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

Abstract

According to one embodiment of the present invention, a positive active material for a lithium secondary battery, a preparation method therefor, a positive electrode comprising same, and a lithium secondary battery are provided, the positive active material comprising: a lithium compound represented by chemical formula 1; and a coating layer formed on the surface of the particles of the lithium compound, wherein the coating layer comprises carbon and a surface modifier, and the D / G band ratio, measured by means of Raman spectroscopy, on the surface of the positive active material is 0.7-0.89. [Chemical formula 1] Li1+aTibMncO2-dXd In chemical formula 1, 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2, and X is a halogen element.

Description

Positive electrode active material for lithium secondary battery, method for producing same, positive electrode including same, and lithium secondary battery

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0169859, filed November 29, 2023, and Korean Patent Application No. 10-2024-0173826, filed November 28, 2024, the entire contents of which are incorporated herein by reference.

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

[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 purpose of the present invention is to provide a positive electrode active material for a lithium secondary battery capable of exhibiting high capacity, high rate, and excellent lifespan characteristics, and a method for producing the same.

[0015] The present invention also aims to provide a positive electrode including such a positive electrode active material, and a lithium secondary battery including the same.

[0016] According to one embodiment of the present invention,

[0017] As a positive electrode active material for lithium secondary batteries,

[0018] A lithium compound represented by the following chemical formula 1, and a coating layer formed on the particle surface of the lithium compound,

[0019] The above coating layer includes carbon and a surface modifier,

[0020] The above cathode active material is provided as a cathode active material having a D / G band ratio value of 0.7 to 0.89 measured on its surface by Raman spectroscopy.

[0021] [Chemical Formula 1]

[0022] Li 1+a Ti b Mn c O 2-d X d

[0023] In the above chemical formula 1,

[0024] 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2,

[0025] X is a halogen element.

[0026] Specifically, in the above chemical formula 1, b+c=0.8.

[0027] These positive electrode active materials may have an average diameter (D50) of primary particles of 10 to 100 nanometers and an average diameter (D50) of secondary particles of 0.5 to 1.5 micrometers.

[0028] Meanwhile, the content of the carbon and the surface modifier may be 0.5 to 1.5 wt% based on the total weight of the positive electrode active material, and the total content thereof may be 1 to 3 wt% based on the total weight of the positive electrode active material.

[0029] The above surface modifier is a nonionic surface modifier, and more specifically, may be at least one selected from the group consisting of polyvinylpyrrole (PVP) and polyvinyl chloride (PVC).

[0030] According to another embodiment of the present invention, a method for producing a positive electrode active material for a lithium secondary battery is provided, wherein the positive electrode active material is produced by a solid-state method based on a mixture including an active material precursor, a carbon precursor, and a surface modifier.

[0031] At this time, the active material precursor may be a lithium source, a manganese source, and a titanium source.

[0032] Additionally, the carbon precursor may be at least one selected from the group consisting of citric acid and sucrose.

[0033] Furthermore, the surface modifier may be a nonionic surface modifier, and may be at least one selected from the group consisting of polyvinylpyrrole (PVP) and polyvinyl chloride (PVC).

[0034] Specifically, the above-mentioned high-temperature method may be to calcinate the mixture at 550°C to 1050°C in an inert atmosphere.

[0035] According to another embodiment of the present invention, a positive electrode is provided in which a positive electrode composite layer including the positive electrode active material is formed on one or both sides of a positive electrode current collector.

[0036] Here, the content ratio of carbon to the content of carbon and metal (Ti and Mn) represented by the following formula 1 of the positive electrode active material may be 0.75 to 0.9.

[0037] [Formula 1]

[0038] C content / (C+Metal) content.

[0039] Furthermore, according to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

[0040] Figure 1 is an SEM photograph of a portion of the anode surface 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 mentioned components.

[0045]

[0046] positive electrode active material

[0047] According to one embodiment of the present invention, a positive electrode active material for a lithium secondary battery is

[0048] A lithium compound represented by the following chemical formula 1, and a coating layer formed on the particle surface of the lithium compound,

[0049] The above coating layer comprises carbon and a surface modifier,

[0050] The above positive electrode active material is characterized in that the D / G band ratio measured on its surface by Raman spectroscopy has a value of 0.7 to 0.89.

