KR20180119336A - Manufacturing method of a positive electrode active material for rechargeable lithium battery, positive electrode active material for rechargeable lithium battery manufacture using the same, and rechargeable lithium battery including the same - Google Patents

Abstract

A method for manufacturing a cathode active material for a rechargeable lithium battery according to an embodiment of the present invention includes a step of mixing a lithium compound, a metal hydroxide, and an organic acid to prepare a mixture and a step of firing the mixture. It is possible to reduce residual lithium carbonate while reducing manufacturing costs.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, a positive electrode active material for a lithium secondary battery produced using the same, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive active material for lithium secondary batteries, THE SAME, AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME}

The present invention relates to a method for producing a cathode active material for a lithium secondary battery, a cathode active material for a lithium secondary battery manufactured using the same, and a lithium secondary battery comprising the cathode active material.

Lithium secondary batteries are widely used as energy storage devices for mobile communication devices, hybrid electric vehicles, and household appliances because of their high energy density, excellent output characteristics, and light weight.

The core material of the lithium secondary battery is classified into an anode, a cathode, an electrolyte, and a separator. As the cathode material of a lithium secondary battery currently used, a cathode active material of LiCoO ₂ or NCM (Nickel Cobalt Manganese) may be used. Such a cathode active material can be produced by a method in which a powdery raw material is placed in a sagger, which is a sintering vessel, and the sintered body is sintered at a high temperature in a sintering furnace.

In the process of manufacturing the active material, the firing process is performed in an atmosphere of air containing oxygen. In the firing process, the firing atmosphere gas containing oxygen such as oxygen and air supplied from the outside must be easily circulated, It is possible to improve the firing efficiency by contacting oxygen with the raw material.

In particular, since carbon dioxide is heavier than oxygen and air used for controlling the firing atmosphere, the carbon dioxide remains in the inner chamber, and during the firing process, And reacts with the lithium oxide on the surface of the active material to form lithium carbonate.

An increase in the residual lithium carbonate concentration causes a problem that the dispersibility of the slurry in the coating process of the cathode active material is lowered or the capacity of the battery is decreased. Therefore, it is necessary that the sintering process of the cathode active material smoothly discharges carbon dioxide generated during the process in the inner shell.

In order to reduce the firing process ratio, it is necessary to increase the amount of powder per unit sagger. However, since the discharge of carbon dioxide during the firing process is not smooth when the powder load is increased, the concentration of residual lithium carbonate increases due to the reaction of the cathode active material and carbon dioxide there is a problem.

An embodiment of the present invention provides a method for manufacturing a cathode active material for a secondary battery and a cathode active material for a secondary battery, which can reduce lithium carbonate remaining while reducing manufacturing cost.

A method for producing a cathode active material for a lithium secondary battery according to an embodiment of the present invention includes mixing a lithium compound, a metal hydroxide, and an organic acid to prepare a mixture, and firing the mixture.

The step of mixing a lithium compound, a metal hydroxide and an organic acid to prepare a mixture may include the steps of mixing a lithium compound and an organic acid to prepare a linear mixture, and mixing the linear hydroxide with the metal hydroxide to prepare a mixture .

The lithium compound may include at least one of lithium carbonate and lithium hydroxide.

The metal hydroxide may be represented by the following formula (1) or (2).

[Chemical Formula 1]

M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}

(Wherein M ¹ , M ² and M ³ are selected from the group consisting of Ni, Co, Mn and combinations thereof, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0.0??? 0.02, 0 < x + y + z?

(2)

M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}

Wherein M ¹ , M ² , and M ³ are selected from the group consisting of Ni, Co, Al, and combinations thereof, and 0.8 ≦ x ≦ 1, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0.0??? 0.02, 0 < x + y + z?

The organic acid may include at least one selected from carboxylic acid, and imidic acid.

The organic acids are acetic acid (C ₂ H ₄ O ₂ ), formic acid (CH ₂ O ₂ ), lactic acid (C ₃ H ₆ O ₃ ), oxalic acid (C ₂ H ₂ O ₄ ), citric acid (C ₆ H ₈ O ₇ ) And may include at least one selected from acetone (C ₃ H ₆ O), ascorbic acid (C ₆ H ₈ O ₆ ), benzoic acid (C ₇ H ₆ O ₂ ), and propionic acid (C ₃ H ₆ O ₂ ).

