Anode active material, method for producing anode active material, anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

1. A negative electrode active material comprising a silicon-based active material, the silicon-based active material comprising silicon-based crystal grains, wherein a high-angle grain boundary ratio within the silicon-based crystal grains is 30% or more, and the silicon-based active material has a chemical structure that satisfies the following formulas 1 and 2: [Formula 1] 1 μm≦particle size of silicon-based active material (D50)≦10 μm [Formula 2] 2 nm≦crystal grain size of silicon-based active material≦1 μm.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0052006, filed with the Korean Intellectual Property Office on April 20, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present 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 including the same, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses electrochemical energy is a secondary battery, and the range of its use is expanding.

[0005] With the development of mobile device technologies and the increase in demand, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[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 extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a large discharge capacity. Therefore, research into improving the performance of negative electrode active materials using silicon-based particles has been actively conducted. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0008] As a result of research into reducing the grain size, it was confirmed that if a plate-shaped silicon precursor is formed by adjusting the cooling rate of the rapid cooling process prior to the conventional grinding of MG (Metallurgical Grade)-Si and then grinded, the desired grain size can be reduced and the high-angle boundary ratio can be controlled.

[0009] The present 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 including the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0010] One embodiment of the present specification provides an anode active material including a silicon-based active material, wherein the silicon-based active material includes silicon-based crystal grains, a high-angle grain boundary ratio within the silicon-based crystal grains is 30% or more, and the silicon-based active material satisfies the following formulas 1 and 2: [Formula 1] Approximately 1 μm≦particle size of silicon-based active material (D50)≦approximately 10 μm [Formula 2] Approximately 2 nm≦crystal grain size of silicon-based active material≦approximately 1 μm

[0011] In yet another embodiment, there is provided a method for producing an anode active material, the method including: rapidly cooling metal silicon to form a silicon precursor; and pulverizing the silicon precursor to form a silicon-based active material, wherein the rapidly cooling step includes melt spinning, suction casting, or injection casting.

[0012] In yet another embodiment, there is provided a negative electrode composition including the negative electrode active material according to the present application, a negative electrode conductive material, and a negative electrode binder.

[0013] In yet another embodiment, there is provided 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 surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer comprises the negative electrode composition according to the present application or a cured product thereof.

[0014] The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode for a lithium secondary battery according to the present application, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0015] In the case of the negative electrode active material according to an embodiment of the present invention, unlike conventional milling processing methods, a rapid cooling process is performed prior to MG (Metallurgical Grade)-Si milling to form a plate-shaped silicon precursor, and the crystal grain size and high-angle grain boundary ratio of the silicon-based active material can be optimized by controlling the cooling rate.

[0016] As described above, a silicon-based active material having nano-sized crystal grains can be obtained by pulverizing a plate-shaped silicon precursor having nano-sized crystal grains. When a negative electrode is manufactured using the silicon-based active material, the cycle capacity retention rate and initial capacity efficiency are increased.

[0017] The negative electrode active material of the present invention contains SiO as a silicon-based active material. x (x=0) and SiOx It contains one or more selected from the group consisting of (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x It contains, for example, about 70 parts by weight or more of (x = 0), and while having a pure silicon (Pure Si) active material, the problem of volume expansion due to charge and discharge, which is a problem with this, is solved by adjusting the grain size.

Brief Description of the Drawings

[0018] [Figure 1] It is a flowchart of a manufacturing process of a silicon-based active material according to an embodiment of the present application. [Figure 2] It is a diagram showing an enlarged view of a silicon-based active material according to an embodiment of the present application. [Figure 3] It is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 4] It is a diagram showing a laminated structure of a lithium secondary battery according to an embodiment of the present application. [Figure 5] It is a diagram showing a method for calculating the grain size. [Figure 6] It is a diagram showing the misorientation angle.

Modes for Carrying Out the Invention

[0019] In some of the accompanying drawings, the same reference numerals are given to corresponding components. Those skilled in the art should understand that the drawings clearly show the elements simply and are not necessarily drawn to scale. For example, for the purpose of assisting in the understanding of various embodiments, the dimensions of some elements shown in the drawings may be exaggerated compared to other elements. Also, elements of known technology that are useful or essential in commercially feasible embodiments may not be depicted so as not to obscure the gist of various embodiments of the present invention.

[0020] Before explaining the present invention, first, some terms are defined.

[0021] In this specification, when a part is said to "comprise" a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary, but rather that it does not exclude other components.

[0022] In this specification, "p to q" means "not less than p and not more than q."

[0023] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above-mentioned measurement method.

[0024] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, the average particle size may be measured using the laser diffraction method. For example, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). When the particles pass through a laser beam, the difference in diffraction pattern due to particle size is measured to calculate the particle size distribution.

[0025] In one embodiment of the present application, the particle size or particle size may refer to the average particle size or representative particle size of each particle constituting the metal powder.

[0026] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0028] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0029] As used in this specification, the terms "about," "approximately," and "substantially" are used to mean a range of values or degrees or their approximations, taking into consideration inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting the disclosure content in which precise or absolute values provided to aid in the understanding of the present invention are mentioned.

[0030] The limitations of numerical ranges used in this specification (e.g., ≦, parts by weight, thickness, greater than or equal to, less than or equal to, etc.) are used in the sense of a range of numerical values or degrees or their approximate meanings, taking into consideration inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting the disclosure content in which precise or absolute numerical values provided to aid in the understanding of the present invention are recited.

[0031] Recently, with the demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than graphite-based materials, have been used as negative electrode active materials. xResearch is being conducted into methods to increase battery capacity by using silicon-based compounds such as graphite. Silicon-based compounds, which are high-capacity materials, have a higher capacity than conventional graphite, but they have the problem of rapidly expanding during charging, cutting off the conductive path and degrading battery performance.

[0032] Therefore, various researches have been conducted to solve the problems when using silicon-based compounds as negative electrode active materials. For example, in order to use silicon-based compounds as negative electrode active materials, methods for adjusting the driving potential, methods for coating a thin film on the active material layer, methods for suppressing volume expansion itself such as methods for adjusting the particle size of the silicon-based compound, and various methods for preventing the conductive path from being broken have been discussed, but each method has its own advantages and disadvantages.

