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

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.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0130500 filed with the Korean Intellectual Property Office on September 27, 2023, and Korean Patent Application No. 10-2024-0130793 filed with the Korean Intellectual Property Office on September 26, 2024, 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 areas as part of this is the field of power generation and storage using electrochemical reactions.

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

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these 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 contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, active research is being conducted into methods of increasing capacity by using silicon-based compounds such as Si / C and SiOx as anode active materials, which have capacities more than 10 times larger than graphite-based materials. However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite, they suffer from the problem of rapid volume expansion during charging, which breaks the conductive path and reduces battery performance.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as anode active materials, various methods have been discussed, such as methods for controlling the driving potential, methods for additionally coating a thin film on the active material layer, methods for suppressing the volume expansion itself, such as methods for controlling the particle size of the silicon-based compound, or methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade the performance of the battery, and there are still limitations in the commercialization of anode batteries with a high content of silicon-based compounds.

[0009] In recent years, when using silicon-based active materials, adjusting the porosity to a high level within a certain range has been used to alleviate stress caused by particle expansion / contraction that occurs in response to lithium insertion / extraction during charge / discharge, preventing cracking of the silicon-based active material and providing Li-ion passages that facilitate the penetration of electrolyte into the active material, thereby improving life performance. However, with silicon-based active materials with adjusted porosity, as cycling continues, an SEI side reaction layer accumulates on the surface, blocking the particle pores, resulting in a rapid decrease in life performance as certain cycles progress.

[0010] Therefore, even when a silicon-based active material is used as a negative electrode active material to improve capacity performance, research is needed into silicon-based active materials themselves that can prevent the deterioration of life performance due to the volume expansion of the silicon-based compound. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0012] When a double layer structure of a silicon-based active material with small crystal grains is formed on the surface of a conventional silicon-based active material with pores due to a Si deposition reaction, the silicon-based active material with pores is continuously exposed directly to the electrolyte, preventing pore blockage due to the SEI layer formation reaction. In addition, it was found that the coating of the silicon-based active material with small crystal grains results in many grain boundaries, which are not blocked by Li ions even as the reaction proceeds, allowing the material to function as Li.

[0013] Therefore, the present application relates to a negative electrode active material, a method for 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, which can solve the above-mentioned problems. [Means for solving the problem]

[0014] One embodiment of the present specification provides an anode active material including: a first silicon-based active material containing pores; and a coating layer provided on a surface of the first silicon-based active material, wherein the coating layer includes a second silicon-based active material, and the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less.

[0015] Another embodiment provides a method for manufacturing an anode active material, the method including: etching a silicon raw material to prepare a first silicon-based active material having pores; and depositing a silicon-containing gas onto the first silicon-based active material to form a coating layer on a surface of the first silicon-based active material, wherein the coating layer includes a second silicon-based active material, and the second silicon-based active material has a crystal grain size of 20 nm to 200 nm.

[0016] Yet another embodiment provides a negative electrode composition comprising the negative electrode active material according to the present application; a negative electrode conductive material; and a negative electrode binder.

[0017] Yet another embodiment provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both 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.

[0018] Finally, yet another embodiment 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]

[0019] In accordance with an embodiment of the present invention, the anode active material is characterized in that, in recognition of the above-mentioned problems, a silicon-based active material having small crystal grains is coated on the surface of a conventional silicon-based active material having pores formed thereon by a Si deposition reaction.

[0020] The silicon-based active material with pores formed through the coating layer is continuously and directly exposed to the electrolyte, preventing pore blockage due to the SEI layer formation reaction. In addition, by using a silicon-based active material with small crystal grains for the coating layer, there are many crystal grain boundaries, which are not blocked by Li ions even when the reaction proceeds, and can act as a Li ion channel.

[0021] In other words, the initial efficiency can be improved by suppressing side reactions in the SEI layer of the first silicon-based active material, which contains pores. The pores in the first silicon-based active material and the grain boundaries in the surface portion of the second silicon-based active material relieve stress generated by the reaction between lithium and silicon, and reduce particle cracking, resulting in improved life performance. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing a manufacturing process of a silicon-based active material according to Example 1 of the present application. [Figure 2] FIG. 2 is a diagram showing a manufacturing process of a silicon-based active material according to Comparative Example 1 of the present application. [Figure 3] FIG. 1 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] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 5] FIG. 1 is a diagram showing a method for calculating grain size. [Figure 6] FIG. 10 is a diagram relating to a method for calculating the surface area porosity of the first silicon-based active material. [Figure 7] FIG. 3 is a diagram relating to a method for calculating the volume porosity of the first silicon-based active material. DETAILED DESCRIPTION OF THE INVENTION

[0023] Before describing the present invention, some terms will first be defined.

[0024] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0025] In this specification, "p to q" means a range of "not less than p and not more than q."

[0026] 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 may mean the specific surface area measured by the above-mentioned measurement method.

[0027] 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 according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, 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). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through a laser beam.

[0028] In one embodiment of the present application, the particle size or particle size may refer to the average diameter or typical diameter of the individual particles that make up the metal powder.

