Nanosilicon agglomerate composite negative electrode material and its preparation method

Abstract

The present invention provides a pine needle and branch-like three-dimensional network structure nanosilicon agglomerate composite anode material and a preparation method thereof. The nanosilicon agglomerate composite anode material includes a nano-sized core particle, a pine needle and branch-like three-dimensional network structure nanosilicon agglomerate grown around the nano-sized core particle, and a composite coating layer covering the pine needle and branch-like three-dimensional network structure nanosilicon agglomerate. Measurements have revealed that the nanosilicon agglomerate composite anode material has excellent battery charge-discharge cycle performance and output characteristics when applied to a lithium ion battery, with an initial discharge capacity per gram of 2600mAh / g or more and an initial coulombic efficiency of 85% or more.

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium battery materials, in particular to nanosilicon agglomerate composite anode materials and methods for preparing same. [Background technology]

[0002] Silicon-based anode materials have an ultra-high theoretical capacity of up to 4200mAh / g. The raw silicon used in silicon-based anode materials is a particularly abundant natural resource, making them low-cost and environmentally friendly. Furthermore, silicon-based anode materials have a low lithium intercalation / deintercalation potential (approximately 0.4V vs. Li / Li). + ), therefore, lithium dendrites are not able to form on the surface of silicon-based anode materials even when the battery is fully charged. Therefore, the safety performance of silicon-based anode materials is superior to that of graphite anode materials. Due to the above advantages, silicon-based anode materials are well-known as the most promising anode materials for new high-capacity lithium-ion batteries.

[0003] However, existing silicon-based anode materials have a fatal flaw that makes their practical application difficult. When silicon is used as an anode material in lithium batteries, the crystalline silicon expands in volume by 3 to 4 times after lithium intercalation and then contracts dramatically after lithium deintercalation. After multiple cycles, the battery experiences severe pulverization of silicon particles, the formation of new interfaces, the continuous fracture and regeneration of the SEI film, and the rapid consumption of lithium in the electrolyte. All of these flaws result in rapid decay of the battery's capacity. Existing material formulation and coating technologies are unable to resolve this fatal flaw: the rapid decay of discharge capacity in batteries using silicon-based anode materials.

[0004] Furthermore, silicon-based anode materials have a conductivity of only 6.7 x 10 -4S / cm. This conductivity is very low, which also seriously affects the electrochemical performance of the battery. The above deficiencies significantly limit the practical application of silicon-based anode materials in the field of lithium-ion batteries. Currently used silicon-carbon cathode materials are formed by blending approximately 10% silicon into a graphite anode, and the capacity of the resulting silicon-carbon anode is only approximately 500 mAh / g, which is far lower than the theoretical capacity of silicon-based cathode materials.

[0005] The new silicon nanowire cluster material, formed by one-dimensional silicon nanowires, has larger spaces within the wire clusters, and the silicon nanowires have diameters less than 100 nm. When used as an anode material, the volume expands upon lithium intercalation, but the silicon nanowire clusters have sufficient space to withstand this expansion. This material is a known material. When these one-dimensional silicon nanowires are wound and weakly aggregated into agglomerates, there are no riveting points between the wires because there are no Si-Si covalent bonds between them. Therefore, when used as an anode material for lithium batteries, these silicon nanowire clusters are easily crushed during the electrode sheet rolling process. While this material can withstand the volume expansion upon lithium intercalation and the volume contraction upon lithium deintercalation, the lack of anchoring points between the silicon nanowires prevents the nanowires from making sufficient contact with each other, resulting in poor electrical contact and making it very difficult for electrons to transfer from the nanowires to the copper foil current collector.

[0006] Methods for preparing silicon nanowires include laser ablation, thermal evaporation, hydrothermal, metal-catalyzed chemical etching (MACE), and CVD. These existing methods have problems such as high raw material costs, very low manufacturing efficiency, and serious chemical pollution, making them unsuitable for industrial mass production.

[0007] Reference 1 (Zhang Zheng, Shandong University Master's Degree Theses, May 2012, "Preparation of Silicon Nanowires and Nanotubes and Studies on Their Related Physical Properties") reports the preparation of silicon nanowires at high temperatures in a sealed stainless steel container using metallic zinc powder and SiCl4. The results obtained in this document are needle-like silicon nanowires with micrometer lengths, and no wire clusters are formed. In this document, the preparation environment is completely static, and there are no connections between the resulting silicon nanowires. Since a pressure-resistant, completely sealed container is used for preparation, continuous industrial production is not feasible.

[0008] Reference 2 (“Microclusters of Linked Silicon Nanowings Synthesized by a Recyclable Iodide Process for High-Performance Lithium-Ion battery Anodes, Adv. Energy Mater. 2020, (2002, pp. 81-88) reported the formation of silicon nanowire clusters by decomposing SiI4 under high vacuum (<1.33 Pa) and high temperature (900 °C). As can be clearly seen from the SEM (scanning electron microscope) images in the above publication, the silicon nanowire clusters are loose silicon nanowire clusters formed by winding one-dimensional silicon nanowires. One-dimensional silicon nanowires lack branching, forking, and interconnected structures. In the process described in the above publication, the reactant SiI4 is in the gas phase at a high temperature of 900 °C, and the decomposition reaction of SiI4 is thermodynamically feasible only under high vacuum conditions of <1.33 Pa. Because the reactants are in the gas phase, the amount of reactants added must be kept very small to maintain the pressure in the reaction vessel below 1.33 Pa. Otherwise, the pressure would exceed 1.33 Pa, preventing the decomposition reaction. Therefore, the efficiency of this reaction is extremely low, making industrial production unfeasible.

[0009] Document 3 (China Patent Publication No. 105271235) discloses silicon nanowire materials and a method for preparing them. In this method, a copper-based catalyst and silicon are preheated to 200-500°C in an inert atmosphere to obtain a contact mass. The contact mass is then reacted with chloromethane while controlling the silicon so that it does not completely react. Impurities are removed from the reactant, and unreacted silicon is separated, thereby obtaining one-dimensional silicon nanowires. One-dimensional silicon nanowires do not have any branched or unbranched structures. The method for removing impurities (carbon deposits) and separating unreacted silicon from the reactant described in the above document is described below. The product is heated to 500°C in a tubular furnace filled with air and baked for 1 hour to remove the deposited carbon. During this time, most of the carbon nanowires are oxidized to form silicon dioxide. The silicon dioxide is then removed using a sodium hydroxide solution. The resulting silicon nanowires have a radius of less than 100 nm and are therefore highly chemically active, even dissolving in sodium hydroxide solution. This method results in a very low yield, even if silicon nanowires are obtained, because a large amount of silicon is oxidized and dissolved away. The method described in the above document generates a large amount of wastewater due to the use of acid and base washing steps. This method cannot be used for industrial production due to its low yield and the large amount of acidic and alkaline industrial wastewater it generates.

