Negative electrode active material, method for producing the same, and lithium secondary battery including 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 an anode active material, a method for producing the same, and a lithium secondary battery including the same, and more specifically to an anode active material having a two-layer shell structure, a method for producing the same, and a lithium secondary battery including the same that has excellent initial efficiency, life characteristics, and output characteristics. [Background technology]

[0002] Lithium ion batteries (LIBs) have high energy density and are easy to design, and are used as the main power source for mobile electronic devices. In the future, their range of applications will expand further to include electric vehicles and power storage devices for new and renewable energy sources.

[0003] In order to apply LIBs to new fields, there is a continuing demand for research into LIB materials with properties such as higher energy density and longer life.

[0004] In particular, when it comes to negative electrode materials, research has been conducted on a variety of substances, including carbon, silicon, tin, and germanium.

[0005] Among these, silicon-based anode materials have attracted much attention because they have a much higher energy density than the currently commercially available graphite anode materials.

[0006] However, silicon-based anode materials have fatal drawbacks, such as the formation of an unstable SEI layer due to a side reaction between the silicon surface and the electrolyte, which reduces electrochemical properties, and the internal stress caused by the sudden volume expansion that occurs during charging and discharging, which can cause the electrode material to shatter.

[0007] To solve this problem, much research has been conducted into improving the reversibility of silicon-based negative electrode materials through various surface treatments, and in particular, methods of surface coating or compounding with carbon materials have been widely studied.

[0008] On the other hand, various surface treatments using carbon materials require complex and expensive processes, and while surface treatments using carbon materials have improved the lifespan characteristics of some silicon-based anode materials, the ionic conductivity of silicon-based anode materials has been low, limiting the improvement of output characteristics required to realize high-speed charge / discharge LIBs, which have recently seen increasing demand.

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

[0010] Therefore, there is a current demand for the development of a technology for surface treatment of high-capacity silicon-based negative electrode active materials that suppresses the volume expansion of silicon-based negative electrode materials while improving the low ionic conductivity of silicon-based negative electrode materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Republic of Korea Patent Publication No. 2016-0104720 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, an object of the present invention is to provide a negative electrode active material for a secondary battery that is excellent in initial efficiency, life characteristics, and output characteristics.

[0013] Another object of the present invention is to provide a method for producing the negative electrode active material with high efficiency and low cost.

[0014] Another object of the present invention is to provide an electrode and a lithium secondary battery containing the negative electrode active material.

[0015] However, the problems to be solved by the present application 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 application is a composite material comprising: a core comprising at least one metal-containing particle; a first shell surrounding the core; a second shell surrounding the first shell, The metal-containing particles contain at least one selected from the group consisting of Mg, Al, Si, Ca, Fe, Mg, Mn, Co, Ni, Zn, and Ge. A negative electrode active material is provided.

[0017] Another aspect of the present application is a method for producing the negative electrode active material, comprising: spray-drying a solution containing metal-containing particles and nanocarbon particles to produce a precursor powder; a first compounding step of mixing and compounding the precursor powder and the first amorphous carbon to produce a primary compound; a second compounding step of mixing and compounding the primary compound, the second amorphous carbon, and the crystalline carbon to produce a secondary compound; and heat treating the resulting product. The metal is one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb. A method for producing a negative electrode active material is provided.

[0018] Yet another aspect of the present application is a negative electrode active material comprising: An electrode is provided.

[0019] Yet another aspect of the present application is a battery comprising a negative electrode including the negative electrode active material; a positive electrode positioned opposite the negative electrode; and 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 excellent in initial efficiency, life characteristics and output characteristics.

[0021] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating a negative electrode active material having a two-layer shell structure according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention.

[0024] Therefore, it should be understood that the configuration of the embodiment described in this specification is merely one of the most preferred embodiments of the present invention and does not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0025] In this specification, the singular includes the plural unless the context clearly indicates otherwise. It should be understood that in this specification, the terms "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0026] In this specification, the terms "from" and "to" in "from a to b" and "a to b" that indicate a numerical range are defined as ≧a and ≦b.

