Positive electrode active material for lithium secondary battery, method for preparing same, and positive electrode and lithium secondary battery comprising same

Abstract

According to one embodiment of the present invention, provided are a positive electrode active material for a lithium secondary battery, a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the same, the positive electrode active material comprising a lithium compound represented by the following Chemical Formula 1 and a carbon coating layer formed on particle surfaces of the lithium compound, wherein the lithium compound has the form of secondary particles having a structure in which the primary particles agglomerate with each other, an average diameter (D50) of the secondary particles is 0.2 to 10 [mu] m, an average diameter (D50) of the primary particles is 10 to 300 nm, and a ratio of an average diameter (D90) / average diameter (D10) of the secondary particles is 15 to 80, [Chemical Formula 1] Li1 + aM1bM2cO2-dXd, where in Chemical Formula 1, in chemical Formula 1, R1 represents a hydrogen atom, R2 represents a hydrogen atom, and X represents a hydrogen atom; m1 is one or more selected from the group consisting of Ni, V, Mn, Mo, Cr and Fe, and M2 is one or more selected from the group consisting of Ti, Zr, Nb, Mo, Ta and W, 0.1 < = a < = 0.5, 0.2 < = b < = 0.6, 0.2 < = c < = 0.6, 1.05 < = (1 + a) / (b + c) < = 1.5, 0 < = d < = 0.2, and X is a halogen element.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0104686, filed on August 6, 2024, and Korean Patent Application No. 10-2025-0107390, filed on August 5, 2025, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This invention relates to a positive electrode active material for lithium secondary batteries, its preparation method, a positive electrode containing the material, and a lithium secondary battery. Background Technology

[0004] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is growing, and as part of this, the most active area of ​​research is in the field of power generation and energy storage using electrochemistry.

[0005] Currently, secondary batteries are a representative example of electrochemical devices that utilize this electrochemical energy, and their application is gradually expanding.

[0006] Recently, with the technological advancements and increasing demand for mobile devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as energy sources has increased rapidly. Among these secondary batteries, lithium-ion batteries, exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate, have been extensively studied and have been commercialized and widely used.

[0007] Furthermore, with increasing concern about environmental issues, research is frequently being conducted on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels (such as gasoline and diesel vehicles), which are one of the main causes of air pollution. Although nickel-metal hydride secondary batteries are mainly used as power sources for electric and hybrid electric vehicles, much research has been actively undertaken to utilize lithium secondary batteries with high energy density and high discharge voltage, some of which are already in the commercialization stage.

[0008] Lithium-ion secondary batteries typically have the following structure: a non-aqueous electrolyte is impregnated into an electrode assembly comprising a positive electrode, a negative electrode, and a porous separator. Generally, the positive electrode is prepared by coating a positive electrode mixture containing positive electrode active material onto an aluminum foil, and the negative electrode is prepared by coating a negative electrode mixture containing negative electrode active material onto a copper foil.

[0009] Typically, the positive electrode active material is a lithium transition metal oxide, and the negative electrode active material is a carbon-based material.

[0010] However, recently, as lithium secondary batteries have been used in various industrial fields, high capacity and high rate characteristics are being studied as important performance parameters. As a result, there are active attempts to develop positive electrode active materials that can achieve these characteristics.

[0011] Recently, one type of positive electrode active material that has attracted attention is DRX (cationically disordered rock salt transition metal oxide), which is a high-capacity material that can exhibit additional capacity not only through cation oxidation / reduction but also through anion oxidation / reduction (oxygen oxidation-reduction).

[0012] However, these materials have problems such as gas emission during the high-voltage operation of lithium secondary batteries and reduced lifetime characteristics due to increased material resistance, and improving them remains a challenge.

[0013] Therefore, there is an urgent need to develop technologies that can solve these problems and achieve secondary battery performance such as high capacity, high rate capability, and excellent lifespan characteristics. Summary of the Invention

[0014] Technical issues

[0015] One object of the present invention is to provide a positive electrode active material for lithium secondary batteries, a method for preparing the same, a positive electrode comprising the same, and a lithium secondary battery, wherein the positive electrode active material is prepared such that it has an optimized particle size distribution.

[0016] Technical solution

[0017] According to one aspect of the present invention, a positive electrode active material for lithium secondary batteries is provided, the positive electrode active material comprising: Lithium compounds represented by the following chemical formula 1 and carbon coatings formed on the surface of lithium compound particles, The lithium compound exists in the form of secondary particles, which have a structure in which the primary particles are aggregated together. The average diameter (D50) of the secondary particles ranges from 0.2 to 10 μm. The average diameter (D50) of primary particles ranges from 10 to 300 nm, and The ratio of the average diameter (D90) to the average diameter (D10) of secondary particles is between 15 and 80. [Chemical Formula 1] Li 1+a M1 b M2 c O 2-d X d In chemical formula 1, M1 is selected from one or more of Ni, V, Mn, Mo, Cr, and Fe, and M2 is selected from one or more of Ti, Zr, Nb, Mo, Ta, and W. 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.05≤(1+a) / (b+c)≤1.5, 0≤d≤0.2, and X is a halogen element.

[0018] Specifically, in chemical formula 1, b + c = 0.8.

[0019] The carbon coating content can be from 1 to 10 parts by weight, based on 100 parts by weight of lithium compound.

[0020] On the other hand, according to another aspect of the present invention, a method for manufacturing a positive electrode active material for lithium secondary batteries is provided, the method comprising: Lithium compounds are synthesized based on a mixture containing active material precursors and carbon precursors. The synthesis process includes primary ball milling, calcination, secondary ball milling, and jaw crushing.

[0021] Specifically, for example, the synthesis can be carried out in the order of primary ball milling, calcination, jaw crushing and secondary ball milling, or in the order of primary ball milling, calcination, secondary ball milling and jaw crushing.

[0022] Here, ball milling can be carried out under an inactive atmosphere. The first ball milling can be carried out at 100 rpm to 500 rpm, and the second ball milling can be carried out at 100 rpm to 500 rpm. The first ball milling can be repeated 1 to 2 times by grinding for 3 to 8 hours and then letting it stand for 5 to 120 minutes. The second ball milling can be repeated 1 to 2 times by grinding for 1 to 8 hours and then letting it stand for 5 to 120 minutes.

[0023] In addition, jaw crushing can be performed once or twice.

[0024] Jaw crushing can be performed at 600 rpm to 1200 rpm.

