KR101523082B1 - Positive electrode active material for rechargeable lithium battery and method of manufacturing the same and rechargeable lithium battery including the positive electrode active material - Google Patents

Abstract

A core comprising a lithium manganese-based oxide; And a coating layer coated on the surface of the core with an oxyfluoride compound containing zirconium (Zr), a method for producing the same, and a lithium secondary battery including the cathode active material.

Description

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

To a lithium secondary battery including the positive electrode active material, a method for producing the same, and a lithium secondary battery including the positive electrode active material.

A battery is a device that converts the chemical energy generated by an electrochemical oxidation-reduction reaction of an internal chemical substance into electrical energy. When the energy inside the battery is exhausted, the primary battery and the rechargeable secondary battery . Among them, the secondary battery can be used by charging and discharging several times by using reversible conversion between chemical energy and electric energy.

On the other hand, the development of high-tech electronic industry has made it possible to miniaturize and lighten electronic equipment, and the use of portable electronic devices 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.

Such a lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium and a negative electrode including a negative active material capable of intercalating and deintercalating lithium And the electrolyte is injected into the battery cell.

Among them, studies have been made to improve the battery characteristics by using an oxide containing various transition metals as a cathode active material. Examples of the oxide containing the transition metal include lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide.

Lithium cobalt oxide such as LiCoO ₂ has excellent cycle characteristics and is easy to manufacture, but has a limitation in application to a large-capacity battery such as a hybrid automobile or an electric automobile since a large amount of expensive cobalt is used. Lithium nickel-based oxides such as LiNiO ₂ are attracting attention as high-capacity materials, but they are limited in terms of stability.

Lithium manganese based oxides such as LiMn ₂ O ₄ are advantageous in that they have a resource-rich and environmentally friendly manganese structure and have a spinel structure having a three-dimensional structure such as a cubic system structure. . Therefore, lithium manganese oxide has attracted much attention as a cathode active material which can replace lithium cobalt oxide or lithium nickel oxide.

However, the lithium manganese-based oxide can release manganese ions (Mn ^{2 +} ) at a high temperature, and the eluted manganese ions (Mn ^{2 +} ) may precipitate from the surface of the negative electrode and cause a decrease in capacity.

One embodiment provides a cathode active material capable of preventing a capacity drop at high temperatures.

Another embodiment provides a method of manufacturing the cathode active material.

Another embodiment provides a lithium secondary battery comprising the cathode active material.

According to one embodiment, a core comprising a lithium manganese based oxide; And a coating layer coated on the surface of the core with an oxyfluoride compound containing zirconium (Zr). The present invention also provides a cathode active material for a lithium secondary battery.

The lithium manganese-based oxide may be represented by the following formula (1).

[Chemical Formula 1]

Li _{1 + x} Mn _{2 -x- y} M _y O ₄

In Formula 1,

M is at least one selected from boron (B), magnesium (Mg) and transition metal,

0? X <0.1 and 0? Y <0.3.

The lithium manganese-based oxide may be doped with aluminum (Al).

The doping concentration of aluminum (Al) may be about 0.02 M to 0.2 M.

The cathode active material for lithium secondary batteries may contain about 0.04 wt% or more and 0.06 wt% or less of fluorine (F) based on 100 wt% of the active material.

The oxyfluoride compound containing zirconium (Zr) may contain about 40 wt% or more and 60 wt% or less of fluorine (F) based on 100 wt% of the oxyfluoride compound containing zirconium.

The oxyfluoride compound containing zirconium (Zr) may be coated on the surface of the core containing lithium manganese oxide in the form of an island.

The oxyfluoride compound containing zirconium (Zr) may be represented by the following general formula (2).

(2)

ZrO _a F _b

In Formula 2,

0 < a? 1.5 and 1? B <4.

The coating layer may further include ZrO ₂ .

The thickness of the coating layer may be about 5 nm to 100 nm or less.

About 0.002 mole to 0.1 mole of the oxyfluoride compound containing zirconium (Zr) may be included relative to 100 moles of the core.

According to another embodiment, there is provided a method for preparing a coating solution, comprising the steps of: preparing a salt solution containing zirconium (Zr) as a coating solution; Mixing the coating solution with a core containing lithium manganese oxide to prepare a precursor solution; Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And a step of subjecting the coprecipitation compound to filtration, drying, and heat treatment in an oxidizing atmosphere. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

The salt solution containing zirconium (Zr) may be selected from the group consisting of water, alcohol, ether, and combinations thereof.

The molar concentration of the salt solution containing zirconium (Zr) may be about 0.0001M to 0.02M.

The step of preparing a salt solution containing zirconium (Zr) as the coating solution may be a step of preparing a coating solution by mixing a salt solution containing zirconium (Zr) with a buffer solution.

The method for preparing the cathode active material for a lithium secondary battery may be performed at a pH of 4.0 or higher.

The method for preparing the cathode active material for a lithium secondary battery may be performed at a pH of 5.0 or higher.

The lithium manganese-based oxide may be represented by the following formula (1).

