Silicon anode material for lithium-ion secondary battery, comprising granular porous silicon composite with controlled porosity

Abstract

The present invention relates to a silicon anode material for a lithium-ion secondary battery, comprising a granular porous silicon composite formed by the agglomeration of silicon composites, wherein the silicon composite is a flake-shaped silicon composite in which a composite layer, which comprises an oxide layer and a carbon-containing layer, is formed on flake-shaped silicon obtained from waste silicon kerf. A silicon anode material for a lithium-ion secondary battery, comprising the porous silicon composite, and an anode and a lithium-ion secondary battery, which comprise same, can be provided. If composited with graphite, the silicon anode material exhibits excellent packing density, allows more lithium to be charged per unit volume, and uses waste silicon kerf so as to have superior economic feasibility.

Description

Silicon anode material for lithium-ion secondary batteries comprising a granular porous silicon composite with controlled porosity

[0001] The present invention relates to a silicon-containing negative electrode material for a lithium-ion secondary battery and a lithium-ion secondary battery including the same, and more specifically, to a silicon-containing negative electrode material including a granular porous silicon composite formed by agglomerating plate-like silicon composites, wherein the plate-like silicon composite has an oxide layer, a silicon carbide layer, and a carbon coating layer formed on plate-like silicon particles, and wherein the porosity of the granular porous silicon composite is controlled to provide a silicon negative electrode material for a lithium-ion secondary battery having excellent charge capacity and lifespan, and a lithium-ion secondary battery including the same.

[0002]

[0003] Graphite is a representative anode material for lithium-ion secondary batteries. It has a layered structure and a mechanism for lithium ion insertion and charging between layers. Graphite-based anode materials have a theoretical capacity of 372 mAh / g, but in practice, they exhibit a capacity of 360 mAh / g. With the growing demand for higher capacities, research and development is actively underway to develop materials with higher capacities than graphite-based anode materials.

[0004] Among the materials with higher capacity than graphite, silicon (Si)-based anode materials have a theoretical capacity of 4200 mAh / g, which is more than 10 times that of graphite, and silicon anode materials are attracting attention as a major material that can replace graphite anode materials. However, silicon anode materials have a short lifespan. This is because during the charge and discharge process, in which four lithium ions bind to and then leave one silicon cell, a volume change of up to 300% occurs, and cracks occur in the parts of the silicon that cannot return to their original state after the volume expansion. Moreover, during this process, they separate into fine nanoparticles, which cuts off the electrical connection with the electrolyte or electrolytic solution, making it impossible to recharge lithium.

[0005] These problems with silicon anode materials are widely known, and active research and development is underway to suppress cracking that occurs in silicon anode materials during charge and discharge. For example, Korean Patent No. 2476118 discloses a technology for increasing cycle life by creating nanoscale fine silicon particles, and Korean Patent No. 2019-0083613 discloses a technology for improving the lifespan of silicon anode materials by coating porous silicon clusters with amorphous carbon.

[0006] However, despite the progress in technological development, the amount of silicon anode material used in the anode of lithium-ion secondary batteries is still small, and silicon anode material technology that can replace the majority of graphite anode materials is still in demand worldwide.

[0007]

[0008] The present invention aims to provide a granular porous silicon composite formed by agglomeration of plate-like silicon composites in order to solve the problems of silicon-based negative electrode materials, and specifically, by forming an oxide layer, a silicon carbide layer, and a carbon coating layer on plate-like silicon particles obtained from a silicon kerf and controlling the porosity of the granular porous silicon composite in which the plate-like silicon composite is agglomerated, a silicon negative electrode material having significantly improved filling rate and lifespan can be provided, and the silicon-based negative electrode material of the present invention is also excellent in commerciality and economic feasibility.

[0009] The present invention provides a silicon anode material for a lithium ion secondary battery, which comprises a granular porous silicon composite formed by agglomerating plate-like silicon composites, wherein the plate-like silicon composite comprises polycrystalline plate-like silicon particles formed by a waste silicon kerf, an oxide layer formed by oxidizing the surface of the polycrystalline plate-like silicon particles, a silicon carbide layer formed on the outer surface of the oxide layer, and a carbon coating layer formed by coating the silicon carbide layer with conductive carbon so as to surround the silicon carbide layer, and the silicon carbide layer is a silicon carbide layer formed by supplying hydrocarbon gas to the silicon oxide layer and heating it.

[0010] In the silicon anode material of the present invention, a carbon coating layer can be provided, which is a silicon anode material for a lithium ion secondary battery, in which a pyrolysis carbon formed by heating hydrocarbon gas covers the outer shell of a silicon carbide layer.

[0011] In the silicon anode material of the present invention, the porosity of the granular porous silicon composite may be 15 to 50%.

[0012] In the silicon anode material of the present invention, the plate-shaped silicon may have an average thickness of 10 to 200 nm and an average length of 10 μm or less.

[0013] In the silicon anode material of the present invention, the oxide layer may have an average thickness of 2 to 10 nm.

[0014] In the silicon anode material of the present invention, the silicon carbide layer may have an average thickness of 1 to 5 nm.

[0015] In the silicon anode material of the present invention, the silicon carbide layer can be formed by replacing some of the oxygen in the oxide layer with carbon.

[0016] In the silicon negative electrode material of the present invention, the carbon coating layer may have an average thickness of 1 to 10 nm.

[0017] The silicon anode material of the present invention may further include graphite.

[0018] The present invention can provide a negative electrode including a silicon negative electrode material according to the present invention.

[0019] The present invention can provide a lithium ion secondary battery including a negative electrode according to the present invention.

[0020] The silicon anode material for a lithium ion secondary battery of the present invention is a granular porous silicon composite manufactured by agglomerating a silicon composite having an oxide layer, a silicon carbide layer, and a carbon coating layer formed on polycrystalline plate silicon formed with a waste silicon kerf, and the porosity of the porous structure is controlled to provide an excellent filling rate when composited with graphite, and more lithium can be charged based on the same volume, and the cost-effectiveness is also excellent by using a waste silicon kerf.

[0021]

[0022] FIG. 1 is an SEM photograph of plate-shaped silicon used in the manufacture of a silicon negative electrode material for a lithium-ion secondary battery according to an embodiment of the present invention.

[0023] Figure 2 is an exemplary diagram showing an oxide layer formed on a plate-shaped silicon particle according to an embodiment of the present invention.

[0024] Figure 3 is an exemplary drawing showing a silicon carbide layer formed on a plate-shaped silicon particle having an oxide layer formed in Figure 2.

[0025] Figure 4 is an exemplary drawing showing the appearance of a plate-shaped silicon composite in which a carbon layer is formed on the silicon particles of Figure 3.

[0026] Figure 5 is a TEM image of plate-like silicon particles from which carbon has been removed from the plate-like silicon composite.

[0027] Figure 6 is a flow chart schematically showing a method for manufacturing a silicon negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention.

[0028] Figure 7 shows a granular porous silicon composite and a cross-sectional photograph thereof according to an embodiment of the present invention.

