KR20160105348A - Positive electrode active material, and positive electrode and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, which comprises a lithium nickel-manganese-cobalt oxide represented by chemical formula 1: Li_aNi_xMn_yCo_zO_2, wherein 1<= a <= 1.2, x = 1 - y - z, 0 < y < 1, and 0 < z <1; x > y; and z = ny or y = nz, and n > 1. The lithium nickel-manganese-cobalt oxide included in the positive electrode active material according to the present invention has a nickel content higher than a manganese content, and thus can suppress generation of Ni^(2+), thereby preventing Ni^(2+) from moving to a lithium layer and deteriorating electrochemical performance. Furthermore, improvement on output and high capacity can be adjusted and achieved by appropriately adjusting manganese and cobalt contents as desired. Accordingly, the positive electrode active material according to the present invention can be advantageously used for manufacture of a positive electrode for a lithium secondary battery and manufacture of a lithium secondary battery including the positive electrode.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery,

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

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like.

Such electric vehicles (EV) and hybrid electric vehicles (HEV) use nickel metal hydride (Ni-MH) secondary batteries as a power source or lithium secondary batteries having high energy density, high discharge voltage and output stability. Is required to be used for an electric vehicle for 10 years or more under severe conditions in addition to high energy density and characteristics capable of exhibiting large output in a short period of time. Therefore, it is inevitable that safety and long- . In addition, a secondary battery used in an electric vehicle (EV), a hybrid electric vehicle (HEV), and the like requires excellent rate characteristics and power characteristics depending on operating conditions of the vehicle.

At present, as a cathode active material of a lithium ion secondary battery, a lithium-containing cobalt oxide such as LiCoO ₂ of a layered structure, a lithium-containing nickel oxide such as LiNiO ₂ of a layered structure, LiMn ₂ O ₄ of a spinel crystal structure And lithium-containing manganese oxides such as lithium manganese oxide and lithium manganese oxide.

LiCoO ₂ has excellent properties such as excellent cycle characteristics and is widely used at present but its safety is low and there is a limitation on mass use as a power source for fields such as electric vehicles due to a problem of price due to the resource limit of raw material cobalt . In addition, LiNiO ₂ is difficult to apply to an actual mass production process at a reasonable cost due to the characteristics of the production method thereof.

On the other hand, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have a great interest as a cathode active material capable of replacing LiCoO ₂ because they have the advantage of using manganese rich in raw material resources and environmentally friendly. However, But also has a disadvantage in that the cycle characteristics are poor. Specifically, LiMnO ₂ has a disadvantage in that the initial capacity is small and several dozens of charge-discharge cycles are required until a certain capacity is reached. In addition, LiMn ₂ O ₄ has a disadvantage in that the cycle capacity is seriously deteriorated as the cycle continues, and in particular, at a high temperature of 50 ° C or higher, the cycle characteristics are drastically lowered due to decomposition of the electrolytic solution and elution of manganese.

On the other hand, in the LiNiO ₂ cathode active material, there is a disadvantage in that a rapid phase transition of the crystal structure occurs depending on the volume change accompanied by the charge / discharge cycle and the stability is rapidly lowered when exposed to air and moisture. However, When charged to 4.3 V, it has the advantage of exhibiting a high discharge capacity.

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

The positive electrode active material prepared by mixing nickel, cobalt or manganese has improved physical properties in comparison with a battery prepared by using the respective transition metals separately, but still needs to be improved in terms of high-rate characteristics, and nickel and manganese when composed of, Mn ^{4 +} ions are Ni ^{2 +} moves to the Li site (site) to lower the electrochemical performance formed by inducing the formation of Ni ^{2 +} ion has a problem,

Therefore, it is required to develop a lithium nickel-manganese-cobalt composite oxide having a layered structure as an active material having excellent battery performance balance, overcoming or minimizing defects of each cathode active material.

An object of the present invention is to provide a cathode active material for a lithium secondary battery which can improve the output and achieve a high capacity by controlling the contents of manganese and cobalt.

Another object of the present invention is to provide a positive electrode for a lithium secondary battery comprising the positive electrode active material.

