PROCESS FOR PRODUCING POLYMER CAPACITORS FOR HIGH RELIABILITY APPLICATIONS

Abstract

The present invention relates to a method for manufacturing a capacitor, comprising the method steps: a) provision of a porous electrode body made of an electrode material, wherein a dielectric at least partially covers a surface of this electrode material; b) introduction of a liquid composition which comprises an electrically conductive polymer, at least one high-boiling solvent; c) filling at least a part of the pores of the porous electrode body obtained in process step b) with an impregnation solution comprising at least one impregnation solvent, wherein the at least one impregnation solvent comprises at least one hydroxy group and has a molecular weight in the range from 70 to 180 g/mol; d) encapsulation of the porous electrode body obtained in process step c). The invention also relates to capacitor manufactured with this method, the use of an electrolytic capacitor and electronic circuits.

Claims

1. A method for manufacturing a capacitor, comprising the method steps: a) provision of a porous electrode body made of an electrode material wherein a dielectric at least partially covers a surface of this electrode material; b) introduction of a liquid composition which comprises an electrically conductive polymer, at least one high-boiling solvent having a boiling point (determined at 1013.25 hPa) of at least 150° C. and of not more than 275° C. and optionally a dispersing agent into at least a part of the porous electrode body provided in process step a) and at least partial removal of the high-boiling solvent and, if present, of the dispersing agent for the formation of a solid electrolyte that at least partially covers a surface of the dielectric; c) filling at least a part of the pores of the porous electrode body obtained in process step b) with an impregnation solution comprising at least one impregnation solvent, wherein the at least one impregnation solvent comprises at least one hydroxy group and has a molecular weight in the range from 70 to 180 g/mol; and, d) encapsulation of the porous electrode body obtained in process step c).

2. The method according to claim 1, wherein the electrically conductive polymer is poly(3,4-ethylenedioxythiophene) or derivative thereof.

3. The method according to claim 1, wherein the at least one high-boiling solvent has a molecular weight of less than 180 g/mol.

4. The method according to claim 1, wherein in process step b) at least 50 wt.-% of the total amount of high-boiling solvent is at least partially removed when forming the solid electrolyte.

5. The method according to claim 1, wherein the impregnation solution has an ionic conductivity of less than 1000 pS/cm.

6. The method according to claim 1, wherein the at least one impregnation solvent is a mono, di- or tri alkylene glycol, a mono-, di- or tri alkylene glycol monoether, an alkanediol or an alkanediol monoether.

7. The method according to claim 6, wherein the alkanediol is selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hexanediol, 2,5-hexanediol, 3,4-hexanediol, 1,2-heptanediol, 1,3-heptanediol, 1,4-heptanediol, 1,5-heptanediol, 1,6-heptanediol, 1,7-heptanediol, 2,3-heptanediol, 2,4-heptanediol, 2,5-heptanediol, 2,6-heptanediol, 3,4-heptanediol, 3,5-heptanediol, 1,2-octanediol, 1,3-octanediol, 1,4-octanediol, 1,5-octanediol, 1,6-octanediol, 1,7-octanediol, 1,8-octanediol, 2,3-octanediol, 2,4-octanediol, 2,5-octanediol, 2,6-octanediol, 2,7-octanediol, 3,4-octanediol, 3,5-octanediol, 3,6-octanediol and 4,5-octanediol.

8. The method according to claim 1, wherein the at least one impregnation solvent has a boiling point (determined at 1013.25 hPa) of more than 205° C.

9. The method according to claim 1, wherein the at least one impregnation solvent has a melting point of less than 15° C.

10. A capacitor comprising as components: i) a porous electrode body made of an electrode material, wherein a dielectric at least partially covers a surface of this electrode material; ii) a solid electrolyte comprising an electrically conductive polymer, wherein the solid electrolyte layer at least partially covers a surface of the dielectric; iii) an impregnation solution that fills at least a part of the open pore volume of the porous electrode body, wherein the impregnation solution has a conductivity of less than 1000 pS/cm and comprises at least one impregnation sol vent, wherein the at least one impregnation solvent comprises at least one hydroxy group and has a molecular weight in the range from 70 to 180 g/mol; and iv) an encapsulation that encloses the porous electrode body; wherein the capacitor has (a1) a decrease of the capacitance of at most 20% on reducing the temperature from 20° C. to −55° C., and (a2) a decrease of the capacitance of at most 20% after storage of the capacitor for 1000 hours at 125° C.

