KR20140069567A - Positive active material for a lithium secondary battery, method of preparing the same, and lithium secondary battery using the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery using the same, and more specifically, to a cathode active material for a lithium secondary battery which comprises a lithium metal oxide represented by chemical formula 1, has a high degree of crystallinity by understanding the relationship between the full width at half maximum of the lithium metal oxide and the performance of the battery, and is able to improve the capacity and the rate capability of a lithium secondary battery; a manufacturing method thereof; and a lithium secondary battery using the same. In chemical formula 1, a is 1.17<=a<=1.33; x,y and z are 0<x<1, 0<y<1, and 0<z<1; and a+x+y+z=2.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a positive active material for lithium secondary batteries, a method for producing the positive active material, and a lithium secondary battery using the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

Embodiments of the present invention relate to a cathode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery using the same.

Background Art [0002] With the recent development of high-tech electronic industry, it is possible to miniaturize and lighten electronic equipments, and the use of portable electronic equipments is increasing. The need for a battery having a high energy density as a power source for such portable electronic devices has been increased, and research on lithium secondary batteries has been actively conducted. The lithium _secondary battery uses a transition metal oxide capable of reversibly intercalating and deintercalating lithium ions as an anode, and LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Co _y Mn _{21 -x- y} O ₂ , LiMnO ₂ Have been studied. Among the above cathode active materials, a Co-based cathode active material such as LiCoO ₂ is most widely used as a cathode active material because it exhibits a high energy density (theoretical capacity of 274 mAh / g) and an excellent life characteristic (capacity retention rate). However, due to the structural instability of LiCoO ₂ , it is practically assumed that about 50% of the theoretical capacity, that is, 0.5 or more of lithium (Li) remains in Li _{2 x} CoO ₂ (x> 0.5) And only 140 mAh / g is used. In order to utilize the theoretical capacity of LiCoO ₂ more than 50%, it is necessary to increase the charge voltage to more than 4.2 V. In this case, lithium is less than 0.5 in Li _x CoO ₂ , and hexagonal monoclinic phase And it is structurally unstable. As the lifespan progresses, rapid capacity decrease occurs.

Of the above cathode active materials, LiCoO ₂ is most widely used because it has excellent lifetime characteristics and charge / discharge efficiency. However, since it has low safety at high temperature and cobalt used as a raw material is an expensive material due to its resource limit, Have. LiMnO ₂ , LiMn ₂ O ₄ Lithium manganese oxides are excellent in thermal stability, low in cost, and easy to synthesize, but have a problem of low capacity, poor high temperature characteristics, and low conductivity. The LiNiO ₂ cathode active material exhibits a relatively low cost and high discharge capacity, but exhibits rapid phase transition of the crystal structure in accordance with the volume change accompanying the charging / discharging cycle. When exposed to air and moisture, There is a problem of deterioration.

Accordingly, the present inventors have found that by providing a positive electrode active material composed of a lithium metal oxide whose crystallinity is enhanced by controlling the mixing ratio of lithium in the lithium metal oxide as the positive electrode active material, and the capacity and rate characteristics of the lithium secondary battery including the thus obtained positive electrode active material The present invention has been accomplished.

According to one embodiment of the present invention, an object of the present invention is to provide a lithium secondary battery, which is an approach for maximizing capacity and rate characteristics for a cathode active material, which comprises adjusting a mixing ratio of lithium to a transition metal in producing a cathode active material for a lithium secondary battery, A cathode active material for a lithium secondary battery, which is capable of measuring the full width at half maximum (FWHM) through XRD analysis of a lithium metal oxide and investigating a corresponding electrochemical relationship to thereby improve the crystallinity and the capacity and rate characteristics of the battery, Lithium provides a secondary battery.

According to an embodiment of the present invention, another object of the present invention is to provide a method of manufacturing a cathode active material for a lithium secondary battery.

In one embodiment of the present invention, one aspect of the present invention relates to a cathode active material for a lithium secondary battery comprising a lithium metal oxide represented by the following general formula (1), wherein one of the main peaks in the XRD pattern of the lithium metal oxide The full width at half maximum (FWHM) of the phosphorus (104) plane peak (2? = 44.5 占) may be more than 0 and less than 0.2 占.

