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 shell containing metal particles whose surfaces are entirely or partially coated with metal carbide, a method for producing the same, and a lithium secondary battery including the same.

Description

[Technical Field]

[0001] The present invention relates to an anode active material, a manufacturing method thereof, and a lithium secondary battery including the same, and more particularly to an anode active material that improves battery life by incorporating metal particles whose surfaces are entirely or partially coated with metal carbide, a manufacturing method thereof, and a lithium secondary battery including the same. [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 be further expanded to include electric vehicles and power storage devices for renewable energy sources.

[0003] In order to apply LIBs to new fields, there is a continuous demand for research into LIB materials with higher energy density and longer lifespan.

[0004] In particular, when it comes to negative electrode materials, research has been progressing 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 currently commercially available graphite anode materials.

[0006] However, silicon-based anode materials have fatal disadvantages, 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 battery performance through various surface treatments of silicon-based anode materials, and in particular, methods of surface coating or compounding with carbon materials have been widely studied.

[0008] However, there are still limits to how much battery life can be improved, and there is currently a need to develop technology for surface treatment of silicon-based negative electrode active materials that will suppress the volume expansion of silicon-based negative electrode materials while also improving battery life. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Republic of Korea Patent Publication No. 2018-0002715 [Patent Document 2] Republic of Korea Patent Registration No. 10-1666878 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide a negative electrode active material for a long-life secondary battery having a high capacity and a high energy density.

[0011] Another object of the present invention is to provide a method for producing the negative electrode active material with high efficiency and low cost.

[0012] Another object of the present invention is to provide an electrode and a lithium secondary battery containing the negative electrode active material.

[0013] 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]

[0014] One aspect of the present application is a semiconductor device comprising: a core; a shell surrounding the core, the shell comprises metal particles whose surfaces are entirely or partially coated with metal carbide; The metal includes any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P and Ag, A negative electrode active material is provided.

[0015] Another aspect of the present application is a method for producing a powder comprising the steps of: milling metal particles; mixing the pulverized metal particles, amorphous carbon, and crystalline carbon to form a composite; a heat treatment step, The metal includes any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P and Ag, A method for producing a negative electrode active material is provided.

[0016] Yet another aspect of the present application is a negative electrode active material comprising: An electrode is provided.

[0017] 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]

[0018] The negative electrode active material according to the present invention has the effect of providing a secondary battery having a high capacity, a high energy density and a long life.

[0019] 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]

[0020] [Figure 1] 1 is a schematic diagram illustrating a core-shell structured negative electrode active material according to one embodiment of the present invention. [Figure 2a] FIG. 2a shows XRD and Raman spectra of the negative electrode active materials according to Example 1, Example 3 and Comparative Example 3 of the present invention. [Figure 2b]FIG. 2b shows XRD and Raman spectra of the negative electrode active materials according to Examples 1 and 3 of the present invention and Comparative Example 3. [Figure 3a] FIG. 3a is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 3b] FIG. 3b is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 3c] FIG. 3c is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1 of the present invention. [Figure 4a] FIG. 4a shows the result of an energy dispersive X-ray spectroscopy (EDS) line scan analysis of a cross section of the negative electrode active material according to Example 1 of the present invention. [Figure 4b] FIG. 4b shows the result of an energy dispersive X-ray spectroscopy (EDS) line scan analysis of a cross section of the negative active material according to Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] 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.

[0023] 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.

[0024] As shown in FIG. 1 , a negative electrode active material according to one embodiment of the present application includes a core and a shell surrounding the core, the shell including metal particles whose surfaces are entirely or partially coated with metal carbide, and the metal may include any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag.

[0025] The surfaces of the metal particles of the negative electrode active material are partially or entirely coated with the metal carbide.

[0026] For example, the metal carbide may coat 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100% of the entire surface of the metal particles, and the degree of coating can be adjusted by changing process conditions during the preparation of the negative electrode active material.

[0027] In one embodiment, the core of the negative electrode active material includes metal particles, and the metal may include any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag.

