KR101816945B1 - Cathode active material, preparation method thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

Lithium transition metal oxide; And a coating layer on the surface of the lithium-transition metal oxide, wherein the coating layer comprises lithium boroxide oxide and a lithium-phosphorus-containing compound, a method for producing the same, and a lithium secondary battery comprising the lithium-transition metal oxide .
The cathode active material according to an embodiment of the present invention reduces lithium impurities existing on the lithium transition metal oxide and forms a coating layer on the surface of the lithium transition metal oxide to generate moisture due to side reactions between the electrolyte and the electrolyte The generation of HF that can be suppressed can be suppressed, so that the cycle characteristics of the lithium secondary battery can be further improved.
In addition, the method for producing a cathode active material according to an embodiment of the present invention can perform surface treatment at optimum temperature conditions depending on use of a phosphoric acid-containing compound and a boron-containing compound by performing a two-step heat treatment process, The performance degradation phenomenon can be improved and the increase in resistance can be suppressed.

Description

TECHNICAL FIELD The present invention relates to a cathode active material, a method for producing the cathode active material, and a lithium secondary battery including the cathode active material,

The present invention relates to a positive electrode active material, a method for producing the same, and a lithium secondary battery including the same, and more particularly, to a lithium secondary battery comprising a lithium transition metal oxide and a coating layer comprising lithium borate oxide and lithium- A cathode active material, a method for producing the same, and a lithium secondary battery comprising the same.

Lithium rechargeable batteries have been widely used as power sources for portable devices since they appeared in 1991 as small-sized, lightweight, and large-capacity batteries. In recent years, with the rapid development of the electronics, communication, and computer industries, camcorders, mobile phones, and notebook PCs have been remarkably developed and demand for lithium secondary batteries as a power source for driving these portable electronic information communication devices is increasing day by day .

The lithium secondary battery has a problem in that its service life is rapidly deteriorated by repeated charging and discharging. This problem is particularly serious at high temperatures. This is due to the phenomenon that electrolytes are decomposed or deteriorated due to moisture and other influences inside the battery, and the internal resistance of the battery is increased.

To solve these problems, a technique has been developed in which a metal oxide such as Mg, Al, Co, K, Na, or Ca is coated on the surface of a cathode active material by heat treatment. In addition, TiO ₂ was added to LiCoO ₂ active material to improve energy density and high-rate characteristics.

However, the problem of deterioration of lifetime and the problem of generation of gas due to decomposition of electrolyte during charging and discharging are not completely solved yet.

In addition, when impurities are present on the surface of the positive electrode active material during the electrode manufacturing process of the lithium secondary battery, it is possible not only to affect the change over time in the manufacturing step of the electrode slurry during the electrode manufacturing process of the lithium secondary battery, A swelling phenomenon may occur in the lithium secondary battery by reacting with the injected electrolyte.

Specifically, when the electrolytic solution contains a substance containing fluorine (F) such as LiPF ₆ , the fluorine meets with moisture or lithium impurities during charging and discharging to generate hydrofluoric acid (HF) This can degrade.

Therefore, it is urgently required to develop a cathode active material which can minimize the amount of lithium impurities present in the cathode active material for a lithium secondary battery and has excellent cycle characteristics.

A first object of the present invention is to minimize the swelling phenomenon that may occur due to lithium impurities existing on the lithium transition metal oxide, To thereby suppress the generation of HF that can be generated due to the side reaction of the cathode active material.

A second technical object of the present invention is to provide a method for producing the cathode active material.

A third object of the present invention is to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

In order to solve the above problems, the present invention provides a lithium secondary battery comprising: a lithium transition metal oxide; And a coating layer on the surface of the lithium transition metal oxide, wherein the coating layer comprises lithium borate oxide and lithium-phosphorus-containing compound.

The present invention also provides a method for producing a lithium secondary battery, comprising: mixing a lithium-transition metal oxide and a phosphoric acid-containing compound and performing a primary heat treatment; And a step of mixing the product obtained by the first heat treatment and the boron-containing compound and performing a secondary heat treatment.

In addition, the present invention provides a positive electrode comprising the positive electrode active material.