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z O ₂

(Wherein a is 1.17? A? 1.33 and x, y and z are 0 <x <1, 0 <y <1, 0 <z <1, and a + x + y + z = 2.

In one embodiment, in the X-ray diffraction analysis (XRD), the lithium metal oxide may have a full width at half maximum (FWHM) of the (104) plane peak (2θ = 44.5 °) which is one of the main peaks, from 0.180 to 0.191 ° .

In another embodiment of the present invention,

1. A process for producing a cathode active material comprising a lithium metal oxide represented by the following general formula (1)

Cobalt and manganese on an aqueous solution to prepare a transition metal precursor represented by the following Chemical Formula 2;

A drying step of drying the transition metal precursor;

Mixing the transition metal precursor and the lithium precursor;

And calcining the mixture at a temperature of 600 to 1,000 DEG C for 10 to 30 hours after the mixing step. The present invention also relates to a method for producing a cathode active material for a lithium secondary battery.

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z O ₂

(Wherein a is 1.17? A? 1.33, x, y and z are 0 <x <1, 0 <y <1, 0 <z <1, and a + x + y + z = 2.

(2)

Ni _l Co _m Mn _n (OH) ₂

(1, m and n are 0 < l < 1, 0 <m <1, 0 <n <1 and l + m + n = 1.

According to another aspect of the present invention, there is provided a positive electrode comprising a positive electrode active material according to the present invention; A negative electrode comprising a negative electrode active material; A separator existing between the anode and the cathode, and a non-aqueous electrolyte.

The present invention provides a positive electrode active material capable of improving the capacity and rate characteristics of a lithium secondary battery by controlling the mixing ratio of lithium in the production of the positive electrode active material for a lithium secondary battery and controlling the degree of crystallization thereby to provide a lithium secondary battery comprising the same have.

FIG. 1 is a graph showing a change in full width at half maximum according to a mixing ratio of lithium to transition metal of the lithium metal oxide in the lithium metal oxide obtained according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the electrochemical characteristics (capacity, percentage characteristics (%), and the like) of the lithium metal oxide according to the mixing ratio of lithium to the transition metal in the lithium metal oxide obtained according to an embodiment of the present invention. ) In the first embodiment.

Hereinafter, the present invention will be described in more detail. In the following detailed description, embodiments of the invention are presented and described for purposes of illustration. It will be appreciated by those skilled in the art that the present invention may be illustrated in various forms and that the embodiments described below can not be construed as limiting the present invention.

According to one embodiment of the present invention, the present invention relates to a cathode active material comprising a lithium metal oxide represented by the following formula (1).

More specifically, the lithium metal oxide represented by the following formula (1) is an excess of lithium added to the transition metal (nickel, cobalt and manganese), and two phases are formed by this excessive amount of lithium. One is a layered LiNi _b Co _c Mn _d O ₂ (hereinafter referred to as LiMO ₂ , b + c + d = 1, M is Ni, Co, Mn) and the other is a layered Li ₂ MnO ₃ phase. The LiMO ₂ Phase is an active region for reversible charge and discharge, and Li ₂ MnO ₃ is an inactive region having Mn ^{4 +} at 4.4 V or lower, but an electrochemical reaction occurs at 4.4 V or higher. As a result, MnO ₂ is converted into an active material while being produced, and a high capacity is provided at 4.4 V or more. Accordingly, the present invention aims to maximize the capacity and rate characteristics of a lithium secondary battery by controlling the chemical equivalent ratio and the crystal size of each lithium metal oxide containing lithium to each metal, In the preparation of the metal oxide, the mixing ratio condition of the transition metal precursor (nickel cobalt manganese hydroxide) and the lithium carbonate is controlled according to the following formula 1, and the crystallinity obtained from the full width at half maximum value of the lithium metal oxide according to the mixing ratio, And a quantitative relationship is defined so as to provide a cathode active material having high crystallinity and capable of improving the capacity and rate characteristics of the battery.