[0029] FIG. 8 is an image analysis photograph showing the porosity of a granular porous silicon composite in a granular porous plate-shaped silicon composite according to an embodiment of the present invention. ((A): Example 1, porosity 18% / (B): Example 2, porosity 34%)

[0030] FIG. 9 is an image analysis photograph showing the porosity of a granular porous plate-shaped silicon composite according to a comparative example of the present invention. ((A): Comparative Example 1, porosity 10% / (B): Comparative Example 2, porosity 53%)

[0031]

[0032] The following description of the present invention with reference to the drawings is not limited to specific embodiments, and various modifications and embodiments may be made. Furthermore, the following description should be understood to encompass all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0033] In the following description, terms such as first, second, etc. are used to describe various components, and are not limited in meaning in themselves, but are used only for the purpose of distinguishing one component from another.

[0034] Like reference numbers used throughout this specification represent like components.

[0035] As used herein, singular expressions include plural expressions unless the context clearly dictates otherwise. In addition, terms such as "comprise," "include," or "have" used herein should be interpreted to indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood to not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0036]

[0037] The present invention relates to a silicon anode material for a lithium ion secondary battery, comprising a granular porous silicon composite formed by agglomerating plate-like silicon composites, wherein the porous silicon composite has a controlled porosity, and the plate-like silicon composite is a plate-like silicon composite in which a composite layer including an oxide layer, a silicon carbide layer, and a carbon coating layer is formed on plate-like silicon obtained from waste silicon kerf. The present invention can provide a silicon anode material for a lithium ion secondary battery comprising a granular porous silicon composite, and an anode and a lithium ion secondary battery comprising the same.

[0038]

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached FIGS. 1 to 9.

[0040] The present invention relates to a cathode material comprising a granular porous silicon composite formed by agglomerating plate-like silicon composites. The plate-like silicon composite forming the granular porous silicon composite will first be described.

[0041] FIG. 4 is an exemplary view showing the appearance of a plate-shaped silicon composite (1) of a silicon anode material for a lithium ion secondary battery according to an embodiment of the present invention, FIG. 1 is an SEM photograph of plate-shaped silicon used in the manufacture of a silicon anode material for a lithium ion secondary battery according to an embodiment of the present invention, FIG. 2 is an exemplary view showing the appearance of an oxide layer formed on the plate-shaped silicon particle of FIG. 1, and FIG. 3 is an exemplary view of plate-shaped silicon particles in which a silicon carbide layer is formed on the oxide layer of FIG. 2.

[0042] Figure 5 is a TEM photograph of the plate-shaped silicon on which the silicon carbide layer of Figure 3 is formed.

[0043] The present invention relates to a silicon anode material having a low unit price using plate-shaped silicon formed by a silicon kerf and having an excellent filling rate by being composited with plate-shaped graphite.

[0044] The waste silicon kerf used in the present invention is generated during the process of thinly slicing a lump of metallic silicon to obtain silicon wafers in the solar cell or semiconductor industry. Here, the waste silicon kerf is high-purity silicon with a purity of 99.9999999% to 99.999999999% used in the solar cell or semiconductor industry, and is separated into a nano-thick plate-like material using a wire-shaped saw. This high-purity plate-like silicon is a good candidate for an anode active material for lithium secondary batteries.

[0045] Referring to FIG. 4, a silicon negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention may include a plate-shaped silicon composite (1).

[0046] The above-mentioned plate-shaped silicon composite (1) is manufactured from plate-shaped silicon formed by a silicon kerf, and may include polycrystalline plate-shaped silicon particles (10), an oxide layer (11), and a silicon carbide layer (12).

[0047] The polycrystalline plate silicon (10) used here may be a powder formed in a plate shape, as shown in Fig. 1, and may be formed from waste silicon kerf (cutting fines) generated during the process of thinly slicing a silicon ingot for solar cells or semiconductors.

[0048] There are three or four general methods for cutting silicon ingots, all of which involve sorting, washing, precipitation, and drying steps to produce a waste silicon kerf. To obtain a waste silicon kerf with a high thickness uniformity, it is preferable to use one made using a diamond wire saw, but this is not a limitation.

[0049] Specifically, a diamond wire saw is a method of cutting a silicon ingot using water or diethylene glycol as a lubricant by randomly embedding diamond particles on the surface of a carbon steel wire called piano wire, which is approximately 50㎛ in diameter. The silicon cutting fines generated during this process are suitable as a raw material for the polycrystalline plate silicon (10) of the present invention.

[0050] Here, if the average thickness of the polycrystalline plate silicon (10) is less than 10 nm, the loss during formation of the oxide layer (11) is so great that the initial capacity may not even be 30% of that before processing, which may significantly reduce economic feasibility. In addition, if the average thickness exceeds 200 nm, the ratio of the central silicon layer may be high at 80% or more, which may significantly reduce the performance improvement effect.

[0051] In addition, when the average length of the polycrystalline plate-like silicon (10) exceeds 10 ㎛, when mixed with graphite, a large amount of empty space is formed between the particles of the graphite and plate-like silicon composite (1), so that the porosity in the same space increases and the filling rate decreases, and the discharge capacity in the same volume may drop significantly.

[0052] Polycrystalline plate silicon (10) is subjected to strong force during the cutting process, causing the silicon to break off from the single crystal into a plate shape, which causes it to warp and curl, and can be made into a form in which many fine crystal grains are weakly attached. Accordingly, polycrystalline plate silicon (10) can be made into a state more suitable for use as a negative electrode material through a pulverization pretreatment.

[0053] Meanwhile, the polycrystalline plate silicon (10) can be pretreated, for example, by wet grinding and drying. Through the pretreatment, the thickness and particle size distribution of the polycrystalline plate silicon (10) can be controlled to fall within the scope of the present invention.

[0054] At this time, the wet milling method for polycrystalline plate silicon (10) may be a bead mill (ball mill), ultrasonic dispersion, or high-pressure homogenizer dispersion method.

[0055] First, the bead mill method is a method in which polycrystalline plate silicon (10) is mixed in water or an organic solvent in a range of 5 to 30 wt%, and then rotated together with zirconia or alumina beads in a zirconia or alumina container to crush the beads by frictional force and impact force between the balls. It is preferable that the bead mill use beads with a diameter of 0.1 to 3 mm and rotate at 1,000 to 5,000 rpm based on a container diameter of 100 mm for crushing.

[0056] When using a bead mill, if the diameter of the beads is less than 0.1 mm, the impact force may be weak and crushing may be almost impossible. If it is more than 3 mm, the number of beads may be too small and the probability of collision with the polycrystalline plate silicon (10) may be reduced, which may unnecessarily lengthen the crushing time.

[0057] In addition, if the rotation speed is less than 1,000 rpm, the energy required for crushing may be insufficient due to low energy, and crushing may not occur at all. If it exceeds 5,000 rpm, excessive high energy may cause bead wear and may mix with plate silicon as impurities.

