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

Abstract

The present invention relates to a negative electrode active material including a core containing at least one metal-containing particle, a first shell surrounding the core, and a second shell surrounding the first shell, wherein the metal-containing particle includes one or more elements selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge; a method for producing the negative electrode active material; and a lithium secondary battery including the negative electrode active material.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material, a method for producing the same, and a lithium secondary battery comprising the same, and specifically relates to a negative electrode active material having a two-layer shell structure introduced therein, a method for producing the same, and a lithium secondary battery comprising the same that is excellent in initial efficiency, life characteristics and output characteristics.

Background Art

[0002] Lithium Ion Batteries (LIBs) have high energy density, are easy to design, are adopted and used as a main power supply source for mobile electronic devices, and their application scope is further expanding to fields such as electric vehicles and power storage devices for new renewable energy in the future.

[0003] For application to new application fields, continuous research on LIB materials having characteristics such as higher energy density and long service life is continuously required.

[0004] In particular, for negative electrode materials, research has been progressed on various substances including carbon, such as silicon, tin, germanium, and the like.

[0005] Among these, silicon-based negative electrode materials have a much higher energy density than currently commercialized graphite negative electrode materials, and have attracted much attention.

[0006] However, silicon-based negative electrode materials have fatal disadvantages such as: an unstable SEI layer is formed due to a side reaction between the silicon surface and an electrolyte, leading to degradation of electrochemical characteristics; and pulverization of the electrode material occurs due to internal stress caused by abrupt volume expansion that occurs during charge and discharge.

[0007] To solve this problem, many studies have been progressed to improve the reversibility on the surface through various surface treatments of silicon-based negative electrode materials, and in particular, methods of surface-coating or compounding carbon materials have been widely studied.

[0008] On the other hand, various surface treatments using carbon materials require complex and costly processes. While surface treatments using carbon materials have improved the lifespan characteristics of some silicon-based anode materials, they have resulted in lower ionic conductivity of silicon-based anode materials, limiting the improvement of output characteristics necessary for realizing high-speed charge-discharge lithium-ion batteries (LIBs), for which demand has been growing recently.

[0009] In other words, conventional surface treatments using carbon materials proceeded with the composite formation with carbon without improving the low ionic conductivity of the silicon-based anode material, making it difficult to achieve the output characteristics required for high-speed charge-discharge lithium-ion batteries (LIBs).

[0010] Therefore, there is currently a need to develop surface treatment technologies for high-capacity silicon-based anode active materials that suppress volume expansion of silicon-based anode materials while simultaneously improving their low ionic conductivity. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Republic of Korea Patent Publication No. 2016-0104720 [Overview of the project] [Problems that the invention aims to solve]

[0012] Therefore, the objective of this invention is to provide a negative electrode active material for a secondary battery that has excellent initial efficiency, lifespan characteristics, and output characteristics.

[0013] Furthermore, the objective is to provide a manufacturing method that enables the production of the anode active material with high efficiency and low cost.

[0014] Along with this, the objective is to provide an electrode containing the aforementioned negative electrode active material and a lithium secondary battery.

[0015] However, the problems that this application seeks to solve are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0016] One aspect of the present invention comprises a core containing at least one metal-containing particle, A first shell surrounding the core, Including a second shell surrounding the first shell, The aforementioned metal-containing particles include one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge. We provide a negative electrode active material.

[0017] Another aspect of the present invention is a method for producing the negative electrode active material, A step of producing a precursor powder by spray-drying a solution containing metal-containing particles and nanocarbon particles, A first compounding step involves mixing the precursor powder and first amorphous carbon and compounding them to produce a primary composite, A second compounding step involves mixing the primary composite, a second amorphous carbon, and crystalline carbon, and compounding them to produce a secondary composite. The step includes a heat treatment step, The aforementioned metal is one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb. The present invention provides a method for producing a negative electrode active material.

[0018] Further embodiments of the present application include the negative electrode active material, Provide electrodes.

[0019] A further embodiment of the present application is a negative electrode comprising the negative electrode active material, A positive electrode located opposite the negative electrode, The present invention provides a lithium secondary battery comprising an electrolyte disposed between the negative electrode and the positive electrode. [Effects of the Invention]

[0020] The negative electrode active material according to the present invention has the effect of providing a secondary battery with excellent initial efficiency, lifespan characteristics, and output characteristics.

[0021] Furthermore, it has the effect of enabling the production of negative electrode active materials with high efficiency and low cost. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram showing a negative electrode active material with a two-layer shell structure according to one embodiment of the present invention. [Modes for carrying out the invention]

[0023] Terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0024] Therefore, the configurations of the embodiments described herein represent only one of the most preferred embodiments of the present invention and do not represent the entire technical concept of the invention. It should be understood that, at the time of filing, there are various equivalents and modifications that can be substituted for these embodiments.

[0025] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of an implemented feature, number, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, numbers, stages, components, or combinations thereof.

[0026] In this specification, the terms "from" and "~" in "a to b" and "a~b" which indicate a numerical range are defined as ≥ a and ≤ b.