[0033] Meanwhile, research has shown that in the case of Si anode active materials, grain boundaries act as lithium diffusion paths, so wider grain boundaries, i.e., smaller grain sizes, are more beneficial for the performance characteristics of secondary batteries. However, when manufacturing anode active materials by pulverizing metallic grade silicon (MG-Si), the typical grain size of MG-Si is several hundred mm to several mm, which limits how much the grain size of the Si active material can be reduced, thereby limiting the improvement of secondary battery performance characteristics.

[0034] The present invention provides a technology that can control the size of crystal grains in Si particles, for example, by reducing the size of the crystal grains in Si particles to a size of several nm to several tens of nm, so as to prevent damage to the conductive paths due to volume expansion of the silicon-based compound even when the silicon-based active material is used as a negative electrode active material in order to improve the capacity performance of the secondary battery.

[0035] Hereinafter, in order for those with ordinary knowledge in the technical field to which the present invention belongs to easily implement the present invention, it will be described in detail by combining the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0036] One embodiment of the present specification is an anode active material containing a silicon-based active material, wherein the silicon-based active material contains silicon-based crystal grains, and the high angle grain boundary ratio in the silicon-based crystal grains is 30% or more, and the silicon-based active material provides an anode active material that satisfies the following formulas 1 and 2. [Formula 1] Approximately 1 μm ≤ particle size (D50) of silicon-based active material ≤ approximately 10 μm [Formula 2] Approximately 2 nm ≤ crystal grain size of silicon-based active material ≤ approximately 1 μm

[0037] In the case of the anode active material according to one embodiment of the present invention, different from the conventional pulverization process, prior to pulverizing MG-Si, a rapid cooling process is carried out first to form a plate-like silicon precursor, and as a result, the crystal grain size and high angle grain boundary (HAGB) ratio of the silicon-based active material produced by adjusting the cooling rate can be optimized.

[0038] As described above, a silicon-based active material having nano-sized crystal grains can be ensured by pulverizing the plate-like silicon precursor having nano-sized crystal grains, and when using this to manufacture the anode of a lithium secondary battery, the cycle capacity maintenance rate and initial capacity efficiency of the lithium secondary battery are increased.

[0039] In one embodiment of the present application, the silicon-based active material contains one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be contained in an amount of about 70 parts by weight or more.

[0040] In one embodiment of the present application, the silicon-based active material is SiO x (x=0), and based on 100 parts by weight of the silicon-based active material, x (x=0) may be contained in an amount of about 70 parts by weight or more.

[0041] In another embodiment, the SiO x (x=0) may be included in an amount of about 70 parts by weight or more, for example, about 80 parts by weight or more, or about 90 parts by weight or more, and may be included in an amount of about 100 parts by weight or less, for example, about 99 parts by weight or less, or about 95 parts by weight or less.

[0042] In one embodiment of the present application, pure silicon (Si) particles may be used as the silicon-based active material. The use of pure silicon (Si) particles as the silicon-based active material means, as described above, pure Si particles (SiO ) that are not bonded with other particles or elements, based on 100 parts by weight of the total silicon-based active material. x (x=0)) may be included in the range.

[0043] In one embodiment of the present application, the silicon-based active material is SiO 2 based on 100 parts by weight of the silicon-based active material. x (x=0) 100 parts by weight of silicon-based particles.

[0044] In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities may be metals that are generally contained in silicon-based active materials, and may be contained in an amount of, for example, about 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0045] Silicon-based active materials used as negative electrode active materials in lithium secondary batteries have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them have been increasing. However, due to their high volume expansion during charge and discharge, such attempts have been limited to mixing a small amount of silicon-based active material with a graphite-based active material.

[0046] Therefore, in the present invention, a silicon-based active material is used as a negative electrode active material to improve capacity performance, but the problems of the silicon-based active material described above are solved by adjusting the crystal grain size of the silicon-based active material itself rather than adjusting the composition of the conductive material and binder.

[0047] In the present application, in order to reduce the crystal grain size, a rapid cooling process is performed prior to MG-Si pulverization during the process of manufacturing the negative electrode active material, thereby producing a plate-shaped silicon precursor, which is then pulverized to produce a silicon-based active material.

[0048] In one embodiment of the present application, the silicon precursor satisfies the following formulas 3 and 4: [Equation 3] Approximately 10 μm≦ silicon precursor plate thickness≦ approximately 2 mm [Equation 4] Approximately 2 nm ≦ size of crystal grains in silicon precursor ≦ approximately 1 μm

[0049] In one embodiment of the present application, the above formula 3 may satisfy about 10 μm≦plate thickness of silicon precursor≦2 mm, or about 13 μm≦plate thickness of silicon precursor≦1.5 mm, or about 15 μm≦plate thickness of silicon precursor≦1 mm.

[0050] In one embodiment of the present application, the above formula 4 satisfies about 2 nm≦size of the crystal grains in the silicon precursor≦1 μm, and can, for example, satisfy about 10 nm≦size of the crystal grains in the silicon precursor≦1 μm, or about 40 nm≦size of the crystal grains in the silicon precursor≦1 μm.

[0051] Referring to FIG. 1, in one embodiment of the present invention, MG silicon is placed in a graphite crucible and a current of approximately 10 kA is applied to a copper coil to produce molten silicon at approximately 2000°C (S1). The molten silicon is then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at 3000 rpm to produce a plate-shaped silicon precursor (S2). The produced precursor is then checked to see if it satisfies Equations 3 and 4 (S3). If it does (S3, YES), the produced silicon precursor is pulverized using a method such as a ball mill, pin mill, disk mill, or jet mill to form a silicon-based active material (S4). If the precursor produced in S3 does not satisfy Equations 3 and 4, the process returns to step S1 to produce molten silicon metal, or returns to step S2 to repeat the process of rapidly cooling the molten silicon metal to produce a plate-shaped silicon metal. Meanwhile, the active material formed in step S5 is checked to see if it satisfies formulas 1 and 2. If it does (YES, S5), the silicon-based active material is secured in step S6, and the process ends. The secured silicon-based active material can then be used to manufacture, for example, a negative electrode for a lithium secondary battery. On the other hand, if the active material formed in step S5 does not satisfy formulas 1 and 2 (NO, S5), the process returns to step S4 and is repeated.

