JPH01167965A - Electric element - Google Patents

Abstract

PURPOSE:To prevent the tendency to come to a low molecular weight by using at least a pair of electrodes, an electrolyte, and a polyolefin type separator, to form an electric element, and including 0.001 to 5wt.% of oxidation preventive agent for polyolefin at least in the electrolyte. CONSTITUTION:In an electric element in which a polyolefin type separator is used for the separator of a cell, an electrolyte capacitor, an electric double- layer capacitor, and the like, 0.001 to 5wt.% of an oxidation preventive agent for polyolefin is included at least in the electrolyte. As a result, the separator is protected from the oxygen, the radical, and the like generated in the element, and the tendency to make a low molecular weight owing to the oxidation deteri oration is suppressed, the deterioration of mechanical strength is minimized, and the solution of the low molecular weight substance into the electrolyte is reduced even though the element is used for a long period high temperature service. In this case, as the polyolefin type resin, polyethylene, polypropylene, or the like is used, and as the electrolyte, non-proton type solvent is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the improvement of electrical elements such as batteries, electrolytic capacitors, electric double layer capacitors, and the like.

[Prior art] Polyolefin microporous membranes, which have excellent pore uniformity and mechanical strength, are being used in electrical devices such as batteries, electrolytic capacitors, and electric double layer capacitors (Japanese Patent Application No. 1983).
1-18851, JP-A No. 61-13614, Utility Model Application No. 59-140429, etc.).

[Problems to be Solved by the Invention] However, there is a problem with the use of such microporous membranes due to the generation of oxygen contained in the device or peroxides/radicals. When used at high temperatures, the polyolefin resin often undergoes oxidative deterioration, becomes lower in molecular weight, becomes mechanically brittle, and may cause short circuits.

In view of this situation, the present invention aims to prevent a decrease in mechanical strength due to oxidative deterioration in the element and provide long-term reliability.

[Means for Solving the Problems] The present invention comprises at least one pair of electrodes, an electrolyte, and a polyolefin separator, and contains at least 0.001 to 5 wt% of an antioxidant for polyolefin in the electrolyte. The present invention relates to an electric element characterized by the following.

In the present invention, an electric element refers to an element such as an electrolytic capacitor, an electric double layer capacitor, a lithium battery, an alkaline battery, etc., and its constituent elements include at least one pair of electrodes, a separator separating them, and an electrolyte, and It is a necessary requirement to use a separator made of polyolefin resin as the separator. Here, polyolefin resins are homopolymers, copolymers, or blends of α-olefins such as polyethylene, polypropylene, poly(4-methylpentene), and polybutene, and among these, high-density polyethylene has excellent solvent resistance and mechanical properties. , polypropylene are preferred as objects of the present invention. Here, the weight average molecular weight of high density polyethylene is 2
X105 or more, preferably 3X105 or more is preferable because mechanical strength will be good. In the case of polypropylene, the intrinsic viscosity is 1.7 to 3.3 dl/g, preferably 2.
1 to 3.3 dl/Q, more preferably 2.7 to 3.2
When it is dl/g, mechanical properties and pinhole resistance are excellent, and long-term reliability is good. Moreover, it is preferable that the isotactic index is 93% or more, preferably 97% or more, since this provides excellent chemical resistance and increases stability against electrolytes.

In addition, in the present invention, the separator may be a nonwoven fabric, a microporous membrane, or a laminate thereof, and among these, the surface pore size is 0.01 to 5 μm, preferably 0.
．． If it is 6 to 4 μm, the short ratio will be small, so it is preferable, and the porosity is 30 to 90%, preferably 50 to 75%.
This is preferable because the amount of electrolyte impregnated is large and long-term reliability is increased.

In addition, if the micropore shape is a network structure or a layered structure resulting from a phase separation method, rather than a shape penetrating in the thickness direction resulting from the lamellar structure of polyolefin, the trap site for conductive particles becomes larger, which may cause leakage current. is preferable because it reduces

In the present invention, at least the electrolyte contains an antioxidant for polyolefins of 0.001. The content is 5 wt%, preferably 0.01 to 2 wt%.

If the amount of the antioxidant added is less than 0.001 wt%, deterioration during long-term high temperature use will cause problems. On the other hand, if the amount added exceeds Swt%, problems often occur in electrical characteristics.

The antioxidant as used in the present invention refers to antioxidants for polyolefins described in "Antioxidant Handbook J (Taisei Column)" and "Polymer Additives/Modifiers Evaluation and Market J (Published by CMC Co., Ltd. Column Column). 2,6-di-t-butyl-p-cresol [BIT], 2,6-di-t-butyl-p-phenol, tetrakis[methylene-3-(3,5-di-t-
Phenolic antioxidants such as butyl-4-hydroxyphenol)-propionate comethane [Irgano x 1010], amine antioxidants such as N,N-diphenyl-p-phenylenediamine, dilauryl Examples include organic sulfur-based antioxidants exemplified by thiodipropionate, phosphite-based antioxidants exemplified by triphenylphosphite, and among these, any one selected from phenolic antioxidants. or a combination thereof is preferable because it has a large effect of inhibiting molecular weight reduction.

The solvent used as the electrolytic solution in the present invention may be any solvent as long as it can dissolve the antioxidant for polyolefin, and among these, propylene carbonate, γ-butyrolactone, dimethylformamide, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, acetonitrile, Aprotic solvents such as dimethyl sulfoxide, dioxolane, and sulfolane are preferred because they have high solubility of antioxidants and excellent affinity for polyolefins.

Furthermore, known solutes such as ammonium salts, amine salts, phthalic acid, and various metal salts can be used.

