Anode active material for lithium ion battery, preparing method for the same and lithium ion battery comprising the same

Abstract

The present invention relates to a negative electrode active material that can be used in a lithium-ion battery, more specifically comprising silicon particles and a carbon-based material surrounding the silicon particles, wherein the crystal size ratio of the carbon-based material to the silicon particles is 1.9 to 3.6, and the crystal size is calculated from the full-width at half maximum (FWHM) of the X-ray diffraction spectrum (XRD spectrum) peak.

Description

Technology Field

[0001] The following various embodiments relate to a negative electrode active material that may be included in a lithium-ion battery, a method for manufacturing the same, and a lithium-ion battery including the same. Background Technology

[0003] Lithium-ion batteries (LIBs) can achieve high energy density while remaining lightweight, and are currently widely used as the primary power source for portable devices such as laptops and mobile devices including smartphones; furthermore, active research is underway to apply them to various fields, ranging from transportation methods like electric vehicles to large-capacity energy storage systems.

[0004] At this time, 'active materials' that are directly involved in the production and storage of electrical energy through chemical reactions exist within the electrodes of lithium-ion batteries. In particular, the 'negative electrode active material' refers to a substance capable of storing lithium ions transferred from the positive electrode during charging and releasing them to the positive electrode during discharge. Currently, graphite is primarily used as the negative electrode active material in commercially available lithium-ion batteries due to its stability in lithium ion insertion and extraction, as well as its economic feasibility.

[0005] However, as mentioned above, as the applications of lithium-ion batteries expand beyond portable mobile devices to fields such as transportation and power generation, there is a growing need to develop lithium-ion batteries with higher capacities than those currently available. Graphite is a material with a theoretical capacity of 372 mAh / g, which can be seen as having fundamental limitations in meeting the market's demand for higher capacity. On the other hand, silicon, which has recently been attracting attention as a substitute for the aforementioned graphite, possesses a high theoretical capacity of approximately 4,200 mAh / g and can be considered a next-generation anode active material with superior potential compared to graphite in terms of increasing battery capacity.

[0006] While silicon materials have the advantage of providing high capacity and energy density, they have the problem of undergoing significant volume changes as they react with lithium during battery use. Generally, when lithium ions are inserted into silicon, it swells or contracts by more than 300%, and such extreme volume changes significantly impair the mechanical stability of the anode material. Furthermore, from the perspective of the battery, the volume expansion of the silicon anode material leads to unstable contact between the electrode and the electrolyte, which not only increases the internal resistance of the battery but also damages the structure of the anode material due to volume changes during repeated charging and discharging processes, potentially shortening the cycle life. Additionally, structural damage can cause physical separation of the electrode and infiltration of the electrolyte, thereby reducing the battery's capacity and energy density.

[0007] Therefore, in order to commercialize lithium-ion batteries with high capacity, it is necessary to develop new silicon-based negative electrode active materials that can solve the problems of battery performance degradation and reduced long-term reliability caused by silicon volume expansion. The problem to be solved

[0009] In order to solve the above-mentioned problems, a negative electrode active material is provided that can solve the problems of reduced battery performance and decreased long-term reliability due to volume expansion of silicon by including silicon particles and a carbon-based material surrounding the silicon particles, wherein the crystal size ratio of the carbon-based material to the silicon particles is 1.9 to 3.6.

[0010] However, the problems intended to be solved in this specification are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below. means of solving the problem

[0012] A negative electrode active material according to one embodiment comprises silicon particles and a carbon-based material surrounding the silicon particles, wherein the crystal size ratio of the carbon-based material to the silicon particles is 1.9 to 3.6, and the crystal size may be calculated from the full-width at half maximum (FWHM) of the X-ray diffraction spectrum (XRD spectrum) peak.

[0013] The above silicon particles may include silicon (Si) and a silicon oxide film formed on the surface of the silicon.

[0014] The above silicon particles may include flake-like silicon particles.

[0015] The above-mentioned negative electrode active material may include secondary particles formed by aggregating two or more primary particles, which are silicon particles.

[0016] The average particle size of the primary particles is 10 nm to 200 nm, and the average particle size of the secondary particles may be 1 μm to 10 μm.

[0017] The above carbon-based material may include hard carbon and soft carbon.

[0018] The above-described cathode active material may be in a form in which hard carbon is formed on the outer surface of the primary particles, and soft carbon is partially or entirely filled between the primary particles.

