KR20090111130A - Positive active material for lithium secondary battery, method for preparing the same, and lithium secondary battery using the same - Google Patents

Abstract

PURPOSE: A cathode active material for lithium secondary battery and a method for manufacturing the same are provided to prevent structure change and improve structural stability. CONSTITUTION: A method for manufacturing a cathode active material for lithium secondary battery comprises: a step of uniformly mixing lithium composite, cobalt oxide, metal oxide (or metal hydroxide) and fluoride (S100); a step of heating the mixture; and a step of synthesizing lithium cobalt complex oxide (S120).

Description

Positive active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery using same {Positive active material for lithium secondary battery, method for preparing the same, and lithium secondary battery using the same}

The present invention relates to a cathode active material for a lithium secondary battery, and more particularly, to a cathode active material in the form of a lithium cobalt composite oxide having a configuration capable of high voltage charging, a method of manufacturing the same, and a lithium secondary battery using the same.

Recently, the demand for portable electronic devices for information and communication such as mobile phones, portable personal digital assistants (PDAs), notebook computers, and portable electronic devices such as digital cameras, camcorders, and MP3s, electric bicycles, and electric vehicles is increasing. As a result, there is an increasing demand for a nonaqueous electrolyte secondary battery such as a lithium secondary battery having a small size, a light weight, and a high energy density.

The lithium secondary battery has an advantage of having a high energy density because a high voltage of 4V is obtained. Lithium composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and LiFeO ₂ are widely used as positive electrode active materials of such lithium secondary batteries. Among them, LiCoO ₂ is preferred because of its excellent electrochemical characteristics compared to other composite oxides. However, there is a problem of insufficient cobalt (Co) resources and high price. Therefore, LiCoO ₂ is continuously used for high performance and high lifetime. Is required.

Recently, research and development have been actively conducted on a cathode active material that provides various electrochemical properties equivalent to or higher than that of cobalt (Co) using another transition element replacing cobalt (Co).

For example, Japanese Unexamined Patent Application Publication No. Hei 4-319260 discloses a method showing excellent charge and discharge characteristics and cycle characteristics by adding dissimilar elements such as zirconium (Zr) and magnesium (Mg) to LiCoO ₂ .

Japanese Laid-Open Patent Publication No. 2004-299975 discloses a technique for improving cycle characteristics by adding not only zirconium (Zr) and magnesium (Mg) but also titanium (Ti) and fluorine (F) as heterologous elements added to LiCoO ₂ . It is.

Japanese Patent Laid-Open No. 3-201368 discloses cycle characteristics by replacing 5 to 35% of cobalt (Co) atoms with tungsten (W), manganese (Mn), tantalum (Ta), titanium (Ti), or niobium (Nb). Techniques for improving this are disclosed.

In addition, recently published in Chem . Mater . 2005,17,1284-1286] has a cathode active material for a lithium secondary battery of _{LiM 0 .05 Co 0 .95 O 2} [M = Cr, Bi, Sn, and Zr] material available in a high voltage of 4.5V is provided, J ournal of Power Sources 148 (2005) 90-94 ] have LiCo _1-X Zr _{X / 2} Mg _{X / 2} O ₂ [x = 0, 0.02, 0.06, 0.1, 0.2] with zirconium (Zr) at cobalt (Co) atoms , A method of adding magnesium (Mg) at the same time is presented.

 The present invention has been made based on the development of the cathode active material as described above, the cathode active material for lithium secondary battery improved the structure of the lithium composite oxide through elemental substitution by a fluorine compound to have improved structural stability and thermal stability at high voltage And to provide a method for manufacturing the same and a lithium secondary battery using the same.

In order to achieve the above object, the present invention, in the positive electrode active material for a lithium secondary battery, a part of the cobalt atom is replaced with a metal atom by a fluorine compound and at the same time a part of the oxygen atom is substituted with a fluorine atom, having a lithium cobalt composite oxide form Disclosed is a cathode active material characterized in that.

The composition formula of the lithium cobalt composite oxide is Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z (M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, 0≤x ≤ 0.1, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2).

