JPH11102703A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery which is superior in high- temperature characteristic. SOLUTION: In a secondary battery using lithium or a material capable of absorbing/releasing lithium in a negative electrode, having a nonaqueous electrolyte, and a positive electrode, a positive active material is a lithium manganese oxide having spinel structure, in which in an X-ray absorption spectrum measured by an X-ray absorption fine structure (XAFS) analysis method, peak, intensity in the vicinity of 2.5 Å in a radius vector structure function obtained by Fourier transform of a wide region X-ray absorption fine structure spectrum (EXAFS) of MnK absorption edge is 17.5 or less, when 90% of lithium capable of theoretically being discharged is discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in characteristics of a nonaqueous secondary battery using a spinel lithium manganese composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art As electronic devices become smaller and lighter, there is an increasing demand for high energy density secondary batteries as power sources. In recent years, lithium ion secondary batteries using LiCoO _2, which can provide a voltage as high as about 4 V with respect to metallic lithium, as a positive electrode active material and using a carbon material as a negative electrode active material have come to be marketed.

[0003] However, LiCoO ₂ is a material having a low production of Co, so that the price of the Co compound as a raw material is high, and there is concern about stable supply. Therefore, the development of a substitute material is desired. . As an example, LiM
n ₂ O ₄ has been proposed. Since LiMn ₂ O ₄ is abundant in raw materials, inexpensive, and inexpensive in production, various studies have been made toward practical use. Generally LiMn ₂ O
No. ₄ can be easily synthesized by a method of mixing a manganese oxide such as MnO ₂ and a manganese oxide such as Li ₂ CO ₃ and a lithium salt such that the molar ratio of lithium and manganese is 1: 2, followed by heat treatment. However, this material has a problem that cycle characteristics, which are the basics of battery characteristics, are poor.

In order to solve this, for example, Japanese Patent Publication No.
No. 24043 discloses that the lattice constant a of a crystal is 8.22 °.
It has been proposed to use the following LiMn ₂ O ₄ as an active material. Japanese Patent Application Laid-Open No. Hei 6-187993 proposes a lithium-excess composition in order to increase the oxidation state of manganese. In Japanese Patent No. 2058834, a part of Mn in LiMn ₂ O ₄ is converted to Co, Cr,
It is proposed to substitute Fe. These are aimed at improving the cycle characteristics by modifying the lithium manganese oxide by focusing on the crystal lattice and the oxidation number of manganese. Although such a method can certainly be expected to improve the cycle characteristics at room temperature, there is a problem that the capacity is reduced due to storage at high temperatures and charge / discharge cycles.

[0005]

SUMMARY OF THE INVENTION The present invention is to solve such a problem of a lithium ion secondary battery, and is capable of repeatedly charging and discharging at a high energy density and at a high temperature for a long period of time, or even when stored at a high temperature. Is extremely low,
An object is to obtain a long-life non-aqueous secondary battery.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and shows an MnK spectrum in an X-ray absorption spectrum measured by an X-ray absorption fine structure analysis (XAFS). Wide-range X-ray absorption fine structure at the absorption edge (E
It has been found that the peak intensity around 2.5 ° in the radial structure function obtained by Fourier transform of the (XAFS) spectrum is deeply related to the high temperature characteristics of the secondary battery.

Hereinafter, the present invention will be described in detail. As described above, proposals for improving the characteristics of the spinel-type lithium manganese oxide generally involve stabilizing the crystal by increasing the average oxidation number to more than 3.5. The present inventors have conducted thorough studies on manganese elements and high-temperature characteristics based on the recognition that the proposed active materials are insufficient for high-temperature characteristics.

That is, spinel-type lithium manganese oxides having different synthesis conditions such as firing conditions and compositions were synthesized, and after a test at a high temperature, the electronic state of manganese was examined in detail by XAFS measurement. Those whose capacity is extremely small even after repeated charge / discharge or storage at a high temperature are those which have a wide range of MnK absorption edges determined from X-ray absorption spectra measured by X-ray absorption fine structure analysis (XAFS). The peak intensity around 2.5 ° in the radial structure function obtained by Fourier transforming the structure (EXAFS) spectrum indicates that the amount of lithium that can be theoretically released is 90%.
% Was found to be less than 17.5.