[0029] 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 contained in the polymer as a repeating unit. In this specification, when a polymer contains a monomer, it is interpreted in the same way as when a polymer contains a monomer as a monomer unit.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0031] 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) of various degrees of polymerization as standard substances for molecular weight measurement. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0032] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention, although the present invention may be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification provides an anode active material including: a first silicon-based active material containing pores; and a coating layer provided on a surface of the first silicon-based active material, wherein the coating layer includes a second silicon-based active material, and the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less.

[0034] With the above-described configuration, it is possible to improve initial efficiency by suppressing side reactions in the SEI layer of the first silicon-based active material, which includes pores. The pores in the first silicon-based active material and the grain boundaries in the surface portion of the second silicon-based active material relieve stress generated by the reaction between lithium and silicon, and reduce particle cracking, resulting in improved life performance.

[0035] Specifically, the first silicon-based active material (core) is made of silicon with large crystal grains or pores, which means that there is little particle cracking even when the volume expands. Furthermore, by forming a double layer structure with the second silicon-based active material with small crystal grains, a path for the movement of Li ions entering the interior is secured, resulting in the core not cracking even when charging and discharging.

[0036] This will be explained in more detail below.

[0037] An embodiment of the present application may include a first silicon-based active material that includes pores.

[0038] In the present application, the first silicon-based active material including the pores can be referred to as a core portion.

[0039] In the present application, there is provided a negative electrode active material, wherein the porosity of the first silicon-based active material is 10% or more and 40% or less.

[0040] In another embodiment, the porosity of the first silicon-based active material may be 10% or more and 40% or less, preferably 12% or more and 35% or less, and more preferably 15% or more and 30% or less.

[0041] In this application, the porosity may refer to the percentage of the total volume of a porous material that is open, or may refer to the percentage of the surface area of ​​a material that is perforated with holes.

[0042] Specifically, the present application provides a negative electrode active material in which the surface area porosity of the first silicon-based active material satisfies the following formula 1:

[0043] [Formula 1] 1.0≦Sp≦12.0 In the formula 1, Sp means the surface area of ​​the first silicon-based active material including pores / the surface area of ​​the first silicon-based active material before pores are formed.

[0044] That is, the surface area porosity may refer to the ratio of the surface area after the etching process (i.e., the first silicon-based active material after pore formation) to the surface area before the etching process (i.e., the first silicon-based active material before pore formation) when an etching process described below is performed to form pores in the first silicon-based active material.

[0045] In the present application, the formula 1 may be 1.0≦Sp≦12.0, preferably 1.1≦Sp≦9.9, and more specifically 1.3≦Sp≦9.85.

[0046] In the present application, there is provided a negative electrode active material, wherein the volume porosity of the first silicon-based active material satisfies the following formula 2:

[0047] [Formula 2] 1.0≦Vp≦11.0 Vp means the volume of the first silicon based active material including pores / the volume of the first silicon based active material before pores are formed.

[0048] That is, the volumetric porosity may refer to the volume ratio after the etching process (i.e., the first silicon-based active material after pore formation) to the volume before the etching process (i.e., the first silicon-based active material before pore formation) when the etching process described below is performed to form pores in the first silicon-based active material.

[0049] In the present application, the formula 2 may satisfy the range of 1.0≦Vp≦11.0, preferably 1.1≦Vp≦8.0, and more preferably 1.3≦Vp≦6.5.

[0050] In the present application, the first silicon-based active material has the porosity of Formula 1 and Formula 2 as described above, thereby alleviating stress generated in response to lithium insertion / extraction during charge / discharge, preventing particle cracking, and serving as a Li ion passage that facilitates the penetration of electrolyte into the active material, thereby improving life performance.

[0051] However, the main feature is that the problem of the SEI side reaction layer that occurs due to the high surface area of ​​the first silicon-based active material accumulating and blocking the pores of the particles, resulting in reduced life performance, is solved by forming a coating layer containing the second silicon-based active material, which will be described later.

[0052] FIG. 6 is a diagram relating to a method for calculating the surface area porosity of the first silicon-based active material, and FIG. 7 is a diagram relating to a method for calculating the volume porosity of the first silicon-based active material.

[0053] Specifically, in FIG. 6, Eqn ,

[0058] , ,

[0057] , , is an equation using the surface area of the particles (the dark frame part in the drawing). S1 is the surface area per weight of the first silicon-based active material before pore generation (before etching), S2 is the surface area per weight of the first silicon-based active material after pore generation (after etching), m1 is the weight before etching, and m2 is the weight after etching.

[0054] At this time, S1 and S2 respectively utilize the values measured within the BET method by using N2 adsorption, and calculate the surface area when assuming the same number of particles. It is calculated with the factor (m2 / m1) for considering the weight reduction due to etching.

[0055] Also, in FIG. 7, Eqn V is an equation using the pore volume within the particles (the blue part in the drawing). V1 is the pore volume per weight of the first silicon-based active material before pore generation (before etching), V2 is the pore volume per weight of the first silicon-based active material after pore generation (after etching), m1 is the weight before etching, and m2 is the weight after etching.

[0056] At this time, V1 and V2 respectively utilize the values measured within the BET method by using N2 adsorption, and calculate the pore volume ratio per particle number when assuming the same number of particles. It is a value calculated by correcting through the mass ratio (m2 / m1) before and after etching.