Further, the present invention provides a lithium secondary battery including the positive electrode.

The cathode active material according to an embodiment of the present invention reduces lithium impurities existing on the lithium transition metal oxide and forms a coating layer on the surface of the lithium transition metal oxide to generate moisture due to side reactions between the electrolyte and the electrolyte The generation of HF that can be suppressed can be suppressed, so that the cycle characteristics of the lithium secondary battery can be further improved.

In addition, the method for producing a cathode active material according to an embodiment of the present invention can perform surface treatment at optimum temperature conditions depending on use of a phosphoric acid-containing compound and a boron-containing compound by performing a two-step heat treatment process, The performance degradation phenomenon can be improved and the increase in resistance can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a schematic view of a cathode active material according to an embodiment of the present invention.
FIG. 2 is a graph showing pH titration results for examining the amount of lithium impurities in the cathode active material prepared in Example 1 and Comparative Example 1 of the present invention. FIG.
3 is a graph showing the cycle characteristics of the lithium secondary battery manufactured in Example 2 and Comparative Example 2 of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As shown in FIG. 1, the cathode active material according to one embodiment of the present invention includes a lithium transition metal oxide; And a coating layer on the surface of the lithium-transition metal oxide, wherein the coating layer comprises lithium borate oxide and lithium-phosphorus-containing compound.

Generally, when lithium impurities are present on the lithium transition metal oxide, the lithium impurities react with the electrolyte injected into the lithium secondary battery, thereby swelling the lithium secondary battery, that is, swelling may occur .

Particularly, when a lithium salt containing fluorine (F) such as LiPF ₆ is used as an electrolytic solution, HF can be produced as shown in the following reaction formula (1). Specifically, when the lithium secondary battery is charged and discharged, LiPF ₆ contained in the electrolytic solution is decomposed into LiF and PF ₅ , and F can generate HF with water or lithium impurities such as LiOH. The generation of HF can cause corrosion of the electrode and degrade the cycle characteristics of the secondary battery:

<Reaction Scheme 1>

LiPF ₆ - > LiF + PF ₅

PF ₅ + 2LiOH - > 2LiF + HF + H ₂ O + POF ₃

However, the cathode active material according to an embodiment of the present invention can suppress the formation of HF by reducing the amount of lithium impurities existing on the lithium transition metal oxide, and by forming a coating layer on the surface of the lithium transition metal oxide, The reaction with the lithium impurity existing on the lithium transition metal oxide can be prevented.

That is, according to one embodiment of the present invention, by using at least a portion of the lithium impurities existing on the lithium transition metal oxide to be converted into the lithium-phosphorus containing compound by using the phosphoric acid-containing compound, lithium Impurities can be reduced.

The surface of the lithium transition metal oxide may be protected by protecting the surface of the lithium transition metal oxide with lithium boron oxide in the coating layer so as to protect the surface of the lithium transition metal oxide with the lithium- It is possible to prevent the reaction between the lithium salt of the electrolytic solution and the lithium impurity existing on the lithium transition metal oxide, reduce the production of HF, and improve the structural stability of the cathode active material. In addition, when applied to a secondary battery, deterioration of high-temperature performance can be improved, and resistance increase can be suppressed.

In the cathode active material according to an embodiment of the present invention, the lithium transition metal oxide may be a commonly used lithium transition metal oxide, and examples thereof include lithium-cobalt oxide, lithium-manganese oxide, lithium- Nickel-manganese-based oxide, lithium-manganese-cobalt oxide, and lithium-nickel-manganese-cobalt oxide, or a mixture of two or more thereof. Particularly, a layered lithium transition metal oxide having a high capacity characteristic is preferable and can be represented by the following formula (1)

&Lt; Formula 1 >

Li _{1 + a} [Ni _x Mn _y Co _z M _v ] O _{2 - ca c}

Wherein M is at least one element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga and In, or at least two elements thereof; A is at least one member selected from the group consisting of P, F, S and N and 0? X? 1.0, 0? Y <0.6, 0? Z <0.6, 0? V? 0.1, 0? C? 0.2 and a + x + y + z + v = 1.

