JP2000268831A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain increase of internal resistance during long time storage at a room temperature for several years after partial discharge, by adding aromatic mono-carboxylic acid ester at a specific concentration to nonaqueous electrolyte. SOLUTION: Aromatic mono-carboxylic acid ester is added to nonaqueous electrolyte, decomposition of low-boiling solvent by a catalyst reaction of manganese dioxide or the like is prevented, and a discharge characteristic of a battery can be kept for several years. It is effective that this aromatic mono-carboxylic acid ester is contained at 1500-10000 ppm concentration in the nonaqueous electrolyte. Added weight in the nonaqueous electrolyte is restrained, the aromatic mono-carboxylic acid ester with relatively low molecular weight, such as methyl benzonate so as not to excessively dilute the electrolyte is preferably used. As an alkyl group constituting ester by substituting hydrogen in a carboxyl group, a methyl group, an ethyl group, or an n-butyl group with low molecular weight is preferable.

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 battery, and more particularly to an improvement in an electrolyte used for this type of battery.

[0002]

2. Description of the Related Art At present, non-aqueous electrolyte batteries have a relatively high energy density and are suitable for miniaturization. Therefore, various batteries are used for various purposes, including memory backup and power supplies for cameras and the like. . Non-aqueous electrolyte batteries, for example,
It has the following structure. That is, a positive electrode formed by pressing a metal oxide (such as manganese dioxide) or graphite fluoride on a stainless steel core, and a lithium metal or lithium metal.
A negative electrode made of an aluminum alloy is overlapped with a separator interposed therebetween, and this is wound to form a power generating element. For the purpose of improving the flow of lithium ions and the like moving in the electrolyte, a microporous resin film is generally used for the separator.

Further, the power generating element is housed in an outer can and is immersed in a non-aqueous electrolyte. Here, an organic solvent is generally used for the non-aqueous electrolyte. Lithium perchlorate LiCl is used as a mixed solvent of a carbonate such as propylene carbonate and a low-boiling solvent such as 1,2-dimethoxyethane.
0 ₄ or lithium trifluoromethanesulfonate Li
It is constituted by dissolving a solute such as CF ₃ SO ₃ . Note that the outer can houses the power generation element, and is immersed in the non-aqueous electrolyte, and then sealed by the sealing body.

[0004]

The non-aqueous electrolyte battery having the above-mentioned structure has excellent discharge characteristics even under a low temperature condition of minus 10 ° C. since it uses a low boiling point solvent. On the other hand, if the battery is left at room temperature for a long time while discharging at least half its discharge capacity, the internal resistance of the battery may gradually increase. If the internal resistance increases, it becomes difficult to take out a large current, and the discharge characteristics deteriorate.

[0005] Such a problem can be expected to be suppressed by reducing the amount of the low boiling point solvent in the electrolytic solution. However, in practice, this leads to an increase in the viscosity of the electrolytic solution, which hinders the movement of ions. . On the other hand, when salicylic acid ester or aromatic dicarboxylic acid ester is added to the electrolytic solution,
It is known that there is an effect of suppressing an increase in internal resistance during storage at room temperature (Japanese Patent Application Laid-Open Nos. 58-68878 and 7-2202069). However, although these techniques are effective in suppressing the increase in the internal resistance of the battery for about one year, when the battery capacity is discharged by 70% or more and stored at room temperature for a long time (about two years or more), Internal resistance increases, and it is easy to suppress the internal resistance.
This is a problem to be solved, for example, in a case where a non-aqueous electrolyte battery is used as a power source for various meters such as a gas meter, in an environment where the battery is used for two years or more, a driving failure due to a voltage drop or the like occurs. is there.

[0006] From the above, it is considered that there is still room for improvement on this subject. The present invention has been made in view of the above problems, and has as its object the internal resistance during long-term storage at room temperature for several years after partial discharge while maintaining the excellent low-temperature discharge characteristics of nonaqueous electrolyte batteries. It is an object of the present invention to provide a non-aqueous electrolyte battery which can suppress the rise of the battery and is suitable for a power supply of various meters.

[0007]

Means for Solving the Problems In view of the above problems, the inventors of the present invention have conducted intensive studies, and have found that an aromatic monocarboxylic acid ester is added as an additive to an electrolytic solution of a non-aqueous electrolyte battery by 1500.
It has been found that the use in the range of 1 to 10,000 ppm realizes the storage characteristics of the battery for two years or more, which was difficult in the past. Accordingly, in order to solve the above problems, the present invention provides a negative electrode made of lithium or a lithium alloy or a carbon material capable of electrochemically storing and releasing lithium, a positive electrode using a metal oxide as an active material, And a non-aqueous electrolyte solution comprising a liquid and an aromatic monocarboxylic acid ester at a concentration of 1500 to 10000 ppm as an additive to the non-aqueous electrolyte.

