Anode active material, method for manufacturing same, and lithium secondary battery comprising same

Abstract

The purpose of one aspect of the present invention is to provide an anode active material. The anode active material includes: silicon-based particles; and a coating layer disposed on the surfaces of the silicon-based particles, wherein an average particle diameter (D50) of the silicon-based particles is 1.0-2.8 ㎛, the coating layer includes a polymer, and in the Raman spectrum of the anode active material, a full width at half maximum of a peak positioned in a 480-540 cm-1 region may be greater than 23 cm-1.

Description

Negative active material, method for producing same, and lithium secondary battery including same

[0001] The present invention relates to a negative electrode active material, a method for producing the same, and a lithium secondary battery including the same.

[0002] As the market for electronic devices such as mobile phones, laptops, and PCs grows, the market for lithium secondary batteries, the power sources for these devices, is also growing rapidly. Furthermore, growing concern over environmental issues has led to a surge in demand for eco-friendly vehicles like electric vehicles, leading to research into lithium secondary batteries that can meet a variety of applications.

[0003] Among the components that make up lithium secondary batteries, the anode active material stores lithium ions during charging and plays a crucial role in determining charging speed and battery capacity. Among these anode active materials, silicon-based active materials are attracting attention due to their superior electrochemical properties, such as capacity and energy output, compared to carbon-based materials.

[0004] However, silicon-based active materials typically exhibit significant volumetric expansion and contraction during charge and discharge, leading to reduced battery life. Furthermore, side reactions between silicon-based active materials and the electrolyte can lead to the formation of a thick SEI layer.

[0005] Therefore, there is a need for research on silicon-based negative electrode active materials that can suppress side reactions with the electrolyte while minimizing volume expansion due to continuous charge and discharge.

[0006] One aspect of the present invention is to provide a negative electrode active material capable of improving life characteristics by reducing volume expansion and minimizing side reactions with an electrolyte, a method for producing the same, and a lithium secondary battery including the same.

[0007] The objectives of the present invention are not limited to the above-described matters. Additional objectives of the present invention are described throughout the specification, and those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the contents described in the specification.

[0008] One aspect of the present invention provides a negative electrode active material. The negative electrode active material comprises: silicon particles; a coating layer disposed on the surface of the silicon particles, wherein the silicon particles have an average particle diameter (D50) of 1.0 to 2.8 μm, the coating layer comprises a polymer, and a Raman spectrum of the negative electrode active material has a wavelength of 480 to 540 cm. -1 The half-width of the peak located in the area is 23 cm -1 It may be excessive.

[0009] In addition, in the above-mentioned negative active material, the value of the Raman shift corresponding to the maximum peak in the Raman spectrum of the negative active material is 499 cm -1 It could be strange.

[0010] Additionally, in one of the aforementioned negative active materials, the cyclization reaction temperature or condensation reaction temperature of the polymer may be 200 to 350°C.

[0011] In addition, in one of the above-mentioned negative electrode active materials, the polymer may include polyacrylonitrile, nitrile butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyaniline or a mixture thereof, which is cyclized or condensed on the surface of silicon particles.

[0012] Additionally, in one of the aforementioned negative active materials, the polymer may include a cyclized polyacrylonitrile-based polymer.

[0013] Additionally, in one of the above-described negative electrode active materials, the polymer may be included in an amount of 0.5 to 10.0 wt% based on the total weight of the negative electrode active material.

[0014] Additionally, in one of the aforementioned negative active materials, the coating layer may further include fibrous carbon.

[0015] In addition, in one of the aforementioned negative active materials, the fibrous carbon may include at least one selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs).

[0016] Additionally, in one of the aforementioned negative electrode active materials, the fibrous carbon may be included in an amount of 0.1 to 1.0 wt% based on the total weight of the negative electrode active material.

[0017] Additionally, in one of the aforementioned negative active materials, the silicon-based particles may be silicon particles (Pure Si).

[0018] Additionally, in one of the aforementioned negative active materials, the D10 of the silicon-based particles may be 0.1 to 1.4 μm.

[0019] Additionally, in one of the aforementioned negative electrode active materials, the silicon-based particles may be included in an amount of 80 wt% or more based on the total weight of the negative electrode active material.

[0020] Another aspect of the present invention provides a method for manufacturing a negative electrode active material. The method comprises the steps of: preparing a precursor solution containing a polymer; adding silicon particles to the precursor solution to obtain a mixture; and heat-treating the mixture at a temperature of 200 to 350°C. The average particle diameter (D50) of the silicon particles may be 1.0 to 2.8 μm.

[0021] Additionally, in the method described above, in the step of preparing the precursor solution, the precursor solution may further include fibrous carbon.

[0022] Another aspect of the present invention provides a lithium secondary battery. The lithium secondary battery includes a negative electrode; a positive electrode; and an electrolyte, wherein the negative electrode may include one of the negative electrode active materials described above.

[0023] According to the present invention, a coating layer containing a polymer is formed on the surface of silicon particles, thereby applying strong compressive stress to the silicon particles. Accordingly, volume expansion of the negative electrode active material due to continuous charge / discharge can be improved, and life characteristics can be enhanced.

[0024] In addition, the negative active material according to one specific example may have improved electrical conductivity by further including fibrous carbon in the coating layer, and a stronger compressive stress may be applied to the silicon-based particles.

[0025] In addition, according to the present invention, the coating layer can minimize direct contact between silicon particles and the electrolyte, thereby suppressing the formation of a thick and unstable SEI due to a side reaction with the electrolyte.

[0026] In addition, according to the present invention, the coating layer can prevent the negative active material from being detached from the electrode plate even if cracking of silicon particles occurs.

