WO2016137287A1 - Cathode active material, cathode comprising same, and lithium secondary battery - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery comprising a lithium nickel-manganese-cobalt oxide represented by chemical formula 1. The lithium nickel-manganese-cobalt oxide included in the cathode active material according to the present invention contains nickel of which the content is greater than the content of manganese, thereby suppressing generation of Ni²⁺ and preventing degradation of electrochemical performance caused if Ni²⁺ moves to a lithium layer. Also, it is possible to appropriately adjust and achieve an increase in output and high capacity, if necessary, by appropriately adjusting the content of manganese and cobalt. Thus, the cathode active material can be usefully used in the manufacture of a cathode for a lithium secondary battery, and the manufacture of a lithium secondary battery comprising the same.

Description

Positive electrode active material, positive electrode and lithium secondary battery comprising same

[Cross-cited with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2015-0028378 dated February 27, 2015, and all contents disclosed in the literature of that Korean patent application are incorporated as part of this specification.

[Technical Field]

The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery capable of achieving high output and high capacity.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

Also, as interest in environmental issues has increased recently, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, There is a lot of research on the back.

Such electric vehicles (EVs) and hybrid electric vehicles (HEVs) use nickel-metal hydride (Ni-MH) secondary batteries or lithium secondary batteries with high energy density, high discharge voltage, and output stability as power sources. When used in electric vehicles, it must be able to be used for 10 years or more under severe conditions as well as high energy density and high output in a short time. Therefore, superior safety and long life characteristics are inevitably superior to conventional small lithium secondary batteries. Is required. In addition, secondary batteries used in electric vehicles (EVs) and hybrid electric vehicles (HEVs) require excellent rate characteristics and power characteristics according to vehicle operating conditions.

Currently, the positive electrode active material of a lithium ion secondary battery includes a lithium-containing cobalt oxide such as LiCoO ₂ having a layered structure, a lithium-containing nickel oxide such as LiNiO ₂ having a layered structure, and a LiMn ₂ O _{4 having a} spinel crystal structure. Lithium-containing manganese oxide such as is used.

LiCoO ₂ is widely used because of its excellent physical properties such as excellent cycle characteristics, but it is low in safety and has a limitation in mass use as a power source in electric vehicles such as electric vehicles due to price problems due to resource limitations of cobalt as a raw material. . In addition, LiNiO ₂ is difficult to apply to the actual mass production process at a reasonable cost, due to the characteristics of the manufacturing method.

Meanwhile, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have a lot of interest as a cathode active material that can replace LiCoO ₂ because of the advantage of using abundant raw materials and environmentally friendly manganese. It also has the disadvantage of poor cycle characteristics. Specifically, LiMnO ₂ has a disadvantage that the initial capacity is small, dozens of charge and discharge cycles are required until a certain capacity is reached. In addition, LiMn ₂ O ₄ has a disadvantage in that the capacity deterioration is serious as the cycle continues, and particularly, the cycle characteristics are rapidly deteriorated due to decomposition of the electrolyte, elution of manganese, and the like at a high temperature of 50 ° C. or higher.

On the other hand, LiNiO ₂ based positive electrode active material has the disadvantage of a sudden phase transition of the crystal structure according to the volume change accompanying the charge and discharge cycle, and the stability is sharply lowered when exposed to air and moisture, but is cheaper than the cobalt oxide When charged to 4.3 V, it has the advantage of showing high discharge capacity.

In order to solve the shortcomings of the LiNiO ₂ based positive electrode active material, a lithium transition metal oxide in which a part of nickel is replaced with another transition metal such as manganese and cobalt has been proposed. For example, nickel-manganese and nickel-cobalt-manganese have been proposed. Attempts and studies have been made to use lithium oxide mixed 1: 1 or 1: 1: 1 in positive electrode active materials.

The positive electrode active material prepared by mixing nickel, cobalt or manganese has improved overall physical properties compared to the battery prepared by using the transition metals separately, but still needs improvement in terms of high rate characteristics, and the equivalent of nickel and manganese In the case of forming, there is a problem that Ni ^{2 +} formed by Mn ^{4 +} ions induces the formation of Ni ^{2 +} ions moves to the Li site, thereby lowering the electrochemical performance.