0.01 to 0.6 mol of an organic acid may be mixed per 1 mol of the lithium compound.

In the step of preparing the mixture, the inorganic additive may be further mixed.

The inorganic additives may be oxides or hydroxides of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, La, Ce, Ta, Sr, Al, Ag, Ba, Zr, Nb, Mo, , And combinations thereof. &Lt; / RTI &gt;

After the step of preparing the mixture, the step of molding the mixture to produce the shaped body may be further included.

The binder may be further mixed in the step of preparing the mixture.

The binder may comprise at least one of water, polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

The binder includes at least one of polyvinyl alcohol (PVA) and polyvinyl butyral (PVB), and the binder may be mixed with 0.01 to 1% by weight of the binder.

The binder includes water, and the binder may be mixed in an amount of 5 to 15% by weight with respect to the entire mixture.

The density of the molded body may be from 1.5 g / cc to 3.0 g / cc.

The shape of the molded body may be spherical, cylindrical, hexahedron, toroidal, briquetted or a combination thereof.

The step of firing comprises the steps of: placing the mixture in an inner shell and disposing an inner shell on the firing furnace; And supplying and firing a gas containing oxygen to the firing furnace.

After the firing step, the firing step may further include pulverizing the fired product.

The cathode active material for a lithium secondary battery according to one embodiment of the present invention includes on average 1 to 3 concave portions having a diameter of 100 nm to 200 nm and a depth of 50 nm to 100 nm on the surface of primary particles having a size of 1um or more.

The specific surface area of the cathode active material may be 0.5 to 1.0 m ² / g.

A lithium secondary battery according to an embodiment of the present invention includes: a positive electrode; cathode; And an electrolyte; and the positive electrode includes a positive electrode active material for a lithium secondary battery manufactured by the above-described method.

The method for manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention can reduce lithium carbonate remaining while reducing manufacturing cost.

Also, the use of the cathode active material for a lithium secondary battery manufactured by the manufacturing method according to an embodiment of the present invention has high discharge capacity and initial charge / discharge efficiency.

1 is a schematic view of a molded body formed during a process of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
2 is a schematic view of a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
Fig. 3 is a photograph of a molded article mounted on an inner door.
FIG. 4 is a scanning electron microscope (SEM) photograph of a cathode active material for a lithium secondary battery manufactured in Example.
5 is a scanning electron microscope (SEM) photograph of the cathode active material for a lithium secondary battery manufactured in the example.
6 is a scanning electron microscope (SEM) photograph of the cathode active material for a lithium secondary battery produced in the example.
7 is a scanning electron microscope (SEM) photograph of the cathode active material for a lithium secondary battery manufactured in Comparative Example.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings 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.

A method for producing a cathode active material for a lithium secondary battery according to an embodiment of the present invention includes mixing a lithium compound, a metal hydroxide, and an organic acid to prepare a mixture, and firing the mixture.

First, a lithium compound, a metal hydroxide and an organic acid are mixed to prepare a mixture.

The lithium compound can be used without particular limitation as long as it is a compound capable of supplying lithium in the positive electrode active material. Specifically, the lithium compound may include at least one of lithium carbonate and lithium hydroxide. As will be described later, in one embodiment of the present invention, residual lithium carbonate can be remarkably reduced through the mixing of organic acids, so that lithium carbonate can be contained as a lithium compound in a large amount. More specifically, the lithium compound may include only lithium carbonate. Even when lithium hydroxide is used as the lithium compound, lithium carbonate may be present as impurities in the lithium hydroxide, and lithium carbonate may be generated during the calcination. In one embodiment of the present invention, the residual lithium carbonate can be remarkably reduced through the mixing of the organic acid, so that the effect of the present invention can be obtained even when only lithium hydroxide is used as the lithium compound. The lithium compound may be contained in an amount of 28 to 33% by weight based on the sum of the lithium compound and the metal hydroxide.

