Silicon-carbon composite material, method for preparing the same, and use thereof

Abstract

The application relates to the technical field of negative electrode material preparation, in particular to a silicon-carbon composite material and a preparation method and application thereof. The silicon-carbon composite material comprises a silicon-carbon inner core, a first shell layer covering the silicon-carbon inner core and a second shell layer covering the first shell layer; the silicon-carbon inner core comprises doped porous carbon and nano-silicon arranged on the doped porous carbon, and the doped porous carbon is doped with metal and rare earth oxide; the first shell layer comprises a polymer-based positive temperature coefficient thermosensitive material; and the second shell layer comprises lithium-doped amorphous carbon. The silicon-carbon composite material has excellent initial efficiency, cycle performance, rate performance, fast charging performance and safety performance.

Description

Technical Field

[0001] This application relates to the field of negative electrode material preparation technology, and in particular to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of portable electronics and new energy vehicle industries, the increasing market demand for high-energy-density batteries necessitates improvements in the cycle performance and safety of anode materials, especially silicon-carbon materials, in addition to high energy density. Currently, although silicon-carbon anode materials have shown some improvement in power performance, expansion, and initial efficiency, poor safety performance remains a concern. Summary of the Invention

[0003] Based on this, in order to address the problem that existing silicon-carbon anode materials cannot simultaneously possess conductivity and safety, this application provides a silicon-carbon composite material, its preparation method, and its application.

[0004] A first aspect of this application provides a silicon-carbon composite material, the silicon-carbon composite material comprising a silicon-carbon core, a first shell layer covering the silicon-carbon core, and a second shell layer covering the first shell layer;

[0005] The silicon-carbon core includes doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with metals and rare earth oxides.

[0006] The first shell layer comprises a polymer-based positive temperature coefficient thermosensitive material;

[0007] The second shell comprises lithium-doped amorphous carbon.

[0008] In some embodiments, the metal includes at least one selected from magnesium, lithium, molybdenum, and cobalt; and / or,

[0009] The polymer in the polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide, polyphenylene sulfide, polysulfone, aromatic polyamide, and polyarylate; and / or,

[0010] The rare earth oxides include at least one of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, and samarium oxide.

[0011] In some embodiments, the content of the first shell layer in the silicon-carbon composite material is 1% to 5% by mass fraction.

[0012] A second aspect of this application provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0013] A silicon-carbon core is provided, the silicon-carbon core comprising doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with metals and rare earth oxides;

[0014] A first shell layer is coated on the surface of the silicon-carbon core, and the first shell layer includes a polymer-based positive temperature coefficient thermistor to obtain a silicon-carbon composite precursor.

[0015] A second shell layer is coated on the surface of the silicon-carbon composite precursor, the second shell layer comprising lithium-doped amorphous carbon.

[0016] In some embodiments, the fabrication process of the silicon-carbon core includes:

[0017] Organic resin, organic solvent, rare earth compound and metal chloride are mixed and dried to obtain a mixture;

[0018] The mixture is subjected to pore-forming and reduction treatments to obtain porous carbon doped with metal and rare earth oxides.

[0019] The silicon-carbon core is obtained by doping the metal and rare earth oxide with porous carbon to deposit nano-silicon.

[0020] In some embodiments, the mass ratio of the organic resin, the organic solvent, the rare earth compound, and the metal chloride is 100:500~2000:1~5:1~5; and / or,

[0021] The organic resin includes at least one selected from acrylic resin, malic resin, alkyd resin, and fumaric resin; and / or,

[0022] The organic solvent includes at least one selected from N,N-dimethylformamide, chloroform, ethyl acetate, and N-methylpyrrolidone; and / or,

[0023] The metal chloride includes at least one of magnesium chloride, lithium chloride, molybdenum chloride, and cobalt chloride; and / or,

[0024] The rare earth compound includes at least one of the oxalate compounds of lanthanum, cerium, praseodymium, neodymium, promethium, and samarium; and / or,

[0025] The steps of performing pore-forming and reduction treatments on the mixture include:

[0026] The mixture is subjected to pore-forming treatment using a gaseous pore-forming agent to obtain porous carbon material; then, the porous carbon material is reduced using a reducing gas to obtain metal and rare earth oxide-doped porous carbon; and / or,

[0027] The step of doping the metal and rare earth oxides with porous carbon-deposited nano-silicon includes:

[0028] Under a system pressure of 0.01 MPa to 0.1 MPa, silane and the metal and rare earth oxide-doped porous carbon are heated at 500°C to 700°C for 1 to 3 hours to deposit nano-silicon on the rare earth oxide-doped porous carbon.

[0029] In some embodiments, the step of coating the surface of the silicon-carbon core with a first shell layer includes:

[0030] A polymer-based positive temperature coefficient thermistor material is deposited on the surface of a silicon-carbon core using physical vapor deposition to obtain a silicon-carbon composite precursor; and / or,

[0031] The polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide-based PTC, polyphenylene sulfide-based PTC, polysulfone-based PTC, aromatic polyamide-based PTC, and polyarylate-based PTC.

[0032] In some embodiments, the step of coating the surface of the silicon-carbon composite precursor with a second shell layer includes:

[0033] The organic lithium compound and carbon source are melt-mixed and then mixed with the silicon-carbon composite precursor, followed by carbonization treatment under an inert atmosphere.

[0034] A third aspect of this application provides the application of the silicon-carbon composite material described above or the silicon-carbon composite material prepared according to the preparation method of the silicon-carbon composite material described above in the preparation of batteries.

