JP2006216305A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means to suppress deterioration of a capacity caused by repeated charge and discharge, in a secondary battery using a lithium manganese oxide as a positive electrode active material. <P>SOLUTION: This secondary battery has a lithium nickel oxide and the lithium manganese oxide as positive electrode active materials. In this secondary battery, the average particle diameter of the lithium nickel oxide is smaller than the average particle diameter of the lithium manganese oxide, and the content of the lithium nickel oxide is 22 wt.% to 38 wt.% of the total quantity of the lithium nickel oxide and the lithium manganese oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary battery having lithium nickel oxide and lithium manganese oxide.

  In recent years, development of electric vehicles (EV), hybrid vehicles (HEV), and fuel cell vehicles (FCV) has been promoted against the background of raising awareness of environmental problems. As these power sources, secondary batteries that can be repeatedly charged and discharged are optimal, and lithium ion secondary batteries that can be expected to have a high output are attracting attention. By the way, lithium manganese oxide is one of positive electrode materials for lithium ion secondary batteries, and has advantages such as low cost and excellent thermal stability. However, a lithium ion secondary battery using lithium manganese oxide as a positive electrode active material has a drawback that it tends to cause a decrease in charge / discharge capacity due to repeated charge / discharge, and should be avoided in practical use of a lithium ion battery. It is a big problem that cannot be done.

As a conventional technique for effectively suppressing a decrease in capacity due to repeated charge and discharge, for example, there is one described in Patent Document 1. The lithium ion secondary battery of Patent Document 1 is a secondary battery that uses lithium manganese oxide as a positive electrode active material, and is characterized in that a hydrogen ion scavenger is disposed at a location in contact with the electrolyte in the battery. It is said. It is thought that the cause of the capacity | capacitance fall by repeated charging / discharging is the increase in Mn density | concentration in electrolyte solution by elution of Mn from lithium manganese oxide. It has also been suggested that hydrogen ions (H ⁺ ) present in the electrolyte promote elution of Mn in the lithium manganese oxide. Therefore, the hydrogen ion scavenger reduces the hydrogen ion concentration in the electrolytic solution and prevents the elution of Mn from the lithium manganese oxide, thereby suppressing the decrease in capacity.

  By the way, in the said patent document, lithium nickel oxide is used as a hydrogen ion scavenger. Further, it is shown that the Mn concentration in the electrolytic solution becomes lower as the content of the lithium nickel oxide with respect to the total amount of the lithium nickel oxide and the lithium manganese oxide becomes lower, and when the content is 20%, the electrolytic solution It has been shown that the Mn concentration in the inside becomes almost zero (see Table 1 of Patent Document 1).

However, even in the lithium ion secondary battery as described above, although it is possible to suppress the decrease in capacity due to repeated charge and discharge, there is a demand for further suppression of the decrease in capacity.
JP 2000-077097 A

  Therefore, an object of the present invention is to provide means for suppressing a decrease in capacity due to repeated charge and discharge in a secondary battery using lithium manganese oxide as a positive electrode active material.

  The present invention provides a secondary battery having lithium nickel oxide and lithium manganese oxide as a positive electrode active material, wherein the average particle diameter of the lithium nickel oxide is smaller than the average particle diameter of the lithium manganese oxide. And it is a secondary battery whose content of the said lithium nickel oxide is 22 wt%-38 wt% with respect to the total amount of the said lithium nickel oxide and the said lithium manganese oxide.

  According to the secondary battery of the present invention, the life characteristics are greatly improved in order to effectively suppress the decrease in capacity due to repeated charge and discharge.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the secondary battery using lithium nickel oxide and lithium manganese oxide as the positive electrode active material, the present invention defines the size relationship between the average particle diameters of lithium nickel oxide and lithium manganese oxide, and lithium nickel oxide It was completed by finding a heterogeneous effect that significantly improves the life characteristics by setting the oxide content in an optimum range.

