Silicon-based anode materials, silicon-carbon composite anode materials, their preparation methods and applications

Abstract

This invention relates to silicon-based anode materials, silicon-carbon composite anode materials, their preparation methods, and applications, belonging to the technical field of lithium-ion batteries. The silicon-based anode material comprises micron-sized silicon particles and silicon oxide layers. The outer surface of the micron-sized silicon particles is coated with multiple layers of silicon oxide, with the oxygen content of the multiple silicon oxide layers gradually decreasing from the outermost to the innermost layers. Carbon material is uniformly distributed in the outermost silicon oxide layer of the multiple silicon oxide layers, or the outermost silicon oxide layer of the multiple silicon oxide layers is coated with a layer of carbon material. The silicon-based anode material of this invention has a multi-layered core-shell structure, with a high-capacity micron-sized silicon inner layer, a silicon-rich silicon oxide middle layer, and an oxygen-rich silicon oxide outer layer, effectively ensuring the high capacity and structural stability of the material. The silicon-based anode material of this invention exhibits high initial coulombic efficiency, high capacity, and excellent cycle performance in secondary lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a silicon-based anode material, a silicon-carbon composite anode material, their preparation methods, and applications. Background Technology

[0002] Silicon-based anode materials undergo significant volume expansion and contraction during charge and discharge, leading to material pulverization, structural collapse, and the rupture and regeneration of the solid-liquid interface layer. This severely impacts the battery's coulombic efficiency and cycle life during cycling. Furthermore, during the initial charge and discharge cycle, silicon-based anode materials consume some lithium to form the solid-liquid interface layer and participate in irreversible reactions, resulting in low initial coulombic efficiency and wasting silicon-based materials, thus limiting the further application of silicon-based anodes.

[0003] Currently, to address the aforementioned problems, active materials that combine various silicon-based materials with carbon materials are employed. These active materials are an effective method to improve the electrochemical performance of silicon-based materials. Two common approaches are: one is to use nanoscale or sub-nanometer silicon elemental composites with carbon to create nanoscale silicon-carbon anode materials; the other is to use silicon oxides (SiO₂) with smaller volume changes. x Silicon-oxygen-carbon anode materials can be synthesized by combining silicon with carbon materials. However, the preparation of nanoscale or sub-nanometer-scale elemental silicon is difficult, and composite materials with large specific surface areas and low tap densities are easily obtained, resulting in low initial coulombic efficiency and poor cycle stability; while SiO2... x The oxygen itself brings an irreversible phase, resulting in a large irreversible capacity loss. It is necessary to supplement the lithium source to improve the initial coulombic efficiency. At the same time, the capacity of silicon oxide is lower than that of elemental silicon, and the capacity advantage is even less obvious after being combined with carbon materials.

[0004] Chinese patent CN112751029A provides a silicon-oxygen composite anode material, wherein the composite material includes SiO₂. x Li2Si2O5 and non-Li2Si2O5 lithium-containing compounds, SiO x Located within a non-Li₂Si₂O₅ lithium-containing compound, Li₂Si₂O₅ is coated onto the surface of the non-Li₂Si₂O₅ lithium-containing compound. This invention achieves this by coating a pre-lithiated SiO₂ compound with dense, water-insoluble Li₂Si₂O₅ that does not negatively impact battery performance. x The outer surface effectively prevents water from contacting the internal non-Li2Si2O5 lithium-containing compounds, thus preventing the formation of alkalinity and affecting processing performance. The provided silicon-oxygen composite anode material has an initial reversible capacity of up to 1420 mAh / g and an initial coulombic efficiency of 90.5%. However, this invention uses pre-lithiated silicon oxide as the matrix, which limits the capacity utilization. Furthermore, in order to obtain better cycle stability, it is used in combination with graphite materials as a negative electrode active material, which further reduces the capacity advantage and cannot meet the demand for higher energy density batteries.

[0005] Chinese patent CN111653737A discloses a silicon oxide composite material with a gradient pre-lithiation structure. This composite material has a core-shell structure consisting of a lithium-containing silicon oxide layer, a silicon oxide layer, and a carbon coating layer, arranged sequentially from the inside out. However, this invention uses a high-temperature condition of 1500℃ to react a silicon source with a lithium source to generate silicon oxide. The resulting silicon oxide has a fixed oxygen content, a high degree of disproportionation, and poor cycle stability, resulting in a cycle capacity retention of only 85% after 50 cycles.

[0006] Therefore, no silicon-based anode material has yet been proposed that meets the requirements of high capacity, high initial coulombic efficiency, and high cycle stability. Summary of the Invention

[0007] In order to solve one or more of the above-mentioned technical problems, the present invention provides a silicon-based anode material, a silicon-carbon composite anode material, its preparation method and application.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a silicon-based anode material, comprising micron-sized silicon particles and silicon oxide layers, wherein the outer surface of the micron-sized silicon particles is coated with multiple layers of the silicon oxide layers, and the oxygen content of the multiple layers of the silicon oxide layers gradually decreases from the outer layer to the inner layer;

[0009] Carbon material is uniformly distributed in the outermost silicon oxide layer of a multilayer silicon oxide layer, or the outer surface of the outermost silicon oxide layer of a multilayer silicon oxide layer is covered with a carbon material layer.

