JP2002308626A - Method for manufacturing spinel type lithium manganate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing spinel type lithium manganate, by which the high temperature properties of a battery such as high temperature preservation properties or high temperature cycle property is improved. SOLUTION: The spinel type lithium manganate is manufactured by adding phosphoric acid in an electrolyte, pulverizing manganese dioxide electrodeposited in the presence of phosphoric acid, neutralizing the resultant manganese dioxide with the phosphoric acid with sodium hydroxide or sodium carbonate to adjust the pH to >=2, mixing the electrodeposited manganese dioxide having >=50 m<2> /g specific surface area and containing 0.1-1 wt.% phosphor with a lithium raw material and firing the mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spinel-type lithium manganate, and more particularly, to a method for producing a positive electrode material for a non-aqueous electrolyte secondary battery, which suppresses the amount of Mn eluted,
The present invention relates to a method for producing a spinel-type lithium manganate having improved high-temperature characteristics of a battery such as high-temperature storage characteristics and high-temperature cycle characteristics.

[0002]

2. Description of the Related Art With the rapid progress of portable and cordless personal computers and telephones in recent years, the demand for secondary batteries as power sources for driving them has been increasing. Among them, non-aqueous electrolyte secondary batteries are particularly expected because they have the smallest size and high energy density. Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ) are used as the positive electrode material of the non-aqueous electrolyte secondary battery satisfying the above requirements.
Etc. Since these composite oxides have a voltage of 4 V or more with respect to lithium, a battery having a high energy density can be obtained.

[0003] Among the above composite oxides, LiCoO ₂ and LiNiO ₂ have a theoretical capacity of about 280 mAh / g, while LiMn ₂ O ₄
Is small at 148 mAh / g, but is considered to be suitable for EV applications because it is abundant and inexpensive with manganese oxide as a raw material and does not have thermal instability during charging like LiNiO _2. I have.

However, this lithium manganate (L
Since iMn ₂ O ₄ ) elutes Mn at a high temperature, there is a problem that the battery characteristics at a high temperature such as a high-temperature storage property and a high-temperature cycle characteristic are inferior.

Accordingly, an object of the present invention is to provide a positive electrode material for a non-aqueous electrolyte secondary battery, which suppresses the amount of Mn elution during charging and improves battery characteristics at high temperatures such as high-temperature preservability and high-temperature cycle characteristics. Another object of the present invention is to provide a method for producing spinel-type lithium manganate, a cathode material comprising the lithium manganate, and a non-aqueous electrolyte secondary battery using the cathode material.

[0006]

Various manganese compounds have been studied as a manganese raw material for spinel-type lithium manganate. Since electrolytic manganese dioxide is inexpensive and abundant, it is suitable as a manganese raw material for spinel-type lithium manganate. As a positive electrode active material of a lithium primary battery, a material obtained by firing electrolytic manganese dioxide having a high specific surface area at a specific temperature is used. The specific surface area of this electrolytic manganese dioxide depends on the electrolytic conditions. As one of the methods, there is a method in which phosphoric acid is added to an electrolytic solution during electrolysis to perform electrolysis, and it is known that a small amount of phosphorus remains in electrolytic manganese dioxide. Soda neutralization is applied to alkaline manganese batteries. It is known that a small amount of sodium remains in soda-neutralized electrolytic manganese dioxide, and the amount of sodium depends on neutralization conditions.

The present inventors have focused on the specific surface area, phosphorus content and neutralization conditions of electrolytic manganese dioxide, and by specifying these, the obtained spinel-type lithium manganate can achieve the above object. Was found.

The present invention has been made based on the above findings. The first invention of the method for producing spinel-type lithium manganate is characterized in that phosphoric acid is added to an electrolytic solution and electrolytic deposition is performed in the presence of phosphoric acid. After pulverizing manganese dioxide, it is neutralized with sodium hydroxide or sodium carbonate to adjust the pH to 2 or more, the specific surface area is 50 m ² / g or more, and the phosphorus content is 0.1 to 1% by weight. A method for producing spinel-type lithium manganate, comprising mixing electrolytic manganese dioxide and a lithium raw material, followed by firing.

