KR101551355B1 - The Method for Preparing Cathode Active Material for Secondary Battery and Cathode Active Material Using The Same - Google Patents

Abstract

The present invention relates to a method for producing a cathode active material for a secondary battery,
(a) preparing a lithium metal oxide represented by the following formula (1);
Li _{1 + z} Ni _a Mn _b Co _{1 - (a + b)} O ₂ (1)
(Where 0? Z? 0.1, 0.1? A? 0.8, 0.1? B? 0.8 and a + b <1)
(b) diluting the zirconium-containing precursor with an organic solvent, and mixing and stirring the lithium metal oxide;
(c) performing a first heat treatment to remove the organic solvent; And
(d) performing a second heat treatment to convert the zirconium-containing precursor to zirconia (ZrO ₂ );
The present invention also provides a method for producing a zirconia-coated cathode active material and a cathode active material prepared using the same.
The lithium secondary battery including the lithium secondary battery has improved safety due to minimization of the swelling phenomenon and exhibits an effect of improving cycle characteristics.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a cathode active material for a secondary battery and a cathode active material using the same,

The present invention relates to a method for producing a cathode active material for a secondary battery and a cathode active material produced using the same,

(a) preparing a lithium metal oxide represented by the following formula (1);

Li _{1 + z} Ni _a Mn _b Co _{1 - (a + b)} O ₂ (1)

(Where 0? Z? 0.1, 0.1? A? 0.8, 0.1? B? 0.8 and a + b <1)

(b) diluting the zirconium-containing precursor with an organic solvent, and mixing and stirring the lithium metal oxide;

(c) performing a first heat treatment to remove the organic solvent; And

(d) conducting a second heat treatment to convert the zirconium-containing precursor to zirconia (ZrO ₂ ), and a cathode active material for a secondary battery manufactured using the same.

As the technology development and demand for mobile devices have increased, the demand for secondary batteries has increased sharply as an energy source. Among such secondary batteries, lithium secondary batteries having high energy density and operating potential, long cycle life, Have been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

Lithium-containing cobalt oxide (LiCoMO ₂ ) is mainly used as a cathode active material of a lithium secondary battery, and lithium-containing nickel oxide (LiNiMO ₂ ), lithium manganese oxide (LiMnMO ₂ ) having a layered structure, lithium manganese oxide (LiMn ₂ MO ₄ ) is also considered, and recently, LiMO ₂ (M is Co, Ni, and Mn) is used.

On the surface of LiMO ₂ (M is Co, Ni, and Mn), a large amount of Li by-products are generated during the synthesis process. Most of these Li by-products are composed of a compound of LiOH and Li ₂ CO ₃ , and the generation of gas due to the progress of charge / discharge after manufacturing the electrode.

On the other hand, in the lithium secondary battery, an electrolyte is essential as an agent for transferring ions. The electrolyte is generally composed of a solvent and a lithium salt. The lithium salt is preferably lithium tetrafluoroborate LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and the like are mainly used. However, as described above, the electrolyte in which the lithium salt containing fluorine (F) is dissolved reacts with a trace amount of moisture in the electrolyte to form hydrofluoric acid (HF).

Since the lithium carbonate (Li ₂ CO ₃ ) is not dissolved in the non-aqueous pure solvent but stably exists, it reacts with hydrofluoric acid (HF) to elute into the electrolyte to generate carbon dioxide (CO ₂ ) An excessive amount of gas is generated. Thereby causing swelling of the battery and deteriorating high-temperature safety.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments. As described later, when a zirconia-coated lithium transition metal oxide is produced by using a predetermined method, damage to the surface of the cathode active material particle, The present inventors have completed the present invention by confirming that the desired effect can be achieved.

Accordingly, the present invention provides a method for producing a cathode active material for a secondary battery,

(a) preparing a lithium metal oxide represented by the following formula (1);

Li _{1 + z} Ni _a Mn _b Co _{1 - (a + b)} O ₂ (1)

(Where 0? Z? 0.1, 0.1? A? 0.8, 0.1? B? 0.8 and a + b <1)

(b) diluting the zirconium-containing precursor with an organic solvent, and mixing and stirring the lithium metal oxide;

(c) performing a first heat treatment to remove the organic solvent; And

(d) performing a second heat treatment to convert the zirconium-containing precursor to zirconia (ZrO ₂ );

Wherein the cathode active material is coated with zirconia.

The zirconia (ZrO ₂ ) coating according to the production method of the present invention can prevent the contact between the impurities (Li ₂ CO ₃ , LiOH) present on the surface of the cathode active material and the hydrofluoric acid (HF) in the electrolyte, ) To form a stable form of ZrO ₂ O ₅ HF H H ₂ O, thereby stabilizing the surface of the cathode active material.

Therefore, the cathode active material produced according to the present invention can suppress the structural collapse of the cathode active material due to contact with the electrolyte and the generation of carbon dioxide as a side reaction product. Therefore, the lithium secondary battery including the lithium secondary battery has improved safety And exhibits an effect of improving cycle characteristics.

