Negative electrode active material, and negative electrode and secondary battery containing the same

Abstract

The present invention relates to a negative electrode active material, comprising: a silicon-based core; and an outer coating layer formed on the silicon-based core and comprising polyimide, wherein the polyimide comprises a fluorine-containing imide unit.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0010814, filed on January 30, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a negative electrode active material, and a negative electrode and a secondary battery comprising the negative electrode active material. Background Art

[0005] Recently, with the rapid popularization of electronic devices using batteries, such as mobile phones, laptop computers, electric vehicles, etc., the demand for secondary batteries with relatively high capacity, small size and light weight has increased dramatically. In particular, lithium secondary batteries have become a focus of attention as driving power sources for portable devices because they are lightweight and have high energy density. Therefore, research and development efforts have been continuously made to improve the performance of lithium secondary batteries.

[0006] Lithium secondary batteries typically include a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, an electrolyte, an organic solvent, and the like. In addition, an active material layer containing a positive electrode active material or a negative electrode active material may be formed on the current collector of the positive and negative electrodes. Lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are commonly used as positive electrode active materials in the positive electrode, while lithium-free carbon-based active materials or silicon-based negative electrode active materials are used as negative electrode active materials in the negative electrode.

[0007] Silicon-based negative electrode active materials, in particular, have attracted considerable attention due to their capacity, which is approximately 10 times higher than that of carbon-based negative electrode active materials. Their advantage lies in their high capacity, enabling high energy density even with thin electrodes. However, silicon-based negative electrode active materials exhibit significant volume expansion during charge and discharge, leading to significant side reactions with the electrolyte. Consequently, silicon-based negative electrode active materials exhibit poor performance in terms of cycle attenuation, high-temperature lifespan characteristics, and high-temperature storage characteristics, making them less commonly used.

[0008] Therefore, there is a need to develop a secondary battery that can prevent a side reaction with an electrolyte and improve lifespan characteristics while achieving high capacity and energy density of a silicon-based negative electrode active material.

[0009] Korean Unexamined Patent Publication No. 10-2017-0074030 relates to a negative electrode active material for a lithium secondary battery, a preparation method thereof, and a lithium secondary battery including the same, and discloses a negative electrode active material including a porous silicon-carbon composite, but has limitations in solving the above-mentioned problems.

[0010] [Prior Art Document]

[0011] [Patent Document]

[0012] Korean Unexamined Patent Publication No. 10-2017-0074030 Summary of the Invention

[0013] Technical issues

[0014] The present invention aims to provide a negative electrode active material having excellent high-temperature life performance, high-temperature storage performance and output performance when using a silicon-based negative electrode active material.

[0015] The present invention also provides a negative electrode comprising the negative electrode active material.

[0016] The present invention also provides a secondary battery comprising the negative electrode.

[0017] Technical Solution

[0018] One aspect of the present invention provides a negative electrode active material comprising: a silicon-based core; and an outer coating layer formed on the silicon-based core and comprising polyimide, wherein the polyimide comprises a fluorine-containing imide unit.

[0019] Another aspect of the present invention provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and comprising a negative electrode material, wherein the negative electrode material comprises the above-mentioned negative electrode active material.

[0020] Another aspect of the present invention provides a secondary battery including: the above-mentioned negative electrode; a positive electrode disposed to face the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0021] Beneficial effects

[0022] The negative electrode active material according to the present invention is characterized in that it comprises an outer coating formed on a silicon core and containing a polyimide, wherein the polyimide comprises a fluorine-containing imide unit. Since the polyimide coating is formed on the silicon core, it is possible to control the volume expansion / contraction of the silicon core as it charges and discharges, while preventing side reactions with the electrolyte at an excellent level, thereby improving life characteristics. In addition, the outer coating containing polyimide (the polyimide comprising a fluorine-containing imide unit) can be used as a solid electrolyte interface layer (SEI layer) on the negative electrode active material to achieve a more excellent level in preventing side reactions with the electrolyte, and due to the high electronegativity of fluorine, lithium can be smoothly embedded in / deintercalated from the active material. Therefore, the resistance of the negative electrode active material can be reduced, and the output performance can be improved to an excellent level.

[0023] Therefore, the high-temperature life performance, high-temperature storage performance, and output performance of a negative electrode and a secondary battery using the above-mentioned negative electrode active material can be simultaneously improved. DETAILED DESCRIPTION

[0024] The words or terms provided herein should not be interpreted as the commonly used meanings or the meanings defined in the dictionary, but should be interpreted with the meanings and concepts consistent with the technical scope of the present invention, on the basis that the inventor can appropriately define the concepts of the terms to describe the principles of the present invention in the best manner.

[0025] The terminology provided herein is for describing exemplary embodiments only and is not intended to limit the present invention.Unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms as well.

[0026] It should be understood that when used in this document, the terms "comprises", "comprising", "includes", "including", "has" or "having" specify the presence of the stated features, numbers, steps, elements or their combination, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or their combination.

[0027] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution and can be measured using a laser diffraction method. Specifically, the average particle size (D 50 ) can be calculated as follows: disperse the target particles in a dispersion medium, inject the resultant into a commercial laser diffraction particle size analyzer (e.g., Horiba Partica LA-960), and determine the average particle diameter (D) corresponding to 50% of the cumulative volume in the particle size distribution. 50 ), the particle size distribution corresponds to the particle size measured by scattered light.

