JPH06333596A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To provide excellent battery characteristics such as storing characteristic and cycle characteristic by adding a specified azo compound to an nonaqueous electrolyte. CONSTITUTION:An nonaqueous electrolyte battery has a negative electrode using a material capable of storing and releasing metal lithium or lithium as the negative electrode material, a positive electrode, and an nonaqueous electrolyte. In the nonaqueous electrolyte battery, an azo compound represented by the formula is added to the nonaqueous electrolyte. In the formula, R<1>, R<2>, R<3>, R<4> each represents a hydrogen atom or hydrocarbon group independently. Examples of the azo compound include 4,4'-tetramethyldiamino azobenzene, 4,4'-tetraethyldiamino azobenzene, 4,4'-tetrapropyldiamino azobenzene, 4,4'- tetrabutyldiamino azobenzene, and 4,4'-tetraphenyldiamino azobenzene.

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 specifically, to prevent deterioration of storage characteristics, cycle characteristics, etc. due to decomposition and deterioration of a solvent in the non-aqueous electrolyte on the positive electrode side. To improve the non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years,
Non-aqueous electrolyte batteries such as lithium batteries differ from batteries that use water-containing electrolytes such as nickel-cadmium batteries,
Since it is not necessary to consider the decomposition voltage of water, it is possible to design a high voltage of 3 V or more, and it is in the spotlight.

As a positive electrode active material for such a high voltage type non-aqueous electrolyte battery, manganese, cobalt,
Oxides of metals such as nickel, vanadium, and niobium, or composite oxides containing two or more of these metals are used.

However, the above metal oxide or composite oxide easily reacts with the non-aqueous electrolyte, so that the solvent in the non-aqueous electrolyte decomposes during storage of the battery, and its decomposition product (polymerized product). Etc.) adhere to the electrodes, resulting in an increase in the internal resistance (internal impedance) of the battery after storage and a decrease in the discharge characteristics, or in the case of a secondary battery, a further decrease in the cycle characteristics. There was a problem. Incidentally, such a decomposition reaction of the solvent remarkably occurs when the positive electrode is charged at a high potential.

By the way, attempts to improve the storage characteristics and cycle characteristics by suppressing the decomposition reaction of the above-mentioned solvent have been made in the past, and, for example, tetrahydrofuran (TH
F), 1,3-dioxolane (DOXL) and other cyclic ethers have been proposed in an attempt to stabilize some of the hydrogen atoms by substituting them with an alkyl group or the like to prevent decomposition and deterioration (J.
L. Goldman, RM Mank, JH Young and VR Koc
h: J. Electrochem. Soc., 127,1461 (1980)).

However, it is difficult to sufficiently stabilize the non-aqueous electrolyte even by such modification by alkylation of the cyclic ether, and it is possible to effectively suppress the decomposition reaction of the non-aqueous electrolyte on the high potential positive electrode side. The reality is that it has not arrived. In particular, in the case of a secondary battery, it has been pointed out that, when overcharged, the decomposition reaction of the solvent accompanied by the generation of carbon dioxide gas on the positive electrode rapidly progresses, and the battery characteristics are significantly deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a non-aqueous electrolyte battery having excellent battery characteristics such as storage characteristics and cycle characteristics.

[0008]

A non-aqueous electrolyte battery according to the present invention (hereinafter, referred to as "the battery of the present invention") for achieving the above object is a negative electrode made of metallic lithium or a substance capable of occluding and releasing lithium. In a non-aqueous electrolyte battery including a negative electrode as a material, a positive electrode, and a non-aqueous electrolyte, an azo compound represented by the following chemical formula 2 is added to the non-aqueous electrolyte.

[0009]

[Chemical 2]

However, R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom or a hydrocarbon group.

Specific examples of the azo compound in the present invention include 4,4'-tetramethyldiaminoazobenzene,
4,4'-tetraethyldiaminoazobenzene, 4,
4'-tetrapropyldiaminoazobenzene, 4,4 '
-Tetrabutyldiaminoazobenzene and 4,4'-tetraphenyldiaminoazobenzene. These azo compounds may be added alone or in combination of two or more as required.