The lithium impurity that may be present on the surface of the lithium transition metal oxide may include at least one of LiOH and Li ₂ CO ₃ .

The lithium impurity may be included in the lithium transition metal oxide, for example, in the form of the following chemical formula 2:

(2)

(1-st) [Li (Li _a Mn _(1-axz) Ni _x CO _z ) O ₂ ] s [Li ₂ CO ₃ ]

0 <x <0.9, 0? Z <0.6, 0 <s <0.05, and 0 <t <0.05.

In the cathode active material according to one embodiment of the present invention, the lithium-phosphorus-containing compound contained in the coating layer may be represented by LixPyOz (1? X? 4, 1? Y? 4, 0? Z? 7) , Specifically, Li ₃ PO ₄ , LiPO ₃ , Li ₄ P ₂ O ₇ , LiP and Li ₃ P, or a mixture of two or more thereof. Of these, Li ₃ PO ₄ having a particularly high ionic conductivity and being stable is preferable.

In the cathode active material according to an embodiment of the present invention, the lithium-phosphorus-containing compound contained in the coating layer may be one in which at least a part of the phosphorus-containing compound and the lithium impurity on the lithium transition metal oxide are reacted and modified.

The lithium impurity present on the lithium transition metal oxide may be 0.1% by weight to 0.6% by weight based on the total weight of the lithium transition metal oxide.

According to one embodiment of the present invention, at least a part of the lithium impurity on the lithium transition metal oxide reacts with the lithium-phosphorus-containing compound to modify the amount of the lithium impurity to about 30% To 70%, preferably 40% to 70%.

More specifically, the amount of lithium impurity present in the cathode active material according to the present invention is preferably less than 0.3 wt% based on the total weight of the cathode active material. Lithium impurities such as LiOH or Li ₂ CO ₃ have a high reactivity with respect to the electrolytic solution. Therefore, when the amount of lithium impurity present on the surface of the lithium transition metal oxide is 0.3 wt% or more, excessive swelling phenomenon occurs It is because.

In the cathode active material according to one embodiment of the present invention, the lithium-phosphorus-containing compound contained in the coating layer is contained in an amount of 0.01 to 2% by weight, preferably 0.1 to 2% by weight based on the total weight of the cathode active material &Lt; / RTI &gt;

When the content of the lithium-phosphorus-containing compound is less than 0.01% by weight, the effect of reducing the amount of lithium impurities may be insignificant. When the content is more than 2% by weight, an excessive amount of the phosphoric acid-containing compound is required.

In addition, in the cathode active material according to an embodiment of the present invention, the coating layer may include boron lithium oxide together with the lithium-phosphorus-containing compound. The boron lithium oxide contained in the coating layer may be contained in an amount of 0.01 to 0.5% by weight, preferably 0.1 to 0.5% by weight based on the total weight of the cathode active material.

If the amount of the boron lithium oxide is less than 0.01 wt%, the coating layer formed on the surface of the lithium transition metal oxide becomes thin, and the effect of suppressing the side reaction between the electrolytic solutions during charging and discharging may be insufficient. The excessive thickness of the boron lithium oxide increased the thickness of the coating layer, and the increase of the resistance caused the deterioration of the electrochemical characteristics of the lithium secondary battery.

The boron lithium oxide may be LiBO ₂ , Li ₂ B ₄ O ₇ , or a mixture thereof.

In the cathode active material according to an embodiment of the present invention, the coating layer may contain B and P in a weight ratio of 1: 2 to 5. Specifically, the coating layer may contain P in an amount of 1000 ppm to 1500 ppm, and B in an amount of 300 ppm to 500 ppm.

The weight ratio of B and P contained in the coating layer of the cathode active material can be measured by, for example, ICP mass analysis.

The coating layer containing the boron lithium oxide and the lithium-phosphorus-containing compound is preferably formed in an amount of 0.01 wt% to 3 wt% with respect to the total weight of the cathode active material.

According to an embodiment of the present invention, a portion P of the lithium-phosphorus-containing compound, a portion B of lithium borate oxide, or a mixed element thereof may be doped into the lithium transition metal oxide in a small amount.

