Silicon negative electrode material for lithium-ion secondary battery, comprising polycrystalline flake-shaped silicon particles

Abstract

The present invention relates to a silicon negative electrode material for a lithium-ion secondary battery, manufactured from waste silicon kerf, and may provide: a silicon negative electrode material for a lithium-ion secondary battery, comprising a flake-like silicon composite in which a composite layer comprising an oxide layer and a carbon-containing layer is formed on flake-shaped silicon obtained from waste silicon kerf; and a negative electrode and lithium-ion secondary battery comprising same, wherein the silicon negative electrode material, when formed into a composite with graphite, exhibits excellent packing density and allows more lithium to be charged per unit volume, while also providing superior economic efficiency through the use of waste silicon kerf.

Description

Silicon anode material for lithium-ion secondary batteries containing polycrystalline plate-shaped silicon particles

[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 particularly, to a silicon negative electrode material for a lithium-ion secondary battery having excellent charge capacity and lifespan, in which polycrystalline plate-shaped silicon particles having a controlled crystal structure are obtained from plate-shaped waste silicon kerfs, and a composite layer including an oxide layer, a silicon carbide layer, and carbon is formed on the polycrystalline plate-shaped silicon particles, 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 solve the problem of silicon-based negative electrode materials by obtaining polycrystalline plate-shaped silicon particles having a controlled crystal structure from waste silicon kerf, and using the polycrystalline plate-shaped silicon particles, a silicon negative electrode material having a significantly improved filling factor and lifespan can be provided. The silicon-based negative electrode material of the present invention also has excellent commerciality and economic feasibility.

[0009] The present invention is a silicon anode material for a lithium ion secondary battery comprising a plate-like silicon composite manufactured from plate-like silicon formed by a silicon kerf, wherein the plate-like silicon composite comprises polycrystalline plate-like silicon particles, 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 with conductive carbon to surround the silicon carbide layer.

[0010] In the silicon anode material of the present invention, the silicon carbide layer may be a silicon carbide layer formed by supplying hydrocarbon gas to a silicon oxide layer and heating it.

[0011] In the silicon anode material of the present invention, the carbon coating layer may be a carbon coating layer formed by heating hydrocarbon gas so that pyrolysis carbon covers the outer shell of the silicon carbide layer.

[0012] In the silicon anode material of the present invention, the polycrystalline plate-shaped silicon particles may have an average grain size of 10 to 50 nm as measured by XRD analysis.

[0013] In the silicon anode material of the present invention, the average grain size in the polycrystalline plate silicon may be the average grain size measured according to the Scherer Equation of the Si(002) plane in XRD analysis.

[0014] In the silicon anode material of the present invention, the full width at half maximum of the polycrystalline plate silicon may be 0.1500° to 0.4000°.

[0015] 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.

[0016] In the silicon anode material of the present invention, the oxide layer may have an average thickness of 2 to 10 nm.

[0017] In the silicon anode material of the present invention, the silicon carbide layer may have an average thickness of 1 to 5 nm.

[0018] 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.

[0019] In the silicon negative electrode material of the present invention, the carbon coating layer may have an average thickness of 1 to 10 nm.

[0020] The silicon anode material of the present invention may further include graphite.

[0021] The present invention can provide a negative electrode including a silicon negative electrode material according to the present invention.

[0022] The present invention can provide a lithium ion secondary battery including a negative electrode according to the present invention.

[0023] The silicon anode material for a lithium ion secondary battery of the present invention forms a multilayer structure including an oxide layer and a carbon-containing layer on a polycrystalline plate silicon having a controlled crystal structure formed by using a waste silicon kerf, so that when combined 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 a waste silicon kerf.

[0024]

[0025] FIG. 1 is a SEM (Scanning electron microscope) 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Figure 5 is a TEM (Transmission electron microscope) image of plate-like silicon particles from which carbon has been removed from the plate-like silicon composite.

[0030] 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.

[0031] Figure 7 is a flow chart that further includes a pretreatment step, a secondary disintegration step, and a silicon carbide formation step in Figure 6.

