DE2449282A1 - ELECTROLYTE FOR ELECTROLYTIC CAPACITORS AND CAPACITOR WITH SUCH ELECTROLYTE - Google Patents

Description

Dipl.-Phys. L.Thul

Stuttgart

M.G.Pringuet 2

International Standard Electric Corporation, New York

Electrolyte for electrolytic capacitors and capacitors with such an electrolyte

The present invention relates to electrolytic capacitors, particularly to anhydrous electrolytes for such capacitors, whereby the capacitors are operated at ambient temperatures of - 55 C to + 105 C. and the electrical properties remain stable.

The development of new anhydrous electrolytes became necessary because aqueous electrolytes have the disadvantage that a gradual hydration of the anodic dielectric layer occurs, so that the oxide in an ineffective Oxide is converted. This phenomenon can be observed from the fact that both the capacity of the Capacitor as well as the residual current increase over time.

It has already been proposed to determine the water content in the known To reduce electrolytes, but on the other hand one achieves that the resistance increases, whereby the Series resistance and the loss factor of the capacitor increase. ...

Fri / b - 27.9.197U. /.

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M.G.Pringuet 2

For these reasons, aqueous electrolytes cannot be used for extreme temperatures from - 55 C to + 10 5 C. will. In order to overcome the above difficulties, various manufacturers have tried anhydrous electrolytes to manufacture. Most of the non-aqueous solvents have a low specific inductive capacity with little dissociative force with respect to compounds dissolved in these solvents will. This creates additional difficulties in obtaining an acceptable resistance, especially in the case of extreme Temperatures. Furthermore, anhydrous electrolyte components must be used be thermally stable so that capacitors containing such electrolytes do not age have their electrical properties. It is also known that traces of water can also be found in anhydrous electrolytes must be present for the electrolytic capacitor to operate satisfactorily.

The object of the present invention is to provide an anhydrous electrolyte for the impregnation of electrolytic Capacitors with one or more electrodes covered with an insulating dielectric layer, to accomplish.

This object is achieved in that the electrolyte has the following composition:

Probylene carbonate from 3 5.5% to 43.5% ^ "- Butyolactone from 35.5% to 43.5% N methylacetamide from 1.4% to 16.2% picric acid from 7.5% to 8.7% crystallized citric acid from 0.5% to 0.6% tetramethylguanxdxn from 3, §% to 3.6%

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M.G.Pringuet 2

In the case of the electrolyte according to the invention, the electrical properties of the impregnated with the mixture To change capacitors, the propylene carbonate is replaced by a mixture containing 3.2% to 4.3% Ethylene carbonate and 3 2% to 3 8.15% propylene carbonate. The N methylacetamide can be replaced by NN dimethylacetamide in a proportion of 1.5% to 20%.

The invention further consists in electrical capacitors which contain this electrolyte, as well as one or several electrodes made of aluminum, which are covered with a dielectric aluminum layer.

In the following description, the term "electrode" is used to refer to either the capacitor anode or the capacitor cathode Understood.

The invention will be explained in more detail using an exemplary embodiment and the drawings.

Figure 1 shows a schematic perspective view a coil for an electrolytic capacitor according to the invention;

Figure 2 shows schematically a cross section through an electrolytic capacitor according to the invention.

In Figure 1 is a manufactured according to the known method Capacitor winding 1 is shown, a part of which is unwound. The winding 1 consists of four wound one on top of the other Foils 2, 3, U and 5. The metal foil 2 is

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the anode and the metal foil 4 is the cathode of the capacitor, while the foils 3 and 4 are between the foils 2 and 4 are arranged and consist of more or less porous dielectric material. For example, can the dielectric material will be paper. The anode, which is preferably made of aluminum, is provided with an insulating dielectric layer covered by alumina. The foils 3 and 5 are wider than the anode 2 and the Cathode 4. A metal strip 6 is attached to the anode 2 and a metal strip 7 is attached to the cathode 4. These form the electrical connections for the roll 1.

