Silicon-based active material, negative electrode composition, and negative electrode and secondary battery comprising same

Abstract

The present invention relates to a silicon-based active material, a negative electrode composition, a negative electrode, a secondary battery, a battery pack, and a battery module and, specifically, to a silicon-based active material comprising two types of silicon-carbon composites having different silicon contents and different sphericities, mixed in optimal amounts.

Description

Silicon-based active material, negative electrode composition, negative electrode and secondary battery including the same

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2024-0192255 filed with the Korean Intellectual Property Office on December 20, 2024, the entire contents of which are incorporated herein.

[0002] The present invention relates to a silicon-based active material, a negative electrode composition, a negative electrode comprising the same, and a secondary battery. Furthermore, the present invention relates to a battery module comprising the secondary battery and a battery pack comprising the secondary battery or the battery module.

[0003] Recently, products utilizing various types of electrochemical energy, such as electric vehicles and energy storage systems, have been receiving significant attention in the market, leading to a rapid increase in demand for high-performance lithium-ion batteries. Due to their high energy density, high voltage, and long lifespan, lithium-ion batteries are the most widely used among various electrochemical devices and have established themselves as essential energy storage devices in applications requiring high-capacity energy, such as electric vehicles. In particular, active research is underway to develop high-density electrodes with higher energy density per unit volume to manufacture electrodes for high-capacity lithium-ion batteries.

[0004] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode, and silicon-based particles with a high discharge capacity can be used as this negative electrode active material.

[0005] In particular, with the recent increase in demand for high-density energy batteries, research is actively underway on methods to increase capacity by using silicon-based compounds, such as Si / C or SiOx, as negative electrode active materials, which offer higher capacity compared to graphite-based materials. While silicon-based compounds, as high-capacity materials, have the advantage of higher capacity compared to conventionally used graphite, they present a problem in that their volume expands rapidly during the charging process, severing conductive pathways and degrading battery performance.

[0006] Accordingly, various measures are being discussed to resolve the problems associated with using silicon-based active materials as negative electrode active materials, such as controlling the driving potential, suppressing volume expansion itself by additionally coating a thin film on the surface of the active material layer, or preventing the interruption of conductive paths. However, since these measures can actually degrade battery performance, their application is limited, and thus there are still limitations to the commercialization of manufacturing negative electrode batteries with a high content of silicon-based compounds.

[0007] Therefore, when using silicon-based active materials as negative electrode active materials, research is needed on methods to solve the aforementioned problems.

[0008] The present invention aims to provide a silicon-based compound, a cathode composition, a cathode including the same, and a secondary battery capable of solving the above-mentioned problems.

[0009] According to one embodiment of the present invention, a silicon-based active material is provided, comprising a first silicon carbon composite and a second silicon carbon composite, wherein the first silicon carbon composite comprises a first porous carbon and silicon provided on the first porous carbon, and the second silicon carbon composite comprises a second porous carbon and silicon provided on the second porous carbon, wherein the ratio (A) of the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite and the ratio (B) of Si content (wt%) to C content (wt%) of the second silicon carbon composite (A / B) is 0.1 to 0.9, the degree of sphericity of the first silicon carbon composite is smaller than the degree of sphericity of the second silicon carbon composite, and the degree of sphericity of the second silicon carbon composite is greater than 0.8 and less than or equal to 1, and the second silicon carbon composite is included in an amount of 0.01 to 25 parts by weight based on 100 parts by weight of a silicon-based active material.

[0010] According to another embodiment, a cathode composition comprising the silicon-based active material is provided.

[0011] According to another embodiment, a cathode is provided comprising: a cathode current collector; and a cathode active material layer provided on one or both sides of the cathode current collector, wherein the cathode active material layer comprises the cathode composition.

[0012] In another embodiment, a secondary battery comprising a positive electrode and a negative electrode is provided.

[0013] In another embodiment, a battery module or battery pack including the secondary battery is provided.

[0014] Finally, a battery pack including the above-mentioned battery module is provided.

[0015] According to one embodiment of the present invention, a silicon carbon composite comprising porous carbon and silicon provided on the porous carbon is applied as a silicon-based active material to provide a negative electrode having high energy density and a secondary battery including the same.

[0016] According to one embodiment of the present invention, by applying two types of silicon-carbon composites with different degrees of sphericity at an optimal content, the ratio of silicon content to carbon content satisfies a specific ratio, thereby effectively buffering the structural instability of the silicon-carbon composite, and thereby providing a negative electrode with improved capacity and lifespan characteristics and a secondary battery including the same.

[0017] According to one embodiment of the present invention, by applying a second silicon carbon composite with a high degree of sphericity in an optimal amount, particle breakage is minimized when mixing a negative electrode slurry containing a silicon-based active material, thereby reducing the amount of Si exposed on the surface and improving water-based processability.

[0018] In addition, by satisfying a specific ratio (A / B) of the ratio of silicon content (wt%) to carbon content (wt%) within the first silicon carbon composite with low sphericity (A) and the ratio of silicon content (wt%) to carbon content (wt%) within the second silicon carbon composite with high sphericity (B), the uniformity of silicon per particle is secured, thereby improving long-term lifespan performance.

[0019] Further scopes of the applicability of the present invention will become apparent from the following detailed description. However, since various changes and modifications within the spirit and scope of the present invention are clearly understood by those skilled in the art, specific embodiments, such as the detailed description and preferred embodiments of the present invention, should be understood as being given merely as examples.

[0020] FIG. 1 is a figure showing a negative electrode of a lithium secondary battery according to one embodiment of the present invention.

[0021] FIG. 2 is a figure showing a positive electrode of a lithium secondary battery according to one embodiment of the present invention.

[0022] Figure 3(a) shows an SEM image of the silicon-based active material of Example 1, and Figure 3(b) shows an SEM image of the cathode cross-section of Example 1.

[0023] Figure 4(a) shows an SEM image of the silicon-based active material of Comparative Example 1, and Figure 4(b) shows an SEM image of the cathode cross-section of Comparative Example 1.

[0024] Figure 5 shows an SEM image of the silicon-based active material of Example 2.

[0025] Figure 6 shows an SEM image of the silicon-based active material of Comparative Example 2.

[0026] Figure 7 shows an SEM image of the silicon-based active material of Comparative Example 3.

[0027] Figure 8 shows an SEM image of the silicon-based active material of Comparative Example 4.

[0028] Figure 9 is a figure showing the EDS analysis method of the silicon-based active material of Example 1.

[0029] The present invention is described in detail below so that those skilled in the art can easily practice it. However, the present invention may be embodied in various different forms and is not limited to the description below.

[0030] Before describing the present invention, some terms are defined first.

[0031] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0032] In this specification, "p to q" means a range of p or more and q or less.

[0033] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL SORP-mini II from BEL Japan. That is, in the present invention, the BET specific surface area may refer to the specific surface area measured by the above measurement method. The BET specific surface area may be measured according to DIN 66131 using N2.

[0034] In this specification, "Dn" refers to the particle size distribution and represents the particle size at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size (central particle size), D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the central particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0035] In this specification, particularly when the particle is spherical or circular, the particle size or particle diameter may refer to the average diameter or representative diameter of each individual grain forming the particle powder.

[0036] In this specification, particularly when the particle is not only spherical or circular but also has an amorphous shape, the particle size or particle diameter may be defined as (major axis length + minor axis length) / 2 of the particle.

[0037] In addition, the above average particle size can be measured through cross-sectional analysis of the cathode. Specifically, for the cross-sectional analysis of the cathode, a cathode electrode cut to a width of 0.5 cm and a length of 0.5 cm is mounted on an ion milling holder, the electrode sample is milled using a Hitachi IM4000 device, and an ion beam is fired at a voltage of 5 kV for about 1 to 2 hours per sample, after which a cross-sectional image of the electrode is measured using a scanning electron microscope (SEM) from JEOL. For each particle observed in the SEM image obtained from the cross-sectional image, the major axis length and minor axis length are measured, and the average value of (major axis length + minor axis length) / 2 is calculated to determine the value. Five regions of the cross-section were randomly selected, and the cross-section was magnified by 2.5 K and photographed (WD 8.5~10.5 mm) to obtain images for measurement.

[0038] In the present specification, the content of Si and C within the silicon-carbon composite can be determined using an energy-dispersive X-ray spectroscopy (EDS), and the energy-dispersive X-ray spectroscopy can be used that is attached to a scanning electron microscope (SEM). Specifically, a scanning electron microscope (SEM) is a device capable of observing the fine surface shape of a sample by irradiating the surface of the sample with an electron beam and detecting secondary electrons emitted from the sample. When the electron beam irradiates the sample, characteristic X-rays are emitted from the atoms constituting the sample, and the elemental composition of the sample can be confirmed by detecting these characteristic X-rays and analyzing them through an energy-dispersive X-ray spectroscopy (EDS).

[0039] In this specification, the particle may be in the form of a single particle or in the form of a secondary particle formed by the aggregation of a plurality of primary particles. Additionally, the central particle size of a particle may be used interchangeably with the average particle size, D50, or particle size, and the central particle size may refer to the size of a particle.

[0040] In this specification, "particle" may include all forms of single particles, pseudo-single particles, and secondary particles.

[0041] In this specification, "single particle" may mean one primary particle and may include a pseudo-single particle formed by aggregating, combining, or assembling 30 or fewer primary particles.

[0042] The term "secondary particles" used in the present invention refers to particles formed by the aggregation of dozens to hundreds, for example, more than 30 primary particles, by combining, bonding, or assembling.

[0043] In this specification, the meaning that a polymer contains a monomer in monomer units means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. In this specification, when it is stated that a polymer contains a monomer, this is interpreted as the same as the polymer containing the monomer in monomer units.

[0044] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless specified as "homopolymer."

[0045] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are polystyrene equivalent molecular weights measured by gel permeation chromatography (GPC), using commercially available monodisperse polystyrene polymers of various degrees of polymerization (standard samples) for molecular weight measurement as standard materials. In this specification, the term "molecular weight" means weight-average molecular weight unless otherwise specified.