It is still another object of the present invention to provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

According to the above object, the present invention provides a cathode active material for a lithium secondary battery having the following constitution.

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

[Chemical 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 <

x > y,

z = ny or y = nz, and n >

(2) The positive electrode active material for a lithium secondary battery 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 positive electrode for lithium secondary battery according to (3), wherein nickel in an amount exceeding a content corresponding to the manganese content in the nickel contained in the lithium nickel-manganese-cobalt oxide exists in the form of Ni ^{3 +} Active material.

(5) The positive electrode active material for a lithium secondary battery 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 a lithium secondary battery according to any one of (1) to (5), wherein an average oxidation number of Ni, Mn and Co other than Li is 3.0 or more.

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

(8) The lithium ^secondary battery according to (7), wherein the content of Ni ^{2 +} inserted into the reversible lithium layer is 5 mol% or less as a proportion of sites occupied by Ni ^{2 +} in the entire Li sites included in the reversible lithium layer Cathode active material for secondary battery.

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

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

(11) A positive electrode for a lithium secondary battery comprising the positive electrode active material for a lithium secondary battery according to any one of (1) to (10).

Further, the present invention provides (12) a lithium secondary battery comprising the positive electrode for a lithium secondary battery. (13) The lithium secondary battery may be used for power supply 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 And the content of manganese and cobalt can be appropriately controlled so that the output can be improved and the capacity of the battery can be appropriately adjusted as required. Therefore, the production of a positive electrode for a lithium secondary battery and the production of a lithium secondary battery comprising the same Can be usefully used.

1 and 2 are scanning electron microscope (SEM) photographs of the lithium nickel-manganese-cobalt oxide prepared in Example 1 and Comparative Example 1, respectively.
3 is a graph showing the results of an evaluation test of cycle characteristics of the lithium secondary batteries manufactured in Example 5 and Comparative Example 4, respectively.
4 is a graph showing the results of an evaluation test of cycle characteristics of lithium secondary batteries manufactured in Examples 6 to 8 and Comparative Examples 4 to 6, respectively.
5 is a graph showing resistance measurement results of a lithium secondary battery using HPPC for the lithium secondary battery manufactured in Example 5 and Comparative Example 4. FIG.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

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

[Chemical Formula 1]

Li _a Ni _x Mn _y Co _z O ₂

1, 0 < z < 1, x> y, z = ny or y = nz, and n &gt; 1.

The lithium nickel-manganese-cobalt oxide contained in the positive electrode active material for a lithium secondary battery according to the present invention satisfies the relationship x> y. That is, in one embodiment of the present invention, the lithium nickel-manganese-cobalt oxide may contain a relatively large amount of nickel (Ni) relative to manganese (Mn) May have an excess nickel composition. Specifically, the content (x) of the nickel may have a value of 0.4? X? 0.95, preferably 0.6? X? 0.85, more preferably 0.6? X? Lt; / RTI &gt;

When the content of nickel is 0.4 or more, a high capacity can be expected. When the content of nickel is 0.95 or less, safety can be prevented from being deteriorated.

When the content of manganese and nickel in the lithium nickel-manganese-cobalt oxide is substantially the same, Mn ^{4 +} ions induce the formation of Ni ^{2 +} ions. Therefore, in the lithium nickel-manganese-cobalt oxide, Reducing the relative manganese content can reduce the formation of Ni ^{2 +} ions, and thus the possibility that the formed Ni ^{2 +} ions migrate to the reversible Li sites and form a salt structure, degrading the electrochemical performance Can be reduced.

Therefore, the lithium nickel-manganese-cobalt oxide included in the positive electrode active material according to an embodiment of the present invention contains a relatively large amount of nickel (Ni) compared to manganese (Mn) The relative content of Ni ^{2 +} in transition metals can be reduced.

Among the lithium nickel-manganese-cobalt oxides included in the cathode active material according to an exemplary embodiment of the present invention, nickel in an amount corresponding to the manganese content may exist in the form of Ni ^{2 +} , and the content corresponding to the manganese content An excess amount of nickel may be present in the form of Ni &lt; ^{3 +} &gt;.

