JP3856518B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００２７】
【発明の効果】
以上説明してきたように、本発明のＸ線回折ピークを少なくとも２．７５±０．０２Åには有せず、４．７４±０．０２Å、２．４７±０．０２Å、２．０５±０．０２Åに有し、その半価巾が各々０．１±０．０５であるＬｉ［Ｌｉ_x Ｍｎ_2-x ］Ｏ₄ で示されるスピネル系のリチウムマンガン酸化物を使用した非水電解質二次電池では、初期容量が高く、かつ、室温以上の温度下でもＭｎの溶出が起こらなくなり良好なサイクル性能が維持される。また、ＬｉＯＨが残存しないためにペーストのゲル化も起こらない。さらに、高価な他の元素を使用しないので安価である。その結果、安価な材料のリチウムマンガン酸化物を使用して、高価なリチウムコバルト酸化物を使用した場合と遜色のない非水電解質二次電池を提供できる。高性能な非水電解質二次電池が安価で供給できるようになりその工業的価値は大きい。
【図面の簡単な説明】
【図１】実施例１で得られたリチウムマンガン酸化物のＸ線回折模様である。
【図２】比較例で得られたリチウムマンガン酸化物のＸ線回折模様である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in cycle performance at high temperature of a nonaqueous electrolyte secondary battery using lithium manganese oxide as a positive electrode active material.
[0002]
[Prior art]
In recent years, the development of electronic technology is remarkable, and downsizing and weight reduction of devices are being promoted. For this reason, mobile devices such as mobile communication devices and portable computers have become widespread, and secondary batteries with high energy density are demanded as power sources for these mobile devices. In particular, non-aqueous electrolyte secondary batteries are expensive. Since voltage can be expected, there is a craving for further miniaturization and weight reduction of equipment. However, in non-aqueous electrolyte secondary batteries using lithium metal and lithium alloys as negative electrode materials, lithium dendrites are formed on the negative electrode when charging and discharging are repeated, resulting in poor cycle performance and reliability at high temperatures. It was difficult to put it to practical use because of problems such as sex.
[0003]
As a means for solving these problems, a non-aqueous electrolyte secondary battery using a carbon material capable of occluding and releasing lithium as a negative electrode active material and a composite oxide of lithium and cobalt as a positive electrode active material (Japanese Patent No. 1989293). No. specification) has been developed and has a voltage of 4 V or more in a charged state, and therefore has become widely used as a power source for mobile devices. However, current non-aqueous electrolyte secondary batteries are expensive because they contain a large amount of cobalt, and there has been a limit to reducing the price of the power supply. For this reason, attempts to replace cobalt with other transition metals are active. Among the transition metals, manganese, which is inexpensive, is most expected to replace cobalt. However, the lithium manganese oxide having a stoichiometric composition has poor cycle performance, and as a method for improving this, for example, as disclosed in JP-A-5-205744, a part of manganese can be replaced with lithium. Proposed.
[0004]
Thus, the conventional synthesis method of lithium manganese oxide in which a part of manganese is substituted with lithium is obtained by mixing Mn raw material and Li raw material in a desired ratio and heat-treating at a relatively low temperature of 700 ° C. or lower. It was a thing. In particular, heat treatment at a temperature of 500 ° C. or less has been proposed by using lithium hydroxide having a low melting point (an anhydride, melting point: 445 ° C.) or lithium nitrate (melting point: 255 ° C.) instead of lithium carbonate as a Li raw material. . However, in any case, since the heat treatment is performed at a low temperature, the crystallinity does not increase, and as a result, there is a problem that the reversible capacity in the vicinity of about 4 V is lowered with respect to the oxidation-reduction potential of the lithium metal. Furthermore, when lithium hydroxide is used as the Li raw material, if it remains unreacted, the paste will gel due to its alkaline components when making a paste by wet mixing with a binder to form a battery. There is a problem that it becomes impossible to use it.
Further, when heat treatment is performed at a high temperature of 700 ° C. or higher, a secondary phase such as Li ₂ MnO ₃ is likely to be formed, and manganese is not sufficiently substituted with lithium. Elution occurred, and there was a problem in cycle performance at high temperatures.
