JPH10302766A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase initial charging and discharging capacity and improve the cycle characteristic of service capacity by forming a lithium secondary battery so that a negative electrode contains a material capable of storing and releasing lithium ions as an active material, a positive electrode contains lithium-manganese composite oxide as an active material and a water electrolyte is contained. SOLUTION: A lithium secondary battery is formed so that a negative electrode contains a material capable of storing and releasing lithium ions as an active material, a positive electrode contains the lithium-manganese composite oxide expressed by the formula of Li2 Mn2-x Mx O4 as an active material, and further an water electrolyte is contained. In the formula, M stands for metal selected from Fe, Co and Ni, and (x) for a value in the range of 0.05<=(x)<=0.2. In this case, each component is mixed to obtain the composition as per the formula, and thermally treated at temperature between 700 deg.C and 850 deg.C in atmospheric environment. Then, a generated compound having 10 times or more of a mole ratio is added to LiI and dissolved with acetonitrile. Then, heating and reflux processes are applied to manufacture the lithium secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery having an improved positive electrode active material.

[0002]

2. Description of the Related Art A lithium ion secondary battery including a positive electrode containing a lithium manganese composite oxide as a positive electrode active material and a negative electrode containing a substance that absorbs and releases lithium such as a carbonaceous material is mainly used for cordless phones and personal computers. It is used as a power supply.

Meanwhile, the lithium manganese composite oxide has a spinel structure because of its electrochemical characteristics.
Mn ₂ O ₄ , LiMnO ₂ having a layered structure, and Li ₂ Mn ₂ O ₄ having a rock salt structure are roughly classified into three types. Among them, Li ₂ Mn ₂ O ₄ has a very high theoretical discharge capacity of 285.5 mAh / g, and is expected to be applied as a positive electrode active material of a lithium ion secondary battery.

[0004] Such Li ₂ Mn ₂ O ₄ has been conventionally synthesized by the following method. (1) LiMn ₂ O ₄ having a spinel structure and lithium iodide (LiI) in acetonitrile at 80 to 90 ° C.
And heat to reflux to synthesize Li ₂ Mn ₂ O ₄ .

(2) LiMn ₂ O having a spinel structure
₄ and lithium iodide (LiI) are housed in a vacuum-sealed reaction vessel, and the reaction vessel is kept at about 150 ° C. for 2 to 2 hours.
Li ₂ Mn ₂ O ₄ is synthesized by heating for 3 hours.

Li ₂ M synthesized by the lithium iodide method
When a lithium ion secondary battery having a positive electrode containing n ₂ O ₄ powder as a positive electrode active material is charged and discharged in a voltage range of 2.7 to 4.3 V, the initial charge and discharge capacity is large, but the charge and discharge are large. Occlusion and release of lithium during the process (intercalation
Deintercalation) causes a problem in that the crystal phase rearrangement of the substance causes a significant deterioration in capacity with respect to the cycle.

[0007] Also, Thackeray et al.
receiveds of 11th Internationala
tional semiminer on Primary
and Secondary Battery Te
ch. and Appl. , Feb. 28-Ma
r. 4 (1994). Deerfied Beach
(Florida), "Spinel Electr
odes for Rechargeable Lit
H Batteris-A Review “F
IG. In 3, Li ₂ Mn ₂ O ₄ is 4.45 to 2.
It is reported that when charging / discharging is performed between 0 V, the capacity is significantly deteriorated, and the charge / discharge at the 10th cycle is reduced to about half of the initial capacity.

On the other hand, K. Amine et al. .
J. Electrochem. Soc. , 143 16
07 (1996) discloses lithium in which part of the manganese site of Li ₂ Mn ₂ O ₄ has been replaced by nickel as a starting material when reducing a manganese oxide such as LiMn ₂ O _{4 with} lithium iodide in acetonitrile. It is disclosed that Li ₂ Mn _1.5 Ni _0.5 O ₄ was successfully synthesized using a manganese oxide. This substance has a cubic system, and the discharge potential of a unipolar cell having lithium metal as a counter electrode is 3%.
It describes that V exhibits potential flatness.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion secondary battery having a large initial charge / discharge capacity and improved cycle characteristics of the discharge capacity.