[0025] Calcination can be carried out in an inactive atmosphere at a temperature ranging from 650 to 1200°C for 6 to 30 hours.

[0026] The active material precursor can be an M1 source, an M2 source, or a lithium source, and the carbon precursor can be selected from one or more of citric acid and sucrose.

[0027] According to another aspect of the present invention, a positive electrode for a lithium secondary battery is provided, the positive electrode having a positive electrode mixture layer formed on one or both surfaces of the entire positive electrode. The positive electrode mixture layer contains positive electrode active materials, binders, and conductive materials.

[0028] In this case, the conductive material can be a dot-shaped conductive material.

[0029] On the other hand, according to yet another aspect of the present invention, a lithium secondary battery comprising the positive electrode is provided. Detailed Implementation

[0030] In the following description and claims, the terms or words used should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the technical concept of the invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their own invention.

[0031] Unless otherwise defined, all terms used herein (including technical and scientific terms) are to be used in the sense that would be commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, unless specifically and explicitly defined, terms as defined in commonly used dictionaries should not be idealized or over-interpreted.

[0032] The terminology used herein is provided to describe embodiments and not to limit the concept of the invention. In this specification, the singular forms include the plural forms unless the context clearly indicates otherwise. The terms “comprising” and / or “including” as used herein do not exclude the presence or addition of more than one element in addition to those mentioned.

[0033] On the other hand, the terms “composed of” and / or “constituting of” as used herein mean that, in addition to the stated constituent elements, the extent to which other constituent elements are included is such that they contain only very small amounts at the impurity level and do not exceed trace amounts.

[0034] In this specification, "average particle sizes D10, D50, and D90" refer to the particle sizes at 10%, 50%, and 90% of the cumulative volume distribution of the tested particle powder (e.g., positive electrode active material powder, negative electrode active material powder, etc.). The average particle sizes D10, D50, and D90 can be measured using laser diffraction. For example, the average particle size can be measured by a process including the following steps: dispersing the tested particle powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasound at a frequency of approximately 28 kHz and an output of 60 W, obtaining a cumulative volume particle size distribution map, and then determining the particle sizes corresponding to 10%, 50%, and 90% of the cumulative volume.

[0035] Positive electrode active material

[0036] According to one embodiment of the present invention, a positive electrode active material for lithium secondary batteries is provided, the positive electrode active material comprising: Lithium compounds represented by the following chemical formula 1 and carbon coatings formed on the surface of lithium compound particles, The lithium compound exists in the form of secondary particles, which have a structure in which the primary particles are aggregated together. The average diameter (D50) of the secondary particles ranges from 0.2 to 10 μm. The average diameter (D50) of primary particles ranges from 10 to 300 nm, and The ratio of the average diameter (D90) to the average diameter (D10) of secondary particles is between 15 and 80. [Chemical Formula 1] Li 1+a M1 b M2 c O 2-d X d In chemical formula 1, M1 is selected from one or more of Ni, V, Mn, Mo, Cr, and Fe, and M2 is selected from one or more of Ti, Zr, Nb, Mo, Ta, and W. 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.05≤(1+a) / (b+c)≤1.5, 0≤d≤0.2, and X is a halogen element.

[0037] Here, the lithium compound represented by Formula 1 can be DRX, and more specifically, in Formula 1, b+c=0.8.

[0038] Additionally, 0.2≤a≤0.4, 0.3≤b≤0.5, 0.3≤c≤0.5, and M1 can be Mn, and M2 can be Ti.

[0039] Most specifically, lithium compounds can be Li 1.2 Mn 0.4 Ti 0.4 O2.

[0040] This lithium compound can have the form of secondary particles, which have a structure in which the primary particles are clustered together.

[0041] Here, the average diameter (D50) of the secondary particles can be 0.2 to 10 micrometers, specifically 0.5 to 7 micrometers, and more specifically 0.7 to 2 micrometers.

[0042] In addition, the average diameter (D50) of the primary particles that make up the secondary particles can be 10 to 300 nanometers, specifically 20 to 200 nanometers, and more specifically 30 to 100 nanometers.

[0043] If the average diameter (D50) of the secondary particles is too large and falls outside the aforementioned range, the lithium-ion migration path becomes longer, resulting in poorer capacity and output, and reduced ability to cover the particles during carbon coating. Conversely, if the average diameter of the secondary particles is too small, the particles may agglomerate, leading to clumping during contact with conductive materials and slurry mixing, which can adversely affect output and lifetime characteristics.

[0044] Furthermore, if the average diameter (D50) of the primary particles is too large, the agglomeration properties of the secondary particles may decrease; if the average diameter (D50) of the primary particles is too small, the amount of fine powder produced may increase, which is undesirable.

[0045] On the other hand, according to the present invention, since the lithium compound of the present invention is prepared by the preparation method described later, the lithium compound is able to have an optimized particle size distribution, which eliminates agglomeration, optimizes the coverage of the carbon coating and improves the rolling density, and as a characterization index, the average diameter (D90) / average diameter (D10) of the secondary particles can be 15 to 80, specifically 15 to 70, more specifically 20 to 70.

[0046] If the average diameter (D90) / average diameter (D10) of the secondary particles is large and falls outside the above range, the range of lithium compounds is too wide, resulting in reduced capacity and resistivity performance, and it is difficult to prepare secondary particles with an average diameter (D90) / average diameter (D10) ratio greater than the above range.

[0047] The lithium compound is used in the form of a carbon coating on its surface to enhance conductivity, and the carbon coating content can be from 1 to 10 parts by weight based on 100 parts by weight of the lithium compound. Specifically, the carbon coating content can be from 1 to 7 parts by weight, and more specifically, from 1 to 5 parts by weight based on 100 parts by weight of the lithium compound.

[0048] If the carbon coating content is too low and falls outside the aforementioned range, a sufficient conductive network cannot be formed, which is undesirable. If the carbon coating content is too high, agglomeration occurs due to these clusters coming together, making uniform coating impossible.