[0005]
[Problems to be solved by the invention]
Lithium manganese oxide in which a part of manganese was replaced with lithium was able to improve the cycle performance near room temperature, but manganese was still eluted under higher temperatures and severer conditions. Had the problem of lowering. Furthermore, the crystallinity is low and the capacity is greatly reduced.
The object of the present invention is to replace a part of manganese with lithium and to use a lithium manganese oxide with good crystallinity, so that the cycle performance is good especially at a temperature of room temperature or higher while maintaining a high capacity. And providing a non-aqueous electrolyte secondary battery.
[0006]
[Means for Solving the Problems]
As a result of intensive studies on the heat treatment conditions and substitution method of spinel-type lithium manganese oxide in which a part of manganese is substituted with lithium, the present inventors have obtained a desired substitution amount while maintaining high crystallinity. The present inventors have found a spinel lithium manganese oxide suitable as a positive electrode material for an electrolyte secondary battery and have reached the present invention.
That is, the present invention
(1) A negative electrode active material capable of occluding and releasing lithium ions, a lithium ion conductive non-aqueous electrolyte, and a positive electrode active material comprising a lithium-containing metal oxide capable of occluding and releasing lithium ions In the non-aqueous electrolyte secondary battery, the lithium-containing metal oxide is a spinel-type lithium manganese oxide represented by the following general formula, and the X-ray diffraction peak is 4.26 ± 0.02Å, 4.08 ±. 0.02 mm, 2.75 ± 0.02 mm, and at least 4.74 ± 0.02 mm, 2.47 ± 0.02 mm, 2.05 ± 0.02 mm, and the X-ray A non-aqueous electrolyte secondary battery characterized in that the half-value widths of diffraction peaks are each 0.1 ± 0.05,
Li [Li _x Mn _2-x ] O ₄ (where 0.07 ≦ x ≦ 0.18 )
(2) The lattice constant of the spinel-type lithium manganese oxide represented by the general formula Li [Li _x Mn _2−x ] O ₄ (where 0.07 ≦ x ≦ 0.18 ) is 8.20 to 8.24 A non-aqueous electrolyte secondary battery characterized in that
(3) After heat-treating a mixture of electrolytic manganese dioxide and lithium hydroxide or lithium nitrate in air at a temperature of 700 ° C. or higher, heat-treat again at a temperature of 300 ° C. or higher and 600 ° C. or lower to obtain an X-ray diffraction peak. 4.26 ± 0.02 mm, 4.08 ± 0.02 mm, 2.75 ± 0.02 mm, and at least 4.74 ± 0.02 mm, 2.47 ± 0.02 mm, 2. The general formula Li [Li _x Mn _2−x ] O ₄ (where 0.07 ≦ x is 0.5 ± 0.02 mm) and the half width of each X-ray diffraction peak is 0.1 ± 0.05. The method for producing a nonaqueous electrolyte secondary battery according to claim 1 , further comprising a step of obtaining a spinel lithium manganese oxide represented by ≦ 0.18) .
[0007]
Hereinafter, the present invention will be specifically described.
Examples of the manganese raw material of the lithium manganese oxide used in the present invention include EMD (Electrolytic Manganese Dioxide), CMD (Chemical Manganese Dioxide), and γ-MnOOH, but EMD having a high tetravalent Mn content is preferable. . Examples of the lithium raw material include Li ₂ CO ₃ , LiOH, LiCl, LiNO ₃ , Li ₂ SO ₄ , and CH ₃ COOLi, and Li ₂ CO ₃ , LiOH, or LiNO ₃ is preferable.
[0008]
The lithium manganese oxide used in the present invention can be prepared as follows.
For example, after mixing EMD and LiOH or LiNO ₃ or Li ₂ CO ₃ pulverized so as to have an average particle diameter of 5 to 25 μm so that the Mn / Li ratio is 0.5, 800 to 900 ° C. in the atmosphere. It can be obtained by performing heat treatment at room temperature, cooling to near room temperature, adding LiOH or LiNO ₃ so as to obtain a desired amount of Li, mixing and heat-treating at 300 to 600 ° C., more preferably at 300 to 500 ° C. it can. If the temperature of the second heat treatment is less than 300 ° C., LiOH may remain particularly, and it is not preferable because a paste for forming an electrode cannot be formed. If it exceeds 600 ° C., subphases such as Li ₂ MnO ₃ are easily synthesized, which is also not preferable.
