JPH07282798A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve cycle characteristic of a nonaqueous electrolyte secondary battery having positive electrode active material of spinel system lithium manganese oxide. CONSTITUTION:Spinel system lithium manganese oxide, shown in a general formula Li [Mn2-XLi]XO4 (0.020<=x<=0.081), is used for the active material of a positive electrode 2. It becomes Li3X [Mn2-x]O4 when charged, and at the point of the time, all manganese in a crystal is Mn<4+> to cause no Mn<3+> in the crystal to make the crystallization structure change of the active material of the positive electrode 2 difficult to be caused. Even at the point of time when all manganese in the active material becomes Mn<4+>, a lithium ion located in a 8a site remains 0.06 or more, and ion conductivity induced by the movement of the lithium ion in an active material crystal is kept in well to effectively charge/discharge all active material, providing a battery less in capacity deterioration following a cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to improve the cycle characteristics of a non-aqueous electrolyte secondary battery using a spinel type lithium manganese oxide as a positive electrode active material.

[0002]

2. Description of the Related Art As electronic devices are becoming smaller and lighter, there is an increasing demand for high energy density secondary batteries as their power sources. As a high energy density secondary battery, it has been expected to be a non-aqueous electrolyte secondary battery that can be expected to have a high voltage, but there is a problem in the cycle performance of the negative electrode.
It just didn't happen. However, only recently has a non-aqueous electrolyte secondary battery with a carbon electrode as a negative electrode, which utilizes the movement of lithium ions into and out of carbon, developed, and the non-aqueous electrolyte secondary battery has entered the stage of commercialization all at once. It was This battery was first introduced to the world in 1990 by the present inventors under the name of lithium-ion secondary battery (the magazine Progress In Batteri).
es & Solar Cells, Vol. 9, 19
90, p209), and nowadays it is recognized in the battery industry and academic societies as to be called the next-generation secondary battery "lithium-ion secondary battery", and its development and commercialization competition is intensifying. Typically, a lithium cobalt-containing composite oxide (LiCoO ₂ ) is used for the positive electrode material, and a carbonaceous material such as coke or graphite is used for the negative electrode. In fact 2
Lithium ion secondary batteries having an energy density of about 40 Wh / l have already been put into practical use in small quantities as power sources for video cameras, mobile phones, and the like. The energy density of existing nickel-cadmium batteries is 100-150 Wh / l,
The energy density of lithium-ion secondary batteries is much higher than that of existing batteries. However, a major drawback of the lithium-ion secondary battery using LiCoO ₂ as the positive electrode material is that the cost of raw materials is much higher than that of existing batteries because expensive cobalt is used. In addition to lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) and lithium manganese oxide (LiMn ₂ O ₄ ) are known as materials that can be combined with a carbon negative electrode to form a lithium ion secondary battery. ing.
LiMn ₂ O ₄ attracts attention because it is an inexpensive material.
In recent years, lithium ion secondary batteries using Mn ₂ O ₄ as a positive electrode active material have been actively developed. LiC
Another drawback of the lithium-ion secondary battery using oO ₂ as a positive electrode material is that it causes a fire or smoke due to overcharging, which leaves a problem in safety performance. For this reason, for example, a battery pack of a lithium-ion secondary battery that is currently in practical use as a power source for a video camera incorporates an overcharge prevention circuit and measures against it are taken. Therefore, in addition to the battery price, the price of the overcharge prevention circuit is added,
Battery packs using lithium-ion batteries are very expensive, which is a major obstacle to the widespread use of lithium-ion batteries. The present inventor has found that a lithium-ion secondary battery using lithium manganese oxide (LiMn ₂ O ₄ ) for the positive electrode does not cause ignition due to overcharging, and the temperature inside the battery rises due to overcharging, and It was found that the porous membrane separator of No. 1 softens or melts, loses its porosity, becomes inoperable, and the battery is safely broken. However, unfortunately, lithium ion secondary batteries that use lithium manganese oxide (LiMn ₂ O ₄ ) as a positive electrode material have poor cycle characteristics, which means that they have great features in terms of price and safety. It has not been put to practical use yet because of its large deterioration. As a method for improving this cycle characteristic, lithium is excessively used to obtain i _{1 + X} Mn ₂ O ₄ , or a part of manganese is replaced with another metal such as Co to obtain LiMn.
It has been proposed that the lithium manganese oxide be modified by using _2-X Co _X O ₄ or the like to improve the cycle characteristics, but the capacity associated with the charge / discharge cycle at high temperature (35 ° C. or higher) is proposed. However, the lithium-ion secondary battery using lithium manganese oxide as a positive electrode material has not yet been put to practical use.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to provide a lithium ion secondary battery using spinel-type lithium manganese oxide as a positive electrode active material, which has a small capacity deterioration due to charge and discharge cycles.

