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 containing metal-containing particles, wherein at least one of the angles between a line connecting a center point of the negative electrode active material and a center point of the metal-containing particle and a major axis of the metal-containing particle is 60° or more and 90° or less, a manufacturing method thereof, and a lithium secondary battery containing 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 having improved performance by adjusting the alignment direction (angle) of metal-containing particles contained in the anode active material, 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 expand further to include electric vehicles and power storage devices for renewable energy sources.

[0003] In order to apply them to new fields of application, there is a continuous 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 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 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 although surface treatments using carbon materials have improved some of the properties of silicon-based anode materials, there are limitations to realizing high-power, long-life, and fast-charging LIBs.

[0009] Therefore, there is a current demand for technological development related to high-capacity silicon-based negative electrode active materials that can further improve battery characteristics while suppressing the volume expansion of silicon-based negative electrode materials. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Republic of Korea Patent Publication No. 10-2019-0090024 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, an object of the present invention is to provide a negative electrode active material for a secondary battery that has a high capacity and a high energy density, and also has a long life.

[0012] Another object of the present invention is to provide a method for producing the negative electrode active material with high efficiency and low cost.

[0013] Another object of the present invention is to provide an electrode and a lithium secondary battery containing the negative electrode active material.

[0014] 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]

[0015] A negative electrode active material containing metal-containing particles, the metal-containing particles have at least one angle between a line connecting a center point of the negative electrode active material and a center point of the metal-containing particle and a major axis of the metal-containing particle of 60° or more and 90° or less; A negative electrode active material is provided.

[0016] Another aspect of the present application includes the negative electrode active material, 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 and a high energy density, and also having 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] 3 is a schematic diagram showing an angle formed by a line connecting the center point of a negative electrode active material according to an embodiment of the present invention and the center point of a metal-containing particle, and the major axis of the metal-containing particle. FIG. [Figure 2] 1A and 1B are schematic diagrams showing anode active materials with a core-shell structure and a hollow structure according to an embodiment of the present invention. [Figure 3] 1A and 1B are scanning electron microscope (SEM) photographs of cross sections of negative electrode active materials having a core-shell structure (a and b) and a hollow structure (c) according to embodiments of the present invention. [Figure 4] 1 is a charge / discharge graph of a cell in which the negative electrode is an electrode using the negative electrode active materials of Example 1 of the present invention and Comparative Example 2. [Figure 5]1 shows the results of measuring the capacity retention rate depending on the number of charge / discharge cycles of cells in which the negative electrode was an electrode using the negative electrode active materials of Example 1 of the present invention and Comparative Example 2. 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 configurations of the embodiments described in this specification are merely one of the most preferred embodiments of the present invention and do 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] 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.

[0025] As shown in FIG. 1, an anode active material according to one embodiment of the present application may include metal-containing particles, wherein at least one of the angles formed between a line connecting a center point of the anode active material and a center point of the metal-containing particle and a major axis of the metal-containing particle is 60° or more and 90° or less.

[0026] As shown in FIG. 1(a), the center point of the negative electrode active material can correspond to a point located at the center of a cross section of the negative electrode active material having any closed curved surface shape, including a sphere, cut along a plane including the central axis of the negative electrode active material.

[0027] On the other hand, in the case of a negative electrode active material having a non-uniform curved shape, as shown in FIG. 1(b), the center of curvature of the negative electrode active material cut along a plane including the central axis of the negative electrode active material is the central point.

[0028] The center point of the metal-containing particle may correspond to a point located at the center of a cross section of the negative electrode active material cut along a plane including the major axis or minor axis of the metal-containing particle.

[0029] The major axis may correspond to the longest linear distance of a cross section passing through the center point of the metal-containing particle, and the minor axis may correspond to the shortest linear distance of a cross section passing through the center point of the metal-containing particle.

[0030] As shown in FIG. 1, at least one angle (θ) formed between an imaginary line (r) connecting the center point of the negative electrode active material and the center point of the metal-containing particle and the major axis (d) of the metal-containing particle may be 60° or more and 90° or less.

