Composite negative electrode material and manufacturing method therefor

Abstract

To provide a silicon-carbon composite negative electrode material achieving uniform distribution of silicon particles, and a method for manufacturing the same.SOLUTION: The present invention provides a composite negative electrode material containing graphite, a plurality of silicon particles, and a carbon coating layer. The graphite is surface-modified by pretreatment with an organic polymer material. The plurality of silicon particles coat the graphite, and the carbon coating layer coats the graphite and the plurality of silicon particles. The carbon coating layer is formed by carbonizing the organic polymer material through a heat treatment process. A manufacturing method for the composite negative electrode material includes the following steps: first, the graphite and a first solution containing the organic polymer material are mixed and dried to form first composite particles; next, the first composite particles and a second solution including a plurality of silicon particles are mixed to form second composite particles; and finally, the second composite particles are subjected to the heat treatment process to form the composite negative electrode material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite anode material and a manufacturing method thereof, and in particular to a silicon-carbon composite anode material (silicon-carbon composite anode material) and a manufacturing method thereof. The present invention achieves uniform distribution of silicon particles by surface-modifying graphite with an organic polymer material. [Background technology]

[0002] With the rapid development of technology, reusable secondary batteries are now widely used in fields such as electric vehicles and energy storage. To achieve superior efficiency and convenience, the demand for high-performance secondary batteries is increasing day by day. The performance of secondary batteries is closely related to the anode material used, and graphite has attracted attention as one of the mainstream options.

[0003] Currently used graphite anode materials are approaching the theoretical limit of capacitance per gram, and as a method for improving the capacitance of anode materials, it has been proposed to mix graphite with silicon particles having a high capacitance per gram to form a silicon-carbon composite anode material having a high capacitance per gram. However, because the surfaces of graphite and silicon particles have negative potentials, when graphite and silicon particles are mixed to form a silicon-carbon composite anode material, the silicon particles cannot be uniformly distributed on the surface of the graphite due to the similar surface potentials of the graphite and silicon particles, resulting in poor performance of the silicon-carbon composite anode material.

[0004] Therefore, to solve these problems, it is necessary to provide a silicon carbon composite anode material and a manufacturing method thereof that can achieve uniform distribution of silicon particles. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a silicon-carbon composite anode material and a manufacturing method thereof, in which graphite is surface-modified using an organic polymer material to achieve a uniform distribution of silicon particles. The composite anode material is manufactured by first liquid-phase mixing graphite with an organic polymer material, and then surface-modifying the graphite surface using the organic polymer material to form first composite particles. The first composite particles are then liquid-phase mixed with silicon particles to form second composite particles. For example, graphite is surface-modified using organic polymer materials such as polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA) to form first composite particles with a positive surface potential. This allows silicon particles with a negative surface potential to be adsorbed uniformly on the graphite surface, without the need for a binder. Furthermore, graphite is mixed with a cross-linking agent, such as glutaraldehyde (GA), and an organic polymer material. This cross-linking reaction between the cross-linking agent and the organic polymer material strengthens the bond with the graphite surface, improving the surface modification effect. Finally, the second composite particles are heat-treated to form a composite anode material. The composite anode material includes graphite, a plurality of silicon particles, and a carbon coating layer. The plurality of silicon particles coat the graphite, and the carbon coating layer coats the graphite and the plurality of silicon particles. The carbon coating layer is formed by carbonizing the organic polymer material used for graphite surface modification through a heat treatment process. In other words, the addition of the organic polymer material not only achieves uniform distribution of the silicon particles, but also bonds them to form a carbon coating layer, further improving the electrochemical performance of the composite anode material. [Means for solving the problem]

[0006] To achieve the above object, the present invention provides a composite anode material comprising graphite, a plurality of silicon particles, and a carbon coating layer. The graphite is surface-modified by pre-treatment with an organic polymer material. A plurality of silicon particles coat the graphite. The carbon coating layer is formed by coating the graphite and the plurality of silicon particles and carbonizing the organic polymer material through a heat treatment process.

[0007] In a preferred embodiment, the organic polymeric material comprises polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA).

[0008] In a preferred embodiment, the carbon coating layer is formed by carbonizing the organic polymer material and the cross-linking agent through the heat treatment step.