  As described above, Patent Document 1 suggests that reducing elution of Mn from the lithium-manganese composite oxide is indispensable for improving the life characteristics of the secondary battery (see “0025 of Patent Document 1”). ). Moreover, in order to reduce the Mn concentration in the electrolytic solution, it has been shown that the content of lithium nickel oxide relative to the total amount of lithium-manganese composite oxide may be increased, but when the content is 20% It has been shown that the Mn concentration in the electrolytic solution becomes almost zero (see Table 1 of Patent Document 1). Therefore, in order to reduce the Mn concentration in the electrolytic solution, the above content is sufficient up to 20%, and even if lithium nickel oxide is further added, the life characteristics should not change.

  However, in the present invention, when the average particle diameter of lithium nickel oxide is smaller than the average particle diameter of lithium manganese oxide, the content of lithium nickel oxide is 22 wt% with respect to the total amount of lithium-manganese composite oxide. It has been found that the life characteristics are further greatly improved in the range of ˜38 wt%. In particular, it was found that the life characteristics were the highest when the content was 30 wt%. Therefore, the effect in the present invention is not caused by reducing the concentration of Mn in the electrolytic solution as in the prior art, but is considered to be caused by some other mechanism. In addition, the secondary battery of patent document 1 does not prescribe | regulate the magnitude relationship of the average particle diameter of lithium nickel oxide and lithium manganese oxide.

  In the secondary battery according to the present invention, the average particle diameter of lithium nickel oxide is smaller than the average particle diameter of lithium manganese oxide, and the content of lithium nickel oxide is lithium nickel oxide and lithium manganese oxide. It is 22 wt%-38 wt% with respect to the total amount of a thing. When these conditions are satisfied, the effect of improving the life characteristics is significantly improved as compared with the conventional secondary battery. The mechanism that brings about this effect is not clear, but in the range from 22 wt% to 38 wt%, the positive electrode density is higher than the other ranges, and the life characteristics are improved by this high positive electrode density. I think that the. Here, the average particle diameter is a 50% cumulative particle diameter, and is a particle diameter when the volume integrated from 0 μm is 50% in the particle size distribution diagram. In order to calculate the average particle size, the number of particles n and the diameter d per particle are measured by laser light scattering using a Microtrac particle size distribution analyzer. The particle size analyzer is not limited to the above device, but when a significant blur occurs in the numerical value by the particle size analyzer, the value measured by the device is used as the average particle size.

  In addition, the more preferable range of content of lithium nickel oxide with respect to the total amount of lithium nickel oxide and lithium manganese oxide is 28 wt%-32 wt%. The effect of improving the life characteristics increases as the content approaches 30 wt%, and the effect is maximized when the content is 30 wt%.

  Hereinafter, the secondary battery of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a secondary battery according to the present invention. 1 is a configuration diagram of a polymer secondary battery, the secondary battery according to the present invention may be a liquid type or a gel type, and is not particularly limited.

  In the polymer secondary battery 10, an electrolyte layer 40 is sandwiched between a positive electrode (electrode) 20 and a negative electrode (electrode) 30. The electrolyte layer 40 is a polymer solid electrolyte layer, and is composed of a polymer gel electrolyte having a polymer component or an all solid (intrinsic) polymer electrolyte.

  The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24. A positive electrode active material layer 24 is formed on the positive electrode current collector 22 and is electrically connected to each other. The positive electrode current collector 22 is formed of, for example, an aluminum foil.

  The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34. A negative electrode active material layer 34 is formed on the negative electrode current collector 32 and is electrically connected to each other. The negative electrode current collector 32 is formed of, for example, a copper foil.

  Next, the manufacturing method of the secondary battery of this invention is demonstrated.

  FIG. 2 is a diagram illustrating a state in which the constituent elements of the polymer secondary battery 10 are sequentially stacked. First, the positive electrode 20 is formed by the positive electrode current collector 22 and the positive electrode active material layer 24. The negative electrode 30 is formed by the negative electrode current collector 32 and the negative electrode active material layer 34. Subsequently, the electrolyte layer 40 is prepared, and the electrolyte layer 40 is overlaid on the positive electrode 20. On the electrolyte layer 40, a negative electrode 30 is further stacked. Thereby, the electrolyte layer 40 is sandwiched between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30, and the polymer secondary battery 10 is formed.

