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. 10-2022-0170486, filed with the Korean Intellectual Property Office on December 8, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Background technology]

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

[0004] Currently, a typical example of an electrochemical element that utilizes 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. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] In recent years, in response to the demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than those of graphite-based materials, have been used as negative electrode active materials. x Research is being actively conducted into methods of increasing capacity by using silicon-based compounds such as graphite together with silicon dioxide to increase capacity. However, silicon-based compounds, which are high-capacity materials, have a problem in that while they have a large capacity compared to conventionally used graphite, they suddenly expand in volume during charging, cutting off the conductive path and reducing battery performance.

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

[0009] Therefore, even when silicon-based active materials are used as negative electrode active materials to improve capacity performance, research is needed into silicon-based active materials themselves that can mitigate the cracking phenomenon of silicon caused by lithium insertion and extraction during charge and discharge. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0011] When adjusting the distribution of crystal planes and the sphericity in a silicon-based active material by controlling the plate-like degree of the silicon-based active material through a silicon processing method, it was confirmed that during the lithium insertion / desorption reaction, the reaction occurs uniformly, reducing the stress on the silicon-based active material. In particular, when specifically setting the milling temperature, pressure, and time in the processing method, it was confirmed through research that the plate-like degree of the silicon-based active material itself can be specifically controlled, and through this, it was confirmed that the insertion and desorption of lithium ions occur uniformly.

[0012] Accordingly, the present application relates to a negative electrode active material, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode, which can solve the above problems.

Means for Solving the Problem

[0013] One embodiment of the present specification is a negative electrode active material including a silicon-based active material satisfying the plate-like degree of the following Formula 1, wherein the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x (x = 0). A negative electrode active material is provided.

[0014] [Formula 1] 45 ≦ (A / B) × 100 In Formula 1 above, A means the length of the short axis of the silicon-based active material, B means the length of the long axis of the silicon-based active material.

[0015] In another embodiment, a method for manufacturing a negative electrode active material includes a step of preparing metal silicon; and a step of pulverizing the metal silicon to form a silicon-based active material, wherein the silicon-based active material satisfies the plate-like degree of Formula 1. A method for manufacturing a negative electrode active material is provided.

[0016] In another embodiment, a negative electrode composition including a negative electrode active material; a negative electrode conductive material; and a negative electrode binder according to the present application is to be provided.

[0017] In another embodiment, a negative electrode for a lithium secondary battery including 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 active material layer including the negative electrode composition according to the present application or a cured product thereof is to be provided.

[0018] Finally, a lithium secondary battery including a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte is provided.

Advantages of the Invention

[0019] The negative electrode active material of the present invention, as a silicon-based active material, includes at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of the SiO x (x = 0), that is, while having a pure Si (Pure Si) active material, it improves the conventional processing method and controls the pulverization conditions to produce it. Thus, it contains a silicon-based active material that satisfies certain physical properties. When using the silicon-based active material manufactured in this way, it becomes possible to react uniformly during the insertion and desorption reactions of lithium during charge and discharge, reduce the stress received by the silicon-based active material, and relieve the cracking of particles, thereby improving the electrode life retention rate.

[0020] In particular, as described above, the present application is characterized in that when manufacturing the silicon-based active material, the plate-like degree satisfying the range of Formula 1 is controlled. That is, when the plate-like degree satisfies the range of Formula 1, the silicon-based active material contains a large proportion of the 220 crystal plane differently from the conventional case, and lithium uniformly enters and exits during the insertion and desorption reactions of lithium, and the silicon cracking phenomenon on the electrode surface can be alleviated, thereby having the characteristic of strengthening the electrode life characteristics. [Brief explanation of the drawings]

[0021] [Figure 1] 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 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 3] FIG. 1 illustrates a method for calculating grain size. [Figure 4] 1 is a diagram showing a unit structure of a silicon-based active material according to the present application. FIG. [Figure 5] FIG. 2 is a diagram showing the 220 and 111 faces of the silicon-based active material according to the present application. [Figure 6] FIG. 1 is a diagram comparing the densities of the 220 and 111 planes of silicon-based active materials. DETAILED DESCRIPTION OF THE INVENTION

[0022] Before describing the present invention, some terms will first be defined.

[0023] In this specification, when a part is said to "comprise" a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary, but rather that it does not exclude other components.

[0024] In this specification, "p to q" means a range of "not less than p and not more than q."

[0025] 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.

[0026] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, the average particle size 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 diffraction patterns due to particle size when the particles pass through a laser beam.

[0027] In one embodiment of the present application, the particle size or particle size may refer to the average diameter or representative diameter of each grain constituting the metal powder.

