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

Abstract

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. 10-2022-0097513, filed with the Korean Intellectual Property Office on August 4, 2022, and all of its contents are incorporated herein by reference.

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

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative and clean energies. As part of this, the fields of power generation and power storage using electrochemical reactions are the most actively studied areas.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage area is expanding more and more.

[0005] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commonly used and widely used. In addition, research on methods for manufacturing high-density electrodes having a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles having 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, research is actively being conducted on methods to increase capacity using silicon-based compounds such as Si / C and SiOx as negative electrode active materials, which have a capacity more than 10 times greater than graphite-based materials. However, while silicon-based compounds are high-capacity materials, they have the problem that, compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems that arise when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as adjusting the driving potential, further coating a thin film on the active material layer, suppressing volume expansion itself by adjusting the particle size of the silicon-based compound, or preventing the conduction path from being interrupted. However, in the case of the aforementioned methods, there is a possibility that the performance of the battery may actually decrease, so there are limitations to their application, and the commercialization of negative electrode batteries with a high content of silicon-based compounds remains limited.

[0009] Therefore, even when using silicon-based active materials as negative electrode active materials to improve capacity performance, research is needed on the silicon-based active materials themselves that can prevent the conduction path from being interrupted due to the volume expansion of silicon-based compounds. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] A silicon-based active material is produced by a chemical processing method that is not a conventional grinding processing method. In particular, as shown by research, in the case of a silicon-based active material grown by the formation of crystal nuclei, it is possible to adjust the surface area and roughness. By adjusting the surface area within a predetermined range, it was confirmed that during the insertion / desorption reaction of lithium, the reaction occurs uniformly, reducing the stress on the silicon-based active material.

[0012] This 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 Problems

[0013] One embodiment of this specification includes a silicon-based active material with a specific surface area of 0.30 m 2 / g or more and 4.00 m 2 / g or less. The silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, it provides a negative electrode active material containing 70 parts by weight or more of the SiOx (x = 0).

[0014] In another embodiment, a method for manufacturing a negative electrode active material includes the steps of chemically reacting silane gas to deposit a silicon-based active material on a substrate; growing the silicon-based active material by the formation of crystal nuclei; and obtaining the silicon-based active material deposited on the substrate. The specific surface area of the silicon-based active material is 0.30 m 2 / g or more and 4.00 m 2 / g or less, and provides a method for manufacturing a negative electrode active material according to this application.

[0015] In another embodiment, it provides a negative electrode composition including the negative electrode active material according to this application; a negative electrode conductive material; and a negative electrode binder.

[0016] In another embodiment, a negative electrode for a lithium secondary battery is provided, which includes 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 contains the negative electrode composition according to the present application or a cured product thereof.

[0017] Finally, a lithium secondary battery is provided, which includes 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.

Advantages of the Invention

[0018] In the case of the negative electrode active material according to an embodiment of the present invention, different from the conventional pulverization processing method, a chemical method is used, and a silicon-based active material is grown by the formation of crystal nuclei. Thus, it is characterized by having a silicon-based substance with a specific surface area greater than a predetermined range.

[0019] The negative electrode active material of the present invention includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2) as a silicon-based active material. Based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of the SiOx (x = 0). That is, while having a pure silicon (Pure Si) active material, the main feature is that the problem of volume expansion due to charge and discharge, which is a problem caused by this, is solved by adjusting the specific surface area of the silicon-based active material within a predetermined range.

[0020] That is, by using a silicon-based active material whose specific surface area satisfies the range according to the present invention, the rough surface enables the particles with the same particle size to have a large surface area, and the binding force with the binder increases, thereby relaxing the cracks (Crack) of the electrode due to repeated charge and discharge cycles. Also, it can uniformly react during the insertion and desorption reactions of lithium during charge and discharge, reduce the stress received by the silicon-based active material, and relax the cracking of the particles, thereby improving the electrode life maintenance rate.

Brief Description of the Drawings

[0021] [Figure 1] This figure shows the manufacturing process of a silicon-based active material according to Example 1 of this application. [Figure 2] This figure shows the manufacturing process of a silicon-based active material according to Comparative Example 1 of this application. [Figure 3] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 4] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Figure 5] This illustrates the concept of the degree of spheroidization of silicon-based active materials. [Figure 6] This illustrates the concept of convexity in silicon-based active materials. [Modes for carrying out the invention]

[0022] Before describing the present invention, let us first define some terms. In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0023] In this specification, "p~q" means "greater than or equal to p and less than or equal to q". In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0024] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the average particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam.

