Silicon composite material, preparation method thereof, negative active material, and negative electrode sheet

Abstract

This invention relates to the field of lithium-ion battery technology, and more particularly to a silicon composite material and its preparation method, a negative electrode active material, and a negative electrode sheet. The silicon composite material includes a core structure and a shell structure; the core structure includes liquid metal particles and a first carbon coating layer located on the outer periphery of the liquid metal particles; the shell structure includes a silicon layer located on the outer periphery of the first carbon coating layer and a second carbon coating layer located on the outer periphery of the silicon layer. This silicon composite material can effectively suppress cracking caused by large deformation during charging and discharging, improve the lithium-ion and electronic conductivity inside the silicon particles, reduce internal polarization, eliminate dead lithium and provide high specific capacity, and improve battery cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon composite material and its preparation method, a negative electrode active material, and a negative electrode sheet. Background Technology

[0002] With the development of electric vehicle technology and people's increasing demands for range, improving battery energy density has become an urgent issue. Graphite anodes occupy a dominant position in the anode market due to their extremely high stability and low price. However, their theoretical capacity is low and cannot meet the growing demand for high power and high energy density. Silicon materials, with a theoretical energy density more than ten times that of graphite, have stood out among anode materials. However, the enormous stress during lithium-ion insertion and extraction causes silicon anodes to expand dramatically (approximately 300%). Such high expansion often leads to problems such as SEI film decomposition, active particle breakage, binder detachment, reduced peel strength, and electrode cracking on the silicon anode surface, ultimately resulting in battery capacity loss.

[0003] Currently, the focus is mainly on optimizing the binder, using novel binders such as star-shaped binders and reversible crosslinking binders to improve their interaction with silicon particles. However, repeated expansion and contraction can cause binder displacement and breakage, ultimately leading to reduced adhesion and collapse of the negative electrode structure. Therefore, optimizing the binder needs to be combined with optimizing the silicon particle structure. A common approach is to provide appropriate external or internal space for silicon expansion. For external expansion space, silicon particles with a villous surface structure are mainly prepared through the stepwise growth of carbon fibers; however, the degree of coating of this core-shell structure and the growth effect of the surface villous layer are difficult to control. For internal expansion space, hollow silicon particles are typically prepared, and their structural design and preparation methods have a significant impact on the performance of the silicon particles. Specifically, a porous structure can be introduced by magnesium thermoreduction of silicates and subsequent acid washing. However, residual magnesium can cause significant bulk diffusion resistance, and residual acid can affect the stability of the SEI and the binder. Using metal-organic frameworks (MOFs) as a framework to coat silicon materials on the surface, followed by calcination, produces a porous cage-like Si / C composite material, providing a new approach for preparing porous silicon using MOF structures. However, MOFs are costly and have a low success rate, making them unsuitable for large-scale production. Mixing silicon particles and carbon source gel, granulating them, coating them with a carbon source, and then calcining them produces hollow and porous spherical silicon-carbon composite particles. This method allows for maximum contact between silicon particles and carbon materials, improving electron transport rates. However, silicon particles are difficult to disperse in the gel composition, and under extremely high deformation, the inner carbon layer easily separates from the silicon particles, leading to increased internal polarization and impaired capacity utilization.

[0004] Therefore, optimizing the internal structure of the silicon anode and uniformly discharging the enormous stress generated during the charging and discharging process has become a key focus. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a silicon composite material and its preparation method, a negative electrode active material, and a negative electrode sheet. This silicon composite material can effectively suppress cracking caused by large deformation during charging and discharging, improve the lithium-ion and electronic conductivity inside silicon particles, reduce internal polarization, eliminate dead lithium and provide high specific capacity, and improve battery cycle life.

[0006] Therefore, in a first aspect, the present invention provides a silicon composite material, the silicon composite material comprising a core structure and a shell structure;

[0007] The core structure includes liquid metal particles and a first carbon coating layer located on the outer periphery of the liquid metal particles;

[0008] The shell structure includes a silicon layer located on the periphery of the first carbon coating layer and a second carbon coating layer located on the periphery of the silicon layer.

[0009] This silicon composite material features a hollow structure with a liquid metal core, a silicon shell, and a carbon coating. The liquid metal core not only enhances the lithium-ion and electronic conductivity within the silicon particles but also acts as an active material, alloying with lithium metal, suppressing dendrite growth, and providing high specific capacity. The hollow structure provides inward expansion space for the silicon particles, reducing overall electrode deformation and binder rearrangement, thus improving the cycle stability of the electrode material. The carbon coating on the shell surface enhances both the electronic conductivity of the silicon particles and their interfacial stability, reducing side reactions with the electrolyte / electrolyte.

[0010] According to an embodiment of the present invention, the silicon composite material contains 70-98% silicon by mass, 1-20% liquid metal by mass, and 1-10% carbon by mass.