[0028] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0029] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer."

[0030] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0031] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0032] One embodiment of the present specification is a negative electrode active material containing a silicon-based active material satisfying the plate shape degree of the following formula 1, wherein the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) contains 70 parts by weight or more, providing a negative electrode active material.

[0033] [Formula 1] 45 ≦ (A / B) × 100 In the above formula 1, A means the length of the short axis of the silicon-based active material, B means the length of the long axis of the silicon-based active material.

[0034] This application is characterized in that when manufacturing a silicon-based active material, the plate shape degree satisfying the range of formula 1 is controlled. That is, when the plate shape degree satisfies the range of formula 1, the silicon-based active material contains a large proportion of the 220 crystal plane differently from the conventional one, and lithium uniformly enters and exits in the lithium insertion and desorption reaction, which can alleviate the silicon cracking phenomenon on the electrode surface, thereby having the characteristic of enhancing the life characteristics of the electrode.

[0035] In one embodiment of this application, A means the length of the short axis of the silicon-based active material, and B means the length of the long axis of the silicon-based active material. For the measurement of the long axis and the short axis, after taking a SEM image of the cross-section of the electrode containing the silicon-based negative electrode active material, the cross-sectional image of individual particles is analyzed through an image processing program to measure the ratio of the long axis and the short axis of the silicon-based active material.

[0036] In this case, the length of the major axis of the silicon-based active material may refer to the length of the longest axis of the silicon-based active material particle obtained by observing individual particles through the above-mentioned SEM image capturing and image processing program, and the length of the minor axis may refer to the length of the shortest axis.

[0037] In one embodiment of the present application, the formula 1 may satisfy the range of 45≦(A / B)×100, preferably 46≦(A / B)×100, more preferably 47≦(A / B)×100, and may satisfy the range of (A / B)×100≦100, preferably (A / B)×100≦90, and further preferably (A / B)×100≦88.

[0038] In the present application, when the silicon-based active material satisfies the range of the plate-like degree (Equation 1), the particles with high lithium mobility can be distributed relatively frequently within the particles through the particle shape control, resulting in the ease of lithium intercalation and deintercalation within the active material. In other words, the uniformity of lithium intercalation / deintercalation between active materials within an electrode is improved, and particle cracking at the upper end of the electrode is alleviated, thereby improving the lifespan of batteries containing the silicon-based active material.

[0039] In the present application, the silicon-based active material that satisfies the plate-like degree of the formula 1 can be prepared by the manufacturing method described below, the specific details of which will be described later.

[0040] In one embodiment of the present specification, there is provided a negative electrode active material, wherein the silicon-based active material includes a 220 crystal face and a 111 crystal face, and the silicon-based active material satisfies the following formula 2:

[0041] [Formula 2] 37≦(X / Y)×100 In the formula 2, Y means the proportion of 111 crystal faces in the silicon-based active material, X means the proportion of 220 crystal faces in the silicon-based active material.

[0042] The present application is characterized by controlling the plate-likeness of the above formula 1 and the crystal grain orientation distribution that satisfies the range of formula 2 when manufacturing a silicon-based active material. That is, when a relatively large proportion of 111 crystal faces is formed, as in the conventional case, the 111 crystal faces have lower lithium mobility than the 220 crystal faces, making it difficult for lithium to enter and exit uniformly during lithium insertion and desorption reactions. However, the silicon-based active material of the present application contains a high proportion of 220 crystal faces, which is different from the conventional case, allowing lithium to enter and exit uniformly during lithium insertion and desorption reactions, thereby mitigating silicon cracking on the electrode surface and improving the electrode's lifespan.

[0043] Figure 4 shows the unit structure of the silicon-based active material according to the present application. It includes crystal planes, and specifically, the 220 and 111 planes of the silicon-based active material can be seen in Figure 5. Figure 6 is a diagram comparing the density of the 220 and 111 planes of the silicon-based active material. Specifically, when the density and orientation of the 220 and 110 planes were examined, it was found that the particle density within the same area was lower on the 220 plane, making the 220 plane, with its lower particle density, more advantageous for Li migration.

[0044] In one embodiment of the present application, the X means the proportion of 220 crystal faces in the silicon-based active material, and means the proportion based on the entire surface of the silicon-based active material, and the X may be 30 to 60, preferably 35 to 60, and more preferably 35 to 55.

[0045] In one embodiment of the present application, the Y refers to the proportion of 111 crystal faces in the silicon-based active material, and refers to the proportion based on the entire surface of the silicon-based active material, and the Y may be 50 to 80, preferably 55 to 80, and more preferably 55 to 75.

[0046] In one embodiment of the present application, the silicon-based active material may further include various crystal planes.