[0032] Figure 8 shows the XRD analysis results before the oxidation step of the plate-shaped silicon particles according to an embodiment of the present invention, and the grain size can be obtained by measuring the full width at half maximum (FWHM) value according to the equation below.

[0033] Full width at half maximum (FWHM) = Kλ / LCosθ (K=0.9~0.94, λ=0.154nm, L=crystal size, θ=half value of 2θ (28.4))

[0034] FIG. 9 is a TEM photograph showing the crystal grains and sizes of plate-like silicon particles before the oxidation step in a plate-like silicon composite according to an embodiment of the present invention (the crystal grains of plate-like silicon particles are indicated by the white boundary lines).

[0035]

[0036] 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.

[0037] 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.

[0038] Like reference numbers used throughout this specification represent like components.

[0039] 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.

[0040]

[0041] The present invention relates to a silicon anode material for a lithium ion secondary battery manufactured from waste silicon kerf, and can provide a silicon anode material for a lithium ion secondary battery including a plate-like silicon composite in which a composite layer including an oxide layer, a silicon carbide layer, and a carbon layer is formed on polycrystalline plate-like silicon obtained from waste silicon kerf, and an anode and a lithium ion secondary battery including the same.

[0042]

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached FIGS. 1 to 9.

[0044] 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.

[0045] Figure 5 is a TEM photograph of the plate-shaped silicon on which the silicon carbide layer of Figure 3 is formed.

[0046] 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.

[0047] 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.

[0048] 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).

[0049] 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).

[0050] 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.

[0051] 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.

[0052] 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 a piano wire of 50㎛ to 400㎛. The silicon cutting fines generated during this process are suitable as a raw material for the polycrystalline plate silicon (10) of the present invention.

[0053] The polycrystalline platelet silicon particles (10) of the present invention have an average grain size of 50 nm or less, 5 to 50 nm, and preferably 10 to 50 nm, as measured by XRD (X-ray diffraction) analysis. The platelet silicon particles having the desired grain size can be obtained by adjusting the process conditions appropriate for each process for obtaining platelet silicon particles from waste silicon kerf. The grain size of the waste silicon kerf varies depending on the diameter and cutting speed of the diamond wire saw, and the larger the diameter of the wire saw and the faster the cutting speed, the thicker the thickness of the waste silicon kerf, the larger the plate size, and the larger the grain size. The performance of a lithium secondary battery using a silicon anode material including a platelet silicon composite (1) may be affected by the grain size of the polycrystalline platelet silicon (10) particles included in the platelet silicon composite (1). According to one embodiment of the present invention, if the crystal grain size of the polycrystalline plate-shaped silicon (10) particles exceeds 50 nm, the expansion and contraction of individual crystal grains are large, so that they are easily destroyed during charge and discharge cycles, which may cause a rapid decrease in battery capacity or a significantly shortened lifespan of the battery.

[0054] The average grain size of the polycrystalline platelet silicon particles (10) of the present invention may be the average grain size measured according to the Scherer Equation of the Si (002) plane in XRD analysis, and may also be derived by measuring the full width at half maximum (FWHM) of the polycrystalline platelet silicon and using the following equation (1). According to one embodiment of the present invention, the full width at half maximum (FWHM) in the polycrystalline platelet silicon particles having the desired average grain size of the present invention may be 0.1500° to 0.4000°. If the range of the FWHM is less than 0.1500°, the battery life may be significantly reduced or the battery capacity improvement by the platelet silicon particles may not be sufficient.

[0055] Equation (1): Full width at half maximum (FWHM) =

[0056] (K is the Scherer constant (λ = wavelength of the X-ray used, L = grain size, θ = half value of 2θ)

[0057] The polycrystalline plate silicon (10) formed with a silicon kerf can be formed with an average thickness of 10 to 200 nm and an average length of 10 μm or less, preferably an average length of 1 to 10 μm.

[0058] 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.

[0059] 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.