[0009] In a preferred embodiment, the cross-linking agent comprises glutaraldehyde (GA).

[0010] In a preferred embodiment, the average particle size of the graphite is 5 μm to 50 μm.

[0011] In a preferred embodiment, the plurality of silicon particles have an average particle size of 100 nm to 200 nm.

[0012] In a preferred embodiment, the temperature of the heat treatment step is 900°C to 1100°C.

[0013] In a preferred embodiment, the heat treatment step is carried out in a non-oxidizing atmosphere.

[0014] In order to achieve the above object, the present invention provides a method for producing a composite anode material, including: step (a) of providing graphite; step (b) of mixing the graphite with an organic polymer material, whereby the organic polymer material coats the surface of the graphite to form first composite particles; step (c) of mixing the first composite particles with a plurality of silicon particles, whereby the plurality of silicon particles coat the surfaces of the first composite particles to form second composite particles; and step (d) of performing a heat treatment process on the second composite particles to carbonize the organic polymer material to form a composite anode material, wherein the composite anode material includes graphite, a plurality of silicon particles, and a carbon coating layer, whereby the plurality of silicon particles coat the graphite and the carbon coating layer coats the graphite and the plurality of silicon particles, and the carbon coating layer is formed by carbonizing the organic polymer material through a heat treatment process.

[0015] In a preferred embodiment, the weight of the organic polymer material is 5% to 10% of the weight of the graphite.

[0016] The organic polymeric materials include polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA).

[0017] In a preferred embodiment, the weight of polydiallyldimethylammonium chloride (PDDA) is 5% to 10% of the weight of graphite, and the weight of polyvinyl alcohol (PVA) is 0.5% to 1.5% of the weight of graphite.

[0018] In a preferred embodiment, the graphite and the organic polymer material are mixed with a cross-linking agent to form the first composite particles, and the carbon coating layer is formed by carbonizing the organic polymer material and the cross-linking agent through a heat treatment process.

[0019] In a preferred embodiment, the weight of the cross-linking agent is 0.5% to 1.5% of the weight of the graphite.

[0020] In a preferred embodiment, the cross-linking agent comprises glutaraldehyde (GA).

[0021] In a preferred embodiment, the average particle size of the graphite is 5 μm to 50 μm.

[0022] In a preferred embodiment, the plurality of silicon particles have an average particle size of 100 nm to 200 nm.

[0023] In a preferred embodiment, the temperature of the heat treatment step is 900°C to 1100°C.