[0010]

A lithium ion secondary battery according to the present invention comprises a negative electrode containing a material capable of occluding and releasing lithium ions as an active material, and a general formula Li ₂ Mn.
_{As an} active material, a lithium manganese-based composite oxide represented by _2-x M _x O ₄ (where M is a metal selected from Fe, Co and Ni, and x represents 0.05 ≦ x ≦ 0.2) It is characterized by comprising a positive electrode and a non-aqueous electrolyte.

The lithium-manganese-based composite oxide includes, for example, a lithium salt, a manganese compound, and a compound of a metal selected from Fe, Co, and Ni which is converted into an oxide during the reaction. Is 1: 2-x: x in element ratio (where x is 0.05 ≦ x ≦
0.2 and a heat treatment of the mixture at 700 to 850 ° C. in the air atmosphere to obtain LiMn _2-x M _x O ₄ (where M is Fe, Co
And a metal selected from Ni and x is 0.05 ≦ x ≦ 0.
2) and a molar ratio (LiMn) of the compound to lithium iodide (LiI).
_2-x M _x O ₄ / LiI) is produced by dissolving with acetonitrile so as to be 10 or more and heating and refluxing.

In the secondary battery, (a) the initial charge is started from an open circuit voltage, the battery is charged to a voltage having a positive electrode voltage of 4.7 V or less based on lithium metal, and (b) the initial discharge is performed using lithium metal. (C) The second and subsequent charging / discharging is performed while the positive electrode voltage based on lithium metal is between 3.0 and 4.7 V.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lithium ion secondary battery according to the present invention will be described in detail with reference to FIG. For example, a positive electrode 2 is housed in a positive electrode can 1 made of stainless steel. The separator 3 is disposed on the positive electrode 2.
The separator 3 is impregnated with a non-aqueous electrolyte in which an electrolyte is dissolved in an organic solvent. The negative electrode 4 is disposed on the separator 3. At the opening of the positive electrode can 1, a negative electrode can 6 is provided via an insulating gasket 5. By caulking the negative electrode can 6 and the positive electrode can 1, the negative electrode can 6 is inserted into the positive electrode can 1 and the negative electrode can 6. The positive electrode 2, the separator 3, and the negative electrode 4 are sealed.

Next, the positive electrode 2, the negative electrode 4, the separator 3, and the non-aqueous electrolyte will be described in detail. (1) Positive electrode 2 This positive electrode 2 is made of a general formula Li ₂ Mn _2-x M _x O ₄ (where M is a metal selected from Fe, Co and Ni, and x represents 0.05 ≦ x ≦ 0.2) ) Is produced by pressure-forming a mixture containing a positive electrode active material composed of a lithium manganese-based composite oxide represented by the following formula, a conductive additive such as graphite, and a binder such as polytetrafluoroethylene. .

Fe, Co and N represented by M in the above general formula
Among i, Fe is particularly preferable because it easily synthesizes the lithium manganese-based composite oxide represented by the general formula. The reason for defining x in the above general formula is as follows. If x is less than 0.05, it becomes difficult to improve the charge / discharge cycle with respect to capacity in a lithium ion secondary battery provided with a positive electrode containing a lithium-manganese composite oxide. On the other hand, if x exceeds 0.2, phase separation occurs in the solid-phase reaction during synthesis, so that not only cannot a lithium-manganese composite oxide having the desired composition be obtained, but also a lithium-manganese composite oxide is contained. The initial capacity of a lithium ion secondary battery having a positive electrode decreases. More preferably, x is 0.1 ≦ x ≦ 0.2.

The lithium manganese composite oxide is produced, for example, by the following method. First, a lithium salt such as lithium carbonate or lithium hydroxide, a manganese compound such as electrolytic manganese dioxide, and a compound of a metal selected from Fe, Co, and Ni which are converted into an oxide during the reaction are converted into a lithium salt: manganese. Compound: metal compound in an element ratio of 1: 2-x: x (where x is 0.05 ≦ x)
≤ 0.2). Subsequently, the mixture is subjected to a heat treatment at 700 to 850 ° C. in an air atmosphere to obtain LiMn _2-x M _x O ₄ (where M is F
e, a metal selected from Co and Ni, x is 0.05 ≦
(indicating x ≦ 0.2). Then, the compound was dissolved in acetonitrile so that the molar ratio of lithium iodide _{(LiI) (LiI / LiMn 2} -x M x O 4) is 10 or more, Li ₂ Mn _2-x M by heating to reflux producing lithium manganese composite oxide represented by _x O _4.