[0060] Polycrystalline plate silicon (10) is subjected to rapid heating and cooling during the cutting process when strong force is applied, causing the silicon to separate 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.

[0061] Meanwhile, the polycrystalline plate silicon (10) can be pretreated, for example, by wet grinding and drying. Through the pretreatment, the crystal grain size or plate size of the polycrystalline plate silicon (10) can be controlled to fall within the scope of the present invention.

[0062] 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.

[0063] 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.

[0064] 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, and 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 powders with high apparent density.

[0076] 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.

[0077] 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.

[0078] 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).

[0079] 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.

[0080] Referring to FIG. 2, the oxide layer (11) can be formed by oxidizing the surface of polycrystalline plate-shaped silicon particles (10).

[0081] 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.

[0082] 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.

[0083] 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).

[0084] 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.

[0085] Additionally, the oxide layer (11) may have an average thickness of 2 to 10 nm.

[0086] 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.

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] At this time, if the average thickness of the carbon coating layer (13) is less than 1 nm, the carbon coating layer (13) is formed unevenly in the form of dots on the surface, so that many uncoated areas occur, and the lifespan improvement effect may not be significant. If it exceeds 20 nm, excessive coating may cause many pores to form inside the carbon coating layer (13), so that lithium fills the pores and does not escape again, and the irreversible capacity may increase significantly.

[0110] 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.

[0111] Additionally, silicon anode materials for lithium-ion secondary batteries may further contain graphite.

[0112] Here, graphite is a plate-shaped material, and even when spherical, empty space is formed.

[0113] 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.

[0114] Here, there are two possible methods for mixing the plate-like silicon composite (1) of the silicon negative electrode material for lithium-ion secondary batteries and graphite: 1) a method of introducing the plate-like silicon composite (1) during the process of spheroidizing graphite, and 2) a method of mixing the plate-like silicon composite (1) and graphite that have completed the spheroidizing or spheroidizing process.

[0115] 1) When manufacturing a silicon anode material for a lithium-ion secondary battery by inserting a plate-shaped silicon complex (1) in the process of spheroidizing graphite, a spheroidized silicon anode material for a lithium-ion secondary battery in the form of spheroidized or spheroidized graphite can be formed by inserting the plate-shaped silicon complex (1) between the graphite plates.

[0116] On the other hand, 2) when manufacturing a silicon anode material for a lithium-ion secondary battery by mixing a graphite and a plate-shaped silicon complex (1) that have undergone a spheroidization or spheroidization process, a silicon anode material for a lithium-ion secondary battery in a simple mixed form in which the plate-shaped silicon complex (1) is arranged between graphite can be formed.

[0117] 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.

[0118] 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.

[0119] 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.

[0120]

[0121] FIG. 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, and FIG. 7 is a flow chart further including a pretreatment step, a secondary disintegration step, and a silicon carbide formation step in FIG. 6.

[0122] 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 first disintegration step (S10), an oxidation step (S20), a silicon carbide layer formation step (S30), and a carbon coating step (S40).

[0123] The first 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.

[0124] 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).

[0125] At this time, as illustrated in FIG. 7, 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 first disintegration step (S10).

[0126] The preprocessing step (S1) can be used to wet-mill and dry polycrystalline plate silicon (10) before the first crushing step (S10) to produce crushed plate silicon particles.

[0127] 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) can be crushed in the first crushing step (S10) to form spaces between the particles.

[0128] 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 first crushing step (S10), polycrystalline plate-shaped silicon particles (10) having an apparent density of 0.1 to 0.4 g / cm3 can be obtained.

[0129] 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 first crushing step (S10) can enable the oxidation layer (11) to be uniformly formed in the subsequent oxidation step (S20).

[0130] The oxidation step (S20) can form an oxide layer (11) by oxidizing the surface of polycrystalline plate-shaped silicon particles (10).

[0131] 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.

