KR100868259B1 - Cathode Active Material for Lithium Secondary Battery and Lithium Secondary Battery Having the Same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the same, comprising a spinel structure lithium manganese oxide and a lithium metal oxide having a relatively low operating voltage, and thus having excellent high temperature storage characteristics and cycle life. It is to provide a positive electrode active material having a, and a lithium secondary battery containing it as a component of the positive electrode.

Description

Cathode Active Material for Lithium Secondary Battery and Lithium Secondary Battery Having the Same}

1 and 2 are schematic diagrams of one exemplary battery usable in the present invention.

[Explanation of symbols on the main parts of the drawings]

10: cathode 20: separator

30: positive electrode 40: positive terminal

50: negative terminal 60: battery case

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a lithium manganese oxide having a spinel structure and a lithium metal oxide having a relatively low operating voltage, and thus having excellent high temperature. The present invention provides a cathode active material having storage characteristics and cycle life, and a lithium secondary battery including the same as a component of a cathode.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used.

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. Reaction in lithium secondary jersey 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 occluded in the spinel electrode are ejected and 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 and are external The electrons are sent out to flow current.

The spinel-structured lithium manganese oxide has the advantages of excellent thermal safety, low cost, and easy synthesis, but has a problem of small capacity, low lifetime characteristics due to side reactions, high temperature characteristics, and low conductivity.

In order to solve this problem, attempts have been made to use spinel structure lithium manganese oxide in which some other metal is substituted. 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, attempts have been made to maintain the stability of the structure by doping or replacing other metals. For example, Korean Patent Application Publication No. 2002-24520 uses a lithium manganese oxide having a side structure to form a charge. 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.

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.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the present inventors have used LiMn ₂ O ₄ having a spinel structure as a positive electrode active material which is not stable at high SOC as a positive electrode, and has a negative electrode limiting capacity in a lithium secondary battery. Lithium metal oxide, such as o-LiMO ₂ , having a low operating voltage was added to the positive electrode active material to cause an irreversible reaction on the surface of the negative electrode during initial charging by lithium ions of the lithium metal oxide to form LiMn ₂ O ₄ as a positive electrode active material. By regulating the operating SOC, it has been found that the high temperature storage and cycle life of the anode can be greatly improved and the present invention has been completed.

The cathode active material according to the present invention for achieving the above object is a cathode active material for a lithium secondary battery having a negative electrode limiting capacity, the lithium manganese oxide of the spinel structure of 70 to 90% by weight, lithium metal oxide having a relatively low operating voltage 10 And 30 wt%.

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.

The lithium manganese oxide has a spinel structure and is a material represented by the following Chemical Formula 1.

Li _{1 + x} Mn _2-xy 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.

In a lithium secondary battery with a negative electrode limiting capacity, the actual use of charge (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 first charge-display cathode, in which a large amount of lithium ions emitted from the anode is used, and substantially the lithium ions participating in charge and discharge are used. The amount will be reduced.

In the present invention, using a lithium metal oxide having a low operating voltage of less than the operating voltage of the battery together with the lithium manganese oxide which is the main component of the positive electrode active material, the lithium source for the initial irreversible reaction on the negative electrode surface as described above By providing from the lithium metal oxide, it is possible to control the operating SOC of the positive electrode active material.

Thus, the term "relatively low operating voltage" as used above means an operating voltage lower than the operating voltage of the battery. Lithium metal oxides having a relatively low operating voltage include, but are not limited to, LiMnO ₂ , LiFePO ₄ , and the like. When using LiMn ₂ O ₄ as the main component of the positive electrode active material, the lithium metal oxide is particularly preferably LiMnO ₂ (o-LiMnO ₂ ) having an orthorhombic crystal structure. Since o-LiMnO ₂ consists of the same constituents as LiMn ₂ O ₄ , it is preferable in terms of homogeneity of the material, and the reason will be described later.

Since the positive electrode active material of the LiMn ₂ O ₄ having the spinel structure shows a difference in high temperature storage performance according to the operating SOC, the storage performance of the battery largely depends 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 o-LiMnO ₂ is added 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 initial charging are provided from o-LiMnO ₂ at a low voltage. At higher voltages, lithium ions provided from LiMn ₂ O ₄ and inserted into the cathode contribute to the actual capacity of the battery. As a result, lithium ions of o-LiMnO ₂ that do not act at the actual operating voltage of the battery are consumed for the irreversible reaction on the surface of the negative electrode, and lithium ions of LiMn ₂ O _{4 which} act at the actual operating voltage of the battery are consumed for the irreversible reaction. The amount to be reduced can be greatly reduced. This can extend the range in which Li-ion reacts in LiMn ₂ O ₄ to a low SOC range, resulting in improved high temperature storage properties and high temperature cycle life.

The operating voltage of the battery, that is, the operating voltage of LiMn ₂ O ₄ is approximately 3.5 to 4.5 V, and the operating voltage of o-LiMnO ₂ is approximately 2.5 to 3.5 V.