Accordingly, there is a need to develop a lithium nickel-manganese-cobalt-based composite oxide having a layered structure as an active material having excellent battery performance balance, overcoming or minimizing defects of each positive electrode active material.

An object of the present invention is to provide a cathode active material for a lithium secondary battery that can achieve a high output and improved output by adjusting the content of manganese and cobalt.

Another object of the present invention to provide a cathode for a lithium secondary battery containing the cathode active material.

Still another object of the present invention is to provide a lithium secondary battery including the cathode for a lithium secondary battery.

In accordance with the above object, the present invention provides a cathode active material for a lithium secondary battery having the following configuration.

(1) A cathode active material for a lithium secondary battery containing lithium nickel-manganese-cobalt oxide represented by the following formula (1):

[Formula 1]

Li _a Ni _x Mn _y Co _z O ₂

In Chemical Formula 1,

1≤a≤1.2, x = 1-y-z, 0 <y <1, 0 <z <1,

x> y

z = ny or y = nz and n> 1.

(2) The positive electrode active material for lithium secondary batteries according to (1), wherein x has a value of 0.4 ≦ x ≦ 0.95.

3, the lithium-nickel-manganese-of the nickel containing cobalt oxide, a lithium secondary battery positive electrode according to (1) or (2) the amount of nickel corresponding to the manganese content in the form of Ni ^{2 +} Active material.

4, the lithium nickel-manganese-of the nickel containing cobalt oxide, a lithium secondary battery positive electrode according to (3) to the amount of nickel in excess of the amount corresponding to the manganese content in the form of Ni ^{3 +} Active material.

(5) The positive electrode active material for lithium secondary batteries according to any one of (1) to (4), wherein the Ni has an average oxidation number greater than +2.

(6) The positive electrode active material for lithium secondary batteries according to any one of (1) to (5), wherein the average oxidation number of Ni, Mn, and Co except for Li exceeds 3.0.

(7) the lithium nickel-manganese-cobalt oxide comprises a transition metal-oxide layer (MO layer) containing a transition metal and a Li-oxide layer (reversible lithium layer) containing lithium, wherein the MO layer is Ni ^{+ 2} and Ni ^{+ 3,} and containing, the Ni ^{2 +} part of cathode active material for a lithium secondary battery according to any one of (1) to (6), which is inserted into the reversible lithium layer of.

8 lithium according to (7) 5 mol% or less, the content of Ni ^{2 +,} across the Li sites in the reversible lithium layer as a percentage of the sites and Ni ^{2 +} is occupied to be inserted into the reversible lithium layer Positive electrode active material for secondary batteries.

9, the Ni ^{+ 2} 0.1 to 2% by weight of a lithium secondary battery positive electrode active material according to (7), based on the total weight of the nickel ions.

(10) The positive electrode active material for lithium secondary batteries according to any one of (1) to (8), wherein n is a natural number of 2 to 5.

Moreover, this invention provides the positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries in any one of (11) said (1)-(10).

Furthermore, the present invention provides a lithium secondary battery comprising (12) the positive electrode for a lithium secondary battery. The lithium secondary battery may be used for a power source of an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

Lithium nickel containing a cathode active material for a lithium secondary battery according to the present invention - manganese - because cobalt oxide is many a content of nickel as compared to manganese and to suppress the formation of Ni ^{2 +} Ni ^{2 +} moves to the lithium layer electrochemical performance It can be prevented from being lowered and can be achieved by appropriately adjusting the content of manganese and cobalt to improve the output and appropriately adjust the high capacity, if necessary, to manufacture a positive electrode for a lithium secondary battery, and to manufacture a lithium secondary battery including the same. It can be usefully used.

1 and 2 are scanning electron microscope (SEM) photographs of lithium nickel-manganese-cobalt oxide prepared in Example 1 and Comparative Example 1, respectively.

