Positive electrode containing positive electrode additive for lithium secondary battery

Abstract

In order to complement the structural stability of the high-nickel positive electrode active material, the present invention uses ZrO 2-x (0

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0106870, filed on August 12, 2021, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a cathode additive included in a cathode comprising a high-Ni lithium transition metal oxide. [Background technology]

[0003] Recently, with the development of technologies such as electric vehicles, the need for high-capacity secondary batteries is increasing, and as a result, research on high-nickel (high-Ni) positive electrode active materials with excellent capacity characteristics is being actively conducted.

[0004] High-nickel cathode active materials are cathode active materials with a nickel content of 60 atm% or more, which can achieve high capacity. However, as the nickel content increases, the structural stability of the cathode active material decreases, resulting in problems such as poor life characteristics and stability at high voltages.

[0005] For example, high-nickel positive electrode active materials are prone to cracking due to changes in lattice constant, i.e., changes in the volume within the unit lattice, during the process of lithium ion insertion and extraction during charge and discharge. These cracks allow the electrolyte to penetrate into the positive electrode active material, deteriorating the structure of the positive electrode active material and accelerating the decomposition of the electrolyte, reducing lifespan characteristics. Furthermore, the formation of a coating due to the decomposition of the electrolyte increases resistance, reducing output characteristics.

[0006] Therefore, there is a need to develop a positive electrode active material that can achieve high capacity and has excellent life characteristics, and various positive electrode additives have been proposed to solve the structural instability of high-nickel positive electrode active materials. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is for solving the above problems, and in order to complement the structural stability of the high-nickel cathode active material, a cathode additive of ZrO 2-x (0 < x < 2) is used to achieve a high capacity and provide a cathode with excellent life characteristics, a method for manufacturing the same, and a lithium secondary battery including the same.

Means for Solving the Problems

[0008] On one aspect, the present invention is a cathode including a cathode active material layer containing a cathode active material, a conductive material, a binder, and a cathode additive, wherein the cathode additive is ZrO 2-x (0 < x < 2).

[0009] On another aspect, the present invention includes a step of reducing a precursor containing Zr to prepare ZrO 2-x (0 < x < 2), a step of mixing the ZrO 2-x with a cathode active material, a conductive material, and a binder as a cathode additive to manufacture a cathode slurry, and a step of manufacturing a cathode active material layer using the cathode slurry, and provides a method for manufacturing a cathode.

[0010] On still another aspect, the present invention provides a secondary battery including the cathode.

Effects of the Invention

[0011] The cathode according to the present invention uses a high-nickel cathode active material, has a large initial capacity, and the structural stability of the high-nickel cathode active material is improved by the additive of ZrO 2-x (0 < x < 2). The secondary battery including the cathode according to the present invention has an effect of excellent cycle characteristics.

[0012] In addition, the cathode according to the present invention has improved structural stability, is excellent in high-rate characteristics when applied to a secondary battery, and ZrO 2-xThe positive electrode additive in the range of (0 < x < 2) has the effect of collecting the gas generated during charge and discharge, thereby reducing the generation of gas.

[0013] Therefore, the positive electrode according to the present invention can be usefully applied to a lithium secondary battery.

Brief Description of the Drawings

[0014] [Figure 1] The results of observing the XRD patterns for (a) ZrO2-x (0 < x < 2) particles and (b) ZrO2 particles using an X-ray diffractometer. [Figure 2] The results of observing the XRD patterns for the positive electrodes manufactured in Example 1 and Comparative Examples 1-2 using an X-ray diffractometer. [Figure 3] The results of measuring the generation amounts of CO2, CO, and O2 for each of the secondary batteries manufactured in Example 1 and Comparative Example 1 using Differential Electrochemical Mass Spectrometry (DEMS).

Modes for Carrying Out the Invention

[0015] In this specification and the claims, terms and words used should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, following the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0016] In this specification, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0017] The present invention will now be described in more detail.

