Negative electrode active material, method for producing a negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery containing the same, and lithium secondary battery containing the negative electrode

Abstract

This application relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0140485, filed with the Korean Intellectual Property Office on October 19, 2023, and all of its content is incorporated herein.

[0002] This application relates to a negative electrode active material, a method for manufacturing the same, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the field of power generation and energy storage using electrochemical reactions is one of the most actively studied areas.

[0004] Currently, secondary batteries are representative examples of electrochemical devices using such electrochemical energy, and their usage areas are increasingly expanding.

[0005] As technology development and demand related to mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. Also, research on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and as the negative electrode active material, silicon-based particles with a large discharge capacity can be used.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO2, which have more than 10 times the capacity of graphite-based materials, are being used as negative electrode active materials. x Active research is being conducted on methods to increase capacity by using silicon-based compounds such as those mentioned above. However, while silicon-based compounds are high-capacity materials, they have the problem that, compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems that arise when silicon-based compounds are used as negative electrode active materials, various methods have been discussed, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or methods to prevent the conduction path from being interrupted. However, in the case of the above methods, there is a limit to their application because they may actually degrade the performance of the battery, and there are still limitations to the commercialization of negative electrode battery manufacturing with a high content of silicon-based compounds.

[0009] Furthermore, research has revealed that in the case of Si negative electrode active materials, grain boundaries act as diffusion pathways for lithium, and therefore, wider grain boundaries, i.e., smaller grain size, are advantageous for the performance characteristics of secondary batteries.

[0010] However, when manufacturing negative electrode active materials by casting and grinding conventional MG-Si (metallurgical grade silicon), the high crystallinity of silicon results in a typical grain size of several hundred to several millimeters for MG-Si. This limits the reduction in grain size of the Si active material, and thus still limits the improvement of the performance characteristics of secondary batteries.

[0011] Therefore, even when using silicon-based active materials as negative electrode active materials to improve capacity performance, it is necessary to develop technologies that can form pathways for easy diffusion of lithium ions within the active material, so as to prevent the conduction pathway from being impaired due to the volume expansion of the silicon-based compound. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] Research into creating pathways for easy lithium ion diffusion revealed limitations in reducing grain size. Therefore, studies have confirmed that forming a layered silicon-based active material by alloying silicon with a metal element that reacts eutectically with silicon creates a boundary between the two phases within the active material, which acts as a lithium ion diffusion pathway, thereby improving cycle capacity maintenance.

[0014] Therefore, this application relates to a negative electrode active material that can solve the aforementioned problems, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode. [Means for solving the problem]

[0015] One embodiment of this specification provides a negative electrode active material comprising a layered silicon-based active material, wherein the layered silicon-based active material is represented by the following formula 1, and satisfies the following formulas 2 and 3.

[0016] [Formula 1] Si 100-x M x In the above formula 1, x has an atomic weight in the range of greater than 0 and less than 100. M comprises one or more elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au. [Formula 2] 10nm ≤ Y ≤ 1μm [Formula 3] 10 nm ≤ X ≤ 1 μm In equations 2 and 3, X is the size of the primary silicon crystal (primary Si) in the layered silicon-based active material. Y represents the interlamellar spacing in a layered silicon-based active material.

[0017] Another embodiment provides a method for producing a negative electrode active material, comprising the steps of: pulverizing a silicon precursor to form a silicon-based active material; mixing the silicon-based active material with one or more metal elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au; melting the silicon-based active material and the metal elements; and cooling the silicon-based active material and the metal elements.

[0018] Another embodiment provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder according to the present application.

[0019] Another embodiment provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises the negative electrode composition or a cured product thereof according to this application.

[0020] Finally, the present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator provided between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0021] In the case of a negative electrode active material according to one embodiment of the present invention, unlike conventional casting and grinding processing methods, a layered silicon-based active material layer is formed by alloying the MG-Si pulverized material with a metal element that undergoes a eutectic reaction, and the size of the primary silicon crystals and the interlamellar spacing of the layered silicon-based active material are adjusted.

