Negative electrode active material, method for manufacturing negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery comprising same, and lithium secondary battery comprising negative electrode

Abstract

The present application relates to a negative electrode active material, a method for preparing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery comprising the same, and a lithium secondary battery comprising the negative electrode, the negative electrode active material comprising a silicon-based active material which is a mixture of silicon-based particles and a binder, wherein the grain size of the silicon-based particles is 100 nm or less, the particle size (D50) of the silicon-based active material is 1-20 [mu] m, and the content of the binder is 1-15 parts by weight with respect to 100 parts by weight of the silicon-based active material.

Description

Technical Field

[0001] This application claims the priority and benefit of Korean Patent Application No. 10-2023-0091763, filed with the Korean Intellectual Property Office on July 14, 2023, the entire contents of which are incorporated herein by reference.

[0002] This application relates to a negative electrode active material, a method of manufacturing the 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 Art

[0003] Due to the rapid growth in the use of fossil fuels, there is an increasing demand for the use of alternative or clean energy. As part of this trend, the most actively studied area is the field of power generation and power storage using electrochemical reactions.

[0004] Currently, secondary batteries are representative examples of electrochemical devices that utilize this electrochemical energy, and their range of use tends to gradually expand.

[0005] With the increase in the development of mobile devices and demand, the demand for secondary batteries as an energy source has grown rapidly. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used. In addition, as an electrode for such high-capacity lithium secondary batteries, a method of manufacturing a high-density electrode having a higher energy density per unit volume is being actively studied.

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for inserting and extracting lithium ions from the positive electrode, and as the negative electrode active material, silicon-based particles having a high discharge capacity can be used.

[0007] In particular, according to the recent demand for high-density energy batteries, a method of increasing the capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity more than 10 times that of a graphite-based material, as a negative electrode active material is being actively studied. However, compared with the commonly used graphite, the silicon-based compounds as high-capacity materials have a large capacity, but undergo rapid volume expansion during charging, thereby disconnecting the conduction path and reducing the battery characteristics.

[0008] Therefore, in order to solve the problems that occur when a silicon-based compound is used as a negative electrode active material, the following have been discussed: methods for suppressing volume expansion itself, such as methods for controlling the driving potential, methods for further coating a film on the active material layer, and methods for controlling the particle size of the silicon-based compound; or various methods for preventing the disconnection of the conduction path. However, the above methods may instead reduce the battery performance, so their applications are limited. Therefore, there are still limitations in the commercialization of manufacturing a battery including a negative electrode having a high content of a silicon-based compound.

[0009] In addition, as a result of research on the above problems, it has been found that the smaller the grain size of the silicon-based active material, the higher the life performance. However, as the grain size of the silicon-based active material is reduced to improve the life performance, problems such as a deteriorated coating state on the electrode and a reduced electrode adhesion force occur, resulting in problems such as detachment from the negative electrode current collector during the evaluation of the battery life performance.

[0010] Therefore, it is necessary to research methods that can solve the above problems when using a silicon-based active material as a negative electrode active material to improve the capacity performance.

[0011] Prior art documents

[0012] Patent documents

[0013] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention

[0014] Technical problem

[0015] As a result of research on methods that can improve the life performance of a negative electrode including a silicon-based active material, it has been found that when the nano-sized silicon-based particles used in the prior art are mixed with a binder to form secondary particles, the binder acts as a buffer and reduces the particle pulverization phenomenon.

[0016] Therefore, the present application relates to a negative electrode active material, a method for manufacturing 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, which can solve the above problems.

[0017] Technical solution

[0018] An exemplary embodiment of the present specification provides a negative electrode active material including: a silicon-based active material, wherein the silicon-based active material is a mixture of silicon-based particles and a binder, the grain size of the silicon-based particles is 100 nm or less, the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and the content of the binder is 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the silicon-based active material.

[0019] Another exemplary embodiment provides a method for manufacturing a negative electrode active material, the method comprising: preparing a silicon raw material; pulverizing the silicon raw material to form silicon-based particles; and mixing the silicon-based particles with a solvent and a binder to form a silicon-based active material, wherein the crystal grain size of the silicon-based particles is 100 nm or less, the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and the content of the binder is 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the silicon-based active material.

[0020] Another exemplary embodiment provides a negative electrode composition comprising: a negative electrode active material according to the present application; a negative electrode conductive material; and a negative electrode binder.

[0021] Another exemplary 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 surface or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer contains the negative electrode composition according to the present application or a cured product thereof.

[0022] Finally, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0023] Advantageous Effects

[0024] The negative electrode active material according to an exemplary embodiment of the present invention comprises a spherical silicon-based active material having a micron-sized particle size formed by mixing nano-sized silicon-based particles with a binder.

[0025] That is, the silicon-based active material is a mixture of silicon-based particles and a binder, wherein the crystal grain size of the silicon-based particles is 100 nm or less, and the particle size (D50) of the silicon-based active material is in the range of 1 μm or more and 20 μm or less, thereby solving problems related to life performance and facilitating electrode manufacturing.

[0026] In addition, the content of the binder constituting the secondary particles (a mixture of silicon-based particles and a binder) is 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the silicon-based active material, thereby acting as a buffer within the silicon-based active material and further reducing the particle pulverization phenomenon compared to micron-sized polycrystalline particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a view showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application.

[0028] Figure 2It is a view showing the stacked structure of a lithium secondary battery according to an exemplary embodiment of the present application.

[0029] <Description of Reference Numerals and Symbols>

[0030] 10: Negative electrode current collector layer

[0031] 20: Negative electrode active material layer

[0032] 30: Separator

[0033] 40: Positive electrode active material layer

[0034] 50: Positive electrode current collector layer

[0035] 100: Negative electrode for lithium secondary battery

[0036] 200: Positive electrode for lithium secondary battery Detailed Description of the Invention

[0037] Before describing the present invention, some terms are first defined.