[0027] The various advantageous and beneficial advantages and effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0028] In order to more fully understand the drawings cited in the detailed description of the present invention, a brief description of each drawing is provided.

[0029] FIG. 1 is a diagram showing the Raman spectra of the negative active materials of Example 1, Example 2, and Comparative Example 1.

[0030] Figure 2 is a photograph of the negative active material of Example 2 observed using a scanning electron microscope (SEM).

[0031] Figure 3 is a graph showing the capacity retention rate at 50 cycles of lithium half-cells manufactured in Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0032] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified in various other forms, and the terminology used herein is for the purpose of describing the present invention and is not intended to limit the present invention. Furthermore, the singular forms used herein also include plural forms, unless the relevant definition clearly indicates a contrary meaning.

[0033] In this specification, the term "including" is used to indicate that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0034] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0035] In addition, in this specification, “Dn” means particle size distribution, and can mean the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. For example, D50 is the particle size (average particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the particle size distribution can be measured using a laser diffraction method. Specifically, after the target powder is dispersed in a dispersion medium, it is introduced into a laser diffraction particle size measuring device, and when the particles pass through a laser beam, the difference in diffraction pattern according to particle size can be measured, thereby calculating the particle size distribution.

[0036] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in the dictionary are to be interpreted to have meanings consistent with the relevant technical literature and the present disclosure.

[0037] Hereinafter, a negative electrode active material according to one embodiment of the present invention will be described. The negative electrode active material according to one embodiment of the present invention may include silicon-based particles; a coating layer disposed on the surface of the silicon-based particles and containing a polymer. In other words, the negative electrode active material may include a core that is a silicon-based particle and a shell disposed on the surface of the core and containing a polymer.

[0038] Silicon particles can be the base of the negative electrode active material. For example, silicon particles are materials whose main component is silicon atoms, and for example, they can be particles composed purely of silicon atoms (Si), i.e. silicon particles (Pure Si, Si purity >98%). Silicon particles are silicon oxide (SiOx(0 <x≤2)) 또는 탄화규소(SiC) 등과 대비하여 초기 충방전 용량 및 효율이 향상될 수 있으며, 제조 비용이 낮아 상용화가 우수하다는 장점이 있다.

[0039] The average particle diameter (D50) of the silicon particles may be 1.0 to 2.8 ㎛. If the average particle diameter (D50) of the silicon particles is less than 1.0 ㎛, the specific surface area of ​​the silicon particles may increase excessively, which may cause an unintended side reaction with the electrolyte, and the content of the coating layer relative to the silicon particles in the negative electrode active material may increase excessively, which may damage the advantage of silicon showing high capacity. In addition, if the average particle diameter (D50) of the silicon particles, which are the core in the negative electrode active material having a core-shell structure, is less than 1.0 ㎛, there is a risk that smooth contact with the electrolyte may not be achieved due to insufficient interparticle space of the negative electrode active material.

[0040] The maximum size of the average particle diameter (D50) of the silicon-based particles should be such that the coating layer (shell) containing the polymer is not damaged by the volume change of the silicon-based particles caused by repeated charge and discharge. However, if the volume change of the silicon-based particles is excessively large, the silicon-based coating layer may be damaged by the repeated volume change, the layer (film) shape may be broken, and the coating layer may not be able to apply compressive stress to the silicon-based particles and may simply function as a resistive component. In order to prevent the coating layer from being damaged even by repeated volume changes, the average particle diameter (D50) of the silicon-based particles may be 2.8 ㎛ or less. That is, the average particle diameter (D50) of the silicon-based particles may be 1.0 to 2.8 ㎛, more advantageously 1.0 to 2.5 ㎛, and even more advantageously 1.0 to 2.0 ㎛.

[0041] For example, the D10 of the silicon-based particles may be 0.1 to 1.4 ㎛. If the D10 of the silicon-based particles is less than 0.1 ㎛, a side reaction with the electrolyte may occur, uniform coating may be difficult on the negative electrode, and the pore structure may not be properly secured, making it difficult to reduce the resistance to charge transfer. In addition, if the D10 of the silicon-based particles exceeds 1.4 ㎛, the degree of volume expansion of the silicon-based particles may be severe, or the thickness change of the electrode may excessively increase due to continuous charge and discharge. That is, the D10 of the silicon-based particles may be 0.1 to 1.4 ㎛, more specifically, 0.5 to 1.2 ㎛, and even more specifically, 0.8 to 1.0 ㎛.

[0042] For example, the silicon-based particles may be included in an amount of 80 wt% or more based on the total weight of the negative electrode active material. If the content of the silicon-based particles is less than 80 wt%, it may be difficult to secure sufficient capacity of the negative electrode active material. In addition, if the content of the silicon-based particles is excessively high, it may be difficult to improve volume expansion of the silicon-based particles. That is, the content of the silicon-based particles may be 80 wt% or more, more specifically 85.0 to 99.5 wt%, even more specifically 90.0 to 99.5 wt%, and even more specifically 95.0 to 99.5 wt%.

[0043] The coating layer can improve the volume expansion of silicon particles, thereby enhancing electrochemical properties (e.g., initial efficiency, life characteristics, or battery capacity of a secondary battery). Furthermore, the coating layer can minimize direct contact between silicon particles and the electrolyte, thereby suppressing the formation of a thick SEI due to side reactions with the electrolyte and preventing the continuous generation of SEI. Furthermore, the coating layer can prevent the negative active material from being detached from the electrode plate even if cracking of the silicon particles occurs.

