JP2001093528A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery with a good characteristics of charging discharging cycle. SOLUTION: The activating material of positive electrode is complex oxide of manganese including lithium expressed by the formula: Lia[Mn2-b-cFebMc]Od, where M in the formula represents at least one element selected from the group of elements consisted of Li, Mg, Cr and Co, meanwhile 0.02<=a<=2.00, 0.1<=b<=0.6, 0<=c<=0.4 and 3.9<=d<=4.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a positive electrode, a negative electrode containing a substance capable of electrochemically storing and releasing lithium ions or a lithium metal as an active material, and an electrolyte salt dissolved in a non-aqueous solvent. More specifically, the present invention relates to an improvement in a positive electrode active material for the purpose of improving the charge / discharge cycle characteristics of the lithium secondary battery.

[0002]

2. Description of the Related Art
As a positive electrode active material of a lithium secondary battery, LiCoO_Two
And LiNiO _TwoIs well known. But these
Are expensive, and there is a problem in terms of raw material cost.
is there.

Therefore, LiMn ₂ O ₄ having a spinel type crystal structure has been proposed as a positive electrode active material instead of them. LiMn ₂ O ₄ is relatively inexpensive because one of the raw materials, manganese, is abundant in nature.

However, LiMn ₂ O ₄ is 4.3
When charged to a potential higher than V (vs. Li ^/ Li ⁺ ), the crystal structure is destroyed, so that the capacity is significantly reduced due to repeated charge and discharge.

As a positive electrode active material having improved crystal structure instability at a high potential of LiMn ₂ O ₄ , LiMn ₂ O ₄ is used as a positive electrode active material.
LiMn ₂ such as _1.5 Fe _0.5 O ₄ and LiMnFeO ₄
It has been proposed that a part of Mn in O ₄ is replaced by Fe (K. Amine et al./Journal of Power Sources 68
(1997) 604-608).

[0006] However, simply replacing a part of Mn in LiMn ₂ O ₄ with Fe cannot effectively suppress a decrease in capacity due to repetition of charge and discharge (K. Amine).
etal./Journal of Power Sources 68 (1997) 607 Fig.
6).

Accordingly, the present invention uses a lithium-containing manganese composite oxide whose crystal structure is unlikely to collapse even after repeated charge / discharge with high-potential charge as a positive electrode active material.
It is an object to provide a lithium secondary battery having good charge / discharge cycle characteristics.

[0008]

A lithium secondary battery (battery of the present invention) according to the present invention comprises a positive electrode, a material capable of electrochemically absorbing and releasing lithium ions or a lithium metal as an active material. negative electrode and, a non-aqueous electrolyte formed by dissolving an electrolyte salt in a nonaqueous solvent, wherein the active material of positive electrode, composition _{formula: Li a [Mn 2-bc} Fe b M c] O d wherein, M Is at least one element selected from the group consisting of Li, Mg, Cr and Co, 0.02 ≦ a ≦ 2.00,
0.1 ≦ b ≦ 0.6, 0 <c ≦ 0.4, 3.9 ≦ d ≦
4.1. ] It is a lithium-containing manganese composite oxide represented by these.

Mn in LiMn ₂ O _{4 is} added in a predetermined amount (b)
The crystal structure is stabilized even at a high potential of 4.3 V or more by substituting with Fe. Further, LiMn ₂ O
By replacing Mn in ₄ with a predetermined amount (c) of M, a decrease in capacity due to repetition of charge and discharge is suppressed. M
The substitution energy reduces the ordering energy,
It is considered that the distortion of the crystal structure accompanying the repetition of charge and discharge is reduced. Therefore, the battery of the present invention has LiMn ₂
It has better charge / discharge cycle characteristics than a lithium secondary battery using a conventional cathode active material such as O ₄ , LiMn _1.5 Fe _0.5 O ₄ , and LiMnFeO ₄ .