[0010] Reference 4 (US Patent Application Publication No. 2015 / 0072233) discloses an anode active material in which one-dimensional silicon-based nanowires are grown on the surface of spherical particles (having a diameter of 1 to 30 μm) of a non-carbonaceous conductive metal, crystalline silicon, or alloy. The one-dimensional silicon-based nanowires account for 1 to 40% by weight. The nanowires are then coated on the outside with a layer of amorphous carbon, so that at least 50% of the one-dimensional silicon-based nanowires are covered with the amorphous carbonaceous coating layer. The above reference defines silicon-based nanowires as follows (see paragraph 0043): At least a portion of the nanowires may be linear, gently or sharply curved, or branched. The silicon-based nanowire layer (1 to 50% by weight) is statically grown on the surface of micrometer-sized non-carbonaceous conductive particles, and more than 50% of the silicon nanowires are covered with the amorphous carbon. Therefore, the anode active material listed in the above reference has the following structure: The inner core contains spherical (1-30 μm diameter) non-carbonaceous conductive metal, crystalline silicon, or alloy, and the second layer contains one-dimensional silicon-based nanowires with no or few wire-wire nodes. The lack of connectivity between the nanowires makes rapid electron transport difficult and requires assistance from conductive materials. More than 50% of the outer layer is covered with amorphous carbon, so the surface morphology of the composite particles is dominated by amorphous carbon. In the anode material, silicon-based nanowires account for 1-40 wt% and are therefore not the main phase.

[0011] Reference 5 (Chinese Patent No. 103035915) discloses an anode active material in which a layer of one-dimensional nanowires is grown on a spherical carbonaceous substrate having a diameter of about 1 to about 30 μm by using a vapor-liquid-solid (VLS) growth method, with the one-dimensional silicon-based nanowires accounting for 1 to 40 wt %. Therefore, the anode active material is a carbon-silicon-based nanowire composite anode material containing carbon as the primary phase and silicon-based nanowires as the secondary phase. The reference defines silicon-based nanowires as follows: The term "nanowire" refers to a wire structure having a nanometer cross section, at least a portion of which may be linear, gently or sharply curved, or branched. In other words, the nanowires in the reference are not multi-connected and multi-node network structures. Due to the lack of connectivity between nanowires, rapid electron transport is difficult and requires the use of conductive agents. In the examples disclosed in the above document, the maximum initial capacity per gram of the negative electrode active material is less than 670 mAh / g, because the main phase of the negative electrode material is carbon, while the secondary phase is silicon nanowires in a small amount.

[0012] As can be seen from SEM images of silicon nanowires reported in all published literature, under quiescent conditions, silicon nanowires grow along the direction of the

[0111] crystal plane and grow into one-dimensional linear structures when the outer layer is Si-Ox. During the growth of the one-dimensional linear structure of silicon nanowires, turning occurs only when impurity atoms are deposited within the nanowire. Therefore, branching is rarely observed.

[0013] Reference 6 (China Patent Publication No. 106941153) discloses a method for producing high-purity gaseous silicon by heating high-purity silicon using a plasma torch (which may condense to form cotton-like elemental silicon nanowire clusters). The silicon nanowire clusters are then blended with a medium- to high-molecular-weight polymer and carbonized at a carbonization temperature of 900 to 1600°C for 2 to 24 hours. Above 900°C, these silicon nanowires readily react with the amorphous carbon obtained from the cleavage of the medium- to high-molecular-weight polymer to produce silicon carbide. Silicon nanowire morphology is not observed in Figures 5 to 7 of the reference. Furthermore, as can be seen from Figure 1, the resulting material is a linear, one-dimensional structure that forms a very loose agglomerate structure with no inter-wire connections. In this case, the lack of interconnections between the silicon nanowires makes rapid electron transport difficult and requires the addition of a conductive agent. Furthermore, the cycling curves of the sample button cells, such as those shown in FIG. 3 above, will likely involve fluctuations in discharge capacity and are unlikely to be standard straight lines.

[0014] Therefore, there is an urgent need for high performance nanosilicon-based anode materials that are not loosely structured in one dimension and can be produced in large quantities using low-cost, highly efficient, and clean continuous manufacturing techniques. Summary of the Invention

[0015] The present invention aims to solve the technical problem that silicon-based negative electrode materials have poor cycle performance, low charge / discharge capacity, and low initial coulomb efficiency when applied to lithium batteries.

[0016] The present invention aims to solve other technical problems that arise when preparing silicon-based negative electrode materials based on silicon nanowires: poor dispersion of silicon nanowires, low conductivity of silicon nanowire clusters, and the fact that silicon nanowire clusters are crushed when the electrode sheet is rolled.

[0017] The present invention aims to solve a further technical problem of realizing wastewater-free, continuous, and low-cost industrial production of nanosilicon agglomerate composite anode materials.

[0018] The present invention solves the above problems through the following technical solutions.

[0019] Provided is a nanosilicon agglomerate composite negative electrode material comprising: nano-sized core particles; nanosilicon agglomerates with a pine needle and branch-shaped three-dimensional network structure growing around the nano-sized core particles; and a composite coating layer covering the pine needle and branch-shaped three-dimensional network structured nanosilicon agglomerates, wherein the nano-sized core particles comprise metal particles and / or carbon particles, the pine needle and branch-shaped three-dimensional network structured nanosilicon agglomerates are formed by interconnected silicon nanowires with a diameter of 50 to 150 nm and a length of 0.5 to 2 μm, and the composite coating layer comprises conductive carbon and an inorganic metal oxide.

[0020] In one exemplary embodiment, the metal particles are at least one particle selected from the group consisting of silver, copper, iron, nickel, and cobalt.

[0021] In one exemplary embodiment, the inorganic metal oxides include titanium dioxide and / or zirconium dioxide.

[0022] In one exemplary embodiment, the pine needle and branch three-dimensional network structured nanosilicon agglomerates are present in an amount of 90.6 to 96.17 wt %, based on the weight of the nanosilicon agglomerate composite anode material.

[0023] In one exemplary embodiment, the nano-sized core particles are present in an amount of 1.4-3.3 wt %, the metal particles are present in an amount of 0-2.6 wt %, and the carbon particles are present in an amount of 0-2.7 wt %, based on the weight of the nanosilicon agglomerate composite anode material.

[0024] In one exemplary embodiment, the composite coating layer is present in an amount of 2.1 to 7.0 wt %, the conductive carbon is present in the composite coating layer in an amount of 1.0 to 4.5 wt %, and the inorganic metal oxide is present in an amount of 1.0 to 3.0 wt %, based on the weight of the nanosilicon agglomerate composite anode material.