[0024] In a preferred embodiment, the heat treatment step is carried out in a non-oxidizing atmosphere. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a conceptual structural diagram of a composite negative electrode material according to one embodiment of the present invention. [Figure 2A] 1 is an SEM image of a composite negative electrode material in one embodiment of the present invention. [Figure 2B] 1 is an SEM image of a composite negative electrode material in one embodiment of the present invention. [Figure 2C] 1 is an SEM image of a composite negative electrode material in one embodiment of the present invention. [Figure 2D] 1 is an SEM image of a composite negative electrode material in one embodiment of the present invention. [Figure 3] 1 is a flowchart of a method for manufacturing a composite negative electrode material in accordance with one embodiment of the present invention. [Figure 4A] 4 is a flowchart showing SEM images of second composite particles in one embodiment of the present invention. [Figure 4B] 1 is an SEM image of silicon carbon composite particles without surface modification. [Figure 5A] FIG. 2 is a SEM-EDS diagram of a second composite particle in one embodiment of the present invention. [Figure 5B] FIG. 1 is an SEM-EDS image of a silicon carbon composite particle without surface modification. [Figure 6A] 10 is a graph showing charge / discharge measurement curves at a 0.1C charge / discharge rate (C-rate) according to a fourth embodiment of the present invention. [Figure 6B] 10 is a charge / discharge measurement curve at a 0.1 C charge / discharge rate (C-rate) of a second comparative example. [Figure 7A] 10 is an SEM image of the fourth embodiment of the present invention. [Figure 7B] 10 is an SEM image of a second comparative example. [Figure 8A] FIG. 10 is an XPS diagram of the fourth example of the present invention and the second comparative example. [Figure 8B] FIG. 10 is an XPS diagram of the fourth example of the present invention and the second comparative example. [Figure 9]10 shows conductivity test curves of the fourth embodiment of the present invention and the second comparative example. [Figure 10A] 10 is a graph showing charge / discharge measurement curves at a 0.3C charge / discharge rate (C-rate) of a fourth embodiment of the present invention. [Figure 10B] 10 is a charge / discharge measurement curve at a 0.3 C charge / discharge rate (C-rate) of a second comparative example. [Figure 11A] 10 is a coulomb efficiency curve at a 0.3C charge / discharge rate (C-rate) of a fourth embodiment of the present invention. [Figure 11B] 10 is a coulomb efficiency curve at a charge / discharge rate (C-rate) of 0.3 C in the second comparative example. [Figure 12] 10 shows charge / discharge measurement curves at different charge / discharge rates for the fourth embodiment of the present invention and the second comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0026] Several exemplary embodiments embodying the features and advantages of the present invention are described in detail below. The present invention is susceptible to various modifications without departing from its scope. The following description and drawings are used to explain the present invention, not to limit it. Furthermore, in the detailed description of the present invention, a first feature being disposed on or above a second feature includes an embodiment in which the disposed first feature and the second feature are directly connected, as well as an embodiment in which the first feature and the second feature are not directly connected via another structure between them. Although the broad numerical ranges and parameters described in the details of the invention are approximations, the numerical values ​​are described as precisely as possible. Furthermore, the term "and / or" refers to one or more related elements or any combination thereof. The term "approximately" refers to a mean value within a standard error range generally accepted by those skilled in the art. Unless expressly defined in embodiments relating to operations / operations, all numerical ranges, amounts, values, percentages, etc. (e.g., angles, durations, temperatures, operating conditions, ratios, and corresponding percentages) described herein should be understood in all embodiments to be "about" or "substantially." Furthermore, unless otherwise specified in the context, all numerical values ​​in the present invention and claims may be approximated, subject to variations as necessary. For example, each parameter may be interpreted in light of at least the stated number of significant digits and by applying ordinary rounding rules. Numerical ranges herein may also be expressed as ranges from one endpoint to the other endpoint or between two endpoints. Please note that all ranges described herein include the endpoints unless otherwise specified.

[0027] Please refer to FIG. 1. FIG. 1 is a conceptual structural diagram of a composite negative electrode material according to one embodiment of the present invention. In this embodiment, the composite negative electrode material 1 includes graphite 10, a plurality of silicon particles 20, and a carbon coating layer 30. The graphite is surface-modified by pretreatment with an organic polymer material. The plurality of silicon particles 20 coat the graphite 10. The carbon coating layer 30 covers the graphite 10 and the plurality of silicon particles 20 and is formed by carbonizing the organic polymer material through a heat treatment process. In this embodiment, the organic polymer material includes, for example, polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA). The carbon coating layer 30 is formed, for example, by carbonizing the organic polymer material and a crosslinker through a heat treatment process. The crosslinker includes, for example, glutaraldehyde (GA). Note that the present invention also allows for the carbon coating layer 30 to be formed by heat treatment using other types of organic polymer materials or crosslinkers. In this embodiment, the graphite 10 has an average particle size (D50) of, for example, 5 μm to 50 μm, and the plurality of silicon particles 20 has an average particle size (D50) of, for example, 100 nm to 200 nm. The temperature of the heat treatment process is in the range of 900°C to 1100°C, and the heat treatment process is performed in a non-oxidizing atmosphere. The organic polymer material and the crosslinking agent are carbonized by the high-temperature heat treatment to form a carbon coating layer, thereby improving the electrochemical performance of the composite negative electrode material. The gas in the non-oxidizing atmosphere can be selected from the group consisting of, for example, helium gas, neon gas, argon gas, nitrogen gas, and hydrogen gas.

[0028] Please refer to Figures 2A to 2D. Figures 2A to 2D are SEM images of a composite negative electrode material according to one embodiment of the present invention. Figures 2A to 2D were measured using a focused ion beam scanning electron microscopy (FIB-SEM). Figure 2A shows graphite 10 and multiple silicon particles 20 coating the graphite 10 in the composite negative electrode material. Figure 2B is an enlarged view of Figure 2A, showing a carbon coating layer 30 formed by multiple carbon particles between the graphite 10 and the silicon particles 20. Figure 2C shows the coating structure of multiple silicon particles 20. Figure 2D shows the silicon particles 20 and the carbon coating layer 30 coating the silicon particles 20.