[0038] In this specification, unless otherwise specifically stated, when a part "includes", "contains", or "has" a constituent element, this does not mean excluding another constituent element, but means that another constituent element can also be included.

[0039] In this specification, "p to q" means a range of "p or more and q or less".

[0040] In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen adsorption amount at the liquid nitrogen temperature (77 K) using the BELSORP-mini II available from BEL Japan Inc. That is, in the present application, the BET specific surface area may refer to the specific surface area measured by the above measurement method.

[0041] In this specification, "Dn" refers to the particle size distribution and is the particle size at the n% point in the cumulative particle number distribution according to the particle diameter. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to the particle diameter, D90 is the particle size at the 90% point in the cumulative particle number distribution according to the particle diameter, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to the particle diameter. On the other hand, the average particle size can be measured by the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device (such as Microtrac S3500), where the diffraction pattern is measured according to the difference in particle size when the laser beam passes through the particles, and then the particle size distribution is calculated.

[0042] In an exemplary embodiment of the present application, the particle size or grain size may refer to the average diameter or representative diameter of each crystal grain constituting the metal powder.

[0043] In this specification, the description that "a polymer contains a certain monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included in the polymer as a repeating unit. In this specification, when a polymer contains a monomer, this should be interpreted as the same as when the polymer contains the monomer as a monomer unit.

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

[0045] 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) while using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization for measuring molecular weights as standard materials. In this specification, unless otherwise specifically stated, the molecular weight refers to the weight-average molecular weight.

[0046] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0047] An exemplary embodiment of this specification provides a negative electrode active material including a silicon-based active material, wherein the silicon-based active material is a mixture of silicon-based particles and a binder, the crystal grain size of the silicon-based particles is 100 nm or less, the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and with respect to 100 parts by weight of the silicon-based active material, the content of the binder is 1 part by weight or more and 15 parts by weight or less.

[0048] In an exemplary embodiment of the present application, the silicon-based active material contains a binder. Therefore, for example, when nano-sized silicon-based particles are mixed with a binder and compounded into the form of secondary particles, compared with the case where the silicon-based active material does not contain a binder and is not compounded, volume expansion can be effectively controlled, so that a higher content of the negative electrode active material can be included. In addition, the binder acts as a buffer, thereby reducing the particle pulverization phenomenon, which is also effective in increasing the content of the Si active material in the electrode.

[0049] The negative electrode active material according to an exemplary embodiment of the present invention includes a spherical silicon-based active material having a micron-sized particle size formed by mixing nano-sized silicon-based particles with a binder. That is, the silicon-based active material is a mixture of silicon-based particles and a binder, wherein the grain size of the silicon-based particles is 100 nm or less, and the particle size (D50) of the silicon-based active material is in the range of 1 μm or more and 20 μm or less, thereby solving problems related to life performance and facilitating electrode manufacturing.

[0050] In an exemplary embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC.

[0051] In an exemplary embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and the content of SiOx (x = 0) may be 70 parts by weight or more with respect to 100 parts by weight of the silicon-based active material.

[0052] In an exemplary embodiment of the present application, the silicon-based active material may include SiOx (x = 0), and the content of SiOx (x = 0) may be 70 parts by weight or more with respect to 100 parts by weight of the silicon-based active material.

[0053] In an exemplary embodiment of the present application, the silicon-based active material may further include SiOx (0 < x < 2).

[0054] In another exemplary embodiment, the content of SiOx (x = 0) may be 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less with respect to 100 parts by weight of the silicon-based active material.

[0055] In an exemplary embodiment of the present application, pure silicon (Si) particles may be particularly used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material may mean that pure Si particles (SiOx (x = 0)) not combined with other particles or elements are included within the above range with respect to 100 parts by weight of all the silicon-based active materials as described above.

[0056] In an exemplary embodiment of the present application, the silicon-based active material may be formed of silicon-based particles having 100 parts by weight of SiOx (x = 0) with respect to 100 parts by weight of the silicon-based active material.

[0057] In an exemplary embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities are metals that can generally be contained in the silicon-based active material. Specifically, relative to 100 parts by weight of the silicon-based active material, the content may be 0.1 part by weight or less.

[0058] It should be noted that in an exemplary embodiment of the present application, the particle size of the silicon-based active material, i.e., the average particle diameter (D50), may be 1 μm or more and 20 μm or less, 5 μm to 10 μm, specifically 5 μm to 8 μm, and more specifically 5 μm to 7 μm. If the average particle diameter is less than 5 μm, the specific surface area of the particles increases excessively, resulting in an excessive increase in the viscosity of the negative electrode slurry. Therefore, the particles constituting the negative electrode slurry cannot be smoothly dispersed. In addition, if the silicon-based active material is too small, the contact area between the silicon-based particles and the conductive material decreases due to the composite material composed of the conductive material and the binder in the negative electrode slurry, so the possibility of disconnecting the conductive network increases, thereby reducing the capacity retention rate. On the other hand, if the average particle diameter is greater than 10 μm, there are excessively large silicon-based particles, making the surface of the negative electrode uneven and resulting in uneven current density during charging and discharging. In addition, if the silicon-based particles are too large, the phase stability of the negative electrode slurry becomes unstable, leading to a decrease in processability. As a result, the capacity retention rate of the battery decreases.