The positive electrode active material of the battery of the present invention has a composition formula: Li
_a in _{[Mn 2-bc Fe b M} c] O d [wherein, M is Li, M
g, Cr and Co, at least one element selected from the group consisting of 0.02 ≦ a ≦ 2.00, 0.1 ≦ b ≦ 0.
6, 0 <c ≦ 0.4, 3.9 ≦ d ≦ 4.1. ] It is a lithium-containing manganese composite oxide represented by these. Mn
Is preferably at least one element selected from the group consisting of Li and Mg. Note that M
Li as a partial substitution element M of n does not participate in charge / discharge and only contributes to stabilization of the crystal structure. The reason that the composition formula is limited to 0.02 ≦ a ≦ 2.00 is that in the case of a <0.02, it is difficult to electrochemically extract lithium ions without collapsing the crystal structure, On the other hand, in the case of a> 2.00, after charging to a high potential of 4.3 V or more, since the change in the lattice constant of the crystal when discharged is large, the crystal structure is likely to collapse due to repeated charge and discharge. is there. Further, the reason why the composition formula is limited to 0.1 ≦ b ≦ 0.6 is that when b <0.1, the crystal lattice is charged to a high potential of 4.3 V or more and then discharged. Since the change in the constant is large, the crystal structure is easily broken by repeated charge and discharge, while b> 0.
No. 6 contains impurities (such as Fe ₂ O ₃ ) that adversely affect the charge / discharge cycle characteristics. Further, the reason why c is less than 0.4 in the above composition formula is that c>
This is because 0.4 contains impurities (such as Li ₂ MnO ₃ ) that adversely affect the charge / discharge cycle characteristics. 0.
Those with 1 ≦ c ≦ 0.3 are particularly preferred. Furthermore, the reason why 3.9 ≦ d ≦ 4.1 in the above composition formula is limited is that the synthesis conditions (firing temperature, firing time, firing atmosphere, etc.)
This is because, although it is slightly different depending on the above, usually, only the value of d within this range can be obtained.

The particle size and shape of the lithium-containing manganese composite oxide are not particularly limited, but the median diameter is 1
When substantially spherical particles of about 100 μm are charged to a high potential of 4.3 V or more and then discharged, the change in the lattice constant of the crystal is small, and the crystal structure is not easily collapsed by repeated charge and discharge, which is preferable. .

The non-aqueous electrolyte of the battery of the present invention contains a lithium salt.
It is formed by dissolving in a non-aqueous solvent. As lithium salt
Is a composition formula: LiN (C_mF_{2m + 1}SO_Two) (C_nF_{2n + 1}
SO _TwoWherein 1 ≦ m ≦ 4 and 1 ≦ n ≦ 4. 〕so
Those containing 50 mol% or more of the imide salt represented
The lithium-containing manganese composite oxide has a high voltage of 4.3 V or more.
It is particularly effective in stabilizing the potential,
Good. As the non-aqueous solvent, propylene carbonate,
Ethylene carbonate, vinylene carbonate, butylene
Cyclic carbonates such as carbonate, dimethyl carbonate
, Diethyl carbonate, methyl ethyl carbonate
Chain carbonates such as
, 1,2-diethoxyethane, ethoxymethoxyethane
Examples thereof include ethers such as butane and mixed solvents thereof.

The negative electrode of the battery of the present invention uses a substance capable of electrochemically storing and releasing lithium ions or a lithium metal as an active material. Materials capable of electrochemically storing and releasing lithium ions include lithium-aluminum alloy, lithium-lead alloy, lithium-
Lithium alloys such as tin alloys, carbon materials such as graphite, coke, and fired organic materials, SnO ₂ , SnO, TiO ₂ , Nb ₂
A metal oxide having a lower potential than a positive electrode active material such as O ₃ is exemplified.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope of the invention without changing its gist. It is something.

(Experiment 1) A battery of the present invention and a comparative battery were prepared, and charge / discharge cycle characteristics were examined.

(Example 1) [Preparation of positive electrode] Manganese acetate (Mn (CH ₃ CO
O) ₂ ) and iron nitrate (Fe (NO ₃ ) ₃ ) are mixed at a molar ratio of 1.4: 0.4, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia to obtain a precipitate. Was. The obtained precipitate and lithium nitrate (LiNO ₃ )
The total of n and Fe and Li were mixed at an atomic ratio of 1.8: 1.2, calcined at 700 ° C. for 20 hours in an oxygen gas stream, pulverized by a jet mill, and a composition formula having a median diameter of 10 μm. : was prepared _{Li [Mn 1.4 Fe 0.4 Li 0.2} ] lithium-containing manganese composite oxide represented by O _4. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

The above-mentioned lithium-containing manganese composite oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are kneaded at a weight ratio of 90: 6: 4 to prepare a positive electrode mixture. 2 tons / c of this positive electrode mixture
After press-molding into a disc shape with a diameter of 20 mm at a pressure of m ² ,
Heat treatment was performed at 250 ° C. for 2 hours under vacuum to produce a positive electrode.