[0011] According to an embodiment of the present invention, the particle size of the silicon composite material is 1-15 μm;

[0012] And / or, the D of the liquid metal particles 50 It is 0.5-5μm;

[0013] And / or, the thickness of the first carbon coating layer is 0.2-0.6 μm;

[0014] And / or, the thickness of the silicon layer is 1.5-5 μm;

[0015] And / or, the thickness of the second carbon coating layer is 0.08-0.2 μm.

[0016] According to an embodiment of the present invention, the liquid metal particles include at least one of gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, rubidium, and cesium.

[0017] According to an embodiment of the present invention, the core structure further includes an oxide layer located on the periphery of the liquid metal particles, wherein the first carbon coating layer is located on the periphery of the oxide layer;

[0018] And / or, the thickness of the oxide layer is 0.5-3 nm.

[0019] A second aspect of the present invention provides a method for preparing the silicon composite material described in the first aspect, the method comprising:

[0020] Liquid metal and thiol surfactants are dissolved in a first solvent and then pulverized to obtain liquid metal particles;

[0021] The liquid metal particles, amphiphilic macromolecules, and polysaccharides are mixed to obtain micelle particles; the micelle particles are then mixed with a crosslinking agent to obtain a coating.

[0022] The coupling agent and silicon particles are dissolved in a second solvent to obtain silicon-coupling agent particles;

[0023] The coating and the silicon-coupling agent particles are mixed to obtain the precursor;

[0024] The precursor and organic carbon source are mixed and sintered to obtain the silicon composite material.

[0025] According to embodiments of the present invention, the thiol surfactant includes at least one of 3-mercaptopropyltriethoxysilane, n-octadecyl mercaptan, dodecathyl mercaptan, and 3-mercapto-N-nonylpropionamide;

[0026] And / or, the mass ratio of the liquid metal to the thiol surfactant is 100:(0.7-3);

[0027] And / or, the first solvent includes one of n-hexane, cyclohexane, and anhydrous ethanol.

[0028] According to embodiments of the present invention, the amphiphilic macromolecule includes at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium dodecyl phosphate, tetradecyltrimethylammonium bromide, hexadecyltrimethylsodium bromide, dihexadecyldimethylammonium bromide, dihexadecyldimethylammonium chloride, octadecyldimethylammonium bromide, and dioctadecyldimethylammonium chloride.

[0029] And / or, the polysaccharide includes at least one of sucrose, lactose, maltose, fructose, and glucose;

[0030] And / or, the crosslinking agent includes at least one of polydopamine, maleimide-polyethylene glycol-dopamine, multi-arm polyethylene glycol, polymaleic acid, citric acid, polycarboxylic acid, and polyol;

[0031] And / or, the micelle particles and crosslinking agent are mixed at 40-60°C for 15-30 minutes.

[0032] According to an embodiment of the present invention, the mass ratio of the silicon particles to the coupling agent is 100:(0.05-2), preferably 100:(0.2-1);

[0033] And / or, the coupling agent includes a silane coupling agent;

[0034] And / or, the coupling agent includes at least one of alkyl silane coupling agents, vinyl silane coupling agents, epoxy silane coupling agents, acyloxy silane coupling agents, acylurea silane coupling agents, chloropropyl silane coupling agents, amino silane coupling agents, and sulfur-containing silane coupling agents;

[0035] And / or, the second solvent includes an alcohol-water solvent;

[0036] And / or, the second solvent includes at least one of methanol aqueous solvent, ethanol aqueous solvent, butanol aqueous solvent, pentanol aqueous solvent, ethylene glycol aqueous solvent, and propylene glycol aqueous solvent;

[0037] And / or, the mass ratio of alcohol, water and coupling agent in the alcohol-water solvent is (63-74):(8-19):(15-23), preferably 72:(8-10):(18-20);

[0038] And / or, the silicon particles include at least one of pure silicon, silicon oxide, and silicon-carbon materials;

[0039] And / or, the D of the silicon particles 50 It ranges from 0.5 to 3 μm.

[0040] According to embodiments of the present invention, the organic carbon source includes at least one of polyethylene glycol, polyethylene oxide, epoxy resin, phenolic resin, acrylic resin, furfural resin, asphalt, polyvinyl chloride, and polyacrylonitrile;

[0041] And / or, the mass ratio of the precursor to the organic carbon source is 1:(0.05-0.2);

[0042] And / or, the sintering is performed under a protective atmosphere;

[0043] And / or, the sintering temperature is 900-1200℃;

[0044] And / or, the sintering time is 0.5-10h.

[0045] A third aspect of the present invention provides a negative electrode active material, the negative electrode active material comprising the silicon composite material described in the first aspect or the silicon composite material obtained according to the preparation method described in the second aspect.

[0046] This negative electrode active material has all the advantages of the aforementioned silicon composite materials, which will not be repeated here.

[0047] A fourth aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode active material described in the third aspect.

[0048] The negative electrode plate has minimal deformation during charging and discharging, which can improve the cycle life of the battery containing it.

[0049] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0050] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0051] Figure 1 One of the structural diagrams of the silicon composite material provided by the present invention is shown;

[0052] Figure 2 The second structural diagram of the silicon composite material provided by the present invention is shown;

[0053] Figure 3 The image shows a SEM image of the negative electrode material prepared according to Example 1 after 50 battery cycles.