[0027] As shown in FIG. 1 , a negative electrode active material according to one embodiment of the present application can include a core including at least one metal-containing particle, a first shell surrounding the core, and a second shell surrounding the first shell.

[0028] 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 flake-shaped.

[0029] The first shell effectively bonds the core and the second shell, thereby stably maintaining the structure of the negative electrode active material against volume expansion of the metal-containing particles (e.g., silicon) that occurs during charge and discharge.

[0030] If the first shell is absent, the adhesive strength between the core and the second shell of the negative electrode active material may be weakened, which may cause the second shell to be easily broken during electrode manufacturing, reducing processability. In addition, electrolyte solvent molecules may be inserted through the broken portions, reducing the electrochemical reactivity of the second shell and the core.

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

[0032] Without the second shell, hydrocarbons in the first shell may react with lithium ions to generate irreversible capacity, thereby reducing the battery's lifespan. Additionally, microscopic defects in the first shell may accelerate side reactions such as the reduction and decomposition of the electrolyte.

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

[0034] [C1] SiOx(0≦x≦0.5)

[0035] In the above formula 1, if x exceeds 0.5, it may have a detrimental effect on the battery capacity and efficiency. That is, lithium ions react with oxygen to form Li2O, Li-silicate (Li x Si y O z As a result, the lithium ions that react with the anode material are trapped inside the anode instead of returning to the electrolyte or cathode material, preventing the battery from achieving full 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 an organic solution in which the silicon-containing particles were dispersed, using a particle size analyzer (Mastersizer 3000, Malvern Panalytical).

[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 significantly shortened. If the average particle size of the silicon-containing particles is less than 50 nm, the battery capacity and efficiency will be low and the manufacturing costs will be high.

[0039] In one embodiment, the metal-containing particles may account for 50 to 98 wt % of the total weight of the core, i.e., when the weight of the entire core is taken as 100 wt %, 50 to 98 wt % of the total weight of the core may correspond to the weight of the metal-containing particles.

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

[0041] The average particle size of the negative active material was measured using an organic solution in which the negative active material was dispersed, using a particle size analyzer (Mastersizer 3000, Malvern Panalytical).

[0042] In one embodiment, the negative electrode active material can 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 included in an amount of 0.5 wt % or more and 10 wt % or less, based on the total weight of the metal-containing particles (100 wt %).

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

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

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

[0048] Meanwhile, the core may additionally contain amorphous carbon.

[0049] The first shell contains the amorphous carbon, which can effectively bond the core and the second shell and stably maintain the structure of the negative electrode active material against volume expansion of the metal-containing particles (e.g., silicon) that occurs during charge and discharge.

[0050] The second shell, containing the crystalline carbon, effectively prevents contact between the metal-containing particle (e.g., silicon) of the core and the electrolyte solvent, contributing to stable electrochemical reversibility of the metal-containing particle. At the same time, the outermost shell has stable electrochemical stability with the electrolyte solvent, improving the life characteristics of the negative electrode active material.

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

[0052] If the carbon content is below the range of the present application, the electrical conductivity of the negative electrode active material may decrease and the porosity may increase, and the initial efficiency, life characteristics, and output characteristics of a secondary battery using the negative electrode active material may decrease.

[0053] On the other hand, if the carbon content exceeds the range of the present application, the porosity of the negative electrode active material may be reduced, and the initial efficiency, life characteristics, and output characteristics of a secondary battery using the negative electrode active material may be reduced.

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

[0055] If the carbon content of the first shell is below the range of the present application, the binding strength between the core and the second shell may be weakened, resulting in a decrease in the life characteristics of the secondary battery.

[0056] Furthermore, if the carbon content of the first shell exceeds the range of the present application, the thickness of the first shell increases, and the strength of the first shell and the second shell may be weakened overall.

[0057] On the other hand, if the carbon content of the second shell is below the range of the present application, the electrical conductivity of the negative electrode active material may decrease, and the life characteristics of the secondary battery may deteriorate.

[0058] Furthermore, if the carbon content of the second shell exceeds the range of the present application, the specific capacity may decrease, resulting in a decrease in the energy density of the secondary battery.