[0009]
As another example, the pulverized EMD and LiOH or LiNO ₃ may be mixed in advance at a desired Mn / Li ratio and heat-treated. The heat treatment must first be performed at 800 to 900 ° C., then 300 to 600 ° C., more preferably 300 to 500 ° C. Also in this case, it is important to perform the second heat treatment. If the second heat treatment is not performed, a phase other than spinel such as Li ₂ MnO ₃ is generated, which is not preferable.
[0010]
The amount of substitution of Mn by Li is preferably in the range of 0.05 to 0.18 atomic%, and more preferably in the range of 0.07 to 0.16 atomic%. When the substitution amount is less than 0.05 atomic%, the effect of substituting manganese with lithium is small, and the cycle performance at room temperature is lowered. On the other hand, if it exceeds 0.18 atomic%, the capacity decreases greatly, which is not preferable.
[0011]
Next, an X-ray diffraction pattern measurement method in the present invention will be described.
For the measurement of the X-ray diffraction pattern, RINT 2500 manufactured by Rigaku Corporation was used. The test was performed under the following equipment conditions using Cu-Kα1 (wavelength 1.5405 mm) as the X-ray source. The tube voltage and current were 50 kV and 160 mA, the divergence slit was 0.5 °, the scattering slit was 0.5 °, the light receiving slit width was 0.15 mm, and a monochromator was used. The measurement was performed under the conditions of a scanning speed of 2 ° / min, a scanning step of 0.01 °, and a scanning axis of 2θ / θ. Further, the half width was obtained by subtracting the background from the measured value of the diffraction pattern expressed by the 2θ axis, and setting the width of the peak at half the height (h / 2) of the diffraction peak intensity (h).
[0012]
The lithium manganese oxide synthesized by the method described above has X-ray diffraction peaks derived from at least the (111) plane, the (311) plane, and the (222) plane by 4.74 ± 0.02Å, 2.47 ± 0. 0.02% and 2.05 ± 0.02%, and the half-value width as an index of crystallinity of these diffraction peaks is 0.1 ± 0.05. If the half width is 0.1 ± 0.05 or more, Mn elution is likely to occur and the capacity is also reduced, which is not preferable. Further, a diffraction peak of 2.75 ± 0.02Å caused by Mn ₂ O ₃ or Mn ₃ O ₄ , and 4.26 ± 0.02Å, 4.08 ± 0 caused by LiOH and / or Li ₂ MnO ₃ .02 Å does not have.
[0013]
According to JCPDS (The Joint Commitment on Power Diffraction Standards) card 35-782, LiMn ₂ O _4, which is a conventional stoichiometric composition, has a lattice constant of 8.248 Å. The lattice constant of the lithium manganese oxide of the present invention is preferably 8.20 to 8.24. The reason why the lattice constant of the lithium manganese oxide of the present invention is small is thought to be that a part of Mn in the crystal unit cell was replaced with Li having an ionic radius smaller than that of Mn. When the lattice constant is 8.20 mm or less, the capacity is remarkably reduced. This is presumably because the average valence of Mn is too close to 4. On the other hand, if it is 8.24 mm or more, the effect of substituting part of Mn with Li cannot be obtained, and elution of Mn occurs and the cycle performance deteriorates.
[0014]
The negative electrode material used in the present invention is not particularly limited as long as lithium can be occluded and released in an ionic state. For example, carbon materials such as coke, natural graphite, artificial graphite and non-graphitizable carbon, metal oxides such as SiSnO, LiCoN A metal nitride such as ₂ can be mentioned, and a carbon material is preferable.
