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

Abstract

The present invention relates to an anode active material including at least one metal-containing particle, wherein the ratio (r2 / r1) of the length (r2) of the longest straight line connecting the center point of the anode active material to the end of the metal-containing particle located farthest from the center point of the anode active material to the radius (r1) of the anode active material is 0.8 or more and 0.95 or less, a method for producing the anode active material, and a lithium secondary battery including the anode active material.

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. Specifically, the present invention relates to an anode active material having improved performance by adjusting the ratio (r2 / r1) of the length (r2) of the longest line connecting the center point of the anode active material to the end of the metal-containing particle located farthest from the center point of the anode active material relative to the radius (r1) of the anode active material, and / or the porosity. [Background technology]

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

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

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

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

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

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

[0008] On the other hand, various surface treatments using carbon materials require complex and expensive processes, and 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 the development of technology relating 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. 10-2017-0044360 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 high capacity and high energy density, as well as high output and 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 comprising at least one metal-containing particle, a ratio (r2 / r1) of the length (r2) of the longest straight line connecting the center point of the negative electrode active material of the metal-containing particle located at the farthest distance from the center point of the negative electrode active material to the radius (r1) of the negative electrode active material is 0.8 or more and 0.95 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 that has high capacity and high energy density, as well as high output and 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 showing the radius (r1) of a negative electrode active material according to an embodiment of the present invention and the length (r2) of the longest straight line connecting the center point of the negative electrode active material and the end of the metal-containing particle located at the farthest distance from the center point of the negative electrode active material. [Figure 2] 1 is a graph showing the capacity / efficiency characteristics of cells using the negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 6. [Figure 3]1 is a graph showing the life characteristics of cells using the negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 6. [Figure 4] 1 is a graph showing the output characteristics of cells using the negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 6. 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] 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] In the negative electrode active material according to one embodiment of the present application, the ratio (r2 / r1) of the length (r2) of the longest straight line connecting the center point of the negative electrode active material and the end of the metal-containing particle located farthest from the center point of the negative electrode active material to the radius (r1) of the negative electrode active material may be 0.8 or more and 0.95 or less.

[0026] The r1 and r2 of the negative electrode active material are as shown in Fig. 1. For example, when the metal-containing particle of the negative electrode active material is scaly as shown in Fig. 1, the r2 is the distance between the end of the metal-containing particle and the end that is farthest from the center point of the negative electrode active material (the longest straight line distance).

[0027] If the r2 / r1 of the negative electrode active material is above or below the range of the present application, the life and output characteristics of the secondary battery may be reduced.

[0028] This is because if r2 / r1 exceeds the range of the present application, the carbon matrix may be destroyed due to the volume expansion of the metal-containing particles (e.g., silicon particles), and if r2 / r1 is below the range of the present application, the migration of lithium ions to the metal-containing particles (e.g., silicon particles) may be inhibited.

[0029] The negative electrode active material may include a core and a shell surrounding the core, the metal-containing particles may include any 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 may be contained in the core.

[0030] In one embodiment, the metal-containing particles may be silicon (Si)-containing particles, and the silicon (Si)-containing particles may include any one or more selected from the group consisting of silicon particles, silicon oxide particles, silicon carbide particles, and silicon alloy particles.

[0031] 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 represented by the following chemical formula 1.

[0032] chemical formula 1 SiO x (0≦x≦0.5)

[0033] 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.

[0034] 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).

[0035] The average particle size of the silicon-containing particles was measured using an organic solution in which the silicon-containing particles were dispersed, using a particle size analyzer (Mastersizer 3000, Malvern Panalytical).

[0036] 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 costs will be high.

[0037] In one embodiment, the negative electrode active material may include 30 wt % to 80 wt % of a carbon-based material.

[0038] For example, the carbon content of the negative electrode active material may be 50% or more and 55% or less, and the oxygen content may be 5.5% or more and 6.5% or less.

[0039] The carbon-based material may be one or more of amorphous carbon and crystalline carbon.

[0040] 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.

[0041] 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.

[0042] Natural graphite is graphite that occurs naturally and includes flake graphite, highly crystalline graphite, and amorphous (microcrystalline or cryptocrystalline; amorphous) graphite. Artificial graphite is artificially synthesized graphite made by heating amorphous carbon to high temperatures and includes primary or electrographite, secondary graphite, and graphite fiber.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Furthermore, flake graphite can be suitable for increasing electrical conductivity by contacting with metal-containing particles.

