KR20180027260A - Positive active material for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery comprising a lithium metal oxide represented by chemical formula 1: Li_p(Ni_xCo_yMe_z)O_2, and to a lithium secondary battery comprising the same. In chemical formula 1, Me is at least one selected from a group consisting of Al, Mn, Mg, Ti and Zr, and the following conditions are satisfied: 0.9<=p<=1.1; 0.81<=x<=0.87; 0<y<=0.3; 0<z<=0.3; and x+y+z=1. One embodiment of the present invention is to provide the positive electrode active material for a lithium secondary battery having high capacity and excellent lifetime characteristics.

Description

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

The present invention relates to a cathode active material for a lithium secondary battery and a lithium secondary battery comprising the same.

BACKGROUND ART [0002] In recent years, miniaturization and lightening of a mobile information terminal have progressed rapidly, and a lithium secondary battery, which is a driving power source thereof, is required to have a higher capacity.

Also, as the market for hybrid vehicles or electric vehicles is expanding, researches for using lithium secondary batteries as their driving power sources or power storage sources are actively conducted.

Examples of the positive electrode active material of such a lithium secondary battery include LiCoO ₂ , LiMn ₂ O ₄ , lithium having a structure capable of intercalating lithium ions such as LiNi _{1 - x} Co _x O ₂ (0 <x <1) Oxides formed are mainly used.

One embodiment of the present invention is to provide a cathode active material for a lithium secondary battery having a high capacity and excellent lifetime characteristics.

Another embodiment of the present invention is to provide a lithium secondary battery comprising the cathode active material.

In one aspect, the present invention provides a cathode active material for a lithium secondary battery comprising a lithium metal oxide represented by the following general formula (1).

[Chemical Formula 1]

Li _p (Ni _x Co _y Me _z ) O ₂

In Formula 1, 0.9? P? 1.1, 0.81? X? 0.87, 0 <y? 0.3, 0 <z? 0.3, x + y + z = 1, Me represents Al, Mn, Mg, Ti and Zr At least one.

In another aspect, the present invention provides a lithium secondary battery comprising a positive electrode including the positive electrode active material, a negative electrode including the negative electrode active material, and an electrolyte.

The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention has excellent structural stability even when charged because it contains a compound having a high nickel content.

Therefore, the lithium secondary battery according to the present invention using the positive electrode containing the positive electrode active material can remarkably improve the life characteristics while having a high capacity.

1 schematically shows a structure of a lithium secondary battery according to an embodiment of the present invention.
2 is a graph showing a specific capacity measurement result of a lithium secondary battery according to Examples 1 and 2 and Comparative Examples 1 and 2 with respect to a voltage.
FIG. 3 shows the results of dQ / dV measurement of the voltage of the lithium secondary battery according to Examples 1 and 2 and Comparative Examples 1 and 2.
4 is an enlarged view of the dQ / dV measurement result for a voltage in the range of 4V to 4.4V in Fig.
5 shows the results of measurement of capacity retention ratios of the lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 and 2 for each cycle.
6 is an x-ray diffraction graph of a cathode active material according to Example 1. Fig.
7 is an x-ray diffraction graph of a cathode active material according to Comparative Example 1. Fig.
FIG. 8 is an enlarged view of FIG. 7 over the range of 2? = 27 degrees (degrees) to 39 degrees (degrees).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

There are several kinds of cathode active materials used in lithium secondary batteries. Among them, cathode active materials using lithium cobalt oxide, that is, LiCoO ₂ , are most widely used today. However, the cathode active material using lithium cobalt oxide causes an increase in manufacturing cost due to the ubiquitous nature and scarcity of cobalt, and thus it is difficult to supply the cathode active material with stability.

In order to solve this problem, various studies have been made to apply a substitute material for cobalt. For example, a cathode active material using one or a combination of inexpensive nickel (Ni) and manganese (Mn) instead of expensive cobalt There is an attempt to do so.