[0057] In one embodiment of the present application, the first silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may include 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the first silicon-based active material.

[0058] In one embodiment of the present application, the first silicon-based active material includes SiOx (x = 0), and may include 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the first silicon-based active material.

[0059] In another embodiment, the first silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0060] In one embodiment of the present application, pure silicon (Si) particles may be used as the first silicon-based active material. The use of pure silicon (Si) particles as the first silicon-based active material may mean that the first silicon-based active material contains pure Si particles (SiOx (x=0)) that are not bonded to other particles or elements in the above range, based on 100 parts by weight of the first silicon-based active material.

[0061] In one embodiment of the present application, the first silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0062] The present application includes an anode active material including a first silicon-based active material containing pores; and a coating layer provided on a surface of the first silicon-based active material, wherein the coating layer includes a second silicon-based active material, and the crystal grain size of the second silicon-based active material may be 20 nm or more and 200 nm or less.

[0063] In one embodiment of the present application, the second silicon-based active material may be 50 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, or may be 100 parts by weight or less, based on 100 parts by weight of the coating layer.

[0064] In one embodiment of the present application, the coating layer may be made of a second silicon-based active material, i.e., when the second silicon-based active material is 100 parts by weight based on 100 parts by weight of the coating layer, the coating layer can be said to be made of the second silicon-based active material.

[0065] In the present application, the negative electrode active material may have a first silicon-based active material containing pores as a core, and the core may be formed in a form surrounded by the coating layer.

[0066] By forming the coating layer on the surface of the first silicon-based active material as described above, it will have the characteristic that the initial efficiency can be improved by suppressing the side reaction of the SEI layer of the porous first silicon-based active material.

[0067] In one embodiment of the present application, the second silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the second silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more.

[0068] In one embodiment of the present application, the second silicon-based active material contains SiOx (x = 0), and based on 100 parts by weight of the second silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more.

[0069] In another embodiment, based on 100 parts by weight of the second silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0070] In one embodiment of the present application, particularly, pure silicon (Si) particles may be used as the second silicon-based active material. Using pure silicon (Si) particles as the second silicon-based active material may mean that, as described above, when based on 100 parts by weight of the second silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are contained within the above range.

[0071] In one embodiment of the present application, the second silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0072] In one embodiment of the present application, the crystal grain size of the second silicon-based active material may be 20 nm or more and 200 nm or less.

[0073] In another embodiment, the crystal grain size of the second silicon-based active material may be 20 nm or more and 200 nm or less, preferably 22 nm or more and 180 nm or less, more preferably 25 nm or more and 150 nm or less, 30 nm or more and 130 nm or less, or 40 nm or more and 110 nm or less.

[0074] The second silicon-based active material has the above-mentioned crystal grain size, and the crystal grain size of the second silicon-based active material can be adjusted by changing the process conditions in the manufacturing process described below. By satisfying the above range, the crystal grain boundaries are widely distributed, allowing lithium ions to be inserted uniformly during insertion, reducing the stress exerted during lithium ion insertion into silicon particles and thereby mitigating particle cracking. As a result, the negative electrode has the characteristic of improving its life stability. If the crystal grain size exceeds the above-mentioned range, the crystal grain boundaries within the particles are narrowly distributed, causing lithium ions to be inserted non-uniformly within the particles, resulting in large stress due to ion insertion and particle cracking.

[0075] In one embodiment of the present application, there is provided a negative electrode active material, wherein the second silicon-based active material includes a crystalline structure having a crystal grain distribution of 20 nm or more and 200 nm or less, and an area ratio of the crystalline structure based on the area of ​​the entire second silicon-based active material is 5% or less.

[0076] In another embodiment, the area ratio of the crystalline texture based on the area of ​​the entire second silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0077] That is, the second silicon-based active material according to the present application has a crystal grain size of 200 nm or less, and the size of each crystal structure is small, so that the above-mentioned area ratio can be satisfied, which allows the distribution of the crystal grain boundaries to be widened, thereby achieving the above-mentioned effects.

[0078] In one embodiment of the present application, there is provided a negative electrode active material, wherein the number of crystalline structures contained in the second silicon-based active material is 20 or more.

[0079] In another embodiment, the number of crystalline structures contained in the second silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy the range of 60 or less, or 50 or less.

[0080] That is, as described above, when the size of the crystal grains of the second silicon-based active material satisfies the above range and the number of crystalline structures satisfies the above range, the strength of the silicon-based active material itself will have an appropriate range, and when contained in an electrode, it will be able to impart flexibility and have the characteristics of being able to efficiently suppress volume expansion.

[0081] In this application, the term "crystal grain" refers to a collection of irregularly shaped microscopic crystal particles in a metal or material, and the term "crystal grain size" may refer to the diameter of the observed crystal grain. That is, in this application, the term "crystal grain size" refers to the size of a domain that shares the same crystal orientation within a particle, and is a different concept from the grain size or particle size, which represent the size of a substance.