[0047] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be included in an amount of 70 parts by weight or more.

[0048] In one embodiment of the present application, the silicon-based active material includes SiO x (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be included in an amount of 70 parts by weight or more.

[0049] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be included 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 included 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.

[0050] In one embodiment of the present application, as the silicon-based active material, those containing particularly pure silicon (Si) particles may be used. Using pure silicon (Si) particles as the silicon-based active material means that, as described above, based on a total of 100 parts by weight of the silicon-based active material, pure Si particles (SiO x (x = 0)) that are not bonded to other particles or elements are included within the above range.

[0051] In one embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

[0052] In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities are metals that may be generally contained in silicon-based active materials, and specifically, the impurities may be contained in an amount of 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0053] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion rate during charging and discharging, they are only used in small amounts by mixing with graphite-based active materials.

[0054] Therefore, in the present invention, while only a silicon-based active material is used as a negative electrode active material to improve capacity performance, the above-mentioned problems are solved by adjusting the size or surface area of ​​the crystal grains of the silicon-based active material itself, rather than adjusting the composition of the conductive material and binder.

[0055] In one embodiment of the present application, the silicon-based active material may have a crystal grain size of 500 nm or less.

[0056] In another embodiment, the crystal grain size of the silicon-based active material may be 500 nm or less, preferably 400 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, and more specifically 91 nm or less. The crystal grain size of the silicon-based active material may be 10 nm or more, preferably 15 nm or more.

[0057] The silicon-based active material has the above-described crystal grain size, and the crystal grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. By satisfying this range, the crystal grain boundaries are widely distributed, allowing lithium ions to be inserted uniformly during insertion, reducing the stress exerted when lithium ions are inserted 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 this range, the crystal grain boundaries within the particles are narrowly distributed, causing lithium ions to be inserted non-uniformly within the particles, increasing the stress due to ion insertion and resulting in particle cracking.

[0058] In one embodiment of the present application, there is provided a negative electrode active material, wherein the silicon-based active material includes a crystalline structure having a crystal grain distribution of 1 nm or more and 200 nm or less, and the area ratio of the crystalline structure is 5% or less based on the total area of ​​the silicon-based active material.

[0059] In another embodiment, the area ratio of the crystalline structure may be 5% or less, 3% or less, or 0.1% or more, based on the total area of ​​the silicon-based active material.

[0060] That is, the 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, and thus the distribution of the grain boundaries can be widened, thereby achieving the above-mentioned effects.

[0061] In one embodiment of the present application, there is provided a negative electrode active material, wherein the silicon-based active material contains 20 or more crystalline structures.

[0062] In another embodiment, the number of crystalline structures contained in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may be in the range of 60 or less, or 50 or less.

[0063] That is, as described above, when the silicon-based active material has a crystal grain size that satisfies the above range and the number of crystalline structures that satisfies the above range, the strength of the silicon-based active material itself falls within an appropriate range, and when contained in an electrode, the silicon-based active material can be provided with flexibility and has the characteristic of being able to efficiently suppress volume expansion.

[0064] 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 an 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.

[0065] In one embodiment of the present application, the crystal grain size can be calculated as a FWHM (Full Width at Half Maximum) value through XRD analysis. Specifically, a method for calculating the crystal grain size can be seen from FIG. 6. In FIG. 6, the remaining values ​​excluding L are measured through XRD analysis of the silicon-based active material, and the crystal grain size can be calculated based on the inverse relationship between FWHM and crystal grain size using the Debye-Scherrer equation. In this case, the Debye-Scherrer equation is as follows:

[0066] [Formula 1-1] FWHM=Kλ / LCosθ In the formula 1-1, L is the grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0067] The shape of the crystal grains is diverse and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured by a commonly used circle method or diameter measurement method, but is not limited thereto.

[0068] The diameter measurement method involves drawing 5 to 10 parallel lines, each L mm long, on a micrograph of the target particle, counting the number of crystal grains z along the lines, and averaging them. Only those grains that are fully contained are counted, and those that overlap are excluded. If the number of lines is P and the magnification is V, the average particle diameter can be calculated using the following formula 1-2.

[0069] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0070] The circle method involves drawing a circle of a specified diameter on a micrograph of the target particle, and then calculating the average area of ​​the crystal grains from the number of crystal grains that fit within the circle and the number of crystal grains that cross the boundary line. This can be calculated using the following formula 1-3.

[0071] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 ) In the above formulas 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles that fit inside the circle, n is the number of particles that span the arc, and V is the magnification of the microscope.

[0072] In one embodiment of the present application, the negative electrode active material has a surface area of ​​0.25 m 2 / g or more of a silicon-based active material.