[0035] A fourth aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector;

[0036] The negative electrode active material layer includes the silicon-carbon composite material described above or the silicon-carbon composite material prepared according to the preparation method of the silicon-carbon composite material described above.

[0037] A fifth aspect of this application provides a battery comprising the negative electrode sheet described above.

[0038] Compared with related technologies, this application has at least the following beneficial effects:

[0039] The silicon-carbon composite material provided in this application has a core-shell structure, comprising a silicon-carbon core, a first shell layer, and a second shell layer from the inside out. The polymer-based positive temperature coefficient (PTC) thermistor material in the first shell layer improves the material's safety performance, reducing the probability of battery fire and explosion in the event of thermal runaway. The lithium-doped amorphous carbon in the second shell layer tightly encapsulates the polymer-based PTC thermistor material, preventing it from reacting during battery use and affecting the battery's initial efficiency and cycle performance. Simultaneously, the lithium-doped amorphous carbon has a high diffusion coefficient, reducing gas generation and increasing the lithium-ion insertion / extraction rate during charging and discharging, thereby improving ionic conductivity. Based on this, the silicon-carbon composite material possesses both excellent electrical and safety performance; specifically, it exhibits excellent initial efficiency, cycle performance, rate capability, fast charging performance, and safety performance.

[0040] In addition, doping porous carbon with elemental metals and rare earth oxides can improve the conductivity of the silicon-carbon core, and the introduction of rare earth elements can also reduce the impedance of the material. Elemental metals are beneficial to the structural stability of the material during charging and discharging. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a flowchart illustrating a method for preparing silicon-carbon composite materials according to some embodiments of this application;

[0043] Figure 2 The image shows a SEM image of the silicon-carbon composite material prepared in Example 1. Detailed Implementation

[0044] To facilitate understanding of this application, a more comprehensive description of the application will be provided below in conjunction with specific embodiments. Preferred embodiments of the application are given in the specific embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings:

[0047] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0048] In this application, terms such as "further," "even more," "particularly," "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate a connection in the coverage of different technical solutions presented earlier and later, but should not be construed as limiting the preceding technical solution or restricting the scope of protection herein. Unless otherwise specified herein, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0049] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "present" or "absent." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain." "Optional component X" indicates whether component X exists or does not exist, or whether component X is contained or not.

[0050] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0051] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0052] The terms "comprising" and "having," and any variations thereof, used in the embodiments of this application, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to such processes, methods, products, or devices.

[0053] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0054] In the flowchart of this application, although the steps are shown sequentially according to the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps. They can be executed in other orders. Moreover, at least some of the steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. Their execution order is not necessarily sequential, but can be performed alternately or in turn with at least some of other steps or other sub-steps or stages.

[0055] A first aspect of this application provides a silicon-carbon composite material, the silicon-carbon composite material comprising a silicon-carbon core, a first shell layer covering the silicon-carbon core, and a second shell layer covering the first shell layer;

[0056] The silicon-carbon core consists of doped porous carbon and nano-silicon disposed on the doped porous carbon, which is doped with metals and rare earth oxides.

[0057] The first shell layer comprises a polymer-based positive temperature coefficient thermistor material;

[0058] The second shell consists of lithium-doped amorphous carbon.

[0059] The aforementioned silicon-carbon composite material has a core-shell structure, comprising a silicon-carbon core, a first shell layer, and a second shell layer from the inside out. The polymer-based positive temperature coefficient (PTC) thermistor material in the first shell layer enhances the material's safety performance, preventing battery fire and explosion in the event of thermal runaway. The lithium-doped amorphous carbon in the second shell layer tightly encapsulates the PTC thermistor material, preventing it from reacting during battery use and affecting the battery's initial efficiency and cycle performance. Simultaneously, the lithium-doped amorphous carbon has a high diffusion coefficient, reducing gas generation and increasing the lithium-ion insertion / extraction rate during charging and discharging, thus improving ionic conductivity. Based on this, the silicon-carbon composite material exhibits both excellent electrical and safety performance; specifically, it demonstrates superior initial efficiency, cycle performance, rate capability, fast charging performance, and safety performance.

[0060] Furthermore, doping porous carbon with elemental metals and rare earth oxides can improve the conductivity of the silicon-carbon core, and the introduction of rare earth elements can also reduce the impedance of the material, while elemental metals can improve the stability of the material.

[0061] Understandably, the aforementioned metals are non-rare earth metals. In some examples, the metal includes at least one of magnesium, lithium, molybdenum, and cobalt, and the metal may exist in elemental form within the silicon-carbon core. These metals contribute to the stability of the material structure during charging and discharging.

[0062] As is understandable, polymer-based positive temperature coefficient (PTC) thermistors are positive temperature coefficient (PTC) thermistors based on polymer materials, typically comprising a polymer matrix and conductive fillers. They are commercially available.

[0063] In some embodiments, the content of conductive filler in the polymer-based positive temperature coefficient thermistor can be 5wt% to 20wt%.

[0064] In some embodiments, the polymer in the polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide, polyphenylene sulfide, polysulfone, aromatic polyamide, and polyarylate.

[0065] Understandably, this application does not have specific requirements for the conductive filler in the polymer-based positive temperature coefficient thermistor, and conventional choices in the art are acceptable. In some embodiments, the conductive filler may be one or more of carbon black, silver, and silver oxide.