[0132] The silicon carbide layer (12) formation step (S30) can be used to form an electrically conductive silicon carbide layer (12) by replacing some of the oxygen in the oxide layer with carbon. The method for forming the silicon carbide layer has been described in detail above.

[0133] The carbon coating step (S40) 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 (S40) 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).

[0134] In the oxidation step (S20) described above, the oxide layer (11) has good lithium permeability and can improve the battery life.

[0135] The silicon carbide layer formation step (S30) and the carbon coating step (S40) 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 layer (13) can also be formed simultaneously.

[0136] First, the case where the silicon carbide layer formation step (S30) and the carbon coating step (S40) are performed separately will be described.

[0137] The silicon carbide layer formation step (S30) is to pass polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) is formed through a kiln at 900 to 1100°C, and C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H decompose 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, or pitch is injected, a silicon carbide layer (12) is formed. At this time, a residence time of 1 to 30 minutes at 900℃ 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.

[0138] The carbon coating step (S40) passes the plate-shaped silicon particles on which the silicon carbide layer (12) is formed through a kiln at 750 to 1,000°C to form C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), C4H 10When a large amount of vaporized gas of 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 layer (13) is formed.

[0139] This describes a case where the silicon carbide layer formation step (S30) and the carbon coating step (S40) are performed simultaneously.

[0140] Plate-shaped silicon particles on which an oxide layer (11) has been formed are passed through a kiln at 900 to 1100°C, and decomposition occurs at 900°C or higher to produce C2H2 (acetylene), C2H6 (ethane), C2H4 (ethylene), CH4 (methane), C3H8 (propane), and 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 silicon carbide layer (12) is formed first, and then an excess of carbon is accumulated to form a carbon layer (13). The formation speed of the silicon carbide layer (12) is slower than that of the carbon layer (13), so that the residence time at 900 degrees or higher is based on the residence time standard of the silicon carbide layer formation step (S30). 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. Recombination time refers to the time it takes for five or more carbon atoms to clump together and convert to carbon black or graphene structure through thermal decomposition of hydrocarbon molecules.

[0141] Additionally, the method for manufacturing a silicon negative electrode material for a lithium ion secondary battery may further include a secondary disintegration step (S24) after the oxidation step (S20).

[0142] The secondary disintegration step (S24) can crush and reduce the density of the polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) has been formed after the oxidation step (S20). The secondary disintegration step (S24) can crush the polycrystalline plate-shaped silicon particles (10) on which an oxide layer (11) has been formed together with air in a pin mill with a radius of 110 to 130 mm and a speed of 3300 to 3500 rpm.

[0143] This secondary disintegration step (S24) separates the polycrystalline plate-shaped silicon particles (10) on which the coagulated oxide layer (11) is formed, and, like the primary disintegration step (S10), the particles can have an apparent density of 0.1 to 0.4 g / cm3. Accordingly, the secondary disintegration step (S24) can enable the silicon carbide layer (12) to be uniformly formed in the subsequent silicon carbide layer forming step (S30).

[0144] 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 (S40).

[0145] The graphite and mixing step can be performed after the carbon coating step (S40) by mixing the plate-shaped silicon composite (1) and 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.

[0146] In the graphite and mixing step, the plate-shaped silicon complex (1) can be added during the process of spheroidizing graphite, or the graphite and plate-shaped silicon complex (1) that have completed the spheroidizing or spheroidizing process can be mixed.

[0147] Specifically, when a plate-shaped silicon complex (1) is introduced in the process of spheroidizing graphite in the mixing step with graphite, a spheroidized silicon negative electrode material for a lithium-ion secondary battery in the form of spheroidized or spheroidized graphite can be manufactured by inserting the plate-shaped silicon complex (1) between the graphite plates.

[0148] On the other hand, when a graphite and plate-shaped silicon composite (1) that have undergone a spheroidization or spheroidization process in the mixing step are mixed, a silicon negative electrode material for a simple lithium-ion secondary battery can be manufactured in the form of a plate-shaped silicon composite (1) arranged between graphite.