[0051] [Chemical Formula 1]

[0052] Li 1+a Ti b Mn c O 2-d X d

[0053] In the above chemical formula 1,

[0054] 0.1≤a≤0.5, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2,

[0055] X is a halogen element.

[0056] 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.

[0057] Additionally, 0.2≤a≤0.4, 0.3≤b≤0.5, 0.3≤c≤0.5 may be satisfied.

[0058] In most detail, the lithium compound is Li 1.2 Ti 0.4Mn 0.4 It could be O2.

[0059] The above lithium compound is used in a form in which a carbon coating is formed on its surface to improve conductivity. However, due to the nature of the carbon, the carbon coating tends to aggregate rather than distribute evenly, making it difficult to evenly coat the carbon, and thus there was a problem in that an excellent conductive network could not be formed.

[0060] However, it was confirmed that the positive electrode active material according to the present invention can exhibit excellent effects by solving this problem by including a surface modifier together with the carbon coating of the lithium compound, and by forming a coating layer including the carbon and the surface modifier, the D / G band ratio value can be increased to 0.7 to 0.89, thereby increasing surface crystallinity and improving the uniformity of the coating.

[0061] Here, the D / G band ratio value is an indicator indicating the crystallinity of the surface of the positive electrode active material.

[0062] The above D / G band ratio value can be measured and calculated by Raman spectroscopy, and specifically, the crystallinity can be determined from the peak intensity ratio value for the G band 1700 / cm and D band 1400 / cm, which are the main peak regions of carbon, in addition to the peak appearing by the lithium compound in the Raman spectrum measured by Raman spectroscopy, and it is considered that the crystallinity increases as this value decreases.

[0063] The positive electrode active material according to the present invention may have a D / G band ratio value of its surface of 0.7 to 0.89, specifically 0.7 to 0.85, and more specifically 0.75 to 0.8.

[0064] Compared to cases where a surface modifier is not used or where a cathode active material, carbon, and a surface modifier are simply mixed, which mostly have a value of 0.9 or higher, the cathode active material of the present invention forms a coating layer including carbon by using a surface modifier from the precursor stage of the cathode active material as described below, and therefore has excellent surface crystallinity and enables uniform coating.

[0065] At this time, it was found that the content of carbon and the content of the surface modifier included in the coating layer are very important factors influencing these characteristics, and here, the content of the carbon and the surface modifier showing the best effect may be 0.1 to 3 wt%, specifically 0.5 to 2 wt%, and more specifically 0.5 to 1.5 wt%, respectively, based on the total weight of the positive electrode active material.

[0066] Most specifically, the content of the carbon may be 1 to 1.5 wt%, 1.1 to 1.4 wt% based on the total weight of the positive electrode active material, and the content of the surface modifier may be 0.5 to 1 wt%, 0.6 to 0.9 wt% based on the total weight of the positive electrode active material.

[0067] Additionally, the total content of these may be 0.5 to 5 wt%, specifically 1 to 3 wt%, and more specifically 1.5 to 2 wt%, based on the total weight of the positive electrode active material.

[0068] Beyond the above range, if the carbon content 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.

[0069] In addition, if the content of the surface modifier is too small, the agglomeration of carbon cannot be resolved, so the conductivity cannot be improved. If the content of the surface modifier is too large, the resistance increases due to the resistance of the surface modifier, which causes a problem in that the life characteristics are reduced.

[0070] Moreover, when the total content increases, there is also the problem of increased resistance, and when the total content is small, the carbon content decreases, so the effect of improving conductivity cannot be achieved.

[0071] Here, the surface modifier is not limited to any type of surfactant that can be used in a lithium secondary battery, but specifically, it may be a nonionic surface modifier, and for example, polyethylene glycol, ethoxylated fatty alcohol, ethoxylated fatty acid, ethoxylated alkyl phenol, alkanolamide (fatty acid alkanolamide), ethoxylated fatty acid alkanolamide, fatty amine oxide, fatty amido amine oxide, glyceryl fatty acid ester, sorbitan, ethoxylated sorbitan ester, alkyl poly glycoside, ethylene / propylene oxide block It may be at least one selected from the group consisting of copolymer (ethylene / propylene oxide copolymer), ethoxylated-propoxylated fatty alcohol, polyvinylpyrrolidone (PVP), and polyvinyl chloride (PVC), and more specifically, it may be at least one selected from the group consisting of polyvinylpyrrolidone (PVP) and polyvinyl chloride (PVC), and more specifically, it may be polyvinylpyrrolidone (PVP).

[0072] Here, the number average molecular weight of polyvinylpyrrolidone (PVP) may be 20,000 to 40,000.

[0073] The above number average molecular weight was measured using gel permeation chromatography (GPC: PL GPC220, Agilent Technologies) under the following conditions.

[0074] - Column: PL MiniMixed B x 2

[0075] - Solvent: THF

[0076] - Flow rate: 0.3 ml / min

[0077] - Sample concentration: 2.0 mg / ml

[0078] - Injection volume: 10 ㎕

[0079] - Column temperature: 40℃

[0080] - Detector: Agilent RI detector

[0081] - Standard: Polystyrene (corrected with a cubic function)

[0082] - Data processing: ChemStation

[0083] Outside the above range, if the average molecular weight is less than 20,000, coating is not performed well, and if it exceeds 40,000, dispersibility is reduced, which is not preferable.

[0084] Meanwhile, the positive electrode active material having such a composition and structure may have the form of secondary particles having a structure in which primary particles are aggregated.

[0085] At this time, the average diameter (D50) of the primary particles may be 10 to 100 nanometers, and the average diameter (D50) of the secondary particles may be 0.5 to 1.5 micrometers.

[0086] 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., Microtrac S3500), and the difference in diffraction pattern according to particle size is measured when the particles pass through the laser beam, thereby calculating the particle size distribution. By calculating the particle diameter at the point where it becomes 50% of the cumulative particle volume distribution according to particle size in the measuring device, the D50 can be measured.

[0087]

[0088] Method for manufacturing positive electrode active material

[0089] The above-mentioned positive electrode active material is manufactured by a solid-state method based on a mixture including an active material precursor, a carbon precursor, and a surface modifier.

[0090] 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.

[0091] The lithium source may be one or more substances selected from lithium carbonate, lithium hydroxide, and lithium phosphate, and specifically may be lithium hydroxide (LiOH). The 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 specifically may be manganese oxide (MnO2).

[0092] 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).

[0093] In addition, in order to improve the conductivity of these active materials, the carbon precursor is introduced together with the lithium compound from the synthesis stage. That is, it is mixed together with the active material precursor.

[0094] 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.

[0095] In addition, the surface modifier is also added together to ensure even dispersion of the carbon precursor in the synthesis step. Here, the surface modifier may be a nonionic surface modifier, and materials such as those described above may be used. Specifically, it may be at least one selected from the group consisting of polyvinylpyrrolidone (PVP) and polyvinyl chloride (PVC), and more specifically, it may be polyvinylpyrrolidone (PVP).

[0096] Meanwhile, the positive electrode active material is manufactured by synthesizing a mixture of these materials using a solid-state method.

[0097] The above method is a method that is achieved by mixing these mixtures in a dry form through ball milling and then calcining them.

[0098] According to the present invention, the active material precursor sources are mixed in accordance with the stoichiometric ratio of the chemical formula 1, and the carbon precursor and the surface modifier may be added so that the content of carbon and the surface modifier based on these raw materials is in the above range, that is, 0.1 to 3 wt%, specifically 0.5 to 2 wt%, and more specifically 0.5 to 1.5 wt%, based on the total weight of the positive electrode active material, and most specifically, the content of the carbon is 1 to 1.5 wt% based on the total weight of the positive electrode active material, and the content of the surface modifier is 0.5 to 1 wt% based on the total weight of the positive electrode active material.

[0099] In addition, the carbon precursor and the surface modifier may be added so that the total content of carbon and the surface modifier is 0.5 to 5 wt%, specifically 1 to 3 wt%, and more specifically 1.5 to 2 wt%, based on the total weight of the positive electrode active material.

[0100] These active material precursors, carbon precursors, and surface modifiers can be mixed in powder form and placed in a zirconia container, milled using zirconia balls, and then sintered to produce a composite material.

[0101] At this time, the calcination may be performed by heat treating the mixture at 550°C to 1050°C in an inert atmosphere.

[0102] More specifically, the firing may be carried out in two stages, for example, stage 1 may be carried out under an inert atmosphere at a temperature in the range of 500 to 800°C for 1 to 6 hours, and stage 2 may be carried out under an inert atmosphere at a temperature in the range of 800 to 1200°C for 6 to 20 hours.

[0103] The positive electrode active material manufactured by the solid-state method can be obtained in a form in which carbon is evenly coated on the surface of the lithium compound represented by the chemical formula 1 containing lithium, manganese, and titanium, and the carbon precursor and the surface modifier are mixed together from the precursor stage and then fired, so that the surface crystallinity is improved, and the value of the D / G band ratio measured by the Mann spectroscopy can satisfy the range of 0.7 to 0.89.

[0104] Therefore, according to the present invention, not only can the crystallinity of the material surface of the positive electrode active material be increased and uniform coating be achieved even with a small amount of carbon, thereby sufficiently improving conductivity, but also improving surface stability and life characteristics.

[0105]

[0106] anode

[0107] According to another embodiment of the present invention, a positive electrode is provided in which a positive electrode composite layer including the positive electrode active material is formed on one or both sides of a positive electrode current collector.

[0108] After manufacturing the positive electrode, the content ratio of carbon to the content of carbon and metal (Ti and Mn) represented by the following formula 1 of the positive electrode active material may be 0.75 to 0.9, and specifically, 0.77 to 0.85.

[0109] [Formula 1]

[0110] C content / (C+Metal) content

[0111] The ratio of carbon content to the content of carbon and metals (Ti and Mn) represented by the above equation 1 can be determined by photographing the surface of the anode with an SEM, selecting an area within a few hundred nm in diameter, and measuring the Auger spectrum using an Auger electron spectroscopy (AES) device (PHI 710, ULVAC-PHI INC). Specifically, 24 measurement areas were selected for each sample and measured, and after obtaining the Auger spectrum obtained at each point, the ratio can be obtained by dividing the C content by the sum of the contents of C and metals (Ti and / or Mn).

[0112] From this, it can be seen that the closer the value is to 1, the smaller the metal content on the surface and the better the carbon coating is formed, indicating the uniformity of the coating.

[0113] 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.

[0114] 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.

[0115] The above positive electrode composite layer includes a positive electrode active material and, if necessary, may include a conductive agent, a binder, and other additives.

[0116] The above-mentioned positive electrode active material layer may further include a compound capable of reversible intercalation and deintercalation of lithium in addition to the above-mentioned positive electrode active material, and 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., Li1+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.

[0117] Of course, the positive electrode active material according to the present invention may be included as a main material, and based on the total amount of materials acting as active materials capable of reversible intercalation and deintercalation of lithium, the positive electrode active material 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 the material acting as an active material may include only the positive electrode active material according to the present invention in an amount of 100 wt%.

[0118] The conductive agent is a component for further improving the conductivity of the positive electrode active material, and the conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and 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; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0119] The above-mentioned conductive material may be included in an amount of 0.1 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.

[0120] The above binder is a component that assists in bonding between the conductive material, the positive electrode active 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.

[0121] 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.

[0122] In addition, the above-mentioned other additives may further include, for example, fillers as components that suppress expansion. The fillers are not particularly limited as long as they 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.

[0123]

[0124] lithium secondary battery

[0125] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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

[0162] 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.

[0163] In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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 and linear ester compounds, such as dimethyl carbonate and diethyl carbonate, are mixed and used in an appropriate ratio with these cyclic carbonate compounds, an electrolyte with high electrical conductivity can be produced, and thus the compounds can be used more preferably.

[0173] 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.

[0174] 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.

[0175] 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 electrolyte. When the content of the sultone-based compound in the 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.

[0176] 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 electrolyte.

[0177] 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 electrolyte.

[0178] 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 electrolyte.

