KR20080050645A - Cathode active material with high power and lithium secondary batter having the same - Google Patents

Abstract

A high-output cathode active material is provided to realize improved high-temperature storage characteristics, to enlarge the driving range of a spinel-like lithium manganese oxide, thereby imparting improved high-temperature cycle characteristics to a lithium secondary battery. A cathode active material for a lithium secondary battery with a limited capacity of an anode comprises: (i) a lithium manganese oxide having a spinel structure(referred to as spinel-like lithium manganese oxide); and (ii) an electrode active material having a plateau where gas generation occurs in a charging region(referred to as an electrode active material having a plateau). The cathode active material comprises 50-90 wt% of the lithium manganese oxide and 10-50 wt% of a lithium metal oxide.

Description

High Power Cathode Active Material and Lithium Secondary Battery Containing It {Cathode Active Material With High Power and Lithium Secondary Batter Having the Same}

The present invention relates to a high output positive electrode active material and a lithium secondary battery including the same. More particularly, the present invention relates to a positive electrode active material having (i) a lithium manganese oxide having a spinel structure and (ii) a flat state section in which gas is generated during charging. The present invention relates to a high output lithium secondary battery, which is composed of a mixture of electrode active materials and has improved high temperature storage performance.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage are commercially used in such secondary batteries.

Among lithium secondary batteries, a battery using lithium cobalt oxide as a cathode active material is the most used battery because of its excellent electrode life and high fast charge and discharge efficiency. However, such lithium cobalt oxide has a disadvantage in that it is inferior in price competitiveness because it is inferior in high temperature stability and cobalt used as a raw material is expensive material.

A cathode active material, which is proposed as one of the methods for solving the problems of the lithium cobalt oxide battery, is a lithium manganese oxide. The reaction in a lithium secondary battery using lithium manganese oxide as a positive electrode active material and a carbon material as a negative electrode active material is as follows.

Anode Reaction: xLi ⁺ + MnO ₂ + xe ^- ↔ Li _x Mn ₂ O ₄ (0 <x≤2)

Cathode reaction: LixC ↔ C + xLi + + xe-

Total reaction: Li _{1 - x} Mn ₂ O ₄ + Li _x C ↔ LiMn ₂ O ₄ + C

That is, during charging, electrons are sent to the cathode, and lithium ions stored in the spinel electrode come out and are inserted into the cathode to generate a potential difference. On the contrary, when discharged, lithium ions inserted into the cathode enter the spinel anode through the electrolyte. The electrons are sent out to flow current.

In general, spinel-type lithium manganese oxides have advantages of excellent thermal stability, low cost, and easy synthesis, but have a small capacity, deterioration of life characteristics due to side reactions, high temperature characteristics, and low conductivity. There was this.

In order to solve this problem, attempts have been made to use spinel structure lithium manganese oxide in which some other metal is substituted. For example, Korean Patent Application Publication No. 2002-65191 discloses a spinel structure lithium manganese oxide having excellent thermal safety, but has a problem of low battery capacity and low temperature storage characteristics and cycle life. .

Many attempts have been made to use a layered lithium manganese oxide to compensate for the small capacity of spinel and to ensure good thermal stability of the manganese-based active material. In this case, the structure is unstable, so phase change occurs during charging and discharging, the capacity is rapidly decreased, and the life characteristics are deteriorated. In order to solve this problem, there have been attempts to maintain the stability of the structure by doping or substituting other metals, for example, Korean Patent Application Publication No. 2002-24520 uses a layered lithium manganese oxide, A positive electrode active material in which phase transition does not occur during discharge is disclosed, but high temperature storage characteristics and cycle life are not greatly improved.

In addition, a method of mixing lithium nickel cobalt manganese oxide with lithium manganese oxide and using it as a cathode active material has been disclosed. In this case, although there are some effects of improving the output and regenerative characteristics of the battery, there is room for improvement in improving the cycle life because the capacity is small and the slope of the voltage range is also small.

Therefore, there is a high demand for a positive electrode active material having excellent high temperature storage characteristics and cycle life while using thermally safe lithium manganese oxide as a main component.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application have continued in-depth research and various experiments, and in the lithium secondary battery having a negative electrode limiting capacity, for example, LiMn ₂ O ₄ having a spinel structure, which is not stable at high SOC, and When using the electrode active material having a generated flat level section as the positive electrode active material, it was found that the high temperature storage and cycle life of the positive electrode can be greatly improved, and the present invention has been completed.

