DE2018540B2 - Electrolyte for electrolytic capacitors - Google Patents

Description

The invention relates to an electrolyte for Elektrolytkoiidensatoren containing a salt of a acidic nitrobenzene derivative, an organic solvent and, based on its total weight, 0.05 to 5 percent by weight water.

As is known in the art, this is electrolytic Capacitor has been the subject of intense research, and it became this - during the last half a century of use. In particular, capacitors of this type were using Anodes are made up of molded aluminum or tanta .. Electrolytes are made up of numerous Categories selected, and the patent and technical literature is not often preoccupied with suggestions for ionogens and electrolytes for electrolytic capacitors with a content of in a suitable solvent, such as water and polyhydric alcohol such as ethylene glycol, dissolved boric acid or borate, such as ammonium borate, are known.

The electrolytes of the type mentioned are for use in capacitors, which are extremely high or low temperatures and other specific Working conditions should be exposed to unsatisfactory, since the electrolyte is an unstable Have electrical conductivity which varies considerably with temperatures. Anodes under Use of tantalum as a so-called valve metal have technical importance because of the large Stability of the formed oxide film gained. In known tantalum capacitors which are used for operation are suitable at temperatures above 100 ° C, sulfuric acid is used as the electrolyte. Although sulfuric acid produces sufficient conductivity, there are other serious problems related to it the selection of the components, the seal, the gas discharge device and the like. in particular because sulfuric acid occurs in the liquid phase.

On the other hand, aluminum capacitors using the electrolyte are subject to the above Type disturbances of the oxide film formed on the aluminum anode when the capacitors are high Temperatures during the initial formation or subsequent regression of the anode oxide film get abandoned. The disturbance of the dielectric properties of the oxide film increases the Leakage current. When the leakage current of the capacitor is increased during operation, it becomes hydrogen gas generated at the cathode of the capacitor, which leads to an increase in pressure in the capacitor housing.

Furthermore, electrolytes are known which contain ammonium picrate, a glycol ether and water and also those made of dimethylformamide or its homologues, as well as a small amount of water and as ionogenic picric acid and / or an alkali

, 5 picrates included.

Finally, electrolytes for electrolytic capacitors with aluminum electrodes are proposed which contain a picrate dissolved in an anhydrous solvent, the picrate

: io in the form of cyclohexylamine picrate in Äthi lenglycolmonomethyläther is resolved.

All of these known electrolytes contain a picrate salt as an ionogen. However, it turned out that for a given stiom density the formation span

voltage with such electrolytes is relatively low and a discharge occurs even at a relatively low voltage.

Accordingly, it is an object of the invention to provide a new electrolyte for electrolyte customers with

so high and stable conductivity over a wide area To create at working temperatures.

The solution to this problem is according to the invention that the electrolyte according to the invention Ammonium, triethylammonium, calcium or barium p-nitro-phenolate, an amide, a polyvalent one Alcohol or an alkyl ether of a polyhydric alcohol as an organic solvent and, based on its total weight, contains 0.05 to 5 percent by weight of water.

Experiments have shown that the p-nitrophenolate containing electrolyte according to the invention has a considerably higher formation voltage than the picrate-containing electrolyte, in which a discharge occurs at a relatively low voltage of about 100 volts in the Compared to 175 volts or 148 volts of p-nitrophenolate containing electrolytes occurs. In general, the formation voltage of an electrolyte increases with the increase in the water content in the electrolyte: nevertheless an electrolyte is known Type containing as ionic ammonium picrate even with a water content of 10% by weight in terms of forming voltage significantly inferior to the p-nitrophenolate-containing electrolyte of the invention. Finally toilet the known electrolytes containing picric acid and picrate have the further disadvantage. that they are difficult to handle due to the severe discoloration, reducing the appearance of the electrolyte is adversely affected.

5p More specifically, the invention is described below in Connection described with the drawings.

FIGS. 1 and 2 are graphical representations of the dependence of the increase in voltage of the capacitor on its moisture content when a constant current density is applied;

3 is a perspective view showing a Example of a practical construction device of the electrolytic capacitor according to the invention represents.

The electrolytes of the invention have film-forming properties for the surfaces of the valve metal.

In general, an electrolyte applicable to electrolytic capacitors should meet the following requirements fulfill:

1. The ability to provide oxygen to the oxide film on the metal anode.

2. Electrolytic conductivity from 5 X 10 "'to

I χ ΙΟ " ¹ υ cm"¹; and

3. no formation of hydrogen gas,

The first requirement means that the scintillation or saturation voltage should be at least that 1.5 times the working voltage are solite.

The invention is based on the discovery that the ionic electrolyte component consists of an organic Salt with a special type of anion

should, in this case, a phenolate anion with a - .— ₆ w ..., "_ .. _o , _.

Nitrogrnppe or nitrogroups that becomes a water 10 that it is not an oxidizing agent. It became a

of the oxide film on the anodic metal surfaces. From this it can be concluded that the rate of increase depends considerably on the water content and that no oxide film is formed when the solvent does not contain water.

