Cathode for lithium secondary battery, manufacturing method therefor, and lithium secondary battery comprising same

Abstract

According to an embodiment of the present invention, there are provided a cathode for a lithium secondary battery, a manufacturing method therefor, and a lithium secondary battery comprising same. The cathode comprises a cathode mixture layer formed on one side or both sides of a cathode current collector, wherein the cathode mixture layer comprises a cathode active material and a mixed conductive material, the cathode active material comprises a carbon coating layer on the surface thereof and a lithium compound represented by chemical formula 1, and the mixed conductive material comprises a first conductive material having a specific surface area (BET) of 50 m2 / g to 70 m2 / g and a second conductive material having a BET of 100 m2 / g to 300 m2 / . [Chemical formula 1] Li1+aTibMncO2-dXd In chemical formula 1, 0.1≤a≤0.5, 0.3≤b≤0.5, 0.3≤c≤0.5, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2, and X is a halogen element.

Description

Anode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery comprising the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0100441, filed July 29, 2024, and Korean Patent Application No. 10-2025-0102536, filed July 28, 2025, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a positive electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

[0004] Due to the rapid increase in fossil fuel use, the demand for alternative and clean energy is increasing, and as part of this, the most actively researched field is the field of power generation and storage using electrochemistry.

[0005] A representative example of an electrochemical device that currently utilizes this type of electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0006] Recently, with the increase in technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has been rapidly increasing. Among them, much research has been conducted on lithium secondary batteries that exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, and they have also been commercialized and widely used.

[0007] Furthermore, with growing concern about environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles as alternatives to fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution. While nickel-metal hydride secondary batteries are primarily used as power sources for these electric and hybrid electric vehicles, research into the use of lithium secondary batteries, which boast high energy density and discharge voltage, is actively underway, and some are nearing commercialization.

[0008] Typically, lithium secondary batteries are structured to have an electrode assembly comprising a positive electrode, a negative electrode, and a porous separator, each impregnated with a non-aqueous electrolyte. Furthermore, the positive electrode is typically manufactured by coating a positive electrode mixture containing a positive electrode active material onto aluminum foil, while the negative electrode is typically manufactured by coating a negative electrode mixture containing a negative electrode active material onto 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, as lithium secondary batteries are being used in various industrial fields recently, high capacity and high rate characteristics are being studied as important performances, and the development of positive electrode active materials that can exhibit these characteristics is actively underway.

[0011] A material that has recently been in the spotlight as a positive electrode active material is DRX (cation-disordered rocksalt transition metal oxide), which is a high-capacity material that can express additional capacity through not only cation oxidation / reduction but also anion oxidation / reduction reaction (oxygen redox).

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

[0013] Therefore, there is an urgent need to develop a technology that can solve these problems and provide secondary battery performance such as high capacity, high rate, and excellent lifespan characteristics.

[0014] The present invention aims to provide a positive electrode having improved conductivity and thus capable of improving capacity, lifespan characteristics, and output characteristics, a method for manufacturing the same, and a lithium secondary battery including the same.

[0015] According to one embodiment of the present invention,

[0016] A positive electrode for a lithium secondary battery in which a positive electrode composite layer is formed on one or both sides of a positive electrode collector,

[0017] The above positive electrode composite layer includes a positive electrode active material and a conductive material mixture,

[0018] The above positive electrode active material has a carbon coating layer formed on the surface and includes a lithium compound represented by the following chemical formula 1,

[0019] The above-mentioned mixture of the challenge materials has a specific surface area (BET) of 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / An anode including a second challenger is provided.

[0020] [Chemical Formula 1]

[0021] Li 1+a Ti b Mn c O 2-d X d

[0022] In the above chemical formula 1,

[0023] 0.1≤a≤0.5, 0.3≤b≤0.5, 0.3≤c≤0.5, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2,

[0024] X is a halogen element.

[0025] The lithium compound is in the form of secondary particles, and the average diameter (D50) of the secondary particles may be 0.5 to 1.5 micrometers, and the average diameter (D50) of the primary particles forming the secondary particles may be 10 to 100 nanometers.

[0026] The carbon coating layer may be included in an amount of 1 to 10 parts by weight per 100 parts by weight of the lithium compound.

[0027] Meanwhile, the first challenge material has a specific surface area (BET) of 60 m 2 / g to 70 m 2 / g, and the second challenge material has a specific surface area (BET) of 150 m 2 / g to 250 m 2 / g may be.

[0028] Here, both the first conductive material and the second conductive material may be point-shaped conductive materials.

[0029] The conductive material mixture may include the first conductive material and the second conductive material in a weight ratio of 90:10 to 30:70, and the conductive material mixture may be included in an amount of 1 to 10 wt% based on the total weight of the positive electrode mixture layer.

[0030] The conductive mixture can coat the surface of the positive electrode active material at a rate of 50 wt% or more based on the total weight of the conductive mixture.

[0031] Specifically, on the surface of the positive electrode active material, the first conductive material among the conductive material mixture may be positioned on the inner side of the surface, and the second conductive material may be formed on the surface of the first conductive material and in a portion where the first conductive material is not positioned.

[0032] Meanwhile, the above-mentioned positive electrode composite layer may further include a binder.

