JP2000231919A - Positive electrode active material and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with less deteriorated charging/discharging characteristics even when used under high temperature conditions using inexpensive manganese oxides for a positive active material. SOLUTION: This positive active material has a manganese oxide particle mainly containing a manganese oxide and an elution suppressing layer of a non-polymer film covering the manganese oxide particle for suppressing elution of a manganese. This nonaqueous electrolyte secondary battery has the positive active material in a positive electrode. A nonaqueous electrolyte (an electrolyte solution, for example) is not brought into contact with a manganese element highly active by blocking the elution suppressing layer so that the nonaqueous electrolyte is prevented from being electrolyzed by the manganese. A negative electrode is not badly affected by eluting the manganese from the positive active material. Therefore, this nonaqueous electrolyte secondary battery can maintain large discharging capacity even if stored or charged/discharged under high temperature conditions for a long time and deterioration of charging/ discharging characteristics is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of lithium ion secondary batteries and non-aqueous electrolyte secondary batteries including lithium secondary batteries.

[0002]

2. Description of the Related Art In recent years, cordless electronic devices such as video cameras, portable telephones and portable personal computers have been remarkably developed, and non-aqueous electrolyte batteries capable of being charged with a high battery voltage and a high energy density have been used as power supply batteries. The next battery is attracting attention. As the positive electrode active material used in such a non-aqueous electrolyte secondary battery, LiV ₃ O ₈ , LiCo
The use of various lithium transition metal composite oxides such as O ₂ , LiNiO ₂ and LiMn ₂ O ₄ has been studied. Among these, manganese-based oxides such as LiMn ₂ O ₄ are particularly promising because they are very inexpensive.

However, it has been known that the use of manganese oxide as a positive electrode active material causes the following disadvantages. First, since a charging voltage exceeding 4 V is applied to the non-aqueous electrolyte secondary battery, the electrolytic solution is decomposed by the catalysis of highly active manganese, which causes a disadvantage that the battery characteristics deteriorate. Secondly, manganese dissolved from the surface of the positive electrode active material moves in the non-aqueous electrolyte and acts on the negative electrode, thereby inhibiting charging and discharging. These disadvantages are particularly remarkable in a high-temperature environment, and cause remarkable deterioration of charge / discharge cycle characteristics and deterioration of storage characteristics.

[0004] In order to solve the first inconvenience,
Japanese Patent Application Laid-Open No. 9-35712 discloses a technique for replacing manganese on the surface of a spinel-type lithium manganese oxide with another transition metal (prior art 1). However, with this technique, manganese is still distributed over most of the surface of the lithium manganese oxide,
The dissolution of manganese cannot be sufficiently suppressed, and the second disadvantage cannot be solved.

For the same purpose, Japanese Patent Application Laid-Open No. 10-125
No. 306 discloses a technique of coating a positive electrode active material with a lithium ion conductive polymer (prior art 2). However, even with this technology, when manganese oxide is used as the positive electrode active material, the electrolyte penetrates into the lithium ion conductive polymer and comes into contact with the surface of the manganese oxide. Manganese begins to dissolve in the liquid. Therefore, the second problem cannot be solved by the second conventional technique.

As a result, in both the prior art 1 and the prior art 2, as long as an inexpensive manganese oxide is used as the positive electrode active material, the non-aqueous electrolyte whose charge / discharge characteristics are deteriorated when used in a high temperature environment. Only liquid rechargeable batteries can be provided.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a non-aqueous electrolyte secondary battery using an inexpensive manganese oxide as a positive electrode active material and having less deterioration in charge / discharge characteristics even when used in a high-temperature environment. Is the task to be solved. At the same time, it is another object of the present invention to provide an inexpensive positive electrode active material containing manganese oxide as a main component, which is used for such a nonaqueous electrolyte secondary battery.

[0008]

In order to solve the above problems, the inventor has invented the following means. (First Means) A first means of the present invention is the positive electrode active material according to claim 1. By using the positive electrode active material of this means, a non-aqueous electrolyte secondary battery having the following advantages can be manufactured.

That is, in this means, as shown in FIG. 1, the surface of the manganese oxide particles, which is the main component of the positive electrode active material, has the surface of the elution suppressing layer for suppressing the dissolution of manganese from the manganese oxide particles. It is covered by a molecular coating. Here, when the non-aqueous electrolyte secondary battery is configured, the elution suppression layer not only suppresses the dissolution of manganese from the manganese oxide particles into the non-aqueous electrolyte, but also suppresses the elution suppression layer itself. It is desirable not to release manganese into the non-aqueous electrolyte. In addition, even when a relatively high voltage is applied during charging, the elution suppressing layer covers the non-aqueous electrolyte so that the non-aqueous electrolyte does not touch the manganese oxide particles through the elution suppressing layer and is not denatured by the manganese activation action. It is desirable to have the property of not allowing transmission. Therefore, it is desirable that a manganese element is not contained in the elution suppression layer itself by using a lithium-based composite oxide containing no manganese element for the elution suppression layer.

[0010] Therefore, in the positive electrode of the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte is prevented from directly contacting the highly active manganese. The first disadvantage of deteriorating properties is avoided. Also, for similar reasons,
Since the elution of manganese from the manganese oxide particles of the positive electrode active material into the nonaqueous electrolyte is suppressed, the eluted manganese moves in the nonaqueous electrolyte and acts on the negative electrode to charge and discharge the nonaqueous electrolyte secondary battery. The second disadvantage of inhibition is also prevented. As a result, the first and second disadvantages described above are eliminated, so that the battery characteristics do not deteriorate even when charged at a relatively high voltage, and the charge / discharge characteristics are maintained even when stored or used at a relatively high temperature. Deterioration is prevented.