The azo compound in the present invention must be a substance whose oxidation potential is nobler than the charging voltage of the battery and less noble than the decomposition voltage of the non-aqueous electrolyte.
This is because if the oxidation potential is lower than the charging voltage, charging becomes impossible, and if it is nobler than the decomposition voltage of the non-aqueous electrolyte, decomposition of the non-aqueous electrolyte cannot be suppressed.

The proportion of the azo compound added to the non-aqueous electrolyte varies slightly depending on the total amount of the non-aqueous electrolyte in the battery, but it is usually 1 × 10 ^-3 mol / mol in order to obtain a significant addition effect.
It is necessary to add more than 1 liter. 0.01-1 mol /
It is preferable to add in the range of 1 liter. If the addition ratio is less than 0.01 mol / l, the effect of addition is not sufficiently exhibited, and if it exceeds 1 mol / l, the conductivity decreases due to the relative decrease in the amount of electrolyte. Or the excess azo compound gradually reacts with the positive electrode or the negative electrode, so that the storage characteristics and the cycle characteristics tend to deteriorate.

In the present invention, metallic lithium or a substance capable of inserting and extracting lithium is used as the negative electrode material. Examples of the substance capable of inserting and extracting lithium include lithium alloys, carbon materials such as graphite and coke,
Graphite is particularly preferable because it has a large amount of lithium storage and release (capacity).

The positive electrode material (active material) in the present invention is, for example, an oxide of a metal such as manganese, cobalt, nickel, vanadium or niobium, which is conventionally used in a non-aqueous electrolyte battery having a battery voltage of 3 V or more. (LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ etc.)
Alternatively, a composite oxide containing two or more of these metals (Li
_{Ni x Co 1-x O 2} ( where, 0 <x <1), etc.).

The effect of the present invention is remarkably exhibited when a high-potential type positive electrode material having a high potential and which easily induces decomposition and deterioration of the non-aqueous electrolyte is used, but it is used as an additive to the positive electrode active material. Since the azo compound also has a function of suppressing decomposition and degradation of the non-aqueous electrolyte during overcharge, the positive electrode material in the present invention exhibits a high potential of 3 V or more in the normal state (storage or normal charging). The material is not necessarily limited.

The present invention is characterized in that an azo compound is added to a non-aqueous electrolyte to prevent decomposition and deterioration in order to obtain a non-aqueous electrolyte battery having excellent battery characteristics such as storage characteristics and cycle characteristics. Therefore, other members constituting the battery such as non-aqueous electrolyte is not particularly limited, it is possible to use various materials conventionally used for non-aqueous electrolyte battery, or proposed various materials without particular limitation. is there.

For example, as the solvent for the non-aqueous electrolytic solution, organic solvents such as ethylene carbonate, vinylene carbonate and propylene carbonate, and dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane and 1,2-diethoxyethane are used. And a mixed solvent with a low boiling point solvent such as ethoxymethoxyethane.

As the solute of the non-aqueous electrolyte, lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoroantimonate (LiSbF ₆₎ are exemplified.

As the non-aqueous electrolyte in the present invention, a solid electrolyte may be used instead of the above liquid electrolyte.

[0021]

In the battery of the present invention, since at least one azo compound is added to the non-aqueous electrolyte, the reaction between the positive electrode active material and the non-aqueous electrolyte occurs even after long-term storage or overcharging. Difficult to decompose and deteriorate the non-aqueous electrolyte. The reason for this is presumed as follows.

That is, since the azo compound has a conjugated double bond in the molecule, it has a high resonance stabilizing effect on the molecule. Therefore, when the positive electrode potential becomes high due to charging or the like, it is oxidized on the positive electrode side, as shown in the following chemical formula 3. Generates cations (cations). When the oxidation potential of this azo compound is lower than that of the non-aqueous electrolyte, the oxidation reaction of the azo compound shown in Chemical formula 3 takes precedence over the oxidation reaction of the non-aqueous electrolyte. In other words, the azo compound acts as a sacrifice (dummy) and is oxidized to suppress the decomposition of the solvent in the non-aqueous electrolyte. Since the azo compound is excellent in the reversibility of the redox reaction, the generated cation diffuses in the non-aqueous electrolyte and is reduced on the negative electrode side as shown in Chemical Formula 4 below to return to the original azo compound. , Is repeatedly used as a dummy for the oxidation reaction on the positive electrode side.

