JP2014002849A - Lithium manganese-containing oxide and method for producing the same, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium manganese-containing oxide, when used as a positive electrode active material for a lithium ion secondary battery, capable of improving charge/discharge characteristics in an initial state and after repeated charging/discharging in use at a high potential of 4.5 V or more, and including a crystal phase where lithium is introduced within a crystal structure of γ-type manganese dioxide.SOLUTION: A lithium manganese-containing oxide has an average composition formula represented by the following general formula (I), includes a crystal phase where lithium is introduced within a crystal structure of γ-type manganese dioxide, and has a peak top within a range of 41.62<2θ<42.66 in an X-ray diffraction pattern. LiMnO(where, 0<x/(1-x)<1.3)...(I)

Description

  The present invention relates to a lithium manganese-containing oxide and a method for producing the same, a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery.

  A lithium ion secondary battery is generally composed of a positive electrode and a negative electrode capable of reversibly inserting and removing lithium ions, and a liquid, gel or solid electrolyte, and has advantages such as high output and high energy density. Yes.

Conventionally, as a positive electrode active material of a lithium ion secondary battery, LiCoO ₂ , LiNiO ₂ , or a substitution system thereof such as a formula LiMO ₂ (wherein M is at least one transition metal having an average valence of 4+) A lithium composite oxide having a layered rock salt structure represented by the formula is widely used.

  On the other hand, manganese dioxide is widely used as a positive electrode active material for lithium ion primary batteries. Manganese dioxide is abundant in resources, inexpensive, and chemically stable. Then, applying manganese dioxide to the positive electrode active material of a lithium ion secondary battery is examined.

In paragraphs 0006 to 0007 of Patent Document 1, a mixture of Li ₂ MnO ₃ and manganese dioxide in which lithium is introduced into a γ-type crystal structure is described as a conventional technique. All of these are manufactured by firing a mixture of manganese dioxide having a γ-type crystal structure and a lithium-containing material at a high temperature of 300 ° C. or higher.
Patent Document 1 proposes to use, as a raw material manganese dioxide, acid-treated γ-type manganese dioxide having a BET specific surface area of 150 to 500 m ² / g (Claim 1).

Japanese Unexamined Patent Publication No. 06-029019

  A lithium ion secondary battery mounted on a plug-in hybrid vehicle (PHV) or an electric vehicle (EV) has good charge / discharge characteristics after repeated initial and charge / discharge cycles when using a high potential of 4.5V or higher. It is required to be.

If the positive electrode active material containing _Li 2 MnO _3, in a high potential use at 4.5V or _more, occur discharge of oxygen gas from Li 2 MnO _3, lowering the charge and discharge characteristics such as initial discharge capacity and the capacity retention rate There is a fear. In a conventional manufacturing method in which high-temperature baking is performed at 300 ° C. or higher, Li ₂ MnO _{3 that} is stable at high temperatures is easily generated.
In addition, in the conventional manufacturing method in which high-temperature baking is performed at 300 ° C. or higher, a spinel-type crystal phase that is stable at high temperatures may be generated. When a spinel crystal phase is generated, the battery capacity tends to decrease when using a high potential at 4.5 V or higher.

The present invention has been made in view of the above circumstances, and when used as a positive electrode active material of a lithium ion secondary battery, the charge / discharge characteristics after repeated initial and charge / discharge operations at a high potential of 4.5 V or higher are used. It is an object of the present invention to provide a lithium manganese-containing oxide containing a crystal phase in which lithium is introduced into the crystal structure of γ-type manganese dioxide, and a method for producing the same.
In addition, although the lithium manganese containing oxide of this invention is a thing suitable for high potential use of 4.5V or more, it can be used on arbitrary charging / discharging conditions.

  In this specification, unless otherwise specified, a high potential is defined as “4.5 V or more”. Unless otherwise specified, “initial characteristics” means initial charge / discharge characteristics, and “cycle characteristics” means charge / discharge characteristics after repeated charge / discharge.