[0031] The unit of angle (θ) is "° (degrees)", which is defined as 360 equal parts of one rotation, and 1° is equal to π / 180 radians.

[0032] The negative electrode active material includes a core and a shell surrounding the core, and 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, and the metal-containing particles are contained in the shell.

[0033] In particular, the metal-containing particles may be scale-like having a major axis and a minor axis.

[0034] In one embodiment, the negative electrode active material may further include the metal-containing particles in the core of a core-shell structure, as shown in Figure 2(a). SEM images of the negative electrode active material observed to measure the angular fraction of the core-shell negative electrode active material containing the metal-containing particles in the core are shown in Figures 3(a) and 3(b), respectively.

[0035] The negative electrode active material may have a hollow structure with a hollow core, as shown in FIG. 2(b).

[0036] The SEM photograph of the negative electrode active material observed to measure the angular fraction of the hollow negative electrode active material is shown in FIG. 3(c).

[0037] As shown in Figures 3(a) to 3(c), cells of the core-shell structure and hollow structure negative electrode active material contain scaly metal-containing particles, and as described above, at least one of the angles formed between a line connecting the center points of the scaly metal-containing particles contained in the shell and the long axis of the scaly metal-containing particles contained in the shell is 60° or more and 90° or less.

[0038] In one embodiment, the ratio of the number of metal-containing particles in which at least one of the angles is 60° or more and 90° or less among the metal-containing particles contained in the shell may be 40% or more.

[0039] That is, the angular fraction, which is the ratio of the number of metal-containing particles in which at least one of the angles formed by a line connecting the center point of the negative electrode active material and the center point of a scaly metal-containing particle contained in the shell of the negative electrode active material with the long axis of the scaly metal-containing particle contained in the shell is 60° or more and 90° or less, among all the scaly silicon particles contained in the shell, may be 40% or more.

[0040] For example, the angular fraction may be 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100%.

[0041] As the angular fraction of the negative electrode active material increases, the initial electrode expansion rate and the electrode expansion rate of the electrode using the negative electrode active material decrease, thereby improving the life characteristics of the battery.

[0042] In one embodiment, the metal 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.

[0043] The silicon (Si)-containing particles may have an average particle size (D50) of 80 nm or more and 200 nm or less, and may be expressed by the following formula 1.

[0044] (chemical 1) SiOx(0≦x≦0.5)

[0045] 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.

[0046] 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).

[0047] The average particle size of the silicon-containing particles was measured using an organic solution in which the silicon-containing particles were dispersed, with a particle size measuring device (Mastersizer 3000, Malvern Panalytical).

[0048] 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 80 nm, the battery capacity and efficiency will be low and the manufacturing cost will be high.

[0049] In one embodiment, the average crystal grain size of the metal-containing particles may be 13 nm or more and 18 nm or less.

[0050] If the crystal grain size of the metal-containing particles is less than 13 nm, it may be advantageous in terms of battery life but disadvantageous in realizing capacity, and if the crystal grain size exceeds 18 nm, it may be disadvantageous in terms of battery manufacturing costs and life stability.

[0051] The metal-containing particles may have a sphericity (minor axis length / major axis length) of 0.5 or less. In one embodiment, the negative electrode active material may include 40 wt % to 80 wt % of a carbon-based material.

[0052] The carbon-based material may have an XRD diffraction peak at 25° or more and 27° or less, and the full width at half maximum of the XRD diffraction peak may be 0.1 or more and 0.5 or less.

[0053] The carbon-based material may be one or more of amorphous carbon and crystalline carbon.

[0054] In one embodiment, the amorphous carbon may 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.

[0055] 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.

[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 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.

[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 is suitable for increasing conductivity by contacting with metal-containing particles.

[0062] In one embodiment, the core may additionally comprise amorphous carbon and the shell may comprise crystalline carbon.

[0063] However, in the case of a hollow negative electrode active material, the hollow core does not necessarily need to contain a carbon-based material.

[0064] In particular, the shell may consist mostly of crystalline carbon, and the additional carbon component of the core may be mostly amorphous carbon.

