JP3029889B2 - Manganese dioxide for lithium secondary battery and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an .alpha.-type manganese dioxide used as an anode active material of a lithium secondary battery and a method for producing the same.

[0002]

2. Description of the Related Art As a positive electrode active material of a lithium primary battery using lithium or a lithium alloy as a negative electrode active material, manganese dioxide, carbon fluoride and the like are known as typical ones, and these have already been put to practical use. .

[0003] Among such anode active materials, manganese dioxide, in particular, has the advantage of being excellent in preservability and inexpensive.

However, when manganese dioxide, which is currently used as an anode active material of a lithium primary battery, is used as an anode active material of a lithium secondary battery, reproducibility of charge / discharge cycles is poor and sufficient characteristics are not obtained. At present, there is no secondary battery available.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and provides a manganese dioxide which can be used for an anode active material of a lithium secondary battery and has high performance, and a method for producing the same. The ultimate purpose is to significantly increase the discharge capacity of the lithium secondary battery.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by obtaining a certain amount of ammonia and lithium-containing α-type manganese dioxide which is further heat-treated and used as an anode active material of a lithium secondary battery.

That is, according to the present invention, ammonia is added at a concentration of 0.2%.
Α-manganese dioxide for a lithium secondary battery, characterized in that the α-manganese dioxide contains 1.0 to 3.5% by weight of lithium and 1.0 to 3.5% by weight of lithium.

[0008] The α-type manganese dioxide of the present invention contains 0.2 to 0.6% by weight of ammonia as described above.
When the content of ammonia is less than 0.2% by weight, the effect of the content on the discharge performance of the lithium secondary battery is small,
If it exceeds 6% by weight, the discharge characteristics of manganese dioxide when used in a lithium secondary battery tend to be impaired.

[0009] Lithium is contained in an amount of 1.0 to 3.5% by weight. When the lithium content is less than 1.0% by weight, the effect on the discharge performance of the lithium secondary battery is small, and when it exceeds 3.5% by weight, the discharge performance of the lithium secondary battery does not improve. The resulting discharge characteristics are impaired.

[0010] The α-type manganese dioxide of the present invention containing a certain amount of ammonia and lithium is obtained by the following method.

That is, first, manganese sulfate and a sulfuric acid solution to which an ammonium salt has been added are electrolyzed to obtain α-type manganese dioxide containing a certain amount of ammonia.

In this electrolysis, a solution of manganese sulfate and sulfuric acid is used as an electrolytic solution. The manganese concentration in this electrolyte is 20 to 50 g / l, and the sulfuric acid concentration is 30 to 80 g.
/ L is common. In addition, titanium or the like is used for an anode and carbon or the like is used for a cathode as an electrode.

As the ammonium salt, ammonium sulfate, ammonium chloride and the like are used. This ammonium salt is added uniformly, for example, together with the replenished manganese sulfate solution from above the electrolytic cell to between the electrode plates.

The electrolytic conditions of the electrolytic manganese dioxide are usually as follows: bath temperature 90 to 100 ° C., current density 50 to 100 A /
m ² .

The concentration of the ammonium salt in the electrolytic solution is 0.1 to 2.0 mol / l, and the ammonium salt is added to the obtained electrolytic manganese dioxide so that the above range of ammonia is contained.

Next, the ammonia-containing α-type manganese dioxide is neutralized using an aqueous solution of a lithium salt such as lithium hydroxide or lithium nitrate, and further filtered and dried to obtain the manganese dioxide of the present invention ( Hereinafter, manufacturing method I
).

That is, in this production method, the ammonia-containing α-type manganese dioxide is neutralized using an aqueous solution of a lithium salt such as lithium hydroxide or lithium nitrate. At this time, the concentration of the lithium salt is 0.1 to 10 mol / l.
Is desirable. The time for the neutralization treatment is appropriately 1 to 24 hours, and the temperature condition is desirably 20 to 80 ° C.

In another production method, the ammonia-containing α-manganese dioxide is mixed with a lithium salt such as lithium hydroxide or lithium nitrate to obtain the manganese dioxide of the present invention (hereinafter referred to as production method II). .

That is, in this production method, ammonia-containing α-type manganese dioxide is sufficiently mixed with a lithium salt such as lithium hydroxide or lithium nitrate.