3 is a graph showing a cycle characteristic evaluation results for the lithium secondary battery prepared in Example 5 and Comparative Example 4, respectively.

4 is a graph showing the results of the cycle characteristics evaluation for the lithium secondary battery prepared in Examples 6 to 8 and Comparative Examples 4 to 6, respectively.

FIG. 5 is a graph showing the results of resistance measurement experiments of lithium secondary batteries using HPPC for lithium secondary batteries prepared in Example 5 and Comparative Example 4. FIG.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The cathode active material for a lithium secondary battery according to the present invention includes lithium nickel-manganese-cobalt oxide represented by the following formula (1).

[Formula 1]

Li _a Ni _x Mn _y Co _z O ₂

In Formula 1, 1 ≦ a ≦ 1.2, x = 1-y-z, 0 <y <1, 0 <z <1, x> y, z = ny or y = nz and n> 1.

The lithium nickel-manganese-cobalt oxide included in the cathode active material for a lithium secondary battery according to the present invention satisfies the relationship of x> y. That is, in one embodiment of the present invention, the lithium nickel-manganese-cobalt oxide may include a relatively large amount of nickel (Ni) than manganese (Mn), and also relative to manganese and cobalt (Co) It may have a composition of nickel excess. Specifically, the nickel content (x) may have a value of 0.4 ≦ x ≦ 0.95, preferably of 0.6 ≦ x ≦ 0.85, and more preferably of 0.6 ≦ x ≦ 0.82. Can have

When the nickel content is 0.4 or more, a high capacity can be expected, and when the content of nickel is 0.95 or less, a problem of deterioration of safety can be prevented.

The lithium-nickel-manganese-If in the cobalt oxide content of manganese and nickel are substantially equal, the Mn ^{4 +} ions, so to induce the formation of Ni ^{2 +} ions, and the lithium nickel-on nickel in the cobalt oxide-manganese Let it reduces the amount of relative manganese can reduce the formation of Ni ^{2 +} ions, whereby Ni ^{2 +} ions formed in accordance with the movement in the reversible Li site (site) and by forming the rock-salt structure, the possibility is thereby degraded electrochemical performance Can be reduced.

Therefore, the lithium nickel-manganese-cobalt oxide included in the cathode active material according to an example of the present invention includes a relatively large amount of nickel (Ni) compared to manganese (Mn), thereby being included in the lithium nickel-manganese-cobalt oxide. of transition metals can reduce the relative amount of Ni ^{+ 2.}

The lithium nickel containing this the positive electrode active material according to an example of the invention - manganese - of cobalt oxide, the amount of nickel corresponding to the manganese content may be in the form of Ni ^{2 +,} the content corresponding to the manganese content the amount of nickel in excess may be in the form of Ni ^{3 +.}

Accordingly, the nickel included in the cathode active material may have an average oxidation number of more than +2, and the average oxidation number of nickel, manganese, and cobalt excluding the lithium in the lithium nickel-manganese-cobalt oxide as a whole may exceed +3.0. have.

The lithium nickel-manganese-cobalt oxide includes a transition metal oxide layer (MO layer) containing a transition metal and a lithium oxide layer (reversible lithium layer) containing lithium, and the transition metal oxide layer ( MO layer) and has a Ni ^{+ 2} and Ni ^{+ 3} co-exist, the portion of the Ni ^{+ 2} is inserted into the reversible lithium layer may be in the form of cross-coupled with the MO layers.

On the other hand, the Ni ^{3 +} is because the size smaller than that of a Ni ^{2 +} having the same size as Li ^+, the Ni ^{3 +} increases as along the transition transition, which contains the metal the metal-oxide layer (MO layer) and lithium The lithium-oxide layer (reversible lithium layer) containing can be properly separated by the size difference of the ions occupying each layer. That is, since the average oxidation number of the transition metals except lithium is greater than +3, the positive electrode active material has a smaller overall size of the transition metal ions than the case where the average oxidation number is +3, and thus the size difference with the lithium ions Since it becomes large and the separation between layers is performed well, a stable layered crystal structure can be formed.