The metal compound selected from the group consisting of Fe, Co and Ni includes, for example, oxides, carbonates and hydroxides. The reason for defining the molar ratio (LiMn _2-x M _x O ₄ / LiI) between the compound represented by LiMn _2-x M _x O ₄ and lithium iodide (LiI) is as follows:
If the value is less than 10, the general formula Li ₂ Mn _2-x M _x
It becomes difficult to produce a lithium manganese-based composite oxide represented by O ₄ .

It is preferable that the mixing ratio of the positive electrode active material, the conductive additive, and the binder is 90: 7: 3 to 100: 10: 1. (2) Negative Electrode 4 The negative electrode 4 is produced by pressure-forming a mixture comprising a carbonaceous material, a conductive agent and a binder.

As the carbonaceous material, for example, artificial graphite, natural graphite, pyrolytic carbon, coke, resin fired body, mesophase sphere, mesophase pitch and the like can be used.

As the conductive material, for example, acetylene black, carbon black or the like can be used. Examples of the binder include styrene-butadiene latex (SBR), carboxymethyl cellulose (CM)
C), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDE), ethylene-propylene-diene copolymer (EPDM), nitrile-butadiene rubber (NBR), vinylidene fluoride-hexafluoropropylene copolymer, fluorine Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer,
Polytrifluoroethylene (PTrFE), vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, or the like can be used.

(3) Separator 3 The separator 3 is made of, for example, a polypropylene nonwoven fabric, a microporous polyethylene film, or the like.

(4) Non-aqueous electrolyte This non-aqueous electrolyte has a composition in which an electrolyte is dissolved in a non-aqueous solvent. Examples of the electrolyte include lithium borofluoride (LiBF ₄ ) and lithium hexafluorophosphate (LiPF
₆ ), one or two selected from lithium perchlorate (LiClO ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and lithium aluminum chloride (LiAlCl)
More than one lithium salt can be mentioned.

Examples of the nonaqueous solvent include ethylene carbonate, 2-methyltetrahydrofuran, 1,2
1 selected from dimethoxyethane, diethoxyethane, 1,3-dioxolan, and 1,3-dimethoxypropane
Species or mixtures of two or more can be mentioned.

The amount of the electrolyte dissolved in the non-aqueous solvent is as follows:
It is desirably 0.5 to 1.5 mol / l. The lithium ion secondary battery according to the present invention has the following (a)
It is preferable to perform charging and discharging in the modes shown in FIGS.

(A) The initial charge is started from the open circuit voltage, and is charged to a voltage having a positive electrode voltage of 4.7 V or less based on lithium metal. (B) The first discharge is performed while the positive electrode voltage based on lithium metal becomes a voltage of 3.0 V or more.

(C) The second and subsequent charging / discharging is performed while the positive electrode voltage is 3.0 to 4.7 V based on lithium metal. The charging / discharging conditions (a) to (c) are defined for the following reasons.

If the voltage at the first discharge in (a) exceeds 4.7 V, the non-aqueous electrolyte may be decomposed. A more preferable voltage at the initial discharge is 4.3 to 4.7 V. If the voltage at the initial charge in (b) is less than 3.0 V, the lithium manganese-based composite oxide represented by the general formula, which is the positive electrode active material, may undergo a phase change and the charge / discharge cycle characteristics may be deteriorated. is there. More preferably, the voltage at the first charge is 2.7 to
2.9V.

When the voltage in the second and subsequent charging / discharging of (c) is less than 3.0 V, the phase in which the crystal structure of the lithium manganese-based composite oxide represented by the general formula as the positive electrode active material changes is changed. Since the rearrangement is repeated, the charge / discharge cycle characteristics may be degraded. On the other hand, when the charge / discharge voltage exceeds 4.7 V, the electrolyte may be decomposed.