[0044] The coating layer may be disposed on the surface of the silicon-based particle. For example, the coating layer may be disposed at least partially on the surface of the silicon-based particle, and more specifically, may be provided entirely on the surface of the silicon-based particle. In other words, the coating layer may cover the surface of the silicon-based particle, and more specifically, may completely cover the surface of the silicon-based particle.

[0045] The coating layer may include a polymer. However, the present invention is not limited thereto, and the coating layer may further include crystalline carbon or conductive carbon, including artificial graphite, natural graphite, expanded graphite, or carbon black, or may further include amorphous carbon derived from petroleum pitch, coal pitch, sucrose, glucose, or galactose.

[0046] Since the polymer is elastic, it can effectively suppress the volume expansion of silicon particles, and even if the silicon particles are fragmented by cracking, the silicon fragments can be maintained in a similar or identical form to the silicon particles before cracking, and the negative active material can be prevented from being detached from the electrode plate.

[0047] The polymer contained in the coating layer may be a polymer that has undergone a cyclization reaction or a condensation reaction. Specifically, the polymer contained in the coating layer may be a polymer that has undergone a cyclization reaction or a condensation reaction while being provided on the surface of the silicon-based particles. The cyclization reaction temperature or the condensation reaction temperature of the polymer may be 200 to 350°C. When the cyclization reaction temperature or the condensation reaction temperature is within the above range, the molecular structure of the polymer is rearranged, and a strong compressive stress can be applied to the silicon-based particles by the polymer. Accordingly, the structural stability and electrical conductivity of the negative electrode active material can be improved. In addition, since the polymer is cyclized or condensed without being carbonized, the phenomenon of the coating layer being broken can be improved compared to general carbon materials, and the phenomenon of silicon-based particles being detached from the negative electrode active material due to volume expansion and contraction can also be improved due to improved elasticity.

[0048] In detail, the cyclization reaction or condensation reaction polymer may be a polymer in which one or more reactions have occurred among a cyclization reaction of a nitrile group, a condensation reaction by a nitrile group, a condensation reaction by a carboxyl group or a hydroxyl group, a cyclization reaction by an aniline group, and a condensation reaction by an aniline group.

[0049] As an advantageous example in which a stronger compressive stress can be applied to the silicon-based particles by the coating layer, the polymer contained in the coating layer may be a polymer having an aromatic ring formed by a cyclization reaction of a nitrile group that occurs in a state in which the polymer is disposed on the surface of the silicon-based particles.

[0050] An example of a polymer having an aromatic ring formed by a cyclization reaction of a nitrile group is a cyclized polyacrylonitrile polymer. The polyacrylonitrile polymer may be a polymer in which acrylonitrile accounts for 90 to 100 mass% of the polymer backbone. Specifically, the polyacrylonitrile polymer may be a polymer containing 90 to 100 mass% of a structure derived from acrylonitrile and 10 mass% or less of a structure derived from a copolymerizable monomer such as itaconic acid, acrylamide, or methacrylic acid. At this time, the number average molecular weight of the polyacrylonitrile polymer may be on the order of 10,000 to 500,000 g / mol, but is not necessarily limited thereto.

[0051] Other examples of polymers capable of cyclization or condensation include at least one selected from the group consisting of polyacrylonitrile, nitrile butadiene rubber, carboxymethyl cellulose, polyacrylic acid, and polyaniline. In this case, the coating layer may include polyacrylonitrile, nitrile butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyaniline, or a mixture thereof that has undergone a cyclization or condensation reaction on the surface of the silicone particles.

[0052] For example, the polymer may be included in an amount of 0.5 to 10.0 wt%, specifically 0.6 to 5.0 wt%, more specifically 0.7 to 2.0 wt%, and even more specifically 0.7 to 1.5 wt%, based on the total weight of the negative electrode active material. If the polymer content is less than 0.5 wt%, a coating layer may not be sufficiently formed on the surface of the silicon-based particles, making it difficult to secure the above-described effect. In addition, if the polymer content is excessively large, the thickness of the coating layer increases, which may cause a problem of increased resistance to charge and ion movement.

[0053] For example, the coating layer may further include fibrous carbon. In one embodiment of the present invention, the coating layer simultaneously includes both polymer and fibrous carbon. In this case, the synergistic effect (composite) of the polymer and fibrous carbon can exert a stronger compressive stress on the silicon particles. Accordingly, the volume expansion rate of the negative electrode active material due to continuous charge and discharge can be improved.

[0054] Fibrous carbon can impart excellent conductivity to the negative electrode active material. For example, the fibrous carbon may include at least one selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs).

[0055] As an advantageous example, the fibrous carbon may be a carbon nanotube. The carbon nanotube may include a single-wall carbon nanotube (SWCNT) and / or a multi-wall carbon nanotube (MWCNT). The number of walls in the multi-wall carbon nanotube may be 2 to 20. Carbon nanotubes have a high aspect ratio and flexibility, so that they can easily form a network structure in which carbon nanotubes are randomly entangled or in contact with each other on the surface of silicon-based particles, and a conductive network can be uniformly formed over the entire surface of the silicon-based particles. In addition, since the coating layer has a composite form including a polymer matrix and a dispersed phase of carbon nanotubes, a greater compressive stress can be applied to the silicon-based particles by the coating layer, and the durability of the coating layer is greatly increased, thereby further improving the cycle characteristics of the negative electrode active material. The aspect ratio (ratio of major axis length / minor axis diameter) of the carbon nanotubes contained in the coating layer may be 10 to 50,000, specifically 50 to 10,000.