[0019] A method for manufacturing a negative electrode active material according to one embodiment may include the steps of: introducing silicon powder and a polymer material into a solvent to prepare a solution and grinding it; spray-drying the solution to prepare a precursor; introducing the precursor and a carbon raw material and compounding them to prepare a composite; and heat-treating the composite at a temperature of 600 to 1,100 ℃ under an inert atmosphere.

[0020] In the step of preparing a solution by adding silicone powder and a polymer material to the solvent and grinding, the polymer material may include one or more of polyvinylpyrrolidone, polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, phenolic resin, polyacrylic acid, epoxy resin, and polyfurfuryl alcohol resin.

[0021] In the step of manufacturing a composite by introducing and compounding the above-mentioned precursor and carbon raw material, the carbon raw material may include one or more of petroleum pitch, coal tar pitch, graphite, and graphene.

[0022] In the step of manufacturing a composite by introducing and compounding the above precursor and carbon raw material, the weight ratio of the above precursor and carbon raw material may be 3:1 to 1:3.

[0023] The carbon raw material comprises a first carbon raw material and a second carbon raw material of different types, and the weight ratio of the first carbon raw material and the second carbon raw material may be 5:1 to 1:5.

[0024] A lithium-ion battery according to one embodiment may include a negative electrode active material according to one embodiment. Effects of the invention

[0026] A negative electrode active material according to one embodiment comprises silicon particles and a carbon-based material surrounding the silicon particles, and by controlling the crystal size ratio of the carbon-based material to the silicon particles to a specific range, a lithium-ion battery with improved battery capacity and lifespan retention rate compared to conventional batteries can be manufactured.

[0027] The effects according to one embodiment in this specification are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims in this specification. Brief explanation of the drawing

[0029] FIG. 1 is a drawing showing a negative electrode active material (100) according to one embodiment. Figure 2 is a figure showing the X-ray diffraction spectrum (XRD spectrum) of the cathode active material of the example and comparative example. Figure 3 is a graph showing the life retention rate according to the cycle for lithium-ion batteries containing the negative electrode active materials of the examples and comparative examples. Specific details for implementing the invention

[0030] Embodiments are described in detail below. However, various modifications may be made to the embodiments, and thus the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, and substitutions to the embodiments are included within the scope of the rights.

[0031] To those skilled in the art, the scope of the present invention is not limited by these embodiments according to the gist of the invention.

[0032] The terms used in the embodiments are for illustrative purposes only and should not be interpreted as intended to be limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0033] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the embodiments pertain. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0034] In addition, when describing the embodiments, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the embodiments, such detailed description is omitted.

[0035] In addition, terms such as first, second, A, B, (a), (b), etc. may be used when describing the components of the embodiments. These terms are used only to distinguish the components from other components, and the essence, order, or sequence of the components is not limited by the terms.

[0036] Components included in any one embodiment and components having common functions shall be described using the same names in other embodiments. Unless otherwise stated, the descriptions given in any one embodiment may also apply to other embodiments, and specific descriptions shall be omitted to the extent of overlap.

[0037] Throughout the specification, when a part is described as "including" a certain component, this means that it does not exclude other components but may include additional components.

[0039] A negative electrode active material (100) according to one embodiment comprises silicon particles (110) and a carbon-based material (120) surrounding the silicon particles, and the crystal size ratio of the carbon-based material to the silicon particles may be 1.9 to 3.6. In this case, the crystal size may be calculated from the full-width at half maximum (FWHM) of the X-ray diffraction spectrum (XRD spectrum) peak.

[0040] A negative electrode active material according to one embodiment is manufactured based on silicon (Si) particles having a high theoretical capacity and high energy density so as to manufacture a high-capacity lithium-ion battery. However, silicon particles have a disadvantage that can reduce the long-term durability of the lithium-ion battery due to frequent volume expansion and contraction that occur as several charge-discharge cycles proceed. This was intended to be resolved by introducing a carbon-based material surrounding the silicon particles.

[0041] In addition, the inventors have discovered that by controlling the crystal size ratio of the carbon-based material to the silicon particles to a specific range, they can contribute to the long lifespan of the lithium-ion battery. As a method for controlling the crystal size ratio to a specific range, the manufacturing method according to one embodiment described below can be cited as an example, and in particular, the method of controlling the heat treatment temperature of the material after the composite formation of the silicon precursor and the carbon raw material can be cited as an example.