[0022] In other words, a layered silicon-based active material satisfying the ranges of Equations 2 and 3 forms a phase boundary between two phases (primary Si crystal and alloy) within the silicon-based active material. This boundary acts together with grain boundaries as a diffusion pathway for lithium ions, thereby improving cycle capacity maintenance and initial capacity efficiency. [Brief explanation of the drawing]

[0023] [Figure 1] This is an enlarged view of a layered silicon-based active material according to one embodiment of this application. [Figure 2] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 3] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0024] Before describing the present invention, let us first define some terms.

[0025] In this specification, when a part "includes" a component, it means that it may include other components rather than excluding them, unless otherwise stated.

[0026] In this specification, "p~q" means the range "p or greater and q or less".

[0027] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution corresponding to the particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution corresponding to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution corresponding to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution corresponding to the particle size. On the other hand, the average 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 analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns corresponding to the particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0029] In one embodiment of this application, particle size may refer to the average diameter or representative diameter of individual particles making up the metal powder.

[0030] In this specification, when a polymer is said to contain a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this specification, when a polymer is said to contain a monomer, it is interpreted the same way as when a polymer contains a monomer as a monomer unit.

[0031] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0032] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0033] The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention may be realized in various different forms and is not limited to the following description.

[0034] One embodiment of this specification provides a negative electrode active material comprising a layered silicon-based active material, wherein the layered silicon-based active material is represented by the following formula 1, and satisfies the following formulas 2 and 3.

[0035] [Formula 1] Si 100-x M x In the above formula 1, x has an atomic weight in the range of greater than 0 and less than 100. M comprises one or more elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au. [Formula 2] 10nm ≤ Y ≤ 1μm [Formula 3] 10 nm ≤ X ≤ 1 μm In equations 2 and 3, X is the size of the primary silicon crystal (primary Si) in the layered silicon-based active material. Y represents the interlamellar spacing in a layered silicon-based active material.

[0036] In the case of a negative electrode active material according to one embodiment of the present invention, a layered silicon-based active material satisfying the ranges of formulas 2 and 3 forms a phase boundary between two phases (primary Si crystal and alloy) within the silicon-based active material. This boundary acts together with the grain boundaries as a diffusion pathway for lithium ions, thereby improving the cycle capacity retention rate and initial capacity efficiency.

[0037] Figure 1 is an enlarged view of a layered silicon-based active material according to one embodiment of the present application. Specifically, the primary silicon crystals can be seen, and the silicon-based active material having both primary silicon crystals and a layered structure can be seen. When a Si-rich molten metal solidifies, Si solidifies first in a spherical shape, which is the primary silicon crystal (primary Si). When the remaining molten metal falls below the eutectic temperature, the two phases of Si and M separate and solidify into a layered structure. At this time, Si can be represented as eutectic Si, and the remaining M can be represented as eutectic M. In Figure 1, M may also be Al.

[0038] In this case, eutectic silicon (Si) and primary silicon have no difference in composition; they can be distinguished by whether their shape is spherical or layered.

[0039] In one embodiment of this application, the negative electrode active material includes a layered silicon-based active material. That is, the negative electrode active material produced by the manufacturing method described later is not a general silicon-based active material, but includes a layered silicon-based active material, and may satisfy the conditions of formulas 2 and 3 described above.

[0040] In one embodiment of this application, the layered silicon-based active material may be represented by the following formula 1.

[0041] [Formula 1] Si 100-x M x In the above formula 1, x has an atomic weight in the range of greater than 0 and less than 100. M includes one or more elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au.

[0042] In the above formula 1, M represents a metallic element, and any metallic element that undergoes a eutectic reaction with silicon can be used without limitation.

[0043] In this application, the layered silicon-based active material is characterized in that it is in the form of an alloy of silicon and a metallic element, and a boundary is formed between the two phases.

[0044] In one embodiment of this application, x may satisfy the range of greater than 0 and less than 100 in atomic weight %, preferably 5 to 95, and more preferably 10 to 80.

[0045] The above-mentioned x satisfies the above range. If the above range is exceeded, the capacity of the silicon-based active material itself decreases, which can cause problems. If the above range is less than the above range, the content of the metal constituting the alloy is low, and it is not possible to have the desired layered shape, and the ranges of Equations 2 and 3 are not satisfied, which presents a problem in that it is difficult to secure the lithium ion pathway.

