WO2018048156A1 - Cathode active material for lithium secondary battery, and lithium secondary battery comprising same - Google Patents

Abstract

The present disclosure relates to a cathode active material for a lithium secondary battery, and a lithium secondary battery comprising same, the cathode active material comprising a lithium metal oxide represented by the following chemical formula 1: [chemical formula 1] Li_p(Ni_xCo_yMe_z)O₂, wherein 0.9 ≤ p ≤ 1.1, 0.81 ≤ x ≤ 0.87, 0 < y ≤ 0.3, 0 < z ≤ 0.3, x + y + z =1, and Me is at least one of Al, Mn, Mg, Ti and Zr.

Description

Cathode active material for lithium secondary battery and lithium secondary battery comprising same

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

In recent years, the miniaturization and weight reduction of mobile information terminals have progressed rapidly, and a higher capacity has also been required for a lithium secondary battery as a driving power source.

In addition, as the hybrid vehicle or electric vehicle market expands, studies for using lithium secondary batteries as driving power or power storage power sources are being actively conducted.

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

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

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

In one aspect, the present disclosure provides a cathode active material for a lithium secondary battery including a lithium metal oxide represented by the following Formula 1.

[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, and Me is selected from Al, Mn, Mg, Ti, and Zr. At least one.

In another aspect, the present disclosure provides a lithium secondary battery including a cathode including the cathode active material, an anode including an anode active material, and an electrolyte.

Since the positive electrode active material for a rechargeable lithium battery according to one embodiment of the present disclosure includes a compound having a high nickel content, even when charged, the structural stability is excellent.

Therefore, the lithium secondary battery according to the present invention to which the cathode including the cathode active material is applied may significantly improve life characteristics while having a high capacity.

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

2 is a specific capacity measurement result of the voltage of the lithium secondary battery according to Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 3 shows dQ / dV measurement results of voltages of lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

4 is an enlarged view of a dQ / dV measurement result for a voltage in the range of 4V to 4.4V in FIG. 3.

5 is a result of measuring the capacity retention rate of each lithium secondary battery according to Examples 1 to 2 and Comparative Examples 1 to 2 by cycle.

6 shows an x-ray diffraction graph of the cathode active material according to Example 1. FIG.

7 shows an x-ray diffraction graph of the cathode active material according to Comparative Example 1. FIG.

FIG. 8 is an enlarged view of a range of 2θ = 27 degrees (°) to 39 degrees (°) in FIG. 7.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In addition, throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding the other components unless otherwise stated.

There are several kinds of positive electrode active materials used in a lithium secondary battery, and among them, a positive electrode active material using lithium cobalt oxide, that is, LiCoO ₂ is most widely used at present. However, a positive electrode active material using lithium cobalt oxide causes an increase in manufacturing cost due to cobalt resource ubiquity and scarcity, and it is always difficult to provide a stable supply.

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

Among these, nickel (Ni) -based composite oxide is a material capable of overcoming the limitations of cost, stability, and capacity of materials such as LiCoO ₂ , LiNiO ₂ , Li ₂ MnO _3, and the like, and active researches have been conducted recently.

In this regard, the nickel (Ni) -based composite oxide reacts with Ni ^{2 +} → Ni ^{4 +} + 2e to generate two electrons during a charging reaction in which one lithium atom escapes, thereby generating only one electron. Compared with other elements such as Co) and manganese (Mn), the capacity increases as the nickel (Ni) content increases.

However, when the oxide having a high nickel (Ni) content is used as the positive electrode active material, the crystal structure of the nickel-containing oxide is more easily compared to the case where lithium cobalt oxide is used as the positive electrode active material. There is a problem of collapse. More specifically, a high content of nickel-containing oxide changes the crystal structure at a voltage of 4V or more during charging to cause a phase transition from H2 to H3. Since the phase transition from H2 to H3 is partially irreversible and the lithium ions that can be intercalated and deintercalated in the H3 phase structure can be reduced, as described above, when the phase transition from H2 to H3 occurs, There is a problem that the life characteristics are significantly reduced. Therefore, when an oxide having a high nickel content is used as the positive electrode active material, it is necessary to suppress the phase transition of the nickel-containing oxide from H2 to H3 during charging.

Therefore, the inventors of the present invention have repeatedly studied to simultaneously realize high capacity and excellent life characteristics while using nickel (Ni) -based composite oxide as a cathode active material for a lithium secondary battery, and have a nickel-containing oxide containing nickel (Ni) in a specific content. When using as a positive electrode active material it was found that the above object can be achieved and implemented an embodiment of the present disclosure.

More specifically, the cathode active material for a lithium secondary battery according to an embodiment of the present disclosure is characterized by including a lithium metal oxide represented by the following Chemical Formula 1.