[0048] On the other hand, the weight ratio of amorphous carbon to crystalline carbon in the negative electrode active material (weight of amorphous carbon / weight of crystalline carbon) may be 0.6 or more and 1 or less.

[0049] For example, it may be 0.7 or more and 0.99 or less.

[0050] If the weight ratio of amorphous carbon to crystalline carbon (weight of amorphous carbon / weight of crystalline carbon) of the negative electrode active material is above or below the range of the present application, the value of r2 / r1 of the negative electrode active material may exceed the range of the present application, which may degrade the characteristics of the secondary battery.

[0051] In one embodiment, the core and the cells may include one or more selected from the group consisting of amorphous carbon and crystalline carbon.

[0052] For example, the core may include both the amorphous carbon and the crystalline carbon, and the shell may include both the amorphous carbon and the crystalline carbon.

[0053] The carbon component added to the core and the shell may serve to reduce volume expansion of the metal-containing particles during charge and discharge.

[0054] In one embodiment, the negative electrode active material may have an average particle size (D50) of 3 μm or more and 20 μm or less.

[0055] Meanwhile, the negative electrode active material may include voids. In particular, the voids may be formed mainly in the core of the negative electrode active material. The voids may reduce the initial irreversible capacity of the secondary battery and help alleviate the volume expansion of the metal-containing particles.

[0056] In one embodiment, the porosity of the negative electrode active material may be 10% or less. If the porosity of the negative electrode active material exceeds the range of the present application, the life and output characteristics of the secondary battery may be reduced.

[0057] This is because if the porosity exceeds 10%, destruction of the carbon matrix allows the electrolyte solvent to penetrate into the voids, which can damage metal-containing particles (e.g., silicon particles), reducing the lifespan characteristics. Also, a decrease in the density of electron transport pathways can hinder smooth electrochemical reactions, reducing output characteristics.

[0058] A method for manufacturing a negative electrode active material according to another aspect of the present application may include spray-drying a solution containing metal-containing particles to prepare a precursor powder, mixing the precursor powder, amorphous carbon, and crystalline carbon to form a composite, and heat-treating the composite.

[0059] The metal-containing particles provided in the step of preparing the precursor powder may be prepared by being pulverized to have a desired average particle size through a pulverization process.

[0060] The metal may be one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe and Nb.

[0061] In one embodiment, the complexing step may be carried out by a physical method.

[0062] 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.

[0063] For example, the compounding step may be performed by ball milling. In particular, a planetary ball mill can efficiently mix and grind the mixture by rotating and revolving the composition in a non-contact manner.

[0064] 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.

[0065] On the other hand, the reaction time of the composite step may be 1 minute to 24 hours, the reaction temperature may be 40 to 250° C., and the reaction atmosphere may be air or an inert atmosphere.

[0066] In one embodiment, the heat treatment step can include a first heat treatment step and a second heat treatment step.

[0067] The heat treatment temperature in the first heat treatment step may be 100 to 500° C., the heat treatment time may be 10 to 48 hours, and the heat treatment may be performed in a vacuum atmosphere.

[0068] The heat treatment temperature in the second heat treatment step may be 600 to 1,000° C., the heat treatment time may be 1 to 48 hours, and the heat treatment may be performed in an inert gas (for example, nitrogen, argon, etc.) atmosphere.

[0069] The weight ratio of the amorphous carbon and the crystalline carbon mixed in the compounding step (weight of amorphous carbon / weight of crystalline carbon) may be 0.6 or more and 1 or less.

[0070] 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.

[0071] The negative electrode may include the negative electrode active material. For example, the negative electrode active material, a binder, and optionally a conductive agent may be mixed in a solvent to prepare a negative electrode active material composition, which may then be molded into a predetermined shape or applied to a current collector such as copper foil.

[0072] 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.

[0073] For example, the metal capable of alloying 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.

[0074] For example, the transition metal oxide may be lithium titanate, vanadium oxide, lithium vanadate, etc.

[0075] For example, the non-transition metal oxide may be SnO2, SiO x (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.

[0076] 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 electrical conductivity can be improved to further improve the charge and discharge characteristics of lithium.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The conductive agent can be any of those commonly used in lithium batteries. Examples include carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fiber (e.g., vapor-grown carbon fiber); metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof. The amount of conductive agent can be adjusted appropriately. For example, the weight ratio of the negative electrode active material to the conductive agent can be in the range of 99:1 to 90:10.