[0010] The beneficial effects of this invention are as follows: The silicon-based anode material of this invention has a multi-layered core-shell structure with a gradient distribution of active materials. The inner layer is high-capacity micron-sized silicon, the middle layer is silicon-rich silicon oxide, and the outer layer is oxygen-rich silicon oxide, effectively ensuring the high capacity and structural stability of the material. The silicon oxide coating of this invention forms the active material in situ, providing excellent electron transport performance. The silicon-based anode material of this invention exhibits high initial coulombic efficiency, high capacity, and excellent cycle performance in secondary lithium-ion batteries.

[0011] This invention generates some carbon materials during the preparation of silicon-based anode materials. These carbon materials can be uniformly distributed in the outermost silicon oxide layer or coated on the surface of the outermost silicon oxide layer.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, the multilayer silicon oxide layer includes a first silicon oxide layer and a second silicon oxide layer arranged from the inside out, wherein the atomic ratio of oxygen to silicon in the first silicon oxide layer is (0.1 to 1.0):1, and the atomic ratio of oxygen to silicon in the second silicon oxide layer is (1.0 to 1.5):1.

[0014] The advantages of adopting the above-mentioned further scheme are: using two silicon oxide layers facilitates fabrication and molding, and the structure is stable and reliable.

[0015] Furthermore, the silicon oxide layer also contains a lithium compound, and the lithium content in the lithium compound is distributed in a gradient from the outer layer to the inner layer in the multilayer silicon oxide layer.

[0016] The beneficial effects of adopting the above-mentioned further solution are: the lithium content gradient distribution in the multilayer silicon oxide layer of the silicon-based anode material provided by the present invention forms a gradient lithium replenishment, providing an additional lithium source during the initial cycling process of the anode, promoting the transport of lithium ions from the outside to the inside, and greatly improving the first coulombic efficiency.

[0017] Furthermore, the lithium content in the lithium compound gradually decreases from the outermost to the innermost layer in the multilayer silicon oxide layers.

[0018] Furthermore, the lithium compound includes any one or a combination of several of Li2Si2O5, Li2SiO3 and Li4SiO4; the lithium content in the multilayer silicon oxide accounts for 0.05% to 5% of the mass percentage of the silicon-based anode material.

[0019] Furthermore, the micron-sized silicon particles are elemental silicon, and the volume average diameter M of the micron-sized silicon particles is... V The thickness is 1–5 μm, and the thickness of the multilayer silicon oxide layer gradually decreases from the outer layer to the inner layer.

[0020] For example, the thickness of the first silicon oxide layer is 1–100 nm, preferably 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm, 62 nm, etc. The thickness of the second silicon oxide layer is 0.1–1 μm, preferably 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm.

[0021] A silicon-carbon composite anode material includes the aforementioned silicon-based anode material and further includes a carbon coating layer, wherein the carbon coating layer coats the surface of the outermost silicon oxide layer in a multilayer silicon oxide layer, or the carbon coating layer coats the surface of the carbon material layer.

[0022] The beneficial effect of adopting the above-mentioned further scheme is that the carbon coating layer is located on the outermost layer of the silicon-based anode material and is tightly connected with the silicon-based anode material to form the carbon coating layer.

[0023] Furthermore, the carbon source of the carbon coating layer includes any one or a combination of several of the following: natural graphite, pitch carbon, petroleum coke, needle coke, epoxy resin, polyacrylonitrile, polyacrylamide, polyimide, graphene oxide, and graphene; the thickness of the carbon coating layer is 5–100 nm, preferably 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm; the carbon coating layer accounts for 20%–45% of the mass percentage of the silicon-based anode material, preferably 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, and 45%.

[0024] A method for preparing the above-mentioned silicon-based anode material includes the following steps:

[0025] Pretreatment: Disperse micron-sized silicon particles in hydrofluoric acid solution to remove the oxide layer on the surface of the micron-sized silicon particles;

[0026] Oxidation of micron-sized silicon particles: In an inert atmosphere, pretreated micron-sized silicon particles are heated and oxidizing gas is introduced to generate a first silicon oxide layer on the outer layer of the micron-sized silicon particles, thereby obtaining the first product;

[0027] Second silicon oxide layer coating: The first product is mixed with a silane solution, dried and pyrolyzed to obtain a second product coated with a second silicon oxide layer;

[0028] Pre-lithiation: The second product is mixed with a lithiation reagent and heated in an inert atmosphere to obtain a silicon-based anode material.

