JP3157209B2 - 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 non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, and more particularly to an improvement in the electrolyte.

[0002]

2. Description of the Related Art A positive electrode, a negative electrode using lithium as an active material ,
Nonaqueous electrolyte secondary battery using, the such as high energy density and superior storage characteristics are noted, are still conducted active research and development. Among them, a non-aqueous electrolyte using a material (for example, cobalt oxide or manganese oxide) having a charging voltage of 3.8 V or more for the positive electrode and a carbon material for the negative electrode
A secondary battery is a promising battery system because of its extremely high energy density and excellent cycle characteristics. The most important issue in putting this battery system to practical use is the search for a stable electrolyte solution.

In particular, in this type of secondary battery , the electrolyte is easily decomposed because the high potential is maintained on the positive electrode side. Therefore, it is indispensable to select a composition in consideration of these points in selecting an electrolyte solution. For this reason, it has been proposed to use various electrolytic solutions, but most of them are mixed with 1,2-dimethoxyethane in a high boiling point solvent such as propylene carbonate, ethylene carbonate, and γ -butyrolactone. And 1,3
-It is a mixture of a low-viscosity solvent such as dioxolane, while using a solute such as lithium perchlorate or lithium tetrafluoroborate is disclosed.

[0004]

However, even if the above-mentioned electrolytic solution is used, sufficient characteristics cannot always be obtained. Therefore, the present invention has been made in view of the above problems, and by controlling the reactivity between the highly active positive and negative electrodes and the electrolytic solution of this type of battery, storage characteristics, and excellent cycle characteristics. And a non-aqueous electrolyte secondary battery .

[0005]

SUMMARY OF THE INVENTION The non-aqueous electrolyte solution of the present invention
The secondary battery has a positive electrode whose voltage at the time of charging is 3.8 V or more,
A negative electrode made of an electrically conductive carbon material and propylene carbonate.
And ethylene carbonate and dimethyl carbonate
And a non-aqueous electrolyte solution containing
The solute is characterized in that it is lithium hexafluorophosphate .

[0006]

As described above, in this type of non-aqueous electrolyte secondary battery , a decomposition reaction of the electrolyte is likely to occur, which is considered to be the main cause of deteriorating various battery characteristics. In contrast, according to the present invention, the solvent is propylene carbonate.
And ethylene carbonate and dimethyl carbonate
When a non-aqueous electrolyte containing lithium and the solute of the electrolyte is lithium hexafluorophosphate is used, decomposition of the electrolyte is suppressed, and as a result, a non-aqueous electrolyte secondary having excellent storage characteristics and cycle characteristics is obtained. A battery is obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The non-aqueous electrolyte secondary battery of the present invention will be described below.
Reference Examples and Comparative Examples 1 and 2 to assist
The example and the comparative examples 3 and 4 will be described in detail.

Reference Example FIG. 1 is a sectional view of a flat nonaqueous electrolyte secondary battery as a reference example for explaining the present invention . Reference numeral 1 denotes a negative electrode made of a chargeable / dischargeable coke material, which is pressure-bonded to a negative electrode current collector 3 fixed to the inner bottom surface of a negative electrode can 2. Reference numeral 4 denotes a positive electrode, which is a chargeable active material having a voltage of 3.8 V during charging.
To 85% by weight of the above cobalt oxide, 10% by weight of acetylene black as a conductive agent and 5% by weight of a fluororesin as a binder were added, and the mixture was sufficiently mixed and then molded. Then, this is pressure-bonded to a positive electrode current collector 6 fixed to the inner bottom surface of the positive electrode can 5. 7 is a separator made of polypropylene porous membrane, a mixed solvent of propylene carbonate and dimethyl carbonate (volume ratio 50:
50) is impregnated with an electrolytic solution in which lithium hexafluorophosphate (fluorine-based lithium Lewis acid) as a lithium salt is dissolved at a ratio of 1 mol / l. Numeral 8 denotes an insulating packing, which has a battery size of 24 mm in diameter and 3 mm in height. This battery was used as Reference Battery S.

Comparative Example 1 A battery was manufactured in the same manner as in the reference example except that propylene carbonate was used as the organic solvent. This battery was used as Comparative Battery X.

[Comparative Example 2] The above-mentioned procedure was repeated except that propylene carbonate and 1,2-dimethoxyethane (volume ratio: 50:50) were used as organic solvents.
A battery similar to the reference example was produced. This battery was designated as Comparative Battery Y.

The cycle characteristics of these batteries S , X, and Y were compared. The charge / discharge conditions at this time were a charge / discharge current of 3 mA, a charge-start voltage of 4.2 V, and a discharge-start voltage of 3.0 V. The result is shown in FIG. As is clear from FIG. 2, the reference battery S has superior cycle characteristics as compared with the comparative batteries X and Y.