[0054] Figure 4 The image shows a SEM image of the negative electrode material prepared based on Comparative Example 1 after 50 battery cycles.

[0055] Figure label:

[0056] Liquid metal particles 1, first carbon coating layer 2, silicon layer 3, second carbon coating layer 4, oxide layer 5. Detailed Implementation

[0057] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0058] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0059] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0060] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0061] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0062] According to embodiments of the present invention, a first aspect provides a silicon composite material, the specific structure of which is shown below. Figure 1 The silicon composite material includes a core structure and a shell structure;

[0063] The core structure includes liquid metal particles 1 and a first carbon coating layer 2 located on the outer periphery of the liquid metal particles 1;

[0064] The shell structure includes a silicon layer 3 located on the outer periphery of the first carbon coating layer 2 and a second carbon coating layer 4 located on the outer periphery of the silicon layer 3.

[0065] The inventors have proposed a hollow core-shell structure silicon material. This material has a hollow structure with a liquid metal core, a silicon shell, and a carbon coating. The liquid metal, as the core, not only enhances the lithium-ion and electronic conductivity within the silicon particles but also acts as an active material, alloying with lithium metal, suppressing dendrite growth, and providing high specific capacity. The hollow structure provides inward expansion space for the silicon particles, reducing overall electrode deformation and binder rearrangement, thus improving the cycle stability of the electrode material. Simultaneously, the carbon coating on the shell surface enhances both the electronic conductivity of the silicon particles and the interfacial stability, reducing side reactions with the electrolyte / electrolyte.

[0066] According to specific embodiments of the present invention, the silicon mass percentage in the silicon composite material is 70-98%, and as some specific examples, the silicon mass percentage in the silicon composite material can be 70%, 80%, 90%, 95%, 98%, etc. The liquid metal mass percentage is 1-20%, and as some specific examples, the liquid metal mass percentage can be 1%, 10%, 20%, etc. The carbon mass percentage is 1-10%, and as some specific examples, the carbon mass percentage can be 1%, 5%, 10%, etc. If the silicon mass percentage is too high, the specific capacity of the silicon material decreases, the strain during the expansion and contraction of silicon particles is greater, structural collapse is accelerated, and cycling performance deteriorates. If the silicon mass percentage is low, the specific capacity increases, but the electrode thickness corresponding to the same active layer density increases, polarization increases, rate performance decreases, and uneven ion concentration distribution is easily caused, resulting in excessive local stress or lithium plating problems.

[0067] According to specific embodiments of the present invention, the thickness of each layer is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, the particle size of the silicon composite material is 1-15 μm. As some specific examples, the particle size of the silicon composite material can be 1 μm, 5 μm, 10 μm, 15 μm, etc. The D of the liquid metal particles... 50 The diameter is 0.5-5 μm. As some specific examples, the D of liquid metal particles... 50 The thickness of the first carbon coating layer is 0.2-0.6 μm, and for some specific examples, the thickness of the first carbon coating layer is 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, etc. The thickness of the silicon layer is 1.5-5 μm, and for some specific examples, the thickness of the silicon layer is 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. The thickness of the second carbon coating layer is 0.08-0.2 μm, and for some specific examples, the thickness of the second carbon coating layer is 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, etc.

[0068] According to specific embodiments of the present invention, the type of liquid metal particles is not particularly limited, including but not limited to gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, rubidium, and cesium. Gallium-based liquid metals are preferred because they have high thermal conductivity, high electrical conductivity, low melting point, low viscosity, low toxicity, and a high theoretical specific capacity (769 mAh / g).

[0069] According to a specific embodiment of the present invention, the core structure further includes an oxide layer 5 located on the outer periphery of the liquid metal particles 1, and the first carbon coating layer 2 is located on the outer periphery of the oxide layer 5. The oxide layer is an oxide passivation film generated by the reaction of liquid metal and oxygen. The surface of this oxide layer is wrinkled and physically unstable, which promotes the refinement of liquid metal particles. When the particles are refined to a certain extent, the oxide layer has a moderate thickness and a stable structure, thus becoming a protective layer for the liquid metal.

[0070] Specifically, the thickness of the oxide layer is 0.5-3 nm. As some specific examples, the thickness of the oxide layer can be 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, etc.

[0071] A second aspect of the present invention provides a method for preparing the silicon composite material described in the first aspect, comprising:

[0072] (1) Dissolve liquid metal and thiol surfactant in a first solvent and pulverize to obtain liquid metal particles.

[0073] Thiol surfactants are excellent polymeric complexing agents that can form complexes with various heavy metal ions, promoting the formation of stable spherical nanoparticles from liquid metals, while also exhibiting good wettability to non-metallic materials. When liquid metals are mixed with thiol surfactants, an organic-based self-assembled molecular layer is formed on the surface of the liquid metal. This layer, through complexation, maintains the spherical particle shape of the liquid metal and prevents it from re-fusion in the mixture. The thickness of this molecular layer is 4-8 nm.

