KR101904895B1 - Positive active material for rechargeable lithium battery, and positive electrode for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

A lithium manganese oxide-based solid solution having a specific surface area of 3 to 12 m ² / g and a crystallite diameter of 40 to 120 nm, and a positive electrode and a lithium secondary battery for the lithium secondary battery comprising the same.

Description

FIELD OF THE INVENTION The present invention relates to a positive electrode active material for a lithium secondary battery, and a positive electrode and a lithium secondary battery for the same, and a positive electrode and a lithium secondary battery for the same. BACKGROUND ART < RTI ID =

A positive electrode active material for a lithium secondary battery, and a positive electrode and a lithium secondary battery for a lithium secondary battery comprising the same.

Lithium manganese oxide solid solution exhibits a high capacity when charged at a high voltage, and accordingly, research is being actively conducted as a material for a cathode active material for a lithium secondary battery.

However, when the charging / discharging cycle is repeated at a high voltage, there is a limit to the lifetime characteristics of the battery.

One embodiment is to provide a positive electrode active material for a lithium secondary battery that suppresses a decrease in discharge capacity due to repetition of a charge-discharge cycle and improves cycle life characteristics.

Another embodiment is to provide a positive electrode for a lithium secondary battery comprising the positive electrode active material.

Another embodiment is to provide a lithium secondary battery comprising the positive electrode.

One embodiment provides a cathode active material for a lithium secondary battery comprising a lithium manganese oxide-based solid solution having a specific surface area of 3 to 12 m ² / g and a crystallite diameter of 40 to 120 nm.

The specific surface area of the lithium manganese oxide solid solution may be 6 to 12 m ² / g.

The crystallite diameter of the lithium manganese oxide solid solution may be 40 to 70 nm.

The lithium manganese oxide solid solution may be represented by the following general formula (1).

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) LiMO ₂

(In the formula 1,

M is represented by the following formula (2) and 0.2? X? 0.5.)

(2)

Mn _a Co _b Ni _c M ' _d

(In the formula (2)

M 'is a transition metal except for Mn, Co and Ni,

D? 0.5 and a + b + c + d = 1).

Another embodiment provides a positive electrode for a lithium secondary battery comprising the positive electrode active material.

Yet another embodiment includes the anode; cathode; And a lithium secondary battery comprising the electrolyte.

The details of other embodiments are included in the detailed description below.

It is possible to realize a lithium secondary battery in which cracking of the lithium manganese oxide solid solution due to repetition of the charge-discharge cycle and reduction of the discharge capacity are suppressed and cycle life characteristics are improved.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.
2 is a graph showing the correspondence between the specific surface area and the voltage drop amount of the lithium manganese oxide solid solution.
3 is a graph showing the correspondence between the crystallite diameter and the voltage drop amount of the lithium manganese oxide solid solution.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

A lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.

1, the lithium secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator 40 disposed between the positive electrode 20 and the negative electrode 30.

The charge reached voltage of the lithium secondary battery, that is, the redox potential may be, for example, 4.5V to 5.0V (vs. Li / Li +).

The shape of the lithium secondary battery is not particularly limited. In other words, the lithium secondary battery can have any shape such as a cylindrical shape, a square shape, a laminate shape, and a button shape.

The anode 20 includes a current collector 21 and a cathode active material layer 22 formed on the current collector 21.

The collector may be, for example, aluminum.

The cathode active material layer may include a cathode active material and a conductive material, and may further include a binder.

The cathode active material may include a lithium manganese oxide solid solution.

The lithium manganese oxide-based solid solution may be a solid solution containing Li ₂ MnO ₃ , and specifically may be represented by the following general formula (1).

[Chemical Formula 1]

xLi ₂ MnO ₃ (1-x) LiMO ₂

(In the formula 1,

M is represented by the following formula (2) and 0.2? X? 0.5.)

(2)

Mn _a Co _b Ni _c M ' _d

(In the formula (2)

M 'is a transition metal except for Mn, Co and Ni,

D? 0.5 and a + b + c + d = 1).

