KR20150021809A - Lithium transition metal cathode active material, preparation method thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium transition metal cathode active material containing a coating layer containing Al_2O_3 and LiF on the surface, a method for preparing the same, and a lithium secondary battery including the same. The lithium transition metal cathode active material according to the present invention is highly acid-resistant and suppresses an electrolytic reaction so that battery capacity reduction can be addressed and improves lithium ion mobility so that the electrochemical characteristics of the lithium secondary battery such as charging and discharging characteristics, life characteristics, high-rate characteristics, and thermal stability can be improved. According to the present invention, AlF_3 is added to a lithium transition metal oxide containing excess lithium before plastification, and thus a uniform surface coating can be formed on the lithium transition metal cathode active material. In addition, the simple process can result in reduced preparation costs.

Description

TECHNICAL FIELD [0001] The present invention relates to a lithium transition metal cathode active material, a method for producing the same, and a lithium secondary battery comprising the lithium transition metal cathode active material,

The present invention relates to a lithium transition metal cathode active material including a coating layer containing Al ₂ O ₃ and LiF on its surface, a method for producing the lithium transition metal cathode active material, and a lithium secondary battery comprising the lithium transition metal cathode active material.

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.

Further, recently, a technique of coating a surface of a cathode active material with a coating agent such as a metal oxide or a metal fluoride compound has been developed. This coating method is a method in which a coating agent is adhered to the surface of a cathode active material by a sol-gel method or a colloid method using an aqueous or organic material as a solvent and then heat-treated.

LiCoO ₂ , a structurally stable LiCoO ₂ , improves its electrochemical properties, but Li [Ni _{1 - x} M _x ] O ₂ or Li [Ni _x Co _{1 -2 x} Mn _x ] O ₂ , the surface modification effect may not be exhibited due to the structural change thereof, or the electrochemical performance of the secondary battery may be significantly deteriorated. In addition, such a wet process may cause another problem that the manufacturing process is complicated and the process cost is increased.

A first technical object of the present invention is to provide a lithium secondary battery which is capable of improving electrochemical characteristics such as charging / discharging characteristics, lifetime characteristics, high rate characteristics and thermal stability of a secondary battery through surface coating of a lithium transition metal cathode active material, To provide a cathode active material.

A second 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 comprising the positive electrode active material.

A fourth aspect of the present invention is to provide a lithium secondary battery including the positive electrode.

In order to solve the above problems, the present invention provides a lithium transition metal cathode active material comprising a coating layer containing Al ₂ O ₃ and LiF on its surface.

The present invention also relates to a method for preparing a lithium transition metal oxide, comprising: mixing a mixed transition metal precursor and a lithium source and subjecting the mixture to a first calcination to obtain an excess lithium-containing lithium transition metal oxide; And

A step of adding AlF ₃ to the excess lithium-containing lithium transition metal oxide and performing secondary firing to coat the surface of the lithium transition metal oxide with Al ₂ O ₃ and LiF.

Furthermore, the present invention provides a positive electrode and a lithium secondary battery comprising the lithium transition metal positive electrode active material.

The lithium transition metal cathode active material including a coating layer containing Al ₂ O ₃ and LiF on the surface according to an embodiment of the present invention has an increased resistance to an acid and suppresses a reaction with an electrolyte, In addition, it is possible to improve the electrochemical characteristics such as charge / discharge characteristics, lifetime characteristics, high rate characteristics and thermal stability of lithium secondary batteries by improving the mobility of lithium ions.

In addition, according to the method of the present invention, since AlF ₃ is added to a lithium-containing transition metal oxide containing an excess amount of lithium and fired, a uniform surface coating layer can be formed on the lithium transition metal cathode active material, Cost can be reduced.

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 graph showing the results of X-ray diffraction analysis of AlF ₃ before and after calcination at 500 ° C.
2 is a graph showing the results of X-ray diffraction analysis for analyzing reactants obtained by the reaction of AlF ₃ and Li ₂ CO ₃ .

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.

According to one embodiment of the present invention, there is provided a lithium transition metal cathode active material comprising a coating layer comprising Al ₂ O ₃ and LiF on its surface.