A similar attempt was made to address the Determine the role of the water to be added to the solvent. In this attempt, pyrrole became used as lonogenes by the angtnowmen ß ki Odiittel is It became a

gpp gpp

Substitute substance atom or atoms. This nitrophenol, which is known to have the property of reforming the oxide film, has a relative low conductivity because of its low ionization becomes that there is no xy

Comparison at a constant current density of 1 mA / cn between a nicbc aqueous solution with a content on pyrrole and dimethylformamide and a solution which also contained 5% water, employed, ll ie di dhenes or dashed lines

"" ■ "" f - ~ """" ₆ ? - "" * -5 ^ "uv _M " ii _B yn U ₆ ^. X _U i .. _ai ^ - solution, which also contains 5% water e, g tionSKonstante with dissolution in water or organic 15 represented by the solid or dashed lines in Fig. 2 As from this figure he

see solvents on. However, it has been found that the anion has a high conductivity of 5 × 10 ^−λ to IX 10 " ² ½ cm" ¹ when it is used as an electrolyte with a suitable cation such as an ammonium ion. It has also been found that the nitro group of the anion ^{reacts with the proton (H 4} ) which is generated in the electrolyte solution with ionogens and solvents, so that the generation of hydrogen gas is avoided during operation. This effect is particularly prevalent in the holien temperature range, whereby an »extremely stable mode of operation is guaranteed even at around 125 ° C.

In addition, it was found that the Nachford represented by the dugg
As can be seen from this figure, the forming voltage increases considerably with the lapse of time and the formation of the oxide film on the metal anode on the counter

-.VJ was returned by water, even if pyrrole without oxidizing effect, used in this experiment will:.

The practical importance Keyring can advertising derived ^c e of the above discussed tests

the fact that the production of an oxide film depends solely on the water content in a solvent, since this generation occurs in the electrolysis of water, and that the nature of an ionogen for the properties of the generated oxide film in close relation

Vlilmetalls ver

mation of the oxide film in the presence of moisture to corrode the valve metal used ·; verity becomes very effective, although such an effective one is responsible. It follows, therefore, that the one in an elekkeit preferably used in the non-aqueous system essentially trolytic condenser Is negligible. This is explained in more detail under Electrolyte contains such an ionogen that is not referred to to Figs. 1 and 2 explained. Building on an Oxydiilm acts and a suitable one In addition, it was found that ^ the discharge voltage, 35 organic solvent and a given amount of water should contain. The amount of water should preferably be within a range from 0.05 to 5 percent, based on the total weight of the electrolyte, because there is too much water for impairment 40 of the capacitor performance and leads to corrosion of the protective oxide film on the metal.

If desired, the anions and cations of the octrolyte according to the invention can be in the form of their Ionic applied ·, 'earth, which - hereinafter in its non-dissociated form, ammonium p-nitrophenolate, Triethylammoium-pnitrophenolaUTriiithunolaiiimonium-p-nitrophenohit and are culicum or barium p-nitrophenolate Various solvents can be used according to

which can be defined as the maximum voltage of the capacitor formed at constant current, assumes a value which varies from 150 to 500 volts depending on the conductivity of the electrolyte used. The dependence of the discharge voltage (K) on the conductivity can be empirically called algebraic Equation can be expressed as follows:

V = V ₀ - V.lügk, and k are variable quantities which for

where K ₁₁ y

the type of electrolyte used are specific. As can be seen from this equation, any suitable discharge voltage can be obtained within a wide range of 150 to 500 V if

Range from 150 to 500 V can be obtained if _

the amount of the anion as well as the types of the cation 50 invention are used, some of them

and the solvent selected accordingly "' ^A '<*'· ■ · (,,;. * _r ,

will.

In Fig. I the behavior of the forming tension plotted as a function of time, with variation of the Fhikihl i d Elktlt it

ncn are specified for certain limited applications. In some systems, however, the solvent should exactly M) are selected that the desired Löjilichkitscigcnschaften and the desired

i h Säi

Moisture content in the electrolyte shown. 55 Conductivity to generate a desired saturation Ammonium picrate can be achieved as ionogenes and directional voltage and furthermore for the

¹ "'· -' ■ - - '■ < -—u ;; i. Possible film formation - be it film formation

/ u Beginning or discontinuation of a film In

p g

Contains thylformamide and water as solvents. Measurements were made at a constant current density of 0.5 mA / cm ⁵ while varying the water level

/ u start d g

• This relationship can be the solvent from the ■ "" 'including di-

running content of 0.1 to 100 percent by weight. 60 amide groups can be selected, including Di-Aus Fig. 1 can be seen that the forming tension methylformamide and dimeihylacetamide, inehrwertibei the applied constant current gradually fond of alcohol, such as ethylene glycol, and alkyl ethers of increases over time. In addition, to polyhydric alcohol, however, it is preferred that note that the increase with the increase in the dimethylformamide and ethylene glycol monomethyl water content increases, and furthermore that no increase is required because of its higher conductivity occurs when a non-aqueous solvent is used, especially when used over a wide Tcm will. This increase in the forming voltage should be applied pcraturbercich, is, as is believed, the result of formation The type of anode metal used depends on

door borrowed from the type of end use. Aluminum and tantalum can advantageously be used as anode metals in high temperature electrolytic capacitors of the invention. However, other valve metals such as titanium, zirconium, magnesium, and bismuth can be used provided their specific anodic properties suit the application .