[0065] Additionally, the shell may contain a small amount of amorphous carbon, and the core may contain a small amount of crystalline carbon.

[0066] When the core contains a small amount of crystalline carbon, the specific gravity of the graphite can increase with increasing distance from the center of the core.

[0067] The amorphous carbon core may be located between and surround the metal particles, i.e., the amorphous carbon may be a matrix with dispersed metal particles forming a core.

[0068] The carbon component added to the shell and core may serve to reduce volume expansion of the metal-containing particles during charge and discharge.

[0069] In one embodiment, the negative electrode active material may have an average particle size (D50) of 5 μm or more and 20 μm or less.

[0070] The thickness of the shell of the negative electrode active material may be 5 μm or more and 10 μm or less.

[0071] Meanwhile, the core of the negative electrode active material may contain voids, which may reduce the initial irreversible capacity of the battery and help alleviate volume expansion of the metal-containing particles.

[0072] A method for manufacturing a negative electrode active material according to another aspect of the present disclosure may include mixing metal-containing particles, amorphous carbon, and crystalline carbon to form a composite, and performing a heat treatment.

[0073] The metal may be one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe and Nb.

[0074] In one embodiment, the conjugation step is carried out by a physical method.

[0075] 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.

[0076] 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.

[0077] 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 balls may be, for example, about 0.3 mm to 10 mm, but is not limited thereto.

[0078] In the compounding step, the angular fraction of the metal-containing particles contained in the shell of the negative electrode active material can be adjusted by adjusting the rotation speed of the milling machine. The angular fraction of the metal-containing particles can be increased by increasing the rotation speed of the milling machine.

[0079] 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.

[0080] In one embodiment, the heat treatment temperature may be 700 to 1,100°C.

[0081] The heat treatment time is not particularly limited, but is carried out for a period of time ranging from 10 minutes to 24 hours, for example.

[0082] 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.

[0083] 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 coated on a current collector such as copper foil.

[0084] 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.

[0085] 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 13-16 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.

[0086] For example, the transition metal oxide may be lithium titanate, vanadium oxide, lithium vanadate, etc.

[0087] 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 fired carbon) or hard carbon, mesophase pitch carbide, fired coke, etc.

[0088] When both the negative electrode active material and the carbon-based material are used, the oxidation reaction of the silicon-based active material can be suppressed, an SEI film can be effectively formed to form a stable film, and the electrical conductivity can be improved to further improve the charge and discharge characteristics of lithium.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] The conductive agent may be any material 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 the conductive agent may be adjusted appropriately. For example, the weight ratio of the negative electrode active material to the conductive agent may be in the range of 99:1 to 90:10.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The positive electrode active material may be any lithium-containing metal oxide that is commonly used in the art.

[0101] 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.

[0102] 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.

[0103] Of course, the 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 the coating layer may be amorphous or crystalline. The coating element contained in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture 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.

[0104] 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.

[0105] 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 contents of the positive electrode active material, conductive agent, binder, and solvent are at levels typically used in lithium batteries.

[0106] 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.

[0107] 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.

[0108] 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 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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 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.

[0114] 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.

[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] Scaly silicon particles (average particle size (D 50Spherical porous secondary particles consisting of graphite (100 nm) were mixed with pitch and graphite in a 1:1:1 weight ratio in a THF solvent, then placed in a compositer and milled at a rotation speed of 15,000 rpm for 15 minutes to composite. The mixture was then heat-treated in a nitrogen atmosphere at 950°C in a furnace to produce a reaction product. The reaction product was then sieved to a 325 mesh to obtain the negative electrode active material.

[0118] [Example 2] A negative electrode active material was produced in the same manner as in Example 1, except that the milling rotation speed in the compounding step was set to 10,000 rpm.

[0119] [Example 3] A negative electrode active material was produced in the same manner as in Example 1, except that the milling rotation speed in the compounding step was 20,000 rpm.

[0120] [Comparative Example 1] A negative electrode active material was produced in the same manner as in Example 1, except that the milling rotation speed in the compounding step was 3,000 rpm.