[0023]

[Chemical 3]

[0024]

[Chemical 4]

[0025]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples, and various modifications can be made without departing from the scope of the invention. Is possible.

Example 1 A flat type non-aqueous electrolyte secondary battery was prepared.

[Cathode] As the cathode active material, manganese dioxide heat-treated at 375 ° C. is used.
Carbon powder as a conductive agent and fluororesin powder as a binder were mixed at a weight ratio of 85: 10: 5, and then this mixture was pressure-molded and then heat-treated at 250 ° C to give a disc shape. The positive electrode of was produced.

[Negative Electrode] A rolled lithium plate was punched into a predetermined size to prepare a disk-shaped negative electrode.

[Electrolyte] Ethylene carbonate (EC)
Lithium trifluoromethanesulfonate (LiCF) in a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 5: 3: 2.
₃ SO ₃ ) in a 1M solution,
4'-Tetramethyldiaminoazobenzene was added at a rate of 0.01 mol / liter to prepare an electrolytic solution.

[Production of Battery] A flat type battery BA1 of the present invention (outer diameter: 20 mm;
Thickness: 2.5 mm) was produced. As the separator, a polypropylene microporous film (made by Celanese,
The product name "Celgard") was used and impregnated with the electrolytic solution.

FIG. 1 is a cross-sectional view schematically showing the produced battery BA1 of the present invention. The battery BA1 of the present invention shown in FIG.
It comprises a positive electrode 1, a negative electrode 2, a separator 3 separating these electrodes 1 and 2 from each other, a positive electrode can 4, a negative electrode can 5, a positive electrode current collector 6, a negative electrode current collector 7 and an insulating packing 8 made of polypropylene.

The positive electrode 1 and the negative electrode 2 are housed in a battery case formed by positive and negative bipolar cans 4 and 5 which face each other with a separator 3 impregnated with an electrolytic solution interposed therebetween. The positive electrode 1 has a positive electrode current collector 6. To the positive electrode can 4 and the negative electrode 2 to the negative electrode can 5 via the negative electrode current collector 7 so that the chemical energy generated inside the battery can be output as electrical energy from both terminals of the positive electrode can 4 and the negative electrode can 5 to the outside. You can take it out.

Example 2 A battery BA2 of the present invention was produced in the same manner as in Example 1 except that lithium hexafluorophosphate was used as the solute of the electrolytic solution instead of lithium trifluoromethanesulfonate.

Example 3 As a solvent for the electrolytic solution, instead of a mixed solvent of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 5: 3: 2, ethylene carbonate, propylene carbonate and ethoxymethoxy were used. Volume ratio with ethane (EME) 5: 3:
Battery BA3 of the present invention was produced in the same manner as in Example 2 except that the mixed solvent of No. 2 was used.

(Comparative Example 1) In the preparation of the electrolytic solution,
Comparative battery BC1 was prepared in the same manner as in Example 1 except that 4′-tetramethyldiaminoazobenzene was not added.
Was produced.

Comparative Example 2 A comparative battery BC2 was prepared in the same manner as in Comparative Example 1 except that lithium hexafluorophosphate was used instead of lithium trifluoromethanesulfonate as the solute of the electrolytic solution.

(Comparative Example 3) As a solvent for the electrolytic solution, a mixed solvent of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 5: 3: 2 was used, and ethylene carbonate, propylene carbonate and ethoxymethoxy were used. Volume ratio with ethane (EME) 5: 3:
A comparative battery BC3 was produced in the same manner as in Comparative Example 2 except that the mixed solvent of No. 2 was used.

[Cycle characteristics] Under normal temperature (25 ° C), 2
A charging / discharging cycle test in which one cycle includes a step of discharging at 2 mA for 4 hours after charging to a cutoff voltage of 3.5 V at mA, and the cycle characteristics of each battery were investigated. The time when the discharge voltage reached 2.4 V within the discharge time was determined as the life of each battery, and the charge / discharge cycle test was terminated at that time. The results are shown in FIGS. 2, 3 and 4.

2 to 4 show the cycle characteristics of each battery,
It is a graph in which the vertical axis represents the discharge end voltage (V) in each cycle, and the horizontal axis represents the number of cycles (times).
From these figures, batteries BA1 to BA3 of the present invention in which 4,4′-tetramethyldiaminoazobenzene was added to the electrolytic solution
Indicates that the cycle life is long and the cycle characteristics are excellent as compared with the comparative batteries BC1 to BC3 in which it was not added, because the decomposition degradation of the electrolytic solution is small.

