JP5895730B2 - 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

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.

Patent Document 1 has a layered structure, and has the general formula Li _2-x Mn _1-y O _3-p (0 ≦ x ≦ 2/3, 0 ≦ y ≦ _1/3, 0 ≦ p ≦ 1). A positive electrode active material for a lithium secondary battery is disclosed that has a peak width of (001) crystal plane measured by X-ray diffraction of 0.22 ° or more and an average particle diameter of 130 nm or less. (Claim 1).
In Patent Document 1, examples of the lithium manganese oxide represented by the above formula include Li ₂ MnO ₃ and Li [Li _0.33 Mn _0.67 ] O ₂ (Claim 2).

As described in Patent Document 1, since the general _Li 2 MnO ₃ and Li _[Li 0.33 _{Mn 0.67] O 2,} the valence of Mn is ^{4 +,} the Li ⁺ ions It is considered difficult to discharge during charging (paragraph 0002).
Patent Document 1 states that “in the present invention, the half width of the peak of the (001) crystal plane measured by X-ray diffraction is 0.22 ° or more, so the crystallinity is low and the crystal structure is unstable. Therefore, it is considered that lithium is easily released from the active material, so that the discharge capacity can be increased.The average particle diameter of the lithium manganese oxide of the present invention is 130 nm or less. For this reason, the distance that lithium diffuses in the active material particles is shortened, and lithium is more easily released from the active material, so that the discharge capacity can be increased. ” (Paragraph 0018).

In Examples 1 to 5 of Patent Document 1, a mixture of lithium hydroxide and manganese carbonate is pulverized in acetone, dried at 60 ° C., calcined at 400 to 800 ° C., and Li [Li _0.33 Mn _0.67 ] O ₂ is produced (paragraphs 0048-0049).

JP 2010-135285 JP

  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.

When the present inventor manufactured and evaluated a positive electrode active material according to the method described in Patent Document 1, the initial discharge capacity and the initial charge / discharge efficiency were low when using a high potential of 4.5 V or higher. It was revealed that the capacity retention rate after repetition was low (see Comparative Example 1 below).
In the positive electrode active material of Patent Literature 1, lithium can be released by making the crystal structure unstable. Since the structure of the positive electrode active material of Patent Document 1 is unstable, high performance cannot be obtained when using a high potential, and it is considered that the durability is not good.

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. An object of the present invention is to provide a lithium manganese-containing oxide that can be improved 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 is
The average composition formula is represented by the following formula (I):
Including lithium manganate having a Li ₂ MnO ₃ crystal structure,
In the X-ray diffraction (XRD) pattern, I1 / I2, which is the ratio of the peak intensity I1 near 2θ = 18 ° and the peak intensity I2 near 2θ = 45 °, satisfies 0.6 to 1.4. .
Li _x Mn _y O ₃ (where 1.3 ≦ x / y ≦ 1.8) (I)

The second lithium manganese-containing oxide of the present invention is
The average composition formula is represented by the following formula (I):
Including lithium manganate having a Li ₂ MnO ₃ crystal structure,
In the X-ray diffraction (XRD) pattern, I3 / I4, which is the ratio of the peak intensity I3 near 2θ = 64 ° and the peak intensity I4 near 2θ = 66 °, satisfies 0.8 to 1.8. .
Li _x Mn _y O ₃ (where 1.3 ≦ x / y ≦ 1.8) (I)

Li ₂ MnO ₃ has a layered rock salt type crystal structure.
“Lithium manganate having a Li ₂ MnO ₃ crystal structure” means lithium manganate having a crystal structure identical to that of Li ₂ MnO ₃ .
The first and second lithium manganese-containing oxides of the present invention have a Li ₂ MnO ₃ crystal structure and include a crystal phase composed of lithium manganate with a Li / Mn molar ratio deviating from 2.
First, second lithium manganese-containing oxide of the present invention, in addition to the crystalline phase can containing Li ₂ MnO ₃ crystal phase.