The content of Ni ^{2 +} is inserted into the reversible lithium layer may be may be 5 mol% or less, preferably% 3 mol or less as a percentage of the sites and Ni ^{2 +} occupied in the lithium site, for example, 0.01 to 5 mol %, 0.01 to 3 mol%, 0.1 to 5 mol%, 0.1 to 3 mol% and the like. The content of the Ni ^{2 +} inserted into the reversible lithium layers can exhibit a superior rate characteristics if more than 5 mol% Ni ^{+ 2} to be inserted into the reversible lithium layer is to minimize the disturbance to cause the occlusion and release of lithium ions.

On the other hand, the amount of Ni ^{2 +} may be 0.1 to 2% by weight, specifically 0.5 to 1.5% by weight, based on the total weight of nickel ions.

As such, when the layered crystal structure of the cathode active material is more stably formed, high rate charge / discharge characteristics may be improved.

If the average oxidation number of the transition metal is too large, the amount of charge that can move the lithium ions is reduced and the capacity is reduced, the average oxidation number of the transition metal may be more than 3 to less than 3.5, preferably more than 3 To 3.3, more preferably greater than 3 to 3.1.

On the other hand, in the composition of the lithium nickel-manganese-cobalt oxide, the content (a) of lithium satisfies 1 ≦ a ≦ 1.2, and when the a value is 1.2 or less, an appropriate high temperature safety may be exhibited and the a value If it is 1 or more, the reversible capacity may not be lowered while exhibiting an appropriate rate characteristic.

In the composition of the lithium nickel-manganese-cobalt oxide included in the cathode active material according to an embodiment of the present invention, the content of manganese (y) and the content of cobalt (z) may satisfy z = ny, where n is n> 1. Alternatively, n may be a natural number except 1, and may be a natural number of 2 to 5. That is, the lithium nickel-manganese-cobalt oxide may have a higher cobalt content than manganese, and the cobalt may be included as a multiple of n of the manganese content.

Lithium nickel-manganese-cobalt oxide included in the positive electrode active material according to an embodiment of the present invention includes the cobalt in a larger amount than the manganese, so that the electrical conductivity is relatively increased to improve the rate characteristics, Powder density can be achieved.

On the other hand, in the composition of the lithium nickel-manganese-cobalt oxide included in the cathode active material according to another embodiment of the present invention, the content (y) and the content (z) of cobalt (z) may satisfy y = nz, In this case, n may be n> 1. Alternatively, n may be a natural number except 1, and may be a natural number of 2 to 5. That is, the lithium nickel-manganese-cobalt oxide may be more manganese than cobalt, and the manganese may be included as a multiple of n of the cobalt content.

Lithium nickel-manganese-cobalt oxide included in the positive electrode active material according to another embodiment of the present invention includes the manganese in a larger amount than the cobalt, lithium nickel-manganese-cobalt oxide containing much cobalt than manganese, or manganese and cobalt are contained in the same amount of lithium nickel-manganese-many content of relatively manganese compared with the cobalt oxide, the effect of the content of Ni ^{2 +} induced by the presence of the manganese also increases relatively and the battery capacity increases in Can exert. In addition, manganese contributes to the stabilization of the structure of lithium nickel-manganese-cobalt oxide to properly implement the characteristics required for high-capacity lithium secondary batteries, and the relatively low cobalt content reduces the effect of unstable Co ^{4+ in} the state of charge. Stability can be improved.

In the lithium transition metal oxide of the present invention, the transition metals nickel, manganese and cobalt may be partially substituted with other metal elements within a range capable of maintaining a layered crystal structure, for example, a small amount of metal elements and cationic elements within 5 mol%. And some substitutions.

In addition, the present invention provides a cathode including the cathode active material.

The positive electrode can be prepared by conventional methods known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in a positive electrode active material, and then applying the coating (coating) to a current collector of a metal material, compressing it, and drying the same to prepare a positive electrode.