[0042] The crystal size ratio of the carbon-based material to the silicon particles included in the above-mentioned cathode active material may be 1.9 to 3.6, preferably 1.9 to 3.0, more preferably 2.0 to 3.0, even more preferably 2.0 to 2.85, and most preferably 2.0 to 2.6. If the crystal size ratio of the carbon-based material to the silicon particles exceeds the above range or is below the above range, a sufficient amount of electrical capacitance may not be secured, or the lifespan retention rate may decrease rapidly as the number of cycles increases.

[0043] Meanwhile, the above crystal size ratio may be calculated based on the full-width at half maximum (FWHM) for a specific peak of the spectrum obtained from X-ray diffraction (XRD), and as a specific calculation method, it may be calculated from Scherrer's equation according to Equation 1 below, which is widely known in the art.

[0044] [Equation 1]

[0045] D = Kλ / βcosθ

[0046] In Equation 1 above, D represents the crystalline size (unit is nm), K is the shape factor determined by the shape of the crystal, λ is the wavelength of the X-ray used for measurement (unit is nm), β is the full width at half maximum along the 2θ axis of the spectrum (unit is radian), and θ is the Bragg's angle of the peak corresponding to the crystal.

[0047] In particular, the crystal size of the silicon particles and carbon-based material according to one embodiment may be measured from the peaks corresponding to 2θ = 28.4±0.1° and 26.5±0.1° of the XRD spectrum, respectively, or may be measured from the peaks corresponding to the silicon (Si) (111) crystal plane and the amorphous carbon (002) crystal plane of the XRD spectrum, respectively.

[0049] According to one embodiment, the silicon particles may comprise silicon (Si) and a silicon oxide film formed on the silicon surface, and may comprise flake-like silicon particles. The composition of the silicon oxide film is SiO x (where x is a value greater than 0 and less than or equal to 2). Also, in the case where the silicon particles have a major axis and a minor axis, such as in a flake-like structure, the major axis and the minor axis may be 80 nm to 200 nm and 20 nm to 100 nm, respectively. However, it is not limited thereto.

[0050] According to one embodiment, the negative electrode active material may include secondary particles formed by aggregating two or more primary particles, which are silicon particles. The aggregation may be formed by a plurality of primary particles directly contacting each other surface-to-surface to form a group of secondary particles, or by a carbon material being generated in the space between the plurality of primary particles and partially or completely filling it to form a group and physically connecting them to form secondary particles, and both of the above cases may be included.

[0051] According to one embodiment, the average particle size of the primary particle may be 10 nm to 200 nm, or 50 nm to 150 nm, or 80 nm to 120 nm, and the average particle size of the secondary particle may be 1 μm to 10 μm, or 3 μm to 9 μm, or 5 μm to 8 μm. In particular, the primary particle is composed of nanoparticles having a size in the nanometer range, so it may be easier to suppress the change in silicon volume during charging and discharging of a battery containing the same. If the average particle size of the primary particle is less than the lower limit of the above range, there is a possibility that the battery capacity and efficiency will decrease, and if it exceeds the upper limit of the above range, the effect of suppressing volume change decreases sharply, which may have an adverse effect on the lifespan of the battery.

[0053] According to one embodiment, the carbon-based material may include hard carbon and soft carbon. Carbon-based materials can be broadly classified into crystalline carbon, such as graphite, or amorphous carbon, and both the hard carbon and soft carbon belong to amorphous carbon.

[0054] Among these, hard carbon is also called non-graphitizable carbon and has a structure in which crystals on small graphite layers consisting of several layers are arranged somewhat irregularly. Although the mechanical strength of hard carbon is relatively superior to that of soft carbon, it is characterized by the fact that graphitization does not occur easily even at high temperatures above 2,500°C. On the other hand, soft carbon is also called graphitizable carbon and has the characteristic that the crystals on the graphite layers are arranged with a certain degree of orientation compared to hard carbon, allowing graphitization to occur at high temperatures above 2,500°C. Meanwhile, the two types of carbon mentioned above can also be distinguished depending on the raw materials used for manufacturing, and their electrochemical properties may differ accordingly.

[0056] According to one embodiment, the negative electrode active material may be in a form in which hard carbon is formed on the outer surface of the primary particles and soft carbon is partially or entirely filled between the primary particles. The negative electrode active material according to one embodiment may form a structure in which silicon particles, hard carbon, and soft carbon are formed at specific locations by a method for manufacturing a negative electrode active material according to one embodiment below, which is illustrated in the schematic diagram of FIG. 1.