A lithium secondary battery using the lithium manganese oxide-based solid solution as a cathode active material exhibits a high capacity of 200 mAh / g or more when charged at a high voltage of 4.5 V or higher. The crystalline structure of the lithium manganese oxide solid solution is changed from a layered crystal structure to a spinel crystal structure during charging and a layered structure in a spinel crystal structure at the time of discharging because the lithium manganese oxide based solid solution causes a phase change during charging and discharging, The crystal structure is changed, so that such a phase change can contribute to the improvement of the discharge capacity.

However, the phase change may not be reversible as the charge / discharge cycle is repeated at high voltage charging. In other words, during the discharge, some crystallizers do not return to the layered crystal structure in the spinel crystal structure, and crystallites having a spinel crystal structure increase as the charge and discharge cycles are repeated. As a result, the number of crystallites contributing to charge and discharge decreases, and cycle life characteristics may be degraded. Also, as the number of crystallites having a spinel crystal structure increases, the stress in the solid solution increases, and cracks may be generated on the solid solution surface due to such stress.

According to one embodiment, by controlling the specific surface area and the crystallite diameter of the lithium manganese oxide solid solution, it is possible to suppress the generation of cracks even when the charge / discharge cycle is repeated at high voltage and to maintain the high capacity characteristics, Lt; / RTI >

Specifically, the specific surface area of the lithium manganese oxide solid solution may be 3 to 12 m ² / g, and more specifically, 6 to 12 m ² / g. When the specific surface area of the lithium manganese oxide solid solution is within the above range, the crystallinity of each crystallite is excellent in the solid solution and the crystallite is hardly broken, so that the phase change can be reversibly caused during charging and discharging. As a result, it is possible to suppress the generation of cracks on the surface of the lithium manganese oxide solid solution during charge and discharge at a high voltage and to improve cycle life characteristics.

The specific surface area can be measured by, for example, a nitrogen adsorption method.

The crystallite diameter of the lithium manganese oxide solid solution may be 40 to 120 nm, specifically 40 to 70 nm. When the crystallite diameter of the lithium manganese oxide solid solution is within the above range, the crystallinity of each crystallite is excellent in the solid solution and the crystallite is hard to break, so that the phase change can be reversibly caused during charging and discharging. As a result, it is possible to suppress the generation of cracks on the surface of the lithium manganese oxide solid solution during charge and discharge at a high voltage and to improve cycle life characteristics.

The crystallite may be a single crystal having a fine size, and the lithium manganese oxide solid solution may be a polycrystalline material composed of such crystallizers.

Specifically, the crystallite diameter can be defined by the following equation (1).

[Equation 1]

D = (K *?) / (? * Cos?)

(In the above formula (1)

D is the crystallite diameter,

K is a Scherrer constant and can be, for example, 0.9,

β is a half-value width (rad) of a peak observed near the diffraction angle by X-ray diffraction (XRD), wherein the peak is the diffraction peak of the (003)

θ is the diffraction angle (rad).)

The units of? And? Are all radians.

The specific surface area and crystallite diameter can be controlled by controlling the stirring speed, stirring time, baking temperature, baking time and the like in the production of the lithium manganese oxide solid solution.

The method for producing the lithium manganese oxide solid solution is not particularly limited, and for example, it can be produced by coprecipitation.

Specifically, nickel sulfate hexahydrate, manganese sulfate heptahydrate, and cobalt sulfate heptahydrate are dissolved in ion exchanged water to prepare a mixed aqueous solution.

The total amount of the nickel sulfate hexahydrate, the manganese sulfate heptahydrate and the cobalt sulfate heptahydrate may be 20 wt% based on the total amount of the mixed aqueous solution. The nickel sulfate hexahydrate, the manganese sulfate heptahydrate and the cobalt sulfate heptahydrate are mixed so that the molar ratio of each element of Ni, Co and Mn is a desired value. The molar ratio of each element is determined according to the composition of the lithium manganese oxide solid solution. For example, when 0.4Li ₂ MnO ₃ -0.6 Li (Mn _0.33 Co _0.33 Ni _0.33 ) O ₂ is produced, the molar ratio of each element is Mn: Co: Ni of 60:20:20.

On the other hand, a predetermined amount of ion exchange material can be put into the reaction vessel, and the temperature of the ion exchange material can be maintained at 50 캜.