[0029] Please refer to FIG. 3. FIG. 3 is a flowchart of a method for manufacturing a composite negative electrode material according to one embodiment of the present invention. In this embodiment, the method for manufacturing a composite negative electrode material includes the following steps. First, as shown in steps S1 and S2, graphite is provided (prepared), and the graphite is mixed with an organic polymer material so that the organic polymer material coats the surface of the graphite to form first composite particles. In this embodiment, the average particle size (D50) of the graphite 10 is, for example, 5 μm to 50 μm, and the average particle size (D50) is measured using a laser particle size analyzer (LPSA). The organic polymer material includes, for example, polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA). The weight of the organic polymer material is, for example, 5% to 10% of the weight of graphite, the weight of polydiallyldimethylammonium chloride (PDDA) is, for example, 5% to 10% of the weight of graphite, and the weight of polyvinyl alcohol (PVA) is, for example, 0.5% to 1.5% of the weight of graphite. The organic polymer material is provided, for example, in the form of a solution using water as a solvent. The first composite particles are formed by adding graphite 10 to the organic polymer solution, stirring and mixing, and finally drying.

[0030] In this embodiment, first composite particles are formed by mixing graphite 10 and an organic polymer material with, for example, a crosslinking agent. The crosslinking agent may, for example, contain glutaraldehyde (GA), and the weight of the crosslinking agent is 0.5% to 1.5% of the weight of the graphite. When graphite is mixed with the crosslinking agent and the organic polymer material, a crosslinking reaction between the crosslinking agent and the organic polymer material strengthens the bond with the graphite surface, improving the surface modification effect. After the graphite 10 and the organic polymer are mixed in a liquid phase, the mixture is dried, for example, by spray drying. This causes the organic polymer material to coat the graphite 10, achieving surface modification and forming first composite particles having a positive surface potential. The temperature in the spray drying step is, for example, 100°C to 180°C. In this embodiment, the first composite particles formed after drying may be subjected to a heat treatment, for example, at 80°C to 120°C. This promotes the crosslinking reaction between the organic polymer material and the crosslinking agent, and prevents the organic polymer material from dissolving in the solvent again.

[0031] Furthermore, as shown in step S3, the first composite particles are mixed with a plurality of silicon particles 20, and the surfaces of the first composite particles are coated with the plurality of silicon particles 20 to form second composite particles. Since the surfaces of the first composite particles have a positive potential, they can adsorb the silicon particles 20, which have a negative potential, and uniformly distribute the silicon particles 20 on the surfaces of the first composite particles. This method also eliminates the need for a binder. In this embodiment, the plurality of silicon particles 20 are provided in the form of a solution using, for example, ethanol as a solvent. The second composite particles are formed by adding the first composite particles to the silicon particle solution, stirring and mixing, and then filtering and drying. The silicon particles 20 are nanoscale particles, and their average particle size (D50) is, for example, 100 nm to 200 nm, as measured by a laser particle size analyzer (LPSA). The average particle size of the silicon particles can be adjusted, for example, between 10 nm and 100 nm according to actual needs, but the present invention is not limited thereto. In this embodiment, the weight of the plurality of silicon particles 20 is, for example, 0.5% to 7% of the weight of the first composite particles, and preferably 5% to 7%, thereby obtaining a composite negative electrode material with relatively excellent electrochemical performance.

[0032] Finally, as shown in step S4, the second composite particles are subjected to a heat treatment process to carbonize the organic polymer material, thereby forming a composite negative electrode material 1. The composite negative electrode material 1 includes (is provided with) graphite 10, a plurality of silicon particles 20, and a carbon coating layer 30. The plurality of silicon particles 20 coat the graphite 10, and the carbon coating layer 30 coats the graphite 10 and the plurality of silicon particles 20. The carbon coating layer 30 may be formed by carbonizing the organic polymer material through a heat treatment process, or by carbonizing the organic polymer material and a crosslinking agent through a heat treatment process. In this embodiment, the temperature of the heat treatment process is, for example, 900°C to 1100°C, and the heat treatment process is performed in a non-oxidizing atmosphere. Carbonizing the organic polymer material and the crosslinking agent through high-temperature heat treatment forms a carbon coating layer that coats the graphite 10 and the plurality of silicon particles 20, thereby improving the electrochemical performance of the composite negative electrode material. The type of gas in the non-oxidizing atmosphere may be a gas selected from the group consisting of helium gas, neon gas, argon gas, nitrogen gas, and hydrogen gas.

