JP2003086180A - Positive electrode active material of nonaqueous electrolyte secondary battery and secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material of a nonaqueous secondary battery having a high capacity and an excellent cycle characteristic. SOLUTION: The positive electrode active material of the nonaqueous secondary battery is a rhombic system LiMnO2 where manganese ions have an average oxidation number of not less than 3.03 nor more than 3.08, with a BET specific surface ration of 8 m<2> /g or more.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery positive electrode active material and a secondary battery using the same. Specifically, in orthorhombic LiMnO ₂ , the average oxidation number of manganese ions is 3.03 or more and 3.08 or less, and B
The present invention relates to a positive electrode active material having a high capacity and excellent cycle characteristics by setting the ET specific surface area to 8 m ² / g, and a secondary battery using the same.

[0002]

2. Description of the Related Art A 4-volt high energy density type lithium battery
As a positive electrode active material for a lithium secondary battery, LiMnO 2_TwoOther
LiCoO_Two, LiMn_TwoO_FourCan be used. Li
CoO _TwoBatteries using as a positive electrode active material are already on the market.
It However, cobalt has a small amount of resources and is expensive.
Therefore, it is not suitable for mass production due to the spread of batteries. Resource amount
Positive electrode materials with promising manganese compounds in terms of price
Is. Manganese dioxide, which can be used as a raw material, is currently dry.
It is inexpensive because it is mass-produced as a battery material.

The orthorhombic o-LiMnO ₂ has a 4 V region and 3
Although it is a compound having a charge / discharge profile in the V region,
In the charge / discharge behavior at room temperature, which has been conventionally reported, the capacity is very small at the beginning, for example, about 40 mAh / g, and the charge / discharge is gradually repeated until the capacity becomes 100 at about 50 cycles.
It shows a behavior of reaching mAh / g or more and reaching the maximum capacity. As described above, it was confirmed that the battery material has a small capacity, and particularly has a fatal defect that the capacity is low during the first several tens of cycles. To improve these behaviors and increase the capacity, stabilize the orthorhombic structure and stabilize the surface structure so that lithium ions can be diffused even by charging and discharging in a wide range of 4 to 3V. It is necessary to plan.

Regarding the structure stabilization, it has been found that the presence of a trace amount of Li ₂ MnO ₃ having a rock salt structure is suitable for the orthorhombic structure. The oxidation number of the manganese ion of Li ₂ MnO ₃ is 4, whereas the oxidation number of the manganese ion of LiMnO ₂ is 3. Therefore, the structure-stabilized LiMnO ₂ can be synthesized by controlling the average oxidation number of the manganese ion. It is necessary to plan.

[0005]

However, LiMn ₂ O ₄ having a spinel structure has a drawback that the capacity decreases with repeated cycles, and in order to improve this drawback, Mg and Z are added.
n addition (Thackeray et al., Solid State Ionics, 69, 59
(1994)) and addition of Co, Ni, Cr, etc. (Okada et al., Battery Technology, Vol.5, (1993)), and their effectiveness has already been clarified. However, when this addition is carried out, the capacity is lowered to 100 to 120 mAh / g, so that the energy density is lowered.

On the other hand, the capacity of orthorhombic LiMnO ₂ is 190 m.
Since it has a large capacity of Ah / g or more, it is known to be a positive electrode material having a higher energy density than spinel structure LiMn ₂ O ₄ . It is known that this compound has the following two kinds of materials by a synthetic method. That is, low temperature firing (LT, o-LiMnO ₂ ) and high temperature firing (H
T, o-LiMnO ₂ , and baked at 800 ° C. or higher). It is known that LT and o-LiMnO ₂ are fired at 450 ° C. or lower, but when used as a positive electrode, their structure changes to a spinel structure, so that the capacity decreases and the cycle characteristics are poor. For example JNReimers et al., J.
See Electrochem. Soc., 140, 3396 (1993).

It has been reported that HT and o-LiMnO ₂ also have good cycle characteristics between 4.4 V and 2.0 V at room temperature, but poor cycle characteristics at 55 ° C. For example YM Chiang et al., J. Electrochem. Solid-State
See Left., 2, 1 (1999). Therefore, it has been found that conventional firing alone does not provide a battery material having a high energy density.

The present invention was devised in view of the above points, and has an orthorhombic Li system having a high capacity and excellent cycle characteristics.
As a result of diligent study on MnO _2, it was found that the rock salt structure Li ₂ MnO ₃ as observed by the X-ray diffraction method was orthorhombic LiM.
The inventors have come to the finding that the structure of nO ₂ should be stabilized. Therefore, the present invention is based on this finding,
It is an object of the present invention to provide a non-aqueous solution secondary battery positive electrode active material having a high capacity and good cycle characteristics, and a secondary battery using the same.

