Anode and secondary battery including said anode

Abstract

The present invention relates to a negative electrode including a negative electrode active material layer, wherein the negative electrode active material layer includes a silicon-containing negative electrode active material and a conductive material, the silicon-containing negative electrode active material includes a core and a carbon layer provided on the core, and the core includes SiO x (0 < x < 2) and at least one metal atom, the at least one metal atom includes at least one selected from the group consisting of Mg, Li, Al, and Ca, and the D5 / D of the silicon-containing negative electrode active material 50 is 0.5 or more, the D5 of the silicon-containing negative electrode active material is 3 μm or more, and D 50 is 4 μm or more and 11 μm or less, and relates to a negative electrode in which the conductive material includes single-walled carbon nanotubes and a secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0107510 filed with the Korean Intellectual Property Office on August 13, 2021, and Korean Patent Application No. 10-2022-0008551 filed with the Korean Intellectual Property Office on January 20, 2022, the contents of which are incorporated herein in their entirety.

[0002] The present invention relates to a negative electrode containing a silicon-containing negative electrode active material having a specific particle size distribution and single-walled carbon nanotubes, and a secondary battery containing the negative electrode. [Background technology]

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

[0004] Currently, secondary batteries are a typical example of electrochemical elements that use electrochemical energy, and their range of use is expanding. In recent years, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as energy sources has rapidly increased. Among these secondary batteries, much research has been conducted on high-energy density, i.e., high-capacity lithium secondary batteries, which have been commercialized and are widely used.

[0005] 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 extracts lithium ions from the positive electrode. The negative electrode active material can be a silicon-containing active material with a large discharge capacity.

[0006] However, silicon-containing active materials undergo excessive volume change during battery operation, resulting in reduced battery life. Previous approaches to address this issue have involved reducing the proportion of silicon-containing active materials used or using binders capable of exhibiting high anode adhesive strength. However, these approaches have been limited in their effectiveness because they do not involve improving the silicon-containing active material itself. Another approach has been to make silicon-containing active materials porous to accommodate volume expansion internally, but this approach reduces the capacity per weight of the anode and reduces its effectiveness due to particle destruction during rolling after electrode fabrication.

[0007] Therefore, there is an urgent need to develop a negative electrode that can effectively improve the life characteristics of a battery while using a silicon-containing negative electrode active material. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-1586816 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a negative electrode capable of improving the capacity, efficiency, and / or life characteristics of a battery, and a secondary battery including the negative electrode. [Means for solving the problem]

[0010] One embodiment of the present invention is an anode including an anode active material layer, the anode active material layer including a silicon-containing anode active material and a conductive material, the silicon-containing anode active material including a core and a carbon layer present on the core, the core being made of SiO x(0 < x < 2) and contains at least one kind of metal atom, and the at least one kind of metal atom includes at least one selected from the group consisting of Mg, Li, Al, and Ca, and the D5 / D of the silicon-containing negative electrode active material 50 is 0.5 or more, the D5 of the silicon-containing negative electrode active material is 3 μm or more, and D 50 is 4 μm or more and 11 μm or less, and the conductive material includes single-walled carbon nanotubes, and provides a negative electrode.

[0011] Another embodiment of the present invention provides a secondary battery including the negative electrode.

Advantages of the Invention

[0012] The negative electrode according to one embodiment of the present invention has D5 / D 50 of 0.5 or more, D5 of 3 μm or more, and D 50 of 4 μm or more and 11 μm or less, and includes a silicon-containing negative electrode active material and single-walled carbon nanotubes. Therefore, while not causing an excessive side reaction with the electrolytic solution, it has ease of insertion / desorption of lithium ions during charge and discharge and does not cause excessive swelling, so the life characteristics of the battery can be improved. In addition, since the silicon-containing negative electrode active material contains at least one kind of metal atom and the at least one kind of metal atom exists in the form of a metal compound such as a metal silicate, the initial efficiency of the battery can be improved.

[0013] Also, by using both the silicon-containing negative electrode active material having the above-described particle size distribution and single-walled carbon nanotubes, the conductive path between the negative electrode active material particles can be improved, and the capacity, efficiency, and life performance of the battery can be enhanced.

[0014]

Modes for Carrying Out the Invention

[0015] Hereinafter, in order to assist the understanding of the present invention, the present invention will be described in more detail.

[0015] ​​​​​​The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0016] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0017] It should be understood that in this specification, the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] In this specification, D5 and D 50 can be defined as particle sizes corresponding to 5% and 50% of the cumulative volume on the particle size distribution curve (graph curve of particle size distribution diagram). max and D min may correspond to the largest particle size and the smallest particle size, respectively, in the particle size distribution curve of the particles. 50 , D max , and D min can be measured using, for example, the laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution. 50The measurement can be confirmed using a Microtrac device (manufacturer: Microtrac, model name: S3500) under the condition of a refractive index of 1.97, using water and a triton-X100 dispersant.

[0019] In this specification, the average length or diameter of the conductive material was measured using SEM or TEM.

[0020] In this specification, the specific surface area can be measured by using a BET measurement device (BEL-SORP-MAX, Nippon Bell) for the measurement target, removing gas (degassing) at 130 °C for 2 hours, and performing N2 adsorption / desorption at 77K.