[0028] Hereinafter, the present invention will be described in detail.

[0029] <Negative Electrode Active Material>

[0030] The present invention relates to a negative electrode active material, in particular to a negative electrode active material for a lithium secondary battery.

[0031] The negative active material of the present invention comprises: a silicon-based core; and an outer coating layer formed on the silicon-based core and comprising polyimide, wherein the polyimide comprises a fluorine-containing imide unit.

[0032] The negative electrode active material of the present invention is characterized in that the polyimide (the polyimide contains a fluorine-containing imide unit) is contained in an outer coating on the silicon core to prevent the shortcomings of general silicon-based negative electrode active materials, such as volume expansion / contraction accompanying charging and discharging, side reactions with the electrolyte due to volume expansion / contraction, degradation of high temperature life performance and high temperature storage performance, etc. The outer coating can prevent side reactions caused by contact between the silicon core with volume expansion / contraction and the electrolyte. In particular, the polyimide containing the fluorine-containing imide unit can be used as a solid electrolyte interface layer (hereinafter referred to as "SEI layer") to further prevent side reactions with the electrolyte, thereby improving high temperature life performance and high temperature storage performance. In addition, since the fluorine contained in the outer coating has a high electronegativity, it can reduce resistance as lithium ions are inserted into / deintercalated from the silicon core, thereby further enhancing the output performance of the active material. Therefore, the high temperature life performance, high temperature storage performance and output performance of the negative electrode and secondary battery using the negative electrode active material according to the present invention can be enhanced at the same time.

[0033] The silicon-based core enables intercalation / deintercalation of lithium and can be used as a core particle of a negative electrode active material.

[0034] The silicon-based core may include silicon-based particles including a compound represented by the following Chemical Formula 2.

[0035] [Chemical Formula 2]

[0036] SiO x (0≤x<2)

[0037] When Chemical Formula 2 is SiO2 (x=2 in Chemical Formula 2), SiO2 does not react with lithium ions and therefore cannot store lithium. Therefore, it is preferred that x be within the above range. Specifically, in terms of structural stability of the active material, in Chemical Formula 2, x may be 0.5≤x≤1.5.

[0038] Based on the silicon-based particles comprising the compound represented by Chemical Formula 2, the silicon-based core may further comprise a metal distributed on the surface of the silicon-based particles, within the silicon-based particles, or on and within the silicon-based particles. The metal may be distributed on the surface and / or within the silicon-based particles in the form of being doped in the silicon-based particles.

[0039] The metal distributed on the surface and / or within the silicon-based particles can be used to control the volume expansion / contraction of the silicon-based core to an appropriate level and prevent damage to the active material. Furthermore, the metal can be included to reduce the proportion of irreversible phases (e.g., SiO2) in the silicon-based core, thereby improving the efficiency of the active material.

[0040] The metal may be contained in the negative electrode active material in an amount of 0.1 wt % to 25 wt %, preferably 1 wt % to 20 wt %, more preferably 2 wt % to 15 wt %, and the above range is preferred in terms of preventing damage to the silicon-based core, achieving more preferred life characteristics, and not impairing the excellent capacity characteristics of the silicon-based core.

[0041] The metal may be at least one selected from the group consisting of lithium (Li), magnesium (Mg), aluminum (Al), calcium (Ca), and titanium (Ti), and is preferably at least one selected from lithium and magnesium. Specifically, in order to achieve the aforementioned effect of preventing damage to the silicon-based core and further improve initial efficiency, the metal may be at least one selected from lithium and magnesium, and is more preferably magnesium.

[0042] The content of the silicon-based core in the negative electrode active material may be 50 to 99 wt %, preferably 70 to 97 wt %, more preferably 85 to 95 wt %. The above range is preferred in terms of increasing the capacity of the negative electrode.

[0043] The outer coating is formed on the silicon-based core.

[0044] Furthermore, the overcoat layer includes polyimide, and the polyimide includes a fluorine-containing imide unit.

[0045] The outer coating layer can function as the SEI layer of the negative electrode active material by containing a polyimide (the polyimide containing a fluorine-containing imide unit). Therefore, the electrolyte side reaction caused by the contact between the silicon core and the electrolyte can be prevented at an excellent level, thereby improving the high-temperature life performance and high-temperature storage performance of the negative electrode active material at an excellent level. In addition, the outer coating layer contains fluorine with high electronegativity, which enables lithium ions to be smoothly inserted into / deinserted from the negative electrode active material, and is therefore preferred in terms of reducing the resistance of the negative electrode active material and enhancing output performance.

[0046] The polyimide includes a fluorinated imide unit. The inclusion of the fluorinated imide unit in the polyimide can effectively prevent side reactions between the silicon core and the electrolyte, while also improving high-temperature lifespan, high-temperature storage performance, and output performance. If the polyimide does not contain the fluorinated imide unit, the aforementioned effects of preventing electrolyte side reactions and reducing resistance may not be achieved.

[0047] The fluorine-containing imide unit may be contained in the polyimide in an amount of preferably 10 wt % or more, more preferably 40 wt % or more, and even more preferably 80 wt % or more. Within the above range, the high-temperature life performance, high-temperature storage performance, and output performance of the negative electrode active material can be simultaneously improved at excellent levels.

[0048] The fluorine-containing imide unit may be represented by the following Chemical Formula 1.