[Chemical Formula 1]

Li _{1 + x} Mn _{2 -x- y} M _y O ₄

In Formula 1,

M is at least one selected from boron (B), magnesium (Mg) and transition metal,

0? X <0.1 and 0? Y <0.3.

The fluoride compound may be any one selected from the group consisting of NH ₄ F, HF, Anhydrous hydrogen fluoride (AHF), and combinations thereof.

The fluoride compound solution may be selected from the group consisting of water, alcohols, ethers, and combinations thereof.

The drying can be carried out at about 60 ° C to 150 ° C.

The oxidizing atmosphere may be performed by introducing oxygen or oxygen-containing air.

The heat treatment may be performed at about 300 ° C to 700 ° C.

According to another embodiment, there is provided a lithium secondary battery comprising a cathode, a cathode, and an electrolyte including the cathode active material.

By using the lithium manganese-based oxide as the cathode active material, it is possible to economically produce the cathode active material while improving the cycle, lifetime, and capacity characteristics.

FIG. 1 shows X-ray diffraction (XRD) measurement results of the cathode active materials according to Production Examples 1, 2 and 3 and Comparative Production Example 1. FIG.
2 is a scanning electron microscope (SEM) photograph of the surface of a cathode active material according to Comparative Production Example 1. Fig.
3 is a scanning electron microscope (SEM) photograph of the surface of the positive electrode active material according to Production Example 1. Fig.
4 is a transmission electron microscope (TEM) photograph of the cathode active material according to Production Example 1. Fig.
FIG. 5 is an analysis result of mapping chemical components of a cathode active material according to Production Example 1 using EELS (Electron Energy Loss Spectroscopy).
FIG. 6 is an X-ray photoelectron spectroscopy (XPS) analysis result of the positive electrode active material according to Production Example 1. FIG.
FIG. 7 is a graph showing changes in pH during the cathode active material production process according to Production Examples 1 and 4 and Comparative Production Examples 2, 3 and 4.
8 is a graph showing the cycle life characteristics at room temperature of the lithium secondary batteries according to Examples 1, 2, 3, and Comparative Example 1. FIG.
FIG. 9 is a graph showing the cycle life characteristics at room temperature of the lithium secondary battery according to Example 1 and Comparative Examples 1, 2, and 3. FIG.
10 is a graph showing the high temperature cycle life characteristics of the lithium secondary battery according to Example 5 and Comparative Example 5. FIG.
11 is a graph showing the high temperature cycle life characteristics of the lithium secondary battery according to Example 1 and Example 4. FIG.

Hereinafter, exemplary 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.

Hereinafter, a cathode active material for a lithium secondary battery according to one embodiment will be described.

The cathode active material for a lithium secondary battery according to an embodiment includes a core containing lithium manganese oxide; And a coating layer coated with an oxyfluoride compound containing zirconium (Zr) on the surface of the core.

Generally, a lithium salt such as LiPF ₆ is used for a lithium secondary battery, and PF ₆ ^- of LiPF ₆ is oxidized to reduce Mn ^{4 +} in the cathode active material to Mn ^{3 +} . In addition, the H ₂ O in the electrolyte sikineunde generate HF, HF is dissolved the Mn ^{+ 3} as a strong oxidant, the molten Mn ³⁺ is there is again separated by Mn ^{+ 4} and Mn ^{+ 2,} the Mn ^{+ 4} is oxygen And MnO ₂ (s) is precipitated on the surface of the cathode active material. However, Mn ^{2 +} is present as an ion and moves to the surface of the negative electrode through the electrolyte, and is reduced to Mn metal on the surface of the negative electrode to form a coating, Or short-circuiting, heat generation, or battery deterioration. Particularly, the battery deterioration phenomenon occurs more frequently at a high temperature (above 55 캜).

However, the cathode active material for a lithium secondary battery according to one embodiment includes a coating layer of an oxyfluoride compound containing zirconium (Zr), and the HF in the electrolyte does not react with the surface of the cathode active material by the coating layer, It is possible to prevent elution of manganese ions (Mn &lt; ^{2 +} & gt ^; ) from the oxide. Therefore, it is possible to prevent the formation of a film on the surface of the negative electrode due to the elution of manganese ions (Mn ^{2 +} ) at a high temperature, thereby preventing deterioration of battery capacity and improving lifetime characteristics, cycle characteristics, and thermal stability.

The lithium manganese-based oxide is a compound having a spinel structure having a three-dimensional structure such as a cubic structure, and can be represented, for example, by the following formula (1).

[Chemical Formula 1]

Li _{1 + x} Mn _{2 -x- y} M _y O ₄

In Formula 1,

M is at least one selected from boron (B), magnesium (Mg) and transition metal,

0? X <0.1 and 0? Y <0.3.

The transition metal means an element of the d-zone on the periodic table, and includes all the elements from group 3 to group 12 of the periodic table.

The lithium manganese-based oxide has a short lithium ion migration path and high ion conductivity, which is advantageous for high rate charging and discharging and has high thermal stability in a charged state. The lithium manganese-based oxide is located in the core of the cathode active material to ensure a high rate charge-discharge characteristic and thermal stability.

