KR101748037B1 - Cathode active material having high electrochemical properties and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium transition metal oxide-based particle; And an organic phosphate coating layer formed on a part or the whole of the particle surface, a method for producing the same, and a lithium secondary battery comprising the cathode active material.
The positive electrode active material of the present invention effectively inhibits the decomposition reaction of the electrolytic solution by the organic phosphate coating layer formed on the surface thereof, thereby significantly improving the electrochemical performance of the electrochemical device, preferably the lithium secondary battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material having excellent electrochemical performance and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present invention relates to a novel cathode active material capable of significantly inhibiting the decomposition reaction of a cathode material and an electrolytic solution and of improving the electrochemical performance of a lithium secondary battery by coating and heat treating an organic phosphate on the surface of a cathode material, To an electrochemical device having an active material, preferably a lithium secondary battery

2. Description of the Related Art In recent years, a secondary battery with a high capacity has been required due to miniaturization of electronic devices. In particular, lithium secondary batteries having higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries have attracted attention.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of a lithium secondary battery, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, The use of LiNiO ₂ , which is a non-aqueous electrolyte, is also considered. Of the above cathode active materials, LiCoO ₂ is most widely used because of its excellent lifetime characteristics and charge / discharge efficiency. However, LiCoO ₂ is expensive because of its small capacity and resource limitations of cobalt used as a raw material, so it is used as a power source for mid- There is a disadvantage in that price competitiveness is limited. Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ are advantageous in that they are rich in manganese resources used as raw materials, are inexpensive, environmentally friendly, and excellent in thermal stability. However, they have small capacity, high temperature characteristics, This is a poor problem.

In order to overcome such disadvantages, the demand for a nickel rich system as a cathode active material of a secondary battery has begun to increase. However, the active material of the nickel rich system has excellent advantages of high capacity, Deterioration phenomenon of the cell performance due to the reaction with the electrolytic solution appears.

Techniques for effectively suppressing the reaction between the above-described cathode active material and an electrolyte have been developed at present, but satisfactory results have not yet been obtained. Accordingly, there is an urgent need to develop a novel cathode active material capable of improving the electrochemical performance and reliability of lithium secondary batteries over the long term.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems of the prior art as described above, and it is an object of the present invention to suppress the oxidation reaction of the electrolyte solution on the anode surface by coating and heat treating an organic compound including P element, for example, organic phosphate, Thereby realizing a significant improvement in the electrochemical performance of the lithium secondary battery.

Accordingly, it is an object of the present invention to provide a cathode active material having the organic phosphate coating layer formed thereon and a method for producing the same.

It is another object of the present invention to provide a lithium secondary battery having the above-described cathode active material and improved electrochemical performance and reliability.

In order to achieve the above object, the present invention provides a lithium transition metal oxide-based particle; And an organic phosphate coating layer formed on a part or the whole of the particle surface, preferably a cathode active material for a lithium secondary battery.

According to a preferred embodiment of the present invention, the organic phosphate coating layer may be a compound represented by the following general formula (1).

In Formula 1,

R ₁ to R ₃ are the same or different and each independently represents a C ₁ to C ₄₀ alkyl group, a C ₂ to C ₄₀ alkenyl group, a C ₂ to C ₄₀ alkynyl group, a C ₆ to C ₄₀ aryl group , A heteroaryl group having 5 to 40 nuclear atoms, a C ₆ to C ₄₀ aryloxy group, a C ₁ to C ₄₀ alkyloxy group, a C ₆ to C ₄₀ arylamine group, a C ₃ to C ₄₀ cycloalkyl group , A heterocycloalkyl group having 3 to 40 nuclear atoms, a C ₁ to C ₄₀ alkylsilyl group, a C ₁ to C ₄₀ alkylboron group, and a C ₆ to C ₄₀ arylboron group, and C ₆ to C ₄₀ And arylsilyl groups, each of which may be substituted with at least one substituent selected from the group consisting of a halogen, a cyano group, and a C ₁ to C ₂₀ alkyl group.