[0059] In an exemplary embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of the silicon-based active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, and most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0060] In an exemplary embodiment of the present application, the silicon-based active material may exist, for example, in crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or fragmented particles. Alternatively but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0061] In an exemplary embodiment of the present application, the silicon-based active material may have a non-spherical shape, and its sphericity (circularity) is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0062] In the present application, the circularity is determined by Equation 1 below, where A is the area and P is the boundary line.

[0063] [Equation 1]

[0064] 4πA / P 2

[0065] The capacity of the silicon-based active material is significantly higher than that of the commonly used graphite-based active material, so more attempts have been made to apply it. However, the silicon-based active material has a high volume expansion rate during charging and discharging. Therefore, for example, only a small amount of it is mixed with the graphite-based active material for use.

[0066] Therefore, in the present invention, in order to improve the capacity performance, only the silicon-based active material is used as the negative electrode active material. At the same time, in order to solve the above problems, instead of controlling the composition of the conductive material and the binder, the silicon-based active material is made into the form of secondary particles, thereby solving the problems found in the prior art.

[0067] In an exemplary embodiment of the present application, the silicon-based active material is in the form of secondary particles as a mixture of silicon-based particles and a binder.

[0068] That is, the silicon-based active material contains silicon-based particles as primary particles and may be composed of secondary particles as a mixture of primary particles and a binder.

[0069] In an exemplary embodiment of the present application, the grain size of the silicon-based particles may be 100 nm or less.

[0070] In an exemplary embodiment of the present application, the grain size of the silicon-based particles may be 10 nm or more and 80 nm or less.

[0071] In another exemplary embodiment, the grain size of the silicon-based particles may be 100 nm or less, 95 nm or less, 90 nm or less, or 80 nm or less, and may be 1 nm or more, 5 nm or more, 7 nm or more, or 10 nm or more.

[0072] In another exemplary embodiment, the grain size of the silicon-based particles may be 10 nm or more and 80 nm or less.

[0073] The grain size of the silicon-based particles is within the above range, resulting in a wide distribution of grain boundaries. As a result, during lithium-ion insertion, lithium ions can be inserted uniformly, thereby reducing the stress applied during the insertion of lithium ions into the silicon particles. Correspondingly, particle cracking is alleviated. As a result, the characteristics that can improve the life stability of the negative electrode are obtained. If the grain size exceeds the above range, the distribution of grain boundaries within the particles is narrow. In this case, lithium ions are not inserted into the particles uniformly, resulting in a large stress during ion insertion, and correspondingly, particle cracking occurs.

[0074] In this application, a grain refers to a crystal particle in a metal or material, which is a collection of microscopic irregular shapes, and the grain size can refer to the diameter of the observed grain particles. That is, in this application, the grain size refers to the size of the domain with the same crystal orientation in the particle, and has a different concept from the particle size or particle diameter size representing the material size.

[0075] In an exemplary embodiment of this application, the grain size can be calculated as the value of the full width at half maximum (FWHM) through XRD analysis. Other values except L are measured through XRD analysis of the silicon-based active material, and the grain size can be measured through the Debye-Scherrer formula indicating that FWHM is inversely proportional to the grain size. The Debye-Scherrer formula is shown in Equation 1-1 below.

[0076] [Equation 1-1]

[0077] FWHM = Kλ / LCosθ

[0078] In Equation 1-1,

[0079] L is the grain size, K is a constant, θ is the Bragg angle, and λ refers to the wavelength of the X-ray.

[0080] In addition, the shapes of grains are various and can be measured three-dimensionally. Generally, the size of grains can be measured by the common circular method and diameter measurement method, but the present invention is not limited thereto.

[0081] In the diameter measurement method, the size of grains can be measured by drawing 5 to 10 parallel lines each with a length of L mm on the micrograph of the target particles, counting the number of grains z on each line and taking the average. In this case, only the grains completely contained within the line are counted, and the grains partially placed (straddling) on the line are excluded. When the number of lines is P and the magnification is V, the average particle diameter can be calculated by Equation 1-2 below.

[0082] [Equation 1-2]

[0083] Dm = (L×P×10 3 ) / (zV) (µm)

[0084] The circular method is a method in which a circle with a predetermined diameter is drawn on a micrograph of a target particle, and then the average area of the crystal grains is calculated by the number of crystal grains within the circle and the number of crystal grains straddling the boundary line, and the average area can be calculated by Formula 1-3 below.

[0085] [Formula 1-3]

[0086] Fm = (Fk×10 6 ) / ((0.67n + z) V 2 ) (µm 2 )

[0087] In Formula 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles within the circle, n is the number of particles straddling the circle, and V is the magnification of the microscope.

[0088] In an exemplary embodiment of the present application, the negative electrode active material is provided, wherein the silicon-based particles are single-crystalline silicon-based particles or polycrystalline silicon-based particles.

[0089] In an exemplary embodiment of the present application, the silicon-based particles may be single-crystalline silicon-based particles.

[0090] In an exemplary embodiment of the present application, the silicon particles may be polycrystalline silicon-based particles.

[0091] In an exemplary embodiment of the present application, the silicon-based active material is in the form of secondary particles as a mixture of silicon-based particles and a binder. In this case, the binder serves to form secondary particles by mixing the silicon-based particles as primary particles with each other.

[0092] In an exemplary embodiment of the present application, the negative electrode active material is provided, wherein the binder is a binder having a linear structure.

[0093] In an exemplary embodiment of the present application, the negative electrode active material is provided, wherein the binder contains an aqueous binder, and the aqueous binder contains one or more selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0094] In an exemplary embodiment of the present application, relative to 100 parts by weight of the silicon-based active material, the content of the binder may be 1 part by weight or more and 15 parts by weight or less.