[0057] According to the schematic diagram of FIG. 1, a negative electrode active material (100) according to one embodiment comprises silicon particles (primary particles, 110) and a carbon-based material (120). The silicon particles consist of a central silicon (111) and a silicon oxide film (112) formed on the outside of the silicon surface, and a hard carbon (121) is formed on the outside of the surface of the silicon particles (i.e., the surface of the silicon oxide film). Furthermore, a soft carbon (122) is formed between the silicon particles on which the hard carbon is formed on the surface, physically connecting the silicon particles, and thereby the silicon particles may be in the form of a secondary particle formed by aggregation.

[0059] A method for manufacturing a negative electrode active material according to one embodiment may include the steps of: introducing silicon powder and a polymer material into a solvent to prepare a solution and grinding it; spray-drying the solution to prepare a precursor; introducing the precursor and a carbon raw material and compounding them to prepare a composite; and heat-treating the composite at a temperature of 600 to 1,100 ℃ under an inert atmosphere.

[0061] The step of preparing a solution by introducing silicon powder and a polymer material into the above solvent and grinding may include wet grinding (wet milling) using ball mill or bead mill equipment, and the solvent may include water (distilled water) or an organic solvent such as isopropyl alcohol, ethanol, or methanol, and the silicon powder after grinding may have a size according to the average particle size of the primary particles described above. In addition, as the wet grinding proceeds, carbonization of the introduced polymer material may occur to form a hard carbon layer on the outside of the surface of the silicon powder.

[0062] According to one embodiment, in the step of preparing a solution by adding silicone powder and a polymer material to the solvent and grinding, the polymer material may include one or more of polyvinylpyrrolidone, polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, phenolic resin, polyacrylic acid, epoxy resin, and polyfurfuryl alcohol resin, and preferably one or more of polyvinylpyrrolidone, polyvinylidene fluoride, and styrene-butadiene rubber. It can be included.

[0064] From the step of preparing a precursor by spray-drying the above solution, secondary particles formed by aggregation of the prepared primary particles may be formed, and the secondary particles may have a size different from the average particle size of the secondary particles described above.

[0065] The step of manufacturing a composite by introducing and compounding the above-mentioned precursor and carbon raw material may involve introducing the precursor produced in the previous step and one or more types of carbon raw materials into a compounder at a specific ratio to proceed with compounding.

[0066] According to one embodiment, in the step of manufacturing a composite by introducing and compounding the precursor and carbon raw material, the carbon raw material may include one or more of petroleum pitch, coal tar pitch, graphite, and graphene.

[0067] According to one embodiment, in the step of manufacturing a composite by introducing and compounding the precursor and carbon raw material, the weight ratio of the precursor and carbon raw material may be 3:1 to 1:3, or 3:2 to 2:3.

[0068] According to one embodiment, the carbon raw material comprises a first carbon raw material and a second carbon raw material of different types, and the weight ratio of the first carbon raw material and the second carbon raw material may be 5:1 to 1:5, or 3:1 to 1:3, or 2:1 to 1:2.

[0069] Depending on the ratio of the above precursor and carbon raw material, the amount of soft carbon included in the cathode active material can be controlled, and depending on the ratio of the first carbon raw material and the second carbon raw material, the characteristics of the soft carbon can be controlled.

[0071] The step of heat-treating the composite at a temperature of 600 to 1,100 ℃ under an inert atmosphere may be a process of applying heat to the composite to induce carbonization of hard carbon or soft carbon, and in particular, as the carbon raw material is carbonized, it may be impregnated into the interior of the secondary particles within the composite, and ultimately manufactured in a form that surrounds the silicon particles-hard carbon.

[0072] In particular, the temperature of the heat treatment is the most important factor in controlling the crystal size ratio of the carbon-based material to the silicon particles in the cathode active material according to one embodiment. As the temperature increases, the silicon crystal size increases and silicon carbide (SiC) is generated on the side of the silicon particles, leading to a decrease in reversible capacity. On the other hand, on the side of the carbon-based material, carbon functional groups are removed, leading to an increase in reversible capacity. Therefore, it is considered important to perform the heat treatment within an appropriate temperature range to maintain a balance regarding the characteristics of each component according to the heat treatment.

[0073] Accordingly, the heat treatment temperature range may be 600 to 1,100 ℃, preferably 600 to 1,000 ℃, more preferably 750 to 1,000 ℃, more preferably 850 to 1,000 ℃, and most preferably 850 to 950 ℃. At this time, if the heat treatment temperature is below the lower limit of the above range, carbon functional groups are not properly removed, and the electrical capacity of the battery containing the same may decrease, and if it exceeds the upper limit of the above range, the crystal size of the silicon particles and the amount of silicon carbide increase excessively, and likewise the electrical capacity of the battery containing the same may decrease.