On the other hand, when the capacity clearly decreases due to the high-temperature cycle or high-temperature storage, that is, when the high-temperature characteristic deteriorates, the peak intensity around 2.5 ° in the radial structure function indicates the amount of lithium that can be theoretically released. It has been found that when it releases 90%, it becomes 17.5 or more, and the present invention has been completed. The peak intensity around 2.5 ° in the radial structure function indicates the degree of scattering from Mn-Mn atoms,
In the case of the lithium manganese composite oxide of the present invention, although details are unknown, Mn-M in the second coordination sphere is formed by elimination of lithium.
It is presumed that scattering from n atoms does not increase as in a general lithium manganese oxide, and the local structure of Mn atoms is slightly different.

That is, the present invention relates to a lithium-manganese composite oxide in which a positive electrode active material has a spinel structure in a secondary battery comprising lithium or a substance capable of inserting and extracting lithium as a negative electrode, and a nonaqueous electrolyte and a positive electrode. And X
In the X-ray absorption spectrum measured by the X-ray absorption fine structure analysis (XAFS) method, around 2.5 ° in the radial structure function obtained by Fourier-transforming the broad-range X-ray absorption fine structure (EXAFS) spectrum at the MnK absorption edge A non-aqueous secondary battery characterized in that the peak intensity is 17.5 or less when 90% of the theoretically releasable lithium amount is released.

Here, measurement of general X-ray absorption fine structure analysis (XAFS) will be described. Although light such as IR and UV is absorbed by the substance, X-rays are also absorbed by the substance without exception, and the energy of the absorbed amount is converted into photoelectrons, fluorescent X-rays, and heat. At this time, part of the photoelectrons generated by the absorption of X-rays is reflected as structural information on the amount of X-ray absorption by scattering and interference by a plurality of atoms. That is, by monitoring the amount of X-ray absorption, information on the atomic structure can be obtained.

[0012] When placing material on beamline X-rays, X-rays irradiated to the substance (incident X-ray: I ₀₎ strength and substance X-rays having passed through the (transmitted X-rays: I _t) and strength Then, the amount of X-ray absorption (X-ray absorption coefficient) by the substance is calculated. When the X-ray energy (wavelength) is changed while monitoring the increase / decrease of the X-ray absorption coefficient and the X-ray absorption spectrum is measured, a sharp rise (absorption edge) of the X-ray absorption coefficient is observed at a certain energy position. Since the energy position of the absorption edge is unique to an element, if structural information can be extracted in the energy region near the absorption edge, it means that the information is information unique to the element.

When the X-ray absorption spectrum is measured with sufficient accuracy in the energy region near the absorption edge of a certain element of interest,
Large structural vibration accompanied by attenuation is observed in the energy region of several tens eV from the absorption edge. This is called X-ray absorption near edge stru
cture), which mainly contains information on the electronic state and three-dimensional structure of the element of interest. Further, in the energy region of several hundred eV on the higher energy side than XANES, fine structural vibration accompanied by similar attenuation is observed. This is called the wide area X-ray absorption fine structure (EXAFS: Extend).
It is called “ed X-ray absorption Fine structure” and contains information about the local structure (interatomic distance and coordination number) near the element of interest.

EXA extracted from X-ray absorption spectrum
When a Fourier transform is performed on an FS spectrum in an appropriate region, a radial distribution function can be obtained. This function is a one-dimensional distribution of the electron density centered on the element of interest, some atoms are located at the distance where the local maximum is shown, and the intensity is proportional to the electron density of the located atom. Therefore, structural information on the element of interest can be obtained by numerically examining the radial distribution function. In recent years, the above-mentioned XANES and EXAFS are collectively called XAFS.

In order to search for a high-performance active material in a lithium ion secondary battery or the like, the local crystal structure of each active material having a different charge / discharge amount and details of the structural change due to charge / discharge are measured. It will be an effective guideline to clarify this. To make such a measurement with XAFS,
A method of preparing an active material charged and discharged to a predetermined charge / discharge amount in advance and transmitting X-rays to the active material can be considered. However, in such a measurement method, when the active material is taken out from the closed cell for charge and discharge and moved to the XAFS measurement cell, the physical properties of the active material may be changed due to careless contact with air or the like. As a result, accurate measurement may not be performed.

Further, it is necessary to perform charging and discharging of the active material in another place, and it is necessary to prepare various kinds of active materials having different charging and discharging amounts. Was. In order to solve this problem, charging and discharging of the active material can be made possible in a sealed cell, and the details of the local crystal structure of each active material having a different charge / discharge amount and the structural change due to the charge / discharge can be easily and simply described. A cell for X-ray absorption fine structure measurement of a battery material that can be accurately measured was prepared.