[0033] According to another embodiment of the present invention, a method for manufacturing a positive electrode for a lithium secondary battery is provided,

[0034] The active material precursor and the carbon precursor are first ball milled and calcined, and the calcined material and the specific surface area (BET) are 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / The slurry is prepared by dispersing the mixed powder obtained by secondary ball milling of the conductive mixture containing the second conductive agent under a solvent,

[0035] A method for manufacturing a cathode is provided, which comprises applying, drying, and rolling the above slurry on one or both sides of a cathode current collector.

[0036] The above active material precursor may be a lithium source, a manganese source, and a titanium source, and the carbon precursor may be at least one selected from the group consisting of citric acid and sucrose.

[0037] The above conductive material mixture may be a mixture of the first conductive material and the second conductive material in a weight ratio of 90:10 to 30:70.

[0038] In another embodiment according to the present invention, a lithium secondary battery including the positive electrode is provided.

[0039] Figure 1 is an SEM photograph according to Experimental Example 1.

[0040] Figure 2 is a capacity comparison graph according to Experimental Example 2.

[0041] Hereinafter, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense to those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0043] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0044] Meanwhile, the terms "consists of" and / or "consisting of" used in the specification mean that other components are not included in amounts greater than trace amounts, i.e., impurities, other than the components mentioned.

[0045] In this specification, the “specific surface area” is measured by the BET method, and can be specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan.

[0046]

[0047] According to one embodiment of the present invention,

[0048] A positive electrode for a lithium secondary battery in which a positive electrode composite layer is formed on one or both sides of a positive electrode collector,

[0049] The above positive electrode composite layer includes a positive electrode active material and a conductive material mixture,

[0050] The above positive electrode active material has a carbon coating layer formed on the surface and contains a lithium compound represented by the following chemical formula 1 as the positive electrode active material,

[0051] The above-mentioned mixture of the challenge materials has a specific surface area (BET) of 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / A positive electrode for a lithium secondary battery including a second conductive material is provided.

[0052] [Chemical Formula 1]

[0053] Li 1+a Ti b Mn c O 2-d X d

[0054] In the above chemical formula 1,

[0055] 0.1≤a≤0.5, 0.3≤b≤0.5, 0.3≤c≤0.5, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2,

[0056] X is a halogen element.

[0057]

[0058] positive current collector

[0059] The positive electrode current collector is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0060] The above-mentioned positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material layer. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0061]

[0062] anode composite layer

[0063] The above positive electrode composite layer may include a positive electrode active material and a conductive material mixture.

[0064] The above positive electrode active material is,

[0065] A carbon coating layer is formed on the surface, and may include a lithium compound represented by the following chemical formula 1.

[0066] [Chemical Formula 1]

[0067] Li 1+a Ti b Mn c O 2-d X d

[0068] In the above chemical formula 1,

[0069] 0.1≤a≤0.5, 0.3≤b≤0.5, 0.3≤c≤0.5, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2,

[0070] X is a halogen element.

[0071] Here, the lithium compound represented by the above chemical formula 1 may be DRX, and more specifically, in the above chemical formula 1, b+c=0.8.

[0072] Additionally, 0.2≤a≤0.4, 0.3≤b≤0.5, 0.3≤c≤0.5 may be satisfied.

[0073] In most detail, the lithium compound is Li 1.2 Ti 0.4 Mn 0.4 It could be O2.

[0074] These lithium compounds may have the form of secondary particles having a structure in which primary particles are aggregated. Here, the average diameter (D50) of the secondary particles may be 0.5 to 1.5 micrometers, and specifically, 0.7 to 1.2 micrometers.

[0075] Additionally, the average diameter (D50) of the primary particles forming the secondary particles may be 10 to 100 nanometers, specifically 20 to 70 nanometers, and more specifically 30 to 60 nanometers.

[0076] The above average diameter D50 is the diameter at the 50% point of the cumulative particle volume distribution according to particle size. The D50 can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern Mastersizer 3000), and when the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle diameter at the point where it becomes 50% of the cumulative particle volume distribution according to the particle size in the measuring device, the D50 can be measured.

[0077] The above lithium compound can be used in a form in which a carbon coating layer is formed on its surface to improve conductivity.

[0078] At this time, the carbon coating layer may be included in an amount of 1 to 10 parts by weight relative to 100 parts by weight of the lithium compound. Specifically, the carbon coating layer may be included in an amount of 1 to 7 parts by weight or 1 to 5 parts by weight relative to 100 parts by weight of the lithium compound.

[0079] Beyond the above range, if the content of the carbon coating layer is too small, it is not desirable to form a sufficient conductive network, and if it is too large, there is a problem in that agglomeration occurs due to the phenomenon of them clumping together, making even coating impossible.

[0080] Meanwhile, in addition to the lithium compound, the cathode active material may further include a compound capable of reversible intercalation and deintercalation of lithium, for example, a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum, specifically, a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (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(here, -0.5≤x'''≤0.5, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, Li 1+x'''' Co 1-Y2 Mn Y2 O2(here, -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 (wherein, -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) oxide (e.g., Li 1+a3 (Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and a3, p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, -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 (e.g., Li 1+a4 Fe 1-p3 M p3 (PO 4-b4 )X b4 (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, and -0.5≤a4≤0.5, 0≤p3≤0.5, 0≤b4≤0.1) and the like, and any one or two or more compounds thereof may be included.