[0082] In one embodiment of the present application, the crystal grain size can be calculated from the FWHM (Full Width at Half Maximum) value by XRD analysis. Specifically, a method for calculating the crystal grain size can be seen from FIG. 5. The crystallite size (=crystal grain size (L)) shown in FIG. 5 is measured by XRD analysis, and the crystal grain size can be calculated according to the Debey-Scherrer equation, since FWHM and crystal grain size are inversely proportional to each other. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0083] [Formula 1-1] FWHM=(Kλ) / (LCOSθ)

[0084] 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.

[0085] Furthermore, the crystal grains have various shapes and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured by commonly used circle method and diameter measurement method, but is not limited thereto.

[0086] The diameter measurement method involves drawing 5 to 10 equilibrium lines, each with a length of L mm, on a micrograph of the target particle, counting the number of crystal grains z on the lines, and averaging them. Only those grains that fit completely are counted, and those that do not fit are excluded. If the number of lines is P and the magnification is V, the average grain size can be calculated using the following formula 1-2.

[0087] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0088] The circle method is a method in which a circle of a specified 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 cross the boundary line, and can be calculated using the following formula 1-3.

[0089] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 )

[0090] 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 within the circle, n is the number of particles that span the arc, and V is the magnification of the microscope.

[0091] In one embodiment of the present application, the second silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0092] The second silicon-based active material containing silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less means that the second silicon-based active material contains a plurality of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles contained is not limited.

[0093] The particle size of the silicon-based particles may be represented by their diameter if they are spherical, but even if they are non-spherical in shape, the particle size can be measured by comparing it with the spherical shape, and the particle size of each silicon-based particle can be measured by a method commonly used in the art.

[0094] Meanwhile, the average particle size (D50 particle size) of the second silicon-based active material of the present invention is 1 μm or more and 10 μm or less, specifically 2 μm to 8 μm, and more specifically 3 μm to 8 μm. When the average particle size is within this range, the specific surface area of ​​the particles is within an appropriate range, and therefore the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the contact area between the silicon particles and the conductive material is improved by the complex consisting of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of the conductive network being maintained, and improving the capacity retention rate. Meanwhile, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0095] The present application provides a negative electrode active material in which the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less, and an average grain size (D50) of the second silicon-based active material of 1 μm or more and 10 μm or less.

[0096] In one embodiment of the present application, there is provided a negative electrode active material, wherein the negative electrode active material has an average particle size (D50) of 3 μm or more and 15 μm or less.

[0097] In particular, the second silicon-based active material according to the present application has a controlled average particle size (D50) and crystal grain size. It is generally known that using a silicon-based active material with a large average particle size makes it easier to secure lithium ion paths. However, as the average particle size increases, the adhesive strength with the negative electrode current collector layer decreases, resulting in a rapid deterioration in life characteristics. Therefore, simply using a silicon-based active material with a small average particle size (D50) ensures life performance, but it is difficult to secure lithium ion paths, resulting in increased resistance.

[0098] In recognition of the above-mentioned problems, the present application adjusts the average particle size (D50) of the second silicon-based active material within the above-mentioned range to ensure life characteristics, and also adjusts the crystal grain size of the silicon-based particles as described above to widely distribute the crystal grain boundaries (crystal grain boundaries), which allows lithium ions to be inserted uniformly during insertion, thereby reducing the stress applied during insertion of lithium ions into the silicon particles, thereby mitigating particle cracking and, as a result, further improving the life stability of the negative electrode.

[0099] In one embodiment of the present application, the first 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 to 150 m 2 / g, more preferably 0.1 to 100m 2 / g, particularly preferably 0.2 to 80m 2 / g, most preferably 0.2 to 18m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0100] In one embodiment of the present application, the surface area of ​​the negative electrode active material is 10 m 2 / g or less.

[0101] The surface area of ​​the negative electrode active material is 8 m 2 / g or less, 6m 2 / g or less, or 4m 2 / g or less, and 2 / g or more, or 0.7m 2 / g or more.

[0102] That is, as described above, the first silicon-based active material has an increased surface area due to the formation of pores. When the surface area is increased, the material is directly exposed to the electrolyte, causing the pores to be blocked. However, by forming a coating layer to adjust the surface area as described above, the pore blocking phenomenon can be prevented even when the reaction proceeds, resulting in improved life performance.

[0103] The surface area of ​​the negative electrode active material may be expressed as S_total, and specifically, it refers to the surface area of ​​the entire negative electrode active material obtained by coating a porous first silicon-based active material with another second silicon-based active material.

[0104] In one embodiment of the present application, the first and second silicon-based active materials can be, for example, in crystalline or amorphous form, and are preferably non-porous.Silicon particles are preferably spherical or shard particles.Alternatively, but less advantageously, silicon particles can have a fibrous structure or be in the form of silicon-containing film or coating.

[0105] In one embodiment of the present application, the first and second silicon-based active materials may have a non-spherical shape, and the sphericity thereof 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.

[0106] In this application, the circularity is determined by the following formula 1-A, where A is the area and P is the perimeter.

