Precursor for negative electrode material of lithium secondary battery and method for preparing the same

Abstract

An aspect of the present application provides a precursor for a negative electrode material of a lithium secondary battery and a method of manufacturing the same, in which by controlling the molding density of the precursor for the negative electrode material of the lithium secondary battery, high capacity characteristics and excellent life characteristics of the negative electrode material can be ensured.

Description

Technical Field

[0001] This invention relates to a precursor for a negative electrode material of a lithium secondary battery and a negative electrode material prepared from the precursor. Background Technology

[0002] Lithium-ion rechargeable batteries typically consist of a positive electrode containing a positive electrode material, a negative electrode containing a negative electrode material, a separator, and an electrolyte. They are charged and discharged through the intercalation and decalation of lithium ions. Lithium-ion rechargeable batteries have advantages such as high energy density, high electromotive force, and high capacity, and are therefore used in various fields including mobile devices, electric vehicles, and hybrid electric vehicles.

[0003] In lithium secondary batteries, metal oxides such as LiCoO2, LiMnO2, LiMn2O4, or LiCrO2 are used as positive electrode materials, while metal-based materials such as metal lithium, graphite, or activated carbon, and silicon oxide (SiOx) are used as negative electrode materials.

[0004] Various forms of materials are used as the carbon-based anode material, such as natural graphite and artificial graphite as crystalline carbon-based materials, or hard carbon and soft carbon as amorphous carbon-based materials. Among them, graphite-based anode materials are the most widely used, as they have excellent reversibility, which is beneficial to the lifespan characteristics of lithium secondary batteries.

[0005] However, the theoretical capacity of graphite-based anode materials (e.g., approximately 372 mAh / g in the case of LiC6 anodes) is relatively low, and therefore currently insufficient to meet the electrochemical characteristics required by the relevant markets.

[0006] Therefore, many researchers are focusing on Group IV elements (Si, Ge, Sn) in the periodic table, especially silicon due to its very high theoretical capacity (Li). 15 Si4 has attracted considerable attention as a highly attractive material due to its characteristics of 3600 mAh / g and low operating voltage (~0.1V vs. Li / Li+). However, during charge and discharge, silicon undergoes significant volume expansion and contraction due to its reaction with lithium, which may lead to micronization of the silicon active material powder and poor electrical contact between the silicon active material powder and the current collector. Because of this phenomenon, silicon-containing lithium secondary batteries suffer from the problem that the battery capacity may decrease sharply with charge-discharge cycles. Summary of the Invention

[0007] (a) Technical problems to be solved One aspect of the present invention is to provide a precursor for a negative electrode material of a lithium secondary battery that can ensure high capacity characteristics and excellent lifespan characteristics, and a method for preparing the same.

[0008] The technical problem addressed by this invention is not limited to the above description. Those skilled in the art will readily understand the additional technical problems addressed by this invention from the entirety of this specification.

[0009] (II) Technical Solution According to one aspect of the present invention, the precursor for the negative electrode material of a lithium secondary battery may comprise silicon nanoparticles, conductive materials and carbon-based materials, and the molding density of the precursor for the negative electrode material of the lithium secondary battery may be greater than 1.3 g / cm³ (cc) and less than 1.6 g / cm³.

[0010] The aforementioned conductive material can be at least one of natural graphite and artificial graphite.

[0011] The aforementioned carbon-based material may be at least one of coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

[0012] The fixed carbon ratio of the above-mentioned coal-based pitch and petroleum-based pitch can be above 60%, and the β-resin value can be above 10%.

[0013] The aforementioned carbon-based materials may further include binding additives.

[0014] The aforementioned adhesive additives may be viscoelastic olefin-based oligomers or polymers, or organic compounds with adhesive properties.

[0015] A method for preparing a precursor for a negative electrode material of a lithium secondary battery according to another aspect of the present invention may include the following steps: preparing silicon nanoparticles, a conductive material, and a carbon-based material; mixing the silicon nanoparticles, the conductive material, and the carbon-based material to prepare a mixture; and subjecting the mixture to pressure molding, wherein the pressure molding step can be performed by applying an pressure of 6 tons / cm². 2 Above and 20 tons / cm 2 The following pressures will be applied.

[0016] The aforementioned conductive material can be at least one of natural graphite and artificial graphite.

[0017] The aforementioned carbon-based material may be at least one of coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

[0018] The fixed carbon ratio of the above-mentioned coal-based pitch and petroleum-based pitch can be above 60%, and the β-resin value can be above 10%.