[0004]

[Means for Solving the Problem] The means for solving the problem is as a main active material of a positive electrode, which is represented by the general formula: Li [Mn _2−X Li _X ] O ₄ (where 0.020 ≦ x
The spinel-based lithium manganese oxide represented by ≦ 0.081) is used.

[0005]

In a battery using lithium manganese oxide (LiMn ₂ O ₄ ) as a positive electrode active material, an ideal positive electrode charging reaction is represented by the following equation. LiMn ₂ O ₄ → Li _1-X Mn ₂ O ₄ + XLi ⁺ + Xe ⁻ → Mn ₂ O ₄ (λ-MnO ₂ ) + Li ⁺ + e ⁻ (1) That is, LiMn ₂ O ₄ is a crystal. The lithium ion therein is extracted, and the oxidation valence of manganese in the crystal is changed from 3.5 to 4.0. Therefore, the theoretical capacity of LiMn ₂ O ₄ is 148 mAh / g. However, the actual battery has a capacity of about 139 mAh / g. The difference between this theoretical value and the actual capacity is considered as follows. In order for the above formula (1) to proceed as an electrochemical oxidation reaction, it is necessary that Li _1-X Mn ₂ O _{4 during} oxidation has electronic conductivity and ionic conductivity. However, when the reaction proceeds and the amount of lithium ions in the crystal decreases, the ionic conductivity brought about by the movement of lithium ions in the crystal is greatly impaired. Therefore, since the charging time is limited in an actual battery, it is considered that the electrochemical oxidation reaction reaches the limit when X≈0.94 in the above formula (1). Therefore, in a battery using LiMn ₂ O ₄ as the positive electrode active material, Li _0.06 Mn ₂ O ₄ can be used even with a sufficiently charged positive electrode active material.
it is conceivable that. That is, the fully charged positive electrode active material is (Li _0.06 □ _0.94 ) _8a [Mn ₂ ] _16d O ₄
It is considered that the spinel structure represented by the above is conversely considered, and conversely, in order for the spinel-type lithium manganese oxide to be electrochemically oxidized, it is necessary that 0.06 or more of the lithium ions located at the 8a site remain. On the other hand, Li _0.06 Mn
₂ O ₄ is Li _0.06 Mn ⁴⁺ _1.94 Mn ³⁺
_{It is 0.06} O ₄ , Mn ³⁺ still exists in the crystal, the next reaction gradually progresses, and Mn ²⁺ is dissolved in the electrolytic solution, so that the crystal structure gradually changes. 2Mn ³⁺ (solid) → Mn ⁴⁺ (solid) + Mn ²⁺ (solution) (2) As a result of a gradual change in the crystal structure of the positive electrode active material, the charge / discharge function is gradually lost. This is considered to be the mechanism of capacity deterioration with cycles of a lithium ion secondary battery using LiMn ₂ O ₄ as a positive electrode material. Therefore, the inventor of the present invention has come up with the idea of the present invention, considering that the following conditions are ideal for the active material in a charged state. Condition 1. 0.06 or more of lithium ions located at the 8a site in the spinel crystal structure remain. (To maintain good ionic conduction of the active material) Condition 2. The absence of Mn ³⁺ . (To suppress crystal structure change) As described above, in the lithium manganese oxide LiMn ₂ O ₄ which has been conventionally studied as a positive electrode material, the above Condition 2 is used.
Is not satisfied. However, the general formula Li [Mn _2−X L
The present inventor has noticed that a series of spinel-type lithium manganese oxides represented by i _X ] O ₄ (0 ≦ X ≦ 0.33) meet the above conditions if the range of X is appropriately selected.
(Note that the conventional LiMn ₂ O ₄ is also a spinel-type lithium manganese oxide represented by the general formula, where X = 0.) That is, the general formula Li [Mn _{2 −X} Li _X ] O ₄ (0 ≦ X ≤
When charged, the spinel-type lithium manganese oxide represented by the formula (0.33) produces Li as shown in the following formula (3).
_3X [Mn _2−X Li _X ] O ₄ is obtained, and 3X remains in the lithium ion located at the 8a site. Therefore, the spinel type lithium manganese oxide represented by the general formula Li [Mn _2−X Li _X ] O ₄ is set to 0.02 ≦ X,
At least 0.06 or more of lithium ions located at the a site will remain, so that the above condition 1 is satisfied. Also Li
_{3X [Mn 2-X Li X} ] all manganese in the crystal at the time when the _{O 4} is ^{Mn 4+, Mn 3+} is the condition 2 is also satisfied because there. However, as shown in the formula (4), the lithium ion (1-3X) desorbed from the active material is the charge capacity of the active material, and naturally the battery capacity itself becomes small when the composition of X is too large. Therefore, 0.020 ≦ x ≦ 0.081
Is preferred. Based on the above idea, the general formula Li [Mn
As a result of extensive studies on a method for producing a spinel-based lithium manganese oxide represented by _2-X Li _X ] O ₄ ,
Li [Mn _2−X Li _X ] O ₄ (however, 0.020 ≦ x
≦ 0.081) is 2θ of the X-ray diffraction angle (Fe-Kα).
= 0.33 °, the half value width of the diffraction peak on the 110 plane is β-type MnO ₂ in which the crystal has developed to a value of 2.0 ° or less, and a lithium compound is used in an atomic ratio of lithium to manganese of 0.515 ≦ L.
i / Mn ≦ 0.563 is mixed, and the heat treatment temperature (T) is 4
The present invention has been completed by finding that it can be manufactured by heat treatment at 50 ° C. ≦ T ≦ 850 ° C. If LiMn ₂ O ₄ has been studied as a conventional positive electrode material, a lithium compound is added to manganese oxide as Li / Mn =
It can be manufactured by mixing at 0.5 and heat treating in air at 600 to 900 ° C. However, in this method, even if the lithium mixing ratio is increased and synthesis is attempted with Li / Mn> 0.5, Li ₂ MnO ₃ is generated as an impurity, and Li [Mn
_2-X Li _X ] O ₄ (however, 0.020 ≦ x ≦ 0.08
It is difficult to synthesize 1).