Of these, nickel (Ni) based composite oxides have been actively studied as materials capable of overcoming limitations such as cost, stability, and capacity of materials such as LiCoO ₂ , LiNiO ₂ , and Li ₂ MnO ₃ .

In this regard, the Ni-based composite oxide reacts with Ni ^{2 +} → Ni ^{4 +} + 2e to generate two electrons in a charging reaction in which one lithium atom exits, so that cobalt Co), and manganese (Mn), the capacity is increased as the content of nickel (Ni) increases.

However, when an oxide having a high nickel (Ni) content is used as a cathode active material, the amount of lithium to be eliminated at the time of the charging reaction is large as compared with the case where lithium cobalt oxide is used as a cathode active material, There is a problem that it collapses. More specifically, a high content of the nickel-containing oxide changes its crystal structure at a voltage of 4 V or more at the time of charging, and phase transition occurs from H2 to H3. Since the phase transition from H2 to H3 is partially irreversible and lithium ions which can be intercalated and deintercalated in the H3 phase structure can be reduced, as described above, when phase transition from H2 to H3 occurs, There is a problem that the life characteristic is remarkably lowered. Therefore, when an oxide having a high nickel content is used as a cathode active material, it is necessary to suppress the phase transition of the nickel-containing oxide from H2 to H3 during charging.

Accordingly, the inventors of the present invention have conducted studies to simultaneously realize high capacity and excellent lifetime characteristics while using a nickel (Ni) based composite oxide as a cathode active material for a lithium secondary battery, and as a result, found that a nickel- Is used as a cathode active material, the above-mentioned object can be achieved and an embodiment of the present disclosure is realized.

More specifically, the cathode active material for a lithium secondary battery according to one embodiment of the present invention is characterized by containing a lithium metal oxide represented by the following formula (1).

[Chemical Formula 1]

Li _p (Ni _x Co _y Me _z ) O ₂

In Formula 1, 0.9? P? 1.1, 0.81? X? 0.87, 0 <y? 0.3, 0 <z? 0.3, x + y + z = 1, Me represents Al, Mn, Mg, Ti and Zr At least one.

When a nickel-containing lithium metal oxide having a high nickel content such as the lithium metal oxide represented by the general formula (1) is used as the cathode active material, a lithium secondary battery having a high capacity can be realized.

More specifically, the content of nickel in the lithium metal oxide according to the present invention can be 0.81 or more and 0.87 or less, as can be seen from the general formula (1). More specifically, the content of nickel in Formula (1) is 0.82 or more, and may be 0.86 or less. When the content of nickel contained in the lithium metal oxide satisfies the above range, a lithium secondary battery having a high capacity and excellent lifetime characteristics can be realized.

In Formula 1, the molar ratio of Li and Ni + Co + Me may be 1.05: 1.0 to 0.95: 1.0. More specifically, the molar ratio of Li and Ni + Co + Me may be 1.03: 1.0 to 1.01: 1.0 or 1.05: 1 to 1.01: 1.0. When the molar ratio of Li and Ni + Co + Me satisfies the above-described numerical range, the content of lithium remaining on the surface of the lithium metal oxide can be reduced.

That is, the lithium metal oxide may include a lithium compound positioned on the surface of the lithium metal oxide. At this time, the content of lithium contained in the lithium compound may be 0.25 parts by weight or less, more specifically 0.05 parts by weight to 0.15 parts by weight based on 100 parts by weight of the positive electrode active material.

The lithium compound positioned on the surface of the lithium metal compound may be Li ₂ CO ₃ , LiOH or a combination thereof.

When the molar ratio of Li: (Ni + Co + Al) satisfies the above-described numerical value range, a precursor having a high Ni content is excellent in reactivity with Li and can produce a highly crystalline cathode active material. In this case, it is possible to realize a lithium secondary battery which can improve cycle life characteristics of the lithium secondary battery and exhibit excellent electrochemical characteristics.