[0052] In the present application, in order to reduce the crystal grain size during the manufacturing process of the negative electrode active material, a rapid cooling process is performed on molten MG-Si prior to pulverizing the MG-Si to prepare a plate-shaped silicon precursor, and through this adjustment, a silicon precursor satisfying the above formulas 3 and 4 is prepared.

[0053] By pulverizing the plate-shaped silicon precursor having nano-sized crystal grains, a silicon-based active material having nano-sized crystal grains can be obtained, and by using this to manufacture a negative electrode, for example, the cycle capacity retention rate and initial capacity efficiency of a secondary battery can be increased.

[0054] In one embodiment of the present application, the plate-shaped silicon precursor as described above can be pulverized to form a silicon-based active material, and the silicon-based active material according to the present application satisfies the following formulas 1 and 2. [Formula 1] Approximately 1 μm≦particle size of silicon-based active material (D50)≦10 μm [Formula 2] Approximately 2 nm≦crystal grain size of silicon-based active material≦1 μm

[0055] The formula 1 can satisfy, for example, the range of about 3 μm≦particle size (D50) of the silicon-based active material≦9 μm, or about 3 μm≦particle size (D50) of the silicon-based active material≦7 μm.

[0056] Furthermore, the formula 2 can satisfy, for example, about 5 nm≦crystal grain size of silicon-based active material≦700 nm, or about 20 nm≦crystal grain size of silicon-based active material≦500 nm.

[0057] As described above, the crystal grain size is controlled during the formation of the silicon precursor, and then the crystal grain size is finally set within the range of Equation 2 through a pulverization process, thereby increasing the cycle capacity retention rate and initial capacity efficiency of the secondary battery.

[0058] In one embodiment of the present application, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. For example, a method for calculating the crystal grain size can be seen in FIG. 5. In FIG. 5, the remaining values excluding L are measured through XRD analysis of the silicon-based active material, and the crystal grain size can be calculated based on the fact that FWHM and crystal grain size are inversely proportional to each other through the Debye-Scherrer equation. In this case, the Debye-Scherrer equation is as follows:

[0059] [Formula 1-1] FWHM=Kλ / LCosθ In the formula 1-1, L is the size of the crystal grain, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0060] The shape of the crystal grains may be measured in various ways and three-dimensionally, and the size of the crystal grains may be measured by a commonly used circle method or diameter measurement method, but is not limited thereto.

[0061] The diameter measurement method involves drawing 5 to 10 parallel lines, each L mm long, on a micrograph of the target particle, and counting and averaging the number of crystal grains z along the lines. Only those that fit completely within the lines are counted, and those that overlap are excluded. If the number of lines is P and the magnification is V, the average particle size can be calculated using the following formula 1-2.

[0062] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0063] In addition, the circle method is a method in which a circle of a predetermined diameter is drawn on a micrograph of the target particle, and then the average area of the crystal grains is calculated from the number of crystal grains that fit within the circle and the number of crystal grains that overlap the boundary, and can be calculated using the following formula 1-3.

[0064] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 ) In the above formulas 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles that fit inside the circle, n is the number of particles that span the arc, and V is the magnification of the microscope.

[0065] In one embodiment of the present application, there is provided a negative electrode active material, wherein the silicon-based active material includes silicon-based crystalline grains, and a high-angle boundary ratio within the silicon-based crystalline grains is about 30% or more.

[0066] In yet another embodiment, the silicon-based active material includes silicon-based crystalline grains, and the high-angle boundary ratio within the silicon-based crystalline grains may be about 30% or more, 35% or more, or 40% or more, or about 80% or less, 75% or less, or 70% or less.

[0067] In the present application, the silicon-based crystalline grain may refer to each particle constituting a silicon-based active material, and the silicon-based crystalline grains are gathered together to form the silicon-based active material. In this case, the grain boundary may be defined as a defect between the corresponding crystalline grains.

[0068] When fabricated using the above-mentioned method, many high-angle grain boundaries (HAGBs) with high grain boundary energy are formed, and lithium ions diffuse more easily through high-angle boundaries than through low-angle grain boundaries (LAGBs).

[0069] In the present application, the high-angle boundary ratio may refer to the ratio of grain boundaries having a boundary angle of about 15° or more in the entire silicon-based active material.

[0070] In this application, the high angle grain boundary may refer to a grain boundary misorientation angle > about 15°, and the low angle grain boundary may refer to a grain boundary misorientation angle < about 2° < misorientation angle < 15°.

[0071] 6 is a diagram showing a misorientation angle. The misorientation angle 4 may be defined as an angle relative to the crystal orientation difference between two adjacent silicon-based crystal grains 2. In this case, a grain boundary may be defined as a crystal defect between different silicon-based crystal grains 2.

[0072] The silicon-based active material according to the present application can have a relatively high ratio of high-angle boundaries across all grain boundaries, thereby improving battery performance.

[0073] In one embodiment of the present application, there is provided a negative electrode active material, wherein the silicon-based crystal grains have an average misorientation angle of about 5° or more.

[0074] 2 is an enlarged view of a silicon-based active material according to an embodiment of the present application. For example, a silicon-based active material 1 is composed of a plurality of silicon-based crystalline grains 2, and the crystalline grains have the size of the crystalline grains represented by the formula 2. In addition, a crystal defect between silicon-based crystalline grains can be defined as a grain boundary.

[0075] In one embodiment of the present application, the silicon-based active material may include silicon-based particles having a particle size distribution of about 0.01 μm or more and 30 μm or less.

[0076] The silicon-based active material containing silicon-based particles having a particle size distribution of about 0.01 μm to 30 μm means that the silicon-based active material contains a large number of individual silicon-based particles having particle sizes within this range, and the number of silicon-based particles contained is not limited.

