KR101798154B1 - Positive electrode active material for rechargable lithium battery, method for synthesis the same, and rechargable lithium battery including the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the lithium metal oxide. And a coating layer disposed on the surface of the lithium metal oxide and including a silicate compound represented by the following formula (2), a method for producing the same, and a lithium secondary battery comprising the same.
[Chemical Formula 1]
LiNi _{1- x- y} Co _x Mn _y O ₂
(2)
G _s O _t · zSiO ₂

Description

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

A cathode active material for a lithium secondary battery, a production method thereof, and a lithium secondary battery comprising the same.

The lithium secondary battery is manufactured as a high-performance small-sized battery, and is used not only as an energy storage source for mobile information communication devices including smart phones, notebooks, and computers, but also recently as a battery for high- (Electric Vehicle) and hybrid electric vehicle (hybrid electric vehicle).

In order to cover all of these small and large fields, a secondary battery having excellent charge / discharge characteristics, lifetime characteristics, high rate characteristics and stability at a high temperature of G is required. In this regard, in the case of a lithium secondary battery, Because it has a high energy density, it meets the above requirements, but there are still issues to be addressed in large-scale applications.

Specifically, the cathode active material among the major constituent elements of the lithium secondary battery has a higher production cost than other elements, and LiCoO ₂ and the like are currently commercially available cathode active materials.

However, not only the cost of the cathode active material is reduced but also the problem that the main component of the cathode active material is eluted due to repeated charging and discharging and the deterioration of the cathode active material when the electrolyte is decomposed due to moisture inside the battery, And the problem of increased internal resistance. These problems have not been solved yet.

One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery capable of improving the thermal stability, lifetime characteristics, and discharge efficiency of a lithium secondary battery by solving the above-mentioned problems, a method for producing the same, and a lithium secondary battery comprising the same. .

One embodiment of the present invention is a lithium metal oxide represented by the following general formula (1); And a coating layer disposed on the surface of the lithium metal oxide and including a silicate compound represented by the following formula (2): < EMI ID = 2.0 >

[Chemical Formula 1]

LiNi _1-xy Co _x Mn _y O ₂

(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂

In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a real number of 0.5 to 10, and s and t are variables that are determined according to the valence of G, respectively.)

The content of the coating layer may be 3 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the lithium metal oxide.

In Formula 2, G may be Li. Specifically, the above formula (2) than is, may be one of Li ₂ O · 5SiO _2.

The thickness of the coating layer may be 40 nm or more, and 150 nm or less.

According to another embodiment of the present invention, there is provided a method for manufacturing a lithium secondary battery, comprising: preparing a mixed solution including a lithium metal oxide, a silicate compound, and a solvent; Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; And a step of firing a lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material, wherein the lithium metal oxide is represented by the following Formula 1, and the silicate compound is represented by the following Formula 2 The present invention provides a method for producing a positive electrode active material for a lithium secondary battery.

[Chemical Formula 1]

LiNi _1-xy Co _x Mn _y O ₂

(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂

In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a real number of 0.5 to 10, and s and t are variables that are determined according to the valence of G, respectively.)

Preparing a mixed solution comprising the lithium metal oxide, the silicate compound, and the solvent, wherein the silicate compound is added in an amount of 3 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the lithium metal oxide, 50 parts by weight or more, and 200 parts by weight or less of a solvent may be added.

Preparing a mixed solution comprising the lithium metal oxide, the silicate compound, and a solvent, the silicate compound being dissolved in a solvent, followed by stirring and dissolving; And adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring to prepare a slurry of a cathode active material coated with a silicate compound on the surface of the lithium metal oxide.

Preparing a slurry of the cathode active material coated with a silicate compound on the surface of the lithium metal oxide by adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring the slurry of the lithium metal oxide in the slurry at a rate of 150 rpm or more and 300 rpm or less It can be done.

Wherein the lithium metal oxide is added to the solution in which the silicate compound is dissolved and stirred to prepare a slurry of the cathode active material coated with the silicate compound on the surface of the lithium metal oxide, Lt; / RTI &gt; of time.

The calcination of the lithium metal oxide coated on the surface of the silicate compound to obtain the cathode active material may be performed at a temperature of 500 ° C or higher and 700 ° C or lower.

The calcination of the lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material may be performed for 3 hours or more and 7 hours or less.

Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; , The drying may be performed at a temperature of 100 ° C or higher, and 300 ° C or lower.