A second invention is characterized in that, in the first invention, the amount of phosphoric acid added to the electrolyte is less than 3 g / l.

A third invention is characterized in that, in the first or second invention, the calcination is performed at 750 ° C. or higher.

A fourth invention is characterized in that, in any one of the first to third inventions, the manganese dioxide after pulverization has an average particle size of 5 to 30 μm. Manufacturing method.

A fifth invention of a cathode material for a non-aqueous electrolyte secondary battery is characterized by comprising the spinel-type lithium manganate obtained by any one of the first to fourth inventions.

The invention of a fifth non-aqueous electrolyte secondary battery is characterized by comprising a positive electrode using the fourth positive electrode material, a negative electrode capable of inserting and extracting lithium and a non-aqueous electrolyte.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, electrolytic manganese dioxide is used as a manganese raw material for spinel-type lithium manganate.

The electrolytic manganese dioxide in the present invention is obtained by the following method. Using a manganese sulfate solution of a predetermined concentration as the electrolytic solution, using a carbon plate for the cathode and a titanium plate for the anode, performing electrolysis at a constant current density while heating,
Manganese dioxide is electrodeposited on the anode. At this time, a predetermined phosphoric acid is added to the electrolytic solution. Next, the deposited manganese dioxide is peeled off from the anode and pulverized to a predetermined particle size.

Here, the amount of phosphoric acid added to the electrolytic solution during electrolysis is preferably less than 3 g / l, more preferably 0.2 to 2 g / l. This is because if it is 3 g / l or more, the initial discharge capacity decreases, which is not preferable.

Here, the pulverized manganese dioxide is preferably pulverized to an average particle size of 5 to 30 μm. This is preferable because the finer the particle size, the better the current load factor is. On the other hand, when the average particle size exceeds 30 μm, cracks and the like are generated in the film formed as the positive electrode material, and it is difficult to form a uniform film thickness. Because.

The electrolytic manganese dioxide ground to a predetermined particle size is neutralized with sodium, washed with water and dried. As the sodium neutralization, specifically, it is neutralized with sodium hydroxide or sodium carbonate. The order of pulverization and neutralization is not particularly limited, and pulverization may be performed after neutralization.

The pH of the neutralized electrolytic manganese dioxide is 2
As mentioned above, it is preferably 2 to 5.5, more preferably 2 to 4. The higher the pH, the lower the Mn elution amount at high temperatures, but the lower the initial discharge capacity. If the pH is less than 2, the effect is insufficient.

The specific surface area of this electrolytic manganese dioxide is 50
m ² / g or more. When the specific surface area is 50 m ² / g or less, the reactivity with the lithium raw material is deteriorated, and a uniform product cannot be obtained. Specific surface area is 50m ² /
Even if electrolytic manganese dioxide of g or more does not contain sodium, uniform spinel-type lithium manganate can be obtained, but the specific surface area of the obtained spinel-type lithium manganate also increases. Therefore, the reaction area with the electrolytic solution also increases, and the amount of Mn eluted is not reduced. Then, sodium is neutralized, and sodium remains in the electrolytic manganese dioxide, so that sodium is also uniformly dispersed and reacted, so that the amount of Mn eluted is reduced.

The specific surface area of the electrolytic manganese dioxide is 5
To increase the current density to 0 m ² / g or more, it is possible to increase the current density during electrolysis or to lower the concentration of the electrolyte, the concentration of the acid, and the temperature. Difficult. Therefore, in the present invention, the specific surface area can be continuously adjusted to 5 by understanding the presence of phosphoric acid in the electrolytic solution.
Electrolytic manganese dioxide of 0 m ² / g or more can be electrolytically deposited. At this time, phosphorus remains in the electrolytic manganese dioxide. Although the effect is unknown, it reduces the amount of Mn eluted. As content in electrolytic manganese dioxide
0.1-1% by weight is preferred. This is because if it exceeds 1% by weight, the initial capacity decreases.