The present invention uses the above-described cell to charge and discharge various spinel-type lithium manganese composite oxides,
The AFS measurement is performed, and the peak intensity around 2.5 ° in the radial structure function obtained by Fourier transforming the broad X-ray absorption fine structure (EXAFS) spectrum at the MnK absorption edge obtained from the X-ray absorption spectrum and the active material As a result of examining the relationship with the battery characteristics in detail, it has been found that there is a strength relationship suitable for the high-temperature characteristics.

The measurement of the X-ray absorption fine structure (XAFS) in the present invention was carried out by analyzing Si (111) as a spectral crystal.
Using a channel cut monochromator, X-ray energy was scanned between 6490 eV and 6750 eV, and transmission was performed by a transmission method. The integration time was 2 seconds / point. Angle correction is performed by setting the K absorption edge of Cu of 8980.3 eV to 12.71.
The test was performed at 85 degrees.

The positive electrode active material of the present invention can be synthesized by the following method. For example, it can be obtained by mixing a lithium compound and a manganese compound and then performing a heat treatment. The lithium compound is not particularly limited, for example, lithium hydroxide, lithium carbonate, lithium nitrate,
Examples thereof include lithium oxide, lithium chloride, lithium sulfate, lithium acetate, lithium iodide, and alkyl lithium. Particularly, lithium hydroxide, lithium carbonate, and lithium nitrate are preferable.

The manganese compound is not particularly limited. For example, electrolytic manganese dioxide (EMD), chemically synthesized manganese dioxide (CMD), Mn ₂ O ₃ , MnOOH
And manganese oxides and hydroxides such as Mn ₃ O ₄ . Particularly, electrolytic manganese dioxide, chemically synthesized manganese dioxide, and MnOOH are preferable. The mixing ratio of Li and Mn (Li / Mn ratio) varies depending on the starting compound and heating conditions, but is usually preferably 0.52 to 0.60.

The heat treatment conditions vary slightly depending on the starting compound, but can be obtained by heat treatment at 600 to 950 ° C. The heating atmosphere is nitrogen, argon,
Air, oxygen or a mixed gas thereof can be used. The average particle diameter of the positive electrode active material in the present invention is preferably in the range of 5 to 50 μm, more preferably 5 to 30 μm. The negative electrode material used in the present invention,
The substance is not particularly limited as long as it is a substance capable of reversibly storing and releasing lithium. Examples thereof include metallic materials such as metallic lithium and aluminum, carbon materials, carbon materials, graphite and graphite-like compounds, metal oxides, and metal nitrides. Can be used.

The lithium ion transfer medium used in the present invention may be, for example, an electrolyte in which a lithium salt is dissolved in an aprotic organic solvent, a solid or semisolid in which a lithium salt is dispersed in a polymer matrix, or a mixture of both. Although not limited, examples of the lithium salt include lithium perchlorate, L
iBF ₄ , LiPF ₆ , LiAsF ₆ , CF ₃ SO ₃ L
i, (CF ₃ SO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ C
Li, lithium organic carboxylate, lithium fluorocarboxylate, lithium polymer sulfonate, lithium polymer carboxylate, or the like can be used. Examples of the aprotic organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, organic carbonates such as methyl propyl carbonate, butyrolactone, propiolactone, ethyl acetate, butyl acetate, propyl acetate, and propion. Organic esters such as ethyl acetate and butyl propionate, organic ethers such as glyme, diglyme, triglyme, tetrahydrofuran, dioxane, diethyl ether, and silicon oil; organic amines such as pyridine and triethylamine; organic nitriles such as acetonitrile and propionitrile; Containing at least a part of a simple substance or a mixture of an organic nitrile of the present invention, to which other aprotic organic solvents such as benzene , Toluene, xylene, aromatic hydrocarbons such as decalin, hexane, pentane, aliphatic hydrocarbons such as decane, phenol, catechol, alkyl esters such as bisphenol, aromatic esters and chloroform,
It is also possible to use a mixture of halogenated hydrocarbons such as carbon tetrachloride and dichloromethane.