[0006]

EXAMPLES Hereinafter, examples in which the present invention is applied to a coin type non-aqueous electrolyte secondary battery using a graphite carbon material as a negative electrode active material will be described with reference to the drawings.

Example 1 A coin type non-aqueous electrolyte secondary battery shown in FIG. 1 was prepared as follows. First, Li [Mn _{2-X used as the} positive electrode active material
A β-type MnO ₂ sample was prepared as a starting material for synthesizing Li _X ] O ₄ (0 ≦ X ≦ 0.12) as follows. 3 mol / l of the same concentration of MnSO ₄ and (NH ₄ ) ₂
CO ₃ was parallel charged into the reaction vessel at a dropping rate of 150 cc / h, kept at a reaction temperature of 5 ° C. or lower, and reacted for 6 hours to synthesize MnCO ₃ having an average particle diameter of 0.008 mm. Next, the MnCO ₃ was heat-treated at 600 ° C. for 20 hours to form Mn ₂ O _3, and the amount of Mn ₂ O ₃ was 0.6 g / g.
The operation of adding 13N-HNO ₃ at a ratio of cc and thermally decomposing at 280 ° C. was repeated 3 times to obtain a β-type MnO ₂ sample (A) having extremely fine particles of about 0.001 mm. This β-type MnO ₂ sample (A) shows a typical β-type MnO 2 diffraction pattern as shown in FIG. 2 as an X-ray diffraction result, and appears at 2θ = 36.3 ° (Fe-Kα). 11
The half-value width of the diffraction peak on the 0-face is about 1.5 °, and the crystallinity is high.