More specifically, a comparison between a non-aqueous electrolyte secondary battery consisting only of bare manganese oxide particles and a non-aqueous electrolyte secondary battery as an embodiment of the present invention shows that FIG. 2 and FIG. As shown, excellent charge / discharge cycle characteristics and storage characteristics at high temperatures are demonstrated. That is, FIG. 2 shows the comparative example in which the manganese oxide particles did not have the elution suppressing layer, and the non-aqueous electrolyte secondary battery of the present invention in which the predetermined elution suppressing layer was used.
5 is a graph showing a decrease in discharge capacity when charge and discharge are repeated in an atmosphere of ° C. From FIG. 2, it can be seen that only the initial capacity up to about 20 charge / discharge cycles is slightly better in the comparative example, but if the number of cycles exceeds about 40, the non-aqueous solution of the present invention having the positive electrode active material of the present means is used. It is clear that the electrolyte secondary battery is superior in the discharge capacity and is superior in the high-temperature charge / discharge cycle characteristics. Regarding the initial capacity, it is possible to manufacture an example that is superior to the comparative example by means such as forming the elution suppression layer with a lithium-cobalt composite oxide as described later. On the other hand, FIG. 3 shows the recovery rate of the discharge capacity of the charged non-aqueous electrolyte secondary battery left for 300 hours in an atmosphere at 60 ° C., with the initial discharge capacity being 100%. 4 is a bar graph showing a comparison between high-temperature storage characteristics and an example of the present invention. As is clear from FIG. 3, the embodiment of the present invention has about several percent improvement in discharge capacity reduction due to high-temperature storage.

Therefore, according to this means, the cathode active material of the non-aqueous electrolyte secondary battery, which is inexpensive because it uses manganese oxide as a main component and has little deterioration in charge / discharge characteristics even when used in a high temperature environment, is inexpensive. There is an effect that the substance can be provided. Here, the non-aqueous electrolyte is a concept including not only a non-aqueous electrolyte but also a gel non-aqueous electrolyte and a solid electrolyte (a kind of polymer, etc.). This is a concept that includes media in general. Therefore, the non-aqueous electrolyte secondary battery includes a non-aqueous electrolyte secondary battery, but indicates a broader concept than the non-aqueous electrolyte secondary battery.

The manganese oxide is typically a composite oxide of lithium and manganese or manganese dioxide, but other manganese oxides may be used as long as battery performance and cost permit. It is most desirable that the entire surface of the manganese oxide particles is covered with the elution suppressing layer. However, even if there is a part of the surface that is not covered, the cycle capacity and storage characteristics are only slightly reduced. Therefore, it is not always necessary that the entire surface of the manganese oxide particles is covered with the elution suppressing layer, but it is desirable that as much of the surface of the manganese oxide particles as possible is covered with the elution suppressing layer.

Further, as a method for producing the positive electrode active material of the present means, for example, there is the following method. First, as a raw material for forming the elution suppression layer, a lithium raw material and a metal element raw material other than manganese are mixed, and this mixture fine powder is added to manganese oxide particles and mixed. Thereafter, the mixture of the mixture fine powder and the manganese oxide particles forming the elution suppression layer is fired to obtain the positive electrode active material of the present means.
Here, as the lithium raw material, for example, Li ₂ C
O ₃ , LiOH.H ₂ O, LiOH and the like can be mentioned. Further, as the metal element raw material, for example, TiO ₂ ,
Oxides such as V ₂ O ₅ , WO ₃ and MoO ₃ , H ₂ WO ₄ ,
Acids such as H ₂ MoO ₄ can be mentioned. When the firing temperature is set at 500 to 900 ° C., a sufficient firing action can be obtained. Further, the maintenance time of the firing temperature is preferably 1 to 30 hours, and more preferably 3 to 20 hours. However, the method for producing a positive electrode active material according to this means is not limited to the above method.

(Second Means) A second means of the present invention is the positive electrode active material according to claim 2. That is, in the present means, the elution suppressing layer is composed mainly of a lithium composite oxide with any of Ti, V, Mo, W, Co and Ni. Therefore, the elution suppression layer contains little (or no) Mn, and the Mn does not dissolve into the non-aqueous electrolyte from the elution suppression layer. When used in a battery, the non-aqueous electrolyte secondary battery can exhibit good durability.

In the case where Ti, V, Mo or W is adopted, the excellent performance of the non-aqueous electrolyte secondary battery is clarified in each of the embodiments described later.
In the case of employing the same, excellent battery performance is similarly exhibited. When Co or Ni is adopted for the elution suppressing layer,
Since the elution suppressing layer exhibits not only the function as the elution suppressing layer but also the function as the positive electrode active material, there is almost no decrease in the initial capacity as described later, and more excellent battery performance can be obtained.

