KR20190078100A - Manufacturing method of a positive electrode active material for rechargeable battery, and rechargeable battery including positive electrode active material for rechargeable battery manufacture using the same - Google Patents

Abstract

The present invention relates to a manufacturing method of a positive electrode active material for lithium secondary battery. The positive electrode active material manufacturing method includes: a step of preparing lithium composite oxide represented by chemical formula 1, Li_xNi_aCo_bMn_cM1_dO_2; and a step of washing the lithium composite oxide. The washing liquid of the washing step includes lithium hydroxide, tungsten oxide, and a solvent. In chemical formula 1, M1 is at least one of Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo, and W; x satisfies the inequation, 0.90 <= x <= 1.07; a satisfies the inequation, 0.83 <= a < 1; b satisfies the inequation, 0 < b <= 0.3; c satisfies the inequation, 0 < c <= 0.3; d satisfies the inequation, 0 < d < 0.01; and a+b+c+d = 1. The present invention is able to achieve high capacity and structural stabilization at the same time.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery comprising a lithium secondary battery and a lithium secondary battery including the lithium secondary battery and a lithium secondary battery including the lithium secondary battery. 2. Description of the Related Art [0002] }

An embodiment of the present invention relates to a method for producing a cathode active material and a lithium secondary battery comprising the cathode active material produced using the method. More specifically, the manufacturing processability is improved by using a wash liquid containing a coating element in a washing process And a method for producing a cathode active material having excellent characteristics at the same time.

The cathode active material, which is one of the constituent elements of the lithium secondary battery, contributes directly to the expression of the energy density of the battery.

In this regard, in the case of a positive electrode active material containing nickel, since a high capacity battery can be realized as the content of nickel (Ni) increases, recent studies have been actively conducted.

However, in the case of the positive electrode active material containing nickel, the higher the content of nickel (Ni) becomes, the more unstable the structure becomes, and the stability and the life characteristic become worse in a high temperature environment.

Therefore, it is urgent to develop a cathode active material having a high nickel content and excellent resistance characteristics in a high temperature environment and excellent structural stability.

The embodiments are to provide a method for producing a cathode active material which is excellent in processability and excellent in resistance characteristics even in a high temperature environment, and can simultaneously realize high capacity and structural stability, and a lithium secondary battery comprising the cathode active material produced using the method.

A method for preparing a cathode active material for a lithium secondary battery according to an exemplary embodiment of the present invention includes preparing a lithium composite oxide represented by Formula 1 below and washing the lithium composite oxide with water, , Lithium hydroxide, tungsten oxide, and a solvent.

[Chemical Formula 1]

Li _x Ni _a Co _b Mn _c M _{d d} O ₂

In the formula 1, M1 is at least one of Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo and W, x is 0.90? X? 1.07, a is 0.83? A < 0 <b? 0.3, c is 0 <c? 0.3, d is 0 <d <0.01, and a + b + c + d = 1.

The lithium secondary battery according to an embodiment may include a cathode, a cathode, and an electrolyte, and the cathode may include a cathode active material prepared by a method for producing a cathode active material for a lithium secondary battery according to an embodiment of the present disclosure .

The cathode active material for a lithium secondary battery manufactured according to the embodiments has excellent resistance characteristics even in a high temperature environment and can minimize the rate of increase in resistance even after a charge / discharge cycle.

In addition, when the cathode active material is manufactured according to the embodiments, the cathode active material having improved processability and improved lifetime characteristics can be manufactured.

FIG. 1 shows measurement results for confirming the structural stability of a cathode active material applied to a lithium secondary battery produced according to Examples 2 to 3, Comparative Example 1 and Reference Example 1. FIG.

Below, The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

Hereinafter, a method of manufacturing a cathode active material according to an embodiment of the present invention will be described.

The method for preparing a cathode active material for a lithium secondary battery according to an exemplary embodiment may include preparing a lithium composite oxide and washing the lithium composite oxide.

First, a step of preparing a lithium composite oxide will be described.

In the present embodiment, the lithium composite oxide may be represented by the following general formula (1).

[Chemical Formula 1]

Li _x Ni _a Co _b Mn _c M _{d d} O ₂

In the formula 1, M1 is at least one of Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo and W, x is 0.90? X? 1.07, a is 0.83? A < 0 <b? 0.3, c is 0 <c? 0.3, d is 0 <d <0.01, and a + b + c + d = 1.