  The configuration of the polymer secondary battery 10 is not particularly limited as long as it is a known material used for a general lithium ion secondary battery, except for those specifically described.

  Hereinafter, the current collectors 22 and 32, the positive electrode active material layer 24, the negative electrode active material layer 34, and the electrolyte layer 40 will be described. However, the substances exemplified below are merely examples, and the technical scope of the present invention is not limited to the embodiments using the following materials.

  First, the current collector will be described.

  The current collector includes a positive electrode current collector used for the positive electrode and a negative electrode current collector used for the negative electrode. The positive electrode current collector is made of aluminum, for example. Moreover, the negative electrode current collector is made of copper, for example. The current collector needs to be formed by laminating and stacking on any shape using thin film manufacturing techniques such as spray coating, for example, aluminum, copper, titanium, nickel, stainless steel ( SUS), a metal powder such as an alloy thereof as a main component, and a current collector metal paste containing a binder (resin) and a solvent is heated and molded. These metal powders may be used alone or in combination of two or more. Taking advantage of the characteristics of the manufacturing method, different types of metal powders may be laminated in multiple layers. The binder is not particularly limited. For example, a conventionally known resin binder material such as an epoxy resin can be used, and a conductive polymer material may be used. Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers.

  Subsequently, the positive electrode active material layer will be described.

  The positive electrode active material layer includes at least a positive electrode active material and may include a binder and a conductive additive.

  In this invention, although lithium nickel oxide and lithium manganese oxide are employ | adopted as a positive electrode active material, the compound which can be used as a positive electrode active material other than the said oxide may be included.

Lithium nickel oxide is a composite oxide composed of lithium, nickel, and oxygen. For example, for LiNiO ₂ , Li ₂ NiO ₂ , LiNi ₂ O ₄ , and Li ₂ Ni ₂ O ₄ , and these oxides, The thing etc. which contain another element in part can be mentioned. Note that since the lithium nickel oxide is an alloy, it may contain some impurities.

Among these lithium nickel oxides, it is particularly preferable to use lithium nickelate (LiNiO ₂ ) and those containing other elements in part. That is, the lithium nickel oxide is LiNi _1-x M _x O ₂ (wherein M is at least one metal atom selected from the group consisting of cobalt, manganese, aluminum, iron, copper, and strontium). And 0 ≦ X ≦ 0.5). By doping the lithium nickel oxide composed of lithium, nickel, and oxygen with another metal element, the secondary battery can be stabilized, increased in capacity, improved in safety, and the like. In particular, lithium nickelate and those containing a part of other metal elements can be expected to have a greater effect.

The lithium manganese oxide is a composite oxide composed of lithium, manganese, and oxygen. For example, lithium manganate having a spinel structure such as LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , LiMnO _2, and Li ₂ MnO ₃ , and Examples of these oxides include those containing other elements in part. Among these lithium manganese oxides, those having a spinel structure such as LiMn ₂ O ₄ are preferable. Note that since the lithium manganese oxide is an alloy, it may contain some impurities.

  In order to reduce the electrode resistance of the polymer battery, the positive electrode active material may have a particle size smaller than that generally used in a solution type lithium ion battery in which the electrolyte is not solid. Specifically, the average particle diameter of the positive electrode active material is preferably 0.1 to 5 μm.

  Examples of the conductive assistant include acetylene black, ketjen black, carbon black, graphite and the like, copper powder, silver powder and the like, and metal powder made of a mixture thereof. However, it is not necessarily limited to these.

  The blending amount of the positive electrode active material, the binder and the conductive assistant in the positive electrode active material layer should be determined in consideration of the purpose of use of the battery such as emphasis on output and energy, and ion conductivity. Further, the thickness of the positive electrode active material layer is not particularly limited, and should be determined in consideration of the purpose of use of the battery such as emphasis on output and energy, and ion conductivity. By the way, the thickness of a general positive electrode active material layer is about 5-500 micrometers.