[0107] [Formula 1-A] 4πA / P 2

[0108] The present application provides a negative electrode active material in which the thickness of the coating layer satisfies the following formula 3:

[0109] [Formula 3] 0.1≦Coating layer thickness / diameter of negative electrode active material particle cross section≦0.6

[0110] The coating layer is provided on the surface of the first silicon-based active material and is deposited on the outer layer of the structure. When a cross-sectional analysis is performed, the coating layer may appear in the form of a shell rather than a porous form.

[0111] That is, the coating layer has a structure surrounding the entire surface of the first silicon-based active material including pores, and has a structure different from that of a negative electrode active material having silicon crystal grains on the surface of the silicon-based active material. The coating layer includes a second silicon-based active material having crystal grains within a certain range, and therefore prevents the first silicon-based active material having pores from being directly exposed to the electrolyte.

[0112] In contrast, when silicon crystal grains are positioned on the surface of the first silicon-based active material, the deposition of particles occurs throughout the structure, forming a porous material structure, and when a cross-sectional analysis is performed, only the porous structure, not the shell, can be observed.

[0113] In Equation 3, the thickness of the coating layer and the diameter of the cross-section of the negative electrode active material particle are calculated by selecting a particle in an SEM cross-sectional image, measuring the thickness of the shell morphology (a layer where no porous morphology is observed when observing the particle cross-section), and dividing the thickness by the diameter value of the particle cross-section.

[0114] In the present application, the formula 3 may be 0.1 or more, 0.12 or more, or 0.25 or more, or 0.6 or less, 0.57 or less, 0.52 or less, 0.45 or less, or 0.42 or less. When the formula 3 satisfies this range, even if the surface area of ​​the first silicon-based active material increases due to the formation of pores, the phenomenon of pore blockage due to the formation of a side reaction layer caused by direct exposure to the electrolyte can be prevented, thereby improving the life performance.

[0115] In one embodiment of the present application, there is provided an anode active material, in which the first silicon-based active material and the second silicon-based active material are different from each other.

[0116] One embodiment of the present application provides a negative electrode composition comprising the negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0117] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0118] In another embodiment, the amount of the negative electrode active material may be 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0119] The negative electrode composition according to the present application is characterized in that even when a negative electrode active material with extremely high capacity is used within the above range, the negative electrode composition does not deteriorate the performance of the negative electrode and has excellent output characteristics during charging and discharging, by using a second silicon-based active material as a coating layer that satisfies the specific crystal grain size that can suppress the volume expansion rate during charging and discharging, even when the content is within the above range.

[0120] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials are adjusted as described above, their volume can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0121] Therefore, in one 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, sheet-shaped conductive materials, and linear conductive materials.

[0122] 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, does not cause chemical changes, and has conductivity. Specifically, 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, and preferably includes carbon black, which achieves high conductivity and excellent dispersibility.

[0123] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0124] In one embodiment of the present application, the dot-like conductive material may have a volatile matter content 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.

[0125] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, the functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent. In particular, by using a specific silicon-based active material, the present invention can reduce the content of functional groups in the dot-like conductive material, thereby achieving an excellent effect of improving dispersibility.

[0126] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the content of the functional group can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0127] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0128] In one embodiment of the present application, the negative electrode conductive material may include a sheet-shaped conductive material.

[0129] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion. The sheet-like conductive material can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0130] In one embodiment of the present application, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0131] In one embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the average particle size satisfies the above range, the particle size is sufficient to prevent an excessive increase in the viscosity of the negative electrode slurry and facilitate dispersion. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0132] In one embodiment of the present application, the sheet-shaped conductive material may have a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 6.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less. When these ranges are satisfied, the particle size is sufficient to prevent an excessive increase in viscosity of the negative electrode slurry and to facilitate dispersion.

[0133] In one embodiment of the present application, the sheet-shaped conductive material may be a sheet-shaped conductive material having a high BET specific surface area; or a sheet-shaped conductive material having a low specific surface area.

[0134] In one embodiment of the present application, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since the dispersion of the sheet-like conductive material in the present application can have a certain degree of influence on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0135] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0136] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0137] The sheet-shaped conductive material according to the present application may be a sheet-shaped conductive material with a high specific surface area or a sheet-shaped conductive material with a low specific surface area.

[0138] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0139] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and a BET specific surface area of ​​1 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0140] 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. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in a substantially uniform direction, forming a bundle or rope-like structure. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the curved 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, smoothly forming a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0141] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0142] In another embodiment, the negative electrode conductive material may be 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0143] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a sheet-shaped conductive material and a linear conductive material.

[0144] 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, 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0145] In another embodiment, the negative electrode conductive material may contain 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, and more preferably 95 parts by weight or more and 98 parts by weight or less of the sheet-like conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0146] In another embodiment, the negative electrode conductive material may contain 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, and more preferably 2 parts by weight or more and 5 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0147] In one embodiment of the present application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and by satisfying the above-mentioned composition and proportions, the battery does not have a significant effect on the life characteristics of conventional lithium secondary batteries. In particular, when the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, the battery has the following characteristics: there are more points at which charging and discharging are possible, output characteristics are excellent at a high C-rate, and the amount of high-temperature gas generated is reduced.

[0148] In one embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material.