[0049] On the other hand, in addition to lithium compounds, the positive electrode active material may further comprise compounds capable of reversibly inserting and deintercalating lithium, and examples may include lithium metal oxides containing lithium and at least one metal such as cobalt, manganese, nickel, or aluminum, specifically including: lithium manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt oxides (e.g., LiCoO2, etc.), lithium nickel oxides (e.g., LiNiO2, etc.), lithium nickel manganese oxides (e.g., Li... 1+x' Ni 1-Y Mn Y O2 (where -0.5 ≤ x' ≤ 0.5, 0 < Y < 1), Li 1+x'' Mn 2-Z Ni Z O4 (where -0.5 ≤ x'' ≤ 0.5, 0 < Z < 2), etc.), lithium nickel cobalt oxides (e.g., Li 1+x''' Ni 1-Y1 Co Y1 O2 (where -0.5 ≤ x''' ≤ 0.5, 0 < Y1 < 1), etc.), lithium manganese cobalt oxides (e.g., Li 1+x'''' Co 1-Y2 Mn Y2 O2 (where -0.5 ≤ x'''' ≤ 0.5, 0 < Y2 < 1), Li 1+x''''' Mn 2-Z1 Co Z1 O4 (where -0.5 ≤ x''''' ≤ 0.5, 0 < Z1 < 2), etc.), lithium nickel manganese cobalt oxides (e.g., Li 1+a1 (Ni p Co q Mn r O2 (where -0.5 ≤ a1 ≤ 0.5, 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li 1+a2 (Ni p1 Co q1 Mn r1 O4 (where -0.5≤a2≤0.5, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2, etc.) or lithium nickel cobalt transition metal (M) oxides (e.g., Li 1+a3 (Ni p2 Co q2 Mn r2 M s2O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and a3, p2, q2, r2, and s2 are the atomic fractions of each independent element, where -0.5 ≤ a3 ≤ 0.5, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate oxides (e.g., Li... 1+a4 Fe 1-p3 M p3 (PO 4-b4 )X b4 (where M is at least one selected from Al, Mg and Ti, X is at least one selected from F, S and N, -0.5≤a4≤0.5, 0≤p3≤0.5, 0≤b4≤0.1)), etc., and any one of them or a mixture of two or more of them can be used.

[0050] Of course, the lithium compound according to the invention may be included as the main active material, and based on the total amount of the positive electrode active material, the content of the lithium compound according to the invention may be 80% by weight or more, specifically 90% by weight or more and 100% by weight or less. The content of the lithium compound alone may be 100% by weight.

[0051] Methods for preparing positive electrode active materials

[0052] Methods for preparing positive electrode active materials for lithium secondary batteries include the preparation of lithium compounds.

[0053] There are no restrictions on the method for preparing lithium compounds as positive electrode active materials, and it can be prepared by solid-phase methods, but specifically, it can be prepared by grinding and calcining a mixture containing active material precursors and carbon precursors.

[0054] In this case, the mixture may further contain additives, such as surface modifiers, as needed.

[0055] Here, the active material precursor is a component constituting the lithium compound represented by chemical formula 1, and can be a source of M1, a source of M2, and a lithium source. In this case, M1 and M2 are defined as they are defined for the positive electrode active material.

[0056] In this case, the lithium source can be one or more materials selected from lithium carbonate, lithium hydroxide and lithium phosphate, more specifically lithium hydroxide (LiOH).

[0057] The M1 source can be one or more materials selected from sulfates, nitrates, carbonates, acetates, hydrochlorides, hydroxides, oxides, and phosphates, each containing M1, and more specifically, oxides containing M1.

[0058] The M2 source can be one or more materials selected from sulfates, nitrates, carbonates, acetates, hydrochlorides, hydroxides, oxides, and phosphates, each containing M2, and more specifically, oxides containing M2.

[0059] In addition, carbon precursors are introduced simultaneously from the lithium compound synthesis stage to enhance the conductivity of the synthesized lithium compounds.

[0060] In this case, the carbon precursor can be one or more materials selected from citric acid, glucose, sucrose, graphite, carbon nanotubes and carbon black, and more specifically, it can be one or more materials selected from citric acid and sucrose.

[0061] These precursors can typically be prepared using solid-state methods, which involve mixing followed by calcination. However, when prepared using conventional methods, the lithium compounds after calcination exhibit a wide diameter distribution, making it difficult to achieve the improved capacity and electrochemical performance desired by this invention.

[0062] Therefore, according to the present invention, even after mixing and calcination, the precursor can be synthesized by performing a further grinding step.

[0063] In this case, the precursor can be mixed by a single ball milling process. The single ball milling can be specifically carried out by dry mixing, or more specifically by mixing and grinding the precursor with zirconia balls, etc.

[0064] In this case, a single ball milling can be carried out in an inactive atmosphere, specifically, in an Ar atmosphere, and can be repeated 1 to 2 times by milling at 100 to 500 rpm for 3 to 8 hours and then letting it stand for 5 to 120 minutes.

[0065] Subsequently, once thoroughly mixed, the mixture can be calcined.

[0066] In this case, calcination can be carried out for 6 to 30 hours in an inert atmosphere, specifically an Ar atmosphere, at a temperature ranging from 650 to 1200°C. Alternatively, calcination can be carried out in two steps. For example, the first step can be carried out for 1 to 6 hours in an inert atmosphere at a temperature ranging from 500 to 800°C, and the second step can be carried out for 6 to 20 hours in an inert atmosphere at a temperature ranging from 800 to 1200°C.

[0067] Subsequently, by further grinding according to the present invention, the particle size distribution can be controlled and optimized. In this case, further grinding can be carried out by secondary ball milling and jaw crushing. For example, grinding can be carried out in the order of primary ball milling and calcination, followed by the above-mentioned jaw crushing and secondary ball milling. As another example, grinding can also be carried out in the order of primary ball milling and calcination, followed by secondary ball milling and jaw crushing.

[0068] Here, similar to primary ball milling, secondary ball milling can be carried out through dry mixing. More specifically, it can be achieved by mixing and grinding the precursor with zirconia balls, etc.

[0069] In addition, secondary ball milling can also be carried out in a non-active atmosphere, specifically in an Ar atmosphere.

[0070] In addition, secondary ball milling can be repeated 1 to 2 times by grinding at 100 rpm to 500 rpm for 1 to 8 hours and then letting it stand for 5 to 120 minutes.

[0071] It is undesirable for the grinding speed to be too high or the duration to be too long, as this not only prolongs the preparation process time and reduces the process efficiency, but also may cause the calcined lithium compound to crack due to the high speed. On the other hand, it is also undesirable for the grinding speed to be too low or the duration to be too short, as this will not achieve the particle size distribution expected by the present invention.

[0072] On the other hand, jaw crushing can be performed once, but it can also be repeated more than twice. Specifically, it can be performed one to five times, and more specifically, it can be performed one to two times.