[0081] Of course, the lithium compound according to the present invention may be included as a main material, and based on the total amount of the positive electrode active material, the lithium compound according to the present invention may be included in an amount of 80 wt% or more, specifically 90 wt% or more and 100 wt% or less, and only the positive electrode active material may be included in an amount of 100 wt%.

[0082] Meanwhile, the carbon coating layer was difficult to coat evenly due to the nature of the carbon, which tended to clump together rather than being evenly distributed, and thus there was a problem in that an excellent conductive network could not be formed simply by forming the carbon coating layer.

[0083] Accordingly, according to the present invention, in addition to the carbon coating layer, a conductive material may be further included to increase the conductivity of the active material, and at this time, the conductive material may include a mixture of two types of conductive materials having different specific surface areas.

[0084] Specifically, the above-mentioned conductive mixture has a specific surface area (BET) of 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / may include a second conductive agent, and in detail, the first conductive agent has a specific surface area (BET) of 60 m 2 / g to 70 m 2 / g, and the second challenge material has a specific surface area (BET) of 150 m 2 / g to 250 m 2 / g, and more specifically, the first challenge material has a specific surface area (BET) of 60 m 2 / g to 70 m 2 / g, and the second challenge material has a specific surface area (BET) of 200 m 2 / g to 250 m 2 / g may be.

[0085] The above first conductive material has a small specific surface area (BET) and an average diameter (D50) of 0.5 to 2 micrometers, and more specifically, 0.5 to 1.2 micrometers.

[0086] The above first conductive agent has a small specific surface area and a large size, so particle aggregation does not occur, and thus can play a role in improving conductivity between the positive electrode active material particles.

[0087] However, the first conductive material does not sufficiently cover the surface of the positive electrode active material, so that resistance at the interface may be improved, and accordingly, a sufficient conductivity improvement effect cannot be obtained with the first conductive material alone.

[0088] Therefore, according to the present invention, a second conductive material having a larger specific surface area may be additionally included as the conductive material.

[0089] The second conductive material has a large surface area and a small size, so it can be densely positioned on the surface of the positive electrode active material, and can contribute to improving conductivity in the interstitial space that is difficult to cover with the first conductive material.

[0090] The above second challenge material may specifically have an average diameter (D50) of 2 to 10 micrometers, and more specifically, 2 to 5 micrometers.

[0091] The first conductive material and the second conductive material may be, for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers such as carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc.

[0092] Here, the first conductive material may be a point-shaped conductive material, and the second conductive material may be a linear conductive material.

[0093] Specifically, the first conductive material may be carbon black, and more specifically, may be Super-P among the carbon blacks. The second conductive material may be acetylene black or carbon nanotubes, specifically.

[0094] The first conductive material and the second conductive material may be included in a weight ratio of 90:10 to 30:70, and specifically, the first conductive material and the second conductive material may be included in a weight ratio of 80:20 to 30:70, and more specifically, 80:20 to 60:40.

[0095] Beyond the above range, if the content of the first conductive agent is too high, the contact area between the positive electrode active material and the conductive agent mixture decreases, resulting in increased resistance. If the content of the second conductive agent is too high, agglomeration of the second conductive agent occurs frequently, which also fails to properly coat the positive electrode active material, resulting in a problem of reduced conductivity.

[0096] The above-described conductive mixture may be included in an amount of 1 to 10 wt%, specifically 1 to 8 wt%, and more specifically 1 to 5 wt%, based on the total weight of the positive electrode composite layer.

[0097] At this time, the conductive material mixture may be included in a form that coats the surface of the positive electrode active material in an amount of 50 wt% or more, specifically 60 wt% to 90 wt%, and more specifically 60 wt% to 80 wt% based on the total weight of the conductive material mixture.

[0098] More specifically, the first conductive material among the conductive material mixture may be coated on the surface of the positive electrode active material in a manner such that the first conductive material is positioned on the surface of the positive electrode active material, and the second conductive material is formed on a portion where the first conductive material is not positioned and on the surface of the first conductive material.

[0099] Therefore, the positive electrode active material according to the present invention can form a dense conductive network through the conductive material mixture including two types of conductive materials without any empty space on the surface of the positive electrode active material, thereby exhibiting better conductivity and reducing resistance, thereby improving the overall performance of a lithium secondary battery including the positive electrode active material.

[0100] Meanwhile, the above-mentioned positive electrode composite layer may further include a binder.

[0101] The above binder is a component that assists in bonding between the positive electrode active material, the conductive material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0102] Typically, the binder may be included in an amount of 0.5 to 20 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode composite layer.

[0103] In addition, the positive electrode composite layer may further include other additives, and as the other additives, for example, a filler as a component that suppresses expansion may be further included. The filler is not particularly limited as long as it can suppress expansion of the electrode without causing chemical changes in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0104]

[0105] Method for manufacturing anode

[0106] The positive electrode for the lithium secondary battery is manufactured by first preparing a slurry containing a positive electrode active material, and then applying, drying, and rolling the slurry to one or both sides of the positive electrode current collector.

[0107] At this time, the slurry can be manufactured by first manufacturing the positive electrode active material and then mixing the positive electrode active material and conductive material mixture together.

[0108] More specifically, at least a portion of the conductive material may be first mixed with the positive electrode active material through dry mixing, more specifically high shear dry mixing, and then the remaining conductive material mixture may be simply mixed under a solvent together with other components of the positive electrode active material layer.