The metal hydroxide may be a compound represented by the following formula (1) or (2).

 [Chemical Formula 1]

M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}

(Wherein M ¹ , M ² and M ³ are selected from the group consisting of Ni, Co, Mn and combinations thereof, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0.0??? 0.02, 0 < x + y + z?

(2)

M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}

Wherein M ¹ , M ² , and M ³ are selected from the group consisting of Ni, Co, Al, and combinations thereof, and 0.8 ≦ x ≦ 1, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0.0??? 0.02, 0 < x + y + z?

A compound represented by the general formula (1) include, for example, Ni _x Co _y Mn _z (OH) may use the _{2 + δ,} with a compound represented by the formula (2) include, for example, Ni _x Co _y Al _z (OH) _{2 + delta} can be used. These metal hydroxides can be prepared by methods known in the art, for example, solid phase reaction, coprecipitation, sol-gel process, hydrothermal synthesis and the like. The metal hydroxide may be contained in an amount of 67% by weight to 72% by weight based on the sum of the lithium compound and the metal hydroxide.

In an embodiment of the present invention, an organic acid is added and mixed to lower the amount of lithium carbonate present in the cathode active material.

Since the melting point of lithium carbonate is 723 deg. C, the reaction between lithium carbonate and metal hydroxide may not be sufficient at a calcination temperature of 700 to 900 deg. Accordingly, lithium carbonate may partially remain in the production of the cathode active material. Also, in the firing process, the cathode active material and the carbon dioxide react with each other to generate residual lithium carbonate.

If the residual lithium carbonate is present in a large amount, the battery may explode due to the generation of carbon dioxide during use of the battery. Therefore, it is very important to reduce the residual lithium carbonate in order to secure the reliability of the battery.

In an embodiment of the present invention, the amount of lithium carbonate remaining can be reduced through the reaction of organic acid and lithium carbonate by mixing an organic acid in addition to a lithium compound and a metal hydroxide. The organic acid is not particularly limited as long as it is an organic acid capable of reacting with lithium carbonate to remove lithium carbonate. Specifically, the organic acid may include at least one selected from carboxylic acid, and imidic acid. Sulfuric acid may be included as an organic acid, but sulfonic acid may contain sulfur and may not be completely removed in the firing step. Since imidacic acid contains nitrogen, it can be applied only when the calcination temperature is high. Therefore, as the organic acid, it is most preferable to include a carboxylic acid.

More specifically, the organic acid is acetic acid _{(C 2 H 4 O 2)} , formic acid (CH ₂ O _2), lactic acid _{(C 3 H 6 O 3)} , oxalic acid _{(C 2 H 2 O 4)} , citric acid (C ₆ H ₈ O ₇ ), acetone (C ₃ H ₆ O), ascorbic acid (C ₆ H ₈ O ₆ ), benzoic acid (C ₇ H ₆ O ₂ ) and propionic acid (C ₃ H ₆ O ₂ ) .

Hereinafter, the mechanism of removing lithium carbonate will be described by taking acetic acid as an example of an organic acid. However, the present invention is not limited thereto.

When lithium carbonate and acetic acid are reacted, lithium acetate, water, and carbon dioxide are generated as shown in the following reaction formula (1).

[Reaction Scheme 1]

The melting point of lithium acetate is 286 ° C., which is lower than the melting point of lithium hydroxide. Therefore, if lithium carbonate and acetic acid are reacted in advance and then mixed with a precursor and then calcined, the calcination temperature is low.

The mixing amount of the organic acid may be 0.01 to 0.6 moles per 1 mole of the lithium compound. If too little organic acid is mixed, lithium carbonate removal may not be sufficiently achieved. When the organic acid is mixed too much, the lithium reactant (for example, lithium acetate) may melt and flow down, and the Li concentration may vary depending on the position of the mixture in the firing process during the firing process. Therefore, the Li / Me ratio of the cathode active material is not uniform, There arises a problem that scattering of lithium concentration or the like increases. In addition, a problem may arise in that the lithium compound reacts with the metal hydroxide because the molten lithium reactant flows down.