  Next, the negative electrode active material layer will be described.

  The negative electrode active material layer contains at least a negative electrode active material and may contain a binder. Except for the type of the negative electrode active material, the description is basically the same as that described for the positive electrode active material. Examples of the negative electrode active material that can absorb and release lithium ions of the positive electrode active material, such as amorphous carbon such as hard carbon, non-graphitizable carbon, graphitizable carbon, or graphite. Materials can be mentioned.

  Next, the electrolyte layer will be described.

  The electrolyte layer is a layer composed of a polymer having ion conductivity, and the material is not limited as long as it exhibits ion conductivity. For example, an intrinsic polymer electrolyte, a polymer gel electrolyte, etc. are mentioned as an electrolyte layer.

Examples of the intrinsic polymer electrolyte include known solid polymer electrolytes such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. The solid polymer electrolyte layer preferably contains a supporting salt (lithium salt) in order to ensure ionic conductivity. As the supporting salt, LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , or a mixture thereof can be used. However, it is not necessarily limited to these. A polyalkylene oxide polymer such as PEO and PPO can dissolve lithium salts such as LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ well. Moreover, excellent mechanical strength is exhibited by forming a crosslinked structure.

The polymer gel electrolyte generally refers to an electrolyte solution held in an all-solid polymer electrolyte having ion conductivity. In the case of forming an electrolyte layer with a polymer gel electrolyte, the electrolytic solution is maintained at more than 0 wt% and not more than 98 wt%. The electrolytic solution (electrolyte salt and plasticizer) is not particularly limited, and various conventionally known electrolytic solutions can be appropriately used. For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiTaF ₆ , LiAlCl ₄ , Li ₂ B ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N or an organic acid anion salt selected from at least one lithium salt (electrolyte salt), cyclic carbonates such as propylene carbonate and ethylene carbonate; dimethyl carbonate; Chain carbonates such as methyl ethyl carbonate and diethyl carbonate; ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; γ-butyrolactone, etc. Lactones; Nitriles such as acetonitrile Esters such as methyl propionate; amides such as dimethylformamide; plasticizers such as aprotic solvents (organic solvents) mixed with at least one selected from methyl acetate and methyl formate ) Can be used. However, it is not necessarily limited to these.

  In the present application, a polymer electrolyte having a similar electrolyte solution held in a polymer skeleton having no lithium ion conductivity is also included in the polymer gel electrolyte. The type of electrolyte solution (electrolyte salt and plasticizer) used is not particularly limited.

  Examples of the solid polymer electrolyte having ion conductivity include known solid polymer electrolytes such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

  For example, polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), etc. are used as the polymer having no lithium ion conductivity used in the polymer gel electrolyte. it can. However, it is not necessarily limited to these. Note that PAN, PMMA, etc. are in a class that has almost no ionic conductivity, and can be a polymer having the above ionic conductivity, but here, they are used for polymer gel electrolytes. This is exemplified as a polymer having no lithium ion conductivity.

  When the electrolyte layer is made of a polymer gel electrolyte, the electrolyte layer is formed by impregnating a separator such as a nonwoven fabric with a polymer gel raw material solution and then polymerizing using the above-described various methods. It may be. By using the separator, the filling amount of the electrolytic solution can be increased, and the thermal conductivity inside the battery is ensured.

  Hereinafter, the present invention will be described specifically by way of examples.

(Relationship between lithium nickel oxide content and internal resistance increase rate)
In order to verify the relationship between the content of lithium nickel oxide in lithium nickel oxide and lithium manganese oxide and the rate of increase in internal resistance after 1000 charge / discharge cycles, for the secondary battery according to the present invention, A charge / discharge cycle test was conducted.