Accordingly, the positive electrode active material according to the present invention is a positive electrode active material for a lithium secondary battery having a negative electrode limiting capacity, wherein (i) a lithium manganese oxide having a spinel structure (abbreviated as "spinel lithium manganese oxide") and (ii) gas in the charging section It consists of including the electrode active material (abbreviated as "electrode active material which has a flat level section") which has a flat level section which generate | occur | produces.

In the above, the lithium secondary battery having a negative electrode limiting capacity is a lithium secondary battery using a negative electrode active material having a capacity larger than that of the positive electrode active material, preferably a lithium manganese having a spinel structure using a carbon-based material as the negative electrode active material and a positive electrode active material The lithium secondary battery using an oxide of the type | system | group is mentioned.

In such a negative electrode limited capacity lithium secondary battery, the actual use rate (SOC) of the positive electrode is limited by the initial irreversible reaction at the negative electrode surface. That is, a solid electrolyte interface (SEI) film is formed on the surface of the negative electrode during initial charging, in which a large amount of lithium ions emitted from the positive electrode is used, and the amount of lithium ions participating in charging and discharging is substantially reduced. do.

Therefore, in the present invention, the electrode active material (ii) having a flat level section is used together with the lithium manganese oxide (i) which is a main component of the positive electrode active material, so that the lithium source for the initial irreversible reaction on the surface of the negative electrode as described above By providing, to control the operating SOC of the positive electrode active material.

More specifically, when the charge is generated to the flat level, for example, 4.8 V at the time of initial charging, the gas generated in the charging section is removed and then discharged again, the discharge voltage of the electrode active material (ii) having the flat level section is reduced. As it becomes very low, it is very different from the discharge voltage of spinel lithium manganese oxide (i). Therefore, during initial charging, the spinel lithium manganese oxide (i) and the lithium ions of the electrode active material (ii) having the flat level section are moved to the negative electrode to participate in an irreversible reaction and an intercalation reaction. In discharge, lithium ions participating in the occlusion reaction move to a lithium manganese oxide having a relatively high potential.

This is because when only 100% spinel lithium manganese oxide (i) is used, all of the lithium ions moved to the cathode cannot be returned to the lithium manganese oxide due to the irreversible reaction, resulting in an increase in the state of charge (SOC) of the lithium manganese oxide. do.

Therefore, when the battery is operated in the voltage range of 3.0 to 4.2 V from the second charge and discharge, most of the lithium ions move to the spinel lithium manganese oxide (i) and the cathode, and the operating range of the spinel lithium manganese oxide (i) is also wide. The high temperature storage performance is improved.

In the cathode active material of the present invention, the content of the lithium manganese oxide is preferably 50 to 90% by weight, and the content of the electrode active material having the flat level section is preferably 10 to 50% by weight.

If the content of the lithium manganese oxide is too small, the voltage range is not wide enough to improve the high temperature storage performance, and even if the content is too high, the high temperature storage performance is not preferable. In addition, when the content of the electrode active material having the flat level range is less than 10% by weight, it is difficult to expect the effect of the addition, while if it exceeds 50% by weight, there is a problem in high temperature storage and life and contribute to the actual capacity It is not preferable because there is a problem that the capacity of the battery is reduced by reducing the amount of lithium of lithium manganese oxide.

The spinel lithium manganese oxide (i) has a spinel structure, preferably may be a material represented by the following formula (1).

[Formula 1]

Li _{1 + x} Mn _{2 -x- y} M _y O ₄

Where

0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.1, and M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Ti, V, Zr and Zn.

Particularly preferred lithium manganese oxide is LiMn ₂ O ₄ in which x and y are zero.

Since the positive electrode active material of the LiMn ₂ O ₄ having the spinel structure shows a difference in high temperature storage performance depending on the operating SOC, the storage performance of the battery is largely dependent on the SOC of the positive electrode active material. LiMn ₂ O ₄ as a positive electrode active material is unstable at high SOC. Due to the initial irreversible reaction at the negative electrode surface, the LiMn ₂ O ₄ actually operates in the high SOC region during subsequent charge and discharge processes.