[Overcharge Characteristics] Ten batteries BA1 of the present invention and 10 batteries of the comparative battery BC2 were prepared, and the battery voltage of each battery was changed to 4V which was higher than the normal end-of-charge voltage.
It was maintained for 0 days (overcharged state), and changes in the internal impedance and battery thickness of each battery at that time were examined. The results are shown in Table 1.

[0041]

[Table 1]

As shown in Table 1, the battery BA1 of the present invention is
It can be seen that, as compared with the comparative battery BC2, the decomposition and deterioration of the electrolytic solution is small, so that the increase in the internal impedance and the increase in the battery thickness in the overcharged state are generally small and the reliability is high.

(Examples 4 to 7) 4,4'-tetramethyldiaminoazobenzene was replaced with 0.01 mol / liter of 4,4'-tetraethyldiaminoazobenzene,
4,4'-tetrapropyldiaminoazobenzene, 4,
4'-Tetrabutyldiaminoazobenzene or 4,4 '
-Invention batteries BA4 to BA7 were sequentially manufactured in the same manner as in Example 1 except that tetraphenyldiaminoazobenzene was used in the same ratio.

[Cycle Characteristics] A charge / discharge cycle test was conducted under the same conditions as above to examine the cycle characteristics of each battery. The results are shown in FIG. 5, which is a graph of the same coordinate system as in FIGS. For comparison, the cycle characteristics of the comparative battery BC1 described above are also shown in the figure. From the figure, it is understood that the batteries BA4 to BA7 of the present invention in which the azo compound is added to the electrolytic solution have a longer cycle life and excellent cycle characteristics as compared with the comparative battery BC1 in which nothing is added.

In the above embodiments, the case where the present invention is applied to the flat rectangular non-aqueous electrolyte battery has been described as an example, but the shape of the battery is not particularly limited, and various types such as a cylindrical type and a square type are used. It can be applied to a non-aqueous electrolyte battery having the above shape.

In the above embodiments, the case where the present invention is applied to the secondary battery has been described. However, since the present invention battery has a small increase in internal impedance and increase in battery thickness in an overcharged state, the present invention Can be suitably applied to a primary battery for memory backup which is stored in an overcharged state.

[0047]

Since the azo compound is added to the non-aqueous electrolyte in the battery of the present invention, decomposition and deterioration of the non-aqueous electrolyte is less likely to occur, and therefore the battery characteristics such as storage characteristics and cycle characteristics are excellent. Has an excellent and unique effect.

[Brief description of drawings]

FIG. 1 is a flat type non-aqueous electrolyte battery (invention battery BA
It is a sectional view of 1).

FIG. 2 is a graph showing cycle characteristics of a battery BA1 of the present invention and a comparative battery BC1 manufactured in Examples.

FIG. 3 is a graph showing cycle characteristics of the battery BA2 of the present invention and the comparative battery BC2 manufactured in Examples.

FIG. 4 is a graph showing cycle characteristics of a battery BA3 of the present invention and a comparative battery BC3 manufactured in an example.

FIG. 5 is a graph showing cycle characteristics of inventive batteries BA4 to BA7 and comparative battery BC1 produced in Examples.

[Explanation of symbols]

 BA1 non-aqueous electrolyte battery (the battery of the present invention) 1 positive electrode 2 negative electrode 3 separator

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Toshihiko Saito 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a negative electrode having a negative electrode material of metallic lithium or a substance capable of inserting and extracting lithium, a positive electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is represented by the following chemical formula 1. A non-aqueous electrolyte battery, wherein an azo compound is added. [Chemical 1] (However, R ¹ , R ² , R ³ , and R ⁴ are each independently a hydrogen atom or a hydrocarbon group.) 2. The azo compound is 4,4′-tetramethyldiaminoazobenzene, 4,4′-tetraethyldiaminoazobenzene, 4,4′-tetrapropyldiaminoazobenzene, 4,4′-tetrabutyldiaminoazobenzene and 4 The non-aqueous electrolyte battery according to claim 1, which is at least one azobenzene derivative selected from the group consisting of 4,4'-tetraphenyldiaminoazobenzene.