Reference is now made to FIG. Numeral 10 generally denotes a capacitor.

The capacitor film or the capacitor winding is shown partially unwound. Reference symbol 11 denotes the anode of the capacitor, which consists of a so-called valve metal, such as aluminum and tantalum, with a corresponding oxide film formed on its surface. Reference number 12 represents a cathode which is usually also made from a valve metal. For direct current applications, the cathodes 12 can consist of a silver or other metal foil. The anode and / or cathode can be etched, perforated, or otherwise removed in order to increase the effective surface area. Oe / ugszcidicn 13 represents a porous or perforated spacer. Made of a material which is inert in the electrochemical system and is impregnated with an electrolyte of the invention. A pair of connecting terminals 14 and 15 are connected to the two electrical cables 11 and 12. The housing (not shown) for the capacitor can be made of a metal or non-metal container, for example aluminum. Consist of silver or glass. The housing can be tightly sealed using conventional sealing means, which are selected depending on the working temperature range and the viscosity of the electrolyte and the like.

In addition to the wound capacitor shown, the invention applies to sintered, porous anodes. Rod- and wire anodes and the like are applicable for special purposes. The electrolytes are particularly suitable except for use for ek small blind capacitors for rectifiers and changes' systems where their Properties are adapted to the specific requirements.

The following examples of the manufacture of the electrolyte and the electrolytic capacitors serve to further illustrate the invention.

example 1

An electrolyte was prepared by dissolving 4 g of triethylammonium p-nitrophenolate in KMIg of ethylene glycol monomethyl ether. The electrolyte had the specific conductivity of 3.8 X 10 ^-3 ü crn 'on at room temperature of 25 ° C. The scintillation voltage of the capacitor with a molded aluminum anode was 180 V when 0.5 weight percent water was added to the electrolyte.

B e i s ρ i c I 2

An electrolyte was prepared by dissolving 5 g of nitrophenol and 8 g of triethanolammonium in 100 g of dimethylformamide. The specific conductivity of this electrolyte was 9 X ΙΟ ^"1 υ cm"'at 25 "C in the presence .of 0.5 weight percent water.

B e i s ρ i e I 3

An electrolyte system containing 5 g of barium p-nitrophenolate in 100 g of ethylene glycol monomethyl alcohol was prepared. The system had the specific conductivity of 7.5 XlO ' ν cm ^! . The scintillation voltage of the aluminum condenser exceeded 300 V in the presence of 2 weight percent water in the system.

Example 4

An Elcktroiytsyslem was prepared by dissolving v (·., 5 g of ammonium p-nitrophenolate in K) Og of dimethylformamide. The specific conductivity of this system was! <K) i'cm '. The scintillation voltage was 145 V for a capacitor with a formed aluminum anodc and the electrolyte with a content of 0.5 percent by weight water. The leakage ^{current was reduced to c} · inA cm, measured 1 hour after an aluminum foil formed at a voltage up to K) (IV was placed in this electrolyte, and a constant voltage of 9 (1 V was applied found that the extent of the I lcabsetzung the crawl mines considerably the one de- · Elcktrolytsystems exceeded using picric acid l ^-. .s was no occurrence of gases in the

4 ' ¹ cathode found neither be. Room temperature con 25 "C still at a temp. Atm of K) O ⁰ C

As can be seen from the above description, an excellent electrolyte for use in a electrolytic capacitor is created ^{by tue Erl'indu - g.} The electrolyte has a number of favorable property for 11 ek ^{l-symmetrical} capacitors and other htunecn Einru. in which known electrolyte systems flour were satisfactory . For example, the electrolyte has a high and stable electrical conductivity over a wide temperature range from -55 to + 125 ° C. Therefore, it can be operated stably even at such a high temperature for a longer period of time. Furthermore, the electrolyte of the invention is able to reformulate the once formed oxide film on anodic metal surfaces and avoid gas formation at the cathode.

For this ! Sheet drawings

Claims (1)

Claim: Electrolyte for electrolytic capacitors containing a salt of an acidic nitrobenzene derivative, an organic solvent and water, characterized in that it is an ammonium, Triethylammonium, calcium or barium p-nitrophenolate, an amide, a polyvalent one Alcohol or an alkyl ether of a polyhydric alcohol as an organic solvent and, based on its total weight, contains 0.05 to 5 percent by weight of water.