Next, examples of the polymer matrix include aromatic polyethers such as polyethylene oxide, polytetramethylene oxide, polyvinyl alcohol and polyvinyl butyral, polyethylene sulfide, and the like.
Aliphatic polythioethers such as polypropylene sulfide, aliphatic polyesters such as polyethylene succinate, polybutylene adipate and polycaprolactone, polyethyleneimine, polyimide and precursors thereof can be used.

As the separator used in the present invention, for example, a porous sheet of a polyolefin resin such as polyethylene or polypropylene, or a nonwoven fabric thereof may be used. The battery of the present invention is a conventional lithium secondary battery (metal lithium secondary battery or lithium secondary battery) except that a lithium manganese composite oxide having a spinel structure having the features of claim 1 is used as a positive electrode active material. Ion secondary battery).

[0025]

Embodiments of the present invention will be described below. Various lithium manganese oxides A to H were prepared by applying various raw materials and firing conditions as shown in Table 1 as the positive electrode active material.

【Example】

(Example 1) In the synthesis of a positive electrode active material, Li ₂ CO ₃ was used as a lithium compound, electrolytic manganese dioxide (EMD) was used as a manganese compound, and Li / Mn was mixed at an atomic ratio of 0.50. Oxygen concentration 20 vol%) 850 ° C
For 20 hours. Then, Li ₂ CO is added so that the final composition becomes Li _1.08 Mn _1.92 O _4.
3 was added, and the mixture was further heated at 650 ° C. for 20 hours to obtain a lithium manganese oxide. The resulting product, Li a spinel structure by X-ray diffraction and chemical analysis _1.080 Mn _1.916 O ₄
Met.

Next, 7 parts by weight of carbon powder as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder are added to 100 parts by weight of the positive electrode active material, and a paste is formed using N-methyl-2-pyrrolidone. And applied to a current collector of aluminum foil, dried and pressed to obtain a positive electrode. Subsequently, the positive electrode and the lithium metal of the counter electrode are provided with an X-ray transmission hole in an argon dry box controlled to a moisture content of 1 ppm or less, and the positive electrode and the lithium counter electrode face each other on the X-ray optical path. A mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in which 1.0 mol / l of LiPF ₆ is dissolved is incorporated in a chargeable / dischargeable closed X-ray absorption fine structure measurement cell, It was injected and used for measurement.

Using the positive electrode prepared above, a battery was prepared according to the following procedure. As the negative electrode, 5 parts by weight of flaky graphite, 1 part by weight of carboxymethyl cellulose as a binder, and 2 parts by weight of styrene-butadiene rubber were added to 100 parts by weight of graphitized mesocarbon fiber as an active material, and purified water was used. It was used as a paste, applied to a copper foil current collector, dried and pressed. A 25 μm-thick polyethylene microporous membrane was sandwiched between the positive electrode and the negative electrode as a separator to form a roll.

An insulating film was inserted into the bottom of a rectangular iron can, and the wound body was crushed and inserted. Next, the negative electrode tab taken out from the wound body was welded to the closing lid, and the positive electrode tab was welded to the positive electrode pin of the closing lid. An electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a 1: 2 mixed solvent of ethylene carbonate and dimethyl carbonate was poured into the battery can, and then the closure lid was welded to a thickness of 8.6 m.
m, a width of 34 mm, and a height of 48 mm were prepared and subjected to evaluation of high-temperature characteristics.