Subsequently, an aqueous solution of NaOH (containing 40% by weight of NaOH) is dropped into the ion-exchanged material to adjust the pH of the reaction vessel aqueous solution to 11.5. Subsequently, the ion exchanged material is bubbled with an inert gas such as nitrogen to remove dissolved oxygen.

The reaction vessel aqueous solution is stirred, the temperature of the reaction vessel aqueous solution is maintained at 50 占 폚, and the mixed aqueous solution is dropped into the reaction solution aqueous solution. The dropping rate is not particularly limited, but may be, for example, about 3 ml / min.

An aqueous solution of NaOH (containing 40 wt% of NaOH) and an aqueous NH ₃ solution (containing 10 wt% of NH ₃ ) were further added dropwise to the reaction vessel aqueous solution and stirred. The pH of the reaction vessel aqueous solution was maintained at 11.5, Is co-precipitated.

At this time, stirring can be performed at a predetermined speed and time. For example, the stirring speed may be 1 to 10 m / s, and the stirring time may be performed for 5 hours or more. When the stirring speed and agitation time are within the above ranges, the specific surface area and the crystallite diameter within the range according to one embodiment can be obtained.

The coprecipitate hydroxide is then removed from the reaction vessel aqueous solution by solid liquid separation, for example, suction filtration, and washed with ion exchanged water.

The coprecipitate hydroxide is then vacuum dried. The drying temperature may be, for example, 100 占 폚, and the drying time may be, for example, 10 hours. After drying, the coprecipitate hydroxide is pulverized with a mortar for several minutes to obtain a dry powder. The dry powder and lithium carbonate are mixed to produce a mixed powder. The molar ratio of Li to M (Ni + Mn + Co) is determined depending on the composition of the solid solution. For example, 0.4Li ₂ MnO ₃ -0.6Li when manufacturing the _{(Mn 0 .33 Co 0 .33 Ni} 0 .33) O 2 molar ratio of Li and M Li: M is 1.4: 1.

Subsequently, the mixed powder is fired at a predetermined time and temperature. Whereby a lithium manganese oxide solid solution can be produced. At this time, the firing time may be 4 to 24 hours, the firing temperature may be 710 to 980 ° C, and more specifically, 720 to 930 ° C.

The content of the lithium manganese oxide solid solution is not particularly limited and may be a content that is applied to the positive electrode active material layer of the lithium secondary battery.

The conductive material may include, for example, carbon black such as KETJEN BLACK, acetylene black or the like; Graphite such as natural graphite and artificial graphite. However, it is not particularly limited as long as it is for increasing the conductivity of the anode.

The content of the conductive material is not particularly limited and may be any content as long as it is applied to the positive electrode active material layer of the lithium secondary battery.

Examples of the binder include polyvinylidene fluoride, ethylene propylene diene terpolymer, styrene butadiene rubber, acrylonitrile butadiene rubber, fluor rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like However, it is not particularly limited as long as it can bind the positive electrode active material and the conductive material on the current collector.

The content of the binder is not particularly limited and may be a content that is applied to the positive electrode active material layer of the lithium secondary battery.

The cathode active material layer may be formed by, for example, dispersing the cathode active material, the conductive material, and the binder in an organic solvent such as N-methyl-2-pyrrolidone to form a slurry, And drying it.

The coating method is not particularly limited, and examples thereof include a knife coating method and a gravure coating method.

Subsequently, the positive electrode active material layer is rolled to a desired thickness by a press machine to produce a positive electrode. At this time, the thickness of the positive electrode active material layer is not particularly limited.

The cathode 30 includes a current collector 31 and a negative electrode active material layer 32 formed on the current collector 31.

The current collector 31 may be, for example, copper, nickel, or the like.

The negative electrode active material layer may be any negative electrode active material layer as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the negative electrode active material layer includes a negative electrode active material, and may further include a binder.

Examples of the negative electrode active material include graphite such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite; A mixture of fine particles of silicon, tin or an oxide thereof, and graphite; Fine particles of silicon or tin; An alloy containing silicon or tin; Li ₄ Ti ₅ O ₁₂ , And the like. The oxide of silicon may be represented by SiOx (0? X? 2). Metal lithium or the like may also be used.

The binder may be the same as the binder constituting the positive electrode active material layer.