Here, it is preferable that the organic phosphate reacts with a part of the lithium compound on the surface of the anode through heat treatment to convert it into an organic lithium phosphate.

The present invention also provides a positive electrode comprising the above-mentioned positive electrode active material and an electrochemical device having the same, preferably a lithium secondary battery.

Further, the present invention provides a method for producing a lithium transition metal oxide-based particle, comprising: (i) coating an organic phosphate on the surface of a lithium transition metal oxide-based particle; And (ii) heat-treating the coated lithium-metal composite oxide-based particles. The present invention also provides a method for producing the cathode active material for a lithium secondary battery.

In the present invention, it is possible to inhibit the oxidative decomposition reaction with the electrolytic solution compared to the conventional cathode active material by coating and heat-treating the surface of the cathode active material with phosphoric (P) -containing organic compound. As a result, the electrochemical performance and long- Can be significantly improved.

Therefore, it is possible to secure long-term reliability and high capacity at the same time by applying the present invention to a Ni-rich system active material exhibiting deterioration of battery performance according to a reaction with an electrolyte, as well as existing cathode active materials.

FIG. 1 is a graph showing changes in the capacity retention rate of a battery during 100 cycles using the lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

Hereinafter, the present invention will be described in detail.

In the present invention, an organic phosphate coating layer is formed on the surface of the lithium transition metal oxide in order to suppress the oxidative decomposition reaction between the cathode active material and the electrolytic solution and significantly improve the electrochemical performance and long-term reliability of the lithium secondary battery .

Conventionally, organic phosphates have been mainly used as an electrolyte additive component of a lithium secondary battery in order to improve stability during overcharging of a battery or to enhance high-temperature storage characteristics, lifetime characteristics and the like. Since such an organic phosphate has high stability within the operating range of the battery, it is difficult to exhibit the side reaction inhibitory effect between the positive electrode active material and the electrolytic solution itself, because it exists as an additive in the electrolyte solution without a separate chemical reaction with other materials .

In addition, conventionally, inorganic phosphate (e.g., phosphoric acid) coating layer is formed on the surface of the cathode active material. However, since such inorganic phosphate is mainly solid, the coating process itself is not easy, and even if a coating layer is formed There is a problem in that it can not be uniformly formed on the surface of the positive electrode active material particles. For example, in the case of phosphoric acid, since the acid component of phosphoric acid and the base component of the anode surface react with each other before coating on the anode surface layer in the coating process, the aggregation of the anode particles occurs, Resulting in degraded problems. Therefore, the oxidation decomposition reaction between the cathode active material and the electrolytic solution was inhibited and the performance and safety of the battery were not improved.

In contrast, according to the present invention, the organic phosphate which is an organic material is adopted to form a uniform thin coating layer on the surface of the cathode active material particles, thereby effectively suppressing the oxidative decomposition reaction between the cathode active material and the electrolyte solution without interfering with the movement of lithium ions And thus the electrochemical performance and long-term reliability of the lithium secondary battery can be significantly improved. Particularly, the organic phosphate employed in the present invention does not cause an acid-base reaction with the surface of the anode, so that a uniform coating layer can be formed without aggregation between the anode particles, and a side reaction between the electrolyte and the anode occurs after the coating layer is formed. And protects the cathode active material continuously.

Further, since the organic phosphate is easy to handle, the simplicity and economy of the coating process and the manufacturing process can be improved.

<Cathode Active Material>

The cathode active material according to the present invention includes cathode active material particles capable of occluding and releasing lithium and an organic phosphate coating layer formed on the particle surface.

More specifically, the cathode active material comprises (a) lithium transition metal oxide-based particles; And (b) an organic phosphate coating layer formed on part or all of the particle surface.