According to the present invention described above, the positive electrode has the general formula Li ₂ Mn _2-x M _x O ₄ (where M is a metal selected from Fe, Co and Ni, and x is 0.05 ≦ x ≦ 0) .2
Since the active material comprises a lithium-manganese-based composite oxide represented by the formula (1), a lithium ion secondary battery having a high initial capacity and a long charge-discharge cycle life can be obtained.

In particular, a lithium-ion secondary battery having a longer charge / discharge cycle life can be realized by using a lithium-manganese-based composite oxide in which M in the above general formula is Fe as the positive electrode active material.

By performing charging / discharging in the above-described modes (a) to (c), the charge / discharge cycle life of the lithium ion secondary battery can be further extended.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. (Example 1) <Production of lithium manganese composite oxide> First, lithium carbonate (Li ₂ CO ₃ ) and electrolytic manganese dioxide (MnO ₂ )
₂ ) and tetrairon trioxide were weighed so that the molar ratio of lithium, manganese and iron was 1: 1.95: 0.05, and uniformly mixed by a dry method to prepare a mixed powder. Then,
This mixed powder was heated at 800 ° C. for 24 hours in an air atmosphere. Subsequently, after cooling to room temperature, the mixture was again uniformly mixed by a dry method. This powder was again kept in the air atmosphere at 800 ° C. for 48 hours. After this, 10 ° C / h
Cooled at a rate of r.

The obtained powder was measured by XDR. As a result, the diffraction peak was indexed by a spinel having a cubic crystal structure, and its lattice constant was 0.825 nm.
The powder had a composition formula of LiMn _1.95 Fe _0.05 O ₄ .

Next, the LiM having the spinel structure
n _1.95 Fe _0.05 O ₄ powder and lithium iodide (LiI) powder have a molar ratio of LiI / LiMn _1.95 Fe _0.05 O ₄ of 1
The resulting solution was dissolved in acetonitrile so as to obtain a solution No. 2 and refluxed for 6 hours. The reaction temperature was 82 ° C, and the reaction was stirred using a stirrer. After completion of the reaction, the reaction solution was filtered, and the obtained powder was washed with acetonitrile and dried.

The obtained powder was measured by XDR. As a result, the diffraction peak is indexed by the tetragonal crystal structure, and its lattice constant is 0.557 nm for the a-axis and 0.885 nm for the c-axis.
nm. The powder has a composition formula of Li ₂ Mn.
_1.95 Fe _0.05 O ₄ .

Next, the obtained synthetic powder (Li ₂ Mn)
_1.95 Fe _0.05 O ₄ ), acetylene black as a conductive material, and polytetrafluoroethylene as a binder are uniformly mixed at a weight ratio of 80: 17: 3, and this mixture is rolled by a roller. To produce a positive electrode sheet.
Subsequently, the positive electrode sheet was rolled into a stainless steel net to prepare a positive electrode.

Next, FIG. 2 and FIG.
A test cell having the structure shown in FIG. 2 and 3, a positive electrode 11 and a negative electrode 12 in which a lithium metal foil is pressure-bonded to a nickel mesh body are opposed to each other with a glassy separator 13 interposed therebetween. On the side of the positive electrode 11 opposite to the separator 13, a reference electrode 14 in which a lithium metal foil is pressure-bonded to a stainless steel mesh body is disposed in close proximity.
The negative electrode 12, the separator 13, and the reference electrode 14 are sandwiched between two polypropylene insulating plates 15a and 15b. The polypropylene insulating plates 15a and 15b sandwiching each of the battery elements are immersed in a glass container 17 containing an electrolytic solution 16. In addition, lead wires 18-2
0 has one end connected to the positive electrode 11, the negative electrode 12, and the reference electrode 14, and the other end extending outside the container 17. As the electrolytic solution 16, a solution prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (mixing volume ratio 1: 2) at 1.0 mol / l was used.

Example 2 First, lithium carbonate (Li ₂
CO ₃ ), electrolytic manganese dioxide (MnO ₂ ), and tetrairon trioxide at a molar ratio of lithium, manganese, and iron of 1: 1.9:
The mixture was weighed so as to be 0.1 and uniformly mixed by a dry method to prepare a mixed powder. Subsequently, the mixed powder was subjected to heat treatment in the air atmosphere, mixing by a dry method, heat treatment in the air atmosphere, and cooling in the same manner as in Example 1. Further, the obtained powder was mixed with lithium iodide (LiI). The powder was dissolved in acetonitrile, refluxed, and the resulting reaction solution was filtered,
By drying, a predetermined powder was produced. In the obtained powder, the diffraction peak is indexed by a tetragonal crystal structure as measured by XDR, and its composition formula is Li ₂ Mn _1.90 Fe.
_0.1 O ₄ .