[0073] This jaw crusher can operate at 600 to 1200 rpm, with a blade spacing of 2 to 30 mm.

[0074] When this secondary ball milling and jaw crushing are performed, the particle size of the lithium compound can have the particle size distribution expected in this invention.

[0075] Specifically, as described above, the average diameter (D50) of the secondary particles of the lithium compound can be from 0.2 to 10 μm, the average diameter (D50) of the primary particles can be from 10 to 300 nm, and the ratio of the average diameter (D90) of the secondary particles to the average diameter (D10) can be from 15 to 80.

[0076] When lithium compounds with optimized particle size distribution are prepared by the above method, electrochemical performance can be improved while minimizing particle agglomeration.

[0077] positive electrode

[0078] According to another aspect of the invention, a positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector, followed by drying and calendering. Therefore, the positive electrode can have a structure in which a positive electrode mixture layer formed by drying the positive electrode slurry is formed on one or both surfaces of the positive electrode current collector.

[0079] There are no particular restrictions on the positive current collector, as long as it does not cause chemical changes in the corresponding battery and is conductive, and materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. can be used.

[0080] Positive current collectors can typically have a thickness ranging from 3 μm to 500 μm. They can also have fine irregularities formed on their surface to enhance the adhesion of the positive electrode active material. For example, positive current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0081] In addition to the positive electrode active material, the positive electrode mixture layer may further contain conductive materials, binders and other additives as needed.

[0082] Conductive materials are components used to further improve the conductivity of the positive electrode active material. There are no particular limitations on such conductive materials, as long as they are conductive and do not cause any chemical changes in the corresponding battery. Examples include: carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powders such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive fibers such as carbon nanotubes, carbon fibers, or metal fibers; fluorocarbon powders; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives, etc.

[0083] Specifically, the conductive material can be a dot-like conductive material, such as carbon black or furnace black, more specifically super-P carbon black.

[0084] Based on the total weight of the positive electrode mixture layer, the content of conductive material can be 0.1 to 20% by weight, specifically 0.5 to 10% by weight, or more specifically 0.5 to 5% by weight.

[0085] Adhesives are components that facilitate the bonding between conductive materials, positive electrode active materials, and positive electrode current collectors. Examples of such adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0086] Typically, based on the total weight of the cathode mixture layer, the binder content can be 0.5 to 20% by weight, specifically 0.5 to 10% by weight, and more specifically 0.5 to 5% by weight.

[0087] In addition, as other additives, fillers may be further included as components to suppress expansion. There are no particular limitations on the fillers, as long as they can suppress electrode expansion without causing any chemical changes in the corresponding battery, and examples may include: olefinic polymers, such as polyethylene and polypropylene; fibrous materials, such as glass fiber and carbon fiber, etc.

[0088] Lithium secondary batteries

[0089] On the other hand, according to another aspect of the present invention, a lithium secondary battery comprising the positive electrode is provided.

[0090] A lithium secondary battery has the following structure: an electrode assembly, including a positive electrode, a negative electrode, and a separator, is introduced into the secondary battery case along with an electrolyte.

[0091] Here, the negative electrode has the following structure: a negative electrode mixture layer containing a negative electrode active material is formed on one or both surfaces of the negative electrode current collector. In addition to the negative electrode active material, the negative electrode mixture layer may further contain electrode materials, such as conductive materials, and binders, as described for the positive electrode.

[0092] There are no particular restrictions on the negative electrode current collector, as long as it does not cause chemical changes in the corresponding battery and is conductive. It can be made of materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys.

[0093] Negative electrode current collectors can typically have a thickness ranging from 3 μm to 500 μm. Similar to positive electrode current collectors, negative electrode current collectors can have fine irregularities formed on their surface to enhance the adhesion of the negative electrode active material. For example, negative electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric structures.

[0094] Negative electrode active materials may include lithium metal, carbon materials capable of reversibly inserting / deintercalating lithium ions, metals or alloys of lithium with these metals, metal composite oxides, materials capable of doping and dedoping lithium, and transition metal oxides.

[0095] Carbon materials capable of reversibly inserting / deintercalating lithium ions can be used without particular restrictions, as long as they are carbon-based anode active materials commonly used in lithium-ion secondary batteries. Typical examples include crystalline carbon, amorphous carbon, or both. Examples of crystalline carbon include graphite, such as irregular, planar, flake, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbides, calcined coke, etc.

[0096] As a metal or an alloy of lithium with these metals, a metal selected from Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of lithium with these metals can be used.

[0097] As a metal composite oxide, at least one of the following substances can be used: PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (where 0≤x≤1), Li x WO2 (where 0≤x≤1) and Sn x Me 1-x Me' y O z (Where Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of groups I, II and III in the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0098] Materials that can be doped and dedoped with lithium include: Si, SiO x (where 0 < x ≤ 2), Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, but not Si), Sn, SnO2, Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, but not Sn), etc., and at least one of these substances can be mixed and used with SiO2. Element Y can be selected from: 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0099] Transition metal oxides can include lithium-containing titanium oxides (LTO), vanadium oxides, lithium vanadium oxides, etc.

[0100] Based on the total weight of the negative electrode mixture layer, the content of the negative electrode active material can be 60 to 99% by weight, preferably 80 to 99% by weight, and more preferably 90 to 98% by weight.

[0101] When using the metal itself without forming a negative electrode mixture layer on the negative electrode, it can be prepared by physically bonding, rolling, or depositing the metal on the metal thin film itself or on the negative electrode current collector. As deposition methods, metal electrodeposition or chemical vapor deposition can be used.

[0102] For example, the metal film itself or the metal bonded / rolled / deposited on the negative electrode current collector may include: one metal selected from lithium (Li), nickel (Ni), tin (Sn), copper (Cu) and indium (In) or an alloy of two of them.

[0103] The membrane can be used without particular restrictions, as long as it is commonly used as a membrane in lithium secondary batteries, and those membranes with excellent electrolyte liquid moisture-holding capacity and low resistance to ion migration of the electrolyte liquid are particularly preferred.

[0104] For example, as a separator, a porous polymer membrane comprising polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer can be used; or a laminated structure of two or more layers thereof. Furthermore, as a separator, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0105] Alternatively, it can be an SRS (Safety Reinforced Separator) diaphragm, as described above, which has the following structure: a coating containing binding materials and inorganic particles is formed on one or both surfaces of a polymer substrate.