In this case, a may be 0.90? A <1, more specifically 0.85? A <1.

B may be 0 <b? 0.2 or 0 <b? 0.1, and c may be 0 <c? 0.2 or 0 <c? 0.1.

When a is less than 0.83 in formula (1), the cathode active material becomes susceptible to moisture in the water, and the residual lithium content on the surface rapidly increases. Further, when such a cathode active material is employed in a battery, the initial resistance rapidly increases at room temperature.

Therefore, as in this embodiment, it is preferable that the range of a, which is the molar ratio of Ni in Chemical Formula 1, satisfies the above range. Since the cathode active material of this embodiment having such a composition has a high energy density per volume, it is possible to improve the capacity of a battery to which the cathode active material is applied and is also suitable for use in an electric vehicle having a traveling distance of 600 km or more.

The nickel-based lithium metal oxide preferably has a core portion which is a region where a molar amount of nickel is constant and a nickel portion which surrounds the outer surface of the core portion and has a molar content of nickel gradually from the interface with the core portion to the outermost portion Lt; RTI ID = 0.0 &gt; a &lt; / RTI &gt; concentration gradient.

As mentioned above, there is a problem that the nickel-based lithium metal oxide becomes structurally unstable as the content of nickel (Ni) increases. However, in this embodiment, nickel-based lithium metal oxide particles having a CSG form as the lithium composite oxide are used, which is advantageous for stabilizing the structure.

Specifically, the CSG type has a core-shell gradient (CSG) in which a high concentration of nickel is constantly maintained in the core portion and a concentration of nickel is reduced in the shell portion. Therefore, while the molar content of nickel in the core portion is kept high, the molar content of nickel in the shell portion is decreased while the molar content of the different metals (e.g., Mn, Co, Al, etc.) is increased while stabilizing the structure have.

After preparing the lithium composite oxide as described above, the step of washing the lithium composite oxide is performed.

The washing liquid in the washing step may include lithium hydroxide (LiOH), tungsten oxide (WO ₃ ) and a solvent.

Lithium hydroxide in the wash liquor protects the surface of the cathode active material because it prevents proton exchange. Accordingly, it is possible to improve the initial capacity and lifetime characteristics of a battery employing a cathode active material manufactured by the same method as the present embodiment and having a coating layer formed thereon.

The content of lithium hydroxide in the washing liquid may be, for example, from 0.05 to 0.2 parts by weight, more specifically from 0.07 to 0.15 parts by weight, based on 100 parts by weight of the lithium composite oxide. If the content of lithium hydroxide in the washing liquid is less than 0.05 parts by weight, there is no advantage in that the washing process is carried out using lithium hydroxide. If the content of lithium hydroxide in the washing liquid exceeds 0.2 parts by weight, the residual lithium removal effect on the surface of the produced positive electrode active material is insignificant and the initial resistance value becomes large.

The weight ratio of lithium hydroxide and tungsten oxide in the wash liquor may range from 1: 4 to 1:30, more specifically from 1: 5 to 1:18. When the weight ratio of lithium hydroxide and tungsten oxide satisfies the above range, tungsten is completely dissolved in the preparation of the wash liquor and is not changed to lithium tungstate. That is, when lithium hydroxide and tungsten oxide are mixed at the same weight ratio to prepare a washing solution and the washing process of the cathode active material is performed, the initial resistance of the lithium secondary battery can be remarkably reduced. That is, the tungsten oxide serves to lower the initial resistance of the cathode active material. When the positive electrode active material is prepared by using the washing liquid containing tungsten oxide as described above, the positive electrode active material can obtain a positive electrode active material having a coating layer containing tungsten on its surface.

The content of the solvent in the washing solution may be 50 parts by weight to 200 parts by weight, more specifically 75 parts by weight to 120 parts by weight, based on 100 parts by weight of the lithium composite oxide. If the content of the solvent in the washing liquid is less than 50 parts by weight, the residual lithium removal effect is insignificant. Further, when the content of lithium hydroxide in the washing liquid exceeds 200 parts by weight, proton exchange rapidly occurs, which lowers the initial capacity and lifetime characteristics of the cathode active material.

As the solvent, for example, at least one of distilled water, ethanol and methanol may be used.