(Experiment 1)
As the positive electrode active material, lithium manganese oxide (Li _1.2 Mn _1.8 O ₄ ) having an average particle diameter of 10 μm and lithium nickel oxide (LiNi _0.81 Co _0.15 Al _0.04 ) having an average particle diameter of 5 μm. O ₂ ) was employed. Moreover, hard carbon was employ | adopted as a negative electrode active material, and the mixing ratio of hard carbon and PVdF was 90:10. Furthermore, carbon black was used as the conductive agent, and polyvinylidene fluoride (PVdF) was used as the binder (binder). First, a positive electrode active material and a conductive agent are mixed, and the mixed positive electrode active material and the conductive agent are uniformly dispersed in N methyl-2-pyrrolidone (NMP) in which polyvinylidene fluoride as a binder is dissolved. It was created. Subsequently, the prepared slurry was uniformly applied onto an aluminum metal foil serving as a positive electrode side current collector, and NMP was evaporated to form a positive electrode layer. The weight ratio of the positive electrode active material, the conductive agent and PVDF is 89: 8: 3, and the content of lithium nickel oxide in the positive electrode active material (lithium nickel oxide and lithium manganese oxide) is 0 wt% to 50 wt%. %.

  The secondary battery using the positive electrode active material was charged and discharged 1000 times at a current value of 1 CA at 45 ° C., and the rate of increase in internal resistance after 1000 times was calculated. The charge / discharge cycle was performed by charging and discharging the battery with a constant current. Further, one charge / discharge cycle has four steps of charge-charge stop-discharge-discharge stop. Table 1 shows the charge / discharge cycle conditions.

  The internal resistance is calculated by Ohm's law using the voltage drop at the time when the battery is discharged at a constant current. The rate of increase in internal resistance (%) is calculated by “(internal resistance before charge / discharge / internal resistance after charge / discharge−1) × 100”.

  FIG. 3 shows the lithium nickel oxide content and charge / discharge in the lithium nickel oxide and lithium manganese oxide when the average particle sizes of lithium manganese oxide and lithium nickel oxide are 10 μm and 5 μm, respectively. The relationship of the rate of increase in internal resistance after 1000 cycles is shown. From FIG. 3, it can be seen that when the content of lithium nickel oxide is in the range of 22 wt% to 38 wt%, the rate of increase in internal resistance is significantly lower than in other ranges, and is particularly low at 30 wt%. I understand. This mechanism is not clear, but in the range from 22 wt% to 38 wt%, the positive electrode density is higher than the other ranges, and it seems that the life characteristics are improved by this high positive electrode density. .

(Experiment 2)
The lithium nickel oxide (LiNi _0.81 Co _0.15 Al _0.04 O ₂ ) used as the positive electrode active material was charged in the same procedure as in Experiment 1 except that the average particle size was changed from 5 μm to 10 μm. A discharge cycle test was conducted. FIG. 4 shows the lithium nickel oxide content and charge / discharge in the lithium nickel oxide and lithium manganese oxide when the average particle sizes of lithium manganese oxide and lithium nickel oxide are 10 μm and 10 μm, respectively. The relationship of the rate of increase in internal resistance after 1000 cycles is shown. In FIG. 4, there was no portion where the rate of increase in internal resistance as seen in FIG. 3 was significantly reduced. Therefore, in improving the life characteristics of the secondary battery according to the present invention, it is considered preferable that the average particle diameter of the lithium nickel oxide is smaller than the average particle diameter of the lithium manganese oxide.

(Experiment 3)
Experiment 1 except that the lithium nickel oxide employed as the positive electrode active material was changed from LiNi _0.81 Co _0.15 Al _0.04 O ₂ to LiNi _1/3 Co _1/3 Mn _1/3 O ₂ A charge / discharge cycle test was conducted by the same procedure as described above. FIG. 5 shows the content of lithium nickel oxide in lithium nickel oxide and lithium manganese oxide when LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the lithium nickel oxide. The relationship of the internal resistance increase rate after 1000 charge / discharge cycles is shown. From FIG. 5, in the range of lithium nickel oxide content from 22 wt% to 38 wt%, the decrease in the rate of increase in internal resistance is small compared to the case of Experiment 1, but it is lower than the other ranges. It can be seen that it is particularly low at 30 wt%.