[0033] Please refer to Figures 4A to 5B. Figure 4A is an SEM image of a second composite particle according to one embodiment of the present invention. Figure 4B is an SEM image of a silicon carbon composite particle that has not been surface-modified. Figure 5A is an SEM-EDS image of a second composite particle according to one embodiment of the present invention. Figure 5B is an SEM-EDS image of a silicon carbon composite particle that has not been surface-modified. Figures 4A to 5B were measured using a scanning electron microscope (SEM). Figures 5A and 5B are the results of surface elemental analysis of silicon using an energy dispersive spectrometer (EDS). Figures 5A and 5B show second composite particles composed of surface-modified graphite and silicon particles, which clearly contain silicon, while the presence of silicon is not clearly observed in the silicon carbon composite particles that have not been surface-modified. This demonstrates that uniform distribution of silicon particles can be achieved by surface-modifying graphite using an organic polymer material.

[0034] The method for producing the carbon-coated lithium iron phosphate material of the present invention will be described in detail below with reference to examples.

[0035] First Example

[0036] A first solution was prepared by adding 3.43 g of a polydiallyldimethylammonium chloride (PDDA) solution, 0.227 g of polyvinyl alcohol (PVA), and 0.4 g of glutaraldehyde (GA) solution to 100 ml of deionized water and stirring. (The first solution was prepared by mixing 3.43 g of a 35 wt% polydiallyldimethylammonium chloride solution with a weight-average molecular weight of less than 100,000, 0.227 g of polyvinyl alcohol with a hydrolysis rate of 88% and a weight-average molecular weight of 88,000, 0.4 g of a 50 wt% glutaraldehyde solution, and 100 ml of deionized water.) 20 g of graphite was then added to the first solution and stirred to form a second solution. The weight percentage concentration of the PDDA solution is 35 wt%, the solvent is deionized water, and the weight-average molecular weight is less than 100,000. The degree of hydrolysis of PVA is 88%, and the weight-average molecular weight is 88,000. The weight percentage concentration of the GA solution is 50 wt%, and the solvent is deionized water. In other words, the weight of PDDA actually added is 1.2 g (6% of the weight of graphite), the weight of PVA is 0.2 g (1% of the weight of graphite), and the weight of GA is 0.2 g (1% of the weight of graphite). The average particle size (D50) of the graphite is 13 μm.

[0037] The second solution is used to form first composite particles by spray granulation at 120°C, and the first composite particles are then heated at 100°C for 2 hours under vacuum to promote the crosslinking reaction between the organic polymer material and the crosslinking agent and prevent the organic polymer material from redissolving in a solvent in a subsequent process.

[0038] 5 g of the first composite particles are added to 0.5 g of the silicon particle solution and stirred to form a mixed solution, with the silicon particles having a negative potential adsorbing onto the surface of the first composite particles having a positive potential. The weight percentage concentration of the silicon particle solution is 10 wt%, and the solvent is ethanol. The particle diameter of the silicon particles is 150 nm. In other words, the weight of the silicon particles actually added is 0.05 g (1% of the weight of the first composite particles). Next, the mixed solution is filtered through filter paper to obtain a mixture, which is then heated and dried at 100°C for 2 hours in a vacuum environment to obtain second composite particles.

[0039] The second composite particles are placed in an alumina crucible and heat-treated in a non-oxidizing atmosphere to produce a composite anode material. The heat treatment begins at room temperature (25°C), is heated to 1000°C at a rate of 2°C per minute, and is maintained at 1000°C for three hours before the heat treatment is completed. The gas in the non-oxidizing atmosphere is a mixture of argon gas and 3% hydrogen gas.

[0040] The manufacturing process of the second embodiment is substantially the same as that of the first embodiment, except that 5 g of the first composite particles are added to 1.5 g of the silicon particle solution and stirred to form a mixed solution, i.e., the weight of the silicon particles actually added is 0.15 g (3% of the weight of the first composite particles).