[0066] In some embodiments, the rare earth oxides include at least one of lanthanum (La) oxide, cerium (Ce) oxide, praseodymium (Pr) oxide, neodymium (Nd) oxide, promethium (Pm) oxide, and samarium (Sm) oxide.

[0067] In some of these examples, among the rare earth oxides, lanthanum oxide includes lanthanum pentoxide, cerium oxide includes cerium trioxide, praseodymium oxide includes praseodymium undecaoxide, neodymium oxide includes neodymium trioxide, promethium oxide includes promethium trioxide, and samarium oxide includes samarium trioxide.

[0068] In some specific examples, the silicon-carbon core contains 0.5% to 2 wt% metal and 0.5-2 wt% rare earth oxides.

[0069] In some embodiments, the silicon-carbon composite material comprises 1% to 5% of a first shell by mass fraction. Exemplarily, it can be 1%, 2%, 3%, 4%, or 5%; in some examples, it can be a range consisting of any two of these point values ​​as endpoints.

[0070] In some embodiments, the silicon-carbon composite material comprises 5% to 10% of a second shell by mass fraction. Exemplary values ​​may be 5%, 6%, 7%, 8%, 9%, or 10%; in some examples, it may be a range consisting of any two of these point values ​​as endpoints.

[0071] In some embodiments, the silicon-carbon core comprises, by mass fraction, 40% to 45% porous carbon, 40% to 45% nano-silicon, 1% to 5% elemental metal, and 1% to 5% rare earth oxides.

[0072] In some embodiments, the lithium content in the second shell is 1% to 10% by mass fraction. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%; in some examples, it can be a range consisting of any two of these point values ​​as endpoints.

[0073] A second aspect of this application provides a method for preparing a silicon-carbon composite material, in conjunction with reference to... Figure 1 The preparation method includes the following steps:

[0074] S1: Provides a silicon-carbon core, which includes doped porous carbon and nano-silicon disposed on the doped porous carbon, and the doped porous carbon is doped with metals and rare earth oxides.

[0075] S2: A first shell layer is coated on the surface of a silicon-carbon core, the first shell layer including a polymer-based positive temperature coefficient thermistor material, to obtain a silicon-carbon composite precursor;

[0076] S3: A second shell is coated on the surface of the silicon-carbon composite precursor, the second shell comprising lithium-doped amorphous carbon.

[0077] In some embodiments, the fabrication process of the silicon-carbon core includes:

[0078] Organic resin, organic solvent, rare earth compound and metal chloride are mixed and dried to obtain a mixture;

[0079] The mixture was subjected to pore-forming and reduction treatments to obtain porous carbon doped with metals and rare earth oxides.

[0080] Porous carbon was deposited into nano-silicon by doping metals and rare earth oxides, resulting in a silicon-carbon core.

[0081] In some embodiments, the step of mixing the organic resin, organic solvent, rare earth compound, and metal chloride includes:

[0082] The organic resin is dissolved in an organic solvent, then rare earth compounds are added and mixed, and then metal chlorides are added and mixed evenly.

[0083] In some embodiments, the drying method may be spray drying. There are no special requirements for the conditions of spray drying, and it can be carried out according to the conditions conventional in the art.

[0084] In some embodiments, the mass ratio of organic resin, organic solvent, rare earth compound, and metal chloride is 100:500~2000:1~5:1~5. For example, the mass ratio of resin to organic solvent can be 100:500, 100:1000, 100:1500, or 100:2000; the mass ratio of resin to organic rare earth compound can be 100:1, 100:2, 100:3, 100:4, or 100:5; the mass ratio of resin to metal chloride can be 100:1, 100:2, 100:3, 100:4, or 100:5; in some examples, it can be a range consisting of any two of these point values ​​as endpoints.

[0085] In some embodiments, the organic resin includes at least one of acrylic resin, malic resin, alkyd resin and fumaric resin.

[0086] In some embodiments, the organic solvent includes at least one of N,N-dimethylformamide, chloroform, ethyl acetate, and N-methylpyrrolidone.

[0087] In some embodiments, the metal chloride includes at least one of magnesium chloride, lithium chloride, molybdenum chloride, and cobalt chloride.

[0088] In some embodiments, the rare earth compound includes at least one of oxalate compounds of lanthanum, cerium, praseodymium, neodymium, promethium, and samarium.

[0089] In some embodiments, the steps of pore-forming treatment and reduction treatment of the mixture include:

[0090] A porous carbon material is obtained by using a gaseous pore-forming agent to create pores in the mixture; then, the porous carbon material is reduced by a reducing gas to obtain metal and rare earth oxide-doped porous carbon.

[0091] In some embodiments, the gaseous pore-forming agent includes at least one of carbon dioxide and water vapor.

[0092] In some embodiments, the conditions for the pore-forming process include: a temperature of 1100°C to 1500°C and a time of 60 min to 600 min. Exemplarily, the temperature for the pore-forming process can be 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C; in some examples, it can be a range consisting of any two of these values ​​as endpoints. Exemplarily, the time for the pore-forming process can be 60 min, 80 min, 100 min, 120 min, 180 min, 240 min, 300 min, 360 min, 480 min, or 600 min; in some examples, it can be a range consisting of any two of these values ​​as endpoints.

[0093] In some embodiments, the reducing gas includes carbon monoxide and / or hydrogen.