In general, lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) lithium inevitably exist in the surface of the lithium composite oxide containing Ni, Co, and Mn inevitably, .

The battery in which the lithium composite oxide having the residual lithium on the surface is applied to the positive electrode as the positive electrode active material causes generation of gas by the residual lithium during charging and discharging, and problems such as the initial capacity decrease and the initial charge- have.

Therefore, in this embodiment, the residual lithium on the surface of the positive electrode active material can be effectively removed by performing the washing step using the washing liquid containing the solvent as described above.

In the present embodiment, the step of washing the lithium composite oxide comprises a step of adding the lithium composite oxide to the washing solution and stirring to produce a slurry, and a step of filtering the slurry to obtain a washed lithium composite oxide .

At this time, the step of adding the lithium composite oxide to the washing liquid and stirring to prepare a slurry is carried out at a temperature range of 5 ° C to 25 ° C for 1 minute to 60 minutes at a stirring rate of 50 rpm to 200 rpm . This is a sufficient time for carrying out the removal of residual lithium on the surface of the positive electrode active material while preventing lithium loss therein, and the stirring speed is not limited thereto.

Next, the step of filtering the slurry to obtain a washed lithium complex oxide may further include a step of drying the washed lithium complex oxide.

The step of drying the washed lithium composite oxide may be performed at a temperature ranging from 80 캜 to 300 캜 for 1 hour to 30 hours. This is a temperature and a time range sufficient to remove moisture and the like remaining on the surface of the cathode active material treated with the washing liquid, but is not limited thereto.

In this embodiment, the method may further include a step of heat-treating the washed lithium composite oxide after the step of washing the lithium composite oxide.

At this time, the step of heat-treating the washed lithium composite oxide may be performed by heating air, oxygen (O ₂ ), or nitrogen (N ₂ , for example) at a temperature of 200 ° C. to 800 ° C. for 1 hour to 10 hours ) Atmosphere. This is a temperature and a time range sufficient to further improve the performance of the cathode active material subjected to the washing step, but the present invention is not limited thereto.

In this embodiment, after the lithium composite oxide is prepared, the water washing step is performed using a wash solution containing lithium hydroxide, tungsten oxide and a solvent.

The cathode active material prepared by the above-described method can be usefully used for the anode of a lithium secondary battery. That is, the lithium secondary battery according to one embodiment includes a cathode and an electrolyte including a cathode active material prepared by the above-described method together with a cathode.

The lithium secondary battery according to an embodiment may include an electrode assembly including an anode, a cathode, and a separator disposed between the anode and the cathode. Such an electrode assembly is wound or folded and accommodated in a case to constitute a lithium secondary battery.

At this time, the case may have a cylindrical shape, a square shape, a thin film shape, or the like, and may be appropriately modified according to the type of apparatus to be applied.

The negative electrode may be prepared by preparing a composition for forming a negative electrode active material layer by mixing a negative electrode active material, a binder and a conductive material, and then applying the composition to an anode current collector such as copper.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used. Examples of the negative active material include lithium metal, lithium alloy, coke, artificial graphite, natural graphite, Lt; / RTI &gt;

Examples of the binder include polyvinyl alcohol, carboxymethylcellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene Polypropylene and the like can be used, but the present invention is not limited thereto. The binder may be mixed in an amount of 1% by weight to 30% by weight based on the total amount of the composition for forming the anode active material layer.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and specifically includes graphite such as natural graphite and artificial graphite; Carbon black such as 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 conductive material may be mixed in an amount of 0.1% by weight to 30% by weight based on the total amount of the composition for forming the negative electrode active material layer.

The anode may include a cathode active material for a lithium secondary battery manufactured according to an embodiment.

That is, the cathode active material prepared by the above-described method, a binder and optionally a conductive material are mixed to prepare a composition for forming a cathode active material layer, and the composition is applied to a cathode current collector such as aluminum. The conductive material, the binder and the solvent are used in the same manner as in the case of the above-mentioned negative electrode.

As the electrolyte to be filled in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used.

The lithium salt may be, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI may be used.

Examples of the solvent of the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and? -Butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide, and the like can be used, but the present invention is not limited thereto. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used.

As the electrolyte, a gelated polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The separator may be an olefin-based polymer such as polypropylene, which is chemically resistant and hydrophobic; A sheet or a nonwoven fabric made of glass fiber, polyethylene or the like can be used. When a solid electrolyte such as a polymer is used as the electrolytic solution, the solid electrolytic solution may also serve as a separation membrane.