In view of the manufacturing process and cost of the cathode active material, Me in Formula 1 is preferably Al or Mn.

The positive electrode active material of the present invention has no other diffraction peaks appearing in the range of 2θ = 25 ° (°) to 38 ° (°) other than the diffraction peak of the (101) plane in the X-ray diffraction (XRD) measurement. In other words, the lithium metal oxide of the present invention exhibits a crystal structure of R-3m, that is, a crystal structure of rhombohedral. Therefore, in X-ray diffraction (XRD) measurement, ) Diffraction peaks do not appear.

In the present specification, the X-ray diffraction measurement is a measurement using a CuK? Line as a target line. For example, Co ₃ O ₄ is formed when diffraction peaks other than the diffraction peak of the (101) plane at 2θ = 25 ° (°) to 38 ° (°) in measurement of the XRD of the cathode active material, . If the cathode active material contains impurities as described above, it is not an electrochemically active material and thus does not contribute to the capacity of the battery. Moreover, such impurities lower the migration speed of lithium ions on the surface of the positive electrode active material, which can act as a cause of increase in resistance and deteriorate capacity and cycle life characteristics of the battery.

However, it can be understood that the positive electrode active material according to the present invention will exhibit better capacity and cycle life characteristics since no impurities, i.e., Co ₃ O ₄ , are produced as described above.

The cathode active material according to one embodiment of the present invention described above can be manufactured by a general cathode active material manufacturing process widely known in the art and will be briefly described.

A nickel precursor and a lithium precursor are mixed to prepare a mixture. At this time, the mixing ratio of the nickel precursor and the lithium precursor can be appropriately controlled so as to obtain the compound of Formula 1 above.

The lithium precursor may be, for example, lithium acetate, lithium nitrate, lithium hydroxide, lithium carbonate, lithium acetate, hydrates thereof, or combinations thereof.

The nickel precursor may be, for example, nickel acetate, nickel nitrate, nickel carbonate, hydrates thereof, or a combination thereof.

The mixture is firstly fired to produce a first fired product. The mixing process can be performed by a mechanical mixing process such as ball milling or the like.

The first firing process may be performed at 650 ° C to 850 ° C, where the heat treatment time may be 10 hours to 30 hours. The heat treatment may be performed in an oxygen (O ₂ ) atmosphere.

Thereafter, the primary sintered body is pulverized and pulverized, and then subjected to a cleaning process to reduce the residual amount of lithium contained in the lithium compound on the surface of the primary sintered body.

The cleaning process can be carried out by mixing cleaning water such as distilled water and powdered primary firing at a ratio of 1: 1 to 1: 5.

Next, the first sintered material having undergone the washing step is dehydrated and then secondarily sintered to produce a second sintered material. The secondary firing process may be performed at 650 ° C to 850 ° C, where the heat treatment time may be 10 hours to 30 hours. The heat treatment may be performed in an oxygen (O ₂ ) atmosphere.

Next, the secondary sintered material is pulverized to prepare a cathode active material.

Hereinafter, a lithium secondary battery according to another embodiment of the present invention will be described.

1 schematically shows a structure of a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment may include a case 50 in which an electrode assembly and an electrode assembly are accommodated, and a sealing member 40 that seals the case 50.

The electrode assembly includes a positive electrode 10 including the positive electrode active material described above, a negative electrode 20 including a negative active material, and a separator 30 disposed between the positive electrode 10 and the negative electrode 20. The anode 10, the cathode 20 and the separator 30 may be impregnated with an electrolyte solution (not shown).

The electrode assembly may be formed by winding a separator 30 between the anode 10 and the cathode 20. In Fig. 1, the wound electrode assembly is assembled for convenience, but the contents of the present invention are not limited thereto. For example, the electrode assembly may have a structure in which a plurality of sheet-shaped positive electrodes and negative electrodes are alternately stacked with a separator interposed therebetween.

