recorded.

[0233] The test results are shown in Table 3.

[0234] Examples 2 to 17 and Comparative Examples 1 to 2

[0235] The differences between the porous carbon in each embodiment and comparative example and Example 1 are shown in Table 1, the differences in preparation process parameters are shown in Table 1, and the test results of the prepared silicon-carbon negative electrode material and the assembled battery are shown in Table 2.

[0236] Table 1 Selection and preparation process parameters of porous carbon

[0237]

[0238] In Table 1, nitrogen:silane refers to the gas flow rate ratio of nitrogen to silane, and nitrogen:acetylene refers to the gas flow rate ratio of nitrogen to acetylene.

[0239] Table 2 Test results

[0240]

[0241] From Table 1 and Table 2, it can be seen that the silicon-carbon negative electrode material provided in the embodiment of the present application has a crystalline phase in the silicon particles and a crystallinity of at least 90%. Under the condition that the average grain size of the silicon particles is less than 4 nm, when it is used in a battery, the battery has high capacity, better cycle stability and high first coulombic efficiency.

[0242] According to Examples 1 and 2, since Example 2 is not carbon-coated, the BET of the silicon-carbon negative electrode material prepared in Example 2 is slightly larger than that in Example 1, and since it is not carbon-coated, a certain amount of silicon oxide exists on the surface of the silicon-carbon negative electrode material prepared in Example 2. Silicon oxide consumes active lithium and has no reversible capacity, resulting in its capacity and first efficiency being lower than those in Example 1, and the cycle performance is also slightly lower than that in Example 1 due to the influence of the first efficiency.

[0243] According to Examples 1, 3, and 4, the main differences between the products of Examples 3 and 4 and Example 1 are the enlargement of silicon grains and the reduction of porosity. Therefore, compared with Example 1, the cycle performance of Examples 3 and 4 is slightly worse under the premise of similar capacity and first effect.

[0244] According to Examples 1 and 5 to 8, when the silicon deposition temperature is 400°C to 550°C, especially 430°C to 530°C, the prepared silicon-carbon negative electrode material, when used in a battery, has high capacity, better cycle stability and high first coulombic efficiency.

[0245] According to Examples 1 and 9 to 11, when the flow rate ratio of the protective gas to the silicon source gas is 90:10 to 70:30, the battery has better capacity, coulombic efficiency and cycle performance.

[0246] According to Examples 1, 12, and 13, it can be seen that deposition time affects crystallinity and cycle performance. In Example 12, the deposition time is reduced, so the amount of silicon deposition is small. Under the same other process conditions, it can be seen that the crystallinity increases slightly with the increase of deposition time. The decrease in crystallinity leads to a decrease in capacity, which leads to a decrease in first efficiency. The low first efficiency but high porosity leads to low expansion, thereby improving the cycle performance. Compared with Example 1, Example 13 has a slightly higher crystallinity, which is mainly due to the increase in deposition time, thereby improving its capacity. However, because the porosity is lower than that of Example 1, the cycle deviation is

[0247] According to Examples 1, 14 and 15, the carbon coating temperature (that is, the temperature of the pyrolysis carbon source) affects the first efficiency and cycle performance of the battery. In Example 14, the carbon coating temperature is 800°C. Since the coating temperature is increased compared to Example 1, the decomposition efficiency of acetylene is improved, resulting in a decrease in the percentage of silicon and a decrease in BET. However, the increase in coating temperature leads to an increase in crystallinity, and the orientation of silicon grain expansion is stronger, that is, the overall expansion of the silicon-carbon negative electrode material increases, so the cycle performance is slightly lower than that of Example 1. In Example 15, due to the excessively high carbon coating temperature, silicon carbide is generated, resulting in a loss of the first discharge capacity and first efficiency of the battery. Moreover, the excessively high temperature further increases the crystallinity, and the cycle is slightly deteriorated.

[0248] According to Examples 1 and 16 to 17, the gas flow ratio during the carbon coating process mainly affects the thickness of the carbon coating layer on the surface of the finished product. When the gas flow ratio of the inert gas to the carbon source is 1: (1.5 to 5), as the acetylene gas flow rate increases, the thickness of the carbon coating layer increases, and the BET decreases. In addition, due to the increase in the carbon coating layer, the silicon content decreases slightly, and it has little effect on the capacity, first effect, porosity, crystallinity, etc., and the cycle is basically unaffected.

[0249] Because nano-silicon particles are prone to agglomeration, if there is no framework to restrict them, they can grow freely and without restrictions. Therefore, according to Example 1 and Comparative Example 1, the average pore size of the porous carbon in Comparative Example 1 is large and the micropores are relatively few. Therefore, under the same deposition conditions, the average silicon grain size in the final product is larger. The larger grain size will increase the difference in silicon expansion force in all directions, resulting in a significant reduction in the number of cycles. In addition, because the carbon substrate in Comparative Example 1 has more mesopores and macropores, while maintaining the same porosity level, Comparative Example 1 is less pressure-resistant. The material partially cracks during the cold pressing process, resulting in a low initial efficiency of the battery.

[0250] According to Example 1 and Comparative Example 2, in Comparative Example 2, amorphous silicon is generated due to the silicon deposition parameters during the silicon deposition process, resulting in a significant reduction in the first efficiency.