(Relationship between average particle size of lithium nickel oxide and rate of increase in internal resistance)
Then, in order to verify the relationship between the average particle diameter of lithium nickel oxide and the internal resistance increase rate after 1000 charge / discharge cycles, a charge / discharge cycle test was performed on the secondary battery according to the present invention.

(Experiment 4)
The content of lithium nickel oxide in the positive electrode active material was fixed at 30 wt%, and the average particle diameter of the lithium nickel oxide was changed from 0.5 μm to 20 μm. The average particle size of the lithium manganese oxide was fixed at 10 μm. Other than that, the procedure is the same as in Experiment 1. FIG. 6 shows the relationship between the average particle diameter of lithium nickel oxide having a lithium nickel oxide content of 30 wt% and the rate of increase in internal resistance after 1000 charge / discharge cycles. FIG. 6 shows that the rate of increase in internal resistance is constant when the average particle diameter of lithium nickel oxide is greater than or equal to the average particle diameter of lithium manganese oxide. In addition, in the range where the average particle diameter of lithium nickel oxide is smaller than the average particle diameter of lithium manganese oxide, it can be seen that the lower the average particle diameter of lithium nickel oxide, the lower the internal resistance increase rate. . Therefore, in improving the life characteristics of the secondary battery according to the present invention, it is considered preferable that the average particle diameter of the lithium nickel oxide is smaller than the average particle diameter of the lithium manganese oxide.

  The secondary battery according to the present invention can be applied to a driving battery such as an electric vehicle.

It is a block diagram of the secondary battery which concerns on this invention. It is a figure which shows a mode that the component of the secondary battery of this invention is laminated | stacked sequentially. Lithium nickel oxide content and lithium nickel oxide content in lithium nickel oxide and lithium manganese oxide when the average particle diameters of lithium manganese oxide and lithium nickel oxide are 10 μm and 5 μm, respectively, and after 1000 charge / discharge cycles It is a graph which shows the relationship of the internal resistance increase rate of. Content of lithium nickel oxide in lithium nickel oxide and lithium manganese oxide when the average particle diameters of lithium manganese oxide and lithium nickel oxide are 10 μm and 10 μm, respectively, and after 1000 charge / discharge cycles It is a graph which shows the relationship of the internal resistance increase rate of. Lithium nickel oxide content in lithium nickel oxide and lithium manganese oxide when LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the lithium nickel oxide, and charge / discharge cycle 1000 It is a graph which shows the relationship of the internal resistance increase rate after rotation. It is a graph which shows the relationship between the average particle diameter of lithium nickel oxide whose content of lithium nickel oxide is 30 wt%, and the internal resistance increase rate after 1000 charge / discharge cycles.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Polymer-type secondary battery, 20 ... Positive electrode (electrode), 22 ... Positive electrode collector, 24 ... Positive electrode active material layer, 30 ... Negative electrode (electrode), 32 ... Negative electrode collector, 34 ... Negative electrode active material layer, 40 ... electrolyte layer.

Claims (3)

A secondary battery having lithium nickel oxide and lithium manganese oxide as a positive electrode active material,
The average particle size of the lithium nickel oxide is smaller than the average particle size of the lithium manganese oxide, and the content of the lithium nickel oxide is equal to the total amount of the lithium nickel oxide and the lithium manganese oxide. On the other hand, the secondary battery is 22 wt% to 38 wt%.   The secondary battery according to claim 1, wherein a content of the lithium nickel oxide is 28 wt% to 32 wt% with respect to a total amount of the lithium nickel oxide and the lithium manganese oxide. The lithium nickel oxide is LiNi _1-x M _x O ₂ (wherein M is at least one metal atom selected from the group consisting of cobalt, manganese, aluminum, iron, copper, and strontium, The secondary battery according to claim 1, wherein the secondary battery has a structure represented by 0 ≦ X ≦ 0.5.

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