[0094] In some embodiments, the reduction treatment conditions include: a temperature of 300°C to 500°C, a time of 30 min to 300 min, and a reducing gas flow rate of 10 SCCM to 100 SCCM. For example, the reduction treatment temperature can be 300°C, 350°C, 400°C, 450°C, or 500°C; the reduction treatment time can be 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 240 min, or 300 min; and the reducing gas flow rate can be 10 SCCM, 20 SCCM, 30 SCCM, 50 SCCM, 80 SCCM, or 100 SCCM.

[0095] Understandably, when the mixture is subjected to pore-forming treatment under the above conditions, porous carbon will be formed, and metal chlorides and rare earth compounds will be transformed into metal oxides and rare earth oxides at high temperatures. Then, when the mixture is subjected to reduction treatment under the above conditions, the rare earth oxides will not be reduced, while the metal oxides will be reduced to elemental metals. Based on this, metal and rare earth oxide-doped porous carbon is obtained.

[0096] In some embodiments, the pore-forming treatment and the reduction treatment can be performed continuously in the same equipment. In one embodiment, the steps of performing pore-forming treatment and reduction treatment on the mixture include: heating the mixture to 1100-1500°C, activating and creating pores by introducing carbon dioxide for 60-600 min, then cooling it to 300-500°C and introducing carbon monoxide reducing gas at a flow rate of 10-100 SCCM for 30-300 min.

[0097] In some embodiments, the step of doping porous carbon-deposited nano-silicon with metals and rare earth oxides includes:

[0098] Under system pressure of 0.01 MPa to 0.1 MPa, porous carbon doped with silane, metal and rare earth oxides is heated at 500℃ to 700℃ for 1 h to 3 h to deposit nano-silicon on the rare earth oxide doped porous carbon.

[0099] In some implementations, the step of doping porous carbon-deposited nano-silicon with metals and rare earth oxides can be carried out in a fluidized bed.

[0100] In some implementations, the silane can be a liquid silane.

[0101] In some embodiments, the silane includes at least one of chloromethyldimethylchlorosilane, chloromethyltrichlorosilane, chloromethyldichlorosilane, trimethoxysilane, triethoxysilane, and tripropoxysilane.

[0102] Understandably, in a fluidized bed, under vacuum conditions of 0.01 MPa to 0.1 MPa, silane will be converted into a gaseous state. After heating and holding, the gaseous silane will decompose to generate nano-silicon, which can be uniformly deposited in the pores of the aforementioned metal and rare earth oxide-doped porous carbon.

[0103] In some embodiments, based on the total mass of silane and metal and rare earth oxide-doped porous carbon, the amount of silane used is 40% to 60% by mass fraction, and the amount of metal and rare earth oxide-doped porous carbon used is 40% to 60%.

[0104] In some embodiments, the step of coating the surface of the silicon-carbon core with a first shell includes:

[0105] A polymer-based positive temperature coefficient thermistor was deposited on the surface of a silicon-carbon core using physical vapor deposition to obtain a silicon-carbon composite precursor.

[0106] Understandably, physical vapor deposition can be used to tightly encapsulate the aforementioned silicon-carbon core with polymer-based positive temperature coefficient (PTC) thermistors, preventing structural changes or decomposition of the polymer-based PTC thermistors.

[0107] In some implementations, the silicon-carbon core can be transferred to a vacuum furnace, and then coated with a polymer-based positive temperature coefficient thermistor material through physical vapor deposition.

[0108] In some embodiments, the polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide-based PTC, polyphenylene sulfide-based PTC, polysulfone-based PTC, aromatic polyamide-based PTC, and polyarylate-based PTC.

[0109] In some embodiments, the physical vapor deposition conditions include: a vacuum of 0.01 Pa to 0.05 Pa, a deposition rate of 0.1 nm / min to 1 nm / min, and a deposition time of 30 min to 60 min.

[0110] In some embodiments, the step of coating the surface of the silicon-carbon composite precursor with a second shell includes:

[0111] The organic lithium compound and carbon source are melt-mixed and then mixed with a silicon-carbon composite precursor, followed by carbonization under an inert atmosphere.

[0112] In some embodiments, the mass ratio of the organolithium compound, the carbon source, and the silicon-carbon composite precursor is 1 to 5:1 to 5:100. Exemplarily, the mass ratio of the organolithium compound to the silicon-carbon composite precursor can be 1:100, 2:100, 3:100, 4:100, or 5:100; the mass ratio of the carbon source to the silicon-carbon composite precursor can be 1:100, 2:100, 3:100, 4:100, or 5:100.

[0113] In some of these examples, the carbon source can be oxidized asphalt. Oxidized asphalt has good processability and low cost. Choosing oxidized asphalt as a carbon source can reduce the material preparation cost while ensuring the material performance.

[0114] In some embodiments, the step of coating the surface of the silicon-carbon composite precursor with a second shell includes:

[0115] Organic lithium compounds and oxidized asphalt are melt-mixed at 200℃~300℃, then silicon-carbon composite precursors are added and mixed, and then carbonization is carried out under an inert atmosphere.

[0116] In some implementations, the inert atmosphere may be provided by inert gases or nitrogen, which are common in the art.

[0117] In some embodiments, the carbonization treatment conditions include a temperature of 1100°C to 1300°C and a time of 1 hour to 6 hours. For example, the carbonization temperature can be 1100°C, 1150°C, 1200°C, 1250°C, or 1300°C; in some examples, it can be a range consisting of any two of these values ​​as endpoints. For example, the carbonization time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours; in some examples, it can be a range consisting of any two of these values ​​as endpoints.