[0056] For example, the fibrous carbon may be included in an amount of 0.1 to 1.0 wt% based on the total weight of the negative electrode active material. When the content of the fibrous carbon is less than 0.1 wt%, the electrical conductivity of the negative electrode active material may decrease, and since it is difficult to compensate for the low electrical conductivity of the polymer, the resistance to charge transfer may increase. When the content of the fibrous carbon exceeds 1.0 wt%, the efficiency of improving the electrochemical properties of the negative electrode active material is not good compared to the cost of the raw material, which may cause a problem of increased manufacturing cost. In addition, when the content of the fibrous carbon exceeds 1.0 wt%, the specific surface area increases, which may cause a side reaction with the electrolyte, which may cause problems such as lithium ion depletion in the electrolyte, gas generation, and decreased electrochemical efficiency. That is, the content of the fibrous carbon may be 0.1 to 1.0 wt%, more specifically, 0.1 to 0.8 wt%, and even more specifically, 0.1 to 0.5 wt%.

[0057] The coating layer may further contain conductive two-dimensional nanostructures together with or independently of the fibrous carbon. Representative examples of conductive two-dimensional nanostructures include graphene and reduced graphene oxide (RGO). When the coating layer further contains conductive two-dimensional nanostructures, the conductive two-dimensional nanostructures may be included in an amount of 0.05 to 0.50 wt% based on the total weight of the negative electrode active material.

[0058] 480 to 540 cm in the Raman spectrum of the negative active material -1 Area, specifically 485 to 520 cm -1 The half-width of the peak located in the area is 23 cm -1 It may be over, more specifically 23 cm -1 Over 30 cm -1 It may be less than or equal to 24 to 30 cm, more specifically -1 It can be, more specifically, 25 to 30 cm-1 It can be. Here, the half-width is 480 to 540 cm in the Raman spectrum of the negative active material. -1 Area, specifically 485 to 520 cm -1 At the peak located in the region, the maximum intensity of the peak (maximum Raman scattering intensity) I max 1 / 2I of max It can be calculated by measuring the width of the peak at the point.

[0059] The negative active material according to one embodiment of the present invention is characterized in that the half-width is increased compared to the half-width of a typical uncoated silicon-based active material. That is, when a coating layer including a polymer is formed on the surface of a silicon-based particle, compressive stress is applied to a wider area of ​​the silicon-based particle, thereby improving the volume expansion of the silicon-based particle.

[0060] For example, in the Raman spectrum of the negative active material, 480 to 540 cm -1 Area, specifically 485 to 520 cm -1 Maximum intensity of the peak located in the region I max The value of the corresponding Raman shift is 499 cm -1 It could be more than 499 cm, more specifically -1 515 cm in length -1 It may be less than or equal to 500 to 515 cm, more specifically -1 It can be, more specifically, 503 to 510 cm -1 It can be, and more specifically, 505 to 509 cm -1 It could be.

[0061] The negative active material according to one embodiment of the present invention is characterized in that the Raman shift value increases compared to the Raman shift value of the uncoated silicon-based active material. That is, when a coating layer including a polymer is formed on the surface of the silicon-based particles, a stronger compressive stress can be applied to the silicon-based particles, and thus the volume expansion rate of the negative active material due to continuous charge and discharge can be improved.

[0062] Hereinafter, a method for manufacturing a negative electrode active material according to an embodiment of the present invention will be described. However, this does not necessarily mean that the negative electrode active material according to an embodiment of the present invention must be manufactured using the manufacturing method described below.

[0063] [Preparation of precursor solution]

[0064] A precursor solution containing a polymer can be prepared. In this step, the polymer can be converted into the polymer of the aforementioned negative electrode active material through a cyclization reaction and / or a condensation reaction. Accordingly, the polymer subjected to the cyclization reaction and / or condensation reaction can correspond to the polymer of the aforementioned negative electrode active material.

[0065] For example, the polymer's cyclization or condensation reaction temperature may be between 200 and 350°C. When the cyclization or condensation reaction temperature is within the above range, the polymer is not carbonized and its molecular structure is rearranged, thereby applying strong compressive stress to the silicon particles of the ultimately manufactured negative electrode active material. Accordingly, the structural stability and electrical conductivity of the negative electrode active material can be improved.

[0066] For example, the polymer may be a polyacrylonitrile-based polymer. The polyacrylonitrile-based polymer may be a polymer in which acrylonitrile accounts for 90 to 100 mass% of the polymer backbone. Specifically, the polyacrylonitrile-based polymer may be a polymer containing 90 to 100 mass% of a structure derived from acrylonitrile and containing 10 mass% or less of a structure derived from a copolymerizable monomer, such as itaconic acid, acrylamide, or methacrylic acid.

[0067] For example, the polymer may include at least one selected from the group consisting of polyacrylonitrile, nitrile butadiene rubber, carboxymethyl cellulose, polyacrylic acid, and polyaniline.

[0068] For example, a polymer-containing solution can be prepared by dissolving the polymer in a solvent. For example, the solvent may include N-methyl-2-pyrrolidone (NMP). However, the solvent is not limited thereto, and various types of solvents in which the polymer can be dissolved, such as N,N-dimethylformamide (DMF), dimethyl sulfone (DMSO2), dimethyl sulfoxide (DMSO), N,N-dimethyl acetamide (DMAc), ethylene carbonate (EC), or propylene carbonate (PC), can be used.

[0069] For example, the solution may further include fibrous carbon. For example, the fibrous carbon may include at least one selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs).

[0070] For example, if the solution contains fibrous carbon, the step of preparing the precursor solution may include, after the step of preparing a solution containing a polymer, adding fibrous carbon to the solution containing the polymer and stirring the solution containing the polymer and fibrous carbon. For example, stirring may be performed until the color of the solution becomes uniform.