[0106] Inorganic particles can form empty spaces between themselves, thus acting as spacers that create micropores while maintaining their physical shape. Because inorganic particles are typically characterized by their unchanged physical properties even at temperatures exceeding 200°C, the resulting organic / inorganic mixture layer exhibits excellent heat resistance.

[0107] There are no particular limitations on the inorganic particles, as long as they are electrochemically stable. That is, there are no particular limitations on the inorganic particles that can be used in this invention if oxidation and / or reduction reactions do not occur within the operating voltage range of the battery during use. In particular, when inorganic particles with ion transport capabilities are used, ion conductivity can be increased and performance enhancement within the electrochemical device can be promoted; therefore, inorganic particles with higher ion conductivity are preferred if possible. Furthermore, when inorganic particles have a high density, not only is it difficult to disperse them during manufacturing, but there is also a problem of weight increase during the manufacture of secondary batteries; therefore, inorganic particles with a lower density are preferred if possible. In addition, inorganic particles with a high dielectric constant can help increase the degree of dissociation of electrolyte salts such as lithium salts in liquid electrolytes, thereby enhancing the ion conductivity of the electrolyte. Finally, inorganic particles with thermal conductivity have excellent endothermic capabilities; therefore, heat is locally concentrated to form a heating point, thereby suppressing phenomena leading to thermal runaway, which is more preferable.

[0108] For the reasons stated above, the inorganic particles may preferably be selected from at least one of the following substances: (a) inorganic particles having a high dielectric constant of 1 or more, 5 or more, preferably 10 or more, (b) inorganic particles having piezoelectricity, (c) inorganic particles having thermal conductivity, and (d) inorganic particles having lithium-ion transport capability.

[0109] Piezoelectric inorganic particles are materials that are non-conductive under normal pressure but exhibit conductive properties due to changes in their internal structure when a certain pressure is applied. They are materials that not only possess high dielectric constant characteristics (such as a dielectric constant above 100), but also have the following function: when a piezoelectric material is subjected to a certain pressure and stretched or compressed, it generates an electric charge, causing one surface to become positively charged and the opposite surface to become negatively charged, thus creating a potential between the two surfaces.

[0110] Examples of piezoelectric inorganic particles include: BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1- x La x Zr 1-y Ti y O3 (PLZT), PB (Mg) 1 / 3 Nb 2 / 3 O3-PbTiO3 (PMN-PT), Hafnium oxide (H f O2) or mixtures thereof, but not limited to these.

[0111] Inorganic particles with lithium-ion transport capability refer to inorganic particles that contain lithium atoms and have the ability to move lithium ions without storing lithium. Due to a defect in the particle structure, inorganic particles with lithium-ion transport capability can transfer and move lithium ions, thus preventing a decrease in lithium mobility and consequently preventing a decrease in battery capacity.

[0112] Examples of inorganic particles capable of lithium-ion transport include: lithium phosphate (Li3PO4), lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y Glass-like substances (0 < x < 4, 0 < y < 13) such as 14Li₂O-9Al₂O₃-38TiO₂-39P₂O₅, lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0<x<4, 0<y<1, 0<z<1, 0<w<5) as Li 3.25 Ge 0.25 P 0.75 S4, Lithium nitride (Li x N y (0 < x < 4, 0 < y < 2) such as Li3N and SiS2 type glasses (Li x Si y S z (0 < x < 3, 0 < y < 2, 0 < z < 4) such as Li3PO4-Li2S-SiS2, P2S5 type glass (Li x P y S z (0 < x < 3, 0 < y < 3, 0 < z < 7) such as LiI-Li2S-P2S5 or mixtures thereof, but not limited thereto.

[0113] In addition, examples of inorganic particles with a dielectric constant of 1 or higher may include, but are not limited to: SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC or mixtures thereof.

[0114] Thermally conductive inorganic particles are materials that provide low thermal resistance but not electrical conductivity and thus have insulating properties, and examples of such particles may be selected from at least one of the following substances: aluminum nitride (AlN), boron nitride (BN), aluminum oxide (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but are not limited thereto.

[0115] When the above-mentioned inorganic particles with high dielectric constant, piezoelectricity, thermal conductivity, and lithium-ion transport capability are used in combination, the synergistic effect of these inorganic particles can be doubled.

[0116] There are no restrictions on the size of the inorganic particles, but to ensure appropriate porosity between the particles, a size in the range of 0.001 to 10 μm is preferred, if possible. When the size is less than 0.001 μm, dispersibility decreases and it becomes difficult to adjust physical properties. When the size is greater than 10 μm, the thickness increases and mechanical properties decrease. Furthermore, due to excessively large pore sizes, the coating cannot function effectively, and the possibility of internal short circuits during battery charging and discharging increases.

[0117] There is no particular limitation on the content of inorganic particles, but based on a mixture of 100% by weight of inorganic particles and binder material, the content is preferably in the range of 1 to 99% by weight, especially 10 to 95% by weight. If the content of inorganic particles is less than 1% by weight, the content of binder material may be too high, resulting in a decrease in pore size and porosity due to the reduced space between inorganic particles, thereby reducing lithium-ion mobility. On the other hand, when the content exceeds 99% by weight, the content of binder material is too low, thus weakening the adhesion between inorganic materials and reducing the mechanical properties of the coating.

[0118] On the other hand, there are no restrictions on the bonding material, as long as it does not cause side reactions with the electrolyte. However, in particular, it is possible to use materials with the lowest possible glass transition temperature (T0). g The bonding material is preferably in the range of -200 to 200°C. This is because it can improve the mechanical properties of the final insulating film.

[0119] Furthermore, while the bonding material does not necessarily have ion conductivity, it is preferable to use a polymer with ion conductivity.

[0120] Therefore, if possible, the bonding material preferably has a high dielectric constant. In fact, since the degree of dissociation of salt in an electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the greater the improvement in the degree of salt dissociation in the electrolyte. The dielectric constant of the polymer can be 1 or higher, specifically in the range of 1.0 to 100 (measurement frequency = 1 kHz), and particularly preferably 10 or higher.