11. The capacitor according to claim 10, wherein the electrically conductive polymer is poly(3,4-ethylenedioxythiophene) or a derivative thereof.

12. The capacitor according to claim 10, wherein the at least one impregnation solvent is a mono, di- or tri-alkylene glycol, a mono- di- or tri alkylene gylcol monoether, an alkanediol or an alkanediol monoether.

13. The capacitor according to claim 10, wherein at least 50 vol-% of the open pore volume of the porous electrode body are filled with the at least one impregnation solvent.

14. The use of capacitors according to claim 10, in electronic circuits.

15. An electronic circuit comprising capacitors according to claim 10.

16. The use of a capacitor obtainable by the method according to claim 1 in electronic circuits.

17. An electronic circuit comprising a capacitor obtainable by the method according to claim 1.

Description

[0181] The invention is now explained in greater detail with reference to non-limiting drawings and examples.

[0182] FIG. 1 shows a schematic sectional view through a part of a capacitor according to the invention. The latter comprises a porous electrode body 1, made mostly from a porous electrode material 2 such as aluminium. On the surface of the electrode material 2, a dielectric 3 is formed as a thin layer, so that an anode body is formed which is still porous, comprising the electrode body 1 made of the electrode material 2 and the dielectric 3. On the dielectric 3, there follows, optionally after further layers, a layer of a solid electrolyte 4 (for example, made of PEDOT/PSS particles), so that a capacitor body is formed, comprising the electrode body 1 made of the electrode material 2, the dielectric 3 and the solid electrolyte 4. The pores 5 of the porous electrode body 1 are at least partially filled with an impregnation solvent (for example, with an alkanediol; see the grey shading in FIG. 1), so that a capacitor is formed, comprising the porous electrode body 1 made of the electrode material 2, the dielectric 3, the solid electrolyte 4 and the impregnation solvent 6.

[0183] FIG. 2 shows an aluminium capacitor according to the present invention that comprises capacitor element 8 (porous electrode material 2 coated with dielectric 3 and solid electrolyte 4 and comprising the impregnation solvent) and lead wires 10 which contact the porous anode foil and an opposite cathode foil, both foils being wound with two separator papers between both foils and being fixed with a winding end tape). Capacitor element 8 is held in an aluminium casing 7 in the shape of a bottomed cylinder, a rubber packing 9 is attached in the opening of the casing.

[0184] MEASUREMENT METHODS:

[0185] Equivalent Series Resistance (ESR)

[0186] The equivalent series resistance (in mΩ) was determined at 20° C. at 100 kHz by means of an LCR meter (Agilent 4284A). In each capacitor experiment 2 capacitors have been prepared and the average ESR-value was determined.

[0187] Capacitance (CAP)

[0188] The capacitance was determined at 20° C. and −55° C. at 120 Hz by means of an LCR meter (Agilent 4284A). In each capacitor experiment 2 capacitors have been prepared and the average capacitance-value was determined.

[0189] Ionic Conductivity of the Impregnation Solvent

[0190] The ionic conductivity of the impregnation solvent is measured with a conductivity meter (Knick 703 or equivalent conductivity meters).

[0191] Viscosity

[0192] The viscosity of the dispersion was determined with a shear rate of 100 Hz and 20° C. using a rheometer (Haake Type RotoVisco 1 with a double-gap cylinder-system DG43).

[0193] Solids Content

[0194] In order to determine the solids content, 5 g of the dispersion were dried for 15 hours at 100° C., and the solids content was determined by differential weighing.

[0195] pH-Value

[0196] pH Measurement: pH value is determined with a pH meter. After calibration the pH electrode is put into the slowly stirred dispersion or solution until the reading of the pH is constant.

EXAMPLES

[0197] Process Step a)

[0198] A porous electrode body for a cylindrical aluminium capacitor (as described in FIG. 2) having a rated voltage of 16 V and a rated capacitance of 100 g was produced in the following way.