In Formula 2, G may be Li. Specifically, the above formula (2) than may be one of Li ₂ O · 5SiO _2.

Preparing a mixed solution containing the lithium metal oxide, the silicate compound, and a solvent, and the solvent may be de-ionized water.

Stirring the silicate compound in a solvent and dissolving it may be performed at a speed of 150 rpm or more and 300 rpm or less.

According to another embodiment of the present invention, cathode; And an electrolyte, wherein the positive electrode includes the positive electrode active material according to an embodiment of the present invention.

An embodiment of the present invention can provide a positive electrode active material for a lithium secondary battery capable of improving thermal stability, life characteristics, and discharge efficiency of the lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery comprising the same.

1 is a TEM image of a cathode active material according to a comparative example of the present invention.
2 is a TEM image of a cathode active material according to Example 3 of the present invention.
3 is a TEM image of a cathode active material according to Example 4 of the present invention.
4 is initial discharge efficiency evaluation data of coin cells employing the cathode active materials of Examples 1 to 4 and Comparative Examples of the present invention.
5A is data for evaluating the life characteristics of coin cells employing the positive electrode active materials of Examples 1 to 4 and Comparative Examples of the present invention.
FIG. 5B is data for evaluating life characteristics of coin cells employing the cathode active materials of Examples 1 to 4 and Comparative Examples of the present invention.
6 is thermal stability evaluation data of coin cells employing the cathode active materials of Examples 2, 3 and Comparative Example of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

One embodiment of the present invention is a lithium metal oxide represented by the following general formula (1); And a coating layer disposed on the surface of the lithium metal oxide and including a silicate compound represented by the following formula (2): &lt; EMI ID = 2.0 &gt;

[Chemical Formula 1]

LiNi _1-xy Co _x Mn _y O ₂

(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂

In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a real number of 0.5 to 10, and s and t are variables that are determined according to the valence of G, respectively.)

More specifically, the range of x may be 0 <x? 0.3, 0 <x? 0.2, 0.1? X? 0.3, 0.15? X? 0.25, or 0.2? X? 0.3.

More specifically, the range of y may be 0 <y? 0.3, 0 <y? 0.2, 0.1? Y? 0.3, 0.15? Y? 0.25, or 0.2? Y? 0.3.

In general, the high nickel-based cathode active material has a problem in that it is difficult to commercialize it because of the thermal stability problem.

However, in one embodiment of the present invention, the surface of the lithium metal oxide is coated with a silicate compound to treat the surface with an oxide, thereby solving the thermal stability, the initial capacity, and the life characteristic problem.

The content of the silicate compound coating layer coated on the surface of the lithium metal oxide may be 3 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the lithium metal oxide. More specifically not less than 5 parts by weight, and not more than 10 parts by weight; 5 parts by weight or more, and 7 parts by weight or less; 7 parts by weight or more, and 10 parts by weight or less.

If the content of the silicate compound coating layer is too large, there may arise a problem of deterioration of the thermal stability and lifetime characteristics due to the increase in resistance due to the coating layer on the surface of the active material. When the content of the silicate compound coating layer is too small, the formation of the coating layer may result in deterioration of thermal stability and lifetime characteristics.

In Formula 2, G may be Li. More specifically, Formula 2 may be Li ₂ Si ₅ O ₁₁ .

The thickness of the coating layer may be 40 nm or more, and 150 nm or less. If the thickness of the coating layer is too thick, problems of initial capacity and efficiency reduction due to an increase in surface resistance may occur. If the thickness of the coating layer is too thin, a degradation in lifetime characteristics may occur.

Another embodiment of the present invention is a method for manufacturing a lithium secondary battery including: preparing a mixed solution including a lithium metal oxide, a silicate compound, and a solvent; Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; And a step of firing a lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material, wherein the lithium metal oxide is represented by the following Formula 1, and the silicate compound is represented by the following Formula 2 The present invention provides a method for producing a positive electrode active material for a lithium secondary battery.

[Chemical Formula 1]

LiNi _1-xy Co _x Mn _y O ₂

(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂

In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a real number of 0.5 to 10, and s and t are variables that are determined according to the valence of G, respectively.)

More specifically, the range of x may be 0 <x? 0.3, 0 <x? 0.2, 0.1? X? 0.3, 0.15? X? 0.25, or 0.2? X? 0.3.

More specifically, the range of y may be 0 <y? 0.3, 0 <y? 0.2, 0.1? Y? 0.3, 0.15? Y? 0.25, or 0.2? Y? 0.3.