[0029] The beneficial effects of this invention are: the preparation method of this invention can obtain micron-sized particles with higher tap density, which is suitable for existing manufacturing processes of secondary lithium-ion batteries. The different silicon oxide coating methods and pre-lithiation methods used in this invention can easily obtain a structure in which the thickness of the silicon oxide coating layer gradually decreases from the outer layer to the inner layer, the oxygen content gradually decreases from the outer layer to the inner layer, and the lithium content gradually decreases from the outer layer to the inner layer, thereby achieving optimal capacity, initial coulombic efficiency, and cycle performance.

[0030] A method for preparing a silicon-carbon composite anode material, based on the above-mentioned method for preparing silicon-based anode materials, further includes the following steps:

[0031] Carbon composite: The silicon-based anode material is directly mixed with a first carbon source, or the silicon-based anode material is mixed with a second carbon source and then subjected to heat treatment to obtain a silicon-carbon composite anode material coated with a carbon coating layer.

[0032] The micron-sized silicon particles used in the preparation method of this invention are elemental silicon powder, and the volume average diameter M of the powder particles is... V The size ranges from 1 to 5 μm, with 1 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, and 5 μm being preferred.

[0033] The pretreatment specifically involves dispersing micron-sized silicon particles in a 5% hydrofluoric acid solution, stirring vigorously for at least 30 minutes, filtering, washing with water and ethanol, and then transferring the solution to a vacuum at 80°C for drying.

[0034] The oxidation of the micron-sized silicon particles specifically involves transferring the pretreated micron-sized silicon particles into a high-purity inert atmosphere (e.g., high-purity argon, purity ≥ 99.999%), heating to 100–200°C, maintaining the temperature, and simultaneously introducing an oxidizing gas with a purity ≥ 99.999%. The ratio of the oxidizing gas rate to the inert gas rate is 1:10. After introducing the oxidizing gas for 0.5–1 hour, the introduction is stopped and heating is ceased, allowing the mixture to cool naturally to obtain the first product. The inert atmosphere can be argon, nitrogen, helium, etc., and the oxidizing gas can be oxygen or ozone.

[0035] The second silicon oxide layer coating is specifically performed by dispersing the first product in an organic solution and adding an organosilicon compound while stirring. After complete addition, stirring is continued for 0.5 to 1 hour. Then, the mixture is transferred to an inert atmosphere and heated to 100°C for 1 hour. The temperature is then further increased to 450 to 800°C for 0.5 to 3 hours of heat treatment to obtain the second product.

[0036] The organic solution mentioned in this step is a mixed solution of ammonia and alcohols, with the ammonia concentration being 20% ​​to 40%. The alcohols include one or more of ethanol, n-propanol, and isopropanol. The organosilicon compounds include one or more of tetraethoxysilane, triethoxysilane, diethoxymethylsilane, dimethyldichlorosilane, and dimethylsiloxane.

[0037] During the mixing process of the organosilicon compound described in this step, the mixture is simultaneously heated and stirred at a constant temperature of 40–75°C. This constant temperature heating and stirring accelerates the hydrolysis reaction of the organosilicon compound and the organic solution, promotes the nucleation of silicon oxide particles, and allows silicon oxide to precipitate uniformly on the surface of micron-sized silicon particles. Furthermore, after pyrolysis in an inert atmosphere, a silicon oxide layer with a higher oxygen content is generated, which is beneficial for forming a negative electrode active material with a gradient distribution of oxygen content inside and outside the silicon oxide.

[0038] The pre-lithiation specifically involves mixing the second product with a lithiation reagent at a mixing temperature of 10–80°C for 10–120 min, followed by heating under an inert atmosphere at a heating temperature of 100–300°C, and then further heating to 800–1100°C for stabilization.

[0039] In this step, the lithium reagent is obtained by dissolving a lithium source and a methyl-substituted polycyclic aromatic hydrocarbon in an organic solvent; the lithium source includes metallic lithium or lithium salts, and the lithium salts include one or more of lithium fluoride, lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, and lithium acetate; the methyl-substituted polycyclic aromatic hydrocarbons include one or more of monomethylbiphenyl, dimethylbiphenyl, tetramethylbiphenyl, and their derivatives; the organic solvent includes one or more of hexane, cyclohexane, tetrahydrofuran, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and dimethyl glycol ether.

[0040] Furthermore, the lithium metal includes lithium foil, lithium sheets, lithium wire, lithium powder, etc. Lithium metal can form an organolithium solution with methyl-substituted polycyclic aromatic hydrocarbons, exhibiting reactivity far exceeding that of lithium salts as a lithiation reagent. When mixed with negative electrode active material particles, it can diffuse into the interior of the particles, forming a gradient distribution of lithium concentration from the outside to the inside.

[0041] The carbon coating layer is prepared by directly mixing a silicon-based anode material with a first carbon source, or by mixing a third product with a second carbon source and then heating the mixture at a temperature of 600–900°C. The first carbon source is selected from one or more of natural graphite, pitch carbon, petroleum coke, and needle coke, and is directly mixed without further high-temperature heat treatment. The second carbon source can be selected from one or more of epoxy resin, polyacrylonitrile, polyacrylamide, polyimide, and graphene oxide.