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

[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 can additionally include at least one metal-containing particle.

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

[0063] If the electrical conductivity and / or porosity of the negative electrode active material is higher or lower than the range of the present application, one or more of the initial efficiency, life characteristics, and output characteristics of a secondary battery using the negative electrode active material may be reduced.

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

[0065] The 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 preparing the precursor powder may be prepared by being pulverized to have a desired average particle size through a pulverization process.

[0067] In one embodiment, the first and second amorphous carbons may each be at least one 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, vinyl chloride resin, block copolymer, polyol, and polyimide resin.

[0068] The crystalline carbon may be at least one 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, highly crystalline graphite, and amorphous (microcrystalline or cryptocrystalline; amorphous) graphite. Artificial graphite is artificially synthesized graphite made by heating amorphous carbon to high temperatures and includes primary or electrographite, secondary graphite, and graphite fiber.

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

[0071] Carbon black is a crystalline material with less regularity than graphite, and can be converted into graphite by heating it at approximately 3,000°C for a long period of time. Fullerene is a carbon mixture containing at least 3 wt% fullerene, a polyhedral bundle-shaped compound consisting of 60 or more carbon atoms. The first carbon-based material can be one type of crystalline carbon or a combination of two or more types. For example, natural graphite or artificial graphite can be used. The crystalline carbon can be in the form of spheres, plates, fibers, tubes, or powder.

[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 with a QI (Quinolone Insoluble) content of 5% by weight or less, more preferably 1% by weight or less can be used.

[0073] On the other hand, natural graphite can be preferably used as the crystalline carbon, and the purity of the graphite to be used is high, with a fixed carbon content of 99% by weight or more, more preferably 99.95% by weight or more.

[0074] Furthermore, flake graphite can be suitable for increasing electrical conductivity by contacting with silicon.

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

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

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

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

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

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

[0081] The weight ratio of the precursor powder and 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] The weight ratio of the primary composite, second amorphous carbon, and crystalline carbon in the second composite forming 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 to the first amorphous carbon in the first compounding step and / or the weight ratio of the primary compound, the second amorphous carbon, and the crystalline carbon in the second compounding step is above or below the range of the present invention, the initial efficiency, life characteristics, and output characteristics may be reduced when the negative electrode active material is applied to a secondary battery.

[0084] According to yet another aspect of the present application, an electrode may include the negative electrode active material, and a lithium secondary battery may include an electrode including the negative electrode active material as a negative electrode, a positive electrode positioned opposite 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. For example, the negative electrode active material, a binder, and optionally a conductive agent may be mixed in a solvent to prepare a negative electrode active material composition, which may then be molded into a predetermined shape or applied to a current collector such as copper foil.

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

[0087] For example, the metal that can form an alloy with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination of these elements and is not Si), Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 to Group 16 element, transition metal, rare earth element, or a combination of these elements and is not Sn), etc. 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 of these.

[0088] For example, the transition metal oxide may be lithium titanate, vanadium oxide, lithium vanadate, etc.

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

[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 suppressed, the SEI film can be effectively formed to form a stable film, the electrical conductivity can be improved, and the charge and discharge characteristics of lithium can be further improved. <000038�> A typical negative electrode active material may be mixed and blended with the above-mentioned negative electrode active material, coated on the surface of the above-mentioned negative electrode active material, or used in any other combined form.

[0092] The binder used in the negative electrode active material composition is a component that aids in bonding the negative electrode active material to the conductive agent and the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. For example, the binder may be added in an amount 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resins, epoxy resins, polyethylene terephthalate, polytetrafluoroethylene, polyphenylsulfide, polyamideimide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

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

[0095] The conductive agent can be any of those commonly used in lithium batteries. Examples include carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fiber (e.g., vapor-grown carbon fiber); metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof. The amount of conductive agent can be adjusted appropriately. 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 may be N-methylpyrrolidone (NMP), acetone, water, etc. The content of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the content of the solvent is within this range, the process of forming the active material layer is easy.

[0097] The current collector is generally formed to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery, and examples that can be used include copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys.