The coating layer may be formed on the surface of the lithium manganese-based oxide in the form of a shell by coating and heat treatment, and may be located on all or a part of the surface of the lithium manganese-based oxide. For example, the oxyfluoride compound containing zirconium (Zr) may be coated on the surface of the core containing the lithium manganese oxide in the form of an island.

The lithium manganese-based oxide may be doped with aluminum (Al). When the lithium manganese oxide doped with aluminum (Al) is used as the core of the cathode active material, the capacity is somewhat reduced, but the structure can be stabilized by increasing the manganese oxidation number in the cathode active material. As a result, Mn ^{3 +} Can be inhibited.

The doping concentration of the aluminum (Al) may be 0.02M to 0.2M. When aluminum (Al) is doped to the above range, high temperature stability and cycle life characteristics can be improved.

The cathode active material for the lithium secondary battery may include 0.04 wt% or more and 0.06 wt% or less, for example, 0.04 wt% to 0.05 wt% of fluorine (F) based on 100 wt% of the active material. The oxyfluoride compound containing zirconium (Zr) may be used in an amount of 40 to 60% by weight, for example, 40 to 50% by weight, based on 100% by weight of the oxyfluoride compound containing zirconium % &Lt; / RTI &gt; When fluorine (F) is contained within the above range, it is possible to inhibit HF in the electrolytic solution from reacting directly with the surface of the cathode active material.

The oxyfluoride compound containing zirconium (Zr) may be represented by the following general formula (2).

(2)

ZrO _a F _b

In Formula 2,

0 < a? 1.5 and 1? B <4.

For example, in the above formula (2), 0 <a <1 and 2 <b <4.

The coating layer may further include ZrO ₂ .

The thickness of the coating layer may be 5 nm to 100 nm. When the thickness of the coating layer is within the above range, high-rate characteristics and cycle life characteristics can be improved without increasing the resistance.

0.002 mole to 0.1 mole of the oxyfluoride compound containing zirconium (Zr) may be included in 100 mole of the core. When the oxyfluoride compound containing zirconium (Zr) is included within the above range, the coating effect is excellent and the high-rate characteristics can be improved without lowering the initial discharge capacity.

Hereinafter, a method for producing a cathode active material for a lithium secondary battery according to one embodiment will be described.

According to an embodiment, there is provided a method of preparing a cathode active material for a lithium secondary battery, comprising: preparing a salt solution containing zirconium (Zr) as a coating solution; Mixing the coating solution with a core containing lithium manganese oxide to prepare a precursor solution; Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And a step of subjecting the coprecipitation compound to filtration and drying, followed by heat treatment in an oxidizing atmosphere.

The cathode active material for a lithium secondary battery may be prepared by a wet coating method such as a wet aqueous coating using a solvent. For example, the solvent, the lithium manganese oxide powder, the coating solution, and the fluoride compound solution are mixed to form lithium After the coating layer is formed on the surface of the core containing the manganese-based oxide, it may be dried at a predetermined temperature to remove the solvent.

The solvent is not limited as long as it can dissolve the compound or solution to be added together with the lithium manganese based oxide and the lithium manganese based oxide, but is not limited to, for example, deionized water, methanol, ethanol, Ethoxyethanol, 2-propoxyethanol 2-butoxyethanol, methyl cellosolve, ethyl cellosolve, diethylene glycol methyl ether, diethylene glycol ethyl ether, dipropylene glycol methyl ether, toluene, xylene, hexane, Propyleneglycol methyl ether, propyleneglycol propyl ether, propyleneglycol propyl ether, propyleneglycol propyl ether, butyl acetate, butyl acetate, diethyleneglycol dimethyl ether, diethyleneglycol dimethylethylether, methylmethoxypropionic acid, ethylethoxypropionic acid, ethyl lactic acid, Methyl cellosolve acetate, ethyl cellosolve acetate, diethylene glycol methyl ether (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, gamma -butyl May be selected from lactone, diethyl ether, ethylene glycol dimethyl ether, diglyme, tetrahydrofuran, acetylacetone, and acetonitrile, and may include at least one selected from these.

The lithium manganese-based oxide is a compound having a spinel structure as described above, and can be represented, for example, by the following formula (1).

[Chemical Formula 1]

Li _{1 + x} Mn _{2 -x- y} M _y O ₄

In Formula 1,

M is at least one selected from boron (B), magnesium (Mg) and transition metal,

0? X <0.1 and 0? Y <0.3.

The salt solution containing zirconium (Zr) may be selected from the group consisting of water, alcohol, ether, and combinations thereof. For example, the alcohol may be a C1 to C4 lower alcohol selected from the group consisting of methanol, ethanol, isopropanol, and combinations thereof. For example, the ether may be ethylene glycol or butylene glycol.

The molar concentration of the salt solution containing zirconium (Zr) may be 0.0001M to 0.02M. When the molar concentration of the salt solution containing zirconium (Zr) is within the above range, the high-rate characteristics and the cycle life characteristics can be improved without increasing the resistance due to the coating layer.