The anode 10 includes a cathode active material layer and a current collector for supporting the cathode active material. In the cathode active material layer, the content of the cathode active material may be 90 wt% to 98 wt% with respect to the total weight of the cathode active material layer.

In one embodiment of the present invention, the cathode active material layer may further include a binder and a conductive material. At this time, the content of the binder and the conductive material may be 1 wt% to 5 wt% with respect to the total weight of the cathode active material layer.

The binder serves to adhere the positive electrode active materials to each other and to adhere the positive electrode active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl pyrrolidone But are not limited to, water, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon .

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used for the battery without causing any chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof.

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

The cathode 20 includes a current collector and a negative electrode active material layer including a negative electrode active material formed on the current collector.

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.

As a material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium ion secondary batteries can be used as the carbonaceous material. Typical examples thereof include crystalline carbon , Amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fibrous type. Examples of the amorphous carbon include soft carbon or hard carbon hard carbon, mesophase pitch carbide, fired coke, and the like.

As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used.

As the material capable of being doped and dedoped into lithium, Si, Si-C composite, SiO _x (0 <x <2), Si-Q alloy (Q is an alkali metal, an alkaline earth metal, a Group 13 element, Sn, SnO ₂ , Sn-R alloy (R is an element selected from the group consisting of Group 15 elements, Group 16 elements, transition metals, rare earth elements and combinations thereof, An element selected from the group consisting of a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn) SiO ₂ may be mixed and used. The element Q and the element R may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and lithium titanium oxide.

The content of the negative electrode active material in the negative electrode active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative electrode active material layer.

In one embodiment of the present invention, the negative electrode active material layer includes a binder, and may further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% with respect to the total weight of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material may be used in an amount of 90 to 98 wt%, the binder may be used in an amount of 1 to 5 wt%, and the conductive material may be used in an amount of 1 to 5 wt%.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include a rubber-based binder or a polymeric resin binder. The rubber binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluorine rubber and combinations thereof. The polymeric resin binder may be selected from the group consisting of polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, Polyvinyl pyrrolidone, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further contained as a thickener. As the cellulose-based compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, alkali metal salts thereof or the like may be used in combination. As the alkali metal, Na, K or Li can be used. The content of the thickener may be 0.1 part by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used for the battery without causing any chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The collector may be selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foil, a polymer substrate coated with a conductive metal, and a combination thereof.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol, or aprotic solvent.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, caprolactone, Etc. may be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. As the ketone-based solvent, cyclohexanone and the like can be used. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, , A double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used .

The organic solvent may be used singly or in a mixture of one or more. If one or more of the organic solvents are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired battery, and this may be widely understood by those skilled in the art have.

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1: 1 to 1: 9, the performance of the electrolytic solution may be excellent.

The organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1: 1 to 30: 1.

The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound represented by the following formula (2).

(2)

Wherein R ₁ to R ₆ are the same or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and a combination thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, Examples of the solvent include 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4- Dichlorotoluene, 2,3-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3-dichlorotoluene, 3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2 , 5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by the following formula (3) as a life improving additive in order to improve battery life.

(3)

(Wherein R ₇ and R ₈ are the same or different and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and an alkyl group having 1 to 5 fluorinated carbon atoms , At least one of R ₇ and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and an alkyl group having 1 to 5 fluorinated carbon atoms, provided that R ₇ and R ₈ both It is not hydrogen.)

Representative examples of the ethylenic carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. . When such a life improving additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the anode and the cathode. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiN (SO 2 C 2 F 5) 2, Li (CF 3 SO 2) 2 N, LiN (SO 3 C 2 F 5) 2, _{LiC 4 F 9 SO 3, LiClO} 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) ( where, x and y are natural numbers, e.g. 1 to 20), LiCl, LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate: LiBOB) The concentration of the lithium salt is preferably in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, Lithium ions can move effectively.