[0021] In this specification, the presence and content of metal elements in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICP-OES manufactured by Perkin-Elmer 7300, AVIO 500).

[0022] <Negative electrode> The negative electrode according to an embodiment of the present invention is a negative electrode including a negative electrode active material layer, the negative electrode active material layer includes a silicon-containing negative electrode active material and a conductive material, the silicon-containing negative electrode active material includes a core and a carbon layer present on the core, and the core is SiO x (0 < x < 2) and contains metal atoms, the metal atoms include at least one selected from the group consisting of Mg, Li, Al, and Ca, and the D5 / D of the silicon-containing negative electrode active material 50 is 0.5 or more, the D5 of the silicon-containing negative electrode active material is 3 μm or more, and D 50 is 4 μm or more and 11 μm or less, and the conductive material includes single-walled carbon nanotubes.

[0023] In one embodiment of the present invention, the silicon-containing negative electrode active material includes a core and a carbon layer present on the core.

[0024] In one embodiment of the present invention, the core contains SiO x (0 < x < 2).

[0025] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-containing negative electrode active material. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-containing negative electrode active material contains the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0026] In one embodiment of the present invention, the core may contain metal atoms. The at least one kind of metal atom may exist in at least one of the forms of metal atoms, metal silicates, metal silicides, and metal oxides in the silicon-containing negative electrode active material.

[0027] The at least one kind of metal atom may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Thereby, the initial efficiency of the silicon-containing negative electrode active material can be improved.

[0028] Specifically, the metal atom may contain one or more of Mg, Li, or Al. The silicon-containing negative electrode active material of the present invention may be in a form in which relatively small-sized particles are removed. When the metal atom is one or more of Mg, Li, or Al, doping can be uniformly performed up to the inside of the core, so that the production of the silicon-containing negative electrode active material having the above characteristics can be facilitated. Further, in the silicon-containing negative electrode active material having the particle size distribution of the present invention, the size of the metal atom having a low atomic number is small and can be doped more uniformly to the inside, so the metal atom is most preferably Mg or Li.

[0029] The metal atoms (such as Li, Mg, etc.) may be distributed on the surface and / or inside of the silicon-containing particles in a doped form. The metal atoms are distributed on the surface and / or inside of the silicon-containing particles, and can control the expansion / contraction of the volume of the silicon-containing particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the metal atoms may be included in terms of reducing the proportion of the irreversible phase (for example, SiO2) in the SiO x (0 < x < 2) particles and increasing the efficiency of the active material.

[0030] The metal atoms may exist in the form of metal silicate. The metal silicate can be classified into crystalline metal silicate and amorphous metal silicate.

[0031] When the metal atom is Li, Li may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the core.

[0032] When the metal atom is Mg, Mg may exist in the form of at least one magnesium silicate of Mg2SiO4 and MgSiO3 within the core.

[0033] In one embodiment of the present invention, the metal atoms may be included in an amount of 0.1 parts by weight or more and 40 parts by weight or less based on 100 total parts by weight of the silicon-containing negative electrode active material. Specifically, it may be included in an amount of 1 part by weight or more and 25 parts by weight or less. More specifically, it may be included in an amount of 2 parts by weight or more and 20 parts by weight or less, or 2 parts by weight or more and 10 parts by weight or less. When the content of the metal atoms exceeds the range of 0.1 parts by weight or more and 40 parts by weight or less, although the initial efficiency increases as the content of the metal atoms increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, an appropriate discharge capacity and initial efficiency can be realized.

[0034] In one embodiment of the present invention, the metal atoms may be included in an amount of 1 to 25 parts by weight, more specifically, 2 to 20 parts by weight, or 2 to 10 parts by weight, based on a total of 100 parts by weight of the core. If the content of the metal atoms exceeds the range of 1 to 25 parts by weight, the initial efficiency increases as the content of the metal atoms increases, but the discharge capacity decreases. Therefore, when the content of the metal atoms satisfies the above range, suitable discharge capacity and initial efficiency can be achieved.

[0035] In one embodiment of the present invention, the silicon-containing negative electrode active material may include a carbon layer. The carbon layer may be disposed on the core and cover at least a portion of the surface of the core. That is, the carbon layer may partially cover the surface of the core, or may cover the entire surface of the core. The carbon layer imparts conductivity to the silicon-containing negative electrode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0036] The carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0037] The crystalline carbon may further improve the conductivity of the silicon-containing negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0038] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-containing composite particles. The amorphous carbon may be a carbon-containing material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a hydrocarbon as a source in a chemical vapor deposition process.

[0039] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0040] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0041] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on a total of 100 parts by weight of the silicon-containing negative electrode active material. More specifically, the carbon layer may be included in an amount of 0.5 to 15 parts by weight. When the amount is within the range of 0.1 to 50 parts by weight, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0042] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the thickness is in the range of 1 nm to 500 nm, the conductivity of the silicon-containing negative electrode active material is improved, and the initial efficiency and lifespan of the battery are improved.