This is a method of coating a silicate compound to a lithium metal oxide in a wet state, and has a more uniform coating formation advantage than a dry coating.

Preparing a mixed solution comprising the lithium metal oxide, the silicate compound, and the solvent, wherein the silicate compound is added in an amount of 3 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the lithium metal oxide, 50 parts by weight or more, and 200 parts by weight or less of a solvent may be added.

The content of the silicate compound has been described above and therefore will be omitted.

The content of the solvent is more specifically 50 parts by weight or more and 150 parts by weight or less based on 100 parts by weight of the lithium metal oxide; Not less than 50 parts by weight, and not more than 125 parts by weight; Not less than 75 parts by weight, and not more than 200 parts by weight; Not less than 75 parts by weight, and not more than 150 parts by weight; Not less than 75 parts by weight, and not more than 125 parts by weight.

If the amount of the solvent is too small, difficulties may be encountered in the coating. If the amount of the solvent is too large, damage to the surface of the active material may occur due to excessive coating mixing.

Preparing a mixed solution containing the lithium metal oxide, the silicate compound, and a solvent, and the solvent may be de-ionized water.

Preparing a mixed solution comprising the lithium metal oxide, the silicate compound, and a solvent, the silicate compound being dissolved in a solvent, followed by stirring and dissolving; And adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring to prepare a slurry of a cathode active material coated with a silicate compound on the surface of the lithium metal oxide.

Stirring the silicate compound in a solvent and dissolving it may be performed at a speed of 150 rpm or more and 300 rpm or less.

However, the present invention is not limited thereto, and the silicate compound can be appropriately controlled within a range in which the silicate compound is sufficiently dissolved in the solvent.

Preparing a slurry of the cathode active material coated with a silicate compound on the surface of the lithium metal oxide by adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring the slurry of the lithium metal oxide in the slurry at a rate of 150 rpm or more and 300 rpm or less It can be done. However, the present invention is not limited thereto, and can be appropriately adjusted within a range in which the materials are sufficiently mixed.

Wherein the lithium metal oxide is added to the solution in which the silicate compound is dissolved and stirred to prepare a slurry of the cathode active material coated with the silicate compound on the surface of the lithium metal oxide, Lt; / RTI &gt; of time.

However, the present invention is not limited thereto, and can be suitably controlled within a range in which the silicate compound, the solvent, and the lithium metal oxide are sufficiently mixed.

Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; , The drying may be performed at a temperature of 100 ° C or higher, and 300 ° C or lower.

Further, in the step of drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound, the drying is performed in a short time by rapid drying.

However, the present invention is not limited thereto, and the drying temperature and time may be appropriately adjusted so that the solvent is sufficiently dried.

The calcination of the lithium metal oxide coated on the surface of the silicate compound to obtain the cathode active material may be performed at a temperature of 500 ° C or higher and 700 ° C or lower.

If the firing temperature is too low, the coating oxide may not be formed and the coating effect may be insufficient. If the firing temperature is too high, the performance may be degraded due to the over-heating.

The calcination of the lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material may be performed for 3 hours or more and 7 hours or less.

If the baking time is too short, the coating oxide may not be formed and the coating effect may be insufficient. If the sintering time is too long, the performance may be deteriorated due to the inferiority.

In another embodiment of the present invention, there is provided a lithium secondary battery including the positive electrode, the negative electrode, and the electrolyte containing the positive electrode active material.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

As the collector, aluminum may be used, but the present invention is not limited thereto.

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

The binder may be selected from, for example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, Styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like can be used.

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

The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The negative electrode active material layer includes a negative electrode active material, a binder composition, and / or a conductive material.

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

Descriptions of the negative electrode active material, the binder composition and the conductive material will be omitted.

The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent and the lithium salt can be used as long as they are compatible with each other, so that detailed explanation is omitted.

Hereinafter, preferred embodiments and comparative examples of the present invention 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.

Preparation Example: Preparation of lithium metal oxide

LiOH and Ni _{0 . 8} Co _{0 . 1} Mn _{0 . 1} (OH) ₂ were mixed in a weight ratio of 1: 1.05 (Metal: Li) using a mixer, and then heated for 8 hours in an oxygen atmosphere, at 800 ° C for 10 hours, The sintering time was 27 hours.

Slowly cooling the resulting fired body, and then pulverized, LiNi _{0. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ Lithium metal oxide powder was prepared.