The fluorine compound is CsF, KF, NaF, RbF, TiF, AgF, AgF₂, BaF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , HgF ₂ , Hg ₂ F ₂ , MnF ₂ , MgF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , InF ₃ , LaF ₃ , LuF ₃ , MnF ₃ , NdF ₃ , VOF ₃ , PrF ₃ , SbF ₃ , ScF ₃ , SmF ₃ , TbF ₃ , TiF ₃ , TmF ₃ , YF ₃ , YbF ₃ , TIF ₃ , CeF ₄ , GeF _{4, HfF 4, SiF 4,} SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, at least one selected from the group consisting of SF ₆ and WF ₆ It is preferable that it is above.

Other portions of the cobalt atoms may be substituted with metal atoms by metal oxides or metal hydroxides.

According to another aspect of the present invention, a step of uniformly mixing the lithium complex, cobalt oxide, metal oxide (or metal hydroxide) and fluorine compound and then grinding (grinding) to prepare a mixture; And heat-treating the mixture to synthesize a lithium cobalt composite oxide in which a part of cobalt atoms is replaced with a metal atom by a fluorine compound and at the same time a part of oxygen atoms is substituted with a fluorine atom. A manufacturing method is provided.

The composition formula of the lithium cobalt composite oxide is Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z (M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, 0≤x ≤ 0.1, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2).

The heat treatment may be performed by calcining the mixture at 700 to 1000 ° C. for 10 to 30 hours under an oxidizing atmosphere, a reducing atmosphere or a vacuum. More preferably, the heat treatment may be performed by calcining the mixture at 800 to 900 ° C. under an oxidizing atmosphere for 15 to 25 hours.

The lithium composite is Li ₂ CO ₃ , the cobalt oxide is preferably Co ₃ O ₄ .

According to another aspect of the present invention, a lithium secondary including a cathode active material, characterized in that a part of the cobalt atom is replaced with a metal atom by a fluorine compound and at the same time a part of the oxygen atom is replaced with a fluorine atom, and has a lithium cobalt composite oxide form A battery is provided.

According to the present invention, it is possible to obtain a cathode active material for a lithium secondary battery having excellent crystallinity, preventing structural deformation generated during high voltage charging, and improving structural stability. In particular, due to the fluorine atom, a strong fluorine bond is formed not only on the surface of the positive electrode active material but also inside the particle, thereby reducing the influence on the acid generated near the positive electrode active material. By suppressing the reaction, a phenomenon in which the capacity of the battery is drastically reduced can be prevented.

Accordingly, the present invention can provide a positive electrode active material excellent in charge and discharge characteristics, life characteristics, high voltage, rate (C-rate) characteristics, thermal stability, etc., and can provide a lithium secondary battery that can be charged at a high voltage of 4.5V or more. There is an advantage.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

1 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to a preferred embodiment of the present invention.

Referring to Figure 1, the method for producing a cathode active material for a lithium secondary battery according to a preferred embodiment of the present invention is carried out through a solid state reaction method (solid state reaction method), a mixture formation process of mixing the starting material (step S100), Heat-treating the mixture to synthesize a lithium cobalt composite oxide in the form of Li [Li _x M _y Co _1-xy ] O _2-z F _{z in} which part of cobalt atoms is replaced with metal atoms and part of oxygen atoms is replaced with fluorine atoms (Steps S110, S120). Here, M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, the range of x, y, z is 0≤x≤0.1, 0≤y≤0.2, 0≤z≤0.2 It is decided.

In the mixture formation process (step S100), it is preferable to use lithium complex (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), metal oxide (MO _X ) and fluorine compound (MF _X ) as starting materials. Here, the fluorine compound (MF _X ) is used to replace a part of the oxygen atom with a fluorine atom and a part of the cobalt atom with a metal atom in Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z . . Metal oxides (MO _X ) are used to compensate for the shortage of metal atoms substituted by fluorine compounds (MF _X ). That is, for example, Li ₂ CO ₃ , ZrO ₂ , ZrF ₄ And Co ₃ O ₄ to synthesize the lithium cobalt oxide of _{LiZr 0 .05 Co 0 .95 O 1} .95 F 0.05 using a fluorine atom are both provided from ZrF _4, the metal atom is ZrO ₂ and ZrF ₄ From. The metal oxide (MO _X ) may be replaced with a metal hydroxide (M (OH) _X ).