[0071] [Mixture Obtaining Step]

[0072] A mixture can be obtained by adding silicon particles to a precursor solution. The description of the silicon particles in this step is identical to the description of the silicon particles of the negative active material described above. For example, the average particle diameter (D50) of the silicon particles may be 1.0 to 2.8 μm, more specifically 1.0 to 2.5 μm, and even more specifically 1.0 to 2.0 μm.

[0073] For example, the step of obtaining a mixture can be performed by adding silicon particles to a precursor solution and then stirring a dispersion containing the polymer and silicon particles.

[0074] For example, after the step of obtaining the mixture, a step of drying the mixture at 100 to 200°C, specifically 100 to 170°C, may be further included. The drying step may evaporate the solvent contained within the mixture. For example, the drying step may utilize various drying methods known in the art, such as spray drying, vacuum drying, and hot air drying.

[0075] [Heat treatment stage]

[0076] The mixture can be heat-treated at a temperature of 200 to 350°C. When the mixture is heat-treated, a coating layer including a polymer subjected to a cyclization reaction and / or condensation reaction can be uniformly formed on the surface of the silicon-based particles. In one embodiment of the present invention, when the precursor solution is prepared in the step of preparing the precursor solution and the solution includes a polymer and fibrous carbon, a coating layer including a polymer subjected to a cyclization reaction and / or condensation reaction and fibrous carbon can be formed on the surface of the silicon-based particles in the step of heat-treating.

[0077] In this step, the polymer is not carbonized but undergoes a cyclization reaction or a condensation reaction, so that the molecular structure can be rearranged (for example, a chain-like molecular structure can be rearranged into a regular cyclic structure). Accordingly, the polymer in the coating layer maintains a regular molecular structure, thereby increasing the mechanical strength of the negative electrode active material and improving the volume expansion of the silicon particles due to charge and discharge. In addition, in one embodiment of the present invention, the coating layer may further include fibrous carbon, in which case the electrical conductivity of the negative electrode active material can be improved and the resistance to charge transfer can be reduced.

[0078] When the heat treatment temperature is less than 200°C, the polymer cyclization or condensation reaction is not performed, so the degree of compressive stress applied to the silicon-based particles is reduced, which may reduce the improvement effect of volume expansion. In addition, when the heat treatment temperature exceeds 350°C, an unintended polymer decomposition reaction may occur, and as the decomposed polymer is carbonized, a problem may arise in that it is difficult to form an elastic coating layer (specifically, a soft coating) on ​​the surface of the silicon-based particles. That is, the heat treatment temperature may be 200 to 350°C, more specifically 230 to 330°C, and even more specifically 280 to 310°C.

[0079] For example, the heat treatment step may be performed for 2 to 6 hours. When the heat treatment time is within the above range, a coating layer may be uniformly formed on the surface of the silicon-based particles.

[0080] For example, the heat treatment step may be performed in an inert atmosphere. For example, the inert atmosphere may be a nitrogen atmosphere. However, this is not a limitation, and the inert atmosphere may be adjusted to various other atmospheres, such as an argon atmosphere or a helium atmosphere, as long as the effects of the present invention are not impaired.

[0081] For example, prior to the heat treatment step, a step of disintegrating the dried mixture may be further included. For example, the disintegration step may be performed using a device typically used to break up agglomerates by applying shear force, such as an agitator or a disintegrating mill.

[0082] Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described. A lithium secondary battery according to an embodiment of the present invention may include a negative electrode; a positive electrode; and an electrolyte.

[0083] The negative electrode may include a negative electrode active material layer including the above-described negative electrode active material; and a current collector.

[0084] Current collectors can serve to impart conductivity. There are no specific limitations on the materials that can be used as current collectors, and any material that possesses conductivity without causing chemical changes to the battery can be used. For example, current collectors can include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0085] The negative electrode active material layer may be disposed on at least one surface of the current collector, and specifically, may be disposed on one or both surfaces. For example, the negative electrode active material may be included in an amount of 80 to 98 wt% based on the total weight of the negative electrode active material layer.

[0086] The negative electrode active material layer may further include a binder and / or a conductive agent. The binder may serve to bond the particles constituting the negative electrode active material to each other and improve the adhesion performance of the negative electrode active material to the current collector. For example, the binder may be included in an amount of 1 to 5 wt% based on the total weight of the negative electrode active material layer.

[0087] For example, the binder may include a non-aqueous binder, an aqueous binder, or a combination thereof. For example, the non-aqueous binder may include at least one selected from the group consisting of an ethylene / propylene copolymer, polyacrylonitrile (PAN), polystyrene (PS), polyvinyl chloride (PVC), carboxylated polyvinyl chloride, poly(vinylidene fluoride; PVDF), polyurethane, polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polyamide-imide (PAI), and polyimide (PI). However, it is not limited to this.

[0088] Water-based binders include polymers including Styrene Butadiene Rubber (SBR), Acrylated Styrene Butadiene Rubber, Nitrile Butadiene Rubber (NBR), Acrylic Rubber, Butyl Rubber, Fluoro Rubber, Ethylene oxide, Polyvinyl pyrrolidone (PVP), Polyepichlorohydrine, Polyphosphazenes, Ethylene Propylene Diene Terpolymer (EPDM), Poly(vinyl pyridine), Chlorosulphonated Polyethylene (CSM), Latex, It may include at least one selected from the group consisting of polyester resin, acrylic resin, phenol resin, epoxy resin, and polyvinyl alcohol (PVA), but is not limited thereto.