[0098] In addition, the bonding strength of the negative electrode active material can be strengthened by forming minute irregularities on the surface, and the material can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0099] The negative electrode active material composition thus prepared can be directly coated on a current collector to produce a negative electrode plate, or can be cast onto a separate support, peeled off from the support, and the resulting negative electrode active material film can be laminated onto a copper foil current collector to produce a negative electrode plate. The negative electrode is not limited to the above-listed forms and may have other forms.

[0100] The negative electrode active material composition can be used not only to manufacture an electrode for a lithium secondary battery, but also to manufacture a printable battery by being printed on a flexible electrode substrate.

[0101] Separately, to produce a positive electrode, a positive electrode active material composition is prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent.

[0102] Any lithium-containing metal oxide that is 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 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b B b O 2-c D c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B b O 4-c D c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B c Dα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co 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 Co 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 Bc Dα (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 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 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (wherein 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 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 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 expressed by any one of the chemical formulas Fe2(PO4)3(0≦f≦2);LiFePO4 can be used.

[0104] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, 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; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0105] Of course, this compound may have a coating layer on its surface, or the compound may be mixed with a compound having a coating layer. The coating layer may include a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. Examples of the coating element included in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation process may be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material. Since this method is well understood by those skilled in the art, a detailed description 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] The conductive agent, binder, and solvent in the positive electrode active material composition may be the same as those in the negative electrode active material composition. In some cases, a plasticizer may be added to the positive electrode active material composition and the negative electrode active material composition to form voids within the electrode plate. The amounts of the positive electrode active material, conductive agent, binder, and solvent are 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, does not induce chemical changes in the battery, and has high conductivity, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector may have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0108] The prepared positive electrode active material composition can be directly coated on a positive electrode current collector and dried to produce a positive electrode plate, or the positive electrode active material composition can be cast on a separate support, peeled off from the support, and the resulting film can be laminated on a 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, separators with low resistance to the movement of electrolyte ions and excellent electrolyte humidifying capacity are preferred. For example, the separator may be made of a material selected from glass fiber, polyester, Teflon (registered trademark), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven or woven fabric. The separator has a pore size of 0.01 to 10 μm and a thickness of generally 5 to 300 μm.

[0110] The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and lithium. The non-aqueous electrolyte may be a non-aqueous electrolytic solution, a solid electrolyte, or an inorganic solid electrolyte.

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

[0112] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociative groups. Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0113] Any lithium salt commonly used in lithium batteries can be used as the lithium salt. Examples of substances that are easily dissolved in the non-aqueous electrolyte include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic lithium carboxylates, lithium tetraphenylborate, imides, and the like can be used in one or more of the following materials.

[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 be classified into cylindrical, prismatic, coin-shaped, pouch-shaped, etc. depending on the shape, and into bulk type and thin film type depending on the size.

[0115] The manufacturing methods of these batteries are well known in the art and will not be described in detail. [Example]

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

[0117] [Example 1] Silicon particles (average particle size (D 50 Five parts by weight of silicon dioxide (5 μm): 5 μm) and 95 parts by weight of isopropyl alcohol (IPA) were mixed and charged into a bead mill, and ground until the average particle size (D50) of the silicon particles became 110 nm, thereby preparing a ground silicon solution.

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

[0119] The prepared silicon precursor was mixed with petroleum-based pitch in a weight ratio of 80:20 and placed in a compounder (manufactured by Hansol Chemical) for primary compounding to 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 compounder for secondary compounding to produce a secondary composite.

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

[0121] [Example 2] A negative electrode active material was prepared 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] A negative electrode active material was prepared 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] An anode active material was prepared in the same manner as in Example 1, except that the silicon precursor and petroleum-based pitch were mixed in a weight ratio of 85:15 during the primary compounding process, and the primary composite, pitch, and graphite were mixed in a weight ratio of 48:22:30 during the secondary compounding process.

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

[0125] [Comparative Example 1] A negative electrode active material was produced in the same manner as in Example 1, except that no carbon nanotubes were added.

[0126] Comparative Example 2 A 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 in Example 1 was not carried out, and only the process corresponding to the secondary compounding was carried out by adjusting the weight ratio of the silicon precursor, petroleum-based pitch, and graphite).