[0015]
In the present invention, when the active material is formed into an electrode, a conductive agent can be added as necessary and fixed to the current collector with a binder. Examples of the conductive agent include natural graphite, artificial graphite, carbon black, ketjen black, acetylene black, etc., and graphite or a combination of graphite and acetylene black is preferable. The addition amount is not particularly limited, but is preferably 1 to 20% by weight, more preferably 3 to 10% by weight. When the addition amount is less than 1% by weight, the conductivity is not uniform, and when it exceeds 20% by weight, the capacity per unit volume is lowered. Further, as the binder, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, carboxymethylcellulose, styrene butadiene rubber, fluororubber, etc. are usually used alone or mixed, but particularly limited. Not. These addition amounts are preferably 1 to 20% by weight, more preferably 1 to 10% by weight. When the addition amount is less than 1% by weight, the binding force is weak, and when it exceeds 20% by weight, the movement of Li ions is inhibited, and the performance as a battery is deteriorated.
[0016]
As the electrolytic solution, a mixture in which a lithium salt is used as an electrolyte and is dissolved in various organic solvents is used. The electrolyte is not particularly _limited, it may be used _{LiClO 4, LiBF 4, LiPF 6} , LiAsF 6, alone or a mixture of such LiCF ₃ SO _3. Further, the organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran and the like alone or two or more kinds Mixed solvents can be used.
[0017]
[Action]
Since the lithium manganese oxide of the present invention does not contain Mn ₂ O ₃ and / or Mn ₃ O ₄ , it is possible to prevent elution of Mn from the by-product. In addition, since the heat treatment is performed at a low temperature after the heat treatment at a high temperature, Li ₂ Mn ₃ O _{4 as} a by-product disappears, and substitution of Mn and Li can be accurately performed in a desired amount. Furthermore, since the heat treatment is once performed at a high temperature of 700 ° C. or higher, the crystallinity can be increased as shown by the half-value width of the peak of the X-ray diffraction pattern. As a result, in the non-aqueous electrolyte secondary battery using the lithium manganese oxide of the present invention, the elution amount of Mn at a high temperature is reduced as compared with the battery using the conventional lithium manganese oxide, which is favorable. Cycle characteristics can be obtained.
[0018]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated still in detail using a specific Example etc., this invention is not limited at all more than these Examples.
Example 1
EMD with an average particle size of 20 μm as a starting material and Li ₂ CO ₃ were mixed at a composition ratio of Li / Mn = 0.5 (atomic ratio), heat-treated in air at 850 ° C. for 20 hours, and then cooled to near room temperature. did. From the result of comparing the X-ray diffraction pattern of this lithium manganese oxide and the JCPDS card, it was confirmed that this lithium manganese oxide was LiMn ₂ O ₄ . Next, the obtained LiMn ₂ O ₄ and LiOH were mixed at a composition ratio of Li / Mn = 0.61 (atomic ratio), and heat-treated at 400 ° C. for 10 hours in the air to obtain the lithium manganese oxide of the present invention. Obtained. As shown in FIG. 1, the X-ray diffraction pattern of this lithium manganese oxide shows diffraction peaks derived from the (111) plane, (311) plane, and (222) plane as 4.741４, 2.476Å, and 2.053Å, respectively. And the half widths thereof are 0.094, 0.118, and 0.118, respectively, and the crystallinity is high, and subphases such as Mn ₂ O ₃ , Mn ₃ O _4, Li ₂ MnO ₃ , and LiOH are included. Since it has no diffraction peak, it was confirmed to be a single cubic spinel.
[0019]
When the lattice constant was accurately determined using Si as a standard material, it was 8.213 mm. Furthermore, it was confirmed from the results of elemental analysis that it was Li [Li _0.12 Mn _1.88 ] O ₄ . As a result of observing the surface of the lithium manganese oxide thus prepared with a scanning electron microscope, it is confirmed that the secondary particles are formed by an aggregate of primary particles having a diameter of approximately 0.3 to 1.0 μm. It could be confirmed.
Specific battery creation in the present invention will be described.