Preferably, ZrO ₂ may be used as the metal oxide, and ZrF ₄ may be used as the fluorine compound (MF _X ), but the present invention is not limited thereto. Other fluorine compounds (MF _X ) include CsF, KF, NaF, RbF, TiF, AgF, AgF₂, BaF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , HgF ₂ , Hg ₂ F ₂ , MnF ₂ , MgF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , _{HoF 3, InF 3, LaF 3} , LuF 3, MnF 3, NdF 3, VOF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, YbF 3, TIF 3 , such as _{CeF 4, GeF 4, HfF 4} , SiF 4, SnF 4, TiF 4, VF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6, WF 6 can be used .

In the mixture formation process (step S100), the lithium complex (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), metal oxide (MO _X ) and fluorine compound (MF _X ) are uniformly mixed (mixed) and then ground ( grinding) to form a mixture. As the equipment for uniformly mixing the mixture, it is preferable that a known mortar agate, a mixer, or the like is employed.

After forming the lithium cobalt composite mixture, the mixture is preferably calcined (calcine) and heat treated under an oxidizing atmosphere at 850 ° C. for 20 hours (step S110), and then for controlling particle size of the powder or removing impurities. Grinding is performed to synthesize Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z having a layered structure (step S120). Here, the heat treatment conditions are sufficient to be carried out in an oxidizing atmosphere, a reducing atmosphere or a vacuum for 10 to 30 hours at 700 ~ 1000 ℃, more preferably carried out in an oxidizing atmosphere for 15 to 25 hours at 800 ~ 900 ℃.

When the lithium secondary battery is manufactured using the cathode active material prepared according to the present invention, it is preferable that an ester is used as the electrolyte. For example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC) ), Dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and non-cyclic carbonates such as zipurofilcarbonato (DPC) ), Aliphatic carboxylic acid esters such as methyl formate (methyl) IMF), methyl acetate (MA), methyl propionate (MP) and ethyl propionate (MA), butyrolactone Cyclic carboxylic acid esters such as (GBL) can be used. As the cyclic carbonate, EC, PC, VC or the like is preferably used. Moreover, it is also preferable to use aliphatic carboxylic acid ester in 20% or less range as needed.

Lithium salts dissolved in such solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , LiBOB (Lithium Bis (oxalato) borate), LiBoB, lower aliphatic lithium carbonate, lithium chloroborane, lithium tetraphenylborate, and LiN (CF ₃ SO ₂ ) ( Imides such as C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) And the like can be used. The lithium salts may be used alone or in any combination within a range not impairing the effects of the present invention, and among them, it is preferable to use LiPF ₆ .

The electrolyte may further include carbon tetrachloride, ethylene trifluoride chloride, or phosphate containing phosphorus to impart nonflammability.

Meanwhile, an inorganic or organic solid electrolyte may be used as the electrolyte. Inorganic solid electrolytes include Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiAl-LiOH, xLi ₃ PO _{4- (1-x)} Li ₄ SiO ₄ , Li ₂ SiS ₃ , Li ₃ PO ₄ -Li ₂ S-SiS ₂ And phosphorus sulfide compounds are effective. As the organic solid electrolyte, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, fluoropropylene and the like, and polymer materials such as derivatives, mixtures and composites are effective.

The separator of a lithium secondary battery mainly uses a polyethylene-based or polypropylene-based polymer such as porous polyethylene.

As a negative electrode material of a lithium secondary battery, a compound capable of adsorbing and releasing lithium ions such as lithium, a lithium alloy, an alloy / intermetallic compound, carbon, an organic compound, an inorganic compound, a metal complex, and an organic polymer compound is used. Each of the above compounds can be used alone or in any combination within a range that does not impair the effects of the present invention.

