Composite silicon-carbon negative electrode material and preparation method thereof, negative electrode plate and battery

Abstract

The invention provides a composite silicon-carbon negative electrode material and a preparation method thereof, a negative electrode plate and a battery. The composite silicon-carbon negative electrode material comprises a silicon-carbon composite core, and a gradient pore carbon buffer layer and a dynamic self-healing binder layer which sequentially coat the surface of the silicon-carbon composite core, a branched carbon nanostructure grows in the pore wall of the gradient pore carbon buffer layer, the dynamic self-healing binder layer partially permeates into the pores of the gradient pore carbon buffer layer, the dynamic self-healing binder layer contains dynamic disulfide bonds, and the dynamic self-healing binder layer comprises a composite binder and a conductive high-molecular polymer. According to the invention, the gradient pore buffer layer is arranged on the surface of the silicon-carbon particles, and meanwhile, the self-healing binder containing dynamic disulfide bonds is used for permeation filling, so that three-dimensional cooperative regulation and control of graded dissipation of expansion stress, self-repairing of microcracks and ion / electron dual-path conduction are realized; the three core problems of electrode pulverization caused by volume expansion, interface impedance sharp increase and long circulation capacity attenuation are thoroughly solved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a composite silicon-carbon anode material and its preparation method, anode sheet and battery. Background Technology

[0002] Silicon-based materials are considered one of the most promising next-generation high-capacity anode materials to replace traditional graphite anodes due to their significant advantages, such as extremely high theoretical specific capacity (4200 mAh / g), low lithium insertion / extraction potential, and abundant crustal reserves. However, silicon-based materials experience volume expansion of over 200% during lithium-ion insertion / extraction. This inherent defect causes a series of serious problems, greatly limiting their commercial application. This is because the drastic volume expansion leads to the pulverization and cracking of silicon particles, causing significant structural collapse and peeling of the anode sheet, damaging the integrity of the electrode. Moreover, the electrode structure damage caused by volume expansion leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, which not only consumes electrolyte and lithium ions but also causes a sharp increase in interfacial impedance, significantly reducing the rate performance of the battery. During long-term cycling, the problems of electrode pulverization and surge in interfacial impedance caused by volume expansion will continue to accumulate, ultimately leading to rapid capacity decay and a significant reduction in cycle life.

[0003] CN120589757A discloses a method for preparing high-rate silicon-carbon anode materials and their applications. The method for preparing high-rate silicon-carbon anode materials includes steps such as silicon powder pretreatment, silicon-carbon powder composite ball milling, phosphoric acid treatment, and high-temperature carbonization.

[0004] CN119430129A discloses a biomass-derived silicon-carbon anode material and its preparation method and application. The preparation method includes mixing biomass-derived carbon obtained by acid washing, alkali extraction, reprecipitation, drying, carbonization and ball milling with diatomaceous bio-silica obtained by precipitation collection, oxidative acid hydrolysis, filtration washing, drying and calcination, and ball milling to finally obtain a synergistic composite silicon-carbon material.

[0005] Although the silicon-carbon anode material prepared by the above scheme can reduce the expansion during cycling, it still cannot avoid expansion, and irreversible structural damage will occur after expansion, so the performance of the silicon-carbon anode material needs to be improved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite silicon-carbon anode material and its preparation method, anode sheet, and battery. The present invention forms a gradient pore buffer layer with dense inner and sparse outer pores on the surface of silicon-carbon particles, and simultaneously fills it with a self-healing binder containing dynamic disulfide bonds, thereby achieving three-dimensional synergistic regulation of expansion stress graded dissipation, microcrack self-repair, and ion / electron dual-pathway conduction. This completely solves the three core problems of electrode pulverization caused by volume expansion, surge in interface impedance, and capacity decay over long cycles.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite silicon-carbon anode material, the composite silicon-carbon anode material comprising primary particles and secondary particles composed of primary particles;

[0009] The primary particles include a silicon-carbon composite core and a gradient porous carbon buffer layer and a dynamic self-healing adhesive layer sequentially coated on the surface of the silicon-carbon composite core.

[0010] The composite silicon-carbon anode material has branched carbon nanostructures between its particles. The dynamic self-healing binder layer partially penetrates into the pores of the gradient pore carbon buffer layer. The dynamic self-healing binder layer contains dynamic disulfide bonds and includes a composite binder and a conductive polymer.

[0011] In the composite silicon-carbon anode material of this invention, a gradient porous carbon buffer layer is formed on the surface of the silicon-carbon composite core. Through the capillary confinement effect of the dense inner carbon layer and the volumetric capacity of the outer buffer carbon layer, a radial gradient stress dissipation network is formed, completely replacing the traditional single-stage buffer mode of uniform porous structures. This reduces silicon expansion strain from >120% to <20%. The dynamic self-healing binder layer contains dynamic disulfide bonds. These dynamic disulfide bonds (-SS- bond energy ≈ 268 kJ / mol) undergo reversible breakage / recombination during charge-discharge processes (3.0V~3.5V), avoiding the permanent interface failure of traditional static binders and achieving in-situ repair of microcracks. The self-healing binder penetrates and fills the pores of the gradient porous carbon buffer layer, forming a dual dynamic repair network of hydrogen bonds and dynamic disulfide bonds. Branched carbon nanostructures are arranged between the particles of the composite silicon-carbon anode material, providing high-speed electron channels (bulk conductivity >10). 2 (S / cm), branched carbon nanostructures also exist in the gaps between the composite silicon-carbon anode material and the current collector, while conductive polymers construct Li in the binder. + Transport pathway (ionic conductivity > 10) -4 (S / cm), breaking through the transmission bottleneck of traditional silicon-carbon anodes where "electrons are conducting but ions are blocking".

[0012] Preferably, the silicon-carbon composite core is made of silicon nanoparticles and acetylene black.

[0013] Preferably, in the silicon-carbon composite core, the mass fraction of silicon nanoparticles is 28% to 32%, for example: 28%, 29%, 30%, 31% or 32%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, the median particle size D50 of the silicon nanoparticles is 70nm~90nm, for example: 70nm, 75nm, 80nm, 85nm or 90nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the median particle size D50 of the silicon-carbon composite core is 1μm to 5μm, for example: 1μm, 2μm, 3μm, 4μm or 5μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the gradient porous carbon buffer layer comprises an inner porous carbon layer close to the silicon-carbon composite core and an outer porous carbon layer away from the silicon-carbon composite core.