[0025] In one exemplary embodiment, the nanosilicon agglomerate composite anode material has an average particle size of 5-20 μm.

[0026] In one exemplary embodiment, chemical crosslinks are formed between at least some of the silicon nanowires in the pine needle and branch three-dimensional network structure of nanosilicon agglomerates, for example to form Si-Si covalent bonds.

[0027] A method for preparing the above nanosilicon agglomerate composite anode material is also provided, which includes the following steps: (1) carrying out a surface metal substitution reaction by placing a powder of metal A in a salt solution of metal B to partially produce nano-sized metal B particles on a portion of the surface of the powder of metal A to form a composite powder; (2) continuously feeding the composite powder, which acts as a reactant and a nucleating agent, into a reaction chamber; (3) delivering SiCl gas into the reaction chamber together with an inert gas or nitrogen; (4) setting the temperature of the reaction chamber to 500-950°C to carry out a high-temperature reaction with continuous stirring, which causes nanosilicon aggregates with a pine needle and branch-like three-dimensional network structure to dynamically grow and wrap around the nano-sized metal B particles; (5) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon aggregates discharged from the reaction chamber to vacuum heat treatment; and (6) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates obtained in step (5) to a composite coating process using conductive carbon and inorganic metal oxide.

[0028] In one exemplary embodiment, in step (1), the surface metal replacement reaction is carried out by placing an alloy powder containing metal A and carbon into a salt solution of metal B, generating nano-sized metal B particles on a portion of the surface of the alloy powder to form a composite powder; and in step (4), the reaction causes pine needle and branch-like three-dimensional network structured nano-silicon agglomerates to wrap around and grow on the nano-sized carbon particles and around the nano-sized metal B particles produced by the alloy powder.

[0029] In an exemplary embodiment, metal A is at least one selected from the group consisting of magnesium and zinc, and metal B is at least one selected from the group consisting of silver, copper, iron, nickel, and cobalt.

[0030] In one exemplary embodiment, the inorganic metal oxides include titanium dioxide and / or zirconium dioxide.

[0031] In one exemplary embodiment, the vacuum heat treatment of step (5) and the composite coating treatment of step (6) are performed simultaneously.

[0032] In one exemplary embodiment, the composite coating process includes applying an organic titanium source and / or an organic zirconium source, and applying an organic carbon source to the pine needle and branch-like three-dimensional network structured nanosilicon agglomerates by high temperature hydrolysis to form a composite coating layer of titanium dioxide and / or zirconium dioxide and carbon.

[0033] Another method for preparing the above nanosilicon agglomerate composite anode material is also provided, which includes the following steps: (1) continuously introducing alloy powder containing metal A and carbon, which serves as a reactant and a nucleating agent, into a reaction chamber; (2) delivering SiCl gas into a reaction chamber together with an inert gas or nitrogen; (3) carrying out a high-temperature reaction with continuous stirring by setting the temperature of the reaction chamber at 500-950°C, which causes the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates to roll and grow on the nano-sized carbon particles made by the alloy powder; (4) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates discharged from the reaction chamber to vacuum heat treatment; and (5) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates obtained in step (4) to a composite coating treatment using conductive carbon and inorganic metal oxide.

[0034] In one exemplary embodiment, the metal A is at least one selected from the group consisting of magnesium and zinc.

[0035] In one exemplary embodiment, the inorganic metal oxides include titanium dioxide and / or zirconium dioxide.

[0036] In one exemplary embodiment, the vacuum heat treatment of step (4) and the composite coating treatment of step (5) are performed simultaneously.

[0037] In one exemplary embodiment, the composite coating process includes applying an organic titanium source and / or an organic zirconium source, and applying an organic carbon source to the pine needle and branch-like three-dimensional network structured nanosilicon agglomerates by high temperature hydrolysis to form a composite coating layer of titanium dioxide and / or zirconium dioxide and carbon.

[0038] At the high temperature of step (4), metal A, with its low boiling point and high vapor pressure, rapidly evaporates. The evaporated metal A reacts with gas-phase SiCl4 to produce silicon and metal A chloride. In the high-temperature reaction chamber, after metal A evaporation, only nanosized carbon particles (if present) and nanosized metal B particles (if present) remain in the alloy and composite powders. Note that at least one of nanosized carbon particles and nanosized metal B particles must be present as nucleating agents. In the presence of core particles, the silicon generated in the gas phase can rapidly generate silicon nanowires. Under continuous high-speed stirring at a boiling state, in the presence of core carbon (if present) and metal B (if present), the silicon nanowires coil to form interconnected nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches. The nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches are continuously and spirally discharged. Due to their low boiling point, the generated metal A chlorides are discharged through a chimney and condense to form by-products. In step (5), a vacuum heat treatment is carried out to completely remove any remaining chloride of metal A by volatilization.

[0039] The present invention relates to nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, dynamically grown on a dynamic nucleation source (nano-sized silver, copper, iron, nickel, cobalt, and carbon particles). It should be noted that these agglomerates are completely different from the perfectly long, one-dimensional linear silicon nanowires in prior art (e.g., References 1 to 6 mentioned in the Background Art section) statically grown on a static nucleation source. Figure 1A is a schematic diagram of a silicon nanowire cluster prepared under static conditions reported in the literature. The one-dimensional structure of the grown silicon nanowires lacks winding and wire-to-wire connections. Figure 1B is a schematic diagram of a three-dimensional network structure nanosilicon agglomerate with a pine needle and branch structure, dynamically prepared as disclosed in the present invention, in which the pine needles and branches are interconnected. SEM photographs of actual samples disclosed in the present invention (e.g., Figure 2) show closer connections between the pine needles and branches. FIG. 1C is a schematic diagram of the connections between pine needles and between pine needles and pine branches in the nanowire aggregate disclosed in the present invention, where the pine needles and pine branches are structurally connected.

[0040] In a boiling reaction system with high-speed stirring, dynamic growth of the spatially heterogeneous phase is carried out to produce pine needle- and branch-like nanosilicon agglomerates with nano-sized conductive metal particles and nano-sized carbon particles (if present) as cores, where the pine needles and pine needles and pine branches are interconnected (e.g., chemically cross-linked) to form a three-dimensional network structure with specific compressive strength and good electrical conductivity.

[0041] The pine needle and branch-like three-dimensional network structure nanosilicon agglomerates prepared in the present invention are micron-sized, which solves the problem that nanosilicon has poor dispersibility and is difficult to uniformly disperse in N-methylpyrrolidone during the slurry formation step of the negative electrode material.