[0042] Furthermore, the carbon coating layer is selected from in-situ generated graphene. The silicon-based anode material is mixed with graphene oxide slurry and a reducing agent, followed by heat treatment. The reducing agent includes one or more of L-ascorbic acid, reducing sugars, proteins, peptides, and amino acids. After heat treatment, a silicon-carbon composite material with a graphene coating is obtained. The silicon-based anode material and graphene are tightly bonded, compensating for the low intrinsic conductivity of silicon-based materials. Graphene encapsulation of the silicon-based anode material effectively improves the material's resistance to expansion, significantly contributing to improved cycle stability.

[0043] A battery made from the above-mentioned silicon-based anode material or the above-mentioned silicon-carbon composite anode material.

[0044] The beneficial effects of this invention are: by applying the above-mentioned silicon-based anode material or silicon-carbon composite anode material to a battery, the battery has the characteristics of high initial coulombic efficiency, high capacity and excellent cycle performance. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of the silicon-based anode material of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of the silicon-carbon composite anode material of the present invention.

[0047] The attached diagram lists the components represented by each number as follows:

[0048] Figure 1 and Figure 2 The reference numerals are 1. Micron-sized silicon particles; 2. First silicon oxide layer; 3. Second silicon oxide layer; 4. Carbon coating layer.

[0049] Figure 3 The images shown are SEM images of the silicon-based anode material prepared in Example 1 of the present invention, where (a) is a particle of the anode active material and (b) is a magnified image of a single particle. Detailed Implementation

[0050] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0051] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0052] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0053] Product Example 1

[0054] One example of this product embodiment is a silicon-based anode material, such as... Figure 1 As shown, it includes micron-sized silicon particles 1 and a silicon oxide layer. The outer surface of the micron-sized silicon particles 1 is covered with a first silicon oxide layer 2 and a second silicon oxide layer 3 from the inside to the outside. The oxygen content of the second silicon oxide layer 3 and the first silicon oxide layer 2 gradually decreases from the outer layer to the inner layer. Carbon material is uniformly distributed in the second silicon oxide layer 3, or the outer surface of the second silicon oxide layer 3 is covered with a carbon material layer.

[0055] The micron-sized silicon particles in this product embodiment are elemental silicon, and the volume average diameter M of the micron-sized silicon particles is... V The thickness is 1 μm. In this embodiment, the atomic ratio of oxygen to silicon in the first silicon oxide layer is 0.1:1, and the atomic ratio of oxygen to silicon in the second silicon oxide layer is 1:1. The thickness of the first silicon oxide layer is 1 nm, and the thickness of the second silicon oxide layer is 0.1 μm.

[0056] In this product embodiment, both the first and second silicon oxide layers contain lithium compounds. The lithium compound content accounts for 0.05% of the mass percentage of the silicon-based anode material, and the lithium compound content in the first silicon oxide layer is less than that in the second silicon oxide layer. The lithium compound includes Li₂Si₂O₅.

[0057] One example of this product is a silicon-carbon composite material, such as... Figure 2 As shown, a carbon coating layer 4 is further coated on the aforementioned silicon-based anode material. The carbon coating layer 4 is coated on the surface of the second silicon oxide layer 3, or the carbon coating layer 4 is coated on the surface of the carbon material layer. The thickness of the carbon coating layer is 5 nm, and the carbon coating layer accounts for 20% of the mass percentage of the silicon-based anode material.

[0058] Product Examples 2-5

[0059] Product Examples 2-5 respectively provide a silicon-based anode material and a silicon-carbon composite material, and the parameters that differ from those in Product Example 1 are shown in the following table:

[0060] Table 1-1 Comparison of Parameters for Product Examples 1-5

[0061]

[0062] Product Examples 6-8 provide a silicon-based anode material and a silicon-carbon composite material, respectively. The parameters that differ from those in Product Example 4 are shown in the table below, while the rest are the same as those in Product Example 4.

[0063] Table 1-2 Comparison of Parameters for Product Examples 6-8

[0064]

[0065] Method Example 1

[0066] Pretreatment: Micron-sized silicon powder with an average particle size of 2 μm was dispersed in a 5% hydrofluoric acid solution and stirred at 1000 rpm for 40 min. The mixture was then filtered and washed with water and ethanol, and then transferred to a vacuum oven and dried under vacuum at 80 °C to obtain micron-sized silicon particles with the oxide layer removed.

[0067] Oxidation of micron-sized silicon particles: Take 2g of the micron-sized silicon particles obtained in the previous step and transfer them to a tube furnace under a high-purity argon atmosphere. Heat the furnace to 100℃ at a heating rate of 2℃ / min, maintaining an argon flow rate of 200 sccm. Simultaneously, open the oxygen valve and introduce oxygen at a flow rate of 20 sccm for 1 hour. Close the oxygen valve and stop heating. After natural cooling, close the argon valve and remove the first product with the first silicon oxide layer. The atomic ratio of oxygen to silicon in the first silicon oxide layer is 0.8.