[0095] In another exemplary embodiment, based on 100 parts by weight of the silicon-based active material, the content of the binder may be 1 part by weight or more and 15 parts by weight or less, preferably 3 parts by weight or more and 15 parts by weight or less, and more preferably 5 parts by weight or more and 15 parts by weight or less.

[0096] The binder satisfies the above range. However, if the content of the binder exceeds the range, the capacity and life performance of the battery may decrease. If the content is below the range, the binder may not be suitable for acting as a buffer, resulting in a decrease in life performance due to particle pulverization.

[0097] In particular, based on 100 parts by weight of the silicon-based active material, if the content of the binder exceeds 15 parts by weight, for example, if the binder contained in the silicon-based active material exceeds the above range, the binder itself becomes a resistor, resulting in a decrease in efficiency characteristics and a reduction in energy density and capacity characteristics.

[0098] The binder according to an exemplary embodiment of the present application has a different composition from the negative electrode binder described later.

[0099] An exemplary embodiment of the present application provides a method for manufacturing a negative electrode active material, the method including the steps of: preparing a silicon raw material; pulverizing the silicon raw material to form silicon-based particles; and mixing the silicon-based particles with a solvent and a binder to form a silicon-based active material, wherein the grain size of the silicon-based particles is 100 nm or less, the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and based on 100 parts by weight of the silicon-based active material, the content of the binder is 1 part by weight or more and 15 parts by weight or less.

[0100] In the manufacturing method, each composition and content are the same as above.

[0101] In the present application, the method for manufacturing the negative electrode active material is provided, and further includes a step of drying the mixture after mixing the silicon-based particles with the solvent and the binder.

[0102] In the present application, in the step of mixing the silicon-based particles with the solvent and the binder to form a silicon-based active material, the mixing rpm may be 2000 rpm or more and 3000 rpm or less.

[0103] In the present application, the silicon raw material may be a raw material used in the art for manufacturing a silicon active material, and may include silicon blocks, MG-Si, etc.

[0104] In an exemplary embodiment of the present application, a negative electrode composition is provided, which includes the above-mentioned negative electrode active material, negative electrode conductive material, and negative electrode binder.

[0105] In an exemplary embodiment of the present application, the negative electrode composition is provided, wherein, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode active material is 40 parts by weight or more.

[0106] In another exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode active material can be 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, further preferably 70 parts by weight or more, and can be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0107] The negative electrode composition according to the present application uses a negative electrode active material with a specific surface area size that can control the volume expansion rate during charging and discharging even when using a negative electrode active material with a significantly high capacity within the above range. Therefore, even when the negative electrode active material is within the above range, the negative electrode composition will not reduce the performance of the negative electrode and has excellent output characteristics during charging and discharging.

[0108] In the prior art, generally only graphite-based compounds are used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, in order to increase the capacity, attempts to mix and use silicon-based active materials have also increased. However, in the case of silicon-based active materials, even when adjusting the characteristics of the silicon-based active material itself as described above, the volume may rapidly expand during charging and discharging, causing some problems such as damaging the conduction path formed in the negative electrode active material layer.

[0109] Therefore, in an exemplary embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-shaped conductive materials, planar conductive materials, and linear conductive materials.

[0110] In an exemplary embodiment of the present application, the dot-shaped conductive material refers to a dot-shaped or spherical conductive material that can be used to improve the conductivity of the negative electrode and has conductivity without causing chemical changes. Specifically, the dot-shaped conductive material may be one or more selected from the group consisting of the following substances: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black in terms of high conductivity and excellent dispersibility.

[0111] In an exemplary 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.

[0112] In an exemplary embodiment of the present application, the content of the functional groups (volatile substances) of the dot-shaped conductive material may satisfy the range of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0113] In particular, when the content of the functional groups of the dot-shaped conductive material satisfies the above range, the functional groups are present on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, due to the use of a specific silicon-based active material, the content of the functional groups of the dot-shaped conductive material can be reduced, which shows excellent effects in improving dispersibility.

[0114] In an exemplary embodiment of the present application, on the basis of including the silicon-based active material, the dot-shaped conductive material with the functional group content within the above range is further included, and the content of the functional groups can be adjusted according to the heat treatment degree of the dot-shaped conductive material.

[0115] In an exemplary embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0116] In an exemplary embodiment of the present application, the conductive material may include a planar conductive material.

[0117] The planar conductive material improves the conductivity by increasing the surface contact between the silicon-based particles in the negative electrode, and can be used to suppress the disconnection of the conduction path caused by volume expansion. The planar conductive material may be represented as a plate-shaped conductive material or a block-shaped conductive material.

[0118] In an exemplary embodiment of the present application, the planar conductive material may include one or more selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0119] In an exemplary embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 3.5 μm to 5 μm. When the above range is satisfied, sufficient particle size results in easy dispersion and does not cause an excessive increase in the viscosity of the negative electrode paste. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0120] In an exemplary embodiment of the present application, the negative electrode composition is provided, wherein D10 of the sheet-like conductive material is 0.5 μm or more and 2.0 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 6.5 μm or more and 15.0 μm or less.

[0121] In an exemplary embodiment of the present application, for the sheet-like conductive material, a high specific surface area sheet-like conductive material or a low specific surface area sheet-like conductive material having a high BET specific surface area may be used.

[0122] In an exemplary embodiment of the present application, a high specific surface area sheet-like conductive material or a low specific surface area sheet-like conductive material may be used for the sheet-like conductive material without limitation. However, particularly, the sheet-like conductive material according to the present application can affect the electrode performance to a certain extent due to the dispersion effect. Therefore, it is particularly preferred to use a low specific surface area sheet-like conductive material that does not cause dispersion problems.