[0179] 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 electrolyte. If the content of the halogen-substituted carbonate compound in the electrolyte exceeds 5 wt%, cell swelling performance may deteriorate.

[0180] 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.

[0181] 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 electrolyte. If the content of the cyclic carbonate compound in the electrolyte exceeds 3 wt%, the cell swelling suppression performance may deteriorate.

[0182] 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 electrolyte.

[0183] 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 electrolyte.

[0184] The above 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 bisoxalatoborate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3 wt% or less based on the total weight of the electrolyte.

[0185] 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.

[0186]

[0187] Hereinafter, examples will be described to demonstrate that a lithium secondary battery according to one embodiment of the present invention exhibits improved effects.

[0188]

[0189] <Example 1>

[0190] Under an Ar atmosphere, 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 0.66 wt%, and polyvinylpyrrolidone (PVP) was added to improve dispersibility so that the content in the final cathode active material was 1.34 wt%, thereby producing a mixed powder.

[0191] The above-mentioned mixed powder was manufactured by placing the above-mentioned active material raw material, sucrose, and PVP 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.

[0192] 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.

[0193] From this, a coating layer containing carbon and PVP is formed. 1.2 Ti 0.4 Mn 0.4 O2 positive electrode active material was manufactured.

[0194]

[0195] <Example 2>

[0196] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere, sucrose was added to improve conductivity so that the content in the final positive electrode active material was 1.0 wt%, and polyvinylpyrrolidone (PVP) was added to improve dispersibility so that the content in the final positive electrode active material was 1.0 wt%, and a mixed powder was prepared, except that a positive electrode active material was prepared in the same manner as in Example 1.

[0197]

[0198] <Example 3>

[0199] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere, sucrose was added to improve conductivity so that the content in the final positive electrode active material was 1.2 wt%, and polyvinylpyrrolidone (PVP) was added to improve dispersibility so that the content in the final positive electrode active material was 0.8 wt%, and a mixed powder was prepared, except that a positive electrode active material was prepared in the same manner as in Example 1.

[0200]

[0201] <Example 4>

[0202] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were each mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere, sucrose was added to improve conductivity so that the content in the final positive electrode active material was 1.34 wt%, and polyvinylpyrrolidone (PVP) was added to improve dispersibility so that the content in the final positive electrode active material was 0.66 wt%, and a mixed powder was prepared, except that a positive electrode active material was prepared in the same manner as in Example 1.

[0203]

[0204] <Comparative Example 1>

[0205] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere, and only sucrose was added to improve conductivity so that the content in the final positive electrode active material was 2.0 wt%, thereby manufacturing a mixed powder, except that a positive electrode active material was manufactured in the same manner as in Example 1.

[0206]

[0207] <Comparative Example 2>

[0208] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere, and only sucrose was added to improve conductivity so that the content in the final positive electrode active material was 1.34 wt%, and a mixed powder was prepared, except that a positive electrode active material was prepared in the same manner as in Example 1.

[0209]

[0210] <Comparative Example 3>

[0211] In the above Example 1, the active material raw materials of LiOH, MnO2, and TiO2 were mixed in a molar ratio of 3:1:1 in accordance with the stoichiometric ratio under an Ar atmosphere to prepare a mixed powder, and the mixed powder was heat-treated in an Ar atmosphere using a tube furnace. The heat treatment was performed at 600°C for 3 hours and at 900°C for 12 hours at a heating rate of 5°C / min. As a result, Li 1.2 Ti 0.4 Mn 0.4 O2 positive electrode active material was manufactured.

[0212] Afterwards, carbon black and PVP were added to N-methylpyrrolidone (NMP) so that the final material had 0.66 wt% and 1.34 wt%, respectively, and the dispersion was stirred, and the positive electrode active material and PVDF were added and stirred.

[0213]

[0214] Experimental Example 1

[0215] Raman spectroscopy was performed on the positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 3. Specifically, a Raman spectrum was obtained on the surface of the active material using a 532 nm laser, and peak analysis was performed based on the average spectrum for 50 points.