[0127] Comparative Example 3 An anode active material was prepared in the same manner as in Example 1, except that the silicon precursor and petroleum-based pitch were mixed in a ratio of 95:5 parts by weight during the primary compounding process, and the primary composite, pitch, and graphite were mixed in a weight ratio of 44:26:30 during the secondary compounding process.

[0128] Comparative Example 4 An anode active material was prepared in the same manner as in Example 1, except that the silicon precursor and petroleum-based pitch were mixed in a ratio of 70:30 parts by weight during the primary compounding process, and the primary composite, pitch, and graphite were mixed in a weight ratio of 56:14:30 during the secondary compounding process.

[0129] [Manufacturing example] Fabrication of coin half-cells The negative electrode active materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4, a conductive agent (Super P), and a binder (SBR-CMC) were uniformly mixed in a weight ratio of 94:2:4 to prepare negative electrode slurries. The prepared negative electrode slurry was coated on a copper thin film current collector having a thickness of 10 μm, and the coated electrode plate was dried at 120° C. for 20 minutes and then pressed to prepare a negative electrode.

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

[0131] Fabrication of a coin full cell The negative electrode used in the coin half-cell was used to prepare a positive electrode as follows: LiNi 0.6 Co 0.2 Mn 0.2 O2, a conductive agent (Super P), and a binder (PVDF) were mixed in a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil current collector with a thickness of 12 μm. The coated electrode plate was dried at 120°C for 15 minutes and then pressed to prepare a positive electrode.

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

[0133] Evaluation example 1: Analysis of negative electrode active material The properties of the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 4 were analyzed and are shown in Table 1 below.

[0134] [Table 1]

[0135] In Table 1, the particle size (D50) of the negative electrode active material (composite) was measured with a particle size analyzer (Mastersizer 3000, Malvern Panalytical) using an organic solution in which the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 4 were dispersed.

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

[0137] Meanwhile, the carbon contents of the first shell and the second shell of the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 4 were determined by measuring the quantity of carbon-containing gases such as carbon dioxide and carbon monoxide generated by burning the carbon contents of the silicon precursor, the primary composite, and the negative electrode active material at high temperatures using an ELEMENTRAC CS-i (ELTRA), and then multiplying the values ​​calculated by 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] The carbon contents of the first shell and the second shell were calculated for the negative electrode active materials of Examples 1 to 4 and Comparative Examples 1, 3, and 4. However, the carbon content of the shell of Comparative Example 2, in which only one shell layer was formed, was shown as the carbon content of the second shell.

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

[0143] The negative electrode active materials produced in Examples 1 to 5 and Comparative Examples 1, 3 and 4 were pelletized, and the electrical conductivity of the powder was measured by a 4-probe measurement method.

[0144] That is, 500 mg of each negative electrode active material powder was placed in a powder resistance measurement container, and the generated electrical resistance was measured and converted into electrical conductivity. At this time, the negative electrode active material pellet was compressed, and the electrical resistance was measured in real time.

[0145] Meanwhile, the porosity was calculated using the following equation 3. In the following equation 1, the true density was 2.33 g / cc. The total pore volume of the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 4 was measured using a TriStar II 3020 device manufactured by Micromeritics. The total pore volume was measured by measuring 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, by comparing the negative electrode active materials of Examples 1 to 3, it was confirmed that as the carbon nanotube content increases, the electrical conductivity and porosity of the negative electrode active material increase.

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

[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 the silicon precursor and petroleum-based pitch to 75-85:15-25 in 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 in the secondary compounding process.

[0150] On the other hand, it was confirmed that the negative electrode active materials of Comparative Examples 3 and 4, in which the weight ratio of the silicon precursor and petroleum-based pitch in the primary compounding process and the weight ratio of the first composite, petroleum-based pitch and graphite in the secondary compounding process were adjusted to be different from those of the negative electrode active materials of the Examples, had particularly low electrical conductivity and low porosity.

[0151] Evaluation example 2: Battery characteristic analysis The characteristics of the cells using the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 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 manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated as follows.