As the lithium alloy, a Li-Al alloy, a Li-Al-Mn alloy, a Li-Al-Mg alloy, a Li-Al-Sn alloy, a Li-Al-In alloy, or a Li-Al-Cd alloy , Li-Al-Te based alloy, Li-Ga based alloy, Li-Cd based alloy, Li-In based alloy, Li-Pb based alloy, Li-Bi based alloy, Li-Mg based alloy and the like can be used. As the alloy / intermetallic compound, compounds of transition metals and silicon, compounds of transition metals and tin, and the like can be used. Particularly, compounds of nickel and silicon are preferable.

Carbonaceous materials include cokes, pyrolytic carbons, natural graphites, artificial graphites, meso carbon micro beads, graphitized meso phase globules, glassy carbons, and carbon fibers (polyacrylics). And polynirylonitrile-based, pitch-based, cellulose-based, vapor-grown carbon-based), amorphous carbon, and carbon from which organic materials are fired. These may be used alone or in any combination within a range that does not impair the effects of the present invention.

As the exterior material of the lithium secondary battery, a packaging material composed of a metal can or aluminum and several polymer layers is mainly used.

Hereinafter, a specific method of manufacturing a cathode active material for a lithium secondary battery and characteristics of the cathode active material manufactured accordingly will be described.

Lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), zirconium oxide (ZrO ₂ ), and zirconium fluorine compound (ZrF ₄ ) were used as starting materials. The starting materials were quantified at 0.2 mole relative to the composition ratio, and uniformly ground with a mortar agate for a predetermined time to prepare a mixture. The mixture was placed in an alumina vessel and calcined at 850 ° C. for 20 hours, followed by grinding to form Li [Li _x Zr _y Co _{1 -xy} ] O _2-z F _z (0≤x≤0.1, 0≤). y ≦ 0.2, 0 ≦ z ≦ 0.2). In order to find the optimal composition by varying the amount of the zirconium (Zr) and fluorine (F) to be substituted was prepared a lithium cobalt composite oxide of various compositions.

In order to confirm the XRD characteristics of the lithium cobalt composite oxide prepared as described above, an X-ray diffraction pattern was measured using an X-ray diffraction analyzer (trade name: Rint-2000, company name: Rigaku, Japan). 2 and 3, the zirconium (Zr) can be clearly observed in the X-ray diffraction pattern as the amount of zirconium (Zr), which is a metal atom replacing a part of the cobalt atom, increases. In FIG. 2, y and z of Li [Li _x Zr _y Co _{1 -xy} ] O _{2 z} F _z were adjusted in the range of 0.005 ≦ y ≦ 0.05 and 0.005 ≦ z ≦ 0.2, respectively. In FIG. 3, _z of Li [Li _x Zr _y Co _{1 -xy} ] O _{2 z} F _z was fixed at 0.05, and y was adjusted in a range of 0.02 ≦ y ≦ 0.05.

4 and 5 are FE-SEM (Field Emission Scanning Electron Microscopy, trade name: JSM 6400, company name: JEOL, Japan) of the prepared lithium cobalt composite oxide is shown. 4 and 5, it can be observed that the morphology changes as the amount of zirconium (Zr) for substituting a part of the cobalt atom and fluorine (F) for substituting a part of the oxygen atom increases. In particular, when zirconium (Zr) is fixed and the amount of fluorine (F) is increased, it can be observed that crystallinity is further improved (see FIG. 4).

In order to manufacture a positive electrode for a lithium secondary battery, a slurry was prepared by mixing a lithium cobalt composite oxide prepared by the above method, acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 80:10:10. It was. This slurry was uniformly applied to an aluminum foil having a thickness of 20 μm, and vacuum dried at 120 ° C. to prepare a cathode for a lithium secondary battery.

A positive electrode prepared by the above method and a lithium foil as a counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) 1 mol LiPF6 of a mixed solvent Using a solution as a liquid electrolyte, a coin cell of the 2032 standard was manufactured according to a conventional manufacturing process of a lithium battery.