Li [Mn _2−X Li _X ] O ₄ (0 ≦ X ≦
Synthesis of 0.12). According to Table 1, X is varied in 10 steps in the range of X = 0 to 0.12, the above β-MnO ₂ sample (A) is mixed with lithium carbonate (Li ₂ CO ₃ ), and the mixture is placed in a porcelain container to be electrically charged. It was placed in a furnace, heated to 450 ° C., and kept at this temperature for 12 hours for heat treatment. Thereafter, a final heat treatment was performed by further holding the temperature at 450 to 850 ° C. for 12 hours. As a result of preliminary experiments, the proper temperature for the final heat treatment differs depending on the X value, and the proper temperature at which unreacted β-MnO ₂ , Mn ₂ O _3, etc. are not mixed as impurities was determined in advance. In X-ray diffraction, the diffraction peaks appearing on the wide-angle side of the 10 kinds of products (X value 0 to 0.12) after the heat treatment shift to the very wide-angle side as the X increases, but they are all cubic crystals. This was in agreement with the diffraction pattern of spinel type LiMn ₂ O ₄ , and the presence of other impurities was not seen. In addition to chemical analysis, each product has the composition shown in Table 1,
Cubic spinel type Li [Mn _2−X Li _X ] O ₄ (0 ≦
It was confirmed that X ≦ 0.12) was satisfied.

10 kinds of reaction products having different X values [Li
_{1 + X} Mn _2-X O ₄ ], 88 parts by weight of each of them was added with 3 parts by weight of acetylene black and 6 parts by weight of graphite and mixed well, and further 3 parts by weight of polyvinylidene fluoride as a binder and N- which was a solvent. Methyl-2-pyrrolidone was added and wet mixed to obtain a positive electrode mixture paste.
This positive electrode material mixture paste was uniformly applied to one side of an aluminum foil having a thickness of 0.02 mm, dried, and then pressure-molded with a roller press machine to form a sheet, and 10 kinds of [Li _{1 + X} Mn _{2 having} different X values were used. 10 to the _-X O _4] as a positive electrode active material
A variety of sheet electrodes were obtained. A disk-shaped positive electrode (2) with a diameter of 17.6 mm for coin-type batteries was punched out from each of 10 types of sheet-shaped electrodes, and the temperature was 100 ° C for 12 hours in a vacuum dryer. Dried.

The negative electrode was prepared as follows. 28
86 parts by weight of mesocarbon microbeads (d002 = 3.37Å) heat-treated at 00 ° C., 4 parts by weight of carbon black and polyvinylidene fluoride (P
VDF) 10 parts by weight is added, and the solvent is N-methyl-2.
Wet mixed with pyrrolidone to form a slurry (paste). Then, this negative electrode mixture slurry is made to have a thickness of 0.02 mm.
Was uniformly applied to one surface of the copper foil, dried and pressure-molded with a roller press machine to obtain a sheet-shaped carbon electrode. This sheet-shaped carbon electrode was punched into a disc having a diameter of 18.5 mm to form a disc-shaped negative electrode (1) for a coin-type battery,
It was dried in a vacuum dryer at a temperature of 100 ° C. for 12 hours.

Next, as shown in FIG. 1, an aluminum foil (10) is laid on the bottom of the battery can (4) and a gasket (6) is provided.
The prepared negative electrode (1) and positive electrode (2) were placed in the center of the battery can (4) with the active material layers facing each other with the porous polypropylene separator (3) interposed therebetween. , 1 mol / l L as electrolyte in the battery can
A mixed solution of ethylene carbonate (EC) in which iPF ₆ was dissolved and diethyl carbonate (DEC) was injected.
After that, the electrode pressing plate (7) was installed, the battery lid (5) was overlaid, and the battery can and the battery lid were caulked with a gasket to seal and seal the battery. The batteries prepared in this manner are 10 types of batteries (A) to (J), which differ only in the positive electrode active material.

Test Results The batteries thus prepared in Example 1 were (A) to
(J) shows a charging voltage of 4.2 V after an aging period of 12 hours has passed for the purpose of stabilizing the inside of the battery.
Set to, and charge for 8 hours in each case, and discharge all batteries with a constant current of 2 mA and a final voltage of 3.0 V.
Then, the initial capacity of each battery was obtained. The results are shown in Table 2. Then, each battery was subjected to a charge / discharge cycle test in an atmosphere of 40 ° C. Charging current is 2mA
Then, the charge upper limit voltage is set to 4.2V and charging is performed for 4 hours, and the discharge is a constant current discharge of 2mA, and the final voltage is 3.0V.
And repeated charging and discharging. The capacity of each battery after 100 cycles and 200 cycles is also shown in Table 2.