[0109] Meanwhile, the method for producing a lithium compound as the positive electrode active material is not limited and may be produced by a solid-state method, but specifically, may be produced by calcining a mixture including an active material precursor and a carbon precursor.

[0110] At this time, the mixture may further include additives such as surface modifiers, if necessary.

[0111] Here, the active material precursor is a composition material forming a lithium compound represented by the chemical formula 1, and may be a lithium source, a manganese source, and a titanium source.

[0112] The above lithium source may be one or more substances selected from lithium carbonate, lithium hydroxide and lithium phosphate, and more specifically, may be lithium hydroxide (LiOH).

[0113] The above manganese source may be one or more substances selected from manganese sulfate, manganese nitrate, manganese carbonate, manganese acetate, manganese chloride, manganese hydroxide, manganese oxide, and manganese phosphate, and more specifically, manganese oxide (MnO2).

[0114] The above titanium source may be one or more substances selected from titanium sulfate, titanium nitrate, titanium carbonate, titanium acetate, titanium chloride, titanium hydroxide, titanium oxide, and titanium phosphate, and more specifically, may be titanium oxide (TiO2).

[0115] Additionally, in order to improve the conductivity of these active materials, the carbon precursor is added together from the synthesis stage of the lithium compound.

[0116] At this time, the carbon precursor may be one or more substances selected from citric acid, glucose, sucrose, graphite, carbon nanotubes, and carbon black, and more specifically, may be one or more substances selected from the group consisting of citric acid and sucrose.

[0117] These precursors can be mixed and then calcined, wherein the mixing can be performed by ball milling, and the ball milling mixing can be specifically dry mixing, and more specifically, can be performed in the form of mixing and milling the precursors together with zirconia balls or the like.

[0118] After sufficient mixing is achieved, the mixture can be calcined to synthesize a lithium compound.

[0119] At this time, the firing can be carried out in an inert atmosphere at a temperature in the range of 650 to 1200°C for 6 to 30 hours, or the firing can be carried out in two stages, for example, the first stage can be carried out in an inert atmosphere at a temperature in the range of 500 to 800°C for 1 to 6 hours, and the second stage can be carried out in an inert atmosphere at a temperature in the range of 800 to 1200°C for 6 to 20 hours.

[0120] A lithium compound manufactured by a solid-state method in this way can be obtained in the form of a lithium compound represented by the chemical formula 1 containing lithium, manganese, and titanium, with carbon coated on the surface.

[0121] In this way, after manufacturing a lithium compound, a slurry containing the compound as a positive electrode active material can be manufactured.

[0122] At this time, the positive electrode active material and the conductive material mixture can be directly mixed under a solvent, but more specifically, in order to further improve the conductive network of the positive electrode active material according to the present invention, it is more preferable that the conductive material mixture is present in a form coated on the surface of the positive electrode active material.

[0123] Therefore, in this case, the prepared positive electrode active material and the conductive material mixture including the first conductive material and the second conductive material are first mixed by secondary ball milling, and the resulting mixed powder is dispersed in a solvent to prepare a slurry.

[0124] The above conductive material mixture may include the first conductive material and the second conductive material in a weight ratio of 90:10 to 30:70 as described above, and specifically, the first conductive material and the second conductive material may be in a weight ratio of 80:20 to 30:70, and more specifically, 80:20 to 60:40.

[0125] Additionally, the above secondary ball milling may also be dry mixing, and more specifically, high-shear dry mixing.

[0126] Through this secondary ball milling, the conductive mixture can be coated in a layer on the surface of the positive electrode active material, thereby exhibiting further improved conductivity.

[0127] In addition, the amount of the conductive material mixture introduced during the secondary ball milling may be 50 wt% or more of the amount of the conductive material mixture included in the final positive electrode mixture layer, specifically 60 wt% to 90 wt%, and more specifically 60 wt% to 80 wt%.

[0128] If the entire amount of the conductive material mixture is not added during the second ball milling, the remaining conductive material mixture may be added when the mixed powder is dispersed under a solvent.

[0129] Furthermore, when dispersing the mixed powder under the solvent, the binder and other additives may be added together.

[0130]

[0131] lithium secondary battery

[0132] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

[0133] The above lithium secondary battery has a structure in which an electrode assembly including the positive electrode, negative electrode, and separator is built into a secondary battery case together with an electrolyte.

[0134] Here, the negative electrode has a structure in which a negative electrode composite layer including a negative electrode active material is formed on one or both sides of a negative electrode current collector, and the negative electrode composite layer may further include electrode materials such as a conductive material and a binder as described in the positive electrode in addition to the negative electrode active materials.

[0135] The negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes 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., aluminum-cadmium alloy, etc. can be used.

[0136] The above-mentioned negative electrode collector may typically have a thickness of 3 μm to 500 μm, and like the positive electrode collector, it may be provided with fine irregularities on the surface of the negative electrode collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0137] The above negative active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0138] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0139] As the above metal or an alloy of these metals with lithium, a metal selected from the group consisting of 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 these metals with lithium may be used.

[0140] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, LixFe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0141] Materials capable of doping and dedoping the above lithium include Si, SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 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 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0142] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0143] The negative electrode active material may be included in an amount of 60 to 99 wt%, preferably 80 to 99 wt%, and more preferably 90 to 98 wt%, based on the total weight of the negative electrode composite layer.