[0020]
After mixing 3 parts by weight of acetylene black and 3 parts by weight of scale-like natural graphite as a conductive agent with respect to 100 parts by weight of the lithium manganese oxide, fluorine rubber is mixed at a ratio of 3 parts by weight with respect to the total weight. A solvent mixture of ethyl acetate / ethyl cellosolve was added and wet-mixed to obtain a paste. Next, this paste was uniformly applied to both surfaces of a 20 μm-thick aluminum foil serving as a positive electrode current collector, dried, and then subjected to pressure molding with a roller press to prepare a belt-like positive electrode. Next, with respect to a mixture of 95 parts by weight of mesocarbon fiber graphitized at 3000 ° C. and 5 parts by weight of scale-like natural graphite, 1 part by weight of carboxymethylcellulose, 2 parts by weight of styrene butadiene rubber, and purified water as a solvent are added and wet mixed. To make a paste. Next, this paste was uniformly applied to both sides of a 12 μm thick copper foil serving as a negative electrode current collector, dried, and then pressure-formed by a roller press to prepare a belt-like negative electrode. Further, a wound body was obtained by winding a 25 μm thick polyethylene microporous film as a separator between the positive electrode and the negative electrode in a roll shape.
[0021]
An insulating film was inserted into the bottom of a nickel-plated iron cylindrical can, and the wound body was inserted. Next, the negative electrode tab taken out from the wound body was welded to the bottom of the can, and the positive electrode tab was welded to a closed lid made of a gasket, an explosion-proof disk, and a PTC element. An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate and diethyl carbonate was poured into a battery can, and an insulating film was inserted into the upper part of the winding body, and then the plug was closed. A cylindrical body of a nonaqueous electrolyte secondary battery having an outer shape of 17 mm and a height of 500 mm was prepared by inserting a lid and caulking the end of the battery can.
[0022]
(Example 2)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the synthesis method of lithium manganese oxide was changed as follows. EMD having an average particle size of 15 μm as a starting material and LiOH were mixed at a composition ratio of Li / Mn = 0.61 (atomic ratio), heat-treated in air at 900 ° C. for 20 hours, and then cooled to 500 ° C. to 12 The lithium manganese oxide of the present invention was obtained by heat treatment for a period of time. The X-ray diffraction pattern of the obtained substance has diffraction peaks derived from at least the (111) plane, the (311) plane, and the (222) plane at 4.751 mm, 2.479 mm, and 2.055 mm, and The half widths were 0.094, 0.094, and 0.094, respectively, and they were single cubic spinels with high crystallinity and no secondary phase peak. When the lattice constant was accurately determined using Si as a standard material, it was 8.215 mm. Furthermore, it was confirmed from the results of elemental analysis that it was Li [Li _0.11 Mn _1.89 ] O ₄ . As a result of observing the surface of the lithium manganese oxide thus prepared with a scanning electron microscope, the secondary particles were found to be formed of aggregates of primary particles having a diameter of approximately 0.5 to 1.5 μm. It could be confirmed.
[0023]
(Comparative example)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the synthesis method of lithium manganese oxide was changed as follows. EMD with an average particle diameter of 20 μm as a starting material and LiOH were mixed at a composition ratio of Li / Mn = 0.6 (atomic ratio), heat-treated in air at 650 ° C. for 12 hours, and then heated to 900 ° C. Lithium manganese oxide was obtained by heat treatment for 12 hours. As shown in FIG. 2, the X-ray diffraction pattern of this lithium manganese oxide shows diffraction peaks derived from the (111) plane, (311) plane, and (222) plane as 4.767４, 2.487Å, and 2.063Å, respectively. And half-widths of 0.094, 0.118, and 0.141, respectively, and the crystallinity is high, but the diffraction peak is considered to be attributed to Mn ₂ O ₃ or Mn ₃ O ₄ at 2.767Å. And there was a diffraction peak believed to be due to Li ₂ MnO ₃ . Furthermore, when the lattice constant was accurately determined using Si as a standard material, it was 8.247 mm. From this result, it was considered that it was a mixture of LiMn ₂ O ₄ and Mn ₂ O _3, Mn ₃ O ₄ and Li ₂ MnO ₃ and not a uniform cubic spinel single phase.
[0024]
〔Test results〕
In each of the batteries prepared in Examples 1 and 2 and the comparative example, after the aging period of 24 hours has elapsed for the purpose of stabilizing the inside of the battery, the charging voltage is set to 4.2 V and charging is performed in 5 hours. I did it. Subsequently, the battery was discharged to 2.7 V at a constant current of 500 mA, the initial capacity of each battery was measured, and the capacity per unit positive electrode active material in the battery was determined. Next, the battery was placed in a thermostatic chamber adjusted to 60 ° C., charged at a charging voltage of 4.2 V for 3 hours, and subjected to a cycle test in which discharging was repeated up to 2.7 V at a constant current of 1 A. 50 The discharge capacity at the cycle was measured, and the capacity per unit positive electrode active material in the battery was determined. Based on these, the deterioration rate of the discharge capacity (Y) at the 50th cycle relative to the initial capacity (X) was calculated according to the following equation.
