Negative electrode active material, method for producing the same, and lithium secondary battery containing 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 a negative electrode active material, a method for manufacturing the same, and a lithium secondary battery including the same. Specifically, 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 distance from the center point of the negative electrode active material to the metal-containing particle located at the farthest distance from the center point of the negative electrode active material with respect to the radius (r1) of the negative electrode active material and / or the porosity are adjusted to improve the performance of the negative electrode active material, a method for manufacturing the same, and a lithium secondary battery including the same.

Background Art

[0002] Lithium ion batteries (LIBs) have a high energy density, are easy to design, and are adopted and used as the main power supply for mobile electronic devices. In the future, their application scope will be further expanded to electric vehicles or power storage devices for new renewable energy.

[0003] For application to new fields, research on LIB materials with characteristics such as higher energy density and longer life has been continuously demanded.

[0004] Especially in the case of negative electrode materials, research has been carried out on various substances such as silicon, tin, and germanium in addition to carbon.

[0005] Among these, silicon-based negative electrode materials have a very high energy density compared to currently commercialized graphite negative electrode materials and have received much attention.

[0006] However, silicon-based negative electrode materials have fatal disadvantages such as the formation of an unstable SEI layer due to the side reaction between the silicon surface and the electrolyte, resulting in a decrease in electrochemical properties, or the pulverization of the electrode material due to internal stress caused by the rapid volume expansion during charge and discharge.

[0007] To address this, much research has been conducted on improving the reversibility of silicon-based anode materials through various surface treatments. In particular, methods of surface coating or composite formation with carbon materials are being widely studied.

[0008] On the other hand, various surface treatments using carbon materials require complex and costly processes. While surface treatments using carbon materials have improved some properties of silicon-based anode materials, there were limitations to realizing high-power, long-life, high-speed charge-discharge LIBs.

[0009] Therefore, there is currently a need for the development of technologies related to high-capacity silicon-based anode active materials that can further improve battery characteristics while suppressing the volume expansion of silicon-based anode materials. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Republic of Korea Patent Publication No. 10-2017-0044360 [Overview of the project] [Problems that the invention aims to solve]

[0011] Therefore, the present invention aims 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 lifespan.

[0012] Furthermore, the objective is to provide a manufacturing method that enables the production of the anode active material with high efficiency and low cost.

[0013] Along with this, the objective is to provide an electrode containing the aforementioned negative electrode active material and a lithium secondary battery.

[0014] However, the problems that this application seeks to solve are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0015] A negative electrode active material comprising at least one metal-containing particle, The ratio (r2 / r1) of the length of the longest straight line (r2) connecting the farthest point of the metal-containing particle to the farthest point of the center 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. We provide a negative electrode active material.

[0016] Other aspects of the present application include the negative electrode active material, Provide electrodes.

[0017] A further embodiment of the present application is a negative electrode comprising the negative electrode active material, A positive electrode located opposite the negative electrode, The present invention provides a lithium secondary battery comprising an electrolyte disposed between the negative electrode and the positive electrode. [Effects of the Invention]

[0018] The negative electrode active material according to the present invention has the effect of providing a secondary battery with high output and long lifespan while possessing high capacity and high energy density.

[0019] Furthermore, it has the effect of enabling the production of negative electrode active materials with high efficiency and low cost. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram showing the radius (r1) of the negative electrode active material and the length (r2) of the longest straight line connecting the furthest point of the metal-containing particle located at the center point of the negative electrode active material to the furthest point of the negative electrode active material. [Figure 2] This graph shows the capacity / efficiency characteristics of cells using the negative electrode active materials produced by Examples 1 to 3 and Comparative Examples 1 to 6. [Figure 3]This graph shows the life characteristics of cells using the negative electrode active materials produced by Examples 1 to 3 and Comparative Examples 1 to 6. [Figure 4] This graph shows the output characteristics of cells using the negative electrode active materials produced by Examples 1 to 3 and Comparative Examples 1 to 6. [Modes for carrying out the invention]

[0021] Terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0022] Therefore, the configurations of the embodiments described herein represent only one of the most preferred embodiments of the present invention and do not represent the entire technical concept of the invention. It should be understood that, at the time of filing, there are various equivalents and modifications that can be substituted for these embodiments.