[0149] In particular, when linear conductive materials are used alone, the electrode tortuosity, which is a problem with silicon-based negative electrodes, can be simplified, improving the electrode structure and thereby reducing the resistance to lithium ion migration within the electrode.

[0150] 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 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0151] The negative electrode conductive material according to the present application has a structure that is completely different from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact between the silicon-based active materials, which undergo a very large volume expansion of the electrode upon charge and discharge, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and therefore has a structure and role that are completely different from the negative electrode conductive material of the present invention.

[0152] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having 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, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0153] In one embodiment of the present application, the sheet-like conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dotted shape to facilitate the storage and release of lithium ions.

[0154] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but refers to a material that ensures a conductive path in a sheet shape inside the negative electrode active material layer.

[0155] That is, in this application, the term "platy graphite is used as a conductive material" means that it is processed into a sheet or plate shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

[0156] In contrast, 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.

[0157] That is, 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 sheet-shaped conductive material, plate-shaped graphite, may be in the form of a sheet and have a BET specific surface area of ​​5 m 2 / g or more.

[0158] 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, polytetrafluoroethylene, 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.

[0159] The negative electrode binder according to one embodiment of the present application serves to hold the active material and the conductive material together to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. Any common binder that fulfills the above-mentioned role can be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0160] In one embodiment of the present application, the amount of the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, or may be 5 parts by weight or more, or 10 parts by weight or more.

[0161] One embodiment of the present application provides a method for manufacturing an anode active material, the method including: etching a silicon raw material to prepare a first silicon-based active material having pores; and depositing a silicon-containing gas onto the first silicon-based active material to form a coating layer on a surface of the first silicon-based active material, wherein the coating layer includes a second silicon-based active material, and the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less.

[0162] According to one example, the silicon-containing gas may be silane gas.

[0163] In one embodiment of the present application, there is provided a method for producing a negative electrode active material, wherein the silicon-containing gas contains one or more gases selected from monosilane, dichlorosilane, and trichlorosilane.

[0164] According to one example, the silane gas may include one or more gases selected from monosilane, dichlorosilane, and trichlorosilane, and may specifically be trichlorosilane gas.

[0165] In one embodiment of the present application, the step of chemically reacting silane gas to deposit a silicon-based active material on a substrate may be performed under a pressure condition of 10 Pa to 150 Pa. Such a low pressure reduces the silicon growth rate, thereby allowing the formation of small crystal grains. This step may be performed at a temperature condition of 100°C or higher, specifically 500°C or higher, preferably 800°C or higher, more preferably 800°C to 1300°C, or 800°C to 1100°C. This is a lower temperature than the conventional gas atomizing method, which heats the substrate to 1600°C or higher to melt Si.

[0166] One embodiment of the present application provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both 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.

[0167] 3 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. Although FIG. 3 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0168] 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.

[0169] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0170] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0171] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0172] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0173] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is suitable, and particle aggregation of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0174] In one embodiment of the present application, the slurry solvent can be any solvent that can dissolve the negative electrode composition, and specifically, water or NMP may be used.

[0175] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be formed with fine irregularities to strengthen the binding force 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, mesh, porous material, foam, or nonwoven fabric.

[0176] 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 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.

[0177] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0178] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0179] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% to 60%, preferably 20% to 50%, more preferably 30% to 45%.

[0180] 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, the silicon-based active material and conductive material according to the present application are contained in a specific composition and content, thereby satisfying the above range, and the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0181] One embodiment of the present application 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.

[0182] 4 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side 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 side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are stacked with a separator 30 interposed therebetween.

[0183] A secondary battery according to an embodiment of the present specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0184] 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.

[0185] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0186] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 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 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides 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); or 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.

[0187] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0188] In this case, 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 that is constructed. Specific 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 of two or more.

[0189] 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. Specific examples of the positive electrode binder 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, and various copolymers thereof. These binders may be used singly or in combination.

[0190] 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 limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0191] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0192] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0193] 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, γ-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.

[0194] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear 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, and therefore such cyclic carbonates can be more preferably used.

[0195] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. 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:

[0196] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0197] 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 can 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.

[0198] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating 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, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0199] [Example] <Production example> <Production of Examples 1 to 9> After applying heat to the SiOx raw material to turn it into a liquid phase, an electrochemical reaction is performed to produce MG-Si (Metallic Grade Silicon).The MG-Si is then crushed and classified to control the desired particle size and particle size distribution, and pores are formed within the silicon particles using a strong acid (HF, H2SO4) or a strong base (NaOH).The porosity is as shown in Table 1 below.

[0200] Next, a fluid was passed through the reactor to allow the particles to flow, and then heat was applied while a silicon-containing gas was passed through, producing a double-layered anode active material in which a polycrystalline silicon layer (Si) was formed within the conventional particles. The crystal grain size (nm) of the silicon layer (Si), i.e., the crystal grain size (nm) of the second silicon-based active material, is shown in Table 1 below.

[0201] <Production of Example 10> After applying heat to the SiOx raw material to turn it into a liquid phase, an electrochemical reaction is performed to produce MG-Si (Metallic Grade Silicon).The MG-Si is then crushed and classified to control the desired particle size and particle size distribution, and pores are formed within the silicon particles using a strong acid (HF, H2SO4) or a strong base (NaOH).The porosity is as shown in Table 1 below.