[0082] 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.

[0083] 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.

[0084] In addition, the bonding strength of the negative electrode active material can be strengthened by forming minute irregularities on the surface, and the material can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0085] 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.

[0086] The negative electrode active material composition can be used not only to manufacture an electrode for a lithium secondary battery, but also to manufacture a printable battery by being printed on a flexible electrode substrate.

[0087] 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.

[0088] Any lithium-containing metal oxide that is commonly used in the art can be used as the positive electrode active material.

[0089] 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.

[0090] 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.

[0091] Of course, this compound may have a coating layer on its surface, or the compound may be mixed with a compound having a coating layer. The coating layer may include a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. Examples of the coating element included in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation process may be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material. Since this method is well understood by those skilled in the art, a detailed description will be omitted.

[0092] 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.

[0093] The conductive agent, binder, and solvent in the positive electrode active material composition may be the same as those in the negative electrode active material composition. In some cases, a plasticizer may be added to the positive electrode active material composition and the negative electrode active material composition to form voids within the electrode plate. The amounts of the positive electrode active material, conductive agent, binder, and solvent are at levels typically used in lithium batteries.

[0094] The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm, does not induce chemical changes in the battery, and has high conductivity, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector may have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0095] 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.

[0096] The positive and negative electrodes can be separated by a separator, and any separator commonly used in lithium batteries can be used. In particular, separators with low resistance to the movement of electrolyte ions and excellent electrolyte humidifying capacity are preferred. For example, the separator may be made of a material selected from glass fiber, polyester, Teflon, 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Any lithium salt commonly used in lithium batteries can be used as the lithium salt. Examples of substances that are easily dissolved in the non-aqueous electrolyte include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 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.

[0102] Lithium secondary batteries may be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and may be classified into cylindrical, prismatic, coin-shaped, pouch-shaped, etc. depending on the shape, and into bulk type and thin film type depending on the size.

[0103] The manufacturing methods of these batteries are well known in the art and will not be described in detail. [Example]

[0104] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited thereto.

[0105] [Example 1] Scaly silicon particles (average particle size (D 505 parts by weight of silicon dioxide (5 μm), 94 parts by weight of isopropyl alcohol (IPA), and 1 part by weight of stearic acid were mixed and charged into a bead mill to measure the average particle size (D 50 ) was ground to 110 nm to prepare a ground silicon solution.

[0106] The prepared crushed silicon solution is spray-dried to obtain a silicon powder having an average particle size (D 50 ) produced 6 μm silicon precursors.

[0107] The silicon precursor was then placed in a compounder (manufactured by Hansol Chemical) with petroleum pitch and graphite in a weight ratio of 45:25:30, and compounded for 10 minutes. After that, the compound was subjected to a primary heat treatment at 180°C for 24 hours under a vacuum atmosphere.

[0108] Then, a secondary heat treatment was performed in an inert atmosphere at 900°C for 3 hours to produce a composite material.

[0109] The composite material was classified into 325 mesh to obtain a negative electrode active material.

[0110] [Example 2] A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:23:32 parts by weight, respectively.

[0111] [Example 3] A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:27:28 parts by weight, respectively.

[0112] [Comparative Example 1] A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:30:25 parts by weight, respectively.

[0113] Comparative Example 2 A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:33:22 parts by weight, respectively.

[0114] Comparative Example 3 A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:20:35 parts by weight, respectively.

[0115] Comparative Example 4 A negative electrode active material was produced in the same manner as in Example 1, except that the weight ratio of the silicon precursor, pitch, and graphite was 45:18:37 parts by weight, respectively.

[0116] Comparative Example 5 After the composite was formed, a negative electrode active material was produced in the same manner as in Example 1, except that a primary heat treatment was carried out at 180° C. for 24 hours in a nitrogen atmosphere, not a vacuum atmosphere.

[0117] Comparative Example 6 After the composite was formed, a negative electrode active material was produced in the same manner as in Example 1, except that the primary and secondary heat treatments were not carried out.

[0118] [Manufacturing example] Fabrication of coin half-cells The negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6, a conductive agent (Super P), and a binder (SBR-CMC) were uniformly mixed in a weight ratio of 94:2:4 to prepare negative electrode slurries.

[0119] The prepared negative electrode slurry was coated on a copper thin film current collector having a thickness of 10 μm, and the coated electrode plate was dried at 120° C. for 20 minutes and then pressed to prepare a negative electrode.