(Third Means) A third means of the present invention is the positive electrode active material according to claim 3. That is, in this means, the manganese oxide is one of a composite oxide of lithium and manganese and manganese dioxide. In the above-mentioned first means, other manganese oxides can be used. However, in the present means, there is a limitation from the viewpoint of being relatively inexpensive and easy to obtain and manufacture raw materials. As the composite oxide of lithium and manganese (lithium-manganese composite oxide), for example, LiMn ₂ 0 _4, Li
_{1 + X} Mn _2-x O ₄ , Li _{1 + X} Mn _2-xy Me _y O ₄ (M
e can be a metal element other than Mn).

Therefore, according to this means, in addition to the effects of the above-mentioned first means or second means, there is an effect that it is relatively inexpensive and it is easy to obtain and manufacture raw materials. (Fourth Means) A fourth means of the present invention is the positive electrode active material according to claim 4. In this means, there is an additional limitation that the mixing ratio between the manganese oxide particles and the elution suppressing layer is 1: 0.001 to 1: 0.01. Here, if the compounding weight ratio of the manganese oxide particles to the elution suppressing layer is less than 1: 0.001, and the manganese elution suppressing effect of the elution suppressing layer becomes small under a high temperature environment, However, the storage characteristics of the non-aqueous electrolyte secondary battery deteriorate. Conversely, if the same weight ratio exceeds 1: 0.01, the coating of the elution suppressing layer becomes thicker, the electrical resistance of the coating increases, and the internal resistance of the nonaqueous electrolyte secondary battery increases. Causes inconvenience. Therefore, if the range of the blending weight ratio is limited as in this means, the storage characteristics of the non-aqueous electrolyte secondary battery can be effectively prevented from deteriorating in storage characteristics at high temperatures, but not so much. The internal resistance does not need to be large. As a result, it is possible to provide a non-aqueous electrolyte secondary battery that is durable even at high temperatures without significantly lowering the initial performance of the non-aqueous electrolyte secondary battery.

Therefore, according to this means, in addition to the effects of the first to third means, it is possible to manufacture a non-aqueous electrolyte secondary battery that has little initial performance and is durable even at high temperatures. There is an effect that it becomes. (Fifth Means) A fifth means of the present invention is a nonaqueous electrolyte secondary battery according to the fifth aspect.

That is, this means is characterized in that any one of the above-described first to fourth means has a positive electrode active material on the positive electrode, so that any of the effects of each means is exhibited. That is, it is possible to provide a non-aqueous electrolyte secondary battery in which inexpensive manganese oxide is used as a main component of the positive electrode active material and whose charge / discharge characteristics are less deteriorated even when used in a high-temperature environment.

Therefore, according to the non-aqueous electrolyte secondary battery of the present means, it is possible to exhibit excellent durability even at a low price without a significant decrease in initial performance and for long-term use at high temperatures. effective. In addition, as the negative electrode active material of the nonaqueous electrolyte secondary battery of this means, in addition to lithium metal and lithium alloy, various materials capable of electrochemically absorbing and releasing lithium ions may be used. it can. For example, a carbon-based material such as graphite, coke, and an organic polymer compound, and a metal oxide such as SnO and TiO ₂ having a lower potential than the positive electrode active material can be used.

Further, the non-aqueous electrolyte secondary battery of this means
The electrolyte is limited to the non-aqueous electrolyte as described above.
However, lithium salt is used as the supporting electrolyte,
Non-aqueous electrolytes with dissolution dissolved in various organic solvents are typical
It is. Here, as the supporting electrolyte, for example, LiC
10_Four, LiBF_Four, LiPF₆, LiCF_ThreeSO_Three, L
iN (CF_ThreeSO_Two)_Two, LiN (C_TwoF_FiveSO_Two)_Two, Li
N (CF_ThreeSO_Two) (C _FourF₉SO_Two)
Can be. Among these, a supporting electrolyte containing fluorine is included.
In the mixed nonaqueous electrolyte, the positive electrode active material
Leaching of manganese from sediment is effective by elution suppression layer
The effect of this measure is remarkably exhibited
You. On the other hand, as the organic solvent of the non-aqueous electrolyte, for example,
Propylene carbonate, ethylene carbonate, 1,
2-dimethoxyethane, dimethyl carbonate, diethyl
Leucarbonate, ethyl methyl carbonate, tetrahi
Drofuran, 2-methyltetrahydrofuran, tetrahi
Dropyran or the like can be employed. Among these
In a non-aqueous electrolyte containing a carbonate-based organic solvent, 4 V
Since charging and discharging are performed at the relatively high voltage,
Manganese in most of the materials comes into contact with non-aqueous electrolyte
The effect of the non-aqueous electrolyte secondary battery of this means is notable
You.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the positive electrode active material and the nonaqueous electrolyte secondary battery of the present invention will be understood by those skilled in the art. A clear and thorough explanation will be made by contrasting the embodiment of the water electrolyte secondary battery with the comparative example. [Examples] (Example 1: A1) A positive electrode active material as a first example of the present invention and a nonaqueous electrolyte secondary battery having the same positive electrode active material as a positive electrode are as follows.
It was prepared as follows.