[0023] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of an implemented feature, number, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, numbers, stages, components, or combinations thereof.

[0024] In this specification, the terms "from" and "~" in "a to b" and "a~b" which indicate a numerical range are defined as ≥ a and ≤ b.

[0025] In one aspect of the present invention, the negative electrode active material may have a ratio (r2 / r1) of the length of the longest straight line connecting the farthest point of the metal-containing particle to the farthest point of the center of the negative electrode active material to the radius (r1) of the negative electrode active material of 0.8 or more and 0.95 or less.

[0026] The values ​​of r1 and r2 of the negative electrode active material are as shown in Figure 1. For example, if the metal-containing particles of the negative electrode active material are in the form of flakes as shown in Figure 1, then r2 is the distance (longest straight line distance) between the two ends of the metal-containing particles and the end that is furthest from the center point of the negative electrode active material.

[0027] If the r2 / r1 ratio of the negative electrode active material exceeds or falls below the range of this application, the lifespan and output characteristics of the secondary battery may deteriorate.

[0028] This is because if r2 / r1 exceeds the scope 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 falls below the scope of the present application, the movement of lithium ions to the metal-containing particles (e.g., silicon particles) may be inhibited.

[0029] Furthermore, 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 may be included 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 one or more selected from the group consisting of silicon particles, silicon oxide particles, silicon carbide particles, and silicon alloy particles.

[0031] Furthermore, the average particle size (D50) of the silicon (Si)-containing particles may be 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 chemical formula 1, if x exceeds 0.5, there may be unfavorable effects on battery capacity and efficiency. That is, lithium ions react with oxygen to form Li2O, Li-silicate(Li x Si y O z Irreversible products such as ) are generated. As a result, lithium ions that have reacted with the negative electrode material are trapped inside the negative electrode instead of returning to the electrolyte or positive electrode material, preventing them from exhibiting capacity and reducing efficiency.

[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 a particle size analyzer (Mastersizer3000, Malvern Panalytical) with an organic solution in which the silicon-containing particles were dispersed.

[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 very short. If the average particle size of the silicon-containing particles is less than 80 nm, the battery capacity and efficiency will be low, and manufacturing costs may be high.

[0037] In one embodiment, the negative electrode active material may contain 30% or more and 80% or less by weight 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 amorphous carbon and crystalline carbon.

[0040] In one embodiment, the amorphous carbon may be one or more selected from the group consisting of coal-based pitch, mesophase pitch, petroleum-based pitch, tar, coal-based oil, petroleum-based heavy oil, organic synthetic pitch, sucrose, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, phenol resin, furan resin, cellulose resin, styrene resin, epoxy resin or vinyl chloride resin, block copolymer, polyol, and polyimide resin.

[0041] Furthermore, the crystalline carbon may be one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene.

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

[0043] Expanded graphite is produced by intercalating chemicals such as acids or alkalis between layers of graphite and then heating it to expand the vertical layers of its molecular structure. Graphene contains a single layer or multiple single layers of graphite.

[0044] Carbon black is a crystalline substance with less regularity than graphite, and can be converted to graphite by heating it at approximately 3,000°C for a long period of time. Fullerene is a carbon mixture containing at least 3% by weight of fullerene, which is a polyhedral bundle compound consisting of 60 or more carbon atoms. The first carbon-based material can use one type of such crystalline carbon alone or in combination of two or more types. For example, natural graphite or artificial graphite can be used. The crystalline carbon can be spherical, plate-shaped, fibrous, tubular, or powder-shaped.

[0045] Preferably, pitch can be used as the amorphous carbon. The pitch can have a softening point of 100 to 250°C, and in particular, petroleum-based or coal-based pitch can be used that has a QI (Quinolone Insoluble) component of 5% by weight or less, more preferably 1% by weight or less.

[0046] On the other hand, natural graphite can preferably be used as the crystalline carbon. The purity of the graphite should be such that it has a fixed carbon content of 99% by weight or more, and more preferably 99.95% by weight or more.