[0049] [Chemical Formula 1]

[0050]

[0051] In Chemical Formula 1, A1 is C4 to C 30 A tetravalent organic group, B1 is C6 to C 30 A divalent organic group, and at least one of A1 and B1 contains fluorine.

[0052] When A1 in Chemical Formula 1 contains fluorine, A1 may be a tetravalent organic group selected from the group consisting of the following Chemical Formulas 1-1-A to 1-4-A. Specifically, A1 may be the following Chemical Formula 1-1-A.

[0053] [Chemical Formula 1-1-A]

[0054]

[0055] [Chemical Formula 1-2-A]

[0056]

[0057] [Chemical Formula 1-3-A]

[0058]

[0059] [Chemical Formula 1-4-A]

[0060]

[0061] In Chemical Formulas 1-1-A to 1-4-A, * represents a binding site.

[0062] When B1 in Chemical Formula 1 contains fluorine, B1 may be a divalent organic group selected from the group consisting of the following Chemical Formulas 1-1-B to 1-6-B. Specifically, B1 may be the following Chemical Formula 1-1-B.

[0063] [Chemical Formula 1-1-B]

[0064]

[0065] [Chemical Formula 1-2-B]

[0066]

[0067] [Chemical Formula 1-3-B]

[0068]

[0069] [Chemical Formula 1-4-B]

[0070]

[0071] [Chemical Formula 1-5-B]

[0072]

[0073] [Chemical Formula 1-6-B]

[0074]

[0075] In Chemical Formulas 1-1-B to 1-6-B, * represents a binding site.

[0076] In Chemical Formula 1, A1 and B1 may contain fluorine, and when both A1 and B1 contain fluorine, the above-mentioned effects of preventing resistance increase, improving life performance, and improving output performance may be achieved at an excellent level.

[0077] Specifically, Chemical Formula 1 may be at least one unit selected from the following Chemical Formulas 1-1 and 1-2, and is preferably a unit represented by the following Chemical Formula 1-1.

[0078] [Chemical Formula 1-1]

[0079]

[0080] [Chemical formula 1-2]

[0081]

[0082] In Chemical Formulas 1-1 and 1-2, * is a binding site.

[0083] In addition to the fluorine-containing imide unit, the polyimide may further include a fluorine-free imide unit, specifically, a unit represented by the following Chemical Formula 3-1, but the present invention is not limited thereto.

[0084] [Chemical Formula 3-1]

[0085]

[0086] In Chemical Formula 3-1, * represents a binding site.

[0087] The outer coating layer may contain fluorine in an amount of 10 to 50 wt %, preferably 20 to 40 wt %. The above range is preferred in terms of improving life performance and output characteristics while preventing an increase in resistance due to excessive fluorine.

[0088] In the negative electrode active material, the content of the outer coating layer may be higher than 0 wt % and less than 4.5 wt %, preferably 0.1 wt % to 1.5 wt %, more preferably 0.35 wt % to 0.75 wt %. When the outer coating layer in the above amount is included in the negative electrode active material layer, the electrolyte side reaction can be prevented at an excellent level while preventing the increase in resistance due to excessive formation of the coating layer, thereby simultaneously improving high temperature life performance, high temperature storage performance, and output performance. In addition, when an excessive amount of the outer coating layer is formed in the negative electrode active material, excessive aggregation may occur between the active material particles, making it difficult to form an electrode. Therefore, it is preferred to form the outer coating layer within the above range.

[0089] The negative electrode active material of the present invention may further include an inner carbon coating formed between the silicon-based core and the outer coating. The inner carbon coating may serve as a protective layer, inhibiting volume expansion of the silicon-based core and further preventing side reactions with the electrolyte.

[0090] The content of the inner carbon coating layer may be 1 to 10 wt %, preferably 3 to 7 wt %, based on the total weight of the silicon-based core and the inner carbon coating layer. This range is preferred in terms of the inner carbon coating layer excellently controlling the volume expansion of the silicon-based core and preventing side reactions with the electrolyte.

[0091] The inner carbon coating layer may be an amorphous carbon coating layer. Specifically, the inner carbon coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0092] The average particle size (D) of the negative electrode active material is preferably 0.0547 W / m in terms of ensuring the structural stability of the active material during charge and discharge, preventing the degree of volume expansion / contraction from increasing due to excessive increase in particle size, and preventing the initial efficiency from decreasing due to excessively low particle size. 50) may be 0.1 μm to 20 μm, preferably 1 μm to 10 μm, more preferably 2 μm to 8 μm.

[0093] In addition, the present invention provides a method for preparing the above-mentioned negative electrode active material.

[0094] The method of preparing the negative active material includes mixing a silicon-based core and a polyimide precursor including a fluorine-containing unit, and subjecting the resulting mixture to a heat treatment.

[0095] The polyimide precursor is a precursor of polyimide and can be cured by heat treatment to form an outer coating layer comprising polyimide on a silicon-based core and comprising a fluorine-containing unit.

[0096] Specifically, the polyimide precursor may include polyamic acid and / or polyamic acid ester, and more specifically, the polyimide precursor may include a unit represented by the following Chemical Formula 1′.

[0097] [Chemical Formula 1']

[0098]

[0099] In Chemical Formula 1', A1 and B1 are the same as A1 and B1 described in Chemical Formula 1, and R1 and R2 are each independently selected from hydrogen and a C1 to C5 alkyl group.

