JP2979641B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte secondary battery using manganese dioxide as a positive electrode active material and lithium as a negative electrode active material.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery uses a non-aqueous electrolyte and combines a negative electrode using lithium as an active material (a lithium negative electrode, a lithium alloy negative electrode, etc.) with a positive electrode via a separator. Is commonly adopted. Also,
Oxides and sulfides such as V ₂ O ₅ , MnO ₂ (manganese dioxide), TiO ₂ and MoS ₂ are used as the positive electrode active material.

As the manganese dioxide, lithium-containing manganese dioxide obtained by doping lithium ions into manganese dioxide is known. This type of manganese dioxide includes, for example, the following 1) to 3). That is, 1) JP-A-1-29
As described in Japanese Patent No. 4359, manganese dioxide obtained by immersing manganese dioxide powder in an aqueous solution of a lithium salt, evaporating water, drying and solidifying, and then heat-treating. 2) JP
Manganese dioxide obtained by immersing manganese dioxide powder in an aqueous solution of a lithium salt and heat-treating it under pressure, as described in JP-A-61-16473. 3) JP-A-63-114064
Manganese dioxide obtained by heat-treating a mixture of a lithium salt powder and a manganese dioxide powder as disclosed in Japanese Patent Application Publication

[0004]

By the way, since lithium salts, for example, lithium hydroxide (LiOH) have low solubility, the concentration of lithium ions in the aqueous solution of the lithium salt is small.

[0005] Therefore, in the case of manganese dioxide of the above 1), it is difficult to sufficiently transfer lithium ions into manganese dioxide by impregnation. When dried, LiOH or LiCO ₃ precipitates to increase the lithium concentration on the surface of manganese dioxide, resulting in inactive Li ₂ Mn.
Since O ₃ is easily generated, the battery using this battery has a small charge / discharge capacity, and the number of cycles that can be charged / discharged in practice is small, and the cycle characteristics are not good.

In the case of manganese dioxide of 2), since the lithium concentration in manganese dioxide is low as in 1), even if heat treatment is performed under pressure, the effect is not so different, and a good crystal structure is formed. Can not.

In the case of 3), Li ₂ MnO ₃ is similarly produced since the distribution of lithium is only on the surface of manganese dioxide, and the central portion of manganese dioxide is changed to β-type manganese dioxide having low activity by heat treatment. Therefore, there is a problem that the cycle characteristics of the battery are not good as described above.

It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a large charge / discharge capacity and good cycle characteristics.

[0009]

A non-aqueous electrolyte secondary battery according to the present invention includes a negative electrode using lithium as an active material and a positive electrode using manganese dioxide as an active material. manganese powder and 100% or less of water pore volume of the mixed powder to the mixed powder of a lithium salt powder was added, and stored at 60 to 90 ° C. in a sealed state, then 200-4
The gist is that it is obtained by heat treatment at 30 ° C.

As the lithium salt, lithium nitrate, lithium hydroxide, lithium chloride, lithium acetate, lithium bromide and the like can be used.

The mixing ratio of manganese dioxide and lithium salt in the above mixed powder may be such that the lithium salt is about 0.015 to 0.05 per manganese dioxide by weight.

The lower limit of the water content to be added to the mixed powder is not particularly limited. For example, good results can be obtained at 30% or less.

The storage in the closed state may be performed for about 24 hours, depending on the temperature.

[0014]

[Function] As described above, a water content of 100% or less of the pore volume of the mixed powder is added to the mixed powder of the manganese dioxide powder and the lithium salt powder, and the mixed powder is stored at 60 to 90 ° C in a closed state. Thus, lithium-containing manganese dioxide in which lithium ions are uniformly distributed up to the center of the manganese dioxide powder can be obtained.

[0015] This is because the water added to the mixed powder is reduced to 100% or less, so that the liquid phase of the aqueous lithium salt solution is always saturated with the lithium salt even when the reaction of incorporating lithium ions into manganese dioxide proceeds. Therefore, it is considered that lithium ions move smoothly to the inside of the manganese dioxide powder through the liquid phase on the surface of the manganese dioxide powder.