[0058] The ultrasonic dispersion method is a method of applying ultrasonic vibration to a solution by attaching an amplifying horn and a vibrating horn to an ultrasonic vibrator to disperse or destroy grains in the solution. It is preferable to process plate-shaped silicon (10) under the conditions of a frequency of 20 to 35 KHz, an amplitude of 20 to 200 μm, and a vibrator power consumption of 200 W or more for ultrasonic dispersion. In addition, ultrasonic dispersion is possible by mixing plate-shaped silicon (10) in water or an organic solvent in a range of 30 wt% or less, and then passing the mixture through a path in which multiple vibrators are arranged in a row to receive ultrasonic vibrations from multiple vibrators, thereby crushing the grains.

[0059] At this time, if the vibrator power consumption is less than 200W, the energy consumption may be too low to achieve significant shredding. Furthermore, if the frequency is below 20kHz, operation may be difficult due to the inability to exceed the audible frequency. If the frequency exceeds 35kHz, the durability of the vibrator and vibration generator will be reduced, with no effect on shredding or improving the working environment.

[0060] In addition, when polycrystalline plate silicon (10) is mixed in water or an organic solvent in an amount exceeding 30 wt%, the viscosity may become too high and the transmission range of ultrasonic vibration may not be wide.

[0061] A high-pressure homogenizer is a device that disperses or destroys powder in a solution by applying pressure using a pump to force the solution through micro-nozzles in opposite directions. There are also methods for using high-pressure homogenizers that combine collisions, such as a method of colliding the solution with a diamond plate after passing through a micro-nozzle, or a method of colliding the solution with each other by passing the nozzles in both directions. In the present invention, it is preferable to use a method in which polycrystalline plate-shaped silicon (10) is mixed in water or an organic solvent in an amount of 30 wt% or less, and then pressurized to 500 bar or more to pass through micro-nozzles of 50 to 200 μm and collide with a diamond plate or with each other by passing the solution through a micro-nozzle.

[0062] At this time, if polycrystalline plate silicon (10) is mixed in water or an organic solvent in an amount exceeding 30 wt%, the viscosity may become too high, making it difficult to inject into a fine nozzle. In addition, if the pressure is less than 500 bar, the collision energy may become weak, making crushing almost impossible.

[0063] In addition, if the micro nozzle diameter is less than 50㎛, nozzle clogging may occur frequently, making process operation difficult, and if it exceeds 200㎛, the collision energy may be too weak, resulting in almost no crushing.

[0064] In addition, it is preferable that the plate-shaped silicon particles obtained from one of the above bead mills, dispersers and homogenizers are recovered in a dried powder state.

[0065] At this time, various devices with moisture and organic solvent vaporization functions can be used as drying devices, but it is preferable to use a spray dryer or disk dryer.

[0066] Here, the spray dryer is a device that spreads a dispersion solution containing crushed plate-shaped polycrystalline silicon particles (10) into the air through a spray nozzle or a rotating disk nozzle (Atomizer) and injects a heated gas to rotate around the nozzle to dry the solution in a scattered state. This device has the advantage of being able to obtain a dry powder with a low apparent density, but has poor thermal efficiency.

[0067] A disk dryer has high thermal efficiency, and is a method of drying by dropping a dispersion solution containing crushed polycrystalline plate-shaped silicon particles (10) little by little onto a heated rotating disk, and then scraping the crushed and dried plate-shaped polycrystalline silicon particles (10), which are the dried residue, with a ceramic knife to recover them. Although a disk dryer has high thermal efficiency, it has the disadvantage of recovering powder with a high apparent density.

[0068] Through the above pretreatment process, the polycrystalline plate-shaped silicon particles (10) that have been crushed and dried have the moisture and lubricant in the waste silicon cuff removed, but in order to facilitate reaction with gas in the post-process, the polycrystalline plate-shaped silicon particles (10) can be crushed to form spaces between the particles.

[0069] The crushed and dried polycrystalline plate-shaped silicon particles (10) have an apparent density of 1 to 2 g / cm3, and by crushing them at 3,000 rpm in air, polycrystalline plate-shaped silicon particles (10) having an apparent density of 0.1 to 0.4 g / cm3 can be obtained.

[0070] The average distance between the particles of the crushed polycrystalline plate-shaped silicon particles (10) can be increased by 3 to 10 times compared to the crushed and dried polycrystalline plate-shaped silicon particles (10).

[0071] In this way, by using polycrystalline plate silicon (10) in the form of crushed polycrystalline plate silicon particles (10) instead of using it as is, the oxide layer (11) can be formed more uniformly.

[0072] Referring to FIG. 2, the oxide layer (11) can be formed by oxidizing the surface of polycrystalline plate-shaped silicon particles (10).

[0073] This oxide layer (11) is formed to solve the problem that silicon fragmentation occurs quickly due to rapid charging and discharging, although the polycrystalline plate-shaped silicon particles (10) have a high surface area of ​​10 m2 / g or more, which ensures a high charge / discharge speed and a large contact area with the electrolyte or electrolyte, and can reduce the charge / discharge speed.

[0074] Specifically, the oxide layer (11) is formed by further oxidizing the natural oxide layer that is naturally formed on the surface of the polycrystalline plate-shaped silicon particles (10), and can be said to be formed thicker than the natural oxide layer.

[0075] At this time, the oxide layer (11) is formed in an amorphous state, and when lithium approaches the oxide layer (11), lithium fills the gaps of the oxide layer (11), and an electrically conductive line penetrating the oxide layer (11) can be formed. Accordingly, the oxide layer (11) can allow lithium of the electrolyte or electrolyte to slowly diffuse into the polycrystalline plate-shaped silicon particles (10).

[0076] In this way, by lowering the bonding speed of lithium and polycrystalline plate-shaped silicon particles (10) through the oxide layer (11), the charge capacity is somewhat lower than that of conventional silicon, but the charge / discharge life can be dramatically increased.

[0077] Additionally, the oxide layer (11) may have an average thickness of 2 to 10 nm.

[0078] When the average thickness of the oxide layer (11) is less than 2 nm, a non-uniform oxide layer (11) in the form of dots may be formed on the surface of the polycrystalline plate-shaped silicon particles (10), and as a result, a large number of non-oxidized portions on the surface of the polycrystalline plate-shaped silicon particles (10) occur between the dot-shaped oxide layers (11), and thus the effect of the uniform oxide layer (11) cannot be exhibited. In other words, the life performance improvement effect may not be exhibited as desired.

[0079] In addition, if the oxide layer (11) exceeds 10 nm, the irreversible capacity, which is the main reason for the decrease in the initial discharge capacity, may increase significantly by more than 30%, which may lead to severe lithium consumption.

[0080] The oxide layer (11) can be formed thicker by further oxidizing the naturally formed natural oxide layer on the surface of the polycrystalline plate-shaped silicon particles (10).

[0081] The oxide layer (11) can be formed by injecting an oxidizing agent into polycrystalline plate-shaped silicon particles (10) using a rotary kiln and heating them to 700 to 1,100°C.