The lithium transition metal cathode active material including a coating layer containing Al ₂ O ₃ and LiF on the surface according to an embodiment of the present invention may be obtained by mixing a mixed transition metal precursor and a lithium source and then performing a first calcination to obtain an excessive amount of lithium To obtain a lithium transition metal oxide; And a step of adding AlF ₃ to the excess lithium-containing lithium transition metal oxide and performing secondary firing to coat the surface of the lithium transition metal oxide with Al ₂ O ₃ and LiF.

Specifically, the manufacturing method of the present invention may include a step of obtaining an excess lithium-containing lithium transition metal oxide (Step 1).

According to one embodiment of the present invention, in the excess lithium-containing lithium-transition metal oxide, the lithium source is excessively added so that the ratio of lithium (Li) to transition metal (Me) is 1.05 or more, preferably 1.05 to 1.20 . ≪ / RTI > That is, the mixed transition metal precursor and the lithium source can be mixed at a molar ratio of 1: 1.05 or more, preferably 1: 1.05 to 1.20.

Generally, excessive amounts of lithium in the production of a cathode active material cause degradation of the electrochemical characteristics and reliability of the cathode active material by decomposing the electrolyte, so that the molar ratio of the mixed transition metal precursor to the lithium source (Li / transition metal (Me) ) Was used at less than 1: 1.05.

However, according to one embodiment of the invention, in the case of using the AlF ₃ with a surface coating material, AlF ₃ is reacted with a lithium source to form an Al ₂ O ₃ and LiF, Al ₂ O ₃ and LiF formed in the positive electrode active material Can be coated on the surface.

Specifically, when a lithium source is added in excess by using a molar ratio of a mixed transition metal precursor to a lithium source of 1: 1.05 or more, excess lithium sources reacting with AlF ₃ are increased, The surface coating layer can be more uniformly formed and the specific surface area can be reduced. That is, the specific surface area of the lithium transition metal cathode active material according to an embodiment of the present invention may be reduced by about 3% to 30% as compared to the cathode active material not including the coating layer containing Al ₂ O ₃ and LiF on the surface.

Lithium transition metal Al ₂ O ₃ coated on the surface of the cathode active material is produced as a side reaction in the process of manufacturing a lithium secondary battery, and is capable of promoting deterioration of battery performance such as capacity reduction and swelling of lithium secondary battery. And LiF coated on the surface of the lithium transition metal cathode active material is formed as a protective layer on the surface of the cathode active material, thereby improving the electrochemical characteristics such as charge / discharge characteristics, high rate characteristics and lifetime characteristics of the lithium secondary battery. Can be improved.

The mixed transition metal precursor may be a mixed transition metal precursor commonly used in the art for the production of a cathode active material, but is not limited thereto. For example, MOOH or M (OH) ₂ (M = Ni _x Mn _y Co _z , 0.3? X? 0.9, 0? Y? 0.45 and 0? Z? 0.4, x + y + z = 1) can be used.

Meanwhile, the lithium source may be Li ₂ CO ₃ , LiOH, or a mixture thereof.

According to an embodiment of the present invention, the primary firing to obtain the lithium-containing lithium-containing lithium metal oxide may be performed at 700 ° C to 1100 ° C for 5 hours to 15 hours.

Further, the manufacturing method of the present invention may include a step of surface coating the lithium transition metal oxide with Al ₂ O ₃ and LiF (Step 2).

According to one embodiment of the present invention, the amount of AlF ₃ is preferably 0.01 wt% to 2 wt% based on the total weight of lithium-containing metal oxide containing excessive lithium. If the amount of AlF ₃ is less than 0.01 wt%, the surface coating effect of the cathode active material may be insignificant. When the amount of AlF ₃ is more than 2 wt%, solid AlF ₃ aggregates are strong, .

In addition, the second firing is Al ₂ O ₃ and LiF AlF ₃ to form the Al ₂ O ₃ and LiF can react with in excess of the lithium source anode active material, and thus formed as a plastic for coating the positive electrode active material surface, 300 ℃ Deg.] C to 800 [deg.] C, preferably 400 [deg.] C to 700 [deg.] C for 2 hours to 8 hours.