[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, and Me is selected from Al, Mn, Mg, Ti, and Zr. At least one.

When using a nickel-containing lithium metal oxide having a high nickel content as a positive electrode active material, such as the lithium metal oxide represented by Formula 1, it is possible to implement a lithium secondary battery having a high capacity.

More specifically, the content of nickel in the lithium metal oxide according to the present disclosure may be 0.81 or more and 0.87 or less, as can be seen in Formula 1. More specifically, the content of nickel in Formula 1 may be 0.82 or more and 0.86 or less. When the nickel content included in the lithium metal oxide satisfies the above range, a lithium secondary battery having high capacity and excellent life characteristics may be implemented.

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 numerical range, the content of lithium remaining on the surface of the lithium metal oxide may be reduced.

That is, the lithium metal oxide may include a lithium compound located on the surface of the lithium metal oxide. In this case, the lithium content 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 located 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-mentioned numerical range, it is possible to prepare a cathode active material having high reactivity with Li when the precursor having high Ni content is excellent. In this case, the cycle life characteristics of the lithium secondary battery may be improved, and a lithium secondary battery exhibiting excellent electrochemical characteristics may be implemented.

In addition, Me of Formula 1 is preferably Al or Mn in consideration of the manufacturing process and cost of the positive electrode active material.

The positive electrode active material of the present substrate does not have other diffraction peaks appearing other than the diffraction peak of the (101) plane in the range of 2θ = 25 degrees (°) to 38 degrees (°) when measured by X-ray diffraction (XRD). In other words, the lithium metal oxide of the present disclosure exhibits an R-3m crystal structure, that is, a crystalline structure of a rhombohedral, and thus, when measuring X-ray diffraction (XRD), the diffraction peak and (101) plane of (003) plane are measured. No other additional phase appears between the diffraction peaks of the plane.

In the present specification, the X-ray diffraction measurement is measured using a CuKα ray as a target line. When XRD measurement of the positive electrode active material shows a diffraction peak other than the diffraction peak of the (101) plane at 2θ = 25 degrees (°) to 38 degrees (°), that is, an additional phase, impurities, such as Co ₃ O _4, are formed. . When impurities are included in the cathode active material as described above, they do not contribute to the capacity of the battery because they are not electrochemically activated materials. In addition, such an impurity may act as a cause of an increase in resistance since the rate of movement of lithium ions on the surface of the positive electrode active material is reduced, and the capacity and cycle life characteristics of the battery may be lowered, which is not appropriate.

However, it can be seen that the cathode active material according to the present invention will exhibit more excellent capacity and cycle life characteristics because impurities, that is, Co ₃ O _4, etc. are not generated as described above.

The cathode active material according to the exemplary embodiment of the present disclosure described above may be manufactured by a general cathode active material manufacturing process well known in the art, and will be briefly described.

The mixture is prepared by mixing the nickel precursor and the lithium precursor. At this time, the mixing ratio of the nickel precursor and the lithium precursor can be appropriately adjusted so that the compound of Formula 1 is obtained.

Examples of the lithium precursors include lithium acetate, lithium nitrate, lithium hydroxide, lithium carbonate, lithium acetate, hydrates thereof, and combinations thereof.

Examples of the nickel precursors include nickel acetate, nickel nitrate, nickel carbonate, hydrates thereof, and combinations thereof.

The mixture is first calcined to produce a primary calcined product. The mixing step can be carried out by a mechanical mixing step such as, for example, ball milling.

The primary firing process may be carried out at 650 ℃ to 850 ℃, the heat treatment time may be 10 hours to 30 hours. The heat treatment step may be carried out in an oxygen (O ₂ ) atmosphere.

Thereafter, the primary fired material is pulverized and powdered, followed by a washing process to reduce the amount of lithium contained in the lithium compound on the surface of the primary fired product.

For example, the washing process may be performed by mixing the washing water such as distilled water and the powdered primary fired product in a ratio of 1: 1 to 1: 5.

Next, after the dehydrated primary calcined product is dehydrated, secondary calcined product is manufactured. Secondary firing process may be carried out at 650 ℃ to 850 ℃, wherein the heat treatment time may be 10 hours to 30 hours. The heat treatment step may be carried out in an oxygen (O ₂ ) atmosphere.

Next, the secondary fired material is ground to prepare a cathode active material.

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

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

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment may include an electrode assembly, a case 50 in which the electrode assembly is accommodated, and a sealing member 40 sealing 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 electrode active material, and a separator 30 disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown).

The electrode assembly may have a shape in which the electrode assembly is sandwiched between the positive electrode 10 and the negative electrode 20 via a separator 30. In FIG. 1, a wound electrode assembly is assembled for convenience, but the contents of the present disclosure are not limited thereto. For example, the electrode assembly may have a structure in which a plurality of anodes and cathodes having a sheet shape are alternately stacked with separators interposed therebetween.