[0077] The particle size of the silicon-based particles may be expressed as their diameter if they are spherical, but if they have other shapes other than spherical, the particle size may be measured by comparing them with the spherical shape, and the particle size of individual silicon-based particles may be measured by a method commonly used in the art.

[0078] In one embodiment of the present application, the silicon-based active material may be, for example, in a crystalline or amorphous form, and may be, for example, non-porous. The silicon particles may be, for example, spherical or platelet-shaped particles. In one embodiment, the silicon particles may also have a fibrous structure, or may exist in the form of a silicon-containing thin film or coating, although this is less preferred.

[0079] In one embodiment of the present application, there is provided a negative electrode composition comprising the negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0080] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode active material is about 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0081] In yet another embodiment, the negative electrode active material may be included in an amount of about 40 parts by weight or more, for example, 60 parts by weight or more, or 65 parts by weight or more, or 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, or 90 parts by weight or less, or 85 parts by weight or less.

[0082] The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific surface area size that can control the volume expansion rate during charge and discharge, even when a silicon-based active material with significantly high capacity is used within the above range, and is characterized by improved output characteristics during charge and discharge compared to conventional secondary batteries without reducing the performance of the negative electrode even when the range is included.

[0083] While graphite-based compounds have traditionally been used as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have recently been increasing in response to the growing demand for high-capacity batteries. However, even if silicon-based active materials can adjust their properties as described above, they can still experience problems such as rapid volume expansion during charge / discharge cycles, damaging the conductive pathways formed within the negative electrode active material layer.

[0084] In one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-like conductive materials, planar conductive materials, and linear conductive materials.

[0085] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without inducing a chemical change. For example, the dot-like 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 derivatives. In one embodiment, the dot-like conductive material may include carbon black to achieve high conductivity and improve dispersibility.

[0086] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of about 40 m 2 / g or more 70m 2 / g or less, for example, 45m 2 / g or more 65m 2 / g or less, or 50m 2 / g or more 60m 2 / g or less.

[0087] In one embodiment of the present application, the dot-like conductive material may have a volatile matter content in the range of about 0.01% to about 1%, for example, about 0.01% to about 0.3%, or about 0.01% to about 0.1%.

[0088] When the functional group content of the dot-like conductive material satisfies the above range, the functional groups present on the surface of the dot-like conductive material allow the dot-like conductive material to be smoothly dispersed in water as a solvent. For example, in the present invention, by using a specific silicon-based active material, the functional group content of the dot-like conductive material can be reduced, thereby improving dispersibility.

[0089] In one embodiment of the present application, a dot-like conductive material having a functional group content within the above range is included together with a silicon-based active material, and the functional group content can be adjusted by adjusting the degree of heat treatment of the dot-like conductive material.

[0090] In one embodiment of the present application, the particle size of the dotted conductive material may be about 10 nm to about 100 nm, for example, about 20 nm to 90 nm, or about 20 nm to 60 nm.

[0091] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0092] The planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and simultaneously prevent the conductive path from being broken due to volume expansion. The planar conductive material may be referred to as a plate-type conductive material or a bulk-type conductive material.

[0093] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and in one embodiment, may be platelet graphite.

[0094] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be about 2 μm to 7 μm, for example, about 3 μm to 6 μm, or about 3.5 μm to 5 μm. When the above range is satisfied, the particle size is sufficient to facilitate dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, the dispersion effect is improved when dispersing using the same equipment and time.

[0095] In one embodiment of the present application, the planar conductive material provides a negative electrode composition having a D10 of about 0.5 μm or more and 2.0 μm or less, a D50 of about 2.5 μm or more and 3.5 μm or less, and a D90 of about 6.5 μm or more and 15.0 μm or less.

[0096] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low BET specific surface area.

[0097] In one embodiment of the present application, the planar conductive material may be a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without any restrictions. However, the planar conductive material in one embodiment may be affected to some extent by dispersion in terms of electrode performance, and a planar conductive material with a low specific surface area that does not cause dispersion problems may also be used.

[0098] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of about 0.25 m 2 / g or more.

[0099] In another embodiment, the sheet conductive material has a BET specific surface area of about 1 m 2 / g or more 500m 2 / g or less, for example, about 5m 2 / g or more 300m 2 / g or less, or 5m 2 / g or more 250m 2 / g.

[0100] The sheet conductive material according to the present application may be a sheet conductive material with a high specific surface area; or a sheet conductive material with a low specific surface area.

[0101] In another embodiment, the sheet conductive material is a sheet conductive material with a high specific surface area, and has a BET specific surface area of about 50 m 2 / g or more 500m 2 / g or less, for example, about 80m 2 / g or more 300m 2 / g or less, or 100m 2 / g or more 300m 2 / g or less.

[0102] In another embodiment, the sheet conductive material is a sheet conductive material having a low specific surface area, and a BET specific surface area of about 1 m 2 / g or more 40m 2 / g or less, for example, about 5m 2 / g or more 30m 2 / g or less, or 5m 2 / g or more 25m 2 / g or less.

[0103] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. For example, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged parallel to each other or twisted with the longitudinal axes of the carbon nanotube units in substantially the same orientation, forming a bundle or rope. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the carbon nanotube unit may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication and can smoothly form a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0104] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is about 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0105] In yet another embodiment, the negative electrode conductive material may comprise, based on 100 parts by weight of the negative electrode composition, about 0.1 parts by weight to 40 parts by weight, for example, about 0.2 parts by weight to 30 parts by weight, or about 0.4 parts by weight to 25 parts by weight, or about 0.4 parts by weight to 10 parts by weight.

