JPH03289064A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve charge-discharge cycle and reservation characteristics by using as nonaqueous electrolyte one in which a soluble material comprising lithium salt including fluorine is solved in a solvent including at least butylene carbonate. CONSTITUTION:There are used positive electrode 1 mainly composed of manganese dioxide, a negative electrode 2 made of lithium or lithium - aluminium alloy, a material where a substance comprising lithium salt including florine is solved in a solvent including at least butylene carbonate. Since the lithium salt including fluorine is chemically stable in itself, it is hard to react with electrodes 1, 2 under highly active conditions so that the reaction between the solvent and manganese dioxide is restrained, thereby dissolution of the solvent in electrolyte is hard to occur with butylene carbonate being high at its oxide electric potential and a excellent in its oxidation resistance. It is thus possible to improve charge-discharge cycle and reservation characteristics.

Description

[Detailed Description of the Invention] Riwayo Ω and Li Corporation The present invention provides a non-aqueous electrolyte comprising a positive electrode mainly made of manganese dioxide, a negative electrode made of lithium or a lithium-aluminum alloy, and a non-aqueous electrolyte. This paper applies to secondary batteries, and particularly relates to improvements in non-aqueous electrolytes.

Conventional ■ Late An This type of battery has high voltage and high energy density, so it has been actively researched in recent years, but in order to put it into practical use, it is necessary to develop battery materials with even better cycle characteristics and storage characteristics. This is what is desired.

In particular, it is known that the electrolyte greatly influences the above characteristics. That is, in a lithium secondary battery, both the positive electrode and the negative electrode become highly active due to repeated charging and discharging, so the battery characteristics change depending on the stability of the electrolyte in contact with these two electrodes.

Therefore, for example, JP-A-59-167971 proposes using a mixed solvent of T-butyrolactone and tetrahydrofuran as a solvent for the electrolytic solution;
JP-A No. 63-32870 proposes the use of acetyl group-substituted propylene carbonate as a solvent for an electrolytic solution.

However, when manganese dioxide, which has a relatively high potential and has a strong oxidation catalytic effect, is used as the positive electrode active material of the battery, decomposition of the electrolyte is likely to occur, especially during charging. Such decomposition of the electrolytic solution occurs even when the above-mentioned electrolytic solution is used, so a battery with a conventional structure has a problem in that its characteristics cannot be sufficiently improved.

Specifically, some of the decomposed products adhere to the surface of the positive electrode, resulting in an increase in the internal resistance of the battery, a decrease in the utilization rate of the active material, and a deterioration in the charge/discharge cycle characteristics of the battery. In addition, when charging and discharging cycles are repeated or when stored for a long period of time, gaseous decomposition products accumulate in the battery, causing problems such as blistering of the battery.

The present invention has been made in view of the current situation, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery with excellent charge/discharge cycle characteristics and storage characteristics.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary comprising a positive electrode mainly made of manganese dioxide, a negative electrode made of lithium or lithium-aluminum alloy, and a non-aqueous electrolyte. In the battery, the non-aqueous electrolyte is characterized in that a solute made of a fluorine-containing lithium salt is dissolved in a solvent containing at least butylene carbonate.

As mentioned above, when a fluorine-containing lithium salt is used as a solute in the electrolyte, the fluorine-containing lithium salt itself is chemically stable, so it becomes difficult to react with the electrode in a highly active state. . In addition, since the surface groups of manganese dioxide in an active state react with some free fluorine ions, the reaction between the solvent and manganese dioxide is suppressed. These things make it possible to improve cycle characteristics.

In addition, butylene carbonate has a higher oxidation potential and excellent oxidation resistance than propylene carbonate and the like.

Therefore, even when stored for a long period of time or when charge/discharge cycles are repeated, decomposition of the solvent in the electrolytic solution is less likely to occur. As a result, it is possible to suppress a decrease in the utilization rate of the active material of the positive electrode, an increase in the internal resistance of the battery, and a phenomenon of blistering in the battery.