As the aromatic monocarboxylic acid ester, specifically, a benzoic acid ester is desirable. Benzoic acid ester is an aromatic monocarboxylic acid ester having a relatively low molecular weight, and the weight to be added to the non-aqueous electrolyte can be suppressed with a small amount. Therefore, the non-aqueous electrolyte is prevented from being excessively diluted. In addition, as the alkyl group that substitutes for the hydrogen of the carboxyl group of the aromatic monocarboxylic acid ester, any of a methyl group, an ethyl group, an n-butyl group, an isobutyl group, and a 2-ethylhexyl group has a relatively low molecular weight. desirable.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Configuration of Nonaqueous Electrolyte Battery) FIG.
FIG. 1 is a cross-sectional perspective view showing a configuration of a lithium battery as one application example of the nonaqueous electrolyte battery of the present invention. A lithium battery 100 shown in FIG. 1 has a sheet-shaped positive electrode plate 103 and a negative electrode plate 1 placed on a bottomed cylindrical outer can 101 via a separator 102.
04 is housed in a spiral (spiral) state, and the opening of the outer can 101 is swaged by a sealing plate 106 via an insulating gasket 105 and sealed.

The positive electrode plate 103, the negative electrode plate 104, and the separator 102 are impregnated with a non-aqueous electrolyte. An insulating plate 10 is provided between the power generation element including the separator 102, the positive electrode plate 103, the negative electrode plate 104, and the outer can 101.
7, 108 are interposed. The negative electrode plate 104 is made of a lithium-aluminum alloy, and uses lithium as a negative electrode active material. Alternatively, lithium or a carbon material capable of electrochemically storing and releasing lithium may be used.

The positive electrode plate 103 uses a stainless steel lath core as a current collector and manganese dioxide MnO ₂ as a positive electrode active material. In addition, a metal oxide such as a titanium oxide and a nickel oxide may be used. Separator 10
Reference numeral 2 denotes a polyethylene microporous membrane having a micro-order perforated in the thickness direction so that various components (electrolytic ions) of the nonaqueous electrolyte can flow between the positive electrode plate 103 and the negative electrode plate 104 during power generation. It has become.

In the present embodiment, the solvent of the non-aqueous electrolyte is a low boiling point solvent such as ethylene carbonate (EC), butylene carbonate (BC), or 1,2-dimethoxyethane (DME) in a weight ratio of 25:25:50. Are mixed. In addition, propylene carbonate (P
C), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethoxymethoxyethane (E
Low-boiling solvents such as ME), tetrahydrofuran (THF), and dioxolane (DOL) can be appropriately mixed and used.

On the other hand, the electrolyte of the non-aqueous electrolyte is lithium trifluoromethanesulfonate LiCF in the present embodiment.
₃ SO ₃ is used. In addition, lithium perchlorate LiClO ₄ , lithium hexafluorophosphate LiP
F ₆ , lithium hexafluoroborate LiBF ₆ , lithium hexafluoroarsenate LiAsF ₆ , lithium trifluoromethanesulfonimide (CF ₃ SO ₂ ) ₂ NLi,
Lithium pentafluoroethanesulfonimide (C ₂
F ₅ SO ₂ ) ₂ NLi or the like can be used.

The nonaqueous electrolyte further contains an additive as a feature of the present invention. The additive is an aromatic monocarboxylic acid ester, in which methyl benzoate Ph @ COOCH ₃ is used, and 50% of the additive is contained in the non-aqueous electrolyte.
The concentration is adjusted to be 00 ppm. This methyl benzoate has the following important roles. That is, the non-aqueous electrolyte battery uses a low-boiling solvent to provide excellent discharge characteristics, especially at low temperatures, but when discharged to some extent, it is catalyzed by components such as manganese dioxide contained in the positive electrode, and is subject to aging. There is a tendency to be gradually decomposed. The decomposed solvent component adheres to the surface of the negative electrode, where it forms an inert film. This is a cause of lowering the discharge characteristics of the battery. Under conditions in which the battery is used for a long period of about two years or more (for example, when used as a backup power supply for a gas meter), the amount of electricity is reduced and the drive target is reduced. Is liable to malfunction, which is not preferable. Methyl benzoate is added to suppress such deterioration in the discharge characteristics of batteries, and prevents the decomposition of low-boiling solvents due to the catalytic action of manganese dioxide, etc., and maintains the battery's discharge characteristics for several years. have.