[0041] The manufacturing process of the third embodiment is substantially the same as that of the first embodiment, except that 5 g of the first composite particles are added to 2.5 g of the silicon particle solution and stirred to form a mixed solution, i.e., the weight of the silicon particles actually added is 0.25 g (5% of the weight of the first composite particles).

[0042] The manufacturing process of Example 4 is substantially the same as Example 1, except that 5 g of the first composite particles are added to 3.5 g of the silicon particle solution and stirred to form a mixed solution, i.e., the weight of the silicon particles actually added is 0.35 g (7% of the weight of the first composite particles).

[0043] The first comparative example is graphite.

[0044] The manufacturing process of the second comparative example is generally the same as the manufacturing process of the fourth example, except that the final heat treatment step is omitted and the second composite particles are directly manufactured into an electrode sheet without high-temperature heat treatment.

[0045] See Figures 6A to 6B and Table 1. Figures 6A and 6B are charge / discharge measurement curves at a 0.1C charge / discharge rate (C-rate) for Example 4 of the present invention and Comparative Example 2. Figure 6A is the charge / discharge curve for the first cycle of Example 4 of the present invention. Figure 6B is the charge / discharge curve for the first cycle of Comparative Example 2. Table 1 shows the charge / discharge measurement results for Examples 1 to 4 of the present invention, Comparative Example 1, and Comparative Example 2. Charge / discharge measurements were performed by preparing electrode sheets from each of the Examples and the embodiment, and then using the electrode sheets, lithium metal, electrolyte, and separator to form button batteries. The battery case specifications are CR2032. The electrode sheets are composed of 90 wt% active material (Example or Comparative Example), 4 wt% Super P, and 6% sodium alginate. The electrolyte solution contained 1 M lithium hexafluorophosphate (LiPF6) dissolved in a 1:2 volume ratio of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), 2 wt% vinylene carbonate (VC), and 10 wt% fluorinated ethylene carbonate. The separator was a polyethylene separator. The voltage window for charge / discharge measurements was 1 mV to 1.5 V. The discharge process was performed in constant current (CC) mode at a 0.1 C charge / discharge rate, discharging to 1 mV, and then in constant voltage (CV) mode until the current reached 0.1 times the CC charge / discharge rate. The charge process was performed in constant current (CC) mode at a 0.1 C charge / discharge rate, charging to 1.5 V. [Table 1]

[0046] As shown in Table 1, after two charge / discharge cycles, the charge / discharge capacities of Examples 1 to 4 were all superior to those of Comparative Example 1, which used a graphite anode. The charge / discharge capacities, in descending order, were as follows: Example 4, in which the weight of the silicon particles was 7% of the weight of the first composite particles; Example 3, in which the weight of the silicon particles was 5% of the weight of the first composite particles; Example 2, in which the weight of the silicon particles was 3% of the weight of the first composite particles; and Example 1, in which the weight of the silicon particles was 1% of the weight of the first composite particles. Thus, when the silicon particles are added in a ratio of 0.5% to 7% of the weight of the first composite particles, as in the present invention, a composite anode material with better electrochemical performance can be obtained; and a ratio of 5% to 7% of the weight of the first composite particles is more preferable, which further improves the electrochemical performance of the composite anode material.

[0047] 6A-6B and Table 1, the same ratios of organic polymer material and silicon particles were added to the fourth example and the second comparative example, but the charge / discharge capacity and Coulombic efficiency (CE) of the fourth example are significantly better than those of the second comparative example. This indicates that the organic polymer material is carbonized by high-temperature heat treatment to form a carbon coating layer that covers the graphite and silicon particles, improving the electrochemical performance of the composite negative electrode material.