[0043] In one embodiment of the present invention, D of the silicon-containing negative electrode active material 50 The D of the silicon-containing negative electrode active material may be 4 μm or more and 11 μm or less. 50If the D of the silicon-containing negative electrode active material is less than 4 μm, the particle size is too small and the specific surface area of ​​the material is large, which causes many side reactions with the electrolyte and leads to an extreme deterioration in the lifespan. 50 If the D of the silicon-containing negative electrode active material is more than 11 μm, the particle size is too large, making it difficult to charge and discharge, and thus it is difficult to achieve the capacity / efficiency during charging and discharging. 50 When the D of the silicon-containing negative electrode active material is 4 μm or more and 11 μm or less, the charge and discharge are easy, the capacity / efficiency is sufficiently realized, and the life characteristics are stable. 50 The thickness may be 4.2 μm or more and 10 μm or less, specifically 4.5 μm or more and 9 μm or less, and more specifically 5 μm or more and 7 μm or less. In this case, in addition to the above-mentioned effects, the effect of facilitating the production of the electrode can be obtained.

[0044] In one embodiment of the present invention, the silicon-containing negative electrode active material may have a D5 of 3 μm or more. If the silicon-containing negative electrode active material has a D5 of less than 3 μm, the particle size is small and oxidation occurs frequently, resulting in relatively low capacity and efficiency. Furthermore, the small particle size increases side reactions with the electrolyte during charge / discharge, resulting in poor battery life characteristics. Therefore, when the D5 satisfies the above range, the content of silicon-containing negative electrode active material with excessively small particle size in the negative electrode is reduced, thereby reducing side reactions with the electrolyte and improving battery life and stability. In particular, the silicon-containing negative electrode active material may have a D5 of 3 μm to 5.5 μm, specifically 3 μm to 5 μm, more specifically 3 μm to 4 μm or 3 μm to 3.6 μm.

[0045] D5 / D of the silicon-containing negative electrode active material 50 The D5 / D may be 0.5 or more, and specifically may be 0.6 or more. 50If the D5 / D is less than 0.5, the volume occupied by the excessively small silicon-containing negative active material in the negative electrode increases, which increases the specific surface area of ​​the material and increases the side reaction with the electrolyte, resulting in a decrease in the battery life. 50 The D5 / D of the silicon-containing negative electrode active material is set to be 0.5 or more, thereby improving the life characteristics of the battery. 50 The upper limit of may be 1.

[0046] At this time, D5 and D 50 Even if D5 / D satisfies the above range, 50 If the value is less than 0.5, the negative electrode contains D 50 The volume occupied by the much smaller active material increases, which increases side reactions with the electrolyte and reduces the battery life. 50 Even if the value is 0.5 or more, D5 or D 50 If D does not satisfy the above range, the average particle size will be too small or too large, resulting in problems such as difficulty in achieving the required life and / or efficiency. 50 If the value is small, the silicon-containing negative electrode active material particles are oxidized to a large extent, resulting in a decrease in capacity and efficiency, and a decrease in lifespan due to excessive side reactions with the electrolyte. 50 If the particle size is too large, it is difficult to charge and discharge the battery, which makes it difficult to achieve the required capacity and efficiency during charging and discharging.

[0047] Therefore, as in the present invention, D5 and D of the silicon-containing negative electrode active material 50 , and D5 / D 50 When these ranges are simultaneously satisfied, the capacity, efficiency, and / or life of the battery can be improved.

[0048] In one embodiment of the present invention, the BET specific surface area of ​​the silicon-containing negative electrode active material is 1 m 2 / g or more 20m 2 / g or less, and 2 / g or more 15m 2 / g or less, and 2 / g over 10m 2 / g or less than 2.5m 2 / g or more 8m 2 / g or less.

[0049] The upper limit of the BET specific surface area is 20 m 2 / g, 18m 2 / g, 15m 2 / g, 10m 2 / g, 8m 2 / g, 5m 2 / g, or 4m 2 / g, with a lower limit of 1m 2 / g, 1.5m 2 / g, 2m 2 / g, or 2.5m 2 / g.

[0050] In one embodiment of the present invention, D of the silicon-containing negative electrode active material max The particle size may be 35 μm or less, specifically 30 μm or less, more specifically 25 μm or less, or 20 μm or less. If the particle size is not within the 35 μm or less range, the particles are too large, which can cause problems such as the electrodes not being manufactured smoothly and the electrodes being manufactured unevenly during rolling.

[0051] D of the silicon-containing negative electrode active material min The specific surface area of ​​the material may be 1.3 μm or more, specifically 1.5 μm or more, more specifically 1.7 μm or more, or 2 μm or more. When the specific surface area of ​​the material is in the range of 1.3 μm or more, the specific surface area of ​​the material does not become excessively large, which has the effect of reducing side reactions with the electrolyte.

[0052] In one embodiment of the present invention, the silicon-containing negative electrode active material may be formed by the steps of: preparing a preliminary silicon-containing negative electrode active material; adjusting the particle size of the preliminary silicon-containing negative electrode active material; and forming a carbon layer on the preliminary silicon-containing negative electrode active material having the controlled particle size.

[0053] Specifically, in the step of preparing the preliminary silicon-containing negative electrode active material, the preliminary silicon-containing negative electrode active material may be formed by the steps of: mixing Si powder, SiO powder, and metal powder, followed by vaporizing the mixed gas; condensing the vaporized mixed gas into a solid phase; and heat-treating the mixed gas in an inert atmosphere.