Accordingly, the nickel contained in the positive electrode active material may have an average oxidation number greater 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.

Wherein 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, wherein the transition metal- MO layer), Ni ^{2 +} and Ni ^{3 +} coexist, and a part of the Ni ^{2 +} may be inserted into the reversible lithium layer to mutually bond 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 lithium can be appropriately separated by the difference in size of the ions occupying each layer. That is, since the average oxidation number of the transition metal except for lithium is greater than +3, the overall size of the transition metal ion becomes smaller as compared with the case where the average oxidation number is +3, So that a stable layered crystal structure can be formed.

The content of Ni ^{2 +} inserted into the reversible lithium layer may be 5 mol% or less, preferably 3 mol% or less, and 0.01 to 5 mol%, for example, as a ratio of sites occupied by Ni ^{2 +} %, 0.01 to 3 mol%, 0.1 to 5 mol%, or 0.1 to 3 mol%, and the like. When the content of Ni ^{2 +} inserted into the reversible lithium layer is 5 mol% or less, Ni ^{2 +} inserted in the reversible lithium layer minimizes interference with the occlusion and release of lithium ions, and excellent rate characteristics can be exhibited.

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 described above, when the layered crystal structure of the cathode active material is formed more stably, the high rate charge / discharge characteristics can be improved.

If the average oxidation number of the transition metal is excessively large, the amount of charge capable of moving lithium ions is reduced and the capacity is reduced. Therefore, the average oxidation number of the transition metal may be more than 3 and less than 3.5, To 3.3, and more preferably from more than 3 to 3.1.

In the composition of the lithium nickel-manganese-cobalt oxide, the lithium content (a) satisfies 1? A? 1.2 and the a value is 1.2 or less, Is equal to or larger than 1, the reversible capacity may not be lowered while exhibiting an appropriate rate characteristic.

The content (y) of manganese and the content (z) of cobalt in the composition of the lithium nickel-manganese-cobalt oxide included in the cathode active material according to an example of the present invention may satisfy z = ny, n > 1. Alternatively, n may be a natural number other than 1, and may be a natural number of 2 to 5. That is, the lithium nickel-manganese-cobalt oxide may have a larger content of cobalt than that of manganese, and the cobalt may be contained in a multiples of n of manganese content.

The lithium nickel-manganese-cobalt oxide included in the cathode active material according to an example of the present invention contains cobalt in a larger amount than manganese, so that the electric conductivity is increased and the rate characteristics can be improved. Powder density can be achieved.

In the composition of the lithium nickel-manganese-cobalt oxide of the cathode active material according to another embodiment of the present invention, the content (y) of manganese and the content (z) of cobalt may satisfy y = Here, n may be n> 1. Alternatively, n may be a natural number other than 1, and may be a natural number of 2 to 5. That is, the lithium nickel-manganese-cobalt oxide may have a larger content of manganese than cobalt, and the manganese may be contained in multiples of n of the cobalt content.

Since the lithium nickel-manganese-cobalt oxide included in the cathode active material according to another embodiment of the present invention contains the manganese in a larger amount than the cobalt, the lithium nickel-manganese-cobalt oxide containing more cobalt than manganese, Or manganese-cobalt oxide, the content of manganese is relatively larger than that of lithium nickel-manganese-cobalt oxide, and the content of Ni ^{2 +} induced by the presence of manganese is also relatively increased, . Further, manganese contributes to the structural stabilization of the lithium nickel-manganese-cobalt oxide, so that the characteristics required for a high capacity lithium secondary battery can be appropriately realized, and the content of cobalt is relatively reduced, thereby reducing the influence of unstable Co ⁴⁺ Stability can be enhanced.

In the lithium transition metal oxide of the present invention, nickel, manganese, and cobalt, which are transition metals, can be partially substituted with other metal elements within a range capable of maintaining a layered crystal structure. For example, small amounts of metal elements within 5 mol% And the like.

The present invention also provides a positive electrode comprising the positive electrode active material.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant, if necessary, in a cathode active material, coating the cathode active material with a collector of a metal material, compressing the anode active material, and drying the slurry.