[0028] That is, the core of the negative electrode active material may include metal particles whose surfaces are not coated with metal carbide, and the shell of the negative electrode active material may include metal particles whose surfaces are partially or entirely coated with metal carbide.

[0029] The metal particles whose surfaces are partially or entirely coated with metal carbide can improve the life stability of the battery.

[0030] In one embodiment, the metal particles may be silicon particles, silicon oxide particles, silicon carbide particles, silicon alloy particles, or a combination thereof.

[0031] The silicon-containing particles are represented by the following formula 1. SiOx(0≦x≦0.5) (Chem.1)

[0032] In the formula 2, if x is greater than 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 reacted with the anode material cannot return to the electrolyte or cathode material and are trapped inside the anode, preventing the battery from achieving full capacity and reducing efficiency.

[0033] 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).

[0034] The silicon-containing particles may have an average particle size (D50) of 50 to 1,000 nm, and preferably 600 to 900 nm.

[0035] If the average particle size of the silicon-containing particles exceeds 1,000 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.

[0036] In one embodiment, the crystal grain size of the metal particles may be 5 to 50 nm, and preferably 10 to 35 nm.

[0037] If the crystal grain size of the metal particles exceeds 50 nm, the manufacturing cost may increase and the life stability may decrease, and if the crystal grain size of the metal particles is less than 5 nm, the battery capacity may decrease.

[0038] The size of the crystal grains of the metal carbide may be 1 to 50 nm, preferably 5 to 20 nm.

[0039] If the size of the crystal grains of the metal carbide exceeds 50 nm, it may hinder the development of battery capacity, and if the size of the crystal grains of the metal carbide is less than 1 nm, the effect of improving the battery life is not achieved.

[0040] In one embodiment, the ratio of the height of the peak of the metal carbide to the height of the peak of the metal in an XRD analysis of the negative electrode active material (height of the peak of the metal carbide / height of the peak of the metal) may be 0.01 to 0.55, preferably 0.01 to 0.2, and more preferably 0.02 to 0.1.

[0041] If the ratio of the height of the peak of the metal carbide to the height of the peak of the metal exceeds 0.55, the capacity characteristics of the battery may be reduced, and if the ratio of the height of the peak of the metal carbide to the height of the peak of the metal is less than 0.01, the life of the battery may be shortened.

[0042] In one embodiment, the peak (I d ) and the corresponding peak of crystalline carbon (I g ) and the height ratio (I d / I g ) may be 0.1 to 1.8.

[0043] Furthermore, the ratio (I metal carbide / I metal) of the height of the peak corresponding to the metal carbide (I metal carbide) to the height of the peak corresponding to the metal (I metal) in Raman analysis of the negative electrode active material may be 0.01 to 0.2, and preferably 0.05 to 0.1.

[0044] If the ratio of I metal carbide to I metal exceeds 0.2, the capacity characteristics of the battery may be reduced, and if the ratio of I metal carbide to I metal is less than 0.01, the battery life may be shortened.

[0045] Meanwhile, the height of the peak corresponding to the metal carbide (I metal carbide) and the peak corresponding to the amorphous carbon (I d ) and the ratio (I metal carbide / I d ) may be 0.005 to 0.1, and preferably 0.02 to 0.07.

[0046] I metal carbide / I d If the value exceeds 0.1, the capacity characteristics of the battery are reduced, and the I metal carbide / I d If it is less than 0.005, the battery life may be shortened.

[0047] In one embodiment, the shell may comprise crystalline carbon.

[0048] That is, the shell may be a carbon-based shell, and may be composed mostly of crystalline carbon with a small amount of amorphous carbon.

[0049] The carbon component of the carbon-based shell may serve to mitigate volume expansion of metal particles whose surfaces are entirely or partially coated with metal carbide during charging and discharging.

[0050] Meanwhile, the core of the negative electrode active material has voids formed therein, and the internal pores of the core can reduce the initial irreversible capacity of the battery and help alleviate the volume expansion of Si.

[0051] The volume of the voids formed in the core may be 0.01 to 0.5 cc / g, and the specific gravity of the voids may decrease as they are located farther from the center of the core.