Here, the organic phosphate coating layer may be formed by using any conventional organic phosphate compound known in the art without limitation, preferably by coating and heat-treating a compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1,

R ₁ to R ₃ are the same or different and each independently represents a C ₁ to C ₄₀ alkyl group, a C ₂ to C ₄₀ alkenyl group, a C ₂ to C ₄₀ alkynyl group, a C ₆ to C ₄₀ aryl group , A heteroaryl group having 5 to 40 nuclear atoms, a C ₆ to C ₄₀ aryloxy group, a C ₁ to C ₄₀ alkyloxy group, a C ₆ to C ₄₀ arylamine group, a C ₃ to C ₄₀ cycloalkyl group , A heterocycloalkyl group having 3 to 40 nuclear atoms, a C ₁ to C ₄₀ alkylsilyl group, a C ₁ to C ₄₀ alkylboron group, and a C ₆ to C ₄₀ arylboron group, and C ₆ to C ₄₀ And arylsilyl groups, each of which may be substituted with at least one substituent selected from the group consisting of a halogen, a cyano group, and a C ₁ to C ₂₀ alkyl group.

In the present invention, R ₁ to R ₃ are the same or different and each independently represents an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, And an aryl group. Wherein R ₁ to R ₃ may each be substituted with at least one substituent selected from the group consisting of halogen, cyano group and C ₁ to C ₂₀ alkyl group.

Non-limiting examples of organic phosphates that can be used include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, triisobutyl phosphate, tripentyl phosphate, triphenyl phosphate or mixtures thereof.

The organophosphate is coated on the lithium transition metal oxide particles and then subjected to a heat treatment process. A part of R ₁ , R ₂ , and R ₃ in the organic phosphate of Formula 1 reacts with the lithium compound on the surface of the anode through the heat treatment Organic lithium phosphate (organic lithium compound).

In the case of conventional phosphoric acid, a lithium phosphate coating layer is formed after the heat treatment, whereas in the present invention, a part of the organic functional group reacts with the lithium source on the surface of the anode after the heat treatment to form an organic phosphate coating layer containing lithium. Such an organic lithium phosphate coating layer prevents the deterioration of the cathode active material by preventing side reactions between the cathode active material and the electrolyte solution while preventing the lithium ion migration during charging and discharging of the battery, and can continuously protect the cathode active material.

The lithium source forming the organic lithium phosphate bond may be a lithium ion in the lithium transition metal oxide or a residual lithium compound present on the surface of the oxide. That is, a lithium compound such as lithium oxide (Li ₂ O), lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), or the like can be formed on the surface of the lithium transition metal oxide- Lithium carbide (Li ₂ C) or the like may be present. This residual lithium compound can react with a specific substance in the electrolyte in the secondary battery and the reactant can accumulate on the surface of the cathode active material and interfere with the movement of lithium ions. For example, the residual lithium compound reacts with HF or the like in the electrolyte to generate LiF, which may lead to deterioration of the performance of the battery. In the present invention, the organic phosphate coating layer coated on the cathode active material reacts with the lithium source in the cathode to convert into organic lithium phosphate, thereby reducing the amount of the lithium compound that may remain on the surface and cause deterioration of the performance of the battery, It is possible to simultaneously exhibit the effect of suppressing the surface deterioration due to the reaction with.

The cathode active material may have a structure in which an organic phosphate coating layer is formed on a part of a surface of the lithium transition metal oxide, or may include a core part including a lithium transition metal oxide; And a shell part formed by coating organic phosphate on the surface of the core part.

In the present invention, the thickness of the organic phosphate coating layer can be adjusted within a conventional range known in the art. For example, in the range of 10 to 500 nm, and preferably in the range of 200 to 300 nm.

The content of the organic phosphate coating layer may be in the range of 1 to 20 parts by weight, preferably 3 to 15 parts by weight, based on the total weight of the cathode active material.

In the present invention, an object on which an organic phosphate coating layer is formed is a cathode active material for a lithium secondary battery.