[0042] The pine needle- and branch-like three-dimensional network-structured nanosilicon agglomerates prepared in the present invention are completely different in morphology from the one-dimensional silicon nanowires and silicon nanowire clusters disclosed in the prior art (e.g., References 1-6). While the one-dimensional silicon nanowires disclosed in the prior art have almost no wire-to-wire connections, the pine needle- and branch-like three-dimensional network-structured nanosilicon agglomerates of the present invention are characterized by interconnections between pine needles and between pine needles and pine branches, forming a multi-node three-dimensional network structure. This multi-node three-dimensional network structure may be very useful for increasing the compressive strength of powder particles during rolling of electrode sheets and for increasing electron mobility of nanosilicon during lithium intercalation / deintercalation. Furthermore, the key to forming such unique interconnected pine needle- and branch-like three-dimensional network-structured nanosilicon agglomerates is that the very fine nucleation sources formed in the reaction system are constantly stirred at high speed, allowing the silicon nanowires to grow dynamically, rather than statically, as described in the prior art.

[0043] A composite coating of conductive carbon and inorganic metal oxide is applied onto the surface of the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates prepared in this invention to prevent the occurrence of harmful side reactions between silicon and electrolyte and further optimize dispersibility and conductivity.

[0044] In the nanosilicon agglomerate composite anode material prepared in the present invention, the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates account for 90.6-96.17 wt %, i.e., nanosilicon is the main phase, and therefore the composite anode material obtained in this way has a higher discharge capacity per gram, which is more beneficial for improving the energy density of lithium batteries. [Effects of the Invention]

[0045] The nanosilicon agglomerate composite anode material and its preparation method provided by the present invention have the following beneficial effects: (1) The material has excellent battery charge-discharge cycle performance and rate capability, with an initial discharge capacity per gram exceeding 2600 mAh / g and an initial coulombic efficiency of 85% or higher. (2) The nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches have a morphology close to that of micron-sized spheres, and the product has good processability for electrode sheets. (3) The nanosilicon agglomerate composite anode material is dynamically fabricated, with pine needles and pine branches interconnected to form a multi-node network. This material is not easily crushed when the electrode sheet is rolled. During battery charging and discharging, the complete connection between the pine needles and between the pine branches facilitates electron transfer, and the agglomerates therefore have excellent electrical conductivity. (4) Continuous supply and discharge enable continuous production and high production efficiency. (5) Low cost: There is no loss of silicon source, and the SiCl4 raw material used is a by-product of the polysilicon industry, so the raw material cost is low. This method has a low firing temperature, a short time, low energy consumption, and the overall production cost is low. (6) Environmental friendliness: The chloride by-products are in the gas phase at high temperatures and are completely condensed into by-products after volatilization from the reactor. No wastewater or waste gas is emitted during the manufacturing process. [Brief explanation of the drawings]

[0046] For a better understanding of the invention and to show how the same may be carried into effect, embodiments of the invention will now be described, by way of example only, by reference to the drawings in which: [Figure 1] Figure 1 shows a schematic diagram of silicon nanowire clusters (A) reported in prior art documents, and nanosilicon aggregates with a three-dimensional network structure resembling pine needles and branches (B) disclosed in this patent application, as well as the control of the pine needle-pine needle and pine needle-pine branch connectivity (C) therein. [Figure 2]FIG. 2 is an SEM photograph of nanosilicon aggregates with a three-dimensional network structure resembling pine needles and branches, prepared in Example 1, using silver as core particles (magnification: 10,000, scale in the figure: 2 μm). [Figure 3] FIG. 3 is the XRD pattern of the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates prepared in Example 1 using silver as the core particles. [Figure 4] FIG. 4 shows the initial charge-discharge curves of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 1. [Figure 5] FIG. 5 is the cycle curve of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 1. [Figure 6] FIG. 6 is an SEM photograph of nanosilicon aggregates with a three-dimensional network structure resembling pine needles and branches, prepared in Example 2, using copper as core particles (magnification: 5,000, scale in the figure: 5 μm). [Figure 7] FIG. 7 is the XRD pattern of the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates prepared in Example 2 using copper as the core particles. [Figure 8] FIG. 8 shows the initial charge-discharge curves of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 2. [Figure 9] FIG. 9 is the cycle curve of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 2. [Figure 10] FIG. 10 shows the initial charge-discharge curves of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 3. [Figure 11] FIG. 11 shows the initial charge-discharge curves of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 4. [Figure 12] FIG. 12 shows the initial charge-discharge curves of the button cell containing the nanosilicon agglomerate composite anode material prepared in Example 5. [Figure 13]FIG. 13 is an SEM photograph of the negative electrode material prepared in Comparative Example 1 (magnification: 3,000, scale in the figure: 8 μm). [Figure 14] FIG. 14 is an SEM photograph of the negative electrode material prepared in Comparative Example 2 (magnification: 5,000, scale in the figure: 5 μm). DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention will be further described with reference to the following specific examples. It should be understood that these examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. The present invention may be embodied in many different forms and is not limited to the examples exemplified herein.

[0048] In the following examples, experimental methods that are not specified in specific conditions are typically carried out according to conventional conditions or conditions recommended by manufacturers.Unless otherwise specified, all percentages, ratios, proportions, or parts are by weight.Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as those commonly understood by those skilled in the art.In addition, any methods and materials similar or equivalent to those described herein can be used in the method of the present invention.The preferred embodiments and materials described herein are merely illustrative.

[0049] All numbers indicating dimensions, physical properties, processing parameters, component amounts, reaction conditions, and the like used in the description and claims should be understood as being modified in all instances by the term "about."

[0050] All ranges disclosed herein should be understood to encompass the beginning and ending values ​​of the range, as well as all subranges subsumed therein. For example, a range of "1 to 10" should be considered to include any and all subranges between (and including) the minimum value of 1 and the maximum value of 10, i.e., all subranges beginning with a minimum value of 1 or greater and ending with a maximum value of 10 or less, e.g., 1 to 2, 3 to 5, 8 to 10, etc.

[0051] Example 1 Ten kilograms of 200-mesh zinc powder with a purity of 99.9% was added to 10 L of a 0.05 M silver nitrate solution, stirred at 5°C for 30 minutes, and then allowed to stand for 1 hour. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce zinc powder with a partial silver coating on its surface. The silver content was 0.54 wt%. The temperature of the stirred boiling furnace (fluidized bed) was set to 550°C. The silver-coated zinc powder prepared above was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the stirring boiling furnace was set to 60 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge began, yielding a dark yellow-green powder containing a small amount of zinc chloride. Figure 2 shows an SEM image of the powder, clearly showing micron-sized agglomerates of pine-leaf and branch-like three-dimensional network structure formed by silicon nanowires. The silicon nanowires had a diameter of approximately 100 nm and a length of approximately 1 μm. Figure 3 shows the X-ray diffraction spectrum of the powder, indicating that the powder is crystalline silicon containing a small amount of silver. The prepared agglomerate powder was measured by a laser particle size analyzer and had the following particle size distribution: D10=5.8 μm, D50=10.5 μm, D90=14.3 μm.