[0121] In addition to the aforementioned functions, the binder material can also exhibit high electrode impregnation (swelling degree) through gelation when immersed in a liquid electrolyte. When the binder material has virtually excellent electrode impregnation properties, the electrolyte injected after battery assembly can permeate into the polymer, and the polymer containing the absorbed electrolyte possesses electrolyte ion conductivity. Therefore, if possible, a solubility parameter of 15 to 45 MPa is preferred. 1 / 2 The polymer, more preferably 15 to 25 MPa 1 / 2 and 30 to 45 MPa 1 / 2 The range. When the solubility parameter is less than 15 MPa. 1 / 2 When and greater than 45MPa 1 / 2 At that time, it becomes difficult to be impregnated (swelled) by the liquid electrolyte typically used in batteries.

[0122] Examples of materials include at least one selected from the following substances: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, and polyvinyl alcohol.

[0123] The total thickness of the separator can range from 5 micrometers to 20 micrometers, specifically 5 micrometers to 15 micrometers, and more specifically 6 micrometers to 13 micrometers. If the separator thickness meets these ranges, short circuits between the positive and negative electrodes can be effectively prevented, while minimizing the resistance of the lithium-ion battery. As a result, the energy density of the lithium-ion battery can be prevented from decreasing, and its lifespan characteristics can be improved.

[0124] The electrolyte can be a lithium non-aqueous electrolyte, and the lithium non-aqueous electrolyte can contain lithium salts and non-aqueous organic solvents.

[0125] In this context, lithium salts are used as a medium for transferring ions within a lithium secondary battery. For example, the lithium salt may contain Li. + It is a cation, and may contain at least one selected from the following substances as an anion: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10- AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - (CF3CF2SO2)2N - (CF3SO2)2N - (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - and SCN - .

[0126] Specifically, lithium salts may include one or a mixture of two or more materials selected from the following: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), but LiN(SO2CF3)2 is preferred for its excellent stability.

[0127] In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without particular restrictions.

[0128] The concentration of lithium salt can be appropriately varied within a generally applicable range, but lithium salt can be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically 1 M to 2.5 M, and more specifically 1 M to 2 M, to achieve the best effect in forming a coating on the electrode surface to prevent corrosion. When the concentration of lithium salt meets the above range, it is sufficient to improve the cycle characteristics of lithium secondary batteries during high-temperature storage, and the viscosity of the electrolyte is appropriate, thereby improving electrolyte impregnation.

[0129] There are no restrictions on non-aqueous organic solvents, as long as they minimize decomposition caused by oxidation reactions during the charging / discharging process of lithium secondary batteries and exhibit the desired properties together with additives. For example, carbonate organic solvents, ether organic solvents, ester organic solvents, etc., can be used alone or in mixtures of two or more of them; specifically, carbonate organic solvents can be used.

[0130] The carbonate organic solvent in the organic solvent can include at least one selected from the following: cyclic carbonate organic solvents and linear carbonate organic solvents. Specifically, the cyclic carbonate organic solvent can include at least one selected from the following: ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it can include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0131] In addition, linear carbonate organic solvents are solvents with low viscosity and low dielectric constant, and may include at least one selected from the following substances: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, more specifically, it may include dimethyl carbonate.

[0132] Ether organic solvents may include, but are not limited to, any one or a mixture of two or more of the following substances: ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0133] Ester organic solvents may include at least one of the following: linear ester organic solvents and cyclic ester organic solvents.

[0134] Specific examples of linear ester organic solvents may include, but are not limited to, any one or a mixture of two or more of the following substances: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

[0135] Specific examples of cyclic ester organic solvents may include, but are not limited to, any one or a mixture of two or more of the following substances: γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

[0136] In ester solvents, cyclic carbonate compounds are preferred because they are high-viscosity organic solvents that readily dissociate lithium salts from the electrolyte due to their high dielectric constant. When cyclic carbonate compounds are mixed with low-viscosity, low-dielectric-constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate in appropriate proportions, a gel-type electrolyte with high conductivity can be prepared, and this gel-type electrolyte is even more preferred.

[0137] In addition, the lithium non-aqueous electrolyte can further contain functional additives, which can prevent the negative electrode from collapsing in a high-power environment, or further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion suppression during high-temperature storage.

[0138] Specifically, as a representative example, functional additives may include at least one functional additive selected from the following substances: sulfonyl lactones, sulfites, sulfones, sulfates, halogen-substituted carbonates, nitriles, cyclic carbonates, phosphates, borates, and lithiums.

[0139] The sulfonyl compounds may include at least one compound selected from the group consisting of 1,3-propanesulfonyl (PS), 1,4-butanesulfonyl, ethanesulfonyl, 1,3-propenesulfonyl (PRS), 1,4-butenesulfonyl, and 1-methyl-1,3-propenesulfonyl, and the content based on the total weight of the gel electrolyte may be from 0.3% by weight to 5% by weight, specifically from 1% by weight to 5% by weight. When the amount of sulfonyl compounds in the gel electrolyte exceeds 5% by weight, an excessively thick layer may form on the electrode surface, leading to increased resistance and decreased output. Furthermore, the increased resistance due to excessive additives may degrade output characteristics.

[0140] The sulfite compounds may include at least one compound selected from the following substances: ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butanediol sulfite, and the content based on the total weight of the gel electrolyte may be less than 3% by weight.

[0141] Sulfone compounds may include at least one compound selected from the following: divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and the content based on the total weight of the gel electrolyte may be less than 3% by weight.

[0142] Sulfate compounds may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS), and the content based on the total weight of the gel electrolyte may be less than 3% by weight.

[0143] Furthermore, the halogen-substituted carbonate compounds may include fluoroethylene carbonate (FEC), and their content based on the total weight of the gel electrolyte may be less than 5% by weight. If the amount of halogen-substituted carbonate compounds in the gel electrolyte exceeds 5% by weight, the battery swelling performance may decrease.

[0144] In addition, nitrile compounds may include at least one compound selected from the following substances: succinic acid nitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyric acid nitrile, valerate nitrile, octanoic acid nitrile, heptanonitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0145] Cyclic carbonate compounds may include vinylene carbonate (VC) or vinylene ethylene carbonate, and their content based on the total weight of the gel electrolyte may be less than 3% by weight. If the content of cyclic carbonate compounds in the gel electrolyte is greater than 3% by weight, the battery swelling suppression performance may be reduced.

[0146] Phosphate compounds may include at least one compound selected from the following: lithium difluoro(bis(oxalate)phosphate), lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(2,2,2-trifluoroethyl) phosphite, and the content based on the total weight of the gel electrolyte may be less than 3% by weight.

[0147] The borate compounds may include lithium oxaloyl difluoroborate, and the content based on the total weight of the gel electrolyte may be less than 3% by weight.