In order to evaluate the characteristics of the manufactured battery, using an electrochemical analyzer (Toyo's Toscat3000U, Japan) at room temperature (30 ° C), the first 2 cycles in the potential region of 3.0 to 4.5V, 0.2 mA / cm 2, from 3 cycles Charge and discharge experiments were conducted under a current density of 0.8 mA / cm 2. 6 and 7 show changes in discharge capacity with cycles. 6 and 7, the present invention shows very good cycle characteristics with almost no capacity reduction up to 30 cycles in general, whereas a battery employing a positive electrode active material having a composition of LiCoO ₂ simply shows a rapid decrease in capacity. You can check it. The present invention can improve the phenomenon that the capacity of the battery is drastically reduced by reducing the influence on the acid generated by the electrolyte side reaction near the positive electrode active material or suppressing the reaction between the positive electrode active material and the electrolyte. 6 and 7, the reason why the capacity decreases after 30 cycles is that the positive electrode active material containing fluorine may rapidly undergo corrosion of the lithium metal as a counter electrode during charging and discharging with a current density of 0.5C or higher at high voltage. Because there is.

In order to evaluate the C-rate characteristics of the manufactured battery, using an electrochemical analyzer (Toyo's Toscat3000U, Japan), the battery was charged under various current density conditions at room temperature (30 ° C.) and a potential region of 3.0 to 4.5 V. , Discharge experiments were performed. In FIG. 8A, the capacity change according to the cycle is shown, and in FIG. 8B, the capacity of the 20 mA / g current density is shown in%. Referring to FIG. 8, Li [Li _x Zr _y Co _{1 -xy} ] O _{2- z} F _z The present invention having a positive electrode active material composition of (0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2) has a very good capacity characteristic under various current density conditions compared to a battery employing a positive electrode active material having a composition of LiCoO ₂ . When compared with the basis of the current density of 20 mA / g, it was confirmed that the more excellent output characteristics at higher rates (see FIG. 8B).

The prepared lithium cobalt composite oxide Li [Li _x Zr _y Co _{1 -xy} ] O _{2- z} F _z In order to evaluate the thermal stability of (0≤x≤0.1, 0≤y≤0.2, 0≤z≤0.2), a coin battery was manufactured as described above, charged to 4.5V, and the electrodes were separated to perform differential thermogravimetric analysis ( Differential Scanning Calorimetry; DSC, NETZSCH-TA4, Germany). Referring to FIG. 9 (A) and (B), the case of LiCoO ₂ according to the prior art appear, but the main exothermic peak in the vicinity of _{241 ℃, LiZr 0 .05 Co 0} .95 O in accordance with an embodiment of the present _{invention; In the case of} 95F _0.05 , the main exothermic peak appeared at about 242 ℃. In general, the location of the exothermic peak of the lithium cobalt composite oxide prepared according to the present invention was confirmed to have a lower calorific value (J / g) than LiCoO ₂ according to the prior art.

Example  One

Lithium cobalt oxide _{LiZr 0 .05 Co 0 .95 O 1} .95 F lithium carbonate as a starting material for the production of _0.05 (Li ₂ CO _3), cobalt oxide (Co ₃ O _4), zirconium oxide (ZrO _2), and Zirconium fluorine compound (ZrF ₄ ) was used. The starting material was quantitated to 0.2 mol based on the composition ratio, and uniformly ground with a mortar agate for a predetermined time to prepare a mixture. The mixture to yield the final oxide, lithium cobalt oxide _{LiZr 0 .05 Co 0 .95 O 1} .95 F 0. 05 to grinding after calcining into 850 ℃ for 20 hours in an alumina vessel.

Example  2

Example 1 except for quantitative determination using lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), aluminum hydroxide (Al (OH) ₃ ), aluminum fluorine compound (AlF ₃ ) as starting materials the lithium cobalt oxide _{LiAl 0 .05 Co 0 .95 O 1} .95 F 0.05 was obtained in the same manner.

Example  3

Examples were quantified using lithium carbonate (Li ₂ CO ₃ ), cobalt oxide (Co ₃ O ₄ ), magnesium hydroxide (Mg (OH) ₂ ) and magnesium fluorine compound (MgF ₂ ) as starting materials in the same manner as in 1 to give a lithium-cobalt composite oxide _{LiMg 0 .05 Co 0 .95 O 1} .95 F 0.05.