[0123] In an exemplary embodiment of the present application, the BET specific surface area of the sheet-like conductive material may be 0.25 m 2 / g or more.

[0124] In another exemplary embodiment, the BET specific surface area of the sheet-like conductive material may be 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0125] For the sheet-like conductive material of the present application, a high specific surface area sheet-like conductive material or a low specific surface area sheet-like conductive material may be used.

[0126] In another exemplary embodiment, the sheet-like conductive material is a high specific surface area sheet-like conductive material, and the BET specific surface area may satisfy 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m2 above / g and 300 m 2 below / g, more preferably 100 m 2 above / g and 300 m 2 below / g.

[0127] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area can satisfy 1 m 2 above / g and 40 m 2 below / g, preferably 5 m 2 above / g and 30 m 2 below / g, more preferably 5 m 2 above / g and 25 m 2 below / g.

[0128] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a secondary shape of a bundle or rope in which a plurality of carbon nanotube units are arranged side by side or entangled in an orientation where the longitudinal axes of the carbon nanotube units are substantially the same. The carbon nanotube unit has a cylindrical graphite sheet with a nanoscale diameter and has a sp 2 bonding structure. In this case, depending on the rolling angle and structure of the graphite sheet, it can exhibit the characteristics of a conductor or a semiconductor. Compared with entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during the manufacture of the negative electrode and can more smoothly form a conductive network in the negative electrode, thereby improving the conductivity of the negative electrode.

[0129] In an exemplary embodiment of the present application, there is provided the negative electrode composition, wherein, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less.

[0130] In another exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the content of 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.

[0131] In an exemplary embodiment of the present application, there is provided the negative electrode composition, wherein the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0132] In an exemplary embodiment of the present application, the negative electrode composition is provided, wherein, based on 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material includes 80 parts by weight or more and 99.9 parts by weight or less of the planar conductive material and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0133] In another exemplary embodiment, based on 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may include 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 98 parts by weight or less of the planar conductive material.

[0134] In another exemplary embodiment, based on 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may include 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 15 parts by weight or less, more preferably 0.2 parts by weight or more and 5 parts by weight or less of the linear conductive material.

[0135] In an exemplary embodiment of the present application, the negative electrode conductive material includes the planar conductive material and the linear conductive material and satisfies the above compositions and ratios respectively, so that the life characteristics of the existing lithium secondary battery are not significantly affected. In particular, when the planar conductive material and the linear conductive material are included, the number of charge and discharge cycles increases, so that the output characteristics at a high C rate are excellent, and the amount of gas generated at high temperature is reduced.

[0136] In an exemplary embodiment of the present application, the negative electrode conductive material may be composed of a linear conductive material.

[0137] In particular, when the linear conductive material is used alone, the electrode tortuosity (which is a problem of the silicon-based negative electrode) can be simplified, so that the electrode structure can be improved, and correspondingly, the movement resistance of lithium ions in the electrode is reduced.

[0138] In an exemplary embodiment of the present application, when the negative electrode conductive material solely includes a linear conductive material, based on 100 parts by weight of the negative electrode composition, the content of the linear conductive material may be 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, more preferably 0.4 parts by weight or more and 1 part by weight or less.

[0139] The negative electrode conductive material according to the present application has a structure completely different from that of the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application is used to maintain the contact between silicon-based active materials with a very large volume expansion of the electrode due to charging and discharging, while the positive electrode conductive material is used to impart a certain conductivity and act as a buffer during rolling, and is completely different from the negative electrode conductive material of the present invention in terms of structure and function.

[0140] In addition, the negative electrode conductive material according to the present application is applied to silicon-based active materials and has a structure completely different from that of the conductive material applied to graphite-based active materials. That is, since the conductive material for an electrode having a graphite-based active material only has particles smaller than the active material, the conductive material has the characteristics of improving output characteristics and imparting a certain conductivity, and is completely different from the negative electrode conductive material applied with silicon-based active materials in the present invention in terms of structure and function.

[0141] In an exemplary embodiment of the present application, the planar conductive material used as the above-mentioned negative electrode conductive material has a different structure and function from the carbon-based active material usually used as the 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 processed into a spherical or dot shape and used to facilitate the storage and release of lithium ions.

[0142] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate shape, and can be represented as plate graphite. That is, the planar conductive material is a material included in the negative electrode active material layer to maintain a conductive path, and refers to a material used to fix the planar conductive path inside the negative electrode active material layer rather than acting in the storage and release of lithium.

[0143] That is, in the present application, using plate graphite as the conductive material means processing graphite into a planar or plate shape and using it as a material for fixing the conductive path rather than acting in the storage or release of lithium. In this case, the included negative electrode active material has a high-capacity characteristic in terms of the storage and release of lithium and acts to store and release all lithium ions transferred from the positive electrode.

[0144] On the other hand, in the present application, using a carbon-based active material as the active material means processing the carbon-based active material into a dot or spherical shape and using it as a material for storing or releasing lithium.

[0145] That is, in an exemplary embodiment of the present application, artificial graphite or natural graphite as the carbon-based active material has a dot shape, and its BET specific surface area can satisfy 0.1 m 2 / g or more and 4.5 m 2in the range below / g. In addition, the plate-shaped graphite as the planar conductive material has a planar shape, and its BET specific surface area can be 5 m 2 / g or more.

[0146] In an exemplary 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, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0147] The negative electrode binder according to an exemplary embodiment of the present application is used to hold the active material and the conductive material so as to prevent distortion and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. When such functions are satisfied, all conventional binders can be applied. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0148] In an exemplary embodiment of the present application, relative to 100 parts by weight of the negative electrode composition, the content of 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, and may be 5 parts by weight or more and 10 parts by weight or more.