Man-LiJL Masu The first embodiment of the present invention is based on FIGS. 1 to 3,
This will be explained below.

〔Example〕

As shown in FIG. 1, a negative electrode 2 made of a lithium-aluminum alloy is crimped to the inner surface of a negative electrode current collector 7, and this negative electrode current collector 7 is attached to a negative electrode can 5 made of stainless steel and having a substantially U-shaped cross section. It is fixed to the inner bottom. The peripheral end of the negative electrode can 5 is fixed inside an insulating backing 8 made of polypropylene, and the outer periphery of the insulating backing 8 is a positive electrode can made of stainless steel and having a substantially U-shaped cross section in the opposite direction to the negative electrode can 5. 4 is fixed. A positive electrode current collector 6 is fixed to the inner bottom surface of the positive electrode can 4, and a positive electrode 1 is fixed to the inner surface of this positive electrode current collector 6. This positive electrode 1 was prepared by adding 10 parts by weight of acetylene blank as a conductive agent and 5 parts by weight of fluororesin powder as a binder to 85 parts by weight of manganese oxide as an active material, and mixing these thoroughly. ,
This mixture was produced by pressure molding. Also,
A separator 3 made of a porous polypropylene membrane and impregnated with an electrolyte is interposed between the positive electrode 1 and the negative electrode 2. The battery dimensions are 24 mm in diameter, 3 mm in thickness. It is 0mn+.

Here, the electrolyte is butylene carbonate (
Lithium trifluoromethanesulfonate (Li CF, SO, ,
A solution prepared by melting 1 mol/I is used.

The battery thus produced is hereinafter referred to as the (A) battery.

[Comparative Example I]

Propylene carbonate (hereinafter referred to as
A battery was produced in the same manner as in the above example except that a mixed solvent of equal volumes of PC (abbreviated as PC) and DME was used.

The battery thus produced is hereinafter referred to as a (χ1) battery.

[Comparative example ■]

Ethylene carbonate (hereinafter referred to as E) is used as a solvent for the electrolytic solution.
In addition to using an equal volume mixed solvent of C) and DME,
A battery was produced in the same manner as in the above example.

The battery thus produced is hereinafter referred to as an (X2) battery.

[Comparative example ■]

γ-butyrolactone (hereinafter referred to as r-
A battery was produced in the same manner as in the above example except that a mixed solvent of equal volumes of BL (abbreviated as BL) and DME was used.

The battery thus produced is hereinafter referred to as an (X3) battery.

[Experiment I]

The (A) battery of the present invention and the (xl) battery of the comparative example ~ (X
3) The cycle characteristics with the battery were investigated, and the results are shown in Figure 2. The charging and discharging conditions are that after charging for 3 hours at a charging current of 2mA, the battery is discharged at a discharging current of 2mA until the battery voltage reaches 1.5cm.As is clear from Figure 2, (A) battery is It is recognized that the cycle characteristics are improved compared to the (X,) battery to the (X,) battery.

[Experiment■]

The (A) battery of the present invention and the (XI) battery of the comparative example ~ (
χ, ) Battery (Xl) Store the battery at 3.25V for one week,
We investigated the change in internal resistance of the battery and the amount of battery swelling.
The results are shown in Table 1 below.

Table 1 As is clear from Table 1 above, initially the internal resistances of both batteries are the same, but after charging, (XI) battery ~ (X3
) Batteries have a significantly increased internal resistance, whereas (
A) It is observed that the internal resistance of the battery does not increase much.

Also, regarding battery swelling, (Xl) battery ~ (X3
It is observed that the battery (A) has not been charged much, while the battery (A) has been significantly overloaded.

A second embodiment of the present invention will be described below with reference to FIG.

〔Example〕

A battery was produced in the same manner as in the first example, except that an equal volume mixed solvent of BC and tetrahydrofuran (hereinafter abbreviated as THF) was used as a solvent for the electrolytic solution.

