DE1190578B - Electrolyte for electrolytic capacitors - Google Patents

Description

Electrolyte for electrolytic capacitors The invention relates to a improved electrolytes for electrolytic capacitors, the N, N-dimethylformamide and contains an ammonium borate.

The object of the invention is an anhydrous electrolyte with which electrolytic capacitors can be produced which, when operated at high voltages, have a temperature range of about -55 to - # -125'C and an improved service life, as well as their capacitance and ohmic resistance in the specified temperature range change little.

The use of dimethylformamide as a diluent for aqueous Electrolytes of electrolytic capacitors are known. This consists of several components However, existing, known electrolytes are only within a limited temperature range useful because they change their composition when the temperature changes.

According to the invention, the electrolyte for an electrolytic capacitor, which meets the requirements, consists of 99.8 percent by weight of N, N-dimethylformamide and 0.2 percent by weight ammonium borate.

This electrolyte, designated by the letter A , is suitable for capacitors, one electrode of which is made of tantalum or another film-forming material.

The ammonium pentaborate is only present in such small quantities that it does not fail at about -55'C. Subject to the above conditions, operation at low voltage, higher concentrations of the ion generator and lower concentrations can be used for operation at higher voltages.

The properties of this electrolyte A are much better than those using a mixture of an ion former, e.g. B. ammonium pentaborate, a glycol and water. A known electrolyte of the latter type, which was tested in comparison with electrolyte A according to the invention, has the following composition in percent by weight: electrolyte B ammonium pentaborate ........... 3.50 /, ethylene glycol .... ............... 60.3 "/, water .......................... 362 0 /, The properties of the above electrolytes are summarized in the following table: Table 1 1 electrolyte A electrolyte B Freezing point, 0 C .... -61 below -55 Boiling point, 'C ......... 153 118 Vapor pressure, mm Hg at 85'C ............. 85 290 at 125'C ............ 340 1240 Specific resistance, Ohm-cm at -55'C ........... 32000 30000 at 25'C ............. 4200 250 at 85'C ............. 2400 75 at 125'C ............. 1250 - at 150'C ............ 840 The table above shows the further temperature range, the lower vapor pressure and the lower dependence of the specific resistance on the temperature of the electrolyte according to the invention.

The service life of capacitors containing the above electrolytes was tested in which the capacitors contained 12.70 mm thick tantalum foils as anodes and cathodes, which were separated by a paper strip about 30.48 mm thick. Lifetime tests carried out on such capacitors at 125 ° C and a direct voltage of 150 volts showed that the capacitors containing the known electrolyte B all failed before Albauf for 528 hours, while the capacitor containing electrolyte A was still in operation after 1080 hours was. After this time had elapsed, the capacitor according to the invention still had 78 Ω / □ of its original capacity at room temperature, while the electrolyte B had only 790 Ω / □ after 168 hours. These results show a six-fold improvement in life using the electrolyte of the invention.

In a similar series of tests, in which the capacitors were operated at 85 ° C and a direct voltage of 300 volts, the capacitor according to the invention still retained 880/0 of its original capacity at room temperature after 2160 hours, while the capacitor after 288 when using electrolyte B Hours only 840 / that had capacity, which is an eight-fold improvement. In a further test in which the capacitors containing the electrolyte according to the invention were measured at 125 ° C. and a direct voltage of 300 volts, these capacitors still had 97.50% of their original capacity at room temperature after 1600 hours.

The following table shows the low temperature properties of capacitors containing electrolyte A. Table 11 temperature .c HZ capacity tg c25 25 120 1.09 7.0 100 25 1000 1.06 11.0 100 -55 120 1.01 80 92, 7 -55 1000 0.94 40: 3 88.7 In the table above, Hz means the number of oscillations, 0 /, tgb means the loss factor, and 0 /, C "is the percentage capacity, based on the output capacity at 25'C. As can be seen from the table, the capacity at - 25'C extremely high both in the experiment with 120 Hz and in the experiment with 1000 Hz, and the loss factor is still completely satisfactory even at these low temperatures.

The dimethylformamide electrolyte is extremely stable and resistant and has a considerably lower freezing point than conventional electrolytes. It is opposite to the metals commonly used as capacitor housings non-corrosive and has no dissolving effect on the capacitor electrodes formed oxide films. The electrolyte also retards the speed of the Formation of crystalline oxides in the dielectric film, which is often the case with previous electrolytes occurred, and thus protects the connection point of the foils with the connecting wire, which is usually the weak point of every capacitor. The electrolyte possesses at 25'C a higher specific resistance than conventional electrolytes. The dimethylformamide electrolyte furthermore, its viscosity hardly changes at fluctuating temperatures, with the result has that the specific resistance and the capacitance also change with temperature change less.

Since the electrolyte is anhydrous, it has a lower vapor pressure, so that the problem of maintaining a tight seal of the capacitor does not arise here. The electrolyte also does not have the difficulties which occur when known electrolytes containing solvent mixtures are used, in which one or the other solvent evaporates more easily and thus the composition, viscosity, specific resistance and solidification point of the electrolyte change. When using the electrolyte, practically 100 ", /, of N, N-dimethylformamide, up to 5001, of the electrolyte can be lost (e.g. due to a faulty seal) without affecting the electrical properties or the operation of the Capacitor changes noticeably.

Since the dimethylformamide-containing capacitors for higher Voltages are suitable as they were previously used for electrolytic capacitors, is their use as high voltage capacitors instead of in series Capacitors possible.

Claims (1)

Claim -. Electrolyte for electrolytic capacitors containing N, N-dimethylformamide and an ammonium borate, characterized in that it contains 99.8 "/, N, N-dimethylformamide and 0.20 /, ammonium borate. Documents considered: French Patent No. 1086 115.