The layered o-LiMnO ₂ releases one lithium ion per two oxygen atoms during initial charging and is expected to be converted to a spinel structure after such charge and discharge. By such structural conversion, it is converted into a material capable of occluding and releasing one lithium ion per two oxygen atoms. Thus, the use of LiMnO ₂ is more preferred when using LiMn ₂ O ₄ .

In the cathode active material of the present invention, the content of the lithium metal oxide is 10 to 30% by weight based on the weight of the lithium manganese oxide, as described above, if the content is too small, the effect of the addition of lithium metal oxide On the other hand, too much is not preferable because there is a problem in high temperature storage and life and there is a problem that the capacity of the battery is reduced by reducing the amount of lithium of LiMn ₂ O ₄ which contributes to the actual capacity.

The present invention also relates to a lithium secondary battery 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.

1 and 2 illustrate one exemplary structure of a lithium secondary battery according to the present invention.

1 and 2, in the lithium secondary battery, the negative electrode 10 and the positive electrode 30 are sealed inside the battery case 60 with a separator 20 interposed therebetween. A negative terminal 50 is formed on the top of the negative electrode 10 for electrical connection with other devices constituting a battery and an external device, and a positive terminal 40 for such electrical connection is also formed on the top of the positive electrode 20. Formed.

As shown in the figure, a battery composed of a case 60 of a shape is called a pouch-type battery, and the present invention can be applied to not only such a pouch-type battery but also a cylindrical battery and a square battery.

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 agent, and a binder onto a positive electrode current collector, followed by drying, and optionally, a filler may be 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 agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent 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, addition of the conductive agent may be omitted because the conductive second coating layer is added to the positive electrode active material.

The binder is a component that assists in bonding the active material and the conductive agent 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, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

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' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, 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.

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 non-woven fabrics 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 lithium. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxorone, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and 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.

As the inorganic solid electrolyte, for example, 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

A lithium active material was prepared by mixing lithium manganese oxide of Li _1.1 Mn _1.85 Al _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 90:10 (weight ratio). 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, a button-type battery was manufactured using lithium metal as a negative electrode and a porous polyethylene film as a separator, and a 1M LiPF ₆ EC / EMC solution was used as an electrolyte. In the battery manufactured as described above, the capacity per gram of the positive electrode was measured at 4.3 V charge / 3.4 V discharge operating voltage, and in order to evaluate the high temperature life, 50 charge / discharge experiments were performed at a current density of 0.2 C at a high temperature of 50 ° C. The discharge capacity retention rate was calculated according to Equation 1 below, and the results are shown in Table 1.

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

The basis for 50 times is to find the optimum of relative comparison.

[Examples 2 and 3]

As described in Table 2 below, a positive electrode active material was prepared by adjusting a mixing ratio of lithium manganese oxide of Li _1.1 Mn _1.85 Al _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ , and Example 1 The cells were assembled in the same manner to evaluate the capacity per gram of positive electrode and the high temperature life. The results are shown in Table 1 below.

Comparative Example 1

A positive electrode active material was manufactured by using lithium manganese oxide of Li _1.1 Mn _1.85 Al _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 100: 0 (weight ratio), and a battery was prepared in the same manner as in Example 1. The assembly was performed to evaluate the capacity per gram of the positive electrode and the high temperature life. The results are shown in Table 1 below.

Comparative Example 2

A positive electrode active material was prepared by using lithium manganese oxide of Li _1.1 Mn _1.85 Al _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 0: 100 (weight ratio), and a battery was prepared in the same manner as in Example 1. The assembly was performed to evaluate the capacity per gram of the positive electrode and the high temperature life. The results are shown in Table 1 below.

As shown in Table 1, the capacity per gram of the positive electrode in the battery having an operating voltage of 3.4 ~ 4.3 V can be seen that as the ratio of o-LiMnO ₂ increases as the discharge capacity is increased. This indicates that the Li of the positive electrode, which was moved to Li metal as the negative electrode during 4.3 V charging, did not return in the discharge up to 3.4 V because the operating voltage of the o-LiMnO ₂ cathode active material was lower than 3.4 V. The reason for limiting the discharge voltage to 3.4 V is that the actual spinel lithium manganese oxide does not fall below 3.4 V.

In the case of 50 ° C high temperature cycles, the proportion of spinel lithium manganese oxide is preferably 70% or more. The reason is that when a large amount of o-LiMnO ₂ is present, as shown in Table 1 above, The cycle life is not good because the temperature of 50 ℃ is high, but if it contains up to 30%, o-LiMnO ₂ is charged to 4.3 V and then discharged to 3.4 V, and the structure is changed to the structure of spinel LiMn ₂ O ₄ . It is believed that the new spinel LiMn ₂ O ₄ compensates for the capacity reduction of the existing spinel LiMn ₂ O ₄ .