[0144] When the metal itself is used without including a cathode composite layer in the above cathode, it can be manufactured by physically bonding, rolling, or depositing the metal onto the metal thin film itself or the cathode current collector. The deposition method can use an electrical deposition method or a chemical vapor deposition method.

[0145] For example, the metal to be bonded / rolled / deposited on the metal thin film itself or the negative electrode current collector may include one metal selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two metals.

[0146] The above separator can be used without any special restrictions as long as it is commonly used as a separator in a lithium secondary battery, and it is particularly preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity.

[0147] For example, as a separator, a porous polymer film including a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can also be used as a separator.

[0148] Alternatively, it may be a Safety Reinforced Separator (SRS) membrane having a coating layer including a binder and inorganic particles formed on one or both sides of a polymer substrate as described above.

[0149] The above-mentioned inorganic particles enable the formation of voids between the inorganic particles, thereby forming micropores, and also serve as a type of spacer that maintains the physical shape. Furthermore, since the inorganic particles generally have a property of not changing their physical properties even at high temperatures of 200°C or higher, the formed organic-inorganic mixed layer possesses excellent heat resistance.

[0150] The inorganic particles described above are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the battery to which they are applied. In particular, when using inorganic particles with ion transfer capabilities, it is preferable to use particles with as high an ion conductivity as possible, as this can enhance performance by increasing the ionic conductivity within the electrochemical device. In addition, when the inorganic particles have a high density, it is difficult to disperse them during manufacturing, and there is also the problem of weight increase during the manufacturing of the secondary battery, so it is preferable to use particles with as low a density as possible. In addition, when using inorganic particles with a high dielectric constant, they can contribute to an increase in the dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte. Finally, inorganic particles with thermal conductivity are even more preferable, as they have excellent heat absorption capabilities, which prevents heat from being concentrated locally, forming a heating point and leading to thermal runaway.

[0151] For the reasons mentioned above, the inorganic particles are preferably at least one selected from the group consisting of (a) high-dielectric constant inorganic particles having a dielectric constant of 1 or more, 5 or more, preferably 10 or more, (b) inorganic particles having piezoelectricity, (c) thermally conductive inorganic particles, and (d) inorganic particles having lithium ion transfer capability.

[0152] The above piezoelectric inorganic particles are non-conductive at normal pressure, but when a certain pressure is applied, they are materials that have the property of conducting electricity due to a change in their internal structure. In addition, when a certain pressure is applied and they are stretched or compressed, they generate electric charges, so that one side is charged positively and the other side is charged negatively, and they are materials that have the function of generating a potential difference between the two sides.

[0153] Examples of the above piezoelectric inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT) hafnia (H f O2) or mixtures thereof, but are not limited thereto.

[0154] The above inorganic particles having lithium ion transfer capability refer to inorganic particles that contain lithium elements but do not store lithium and have the function of transferring lithium ions. Since the inorganic particles having lithium ion transfer capability can transfer and move lithium ions due to a type of defect existing within the particle structure, they can prevent a decrease in lithium mobility and thus a decrease in battery capacity.

[0155] Examples of inorganic particles having the above lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O5등과 같은 (LiAlTiP)x O y Series glass (0 <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w , 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS2등과 같은 SiS2계열 glass (Li x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass (Li x P y S z , 0 <x<3, 0<y<3, 0<z<7), 또는 이들의 혼합물 등이 있으나, 이에 한정되는 것은 아니다.

[0156] Additionally, examples of inorganic particles having a dielectric constant of 1 or greater include, but are not limited to, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, or mixtures thereof.

[0157] The above thermally conductive inorganic particles are materials having insulating properties by providing low thermal resistance but no electrical conductivity, and may be, for example, at least one selected from the group consisting of aluminum nitride (AlN), boron nitride (BN), alumina (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but are not limited thereto.

[0158] When the aforementioned high-k inorganic particles, piezoelectric inorganic particles, thermally conductive inorganic particles, and inorganic particles having lithium ion transfer capability are mixed, their synergistic effect can be doubled.

[0159] The size of the above-mentioned inorganic particles is not limited, but it is preferably in the range of 0.001 to 10 ㎛ to ensure an appropriate porosity between the inorganic particles. If it is less than 0.001 ㎛, dispersibility is reduced, making it difficult to control physical properties. If it exceeds 10 ㎛, the thickness increases, resulting in a deterioration in mechanical properties. In addition, due to the excessively large pore size, the coating layer cannot sufficiently function, increasing the probability of an internal short circuit occurring during battery charging and discharging.

[0160] The content of the above-mentioned inorganic particles is not particularly limited, but is preferably in the range of 1 to 99 wt%, and particularly 10 to 95 wt%, per 100 wt% of the mixture of inorganic particles and binder. When it is less than 1 wt%, the content of the binder becomes too high, which may reduce the pore size and porosity due to a decrease in the empty space formed between the inorganic particles, thereby reducing the mobility of lithium ions. Conversely, when it exceeds 99 wt%, the content of the binder becomes too low, which may result in a decrease in the adhesive strength between the inorganic particles, thereby reducing the mechanical properties of the coating layer.

[0161] Meanwhile, the binder is not limited as long as it does not cause a side reaction with the electrolyte, but in particular, one having a glass transition temperature (Tg) as low as possible can be used, preferably in the range of -200 to 200°C. This is because the mechanical properties of the final insulating film can be improved.

[0162] In addition, the above-mentioned binder does not necessarily need to have ion conducting ability, but it is more preferable to use a polymer having ion conducting ability.