[0068] Second silicon oxide layer coating: All the first product obtained in the previous step was dispersed in a mixed solution of 25% ammonia and anhydrous ethanol. The solution was heated to 40°C in a water bath and stirred at 150 rpm. 4 g of tetraethoxysilane was added while stirring. After addition, stirring continued for 1 hour. After centrifugation and washing, the product was transferred to an inert atmosphere furnace and heated to 100°C for 1 hour. The temperature was then increased to 600°C and held for 2 hours. The product was then naturally cooled to room temperature to obtain the second product coated with a second silicon oxide layer. The atomic ratio of oxygen to silicon in the second silicon oxide layer was 1.4.

[0069] Pre-lithiation: In a constant temperature and humidity chamber with a dew point < -50℃, all the obtained second product was placed in an inert atmosphere glove box and mixed with a solution of ethylene glycol dimethyl ether containing dissolved lithium metal and 4,4'-dimethylbiphenyl. The concentration of 4,4'-dimethylbiphenyl was 0.2 mol / L, and the molar ratio of lithium metal to 4,4'-dimethylbiphenyl was 4:1. The mixing temperature was 60℃, and the mixture was stirred at this temperature for 1 h. After cooling to room temperature, stirring was continued for 30 min. The mixture was then transferred to an inert atmosphere furnace for heating treatment. The temperature was increased to 100℃ at a rate of 0.5℃ / min and held for 1 h. The temperature was then increased to 300℃ and held for 1 h. Finally, the temperature was increased to 1000℃ at a rate of 2℃ / min and held for 2 h. After natural cooling, the mixture was removed to obtain the third product. The lithium content of the third product accounted for 1% of the mass percentage of the silicon-based anode material.

[0070] Preparation of the carbon coating layer: All the third product obtained in the previous step was added to 50 ml of graphene oxide slurry dispersed in N-methylpyrrolidone, with a graphene oxide concentration of 0.02 g / ml. The mixture was ultrasonically dispersed for 1 h, then 5 g of L-ascorbic acid reducing agent was added, and the mixture was stirred for 30 min and allowed to stand for 12 h. The resulting solid product was freeze-dried and then transferred to an inert atmosphere furnace. The temperature was increased to 800 °C at 2 °C / min and held for 2 h. After natural cooling, the silicon-based anode material was obtained. The total carbon content of the silicon-based anode material was approximately 30%.

[0071] The silicon-based anode material and silicon-carbon composite material obtained by method embodiment 1 are as described in product embodiment 4 above.

[0072] Method Example 2

[0073] The preparation process and method of silicon-based anode material in this embodiment are basically the same as those in Embodiment 1. The difference is that in the oxidation step of micron-sized silicon particles, the micron-sized silicon particles that have undergone the pretreatment step are heated to 200°C in a high-purity inert atmosphere. The flow rate and time of oxygen introduction are the same as those in Embodiment 1. The remaining preparation steps and battery testing methods are the same as those in Embodiment 1.

[0074] Method Example 3

[0075] The preparation process of the silicon-based anode material in this embodiment is basically the same as that in embodiment 1. The difference is that the micron-sized silicon particles do not undergo pretreatment and oxidation steps, but directly undergo the second silicon oxide layer coating step. The remaining preparation steps and battery testing methods are the same as those in embodiment 1.

[0076] Table 2. Parameter Comparison Table for Method Examples 1-3

[0077]

[0078] Method Example 4

[0079] The difference between Method Example 4 and Method Example 1 is that the average particle size of the micron-sized silicon particles used is different, while the rest of the preparation steps and battery testing methods are the same as those in Method Example 1.

[0080] Method Example 5

[0081] The difference between Method Example 5 and Method Example 1 is that the ammonia concentration is different in the second silicon oxide layer coating step, while the other preparation steps and battery testing methods are the same as in Method Example 1.

[0082] Method Example 6

[0083] The difference between Method Example 6 and Method Example 1 is that the reaction temperature of the organosilicon source with ammonia is different in the second silicon oxide layer coating step, while the other preparation steps and battery testing methods are the same as in Method Example 1.

[0084] Table 3. Parameter Comparison Table for Method Examples 4-6

[0085]

[0086] Method Example 7

[0087] The difference between Method Example 7 and Method Example 1 lies in the pre-lithiation step. The same pre-lithiation method is used, but the solution pre-lithiation only undergoes heat treatment at both ends of 100 and 300°C, without undergoing high-temperature treatment at 1000°C. The remaining preparation steps and battery testing methods are the same as in Method Example 1.

[0088] Method Example 8

[0089] The difference between Method Example 8 and Method Example 1 is that the final high-temperature treatment temperature of the pre-lithiation step is different, while the other preparation steps and battery testing methods are the same as those in Method Example 1.

[0090] Method Example 9

[0091] The difference between Method Example 9 and Method Example 1 lies in the carbon coating preparation steps. In Method Example 9, pitch is used as the carbon source. The third product obtained in the previous step is added to the pitch solution, spray-dried, and then pyrolyzed and carbonized in an inert atmosphere at 800°C to obtain a pitch-carbon composite silicon-based anode material. The remaining preparation steps and battery testing methods are the same as in Method Example 1.