[0046] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are presented and described in detail in the detailed description. However, this is not intended to limit the scope of the invention by the embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0047] Recently, the development of silicon (Si)-based active materials has been actively pursued to create next-generation batteries with high energy density. Since Si-based active materials possess a higher theoretical capacity compared to conventional graphite, utilizing them can significantly improve the energy density of lithium-ion batteries. However, because silicon undergoes significant volume expansion during the charging and discharging process, the application of silicon-based active materials presents problems such as reduced structural stability of the anode and degradation of battery performance due to the disruption of conductive pathways.

[0048] To solve the above problem, SiOx(0 <x<2), pure Si 등의 물질이 실리콘 계 음극 활물질로 연구되어 왔으나, 이들 물질은 충방전 성능 또는 초기 효율이 저조하게 나타나는 등 기존 문제점을 해결하지 못했다. 특히, 충·방전 과정에서 발생하는 부피 팽창으로 인한 구조적 불안정성과 수명 감소의 문제는 여전히 해결해야 할 과제였다.

[0049] Accordingly, the inventors of the present invention have confirmed that using a silicon-carbon composite containing silicon on porous carbon can effectively mitigate structural instability caused by volume expansion while maintaining the high capacity of silicon. In other words, by uniformly depositing silicon within the porous carbon structure, it has been discovered that the structural stability of silicon-based active materials can be improved and active materials of a uniform form can be manufactured more easily.

[0050] In particular, it was discovered that by appropriately mixing silicon-carbon composites having different degrees of sphericity, the water-based processability can be improved and the lifespan of the battery can be improved by preventing the interruption of conductive paths during charging and discharging.

[0051]

[0052] Silicon-based active material

[0053] According to one embodiment of the present invention, a silicon-based active material is provided, comprising a first silicon carbon composite and a second silicon carbon composite, wherein the first silicon carbon composite comprises a first porous carbon and silicon provided on the first porous carbon, and the second silicon carbon composite comprises a second porous carbon and silicon provided on the second porous carbon, wherein the ratio (A) of the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite and the ratio (B) of Si content (wt%) to C content (wt%) of the second silicon carbon composite (A / B) is 0.1 to 0.9, the degree of sphericity of the first silicon carbon composite is smaller than the degree of sphericity of the second silicon carbon composite, and the degree of sphericity of the second silicon carbon composite is greater than 0.8 and less than or equal to 1, and the second silicon carbon composite is included in an amount of 0.01 to 25 parts by weight based on 100 parts by weight of a silicon-based active material.

[0054] In the present specification, the C content (wt%) and Si content (wt%) of the first silicon carbon composite refer to the mass parts of each element based on 100 wt% of the first silicon carbon composite.

[0055] In this specification, the C content (wt%) and Si content (wt%) of the second silicon carbon composite refer to the mass parts of each element based on 100 wt% of the first silicon carbon composite.

[0056] According to one embodiment of the present invention, the ratio (A) of the Si content (wt%) to the C content (wt%) of the first silicon carbon composite is lower than the ratio (B) of the Si content (wt%) to the C content (wt%) of the second silicon carbon composite.

[0057] In this specification, the C content and the Si content may each have a unit of mol% representing the ratio of atoms.

[0058] In this specification, the ratio of Si content to C content may be a dimensionless number.

[0059] According to one embodiment of the present invention, the ratio (A / B) of the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite (A) and the ratio of Si content (wt%) to C content (wt%) of the second silicon carbon composite (B) may be 0.1 to 0.9. For example, A / B may be 0.1 or more, 0.2 or more, or 0.25 or more, and may be 0.9 or less, 0.8 or less, or 0.75 or less.

[0060] By satisfying the above range, the ratio (A / B) of the ratio (A) of the Si content (wt%) to the C content (wt%) of the first silicon carbon composite and the ratio (B) of the Si content (wt%) to the C content (wt%) of the second silicon carbon composite can ensure the uniformity of silicon per particle, thereby improving long-term life performance. Specifically, when the ratio satisfies the above numerical range, an appropriate amount of silicon is deposited on the second silicon carbon composite, thereby suppressing side reactions in the electrolyte, preventing cell performance degradation and swelling, and ensuring the stability of the aqueous slurry.

[0061] According to one embodiment of the present invention, the degree of sphericity of the first silicon carbon composite is smaller than the degree of sphericity of the second silicon carbon composite.

[0062] According to one embodiment of the present invention, the degree of sphericity of a first silicon carbon composite having a relatively low ratio of Si content (wt%) to C content (wt%) (A) may be smaller than the degree of sphericity of a second silicon carbon composite having a relatively high ratio of Si content (wt%) to C content (wt%) (B).

[0063] One feature of the present invention is that by increasing the degree of sphericity of a second silicon carbon composite having a higher silicon content as a silicon-based active material, the effect of suppressing electrolyte side reactions and improving the cycle can be obtained.

[0064] Specifically, as the degree of sphericity of the silicon-carbon composite increases, the strength of the particles increases. When the degree of sphericity of the second silicon-carbon composite with a higher silicon content is increased, not only is the capacity superior by increasing the Si content in the negative electrode active material, but side reactions with the electrolyte can also be suppressed by minimizing particle breakage during rolling.

[0065] One feature of the present invention is that, as a silicon-based active material, a small amount of a second silicon carbon composite with a relatively larger degree of sphericity is included to increase the particle strength of the active material and, at the same time, improve the rolling resistance of the cathode when applied to the cathode, thereby improving water-based processability and mitigating volume expansion during charging and discharging.

[0066] The above sphericity can be defined as the aspect ratio of the minor axis to the major axis and can be measured through SEM image analysis of the cathode active material powder. Specifically, after attaching carbon tape to an SEM holder, a small amount of cathode active material powder is scattered onto the carbon tape. Then, the ratio of the minor axis to the major axis of the cathode active material observed in the SEM image is calculated and measured by magnifying it to 1K using a JEOL SEM instrument. The above sphericity may be the average value obtained by repeating the above process five times.

[0067] In addition, the sphericity can be measured through cross-sectional analysis of the cathode. Specifically, for the cross-sectional analysis of the cathode, a cathode electrode cut to a width of 0.5 cm and a length of 0.5 cm is mounted on an ion milling holder, the electrode sample is milled using a Hitachi IM4000 device, and an ion beam is fired at a voltage of 5 kV for about 1 to 2 hours per sample, after which the cross-sectional image of the electrode is measured using a SEM instrument from JEOL. The measurement can be performed by calculating the average value of the ratio of the minor axis to the major axis for each particle observed in each SEM image obtained from the cross-sectional image. Five regions of the cross-section were randomly selected, and the cross-section was magnified by 2.5 K and photographed (WD 8.5~10.5 mm) to measure the value using the obtained images.

[0068] In one embodiment of the present invention, the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite and the second silicon carbon composite can be obtained simultaneously with the SEM image through an energy-dispersive X-ray spectroscopy (EDS) device attached to the SEM equipment. Specifically, the degree of sphericity is calculated for each particle observed on each SEM image obtained from the SEM image to distinguish between the first silicon carbon composite and the second silicon carbon composite, and the ratio of Si content (wt%) to C content (wt%) for each particle is calculated. Then, the average value can be set as the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite (A) and the ratio of Si content (wt%) to C content (wt%) of the second silicon carbon composite (B).

[0069] Specifically, as illustrated in Fig. 9, silicon carbon composites within the cathode can be distinguished through SEM images, and the Si content (wt%) relative to the C content (wt%) can be determined by analyzing the EDS spectrum of each silicon carbon composite. In Fig. 9, 25 particles were identified as silicon carbon composites, Spectrums 1 to 17 were classified as first silicon carbon composites, and the average ratio of Si content (wt%) relative to C content (wt%) was calculated and assigned as A, while Spectrums 18 to 25 were classified as second silicon carbon composites, and the average ratio of Si content (wt%) relative to C content (wt%) was calculated and assigned as B.

[0070] According to one embodiment of the present invention, the ratio (A) of the Si content to the C content of the first silicon carbon composite may be 0.45 or more, 0.55 or more, or 0.60 or more, and may be 2.3 or less, 1.9 or less, or 1.5 or less.

[0071] According to one embodiment of the present invention, the ratio (B) of the Si content to the C content of the first silicon carbon composite of the second silicon carbon composite may be 0.8 or more, 0.9 or more, or 1.0 or more, and may be 5.7 or less, 4.2 or less, or 3.0 or less.

[0072] According to one embodiment of the present invention, the degree of sphericity of the second silicon carbon composite is greater than 0.8 and less than or equal to 1. For example, the degree of sphericity may be greater than 0.8, greater than or equal to 0.85, or greater than or equal to 0.90, and may be less than or equal to 1 or less than or equal to 0.95.

[0073] The above silicon-based active material includes a second silicon carbon composite with a high degree of sphericity, thereby providing excellent strength to the silicon-based active material and improving ductility when applied as a negative electrode, which can reduce the probability of cracks occurring due to particle breakage.

[0074] According to one embodiment of the present invention, the second silicon carbon composite may be included in an amount of 0.01 to 25 parts by weight based on 100 parts by weight of a silicon-based active material. For example, the second silicon carbon composite may be included in an amount of 0.01 parts by weight or more, 1 part by weight or more, or 5 parts by weight or more based on 100 parts by weight of a silicon-based active material, and may be included in an amount of 25 parts by weight or less, or 20 parts by weight or less. When the second silicon carbon composite is included within the above range, aqueous processability is improved, and volume expansion during charging and discharging may be mitigated.

[0075] That is, according to one embodiment of the present invention, the first silicon carbon composite and the second silicon carbon composite may be mixed and included in a weight ratio of 99.99:0.01 to 75:25. For example, the first silicon carbon composite and the second silicon carbon composite may be mixed in a weight ratio of 99.99:0.01 to 75:25, 99:1 to 75:25, 95:5 to 75:25, or 99:1 to 80:20.

