JP2002175801A - Cathode for lithium secondary battery, its manufacturing method and the lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lithium secondary battery of superior preservation characteristics by suppressing manganese which is eluted from lithium manganese oxide, when it is stored in a state of charging/discharging or charging in a lithium secondary battery using the lithium manganese oxide, which has a spinel structure that can occlude/release lithium, in the cathode. SOLUTION: In the lithium secondary battery which uses lithium manganese oxide, having a spinel structure that can occlude/release lithium, for the cathode 1, a thing, in which a covering layer that is formed with boron oxide and lithium cobalt compound oxide in the surface of the lithium manganese oxide, or a substance, in which a 1st covering layer using the boron oxide on the surface of the lithium manganese oxide, and a 2nd covering layer using the lithium cobalt composite oxide are formed, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode for a lithium secondary battery using a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium, a method for manufacturing the same, and a method for manufacturing the lithium secondary battery. The present invention relates to a lithium secondary battery using a positive electrode, and particularly has a feature in that the above-described positive electrode for a lithium secondary battery is improved to improve storage characteristics in the lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, secondary batteries have been used in various fields such as electronic devices. In particular, as one of new batteries having a high output and a high energy density, a high battery utilizing oxidation and reduction of lithium has been used. Power rechargeable lithium batteries have come to be used.

[0003] In such a lithium secondary battery, in order to obtain a high battery voltage and reduce the cost, use of a lithium manganese oxide having a spinel structure for its positive electrode has been studied. .

However, in the case of a lithium secondary battery using lithium manganese oxide having a spinel structure for the positive electrode, the above lithium manganese in the positive electrode is charged and discharged or stored while being charged. Manganese elutes from the oxide and reacts with the non-aqueous electrolyte, which causes a problem that the capacity of the lithium secondary battery gradually decreases and storage characteristics deteriorate.

For this reason, in recent years, Japanese Patent Application Laid-Open No. 9-2
As shown in Japanese Patent No. 65984, it has been proposed to coat the surface of the above-mentioned lithium manganese oxide having a spinel structure with boron oxide to suppress the elution of manganese from the lithium manganese oxide.

However, when the surface of the lithium manganese oxide having a spinel structure is coated with boron oxide, the boron in the boron oxide is dissolved in the lithium manganese oxide, and the lithium secondary battery is still in use. Could not be sufficiently improved.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-described problems in a lithium secondary battery using a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium as a positive electrode. During charging and discharging of the lithium secondary battery and during storage of the lithium secondary battery in a charged state, manganese elutes from the lithium manganese oxide in the positive electrode of the lithium secondary battery. It is an object of the present invention to provide a lithium secondary battery which is sufficiently suppressed and has excellent storage characteristics.

[0008]

In order to solve the above-mentioned problems, a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium is provided in the first lithium secondary battery positive electrode according to the present invention. In a positive electrode for a lithium secondary battery using the above, a coating layer using boron oxide and a lithium cobalt composite oxide is formed on the surface of the lithium manganese oxide having the spinel structure.

In manufacturing the first positive electrode for a lithium secondary battery, lithium manganese oxide having a spinel structure capable of inserting and extracting lithium, boron oxide, and lithium cobalt composite oxide are used. The mixture is heat-treated to form a coating layer using boron oxide and a lithium-cobalt composite oxide on the surface of the lithium manganese oxide having a spinel structure.

In the second positive electrode for a lithium secondary battery according to the present invention, the positive electrode for a lithium secondary battery using a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium is provided. A first coating layer using boron oxide is formed on the surface of the lithium manganese oxide having a spinel structure, and a second coating layer using lithium cobalt composite oxide is formed on the first coating layer. It was.

In manufacturing such a second positive electrode for a lithium secondary battery, lithium manganese oxide having a spinel structure capable of inserting and extracting lithium and boron oxide are mixed and heat-treated. After forming a first coating layer using boron oxide on the surface of lithium manganese oxide having a spinel structure, this is mixed with a lithium-cobalt composite oxide and heat-treated. To form a second coating layer using a lithium-cobalt composite oxide.