Next, the obtained synthetic powder (Li ₂ Mn)
_1.90 Fe _0.1 O ₄ ), acetylene black as a conductive material, and polytetrafluoroethylene as a binder are uniformly mixed at a weight ratio of 80: 17: 3, and this mixture is rolled by a roller. To produce a positive electrode sheet.
Subsequently, the positive electrode sheet was rolled into a stainless steel net to prepare a positive electrode. FIG. 2 described above using the obtained positive electrode.
Then, a test cell having the structure shown in FIG. 3 was assembled.

Comparative Example 1 First, lithium carbonate (Li ₂
CO ₃ ) and electrolytic manganese dioxide (MnO ₂ ) were weighed so that the molar ratio of lithium, manganese and iron was 1: 2, and uniformly mixed by a dry method to prepare a mixed powder. Subsequently, this mixed powder was placed in an air atmosphere at 800 ° C. for 24 hours.
Heated for hours. After cooling to room temperature,
Again, they were uniformly mixed by a dry method. This powder was again kept in the air atmosphere at 800 ° C. for 48 hours. After this, 10
Cooled at a rate of ° C / hr.

The obtained powder was measured by XDR. As a result, the diffraction peak was indexed by a spinel having a cubic crystal structure, and its lattice constant was 0.825 nm.
The powder had a composition formula of LiMn ₂ O ₄ .

Next, the LiM having the spinel structure
The n ₂ O ₄ powder and lithium iodide (LiI) powder were dissolved in acetonitrile so that the molar ratio of LiI / LiMn ₂ O ₄ became 12, and the mixture was refluxed for 6 hours. The reaction temperature was 82
In the reaction, the solution was stirred using a stirrer. After completion of the reaction, the reaction solution was filtered, and the obtained powder was washed with acetonitrile and dried.

The obtained powder was measured by XDR. As a result, the diffraction peak is indexed by the tetragonal crystal structure, and its lattice constant is 0.565 nm for the a-axis and 0.924 nm for the c-axis.
nm. The powder has a composition formula of Li ₂ Mn.
₂ O ₄ .

Next, the obtained synthetic powder (Li ₂ Mn ₂
O ₄ ), acetylene black as a conductive material, and polytetrafluoroethylene as a binder in a weight ratio of 8%.
The mixture was uniformly mixed at a ratio of 0: 17: 3, and this mixture was rolled by a roller to produce a positive electrode sheet. Subsequently, the positive electrode sheet was rolled into a stainless steel net to prepare a positive electrode. Using the obtained positive electrode, a test cell having the structure shown in FIGS. 2 and 3 was assembled.

Comparative Example 2 First, lithium carbonate (Li ₂
CO ₃ ), electrolytic manganese dioxide (MnO ₂ ), and tetrairon trioxide at a molar ratio of lithium, manganese, and iron of 1: 1.7.
5: 0.25 was weighed and uniformly mixed by a dry method to prepare a mixed powder. Subsequently, the mixed powder was subjected to heat treatment in the air atmosphere, mixing by a dry method, heat treatment in the air atmosphere, and cooling in the same manner as in Example 1.
Further, the obtained powder and lithium iodide (LiI) powder were dissolved in acetonitrile, refluxed, and the obtained reaction liquid was filtered and dried to produce a predetermined powder. In the obtained powder, the diffraction peak was indexed by a tetragonal crystal structure as measured by XDR, and its composition formula was Li ₂ Mn _1.75.
Fe _0.25 O ₄ .

Next, the obtained synthetic powder (Li ₂ Mn)
_1.75 Fe _0.25 O ₄ ), acetylene black as a conductive material, and polytetrafluoroethylene as a binder were uniformly mixed at a weight ratio of 80: 17: 3, and this mixture was rolled by a roller. To produce a positive electrode sheet.
Subsequently, the positive electrode sheet was rolled into a stainless steel net to prepare a positive electrode. FIG. 2 described above using the obtained positive electrode.
Then, a test cell having the structure shown in FIG. 3 was assembled.