[0163] Therefore, it is preferable that the binder have a permittivity constant as high as possible, and since the degree of salt dissociation in the electrolyte actually depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the polymer, the better the degree of salt dissociation in the electrolyte. The permittivity constant of the polymer is preferably 1 or more, specifically, in the range of 1.0 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or more.

[0164] In addition to the aforementioned functions, the binder may have the characteristic of being gelled when impregnated with a liquid electrolyte, thereby exhibiting a high degree of swelling. In fact, if the binder is a polymer having an excellent electrolyte impregnation rate, the electrolyte injected after battery assembly permeates the polymer, and the polymer retaining the absorbed electrolyte has electrolyte ion conductivity. Therefore, if possible, the solubility index should be set to be 15 to 45 MPa. 1 / 2 Polymers are preferred, with a viscosity of 15 to 25 MPa. 1 / 2 and 30 to 45 MPa 1 / 2 The range is more desirable. The solubility index is 15 MPa. 1 / 2 Less than and 45 MPa 1 / 2 If it exceeds , it becomes difficult to be impregnated (swelled) by a conventional battery liquid electrolyte.

[0165] Examples of such binders include polyvinylidene fluorideco-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, It may be at least one selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

[0166] The total thickness of the separator may be 5 micrometers to 20 micrometers, specifically 5 micrometers to 15 micrometers, and more specifically 6 micrometers to 13 micrometers. When the thickness of the separator satisfies the above range, the resistance value of the lithium secondary battery can be minimized while effectively preventing a short circuit between the positive and negative electrodes. As a result, the reduction in energy density of the lithium secondary battery can be prevented and the life characteristics can be improved.

[0167] The above electrolyte may be a lithium non-aqueous electrolyte, and the lithium non-aqueous electrolyte may include a lithium salt and a non-aqueous organic solvent.

[0168] At this time, the lithium salt is used as a medium for transferring ions within a lithium secondary battery. Lithium salt is, for example, Li as a cation. + , and the anion is 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 - At least one selected from the group consisting of

[0169] Specifically, the lithium salt is 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 it is preferable to include Li(N(SO2CF3)2) in terms of excellent stability.

[0170] In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0171] The lithium salt may be appropriately changed within a generally usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion on the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically, at a concentration of 1 M to 2.5 M, and more specifically, at a concentration of 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of a lithium secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so that the electrolyte impregnation property can be improved.

[0172] The above non-aqueous organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charge / discharge process of a lithium secondary battery and can exhibit the desired properties together with additives. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used alone or in combination of two or more, and specifically, carbonate-based organic solvents can be used.

[0173] Among the organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC), and specifically, may 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.

[0174] In addition, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically, may include dimethyl carbonate.

[0175] The above ether organic solvent may be any one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more thereof, but is not limited thereto.

[0176] The above ester organic solvent may include at least one selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0177] Specific examples of the linear ester organic solvent include, but are not limited to, one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more thereof.

[0178] The above cyclic ester organic solvent may be, as a specific example, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0179] Among the above ester solvents, cyclic carbonate compounds are preferably used as high-viscosity organic solvents with high dielectric constants, which facilitate the dissociation of lithium salts in the electrolyte. When low-viscosity, low-dielectric constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate, and linear ester compounds are mixed and used in an appropriate ratio with these cyclic carbonate compounds, a gel-type electrolyte with high electrical conductivity can be produced, and thus, the compounds can be used more preferably.

[0180] Furthermore, the lithium non-aqueous electrolyte further includes a functional additive, and the functional additive may be included to prevent cathode collapse from occurring in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0181] Specifically, the functional additive may include at least one functional additive selected from the group consisting of, as representative examples, sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0182] The above sultone-based compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone, and may be included in an amount of 0.3 wt% to 5 wt%, specifically 1 wt% to 5 wt%, based on the total weight of the gel electrolyte. When the content of the sultone-based compound in the gel electrolyte exceeds 5 wt%, an excessively thick film may be formed on the electrode surface, which may cause an increase in resistance and a deterioration in output, and the resistance may also increase due to an excessive amount of additive, which may deteriorate the output characteristics.

[0183] The above sulfite compound may include at least one compound selected from the group consisting of 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-butylene glycol sulfite, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0184] The above sulfone compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0185] The above sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0186] In addition, the halogen-substituted carbonate compound may include fluoroethylene carbonate (FEC) and may be included in an amount of 5 wt% or less based on the total weight of the gel electrolyte. If the content of the halogen-substituted carbonate compound in the gel electrolyte exceeds 5 wt%, cell swelling performance may deteriorate.

[0187] In addition, the nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0188] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte. If the content of the cyclic carbonate compound in the gel electrolyte exceeds 3 wt%, the cell swelling suppression performance may deteriorate.

[0189] The above phosphate compound may include at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0190] The above borate compound may include lithium oxalyldifluoroborate, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0191] The lithium salt-based compound is a compound different from the lithium salt included in the lithium non-aqueous electrolyte, and may include at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3 wt% or less based on the total weight of the gel-type electrolyte.