[0046] In one embodiment of this application, formula 2 may satisfy 10 nm ≤ Y ≤ 1 μm, preferably 10 nm ≤ Y ≤ 800 nm, more preferably 10 nm ≤ Y ≤ 400 nm, specifically 10 nm ≤ Y ≤ 200 nm.

[0047] In one embodiment of this application, formula 3 may satisfy 10 nm ≤ X ≤ 1 μm, preferably 10 nm ≤ X ≤ 800 nm, more preferably 10 nm ≤ X ≤ 500 nm, specifically 10 nm ≤ X ≤ 400 nm.

[0048] In this application, a negative electrode active material is provided in which the fraction of primary silicon in the layered silicon-based active material is 0% or more and less than 90%.

[0049] In another embodiment, the fraction of primary silicon in the layered silicon-based active material may be 0% or more and less than 90%, 2% or more and 60%, or 5% or more and 40%.

[0050] The fraction of primary silicon in the layered silicon-based active material may mean 0% or more and less than 90% based on 100 parts by weight of the layered silicon-based active material.

[0051] The fraction of primary silicon refers to particulate silicon that solidifies before the layered structure in a layered silicon-based active material. In other words, in the manufacturing method described later, the solidification order is that primary silicon solidifies first, followed by the solidification of the layered structure.

[0052] The fraction of the silicon primary crystal decreases as the alloy composition, based on atomic weight % x, approaches the eutectic composition, or as the cooling rate increases. When the cooling rate increases, the solidification of the primary crystal may not occur sufficiently, the temperature may fall below the eutectic temperature, and a eutectic reaction may occur. This can lead to the alloy composition becoming closer to the eutectic composition, and the solidification start temperature decreasing.

[0053] When the fraction of silicon primary crystals satisfies the aforementioned range, the fraction of layered structure increases, leading to an increase in lithium diffusion pathways and resulting in superior battery performance. In other words, when the proportion of primary crystals decreases, the microstructure becomes finer, and the number of interphase boundaries increases, resulting in more lithium ion diffusion pathways and easier diffusion.

[0054] The layered silicon-based active material according to this application satisfies the size and interlayer spacing of the silicon primary crystal as described above. In the case of conventional silicon-based active materials, there have been attempts to minimize the size of the crystal grains and secure a wide grain boundary.

[0055] However, minimizing the size of the crystal grains is difficult, and even if the crystal grain size is reduced, there is a problem that the lifetime characteristics further deteriorate due to an increase in side reactions. In the case of the negative electrode active material according to this application, the crystal grain size of the silicon-based active material itself is not adjusted, but rather a layered silicon-based active material is formed by alloying with a metal, and it is manufactured in such a way that it satisfies the ranges of Equations 2 and 3 during the manufacturing process.

[0056] By satisfying the ranges of Equations 2 and 3 as described above, the capacity characteristics of the silicon-based active material can be maximized, and a layered structure can be formed in the active material to secure lithium diffusion pathways, thereby improving initial capacity efficiency and cycle capacity maintenance rate.

[0057] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities are metals that are commonly contained in silicon-based active materials, and specifically, may be contained in an amount of 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0058] In the case of silicon-based active materials, the capacity is significantly higher compared to conventionally used graphite-based active materials, and attempts to apply them are increasing. However, because of their high volume expansion rate during the charge-discharge process, their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0059] Therefore, in the present invention, in order to improve capacity performance, only silicon-based active material is used as the negative electrode active material, and in order to resolve the aforementioned problems, the conventional problems are solved by adjusting the morphology of the silicon-based active material itself, rather than adjusting the composition of the conductive material and binder.

[0060] In this application, a negative electrode active material is provided in which the average particle size (D50) of the layered silicon-based active material is 1 μm or more and 10 μm or less.

[0061] In another embodiment, the average particle size (D50) of the layered silicon-based active material may be 1 μm or more and 10 μm or less, 2 μm or more and 9 μm or less, or 3 μm or more and 8 μm or less, and more specifically, 4 μm or more and 6 μm or less.

[0062] One embodiment of this application provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0063] In one embodiment of this application, a negative electrode composition is provided in which the negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0064] In another embodiment, the negative electrode active material may be 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, even more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0065] The negative electrode composition according to this application has the characteristic of not degrading the performance of the negative electrode and having excellent output characteristics in charging and discharging, even when a silicon-based active material with a remarkably high capacity is used within the aforementioned range, by using a negative electrode active material that satisfies a specific surface area size that can suppress the volume expansion rate during the charging and discharging process.