Deterioration rate (%) = [(X−Y) / X] × 100
[0025]
Table 1 shows the discharge amount per unit positive electrode active material calculated from the initial discharge amount and the discharge capacity at the 50th cycle, and the deterioration rate calculated therefrom.
As shown in Table 1, the batteries of Examples 1 and 2 have a lower initial capacity than that of the comparative example, but the deterioration rate at 50 cycles is small.
This is because once heat-treated at 700 ° C. or higher, a uniform spinel with high crystallinity can be created and the subphase disappears, so that the charged lithium accurately replaces a part of manganese. Conceivable.
[0026]
[Table 1]

[0027]
【The invention's effect】
As described above, the X-ray diffraction peak of the present invention does not have at least 2.75 ± 0.02Å, 4.74 ± 0.02Å, 2.47 ± 0.02Å, 2.05 ± 0. Nonaqueous electrolyte secondary using a spinel-type lithium manganese oxide represented by Li [Li _x Mn _2−x ] O ₄ having a half width of 0.1 ± 0.05 each In the battery, the initial capacity is high, and the elution of Mn does not occur even at a temperature equal to or higher than room temperature, and good cycle performance is maintained. Further, since no LiOH remains, the gelation of the paste does not occur. Furthermore, it is inexpensive because it does not use other expensive elements. As a result, it is possible to provide a non-aqueous electrolyte secondary battery that is inferior to the case of using expensive lithium cobalt oxide by using lithium manganese oxide that is an inexpensive material. A high-performance non-aqueous electrolyte secondary battery can be supplied at low cost, and its industrial value is great.
[Brief description of the drawings]
1 is an X-ray diffraction pattern of lithium manganese oxide obtained in Example 1. FIG.
FIG. 2 is an X-ray diffraction pattern of lithium manganese oxide obtained in a comparative example.

Claims (3)

A non-aqueous device comprising a negative electrode active material capable of occluding and releasing lithium ions, a lithium ion conductive non-aqueous electrolyte, and a positive electrode active material comprising a lithium-containing metal oxide capable of occluding and releasing lithium ions In the electrolyte secondary battery, the lithium-containing metal oxide is a spinel-type lithium manganese oxide represented by the following general formula, and an X-ray diffraction peak is 4.26 ± 0.02Å, 4.08 ± 0.02Å. 2.75 ± 0.02 mm, and at least 4.74 ± 0.02 mm, 2.47 ± 0.02 mm, 2.05 ± 0.02 mm, and the X-ray diffraction peak A non-aqueous electrolyte secondary battery having a half width of 0.1 ± 0.05.
Li [Li _x Mn _2-x ] O ₄ (where 0.07 ≦ x ≦ 0.18 ) The lattice constant of the spinel-type lithium manganese oxide represented by the general formula Li [Li _x Mn _2−x ] O ₄ (where 0.07 ≦ x ≦ 0.18 ) is 8.20 to 8.24. The nonaqueous electrolyte secondary battery according to claim 1. A mixture of electrolytic manganese dioxide and lithium hydroxide or lithium nitrate was heat-treated at a temperature of 700 ° C. or higher in the air atmosphere, and then heat-treated again at a temperature of 300 ° C. or higher and 600 ° C. or lower to give an X-ray diffraction peak of 4.26. ± 0.02Å, 4.08 ± 0.02Å, 2.75 ± 0.02Å, and at least 4.74 ± 0.02Å, 2.47 ± 0.02Å, 2.05 ± 0 , And the half width of the X-ray diffraction peak is 0.1 ± 0.05, respectively. General formula Li [Li _x Mn _2−x ] O ₄ (where 0.07 ≦ x ≦ 0. The method for producing a nonaqueous electrolyte secondary battery according to claim 1 , further comprising a step of obtaining a spinel-type lithium manganese oxide represented by 18) .

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