[0121] Comparative Example 2 Scaly silicon particles (average particle size (D 50 Spherical porous secondary particles consisting of graphite (100 nm) were mixed with pitch and graphite in a 1:1:1 weight ratio in a THF solvent, and the solvent was heated and dried at 60°C to form a composite. The mixture was then heat-treated in a nitrogen atmosphere furnace at 950°C to produce a reaction product. The reaction product was then classified into 325 mesh to obtain the negative electrode active material.

[0122] Comparative Example 3 Spherical silicon particles (average particle size (D 50 A negative electrode active material was produced in the same manner as in Example 1, except that a 100 nm (100 nm) SiO 2 was used.

[0123] [Manufacturing example] Fabrication of coin half-cells The negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, 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.

[0124] The prepared negative electrode slurry was coated on a copper foil current collector having 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.

[0125] 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 a 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.

[0126] 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, and the coated electrode plate was dried at 120°C for 15 minutes and then pressed to prepare a positive electrode.

[0127] 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%.

[0128] Evaluation example 1: Analysis of negative electrode active material The properties of the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed and are shown in Table 1 below.

[0129] [Table 1]

[0130] In Table 1, the angular fraction indicates the specific gravity of silicon particles for which at least one of the angles formed by a line connecting the center point of the negative electrode active material and the center point of a scaly silicon particle contained in the shell of the negative electrode active material and the long axis of the scaly silicon particle contained in the shell is 60° or more and 90° or less (the number of silicon particles for which at least one of the angles is 60° or more and 90° or less among the number of scaly silicon particles contained in the shell).

[0131] The angular fraction was measured by subjecting the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 to FIB processing and then observing the cross section of the negative electrode active material with an SEM.

[0132] It was confirmed that the angular fraction can be adjusted by adjusting the milling rotation speed in the compounding step, i.e., the higher the milling rotation speed, the higher the angular fraction.

[0133] The sphericity was determined by observing the scaly silicon particles with an SEM, measuring the lengths of the minor axis and major axis of the scaly silicon particles, and calculating the ratio (minor axis length / major axis length).

[0134] Meanwhile, the size of the Si crystal grains was measured by X-ray diffraction (XRD), that is, the size of the crystal grains of the metal particles was measured by applying the Scherrer equation to a specific peak measured by XRD.

[0135] The full width at half maximum of the carbon (C)-based material was measured by X-ray diffraction (XRD) of the negative electrode active material, and the XRD diffraction peak of the carbon-based material was observed at 25 to 27°.

[0136] The oxygen content was measured using an oxygen analyzer (O836, LECO Co.) The prepared negative active material was placed in a carbon crucible and heated to a high temperature, and the CO and CO generated were measured to calculate the oxygen content of the sample.

[0137] The average particle size of the secondary particles was measured with a particle size analyzer (Mastersizer 3000, Malvern Panalytical) using an organic solution in which spherical porous secondary particles made of scaly silicon particles were dispersed.

[0138] Evaluation example 2: Electrode characteristic analysis The properties of the electrodes using the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed and are shown in Table 2 below.

[0139] [Table 2]

[0140] The initial electrode expansion ratio and the electrode expansion ratio in Table 2 were calculated using the following equations 1 and 2.

[0141] <Number 1> Initial electrode expansion rate [%] = [electrode thickness at first charge / initial electrode thickness] x 100

[0142] <Number 2> Electrode expansion rate [%] = [electrode thickness at 100th discharge / initial electrode thickness] x 100

[0143] In the above equations 1 and 2, the initial electrode thickness is the thickness of the electrode measured immediately after the electrode is manufactured, and is the thickness of the electrode without any charge / discharge.

[0144] It was confirmed that the electrodes using the negative electrode active materials of Examples 1 to 3 with high angular fractions had lower initial electrode expansion coefficients and electrode expansion coefficients than the electrodes using the negative electrode active materials of Comparative Examples 1 to 3 with low angular fractions.

[0145] Therefore, it was confirmed that the initial electrode expansion rate and the electrode expansion rate can be reduced by adjusting the angular fraction of the negative electrode active material, thereby maximizing battery performance.