[Chemical Formula 1]

Li _a Ni _x Co _y Mn _z O ₂

1, 0 < z < 1, and a + x + y + z = 2 to be. When the value of a is less than 1.17 or more than 1.33, the degree of crystallization of the lithium metal oxide as the obtained positive electrode active material is not high and it is difficult to secure a high capacity, especially 200 mAh / g or more of a standard capacity of the battery. Which is undesirable. According to an embodiment of the present invention, it is preferable that the value of a is 1.17 a 1.20. If the value of a + x + y + z is outside 2, the capacity is lowered and the degree of crystallization is lowered, which makes it difficult to obtain an effect of improving the life characteristics of the battery.

According to an embodiment of the present invention, the lithium metal oxide LiMO ₂ (Ni _, Co (Mn) and Li ₂ MnO ₃ were observed. The full width at half maximum (FWHM) of the (104) plane peak (2θ = 44.5 °), which is one of the main peaks of the X-ray diffraction analysis, The degree of crystallization thereof can be confirmed.

In addition, according to one embodiment of the present invention, the correlation between the degree of crystallization of the lithium metal oxide and the corresponding cell performance was measured by the full width at half maximum, and the value of the full width at half maximum (FWHM) And inversely proportional to the properties.

According to one embodiment of the present invention, in order to improve the battery performance, the full width at half maximum (FWHM) may be more than 0 and less than 0.2 degrees, preferably 0.180 to 0.191 degrees, more preferably 0.188 to 0.191 degrees Lt; / RTI &gt; If the full width at half maximum (FWHM) is out of the above range, the crystallinity may be lowered. In particular, it is difficult to obtain a high capacity of 200 mAh / g or more or to obtain a rate characteristic improvement effect.

According to one embodiment of the present invention, the present invention relates to a method for producing the lithium metal oxide. More specifically, the present invention relates to a process for producing a transition metal precursor, Mixing step; And a firing step.

The step of preparing the transition metal precursor is a step of forming a nickel cobalt manganese hydroxide represented by the following Chemical Formula 2 by adding a basic aqueous solution to a transition metal mixed aqueous solution in which raw material compounds of nickel, cobalt and manganese are dissolved.

(2)

Ni _l Co _m Mn _n (OH) ₂

1, 0 < n < 1, and l + m + n = 1.

The basic aqueous solution may be 1 to 3 M of ammonia water or an aqueous solution of sodium hydroxide. After the aqueous solution of the transition metal is administered to an aqueous solution of sodium hydroxide of 1 M according to an embodiment of the present invention, The coprecipitation can be induced by adding an aqueous ammonia solution having the same equivalent ratio as the equivalence ratio.

The raw material compound of nickel, cobalt and manganese may be at least one selected from the group consisting of hydroxide, ammonium, sulfate, alkoxide, oxalate, nickel, cobalt, and manganese, (S), phosphate, halide, oxyhalide, sulfide, oxide, peroxide, acetate, nitrate, carbonate, sheet, May be at least one of citrate, phthalate, perchlorate, acetylacetonate, acrylate, formate, oxalate compounds and their hydrates, , But is not limited thereto.

The drying step is a step of drying the transition metal precursor at a temperature of 100 ° C to 200 ° C for 5 to 50 hours.

In the mixing step, the transition metal precursor and the lithium precursor are dry-mixed according to the equivalent ratio of the following formula (1). According to one embodiment of the present invention, the chemical equivalent ratio of lithium to transition metal in the mixing step may be from 1.409 to 2: 1, and from 1.45 to 1.5: 1, according to one embodiment of the present invention. By applying the transition metal precursor formed by coprecipitation in the mixing step, it can be more effective in improving the physical properties of the battery as compared with the case where each transition metal is mixed with the lithium precursor.

The lithium precursor may be selected from the group consisting of lithium hydroxide, ammonium, sulfate, alkoxide, oxalate, phosphate, halide, oxyhalide, ), Sulfide, oxide, peroxide, acetate, nitrate, carbonate, citrate, phtalate, perchlorate, But are not limited to, one or more of acetylacetonate, acrylate, formate, oxalate compounds, and hydrates thereof.