In the step of preparing the mixture, the inorganic additive may be further mixed. The inorganic additive enhances stability by replacing the metal ion of the cathode active material or acts as an oxide on the surface of the cathode active material to prevent the reaction with the electrolyte. Specifically, the inorganic additive is an oxide of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, La, Ce, Ta, Sr, Al, Ag, Ba, Zr, Or a hydroxide thereof, and combinations thereof.

The mixture thus prepared can be immediately fired, but the mixture can be molded to produce a molded body and then fired. When a molded body is produced and fired, voids are formed between the molded bodies. The atmospheric gas is supplied into the inner shell through the gap, whereby the atmospheric gas can be uniformly supplied to the raw material of the cathode active material loaded in the inner shell, thereby achieving a more uniform firing quality.

On the other hand, in the case of firing without forming a molded body, the atmospheric gas flows through the upper surface of the inner shell, but the atmospheric gas mainly comes into contact with the upper shell of the raw material loaded in the inner shell, It is difficult to obtain a uniform firing quality because the contact probability is relatively small with respect to the raw material located at a deep portion such as the bottom surface.

In order to increase the bonding force between the mixtures, the binder may be further mixed in the step of preparing the above-mentioned mixture. The binder may comprise at least one of water, polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

When the binder contains at least one of polyvinyl alcohol (PVA) and polyvinyl butyral (PVB), the binder may be mixed in an amount of 0.01 to 1% by weight with respect to the whole mixture. If too much of at least one of polyvinyl alcohol (PVA) and polyvinyl butyral (PVB) is mixed, a large amount of carbon dioxide may be generated during the firing process, and the residual lithium carbonate concentration on the surface of the cathode active material may increase.

When the binder includes water, the binder may be mixed in an amount of 5 to 15% by weight with respect to the whole mixture. When the amount of water is too small, the amount of moisture adsorbed on the surface of the metal hydroxide and the lithium compound powder is insufficient and the binding property is lowered, so that molding may be difficult. If too much water is involved, the viscosity of the mixture may become too low.

When a molded body is manufactured and fired, a molded body having a high density is fired, so that a larger amount of mixture can be stacked in a predetermined volume of an inner shell, and productivity can be improved.

Specifically, the density of the molded body may be 1.5 g / cc to 3.0 g / cc. If the density of the molded body is too low, the amount of powder per unit weight in the unit is not different from that in the case of powder calcining, so the productivity improvement may be insignificant. If the density is too high, the discharge of carbon dioxide and water vapor generated inside the molded body during the firing process is not smooth, so that the capacity per unit weight of the produced cathode active material may decrease.

On the other hand, the size of the formed body may be 5 mm to 100 mm. If the size of the molded body is too small, the size of the gap formed between the molded bodies is small, so that the gas may not flow in and out smoothly. If the size of the molded body is too large, the molded body may be deformed during the firing process, thereby increasing the contact area between the inner shell and the molded body and reducing the life of the inner shell. At this time, the size of the molded body means the diameter of the cross section or the length of one side. By manufacturing the molded article in the above-mentioned size, the size of the gap formed between the molded articles can be formed to be 0.1 to 10 mm.

The shape of the molded body is not particularly limited. Any shape of a regular or irregular shape may be used as long as it can introduce atmospheric gas and discharge reaction by-products. The shape of the molded body may be, for example, a spherical shape, a cylindrical shape, a hexagonal shape, or the like, or a combination of two or more shapes thereof may be used. For the heat transfer to the inside during firing, it is also possible to use a form having a hole formed therein such as a donut type or a briquetting type.

Fig. 1 exemplarily shows the shape of a molded body manufactured in a spherical shape. Referring to FIG. 1, the molded body 100 may include a metal hydroxide 10 and a lithium compound 20.

Next, the mixture is baked. After the mixture is prepared as described above, if the mixture is molded to produce a molded body, the molded body is fired.

The firing can be performed at a temperature of 700 to 1100 DEG C for 10 to 30 hours under a gas atmosphere containing oxygen, but is not limited thereto. The temperature and time of firing can be appropriately selected depending on the kind of raw material.