[0073] In another embodiment, the silicon-based active material has a surface area of ​​0.25 m 2 / g or more, preferably 0.28m 2 / g or more, more preferably 0.30m 2 / g or more, specifically 0.31m 2 / g or more, more specifically 0.32m 2 The silicon-based active material may have a surface area of ​​3 m / g or more. 2 / g or less, preferably 2.5m 2 / g or less, more preferably 2.2m 2 The surface area can be measured (using nitrogen) according to DIN 66131:

[0074] The silicon-based active material has the above surface area, and the size of the surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material, which will be described later. That is, when a negative electrode active material is manufactured using the manufacturing method of the present application, the rough surface results in a larger surface area than particles having the same particle size. In this case, by satisfying the above range and increasing the binding strength with the binder, it has the characteristic of being able to mitigate cracks in the electrode caused by repeated charge-discharge cycles.

[0075] Furthermore, lithium ions are inserted uniformly during insertion, reducing the stress applied when lithium ions are inserted into silicon particles, thereby mitigating particle cracking. As a result, the negative electrode has the characteristic of improving its life stability. If the surface area is less than the above range, even if the particle size is the same, the surface will be smooth, reducing the binding strength with the binder and causing electrode cracking. In this case, lithium ions will be inserted non-uniformly within the particles, resulting in greater stress due to ion insertion and particle cracking.

[0076] In one embodiment of the present application, the silicon-based active material provides a negative electrode active material that satisfies the range of the following formula 2-1.

[0077] [Formula 2-1] X1 / Y1≦0.960 In the formula 2-1, X1 is the actual area of ​​the silicon-based active material, Y1 means the area of ​​a spherical particle having the same circumference as the silicon-based active material.

[0078] The formula 2-1 can be measured using a particle shape analyzer. Specifically, the silicon-based active material according to the present application is scattered on a glass plate using an air jet, and then a shadow image of the scattered silicon-based active material particles is taken, and the particle shapes of 10,000 silicon-based active material particles in the photograph can be measured. In this case, the formula 2-1 represents an average value for 10,000 particles. From the image, the formula 2-1 according to the present application can be measured, and the formula 2-1 can be expressed as the sphericity of the silicon-based active material. The sphericity can be calculated using the formula [4π * actual area of ​​silicon-based active material / (boundary)]. 2 ] may also be expressed as

[0079] In one embodiment of the present application, the sphericity of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The sphericity of the silicon-based active material may be 0.8 or more, for example, 0.9 or more, specifically 0.93 or more, more specifically 0.94 or more, for example, 0.941 or more.

[0080] In one embodiment of the present application, there is provided a negative electrode active material, in which the silicon-based active material satisfies the range of the following formula 2-2.

[0081] [Formula 2-2] X2 / Y2≦0.995 In the formula 2-2, Y2 is the actual circumference of the silicon-based active material, X2 is the circumference of the circumscribing figure of the silicon-based active material.

[0082] The formula 2-2 can be measured using a particle analyzer. Specifically, the silicon-based active material according to the present application is scattered on a glass plate using an air jet, and then a shadow image of the scattered silicon-based active material particles is taken. The shape of 10,000 silicon-based active material particles in the image can be measured. In this case, the formula 2-2 represents an average value for 10,000 particles. The formula 2-2 according to the present application can be measured from the image, and the formula 2-2 can be expressed as the convexity of the silicon-based active material.

[0083] In one embodiment of the present application, the range of X2 / Y2≦0.996, preferably X2 / Y2≦0.995, may be satisfied, and the range of 0.8≦X2 / Y2, preferably 0.9≦X2 / Y2, more preferably 0.95≦X2 / Y2, specifically 0.98≦X2 / Y2 may be satisfied.

[0084] The smaller the value of the formula 2-1 or 2-2, the greater the roughness of the silicon-based active material. By using a silicon-based active material having such a range, the bonding strength with the binder increases, thereby providing the characteristic of being able to alleviate cracks in the electrode caused by repeated charge-discharge cycles.

[0085] In one embodiment of the present application, the silicon-based active material may contain silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0086] The silicon-based active material containing silicon-based particles having a particle size distribution of 0.01 μm to 30 μm means that the silicon-based active material contains a large number of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles contained is not limited.

[0087] The particle size of the silicon-based particles may be expressed as their diameter if they are spherical. However, even if the particles are not spherical, the particle size may be measured by comparing it with the spherical shape. The particle size of individual silicon-based particles may be measured by a method generally used in the art.

[0088] Meanwhile, the average particle size (D50 particle size) of the silicon-based active material of the present invention may be 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles falls within an appropriate range, and 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 composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and improving the capacity retention rate. On the other hand, 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.