In the present invention, this electrolytic manganese dioxide is mixed with a lithium raw material and fired to obtain a spinel type lithium manganate. Examples of the lithium raw material include lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), and lithium hydroxide (LiOH). The Li / Mn molar ratio between the electrolytic manganese dioxide and the lithium raw material is preferably 0.50 to 0.60.

These electrolytic manganese dioxide and lithium raw materials are preferably ground before or after mixing the raw materials in order to obtain a larger reaction area. The weighed and mixed raw materials may be used as they are or may be granulated. The granulation method may be wet or dry, and may be extrusion granulation, tumbling granulation, flow granulation, mixing granulation, spray drying granulation, pressure molding granulation, or flake granulation using a roll or the like. .

The raw material thus obtained is put into a firing furnace and fired at 600 to 1000 ° C. to obtain a spinel type lithium manganate. A temperature of about 600 ° C. is sufficient to obtain a single-phase spinel-type lithium manganate, but a firing temperature of 750 ° C. or higher, preferably 850 ° C. or higher is necessary because a low firing temperature does not promote grain growth. Becomes Examples of the firing furnace used here include a rotary kiln and a stationary furnace. The firing time is 1 hour or more, preferably 5 to 20 hours.

Thus, a spinel-type lithium manganate containing a certain amount of sodium is obtained. The content of sodium is preferably from 0.07 to 2.5% by weight. This sodium-containing spinel-type lithium manganate is used as a positive electrode material of a nonaqueous electrolyte secondary battery.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode material, a conductive material such as carbon black, and a binder such as Teflon (registered trademark) are mixed to form a positive electrode mixture, and Is made of a material capable of occluding and desorbing lithium such as lithium or carbon. As a non-aqueous electrolyte, a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent such as ethylene carbonate-dimethyl carbonate. However, there is no particular limitation.

Since the non-aqueous electrolyte secondary battery of the present invention can suppress the elution of manganese in a charged state, the battery characteristics at high temperatures such as high-temperature storage and high-temperature cycle characteristics can be improved.

[0028]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and the like, but the present invention is not particularly limited thereto.

Example 1 As a manganese electrolyte, sulfuric acid was used.
Acid concentration 30 g / l, manganese concentration 50 g / l, phosphoric acid 0.
A 5 g / l manganese sulfate aqueous solution was prepared. This electrolyte
Is heated to 95 ° C., and the carbon is
60A / m using titanium plate for plate and anode ^TwoCurrent density
Electrolysis was performed. Next, the manganese dioxide manganese electrodeposited on the anode
And crushed into chips of 7 mm or less.
The chips were ground to an average particle size of about 20 μm.

10 kg of this manganese dioxide was washed with 20 liters of water, and after washing water was discharged, 20 liters of water was added again. Here, 110 g of sodium hydroxide was dissolved, neutralized for 24 hours with stirring, washed with water, filtered,
It was dried (50 ° C., 12 hours). About the obtained powder, p measured according to JISK14677-1984
Table 1 shows the H, sodium content, specific surface area and P content.

Lithium carbonate was added to 1 kg of this manganese dioxide having an average particle size of about 20 μm and mixed so that the Li / Mn molar ratio became 0.54. Lithium manganate was obtained. The spinel-type lithium manganate obtained in this manner is
By weight, 15 parts by weight of carbon black as a conductive agent and 5 parts by weight of polytetrafluoroethylene as a binder were mixed to prepare a positive electrode mixture.

Using this positive electrode mixture, a coin-type nonaqueous electrolyte secondary battery shown in FIG. 1 was produced. That is, the current collector 3 also made of stainless steel is spot-welded inside the positive electrode case 1 made of stainless steel having resistance to organic electrolyte.
On the upper surface of the current collector 3, a positive electrode 5 made of the above positive electrode mixture is pressed. On the upper surface of the positive electrode 5, a separator 6 made of microporous polypropylene resin impregnated with an electrolytic solution is arranged. At the opening of the positive electrode case 1, a sealing plate 2 to which a negative electrode 4 made of metallic lithium is joined is disposed below a gasket 7 made of polypropylene, whereby the battery is sealed. The sealing plate 2 also serves as a negative electrode terminal,
It is made of the same stainless steel as the positive electrode case 1. The diameter of the battery is 20 mm, and the total height of the battery is 1.6 mm. In the electrolyte,
A solution obtained by mixing ethylene carbonate and 1,3-dimethoxyethane in equal volumes was used as a solvent, and a solution in which lithium hexafluorophosphate was dissolved at 1 mol / liter as a solute was used.