The step of firing comprises the steps of: placing the mixture in an inner shell and disposing an inner shell on the firing furnace; And supplying and firing a gas containing oxygen to the firing furnace. Furthermore, there can be one or more inner flare arranged in the firing furnace. At this time, the inner shell can be arranged as a single layer of a plurality of inner shells, or two or more inner shells can be stacked and arranged in two or more layers.

As the firing vessel, for example, alumina, mullite, or a coating layer formed thereon can be used, and any material that is inert to the raw material and has durability under the firing temperature can be used without limitation.

After the firing step, cooling the fired product may further comprise cooling the fired product.

The cooling can be carried out at a cooling rate of, for example, 1 / min to 10 / min from a firing temperature to at least 200.

After the firing step, the firing step may further include pulverizing the fired product.

The cathode active material for a lithium secondary battery manufactured by the above-described method can reduce lithium carbonate remaining while reducing manufacturing cost.

As described above in one embodiment of the present invention, the organic acid is reacted with the lithium compound or the metal hydroxide and is eroded by adding the organic acid to the mixture and firing, so that erosion marks may remain on the surface of the finally prepared cathode active material.

For example, in the case of baking a mixture having a hexahedron shape, if the organic acid is not added to the mixture, it remains in a hexahedron shape. However, in one embodiment of the present invention, the organic acid is included in the mixture, and the organic acid reacts with the lithium compound or the metal hydroxide in the firing process and is eroded to form the concave portion 30 on the surface.

FIG. 2 schematically illustrates a cathode active material 200 having a concave portion 30 formed on its surface. At this time, the recess 30 may have a diameter of 100 nm to 200 nm and a depth of 50 nm to 100 nm. In this case, the diameter and the depth of the concave portion mean the diameter of the circle equivalent of the concave portion formed on the imaginary surface, and the depth from the imaginary surface, assuming a surface on which no erosion by the organic acid has occurred. Such recesses are formed with specific diameters and depths, and the recesses due to erosion are not formed in the manufacturing process of the conventional positive electrode active material, so that they are distinguished from each other.

In addition, an average of 1 to 3 concave portions per primary particle having a size of the cathode active material 200 of 1 um or more can be formed. As described above, since the mixing amount of the lithium compound and the organic acid is appropriately controlled in the process of manufacturing the cathode active material, a suitable number of the concave portions 30 are formed in the cathode active material 200. FIG. 2 shows a case where two concave portions 30 are formed on one particle of the cathode active material 200. In the case of the primary particles having a size of less than 1 탆, the production deviation of the concave portions 30 per particle may occur to a large extent. Therefore, in one embodiment of the present invention, the primary particles having a size of 1 탆 or more are assumed, Is calculated. At this time, the size of the positive electrode active material means the particle diameter of the particles.

In this embodiment of the present invention, since the concave portion 30 is formed in the particles of the cathode active material 200, the specific surface area of the cathode active material is increased as compared with the cathode active material generally manufactured. Specifically, the specific surface area of the cathode active material may be 0.5 to 1.0 m ² / g.

As described above in one embodiment of the present invention, by adding an organic acid to the mixture and firing, the content of residual lithium carbonate in the finally produced cathode active material is remarkably reduced.

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

Specifically, the lithium secondary battery according to an embodiment of the present invention may include an electrode assembly including a cathode, a cathode, and a separator disposed between the anode and the cathode.

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 to 30% by weight based on the total amount of the composition for forming the negative electrode 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 to 30% by weight based on the total amount of the composition for forming the anode active material layer.

The anode includes the cathode active material prepared by the method for producing a cathode active material according to an embodiment. That is, the cathode active material, the binder and optionally the conductive material may be mixed to prepare a composition for forming a cathode active material layer, and then the composition may be applied to a cathode current collector such as aluminum. Further, the conductive material, binder and solvent are used in the same manner as in the case of the above-mentioned anode.