When the first and second positive electrodes for lithium secondary batteries as described above are used in a lithium secondary battery, a coating layer covering the surface of a lithium manganese oxide having a spinel structure, a second coating layer, or the like can be used. The manganese elution from the lithium manganese oxide is suppressed by the boron oxide in the first coating layer, and the boron in the boron oxide is reduced by the lithium manganese oxide by the lithium cobalt composite oxide in the coating layer and the second coating layer. And the manganese elution from the lithium manganese oxide is sufficiently suppressed, and the storage characteristics of the lithium secondary battery are improved. In particular, a first coating layer using boron oxide was formed on the surface of lithium manganese oxide having a spinel structure, and a second coating layer using lithium cobalt composite oxide was formed on the first coating layer. When the second positive electrode for a lithium secondary battery is used, boron oxide is more stably present even during charging and discharging, and the storage characteristics of the lithium secondary battery are further improved.

Here, as described above, when forming a coating layer using boron oxide and lithium cobalt composite oxide on the surface of lithium manganese oxide, or forming a first coating layer using boron oxide, If the amount of boron oxide in these coating layers is small, it is not possible to sufficiently suppress manganese from being eluted from the lithium manganese oxide, while if the amount of boron oxide is too large,
Since the load when charging and discharging the lithium secondary battery is increased, the atomic ratio of boron in boron oxide to manganese in lithium manganese oxide is set to 0.01.
It is preferable to set the range to 0.2.

The lithium-cobalt composite oxide used for the coating layer and the second coating layer is LiCo _a M _b
O ₂ (where M is Ni, Mn, Fe, Zn, Ti, C
At least one element selected from r, Mg, Al, Cu, and Ga, and satisfies the condition of a + b = 1, 0 ≦ b ≦ 0.2. ) Can be used. When the atomic ratio of M in the lithium-cobalt composite oxide increases, the charge / discharge capacity and the charge / discharge efficiency decrease, so that b is set to 0.2 or less as described above.

The lithium-cobalt composite oxide contains L
Upon iCo _a M _b O ₂ using a forming the coating layer and the second covering layer, the amount of the lithium cobalt composite oxide is small, boron in the boron oxide from being dissolved in the lithium manganese oxide sufficiently On the other hand, if the amount of the lithium-cobalt composite oxide is too large, the oxidation number of the lithium manganese oxide is affected, and the storage characteristics of the lithium secondary battery deteriorate. it is preferable to in LiCo _a M _b O ₂ to manganese in the object the atomic ratio of (Co + M) in the range of 0.05 to 2.0.

Here, the lithium secondary battery in the present invention is characterized by using the above-mentioned positive electrode for a lithium secondary battery, and the nonaqueous electrolyte and the negative electrode to be used are not particularly limited.

As the non-aqueous electrolyte used in the lithium secondary battery according to the present invention, a conventionally used one obtained by dissolving a solute in an organic solvent can be used.

Here, as the organic solvent used for the non-aqueous electrolyte, a conventionally used organic solvent can be used, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and dimethyl carbonate. , Diethyl carbonate,
A chain carbonate such as ethyl methyl carbonate can be used, and a mixed solvent of the above-mentioned cyclic carbonate and chain carbonate can also be used.

In the non-aqueous electrolyte, as the solute to be dissolved in the above-mentioned organic solvent, a conventionally used solute can be used.
₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiC
F ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ S
O ₂₎ and _2, LiOSO ₂ (CF ₂₎ a lithium compound such as ₃ CF ₃ can be used.

In the nonaqueous electrolyte battery according to the present invention, as the negative electrode material used for the negative electrode, a conventionally known negative electrode material can be used. For example, lithium metal, Li-Al, Li-In , Li-S
n, Li-Pb, Li-Bi, Li-Ga, Li-S
r, Li-Si, Li-Zn, Li-Cd, Li-C
a, a lithium alloy such as Li-Ba, a graphite material capable of occluding and releasing lithium ions, a coke, and a carbon material such as a fired organic material can be used.