Next, these batteries S, X, and Y are taken out after charging and stored at 60 ° C. for 20 days, and the battery thickness and internal resistance are shown in the following table.

[0013]

[Table 1]

[0014] As described above, when a mixed solvent of propylene carbonate and dimethyl carbonate having excellent oxidation resistance in the non-aqueous electrolyte is suppressed decomposition at a high potential, no gas generation or increase in internal resistance, cycles A battery having excellent characteristics and storage characteristics can be obtained. However, it can be understood from FIG.
Thus, the battery discharge capacity of the reference battery S is about 80 mAh.
It is.

EXAMPLE A chargeable / dischargeable manganese oxide was used for a positive electrode, and a chargeable / dischargeable pyrolytic carbon material was used for a negative electrode. Propylene carbonate, ethylene carbonate, and dimethyl carbonate were used as electrolyte solvents.
A battery was manufactured in the same manner as in the above reference example, except that a sheet (volume ratio 30:30:40) was used. This battery was designated as battery A of the present invention.

Comparative Example 3 A battery similar to that of the above example was produced except that a mixed solvent of propylene carbonate and ethylene carbonate (volume ratio: 50:50) was used as an electrolyte solvent. This battery was used as Comparative Battery V.

Comparative Example 4 A mixed solvent of propylene carbonate, ethylene carbonate and tetrahydrofuran (volume ratio: 3) was used as the electrolyte solvent.
0:30:40) except for using was prepared in the same manner as the battery with the embodiment. This battery was used as comparative battery W.

[0018] These batteries A, V, and X used, the reference
The cycle characteristics of the battery were examined under the same conditions as in the example, and the results are shown in FIG . FIG. 3 shows that when a mixed solvent of propylene carbonate, ethylene carbonate and dimethyl carbonate is used as the electrolyte solution solvent, excellent cycle characteristics are exhibited. As can be understood from FIG.
The battery discharge capacity of A is about 90 mAh.

[0019]

By the way, from the comparison between FIG. 2 and FIG.
Battery A is composed of propylene carbonate and dimethyl carbonate.
Hexafluoro as lithium salt in mixed solvent
Dissolve lithium phosphate (fluorine-based lithium Lewis acid)
Battery discharge capacity compared to the reference battery S using
large. It consists of propylene carbonate and ethylene carbonate.
Mixed solution containing carbonate and dimethyl carbonate
From medium and lithium hexafluorophosphate as solute
This is presumed to be an effect using a non-aqueous electrolyte solution. Ma
The negative electrode 1 may be a chargeable / dischargeable coke or a heat component.
Besides graphite, graphite can also be used. In addition, the positive electrode
Manganese acid whose voltage at the time of charge is 3.8 V or more
Other than oxides, such as cobalt oxide and nickel oxide
Can be.

[0021]

As is apparent from the above description, the present invention provides a positive electrode having a charging voltage of 3.8 V or more, a negative electrode made of a chargeable / dischargeable carbon material, propylene carbonate,
A non-aqueous electrolyte containing ethylene carbonate and dimethyl carbonate is provided, and since the solute of the non-aqueous electrolyte is lithium hexafluorophosphate, decomposition of the electrolyte is suppressed, and as a result, The storage characteristics and cycle characteristics of the seed non-aqueous electrolyte secondary battery can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an internal configuration of a non-aqueous electrolyte secondary battery of a reference example .

FIG. 2 is a cycle characteristic diagram of a reference battery and a comparative battery .

FIG. 3 is a cycle characteristic diagram of a battery of the present invention and a comparative battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Negative electrode 4 Positive electrode 7 Separator A Battery of the present invention S Reference battery X, Y, V, W Comparative battery

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Yoshimura 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Nobuhiro Furukawa 2--18 Keihanhondori, Moriguchi-shi, Osaka JP-A-2-195661 (JP, A) JP-A-2-165576 (JP, A) JP-A-2-10666 (JP, A) JP-A-63-121260 (JP, A) JP-A-5-74441 (JP, A) JP-A-5-41245 (JP, A) JP-A-6-267075 (JP, A) JP-A-4-171674 (JP, A) Kaihei 3-250565 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4/38-4/62 H01M 6/16

Claims (3)

(57) [Claims] (1) A positive electrode whose voltage at the time of charging is 3.8 V or more;
A negative electrode made of a chargeable and dischargeable carbon material;
Carbonate, ethylene carbonate and dimethyl carbonate
And a non-aqueous electrolytic solution containing
That the solute of the liquid is lithium hexafluorophosphate
Characteristic non-aqueous electrolyte secondary battery. 2. The method according to claim 1, wherein the negative electrode is a chargeable / dischargeable coke,
2. A pyrolytic carbon or graphite.
The non-aqueous electrolyte secondary battery according to the above. 3. The method according to claim 1, wherein the positive electrode is manganese oxide, cobalt,
Oxide or nickel oxide
The non-aqueous electrolyte secondary battery according to claim 1.