[0082] At this time, if the heating temperature is less than 700°C, the formation speed of the oxide layer (11) becomes too slow, and as the reaction time becomes excessively long, the oxide layer (11) may not be formed entirely or may be difficult to form to the desired thickness, and if it exceeds 1,100°C, the plate-shaped silicon particles (10) may be damaged by the excessive temperature or the process cost may increase unnecessarily, which may be inefficient.

[0083] Here, the oxidizing agent may be one or more of oxygen, water, and hydrogen peroxide, and the heating temperature may be controlled depending on the type of oxidizing agent.

[0084] Specifically, when hydrogen peroxide is used as an oxidizing agent, it can be heated to 700 to 1,100°C, and when oxygen is used as an oxidizing agent, it can be heated to 900 to 1,100°C.

[0085] Here, the rotary kiln uses a continuous heating furnace, so it has high thermal efficiency and can shorten the working time. The rotary kiln is composed of an inlet for feeding the material to be treated into the kiln body, a heat treatment section having a kiln body for heating, and a discharge section for discharging the heated material to be treated. Since the material to be treated is continuously mixed and moved in the rotary kiln, a uniform and thick oxide layer (11) is formed, and the difference in the ratio of the oxide layer (11) between particles can be reduced.

[0086] A silicon carbide layer (12) can be formed on the outer surface of the oxide layer (11) to surround the oxide layer (11). The oxide layer (11) is amorphous and forms a passage for lithium and electrons to move while increasing the irreversible capacity when combined with lithium, but the silicon carbide layer (12) can control the diffusion or movement speed of lithium while forming a passage for lithium and electrons while reducing the increase in irreversible capacity to less than 1 / 10 of the oxide layer. The life performance can be improved through the formation of the silicon carbide layer (12) on the outer surface of the oxide layer (11).

[0087] The thickness of the silicon carbide layer (12) may be 1 to 5 nm. If it is less than 1 nm, it is formed in an uneven dot shape, so the exposed area of ​​the oxide layer (11) is large, making it difficult to expect an improvement in life performance. If it is more than 5 nm, the discharge speed of lithium is greatly reduced compared to when there is no silicon carbide layer (12), which significantly reduces the high-speed charge / discharge performance.

[0088] The silicon carbide layer (12) can be formed by supplying hydrocarbon gas to the silicon oxide layer (11) and heating it. The silicon carbide layer (12) formed on the outer surface of the oxide layer (11) is formed by replacing two oxygen atoms of silicon oxide with one carbon atom from the outermost surface of the oxide layer (11). There are two possible methods for replacing silicon oxide with silicon carbide. One is to mix crystalline silicon oxide with pitch and heat it at 1200 to 1400 degrees for a long time to replace carbon with a stronger bond to silicon, and then burn the residual carbon. The other is to heat amorphous silicon oxide with pitch or another carbon source at 1000 degrees or more for a long time to replace oxygen attached to silicon with carbon with a stronger bond to silicon, and then burn the residual carbon.

[0089] In this technology, it was discovered that the outer shell of amorphous silicon oxide of 1 to 5 nm can be rapidly replaced even at a lower temperature when reacted with gasified carbon, and this was applied. When silicon particles (10) on which an oxide layer (11) of 2 to 20 nm in thickness is formed by the above oxidation process are passed through a kiln heated to 900 to 1100°C and hydrocarbon gas is flowed into the same reactor, the hydrocarbon is decomposed, causing carbon atoms to approach the oxide layer (11), and the outermost oxygen of the amorphous oxide layer (11) is replaced with carbon even at a relatively low temperature of 900°C. Due to the characteristics of the amorphous layer, carbon with a small atomic size can easily penetrate, so replacement is possible at a high speed up to a depth of 5 nm.

[0090] The hydrocarbon gases available at this time are C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H 10 (Butane), C3H6 (propylene), C4H8 (butylene), etc. can be used. Hydrocarbon gas can be used by vaporizing hydrocarbon solutions composed of C, H, O, such as ethanol, methanol, toluene, tar, and pitch.

[0091] The method for confirming whether a silicon carbide layer (12) has been formed can be as follows: particles that have completed the silicon carbide layer (12) formation step are heated at 800 degrees in an oxygen atmosphere to burn off all residual carbon, and the resultant product is then checked for the presence of silicon carbide in the outermost layer. From the inside to the outside, polycrystalline plate-shaped silicon particles (10), a silicon oxide layer (11), and a silicon carbide layer (12) remain in that order, and this can be confirmed by transmission electron microscopy or electron microscopy analysis after ion milling.

[0092] Referring to FIGS. 1 and 5, a carbon coating layer (13) can be formed by coating with conductive carbon to surround a silicon carbide layer (12) on the outer surface of a polycrystalline plate-shaped silicon particle (10).

[0093] The carbon coating layer (13) may be a carbon coating layer (13) formed by heating hydrocarbon gas to form pyrolysis carbon to cover the outer shell of the silicon carbide layer (12). This carbon coating layer (13) is formed to provide electrical conductivity and smooth electron flow to the oxide layer (11), which is an insulating layer, and the silicon carbide layer (12), which is an electrically conductive layer. That is, the carbon coating layer (12) plays a role in maintaining the formation amount and formation relationship of SEI (Solid electrolyte interface), which is an interface between graphite and the electrolyte (or electrolyte) in a conventional lithium ion secondary battery, and can eliminate the inconvenience of having to change the electrolyte (or electrolyte) due to a change in material.

[0094] The carbon coating layer (13) can be formed by supplying one of hydrocarbon gas, liquefied natural gas, and liquefied petroleum gas to plate-shaped silicon particles on which a silicon carbide layer (12) is formed using a rotary kiln or a kiln, and thermally decomposing the same at 750 to 1000°C.

[0095] The carbon coating layer (13) can be formed by introducing one of hydrocarbon gas, liquefied natural gas, and liquefied petroleum gas into plate-shaped silicon particles on which an oxide layer (11) or a silicon carbide layer (12) is formed using a rotary kiln or a kiln, and thermally decomposing the particles at 750 to 1000°C.

[0096] Here, hydrocarbon gas is a gas composed of carbon and hydrogen bonds, such as C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H 10 (Butane), C3H6 (propylene), C4H8 (butylene), etc. can be used. Hydrocarbon gas can be produced by vaporizing and thermally decomposing hydrocarbon solutions composed of C, H, O, such as ethanol, methanol, toluene, tar, and pitch.

[0097] The carbon coating layer (13) is preferably formed by thermally decomposing plate-shaped polycrystalline silicon particles (10) on which an oxide layer (11) or a silicon carbide layer (12) is formed using ethylene gas as a hydrocarbon gas at 750 to 800°C, or by thermally decomposing polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) or a silicon carbide layer (12) is formed using liquefied natural gas at 950 to 1,000°C, but is not limited thereto.

[0098] When using ethylene gas, if the temperature is below 750℃, the decomposition rate is less than 50%, resulting in unnecessary consumption of gas. If the temperature exceeds 800℃, the decomposition rate becomes faster, which can produce a large amount of unnecessary byproduct called carbon black.