[0202] Next, a fluid was passed through the reactor to allow the particles to flow, and then a silicon-containing gas was passed through while heat was applied, producing a double-layered anode active material in which a polycrystalline silicon layer (Si) was formed within the conventional particles. Heat was then applied under inert gas conditions to control the grain size of the active material, increasing the grain size of the active material. The grain size (nm) of the silicon layer (Si), i.e., the grain size (nm) of the second silicon-based active material, is shown in Table 1 below.

[0203] <Production of Comparative Examples 1 to 3> After applying heat to the SiOx raw material to turn it into a liquid phase, an electrochemical reaction is performed to produce MG-Si (Metallic Grade Silicon).The MG-Si is then crushed and classified to control the desired particle size and particle size distribution, and pores are formed within the silicon particles using a strong acid (HF, H2SO4) or a strong base (NaOH).The porosity is as shown in Table 1 below.

[0204] <Production of Comparative Examples 4 to 6> After producing Comparative Example 3, a fluid was passed through the reactor to allow the particles to flow, and then a silicon-containing gas was passed through while heat was applied, thereby producing Comparative Examples 4 and 5, which are anode active materials having a double layer in which a polycrystalline silicon layer (Si) was formed within conventional particles.

[0205] Furthermore, to confirm a structure with more pores than Comparative Example 3, Comparative Example 6 was prepared using a different synthesis method than Comparative Example 3. Silicon and metal alloy particles were treated with acid to form a porous silicon structure. Then, a silicon-containing gas was passed through the material while heat was applied, thereby forming a polycrystalline silicon layer (Si) on the surface of the Si particles. This produced Comparative Example 6, an anode active material.

[0206] At this time, the crystal grain size (nm) of the silicon layer (Si), that is, the crystal grain size (nm) of the second silicon-based active material, is as shown in Table 1 below.

[0207] [Table 1A]

[0208] [Table 1B]

[0209] In Table 1, Equation 1 represents the surface area ratio after the etching process (i.e., the first silicon-based active material after pore formation) to the surface area before the etching process (i.e., the first silicon-based active material before pore formation). Equation 2 represents the volume ratio after the etching process (i.e., the first silicon-based active material after pore formation) to the surface area before the etching process (i.e., the first silicon-based active material before pore formation). In addition, in Table 1, the thickness of the coating layer and the diameter of the cross-section of the negative electrode active material particle are calculated by selecting a particle in an SEM cross-sectional image, measuring the thickness of the shell morphology (a layer where no porous morphology is observed when examining the particle cross-section), and dividing the thickness by the diameter of the particle cross-section.

[0210] <Production of negative electrodes> The negative electrode active material including the silicon-based active material in Table 1, the first conductive material, the second conductive material, and polyacrylamide as a binder were added in a weight ratio of 80:10:10 to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry (solid concentration: 28 wt %).

[0211] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0212] Specifically, the first conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, the second conductive material was added and dispersed for 10 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0213] The negative electrode current collector layer was made by applying 227 mg / 50 cm of the negative electrode slurry to one side of a copper current collector (thickness: 15 μm). 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 23 μm), which was used as a negative electrode (negative electrode thickness: 38 μm, negative electrode porosity: 40.0%).

[0214] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0215] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 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: 77 μm, porosity: 26%).

[0216] 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 into the separator to prepare a lithium secondary battery.

[0217] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, to which 3 wt% vinylene carbonate was added based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0218] <Experimental Example> Experimental example 1: Cycle life data The secondary batteries including the negative electrodes prepared using the negative electrode active materials of the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the 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 the capacity retention was measured by charging / discharging at 0.33 C / 0.33 C (4.2-3.0 V) every 50 cycles during the test.

[0219] Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0220] [Table 2]

[0221] Experimental example 2: Pulse resistance after 200 cycles 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 30 seconds after discharging at SOC50 with a 2.5C pulse to determine the degree of difference in resistance value after the cycles.

[0222] The data at 200 cycles for each of the resistance increase rates was calculated, and the results are shown in Table 3 below.

[0223] [Table 3]

[0224] As can be seen from Tables 2 and 3, when the anode active materials of Examples 1 to 10 of the present invention are used, initial efficiency can be improved by suppressing side reactions in the SEI layer of the first silicon-based active material containing pores. Furthermore, the pores in the first silicon-based active material and the grain boundaries in the surface of the second silicon-based active material relieve stress generated by the reaction between lithium and silicon, and reduce particle cracking, thereby improving life performance. Comparative Examples 1 to 3 correspond to cases where a silicon-based active material containing pores was used alone. In these cases, because the porous region was directly exposed to the electrolyte, a rapid decrease in life performance occurred as the number of cycles progressed, regardless of particle size. This phenomenon occurs when the pores that relieve stress during conventional charging and discharging are blocked by the formation of a side reaction layer (SEI layer) as the cycles progress.

[0225] When checking the resistance values ​​in Table 3, it was also possible to confirm that the resistance increased sharply compared to the conventional method.