Example 2 The synthesis of the positive electrode active material was carried out by using LiOH.H ₂ O as a lithium compound and electrolytic manganese dioxide (EMD) as a manganese compound.
= 0.50, and heat-treated at 750 ° C. for 20 hours in a mixed gas of air and N ₂ (oxygen concentration: 15 vol%). Then, the final composition is Li _1.04 M
LiOH.H ₂ O was added so as to be n _1.96 O _4, and the mixture was further heated at 550 ° C. for 12 hours to obtain a lithium manganese oxide. The obtained product was found to be Li _1.037 Mn _1.960 O ₄ having a spinel structure by X-ray diffraction and chemical analysis. Next, after producing a positive electrode and an XAFS cell in the same manner as in Example 1, an X-ray absorption spectrum measured by an X-ray absorption fine structure analysis (XAFS) method was obtained. Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Example 3 In the synthesis of the positive electrode active material, LiNO ₃ was used as a lithium compound and γ was used as a manganese compound.
Using MnOOH, mixing at an atomic ratio of Li / Mn = 0.54, 24 hours at 650 ° C. in N ₂ (oxygen concentration 0 vol%).
The heat treatment was performed for a time. The obtained lithium manganese oxide was found to have a spinel structure of Li _1.06 Mn _1.927 O ₄ by X-ray diffraction and chemical analysis. Next, after a positive electrode and an XAFS cell were manufactured in the same manner as in Example 1, X was measured by X-ray absorption fine structure analysis (XAFS).
A linear absorption spectrum was obtained. Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Example 4 The synthesis of a positive electrode active material was performed using LiOH.H ₂ O as a lithium compound and chemically synthesized manganese dioxide (CMD) as a manganese compound.
Mn is mixed at an atomic ratio of 0.53, and mixed in O ₂ (oxygen concentration 1
(00 vol%) by performing a heat treatment at 800 ° C. for 20 hours. The obtained lithium manganese oxide was found to have a spinel structure of Li _1.05 Mn _1.95 by X-ray diffraction and chemical analysis.
O ₄ . Next, after producing a positive electrode and an XAFS cell in the same manner as in Example 1, an X-ray absorption spectrum measured by an X-ray absorption fine structure analysis (XAFS) method was obtained.
Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Example 5 A positive electrode active material was synthesized by using Li ₂ CO ₃ as a lithium compound and electrolytic manganese dioxide (EMD) as a manganese compound.
Mix at an atomic ratio of 0.57, and in air (oxygen concentration 20 vo
1%) by heating at 900 ° C. for 24 hours. The obtained lithium manganese oxide was found to have a spinel structure of Li _1.120 Mn _1.876 O ₄ by X-ray diffraction and chemical analysis.
Next, in the same manner as in Example 1, the positive electrode and XA
After fabricating the FS cell, X-ray absorption fine structure analysis (XAF
An X-ray absorption spectrum measured by the S) method was obtained. continue,
A battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Comparative Example 1 A positive electrode active material was synthesized by using LiNO ₃ as a lithium compound, electrolytic manganese dioxide (EMD) as a manganese compound, and Li / Mn = 0.
Mixed at an atomic ratio of 50 and in air (oxygen concentration 20 vol
%) By performing a heat treatment at 450 ° C. for 24 hours. The obtained lithium manganese oxide was found to have a spinel structure of Li _0.997 Mn _1.996 O ₄ by X-ray diffraction and chemical analysis.
Met. Next, in the same manner as in Example 1, the positive electrode and X
After fabricating the AFS cell, X-ray absorption fine structure analysis (XA
An X-ray absorption spectrum measured by the FS) method was obtained. Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Comparative Example 2 A positive electrode active material was synthesized by using LiOH.H ₂ O as a lithium compound and chemically synthesized manganese dioxide (CMD) as a manganese compound.
Mixing was performed at an atomic ratio of Mn = 0.54, and heat treatment was performed at 750 ° C. for 20 hours in a mixed gas of air and O ₂ (oxygen concentration: 50 vol%). The obtained lithium manganese oxide was identified as having a spinel structure L by X-ray diffraction and chemical analysis.
i _1.069 Mn _1.926 O ₄ . Next, after producing a positive electrode and an XAFS cell in the same manner as in Example 1, an X-ray absorption spectrum measured by an X-ray absorption fine structure analysis (XAFS) method was obtained. Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

Comparative Example 3 A positive electrode active material was synthesized by mixing Li ₂ CO ₃ as a lithium compound and Mn ₂ O ₃ as a manganese compound at an atomic ratio of Li / Mn = 0.57. (Oxygen concentration 100 vol%) 2 at 700 ° C
The heating was performed for 0 hours. The obtained lithium manganese oxide was found to have a spinel structure of Li _1.112 Mn _1.879 O ₄ by X-ray diffraction and chemical analysis. Next, after producing a positive electrode and an XAFS cell in the same manner as in Example 1, an X-ray absorption spectrum measured by an X-ray absorption fine structure analysis (XAFS) method was obtained. Subsequently, a battery was manufactured in the same manner as in Example 1, and the high-temperature characteristics were evaluated.