[0054] Alternatively, the preliminary silicon-containing negative electrode active material may be formed by the steps of: heating Si powder and SiO powder in a vacuum to vaporize them, and then depositing the vaporized mixed gas to form silicon-containing particles; and mixing the formed silicon-containing particles with a metal powder, followed by heat treatment.

[0055] The heat treatment step may be performed at 700° C. to 900° C. for 4 to 6 hours, and specifically at 800° C. for 5 hours.

[0056] The metal powder may be Mg powder or Li powder.

[0057] When Mg powder is used as the metal powder, it may be vaporized to produce the negative electrode active material.

[0058] When Li powder is used as the metal powder, the negative electrode active material may be prepared by mixing silicon-containing particles and Li powder and then heat-treating the mixture.

[0059] The silicon-containing particles are SiO x (x=1) is also acceptable.

[0060] In the preliminary silicon-containing negative electrode active material, the Mg compound phase may include the above-mentioned Mg silicate, Mg silicide, Mg oxide, and the like.

[0061] In the preliminary silicon-containing negative electrode active material, the Li compound phase may include the above-mentioned Li silicate, Li silicide, Li oxide, and the like.

[0062] In the step of adjusting the particle size of the preliminary silicon-containing negative active material, the particle size may be adjusted by a method such as, but not limited to, a ball mill, a jet mill, or air classification. For example, when adjusting the particle size of the preliminary silicon-containing negative active material using a ball mill, 5 to 20 sus ball media may be added, specifically, 10 to 15 sus ball media may be added, but is not limited to this.

[0063] In the step of adjusting the particle size, the grinding time of the preliminary silicon-containing negative electrode active material may be 2 hours to 5 hours, specifically 2 hours to 4 hours, and more specifically 3 hours, but is not limited thereto.

[0064] In the step of forming the carbon layer, the carbon layer may be manufactured by using a chemical vapor deposition (CVD) method using a hydrocarbon gas, or by carbonizing a material serving as a carbon source.

[0065] Specifically, the silicon-containing negative electrode active material may be charged into a reactor, and then subjected to chemical vapor deposition (CVD) of a hydrocarbon gas at 600°C to 1200°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

[0066] In one embodiment of the present invention, the negative electrode may further include a carbon-containing negative electrode active material, which may include at least one selected from natural graphite and artificial graphite.

[0067] In one embodiment of the present invention, the silicon-containing negative electrode active material and the carbon-containing negative electrode active material may satisfy the following formula A. [Formula A] 2.415≦D Gr / D SiO ≦6.452 In the formula A, D SiOis the average particle size (D 50 ) and D Gr is the average particle size (D 50 ) means

[0068] When the carbon-containing negative electrode active material satisfying Formula A is used together with the silicon-containing negative electrode active material, the silicon-containing negative electrode active material is easily positioned in the space between the carbon-containing negative electrode active materials during the preparation of the negative electrode, improving contact characteristics, and thus easily forming a conductive path between particles, resulting in excellent conductivity within the electrode.

[0069] In one embodiment of the present invention, Gr / D SiO may be 2.5 or more and 5 or less, 2.5 or more and 4 or less, or 3.0 or more and 3.5 or less.

[0070] In one embodiment of the present invention, in the negative electrode, the weight ratio of the silicon-containing negative electrode active material to the carbon-containing negative electrode active material may be 10:90 to 90:10, specifically 10:90 to 50:50, and more specifically 10:90 to 30:70.

[0071] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. The negative electrode active material layer may further include a binder and / or a conductive material.

[0072] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0073] In one embodiment of the present invention, the conductive material may include single-walled carbon nanotubes (SWCNTs). The term "SWCNTs" refers to a tubular carbon structure containing one carbon layer. When the conductive material in the negative electrode active material layer includes the SWCNTs, the charge / discharge capacity and / or lifespan of the battery may be improved. Specifically, the SWCNTs smoothly connect conductive paths between particles, thereby preventing loss of the conductive paths due to swelling of the silicon-containing negative electrode active material. As a result, when the SWCNTs are included, the lifespan of the battery may be improved.

[0074] In this specification, the length of a carbon nanotube refers to the length of the major axis passing through the center of a carbon nanotube unit, and the diameter of a carbon nanotube refers to the length of the minor axis passing through the center of the unit and perpendicular to the major axis.

[0075] The average length of the single-walled carbon nanotubes may be 0.1 μm to 50 μm, specifically 0.5 μm to 25 μm or 0.5 μm to 20 μm, or more specifically 5 μm to 15 μm. The lower limit of the average length may be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm, and the upper limit may be 50 μm, 30 μm, 25 μm, 20 μm, 15 μm, 14 μm, 13 μm, 12 μm, 11 μm, or 10 μm.

[0076] When single-walled carbon nanotubes satisfying the conductivity, strength, and average length range of 0.1 μm to 50 μm are used with a silicon-containing negative electrode active material having the above characteristics, the carbon nanotubes have a length equal to the distance between particles of the negative electrode active material, which facilitates the formation of conductive paths between the particles and improves the conductivity, strength, and / or storage stability of the electrolyte of the negative electrode. On the other hand, if the average length of the carbon nanotubes is too short, it may be difficult to efficiently form conductive paths, which may result in reduced conductivity, and if the average length of the carbon nanotubes is too long, dispersibility may be reduced.