[0092] Table 4. Parameter Comparison Table for Method Examples 7-9

[0093]

[0094] Method Example 10

[0095] Method Example 10 uses silicon oxide particles with an average particle size of 5 μm and an atomic ratio of oxygen to silicon of 1:1. The second silicon oxide layer coating step in Method Example 1 is performed directly. The subsequent preparation steps and battery testing methods are the same as in Method Example 1.

[0096] Method Example 11

[0097] Method Example 11 is basically the same as Method Example 1, except that the final carbon coating layer preparation composite step is not performed. The resulting third product is directly used as the negative electrode active material, and electrochemical testing is performed using the same battery testing method as Method Example 1.

[0098] Method Example 12

[0099] In Method Example 12, the product obtained from the pretreatment step of micron-sized silicon particles in Method Example 1 is directly used for graphene composite without the preparation of multilayer silicon oxide layers and pre-lithiation steps. The composite material is used as a silicon-based anode material for electrochemical characterization, and the battery testing method is the same as that in Method Example 1.

[0100] Table 5. Parameter Comparison Table for Method Examples 10 to 12

[0101] Micron-sized silicon pretreatment none Same method as Example 1 Same method as Example 1 Micron silicon oxide none Same method as Example 1 none Silicon oxide coating Same method as Example 1 Same method as Example 1 none Pre-lithiation Same method as Example 1 Same method as Example 1 none Graphite composite Same method as Example 1 none Same method as Example 1

[0102] The silicon-carbon composite anode materials obtained from the above product examples and method examples were subjected to coin cell half-cell tests to evaluate their electrochemical performance. The test methods are as follows:

[0103] The prepared silicon-carbon composite anode material was mixed with carbon black conductive agent, carbon nanotube conductive agent, and binder in a mass ratio of 90:3:1:6 to form a homogenous slurry. The slurry was then coated onto a 10μm copper foil using a doctor blade coater. The foil was dried at 80℃ for 1 hour under forced air and then at 120℃ under vacuum for 12 hours, resulting in an electrode areal density of 8.5±0.1 mg / cm³. 2 The electrode sheets are rolled to a compaction density of 1.05 ± 0.05 g / m³. 3 The electrode sheets were cut into 12mm diameter discs and assembled with the counter electrode lithium metal sheet, Celgard 2400 separator, and electrolyte (1M LiPF6, EC / DMC 1:1v / v) to form a CR2025 coin cell. The assembled coin cell was tested for charge and discharge using a 5V 50mA battery testing system.

[0104] The material capacity and initial coulombic efficiency were tested as follows: at 25±1℃, the material was discharged at a constant current of 0.05C to 0.005V, left to stand for 5 minutes, and then charged at a constant current of 0.1C to 1.5V. The charge capacity was taken as the material capacity, and the ratio of the charge capacity to the discharge capacity was used to obtain the initial coulombic efficiency.

[0105] The material's cycle performance was tested as follows: The battery was placed in a 25°C constant temperature chamber. For the first discharge, it was discharged at a constant current rate of 0.05C to 0.005V, left to stand for 5 minutes, and then charged at a constant current rate of 0.1C to 1.5V. For the second discharge, it was discharged at 0.33C to 0.005V and charged at 0.33C to 1.5V. Then, it was cycled for 50 cycles at the same rate and upper and lower limit voltages. The cycle capacity retention rate was obtained by comparing the charging capacity after 50 cycles with the second charging capacity.

[0106] The electrochemical performance results of the silicon-based anode materials prepared in Examples 1-8 are shown in Table 6.

[0107] Table 6 Electrochemical performance test results

[0108] Product Example 1 2010 90.5 94.5 Product Example 2 1721 93.4 95.8 Product Example 3 1690 94.9 96.5 Product Example 4 1943 92.2 95.0 Product Example 5 1628 96.9 97.0 Product Example 6 1960 93.2 94.4 Product Example 7 2005 93.2 92.5 Product Example 8 1939 90.1 92.8

[0109] As shown in Table 6, all product examples 1-5 exhibit high reversible capacity, high initial coulombic efficiency, and high cycle stability, making them relatively ideal silicon-based anode materials. The significant capacity differences among product examples 1-5 are mainly due to the proportion of carbon coating (the carbon coating thickness in product example 5 is 100 nm, accounting for 45%). Combining a suitable amount of graphite material to form a carbon coating can improve the cycle performance of the material while ensuring capacity; however, an excessive proportion of carbon coating will sacrifice the high capacity advantage of silicon-based materials. The different coating thicknesses in product examples 1-5 affect the particle size of the final product. By controlling the silicon oxide layer coating thickness within the design range, the product particle size will mainly be related to the initial micron-sized silicon particles, while the particle size has no significant impact on electrochemical performance.