[0089] For example, when a water-based binder is used as a binder, the negative electrode active material layer may further include a thickener capable of providing viscosity. The thickener may include a cellulose-based compound. For example, the cellulose-based compound may include at least one selected from the group consisting of carboxymethyl cellulose, hydroxypropyl methylcellulose, methylcellulose, and alkali metal salts in which hydrogens of these are substituted with Na, K, or Li. For example, the thickener may be included in an amount of 0.1 to 3 wt% based on the total weight of the negative electrode active material layer.

[0090] Conductive materials can be used to impart conductivity to electrodes. There are no specific limitations on the materials that can be used as conductive materials, and any material that has conductivity without causing chemical changes in the battery can be used. For example, conductive materials can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0091] The negative electrode can be obtained by mixing a binder and / or a conductive agent with a negative electrode active material in a solvent to prepare an active material composition, and then applying this active material composition to a current collector. For example, the solvent may include water. Since the method for preparing such a negative electrode can be applied using methods commonly used in the art, a detailed description thereof will be omitted herein.

[0092] The positive electrode comprises a current collector; and a positive electrode active material layer formed on at least one surface of the current collector and including a positive electrode active material. For example, the positive electrode active material may be included in an amount of 80 to 98 wt% based on the total weight of the positive electrode active material layer.

[0093] Current collectors can serve to impart conductivity. There are no specific limitations on the materials that can be used as current collectors, and any material that possesses conductivity without causing chemical changes to the battery can be used. For example, current collectors can include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or other materials.

[0094] The cathode active material may include a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound). The cathode active material may be a commonly used cathode active material, and may include, for example, at least one of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. Specifically, the cathode active material may include a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; and a compound having the chemical formula Li. 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide expressed as O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a portion of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0095] For example, a compound having a coating layer on the surface of the compound may be used, or a compound having the compound and a coating layer may be mixed and used. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compound forming the coating layer may be amorphous or crystalline. The coating element included in the coating layer may include at least one selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, and Zr. The coating layer forming process may use any coating method as long as it can coat the compound with these elements by a method (for example, spray coating, dipping, etc.) that does not adversely affect the properties of the positive electrode active material, and a method commonly used in the art may be applied, so a detailed description thereof will be omitted herein.

[0096] The positive electrode active material layer may further include a binder and / or a conductive agent. The binder may serve to bond the particles constituting the positive electrode active material to each other and improve the adhesion performance of the positive electrode active material to the current collector. For example, the binder may be included in an amount of 1 to 5 wt% based on the total weight of the positive electrode active material layer.

[0097] Binders include polyvinylidene fluoride (PVDF), vinylidene fluoride-co-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl chloride (PVC), carboxylated polyvinyl chloride, polyvinyl pyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), It may include at least one selected from the group consisting of polypropylene (PP), ethylene-propylene-diene copolymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof.

[0098] A conductive material can be used to provide conductivity to an electrode. There are no specific limitations on the materials that can be used as a conductive material, and any material that has conductivity without causing a chemical change in the battery can be used. For example, conductive materials include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more may be used.

[0099] The positive electrode can be obtained by mixing a binder and / or a conductive agent with a positive electrode active material in a solvent to prepare an active material composition, and then applying this active material composition to a current collector. For example, the solvent may include water. Since methods commonly used in the art can be applied to prepare such a positive electrode, a detailed description thereof will be omitted herein.

[0100] The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that are commonly used in the industry when manufacturing lithium secondary batteries. Specifically, the electrolyte may include a non-aqueous organic solvent and / or a lithium salt.

[0101] Non-aqueous organic solvents can serve as a medium through which ions involved in the electrochemical reaction of a battery can move. For example, the non-aqueous organic solvent may include one or more selected from the group consisting of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.

[0102] Examples of the above carbonate solvent that can be used include dimethyl carbonate, diethyl carbonate, dicaprylyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, or caprolactone. Examples of the ether solvent that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Cyclohexanone, etc. can be used as the above ketone solvent. Ethanol or isopropyl alcohol, etc. can be used as the above alcohol solvent.As the aprotic solvent, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used.

[0103] The above lithium salt can be dissolved in an organic solvent and act as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. The anion of the lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0104] For example, the concentration of the lithium salt may be 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and thus lithium ions may move more effectively.

[0105] For example, depending on the type of lithium secondary battery, the lithium secondary battery may further include a separator formed between the positive and negative electrodes. The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator used in the industry as a separator for secondary batteries may be used without particular limitations. For example, the separator may be a multilayer film made of polyethylene, polypropylene, polyvinylidene fluoride, or two or more layers thereof. However, the present invention is not limited thereto, and the separator may be a mixed multilayer film, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0106] The above lithium secondary battery may be placed within a battery case. The shape of the battery case may be at least one selected from the group consisting of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape. However, the shape of the battery case is not limited thereto, and may have various shapes used in the relevant industry.

[0107] Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are intended only to illustrate and further illustrate the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0108] (Example 1)

[0109] A precursor solution was prepared by dissolving 1 g of PAN (number average molecular weight = 150,000) in NMP solvent. Then, 99 g of Si powder was added to the precursor solution. At this time, the Si powder was a metallurgical grade with a purity of 99% or more and an oxygen content of 1% or less, and a D50 of 1.3 ㎛ (D10 of 0.5 ㎛ or more and D90 of 10 ㎛ or less). Thereafter, the precursor solution with the Si powder added was sufficiently stirred to obtain a mixture. While maintaining the stirring state, the mixture was dried at 150°C, and the dried mixture was pulverized using an agitator and heat-treated at 300°C for 4 hours in a nitrogen atmosphere to manufacture the negative active material of Example 1.