[0089] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.01 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET surface area is determined according to DIN 66131 (using nitrogen).

[0090] In one embodiment of the present application, there is provided a negative electrode active material, wherein the silicon-based active material satisfying the plate-like degree of the formula 1 is contained in an amount of 80 parts by weight or more and 100 parts by weight or less, based on 100 parts by weight of the negative electrode active material.

[0091] In yet another embodiment, the silicon-based active material satisfying the plate-like degree of the formula 1 may be contained in an amount of 80 parts by weight or more and 100 parts by weight or less, preferably 85 parts by weight or more and 99 parts by weight or less, and more preferably 90 parts by weight or more and 99 parts by weight or less, based on 100 parts by weight of the negative electrode active material.

[0092] That is, the negative electrode active material according to the present application includes a silicon-based active material that satisfies the range of the above formula 1 within the above range, and may further include a silicon-based active material or a carbon-based active material that may be generally included.

[0093] In one embodiment of the present application, there is provided a negative electrode composition comprising the negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0094] In one embodiment of the present application, the negative electrode composition is provided in which the negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0095] In one embodiment of the present application, the negative electrode composition is provided in which the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0096] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0097] The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific crystal grain size that can suppress the volume expansion rate during charge and discharge even when a silicon active material with extremely high capacity is used within the above range, and therefore does not reduce the performance of the negative electrode even when the above range is included, and has the characteristic of excellent output characteristics during charge and discharge.

[0098] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into them 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 themselves are adjusted as described above, the volume of silicon-based active materials can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed within the negative electrode active material layer.

[0099] Therefore, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of dot-like conductive materials, planar conductive materials, and linear conductive materials.

[0100] 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 conductivity to the negative electrode and has conductivity without inducing a chemical change. 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 realizes high conductivity and excellent dispersibility.

[0101] 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.

[0102] 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.

[0103] In particular, when the functional group content of the dot-like conductive material satisfies the above range, 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, in the present invention, by using a specific silicon-based active material, the functional group content of the dot-like conductive material can be reduced, thereby having an excellent effect of improving dispersibility.

[0104] In one embodiment of the present application, the active material is characterized by including a dot-like conductive material having a functional group content within the above range together with a silicon-based active material, and the functional group content can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0105] 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.

[0106] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0107] The planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, and can also serve to prevent the conductive path from being broken due to volume expansion. The planar conductive material can be referred to as a plate-type conductive material or a bulk-type conductive material.

[0108] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0109] In one embodiment of the present application, the average particle size (D50) of the sheet 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 this range, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0110] In one embodiment of the present application, the sheet conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0111] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0112] In one embodiment of the present application, the sheet conductive material can be a high-specific surface area sheet conductive material or a low-specific surface area sheet conductive material without any restrictions. However, the sheet conductive material of the present application in particular may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area sheet conductive material that does not cause dispersion problems.

[0113] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0114] In another embodiment, the sheet 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 The sheet conductive material according to the present application may be a high-specific surface area sheet conductive material or a low-specific surface area sheet conductive material.

[0115] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having 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.

[0116] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​1 m 2 / g or more 40m 2 / g or less, preferably 5m2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0117] 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 substantially the same direction, forming a bundle or rope-like shape. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the carbon nanotube unit may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, and improving the conductivity of the negative electrode.

[0118] In one embodiment of the present application, the negative electrode composition is provided in which 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.

[0119] In another embodiment, the negative electrode conductive material may comprise, based on 100 parts by weight of the negative electrode composition, 0.1 parts by weight to 40 parts by weight, preferably 0.2 parts by weight to 30 parts by weight, more preferably 0.4 parts by weight to 25 parts by weight, and most preferably 0.4 parts by weight to 10 parts by weight.

[0120] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0121] In one embodiment of the present application, there is provided a negative electrode composition comprising, 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 conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0122] 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 conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0123] 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 0.2 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.

[0124] In one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and ratio, so that it does not significantly affect the life characteristics of existing lithium secondary batteries. In particular, when the negative electrode conductive material includes a planar conductive material and a linear conductive material, there are more points at which charging and discharging are possible, and the negative electrode conductive material has the characteristics of excellent output characteristics at a high C-rate and reduced generation of high-temperature gas.

[0125] In one embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material.

[0126] In particular, when a linear conductive material is used alone, it is possible to simplify the tortuosity of the electrode, which is a problem with silicon-based negative electrodes, and improve the electrode structure, thereby reducing the resistance to lithium ion migration within the electrode.