When a portion P of the lithium-phosphorus-containing compound, a portion B of the lithium-boron oxide, or a mixed element thereof is doped in the lithium-transition metal oxide, the content of P or B is increased from the surface of the lithium- And may be represented by the following formula (3): &lt; EMI ID =

(3)

Li _{1 + a} [Ni _x Mn _y Co _z P _s B _w M _v ] O _{2 - ca c}

Wherein M is at least one element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga and In, or at least two elements thereof; A is at least one member selected from the group consisting of P, F, S and N and 0? X? 1.0, 0? Y <0.6, 0? Z <0.6, 0? V? 0.1, 0? C? 0.2, a + x + y + z + v = 1, 0? S? 0.1 and 0? W? 0.1.

The present invention also provides a method for producing a lithium secondary battery, comprising: mixing a lithium-transition metal oxide and a phosphoric acid-containing compound and performing a primary heat treatment; And a step of mixing the product obtained by the primary heat treatment and the boron-containing compound and performing a secondary heat treatment.

A method for producing a cathode active material according to an embodiment of the present invention includes a step of performing a two step heat treatment step, that is, a first heat treatment is performed by mixing a lithium transition metal oxide and a phosphoric acid-containing compound, By performing the secondary heat treatment by mixing the compounds, the surface treatment can be carried out at the optimal temperature conditions depending on the use of the phosphoric acid-containing compound and the boron-containing compound, so that degradation of the high temperature performance of the secondary battery can be improved, .

In the method for producing a cathode active material according to an embodiment of the present invention, the first heat treatment using the phosphoric acid-containing compound is performed by reacting the phosphoric acid-containing compound with at least a part of lithium impurities existing on the lithium transition metal oxide This is because the lithium impurity existing on the lithium transition metal oxide can be preferentially reduced by converting it into the lithium-phosphorus-containing compound. Then, the resultant having reduced lithium impurities is mixed with the boron-containing compound and subjected to a secondary heat treatment to stably form a coating layer containing the boron-containing compound together with the lithium-phosphorus-containing compound on the lithium transition metal oxide having reduced lithium impurity It is preferable.

A method of forming a coating layer on the surface of the lithium transition metal oxide generally includes a dry mixing method and a wet mixing method. When the wet mixing method is used, there is an advantage that the coating layer formed on the surface of the lithium transition metal oxide can be obtained more uniformly. However, in the case of the wet mixing method, the phosphoric acid-containing compound must be used in the form of an aqueous solution. In this case, the aqueous solution may cause damage to the lithium transition metal oxide. Therefore, in consideration of this point, it is preferable to use the dry mixing method in the present invention.

In the manufacturing method according to an embodiment of the present invention, the dry mixing method may be performed using a mixing method using a shaker, a mortar grinder mixing method, and a mechanical milling method, It may be preferable to use a mechanical milling method to form a uniform coating layer.

Specifically, the shaker mixing method may be performed by hand mixing the lithium transition metal oxide and the phosphoric acid-containing compound or the product obtained by the first heat treatment and the boron-containing compound by shaking them several times.

The mortar grinder mixing method is a method of homogeneously mixing a lithium transition metal oxide and a phosphoric acid-containing compound or a product obtained by the above primary heat treatment with a boron-containing compound using a mortar.

In addition, the mechanical milling may be performed by using a roll mill, a ball mill, a high energy ball mill, a planetary mill, a stirred ball mill, The lithium transition metal oxide and the phosphoric acid-containing compound or the product obtained by the above primary heat treatment and the boron-containing compound can be mixed by mechanical friction using a vibrating mill or a jet mill And can be mechanically compressively stressed, for example, by rotating at a revolution of 100 rpm to 1000 rpm.