[0148] Lithium salt compounds are compounds that differ from the lithium salts contained in lithium non-aqueous electrolytes. Lithium salt compounds may include at least one compound selected from the following substances: LiPO2F2, LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C2O4)2) and LiBF4), and the content based on the total weight of the lithium non-aqueous electrolyte may be less than 3% by weight.

[0149] Two or more functional additives can be mixed, and their content based on the total weight of the lithium non-aqueous electrolyte can be less than 20% by weight, specifically from 0.1% to 10% by weight. If the content of the functional additive is greater than 20% by weight, there is a possibility that excessive side reactions may occur in the lithium non-aqueous electrolyte during battery charge and discharge. In particular, it cannot be fully decomposed at high temperatures and may exist as an unreacted material or in a precipitated state in the lithium non-aqueous electrolyte at room temperature. Therefore, side reactions may occur, resulting in a decrease in the lifespan or resistivity characteristics of the lithium metal battery.

[0150] In the following description, a lithium secondary battery according to one embodiment of the present invention will be explained with reference to examples, thereby demonstrating that it exhibits improved performance.

[0151] <Example 1> (Single ball milling - sintering - jaw crushing - secondary ball milling)

[0152] Under an Ar atmosphere, the active material raw materials LiOH, MnO2 and TiO2 are mixed in a molar ratio of 3:1:1 according to the stoichiometric ratio, and sucrose is added to improve conductivity, so that the content in the final positive electrode active material is 8% by weight, thereby preparing a mixed powder.

[0153] The mixed powder was prepared by the following steps: the active material raw materials and sucrose were placed in a zirconia container using bimodal zirconia balls (10 mm, 5 mm, large diameter / small diameter weight ratio = 0.1, 1.5 times the weight of the mixed powder), purged with Ar for 1 hour, ground at 350 rpm for 1 hour, allowed to stand for 30 minutes, and the grinding cycle was repeated 12 times.

[0154] Subsequently, the mixed powder, in which the above-described mixture was prepared, was heat-treated in a tube furnace under an Ar atmosphere. The heat treatment was carried out at 600°C for 3 hours at a heating rate of 5°C / min, followed by heat treatment at 900°C for 12 hours.

[0155] When calcination is completed in this manner, a lithium compound (Li) with a carbon coating is obtained. 1.2 Ti 0.4Mn 0.4 O2).

[0156] The lithium compound was subjected to jaw crushing (Retsch, BB50, 600 to 1,200 rpm, blade spacing of 2 to 30 mm, 4 cycles per process).

[0157] After jaw crushing, the lithium compound was placed again in a zirconia container using bimodal zirconia balls (10 mm, 5 mm, large diameter / small diameter weight ratio = 0.1, 1.5 times the weight of the mixed powder) and purged with Ar for 1 hour. It was then ball-milled twice by grinding at 300 rpm for 6 hours followed by a 30-minute resting period. This yielded the final lithium compound.

[0158] <Example 2>

[0159] After completing the calcination in Example 1, the lithium compound (Li) with the carbon coating was first subjected to... 1.2 Ti 0.4 Mn 0.4 O2) was used for a second ball milling process as described in Example 1. After the second ball milling was completed, jaw crushing as described in Example 1 was performed to obtain the final lithium compound.

[0160] <Example 3>

[0161] The final lithium compound was obtained in the same manner as in Example 2, except that the number of jaw crushing operations was set to eight (twice for each process).

[0162] <Example 4>

[0163] The final lithium compound was obtained in the same manner as in Example 1, except that in Example 1, ball milling was performed once at 600 rpm.

[0164] <Example 5>

[0165] The final lithium compound was obtained in the same manner as in Example 1, except that in Example 1, the compound was heat-treated at 400°C for 3 hours at a heating rate of 5°C / min, and then heat-treated at 600°C for 12 hours.

[0166] <Example 6>

[0167] The final lithium compound was obtained in the same manner as in Example 1, except that in Example 1, a second ball milling was performed at 600 rpm.

[0168] <Comparative Example 1>

[0169] In Example 1, neither jaw crushing nor secondary grinding was performed, and the final lithium compound obtained after calcination was used as the final lithium compound.

[0170] <Comparative Example 2>

[0171] In Example 2, the lithium compound obtained after only two ball milling processes was used as the final lithium compound.

[0172] <Experimental Example 1>

[0173] The PSD of the final lithium compound powders obtained in Examples 1 to 3 and Comparative Examples 1 to 2 was measured using a Malvern Mastersizer 3000 PSD particle size analyzer as a powder morphology analyzer, and the results are shown in Table 1 below.

[0174] [Table 1]

[0175] Referring to Table 1, it can be confirmed that the positive electrode active material according to the present invention has a larger D90 / D10 value.

[0176] <Experimental Example 2>

[0177] The lithium compound, conductive material (CNT), and binder prepared in Examples 1 to 6 and Comparative Examples 1 and 2 as positive electrode active materials were mixed in NMP solvent at a weight ratio of 85:5:10 to prepare a positive electrode slurry. This positive electrode slurry was coated onto a surface of an aluminum current collector (thickness: 12 μm) with a thickness of 60 μm, and then dried (130°C) and rolled (porosity: 30% by volume) to manufacture a positive electrode.

[0178] A lithium metal foil is used as the negative electrode, and a separator (polyethylene) is inserted between the positive and negative electrodes to prepare an electrode assembly. An electrolyte prepared by dissolving LiPF6 at 1.0 M in a non-aqueous organic solvent with a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 50:50 (volume ratio) is injected into the electrode assembly to manufacture a half cell.

[0179] At 25°C, the half-cell was charged with a constant current of 0.1 C until the voltage reached 4.65 V, and then discharged with a constant current of 0.1 C until the voltage reached 2.0 V. The initial charge capacity and initial discharge capacity obtained are shown in Table 2 below, and the ratio of the initial discharge capacity to the initial charge capacity is shown in Table 2 below as the initial efficiency.

[0180] In addition, the battery capacity was measured while repeating 50 charge / discharge cycles at 0.1 C in the range of 2.5 to 4.45 V at 45°C. The capacity ratio of the 50th cycle to the 1st cycle is shown in Table 2 below as the capacity retention rate.

[0181] [Table 2]

[0182] Referring to Table 2, it can be confirmed that the lithium secondary battery using the positive electrode active material of the present invention exhibits a better capacity retention rate than the positive electrode active material of the comparative example.