The mixing weight ratio of the negative electrode active material and the binder is not particularly limited.

The negative electrode may be manufactured in the same manner as the positive electrode.

Specifically, the negative electrode active material and the binder are mixed in a predetermined ratio and dispersed in an organic solvent such as N-methyl-2-pyrrolidone to form a slurry. Subsequently, the slurry is coated on a current collector and dried to form a negative electrode active material layer. Subsequently, the negative electrode active material layer is rolled to a desired thickness by a press machine to produce a negative electrode. At this time, the thickness of the negative electrode active material layer is not particularly limited.

When metal lithium is used for the negative electrode active material layer, a metal lithium foil can be formed on the current collector.

The separator 40 is not particularly limited, and any separator may be used as long as it is used as a separator of a lithium secondary battery. Concretely, a porous film or nonwoven fabric exhibiting excellent high rate discharge performance can be used alone or in combination.

As the material of the separator, for example, a polyolefin resin such as polyethylene and polypropylene; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Vinylidene fluoride-vinylidene fluoride copolymer, vinylidene fluoride-vinylidene fluoride-vinylidene fluoride copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride- Vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinyl fluoride Fluorene resins such as vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, diene-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-ethylene-tetrafluoroethylene copolymer.

The porosity of the separator is not particularly limited.

The separator may be impregnated with an electrolytic solution.

The electrolytic solution is not particularly limited as long as it can be used in a lithium secondary battery. Specifically, the electrolytic solution may include a non-aqueous solvent and an electrolyte salt.

Examples of the non-aqueous solvent include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as? -butyrolactone and? -valerolactone; Chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; Chain esters such as methyl formate, methyl acetate and methyl butyrate; Tetrahydrofuran or a derivative thereof; Ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyl diglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof, and these may be used alone or in combination of two or more.

As the electrolyte salt, for example, LiClO _4, LiBF _4, LiAsF _6, LiPF _6, LiSCN, LiBr, LiI, Li ₂ SO _4, Li ₂ B ₁₀ C _l1 0, NaClO _4, NaI, NaSCN, NaBr, Inorganic ion salts such as KClO ₄ and KSCN; _{LiCF 3 SO 3, LiN (CF} 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, _{LiC (C 2 F 5 SO 2} ) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, (C 2 H 5) 4 NI, (C 3 H 7 _{) 4 NBr, (nC 4 H} 9) 4 NClO 4, (nC 4 H 9) 4 Ni, (C 2 H 5) 4 N- _{maleate, (C 2 H 5) 4} N- benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearylsulfonate, lithium octylsulfonate, lithium dodecylbenzenesulfonate, and the like, and they may be used singly or in combination of two or more.

The concentration of the electrolyte salt is not particularly limited, but may be specifically used in a concentration of 0.5 to 2.0 mol / L.

The lithium secondary battery can be manufactured by the following method.

The separator (40) is disposed between the anode (20) and the cathode (30) to produce an electrode structure. Next, the electrode structure is processed into a desired shape, for example, a cylindrical shape, a square shape, a laminate shape, a button shape, or the like, and inserted into the container of the above-described shape. Subsequently, the electrolyte solution is injected into the container, and each of the pores in the separator is impregnated with an electrolytic solution to prepare a lithium secondary battery.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

Example  1 to 5 and Comparative Example  1 and 2

(Lithium manganese oxide solid solution product)

Nickel sulfate hexahydrate, manganese sulfate heptahydrate and cobalt sulfate heptahydrate were dissolved in ion exchanged water to prepare a mixed aqueous solution. The total amount of the nickel sulfate hexahydrate, the manganese sulfate heptahydrate and the cobalt sulfate heptahydrate was 20 wt% based on the total amount of the mixed aqueous solution. The nickel sulfate hexahydrate, the manganese sulfate heptahydrate and the cobalt sulfate heptahydrate were mixed so that the molar ratio of Mn, Co and Ni was Mn: Co: Ni of 60:20:20.

On the other hand, 500 ml of ion exchanged product was put into the reaction vessel, and the temperature of the ion exchanged product was maintained at 50 캜. An aqueous solution of NaOH (containing 40% by weight of NaOH) was dropped into the ion exchange material to adjust the pH of the aqueous solution in the reaction vessel to 11.5. The ion exchanger was then bubbled with nitrogen gas to remove dissolved oxygen.