[0118] Understandably, after the organic lithium compound and carbon source are melted and mixed, they are mixed with the silicon-carbon composite precursor. The organic lithium compound and carbon source are coated on the surface of the silicon-carbon composite precursor. Then, after carbonization treatment, the carbon source is transformed into amorphous carbon, and the organic lithium compound decomposes to generate lithium oxide doped in the amorphous carbon. Based on this, the surface of the silicon-carbon composite precursor is coated with lithium-doped amorphous carbon.

[0119] In some embodiments, the organolithium compound includes at least one of lithium pyruvate, lithium octanoate, lithium acetate, lithium perfluorohexanesulfonate, lithium benzoate, lithium oxalate, and lithium lactate.

[0120] A third aspect of this application provides the use of the aforementioned silicon-carbon composite material or the silicon-carbon composite material prepared according to the aforementioned method for preparing the silicon-carbon composite material in the manufacture of batteries.

[0121] A fourth aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector;

[0122] The negative electrode active material layer includes the above-mentioned silicon-carbon composite material or a silicon-carbon composite material prepared according to the above-mentioned method for preparing silicon-carbon composite material.

[0123] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0124] In some embodiments, the negative current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil.

[0125] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0126] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as silicon-carbon composite material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0128] A fifth aspect of this application provides a battery comprising the aforementioned negative electrode.

[0129] The aforementioned battery may optionally include, but is not limited to, a secondary battery. As a non-limiting example, the battery may be a lithium-ion battery, a lead-acid battery, a sodium-ion battery, etc.

[0130] The aforementioned batteries can be either liquid or solid-state batteries.

[0131] In some embodiments, the battery also includes a positive electrode. This application does not impose any particular limitation on the type of positive electrode; it can be selected according to requirements.

[0132] In some embodiments, the battery also includes an electrolyte that facilitates ion conduction between the positive and negative electrodes. This application does not impose any particular limitation on the type of electrolyte; it can be selected according to requirements.

[0133] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0134] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0135] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0136] In some embodiments, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging can also be a soft pack, such as a pouch.

[0137] To make the objectives and advantages of this application clearer, the silicon-carbon composite material and its effects are further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and should not be used to limit this application. Unless otherwise specified, the following embodiments do not include components other than unavoidable impurities. Unless otherwise specified, the drugs and instruments used in the embodiments are conventional choices in the art. Experimental methods in the embodiments that do not specify specific conditions are implemented according to conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0138] Example 1

[0139] Preparation of silicon-carbon composite materials:

[0140] S1: Dissolve 100g of acrylic resin in 1000g of N,N-dimethylformamide and disperse evenly. Then add 3g of lanthanum oxalate and disperse evenly. Then add 3g of magnesium chloride and mix evenly to obtain a mixture. Spray dry the mixture and then heat it to 1300℃. Then introduce carbon dioxide to activate and form pores for 300min. Then cool it down to 400℃ and introduce reducing gas carbon monoxide at a flow rate of 50SCCM for 150min to obtain porous carbon doped with magnesium and lanthanum oxide.

[0141] 50g of chloromethyldimethylchlorosilane and 50g of magnesium and lanthanum oxide-doped porous carbon were added to a fluidized bed, evacuated to 0.05 MPa, and then heated to 600℃ and held for 2 hours to obtain a carbon-silicon core.

[0142] S2: The obtained silicon-carbon core is transferred to a vacuum furnace, and polyimide-based PTC is deposited on the surface of the silicon-carbon core using physical vapor deposition (PVD) with a vacuum of 0.03 Pa and a deposition rate of 0.5 nm / min for 30 min, to obtain a silicon-carbon composite precursor. The conductive filler in the polyimide-based PTC is carbon black, with a content of 10 wt%.

[0143] S3: Mix 3g of lithium pyruvate and 3g of oxidized asphalt evenly and heat to 250℃ for hot melting. Then add 100g of silicon-carbon composite precursor and mix evenly. Then heat to 1200℃ under nitrogen for 3h to obtain silicon-carbon composite material.

[0144] The prepared silicon-carbon composite material includes a silicon-carbon core, a first shell layer covering the silicon-carbon core, and a second shell layer covering the first shell layer;

[0145] The silicon-carbon core includes doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with elemental magnesium and lanthanum oxide.

[0146] The first shell layer comprises polyimide-based PTC, and the content of the first shell layer is approximately 3% by mass fraction;

[0147] The second shell comprises lithium-doped amorphous carbon.

[0148] Example 2

[0149] Preparation of silicon-carbon composite materials:

[0150] S1: Dissolve 100g of malic acid resin in 500g of chloroform and disperse evenly. Then add 1g of cerium oxalate and disperse evenly. Then add 1g of lithium chloride and mix evenly to obtain a mixture. Spray dry the mixture and then heat it to 1100℃. Then pass carbon dioxide through it to activate and form pores for 600min. Then cool it down to 300℃ and pass carbon monoxide, a reducing gas, through it at a flow rate of 10SCCM for 300min to obtain lithium elemental and cerium oxide doped porous carbon.

[0151] 40g of chloromethyltrichlorosilane and 60g of lithium elemental and cerium oxide-doped porous carbon were added to a fluidized bed, evacuated to 0.01 MPa, and then heated to 500℃ and held for 3 hours to obtain a silicon-carbon core.