In the present invention, the Li / Mn molar ratio (x / y) is determined by ICP emission spectroscopic analysis.
In the present invention, the peak intensity in the XRD pattern means the integrated intensity of the peak.
For the specific methods for measuring the Li / Mn molar ratio, the XRD pattern, and the peak intensity in the XRD pattern by ICP emission spectroscopic analysis, refer to the section of [Example].

The lithium manganese-containing oxide of the present invention may contain a crystal phase other than lithium manganate having a Li ₂ MnO ₃ crystal structure.

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,
The lithium-containing material and manganese dioxide are subjected to a hydrothermal synthesis reaction 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 lithium manganese-containing oxide of the present invention is used as a positive electrode active material.

  According to the present invention, when used as a positive electrode active material of a lithium ion secondary battery, lithium manganese capable of improving the charge / discharge characteristics after repeated initial and charge / discharge when using a high potential of 4.5 V or higher A contained oxide and a method for producing the same can be provided.

2 is a SEM image of the positive electrode active material obtained in Example 1. 4 is a SEM image of the positive electrode active material obtained in Example 2. 4 is a SEM image of the positive electrode active material obtained in Example 3. 3 is a SEM image of the positive electrode active material obtained in Comparative Example 1. 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. 2 is an XANES spectrum of the positive electrode active material obtained in Example 1. 3 is an XANES spectrum of the positive electrode active material obtained in Example 2. 3 is an XANES spectrum of the positive electrode active material obtained in Example 3. 3 is an XANES spectrum of the positive electrode active material obtained in Comparative Example 1. It is a XANES spectrum of the positive electrode active material obtained in Examples 1 to 3 and Comparative Example 1. 4 is a graph showing evaluation results of initial characteristics in a charge / discharge test of the lithium ion secondary battery obtained in Example 1. FIG. 4 is a graph showing evaluation results of initial characteristics in a charge / discharge test of a lithium ion secondary battery obtained in Example 2. 4 is a graph showing evaluation results of initial characteristics in a charge / discharge test of a lithium ion secondary battery obtained in Example 3. 6 is a graph showing evaluation results of initial characteristics in a charge / discharge test of a lithium ion secondary battery obtained in Comparative Example 1.

  Hereinafter, the present invention will be described in detail.

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

The first lithium manganese-containing oxide of the present invention is
The average composition formula is represented by the following formula (I):
Including lithium manganate having a Li ₂ MnO ₃ crystal structure,
In the X-ray diffraction (XRD) pattern, I1 / I2, which is the ratio of the peak intensity I1 near 2θ = 18 ° and the peak intensity I2 near 2θ = 45 °, satisfies 0.6 to 1.4. .
Li _x Mn _y O ₃ (where 1.3 ≦ x / y ≦ 1.8) (I)

The second lithium manganese-containing oxide of the present invention is
The average composition formula is represented by the following formula (I):
Including lithium manganate having a Li ₂ MnO ₃ crystal structure,
In the X-ray diffraction (XRD) pattern, I3 / I4, which is the ratio of the peak intensity I3 near 2θ = 64 ° and the peak intensity I4 near 2θ = 66 °, satisfies 0.8 to 1.8. .
Li _x Mn _y O ₃ (where 1.3 ≦ x / y ≦ 1.8) (I)

In the above formula (I), when x / y <1.3, the amount of Li is too small to maintain the Li ₂ MnO ₃ crystal structure. A Li ₂ MnO ₃ crystal structure satisfying x / y ≧ 2.0 is not known. In addition, if x / y is excessive, excess lithium element may increase the irreversible capacity.
The first and second lithium manganese-containing oxides of the present invention satisfy 1.3 ≦ x / y ≦ 1.8 (see Examples 1 to 3 below).
Since higher characteristics are obtained, 1.3 ≦ x / y ≦ 1.5 is preferable (see Examples 2 and 3 below).