[Preparation of Negative Electrode] A rolled sheet of lithium metal having a thickness of 1.0 mm was punched into a disc having a diameter of 20 mm to prepare a negative electrode.

[Preparation of Nonaqueous Electrolyte] LiN (C ₂ F ₅ SO ₂ ) ₂ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: ₂ at 1 mol / liter to prepare a nonaqueous electrolyte. .

[Preparation of Lithium Secondary Battery]
Using the negative electrode and the nonaqueous electrolyte, a flat lithium secondary battery A1 (battery of the present invention) was produced. As a separator,
A lithium ion permeable polypropylene film was used.

FIG. 1 is a sectional view of a manufactured lithium secondary battery. The illustrated lithium secondary battery A1 has a negative electrode 1, a positive electrode 2, a separator 3 separating them, a negative electrode can 4, a positive electrode can 5, polypropylene Made of insulating packing 8 or the like. The negative electrode 1 and the positive electrode 2 face each other via a separator 3 impregnated with a non-aqueous electrolyte, and are housed in a battery can formed by a negative electrode can 4 and a positive electrode can 5. Are connected to the positive electrode can 5, respectively, so that chemical energy generated in the battery can can be taken out to the outside as electric energy.

Example 2 Manganese acetate, iron nitrate and magnesium nitrate (Mg (NO ₃ ) ₂ ) were used in a molar ratio of 1.
The mixture was mixed at 4: 0.4: 0.2, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia to obtain a precipitate. The obtained precipitate and lithium nitrate were converted into Mn, Fe
And a mixture of Mg and Li at an atomic ratio of 2.0: 1.0, and calcined in an oxygen gas stream at 700 ° C. for 20 hours,
By pulverizing with a jet mill, a lithium-containing manganese composite oxide represented by a composition formula of Li [Mn _1.4 Fe _0.4 Mg _0.2 ] O ₄ having a median diameter of 10 μm was produced. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

A lithium secondary battery A2 (battery of the present invention) was produced in the same manner as in Example 1 except that the above-mentioned lithium-containing manganese composite oxide was used as the positive electrode active material.

Example 3 Manganese acetate, iron nitrate and chromium nitrate (Cr (NO ₃ ) ₃ ) were used in a molar ratio of 1.4: 0.
The mixture was mixed at 4: 0.2, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia to obtain a precipitate. The obtained precipitate and lithium nitrate are mixed at an atomic ratio of 2.0: 1.0 of the total of Mn, Fe and Cr and Li, and calcined at 700 ° C. for 20 hours in an oxygen gas stream. Pulverized by a jet mill to obtain a composition formula of Li [M
The n _1.4 Fe _0.4 Cr _0.2] lithium-containing manganese composite oxide represented by O ₄ was prepared. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

A lithium secondary battery A3 (battery of the present invention) was produced in the same manner as in Example 1 except that the above-mentioned lithium-containing manganese composite oxide was used as the positive electrode active material.

Example 4 Manganese acetate, iron nitrate and cobalt acetate (Co (CH ₃ COO) ₂ ) were used in a molar ratio of 1.
The mixture was mixed at 4: 0.4: 0.2, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia to obtain a precipitate. The obtained precipitate and lithium nitrate were converted into Mn, Fe
And the total of Co and Li were mixed at an atomic ratio of 2.0: 1.0, and calcined in an oxygen gas stream at 700 ° C. for 20 hours.
And pulverized with a jet mill to formula median diameter 10 [mu] m: to prepare a _{Li [Mn 1.4 Fe 0.4 Co 0.2} ] lithium-containing manganese composite oxide represented by O _4. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

A lithium secondary battery A4 (battery of the present invention) was produced in the same manner as in Example 1 except that the above-mentioned lithium-containing manganese composite oxide was used as the positive electrode active material.

Example 5 Manganese acetate, iron nitrate and magnesium nitrate were mixed at a molar ratio of 1.4: 0.4: 0.1, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia. A precipitate was obtained. The obtained precipitate and lithium nitrate are mixed at an atomic ratio of 1.9: 1.1 of the total of Mn, Fe, and Mg to Li, and mixed in an oxygen gas stream at a flow rate of 7: 1.
Fired at 00 ° C for 20 hours, crushed by jet mill,
Composition formula of median diameter 10 μm: Li [Mn _1.4 Fe _0.4
To prepare a Li _0.1 Mg _0.1] lithium-containing manganese composite oxide represented by O _4. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

A lithium secondary battery A5 (battery of the present invention) was produced in the same manner as in Example 1, except that the above-mentioned lithium-containing manganese composite oxide was used as the positive electrode active material.