[0100] In Chemical Formula 1′, A1 may be a tetravalent organic group selected from the group consisting of Chemical Formulas 1-1-A to 1-4-A described for Chemical Formula 1.

[0101] In Chemical Formula 1′, B1 may be a divalent organic group selected from the group consisting of Chemical Formulas 1-1-B to 1-6-B described for Chemical Formula 1.

[0102] The heat treatment can be performed at 250°C to 500°C, preferably 300°C to 400°C, to fully convert the polyimide precursor into the polyimide and enhance the chemical and physical resistance of the polyimide. When heat treated within this temperature range, the degree of π-π stacking in the polyimide can be increased, resulting in a polyimide with high physical strength and high chemical resistance. A coating with high coverage can also be formed, preventing the polyimide from pyrolysis while improving heat resistance through imidization of the polyimide precursor particles.

[0103] The heat treatment may be performed for 0.5 to 5 hours, preferably 1 to 3 hours, to form a polyimide coating with high coverage and prevent the polyimide coating from being dissolved in a solvent or the like due to insufficient imidization and falling off from the surface.

[0104] <Negative electrode>

[0105] The present invention also provides a negative electrode comprising the negative electrode active material.

[0106] Specifically, the negative electrode of the present invention includes: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode material, wherein the negative electrode material includes the above-mentioned negative electrode active material.

[0107] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used as the negative electrode current collector.

[0108] The thickness of the negative electrode current collector may generally be 3 μm to 500 μm.

[0109] The negative electrode current collector may have fine concavoconvexities formed on its surface to increase the adhesion of the negative electrode active material. In addition, the negative electrode current collector may be used in any of various forms such as a film, a sheet, a foil, a net, a porous material, a foam, a non-woven fabric, etc.

[0110] The negative electrode active material layer is formed on the negative electrode current collector.

[0111] The negative electrode active material layer includes a negative electrode material, and the negative electrode material includes the above-mentioned negative electrode active material.

[0112] The negative electrode active material may be included in the negative electrode to exhibit excellent capacity characteristics and lifespan characteristics. The negative electrode active material has been described above.

[0113] In addition to the negative electrode active material, the negative electrode material may further include a carbon-based active material. The carbon-based active material having a low volume expansion during charge and discharge can reduce the volume expansion of the entire negative electrode material.

[0114] The carbon-based active material may include at least one selected from the group consisting of graphite, artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of artificial graphite and natural graphite.

[0115] In terms of ensuring structural stability during charge and discharge and reducing side reactions with the electrolyte, the average particle size (D 50 ) can be 1 μm to 50 μm, preferably 3 μm to 25 μm.

[0116] Specifically, in order to improve both capacity characteristics and cycle characteristics, the negative electrode material preferably contains both the negative electrode active material and the carbon-based active material. Specifically, the negative electrode material preferably contains the negative electrode active material and the carbon-based active material in a weight ratio of 1:99 to 50:50, preferably 2:98 to 30:70.

[0117] The negative electrode material may be included in the negative electrode active material layer in an amount of 80 wt % to 99 wt %, preferably 90 wt % to 98.5 wt %.

[0118] The negative active material layer may include a binder.

[0119] In terms of enhancing electrode adhesion and imparting sufficient resistance to volume expansion / contraction of the active material, the binder may include at least one selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM). In terms of having high strength, excellent resistance to volume expansion / contraction of the silicon-based negative electrode active material, and imparting excellent flexibility to prevent electrode warping, bending, etc., the binder preferably includes SBR.

[0120] The binder may be included in the negative electrode active material layer in an amount of 0.5 wt % to 10 wt %. The above range is preferred in terms of more effectively controlling the volume expansion of the active material.

[0121] The negative electrode active material layer may further include a conductive material. The conductive material can be used to enhance the conductivity of the negative electrode, and preferably the conductive material does not cause chemical changes and has conductivity. Specifically, the conductive material can 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, carbon nanotubes (CNTs), fluorocarbons; aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. In terms of achieving high conductivity, carbon black is preferably included.

[0122] The conductive material may be included in an amount of 0.5 wt % to 10 wt % in the negative active material layer.

[0123] In terms of increasing electrical contact between components of the negative electrode material, the negative electrode active material layer may have a thickness of 10 μm to 100 μm, preferably 15 μm to 80 μm.

[0124] The negative electrode may be prepared by dispersing a negative electrode material, a binder, and a conductive material in a solvent for forming a negative electrode slurry to form a negative electrode slurry, applying the negative electrode slurry to a negative electrode collector, and then drying and roll-pressing.

[0125] The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, and is preferably distilled water in terms of ease of dispersing the components.

[0126] <Secondary Battery>

[0127] The present invention provides a secondary battery comprising the negative electrode, and more specifically, provides a lithium secondary battery.

[0128] Specifically, the secondary battery according to the present invention includes: the above-mentioned negative electrode; a positive electrode provided to face the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0129] The positive electrode may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector.

[0130] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used as the positive electrode current collector.

[0131] The thickness of the positive electrode current collector may generally be 3 μm to 500 μm.

[0132] The positive electrode current collector may have fine concavo-convex portions formed on its surface to increase the adhesion of the positive electrode active material. In addition, the positive electrode current collector may be used in any of various forms such as a film, sheet, foil, net, porous material, foam, non-woven fabric, etc.

[0133] The positive electrode active material layer may include a positive electrode active material.