[0021]

EXAMPLES Hereinafter, the positive electrode for a lithium secondary battery according to the present invention, a method for producing the same, and a lithium secondary battery will be specifically described with reference to examples. It is clarified that the storage characteristics are improved with reference to comparative examples. The positive electrode for a lithium secondary battery according to the present invention, the method for manufacturing the same, and the lithium secondary battery are not limited to those shown in the following examples, and may be changed as appropriate without departing from the gist thereof. Can be implemented.

Example 1 In Example 1, the positive electrode 1
A negative electrode 2 was prepared as described below, and a non-aqueous electrolyte was prepared as described below, thereby preparing a flat coin-type lithium secondary battery as shown in FIG.

[Preparation of Positive Electrode] To prepare a positive electrode, LiMn ₂ O ₄ which is a lithium manganese oxide having a spinel structure was used as a positive electrode active material.
When mixing Mn ₂ O ₄ , boron oxide B ₂ O ₃ and lithium cobalt composite oxide LiCoO ₂ , as shown in Table 1 below, manganese Mn in LiMn ₂ O ₄ was mixed with boron oxide B ₂ These were mixed so that the atomic ratio of boron B in O ₃ (B / Mn) was 0.03 and the atomic ratio of cobalt Co in LiCoO ₂ of the lithium cobalt composite oxide (Co / Mn) was 0.2. The mixture was heat treated at 400 ° C. to give LiMn ₂ O
_On the surface of No. ₄ , a coating layer composed of B ₂ O ₃ and LiCoO ₂ was formed.

[0024] The LiMn ₂ O ₄ having the coating layer formed on the surface as described above is provided with carbon powder as a conductive agent and N-
A solution in which polyvinylidene fluoride as a binder is dissolved is added to a methyl-2-pyrrolidone solution, and the above LiMn ₂ is added.
A slurry was prepared in which O ₄ , the carbon material of the conductive agent, and the polyvinylidene fluoride of the binder had a weight ratio of 90: 5: 5, and this slurry was applied to one surface of a positive electrode current collector made of aluminum foil by a doctor. The coating was applied by a blade method, rolled, and then punched into a disk having a diameter of 20 mm to produce a positive electrode.

[Preparation of Negative Electrode] In preparing the negative electrode, a natural graphite powder was used as a negative electrode active material, and the natural graphite powder and polyvinylidene fluoride as a binder were used for 90:
The mixture was mixed to a weight ratio of 10 and an N-methyl-2-pyrrolidone solution was added to the mixture to prepare a slurry. The slurry was applied to one surface of a negative electrode current collector made of copper foil by a doctor blade method. And after rolling this, the diameter 2
A negative electrode was produced by punching out a 2 mm disc.

[Preparation of Non-Aqueous Electrolyte] In preparing a non-aqueous electrolyte, a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 is used.
PF ₆ was dissolved at a rate of 1 mol / l to prepare a non-aqueous electrolyte.

[Preparation of Battery] In preparing a battery, as shown in FIG. 1, a polypropylene impregnated with the above-described non-aqueous electrolyte between the positive electrode 1 and the negative electrode 2 prepared as described above was used. A separator 3 made of a microporous film made of a metal is interposed, and these are accommodated in a battery case 4 formed of a positive electrode can 4a and a negative electrode can 4b. 4a, the negative electrode 2 is connected to the negative electrode can 4b via the negative electrode current collector 6, and the positive electrode can 4a and the negative electrode can 4b are electrically insulated by a polypropylene insulating packing 7, 24mm in diameter,
A flat coin-shaped lithium secondary battery having a thickness of 3.0 mm was obtained.

[0028] In (Example 2) Example 2, in preparation of the positive electrode in Example 1 above, with respect to manganese Mn in LiMn ₂ O ₄ which was above a spinel structure, the boron oxide B ₂ O ₃ The atomic ratio (B / Mn) of boron B is set to 0.05, and LiMn ₂
O ₄ and B ₂ O ₃ were mixed, first consisting of LiMn ₂ O surface B ₂ O ₃ of ₄ by heat-treating the mixture at 400 ° C.
After forming the coating layer, the manganese Mn in LiMn ₂ O ₄ is compared with the lithium cobalt composite oxide LiCo.
Li in which the first coating layer was formed such that the atomic ratio (Co / Mn) of cobalt Co in O ₂ was 0.2.
Mn ₂ O ₄ and LiCoO ₂ are mixed, and this mixture is mixed with 4
Heat treatment at 00 ° C. to form LiCo on the first coating layer.
A second coating layer of O ₂ was formed.