[0047] Furthermore, flake graphite can be suitable for increasing conductivity through contact 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 could be between 0.7 and 0.99.

[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 exceeds or falls below the range specified in this application, the r2 / r1 value of the negative electrode active material may exceed the range specified in this application, which may degrade the characteristics of the secondary battery.

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

[0052] For example, the core may contain all of the amorphous carbon and crystalline carbon, and the shell may contain all of the amorphous carbon and crystalline carbon.

[0053] The additional carbon components in the core and shell can play a role in mitigating the volume expansion of metal-containing particles during charging and discharging.

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

[0055] On the other hand, the negative electrode active material may contain voids. In particular, voids can be formed mainly in the core of the negative electrode active material. These voids can reduce the initial irreversible capacity of the secondary battery and help mitigate 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 lifespan and output characteristics of the secondary battery may decrease.

[0057] This is because, if the porosity exceeds 10%, the breakdown of the carbon matrix allows the electrolyte solvent to penetrate the voids, potentially damaging metal-containing particles (e.g., silicon particles) and reducing the lifetime characteristics. Furthermore, a decrease in the density of the electron transport pathway can hinder smooth electrochemical reactions, potentially reducing the output characteristics.

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

[0059] The metal-containing particles provided in the step of producing the precursor powder may be prepared by grinding them in a grinding process to have a desired average particle size.

[0060] The aforementioned 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 compounding step may be carried out by a physical method.

[0062] The aforementioned physical method may include one or more high-energy processes selected from the group consisting of milling, stirring, mixing, and compression.

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

[0064] The balls that can be used for ball milling may be, for example, zirconia balls, and there are no restrictions on the type of ball. The size of the ball may be, for example, approximately 0.3 to 10 mm, but is not limited to this.

[0065] On the other hand, the reaction time for the compounding 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 may 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, and the heat treatment time may be 10 to 48 hours, and the process may be carried out under a vacuum atmosphere.

[0068] The heat treatment temperature in the second heat treatment step may be 600 to 1,000°C, and the heat treatment time may be 1 to 48 hours. The heat treatment can be carried out under an inert gas atmosphere (e.g., nitrogen, argon, etc.).

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

[0070] An electrode according to yet another aspect of the present application may include the negative electrode active material, and the lithium secondary battery may include a positive electrode positioned opposite the negative electrode, with the electrode containing the negative electrode active material as the negative electrode, and an electrolyte disposed between the negative electrode and the positive electrode.

[0071] The negative electrode may include the negative electrode active material and may be manufactured, for example, by mixing the negative electrode active material, a binder, and a selectively conductive agent in a solvent to produce a negative electrode active material composition, and then molding it into a certain shape or by applying it to a current collector such as copper foil.

[0072] The negative electrode may further include, in addition to the negative electrode active material described above, negative electrode active material materials commonly used as negative electrode active materials for lithium batteries in the art. Commonly used negative electrode active material materials may include, for example, one or more selected from the group consisting of lithium metal, metals alloyable with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0073] For example, the metal that can form an alloy with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a 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), a Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 to 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, Tl, 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, the electrical conductivity can be improved, and the charge and discharge characteristics of lithium can be further improved.

[0077] Conventional negative electrode active material may be used by mixing and blending it with the negative electrode active material described above, by coating it on the surface of the negative electrode active material described above, or in any other combination form.

[0078] The binder used in the negative electrode active material composition is a component that assists in the bonding of the negative electrode active material to a conductive agent and to the current collector, and is added in amounts of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. For example, the binder can be added in the range of 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the negative electrode active material.

[0079] Examples of such binders include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resins, epoxy resins, polyethylene terephthalate, polytetrafluoroethylene, polyphenyl sulfide, polyamide-imide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0080] The negative electrode may further selectively contain a conductive agent to provide conductive passages to the negative electrode active material and further improve electrical conductivity.

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

[0082] The solvent can be N-methylpyrrolidone (NMP), acetone, water, etc. The solvent content is 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the solvent content is within this range, the process of forming the active material layer is easy.

[0083] Furthermore, the current collector is generally made to a thickness of 3 to 500 μm. The current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used.