[0066] Traditionally, graphite-based compounds were used exclusively as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, in the case of silicon-based active materials, even if the properties of the silicon-based active material itself are adjusted as described above, a problem can still occur where the volume expands rapidly during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer.

[0067] Therefore, in one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, sheet conductive materials, and linear conductive materials.

[0068] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, means a dot-shaped or spherical conductive material that does not cause chemical changes and has conductivity. Specifically, the dot-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, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may contain carbon black in terms of achieving high conductivity and excellent dispersibility.

[0069] In one embodiment of the present application, the BET specific surface area of the dot-shaped conductive material may be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0070] In one embodiment of the present application, the dot-shaped conductive material may satisfy that the content (Volatile matter) of functional groups is 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.1% or less.

[0071] Particularly when the content of the functional groups of the dot-shaped conductive material satisfies the above range, functional groups exist on the surface of the dot-shaped conductive material, and when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, the present invention can lower the content of the functional groups of the dot-shaped conductive material by using a specific silicon-based active material, and thereby has an excellent effect of improving dispersibility.

[0072] In one embodiment of this application, a silicon-based active material is provided along with a point-type conductive material having a functional group content within the range described above, wherein the content of the functional group can be adjusted according to the degree to which the point-type conductive material is heat-treated.

[0073] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0074] In one embodiment of this application, the conductive material may include a sheet-like conductive material.

[0075] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and can also suppress the disruption of the conductive path due to volume expansion. The sheet-like conductive material can also be described as a plate-like conductive material or a bulk conductive material.

[0076] In one embodiment of this application, the sheet-like conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0077] In one embodiment of this application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When this range is met, the particle size is sufficient to prevent an excessive increase in the viscosity of the negative electrode slurry and facilitates dispersion. Therefore, the dispersion effect is excellent when dispersed using the same apparatus and time.

[0078] In one embodiment of this application, a negative electrode composition is provided in which the sheet-like conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0079] In one embodiment of this application, the sheet-like conductive material may be a high-specific-surface-area sheet-like conductive material with a high BET specific-surface-area; or a low-specific-surface-area sheet-like conductive material.

[0080] In one embodiment of this application, the sheet-like conductive material can be any sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area without limitation. However, since dispersion can affect electrode performance to some extent in the sheet-like conductive material according to this application, it is particularly preferable to use a sheet-like conductive material with a low specific surface area that does not cause dispersion problems.

[0081] In one embodiment of this application, the sheet-like conductive material has a BET specific surface area of ​​0.25 m². 2 It may be more than / g.

[0082] In another embodiment, the sheet-like conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0083] The sheet-like conductive material relating to this application may be a sheet-like conductive material with a high specific surface area, or a sheet-like conductive material with a low specific surface area.

[0084] In another embodiment, the sheet-like conductive material is a sheet-like conductive material with a high specific surface area, and has a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 Less than / g, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0085] In another embodiment, the sheet-like conductive material is a low specific surface area sheet-like conductive material, with a BET specific surface area of ​​1 m². 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 The range of / g or less may also be satisfied.

[0086] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a bundle-like or rope-like secondary shape in which multiple carbon nanotube units are arranged side by side or intertwined with substantially the same orientation along the length direction of the carbon nanotube units. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the graphite sheet can exhibit conductive or semiconductor properties depending on the angle and structure at which it is curled. Compared to entangled-type carbon nanotubes, the bundle-type carbon nanotubes can be dispersed more uniformly during anode manufacturing, smoothly forming a conductive network within the anode and improving the conductivity of the anode.

[0087] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0088] In another embodiment, the negative electrode conductive material may be 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0089] In one embodiment of this application, the negative electrode composition is provided, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

[0090] In one embodiment of this application, the negative electrode conductive material is provided as a negative electrode composition comprising 80 to 99.9 parts by weight of the sheet-like conductive material and 0.1 to 20 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0091] In another embodiment, the negative electrode conductive material may contain 80 to 99.9 parts by weight, preferably 85 to 99.9 parts by weight, and more preferably 95 to 98 parts by weight, of the sheet-like conductive material based on 100 parts by weight of the negative electrode conductive material.