[0152] S2: The obtained silicon-carbon core is transferred to a vacuum furnace, and polyphenylene sulfide-based PTC is deposited on the surface of the silicon-carbon core by physical vapor deposition (PVD) using PTC as the target material at a vacuum of 0.01 Pa and a deposition rate of 0.1 nm / min for 60 min, thus obtaining a silicon-carbon composite precursor. The conductive filler in the PTC is carbon black, with a content of 10 wt%.

[0153] S3: Mix 1g of lithium octanoate and 1g of oxidized asphalt evenly and heat to 200℃ for hot melting. Then add 100g of silicon-carbon composite precursor and mix evenly. Then heat to 1100℃ under argon for 6 hours to obtain silicon-carbon composite material.

[0154] The prepared silicon-carbon composite material includes a silicon-carbon core, a first shell layer covering the silicon-carbon core, and a second shell layer covering the first shell layer;

[0155] The silicon-carbon core includes doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with elemental lithium and cerium oxide.

[0156] The first shell layer comprises polyphenylene sulfide-based PTC, and the content of the first shell layer is 1% by mass fraction;

[0157] The second shell comprises lithium-doped amorphous carbon.

[0158] Example 3

[0159] Preparation of silicon-carbon composite materials:

[0160] S1: Dissolve 100g of alkyd resin in 2000g of ethyl acetate and disperse evenly. Then add 5g of praseodymium oxalate and disperse evenly. Then add 5g of molybdenum chloride and mix evenly to obtain a mixture. Spray dry the mixture and then heat it to 1500℃. Then introduce carbon dioxide to activate and form pores for 600min. Then cool it to 500℃ and introduce the reducing gas carbon monoxide at a flow rate of 100SCCM for 30min to obtain porous carbon doped with molybdenum and praseodymium oxide.

[0161] 60g of chloromethyldichlorosilane, 40g of elemental molybdenum and praseodymium oxide-doped porous carbon were added to a fluidized bed, the vacuum was drawn to 0.1 MPa, and then heated to 700℃ and held for 1 h to obtain a silicon-carbon core.

[0162] S2: The obtained silicon-carbon core is transferred to a vacuum furnace, and polysulfone-based PTC is deposited on the surface of the silicon-carbon core by physical vapor deposition at a vacuum of 0.05 Pa and a deposition rate of 1 nm / min for 60 min, forming a silicon-carbon composite precursor. The polysulfone-based PTC contains carbon black as a conductive filler at a content of 10 wt%.

[0163] S3: Mix 5g of lithium acetate and 5g of oxidized asphalt evenly and heat to 300℃ for hot melting. Then add 100g of silicon-carbon composite precursor and mix evenly. Then heat to 1300℃ under argon for 1 hour to obtain silicon-carbon composite material.

[0164] The prepared silicon-carbon composite material includes a silicon-carbon core, a first shell layer covering the silicon-carbon core, and a second shell layer covering the first shell layer;

[0165] The silicon-carbon core includes doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with molybdenum and praseodymium oxide.

[0166] The first shell layer comprises polysulfone-based PTC, and the content of the first shell layer is 5% by mass fraction;

[0167] The second shell comprises lithium-doped amorphous carbon.

[0168] Example 4

[0169] The method is basically the same as in Example 2, except that in step S3, the amount of lithium octanoate is adjusted to 0.5g.

[0170] Example 5

[0171] The process is basically the same as in Example 2, except that in step S3, the amount of polyphenylene sulfide-based PTC deposition is reduced, so that the content of the first shell layer in the prepared silicon-carbon composite material is reduced to 0.5%.

[0172] Comparative Example 1

[0173] It is basically the same as Example 1, except that lanthanum oxalate and magnesium chloride are not added in step S1.

[0174] Comparative Example 2

[0175] The process is basically the same as in Example 1, except that step S2 is omitted and step S3 is performed directly using the silicon-carbon core obtained in S1.

[0176] The specific preparation process is as follows:

[0177] 100g of acrylic resin was dissolved in 1000g of N,N-dimethylformamide and dispersed evenly. Then, 3g of lanthanum oxalate was added and dispersed evenly. Then, 3g of magnesium chloride was added and mixed evenly to obtain a mixture. The mixture was spray-dried and then heated to 1300℃. Carbon dioxide was introduced for activation and pore formation for 300min. Then, the temperature was lowered to 400℃ and carbon monoxide, a reducing gas, was introduced at a flow rate of 50SCCM for 150min to obtain porous carbon doped with metal and rare earth compounds.

[0178] 50g of chloromethyldimethylchlorosilane and 50g of metal and rare earth compound-doped porous carbon were added to a fluidized bed, vacuumed to 0.05 MPa, and then heated to 600℃ and held for 2 hours to obtain a carbon-silicon core.

[0179] Mix 3g of lithium pyruvate and 3g of oxidized asphalt evenly and heat to 250℃ for hot melting. Then add 100g of carbon silicon core and mix evenly. Then heat to 1200℃ under nitrogen for carbonization for 3 hours.

[0180] Comparative Example 3

[0181] It is basically the same as Example 1, except that step S3 is not performed.

[0182] Comparative Example 4

[0183] It is basically the same as Example 1, except that step S3 is performed first, and then step S2 is performed.