The phosphoric acid-containing compounds usable according to the method of the present invention include NH ₄ HPO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) ₃ HPO ₄ , Mg ₃ (PO ₄ ) ₂ , _{4, Co 3 (PO 4)} 2, (C 2 H 5 O) 2 P (O) H, (C 4 H 9 O) 2 P (O) OH and Ni ₃ (PO ₄₎ selected from the group consisting of ₂ either or may be a mixture of two or more of these, and preferably NH ₄ HPO _4, (NH _{4) 2} HPO ₄ and (NH _{4) 3} which is selected from the group consisting of _4-one HPO or a mixture of two or more of these Lt; / RTI &gt;

The phosphoric acid-containing compound may be used in an amount of 0.01 to 2% by weight, preferably 0.1 to 2% by weight based on the total weight of the lithium-transition metal oxide.

The boron-containing compound that can be used in accordance with one embodiment of the present invention can be selected from the group consisting of H ₃ BO ₃ , B ₂ O ₃ , C ₆ H ₅ B (OH) ₂ , (C ₆ H ₅ O) ₃ B, _{[CH 3 (CH 2) 3} O] 3 B, C 13 H 19 BO 3, C 3 H 9 B 3 O 6 , and (C ₃ H ₇ O) 2 species of at least one selected thereof from the group consisting of ₃ B Or more.

The boron-containing compound may be used in an amount of 0.01 wt% to 0.5 wt%, preferably 0.1 wt% to 0.5 wt% with respect to the total weight of the lithium transition metal oxide.

According to the method for producing a cathode active material according to an embodiment of the present invention, the mixing weight ratio of the boron-containing compound to the phosphoric acid-containing compound is preferably 1: 1 to 1: 4.

Meanwhile, according to the method of the present invention, the first heat treatment may be performed at 400 ° C to 800 ° C for about 3 hours to 10 hours.

If the heat treatment temperature is lower than 400 ° C, the reaction between the lithium transition metal oxide and the phosphoric acid-containing compound may not be carried out to form a coating layer. If the heat treatment temperature is higher than 800 ° C, the structure of the cathode active material may be changed Side reactions may occur.

The first heat treatment may include a lithium-phosphorus-containing compound on the surface of the lithium-transition metal oxide. Depending on the heat treatment conditions, the lithium-transition metal oxide may be doped with a portion P of the lithium- have.

According to the manufacturing method of the present invention, the secondary heat treatment may be performed at 300 ° C to 600 ° C for about 3 hours to 10 hours.

When the temperature of the heat treatment is less than 300 ° C, the reaction between the product obtained by the first heat treatment and the boron-containing compound may not be carried out to form a coating layer. When the temperature exceeds 600 ° C, Or a side reaction may occur.

The surface of the lithium transition metal oxide may include lithium boroxide oxide by the secondary heat treatment, and the lithium transition metal oxide may be doped with a part of boron lithium oxide B according to a heat treatment condition.

In addition, the method for producing a cathode active material according to an embodiment of the present invention may be performed in a single step without performing a two-step heat treatment by mixing a lithium transition metal oxide, a phosphoric acid-containing compound, and a boron-containing compound and performing a heat treatment.

When the first step heat treatment is performed, the heat treatment temperature may be performed at 400 ° C to 700 ° C for 5 hours to 12 hours, and the mixing method may be performed using the dry mixing method as described above. In this case, the reduction effect of the impurities is less than that of the two-step heat treatment process, but the process may be simplified and advantageous in terms of the process.

The present invention provides a positive electrode comprising the positive electrode active material.

The present invention also provides a positive electrode comprising the positive electrode active material.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive agent, and a dispersant, if necessary, in a cathode active material, coating the cathode active material with a collector of a metal material, have.

The current collector of the metal material is a metal having high conductivity and can be easily adhered to the slurry of the cathode active material, and any material can be used as long as it is not reactive in the voltage range of the battery. Non-limiting examples of the positive electrode current collector include foil produced by aluminum, nickel, or a combination thereof.

Examples of the solvent for forming the anode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the cathode active material, the binder and the conductive agent in consideration of the coating thickness of the slurry and the production yield.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or Various kinds of binder polymers such as various copolymers can be used.

The conductive agent is not particularly limited as long as it has electrical conductivity without causing any chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers 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 present invention also provides a lithium secondary battery including the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode.