When the temperature of the second firing is higher than 800 ° C., the reaction rate is too fast to obtain a uniform surface coating. When the temperature of the second firing is less than 300 ° C., AlF ₃ is added to the excess lithium source in the cathode active material The reaction may be difficult.

The method for producing the positive electrode active material can prevent the structural transition occurring on the surface of the lithium transition metal positive electrode active material and can produce a positive electrode active material having a uniform surface coating. Also, since the surface coating process is simple, the cost increase due to the coating can be minimized.

In addition, the lithium transition metal cathode active material prepared according to the present invention has an increased resistance to an acid and inhibits the reaction with an electrolyte, thereby improving the capacity reduction of the battery and improving the mobility of lithium ions to improve the discharge potential Thereby improving the charge / discharge characteristics, lifetime characteristics, and high-rate characteristics of the lithium secondary battery.

The present invention can provide a lithium transition metal cathode active material produced according to the above production method.

The lithium transition metal cathode active material may preferably be a compound of the following formula 1:

≪ Formula 1 >

Li _a M _b O ₂

In this formula,

M = Ni _x Mn _y Co _z , (0.3? X? 0.9, 0? Y? 0.45 and 0? Z? 0.4, x + y + z = 1);

a + b? 2, and 0.95? a? 1.05.

According to an embodiment of the present invention, the thickness of the coating layer formed on the surface of the lithium transition metal cathode active material may be 1 nm to 100 nm, preferably 10 nm to 50 nm.

If the thickness of the surface coating layer is less than 1 nm, the amount of Al ₂ O ₃ serving as a remover for HF and the amount of LiF as a protective layer may be reduced with an insufficient coating thickness, and the desired effect of the present invention may be insignificant, If the thickness of the surface coating layer exceeds 100 nm, the resistance of the lithium ion may be increased and the resistance may increase.

According to an embodiment of the present invention, there is provided a positive electrode comprising the lithium transition metal 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 positive electrode 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 vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, poly Polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), liquefied petroleum resin (EPDM), polyvinyl alcohol, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers in which hydrogen is substituted with Li, Na, Ca, or the like, 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 dispersing agent may be an aqueous dispersing agent or an organic dispersing agent such as N-methyl-2-pyrrolidone.

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. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

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. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

The lithium salt that can be used as the electrolyte used in the present invention may be any of those conventionally used in an electrolyte for a lithium secondary battery. For example, the anion of the lithium salt may include F ^- , Cl ^- , Br ^- , I ^{- _{NO 3 -, N (CN)}} 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, ^{_{(CF 3) 5 PF -,}} (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 _{CF 2 (CF 3) 2 CO} -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^-, and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. no.

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 of the present invention can be used as a power source for various electronic products. For example, a portable telephone, a mobile phone, a game machine, a portable television, a notebook computer, a calculator, and the like, but is not limited thereto.

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.

Example  One

<Preparation of cathode active material surface-coated with Al ₂ O ₃ and LiF>

Step 1) Preparation of an excess lithium-containing lithium transition metal oxide

With a mixed transition metal precursor _{(Ni 0 .5 Mn 0 .3 Co} 0 .2) OOH and a lithium source and mixed so that the molar ratio of 1.05 (the ratio of Li / Me) of Li ₂ CO _3, the mixture is about 950 Lt; 0 &gt; C for about 10 hours to obtain an excess lithium-containing lithium transition metal oxide.

Step 2) Preparation of cathode active material surface-coated with Al ₂ O ₃ and LiF

0.2% by weight of AlF ₃ was added to the excess lithium-containing lithium-containing metal oxide obtained in the step 1), and this was subjected to secondary calcination at about 400 ° C. for 5 hours in an inert atmosphere to form Al ₂ O ₃ and LiF Thereby obtaining a positive electrode active material containing a coating layer containing the above-mentioned negative electrode active material.

Example  2

A cathode active material including a coating layer containing Al ₂ O ₃ and LiF on the surface was obtained in the same manner as in Example 1 except that 0.5 wt% of AlF ₃ was used in the step 2 of Example 1.