[0092] In another embodiment, the negative electrode conductive material may contain 0.1 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 0.2 to 5 parts by weight, of the linear conductive material based on 100 parts by weight of the negative electrode conductive material.

[0093] In one embodiment of this application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, satisfying the aforementioned composition and proportions, thereby not significantly affecting the life characteristics of conventional lithium secondary batteries. In particular, when a sheet-like conductive material and a linear conductive material are included, the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate and reduced high-temperature gas generation.

[0094] In one embodiment of this application, the negative electrode conductive material may be a linear conductive material.

[0095] In particular, when linear conductive materials are used alone, the electrode tortuosity, which is a problem with silicon-based negative electrodes, can be simplified, thereby improving the electrode structure and reducing the resistance to lithium ion movement within the electrode.

[0096] In one embodiment of this application, when the negative electrode conductive material includes a linear conductive material alone, the negative electrode conductive material may be included in an amount of 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0097] The negative electrode conductive material described in this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. Specifically, the negative electrode conductive material described in this application plays the role of providing contact between silicon-based active materials, which undergo very large volume expansion during charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling and also imparts some conductivity. Thus, its structure and role are completely different from the negative electrode conductive material of the present invention.

[0098] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and thus have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0099] In one embodiment of this application, the sheet-like conductive material used as the negative electrode conductive material described above has a different structure and role from the carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0100] In contrast, sheet-like conductive materials used as negative electrode conductive materials are substances that have a sheet-like or plate-like shape and can be described as plate-like graphite. That is, they are substances included in the negative electrode active material layer to maintain conductive pathways, and do not play a role in the storage and release of lithium, but rather are substances that secure conductive pathways in a sheet-like form within the negative electrode active material layer.

[0101] In other words, in this application, when plate-shaped graphite is used as a conductive material, it means that it is processed into a sheet or plate shape and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0102] In contrast, in this application, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0103] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is point-like and has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate graphite, which is a sheet-like conductive material, is in sheet form and has a BET specific surface area of ​​5m². 2 It may be more than / g.

[0104] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0105] The negative electrode binder according to one embodiment of this application plays a role in holding the active material and conductive material to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any general binder that fulfills the above role can be applied, and specifically, an aqueous binder may be used, or more specifically, a PAM-based binder may be used.

[0106] In one embodiment of this application, the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may also be 5 parts by weight or more, or 10 parts by weight or more.

[0107] One embodiment of this application provides a method for producing a negative electrode active material, comprising the steps of: crushing a silicon precursor to form a silicon-based active material; mixing the silicon-based active material with one or more metal elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au; melting the silicon-based active material and the metal elements; and cooling the silicon-based active material and the metal elements.

[0108] As described above, instead of casting and crushing silicon itself, the silicon-based active material is mixed with metal elements that form an alloy, melted, and then a layered silicon-based active material is formed by a rapid cooling process.

[0109] In this application, the step of pulverizing the silicon-based active material and the metal element may be further included after the cooling step.

[0110] In this application, a method for producing a negative electrode active material is provided, wherein, after the step of cooling the silicon-based active material and a metal element, the silicon-based active material satisfies the following formulas 2 and 3.

[0111] [Formula 2] 10nm ≤ Y ≤ 1μm [Formula 3] 10 nm ≤ X ≤ 1 μm In equations 2 and 3, X is the size of the primary silicon crystal (primary Si) in the layered silicon-based active material. Y represents the interlamellar spacing in a layered silicon-based active material.

[0112] In this application, the invention provides a method for producing a negative electrode active material, wherein the cooling step includes melt spinning, suction casting, injection casting, or gas spraying.

[0113] Generally, melt spinning can refer to the process of spinning molten material onto a rotating copper wheel (Cu wheel) and rapidly cooling it. Suction casting refers to the process of casting by sucking molten material from below a mold using a vacuum, and injection casting refers to the process of casting by injecting molten material into a mold with high-pressure gas. Gas atomization is one of the processes for producing metal powder, in which high-pressure gas is injected into molten metal to produce powder, and can refer to a process of rapid cooling.