[0184] The specific preparation process is as follows:

[0185] 100g of acrylic resin was dissolved in 1000g of N,N-dimethylformamide and dispersed evenly. Then, 3g of lanthanum oxalate was added and dispersed evenly. Then, 3g of magnesium chloride was added and mixed evenly to obtain a mixture. The mixture was spray-dried and then heated to 1300℃. Carbon dioxide was introduced for activation and pore formation for 300min. Then, the temperature was lowered to 400℃ and carbon monoxide was introduced at a flow rate of 50SCCM for 150min to obtain porous carbon doped with magnesium and lanthanum oxide.

[0186] 50g of chloromethyldimethylchlorosilane and 50g of metal and rare earth compound-doped porous carbon were added to a fluidized bed, vacuumed to 0.05 MPa, and then heated to 600℃ and held for 2 hours to obtain a carbon-silicon core.

[0187] 3g of lithium pyruvate and 3g of oxidized asphalt were mixed evenly and heated to 250℃ for hot melting. Then, 100g of carbon silicon core was added and mixed evenly. After that, the mixture was heated to 1200℃ under nitrogen for 3 hours to obtain intermediate material.

[0188] The obtained intermediate material was transferred to a vacuum furnace, and polyimide-based PTC was deposited on the surface of the intermediate material by physical vapor deposition at a vacuum of 0.03 Pa and a deposition rate of 0.5 nm / min for 30 min, using polyimide-based PTC as the target material, to obtain a silicon-carbon composite material.

[0189] Test Example 1

[0190] The silicon-carbon composite material prepared in Example 1 was characterized using SEM, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen, the material exhibits a porous structure with relatively large pores and a particle size between 5 and 15 µm.

[0191] Test Example 2

[0192] 1. The tap density and specific surface area of ​​the products of Examples 1-5 and Comparative Examples 1-4 were tested according to the methods in the national standard GB / T38823-2020 "Silicon Carbon". The results are shown in Table 1.

[0193] The powder resistivity of the products of Examples 1-5 and Comparative Examples 1-4 was detected using the four-probe method, and the results are shown in Table 1.

[0194] Table 1

[0195]

[0196] As shown in Table 1, compared with the comparative examples, the silicon-carbon composite materials provided in Examples 1-5 of this application have a higher specific surface area, a larger tap density, and a lower powder resistivity.

[0197] 2. Button cell battery test

[0198] The products of Examples 1-5 and Comparative Examples 1-4 were used as active materials for the negative electrode sheets of batteries to prepare nine coin cells, which were labeled as A1-A5 and B1-B4 respectively.

[0199] The specific manufacturing process of each coin cell is as follows:

[0200] Preparation of battery negative electrode sheet: Add binder, conductive agent and solvent to active material, stir to form slurry, coat on copper foil, dry and roll to obtain battery negative electrode sheet; wherein, LA132 binder is used as binder, SP (conductive carbon black) is used as conductive agent, double distilled water is used as solvent, and the ratio of active material: SP:LA132:double distilled water = 94g:1g:5g:220mL.

[0201] Coin cell preparation: The electrolyte is a LiPF6 solution with a concentration of 1.1 mol / L. The solvent used is a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a weight ratio of 1:1. A lithium metal sheet is used as the counter electrode, and polyethylene (PE) is used as the separator. The simulated battery is assembled in an argon-filled glove box.

[0202] Electrochemical performance was tested on a Wuhan Landian CT2001A battery tester under the following conditions: charge / discharge voltage range of 0.005V to 2.0V, and charge / discharge rate of 0.1C. The rate performance (0.1C / 1C) and cycle performance (test conditions: 0.1C / 0.1C, 100 cycles) of the coin cells were also tested.

[0203] Full charge expansion test: The thickness of the electrode after rolling is D1. When fully charged to 100% SOC, the thickness of the electrode is D2. Full charge expansion = (D2-D1) / D1.

[0204] The test results are shown in Table 2.

[0205] Table 2

[0206]

[0207] As shown in Table 2, compared to the comparative example, the coin cell prepared using the silicon-carbon composite material provided in the examples as the active material of the negative electrode exhibits higher initial discharge specific capacity, initial efficiency, and cycle performance, while also showing lower full-charge expansion. The silicon-carbon composite material prepared in the examples has a core-shell structure, with the core consisting of porous carbon doped with rare earth oxides and elemental metals, which can reduce impedance and expansion, and improve cycle performance. Simultaneously, the lithium-doped amorphous carbon coating on the surface further enhances the ionic conductivity of the material, reduces irreversible capacity, and improves initial efficiency and cycle performance.

[0208] 3. Soft-pack battery test

[0209] The products of Examples 1-5 and Comparative Examples 1-4 were doped with 90% artificial graphite as negative electrode materials (i.e. negative electrode sheets), and nine kinds of soft-pack batteries were prepared accordingly, which were denoted as C1-C5 and D1-D4, respectively.

[0210] The specific manufacturing process of a pouch cell is as follows:

[0211] The negative electrode material, positive electrode material, electrolyte and separator are assembled into a 5Ah soft pack battery;

[0212] Among them, ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is the positive electrode material, the separator is Celegard 2400, and the electrolyte is a LiPF6 solution, wherein the solvent of the LiPF6 solution is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 is 1.3 mol / L.

[0213] Rate performance was tested: the charge / discharge voltage range was 2.5-4.2V, the temperature was 25±3.0℃, and each soft pack battery was charged at 1C, 3C, and 5C respectively, and discharged at 1C.

[0214] The test results are shown in Table 3.