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

[0026] In this specification, the meaning of a polymer containing a monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

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

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

[0029] 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.

[0030] One embodiment of this specification has a silicon-based active material with a specific surface area of 0.30 m 2 / g or more and 4.00 m 2 / g or less. The silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, it provides a negative electrode active material containing 70 parts by weight or more of the SiOx (x = 0).

[0031] The negative electrode active material of the present invention includes, as the silicon-based active material, one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of the SiOx (x = 0). That is, while having a pure silicon (Pure Si) active material, the main feature is that the problem of volume expansion due to charge and discharge, which is a problem caused by it, is solved by adjusting the specific surface area of the silicon-based active material to a predetermined range.

[0032] That is, by using a silicon-based active material whose specific surface area satisfies the range according to the present invention, the rough surface makes the particles with the same particle size have a wider surface area, and the binding force with the binder becomes higher, thereby relaxing the cracks in the electrode due to repeated charge and discharge cycles. Also, it can react uniformly during the insertion and desorption reactions of lithium during charge and discharge, reducing the stress received by the silicon-based active material and relaxing the cracking of the particles, thereby improving the electrode life retention rate.

[0033] In one embodiment of the present application, the 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 silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more.

[0034] In one embodiment of the present application, the silicon-based active material contains SiOx (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more.

[0035] In another embodiment, based on 100 parts by weight of the 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.

[0036] In one embodiment of the present application, particularly, pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material may mean, as described above, that when based on 100 parts by weight of the entire silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are contained within the above range.

[0037] 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 SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0038] 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 generally be contained in the silicon-based active material. Specifically, based on 100 parts by weight of the silicon-based active material, the impurities may be contained in an amount of 0.1 part by weight or less.

[0039] In the case of silicon-based active materials, when compared with the conventionally used graphite-based active materials, the capacity is significantly higher, and attempts to apply them are increasing. However, the volume expansion rate during charge and discharge is high, and it has remained at the level of using a small amount mixed with graphite-based active materials.

[0040] Therefore, in the case of the present invention, in order to improve the capacity performance, while using only the silicon-based active material as the negative electrode active material, in order to solve the above problems, rather than adjusting the composition of the conductive material and the binder, the surface area (surface roughness) of the silicon-based active material itself is adjusted to solve the conventional problems.

[0041] In one embodiment of the present application, the negative electrode active material may include a silicon-based active material having a specific surface area of 0.30 m 2 / g or more and 4.00 m 2 / g or less.

[0042] In another embodiment, the silicon-based active material may have a specific surface area of 0.30 m 2 / g or more, preferably 0.31 m 2 / g or more, more preferably 0.32 m 2 / g or more. The silicon-based active material may have a specific surface area of 4.00 m 2 / g or less, preferably 2.50 m 2 / g or less, more preferably 2.20 m 2 / g or less. The specific surface area may be measured by DIN 66131 (using nitrogen).

[0043] The silicon-based active material has the above specific 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 described later. That is, when manufacturing the negative electrode active material by the manufacturing method according to the present application, the rough surface makes the particles having the same particle size have a large surface area. At this time, by satisfying the above range and increasing the binding force with the binder, it has the characteristic of being able to relieve the cracks of the electrode due to repeated charge and discharge cycles.

[0044] Furthermore, lithium ions are inserted uniformly, reducing the stress on the silicon particles during insertion, thereby mitigating particle cracking. As a result, the life stability of the negative electrode can be improved. When the specific surface area is less than the range mentioned above, even with the same particle size, the surface is formed smoothly, reducing the bonding force with the binder and causing electrode cracks. In this case, lithium ions are inserted non-uniformly within the particles, resulting in high stress due to ion insertion and causing particle cracking. In one embodiment of this application, the SiOx(x=0) has a crystal grain size of 200 nm or less. When a silicon-based active material with a crystal grain size satisfying the range mentioned above is used, the lithium can react uniformly during the insertion and desorption reactions during charging and discharging, reducing the stress on the silicon-based active material and mitigating particle cracking, thereby improving the life maintenance rate of the electrode.