[0074] According to specific embodiments of the present invention, the types of thiol surfactants are not particularly limited, including but not limited to 3-mercaptopropyltriethoxysilane (KH580) and n-octadecyl mercaptan (C 18 H 38 S), dodecanthiol (C) 12 H 26 S), 3-mercapto-N-nonylpropionamide (1ATC9). The above-mentioned thiol surfactants contain thiol groups. Since the sulfur atoms in the thiol groups have a chemical adsorption effect on the liquid metal surface, they can inhibit the formation of excessive and irregular oxide layers on the liquid metal surface, thereby controlling the size of liquid metal particles.

[0075] According to specific embodiments of the present invention, the mass ratio of the liquid metal to the thiol surfactant is 100:(0.7-3). As some specific examples, the mass ratio of the liquid metal to the thiol surfactant is 100:0.7, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, etc.

[0076] According to specific embodiments of the present invention, the type of the first solvent is not particularly limited, including but not limited to n-hexane, cyclohexane, and anhydrous ethanol.

[0077] According to specific embodiments of the present invention, the volume ratio of the liquid metal to the first solvent is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the volume ratio of the liquid metal to the first solvent is 1:(120-180). As some specific examples, the volume ratio of the liquid metal to the first solvent is 1:120, 1:130, 1:140, 1:150, 1:160, 1:170, 1:180, etc.

[0078] According to specific embodiments of the present invention, the pulverization method is not particularly limited, and those skilled in the art can choose according to the actual situation. For example, it can be carried out by ultrasound, that is, under the action of ultrasound, the liquid metal is pulverized into spherical droplets, and then liquid metal particles can be obtained by centrifugation.

[0079] According to a specific embodiment of the present invention, when this step is performed in an oxygen-free environment, there is no oxide layer on the surface of the liquid metal particles; when this step is performed in a weak oxygen environment, an oxide layer is formed on the surface of the liquid metal particles, and the thickness of the oxide layer can be 0.5-3 nm.

[0080] (2) The liquid metal particles, amphiphilic macromolecules and polysaccharides are mixed to obtain micelle particles; the micelle particles are mixed with a crosslinking agent to obtain a coating.

[0081] The amphiphilic macromolecule comprises a hydrophilic portion and a lipophilic portion. The lipophilic portion connects to the liquid metal particles, while the hydrophilic portion connects to the polysaccharide. This allows the liquid metal nanoparticles and polysaccharide to form a stable micelle structure, preventing the liquid metal from being unevenly dispersed in the polysaccharide solution. The polysaccharide serves as a low-carbon carbon source, generating ample space after sintering. Furthermore, it is grafted onto the silicon surface through the reaction of the carboxyl and hydroxyl functional groups of the polysaccharide with subsequently added coupling agents. Thus, the micelle particles contain both an amphiphilic macromolecule layer and a polysaccharide layer. The thickness of the amphiphilic macromolecule layer can be 5-15 nm; for specific examples, the thickness of the amphiphilic macromolecule can be 5 nm, 10 nm, 15 nm, etc.; the thickness of the polysaccharide layer is 1-3 μm.

[0082] According to specific embodiments of the present invention, the type of the amphiphilic macromolecule is not particularly limited, including but not limited to sodium dodecyl sulfonate (SDS), sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SLS), sodium dodecyl phosphate, tetradecyltrimethylammonium bromide, hexadecyltrimethylsodium bromide, dihexadecyldimethylammonium bromide, dihexadecyldimethylammonium chloride, octadecyldimethylammonium bromide, and dioctadecyldimethylammonium chloride.

[0083] According to specific embodiments of the present invention, the type of polysaccharide is not particularly limited, and includes, but is not limited to, sucrose, lactose, maltose, fructose, and glucose.

[0084] According to specific embodiments of the present invention, the type of crosslinking agent is not particularly limited, including but not limited to polydopamine, maleimide-polyethylene glycol-dopamine (mal-PEG-Do), multi-arm polyethylene glycol, polymaleic acid, citric acid (CA), polycarboxylic acids, and polyols.

[0085] According to specific embodiments of the present invention, the mixing conditions of the micelle particles and the crosslinking agent are not particularly limited, and those skilled in the art can select them according to actual conditions. For example, the mixing temperature is 40-60°C, and as some specific examples, the mixing temperature is 40°C, 50°C, 60°C, etc.; the mixing time is 15-30 min, and as some specific examples, the mixing time is 15 min, 20 min, 25 min, 30 min, etc. This allows the polysaccharides on the surface of the micelle particles to form a stable three-dimensional coating structure.

[0086] (3) Dissolve the coupling agent and silicon particles in a second solvent to obtain silicon-coupling agent particles.

[0087] According to specific embodiments of the present invention, the coupling agent includes silane coupling agents, preferably alkyl silane coupling agents, vinyl silane coupling agents, epoxy silane coupling agents, acyloxy silane coupling agents, acylurea silane coupling agents, chloropropyl silane coupling agents, amino silane coupling agents, and sulfur-containing silane coupling agents. More preferably, vinyl silane coupling agents, epoxy silane coupling agents, and amino silane coupling agents can rapidly undergo a condensation reaction with carboxyl / hydroxyl groups.