[0027] A negative electrode active material according to one aspect of the present invention may include a core containing at least one metal-containing particle, a first shell surrounding the core, and a second shell surrounding the first shell, as shown in Figure 1.

[0028] Furthermore, the metal-containing particles may contain one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge, and may be spherical or flaky.

[0029] The first shell effectively bonds the core and the second shell, thereby stably maintaining the structure of the negative electrode active material from the volume expansion of the metal-containing particles (e.g., silicon) generated during charging and discharging.

[0030] If the first shell is absent, the adhesion between the core and the second shell of the negative electrode active material weakens, making the second shell more prone to breakage during electrode manufacturing and potentially reducing processability. Electrolyte solvent molecules may then be inserted through the broken portion, reducing the electrochemical reactivity of the second shell and the core.

[0031] The second shell effectively prevents contact between the metal-containing particles of the core and the electrolyte solvent, contributing to the stable electrochemical reversibility of the metal-containing particles, while simultaneously improving the lifetime characteristics of the negative electrode active material based on stable electrochemical stability with the electrolyte solvent at the outermost layer.

[0032] In the absence of the second shell, hydrocarbons and other substances in the first shell react with lithium ions, generating irreversible capacity, which can degrade the battery's lifespan. Furthermore, microscopic defects in the first shell can accelerate side reactions such as electrolyte reductive decomposition.

[0033] In one embodiment, the metal-containing particles may be silicon (Si)-containing particles, and the silicon (Si)-containing particles may include one or more selected from the group consisting of silicon particles, silicon oxide particles, silicon carbide particles, and silicon alloy particles. Furthermore, the average particle size (D50) of the silicon (Si)-containing particles may be 50 to 200 nm and represented by the following chemical formula 1.

[0034] [C1] SiOx (0 ≤ x ≤ 0.5)

[0035] In the above chemical formula 1, if x exceeds 0.5, there may be unfavorable effects on battery capacity and efficiency. That is, lithium ions react with oxygen to form Li2O, Li-silicate(Li x Si y O z Irreversible products such as ) are generated. As a result, lithium ions that have reacted with the negative electrode material are trapped inside the negative electrode instead of returning to the electrolyte or positive electrode material, preventing them from exhibiting capacity and reducing efficiency.

[0036] Furthermore, for example, the silicon carbide may be SiC, and the silicon alloy may be, for example, a Si-Z alloy (where Z is one or more elements selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si).

[0037] The average particle size of the silicon-containing particles was measured using a particle size analyzer (Mastersizer3000, Malvern Panalytical) with an organic solution in which the silicon-containing particles were dispersed.

[0038] If the average particle size of the silicon-containing particles exceeds 200 nm, a high battery capacity can be obtained, but the battery life will be very short. If the average particle size of the silicon-containing particles is less than 50 nm, the battery capacity and efficiency will be low, and manufacturing costs may be high.

[0039] In one embodiment, the metal-containing particles may be present in an amount of 50 to 98% by weight based on the total weight of the core. That is, when the total weight of the core is 100% by weight, 50 to 98% of this amount can correspond to the weight of the metal-containing particles.

[0040] In one embodiment, the average particle size (D50) of the negative electrode active material may be 5 to 20 μm.

[0041] The average particle size of the negative electrode active material was measured using a particle size analyzer (Mastersizer3000, Malvern Panalytical) with an organic solution in which the negative electrode active material was dispersed.

[0042] In one embodiment, the negative electrode active material may include at least one nanocarbon particle.

[0043] The nanocarbon particles may be single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black, or a combination thereof.

[0044] In one embodiment, the nanocarbon particles may be present in an amount of 0.5% by weight or more and 10% by weight or less, based on 100% by weight of the total weight of the metal-containing particles.

[0045] If the content of the nanocarbon particles falls below the content range specified in this application, the electrical conductivity and porosity of the negative electrode active material will be significantly reduced, which may lead to a decrease in initial discharge capacity, initial efficiency, life characteristics, and output characteristics when used in a secondary battery.

[0046] In one embodiment, the first shell may contain amorphous carbon, and the second shell may contain crystalline carbon.

[0047] Furthermore, the first shell may contain a small amount of crystalline carbon, and the second shell may contain a small amount of amorphous carbon.

[0048] On the other hand, the core may additionally contain amorphous carbon.

[0049] The first shell, by containing amorphous carbon, can effectively bond the core and the second shell, and can stably maintain the structure of the negative electrode active material from the volume expansion of the metal-containing particles (e.g., silicon) generated during charging and discharging.

[0050] The second shell, by containing the crystalline carbon, effectively prevents contact between the metal-containing particles (e.g., silicon) of the core and the electrolyte solvent, thereby contributing to the stable electrochemical reversibility of the metal-containing particles. At the same time, it can improve the lifetime characteristics of the negative electrode active material based on stable electrochemical stability with the electrolyte solvent at the outermost layer.

[0051] In one embodiment, the negative electrode active material may have a carbon content of 30% by weight or more and 85% by weight or less, based on 100% by weight of the total weight of the negative electrode active material.