The first lithium manganese-containing oxide of the present invention,
The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
In the X-ray diffraction (XRD) pattern, the lithium manganese-containing oxide has a peak top in the range of 41.62 <2θ <42.66.
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I)

The second lithium manganese-containing oxide of the present invention is
The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
The lithium manganese-containing oxide has a Li ₂ MnO ₃ content of 10% by mass or less.
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I)

In the present invention, the Li / Mn molar ratio x / (1-x) is determined by ICP emission spectroscopic analysis.
In the present invention, the content of Li ₂ MnO ₃ is determined from the XRD pattern. Specifically, when there is a peak derived from Li ₂ MnO ₃ in the vicinity of 2θ = 44.7 ° in the XRD pattern, the Li ₂ MnO ₃ content (% by mass) is obtained from the integrated intensity.
For specific methods for measuring the Li / Mn molar ratio, the XRD pattern, and the Li ₂ MnO ₃ content, see the section “Examples”.

The method for producing the lithium manganese-containing oxide of the present invention comprises:
A method for producing the first or second lithium manganese-containing oxide of the present invention,
A hydrothermal synthesis reaction is performed between a lithium-containing material and manganese dioxide having a γ-type crystal structure at a reaction temperature of less than 300 ° C. under pressure.

The positive electrode active material for the lithium ion secondary battery of the present invention is
The above-described first or second lithium manganese-containing oxide of the present invention is included.

The lithium ion secondary battery of the present invention is
The first or second lithium manganese-containing oxide of the present invention is used as a positive electrode active material, and a lithium-containing material is used as a negative electrode active material.

  According to the present invention, when used as a positive electrode active material for a lithium ion secondary battery, the charge and discharge characteristics after repeated initial and charge / discharge operations at a high potential of 4.5 V or higher can be improved. It is possible to provide a lithium manganese-containing oxide containing a crystal phase in which lithium is introduced into the crystal structure of the type manganese dioxide and a method for producing the same.

3 is an XRD pattern of a positive electrode active material obtained in Example 1. 3 is an XRD pattern of a positive electrode active material obtained in Example 2. 3 is an XRD pattern of a positive electrode active material obtained in Example 3. 3 is an XRD pattern of a positive electrode active material obtained in Comparative Example 1. 3 is an XRD pattern of a positive electrode active material obtained in Comparative Example 2.

  Hereinafter, the present invention will be described in detail.

[Lithium manganese-containing oxide and its production method]
The lithium manganese-containing oxide of the present invention is suitable for a positive electrode active material of a lithium ion secondary battery.

The positive electrode active material of Patent Document 1 listed in the section “Background Art” is manufactured by firing a mixture of manganese dioxide having a γ-type crystal structure and a lithium-containing material at a high temperature of 300 ° C. or higher. . In the conventional production method in which high-temperature baking is performed at 300 ° C. or higher, Li ₂ MnO ₃ that is stable at high temperatures is easily generated, and a spinel-type crystal phase that is stable at high temperatures may be generated.

  The present inventor optimized the Li / Mn molar ratio and hydrothermally reacted the lithium-containing material and manganese dioxide having a γ-type crystal structure under pressure at a reaction temperature of less than 300 ° C. We have succeeded in synthesizing a lithium manganese-containing oxide containing a crystal phase in which lithium is introduced into the crystal structure of γ-type manganese dioxide.

According to the above method, since synthesis at a lower temperature than before is possible, the generation of Li ₂ MnO ₃ and a spinel crystal phase can be suppressed.
When the lithium manganese-containing oxide produced by the above method is used as the positive electrode active material of a lithium ion secondary battery, the charge / discharge characteristics after repeated initial and charge / discharge operations at a high potential of 4.5 V or higher are improved. be able to.

The lithium manganese-containing oxide of the present invention is
The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
In the X-ray diffraction (XRD) pattern, the lithium manganese-containing oxide has a peak top in the range of 41.62 <2θ <42.66.
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I)

  The peak around 2θ = 42.0 in the XRD pattern is a peak derived from the γ-type crystal structure (in the present invention, a crystal phase in which lithium is introduced into the crystal structure of γ-type manganese dioxide).

  According to the lithium manganese-containing oxide of the present invention, when used as a positive electrode active material of a lithium ion secondary battery, cycles such as initial characteristics such as initial discharge capacity and capacity maintenance rate are used at a high potential of 4.5 V or higher. The characteristics can be improved.