Otherwise, in the same manner as in Example 1 described above, a positive electrode was prepared, and a lithium secondary battery was prepared using the positive electrode thus prepared.

(Comparative Example 1) In Comparative Example 1, boron oxide B ₂ was added to LiMn ₂ O ₄ having the spinel structure in the preparation of the positive electrode in Example 1 described above.
A positive electrode was prepared in the same manner as in Example 1 except that O ₃ and LiCoO ₂ of the lithium-cobalt composite oxide were not mixed, and a lithium was prepared using the positive electrode thus prepared. A secondary battery was manufactured.

(Comparative Example 2) In Comparative Example 2, the manganese Mn in LiMn ₂ O ₄ having the spinel structure described above was compared with the manganese Mn in boron oxide B ₂ O ₃ in the preparation of the positive electrode in Example 1 described above. LiMn _{2 is} adjusted so that the atomic ratio (B / Mn) of boron B becomes 0.03.
O ₄ and B ₂ O ₃ were mixed, and the mixture was heat-treated at 400 ° C. to form a coating layer consisting of only B ₂ O _{3 on} the surface of LiMn ₂ O _4. In the same manner as in the above case, a positive electrode was produced, and a lithium secondary battery was produced using the positive electrode produced in this manner.

Next, each of the lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 manufactured as described above was
After charging at a charging current of 0.8 mA to an end-of-charging voltage of 4.2 V in an atmosphere of 100 ° C.
The battery was discharged at A to a discharge end voltage of 3.0 V, and the discharge capacity Q0 of each lithium secondary battery before storage was measured.

Thereafter, each of the above-mentioned lithium secondary batteries was charged at a charging current of 0.8 mA to an end-of-charge voltage of 4.2 V in an atmosphere of 25 ° C. as described above.
After storing for 2 weeks in an atmosphere of 0 ° C., each lithium secondary battery was returned to an atmosphere of 25 ° C., and a discharge current of 0 ° C.
The battery was discharged at a discharge end voltage of 3.0 V at 8 mA, and the discharge capacity Q1 of each lithium secondary battery after storage was measured.
The self-discharge rate (%) of each lithium secondary battery was determined based on the following equation, and the results are shown in Table 1 below.

Self-discharge rate (%) = (1−Q1 / Q0) × 100

[0035]

[Table 1]

As is apparent from the results, the spinel structure
LiMn made_TwoO_FourB on the surface of_TwoO_ThreeAnd LiCo
O_TwoThe one having a coating layer consisting of
The lithium secondary battery of Example 1 and a spinel structure were obtained.
LiMn_TwoO_FourB on the surface of_TwoO_ThreeA first coating layer comprising
LiCoO_TwoThe second coating layer made of
The lithium secondary battery of Example 2 used for the electrode was a spinel
Structured LiMn _TwoO_FourThese coatings on the surface of
Lithium of Comparative Example 1 using a non-formed one for the positive electrode
Battery or LiMn with spinel structure_TwoO_Fourof
B on the surface_TwoO_ThreeWith a coating layer consisting of only
As compared with the lithium secondary battery of Comparative Example 2 used for the electrode.
Self-discharge rate is greatly reduced, and storage characteristics are greatly improved
Was.

When the lithium secondary batteries of Examples 1 and 2 were compared, a first coating layer made of B ₂ O ₃ and a second coating made of LiCoO ₂ were formed on the surface of LiMn ₂ O ₄ having a spinel structure. In the lithium secondary battery of Example 2 using the layer and the layer, the self-discharge rate was further reduced, and the storage characteristics were further improved.