Therefore, as in the present invention, when the electrode active material (ii) having the flat level section is added together to LiMn ₂ O ₄ to form a positive electrode active material, lithium ions consumed for irreversible reaction on the surface of the negative electrode during the initial charging process are LiMn _It is provided from the electrode active material (ii) having ₂ O ₄ and the flat level section, and the discharge voltage of the electrode active material (ii) having the flat level section is lowered after the discharge. As a result, the lithium ions of the electrode active material (ii) having the potential plateau region does not function in the real operating voltage of the cell is therefore a relatively to the discharge voltage is moved to the high LiMn ₂ O ₄ lithium ions in the LiMn ₂ O ₄ reaction Can be extended to a low SOC range, resulting in improved high temperature storage characteristics and high temperature cycle life.

The electrode active material (ii) having the flat level section is not particularly limited as long as it has a flat level of a certain section above an oxidation / reduction potential exhibited by a change in the oxidation number of a component in the electrode active material during charge and discharge. It may be a material represented by the formula (2).

[Formula 2]

XLi solid solution (solid solution) of _{(Li 1/3 M 2/} 3) O 2 + YLiM'O 2

Where

At least one element selected from metals having an oxidation number of M = 4 ⁺ , preferably at least one element selected from Mn, Sn, and Ti metals;

M '= at least one element selected from transition metals, preferably at least one element selected from Ni, Mn, Co, Cr metals;

0 <X <1, 0 <Y <1, and X + Y = 1.

When the compound of Chemical Formula 2 is charged at the oxidation / reduction level of M 'or higher, desorption of oxygen occurs to balance redox while lithium is desorbed at a lithium site, thereby having a flat potential section. .

The flat level section of the electrode active material having the flat level section is a potential higher than the oxidation / reduction potential section of a general transition metal, and preferably may be 4.4 to 4.8 V. Therefore, after charging to a charging voltage of at least a flat level, for example, 4.4 to 4.8 V, even after performing the gas removal process can be used as an electrode active material because it can maintain a stable state in the charge and discharge cycle.

The present invention also includes the positive electrode active material, and the step of filling up to the flat level or more of the electrode active material (ii) having the flat level section; And it provides a secondary battery manufacturing method comprising the step of removing the gas.

In current commercially available lithium secondary battery systems, when the voltage is increased above a certain value, it is difficult to configure the battery by side reaction of the electrode active material and the electrolyte, and thus the limit voltage is about 4.4 V. Therefore, when charging and discharging at a charge voltage (for example, 4.4 to 4.8 V) or more above a flat level in a commercialized electrolyte system stable at 4.2 V, the battery performance is adversely affected by the reaction of the electrode active material and the electrolyte, whereas When charging and discharging below the flat level, the battery capacity becomes very low. In addition, in a battery system including the electrode active material (ii) having the flat level section, a large amount of gas is generated when the flat level is charged.

As a result of the study of the inventors of the present application, since the large amount of gas is generated only at the first charge, the gas is charged to a flat level of a certain section or more, which is present in the redox potential section of the transition metal constituting the electrode active material. After the gas was removed, it was confirmed that there was no problem such as generating a large amount of gas even after charging above the flat level in the charge / discharge cycle.

Therefore, the step of filling up to the flat level of the electrode active material or more and the step of removing gas are preferably performed at the time of initial charge.

If the gas is charged after the charging is performed to the flat level or higher during the first charging, when the gas is charged to the flat level or higher from the second charge / discharge cycle, it is possible to secure an increase in capacity without generating a large amount of gas. . Furthermore, even after the charging voltage was lowered after charging above the flat level, it was confirmed that the capacity increased significantly than when the charging level was not higher than the flat level. Therefore, high capacity can be realized even at a low voltage which does not cause side reaction of the electrolyte.

The present invention also relates to a lithium secondary battery produced by the method comprising the positive electrode active material as a component of the battery. Typically, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte.

Hereinafter, the main components of the battery will be described in more detail with respect to the positive electrode, the negative electrode, the separator, the electrolyte, and the like.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder to a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the positive electrode active material. Such a 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 carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive material may be omitted.

The binder is a component that assists in bonding the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode is manufactured by applying and drying a negative electrode material on the negative electrode current collector, and if necessary, the components as described above may be further included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver and the like on the surface, 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.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 of the periodic table) Metal composite oxides such as a group element, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used, and in the present invention, it is particularly preferable to use amorphous carbon as the negative electrode material.