[0052] The powder was sprayed with a butyl titanate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 700°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl titanate decomposed into titanium dioxide, and the carboxymethyl cellulose decomposed into carbon. The titanium dioxide and carbon were then coated onto the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of titanium dioxide and carbon used for the surface coating and the inner core silver particles were 1.0%, 1.2%, and 2.5%, respectively.

[0053] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating, with a wet thickness of 150 μm, was baked at 100 °C, vacuum dried, rolled, and subjected to imidization at 290 °C for 30 minutes in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. Figure 4 shows the initial charge / discharge curve of the button cell, and Figure 5 shows the cycle curve of the button cell. The nanosilicon agglomerate composite anode material prepared in Example 1 had an initial discharge capacity per gram of 3,105.8 mAh / g and an initial coulombic efficiency of 86.8%. The button cell was subjected to 120 1C charge-discharge cycles. The charge capacity showed almost no decay.

[0054] Example 2 Ten kilograms of 99.9% pure 100-mesh zinc powder was added to 10 L of 0.05 M copper nitrate solution, stirred at 2°C for 20 minutes, and then allowed to stand for 1 hour. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce zinc powder with a partial copper coating on its surface. The copper content was 0.32 wt%. The temperature of the stirred boiling furnace was set to 650°C. The copper-coated zinc powder prepared above was fed into the boiling furnace at a constant rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the stirring boiling furnace was set to 100 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge was initiated, yielding a dark yellow-green powder containing a small amount of zinc chloride. Figure 6 shows an SEM image of the powder, clearly showing micron-sized agglomerates of silicon nanowires with a pine-leaf and branch-like three-dimensional network structure. The silicon nanowires had a diameter of approximately 90 nm and a length of approximately 1 μm. Figure 7 shows the X-ray diffraction spectrum of the powder, indicating that the powder is crystalline silicon. A small amount of copper as core particles was not detected due to the sensitivity limit of the X-ray diffractometer due to its small amount. The prepared agglomerate powder was measured by a laser particle size analyzer and had the following particle size distribution: D10=5.1 μm, D50=9.6 μm, D90=12.7 μm.

[0055] The powder was sprayed with a butyl zirconate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 750°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl zirconate decomposed into zirconium dioxide, and the carboxymethyl cellulose decomposed into carbon. The zirconium dioxide and carbon were coated over the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of the surface-coating zirconium dioxide and carbon and the inner core copper particles were 1.2%, 1.5%, and 1.4%, respectively.

[0056] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 minutes in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. Figure 8 shows the initial charge / discharge curve of the button cell, and Figure 9 shows the cycle curve of the button cell. The nanosilicon agglomerate composite anode material prepared in Example 2 had an initial discharge capacity per gram of 3,009.8 mAh / g and an initial coulombic efficiency of 86.9%. The button cell was subjected to 115 1C charge-discharge cycles. The charge capacity showed almost no decay.

[0057] Example 3 Ten kilograms of 50-mesh zinc powder with a carbon content of 0.5% was added to 10 L of 0.02 M silver nitrate solution, stirred at 0°C for 30 minutes, and then allowed to stand for 1 hour. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce a carbon-containing zinc powder with a partial silver coating on its surface. The silver content was 0.216 wt%. The temperature of the stirred boiling furnace was set to 750°C. The silver-coated carbon-containing zinc powder prepared above was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the stirred boiling furnace was set to 80 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge began, yielding a dark yellow-green powder containing a small amount of zinc chloride. The powder also consisted of nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches. The silicon nanowires had a diameter of approximately 100 nm and a length of approximately 1 μm. X-ray diffraction spectra indicated the powder was crystalline silicon. Due to the presence of small amounts of silver and carbon as inner core particles, the XRD spectrum indicated the presence of silver but not carbon. The carbon content was measured using a carbon analyzer and was found to be 2.37%. The prepared agglomerate powder was measured with a laser particle size analyzer and had the following particle size distribution: D10=5.4 μm, D50=10.2 μm, D90=14.0 μm.

[0058] The powder was sprayed with an isopropyl titanate / sucrose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas and heated to 500°C, evacuated to 100 Pa, and further heated to 750°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the isopropyl titanate decomposed into titanium dioxide, and the sucrose decomposed into carbon. The titanium dioxide and carbon were coated over the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of titanium dioxide and carbon used for the surface coating and the carbon and silver content within the internal silver particles were 1.2%, 1.5%, 2.3%, and 1.0%, respectively.

[0059] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 minutes in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. Figure 10 shows the initial charge / discharge curves of the button cell. The nanosilicon agglomerate composite anode material prepared in Example 3 had an initial discharge capacity per gram of 3,132.5 mAh / g and an initial coulombic efficiency of 87.0%. The button cell was subjected to 115 1C charge-discharge cycles. The charge capacity did not fade.

[0060] Example 4 Ten kilograms of 300-mesh zinc powder with a carbon content of 0.5% was taken, and the temperature of the stirred boiling furnace was set to 600°C. The carbon-containing zinc powder was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). To deliver the gaseous silicon tetrachloride to the boiling furnace, 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring impeller of the stirred boiling furnace was set to 120 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and a solenoid valve located in the chimney automatically opened when the pressure was higher than this positive pressure. The product was continuously discharged from the bottom of the boiling furnace in a spiral. After 3 hours of reaction with continuous feeding, discharge was initiated, yielding a dark yellow-green powder containing a small amount of zinc chloride. SEM images showed nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, with silicon nanowires having a diameter of approximately 80 nm and a length of approximately 1 μm. X-ray diffraction spectra indicated that the powder was crystalline silicon. A small amount of carbon as core particles was not detected due to the sensitivity limit of the X-ray diffractometer due to its small amount. The carbon content was measured using a carbon analyzer and found to be 2.32%. The prepared agglomerate powder was measured using a laser particle size analyzer and found to have the following particle size distribution: D10 = 4.7 μm, D50 = 9.2 μm, D90 = 12.0 μm.

[0061] The powder was sprayed with a butyl titanate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 700°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl titanate decomposed into titanium dioxide, and the carboxymethyl cellulose decomposed into carbon. The titanium dioxide and carbon were then coated onto the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of titanium dioxide and carbon for the surface coating and the inner core carbon particles were 1.0%, 1.2%, and 2.3%, respectively.

[0062] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 minutes in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. Figure 11 shows the initial charge / discharge curves of the button cell. The nanosilicon agglomerate composite anode material prepared in Example 4 had an initial discharge capacity per gram of 2,935.2 mAh / g and an initial coulombic efficiency of 84.9%. The button cell was subjected to 120 1C charge-discharge cycles. The charge capacity did not decay and only increased slightly.