After the reaction vessel aqueous solution was stirred and the temperature was maintained at 50 ° C, the mixed aqueous solution was added dropwise to the reaction vessel aqueous solution at a rate of 3 ml / min.

Further, an aqueous NaOH solution (containing 40 wt% of NaOH) and an NH ₃ aqueous solution (containing 10 wt% of NH ₃ ) were further added dropwise to the reaction vessel aqueous solution to maintain the pH of the reaction vessel aqueous solution at 11.5. The stirring speed was 5 m / s and the time was 10 hours. Thus, hydroxides of the respective metal elements were coprecipitated.

Then, the coprecipitated hydroxide was taken out from the reaction layer aqueous solution by suction filtration and washed with ion exchanged water. The coprecipitate hydroxide was then vacuum dried. The vacuum drying temperature was 100 占 폚 and the drying time was 10 hours.

Subsequently, the coprecipitated hydroxide after drying was pulverized with a mortar for several minutes to obtain a dry powder. Then, the dry powder and lithium carbonate were mixed to produce a mixed powder. At this time, the molar ratio of Li to M (Ni + Mn + Co) was set to 1.4: 1.

Subsequently, the mixed powder was divided into seven samples and each sample was fired. At this time, the firing time was 6 hours in all the samples and the firing temperature was changed in the range of 700 to 1000 占 폚 per sample. That is, the lithium manganese oxide solid solution according to Examples 1 to 5 and Comparative Examples 1 and 2 was prepared by firing samples at different temperatures as shown in Table 1 below.

Example Comparative Example One 2 3 4 5 One 2 Firing temperature (캜) 725 750 800 850 900 700 1000

(Production of lithium secondary battery)

The respective lithium manganese oxide solid solutions prepared above, acetylene black and polyvinylidene fluoride were mixed at a weight ratio of 80: 13: 7. This mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. The slurry was coated on an aluminum foil as a current collector and dried to form a cathode active material layer. The anode active material layer was rolled to a thickness of 50 탆 to prepare a cathode.

* The negative electrode was prepared by placing a metal lithium foil on a copper foil as a current collector.

A porous polyethylene film having a thickness of 12 占 퐉 was prepared as a separator, and the separator was disposed between the positive electrode and the negative electrode to prepare an electrode structure.

Then, the electrode structure was processed into CR2032 coin half cell size and stored in a container of CR2032 coin half cell.

Lithium hexafluorophosphate was dissolved at a concentration of 1.00 mol / L in a nonaqueous solvent in which ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 3: 7 to prepare an electrolytic solution.

The electrolyte solution was injected into the coin half cell to impregnate the electrolyte with the separator to produce a lithium secondary battery.

Rating 1: Lithium manganese oxide system  Solid-state Specific surface area  And crystallizer diameter  Measure

The specific surface area of the lithium manganese oxide solid solution prepared in Examples 1 to 5 and Comparative Examples 1 and 2 was measured by a nitrogen adsorption method, and the results are shown in Table 2 below.

The crystallite diameters of the lithium manganese oxide solid solutions prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were measured by the following method, and the results are shown in Table 2 below.

As a result of the X-ray diffraction test of the lithium manganese oxide solid solution, a peak was detected in the vicinity of the diffraction angle of 18 캜. Then, the crystallite diameter was calculated using the diffraction angle and the half width of the peak and the following equation (1).

[Equation 1]

D = (K *?) / (? * Cos?)

(Where D is the crystallite diameter, K is 0.9, and beta is the half-width of the (003) plane of the crystallite, which is observed near the diffraction angle of 18 DEG C by X-ray diffraction (XRD) ) And? Is 18/360 * 2? (Rad).

Crystallite diameter (nm) Specific surface area (m ² / g) Example 1 40 12 Example 2 50 8 Example 3 70 6 Example 4 90 5 Example 5 120 3 Comparative Example 1 30 15 Comparative Example 2 150 2

Evaluation 2: Lithium secondary battery Charging and discharging  characteristic

Charging and discharging evaluations of the lithium secondary batteries fabricated in Examples 1 to 5 and Comparative Examples 1 and 2 were carried out as shown in Table 3, and the evaluation results are shown in Table 4 and Figs. 2 and 3.