The calcining step is a step of heating the mixture at a temperature of 600 to 1,000 DEG C for 10 to 30 hours after the mixing step. The firing atmosphere may be an atmosphere or an oxygen atmosphere, but is not limited thereto.

After the firing step, a post-treatment process according to a conventional solid-phase method may be further performed. For example, a grinding step and a powder step may be performed to control particle size and remove impurities. The grinding step may be a ball mill, a vibration mill, a satellite ball mill, a tube mill, a rod mill, a jet mill, a hammer mill, or the like.

According to an embodiment of the present invention, there is provided a lithium secondary battery comprising the lithium metal oxide according to the present invention.

The lithium secondary battery may further include a nonaqueous electrolyte containing a positive electrode containing a positive electrode active material, a negative electrode, a separator, and a lithium salt. The structure and the manufacturing method of the secondary battery are known in the technical field of the present invention and can be appropriately selected without departing from the scope of the present invention.

For example, the positive electrode may be prepared by applying a composition for forming a positive electrode active material containing a positive electrode active material and a binder to a positive electrode collector, drying and then rolling.

The cathode active material can mix the lithium metal oxide according to the present invention alone or commonly used cathode active material with the lithium metal oxide.

The binder serves to bind the positive electrode active materials and to fix them to the current collector. Any binders used in the technical field can be used without limitation, and preferable examples include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl Tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer , Vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene - chlorotrifluoroethylene copolymer, vinylidene fluoride-hex Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydrolyzed vinylidene fluoride, Polyethylene, polypropylene, styrene-butylene rubber, and fluorine rubber.

The composition for forming a positive electrode active material may further include a solvent such as NMP (N-methyl-2-pyrrolidone) and an oligomer such as polyethylene or polypropylene to the positive electrode active material and the binder; A filler made of a fibrous material such as glass fiber, carbon fiber, or the like, and may further include a conductive material.

The conductive material may be graphite; Carbon blacks such as carbon black, 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; Zinc oxide, potassium titanate, titanium oxide, polyphenylene derivatives, and the like, but the present invention is not limited thereto.

The positive electrode collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon; Surfaces of copper and stainless steel surface treated with carbon, nickel, titanium or silver; Aluminum-cadmium alloy, and the like, and various shapes such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric can be used.

The negative electrode may be prepared by applying a composition for forming an anode active material containing a negative electrode active material on a negative electrode collector and drying the same, or may be a lithium metal. The composition for forming the negative electrode active material may further include a conventional binder and a conductive material applicable to the negative electrode active material.

The negative electrode active material may be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber or amorphous carbon, an alloy of lithium and Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, quality is a metal alloy such as an alloy, Al alloy compound and a complex containing the metallic compound and the carbonaceous _{material, GeO, GeO 2, SnO,} SnO 2, PbO, PbO 2, Pb 2 O 3, Pb 3 O 4 _{, Sb 2 O 3, Sb 2} O 4, Sb 2 O 5, Bi 2 O 3, Bi 2 O 4, and the like, but the metal oxide such as Bi ₂ O _5, not to limit it.

The negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon; Surfaces of copper and stainless steel surface treated with carbon, nickel, titanium or silver; Aluminum-cadmium alloy, and the like, and various shapes such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric can be used.

The separation membrane is disposed between the cathode and the anode, and includes an olefin-based polymer such as polypropylene; A sheet or a nonwoven fabric made of glass fiber, polyethylene, or the like. For example, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, a polyethylene / polypropylene double-layer separator, And the like, but the present invention is not limited thereto.

The lithium salt wherein the non-aqueous electrolyte comprises a non-aqueous electrolyte and a lithium salt is _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 OCl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, But are not limited to, LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lithium tetraphenylborate and imide.