[0099] When using liquefied natural gas, if the temperature is below 950℃, the decomposition rate is less than 30%, which results in unnecessary consumption of gas, and if it exceeds 1000℃, the decomposition rate becomes faster, which can produce a large amount of unnecessary byproduct called carbon black.

[0100] In addition, the carbon coating layer (13) has a crystallinity of less than 20 layers of average graphite layers, and may have an average thickness of 1 to 20 nm, preferably 1 to 10 nm.

[0101] As described above, the silicon anode material for a lithium-ion secondary battery composed of a plate-shaped silicon composite (1) can have electrical conductivity improved by 3 to 30% compared to existing anode materials for lithium-ion secondary batteries.

[0102] The granular porous silicon composite of the present invention is a composite formed by agglomeration and aggregation of the plate-shaped silicon composite (1) described above, and the porosity appearing in the porous structure may vary.

[0103] The porosity of the granular porous silicon composite of the present invention is 13 to 50%, preferably 15 to 50%. The pores are spaces for expansion due to lithium binding of the plate-like silicon composite (1). If there are no pores, the volume of the granular silicon composite will increase by up to twice due to lithium binding, and will return to its original shape when lithium is removed. At this time, electrical conductivity with the surrounding graphite and conductive material is lost, so that the lithium binding ability is significantly reduced in the next charge / discharge. The porosity should be a ratio suitable for absorbing the expansion due to lithium binding of the plate-like silicon composite (1). If the pores are numerous or large, a lot of empty space remains in the granular porous silicon composite even after lithium binding of the plate-like silicon composite (1), causing lithium ions and additives of the electrolyte to accumulate, accelerating lithium consumption of the electrolyte, and as a result, the charge / discharge cycle performance is significantly reduced due to lithium depletion of the electrolyte. This is the same principle as minimizing empty space through a compression process even when making an anode using only graphite.

[0104] Additionally, silicon anode materials for lithium-ion secondary batteries may further contain graphite.

[0105] Here, graphite can be formed into a plate-shaped or spherical cathode material, and empty space can be formed even if it is spherical.

[0106] Accordingly, by mixing graphite and a plate-like silicon composite (1) to form a silicon anode material for a lithium-ion secondary battery, the plate-like silicon composite (1) fills the empty space of the graphite, thereby preventing the entire electrode from expanding due to expansion when lithium is combined, and maintaining electrical connection with the electrode due to shrinkage. In other words, the plate-like silicon composite (1) is combined in the empty space of the graphite, thereby preventing separation from the electrode when expanded by lithium. At this time, the empty space of the graphite acts as a buffer space.

[0107] At this time, the plate-shaped silicon composite (1) and graphite can be mixed in a weight ratio of 1 to 20:80 to 99, and more preferably, can be mixed in a weight ratio of 10:90.

[0108] At this time, if the content of the plate-shaped silicon composite (1) is lower than 1 wt%, the effect of increasing the charging capacity of the silicon anode material due to graphite mixing is within the charging capacity deviation, making it difficult to determine the effect. If it exceeds 20 wt%, the number of silicon particles becomes significantly greater than the number of graphite particles, which may reduce the uniform dispersion effect between the silicon particles and the graphite.

[0109] Next, a granular porous silicon composite is described.

[0110] The granular porous silicon composite according to the present invention is formed by forming pores between the particles when tens to hundreds of plate-like silicon composites are aggregated, and was developed for the purpose of securing expansion space in advance when the plate-like silicon composite expands in volume during lithium charging, thereby reducing the overall expansion rate of an electrode including the plate-like silicon composite. This has the advantages of increasing the amount of mixing with graphite, a conventional negative electrode material, increasing electrode density, reducing lithium consumption due to SEI formation, and extending the charge-discharge life.

[0111] The granule particle size of the granular porous silicon composite according to the present invention may be 3 to 30 μm, the internal porosity of the granules may be 15 to 50%, and the specific surface area of ​​the granules may be 4 to 30 m 2 / g may be.

[0112] A cross-sectional photograph (Fig. 7) of a granular porous silicon composite made by agglomerating plate-like silicon composites shows that carbon is used as a binder to agglomerate plate-like silicon to make granules, and that this carbon forms the outermost layer of the plate-like silicon composite.

[0113] A method for manufacturing a silicon negative electrode material for a lithium ion secondary battery according to the above-described embodiment of the present invention will be described below.

[0114]

[0115] Figure 6 is a flow chart schematically showing a method for manufacturing a silicon negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention.

[0116] Referring to FIG. 6, a method for manufacturing a silicon negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention may include a disintegration step (S10), an oxidation step (S20), an agglomeration step (S30), a silicon carbide layer formation step (S40), and a carbon coating step (S50).

[0117] The disintegration step (S10) can make polycrystalline plate silicon (10) formed by a silicon kerf into polycrystalline plate silicon (10) having an apparent density of 0.1 to 0.4 g / cm3.

[0118] Polycrystalline plate silicon (10) is subject to bending and rolling during the cutting process, as the silicon is separated from the single crystal into a plate shape when a strong force is applied, and can be formed in a form in which many fine single crystals are weakly attached. Therefore, it is necessary to break up the polycrystalline plate silicon (10).

[0119] At this time, as illustrated in FIG. 6, the method for manufacturing a silicon negative electrode material for a lithium ion secondary battery of the present invention may include a pretreatment step (S1) prior to the disintegration step (S10).

[0120] The preprocessing step (S1) can be used to wet-mill and dry polycrystalline plate silicon (10) before the crushing step (S10) to produce crushed plate silicon particles.

[0121] Through this pretreatment step (S1), moisture and lubricant in the waste silicon kerf are removed from the crushed and dried plate-shaped polycrystalline silicon particles (10). However, in order to facilitate reaction with gas in the post-process, the crushed and dried polycrystalline plate-shaped silicon particles (10) are crushed in the crushing step (S10) to form spaces between the particles.

[0122] The crushed and dried plate-shaped silicon particles (10) have an apparent density of 1 to 2 g / cm3, and by crushing them at 3,000 rpm under air in the crushing step (S10), polycrystalline plate-shaped silicon particles (10) having an apparent density of 0.1 to 0.4 g / cm3 can be obtained.

[0123] Accordingly, the average distance between the particles of the crushed polycrystalline plate-shaped silicon particles (10) can be increased by 3 to 10 times compared to the crushed and dried polycrystalline plate-shaped silicon particles (10). Therefore, the crushing step (S10) can enable the oxidation layer (11) to be uniformly formed in the subsequent oxidation step (S20).

[0124] The oxidation step (S20) can form an oxide layer (11) by oxidizing the surface of polycrystalline plate-shaped silicon particles (10).

[0125] The oxidation step (S20) can further oxidize the naturally formed natural oxide layer on the surface of the polycrystalline plate-shaped silicon particles (10) to form a thick oxide layer.