The separator is interposed between the cathode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or nonwovens made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethoxy ethane. , Tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate , Phosphoric acid triester, trimethoxy methane, dioxolon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyroionate Aprotic organic solvents, such as ethyl propionate, can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

Example 1

_{Li 1 .1 Mn 1 .85 Al 0} .05 O 4 and a lithium manganese oxide _{Li (.2 Li 0 Ni 0 .2} Mn 0 .6) O 2 (3/5 [Li (Li 1/3 Mn 2 / _{3) O 2] + 2/5 [} LiNi 1/2 Mn 1/2] O 2) a mixture of the electrode active material has a potential plateau in a range 90: 10 (weight ratio) to prepare a positive electrode active material. A slurry was prepared by mixing the positive electrode active material and carbon black with PVdF [Poly (vinylidene fluoride)] as a binder and NMP as an organic solvent at 85: 10: 5 (weight ratio). The slurry was applied to both sides of Al foil having a thickness of 20 µm and dried to prepare a positive electrode.

Along with the positive electrode, amorphous carbon powder was mixed with a binder PVdF at a weight ratio of 90:10 and then mixed with NMP to prepare a slurry, and then coated on a 10 μm thick copper foil and dried. A negative electrode was prepared by roll pressing to a thickness of 60 μm.

A positive electrode and a negative electrode were prepared, a porous polyethylene film was used as a separator, and a coin-shaped lithium ion battery was manufactured using 1M LiPF ₆ EC / DEC solution as an electrolyte for the battery.

In order to evaluate the high temperature cycle life of the battery manufactured as described above, 50 charge / discharge experiments were performed at a current density of 0.2 C at a high temperature of 50 ° C., and the discharge capacity retention rate was calculated according to Equation 1 below. It is shown in Table 1 below.

Equation 1: Discharge Capacity Retention Rate (%) = (50 Discharge Capacity / 1 Discharge Capacity) x 100

(Based on 50 times, to find the best of relative comparison)

EXAMPLES 2-4

_{Li 1 .1 Mn 1 .85 Al 0} .05 O 4 and a lithium manganese oxide _{Li (.2 Li 0 Ni 0 .2} Mn 0 .6) O 2 (3/5 [Li (Li 1/3 Mn 2 / _3, except _{for) O 2] + 2/5 [LiNi} 1/2 Mn 1/2] O 2) is adjusted as the mixing ratio of the electrode active material has a potential plateau duration described in Table 1 to the cathode active material was prepared in the point Then, a lithium ion battery was manufactured in the same manner as in Example 1. The high temperature cycle life of the battery produced as described above was evaluated, and the results are shown in Table 1 below, respectively.

Comparative Example 1

_{Li 1 .1 Mn 1 .85 Al 0} .05 O 4 a, except that the lithium manganese oxide only was prepared the positive electrode active material was prepared by using a lithium ion battery in the same manner as in Example 1. The high temperature cycle life of the battery of the battery produced as described above was evaluated, and the results are shown in Table 1 below.

TABLE 1

As shown in Table _{1, Li (Li 0 .2 Ni} 0 .2 Mn 0 .6) O 2 (3/5 [Li (Li 1/3 Mn 2/3) O 2] + 2/5 [LiNi Lithium manganese oxide with a certain amount of Li _1.1 Mn _1.85 Al _0.05 O ₄ , which initially reacts to the irreversible reaction occurring at the negative electrode, up to 50% of the electrode active material having a flat level section of _1/2 Mn _1/2 ] O ₂ ) And Li ions of an electrode active material having a flat level section reacting with Li ions of an electrode active material having a flat level section and reacting with a predetermined amount of Li ions remaining at a high voltage. Participation in the intercalation reaction, after the initial charge and discharge, the lithium intercalation reaction between the lithium manganese oxide Li _1.1 Mn _1.85 Al _0.05 O ₄ and the negative electrode active material, so that the soluble region of the lithium manganese oxide increases, the high temperature cycle life and High temperature storage performance will be improved.

As described above, it was found that the batteries according to the embodiment of the present invention have excellent high temperature cycle performance compared to the battery of Comparative Example 1 using lithium manganese oxide alone as the cathode active material.

Example 5

Except that lithium metal was used as a negative electrode, a battery was prepared in the same manner as in Example 1, and the discharge capacity was obtained after flowing a 2C discharge current after fully charging the battery to determine the high rate discharge performance. , As shown in Table 2 to calculate the high rate discharge capacity retention rate.