[0134] The positive electrode active material may include a compound capable of reversible insertion and extraction of lithium, specifically a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum, preferably a lithium transition metal composite oxide containing lithium and a transition metal including nickel, cobalt and manganese.

[0135] More specifically, the lithium transition metal composite oxide may be a lithium manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt oxide (e.g., LiCoO2, etc.), a lithium nickel oxide (e.g., LiNiO2, etc.), a lithium nickel manganese oxide (e.g., LiNi1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt oxides (e.g., LiNi 1- Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium manganese cobalt oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2- z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium nickel manganese cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M[[ID=4"]] s2 )O2) (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, p2, q2, r3, and s2 are the respective atomic fractions of the respective independent elements, and 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1 and p2 + q2 + r3 + s2 = 1), etc.), and these compounds can be used alone or in combination of two or more of them. Among those listed above, in terms of improving the capacity characteristics and stability of the battery, the lithium transition metal composite oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co0.15 Al 0.05 )O2, etc.). In addition, considering that a significant improvement effect can be achieved by controlling the type and content ratio of the elements constituting the lithium transition metal composite oxide, the lithium transition metal composite oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2、Li(Ni 0.5 Mn 0.3 Co 0.2 )O2、Li(Ni 0.7 Mn 0.15 Co 0.15 )O2、Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc. These compounds can be used alone or in combination of two or more thereof.

[0136] In consideration of sufficiently exhibiting the capacity of the positive electrode active material, the positive electrode active material may be included in the positive electrode active material layer in an amount of 80 wt % to 99 wt %, preferably 92 wt % to 98.5 wt %.

[0137] In addition to containing the above-mentioned positive electrode active material, the positive electrode active material layer may further include a binder and / or a conductive material.

[0138] The binder is used to assist in the bonding between the active material and the conductive material and the bonding with the current collector. Specifically, the binder may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluororubber, preferably including polyvinylidene fluoride.

[0139] In terms of sufficiently ensuring adhesion between components such as a positive electrode active material, the binder may be contained in the positive electrode active material layer in an amount of 1 to 20 wt %, preferably 1.2 to 10 wt %.

[0140] The conductive material can be used to impart conductivity to a secondary battery and improve conductivity, and is not particularly limited as long as it does not cause chemical changes and has conductivity. Specifically, the conductive material may include at least one selected from the group consisting of: graphite, such as natural graphite, artificial graphite, etc.; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers, such as carbon fibers, metal fibers, etc.; conductive tubes, such as carbon nanotubes, etc.; fluorocarbons; metal powders, such as aluminum powder, nickel powder, etc.; conductive whiskers composed of zinc oxide, potassium titanate, etc.; conductive metal oxides, such as titanium oxide, etc.; and polyphenylene derivatives, preferably including carbon black for enhanced conductivity.

[0141] In terms of sufficiently ensuring conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1% by weight to 20% by weight, preferably 1.2% by weight to 10% by weight.

[0142] The positive active material layer may have a thickness of 30 μm to 400 μm, preferably 50 μm to 110 μm.

[0143] The positive electrode may be prepared by applying a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry on a positive electrode current collector, followed by drying and roll-pressing.

[0144] The solvent for forming the positive electrode slurry may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), etc., and may be used in an amount suitable for achieving a preferred viscosity when the positive electrode active material and the optional binder and conductive material are included. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the content of the solid component containing the positive electrode active material, the optional binder and the conductive material is in the range of 50% by weight to 95% by weight, preferably 70% by weight to 90% by weight.

[0145] The diaphragm is used to separate the negative electrode and the positive electrode, and provides a channel for lithium ion migration, and any diaphragm used as a diaphragm in a typical lithium secondary battery can be used without restriction. In particular, it is preferred that the migration of electrolyte ions exhibits low resistance and a diaphragm having excellent electrolyte impregnation ability. Specifically, as a diaphragm, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a stacked structure having two or more layers thereof. In addition, as a diaphragm, a common porous non-woven fabric can be used, for example, a non-woven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a coating diaphragm comprising a ceramic component or a polymer material and optionally having a single-layer or multilayer structure can be used as the diaphragm.

[0146] Examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, inorganic solid electrolytes, molten inorganic electrolytes, etc. that can be used in secondary battery manufacturing, but the present invention is not limited thereto.

[0147] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0148] As the organic solvent, any organic solvent can be used without particular limitation, as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether solvents such as dibutyl ether, tetrahydrofuran, etc.; ketone solvents such as cyclohexanone, etc.; aromatic hydrocarbon solvents such as benzene, fluorobenzene, etc.; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; alcohol solvents such as ethanol, isopropanol, etc.; nitrile, such as R-CN (R is a C2 to C20 hydrocarbon group having a linear, branched or cyclic structure, which may contain a double bond aromatic ring or an ether bond), etc.; amides such as dimethylformamide, etc.; dioxolanes such as 1,3-dioxolanes, etc.; or cyclobutane sulfone. Among the solvents listed above, carbonate solvents are preferred. A mixture of cyclic carbonate compounds (such as EC, PC, etc.) having high ionic conductivity and high dielectric constant and linear carbonate compounds (such as EMC, DMC, DEC, etc.) having low viscosity can improve the charge / discharge performance of the battery and is more preferred. In this case, when a mixture of a cyclic carbonate compound and a linear carbonate compound is used in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be exhibited.