[0077] The average length of the single-walled carbon nanotubes can be calculated from the average value of the results of observation using an SEM.

[0078] The average diameter of the single-walled carbon nanotubes may be 1 nm to 20 nm, specifically 1.5 nm to 15 nm, or more specifically 1.5 nm to 5 nm. The lower limit of the average diameter may be 1 nm, 1.5 nm, or 2 nm, and the upper limit may be 20 nm, 18 nm, 16 nm, 14 nm, 12 nm, 10 nm, 8 nm, 6 nm, or 4 nm.

[0079] Single-walled carbon nanotubes satisfying the above range have flexibility, which prevents the contact between particles of the negative electrode active material from being easily broken even when physically damaged. However, if the average diameter of the carbon nanotubes is too large, the electrode density may decrease, and if the average diameter of the carbon nanotubes is too small, dispersion may be difficult, which may reduce the processability of the dispersion.

[0080] The average diameter of the single-walled carbon nanotubes can be calculated from the average value observed using a TEM.

[0081] The BET specific surface area of ​​the single-walled carbon nanotubes is 200m 2 / g~2,000m 2 / g, specifically 250m 2 / g~1,500m 2 / g. 2 / g~2,000m 2 When single-walled carbon nanotubes satisfying the range of 1 / g are used, dispersion is easy even when a small amount of conductive material is used, and therefore, there is an effect that the particles can be effectively connected.

[0082] The single-walled carbon nanotubes may be included in an amount of 0.005 to 1 part by weight, specifically 0.01 to 0.1 parts by weight, or 0.04 to 0.06 parts by weight, based on a total of 100 parts by weight of the negative electrode active material layer. When the amount is within the range of 0.005 to 1 part by weight, it is possible to facilitate the connection of conductive paths between silicon-containing negative electrode active material particles and minimize side reactions with the electrolyte due to the high specific surface area.

[0083] In the negative electrode active material layer, the weight ratio of the silicon-containing negative electrode active material to the single-walled carbon nanotubes may be 92:8 to 99.99:0.01, specifically 97:3 to 99.98:0.02, or more specifically 99:1 to 99.8:0.2. When the weight ratio is within the range of 92:8 to 99.99:0.01, the conductive path of the silicon-containing negative electrode active material can be more effectively secured.

[0084] In this specification, the average size of the silicon-containing negative electrode active material means the arithmetic mean of the sizes of all silicon-containing negative electrode active materials, and is calculated from the average particle size value measured by number distribution in PSD (Particle Size Distribution) analysis. That is, the average size of the silicon-containing negative electrode active material is D , which means the median of the particle size distribution. 50 is a different value.

[0085] Generally, particle size distribution measured by volume distribution in PSD (Particle Size Distribution) analysis is calculated assuming particles are spheres with the same volume, without taking into account factors related to particle shape. Therefore, particle size measured by SEM observation may differ from the particle size distribution measured by volume distribution in PSD analysis.

[0086] In one embodiment of the present invention, the average size of the silicon-containing negative electrode active material measured by SEM analysis of the surface of the negative electrode is 4.5 μm or more, and the average size may be 20 μm or less, 15 μm or less, or 10 μm or less.

[0087] In one embodiment of the present invention, the average size of the silicon-containing negative electrode active material measured during cross-sectional SEM analysis of the negative electrode is 2 μm or more. The average size may be 15 μm or less, 10 μm or less, or 8 μm or less. In cross-sectional SEM analysis, the particle size tends to be measured smaller than in surface SEM analysis, depending on the position of the particle.

[0088] A battery including a silicon-containing negative electrode active material having the above average size has the effect of improving charge / discharge capacity and / or life performance.

[0089] The SEM analysis may be performed using a scanning electron microscope (SEM), and the scanning electron microscope may be, but is not limited to, S-4800 manufactured by Hitachi Corporation.

[0090] The negative electrode active material layer may further include a binder. The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer rubber (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.

[0091] In one embodiment of the present invention, the negative electrode may be manufactured by the steps of: preparing a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent; applying the negative electrode slurry to at least one surface of a current collector, drying the current collector, and rolling the current collector to form a negative electrode active material layer; and drying the current collector on which the negative electrode active material layer has been formed.

[0092] <Secondary battery> A secondary battery according to another embodiment of the present invention may include the negative electrode of the above-described embodiment. 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. The secondary battery may be a lithium-ion secondary battery.

[0093] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and containing the positive electrode active material.

[0094] The positive electrode current collector in the positive electrode 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, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0095] 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) and lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of the 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 satisfying 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 lithium metal.

[0096] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0097] 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 causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-containing 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 a mixture of two or more of these may be used alone.

[0098] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination.

[0099] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, separators coated with ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0100] 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.

[0101] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0102] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0103] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used as high-viscosity organic solvents, have a high dielectric constant, and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high conductivity can be prepared, and therefore these cyclic carbonates are even more preferably used.