As described above, by employing the hydrothermal synthesis method, synthesis at a relatively low temperature of less than 300 ° C. is possible, so that the generation of Li ₂ MnO ₃ and a spinel crystal phase can be suppressed. However, if the amount of Li is excessive with respect to the amount of Mn, excess Li does not completely enter the γ-type crystal structure, and Li ₂ MnO ₃ is likely to be generated. Therefore, in the present invention, the Li / Mn molar ratio is defined as 0 <x / (1-x) <1.3.

The lithium manganese-containing oxide of the present invention is preferably represented by the following general formula (Ia) because the effect of improving the initial characteristics and cycle characteristics in high potential use can be obtained more effectively. Those represented by Ib) are particularly preferred (see Examples 1 to 3 below).
Li _x Mn _1-x O ₂ (where 0.1 ≦ x / (1-x) ≦ 1.0) (Ia),
Li _x Mn _1-x O ₂ (where 0.1 ≦ x / (1-x) ≦ 0.5) (Ib)

  Since the effect of improving the initial characteristics and cycle characteristics when using a high potential can be obtained more effectively, the lithium manganese-containing oxide of the present invention has a peak in the range of 41.7 ≦ 2θ ≦ 42.6 in the XRD pattern. It preferably has a top, and particularly preferably has a peak top within the range of 41.75 ≦ 2θ ≦ 42.55 (see Examples 1 to 3 below).

According to the present invention,
The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
It is possible to provide a lithium manganese-containing oxide having a Li ₂ MnO ₃ content of 10% by mass or less (see Examples 1 to 3 below).
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I)

According to the present invention,
The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
It is also possible to provide a lithium manganese-containing oxide that does not contain Li ₂ MnO ₃ (see Example 1 below).
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I)

The method for producing the lithium manganese-containing oxide of the present invention comprises:
A method for producing the lithium manganese-containing oxide of the present invention,
A hydrothermal synthesis reaction is performed between a lithium-containing material and manganese dioxide having a γ-type crystal structure at a reaction temperature of less than 300 ° C. under pressure.

  The lithium-containing material used for the hydrothermal synthesis reaction is not particularly limited, and examples thereof include lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, and lithium sulfate. These can be used alone or in combination of two or more.

  In order to perform hydrothermal synthesis, it is necessary to use water as a raw material in addition to lithium-containing material and manganese dioxide having a γ-type crystal structure.

In hydrothermal synthesis, if the reaction temperature is too low, the reaction is difficult to proceed, and if it is too high, undesirable components such as Li ₂ MnO ₃ are likely to be generated.
The reaction temperature is preferably 100 ° C. or higher.
The reaction temperature is preferably 140 to 220 ° C, particularly preferably 160 to 200 ° C.
The reaction pressure is not particularly limited, and is preferably 0.1 to 10 MPa, and more preferably 0.15 to 2 MPa.

After completion of the hydrothermal synthesis reaction, the obtained reaction product is washed and dried by a known method.
For example, the obtained reaction product is preferably subjected to suction filtration and pure water washing, followed by heat drying and vacuum drying.
The temperature for heat drying is not particularly limited. If the heat drying temperature is too low, it is difficult to sufficiently remove moisture, and if it is too high, crystal grains grow and the specific surface area of the particles may be reduced.
The heat drying temperature is preferably, for example, 80 to 600 ° C, and more preferably 120 to 400 ° C.
It is preferable to carry out vacuum drying after the heat drying so that moisture that cannot be removed only by heat drying can be removed.
Heating may be performed during vacuum drying. The heating temperature during vacuum drying is preferably, for example, 80 to 120 ° C.

  The lithium manganese-containing oxide of the present invention is particularly suitable for a positive electrode active material of a lithium ion secondary battery using a high potential of 4.5 V or higher.

  As described above, according to the present invention, when used as a positive electrode active material of a lithium ion secondary battery, the charge / discharge characteristics after repeated initial and charge / discharge operations at a high potential of 4.5 V or higher are improved. It is possible to provide a lithium manganese-containing oxide containing a crystal phase in which lithium is introduced into the crystal structure of γ-type manganese dioxide and a method for producing the same.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present invention uses the above-described lithium manganese-containing oxide of the present invention as a positive electrode active material.
A lithium ion secondary battery can be produced by a known method using a positive electrode, a negative electrode, a separator, a nonaqueous electrolyte, and a battery container.