The step of preparing a salt solution containing zirconium (Zr) as the coating solution may be a step of preparing a coating solution by mixing a salt solution containing zirconium (Zr) with a buffer solution. The addition of the buffer solution can control the initial pH, thereby preventing the elution of manganese ions (Mn ²⁺ ) during the coating process. Na ⁺ acts as an impurity in the cell. The buffer solution is preferably Na ⁺ -free buffer solution. For example, a 0.1 M C ₂ H ₇ NO ₂ aqueous solution can be used as the buffer solution.

The method for preparing a cathode active material for a lithium secondary battery according to an embodiment may be performed at a pH of 4.0 or higher by adding the buffer solution. For example, the method for preparing the cathode active material for a lithium secondary battery may be performed at a pH of 5.0 or higher.

The fluoride compound may be any one selected from the group consisting of NH ₄ F, HF, Anhydrous hydrogen fluoride (AHF), and combinations thereof.

The fluoride compound solution may be prepared by mixing the fluoride compound and a solvent. The solvent used herein may be the same as or different from the solvent of the precursor solution. For example, any one selected from the group consisting of water, alcohol, ether, and combinations thereof may be used as the solvent.

The step of filtering and drying the coprecipitated compound is not limited as long as it is higher than the boiling point of the solvent, but may be carried out at 60 ° C to 150 ° C. The coprecipitation compound comprises an oxyfluoride compound comprising zirconium. In addition, zirconium that has not reacted with the fluoride compound may be included in the coprecipitation compound in the form of ZrO ₂ .

The step of heat-treating the dried coprecipitated compound under an oxidizing atmosphere may be performed at, for example, 300 ° C to 700 ° C. Through this heat treatment, impurities that have not been removed in the drying step can be removed and the bonding force between the core and the coating layer can be further increased. If the temperature of the heat treatment is less than 300 ° C, impurities are not properly removed and the cycle characteristics are reduced. If the heat treatment temperature exceeds 700 ° C, formation of oxyfluoride after heat treatment becomes difficult to reduce the cycle characteristics of the battery, do.

The oxidizing atmosphere may be performed by introducing oxygen or oxygen-containing air into the heat treatment apparatus.

Hereinafter, a lithium secondary battery including the above-mentioned cathode active material will be described.

A lithium secondary battery according to an embodiment includes a positive electrode including the above-mentioned positive electrode active material, a negative electrode including the negative electrode active material, and an electrolyte.

The lithium secondary battery may further include a separator positioned between the anode and the cathode.

The positive electrode includes a current collector and a positive electrode active material layer formed on one or both surfaces of the current collector. The current collector may be an aluminum current collector, but is not limited thereto.

The cathode active material layer includes a cathode active material, a binder, and optionally a conductive material.

As described above, the cathode active material includes a core containing a lithium manganese-based oxide and a coating layer coated with an oxyfluoride compound containing zirconium (Zr) on the core surface. The cathode active material can be produced according to the above-described method for producing a cathode active material. The concrete contents are as described above.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector well. Examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinylchloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Metal fibers such as carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The negative electrode includes a current collector and a negative electrode active material layer formed on one or both surfaces of the current collector.

The negative electrode active material layer includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like.

As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used.

As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-Y alloy (Y is an alkali metal, an alkali earth metal, a Group 13 element, a Group 14 element, Rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is at least one element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Element and an element selected from the group consisting of combinations thereof, and not Sn), and at least one of them may be mixed with SiO ₂ . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, and combinations thereof.

The electrolyte includes a lithium salt and an organic solvent.

The lithium salt serves as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. The lithium salt Specific examples include _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 CF 3) 2, _{LiN (SO 3 C 2 F 5} ) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) (x And y is a natural number), LiCl, and LiI.

The concentration of the lithium salt can be used within the range of about 0.1M to about 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 organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the organic solvent, for example, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate , gamma -butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like can be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. Examples of the non-protonic solvent include R-CN (wherein R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, and examples thereof include methyl, ethyl, propyl, isopropyl, A double bond aromatic ring or an ether bond); amines such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolanes; and the like.

The organic solvents may be used singly or in combination of one or more. If one or more of them are mixed, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

The separator may be a single film or a multilayer film, and may be made of, for example, polyethylene, polypropylene, polyvinylidene fluoride, or a combination thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Preparation of cathode active material

Manufacturing example  1: zirconium Oxyfluoride  The coated cathode active material ( Al this Doped  LiMn ₂ O ₄ )

ZrO (NO ₃ ) ₂ .xH ₂ O (Kanto Co., 99%) was charged into a 7 L reactor and dissolved with ultrapure water to prepare 4 L of 0.005 M coating solution. The coating solution was heated to 80 DEG C by a heater uniformly surrounded by the outside of the reactor. 300 g of Al-doped LiMn ₂ O ₄ powder (Al doping concentration: 0.08 M) was slowly added to the reactor to prepare a precursor solution. Stirring was carried out to increase the dispersibility of the powder in the reactor, wherein the stirring speed was 900 rpm. Ammonium fluoride solution NH ₄ F (samchun, 97%) was charged into a 100 mL plastic measuring cylinder and dissolved with ultrapure water to prepare 40 mL of a fluoride compound solution. This was gradually introduced into the reactor over 2 hours using a peristaltic pump , With the concentration being 0.0184 mol. The stabilization time was maintained for an additional 1 hour after the 2 hour reaction. The coated cathode active material was recovered by filtration using a filter paper attached in a vacuum flask and dried at 100 ° C for 3 hours. Then, the furnace was heat-treated at 400 ° C for 2 hours under the atmosphere, and the heating rate was 2 ° C / min. The heat-treated cathode active material was crushed using agate and classified by using a 40 탆 sieve to finally produce zirconium oxyfluoride-coated cathode active material (Li-doped LiMn ₂ O ₄ ).