[0063] Example 5 Five kilograms of 200-mesh magnesium powder with a carbon content of 1.0% was taken, and the temperature of the stirred boiling furnace was set to 850°C. The carbon-containing magnesium powder was fed into the boiling furnace at a constant feed rate of 1 kg / h using a spiral feeder. 17.5 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 56°C (close to the boiling point of silicon tetrachloride, 57.6°C). To deliver the gaseous silicon tetrachloride to the boiling furnace, 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator. The silicon tetrachloride feed rate was controlled at 3.5 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring impeller of the stirred boiling furnace was set to 120 rpm. The boiling furnace was maintained at a positive pressure of 1,800 Pa, and a solenoid valve located in the chimney automatically opened when the pressure was higher than this positive pressure. The product was continuously discharged from the bottom of the boiling furnace in a spiral. After 3 hours of reaction with continuous feeding, discharge was initiated, yielding a dark yellow-green powder containing a small amount of magnesium chloride. The product was nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, with silicon nanowires having a diameter of approximately 70 nm and a length of approximately 1 μm. X-ray diffraction spectra indicated that the powder was crystalline silicon. A small amount of carbon as core particles was not detected due to the sensitivity limit of the X-ray diffractometer due to its small amount. The carbon content was measured using a carbon analyzer and found to be 1.77%. The prepared agglomerate powder was measured using a laser particle size analyzer and found to have the following particle size distribution: D10 = 4.5 μm, D50 = 9.1 μm, D90 = 12.0 μm.

[0064] The powder was sprayed with a propyl zirconate / starch dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 700°C. The temperature was then maintained for 4 hours to ensure that the small amount of magnesium chloride was completely removed by evacuation. During this time, the propyl zirconate decomposed into zirconium dioxide, and the starch decomposed into carbon. The zirconium dioxide and carbon were coated over the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of the surface-coating zirconium dioxide and carbon and the inner core carbon particles were 1.0%, 1.1%, and 1.73%, respectively.

[0065] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were stirred with the addition of N-methylpyrrolidone to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm and was vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 minutes in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. Figure 12 shows the initial charge / discharge curves of the button cell prepared in Example 5. The nanosilicon agglomerate composite anode material prepared in Example 5 had an initial discharge capacity per gram of 2,806.8 mAh / g and an initial coulombic efficiency of 85.1%. The button cell was subjected to 120 1C charge-discharge cycles. The charge capacity did not decay.

[0066] Example 6 Five kilograms of 200-mesh magnesium powder with a carbon content of 1.6% was taken, and the temperature of the stirred boiling furnace was set to 950°C. The carbon-containing magnesium powder was fed into the boiling furnace at a constant feed rate of 1 kg / h using a spiral feeder. 17.5 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 56°C (close to the boiling point of silicon tetrachloride, 57.6°C). To deliver the gaseous silicon tetrachloride to the boiling furnace, 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator. The silicon tetrachloride feed rate was controlled at 3.5 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring impeller of the stirred boiling furnace was set to 200 rpm. The boiling furnace was maintained at a positive pressure of 1,800 Pa, and a solenoid valve located in the chimney automatically opened when the pressure was higher than this positive pressure. The product was continuously discharged from the bottom of the boiling furnace in a spiral. After 3 hours of reaction with continuous feeding, discharge was initiated, yielding a dark yellow-green powder containing a small amount of magnesium chloride. The resulting nanosilicon agglomerates had a three-dimensional network structure resembling pine needles and branches, with silicon nanowires measuring approximately 50 nm in diameter and approximately 0.5 μm in length. X-ray diffraction spectra indicated that the powder was crystalline silicon. A small amount of carbon as core particles was not detected due to the sensitivity limit of the X-ray diffractometer due to its small amount. The carbon content was measured using a carbon analyzer and found to be 2.8%. The prepared agglomerate powder was measured using a laser particle size analyzer and found to have the following particle size distribution: D10 = 4.1 μm, D50 = 8.9 μm, and D90 = 11.7 μm.

[0067] The powder was sprayed with a dispersion of propyl zirconate, butyl titanate, and starch in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 700°C. The temperature was then maintained for 4 hours to ensure that the small amount of magnesium chloride was completely removed by evacuation. During this time, the propyl zirconate decomposed into zirconium dioxide, the butyl titanate decomposed into titanium dioxide, and the starch decomposed into carbon. The zirconium dioxide, titanium dioxide, and carbon were coated on the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of the surface-coating zirconium dioxide, titanium dioxide, and carbon, and the inner core carbon particles were 1.6%, 1.4%, 1.0%, and 2.7%, respectively.

[0068] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was then vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 min in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. The button cell had an initial discharge capacity per gram of 2,602.6 mAh / g and an initial coulombic efficiency of 85.0%. The button cell had good cycling performance and no capacity fade phenomenon occurred after the first 100 cycles.

[0069] Example 7 Ten kilograms of 99.9% pure 100-mesh zinc powder was added to 10 L of 0.05 M silver nitrate solution, stirred at 10°C for 15 minutes, and allowed to stand for 0.5 hours. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce zinc powder with a partial silver coating on its surface. The silver content was 0.54 wt%. The temperature of the stirred boiling furnace was set to 500°C. The silver-coated zinc powder prepared above was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the stirred boiling furnace was set to 20 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge began, yielding a dark yellow-green powder containing a small amount of zinc chloride. Measurement revealed that the powder was composed of micron-sized agglomerates of silicon nanowires with a three-dimensional network structure resembling pine needles and branches. The silicon nanowires had a diameter of approximately 150 nm and a length of approximately 2 μm. The powder had the following particle size distribution: D10 = 7.5 μm, D50 = 13.8 μm, and D90 = 19.5 μm.

[0070] The powder was sprayed with a butyl titanate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 700°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl titanate decomposed into titanium dioxide, and the carboxymethyl cellulose decomposed into carbon. The titanium dioxide and carbon were then coated onto the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of titanium dioxide and carbon for the surface coating and the inner core silver particles were 2.5%, 4.5%, and 2.4%, respectively.

[0071] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was then vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 min in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. The button cell had an initial discharge capacity per gram of 2,853.2 mAh / g and an initial coulombic efficiency of 86.9%. The button cell was subjected to 80 1C charge-discharge cycles, with little decay in charge capacity.

[0072] Example 8 Ten kilograms of 99.9% pure 100-mesh zinc powder was added to 10 L of 0.05 M ferrous sulfate solution, stirred at 2°C for 20 minutes, and then allowed to stand for 1 hour. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce zinc powder with a partial iron coating on its surface. The iron content was 0.28 wt%. The temperature of the stirred boiling furnace was set to 650°C. The iron-coated zinc powder prepared above was fed into the boiling furnace at a constant rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the stirring boiling furnace was set to 100 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge was initiated, yielding a dark yellow-green powder containing a small amount of zinc chloride. SEM images showed that the dark yellow-green powder was micron-sized agglomerates of silicon nanowires with a three-dimensional network structure resembling pine needles and branches. The silicon nanowires had a diameter of approximately 90 nm and a length of approximately 1 μm. The prepared agglomerate powder had the following particle size distribution: D10 = 5.2 μm, D50 = 9.5 μm, and D90 = 12.3 μm.