It is effective that such methyl benzoate is present in the non-aqueous electrolyte at a concentration of about 1500 to 10000 ppm. This will be clarified in an embodiment described later. A concentration of 5000 ppm is an example of this concentration range. Note that methyl benzoate is an example of an aromatic monocarboxylic acid ester. However, in order to reduce the weight of additives in the electrolytic solution and not to excessively dilute the electrolytic solution, a relatively low molecular weight aromatic monocarboxylic acid ester is used. Selected as acid ester. For the above-mentioned reason, a low-molecular-weight methyl group is also used for an alkyl group constituting an ester by substituting with hydrogen of a carboxyl group. In addition, an ethyl group, an n-butyl group, an isobutyl group, It is desirable to use one having a relatively low molecular weight such as an ethylhexyl group.

In the lithium battery 100 having such an internal structure, the outer surface of the outer can 101 is covered with an outer film (not shown), and the bottom surface of the outer can 101 is connected to the negative electrode terminal 111.
Becomes On the other hand, the positive electrode terminal 110 is disposed at the center of the sealing plate 106. The positive electrode terminal 110 (negative electrode terminal 111) is connected to the positive electrode tab 103 (negative electrode plate 104) with the positive electrode tab 1
09 (negative electrode tab; not shown), whereby electric power is taken out of the battery.

The nonaqueous electrolyte battery of the present invention is not limited to a cylindrical battery, but may be applied to various types such as a prismatic type and a button type.

[0018]

EXAMPLES Based on the above embodiment, a non-aqueous electrolyte battery of an example was manufactured. At that time, the above-mentioned methyl benzoate and ethyl benzoate were used as additives of the non-aqueous electrolyte. By changing the concentrations of these additives, a total of five types of Example batteries A1 to A5 were produced.
0 ppm (A1), ethyl benzoate 1500 ppm (A
2), methyl benzoate 3000 ppm (A3), methyl benzoate 5000 ppm (A4), methyl benzoate 10
000 ppm (A5)).

As a comparative example, no additive was added (B
1) Ethyl salicylate 1000 as additive for non-aqueous electrolyte
ppm (B2), 1000 ppm of diethyl phthalate (B
3), benzoic acid 1500 ppm (B4), ethyl acetate 1
A sample using 500 ppm (B5), a sample using low-concentration methyl benzoate 1000 ppm (B6), and a high-concentration methyl benzoate 12000 ppm (B7) were prepared.

The detailed steps of manufacturing the battery are as follows. 1. Preparation of positive electrode plate; manganese dioxide 8 as positive electrode active material
5 wt%, artificial graphite 5 wt% and Ketjen black 5 wt% as conductive agents, and fluorocarbon resin 5 w as binder
t% was mixed and formed into a sheet. This was overlaid on both sides of a belt-shaped stainless steel lath core, rolled, cut into a predetermined size, and heat-treated to obtain a positive electrode plate.

2. Preparation of Negative Electrode Plate: A lithium-aluminum alloy was cut into a predetermined size to obtain a negative electrode plate. 3. Preparation of electrolyte solution: 25% by weight of ethylene carbonate,
In a mixed solvent obtained by mixing 25 wt% of butylene carbonate and 50 wt% of 1,2-dimethoxyethane, 0.5 M of lithium trifluoromethanesulfonate was dissolved as a solute. Thereafter, if necessary, additives were added at a predetermined concentration.

4. Assembling of the battery: The positive electrode plate and the negative electrode plate prepared as described above are wound around a polyethylene microporous membrane separator, and are wound into a cylindrical outer can (diameter 17 mm × height 33.5 mm). Stowed. Thereafter, the current collecting tabs of the positive electrode and the negative electrode were connected to predetermined locations, and the sealing body was spot-welded to inject the above electrolyte, and then completely sealed to obtain the batteries of the respective examples.

(Performance Comparison Experiment) Next, a performance comparison experiment was performed on the fabricated example batteries A1 to A5 and comparative example batteries B1 to B7. As an experimental method, each battery was discharged until the discharge capacity reached 70%, stored at room temperature (23 ° C.) for 12 months and 24 months, and the internal resistance before and after storage and pulse discharge characteristics were examined. Was. The experimental results are shown in Table 1 (change in internal resistance) and Table 2 (change in pulse discharge characteristics).

The internal resistance values are shown in Table 1 as relative values of internal resistance before and after storage (relative value of internal resistance = internal resistance value after storage / internal resistance value before storage). The pulse discharge is 10Ω × 100m at low temperature (─10 ° C.)
This was performed under the condition of sec. In Table 2, the pulse discharge characteristics of each battery are represented as a pulse discharge voltage difference (pulse discharge voltage value of Example battery A1 / pulse discharge voltage value of each battery).