[0127] In one embodiment of the present application, when the negative electrode conductive material contains only a linear conductive material, the negative electrode conductive material may be contained 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.

[0128] The negative electrode conductive material according to the present application has a completely different structure 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 secure the contact points between the silicon-based active materials, which undergo a large volume expansion during charging and discharging, while the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0129] 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.

[0130] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material 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.

[0131] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like 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 rather a material for ensuring a planar conductive path within the negative electrode active material layer.

[0132] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is used as a material that ensures a conductive path, rather than being processed into a planar or plate-like shape to store or release lithium. In this case, the negative electrode active material included therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0133] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that stores or releases lithium.

[0134] 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 plate-shaped graphite, which is a planar conductive material, may have a planar BET specific surface area of ​​5 m 2 / g or more.

[0135] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0136] The negative electrode binder according to one embodiment of the present application plays a role in holding down the active material and conductive material to prevent twisting and structural deformation of the negative electrode structure when the volume expansion and relaxation of the silicon-based active material occurs. Any common binder can be used as long as it fulfills this role. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0137] In one embodiment of the present application, the amount of the negative electrode binder is 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, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0138] In one embodiment of the present application, there is provided a method for manufacturing an anode active material, the method including the steps of preparing metal silicon; and pulverizing the metal silicon to form a silicon-based active material, wherein the silicon-based active material satisfies the plate-like degree of Equation 1.

[0139] In the present application, there is provided a method for manufacturing a negative electrode active material, wherein the step of preparing metal silicon includes a step of forming metal silicon by pulverization; or a step of forming metal silicon by silane deposition.

[0140] That is, the metal silicon can be formed by physically crushing a general silicon block (unprocessed silicon) or chemically by silane deposition, but is not limited thereto.

[0141] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode active material, wherein the step of forming the pulverized metal silicon includes a step of pulverizing unprocessed silicon (silicon chunks) to form the metal silicon.

[0142] The pulverized metal silicon formation step may involve pulverizing raw silicon (silicon chunks) using physical force.

[0143] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode active material, wherein the silane deposition type metal silicon forming step includes: depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; and obtaining the metal silicon-based active material deposited on the substrate.

[0144] The silane deposition metal silicon formation step corresponds to a chemical method, that is, metal silicon can be formed by depositing a metal silicon-based active material on a substrate or wafer through a chemical reaction of silane gas, and then scraping off the deposited metal silicon-based active material to obtain the metal silicon-based active material.

[0145] In this case, when metal silicon is formed through the silane deposition method (chemical method), it is formed in a bulk and larger size than when metal silicon is formed through the existing pulverization method, and therefore, it can be manufactured to satisfy the plate-like shape requirement of Equation 1 through the pulverization (milling) process described below.

[0146] According to one example, the silane gas may include at least one gas selected from monosilane, dichlorosilane, and trichlorosilane, and specifically may be trichlorosilane gas.

[0147] In one embodiment of the present application, the step of chemically reacting silane gas to deposit a metal 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 enabling 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, and more preferably 800°C to 1300°C, or 800°C to 2200°C. This is a lower temperature than the conventional gas atomizing method, which heats the substrate to 1600°C or higher to melt Si.

[0148] In one embodiment of the present application, the metal silicon-based active material may further include a step of growing the metal silicon-based active material via crystalline nucleation. The step of growing the metal silicon-based active material via crystalline nucleation may be performed at a temperature of 800°C or higher, preferably 800°C to 1300°C. This is a lower temperature than the conventional gas atomizing method, which heats the material to 1600°C or higher to melt silicon. In addition, the step of growing the silicon-based active material via crystalline nucleation may be performed under a pressure of 100 Pa to 150 Pa. Such a low pressure reduces the silicon growth rate, thereby forming smaller crystal grains and achieving a specific surface area.

[0149] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode active material, further comprising: depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; and thereafter, growing the metal silicon-based active material through crystalline nucleation, wherein the growing the metal silicon-based active material through crystalline nucleation comprises generating crystalline nuclei at a temperature of 800°C or higher for 1 hour to 24 hours.

[0150] That is, a metal silicon-based active material can be formed by the above-described method, and then the metal silicon is pulverized to form a silicon-based active material, thereby producing a silicon-based active material.

[0151] In one embodiment of the present application, there is provided a method for producing a negative electrode active material, wherein the step of milling the metal silicon to form a silicon-based active material includes milling the metal silicon under a milling pressure condition of 3 bar to 10 bar for 12 hours to 48 hours.

[0152] In one embodiment of the present application, the step of pulverizing the metal silicon to form a silicon-based active material may satisfy a pulverization pressure condition of 3 bar to 10 bar, preferably 3.5 bar to 9 bar, more preferably 4 bar to 8 bar.