The non-aqueous electrolyte may include non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like. Examples of the non-aqueous organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate Methyl ethyl ketone, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples of the solvent include 1,2-dioxane, 2-methyltetrahydrofuran, acetonitrile, formamide, dimethylformamide, N-methyl-2-pyrrolidinone, dimethylsulfoxide, , Sulfolane, methylsulfolane, dioxolane, dioxolane derivative, methyl nitromethaneacetate, phosphoric acid triester, trimethoxymethane, sulfolane, methylsulfolane, 3-methyl-2-oxazolidinone, propylene Viterbo carbonate but are the derivative, diethyl ether and the like, not to limit it.

The organic solid electrolyte may be a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolytic solution, a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, But are not limited to, polymers containing an ionic dissociation group such as phosphoric acid ester polymer, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene .

Wherein the inorganic solid electrolyte is selected from the group consisting of Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI _{-LiOH, Li 3 PO 4 -Li 2} S-SiS 2, Li 2 SP 2 S 5, Li 2 S-SiS 2, Li 2 S-GeS 2, Li 2 nitride, halides of Li, such as S, oxyacid salt , Sulfides, and the like, but are not limited thereto.

The lithium secondary battery can be separated into a coin type, a prismatic type, a cylindrical type, a pouch type, and the like. Since the structure and manufacturing method of these batteries are known in the art, detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples. The following examples are only illustrative of the present invention and do not limit the scope of protection of the present invention.

[ Synthetic example  One]

Nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ) and manganese sulfate (MnSO ₄ ) were dissolved in water at a molar ratio of 2: 2: 6 and then added to a 1 M NaOH solution. Ammonia water (NH ₄ OH) of the same equivalent ratio as the equivalence ratio of the whole metal was slowly added to the mixed solution. After 12 hours by using a continuous-type reactor, a formed precipitate was filtered off, then washed with water, dried to give a transition metal precursor temperature for 48 hours in a drying oven of _{120 ℃ Ni 0 .2 Co 0 .2} Mn 0 _Lt ; / RTI &gt; (OH) ₂ .

[ Example  One]

Lithium carbonate (Li ₂ CO ₃ ) and nickel cobalt manganese hydroxide (Ni _0.2 Co _0.2 Mn _0.6 (OH) ₂ ) as the transition metal precursor of Synthesis Example 1 were uniformly mixed so that the chemical equivalent ratio of Li: transition metal = 1.425: And then heated (heat-treated) at 900 ° C. for 10 hours to obtain a layered lithium metal oxide having a particle size of about 5 μm (based on D50), a specific surface area of 4 m 2 / g, and a pressed density of 2.4 g / Li [Li _{0 .175} (Ni Co _{0 .165 0 .165 0 .495} Mn)] ₂ O; the positive electrode active material) was obtained.

[ Example  2]

(D50 basis), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m2 / g were carried out in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was changed to 1.450: to 2.65g / ㏄ a layer of Li [Li _{0 .184} (Ni Co _{0 .163 0 .163 0 .490} Mn)] of a positive electrode active material O ₂ was obtained.

[ Example  3]

(D50 standard), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m &lt; 2 &gt; / g, were performed in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.472: to 2.65g / ㏄ a layer of Li [Li _{0 .191} (Ni Co _{0 .162 0 .162 0 .485} Mn)] of a positive electrode active material O ₂ was obtained.

[ Example  4]

(D50 basis), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m2 / g were carried out in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.500: the cathode active material of 2.65g / ㏄ layered Li [Li _{0 .200} (Ni Co _{0 .160 0 .160 0 .480} Mn)] O ₂ was obtained.

[ Comparative Example  One]

(D50 standard), specific surface area 4.5 m &lt; 2 &gt; / g, compression density (press density) of 2.65 g / cm &lt; 2 &gt;, and the like, were performed in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.300: the ㏄ the layered cathode active material of Li [Li _{0 .130} (Ni Co _{0 .174 0 .174 0 .522} Mn)] O ₂ in the solid.

[ Comparative Example  2]

(D50 standard), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m &lt; 2 &gt; / g were carried out in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.325: the cathode active material of 2.65g / ㏄ of a layered Li [Li _{0 .140} (Ni Co _{0 .172 0 .172 0 .516} Mn)] O ₂ was obtained.