[0199] An aluminium foil was etched, thereby to roughen the surface of the aluminium foil. The aluminium foil was then subjected to anodic oxidation using an aqueous ammonium adipate solution, thereby to form a dielectric layer on the surface of the aluminium foil. Thus, an anode foil was produced.

[0200] A second aluminium foil was etched, thereby to roughen the surface of the aluminium foil. Thus, a cathode foil was thus prepared.

[0201] An anode lead wire and a cathode lead wire were connected to the anode and the cathode foil, respectively. The anode and the cathode foil were wound together with two separator papers between both foils. A tape was put on the outside of the wound element to avoid unwinding of the foils. The wound element was then subjected to another anodic oxidation to form a dielectric layer on the cut edges of the anode foil.

[0202] Thus, an anode body comprising an electrode body having a dielectric layer was prepared.

[0203] Process Step b)

[0204] The porous electrode body from process step a) was placed into a chamber with a bath of a liquid composition comprising an electrically conductive polymer. Air pressure in the chamber was reduced to 100 hPa. The anode body was dipped into the liquid composition for 300 s. Then, the anode body was extracted from the liquid composition and the chamber was vented to atmospheric pressure. Thereafter, the anode body was dried at 120° C. for 30 min and then at 150° C. for 30 min. The impregnation and drying were carried out a further time. Thus, a capacitor body was obtained.

[0205] Process Step c)

[0206] The capacitor body of process step b) was placed into a chamber with a bath of an impregnation solution. Air pressure in the chamber was reduced to 100 hPa. The capacitor body was dipped into the impregnation solution for 300 s. Then, the capacitor body was extracted from the impregnation solution and the chamber was vented to atmospheric pressure. Thus, a capacitor body impregnated with the impregnation solution was obtained.

[0207] Process Step d)

[0208] The capacitor body of process step c) was placed in a cylindrical aluminium housing and sealed with a rubber sealing, to obtain a finished capacitor.

[0209] All capacitors prepared by process steps a) to d) showed a capacitance at 20° C. of 95-100 μF.

Synthesis Example 1 (Synthesis of a Conductive Polymer Dispersion)

[0210] 868 g of deionized water and 330 g of an aqueous polystyrenesulphonic acid solution having an average molecular weight of 70000 g/mol and a solids content of 3.8 wt.-% were initially introduced into a 21 three-necked flask with a stirrer and internal thermometer. The reaction temperature was kept between 20 and 25° C. 5.1 g of 3,4-ethylenedioxythiophene were added, while stirring. The solution was stirred for 30 min. 0.03 g of iron(III) sulphate and 9.5 g of sodium persulphate were then added and the solution was stirred for a further 24 h. After the reaction had ended, for removal of inorganic salts 100 ml of a strongly acid cation exchanger and 250 ml of a weakly basic anion exchanger were added and the solution was stirred for a further 2 h. The ion exchanger was filtered off. The poly(3,4-ethylenedioxy-thiophene)/polystyrenesulphonate dispersion was homogenized with a high pressure homogenizer ten times under a pressure of 700 bar. The dispersion was subsequently concentrated to a solids content of 2.5% and then additionally homogenized another three times under a pressure of 1500 bar.

Preparation Example 1

[0211] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of ethylene glycol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 2

[0212] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of diethylene glycol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 3

[0213] 45 g of the conductive polymer from Synthesis Example 1 and 2.6 g of 1,2-propanediol were mixed and the pH was adjusted to 4.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 4

[0214] 45 g of the conductive polymer from Synthesis Example 1 and 8 g of 1,3-propanediol were mixed and the pH was adjusted to 7.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 5

[0215] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of 1,5-pentanediol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 6

[0216] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of 1,2-pentanediol were mixed and the pH was adjusted to 2.5 using 2-dimethylaminoethanol. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 7

[0217] 45 g of the conductive polymer from Synthesis Example 1 and 2.5 g of 2-methyl-2,4-pentanediol and 2.5 g of 1,3-propanediol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 8

[0218] 45 g of the conductive polymer from Synthesis Example 1, 4 g of 2,4-pentanediol and 1 g of 1,3-propanediol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 9

[0219] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of 1,4-pentanediol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 10

[0220] 45 g of the conductive polymer from Synthesis Example 1, 5 g of 1,2,4-butanetriol and 0.1 g surfactant were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 11

[0221] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of glycerol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 12

[0222] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of diglycerol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 13

[0223] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of polyethylene glycol 400 (PEG400) were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 14

[0224] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of polyglycerol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 15

[0225] 45 g of the conductive polymer from Synthesis Example 1, 5 g of 1,3-propanediol and 0.5 g of tannic acid were mixed and the pH was adjusted to 7.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer solution was obtained.