[0088] According to a specific embodiment of the present invention, the second solvent comprises an alcohol-water solvent. The alcohol in the alcohol-water solvent includes, but is not limited to, methanol, ethanol, butanol, pentanol, ethylene glycol, and propylene glycol. The mass ratio of alcohol, water, and coupling agent in the alcohol-water solvent is (63-74):(8-19):(15-23). ​​As some specific examples, the mass ratio of alcohol, water, and coupling agent in the alcohol-water solvent is 63:8:15, 70:10:20, 72:8:20, 74:8:20, 74:19:23, etc., preferably 72:(8-10):(18-20).

[0089] According to specific embodiments of the present invention, the type of silicon particles is not particularly limited, and includes, but is not limited to, pure silicon (Si), silicon oxide (SiOx), silicon carbide (SiC), etc. The D of the silicon particles... 50 The diameter is 0.5-3μm. As some specific examples, silicon particle D 50The sizes are 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc.

[0090] According to specific embodiments of the present invention, the mass ratio of silicon particles to coupling agent is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the mass ratio of silicon particles to coupling agent is 100:(0.05-2). As some specific examples, the mass ratio of silicon particles to coupling agent is 100:0.05, 100:0.1, 100:0.2, 100:1, 100:1.5, 100:2, etc., preferably 100:(0.2-1).

[0091] (4) Mix the coating and the silicon-coupling agent particles to obtain the precursor.

[0092] The coupling agent and the carboxyl / hydroxyl groups on the polysaccharide form chemical bonds, and the silicon particles coat the surface of the liquid metal particles. This step can be carried out under ultrasonic pulverization, followed by centrifugation to obtain the precursor. The ultrasonic pulverization power can be 200-400W, such as 200W, 30W, 400W, etc., and the time can be 20-40min, such as 20min, 30min, 40min, etc.

[0093] (5) The precursor and organic carbon source are mixed and sintered to obtain the silicon composite material.

[0094] According to specific embodiments of the present invention, the type of organic carbon source is not particularly limited, and includes, but is not limited to, polyethylene glycol, polyethylene oxide, epoxy resin, phenolic resin, acrylic resin, furfural resin, asphalt, polyvinyl chloride, and polyacrylonitrile. Preferably, the particle size of the organic carbon source is 1-5 μm, thereby achieving a better coating effect when mixed with the precursor and avoiding the aggregation of the carbon source itself.

[0095] According to specific embodiments of the present invention, the mass ratio of the precursor to the organic carbon source is not particularly limited, and those skilled in the art can select it according to the actual situation. For example, the mass ratio of the precursor to the organic carbon source is 1:(0.05-0.2). As some specific examples, the mass ratio of the precursor to the organic carbon source is 1:0.05, 1:0.1, 1:0.2, etc.

[0096] According to a specific embodiment of the present invention, the sintering is carried out under a protective atmosphere, including but not limited to inert gases such as nitrogen, helium, neon, and argon.

[0097] According to specific embodiments of the present invention, the sintering temperature and time are not particularly limited, and those skilled in the art can select them according to actual conditions. For example, the sintering temperature is 900-1200℃. As some specific examples, the sintering temperature can be 900℃, 1000℃, 1100℃, 1200℃, etc.; the sintering time is 0.5-10h. As some specific examples, the sintering time can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0098] A third aspect of the present invention provides a negative electrode active material, the negative electrode active material comprising the silicon composite material described in the first aspect or the silicon composite material obtained according to the preparation method described in the second aspect.

[0099] A fourth aspect of the present invention provides a negative electrode sheet comprising the negative electrode active material described in the third aspect.

[0100] According to a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode active layer, the areal density of which is 2-5 mg / cm³. 2 As some specific examples, the areal density of the negative electrode active layer is 2 mg / cm³. 2 3mg / cm 2 4mg / cm 2 5mg / cm 2 wait.

[0101] According to a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0102] In some embodiments of the present invention, the negative electrode current collector may be made of copper foil, porous copper foil, carbon-coated copper foil, carbon mesh, carbon cloth, etc. The thickness of the current collector may be 6-20 μm.

[0103] In some embodiments of the present invention, the negative electrode active material may be the aforementioned negative electrode active material, and may also include negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may also include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, and lithium titanate.

[0104] In some embodiments of the present invention, the negative electrode active material layer may optionally include a binder. The binder may include at least one selected from polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polypropylene carbonate (PPC), polyethylene oxide (PEO), and ethylene oxide-propylene oxide copolymer (PEO-PO).

[0105] In some embodiments of the present invention, the negative electrode active material layer may optionally include a solid electrolyte. The solid electrolyte is one or more of oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, and polymer solid electrolytes.

[0106] In some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, binder, solid electrolyte and any other components, in a solvent (e.g., deionized water, toluene, dimethylformamide, etc.) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0107] According to a specific embodiment of the present invention, the mass ratio of the negative electrode active material, the binder and the solid electrolyte is (75-97):(3-5):(0-20), for example 95:5, 96:4, 97:3, 96:3:1, etc.