[0045] In this application, "crystal grain" refers to a crystalline particle in a metal or material consisting of an aggregate of irregularly shaped particles of microscopic size, and the crystal grain size may refer to the diameter of the observed crystal grain. In other words, in this application, the crystal grain size refers to the size of domains within a particle that share the same crystal orientation, and is a different concept from particle size or particle size, which express the size of a substance.

[0046] In another embodiment, the crystal grain size of the silicon-based active material may be 200 nm or less, preferably 130 nm or less, more preferably 110 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 also be in the range of 1 nm or more, preferably 3 nm or more.

[0047] The SiOx(x=0) has the aforementioned grain size, and the grain size can be adjusted by changing the manufacturing process conditions described later. In this case, by satisfying the aforementioned range and ensuring a wide distribution of grain boundaries, lithium ions can be inserted uniformly, reducing the stress on the silicon particles during lithium ion insertion and thereby mitigating particle cracking. As a result, the lifetime stability of the negative electrode can be improved. If the grain size exceeds the aforementioned range, the grain boundaries within the particles become narrowly distributed. In this case, lithium ions are inserted non-uniformly within the particles, resulting in high stress due to ion insertion and causing particle breakage.

[0048] In one embodiment of this application, the silicon-based active material includes a crystalline structure having a grain distribution of 1 nm to 200 nm, and the area ratio of the crystalline structure is 5% or less based on the total area of ​​the silicon-based active material.

[0049] In another embodiment, the area ratio of the crystal 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.

[0050] In other words, the silicon-based active material according to this application has a grain size of 200 nm or less, and the size of each individual crystal structure is formed to satisfy the aforementioned area ratio. This allows for a wider distribution of grain boundaries, thereby achieving the aforementioned effect.

[0051] In one embodiment of this application, the silicon-based active material provides a negative electrode active material that satisfies the range of the following formula 1. [Formula 1] X1 / Y1 ≤ 0.960 In Equation 1, X1 is the orthogonal projection area of ​​the silicon-based active material, Y1 represents the area of ​​the circle that has the same circumference as the orthogonal projection of the silicon-based active material.

[0052] The measurement of Equation 1 can be performed using a particle shape analyzer. Specifically, after dispersing the silicon-based active material according to this application onto a glass plate by air jet, the shape of 10,000 silicon-based active material particles in a photograph taken by orthogonally projecting the dispersed silicon-based active material particles can be measured. In this case, Equation 1 is a value that represents the average for 10,000 particles. Equation 1 according to this application can be measured from the above image, and Equation 1 may be expressed as the degree of spherulity of the silicon-based active material. Figure 5 shows the concept of degree of spherulity. The degree of spherulity is given by the formula [4π * orthogonal projection area of ​​silicon-based active material / (orthogonal projection perimeter of silicon-based active material)] 2 It may also be displayed as ].

[0053] Alternatively, X1 may represent the actual area of ​​the silicon-based active material, and Y1 may represent the area of ​​spherical particles around the silicon-based active material.

[0054] In one embodiment of this application, the degree of spheroidization of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The degree of spheroidization 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.

[0055] In one embodiment of this application, the silicon-based active material is provided as a negative electrode active material satisfying the range of the following formula 2. [Formula 2] X2 / Y2 ≤ 0.996 In the above formula 2, Y2 is the orthogonal projection perimeter of the silicon-based active material. X2 is the perimeter of the polygon circumscribing the orthogonal projection of the silicon-based active material.

[0056] The measurement of Equation 2 can be performed using a particle shape analyzer. Specifically, the silicon-based active material according to this application can be dispersed on a glass plate by air jetting, and then an orthographic projection image of the dispersed silicon-based active material can be taken to measure the shape of 10,000 silicon-based active material particles in the photograph. In this case, Equation 2 is a value that represents the average for 10,000 particles. Equation 2 according to this application can be measured from the image, and Equation 2 may be expressed in terms of the convexity of the silicon-based active material. Figure 6 shows the concept of convexity.

[0057] Alternatively, Y2 may represent the actual perimeter of the silicon-based active material, and X2 may represent the perimeter of the circumscribed figure of the silicon-based active material.

[0058] In one embodiment of this application, the range X2 / Y2 ≤ 0.996, preferably X2 / Y2 ≤ 0.995, may be satisfied, and the range 0.8 ≤ X2 / Y2, preferably 0.9 ≤ X2 / Y2, more preferably 0.95 ≤ X2 / Y2, specifically 0.98 ≤ X2 / Y2 may be satisfied.