Preparation Example 16

[0226] 45 g of 1,2 pentanediol and 5 g of gallic acid were mixed. Thus, an impregnation solution was obtained.

Preparation Example 17

[0227] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of dimethyl sulfoxide were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Preparation Example 18

[0228] 45 g of the conductive polymer from Synthesis Example 1 and 5 g of 1,3-butanediol were mixed and the pH was adjusted to 3.0 using ammonia. Thus, a liquid composition which comprises an electrically conductive polymer was obtained.

Example 1

[0229] Capacitors were produced the following way:

[0230] First anode bodies according to process step a) were prepared. Then, the anode bodies were processed according to process step b) using the liquid composition which comprises an electrically conductive polymer of Preparation Example 1. Next, the obtained capacitor bodies were impregnated according to process step c) using diethylene glycol as impregnation solution. Finally, the capacitor bodies were encapsulated according to process step d) and capacitors were obtained.

[0231] The capacitance of the capacitors was measured at 20° C. and −55° C. The relative capacitance at −55° C. was calculated according to the following formula:

(relative capacitance at −55° C.)=(capacitance at −55° C.)/(capacitance at 20° C.)

Example 2-40

[0232] Capacitors were produced and evaluated the same way as in Example 1, however, liquid compositions which comprise an electrically conductive polymer in process step b) and impregnation solutions in process step c) were used according to Table 1.

[0233] The relative capacitance at −55° C. in % is given in Table 1.

TABLE-US-00001 TABLE 1 relative capacitance at −55° C. of Examples 1-52 impregnation solution 1,3- 1,3- 1,5- liquid diethylene propane- butane- pentane- composition glycol diol diol diol Ex. 1-4 Prep. Ex. 1 93% 91% 92% 92% Ex. 5-8 Prep. Ex. 2 92% 93% 95% 91% Ex. 9-12 Prep. Ex. 3 93% 92% 91% 93% Ex. 13-16 Prep. Ex. 4 92% 92% 92% 91% Ex. 17-20 Prep. Ex. 5 93% 95% 91% 91% Ex. 21-24 Prep. Ex. 6 95% 93% 91% 93% Ex. 25-28 Prep. Ex. 7 92% 91% 93% 93% Ex. 29-32 Prep. Ex. 8 93% 94% 92% 91% Ex. 33-36 Prep. Ex. 9 93% 93% 94% 93% Ex. 37-40 Prep. Ex. 10 95% 91% 93% 92%

Examples 41-53

[0234] Capacitors were produced and evaluated the same way as in Example 1, however, liquid compositions which comprise an electrically conductive polymer in process step b) and impregnation solutions in process step c) were used according to Table 2.

[0235] Additionally, the capacitance of the capacitors was measured at 20° C. before and after a storage for 1000 hours at a storage temperature of 125° C. The relative capacitance after 1000 h storage at 125° C. was calculated according to the following formula:

(relative capacitance after 1000 h at 125° C.)=(capacitance at 20° C. after 1000 h storage at 125° C.)/(capacitance at 20° C. before 1000 h storage at 125° C.)

[0236] The relative capacitance at −55° C. and relative capacitance after 1000 h at 125° C. in % are given in Table 2.

Comparison Examples 1-5

[0237] Capacitors were produced and evaluated the same way as in Examples 41-53, however, liquid compositions which comprise an electrically conductive polymer in process step b) and impregnation solutions in process step c) were used according to Table 2.