[0149] As the lithium salt, any compound can be used without particular limitation, as long as it can provide the lithium ions used in the lithium secondary battery. Specifically, as the lithium salt, the following can be used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt is preferably used in a concentration of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate level of conductivity and viscosity, thereby being able to exhibit excellent electrolyte performance and lithium ions being able to effectively migrate.

[0150] The secondary battery may be manufactured by a conventional method of manufacturing a secondary battery, that is, by interposing a separator between the above-mentioned negative electrode and positive electrode and injecting an electrolyte.

[0151] The secondary battery according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs). In particular, it is preferably used as a battery constituting a medium- to large-sized battery module. Therefore, the present invention also provides a medium- to large-sized battery module comprising the aforementioned secondary battery as a unit cell.

[0152] Such medium and large-sized battery modules are preferably used as power sources requiring high output and high capacity, for example, in electric vehicles, hybrid electric vehicles, power storage systems, and the like.

[0153] Hereinafter, the present invention will be described in detail with reference to embodiments so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is therefore not limited to the embodiments described herein.

[0154] Example

[0155] Example 1

[0156] <Silicon Core>

[0157] SiO (average particle size (D 50 ):5μm).

[0158] The silicon-based oxide particles and magnesium metal as a metal-containing material were mixed at a weight ratio of 92:8, and the resulting mixture was heat-treated at 1050° C. for 2 hours to prepare a silicon-based core including Mg distributed on the surface and / or inside thereof.

[0159] Chemical vapor deposition (CVD) was performed at 950° C. by flowing methane as a hydrocarbon gas over the silicon-based core to form an inner carbon coating on the silicon-based core.

[0160] The inner carbon coating layer was formed in an amount of 5 wt % relative to the total weight of the silicon-based core and the inner carbon coating layer.

[0161] <Formation of Outer Coat Layer>

[0162] 13 g of 2,2'-bis(trifluoromethyl)benzidine was dissolved in 77 g of N-methyl-2-pyrrolidone (NMP) solvent, and 20 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added to the resulting solution. The temperature was then raised to 40° C. and stirred for 16 hours to prepare a polyimide precursor-containing solution having a solid content of 30% by weight. Subsequently, the polyimide precursor-containing solution was diluted to a solid content of 0.5% by weight.

[0163] Subsequently, the silicon-based core having the inner carbon coating formed thereon and the solution containing the polyimide precursor were mixed at a weight ratio of 50:50, and the resulting mixture was heat-treated at 350° C. for 1 hour to form an outer coating layer containing polyimide on the silicon-based core having the inner carbon coating formed thereon, and the resulting product was used as the negative electrode active material (average particle size (D 50 ):6μm).

[0164] In the negative electrode active material of Example 1, the polyimide includes a unit represented by the following Chemical Formula 1-1.

[0165] [Chemical Formula 1-1]

[0166]

[0167] In the negative electrode active material of Example 1, the weight ratio of the silicon-based core on which the inner carbon coating is formed and the outer coating is 99.5:0.5. In addition, the outer coating contains fluorine in an amount of about 33 weight %.

[0168] The weight of the outer coating layer was measured by calculating the difference between the weight of the silicon-based core having the inner carbon coating layer formed thereon before polyimide coating and the weight of the negative active material after polyimide coating by thermogravimetric analysis (TGA).

[0169] Example 2

[0170] <Silicon Core>

[0171] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was used.

[0172] <Formation of Outer Coat Layer>

[0173] The negative active material of Example 2 was prepared by forming an outer coating layer on the silicon-based core having the inner carbon coating layer thereon in the same manner as Example 1, except that 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was used instead of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride.

[0174] In the negative active material of Example 2, the polyimide includes a unit represented by the following Chemical Formula 1-2.

[0175] [Chemical formula 1-2]

[0176]

[0177] In the negative electrode active material of Example 2, the weight ratio of the silicon-based core on which the inner carbon coating is formed and the outer coating is 99.5:0.5. In addition, the outer coating contains fluorine in an amount of about 16 weight %.

[0178] Example 3

[0179] <Silicon Core>

[0180] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was used.

[0181] <Formation of Outer Coat Layer>

[0182] 13g of p-phenylenediamine (PDA) was dissolved in 77g of N-methylpyrrolidone (NMP) solvent, and 20g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the resulting solution. The temperature was then raised to 40°C and stirred for 16 hours to prepare a solution containing a second polyimide precursor with a solid content of 30% by weight.

[0183] The solution containing a polyimide precursor having a solid content of 30 wt % prepared in Example 1 was provided as a solution containing a first polyimide precursor, the solution containing the first polyimide precursor and the solution containing the second polyimide precursor were mixed in a weight ratio of 50:50, and then a solution containing a polyimide precursor having a solid content of 0.5 wt % was prepared.

[0184] The negative active material of Example 3 was prepared in the same manner as in Example 1, except that the prepared solution containing the polyimide precursor was used.

[0185] In the negative electrode active material of Example 3, the polyimide includes a unit represented by the following Chemical Formula 1-1 and a unit represented by the following Chemical Formula 3-1. The unit represented by Chemical Formula 1-1 is derived from a first polyimide precursor in a solution containing a first polyimide precursor, and the unit represented by Chemical Formula 3-1 is derived from a second polyimide precursor in a solution containing a second polyimide precursor.

[0186] [Chemical Formula 1-1]

[0187]

[0188] [Chemical Formula 3-1]

[0189]

[0190] In the negative electrode active material of Example 3, the weight ratio of the silicon-based core on which the inner carbon coating layer is formed and the outer coating layer is 99.5:0.5. In addition, the outer coating layer contains fluorine in an amount of about 16 weight %.