[ Comparative Example  3]

(D50 basis), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m2 / g were carried out in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.350: to 2.65g / ㏄ the layered cathode active material of Li [Li _{0 .149} (Ni Co _{0 .170 0 .170 0 .511} Mn)] O ₂ in the solid.

[ Comparative Example  4]

(D50 basis), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m &lt; 2 &gt; / g, were performed in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was 1.378: the cathode active material of 2.65g / ㏄ of a layered Li [Li _{0 .159} (Ni Co _{0 .168 0 .168 0 .505} Mn)] O ₂ was obtained.

[ Comparative Example  5]

(D50 standard), a specific surface area of 4.5 m &lt; 2 &gt; / g, a pressed density (D50), and a specific surface area of 4.5 m &lt; 2 &gt; / g, were performed in the same manner as in Example 1 except that the chemical equivalent ratio of lithium and transition metal was changed to 1.400: A cathode active material of Li [Li _{0 .166} (Ni _{0 .167} Co _{0 .167} Mn _{0 .500} )] O _{2 having} a layer of 2.65 g / cc was obtained.

 [ Experimental Example  One]

The powder XRD diffraction pattern (analysis conditions: 2? = 10 to 80 占 0.001 占 step, Cu-K? Line (1.5418 占 40 kV / 30 mA) manufactured by BRUKER AXS) was measured, and it was confirmed that LiMO ₂ (M, Ni, Co, Mn) phase and Li ₂ MnO ₃ phase were formed by JCPDS (Joint Committee on Powder Diffraction Standards; 01-070-4314) And the comparative example and the example obtained lithium oxide composed of LiMO ₂ and Li ₂ MnO ₃ in single phase. The XRD pattern was used to determine the presence of the (104) plane according to JCPDS The full width at half maximum for the diffraction peak (44.5 DEG) was calculated.

[ Experimental Example  2]

The cathode active material obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was mixed with a conductive material DenkaBlack and polyvinylpyrrolidone (PVDF) binder in a ratio (by mass ratio) of 94: 3: 3 to prepare Al The electrode plate was coated on the foil with a thickness of 150 ㎛. The electrode plate was rolled again and pressed to a thickness of 30 ~ 50 ㎛. Lithium metal was used as a cathode and a separable membrane was made into a coin cell using a porous polyethylene (PE) material 1.3M LiPF6 ethylene carbonate / dimethylcarbonate / EC = 5: 3: 2 solution (mass ratio). The prepared cells were measured for expression capacity according to the current density (0.2C, 0.33C, 2C) after charging and discharging at 4.6 V at room temperature and the capacity ratio (%, rate characteristics) expressed by 3C versus 2C and 0.33C versus 0.2C, . The results are shown in Table 1 and Figures 1-2.

division
Lithium equivalence ratio
Half full width value
(°)
0.2 CD
(3.0-4.6V) 2C / 0.2C
(2.5 to 4.6 V) 3C / 0.33C
(2.5 to 4.6 V) Capacity (mAh / g) Rate characteristic (%) Rate characteristic (%) Comparative Example 1 1.130 0.222 186.75 75.39 73.55 Comparative Example 2 1.140 0.231 189.36 75.34 74.06 Comparative Example 3 1.149 0.219 192.75 75.60 73.56 Comparative Example 4 1.159 0.207 190.92 74.67 73.54 Comparative Example 5 1.166 0.198 196.38 75.42 74.38 Example 1 1.175 0.188 209.60 77.46 76.29 Example 2 1.184 0.187 210.70 78.65 77.72 Example 3 1.191 0.182 220.61 80.40 79.73 Example 4 1.200 0.191 218.04 79.86 78.74

As shown in Table 1 and FIG. 1 to FIG. 2, in the case of the cathode active material according to the present invention, the full width at half maximum value is decreased by controlling the mixing ratio of lithium to the transition metal in the present invention, The crystallinity of the active material, that is, the lithium metal oxide is increased. It is also confirmed that as the degree of crystallization increases, the capacity and rate characteristics of the lithium secondary battery are improved.