FIG. 2 shows a cross section through an electrolytic capacitor with a coil 1 according to FIG. 1. The coil 1 is arranged in a cylindrical metal housing 8. The connecting strip 6 of the anode 2 is connected to a metal rivet 9, while the connecting strip 7 of the cathode 4 is attached to the bottom of the housing opposite the rivet 4. The housing 8 is sealed around the rivet 9 by two discs 10 and 11 lying one on top of the other, the disc 10 consisting of thermosetting synthetic material and the disc 11 consisting of thermoplastic synthetic rubber. A connection line 12 is attached to the rivet 9 and represents the positive capacitor termination, while the connection 13 is attached to the housing 8 and forms the negative capacitor connection. An anhydrous electrolyte (not shown) with the composition and properties as defined above according to the invention forms the impregnation of the capacitor winding 1. The impregnation is carried out under vacuum before the winding 1 is introduced into the housing 8.

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M.G.Pringuet 2

The above description refers to a polar one Capacitor. However, the invention can also be applied to non-polar electrolytic capacitors. In this case, the cathode, as previously described, the anode, preferably made of aluminum and is with an alumina dielectric layer while the other parts of the capacitor are the same.

The effect of the individual chemical compounds contained in the electrolyte according to the invention, is now to be described in detail on the basis of experiences, which mainly with binary or ternary mixtures with ethylene carbonate, propylene carbonate, Butyrolactone, N methylacetamide and NN dimethylacetamide were made.

Ethylene carbonate (or 1,3-dioxolane 2.1) is preferred together with propylene carbonate (or ^ -Methyl-1,3-dioxolane 2.1) used as a solvent because it has a high dielectric constant (£, = 8 9.1 at 40 ° C). A mixture in a ratio of about 10% ethylene carbonate and 90% ■ propylene carbonate gives mixtures which are still liquid up to about - 50 C.

Propylene carbonate (melting point - 49.2 ° C, boiling point 241.7 ° C) has properties that make it possible to manufacture capacitors with low impedance, this impedance only has little change with temperature. The dissozi " enden power of this substance is excellent in terms of ion formers, which are used in capacitors with a low loss angle can be used due to the low electrolyte viscosity.

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However, electrolytes which contain butyrolactone are already known, especially in mixtures with substituted ones Amides.

However, it was found that the mixture according to Invention of propylene carbonate and ^ -butyrolactone in particular is suitable for the production of non-aqueous electrolytes when the proportion of propylene carbonate is down moved within the limits of 2 5% to 75% of the mixture. With an equimolar ratio (^ -butyrolactone 1 + 5.7% and propylene carbonate 54.3%) the mixture is still liquid up to around - 6 5 ° C.

The addition of NN dimethylacetamide to the propylene carbonate makes it possible to produce a mixture that is very low Has viscosity at the temperatures of interest between the melting point and "the boiling point. With Considering the solidification curve, however, it is recommended that a proportion of between 20% and 70% of NN dimethylacetamide be used not to exceed.

The investigation of the mixtures of propylene carbonate and N methylformamide has shown that electrolytes for the Manufacture of capacitors with very low series resistance and low impedance at low temperature can be obtained. If N methylformamide is not to be used because of its toxicity, it can can be replaced by N methylacetamide with the same result.

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The aforementioned substances can form ternary compounds that act as anhydrous electrolyte solvents suitable for capacitors. Investigations have shown that the two solvents mentioned as examples the manufacture of capacitors of the type described with excellent electrical properties and excellent aging behavior enable:

Example 1 Example 2

Propylene carbonate from 47 to 54.5% 40% j ^ -Butyrolactone from 44 to 50% 40%

N methylacetamide from 1.5 to 3% 20%

The percentages mentioned can be around -5% of the values mentioned for the two substances mentioned first deviate without a significant change in the aging behavior or the electrical properties.

The N-methylacetamide acts in the two compositions as a donor of ions H and indirectly prevents deterioration of the anodic aluminum oxide layer and thereby avoids changes in capacity.

By adding oxidizing and non-oxidizing ionic substances Mixtures I and II contain the complete electrolyte (see also Examples III and IV).