Manufacturing example  2: zirconium Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Filtered The cathode active material was prepared in the same manner as in Preparation Example 1, except that the coated cathode active material was heat-treated at 450 캜 under atmospheric condition using a firing furnace.

Manufacturing example  3: zirconium Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Filtering A cathode active material was prepared in the same manner as in Preparation Example 1, except that the coated cathode active material was heat-treated at 500 캜 under an atmosphere using a firing furnace.

Manufacturing example  4: zirconium Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

4 L of a 0.005 M coating solution was prepared by adding ZrO (NO ₃ ) ₂ .xH ₂ O (Kanto Co., 99%) to a 7 L reactor and dissolving it in ultrapure water. Then, ammonium acetate (C ₂ H ₇ NO ₂ , , 97%) Buffer solution 0.01M was charged into the reactor, and a cathode active material was prepared in the same manner as in Preparation Example 1, above.

Comparative Manufacturing Example  1: None of the uncoated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Al-doped LiMn ₂ O ₄ powder (Al doping concentration: 0.08M) used in Production Example 1 was used.

Comparative Manufacturing Example  2: Aluminum Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Except that Al (NO ₃ ) ₃ .9H ₂ O (Samchun, 98%) was used in place of ZrO (NO ₃ ) ₂ xH ₂ O to obtain aluminum oxyfluoride (Li-doped LiMn ₂ O ₄ ) was prepared.

Comparative Manufacturing Example  3: Magnesium Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Except that Mg (NO ₃ ) ₂揃 6H ₂ O (Samchun, 98%) was used in place of ZrO (NO ₃ ) ₂揃 xH ₂ O to obtain magnesium oxyfluoride (Li-doped LiMn ₂ O ₄ ) was prepared.

Comparative Manufacturing Example  4: Aluminum Oxyfluoride  The coated cathode active material ( Al this Doped LiMn ₂ O ₄ )

Except that Al (NO ₃ ) ₃ .9H ₂ O (Samchun Co., 98%) was used instead of ZrO (NO ₃ ) ₂ xH ₂ O and the concentration of the coating solution was changed to 0.05M. 1, and aluminum oxyfluoride was used instead of To prepare a coated cathode active material (Li-doped LiMn ₂ O ₄ ).

The lithium secondary battery  Produce

Example  One

The cathode active material, the conductive material (denka black, denka), and the binder (PVDF-HFP, kurea) according to Production Example 1 were mixed at a ratio of 92: 4: 4 (wt% / wt% / wt%). Subsequently, the mixture was uniformly applied to an aluminum foil (16 mu m) and uniformly pressed at a pressure of 1 ton in a roll press. And then vacuum-dried in a vacuum oven at 100 DEG C to prepare a positive electrode. At this time, the loading amount of the cathode active material was 0.006 g / cm ² , and the rolling rate was 15.3%. A coin type half cell of the CR2032 standard was manufactured using the PE separator (16 탆, SKI) and metal lithium as the negative electrode plate. At this time, a liquid electrolyte containing 1.0 M of LiPF ₆ was used as a mixed solvent having EC: DMC = 1: 1 (v / v) as an electrolyte.

Example  2

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Production Example 2 was used in place of the cathode active material according to Production Example 1.

Example  3

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Production Example 3 was used in place of the cathode active material according to Production Example 1.

Example  4

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Production Example 4 was used in place of the cathode active material according to Production Example 1.

Example  5

Except that the cathode active material, the conductive material, and the binder were mixed at a ratio of 94: 3: 3 (wt% / wt% / wt%) instead of the ratio of 92: 4: 4 (wt% / wt% / wt% Was prepared in the same manner as in Example 1.

Comparative Example  One

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Comparative Preparation Example 1 was used in place of the cathode active material according to Production Example 1.

Comparative Example  2

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Comparative Preparation Example 2 was used in place of the cathode active material according to Production Example 1.

Comparative Example  3

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Comparative Preparation Example 3 was used in place of the cathode active material according to Production Example 1.

Comparative Example  4

A half cell was prepared in the same manner as in Example 1, except that the cathode active material according to Comparative Preparation Example 4 was used in place of the cathode active material according to Production Example 1.

Comparative Example  5

Except that the cathode active material, the conductive material, and the binder were mixed at a ratio of 94: 3: 3 (wt% / wt% / wt%) instead of the ratio of 92: 4: 4 (wt% / wt% / wt% A half cell was prepared in the same manner as in Comparative Example 1.