[0052] If the carbon content falls below the range specified in this application, the electrical conductivity of the negative electrode active material may decrease, and the porosity may increase. In addition, the initial efficiency, life characteristics, and output characteristics of secondary batteries using the negative electrode active material may decrease.

[0053] On the other hand, if the carbon content exceeds the scope of this application, the porosity of the negative electrode active material may decrease. Furthermore, the initial efficiency, life characteristics, and output characteristics of secondary batteries using the negative electrode active material may decrease.

[0054] In one embodiment, the negative electrode active material may have a carbon content of 15% by weight or more and 40% by weight or less in the core and the first shell, based on 100% by weight of the total weight of the negative electrode active material, and a carbon content of 15% by weight or more and 40% by weight or less in the second shell, based on the total weight of the negative electrode active material.

[0055] If the carbon content of the first shell falls below the scope of this application, the bonding force between the core and the second shell may weaken, which may reduce the lifespan characteristics of the secondary battery.

[0056] Furthermore, if the carbon content of the first shell exceeds the scope of this application, the thickness of the first shell may increase, and the overall strength of the first and second shells may be weakened.

[0057] On the other hand, if the carbon content of the second shell falls below the range of the present invention, the electrical conductivity of the negative electrode active material may decrease, which may reduce the lifespan characteristics of the secondary battery.

[0058] Furthermore, if the carbon content of the second shell exceeds the scope of this invention, the specific capacity may decrease, and the energy density of the secondary battery may decrease.

[0059] In one embodiment, the oxygen content may be 10% by weight or less, based on 100% by weight of the total weight of the negative electrode active material.

[0060] For example, the oxygen content may be 5% by weight or more and 10% by weight or less.

[0061] In one embodiment, the first shell may additionally contain at least one metal-containing particle.

[0062] In one embodiment, the electrical conductivity of the negative electrode active material may be 17 S / cm or more and 20 S / cm or less, and the porosity may be 20% or more and 35% or less.

[0063] If the electrical conductivity and / or porosity of the negative electrode active material exceeds or falls below the range of this application, one or more of the initial efficiency, life characteristics, and output characteristics of the secondary battery to which the negative electrode active material is applied may decrease.

[0064] A method for producing a negative electrode active material according to another aspect of the present invention may include the steps of: producing a precursor powder by spray-drying a solution containing metal-containing particles and nanocarbon particles; a first compounding step of mixing and compounding the precursor powder and first amorphous carbon to produce a primary composite; a second compounding step of mixing and compounding the primary composite, second amorphous carbon and crystalline carbon to produce a secondary composite; and a heat treatment step.

[0065] The aforementioned metal may be one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb.

[0066] The metal-containing particles provided in the step of producing the precursor powder may be prepared by grinding them in a grinding process to have a desired average particle size.

[0067] In one embodiment, the first and second amorphous carbons may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, tar, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, sucrose, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, phenol resin, furan resin, cellulose resin, styrene resin, epoxy resin or vinyl chloride resin, block copolymer, polyol, and polyimide resin.

[0068] Furthermore, the crystalline carbon may be one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene.

[0069] Natural graphite is graphite that occurs naturally and includes flake graphite, high crystalline graphite, and amorphous (microcrystalline or cryptocrystalline) graphite. Synthetic graphite is graphite that is artificially synthesized and produced by heating amorphous carbon at high temperatures, and includes primary or electrographite, secondary graphite, and graphite fiber.

[0070] Expanded graphite is produced by intercalating chemicals such as acids or alkalis between layers of graphite and then heating it to expand the vertical layers of its molecular structure. Graphene contains a single layer or multiple single layers of graphite.

[0071] Carbon black is a crystalline substance with less regularity than graphite, and can be converted to graphite by heating it at approximately 3,000°C for a long period of time. Fullerene is a carbon mixture containing at least 3% by weight of fullerene, which is a polyhedral bundle compound consisting of 60 or more carbon atoms. The first carbon-based material can use one type of such crystalline carbon alone or in combination of two or more types. For example, natural graphite or artificial graphite can be used. The crystalline carbon can be spherical, plate-like, fibrous, tubular, or powder-like.

[0072] Preferably, pitch can be used as the first and second amorphous carbons. The pitch can have a softening point of 100 to 250°C, and in particular, petroleum-based or coal-based pitch can be used that has a QI (Quinolone Insoluble) component of 5% by weight or less, more preferably 1% by weight or less.

[0073] On the other hand, as the crystalline carbon, natural graphite can preferably be used. The purity of the graphite should be such that the fixed carbon content is 99% by weight or more, and more preferably 99.95% by weight or more.

[0074] Furthermore, flake graphite can be suitable for increasing conductivity through contact with silicon.

[0075] In one embodiment, the compounding step may be carried out by a physical method.

[0076] The aforementioned physical method may include one or more high-energy processes selected from the group consisting of milling, stirring, mixing, and compression.

[0077] For example, the compounding step may be carried out by ball milling. In particular, a planetary ball mill can efficiently mix and grind a mixture in a non-contact manner, rotating and revolving with the composition.

[0078] The balls that can be used for ball milling may be, for example, zirconia balls, and there are no restrictions on the type of ball. The size of the ball may be, for example, approximately 0.3 to 10 mm, but is not limited to this.