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, preferred embodiments of the present invention, comparative examples thereof, and evaluation examples thereof will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example

The _{Ni 0 .6 Co 0 .2 Mn 0} .2 (OH) a lithium secondary battery positive electrode active material by using the Li ₂ CO ₃ with ₂ and a lithium compound as a metal hydroxide were prepared. 0.05 mol of benzoic acid and metal hydroxide were mixed with 1 mol of Li ₂ CO ₃ . A spherical molding agent having a diameter of 20 mm was prepared. The density of the molded body was 2.1 g / cc. The molded body was filled with 7 kg of an inner shell and placed in a firing furnace. Fig. 3 shows a state in which the molded body is mounted on an inner shell. And fired at a temperature of 900 캜 for 10 hours while injecting air into the firing furnace.

After firing, the inner wall was removed from the firing furnace and cooled to obtain a cathode active material.

The amount of residual lithium and the number of concave portions were measured with respect to the produced positive electrode active material, and the results are shown in Table 1. The microstructure of the prepared positive electrode active material is shown in FIGS. 4 to 6. FIG.

The residual lithium amount was measured by acid-base titration method using diluted hydrochloric acid (HCl) in the residual lithium content on the surface of the cathode active material.

Comparative Example

Benzoic acid was not added to the solution. The amount of residual lithium and the number of concave portions were measured with respect to the produced positive electrode active material, and the results are shown in Table 1. The microstructure of the prepared positive electrode active material is shown in Fig.

As shown in FIG. 4 to FIG. 6, it can be confirmed that the embodiment has a concave portion formed on the particle surface due to the reaction with the organic acid, and the shape is irregular. On the other hand, as shown in FIG. 7, it can be confirmed that the comparative example does not cause corrosion by organic acid, and the shape thereof is substantially constant as a hexahedron. The average diameter of the recesses formed in the examples was 150 nm and the depth was 70 nm.

Experimental Example  : Preparation of lithium secondary battery

(2) by weight of a conductive material (Denka Black), 2% by weight of a binder (PVDF), and 1% by weight of a thickener (CMC) prepared in Examples and Comparative Examples were mixed with 96% by weight of a positive electrode active material for a lithium secondary battery, (NMP) solvent to prepare a slurry.

The slurry was uniformly applied to an aluminum (Al) current collector, compressed by a roll press, and vacuum-dried in a 100 ° C vacuum oven for 12 hours to prepare a positive electrode.

Lithium metal (Li-metal) was used as a counter electrode, and a mixed solvent of ethylene carbonate (EC: Ethylene Carbonate): dimethyl carbonate (DMC, Dimethyl Carbonate) ₆ solution was used.

Using each of the above components, a 2032 half-coin cell was fabricated according to a conventional manufacturing method.

The lifetime characteristics of the thus prepared half cells were evaluated.

First, charging and discharging were performed at 0.1 C in a range of 2.5 V to 4.25 V at 25 캜 using a charge / discharge device (Maccor) to which a constant current was applied. The initial discharge capacity and initial charge / discharge efficiency were shown in Table 1 . The same method was repeated 50 times to calculate the discharge capacity ratio at 50 times to one discharge capacity to determine the capacity retention rate, which was defined as the cycle life.

Example Comparative Example Residual LiOH (ppm) 758 761 Residual Li ₂ CO ₃ (ppm) 4720 7557 Initial discharge capacity (mAh / g, @ 0.1C) 170 167 Number of recesses (per piece / particle) 2.3 none Specific surface area (m ² / g) 0.67 0.42 Initial Charge / Discharge Efficiency (%) 92 90.8 Cycle life (50 ^th / 1 ^st @ 1C) 98.6 98.2

As can be seen from Table 1, the residual amount of lithium carbonate was reduced by about 38% as compared with the comparative example in which the organic acid was not added, in the case of the example in which the organic acid was further mixed and fired. In addition, it can be seen that the embodiment is superior to the comparative example in initial discharge capacity, initial charge / discharge efficiency, and cycle life.

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.