[0075] A lithium-ion battery according to one embodiment may include a negative electrode active material according to one embodiment. The negative electrode active material may be used in the preparation of a negative electrode slurry together with a binder and a solvent, and the negative electrode may be prepared by applying the negative electrode slurry to a current collector, and the lithium-ion battery may be prepared by assembling a positive electrode, an electrolyte, and a separator together with the negative electrode.

[0077] The present invention will be explained in more detail below through examples. The following examples are described for the purpose of illustrating the present invention and do not limit the scope of the present invention.

[0079] - Preparation Example: Preparation of cathode active material

[0080] <Example 1>

[0081] Silicon powder and isopropyl alcohol were fed into a bead mill in a weight ratio of 10:90, polyvinylpyrrolidone (PVP) was added as a polymer material, and wet grinding was performed until the average particle size was 110 nm. Then, the solution containing the ground silicon powder was spray-dried to produce a precursor with an average particle size of 7.5 μm. Subsequently, the precursor, petroleum pitch, and graphite were fed into a compositer in a weight ratio of 4:4:2 and composited for 25 minutes to produce a composite, and the composite was heat-treated at a temperature of 600 ℃ under an inert atmosphere to produce a final negative electrode active material.

[0082] <Example 2>

[0083] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 700 ℃.

[0084] <Example 3>

[0085] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 800 ℃.

[0086] <Example 4>

[0087] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 900 ℃.

[0088] <Example 5>

[0089] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 990 ℃.

[0090] <Example 6>

[0091] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 1,050 ℃.

[0092] <Comparative Example>

[0093] A negative electrode active material was prepared in the same manner as in Example 1, except that the composite was heat-treated at a temperature of 500 ℃.

[0095] - Experimental Example 1: XRD Analysis of Cathode Active Material

[0096] For the negative electrode active materials of the examples and comparative examples prepared according to the above manufacturing example, the spectrum was measured by X-ray diffraction and illustrated as in Fig. 2.

[0097] According to FIG. 2, in the spectra for the negative electrode active materials of the examples and comparative examples, 2θ corresponding to the amorphous carbon (002) crystal plane = A peak of 26.5° and a peak of 2θ = 28.4° corresponding to the silicon (Si) (111) crystal plane were observed, and from each peak, it was confirmed that the synthesized cathode active material contained carbon-based material and silicon. In addition, in the case of Example 6, which was heat-treated at the highest temperature, a peak corresponding to silicon carbide at 2θ = 35.7° was observed, and it was also confirmed that the amount of silicon carbide increased with increasing heat treatment temperature.

[0099] - Experimental Example 2: Performance evaluation of a lithium-ion battery containing a negative electrode active material

[0100] A lithium-ion battery was manufactured using a cathode comprising the cathode active material of the example and comparative example prepared according to the above manufacturing example, along with the same anode, electrolyte, and separator. The specific capacity, initial efficiency, and life retention rate of the battery were measured and summarized as shown in Table 1 below, and a graph regarding the life retention rate according to the number of cycles was shown in Figure 3. At this time, the initial efficiency is the fraction of the initial discharge capacity relative to the initial charge capacity of the battery (= (initial discharge capacity) / (initial charge capacity) X 100 (%)), and a higher initial efficiency means that the energy storage efficiency of the battery is higher.

[0101] C / Si crystal size ratio Cost (mAh / g) Initial efficiency (%) Lifespan retention rate (%, based on 100 cycles) Comparative example 4.20 1332.4 84.8 93.6 Example 1 3.53 1379.8 86.8 96.0 Example 2 2.86 1395.1 88.5 96.5 Example 3 2.83 1393.7 89.6 97.5 Example 4 2.55 1410.6 89.7 97.8 Example 5 2.11 1436.9 90.0 98.2 Example 6 1.94 1385.2 87.3 96.3

[0103] First, according to Table 1 above, it can be seen that the crystal size ratio of carbon-based materials to silicon particles decreases with increasing heat treatment temperature, and thus it can be confirmed that the temperature of the heat treatment according to the cathode active material manufacturing method is the most important factor in controlling the crystal size ratio.