[0079] On the other hand, the reaction time for the first and second compounding steps may be 1 minute to 24 hours, the reaction temperature may be 40 to 250°C, and the reaction atmosphere may be air or an inert atmosphere. In one embodiment, the heat treatment step may be carried out in an inert atmosphere or under vacuum, and the heat treatment temperature may be 700 to 1,100°C.

[0080] Furthermore, the heat treatment time is not particularly limited, but may be performed in the range of, for example, 10 minutes to 48 hours.

[0081] The weight ratio of the precursor powder to the first amorphous carbon in the first compounding step (weight of precursor powder:weight of first amorphous carbon) may be 75-85:15-25.

[0082] Furthermore, the weight ratio of the primary composite, the second amorphous carbon, and the crystalline carbon in the second compounding step (weight of primary composite:weight of first amorphous carbon:weight of crystalline carbon) may be 45-55:15-25:20-35.

[0083] If the weight ratio of the precursor powder and the first amorphous carbon in the first compounding step of this application and / or the weight ratio of the primary composite, the second amorphous carbon and the crystalline carbon in the second compounding step are above or below the specified range, the initial efficiency, life characteristics, and output characteristics may decrease when the negative electrode active material is applied to a secondary battery.

[0084] An electrode according to yet another aspect of the present application may include the negative electrode active material, and the lithium secondary battery may include a positive electrode positioned opposite the negative electrode, with the electrode containing the negative electrode active material as the negative electrode, and an electrolyte disposed between the negative electrode and the positive electrode.

[0085] The negative electrode may include the negative electrode active material and may be manufactured, for example, by mixing the negative electrode active material, a binder, and a selectively conductive agent in a solvent to produce a negative electrode active material composition, and then molding it into a certain shape or by applying it to a current collector such as copper foil.

[0086] The negative electrode may further include, in addition to the negative electrode active material described above, negative electrode active material materials commonly used as negative electrode active materials for lithium batteries in the art. Commonly used negative electrode active material materials may include, for example, one or more selected from the group consisting of lithium metal, metals alloyable with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0087] For example, the metal capable of alloying with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination element thereof, and is not Si), a Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 to group 16 element, a transition metal, a rare earth element, or a combination element thereof, and is not Sn), or the like. The element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0088] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

[0089] For example, the non-transition metal oxide may be SnO₂, SiOₓ (0<x≦2), or the like. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, platy, flaky, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, or the like.

[0090] When the negative electrode active material and the carbon-based material are used together, the oxidation reaction of the silicon-based active material can be inhibited, an SEI film can be effectively formed to produce a stable coating, electrical conductivity can be improved, and the charge-discharge characteristics of lithium can be further enhanced.

[0091] Conventional negative electrode active material may be used by mixing and blending it with the negative electrode active material described above, by coating it on the surface of the negative electrode active material described above, or in any other combination form.

[0092] The binder used in the negative electrode active material composition is a component that assists in the bonding of the negative electrode active material to a conductive agent and to the current collector, and is added in amounts of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. For example, the binder can be added in the range of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the negative electrode active material.

[0093] Examples of such binders include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resins, epoxy resins, polyethylene terephthalate, polytetrafluoroethylene, polyphenyl sulfide, polyamide-imide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0094] The negative electrode may further selectively contain a conductive agent to provide conductive passages to the negative electrode active material and further improve electrical conductivity.

[0095] Generally, any conductive agent used in lithium batteries can be used. Examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, and carbon fibers (e.g., vapor-grown carbon fibers); metallic materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof. The content of the conductive agent can be adjusted as appropriate. For example, the weight ratio of the negative electrode active material to the conductive agent can be in the range of 99:1 to 90:10.

[0096] The solvent can be N-methylpyrrolidone (NMP), acetone, water, etc. The solvent content is 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the solvent content is within this range, the process of forming the active material layer is easy.

[0097] Furthermore, the current collector is generally made to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used.

[0098] Furthermore, by forming fine irregularities on the surface, the bonding force of the negative electrode active material can be strengthened, and it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0099] The negative electrode plate can be manufactured by directly coating the manufactured negative electrode active material composition onto a current collector, or by casting it onto another support, peeling the negative electrode active material film from the support, and laminating it onto a copper foil current collector. The negative electrode is not limited to the forms listed above, and may take other forms.

[0100] Said negative electrode active material composition is not only used for manufacturing electrodes of lithium secondary batteries, but can also be printed on a flexible electrode substrate and used for manufacturing printable batteries.

[0101] Separately, in order to produce a positive electrode, a positive electrode active material composition in which a positive electrode active material, a conductive agent, a binder and a solvent are mixed is prepared.

[0102] Any lithium-containing metal oxide commonly used in the art can be used as the positive electrode active material.