[0017] Preferably, the pore size of the inner porous carbon layer is 5nm to 10nm, for example: 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the porosity of the inner porous carbon layer is 25% to 35%, for example: 25%, 28%, 30%, 32% or 35%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the pore size of the outer porous carbon layer is 50nm~100nm, for example: 50nm, 60nm, 80nm, 90nm or 100nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the porosity of the outer porous carbon layer is 55% to 65%, for example: 55%, 58%, 60%, 62% or 65%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the porosity ratio of the outer porous carbon layer to the inner porous carbon layer is ≥1.8.

[0022] Preferably, the pore size ratio of the outer porous carbon layer to the inner porous carbon layer is ≥10.

[0023] Preferably, the thickness of the gradient porous carbon buffer layer is 150nm~300nm, for example: 150nm, 180nm, 200nm, 250nm or 300nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] The pore size and layer thickness of the gradient porous carbon buffer layer described in this invention are two completely independent parameters of different dimensions, and there is no direct additive relationship between them.

[0025] Preferably, the penetration depth of the dynamic self-healing adhesive layer in the gradient porous carbon buffer layer is >180nm.

[0026] The penetration depth described in this invention is the average penetration depth.

[0027] Preferably, the composite adhesive comprises butyl acrylate-3-methylcrotonitrile-dithiodipropionic acid copolymer.

[0028] Preferably, the molar percentage of butyl acrylate (BA) groups in the molecule of the composite adhesive is 60% to 80%, for example: 60%, 65%, 70%, 75% or 80%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the molar percentage of 3-methylcrotonitrile (MCN) groups in the molecule of the composite adhesive is 10% to 30%, for example: 10%, 15%, 20%, 25% or 30%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the molar percentage of dithiodipropionic acid (DTDP) groups in the molecule of the composite adhesive is 1% to 10%, for example: 1%, 2%, 5%, 8% or 10%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the density of dynamic disulfide bonds in the composite binder is 0.7 mmol / g to 0.9 mmol / g, for example: 0.7 mmol / g, 0.75 mmol / g, 0.8 mmol / g, 0.85 mmol / g or 0.9 mmol / g, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the recombination activation energy of the dynamic disulfide bond at a potential of 3.0V~3.5V is 38kJ / mol~42kJ / mol, for example: 38kJ / mol, 39kJ / mol, 40kJ / mol, 41kJ / mol or 42kJ / mol, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the conductive polymer comprises poly(3,4-ethylenedioxythiophene) / polystyrene sulfonate (PEDOT:PSS).

[0034] Preferably, the median particle size D50 of the conductive polymer is 70nm~90nm, for example: 70nm, 75nm, 80nm, 85nm or 90nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the mass fraction of conductive polymer in the dynamic self-healing adhesive layer is 7.5% to 8.8%, for example: 7.5%, 7.8%, 8%, 8.5% or 8.8%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the thickness of the dynamic self-healing adhesive layer is 200nm~400nm, for example: 200nm, 250nm, 300nm, 350nm or 400nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] In a second aspect, the present invention provides a method for preparing the composite silicon-carbon anode material as described in the first aspect, the method comprising the following steps:

[0038] Carbon precursor material was obtained by CVD gradient deposition of carbon on silicon-carbon composite material.

[0039] A polymer matrix is ​​formed by copolymerizing monomers containing dynamic disulfide bonds, and a conductive polymer is mixed with the polymer matrix and ultrasonically mixed to obtain a self-healing adhesive solution.

[0040] The precursor material, self-healing adhesive, and conductive agent are mixed and coated onto the substrate surface. After solvent removal, the composite silicon-carbon anode material is obtained by hot pressing.

[0041] This invention involves mixing gradient porous silicon-carbon material, self-healing binder, and conductive agent under high shear to form a homogeneous slurry, which is then coated onto a metal current collector and dried in a stepwise manner to remove the solvent. The pre-cured electrode is placed in a thermo-pressing device and subjected to pressure holding treatment at specific temperatures and pressures. Driven by capillary forces, the molten binder deeply penetrates the gradient pores (especially the outer macroporous structure), forming hydrogen bonds with the functional groups on the carbon layer surface. Simultaneously, dynamic disulfide bonds undergo grafting reactions with carbon defect sites under thermal excitation, establishing a covalent-hydrogen bond synergistic chemical bonding network. This process achieves three-dimensional continuous filling of the binder within the pores, allowing the expansion stress of the silicon particles to dissipate through the gradient of the elastic polymer layer, ultimately forming an integrated composite structure of "silicon-carbon core - gradient porous carbon intermediate layer - self-healing binder shell." This significantly improves the mechanical strength and electrochemical stability. The branched carbon nanostructures formed by the conductive agent, dispersed among the particles of the composite silicon-carbon anode material and between the composite silicon-carbon anode material and the current collector, provide high-speed electron channels.

[0042] Preferably, the CVD gradient deposition carbon treatment includes: placing the silicon-carbon composite material in a fluidized bed reactor, achieving uniform particle suspension under the action of inert gas fluidization, performing a first CVD deposition treatment using a gaseous carbon source mixture, performing a second CVD deposition treatment using a gaseous carbon source mixture containing weak oxidizing components, and performing high-temperature pyrolysis treatment on the obtained material using acetylene to obtain the precursor material.

[0043] This invention first performs a first CVDC deposition treatment on silicon-carbon composite materials, catalytically depositing a nanoscale dense carbon layer on the particle surface. The internal honeycomb micropores are precisely controlled through nucleation growth, and the pore size can directionally constrain the lithium intercalation expansion of the silicon particles. Then, a second CVD treatment is performed in a mixed atmosphere containing weakly oxidizing components. Submicron-level interconnected channels are formed by selectively etching amorphous carbon regions, constructing a volumetric buffer space. Finally, during the high-temperature carbon source pyrolysis stage, a branched conductive network is grown in situ on the inner wall of the channels, achieving simultaneous optimization of pore structure and conductivity. This process, through stepwise control of gas phase composition, temperature, and time, continuously completes the construction of a three-dimensional gradient structure of "dense layer - buffer layer - conductive modification layer" within a single reactor.

[0044] Preferably, the gaseous carbon source mixture includes a gaseous carbon source and a carrier gas.