  In the XRD pattern, the initial discharge capacity, the initial charge / discharge efficiency, and the capacity maintenance ratio can be improved by optimizing the peak intensity ratio I1 / I2 and / or the peak intensity ratio I3 / I4 within the above ranges.

The first and second lithium manganese-containing oxides of the present invention can be produced by a hydrothermal synthesis reaction of a lithium-containing material and manganese dioxide.
It is considered that the crystal structure can be stabilized by using manganese dioxide having a tunnel structure or a layered structure as a raw material, and exchanging manganese and lithium sites in the crystal structure. The exchange amount of manganese and lithium sites in the crystal structure is the XRD main peak near 2θ = 18 ° and the peak intensity ratio I1 / I2 near 2θ = 45 °, or 2θ = 64 ° and 2θ = 66 °. It is considered that the peak intensity ratio in the vicinity corresponds to I3 / I4.

In the XRD pattern, the peak intensity ratio I1 / I2 is preferably 0.6 to 1.1 (see Examples 1 to 3 below), and more preferably 0.6 to 0.8 (described below). See Examples 1-2).
In the XRD pattern, the peak intensity ratio I3 / I4 is preferably 0.9 to 1.8 (see Examples 1 to 3 below), and preferably 1.5 to 1.8 (Examples below). 1-2).

The first and second lithium manganese-containing oxides of the present invention can satisfy an energy value of 6549.0 to 6550.8 eV when the normalized absorption coefficient is 0.5 in the XANES spectrum. This numerical range is different from that of the conventional oxide containing lithium manganese containing the Li ₂ MnO ₃ crystal structure.
In the first and second lithium manganese-containing oxides of the present invention, the energy value when the normalized absorption coefficient of the XANES spectrum is 0.5 is different from the conventional one in that the Mn—O in the crystal structure is different. This is probably because the octahedron is distorted. In the lithium manganese-containing oxide of the present invention, distortion is generated in the Mn—O octahedron in the crystal structure, and it is considered that the distortion suppresses the change in the crystal structure accompanying lithium ion desorption.

The first and second lithium manganese-containing oxides of the present invention have a Li ₂ MnO ₃ crystal structure and include a crystal phase composed of lithium manganate with a Li / Mn molar ratio deviating from 2.
First, second lithium manganese-containing oxide of the present invention, in addition to the crystalline phase can containing Li ₂ MnO ₃ crystal phase.
The lithium manganese-containing oxide of the present invention may contain a crystal phase other than lithium manganate having a Li ₂ MnO ₃ crystal structure.
The lithium manganese-containing oxide of the present invention may contain, for example, a LiMnO ₂ crystal phase, a Mn ₃ O ₄ crystal phase that may contain Li, a MnO ₂ crystal phase that may contain Li, or the like.

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,
The lithium-containing material and manganese dioxide are subjected to a hydrothermal synthesis reaction at a reaction temperature of less than 300 ° C. under pressure.

In the method for producing a lithium manganese-containing oxide of the present invention, the lithium-containing material 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.
Manganese dioxide is not particularly limited and preferably has a tunnel structure or a layered structure. The particle size and particle form of manganese dioxide are not particularly limited.
In order to perform hydrothermal synthesis, it is necessary to use water in addition to the lithium-containing material and manganese dioxide.

In the production method of the present invention, the reaction temperature of hydrothermal synthesis is set to less than 300 ° C.
In the conventional method in which heat treatment is performed at 300 ° C. or higher, particularly 400 ° C. or higher in the atmosphere, a spinel crystal phase that is stable at high temperatures is likely to be generated. When the amount of the spinel crystal phase is increased, the initial discharge capacity tends to be reduced when a high potential is used at 4.5 V or higher.
With the hydrothermal synthesis method in which the reaction is performed under pressure, a desired lithium manganese-containing oxide can be stably produced at a relatively low reaction temperature of less than 300 ° C.
If the reaction temperature is too low, the reaction is difficult to proceed. Therefore, 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 may decrease.
The heat drying temperature is preferably, for example, 80 to 600 ° C, and more preferably 120 to 400 ° C.
It is preferable to perform vacuum drying after the heat drying so that moisture that cannot be removed by only the 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 first and second lithium manganese-containing oxides of the present invention are suitable for a positive electrode active material of a lithium ion secondary battery used under a charging condition 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 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, carbon such as graphite, metallic lithium, lithium alloy, transition metal oxide / transition metal nitride / transition metal sulfide capable of doping / dedoping lithium ions, and these A combination etc. are mentioned.