[0052] A method for manufacturing a negative electrode active material according to another aspect of the present disclosure may include a step of pulverizing metal particles, a step of mixing the pulverized metal particles, amorphous carbon, and crystalline carbon to form a composite, and a step of heat treatment.

[0053] The metal may include any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag.

[0054] That is, the method for producing the negative electrode active material of the present invention does not require a separate step of producing a metal carbide and coating the metal carbide, and the metal particles are coated with the metal carbide through the composite step and heat treatment step.

[0055] In one embodiment, the amorphous carbon may be any 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. The crystalline carbon may be any one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene.

[0056] Natural graphite is graphite that is naturally produced 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.

[0057] 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.

[0058] Carbon black is a crystalline material with less regularity than graphite, and can be converted into graphite by heating carbon black 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.

[0059] Preferably, pitch can be used as the amorphous carbon. The pitch has 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.

[0060] On the other hand, natural graphite can be preferably used as the crystalline carbon. The purity of the graphite to be used is high-purity, with a fixed carbon content of 99% by weight or more, more preferably 99.95% by weight or more.

[0061] Furthermore, flake graphite can be suitable for increasing electrical conductivity by contacting with metal particles.

[0062] In one embodiment, the conjugation step is carried out by a physical method.

[0063] 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.

[0064] For example, the compounding step can 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.

[0065] 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.

[0066] On the other hand, the reaction time for the composite step is 1 minute to 24 hours, the reaction temperature is 40 to 250° C., and the reaction atmosphere is air or an inert atmosphere.

[0067] The treatment temperature in the heat treatment step may be 970°C or higher, and preferably 1,400°C or lower.

[0068] The heat treatment time is not particularly limited, but is carried out for a period ranging from 10 minutes to 5 hours, for example.

[0069] 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.

[0070] The negative electrode includes the negative electrode active material. For example, the negative electrode active material, a binder, and optionally a conductive agent are mixed in a solvent to prepare a negative electrode active material composition, which is then molded into a predetermined shape or coated on a current collector such as copper foil.

[0071] 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.

[0072] 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, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si), or a Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, Group 13 to Group 16 element, transition metal, rare earth element, or a combination thereof, and is not Sn). 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.

[0073] For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

[0074] 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 thereof. 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.

[0075] 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, and the lithium charge and discharge characteristics can be further improved by improving the electrical conductivity.

[0076] The ordinary 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.

[0077] The binder used in the negative electrode active material composition is a component that helps to bind the negative electrode active material and the conductive agent, etc. and to bind to 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 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.

[0078] 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.

[0079] 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.

[0080] The conductive agent can be any of those commonly used in lithium batteries, including 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 powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives, or 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 is in the range of 99:1 to 90:10.

[0081] 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.

[0082] 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.

[0083] Furthermore, 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.

[0084] 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.

[0085] 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 printing it onto a flexible electrode substrate.

[0086] Separately, to prepare 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.

[0087] The positive electrode active material may be any lithium-containing metal oxide that is commonly used in the art.

[0088] 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 Bb 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 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 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, and 0.001≦d≦0.1); Li a Ni b Coc Mn d G e O2 (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.

[0089] 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.

[0090] 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. This method is well understood by those skilled in the art, so a detailed description will be omitted.

[0091] 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 y O2 (0≦x≦0.5, 0≦y≦0.5), LiFeO2, V2O5, TiS, MoS, etc. can be used.

[0092] 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 pores inside the electrode plate. The amounts of the positive electrode active material, conductive agent, binder, and solvent are at levels typically used in lithium batteries.

[0093] The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm, has high conductivity without inducing chemical changes in the battery, and is made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector can have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and can be in a variety of forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0094] 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.

[0095] The positive and negative electrodes are separated by a separator, and any separator commonly used in lithium batteries can be used. In particular, separators with low resistance to ion migration and excellent electrolyte humidification are suitable. 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 5 to 300 μm.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Any lithium salt that is 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 Cl 10, 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.