[0126] After the formation of the oxide layer (11), a coagulation step (S30) is performed to coagulate the plate-shaped silicon particles (10) on which the oxide layer (11) is formed, thereby manufacturing a porous aggregate in the shape of a granule including a spherical shape, a nearly spherical oval shape, and a distorted oval shape. The plate-shaped silicon particles (10) on which the oxide layer (11) is formed are coagulated using a binder, and the porous aggregate in which the plate-shaped silicon particles (10) on which the oxide layer (11) is formed can have a size from several micrometers to several tens of micrometers. The binder used in the coagulation step (S30) is preferably an organic polymer that can be dissolved or gelatinized in a solvent and maintains a solid state when the solvent is removed, and the organic binder may be one or more selected from a thermoplastic aqueous polymer, a thermosetting polymer, a petroleum polymer, a coal polymer, and a plant polymer. Specifically, it may be at least one selected from the group consisting of PVP (polyvinyl pyrolidine), PVA (polyvinyl alcohol), phenol, coaltar pitch, amylose, starch, and cellulose.

[0127] The agglomeration step (S30) is performed by evenly mixing the plate-shaped silicon particles (10) on which an oxide layer (11) has been formed, a binder, and a solvent, and removing the solvent to manufacture a porous aggregate in which the plate-shaped silicon particles (10) on which an oxide layer (11) has been formed and the organic polymer have been agglomerated. In the manufacture of the agglomerated porous aggregate, a process of mixing the plate-shaped silicon particles (10) on which an oxide layer (11) has been formed and a binder in a solvent, and then curing the binder may be performed. The solvent is preferably water, purified water, or distilled water, but is not particularly limited, and a solvent that is easy to remove, such as by vaporization, and easy to dissolve or gelatinize the binder used may be preferred.

[0128] In the agglomeration step (S30), the removal of the solvent can be performed through evaporation of the solvent, etc., and the drying process may preferably be disk drying, spray drying, or freeze drying. Disk drying is a method in which a dispersion is poured onto a high-temperature rotating circular disk and the dried powder is scraped off with a scraper, and spray drying is a method in which a dispersion is dropped onto a sprayer or a rotating disk to spread small droplets and then dried by blowing high-temperature gas so that they remain suspended in the air. Freeze drying is a method in which a solvent is solidified and the surrounding air pressure is lowered to remove the solvent by sublimation. More suitably, it may be desirable to produce a porous aggregate in which plate-shaped silicon particles (10) having an oxide layer (11) formed in a spherical, nearly spherical, or distorted oval shape with few angular parts are aggregated through spray drying. The size of the particles after spray drying or the plate-shaped silicon aggregates crushed after disk drying may have an average diameter of 2 to 40 μm, preferably 3 to 35 μm, and more preferably 3 to 30 μm. The dried porous aggregates can be subjected to a spheroidization crushing process in which the porous spheres collide between two plates with different speeds to form small spheroidized aggregates, and a spheroidization crushing process in which the accelerated aggregates collide against a hard plate to gradually wear away the protrusions. If the aggregates are small, homogeneous dispersion may be difficult when mixed with graphite particles, and if they are too large, a lot of empty space may be formed when mixed with graphite, which may reduce the filling rate of the electrode. The organic polymers in the plate-like silicon aggregates are decomposed at high temperatures, leaving mainly the carbon component of the organic polymer, so that they can be used as high-temperature binders that maintain the aggregate shape even at high temperatures.When the organic polymer is completely vaporized or decomposed, the porous aggregate of plate-shaped silicon particles (10) on which an oxide layer (11) is formed loses its shape and returns to plate-shaped particles, and the entire particle may form a single lump in the subsequent carbon coating. To prevent this, the organic polymer is used such that carbon or hydrocarbon residue remains at high temperatures, so that the shape can be maintained until the subsequent process with the carbon residue.

[0129] Afterwards, a step of forming a silicon carbide layer (12) is performed between the coagulation step (S30) and the carbon coating process.

[0130] The silicon carbide layer (12) formation step (S40) can create an electrically conductive silicon carbide layer (12) by replacing some of the oxygen in the oxide layer with carbon.

[0131] The carbon coating step (S50) can form a plate-shaped silicon composite (1) having a carbon coating layer (13) formed by coating the surface of polycrystalline plate-shaped silicon particles (10) on which a silicon carbide layer (11) is formed with conductive carbon. The carbon coating step (S50) can provide uniform electrical conductivity and smooth electron flow to the surface of the plate-shaped silicon particles having a core-shell structure by forming a carbon coating layer (13) on the surface of the polycrystalline plate-shaped silicon particles (10). The core is a plate-shaped silicon particle (10), and the shell is composed of an oxide layer (11), a silicon carbide layer (12), and a carbon coating layer (13).

[0132] In the oxidation step (S20) described above, the oxide layer (11) has good lithium permeability and can improve the battery life.

[0133] The silicon carbide layer formation step (S40) and the carbon coating step (S50) can be formed step by step by separating them into separate processes and passing them through the kiln for each process, and the silicon carbide layer (12) and the carbon coating layer (13) can also be formed simultaneously.

[0134] First, the case where the silicon carbide layer formation step (S40) and the carbon coating step (S50) are performed separately will be described.

[0135] The silicon carbide layer formation step (S40) is to pass a porous aggregate of polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) is formed through a kiln at 900 to 1100°C, and decompose C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H at 900°C. 10 When a small amount of vaporized gas of a hydrocarbon gas such as (butane), C3H6 (propylene), C4H8 (butylene), or a hydrocarbon solution composed of C, H, O such as ethanol, methanol, toluene, tar, pitch, etc. is injected, a silicon carbide layer (12) is formed. At this time, a residence time of 1 to 30 minutes at 900 degrees or higher is suitable, and if it is less than 1 minute, the inside of the plate-shaped silicon particles that move by being electrostatically agglomerated is not heated evenly, making it difficult to uniformly form a silicon carbide layer (12) between the particles, and if it is more than 30 minutes, the thickness increase speed of the silicon carbide layer (12) drops significantly, resulting in a significant decrease in production economy.

[0136] The carbon coating step (S50) forms a silicon carbide layer (12) on a porous aggregate of polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) is formed, and then passes the porous aggregate through a kiln at 750 to 1,000°C to form C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H 10 When a large amount of vaporized gas of a hydrocarbon gas such as (butane), C3H6 (propylene), C4H8 (butylene), or a hydrocarbon solution composed of C, H, O such as ethanol, methanol, toluene, tar, pitch, etc. is injected, a carbon coating layer (13) is formed.

[0137] This describes a case where the silicon carbide layer formation step (S40) and the carbon coating step (S50) are performed simultaneously.