As shown in Table 2, the initial capacity of each battery depends on the positive electrode active material, and the positive electrode active material Li _{1 + X} Mn
_A battery having a small X value in _2-X O ₄ exhibits a large capacity. However, when charge and discharge are repeated at 40 ° C., the capacity deterioration is large in the positive electrode active material having a small X value. After 200 cycles, the battery (A) with X = 0, which is equivalent to the conventional battery, has half the initial capacity. On the other hand, in the batteries of 0.20 ≦ X, the capacity after 200 cycles was 85% of the initial capacity in all cases.
The above is maintained. However, when the X value is too large, the initial capacity is small, and therefore even if the capacity after 200 cycles, the absolute value does not significantly exceed, and X ≦ 0.81 is substantially effective. After all, a carbonaceous material capable of intercalating lithium is used as the negative electrode active material, and the general formula Li [Mn _2−X Li _X ] O is used as the positive electrode active material.
₄ is used, and 0.20 ≦ X ≦ 0.81 is more preferable, and 0.20 ≦ X ≦ 0.65 is more preferable. Even when used as the positive electrode active material, the lithium ion secondary battery has less capacity deterioration due to charge / discharge cycles.

The spinel-based lithium manganese oxide represented by the general formula Li _{1 + X} Mn _{2 -X} O ₄ is theoretically 0
It exists in the range of ≦ X ≦ 1/3. In the example, the positive electrode active material was 0 ≦ x ≦ 0.12. In the battery (C) of the example, the active material in the positive electrode is charged as follows. Charged active material (Li _0.06 □ _0.94 ) _8a [Mn
_{In 1.98} Li _0.02 ] _16d O ₄ , the oxidation valence of Mn is 4, and Mn is no longer oxidized. Therefore, 0.06 of the lithium ion located at the 8a site remains, but the detachment of the lithium ion out of the crystal can occur only in parallel with the increase of the Mn atom in the crystal to a high oxidation valence. No longer goes out of the crystal. Therefore, for 0.02 ≦ X,
5.9 of lithium that was initially present even when charging was completed
% Of lithium ions will remain at the 8a site, the ionic conductivity brought about by the migration of lithium ions in the active material crystal will be well maintained, and all active materials will be effectively charged and discharged. As in the results of the examples, it is considered that the battery has less capacity deterioration due to cycles.

In the secondary battery using the lithium-containing manganese oxide as the positive electrode active material, the charge / discharge reaction of the positive electrode active material causes the lithium ions to enter / exit the active material and increase the valence of Mn atoms in the active material. / Since the descent can occur in parallel, no matter what lithium-containing manganese oxide is used as the active material, the amount of lithium in the active material + [average valence of Mn x amount of manganese in the active material] regardless of the state of charge and discharge. ] = It is constant. Therefore, when the atomic ratio (Li / Mn) of manganese and lithium in the active material composition is a and the average oxidation valence of manganese is m, a + m = c (constant) regardless of the charge / discharge state. The positive electrode active material in the present invention is Li [Mn
_2-X Li _X ] O ₄ (0.020 ≦ x ≦ 0.081) is a spinel-based lithium manganese oxide, and 4.04 ≦ a + m ≦ 4.17. Therefore, even when m = 4, 0 <a and lithium ions are present in the active material.
However, in the case of conventional LiMn ₂ O ₄ , a + m = 4, and in Li _{1 + X} Mn ₂ O ₄ , m = [8− (1+
X)] / 2 and a = (1 + X) / 2, so a + m =
4, which is fundamentally different from the active material material of the present invention in that a = 0 when m = 4 and lithium ions do not exist in the active material.