Hereinafter, the present invention will be described in more detail with reference to experimental examples. These experimental examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example  One

(1) Preparation of cathode active material

The first and second metal salt aqueous solutions having different concentrations of Ni, Co, and Mn were prepared.

First aqueous metal salt solution for the core portion is formed, the raw materials of the respective elements were mixed in distilled water _{(Ni 0. 98 Co 0.} 02) (OH) so as to satisfy the stoichiometric molar ratio of _2. Independently, the second metal salt aqueous solution for forming the shell part was mixed with the raw materials of the respective elements so as to satisfy the stoichiometric molar ratio of (Ni _0.7 Co _0.2 Mn _0.1 ) (OH) _{2 in} the distilled water.

Next, when the first metal salt aqueous solution was slowly added to the coprecipitation reactor and a proper amount of the first metal salt aqueous solution was added, the second metal salt aqueous solution was slowly added to prepare a coprecipitated compound, and the precipitate was filtered and washed to prepare a cathode active material precursor.

At this time, a mixed solution of sodium hydroxide (NaOH) and ammonium hydroxide (NH ₄ OH) as precipitants at a molar ratio of 1.9: 1 to 2.2: 1 is prepared, and then the first metal salt aqueous solution and the second metal salt aqueous solution .

LiOH.H ₂ O (battery grade), which is a lithium salt, was mixed with the precursor of the cathode active material precursor so that the molar ratio of the precursor: lithium salt was 1: 1.05 and then fired to form Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ core-shell structure.

At this time, the sintered body has a concentration gradient in which the Ni mole content gradually decreases in a direction from the interface of the core portion to the outermost portion of the shell portion. When the Ni concentration in the core portion is taken as 100 mol% Of Ni concentration was gradually decreased to 70 mol%.

For the washing process, LiOH and WO ₃ were dissolved in distilled water (DI water) for 3 minutes to prepare a washing solution. At this time, the contents of LiOH, WO ₃ and distilled water (DI water) are as shown in Table 1 below.

The total composition of the washing liquid is Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g of lithium complex oxide particles having an in-core-shell structure were added and stirred for 10 minutes to prepare a slurry. Thereafter, the slurry was filtered, dried in a vacuum dryer at 130 ° C for 4 hours, and then heat-treated at 300 ° C for 5 hours to obtain a cathode active material which was finally washed.

(2) Production of lithium secondary battery

The cathode active material prepared in the above (1), the binder (PVDF) and the conductive material (Denka black) were prepared so that the weight ratio of the cathode active material: binder: conductive material was 96.5: 1.5: 2, -2-pyrrolidone solvent to prepare a slurry.

This slurry was evenly applied to an aluminum foil, followed by compression in a roll press and vacuum drying in a 100 vacuum oven for 12 hours to prepare a positive electrode.

Li-metal was used as a counter electrode, and 1 mole of LiPF ₆ solution was used as a liquid electrolyte in a mixed solvent of EC: EMC = 1: 2 as an electrolytic solution, and the resultant was formed into a 2032 half coin cell To prepare a lithium secondary battery.

Example  1 to 6 and Comparative Example  1 to 11

The lithium composite oxide particles having the total composition as shown in Table 1 below were prepared by the same method as in (1) of Example 1 except that the stoichiometric ratio of the starting materials was controlled. Next, the same procedure as in (1) of Example 1 was carried out except that the wash water solution was prepared by adjusting the contents of LiOH and WO ₃ as described in the following Table 1, A lithium secondary battery was prepared in the same manner as in (2) of Example 1, except that an active material was prepared.

However, in the case of Reference Example 1, a cathode active material and a lithium secondary battery were prepared as follows.

Reference example  One

A lithium composite oxide particle having a core-shell structure having a total composition of Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ was prepared in the same manner as in (1) of Example 1.

Next, lithium hydroxide monohydrate (LiOH.H ₂ O) and tungsten oxide (WO ₃ ) were mixed at a molar ratio of 2: 1 and reacted. After completion of the reaction, the resultant was dried at 80 DEG C in an air atmosphere to obtain lithium tungstate powder. 1300 g of the lithium composite oxide particles were immersed in 1,300 g of distilled water, and 3.6104 g of the lithium tungstate powder was added and stirred to prepare a slurry. Then, the slurry was filtered and then fired to prepare a cathode active material containing W and Li.