The battery thus obtained was subjected to a charge / discharge test. The charge / discharge test is performed at 20 ° C.
The current density was 0.5 mA / cm ² , and the voltage was 4.3 V to 3.0 V.
Performed in the range of V. Also charge this battery at 4.3V,
After storing for 3 days in an environment of 80 ° C., the storage characteristics of the batteries were confirmed using the discharge capacity of these batteries as the capacity retention ratio.
Table 1 shows the measurement results of the initial discharge capacity and the high-temperature storage capacity retention rate.

Example 2 A spinel-type lithium manganate was synthesized in the same manner as in Example 1, except that the amount of sodium hydroxide added during neutralization of electrolytic manganese dioxide was changed to 45 g. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 using the spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention were measured. "

Example 3 A spinel-type lithium manganate was synthesized in the same manner as in Example 1, except that the amount of sodium hydroxide added during neutralization of electrolytic manganese dioxide was changed to 75 g. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

Example 4 Except that the amount of sodium hydroxide added during the neutralization of electrolytic manganese dioxide was 140 g,
In the same manner as in Example 1, spinel-type lithium manganate was synthesized. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

<Example 5> Except that the amount of sodium hydroxide added during the neutralization of electrolytic manganese dioxide was 200 g,
In the same manner as in Example 1, spinel-type lithium manganate was synthesized. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

<Example 6> Except that the amount of sodium hydroxide added during the neutralization of electrolytic manganese dioxide was 280 g,
In the same manner as in Example 1, spinel-type lithium manganate was synthesized. Table 1 shows the pH, sodium content, and specific surface area after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

Example 7 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the amount of phosphoric acid added to the electrolytic solution during electrolysis was 0.2 g / l. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

<Example 8> A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the amount of phosphoric acid added to the electrolytic solution during electrolysis was 2 g / l. P after neutralization
Table 1 shows the H, sodium content, specific surface area and P content. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

Example 9 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the firing temperature was 900 ° C. Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. Further, the spinel-type lithium manganate was used as a cathode material in Example 1
A coin-type non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial discharge capacity and the high-temperature storage capacity retention rate were measured. The results are shown in Table 1.

Example 10 A spinel-type lithium manganate was synthesized in the same manner as in Example 1, except that the firing temperature was 750 ° C. PH after neutralization, sodium content,
Table 1 shows the specific surface area and the P content. Further, a coin-type nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material,
The initial discharge capacity and the high-temperature storage capacity retention rate were measured, and the results are shown in Table 1.

Comparative Example 1 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the amount of phosphoric acid added to the electrolytic solution during electrolysis was changed to 0 g / l. P after neutralization
Table 1 shows the H, sodium content, specific surface area and P content. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

Comparative Example 2 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the amount of phosphoric acid added to the electrolytic solution during electrolysis was 3 g / l. P after neutralization
Table 1 shows the H, sodium content, specific surface area and P content. In addition, a coin-type nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 using this spinel-type lithium manganate as a positive electrode material, and the initial discharge capacity and the high-temperature storage capacity retention ratio were measured. "

Comparative Example 3 A spinel-type lithium manganate was synthesized in the same manner as in Comparative Example 1, except that the electrolytic manganese dioxide was not neutralized (addition amount of sodium hydroxide was 0 g). Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. Further, the spinel-type lithium manganate was used as a cathode material in Example 1
A coin-type non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial discharge capacity and the high-temperature storage capacity retention rate were measured. The results are shown in Table 1.