The positive electrode 10 includes a positive electrode active material layer and a current collector supporting the positive electrode active material. In the cathode active material layer, the content of the cathode active material may be 90% by weight to 98% by weight based on the total weight of the cathode active material layer.

In one embodiment of the present invention, the positive electrode active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% by weight to 5% by weight based on the total weight of the positive electrode active material layer, respectively.

The binder adheres the positive electrode active material particles to each other well, and also serves to adhere the positive electrode active material to the current collector well. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrroli Don, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto. .

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electron conductive material without causing chemical change in the battery. 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 materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives; Or a conductive material containing a mixture of these.

Al may be used as the current collector, but is not limited thereto.

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

The anode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material doped and undoped with lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon. , Amorphous carbon or these can be used together. Examples of the crystalline carbon include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, calcined coke, and the like.

Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metals selected may be used.

The lithium doped and undoped materials include Si, Si-C composites, SiO _x (0 <x <2), Si-Q alloy (Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, An element selected from the group consisting of Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, not Si), Sn, SnO ₂ , Sn-R alloys (wherein R is an alkali metal, an alkaline earth metal, Element selected from the group consisting of Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and not Sn). SiO ₂ can also be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, One selected from the group consisting of S, Se, Te, Po, and a combination thereof can be used.

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

The content of the negative electrode active material in the negative electrode active material layer may be 95% by weight to 99% by weight 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 optionally may further include a conductive material. The content of the binder in the negative electrode active material layer may be 1% by weight to 5% by weight based on the total weight of the negative electrode active material layer. In addition, when the conductive material is further included, 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material may be used.

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

The water-insoluble binder includes polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

The water-soluble binder may be a rubber binder or a polymer resin binder. The rubber-based 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 polymer resin binder may be polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, Ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When using a water-soluble binder as the negative electrode binder, it may further include a cellulose-based compound that can impart viscosity as a thickener. As this cellulose type compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, these alkali metal salts, etc. can be used in mixture of 1 or more types. Na, K or Li may be used as the alkali metal. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electron conductive material without causing chemical change in the battery. 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 materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives; Or a conductive material containing a mixture thereof.

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

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used. The ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, and caprolactone. And the like can be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent. In addition, cyclohexanone may be used as the ketone solvent. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent, and the aprotic solvent may be R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms. Nitriles such as a double bond aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, and the like can be used. .

The organic solvents may be used alone or in combination of one or more, and the mixing ratio in the case of mixing one or more may be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art. have.

In addition, in the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of 1: 1 to 1: 9, so that the performance of the electrolyte may be excellent.

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

As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound of Formula 2 may be used.

[Formula 2]

(In Formula 2, R _{One To} R _{6 It} is the same as or different from each other and selected from the group consisting of hydrogen, halogen, alkyl group of 1 to 10 carbon atoms, haloalkyl group and combinations thereof.)

Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-dioodobenzene, 1,3-dioiobenzene, 1,4-dioiobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-dioodotoluene, 2,4-diaodotoluene, 2 , 5-diaodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include vinylene carbonate or an ethylene-based carbonate compound represented by Chemical Formula 3 as a life improving additive to improve battery life.

[Formula 3]

(In Formula 3, R ₇ and R ₈ are the same as or different from each other, 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 a fluorinated C1-5 alkyl group, provided that both R ₇ and R ₈ are both Not hydrogen.)

Representative examples of the ethylene-based carbonate compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. Can be mentioned. In the case of further using such life improving additives, the amount thereof can be properly adjusted.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts 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, for example Supporting one or more selected from the group consisting of LiCl, LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB)); It is preferable to use the concentration of lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, Lithium ions can move effectively.

Depending on the type of 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 two or more multilayer films thereof may be used, and polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene Of course, a mixed multilayer film such as a polypropylene three-layer separator can be used.

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

Example  One

(1) Preparation of Positive Electrode Active Material

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

Thereafter, the primary calcined product is powdered through a pulverization process and a cleaning process is performed to remove residual lithium on the surface of the primary calcined product.

The washing process was performed such that the weight ratio of the washing water and the powdered primary fired product was 1: 1.

After the cleaning was completed, the first fired product was subjected to a dehydration process using a filter press, followed by a second fire process. Secondary firing was performed in an atmosphere of O ₂ at 720 ° C., followed by a pulverization process, to represent Li (Ni _0.85 Co _0.14 Al _0.01 ) O ₂ , to prepare a cathode active material having a lithium content of 0.10 wt%. It was.