The current collector of the metallic material is a highly conductive metal, a metal to which the slurry of the positive electrode active material can easily adhere, and any metal may 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 a foil made of aluminum, nickel, or a combination thereof.

The solvent for forming the positive electrode includes an organic solvent such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide or water, and these solvents 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 positive electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers in which hydrogen thereof is replaced with Li, Na or Ca, or the like, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; 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 dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The present invention also provides a secondary battery including the positive electrode, the negative electrode, and a 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, tin, or the like, in which lithium ions may be occluded and released, may be used. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

In addition, the negative electrode current collector is generally made to a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include carbon, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and carbon on the surface of copper or stainless steel. Surface-treated with nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As the binder and the conductive material used for the negative electrode, those that can be commonly used in the art, like the positive electrode, may be used. The negative electrode may be prepared by mixing and stirring the negative electrode active material and the additives to prepare a negative electrode active material slurry, and then coating and compressing the negative electrode active material on a current collector.

In addition, the separator may be a conventional porous polymer film conventionally used as a separator, for example, polyolefin such as ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer and ethylene-methacrylate copolymer The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

A lithium salt which can be included as an electrolyte used in the present invention can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example the lithium salt of the anion is ^{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 may be any one selected from the group consisting of _{^{-, 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 liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. no.

The external shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a pouch type or a coin type using a can.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device but also preferably used as a unit cell in a medium and large battery module including a plurality of battery cells used as a power source for a medium and large device. have.

Preferred examples of the medium-to-large device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited to these Examples and Experimental Examples. Embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1 Preparation of Lithium Nickel-Manganese-Cobalt Oxide

Ni-sulfate, manganese sulfate (Mn-sulfate), and cobalt sulfate (Co-sulfate) were weighed so that the molar ratio of Ni: Mn: Co was 8.2: 0.6: 1.2 and dissolved in water to form an aqueous solution. To obtain a nickel-manganese-cobalt composite metal hydroxide. Li ₂ CO _{3 was added} to the metal hydroxide in such a manner that the molar ratio of Li: nickel-manganese-cobalt was 1: 1 and then heat-treated at 800 ° C. for 20 hours in an electric furnace in an oxygen atmosphere to obtain LiNi _{0 . 82} Co _{0 . 12} Mn _{0 .} A lithium nickel-manganese-cobalt oxide having a composition of ₀₆ O ₂ was obtained.

Example 2 Preparation of Lithium Nickel-Manganese-Cobalt Oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so that the molar ratio of Ni: Mn: Co was 8.2: 1.2: 0.6, dissolved in water to form an aqueous solution, and then co-precipitated to obtain a nickel-manganese-cobalt composite metal hydroxide. Li ₂ CO _{3 was added} to the metal hydroxide in such a manner that the molar ratio of Li: nickel-manganese-cobalt was 1: 1 and then heat-treated at 800 ° C. for 20 hours in an electric furnace in an oxygen atmosphere to obtain LiNi _{0 . 82} Co _{0 . 06} Mn _{0 .} A lithium nickel-manganese-cobalt oxide having a composition of ₁₂ O ₂ was obtained.

Example 3 Preparation of Lithium Nickel-Manganese-Cobalt Oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so that the molar ratio of Ni: Mn: Co was 7.6: 0.6: 1.8, dissolved in water to form an aqueous solution, and then co-precipitated to obtain a nickel-manganese-cobalt composite metal hydroxide. Li ₂ CO _{3 was added} to the metal hydroxide in such a manner that the molar ratio of Li: nickel-manganese-cobalt was 1: 1 and then heat-treated at 800 ° C. for 20 hours in an electric furnace in an oxygen atmosphere to obtain LiNi _{0 . 76} Co _{0 . 18} Mn _{0 .} A lithium nickel-manganese-cobalt oxide having a composition of ₀₆ O ₂ was obtained.