<Positive electrode>
The positive electrode can be manufactured by applying a positive electrode active material to a positive electrode current collector such as an aluminum foil by a known method.
In the present invention, the above lithium manganese-containing oxide of the present invention is used as a positive electrode active material.
As the positive electrode active material, a known positive electrode active material other than the lithium manganese-containing oxide of the present invention may be used in combination. However, the higher the amount of the lithium manganese-containing oxide of the present invention, the higher the effect.

  For example, using a dispersant such as N-methyl-2-pyrrolidone, mixing a positive electrode active material, a conductive agent such as carbon powder, and a binder such as polyvinylidene fluoride (PVDF) to obtain a slurry, This slurry can be applied onto a current collector such as an aluminum foil, dried, and pressed to obtain a positive electrode.

<Negative electrode>
The negative electrode active material is not particularly limited, and a material having a lithium storage capacity of 2.0 V or less on the basis of Li / Li + is preferably used.
As the negative electrode active material, lithium-containing materials such as metallic lithium and / or lithium alloys are preferable. By using such a negative electrode active material, lithium ions involved in charging / discharging can be supplied from the negative electrode, and lithium ion release from the positive electrode side can be supplemented from the negative electrode side. As a result, initial characteristics such as initial charge / discharge efficiency and cycle characteristics such as capacity retention ratio can be improved.
When metallic lithium and / or a lithium alloy are used as the negative electrode active material, the negative electrode active material can be used as the negative electrode without using a current collector.

<Nonaqueous electrolyte>
As the non-aqueous electrolyte, known ones can be used, and liquid, gel-like or solid non-aqueous electrolytes can be used.
For example, a lithium-containing electrolyte is dissolved in a mixed solvent of a high dielectric constant carbonate solvent such as propylene carbonate or ethylene carbonate and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate, or dimethyl carbonate. A water electrolysis solution is preferably used.
As the mixed solvent, for example, a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) is preferably used.
Examples of the lithium-containing electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiPF _n {C _k F _{(2k + 1) )} (6-n) (} n = 1~5 integer, k = 1 to 8 integer) lithium salts such as, and combinations thereof.

<Separator>
The separator may be a film that electrically insulates the positive electrode and the negative electrode and is permeable to lithium ions, and a porous polymer film is preferably used.
As the separator, for example, a porous film made of polyolefin such as a porous film made of PP (polypropylene), a porous film made of PE (polyethylene), or a laminated porous film of PP (polypropylene) -PE (polyethylene) is preferably used. It is done.

<Battery container>
A well-known thing can be used as a battery container.
Secondary battery types include a cylindrical type, a coin type, a square type, a film type, and the like, and a battery container can be selected according to a desired type.

The lithium ion secondary battery of the present invention uses the above-described lithium manganese-containing oxide of the present invention as a positive electrode active material.
ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which can improve the charging / discharging characteristic after repeating an initial stage and charging / discharging in the high potential use of 4.5V or more can be provided.

  Examples and comparative examples according to the present invention will be described.

Example 1
<Synthesis of positive electrode active material>
To a lithium hydroxide aqueous solution in which 0.289 g of LiOH.H ₂ O was dissolved in 50 ml of pure water so that the Li / Mn preparation molar ratio was 0.2, 3 g of electrolytic manganese dioxide (FMH, γ type manufactured by Tosoh Corporation) ) Was added and mixed. The obtained mixture was heat-treated in an autoclave at about 1 MPa at 180 ° C. for 24 hours. The obtained reaction product was subjected to suction filtration and pure water washing, and then heat-dried at 80 ° C. and further vacuum-dried at 120 ° C. to obtain a positive electrode active material composed of particulate lithium manganese-containing oxide.
Table 1 shows main synthesis conditions for the positive electrode active material.