[0106] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0107] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises, based on 100 parts by weight of the negative electrode conductive material, about 80 parts by weight or more and 99.9 parts by weight or less of the sheet conductive material; and about 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0108] In yet another embodiment, the negative electrode conductive material may include about 80 parts by weight or more and 99.9 parts by weight or less of the sheet conductive material, for example, about 85 parts by weight or more and 99.9 parts by weight or less, or 95 parts by weight or more and 98 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0109] In yet another embodiment, the negative electrode conductive material may contain the linear conductive material in an amount of about 0.1 parts by weight to 20 parts by weight, for example, 0.1 parts by weight to 15 parts by weight, or 0.2 parts by weight to 5 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0110] In one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and ratio, so that the life characteristics of conventional lithium secondary batteries are not significantly affected. For example, when the negative electrode conductive material includes a planar conductive material and a linear conductive material, the number of points at which charging and discharging are possible increases, improving the output characteristics of the secondary battery at a high C-rate and reducing the amount of high-temperature gas generated.

[0111] In one embodiment of the present application, the negative electrode conductive material may be a linear conductive material. When a linear conductive material is used alone, it can simplify the tortuosity problem that is a problem with silicon-based negative electrodes, improve the electrode structure, and thereby reduce the resistance to lithium ion migration within the electrode.

[0112] In one embodiment of the present application, when the negative electrode conductive material includes only a linear conductive material, the negative electrode conductive material may be included in an amount of about 0.1 parts by weight to about 5 parts by weight, for example, about 0.2 parts by weight to about 3 parts by weight, or about 0.4 parts by weight to about 1 part by weight, based on 100 parts by weight of the negative electrode composition.

[0113] The anode conductive material according to the present application has a substantially different structure from the cathode conductive material used in the cathode. That is, the anode conductive material according to the present application controls the contact points between the silicon-based active material, which experiences a large volume expansion of the electrode during charging and discharging, while the cathode conductive material acts as a buffer during rolling and provides partial conductivity, and thus has a substantially different structure and role from the anode conductive material of the present invention.

[0114] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a substantially different structure from conductive materials applied to graphite-based active materials. For example, conductive materials used in electrodes with graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity. Therefore, their structure and role are substantially different from those of negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0115] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material typically used as a negative electrode active material. For example, 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-like shape to facilitate the storage and release of lithium ions.

[0116] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, which may be expressed as plate-shaped graphite. For example, it refers to a material contained in the negative electrode active material layer to maintain a conductive path within the negative electrode active material layer, and does not play a role in storing or releasing lithium, but rather to ensure a planar conductive path within the negative electrode active material layer.

[0117] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material that ensures a conductive path, not for storing or releasing lithium. In this case, the negative electrode active material included therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0118] Meanwhile, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that stores or releases lithium.

[0119] For example, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-shaped and has a BET specific surface area of 0.1 m 2 / g or more 4.5m 2 The plate-shaped graphite, which is a planar conductive material, may have a planar shape and a BET specific surface area of about 5 m 2 / g or more.

[0120] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0121] The negative electrode binder according to one embodiment of the present application serves to control the active material and conductive material to prevent twisting and deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. Any binder may be used as long as it fulfills the above-mentioned role. For example, a water-based binder or a PAM-based binder may be used.

[0122] In one embodiment of the present application, the amount of the negative electrode binder may be about 30 parts by weight or less, for example, about 25 parts by weight or less, or about 20 parts by weight or less, or may be about 5 parts by weight or more, or about 10 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0123] One embodiment of the present application provides a method for producing an anode active material, the method including: rapidly cooling metallurgical silicon to form a silicon precursor; and pulverizing the silicon precursor to form a silicon-based active material, wherein the rapidly cooling step includes melt spinning, suction casting, or injection casting.

[0124] As described above, instead of immediately pulverizing the silicon metal itself, the crystal grain size of the silicon precursor formed by controlling the cooling rate through a rapid cooling process is controlled, and the precursor is then pulverized to produce a silicon-based active material.

[0125] That is, when casting molten silicon, the shorter the solidification time (Ts), the faster the cooling rate, and the faster the plate thickness of the silicon-based precursor satisfies the range of Equation 3 (e.g., about 10 μm-2 mm), the shorter the solidification time and the faster the cooling rate can be controlled. Also, as described above, the faster the cooling rate is controlled, the shorter the time for crystal grain growth, and the faster the crystal grain size (e.g., about 2 nm to 11 μm) can be controlled.

[0126] In one embodiment of the present application, there is provided a method for producing a negative electrode active material, further comprising the step of heating the metallurgical silicon in an induction furnace before the step of rapidly cooling the metallurgical silicon to form a silicon precursor.

[0127] As described above, the metallurgical silicon is heated in an induction furnace to form a molten state, and then rapidly cooled, and the rapid cooling includes melt spinning, suction casting, or injection casting. Any method that can rapidly cool the metallurgical silicon in a molten state to form a plate-shaped silicon precursor in accordance with the gist of the present invention can be applied.

[0128] Generally, melt spinning refers to a process in which a molten material is ejected onto a rotating copper wheel and rapidly cooled, suction casting refers to a process in which a molten material is cast by being sucked into a mold using a vacuum, and injection casting refers to a process in which a molten material is cast by being injected into a mold using high-pressure gas.

[0129] In the case of the rapid cooling step, the melt spinning, suction casting, or injection casting process is different and diverse, and it is generally difficult to specify the conditions, but as a result, all silicon-based precursors can be produced in a plate shape.

[0130] In this application, the cooling rate during rapid cooling varies depending on the process. Generally, in melt spinning, the faster the wheel rotation speed, the faster the cooling rate. In suction casting or injection casting, the thinner the mold, the faster the cooling rate. The cooling rate can also be controlled by adjusting the external temperature, such as by cooling the wheel or mold with cooling water or liquid nitrogen. Rapid cooling is a cooling method that rapidly cools MG silicon to form a plate-shaped silicon precursor. Rapid cooling refers to a type of non-equilibrium solidification that suppresses reactions such as phase transformation and grain coarsening that occur in an equilibrium state. For example, when rapidly cooling metallic silicon using melt spinning, the cooling rate can be controlled by adjusting the rotation speed of the copper wheel. The material is cooled from the molten state temperature of approximately 1,500°C to room temperature of approximately 25°C, which takes less than one second.

[0131] In one embodiment of the present application, there is provided a method for producing a negative electrode active material, wherein after the step of rapidly cooling metal silicon to form a silicon precursor, the silicon precursor satisfies the above-mentioned formulas 3 and 4.