[0045] Preferably, the gaseous carbon source includes ethylene and / or acetylene.

[0046] Preferably, the carrier gas includes argon and / or nitrogen.

[0047] Preferably, in the gaseous carbon source mixture, the volume ratio of gaseous carbon source to carrier gas is 1:(8~10), for example: 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the temperature of the first CVD deposition process is 370℃~430℃, for example: 370℃, 380℃, 400℃, 420℃ or 430℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the first CVD deposition process takes 20 to 40 minutes.

[0050] Preferably, the gaseous carbon source mixture containing weak oxidizing components includes carbon dioxide and a gaseous carbon source.

[0051] Preferably, the volume ratio of carbon dioxide to gaseous carbon source in the gaseous carbon source mixture containing weak oxidizing components is 1:(2.5~3.5), for example: 1:2.5, 1:2.8, 1:3, 1:3.2 or 1:3.5, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] Preferably, the temperature of the second CVD deposition process is 550℃~650℃, for example: 550℃, 580℃, 600℃, 620℃ or 650℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the second CVD deposition time is 40 min to 80 min, for example: 40 min, 50 min, 60 min, 70 min or 80 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the heating rate from the first CVD deposition process to the second CVD deposition process is 8℃ / min to 12℃ / min, for example: 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min or 12℃ / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the temperature of the high-temperature pyrolysis treatment is 700℃~800℃, for example: 700℃, 720℃, 750℃, 780℃ or 800℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] Preferably, the high-temperature pyrolysis treatment time is 5 min to 15 min, for example: 5 min, 8 min, 10 min, 12 min or 15 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the copolymerization of monomers containing dynamic disulfide bonds to form a polymer matrix includes: dissolving acrylate monomers, cyano functional monomers and dynamic disulfide bond crosslinking agents in a polar organic solvent, adding a free radical initiator to carry out a copolymerization reaction, and obtaining a copolymer matrix.

[0058] This invention involves dissolving acrylate monomers containing flexible segments, cyano functional monomers, and dynamic disulfide bond crosslinking agents in a polar organic solvent within an inert atmosphere-protected reaction system. A free radical initiator is then added to trigger a ternary copolymerization reaction. Molecular chain growth is controlled by continuous stirring at a constant temperature, forming a copolymer matrix with both an elastic framework and dynamic bonding sites. After the reaction is terminated, a conductive polymer additive is incorporated into the system, followed by high-intensity ultrasonic treatment to ensure uniform dispersion within the polymer matrix, forming a molecularly composite bifunctional adhesive. The core design of this adhesive lies in the reversible breakage / reorganization of dynamic disulfide bonds within a specific potential window during electrode charging and discharging, achieving self-healing of cracks. The conductive additive constructs a dual ion / electron transport channel spanning the polymer phase, overcoming the insulation limitations of traditional adhesives.

[0059] Preferably, the acrylate monomer includes butyl acrylate.

[0060] Preferably, the cyano functional monomer includes 3-methylcrotonitrile.

[0061] Preferably, the molar ratio of the cyano functional monomer to the acrylate monomer is (0.55~0.60):1, for example: 0.55:1, 0.56:1, 0.57:1, 0.58:1, 0.59:1 or 0.60:1, etc.

[0062] Preferably, the dynamic disulfide crosslinking agent includes dithiodipropionic acid.

[0063] Preferably, the molar ratio of the dynamic disulfide crosslinking agent to the acrylate monomer is (0.043~0.046):1, for example: 0.043:1, 0.044:1, 0.045:1 or 0.046:1, etc.

[0064] Preferably, the polar organic solvent includes NMP.

[0065] Preferably, the molar ratio of the polar organic solvent to the acrylate monomer is (9.1~9.9):1, for example: 9.1:1, 9.2:1, 9.5:1, 9.6:1 or 9.9:1, etc.

[0066] Preferably, the free radical initiator comprises AIBN.

[0067] Preferably, the molar ratio of the free radical initiator to the acrylate monomer is (0.0055~0.0058):1, for example: 0.0055:1, 0.0056:1, 0.0057:1 or 0.0058:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] Preferably, the conductive agent comprises conductive carbon black SP.

[0069] Preferably, the mass ratio of the precursor material, the self-healing adhesive, and the conductive agent is (70~90):(5~15):(5~15), for example: 70:15:15, 75:15:10, 80:10:10, 85:4:10, or 90:5:5, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] Preferably, the substrate comprises a copper current collector.

[0071] This invention uses copper current collector as a substrate, which enables the composite silicon-carbon anode material to fuse in situ with the electrode interface, thereby obtaining anode sheet with high bonding strength and good stability.

[0072] Preferably, the temperature of the hot pressing treatment is 75℃~85℃, for example: 75℃, 78℃, 80℃, 82℃ or 85℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0073] Preferably, the pressure of the hot pressing treatment is 8MPa to 12MPa, for example: 8MPa, 9MPa, 10MPa, 11MPa or 12MPa, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0074] Preferably, the holding time of the hot pressing treatment is 3h to 5h, for example: 3h, 3.5h, 4h, 4.5h or 5h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0075] Thirdly, the present invention provides a negative electrode sheet comprising the composite silicon-carbon negative electrode material as described in the first aspect.

[0076] Fourthly, the present invention provides a battery comprising a negative electrode as described in the third aspect.

[0077] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0078] Compared with the prior art, the present invention has the following beneficial effects:

[0079] (1) The present invention forms a gradient pore buffer layer with dense inner and sparse outer on the surface of silicon carbon particles. At the same time, it is filled by a self-healing binder containing dynamic disulfide bonds to achieve three-dimensional synergistic regulation of expansion stress graded dissipation, microcrack self-repair and ion / electron dual-path conduction, which completely solves the three core problems of electrode pulverization caused by volume expansion, interface impedance surge and long cycle capacity decay.

[0080] (2) This invention achieves "graded stress dissipation" through a gradient design of rigid constraint by dense inner carbon (5-10 nm pore size) and elastic buffer by loose outer carbon (50-100 nm pore size). Combined with the reversible breakage / recombination of dynamic disulfide bonds at charge-discharge potential (3.0-3.5V), microcracks caused by expansion can be repaired in real time. This synergistic mechanism of "physical gradient buffer + chemical dynamic repair" allows the overall expansion rate of the electrode to be stably controlled at <20% after long-term cycling, which is far lower than that of traditional silicon-carbon materials (usually >120%), thus fundamentally avoiding electrode pulverization failure.