Comparative Example 1 Manganese acetate and iron nitrate were
The mixture was mixed at a molar ratio of 1.6: 0.4, stirred in an aqueous ethyl alcohol solution, and added with aqueous ammonia to obtain a precipitate. The resulting precipitate and lithium nitrate were combined with Mn and F
e and Li are mixed at an atomic ratio of 2.0: 1.0, calcined in an oxygen gas stream at 700 ° C. for 20 hours, pulverized by a jet mill, and a composition formula of Li having a median diameter of 10 μm: Li
A lithium-containing manganese composite oxide represented by [Mn _1.6 Fe _0.4 ] O _0.4 was produced. As a result of analyzing the composite oxide by powder X-ray diffraction measurement, it was found that the composite oxide had a spinel-type crystal structure.

A lithium secondary battery X1 (comparative battery) was fabricated in the same manner as in Example 1 except that the above-mentioned lithium-containing manganese composite oxide was used as the positive electrode active material.

<Charge / Discharge Cycle Characteristics>
After charging at a current density of 0.15 mA / cm ² to 5.0V, a current density of 0.15 mA / cm ² charge and discharge for discharging to 2.4V for 20 cycles, 20 cycles defined by the following equation for each cell The eye volume maintenance rate (%) was determined. The discharge capacity in the first cycle of each battery was 190 to 19
It was 5 mAh / g. Table 1 shows the results.

Capacity retention rate (%) = (discharge capacity at 20th cycle / discharge capacity at 1st cycle) × 100

[0034]

[Table 1]

Table 1 shows that the batteries A1 to A5 of the present invention had better charge / discharge cycle characteristics than the comparative battery X1. Also, among the batteries of the present invention, batteries A1 and A2 of the present invention
And the charge / discharge cycle characteristics of A5 are particularly good, and as the lithium-containing manganese composite oxide, those in which the partially substituted element of Mn is at least one element selected from the group consisting of Li and Mg are preferable. You can see that.

(Experiment 2) Composition formula: Li _a [Mn _2-bc F
With respect to the lithium-containing manganese composite oxide represented by e _b Li _c ] O ₄ , the relationship between b and c in the composition formula and charge / discharge cycle characteristics was examined.

Manganese acetate and iron nitrate were converted to
Ratios 1.5: 0.4, 1.3: 0.4, 1.2: 0.4,
Mix 1.7: 0.1 and 1.2: 0.6 and add ethyl acetate
Stir in aqueous solution of alcohol and add ammonia water
Precipitates are obtained, and each obtained precipitate and lithium nitrate are
The atomic ratio between the sum of Mn and Fe and Li in order, respectively.
1.9: 1.1, 1.7: 1.3, 1.6: 1.4,
1.8: 1.2 and 1.8: 1.2 mixed, oxygen gas
Fired at 700 ° C for 20 hours in air stream, jet mill
With a composition formula of Li [Mn having a median diameter of 10 μm.
_1.5Fe_0.4 Li_{0. 1}] O_Four, Li [Mn_1.3Fe_0.4 L
i_0.3] O_Four, Li [Mn_1.2Fe_0.4 Li_{0. Four}] O_Four, L
i [Mn_1.7Fe_0.1Li_0.2] O_FourAnd Li [Mn_1.2
Fe_0.6Li _0.2] O_FourLithium-containing manganese represented by
A composite oxide was produced. Powder X-ray diffraction measurement of each composite oxide
As a result of analysis, the spinel type crystal structure was used
It was found to have.