[0104] 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:

[0105] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0106] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0107] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0108] <Examples and Comparative Examples> [Example 1-1] (1) Production of silicon-containing negative electrode active material 94g of powder of Si and SiO2 mixed at a 1:1 molar ratio and 6g of Mg were mixed in a reactor and then vacuum heated at a sublimation temperature of 1,400°C. The vaporized Si, SiO2, and Mg mixed gas was then reacted in a vacuum cooling zone with a cooling temperature of 800°C and solidified. This was followed by heat treatment in an inert atmosphere at a temperature of 800°C (additional heat treatment temperature) to produce a preliminary silicon-containing negative electrode active material. The preliminary silicon-containing negative electrode active material was then milled for 3 hours using a ball mill with 15 sus ball media added. 50 Then, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-containing negative electrode active material was placed in the hot zone of a CVD apparatus, and the methane was blown into the hot zone at 900°C using Ar as a carrier gas for 10 minutes. -1 Torr was used for the reaction for 20 minutes to prepare a silicon-containing negative electrode active material having a carbon layer formed on the surface.

[0109] D5 / D of the silicon-containing negative electrode active material 50 is 0.5 and D 50 is 6 μm, and D max is 19 μm, and D min was 2 μm.

[0110] (2) Manufacturing of the negative electrode The silicon-containing negative electrode active material, artificial graphite, and binders (carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR)) were added to a single-walled carbon nanotube dispersion using distilled water as a dispersion medium and carboxymethyl cellulose (CMC) as a dispersant. After stirring, distilled water was added to prepare a negative electrode slurry (solid content = 50 parts by weight). The negative electrode slurry was applied to a 20 μm-thick copper (Cu) metal thin film negative electrode current collector and dried. The circulating air temperature was 60°C. The mixture was then rolled and dried in a vacuum oven at 130°C for 12 hours to prepare a negative electrode with a negative electrode active material layer disposed on the negative electrode current collector.

[0111] In the negative electrode active material layer, the silicon-containing negative electrode active material, the artificial graphite (D 50 The weight ratio of the single-walled carbon nanotubes, carboxymethyl cellulose (CMC), and styrene-butadiene rubber was 14.63:82.92:0.05:1.2:1.2. The weight of the CMC added as a binder:the weight of the CMC added as a dispersant was 1.14:0.06. The average length of the single-walled carbon nanotube units in the negative electrode active material layer was 10 μm, and the average diameter was 2 nm.

[0112] [Example 1-2] A silicon-containing negative electrode was prepared in the same manner as in Example 1, except that 10 Sus ball media were added.

[0113] [Examples 1-3] A silicon-containing negative electrode was prepared in the same manner as in Example 1, except that single-walled carbon nanotubes having an average length of 25 μm and an average diameter of 16 nm were used.

[0114] [Example 2-1] In the method of Example 1, 94 g of SiO particles were synthesized without using Mg, and then 6 g of Li metal powder was added. The mixture was then heat-treated in an inert atmosphere at a temperature of 800°C to produce a pre-silicon-containing negative electrode active material. The pre-silicon-containing negative electrode active material was then milled for 3 hours using a ball mill with 15 sus ball media added. 50 Then, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-containing negative electrode active material was placed in the hot zone of a CVD apparatus, and the methane was blown into the hot zone at 900°C using Ar as a carrier gas for 10 minutes. -1 Torr was used for the reaction for 20 minutes to prepare a silicon-containing negative electrode active material having a carbon layer formed on the surface.

[0115] Next, a silicon-containing negative electrode was fabricated using the silicon-containing negative electrode active material prepared by the above-described method instead of the silicon-containing negative electrode active material of Example 1.

[0116] [Example 2-2] A silicon-containing negative electrode was prepared in the same manner as in Example 3, except that 10 Sus ball media were added.

[0117] [Comparative Example 1-1] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that the grinding time was changed to 8 hours.

[0118] [Comparative Example 1-2] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that the grinding time was changed to 1 hour.

[0119] [Comparative Example 1-3] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that the grinding time was changed to 5 hours.

[0120] [Comparative Example 1-4] A silicon-containing negative electrode was manufactured in the same manner as in Example 1-1, except that 10 Sus ball media were added and the grinding time was changed to 5 hours.

[0121] [Comparative Example 1-5] A silicon-containing negative electrode was manufactured in the same manner as in Example 1-1, except that 30 pieces of sus ball media were added and the grinding time was changed to 8 hours.

[0122] [Comparative Example 1-6] A silicon-containing negative electrode was manufactured in the same manner as in Example 1-1, except that 30 pieces of sus ball media were added and the grinding time was changed to 1 hour.

[0123] [Comparative Example 1-7] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that 30 Sus ball media were added.

[0124] [Comparative Example 2-1] A silicon-containing negative electrode was prepared in the same manner as in Example 2-1, except that the grinding time was changed to 8 hours.

[0125] [Comparative Example 2-2] A silicon-containing negative electrode was prepared in the same manner as in Example 2-1, except that the grinding time was changed to 1 hour.

[0126] [Comparative Example 2-3] A silicon-containing negative electrode was prepared in the same manner as in Example 2-1, except that the grinding time was changed to 5 hours.

[0127] [Comparative Example 2-4] A silicon-containing negative electrode was manufactured in the same manner as in Example 2-1, except that 10 Sus ball media were added and the grinding time was changed to 5 hours.

[0128] [Comparative Example 2-5] A silicon-containing negative electrode was manufactured in the same manner as in Example 2-1, except that 30 pieces of sus ball media were added and the grinding time was changed to 8 hours.