That is, first, 19.9 g of Li_TwoCO_Three
And 86.3 g of TiO_TwoAnd in a mortar, mix
A mixture having a ratio of Li / Ti = 1/2 (mixture 1) was prepared.
Was. Next, it was prepared by firing at 900 ° C in advance.
1.8 kg of Li_1.12Mn_1.88O_FourFor mixture 1
Add only 10.6g and mix in a mortar until uniform
Thus, a new mixture (mixture 2) was obtained. And the mixture
2 into an alumina crucible and 650 in air.
At 20 ° C. for 20 hours. _1.12M
n_1.88O_FourManganese oxide particles and the surface
Leaching is a coating made of overlying lithium-titanium composite oxide
A suppression layer was formed. At this time, Li _1.12Mn_1.88
O_FourWeight ratio of lithium-titanium composite oxide to water
Rate, that is, the blended weight of the manganese oxide and the elution suppression layer
The ratio is 1: 0.005 (0.5% by weight).

As a result, a manganese oxide particle containing manganese oxide as a main component, and a non-polymer coating covering the surface of the manganese oxide, and an elution suppressing layer for suppressing elution of manganese from the manganese oxide particle Was produced. Here, the manganese oxide is a substantially pure oxide of lithium and manganese, while the elution suppressing layer is a substantially pure lithium titanium composite oxide, that is, a lithium composite oxide with Ti. Further, the value of 1: 0.005 of the blending weight ratio of the manganese oxide and the elution suppressing layer corresponds to an intermediate value in the range of 1: 0.001 to 1: 0.01.

The diameter of the manganese oxide particles in the positive electrode active material is approximately 4 μm, and the thickness of the elution suppressing layer covering the surface of the particles is generally 0.003 to 0.003.
It is estimated by calculation to be 0.01 μm. Further, it is presumed that the elution suppressing layer covers most of the surface of the manganese oxide particles from the high capacity retention ratio of 88%.

In order to confirm the effect of the positive electrode active material of this example, a non-aqueous electrolyte secondary battery having the positive electrode active material as a positive electrode was prepared as follows. The positive electrode was first started by making a paste containing the positive electrode active material. That is, 86% by weight
Of the positive electrode active material of this example and 10% by weight as a conductive material
And 4% by weight of PV as a binder
DF (polyvinylidene fluoride) and N- as a solvent
A paste was prepared by dissolving in methyl-2-pyrrolidone. Thereafter, the paste is uniformly applied to one surface of a current collector made of aluminum foil with a predetermined weight and thickness, and after drying of the paste, the aluminum foil having the positive electrode active material held on one surface is removed. It was punched out into a disk having a diameter of 14 mm. Then, the positive electrode active material and the like held on the surface of the aluminum foil were pressed and somewhat compressed, followed by vacuum drying to prepare a positive electrode.

On the other hand, the negative electrode was prepared by punching a metallic lithium foil having a predetermined thickness into a disk having a diameter of 15 mm. A non-aqueous electrolyte as a non-aqueous electrolyte is prepared by adding LiPF ₆ as a solute electrolyte to a mixed solution of ethylene carbonate and diethyl carbonate mixed at a volume ratio of 3: 7.
Was dissolved at a rate of 1 mol / liter. As the separator, a polyethylene porous film having a thickness of 25 μm and a porosity of 40% was used.

Using the positive electrode, the negative electrode and the non-aqueous electrolyte prepared as described above, the container has a diameter of 20 μm.
A flat non-aqueous electrolyte secondary battery of the present invention having a thickness of 3.0 mm and a thickness of 3.0 mm was assembled to produce a non-aqueous electrolyte secondary battery A1 of Example 1. The main specifications of the non-aqueous electrolyte secondary battery A1 of Example 1 are as shown in Table 1 below.
And the weight ratio of the elution suppressing layer to the manganese oxide particles is 1: 0.005.
(0.5% by weight). Further, the initial discharge capacity per unit weight with respect to Comparative Example B9 in which bare manganese oxide was used as a positive electrode active material as described later was 97%.
Further, as a result of performing a charge / discharge cycle test, the capacity retention ratio with respect to the initial discharge capacity was 0.88 (88%), which was higher than any of the comparative examples described below. The charge / discharge cycle test was performed under the same conditions in each example and each comparative example. That is, the charge / discharge cycle test is performed in a high-temperature environment of 60 ° C. in a thermostat.
After charging to 4.3V at a charging current density of 0.5 mA / cm ^2, it was performed a test step of discharging at a discharging current density of 0.5 mA / cm ² to 3V as one cycle. And 5
The value obtained by dividing the discharge capacity at the 0th cycle by the initial discharge capacity is shown in Table 1 as the capacity retention of the nonaqueous electrolyte secondary battery.

[0030]

[Table 1]

(Example 2: A2) Example 2 is the same as Example 1 except that V ₂ O ₅ was used instead of TiO ₂ as one of the starting materials of the elution suppressing layer. That is,
In this example, 19.2 g of Li ₂ CO ₃ and 94.7 g of V ₂ O ₅ were uniformly mixed in a mortar, and a mixture of Li / V = １ ／ in a molar ratio as in Example 1. (Mixture 1) was prepared. Next, 11.8 g of the mixture 1 was added to 1.8 kg of Li _1.12 Mn _1.88 O ₄ prepared in advance by baking at 900 ° C., and the mixture was further mixed in a mortar until a uniform mixture was obtained. (Mixture 2) was obtained. Then, the mixture 2 was put into an alumina crucible, and 650 in air.
As a result of firing over 20 hours at ℃ temperature, Li _1.12 M
A manganese oxide particle composed of n _1.88 O ₄ and an elution suppressing layer, which is a coating composed of a lithium-vanadium composite oxide, covering the surface thereof were formed. At this time, Li _1.12 Mn
Mixing weight ratio of the lithium vanadium composite oxide to _1.88 O _4, i.e. the ratio by weight of manganese oxide and elution suppressing layer, the same 1 as in Example 1: 0.005 (0.5 wt%).