[0110] As can be seen from the electrochemical performance of Product Examples 6-7 in Table 6, the smaller the difference in the silicon-oxygen atomic ratio between the first silicon oxide layer and the second silicon oxide layer, the higher the material capacity, but the cycle performance is somewhat reduced. Among them, the lower the silicon-oxygen atomic ratio of the first silicon oxide layer, the more obvious the capacity reduction trend. The lithium compound content of Product Example 8 is much lower than that of Product Example 4. Too low a lithium compound content will affect the initial coulombic efficiency, thus affecting both capacity and cycle stability.

[0111] The electrochemical performance results of the silicon-based anode materials prepared in Examples 1-12 are shown in Table 7.

[0112] Table 7 Electrochemical performance test results

[0113] Method Example 1 1943 92.2 95.0 Method Example 2 1699 90.6 90.7 Method Example 3 1157 88.3 92.2 Method Example 4 1911 91.6 90.5 Method Example 5 1760 90.7 98.1 Method Example 6 1798 91.2 88.9 Method Example 7 1385 85.6 87.3 Method Example 8 1762 90.1 89.4 Method Example 9 1970 92.9 88.5 Method Example 10 1282 89.4 91.4 Method Example 11 2455 92.8 85.6 Method Example 12 2320 90.2 77.5

[0114] As shown in Table 7, Method Example 1 exhibits higher specific capacity and cycling stability than Method Examples 2 and 3. The micron-sized silicon oxide heat treatment temperature in Method Example 2 is higher than that in Method Example 1, resulting in a higher oxygen content in the first silicon oxide layer. This hinders the formation of a gradient distribution of increasing oxygen content from the inside out, impedes lithium-ion transport, leads to poor capacity utilization, and causes uneven stress distribution within the material, resulting in even worse cycling performance.

[0115] In Method Example 3, without a pretreatment step, a layer of nanoscale silicon dioxide is formed on the surface of micron-sized silicon, which hinders the conduction of lithium ions and electrons to crystalline silicon. The high capacity of silicon cannot be utilized, and the oxygen content of silicon oxide decreases from the inside to the outside, resulting in poorer cycle performance than in Method Example 1.

[0116] The average particle size of the micron-sized silicon used in Method Example 4 is larger than that in other examples, and the average particle size of the final prepared composite active material will also increase, which is not conducive to improving the compaction density of the material. The ion and electron transport paths in the electrode increase, and the performance of the material is affected compared to Method Example 1.

[0117] Compared to Method 1, Method Examples 5 and 6 show significant differences in capacity and cycling stability, indicating that the silicon oxide coating conditions have a substantial impact on the material. In Method Example 5, increasing the ammonia concentration increases the pH of the reaction system, facilitating the hydrolysis of the organosilicon source and resulting in larger silicon oxide ion particles. This leads to a thicker second layer of silicon oxide coating on the micron-sized silicon, effectively improving the cycling stability of the composite material. In Method Example 6, the reaction is conducted at room temperature, resulting in slower nucleation of silicon oxide particles. Under the same reaction time, the formed silicon oxide particles are smaller and have lower oxygen content, leading to a smaller gradient distribution of oxygen content in the composite material and consequently, poorer cycling performance.

[0118] Compared with Method Example 1, Method Example 7 has lower capacity and initial efficiency. This is because Method Example 7 does not perform high-temperature treatment after pre-lithiation with organic lithium solution. The pre-lithiated material is unstable and easily damaged by subsequent steps, and cannot effectively form lithium silicon oxide active compounds.

[0119] Compared with Method Example 7, Method Example 8, although the pre-lithiation step was subjected to high-temperature treatment, did not improve the cycle performance compared with Method Example 1. This is because the high-temperature treatment temperature is too low to fully carbonize the organic matter remaining in the silicon oxide coating step to form a carbon layer to stabilize the pre-lithiated silicon oxide, and the pre-lithiation gradient effect is still affected.

[0120] Compared with Method Example 1, Method Example 9 uses the same silicon-based active material, but its cycling performance is not as good as the other examples. This shows that the graphite composite step greatly helps to improve the overall performance of the material, especially the cycling stability. The graphene formed in situ on the material surface has a better effect on reducing volume expansion of silicon-based materials than pitch coating, thereby improving the cycling stability.

[0121] Method Example 10 uses micron-sized silicon oxide particles instead of micron-sized silicon. Compared with Method Example 1, it loses the high capacity advantage because silicon oxide itself has low initial efficiency and low reversible capacity.

[0122] As can be seen from Method Example 11, the silicon-based composite active material prepared by this method has high capacity and initial coulombic efficiency, but its cycling performance is not outstanding. It is necessary to further improve the stability of the material structure by combining it with graphite. At the same time, it can reduce the contact between the silicon-based material and the electrolyte, avoid the occurrence of side reactions during cycling, and improve the cycling performance.

[0123] Compared with Method Example 1, Method Example 12 shows that the electrochemical performance of pure micron-sized silicon and graphite composites cannot be fully utilized. Without the constraint of multilayer silicon oxide, the micron-sized silicon suffers severe structural damage and rapid capacity decay during multiple charge-discharge cycles. Therefore, constructing silicon-based materials coated with gradient silicon oxide is the key to obtaining high capacity and excellent cycle performance.