Comparative Example  One

With a mixed transition metal precursor under _{(Ni 0 .5 Mn 0 .3 Co} 0 .2) OOH and a lithium source Li ₂ CO ₃ molar ratio such that the mixed (the ratio of Li / Me) is 1.01, and the mixture in an inert atmosphere of Followed by first firing at about 950 DEG C for about 10 hours to obtain a cathode active material.

Comparative Example  2

0.2 wt% of AlF ₃ was added to the cathode active material obtained in Comparative Example 1, and this was subjected to secondary firing at about 400 ° C for 5 hours in an inert atmosphere to obtain a cathode active material.

Comparative Example  3

A cathode active material was obtained in the same manner as in Comparative Example 2 except that 0.5 wt% of AlF ₃ was used.

Comparative Example  4

With a mixed transition metal precursor _{(Ni 0 .5 Mn 0 .3 Co} 0 .2) OOH, and the molar ratio of the lithium source Li ₂ CO ₃ was mixed to ensure that the 1.05, and the mixture first at about 950 ℃ for about 10 hours Followed by firing to obtain a cathode active material.

&Lt; Production of lithium secondary battery >

Example  3

Anode manufacturing

A cathode active material including a coating layer comprising Al ₂ O ₃ and LiF was used on the surface of the substrate prepared in Example 1 above.

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

As negative active material, 96.3 wt% of carbon powder, 1.0 wt% of super-p as a conductive material, 1.5 wt% and 1.2 wt% of SBR and carboxymethyl cellulose (CMC) as a binder were added to NMP as a solvent to prepare an anode material composition . The negative electrode material composition was coated on 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 the non-aqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as electrolytes in a volume ratio of 30:70 to prepare a 1 M LiPF ₆ non-aqueous electrolyte.

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.

Example  4

A lithium secondary battery was produced in the same manner as in Example 3, except that the cathode active material including a coating layer containing Al ₂ O ₃ and LiF was used on the surface of the lithium secondary battery of Example 2.

Comparative Example  5 to 8

A lithium secondary battery was prepared in the same manner as in Example 3, except that the cathode active materials prepared in Comparative Examples 1 to 4 were used.

Experimental Example  One

In order to confirm the oxidation of AlF ₃ before and after firing, AlF ₃ The sole material was calcined at 500 ° C for 5 hours and X-ray diffraction analysis was performed on AlF ₃ before calcination and after calcination. The results are shown in Fig.

Looking at Figure 1, in the prior 500 ℃ after firing one firing for about 5 hours at AlF ₃ AlF ₃ and firing was not differ only in the intensity of the peak, the peak change before and after the firing. From these results, it was confirmed that AlF ₃ itself was not oxidized even when calcined at 500 ° C.

Experimental Example  2

AlF then to analyze the reaction product obtained by the reaction ₃ and Li ₂ CO _3, a mixture of AlF ₃ and Li ₂ CO ₃ and baked at about 500 ℃, the X- ray diffraction analysis was carried out. The results are shown in FIG. 2 and observed in comparison with X-ray diffraction analysis results of Al ₂ O ₃ bare.

As a result of the X-ray diffraction analysis of FIG. 2, peaks corresponding to Al ₂ O ₃ and LiF were observed, and peaks corresponding to AlF ₃ and Li ₂ CO ₃ were not observed. As a result, it can be confirmed that Al ₂ O ₃ and LiF were formed by the reaction of AlF ₃ and Li ₂ CO ₃ .

Experimental Example  3

<Electrochemical Evaluation Test>

Electrochemical evaluation experiments were conducted as follows to examine the initial charge / discharge capacity, high rate characteristics and life characteristics of the lithium secondary batteries obtained in Examples 3 and 4 and Comparative Examples 5 to 8.

The lithium secondary batteries obtained in Examples 3 and 4 and Comparative Examples 5 to 8 were charged at a constant current (CC) of 4.25 V at a temperature of 25 ° C of 0.1 C, then charged at a constant voltage (CV) of 4.25 V, Was 0.05 mAh, the first charging was performed. Thereafter, the battery was allowed to stand for 20 minutes, and discharged at a constant current of 0.1 C until it reached 3.0 V to measure the discharge capacity of the first cycle. Each of the batteries of Examples 3 and 4 and Comparative Examples 5 to 8 was measured for charging / discharging initial capacity, high rate characteristics and life characteristics by varying charge / discharge conditions as shown in Table 1 below. The results are shown in Table 1 below.