The battery thus produced is hereinafter referred to as the (B) battery.

[Comparative example]

A battery was produced in the same manner as in the above example except that an equal volume mixed solvent of T-BL and THF was used as the electrolyte solvent and lithium perchlorate (1 mol/l) was used as the solute.

The battery thus produced is hereinafter referred to as a (Y) battery.

〔experiment〕

The cycle characteristics of the battery (B) of the present invention and the battery (Y) of the comparative example were investigated, and the results are shown in FIG. still,
The charging and discharging conditions were the same as those in Experiment I of the first example.

As is clear from FIG. 3, it is recognized that the (B) battery has improved cycle characteristics compared to the (Y) battery.

The third embodiment of the present invention is based on FIGS. 4 and 5.
This will be explained below.

〔Example〕

Lithium hexafluorophosphate (
A battery was produced in the same manner as in the first embodiment except for using L IP Fb ).

The battery thus produced is hereinafter referred to as the (C) battery.

[Comparative example]

A battery was produced in the same manner as in the above example except that an equal volume mixed solvent of r-BL and DME was used as the electrolyte solvent and lithium perchlorate (1 mol/liter) was used as the solute.

The battery thus produced is hereinafter referred to as a (Z) battery.

[Experiment■]

The cycle characteristics of the battery (C) of the present invention and the battery (Z) of the comparative example were investigated, and the results are shown in FIG. still,
The charging and discharging conditions were the same as those in Experiment (2) of the first embodiment.

As is clear from FIG. 4, it is recognized that the cycle characteristics of the (C) battery are improved compared to the (Z) battery.

[Experiment ■] The relationship between the number of storage days, the internal resistance of the battery, and the amount of blistering of the battery was investigated for the battery (C) and battery (Z), and the results are shown in FIG. Note that the storage temperature is 60°C.

As is clear from FIG. 5, it is recognized that the (C) battery can suppress an increase in the internal resistance of the battery and an increase in the swelling of the battery even if the storage period becomes longer than that of the (Z) battery.

Incidentally, BC, which is the gist of the present invention, is preferably used in combination with a low-viscosity organic solvent such as the above-mentioned DME, THF, or 2-methyltetrahydrofuran or 4-methyl-1,3 dioxolane, rather than using it alone. Moreover, in this case, if BC is contained at 5 VOL% or more, the effect can be sufficiently exhibited.

As explained above, according to the present invention, the decomposition of the solvent in the electrolyte becomes difficult to occur even when stored for a long time or when charge/discharge cycles are repeated, so that the positive electrode becomes active. It is possible to suppress a decrease in the material utilization rate, an increase in the internal resistance of the battery, and the occurrence of a blistering phenomenon in the battery. As a result, effects such as being able to dramatically improve the charge/discharge cycle characteristics and storage characteristics of the non-aqueous electrolyte secondary battery are achieved.

[Brief explanation of drawings]

FIG. 1 is a half-sectional view showing a non-aqueous electrolyte secondary battery which is an example of the present invention, and FIG. 2 is a half-sectional view showing a battery (A) of the present invention and a comparative example (
A graph showing the cycle characteristics of the battery (Xl) to (X3); FIG. 3 is a graph showing the cycle characteristics of the battery (B) of the present invention and the battery (Y) of the comparative example; FIG. (C
) A graph showing the cycle characteristics of the (C) battery and the (Z) battery of the comparative example. FIG. Figure 1 Figure 2 1... Positive electrode, 2... Negative electrode, 3... Separator.

Claims (1)

[Claims] (1) In a non-aqueous electrolyte secondary battery comprising a positive electrode mainly made of manganese dioxide, a negative electrode made of lithium or a lithium-aluminum alloy, and a non-aqueous electrolyte, the non-aqueous electrolyte is at least butylene carbonate. A non-aqueous electrolyte secondary battery characterized in that a solute consisting of a fluorine-containing lithium salt is dissolved in a solvent containing fluorine-containing lithium salt.