The current collector of the metal material is a metal having high conductivity and can be easily adhered to the slurry of the cathode active material. Any material can be used as long as it is not reactive in the voltage range of the battery. Non-limiting examples of the positive electrode current collector include foil produced by aluminum, nickel, or a combination thereof.

Examples of the solvent for forming the positive electrode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or in combination of two or more Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the cathode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 is substituted with Li, Na, or Ca, 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 electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The dispersing agent may be an aqueous dispersing agent or an organic dispersing agent such as N-methyl-2-pyrrolidone.

The present invention also provides a secondary battery comprising 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, or tin which lithium ions can be occluded and released can be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high-temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a conductive material such as carbon, stainless steel, aluminum, nickel, titanium, fired carbon, Nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

As the binder and the conductive material used for the cathode, those which can be commonly used in the art can be used as the anode. The negative electrode may be prepared by mixing and stirring the negative electrode active material and the additives, preparing the negative electrode active material slurry, applying the slurry to the current collector, and compressing the same.

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

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

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

The outer shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like can be used.

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

Preferable examples of the above medium and large-sized devices 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 by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example 1: Preparation of lithium nickel-manganese-cobalt oxide

Manganese sulfate (Ni-sulfate), Mn-sulfate and cobalt sulfate were weighed so as to have a molar ratio of Ni: Mn: Co of 8.2: 0.6: 1.2, To obtain a nickel-manganese-cobalt composite metal hydroxide. The Li ₂ CO ₃ In the above-mentioned metal hydroxide Li: nickel-manganese-cobalt mole ratio of 1: 1 for 20 hours at 800 ℃ to electrical of the oxygen atmosphere after the heat treatment so that the quasi-put LiNi _{0. 82} Co _{0 . 12} Mn _{0 .} Manganese-cobalt oxide having a composition of &lt; RTI ID = 0.0 &_gt; O2. &_{Lt; /} RTI &_gt;

Example 2: Preparation of lithium nickel-manganese-cobalt oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so as to have a molar ratio of Ni: Mn: Co of 8.2: 1.2: 0.6, and then an aqueous solution was prepared by dissolving in water to prepare nickel-manganese-cobalt composite metal hydroxide. The Li ₂ CO ₃ In the above-mentioned metal hydroxide Li: nickel-manganese-cobalt mole ratio of 1: 1 for 20 hours at 800 ℃ to electrical of the oxygen atmosphere after the heat treatment so that the quasi-put LiNi _{0. 82} Co _{0 . 06} Mn _{0 . 12} O &lt; _{2 &} gt ;.

Example 3: Preparation of lithium nickel-manganese-cobalt oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so as to have a molar ratio of Ni: Mn: Co of 7.6: 0.6: 1.8, and then an aqueous solution was prepared by dissolving in water to prepare nickel-manganese-cobalt composite metal hydroxide. The Li ₂ CO ₃ In the above-mentioned metal hydroxide Li: nickel-manganese-cobalt mole ratio of 1: 1 for 20 hours at 800 ℃ to electrical of the oxygen atmosphere after the heat treatment so that the quasi-put LiNi _{0. 76} Co _{0 . 18} Mn _{0 .} Manganese-cobalt oxide having a composition of &lt; RTI ID = 0.0 &_gt; O2. &_{Lt; /} RTI &_gt;

Example 4: Preparation of lithium nickel-manganese-cobalt oxide

Nickel sulfate, manganese sulfate, and cobalt sulfate were weighed so as to have a molar ratio of Ni: Mn: Co of 5.2: 1.2: 3.6, and then an aqueous solution was prepared by dissolving in water to prepare nickel-manganese-cobalt composite metal hydroxide. The Li ₂ CO ₃ In the above-mentioned metal hydroxide Li: nickel-manganese-cobalt mole ratio of 1: 1 for 20 hours at 800 ℃ to electrical of the oxygen atmosphere after the heat treatment so that the quasi-put LiNi _{0. 52} Co _{0 . 36} Mn _{0 . 12} O &lt; _{2 &} gt ;.

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 so as to have a molar ratio of 8: 1: 1 in Example 1 Lithium nickel-manganese-cobalt oxide was obtained.