[0226] In contrast, it was confirmed that the rapid decline in life performance was improved in Examples 1 to 10. This is because the coating layer (double layer) blocks the direct reaction between porous Si and the electrolyte, improving life performance.

[0227] Furthermore, to confirm the influence of the size of the crystal grains of the second silicon-based active material, the cases of Comparative Examples 4 and 5 were examined. In Comparative Example 4, the crystal grains were formed larger than in the Examples, and it was confirmed that there was a relative decrease in life performance and an increase in resistance. This is because, due to the increase in crystal grains, the layer formed on the surface cracks due to stress generated during lithium insertion, and the pores of the first silicon-based active material formed on the surface and inside due to the formation of a side reaction layer are partially blocked, leading to a decrease in life performance and an increase in resistance.

[0228] In addition, in Comparative Example 5, the crystal grains were smaller than those in the Examples, and the coating layer was not formed to completely cover the surface of the porous first silicon-based active material, which resulted in a failure to suppress side reactions with the electrolyte, resulting in a rapid decrease in life performance and a rapid increase in resistance.

[0229] Furthermore, Comparative Example 6 was investigated to confirm the effect of the coating layer formed on the surface of the first silicon-based active material, i.e., the coating layer containing the second silicon-based active material. In Examples 1 to 10, the coating layer was formed to surround the surface of the first silicon-based active material and was deposited on the outer layer of the structure, which appeared as a shell rather than a porous structure in cross-sectional analysis. However, in Comparative Example 6, silicon crystal grains were positioned on the surface of the first silicon-based active material, forming a porous material structure, and particles were deposited throughout the structure. In cross-sectional analysis, only a porous structure, not a shell, was observed. Therefore, it was not possible to measure the thickness of the coating layer relative to the diameter of the cross-section of the negative electrode active material particle. In this case, because the porous region was directly exposed to the electrolyte, it was confirmed that the formation of a side reaction layer and pore blockage occurred as cycling progressed. To prevent this, a shell morphology must be maintained to maintain the porous structure in the first silicon-based active material, otherwise the porous silicon effect cannot be maintained. [Explanation of symbols]

[0230] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30 Separator 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode active material comprising: a first silicon-based active material having pores; and a coating layer provided on a surface of the first silicon-based active material, the coating layer includes a second silicon-based active material; The negative electrode active material, wherein the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less.

2. The negative electrode active material according to claim 1 , wherein the surface area porosity of the first silicon-based active material satisfies the following formula 1: [Formula 1] 1.0≦Sp≦12.0 In the formula 1, Sp means the surface area of ​​the first silicon-based active material including pores / the surface area of ​​the first silicon-based active material before pore formation.

3. The negative electrode active material according to claim 1 , wherein the volume porosity of the first silicon-based active material satisfies the following formula 2: [Formula 2] 1.0≦Vp≦11.0 Vp means the volume of the first silicon-based active material including pores / the volume of the first silicon-based active material before pores are formed.

4. 2. The negative electrode active material of claim 1, wherein the first silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the first silicon-based active material comprises 70 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first silicon-based active material.

5. 2. The negative electrode active material of claim 1, wherein the second silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the second silicon-based active material comprises 70 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the second silicon-based active material.

6. The size of the crystal grains of the second silicon-based active material is 20 nm or more and 200 nm or less, The negative electrode active material according to claim 1 , wherein the second silicon-based active material has an average particle size (D50) of 1 μm or more and 10 μm or less.

7. The negative electrode active material according to claim 1 , wherein the negative electrode active material has an average particle size (D50) of 3 μm or more and 15 μm or less.

8. The negative electrode active material of claim 1 , wherein the first silicon-based active material and the second silicon-based active material are different from each other.

9. The surface area of ​​the negative electrode active material is 10 m ２ The negative electrode active material according to claim 1 , wherein the SiO 2 content is 1 / g or less.

10. The negative electrode active material according to claim 1 , wherein the thickness of the coating layer satisfies the following formula 3: [Formula 3] 0.1≦thickness of coating layer / diameter of cross section of negative electrode active material particle≦0.6

11. Etching a silicon raw material to prepare a first silicon-based active material containing pores; and depositing a silicon-containing gas on the first silicon-based active material to form a coating layer on the surface of the first silicon-based active material; A method for producing a negative electrode active material, comprising: the coating layer includes a second silicon-based active material; The method for producing a negative electrode active material, wherein the second silicon-based active material has a crystal grain size of 20 nm or more and 200 nm or less.

12. The method for producing a negative electrode active material according to claim 11 , wherein the silicon-containing gas includes one or more gases selected from monosilane, dichlorosilane, and trichlorosilane.

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

14. The negative electrode composition according to claim 13 , 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.

15. The negative electrode composition according to claim 13 , wherein the negative electrode conductive material comprises a sheet-shaped conductive material and a linear conductive material.

16. 16. The negative electrode composition according to claim 15, wherein the negative electrode conductive material comprises: 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

17. 16. The negative electrode composition according to claim 15, wherein the sheet-shaped conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 6.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

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

19. the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, 19. The negative electrode for a lithium secondary battery according to claim 18, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

20. positive electrode; The negative electrode for a lithium secondary battery according to claim 18 ; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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