To achieve the above object, the non-aqueous secondary battery positive electrode active material according to the present invention is an orthorhombic LiMn.
O ₂ , the average oxidation number of manganese ions of LiMnO ₂ is 3.03 or more and 3.08 or less, and BE
The T specific surface area is 8 m ² / g or more.

Here, it is difficult to synthesize orthorhombic LiMnO ₂ having an average oxidation number of manganese ions of less than 3.03, and if the average oxidation number of manganese ions exceeds 3.08, battery characteristics are deteriorated.

The BET specific surface area is 8 m ² /
If it is not more than g, the charge / discharge capacity of the battery cannot be sufficiently secured, so the amount is set to 8 m ² / g or more.

In the non-aqueous solution type secondary battery positive electrode active material according to the present invention, L is obtained by substituting a part of oxide ions of orthorhombic LiMnO ₂ with chloride ions or fluoride ions.
_{iMnO 2-X Z X (Z} = Cl or F, 0 <X <
0.10) and its orthorhombic LiMnO2 _- XZ.
The BET specific surface area of _X is 8 m ² / g or more.

When X ≧ 0.10, the orthorhombic structure cannot be provided and the cycle characteristics are greatly deteriorated. Therefore, X <0.10.

The BET specific surface area is 8 m ² /
If it is not more than g, the charge / discharge capacity of the battery cannot be sufficiently secured, so the amount is set to 8 m ² / g or more.

Further, the non-aqueous solution type secondary battery according to the present invention is positive.
The polar active material is orthorhombic LiMnO 2._TwoSome of the oxygen ions of
LiM substituted with chlorine ion or fluorine ion
nO _2-XZ_X(Z = Cl or F, 0 <X <0.1
0) and its orthorhombic LiMnO_2-XZ_XThe Ma
The average oxidation number of gangan ions is greater than 3.05 and 3.2.
Less than 5 and BET specific surface area of 8 m^Two/ G or more
There is something.

Here, if X ≧ 0.10, the structure cannot have an orthorhombic structure and the deterioration of the cycle characteristics is large, so that X <0.10 is the same as above.

Further, in this case, the orthorhombic structure is not stable when the average oxidation number of manganese ions is 3.25 or more, and conversely, the anion-doped orthorhombic structure in which the average oxidation number of manganese ions is 3.05 or less. Of crystalline LiMnO ₂ is difficult.

The BET specific surface area is 8 m ²
If it is not more than / g, the charge / discharge capacity of the battery cannot be sufficiently secured, so that it is set to 8 m ² / g or more as in the above.

[0019]

EXAMPLES Hereinafter, specific examples of the present invention will be described together with comparative examples with reference to the drawings for the understanding of the present invention, but it goes without saying that the present invention is not limited to these examples. Nor.

Example 1 Lithium hydroxide and Mn ₃ O ₄ were mixed and pulverized in a molar ratio of lithium and manganese of 1: 1. this,
It was heated at 1000 ° C. for 10 hours, taken out from the electric furnace, and immediately quenched in air. The X-ray diffraction diagram of this compound is shown in FIG.
Shown in. High-temperature orthorhombic LiMnO _{2 that} is highly crystalline by X-ray analysis has been obtained because of firing at high temperature. On the other hand, orthorhombic L
In addition to the iMnO ₂ peak, a small amount of Li ₂ MnO ₃ peak is recognized. The average oxidation number of manganese ion was larger than 3 and was 3.053. This compound was pulverized to obtain powders having different BET specific surface areas. The average oxidation number of manganese ions after milling is 3.053 to 3.05.
Rose to 6. A film-like mixture was prepared using 25 mg of the above sample and 10 mg of a conductive binder, and was pressed onto a stainless steel mesh to obtain a positive electrode. The positive electrode is 13
It was vacuum dried at 0 ° C. before use. Metallic lithium was used for the negative electrode, and LiPF ₆ -EC • DMC (volume ratio 1:
2) was used. Charge / discharge current is 1mA (0.4mA / cm
² ) and the charge / discharge voltage range was 4.3 to 2.0V.
The charge / discharge test was performed at 50 ° C. Examples below,
All the evaluations in the comparative examples are based on the above conditions. B
The relationship between the ET specific surface area and the first charge / discharge capacity was as follows. That is, BET specific surface area 8, 10, 13, 1
The first charge / discharge capacity between 4.3 and 2.0 V of 5 m ² / g of the active material was 190, 210, 200, 205 mAh.
/ G. From this, it is understood that the BET specific surface area is preferably 8 m ² / g or more.