The lithium metal oxide represented by Formula 1 may have a nickel content (a) and a manganese content (b) of 0.2 or more to 0.7 or less. More specifically, the lithium metal oxide of Formula 1 may be Li _{1 Ni 1/3 Mn 1/} 3 Co 1/3 O 2 or LiNi _{0 .5} may be a _{Mn 0 .3 Co 0 .2 O 2} .

Such lithium transition metal oxide particles can be prepared by a solid-phase method, coprecipitation method, or the like known in the art, and thus a detailed description thereof will be omitted.

In the production method according to the present invention, the zirconium-containing precursor is not limited as long as it is a compound from which Zr can originate, and examples thereof include Zr (C ₅ H ₇ O ₂ ) ₄ , C ₂₆ H ₄₄ O ₁₆ Zr, Zr [ _{OC (CH 3) 3] 4} , Zr (OC 4 H 9) 4, Zr (OH) 2 CO 3 o _{ZrO 2, ZrCl 4, Zr (} OCC (CH 3) 3 CHCOC (CH 3) 3) 2 (o _{3 H 7) 2, Zr (} OC 2 H 5) 4, ZrH 2, Zr (OH) 4, Zr (OCH (CH 3) 2) 4 o _{(CH 3) 2 CHOH, Zr} (OCH (CH 3) 2 _{) 4, Zr (OCC (CH} 3) 3 CHCOC (CH 3) 3) 4, Zr (C 5 H 4 F 3 O 2) 4, and ZrO (NO ₃₎ may be one selected from the group consisting of ₂ Specifically, It can ZrCl _4.

Examples of the organic solvent include organic solvents such as methanol, ethanol, isopropyl alcohol, acetone, dimethyl sulfoxide, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, acetic acid, methyl formate, An ether, a methyl pyrophosphate, and an ether, and a reaction product of a compound represented by the following general formula (1): wherein R 1 and R 2 are independently selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, And ethyl propionate. In particular, when an anhydrous alcohol-based solvent is used, damage to the cathode active material can be prevented, and more particularly, ethanol can be used.

However, when water is used as a solvent, it is not preferable because it may damage the cathode active material.

In the step (b), the amount of zirconia (ZrO ₂ ) coated on the lithium transition metal oxide may be adjusted to the amount of 0.001 to 0.100 wt% based on the total weight of the cathode active material, More specifically, it may be mixed in an amount of 0.001 to 0.010% by weight.

If the amount of the zirconia is too small, it is difficult to exert the desired effect, and when it is too large, the specific capacity may be reduced, which is not preferable.

The first heat treatment is performed at a temperature of 100 to 200 DEG C for 5 to 15 hours to remove the organic solvent.

After the first heat treatment, if the second heat treatment is performed at a temperature of 400 to 1000 ° C, specifically 500 to 800 ° C for 10 hours in an air atmosphere, the zirconium-containing precursor is converted into zirconia (ZrO ₂ ) A coated lithium transition metal oxide can be produced.

If the temperature range of the first and second heat treatment is excessively high or low, which is the optimum range for obtaining the desired cathode active material in the present invention, problems such as impurities, crystal defects, and specimen breakage may occur.

The present invention also provides a cathode active material for a secondary battery, which is coated with zirconia (ZrO ₂ ) produced by the above-described production method.

The thickness of the zirconia (ZrO ₂ ) coating may be 0.01 to 0.10 탆, and more specifically, 0.04 to 0.06 탆.

If the thickness of the coating layer is too small, contact with the electrolyte can not be prevented or the battery can be easily damaged during operation. If the coating layer is too thick, the specific capacity may be reduced.

The zirconia (ZrO ₂ ) may be applied with a coating area of 60 to 100% based on the surface area of the cathode active material, and more specifically, a coating area of 80 to 100%.

If the area of the coating layer is excessively small, the contact area between the positive electrode active material and the electrolytic solution may increase, which is not preferable.

The present invention also provides a positive electrode mixture for a secondary battery comprising the above-mentioned positive electrode active material and a secondary positive electrode comprising the positive electrode mixture.

In addition to the positive electrode active material, the positive electrode mixture may optionally contain a conductive material, a binder, a filler, and the like.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode according to the present invention can be prepared by applying a slurry prepared by mixing a positive electrode mixture containing the above-described compounds to a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by coating a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the mixture. The negative electrode mixture may contain the above-described components as required.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 _{≤ x ≤} 1), Li _x WO ₂ (0 _{≤ x ≤} 1), Sn _x Me _{1 - x} Me _y O _z (Me: Mn, Fe, Pb, , B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen, 0 <x <1> 1 <y> 3, 1 <z <8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include 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 , Nitrides, halides, sulfates and the like of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide And LiPF ₆ is most preferable.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device but also as a unit cell in a middle or large battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

As described above, the method for producing a cathode active material according to the present invention includes a step of mixing and heating a zirconium precursor and a lithium transition metal oxide in a predetermined solvent, and then the surface of the cathode active material thus prepared is coated with zirconia, It is possible to prevent contact between impurities (Li ₂ CO ₃ , LiOH) present on the surface of the cathode active material and hydrofluoric acid (HF) in the electrolyte, and zirconia reacts with hydrofluoric acid (HF) in the electrolyte to produce a stable substance.