Examples and Comparative Examples: Preparation of cathode active material

Example 1

First, 3 g of Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was dissolved in 100 g of de-ionized water and stirred at 300 rpm for 30 minutes.

Then, the LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ 100 g of the lithium metal oxide powder was added and stirred at 300 rpm for 15 minutes to prepare a lithium metal oxide having a surface coated with lithium polysilicate (Li ₂ Si ₅ O ₁₁ ).

Then, by rapid drying at about 200 ℃ The solvent was evaporated, to give the coated active material powder to the surface _{Lithium polysilicate (Li 2 Si 5 O} 11).

Thereafter, the active material powder was fired at 650 ° C for 5 hours to finally obtain a cathode active material coated with a lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) on the surface of a LiNi _0.8 Co _0.1 Mn _0.1 O ₂ lithium metal oxide.

Example 2

A cathode active material was prepared in the same manner as in Example 1 except that 5 g of lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was used.

Example 3

A cathode active material was prepared in the same manner as in Example 1 except that 7 g of lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was used.

Example 4

A cathode active material was prepared in the same manner as in Example 1 except that 10 g of lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was used.

Comparative Example

A cathode active material was prepared in the same manner as in Example 1, except that the process of mixing and dissolving Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) in deionized water was omitted.

Experimental Example

Manufacture of Coin Cell

92% by weight of the cathode active material prepared in Examples 1 to 4 and Comparative Example, 4% by weight of a conductive material (Super P, Denka black) and 4% by weight of a binder (PVDF) Pyrrolidone (NMP), and mixed to prepare a positive electrode slurry.

The positive electrode slurry was applied to an aluminum (Al) thin film as a positive electrode current collector having a thickness of 20 μm, dried in a 120 ° C. vacuum oven for 12 hours, and rolled to produce a positive electrode.

Li-metal was used as the cathode.

The positive electrode and metal Li- thus prepared as the counter electrode, the electrolyte include ethylene carbonate (EC, Ethylene Carbonate): dimethyl carbonate, the volume ratio of (DMC, Dimethyl Carbonate) 3: 7 in a mixed solvent, LiPF ₆ of 1 mole (CR2032 coin half cell) was produced according to a conventional manufacturing method using a solution prepared by dissolving a solution of a coin cell type half-cell.

Projection electron microscope (TEM) photographing evaluation of cathode active material

Transmission Electron Microscope images were taken and evaluated for the cathode active materials prepared in Examples 3, 4 and Comparative Examples. FIG. 1 is a comparative example, FIG. 2 is a photomicrograph of a cathode active material of Example 3, and FIG. 3 is a photomicrograph of a cathode active material of Example 4.

As can be seen from FIGS. 2 and 3, lithium polysilicate is coated to a thickness of about 40 to 150 nm.

ICP analysis of cathode active material

ICP mass spectrometry was performed on the cathode active materials prepared in Examples 1 to 4 and Comparative Examples. The measuring device was a Perkinelmer Optima 7300DV.

The results are shown in Table 1 below. In Table 1, Bare is a cathode active material of Comparative Example in which Li-polysilicate is not coated, and each content indicates Li-polysilicate content with respect to lithium metal oxide in the cathode active materials of Examples 1 to 4.

Item unit Bare 3 wt% 5 wt% 7 wt% 10 wt% Si content ppm - 330 503 712 1,103

Electrochemical Characterization of Secondary Batteries

(1) Evaluation of initial discharge efficiency

The initial discharge efficiency of the above-prepared coin cells was evaluated under the following conditions.

Charge: 0.2 C CC-CV, 4.25 V, 0.005 C cut-off

Discharge: 0.2C CC, 2.5 V

The results are shown in Table 2 and FIG.

In FIG. 4, Bare represents a coin cell employing a cathode active material of Comparative Example in which Li-polysilicate is not coated, and the content of each element is represented by Li-polysilicate of lithium metal oxide in the cathode active materials of Examples 1 to 4 .

As can be seen from Table 2 and FIG. 4, the initial discharge efficiency of the coin cell adopting the positive electrode active material coated with the lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) on the surface of the NCM 811 lithium metal oxide was higher than that of the positive electrode active material The coin cell of the present invention has a remarkably improved initial discharge efficiency.