[0059] The smaller the value of equation 1 or equation 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, which helps to mitigate electrode cracking caused by repeated charge-discharge cycles.

[0060] In one embodiment of this application, the negative electrode active material does not have a structure containing pores, satisfies formulas 1 and 2, and has an external surface irregularity. That is, the negative electrode active material may have an external surface irregularity configuration, rather than an internal pore configuration.

[0061] In one embodiment of this application, the silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm to 30 μm.

[0062] The fact that the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm to 30 μm means that it contains a large number of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles included is not limited.

[0063] The particle size of the silicon-based particles can be expressed by their diameter if they are spherical, but even if they have other shapes that are not spherical, the particle size can be measured in a way that is more efficient than in the case of spherical particles, and the particle size of individual silicon-based particles can be measured using methods commonly used in this industry.

[0064] On the other hand, the average particle size (D50 particle size) of the silicon-based active material in the present invention may be 3 μm to 10 μm, more specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles is 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 greater than or equal to the lower limit range, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of sustained conductive network formation and increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of uneven current density during charging and discharging.

[0065] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure, or exist in the form of a silicon-containing thin film or coating, but these are less preferred.

[0066] One embodiment of this application provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0067] In one embodiment of this application, the negative electrode composition is provided, wherein the negative electrode active material is 40 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0068] In another embodiment, the negative electrode active material may contain 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 also contain 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0069] The negative electrode composition according to this application uses a negative electrode active material that satisfies a specific surface area size that allows the volume expansion rate to be controlled during the charge-discharge process even when using a silicon-based active material with significantly high capacity within the aforementioned range, and has the characteristic of not degrading the performance of the negative electrode even when including the aforementioned range, and having excellent output characteristics during charging and discharging.

[0070] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, as mentioned above, even if the properties of the silicon-based active material itself are adjusted, a problem can sometimes occur where its volume rapidly expands during the charge / discharge process, disrupting the conductive paths formed within the negative electrode active material layer.

[0071] Therefore, in one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0072] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in the negative electrode and means a point-shaped or spherical conductive material that has conductivity without inducing a chemical change. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0073] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m 2 / g or more 60m 2 It may be less than / g.

[0074] In one embodiment of this application, the point-shaped conductive material may satisfy 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.

[0075] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, functional groups present on the surface of the dot-shaped conductive material are present, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, the present invention makes it possible to reduce the functional group content of the dot-shaped conductive material by using a specific silicon-based active material, thereby having an excellent effect on improving dispersibility.

[0076] In one embodiment of this application, a silicon-based active material is provided along with a point-type conductive material having a functional group content within the aforementioned range, wherein the functional group content can be adjusted by the degree of heat treatment of the point-type conductive material.

[0077] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0078] In one embodiment of this application, the conductive material may include a planar conductive material. The planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. The planar conductive material may also be described as a plate-shaped conductive material or a bulk-type conductive material.

[0079] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0080] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, the particle size is sufficient, making dispersion easy while preventing the viscosity of the negative electrode slurry from increasing too much. Therefore, the dispersion effect is superior when dispersed using the same equipment and time.

[0081] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0082] In one embodiment of this application, the planar conductive material may be a planar conductive material with a high specific surface area of ​​BET specific surface area; or a planar conductive material with a low specific surface area.

[0083] In one embodiment of this application, the planar conductive material may be any planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without limitation. In particular, the planar conductive material according to this application may be affected to some extent by the electrode performance due to dispersion effects, and it is especially preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0084] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​0.25 m². 2 It may be more than / g.

[0085] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g is also acceptable.

[0086] The planar conductive material relating to this application may be a high specific surface area planar conductive material or a low specific surface area planar conductive material.

[0087] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and has a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0088] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area is 1 m². 2 / g or more 40m2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0089] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted into a bundle or rope. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be exhibited depending on the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0090] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0091] 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 1 part by weight or more and 20 parts by weight or less, more preferably 5 parts by weight or more and 15 parts by weight or less, and most preferably 6 parts by weight or more and 13 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0092] The negative electrode conductive material described in this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. Specifically, the negative electrode conductive material described in this application plays a role in controlling the contact points between silicon-based active materials, which experience very large volume expansion of the electrodes due to charging and discharging. The positive electrode conductive material, on the other hand, plays a role in providing partial conductivity while acting as a buffer during rolling, and its structure and role are completely different from those of the negative electrode conductive material of the present invention.