After all of the lithium salts have been dissolved, the manganese dioxide is covered with a solution film.

When heat treatment is performed at 200 to 430 ° C. in this state, lithium ions enter the inside of the manganese dioxide from the surface thereof, whereby the lithium ions become inactive L
Without forming i ₂ MnO ₃ , the manganese dioxide forms a crystal structure effective for charging and discharging.

[0018]

Embodiments will be described below.

A mixed powder was obtained by mixing 180 g of electrolytic manganese dioxide and 40 g of lithium hydroxide (LiOH.H ₂ O). A part of the mixed powder was placed in a container, and its porosity was determined by impregnation using a fluorine-based solvent. The porosity was 22% of the volume of the mixed powder.

The above mixed powder 30 ml (pore volume is 30 ml × 0.
22 = 6.6 ml), 4 ml of pure water was added thereto, and the mixture was placed in a polypropylene container, further placed in a stainless steel closed container, sealed and allowed to stand at 90 ° C for 72 hours. Thereafter, the mixture was transferred to a crucible and heated at 350 ° C. for 20 hours to produce manganese dioxide according to the present invention.

The manganese dioxide 8 was mixed with acetylene black 1 and PTFE powder 1 in a weight ratio, and the mixed powder was pressed into a pellet having a diameter of 15 mm and a thickness of 0.4 mm to form a positive electrode mixture. did.

Then, as shown in FIG. 1, the positive electrode mixture 3 obtained above is pressed into a battery can 2 having a stainless steel net 1 spot-welded to the bottom surface, and a negative electrode 4 using lithium as an active material and a propylene Using a non-aqueous electrolyte prepared by dissolving LiClO ₄ at 1 mol / l in a mixed solvent of carbonate and dimethoxyethane in an equal volume ratio, a CR2016 type coin-type lithium secondary battery (Example) was manufactured. In FIG. 1, reference numerals 5 to 7 denote a separator, an insulating gasket, and a terminal plate, respectively.

Various manganese dioxides were prepared by the following processes.

Lithium hydroxide (LiOH.H ₂ O) 40
g manganese dioxide in an aqueous solution of
Manganese dioxide obtained by immersing 180 g and evaporating water and then performing heat treatment at 350 ° C.

In the above aqueous solution, electrolytic manganese dioxide 180 g
Manganese dioxide obtained by immersing, heating at 200 ° C under pressure in an autoclave, filtering, and then performing a heat treatment at 350 ° C.

Lithium hydroxide (LiOH.H ₂ O) 40
manganese dioxide obtained by heating a mixed powder of g and electrolytic manganese dioxide at 180 g at 350 ° C.

A coin-type lithium secondary battery having the same shape (Comparative Example) was prepared in the same manner as in the above example except that each of these three types of manganese dioxide was used.

The batteries of the above Examples and Comparative Examples 1 to 3 were charged to 3.4 V at a current of 1 mA, and charged at a current of 1 mA.
A charge / discharge cycle of discharging to 2.5 V was repeated, and a cycle change of a discharge capacity ratio {(discharge capacity mAH / discharge capacity of the first cycle of each battery) × 100 (%)} was examined. The result is as shown in FIG.

In the above embodiment, the same coin-type lithium secondary battery was used except that manganese dioxide was similarly prepared except that the amount of water added to the mixed powder was changed in the range of 1 to 9 ml. They were prepared and charged and discharged in the same manner as described above.

From the discharge capacity ratio of these batteries in the 50th cycle {{(discharge capacity mAH in the 50th cycle / discharge capacity mAH in the first cycle of each battery) × 100 (%)}, FIG. ) Was obtained.