As the negative electrode active material used for the negative electrode according to an embodiment of the present invention, a carbon material, lithium metal, silicon, or tin which lithium ions can be occluded and released can be used.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. As the binder and the conductive agent used for the cathode, those which can be commonly used in the art can be used as the anode. The negative electrode may be prepared by preparing a negative electrode active material composition by mixing and stirring the negative electrode active material and the additives, applying the negative electrode active material composition to the current collector, and compressing the negative electrode active material composition to produce a negative electrode.

The separator is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength can be used and is well known in the art, and a detailed description thereof will be omitted herein.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

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

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

&Lt; Preparation of positive electrode active material &

Example  One

As a mixed transition metal precursor was used MOOH (M = Ni Mn _{0 .78 0 .11 0 .11} Co), wherein the mixed transition metal precursor and a stoichiometric ratio of _{Li 2 CO 3 (Li: M} = 1.00: 1) And the mixture was calcined in air at about 800 캜 to 900 캜 for 10 hours to prepare LiNi _0.78 Mn _0.11 Co _0.11 O ₂ .

The _{LiNi 0 .78 Mn 0 .11 Co 0} .11 O 2 and _{(NH 4) 2 HPO 4 100} : 1 by weight as quantified in a dry mixer (ready to mixer, manufactured by Matsumoto whether or sikki beam produced, FM-130D type) And mixed to obtain a mixed powder. The obtained powder was subjected to a primary heat treatment at 500 DEG C for 5 hours in an oxygen atmosphere. Then, the product obtained by the first heat treatment and H ₃ BO ₃ were quantitatively determined at a weight ratio of 100: 0.5 and mixed with a dry mixer (Redige mixer, Model FM-130D, manufactured by Matsubo Kabushiki Kaisha) . The obtained powder was subjected to a secondary heat treatment at 300 DEG C for 5 hours in an oxygen atmosphere to obtain a cathode active material. At this time, in the cathode active material, the coating layer was 0.5% by weight based on the total weight of the cathode active material.

Comparative Example  One

As a mixed transition metal precursor was used MOOH (M = Ni Mn _{0 .78 0 .11 0 .11} Co), wherein the mixed transition metal precursor and a stoichiometric ratio of _{Li 2 CO 3 (Li: M} = 1.02: 1) And the mixture was calcined in air at about 800 캜 to 900 캜 for 10 hours to prepare LiNi _0.78 Mn _0.11 Co _0.11 O ₂ .

&Lt; Production of lithium secondary battery >

Example  2

Anode manufacturing

The LiNi _{0 .78} Mn _{0 .11} Co _{0 .11} O ₂ On the surface, LiBO ₂ , Li ₂ B ₄ O ₇ And a coating layer containing Li ₃ PO ₄ was used as a positive electrode active material.

94 wt% of the positive electrode active material, 3 wt% of carbon black as a conductive agent, and 3 wt% of polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) To prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a roll press to prepare a positive electrode.

Cathode manufacture

A negative electrode active material was prepared by mixing 96.3 wt% of carbon powder, 1.0 wt% of super-p as a conductive material, 1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) To prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to produce a negative electrode, followed by roll pressing to produce a negative electrode.

Non-aqueous  Electrolytic solution manufacturing

On the other hand, LiPF ₆ was added to a nonaqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as electrolytes in a volume ratio of 30:70, to prepare a 1M LiPF ₆ nonaqueous electrolyte solution.

Lithium secondary battery manufacturing

The prepared positive electrode and negative electrode were sandwiched between a polyethylene separator and a polypropylene mixed separator, followed by preparing a polymer type battery by a conventional method, and then injecting the prepared non-aqueous electrolyte solution to complete the production of a lithium secondary battery.

Comparative Example  2

The LiNi _{0 .78} Mn _{0 .11} Co _{0 .11} O ₂ Was used as a positive electrode active material, a lithium secondary battery was produced in the same manner as in Example 2. [

Experimental Example  One : ICP  Mass analysis ICP mass 분석 )

The content of the elements B and P contained in the coating layer of the cathode active material of Example 1 was analyzed by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy).