[0114] In the rapid cooling stage described above, the gas spray method, melt spinning, suction casting, or injection casting processes each differ, making it difficult to generally specify the conditions. However, as a result, all of these methods can produce layered silicon-based active materials.

[0115] In this application, the adjustment of the cooling rate differs for each process, but generally, in melt spinning, the faster the wheel rotation speed, the faster the cooling rate, and in suction casting or injection casting, the thinner the mold, the faster the cooling rate. Furthermore, the cooling rate can be adjusted by controlling the external temperature, such as by flowing cooling water through the mold or by cooling the wheel or mold with liquid nitrogen.

[0116] In one embodiment of this application, the grinding step may include one or more steps selected from the group consisting of a ball mill, a pin mill, a disk mill, and a jet mill.

[0117] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0118] Figure 2 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. Although Figure 2 shows the negative electrode active material layer formed on one side, it may also be included on both sides of the negative electrode current collector layer.

[0119] In one embodiment of this application, the negative electrode for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of a negative electrode current collector layer.

[0120] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0121] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0122] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0123] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0124] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity during the formation of the negative electrode active material layer is suitable, minimizing particle aggregation of the negative electrode composition and enabling efficient formation of the negative electrode active material layer.

[0125] In one embodiment of this application, the slurry solvent can be used without limitation as long as it is capable of dissolving the negative electrode composition, and specifically, water or NMP may be used.

[0126] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0127] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0128] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0129] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0130] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0131] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the aforementioned range is satisfied by including the silicon-based active material and conductive material according to this application in specific compositions and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within a suitable range.

[0132] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0133] Figure 3 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery, including a negative electrode active material layer 20, can be seen on one side of the negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of the positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separator 30 interposed between them.

[0134] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery 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 the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0135] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0136] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also 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 strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0137] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the 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; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where 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 Lithium manganese composite oxides represented as 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); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. The positive electrode may also be Li metal (Li-metal).

[0138] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0139] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0140] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode 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, tetrafluoroethylene, 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.

[0141] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries is acceptable without particular limitations, and it is especially preferable that it has low resistance to electrolyte ion movement and excellent electrolyte moisture retention capacity. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and these may be selectively used as single-layer or multi-layer structures.

[0142] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0143] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0144] As the 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, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0145] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making them even more preferable.

[0146] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble 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 - You may use one or more selected from the group consisting of the following:

[0147] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0148] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Because the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0149] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative examples, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims. [Examples]

[0150] <Manufacturing example> <Example 1> An alloy with a Si-30%Al (Formula 1) composition was rapidly cooled by melt spinning and then pulverized to produce a negative electrode active material having a layered structure inside the particles.

[0151] Specifically, prior to melt spinning, a master alloy with a Si:Al mass ratio of 7:3 was produced using an induction furnace. During this process, the inside of the crucible was maintained in an argon atmosphere, and a current of 10 Ka was passed through a copper coil to produce a molten master alloy at 2000°C, which was then allowed to cool naturally. The produced master alloy was placed in a carbon crucible and melted, then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at a speed of 3000 rpm to produce a ribbon-shaped Si-30%Al alloy.

[0152] Subsequently, to produce a silicon-based active material, the alloy produced by ball milling was pulverized. A wet milling method using n-hexane (n-hexane) as the medium was used, with zirconia (ZrO2) as the ball, and ball milling was performed for 30 minutes at a mass ratio of alloy to ball of 1:40. At this time, the particle size (D50) of the produced active material was 5 μm, the interlayer spacing (Equation 2) was 50 nm, and the size of the primary crystal (Equation 3) was 100 nm.

[0153] <Example 2> The negative electrode active material was manufactured in the same manner as in Example 1, except that an alloy with a Si-20%Al (Formula 1) composition was rapidly cooled by melt spinning and then pulverized to produce a negative electrode active material having a layered structure inside the particles.

[0154] <Example 3> The negative electrode active material was manufactured in the same manner as in Example 1, except that an alloy with a Si-10%Al (Formula 1) composition was rapidly cooled by melt spinning and then pulverized to produce a negative electrode active material having a layered structure inside the particles.

[0155] <Example 4> The negative electrode active material was manufactured in the same manner as in Example 1, except that an alloy with a Si-40%Al (Formula 1) composition was rapidly cooled by melt spinning and then pulverized to produce a negative electrode active material having a layered structure inside the particles.