[0101] Lithium secondary batteries are 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.

[0102] The manufacturing methods of these batteries are well known in the art and will not be described in detail. [Example]

[0103] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited thereto.

[0104] [Example 1] 35 parts by weight of silicon (Si, D) out of 100 parts by weight of the total mixture 50 40 parts by weight of pitch-based carbon and 25 parts by weight of flake graphite were mixed and dry milled at 2,000 rpm for 3 minutes, and then heat-treated in an argon (Ar) gas atmosphere at about 1,150°C for 4 hours to prepare a negative electrode active material.

[0105] [Example 2] A negative electrode active material was produced in the same manner as in Example 1, except that silicon with an average particle size (D50) of 107 nm was used.

[0106] [Example 3] A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature was set to 1,250°C.

[0107] [Example 4] A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment time was set to 1 hour.

[0108] [Example 5] A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment time was changed to 8 hours.

[0109] [Comparative Example 1] A negative electrode active material was produced in the same manner as in Example 1, except that silicon and flake graphite were mixed in a weight ratio of 35:65.

[0110] Comparative Example 2 A negative electrode active material was prepared in the same manner as in Example 1, except that silicon and pitch-based carbon were mixed in a weight ratio of 35:65.

[0111] Comparative Example 3 A negative electrode active material was produced in the same manner as in Example 1, except that the heat treatment temperature was set to 950°C.

[0112] Comparative Example 4 A negative electrode active material was produced in the same manner as in Example 1, except that silicon with an average particle size (D50) of 1.06 μm was used.

[0113] Comparative Example 5 Silicon (Si, D 50 A negative electrode active material was prepared in the same manner as in Example 1, except that the amounts of the carbon nanotube (809 nm), pitch-based carbon, and flake graphite were 35 parts by weight, 15 parts by weight, and 55 parts by weight, respectively.

[0114] Comparative Example 6 Silicon (Si, D 50 A negative electrode active material was prepared in the same manner as in Example 1, except that the amounts of the carbon nanotube (809 nm), pitch-based carbon, and flake graphite were 35 parts by weight, 55 parts by weight, and 10 parts by weight, respectively.

[0115] The particle size of silicon, the mixing ratio of each component, and the heat treatment conditions for Examples 1 to 5 and Comparative Examples 1 to 6 are shown in Table 1 below.

[0116] [Table 1]

[0117] [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 93:3:4 to prepare a negative electrode slurry.

[0118] The prepared negative electrode slurry was coated on a copper foil current collector with a thickness of 20 μm, and the coated electrode plate was dried at 120° C. for 30 minutes and then pressed to prepare a negative electrode.

[0119] A CR2032 type coin half cell was fabricated using metallic lithium as the negative electrode and counter electrode, a PE separator as the separator, and 1.0 M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) (volume ratio 3:5:2) as the electrolyte.

[0120] 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 and PVA-PAA as a binder were mixed in a 1:1 weight ratio 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.

[0121] A CR2032 type coin full cell was manufactured 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 20%.

[0122] Evaluation example 1: XRD, Raman and porosity analysis X-ray diffraction (XRD) experiments were performed on the negative electrode active materials prepared in Example 1, Example 3, and Comparative Example 3, and the results are shown in Figure 2A. XRD measurements were performed using Cu-Kα radiation.

[0123] As shown in Figure 2A, in the case of the negative electrode active materials prepared in Examples 1 and 3, a peak corresponding to silicon carbide (near 36°) was observed along with a peak corresponding to carbon (near 26°). A peak corresponding to silicon (near 26°) was also observed. However, in the case of the negative electrode active material prepared in Comparative Example 3, no peak corresponding to silicon carbide was observed.

[0124] In addition, the negative electrode active materials prepared in Examples 1, 3, and Comparative Example 3 were analyzed using a LabRam HR Evolution Raman spectrometer (Horiba Jobin-Yvon, France), and the results are shown in FIG. 2B.

[0125] The Raman system used an Ar+ ion laser with an excitation wavelength of 514 nm and operating at a power of 10 mW.