The negative electrode can be produced, for example, by applying a negative electrode active material to a negative electrode current collector such as a copper foil by a known method.
For example, using a dispersant such as water, a negative electrode active material, a binder such as a modified styrene-butadiene copolymer latex, and a thickener such as carboxymethyl cellulose Na salt (CMC) are mixed as necessary. Thus, a slurry can be obtained, and this slurry can be applied onto a current collector such as a copper foil, dried, and pressed to obtain a negative electrode.

  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 be made into the charging / discharging characteristic after repeating an initial stage and charging / discharging in 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 8 g of LiOH.H ₂ O was dissolved in 50 ml of pure water, 2 g of electrolytic manganese dioxide (FMSO, γ type manufactured by Tosoh Corporation) was added so that the molar ratio of charged Li / Mn was 8.3. 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 washed with pure water, and then heat-dried at 80 ° C. and 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.

<Production 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 produced in the same manner as in Example 1 except that the conditions for the synthesis 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 the positive electrode active material was produced in accordance with the method described in the Example of Patent Document 1.
Specifically, a positive electrode active material was produced by the following method.
Lithium hydroxide (LiOH.H ₂ O) and manganese carbonate (MnCO ₃ .nH ₂ O, n = about 0.5) were mixed so that the Li / Mn molar ratio = 2. The resulting mixture was ground in acetone for 1 hour using a ball mill. At this time, the amount of acetone was the same as the total amount of lithium hydroxide and manganese carbonate. The obtained pulverized product was dried at 60 ° C. and baked at 450 ° C. for 10 hours in the air. The fired product obtained using a mortar was pulverized and fired again at 450 ° C. for 24 hours in the air.

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

<SEM observation>
The positive electrode active material obtained in each example was observed by SEM (scanning electron microscope). SEM images are shown in FIGS. 1A-1D.

<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.

<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.

<XRD analysis>
The positive electrode active material obtained in each example was subjected to powder XRD analysis to identify the crystal phase.
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.
In the obtained XRD pattern, the peak intensity I near 2θ = 18 °, the peak intensity I2 near 2θ = 45 °, the peak intensity I3 near 2θ = 64 °, and the peak intensity I4 near 2θ = 66 ° are measured, I1 / I2 and I3 / I4 were determined.
The peak intensity was determined by automatic profile processing using integrated powder X-ray analysis software PDXL manufactured by Rigaku Corporation.

The XRD pattern of the positive electrode active material obtained in each example is shown in FIGS. 2A to 2D.
The positive electrode active materials obtained in Examples 1 and 2 had only the Li ₂ MnO ₃ crystal structure.
The positive electrode active material obtained in Example 3 mainly includes a crystal structure in which lithium is introduced into the crystal structure of γ-type manganese dioxide, and includes a Li ₂ MnO ₃ crystal structure.
The positive electrode active material obtained in Comparative Example 1 had only a Li ₂ MnO ₃ crystal structure.
Table 2 shows the evaluation results of the crystal structure and the peak intensity ratios I1 / I2 and I3 / I4.