Except that the above-mentioned positive electrode active material is employed, the method of preparing the positive electrode and the method of preparing the non-aqueous electrolyte secondary battery A2 of Example 2 are the same as those of Example 1. It is. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. As a result, as shown in Table 1, the initial capacity per unit weight is 95%, which is about 2% less than that of Example 1 described above.
Further, the capacity retention ratio at the 50th cycle in the charge / discharge cycle test is 0.87, which is smaller than that of Example 1 by 0.01. However, the capacity retention ratio of the present example also marked a higher value than any of the later-described comparative examples.

(Example 3: A3) Example 3 is the same as Example 1 except that H ₂ WO ₄ was used instead of TiO ₂ as one of the starting materials of the elution suppressing layer. That is, in this example, 13.9 g of Li ₂ CO ₃ and 94.2 g
g of H ₂ WO ₄ were uniformly mixed in a mortar and, unlike in Example 1, a mixture having a molar ratio of Li / W = 1/1 (mixture 1)
It was created. Next, 11.8 g of the mixture 1 was added to 1.8 kg of Li _1.12 Mn _1.88 O ₄ prepared in advance by baking at 900 ° C., and further mixed in a mortar until uniform, and a new mixture was obtained. (Mixture 2) was obtained. And
The mixture 2 was charged into an alumina crucible, and calcined at 650 ° C. for 20 hours in air.
_A manganese oxide particle composed of _1.12 Mn _1.88 O ₄ and an elution suppression layer that covers the surface of the manganese oxide particle were formed of a lithium tungsten composite oxide. At this time, Li
The compounding weight ratio of the lithium tungsten composite oxide to _1.12 Mn _1.88 O ₄ , that is, the compounding weight ratio of the manganese oxide and the elution suppressing layer was the same as in Example 1, 1: 0.005.
(0.5% by weight).

Except for the use of the positive electrode active material described above, the method of preparing the positive electrode and the method of preparing the nonaqueous electrolyte secondary battery A3 of Example 3 are the same as those of Example 1. It is. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. As a result, as shown in Table 1, the initial capacity per unit weight is 96%, which is about 1% less than that of Example 1 described above.
Further, the capacity retention ratio at the 50th cycle in the charge / discharge cycle test is 0.87, which is smaller than that of Example 1 by 0.01. However, the capacity retention ratio of the present example also marked a higher value than any of the later-described comparative examples.

(Example 4: A4) Example 4 is the same as Example 1 except that MoO ₃ was used instead of TiO ₂ as one of the starting materials of the elution suppression layer. That is, in this embodiment, 22.0 g of Li ₂ CO ₃ and 85.9 are used.
g of MoO ₃ was uniformly mixed in a mortar to prepare a mixture (mixture 1) having a molar ratio of Li / Mo = 1/1 different from that of Example 1. Next, with respect to 1.8 kg of Li _1.12 Mn _1.88 O ₄ prepared in advance by firing at 900 ° C.,
10.8 g of the mixture 1 was added and further mixed in a mortar until uniform, to obtain a new mixture (mixture 2). Then, the mixture 2 was put into a crucible made of alumina, and calcined in the air at a temperature of 650 ° C. for 20 hours.
Manganese oxide particles comprising Li _1.12 Mn _1.88 O ₄ ,
An elution suppressing layer, which is a coating made of a lithium-molybdenum composite oxide, covering the surface was formed. At this time, L
The compounding weight ratio of the lithium molybdenum composite oxide to i _1.12 Mn _1.88 O ₄ , that is, the compounding weight ratio of the manganese oxide and the elution suppressing layer was 1: 0.005, the same as in Example 1.
(0.5% by weight).

Except for the use of the positive electrode active material described above, the method of preparing the positive electrode and the method of preparing the nonaqueous electrolyte secondary battery A4 of Example 4 are the same as those of Example 1. It is. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. As a result, as shown in Table 1, the initial capacity per unit weight is 96%, which is about 1% less than that of Example 1 described above.
Further, the capacity retention ratio at the 50th cycle in the charge / discharge cycle test is 0.87, which is smaller than that of Example 1 by 0.01. However, the capacity retention ratio of the present example also marked a higher value than any of the later-described comparative examples.

(Examples 5 to 12: A5 to A12) In the same manner as in Examples 1 to 4, the coating of the elution suppressing layer made of a lithium composite oxide with Ti, V, W or Mo was coated on the surface of lithium manganese oxide. And formed over it. Then, as shown in Table 1, the weight ratio of the coating to the lithium manganese oxide Li _1.12 Mn _1.88 O ₄ was 1: 0.001 (0.
1% by weight) or 1: 0.01 (1% by weight) to prepare a positive electrode active material of each example. These two types of mixed weight ratios have a lower limit and an upper limit in the range of 1: 0.001 to 1: 0.01, which is a desirable mixed weight ratio.