[0018] In the present invention, the term "primary particle" refers to the smallest particle unit distinguishable as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of a single crystal grain or multiple crystal grains. The average particle size of the primary particles may be measured by measuring the particle size of each particle distinguished in a cross-sectional SEM image of the positive electrode active material particle and then calculating the arithmetic mean value of the particle sizes.

[0019] In the present invention, the term "secondary particles" refers to secondary structures formed by aggregation of a plurality of primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer. In the present invention, a Microtrac S3500 particle size analyzer was used.

[0020] In the present invention, "particle size Dn" refers to the particle size at the n% point in the cumulative particle size volume distribution. That is, D50 is the particle size at the 50% point in the cumulative particle size volume distribution, D90 is the particle size at the 90% point in the cumulative particle size volume distribution, and D10 is the particle size at the 10% point in the cumulative particle size volume distribution. Dn 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 analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through a laser beam. D10, D50, and D90 can be measured by calculating the particle sizes at the 10%, 50%, and 90% points in the cumulative particle size volume distribution measured by the analyzer.

[0021] In the present invention, X-ray diffraction analysis can be performed using a D8 Advance (TRIO / TWIN) device manufactured by Bruker under the following conditions to obtain XRD data, and then the XRD data can be processed using a DIFFRAC.EVA program manufactured by Bruker. Here, the full width at half maximum was set to be measured using the Caglioti equation.

[0022] <X-ray Diffraction Analysis Conditions> Light source: Cu-target, 40 kV, 40 mA output, wavelength = 1.54 Å Detector: LYNXEYE XE-T Sample preparation: 0.5 g of the sample was filled into a holder with a diameter of 2 cm and loaded onto a rotating stage (radiation stage). Measurement time: 60 minutes Measurement range: 2θ = 10° to 70°

[0023] Positive Electrode Additive The positive electrode according to the present invention can contain a positive electrode additive of ZrO 2-x (0 < x < 2).

[0024] The positive electrode additive according to the present invention is spherical, and the average particle size (D 50 ) can be 0.2 μm to 50 μm. Preferably, it can be 0.2 μm to 5 μm, and more preferably 0.2 μm to 1 μm. When the average particle size of the positive electrode additive satisfies the above range, when mixed with the positive electrode active material, it can be uniformly distributed on the surface of the positive electrode active material, effectively collect oxygen generated during charge and discharge by the positive electrode active material, and improve the life characteristics of the positive electrode.

[0025] The positive electrode additive ZrO 2-x (0 < x < 2) according to the present invention can satisfy the following formula 1.

[0026] [Formula 1] 5 < P1 / P2 < 8

[0027] In Formula 1, P1 is the peak intensity in the range where 2θ is 29° or more and 31° or less on XRD, and P2 is the peak intensity in the range where 2θ is 35° or more and 37° or less on XRD. For the positive electrode additive of the present invention, the value of P1 / P2 can preferably be more than 5 and less than 7, and more preferably more than 5 and less than 6. When the value of P1 / P2 of the positive electrode additive satisfies the above range, it can be confirmed that the positive electrode additive has a tetragonal crystal structure. When the positive electrode additive has a tetragonal crystal structure, an oxygen-deficient structure can be formed to reduce the band gap energy and increase the conductivity.

[0028] The positive electrode additive ZrO according to the present invention 2-x (0 < x < 2) particles can have a tetragonal crystal structure. ZrO2 before the reduction treatment has a mixed monoclinic crystal structure and tetragonal crystal structure, whereas the positive electrode additive ZrO according to the present invention 2-x (0 < x < 2) particles can have a tetragonal crystal structure. When the positive electrode additive has a tetragonal crystal structure, the band gap energy can be reduced and the conductivity can be increased by forming an oxygen-deficient structure.

[0029] The positive electrode additive according to the present invention can have a band gap energy of 3.0 eV or less, preferably 2.0 to 3.0 eV, and more preferably 2.5 to 3.0 eV. Since the positive electrode additive according to the present invention has a reduced band gap energy and high electron and ion conductivity, the lithium secondary battery using the positive electrode additive according to the present invention has the advantages of improved capacity and possible high-speed charge and discharge.

[0030] In the present invention, the positive electrode additive may be included in an amount of 1 wt % to 5 wt %, preferably 2 wt % to 4 wt %, and more preferably 2.5 wt % to 3.5 wt %, based on the total weight of the positive electrode active material layer. When the content of the positive electrode additive satisfies this range, the positive electrode additive and the positive electrode active material are uniformly mixed, and the battery capacity can be maintained within an appropriate range.

[0031] positive electrode The positive electrode according to the present invention includes the positive electrode additive according to the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode additive according to the present invention. Since the positive electrode additive has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0032] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0033] The positive electrode active material layer can contain a positive electrode active material, and optionally a conductive material and a binder, as well as the above-mentioned positive electrode additive.

[0034] The positive electrode active material according to the present invention may include a lithium transition metal oxide in which the content of nickel among metal elements other than lithium is 80 atm % or more.

[0035] Specifically, the lithium transition metal oxide contained in the positive electrode active material of the present invention can have a composition represented by the following chemical formula 1.

[0036] [Chemical formula 1] Li a Ni 1-x-y Co x M 1 y M 2 z O2

[0037] In the above Chemical Formula 1, M 1 can be one or more selected from Mn and Al, and is preferably Mn or a combination of Mn and Al.

[0038] In the above Chemical Formula 1, M 2 can be any one or more elements selected from the group consisting of Zr, Ti, Mg, Ta, Nb, W, Mo and Cr.

[0039] The a represents the molar ratio of lithium in the lithium transition metal oxide, and can be 1.0≦a≦1.3, 1.0≦a≦1.2, or 1.0≦a≦1.1.

[0040] The 1-xy represents the molar ratio of nickel among metal elements other than lithium in the lithium transition metal oxide, and may be 0.6≦1-xy<1.0, 0.70≦1-xy≦0.98, or 0.80≦1-xy≦0.95.

[0041] When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0042] The x represents the molar ratio of cobalt among the metal elements other than lithium in the lithium transition metal oxide, and is 0 <x<0.4、0<x≦0.2、または0.01≦x≦0.10であることができる。

[0043] The y is M among the metal elements other than lithium in the lithium transition metal oxide.1 indicates the molar ratio of 0 <y<0.4、0<y≦0.2、または0.01≦y≦0.10であることができる。

[0044] The z is M among the metal elements other than lithium in the lithium transition metal oxide. 2 and may be 0≦z≦0.1, or 0≦z≦0.05.

[0045] The lithium transition metal oxide contained in the positive electrode active material of the present invention may be in the form of secondary particles in which a plurality of primary particles are aggregated, or may be in the form of single particles.

[0046] The lithium transition metal oxide contained in the positive electrode active material of the present invention may have an average primary particle size of 0.1 μm to 0.5 μm, preferably 0.1 μm to 0.3 μm. When the average primary particle size satisfies this range, a sufficient secondary battery capacity can be ensured.

[0047] The lithium transition metal oxide contained in the positive electrode active material of the present invention may have a secondary particle D50 of 8 μm to 15 μm, preferably 9 μm to 12 μm. If the secondary particle D50 is smaller than this range, there is a problem that the gas reaction due to a side reaction with the electrolyte in the manufactured secondary battery becomes excessive. If the secondary particle D50 is larger than this range, there is a problem that the electrode current collector breaks when the positive electrode active material is coated on the electrode.

[0048] The positive electrode according to the present invention may contain a positive electrode active material in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer. When the positive electrode active material is contained in this range, excellent capacity characteristics can be exhibited.

[0049] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0050] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0051] Positive electrode manufacturing method The method for manufacturing a positive electrode according to the present invention includes a step of reducing a precursor containing Zr to prepare ZrO 2-x (0 < x < 2), a step of mixing the ZrO 2-x as a positive electrode additive with a positive electrode active material, a conductive material, and a binder to produce a positive electrode slurry, and a step of producing a positive electrode active material layer using the positive electrode slurry.

[0052] First, a precursor containing Zr can be reduced to prepare ZrO 2-x (0 < x < 2).

[0053] Specifically, the reduction can be performed by heat-treating a precursor solution containing Zr in a reducing atmosphere.

[0054] The precursor solution can be produced by mixing a precursor containing Zr with a solvent. Here, as the precursor containing Zr, zirconium acetates, sulfates, nitrates, etc. can be used, and as the solvent, water, for example, deionized water, etc. can be used.

[0055] The reducing atmosphere is composed by injecting a reducing gas, and for example, it can be formed by mixing argon and hydrogen gas.

[0056] The heat treatment can be performed in an atmosphere containing 1 to 10% by volume of hydrogen (H2) in argon (Ar), preferably in an atmosphere containing 1 to 8% by volume, more preferably 3 to 8% by volume.

[0057] The heat treatment can be performed at a temperature of 500°C to 700°C, preferably 500°C to 650°C, more preferably 5,500°C to 600°C. When the heat treatment temperature is less than 500°C, there is a problem that the positive electrode additive cannot grow to a sufficient particle size. When the heat treatment temperature exceeds 700°C, there may be a problem that the particle size of the positive electrode additive grows excessively or a phase change occurs.

[0058] The heat treatment can be carried out for 4 to 6 hours, preferably 4 to 5 hours. When the heat treatment time is less than 4 hours, there is a problem that the positive electrode additive particles cannot grow to a sufficient size. When it exceeds 6 hours, there may be problems such as excessive growth of the positive electrode additive particles or phase change.

[0059] As described above, when the heat treatment is carried out in a reducing atmosphere, hydrogenation occurs on the surface of the ZrO2 nanoparticles formed in the precursor substance. Subsequently, oxygen vacancies are formed by a continuous H2O desorption reaction, and Zr metal cations receive electrons and are reduced, thereby generating ZrO 2-x (0 < x < 2).

[0060] Next, the ZrO 2-x is mixed as a positive electrode additive with a positive electrode active material, a conductive material, and a binder to produce a positive electrode slurry, and a positive electrode active material layer can be produced using the positive electrode slurry.

[0061] As the positive electrode active material, the above-mentioned high-nickel lithium transition metal oxide can be used. The lithium transition metal oxide can be purchased as a commercially available product or manufactured using a manufacturing method of lithium transition metal oxide well-known in the art. For example, the lithium transition metal oxide can be manufactured by mixing a lithium raw material substance and a positive electrode active material precursor and then firing.

[0062] In addition, the positive electrode is manufactured by dissolving or dispersing the above-mentioned positive electrode active material, positive electrode additive, and optionally, a binder, a conductive material, and a dispersant in a solvent to form a positive electrode slurry composition, applying the composition onto a positive electrode current collector, and then drying and rolling. Alternatively, the positive electrode slurry composition can be cast onto another support, and then the positive electrode active material layer obtained by peeling from this support is laminated onto a positive electrode current collector.

[0063] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0064] Electrochemical elements Next, an electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the above-described positive electrode of the present invention. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0065] The lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may further include a battery container that houses the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0066] The positive electrode is as described above, and therefore a detailed description thereof will be omitted. Only the remaining components will be described in detail below.

[0067] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0068] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0069] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0070] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbonaceous material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0071] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0072] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0073] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, specifically 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0074] The negative electrode can be manufactured by, for example, coating a negative electrode mixture slurry, prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector and then drying the coating, or by casting the negative electrode mixture slurry onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector. Alternatively, a graphite electrode made of carbon (C) or a metal itself can be used as the negative electrode.

[0075] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion movement in the electrolyte and excellent humidification ability for the electrolyte solution is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0076] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0077] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0078] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0079] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0080] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0081] The shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0082] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a large number of battery cells.

[0083] Examples of the medium to large size devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0084] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention may be practiced in various different forms, without departing from the spirit or scope of the present invention.

[0085] Example Manufacturing Example 1 A precursor solution was prepared using 12 g of zirconium acetate solution, 5 g of acetic acid, 0.6 g of polyvinylpyrrolidone (PVP), and 27 g of dimethylformamide (DMF). The solution was stirred for about 24 hours until it showed a transparent color.

[0086] By heat-treating and reducing the precursor solution containing zirconium acetate in a hydrogen and argon gas atmosphere at 600 °C, ZrO 2-x (0 < x < 2) was obtained in the form of a black powder. Here, the hydrogen and argon gas atmosphere was obtained by injecting a mixed gas composed of 5 vol% hydrogen and 95 vol% argon at a flow rate of 15 cc / min for 4 hours.

[0087] Production Example 2 ZrO2 was obtained in the form of a white powder by treating it in the same manner as in Production Example 1, except that the precursor solution containing zirconium acetate was heat-treated in an air atmosphere at 800 °C.

[0088] <Measurement of average particle size> Using SEM, the average particle size (D 2-x (0 < x < 2)) of the produced ZrO 50 ) was measured. As a result of the measurement, the average particle size (D 50 ) was 0.20 - 50 μm.

[0089] <XRD measurement>[[ID=二十九]] Figure 1(a) shows the result of observing the XRD pattern for the ZrO 2-x (0 < x < 2) particles of Production Example 1 using an X-ray diffractometer. For comparison, the XRD pattern was also observed for the ZrO2 particles of Production Example 2 and is shown in Figure 1(b).

[0090] Referring to Figure 1, the ZrO 2-x (0 < x < 2) particles heat-treated in a reducing atmosphere had a tetragonal crystal structure and showed 2θ peaks at 30.7 °, 35.5 °, 51.0 °, 60. / 63.4 °.

[0091] On the one hand, ZrO2 particles heat-treated in an air atmosphere have a monoclinic crystal structure, and the 2θ peaks are shown at 24.3°, 28.4°, 31.7°, 34.4°, 38.9°, 41.0°, 45.0°, 45.9°, 49.6°, 50.4°, 54.3°, 55.8°, 57.5°, 58.3°, 61.6°, 62.3°, 64.5°, 66.0°, 69.2°.

[0092] The peak intensities of the 2θ peaks are shown in Table 1 and Table 2 below.

[0093]

Table 1

[0094]

Table 2

[0095] <Measurement of Band Gap Energy> Using ultraviolet, visible, and near-infrared spectroscopy (UV-Visible-NIR Spectrometer), the reflectance was measured for ZrO 2-x (0 < x < 2) particles and ZrO2 particles in the wavelength range of 200 - 800 nm, and the band gap energy for each substance was calculated by the tangent of the Tauc plot.

[0096] As a result, it was confirmed that ZrO 2-x (0 < x < 2) particles have a band gap energy of 2.52 eV and ZrO2 particles have a band gap energy of 5.0 eV.

[0097] Here, the bandgap means the energy difference between the highest energy level where electrons exist (conduction band) and the lowest energy level where electrons do not exist (valence band). The smaller the bandgap, the easier it is to excite electrons and the higher the conductivity. Conversely, the larger the bandgap, the more difficult it is to excite electrons and the lower the conductivity.

[0098] That is, it can be confirmed that ZrO 2-x (0 < x < 2) particles exhibit higher conductivity than ZrO2 particles.

[0099] For reference, the ZrO2 particles of Production Example 2 were white, but it can be confirmed that the ZrO 2-x (0 < x < 2) particles of Production Example 1 have a blackish color. That is, the ZrO 2-x (0 < x < 2) particles according to an embodiment of the present invention can have a high absorbance of visible light.

[0100] Example 1 As the positive electrode active material, 82% by weight of LiNi 0.8 Co 0.1 Mn 0.1 O2, 8% by weight of carbon black Super P as a conductive material, 7% by weight of polyvinylidene pyrrolidone (PVDF) as a binder, and 3% by weight of ZrO 2-x (0 < x < 2) of Production Example 1 were mixed in an NMP solvent (solid content 51.8%) to produce a positive electrode slurry. After applying the positive electrode slurry to one side of an aluminum current collector, it was dried in vacuum at 110°C for 12 hours and then rolled to produce a positive electrode.

[0101] Li metal was used as the counter electrode for the positive electrode, and an electrode assembly was produced with a polypropylene separator interposed between the positive electrode and the negative electrode.

[0102] Ethylene carbonate (EC): Diethyl carbonate (DEC) was mixed in a volume ratio of 1:1, and lithium salt LiPF6 was contained in the organic solvent at a concentration of 1 M, and fluoroethylene carbonate (FEC) as an additive was added at a concentration of 5 wt% to produce an electrolyte solution.

[0103] The electrode assembly was positioned inside the case, and the manufactured electrolyte solution was injected to manufacture a secondary battery.

[0104] Comparative Example 1 As the positive electrode active material, LiNi 0.8 Co 0.1 Mn 0.1 O2 82 wt%, carbon black Super P 8 wt% as a conductive material, and polyvinylidene pyrrolidone (PVDF) 7 wt% as a binder were mixed in NMP solvent (solid content 51.8%) to produce a positive electrode slurry. A secondary battery was manufactured in the same manner as in Example 1 except that no positive electrode additive was used.

[0105] Comparative Example 2 As the positive electrode additive, instead of ZrO 2-x (0 < x < 2), ZrO2 manufactured in Production Example 2 was used, and a secondary battery was manufactured in the same manner as in Example 1.

[0106] <XRD Measurement of the Positive Electrodes of Example 1 and Comparative Examples 1-2> Figure 2 shows the results of observing the XRD patterns of the positive electrodes manufactured in Example 1 and Comparative Examples 1-2 using an X-ray diffractometer. In Figure 2, since the peaks corresponding to the tetragonal and monoclinic structures of each additive are still observed even after mixing with the positive electrode active material, it can be confirmed that each additive structure is maintained even after mixing with the positive electrode active material and the like.

[0107] Experimental Example 1 - Evaluation of Cycle Characteristics Each of the secondary batteries manufactured in Example 1 and Comparative Examples 1 to 2 was charged at a constant current of 0.1 C to 4.3 V at 25°C and discharged at a constant current of 0.1 C to 2.5 V. One cycle was defined as this process, and after performing 50 cycles of charge and discharge, the capacity retention rate with respect to the initial capacity after 50 cycles was measured. The results are shown in Table 3 below.

[0108]

Table 3

[0109] The secondary battery of Example 1 using ZrO 2-x (0 < x < 2) as a cathode additive had better cycle characteristics than Comparative Example 1 that did not use a cathode additive. This is because when using ZrO 2-x (0 < x < 2) as a cathode additive, the surface of the cathode active material is stabilized, and it is considered that oxygen gas generated at a high voltage is collected by ZrO 2-x (0 < x < 2). Also, the secondary battery of Example 1 using ZrO 2-x (0 < x < 2) as a cathode additive had better cycle characteristics than the secondary battery of Comparative Example 2 using ZrO2 as a cathode additive. This is considered to be because ZrO 2-x (0 < x < 2) has Zr 3+ and has a reduced bandgap energy and high electron conductivity.

[0110] Experimental Example 2 - Evaluation of Cycle Characteristics during High-Rate Charging The lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 2 were charged under constant current conditions at a rate of 0.1 C to 4.3 V at 25°C and discharged at a rate of 0.8 C to 2.5 V. One cycle was defined as this process, and after performing 50 cycles of charge and discharge, the capacity after 50 cycles was measured and the capacity retention rate with respect to the initial capacity was calculated. The results are shown in Table 4 below.

[0111]

Table 4

[0112] ZrO as a positive electrode additive 2-x (0 < x < 2) The secondary battery of Example 1 using it had excellent cycle characteristics even when charged and discharged at a high rate compared to Comparative Example 1 that did not use a positive electrode additive. This is because when using ZrO 2-x (0 < x < 2), the surface of the positive electrode active material is stabilized, and it is considered that oxygen gas generated at a high voltage is collected by ZrO 2-x (0 < x < 2). Also, the secondary battery of Example 1 using ZrO 2-x (0 < x < 2) as a positive electrode additive had excellent cycle characteristics even when charged and discharged at a high rate compared to the secondary battery of Comparative Example 2 using ZrO2 as a positive electrode additive. This is because compared to ZrO2, ZrO 2-x (0 < x < 2) has Zr 3+ and is considered to have a decreased bandgap energy and high electron conductivity.