Especially, when the lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was coated more than 5 wt% and 10 wt%, the initial discharge efficiency was more than 90% and the highest efficiency was obtained at 7 wt%.

unit Bare Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) content 3 wt% 5 wt% 7 wt% 10 wt% Charging capacity mAh / g 222.3 222.9 223.8 223.1 223.6 Discharge capacity 192.0 198.9 201.7 203.5 198.4 efficiency % 86.4 89.2 90.1 91.2 88.7

(2) Life characteristics evaluation

The life characteristics of the prepared coin cells were evaluated under the following conditions.

Cycle: 50 cycles 0.5C charge, 0.5C discharge

Rest time: 20 min

The results are shown in Tables 3, 5A and 5B.

In FIGS. 5A and 5B, Bare represents a coin cell employing a cathode active material of Comparative Example in which Li-polysilicate is not coated, and the content of each element is shown in the cathode active materials of Examples 1 to 4, It means the content of Li-polysilicate.

As can be seen from Table 3, FIG. 5A and FIG. 5B, the life characteristics of the coin cell employing the positive electrode active material coated with the lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) on the surface of the NCM 811 lithium metal oxide, The life characteristics of the coin cell employing the positive electrode active material are remarkably improved.

In particular, when 5 wt% or more and 10 wt% of Lithium polysilicate (Li ₂ O 5SiO ₂ ) were coated, the capacity retention ratio was 90% or more after 50 cycles and the highest capacity retention ratio was obtained at 7 wt%.

unit Bare Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) content 3 wt% 5 wt% 7 wt% 10 wt% 1 cycle
Discharge capacity mAh / g 189.7 190.3 193.8 194.3 192.9 50 cycles
Discharge capacity 168.2 169.8 180.3 183.0 179.0 Volume
Retention rate % 88.7 89.2 93.0 94.2 92.8

Evaluation of thermal stability of cathode active material

The prepared coin cells were evaluated for thermal characteristics of the anode / electrolyte.

Specifically, after the battery was charged at 4.25 V and decomposed to separate only the positive electrode, a positive electrode-electrolyte exothermic reaction test was performed using a differential scanning calorimeter (DSC). The DSC analyzer was a METTLER STAR system. Specifically, 9 mg of the decomposed anode was injected with 0.5 ul of sampling water and an electrolyte to prepare a pressure cell, and the exothermic peak was measured at 30 ° C to 350 ° C at a heating rate of 5 ° C / min. As the temperature rises, lithium is desorbed and an exothermic reaction occurs between the unstable cathode active material and the electrolyte, and the point appears as a peak.

The results are shown in Table 4 and FIG. The peak point in FIG. 6 means the temperature at which the exothermic reaction reaches the apex.

In FIG. 6, Bare represents a coin cell employing a cathode active material of Comparative Example in which no Li-polysilicate is coated, and the content of each element is represented by the Li-polysilicate of the lithium metal oxide in the cathode active materials of Examples 2 and 3 .

As can be seen from Table 4 and FIG. 6, the thermal stability of the coin cell employing the positive electrode active material coated with the lithium polymeric material (Li ₂ Si ₅ O ₁₁ ) on the surface of the NCM 811 lithium metal oxide is superior to that of the positive electrode active material The thermal stability of the coin cell employing the coin cell is remarkably improved.

In particular, it showed the most improved thermal stability at the point where 7 wt% of Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) was coated.

unit Bare Lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) content 5 wt% 7 wt% Fever
 Peak temperature ℃ 198 207 216

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 (20)

A lithium metal oxide represented by the following formula (1); And
And a coating layer disposed on the surface of the lithium metal oxide and including a silicate compound represented by Formula 2,
The content of the coating layer is preferably 100 parts by weight or more based on 100 parts by weight of the lithium metal oxide,
3 parts by weight or more, and 10 parts by weight or less.
Cathode active material for lithium secondary battery.