Rating 1: Size size  analysis

Particle size analysis (PSA) results are shown in Table 1 below by measuring the particle size before and after the coating of the cathode active material according to Production Example 1 and Comparative Production Example 1.

Particle size distribution Comparative Preparation Example 1 (占 퐉) Production Example 1 (탆) D _min 4.2 3.7 D10 9.6 9.5 D50 16.1 16.3 D90 26.3 27.1 D _max 67.0 62.2

As shown in Table 1, the particle sizes of D50 did not show a large difference between before and after coating, and the same results were obtained with particles of different sizes. From this, it can be confirmed that there is not a large physical effect on the cathode active material during the coating process.

Evaluation 2: XRD  Measurement result

The XRD measurement results of the cathode active material according to Production Example 1 and Comparative Production Examples 1, 2, and 3 are shown in FIG. From this, it can be confirmed that the (111) plane of the spinel structure appears as the main peak. In addition, since the heat treatment temperature after the coating is 400 ° C for Production Example 1, 450 ° C for Production Example 1, and 500 ° C for Production Example 3, no significant difference is shown between the XRD result graphs shown in FIG. 1 , It can be confirmed that the cathode active material is not greatly affected by the heat treatment temperature after coating, and it can be seen that no structural change occurs in the cathode active material during the coating process.

However, in the XRD measurement results, the coating layer can not be confirmed because the coating layer exists in the nanoparticle size.

Evaluation 3: Scanning electron microscope ( SEM ) Measurement result

2 and 3 are photographs taken by scanning electron microscope (SEM) of the surface of the cathode active material according to Comparative Production Example 1 and Production Example 1, respectively. Unlike FIG. 2, FIG. 3 shows that the fine particles having a size of 100 nm or less are uniformly present on the surface of the cathode active material.

The existence or nonexistence of the coating layer can be confirmed by a scanning electron microscope. However, since the crystallinity and structure of the coating layer can not be known, the following evaluation 4 was conducted using a transmission electron microscope (TEM). The transmission electron microscope (TEM) is suitable for analyzing the structure and morphology of nanoparticle sized fine coating layer.

Evaluation 4: Transmission electron microscope ( TEM ) Measurement result

A photograph of the cathode active material according to Preparation Example 1 taken by a transmission electron microscope (TEM) is shown in FIG. From FIG. 4, it can be seen that the coating layer has a form in which single crystals having a size of 10 nm to 30 nm are aggregated on the surface of the LiMn ₂ O ₄ cathode active material. As a result of the SAED pattern of the core, the core of the positive electrode active material has an fcc structure of LiMn ₂ O _{4. As} a result of the NBD pattern of the coating layer, the coating layer of the positive electrode active material has a tetragonal structure of ZrO _{0 .33} F _3.33 (lattice constant a = 0.7946 nm , c = 0.3970 nm) (JCPDS 36-1335).

Meanwhile, FIG. 5 is a result of mapping the chemical components of the cathode active material using EELS (Electron Energy Loss Spectroscopy). As a result, Zr, F and O are intensively mapped on the surface of the LiMn ₂ O ₄ cathode active material, .

Evaluation 5: Measurement of coating efficiency

The presence and content of fluorine elements in the coating layer of the cathode active material according to Production Example 1 and Comparative Production Examples 2 and 3 were quantitatively analyzed by combustion ion chromatography and the results are shown in Table 2 below. When the beam is irradiated to the coating layer, the light elements such as fluorine can volatilize and the fluorine element embedded in the coating layer lattice is difficult to analyze. The presence or absence of the fluorine element and the content analysis are preferably quantitatively analyzed by combustion ion chromatography Do.

Fluorine ion (wt%) Comparative Production Example 2 0.016 Comparative Production Example 3 0.044 Production Example 1 0.118

From Table 2, fluorine elements were detected in both Production Example 1 and Comparative Production Examples 2 and 3. From this, it can be seen that Production Example 1, which is a production method of a cathode active material comprising a zirconium oxyfluoride coating layer, has a higher fluorine coating efficiency than Comparative Production Examples 2 and 3, which is a process for producing a cathode active material comprising an aluminum oxyfluoride or magnesium oxyfluoride coating layer .

In order to quantitatively measure the coating efficiency, the coating solution was divided into two parts before and after coating, and ICP analysis was carried out, respectively. The results are shown in Table 3 below.

(Coating solution concentration: 0.005M, unit: ppm, parentheses indicate initial solution design value) Al Mg Zr Comparative Production Example 2 Before coating 146.1
(136.4) - - After coating 57.6 - - Comparative Production Example 3 Before coating - 123.6
(122.8) - After coating - 43.2 - Production Example 1 Before coating - - 398.7
(456.0) After coating - - 25.89

It can be seen from Table 3 that the Zr coating efficiency of Production Example 1 is as high as 93% as compared to the Al coating efficiency of Comparative Production Example 2 of 60% and the Mg coating efficiency of Comparative Production Example 3 of 65%.