Example 2 Sodium hydroxide and Mn ₃ O ₄ were mixed and pulverized in a molar ratio of lithium and manganese of 1: 1. this,
It was heated at 1050 ° C. for 10 hours, taken out of the electric furnace, and immediately cooled in air. In the X-ray diffraction pattern of this compound, in addition to the orthorhombic LiMnO ₂ peak, a very small amount of Li ₂ Mn
A peak of O ₃ was observed. Therefore, the average oxidation number of manganese ions was 3.308, which was greater than 3. This compound was pulverized to obtain a powder having a BET specific surface area of 11 m ² / g and an average oxidation number of manganese ion of 3.041. The results of the charge / discharge cycle test are shown in FIG. Good cycle characteristics are exhibited at both 25 ° C and 50 ° C.

Example 3 Lithium hydroxide, Mn ₃ O ₄ and LiF were mixed and pulverized in a molar ratio of lithium: manganese: fluoride of 1: 1: 0.05. This was heated at 1050 ° C. for 10 hours, taken out from the electric furnace, and immediately quenched in air. This compound was pulverized to obtain a BET specific surface area of 11 m ² /
Thus, a powder having an average oxidation number of manganese ions of 3.21 was obtained. 220 mA / g capacity as a result of charge / discharge cycle test
At 25 ° C. and 50 ° C., good cycle characteristics were exhibited. In the case of orthorhombic LiMnO ₂ doped with fluoride ions or chloride ions, when the average oxidation number of manganese ions is 3.25 or more, the orthorhombic structure is not stable and a large amount of Li ₂ MnO ₃ is contained. It forms and mixes into the orthorhombic system. Or spinel phase is mixed. In this case, since the capacity is low and the cycle characteristics are poor, the battery characteristics are deteriorated. Therefore, the average oxidation number of manganese ion is 3.
It is preferably less than 25. Further, it is difficult to synthesize anion-doped orthorhombic LiMnO ₂ having an average oxidation number of manganese ions of 3.05 or less. Further, when X ≦ 0.10, the orthorhombic structure could not be formed, and the cycle characteristics were significantly deteriorated.

Comparative Example 1 Lithium hydroxide and Mn ₃ O ₄ were mixed and pulverized in a molar ratio of lithium and manganese of 1: 1. This one
It was heated at 100 ° C. for 10 hours, taken out of the electric furnace, and immediately cooled in air. In the X-ray diffraction pattern of this compound, in addition to the orthorhombic LiMnO ₂ peak, a little more Li ₂ Mn
A peak of O ₃ was observed. Therefore, the average oxidation number of manganese ions was 3.149, which was considerably higher than 3.
The first-time discharge capacity of this compound was as small as 40 mAh / g, and the capacity after 50 cycles was 100 mAh / g or less. When the average oxidation number of manganese ions exceeds 3.08, the orthorhombic structure is not stable and Li ₂ MnO
_A large amount of ₃ is generated and mixed into the orthorhombic system. Or spinel phase is mixed. In this case, since the capacity is low and the cycle characteristics are poor, the battery characteristics are deteriorated. Therefore, the average oxidation number of manganese ions is preferably 3.08 or less.
Further, it is difficult to synthesize orthorhombic LiMnO ₂ having an average oxidation number of manganese ions of less than 3.03. In addition, the first active material having a BET specific surface area of 8 m ² / g is 4.3 to 2.0 V for the first time.
Discharge capacity is 150 mAh / g, surface area 8 m ²
/ G is the limit, and if it is smaller than this, the initial capacity decreases sharply. Therefore, it is understood that the BET specific surface area is preferably 8 m ² / g or more as described above.

Comparative Example 2 Lithium hydroxide and Mn_ThreeO_FourAnd lithium and manga
The mixture is ground in a molar ratio of 1: 1. This is 9
Heat at 50 ° C for 10 hours, remove from electric furnace and immediately
Quenched in air. The X-ray diffraction diagram of this compound shows
LiMnO_TwoIn addition to the peak of _TwoMnO_Threeof
A peak was observed. Therefore, the average acid of manganese ion
The chemical number was 3.067, which was slightly larger than 3. That B
ET specific surface area is 0.6m^Two/ G. Use this substance
The battery charge / discharge cycle diagram is shown in FIG. Oxidation number is appropriate
However, if the BET specific surface area is small, the charge at room temperature is
Pond characteristics are inferior as shown below. That is, as shown in FIG.
Therefore, the initial discharge capacity at 25 ° C is considerably low.
It was 40 mAh / g. 130m after 100 cycles
The value was considerably small at about Ah / g. However, at high temperature
The battery characteristics were good as shown in FIG.