[0104] In addition, looking at the battery performance measurement results according to Table 1 above, regarding the crystal size ratio of carbon-based materials to silicon particles, Examples 1 to 6, which have a lower crystal size ratio compared to the Comparative Example, were observed to have superior battery performance, such as specific capacity, initial efficiency, and lifespan retention rate, compared to the Comparative Example. In particular, looking at the graph of lifespan retention rate according to cycles in Fig. 3, it was confirmed that the batteries containing the negative electrode active materials of Examples 1 to 6 all exhibited an excellent lifespan retention rate of over 90% even after 200 cycles compared to the Comparative Example.

[0105] In addition, it was observed that as the crystal size ratio decreased, the battery performance generally tended to increase. However, in the case of Example 6, which had the lowest crystal size ratio, the performance seemed to deviate somewhat from the above trend due to the formation of silicon carbide, which was confirmed to be present in the XRD pattern, but it still maintained superior battery performance compared to the comparative example. Accordingly, it was found that securing an appropriate range of crystal size ratios for the negative electrode active material according to one embodiment is important for securing optimal battery performance.

[0106] Therefore, through the above experimental example, it was confirmed that a lithium-ion battery with improved electrical capacity and lifespan retention rate can be manufactured by controlling the crystal size ratio of carbon-based material to silicon particles included in the negative electrode active material to a specific range, such as by controlling the heat treatment temperature in the method of manufacturing the negative electrode active material.

[0108] Although the embodiments have been described above with reference to limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, suitable results can be achieved even if the described techniques are performed in a different order than the described method, and / or the described components are combined or assembled in a form different from the described method, or are replaced or substituted by other components or equivalents.

[0109] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims set forth below. Explanation of the symbols

[0111] 100: Cathode active material 110: Silicon particles (primary particles) 111: Silicon (Si) 112: Silicon oxide film 120: Carbonaceous substances 121: Hard Carbon 122: Soft Carbon

Claims

Claim 1 A negative electrode active material comprising silicon particles and a carbon-based material surrounding the silicon particles, wherein the negative electrode active material comprises secondary particles formed by the aggregation of two or more primary particles, which are the silicon particles, and has a form in which hard carbon is formed on the outer surface of the primary particles and soft carbon is partially or entirely filled between the primary particles, and the crystal size ratio of the carbon-based material to the silicon particles is 1.9 to 3.6, and the crystal size is calculated from the full-width at half maximum (FWHM) of the X-ray diffraction spectrum (XRD spectrum) peak. Claim 2 In claim 1, the silicon particles comprise silicon (Si) and a silicon oxide film formed on the silicon surface, a negative electrode active material. Claim 3 In claim 1, the silicon particles comprise scaly silicon particles, a negative electrode active material. Claim 4 delete Claim 5 A negative electrode active material according to claim 1, wherein the average particle size of the primary particles is 10 nm to 200 nm and the average particle size of the secondary particles is 1 μm to 10 μm. Claim 6 In claim 1, the carbon-based material is a negative electrode active material comprising hard carbon and soft carbon. Claim 7 delete Claim 8 A method for manufacturing a negative electrode active material as described in claim 1, comprising the steps of: introducing silicon powder and a polymer material into a solvent to prepare a solution and grinding it; spray-drying the solution to prepare a precursor; introducing the precursor and a carbon raw material and compounding them to prepare a composite; and heat-treating the composite at a temperature of 600 to 1,100 ℃ under an inert atmosphere. Claim 9 A method for manufacturing a negative electrode active material according to claim 8, wherein, in the step of preparing a solution by adding silicon powder and a polymer material to the solvent and grinding, the polymer material comprises one or more of polyvinylpyrrolidone, polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, phenolic resin, polyacrylic acid, epoxy resin, and polyfurfuryl alcohol resin. Claim 10 A method for manufacturing a negative electrode active material according to claim 8, wherein, in the step of introducing and compounding the above-mentioned precursor and carbon raw material to produce a composite, the carbon raw material comprises one or more of petroleum pitch, coal tar pitch, graphite, and graphene. Claim 11 A method for manufacturing a negative electrode active material according to claim 8, wherein, in the step of introducing and compounding the precursor and carbon raw material to manufacture a composite, the weight ratio of the precursor and carbon raw material is 3:1 to 1:

3. Claim 12 A method for manufacturing a negative electrode active material according to claim 10, wherein the carbon raw material comprises a first carbon raw material and a second carbon raw material of different types, and the weight ratio of the first carbon raw material and the second carbon raw material is 5:1 to 1:

5. Claim 13 A lithium-ion battery comprising the negative electrode active material described in claim 1.

Images