[0154] A coin full cell was used for evaluating the life and output characteristics, and a coin half cell was used for evaluating the initial capacity, discharge capacity, and initial efficiency characteristics.

[0155] Coin half-cells prepared using the negative electrode active materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were each charged at a constant current rate of 0.1 C at 25°C until the voltage reached 0.01 V (vs. Li), and then charged at a constant voltage of 0.05 C while maintaining 0.01 V. After the cells were fully charged, they were rested for 10 minutes and then discharged at a constant current of 0.1 C until the voltage reached 1.5 V (vs. Li) (two runs, initial formation). The "C" represents the cell's discharge rate, calculated by dividing the cell's total capacity by the total discharge time.

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

[0157] The cell was then charged at a constant current of 1.0 C at 25°C until the voltage reached 4.2 V (vs. Li), and then at a constant voltage of 0.05 C while maintaining 4.2 V. After the coin cell was fully charged, it was left to rest for 10 minutes and then repeatedly discharged at a constant current of 1.0 C until the voltage reached 2.7 V (vs. Li) (1st to 200th cycles).

[0158] Meanwhile, the initial charge capacity and initial discharge capacity in Table 2 are the charge and discharge capacities in the first cycle, respectively.

[0159] The initial efficiency, lifespan, and output characteristics were calculated using the following formulas 4 to 6, respectively.

[0160] <Formula 4> Initial efficiency [%] = [discharge capacity at first cycle / charge capacity at first cycle] x 100

[0161] <Formula 5> Life characteristics [%] = [200th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0162] <Formula 6> Output characteristics [%] = [5.0C discharge capacity / 0.1C discharge capacity] x 100

[0163] According to the measurement results shown in Table 2, 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 life characteristic 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, had reduced initial discharge capacity, initial efficiency, life 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, in which only one shell layer was formed, had lower initial efficiency, life characteristics, and output characteristics than the secondary batteries using the negative electrode active materials of Examples 1 to 5.

[0166] On the other hand, it was confirmed that the secondary batteries using the negative electrode active materials of Comparative Examples 3 and 4, in which the weight ratio of the silicon precursor and petroleum-based pitch in the primary compounding process and the weight ratio of the first composite, petroleum-based pitch and graphite in the secondary compounding process were adjusted to be different from those of the negative electrode active materials of the Examples, had lower initial efficiency, life characteristics and output characteristics than the secondary batteries using the negative electrode active materials of Examples 1 to 5.

[0167] The scope of the present invention is indicated by the claims that follow rather than by the above detailed description, and all modifications and variations that fall within the meaning and scope of the claims and their equivalents 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 excellent in initial efficiency, life characteristics and output characteristics.

[0169] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost.

Claims

1. a core comprising at least one metal-containing particle; a first shell surrounding the core; 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, Mg, Mn, Co, Ni, Zn, and Ge. Negative electrode active material.

2. The 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 contained in an amount of 0.5 wt % or more and 10 wt % or less based on the total weight of the metal-containing particles (100 wt %). The negative electrode active material according to claim 3 .

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

6. the first shell comprises amorphous carbon; the second shell comprises crystalline carbon; The negative electrode active material according to claim 1 .

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

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

9. the first shell additionally comprises at least one metal-containing particle; The negative electrode active material according to claim 1 .

10. The electrical conductivity is 17 S / cm or more and 20 S / cm or less, The porosity is 20% or more and 35% or less. The negative electrode active material according to claim 1 .

11. A method for producing the negative electrode active material according to any one of claims 1 to 10, spray-drying a solution containing metal-containing particles and nanocarbon particles to produce a precursor powder; a first compounding step of mixing and compounding the precursor powder and the first amorphous carbon to prepare a primary compound; a second compounding step of mixing and compounding the primary compound, the second amorphous carbon, and the crystalline carbon to produce a secondary compound; and heat treating the resulting product. The metal is one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb. A method for producing a negative electrode active material.

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

13. The negative electrode active material according to any one of claims 1 to 10, electrode.

14. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 10; a positive electrode positioned opposite the negative electrode; an electrolyte disposed between the negative electrode and the positive electrode; Lithium secondary battery.

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