[0153] In one embodiment of the present application, the step of milling the metal silicon to form a silicon-based active material may include milling under the milling pressure conditions for 12 hours to 48 hours, specifically for 12 hours to 30 hours, more specifically for 12 hours to 24 hours.

[0154] By varying the pressure, time, and process conditions as described above, it is possible to form a silicon-based active material that satisfies the range of the above-described formula 1. That is, in the process of crushing metal silicon using physical force to generate particle cracks, the difference in particle shape is controlled by adjusting the crushing pressure and time, and thus the above-described conditions that satisfy the range of the formula 1 have been found.

[0155] In one embodiment of the present application, the milling step may include any process that can cause particle cracks through physical force, and specifically, may include a process using a jet mill, a disk mill, or a ball mill.

[0156] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode composition according to the present application or a cured product thereof.

[0157] 1 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, including a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Although FIG. 1 shows the negative electrode active material layer formed on one surface, it may be formed on both surfaces of the negative electrode current collector layer.

[0158] 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.

[0159] In this case, the negative electrode slurry may include the above-mentioned negative electrode composition; and a slurry solvent.

[0160] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0161] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0162] The solid content of the negative electrode slurry may refer 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.

[0163] 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 appropriate, and the negative electrode active material layer can be efficiently formed by minimizing particle agglomeration of the negative electrode composition.

[0164] In one embodiment of the present application, the slurry solvent may be any solvent that can dissolve the negative electrode composition, and specifically, water or NMP may be used.

[0165] 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 has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. Furthermore, the bonding strength of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0166] 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 20 μm or more and 500 μm or less.

[0167] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0168] 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.

[0169] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0170] 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 specific compositions and content portions to satisfy the above range, thereby providing the electrode with appropriate ranges of electrical conductivity and resistance.

[0171] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0172] 2 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 sandwiched between them.

[0173] A secondary battery according to an embodiment of the present specification may include 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.

[0174] 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.

[0175] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce 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, etc. can be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0176] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.6 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); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0177] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0178] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without undergoing 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, and the like, and one or more of these may be used alone or in combination.

[0179] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0180] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure 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 polymer material may also be used, and may be used in a single-layer or multi-layer structure.

[0181] 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.

[0182] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0183] Examples of the non-aqueous organic solvent that may be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0184] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, and therefore, these cyclic carbonates are more preferably used.

[0185] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0186] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0187] One embodiment of the present invention provides 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, excellent rate-limiting characteristics, and excellent cycle characteristics, and 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.

[0188] Below, preferred examples are presented to help understand the present invention. However, the following examples are 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 of the scope and technical idea of ​​the present description, and it is natural that such changes and modifications fall within the scope of the appended claims. [Example]

[0189] <Production example> <Production of first metal silicon-based active material> After the silicon block was gasified with silane and then chemically reacted, the metal silicon active material was formed on the substrate by deposition. The crystal nucleus growth time was 1 to 30 hours, and the crystal grain size was 58.4 nm, satisfying the grain size (D50) of 5.94 μm.

[0190] <Production of second metal silicon-based active material> Unprocessed silicon (silicon chunks) was crushed by physical force to produce unprocessed silicon-based active material.

[0191] <Production of Silicon-Based Composite of Comparative Example 2> A silicon-based composite was produced, which included a composite (A) containing particles (A1) containing Si with an average primary particle diameter dAV of 5 nm or more and 95 nm or less, particles (A2) made of a substance containing graphite, and a carbonaceous material (A3) formed on the surface of the particles (A1).

[0192] The metal silicon-based active material or the silicon-based composite of Comparative Example 2 was prepared in the above manner, and then the silicon-based active material was manufactured by changing the grinding pressure and grinding time as shown in Table 1 below.

[0193] [Table 1]

[0194] <Production of negative electrodes> The negative electrode active material including the silicon-based active material, the first conductive material, the second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 80:9.6:0.4:10 to prepare a negative electrode slurry (solid concentration 25 wt %).

[0195] 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.

[0196] As a specific mixing method, the first conductive material, the second conductive material, the binder, and the water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0197] The negative electrode current collector layer was made of a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 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: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0198] <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%).

[0199] 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. 2The 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%).

[0200] An electrolyte was injected between the positive electrode and the negative electrode of the example or comparative example via a polyethylene separator to prepare a lithium secondary battery.

[0201] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, to which vinylene carbonate was added at 3 wt% based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0202] Experimental example 1: Monocell life evaluation The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V and 1 C / 0.5 C, and the capacity retention was measured every 50 cycles during the test by charging / discharging at 0.33 C / 0.33 C (4.2-3.0 V). The results are shown in Table 2.