[0149] At this time, the graphite goes through 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 problems such as peeling may occur due to difficulty in forming a coating layer of a certain thickness. Generally, the spheroidization process can be spheroidized by removing rough parts of the flake-shaped carbon material through mechanical rotational motion and smoothing the particle surface.

[0150]

[0151] The silicon anode material for a lithium ion secondary battery of the present invention described above forms a multilayer structure including an oxide layer and a carbon-containing layer on a plate-like silicon formed with a waste silicon kerf, so that when combined 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 due to the use of a waste silicon kerf.

[0152]

[0153] 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 of the present invention may have an initial discharge capacity of 400 mAh / g or more, and a residual capacity (discharge capacity) of 75% or more at 500 cycles, which may be 300 to 350 mAh / g.

[0154] In this way, the silicon negative electrode material for a lithium ion secondary battery of the present invention has a low rate of decrease compared to the initial capacity during charge and discharge, and can be expected to have a significantly improved discharge capacity even in the same cycle.

[0155]

[0156] 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.

[0157]

[0158] [Example]

[0159] [Example 1]

[0160] In the process of slicing a single-crystal silicon ingot, 5,000 ml of a 5% plate-shaped silicon mixture was recovered through cooling, lubrication, and cutting with a 50 μm diameter diamond wio saw using a mixture of water and diethylene glycol. The mixture was milled for 2 hours in a milling machine using 0.3 mm zirconia balls and a zirconia jar to recover polycrystalline plate-shaped silicon with a grain size of 24 nm.

[0161] Afterwards, the dispersion solution containing polycrystalline plate silicon was injected at a rate of 20 ml per minute into 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.

[0162] The polycrystalline plate-shaped silicon particles were confirmed to have a grain size of 24 nm through XRD analysis (Fig. 8) and TEM measurement (Fig. 9). The half width at half maximum (FWHM) and grain size can be accurately determined using the equation below based on the measured values ​​of the half width at half maximum (FWHM) and grain size. The half width at half maximum was 0.3676°.

[0163] Full width at half maximum (FWHM) = Kλ / LCosθ (K = Scherrer constant, λ = 0.154 nm, L = crystal size, θ = half value of 2θ (28.4)) The Scherrer constant (K) is as follows.

[0164]

[0165] K(Scherrer constant) particle size 0.90(Spherical) 22.3nm 0.94(Cubic) 23.4nm

[0166]

[0167] This example used K=0.94 because it was close to a crushed silicon particle.

[0168] 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. The plate-shaped silicon particles with the formed oxide layer were maintained in a rotary kiln at 950°C for 20 minutes, while injecting methane gas at a rate of 0.1 M / min. to replace the surface of the oxide layer and form a silicon carbide layer, and the residual carbon covered the outer shell of the silicon carbide layer to form a carbon layer, thereby forming a plate-shaped silicon composite.

[0169] The manufactured plate-shaped silicon composite was mixed with spheroidized graphite in a weight ratio of 5:95 in a dry ball mill in an inert atmosphere 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 make 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.

[0170]

[0171] [Example 2]

[0172] A full-cell lithium secondary battery was assembled by manufacturing a plate-shaped silicon composite in the same manner as in Example 1, except that the zirconia ball milling time was changed to 30 minutes during the polycrystalline plate-shaped silicon particle manufacturing process to manufacture a polycrystalline plate-shaped silicon grain size of 41 nm.

[0173]

[0174] [Comparative Examples 1 and 2]

[0175] In the process of squaring (slicing) a single crystal silicon ingot, a plate-shaped silicon mixture solution was recovered through cooling, lubrication, and cutting with a 400 μm diameter diamond wio saw using a mixture of water and diethylene glycol. The mixture solution was milled for 2 and 4 hours using a milling machine using 1 mm zirconia balls and a zirconia jar, and polycrystalline plate-shaped silicon with different grain sizes of 69 nm and 84 nm were recovered, respectively.

[0176]

[0177] A plate-shaped silicon composite was manufactured in the same manner as in Example 1, and a full-cell lithium secondary battery was assembled.

[0178] The crystal grain sizes and half-widths of Examples 1 and 2 and Comparative Examples 1 and 2 are as shown in [Table 2] below.

[0179]

[0180] Classification FWHM (°) Grain size (nm) Silicon composite: graphite (weight ratio) Example 10.3676245:95 Example 20.2038415:95 Comparative example 30.1242695:95 Comparative example 40.1017845:95

[0181]

[0182] [Experimental Example 1] Charge / Discharge Performance Evaluation

[0183] To evaluate the charge / discharge performance of the full cells manufactured in Examples 1 and 2 and Comparative Examples 1 and 2, the capacity and lifespan were measured.

[0184] At this time, the capacity was measured under the condition of 1C of charge / discharge current at 25℃, and the lifespan was measured up to 500 cycles under the condition of 1C of charge / discharge current at 25℃.

[0185] The results are shown in [Table 3] below.

[0186]

[0187] Classification FWHM (°) Grain size (nm) Initial capacity (initial discharge capacity, mAh / g) Residual capacity after 500 cycles (%) Example 10.367624414.080.5 Example 20.203841417.176.2 Comparative example 10.124269422.451.1 Comparative example 20.101784425.932.4

[0188]

[0189] Example 1 exhibited a high discharge capacity of 414.0 mAh / g in the first cycle test, and showed a capacity decrease that was nearly linear as the cycle progressed, and showed a residual capacity of 80.5% (333.3 mAh / g) at 500 cycles, and Example 2 exhibited a high discharge capacity of 417.1 mAh / g in the first cycle test, and showed a capacity decrease that was nearly linear as the cycle progressed, and showed a residual capacity of 76.2% (317.8 mAh / g) at 500 cycles.

[0190] On the other hand, Comparative Example 1 showed a high discharge capacity of 422.4 mAh / g in the first cycle test, but showed a rapid decrease in capacity as the cycle progressed, and at 500 cycles, it showed a residual capacity of 51.1% (215.8 mAh / g), which is half the capacity. Comparative Example 2 showed a high discharge capacity of 425.9 mAh / g in the first cycle test, but showed a rapid decrease in capacity as the cycle progressed, and at 500 cycles, it showed a residual capacity of 138.0 mAh / g, which was significantly reduced to 32.4%.

[0191] The above results confirm that the crystal structure and size of polycrystalline platelet silicon particles in a silicon composite embedded in a silicon anode material affect battery performance. Specifically, in polycrystalline platelet silicon, larger grain sizes slightly improve initial capacity, but beyond a certain level, lifespan can be significantly reduced.

[0192] 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.

[0193]

[0194] [Explanation of symbols]

[0195] 1: Plate-shaped silicone composite

[0196] 10: Polycrystalline plate silicon

[0197] 11: Oxide layer

[0198] 12: Silicon carbide layer

[0199] 13: Carbon coating layer

Claims

1. A silicon anode material for a lithium ion secondary battery comprising a plate-shaped silicon composite manufactured from plate-shaped silicon formed with a silicon kerf, The above plate-shaped silicon composite is, polycrystalline plate-shaped silicon particles; A silicon oxide layer formed by oxidizing the surface of the polycrystalline plate-shaped silicon particles; A silicon carbide layer formed on the outer surface of the silicon oxide layer; and A silicon negative electrode material for a lithium ion secondary battery, comprising a carbon coating layer formed by coating with conductive carbon to surround the silicon carbide layer.

2. In paragraph 1, The above polycrystalline plate silicon is a silicon anode material for lithium-ion secondary batteries, which was confirmed to be polycrystalline by XRD analysis of the Si(002) plane.

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

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

5. 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.

6. 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.

7. 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.

8. In paragraph 1, A silicon anode material for lithium-ion secondary batteries containing more graphite.

9. A negative electrode comprising a silicon negative electrode material for a lithium ion secondary battery of paragraph 1.

10. A lithium ion secondary battery comprising the negative electrode of clause 9.

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