Number of cycles Charge rate Discharge rate Cutoff voltage (V) One 0.1C CC-CV 0.1C CC 4.8-2.0 2 0.2C CC-CV 0.2C CC 4.7-2.5 3-49 1C CC-CV 1C CC 4.7-2.5 50 0.2C CC-CV 0.2C CC 4.7-2.5

In Table 3, CC-CV denotes a constant current constant voltage charge, and CC denotes a constant current discharge. The cutoff voltage represents the voltage at the end of charging and the voltage at the end of discharge. For example, the charging of the first cycle was performed until the voltage of the lithium secondary battery reached 4.8 V, and the discharge was performed until the voltage of the lithium secondary battery reached 2.0 V.

In Table 4, the capacity retention rate (%) is obtained as a percentage of the discharge capacity at 50 cycles to the discharge capacity at 2 cycles. The average discharge voltage V is a value obtained by measuring the voltage at the time of discharge at a plurality of points of time and arithmetically averaging the measured values. The voltage drop is the difference between the average discharge voltage in two cycles and the average discharge voltage in fifty cycles. The smaller the difference, the smaller the variation of the discharge curve.

Capacity retention rate (%) Average discharge voltage (V) Voltage drop (mV) 2 cycle time At 50 cycles Example 1 95 3.60 3.57 30 Example 2 95 3.60 3.56 40 Example 3 95 3.60 3.57 30 Example 4 95 3.62 3.56 60 Example 5 95 3.62 3.56 60 Comparative Example 1 80 3.55 3.52 30 Comparative Example 2 92 3.65 3.53 120

2 is a graph showing the correspondence between the specific surface area and the voltage drop amount of the lithium manganese oxide solid solution.

In FIG. 2, the five points P11 are the measured values of Examples 1 to 5, and the points P12 and P13 represent the measured values of Comparative Example 1 and Comparative Example 2, respectively.

3 is a graph showing the correspondence between the crystallite diameter and the voltage drop amount of the lithium manganese oxide solid solution.

In FIG. 3, five points P21 represent the measured values of Examples 1 to 5, and the points P22 and P23 represent the measured values of Comparative Example 1 and Comparative Example 2, respectively.

Referring to Table 4 and FIGS. 2 and 3, it can be seen that the variation of the discharge curve is suppressed in all of Examples 1 to 5, and the cycle life characteristics are also excellent. On the other hand, in Comparative Example 1, although the change of the discharge curve is suppressed, the cycle life characteristics are deteriorated. In Comparative Example 2, the change of the discharge curve is large.

The lithium manganese oxide solid solution after charge / discharge evaluation was observed with an electron microscope. As a result, it was confirmed that cracks were not generated in Examples 1 to 5, but cracks were generated in Comparative Examples 1 and 2.

Thus, it can be seen that when the specific surface area and crystallite diameter of the lithium manganese oxide solid solution have a range according to one embodiment, the occurrence of cracks and the change of the discharge curve are suppressed and the cycle life characteristics are improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

10: Lithium secondary battery
20: anode
21: The whole house
22: cathode active material layer
30: cathode
31: The whole house
32: anode active material layer
40: Separator

Claims (6)

A lithium manganese oxide solid solution having a specific surface area of 6 to 12 m ² / g and a crystallite diameter of 40 to 120 nm,
The lithium manganese oxide-based solid solution is represented by the following formula (1).
[Chemical Formula 1]
xLi ₂ MnO ₃ (1-x) LiMO ₂
(In the formula 1,
M is represented by the following formula (2) and 0.2? X? 0.5.)
(2)
Mn _a Co _b Ni _c M ' _d
(In the formula (2)
M 'is a transition metal except for Mn, Co and Ni,
D? 0.5 and a + b + c + d = 1).
delete The method according to claim 1,
Wherein the lithium manganese oxide solid solution has a crystallite diameter of 40 to 70 nm.
delete The positive electrode active material according to claim 1 or 3,
And a positive electrode for a lithium secondary battery.
A cathode according to claim 5;
cathode; And
Electrolyte
≪ / RTI >

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