[0251] 5 is an XRD diagram of the silicon-carbon negative electrode material provided in Example 1; FIG. 6 is an XRD diagram of the silicon-carbon negative electrode material provided in Comparative Example 1; and FIG. 7 is an XRD diagram of the silicon-carbon negative electrode material provided in Comparative Example 2.

[0252] Comparative Example 1 deposited crystalline silicon, and the silicon grain size was larger than that of Example 1, resulting in a sharper peak between 28° and 29°. Comparative Example 2 deposited amorphous silicon, and XRD showed characteristic peaks for the carbon substrate, showing bulges, with the top of the first bulge being particularly smooth. Because Example 1 contained crystalline silicon and its silicon grain size was smaller, the characteristic silicon peak was partially obscured by the peak of the porous carbon, resulting in a slightly sharper first peak than that of Comparative Example 2.

[0253] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A silicon-carbon negative electrode material, wherein: The invention comprises porous carbon and silicon particles attached to the pore walls of the porous carbon, wherein the silicon particles contain a crystalline phase and have a crystallinity of at least 90%, and the average crystal size of the silicon particles is less than 4 nm.

2. The silicon-carbon negative electrode material according to claim 1, wherein The average grain size of the silicon particles is less than 2 nm.

3. The silicon-carbon negative electrode material according to claim 1 or 2, wherein: The average pore diameter of the porous carbon is ≤4 nm, and can be optionally ≤2 nm.

4. The silicon-carbon negative electrode material according to any one of claims 1 to 3, wherein: The porous carbon satisfies at least one of the following characteristics: (a1) The porous carbon has micropores, mesopores and macropores, and the volume proportion of the micropores is ≥75%; (a2) The specific surface area of ​​the porous carbon is ≥ 1700 m 2 / g; (a3) The pore volume of the porous carbon is ≥ 0.75 m 3 / g; Optionally, the porous carbon satisfies at least one of the following characteristics: (b1) The porous carbon has micropores, mesopores and macropores, and the volume proportion of the micropores is ≥85%; (b2) The specific surface area of ​​the porous carbon is ≥ 1800 m 2 / g; (b3) The pore volume of the porous carbon is ≥ 0.8 m 3 / g.

5. The silicon-carbon negative electrode material according to any one of claims 1 to 3, wherein: The porous carbon and the silicon particles are used together as a main body, and the silicon-carbon negative electrode material further includes a carbon coating layer coated on the main body.

6. The silicon-carbon negative electrode material according to claim 5, wherein: The carbon coating layer is discontinuously coated, and the thickness of the carbon coating layer is 1 to 40 nm.

7. The silicon-carbon negative electrode material according to any one of claims 1 to 6, wherein: The silicon-carbon negative electrode material meets at least one of the following characteristics: (c1) The mass content of the silicon particles in the silicon-carbon negative electrode material is 35-55%; (c2) The porosity of the silicon-carbon negative electrode material is 40% to 60%; (c3) The specific surface area of ​​the silicon-carbon negative electrode material is ≤ 6m 2 / g; (c4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 4 μm to 15 μm.

8. The silicon-carbon negative electrode material according to any one of claims 1 to 6, wherein: The silicon-carbon negative electrode material meets at least one of the following characteristics: (d1) The mass content of the silicon particles in the silicon-carbon negative electrode material is 40% to 50%; (d2) The porosity of the silicon-carbon negative electrode material is 45% to 55%; (d3) The specific surface area of ​​the silicon-carbon negative electrode material is ≤4m 2 / g; (d4) The volume particle size distribution Dv50 of the silicon-carbon negative electrode material is 5 μm to 10 μm.

9. A method for preparing a silicon-carbon negative electrode material according to any one of claims 1 to 8, wherein: include: Depositing the silicon particles on the porous carbon by chemical vapor deposition; Wherein, the average pore diameter of the porous carbon is ≤4nm.

10. The preparation method according to claim 9, wherein: The method of depositing the silicon particles on the porous carbon by chemical vapor deposition includes: Placing the porous carbon in a reaction atmosphere, and keeping the temperature at 400° C. to 550° C. for at least 8 hours, wherein the reaction atmosphere is a mixed atmosphere of a protective gas and a silicon source gas, the gas flow ratio of the protective gas to the silicon source gas is 90:10 to 70:30, and the protective gas includes at least one of an inert gas and hydrogen; Optionally, the temperature of the insulation reaction is 430°C to 530°C; Optionally, the gas flow ratio of the protective gas to the silicon source gas is 85:15 to 75:25; Optionally, the insulation reaction time is 8 hours to 16 hours, and optionally 10 hours to 16 hours.

11. The preparation method according to claim 9 or 10, wherein: The preparation method further comprises: using the product obtained by depositing the silicon particles on the porous carbon as a body, placing the body in a mixed atmosphere of a carbon source and an inert gas, and pyrolyzing the carbon source to form a carbon coating layer coated on the body; Wherein, the carbon source includes one or more of alkanes, alkynes and alkenes; Optionally, the temperature for pyrolyzing the carbon source is 400° C. to 800° C., and the pyrolysis time is 0.2 h to 2 h; Optionally, the gas flow ratio of the inert gas to the carbon source is 1:(1.5-5).

12. A negative electrode sheet, wherein: It comprises the silicon-carbon negative electrode material as described in any one of claims 1 to 8.

13. A battery, wherein: It includes the negative electrode sheet as claimed in claim 12.

14. An electrical device, wherein: It comprises a battery as claimed in claim 13, wherein the battery is used to provide electrical energy.

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