Further, in the same manner as in Example 1, a non-aqueous electrolyte secondary battery having a positive electrode formed by pressing each positive electrode active material or the like on one surface of a current collector made of an aluminum foil was used. 12 (A5 to A12) were prepared. The evaluation of these examples will be described later in the section of comparative evaluation. (Example 13: A13) The positive electrode active material of this example was obtained by adding Li ₂ CO _{3 to} one of the starting materials for forming the elution suppressing layer.
This embodiment differs from the first embodiment in that LiOH is used instead of

That is, in this embodiment, 12.9 g of L
iOH and 86.3 g of TiO ₂ were uniformly mixed in a mortar and, unlike in Example 1, the molar ratio was Li / Ti = 1/1.
(Mixture 1) was prepared. Next, 900
1.8 kg of Li _1.12 Mn prepared by baking at ℃
_{To 1.88} O ₄ , 9.92 g of Mixture 1 was added and further mixed in a mortar until uniform, to obtain a new mixture (Mixture 2). Then, the mixture 2 was put into an alumina crucible, and calcined in air at a temperature of 650 ° C. for 20 hours. As a result, a manganese oxide particle composed of Li _1.12 Mn _1.88 O ₄ and a lithium titanium covering the surface thereof An elution-suppressing layer, which is a coating made of a composite oxide, was formed.
At this time, the compounding weight ratio of the lithium titanium composite oxide to Li _1.12 Mn _1.88 O ₄ , that is, the compounding weight ratio of the manganese oxide and the elution suppressing layer was 1: 0.005 (0. 5% by weight).

The method for producing the nonaqueous electrolyte secondary battery A13 of Example 13 including the method for producing the positive electrode is the same as that in Example 1. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. The evaluation of this example (A13) will also be described in the section on comparative evaluation below. (Example 14: A14) The positive electrode active material of this example is also different from Example 3 in that LiOH was used as one of the starting materials for forming the elution suppression layer.

That is, in this embodiment, 16.4 g of L
iOH and 79.7 g of WO ₃ are evenly mixed in a mortar,
Different from Example 3, a mixture of Li / W = 2/1 (mixture 1) was prepared in a molar ratio. Then, 1.8 kg of Li _1.12 Mn _1.88 O prepared by baking at 900 ° C. in advance was prepared.
To _4, the mixture 1 was mixed until uniform with more mortar added only 9.61 g, to obtain a new mixture (mixture 2). Then, the mixture 2 is put into an alumina crucible,
As a result of calcining in air at 650 ° C. for 20 hours, a manganese oxide particle composed of Li _1.12 Mn _1.88 O ₄ and an elution suppression layer covering the surface thereof, which is a film composed of a lithium tungsten composite oxide, were formed. Formed. At this time, the compounding weight ratio of the lithium tungsten composite oxide to Li _1.12 Mn _1.88 O ₄ , that is, the compounding weight ratio of the manganese oxide and the elution suppressing layer was 1: 0.005 (0. 5% by weight).

The method of forming the non-aqueous electrolyte secondary battery A14 of the fourteenth embodiment, including the method of forming the positive electrode, is the same as that of the first embodiment. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. The evaluation of this example (A14) is also described in the section of comparative evaluation below. (Example 15: A15) The positive electrode active material of this example is also different from Example 4 in that LiOH was used as one of the starting materials for forming the elution suppression layer.

That is, in this embodiment, 24.8 g of L
iOH and 74.5 g of MoO ₃ were uniformly mixed in a mortar and, unlike in Example 4, the molar ratio was Li / Mo = 2/1.
(Mixture 1) was prepared. Next, 900
1.8 kg of Li _1.12 Mn prepared by baking at ℃
_{To 1.88} O ₄ , 9.93 g of Mixture 1 was added and further mixed in a mortar until uniform, to obtain a new mixture (Mixture 2). Then, the mixture 2 was put into an alumina crucible, and calcined in air at 650 ° C. for 20 hours. As a result, manganese oxide particles composed of Li _1.12 Mn _1.88 O ₄ and lithium molybdenum covering the surface thereof An elution-suppressing layer, which is a coating made of a composite oxide, was formed.
At this time, the compounding weight ratio of the lithium molybdenum composite oxide to Li _1.12 Mn _1.88 O ₄ , that is, the compounding weight ratio of the manganese oxide and the elution suppressing layer was 1: 0.005 (0. 5% by weight).

The method for producing the non-aqueous electrolyte secondary battery A15 of Example 15 including the method for producing the positive electrode is the same as that in Example 1. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. The evaluation of this example (A15) will also be described later in the section on comparative evaluation. [Comparative Examples] (Comparative Examples 1 to 8: B1 to B8) In the positive electrode active materials of Comparative Examples 1 to 8, Li _1.12 Mn _1.88 O ₄ is used for the manganese oxide particles, as in each of the above-described examples. Was. Similarly, as a starting material of the elution suppression layer, Li ₂ CO ₃ and an oxide containing four kinds of metal elements corresponding to Examples 1 to 4 are employed,
An elution suppressing layer made of a lithium-based composite oxide is formed. However, as shown in Table 1, the weight ratio of the elution-suppressing layer to the manganese oxide particles is set out of a desirable range (0.1 to 1% by weight).
It is 05% by weight or 5% by weight. Under these conditions, the positive electrode active materials of Comparative Examples 1 to 8 were produced. Since these positive electrode active materials do not satisfy the conditions of the above-described fourth means, but satisfy the conditions of the first to third means, they should be treated as working examples. But,
Comparative Examples 1 to 8 are slightly inferior to the above-mentioned respective examples which also satisfy the condition of the fourth means.