[0132] A silicon precursor is formed through a rapid cooling process, which can mean satisfying Equation 3 and Equation 4.

[0133] In the present application, a method for manufacturing a negative electrode active material is provided, which comprises the steps of: pulverizing the silicon precursor to form a silicon-based active material; and thereafter, the silicon-based active material satisfies the above-mentioned formulas 1 and 2.

[0134] A silicon precursor that satisfies the specific formulas 3 and 4 is formed through a rapid cooling process, and then pulverized to produce a silicon-based active material that satisfies the ranges of the above-mentioned formulas 1 and 2.

[0135] In one embodiment of the present application, the pulverizing 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, but is not limited thereto. Any pulverizing step that can pulverize a plate-shaped metal silicon precursor to produce a silicon-based active material that satisfies the ranges of the above-mentioned formulas 1 and 2 is applicable.

[0136] Through the above-described pulverization process, a silicon-based active material that satisfies the ranges of the above-described formulas 1 and 2 can be produced.

[0137] In one embodiment of the present application, there is provided 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 surfaces of the negative electrode current collector layer, the negative electrode composition according to the present application or a cured product thereof.

[0138] 3 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. For example, a negative electrode for a lithium secondary battery 100 can be seen, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 3 shows the negative electrode active material layer 20 formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0139] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a negative electrode slurry containing the negative electrode composition to one or both surfaces of a negative electrode current collector layer and drying the applied slurry.

[0140] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0141] In one embodiment of the present application, the solid content of the negative electrode slurry may be in the range of about 5% to 40%.

[0142] In another embodiment, the solid content of the negative electrode slurry may be in the range of about 5% to 40%, for example, about 7% to 35%, or about 10% to 30%.

[0143] The solid content of the negative electrode slurry may refer to the content of the negative electrode composition contained in the negative electrode slurry, or may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0144] When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, and the caking phenomenon of particles of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0145] In one embodiment of the present application, the slurry solvent may be any solvent that can dissolve the negative electrode composition, and may be, for example, water or NMP.

[0146] In one embodiment of the present application, the negative electrode current collector layer typically has a thickness of about 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be provided with fine irregularities to strengthen the binding strength of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0147] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector layer is about 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is about 5 μm or more and 500 μm or less.

[0148] However, the thickness may vary depending on the type and application of the negative electrode used.

[0149] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of about 10% to 60%.

[0150] In another embodiment, the porosity of the negative electrode active material layer may be in the range of about 10% to 60%, for example, about 20% to 50%, or about 30% to 45%.

[0151] The 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. For example, the porosity satisfies the above range by including the silicon-based active material and conductive material according to the present application in a specific composition and content, thereby allowing the electrode to have an appropriate range of electrical conductivity and resistance.

[0152] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0153] 4 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. For example, a lithium secondary battery anode 100 including an anode active material layer 20 on one surface of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one surface of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and the lithium secondary battery cathode 200 are stacked with a separator 30 sandwiched between them.

[0154] A secondary battery according to an embodiment of the present specification may include the above-described negative electrode for a lithium secondary battery. For example, 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, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0155] 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 including the positive electrode active material.

[0156] The positive electrode current collector in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. 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. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0157] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≦c2≦0.3); 2-c3 M c3Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0158] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material described above.

[0159] The positive electrode conductive material is used to impart conductivity to the electrode and can be any material that has electronic conductivity without causing chemical changes in the battery. Examples include graphite such as natural graphite and 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, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination.

[0160] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0161] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. For example, any separator that exhibits low resistance to ion movement in the electrolyte and has excellent humidifying properties for the electrolyte can be used. For example, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Coated separators containing ceramic components or polymeric materials for heat resistance or mechanical strength can also be used, and they can be used in either a single-layer or multi-layer structure.

[0162] Examples of the electrolyte include 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 manufacturing lithium secondary batteries, but are not limited to these.

[0163] For example, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0164] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0165] Among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with chain carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared.

[0166] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 -, (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0167] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, and improving the discharge capacity of the battery.

[0168] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore may be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0169] Examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description. Naturally, such changes and modifications fall within the scope of the claims.

[0170] [Manufacturing example] <Production of silicon-based precursors> Example 1 MG silicon was placed in a graphite crucible, melted using an induction furnace, and melt-spun to produce a plate-shaped silicon precursor.

[0171] For example, a 10 kA current was passed through a copper coil to produce molten silicon at 2000°C, which was then injected at a pressure of 1.2 kPa onto a 25 cm diameter copper wheel rotating at 3000 rpm to obtain a plate-shaped silicon precursor. The silicon precursor plate had a thickness of approximately 20 μm and a crystal grain size of approximately 50 nm, satisfying the above-mentioned formulas 3 and 4.

[0172] Silicon-based precursors of Examples 2 and 3 and Comparative Example 3 were prepared in the same manner as in Example 1, except that the rotation speed was changed to the conditions in Table 1 below in order to control the cooling rate during rapid cooling after melt spinning.

[0173] [Table 1]

[0174] In Example 2, when the rotation speed of the copper wheel in the melt spinning process was 4000 rpm, which was higher than the 3000 rpm in Example 1, the plate thickness of the silicon-based precursor was about 15 μm and the crystal grain size was about 40 nm, satisfying the above-mentioned formulas 3 and 4. In Example 3, when the rotation speed of the copper wheel in the melt spinning process was 1000 rpm, the plate thickness of the silicon-based precursor was about 100 μm and the crystal grain size was about 300 nm, satisfying the above-mentioned formulas 3 and 4.

[0175] In Comparative Examples 1 and 2, MG silicon was placed in a graphite crucible, melted using an induction furnace, and then subjected to a melt spinning process to produce a plate-shaped silicon precursor. Instead, the MG silicon itself was used directly to carry out the milling process described below. On the other hand, in Comparative Example 3, the rotation speed of the copper wheel in the melt spinning process was set to 100 rpm. The silicon-based precursor plate thickness was about 3 mm, which was thicker than in the Examples of the present invention, and the crystal grain size was 2.5 μm, which was larger than in the Examples of the present invention, and therefore did not satisfy the above-mentioned formulas 3 and 4.