<Test Results> The X-ray absorption fine structure (XAFS) samples prepared in Examples and Comparative Examples were evaluated as follows. A predetermined amount of lithium is inserted and removed while monitoring the amount of charge and discharge electricity with an X-ray absorption fine structure (XAFS) measurement cell, and the absorption coefficient is sequentially determined for a predetermined amount of lithium insertion and removal while scanning the X-ray energy from 6490 to 6750 eV. Was measured to obtain an X-ray absorption spectrum. Subsequently, the background was subtracted using Victoreen's equation (Cλ ³ −Dλ ⁴ + Const.) To which a constant term was added, and Cubic-Spline (weighing) was performed.
The EXAFS signal was extracted by estimating the absorbance of the isolated atoms by the method t). Weights k ⁿ (n
= 3) to perform a Fourier transform to derive a radial structure function that is a function of the distance from the absorbing atom. The peak intensity around 2.5 ° when 90% of the theoretically releaseable lithium amount was released was determined from the obtained radial structure function.

The following Table 1 shows Examples 1 to 5 and Comparative Examples 1 to
3 shows the peak intensity around 2.5 ° above. X
The X-ray absorption spectrum measured by the X-ray absorption fine structure analysis (XAFS) method is shown in FIG. 1, and further, the broad X-ray absorption fine structure at the MnK absorption edge obtained from the X-ray absorption spectrum (EX
The radial structure function of the (AFS) spectrum is shown in FIG. Further, the Fourier to the ratio of the theoretically released lithium to the amount of lithium that can be theoretically released in the wide area X-ray absorption fine structure (EXAFS) spectrum obtained from the X-ray absorption spectra of the lithium manganese oxides of Examples 1 and 2 and Comparative Example 1 FIG. 3 shows the converted absolute value of the peak intensity around 2.5 A.

Further, the batteries produced in the examples and comparative examples were evaluated as follows. After charging at a charging voltage of 4.2 V for 5 hours, the battery was discharged at a constant current of 700 mA to 2.7 V to obtain a battery capacity. After repeating this charge / discharge cycle for 5 cycles, the battery was charged, stored at 85 ° C. for 120 hours in a 4.2 V charged state, cooled to room temperature, and discharged. The self-discharge rate was determined by {1- (discharge amount at sixth cycle / discharge amount at fifth cycle)} × 100. Further, using another battery manufactured at the same time, the charging voltage was 4.2 V.
After charging for 5 hours at a constant current of 700 mA, 2.7
A cycle of discharging to V was performed at 60 ° C. for 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was determined, which was defined as the cycle maintenance rate at 60 ° C. The results of this high temperature storage and cycle test are shown in Table 2. As shown in Table 2, it can be seen that the non-aqueous secondary battery of the present invention is excellent in storage at high temperatures and cycleability.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

The positive electrode active material of the present invention is a lithium manganese composite oxide having a spinel structure, and in the X-ray absorption spectrum measured by the X-ray absorption fine structure analysis (XAFS) method, the wide area X at the MnK absorption edge is obtained. Line absorption fine structure (E
XAFS) when the peak intensity around 2.5 ° in the radial structure function obtained by Fourier transform of the spectrum emits 90% of the theoretically dischargeable lithium amount, 17.5.
It has the following features. The battery using this is
It is industrially extremely useful because of its excellent properties at high temperatures.

[Brief description of the drawings]

FIG. 1 is an X-ray absorption spectrum of a lithium manganese composite oxide which is an example of an embodiment of the present invention.

FIG. 2 shows Mn determined from an X-ray absorption spectrum of a lithium manganese composite oxide as an example of an embodiment of the present invention.
It is a radial structure function of a broad X-ray absorption fine structure (EXAFS) spectrum at a K absorption edge.

FIG. 3 shows the amount of lithium that can be theoretically released in a broad X-ray absorption fine structure (EXAFS) spectrum obtained from the X-ray absorption spectra of the lithium manganese composite oxides of Examples 1 and 2 and Comparative Example 1 of the present invention. This is the absolute value of the peak intensity around 2.5 ° obtained by Fourier transform with respect to the ratio of the released lithium.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshio Tsubata 1-3-1 Yoko, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Asahi Kasei Kogyo Co., Ltd. No. 1 Inside Asahi Kasei Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A secondary battery comprising lithium or a substance capable of inserting and extracting lithium as a negative electrode, a nonaqueous electrolyte and a positive electrode, wherein the positive electrode active material is a lithium manganese composite oxide having a spinel structure, and an X-ray In an X-ray absorption spectrum measured by an absorption fine structure analysis (XAFS) method, a wide area X-ray absorption fine structure at the MnK absorption edge (EXAF)
S) The peak intensity around 2.5 ° in the radial structure function obtained by Fourier transforming the spectrum is 17.5 or less when 90% of the theoretically dischargeable lithium amount is released. Non-aqueous secondary battery.