The α-type manganese dioxide of the present invention thus obtained contains a certain amount of ammonia and lithium as described above.

This α-type manganese dioxide is used as an anode active material of a lithium secondary battery after further heat treatment. The heat treatment conditions at that time are 30 in the above-mentioned production method I.
0 to 450 ° C. for 3 to 6 hours, and 300 to 450 ° C. for 3 to 24 hours in the above production method II.

In the present invention, the use of α-type manganese dioxide containing ammonia as a processing raw material has a more remarkable effect than the case where ordinary γ-type manganese dioxide is used. Manganese has a large tunnel structure, the ammonia in the tunnel is easily replaced with lithium ions during heat treatment, and it is easy to dope and undope lithium during charge and discharge when used as a positive electrode active material for lithium secondary batteries. Conceivable.

In addition, the presence of lithium in the tunnel structure prevents collapse of the structure due to heat treatment,
It is considered that when used as the anode active material, the cycle characteristics of the lithium secondary battery were improved.

[0024]

The present invention will be specifically described below based on examples and comparative examples.

Example 1 A titanium plate as an anode and a graphite plate as a cathode were alternately suspended in a 3-liter electrolytic cell provided with a heating device, and a manganese sulfate and ammonium salt solution was formed at the bottom of the electrolytic cell. The one provided with an addition tube for the electrolytic replenisher was used.

The electrolytic replenisher was prepared by adding ammonium sulfate to the manganese sulfate solution at 40 g / l.

While injecting this replenisher into the electrolytic cell,
At the time of electrolysis, the composition of the electrolytic solution was changed to manganese 50 g /
1 and sulfuric acid 30 g / l, and the electrolysis was performed at a current density of 100 A / m ² while maintaining the temperature of the electrolytic bath at 95 ± 1 ° C.

After completion of the electrolysis, the anode plate on which the electrolytic manganese dioxide was electrodeposited was taken out and subjected to a usual post-treatment.

Next, 100 g of the ammonia-containing α-type manganese dioxide obtained in this way was poured into 2 mol / l lithium hydroxide filled in a 2 liter internal treatment tank provided with a heating device. After reacting at a reaction temperature of 70 ° C. for 2 hours with stirring, manganese dioxide was prepared by performing conventional filtration and drying treatments (Production Method I). Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

Thereafter, a heat treatment was performed at 400 ° C. for 3 hours to obtain manganese dioxide for an anode active material.

Using the heat-treated manganese dioxide as the anode active material, the following lithium secondary battery was constructed (FIG. 1). Note that the lithium secondary battery has an inner diameter of 10.8 mmφ.
The discharging operation was performed in a dry box under an argon atmosphere.

In FIG. 1, 1 denotes a negative electrode terminal, 2 denotes an insulator (Teflon material), 3 denotes a negative electrode current collector plate, 4 denotes a negative electrode material, 5 denotes a separator, 6 denotes an anode mixture, and 7 denotes an anode terminal.

As the anode mixture 6, 6 mg of graphite and 4 mg of tetrafluoroethylene resin were mixed with 90 mg of the obtained manganese dioxide, and the mixture was molded under pressure with a load of 2 tons to form a mixture having a diameter of 1 mm.
A pellet having a diameter of 0.6 mm was used.

As the electrolytic solution, a solution prepared by dissolving lithium perchlorate (LiClO ₄ ) in a 1: 1 mixed solvent of propylene carbonate and 1,2-dimethoxyethane was used in the separator 5.

As the negative electrode material 4, a lithium-aluminum alloy (Al content: 15% by weight) electrode was used, and was designed to have a sufficient amount (about twice equivalent) with respect to the anode mixture 6.

Using the obtained lithium secondary battery, 1 m
The charge / discharge was repeated at a current of A at a voltage in the range of 3.8 to 2.0 V, and the discharge capacity of the secondary battery was measured every 1 cycle, 10 cycles, and 50 cycles, and the results are also shown in Table 1.

Examples 2-3 The amount of ammonium sulfate added during electrolysis of Example 1 was 40 g / l.
20 g / l (Example 2), 60 g / l (Example 3)
The same operation as in Example 1 was performed, except that the procedure was changed to. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide. These manganese dioxides were further heat-treated under the same conditions as in Example 1 to obtain manganese dioxide for an anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. The results are shown in Table 1.