Example 4 Preparation of Lithium Nickel-Manganese-Cobalt Oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so that the molar ratio of Ni: Mn: Co was 5.2: 1.2: 3.6, dissolved in water to form an aqueous solution, and then co-precipitated to obtain a nickel-manganese-cobalt composite metal hydroxide. Li ₂ CO _{3 was added} to the metal hydroxide in such a manner that the molar ratio of Li: nickel-manganese-cobalt was 1: 1 and then heat-treated at 800 ° C. for 20 hours in an electric furnace in an oxygen atmosphere to obtain LiNi _{0 . 52} Co _{0 . 36} Mn _{0 .} A lithium nickel-manganese-cobalt oxide having a composition of ₁₂ O ₂ was obtained.

Comparative Example 1: Preparation of Lithium Nickel-Manganese-Cobalt Oxide

The composition of LiNi _0.8 Co _0.1 Mn _0.1 O _{2 was prepared in} the same manner as in Example 1, except that nickel sulfate, manganese sulfate, and cobalt sulfate were weighed in a molar ratio of 8: 1: 1. Lithium nickel-manganese-cobalt oxide having was obtained.

Comparative Example 2: Preparation of Lithium Nickel-Manganese-Cobalt Oxide

The composition of LiNi _0.85 Co _0.09 Mn _0.06 O _{2 was prepared in} the same manner as in Example 1, except that nickel sulfate, manganese sulfate, and cobalt sulfate were weighed in a molar ratio of 8.5: 0.6: 0.9 in Example 1. Lithium nickel-manganese-cobalt oxide having was obtained.

Comparative Example 3: Preparation of Lithium Nickel-Manganese-Cobalt Oxide

The composition of LiNi _0.85 Co _0.08 Mn _0.07 O _{2 was prepared in} the same manner as in Example 1, except that nickel sulfate, manganese sulfate, and cobalt sulfate were weighed in a molar ratio of 8.5: 0.7: 0.8 in Example 1. Lithium nickel-manganese-cobalt oxide having was obtained.

Example 5 Fabrication of a Lithium Secondary Battery

<Manufacture of Anode>

94% by weight of lithium nickel-manganese-cobalt oxide prepared in Example 1 as a cathode active material, 3% by weight of carbon black as a conductive material, and 3% by weight of polyvinylidene fluoride (PVdF) as a binder A positive electrode mixture slurry was prepared by addition to phosphorus N-methyl-2-pyrrolidone (NMP). The prepared positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then subjected to roll press to prepare a positive electrode.

<Production of Cathode>

96.3 wt% of carbon powder as a negative electrode active material, 1.0 wt% of super-p as a conductive material, and 1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder, respectively, The negative electrode active material slurry was prepared by adding to NMP. The prepared negative electrode active material slurry was applied to a copper (Cu) thin film, which is a negative electrode current collector having a thickness of 10 μm, dried to prepare a negative electrode, and then roll-rolled to prepare a negative electrode.

<Production of Non-Aqueous Electrolyte Solution>

LiPF ₆ was added to a nonaqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as a electrolyte in a volume ratio of 30:70 to prepare a 1 M LiPF ₆ nonaqueous electrolyte.

<Production of Lithium Secondary Battery>

By using the positive electrode and the negative electrode prepared according to the above method, a mixed battery of polyethylene and polypropylene was interposed, a polymer battery was manufactured by a conventional method, and then the non-aqueous electrolyte solution prepared according to the above method was injected. The manufacture of a lithium secondary battery was completed.

Examples 6 to 8: Preparation of a lithium secondary battery

Lithium nickel-manganese-cobalt oxide prepared in Examples 2 to 4 instead of lithium nickel-manganese-cobalt oxide of Example 1 in the preparation of the positive electrode of Example 5, respectively A positive electrode was prepared in the same manner as in Example 5, except that a negative electrode and a non-aqueous electrolyte were prepared in the same manner as in Example 5, and then the positive electrode prepared above, and the negative electrode and the non-aqueous solution. A lithium secondary battery was manufactured using an electrolyte solution.

Comparative Examples 4 to 6: Preparation of Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 5, except that lithium nickel-manganese-cobalt oxide prepared in Comparative Examples 1 to 3 was used.