[0103] For example, Li a A 1-b B b D2 (in the above formula, 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b B b O 2-c D c (in the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); LiE 2-b B b O 4-c D c (in the above formula, 0≦b≦0.5, 0≦c≦0.05); Li a Ni 1-b-c Co b B c Dα (in the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li a Ni 1-b-c Co b B c O 2- αFα (in the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Co b B c O 2- αFα (in the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Mn b Bc Dα(wherein the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2);Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li a Ni b E c G d O2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1.);Li a Ni b Co c Mn d GeO2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1.);Li a NiG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a CoG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a MnG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Compounds represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2) or LiFePO4 can be used.

[0104] In the above chemical formulas, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0105] Of course, compounds having a coating layer on their surface can also be used, or the compound and the compound having the coating layer may be mixed and used. The coating layer may contain coating element compounds of oxide, hydroxide, oxyhydroxy, oxycarbonate, or hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. The coating elements included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation step can be carried out using any coating method that does not adversely affect the physical properties of the positive electrode active material (e.g., spray coating, immersion method, etc.) using such elements, and since this is something that will be well understood by those engaged in this field, a detailed explanation will be omitted.

[0106] For example, LiNiO2, LiCoO2, LiMn x O 2x (x=1, 2), LiNi 1-x Mn x O2(0 <x<1)、LiNi 1-x-y Co x Mn yO2 (0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.5), LiFeO2, V2O5, TiS, MoS, etc. can be used.

[0107] In the positive electrode active material composition, the conductive agent, binder, and solvent can be the same as those used in the negative electrode active material composition described above. In some cases, a plasticizer can be further added to the positive electrode active material composition and the negative electrode active material composition to form voids inside the electrode plate. The content of the positive electrode active material, conductive agent, binder, and solvent is at levels typically used in lithium batteries. The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm and possesses high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The current collector can also have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0108] The prepared positive electrode active material composition can be directly coated onto a positive electrode current collector and dried to produce a positive electrode plate. Alternatively, the positive electrode active material composition can be cast onto another support, and the resulting film, obtained by peeling it off the support, can be laminated onto the positive electrode current collector to produce a positive electrode plate.

[0109] The positive and negative electrodes can be separated by a separator, and any separator commonly used in lithium batteries can be used. In particular, a separator with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferred. For example, materials selected from glass fiber, polyester, Teflon®, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, may be in the form of a nonwoven or woven fabric. The separator has a void diameter of 0.01 to 10 μm and is generally used with a thickness of 5 to 300 μm.

[0110] Lithium salt-containing non-aqueous electrolytes consist of a non-aqueous electrolyte and lithium. Non-aqueous electrolytes include non-aqueous electrolyte solutions, solid electrolytes, and inorganic solid electrolytes.

[0111] As the non-aqueous electrolyte, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate can be used.

[0112] Examples of the organic solid electrolytes that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups. Examples of the inorganic solid electrolytes that can be used include lithium nitrides, halides, and sulfates such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0113] Any lithium salt commonly used in lithium batteries can be used, and substances that readily dissolve in the non-aqueous electrolyte include, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl10 One or more of the following substances can be used: LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc.

[0114] Lithium secondary batteries may be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and may also be classified into cylindrical, prismatic, coin-type, pouch-type, etc. depending on their form, and into bulk type and thin-film type depending on their size.

[0115] Since the manufacturing methods for these batteries are widely known in this field, a detailed explanation will be omitted. [Examples]

[0116] The present application will be described in more detail below using examples and comparative examples, but the present application is not limited thereto.

[0117] [Example 1] Silicon particles (average particle size (D 50 A mixture of 5 μm (5 part by weight) and 95 parts by weight of isopropyl alcohol (IPA) was placed in a bead mill and ground until the average particle size (D50) of the silicon particles reached 110 nm, thereby preparing a ground silicon solution.

[0118] Carbon nanotubes at a weight ratio of 3% relative to silicon particles were added to the prepared pulverized silicon solution, and then the solution was spray-dried to produce a silicon precursor with an average particle size (D50) of 6 μm.

[0119] The manufactured silicon precursor was mixed with petroleum-based pitch in a weight ratio of 80:20 and placed in a compounding device (uniquely manufactured by Hansol Chemical) to carry out primary compounding and produce a primary composite. Subsequently, the primary composite was mixed with petroleum-based pitch and graphite in a weight ratio of 50:20:30 and placed in the same compounding device to carry out secondary compounding and produce a secondary composite.

[0120] Subsequently, the secondary composite was heat-treated in an inert atmosphere up to 900°C for 3 hours to obtain the negative electrode active material.

[0121] [Example 2] The negative electrode active material was manufactured in the same manner as in Example 1, except that the amount of carbon nanotubes added was 4% by weight relative to the silicon particles.

[0122] [Example 3] The negative electrode active material was manufactured in the same manner as in Example 1, except that the amount of carbon nanotubes added was 2% by weight relative to the silicon particles.

[0123] [Example 4] The negative electrode active material was produced in the same manner as in Example 1, except that in the primary compounding process, the silicon precursor and petroleum-based pitch were mixed in a weight ratio of 85:15, and in the secondary compounding process, the primary composite, pitch, and graphite were mixed in a weight ratio of 48:22:30.