[0216] Li at peak 1.2 Ti 0.4 Mn 0.4 In addition to the peak for O2, the peak intensity ratio values ​​for the main peak regions of carbon, G band 1700 / cm and D band 1400 / cm, are shown in Table 1 below.

[0217] At this time, it is judged that the crystallinity increases as the value of the D / G band ratio decreases.

[0218] D / G band ratio Example 10.84 Example 20.82 Example 30.78 Example 40.76 Comparative Example 10.95 Comparative Example 20.92 Comparative Example 30.90

[0219] Referring to Table 1 above, when PVP is added together with carbon in the active material synthesis step to include carbon and PVP together in the coating layer, it can be confirmed that the PVP material makes the carbon structure porous and increases crystallinity. However, when the coating layer includes only carbon or the formation of the coating layer including carbon and PVP is performed after the manufacture of the lithium compound, it can be confirmed that the crystallinity is reduced.

[0220]

[0221] Experimental Example 2

[0222] The positive electrode slurry prepared by mixing the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 with a conductive agent (CNT) and a binder in a solvent of NMP at a weight ratio of 90:5:5 was coated on one surface of an aluminum current collector (thickness: 12㎛) to a thickness of 60 micrometers, dried (130°C), and rolled (porosity: 30% by volume) to prepare a positive electrode.

[0223] A SEM photograph was taken of a portion of the surface of a positive electrode manufactured using the positive electrode active material manufactured in Example 1, and the results are shown in Fig. 1.

[0224] Referring to Fig. 1, it can be confirmed that the particles are clumped. A relatively less clumped area (within several hundred nm in diameter) was selected by scanning electron microscopy (SEM), and the Auger spectrum was measured using Auger electron spectroscopy (AES) equipment (PHI 710, ULVAC-PHI INC). The measurement conditions are as follows, 24 measurement points were selected for each sample and measured, and after obtaining the Auger spectrum obtained at each point, the ratio was calculated by dividing the C content by the sum of the contents of C and metal (Ti, and / or Mn), and the results are shown in Table 2 below.

[0225] Here, the closer the ratio value is to 1, the smaller the metal content on the surface, which means that the carbon coating is well formed, which means that the coating uniformity is improved.

[0226] C / (C+metal) ratio Example 10.78 Example 20.83 Example 30.80 Example 40.84 Comparative Example 10.64 Comparative Example 20.66 Comparative Example 30.70

[0227] Referring to Table 2, it can be seen that in the comparative examples, as the carbon content increases, the coating uniformity deteriorates due to carbon agglomeration, whereas in the case of adding PVP together with carbon in the active material synthesis step as in the present invention, the coating uniformity rapidly improves as the carbon content increases to 1 wt% or more.

[0228]

[0229] Experimental Example 3

[0230] The positive electrode slurry prepared by mixing the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 with a conductive agent (CNT) and a binder in a solvent of NMP at a weight ratio of 90:5:5 was coated on one surface of an aluminum current collector (thickness: 12㎛) to a thickness of 60 micrometers, dried (130°C), and rolled (porosity: 30% by volume) to prepare a positive electrode.

[0231] A half-cell was manufactured by using lithium metal foil as a cathode and interposing a separator (polyethylene) between the cathode and the anode to manufacture an electrode assembly, and injecting an electrolyte 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).

[0232] The above half-cell was charged at a constant current of 0.1 C at 25°C until the voltage reached 4.8 V, and then discharged at a constant current of 0.1 C until the voltage reached 1.5 V. The initial charge capacity and initial discharge capacity obtained therefrom are shown in Table 3 below, and the ratio of the initial discharge capacity to the initial charge capacity is represented as the initial efficiency, also shown in Table 3 below.

[0233] In addition, the battery capacity was measured by repeating the charge / discharge cycle 30 times in the range of 1.5 to 4.5 V at 0.1 C at 45°C, and the capacity ratio in the 30th cycle compared to the 1st cycle was defined as the capacity retention rate and is shown in Table 3 below.