[0126] As shown in Figure 2B, the peak corresponding to silicon (500 cm -1 around 1320 cm -1 around 1600 cm -1 Peaks corresponding to the peaks around 1000 sq m were confirmed.

[0127] In the case of the negative electrode active materials produced in Examples 1 and 3, a peak corresponding to silicon carbide (900 cm -1 However, in the negative electrode active material produced in Comparative Example 3, no peak corresponding to silicon carbide was observed.

[0128] XRD and Raman analyses confirmed that the negative electrode active material of the present invention contains silicon, silicon carbide, and carbon.

[0129] The porosity (porosity of the core portion) was calculated by the following equation 1. In the following equation 1, the true density was 2.33 g / cc.

[0130] The total pore volume of the following equation (1) 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 according to the change in relative pressure at liquid nitrogen temperature (77K).

[0131]

number

[0132] The porosity calculated by the above equation 1 is shown in Table 2 below.

[0133] [Table 2] In the case of Comparative Example 1, which used only flake graphite, and Comparative Example 3, in which the heat treatment temperature was lowered to 950° C., it was confirmed that silicon carbide was not formed.

[0134] Evaluation example 2: SEM analysis The cross section of the negative active material prepared in Example 1 was analyzed by scanning electron microscope (SEM), and the results are shown in FIG. 3A.

[0135] From FIG. 3A, it can be seen that the core and shell of the negative electrode active material are clearly separated.

[0136] Furthermore, analysis of the core and shell at even higher magnification confirmed the presence of a core containing silicon particles (Fig. 3B) and a carbon-based shell containing silicon particles coated with silicon carbide (SiC) (Fig. 3C).

[0137] In contrast, the negative electrode active materials prepared in Comparative Examples 1 and 2 were analyzed by SEM and found to not have the core-shell structure of the present invention.

[0138] Evaluation example 3: FIB-EDS analysis The negative electrode active material prepared in Example 1 was sampled using FIB (Nova200 manufactured by FEI), and EDS line scan analysis was performed using STEM-EDS (JEOL-2200FS manufactured by JEOL) at an acceleration voltage of 200 kV.

[0139] As shown in FIG. 4A, the concentration ratios of carbon, silicon, and oxygen in the core and shell were analyzed by EDS line scanning along the XY line corresponding to the horizontal axis of the cross section of the negative electrode active material prepared in Example 1.

[0140] As a result of the analysis, as shown in Figure 4B, it was measured that the core had relatively higher concentrations of silicon and oxygen than the shell, and that the shell had a higher concentration of carbon than the core.

[0141] That is, the EDS line scan analysis allowed specific identification of the core and shell components of the core-shell structured negative electrode active material of the present invention.

[0142] Evaluation example 4: Battery characteristics evaluation The battery characteristics of the 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.

[0143] In the case of Comparative Examples 5 and 6, a large number of coarse carbon particles were generated during the manufacturing process, making the batteries unsuitable for measurement of battery characteristics, and therefore the battery characteristics were not measured.

[0144] A coin full cell was used for evaluating the life characteristics, and a coin half cell was used for evaluating other battery characteristics.

[0145] 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.

[0146] Furthermore, 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 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).

[0147] 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 discharged at a constant current of 1.0 C until the voltage reached 2.7 V (vs. Li) (cycles 1 to 100).

[0148] The initial charge capacity, initial discharge capacity, initial efficiency and life characteristics measured for the cells using the negative electrode active materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 3 below.

[0149] The initial charge capacity and initial discharge capacity are the charge and discharge capacities at the first cycle.

[0150] The initial efficiency and life characteristics were calculated using the following equations 2 and 3, respectively.

[0151] <Number 2> Initial efficiency [%] = [discharge capacity at 1st cycle / charge capacity at 1st cycle] x 100

[0152] <Number 3> Life characteristic [%] = [100th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0153] [Table 3] It was confirmed that Examples 1 to 5 had particularly excellent battery life characteristics compared to Comparative Examples 1 to 4.