[0124] [Example 5] The negative electrode active material was produced in the same manner as in Example 1, except that in the primary compounding process, the silicon precursor and petroleum-based pitch were mixed in a weight ratio of 75:25, and in the secondary compounding process, the primary composite, pitch, and graphite were mixed in a weight ratio of 53:17:30.

[0125] [Comparative Example 1] The negative electrode active material was manufactured in the same manner as in Example 1, except that carbon nanotubes were not included.

[0126] [Comparative Example 2] The negative electrode active material was produced in the same manner as in Example 1, except that the silicon precursor, petroleum-based pitch, and graphite were mixed in a weight ratio of 43:27:30 and only the compounding process was carried out (the primary compounding step of Example 1 was not carried out, and only the process corresponding to secondary compounding was carried out by adjusting the weight ratio of the silicon precursor, petroleum-based pitch, and graphite).

[0127] [Comparative Example 3] The negative electrode active material was produced in the same manner as in Example 1, except that in the primary compounding process, the ratio of silicon precursor to petroleum-based pitch was mixed at 95:5 parts by weight, and in the secondary compounding process, the weight ratio of the primary composite, pitch, and graphite was mixed at 44:26:30.

[0128] [Comparative Example 4] The negative electrode active material was produced in the same manner as in Example 1, except that in the primary compounding process, the ratio of silicon precursor to petroleum-based pitch was mixed at 70:30 parts by weight, and in the secondary compounding process, the weight ratio of the primary composite, pitch, and graphite was mixed at 56:14:30.

[0129] [Manufacturing example] Making a coin half cell The negative electrode active material, conductive agent (Super P), and binder (SBR-CMC) produced in Examples 1-5 and Comparative Examples 1-4 were uniformly mixed in a weight ratio of 94:2:4 to prepare a negative electrode slurry. The prepared negative electrode slurry was coated onto a 10 μm thick copper thin film current collector. After the coating was complete, the electrode plate was dried at 120°C for 20 minutes, then rolled (pressed) to produce the negative electrode.

[0130] A CR2032 type coin half-cell was manufactured using metallic lithium as the negative electrode and counter electrode, a PE separator as the separation membrane, and a 1.0 M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate):DEC (diethyl carbonate):DMC (dimethyl carbonate) (volume ratio of 3:5:2) as the electrolyte.

[0131] Coin Full Cell Construction Using the negative electrode from the aforementioned coin half-cell, the positive electrode was manufactured as follows: LiNi 0.6 Co 0.2 Mn 0.2 A positive electrode slurry was prepared by mixing O2, a conductive agent (Super P), and a binder (PVDF) in a weight ratio of 95:2:3. The positive electrode slurry was then coated onto a 12 μm thick aluminum foil current collector. After the coated electrode plate was dried at 120°C for 15 minutes, it was rolled (pressed) to produce the positive electrode.

[0132] Using the aforementioned positive and negative electrodes, a PE separation membrane (separator) was used as the separation membrane, and a mixed solvent of EC (ethylene carbonate):DEC (diethyl carbonate):DMC (dimethyl carbonate) (volume ratio of 2:1:7) + 5% FEC in which 1.5M LiPF6 was dissolved was used as the electrolyte to produce a CR2032 type coin full cell.

[0133] Evaluation Example 1: Analysis of Negative Electrode Active Material The characteristics of the negative electrode active materials of Examples 1-5 and Comparative Examples 1-4 were analyzed and are shown in Table 1 below.

[0134] [Table 1]

[0135] In Table 1 above, the particle size (D50) of the negative electrode active material (composite) was measured using a particle size analyzer (Mastersizer3000, Malvern Panalytical) with an organic solution in which the negative electrode active materials of Examples 1-5 and Comparative Examples 1-4 were dispersed.

[0136] Furthermore, the particle size (D50) of the silicon particles used in the production of the negative electrode active materials in Examples 1-5 and Comparative Examples 1-4 was also measured in the same manner as the particle size measurement method for the negative electrode active materials.

[0137] On the other hand, the carbon content of the first and second shells of the negative electrode active materials in Examples 1-5 and Comparative Examples 1-4 was determined by measuring the carbon content of carbon dioxide and carbon monoxide, which are carbon-containing gases generated by burning the silicon precursor, primary composite, and negative electrode active material at high temperatures using ELEMENTRAC CS-i (ELTRA), and then multiplying the values ​​calculated using the following equations 1 and 2 by 100.

[0138]

number

[0139]

number

[0140] In the above formulas 1 and 2, C1 represents the carbon content of the first shell, C2 represents the carbon content of the second shell, M1 represents the carbon content of the primary composite, and M2 represents the carbon content of the negative electrode active material.

[0141] For Examples 1-4 and Comparative Examples 1, 3, and 4, the carbon content of the first and second shells of the negative electrode active material was calculated. However, for Comparative Example 2, where only one layer of shell was formed, the carbon content of the second shell is shown.

[0142] The oxygen content was determined by quantitatively measuring the oxygen-containing gas generated by burning the negative electrode active materials of Examples 1-5 and Comparative Examples 1-4 at high temperatures using an 836 Series (LECO) analyzer.