Comparative Example 4 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the electrolytic manganese dioxide was not neutralized (the amount of sodium hydroxide added was 0 g). Table 1 shows the pH, sodium content, specific surface area, and P content after neutralization. Further, the spinel-type lithium manganate was used as a cathode material in Example 1
A coin-type non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and the initial discharge capacity and the high-temperature storage capacity retention rate were measured. The results are shown in Table 1.

[0047]

[Table 1]

<Example 11> A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the average particle size of the electrolytic manganese dioxide during pulverization was 5 µm. Using this spinel-type lithium manganate as a positive electrode material, a coin-type nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1, and evaluated at two types of current densities, 0.5 mA / cm ² and 1.0 mA / cm ² . And discharge capacity at a current density of 0.5 mA / cm ² to 100
The discharge capacity ratio at 1.0 mA / cm ² was expressed as a current load ratio. Table 2 shows the current load ratio.

Example 12 The same evaluation as in Example 11 was performed on the coin-type nonaqueous electrolyte secondary battery manufactured in Example 1. Table 2 shows the current load ratio.

Example 13 A spinel-type lithium manganate was synthesized in the same manner as in Example 1 except that the average particle size of the electrolytic manganese dioxide during pulverization was 30 μm. Using this spinel-type lithium manganate as a positive electrode material, a coin-type nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1,
The same evaluation as in Example 11 was performed. Table 2 shows the current load ratio.

Comparative Example 5 A spinel-type lithium manganate was synthesized in the same manner as in Example 1, except that the average particle size of the electrolytic manganese dioxide at the time of pulverization was 35 μm. Example 1 using this spinel-type lithium manganate as a cathode material
A coin-type non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 and evaluated in the same manner as in Example 11. Table 2 shows the current load ratio.

[0052]

[Table 2]

[0053]

As described above, by using the spinel-type lithium manganate obtained by the production method of the present invention as a positive electrode material for a non-aqueous electrolyte secondary battery, the amount of Mn elution during charging can be suppressed, Battery characteristics at high temperatures such as high-temperature storage characteristics and high-temperature cycle characteristics can be improved, and the current load factor can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type nonaqueous electrolyte secondary battery of an example and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode case 2 Sealing plate 3 Current collector 4 Metal negative electrode 5 Positive electrode 6 Separator 7 Gasket

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Numata 1-5-1, Shiomachi, Takehara City, Hiroshima Prefecture Inside Battery Materials Research Laboratory, Mitsui Kinzoku Mining Co., Ltd. Matsushita Electric Industrial Co., Ltd. ) 4G048 AA04 AB01 AB02 AB05 AC06 AD04 AD06 AE05 5H029 AJ04 AJ05 AK03 AL06 AL12 AM04 AM05 AM07 BJ03 CJ02 CJ08 CJ14 EJ01 EJ04 EJ12 HJ01 HJ05 HJ07 HJ10 HJ14 5H050 AA05 AA07 GA10 BA16 GA10

Claims (6)

[Claims] 1. A phosphoric acid is added to an electrolytic solution, manganese dioxide electrolytically precipitated in the presence of phosphoric acid is pulverized, then neutralized with sodium hydroxide or sodium carbonate to a pH of 2 or more, and its specific surface area Of spinel-type lithium manganate, characterized in that electrolytic manganese dioxide having a phosphorus content of 50 m ² / g or more and a phosphorus content of 0.1 to 1% by weight and a lithium raw material are mixed and fired. Method. 2. The method according to claim 1, wherein the amount of phosphoric acid added to the electrolytic solution is less than 3 g / l. 3. The method according to claim 1, wherein the calcination is performed at 750 ° C. or higher. 4. The manganese dioxide according to claim 1, wherein the manganese dioxide has an average particle size of 5 to 30 μm.
A method for producing spinel-type lithium manganate, characterized in that: 5. A positive electrode material for a non-aqueous electrolyte secondary battery, comprising a spinel-type lithium manganate obtained by the production method according to claim 1. Description: 6. A non-aqueous electrolyte secondary battery comprising a positive electrode using the positive electrode material according to claim 5, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte.