WO2019093863A2 - Lithium cobalt-based positive electrode active material, method for preparing same, positive electrode comprising same, and secondary battery - Google Patents

Abstract

The present invention relates to a method for preparing a lithium cobalt-based positive electrode active material and a positive electrode active material prepared thereby, the method comprising a step for dry-mixing particles of lithium cobalt oxide represented by chemical formula 1 and lithium metal oxide particles of at least one selected from the group consisting of lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide, followed by thermal treatment.

Description

Lithium cobalt-based cathode active material, its production method, anode and secondary battery containing same

[Mutual quotation with related application]

This application claims priority from Korean Patent Application No. 10-2017-0150922 filed on November 13, 2017, and Korean Patent Application No. 10-2018-0138704 filed November 13, 2018 , The contents of which are incorporated herein by reference.

[TECHNICAL FIELD]

The present invention relates to a lithium cobalt-based positive electrode active material, a method for producing the same, and a positive electrode and a secondary battery comprising the same. More particularly, the present invention relates to a lithium cobalt- A positive electrode active material, a production method thereof, and a positive electrode and a secondary battery comprising the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

One of the cathode active materials for lithium secondary batteries, which has been actively researched and used at present, is a layered LiCoO ₂ . LiCoO ₂ is most widely used because it is easy to synthesize and has excellent electrochemical performance including life characteristics, but its structural stability is low and thus it is limited to be applied to high capacity battery technology.

A technique has been proposed in which the surface of lithium cobalt oxide particles is coated with an oxide of a metal such as Al, Zr or the like to improve the structural stability of the lithium cobalt oxide. The lithium-cobalt oxide coated with the metal oxide showed excellent electrochemical performance in a battery having a driving voltage of less than 4.45V. However, according to the studies of the present inventors, when lithium cobalt oxide coated with a metal oxide is applied to a battery having a driving voltage of 4.45 V or more, the gas and cobalt elution occurs rapidly, and the lifetime characteristics and high- Respectively.

During the metal oxide coating, lithium reacts with the metal oxide on the surface of the lithium cobalt oxide, thereby forming a lithium-deficient layer in which the molar ratio of Li / Co is less than 1 at the surface of the lithium cobalt oxide. When such a lithium- , Lifetime characteristics and output characteristics are improved, but gas generation and cobalt elution occur at high voltage driving due to increase in reactivity with an electrolyte, and high temperature stability is lowered.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a lithium cobalt-based cathode active material capable of effectively suppressing cobalt dissolution even when driven at a high voltage of 4.45 V or higher.

In one aspect, the present invention provides a method for producing a lithium-cobalt-based cathode active material, comprising dry-mixing lithium-cobalt oxide particles represented by the following formula (1) and lithium metal oxide particles and heat-

[Chemical Formula 1]

LiCo _1-x M _x O ₂

M is at least one selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb.

At this time, the lithium metal oxide particles may be at least one selected from the group consisting of lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide.

Preferably, the heat treatment is performed at 300 ° C to 800 ° C.

The lithium metal oxide particles may be mixed in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the total weight of the lithium cobalt oxide particles and the lithium metal oxide particles.

In another aspect, the present invention provides a lithium cobalt-based oxide particle represented by Formula 1 below; And a coating layer formed on the lithium cobalt oxide particle and including a lithium metal oxide,

And a lithium cobalt based cathode active material having an atomic ratio of Li / Co of 1 or more at an interface between the lithium cobalt oxide particle and the coating layer and in the coating layer.

[Chemical Formula 1]

LiCo _1-x M _x O ₂

M is at least one selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb.

Meanwhile, the cobalt leaching amount measured after charging the secondary battery to which the cathode active material is applied at 4.5 V and stored at 60 ° C. for 2 weeks may be 700 ppm or less.

The lithium metal oxide may be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the total cathode active material.

Meanwhile, the cathode active material according to the present invention may be manufactured according to the cathode active material manufacturing method of the present invention.

In another aspect, the present invention provides a lithium secondary battery including the positive electrode and the positive electrode including the positive electrode active material according to the present invention.

According to the manufacturing method of the present invention, by using the lithium metal oxide as the coating raw material, it is possible to prevent lithium in the lithium cobalt oxide from being consumed by the reaction with the coating raw material during coating, The formation of a defect layer can be prevented. Therefore, gas generation and cobalt leaching caused by the presence of the lithium-deficient layer can be effectively suppressed when operating at a high voltage of 4.45 V or higher.

In addition, the cathode active material of the present invention exhibits excellent electrochemical characteristics due to a small amount of cobalt elution even after storage at high temperature after high voltage charging.

Hereinafter, the present invention will be described in detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The present inventors have conducted intensive research to develop a lithium cobalt-based cathode active material capable of effectively suppressing gas generation and cobalt dissolution even when driven at a high voltage of 4.45 V or more, and as a result, it has been found that lithium metal oxides It is possible to realize excellent electrochemical characteristics and high temperature storability even in a battery having a driving voltage of at least 4.45 V by suppressing the formation of a lithium defect layer, thereby completing the present invention.

Method for producing lithium cobalt-based cathode active material

First, a method for producing a lithium cobalt-based cathode active material according to the present invention will be described.

The method for producing a lithium-cobalt-based cathode active material according to the present invention includes a step of dry-mixing lithium cobalt oxide particles and lithium metal oxide particles and subjecting the mixture to heat treatment.

In the present invention, the lithium cobalt oxide particles may be represented by the following formula (1).

[Chemical Formula 1]

LiCo _{1 - x} M _x O ₂

M is a doping element and may be at least one element selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb, , Ti, or a combination thereof.

X represents the atomic ratio of the doping element in the lithium cobalt oxide particle, and may be 0? X? 0.2, preferably 0? X? 0.1.

The lithium cobalt oxide particles represented by Formula 1 may be prepared by using commercially available lithium cobalt oxide particles or by a method for producing lithium cobalt oxide well known in the art. For example, the lithium cobalt oxide particles represented by Formula 1 are prepared by mixing a cobalt raw material, a lithium raw material, and optionally a doping raw material in an amount satisfying a stoichiometric ratio and then firing .

The cobalt raw material may be, for example, a cobalt-containing oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate or sulfate, ₂ , CO ₂ O ₄ , CoOOH, Co (OCOCH ₃ ) ₂揃 4H ₂ O, Co (NO ₃ ) ₂揃 6H ₂ O, or Co (SO ₄ ) ₂揃 7H ₂ O, Two or more mixtures may be used.

The lithium source material may be, for example, a lithium-containing oxide, a hydroxide, an oxyhydroxide, a halogenated salt, a nitrate, a carbonate, an acetate, a oxalate, a citrate or a sulfate, and more specifically, Li ₂ CO ₃ , LiNO _3, LiNO _2, LiOH, LiOH · H ₂ O, LiH, LiF, LiCl, LiBr, LiI, Li ₂ O, Li ₂ SO _4, CH ₃ COOLi, or Li ₃ C ₆ H ₆ O ₇ and the like, Any one or a mixture of two or more of them may be used.

Wherein the doping element raw material is at least one metal selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca, and Nb or oxides, hydroxides, Halide, nitrate, carbonate acetate, oxalate, citrate or sulfate, and any one or a mixture of two or more thereof may be used.

On the other hand, the firing may be performed at a temperature ranging from 500 to 1100 ° C, preferably from 700 to 900 ° C, and may be carried out in the air or in an oxygen atmosphere. The firing time is preferably 6 hours to 18 hours, and more preferably 8 hours to 12 hours.

Next, the lithium metal oxide particles are used for forming a coating layer on the lithium cobalt oxide particles to prevent direct contact between the electrolyte and the lithium cobalt oxide particles. For example, lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide And the like.

Conventionally, metal oxide particles have been mainly used for forming a coating layer of lithium cobalt oxide. However, when a coating layer is formed using metal oxide particles, lithium in the lithium cobalt oxide reacts with the metal oxide and is consumed in the process of forming the coating layer, so that a lithium defect layer is formed on the surface of the lithium cobalt oxide. The lithium-cobalt-based cathode active material having the lithium-deficient layer as described above did not cause a serious problem when applied to a battery having a driving voltage of less than 4.45 V, but when applied to a battery having a driving voltage of 4.45 V or more, gas generation and cobalt- There is a problem that the battery performance is remarkably deteriorated.

However, when lithium metal oxide is used as a coating raw material as in the present invention, since lithium is contained in the coating material itself, lithium in the lithium cobalt oxide is not consumed at the time of forming the coating layer, so that a lithium-defect layer is not formed. Therefore, even when applied to a battery having a driving voltage of 4.45 V or more, gas generation and cobalt leaching can be suppressed, and excellent battery performance can be realized.

The lithium metal oxide particles may be mixed in an amount of 0.01 to 0.5 parts by weight, preferably 0.04 to 0.2 parts by weight based on 100 parts by weight of the total weight of the lithium cobalt oxide particles and the lithium metal oxide particles. When the mixing amount of the lithium metal oxide particles satisfies the above range, the reaction with the electrolytic solution can be suppressed and the effect of reducing the amount of cobalt dissolution can be sufficiently obtained. Specifically, when the content of the lithium metal oxide is less than the above range, the cobalt dissolution reduction effect is not sufficient. If the content exceeds the above range, the capacity decrease and the surface resistance may increase.

In the present invention, it is preferable that the lithium cobalt oxide particles and the lithium metal oxide particles are mixed by a dry mixing method without using a solvent. When the wet process for dispersing the lithium metal oxide used as the coating material of the present invention in a solvent is used, the lithium metal oxide particles are agglomerated to form a uniform coating layer, and the effect of inhibiting cobalt dissolution is inferior .

Meanwhile, the heat treatment is preferably performed at a temperature of 300 ° C to 800 ° C, preferably 500 ° C to 800 ° C, and more preferably 600 ° C to 800 ° C. When the heat treatment temperature is within the above range, the lithium metal oxide does not react with lithium in the lithium cobalt oxide and lithium can be prevented from being lost by the heat treatment, thereby effectively preventing formation of the lithium defect layer .

In addition, the heat treatment is preferably performed for 1 to 10 hours, preferably 1 to 8 hours, more preferably 2 to 5 hours. When the heat treatment time satisfies the above range, the lithium metal oxide does not react with lithium in the lithium cobalt oxide and lithium can be prevented from being lost by the heat treatment, thereby effectively preventing formation of the lithium defect layer .

The cathode active material according to the present invention produced by the above method has no lithium-defect layer on the surface of lithium cobalt oxide particles, and therefore, when applied to a battery having a driving voltage of 4.45 V or more, gas generation and cobalt elution are suppressed .

Lithium cobalt-based cathode active material

Next, the lithium cobalt based positive electrode active material according to the present invention will be described.

The lithium cobalt-based positive electrode active material prepared according to the present invention comprises lithium cobalt-based oxide particles represented by the following formula (1); And a coating layer formed on the lithium cobalt oxide particle and including lithium metal oxide.

[Chemical Formula 1]

LiCo _{1 - x} M _x O ₂

M is a doping element and may be at least one element selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb, , Ti, or a combination thereof.

X represents the molar ratio of the doping element in the lithium cobalt oxide particle, and may be 0? X? 0.2, preferably 0? X? 0.1.

The coating layer is formed by dry mixing lithium metal oxide particles and lithium cobalt oxide particles and then heat-treating the lithium metal cobalt oxide particles. The coating layer is formed on the surface of the lithium cobalt oxide particles and includes a lithium metal oxide. The lithium metal oxide may be at least one selected from the group consisting of lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide, for example.

Meanwhile, the lithium metal oxide may be included in an amount of 0.01 to 0.5 parts by weight, preferably 0.04 to 0.2 parts by weight based on 100 parts by weight of the entire cathode active material. When the content of the lithium metal oxide satisfies the above range, the reaction with the electrolytic solution is suppressed, and the effect of reducing the amount of cobalt dissolution can be sufficiently obtained. Specifically, when the content of the lithium metal oxide is less than the above range, the cobalt dissolution reduction effect is not sufficient. If the content exceeds the above range, the capacity decrease and the surface resistance may increase.