Evaluation 6: Impurity measurement

ICP analysis was performed to observe impurities in the cathode active material according to Production Example 1 and Comparative Production Examples 1, 2, and 3 to quantify the impurities. The results are shown in Table 4 below.

(Unit: ppm) impurities Comparative Preparation Example 1 Comparative Production Example 2 Comparative Production Example 3 Production Example 1 Na 2,912 56 59 87 Mg 59 67 1,257 111 Si 76 23 43 53 S 4,065 921 951 802 K 93 nd nd Nd Ca 138 47 32 105 Cr nd nd nd Nd Fe 24 26 30 30 Ni nd nd nd Nd Cu nd nd nd Nd Zn nd nd nd Nd

From the above Table 4, it can be seen that Comparative Example 2 including the zirconium oxyfluoride coating layer, Comparative Preparation Example 2 including the aluminum oxyfluoride coating layer, and Comparative Preparation Example 3 including the magnesium oxyfluoride coating layer It can be seen that it contains much less impurities such as Na, S, K than Comparative Production Example 1. [ This is because impurities such as Na, S, K present on the surface of the cathode active material are cleaned during the coating process. However, Mg, Si, Ca, Fe, and the like are impurities existing in the cathode active material, and it is judged that there is no cleaning effect by the coating process. Impurities such as Cr, Ni, Cu, and Zn are not newly introduced during the coating process.

Rating 7: XPS  Analysis

The results of XPS analysis of the cathode active material according to Production Example 1 are shown in Fig. 6, it can be seen that the coating layer is coated in the form of an island on the surface of the cathode active material.

Rating 8: pH  Controlled Mn  Elution

The pH change during the coating processes of Production Examples 1 and 4 and Comparative Production Examples 2 to 4 was measured in order to confirm whether or not the cathode active material was eluted by the pH control, and is shown in FIG. From FIG. 7, the initial 0.005M metal nitrate solution showed acidity, but the pH was increased due to the alkalinity of the active material itself when the cathode active material was added, and the pH was gradually increased with time when the fluorine source NH ₄ F was added .

Comparing Preparation Example 1 and Comparative Preparation Examples 2 and 3, the pH was high in the order of Mg, Zr, and Al at the same concentration, but Zr was strongly acidic at 2.7 at the initial stage. Comparing Comparative Preparation Examples 2 and 4, it can be seen that the higher the concentration, the lower the pH is.

Comparing Production Examples 1 and 4 and Comparative Production Examples 2 to 4, it can be seen that Production Example 4 using a buffer solution does not elute Mn ^{2 +} and the like at an initial pH of 5.3, In Production Examples 2 to 4, it can be seen that Mn ^{2 +} and the like elute at an initial pH of 4.0 or less, which may affect the active material itself. In Comparative Production Example 4 where the pH was kept below 4.0 during the coating process as shown in FIG. 6, the elution amounts of Li and Mn were 220.5 ppm and 154 ppm, respectively, in the filtrate after the coating process, No elution occurred at all. That is, it can be seen that the cathode active material is eluted from the acidic solution.

Evaluation 9: Cycle life characteristics at room temperature

The half cells according to Examples 1 to 3 and Comparative Examples 1 to 3 were charged and discharged at 0.1 C, 0.2 C and 0.5 C, respectively, using a charge-discharge device (Maccor, Series 4600A) And observed for 50 times. The charging and discharging voltage ranges from 4.2V to 3.0V. After charging the battery at a constant current of 4.2V, the charging and discharging life cycle is controlled at room temperature (25 ° C) by controlling the CV section until reaching 2% of the applied current value Respectively.

FIG. 8 is a graph showing the cycle life characteristics at room temperature of the cathode active material according to Examples 1 to 3 and Comparative Example 1. FIG. 9 is a graph showing the cycle life characteristics at room temperature of the cathode active material according to Example 1 and Comparative Examples 1 to 3 It is a graph showing.

In FIG. 8, Comparative Example 1 using a cathode active material without a coating layer showed a capacity maintenance ratio of 95.3% based on the initial capacity, but Examples 1 to 3 using a cathode active material containing a zirconium oxyfluoride coating layer showed 97.8% It can be confirmed that high capacity retention rate is indicated.

In FIG. 9, Comparative Examples 2 and 3, which used the cathode active material including aluminum oxyfluoride and magnesium oxyfluoride coating layer, showed better cycle life characteristics at room temperature than Comparative Example 1 using the cathode active material not including the coating layer, It can be confirmed that Example 1 using a cathode active material containing a zirconium oxyfluoride coating layer has better cycle life characteristics at room temperature than Comparative Examples 2 and 3. [

Evaluation 10: High temperature cycle life characteristics

In order to more clearly observe the coating effect at a high temperature (55 ° C) of the half cell according to Examples 1, 4, 5 and Comparative Example 5, the voltage range was set from 4.3 V to 3.0 V and only the constant current was applied. At this time, the CV section after charging was not added. The composition of the slurry for electrode production was differentiated into the cathode active material: conductive material: binder = 94: 3: 3.

FIG. 10 is a graph showing the high temperature cycle life characteristics of Example 5 and Comparative Example 5, and FIG. 11 is a graph showing the high temperature cycle life characteristics of Examples 1 and 4. FIG.