Specifically, 0.1 g of the cathode active material of Example 1 to be measured was taken, 2 ml of distilled water and 3 ml of concentrated nitric acid were added, and the lid was closed to dissolve the sample. Thereafter, when the sample completely dissolved, 50 ml of ultrapure water was added and diluted. The diluted solution was then diluted 10-fold again and then analyzed by ICPAES (Inductively Coupled Plasma-Atomic Emission Spectroscope). ICP-AES (ICP 5300DV, Perkinelemer) was operated under the following conditions: Forward Power 1300 W; Torch Height 15 mm; Plasma gas flow 15.00 L / min; Sample gas flow 0.8 L / min; Auxiliary gas flow 0.20 L / min and pump speed 1.5 ml / min. As a result, the elements B and P contained in the coating layer of the positive electrode active material of Example 1 were 500 ppm and 1500 ppm, respectively.

Experimental Example  2: To determine the amount of lithium impurities pH  proper( titration ) Experiment

PH titration was performed to examine the amounts of lithium impurities in the cathode active material prepared in Example 1 and Comparative Example 1. The results are shown in FIG. The pH meter was metrohm 794 and the pH was recorded by titration with 0.02 ml.

2 is a graph comparing amounts of reduction of lithium impurities with respect to each of the cathode active materials of Example 1 and Comparative Example 1;

That is, as a result of comparing the amount of 0.1 M HCl with respect to 10 g of the cathode active material, the amount of HCl in Example 1 was reduced to about 8.4 ml and the amount of HCl in Comparative Example 1 was reduced to about 13.9 ml. .

Experimental Example  3

<Evaluation test of cycle characteristics>

To evaluate the relative efficiency of the lithium secondary batteries obtained in Example 2 and Comparative Example 2 according to the number of cycles, electrochemical evaluation experiments were performed as follows.

Specifically, the lithium secondary batteries obtained in Example 2 and Comparative Example 2 were charged at a constant current (CC) of 4.35 V at 45 ° C and then charged at a constant voltage (CV) of 4.35 V to obtain a charging current of 0.05 mAh The first charging was carried out. Thereafter, the resultant was allowed to stand for 20 minutes, discharged at a constant current of 2 C until it reached 3.0 V, and then repeatedly subjected to 1 to 230 cycles. The results are shown in Fig.

3, the slope of the lithium secondary battery of Example 2 relative to the relative efficiency from 1 to 100 cycles was gentler than that of Comparative Example 2, and the relative efficiency was about 60% or more even in 100 cycles Can be maintained.

In contrast, in the case of the lithium secondary battery of Comparative Example 2, the slope with respect to the relative efficiency rapidly dropped from about 20 cycles to about 50% from 150 cycles.

Therefore, it can be seen that by including the coating layer on the surface of the lithium transition metal oxide according to the embodiment of the present invention, the cycle deterioration of the secondary battery is relaxed, and stable cycle characteristics can be exhibited for a long period of time.

Claims (29)