[0156] <Example 5> The negative electrode active material was manufactured in the same manner as in Example 1, except that an alloy with a Si-50%Al (Formula 1) composition was rapidly cooled by melt spinning and then pulverized to produce a negative electrode active material having a layered structure inside the particles.

[0157] <Example 6> The production method was the same as in Example 1, except that the manufactured master alloy was placed in a carbon crucible and melted, and then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at a speed of 2000 rpm to produce a ribbon-shaped Si-30%Al alloy.

[0158] <Example 7> The production method was the same as in Example 1, except that the manufactured master alloy was placed in a carbon crucible and melted, and then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at a speed of 1000 rpm to produce a ribbon-shaped Si-30%Al alloy.

[0159] <Example 8> The production method was the same as in Example 1, except that the manufactured master alloy was placed in a carbon crucible and melted, and then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at a speed of 4000 rpm to produce a ribbon-shaped Si-30%Al alloy.

[0160] <Comparative Example 1> MG-Si with a purity of 99.9% was melt-spinned to produce ribbon-shaped silicon, which was then pulverized to produce a 100% Si polycrystalline anode active material.

[0161] Specifically, a current of 10 Ka was passed through a copper coil to produce molten silicon at 2000°C, and this molten silicon was injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at a speed of 3000 rpm to produce ribbon-shaped silicon.

[0162] The manufactured silicon was pulverized in the same manner as in Example 1, with the particle size (D50) of the active material being 5 μm.

[0163] <Comparative Example 2> MG-Si with a purity of 99.9% was pulverized to produce a 100% Si single-crystal negative electrode active material.

[0164] MG-Si was pulverized in the same manner as in Example 1, and the particle size (D50) of the active material was 5 μm.

[0165] <Comparative Example 3> Except for adjusting the rapid cooling rate, the active material was manufactured in the same manner as in Example 1, with the only difference being that the particle size (D50) was 5 μm, the interlayer spacing (Equation 2) was 500 nm, and the size of the primary crystal (Equation 3) was 1.2 μm.

[0166] <Comparative Example 4> In Example 1, the production was carried out in the same manner as in Example 1, except that the particle size (D50) of the active material was 5 μm, the interlayer spacing (Equation 2) was 1.5 μm, and the size of the primary crystal (Equation 3) was 800 nm, by adjusting the rapid cooling rate.

[0167] The above examples and comparative examples are shown in Table 1 below.

[0168] [Table 1]

[0169] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding the aforementioned silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10 to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0170] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material was SWCNT, with a particle size of 3.5 μm (D50) and an average particle size of 3.5 μm.

[0171] As for the specific mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed again at 2500 rpm for 30 minutes to prepare the negative electrode slurry.

[0172] As the negative electrode current collector layer, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 85 mg / 25 cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was then used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0173] <Manufacturing of secondary batteries> LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the cathode slurry to prepare a cathode slurry (solid content concentration 78% by weight).

[0174] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby manufacturing the positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0175] A polyethylene separator was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0176] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90 in an organic solvent, adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0177] <Example of experiment> Experimental Example 1: Lifetime Performance Results of Monocell The lifespan of secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples was evaluated using an electrochemical charger / discharger, and the capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V 1C / 0.5C, and the lifespan retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test.

[0178] Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0179] [Table 2]

[0180] Experimental Example 2: Resistance Change of Monocell In Experimental Example 1, the life retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during testing. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0181] For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0182] [Table 3]

[0183] Experimental Example 3: Evaluation of Coin Cell Capacity and Efficiency The initial capacity and efficiency of coin half-cells containing the negative electrodes manufactured in the above examples and comparative examples were evaluated using an electrochemical charger / discharger. The coin half-cells were subjected to charge-discharge tests at 0.005-1.5V and 0.1C, and the capacity and efficiency in the first cycle were measured, respectively.