Next, a method for measuring the average oxidation number of manganese ion will be described. First, LiMnO ₂ is dissolved with an acid or the like, and the total amount of manganese is measured by the chelate titration method. Separately, the average oxidation number of manganese ion was determined by the redox method. The redox method was basically Ozawa's method. A. Kozaw
a, Memories of the Faculty of Engineering, Nagoya Un
iversity, vol.11 (see No.1-2,243 (1959)). That is, the sample was dissolved in a sulfuric acid acidic FeSO ₄ solution having a known iron concentration, and the residual Fe (divalent) ion concentration was titrated with a KMnO ₄ solution having a known concentration. The average oxidation number was obtained from these analysis results.

As shown in Examples 1, 2 and 3, the non-aqueous secondary battery positive electrode active material according to the present invention has excellent cycle characteristics and a capacity of about 190 mAh / g or more. I understand. Further, since it has a voltage plateau in the 3V region, the battery can operate the device at the time when the voltage reaches the 3V region, and can also be used as a trigger to start charging, and an action as a kind of fuel gauge can be expected. It is a thing.

[0027]

As described above, according to the present invention,
The conventional orthorhombic LiMnO ₂ has a small initial capacity, and it requires several tens of charge / discharge cycles to reach a certain capacity.
In addition, the discharge capacity is small, and the capacity can be increased, and the charging / discharging cycle can be improved. In particular, the substitution of Cl ⁻ and F ⁻ ions succeeded in controlling the oxidation number of manganese ions. Further, since it can operate in a wide voltage range, it can be used as a battery material in many fields such as a high energy density power storage battery.

Further, according to the present invention, since the voltage plateau is in the 3V region, when the battery voltage reaches 3V,
It also has an effect that it can also serve as a fuel gauge for the battery, such as by generating a trigger for starting charging.

[Brief description of drawings]

1 is an X-ray diffraction diagram of LiMnO ₂ of Example 1. FIG.

FIG. 2 (a) is a graph of LiMnO ₂ of Example ₂ of 25.
It is a graph showing the relationship between voltage and capacity on a charge-discharge curve at ° C, and the numbers in the figure show the number of cycles. Figure below (b)
4 is a graph showing the relationship between the discharge capacity and the number of cycles of LiMnO ₂ of Example 2 at 25 ° C. and 50 ° C.

FIG. 3 is a graph showing the relationship between the discharge capacity and the number of cycles of LiMnO ₂ of Comparative Example 2 at 25 ° C. (a) and 50 ° C. (b).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Lee Yong-jo             5147 Honjo, Honjo, Honjo-cho, Saga City, Saga Prefecture             Uscoat 317 (72) Inventor Kazuyuki Adachi             2-82 Watanabe Dori, Chuo-ku, Fukuoka-shi, Fukuoka               Kyushu Electric Power Co., Inc. F-term (reference) 4G048 AA04 AB05 AC06 AD06 AE05                 5H029 AJ03 AJ05 AK03 AL12 AM03                       AM05 AM07 DJ17 HJ00 HJ02                       HJ07                 5H050 AA07 AA08 BA15 BA16 CA09                       CB12 FA19 HA00 HA02 HA07

Claims (4)

[Claims] 1. An orthorhombic LiMnO ₂ having an average oxidation number of manganese ions of the orthorhombic LiMnO ₂ of 3.03 or more and 3.08 or less, and BET thereof.
A non-aqueous secondary battery positive electrode active material having a specific surface area of 8 m ² / g or more. 2. LiMnO _2−X Z _X (Z = Cl or F, 0 <X <, in which a part of oxide ions of orthorhombic LiMnO ₂ is substituted with chloride ions or fluoride ions.
A 0.10), BET specific surface area of the swash orthorhombic system _{LiMnO 2-X Z} X 8
A non-aqueous secondary battery positive electrode active material, characterized in that it is at least m ² / g. 3. LiMnO _2−X Z _X (Z = Cl or F, 0 <X <, in which a part of oxygen ions of orthorhombic LiMnO ₂ is substituted with chloride ions or fluoride ions.
0.10), the average oxidation number of the manganese ion of the orthorhombic LiMnO _{2 -X} Z _X is more than 3.05 and less than 3.25, and the BET specific surface area is 8 m ² / g or more. A non-aqueous secondary battery positive electrode active material characterized by being present. 4. A non-aqueous solution secondary battery, which is made of the non-aqueous solution secondary battery positive electrode active material according to claim 1, claim 2, or claim 3.