[0076] If the content of the second silicon carbon composite is less than the above range, the content of the second silicon carbon composite is too low to achieve the effect of adding the second silicon carbon composite, and if the content of the second silicon carbon composite exceeds the above range, the adhesion of the electrode is reduced, causing the active material to detach during charging and discharging, which may result in reduced battery performance and a problem where the resistance of the negative electrode becomes excessively high.

[0077] Specifically, since the second silicon carbon composite with a high degree of sphericity has a relatively small specific surface area, the adhesion between silicon carbon composites, or between the silicon carbon composite and the current collector (foil), binder, and conductive material, is low. Therefore, if the second silicon carbon composite is included in an amount exceeding the above range, long-term lifespan performance may deteriorate.

[0078] That is, according to one embodiment of the present invention, by including a silicon carbon composite with a high degree of sphericity, the rolling resistance of the silicon-based active material is improved, thereby lowering the probability of cracks occurring within the particles during electrode rolling, and at the same time, by including a silicon carbon composite with a low degree of sphericity, the adhesion of the electrode can be improved.

[0079] According to one embodiment of the present invention, the degree of sphericity of the first silicon carbon composite is 0.45 to 0.8.

[0080] The above silicon-based active material includes a silicon carbon composite having a low specific surface area by including a first silicon carbon composite with a low degree of sphericity. Accordingly, interaction between the first silicon carbon composite and other components is facilitated, and adhesion can be improved when applied to an electrode.

[0081] According to one embodiment of the present invention, a silicon-based active material can be provided in which the average particle size (D50) of the second silicon carbon composite is smaller than the average particle size (D50) of the first silicon carbon composite.

[0082] Another feature of the present invention is that, as a silicon-based active material, a second silicon carbon composite having a greater degree of sphericity than the first silicon carbon composite and a smaller average particle size (D50) is included within the above range, thereby minimizing the reduction in electrode adhesion and improving the strength of the particles and the ductility of the electrode, so that water-based processability is improved and volume expansion during charging and discharging can be mitigated. In addition, when the average particle size (D50) of the second silicon carbon composite is adjusted to the above range, it may be easy to control the degree of sphericity to greater than 0.8.

[0083] According to one embodiment of the present invention, the average particle size (D50) of the first silicon carbon composite may be greater than 4 μm and less than or equal to 10 μm. For example, the average particle size (D50) of the first silicon carbon composite may be greater than 4 μm, greater than or equal to 6 μm, or greater than or equal to 8 μm, and less than or equal to 10 μm or less than or equal to 9 μm. If the average particle size of the first silicon carbon composite is below the lower limit, the average particle size of the entire silicon-based active material becomes excessively small, causing aggregation between the composites during the process, which may lead to a decrease in water-based processability. On the other hand, if the average particle size exceeds the upper limit, the average particle size of the entire silicon-based active material becomes excessively large, which may increase the possibility of battery performance degradation due to volume expansion of the active material.

[0084] According to one embodiment of the present invention, the average particle size (D50) of the second silicon carbon composite may be 1 μm to 4 μm. For example, the average particle size (D50) of the second silicon carbon composite may be 1 μm or more, 1.5 μm or more, 1.8 μm or more, or 2 μm or more, and may be 4 μm or less, 3 μm or less, or 2.5 μm or less. If the average particle size of the second silicon carbon composite is below the lower limit, it may cause structural instability of the electrode during charging and discharging, thereby degrading battery performance, and if it exceeds the upper limit, it may cause the adhesion of the electrode to degrade, thereby negatively affecting battery performance.

[0085] In this specification, the average particle size or average particle diameter may be defined as (major axis length + minor axis length) / 2 of the particle. In particular, the average particle size or average particle diameter of a particle having a non-spherical / non-circular shape may be defined as (major axis length + minor axis length) / 2.

[0086] The above average particle size can be measured through cross-sectional analysis of the cathode. Specifically, for the cross-sectional analysis of the cathode, a cathode electrode cut to a width of 0.5 cm and a length of 0.5 cm is mounted on an ion milling holder, the electrode sample is milled using a Hitachi IM4000 device, and an ion beam is fired at a voltage of 5 kV for about 1 to 2 hours per sample, after which a cross-sectional image of the electrode is measured using a SEM instrument from JEOL. For each particle observed in the SEM image obtained from the cross-sectional image, the major axis length and minor axis length are measured, and the average value of (major axis length + minor axis length) / 2 is calculated to determine the value. Five regions of the cross-section were randomly selected, and the cross-section was magnified by 2.5K and photographed (WD 8.5~10.5 mm) to obtain images for measurement.

[0087] In this specification, “silicon carbon composite” may be used interchangeably with “Si / C.” That is, in this specification, Si / C refers to a silicon carbon composite.

[0088] The first silicon carbon composite may consist of Si and C that are not bonded to each other, but may include additional components as needed. For example, the first silicon carbon composite may or may not include silicon carbide, denoted as SiC. If the first silicon carbon composite includes silicon carbide, its content is 3 weight percent or less. The first silicon carbon composite may exist in a crystalline, amorphous, or mixed state. According to one example, C in the first silicon carbon composite may exist in an amorphous state.

[0089] According to one embodiment of the present invention, the first silicon carbon composite comprises a first porous carbon and silicon provided on the first porous carbon.

[0090] According to one embodiment of the present invention, the first silicon carbon composite may comprise a first porous carbon and silicon deposited on the first porous carbon. Specifically, the first silicon carbon composite comprises a first porous carbon-based particle and silicon particles located on the surface or within the internal pores of the first porous carbon-based particle.

[0091] The silicon particles formed on the surface and internal pores of the first porous carbon-based particles may be silicon nanoparticles, and these may be crystalline, semicrystalline, amorphous, or a combination thereof.

[0092] According to one embodiment of the present invention, the first porous carbon is 0.75 cm 3 / g to 1 cm 3It has a total pore volume of / g. When the total pore volume is controlled within the above range, silicon can be uniformly deposited inside the pores of the first porous carbon.

[0093] According to one embodiment of the present invention, the first porous carbon may contain at least 70% of micropores having an average diameter (D50) of less than 2 nm. When the fraction of micropores with a relatively small average particle size for Si deposition within the first porous carbon is included in the above range, silicon can be uniformly deposited within the pores of the first porous carbon, thereby reducing the amount of silicon exposed to the outside and reducing the amount of water-based slurry gas generated.

[0094] In addition, according to one embodiment of the present invention, the first porous carbon may further include mesopores with an average diameter of 2 nm to 50 nm and macropores with an average diameter greater than 50 nm.

[0095] A first silicon carbon composite according to one embodiment of the present invention comprises a first carbon layer provided on at least a portion of the first porous carbon. Specifically, the first carbon layer can prevent the deterioration of the lifespan characteristics of the first silicon carbon composite or the generation of gas due to contact with water during an aqueous process by blocking the exposure of silicon on the outer surface of the first porous carbon or by reducing the reactivity of silicon. In addition, the first carbon layer imparts conductivity to the first silicon carbon composite, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of the secondary battery can be improved.

[0096] In one embodiment of the present invention, the first carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0097] Specifically, the first carbon layer may be an amorphous first carbon layer. The amorphous carbon can appropriately maintain the strength of the first carbon layer to suppress the expansion of the first silicon carbon composite. Additionally, the first carbon layer may additionally include or not include crystalline carbon.

[0098] The amorphous carbon can appropriately maintain the strength of the first carbon layer to suppress the expansion of the silicon-carbon composite. The amorphous carbon may be a carbon-based material formed using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source for chemical vapor deposition.

[0099] The above-mentioned other organic carbons may be carbons of organic materials selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or kedohexose and combinations thereof.

[0100] The above hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0101] In one embodiment of the present invention, the first carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on a total of 100 parts by weight of the first silicon carbon composite. More specifically, it may be included in an amount of 0.5 to 15 parts by weight or 1 to 10 parts by weight. When satisfying the above ranges, conductivity can be improved while preventing a decrease in the capacity and efficiency of the first silicon carbon composite.

[0102] In one embodiment of the present invention, the thickness of the first carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm, and more specifically 5 nm to 100 nm. When the above range is satisfied, the conductivity of the first silicon carbon composite is improved, the volume change of the first silicon carbon composite is easily suppressed, and side reactions between the electrolyte and the first silicon carbon composite are suppressed, thereby improving the initial efficiency and / or lifespan of the battery.

[0103] Specifically, the first carbon layer can be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0104] According to another embodiment of the present invention, the Si / C (first silicon carbon composite) may be configured such that carbon material is coated on the surface of particles by firing carbon in a state where carbon is bonded with silicon or silicon oxide particles, or such that carbon is dispersed in an atomic state inside silicon particles, or such that a structure is formed in which graphite, graphene, or amorphous carbon is wrapped around a core in which silicon and carbon are composited.

[0105] According to one embodiment of the present invention, the Si:C elemental ratio on the surface of the first silicon carbon composite is 1:1 to 1:4, for example, 1:2 to 1:4, or 1:3 to 1:4. This means that since the first silicon carbon composite has a first carbon layer on its surface, the carbon ratio appears higher in the surface portion. Having such an elemental ratio implies that the carbon coating on the surface of the first silicon carbon composite is well formed, which can be measured via XPS. Adjusting the elemental ratio can be achieved by adjusting the amount of carbonized material or changing the heat treatment time during the process of introducing the first carbon layer.

[0106] According to one embodiment of the present invention, the Si:C element ratio in the first silicon carbon composite is 0.9:1.1 to 1.1:0.9, and for example, may be 1:0.95 to 1:1.1. Although a higher Si content is advantageous for increasing capacity, it may not be deposited within the carbon pores but is deposited on the surface, which accelerates the generation of aqueous slurry gas and increases surface side reactions, thereby adversely affecting lifespan, processability, etc.