FIG. 1 is a graph showing the change in the full width at half maximum according to the mixing ratio of lithium in the lithium metal oxide as the cathode active material obtained according to the present invention. As shown in Fig. 1, the lithium equivalent shows the best crystallinity at 1.191, which is inversely proportional to the width of the full width at half maximum. Also, it was shown that the crystallinity increases with increasing lithium equivalent (up to 1.191), and the crystallinity tends to decrease thereafter. When the lithium equivalent is 1.175 to 1.2, the full width at half maximum is 0.191 degrees or less. When the lithium equivalent is 1.175 or less, the full width at half maximum is increased to 0.191 degrees or more.

FIG. 2 is a graph showing changes in electrochemical characteristics (capacity (%), rate characteristics) according to the mixing ratio of lithium in the lithium metal oxide as the cathode active material obtained according to the present invention. As shown in FIG. 2, it can be seen that the tendency shown in the relation between the lithium equivalent and crystallinity is reproduced in the tendency of the capacity and the rate characteristic. When the lithium equivalent is 1.191, the capacity is 220 mAh / g, the rate characteristic shows the peak of 80% (2C / 0.2C, 3C / 0.33C), and the capacity and rate characteristics tend to decrease at the lithium equivalent of 1.191 or less have. (3C / 0.33C) of 75% or more at a lithium equivalent of 1.175 to 1.2 and a capacity of 200 mAh / g or less at a lithium equivalent of 1.175 or less. C) is reduced to 75% or less.

Claims (6)

1. A lithium secondary battery comprising a lithium metal oxide represented by the following formula (1)
Wherein a full width at half maximum (FWHM) of peak (2θ = 44.5 °) of (104) which is one of the main peaks in the lithium metal oxide in XRD is more than 0 and not more than 0.2 °, Active material:
[Chemical Formula 1]
Li _a Ni _x Co _y Mn _z O ₂
(Wherein a is 1.17? A? 1.33 and x, y and z are 0 <x <1, 0 <y <1, 0 <z <1, and a + x + y + z = 2.
The method according to claim 1,
Wherein the lithium metal oxide has a full width at half maximum (FWHM) of 0.180 DEG to 0.191 DEG.
1. A process for producing a cathode active material comprising a lithium metal oxide represented by the following general formula (1)
Preparing a transition metal precursor to prepare a transition metal precursor represented by the following formula (2) by coprecipitating nickel, cobalt and manganese in an aqueous solution;
A drying step of drying the transition metal precursor;
Mixing the transition metal precursor and the lithium precursor;
And a calcination step of calcining the mixture obtained after the mixing step at a temperature of 600 to 1,000 DEG C for 10 to 30 hours. The method for producing a cathode active material for a lithium secondary battery according to claim 1,
[Chemical Formula 1]
Li _a Ni _x Co _y Mn _z O ₂
(Wherein a is 1.17? A? 1.33, x, y and z are 0 <x <1, 0 <y <1, 0 <z <1, and a + x + y + z = 2.
(2)
Ni _l Co _m Mn _n (OH) ₂
(1, m and n are 0 < l < 1, 0 <m <1, 0 <n <1 and l + m + n = 1.
The method of claim 3,
Wherein a full width at half maximum (FWHM) of peak (2θ = 44.5 °) of (104) which is one of the main peaks in the lithium metal oxide is in the range of more than 0 and not more than 0.2 ° in X-ray diffraction analysis (XRD) A method for producing a cathode active material.
5. The method of claim 4,
Characterized in that, in X-ray diffraction analysis (XRD) of said lithium metal oxide, the full width at half maximum (FWHM) of peak (2θ = 44.5 °) at one peak of the main peak is 0.180 to 0.191 °. A method for producing an active material.
A cathode comprising the cathode active material of claim 1 or 2;
A negative electrode comprising a negative electrode active material;
A separator existing between the anode and the cathode, and
A lithium secondary battery comprising a non-aqueous electrolyte.

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