[0048] Please refer to Figures 7A to 9. Figures 7A to 7B are SEM images of Example 4 of the present invention and Comparative Example 2. Figures 8A to 8B are XPS diagrams of Example 4 of the present invention and Comparative Example 2 measured by X-ray photoelectron spectroscopy (XPS). Figure 9 is a conductivity test curve of Example 4 of the present invention and Comparative Example 2. As shown in Figure 7A, Example 4 of the present invention is carbonized by high-temperature heat treatment to form a carbon coating layer, which makes the silicon particles coated on the surface less likely to fall off, resulting in a denser structure. As shown in Figure 7B, Example 2, which has a carbon coating layer formed without being carbonized by high-temperature heat treatment, has a looser structure (less dense) due to the falloff of silicon particles. As shown in Figures 8A and 8B, the peak value at a binding energy of 284.8 eV (i.e., the binding energy of C 1s) of Example 4 is much larger than that of Comparative Example 2. The peak value at a binding energy of 102.64 eV (i.e., the binding energy of Si 2p) is much smaller than that of the second comparative example. In other words, the surface of the fourth example contains more carbon and less silicon than that of the second comparative example. Furthermore, as shown in FIG. 9, by having a carbon coating layer, the conductivity of the fourth example is about five times that of the second comparative example. This indicates that the organic polymer material of the second composite particle forms a carbon coating layer that coats the graphite and silicon particles through carbonization by high-temperature heat treatment.

[0049] Please refer to Figures 10A to 11B and Table 2. Figure 10A shows charge / discharge measurement curves at a 0.3C charge / discharge rate (C-rate) for Example 4 of the present invention. Figure 10B shows charge / discharge measurement curves at a 0.3C charge / discharge rate (C-rate) for Comparative Example 2. Figure 11A shows Coulomb efficiency curves at a 0.3C charge / discharge rate (C-rate) for Example 4 of the present invention. Figure 11B shows Coulomb efficiency curves at a 0.3C charge / discharge rate (C-rate) for Comparative Example 2. Table 2 shows the charge / discharge measurement results for Example 4 and Comparative Example 2. The charge / discharge measurements were performed using the button batteries prepared in Example 4 and Comparative Example 2. The voltage window for the charge / discharge measurements was 1 mV to 1.5 V. The discharge process consisted of first discharging to 1 mV in constant current (CC) mode at a 0.3 C charge / discharge rate, and then discharging in constant voltage (CV) mode at a current 0.1 times the charge / discharge rate in CC mode. The charge process consisted of charging to 1.5 V in constant current (CC) mode at a 0.3 C charge / discharge rate. As shown in Figures 10A and 10B and Table 2, the capacitance and capacitance retention rate (retention rate) of Example 4 are significantly superior to those of Comparative Example 2. Furthermore, as shown in Figures 11A and 11B, the Coulombic efficiency of Example 4 is also more stable than that of Comparative Example 2. This indicates that the organic polymer material can be carbonized by high-temperature heat treatment to form a carbon coating layer that covers the graphite and silicon particles, improving the electrochemical performance of the composite anode material. [Table 2]

[0050] Please refer to Figure 12. Figure 12 shows the charge / discharge measurement results of the fourth embodiment of the present invention and the second comparative example, after five cycles at charge / discharge rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 0.1C. The charge / discharge measurements were performed using the button batteries prepared in the fourth embodiment and the second comparative example. As can be seen from the figure, the capacitance and capacitance retention rate of the fourth embodiment at different charge / discharge rates are significantly higher than those of the second comparative example without heat treatment, especially at a high charge / discharge rate (1C).

[0051] As described above, the present invention provides a silicon-carbon composite anode material and a manufacturing method thereof, in which graphite is surface-modified using an organic polymer material to achieve a uniform distribution of silicon particles. To manufacture the composite anode material, first, graphite and an organic polymer material are mixed in a liquid phase, and the graphite surface is surface-modified using the organic polymer material to form first composite particles. Next, the first composite particles are mixed in a liquid phase with silicon particles to form second composite particles. For example, by surface-modifying graphite using organic polymer materials such as polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA), first composite particles with a positive surface potential can be formed. This allows silicon particles with a negative surface potential to be adsorbed and distributed uniformly on the graphite surface, eliminating the need for a binder. Furthermore, graphite is mixed with a cross-linking agent, such as glutaraldehyde (GA), and an organic polymer material. This cross-linking reaction between the cross-linking agent and the organic polymer material strengthens the bond with the graphite surface, improving the surface modification effect. Finally, the second composite particles are heat-treated to form a composite anode material. The composite anode material includes graphite, a plurality of silicon particles, and a carbon coating layer. The plurality of silicon particles coat the graphite, and the carbon coating layer coats the graphite and the plurality of silicon particles. The carbon coating layer is formed by carbonizing the organic polymer material used for graphite surface modification through a heat treatment process. In other words, the addition of the organic polymer material not only achieves uniform distribution of the silicon particles, but also bonds them to form a carbon coating layer, further improving the electrochemical performance of the composite anode material.