[0184] Initial efficiency (%): {(Discharge capacity in the first cycle) / (Charge capacity in the first cycle)} × 100

[0185] [Table 4]

[0186] As can be seen from Experimental Examples 1 to 3, in Examples 1 to 8 of this application, a layered silicon-based active material satisfying the ranges of Equations 2 and 3 forms a phase boundary between two phases (Si primary crystal and alloy) within the silicon-based active material. This boundary acts as a diffusion pathway for lithium ions along with the grain boundaries, improving cycle capacity retention and initial capacity efficiency. As can be seen from Experimental Examples 2 and 3, while the interlayer spacing remains almost the same, the size of the primary crystal decreases as the Si content decreases, resulting in superior lifetime performance. However, Si exhibits a capacity of approximately 3500 mAh / g, and Al exhibits a capacity of approximately 990 mAh / g. The capacity of the coin cell in Experimental Example 3 is determined according to their ratio, and the higher the Si content, the greater the capacity of the coin cell. There is a trade-off relationship between lifetime and capacity depending on the composition, and it was possible to simultaneously satisfy both capacity and lifetime characteristics by matching the optimal ratio.

[0187] Furthermore, in Table 4, while there was no significant difference in coin cell efficiency with increasing Si content, there was a tendency for efficiency to increase with increasing boundary, i.e., with finer structures.

[0188] Furthermore, in Examples 6 to 8, the cooling rate was changed while the rpm was modified. Increasing the rpm had a positive effect on the lifespan without decreasing the capacity, whereas the capacity decreased as the Al content increased. In other words, optimizing the capacity and lifespan by adjusting the alloy composition and rpm of the layered silicon-based active material constitutes the main point of the present invention. [Explanation of Symbols]

[0189] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30 ···Separator 40...Cathode active material layer 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries

Claims

1. A negative electrode active material containing a layered silicon-based active material, The layered silicon-based active material is represented by the following formula 1, The layered silicon-based active material is a negative electrode active material that satisfies the following equations 2 and 3: [Formula 1] Yes １００－ｘ M ｘ In the above formula 1, x has an atomic weight in the range of greater than 0 and less than 100. M comprises one or more elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au. [Formula 2] 10 nm ≤ Y ≤ 1 μm [Formula 3] 10 nm ≤ X ≤ 1 μm In equations 2 and 3, X is the size of the primary silicon crystal (primary Si) of the layered silicon-based active material. Y represents the interlamellar spacing of the silicon-based active material in the layered structure.

2. The negative electrode active material according to claim 1, wherein the average particle size (D50) of the layered silicon-based active material is 1 μm or more and 10 μm or less.

3. The negative electrode active material according to claim 1, wherein the fraction of the primary silicon crystal in the layered silicon-based active material is 0% or more and less than 90%.

4. The above equation 2 is given by 10 nm ≤ Y ≤ 300 nm, The negative electrode active material according to claim 1, wherein formula 3 satisfies 10 nm ≤ X ≤ 350 nm.

5. The step of crushing a silicon precursor to form a silicon-based active material; A step of mixing the silicon-based active material with one or more metallic elements selected from the group consisting of Al, Ni, Co, Ti, Mn, Cu, Cr, Fe, Zr, Ag, and Au; The step of melting the silicon-based active material and the metal element; and A step of cooling the silicon-based active material and the metal element; A method for producing a negative electrode active material, including the material itself.

6. After the cooling step, A method for producing a negative electrode active material according to claim 5, further comprising the step of pulverizing the silicon-based active material and the metal element.

7. The method for producing a negative electrode active material according to claim 5, wherein the cooling step includes melt spinning, suction casting, injection casting, or gas spraying.

8. After the step of cooling the silicon-based active material and the metal element, The silicon-based active material satisfies the following formulas 2 and 3, and is a method for producing a negative electrode active material according to claim 5: [Formula 2] 10 nm ≤ Y ≤ 1 μm [Formula 3] 10 nm ≤ X ≤ 1 μm In equations 2 and 3, X is the size of the primary silicon crystal (primary Si) of the layered silicon-based active material. Y represents the interlamellar spacing of a layered silicon-based active material.

9. A negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder according to any one of claims 1 to 4.

10. The negative electrode composition according to claim 9, wherein the negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

11. The negative electrode composition according to claim 9, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

12. A negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, The negative electrode active material layer comprises the negative electrode composition or a cured product thereof according to claim 9, for use as a negative electrode for a lithium secondary battery.

13. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 12, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

14. Positive electrode; A negative electrode for a lithium secondary battery according to claim 12; A separator provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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