[0120] A CR2032 type coin half cell was fabricated using metallic lithium for the negative electrode and counter electrode, a PE separator as the separator, and 1.0M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) (volume ratio 3:5:2) as the electrolyte.

[0121] Fabrication of a coin full cell The negative electrode used in the coin half-cell was used to prepare a positive electrode as follows: LiNi 0.6 Co 0.2 Mn 0.2 O2, a conductive agent (Super P), and a binder (PVDF) were mixed in a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil current collector with a thickness of 12 μm. The coated electrode plate was dried at 120°C for 15 minutes and then pressed to prepare a positive electrode.

[0122] A CR2032 type coin full cell was fabricated using the positive and negative electrodes, a PE separator as a separator, and an electrolyte of 1.5M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) (volume ratio 2:1:7) + FEC 5%.

[0123] 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.

[0124] [Table 1]

[0125] In Table 1, the particle size (D 50) was measured with a particle size analyzer (Mastersizer 3000, Malvern Panalytical) using an organic solution in which the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 were dispersed.

[0126] The particle size (D50) of the silicon particles used in producing the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 was also measured in the same manner as in the particle size measurement method for the negative electrode active material.

[0127] Meanwhile, the carbon content was measured by measuring the quantity of carbon-containing gases such as carbon dioxide and carbon monoxide generated by burning the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 at high temperatures using an ELEMENTRAC CS-i (ELTRA), and the oxygen content was measured by measuring the quantity of oxygen-containing gases generated by burning the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 at high temperatures using an 836 Series (LECO).

[0128] In order to calculate the r2 / r1, cross sections of the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 were processed using a focused ion beam (FIB), and the cross sections were observed with an FE-SEM to measure r1 and r2.

[0129] Meanwhile, the porosity of the negative electrode active material was calculated using the following equation 1. In the following equation 1, the true density was 2.33 g / cc. The total pore volume of the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 was measured using a TriStar II 3020 device manufactured by Micromeritics. The total pore volume was measured by measuring the amount of nitrogen gas adsorbed due to changes in relative pressure at liquid nitrogen temperature (77 K).

[0130]

number

[0131] According to Table 1, the particle size of the negative electrode active materials of Examples 1 to 3 was 5.87 to 6.11 μm, the carbon content was 50.7 to 51.7%, the oxygen content was 5.8 to 6.3%, the r2 / r1 value was 0.82 to 0.89, and the porosity was 5.8 to 6.9%.

[0132] Furthermore, during the production of the negative electrode active material, as the content of petroleum pitch increased and the content of graphite decreased, the value of r2 / r1 generally tended to decrease.

[0133] That is, it was confirmed that the r2 / r1 value of the negative electrode active material can be adjusted by adjusting the contents of petroleum pitch and graphite during the production of the negative electrode active material.

[0134] Furthermore, when comparing Example 1 with Comparative Examples 5 and 6, which differ only in the heat treatment conditions, it was confirmed that the porosity in particular increases significantly when the primary heat treatment conditions are changed or when the primary and secondary heat treatments are not performed.

[0135] That is, it was confirmed that the porosity of the negative electrode active material can be adjusted by changing the heat treatment conditions during the preparation of the negative electrode active material.

[0136] Evaluation example 2: Battery characteristic analysis The characteristics of the cells using the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 6 were analyzed and are shown in Table 2 below.

[0137] [Table 2]

[0138] 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 6 were evaluated as follows.

[0139] A coin full cell was used for evaluating the life and output characteristics, and a coin half cell was used for evaluating the initial capacity, discharge capacity, and initial efficiency characteristics.

[0140] Coin half-cells prepared using the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 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.

[0141] Coin full cells prepared using the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were each charged at a constant current rate of 0.1 C at 25°C until the voltage reached 4.2 V (vs. Li), and then charged at a constant voltage rate of 0.05 C while maintaining 4.2 V. After the cells were fully charged, they were allowed to rest for 10 minutes and then discharged at a constant current of 0.1 C until the voltage reached 2.7 V (vs. Li) (performed twice, initial formation).

[0142] The cell was then charged at a constant current of 1.0 C at 25°C until the voltage reached 4.2 V (vs. Li), and then at a constant voltage of 0.05 C while maintaining 4.2 V. After the coin cell was fully charged, it was left to rest for 10 minutes and then repeatedly discharged at a constant current of 1.0 C until the voltage reached 2.7 V (vs. Li) (1st to 200th cycles).