Example 4

A positive electrode active material was prepared using lithium manganese oxide of Li _1.1 Mn _1.85 Mg _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 90:10 (weight ratio). 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.

Spherical average particle size 12 artificial graphite powder with high crystallinity was mixed with PVDF as a binder at 90:10 (weight ratio), and then mixed with NMP to prepare a slurry, and then coated on 10 μm thick copper foil and dried. The negative electrode was prepared by roll pressing to a thickness of 60 μm.

Using the prepared positive and negative electrodes, using a 1M LiPF ₆ EC / DEC solution as the electrolyte of the battery, a laminated lithium battery as shown in Figure 1 was prepared. Using the manufactured battery, the initial charge capacity and discharge capacity of the battery having an operating voltage of 4.2 to 2.5 V were evaluated, and the state of charge (SOC) of the battery was adjusted to 50 and 100 for two weeks of storage at a high temperature of 65 ° C. The capacity recovery rate after high temperature storage was calculated according to Equation 2 below, and the results are shown in Table 2 below.

[Examples 5 and 6]

As described in Table 2 below, a positive electrode active material was prepared by adjusting a mixing ratio of lithium manganese oxide of Li _1.1 Mn _1.85 Mg _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ . Assemble the cell in the same way, evaluate the initial charge capacity and discharge capacity of the cell, adjust the state of charge (SOC) to 50 and 100, store for 2 weeks at 65 ℃ high temperature, and display the result. 2 is shown.

[Comparative Example 5]

A positive electrode active material was manufactured by using lithium manganese oxide of Li _1.1 Mn _1.85 Mg _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 100: 0 (weight ratio), and a battery was prepared in the same manner as in Example 4. Assembled and evaluated the initial charge capacity and discharge capacity of the cell, and adjusted the state of charge (SOC) of the cell to 50 and 100 to perform two weeks storage at 65 ℃ high temperature, the results are shown in Table 2 below.

Comparative Example 6

A positive electrode active material was prepared by using lithium manganese oxide of Li _1.1 Mn _1.85 Mg _0.05 O ₄ and lithium manganese oxide of orthorhombic crystal structure of o-LiMnO ₂ at 0: 100 (weight ratio), and a battery was prepared in the same manner as in Example 4. Assembled and evaluated the initial charge capacity and discharge capacity of the cell, and adjusted the state of charge (SOC) of the cell to 50 and 100 to perform two weeks storage at 65 ℃ high temperature, the results are shown in Table 2 below.

As shown in Table 2, up to 30% of the ratio of o-LiMnO ₂ is similar to the discharge efficiency of the charge of the battery, which includes lithium of o-LiMnO ₂ that reacts at an initial low voltage to the irreversible reaction occurring at the negative electrode, This is because lithium of a lithium manganese composite oxide having a spinel structure mainly participates in an intercalation reaction to a negative electrode, which contributes to the capacity of a battery. As in Example 6, when the ratio of o-LiMnO ₂ is increased by more than 30%, the amount of lithium that can represent the capacity of the battery is decreased at the operating voltage of 4.2 to 2.5 V. Therefore, the efficiency of the battery is reduced. Therefore, when a certain amount of o-LiMnO ₂ having a lower operating voltage than spinel lithium manganese composite oxide is added to the spinel lithium manganese composite oxide, the capacity and efficiency are similar because lithium of o-LiMnO ₂ is used for the initial irreversible reaction of the cathode. The amount of lithium used in the spinel lithium manganese composite oxide is increased. Looking at the storage characteristics of 65 ℃, the SOC of the spinel lithium manganese composite oxide of the positive electrode when the battery is stored in SOC100 is almost the same, so there is almost no difference in high temperature storage characteristics, as in Example 6 o-LiMnO ₂ ratio is increased by 30% When the high temperature performance of o-LiMnO ₂ itself is lower than the spinel lithium manganese composite oxide, the storage characteristics of the battery are reduced. However, when the battery is stored in the SOC50 state, the content of o-LiMnO ₂ is increased to a certain level, so that the SOC of the spinel lithium manganese composite oxide itself is lowered, and more stable results are obtained at high temperatures. In the case of Example 6, as described above, the high temperature performance of o-LiMnO ₂ itself is lower than that of the spinel lithium manganese composite oxide, thereby reducing the storage characteristics of the battery.

As described above, the positive electrode active material according to the present invention provides excellent high temperature storage characteristics and 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 (6)

A cathode active material for a lithium secondary battery having a negative electrode limiting capacity, comprising 70 to 90 wt% of a lithium manganese oxide having a spinel structure represented by Formula 1 below, and 10 to 30 wt% of a lithium metal oxide having a relatively low operating voltage. The cathode active material is composed of: Li _{1 + x} Mn _2-xy M _y O ₄ (1) Wherein 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. delete delete The cathode active material according to claim 1, wherein the lithium metal oxide is one or more selected from the group consisting of LiMnO ₂ and LiFePO ₄ . delete A lithium secondary battery comprising the cathode active material according to claim 1.

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