[0234] Initial Charge Capacity (mAh / g) Initial Charge Capacity (mAh / g) Initial Efficiency (%) Capacity Retention Rate (%) Example 1 24822891.973 Example 2 25023192.481 Example 3 25424094.588 Example 4 26125196.293 Comparative Example 1 22019890.060 Comparative Example 2 23221291.371 Comparative Example 3 23621791.570

[0235] Referring to Table 3 above, it can be confirmed that when PVP is added together with a carbon precursor according to the present invention, it has better capacity, efficiency, and life characteristics. In addition, it can be seen that it is better when the carbon content is 1 wt% or more, and this seems to be due to the coating uniformity. Meanwhile, when PVP and carbon are post-treated as in Comparative Example 3, there is a problem that the capacity is reduced due to carbon agglomeration or deterioration of carbon coating uniformity because PVP does not sufficiently play a dispersing role with simple physical stirring, and the capacity retention rate is also reduced, whereas according to the examples of the present invention, since the carbon precursor and PVP increase the coating uniformity due to the sintering reaction, not only is there an effect of further increasing the capacity due to the effect of improving ionic conductivity, but the capacity retention rate is also higher.

[0236]

[0237] 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.

[0238] The positive electrode active material according to the present invention forms a coating layer containing carbon and a surface modifier on the surface of a lithium compound of an amorphous rock salt represented by a specific chemical formula, and increases the surface crystallinity to a value of D / G band ratio of 0.7 to 0.89, thereby enabling a more uniform coating on the surface of the positive electrode active material even with a small amount of carbon, thereby exhibiting high capacity, high rate, and excellent life characteristics.

Claims

1. As a positive electrode active material for lithium secondary batteries, A lithium compound represented by the following chemical formula 1, and a coating layer formed on the particle surface of the lithium compound, The above coating layer comprises carbon and a surface modifier, The above cathode active material is a cathode active material having a D / G band ratio value of 0.7 to 0.89 as measured by Raman spectroscopy on its surface: [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, 0.2≤b≤0.6, 0.2≤c≤0.6, 1.1≤(1+a) / (b+c)≤1.4, 0≤d≤0.2, X is a halogen element.

2. In paragraph 1, A positive electrode active material in which b+c=0.8 in the chemical formula 1 above.

3. In paragraph 1, The above positive electrode active material is a positive electrode active material having an average diameter (D50) of primary particles of 10 to 100 nanometers and an average diameter (D50) of secondary particles of 0.5 to 1.5 micrometers.

4. In paragraph 1, A cathode active material wherein the contents of the carbon and the surface modifier are each 0.5 to 1.5 wt% based on the total weight of the cathode active material.

5. In paragraph 1, A cathode active material having a total content of the carbon and the surface modifier of 1 to 3 wt% based on the total weight of the cathode active material.

6. In paragraph 1, The above surface modifier is a positive electrode active material, wherein the surface modifier is a nonionic surface modifier and is at least one selected from the group consisting of polyvinylpyrrolidone (PVP) and polyvinyl chloride (PVC).

7. A method for manufacturing a positive electrode active material for a lithium secondary battery according to Article 1, A method for producing a positive electrode active material, the method comprising producing the positive electrode active material by a solid-state method based on a mixture comprising an active material precursor, a carbon precursor, and a surface modifier.

8. In paragraph 7, A method for manufacturing a cathode active material, wherein the above active material precursors are a lithium source, a manganese source, and a titanium source.

9. In paragraph 7, A method for producing a cathode active material, wherein the carbon precursor is at least one selected from the group consisting of citric acid and sucrose.

10. In paragraph 7, A method for producing a cathode active material, wherein the surface modifier is a nonionic surface modifier and is at least one selected from the group consisting of polyvinylpyrrolidone (PVP) and polyvinyl chloride (PVC).

11. In paragraph 7, The above solid-state method is a method for producing a positive electrode active material, wherein the mixture is calcined at 550°C to 1050°C in an inert atmosphere.

12. A positive electrode in which a positive electrode composite layer containing a positive electrode active material according to Article 1 is formed on one or both sides of a positive electrode current collector.

13. In paragraph 12, A cathode having a carbon content ratio of 0.75 to 0.9 relative to the content of carbon and metal (Ti and Mn) represented by the following formula 1 of the cathode active material: [Formula 1] C content / (C+Metal) content 14. A lithium secondary battery comprising a positive electrode according to Article 12.

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