In addition, manganese acetate and iron nitrate are
The molar ratios 1.1: 0.4, 1.75: 0.05 and 1.
1: 0.7 mix and put in ethyl alcohol aqueous solution
After stirring, ammonia water was added to obtain a precipitate.
Precipitate and lithium nitrate, respectively, Mn and
The atomic ratio of the total of Fe to Li is 1.5: 1.5, 1.8:
1.2 and 1.8: 1.2 mixed in an oxygen gas stream
Baking at 700 ° C for 20 hours, pulverizing with a jet mill
And a composition formula with a median diameter of 10 μm: Li [Mn _1.1Fe
_0.4 Li_0.5] O_Four, Li [Mn_1.75Fe_0.05Li_0.2] O
_FourAnd Li [Mn_1.1Fe_0.7Li_0.2] O_FourRepresented by
A lithium-containing manganese composite oxide was produced. Each complex acid
As a result of analyzing the compound by powder X-ray diffraction measurement, the composition formula:
Li [Mn_1.75Fe_0.05Li_0.2] O_FourLichu represented by
Manganese composite oxides have a spinel-type crystal structure.
The composition formula: Li [Mn_1.1Fe_0.4 Li_0.5]
O _FourThe lithium-containing manganese composite oxide represented by
Li_TwoMnO_ThreeAnd a composition formula: Li [Mn_1.1
Fe_0.7Li_0.2] O_FourLithium-containing manganese represented by
The composite oxide contains Fe_TwoO_ThreeYou can see that
Was.

Example 1 except that each of the above-mentioned lithium-containing manganese composite oxides was used as a positive electrode active material.
In the same manner as described above, lithium secondary batteries B1 to B5 (batteries of the present invention) and Y1 to Y3 (comparative batteries) were produced.

For each of the above batteries, 20 cycles of charge / discharge under the same conditions as those performed in Experiment 1 were carried out.
The capacity maintenance ratio (%) at the 0th cycle was determined. The first cycle discharge capacity of each battery was 185 to 200 mAh.
/ G. Table 2 shows the results. Table 2 shows the composition formula:
_{Li [Mn 1.4 Fe 0.4 Li 0.2} ] O 4 lithium secondary battery using the lithium-containing manganese composite oxide represented by A1 (present battery) and composition formula: Li [Mn _1.6 Fe
_0.4 ] O _0.4 The results of a lithium secondary battery X1 (comparative battery) using a lithium-containing manganese composite oxide represented by O _0.4 are also transcribed from Table 1.

[0041]

[Table 2]

As shown in Table 2, the batteries A1 and B of the present invention
1 to B5 have a higher capacity than the comparative batteries X1 and Y1 to Y3.
High retention rate and good charge / discharge cycle characteristics. The present invention
Among the ponds, the charge / discharge sensors of the batteries A1, B1 and B2 of the present invention
Since the cycle characteristics are particularly good, the composition formula: Li_a [Mn
_2-bcFe_bLi_c] O_FourC in the range of 0.1 to 0.3
It is preferable to use a lithium-containing manganese composite oxide
I understand that it is good. Charge / discharge cycle characteristics of comparative battery Y1
Poor performance is due to the positive electrode active material used (Li [Mn
_1.1Fe_0.4Li_0.5] O_Four) Has bad charge / discharge cycle characteristics
Influencing Li _TwoMnO_ThreeIt is thought to include.
Poor charge / discharge cycle characteristics of comparative battery Y2
Positive electrode active material (Li [Mn_1.75Fe_0.05Li_0.2] O
_FourChanges in the crystal lattice constant during the charge / discharge cycle
It is thought that the crystal structure collapsed rapidly due to the large size.
available. The charge / discharge cycle characteristics of the comparative battery Y3 are not good.
In addition, the positive electrode active material (Li [Mn_1.1Fe_0.7
Li_0.2] O_Four) Adversely affects the charge-discharge cycle characteristics
Fe_TwoO_ThreeIt is thought to include.

(Experiment 3) The relationship between the type of lithium salt and the charge / discharge cycle characteristics was examined.

Ethylene carbonate and dimethyl carbonate
LiN in a mixed solvent with a volume ratio of 1: 2
(CF_ThreeSO_Two)_Two, LiN (CF_ThreeSO_Two) (C_TwoF
_FiveSO _Two), LiN (CF_ThreeSO_Two) (C_FourF₉S
O_Two), LiN (C_FourF₉SO_Two) _Two, LiBF_Four, L
iPF₆And LiN (C_TwoF_FiveSO_Two)_TwoAnd LiPF₆
1 mol / liter of a mixed lithium salt having a molar ratio of 1: 1
Upon dissolution, a non-aqueous electrolyte was prepared.

Lithium secondary batteries C1 to C7 (the batteries of the present invention) in the same manner as in Example 1 except that each of the above lithium salts was used instead of LiN (C ₂ F ₅ SO ₂ ) _2. Was prepared.