The cathode active material may include a conventional cathode active material that can be used for a cathode of a conventional lithium secondary battery, for example, an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a transition metal, a rare earth element, A lithium-containing metal oxide can be used. Chalcogenide-based compounds are also applicable. Nonlimiting examples thereof include lithium transition metal oxides such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , LiNiO ₂ Lithium cobalt oxide such as LiCoO ₂ , vanadium oxide containing lithium, etc.) or a chalcogenide compound (for example, lithium cobalt oxide such as LiCoO ₂ , etc.) or a substitution of a part of manganese, nickel or cobalt of these oxides with another common transition metal or the like) For example, manganese dioxide, titanium disulfide, molybdenum disulfide, etc.).

More specifically, the lithium transition metal oxide system may be LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiFePO ₄ , Li (Co _x Ni _1-x O ₂ (0.5? x <1) and Li _{1 + x} Mn ₂ -yz-wAl _y Co _z Mg _w O ₄ (0.03 <x <0.25, 0.01 <y <0.2, 0.01 <z <0.2, 0? W <0.1 and x + y + z + w <0.4), and is preferably an active material of a nickel rich system.

According to a preferred embodiment of the present invention, the lithium transition metal oxide may be represented by the following general formula (2).

(2)

Li _a Ni _b Co _c X _d O ₂

In Formula 2, X is at least one selected from the group consisting of Mn and Al, and 0.9? A? 1.10, 0.6? B? 1.0, 0.0? C? 0.2, and 0.0? D? 0.2.

The average particle diameter of the cathode active material is not particularly limited as long as it is a typical range that can be used as an active material. For example, in the range of 5 to 30 mu m, preferably in the range of 5 to 20 mu m.

&Lt; Method for producing positive electrode active material &

Hereinafter, a method for producing the positive electrode active material according to the present invention will be described. However, the present invention is not limited to the following production methods, and the steps of each process may be modified or selectively mixed if necessary.

In one preferred embodiment of the above production method, (i) a step of coating an organic phosphate on the surface of the lithium transition metal oxide-based particle ('S10 step'); And (ii) heat-treating the coated lithium-metal composite oxide-based particles (step S20).

Hereinafter, the manufacturing method will be described separately for each process step as follows.

(1) Organic phosphate coating step (hereinafter referred to as &quot; S10 step &

In the step S10, organic phosphate is coated on the surface of the lithium transition metal oxide particle.

For example, a coating solution is prepared by mixing and dispersing an organic phosphate and a solvent, and then a lithium transition metal oxide is added thereto and homogeneously stirred to effect coating.

As the solvent, a conventional solvent known in the art can be used, and a volatile solvent is preferable. Nonlimiting examples of these solvents include water, organic solvents such as alcohols having 1 to 6 carbon atoms, acetone, and the like.

The ratio of the lithium transition metal oxide to the organic phosphate is not particularly limited and may be, for example, 1 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the lithium metal composite oxide- Can be negative.

In the above step S10, the coating method may be performed by any conventional mixing method known in the art without limitation, and a general mixing can be performed for uniform mixing or a dry or wet mechanical milling method can be used have. Non-limiting examples thereof include solvent evaporation, coprecipitation, precipitation, sol-gel, post-adsorption, sputter, chemical vapor deposition, convective, .

(2) Heat treatment step (hereinafter referred to as step S20)

In the step S20, a heat treatment is performed on the lithium-transition metal oxide particle on which the organic phosphate coating layer is formed so that a part of the organic functional groups in the organic phosphate react with the lithium compound of the anode to form an organic lithium phosphate bond while evaporating the solvent in the coating layer do.

In this case, the heat treatment conditions can be suitably adjusted within the conventional range known in the art. For example, the heat treatment can be maintained at a temperature range of 200 to 700 ° C for 2 to 10 hours, preferably at 300 to 600 ° C, 7 hours.

The cathode active material prepared in the present invention is mainly used as a cathode material for a secondary battery, and may be used in various fields in which the above-described structure can be applied.

<Anode>

The present invention provides a cathode material for a secondary battery and a lithium secondary battery including the same.