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The action of an anion-type oxidizing ionogen is to remove the anodic aluminum oxide layer which is responsible for good condenser functioning is required to maintain and heal. To these ionogens, which are soluble in the said binary and termary mixtures include picric acid, oxalic acid and citric acid, however, other suitable acids such as formic acid, acetic acid and tartaric acid can also be used.

These mixtures can be improved by an ionic additive, which is non-oxidizing but very easily dissociable, and which has the important function of providing stable conditions on the inside of the capacitor to generate and to reduce the electrolyte resistance. Such an agent is 1,1,3,3-tetramethylguanidine, the one is a strong organic base and, depending on the percentage selected, it increases the electrolyte resistance set a predetermined value. Another advantage of 1,1,3,3-tetramethylguanidine is that it has oxidize acids does not form water.

Two other examples of capacitors, as shown in Figures 1 and 2, contain electrolytes, which in their basic composition consist of the above-mentioned substances and their composition in percent by weight is given below:

Example III Example IV

Propylene carbonate 43.5% 35.5%

^ "- butyrolactone 43.5% 35.5%

N methylacetamide 1.4% 16.2%

Picric acid 7.5% 8.7%

crystallized lemon - 0.5% 0.6%

acid

1,1,3,3-tetramethylguanidine 3.6% 3.5%

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The electrolysis mentioned in Examples III and IV allow the manufacture of two types of capacitors, one 100 .uF at 63V and the other 100 .uF at 6.3V. For comparison purposes, identical capacitors were impregnated with electrolytes as used for Belong to the state of the art and contain glycol and boric acid (Example V) and on the other hand with electrolytes, which contain the known solvents butyroactone and NN dimethylecetamide (Example VI).

Example V Example VI 68.60% / ** - butyroiactone 63.10% Ethylene Glyco 1 14.45% NN dimethylacetamide 25.4 5% Boric acid 11.43% Picric acid 6.00% Arno η i-umb or a d 1.00% crystallized lemon 0.95% aniline 4.52% nenic acid water Methyl diethanolamine 3.20% Ethylene glycol 1.30%

These capacitors (Examples III and IV, V, VI) were made investigated during operation at temperatures of 105 ° C, which showed that the capacity value increased by more than 10% changed and that the values of the tangent delta, the impedance and the leakage current have changed from their original values Values doubled that the service life of 300 hours for a known electrolyte with glycol (Example VI) and 2400 hours for an electrolyte with solvents (Example V) and 5600 hours for an electrolyte according to the invention (III and IV).

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List of reference signs

1 Capacitor winding 2 Anode foil CO. Paper liner 4th Cathode foil 5 Paper liner 6, 7 Connecting strips 8th Metal housing e 9: rivet 10 Plastic washer 11 Rubber washer 12, 13 connections

5 claims
1 sheet of drawings

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Claims (5)

M.G.Pringuet 2 claims 1.)) Anhydrous electrolyte for the impregnation of electro-— lytic capacitors, which have one or more electrodes covered with a dielectric layer are covered, characterized in that the electrolyte consists of a mixture of the following Substances in percent by weight consists of: Propylene carbonate ■ from 35.5% to 43.5% ^ ■ Butyrolactone from 3 5.5% to 43.5% N methylacetamide from 1.4% to 16.2% Picric acid from 7.5% to 8.7% crystallized citric acid from 0.5% to 0.6% tetramethylguanidine from 3.5% to 3.6% 2.) Anhydrous electrolyte according to claim 1, characterized in that that the propylene carbonate is replaced by a mixture of 3.20% to 4.3% ethylene carbonate plus 32% to 38.15% propylene carbonate. 3.) electrolyte according to claim 1 and 2, characterized in that that the N methylacetamide is replaced by 1.5 to 20% NN dimethylacetamide. 4.) Anhydrous electrolyte according to claim 1 and 2, characterized in that that the N methylacetamide is replaced by an equal molar amount of N methylformamide. 5.) Electrolytic capacitor with at least one formed aluminum electrode and an electrolyte according to one or several of claims 1 to 4. Fr / b - 27.9.1974 5098Ί 9/0698 L e r s ~ e i t e