Meanwhile, since the cathode active material according to the present invention is prepared by using lithium metal oxide as a coating material and performing heat treatment at a relatively low temperature, lithium in the lithium cobalt oxide does not react with the coating material during formation of the coating layer , And therefore does not include a lithium-defect layer having an atomic ratio of lithium Li / Co of less than 1. That is, in the positive electrode active material according to the present invention, the atomic ratio of Li / Co in the surface portion is 1 or more. Here, the surface portion refers to a region adjacent to the surface of the cathode active material particle, and is a region including the interface between the lithium cobalt oxide particle and the coating layer and the coating layer. But is not limited to, for example, a region having a thickness of 1 to 100 nm, preferably 1 to 50 nm in the center direction from the outermost surface of the cathode active material particle. The Li / Co atomic ratio of the cathode active material particles can be measured by various component analysis methods known in the art such as X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) ), Energy Dispersive X-ray spectroscopy (EDS), Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), Time of Flight Secondary Ion Mass Spectrometry, ToF-SIMS).

As described above, the positive electrode active material of the present invention has excellent structural stability due to the absence of a lithium-deficient layer. Even when applied to a battery having a driving voltage of 4.45 V or more, gas generation and cobalt elution are suppressed, The cobalt dissolution inhibiting effect is excellent. Specifically, the amount of cobalt eluted after charging the battery with the cathode active material of the present invention at 4.5 V and stored at 60 ° C for 2 weeks is 700 ppm or less, preferably 600 ppm or less, and more preferably 500 ppm or less.

Meanwhile, the cathode active material according to the present invention may contain lithium at a constant concentration irrespective of the positions inside the particles, and may have a concentration gradient in which the concentration of lithium gradually increases from the surface to the center of the active material particle. In the case where lithium is distributed so as to have a concentration gradient in the cathode active material, the concentration gradient may be in the form of a linear function or a quadratic function which varies depending on the thickness of the particles from the center of the active material particle to the surface direction.

The concentration of the cathode active material can be measured by various component analysis methods known in the art such as X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy analysis Dispersion x-ray spectroscopy (EDS), Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), Time-Flight Secondary Ion Mass Spectrometry (ToF- SIMS) or the like.

The cathode active material according to the present invention may have an average particle diameter (D ₅₀ ) of 3 to 50 탆, preferably 10 to 50 탆. When the average particle diameter (D ₅₀ ) of the cathode active material satisfies the above range, Specific surface area and anodic cohesion density can be realized. Herein, the average particle diameter (D ₅₀ ) of the cathode active material means a particle diameter at 50% of the volume cumulative distribution. For example, it can be measured using a laser diffraction method. Specifically, after the cathode active material particles are dispersed in a dispersion medium and introduced into a commercially available laser diffraction particle size analyzer (for example, Microtra MT 3000), an ultrasonic wave of about 28 Hz is irradiated at an output of 60 W, Can be measured by a method of calculating the particle size at 50%.

Anode and lithium secondary battery

Next, the anode according to the present invention will be described.

The cathode active material for a secondary battery according to the present invention can be usefully used for manufacturing a cathode for a secondary battery.

Specifically, the cathode for a secondary battery according to the present invention includes a cathode current collector and a cathode active material layer formed on the cathode current collector, wherein the cathode active material layer includes the cathode active material according to the present invention.

The positive electrode may be produced according to a conventional positive electrode manufacturing method, except that the positive electrode active material according to the present invention is used. For example, the positive electrode may be prepared by dissolving or dispersing the components constituting the positive electrode active material layer, that is, the positive electrode active material, the conductive material and / or the binder, in a solvent to prepare a positive electrode composite material, Or by a method in which the film is coated on at least one side and then dried and rolled or by casting the positive electrode material on a separate support and then peeling off the support from the support to laminate the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, the positive electrode current collector may be made of a metal such as stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel, , Titanium, silver, or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The current collector includes the cathode active material according to the present invention on at least one surface thereof and optionally includes at least one of a conductive material and a binder.

The cathode active material may include the cathode active material according to the present invention, and the cathode active material may be contained in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight based on the total weight of the cathode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be included in an amount of 1% by weight to 30% by weight based on the total weight of the cathode active material layer.

In addition, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof. One kind or a mixture of two or more kinds of them may be used. The binder may be included in an amount of 1% by weight to 30% by weight based on the total weight of the cathode active material layer.