Therefore, it is possible to suppress the structural collapse of the cathode active material due to contact with the electrolyte and the generation of carbon dioxide as a side reaction product, and the lithium secondary battery including the lithium secondary battery has improved safety due to minimization of the swelling phenomenon, .

1 is a SEM photograph of a zirconia-coated cathode active material prepared according to Example 1 of the present invention;
2 is an SEM photograph of a zeolite-free cathode active material prepared according to Comparative Example 1 of the present invention; And
3 is a graph showing EDX data of a zirconia-coated cathode active material prepared according to Example 1 of the present invention.

&Lt; Example 1 >

_{LiNi 0 .6 Mn 0 .2 Co 0} .2 O After preparation the lithium metal oxide represented by ₂ to the ZrCl ₄ was diluted with ethanol, and the mixture was stirred and mixed with the lithium metal oxide. Then, after removing the ethanol to a first heat treatment at 130 ℃, the second heat treatment at 500 ℃ to zirconia (ZrO ₂₎ is a coated positive electrode active material, wherein the zirconia (ZrO ₂₎ content based on the total weight of the positive electrode active material To prepare zirconia (ZrO ₂ ) -coated cathode active material having a coating thickness of 0.05 μm and 0.005% by weight.

&Lt; Comparative Example 1 &

The lithium metal oxide represented by _{LiNi 0 .6 Mn 0 .2 Co 0} .2 O 2 was prepared.

<Experimental Example 1>

SEM photographs of the positive electrode active material prepared in Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively. Data obtained by checking the composition of the positive electrode active material prepared in Example 1 using the measuring equipment (EDX) Respectively.

In FIG. 1, zirconia is partially coated on the surface of the cathode active material as compared with FIG. Further, in FIG. 3, it can be confirmed that Zr is contained in the cathode active material according to the first embodiment.

Therefore, it can be easily expected that the contact between the surface of the cathode active material and the electrolytic solution will be relatively small when the cathode is produced due to the zirconia coating.

<Experimental Example 2>

The results of measurement of the amounts of impurities Li ₂ CO ₃ and LiOH on the surface of the cathode active material prepared in Example 1 and Comparative Example 1 using HCl are shown in Table 1 below.

<Table 1>

As shown in Table 1, the amount of Li ₂ CO ₃ and LiOH on the surface of the cathode active material was measured by using HCl. As a result, it was confirmed that the amount of Li ₂ CO ₃ and LiOH was significantly reduced in Example 1 as compared with Comparative Example 1.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

A method for producing a cathode active material for a secondary battery,
(a) preparing a lithium metal oxide represented by the following formula (1);
Li _{1 + z} Ni _a Mn _b Co _{1 - (a + b)} O ₂ (1)
(Where 0? Z? 0.1, 0.1? A? 0.8, 0.1? B? 0.8 and a + b <1)
(b) diluting the zirconium-containing precursor with an organic solvent so that the amount of zirconia (ZrO ₂ ) coated on the lithium transition metal oxide is 0.001 to 0.100 wt% based on the total weight of the cathode active material, Adjusting and mixing and stirring;
(c) performing a first heat treatment at a temperature of 100 to 200 DEG C for 5 to 15 hours to remove the organic solvent; And
(d) subjecting the zirconium-containing precursor to zirconia (ZrO ₂ ) by performing a second heat treatment in an air atmosphere at a temperature of 500 to 800 ° C;
Lt; / RTI &gt;
The zirconium-containing _{precursor, ZrCl 4, Zr (C 5} H 4 F 3 O 2) 4, and ZrO (NO _{3) 2,} the production of the zirconia-coated positive electrode active material, characterized in that at least one selected from the group consisting of Way. The lithium _secondary battery according to claim 1, wherein the lithium metal oxide represented by Formula 1 is Li ₁ Ni _1/3 Mn _1/3 Co _1/3 O _2, LiNi _0.6 Mn _0.2 Co _0.2 O _2, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ . delete The process according to claim 1, wherein the zirconium-containing compound is ZrCl ₄ . The method of claim 1, wherein the organic solvent is selected from the group consisting of methanol, ethanol, isopropyl alcohol, acetone, dimethyl sulfoxide, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, acetic acid, methyl formate, Diethyl ether, tetrahydrofuran derivatives, ethers, methyl pyrophosphate, methyl pyruvate, methyl pyruvate, methyl pyruvate, methyl pyruvate, And ethyl propionate. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 6. The method according to claim 5, wherein the organic solvent is ethanol. delete The method according to claim 1, wherein the amount of the zirconia (ZrO ₂ ) is adjusted to 0.001 to 0.010 wt% based on the total weight of the cathode active material, and the amount of the lithium transition metal oxide is adjusted. delete The method according to claim 1, wherein the zirconia (ZrO ₂ ) is coated to a thickness of 0.01 to 0.10 탆. delete 11. The method of claim 10, wherein the zirconia (ZrO ₂₎ is a production method characterized in that the coating with a coating area of 60 to 100%, based on the positive electrode active material surface area. delete delete delete delete delete

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