[0081] (3) The gradient pore structure of the present invention creates an optimized ion transport environment: the inner nanopores can enrich the electrolyte and promote Li + Desolvation, coupled with the large pores in the outer layer, provides a low-resistance, high-speed ion transport "main channel." This gradient channel, similar to "branch collection - main channel fast charging," significantly reduces Li... + Diffusion resistance within the electrode. Combined with the additional ionic conductivity pathways provided by the PEDOT:PSS binder (ionic conductivity >10). -4 (S / cm), enabling the construction of a bicontinuous ion / electron network inside the electrode.

[0082] (4) The self-healing binder containing dynamic disulfide bonds used in this invention is not only an adhesive medium, but also a "smart-response" interface layer. Its dynamic covalent bond characteristics enable the binder network to continuously adapt to volume changes during charging and discharging, re-establishing and strengthening the electrochemical connections between silicon particles, gradient carbon layers, and conductive carbon black, thereby achieving dynamic maintenance of the contact interface. This allows the utilization rate of active materials to remain high during long-term cycling. Compared with traditional static binders such as PVDF, the electrode material of this invention can still maintain a capacity retention rate of >85% after 1000 cycles.

[0083] (5) The composite silicon-carbon anode material of the present invention can achieve a 200-cycle expansion rate of less than 24.5%, a 200-cycle interface impedance growth rate of less than 31.8%, a 1000-cycle capacity retention rate of more than 82.5%, and a crack repair efficiency of more than 96%. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the repair structure of the composite silicon-carbon anode material prepared in Example 1 after cyclic cracking.

[0085] Figure 2 This is a schematic diagram of the structure of the composite silicon-carbon anode material prepared in Comparative Example 3 after cyclic cracking.

[0086] Among them, 1 is the silicon-carbon composite core, 2 is the carbon buffer layer, 3 is the dynamic self-healing adhesive layer, 4 is the crack repair layer, and 5 is the crack area. Detailed Implementation

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0088] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0089] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0090] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0091] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. 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 invention can be combined with other embodiments.

[0092] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0093] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0094] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0095] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0096] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0097] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0098] Example 1

[0099] This embodiment provides a composite silicon-carbon anode material, which includes primary particles and secondary particles composed of primary particles;

[0100] The primary particles include a silicon-carbon composite core and a gradient porous carbon buffer layer and a dynamic self-healing adhesive layer sequentially coated on the surface of the silicon-carbon composite core.

[0101] The composite silicon-carbon anode material has branched carbon nanostructures between its particles. The dynamic self-healing binder layer penetrates 200 nm into the pores of the gradient porous carbon buffer layer. The dynamic self-healing binder layer includes a composite binder (butyl acrylate-3-methylcrotonitrile-dithiodipropionic acid copolymer, with a molar ratio of BA:MCN:DTDP of 70:25:5) and PEDOT:PSS with a median particle size D50 of 80 nm. The mass fraction of PEDOT:PSS in the dynamic self-healing binder layer is 8%. The dynamic self-healing binder layer contains dynamic disulfide bonds with a density of 0.8 mmol / g and a recombination activation energy of 40 kJ / mol at a potential of 3.0 V to 3.5 V.

[0102] The silicon-carbon composite core includes silicon nanoparticles and acetylene black. The mass fraction of the silicon nanoparticles is 30%, the median particle size D50 of the silicon nanoparticles is 80 nm, and the median particle size D50 of the silicon-carbon composite core is 3.0 μm.

[0103] The gradient porous carbon buffer layer comprises an inner porous carbon layer close to the silicon-carbon composite core and an outer porous carbon layer away from the silicon-carbon composite core. The pore size of the inner porous carbon layer is 8 nm and the porosity is 30%. The pore size of the outer porous carbon layer is 80 nm and the porosity is 60%. The porosity ratio of the outer porous carbon layer to the inner porous carbon layer is 2, the pore size ratio of the outer porous carbon layer to the inner porous carbon layer is 10, and the thickness of the gradient porous carbon buffer layer is 250 nm.

[0104] The composite silicon-carbon anode material is prepared by the following method:

[0105] A silicon-carbon composite material composed of silicon nanoparticles and acetylene black was placed in a fluidized bed reactor. The particles were uniformly suspended under the action of argon gas flow. A mixture of ethylene and argon (volume ratio 1:9) was introduced and subjected to a first CVD treatment at 400℃ for 30 min. Then, the temperature was increased to 600℃ at a heating rate of 10℃ / min, and the introduced gas was changed to a mixture of carbon dioxide and acetylene (volume ratio 1:3) for a second CVD treatment for 60 min. The temperature was increased to 750℃ at a heating rate of 10℃ / min, and the introduced gas was changed to acetylene. The precursor material was obtained by high-temperature pyrolysis for 10 min.

[0106] Under an argon atmosphere, butyl acrylate, 3-methylcrotonitrile, and dithiodipropionic acid were dissolved in NMP (molar ratio of NMP to butyl acrylate was 9.5:1) at a molar ratio of 1:0.58:0.044. AIBN (molar ratio of AIBN to butyl acrylate was 0.0057:1) was added to carry out a copolymerization reaction to obtain a copolymer matrix. The copolymer matrix was mixed with PEDOT:PSS and subjected to high-intensity ultrasonic treatment to make it uniformly dispersed in the polymer matrix, forming a molecular-level composite self-healing adhesive liquid.

[0107] The precursor material, self-healing adhesive, and conductive carbon black SP were mixed in a mass ratio of 80:10:10 and coated onto the surface of a copper foil current collector. After drying to remove the solvent, the mixture was hot-pressed at 80°C and 10MPa for 4 hours to obtain the composite silicon-carbon anode material.

[0108] Example 2

[0109] This embodiment provides a composite silicon-carbon anode material, which includes primary particles and secondary particles composed of primary particles;

[0110] The primary particles include a silicon-carbon composite core and a gradient porous carbon buffer layer and a dynamic self-healing adhesive layer sequentially coated on the surface of the silicon-carbon composite core.