[0084] Furthermore, by forming fine irregularities on the surface, the bonding force of the negative electrode active material can be strengthened, and it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0085] The negative electrode plate can be manufactured by directly coating the manufactured negative electrode active material composition onto a current collector, or by casting it onto another support, peeling the negative electrode active material film from the support, and laminating it onto a copper foil current collector. The negative electrode is not limited to the forms listed above, and may take other forms.

[0086] The negative electrode active material composition is not only used for manufacturing the electrodes of lithium secondary batteries, but can also be printed on a flexible electrode substrate and used for manufacturing printable batteries.

[0087] Separately from this, in order to fabricate the positive electrode, a positive electrode active material composition in which a positive electrode active material, a conductive agent, a binder, and a solvent are mixed is prepared.

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

[0089] For example, Li a A 1-b B b D2 (in the above formula, 0.90 ≦ a ≦ 1.8 and 0 ≦ b ≦ 0.5); Li a E 1-b B b O 2-c D c (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE 2-b B b O 4-c D c (in the above formula, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b B c Dα (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α ≦ 2); Li a Ni 1-b-c Co b B c O 2- αFα (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2- αFα (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b Bc Dα(wherein the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2);Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li a Ni 1-b-c Mn b B c O 2- αFα (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li a Ni b E c G d O2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1.);Li a Ni b Co c Mn d GeO2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1.);Li a NiG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a CoG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a MnG b O2(In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Compounds represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2) or LiFePO4 can be used.

[0090] In the above chemical formulas, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0091] Of course, compounds having a coating layer on their surface can also be used, or the compound and the compound having the coating layer may be mixed and used. The coating layer may contain coating element compounds of oxide, hydroxide, oxyhydroxy, oxycarbonate, or hydroxycarbonate of the coating element. The compounds forming these coating layers may be amorphous or crystalline. The coating elements included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation step can be carried out using any coating method that does not adversely affect the physical properties of the positive electrode active material (e.g., spray coating, immersion method, etc.) using such elements, and since this is something that will be well understood by those engaged in this field, a detailed explanation will be omitted.

[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] In the positive electrode active material composition, the conductive agent, binder, and solvent can be the same as those used in the negative electrode active material composition described above. In some cases, a plasticizer can be further added to the positive electrode active material composition and the negative electrode active material composition to form voids inside the electrode plate. The content of the positive electrode active material, conductive agent, binder, and solvent is at levels typically used in lithium batteries.

[0094] The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm and possesses high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The current collector can also have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0095] The prepared positive electrode active material composition can be directly coated onto a positive electrode current collector and dried to produce a positive electrode plate. Alternatively, the positive electrode active material composition can be cast onto another support, and the resulting film, obtained by peeling it off the support, can be laminated onto the positive electrode current collector to produce a positive electrode plate.

[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, a separator with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferred. For example, materials selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, may be in the form of a nonwoven or woven fabric. The separator has a void diameter of 0.01 to 10 μm and is generally used with a thickness of 5 to 300 μm.

[0097] Lithium salt-containing non-aqueous electrolytes consist of a non-aqueous electrolyte and lithium. Non-aqueous electrolytes include non-aqueous electrolyte solutions, solid electrolytes, and inorganic solid electrolytes.

[0098] As the non-aqueous electrolyte, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate can be used.

[0099] Examples of the organic solid electrolytes that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups.

[0100] Examples of the inorganic solid electrolytes that can be used include lithium nitrides, halides, and sulfates such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0101] Any lithium salt commonly used in lithium batteries can be used, and substances that readily dissolve in the non-aqueous electrolyte include, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 One or more of the following substances can be used: LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc.

[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 also be classified into cylindrical, prismatic, coin-type, pouch-type, etc. depending on their form, and into bulk type and thin-film type depending on their size.

[0103] Since the manufacturing methods for these batteries are widely known in this field, a detailed explanation will be omitted. [Examples]

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

[0105] [Example 1] Scale-like silicon particles (average particle size (D 50Mix 5 parts by weight of silicon particles (D):5μm, 94 parts by weight of isopropyl alcohol (IPA), and 1 part by weight of stearic acid, and put the mixture into a bead mill to obtain the average particle size of silicon particles (D 50 The silicon was ground down to 110 nm to prepare a pulverized silicon solution.