[0025]

[Table 1]

[0026]

[Table 2]

(Consideration of Experimental Results) As is clear from Table 1, when an additive is added to the electrolyte solution in Comparative Example Battery B1 in which no additive is added, the internal resistance increases to some extent. It is suppressed. However, the retention period is 1
In the case of continuing over 2 months and continuing up to 24 months, there is a large difference between the example in which the additive is added and the comparative example.
That is, in Comparative Examples B1 to B6, the internal resistance relative value changed at least five times or more, whereas in Examples Batteries A1 to A5, the result that the internal resistance relative value hardly changed was obtained. . Thus, it became clear that the long-term storage characteristics of about 2 years in the examples are superior to those of the comparative examples.

In Comparative Example Battery B7, since methyl benzoate was used in a large amount of 12000 ppm, the decomposition of the low-boiling-point solvent component in the electrolytic solution was suppressed. It is considered that the relative value was maintained. On the other hand, in Comparative Battery B6, although the same methyl benzoate was used, the internal resistance after storage increased due to the small amount of 1000 ppm. For this reason, it is desirable to add at least 1500 ppm or more of methyl benzoate.

However, the results in Table 2 suggest that it is not preferable that the amount of methyl benzoate added is too large, and that the pulse discharge characteristics are adversely affected. The pulse discharge characteristic expresses the battery characteristic based on the stability of the voltage drop at this time when the battery is discharged instantaneously. Here, FIG.
Shows a discharge characteristic diagram of a manganese dioxide-lithium battery as an example. As shown in this figure, for example, 300 mse
In a discharge time as short as c, it can be said that the lower the drop in the discharge battery voltage at that time, the better the performance.

Therefore, since the pulse discharge voltage difference shown in Table 2 is based on the pulse discharge voltage of A1, the larger the absolute value of the value in the minus direction, the larger the value of the battery A of the embodiment.
It can be said that the pulse discharge voltage is superior (i.e., the discharge voltage is higher) than that of Example 1, and that the larger the absolute value in the positive direction is, the lower the pulse discharge voltage is (the lower the discharge voltage) is than the battery A1 of the embodiment. In the example batteries A2 to A5, since the pulse discharge voltage difference was close to 0 over a storage period of 24 months, it can be seen that there was almost no difference from the pulse discharge voltage of the example battery A1, but the comparative example batteries B1 to B7. Since the pulse discharge voltage difference has a relatively large difference in the plus direction, it can be seen that the pulse discharge voltage difference is lower than that of the battery A1 of Example.

In the battery of Comparative Example B7, when the concentration of methyl benzoate is too high, it is considered that this characteristic is not excellent. When the concentration of the additive is as high as about 12000 ppm, the ionic conductivity of the electrolytic solution itself tends to be adversely affected. From these facts, it is desirable to add methyl benzoate in the range of 1500 to 10000 ppm as described in Examples. This is also considered to be substantially the same when ethyl benzoate or another aromatic monocarboxylic acid ester is used.

[0032]

As is apparent from the above, the present invention provides a negative electrode made of lithium or a lithium alloy or a carbon material capable of electrochemically storing and releasing lithium, a positive electrode using a metal oxide as an active material, A non-aqueous electrolyte battery comprising: a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution contains an aromatic monocarboxylic acid ester at a concentration of 1500 to 10000 ppm as an additive, so that the battery is discharged to some extent. Thus, even if the battery is stored for a long period of two years or more, it is possible to suppress an increase in internal resistance and maintain good discharge characteristics as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view of a non-aqueous electrolyte battery as an application example of the present invention.

FIG. 2 is a diagram showing pulse discharge characteristics of a manganese dioxide-lithium battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Outer can 102 Separator 103 Positive electrode plate 104 Negative electrode plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoru Satoru 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Tetsuya Yamashita 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. F term (reference) 5H024 AA03 AA12 CC02 CC12 FF15 FF16 FF18 FF19 HH01 HH02 5H029 AJ04 AK02 AL12 AM03 AM04 AM05 AM06 AM07 BJ02 BJ14 EJ11 HJ10

Claims (3)

[Claims] 1. A non-aqueous electrolyte battery including a negative electrode made of lithium or a lithium alloy or a carbon material capable of electrochemically storing and releasing lithium, a positive electrode using a metal oxide as an active material, and a non-aqueous electrolyte. In the non-aqueous electrolyte, 1500 to 100 as an additive
A nonaqueous electrolyte battery comprising an aromatic monocarboxylic acid ester at a concentration of 00 ppm. 2. The aromatic monocarboxylic acid ester,
The non-aqueous electrolyte battery according to claim 1, which is a benzoate. 3. The aromatic monocarboxylic acid ester,
Methyl group, ethyl group, n-butyl group, isobutyl group, 2
The non-aqueous electrolyte battery according to claim 1 or 2, wherein any of the alkyl groups of the diethylhexyl group is substituted with hydrogen of a carboxyl group.