10, Comparative Example 5 using a cathode active material without a coating layer showed a capacity maintenance ratio of 79.9% based on the initial capacity, but Example 5 using a cathode active material containing a zirconium oxyfluoride coating layer showed a high capacity of 87.2% The maintenance rate is indicated.

In FIG. 11, Example 1 including the cathode active material prepared without using the buffer solution showed a capacity maintenance ratio of 86.3%, and Example 4 including the cathode active material prepared using the buffer solution had a capacity of 87.2% Retention rate. That is, it was confirmed that the buffer retention capacity of the buffer solution of Example 1 including the zirconium oxyfluoride coating layer was not significantly different from that of Example 4 including the zirconium oxyfluoride coating layer although the buffer solution was not used .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (24)

A core comprising a lithium manganese-based oxide; And
And a coating layer coated with an oxyfluoride compound containing zirconium (Zr) on the surface of the core,
The oxyfluoride compound containing zirconium (Zr) is represented by the following formula (2).
(2)
ZrO _a F _b
In Formula 2,
0 < a? 1.5 and 1? B <4.
The method according to claim 1,
Wherein the lithium manganese-based oxide is represented by the following Formula 1:
[Chemical Formula 1]
Li _{1 + x} Mn _{2 -x- y} M _y O ₄
In Formula 1,
M is at least one selected from boron (B), magnesium (Mg) and transition metal,
0? X <0.1 and 0? Y <0.3.
The method according to claim 1,
The lithium manganese oxide is a cathode active material for a lithium secondary battery doped with aluminum (Al).
The method of claim 3,
Wherein the aluminum (Al) has a doping concentration of 0.02 to 0.2M.
The method according to claim 1,
Wherein the positive electrode active material for lithium secondary batteries comprises 0.04 wt% or more and 0.06 wt% or less of fluorine (F) based on 100 wt% of the active material.
The method according to claim 1,
The oxyfluoride compound containing zirconium (Zr) comprises 40 wt% or more and 60 wt% or less of fluorine (F) based on 100 wt% of the oxyfluoride compound containing zirconium.
The method according to claim 1,
The oxyfluoride compound containing zirconium (Zr) is coated on the surface of the core in the form of an island.
delete The method according to claim 1,
Wherein the coating layer further comprises ZrO ₂ .
The method according to claim 1,
Wherein the thickness of the coating layer is 5 nm to 100 nm.
The method according to claim 1,
Wherein the oxyfluoride compound containing zirconium (Zr) is contained in an amount of 0.002 to 0.1 mole relative to 100 moles of the core.
Preparing a salt solution containing zirconium (Zr) as a coating solution;
Mixing the coating solution with a core containing lithium manganese oxide to prepare a precursor solution;
Adding a fluoride compound solution to the precursor solution to obtain a coprecipitation compound; And
Filtering and drying the coprecipitated compound, followed by heat treatment in an oxidizing atmosphere
Wherein the positive electrode active material is a positive electrode active material.
13. The method of claim 12,
Wherein the salt solution containing zirconium (Zr) is any one selected from the group consisting of water, alcohol, ether, and combinations thereof, as a solvent.
13. The method of claim 12,
Wherein the molar concentration of the salt solution containing zirconium (Zr) is 0.0001M to 0.02M.
13. The method of claim 12,
Wherein the step of preparing a salt solution containing zirconium (Zr) as the coating solution is a step of preparing a coating solution by mixing a salt solution containing zirconium (Zr) with a buffer solution.
16. The method of claim 15,
The method for producing a cathode active material for a lithium secondary battery is performed at a pH of 4.0 or higher.
16. The method of claim 15,
The method for producing the cathode active material for a lithium secondary battery is performed at a pH of 5.0 or higher.
13. The method of claim 12,
Wherein the lithium manganese-based oxide is represented by the following formula (1): < EMI ID =
[Chemical Formula 1]
Li _{1 + x} Mn _{2 -x- y} M _y O ₄
In Formula 1,
M is at least one selected from boron (B), magnesium (Mg) and transition metal,
0? X <0.1 and 0? Y <0.3.
13. The method of claim 12,
Wherein the fluoride compound is any one selected from the group consisting of NH ₄ F, HF, Anhydrous hydrogen fluoride (AHF), and combinations thereof.
13. The method of claim 12,
Wherein the fluoride compound solution is one selected from the group consisting of water, alcohol, ether, and combinations thereof, as a solvent.
13. The method of claim 12,
Wherein the drying is carried out at a temperature of 60 ° C to 150 ° C.
13. The method of claim 12,
Wherein the oxidizing atmosphere is carried out by introducing oxygen or oxygen-containing air into the positive electrode active material for a lithium secondary battery.
13. The method of claim 12,
Wherein the heat treatment is performed at 300 ° C to 700 ° C.
A cathode comprising the cathode active material according to any one of claims 1 to 7, and 9 to 11;
A negative electrode comprising a negative electrode active material; And
Electrolyte
&Lt; / RTI &gt;

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