At this time, the cathode material of the present invention is required to include at least a cathode active material having the above-described organic phosphate coating layer formed thereon. For example, the positive electrode active material itself may be used as a positive electrode active material, or a positive electrode material mixture in which the positive electrode active material and a binder are mixed, a positive electrode material mixture paste obtained by further adding a solvent, It falls within the scope of the anode material of the invention.

The anode may be manufactured by a conventional method known in the art. For example, a slurry is prepared by mixing and stirring a binder, a conductive agent, and a dispersant, if necessary, with an electrode active material, Followed by compression and drying.

The electrode material such as a dispersion medium, a binder, a conductive agent, and a current collector may be a conventional one known in the art, and the binder may be suitably used in an amount of 1 to 10 parts by weight based on the weight of the electrode active material and 1 to 30 parts by weight of the conductive material .

Examples of usable conductive agents include natural graphite, artificial graphite, carbon black, acetylene black or Gulf Oil Company, ketjen black, Vulcan XC-72, Super P, coke, carbon nanotubes, And mixtures of one or more of these.

Typical examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) or a copolymer thereof, styrene butadiene rubber (SBR), cellulose and the like. Representative examples of the dispersing agent include isopropyl alcohol, N Methylpyrrolidone (NMP), acetone, and the like.

The current collector of the metal material may be any metal that has high conductivity and is a metal that can easily adhere the paste of the material and does not have reactivity in the voltage range of the battery. For example, a mesh, a foil, or the like of aluminum, copper, or stainless steel may be used.

<Lithium secondary battery>

In addition, the present invention provides a secondary battery comprising the anode, preferably a lithium secondary battery.

The lithium secondary battery of the present invention is not particularly limited except that the cathode active material having the organic phosphate coating layer described above is used, and can be produced according to a conventional method known in the art. For example, a separation membrane may be inserted between an anode and a cathode, and a nonaqueous electrolyte may be charged.

The lithium secondary battery of the present invention includes a cathode, a cathode, a separator, and an electrolyte as battery components. Components of the anode, the separator, the electrolyte, and other additives, if necessary, other than the cathode described above, Which is the same as that of the lithium secondary battery.

For example, the negative electrode may be a negative electrode active material for a lithium secondary battery known in the art. As a non-limiting example, a material capable of intercalating / deintercalating lithium is used. For example, Lithium alloys, coke, artificial graphite, natural graphite, combustibles of organic polymer compounds, carbon fibers, silicones, and tin-based alloys. The conductive agent, binder and solvent are used in the same manner as in the case of the positive electrode described above.

Also, the non-aqueous electrolyte includes electrolytic components commonly known in the art, such as an electrolyte salt and an electrolyte solvent.

(I) a cation selected from the group consisting of Li ⁺ , Na ⁺ , K ⁺ and (ii) a cation selected from the group consisting of PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- A combination of anions selected from the group consisting of CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N (CF ₃ SO ₂ ) ₂ ^- and C (CF ₂ SO ₂ ) ₃ ^- . Specific examples of the lithium salt include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ . These electrolyte salts may be used alone or in combination of two or more.

The electrolyte solvent may be selected from cyclic carbonates, linear carbonates, lactones, ethers, esters, acetonitriles, lactams, and ketones.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and fluoroethylene carbonate (FEC). Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like. Examples of the ester include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl pivalate and the like. Examples of the lactam include N-methyl-2-pyrrolidone (NMP), and the ketone is polymethyl vinyl ketone. The halogen derivative of the organic solvent may be used, but is not limited thereto. In addition, the organic solvent may be glyme, diglyme, triglyme, or tetraglyme. These organic solvents may be used alone or in combination of two or more.

The separator may use any porous material that interrupts the internal short circuit of both electrodes and impregnates the electrolyte. Examples thereof include polypropylene-based, polyethylene-based, polyolefin-based porous separation membranes, or composite porous separation membranes in which an inorganic material is added to the above-mentioned porous separation membranes.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the scope of the present invention is not limited by the following Examples and Experimental Examples.