Thereafter, a lithium secondary battery was produced in the same manner as in (2) of Example 1.

division The total composition of the lithium composite oxide particles Lithium composite oxide
[g] LiOH
[g] WO ₃
[g] DI water
[g] Comparative Example 1 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 0 g 0 g 1300 g Comparative Example 2 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 1.0909 g 0 g 1300 g Comparative Example 3 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 0 g 9.9459 g 1300 g Example 1 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 1.0909 g 4.9729 g 1300 g Example 2 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 1.0909 g 9.9459 g 1300 g Example 3 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 1.0909 g 14.7681 g 1300 g Example 4 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g 1.6363 g 9.9459 g 1300 g Reference Example 1 Li (Ni _0.9 Co _0.07 Mn _0.03 ) O ₂ 1300 g Li ₂ WO ₄ (3.6104 g) 1300 g Comparative Example 4 Li (Ni _0.85 Co _0.12 Mn _0.05 ) O ₂ 1300 g 0 g 0 g 1300 g Comparative Example 5 Li (Ni _0.85 Co _0.12 Mn _0.05 ) O ₂ 1300 g 1.0909 g 0 g 1300 g Comparative Example 6 Li (Ni _0.85 Co _0.12 Mn _0.05 ) O ₂ 1300 g 0 g 9.9459 g 1300 g Example 5 Li (Ni _0.85 Co _0.12 Mn _0.05 ) O ₂ 1300 g 1.0909 g 9.9459 g 1300 g Example 6 Li (Ni _0.85 Co _0.12 Mn _0.05 ) O ₂ 1300 g 1.0909 g 14.7681 g 1300 g Comparative Example 7 Li (Ni _0.8 Co _0.14 Mn _0.06 ) O ₂ 1300 g 0 g 0 g 1300 g Comparative Example 8 Li (Ni _0.8 Co _0.14 Mn _0.06 ) O ₂ 1300 g 1.0909 g 0 g 1300 g Comparative Example 9 Li (Ni _0.8 Co _0.14 Mn _0.06 ) O ₂ 1300 g 0 g 9.9459 g 1300 g Comparative Example 10 Li (Ni _0.8 Co _0.14 Mn _0.06 ) O ₂ 1300 g 1.0909 g 9.9459 g 1300 g Comparative Example 11 Li (Ni _0.8 Co _0.14 Mn _0.06 ) O ₂ 1300 g 1.0909 g 14.7681 g 1300 g

Experimental Example  1 - Evaluation of initial capacity and high temperature lifetime characteristics

The lithium secondary batteries produced in Examples 1 to 6, Comparative Examples 1 to 11 and Reference Example 1 were subjected to 0.2 C charging / 0.2 C discharge to measure the initial discharge capacity. The results are shown in Table 2 below.

Next, the lithium secondary batteries of Examples 1 to 6, Comparative Examples 1 to 12, and Reference Example 1 were charged at a high temperature (45 ° C) under a constant current-constant voltage of 0.3C, 4.25V, and 0.005C cut- Charge and discharge were carried out 30 times with a method of discharging under the conditions of a constant current of 0.3 C and a voltage of 2.7 V cut-off, and the discharge capacity was measured. At this time, the ratio of the 30th discharging capacity to the one discharging capacity was calculated, and the capacity retention rate was obtained, and this was taken as the high temperature lifetime characteristic. The results are shown in Table 2 below.

division Initial discharge capacity at room temperature [25 ° C, mAh / g, 0.2C] High temperature life characteristics [%]
(45 [deg.] C, 30 ^th / 1 ^st ) Comparative Example 1 211.1 90.9 Comparative Example 2 213.3 91.5 Comparative Example 3 208.8 88.7 Example 1 213.8 92.1 Example 2 215.0 92.7 Example 3 215.9 93.4 Example 4 215.2 92.4 Reference Example 1 207.6 86.5 Comparative Example 4 204.5 92.3 Comparative Example 5 206.7 92.5 Comparative Example 6 202.1 91.8 Example 5 207.2 93.8 Example 6 208.1 95.1 Comparative Example 7 197.6 94.5 Comparative Example 8 198.1 94.7 Comparative Example 9 195.2 92.2 Comparative Example 10 198.7 95.1 Comparative Example 11 198.5 95.2

As shown in Table 2, the lithium secondary batteries of Examples 1 to 6, in which the cathode active material prepared by preparing the lithium composite oxide under the same conditions as those of the present example and used for the washing process, had a high initial discharge capacity, I can confirm that it is also excellent.