[0019] In the step of preparing the above mixture, a binding additive may be further mixed in.

[0020] The aforementioned adhesive additives may be viscoelastic olefin-based oligomers or polymers, or organic compounds with adhesive properties.

[0021] When the carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressure molding step can be carried out at a temperature 10°C higher than the pitch softening point to a temperature 150°C higher than the pitch softening point.

[0022] The above-mentioned pressure molding steps can be performed at room temperature.

[0023] The molding density of the precursor for the negative electrode material of the prepared lithium secondary battery can be greater than 1.3 g / cm³ and less than 1.6 g / cm³.

[0024] (III) Beneficial Effects The precursor for the negative electrode material of the lithium secondary battery of the present invention can provide a negative electrode material with a high-density carbon layer that is physically and chemically stable by controlling the molding density. Therefore, the negative electrode material obtained from the precursor for the negative electrode material of the present invention can ensure high capacity characteristics and excellent lifetime characteristics. Attached Figure Description

[0025] Figure 1 This is a photograph of a molded body formed by carbonizing the precursor of the negative electrode material of the lithium secondary battery of Invention Example 1.

[0026] Figure 2 This is a SEM image of the cross-section of the negative electrode on which the negative electrode material of Comparative Example 1 is coated on the current collector.

[0027] Figure 3 This is a SEM image of the cross-section of the negative electrode on which the negative electrode material of Example 1 of the Invention is coated.

[0028] Figure 4 This is a SEM image of the cross-section of the negative electrode on which the negative electrode material of Comparative Example 2 is coated.

[0029] Figure 5 This is a SEM image of the cross-section of the negative electrode on which the negative electrode material of Comparative Example 3 is coated.

[0030] Figure 6 This is a graph showing the expansion rate (%) of Invention Example 1, Invention Example 2, and Comparative Examples 1 to 3 according to the number of cycles. Best practice

[0031] The preferred embodiments of the present invention will be described below. However, the embodiments of the present invention can be modified into many other embodiments, and the scope of the present invention is not limited to the embodiments described below.

[0032] In this specification, unless otherwise stated to the contrary, the terms “comprising” and “including” are used to indicate that other constituent elements may be further included, rather than excluding other constituent elements.

[0033] Furthermore, in the specification of this invention, unless otherwise specified, the % unit represents weight.

[0034] While not strictly necessary, it should be noted that the technical solutions according to various aspects of the present invention can be effectively used in other technical solutions. Furthermore, the components and various useful parameters of the various aspects of the present invention can be appropriately combined with other aspects to obtain advantageous effects.

[0035] In the case of anode materials containing silicon nanoparticles, during charging and discharging, they not only react with lithium, potentially generating irreversible products such as an SEI layer, carbon monoxide (CO), or carbon dioxide (CO2), but may also cause significant volume expansion and contraction of the silicon nanoparticles.

[0036] In this scenario, some silicon nanoparticles may be partially exposed on the surface and react with the electrolyte, potentially generating a new SEI (Sediment-Insulated Layer), which could lead to continuous lithium consumption. Therefore, existing anode materials containing silicon nanoparticles suffer from poor lifetime characteristics.

[0037] To address the aforementioned problems, the inventors of this invention discovered that when a high-density carbon layer with stable physical and chemical properties is formed inside the negative electrode material, not only can the contact path between silicon nanoparticles and conductive materials be enhanced, but the expansion of silicon nanoparticles can also be controlled.

[0038] Furthermore, the inventors of this invention have discovered that the high-density carbon layer can compensate for the low conductivity of silicon raw materials (10). -4 By using S / cm to induce a reversible reaction with lithium, the capacity of the anode material can be increased while improving its lifetime characteristics.

[0039] Furthermore, the inventors of this invention realized that in order to provide the aforementioned high-density carbon layer, it is necessary to control the molding density of the precursor for the negative electrode material of the lithium secondary battery at a certain level, thereby completing this invention.

[0040] Based on this viewpoint, according to an example of the present invention, the precursor for the negative electrode material of a lithium secondary battery may comprise silicon nanoparticles, conductive materials, and carbon-based materials, and the molding density of the precursor for the negative electrode material of a lithium secondary battery may be greater than 1.3 g / cm³ and less than 1.6 g / cm³. The various components will be described in detail below.

[0041] silicon nanoparticles In one example of the present invention, for the purpose of providing a negative electrode material with high capacity characteristics, the precursor for the negative electrode material of the lithium secondary battery may contain silicon nanoparticles.