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

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

[0108] Subsequently, the composite material was manufactured by performing a secondary heat treatment at 900°C for 3 hours under an inert atmosphere.

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

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

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

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

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

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

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

[0116] [Comparative Example 5] The negative electrode active material was manufactured in the same manner as in Example 1, except that after compounding, a primary heat treatment was performed at 180°C for 24 hours under a nitrogen atmosphere (not a vacuum atmosphere).

[0117] [Comparative Example 6] The negative electrode active material was manufactured in the same manner as in Example 1, except that primary and secondary heat treatments were not performed after compounding.

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

[0119] The prepared negative electrode slurry was coated onto a 10 μm thick copper thin film current collector. After the coating was complete, the electrode plate was dried at 120°C for 20 minutes, then rolled (pressed) to produce the negative electrode.

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

[0121] Coin Full Cell Construction Using the negative electrode from the aforementioned coin half-cell, the positive electrode was manufactured as follows: LiNi 0.6 Co 0.2 Mn 0.2 A positive electrode slurry was prepared by mixing O2, a conductive agent (Super P), and a binder (PVDF) in a weight ratio of 95:2:3. The positive electrode slurry was then coated onto a 12 μm thick aluminum foil current collector. After the coated electrode plate was dried at 120°C for 15 minutes, it was rolled (pressed) to produce the positive electrode.

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

[0123] Evaluation Example 1: Analysis of Negative Electrode Active Material The characteristics of the negative electrode active materials of Examples 1-3 and Comparative Examples 1-3 were analyzed and are shown in Table 1 below.

[0124] [Table 1]

[0125] In Table 1 above, the particle size (D) of the negative electrode active material (composite) 50The particle size was measured using an organic solution containing the negative electrode active materials of Examples 1-3 and Comparative Examples 1-6, with a particle size analyzer (Mastersizer3000, Malvern Panalytical).

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

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

[0128] Furthermore, in order to calculate the r2 / r1 ratio, the cross-sections of the negative electrode active materials of Examples 1-3 and Comparative Examples 1-6 were processed using a Focused-ion beam (FIB), and r1 and r2 were measured by observing the cross-sections with a FE-SEM.

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

[0130]

number

[0131] According to Table 1 above, the particle size of the negative electrode active materials in 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 manufacturing of the negative electrode active material, the r2 / r1 value tended to decrease as the petroleum-based pitch content increased and the graphite content decreased.

[0133] In other words, we were able to confirm that the r2 / r1 value of the negative electrode active material can be adjusted by adjusting the content of petroleum-based pitch and graphite during the manufacturing of the negative electrode active material.

[0134] Furthermore, by comparing Comparative Examples 5 and 6, which differ only in heat treatment conditions from Example 1, it was confirmed that the porosity becomes significantly higher when the primary heat treatment conditions are changed or when primary and secondary heat treatments are omitted.

[0135] In other words, we were able to confirm that the porosity of the negative electrode active material can be adjusted by changing the heat treatment conditions during its manufacture.

[0136] Evaluation Example 2: Battery Characteristic Analysis The characteristics of the cells using the negative electrode active materials of Examples 1-3 and Comparative Examples 1-6 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 produced in Examples 1-3 and Comparative Examples 1-6 were evaluated as follows.

[0139] Coin-full cells were used for evaluating lifespan and power characteristics, while coin-half cells were used for evaluating initial capacity, discharge capacity, and initial efficiency characteristics.

[0140] Coin half-cells manufactured using the negative electrode active materials produced in Examples 1-3 and Comparative Examples 1-6 were each charged with a constant current at 25°C at a rate of 0.1C until the voltage reached 0.01V (vs.Li), and then charged with a constant voltage until the current reached 0.05C while maintaining the voltage at 0.01V. After the fully charged cells were left to rest for 10 minutes, they were discharged at a constant current of 0.1C until the voltage reached 1.5V (vs.Li) (performed twice, initial formation). The term "C" refers to the discharge rate of the cell, and means the value obtained by dividing the total capacity of the cell by the total discharge time.