(Embodiments 1.1 to 1.12) Embodiment 1.1
1 to 12, the positive electrode of Example 1 was used.
In the fabrication, LiMn having the above spinel structure_Two
O_FourBoron oxide B on the surface of_TwoO _ThreeAnd lithium cobalt
Used to form a coating layer consisting of a composite oxide
The type of lithium-cobalt composite oxide to be used was changed.

Here, the lithium cobalt composite oxidation described above is used.
As the material, the above-mentioned LiCo_aM_bO_TwoIs represented by the formula
Using the type of M and the values of a and b changed,
As shown in Table 2, in Examples 1 and 1, LiCo_0.9Ni
_0.1O_TwoIn Examples 1 and 2, LiCo_0.8Ni_0.2O
_TwoIn Examples 1 and 3, LiCo_0.7Ni_0.3O_TwoTo
In Examples 1 and 4, LiCo_0.9Mn_0.1O_TwoThe example
LiCo for 1.5_{0. 9}Fe_0.1O_TwoIn Examples 1.6
Then LiCo_0.9Zn_0.1O_TwoIn Examples 1 and 7, L
iCo_0.9Ti_0.1O_TwoIn Examples 1.8, LiCo
_0.9Cr_0.1O _TwoIn Examples 1.9, LiCo_0.9M
g_0.1O_TwoIn Examples 1 and 10, LiCo_0.9Al
_0.1O_TwoIn Examples 1 and 11, LiCo_0.9Cu_0.1
O_TwoIn Examples 1 and 12, LiCo_0.9Ga_0.1O_Two
Was used.

Then, the atomic ratio (B / Mn) of boron B in boron oxide B ₂ O ₃ to manganese Mn in LiMn ₂ O ₄ is set to be 0.03 as in the case of the first embodiment. while the relative manganese Mn in LiMn ₂ O _4, as the atomic ratio of the above in the lithium cobalt composite oxide _{LiCo a M b O 2 (Co} + M) [(Co + M) / Mn] of 0.2 did.

Other than that, a positive electrode was prepared in the same manner as in Example 1 described above, and each lithium secondary battery was prepared using the positive electrode thus prepared.

Next, the embodiment 1 manufactured as described above was prepared.
For each of the lithium secondary batteries 1 to 1 and 12, the self-discharge rate (%) was determined in the same manner as in the case of the lithium secondary battery of Example 1 above, and the results are shown in Table 2 below. Was.

[0043]

[Table 2]

As is apparent from the results, the surface of the spinel-structured LiMn ₂ O ₄ was covered with boron oxide B ₂ O _3.
In forming the coating layer composed of and the lithium-cobalt composite oxide for the positive electrode, even when the type of the lithium-cobalt composite oxide is changed, the lithium secondary batteries of Comparative Examples 1 and 2 are used. In comparison, the self-discharge rate was reduced, and the storage characteristics were improved.

Further, a comparison of each of the lithium secondary batteries of Examples, the lithium cobalt composite oxide the value of b of the formula of LiCo _a M _b O ₂ becomes 0.2 or less Example 1, 1.1, 1.2, 1.4-1 used
-Each of the lithium secondary batteries of 12 has a lower self-discharge rate than the lithium secondary batteries of Examples 1 and 3 using the lithium-cobalt composite oxide having a value of b of 0.3. And the storage characteristics were further improved.

(Examples 1 and 13 to 1 and 17)
In Nos. 13 to 1/17, in the production of the positive electrode in Example 1 described above, the LiM having the spinel structure described above was used.
In forming a coating layer composed of boron oxide B ₂ O ₃ and lithium cobalt composite oxide LiCoO _{2 on} the surface of n ₂ O ₄ , the atomic ratio of cobalt Co in LiCoO _{2 to} manganese Mn in LiMn ₂ O ₄ ( C
o / Mn) was 0.2, while the atomic ratio (B / Mn) of boron B in boron oxide B ₂ O ₃ to manganese Mn in LiMn ₂ O ₄ was as shown in Table 3 below. In Examples 1 and 13, the value was 0.008, and in Examples 1 and 14
In Examples 1 and 15, it was set to 0.1, in Examples 1 and 16 to 0.2, and in Examples 1 and 17 to 0.3.