On the other hand, the solvent used in the preparation of the positive electrode material may be a solvent commonly used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, (NMP), acetone or water may be used alone or in combination. The amount of the solvent to be used can be appropriately adjusted in consideration of the application thickness of the slurry, the production yield, the viscosity, and the like.

Next, a secondary battery according to the present invention will be described.

The secondary battery according to the present invention includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention.

The secondary battery may further include a battery container for storing the positive electrode, the negative electrode and the electrode assembly of the separator, and a sealing member for sealing the battery container.

In the secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

The negative electrode may be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode may be produced by dissolving or dispersing the components constituting the negative electrode active material layer, that is, the negative electrode active material, the conductive material and / or the binder in a solvent to form a negative electrode mixture, Or a method in which the negative electrode material is coated on at least one surface and then dried or rolled or casting the negative electrode material onto a separate support and then peeling the support from the support to laminate the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides such as SiO _v (0 <v <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide, which can dope and dedoped lithium; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

Meanwhile, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ion. The separator can be used without any particular limitation as long as it is used as a separator in a secondary battery. Particularly, It is preferable that it is a resistance and excellent in an ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

The electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a melt-type inorganic electrolyte, and the like, which are usable in the production of a secondary battery.

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

The organic solvent may be used without limitation as long as it 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,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Ra-CN (Ra is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to 9, the performance of the electrolytic solution may be excellent.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium _{salt, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAl0 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2 _{, LiN (C 2 F 5 SO} 2) 2, LiN (CF 3 SO 2) 2. LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ may be used. The concentration of the lithium salt is preferably within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

The electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like for the purpose of improving the lifetime characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. N, N &lt; RTI ID = 0.0 &gt; (N, &lt; / RTI &gt; N, N'-tetramethyluronium hexafluorophosphate), pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, And at least one additive such as substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the secondary battery including the cathode active material according to the present invention has excellent electrical characteristics and high temperature storability, and can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (HEV) Electric vehicles, and the like. In particular, the secondary battery according to the present invention can be usefully used as a high-voltage battery having a high voltage of 4.45 V or higher.

In addition, the secondary battery according to the present invention can be used as a unit cell of a battery module, and the battery module can be applied to a battery pack. The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example 1

0.07 parts by weight of LiAlO ₂ powder was mixed in a solid phase with 100 parts by weight of LiCoO ₂ powder and then heat-treated at 700 ° C for 4 hours to form LiAlO ₂ on LiCoO ₂ To prepare a coated lithium cobalt based cathode active material.

Example 2

0.05 parts by weight of Li ₂ ZrO ₃ powder was mixed with 100 parts by weight of LiCoO ₂ powder in a solid phase and then heat-treated at 750 ° C for 5 hours to prepare a lithium cobalt-based cathode active material coated with Li ₂ ZrO ₃ on LiCoO ₂ .

Example 3

0.05 parts by weight of Li ₂ TiO ₃ powder was mixed in a solid phase with 100 parts by weight of LiCoO ₂ powder and then heat-treated at 750 ° C for 5 hours to prepare a lithium cobalt-based cathode active material coated with Li ₂ TiO ₃ on LiCoO ₂ .

Comparative Example 1

A lithium cobalt-based cathode active material was prepared in the same manner as in Example 1, except that Al ₂ O ₃ powder was used instead of LiAlO ₂ powder.

Comparative Example 2

A lithium cobalt-based cathode active material was prepared in the same manner as in Example 2, except that ZrO ₂ powder was used instead of Li ₂ ZrO ₃ powder.

Comparative Example 3

A lithium cobalt-based cathode active material was prepared in the same manner as in Example 3, except that TiO ₂ powder was used instead of Li ₂ TiO ₃ powder.

Comparative Example 4

100 parts by weight of LiCoO ₂ powder and 0.07 parts by weight of LiAlO ₂ powder were added to an ethanol solvent and mixed and then heat-treated at 650 ° C for 5 hours to prepare a lithium cobalt-based cathode active material.

Experimental Example 1

Lithium secondary batteries were prepared using the cathode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4, respectively.