[0111] The composite silicon-carbon anode material has branched carbon nanostructures between its particles. The dynamic self-healing binder layer penetrates to a depth of 185 nm into the pores of the gradient porous carbon buffer layer. The dynamic self-healing binder layer includes a composite binder (butyl acrylate-3-methylcrotonitrile-dithiodipropionic acid copolymer, with a molar ratio of BA:MCN:DTDP of 60:30:10) and PEDOT:PSS with a median particle size D50 of 70 nm. The mass fraction of PEDOT:PSS in the dynamic self-healing binder layer is 7.5%. The dynamic self-healing binder layer contains dynamic disulfide bonds with a density of 0.7 mmol / g. The recombination activation energy of the dynamic disulfide bonds at a potential of 3.0 V to 3.5 V is 38 kJ / mol.

[0112] The silicon-carbon composite core includes silicon nanoparticles and acetylene black. The mass fraction of the silicon nanoparticles is 28%, the median particle size D50 of the silicon nanoparticles is 70 nm, and the median particle size D50 of the silicon-carbon composite core is 2.5 μm.

[0113] The gradient porous carbon buffer layer comprises an inner porous carbon layer close to the silicon-carbon composite core and an outer porous carbon layer away from the silicon-carbon composite core. The pore size of the inner porous carbon layer is 5 nm, and the porosity of the inner porous carbon layer is 25%. The pore size of the outer porous carbon layer is 100 nm, and the porosity of the outer porous carbon layer is 65%. The porosity ratio of the outer porous carbon layer to the inner porous carbon layer is 2.6, and the pore size ratio of the outer porous carbon layer to the inner porous carbon layer is 20. The thickness of the gradient porous carbon buffer layer is 280 nm.

[0114] The composite silicon-carbon anode material is prepared by the following method:

[0115] A silicon-carbon composite material composed of silicon nanoparticles and acetylene black was placed in a fluidized bed reactor. The particles were uniformly suspended under the action of argon gas flow. A mixture of ethylene and argon (volume ratio of 1:10) was introduced and subjected to a first CVD treatment at 430℃ for 20 min. Then, the temperature was increased to 650℃ at a heating rate of 12℃ / min, and the introduced gas was changed to a mixture of carbon dioxide and acetylene (volume ratio of 1:3.5) for a second CVD treatment for 40 min. The temperature was increased to 800℃ at a heating rate of 10℃ / min, and the introduced gas was changed to acetylene. The precursor material was obtained by high-temperature pyrolysis for 5 min.

[0116] Under an argon atmosphere, butyl acrylate, 3-methylcrotonitrile, and dithiodipropionic acid were dissolved in NMP (the molar ratio of NMP to butyl acrylate was 9.1:1) at a molar ratio of 1:0.60:0.046. AIBN (the molar ratio of AIBN to butyl acrylate was 0.0055:1) was added to carry out a copolymerization reaction to obtain a copolymer matrix. The copolymer matrix was mixed with PEDOT:PSS and subjected to high-intensity ultrasonic treatment to make it uniformly dispersed in the polymer matrix, forming a molecular-level composite self-healing adhesive liquid.

[0117] The precursor material, self-healing adhesive, and conductive carbon black SP were mixed in a mass ratio of 70:15:15 and coated onto the surface of a copper foil current collector. After drying to remove the solvent, the mixture was hot-pressed at 75°C and 8MPa for 3 hours to obtain the composite silicon-carbon anode material.

[0118] Example 3

[0119] This embodiment provides a composite silicon-carbon anode material, which includes primary particles and secondary particles composed of primary particles;

[0120] The primary particles include a silicon-carbon composite core and a gradient porous carbon buffer layer and a dynamic self-healing adhesive layer sequentially coated on the surface of the silicon-carbon composite core.

[0121] The composite silicon-carbon anode material has branched carbon nanostructures between its particles. The dynamic self-healing binder layer penetrates to a depth of 210 nm into the pores of the gradient porous carbon buffer layer. The dynamic self-healing binder layer includes a composite binder (butyl acrylate-3-methylcrotonitrile-dithiodipropionic acid copolymer, with a molar ratio of BA:MCN:DTDP of 80:15:5) and PEDOT:PSS with a median particle size D50 of 90 nm. The mass fraction of PEDOT:PSS in the dynamic self-healing binder layer is 8.8%. The dynamic self-healing binder layer contains dynamic disulfide bonds with a density of 0.9 mmol / g and a recombination activation energy of 42 kJ / mol at a potential of 3.0 V to 3.5 V.

[0122] The silicon-carbon composite core includes silicon nanoparticles and acetylene black. The mass fraction of the silicon nanoparticles is 32%, the median particle size D50 of the silicon nanoparticles is 90 nm, and the median particle size D50 of the silicon-carbon composite core is 3.5 μm.

[0123] The gradient porous carbon buffer layer comprises an inner porous carbon layer close to the silicon-carbon composite core and an outer porous carbon layer away from the silicon-carbon composite core. The pore size of the inner porous carbon layer is 10 nm, and the porosity of the inner porous carbon layer is 35%. The pore size of the outer porous carbon layer is 100 nm, and the porosity of the outer porous carbon layer is 65%. The porosity ratio of the outer porous carbon layer to the inner porous carbon layer is 1.86, and the pore size ratio of the outer porous carbon layer to the inner porous carbon layer is 10. The thickness of the gradient porous carbon buffer layer is 220 nm.

[0124] The composite silicon-carbon anode material is prepared by the following method:

[0125] A silicon-carbon composite material composed of silicon nanoparticles and acetylene black was placed in a fluidized bed reactor. The particles were uniformly suspended under the action of argon gas flow. A mixture of ethylene and argon (volume ratio 1:8) was introduced and subjected to a first CVD treatment at 370℃ for 40 min. Then, the temperature was increased to 550℃ at a heating rate of 8℃ / min, and the introduced gas was changed to a mixture of carbon dioxide and acetylene (volume ratio 1:2.5) for a second CVD treatment for 80 min. The temperature was increased to 700℃ at a heating rate of 8℃ / min, and the introduced gas was changed to acetylene. The precursor material was obtained by high-temperature pyrolysis for 15 min.

[0126] Under an argon atmosphere, butyl acrylate, 3-methylcrotonitrile, and dithiodipropionic acid were dissolved in NMP (molar ratio of NMP to butyl acrylate was 9.9:1) at a molar ratio of 1:0.55:0.043. AIBN (molar ratio of AIBN to butyl acrylate was 0.0058:1) was added to carry out a copolymerization reaction to obtain a copolymer matrix. The copolymer matrix was mixed with PEDOT:PSS and subjected to high-intensity ultrasonic treatment to make it uniformly dispersed in the polymer matrix, forming a molecular-level composite self-healing adhesive liquid.