[0138] The porous aggregate of polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) is formed is passed through a kiln at 900 to 1100°C, and decomposition occurs at 900°C or higher to form C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H 10 (butane), C3H6 (propylene), C4H8 (butylene), etc. When a large amount of vaporized gas of a hydrocarbon gas or a hydrocarbon solution composed of C, H, O such as ethanol, methanol, toluene, tar, pitch, etc. is injected, a silicon carbide layer (12) is first formed on the outer surface of the plate-shaped silicon particles forming an oxide layer that forms a porous aggregate, and then an excess of carbon is accumulated to form a carbon coating layer (13). The formation speed of the silicon carbide layer (12) is slower than that of the carbon coating layer (13), so that the residence time at 900 degrees or higher follows the residence time standard of the silicon carbide layer formation step (S40). More preferably, it is good to use a hydrocarbon having a carbon atomic ratio of 20% or less among hydrocarbons such as CH4 (methane), ethanol, and methanol at 900 to 1100 degrees Celsius to delay the recombination time of the carbon and make the penetration of the oxide layer easier. The recombination time refers to the time it takes for five or more carbon atoms atomized by thermal decomposition of hydrocarbon molecules to aggregate and transform into carbon black or graphene structures. As the carbon coating layer (13) is formed, the outermost layer of the granular porous silicon composite may be formed with an outermost carbon coating layer coated with pyrolytic carbon.

[0139] In addition, the method for manufacturing a silicon negative electrode material for a lithium ion secondary battery may further include a mixing step with graphite after the carbon coating step (S50).

[0140] The graphite and mixing step can be performed after the carbon coating step (S50) to mix the granular porous silicon composite with graphite to manufacture a silicon anode material for a spherical lithium-ion secondary battery or a silicon anode material for a simple lithium-ion secondary battery.

[0141] The graphite mixed with the porous silicon composite of the present invention is preferably graphite that has undergone a spheroidization or spheroidization process, because spheroidal graphite has low anisotropy, which is advantageous in maintaining uniformity of voltage and current distribution. On the other hand, flake-shaped graphite has poor processability due to reduced fluidity during the subsequent mixing and slurrying process with a solvent or binder due to the anisotropy of the material itself, and it is difficult to form a coating layer of a predetermined thickness, which may cause problems such as peeling. In general, the spheroidization process can be performed by removing rough parts of the flake-shaped carbon material through mechanical rotational motion and smoothing the particle surface to form a spheroid.

[0142]

[0143] The silicon anode material for a lithium ion secondary battery of the present invention described above is a granular porous silicon composite formed by agglomerating plate-like silicon composites, wherein the plate-like silicon composite has an oxide layer, a silicon carbide layer, and a carbon coating layer formed on plate-like silicon obtained from waste silicon kerf, and the carbon coating layer has a uniform thickness, so that when composited with graphite, the filling rate is excellent and more lithium can be charged based on the same volume, and the cost-effectiveness is also excellent by using waste silicon kerf.

[0144]

[0145] In a lithium ion secondary battery comprising a negative electrode, a positive electrode, a separator, and an electrolyte including a silicon negative electrode material for a lithium ion secondary battery of the present invention, the initial discharge capacity (initial capacity) may be 400 mAh / g or more, and the residual capacity (discharge capacity) at 500 cycles may be 300 to 350 mAh / g, which is 75% or more. In addition, the initial coulombic efficiency (ICE) may be 93% or more. According to one embodiment of the present invention, a lithium ion secondary battery including a negative electrode, a positive electrode, a separator, and an electrolyte including a silicon negative electrode material for a lithium ion secondary battery composed of 95 wt% of graphite and 5 wt% of the silicon composite of the present invention has an initial discharge capacity (initial capacity) of 400 mAh / g or more, and the initial coulombic efficiency by graphite can be maintained at a constant level of 93% or more (93 to 96%) while the initial coulombic efficiency of the silicon composite can be 85% or more (85 to 92%), thereby providing a lithium secondary battery having excellent charge / discharge performance in which the overall initial coulombic efficiency is maintained at 93% or more.

[0146] In this way, the silicon anode material for a lithium ion secondary battery including the silicon composite of the present invention has a high initial capacity and a low rate of decrease compared to the initial capacity during charge and discharge, so that it has an excellent lifespan, and can have significantly superior coulombic efficiency compared to existing lithium ion secondary batteries using silicon as an anode material.

[0147]

[0148] Hereinafter, the present invention will be described in more detail by way of examples, but these are only intended to illustrate preferred embodiments of the present invention, and the examples do not limit the scope of the present invention.

[0149]

[0150] [Example]

[0151] [Example 1]

[0152] In the process of slicing a single-crystal silicon ingot, 5,000 ml of a 5% plate-shaped silicon mixture solution was recovered through cooling, lubrication, and cutting with a 50 ㎛ diameter diamond wio saw using a mixture of water and diethylene glycol.

[0153] After the mixed solution was pulverized in a milling machine using zirconia balls and zirconia jars, the dispersion solution containing polycrystalline plate silicon was injected at a rate of 20 ml per minute onto an atomizer disc rotating at 15,000 rpm in a spray dryer and dried at 180 degrees to obtain plate silicon particles. Low-density polycrystalline plate silicon dry particles were produced by pulverizing with air in a pin mill with a radius of 120 mm and 3,400 rpm.

[0154] Next, the polycrystalline plate-shaped silicon particles were oxidized by bubbling and injecting hydrogen peroxide with nitrogen while maintaining them in a rotary kiln at 800°C for 10 minutes, thereby forming an oxide layer.

[0155] Next, an agglomeration step was performed to form a porous aggregate structure. 50 g of plate-shaped silicon particles with an oxide layer formed in 1,000 mL of water as a solvent and 20 g of PVA (polyvinyl alcohol) as an organic polymer were mixed and stirred, injected at a rate of 20 mL per minute into an atomizer plate rotating at 18,000 rpm in a spray dryer, and dried at 180°C. As a result, porous aggregates of approximately 20 μm were obtained by agglomeration of plate-shaped silicon particles with an oxide layer formed in the cyclone recovery section.

[0156] Afterwards, the porous aggregate formed by the agglomeration of plate-shaped silicon particles including an oxide layer was kept in a rotary kiln at 950°C for 20 minutes, and methane gas was injected at a rate of 0.1 M / min. to replace the surface of the oxide layer of the plate-shaped silicon particles in which an oxide layer was formed from the surface of the porous aggregate to the inner center, thereby forming a silicon carbide layer, and the residual carbon covered the outer shell of the silicon carbide layer to form a carbon layer, thereby creating a granular porous silicon composite.

[0157] The formation of a granular porous silicon composite and its cross-section were confirmed (Fig. 7), and the porosity was measured by image analysis, and the porosity was confirmed to be 18% (Fig. 8(A)).

[0158] The manufactured granular porous silicon composite and spheroidized graphite were placed in a dry ball mill at a weight ratio of 5:95 and mixed for 10 seconds to prepare a silicon anode material for lithium-ion secondary batteries. The prepared silicon anode material was mixed with a binder and a conductive agent, coated on copper foil, and punched into a square shape. To manufacture a battery cell, the anode was used by punching out a square shape of aluminum foil coated with NCM811. A separator and electrolyte were placed between the anode and cathode, vacuum-packed in an aluminum pouch, and assembled into a full-cell lithium-ion battery.