[0149] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, including: a negative electrode current collector layer; and a negative electrode active material layer formed on one surface or both surfaces of the negative electrode current collector layer and containing the negative electrode composition according to the present application or its cured product.

[0150] Figure 1 is a view showing the stacked structure of the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, it can be seen that the negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10. Figure 1 It shows that the negative electrode active material layer is formed on one surface of the negative electrode current collector layer, but the negative electrode active material layer can also be formed on both surfaces of the negative electrode current collector layer.

[0151] In an exemplary embodiment of the present application, the negative electrode for the lithium secondary battery can be formed by applying a negative electrode paste containing the negative electrode composition to one surface or both surfaces of the negative electrode current collector layer and drying it.

[0152] In this case, the negative electrode paste may contain the above-mentioned negative electrode composition and a paste solvent.

[0153] In an exemplary embodiment of the present application, the solid content of the negative electrode paste may satisfy the range of 5% or more and 40% or less.

[0154] In another exemplary embodiment, the solid content of the negative electrode paste may satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0155] The solid content of the negative electrode paste may refer to the content of the negative electrode composition contained in the negative electrode paste, and may refer to the content of the negative electrode composition relative to 100 parts by weight of the negative electrode paste.

[0156] When the solid content of the negative electrode paste satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the aggregation of the particles of the negative electrode composition, and thus effectively forming the negative electrode active material layer.

[0157] In an exemplary embodiment of the present application, the paste solvent can be used without limitation as long as it can dissolve the negative electrode composition. Specifically, water or NMP can be used.

[0158] In an exemplary embodiment of the present application, the thickness of the negative electrode current collector layer is generally 1 μm to 100 μm. There is no particular limitation on such a negative electrode current collector layer as long as it has high electrical conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector layer may have fine concavities and convexities formed on the surface to enhance the binding force of the negative electrode active material, and can be used in various forms, such as a film, sheet, foil, net, porous body, foam body, or non-woven fabric body.

[0159] In an exemplary embodiment of the present application, there is provided the negative electrode for the lithium secondary battery, 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.

[0160] However, the thickness can be variously modified depending on the type and use of the negative electrode used, and is not limited thereto.

[0161] In an exemplary embodiment of the present application, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less.

[0162] In another exemplary embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0163] 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. In particular, when the silicon-based active material and conductive material according to the present application are contained in a specific composition and content, the above range is satisfied, so that the electrode has conductivity and resistance within an appropriate range.

[0164] An exemplary embodiment of the present application provides a lithium secondary battery, comprising: 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.

[0165] Figure 2 It is a view showing a stacked structure of a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, it can be seen that the negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10, it can be seen that the positive electrode 200 for a lithium secondary battery includes a positive electrode active material layer 40 on one surface of the positive electrode current collector layer 50, and the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separator 30 interposed therebetween.

[0166] A secondary battery according to an exemplary embodiment of the present specification may particularly include the above-described negative electrode for a lithium secondary battery. 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, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, its detailed description will be omitted.

[0167] 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 a positive electrode active material.

[0168] In the positive electrode, there is no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector can generally be 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies.

[0169] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) or a compound substituted by one or more transition metals; lithium iron oxide such as LiFe3O4; lithium manganese oxide such as the chemical formula Li 1+c1 Mn 2-c1 O4(0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide such as LiV3O8, V2O5, and Cu2V2O7; Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-c2 M c2 O2 (where 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); lithium manganese composite oxide represented by the chemical formula LiMn 2-c3 M c3 O2 (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); LiMn2O4 in which a part of Li in the chemical formula is replaced by an alkaline earth metal ion, etc., but not limited thereto. The positive electrode can be Li metal.

[0170] On the basis of containing the above positive electrode active material, the positive electrode active material layer can further contain a positive electrode conductive material and a positive electrode binder.

[0171] 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 the positive electrode conductive material has electronic conductivity and does not cause chemical changes in the battery to be constructed. Specific examples may 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 cracking carbon 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, etc., and any one of them or a mixture of two or more of them can be used.

[0172] In addition, the positive electrode binder is used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc., and any one of them or a mixture of two or more of them can be used.

[0173] The separator is used to separate the negative electrode and the positive electrode and provide a migration path for lithium ions. Any separator can be used as the separator without particular limitation as long as it is commonly used in secondary batteries. In particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to the migration of electrolyte ions can be preferably used. Specifically, a porous polymer membrane can be used, such as a porous polymer membrane made of polyolefin - based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer; or having a laminated structure of two or more layers thereof. In addition, typical porous non - woven fabrics can be used, such as non - woven fabrics formed of high - melting - point glass fibers, polyethylene terephthalate fibers, etc. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single - layer or multi - layer structure can be selectively used.

[0174] Examples of the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel - type polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0175] Specifically, the electrolyte may contain a non - aqueous organic solvent and a metal salt.

[0176] As the non-aqueous organic solvent, an aprotic organic solvent such as N-methyl-2-pyrrolidone, 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate or ethyl propionate can be used.

[0177] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are high-viscosity organic solvents. Since they have a high dielectric constant, they can dissociate lithium salts well, so they can be preferably used. When the cyclic carbonate is mixed with a linear carbonate such as dimethyl carbonate and diethyl carbonate having a low viscosity and a low dielectric constant in an appropriate ratio and used, an electrolyte having a high conductivity can be prepared. Therefore, such a combined use can be more preferable.

[0178] A lithium salt can be used as the metal salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. As the anion of the lithium salt, for example, one or more species selected from the group consisting of the following anions can be used: 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 - .