On the other hand, the lithium secondary batteries prepared in accordance with Comparative Examples 1 to 12 and Reference Example 1 showed at least one of the initial capacity and the high-temperature lifetime characteristics deteriorated or both were not good.

Therefore, when a cathode active material manufactured by the same method as the present embodiment is employed, a lithium secondary battery having excellent initial capacity and improved high-temperature lifetime characteristics can be realized.

Experimental Example  2 - Residual lithium measurement on the surface of cathode active material

The residual lithium content of the surface of the cathode active material prepared according to Examples 1 to 6, Comparative Examples 1 to 3, and Reference Example 1 was measured by acid-base titration using a 0.1 mol% HCl solution, .

division Residual LiOH [ppm] Residual Li ₂ CO ₃ [ppm] Comparative Example 1 3,203 3,024 Comparative Example 2 3,420 3,152 Comparative Example 3 3,176 2,935 Example 1 3,012 2,673 Example 2 2,675 2,315 Example 3 2,018 1,975 Example 4 2,842 2,512 Reference Example 1 3,321 3,051 Example 5 2,405 2,315 Example 6 2,216 2,174

Referring to Table 3, it can be seen that lithium hydroxide and lithium carbonate were decreased in the cathode active materials 1 to 6 prepared by performing the washing process after preparing the lithium composite oxide under the same conditions as in the present example.

On the contrary, in Comparative Examples 1 to 3 in which lithium hydroxide and / or tungsten oxide were not used in the washing process and in both of them, in the case of the positive electrode active material of Reference Example 1 in which lithium tungstate powder was dissolved in distilled water, The lithium content was generally higher when compared to the examples.

Therefore, when the cathode active material is manufactured as in the embodiments of the present invention, a cathode active material with reduced surface residual lithium content can be obtained. In the case of applying the cathode active material to a lithium secondary battery, slurrying of the electrode is prevented, Excellent in ring characteristics. In addition, the generation of gas such as carbon monoxide or carbon dioxide is reduced by charging / discharging of the lithium secondary battery, thereby reducing the volume expansion of the battery and improving the lifetime characteristics.

Experimental Example  3 - Direct current internal resistance (DC-IR) measurement

Charge and discharge cycles were carried out at a high temperature (45 ° C) under the same conditions as in Experimental Example 2, and the lithium secondary batteries prepared in Examples 1 to 6, Comparative Examples 1 to 3, and Reference Example 1 were charged at 4.25 V, The voltage was measured 60 seconds after the discharge current was applied.

The DC-IR value after one charge / discharge and the DC-IR value after 30 charge / discharge cycles are shown, and the rate of increase is expressed in percentage in Table 4 below.

division Room temperature 1 ^st DC-IR [Ω] High temperature 1 ^st DC-IR [Ω] High temperature 30 ^th DC-IR [Ω] High temperature resistance increase rate
(30 ^th / 1 ^hr ,%) Comparative Example 1 29.8 19.8 73.1 269.2 Comparative Example 2 29.0 19.6 68.4 249.0 Comparative Example 3 27.0 18.5 49.4 167.0 Example 1 25.9 17.6 37.5 113.1 Example 2 24.1 16.3 31.8 95.1 Example 3 22.2 15.9 25.1 57.9 Example 4 24.3 16.2 32.1 98.1 Reference Example 1 27.6 18.7 59.2 216.6 Example 5 21.6 15.4 27.9 81.2 Example 6 19.8 14.7 24.2 64.6

Referring to Table 4, the lithium secondary batteries of Examples 1 to 6, in which the cathode active material prepared by preparing the lithium composite oxide under the same conditions as those of the present example and then washed, had low initial DC-IR values, It can be seen that the DC-IR value after the 30 charge / discharge cycles is low as a whole. In addition, the resistance increase rate is also reduced.