[0215] Table 3

[0216]

[0217] As shown in Table 3, compared to the comparative example, the pouch battery made with the silicon-carbon composite material provided in the examples exhibits better rate charging performance; that is, the pouch battery in the examples has a shorter charging time and higher charging efficiency. This may be because the silicon-carbon composite material provided in the examples has lower powder conductivity and lower expansion, thereby improving rate performance.

[0218] 4. Safety performance test (needle penetration test)

[0219] Take 10 soft-pack batteries of each type: C1, C2, C3, C4, C5, D1, D2, D3, and D4. After fully charging the batteries, insert a 5mm diameter nail through the center of the battery and install a temperature tester at the battery terminal. Leave the nail inside the battery and observe the battery condition, measure the battery temperature, and check if the battery catches fire.

[0220] The average temperature of each group of 10 batteries is shown in Table 4, and the number of batteries that caught fire in each group of 10 batteries is also shown in Table 4.

[0221] Table 4

[0222]

[0223] As shown in Table 4, compared to the comparative example, the pouch battery prepared using the silicon-carbon composite material provided in this embodiment exhibits significantly lower battery temperature and a lower rate of ignition during testing. The silicon-carbon composite material provided in this application has a stable structure and also incorporates a polymer-based positive temperature coefficient thermistor material, thus improving the battery's safety performance.

[0224] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0225] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a silicon-carbon core, a first shell covering the silicon-carbon core, and a second shell covering the first shell. The silicon-carbon core includes doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with metals and rare earth oxides. The first shell layer comprises a polymer-based positive temperature coefficient thermosensitive material; The second shell layer comprises lithium-doped amorphous carbon; By mass fraction, the content of the metal in the silicon-carbon core is 0.5% to 2%, and the content of the rare earth oxide is 0.5% to 2%. The silicon-carbon composite material comprises 1% to 5% of the first shell layer by mass fraction; The silicon-carbon composite material comprises 5% to 10% of the second shell layer by mass fraction; The lithium content in the second shell is 1% to 10% by mass fraction; The metal includes at least one of magnesium, lithium, molybdenum, and cobalt.

2. The silicon-carbon composite material according to claim 1, characterized in that, The polymer in the polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide, polyphenylene sulfide, polysulfone, aromatic polyamide, and polyarylate; and / or, The rare earth oxides include at least one of lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, and samarium oxide.

3. A method for preparing the silicon-carbon composite material as described in any one of claims 1 or 2, characterized in that, The preparation method includes the following steps: A silicon-carbon core is provided, the silicon-carbon core comprising doped porous carbon and nano-silicon disposed on the doped porous carbon, wherein the doped porous carbon is doped with metals and rare earth oxides; A first shell layer is coated on the surface of the silicon-carbon core, and the first shell layer includes a polymer-based positive temperature coefficient thermistor to obtain a silicon-carbon composite precursor. A second shell layer is coated on the surface of the silicon-carbon composite precursor, the second shell layer comprising lithium-doped amorphous carbon.

4. The preparation method according to claim 3, characterized in that, The preparation process of the silicon-carbon core includes: Organic resin, organic solvent, rare earth compound and metal chloride are mixed and dried to obtain a mixture; The mixture is subjected to pore-forming and reduction treatments to obtain porous carbon doped with metal and rare earth oxides. The silicon-carbon core is obtained by doping the metal and rare earth oxide with porous carbon to deposit nano-silicon.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the organic resin, the organic solvent, the rare earth compound, and the metal chloride is 100:500~2000:1~5:1~5; and / or, The organic resin includes at least one selected from acrylic resin, malic resin, alkyd resin, and fumaric resin; and / or, The metal chloride includes at least one of magnesium chloride, lithium chloride, molybdenum chloride, and cobalt chloride; and / or, The rare earth compound includes at least one of the oxalate compounds of lanthanum, cerium, praseodymium, neodymium, promethium, and samarium; and / or, The steps of performing pore-forming and reduction treatments on the mixture include: The mixture is subjected to pore-forming treatment using a gaseous pore-forming agent to obtain a porous carbon material; then, the porous carbon material is reduced using a reducing gas to obtain metal and rare earth oxide-doped porous carbon; and / or, The step of doping the metal and rare earth oxides with porous carbon-deposited nano-silicon includes: Under a system pressure of 0.01 MPa to 0.1 MPa, silane and the metal and rare earth oxide-doped porous carbon are heated at 500°C to 700°C for 1 to 3 hours to deposit nano-silicon on the metal and rare earth oxide-doped porous carbon.

6. The preparation method according to any one of claims 3 to 5, characterized in that, The step of coating the surface of the silicon-carbon core with a first shell layer includes: A polymer-based positive temperature coefficient thermistor material is deposited on the surface of a silicon-carbon core using physical vapor deposition to obtain a silicon-carbon composite precursor; and / or, The polymer-based positive temperature coefficient thermosensitive material includes at least one of polyimide-based PTC, polyphenylene sulfide-based PTC, polysulfone-based PTC, aromatic polyamide-based PTC, and polyarylate-based PTC.

7. The preparation method according to any one of claims 3 to 5, characterized in that, The step of coating the surface of the silicon-carbon composite precursor with a second shell layer includes: The organic lithium compound and carbon source are melt-mixed and then mixed with the silicon-carbon composite precursor, followed by carbonization treatment under an inert atmosphere.

8. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; The negative electrode active material layer includes a silicon-carbon composite material as described in any one of claims 1 to 2 or a silicon-carbon composite material prepared by any one of claims 3 to 5.

9. A battery, characterized in that, The battery includes the negative electrode as described in claim 8.

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