[0191] Example 4

[0192] <Silicon Core>

[0193] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was used.

[0194] <Formation of Outer Coat Layer>

[0195] The negative active material of Example 4 was prepared in the same manner as Example 1, except that the polyimide precursor-containing solution having a solid content of 30 wt % prepared in Example 1 was diluted to 0.25 wt % instead of 0.5 wt %.

[0196] In the negative electrode active material of Example 4, the weight ratio of the silicon-based core on which the inner carbon coating layer is formed to the outer coating layer is 99.75:0.25. In addition, the outer coating layer contains fluorine in an amount of about 33 weight %.

[0197] Example 5

[0198] <Silicon Core>

[0199] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was used.

[0200] <Formation of Outer Coat Layer>

[0201] The negative active material of Example 5 was prepared in the same manner as Example 1, except that the polyimide precursor-containing solution having a solid content of 30 wt % prepared in Example 1 was diluted to have a solid content of 1 wt % instead of 0.5 wt %.

[0202] In the negative electrode active material of Example 5, the weight ratio of the silicon-based core having the inner carbon coating formed thereon and the outer coating layer was 99: 1. In addition, the outer coating layer contained fluorine in an amount of about 33 wt %.

[0203] Comparative Example 1

[0204] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was provided as a negative electrode active material of Comparative Example 1. In the negative electrode active material of Comparative Example 1, the outer coating layer was not formed.

[0205] Comparative Example 2

[0206] <Silicon Core>

[0207] The silicon-based core having the inner carbon coating layer formed thereon prepared in Example 1 was used.

[0208] <Formation of Polyimide Coating>

[0209] 13g of p-phenylenediamine (PDA) was dissolved in 77g of N-methylpyrrolidone (NMP) solvent, and 20g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the resulting solution. The temperature was then raised to 40°C and stirred for 16 hours to prepare a polyimide precursor solution having a solids content of 30% by weight. Subsequently, the polyimide precursor solution was diluted to a solids content of 0.5% by weight.

[0210] A negative active material of Comparative Example 2 was prepared in the same manner as in Example 1, except that the prepared solution containing the polyimide precursor was used.

[0211] In the negative electrode active material of Comparative Example 2, the weight ratio of the silicon-based core having the inner carbon coating formed thereon to the outer coating was 99.5:0.5. The outer coating did not contain fluorine.

[0212] [Table 1]

[0213] Amount of outer coating (based on negative electrode active material, weight %) Amount of fluorine (based on outer coating, weight %) Example 1 0.5 About 33 Example 2 0.5 About 16 Example 3 0.5 About 16 Example 4 0.25 About 33 Example 5 1 About 33 Comparative Example 1 0 - Comparative Example 2 0.5 0

[0214] Experimental example

[0215] <Manufacturing of negative electrode>

[0216] As the negative electrode material, a mixture of the negative electrode active material prepared in Example 1 and natural graphite (average particle size (D 50 ):15 μm) in a weight ratio of 5:95 to obtain a mixture.

[0217] The negative electrode material, styrene butadiene rubber (SBR) as a binder, Super C65 as a conductive material, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96:2:1:1, and the resulting mixture was added to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry.

[0218] At 3mAh / cm 2 The negative electrode slurry was applied to one surface of a copper current collector (thickness: 15 μm) as a negative electrode current collector, and then roll-pressed and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: 60 μm). The resulting product was used as the negative electrode according to Example 1 (negative electrode thickness: 75 μm).

[0219] Furthermore, negative electrodes according to Examples 2 to 5 and Comparative Examples 1 and 2 were prepared in the same manner as above, except that the composite negative electrode active material of Examples 2 to 5 and Comparative Examples 1 and 2 was used instead of the composite negative electrode active material of Example 1.

[0220] <Manufacturing of Secondary Batteries>

[0221] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, Super C65 as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2 to prepare a positive electrode slurry. The positive electrode slurry was applied to an aluminum current collector, then rolled and dried to produce a positive electrode.

[0222] A porous polyethylene separator was interposed between each of the negative electrodes and the positive electrodes according to Examples 1 to 5 and Comparative Examples 1 and 2, and an electrolyte was injected to manufacture a pouch-type secondary battery.

[0223] As the electrolyte, an electrolyte obtained by dissolving 1.5 wt % of vinylene carbonate (VC) in a solution obtained by mixing ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3 and dissolving LiPF 6 therein at a concentration of 1 M was used.

[0224] Experimental Example 1: High-temperature life performance evaluation

[0225] The cycle capacity retention rates of the secondary batteries manufactured according to Examples 1 to 5 and Comparative Examples 1 and 2 were evaluated using an electrochemical charger and discharger.

[0226] To evaluate the cycle capacity retention, charge and discharge were performed at 0.1 C from the 1st to 3rd cycles, and from the 4th cycle onwards, charge and discharge were performed at 1.0 C (charge conditions: CC / CV, 4.25 V / 0.05 C cutoff, discharge conditions: CC, 2.5 V cutoff). Charge and discharge were performed at 45°C.

[0227] The capacity retention rate was calculated as follows.

[0228] Capacity retention (%) = {(discharge capacity at the Nth cycle) / (discharge capacity at the 4th cycle)} × 100

[0229] (In this formula, N is an integer greater than or equal to 4.)