[0154] That is, when the Examples were compared with Comparative Example 1, in which a core-shell structure was not formed and SiC was not formed, Comparative Example 2, in which a core-shell structure was not formed but SiC was formed, and Comparative Example 3, in which a core-shell structure was formed but SiC was not formed, it was confirmed that the life characteristics of the battery in which the negative electrode active material of the Example was applied were superior to those of the batteries in which the negative electrode active materials of Comparative Examples 1 to 3 were applied.

[0155] In addition, it was confirmed that the life characteristics of the battery using the negative electrode active material of the Example were superior to those of the battery using the negative electrode active material of Comparative Example 4, in which the size of silicon particles exceeded 1 μm.

[0156] That is, the anode active material of the present invention has a core-shell structure in which the shell contains metal particles (Si) whose surface is coated with metal carbide (SiC), and it exhibits superior battery life characteristics compared to anode active materials that do not have a core-shell structure or do not contain metal particles (Si) whose surface is coated with metal carbide (SiC).

[0157] 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]

[0158] The negative electrode active material according to the present invention has the effect of providing a secondary battery having a high capacity, a high energy density and a long life.

[0159] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost.

Claims

1. The core and a shell surrounding the core, the core comprises metal particles, silicon oxide particles, or a combination thereof; the metal of the metal particle in the core includes any one or more selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag; the shell comprises metal particles whose surfaces are entirely or partially coated with metal carbide, silicon oxide particles whose surfaces are entirely or partially coated with metal carbide, or a combination thereof; In the shell, the metal of the metal particles whose surfaces are entirely or partially coated with metal carbide includes at least one selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag; the shell comprises crystalline carbon; the metal particles, the silicon oxide particles, or a combination thereof have an average particle size (D50) of 50 to 1,000 nm; The height ratio (I d / I g ) of the corresponding peak of amorphous carbon (I d ) to the corresponding peak of crystalline carbon (I g ) in Raman analysis is 0.92 to 1.8; The negative electrode active material has a ratio (I metal carbide / I d ) of the height of the corresponding peak (I metal carbide) of the metal carbide to the height of the corresponding peak (I d ) of amorphous carbon in Raman analysis of 0.02 to 0.

1.

2. The metal particles include at least one selected from the group consisting of silicon particles and silicon alloy particles. The negative electrode active material according to claim 1 .

3. The silicon oxide of the silicon oxide particles is represented by the following Chemical Formula 1: The negative electrode active material according to claim 1 . SiOx (0≦x≦0.5) (Chemical formula 1)

4. The crystal grain size of the metal particles is 5 to 50 nm. The negative electrode active material according to claim 1 .

5. The crystal grain size of the metal carbide is 1 to 50 nm. The negative electrode active material according to claim 1 .

6. the ratio of the height of the peak of the metal carbide to the height of the peak of the metal (height of the peak of the metal carbide / height of the peak of the metal) in XRD analysis is 0.01 to 0.55; The negative electrode active material according to claim 1 .

7. the ratio (I metal carbide / I metal) of the height of the peak corresponding to the metal carbide (I metal carbide) to the height of the peak corresponding to the metal (I metal) in Raman analysis is 0.01 to 0.2; The negative electrode active material according to claim 1 .

8. milling the metal particles; mixing the pulverized metal particles, amorphous carbon, and crystalline carbon to form a composite; a heat treatment step, The method for producing a negative electrode active material according to any one of claims 1 to 7, wherein the metal includes at least one selected from the group consisting of Si, Al, Sn, Ge, Pb, In, As, Sb, P, and Ag.

9. The amorphous carbon is 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; The crystalline carbon is at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene. The method for producing a negative electrode active material according to claim 8 .

10. The compounding step is carried out by any one or more selected from the group consisting of milling, stirring, mixing, and compression. The method for producing a negative electrode active material according to claim 8 .

11. The treatment temperature of the heat treatment step is 970°C or higher. The method for producing a negative electrode active material according to claim 8 .

12. The negative electrode active material according to any one of claims 1 to 7, electrode.

13. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 7; 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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