[0108] According to a specific embodiment of the present invention, the negative electrode active material, binder, and any other components are dispersed in a solvent and stirred to obtain a negative electrode slurry. The stirring method is not particularly limited, and includes, but is not limited to, ultrasonic stirring, impeller stirring, planetary stirring, degassing machine stirring, and ball milling stirring, and the stirring time can be 3-6 hours.

[0109] According to specific embodiments of the present invention, the drying temperature and time are not particularly limited, and those skilled in the art can select them according to the circumstances, for example, the drying temperature is 80-120°C and the time is 0.25-1h.

[0110] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0111] Example 1

[0112] (1) Liquid gallium and 3-mercaptopropyltriethoxysilane were added to a solvent at a mass ratio of 100:1.5. The mixture was then pulverized for 30 minutes in a water bath using an ultrasonic cell disruptor (2000W power). The working mode was 3 minutes of operation followed by a 2-minute rest period. The water bath temperature did not exceed 60℃. Under ultrasonic action, the liquid metal was pulverized into spherical droplets, forming a particulate emulsion. The emulsion was centrifuged in a centrifuge tube at 3000 r / min. After removing the supernatant, the mixture was washed 2-3 times with anhydrous ethanol to obtain liquid metal particles.

[0113] (2) Sodium dodecyl sulfate, a macromolecular amphiphilic liquid metal particles and polysaccharide sucrose were added to deionized water, and the components were ultrasonically dispersed to form micelles with uniform particle size. The mass ratio of liquid metal particles to polysaccharide was 1:2. Maleimide-polyethylene glycol-dopamine was then added and polymerized at 40°C for 15 min to form a stable three-dimensional coating structure of polysaccharide on the surface of micelles.

[0114] (3) Dissolve the coupling agent vinyltriethoxysilane in an alcohol-water solvent, wherein the mass ratio of coupling agent, alcohol and water is 20:72:8, then add pure silicon particles, stir evenly to generate silicon-coupling agent particles.

[0115] (4) The solutions of (2) and (3) are ultrasonically mixed, and the mixed solution is prepared into a suspension by ultrasonic pulverizer under high shear field. The suspension is centrifuged in a centrifuge tube at a speed of 3000 r / min, and after removing the supernatant, it is washed 2-3 times with anhydrous ethanol to obtain the liquid metal-polysaccharide-silicon particle precursor, wherein the mass ratio of liquid metal particles to silicon particles is 1:13;

[0116] (5) The precursor and organic carbon source polyethylene oxide (weight average molecular weight of 1×10⁻⁶) 5 A hollow core-shell silicon material is obtained by mixing Ga (g / mol) at a mass ratio of 1:0.08 and sintering at 900℃ for 30 min under a protective atmosphere. The D of Ga is... 50 The particle size is 1 μm, the oxide layer thickness is 2 nm, the first carbon coating layer thickness is 0.2 μm, the Si layer thickness is 2 μm, the second carbon coating layer thickness is 0.1 μm, and the total particle size is 7-8 μm.

[0117] A negative electrode slurry was prepared by mixing silicon material with PVDF and sulfide electrolyte LPSCl (Li6PS5Cl, a type of silver sulfide germanite). This slurry was then coated onto carbon-coated copper foil and baked in a 100℃ forced-air oven for 0.5 h to obtain the negative electrode material. The mass ratio of silicon material, PVDF, and sulfide electrolyte LPSCl was 92:4:4, and the single-sided areal density of the active layer was 3 mg / cm³. 2 .

[0118] Example 2

[0119] The liquid metal was replaced with GaInSn, and everything else remained the same as in Example 1.

[0120] Example 3

[0121] The difference between this embodiment and embodiment 1 is that: in step (1), the liquid metal gallium and 3-mercaptopropyltriethoxysilane are in a mass ratio of 100:0.7; in step (2), the mass ratio of liquid metal to polysaccharide is 2:1; and in step (4), the mass ratio of liquid metal to silicon particles is 1:2.

[0122] Furthermore, the anode preparation method, active layer density, and the Ga D in the obtained core-shell structured silicon material are consistent with those in Example 1. 50 The particle size is 3 μm, the oxide layer thickness is 3 nm, the first carbon coating layer thickness is 0.2 μm, the Si layer thickness is 1 μm, the second carbon coating layer thickness is 0.1 μm, and the total particle size is 7-8 μm.

[0123] Example 4

[0124] The difference between this embodiment and embodiment 1 is that the mass ratio of liquid metal particles to polysaccharide in step (2) is 1:12; and the mass ratio of liquid metal particles to silicon particles in step (4) is 1:40.

[0125] Furthermore, the anode preparation method, active layer density, and the Ga D in the obtained core-shell structured silicon material are consistent with those in Example 1. 50 The particle size is 1 μm, the oxide layer thickness is 3 nm, the first carbon coating layer thickness is 0.6 μm, the Si layer thickness is 3 μm, the second carbon coating layer thickness is 0.1 μm, and the total particle size is 13-14 μm.