Li / Me 1 ^st CHQ 1 ^st disQ EFF (%) 0.5 / 0.1 0.5 / 1.0 0.5 / 2.0 30 cycles Example 3 1.05 217.1 197.7 91.0 197.5 182.4
(92.4%) 175.3
(88.8%) 96.6
Example 4 1.05 216.3 196.9 91.0 195.8 180.3
(92.1%) 172.2
(88.0%) 96.9 Comparative Example 5 1.01 215.0 191.5 89.1 192.0 176.6
(92.0%) 169.2
(88.1%) 97.0 Comparative Example 6 1.01 217.2 196.0 90.2 196.0 180.1
(91.9%) 172.5
(88.0%) 97.1 Comparative Example 7 1.01 214.2 192.2 89.7 192.8 176.2
(91.4%) 168.0
(87.1%) 97.0 Comparative Example 8 1.05 214.7 192.8 89.8 192.6 177.5
(92.1%) 170.8
(88.7%) 96.9

As can be seen from the above Table 1, when the excessive lithium source was used to burn LiFe / AlF ₃ with a molar ratio of Li / transition metal (Me) of 1.05 as in Examples 3 and 4 of the present invention, Li / Compared with Comparative Examples 5 to 7 using a cathode active material having a molar ratio of Me less than 1.05, the charge / discharge capacities were excellent in both 0.5C / 0.1C, 0.5C / 1.0C and 0.5C / 2.0C, .

In addition, even if a 1.05 and the molar ratio of Li / Me using excess lithium source, an embodiment of the present invention than in the comparative example 8 is not firing process at 400 ℃ with AlF ₃ 3 and the charge-discharge capacity and efficiency of 4 Is improved.

Claims (15)

And a coating layer comprising Al ₂ O ₃ and LiF on the surface.
The method according to claim 1,
Wherein the thickness of the coating layer is 1 nm to 100 nm.
The method according to claim 1,
Wherein the thickness of the coating layer is 10 nm to 50 nm.
The method according to claim 1,
The lithium transition metal cathode active material according to claim 1,
Li _a M _b O ₂ (1)
In this formula,
M = Ni _x Mn _y Co _z , (0.3? X? 0.9, 0? Y? 0.45 and 0? Z? 0.4, x + y + z = 1);
a + b? 2, and 0.95? a? 1.05.
Mixing a mixed transition metal precursor and a lithium source, and firing the mixture to obtain an excess lithium-containing lithium transition metal oxide; And
Adding AlF ₃ to the excess lithium-containing lithium transition metal oxide and performing secondary firing, and coating the surface of the lithium transition metal oxide with Al ₂ O ₃ and LiF.
6. The method of claim 5,
Wherein the molar ratio of the mixed transition metal precursor to the lithium source is 1: 1.05 or more.
The method according to claim 6,
Wherein the molar ratio of the mixed transition metal precursor to the lithium source is 1: 1.05 to 1: 1.20.
6. The method of claim 5,
Wherein the amount of AlF ₃ is 0.01 to 2% by weight based on the total weight of lithium-containing transition metal oxide containing excess lithium.
6. The method of claim 5,
Wherein the primary firing is performed at 700 ° C to 1100 ° C for 5 hours to 15 hours.
6. The method of claim 5,
Wherein the secondary firing is performed at 300 ° C to 800 ° C for 2 hours to 8 hours.
11. The method of claim 10,
Wherein the secondary firing is performed at a temperature of 400 ° C to 700 ° C.
6. The method of claim 5,
Wherein the mixed transition metal precursor is MOOH or M (OH) ₂ (M = Ni _x Mn _y Co _z , 0.3? X? 0.9, 0? Y? 0.45 and 0? Z? 0.4, x + y + Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt;
6. The method of claim 5,
Wherein the lithium source is Li ₂ CO ₃ , LiOH, or a mixture thereof.
A positive electrode comprising the lithium transition metal positive electrode active material of claim 1.
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode according to Claim 14.

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