[0110] (Example 2)

[0111] A precursor solution was prepared by dissolving 1 g of PAN in an NMP solvent, adding 0.5 g of MWCNT (aspect ratio = 10,000) to the prepared solution, and stirring the solution sufficiently until the color of the solution became uniform. Thereafter, 99 g of Si powder (D10: 0.5 μm, D50: 1.3 μm) was added to the precursor solution, and stirring sufficiently was performed to obtain a mixture. The mixture was dried at 150°C while maintaining the stirring state, and the dried mixture was pulverized using an agitator and heat-treated at 300°C for 4 hours in a nitrogen atmosphere to prepare the negative active material of Example 2.

[0112] (Comparative Example 1)

[0113] The Si powder used as a raw material in Examples 1 and 2 was prepared as a negative electrode active material in Comparative Example 1.

[0114] (Comparative Example 2)

[0115] In the manufacturing method of Example 2, a negative active material of Comparative Example 2 was manufactured in the same manner as Example 2, except that Si powder having a D50 of 3.3 μm was used.

[0116] (Experimental Example 1: Raman analysis of negative electrode active material)

[0117] For each of the negative active materials of the above examples and comparative examples, Raman analysis was performed, and the Raman spectrum of each negative active material is shown in Fig. 1 and Table 1.

[0118] Raman analysis was performed using Bruker's Ram II-Senterra with the following settings: Excitation Wavelength: 532 nm, Laser current: 100%, Excitation Power: 5.08 mW, and Excitation power density: 1.38×10 5 It was performed under the condition of W / ㎠. In the measured Raman spectrum, 480 to 540 cm -1 The half-width of the peak located in the region 480 to 540 cm -1 The values ​​of the Raman shift corresponding to the maximum intensity of the peak located in the region are summarized in Table 1.

[0119] Half width of the peak (cm) -1 ) Raman shift corresponding to the maximum peak (cm) -1 )Example 124.7504.57Example 227.9507.78Comparative Example 123498.13

[0120] Referring to Table 1 and Figure 1, Examples 1 and 2, which satisfy the manufacturing conditions proposed in the present invention, were measured to have larger values ​​of half-width and Raman shift compared to Comparative Example 1, in which no coating layer was formed.

[0121] It was confirmed that the Raman shift corresponding to the maximum peak of Examples 1 and 2 tended to shift to the right compared to Comparative Example 1. That is, when a coating layer including a polymer is formed on the surface of a silicon-based particle, a stronger compressive stress can be applied to the silicon-based particle, and thus, it was found that the volume expansion rate of the negative electrode active material due to continuous charge and discharge is improved.

[0122] In addition, it was confirmed that the half-width of Examples 1 and 2 tended to increase compared to Comparative Example 1. That is, when a coating layer including a polymer is formed on the surface of a silicon-based particle, it was found that compressive stress was applied to a wider area of ​​the silicon-based particle, and thus the volume expansion of the silicon-based particle was improved.

[0123] Specifically, it was found that when a coating layer including a polymer is formed on silicon particles having a purity of 99% or more, an oxygen content of 1% or less, a D10 of 0.5 ㎛ or more, a D50 of 1 ㎛ or more, and a D90 of 10 ㎛ or less, a stronger compressive stress is applied to a wider area of ​​the silicon particles.

[0124] In this regard, as a representative example, a photograph of the negative active material of Example 2 observed using a scanning electron microscope (SEM) is shown in FIG. 2. Specifically, (a) of FIG. 2 is an SEM photograph of the negative active material of Example 2 observed at a magnification of 20,000 times, and (b) of FIG. 2 is an SEM photograph of the negative active material of Example 2 observed at a magnification of 25,000 times.

[0125] Referring to Fig. 2, it was confirmed that a coating layer was uniformly formed on the surface of the silicon-based particles, and that the fibrous carbons were attached to the surface of the silicon-based particles in the form of a network in which they were entangled and in contact with each other.

[0126] (Experimental Example 2: Evaluation of electrochemical properties of negative electrode active material)

[0127] In order to evaluate the electrochemical characteristics of the above examples and comparative examples, lithium half-cells were manufactured using each negative active material.

[0128] Specifically, a negative electrode slurry was prepared by mixing a negative electrode active material, polyacrylic acid (PAA), and conductive carbon black (C-65) in a weight ratio of 6:3:1 and then dispersing the mixture in distilled water. Thereafter, the negative electrode slurry was applied to a copper foil current collector and rolled to prepare a negative electrode.

[0129] A coin-type 2032 half-cell was manufactured using the above-mentioned negative electrode as a working electrode and lithium metal as a counter electrode. At this time, a separator made of a porous polypropylene film was interposed between the negative electrode and the lithium metal. In addition, an electrolyte was used in which 1 M LiPF6 was dissolved in a solution in which EC (Ethylene Carbonate) and EMC (ethylmethyl carbonate) were mixed in a volume ratio of 3:7, and 1.5 wt% VC (vinylene carbonate) and 10 wt% FEC (fluoroethylene carbonate) were added.

[0130] For the half-cells manufactured in Examples and Comparative Examples, the initial efficiency, initial discharge capacity, and capacity retention rate at 50 cycles were measured, and the results are shown in Table 2 and Fig. 3. Specifically, Fig. 3 is a graph showing the capacity retention rate at 50 cycles of the lithium half-cells manufactured in Examples 1, 2, Comparative Examples 1, and 2.

[0131] Specifically, the battery was charged to 5 mV in the initial cycle (CC / CV mode, 0.1C charge, 0.005C cut-off) and then discharged to 1.5 V (CC mode, 0.1C discharge). At this time, the initial discharge capacity was measured, and the initial efficiency was measured as the percentage of the initial discharge capacity to the initial charge capacity.