[0107] According to one embodiment of the present invention, the silicon is included in an amount of 50 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the first silicon carbon composite. That is, the first silicon carbon composite contains silicon in an amount of 50 parts by weight or more and less than 100 parts by weight. The silicon content may refer to the silicon content contained within the first silicon carbon composite (final product). While a higher silicon content is advantageous for increasing capacity, excessive swelling of the silicon carbon composite may occur. Furthermore, during the manufacturing process of the silicon carbon composite, silicon may not be deposited within the carbon pores but rather deposited on the surface, increasing the likelihood of side reactions occurring during water-based processes, which may adversely affect lifespan, processability, etc. The above silicon content range is advantageous for satisfying capacity, lifespan, and processability. The above Si / C is mainly composed of two elements, Si and C, and the influence of the remaining elements is excluded. C is measured through a CS analyzer, and the value obtained by subtracting its ratio from the total can be calculated as the Si content. The above silicon content can be controlled by silicon deposition conditions or the pore volume of porous carbon.

[0108] The first silicon carbon composite can be manufactured by including the steps of forming a core comprising a first silicon carbon composite (Si / C) and forming a first carbon layer provided on at least a portion of the core.

[0109] According to one embodiment, the step of forming a core including the first silicon carbon composite may be manufactured by a method comprising: etching carbon-based particles containing internal pores (e.g., porous carbon or coconut shell-derived powder) to expand the internal pores of the carbon-based particles; and forming silicon particles on the surface and internal pores of the carbon-based particles with expanded internal pores.

[0110] The step of expanding the internal pores of the carbon-based particles can be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, an air atmosphere, or a water vapor (H2O) atmosphere. Specifically, the flow rate of the oxygen (O2), the air containing the oxygen, or the water vapor (H2O) can be controlled to 0.1 L / min to 10 L / min.

[0111] The step of expanding the internal pores of the carbon-based particles can be performed for 30 minutes to 4 hours at a temperature range of 400℃ to 1200℃.

[0112] Depending on the conditions for expanding the internal pores of the carbon-based particles, the pore characteristics of the first porous carbon-based particles obtained may vary.

[0113] An etching agent may be used to expand the internal pores of the carbon-based particles, and a basic material such as KOH may be used. For example, the internal pores of the carbon-based particles may be expanded by mixing the carbon-based particles and KOH in a weight ratio of 1:1 to 1:5.

[0114] The step of forming the silicon particles can be performed using chemical vapor deposition (CVD). At this time, silicon nanoparticles are deposited on the surface and / or internal pores of the carbon-based particles with expanded internal pores, thereby forming a silicon coating layer in the form of a film, an island, or a mixture thereof.

[0115] The step of forming the silicon particles above can be performed by flowing SiH4 / H2 gas through carbon-based particles at 500°C to 900°C using a chemical vapor deposition (CVD) apparatus to form a first silicon-carbon composite.

[0116] The step of forming the first carbon layer above can be performed by using a chemical vapor deposition (CVD) method using a carbon-based material, for example, a hydrocarbon gas, or by carbonizing a material that serves as a carbon source.

[0117] Specifically, the core including the first silicon carbon composite can be formed by introducing it into a reactor and then chemically vaporizing (CVD) a hydrocarbon gas at 500°C to 700°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group comprising methane, ethane, propane, and acetylene.

[0118] The second silicon carbon composite may consist of Si and C that are not bonded to each other, but may include additional components as needed. For example, the second silicon carbon composite may or may not include silicon carbide, denoted as SiC. If the second silicon carbon composite includes silicon carbide, its content is 3 weight percent or less. The second silicon carbon composite may exist in a crystalline, amorphous, or mixed state. According to one example, C in the second silicon carbon composite may exist in an amorphous state.

[0119] According to one embodiment of the present invention, the second silicon carbon composite comprises a second porous carbon and silicon provided on the second porous carbon.

[0120] According to one embodiment of the present invention, the second silicon carbon composite may comprise a second porous carbon and silicon deposited on the second porous carbon. Specifically, the second silicon carbon composite comprises a second porous carbon-based particle and silicon particles located on the surface or within the internal pores of the second porous carbon-based particle.

[0121] The silicon particles formed on the surface and internal pores of the second porous carbon-based particle may be silicon nanoparticles, and these may be crystalline, semicrystalline, amorphous, or a combination thereof.

[0122] According to one embodiment of the present invention, the first porous carbon and the second porous carbon may be different.

[0123] In this specification, the expression "different" may include cases where the type of compound constituting the substance is different, the composition of the compound constituting the substance is different, or both the type and composition of the compound are different.

[0124] According to one embodiment of the present invention, the second porous carbon is 0.75 cm 3 / g to 1 cm 3 It has a total pore volume of / g. When the total pore volume is controlled within the above range, silicon can be uniformly deposited inside the pores of the second porous carbon.

[0125] According to one embodiment of the present invention, the second porous carbon may contain at least 70% of micropores having an average diameter (D50) of less than 2 nm. When the fraction of micropores with a relatively small average particle size for depositing Si within the second porous carbon is included in the above range, silicon can be uniformly deposited within the pores of the second porous carbon.

[0126] In addition, according to one embodiment of the present invention, the second porous carbon may further include mesopores with an average diameter of 2 nm to 50 nm and macropores with an average diameter greater than 50 nm.

[0127] A second silicon carbon composite according to one embodiment of the present invention comprises a second carbon layer provided on at least a portion of the second porous carbon. Specifically, the second carbon layer can prevent gas generation caused by contact with water during an aqueous process or the deterioration of the lifespan characteristics of the second silicon carbon composite by blocking the exposure of silicon on the outer surface of the second porous carbon or by reducing the reactivity of silicon. In addition, conductivity is imparted to the second silicon carbon composite by the second carbon layer, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of the secondary battery can be improved.

[0128] In one embodiment of the present invention, the second carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0129] Specifically, the second carbon layer may be an amorphous second carbon layer. The amorphous carbon can appropriately maintain the strength of the second carbon layer to suppress the expansion of the second silicon carbon composite. Additionally, the second carbon layer may additionally include or not include crystalline carbon.

[0130] The amorphous carbon can appropriately maintain the strength of the second carbon layer to suppress the expansion of the silicon-carbon composite. The amorphous carbon may be a carbon-based material formed using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source for chemical vapor deposition.

[0131] The above-mentioned other organic carbons may be carbons of organic materials selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or kedohexose and combinations thereof.

[0132] The above hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0133] In one embodiment of the present invention, the second carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on a total of 100 parts by weight of the second silicon carbon composite. More specifically, it may be included in an amount of 0.5 to 15 parts by weight or 1 to 10 parts by weight. When the above range is satisfied, conductivity can be improved while preventing a decrease in the capacity and efficiency of the second silicon carbon composite.

[0134] In one embodiment of the present invention, the thickness of the second carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm, and more specifically 5 nm to 100 nm. When the above range is satisfied, the conductivity of the second silicon carbon composite is improved, the volume change of the second silicon carbon composite is easily suppressed, and side reactions between the electrolyte and the second silicon carbon composite are suppressed, thereby improving the initial efficiency and / or lifespan of the battery.

[0135] Specifically, the second carbon layer can be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0136] According to another embodiment of the present invention, the Si / C (second silicon-carbon composite) may be configured such that carbon material is coated on the surface of particles by firing carbon in a state where carbon is bonded with silicon or silicon oxide particles, or such that carbon is dispersed in an atomic state inside silicon particles, or such that a structure is formed in which graphite, graphene, or amorphous carbon is wrapped around a core in which silicon and carbon are composited.

[0137] According to one embodiment of the present invention, the Si:C elemental ratio on the surface of the second silicon carbon composite is 1:1 to 1:4, for example, 1:2 to 1:4, or 1:3 to 1:4. This means that since the second silicon carbon composite has a second carbon layer on its surface, the carbon ratio appears higher in the surface portion. Having such an elemental ratio implies that the carbon coating on the surface of the second silicon carbon composite is well formed, which can be measured via XPS. Adjusting the elemental ratio can be achieved by adjusting the amount of carbonized material or changing the heat treatment time during the process of introducing the second carbon layer.

[0138] According to one embodiment of the present invention, the ratio of Si to C elements in the second silicon-carbon composite is 0.9:1.1 to 1.1:0.9, and for example, may be 1:0.95 to 1:1.1. Although a higher Si content is advantageous for increasing capacity, it is not deposited within the carbon pores but is deposited on the surface, which increases side reactions during charging and discharging, and causes problems such as side reactions between silicon and aqueous solvents on the surface during aqueous processes, which may have an adverse effect on lifespan, processability, etc.

[0139] According to one embodiment of the present invention, the silicon is included in an amount of 50 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the second silicon carbon composite. That is, the second silicon carbon composite contains silicon in an amount of 50 parts by weight or more and less than 100 parts by weight. The silicon content may refer to the silicon content contained within the second silicon carbon composite (final product). While a higher silicon content is advantageous for increasing capacity, excessive swelling of the silicon carbon composite may occur. Furthermore, during the manufacturing process of the silicon carbon composite, silicon may not be deposited within the carbon pores but rather deposited on the surface, leading to problems such as side reactions during water-based processes and increased side reactions during charging and discharging, which may adversely affect lifespan and processability. The above silicon content range is advantageous for satisfying capacity, lifespan, and processability. The above Si / C is mainly composed of two elements, Si and C, and excludes the influence of the remaining elements. C is measured through a CS analyzer, and the value obtained by subtracting its ratio from the total can be calculated as the Si content. The above silicon content can be controlled by silicon deposition conditions or the pore volume of porous carbon.

[0140] The second silicon carbon composite can be manufactured by including the steps of forming a core comprising a second silicon carbon composite (Si / C) and forming a second carbon layer provided on at least a portion of the core.

[0141] According to one embodiment, the step of forming a core including the second silicon carbon composite may be manufactured by a method comprising: etching carbon-based particles (e.g., second porous carbon) containing internal pores to expand the internal pores of the carbon-based particles; and forming silicon particles on the surface and internal pores of the carbon-based particles with expanded internal pores.

[0142] The step of expanding the internal pores of the carbon-based particles can be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, an air atmosphere, or a water vapor (H2O) atmosphere. Specifically, the flow rate of the oxygen (O2), the air containing the oxygen, or the water vapor (H2O) can be controlled to 0.1 L / min to 10 L / min.