X-ray diffraction pattern using an X-ray diffraction analyzer (trade name: Rint-2000, company name: Rigaku, Japan) to confirm the XRD characteristics of the lithium cobalt composite oxide prepared according to Examples 1 to 3 of the present invention Was measured. Referring to FIG. 10, zirconium (Zr), aluminum (Al), magnesium (Mg), and the like, which are metal atoms replacing a part of cobalt atoms, may be observed in an X-ray diffraction pattern.

FIG. 11 shows a photograph of Field Emission Scanning Electron Microscopy (trade name: JSM 6400, company name: JEOL, Japan) of a lithium cobalt composite oxide prepared according to Examples 1 to 3 of the present invention. Referring to FIG. 11, it is possible to observe different morphologies depending on the metal atoms (Mg, Al, Zr) replacing a part of the cobalt atoms.

After preparing a positive electrode using a lithium cobalt composite oxide prepared according to Examples 1 to 3 of the present invention, a coin battery was prepared.

In order to evaluate the characteristics of the manufactured coin battery, using an electrochemical analyzer (Toyo's Toscat3000U, Japan) at room temperature (30 ° C.), the first 2 cycles in the potential region of 3.0 to 4.5V, 0.2 mA / cm 2, 3 cycles From the charge and discharge experiments in the current density conditions of 0.8mA / ㎠ shows the capacity change according to the cycle in FIG. Referring to FIG. 12, it can be seen that the batteries manufactured according to Examples 1 to 3 of the present invention have very low lifespan characteristics at high voltage due to a small decrease in capacity according to the number of cycles.

Comparative example  One

LiCoO ₂ , a cathode active material for a lithium secondary battery, in which a part of metal atoms or oxygen atoms were not substituted, was prepared in the same manner as in Example 1, and the characteristics thereof were evaluated. The characteristics are shown in Figs. 2, 4, 6-18.

Comparative example  2

Li [Li _x Zr _y Co _{1 -xy} ] O ₂ (0 ≦ _x ≦ 0.1, 0 ≦ _y ≦ 0.2), which is a positive electrode active material for a lithium secondary battery, in which part of oxygen atoms are not substituted with fluorine atoms, was used in the same manner as in Example 1. The charge and discharge characteristics were evaluated under the same conditions as in Example 1, and the capacity change according to the cycle is shown in FIGS. 13 to 15. As shown in the figure, when the amount of zirconium (Zr) for substituting a part of the cobalt atom is as small as 0.005 or 0.01 (see FIGS. 13 and 14), Comparative Example 2 is not good cycle characteristics compared to Example 1 When the amount of zirconium (Zr) is 0.05 (see FIG. 15), Comparative Example 2 and Example 1 showed similar cycle characteristics. Unlike the Comparative Example 2, the lithium cobalt composite oxide according to Example 1 is formed by an electrolytic solution side reaction near the positive electrode active material even when only a small amount is substituted because a part of the cobalt atom is replaced with a metal atom and a part of the oxygen atom is replaced with a fluorine atom. This is because it is possible to improve the phenomenon that the capacity of the battery is drastically reduced by reducing the influence on the acid or suppressing the reactivity between the positive electrode active material and the electrolyte.

To evaluate the C-rate characteristics, charge and discharge experiments were conducted at room temperature (30 ℃), 3.0 ~ 4.5V potential range, and various current density conditions using an electrochemical analyzer (Toscat3000U, Japan, Toyo). Capacity changes with cycles are shown in FIGS. 16 and 17. Referring to the drawings, Comparative Example 2 can confirm that the capacity characteristics are not as good as in Example 1 in the characteristic that only a part of the cobalt atom is replaced with a metal atom.

Comparative example  3

Magnesium hydroxide (Mg (OH) ₂₎ and lithium fluoride (LiF) with a prepared in the same manner as the cathode active material for a lithium secondary battery of _{LiMg 0 .05 Co 0 .95 O 1} .95 F 0. 05 as in Example 3 And properties were evaluated under the same conditions. Referring to FIG. 18, in Comparative Example 3 in which a part of an oxygen atom is replaced with a fluorine atom using a lithium fluorine compound (LiF), a cobalt atom and a part of an oxygen atom are replaced with a magnesium atom and a fluorine atom using a fluorine compound (MgF ₂ ). It can be seen that the cycle characteristics are not good at high voltage as compared with Example 3 to be replaced.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the detailed description of the present invention serve to further understand the technical spirit of the present invention, the present invention includes matters described in such drawings. It should not be construed as limited to.