[0127] The precursor material, self-healing adhesive, and conductive carbon black SP were mixed in a mass ratio of 90:5:5 and coated onto the surface of a copper foil current collector. After drying to remove the solvent, the mixture was hot-pressed at 85°C and 12MPa for 5 hours to obtain the composite silicon-carbon anode material.

[0128] Example 4

[0129] The only difference between this embodiment and Embodiment 1 is that the pore size of the inner porous carbon layer is controlled to be 10 nm, the pore size of the outer porous carbon layer is controlled to be 50 nm, and the pore size ratio of the inner porous carbon layer to the outer porous carbon layer is 5. All other conditions and parameters are exactly the same as in Embodiment 1.

[0130] Example 5

[0131] The only difference between this embodiment and Embodiment 1 is that the porosity of the inner porous carbon layer is controlled at 35%, the porosity of the outer porous carbon layer is controlled at 55%, and the porosity of the inner and outer porous carbon layers is 1.75. All other conditions and parameters are exactly the same as in Embodiment 1.

[0132] Example 6

[0133] The only difference between this embodiment and Embodiment 1 is that the mass fraction of PEDOT:PSS in the dynamic self-healing adhesive layer is controlled to be 7%, while other conditions and parameters are exactly the same as in Embodiment 1.

[0134] Example 7

[0135] The only difference between this embodiment and Embodiment 1 is that the mass fraction of PEDOT:PSS in the dynamic self-healing adhesive layer is controlled to be 9%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0136] Example 8

[0137] The only difference between this embodiment and Embodiment 1 is that the hot pressing temperature is 70°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0138] Example 9

[0139] The only difference between this embodiment and Embodiment 1 is that the hot pressing temperature is 90°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0140] Comparative Example 1

[0141] This comparative example directly uses a silicon-carbon composite material composed of silicon nanoparticles and acetylene black.

[0142] Comparative Example 2

[0143] The only difference between this comparative example and Example 1 is that the gradient porous carbon buffer layer is replaced with a porous carbon layer with a single pore size of 50 nm and a porosity of 40%. All other conditions and parameters are exactly the same as in Example 1.

[0144] Comparative Example 3

[0145] The only difference between this comparative example and Example 1 is that the self-healing adhesive liquid is replaced with a polyacrylic acid-sodium alginate composite crosslinking adhesive; all other conditions and parameters are exactly the same as in Example 1.

[0146] Performance testing:

[0147] 1) Electrode expansion rate test method after 200 cycles

[0148] 1. Sample preparation: The negative electrode material to be tested is coated on copper foil to prepare an electrode sheet. The original thickness T0 is measured at at least 9 different locations (e.g., 3×3 grid) using a micrometer or laser thickness gauge, and the average value is taken.

[0149] 2. Battery assembly: Using this electrode as the working electrode and the lithium metal sheet as the counter / reference electrode, CR2032 type button half cell is assembled in an argon glove box.

[0150] 3. Cyclic processing: Under the set charge / discharge regime (e.g., 0.5C rate, voltage window 0.01V~1.5V vs Li), + Perform 200 cycles under / Li).

[0151] 4. Post-cycle measurement: After cycling, disassemble the battery in a glove box, carefully remove the electrode plates, gently rinse with an inert solvent (such as DMC) to remove residual electrolyte, and dry. Measure the electrode plate thickness T after cycling using the same method. 200 .

[0152] 5. Calculation: Electrode expansion rate (%) = [(T 200 -T0) / T0]×100%

[0153] 2) Method for testing the growth rate of interfacial impedance after 200 cycles

[0154] 1. Initial Impedance Measurement: After the newly assembled half-cell has been left to stand at open-circuit voltage for 2 hours, an EIS test is performed using an electrochemical workstation. The test conditions are typically: amplitude 5-10mV, frequency range 100kHz to 0.01Hz. The charge transfer resistance (Rc) is obtained through equivalent circuit fitting. et ), denoted as the initial value R et,0 .

[0155] 2. Impedance Measurement After Cycles: After the battery completes 200 cycles, it is left to rest for 2 hours in a fully charged state (or 50% state of charge), and then EIS testing is performed again under the same test conditions to obtain the charge transfer resistance R after cycling. et,200 .

[0156] 3. Calculation: Interface impedance growth rate (%) = [(R et,200 -R et,0 ) / R et,0 ]×100%

[0157] 3) 1000-cycle capacity retention test method

[0158] 1. Initial activation and capacity calibration: Perform 1-2 charge-discharge cycles on the half-cell at a low rate (e.g., 0.1C) to complete activation. Then, perform charge-discharge at a test rate (e.g., 0.5C or 1C), and take the discharge capacity of the third cycle as the initial capacity C3.

[0159] 2. Long-cycle test: Keeping the test conditions unchanged, continue charging and discharging cycles up to 1000 cycles, and record the discharge capacity C each week. n .

[0160] 3. Calculation: Capacity retention rate in week N (%) = (C n / C3)×100%, the capacity retention rate over 1000 cycles is the value when N=1000.

[0161] 4) Crack Repair Rate Test Method

[0162] 1. Artificial pre-crack: A standard crack with a width of micrometers is artificially created in a selected area on the electrode sheet using a nanoindenter or a precision probe. The initial maximum width W0 of the crack is accurately measured and recorded using an atomic force microscope (AFM) or a high-resolution SEM.

[0163] 2. Triggered Repair: Assemble the pre-cracked electrodes into a half-cell and perform one complete charge-discharge cycle (3.0-3.5V window to trigger disulfide bond recombination), or place them in a device with a controllable potential and apply a constant voltage of 3.2V for a period of time (e.g., 180 seconds).

[0164] 3. Post-war observation and calculation: After repair, the crack morphology was observed at the same location using the same equipment, and the maximum width W after repair was measured. r Crack repair rate (%) = [(W0 - W r The test results are shown in Table 1: (W0) × 100%.