[0093] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0094] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material has a different structure and role from the carbon-based active material typically used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0095] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0096] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was processed into a planar or plate-like form and used as a material to secure a conductive path for lithium, rather than to play a role in storing or releasing lithium. In this case, the negative electrode active material included together has high capacity characteristics for storing and releasing lithium and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0097] On the other hand, the fact that carbon-based active materials were used as active materials in this application means that they were processed into point-like or spherical shapes and used as materials that serve to store or release lithium.

[0098] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is punctate and has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate-type graphite, which is a planar conductive material, is planar and has a BET specific surface area of ​​5m². 2 It may be more than / g.

[0099] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0100] The negative electrode binder according to one embodiment of this application plays a role in controlling the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. Any ordinary binder can be applied as long as it fulfills the above role, and specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0101] In one embodiment of this application, the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may also be 5 parts by weight or more, or 10 parts by weight or more.

[0102] One embodiment of this application is a method for producing a negative electrode active material, comprising the steps of: chemically reacting silane gas to deposit a silicon-based active material onto a substrate; growing the silicon-based active material by generating crystal nuclei; and obtaining the silicon-based active material deposited on the substrate, wherein the specific surface area of ​​the silicon-based active material is 0.30 m². 2 / g or more 4.00m 2 This invention provides a method for producing a negative electrode active material that is less than or equal to / g.

[0103] According to one embodiment, the silane gas may contain one or more gases selected from monosilane, dichlorosilane, and trichlorosilane, and specifically, it may be trichlorosilane gas.

[0104] In one embodiment of this application, the step of growing the silicon-based active material by generating crystal nuclei is performed such that the silicon growth rate is reduced by low pressure, thereby enabling the formation of small crystal grains. This may be carried out 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 to 1600°C or higher to melt Si. Furthermore, the step of growing the silicon-based active material by generating crystal nuclei may be carried out under a pressure of 100 Pa to 150 Pa. In this way, the silicon growth rate is reduced by low pressure, thereby enabling the formation of small crystal grains.

[0105] Conventionally, MG-silicon, which is a solid block of silicon, was manufactured by crushing it using physical force. In this manufacturing method, the crystal grain size is generally greater than 100 nm, the surface is smooth, and the specific surface area is 0.30 m². 2 The value will be less than / g. Simply put, when manufacturing silicon-based active materials using conventional methods, there is a disadvantage in that the surface area cannot be controlled, making it difficult to ensure the lifetime stability of the negative electrode.

[0106] However, the method for producing the negative electrode active material according to this application, as described above, includes the step of chemically converting a silicon lump into a silane gas, and then growing the silicon-based active material by generating crystal nuclei, thereby forming silicon particles, and thus it was possible to obtain a silicon-based active material that satisfies the surface area size according to this application.

[0107] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0108] Figure 3 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Figure 3 shows that the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0109] In one embodiment of this application, the negative electrode for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of a negative electrode current collector layer.

[0110] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0111] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0112] 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%.

[0113] The solid content of the negative electrode slurry may mean the content of the negative electrode composition contained in the negative electrode slurry, or it may mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0114] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the caking phenomenon of the particles of the negative electrode composition, and enabling efficient formation of the negative electrode active material layer.

[0115] In one embodiment of this application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode composition, and specifically, water or NMP may be used.

[0116] In one embodiment of this application, the negative electrode current collector layer typically 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, and may be made of materials such as copper, stainless steel, aluminum, nickel, titanium, plastic carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0117] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0118] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited to this.

[0119] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0120] 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%.

[0121] The aforementioned porosity is varied by the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the aforementioned range is satisfied by including the silicon-based active material and conductive material according to this application in specific compositions and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0122] One embodiment of this application provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0123] Figure 4 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, it shows that a negative electrode 100 for a lithium secondary battery, including a negative electrode active material layer 20, can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of a positive electrode current collector layer 50, and that the negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separation membrane 30 in between.

[0124] A secondary battery according to one embodiment of this specification may, in particular, include the negative electrode for lithium secondary batteries described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0125] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0126] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, plastic carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0127] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M can be at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., can be mentioned, but are not limited to these. The positive electrode may also be metallic lithium (Li-metal).

[0128] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0129] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it has electronic conductivity in the battery without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0130] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0131] The separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in secondary batteries, but it is especially preferable to have low resistance to ion movement of the electrolyte and excellent moisture-retaining capacity for the electrolyte. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and they may be selectively used in single-layer or multi-layer structures.