Otherwise, in the same manner as in Example 1 described above, a positive electrode was prepared, and each lithium secondary battery was prepared using the positive electrode thus prepared.

Next, the embodiment 1 manufactured as described above was used.
-Regarding each of the lithium secondary batteries of 13 to 1.17, similarly to the case of the lithium secondary battery of Example 1 described above,
The self-discharge rate (%) was determined, and the results are shown in Table 3 below.

[0049]

[Table 3]

As is apparent from the results, the spinel structure
LiMn made_TwoO_FourB on the surface of_TwoO_ThreeAnd LiCo
O_TwoFor forming a coating layer consisting of
Per LiMn_TwoO_FourFor manganese Mn in
Boron oxide B_TwoO_ThreeAtomic ratio of boron B (B / M
n) was used in the range of 0.01 to 0.2.
The lithium secondary batteries of Examples 1 and 1.14 to 1.16 are:
LiMn_TwoO_FourOxide against manganese Mn in water
Element B_TwoO_ThreeThe atomic ratio (B / Mn) of boron B in
Lithium secondary batteries of Examples 1 and 13 which became 0.008
And LiMn_TwoO _FourTo manganese Mn at room temperature
Boron B_TwoO_ThreeRatio of boron B in (B / Mn)
Is 0.3, the lithium secondary battery of Examples 1 and 17
In comparison, the self-discharge rate has decreased,
Had improved.

(Embodiments 1.18 to 1.22) Embodiment 1
In Nos. 18 to 1.22, in the production of the positive electrode in Example 1 described above, the LiM having the spinel structure described above was used.
on the surface of the n ₂ O _4, in forming a coating layer made of boron oxide B ₂ O ₃ and LiCoO ₂ Metropolitan of lithium cobalt composite oxide, boron in boron oxide B ₂ O ₃ to manganese Mn in LiMn ₂ O ₄ B While the atomic ratio (Co / Mn) of cobalt Co in LiCoO _{2 to} manganese Mn in LiMn ₂ O ₄ was set to 0.03, as shown in Table 4 below. In Example 1.1, it was set to 0.02, and Example 1.1
In Example 9, it was set to 0.05, in Examples 1 and 20 to 1.5, in Examples 1-21 to 2.0, and in Examples 1.22 to 2.5.

Except for this, a positive electrode was produced in the same manner as in Example 1 described above, and each lithium secondary battery was produced using the positive electrode produced in this manner.

Next, the embodiment 1 manufactured as described above was prepared.
-Regarding each of the lithium secondary batteries of 18 to 1.22, similarly to the case of the lithium secondary battery of Example 1 described above,
The self-discharge rate (%) was determined, and the results are shown in Table 4 below.

[0054]

[Table 4]

As is apparent from the results, B ₂ O ₃ and LiCo ₃ are formed on the surface of the spinel-structured LiMn ₂ O _4.
In forming the coating layer composed of O ₂ on the positive electrode, the atomic ratio of cobalt Co in LiCoO _{2 to} manganese Mn in LiMn ₂ O ₄ (Co / M
Each of the lithium secondary batteries of Examples 1, 1.19 to 1.21, and n) in which n) was in the range of 0.05 to 2.0,
LiCo for manganese Mn in LiMn ₂ O ₄
Lithium secondary batteries of Examples 1 and 18 using the one in which the atomic ratio (Co / Mn) of cobalt Co in O ₂ was 0.02, and the ratio of cobalt Co in LiCoO _{2 to} manganese Mn in LiMn ₂ O ₄ Atomic ratio (C
o / Mn) of Examples 1 and 2 using 2.5
The self-discharge rate was lower than that of the lithium secondary battery of No. 2, and the storage characteristics were further improved.