[0124] Furthermore, 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified.

[0125] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0126] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are 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.

[0127] 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-based anode material, characterized in that, It includes micron-sized silicon particles and silicon oxide layers, wherein the outer surface of the micron-sized silicon particles is covered with multiple layers of the silicon oxide layers, and the oxygen content of the multiple layers of silicon oxide layers gradually decreases from the outer layer to the inner layer; Carbon material is uniformly distributed in the outermost silicon oxide layer of a multilayer silicon oxide layer, or the outer surface of the outermost silicon oxide layer of a multilayer silicon oxide layer is covered with a carbon material layer. The multilayer silicon oxide layer includes a first silicon oxide layer and a second silicon oxide layer arranged from the inside out. The atomic ratio of oxygen to silicon in the first silicon oxide layer is (0.1~1.0):1, and the atomic ratio of oxygen to silicon in the second silicon oxide layer is (1.0~1.5):

1. The micrometer silicon particles are elemental silicon, the volume average diameter M V of the micrometer silicon particles is 1-5 μm, and the thickness of the silicon oxide layers gradually decreases from the outer layer to the inner layer.

2. The silicon-based anode material of claim 1, wherein the silicon-based anode material has a capacity of at least 1000 mAh / g. The silicon oxide layer also contains lithium compounds, and the lithium content in the lithium compounds is distributed in a gradient from the outer layer to the inner layer in the multilayer silicon oxide layer.

3. The silicon-based anode material of claim 2, wherein the silicon-based anode material has a capacity of at least 1000 mAh / g. The lithium content in the lithium compound gradually decreases from the outermost to the innermost layer in the multilayer silicon oxide layers.

4. The silicon-based anode material of claim 2, wherein the silicon-based anode material has a capacity of at least 1000 mAh / g. The lithium compound includes any one or a combination of several of Li2Si2O5, Li2SiO3 and Li4SiO4; the lithium content in the multilayer silicon oxide accounts for 0.05% to 5% of the mass percentage of the silicon-based anode material.

5. A silicon-carbon composite negative electrode material, characterized by, The silicon-based anode material according to any one of claims 1 to 4 further includes a carbon coating layer, wherein the carbon coating layer coats the surface of the outermost silicon oxide layer in the multilayer silicon oxide layer, or the carbon coating layer coats the surface of the carbon material layer.

6. The silicon-carbon composite negative electrode material of claim 5, wherein the carbon is selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, and combinations thereof. The carbon source of the carbon coating layer includes any one or a combination of several of the following: natural graphite, pitch carbon, petroleum coke, needle coke, epoxy resin, polyacrylonitrile, polyacrylamide, polyimide, and graphene; the thickness of the carbon coating layer is 5~100nm.

7. The silicon-carbon composite negative electrode material of claim 5, wherein the carbon is selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, and combinations thereof. The carbon coating layer accounts for 20% to 45% of the mass of the silicon-based anode material.

8. A method for producing the silicon-based negative electrode material according to any one of claims 1 to 4, characterized by, Includes the following steps: Pretreatment: Disperse micron-sized silicon particles in hydrofluoric acid solution to remove the oxide layer on the surface of the micron-sized silicon particles; Oxidation of micron-sized silicon particles: In an inert atmosphere, pretreated micron-sized silicon particles are heated and oxidizing gas is introduced to generate a first silicon oxide layer on the outer layer of the micron-sized silicon particles, thereby obtaining the first product; Second silicon oxide layer coating: The first product is mixed with a silane solution, dried and pyrolyzed to obtain the second product; Pre-lithiation: The second product is mixed with a lithiation reagent and heated in an inert atmosphere to obtain the silicon-based anode material.

9. A method for preparing the silicon-carbon composite anode material according to any one of claims 5 to 7, characterized in that, Includes the following steps: Pretreatment: Disperse micron-sized silicon particles in hydrofluoric acid solution to remove the oxide layer on the surface of the micron-sized silicon particles; Oxidation of micron-sized silicon particles: In an inert atmosphere, pretreated micron-sized silicon particles are heated and oxidizing gas is introduced to generate a first silicon oxide layer on the outer layer of the micron-sized silicon particles, thereby obtaining the first product; Second silicon oxide layer coating: The first product is mixed with a silane solution, dried and pyrolyzed to obtain the second product; Pre-lithiation: The second product is mixed with a lithiation reagent and heated in an inert atmosphere to obtain the silicon-based anode material; Carbon composite: The silicon-based anode material is directly mixed with a first carbon source, or the silicon-based anode material is mixed with a second carbon source and then subjected to heat treatment to obtain a silicon-carbon composite anode material coated with a carbon coating layer.

10. A battery prepared from the silicon-based anode material according to any one of claims 1 to 4 or the silicon-carbon composite anode material according to any one of claims 5 to 7.

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