[0052] The present invention can be modified and improved in various ways by those skilled in the art, and all such modifications and improvements are included within the scope of the claims of this application. [Explanation of symbols]

[0053] 1: Composite anode material 10: Graphite 20: Silicon particles 30: Carbon coating layer S1, S2, S3, S4, S5: Steps

Claims

1. A composite anode material comprising: graphite; a plurality of silicon particles; and a carbon coating layer; The graphite is surface-modified by pretreatment with an organic polymer material; the plurality of silicon particles coat the graphite; The carbon coating layer coats the graphite and the plurality of silicon particles, and the carbon coating layer is formed by carbonizing the organic polymer material through a heat treatment process.

2. 2. The composite anode material of claim 1, wherein the organic polymer material comprises polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA).

3. 2. The composite negative electrode material according to claim 1, wherein the carbon coating layer is formed by carbonizing the organic polymer material and the cross-linking agent in the heat treatment process.

4. 4. The composite negative electrode material of claim 3, wherein the cross-linking agent comprises glutaraldehyde (GA).

5. 2. The composite negative electrode material according to claim 1, wherein the average particle size of the graphite is 5 μm to 50 μm.

6. 2. The composite negative electrode material according to claim 1, wherein the average particle size of the silicon particles is 100 nm to 200 nm.

7. 2. The composite negative electrode material according to claim 1, wherein the temperature of the heat treatment is 900 to 1100°C.

8. 2. The composite negative electrode material of claim 1, wherein the heat treatment step is carried out in a non-oxidizing atmosphere.

9. A method for producing a composite negative electrode material, comprising: providing graphite, step (a); Step (b) mixing the graphite with an organic polymer material, and the organic polymer material coating the surface of the graphite to form first composite particles; Step (c) mixing the first composite particles with a plurality of silicon particles, and the plurality of silicon particles coating the surfaces of the first composite particles to form second composite particles; and step (d) of performing a heat treatment process on the second composite particles to carbonize the organic polymer material to form the composite negative electrode material, wherein the composite negative electrode material includes the graphite, the plurality of silicon particles, and a carbon coating layer, the plurality of silicon particles coating the graphite, the carbon coating layer coating the graphite and the plurality of silicon particles, and the carbon coating layer is formed by carbonizing the organic polymer material by the heat treatment process.

10. 10. The method for manufacturing a composite negative electrode material according to claim 9, wherein the weight of the organic polymer material is 5% to 10% of the weight of the graphite.

11. 10. The method for preparing a composite negative electrode material according to claim 9, wherein the organic polymer material comprises polydiallyldimethylammonium chloride (PDDA) and polyvinyl alcohol (PVA).

12. 12. The method for manufacturing a composite negative electrode material according to claim 11, wherein the weight of the polydiallyldimethylammonium chloride (PDDA) is 5% to 10% of the weight of the graphite, and the weight of the polyvinyl alcohol (PVA) is 0.5% to 1.5% of the weight of the graphite.

13. 10. The method for producing a composite negative electrode material according to claim 9, wherein the graphite and the organic polymer material are mixed with a cross-linking agent to form the first composite particles, and the carbon coating layer is formed by carbonizing the organic polymer material and the cross-linking agent through the heat treatment process.

14. 14. The method for manufacturing a composite negative electrode material according to claim 13, wherein the weight of the cross-linking agent is 0.5% to 1.5% of the weight of the graphite.

15. The method for manufacturing a composite negative electrode material according to claim 13, wherein the cross-linking agent comprises glutaraldehyde (GA).

16. 10. The method for manufacturing a composite negative electrode material according to claim 9, wherein the average particle size of the graphite is 5 μm to 50 μm.

17. 10. The method for manufacturing a composite negative electrode material according to claim 9, wherein the average particle size of the silicon particles is 100 nm to 200 nm.

18. 10. The method for manufacturing a composite negative electrode material according to claim 9, wherein the temperature of the heat treatment step is 900 to 1100°C.

19. The method for manufacturing a composite negative electrode material according to claim 9, wherein the heat treatment step is carried out in a non-oxidizing atmosphere.

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