[0056]

As described in detail above, in the lithium secondary battery according to the present invention, boron oxide and lithium cobalt composite oxide are used as the positive electrode on the surface of lithium manganese oxide having a spinel structure. A first positive electrode for a lithium secondary battery using a coating layer formed thereon, a first coating layer using boron oxide on the surface of a lithium manganese oxide having a spinel structure, and a first coating layer using boron oxide on the first coating layer. Since the second positive electrode for a lithium secondary battery using the second coating layer using the lithium-cobalt composite oxide was used, the surface of the lithium manganese oxide having a spinel structure was coated. The manganese oxide is prevented from being eluted from the lithium manganese oxide by the boron oxide in the coating layer and the first coating layer, and the above-described coating layer and the second coating layer. The lithium-cobalt complex oxide in layers, boron in boron oxide was to be inhibited from solid solution in lithium-manganese oxide.

As a result, in the lithium secondary battery of the present invention, manganese is prevented from being eluted from the lithium manganese oxide and reacted with the non-aqueous electrolyte during charge / discharge or when stored in a charged state. As a result, the storage characteristics of the lithium secondary battery were greatly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing an internal structure of a lithium secondary battery produced in an example of the present invention and a comparative example.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyuki Yanagita, Inventor 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Yoshinori Kita 2-5-1 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Atsuhiro Funabashi 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture (72) Inventor Toshiyuki Noma Keihan Hondori, Moriguchi City, Osaka Prefecture 2-5-5 Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 4G048 AA04 AB02 AB04 AC06 AD03 AD06 5H029 AJ04 AK03 AK19 AL07 AM03 AM05 AM07 BJ03 BJ12 BJ13 CJ02 CJ08 DJ17 EJ05 HJ02 5H050 AA09 BA17 CA08 CA09 CA30 DA09 EA12 FA02 FA18 FA19 GA02 GA10 GA26 HA02

Claims (8)

[Claims] 1. A positive electrode for a lithium secondary battery using a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium, wherein the surface of the lithium manganese oxide having a spinel structure is coated with boron oxide. A positive electrode for a lithium secondary battery, wherein a coating layer using a lithium-cobalt composite oxide is formed. 2. A positive electrode for a lithium secondary battery using a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium, wherein boron oxide is formed on the surface of the lithium manganese oxide having a spinel structure. A positive electrode for a lithium secondary battery, wherein a first coating layer used is formed, and a second coating layer using a lithium-cobalt composite oxide is formed on the first coating layer. 3. The positive electrode for a lithium secondary battery according to claim 1, wherein an atomic ratio of boron in the boron oxide to manganese in the lithium manganese oxide is 0.01 to 0.2. A positive electrode for a lithium secondary battery, wherein the positive electrode has a range. 4. A positive electrode for a lithium secondary battery according to any one of claims 1 to 3, the lithium-cobalt composite oxide described above LiCo _a M _b O ₂ (wherein, M represents Ni,
Mn, Fe, Zn, Ti, Cr, Mg, Al, Cu, G
at least one element selected from a, a + b
= 1, 0 ≦ b ≦ 0.2. A) a positive electrode for a lithium secondary battery; 5. A method according to claim 4 for lithium secondary battery positive electrode as described in the atomic ratio of the LiCo _a M _b O ₂ above to manganese in the lithium manganese oxide (Co + M) is 0.05 to 2. A positive electrode for a lithium secondary battery, wherein the positive electrode has a range of 0. 6. A lithium manganese oxide having a spinel structure, wherein a lithium manganese oxide having a spinel structure capable of inserting and extracting lithium, boron oxide, and a lithium cobalt composite oxide are mixed and heat-treated. A method for producing a positive electrode for a lithium secondary battery, comprising forming a coating layer using boron oxide and a lithium-cobalt composite oxide on the surface of a lithium secondary battery. 7. A spinel-structured lithium manganese oxide capable of inserting and extracting lithium and boron oxide are mixed and heat-treated, and boron oxide is used on the surface of the spinel-structured lithium manganese oxide. After forming the first coating layer, the mixture is mixed with the lithium-cobalt composite oxide and heat-treated to form a second coating layer using the lithium-cobalt composite oxide on the first coating layer. A method for producing a positive electrode for a lithium secondary battery, comprising: 8. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has
6. A lithium secondary battery, comprising the positive electrode for a lithium secondary battery according to any one of the above items 5 to 5.