Comparative Example 2: Preparation of lithium nickel-manganese-cobalt oxide

A 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 so as to have a molar ratio of 8.5: 0.6: 0.9 in Example 1 Lithium nickel-manganese-cobalt oxide was obtained.

Comparative Example 3: Preparation of lithium nickel-manganese-cobalt oxide

A 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 so as to have a molar ratio of 8.5: 0.7: 0.8 in Example 1 Lithium nickel-manganese-cobalt oxide was obtained.

Example 5: Preparation of lithium secondary battery

&Lt; Preparation of positive electrode &

94 wt% of the lithium nickel-manganese-cobalt oxide prepared in Example 1, 3 wt% of carbon black as a conductive material, and 3 wt% of polyvinylidene fluoride (PVdF) as a binder were dissolved in a solvent Methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. The prepared positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to prepare a positive electrode, followed by roll pressing to prepare a positive electrode.

&Lt; Preparation of negative electrode &

A mixture of 96.3 wt% of carbon powder, 1.0 wt% of super-p as a conductive material, 1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a binder, NMP to prepare an anode active material slurry. The prepared slurry of the negative electrode active material was applied to a copper (Cu) thin film as a negative electrode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to prepare a negative electrode.

&Lt; Preparation of non-aqueous electrolytic solution &

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

&Lt; Production of lithium secondary battery >

The positive electrode and the negative electrode prepared according to the above method were used to make a polymer type battery by a conventional method after interposing a mixed separator of polyethylene and polypropylene and then injecting the nonaqueous electrolyte solution prepared according to the above method Thereby completing the production of a lithium secondary battery.

Examples 6 to 8: Preparation of lithium secondary battery

The lithium nickel-manganese-cobalt oxide prepared in Examples 2 to 4 was used in place of the lithium nickel-manganese-cobalt oxide of Example 1 as the lithium nickel-manganese-cobalt oxide in the production of the positive electrode of Example 5 A positive electrode was prepared in the same manner as in Example 5 and a negative electrode and a nonaqueous electrolytic solution were prepared in the same manner as in the method described in Example 5. The positive electrode and the negative electrode and the non- A lithium secondary battery was produced using an electrolytic solution.

Comparative Examples 4 to 6: Preparation of lithium secondary battery

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

Experimental Example 1: SEM micrograph

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

Experimental Example 2: Measurement of crystal structure

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) The crystal structure was measured. The lattice constants, crystal size, crystal density, and ratio of Ni ^{2 +} in the a- and c-axes of the lithium nickel-manganese-cobalt oxides prepared in Examples 1 to 4 and Comparative Examples 1 to 3, Respectively. The ratio of Ni ^{2 + in} the above represents the weight of Ni ²⁺ based on the total weight of Ni ions.

a c Crystal size
(nm) Crystal density
(g / cc) The ratio (% by weight) of Ni ^{2 +} 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 ratio of Ni ²⁺ inserted into the lithium sites of Examples 1 to 4 is smaller than that of Comparative Examples 1 to 3.

Experimental Example 3: Evaluation of cycle characteristics

The electrochemical evaluation tests were conducted as follows to investigate the relative efficiencies of the lithium secondary batteries obtained in Examples 5 to 8 and Comparative Examples 4 to 6 according to the number of cycles.

Specifically, the lithium secondary batteries prepared in Example 5 and Comparative Example 4 were charged at a constant current (CC) of 1 C at 4.degree. C. until 4.20 V, and then charged at a constant voltage (CV) of 4.20 V to be charged The first charge was performed until the current reached 0.05 mAh. Thereafter, it was allowed to stand for 20 minutes and then discharged at a constant current of 2 C until the voltage reached 2.5 V (the cut-off was proceeded to 0.05 C). This was repeated in 1 to 100 cycles. The results are shown in Fig.