Further, in the above embodiment, electrolytic manganese dioxide was used.
Lithium hydroxide (LiOH.H ₂ O) mixed with 180g
The same coin shape was prepared except that manganese dioxide was prepared in the same manner except that manganese dioxide was prepared in the same manner except that 30 ml of these mixed powders and 2 ml of pure water were added. Lithium secondary batteries were prepared and charged and discharged in the same manner as described above.

The discharge capacity ratio of these batteries in the first and second cycles {(discharge capacity mAH / discharge capacity in the first cycle of each battery) × 100 (%)} is as shown in FIG. 3 (B). Met.

In the above example, manganese dioxide was prepared in the same manner except that 3 ml of pure water was added to 30 ml of the mixed powder , and the storage temperature in the closed state was appropriately changed in the range of 40 to 90 ° C. A coin-type lithium secondary battery was prepared in the same manner except that the battery was used, and charged and discharged in the same manner as above.

The discharge capacity ratio of these batteries in the 10th cycle {(discharge capacity in the 10th cycle mAH / storage temperature 60
3 (C) was obtained from the discharge capacity in the first cycle of the battery using manganese dioxide at 100 ° C.) × 100 (%).

In the case of manganese dioxide at a storage temperature of 40 ° C. and 50 ° C., a white film was formed on the surface of the manganese dioxide after the heat treatment at 350 ° C.

In the above embodiment, the heat treatment temperature was set to 150 to 500 ° C.
, A coin-shaped lithium secondary battery was produced in the same manner except that manganese dioxide produced in the same manner was used, except that these were charged and discharged in the same manner as described above.

From the discharge capacity ratio of these batteries in the 50th cycle {(discharge capacity in the 50th cycle mAH / discharge capacity in the first cycle of each battery) × 100 (%)}, FIG.
(D) was obtained.

From these results, it was found that the heat treatment temperature was 200 to 430.
It turns out that the range of ° C is preferable. This exceeds 430 ° C
And LiMn ₂ O ₄ are generated to reduce the capacity,
Moisture in less than is believed to be due to not except to take in enough.

[0039]

As described above, according to the present invention, a non-aqueous electrolyte secondary battery having a large charge / discharge capacity and good cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a battery according to an embodiment of the present invention.

FIG. 2 is a graph showing a cycle change of a discharge capacity ratio in a battery of an example and a battery of a comparative example.

FIG. 3 (A) is a graph showing the change in the discharge capacity ratio of the battery with respect to the amount of water added to the mixed powder, and (B) shows the change in the discharge capacity ratio of the battery with respect to the amount of lithium hydroxide in the mixed powder. In the graph, (C) is a graph showing the change in the discharge capacity ratio of the battery with respect to the storage temperature in the sealed state, and (D) is a graph showing the change in the discharge capacity ratio of the battery with the heat treatment temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel net 2 Battery can 3 Positive electrode mixture 4 Negative electrode 5 Separator 6 Insulating gasket 7 Terminal plate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (56) References JP-A-2-139860 (JP, A) JP Japanese Unexamined Patent Publication No. Hei 4-115459 (JP, A) Japanese Unexamined Patent Publication No. Hei 3-219556 (JP, A) Japanese Unexamined Patent Publication No. Hei 3-127453 (JP, A) Japanese Unexamined Patent Publication No. Hei 2-183396 (JP, A) Japanese Unexamined Patent Publication No. Hei 2-170353 (JP, A) , A) JP-A-2-139862 (JP, A) JP-A-1-294359 (JP, A) JP-A-1-234331 (JP, A) JP-A-63-114064 (JP, A) 62-160657 (JP, A) JP-A-61-16473 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/50 H01M 4/02

Claims (1)

(57) [Claims] 1. A negative electrode comprising lithium as an active material and a positive electrode comprising manganese dioxide as an active material, wherein the manganese dioxide is a mixed powder of a manganese dioxide powder and a lithium salt powder. 100% of the pore volume of
A non-aqueous electrolyte secondary battery obtained by adding the following water, storing in a sealed state at 60 to 90 ° C. , and then heat-treating at 200 to 430 ° C.