<XANES analysis>
Using the positive electrode obtained in each example, the surface oxidation state of the positive electrode active material was evaluated by XANES (X-ray Absorption Near Edge Structure) analysis.
XANES analysis of the Mn K edge was performed by the transmission method at SPring-8 BL33XU Toyota Beamline.
Calibration of the detector was performed using Mn metal foil. In the measurement of this Mn metal foil, the K absorption edge was 6539 eV.
The XANES spectra of the positive electrode active material obtained in each example are shown in FIGS. 3A to 3D.
FIG. 3E shows an overlay of XANES spectra of the positive electrode active material obtained in each example.
In the obtained XANES spectrum, the energy value when the normalized absorption coefficient was 0.5 was determined. 3A to 3E, the vertical axis indicates the normalized absorption coefficient. In these figures, a line with a normalized absorption coefficient = 0.5 is indicated by a broken line. The energy value at the intersection of the XANES spectrum and the line with the normalized absorption coefficient = 0.5 was read.
The evaluation results are shown in Table 2.

(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 The charge / discharge test of 3 cycles was done as 2.0V (lithium metal reference | standard).
About the lithium ion secondary battery obtained in each example, the result of the charge / discharge test of 1-2 cycles is shown to FIG. 4A-FIG. 4D.
In each example, the discharge capacity and charge capacity of the first cycle were determined, and the charge / discharge efficiency was determined based on the following formula. Table 3 shows the evaluation results of the discharge capacity and charge / discharge efficiency in the first cycle.
Charge / discharge efficiency (%) = (discharge capacity at the first cycle) / (charge capacity at the first cycle) × 100

[Evaluation of cycle characteristics]
After the above three cycles of charge / discharge, the following 15 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 for 15 cycles.
In the 15-cycle test described above, the discharge capacities of the first cycle and the 15th 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 15th 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), includes lithium manganate having a Li ₂ MnO ₃ crystal structure, and the peak intensity ratio I1 / I2 in the XRD pattern is 0.6. In Examples 1 to 3 using a lithium manganese-containing oxide having a peak intensity ratio I3 / I4 of 0.8 to 1.8, a lithium manganese-containing oxidation outside the range specified in the present invention A lithium ion secondary battery having higher initial discharge capacity, initial charge / discharge efficiency, and capacity retention rate than that of Comparative Example 1 using the product was obtained.
In Examples 1 to 3, the peak intensity ratio I1 / I2 in the XRD pattern was 0.6 to 1.1, and the peak intensity ratio I3 / I4 was 0.9 to 1.8.
In particular, the Li / Mn molar ratio is 1.3 to 1.5, and in the XRD pattern, the peak intensity ratio I1 / I2 is 0.6 to 0.8, and the peak intensity ratio I3 / I4 is 1.5 to 1.5. In Examples 2 and 3 using a lithium manganese-containing oxide of 1.8, a high-performance lithium ion secondary battery 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 (9)

The average composition formula is represented by the following formula (I):
Including lithium manganate having a Li ₂ MnO ₃ crystal structure,
Lithium manganese-containing oxide having an I1 / I2 ratio of 0.6 to 1.1, which is a ratio of a peak intensity I1 near 2θ = 18 ° and a peak intensity I2 near 2θ = 45 ° in an X-ray diffraction pattern.
Li _x Mn _y O ₃ (where 1.3 ≦ x / y ≦ 1.8) (I) The lithium manganese-containing oxide according to claim 1 , wherein in the XANES spectrum, the energy when the normalized absorption coefficient is 0.5 is 6549.0 to 6550.8 eV. A method for producing a lithium manganese-containing oxide according to claim 1 or 2 ,
A method for producing a lithium manganese-containing oxide, comprising subjecting a lithium-containing material and manganese dioxide 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 3 , 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 3 or 4 , wherein the reaction temperature is 100 ° C or higher. The method for producing a lithium manganese-containing oxide according to claim 5 , 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 of Claim 1 or 2 . A lithium ion secondary battery using the lithium manganese-containing oxide according to claim 1 or 2 as a positive electrode active material. The lithium ion secondary battery according to claim 8 , which is used under a charging condition of 4.5 V or more.