10: metal hydroxide 20: lithium compound
30: recess 100: molded article
200: cathode active material

Claims (21)

Mixing a lithium compound, a metal hydroxide and an organic acid to prepare a mixture; and
Firing the mixture
Wherein the positive electrode active material is a positive electrode active material. The method according to claim 1,
The step of mixing the lithium compound, the metal hydroxide, and the organic acid to prepare a mixture includes:
Mixing the lithium compound and the organic acid to prepare a linear mixture; and
And mixing said metal hydroxide with said line mixture to produce a mixture
(Method for producing positive electrode active material for lithium secondary battery). The method according to claim 1,
Wherein the lithium compound comprises at least one of lithium carbonate and lithium hydroxide. The method according to claim 1,
Wherein the metal hydroxide is represented by the following Chemical Formula 1 or Chemical Formula 2.
[Chemical Formula 1]
M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}
(Wherein M ¹ , M ² and M ³ are selected from the group consisting of Ni, Co, Mn and combinations thereof, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0.0??? 0.02, 0 < x + y + z?
(2)
M ¹ _x M ² _y M ³ _z (OH) _{2 + δ}
Wherein M ¹ , M ² , and M ³ are selected from the group consisting of Ni, Co, Al, and combinations thereof, and 0.8 ≦ x ≦ 1, 0 ≦ y ≦ 0.2, 0 ≦ z ≦ 0.2, 0.0??? 0.02, 0 < x + y + z? The method according to claim 1,
Wherein the organic acid comprises at least one selected from carboxylic acid and imidic acid. The method according to claim 1,
The organic acid may be acetic acid (C ₂ H ₄ O ₂ ), formic acid (CH ₂ O ₂ ), lactic acid (C ₃ H ₆ O ₃ ), oxalic acid (C ₂ H ₂ O ₄ ), citric acid (C ₆ H ₈ O ₇ ) Containing at least one selected from acetone (C ₃ H ₆ O), ascorbic acid (C ₆ H ₈ O ₆ ), benzoic acid (C ₇ H ₆ O ₂ ) and propionic acid (C ₃ H ₆ O ₂ ) A method for manufacturing a positive electrode active material for a battery. The method according to claim 1,
Wherein the organic acid is mixed in an amount of 0.01 to 0.6 mol per 1 mol of the lithium compound. The method according to claim 1,
Wherein the inorganic additive is further mixed in the step of preparing the mixture. 9. The method of claim 8,
The inorganic additive may be an oxide of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, La, Ce, Ta, Sr, Al, Ag, Ba, Zr, Nb, Mo, And at least one compound selected from the group consisting of lithium hydroxide, lithium hydroxide, and combinations thereof. The method according to claim 1,
After the step of preparing the mixture,
And then molding the mixture to produce a molded body. 11. The method of claim 10,
Wherein the binder is further mixed in the step of preparing the mixture. 12. The method of claim 11,
Wherein the binder comprises at least one of water, polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). 13. The method of claim 12,
Wherein the binder comprises at least one of polyvinyl alcohol (PVA) and polyvinyl butyral (PVB), and the binder is mixed in an amount of 0.01 to 1 wt% with respect to the entire mixture. 13. The method of claim 12,
Wherein the binder contains water and the binder is mixed in an amount of 5 to 15 wt% with respect to the entire mixture. 11. The method of claim 10,
Wherein the density of the molded body is 1.5 g / cc to 3.0 g / cc. 11. The method of claim 10,
Wherein the shape of the molded body is a spherical shape, a cylindrical shape, a hexahedron shape, a toroidal shape, a briquetting shape, or a combination thereof. The method according to claim 1,
Wherein the firing comprises:
Placing the mixture in an inner shell, placing an inner shell on the firing furnace, and
Supplying a gas containing oxygen to the firing furnace and firing
Wherein the positive electrode active material is a positive electrode active material. The method according to claim 1,
After the firing step,
And pulverizing the fired product. The method for producing a cathode active material for a lithium secondary battery according to claim 1, Wherein the average primary particle size of the primary particles is 1 to 100 nm and the average particle diameter is 100 to 200 nm and the depth is 50 to 100 nm. 20. The method of claim 19,
And a specific surface area of 0.5 to 1.0 m ² / g. anode; cathode; And an electrolyte,
Wherein the positive electrode comprises a positive electrode active material for a lithium secondary battery produced by the method according to any one of claims 1 to 18.

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