[0192] The functional additives may be mixed in an amount of two or more, and may be included in an amount of 20 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the lithium non-aqueous electrolyte. If the content of the functional additive exceeds 20 wt%, there is a possibility that excessive side reactions may occur within the lithium non-aqueous electrolyte during charging and discharging of the battery. In particular, since they may not be sufficiently decomposed at high temperatures, they may exist as unreacted substances or precipitated substances within the lithium non-aqueous electrolyte at room temperature. Accordingly, side reactions that reduce the lifespan or resistance characteristics of the lithium metal battery may occur.

[0193]

[0194] Hereinafter, examples will be described to demonstrate that a lithium secondary battery according to one embodiment of the present invention exhibits improved effects.

[0195]

[0196] <Manufacturing Example>

[0197] Under an Ar atmosphere, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 according to the stoichiometric ratio, and sucrose was added to improve conductivity so that the content in the final cathode active material was 8 wt% to prepare a mixed powder.

[0198] The above-mentioned mixed powder was manufactured by placing the above-mentioned active material raw material and sucrose 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), purging with Ar for 1 hour, milling at 350 rpm for 1 hour, and resting for 30 minutes, and milling 12 times.

[0199] Thereafter, the mixed powder, which had been mixed as described above, was heat-treated in an Ar atmosphere using a tube furnace. The heat treatment was performed at 600°C for 3 hours at a heating rate of 5°C / min and at 900°C for 12 hours.

[0200] From this, a lithium compound (Li) with a carbon coating layer formed 1.2 Ti 0.4 Mn 0.4 O2) was manufactured.

[0201]

[0202] <Example 1>

[0203] The lithium compound manufactured in the above manufacturing example, and Super-P (BET: 63 m) as the first conductive material 2 / g, CNT (bundle type, BET: 230 m) as the second challenger 2 / g) was mixed 90:10 by weight and the conductive mixture was placed in a zirconia container at a weight ratio of 89:1 by weight, and bimodal zirconia balls (10 mm, 5 mm, large diameter / small diameter weight ratio = 0.1, 1.5 times the weight of the mixed powder) were used, and after purging with Ar for 1 hour, 12 secondary millings were performed in the form of milling at 350 rpm for 1 hour and resting for 30 minutes.

[0204] Afterwards, the obtained mixed powder and binder were mixed in a solvent of NMP at a weight ratio of 90:10, and the prepared positive electrode slurry was coated on one side of an aluminum current collector (thickness: 12㎛) with a thickness of 60 micrometers, dried (130℃), and rolled (porosity: 30% by volume) to prepare a positive electrode.

[0205]

[0206] <Example 2>

[0207] A positive electrode was manufactured in the same manner as in Example 1, except that a conductive mixture of Super-P as the first conductive material and CNT as the second conductive material was used in a weight ratio of 80:20.

[0208]

[0209] <Example 3>

[0210] A positive electrode was manufactured in the same manner as in Example 1, except that a conductive material mixture containing Super-P as the first conductive material and CNT as the second conductive material was used in a weight ratio of 70:30.

[0211]

[0212] <Example 4>

[0213] A positive electrode was manufactured in the same manner as in Example 1, except that a conductive mixture of Super-P as the first conductive material and CNT as the second conductive material was used in a weight ratio of 30:70.

[0214]

[0215] <Comparative Example 1>

[0216] In the above Example 1, the positive electrode was manufactured in the same manner as in the above Example 1, except that only the first conductive material, Super-P, was used instead of the conductive material mixture.

[0217]

[0218] <Comparative Example 2>

[0219] In the above Example 1, the positive electrode was manufactured in the same manner as in the above Example 1, except that only the second conductive material, CNT, was used instead of the conductive material mixture.

[0220]

[0221] <Comparative Example 3>

[0222] In the above Example 1, instead of the conductive material mixture, the first conductive material, Super-P, and the third conductive material, GNP (Graphene Nano Plate, BET 600m) 2 The positive electrode was manufactured in the same manner as in Example 1, except that a mixture of conductive materials ( / g) was used in a ratio of 40:60 by weight.

[0223]

[0224] <Comparative Example 4>

[0225] In the above Example 1, instead of the conductive material mixture, the first conductive material, Super-P, and the third conductive material, GNP (Graphene Nano Plate, BET 600m) 2 The positive electrode was manufactured in the same manner as in Example 1, except that a mixture of conductive materials ( / g) was used in a ratio of 30:70 based on weight.

[0226]

[0227] Experimental Example 1

[0228] SEM images of the mixed powder of the lithium compound and conductive material mixture prepared in Example 4 and Comparative Example 1 are shown in Figure 1 below.

[0229] Referring to this, it can be confirmed that the conductive mixture is more thoroughly formed on the surface of the lithium compound in the mixed powder of Example 4.

[0230]

[0231] Experimental Example 2

[0232] An electrode assembly was manufactured by using lithium metal foil as a negative electrode and interposing a separator (polyethylene) between the positive and negative electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 4, and an electrolyte was injected therein in which LiPF6 was dissolved to a concentration of 1.0 M in a non-aqueous organic solvent having a composition of ethylene carbonate (EC) : ethyl methyl carbonate (EMC) = 50 : 50 (volume ratio), thereby manufacturing a half-cell.

[0233] The above half-cell was charged at a constant current of 0.1 C at 25°C until the voltage reached 4.65 V, and then discharged at a constant current of 0.1 C until the voltage reached 2.0 V. The initial charge capacity and initial discharge capacity obtained therefrom are shown in Fig. 2 and Table 1, and the ratio of the initial discharge capacity to the initial charge capacity is represented as the initial efficiency in Table 1.