[0146] Evaluation example 3: Battery characteristic analysis The characteristics of the batteries using the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 as the negative electrode were analyzed and are shown in Table 3 below.

[0147] [Table 3]

[0148] The battery characteristics of coin half cells and coin full cells manufactured using the negative electrode active materials manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows.

[0149] A coin full cell was used for measuring the life characteristics, and a coin half cell was used for evaluating other battery characteristics.

[0150] Coin half-cells prepared using the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 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 total capacity of the cell by the total discharge time.

[0151] Coin full cells prepared using the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 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) (run twice, initial formation).

[0152] 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).

[0153] As an example, charge / discharge curves of cells using the negative electrode active materials prepared in Example 1 and Comparative Example 2 and capacity retention rates as a function of the number of charge / discharge cycles are shown in FIGS. 4 and 5, respectively.

[0154] Meanwhile, the initial discharge capacity in Table 3 is the discharge capacity at the first cycle.

[0155] The initial efficiency and life characteristics were calculated using the following equations 3 and 4, respectively.

[0156] <Number 3> Initial efficiency [%] = [discharge capacity at 1st cycle / charge capacity at 1st cycle] x 100

[0157] <Number 4> Life characteristic [%] = [100th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0158] It was confirmed that the batteries manufactured using the negative electrode active materials of Examples 1 to 3 had improved initial efficiency and life characteristics compared to the batteries manufactured using the negative electrode active materials of Comparative Examples 1 to 3.

[0159] Such improvement in battery characteristics is believed to be due to the fact that the initial expansion rate and expansion rate of the electrodes using the negative electrode active materials of Examples 1 to 3 with adjusted angular fractions were reduced.

[0160] 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]

[0161] The negative electrode active material according to the present invention has the effect of providing a secondary battery having a high capacity and a high energy density, and also having a long life.

[0162] In addition, there is an effect that the negative electrode active material can be produced with high efficiency and low cost.

Claims

1. A negative electrode active material containing metal-containing particles, the metal-containing particles have at least one angle between a line connecting a center point of the negative electrode active material and a center point of the metal-containing particle and a major axis of the metal-containing particle of 60° or more and 90° or less, the ratio of the number of the metal-containing particles having at least one of the angles of 60° or more and 90° or less is 40% or more, The negative electrode active material includes a core and a shell surrounding the core, the core comprises amorphous carbon; the shell comprises crystalline carbon; the metal-containing particles contain Si; The metal-containing particles are contained in the shell. Negative electrode active material.

2. The metal-containing particles further contain one or more selected from the group consisting of Mg, Al, Ca, Fe, Mn, Co, Ni, Zn, and Ge. The negative electrode active material according to claim 1 .

3. The core may additionally contain the metal-containing particles or may be hollow. The negative electrode active material according to claim 1 .

4. The metal-containing particles include at least one selected from the group consisting of silicon particles, silicon oxide particles, silicon carbide particles, and silicon alloy particles. The negative electrode active material according to claim 1 .

5. the metal-containing particles have an average particle size (D50) of 80 nm or more and 200 nm or less; Represented by the following formula 1: The negative electrode active material according to claim 1 . (Chem.1) SiOx (0≦x≦0.5)

6. The average crystal grain size (D50) of the metal-containing particles is 13 nm or more and 18 nm or less. The negative electrode active material according to claim 1 .

7. The sphericity of the metal-containing particles (length of minor axis / length of major axis) is 0.5 or less. The negative electrode active material according to claim 1 .

8. When the entire negative electrode active material is taken as 100% by weight, Contains 40% by weight or more and 80% by weight or less of a carbon-based material; The negative electrode active material according to claim 1 .

9. The carbon-based material has an XRD diffraction peak appearing at 25° or more and 27° or less; The full width at half maximum of the XRD diffraction peak is 0.1 or more and 0.5 or less. The negative electrode active material according to claim 8 .

10. The average particle size (D50) is 5 μm or more and 20 μm or less. The negative electrode active material according to claim 1 .

11. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 10. electrode.

12. 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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