[0165] Table 1

[0166]

[0167] As shown in Table 1, and based on Examples 1-9, the composite silicon-carbon anode material of the present invention achieves a 200-cycle expansion rate of less than 35.2%, a 200-cycle interfacial impedance growth rate of less than 58.9%, a 1000-cycle capacity retention rate of over 73.8%, and a crack repair efficiency of over 92.3%. By adjusting the parameters of each component in the composite silicon-carbon anode material, the 200-cycle expansion rate of the battery made from it can reach less than 24.5%, the 200-cycle interfacial impedance growth rate can reach less than 31.8%, the 1000-cycle capacity retention rate can reach over 82.5%, and the crack repair efficiency can reach over 96%. The inner and outer layer pore size ratio, porosity ratio, and PEDOT:PSS mass fraction in the conductive binder of the gradient pore structure all have clearly optimal values ​​within the preferred range defined in the claims. When these core parameters work synergistically, the composite silicon-carbon anode material can achieve the best balance between mechanical stability, interfacial kinetics, and long cycle life.

[0168] A comparison of Examples 1 and 4-5 shows that in the gradient porous carbon buffer layer of the composite silicon-carbon anode material of the present invention, the pore size ratio and porosity ratio of the outer porous carbon layer and the inner porous carbon layer affect its performance. When the pore size ratio of the outer porous carbon layer and the inner porous carbon layer is controlled at ≥10 and the porosity ratio is controlled at ≥1.8, the composite silicon-carbon anode material has better performance. If the pore size ratio and porosity ratio of the outer porous carbon layer and the inner porous carbon layer are too low, the gradient buffer effect is weakened, resulting in stress concentration, easy cracking of the carbon layer, and a significant increase in the cyclic expansion rate and interfacial impedance, and a decrease in capacity retention.

[0169] A comparison of Examples 1 and 6-7 shows that the mass fraction of conductive polymer in the dynamic self-healing binder layer of the composite silicon-carbon anode material of the present invention affects its performance. When the mass fraction of conductive polymer in the dynamic self-healing binder layer is controlled at 7.5%~8.8%, the composite silicon-carbon anode material exhibits better performance. If the mass fraction of conductive polymer in the dynamic self-healing binder layer is too high, it will disrupt the continuity of the polymer matrix, hinder dynamic bond recombination, reduce self-repair efficiency, and deteriorate mechanical properties. If the mass fraction of conductive polymer in the dynamic self-healing binder layer is too low, it will be difficult to form a complete ion / electron dual conductive network, leading to increased interfacial impedance and accelerated capacity decay.

[0170] A comparison of Examples 1 and 8-9 shows that the hot-pressing temperature affects the performance of the composite silicon-carbon anode material during its preparation. When the hot-pressing temperature is controlled between 75°C and 85°C, the composite silicon-carbon anode material exhibits better performance. If the hot-pressing temperature is too high, it may lead to thermal decomposition or excessive cross-linking of the binder components, causing them to become brittle and reducing their repairability and conductivity. If the hot-pressing temperature is too low, insufficient binder penetration and weak interfacial bonding will prevent effective stress transfer and the construction of a stable conductive interface, resulting in a comprehensive deterioration of all performance characteristics.

[0171] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention forms a gradient porous buffer layer with dense inner and sparse outer layers on the surface of silicon-carbon particles. At the same time, it achieves three-dimensional synergistic regulation of expansion stress graded dissipation, microcrack self-repair, and ion / electron dual-path conduction by penetrating and filling the layer with a self-healing binder containing dynamic disulfide bonds. This completely solves the three core problems of electrode pulverization caused by volume expansion, surge in interface impedance, and capacity decay over long cycles.

[0172] By comparing Example 1 and Comparative Example 2, it can be seen that the present invention, by setting a gradient porous carbon buffer layer on the surface of the silicon-carbon composite core, forms a radial gradient stress dissipation network through the capillary constraint effect of the inner dense carbon and the volume containment capacity of the outer buffer carbon, completely replacing the traditional single-stage buffer mode of uniform porous structure, and reducing the silicon expansion strain from >120% to <20%.

[0173] Example 1 shows a schematic diagram of the repair structure of the composite silicon-carbon anode material after cyclic cracking. Figure 1 As shown, a schematic diagram of the structure of the composite silicon-carbon anode material prepared in Comparative Example 3 after cyclic cracking is shown in the figure. Figure 2As shown, a comparison between Example 1 and Comparative Example 3 reveals that the dynamic self-healing adhesive layer of this invention contains dynamic disulfide bonds. These dynamic disulfide bonds undergo reversible breakage / recombination during the charge-discharge process, avoiding the permanent interface failure of traditional static adhesives and achieving in-situ repair of microcracks. The self-healing adhesive penetrates and fills the pores of the gradient porous carbon buffer layer, forming a dual dynamic repair network of hydrogen bonds and dynamic disulfide bonds. Branched carbon nanostructures grow within the pore walls of the gradient porous carbon buffer layer, providing high-speed electron channels (bulk conductivity > 10). 2 (S / cm), while conductive polymers are constructed in the binder to form Li + Transport pathway (ionic conductivity > 10) -4 (S / cm), breaking through the transmission bottleneck of traditional silicon-carbon anodes where "electrons are conducting but ions are blocking".

[0174] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite silicon-carbon negative electrode material, characterized in that, The composite silicon-carbon negative electrode material comprises primary particles and secondary particles composed of the primary particles; The primary particles comprise a silicon-carbon composite inner core and a gradient porous carbon buffer layer and a dynamic self-healing binder layer successively coated on the surface of the silicon-carbon composite inner core; The composite silicon-carbon negative electrode material is provided with branched carbon nanostructures between the particles, the dynamic self-healing binder layer partially penetrates into the pores of the gradient porous carbon buffer layer, the dynamic self-healing binder layer contains dynamic disulfide bonds, and the dynamic self-healing binder layer comprises a composite binder and a conductive polymer.

2. The composite silicon-carbon anode material of claim 1, wherein, The material of the silicon-carbon composite inner core comprises silicon nanoparticles and acetylene black; Preferably, in the silicon-carbon composite inner core, the mass fraction of the silicon nanoparticles is 28% to 32%; Preferably, the median particle size D50 of the silicon nanoparticles is 70 nm to 90 nm; Preferably, the median particle size D50 of the silicon-carbon composite inner core is 1 μm to 5 μm.