<Manufacture of positive electrode>
Using N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) as a dispersant, a positive electrode active material comprising the above lithium manganese-containing oxide and acetylene black (Electrochemical Industry Co., Ltd.) as a conductive agent ) HS-100) and PVDF (Kureha KF Polymer # 1120) were mixed at 85/10/5 (mass ratio) to obtain a slurry.
The slurry was applied onto an aluminum foil as a current collector by a doctor blade method, dried at 80 ° C. for 30 minutes, and rolled using a press machine to obtain a positive electrode. The positive electrode active material layer had a basis weight of 3.2 mg / cm ² and a thickness of 16 μm.

<Negative electrode>
Metal lithium was used as the negative electrode active material. This was used as a negative electrode as it was.

<Separator>
A commercially available separator made of a PP (polypropylene) porous film was prepared.

<Nonaqueous electrolyte>
A mixed solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3/3/4 (volume ratio) is used as a solvent, and LiPF ₆ which is a lithium salt is used as an electrolyte at a concentration of 1 mol / L. It melt | dissolved and the nonaqueous electric field liquid was prepared.

<Battery container>
As a battery container, a SUS CR2032-type coin cell was prepared.

<Manufacture of lithium ion secondary batteries>
A lithium ion secondary battery was manufactured by a known method using the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte, and the battery container.

(Examples 2 and 3)
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the synthesis conditions of the positive electrode active material were the conditions shown in Table 1.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that electrolytic manganese dioxide (FMH manufactured by Tosoh Corporation) was used as it was as the positive electrode active material.

(Comparative Example 2)
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the synthesis conditions of the positive electrode active material were the conditions shown in Table 1.

(Evaluation of positive electrode active material)
The following evaluation was implemented about the positive electrode active material obtained in each case.

<BET specific surface area>
For the positive electrode active material obtained in each example, manufactured by Shimadzu Corporation TriStar 3000 as measuring device, by BET7 point method using N ₂ adsorption method, the BET specific surface area was measured.
The evaluation results are shown in Table 2.

<XRD analysis>
The positive electrode active material obtained in each example was subjected to powder XRD analysis to identify the crystal phase. In addition, in the obtained XRD pattern, the peak top position near 2θ = 42 ° was read.
As a measuring device, Ultimate IV manufactured by Rigaku Corporation was used. A Cu tube was used as the X-ray source, and a one-dimensional semiconductor detector (D / teX) was used as the detector. The measurement conditions were 2θ = 10 to 80 ° and a scan speed of 10 ° / min.

The XRD pattern of the positive electrode active material obtained in each example is shown in FIGS.
The positive electrode active material obtained in Example 1 had only a crystal structure in which lithium was introduced into the crystal structure of γ-type manganese dioxide.
The positive electrode active materials obtained in Examples 2 and 3 mainly had a crystal structure in which lithium was introduced into the crystal structure of γ-type manganese dioxide, and included a Li ₂ MnO ₃ crystal structure.
The positive electrode active material of Comparative Example 1 was γ-type manganese dioxide.
The positive electrode active material obtained in Comparative Example 2 mainly had a Li ₂ MnO ₃ crystal structure, and contained a crystal structure in which lithium was introduced into the crystal structure of γ-type manganese dioxide.
In the XRD pattern of each example, when there was a peak derived from Li ₂ MnO ₃ in the vicinity of 2θ = 44.7 °, the Li ₂ MnO ₃ content (% by mass) was determined from the integrated intensity.
Table 2 shows the evaluation results of the crystal structure and the Li ₂ MnO ₃ content.

<ICP emission spectroscopic analysis>
About the positive electrode active material obtained in each example, Li / Mn molar ratio was measured by ICP emission spectral analysis.
Using ICPS-8100 manufactured by Shimadzu Corporation, the amount of each element was quantified by a calibration curve method to determine the Li / Mn molar ratio.
The evaluation results are shown in Table 2.
Note that there is a difference between the charged composition and the actual composition by ICP emission spectroscopic analysis because the synthesis reaction was completed with some of the lithium-containing material unreacted, or the lithium was not filtered during filtration or washing after the synthesis reaction. This may be due to a part of the reaction product being desorbed.

(Evaluation of lithium ion secondary battery)
The following evaluation was implemented about the lithium ion secondary battery obtained in each case.