[0176] Example 4 In Example 4, unlike Examples 1, 2, and 3, MG silicon was arc-melted to form a molten metal, which was then subjected to a suction casting process to produce a plate-shaped silicon precursor.

[0177] For example, vacuum level 10 -6 The inside of the torr chamber was filled with argon at a pressure of 0.5 kPa to create a high-purity argon atmosphere, and molten silicon at 2000°C was produced using arc plasma. Then, the vacuum level below the mold was reduced to 10 -5 After maintaining the pressure above torr, the valve between the bottom of the mold and the chamber was opened to suck the molten silicon into the mold, producing a plate-shaped silicon precursor. The mold used was 0.5 mm thick, 10 mm wide, and 50 mm long, and the crystal grain size was 50 nm.

[0178] A silicon-based precursor was prepared in the same manner as in Example 4, except that the mold thickness, which affects the cooling rate during rapid cooling by suction casting, was changed to the conditions in Table 2 below.

[0179] [Table 2]

[0180] In Examples 4, 5, and 6, the plate thickness of the silicon precursor is 500 μm, 400 μm, and 100 μm, respectively, which satisfies the condition of Equation 3, and the size of the crystal grains in the silicon precursor is 400 nm, 500 nm, and 1,000 nm, respectively, which satisfies Equation 4.

[0181] In the case of Comparative Examples 4 and 5, the MG silicon was not melted by arc melting and then subjected to a suction casting process to produce a plate-shaped silicon precursor, but the MG silicon itself was used as is to carry out the milling process described below.

[0182] On the other hand, in the case of Comparative Example 6, in which the thickness of the plate-shaped mold was 3 mm, the plate thickness of the silicon precursor was 3 mm, which did not satisfy the condition of Equation 3, and the size of the crystal grains in the silicon precursor was 2.510 μm, which did not satisfy Equation 4.

[0183] From the values in Tables 1 and 2, it was found that the melt spinning process is generally easier to manufacture a thinner silicon precursor than the suction casting process.

[0184] <Production of silicon-based active materials> The silicon-based precursor prepared above was used in a ball mill to prepare a silicon-based active material.

[0185] For example, a wet milling method using n-hexane as a medium was used, and zirconia (ZrO2) balls were used. The mass ratio of silicon precursor to balls was approximately 1:40, and milling was carried out for 30 minutes. The particle size of the produced negative electrode active material was 5 μm, and the crystal grain size was 50 nm, satisfying Equations 1 and 2, respectively.

[0186] The silicon precursors of the above-mentioned Examples and Comparative Examples were pulverized in the same manner as above, and the results are shown in Table 3.

[0187] [Table 3]

[0188] Table 3 shows that the particle size (D50) of the silicon-based active material in all of Examples 1 to 6 satisfies formula 1, while Comparative Examples 5 and 6 do not. It is also clear that the crystal grain size of the silicon-based active material in all of Examples 1 to 6 satisfies formula 2, while Comparative Examples 1 to 6 do not. It is also clear that the high-angle boundary ratio is 30% or more in all of Examples 1 to 6, but the high-angle boundary ratio is less than 30% in Comparative Examples 4 to 6.

[0189] <Production of negative electrodes> According to one embodiment, a negative electrode active material including a silicon-based active material shown in Table 3, a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 80:9.6:0.4:10 to prepare a negative electrode slurry (solid concentration: 25 wt %).

[0190] For example, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): about 3.5 μm), and the second conductive material was SWCNT.

[0191] As a mixing method, the first conductive material, the second conductive material, the binder, and the water were dispersed using a homomixer at about 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at about 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0192] The negative electrode current collector layer was prepared by applying the negative electrode slurry to both sides of a copper current collector (thickness: 8 μm) at a rate of approximately 85 mg / 25 cm. 2 The coated material was rolled 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 used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0193] <Secondary battery manufacturing> In one embodiment, the positive electrode active material is 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 approximately 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: approximately 78 wt%).

[0194] The positive electrode current collector was an aluminum current collector (thickness: 12 μm) and the positive electrode slurry was applied to both sides of the aluminum current collector at a rate of approximately 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: about 77 μm, porosity: about 26%).

[0195] A polyethylene separator was interposed between the positive electrode and the negative electrode of each of the Examples and Comparative Examples, and an electrolyte was injected thereinto to prepare a lithium secondary battery.

[0196] The electrolyte was prepared by adding vinylene carbonate to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) were mixed in a volume ratio of 10:90, at a concentration of approximately 3 wt % based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of approximately 1 M.

[0197] <Experimental Example> Experimental example 1: Monocell life performance results The secondary batteries including the negative electrodes prepared in the examples and comparative examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate their capacity retention. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V, 1 C / 0.5 C, and a 0.33 C / 0.33 C charge / discharge (4.2-3.0 V) every 50 cycles, and the capacity retention was measured.

[0198] Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} x 100

[0199] [Table 4]

[0200] As can be seen in Table 4, when the capacity retention rates of Examples 1 to 6 in which the present invention was applied and Comparative Examples 1 to 6 in which the present invention was applied were examined with respect to the cycles, it was confirmed that the capacity retention rate of the Comparative Examples to which the present invention was not applied was lower than that of the Examples. This corresponds to the result that when the crystal grain size of the silicon-based active material satisfies the range according to the present invention, the lithium insertion and deintercalation reactions during charge and discharge can be uniformly reacted, the stress on the silicon-based active material can be reduced, and particle cracking can be alleviated, thereby improving the lifespan retention rate of the electrode.

[0201] Experimental example 2: Monocell resistance change In Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test, and then the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0202] For the measurement and evaluation of the resistance increase rate, data was calculated at 200 cycles, and the results are shown in Table 5 below.