[0234] In addition, the battery capacity was measured by repeating the charge / discharge cycle 50 times in the range of 2.5 to 4.45 V at 0.1 C at 45°C, and the capacity ratio in the 50th cycle compared to the 1st cycle was defined as the capacity retention rate and is shown in Table 1 below.

[0235]

[0236] Experimental Example 3

[0237] The initial resistance and resistance increase rate were measured for the half-cells manufactured in the above experimental example 2, and the results are shown in Table 1.

[0238] Specifically, the half-cell was charged at a constant current of 1C at 25°C until the voltage reached 4.4 V, left for 10 seconds, and then discharged at a constant current of 1C until the voltage reached 2.5 V.

[0239] The initial voltage was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the resistance value was calculated from this.

[0240] Conductive material 1 content (wt%) Conductive material 2 content (wt%) Conductive material 3 content (wt%) Arithmetic BET Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) Initial efficiency (%) Capacity retention rate (%) Initial resistance (mohm) Example 10.9 0.17 9.73 16.45 24 0.36 75.96 68.57 1.2 Example 20.8 0.29 6.43 07.15 25 3.93 8 2.67 70.26 5.3 Example 30.7 0.31 13.13 27.68 257.47 78.57 72.26 0.2 Example 40.30.71 79.93 36.81 264.3978.507848.6Comparative Example 11-63264.49214.8781.2462.190.6Comparative Example 2-1230295.41237.3080.3364.563.2Comparative Example 30.40.6385294.3223.575.961.2100.3Comparative Example 40.30.7439290.5218.475.254.2120.8

[0241] Referring to Table 1 above and Figure 2 below, it can be confirmed that a lithium secondary battery using a conductive material mixture according to the present invention exhibits desirable effects when considering both capacity retention and resistance aspects.

[0242] Anyone with ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

[0243] A positive electrode for a lithium secondary battery according to one embodiment of the present invention includes two types of conductive materials having different specific surface areas, thereby improving conductivity and enhancing capacity, life characteristics, and output characteristics.

Claims

1. A positive electrode for a lithium secondary battery in which a positive electrode composite layer is formed on one or both sides of a positive electrode current collector, The above positive electrode composite layer includes a positive electrode active material and a conductive material mixture, The above positive electrode active material has a carbon coating layer formed on the surface and includes a lithium compound represented by the following chemical formula 1, The above-mentioned mixture of the challenge materials has a specific surface area (BET) of 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / Anode containing the second challenger: [Chemical Formula 1] Li 1+a You b Mn c ON 2-d X d In the above chemical formula 1, 0.1≤a≤0.5, 0.3≤b≤0.5, 0.3≤c≤0.5, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2, X is a halogen element.

2. In paragraph 1, A positive electrode in which the lithium compound is in the form of secondary particles, the average diameter (D50) of the secondary particles is 0.5 to 1.5 micrometers, and the average diameter (D50) of the primary particles forming the secondary particles is 10 to 100 nanometers.

3. In paragraph 1, A positive electrode in which the carbon coating layer is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the lithium compound.

4. In paragraph 1, The above first challenge material has a specific surface area (BET) of 60 m 2 / g to 70 m 2 / g, and the second challenge material has a specific surface area (BET) of 150 m 2 / g to 250 m 2 / g is the positive pole.

5. In paragraph 1, An anode in which the first conductive material is a dot-shaped conductive material and the second conductive material is a linear conductive material.

6. In paragraph 1, The above conductive material mixture is an anode comprising the first conductive material and the second conductive material in a weight ratio of 90:10 to 30:

70.

7. In paragraph 1, A cathode in which the above-mentioned conductive mixture is included in an amount of 1 to 10 wt% based on the total weight of the cathode composite layer.

8. In paragraph 1, The above conductive material mixture is a positive electrode that coats the surface of the positive electrode active material by at least 50% by weight based on the total weight of the above conductive material mixture.

9. In paragraph 8, A positive electrode in which the first conductive material among the conductive material mixture is positioned on the inner side of the surface of the positive electrode active material, and the second conductive material is formed on the surface of the first conductive material and in a portion where the first conductive material is not positioned.

10. In paragraph 1, A positive electrode mixture for a lithium secondary battery, wherein the positive electrode mixture layer further comprises a binder.

11. A method for manufacturing a positive electrode for a lithium secondary battery according to Article 1, The active material precursor and the carbon precursor are first ball milled and calcined, and the calcined material and the specific surface area (BET) are 50 m 2 / g to 70 m 2 / g of the first challenge material, and the specific surface area (BET) is 100 m 2 / g to 300 m 2 / The slurry is prepared by dispersing the mixed powder obtained by secondary ball milling of the conductive mixture containing the second conductive agent under a solvent, A method for manufacturing a cathode, comprising applying, drying, and rolling the above slurry to one or both sides of a cathode current collector.

12. In paragraph 11, A method for manufacturing a cathode in which the above active material precursors are a lithium source, a manganese source, and a titanium source.

13. In paragraph 11, A method for manufacturing an anode, wherein the carbon precursor is at least one selected from the group consisting of citric acid and sucrose.

14. In paragraph 11, The above conductive material mixture is a method for manufacturing an anode in which the first conductive material and the second conductive material are mixed in a weight ratio of 90:10 to 30:

70.

15. A lithium secondary battery comprising a positive electrode according to paragraph 1.

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