[0203] Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} x 100

[0204] [Table 2]

[0205] Experimental example 2: @SOC50 2.5C Discharge resistance increase rate (after 200 cycles) evaluation In the test of Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles, and then the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0206] Regarding the resistance increase rate evaluation, data at 200 cycles was calculated, and the results are shown in Table 3 below.

[0207] [Table 3]

[0208] As can be seen from Tables 2 and 3, in Examples 1 to 9 according to the present invention, in which the plate-like shape was adjusted, the life evaluation and the resistance increase rate were superior to those of Comparative Example 1.

[0209] This is because the plate-like degree is controlled to satisfy the range of Equation 1. That is, when a relatively large proportion of 111 crystal faces is formed as in the conventional case, the 111 crystal faces have lower lithium mobility than the 220 crystal faces, which prevents lithium from being uniformly absorbed and desorbed during lithium insertion and desorption reactions. However, the silicon-based active material according to the present application contains a high proportion of 220 crystal faces, which allows lithium to be uniformly absorbed and desorbed during lithium insertion and desorption reactions, thereby mitigating silicon cracking on the electrode surface and improving the lifespan of the electrode.

[0210] In the case of Comparative Example 2, sintering of silicon formed inside Si / C due to high temperature heating (above 1500°C) for graphitization occurred, and the ratio of 111 increased, which did not satisfy the ranges of Equation 1 and Equation 2. As a result, it was confirmed that the life performance was reduced and the resistance increase rate was evaluated high.

[0211] For reference, it can be seen that the plate-likeness (Equation 1) increases from Example 1 to Example 13. In general, it can be seen that as the major and minor axis sizes become more similar, the lifespan performance tends to increase. However, in Example 13, the major and minor axis sizes become the most similar, and as a result, applying too strong a force did not achieve the target D50 level, resulting in a shorter lifespan compared to the other Examples. [Explanation of symbols]

[0212] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode active material containing a silicon-based active material that satisfies the plate-like degree of the following formula 1: The silicon-based active material is SiO ｘ (x=0) and SiO ｘ (0<x<2), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ A negative electrode active material containing 70 parts by weight or more of (x = 0): [Formula 1] 45≦(A / B)×100 In the formula 1, A means the length of the minor axis of the silicon-based active material, B means the length of the major axis of the silicon-based active material.

2. the silicon-based active material includes a 220 crystal plane and a 111 crystal plane; The negative electrode active material according to claim 1, wherein the silicon-based active material satisfies the following formula 2: [Formula 2] 37≦(X / Y)×100 In the formula 2, Y means the proportion of 111 crystal faces in the silicon-based active material; X means the proportion of 220 crystal faces in the silicon-based active material.

3. The negative electrode active material according to claim 1 , wherein the silicon-based active material has a D50 particle size of 3 μm or more and 10 μm or less.

4. The negative electrode active material according to claim 1 , wherein the silicon-based active material has a crystal grain size of 500 nm or less.

5. The negative electrode active material according to claim 1 , wherein the silicon-based active material satisfying the plate-like degree of Equation 1 is contained in an amount of 80 parts by weight to 100 parts by weight based on 100 parts by weight of the negative electrode active material.

6. providing a metal silicon; and pulverizing the metal silicon to form a silicon-based active material; A method for producing a negative electrode active material, comprising: The silicon-based active material satisfies the plate-like degree of the following formula 1, [Formula 1] 45≦(A / B)×100 In the formula 1, A means the length of the minor axis of the silicon-based active material, B means the length of the major axis of the silicon-based active material.

7. The method of claim 6, wherein the step of preparing the metal silicon comprises: forming metal silicon by pulverization; or forming metal silicon by silane deposition.

8. The method of claim 7 , wherein the step of forming the pulverized metal silicon comprises pulverizing raw silicon to form the metal silicon.

9. The silane deposition metal silicon forming step includes depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; and obtaining the metal silicon-based active material deposited on the substrate; The method for producing a negative electrode active material according to claim 7 , comprising:

10. 10. The method for producing an anode active material according to claim 6, wherein the step of milling the metal silicon to form a silicon-based active material comprises milling the metal silicon under a milling pressure condition of 3 bar to 10 bar for 12 hours to 48 hours.

11. A negative electrode composition comprising: the negative electrode active material according to any one of claims 1 to 5; a negative electrode conductive material; and a negative electrode binder.

12. The negative electrode composition according to claim 11 , wherein the negative electrode active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

13. 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 11 or a cured product thereof.

14. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 14. The negative electrode for a lithium secondary battery according to claim 13, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

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

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