FIG. 3 is a graph showing a lifetime characteristic of the lithium secondary battery of Example 5 and Comparative Example 4. As shown in FIG. 3, in the case of the lithium secondary battery of Example 5, the relative capacity Of the lithium secondary battery of Comparative Example 4 was less than that of the lithium secondary battery of Comparative Example 4. It was also confirmed that the lithium secondary battery of Example 5 was more gradual than the lithium secondary battery of Comparative Example 4,

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

The lithium secondary batteries prepared in each of Examples 6 to 8 and Comparative Examples 4 to 6 were charged at a constant current (CC) of 0.5 C at 45 캜 until they reached 4.25 V, and then charged at a constant voltage (CV) of 4.25 V, And the first charge was performed until the charge current became 0.05 mAh. Thereafter, it was allowed to stand for 20 minutes and then discharged at a constant current of 1 C until it reached 3.0 V (the cut-off was proceeded to 0.05 C). This was repeated in 1 to 50 cycles. The results are shown in Fig.

As can be seen from FIG. 4, the slopes of the lithium secondary batteries of Examples 6 to 8 with respect to the relative capacity from 1 to about 40 cycles were more gradual than those of the lithium secondary batteries of Comparative Examples 4 to 6 there was.

Therefore, as in the embodiment of the present invention, the lithium nickel-manganese-cobalt oxide having a small proportion of Ni ^{2 +} inserted into the Li site, including cobalt as a multiple of n of manganese content or manganese as a multiple of n of cobalt content, It was confirmed that when used as an active material, the cycle deterioration of the secondary battery is alleviated, and stable cycle characteristics can be exhibited for a long period of time.

Experimental Example 4: Resistance measurement of lithium secondary battery using HPPC

HPPC (hybrid pulse power characterization) tests were carried out to measure the resistances of the lithium secondary batteries prepared in Example 5 and Comparative Example 4. [ The battery was charged from SOC 10 up to 4.15 V at 1 C (30 mA) to full charge (SOC = 100). After the battery was stabilized for 1 hour, the resistance of the lithium secondary battery was measured according to the HPPC test method. The batteries were discharged from SOC 100 to 10, and the batteries were each stabilized for 1 hour, and the resistance of the lithium secondary batteries was measured by the HPPC test method for each SOC step. The resistance value at the charge / discharge time is shown in Fig.

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 was made of the lithium nickel-manganese-cobalt oxide according to Comparative Example 1 Which is lower than that of the lithium secondary battery.

Claims (13)

A cathode active material for a lithium secondary battery comprising lithium nickel-manganese-cobalt oxide represented by the following formula (1)
[Chemical Formula 1]
Li _a Ni _x Mn _y Co _z O ₂
In Formula 1,
1? A? 1.2, x = 1-yz, 0 <y <1, 0 <z <
x > y,
z = ny or y = nz, and n >
The method according to claim 1,
Wherein x has a value of 0.4? X? 0.95.
The method according to claim 1,
Wherein the amount of nickel corresponding to the manganese content in the nickel contained in the lithium nickel-manganese-cobalt oxide exists in the form of Ni ²⁺ .
The method of claim 3,
The lithium-nickel-manganese-cobalt oxide is contained in the nickel, the corresponding content of the excess amount of the cathode active material for a lithium secondary battery of nickel is present in the form of Ni ^{3 +} to which the manganese content to.
The method according to claim 1,
Wherein the Ni has an average oxidation number greater than +2.
The method according to claim 1,
Wherein an average oxidation number of Ni, Mn and Co other than Li is more than 3.0.
The method according to claim 1,
Wherein 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,
Wherein the MO layer contains Ni ²⁺ and Ni ³⁺ ,
And a part of the Ni ^{2 +} is inserted in the reversible lithium layer.
8. The method of claim 7,
Wherein a content of Ni ^{2 +} inserted into the reversible lithium layer is 5 mol% or less as a ratio of sites occupied by Ni ^{2 +} in the entire Li sites included in the reversible lithium layer.
8. The method of claim 7,
Wherein the Ni ^{2 +} is 0.1 to 2 wt% based on the total weight of nickel ions.
The method according to claim 1,
Wherein n is a natural number of from 2 to 5. &lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
The positive electrode for a lithium secondary battery according to any one of claims 1 to 10, comprising a positive electrode active material for a lithium secondary battery.
12. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 11.
13. The method of claim 12,
Wherein the lithium secondary battery is a power source for an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

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