[0143] Furthermore, the electrical conductivity of the negative electrode active materials produced in Examples 1-5 and Comparative Examples 1, 3, and 4 was measured by pelletizing the materials and using the 4-probe measurement method.

[0144] Specifically, 500 mg of each negative electrode active material powder was placed in a powder resistance measuring container, and the resulting electrical resistance was measured and converted to electrical conductivity. At this time, the negative electrode active material pellet was compressed, and the electrical resistance was measured in real time.

[0145] On the other hand, the porosity was calculated using the following formula 3. In the following formula 1, the true density was 2.33 g / cc. The total porosity volume of the negative electrode active materials in Examples 1-5 and Comparative Examples 1-4 was measured using a TriStar II 3020 instrument from Micromeritics. The total porosity volume was measured by the amount of nitrogen gas adsorbed due to changes in relative pressure at liquid nitrogen temperature (77 K).

[0146]

number

[0147] According to the measurement results shown in Table 1, a comparison of the negative electrode active materials of Examples 1 to 3 confirmed that the electrical conductivity and porosity of the negative electrode active material increased as the carbon nanotube content increased.

[0148] On the other hand, the negative electrode active material of Comparative Example 1, which does not contain carbon nanotubes, exhibited significantly lower electrical conductivity and porosity compared to the negative electrode active materials of Examples 1 to 3, which differed only in their carbon nanotube content.

[0149] Furthermore, by comparing the negative electrode active materials of Examples 1, 4, and 5, it was confirmed that the particle size, carbon shell content ratio, electrical conductivity, and porosity of the negative electrode active material can be adjusted by adjusting the weight ratio of silicon precursor to petroleum-based pitch to 75-85:15-25 during the primary compounding process, and by adjusting the weight ratio of the first composite, petroleum-based pitch, and graphite to 48-53:17-22:30 during the secondary compounding process.

[0150] On the other hand, in Comparative Examples 3 and 4, the anode active materials were adjusted so that the weight ratio of silicon precursor to petroleum-based pitch in the primary composite process and the weight ratio of the first composite, petroleum-based pitch, and graphite in the secondary composite process were different from those of the anode active material in the example. In particular, it was confirmed that the electrical conductivity and porosity of these materials were lower.

[0151] Evaluation Example 2: Battery Characteristic Analysis The characteristics of the cells using the negative electrode active materials of Examples 1-5 and Comparative Examples 1-4 were analyzed and are shown in Table 2 below.

[0152] [Table 2]

[0153] The battery characteristics of coin half-cells and coin full-cells manufactured using the negative electrode active materials produced in Examples 1-5 and Comparative Examples 1-4 were evaluated as follows.

[0154] Coin-full cells were used for evaluating lifespan and power characteristics, while coin-half cells were used for evaluating initial capacity, discharge capacity, and initial efficiency characteristics.

[0155] Coin half-cells manufactured using the negative electrode active materials produced in Examples 1-5 and Comparative Examples 1-4 were each charged with a constant current at 25°C at a rate of 0.1C until the voltage reached 0.01V (vs.Li), and then charged with a constant voltage until the current reached 0.05C while maintaining the voltage at 0.01V. After the fully charged cells were left to rest for 10 minutes, they were discharged at a constant current of 0.1C until the voltage reached 1.5V (vs.Li) (this was done twice, using the initial formation). The term "C" represents the discharge rate of the cell, and is the value obtained by dividing the total capacity of the cell by the total discharge time.

[0156] Coin full cells manufactured using the negative electrode active materials produced in Examples 1-5 and Comparative Examples 1-4 were each charged with a constant current at 25°C at a rate of 0.1C until the voltage reached 4.2V (vs.Li), and then charged with a constant voltage until the current reached 0.05C while maintaining 4.2V. After the fully charged cells were allowed to rest for 10 minutes, they were discharged at a constant current of 0.1C until the voltage reached 2.7V (vs.Li) (performed twice, initial formation).

[0157] Subsequently, the cell was charged with a constant current at a rate of 1.0C at 25°C until the voltage reached 4.2V (vs.Li), and then charged with a constant voltage until the current reached 0.05C while maintaining 4.2V. After the fully charged coin cell was left to rest for 10 minutes, the cycle of discharging with a constant current of 1.0C until the voltage reached 2.7V (vs.Li) was repeated (cycles 1 to 200).

[0158] On the other hand, the initial charge capacity and initial discharge capacity in Table 2 above represent the charge and discharge capacities for the first cycle, respectively.

[0159] Initial efficiency, lifespan, and power characteristics were calculated using equations 4-6 below, respectively.

[0160] <Formula 4> Initial efficiency [%] = [Discharge capacity in the first cycle / Charge capacity in the first cycle] x 100

[0161] <Formula 5> Lifetime characteristic [%] = [Discharge capacity at 200th cycle / Discharge capacity at 1st cycle] x 100

[0162] <Formula 6> Output characteristic [%] = [Discharge capacity at 5.0C / Discharge capacity at 0.1C] x 100

[0163] According to the measurement results shown in Table 2 above, the secondary batteries using the negative electrode active materials of Examples 1 to 5 exhibited an initial charge capacity of 1,658 to 1,673 mAh / g, an initial discharge capacity of 1,457.1 to 1,467.9 mAh / g, an initial efficiency of 87.4 to 88.1%, a lifespan of 79.8 to 81.1%, and an output characteristic of 67.2 to 69.1%.