[0143] The step of expanding the internal pores of the carbon-based particles can be performed for 30 minutes to 4 hours at a temperature range of 400℃ to 1200℃.

[0144] Depending on the conditions for expanding the internal pores of the carbon-based particles, the pore characteristics of the second porous carbon-based particles obtained may vary.

[0145] An etching agent may be used to expand the internal pores of the carbon-based particles, and a basic material such as KOH may be used. For example, the internal pores of the carbon-based particles may be expanded by mixing the carbon-based particles and KOH in a weight ratio of 1:1 to 1:5.

[0146] The step of forming the silicon particles can be performed using chemical vapor deposition (CVD). At this time, silicon nanoparticles are deposited on the surface and / or internal pores of the carbon-based particles with expanded internal pores, thereby forming a silicon coating layer in the form of a film, an island, or a mixture thereof.

[0147] The step of forming the silicon particles above can be performed by flowing SiH4 / H2 gas through carbon-based particles at 500°C to 900°C using a chemical vapor deposition (CVD) apparatus to form a second silicon-carbon composite.

[0148] The step of forming the second carbon layer above can be performed by using a chemical vapor deposition (CVD) method using a carbon-based material, for example, a hydrocarbon gas, or by carbonizing a material that serves as a carbon source.

[0149] Specifically, the core containing the second silicon-carbon composite can be formed by introducing it into a reactor and then chemically vaporizing (CVD) a hydrocarbon gas at 500°C to 700°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group comprising methane, ethane, propane, and acetylene.

[0150]

[0151] cathode composition

[0152] One embodiment of the present invention provides a cathode composition comprising a cathode active material according to one embodiment of the present invention.

[0153] The above cathode composition may further include an additional cathode active material. As the additional cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0154] One embodiment of the present invention provides a cathode composition further comprising a carbon-based active material. The carbon-based active material comprises at least one selected from the group consisting of natural graphite and artificial graphite.

[0155] Specifically, the carbon-based active material may be natural graphite, artificial graphite, or a mixture of natural graphite and artificial graphite.

[0156] The above artificial graphite is generally manufactured by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum-based heavy oils at temperatures above 2,500°C, and is used as a negative electrode active material after undergoing particle size adjustments such as grinding and secondary particle formation following this graphitization. In the case of artificial graphite, crystals are randomly distributed within the particles, and compared to natural graphite, it has a lower degree of sphericity and a somewhat pointed shape.

[0157] In addition, the artificial graphite may have an average particle size (D50) of 5 to 30 μm, preferably 10 to 25 μm.

[0158] The above natural graphite generally exists as plate-like aggregates before processing, and the plate-like particles are manufactured into a spherical shape with a smooth surface through post-processing, such as particle grinding and reassembly, in order to be used as an active material for electrode manufacturing.

[0159] In addition, the natural graphite may have a particle size of 5 to 30 μm, or 10 to 25 μm.

[0160] When the above carbon-based active material is a mixture of artificial graphite and natural graphite, the weight ratio of the artificial graphite and natural graphite may be 9.99 : 0.01 to 0.01 : 9.99, or 9.7 : 0.3 to 7:3. When satisfying this weight ratio range, superior output may be exhibited.

[0161] According to one embodiment of the present invention, the carbon-based active material may be included in an amount of 70 parts by weight or more based on 100 parts by weight of the total negative electrode active material. For example, it may be included in an amount of 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, 98 parts by weight or more, or 99 parts by weight or more, and may be included in an amount of 100 parts by weight or less, less than 100 parts by weight, 99 parts by weight or less, 97 parts by weight or less, or 95 parts by weight or less.

[0162] According to one embodiment of the present invention, the silicon-based active material may be included in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the total negative electrode active material. For example, it may be included in an amount of 0.1 parts by weight or more, 1 part by weight or more, 5 parts by weight or more, or 6 parts by weight or more, and may be included in an amount of 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 9 parts by weight or less. When the silicon-based active material is included within the above range, a secondary battery having high energy density and excellent rapid charging performance can be provided.

[0163] According to one embodiment of the present invention, the cathode composition may include a cathode conductive material and a cathode binder together with the cathode active material described above.

[0164] In one embodiment of the present invention, the conductive material may include one or more selected from the group consisting of point-type conductive materials, planar-type conductive materials, and linear-type conductive materials.

[0165] In one embodiment of the present invention, the point-shaped conductive material can be used to improve conductivity of the cathode and refers to a spherical or point-shaped conductive material that has conductivity without causing chemical changes. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of achieving high conductivity and excellent dispersibility.

[0166] In one embodiment of the present invention, the point-shaped conductive material has a BET specific surface area of ​​40 m² 2 / g or more 70m 2 It may be less than / g, and 45m 2 / g or more 65m 2 / g or less, or 50m 2 / g or more 60m 2 It may be less than / g.

[0167] In one embodiment of the present invention, the conductive material may include a planar conductive material.

[0168] The above-mentioned planar conductive material can be described as a plate-shaped conductive material or a bulk-shaped conductive material, as it can improve conductivity by increasing surface contact between silicon particles within the cathode and simultaneously suppress the interruption of conductive pathways due to volume expansion.

[0169] In one embodiment of the present invention, the planar conductive material may comprise at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0170] In one embodiment of the present invention, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, dispersion is easy without causing an excessive increase in the viscosity of the cathode slurry due to the sufficient particle size. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0171] In one embodiment of the present invention, the planar conductive material may be a high specific surface area planar conductive material having a high BET specific surface area; or a low specific surface area planar conductive material.

[0172] In one embodiment of the present invention, the planar conductive material may be used without limitation as a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area; however, since the planar conductive material according to the present invention may be affected to some extent by dispersion in electrode performance, it may be particularly preferable to use a planar conductive material with a low specific surface area that does not cause problems with dispersion.

[0173] In one embodiment of the present invention, the planar conductive material has a BET specific surface area of ​​5 m² 2 It can be more than / g.

[0174] In another embodiment, the planar conductive material has a BET specific surface area of ​​5m² 2 / g or more than 500m 2 It may be less than / g, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0175] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and has a BET specific surface area of ​​50 m² 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 It can satisfy a range of / g or less.

[0176] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area is 5m² 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 It can satisfy a range of / g or less.

[0177] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may comprise a plurality of carbon nanotube units. Specifically, "bundle type" here refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged parallel or intertwined with the axes along the longitudinal direction of the carbon nanotube units having substantially the same orientation, unless otherwise noted. The carbon nanotube units have a graphite sheet having a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonded structure. At this time, depending on the angle and structure in which the graphite plane is rolled, it may exhibit conductive or semiconductor characteristics. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during cathode manufacturing and smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0178] In one embodiment of the present invention, the linear conductive material may include SWCNT; or MWCNT.

[0179] The content of the cathode conductive material in the above cathode active material layer may be 0.01 to 10 parts by weight, preferably 0.03 to 8 parts by weight, relative to 100 parts by weight of the cathode active material layer.

[0180] The cathode conductive material according to the present invention has a completely separate composition from the anode conductive material applied to the anode. That is, the cathode conductive material according to the present invention serves to hold the contact points between silicon-based active materials, which undergo significant volume expansion of the electrodes due to charging and discharging, whereas the anode conductive material serves as a buffer during rolling and provides partial conductivity; thus, their composition and roles are completely different from those of the cathode conductive material of the present invention.

[0181] Furthermore, the cathode conductive material according to the present invention is applied to a silicon-based active material and has a completely different composition from a conductive material applied to a cathode composition containing only a graphite-based active material. That is, a conductive material used in an electrode having a graphite-based active material simply has particles smaller than the active material, thereby providing characteristics that improve output characteristics and impart partial conductivity; thus, its composition and role are completely different from a cathode conductive material applied together with a silicon-based active material as in the present invention.

[0182] In one embodiment of the present invention, the cathode binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, polyacrylamide (PAM), and materials in which hydrogens thereof are substituted with Li, Na, or Ca, and may also comprise various copolymers thereof.

[0183] A cathode binder according to one embodiment of the present invention serves to hold the active material and the conductive material to prevent distortion or structural deformation of the cathode structure, and any general binder that satisfies the above role can be applied.

[0184] In one embodiment of the present invention, the cathode composition is provided in which the cathode binder comprises 1 part by weight or more and 10 parts by weight or less of the cathode binder based on 100 parts by weight of the cathode active material layer.

[0185] In the case of the negative electrode composition according to the present invention, a silicon-based active material or a modified version thereof is used to maximize capacity characteristics, and compared to a secondary battery using only a conventional carbon-based active material, the volume expansion during charging and discharging is significantly larger. Accordingly, by including the negative electrode binder in the above content portion, it has the characteristic of being able to efficiently control the volume expansion of the silicon-based active material with high rigidity during charging and discharging.

[0186]

[0187] cathode

[0188] According to one embodiment of the present invention, a cathode is provided comprising: a cathode current collector; and a cathode active material layer provided on one or both sides of the cathode current collector, wherein the cathode active material layer comprises a cathode composition according to one embodiment of the present invention.

[0189] FIG. 1 is a diagram showing a stacked structure of a cathode according to one embodiment of the present invention. Specifically, a cathode (100) including a cathode active material layer (20) on one surface of a cathode current collector (10) can be seen, and FIG. 2 shows that the cathode active material layer is formed on one surface, but can be included on both surfaces of the cathode current collector.

[0190] In one embodiment of the present invention, the cathode may be formed by applying and drying a cathode slurry containing the cathode composition on one or both sides of a cathode current collector.

[0191] At this time, the cathode slurry may include the aforementioned cathode composition; and a slurry solvent.

[0192] In one embodiment of the present invention, the solid content of the cathode slurry may satisfy a range of 5% or more and 60% or less. In another embodiment, the solid content of the cathode slurry may satisfy a range of 5% or more and 60% or less, preferably 7% or more and 50% or less, and more preferably 10% or more and 50% or less.

[0193] The solid content of the above cathode slurry may refer to the content of the cathode composition included in the above cathode slurry, and may refer to the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0194] When the solid content of the above cathode slurry satisfies the above range, the viscosity is suitable when forming the cathode active material layer, thereby minimizing particle aggregation of the cathode composition and enabling the cathode active material layer to be formed efficiently.