[0042] As a non-limiting example, the D50 particle size of the silicon nanoparticles can be greater than 50 nm and less than 250 nm. This is to prevent the silicon nanoparticles from expanding due to repeated charging and discharging, while ensuring high capacity. Here, D50 refers to the particle size corresponding to 50% of the volumetric density in the particle size distribution. As another example, the D50 particle size of the silicon nanoparticles can be greater than 50 nm and less than 150 nm; as yet another example, the D50 particle size of the silicon nanoparticles can be greater than 100 nm and less than 150 nm.

[0043] Furthermore, according to one embodiment of the present invention, based on the total weight of the negative electrode material precursor, the weight ratio of silicon nanoparticles contained in the negative electrode material precursor for lithium secondary batteries can be 40% by weight or more and 70% by weight or less.

[0044] According to one embodiment of the present invention, the high capacity characteristics of the negative electrode material for lithium secondary batteries can be ensured by containing more than 40% by weight of the silicon nanoparticles. On the other hand, when the content of the silicon nanoparticles in the negative electrode material precursor is too high, the silicon nanoparticles and the conductive material cannot be completely coated by the carbon coating, either individually or as a whole. In this case, the structure of the negative electrode material, which is a silicon-carbon composite, may collapse. For the above reasons, in one embodiment of the present invention, the content of the silicon nanoparticles can be less than 70% by weight relative to the total weight of the negative electrode material precursor for lithium secondary batteries.

[0045] conductive materials According to one embodiment of the present invention, the precursor for the negative electrode material of the lithium secondary battery may further contain a conductive material to ensure a conductive path with the aforementioned silicon nanoparticles and improve the reversibility of lithium ions, thereby improving the capacity and efficiency of the negative electrode material.

[0046] For the above objectives, in one example of the present invention, the content of the conductive material may be 10% by weight or more relative to the total weight of the negative electrode material precursor for lithium secondary batteries. More specifically, the content of the conductive material may be 20% by weight or more relative to the total weight of the negative electrode material precursor. However, when the content of the conductive material is too high, it may be difficult to be capturing with a carbon coating. Therefore, in one embodiment of the present invention, the weight ratio of the conductive material relative to the total weight of the negative electrode material precursor may be set to 30% by weight or less.

[0047] More specifically, an example of the conductive material may be at least one of natural graphite and artificial graphite.

[0048] carbon-based materials As described above, in one embodiment of the present invention, by forming a high-density carbon layer with stable physical and chemical properties, the high capacity characteristics and excellent lifetime characteristics of the anode material can be ensured.

[0049] Therefore, according to one example of the present invention, for the purpose of forming the carbon layer, the precursor for the negative electrode material of the lithium secondary battery may contain a carbon-based material.

[0050] According to one embodiment of the present invention, the carbon-based material may be at least one selected from coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA). These carbon-based materials can be carbonized to form amorphous carbon, thereby subsequently functioning as a binder to stabilize and support the structure of the negative electrode material. That is, the carbon-based material can be dispersed and located within the pores of the porous silicon-carbon composite, preventing the collapse of the porous structure of the silicon-carbon composite when the negative electrode material precursor of this embodiment is applied to a battery, even with repeated charge-discharge cycles.

[0051] Additionally, as an example, the fixed carbon ratio of the coal-based pitch and the petroleum-based pitch can be 60% or more. More specifically, the fixed carbon ratio can be 70% or more.

[0052] The higher the fixed carbon value of the coal-based pitch and the petroleum-based pitch, the more easily they can form conductive paths with silicon particles that have low conductivity, thereby inducing an increase in capacity and efficiency. Furthermore, when the fixed carbon value meets the above-mentioned range, the internal porosity of the negative electrode material in this embodiment can be reduced. Therefore, side reactions with the electrolyte can also be reduced, which can help improve the initial efficiency of the battery.

[0053] The β-resin value of the coal-based pitch and the petroleum-based pitch can be, for example, 10% or more, and more specifically, the β-resin value can be 25% or more.

[0054] Specifically, the β-resin value refers to the value obtained by subtracting the quinoline insoluble content from the benzene-insoluble content. The β-resin value is directly proportional to the adhesiveness. According to one embodiment of the present invention, when coal-based or petroleum-based pitch with a β-resin value satisfying the above range is used, the porous structure of the silicon-carbon composite can be maintained more stably. Therefore, one embodiment of the present invention can realize a lithium secondary battery with excellent lifespan and electrode expansion characteristics.