Depending on the type of the lithium secondary battery, as shown in Fig. 1, the separator 30 may exist between the positive electrode and the negative electrode. As the separator 30, polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof may be used. The separator may be a polyethylene / polypropylene double layer separator, a polyethylene / polypropylene / polyethylene triple layer separator, a polypropylene / polyethylene / Polypropylene three-layer separator, or the like can be used.

Hereinafter, the present invention will be described in detail with reference to examples.

Example  One

(1) Preparation of cathode active material

Ni _{0 . 85} Co _{0 . 14} Al _{0 .01} (OH) ₂ and LiOH were mixed so that the molar ratio of Li: (Ni + Co + Al) in the final product was 1.02: 1.0. Next, the mixture was fired at 740 ° C in an O ₂ atmosphere for 21 hours to obtain a first fired product.

Thereafter, the primary fired product is pulverized through a pulverizing process, and then a cleaning process is performed to remove residual lithium on the surface of the primary fired product.

The cleaning process was performed so that the weight ratio of the washing water and the powdered primary sintered material was 1: 1, and the residual lithium content on the surface of the primary sintered material subjected to the washing process was 0.10 wt%.

After the washed primary fired product was subjected to a dehydration process using a filter press, a secondary firing process was performed. The secondary firing was carried out in an atmosphere of O ₂ at 720 ° C, followed by pulverization, thereby preparing a cathode active material represented by Li (Ni _0.85 Co _0.14 Al _0.01 ) O ₂ . The Li: (Ni + Co + Al) molar ratio in the prepared positive electrode active material was 1: 1.

(2) Production of lithium secondary battery

94 wt% of the cathode active material prepared in (1), 3 wt% of polyvinylidene fluoride binder and 3 wt% of Ketjen black conductive material were mixed in N-methylpyrrolidone solvent to prepare a cathode active material composition. The positive electrode active material composition was applied to an Al current collector to prepare a positive electrode.

A coin-shaped half-cell was fabricated by a conventional method using an anode, a lithium metal counter electrode, and an electrolyte. A mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 50:50) in which 1.0 M LiPF ₆ was dissolved was used as the electrolyte.

Example  2 and Comparative Example  1 to 2

The same as in Example 1 except that the nickel content of the oxide contained in the produced cathode active material, the molar ratio of Li: (Ni + Co + Al), and the content of lithium remaining on the surface were changed as shown in Table 1 To prepare a cathode active material.

Thereafter, a positive electrode was prepared in the same manner as in Example 1, and a lithium secondary battery was produced.

division Nickel content Li: (Ni + Co + Al) molar ratio Example 1 84 1.02: 1 Example 2 85 1.01: 1 Comparative Example 1 80 1: 1 Comparative Example 2 88 0.98: 1

Experimental Example  One - Charging and discharging  Characterization

The lithium secondary batteries produced according to Examples 1 and 2 and Comparative Examples 1 and 2 were charged and discharged at a current of 0.2 C rate within a range of 2.8 V to 4.4 V at 25 캜 to evaluate initial charging and discharging characteristics. Table 2 shows the initial discharge capacity, and FIG. 2 shows the initial charge / discharge capacity. 3 shows dQ / dV measurement results in the first cycle, and FIG. 4 shows an enlarged view of dQ / dV measurement results with respect to a voltage of 4V to 4.4V in FIG.

Experimental Example  2 - Measurement of capacity retention rate

The lithium secondary batteries produced according to Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to charging and discharging 50 times at 25 ° C within a range of 2.8 V to 4.4 V at 0.2 C to measure the discharge capacity. Further, the capacity retention rate was calculated by calculating the discharge capacity ratio at 50 times to one discharge capacity, and this was defined as the cycle life.