1 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to a preferred embodiment of the present invention.

Figure 2 is a graph showing the XRD pattern for each composition of the lithium cobalt composite oxide provided according to an embodiment of the present invention (in the formula, 0.005≤y≤0.05, 0.005≤z≤0.2) and a comparative example.

Figure 3 is a graph showing the XRD pattern for each composition of the lithium cobalt composite oxide provided according to an embodiment of the present invention (in the formula, 0.02≤y≤0.05, z = 0.05) and a comparative example.

4 is an FE-SEM photograph of each composition of the lithium cobalt composite oxide provided according to an embodiment of the present invention (in formula, 0.005 ≦ y ≦ 0.05, 0.005 ≦ z ≦ 0.2) and a comparative example.

5 is an FE-SEM photograph of each composition of the lithium cobalt composite oxide provided according to an embodiment of the present invention (in the formula, 0.02 ≦ y ≦ 0.05, z = 0.05) and a comparative example.

6 is a graph showing the capacity characteristics according to the cycle of the lithium secondary battery provided according to an embodiment of the present invention (in formula, 0.005≤y≤0.05, 0.005≤z≤0.2) and a comparative example for each composition of the lithium cobalt composite oxide to be.

7 is a graph showing capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in the formula, 0.02 ≦ y ≦ 0.05, z = 0.05) and a comparative example, by composition of a lithium cobalt composite oxide.

8 shows the capacity characteristics of the lithium secondary battery provided according to the embodiment of the present invention (in formula, 0.005≤y≤0.05, 0.005≤z≤0.2) and the comparative example according to the cycle characteristics and the capacity characteristics of the C-rate lithium Graphs and tables showing the composition of cobalt composite oxides.

9 is a thermal analysis by differential thermogravimetric analysis (DSC) performed on a lithium cobalt composite oxide provided according to an embodiment of the present invention (in the formula, 0.005 ≦ y ≦ 0.05, 0.005 ≦ z ≦ 0.2) and a comparative example The results are graphs and tables showing the composition of lithium cobalt composite oxides.

FIG. 10 is a graph illustrating an XRD pattern according to an embodiment of the present invention (in formula, y = 0.05, z = 0.05) and a lithium cobalt composite oxide composition provided according to a comparative example.

FIG. 11 is an FE-SEM photograph according to an embodiment of the present invention (in formula, y = 0.05, z = 0.05) and a composition of a lithium cobalt composite oxide provided according to a comparative example.

12 is a graph showing capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.05, z = 0.05) and a comparative example, by composition of a lithium cobalt composite oxide.

FIG. 13 is a graph showing capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.005 z = 0.005) and a comparative example, by composition of a lithium cobalt composite oxide.

14 is a graph showing the capacity characteristics according to the cycle of the lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.01, z = 0.01) and a comparative example for each composition of the lithium cobalt composite oxide.

FIG. 15 is a graph showing capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.05 z = 0.05) and a comparative example, by composition of a lithium cobalt composite oxide.

16 is a view illustrating capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.005 and z = 0.005) and a comparative example, and capacity characteristics according to C-rate of a lithium cobalt composite oxide. Graphs and tables by composition.

FIG. 17 shows capacity characteristics and cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, y = 0.01, z = 0.01) and a comparative example (in formula, y = 0.01). The capacity characteristics are graphs and tables showing the composition of lithium cobalt composite oxides.

18 is a graph showing capacity characteristics according to cycles of a lithium secondary battery provided according to an embodiment of the present invention (in formula, M = Mg, y = 0.05, z = 0.05) and a comparative example, by composition of a lithium cobalt composite oxide to be.