[0073] The powder was sprayed with a butyl zirconate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 750°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl zirconate decomposed into zirconium dioxide, and the carboxymethyl cellulose decomposed into carbon. The zirconium dioxide and carbon were coated over the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of the surface-coating zirconium dioxide and carbon, and the inner core iron particles, were 1.2%, 1.5%, and 1.2%, respectively.

[0074] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was then vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 min in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. The nanosilicon agglomerate composite anode material prepared in Example 8 had an initial discharge capacity per gram of 2,732 mAh / g and an initial coulombic efficiency of 86.3%. The button cell was subjected to 100 1C charge-discharge cycles, with a capacity retention rate of 97.5%.

[0075] Example 9 Ten kilograms of 99.9% pure 100-mesh zinc powder was added to 10 L of a 0.05 M nickel sulfate and 0.05 M cobalt sulfate mixture, stirred at 1°C for 20 minutes, and then allowed to stand for 1 hour. The material at the bottom was then removed, centrifuged, dried, and then vacuum-dried at 80°C to produce zinc powder partially coated with nickel and cobalt. The nickel content was 0.29 wt% and the cobalt content was 0.29 wt%. The temperature of the stirred boiling furnace was set to 650°C. The nickel- and cobalt-coated zinc powder prepared above was fed into the boiling furnace at a constant rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to 55°C (which is close to the boiling point of silicon tetrachloride, 57.6°C). To deliver gaseous silicon tetrachloride to the boiling furnace, 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator. The silicon tetrachloride supply rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring blade of the boiling furnace was set to 100 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. After 3 hours of reaction with continuous supply, discharge began, yielding a dark yellow-green powder containing a small amount of zinc chloride. SEM images showed that the dark yellow-green powder consisted of micron-sized agglomerates of silicon nanowires with a three-dimensional network structure resembling pine needles and branches. The silicon nanowires had a diameter of approximately 100 nm and a length of approximately 1 μm. The prepared agglomerate powder had the following particle size distribution: D10=5.1 μm, D50=9.3 μm, D90=12.1 μm.

[0076] The powder was sprayed with a butyl zirconate / carboxymethyl cellulose dispersion in ethanol, dried by baking in a vacuum, and then placed in a vacuum furnace. The furnace was filled with high-purity argon gas, heated to 500°C, evacuated to 100 Pa, and further heated to 750°C. The temperature was then maintained for 4 hours to ensure that the small amount of zinc chloride was completely removed by evacuation. During this time, the butyl zirconate decomposed into zirconium dioxide, and the carboxymethyl cellulose decomposed into carbon. The zirconium dioxide and carbon were coated over the entire nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, resulting in the fabrication of a composite anode material. The amounts of the surface-coating zirconium dioxide and carbon, and the inner core nickel and cobalt particles, were 1.2%, 1.5%, 1.3%, and 1.3%, respectively.

[0077] 0.4 g of SuperP conductive carbon powder, 15 g of polyamic acid binder (14.2% solids), 27 g of carbon nanotube / graphene mixed slurry (5.6% solids), and 15 g of the composite anode material prepared above were mixed with N-methylpyrrolidone and stirred to obtain a uniform slurry with a viscosity of 3,800 mPa·s. The slurry was coated onto a 10 μm-thick copper foil. The resulting coating had a wet thickness of 150 μm. It was then vacuum-dried by baking at 100 °C, rolled, and subjected to imidization at 290 °C for 30 min in an argon atmosphere. Next, a CR2032 button cell was fabricated using metallic lithium as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 / EC+DEC as the electrolyte, and its electrochemical properties were evaluated. The nanosilicon agglomerate composite anode material prepared in Example 9 had an initial discharge capacity per gram of 2,673 mAh / g and an initial coulombic efficiency of 86.4%. The button cell was subjected to 100 1C charge-discharge cycles, with a capacity retention rate of 98.2%.

[0078] Comparative Example 1 Ten kilograms of 99.9% pure 200-mesh zinc powder was taken, and the temperature of the stirred boiling furnace was set to 550°C. The zinc powder was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). To deliver the gaseous silicon tetrachloride to the boiling furnace, 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring impeller of the stirred boiling furnace was set to 60 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure was higher than this positive pressure, a solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. The reaction was carried out for 3 hours with continuous feeding, and then discharge was initiated. No powder was discharged throughout the experiment. After opening the apparatus, some deposits were found on the inner walls of the stainless steel muffle tank, the stirring blade, and the stirring shaft of the stirred boiling furnace. Some of the deposits were scraped off and were yellow in color. SEM observation (see Figure 13) revealed that the deposits were nanosilicon powder and a small amount of nanowires. The silicon nanowires were loose, and no three-dimensional network nanosilicon agglomerates were formed, resulting in a very low yield of silicon nanowires.

[0079] Compared to Example 1, Comparative Example 1 shows no silver generated on the surface of the zinc powder through a substitution reaction. In Example 1, ultrafine, highly dispersed silver particles were stirred and suspended in a stirred boiling furnace along with the zinc particles. After the zinc rapidly evaporated, the ultrafine silver particles in the gas phase became a nucleating agent for silicon. High-speed rotation and dynamic growth resulted in the formation of nano-silicon agglomerates with a three-dimensional network structure resembling pine needles and branches. However, in Comparative Example 1, no such nucleating agent was present, and only a small portion of the silicon grew on the inner walls, stirring blades, and stirring shaft of the reactor. The majority of the silicon failed to grow in time and was expelled from the chimney.