[0113] Experimental Example 3 - Evaluation of Gas Generation Amount For each of the secondary batteries manufactured in Example 1 and Comparative Example 1 above, charging was carried out under constant current conditions up to 4.5V at a 0.1C rate, and the amounts of CO2, CO, and O2 generated were measured using Differential Electrochemical Mass Spectrometry (Differential Electrochemical Mass Spectrometer, DEMS) at 25°C. The results are shown in Figure 3.

[0114] Referring to the results in Figure 3, it can be confirmed that the gas generation amounts in Example 1 were significantly reduced compared to Comparative Example 1 that did not use a positive electrode active material. This is because when using ZrO 2-x (0 < x < 2), the surface of the positive electrode active material is stabilized, and oxygen gas generated at a high voltage is collected by ZrO 2-x (0

Claims

1. A positive electrode including a positive electrode active material layer including a positive electrode active material, a conductive material, a binder, and a positive electrode additive, The positive electrode additive is ZrO ２－ｘ (0<x<2), The positive electrode active material includes a lithium transition metal oxide represented by the following chemical formula 1: [Chemical formula 1] Li a Ni 1-x-y Co x M 1 y M 2 z O 2 In the above Chemical Formula 1, M 1 is Al, Mn, or a combination thereof; M 2 is one or more elements selected from the group consisting of Zr, Ti, Mg, Ta, Nb, W, Mo, and Cr; 1.0≦a≦1.3, 0<x<0.4, 0<y<0.4, 0≦z≦0.1, 0.6≦1−x−y<1.

0.

2. The average particle size (D ５０ 2. The positive electrode according to claim 1, wherein the thickness of the first electrode is 200 nm to 50 μm.

3. The ZrO ２－ｘ The positive electrode according to claim 1 , wherein [Formula 1] 5<P1 / P2<8 In formula 1, P1 is the peak intensity in the range of 2θ from 29° to 31° on the XRD, and P2 is the peak intensity in the range of 2θ from 35° to 37° on the XRD.

4. The positive electrode of claim 1 , wherein the positive electrode additive has a tetragonal crystal structure.

5. The positive electrode according to claim 1 , wherein the positive electrode additive has a band gap energy of 3.0 eV or less.

6. The positive electrode according to claim 1 , wherein the positive electrode additive is contained in an amount of 1% by weight to 5% by weight based on the total weight of the positive electrode active material layer.

7. A lithium secondary battery comprising the positive electrode according to claim 1 .

8. ZrO is obtained by reducing a precursor containing Zr. ２－ｘ preparing (0<x<2); The ZrO ２－ｘ as a positive electrode additive, and a positive electrode active material, a conductive material, and a binder to prepare a positive electrode slurry; preparing a positive electrode active material layer using the positive electrode slurry; Including, The positive electrode active material includes a lithium transition metal oxide represented by the following chemical formula 1: [Chemical formula 1] Li a Ni 1-x-y Co x M 1 y M 2 z O 2 In the above Chemical Formula 1, M 1 is Al, Mn, or a combination thereof; M 2 is one or more elements selected from the group consisting of Zr, Ti, Mg, Ta, Nb, W, Mo, and Cr; 1.0≦a≦1.3, 0<x<0.4, 0<y<0.4, 0≦z≦0.1, 0.6≦1−x−y<1.

0.

9. The method for producing a positive electrode according to claim 8 , wherein the precursor is at least one selected from acetate, sulfate, and nitrate of Zr.

10. The ZrO ２－ｘ The method for producing a positive electrode according to claim 8 , wherein (0<x<2) is produced by heat treating a precursor solution containing zirconium in a reducing atmosphere.

11. The method for producing a positive electrode according to claim 10 , wherein the reducing atmosphere is formed by hydrogen and argon.

12. The method for producing a positive electrode according to claim 10, wherein the heat treatment is carried out at a temperature of 500°C to 700°C.

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