[0132] Afterwards, the charge (CC / CV mode, 0.5 C charge, 0.005 C and 5 mV cut-off) and discharge (CC mode, 0.5 C discharge, 1.0 V cut-off) cycles were repeated 50 times, and the capacity retention rate at 50 cycles was calculated by the following equation.

[0133] Capacity retention rate (%) = [(discharge capacity at the 50th cycle) / (discharge capacity at the 1st cycle)] × 100

[0134] Classification Si Powder D50 (㎛) Initial Efficiency (%) Initial Discharge Capacity (mAh / g) Capacity Retention Rate at 50 Cycles (%) Example 11.391.3325164.9 Example 21.392.5351073.2 Comparative Example 11.390.9347638.9 Comparative Example 23.392.6363228.0

[0135] Referring to Table 2 and Figure 3, it was found that Examples 1 and 2 secured significantly higher levels of initial efficiency, initial discharge capacity, and capacity retention rate compared to Comparative Example 1. That is, it was found that a coating layer was formed on the surface of the silicon-based particles, which applied strong compressive stress to the silicon-based particles, and thus the initial efficiency and life characteristics were improved.

[0136] In addition, Comparative Example 2, which was manufactured with silicon particles having an excessively large D50 value, was measured to have a very low capacity retention rate. That is, it was found that when the D50 of the silicon particles is excessively large, the possibility of volume expansion occurring due to continuous charge and discharge increases, thereby deteriorating the life characteristics.

[0137] (Experimental Example 3: Evaluation of electrode expansion properties of a negative electrode manufactured with a negative electrode active material)

[0138] The electrode expansion rate was measured for the lithium half-cells manufactured as examples and comparative examples in the above experimental example 2, and the results are shown in Table 3 below.

[0139] The method for measuring the electrode expansion rate is as follows. After repeating the charge / discharge cycle performed in Experimental Example 2 50 times, lithium was charged to the negative electrode, and the lithium half-cell was disassembled in a dry room. After separating the lithium-charged negative electrode, the thickness of the negative electrode was measured using a thickness gauge, and the electrode expansion rate was calculated by the formula [(thickness after experiment - thickness before experiment) / (thickness before experiment)], and all thicknesses were calculated by applying the value obtained by subtracting the thickness of the copper foil used as the substrate. The electrode expansion rate was calculated by measuring the thickness at more than 5 places for one negative electrode and using the average value as the electrode expansion rate, and after setting the electrode expansion rate of Comparative Example 1 to 1, the relative electrode expansion rate was calculated based on Comparative Example 1.

[0140] Relative electrode expansion rate Example 10.631 Example 20.504 Comparative Example 11

[0141] Referring to Table 3, Examples 1 and 2 were measured to have lower relative electrode expansion rates compared to Comparative Example 1. That is, it was found that strong compressive stress was applied to the silicon particles through the coating layer, thereby improving the expansion of the electrode due to charge and discharge.

[0142] The above embodiments are merely examples and the present invention is not limited thereto. Anything that has substantially the same configuration and achieves the same operational effects as the technical concepts described in the claims of the present invention is included within the technical scope of the present invention.

Claims

1. As a negative active material, silicon-based particles; Comprising a coating layer disposed on the surface of the above silicon particles, The average particle diameter (D50) of the above silicon particles is 1.0 to 2.8 ㎛. The above coating layer comprises a polymer, In the Raman spectrum of the above negative active material, 480 to 540 cm -1 The half width of the peak located in the area is 23 cm -1 Excess, negative active material.

2. In paragraph 1, The value of the Raman shift corresponding to the maximum peak in the Raman spectrum of the above negative active material is 499 cm -1 Ideal, negative active material.

3. In paragraph 1, A negative electrode active material having a cyclization reaction temperature or condensation reaction temperature of the above polymer of 200 to 350°C.

4. In paragraph 1, The above polymer is a negative electrode active material, which is polyacrylonitrile, nitrile butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyaniline or a mixture thereof, which is subjected to a cyclization reaction or condensation reaction on the surface of silicon particles.

5. In paragraph 1, The above polymer is a negative electrode active material comprising a cyclized polyacrylonitrile-based polymer.

6. In paragraph 1, A negative electrode active material, wherein the polymer is included in an amount of 0.5 to 10.0 wt% based on the total weight of the negative electrode active material.

7. In paragraph 1, The above coating layer further comprises a negative active material comprising fibrous carbon.

8. In paragraph 7, The above fibrous carbon is a negative active material including at least one selected from the group consisting of carbon nanotubes (CNT), carbon nanofibers (CNF), and vapor-grown carbon fibers (VGCF).

9. In paragraph 7, A negative electrode active material, wherein the above-mentioned fibrous carbon is included in an amount of 0.1 to 1.0 wt% based on the total weight of the negative electrode active material.

10. In paragraph 1, The above silicon particles are silicon particles (Si), a negative electrode active material.

11. In paragraph 1, A negative active material having a D10 of the above silicon particles of 0.1 to 1.4 ㎛.

12. In paragraph 1, A negative electrode active material, wherein the silicon particles are contained in an amount of 80 wt% or more based on the total weight of the negative electrode active material.

13. A step of preparing a precursor solution containing a polymer; A step of obtaining a mixture by adding silicon particles to the above precursor solution; and Comprising a step of heat treating the above mixture at a temperature of 200 to 350°C, A method for manufacturing a negative electrode active material, wherein the average particle diameter (D50) of the above silicon particles is 1.0 to 2.8 ㎛.

14. In paragraph 13, A method for producing a negative electrode active material, wherein in the step of preparing the precursor solution, the precursor solution further contains fibrous carbon.

15. Cathode; Bipolar; and Contains electrolyte, A lithium secondary battery comprising a negative electrode active material according to any one of claims 1 to 12.

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