[0183] On the other hand, referring to Examples 1 and 4 to 6, it can be confirmed that when the rpm of the first and second ball milling is too high, the capacity retention rate may decrease, and even when the calcination temperature is low, the capacity retention rate is also partially reduced.

[0184] This is because when the rpm is too high, the carbon coating may partially peel off, and when the calcination temperature is too low, the battery may not be fully calcined, which may reduce the structural stability of the positive electrode active material, thus resulting in some loss in capacity retention.

[0185] <Experimental Example 3>

[0186] The initial resistance and resistance increase rate of the half-cell manufactured in Experiment Example 2 were measured, and the results are shown in Table 3.

[0187] Specifically, the half-cell was charged at 25°C with a constant current of 1 C until the voltage reached 4.4 V, then left to stand for 10 seconds, and discharged with a constant current of 1 C until the voltage reached 2.5 V.

[0188] The initial voltage was measured using the PNE-0506 charge / discharge device (manufacturer: PNE SOLUTION, 5 V, 6 A), and the resistance value was calculated from it.

[0189] Next, the lithium secondary battery, which had been initially charged and discharged, was charged at a constant current of 1 C until it reached 4.4 V, stored at 60°C for 6 weeks (100% SOC), and then discharged again at 2.5 C for 10 seconds at 50% SOC. The voltage after high-temperature storage was then measured.

[0190] The voltage was measured using a PNE-0506 charge / discharge device (manufacturer: PNE SOLUTION, 5 V, 6 A). The resistance value was calculated from the voltage after high-temperature storage.

[0191] Substitute the initial resistance value and the resistance value after high-temperature storage into the following mathematical formula 1 to calculate the resistance increase rate.

[0192] [Mathematical Expression 1]

[0193] The rate of increase in resistivity after high-temperature storage (%) = [(resistance after 6 weeks of high-temperature storage / resistance before high-temperature storage) × 100)] – 100

[0194] [Table 3]

[0195] Referring to Table 3, it can be confirmed that the lithium secondary battery using the positive electrode active material of the present invention exhibits superior resistance characteristics compared to the positive electrode active material of the comparative example.

[0196] On the other hand, referring to Examples 1 and 4 to 6, it can be confirmed that when the rpm of the primary and secondary ball milling is too high, or even when the calcination temperature is low, the rate of increase in resistivity due to high-temperature storage is also high.

[0197] This is because when the rpm is too high, part of the carbon coating may peel off, and when the calcination temperature is too low, the calcination may be insufficient, which may reduce the structural stability of the positive electrode active material and lead to a partial increase in resistance.

[0198] Based on the above disclosure, those skilled in the art can make various applications and modifications without departing from the spirit and scope of this invention.

[0199] [Industrial Applicability]

[0200] According to one embodiment of the present invention, the positive electrode active material for lithium secondary batteries has the effect of improving overall electrochemical performance such as capacity, lifetime and output characteristics through particle size optimization.

Claims

1. A positive electrode active material for lithium secondary batteries, the positive electrode active material comprising: A lithium compound represented by the following chemical formula 1 and a carbon coating formed on the surface of the particles of the lithium compound. The lithium compound described therein has the form of secondary particles, wherein the secondary particles have a structure in which the primary particles are aggregated together. The average diameter (D50) of the secondary particles is 0.2 μm to 10 μm. The average diameter (D50) of the primary particles is between 10 nm and 300 nm, and The ratio of the average diameter (D90) to the average diameter (D10) of the secondary particles is between 15 and 80. [Chemical Formula 1] The 1+a M1 b M2 c O 2-d X d in, In chemical formula 1, M1 is selected from one or more of Ni, V, Mn, Mo, Cr, and Fe, and M2 is selected from one or more of Ti, Zr, Nb, Mo, Ta, and W. 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.05≤(1+a) / (b+c)≤1.5, 0≤d≤0.2, and X is a halogen element.

2. The positive electrode active material according to claim 1, In chemical formula 1, b + c = 0.

8.

3. The positive electrode active material according to claim 1, The carbon coating content is from 1 part to 10 parts by weight, based on 100 parts by weight of the lithium compound.

4. A method for preparing the positive electrode active material for lithium secondary batteries according to claim 1, the method comprising: The lithium compound is synthesized based on a mixture containing an active material precursor and a carbon precursor. The synthesis process includes primary ball milling, calcination, secondary ball milling, and jaw crushing.

5. The method for preparing the positive electrode active material according to claim 4, The synthesis is carried out in the order of primary ball milling, calcination, jaw crushing, and secondary ball milling.

6. The method for preparing the positive electrode active material according to claim 4, The synthesis is carried out in the order of primary ball milling, calcination, secondary ball milling, and jaw crushing.

7. The method for preparing the positive electrode active material according to any one of claims 4 to 6, The ball milling is carried out under an inactive atmosphere.

8. The method for preparing the positive electrode active material according to any one of claims 4 to 6, The ball milling process is performed at 100 rpm to 500 rpm, and The secondary ball milling was performed at 100 rpm to 500 rpm.

9. The method for preparing the positive electrode active material according to any one of claims 4 to 6, The ball milling process is repeated once or twice, consisting of grinding for 3 to 8 hours followed by resting for 5 to 120 minutes. The secondary ball milling process is repeated once or twice by grinding for 1 to 8 hours and then letting it stand for 5 to 120 minutes.

10. The method for preparing the positive electrode active material according to any one of claims 4 to 6, The jaw crusher is performed once or twice.

11. The method for preparing the positive electrode active material according to any one of claims 4 to 6, The jaw crushing is performed at 600 rpm to 1200 rpm.

12. The method for preparing the positive electrode active material according to claim 4, The calcination is carried out in an inactive atmosphere at a temperature ranging from 650°C to 1200°C for 6 to 30 hours.

13. The method for preparing the positive electrode active material according to claim 4, The active material precursors are M1 source, M2 source and lithium source.

14. The method for preparing the positive electrode active material according to claim 4, The carbon precursor is selected from one or more of citric acid and sucrose.

15. A positive electrode for a lithium secondary battery, said positive electrode having a positive electrode mixture layer formed on one or both surfaces of the entire positive electrode. The positive electrode mixture layer comprises the positive electrode active material, binder, and conductive material as described in claim 1.

16. The positive electrode according to claim 15, The conductive material mentioned therein is a dot-shaped conductive material.

17. A lithium secondary battery comprising the positive electrode as described in claim 15.

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