[Example 1]

1-1. Cathode active material manufacturing

In order to prepare NCM series cathode active material, first, a precursor of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ was prepared by coprecipitation reaction, LiOH was added as a lithium compound, and heat treatment was performed at 780 ° C. for 12 hours to obtain Li _1.01 Ni _0.8 Co _0.1 Mn _0.1 O was prepared the positive electrode active material represented by the _second.

100 parts by weight of the prepared cathode active material was coated with 10 parts by weight of tributyl phosphate and then heat-treated at 300 ° C for 3 hours to prepare a cathode active material of Example 1.

1-2. Anode manufacturing

95 parts by weight of the cathode active material prepared in Example 1-1, 2.5 parts by weight of the PvdF binder, and 2.5 parts by weight of carbon black as a conductive material were dispersed in an NMP solution to prepare a slurry, which was then applied to the Al current collector. And then rolled by a roll press to produce a positive electrode

1-3. Lithium secondary battery manufacturing

Using a positive electrode and a lithium metal prepared in Example 1-2 as a counter electrode and using an electrolytic solution composed of EC / EMC / DEC (40/30/30, volume ratio) and 1M of LiPF ₄ , coin cells cell.

[Example 2]

The cathode active material of Example 2 was prepared in the same manner as in Example 1 except that triphenyl phosphate instead of tributyl phosphate was used.

A positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, using the positive electrode active material.

[Comparative Example 1]

In order to prepare NCM series cathode active material, first, a precursor of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ was prepared by coprecipitation reaction, LiOH was added as a lithium compound, and heat treatment was performed at 780 ° C. for 12 hours to obtain Li _1.01 Ni _0.8 Co _0.1 Mn _0.1 O was prepared the positive electrode active material represented by the _second.

The positive electrode and the lithium secondary battery of Comparative Example 1 were prepared in the same manner as in Example 1, using the positive electrode active material as it was without coating treatment.

[Comparative Example 2]

10 parts by weight of phosphoric acid was coated on 100 parts by weight of a cathode active material represented by Li _1.01 Ni _0.8 Co _0.1 Mn _0.1 O ₂ prepared in the same manner as in Comparative Example 1 and then heat-treated at 300 ° C for 3 hours to obtain Thereby preparing a cathode active material.

The positive electrode and the lithium secondary battery of Comparative Example 2 were prepared in the same manner as in Example 1, respectively.

[Experimental Example 1] Evaluation of electrochemical performance

The electrochemical performance was evaluated using the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

At this time, the electrochemical performance evaluation was carried out 100 times at 1C in the voltage range of 4.4V to 3.0V based on 1C, and the maintenance ratio was measured relative to the initial capacity.

As a result of the test, the batteries of Comparative Example 1 in which the surface was not treated and Comparative Example 2 in which the inorganic phosphate surface was modified showed a low capacity retention ratio of 63% or less. In the case of Comparative Example 2 in which phosphoric acid is coated with an inorganic phosphate, the difference in the components constituting the coating layer, the aggregation between the anode particles due to the acid-base reaction between the phosphoric acid and the anode surface, and the coating non- The improvement is considered to be low.

In contrast, the batteries of Examples 1 and 2 having the cathode active material coated with organic phosphate showed remarkably improved long-term reliability (see Table 1 and FIG. 1). In particular, the batteries of Examples 1 and 2 improved the capacity retention ratio by about 15 to 20% or more and 13 to 16%, respectively, as compared with the battery of Comparative Example 2 coated with inorganic phosphate, It is confirmed that the effect is exerted.