The results are shown in Table 2 and FIG.

division Initial discharge capacity
[mAh / g] dQ / dV intensity 50 ^th / 1 ^st
Capacity retention rate (%) Example 1 204 260 92.0 Example 2 205 375 88.8 Comparative Example 1 195 190 96.7 Comparative Example 2 207 500 83.5

Referring to Table 2 and FIG. 2 to FIG. 4, it can be seen that the cathode active material according to one embodiment of the present invention can be manufactured according to Examples 1 and 2 including a cathode active material having a nickel content of 0.81 or more and 0.87 or less It can be seen that the phase transition from H2 to H3 is suppressed at a dQ / dV intensity of 400 or less at 4.0 V or more.

However, it was confirmed that the lithium secondary battery of Comparative Example 1 including the cathode active material having a nickel content of less than 0.81 had a low initial discharge capacity. Also, in the case of the lithium secondary battery according to Comparative Example 2 containing a positive electrode active material having a nickel content of more than 0.87, the dQ / dV strength was measured at a value of 4.0 V or more, and it was confirmed that the phase transition from H2 to H3 occurred.

Referring to FIG. 5, it was confirmed that, in the 50th cycle, the lithium secondary batteries according to Examples 1 and 2 exhibited excellent lifespan characteristics as compared with the lithium secondary batteries according to Comparative Examples 1 and 2.

Experimental Example  3

X-ray diffraction (XRD) analysis using Cu-K? Was performed on the cathode active material produced according to Example 1 and Comparative Example 1, and the results are shown in FIGS.

Referring to FIG. 6, the x-ray spectrum confirmed that the cathode active material according to Example 1 had no diffraction peaks other than the (101) plane diffraction peak in the range of 25 ° to 38 ° (°) there was.

Therefore, it was confirmed that the positive electrode active material according to Example 1 had no additive other than the R-3m crystal structure, that is, an impurity.

8, which is an enlarged view of the range of 2? = 27 degrees (inclusive) to 39 degrees (inclusive) in FIG. 7 and FIG. 7, the cathode active material according to Comparative Example 1 has an angle of 25 degrees °) of the (101) plane in addition to the diffraction peak for Co ₃ O ₄ .

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, And all changes to the scope that are deemed to be valid.

101: core
102: Functional layer
100: Lithium secondary battery
10: anode
20: cathode
30: Separator
40: electrode assembly
50: Case

Claims (8)

1. A cathode active material for a lithium secondary battery comprising a lithium metal oxide represented by the following formula (1).
[Chemical Formula 1]
Li _p (Ni _x Co _y Me _z ) O ₂
X + y + z = 1, 0 < y < 0.3, 0 &
Me is at least one of Al, Mn, Mg, Ti and Zr.) The method according to claim 1,
Wherein the molar ratio of Li and Ni + Co + Me in the formula 1 is 1.05: 1.0 to 0.95: 1.0. The method according to claim 1,
In Formula 1, Me is Al or Mn, which is a cathode active material for a lithium secondary battery. The method according to claim 1,
Wherein the positive electrode active material has no other diffraction peak appearing in the range of 2? = 25 degrees to 38 degrees (? 101) other than the diffraction peak of the (101) plane in X-ray diffraction (XRD) . The method according to claim 1,
Wherein the lithium metal oxide comprises a lithium compound positioned on the surface of the lithium metal oxide,
Wherein the content of lithium contained in the lithium compound is 0.25 parts by weight or less based on 100 parts by weight of the positive electrode active material. 6. The method of claim 5,
Wherein the content of lithium contained in the lithium compound is 0.05 to 0.15 parts by weight based on 100 parts by weight of the lithium metal oxide. 6. The method of claim 5,
Wherein the lithium compound includes Li ₂ CO ₃ , LiOH, or a combination thereof. A positive electrode comprising the positive electrode active material of any one of claims 1 to 7;
A negative electrode comprising a negative electrode active material; And
Electrolyte
&Lt; / RTI &gt;

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