Mixing the lithium transition metal oxide and the phosphoric acid-containing compound and performing a first heat treatment; And
Mixing the product obtained by the primary heat treatment and the boron-containing compound and performing a secondary heat treatment.
The method according to claim 1,
Wherein the cathode active material comprises a lithium transition metal oxide; And
And a coating layer formed on a surface of the lithium transition metal oxide, wherein the coating layer comprises lithium borate oxide and a lithium-phosphorus-containing compound.
3. The method of claim 2,
Wherein the coating layer comprises B and P in a weight ratio of 1: 2 to 1: 5.
The method of claim 3,
Wherein the coating layer contains B in an amount of 300 ppm to 500 ppm.
The method of claim 3,
Wherein the coating layer contains P in an amount of 1000 ppm to 1500 ppm.
The method according to claim 1,
A portion of lithium-phosphorus-containing compound P, a portion B of lithium-boron oxide, or a mixed element thereof is doped into the lithium-transition metal oxide, and the content of P or B is increased from the surface of the lithium- Wherein the cathode active material has a decreasing concentration gradient.
The method according to claim 1,
Wherein the lithium transition metal oxide is represented by the following formula (3): < EMI ID =
(3)
Li _{1 + a} [Ni _x Mn _y Co _z P _s B _w M _v ] O _{2 - ca c}
Wherein M is at least one element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga and In, or at least two elements thereof; A is at least one member selected from the group consisting of P, F, S and N and 0? X? 1.0, 0? Y <0.6, 0? Z <0.6, 0? V? 0.1, 0? C? 0.2, a + x + y + z + v = 1, 0? S? 0.1 and 0? W? 0.1.
3. The method of claim 2,
Wherein the coating layer is 0.01 wt% to 3 wt% with respect to the total weight of the cathode active material.
3. The method of claim 2,
Wherein the lithium-phosphorus-containing compound is represented by LixPyOz (1? X? 4, 1? Y? 4, 0? Z? 7).
3. The method of claim 2,
Wherein the lithium-phosphorus-containing compound is any one selected from the group consisting of Li ₃ PO ₄ , LiPO ₃ , Li ₄ P ₂ O ₇ , LiP and Li ₃ P, or a mixture of two or more thereof. Way.
3. The method of claim 2,
Wherein the lithium-phosphorus-containing compound is formed by reacting at least a part of the lithium impurity on the lithium-transition metal oxide with a phosphoric acid-containing compound.
The method according to claim 1,
The phosphate-containing compound is _{NH 4 HPO 4, (NH 4} ) 2 HPO 4, (NH 4) 3 HPO 4, Mg 3 (PO 4) 2, AlPO 4, Co 3 (PO 4) 2, (C 2 H 5 O) ₂ P (O) H, (C ₄ H ₉ O) ₂ P (O) OH and Ni ₃ (PO ₄ ) ₂ , or a mixture of two or more thereof A method for producing an active material.
12. The method of claim 11,
The lithium impurities method of producing a positive electrode active material, characterized in that LiOH, Li ₂ CO ₃ or a mixture thereof.
The method according to claim 1,
Wherein the lithium transition metal oxide includes lithium impurities in an amount of less than 0.3% by weight based on the total weight of the cathode active material.
3. The method of claim 2,
Wherein the boron lithium oxide is LiBO ₂ , Li ₂ B ₄ O ₇ , or a mixture thereof.
The method according to claim 1,
Wherein the lithium transition metal oxide is at least one selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide and lithium- One or a mixture of two or more thereof.
The method according to claim 1,
Wherein the first heat treatment is performed in a range of 400 ° C to 800 ° C.
The method according to claim 1,
Wherein the second heat treatment is performed at a temperature ranging from 300 ° C to 600 ° C.
The method according to claim 1,
Wherein the mixing is performed by a shaker mixing method, a mortar grinder mixing method, or a mechanical milling method.
delete The method according to claim 1,
The boron-containing compounds are _{H 3 BO 3, B 2 O} 3, C 6 H 5 B (OH) 2, (C 6 H 5 O) 3 B, [CH 3 (CH 2) 3 O] 3 B, C 13 H ₁₉ BO ₃ , C ₃ H ₉ B ₃ O _6, and (C ₃ H ₇ O) ₃ B, or a mixture of two or more thereof.
The method according to claim 1,
Wherein the boron-containing compound is used in an amount of 0.01 wt% to 0.5 wt% with respect to the total weight of the lithium transition metal oxide.
The method according to claim 1,
Wherein the phosphoric acid-containing compound is used in an amount of 0.01 to 2% by weight based on the total weight of the lithium-transition metal oxide.
The method according to claim 1,
Wherein the mixed weight ratio of the boron-containing compound to the phosphoric acid-containing compound is 1: 1 to 1: 4.
The method according to claim 1,
Wherein the lithium transition metal oxide is represented by the following formula (1): < EMI ID =
&Lt; Formula 1 &gt;
Li _{1 + a} [Ni _x Mn _y Co _z M _v ] O _{2 - ca c}
Wherein M is at least one element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga and In, or at least two elements thereof; A is at least one member selected from the group consisting of P, F, S and N and 0? X? 1.0, 0? Y? 0.5, 0? Z? 0.5, 0? V? 0.1, 0? C? 0.2 and a + x + y + z + v = 1.
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