Equation 2: High Rate Discharge Capacity Retention Rate (%) = (2C Discharge Capacity / 0.2C Discharge Capacity) x 100

[Examples 6 to 8]

As shown in Table _{2, Li 1 .1 Mn 1 .85} Al 0 .05 O 4 and a lithium manganese oxide _{Li (Li 0.2 Ni 0.2 Mn 0.6} ) O 2 (3/5 [Li (Li 1/3 Mn 2 _{/ 3) O 2] + 2/5} [LiNi 1/2 Mn 1/2] O 2) of adjusting the mixing ratio of the electrode active material has a potential plateau interval to produce a positive electrode active material, and battery in the same manner as in example 5 Was prepared. The high rate discharge capacity retention rate of the battery was evaluated, and the results are shown in Table 2, respectively.

Comparative Example 2

_{Li 1 .1 Mn 1 .85 Al 0} .05 O 4 a, except that the lithium manganese oxide only was prepared the positive electrode active material was prepared by using the battery in the same manner as in Example 5. The high rate discharge capacity retention rate of the battery was evaluated, and the results are shown in Table 2, respectively.

Comparative Example 3

_{Li (Li 0 .2 Ni 0 .2} Mn 0 .6) O 2 (3/5 [Li (Li 1/3 Mn 2/3) O 2] + 2/5 [LiNi 1/2 Mn 1/2] A battery was manufactured in the same manner as in Example 5, except that a cathode active material was manufactured using only an electrode active material having a flat level section of O ₂ ). The high rate discharge capacity retention rate of the battery was evaluated, and the results are shown in Table 2, respectively.

TABLE 2

In the results shown in Table 2, a spinel structure _{Li 1 .1 Mn 1 .85 Al 0} .05 O 4 lithium manganese oxide with the _{Li (Li 0 .2 Ni 0 .2} Mn 0 .6) O 2 ( _{3/5 [Li (Li 1/3} Mn 2/3) O 2] + 2/5 [LiNi 1/2 Mn 1/2] O 2) lithium manganese compound in a mixing ratio by weight of the electrode active material has a potential plateau duration of It can be seen that high rate discharge retention is reduced when the ratio of oxide is less than 0.5 (Example 8). It can be seen that this is due to the low high rate discharge retention of the electrode active material having a flat level section. Therefore, when the ratio of lithium manganese oxide is 0.5 or more, it turns out that both high temperature cycling performance and high rate discharge performance are excellent.

As described above, the positive electrode active material according to the present invention improves high temperature storage performance, expands the operating range of spinel lithium manganese oxide, and improves high temperature cycle life.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (9)

A cathode active material for a lithium secondary battery having a negative electrode limiting capacity, comprising: (i) a lithium manganese oxide having a spinel structure (abbreviated as "spinel lithium manganese oxide") and (ii) an electrode active material having a flat level section in which gas is generated during a charging section ( (Abbreviated as "electrode active material having a flat level section"). The cathode active material according to claim 1, wherein the lithium manganese oxide is 50 to 90% by weight, and the lithium metal oxide is 10 to 50% by weight. The cathode active material according to claim 1, wherein the spinel structure lithium manganese oxide is represented by the following Chemical Formula 1. Li _{1 + x} Mn _{2 -x- y} M _y O ₄ (One) Where 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.1, and M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Ti, V, Zr and Zn. The cathode active material of claim 2, wherein the lithium manganese oxide is LiMn ₂ O ₄ in which x and y are 0. ₄ . The cathode active material according to claim 1, wherein the electrode active material having a flat level section in which gas is generated in the charging section is represented by the following Chemical Formula 2. XLi solid solution (solid solution) of _{(Li 1/3 M 2/} 3) O 2 + YLiM'O 2 (2) Where At least one element selected from metals having an oxidation number of M = 4 ⁺ ; M '= at least one element selected from transition metals; 0 <X <1, 0 <Y <1, and X + Y = 1. The electrode active material of claim 4, wherein the electrode active material having the flat state section is M is at least one element selected from Mn, Sn, and Ti metals, and M ′ is at least one element selected from Ni, Mn, Co, and Cr metals. A positive electrode active material characterized by. The cathode active material according to any one of claims 1 to 3, wherein the electrode active material having the flat level section has a flat level section of 4.4 to 4.8 V. Filling the cathode active material according to claim 1 to a flat level or more; And Method of manufacturing a lithium secondary battery comprising the step of removing gas. A lithium secondary battery prepared by the method according to claim 8.