[0080] Comparative Example 2 Ten kilograms of 99.9% pure 200-mesh zinc powder was mixed with 54 g of silver powder with a particle size of 60 nm. The silver content of the mixed powder was 0.54 wt %. The temperature of the stirred boiling furnace was set to 550°C. The zinc powder was fed into the boiling furnace at a constant feed rate of 2 kg / h using a spiral feeder. 13 kg of analytically pure silicon tetrachloride was added to the silicon tetrachloride evaporator, and the evaporator was heated in a water bath set to a temperature of 55°C (close to the boiling point of silicon tetrachloride, 57.6°C). 99.995% high-purity argon gas was supplied to the silicon tetrachloride evaporator to deliver the gaseous silicon tetrachloride to the boiling furnace. The silicon tetrachloride feed rate was controlled at 2.6 kg / h by adjusting the flow rate of the carrier argon gas. The rotation speed of the stirring boiling furnace's agitator blade was set to 60 rpm. The boiling furnace was maintained at a positive pressure of 1,500 Pa, and when the pressure exceeded this positive pressure, the solenoid valve located on the chimney automatically opened. The product was continuously discharged from the bottom of the boiling furnace in a spiral pattern. The reaction was carried out with continuous supply for 3 hours, after which discharge was initiated. Almost no powder was discharged throughout the experiment. The discharge volume was 1 / 10 of that in Example 1. SEM observation revealed that the powder contained silver powder and silicon nanowires, but no silicon nanowire clusters were formed. After opening the apparatus, some deposits were found on the stainless steel muffle tank, stirring blade, and inner wall of the stirring boiling furnace stirring shaft. Some of the deposits were scraped off and turned yellow. SEM observation (see Figure 14) revealed that the deposits were nanosilicon powder and a small amount of nanowires. The silicon nanowires were loose, and no three-dimensional network nanosilicon agglomerates were formed. The yield of silicon nanowires was very low.

[0081] Compared with Example 1, the raw material of Comparative Example 2 contained the same mass of silver. However, in Example 1, 54 g of silver was generated on the surface of 10 kg of zinc powder through a substitution reaction, and this 54 g of silver was highly dispersed on the surface of the 10 kg of zinc powder. In contrast, in Comparative Example 2, 54 g of nanosilver powder was added to 10 kg of zinc powder by conventional mixing, and the dispersion state of the silver was significantly inferior to that of Example 1. The amount of nanosilver used as a nucleating agent in Comparative Example 2 was low. However, because silver particles are heavy, they are difficult to stir and suspend within the reactor space, making them ineffective as a nucleating agent for silicon growth.

Claims

1. A nanosilicon agglomerate composite anode material comprising: nano-sized core particles; nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches growing around the nano-sized core particles; and a composite coating layer covering the nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches, wherein the nano-sized core particles comprise metal particles and / or carbon particles, the nanosilicon agglomerates with a three-dimensional network structure resembling pine needles and branches are formed by interconnected silicon nanowires with a diameter of 50 to 150 nm and a length of 0.5 to 2 μm, the composite coating layer comprises conductive carbon and an inorganic metal oxide, and the nano-sized core particles are a nucleating agent.

2. 10. The nanosilicon agglomerate composite anode material of claim 1, wherein the metal particles are particles of at least one type selected from the group consisting of silver, copper, iron, nickel, and cobalt.

3. 3. The nanosilicon agglomerate composite anode material of claim 1 or 2, wherein the inorganic metal oxide comprises titanium dioxide and / or zirconium dioxide.

4. 3. The nanosilicon agglomerate composite anode material of claim 1, wherein the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates are present in an amount of 90.6 to 96.17 wt % based on the weight of the nanosilicon agglomerate composite anode material.

5. 3. The nanosilicon agglomerate composite anode material of claim 1, wherein the nano-sized core particles are present in an amount of 1.4 to 3.3 wt %, the metal particles are present in an amount of 0 to 2.6 wt %, and the carbon particles are present in an amount of 0 to 2.7 wt %, based on the weight of the nanosilicon agglomerate composite anode material.

6. 3. The nanosilicon agglomerate composite anode material of claim 1, wherein the composite coating layer is present in an amount of 2.1 to 7.0 wt %, the conductive carbon is present in an amount of 1.0 to 4.5 wt %, and the inorganic metal oxide is present in an amount of 1.0 to 3.0 wt %, based on the weight of the nanosilicon agglomerate composite anode material.

7. 3. The nanosilicon agglomerate composite anode material of claim 1 or 2, wherein the nanosilicon agglomerate composite anode material has an average particle size of 5-20 μm.

8. 1. A method for preparing a nanosilicon agglomerate composite anode material, comprising: (1) carrying out a surface metal substitution reaction by placing a powder of metal A in a salt solution of metal B to generate nano-sized metal B particles on a portion of the surface of the powder of metal A to form a composite powder; (2) continuously feeding the composite powder, which acts as a reactant and a nucleating agent, into a reaction chamber; (3) SiCl ４ delivering a gas into the reaction chamber along with an inert gas or nitrogen; (4) performing a high temperature reaction with continuous stirring by setting the temperature of the reaction chamber at 500-950°C, the reaction causing nanosilicon agglomerates with a pine needle and branch-like three-dimensional network structure to dynamically grow and wrap around the nano-sized metal B particles; (5) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates discharged from the reaction chamber to vacuum heat treatment; (6) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon aggregates obtained in step (5) to a composite coating treatment using conductive carbon and inorganic metal oxide; A method comprising:

9. 9. The method of claim 8, wherein in step (1), the surface metal substitution reaction is carried out by placing an alloy powder containing metal A and carbon into a salt solution of metal B, and the nano-sized metal B particles are generated on a portion of the surface of the alloy powder to form a composite powder; and in step (4), the reaction causes the pine needle and branch-like three-dimensional network structured nano-silicon agglomerates to dynamically grow and wrap around the nano-sized carbon particles and the nano-sized metal B particles generated by the alloy powder.

10. 10. The method according to claim 8 or 9, wherein the metal A is at least one selected from the group consisting of magnesium and zinc, and the metal B is at least one selected from the group consisting of silver, copper, iron, nickel, and cobalt.

11. 10. The method of claim 8 or 9, wherein the inorganic metal oxide comprises titanium dioxide and / or zirconium dioxide.

12. 10. The method of claim 8 or 9, wherein the vacuum heat treatment in step (5) and the composite coating treatment in step (6) are performed simultaneously.

13. 1. A method for preparing a nanosilicon agglomerate composite anode material, comprising: (1) continuously introducing an alloy powder containing metal A and carbon, which serves as a reactant and a nucleating agent, into a reaction chamber; (2) SiCl ４ delivering a gas into the reaction chamber along with an inert gas or nitrogen; (3) carrying out a high temperature reaction with continuous stirring by setting the temperature of the reaction chamber at 500-950°C, the reaction causing nano silicon agglomerates with pine needle and branch-like three-dimensional network structure to dynamically grow and wrap around the nano-sized carbon particles produced by the alloy powder; (4) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon agglomerates discharged from the reaction chamber to vacuum heat treatment; (5) subjecting the pine needle and branch-like three-dimensional network structure nanosilicon aggregates obtained in step (4) to a composite coating treatment using conductive carbon and inorganic metal oxide; A method comprising:

14. The method according to claim 13, wherein the metal A is at least one selected from the group consisting of magnesium and zinc.

15. 15. The method of claim 13 or 14, wherein the inorganic metal oxide comprises titanium dioxide and / or zirconium dioxide.

16. 15. The method of claim 13 or 14, wherein the vacuum heat treatment in step (4) and the composite coating treatment in step (5) are performed simultaneously.

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