[0126] Comparative Example 1

[0127] The negative electrode was prepared using conventional Si active particles, PVDF and carbon black conductive agent. The preparation method and active layer density of the negative electrode sheet were the same as in Example 1. The mass ratio of Si, PVDF and carbon black was 94:2:4.

[0128] Comparative Example 2

[0129] The negative electrode was prepared using conventional Si active particles, PVDF, and carbon black conductive agent. The preparation method of the negative electrode sheet was the same as in Example 1, with a mass ratio of Si, PVDF, and carbon black of 94:2:4. After drying the electrode sheet, liquid metal was sprayed onto the surface of the negative electrode by spraying, followed by hot pressing to promote uniform dispersion of the liquid metal inside the electrode sheet, thus obtaining the negative electrode. The mass ratio of Si to liquid metal was 85:15.

[0130] Comparative Example 3

[0131] When preparing the silicon composite material, no outermost organic carbon source is added, that is, there is no step (5) in Example 1, no design of a second carbon coating layer, and everything else is consistent with Example 1.

[0132] Comparative Example 4

[0133] The difference between this comparative example and Example 3 is that the mass ratio of liquid metal particles to polysaccharide in step (2) is 2:0, that is, no polysaccharide is added in this step.

[0134] The anode preparation method and active layer density remain consistent with those in Example 1. After sintering, the D of Ga... 50 The particle size is 3 μm, the oxide layer thickness is 3 nm, the Si layer thickness is 1 μm, the second carbon coating layer thickness is 0.1 μm, and the total particle size is 5-6 μm.

[0135] Comparative Example 5

[0136] Silicon materials were prepared by replacing liquid metal with organic polymer microspheres (polyethylene oxide, PEO) with a particle size of about 1 μm, and all other aspects remained the same as in Example 1.

[0137] Test case

[0138] (1) Half-cell fabrication: Lithium metal was used as the negative electrode, and the positive electrode used was the electrode sheet prepared in the examples and comparative examples. The electrolyte was a sulfide electrolyte LPSCl. The positive and negative electrodes and the electrolyte were assembled into a coin cell to test the specific capacity of the active materials. The specified test voltage was -0.6V to 1V, and the charge / discharge rate was 0.05C.

[0139] (2) Full cell fabrication: The positive electrode was NCM811, the negative electrode used was the negative electrode sheet prepared in the examples and comparative examples, and the electrolyte was the sulfide electrolyte LPSCl. The positive and negative electrodes and electrolyte were assembled into a pouch cell for routine electrochemical performance testing. The specified test voltage was 2.2V-4.2V, and the charge / discharge rate was 0.5C. The test results are shown in Table 1.

[0140] Table 1

[0141]

[0142]

[0143] From Table 1 and Figure 3-4 It is evident that the silicon composite material prepared by this invention can effectively suppress cracking caused by large deformation during charging and discharging, thereby improving battery cycle life. (Comparatively...) Figure 3-4It can be seen that in Comparative Example 1, obvious interface separation between silicon particles and solid electrolyte, as well as between silicon particles and binder, can be observed during the cycling process. In contrast, in Example 1, due to the absence of irreversible external expansion, the overall deformation of the electrode is small, the silicon particles maintain good contact with other components, and there is no obvious particle breakage.

[0144] The results of Examples 1-2 show that the type of liquid metal has a slight impact on the performance of the negative electrode, mainly because the intrinsic properties and theoretical specific capacity of the liquid metal are different.

[0145] The results from Examples 1-4 and Comparative Examples 1-5 show that the mass ratio of liquid metal to shell silicon particles has a significant impact on the performance of the negative electrode. This mass ratio can be calculated from the corresponding layer thickness in the prepared material, or from the mass ratio of liquid metal particles to silicon particles during the preparation process. An increase in the Si proportion leads to a decrease in specific capacity, and the strain during the expansion and contraction of Si particles is greater, accelerating structural collapse and worsening cycle life. While the liquid metal can provide a small amount of additional specific capacity, a decrease in the Si proportion increases the specific capacity. However, this increases the electrode thickness for the same active layer density, leading to increased polarization, decreased rate performance, and uneven ion concentration distribution, resulting in excessive local stress or lithium plating. This phenomenon also easily leads to severe battery cycle degradation.

[0146] The results of Comparative Examples 1, 2, and 5 show that liquid metal can effectively improve the ionic-electron dual conductivity level of the negative electrode, reduce internal polarization, suppress dendrite growth, and improve cycle performance.

[0147] As can be seen from the results of Example 1 and Comparative Example 3, the second carbon coating layer can isolate the direct contact between the negative electrode particles and the electrolyte, reduce side reactions, and improve the interfacial conductivity.

[0148] In Comparative Example 4, because no polysaccharide was added during the material preparation process, the resulting silicon composite material lacked a first carbon coating layer and a hollow structure. The results from Example 1 and Comparative Example 4 show that a hollow structure can effectively alleviate expansion strain.