[0129] [Comparative Example 2-6] A silicon-containing negative electrode was manufactured in the same manner as in Example 2-1, except that 30 pieces of sus ball media were added and the grinding time was changed to 1 hour.

[0130] [ Comparative Example 2-7 A silicon-containing negative electrode was prepared in the same manner as in Example 2-1, except that 30 Sus ball media were added.

[0131] [Comparative Example 3-1] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that carbon black was used instead of single-walled carbon nanotubes.

[0132] In the negative electrode active material layer, the weight ratio of the silicon-containing negative electrode active material, the artificial graphite, the carbon black, the carboxymethyl cellulose, the styrene-butadiene rubber, and the dispersant was 14.49:82.11:1:1.2:1.2.

[0133] [Comparative Example 3-2] A silicon-containing negative electrode was prepared in the same manner as in Example 1-1, except that multi-walled carbon nanotubes (MWCNTs) were used instead of single-walled carbon nanotubes.

[0134] In the negative electrode active material layer, the weight ratio of the silicon-containing negative electrode active material, the artificial graphite, the multi-walled carbon nanotubes (MWCNT), the carboxymethyl cellulose, the styrene butadiene rubber, and the dispersant was 14.63:82.92:0.05:1.2:1.2.

[0135] The silicon-containing negative electrodes prepared in the examples and comparative examples are as shown in Table 1 below.

[0136] [Table 1]

[0137] The particle size analysis of the silicon-containing negative electrode active material was performed using a Microtrac device (manufacturer: Microtrac, model name: S3500) under the condition of a refractive index of 1.97, using water and a triton-X100 dispersant.

[0138] The specific surface area was measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell) by degassing at 130° C. for 2 hours and then performing N 2 adsorption / desorption at 77K.

[0139] The content of the metal atoms was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

[0140] The physical properties of the conductive materials used in the examples and comparative examples are as shown in Table 2 below.

[0141] [Table 2]

[0142] The average length and / or particle size of the conductive material used was measured using SEM, the average diameter was measured using TEM, and the specific surface area was measured by BET measurement under the conditions of N adsorption / desorption and degassing at 200°C for 8 hours.

[0143] <Experimental example: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> Negative electrodes and batteries were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0144] 1 .7671cm 2A lithium (Li) metal thin film cut into a circular shape was used as the positive electrode. A porous polyethylene separator was placed between the positive electrode and the negative electrode, and an electrolyte solution prepared by dissolving 0.5 parts by weight of vinylene carbonate in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3 and dissolving 1M LiPF6 was injected to prepare a lithium coin half-cell.

[0145] The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 3 below.

[0146] The first and second cycles were charged and discharged at 0.1 C, and from the third cycle onwards, the charge and discharge rate was 0.5 C. The 300th cycle was completed in a charged state (with lithium in the negative electrode).

[0147] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0148] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (discharge capacity after one discharge / one charge capacity) x 100

[0149] The capacity retention rates were calculated as follows. Capacity retention rate (%) = (300 times discharge capacity / 1 time discharge capacity) × 100

[0150] [Table 3]

[0151] The negative electrode according to the present invention is D5 / D 50 is 0.5 or more, D5 is 3 μm or more, and D 50The negative electrode contains a silicon-containing negative electrode active material having a particle size of 4 μm or more and 11 μm or less, and contains single-walled carbon nanotubes as a conductive material. 50 , and D5 / D 50 By having the particle size distribution, side reactions with the electrolyte are suppressed, charge and discharge are easy, capacity / efficiency is sufficiently realized, and life characteristics are stable.

[0152] In addition, when a negative electrode active material satisfying the particle size distribution and single-walled carbon nanotubes are used, conductive paths between particles satisfying the particle size distribution are more easily connected, thereby preventing loss of conductive paths due to swelling of the silicon-containing negative electrode active material.

[0153] If the particle size distribution is not satisfied, i.e., D5 / D 50 is less than 0.5, or D5 is less than 3 μm, or D 50 When a negative electrode active material having a particle size of less than 4 μm is used together with single-walled carbon nanotubes, side reactions with the electrolyte increase, and the negative electrode active material is excessively used during cycles, causing frequent deterioration and resulting in a deterioration in life characteristics. 50 When a negative electrode active material having a particle size exceeding 11 μm is used together with single-walled carbon nanotubes, the volume change due to the swelling phenomenon of the negative electrode active material is so large that it is impossible to prevent the conductive path from being broken, resulting in a problem of shortened lifespan.

[0154] In Table 3, Examples 1-1 to 1-3 and Examples 2-1 to 2-2 use negative electrodes containing negative electrode active materials that satisfy a specific particle size and single-walled carbon nanotubes as a conductive material, and it can be confirmed that they are excellent in all of discharge capacity, initial efficiency, and capacity retention rate.

[0155] In Examples 1-1 and 1-2, the negative electrode active material contains Mg, and D5 / D 50value or D5 value and D 50 It can be seen that the discharge capacity, initial efficiency, and capacity retention rate are all superior to those of Comparative Examples 1-1 to 1-7, which do not satisfy the above values. Furthermore, it can be seen that Examples 2-1 and 2-2, which are negative electrode active materials containing Li, are all superior to those of Comparative Examples 2-1 to 2-7, in terms of discharge capacity, initial efficiency, and capacity retention rate.