(2) Preparation of a Lithium Secondary Battery

A positive electrode active material composition was prepared by mixing 94% by weight of the positive electrode active material prepared in (1), 3% by weight of polyvinylidene fluoride binder, and 3% by weight of Ketjen black conductive material in an N-methylpyrrolidone solvent. This positive electrode active material composition was applied to an Al current collector to prepare a positive electrode.

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

Example  2 and Comparative example  1 to 2

Nickel content of the oxide included in the prepared positive electrode active material, the molar ratio of Li: (Ni + Co + Al) and the amount of lithium remaining on the surface is the same as in Example 1 except that it is adjusted to be adjusted as shown in Table 1 below. A positive electrode active material was prepared by the method.

Then, after manufacturing a positive electrode in the same manner as in Example 1, a lithium secondary battery was produced.

division	Nickel content	Li: (Ni + Co + Al) molar ratio	Lithium content remaining on the active material surface (wt%)
Example 1	84	1.02: 1	0.10
Example 2	85	1.01: 1	0.095
Comparative Example 1	80	1: 1	0.09
Comparative Example 2	88	0.98: 1	0.085

Experimental Example  One - Charging and discharging  Property measurement

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

Experimental Example  2-capacity retention measurement

The lithium secondary batteries prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 were charged and discharged at 0.2 ° C. 50 times in a range of 2.8 V to 4.4 V at 25 ° C., and the discharge capacity was measured. In addition, the capacity retention ratio was calculated by calculating the ratio of the 50th discharge capacity to the onetime discharge capacity, which was defined as the cycle life.

The results are shown in Table 2 and FIG. 5.

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 Figures 2 to 4, the positive electrode active material according to an embodiment of the present disclosure prepared according to Examples 1 and 2 containing a positive electrode active material content of nickel is 0.81 or more and satisfy the range of 0.87 or less In the case of the lithium secondary battery, it is understood that the phase transition from H2 to H3 is suppressed because the dQ / dV intensity is 400 or less at 4.0 V or more while the initial charge and discharge capacity is excellent.

However, the lithium secondary battery according to Comparative Example 1 including the positive electrode active material having a nickel content of less than 0.81 was found to have a low initial discharge capacity. In addition, in the case of the lithium secondary battery according to Comparative Example 2 including the positive electrode active material having a nickel content of more than 0.87, dQ / dV intensity was measured to be high at 4.0 V or higher, and it was confirmed that a phase transition from H2 to H3 occurred.

In addition, referring to FIG. 5, in the 50th cycle, when compared with the lithium secondary batteries according to Comparative Examples 1 and 2, it was confirmed that the lithium secondary batteries according to Examples 1 and 2 exhibited excellent life characteristics.

Experimental Example  3

X-ray diffraction (XRD) analysis using Cu-Kα was performed on the cathode active materials prepared according to Example 1 and Comparative Example 1, and the results are shown in FIGS. 6 to 8.

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

Therefore, in the positive electrode active material according to Example 1, it was confirmed that additional phases other than the R-3m crystal structure, that is, no impurities were present.

However, referring to FIG. 8, which is an enlarged view of 2θ = 27 degrees (°) to 39 degrees (°) of FIGS. 7 and 7, the cathode active material according to Comparative Example 1 is 25 degrees (°) to 38 degrees ( It was confirmed that the diffraction peak for Co ₃ O ₄ in addition to the diffraction peak of the (101) plane in the range (°).

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and easily changed and equalized by those skilled in the art from the embodiments of the present invention. It includes all changes to the extent deemed acceptable.

[Description of the code]

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.

   [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 is at least one of Al, Mn, Mg, Ti and Zr.)
2. The method of claim 1,

   In Formula 1, the molar ratio of the Li and the Ni + Co + Me is 1.05: 1.0 to 0.95: 1.0 positive electrode active material for a lithium secondary battery.
3. The method of claim 1,

   In Formula 1, Me is Al or Mn positive electrode active material for a lithium secondary battery.
4. The method of claim 1,

   The cathode active material does not have another diffraction peak appearing outside the diffraction peak of the (101) plane in the range of 2θ = 25 degrees (°) to 38 degrees (°) when measured by X-ray diffraction (XRD). .
5. The method of claim 1,

   The lithium metal oxide includes a lithium compound located on the surface of the lithium metal oxide,

   The lithium content of the lithium compound is 0.25 part by weight or less based on 100 parts by weight of the positive electrode active material.
6. The method of claim 5,

   The lithium content in the lithium compound is 0.05 part by weight to 0.15 part by weight based on 100 parts by weight of the lithium metal oxide.
7. The method of claim 5,

   The lithium compound is a lithium secondary battery positive electrode active material containing Li ₂ CO ₃ , LiOH or a combination thereof.
8. A positive electrode comprising the positive electrode active material of any one of claims 1 to 7;

   A negative electrode including a negative electrode active material; And

   Electrolyte

   Lithium secondary battery comprising a.

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