[0195] In one embodiment of the present invention, the slurry solvent may be used without limitation as long as it can dissolve the cathode composition, and specifically, water or NMP may be used.

[0196] In one embodiment of the present invention, the negative current collector has a thickness of 1 μm to 100 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0197] In one embodiment of the present invention, a cathode is provided in which the thickness of the cathode current collector is 1 μm to 100 μm or less, and the thickness of the cathode active material layer is 5 μm to 500 μm.

[0198] However, the thickness of the above-mentioned cathode current collector and cathode active material layer may vary depending on the type and application of the cathode used and is not limited thereto.

[0199] In one embodiment of the present invention, the porosity of the negative electrode active material layer is not particularly limited, but may satisfy a range of 10% or more and 60% or less.

[0200] In another embodiment, the porosity of the negative electrode active material layer may satisfy a range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0201] The above porosity varies according to the composition and content of the cathode active material, conductive material, and binder included in the cathode active material layer, and in particular, satisfies the above range by including the cathode active material and conductive material according to the present invention in a specific composition and content, thereby characterized in that the electrical conductivity and resistance of the electrode have an appropriate range.

[0202]

[0203] secondary battery

[0204] In one embodiment of the present invention, a secondary battery comprising a positive electrode; and a negative electrode according to one embodiment of the present invention is provided.

[0205] The above secondary battery further comprises a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0206] FIG. 2 is a diagram showing a stacked structure of a secondary battery according to one embodiment of the present invention. Specifically, a negative electrode (100) including a negative active material layer (20) on one surface of a negative electrode current collector (10) can be seen, and a positive electrode (200) including a positive active material layer (40) on one surface of a positive electrode current collector (50) can be seen, and the negative electrode (100) and the positive electrode (200) are formed in a stacked structure with a separator (30) in between.

[0207] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof is omitted.

[0208] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material.

[0209] In the above-mentioned positive electrode, the positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0210] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. Specifically, the above-mentioned positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3 Examples include lithium manganese composite oxides represented by O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, satisfying 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); and LiMn2O4 in which a portion of the Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The anode may also be Li-metal.

[0211] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0212] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. Specific examples 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, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0213] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0214] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0215] Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0216] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0217] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0218] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0219] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well in the non-aqueous electrolyte; for example, as the anion of the lithium salt, 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 types selected from the group consisting of can be used.

[0220] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0221]

[0222] Battery modules and battery packs

[0223] One embodiment of the present invention provides a battery module including a secondary battery according to one embodiment of the present invention.

[0224] One embodiment of the present invention provides a battery pack including a secondary battery according to one embodiment of the present invention.

[0225] One embodiment of the present invention provides a battery pack including a battery module according to one embodiment of the present invention.

[0226] One embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the secondary battery or the battery module. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0227] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0228]

[0229] <Preparation Example>

[0230] Example 1

[0231] 1) Preparation of silicon-based active materials

[0232] - Preparation of the first silicon carbon composite

[0233] Powder derived from coconut shells was used as an activated carbon precursor. The coconut shells were placed in an electric furnace and carbonized through heat treatment at 900°C under an inert atmosphere, after which the carbonized porous carbon raw material was ground and classified. Subsequently, porous carbon was obtained through physical activation by reacting at 800°C under a steam atmosphere.

[0234] The above porous carbon was classified to produce an average particle size D50 of 8.2 μm. At this time, the pore volume of the obtained porous carbon was 0.80 g / cm³. 3 Up to 1.00 g / cm² 3 was, and the average pore volume was 0.87 g / cm³. 3It was found that the fraction of micropores with an average pore diameter (D50) of less than 2 nm was 87%.

[0235] Subsequently, a silicon carbon composite was formed by flowing a mixed gas with a ratio of SiH4 / N2=95 / 5 at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 600℃ onto the porous carbon formed through the washing and drying steps of the porous carbon.

[0236] Subsequently, the silicon carbon composite was placed in an electric furnace, and acetylene gas was flowed at 650°C to include a carbon layer on the outermost surface, thereby producing a first silicon carbon composite. The degree of sphericity of the produced first silicon carbon composite is 0.77, and the average particle size (D50) is 8.6 μm.

[0237]

[0238] - Manufacture of the second silicon carbon composite

[0239] Phenol and lignin phenol-based resin are added in a 1:1 ratio to a solvent in which phenol and aldehyde are mixed in a 1:1 ratio. Hydrochloric acid is added to the solution, and after reacting at a temperature of 80°C for about 2 hours, the mixture is dried at a temperature of 120°C for 12 hours to obtain a spherical porous carbon raw material.

[0240] The porous carbon raw material obtained above was carbonized by heat treatment at 900°C under an inert gas atmosphere, and then the carbonized porous carbon raw material was ground and classified. Subsequently, porous carbon was obtained through physical activation by reacting at 800°C under a steam atmosphere.

[0241] The above porous carbon was classified to produce an average particle size D50 of 1.7 μm. At this time, the pore volume of the obtained porous carbon was 0.80 g / cm³. 3 Up to 1.00 g / cm² 3 was, and the average pore volume was 0.89 g / cm³3 It was found that the fraction of micropores with an average pore diameter (D50) of less than 2 nm was 98%.

[0242] Subsequently, a silicon carbon composite was formed by flowing a mixed gas with a ratio of SiH4 / N2=95 / 5 at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 600℃ onto the porous carbon formed through the washing and drying steps of the porous carbon.

[0243] Subsequently, the silicon carbon composite was placed in an electric furnace, and acetylene gas was flowed at 650°C to include a carbon layer on the outermost surface, thereby producing a second silicon carbon composite. The degree of sphericity of the produced second silicon carbon composite is 0.91, and the average particle size (D50) is 2.0 μm.

[0244] A silicon-based active material was prepared by mixing the first silicon carbon composite and the second silicon carbon composite in a weight ratio of 95:5.

[0245] Figure 3(a) is an SEM image of the silicon-based active material of Example 1. Referring to Figure 3(a), it can be confirmed that two types of silicon-carbon composites having different degrees of sphericity are mixed.

[0246] 2) Preparation of the cathode

[0247] As a negative electrode active material, the silicon-based active material prepared in 1) above and the carbon-based active material (synthetic graphite (average particle size (D50): 21㎛): natural graphite (average particle size (D50): 9㎛) = 7:3 weight ratio) were mixed in a ratio of 5:95. A negative electrode composition was prepared comprising 95.5 parts by weight of the negative electrode active material, 2.5 parts by weight of SBR as a negative electrode binder, 1.15 parts by weight of CMC as a thickener, and 0.85 parts by weight of SWCNT as a conductive material, for every 100 parts by weight of the negative electrode composition.

[0248] A cathode slurry was prepared by adding the above cathode composition to distilled water as a solvent (solid content 50 wt%). Specifically, the cathode binder, the above thickener, and the conductive material were dispersed using a homo mixer at 2,500 rpm for 30 minutes, and then the cathode active material was added and dispersed at 2,500 rpm for 30 minutes to prepare the cathode slurry.

[0249] The above SWCNT has a BET specific surface area of ​​1,000 to 1,500 m² 2 A solution satisfying / g and having an aspect ratio of 10,000 or higher was used, and a solution dispersed in CMC (Carboxymethyl Cellulose) was used.

[0250] 189 mg / 25 cm of the above cathode slurry is applied to both sides of a copper current collector (thickness 15 μm) as a cathode current collector. 2 A cathode was manufactured by forming a cathode active material layer by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours (cathode thickness 64 μm).

[0251] Figure 3(b) is an SEM image of the cathode of Example 1. Referring to Figure 3(b), it can be confirmed that two types of silicon carbon composites having different degrees of sphericity are mixed.

[0252] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.9, and the Si content / C content (B) of the second silicon carbon composite was measured to be 3.4.

[0253] 3) Manufacturing of secondary batteries

[0254] LiNi as a positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15㎛), carbon black as a conductive material (product name: Super C65, manufacturer: Timcal), and polyvinylidene fluoride (PVdF) as a binder were prepared in a weight ratio of 97:1.5:1.5, and an anode slurry was prepared by adding them to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the anode slurry (solid content concentration 78 wt%).

[0255] 537 mg / 25 cm of the anode slurry is applied to both sides of an aluminum current collector (thickness: 12 μm) as an anode current collector. 2 An anode was manufactured by forming an anode active material layer by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours (anode thickness: 75㎛).

[0256] A lithium secondary battery was manufactured by interposing a polyethylene separator between the anode and the cathode and injecting an electrolyte.

[0257] The above electrolyte was used by adding vinylene carbonate (VC) at 3% by weight based on the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0258]

[0259] Example 2

[0260] In the above 1), the silicon-based active material was prepared by the same method as in Example 1, except that the first silicon carbon composite and the second silicon carbon composite were prepared as follows and mixed in a weight ratio of 99.99:0.01.

[0261]

[0262] - Preparation of the first silicon carbon composite

[0263] It was prepared in the same manner as Example 1, except that porous carbon was obtained through physical activation at 700°C in a carbon dioxide atmosphere.

[0264] The degree of sphericity of the first silicon carbon composite manufactured is 0.79, and the average particle size (D50) is 8.8 μm.

[0265]

[0266] - Manufacture of the second silicon carbon composite

[0267] It was prepared in the same manner as Example 1, except that porous carbon was obtained through physical activation at 700°C in a carbon dioxide atmosphere.

[0268] The degree of sphericity of the manufactured second silicon carbon composite is 0.93, and the average particle size (D50) is 1.8 μm.

[0269]

[0270] Figure 5 is an SEM image of the silicon-based active material of Example 2. Referring to Figure 5, it can be confirmed that two types of silicon-carbon composites having different degrees of sphericity are mixed.

[0271] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.8, and the Si content / C content (B) of the second silicon carbon composite was measured to be 2.3.

[0272]

[0273] Example 3

[0274] In the above 1), the silicon-based active material was prepared by the same method as in Example 1, except that the first silicon carbon composite and the second silicon carbon composite were prepared as follows and mixed in a weight ratio of 75:25.