Retention [%, @ 100th cycle] Example 1 86.9% Example 2 89.3% Comparative Example 1 60.8% Comparative Example 2 62.9%

Claims (15)

Lithium transition metal oxide-based particles; And
And an organic phosphate coating layer formed on part or all of the particle surface,
Wherein the organophosphate coating layer comprises organolithium phosphate converted by reacting a part of the lithium compound on the surface of the anode through heat treatment.
[Chemical Formula 1]

In Formula 1,
R ₁ to R ₃ are the same or different and each independently represents a C ₁ to C ₄₀ alkyl group, a C ₂ to C ₄₀ alkenyl group, a C ₂ to C ₄₀ alkynyl group, a C ₆ to C ₄₀ aryl group , A heteroaryl group having 5 to 40 nuclear atoms, a C ₆ to C ₄₀ aryloxy group, a C ₁ to C ₄₀ alkyloxy group, a C ₆ to C ₄₀ arylamine group, a C ₃ to C ₄₀ cycloalkyl group , A heterocycloalkyl group having 3 to 40 nuclear atoms, a C ₁ to C ₄₀ alkylsilyl group, a C ₁ to C ₄₀ alkylboron group, and a C ₆ to C ₄₀ arylboron group, and C ₆ to C ₄₀ And arylsilyl groups, each of which may be substituted with at least one substituent selected from the group consisting of a halogen, a cyano group, and a C ₁ to C ₂₀ alkyl group. delete delete The method according to claim 1,
Wherein the cathode active material comprises: a core portion containing a lithium transition metal oxide; And a shell part formed by coating an organic phosphate on the surface of the core part. The method according to claim 1,
Wherein the thickness of the organic phosphate coating layer is in the range of 10 to 500 nm. The method according to claim 1,
Wherein the content of the organic phosphate coating layer is in the range of 1 to 20 parts by weight based on the total weight of the cathode active material. The method according to claim 1,
The lithium-transition metal oxide-based particles may be LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiFePO ₄ , Li (Co _x Ni _{1 -x) O 2 (0.5≤ x <} 1), and _{Li 1 + x Mn 2 -yz-} wAl y Co z Mg w O 4 (0.03 <x <0.25, 0.01 <y <0.2, 0.01 <z <0.2, 0 < = w < 0.1, x + y + z + w &lt; 0.4). The method according to claim 1,
Wherein the lithium transition metal oxide-based particles are represented by the following formula (2).
(2)
Li _a Ni _b Co _c X _d O _{2 wherein} X is at least one selected from the group consisting of Mn and Al, 0.9? A? 1.10, 0.6? B? 1.0, 0.0? C? 0.2, being) The method according to claim 1,
Wherein the average particle diameter is in the range of 1 to 30 占 퐉. A positive electrode comprising the positive electrode active material of any one of claims 1 to 9. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte according to claim 10. (i) coating an organic phosphate on the surface of the lithium transition metal oxide-based particle; And
(ii) heat-treating the coated lithium metal composite oxide-based particles,
Wherein the organophosphate of step (i) is a compound represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]

In Formula 1,
R ₁ to R ₃ are the same or different and each independently represents a C ₁ to C ₄₀ alkyl group, a C ₂ to C ₄₀ alkenyl group, a C ₂ to C ₄₀ alkynyl group, a C ₆ to C ₄₀ aryl group , A heteroaryl group having 5 to 40 nuclear atoms, a C ₆ to C ₄₀ aryloxy group, a C ₁ to C ₄₀ alkyloxy group, a C ₆ to C ₄₀ arylamine group, a C ₃ to C ₄₀ cycloalkyl group , A heterocycloalkyl group having 3 to 40 nuclear atoms, a C ₁ to C ₄₀ alkylsilyl group, a C ₁ to C ₄₀ alkylboron group, and a C ₆ to C ₄₀ arylboron group, and C ₆ to C ₄₀ And arylsilyl groups, each of which may be substituted with one or more substituents selected from the group consisting of a halogen or a cyano group. delete 13. The method of claim 12,
Wherein the content of the organic phosphate in the step (i) ranges from 1 to 20 parts by weight based on 100 parts by weight of the lithium metal composite oxide-based particles. 13. The method of claim 12,
Wherein the step (ii) is maintained at 200 to 700 占 폚 for 2 to 10 hours.

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