[0132] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0133] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0134] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with low-viscosity, low-dielectric-constant chain carbonates such as dimethyl carbonate and diethyl carbonate in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0135] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble 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 - You may use one or more selected from the group consisting of the following:

[0136] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0137] 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. Because the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may be used as power sources for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0138] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0139] <Manufacturing example> <Manufacturing of negative electrode active materials in Examples 1-6> Figure 1 shows the manufacturing process of a silicon-based active material according to Example 1 of this application. Specifically, a silicon block in the form of MG-Si was gasified at high temperature, then chemically reacted, and subsequently deposited onto a substrate. After that, the silicon-based active material was grown by generating crystal nuclei. The results are shown in Table 1.

[0140] In this process, the surface area of ​​the silicon-based active materials in Examples 1 to 6 could be controlled by controlling the process conditions (selecting conditions to adjust the surface area within the crystal nucleation temperature and pressure range shown in Table 1 below, and adjusting the temperature and pressure conditions to adjust the surface area), and the results are shown in Table 1.

[0141] <Manufacturing of the negative electrode active material in Comparative Example 1> Figure 2 shows the manufacturing process of a silicon-based active material according to Comparative Example 1 of this application. Specifically, a silicon lump, which is MG-Si, was crushed by physical force, melted, and then gas atomized. As a result, a negative electrode active material with a relatively smooth surface formed by the liquid / gas surface tension was produced, and the specific surface area, circularity, convexity, and D50 particle size of the silicon-based active material in this case are shown in Table 1.

[0142] [Table 1]

[0143] In Comparative Example 2, a silicon block of MG-Si was crushed by physical force, melted, and then subjected to gas atomization. A silicon-based active material with pores was then formed by a strong base etching method. The details of this process are as shown in Table 1.

[0144] Furthermore, in the case of Comparative Example 3, the vapor-deposited silicon-based active material was subjected to strong base treatment to primarily form pores inside the particles rather than surface irregularities. As a result, it has a higher specific surface area compared to the other comparative examples and examples, and Equation 1 (circularity) shows an increased value compared to Examples 1 to 6 of this application, while Equation 2 (convexity) shows a decreased value.

[0145] In other words, in Comparative Example 3, as in Comparative Example 2, pores are formed on a smooth surface, so the roughness increases significantly, but the nearly elliptical particles are scraped off and become rounded.

[0146] As shown in Table 1, the silicon of Examples 1 to 6 has a specific surface area of ​​0.30 m². 2 It was above / g.

[0147] For reference, in the case of Comparative Example 3, where internal pores are formed in the silicon-based active material, rather than having protruding irregularities on the surface, a silicon-based active material with a smooth surface is formed as in Comparative Example 1. By forming pores using a strong base etching method, the specific surface area is larger than in Examples 1 to 6, and it can be confirmed that Equation 1 is formed at a larger size. This is because, when pores are formed, as the roughness of the existing smooth surface increases, Equation 2 (Convexity) decreases, but it is judged that some particles with an elliptical shape are removed and rounded during the etching process.

[0148] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding polyacrylamide, which contains the silicon-based active material listed in Table 1 above, as a negative electrode active material, a negative electrode conductive material, and binder, to distilled water in a weight ratio of 80:10:10 (solid content concentration 25% by weight).

[0149] Specifically, the negative electrode conductive material is carbon black (specific surface area: 45 m²). 2 It is / g, diameter: 30nm~50nm.

[0150] As for the specific mixing method, the negative electrode conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for another 30 minutes to produce the negative electrode slurry.

[0151] As the negative electrode current collector layer, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 85 mg / 25 cm². 2 The material was coated with the specified load, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was then used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0152] <Manufacturing of secondary batteries> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by adding 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 in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0153] As the positive electrode current collector, 537 mg / 25 cm of the positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm). 2The cathode was manufactured by coating with the specified load, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0154] A polyethylene separation membrane was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0155] The aforementioned electrolyte was prepared by adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0156] <Example of experiment> Experimental Example 1: Monocell Life Performance Results The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V and 1C / 0.5C. During the test, the capacity retention rate was measured every 50 cycles by charging / discharging at 0.33C / 0.33C (4.2-3.0V). Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0157] [Table 2]

[0158] As can be seen in Table 2, when the capacity retention rate of Examples 1-6 and Comparative Examples 1-3 was examined by cycle, it was confirmed that the capacity retention rate of Comparative Example 1 was lower than that of the Examples. This corresponds to the fact that when the specific surface area of ​​the silicon-based active material satisfies the range of the present invention, it can react uniformly during the insertion and removal reactions of lithium during charging and discharging, reducing the stress on the silicon-based active material and mitigating particle cracking, thereby improving the capacity retention rate of the electrode.