[0149] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0150] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicon composite material, characterized in that, Includes core structure and shell structure; The core structure includes liquid metal particles and a first carbon coating layer located on the outer periphery of the liquid metal particles; The shell structure includes a silicon layer located on the periphery of the first carbon coating layer and a second carbon coating layer located on the periphery of the silicon layer.

2. The silicon composite material according to claim 1, characterized in that, The silicon composite material contains 70-98% silicon by mass, 1-20% liquid metal by mass, and 1-10% carbon by mass.

3. The silicon composite material according to claim 1, characterized in that, The particle size of the silicon composite material is 1-15 μm; And / or, the D of the liquid metal particles 50 It is 0.5-5μm; And / or, the thickness of the first carbon coating layer is 0.2-0.6 μm; And / or, the thickness of the silicon layer is 1.5-5 μm; And / or, the thickness of the second carbon coating layer is 0.08-0.2 μm.

4. The silicon composite material according to claim 1, characterized in that, The liquid metal particles include at least one of gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, rubidium, and cesium.

5. A silicon composite material according to claim 1, characterized in that, The core structure further includes an oxide layer located on the periphery of the liquid metal particles, and the first carbon coating layer is located on the periphery of the oxide layer; And / or, the thickness of the oxide layer is 0.5-3 nm.

6. A method for preparing a silicon composite material according to any one of claims 1-5, characterized in that, include: Liquid metal and thiol surfactants are dissolved in a first solvent and then pulverized to obtain liquid metal particles; The liquid metal particles, amphiphilic macromolecules, and polysaccharides are mixed to obtain micelle particles; the micelle particles are then mixed with a crosslinking agent to obtain a coating. The coupling agent and silicon particles are dissolved in a second solvent to obtain silicon-coupling agent particles; The coating and the silicon-coupling agent particles are mixed to obtain the precursor; The precursor and organic carbon source are mixed and sintered to obtain the silicon composite material.

7. The preparation method according to claim 6, characterized in that, The thiol surfactants include at least one of 3-mercaptopropyltriethoxysilane, n-octadecyl mercaptan, dodecathyl mercaptan, and 3-mercapto-N-nonylpropionamide; And / or, the mass ratio of the liquid metal to the thiol surfactant is 100:(0.7-3); And / or, the first solvent includes one of n-hexane, cyclohexane, and anhydrous ethanol.

8. The preparation method according to claim 6, characterized in that, The amphiphilic macromolecules include at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium dodecyl phosphate, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dihexadecyldimethylammonium bromide, dihexadecyldimethylammonium chloride, octadecyldimethylammonium bromide, and dioctadecyldimethylammonium chloride. And / or, the polysaccharide includes at least one of sucrose, lactose, maltose, fructose, and glucose; And / or, the crosslinking agent includes at least one of polydopamine, maleimide-polyethylene glycol-dopamine, multi-arm polyethylene glycol, polymaleic acid, citric acid, polycarboxylic acid, and polyol; And / or, the micelle particles and crosslinking agent are mixed at 40-60°C for 15-30 minutes.

9. The preparation method according to claim 6, characterized in that, The mass ratio of silicon particles to coupling agent is 100:(0.05-2), preferably 100:(0.2-1); And / or, the coupling agent includes a silane coupling agent; And / or, the coupling agent includes at least one of alkyl silane coupling agents, vinyl silane coupling agents, epoxy silane coupling agents, acyloxy silane coupling agents, acylurea silane coupling agents, chloropropyl silane coupling agents, amino silane coupling agents, and sulfur-containing silane coupling agents; And / or, the second solvent includes an alcohol-water solvent; And / or, the second solvent includes at least one of methanol aqueous solvent, ethanol aqueous solvent, butanol aqueous solvent, pentanol aqueous solvent, ethylene glycol aqueous solvent, and propylene glycol aqueous solvent; And / or, the mass ratio of alcohol, water and coupling agent in the alcohol-water solvent is (63-74):(8-19):(15-23), preferably 72:(8-10):(18-20); And / or, the silicon particles include at least one of pure silicon, silicon oxide, and silicon-carbon materials; And / or, the D of the silicon particles 50 It ranges from 0.5 to 3 μm.

10. The preparation method according to claim 6, characterized in that, The organic carbon source includes at least one of polyethylene glycol, polyethylene oxide, epoxy resin, phenolic resin, acrylic resin, furfural resin, asphalt, polyvinyl chloride, and polyacrylonitrile. And / or, the mass ratio of the precursor to the organic carbon source is 1:(0.05-0.2); And / or, the sintering is performed under a protective atmosphere; And / or, the sintering temperature is 900-1200℃; And / or, the sintering time is 0.5-10h.

11. A negative electrode active material, characterized in that, The negative electrode active material includes the silicon composite material according to any one of claims 1-5 or the silicon composite material obtained by the preparation method according to any one of claims 6-10.

12. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode active material as described in claim 11.

13. The negative electrode sheet according to claim 12, characterized in that, The negative electrode sheet includes a negative electrode active layer, the areal density of which is 2-5 mg / cm³. 2 .

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