[0164] In contrast, it was confirmed that the secondary battery using the negative electrode active material of Comparative Example 1, which does not contain carbon nanotubes, showed a decrease in initial discharge capacity, initial efficiency, lifespan characteristics, and output characteristics compared to the secondary batteries using the negative electrode active materials of Examples 1 to 5.

[0165] Furthermore, it was confirmed that the secondary battery using the negative electrode active material of Comparative Example 2, which has only one shell formed, exhibited lower initial efficiency, lifespan characteristics, and output characteristics compared to the secondary batteries using the negative electrode active materials of Examples 1 to 5.

[0166] On the other hand, secondary batteries using the negative electrode active materials of Comparative Examples 3 and 4, in which the weight ratio of silicon precursor to petroleum-based pitch in the primary composite process and the weight ratio of the first composite, petroleum-based pitch to graphite in the secondary composite process were adjusted to differ from those of the negative electrode active materials of the Examples, showed a decrease in initial efficiency, life characteristics, and output characteristics compared to secondary batteries using the negative electrode active materials of Examples 1 to 5.

[0167] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or altered forms derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention. [Industrial applicability]

[0168] The negative electrode active material according to the present invention has the effect of providing a secondary battery with excellent initial efficiency, lifespan characteristics, and output characteristics.

[0169] Furthermore, it has the effect of enabling the production of negative electrode active materials with high efficiency and low cost.

Claims

1. A core containing at least one metal-containing particle, A first shell surrounding the core, Including a second shell surrounding the first shell, The metal-containing particles include one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, Ti, Cu, V, Zr, Nb, and Ge. The first shell further comprises at least one metal-containing particle. Negative electrode active material.

2. The aforementioned metal-containing particles are silicon (Si)-containing particles. The negative electrode active material according to claim 1.

3. The core comprises at least one nanocarbon particle, The negative electrode active material according to claim 1.

4. The nanocarbon particles are present in an amount of 0.5% by weight or more and 10% by weight or less, based on 100% by weight of the total weight of the metal-containing particles. The negative electrode active material according to claim 3.

5. Based on 100% by weight of the total weight of the negative electrode active material, the carbon content is 30% by weight or more and 85% by weight or less. The negative electrode active material according to claim 1.

6. The first shell contains amorphous carbon, The second shell contains crystalline carbon, The negative electrode active material according to claim 1.

7. Based on 100% by weight of the total weight of the negative electrode active material, the oxygen content is 10% by weight or less. The negative electrode active material according to claim 1.

8. The carbon content of the first shell is 15% by weight or more and 40% by weight or less, based on 100% by weight of the total weight of the negative electrode active material. The carbon content of the second shell is 15% by weight or more and 40% by weight or less, based on 100% by weight of the total weight of the negative electrode active material. The negative electrode active material according to claim 1.

9. The electrical conductivity is 17 S / cm or higher and 20 S / cm or lower. The porosity is between 20% and 35%. The negative electrode active material according to claim 1.

10. A method for producing a negative electrode active material according to any one of claims 1 to 9, A step of producing a precursor powder by spray-drying a solution containing metal-containing particles and nanocarbon particles, A first compounding step involves mixing the precursor powder and first amorphous carbon and compounding them to produce a primary composite, A second compounding step involves mixing the primary composite, a second amorphous carbon, and crystalline carbon, and compounding them to produce a secondary composite. This includes a heat treatment step, The aforementioned metal is one or more selected from Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, Ti, Cu, V, Zr, Nb, and Ge. A method for producing a negative electrode active material.

11. The weight ratio of the precursor powder to the first amorphous carbon in the first compounding step (weight of precursor powder:weight of first amorphous carbon) is 75-85:15-25. Furthermore, the weight ratio of the primary composite, the second amorphous carbon, and the crystalline carbon in the second composite step (weight of primary composite: weight of first amorphous carbon: weight of crystalline carbon) is 45-55:15-25:20-35. A method for producing a negative electrode active material according to claim 10.

12. A negative electrode active material comprising the material described in any one of claims 1 to 9, electrode.

13. A negative electrode comprising the negative electrode active material described in any one of claims 1 to 9, A positive electrode located opposite the negative electrode, The electrolyte is disposed between the negative electrode and the positive electrode, Lithium-ion rechargeable battery.

14. A core comprising at least one metal-containing particle, A first shell surrounding the core, Including a second shell surrounding the first shell, The metal-containing particles include one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, and Ge. The first shell further comprises at least one metal-containing particle. Negative electrode active material.

15. A core comprising at least one metal-containing particle, A first shell surrounding the core, Including a second shell surrounding the first shell, The metal-containing particles include one or more selected from the group consisting of Mg, Al, Si, Ca, Fe, Mn, Co, Ni, Zn, and Ge. The electrical conductivity is 17 S / cm or higher and 20 S / cm or lower. The porosity is between 20% and 35%. Negative electrode active material.

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