Examples 4 and 5 2 mol / l of lithium hydroxide during the lithium-containing treatment of Example 1 was replaced with 1.0 mol / l of lithium hydroxide (Example 4).
Lithium nitrate 3 mol / l, lithium hydroxide 1 mol / l
The same operation as in Example 1 was performed except that the operation was changed to (Example 5). Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

These manganese dioxides were further heat-treated under the same conditions as in Example 1 to obtain manganese dioxide for the anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. Shown in

Example 6 20 g of lithium nitrate was added to 100 g of the ammonia-containing α-type manganese dioxide obtained by the electrolysis of Example 1, and mixed well to obtain manganese dioxide. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

Thereafter, a heat treatment was performed at 400 ° C. for 5 hours to obtain manganese dioxide for an anode active material.

Using this manganese dioxide, the same battery evaluation as in Example 1 was performed, and the results are shown in Table 1.

Example 7 20 g of lithium nitrate of Example 6 was replaced with 7 g of lithium hydroxide.
The same operation as in Example 6 was performed, except that the procedure was changed to. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

These manganese dioxides were further heat-treated under the same conditions as in Example 6 to obtain manganese dioxide for the anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. Shown in

Comparative Example 1 The same operation as in Example 1 was performed except that ammonium sulfate was not added during the electrolysis of Example 1. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

The manganese dioxide was further heated under the same conditions as in Example 1 to obtain manganese dioxide for an anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. The results are shown in Table 1. Show.

Comparative Example 2 20 g of lithium nitrate was added to 100 g of the manganese dioxide obtained by the electrolysis of Comparative Example 1, and mixed well. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

This manganese dioxide was further heated under the same conditions as in Example 6 to obtain manganese dioxide for an anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. The results are shown in Table 1. Show.

Comparative Example 3 The same operation as in Example 1 was performed except that the treatment with lithium hydroxide in Example 1 was not performed. Table 1 shows the lithium and ammonia contents of the obtained manganese dioxide.

This manganese dioxide was further heated under the same conditions as in Example 1 to obtain manganese dioxide for an anode active material. Using this manganese dioxide, the same battery evaluation as in Example 1 was performed. The results are shown in Table 1. Show.

[0051]

[Table 1]

As is clear from Table 1, the above-mentioned production method I was carried out by using an ammonia-containing α-type manganese dioxide obtained by an electrolytic method as a starting material and immersing it in a lithium salt solution such as lithium hydroxide or lithium nitrate. The lithium secondary batteries using the α-type manganese dioxides of Examples 1 to 5 and the manganese dioxide obtained by further heat treatment as the anode active material have excellent discharge performance in each cycle, and thus have excellent battery performance. .

On the other hand, ordinary manganese dioxide was used as a starting material, and manganese dioxide of Comparative Example 1 containing no ammonia and manganese dioxide of Comparative Example 3 containing no lithium were each heat-treated and used as an anode active material. Lithium secondary batteries have poor battery performance.

Further, the manganese dioxides obtained in Examples 6 and 7 obtained by the above-mentioned production method II and Comparative Example 2 containing no ammonia were each heat-treated to obtain an anode active material of a lithium secondary battery. Almost the same results as those of Examples 1 to 5 and Comparative Examples 1 and 3 were obtained.

[0055]

As described above, a certain amount of ammonia and lithium are contained by the immersion treatment with an aqueous solution of lithium salt or the production method of the present invention in which the mixture is mixed with lithium salt using ammonia-containing α-manganese dioxide as a starting material. α-type manganese dioxide is obtained. Further, the battery performance can be significantly improved by heating this α-type manganese dioxide and using it as an anode active material of a lithium secondary battery.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a lithium secondary battery according to the present invention.

[Explanation of symbols]

1 negative electrode terminal, 2 insulators, 3 negative electrode current collector plate, 4 negative electrode material, 5 separator, 6 anode mix, 7 anode terminal.

Claims (2)

(57) [Claims] An α-type manganese dioxide for a lithium secondary battery, comprising 0.2 to 0.6% by weight of ammonia and 1.0 to 3.5% by weight of lithium. 2. A method for producing α-type manganese dioxide for a lithium secondary battery, comprising immersing ammonia-containing α-type manganese dioxide in a lithium aqueous solution or mixing it with a lithium salt.