[0055] Furthermore, according to one example of the invention, the carbon-based material may further include a binding additive. The binding additive can help maintain the shape of the molded body. The binding additive is not particularly limited to the extent that the above-mentioned objective can be achieved, but as an example, the binding additive may be a viscoelastic olefin-based oligomer or polymer, or an organic material with adhesive function such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), or polyacrylic acid (PAA).

[0056] The precursor for the negative electrode material of a lithium secondary battery according to one embodiment of the present invention will be described in detail below.

[0057] As described above, in one example of the present invention, by forming a high-density carbon layer with stable physical and chemical properties inside the negative electrode material, the capacity of the negative electrode material can be increased while its lifetime characteristics are improved.

[0058] According to one example of the invention, in order to provide such a high-density carbon layer, the molding density of the anode material precursor can be greater than 1.3 g / cm³ and less than 1.6 g / cm³.

[0059] More specifically, according to one example of the present invention, by setting the molding density of the precursor for the negative electrode material of the lithium secondary battery to be greater than 1.3 g / cm³, a high-density internal carbon layer can be provided. Therefore, in one example of the present invention, not only can the porosity in the negative electrode material be removed, but the silicon nanoparticles can also be fully coated by the internal carbon layer, thereby improving the surface coverage of the silicon nanoparticles. Furthermore, in one embodiment of the present invention, the above-mentioned molding density can reduce the distance between the silicon nanoparticles, thereby increasing the number of silicon nanoparticles per unit volume, and thus improving the electrochemical capacity. According to another example, the lower limit of the molding density can be 1.4 g / cm³. On the other hand, when the molding density is too high, the generation of microparticles during subsequent pulverization may increase with the increase in the strength of the negative electrode material; therefore, in one example of the present invention, the upper limit of the molding density can be set to 1.6 g / cm³. According to another example, the upper limit of the molding density can be 1.55 g / cm³, and according to another example, the upper limit of the molding density can be 1.5 g / cm³.

[0060] Furthermore, when the above-mentioned negative electrode material is carbonized with a precursor at a certain temperature and then pulverized and graded, the negative electrode material of the present invention can be obtained. Hereinafter, the negative electrode material of the present invention described above will be specifically explained.

[0061] As described above, in one example according to the present invention, the molding density of the precursor for the negative electrode material can be controlled within a certain range, so the negative electrode material obtained from such a precursor for the negative electrode material can have an appropriate level of tap density and specific surface area, thereby exhibiting excellent electrochemical performance.

[0062] More specifically, according to one embodiment of the present invention, the tap density of the negative electrode material can be above 0.50 g / cm³ and below 0.72 g / cm³, and the specific surface area can be 2 m². 2 / g or more and 7.3m 2 / g or less.

[0063] In addition, according to one embodiment of the present invention, the D50 particle size of the negative electrode material of the lithium secondary battery can be 8.0 μm or more and 15.0 μm or less.

[0064] Specifically, according to one example of the present invention, in order to prevent localized differences in battery performance by ensuring uniform electrode thickness quality, the median particle size (D50) of the negative electrode material of the lithium secondary battery can be set to 8.0 μm or more and 15.0 μm or less. More specifically, the median particle size of the negative electrode material can be 9.0 μm or more and 12.0 μm or less, or 10.0 μm or more and 11.0 μm or less.

[0065] The following describes a method for preparing a precursor for the negative electrode material of a lithium secondary battery according to the present invention. However, it should be noted that the method described below for preparing a precursor for the negative electrode material of a lithium secondary battery is merely an example. The precursor for the negative electrode material of a lithium secondary battery according to the present invention does not necessarily have to be prepared using this method. Any preparation method that satisfies the scope of the claims of the present invention can be used to implement various embodiments of the present invention without any problems.

[0066] According to an example of the present invention, a method for preparing a precursor for a negative electrode material of a lithium secondary battery may include the following steps: preparing silicon nanoparticles, a conductive material, and a carbon-based material; mixing the silicon nanoparticles, the conductive material, and the carbon-based material to prepare a mixture; and subjecting the mixture to pressure molding, wherein the pressure molding step can be performed by applying an pressure of 6 tons / cm². 2 Above and 20 tons / cm 2 The following pressure will be applied. The following will provide a detailed explanation of each step.

[0067] First, in one embodiment of the present invention, silicon nanoparticles, conductive materials, and carbon-based materials can be prepared.

[0068] To obtain the silicon nanoparticles, in one non-limiting embodiment of the present invention, the silicon raw material can be pulverized by mechanical milling. Therefore, as described above, the D50 particle size of the pulverized silicon nanoparticles can be greater than 50 nm and less than 250 nm.

[0069] Furthermore, as an example, the mechanical polishing can be performed using stabilized zirconia. Additionally, in order to suppress the generation of fine particles by improving nano-sizing efficiency and preventing oxidation of silicon particles, the size of the zirconia beads can be less than twice the D99 of the added silicon raw material; however, the zirconia beads used can be in various sizes for process design and are therefore not limited to this.

[0070] Furthermore, the detailed conditions for mechanical grinding are matters that can be fully designed by those skilled in the art according to their purposes, and therefore are not particularly limited. However, as an example, the ball-per-particle ratio (BPR) of the silicon raw material to the stabilized zirconia balls can be set to 5:1, and the rotor speed inside the pulverizer can be maintained at 2500 rpm.

[0071] Furthermore, according to one example of the invention, the solvent used in the mechanical grinding can be an organic solvent such as ethanol or isopropanol (IPA) to prevent oxidation of the silicon raw material.

[0072] The conductive material can be at least one of natural graphite and artificial graphite, and the carbon-based material can be at least one of coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA). Furthermore, the fixed carbon ratio of the coal-based pitch and the petroleum-based pitch can be 60% or more, and the β-resin value can be 10% or more. This part is the same as the above content regarding precursors for anode materials, therefore, the explanation is omitted.

[0073] As described above, after preparing silicon nanoparticles, conductive materials, and carbon-based materials, these materials can be mixed to obtain a mixture. Furthermore, according to another embodiment of the invention, during the above mixing, a binding additive can be further mixed in. As a non-limiting example, the binding additive can be a viscoelastic olefin-based oligomer or polymer, or an organic compound with adhesive properties such as PVDF, SBR, CMC, or PAA.

[0074] The mixing can be performed simultaneously, or at least two of the above substances can be mixed first, followed by the remaining substances. As an example, the silicon nanoparticles and the conductive material can be mixed first, then spray-dried to obtain a spray-dried product, and then the carbon-based material can be added, followed by mixing the spray-dried product and the carbon-based material. Furthermore, the binding additive can be selectively added when adding the carbon-based material. However, this is merely an example and is not a limitation.

[0075] Furthermore, the mixing can be carried out using a milling process that utilizes a medium in contact with the powder. As a non-limiting example, the mixing can be carried out by mechanical fusion or ball milling. When performing such a milling process utilizing a medium in contact with the powder, there is an advantage in reducing the independent flow of silicon nanoparticles when mixing with a solvent.

[0076] According to one embodiment of the present invention, the method for preparing a precursor for a negative electrode material of a lithium secondary battery may include a step of pressurizing and molding the mixture.

[0077] That is, according to one example of the present invention, in order to obtain a precursor for a negative electrode material having the above-mentioned molding density, a specific pressure can be applied to the mixture within a specified time range. More specifically, when such pressure molding is performed, the carbon-based material in the aforementioned negative electrode material precursor can fill the micropores inside the precursor body, thereby reducing the specific surface area of ​​the negative electrode material and thus improving the electrochemical performance of the negative electrode material. As a non-limiting example, the pressure molding can be performed by filling the precursor powder into a self-made mold and using a pressure stamping device, and the resulting semi-finished product can be specified as a block shape.

[0078] In particular, according to a non-limiting embodiment of the invention, the pressure molding step can be achieved by applying 6 tons / cm². 2 Above and 20 tons / cm 2 The following pressures will be applied.

[0079] In the pressure molding step, by applying 6 tons / cm 2 Above and 20 tons / cm 2 The following pressure can control the molding density of the negative electrode material precursor at an appropriate level. More specifically, in one embodiment of the invention, by setting the pressure during press molding to the above range, the molding density of the negative electrode material precursor can be maintained between greater than 1.3 g / cm³ and less than 1.6 g / cm³. As another example, the press molding step can be achieved by applying a pressure of 6 tons / cm³. 2 Above and 15 tons / cm 2 The following pressure is used; as another example, the pressure molding step can be performed by applying 10 tons / cm². 2 Above and 11 tons / cm 2 The following pressures will be applied.

[0080] In addition, according to an example of the present invention, when the carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressure molding step can be carried out at a temperature 10°C higher than the pitch softening point to a temperature 150°C higher than the pitch softening point.

[0081] In one example of the present invention, by performing pressure molding within a temperature range 10°C higher than or equal to the softening point of the asphalt, not only can the viscosity of the asphalt be increased, thereby removing porosity within the negative electrode material precursor, but a high surface coverage of silicon nanoparticles can also be maintained. However, when the temperature in the pressure molding step is higher than 150°C higher than the softening point of the asphalt, the structure and morphology of the molded body may change due to gas generation or deterioration of some components. As another example, the temperature range in the pressure molding step can be from 10°C to 100°C higher than the softening point of the asphalt, or from 50°C to 100°C higher than the softening point of the asphalt.

[0082] However, according to another embodiment of the invention, the pressure molding step can also be performed at room temperature.

[0083] Typically, as mentioned above, heat treatment is required for the successful execution of the pressure molding step. However, according to a non-limiting example of the present invention, when using high-adhesion asphalt with a β-resin value above a certain level or with the addition of further adhesive additives, a precursor for a negative electrode material having the molding density proposed in this invention can be obtained even without separate heat treatment during pressure molding. In this case, since a separate heat treatment process is not required, the energy added can be reduced, thus offering the advantage of saving time and costs.

[0084] The anode material precursor obtained through the above steps can be carbonized, pulverized, and graded to obtain the anode material. The following is a detailed description of the method for preparing anode material from a precursor.

[0085] In a non-limiting example of the present invention, the precursor obtained by the above preparation method can be carbonized to obtain a molded article.

[0086] More specifically, the carbonization can be carried out in a temperature range above 800°C and below 1000°C. In one embodiment of the invention, by carbonizing the precursor at a temperature above 800°C, not only can the volatile components present inside the original precursor evaporate, but the asphalt can also be solidified, thus ensuring the internal structure of the negative electrode material. Furthermore, when the carbonization temperature is too high, silicon carbide and silicon nitride, which lack electrochemical properties, may be generated, potentially leading to a reduction in capacity and efficiency. Therefore, the carbonization can be carried out in a temperature range below 1000°C. In particular, to suppress the oxidation of silicon particles, the carbonization can be carried out in an inert atmosphere.

[0087] By crushing and classifying the molded body obtained as described above, negative electrode material of the target size can be obtained. As a non-limiting example, the crushing can be carried out by dry crushing, which can be performed using an air jet mill or a pin mill.

[0088] According to a non-limiting embodiment of the invention, a step of carbon coating on the surface of the obtained negative electrode material may be further included.

[0089] The carbon coating step can be performed by adding a carbon-based material and then heat-treating it. The carbon-based material can be at least one of petroleum-based asphalt, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA), with a softening point below 250°C. Furthermore, while not limited to these, the coating can be performed using a twisted blade mixer. In this case, process variables include time, rotational speed, etc., which are considered appropriate to the design of those skilled in the art and are not specifically described herein.

[0090] The manufacturing method of the negative electrode of the lithium secondary battery of the present invention will be described in detail below.

[0091] The negative electrode can be manufactured by mixing a negative electrode material prepared according to a specific embodiment of the present invention, an adhesive, and an optional conductive material to prepare a composition for forming a negative electrode material layer, and then coating the composition onto a negative electrode current collector.

[0092] The negative electrode current collector can be, for example, copper foil, nickel foil, stainless steel, titanium foil, foam nickel, foam copper, a polymer substrate coated with a conductive metal, or a combination thereof.

[0093] The adhesive may be made of polyacrylic acid, polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropyl cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene, but is not limited thereto. The amount of the adhesive mixed relative to the total amount of the composition for forming the negative electrode material layer may be from 1% by weight to 30% by weight.

[0094] The conductive material is not particularly limited, as long as it does not cause chemical changes in the battery and is conductive. Specifically, the conductive material can be natural graphite, artificial graphite, etc.; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber and metal fiber; metal powders such as fluorinated carbon, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. The mixing amount of the conductive material can be from 0.1% by weight to 30% by weight relative to the total amount of the composition for forming the negative electrode material layer. Detailed Implementation

[0095] (1) Preparation of negative electrode material precursor First, a silicon raw material (polycrystalline silicon) is prepared. Then, the silicon raw material is pulverized using stabilized zirconium oxide with a size of 0.1 mm to obtain a silicon nanoparticle slurry with a D50 particle size of 150 nm. The pulverization is carried out in 99% pure ethanol solvent with a solids content of 10%. During pulverization, the ball-to-particle ratio (BPR) of the stabilized zirconium oxide is 5:1, and the rotor speed inside the pulverizer is maintained at 2500 rpm. Next, flake graphite with a median particle size (D50) of 8.00 μm (added at 20 wt% relative to the total weight of the precursor) is added to the silicon nanoparticle slurry obtained by the above process, and spray-dried to obtain a powdered product. Then, petroleum-based pitch (added at 40 wt% relative to the total weight of the precursor) is added to the resulting powder, and the mixture is mechanically fused to obtain the anode material precursor. The petroleum-based asphalt has a fixed carbon content of over 70% and a β-resin value of 25%. The precursor is then press-molded to obtain a block-shaped negative electrode material precursor. This press-molding is performed at the temperature and pressure shown in Table 1 below. Pressure is applied to a cylindrical mold with a radius of 1 cm and a height of 5 cm using a pressurizing device. The molding density of the resulting negative electrode material precursor is then measured and is shown in Table 1 below. The molding density is measured by dividing the weight (g) of the molded body by its volume (cubic centimeters).

[0096] (2) Preparation of negative electrode materials Subsequently, the negative electrode material was carbonized at 900°C in an inert atmosphere. Afterward, it was pulverized using a jet mill (JET mill) to uniformly disperse petroleum-based asphalt with a softening point below 250°C onto the surface of the pulverized particles for additional coating. This additional coating was then performed using a twisted blade mixer. Following this, heat treatment was conducted in an inert atmosphere at 900°C, and the negative electrode material was obtained by sieving. The D01, D50, and D90 particle sizes of the obtained negative electrode material were measured using a laser diffraction particle size analyzer, and the measured values ​​are shown in Table 1 below. The D01, D50, and D90 particle sizes refer to the particle sizes corresponding to 1%, 50%, and 90% of the cumulative volume in the particle size distribution, respectively.

[0097] In addition, the tap density and BET specific surface area of ​​the obtained negative electrode material were measured and are shown in Table 1 below.

[0098] (3) Manufacturing of the negative electrode A negative electrode active material slurry is prepared by mixing 75% by weight of the prepared negative electrode material, 24% by weight of the binder containing polyacryl acid (PAA) and 1% by weight of Super P conductive material in distilled water solvent.

[0099] The negative electrode active material slurry was coated onto a copper (Cu) current collector and dried, then pressed in a roller press to a compaction density of 1.0 g / cm³. Subsequently, it was vacuum dried in a vacuum oven to obtain the negative electrode.

[0100] (4) Electrochemical evaluation To evaluate electrochemical characteristics, a lithium-ion secondary battery was manufactured. Specifically, using a negative electrode prepared by the above method, lithium metal (Li-metal) as the counter electrode, and an electrolyte (the electrolyte being an electrolyte in which 1 mole of LiPF6 solution is dissolved in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a volume ratio of 3:7), a 2032 coin-type half-cell was prepared according to a conventional manufacturing method. 10% by weight of fluoroethylene carbonate (FEC) additive was added to the electrolyte.

[0101] The discharge capacity, initial efficiency, and 50-cycle life of the battery were measured and are shown in Table 2 below.

[0102] In the initial cycle, the charge / discharge current was measured at 0.1C. Furthermore, using the first 1C capacity as a baseline, a 0.5C current was applied during charge / discharge, and the cycle life was measured for 50 cycles. At this point, the cut-off current was set to 0.005C.

[0103] [Table 1] [Table 2] In Comparative Example 1, the pressure during the compression molding step is less than 6 tons / cm². 2 Therefore, the density of the molded body is only 1.01 g / cm³. Consequently, the pores in the negative electrode material cannot be removed, and the coverage of silicon nanoparticles is low, resulting in poor initial efficiency and lifespan characteristics of the battery.

[0104] In the cases of Comparative Example 2 and Comparative Example 3, the pressure during the compression molding step exceeded 20 tons / cm². 2 Therefore, the density of the molded body is too high. Consequently, the strength of the molded body increases, and the generation of micronized negative electrode material (D10) during crushing also increases. Therefore, it can be confirmed that the measured specific surface area values ​​of Comparative Example 2 and Comparative Example 3 are larger.

[0105] On the other hand, in the case of Example 1, since all the conditions proposed in this invention are met, the discharge capacity, initial efficiency, and 50-cycle characteristics are all excellent. A photograph of the molded body formed by carbonizing the precursor of the negative electrode material of the lithium secondary battery of Example 1 is shown below. Figure 1 As shown.

[0106] In particular, as can be seen from Example 2 of the invention, the present invention can obtain a precursor for anode materials with excellent electrochemical properties even when pressure molding is performed at room temperature.

[0107] Figures 2 to 5 The image shows SEM images of the cross-sections of negative electrodes coated with negative electrode materials from Comparative Example 1, Invention Example 1, Comparative Example 2, and Comparative Example 3, respectively. According to the above... Figures 2 to 5 It can be confirmed that, compared to Comparative Example 1, Inventive Example 1 is a form in which the pores are relatively removed. Furthermore, according to... Figure 4 and Figure 5 It can be confirmed that in Comparative Examples 2 and 3, although the density of the molded body increased, the morphology after crushing was not uniform, and sharp parts existed after crushing. Therefore, it can be inferred that a large amount of fine powder was generated during the crushing process in Comparative Examples 2 and 3.

[0108] Figure 6This is a graph showing the expansion rate (%) of Invention Example 1, Invention Example 2, and Comparative Examples 1 to 3 according to the number of cycles. Based on the above... Figure 6 It can be confirmed that in Invention Examples 1, 2, and Comparative Example 2, where the molding density exceeds 1.3 g / cm³, the high-density carbon layer controls the expansion of silicon nanoparticles, resulting in a low expansion rate. However, in Comparative Example 1, where the molding density is less than 1.3 g / cm³, the expansion of silicon nanoparticles cannot be suppressed because a high-density carbon layer is not formed, leading to a high expansion rate. In Comparative Example 3, where the molding density is too high, the increased hardness of the molded body leads to an increased content of fine powder during crushing, resulting in the independent existence of silicon nanoparticles and a high expansion rate.

Claims

1. A precursor for the negative electrode material of a lithium secondary battery, comprising: Silicon nanoparticles; Conductive materials; and Carbon-based materials in, The molding density of the precursor for the negative electrode material of the lithium secondary battery is greater than 1.3 g / cm³ and less than 1.6 g / cm³.

2. The precursor for the negative electrode material of a lithium secondary battery according to claim 1, wherein, The conductive material is at least one of natural graphite and artificial graphite.

3. The precursor for the negative electrode material of a lithium secondary battery according to claim 1, wherein, The carbon-based material is at least one of coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

4. The precursor for the negative electrode material of a lithium secondary battery according to claim 3, wherein, The fixed carbon ratio of the coal-based pitch and the petroleum-based pitch is more than 60%, and the β-resin value is more than 10%.

5. The precursor for the negative electrode material of a lithium secondary battery according to claim 1, wherein, The carbon-based material further includes binding additives.

6. The precursor for the negative electrode material of a lithium secondary battery according to claim 5, wherein, The adhesive additive is an olefin-based oligomer or polymer with viscoelasticity, or an organic compound with adhesive function.

7. A method for preparing a precursor for a negative electrode material in a lithium secondary battery, comprising the following steps: Prepare silicon nanoparticles, conductive materials, and carbon-based materials; The silicon nanoparticles, the conductive material, and the carbon-based material are mixed to prepare a mixture; The mixture is then pressurized and molded. The pressure molding step involves applying 6 tons / cm². 2 Above and 20 tons / cm 2 The following pressures will be applied.

8. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 7, wherein, The conductive material is at least one of natural graphite and artificial graphite.

9. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 7, wherein, The carbon-based material is at least one of coal-based pitch, petroleum-based pitch, coal tar, polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

10. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 9, wherein, The fixed carbon ratio of the coal-based pitch and the petroleum-based pitch is more than 60%, and the β-resin value is more than 10%.

11. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 7, wherein, In the step of preparing the mixture, a binding additive is further mixed in.

12. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 11, wherein, The adhesive additive is an olefin-based oligomer or polymer with viscoelasticity, or an organic compound with adhesive function.

13. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 9, wherein, When the carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressure molding step is carried out at a temperature 10°C higher than the pitch softening point to a temperature 150°C higher than the pitch softening point.

14. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 10 or 11, wherein, The pressure molding step is performed at room temperature.

15. The method for preparing a precursor for the negative electrode material of a lithium secondary battery according to claim 8, wherein, The molding density of the precursor for the negative electrode material of the prepared lithium secondary battery is greater than 1.3 g / cm³ and less than 1.6 g / cm³.

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