In addition, if necessary, a copper damage inhibitor for polyolefin (Industrial Chemistry Magazine,
Vol. 71, No. 9 (1068), etc.) may be added. This is particularly preferable when a polyolefin-based separator is used, since the catalytic oxidation deterioration of copper and other heavy metals can be suppressed to a minimum.

The above-mentioned antioxidants, copper damage inhibitors, etc. can be added as an electrolyte composition, coated on a polyolefin separator, or melt-blended with polyolefin. From the viewpoint of controllability or effectiveness of the effect, it is preferable to add it to the electrolytic solution in advance or to coat it on the polyolefin separator.

[Effects of the Invention] According to the present invention, in an electric element using a polyolefin separator as a separator such as a battery, an electrolytic capacitor, an electric double layer capacitor, etc., at least 0.001 to 5 wt% of an antioxidant for polyolefin is contained in the electrolyte. This protects the separator from oxygen, radicals, etc. generated in the element, suppresses lower molecular weight due to oxidative deterioration even during long-term high-temperature use, and minimizes the decrease in mechanical strength.
Moreover, the elution of low molecular weight substances into the electrolytic solution can be reduced, and even during long-term high-temperature use, it is highly reliable and exhibits extremely excellent characteristics.

[Property Evaluation Method and Effect Evaluation Method 1 Next, the characteristics measurement method and effect evaluation method related to the present invention will be summarized.

(1) Surface pore diameter (a) Average value of the long axis of the pore diameter (aχ) and average value of the short axis <av) by scanning electron microscopy (SEM) observation of the sample surface
is measured, and the geometric average shown in the following formula is taken as the surface pore diameter.

a=r-tea@7a7ton (2) Porosity (P) Sample (10xlOcm) Immersed in liquid paraffin for 24 hours, and measured the weight (W2) after thoroughly wiping off the liquid paraffin on the surface layer. , the weight of the sample before immersion! ('Ah) and the density of liquid paraffin (ρ>) using the following formula.

P=(W2-Wl)/(VXρ) Here, ■ is the apparent volume of the sample (a value calculated from the thickness and dimensions).

(3) Mechanical strength Measure the breaking strength in accordance with J I 5K6782.
+/ Expressed in 1.5 mm.

(4) Intrinsic viscosity ([η]) According to ASTM D 1601, 0.1 g of the sample was completely dissolved in 100 ml of tetralin at 135°C, and this solution was measured with a viscometer in a constant temperature bath at 135°C to determine the ratio. It is determined from the viscosity S according to the following formula.

[η]=S/NO,LX (1+0.22XS>)(5
) Isotactic index (II > sample 1
Vacuum dry at 30°C for 2 hours. A sample of weight W (■) is taken from this, placed in a Soxhlet extractor, and extracted with boiling n-hebutane for 12 hours.

Next, take out this sample, wash it thoroughly with acetone, and then
After vacuum drying at 130°C for 6 hours, the weight W' (■) is measured and calculated using the following formula.

II (%)=(W'/W)X100(6) Weight average molecular weight Measured by GPC under the following conditions.

1. Equipment Nigel permeation chromatograph, GPC-150C
(WATER3>2, column: 5hodex KF-90M3,
Solvent: 0-dichlorobenzene (135°C) [Example] Next, Examples and Comparative Examples of this invention will be shown to explain the effects of this invention more specifically.

(Preparation of polyolefin separator) As the polyolefin resin, polypropylene powder (intrinsic viscosity = 3.
0 dl/CI, II=97%) was prepared, and 150 parts by weight of dicyclohexyl phthalate (DCHP) was melt-blended to 100 parts by weight of PP, extruded into a sheet using a T-die, and cooled and solidified. D still included in the sheet
After 99% of CHP was extracted and removed with 1-1-1 trichloroethane, drying was performed. Continue at 120℃ 3
．． Stretched 5 times in the longitudinal direction and further stretched 1 time in the transverse direction at 135°C.
．． It was stretched 4 times and wound up. As a result, the film thickness was 30 μm, the surface pore diameter was 1.2 μm, the porosity was 70%, and the longitudinal strength was 2.6
kg/15mm.

[Example] We prepared an electrolyte in which 1.0M LiBF4 propylene carbonate solution and dimethoxyethane were mixed at a volume ratio of 1:1 (electrolyte 0).

To this, ■rganox 1oio (tetrakis[methylene-3-(3,5-di℃-butyl-4-hydroxyphenol)-propionate comethane>0.1wt%
Added electrolyte (electrolyte 1) and Irganox 10
An electrolyte solution (electrolyte solution 2) to which 0.1 wt% of No. 10 and 0.05 wt% of oxalic acid were added was prepared.

A button-type battery consisting of lithium metal/3 separators/graphite fluoride was constructed using the above electrolyte. (Those using electrolyte 0 → Comparative example 1, hereinafter electrolyte 1 → Example 1,
Electrolyte 2 - Example 2) Regarding the above battery, 60°C x 20
A low-temperature storage test of 00 hours storage → -20° C. x 50 hours was performed, and the device was disassembled and the mechanical strength, intrinsic viscosity, and appearance of the separator were tested.

The above results are summarized in Table 1. In Examples 1 and 2, in which an antioxidant or a copper damage inhibitor was added to the electrolyte, the mechanical strength hardly changed.
In Comparative Example 1, which does not contain such additives, the mechanical strength has decreased to about half of that before the device was fabricated, and cracks have appeared in some areas, indicating that there is a risk of short circuits, etc. if the device is used as is. There is.

Table 1

Claims (2)

[Claims] (1) Consisting of at least one pair of electrodes, an electrolyte, and a polyolefin separator, at least 0.
An electrical element characterized by containing 0.001 to 5 wt% of an antioxidant for polyolefin. (2) The electric device according to claim (1), wherein the electrolyte comprises an aprotic solvent.