Experimental Example 1 SEM Micrograph

Using a scanning electron microscope (SEM), photographs of lithium nickel-manganese-cobalt oxide prepared in Example 1 and Comparative Example 1 were taken at different magnifications, and the results are shown in FIGS. 1 and 2, respectively. .

Experimental Example 2: Crystal structure measurement

Lithium nickel-manganese-cobalt oxides prepared in Examples 1 to 4 and Comparative Examples 1 to 3 using X-ray diffraction [XRD, Rigaku, D / MAX-2500 (18 kW)] using CuKα radiation. The crystal structure was measured. Is manufactured by the measured Examples 1 to 4 and Comparative Examples 1 to 3, the lithium nickel-manganese-to the a- and c- axis lattice constant, the crystal size, crystal density, and the ratio of Ni ^{2 +} cobalt oxide table 1 is shown respectively. The ratio of Ni ^{2 +} in the above represents the weight of the Ni ^2+, based on the total weight of the Ni ions.

	a	c	Crystal size (nm)	Crystal density (g / cc)	The ratio of Ni 2 + (wt%)
Example 1	2.8723	14.1980	188	4.785	1.12
Example 2	2.8721	14.1982	181	4.785	1.25
Example 3	2.8732	14.1985	175	4.786	1.00
Example 4	2.8729	14.1981	179	4.785	1.35
Comparative Example 1	2.8754	14.2161	126	4.761	2.57
Comparative Example 2	2.8755	14.2168	129	4.763	2.10
Comparative Example 3	2.8745	14.2236	150	4.756	2.56

Referring to Table 1, it can be confirmed that the case of Examples 1 to 4 is less than the ratio of Ni ²⁺ inserted into the lithium site compared to Comparative Examples 1 to 3.

Experimental Example 3 Cycle Characteristic Evaluation Experiment

For the lithium secondary batteries obtained in Examples 5 to 8 and Comparative Examples 4 to 6, electrochemical evaluation experiments were performed as follows to determine the relative efficiency according to the cycle number.

Specifically, the lithium secondary batteries prepared in Example 5 and Comparative Example 4, respectively, charged at 45 ° C with a constant current (CC) of 1 C until 4.20 V, and then charged with a constant voltage (CV) of 4.20 V The first charge was performed until the current became 0.05 mAh. After standing for 20 minutes, the battery was discharged to 2.5 V with a constant current of 2C (cut-off proceeded to 0.05C). This was repeated for 1 to 100 cycles. The results are shown in FIG.

3 is a graph showing the life characteristics of the lithium secondary batteries of Example 5 and Comparative Example 4, as can be seen through Figure 3, in the case of the lithium secondary battery of Example 5 relative capacity up to 1 to 100 cycles It was confirmed that the slope for the gentle compared to the lithium secondary battery of Comparative Example 4, the increase in the slope of the lithium secondary battery of Example 5 was also confirmed that the gentle compared to the lithium secondary battery of Comparative Example 4.

That is, it was confirmed that the lithium secondary battery of Example 5 using less manganese than cobalt had better life characteristics than the lithium secondary battery of Comparative Example 4 having the same content of manganese and cobalt.

In addition, the lithium secondary batteries prepared in Examples 6 to 8 and Comparative Examples 4 to 6 were respectively charged at 45 ° C. with a constant current (CC) of 0.5 C until 4.25 V, followed by a constant voltage (CV) of 4.25 V. Charging was carried out for 1st time until charging current became 0.05 mAh. Thereafter, it was left for 20 minutes and discharged until a constant current of 1 C reached 3.0 V (cut-off proceeded to 0.05 C). This was repeated for 1 to 50 cycles. The results are shown in FIG.

As can be seen through Figure 4, in the case of the lithium secondary battery of Examples 6 to 8 it can be confirmed that the slope for the relative capacity up to 1 to about 40 cycles is gentle compared to the lithium secondary battery of Comparative Examples 4 to 6 there was.