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

[0142] Subsequently, the cell was charged with a constant current at a rate of 1.0C at 25°C until the voltage reached 4.2V (vs.Li), and then charged with a constant voltage until the current reached 0.05C while maintaining 4.2V. After the fully charged coin cell was left to rest for 10 minutes, the cycle of discharging with a constant current of 1.0C until the voltage reached 2.7V (vs.Li) was repeated (cycles 1 to 200).

[0143] As an example, Figures 2 to 4 show the measurement graphs of the capacity / efficiency, lifespan, and output characteristics of cells using the negative electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 6, respectively.

[0144] On the other hand, the initial charge capacity and initial discharge capacity in Table 2 above represent the charge and discharge capacities for the first cycle, respectively.

[0145] Initial efficiency, lifespan, and output characteristics were calculated using equations 2-4 below, respectively.

[0146] <Formula 2> Initial efficiency [%] = [Discharge capacity in the first cycle / Charge capacity in the first cycle] x 100

[0147] <Formula 3> Lifetime characteristic [%] = [Discharge capacity at 200th cycle / Discharge capacity at 1st cycle] x 100

[0148] <Formula 4> Output characteristic [%] = [Discharge capacity at 5.0C / Discharge capacity at 0.1C] x 100

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

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

[0151] Furthermore, we were able to confirm that the r2 / r1 value and porosity of the negative electrode active material significantly affect the lifespan 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, where the r2 / r1 value exceeds 0.8 or 0.95, it was confirmed that the lifespan and output characteristics of the secondary batteries were inferior compared to the secondary batteries using the negative electrode active materials of Examples 1 to 3.

[0153] In other words, if the value of r2 / r1 exceeds or falls below the range of this application, it was not possible to obtain a secondary battery with excellent lifespan and output characteristics.

[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%, even if the value of r2 / r1 falls within the range of the present invention, it was confirmed that the life characteristics and output characteristics of the secondary batteries were inferior compared to the secondary batteries using the negative electrode active materials of Examples 1 to 3.

[0155] In other words, even if the value of r2 / r1 falls within the scope of this application, if the porosity exceeds the scope of this application, it was not possible to obtain a secondary battery with excellent lifespan and output characteristics.

[0156] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or altered forms derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention. [Industrial applicability]

[0157] The negative electrode active material according to the present invention has the effect of providing a secondary battery with high output and long lifespan while possessing high capacity and high energy density.

[0158] Furthermore, it has the effect of enabling the production of negative electrode active materials with high efficiency and low cost.

Claims

1. A negative electrode active material comprising at least one metal-containing particle, The radius (r) of the negative electrode active material 1 The longest straight line length (r) connecting the center point of the negative electrode active material with the end of the metal-containing particle located at the furthest distance from the center point of the negative electrode active material. 2 ) ratio (r 2 / r 1 ) is 0.8 or higher and 0.95 or lower, The porosity of the negative electrode active material is 10% or less. Negative electrode active material.

2. The aforementioned 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 included in the core. The negative electrode active material according to claim 1.

3. The metal-containing particles include one or more 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% or more by weight and 80% or less by weight of 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 greater and 1 or less. The negative electrode active material according to claim 1.

6. The core and the shell include one or more 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 larger and 20 μm or smaller. The negative electrode active material according to claim 1.

8. A method for producing a negative electrode active material according to any one of claims 1 to 7, A step of producing a precursor powder by spray-drying a solution containing metal-containing particles, The steps include mixing the precursor powder, amorphous carbon, and crystalline carbon to form a composite, The step includes a heat treatment step, The aforementioned metal is one or more selected from Si, Al, Ti, Mn, Ni, Cu, V, Zr, Mn, Co, Fe, and Nb. The heat treatment step includes a first heat treatment step and a second heat treatment step. A method for producing a negative electrode active material.

9. A negative electrode active material comprising the material described in any one of Claims 1 to 7, electrode.

10. A negative electrode comprising the negative electrode active material described in any one of Claims 1 to 7, A positive electrode located opposite the negative electrode, The electrolyte is disposed between the negative electrode and the positive electrode, Lithium-ion rechargeable battery.

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