In addition to the method for producing the positive electrode, the method for producing the nonaqueous electrolyte secondary batteries B1 to B8 of Comparative Examples 1 to 8 is the same as that of Example 1. Further, the initial discharge capacity and the capacity retention rate were measured by the same test method as in Example 1. The evaluation of each of these comparative examples (B1 to B8) will be described later in the section on comparative evaluation. (Comparative Example 9: B9) The positive electrode active material of this comparative example employs Li _1.12 Mn _1.88 O ₄ for the manganese oxide particles as in the above-described Examples and Comparative Examples. There is no elution suppressing layer covering the surface of the particles. That is, the positive electrode active material of this comparative example is not an example of the present invention in a strict sense, and is a kind that can be called a conventional technology or a conventional technology. The non-aqueous electrolyte secondary battery B9 of this comparative example was prepared in the same manner as in each of the above-described Examples and Comparative Examples except that the positive electrode active material was different.

The initial discharge capacity of each of the examples and comparative examples shown in Table 1 is a value obtained by comparing the initial discharge capacity of the nonaqueous electrolyte secondary battery B9 of this comparative example with a reference value of 100%. . However, the capacity retention rate in the charge / discharge cycle test is a value calculated for each of the examples and the comparative examples, with the initial discharge capacity being 1 for each. [Comparative study] X-ray diffraction measurements were performed on the positive electrode active materials of each of the above Examples and Comparative Examples. The positive electrode active materials of all Examples differed from each other in changes in peak patterns and peak position shifts. Was not seen. That is, in all Examples and Comparative Examples 1 to 8, the same peak pattern and peak position as those of the positive electrode active material including only the manganese oxide particles composed of Li _1.12 Mn _1.88 O _{4 of} Comparative Example 9 were obtained. Therefore, L, which is the core of the positive electrode active material,
There is no structural change in the manganese oxide particles of i _1.12 Mn _1.88 O ₄ , and the surface of the manganese oxide particles is covered with the coating of the elution suppression layer composed of a lithium composite oxide with each of the added elements. It can be estimated that there is. When the table 1 is reviewed again based on the results of the X-ray diffraction measurement, the difference in performance between the nonaqueous electrolyte secondary batteries is caused by the difference in the elution suppression layer attached to the surface of the manganese oxide particles. You can think that there is.

That is, when the nonaqueous electrolyte secondary batteries (A1 to A4) of Examples 1 to 4 are compared with each other and examined, a positive electrode active material having a lithium titanium composite oxide elution suppressing layer is employed. The non-aqueous electrolyte secondary battery A1 exhibits the most excellent performance. That is, the non-aqueous electrolyte secondary battery A1
In (2), the initial discharge capacity is 97% of the reference B9, and the capacity retention as a result of the charge / discharge cycle test in a high-temperature atmosphere is 88% of the initial discharge capacity. That is, even in the result of the charge / discharge cycle test in a high temperature atmosphere, 97% × 88% = 85% as compared with the initial discharge capacity of B9.
% Of the discharge capacity, and exceeds the capacity retention rate of B9 of 74% by 11%.

Therefore, according to the non-aqueous electrolyte secondary battery A1 of Example 1, although the inexpensive manganese oxide is used as the main component of the positive electrode active material, the charge / discharge characteristics even when used in a high temperature environment are reduced. There is an effect that deterioration is reduced. Among the nonaqueous electrolyte secondary batteries A1 to A4 of Examples 1 to 4, the one having the lowest performance is A2 in which a dissolution suppression layer is formed of lithium vanadium oxide. Nevertheless, in the non-aqueous electrolyte secondary battery A2, the initial discharge capacity is inferior to B9 of 95%, but the capacity retention rate after the charge / discharge cycle test is 86%. Therefore, the non-aqueous electrolyte secondary battery A2 maintains a discharge capacity of 95% × 86% = 82%, which is 8% higher than the capacity maintenance ratio of B9 of 74%.
It was proved that the charge / discharge cycle characteristics at a high temperature were superior to Comparative Example 9 as a reference.

Further, the non-aqueous electrolyte secondary batteries A3 and A4 of Examples 3 and 4 using tungsten and molybdenum as additional elements of the elution suppressing layer have the same performance as each other. That is, the non-aqueous electrolyte secondary battery A
3, the initial discharge capacity of A4 was 96% of that of B9, and the capacity retention rate in the charge / discharge cycle test was 87%.
%. Therefore, the non-aqueous electrolyte secondary batteries A3 and A4 of Example 3 and Example 4 have intermediate performance between the non-aqueous electrolyte secondary battery A1 of Example 1 and the non-aqueous electrolyte secondary battery A2 of Example 2. And the charge / discharge cycle characteristics at high temperatures are also superior to Comparative Example 9 as a reference.

From the above examination, the elements to be added to the lithium composite oxide forming the elution suppressing layer include Ti, V,
It is clear that Ti is the best among W and Mo, and the charge / discharge cycle characteristics at high temperatures are extremely excellent. Next, the nonaqueous electrolyte secondary batteries A5, A1, and A6 in which the weight ratio of the elution suppression layer to the manganese oxide particles was 0.1%, 0.5%, and 1%, respectively, were compared with each other. Then, it became clear that the initial discharge capacity tends to be higher when the weight ratio of the elution suppressing layer is lower. However, it was revealed that the capacity retention rate in the charge / discharge cycle test tends to be higher when the weight ratio of the elution suppressing layer is higher. Considering the above, when the weight ratio of the elution suppressing layer is 0.1% by weight, the thickness of the elution suppressing layer is insufficient, or the surface of the manganese oxide particles not covered by the elution suppressing layer is large. It is presumed. As a result, the non-aqueous electrolyte secondary battery A in which the weight ratio of the elution suppression layer of the positive electrode active material is 0.1% by weight.
No. 5 has properties relatively similar to the non-aqueous electrolyte secondary battery B9 of Comparative Example 9 using manganese oxide particles composed of bare manganese lithium oxide as a positive electrode active material.