Specifically, the cathode active material, the carbon black conductive material, and the PVdF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were mixed in the N-methylpyrrolidone solvent in a weight ratio of 90: 5: 5, (Viscosity: 5000 mPa.s) was prepared, applied to an aluminum current collector, dried and rolled to prepare a positive electrode.

Further, mesocarbon microbeads (MCMB), carbon black conductive material and PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 85: 10: 5 as an anode active material to prepare a negative electrode mixture, And then dried and rolled to prepare a negative electrode.

The electrode assembly was fabricated with the porous polyethylene separator interposed between the anode and the cathode fabricated as described above, and the electrode assembly was placed inside the battery case, and then an electrolytic solution was injected into the case to manufacture a coin cell. The electrolyte solution was prepared by dissolving lithium hexafluorophosphate at a concentration of 1.15 M in an organic solvent prepared by mixing ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate at a volume ratio of 3: 4: 3.

The thus prepared coin cells were charged to 4.5V. After charging, the positive electrode was separated, washed with a dichloromethane (DCM) solution, and then the washed positive electrode was placed in a Nilgen bottle together with 4 mL of electrolyte. To prevent the electrolyte from evaporating, the Nalen Bottle is completely sealed with a Parafilm and an aluminum pouch, and then the sealed bottle is kept in a 60 ° C chamber for two weeks. After 2 weeks, the cathode active material, which could be a float in the electrolyte solution, was completely removed using a sealing paper filter to extract the electrolyte solution, and the cobalt content (i.e., cobalt leaching amount) present in the electrolyte solution was measured by ICP analysis by evaporating the electrolyte solution. ICP analysis was carried out using an inductively coupled plasma emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer). Four coin cells were prepared for each of the examples and comparative examples to reduce the deviation between the cells, and the amount of cobalt eluted from the four coin cells was measured and the average value was measured. The measurement results are shown in Table 1 below.

	Cobalt dissolution (ppm)
Example 1	496
Example 2	591
Example 3	559
Comparative Example 1	857
Comparative Example 2	828
Comparative Example 3	1057
Comparative Example 4	842

As shown in Table 1, the amounts of cobalt elution in the coin cells of Examples 1 to 3 using the cathode active material in which the coating layer was formed using the lithium metal oxide particles were significantly higher than those of the coin cells of the coin cells of Comparative Examples 1 to 4 Can be confirmed.

Claims (9)

1. A process for producing a lithium-cobalt-based anode comprising the steps of dry-mixing and heat-treating at least one lithium metal oxide particle selected from the group consisting of lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide, A method for producing an active material.

   [Chemical Formula 1]

   LiCo _{1 - x} M _x O ₂

   M is at least one selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb.
2. The method according to claim 1,

   Wherein the heat treatment is performed at a temperature ranging from 300 ° C to 800 ° C.
3. The method according to claim 1,

   Wherein the lithium metal oxide particles are mixed in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the total weight of the lithium cobalt oxide particles and the lithium metal oxide particles.
4. A lithium cobalt oxide particle represented by the following formula (1); And

   And a coating layer formed on the lithium cobalt oxide particle and containing at least one lithium metal oxide selected from the group consisting of lithium aluminum oxide, lithium zirconium oxide, and lithium titanium oxide,

   A lithium cobalt-based cathode active material having an atomic ratio of Li / Co of 1 or more at an interface between the lithium cobalt oxide particle and the coating layer and in the coating layer;

   [Chemical Formula 1]

   LiCo _{1 - x} M _x O ₂

   M is at least one selected from the group consisting of Al, Mg, W, Mo, Zr, Ti, Fe, V, Cr, Ba, Ca and Nb.
5. 5. The method of claim 4,

   The lithium cobalt-based cathode active material having a cobalt elution amount of 700 ppm or less measured after charging the secondary battery to which the cathode active material is applied at 4.5 V and stored at 60 ° C for 2 weeks.
6. 5. The method of claim 4,

   Wherein the lithium metal oxide is contained in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the total positive electrode active material.
7. An anode comprising the cathode active material according to any one of claims 4 to 6.
8. A lithium secondary battery comprising the positive electrode of claim 7.
9. 8. The method of claim 7,

   Wherein the lithium secondary battery has a driving voltage of 4.45 V or higher.