[0016] The heat treatment of the MnCO ₃ in the embodiment of the present invention the _Mn 2 _{O 3,} further its _Mn 2 _{O 3} in the β-type was synthesized by thermally decomposing in addition to 280 ° C. The HNO ₃ Mn
O ₂ is replaced by Li [Mn _2−X Li _X ] O ₄ (0.020 ≦ x
≦ 0.081) as a synthetic starting material, but a commercially available β-type M
nO ₂ and other methods (eg Mn (NO ₃ ) ₂ at 150 ° C.)
Even if β-type MnO ₂ synthesized by thermal decomposition) was used as a starting material, the same results as those in the above-described examples were obtained. However, which β type M
Also in the nO ₂ sample, 2θ = 36.3 ° (Fe-K
The full width at half maximum of the diffraction peak on the 110 plane appearing in α) is 2.0 °.
The crystals were well developed below. However, γ-type Mn
Β-type similar MnO obtained by heat treatment of O ₂ at 450 ° C.
_{In two} samples, 2θ = 36.3 ° (Fe-K by X-ray diffraction
The half width of the peak appearing in α) is about 2.3 ° and the crystallinity is low. When this is used as a starting material, Li ₂ MnO ₃ is generated as an impurity, and Li [MnO _3
2-X Li _X ] O ₄ (0.020 ≦ x ≦ 0.081) could not be synthesized. Therefore, Li [Mn _2−X L
i _X ] O ₄ (however, 0.020 ≦ x ≦ 0.081) in the production of the spinel-based lithium manganese oxide,
It appears at 2θ = 36.3 ° (Fe-Kα) by X-ray diffraction 1
The starting material was β-type MnO ₂ having a crystal with a half-value width of the diffraction peak on the 10 plane of 2.0 ° or less, and a lithium compound was added to this as an atomic ratio of lithium and manganese of 0.515 ≦ Li.
One effective manufacturing method is to heat-treat and synthesize a mixture mixed with /Mn≦0.563.

[0017]

As described above, when the spinel type lithium manganese oxide represented by the general formula Li [Mn _2−X Li _X ] O ₄ is used as the positive electrode active material, the positive electrode active material is charged. and _{Li 3X [Mn 2-X Li} X] O 4 , and the
At that point all the manganese in the crystals was Mn ⁴⁺ ,
Since Mn ³⁺ does not exist in the product, 2Mn ³⁺ (individual) → Mn ⁴⁺ (individual) + Mn
The crystal structure of the positive electrode active material does not change due to the reaction of ²⁺ (solution). Furthermore, even when all the manganese in the active material becomes Mn ⁴⁺ , 3X remains in the lithium ions located at the 8a site. Therefore, if the X value is selected in the range of 0.020 ≦ x ≦ 0.081, it becomes the 8a site. Lithium ion located is 0.0
6 or more will remain, the ionic conductivity brought about by the movement of lithium ions in the active material crystal will be well maintained, and all the active materials will be effectively charged and discharged, so that the battery will have less capacity deterioration with cycling. Becomes As a result, lithium manganese oxide, which is an inexpensive material, can be used as a positive electrode material, and a high-performance, safe, inexpensive lithium-ion secondary battery can be supplied to a wide range of applications, and its industrial value is great. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a coin-type battery in an example.

FIG. 2 X-ray diffraction of β-MnO ₂

[Explanation of symbols]

1 is a negative electrode, 2 is a positive electrode, 3 is a separator, 4 is a battery can, 5
Is a battery lid, 6 is a gasket, 7 is an electrode pressing plate, 8 is a negative electrode current collector, 9 is a positive electrode current collector, and 10 is an aluminum foil.

Claims (2)

[Claims] 1. A negative electrode active material is a material capable of intercalating lithium, and a positive electrode active material is a lithium-containing metal oxide capable of deintercalating lithium. In a non-aqueous electrolyte secondary battery that produces a normal battery voltage for the first time, the lithium-containing metal oxide has the general formula Li [Mn _2−X Li _X ] O ₄ (where 0.020 ≦ x
≦ 0.081) which is a spinel-based lithium manganese oxide,
In the composition, the lithium manganese oxide in the positive electrode satisfies 4.04 ≦ a + m ≦ 4.17, where a is the atomic ratio of manganese to lithium (Li / Mn) and m is the average oxidation valence of manganese. A non-aqueous electrolyte secondary battery characterized in that 2. An X-ray diffraction angle (Fe) in the production of spinel-based lithium manganese oxide represented by the general formula Li [Mn _2−X Li _X ] O ₄ (where 0.020 ≦ x ≦ 0.081). -Kα) 2θ = 36.3 °, the half-value width of the diffraction peak on the 110 plane is 2.0 ° or less, and β-type MnO ₂ having a developed product has a lithium compound in an atomic ratio of lithium to manganese of 0.515. A method for producing a spinel-based lithium manganese oxide, which comprises synthesizing a mixture obtained by mixing ≦ Li / Mn ≦ 0.563 at a temperature of 450 ° C. or higher.