On the other hand, the maintained discharge capacity in the charge / discharge cycle test was 8% for each of the non-aqueous electrolyte secondary batteries A5, A1, and A6, with the initial discharge capacity of B9 being 100%.
0%, 85% and 87%. Therefore, if the weight ratio of the elution suppression layer is 0.1% by weight to 1% by weight, B9
80% of the initial discharge capacity in the charge / discharge cycle test
It became clear that the discharge capacity of the table was exhibited. Further, the weight ratio of the elution suppressing layer is 0.1% by weight to 1% by weight.
Within the range, the results of the 50 charge / discharge cycle tests were more excellent as the weight ratio of the elution suppressing layer was larger. However,
As in the non-aqueous electrolyte secondary battery B2 of Comparative Example 2, when the weight ratio of the elution suppressing layer is as much as 5% by weight, the result of the charge / discharge cycle test of 50 times is conversely reduced, but over a longer period. If a charge / discharge cycle test is performed, good results may be obtained. Further, as in the non-aqueous electrolyte secondary battery B1 of Comparative Example 1, when the weight ratio of the elution suppressing layer is only 0.05% by weight, the capacity retention ratio is low although the initial discharge capacity is high. Although it is not suitable for long-term use in a high-temperature environment, it can exhibit better results than B9. Therefore, if the operating temperature and the charge / discharge cycle life required for the nonaqueous electrolyte secondary battery are determined, it is considered that an appropriate value is naturally determined for the weight ratio of the elution suppressing layer to the manganese oxide particles.

Similarly, the non-aqueous electrolyte secondary batteries B3, A7, A2, A8, and B4 each having a positive electrode active material in which the elution suppressing layer is formed of a lithium vanadium composite oxide are compared with each other, and the above-described B1, A5 , A1, A6, and B2. A similar tendency is observed when non-aqueous electrolyte secondary batteries B5, A9, A3, A10, and B6 each having a positive electrode active material in which an elution suppression layer is formed of a lithium tungsten composite oxide are compared with each other. Further, non-aqueous electrolyte secondary batteries B7, A11, A4, A12, and B having a positive electrode active material in which an elution suppression layer is formed of a lithium-molybdenum composite oxide.
When 8 are compared with each other, a similar tendency is observed.

When Examples 13 to 15 are compared with Examples 1, 3, and 4, respectively, even if the molar ratio between the additive element and the lithium element of the lithium composite oxide forming the elution suppressing layer is different. It can be seen that there is no significant change in battery characteristics. Therefore, the non-aqueous electrolyte secondary battery having the positive electrode active material of the present invention as the positive electrode has a longer lifetime in a high-temperature environment than a non-aqueous electrolyte secondary battery using bare manganese oxide particles as the positive electrode active material. There is an effect that a large discharge capacity can be exhibited.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of a positive electrode active material of the present invention.

FIG. 2 is a graph showing high-temperature charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery of the present invention.

FIG. 3 is a graph showing the high-temperature storage characteristics of the non-aqueous electrolyte secondary battery of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Masaya Nakamura, Inventor 1-1-1, Showa-cho, Kariya, Aichi Prefecture (72) Inventor Jun Hasegawa 1-1-1, Showa-cho, Kariya, Aichi, Japan DENSO Corporation (72) Inventor Koichi Numata 1-5-1 Shiomachi, Takehara City, Hiroshima Prefecture Inside the Battery Materials Research Laboratories of Mitsui Kinzoku Mining Co., Ltd. (72) Inventor Shintaro Ishida 1-5-1, Shiomachi Takemura City, Hiroshima Prefecture Mining Co., Ltd. Battery Materials Laboratory F-term (reference) 5H003 AA03 AA04 AA07 BB04 BB05 BC01 BC05 BD04 5H014 AA02 EE10 HH01 5H029 AJ04 AJ05 AK02 AK03 AL12 AM05 AM07 BJ03 HJ01

Claims (5)

[Claims] 1. A manganese oxide particle containing manganese oxide as a main component, and a non-polymer coating covering a surface of the manganese oxide particle, the elution suppressing layer suppressing elution of manganese from the manganese oxide particle. And a positive electrode active material comprising: 2. The elution suppressing layer comprises Ti, V, Mo, W,
The positive electrode active material according to claim 1, wherein the positive electrode active material is mainly composed of a lithium composite oxide with one of Co and Ni. 3. The positive electrode active material according to claim 1, wherein said manganese oxide is one of a composite oxide of lithium and manganese and manganese dioxide. 4. The compounding weight ratio of said manganese oxide particles to said elution suppressing layer is from 1: 0.001 to 1: 0.01.
The positive electrode active material according to any one of claims 1 to 3. 5. A non-aqueous electrolyte secondary battery comprising the positive electrode active material according to claim 1 in a positive electrode.