[Chemical Formula 1]
LiNi _1-xy Co _x Mn _y O ₂
(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂
In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a number of more than 2, and less than 10 is a real number, and s and t are variables determined by the valence of G, respectively.) The method of claim 1,
The content of the coating layer is preferably 100 parts by weight or more based on 100 parts by weight of the lithium metal oxide,
3 parts by weight or more, and 7 parts by weight or less.
Cathode active material for lithium secondary battery. delete The method of claim 1,
In Formula 2,
G is Li,
Cathode active material for lithium secondary battery. 5. The method of claim 4,
(2)
Li ₂ O. 5SiO ₂ .
Cathode active material for lithium secondary battery. The method of claim 1,
The thickness of the coating layer,
40 nm, and 150 nm,
Cathode active material for lithium secondary battery. The method of claim 1,
The content of the coating layer is 5 parts by weight or more and 7 parts by weight or less based on 100 parts by weight of the lithium metal oxide,
Wherein the thickness of the coating layer is 40 nm or more and 150 nm or less.
Cathode active material for lithium secondary battery. Preparing a mixed solution including a lithium metal oxide, a silicate compound, and a solvent;
Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; And
And calcining the lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material,
Wherein the lithium metal oxide is represented by the following Formula 1, the silicate compound is represented by the following Formula 2,
The content of the coating layer is preferably 100 parts by weight or more based on 100 parts by weight of the lithium metal oxide,
3 parts by weight or more, and 10 parts by weight or less.
(Method for producing positive electrode active material for lithium secondary battery).

[Chemical Formula 1]
LiNi _1-xy Co _x Mn _y O ₂
(0 < x < 0.4, 0 < y < 0.4 and 0 <

???????? G _s O _t zSiO ₂
In the above formula (2), G is at least one element selected from the group consisting of Na, K, Mg, Ba, Sr, Y, Sn, Ga, In, Th, Pb, Li, Zn, Ca, Cd, Rb, Sc, And Zr, z is a number of more than 2, and less than 10 is a real number, and s and t are variables determined by the valence of G, respectively.) 9. The method of claim 8,
Preparing a mixed solution including the lithium metal oxide, the silicate compound, and a solvent;
Based on 100 parts by weight of the lithium metal oxide,
Wherein the solvent is added in an amount of not less than 50 parts by weight and not more than 200 parts by weight,
(Method for producing positive electrode active material for lithium secondary battery). 9. The method of claim 8,
Preparing a mixed solution including the lithium metal oxide, the silicate compound, and a solvent;
Adding a silicate compound into a solvent and stirring to dissolve the silicate compound; And
And adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring to prepare a slurry of the cathode active material coated with the silicate compound on the surface of the lithium metal oxide.
(Method for producing positive electrode active material for lithium secondary battery). 11. The method of claim 10,
Adding the lithium metal oxide to the solution in which the silicate compound is dissolved and stirring to prepare a slurry of the cathode active material coated with the silicate compound on the surface of the lithium metal oxide;
Wherein the stirring is performed at a speed of 150 rpm or more and 300 rpm or less,
(Method for producing positive electrode active material for lithium secondary battery). 12. The method of claim 11,
Preparing a cathode active material slurry having a silicate compound coated on a surface of a lithium metal oxide by injecting and stirring the lithium metal oxide into a solution in which the silicate compound is dissolved,
Wherein said stirring is carried out for a period of not less than 10 minutes and not more than 30 minutes.
(Method for producing positive electrode active material for lithium secondary battery). 9. The method of claim 8,
Firing the lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material;
Wherein the calcination is performed at a temperature of not less than 500 DEG C and not more than 700 DEG C. [
(Method for producing positive electrode active material for lithium secondary battery). The method of claim 13,
Firing the lithium metal oxide coated on the surface of the silicate compound to obtain a cathode active material;
Wherein the calcination is carried out for not less than 3 hours and not more than 7 hours.
(Method for producing positive electrode active material for lithium secondary battery). 9. The method of claim 8,
Drying the solvent in the mixed solution to obtain a lithium metal oxide coated on the surface of the silicate compound; in,
Wherein the drying is performed at a temperature of 100 ° C or higher, and 300 ° C or lower.
(Method for producing positive electrode active material for lithium secondary battery). 9. The method of claim 8,
In Formula 2,
G is Li,
(Method for producing positive electrode active material for lithium secondary battery). 17. The method of claim 16,
(2)
Li ₂ O. 5SiO ₂ .
(Method for producing positive electrode active material for lithium secondary battery). 9. The method of claim 8,
Preparing a mixed solution containing the lithium metal oxide, the silicate compound, and a solvent;
Wherein the solvent is de-ionized water.
(Method for producing positive electrode active material for lithium secondary battery). 11. The method of claim 10,
Adding the silicate compound into a solvent and stirring and dissolving the silicate compound;
Wherein the stirring is performed at a speed of 150 rpm or more and 300 rpm or less,
(Method for producing positive electrode active material for lithium secondary battery). anode;
cathode; And
An electrolyte;
Wherein the anode comprises the cathode active material of any one of claims 1, 2, and 4 to 7.
Lithium secondary battery.

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