On the other hand, in Comparative Examples 1 to 3 in which lithium hydroxide and / or tungsten oxide were not used in the washing step and in the case of the positive electrode active material of Reference Example 1 in which lithium tungstate powder was prepared by dissolving lithium tungstate powder in distilled water, The initial resistance at room temperature, the initial resistance at high temperature, and the rate of increase in high temperature resistance all have larger values than those in the embodiment.

Therefore, when the cathode active material manufactured according to this embodiment is applied, a lithium secondary battery having excellent resistance characteristics even at room temperature and high temperature environment can be realized.

Experimental Example  4 - Structural stability test

Structural stability tests were conducted on the lithium secondary batteries produced in Examples 2 and 3, Comparative Example 1 and Reference Example 1. [

Specifically, charging and discharging were performed once by charging the battery at 0.2C, 4.25V, and 0.005C cut-off conditions at a constant temperature (50 DEG C) at a constant current to a constant voltage and discharging at a constant current of 0.2C and 2.7V cut- The structure stability test was performed by filling the cells at 0.2C, 4.7V, and 60hr cut-off conditions with a constant current and a constant voltage. The results are shown in Fig.

Referring to FIG. 1, the lithium secondary batteries of Examples 2 to 3 employing the cathode active material prepared by preparing the lithium composite oxide under the same conditions as those of the present example were subjected to a washing treatment at a high voltage of 4.7 V And the structural stability is excellent.

However, in the lithium secondary batteries of Comparative Example 1 and Reference Example 1, the holding current remarkably becomes higher after 40 hours than in the Examples.

Therefore, when the cathode active material is manufactured according to the present embodiments, a cathode active material having excellent structural stability can be realized.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (13)

Preparing a lithium composite oxide represented by Formula 1 below; And
Washing the lithium composite oxide with water
Lt; / RTI &gt;
The washing liquid in the washing step may be,
Lithium hydroxide, tungsten oxide, and a solvent.
[Chemical Formula 1]
Li _x Ni _a Co _b Mn _c M _{d d} O ₂
(Wherein M1 is at least one of Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo and W, x is 0.90? X? 1.07, a is 0.83? A < b is 0 <b? 0.3, c is 0 <c? 0.3, d is 0 <d <0.01 and a + b + c + d = The method according to claim 1,
Wherein a in Formula 1 is 0.85? A <1. The method according to claim 1,
In the lithium composite oxide,
A core portion in which a molar amount of nickel is constant, and
And a shell portion surrounding the outer surface of the core portion and having a concentration gradient in which the molar content of nickel gradually decreases in a direction from the interface with the core portion to the outermost portion. The method according to claim 1,
The content of the lithium hydroxide in the washing liquid is,
And 0.05 part by weight to 0.2 part by weight based on 100 parts by weight of the lithium composite oxide. The method according to claim 1,
Wherein the weight ratio of lithium hydroxide and tungsten oxide in the washing liquid is from 1: 4 to 1:30. The method according to claim 1,
The content of the solvent in the washing liquid may be,
And 50 parts by weight to 200 parts by weight based on 100 parts by weight of the lithium composite oxide. The method according to claim 1,
The step of washing the lithium composite oxide comprises:
Adding the lithium composite oxide to the washing liquid and stirring the slurry to prepare a slurry;
Filtering the slurry to obtain a washed lithium composite oxide
And the cathode active material. 8. The method of claim 7,
The step of adding the lithium composite oxide to the washing liquid and stirring the slurry to prepare the slurry,
Is carried out at a stirring rate of 50 rpm to 200 rpm for 1 minute to 60 minutes at a temperature range of 5 to 25 캜. 8. The method of claim 7,
Further comprising the step of filtering the slurry to obtain a washed lithium composite oxide, followed by drying the washed lithium composite oxide. 10. The method of claim 9,
The step of drying the washed lithium composite oxide comprises:
At a temperature in the range of 80 占 폚 to 300 占 폚 for 1 hour to 30 hours. The method according to claim 1,
After the step of washing the lithium composite oxide,
Further comprising the step of heat-treating the washed lithium composite oxide. 12. The method of claim 11,
The step of heat-treating the washed lithium composite oxide comprises:
(O ₂ ) or nitrogen (N ₂ ) atmosphere in a temperature range of 200 ° C. to 800 ° C. for 1 hour to 10 hours. anode;
cathode; And
Comprising an electrolyte,
Wherein the anode comprises the cathode active material produced by the method according to any one of claims 1 to 12.

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