For each of the above batteries, 20 cycles of charge / discharge under the same conditions as those performed in Experiment 1 were performed.
The capacity maintenance ratio (%) at the 0th cycle was determined. The discharge capacity in the first cycle of each battery was 195 mAh.
/ G. Table 3 shows the results. Table 3 shows that LiN
Lithium secondary battery A1 using (C ₂ F ₅ SO ₂ ) ₂
(Results of the battery of the present invention) are also transcribed from Table 1.

[0047]

[Table 3]

As shown in Table 3, the batteries A1 and C1 of the present invention
C4 and C7 have higher capacity retention rates than the batteries C5 and C6 of the present invention. From this fact, in order to obtain a lithium secondary battery having extremely good charge / discharge cycle characteristics, as a lithium salt, a composition formula: LiN (C _m F _{2m + 1} SO ₂ ) (C _n
F _{2n + 1} SO ₂ ) [where, 1 ≦ m ≦ 4 and 1 ≦ n ≦ 4. It is understood that it is preferable to use one containing 50 mol% or more of the imide salt represented by the formula (1).

[0049]

As described above, a lithium secondary battery having good charge / discharge cycle characteristics is provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a lithium secondary battery (battery of the present invention) manufactured in an example.

[Explanation of symbols]

 A1 lithium secondary battery 1 negative electrode 2 positive electrode 3 separator 4 negative electrode can 5 positive electrode can 8 insulating packing

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shin Fujitani 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5H003 AA04 BB05 BC01 BD00 BD03 5H029 AJ05 AK03 AL02 AL06 AL12 AM03 AM04 AM05 AM07 BJ03 DJ16 HJ01 HJ02

Claims (5)

[Claims] 1. A positive electrode, a negative electrode comprising a substance capable of electrochemically occluding and releasing lithium ions or a lithium metal as an active material, and a non-aqueous electrolyte formed by dissolving a lithium salt in a non-aqueous solvent. In the lithium secondary battery provided, the active material of the positive electrode has a composition formula: Li _a [Mn _2-bc Fe _b
M _c ] O _d [where M is at least one element selected from the group consisting of Li, Mg, Cr and Co, 0.02 ≦
a ≦ 2.00, 0.1 ≦ b ≦ 0.6, 0 <c ≦ 0.4,
3.9 ≦ d ≦ 4.1. ] A lithium secondary battery characterized by being a lithium-containing manganese composite oxide represented by the following formula: 2. The lithium-containing manganese composite oxide,
In particular, the composition _{formula: Li a [Mn 2-bc} Fe b M c] O
_d [wherein, M is at least one element selected from the group consisting of Li, Mg, Cr, and Co, and 0.02 ≦ a ≦ 2.
00, 0.1 ≦ b ≦ 0.6, 0.1 ≦ c ≦ 0.3, 3.
9 ≦ d ≦ 4.1. The lithium secondary battery according to claim 1, which is a lithium-containing manganese composite oxide represented by the following formula: 3. The lithium-containing manganese composite oxide according to claim 1,
In particular, the composition _{formula: Li a [Mn 2-bc} Fe b M 1 c] O d
[Wherein, M ¹ is at least one element selected from the group consisting of Li and Mg, 0.02 ≦ a ≦ 2.00, 0.1
≦ b ≦ 0.6, 0 <c ≦ 0.4, 3.9 ≦ d ≦ 4.1. The lithium secondary battery according to claim 1, which is a lithium-containing manganese composite oxide represented by the following formula: 4. The lithium-containing manganese composite oxide,
In particular, the composition _{formula: Li a [Mn 2-bc} Fe b M 1 c] O d
[Wherein, M ¹ is at least one element selected from the group consisting of Li and Mg, 0.02 ≦ a ≦ 2.00, 0.1
≦ b ≦ 0.6, 0.1 ≦ c ≦ 0.3, 3.9 ≦ d ≦ 4.
It is one. The lithium secondary battery according to claim 1, which is a lithium-containing manganese composite oxide represented by the following formula: 5. The lithium salt has a composition formula: LiN (C _m
F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ ) [where, 1 ≦ m ≦
4, 1 ≦ n ≦ 4. 5. The lithium secondary battery according to claim 1, wherein the lithium secondary battery contains at least 50 mol% of the imide salt represented by the formula (1).