[0159] Experimental Example 2: Monocell Resistance Increase Rate In Experimental Example 1, during the test, the battery was charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure the capacity retention rate. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed. For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0160] [Table 3]

[0161] Tables 2 and 3 confirm that the lifespan characteristics and resistance changes of batteries using silicon produced in Examples 1-6 as the negative electrode active material are excellent.

[0162] Furthermore, in the case of Comparative Example 2, the specific surface area is smaller compared to the present invention, and it corresponds to a structure with internal pores rather than an external uneven surface configuration. In this case, the effect is judged to be superior to that of Comparative Example 1, in which the specific surface area deviates significantly from the range of the present invention. However, it was confirmed that the lifespan performance is reduced and the resistance change is larger compared to this embodiment due to the presence of internal pores.

[0163] For reference, in the case of Comparative Example 3, the silicon-based active material does not have a surface with protruding irregularities, but rather internal pores are formed in the silicon-based active material. This corresponds to forming a silicon-based active material with a smooth surface, as in Comparative Example 2, and then forming pores by a strong base etching method. As a result, the specific surface area is larger than that of Examples 1 to 6, and it can be confirmed that a larger amount of Equation 1 is formed. In this case, as with Comparative Example 2, the internal pore morphology is observed, resulting in a decrease in lifetime performance and a larger change in resistance compared to this example. [Explanation of Symbols]

[0164] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30 ···Separator 40...Cathode active material layer 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. Specific surface area is 0.30 m² ２ / g or more 4.00m ２ Contains silicon-based active material of less than / g, The aforementioned silicon-based active material consists of SiOx (x=0), The silicon-based active material is a negative electrode active material that satisfies the ranges of the following formulas 1 and 2: [Formula 1] 0.930 ≤ X1 / Y1 ≤ 0.960 In the above formula 1, X1 is the orthogonal projection area of ​​the silicon-based active material, Y1 represents the area of ​​a circle having the same circumference as the orthogonal projection of the silicon-based active material. [Formula 2] X2 / Y2≦0.996 In the above formula 2, Y2 is the orthogonal projection perimeter of the silicon-based active material. X2 is the perimeter of the polygon circumscribing the orthogonal projection of the silicon-based active material.

2. The negative electrode active material according to claim 1, wherein the SiOx (x=0) has a crystal grain size of 200 nm or less.

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

4. The step of chemically reacting silane gas to deposit silicon-based active material onto the substrate, The steps include growing the silicon-based active material by generating crystal nuclei, and A step of obtaining the silicon-based active material deposited on the substrate, A method for producing a negative electrode active material, including, The specific surface area of ​​the silicon-based active material is 0.30 m². ２ / g or more 4.00m ２ A method for producing a negative electrode active material according to any one of claims 1 to 3, wherein the amount is less than or equal to / g.

5. The method for producing a negative electrode active material according to claim 4, wherein the silane gas comprises one or more gases selected from monosilane, dichlorosilane, and trichlorosilane.

6. The method for producing a negative electrode active material according to claim 4, wherein the step of growing the silicon-based active material by generating crystal nuclei is carried out at a temperature of 800°C to 1300°C and a pressure of 100 Pa to 150 Pa.

7. A negative electrode composition comprising a negative electrode active material, a negative electrode conductive material, and a negative electrode binder according to any one of claims 1 to 3.

8. The negative electrode composition according to claim 7, wherein the negative electrode active material is 40 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

9. The negative electrode composition according to claim 7, wherein the negative electrode conductive material is 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

10. The material includes a negative electrode current collector layer and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer. The negative electrode for a lithium secondary battery comprises the negative electrode composition or a cured product thereof according to claim 7, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to claim 7.

11. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 10, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

12. positive electrode, A negative electrode for a lithium secondary battery according to claim 10, A separator provided between the positive electrode and the negative electrode, and electrolyte, Lithium-ion batteries, including lithium-ion batteries.

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