The test cells of Examples 1 and 2 and Comparative Examples 1 and 2 were each initially charged from an open circuit voltage to 4.3 V at a current density of 0.5 mA / cm ² , and thereafter, charged at 3.0 to 4.0.
Charge / discharge was repeated 100 times under the condition of a current density of 0.5 mA / cm ² within a range of 3 VV. FIG. 4 shows the relationship between the number of cycles and the capacity in such charge and discharge.

As is apparent from FIG. 4, the general formula Li ₂ Mn
_{2-x Fe x O 4 (} x is 0.05 ≦ x ≦ 0.2) test cells of Examples 1 and 2 having a positive electrode including a lithium manganese-based composite oxide as the positive electrode active material, the composition formula Li ₂ Mn ₂
It has a higher charge / discharge cycle life than the test cell of Comparative Example 1 provided with a positive electrode containing a lithium manganese composite oxide of O ₄ as a positive electrode active material, and has a composition formula of Li ₂ Mn _1.75 Fe
_It can be seen that the battery has a higher discharge capacity than the test cell of Comparative Example 2 including the positive electrode including the lithium manganese composite oxide of _0.25 O ₄ as the positive electrode active material.

In the test cell of Comparative Example 1, the current density was 0.5 mA / cm in the range of 2.7 to 4.3 V from the beginning.
^Under the conditions of ² , charge and discharge were repeated 100 times. as a result,
Although the initial capacity shows a high value of 220 mAh / g, 3
At the 0th cycle, the capacity rapidly dropped to 60 mAh / g.

The lithium ion secondary battery according to the present invention is not limited to a mode in which a separator impregnated with a non-aqueous electrolyte is interposed between a positive electrode and a negative electrode. The same applies to a structure with an electrolyte.

[0051]

As described in detail above, according to the present invention, a lithium ion secondary battery having a large discharge capacity at the time of initial charging and a long charge / discharge cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a button-type lithium ion secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing test cells used in Examples and Comparative Examples.

FIG. 3 is a perspective view of a main part of the test cell of FIG. 2;

FIG. 4 is a diagram showing the relationship between the number of cycles and the capacity in the test cells of Examples 1 and 2 and Comparative Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode can, 2 ... Positive electrode, 4 ... Negative electrode, 6 ... Negative electrode can, 11 ... Positive electrode, 12 ... Negative electrode, 13 ... Separator, 14 ... Reference electrode, 16 ... Electrolyte, 17 ... Glass container.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C01G 51/00 C01G 51/00 A 53/00 53/00 A

Claims (3)

[Claims] 1. A negative electrode containing a material as an active material capable of inserting and extracting lithium ions, and a general formula Li ₂ Mn _2-x M _x O ₄ (where M is Fe, C
a metal selected from o and Ni, x is 0.05 ≦ x ≦
A lithium ion secondary battery comprising: a positive electrode containing a lithium-manganese-based composite oxide represented by 0.2 as an active material; and a non-aqueous electrolyte. 2. The lithium-manganese-based composite oxide includes: a lithium salt, a manganese compound, and a compound of a metal selected from Fe, Co, and Ni that is converted into an oxide during the reaction. The compound has an elemental ratio of 1: 2-x: x (where x is 0.05 ≦ x ≦ 0.2
And a heat treatment of the mixture at 700 to 850 ° C. in the air atmosphere to obtain LiMn _2-x M _x O ₄ (where M is F
e, a metal selected from Co and Ni, x is 0.05 ≦
x ≦ 0.2), and a molar ratio (Li) of the compound to lithium iodide (LiI).
_2. The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is manufactured by dissolving with acetonitrile so that I / LiMn _2-x M _x O ₄ ) becomes 10 or more and heating and refluxing. 3. (a) starting an initial charge from an open circuit voltage;
Charging until the positive electrode voltage based on lithium metal is 4.7 V or less; (b) performing the initial discharge while the positive electrode voltage based on lithium metal is 3.0 V or more; (c) The lithium ion secondary battery according to claim 1, wherein the second and subsequent charging / discharging is performed at a positive electrode voltage of 3.0 to 4.7 V based on lithium metal.