Claims (14)

In the positive electrode active material for a lithium secondary battery, A portion of a cobalt atom is replaced with a metal atom by a fluorine compound, and a portion of an oxygen atom is substituted with a fluorine atom, and has a lithium cobalt composite oxide form. The method of claim 1, The composition formula of the lithium cobalt composite oxide is Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z (M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, 0≤x ≤ 0.1, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2). The method of claim 2, The fluorine compound is CsF, KF, NaF, RbF, TiF, AgF, AgF₂, BaF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , HgF ₂ , Hg ₂ F ₂ , MnF ₂ , MgF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , InF ₃ , LaF ₃ , LuF ₃ , MnF ₃ , NdF ₃ , VOF ₃ , PrF ₃ , SbF ₃ , ScF ₃ , SmF ₃ , TbF ₃ , TiF ₃ , TmF ₃ , YF ₃ , YbF ₃ , TIF ₃ , CeF ₄ , GeF _{4, HfF 4, SiF 4,} SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, at least one selected from the group consisting of SF ₆ and WF ₆ The positive electrode active material for lithium secondary batteries characterized by the above. The method according to claim 1 or 2, The other part of the cobalt atom is a cathode active material for a lithium secondary battery, characterized in that substituted with a metal atom by a metal oxide or metal hydroxide. In the positive electrode active material manufacturing method for a lithium secondary battery, Preparing a mixture by uniformly mixing the lithium complex, cobalt oxide, metal oxide (or metal hydroxide) and fluorine compound and then grinding; And Heat treating the mixture to synthesize a lithium cobalt composite oxide in which a part of cobalt atoms is replaced with a metal atom by a fluorine compound and a part of oxygen atoms is replaced with a fluorine atom; and manufacturing a cathode active material for a lithium secondary battery comprising a Way. The method of claim 5, The composition formula of the lithium cobalt composite oxide is Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z (M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, 0≤x ≤ 0.1, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2). The method of claim 6, The lithium composite is Li ₂ CO ₃ , The cobalt oxide is Co ₃ O _{4 The} method of producing a positive electrode active material for a lithium secondary battery. The method of claim 5, The mixture is calcined in an oxidizing atmosphere, a reducing atmosphere or a vacuum for 10 to 30 hours at 700 ~ 1000 ℃ to perform the heat treatment for a lithium secondary battery positive electrode active material. The method of claim 5, Method for producing a cathode active material for a lithium secondary battery, characterized in that the mixture is calcined in an oxidizing atmosphere for 15 to 25 hours at 800 ~ 900 ℃. A lithium secondary battery comprising a cathode active material prepared by the method of any one of claims 5 to 9. In a lithium secondary battery, A lithium secondary battery comprising a cathode active material, wherein a part of cobalt atoms is replaced with a metal atom by a fluorine compound, and a part of oxygen atoms is replaced with a fluorine atom, and has a lithium cobalt composite oxide form. The method of claim 11, The composition formula of the lithium cobalt composite oxide is Li [Li _x M _y Co _{1 -xy} ] O _{2- z} F _z (M is at least one element selected from the group consisting of Zr, Al, Mg and alkaline earth metal elements, 0≤x ≤ 0.1, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2). The method according to claim 11 or 12, wherein The fluorine compound is CsF, KF, NaF, RbF, TiF, AgF, AgF₂, BaF ₂ , CaF ₂ , CuF ₂ , CdF ₂ , FeF ₂ , HgF ₂ , Hg ₂ F ₂ , MnF ₂ , MgF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , InF ₃ , LaF ₃ , LuF ₃ , MnF ₃ , NdF ₃ , VOF ₃ , PrF ₃ , SbF ₃ , ScF ₃ , SmF ₃ , TbF ₃ , TiF ₃ , TmF ₃ , YF ₃ , YbF ₃ , TIF ₃ , CeF ₄ , GeF _{4, HfF 4, SiF 4,} SnF 4, TiF 4, VF 4, ZrF 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, at least one selected from the group consisting of SF ₆ and WF ₆ The lithium secondary battery characterized by the above. The method of claim 11, And a part of the cobalt atom is replaced with a metal atom by a metal oxide or a metal hydroxide.

Images