[0156] In contrast, Comparative Examples 1 and 5 are D5 / D of the present invention. 50 , D5, D 50 does not satisfy the above. In the cases of Comparative Examples 1-1 to 1-4, the D5 / D 50 Although it satisfies the above, D5 or D 50 It was confirmed that the above conditions were not satisfied and the capacity, efficiency, and lifespan were lower than those of the examples.

[0157] Specifically, D5 / D 50 Even if D5 is 0.5 or more, if D5 is less than 3 μm or D 50 When the particle size is less than 4 μm, the overall particle size is too small, the specific surface area of ​​the material is large, and oxidation occurs frequently. Therefore, it was confirmed that side reactions with the electrolyte occur frequently during charge / discharge, resulting in lower capacity, efficiency, and lifespan than in the examples.

[0158] Also, D5 / D 50 Even if is 0.5 or more, D 50 When the particle size exceeds 11 μm, the overall particle size is too large, making charge / discharge difficult, and it was confirmed that the capacity, efficiency, and lifespan are lower than those of the examples.

[0159] Also, D5 / D 50 If the value is less than 0.5, the negative electrode contains D 50 It was confirmed that the volume occupied by the much smaller negative electrode active material increases, which increases side reactions with the electrolyte, resulting in lower capacity, efficiency, and lifespan than in the examples.

[0160] In Comparative Examples 3-1 and 3-2, carbon black, a dot-like conductive material, or multi-walled carbon nanotubes was used instead of single-walled carbon nanotubes. Although the same negative electrode active material as in Example 1 was used, it was confirmed that the conductive paths between the particles were not easily secured, resulting in a significant decrease in battery life.

[0161] Therefore, D5, D 50 , and D5 / D 50 By using a negative electrode active material with an adjusted range of SiO2 and a single-walled carbon nanotube conductive material, side reactions with the electrolyte can be reduced, a conductive path can be secured, and the capacity, efficiency, and / or lifespan of the battery can be easily improved.

Claims

1. A negative electrode including a negative electrode active material layer, a negative electrode active material layer including a silicon-containing negative electrode active material and a conductive material, the silicon-containing negative electrode active material includes a core and a carbon layer present on the core; The core is made of SiO ｘ (0<x<2) and at least one metal atom; the at least one metal atom includes at least one selected from the group consisting of Mg and Li, D of the silicon-containing negative electrode active material ５ / D ５０ is 0.5 or more, D of the silicon-containing negative electrode active material ５ is 3 μm or more, and D ５０ is 4 μm or more and 11 μm or less, The conductive material comprises a single-walled carbon nanotube.

2. D of the silicon-containing negative electrode active material ５ / D ５０ The negative electrode according to claim 1 , wherein the σ is 0.6 or more.

3. D of the silicon-containing negative electrode active material ５ / D ５０ The negative electrode according to claim 1 , wherein the value of the ρ is 0.5 or more and 1 or less.

4. D of the silicon-containing negative electrode active material ５０ The negative electrode according to claim 1 , wherein the average particle diameter is 4.2 μm or more and 10 μm or less.

5. D of the silicon-containing negative electrode active material ５ The negative electrode according to claim 1 , wherein the average particle size is 3 μm or more and 5.5 μm or less.

6. D of the silicon-containing negative electrode active material ｍａｘ The negative electrode according to claim 1 , wherein the thickness is 35 μm or less.

7. The negative electrode according to claim 1 , wherein the at least one metal atom is contained in an amount of 0.1 parts by weight to 40 parts by weight based on a total of 100 parts by weight of the silicon-containing negative electrode active material.

8. The negative electrode according to claim 1 , wherein the carbon layer is included in an amount of 0.1 parts by weight to 50 parts by weight based on a total of 100 parts by weight of the silicon-containing negative electrode active material.

9. 2. The negative electrode according to claim 1, wherein the single-walled carbon nanotubes have an average length of 0.1 μm to 50 μm.

10. 2. The negative electrode according to claim 1, wherein the single-walled carbon nanotubes have an average diameter of 1 nm to 20 nm.

11. The specific surface area of ​​the single-walled carbon nanotube is 200 m ２ / g to 2,000m ２ The negative electrode according to claim 1 , wherein the anode has a Cr content of 1.0 / g.

12. 2. The negative electrode according to claim 1, wherein a weight ratio of the silicon-containing negative electrode active material to the single-walled carbon nanotubes is 92:8 to 99.99:0.

01.

13. The negative electrode according to claim 1 , wherein the negative electrode active material layer further comprises a carbon-containing negative electrode active material.

14. The negative electrode according to claim 13 , wherein the silicon-containing negative electrode active material and the carbon-containing negative electrode active material satisfy the following formula A: [Formula A] 2.415≦D Ｇｒ / D ＳｉＯ ≦6.452 In the formula A, D ＳｉＯ is the average particle size (D ５０ ) and D Ｇｒ is the average particle size (D ５０ ) means

15. the average size of the silicon-containing negative electrode active material measured by SEM analysis of the surface of the negative electrode is 4.5 μm or more; The negative electrode of claim 1 , wherein the average size of the silicon-containing negative electrode active material measured during cross-sectional SEM analysis of the negative electrode is 2 μm or more.

16. A secondary battery comprising the negative electrode according to claim 1.

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