[0179] For the purposes of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc., in addition to the above electrolyte components, the electrolyte may further contain one or more additives, such as haloalkyl carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, diglyme, hexamethylphosphoramide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0180] An exemplary embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the battery module. Since the battery module and the battery pack include secondary batteries having high capacity, high rate capability, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large-sized devices selected from the group consisting of: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0181] Preferred embodiments will be provided below to better understand the present invention. It will be apparent to those skilled in the art that the embodiments are provided only for the purpose of illustrating the present invention, and various modifications and variations are feasible within the scope and technical gist of the present invention. Such modifications and variations naturally also fall within the scope of the claims included herein.

[0182] Embodiments of the invention

[0183] <Preparation Example>

[0184] <Preparation of silicon-based active material>

[0185] <Example 1>

[0186] MG-Si was pulverized to form primary silicon-based particles in the form of single crystals or polycrystals with a particle size (grain size) of about 100 nm. Then, using water as a solvent, the primary silicon-based particles were mixed with PAA as a binder at a weight ratio of 9:1. Then, the obtained slurry was spray-dried to form particles, thereby preparing a silicon-based active material in the form of secondary particles with a D50 of 5 μm.

[0187] <Example 2>

[0188] The MG-Si is pulverized to form primary silicon-based particles in the form of single crystals or polycrystals with a particle size (grain size) of about 100 nm. Then, using water as a solvent, the primary silicon-based particles are mixed with PAM as a binder at a weight ratio of 9:1. Then, the obtained slurry is spray-dried to form particles, thereby preparing a silicon-based active material in the form of secondary particles with a D50 of 5 μm.

[0189] <Example 3>

[0190] The MG-Si is pulverized to form primary silicon-based particles in the form of single crystals or polycrystals with a particle size (grain size) of about 100 nm. Then, using water as a solvent, the primary silicon-based particles are mixed with PVP as a binder at a weight ratio of 9:1. Then, the obtained slurry is spray-dried to form particles, thereby preparing a silicon-based active material in the form of secondary particles with a D50 of 5 μm.

[0191] <Example 4>

[0192] The MG-Si is pulverized to form primary silicon-based particles in the form of single crystals or polycrystals with a particle size (grain size) of about 100 nm. Then, using water as a solvent, the primary silicon-based particles are mixed with PAA as a binder at a weight ratio of 10:1.5. Then, the obtained slurry is spray-dried to form particles, thereby preparing a silicon-based active material in the form of secondary particles with a D50 of 5 μm.

[0193] <Example 5>

[0194] The MG-Si is pulverized to form primary silicon-based particles in the form of single crystals or polycrystals with a particle size (grain size) of about 100 nm. Then, using water as a solvent, the primary silicon-based particles are mixed with PAA as a binder at a weight ratio of 10:0.5. Then, the obtained slurry is spray-dried to form particles, thereby preparing a silicon-based active material in the form of secondary particles with a D50 of 5 μm.

[0195] <Comparative Example 1>

[0196] The MG-Si is mechanically crushed using a jaw crusher or a roll crusher, and then pulverized using a jet mill that utilizes centrifugal force and particle collisions. Then, a classifier is used to control the particle size to obtain primary silicon-based particles in the form of single crystals or polycrystals with a size of about 5 μm.

[0197] <Comparative Example 2>

[0198] The silicon-based active material is obtained by chemically reacting silane gas to deposit it on a substrate. Then, a classifier is used to control the particle size to obtain silicon-based particles with a particle size of about 5 μm.

[0199] <Comparative Example 3>

[0200] The silicon-based active material was prepared in the same manner as in Example 1, except that in Example 1, water was used as a solvent, and the primary silicon-based particles and PAA as a binder were mixed at a weight ratio of 10:2.5.

[0201] <Comparative Example 4>

[0202] The silicon-based active material was prepared in the same manner as in Example 1, except that in Example 1, water was used as a solvent, and the primary silicon-based particles and PAA as a binder were mixed at a weight ratio of 10:0.2.

[0203] <Preparation of negative electrode>

[0204] A negative electrode paste (solid concentration: 25% by weight) was prepared by adding a negative electrode active material, a first conductive material, a second conductive material, and polyacrylamide as a binder, which included the silicon-based active materials of the examples and comparative examples, to distilled water used as a solvent for forming the negative electrode paste at a weight ratio of 80:9.6:0.4:10.

[0205] Specifically, the first conductive material was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0206] As a specific mixing method, after dispersing the first conductive material, the second conductive material, the binder, and water at 2500 rpm for 30 minutes using a homogenizer, the silicon-based active material was added to the dispersion liquid, and then dispersed at 2500 rpm for 30 minutes to prepare the negative electrode paste.

[0207] The negative electrode paste was coated on both surfaces of a copper current collector (thickness: 8 μm) used as a negative electrode current collector at a loading amount of 85 mg / 25 cm 2 , and then calendered and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (total thickness of the negative electrode active material layer: 33 μm), thereby preparing a negative electrode (thickness of the negative electrode: 41 μm, porosity of the negative electrode: 40.0%).

[0208] <Preparation of secondary battery>

[0209] By using LiNi 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black as a conductive material (product name: Super C65, manufacturer: Timcal), and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode paste in a weight ratio of 97:1.5:1.5 to prepare a positive electrode paste (solid concentration: 78 wt%).

[0210] The positive electrode paste was coated on both surfaces of an aluminum current collector (thickness: 12 μm) used as a positive electrode current collector at a loading amount of 537 mg / 25 cm 2 . Then, it was calendered and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (total thickness of the positive electrode active material layer: 65 μm), thereby preparing a positive electrode (thickness of the positive electrode: 77 μm, porosity: 26%).