3. The composite silicon-carbon negative electrode material of claim 1 or 2, wherein The gradient porous carbon buffer layer comprises an inner porous carbon layer close to the silicon-carbon composite inner core and an outer porous carbon layer away from the silicon-carbon composite inner core; Preferably, the pore size of the inner porous carbon layer is 5 nm to 10 nm; Preferably, the porosity of the inner porous carbon layer is 25% to 35%; Preferably, the pore size of the outer porous carbon layer is 50 nm to 100 nm; Preferably, the porosity of the outer porous carbon layer is 55% to 65%; Preferably, the porosity ratio of the outer porous carbon layer to the inner porous carbon layer is ≥1.8; Preferably, the pore size ratio of the outer porous carbon layer to the inner porous carbon layer is ≥10; Preferably, the thickness of the gradient porous carbon buffer layer is 150 nm to 300 nm; Preferably, the penetration depth of the dynamic self-healing binder layer in the gradient porous carbon buffer layer is >180 nm.

4. The composite silicon-carbon anode material of any one of claims 1-3, wherein, The composite binder comprises a butyl acrylate-3-methylcrotonitrile-dithiodipropionic acid copolymer; Preferably, in the molecule of the composite binder, the molar proportion of the butyl acrylate group is 60% to 80%; Preferably, in the molecule of the composite binder, the molar proportion of the 3-methylcrotonitrile group is 10% to 30%; Preferably, in the molecule of the composite binder, the molar proportion of the dithiodipropionic acid group is 1% to 10%; Preferably, in the composite binder, the density of the dynamic disulfide bond is 0.7 mmol / g to 0.9 mmol / g; Preferably, the recombination activation energy of the dynamic disulfide bond at a potential of 3.0 V to 3.5 V is 38 kJ / mol to 42 kJ / mol; Preferably, the conductive polymer comprises PEDOT:PSS; Preferably, the median particle size D50 of the conductive polymer is 70 nm to 90 nm; Preferably, the mass fraction of the conductive polymer in the dynamic self-healing binder layer is 7.5% to 8.8%; Preferably, the thickness of the dynamic self-healing binder layer is 200 nm to 400 nm.

5. A method for preparing the composite silicon-carbon negative electrode material according to any one of claims 1-4, characterized in that, The preparation method comprises the following steps: CVD gradient deposition carbon treatment is performed on the silicon-carbon composite material to obtain a precursor material; Preferably, the thickness of the gradient porous carbon buffer layer is 150 nm to 300 nm. The monomer containing dynamic disulfide bond is copolymerized to form a polymer matrix under an inert atmosphere, a conductive polymer is mixed with the polymer matrix, and ultrasonic is used to obtain a self-healing adhesive glue solution; The precursor material, the self-healing adhesive glue solution and the conductive agent are mixed, coated on the surface of a substrate, and after the solvent is removed, the composite silicon-carbon negative electrode material is obtained through heat pressing treatment.

6. The production method according to claim 5, wherein The CVD gradient deposition carbon treatment comprises the following steps: placing the silicon-carbon composite material in a fluidized bed reactor, achieving uniform suspension of particles under the fluidization of inert gas, using a gaseous carbon source mixed gas containing a weak oxidizing component for a second CVD deposition treatment after a first CVD deposition treatment using a gaseous carbon source mixed gas, and using acetylene for high-temperature pyrolysis treatment of the obtained material to obtain a precursor material; Preferably, the gaseous carbon source mixed gas comprises a gaseous carbon source and a carrier gas; Preferably, the gaseous carbon source comprises ethylene and / or acetylene; Preferably, the carrier gas comprises argon and / or nitrogen; Preferably, in the gaseous carbon source mixed gas, the volume ratio of the gaseous carbon source and the carrier gas is 1:(8-10); Preferably, the temperature of the first CVD deposition treatment is 370-430℃; Preferably, the time of the first CVD deposition treatment is 20-40min; Preferably, the gaseous carbon source mixed gas containing a weak oxidizing component comprises carbon dioxide and a gaseous carbon source; Preferably, in the gaseous carbon source mixed gas containing a weak oxidizing component, the volume ratio of carbon dioxide and the gaseous carbon source is 1:(2.5-3.5); Preferably, the temperature of the second CVD deposition treatment is 550-650℃; Preferably, the time of the second CVD deposition treatment is 40-80min; Preferably, the temperature rising speed from the first CVD deposition treatment to the second CVD deposition treatment is 8-12℃ / min; Preferably, the temperature of the high-temperature pyrolysis treatment is 700-800℃; Preferably, the time of the high-temperature pyrolysis treatment is 5-15min.

7. The production method according to claim 5 or 6, characterized by, The copolymerization of the monomer containing dynamic disulfide bond to form a polymer matrix comprises the following steps: dissolving an acrylate monomer, a cyano functional monomer and a dynamic disulfide crosslinking agent in a polar organic solvent, and adding a free radical initiator for copolymerization reaction to obtain a copolymer matrix; Preferably, the acrylate monomer comprises butyl acrylate; Preferably, the cyano functional monomer comprises 3-methyl crotonitrile; Preferably, the molar ratio of the cyano functional monomer to the acrylate monomer is (0.55-0.60):1; Preferably, the dynamic disulfide crosslinking agent comprises dithiodipropionic acid; Preferably, the molar ratio of the dynamic disulfide crosslinking agent to the acrylate monomer is (0.043-0.046):1; Preferably, the polar organic solvent comprises NMP; Preferably, the molar ratio of the polar organic solvent to the acrylate monomer is (9.1-9.9):1; Preferably, the free radical initiator comprises AIBN; Preferably, the molar ratio of the free radical initiator to the acrylate monomer is 0.0055-0.0058):

1.

8. The production method according to any one of claims 5 to 7, wherein The conductive agent comprises conductive carbon black SP; Preferably, the mass ratio of the precursor material, the self-healing binder solution and the conductive agent is (70~90):(5~15):(5~15); Preferably, the substrate comprises a copper current collector; Preferably, the temperature of the hot-pressing treatment is 75~85℃; Preferably, the pressure of the hot-pressing treatment is 8~12MPa; Preferably, the pressure-maintaining time of the hot-pressing treatment is 3~5h.

9. A negative electrode sheet characterized by comprising: The negative electrode plate comprises the composite silicon-carbon negative electrode material according to any one of claims 1-4.

10. A battery, characterized by The battery comprises the negative electrode plate according to claim 9.

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