[0275]

[0276] - Preparation of the first silicon carbon composite

[0277] The porous carbon raw material was carbonized by heat treatment at 1050°C under an inert atmosphere, then ground and classified, and finally obtained by physical activation at 650°C in a steam atmosphere, in the same manner as in Example 1.

[0278] The degree of sphericity of the first silicon carbon composite manufactured is 0.80, and the average particle size (D50) is 8.4 μm.

[0279]

[0280] - Manufacture of the second silicon carbon composite

[0281] The porous carbon raw material was carbonized by heat treatment at 1050°C under an inert atmosphere, then ground and classified, and finally obtained by physical activation at 650°C in a steam atmosphere, in the same manner as in Example 1.

[0282] The degree of sphericity of the manufactured second silicon carbon composite is 0.93, and the average particle size (D50) is 1.8 μm.

[0283]

[0284] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.7, and the Si content / C content (B) of the second silicon carbon composite was measured to be 1.1.

[0285]

[0286] Example 4

[0287] In the above 1), the first silicon carbon composite and the second silicon carbon composite were prepared as follows, and a silicon-based active material was prepared by mixing them in a weight ratio of 96:4, except that the silicon-based active material was prepared in the same manner as in Example 1.

[0288]

[0289] - Preparation of the first silicon carbon composite

[0290] By classifying porous carbon, D 50It was prepared in the same manner as Example 1, except that it was prepared to 10.2㎛.

[0291] The degree of sphericity of the first silicon carbon composite manufactured is 0.80, and the average particle size (D50) is 10.6 μm.

[0292]

[0293] - Manufacture of the second silicon carbon composite

[0294] The porous carbon was prepared in the same manner as in Example 1, except that the carbonized porous carbon raw material was carbonized by heat treatment at 950°C under an inert atmosphere, then ground and classified, and then chemically activated in an alkaline KOH atmosphere for 6.5 hours to obtain porous carbon.

[0295] The degree of sphericity of the manufactured second silicon carbon composite is 0.90, and the average particle size (D50) is 1.7 μm.

[0296]

[0297] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.9, and the Si content / C content (B) of the second silicon carbon composite was measured to be 1.2.

[0298]

[0299] Comparative Example 1

[0300] In the above 1), a first silicon carbon composite was prepared as follows as a silicon-based active material, and was prepared in the same manner as Example 1, except that only the first silicon carbon composite was used.

[0301]

[0302] - Preparation of the first silicon carbon composite

[0303] Powder derived from coconut shells was used as an activated carbon precursor. The coconut shells were placed in an electric furnace and carbonized through heat treatment at 1050°C under an inert atmosphere, after which the carbonized porous carbon raw material was ground and classified. Subsequently, porous carbon was obtained through physical activation by reacting at 650°C under a steam atmosphere.

[0304] At this time, the pore volume of the obtained porous carbon is 0.80 g / cm³ 3 Up to 1.00 g / cm² 3 was, and the average pore volume was 0.87 g / cm³ 3 It was found that the fraction of micropores with an average pore diameter D50 of less than 2 nm was 87%.

[0305] Subsequently, a silicon carbon composite was formed by passing a mixture of SiH4 / N2 in a ratio of 95 / 5 to the porous carbon formed through the washing and drying steps of the porous carbon at a flow rate of 75 ml / min under conditions of 3 torr pressure and 600℃ for 2.5 hours.

[0306] Subsequently, the silicon carbon composite was placed in an electric furnace, and acetylene gas was flowed at 600°C to include a carbon layer on the outermost surface, thereby producing a first silicon carbon composite.

[0307] The degree of sphericity of the first silicon carbon composite manufactured is 0.80, and the average particle size (D50) is 9.3 μm.

[0308]

[0309] Figure 4(a) is an SEM image of the silicon-based active material of Comparative Example 1. Referring to Figure 4(a), an amorphous silicon-carbon composite with a sphericity of 0.8 or less can be observed.

[0310] Figure 4(b) is an SEM cross-sectional image of the cathode of Comparative Example 1. Referring to Figure 4(b), an amorphous silicon-carbon composite with a sphericity of 0.8 or less can be observed.

[0311] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.7.

[0312]

[0313] Comparative Example 2

[0314] In the above 1), the second silicon carbon composite was prepared in the following manner, and was prepared in the same manner as Example 1, except that only the second silicon carbon composite was applied as the silicon-based active material.

[0315]

[0316] - Manufacture of the second silicon carbon composite

[0317] Phenol and lignin phenol-based resin are added in a 1:1 ratio to a solvent in which phenol and aldehyde are mixed in a 1:1 ratio. Hydrochloric acid is added to the solution, and after reacting at a temperature of 80°C for about 6 hours, the mixture is dried at a temperature of 120°C for 12 hours to obtain a spherical porous carbon raw material.

[0318] The porous carbon raw material obtained above was carbonized by heat treatment at 900°C under an inert gas atmosphere, and then the carbonized porous carbon raw material was ground and classified. Subsequently, porous carbon was obtained through physical activation by reacting at 800°C under a steam atmosphere.

[0319] The above porous carbon was classified to produce an average particle size D50 of 7.4 μm. At this time, the pore volume of the obtained porous carbon was 0.80 g / cm³. 3 Up to 1.00 g / cm² 3 was, and the average pore volume was 0.89 g / cm³ 3It was found that the fraction of micropores with an average pore diameter (D50) of less than 2 nm was 91%.

[0320] Subsequently, a silicon carbon composite was formed by flowing a mixed gas with a ratio of SiH4 / N2=95 / 5 at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 600℃ onto the porous carbon formed through the washing and drying steps of the porous carbon.

[0321] Subsequently, the silicon carbon composite was placed in an electric furnace, and acetylene gas was flowed at 650°C to include a carbon layer on the outermost surface, thereby producing a second silicon carbon composite. The degree of sphericity of the produced second silicon carbon composite is 0.91, and the average particle size (D50) is 7.8 μm.

[0322] Figure 6 is an SEM image of the silicon-based active material of Comparative Example 2. Referring to Figure 6, it can be seen that it contains a spherical silicon-carbon composite with a sphericity of 0.8 or higher.

[0323] In addition, the Si content / C content (B) of the second silicon carbon composite was measured to be 1.9.

[0324]

[0325] Comparative Example 3

[0326] In the above 1), the silicon-based active material was prepared by the same method as in Example 1, except that the first silicon carbon composite and the second silicon carbon composite were prepared as follows and mixed in a weight ratio of 20:80.

[0327]

[0328] - Preparation of the first silicon carbon composite

[0329] It was prepared in the same manner as Comparative Example 1, except that porous carbon was obtained through physical activation in a carbon dioxide atmosphere at 850°C.

[0330] The degree of sphericity of the first silicon carbon composite manufactured is 0.73, and the average particle size (D50) is 7.7 μm.

[0331]

[0332] - Manufacture of the second silicon carbon composite

[0333] It was prepared in the same manner as Comparative Example 1, except that the porous carbon raw material was carbonized by heat treatment at 950°C under an inert atmosphere, then ground and classified, and then chemically activated for 8 hours in an alkaline KOH atmosphere to obtain porous carbon.

[0334] The degree of sphericity of the manufactured second silicon carbon composite is 0.92, and the average particle size (D50) is 2.3 μm.

[0335]

[0336] Figure 7 is an SEM image of the silicon-based active material of Comparative Example 3. Referring to Figure 7, it can be seen that the silicon-based active material contains an excess amount of spherical silicon-carbon composites with a sphericity of 0.8 or higher.

[0337] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 1.9, and the Si content / C content (B) of the second silicon carbon composite was measured to be 0.8.

[0338]

[0339] Comparative Example 4

[0340] In the above 1), the first and second silicon carbon composites were prepared in the same manner as in Example 1, except that they were prepared in the following manner.

[0341]

[0342] - Preparation of the first silicon carbon composite

[0343] It was prepared in the same manner as Comparative Example 1, except that the porous carbon raw material was carbonized by heat treatment at 1000°C under an inert atmosphere, then ground and classified, and then chemically activated in an alkaline KOH atmosphere for 4 hours to obtain porous carbon.

[0344] The degree of sphericity of the first silicon carbon composite manufactured is 0.71, and the average particle size (D50) is 8.5 μm.

[0345] In addition, the Si content / C content (A) of the first silicon carbon composite was measured to be 0.4.

[0346]

[0347] - Manufacture of the second silicon carbon composite

[0348] Coconut shells were used as an activated carbon precursor. Powder derived from the coconut shells was placed in an electric furnace and carbonized through heat treatment at 900°C under an inert atmosphere. Subsequently, the carbonized porous carbon raw material was crushed and classified. Afterward, porous carbon was obtained through physical activation by reacting at 700°C under a steam atmosphere.

[0349] The above porous carbon was classified to produce an average particle size D50 of 1.7 μm. At this time, the pore volume of the obtained porous carbon was 0.80 g / cm³. 3 Up to 1.00 g / cm² 3 was, and the average pore volume was 0.85 g / cm³ 3 It was found that the fraction of micropores with an average pore diameter (D50) of less than 2 nm was 87%.

[0350] Subsequently, a silicon carbon composite was formed by flowing a mixed gas with a ratio of SiH4 / N2=95 / 5 at a flow rate of 75 ml / min for 2 hours under conditions of 3 torr pressure and 600℃ onto the porous carbon formed through the washing and drying steps of the porous carbon.

[0351] Subsequently, the silicon carbon composite was placed in an electric furnace, and acetylene gas was flowed at 650°C to include a carbon layer on the outermost surface, thereby producing a second silicon carbon composite. The degree of sphericity of the produced second silicon carbon composite is 0.77, and the average particle size (D50) is 2.0 μm.

[0352] Figure 8 is an SEM cross-sectional image of the silicon-based active material of Comparative Example 4. Referring to Figure 8, it is possible to identify an amorphous silicon carbon composite having a silicon carbon composite with a sphericity of 0.8 or less, which contains silicon carbon composites with different degrees of sphericity.