<Charge / discharge test>
[Evaluation of initial characteristics]
With respect to the lithium ion secondary batteries obtained in each example, the charging voltage was set to 4.8 V (lithium metal standard) in a constant temperature bath at 25 ° C. under a constant current condition of a current density of 7.5 mA / g, and the discharging voltage was Charging / discharging of 3 cycles was performed as 2.0V (lithium metal reference | standard).
The discharge capacity at the first cycle was measured as the initial discharge capacity.
The evaluation results are shown in Table 3.

[Evaluation of cycle characteristics]
After the above three cycles of charge / discharge tests, the following 20 cycles of charge / discharge tests were further performed.
After charging to 4.6V (lithium metal standard) in a constant temperature condition at a current density of 50mA / g in a constant temperature bath at 25 ° C, the voltage of 4.6V is maintained until the current density reaches 7.5mA / g. did. Then, it discharged to 2.0V (lithium metal reference | standard) on the constant current conditions with a current density of 50 mA / g. These charge / discharge cycles were performed 20 cycles.
In the 20 cycle test described above, the discharge capacities of the first cycle and the 20th cycle were measured, and the capacity retention rate was determined based on the following formula. The results are shown in Table 3.
Capacity retention rate (%) = (discharge capacity at 20th cycle) / (discharge capacity at 1st cycle) × 100

(result)
As shown in Tables 1 to 3, the average composition formula is represented by the above formula (I), and includes a crystal phase in which lithium is introduced into the crystal structure of γ-type manganese dioxide. In the XRD pattern, 41.62 In Examples 1 to 3 using a lithium manganese-containing oxide having a peak top in the range of <2θ <42.66, Comparative Examples 1 and 2 using a lithium manganese-containing oxide outside the range defined in the present invention As a result, a lithium ion secondary battery having a high initial discharge capacity and a high capacity retention rate was obtained.

  The lithium manganese-containing oxide and the method for producing the same of the present invention can be preferably applied to a positive electrode active material of a lithium ion secondary battery mounted on a plug-in hybrid vehicle (PHV) or an electric vehicle (EV).

Claims (13)

The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
A lithium manganese-containing oxide having a peak top in the range of 41.62 <2θ <42.66 in an X-ray diffraction pattern.
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I) The lithium manganese containing oxide of Claim 1 represented by the following general formula (Ia).
Li _x Mn _1-x O ₂ (where 0.1 ≦ x / (1-x) ≦ 1.0) (Ia) The lithium manganese containing oxide of Claim 2 represented by the following general formula (Ib).
Li _x Mn _1-x O ₂ (where 0.1 ≦ x / (1-x) ≦ 0.5) (Ib)   4. The lithium manganese-containing oxide according to claim 1, which has a peak top in a range of 41.7 ≦ 2θ ≦ 42.6 in an X-ray diffraction pattern.   5. The lithium manganese-containing oxide according to claim 4, which has a peak top in a range of 41.75 ≦ 2θ ≦ 42.55 in an X-ray diffraction pattern. The average composition formula is represented by the following general formula (I):
a crystal phase in which lithium is introduced in the crystal structure of γ-type manganese dioxide,
Lithium manganese-containing oxide content of li ₂ MnO ₃ is not more than 10 wt%.
Li _x Mn _1-x O ₂ (where 0 <x / (1-x) <1.3) (I) A method for producing a lithium manganese-containing oxide according to any one of claims 1 to 6,
A method for producing a lithium manganese-containing oxide, comprising subjecting a lithium-containing material and manganese dioxide having a γ-type crystal structure to a hydrothermal synthesis reaction under pressure at a reaction temperature of less than 300 ° C.   The method for producing a lithium manganese-containing oxide according to claim 7, wherein at least one selected from the group consisting of lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, and lithium sulfate is used as the lithium-containing material.   The method for producing a lithium manganese-containing oxide according to claim 7 or 8, wherein the reaction temperature is 100 ° C or higher.   The method for producing a lithium manganese-containing oxide according to claim 9, wherein the reaction temperature is 140 to 220 ° C.   The positive electrode active material for lithium ion secondary batteries containing the lithium manganese containing oxide in any one of Claims 1-6.   The lithium ion secondary battery which used the lithium manganese containing oxide in any one of Claims 1-6 as a positive electrode active material, and used a lithium containing material as a negative electrode active material.   The lithium ion secondary battery according to claim 12, which is used under a charging condition of 4.5 V or more.

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