JPH06333595A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To provide excellent storing property and cycle characteristic by adding benzine and/or its derivative to an nonaqueous electrolyte. CONSTITUTION:In an nonaqueous electrolyte battery BA1, a positive electrode 1 and a negative electrode 2 are housed in a battery case formed by positive and negative electrode systems 4, 5 in opposition to each other through a separator 3 impregnated with an electrolyte. The negative electrode 2 uses a material capable of storing and releasing metal lithium or lithium as the negative electrode material. Benzine and/or its derivative are added to the nonaqueous electrolyte. As the benzine derivatives are given those in which at least one hydrogen of four hydrogen atoms in total of two amino groups in benzine is substituted by a hydrocarbon group such as alkyl group, phenyl group and benzyl group. Thus, the nonaqueous electrolyte is difficult to decompose and deteriorate.

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, generally, an oxide of a metal such as manganese, cobalt, nickel, vanadium or niobium or two or more kinds of these metals are contained. Complex oxides 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 during charging when the positive electrode has 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, benzidine (4,4′-diaminobiphenyl) and / or its derivative (hereinafter, these benzidine and its derivative) are contained in the non-aqueous electrolyte. May be collectively referred to as “benzidines”).

As the benzidine derivative in the present invention, at least one hydrogen atom out of a total of four hydrogen atoms of two amino groups in benzidine is a hydrocarbon group such as an alkyl group, a phenyl group and a benzyl group. Examples thereof include those substituted with N, N, N ', N'-tetramethylbenzidine, N, N, N', N'-tetraethylbenzidine, N, N, N ', N'-tetra. Examples include propylbenzidine, N, N, N ', N'-tetrabutylbenzidine and N, N, N', N'-tetraphenylbenzidine. In addition, salts having chlorine ion, bromine ion and the like as counter ions are also included in the benzidine derivative of the present invention. These additives may be added alone or in combination of two or more as required.

The benzidines in the present invention must be substances 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 addition ratio of the benzidines to the non-aqueous electrolyte varies slightly depending on the total amount of the non-aqueous electrolyte in the battery, but is usually 1 × 10 ⁻³ mol / liter or more in order to obtain a significant addition effect. There is a need. It is preferably added in the range of 0.01 to 1 mol / 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 benzidines gradually react with the positive electrode or the negative electrode, so that the storage characteristics and 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 has been 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 a non-aqueous electrolyte is used, but it is used as an additive to a positive electrode active material. Since the benzidines also have 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 higher in the normal state (during storage or normal charging). The material is not necessarily limited.

The present invention is characterized in that benzidines are 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, non-aqueous electrolyte, other members constituting the battery such as a separator is not particularly limited, conventionally used for non-aqueous electrolyte battery, or it is possible to use various proposed materials without particular limitation. It is possible.

For example, as the solvent of the non-aqueous electrolyte solution, organic solvents such as ethylene carbonate, vinylene carbonate and propylene carbonate, and these and dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 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, it is possible to use a solid electrolyte instead of the above liquid electrolyte.

[0019]

In the battery of the present invention, since at least one kind of benzidine is added to the non-aqueous electrolyte, the reaction between the positive electrode active material and the non-aqueous electrolyte occurs even when stored for a long time or overcharged. Difficult to decompose and deteriorate the non-aqueous electrolyte. The reason for this is presumed as follows.

That is, since benzidines have a conjugated double bond in the molecule, the resonance stabilizing effect of the molecule is high. Therefore, when the potential of the positive electrode becomes high due to charging or the like, it is oxidized on the positive electrode side, as shown in the following chemical formula 1. Generates cations (cations). When the oxidation potential of the benzidines is lower than the oxidation potential of the non-aqueous electrolyte, the oxidation reaction of the benzidines shown in Chemical formula 1 takes precedence over the oxidation reaction of the non-aqueous electrolyte. In other words, benzidines are sacrificed (dummy)
And is oxidized to suppress the oxidative decomposition of the solvent in the non-aqueous electrolyte. Since benzidines are excellent in the reversibility of redox reaction, the generated cations diffuse in the non-aqueous electrolyte and are reduced on the negative electrode side as shown in the following Chemical formula 2 to return to the original benzidines. , Is repeatedly used as a dummy for the oxidation reaction on the positive electrode side.

[0021]

[Chemical 1]

[0022]

[Chemical 2]

[0023]

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 produced.

[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 solution of 1M, N, N,
0.01 mol of N ', N'-tetramethylbenzidine /
An electrolytic solution was prepared by adding it at a ratio of 1 liter.

[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 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 facing each other with a separator 3 impregnated with an electrolytic solution in between, and the positive electrode 1 includes 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, a mixed solvent of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 5: 3: 2 was used in place of ethylene carbonate, propylene carbonate and ethoxymethoxy. 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, N,
Comparative battery BC1 was prepared in the same manner as in Example 1 except that N, N ′, N′-tetramethylbenzidine was not added.
Was produced.

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

(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 instead of ethylene carbonate, propylene carbonate and ethoxymethoxy. 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 N, N, N ′, N′-tetramethylbenzidine 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 Characteristic] 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.

[0039]

[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) N, N, N ', N'-tetramethylbenzidine, instead of 0.01 mol / liter, N, N, N', N'-tetraethylbenzidine,
N, N, N ', N'-tetrapropylbenzidine, N,
N, N ', N'-tetrabutylbenzidine or N, N,
Inventive batteries BA4 to BA7 were sequentially manufactured in the same manner as in Example 1 except that N ′, N′-tetraphenylbenzidine was used at 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 benzidines are added to the electrolytic solution have a longer cycle life and excellent cycle characteristics as compared with the comparative battery BC1 without addition.

In the above embodiments, the case where the present invention is applied to the flat rectangular type 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.

Further, in the above embodiment, the case where the present invention is applied to the secondary battery has been described. However, since the present invention battery does not increase the internal impedance or the battery thickness in the overcharged state, the present invention Can be suitably applied to a primary battery for memory backup which is stored in an overcharged state.

[0045]

In the battery of the present invention, since benzidine and / or its derivative is added to the non-aqueous electrolyte, decomposition and deterioration of the non-aqueous electrolyte hardly occur.
The present invention has excellent unique effects such as excellent battery characteristics such as cycle characteristics.

[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 using metallic lithium or a substance capable of inserting and extracting lithium as a negative electrode material, a positive electrode, and a non-aqueous electrolyte, wherein benzidine and / or a derivative thereof is contained in the non-aqueous electrolyte. Is added to the non-aqueous electrolyte battery. 2. The derivative is N, N, N ′, N′-tetramethylbenzidine, N, N, N ′, N′-tetraethylbenzidine, N, N, N ′, N′-tetrapropylbenzidine, The non-aqueous electrolyte battery according to claim 1, which is at least one benzidine derivative selected from the group consisting of N, N, N ', N'-tetrabutylbenzidine and N, N, N', N'-tetraphenylbenzidine. .