[0203] [Table 5]

[0204] Tables 4 and 5 confirm that the lifespan characteristics and resistance change of batteries using the silicon prepared in Examples 1 to 6 as anode active materials were excellent. In the case of the anode active material according to one embodiment of the present invention, unlike conventional pulverization-based processing methods, a rapid cooling process is performed prior to MG-Si pulverization to form a plate-shaped silicon precursor, and the crystal grain size is optimized by controlling the cooling rate. As in the examples, by pulverizing the plate-shaped silicon precursor having nano-sized crystal grains, a silicon-based active material with nano-sized crystal grains and a specific high-angle boundary ratio can be obtained. When anodes are manufactured using this, it was confirmed that the cycle capacity retention rate and initial capacity efficiency are increased.

[0205] For reference, Comparative Examples 1 to 3 correspond to cases where the particle size (Equation 1) of the silicon-based active material is the same as the crystal grain size (Equation 2), i.e., where there are no grain boundaries within the particles of the silicon-based active material in a single crystal form, and no high-angle boundaries are present. Comparative Examples 4 to 6 correspond to cases where the value of Equation 1 is greater than the value of Equation 2, where there are grain boundaries within the particles, but the high-angle boundary ratio does not fall within the range of the present application. Examples 1 to 6 of the present application were prepared using the above-described preparation method, and high-angle grain boundaries (HAGBs) with high grain boundary energy were formed at the ratios shown in Table 3. It was confirmed that high-angle boundaries facilitate lithium ion diffusion compared to low-angle grain boundaries (LAGBs), resulting in superior life characteristics and resistance increase rates compared to the comparative examples.

[0206] Although the present invention has been described above with reference to the preferred embodiments, it should be understood that those skilled in the art or those having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as defined in the claims. Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be defined by the claims. [Explanation of symbols]

[0207] 1. Silicon-based active materials 2. Silicon-based crystal grains 3...grain boundary 4...misorientation angle 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode active material containing a silicon-based active material, the silicon-based active material contains silicon-based crystal grains, The high angle grain boundary ratio within the silicon-based crystal grains is 30% or more, The silicon-based active material is a negative electrode active material having a chemical structure satisfying the following formulas 1 and 2: [Formula 1] 1 μm≦particle size (D50) of silicon-based active material≦10 μm [Formula 2] 2 nm≦size of crystal grains of silicon-based active material≦1 μm.

2. The silicon-based active material includes a pulverized silicon precursor, 2. The negative electrode active material of claim 1, wherein the silicon precursor has a chemical structure satisfying the following formulas 3 and 4: [Equation 3] 10 μm≦silicon precursor plate thickness≦2 mm [Equation 4] 2 nm≦size of crystal grains in the silicon precursor≦1 μm.

3. The negative electrode active material of claim 1 , wherein the silicon-based crystalline grains have an average grain boundary misorientation angle of 5° or more.

4. The silicon-based active material is SiO ｘ (x=0) and SiO ｘ (0<x<2), and based on 100 parts by weight of the silicon-based active material, ｘ The negative electrode active material according to claim 1 , comprising 70 parts by weight or more of (x=0).

5. A silicon-based precursor comprising a chemical structure satisfying the following formulas 3 and 4: [Equation 3] 10 μm≦silicon precursor plate thickness≦2 mm [Equation 4] 2 nm≦size of crystal grains in the silicon precursor≦1 μm.

6. performing a rapid cooling process on the metallic silicon to form a silicon precursor; and grinding the silicon precursor to form a silicon-based active material; A method for producing a negative electrode active material, comprising: The method for producing a negative electrode active material, wherein the rapid cooling step is performed by any one of melt spinning, suction casting, and injection casting.

7. Before the step of rapidly cooling the metallurgical silicon, The method of claim 6 , further comprising heating the metal silicon in an induction furnace.

8. After the step of rapidly cooling the metallurgical silicon to form a silicon precursor, The method for producing a negative electrode active material according to claim 6, wherein the silicon precursor has a chemical structure satisfying the following formulas 3 and 4: [Equation 3] 10 μm≦silicon precursor plate thickness≦2 mm [Equation 4] 2 nm≦size of crystal grains in the silicon precursor≦1 μm.

9. pulverizing the silicon precursor to form a silicon-based active material; and thereafter, The method for producing a negative electrode active material according to claim 6, wherein the silicon-based active material has a chemical structure satisfying the following formulas 1 and 2: [Formula 1] 1 μm≦particle size (D50) of silicon-based active material≦10 μm [Formula 2] 2 nm≦crystal grain size of silicon-based active material≦100 nm.

10. The negative electrode active material according to any one of claims 1 to 4; a negative electrode conductive material; and Negative electrode binder; 12. A negative electrode composition comprising:

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

12. The negative electrode composition according to claim 10 , wherein the negative electrode conductive material includes a sheet conductive material and a linear conductive material.

13. 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 for a lithium secondary battery, wherein the negative electrode active material layer comprises the negative electrode composition according to claim 10 or a cured product thereof.

14. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 14. The negative electrode for a lithium secondary battery according to claim 13, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

15. positive electrode; The negative electrode for a lithium secondary battery according to claim 13 ; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

16. producing molten metallurgical silicon; performing a rapid cooling process on the molten metallurgical silicon to form a plate-shaped metallurgical silicon precursor; determining whether the thickness of the formed metallurgical silicon precursor plate is 10 μm or more and 2 mm or less, and whether the size of the crystal grains in the metallurgical silicon precursor is 2 nm or more and 1 μm or less; pulverizing the metallurgical silicon precursor to prepare a silicon-based active material when the plate thickness and crystal grain size of the metallurgical silicon precursor are determined to be 10 μm to 2 mm and 2 nm to 1 μm, respectively; Determining whether the particle size (D50) of the silicon-based active material is 1 μm or more and 10 μm or less, and whether the crystal grain size of the silicon-based active material is 2 nm or more and 1 μm or less; and classifying the silicon-based active material as an active material for manufacturing a negative electrode of a lithium secondary battery when the particle size (D50) and crystal grain size of the silicon-based active material are 1 μm to 10 μm and 2 nm to 1 μm, respectively; A method for producing a negative electrode active material, comprising:

17. The method of claim 16, wherein the rapid cooling step is performed by any one of melt spinning, suction casting, and injection casting.

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