[0143] As an example, graphs showing the capacity / efficiency, life and output characteristics of cells using the negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 6 are shown in FIGS. 2 to 4, respectively.

[0144] Meanwhile, the initial charge capacity and initial discharge capacity in Table 2 are the charge and discharge capacities in the first cycle, respectively.

[0145] The initial efficiency, lifespan, and output characteristics were calculated using the following formulas 2 to 4, respectively.

[0146] <Formula 2> Initial efficiency [%] = [discharge capacity at first cycle / charge capacity at first cycle] x 100

[0147] <Formula 3> Life characteristics [%] = [200th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0148] <Formula 4> Output characteristics [%] = [5.0C discharge capacity / 0.1C discharge capacity] x 100

[0149] According to Table 2, the initial efficiency of the secondary batteries using the negative electrode active materials of Examples 1 to 3 was 87% or more and 90% or less, the life characteristics after 200 charge / discharge cycles were 60% or more, and the output characteristics (C 5.0 / C 0.1 ) may be 70% or more.

[0150] Specifically, the secondary batteries using the negative electrode active materials of Examples 1 to 3 had initial charge capacities of 1606.9 to 1669.2 mAh / g, initial discharge capacities of 1410.9 to 1467.2 mAh / g, initial efficiencies of 87.8 to 88.1%, life characteristics of 62.5 to 63.6%, and output characteristics of 70.9 to 72.3%.

[0151] It was also confirmed that the r2 / r1 value and porosity of the negative electrode active material have a significant effect on the life and output characteristics of the secondary battery.

[0152] In the case of secondary batteries using the negative electrode active materials of Comparative Examples 1 to 4, in which the value of r2 / r1 is greater than or equal to 0.8 and greater than or equal to 0.95, it was confirmed that the life characteristics and output characteristics of the secondary batteries were reduced compared to secondary batteries using the negative electrode active materials of Examples 1 to 3.

[0153] That is, when the value of r2 / r1 is above or below the range of the present invention, a secondary battery with excellent life and output characteristics cannot be obtained.

[0154] On the other hand, in the case of secondary batteries using the negative electrode active materials of Comparative Examples 5 and 6, which have a porosity exceeding 10%, it was confirmed that even if the value of r2 / r1 falls within the range of the present application, the life characteristics and output characteristics of the secondary batteries are reduced compared to secondary batteries using the negative electrode active materials of Examples 1 to 3.

[0155] That is, even if the value of r2 / r1 falls within the range of the present application, if the porosity exceeds the range of the present application, a secondary battery with excellent life and output characteristics cannot be obtained.

[0156] 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]

[0157] The negative electrode active material according to the present invention has the effect of providing a secondary battery that has high capacity and high energy density, as well as high output and long life.

[0158] 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 comprising at least one metal-containing particle, The radius (r 1 ) the length (r 2 ) ratio (r 2 / r 1 ) is 0.8 or more and 0.95 or less, Negative electrode active material.

2. The negative electrode active material is The core and a shell surrounding the core, 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; The metal-containing particles are contained in the core. The negative electrode active material according to claim 1 .

3. 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 .

4. Contains 30% by weight or more and 80% by weight or less of a carbon-based material; The negative electrode active material according to claim 1 .

5. the weight ratio of amorphous carbon to crystalline carbon (weight of amorphous carbon / weight of crystalline carbon) is 0.6 or more and 1 or less; The negative electrode active material according to claim 1 .

6. The core and the cells contain at least one material selected from the group consisting of amorphous carbon and crystalline carbon. The negative electrode active material according to claim 2 .

7. Average particle size (D 50 ) is 3 μm or more and 20 μm or less, The negative electrode active material according to claim 1 .

8. The porosity of the negative electrode active material is 10% or less. The negative electrode active material according to claim 1 .

9. A method for producing the negative electrode active material according to any one of claims 1 to 8, spray drying a solution containing metal-containing particles to produce a precursor powder; mixing the precursor powder, amorphous carbon, and crystalline carbon to form a composite; and heat treating the resulting mixture. the metal is at least one selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb; The heat treatment step includes a first heat treatment step and a second heat treatment step. A method for producing a negative electrode active material.

10. The negative electrode active material according to any one of claims 1 to 8, electrode.

11. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 8; 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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