[0159]

[0160] [Example 2]

[0161] In the process of forming a porous aggregate, 50 g of plate-shaped silicon particles having an oxide layer formed in 1,000 ml of water as a solvent and 10 g of PVA (polyvinyl alcohol) as an organic polymer were mixed and stirred, injected at 10 ml per minute into an atomizer disc rotating at 18,000 rpm in a spray dryer, and dried at 180°C. As a result, a porous aggregate of approximately 12 μm was obtained by agglomeration of plate-shaped silicon particles having an oxide layer formed in the cyclone recovery section. In the remainder, a granular porous silicon composite was manufactured in the same manner as in Example 1, and a full-cell lithium secondary battery was assembled. The porosity of the manufactured granular porous silicon composite was confirmed to be 34% (Fig. 8(B)).

[0162]

[0163] [Comparative Example 1]

[0164] 50 g of plate-shaped silicon particles with an oxide layer formed in 500 ml of water as a solvent and 30 g of PVA (polyvinyl alcohol) as an organic polymer were mixed and stirred, injected at 20 ml per minute into an atomizer plate rotating at 10,000 rpm in a spray dryer, and dried at 180°C. The remainder was manufactured in the same manner as in Example 1, and a full-cell lithium secondary battery was assembled. The porosity of the manufactured granular porous silicon composite was confirmed to be 10% (Fig. 9(A)).

[0165]

[0166] [Comparative Example 2]

[0167] 50 g of plate-shaped silicon particles with an oxide layer formed in 2,000 ml of water as a solvent and 10 g of PVA (polyvinyl alcohol) as an organic polymer were mixed and stirred, injected at 7 ml per minute into an atomizer plate rotating at 18,000 rpm in a spray dryer, and dried at 180°C. The remainder was manufactured in the same manner as in Example 1, and a full-cell lithium secondary battery was assembled. The porosity of the manufactured granular porous silicon composite was confirmed to be 53% (Fig. 9(B)).

[0168]

[0169] The porosity of the granular porous silicon composite manufactured according to Examples 1 and 2 and Comparative Examples 1 and 2 and the lithium secondary battery including the granular porous silicon composite is as shown in [Table 1] below.

[0170]

[0171] Separation porosity (%) Example 118 Example 234 Comparative Example 110 Comparative Example 253

[0172]

[0173] [Experimental Example 1] Evaluation of Charge-Discharge Performance and Initial Coulombic Efficiency (ICE) Performance

[0174] The initial capacity and initial coulombic efficiency (ICE) of the full cells manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. At this time, the capacity was measured under the condition of 1C of charge and discharge current at 25℃, and the initial coulombic efficiency was calculated according to a known method by measuring the initial charge and initial discharge capacities, and the lifespan was measured up to 500 cycles under the condition of 1C of charge and discharge current at 25℃. The results are shown in [Table 2] below.

[0175]

[0176] Separation Porosity (%) Initial Capacity (Initial Discharge Capacity, mAh / g) Initial Coulombic Efficiency (%) Residual Capacity After 500 Cycles (%) Example 1 18 4 15.3 9 3.4 (Graphite 93.5 + Silicon Composite 89) 75.5 Example 2 3 4 12.4 9 3.2 (Graphite 93.5 + Silicon Composite 88) 78.8 Comparative Example 1 10 4 17.4 9 3.5 (Graphite 93.5 + Silicon Composite 90) 52.4 Comparative Example 2 5 3 4 13.8 9 3.5 (Graphite 93.5 + Silicon Composite 83) 69.8

[0177] Example 1 showed a high initial capacity of 415.3 mAh / g in the first cycle test, and the initial Coulombic efficiency was also high at 93.4%. The initial Coulombic efficiency of the silicon composite was confirmed to be remarkably high at 89%. As the cycle progressed, a capacity decrease close to linear was observed, and a residual capacity of 75.5% (313.5 mAh / g) was observed at 500 cycles. Example 2 showed a high initial capacity of 412.4 mAh / g in the first cycle test, and the initial Coulombic efficiency was also high at 93.2%. The initial Coulombic efficiency of the silicon composite was confirmed to be remarkably high at 88%. As the cycle progressed, a capacity decrease close to linear was observed, and a residual capacity of 78.8% (325.0 mAh / g) was observed at 500 cycles.

[0178] On the other hand, Comparative Example 1 showed a high initial capacity of 417.4 mAh / g in the first cycle test, and the initial Coulombic efficiency was also high at 93.5%, and the initial Coulombic efficiency of the silicon composite was confirmed to be significantly high at 90%, but it showed a rapid decrease in capacity as the cycle progressed, and a residual capacity of 52.4% (218.7 mAh / g) at 500 cycles. Comparative Example 2 showed a high initial capacity of 413.8 mAh / g in the first cycle test, and the initial Coulombic efficiency was also high at 92.9%, and the initial Coulombic efficiency of the silicon composite was confirmed to be significantly low at 83%, and it showed a rapid decrease in capacity as the cycle progressed, and a residual capacity of 69.8% (288.8 mAh / g) at 500 cycles.

[0179] The above results confirm that the porosity of the porous structure in granular porous silicon composites affects battery performance. Specifically, if the porosity is excessively low, the battery life is rapidly reduced. However, if the porosity is excessively high, not only is the initial Coulombic efficiency of the graphite maintained constant, but the Coulombic efficiency of the silicon composite can also be significantly reduced.

[0180] Although the embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will understand that the present invention can be implemented in other specific forms without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above are illustrative in all respects and are not limiting.

[0181]

[0182] [Explanation of symbols]

[0183] 1: Plate-shaped silicone composite

[0184] 10: Polycrystalline plate silicon

[0185] 11: Oxide layer

[0186] 12: Silicon carbide layer

[0187] 13: Carbon coating layer

Claims

1. A silicon anode material for a lithium-ion secondary battery comprising a granular porous silicon composite formed by aggregating plate-shaped silicon composites, wherein The above plate-shaped silicon composite comprises plate-shaped silicon particles; Silicon oxide layer formed on the above plate-shaped silicon particles; A silicon carbide layer formed on the outer edge of the silicon oxide layer; and A silicon negative electrode for a lithium-ion secondary battery comprising: a carbon coating layer formed by coating conductive carbon to surround the silicon carbide layer.

2. In paragraph 1, A silicon negative electrode material for a lithium-ion secondary battery, characterized in that the plate-shaped silicon has an average thickness of 10 to 200 nm and an average length of 10 μm or less.

3. In paragraph 1, A silicon anode material for a lithium-ion secondary battery, characterized in that the oxide layer has an average thickness of 2 to 10 nm.

4. In paragraph 1, A silicon negative electrode material for a lithium-ion secondary battery, characterized in that the silicon carbide layer has an average thickness of 1 to 5 nm.

5. In paragraph 1, A silicon negative electrode material for a lithium-ion secondary battery, characterized in that the silicon carbide layer is formed by replacing some of the oxygen in the oxide layer with carbon.

6. In Paragraph 1, A silicon negative electrode material for a lithium-ion secondary battery, characterized in that the carbon coating layer has an average thickness of 1 to 10 nm.

7. In paragraph 1, Silicon anode material for lithium-ion secondary batteries containing additional graphite.

8. A negative electrode comprising the silicon negative electrode material for a lithium-ion secondary battery according to claim 1.

9. A lithium-ion secondary battery comprising the negative electrode of claim 8.

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