[0230] Table 2 below shows the capacity retention (%) after 300 cycles.

[0231] [Table 2]

[0232] Capacity retention after 300 cycles (%) Example 1 87 Example 2 85 Example 3 85 Example 4 84 Example 5 84 Comparative Example 1 80 Comparative Example 2 81

[0233] Referring to Table 2, it can be seen that the secondary battery of the embodiment exhibits an excellent level of high temperature life characteristics compared to the secondary battery of the comparative example by using the negative electrode active material in which a polyimide coating containing a preferred amount of fluorine is formed on a silicon-based core.

[0234] Experimental Example 2: High-temperature storage performance evaluation

[0235] The high-temperature storage performance of the secondary batteries manufactured according to Examples 1 to 5 and Comparative Examples 1 and 2 was evaluated.

[0236] Specifically, the capacity retention rate of the secondary battery after storage at a high temperature of 60° C. for 8 weeks was measured. The results are shown in Table 3 below.

[0237] To evaluate capacity retention, charge and discharge were performed at 0.3 C from the first to third cycles, and at 1.0 C from the fourth cycle onwards (charge conditions: CC / CV, 4.25 V / 0.05 C cutoff, discharge conditions: CC, 2.5 V cutoff). Charge and discharge were performed at 25°C.

[0238] The capacity retention rate was calculated as follows, and the results are shown in Table 3.

[0239] Capacity retention (%) = {(discharge capacity of the third cycle after 8 weeks of high-temperature storage) / (initial discharge capacity)} × 100

[0240] [Table 3]

[0241] Capacity retention rate (%) Example 1 86 Example 2 84 Example 3 84 Example 4 83 Example 5 84 Comparative Example 1 77 Comparative Example 2 80

[0242] Referring to Table 3, it can be seen that the secondary battery of the embodiment exhibits an excellent level of high-temperature storage characteristics compared to the secondary battery of the comparative example by using the negative electrode active material in which a polyimide coating containing a preferred amount of fluorine is formed on a silicon-based core.

[0243] Experimental Example 3: Resistance Performance Evaluation

[0244] The secondary batteries of Examples and Comparative Examples were charged to 4.25 V at 25°C at a constant current (CC) of 0.3C, and then charged at a constant voltage (CV) until the charge current reached 0.05C (cutoff current), thereby performing the first charge of the batteries. The batteries were then allowed to stand for 20 minutes and then discharged to 2.5 V at a constant current (CC) of 0.3C, and the discharge capacity was measured.

[0245] Furthermore, the secondary battery was fully charged again in the same manner and allowed to stand for 1 hour, and the initial resistance was measured by dividing the voltage change until 10 seconds of initial discharge at a current of 3.0 C by the current.

[0246] The measurement results of discharge capacity and initial resistance are shown in Table 4 below.

[0247] [Table 4]

[0248] Discharge capacity (mAh / g) Initial resistance (mΩ) Example 1 80 825 Example 2 80 840 Example 3 80 851 Example 4 80 834 Example 5 80 847 Comparative Example 1 80 860 Comparative Example 2 80 884

[0249] Referring to Table 4, it can be seen that the secondary battery of the example exhibits a superior level of resistance reduction effect compared to the secondary battery of the comparative example by using the negative electrode active material in which a polyimide coating layer containing a preferred amount of fluorine is formed on a silicon-based core.

Claims

1. A negative electrode active material, comprising: Silicon core; and forming an outer coating on the silicon core, wherein the outer coating is polyimide, in, The polyimide comprises a fluorine-containing imide unit, wherein the outer coating layer is contained in the negative electrode active material in an amount greater than 0 wt % and 4.5 wt % or less, and wherein the outer coating layer comprises fluorine in an amount of 10 wt % to 50 wt %.

2. The negative electrode active material according to claim 1, wherein the fluorine-containing imide unit is represented by the following Chemical Formula 1: [Chemical Formula 1] In the chemical formula 1, A1 is C4 to C 30 A tetravalent organic group, B1 is C6 to C 30 A divalent organic group, and at least one of A1 and B1 contains fluorine. 3 . The negative electrode active material according to claim 1 , further comprising an inner carbon coating layer formed between the silicon-based core and the outer coating layer. 4 . The negative active material according to claim 3 , wherein the content of the inner carbon coating layer is 1 wt % to 10 wt % based on the total weight of the silicon-based core and the inner carbon coating layer.

5. The negative electrode active material according to claim 1, wherein the silicon-based core comprises: Silicon-based particles comprising a compound represented by the following Chemical Formula 2, and a metal distributed on the surface of the silicon-based particles, inside the silicon-based particles, or on and inside the silicon-based particles, and The metal is at least one selected from the group consisting of Li, Mg, Al, Ca and Ti: [Chemical Formula 2] SiO x , where 0≤x<2. 6 . The negative electrode active material according to claim 5 , wherein the metal is contained in the silicon-based core in an amount of 0.1 wt % to 25 wt %.

7. The negative electrode active material according to claim 1, wherein the average particle size D of the negative electrode active material is 50 0.1 μm to 20 μm.

8. A negative electrode, comprising: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode material, in, The negative electrode material includes the negative electrode active material according to claim 1 .

9. A secondary battery, comprising: The negative electrode according to claim 8; a positive electrode arranged to face the negative electrode; a separator interposed between the negative electrode and the positive electrode; and electrolytes.

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