[0211] A lithium secondary battery was manufactured by interposing a polyethylene separator between the positive electrode and the negative electrodes of the examples and comparative examples and injecting an electrolyte.

[0212] The electrolyte was obtained by the following steps: adding vinylene carbonate in an amount of 3 wt% relative to the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90, and adding LiPF6 as a lithium salt to a concentration of 1 M.

[0213] <Experimental Example>

[0214] Experimental Example 1: Results of single cell life performance

[0215] For secondary batteries containing the negative electrodes manufactured in the examples and comparative examples, an electrochemical charge-discharge device was used to evaluate the life and capacity retention rate. An in-situ cycle test was performed on the secondary battery at 4.2~3.0 V 1 C / 0.5 C, and during the test, charge / discharge at 0.33 C / 0.33 C (4.2~3.0 V) was performed every 50 cycles to measure the capacity retention rate, and the results are listed in Table 1.

[0216] Capacity retention rate (%) = {(discharge capacity in the Nth cycle) / (discharge capacity in the first cycle)} × 100%

[0217]

[0218] As can be seen in Table 1, it can be confirmed that the capacity retention rates of the negative electrodes according to Embodiments 1 to 5 of the present application are higher than those of the negative electrodes of Comparative Examples 1 to 4. In Embodiments 1 to 3, the type of binder was changed, and in Embodiments 4 and 5, the content of the binder was changed. In Comparative Examples 3 and 4 where the content of the binder exceeded the upper limit or was lower than the lower limit of the optimal range, it was confirmed that when the content of the binder exceeded the upper limit, the proportion of the active material decreased, resulting in a decrease in the capacity retention rate compared to the embodiments. When the content of the binder was lower than the lower limit, the proportion of the active material increased, but the number of fine particles increased, resulting in a decrease in the capacity retention rate. In addition, in Comparative Examples 1 and 2 using a single-particle silicon-based active material alone, it was confirmed that there was no material acting as a buffer in the silicon-based active material, resulting in no alleviation of the pulverization phenomenon and a decrease in the life performance.

[0219] Experimental Example 2: Change in single cell resistance

[0220] In the test of Experimental Example 1, the capacity retention rate was measured by charging / discharging the battery at 0.33 C / 0.33 C (4.2 - 3.0 V) every 50 cycles, and then the resistance increase rate was compared and analyzed by discharging the battery at a 2.5 C pulse at SOC50 to measure the resistance.

[0221] For the evaluation of the resistance increase rate measurement, the data at 200 cycles were calculated for each, and the results are shown in Table 2 below.

[0222]

[0223] Table 2 above shows the change in resistance. As in Table 1, there was no difference in resistance in Embodiments 1 to 3. When the content of the binder exceeded the upper limit, it was confirmed that the resistance increased due to the binder. In addition, it was confirmed that the resistance increase rate in Embodiments 1 to 5 was lower than that in the case where the content of the binder was lower than the lower limit or no binder was included. That is, through the above experiments, it can be confirmed that, with respect to 100 parts by weight of the silicon-based active material, the content of the binder constituting the secondary particles (a mixture of silicon-based particles and the binder) is 1 part by weight or more and 15 parts by weight or less, thereby acting as a buffer in the silicon-based active material, and further alleviating the particle pulverization phenomenon compared to micron-sized polycrystalline particles, thereby improving the life performance and resistance characteristics.

Claims

1. A negative electrode active material comprising a silicon-based active material, wherein the silicon-based active material is a mixture of silicon-based particles and a binder, wherein the grain size of the silicon-based particles is 100 nm or less, wherein the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and wherein, relative to 100 parts by weight of the silicon-based active material, the content of the binder is 1 part by weight or more and 15 parts by weight or less.

2. The negative electrode active material according to claim 1, wherein the silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and relative to 100 parts by weight of the silicon-based active material, the content of SiOx (x = 0) is 70 parts by weight or more.

3. The negative electrode active material according to claim 1, wherein the silicon-based particles are single-crystalline silicon-based particles or polycrystalline silicon-based particles.

4. The negative electrode active material according to claim 1, wherein the grain size of the silicon-based particles is 10 nm or more and 80 nm or less.

5. The negative electrode active material according to claim 1, wherein the binder is a binder having a linear structure.

6. The negative electrode active material according to claim 1, wherein the binder contains an aqueous binder, and wherein the aqueous binder contains one or more selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyacrylamide (PAM).

7. A method for manufacturing a negative electrode active material, the method comprising: preparing a silicon raw material; crushing the silicon raw material to form silicon-based particles; and mixing the silicon-based particles with a solvent and a binder to form a silicon-based active material, wherein the grain size of the silicon-based particles is 100 nm or less, wherein the particle size (D50) of the silicon-based active material is 1 μm or more and 20 μm or less, and wherein, relative to 100 parts by weight of the silicon-based active material, the content of the binder is 1 part by weight or more and 15 parts by weight or less.

8. The method according to claim 7, further comprising drying the mixture after mixing the silicon-based particles with the solvent and the binder.

9. The method according to claim 7, wherein in mixing the silicon-based particles with the solvent and the binder to form a silicon-based active material, the mixing rpm is 2000 rpm or more and 3000 rpm or less.

10. A negative electrode composition comprising: the negative electrode active material according to any one of claims 1 to 6; a negative electrode conductive material; and a negative electrode binder.

11. The negative electrode composition according to claim 10, wherein relative to 100 parts by weight of the negative electrode composition, the content of the negative electrode active material is 40 parts by weight or more.

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

13. 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 surface or both surfaces of the negative electrode current collector layer, The negative electrode active material layer contains the negative electrode composition according to claim 10 or a cured product thereof.

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

15. A lithium secondary battery, comprising: a 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 an electrolyte.

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