Therefore, a multiple of n in the manganese content of cobalt as in the embodiment of the present invention, or manganese to the low lithium n multiple of the ratio of Ni ^{2 +} into the Li site, including the cobalt content of the nickel-manganese-anode cobalt oxide When used as an active material, it was confirmed that the cycle deterioration of the secondary battery can be alleviated to exhibit stable cycle characteristics for a long time.

Experimental Example 4: Measurement of resistance of lithium secondary battery using HPPC

HPPC (hybrid pulse power characterization) test was performed to measure the resistance of the lithium secondary battery prepared in Example 5 and Comparative Example 4. While charging from SOC 10 to full charge (SOC = 100) up to 4.15 V at 1 C (30 mA), the cells were stabilized for 1 hour each, and then the resistance of the lithium secondary battery was measured according to the HPPC test method. After discharging the cells from SOC 100 to 10 and stabilizing the cells for 1 hour, the resistance of the lithium secondary battery was measured by HPPC test method for each SOC step. The resistance values at the time of charging and discharging are shown in FIG. 5.

As can be seen from FIG. 5, the lithium secondary battery using the lithium nickel-manganese-cobalt oxide according to Example 1 in both the charging resistance and the discharging resistance, uses the lithium nickel-manganese-cobalt oxide according to Comparative Example 1. As compared with the lithium secondary battery, it was confirmed that the low output value would indicate high output.

Claims (13)

1. A cathode active material for a lithium secondary battery including lithium nickel-manganese-cobalt oxide represented by Formula 1 below:

   [Formula 1]

   Li _a Ni _x Mn _y Co _z O ₂

   In Chemical Formula 1,

   1≤a≤1.2, x = 1-y-z, 0 <y <1, 0 <z <1,

   x> y

   z = ny or y = nz and n> 1.
2. The method of claim 1,

   The positive electrode active material for lithium secondary batteries, wherein x has a value of 0.4 ≦ x ≦ 0.95.
3. The method of claim 1,

   A cathode active material for a lithium secondary battery, wherein nickel in an amount corresponding to the manganese content is present in the form of Ni ²⁺ in the nickel included in the lithium nickel-manganese-cobalt oxide.
4. The method of claim 3, wherein

   The positive electrode active material for lithium secondary battery, in which nickel in an amount exceeding the content corresponding to the manganese content is present in the form of Ni ^{3 +} of the nickel included in the lithium nickel-manganese-cobalt oxide.
5. The method of claim 1,

   The Ni is a cathode active material for a lithium secondary battery having an average oxidation number greater than +2.
6. The method of claim 1,

   A positive electrode active material for lithium secondary batteries, in which the average oxidation number of Ni, Mn, and Co except for Li exceeds 3.0.
7. The method of claim 1,

   The lithium nickel-manganese-cobalt oxide comprises a transition metal-oxide layer (MO layer) containing a transition metal and a lithium-oxide layer (reversible lithium layer) containing lithium,

   The MO layer contains Ni ²⁺ and Ni ³⁺ ,

   The Ni ^{2 +} part of cathode active material for a lithium secondary battery, which is inserted into the reversible lithium layer of.
8. The method of claim 7, wherein

   The reversible the content of Ni ^{+ 2} that is inserted into the lithium layer, the total Li site, that is a ratio of Ni ^{2 +} sites are occupied at 5 mole% or less, a lithium secondary battery positive electrode active material contained in the reversible lithium layer.
9. The method of claim 7, wherein

   The Ni ^{2 +} 0.1 to 2% by weight of a lithium secondary battery positive electrode active material based on the total weight of the nickel ions.
10. The method of claim 1,

    N is a natural number of 2 to 5 positive electrode active material for lithium secondary batteries.
11. A lithium secondary battery positive electrode comprising the positive electrode active material for lithium secondary battery according to any one of claims 1 to 10.
12. A lithium secondary battery comprising the anode for lithium secondary battery according to claim 11.
13. The method of claim 12,

    The lithium secondary battery is an electric vehicle, a hybrid electric vehicle, or a lithium secondary battery for a power supply of a plug-in hybrid electric vehicle.

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