[0353] In addition, the Si content / C content (B) of the second silicon carbon composite was measured to be 4.0.

[0354]

[0355] The Si / C ratio, sphericity, and weight parts of the silicon carbon composites used in the examples and comparative examples of this experiment are listed in Table 1 below.

[0356] First Silicon Carbon Composite Second Silicon Carbon Composite Si Content / C Content (A) Parts by weight based on 100 parts by weight of spheroidized silicon-based active material Si Content / C Content (B) Parts by weight based on 100 parts by weight of spheroidized silicon-based active material A / B Example 10.9 0.7 79 53.4 0.9 15 0.26 Example 20.8 0.7 99 9.9 2.3 0.9 30.0 10.35 Example 30.7 0.8 07 51.1 0.9 32 50.62 Example 40.9 0.8 09 61.2 0.9 40.75 Comparative Example 10.7 0.8 100 ----Comparative Example 2---1.9 0.9 1100 -Comparative Example 31.9 0.7 32 00.8 0.9 28 0 2.27 Comparative Example 40.40.71954.00.7750.098

[0357]

[0358] <Experimental Example>

[0359] Experimental Example 1: Evaluation of Initial Capacity and Initial Efficiency

[0360] The coin half-cell capacity / efficiency of the negative electrodes prepared in the above examples and comparative examples was evaluated. Specifically, the capacity / efficiency of the first cycle of the secondary battery containing the negative electrode was measured using an electrochemical charge / discharger. The test was conducted using lithium metal as the counter electrode of the negative electrode, and the charging was performed under CC / CV (5mV / 0.005C current cut-off) and the discharging was performed under CC conditions with a 1.5V cut-off condition.

[0361] Discharge capacity (mAh / g) = {(1st cycle discharge capacity (mAh)) / (weight of negative electrode active material (g))}

[0362] Initial efficiency (%) = {(Discharge capacity in 1st cycle) / (Charge capacity in 1st cycle)} * 100%

[0363] Experimental Example 2: Evaluation of Dose Retention Rate

[0364] For the secondary batteries prepared in the above examples and comparative examples, a lifespan evaluation was conducted using an electrochemical charge / discharger, and the capacity retention rate was evaluated. The secondary batteries were subjected to in-situ cycle tests at 4.2-2.5V, 1C charge, and 1C discharge. The test was terminated after 200 cycles of discharge, and the capacity retention rate was measured by performing 0.33C / 0.33C charge / discharge (4.2-2.5V) every 50 cycles and is shown in Table 1.

[0365] Capacity Retention Rate (%) = {(Discharge Capacity at the Nth Cycle) / (Discharge Capacity at the 1st Cycle)} * 100 %

[0366] Experimental Example 3: Rate of change in slurry viscosity (%)

[0367] In order to measure the rate of change in slurry viscosity, the following experiment was performed on the silicon-based active materials prepared in the above examples and comparative examples.

[0368] A slurry was prepared by mixing graphite, the above silicon-based active material, carbon black, CMC, and PAA in a weight ratio of 77:20:1:1:1. The shear viscosity of the prepared slurry was measured at a shear rate of 1 Hz, and the amount of change over time was measured and compared.

[0369] Change in shear viscosity (%) = {(Shear viscosity of slurry after 2 days) - (Shear viscosity of slurry immediately after mixing)} / (Shear viscosity of slurry immediately after mixing) * 100 %

[0370] Experimental Example 4: Pouch Volume Change Rate (%)

[0371] For the silicon-based active materials prepared in the examples and comparative examples, the water-based slurry processability (gas generation) characteristics were evaluated as follows.

[0372] A slurry was prepared by mixing graphite, the above silicon-based active material, carbon black, CMC, and PAA in a weight ratio of 77:20:1:1:1. The mixture was placed in a pouch approximately 10 cm * 15 cm in size, 20 g of the prepared slurry was placed in the pouch, and the pouch was sealed. The pouch was then stored at 40°C for 2 days (48 hours), and the volume was measured to compare the rate of change.

[0373] Pouch Volume Change Rate (%) = {(Pouch Volume After 2 Days) - (Pouch Volume Immediately After Mixing)} / (Pouch Volume Immediately After Mixing) * 100%

[0374] Discharge Capacity (mAh / g) Initial Efficiency (%) Capacity Retention Rate (%) Slurry Viscosity Change Rate (%, after 2 days) Pouch Volume Change Rate (%, @40℃, after 2 days) Example 1 51 192.19 1.5 -2.11.0 Example 2 51 292.29 1.0 -4.73.5 Example 3 50 89 1.79 0.3 -1.00.5 Example 4 50 892.09 0.5 -1.50.0 Comparative Example 1 51 09 1.68 7.4 -35.520.5 Comparative Example 2 48 59 0.18 4.9 -0.350.0 Comparative Example 3 49 29 0.78 6.6 -1.00.5 Comparative Example 4 50 79 1.58 8.0 -38.024.0

[0375] Referring to Tables 1 and 2 and Figures 3 to 9, it is confirmed that Examples 1 to 4 according to one embodiment of the present invention exhibit superior performance in terms of discharge capacity, initial efficiency, capacity retention rate, slurry viscosity change rate, and pouch volume change rate compared to Comparative Examples 1 to 4.

[0376] Comparative Example 1 (Fig. 4) and Comparative Example 4 (Fig. 8) include only an amorphous first silicon carbon composite with a sphericity of 0.8 or less as a silicon-based active material. In this case, the slurry viscosity change rate and pouch volume change rate were found to be inferior, which is understood to be because the content of the second silicon carbon composite was below the lower limit, which reduced the roll resistance of the cathode and consequently lowered the water-based processability.

[0377] In particular, Comparative Example 4 used a mixture of two types of silicon carbon composites with similar sphericity as a silicon-based active material, but did not include a silicon carbon composite with a sphericity greater than 0.8, and the ratio of Si content (wt%) to C content (wt%) of the two types of silicon carbon composites (A / B) was too small, resulting in inferior swelling characteristics and aqueous processability.

[0378] Comparative Example 2 (Fig. 6) contains only a spherical second silicon carbon composite with a sphericity greater than 0.8 as a silicon-based active material, and Comparative Example 3 (Fig. 7) contains an excessive amount of a spherical second silicon carbon composite with a sphericity greater than 0.8, and is a case where the ratio of Si content (wt%) to C content (wt%) of the two types of silicon carbon composites (A / B) is too large. In this case, inferior results were observed in discharge capacity, initial efficiency, and capacity retention rate. This is analyzed to be because the adhesion of the negative electrode active material was reduced due to the excessive content of the second silicon carbon composite with high sphericity, causing active material detachment during the charge-discharge process.

[0379] Although the present invention has been described with reference to embodiments thereof, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above description.

Claims

1. Includes a first silicon carbon composite and a second silicon carbon composite, and The first silicon carbon composite comprises a first porous carbon and silicon provided on the first porous carbon, and The second silicon carbon composite comprises a second porous carbon and silicon provided on the second porous carbon, and The ratio (A) of the ratio of Si content (wt%) to C content (wt%) of the first silicon carbon composite and the ratio (B) of Si content (wt%) to C content (wt%) of the second silicon carbon composite is 0.1 to 0.9, and The degree of sphericity of the first silicon carbon composite is smaller than the degree of sphericity of the second silicon carbon composite, and The degree of sphericity of the second silicon carbon composite is greater than 0.8 and less than or equal to 1, and The above second silicon carbon composite comprises a silicon-based active material in an amount of 0.01 to 25 parts by weight based on 100 parts by weight of the silicon-based active material.

2. In Claim 1, A silicon-based active material in which the ratio (A) of Si content (wt%) to C content (wt%) of the first silicon carbon composite is 0.45 to 2.

3.

3. In Claim 1, A silicon-based active material in which the ratio (B) of Si content (wt%) to C content (wt%) of the second silicon carbon composite is 0.8 to 5.

7.

4. In Claim 1, A silicon-based active material having a degree of sphericity of 0.45 to 0.8 of the first silicon carbon composite.

5. A silicon-based active material in which the average particle size (D50) of the second silicon carbon composite is smaller than the average particle size (D50) of the first silicon carbon composite.

6. In Claim 1, A silicon-based active material having an average particle size (D50) of the first silicon carbon composite greater than 4㎛ and less than or equal to 10㎛.

7. In Claim 1, A silicon-based active material having an average particle size (D50) of the second silicon carbon composite of the above-mentioned second silicon carbon composite of 1 μm to 4 μm.

8. In Claim 1, The first porous carbon and the second porous carbon are different from each other and each independently 0.75 cm 3 / g to 1 cm 3 Silicon-based active material having a total pore volume of / g.

9. In Claim 8, A silicon-based active material wherein the first porous carbon and the second porous carbon are different from each other and each independently comprises at least 70% of micropores having an average diameter (D50) of less than 2 nm.

10. In Claim 1, The silicon in the first silicon carbon composite is a silicon-based active material included in an amount of 50 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the first silicon carbon composite.

11. In Claim 1, The silicon in the second silicon carbon composite is a silicon-based active material included in an amount of 50 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the second silicon carbon composite.

12. A cathode composition comprising a silicon-based active material according to any one of claims 1 to 11.

13. In Claim 12, A cathode composition further comprising a carbon-based active material.

14. In Claim 13, The above-mentioned carbon-based active material comprises at least one selected from the group consisting of natural graphite and artificial graphite, forming a cathode composition.

15. In Claim 13, The above carbon-based active material is included in an amount of 70 parts by weight or more based on 100 parts by weight of the negative electrode active material, forming a negative electrode composition.

16. A negative current collector; and a negative active material layer provided on one or both sides of the negative current collector, comprising The cathode, wherein the cathode active material layer comprises any one of the cathode compositions of claims 12 to 15.

17. A secondary battery comprising a positive electrode; and a negative electrode of claim 16.

18. A battery module comprising a secondary battery according to claim 17.

19. A battery pack comprising a secondary battery according to claim 17.

20. A battery pack comprising a battery module according to claim 18.

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