TABLE-US-00002 TABLE 2 relative capacitance of Example 41-53 and Comparative Examples 1-5 rel. capac- rel. capac- itance liquid impregnation itance after 1000 h composition solution at −55° C. at 125° C. Ex. 41 Prep. Ex. 5 diethylene glycol 93% 90% Ex. 42 Prep. Ex. 5 1,2-propanediol 92% 81% Ex. 43 Prep. Ex. 5 1,3-propanediol 95% 91% Ex. 44 Prep. Ex. 5 50% 1,4-butandiol + 90% 91% 50% 1,3-propanediol Ex. 45 Prep. Ex. 5 1,2-pentanediol + 93% 90% 50% diethylene glycol Ex. 46 Prep. Ex. 5 2-methyl-2,4- 91% 82% pentandiol Ex. 47 Prep. Ex. 5 2,4-pentanediol 86% 82% Ex. 48 Prep. Ex. 5 1,4-pentanediol 89% 83% Ex. 49 Prep. Ex. 5 1,2,4-butanetriol 89% 81% Ex. 50 Prep. Ex. 5 Prep. Ex. 16 93% 95% Ex. 51 Prep. Ex. 15 1,5-pentandiol 91% 97% Ex 52 Prep. Ex. 8 dipropylene glycol 86% 84% Ex 53 Prep. Ex. 8 diethylene glycol 85% 81% monoethyl ether C. Ex. 1 Prep. Ex. 5 ethylene glycol 91% 51% C. Ex. 2 Prep. Ex. 1 ethylene glycol 91% 55% C. Ex. 3 Prep. Ex. 5 γ-butyrolactone 59% 65% C. Ex. 4 Prep. Ex. 1 γ-butyrolactone 63% 66% C. Ex. 5 Prep. Ex. 1 PEG-400 59% 78%

Example 54-58

[0238] Capacitors were produced and evaluated the same way as in Example 1, however, liquid compositions which comprise an electrically conductive in process step b) and impregnation solutions in process step c) were used according to Table 3. Shown in Table 3 is the relative capacitance at −55° C.

TABLE-US-00003 TABLE 4 relative capacitance at −55° C. of Example 54-58 liquid impregnation solution composition 1,5-pentanediol Ex. 54 Prep. Ex. 9 91% Ex. 55 Prep. Ex. 11 81% Ex. 56 Prep. Ex. 12 83% Ex. 57 Prep. Ex. 13 74% Ex. 58 Prep. Ex. 14 75%

Comparison Example 6-19

[0239] Capacitors were produced and evaluated the same way as in Example 1, however, liquid compositions which comprise an electrically conductive in process step b) and impregnation solutions in process step c) used according to Table 4. Shown in Table 4 is the relative capacitance at −55° C.

TABLE-US-00004 TABLE 5 relative capacitance at −55° C. of Comparative Examples 6-19 liquid impregnation solution composition PEG-400 polyglycerol Comp. Ex. 6-7 Prep. Ex. 9 71% 70% Comp. Ex. 8-9 Prep. Ex. 11 58% 62% Comp. Ex. 10-11 Prep. Ex. 12 55% 57% Comp. Ex. 12-13 Prep. Ex. 13 60% 63% Comp. Ex. 14-15 Prep. Ex. 14 59% 57% Comp. Ex. 16-17 Prep. Ex. 17 73% 71% Comp. Ex. 18-19 Prep. Ex. 18 74% 73%

Comparison Example 20-25

[0240] Capacitors were produced and evaluated the same way as in Example 1, however, liquid compositions which comprise an electrically conductive in process step b) and impregnation solutions in process step c) used according to Table 5. For Comparison Example 20 and 23, process step c) was not applied, thus no impregnation solution was used. Shown in Table 5 is the relative capacitance at −55° C.

TABLE-US-00005 TABLE 5 relative capacitance at −55° C. of Comparative Examples 20-25 liquid impregnation solution composition without γ-butyrolactone sulfolane Comp. Ex. 20-22 Prep. Ex. 13 49% 63% 65% Comp. Ex. 23-25 Prep. Ex. 14 52% 56% 58%

KEY TO REFERENCE NUMBERS

[0241] 1 porous electrode body [0242] 2 electrode material [0243] 3 dielectric [0244] 4 solid electrolyte [0245] 5 pore [0246] 6 impregnation solution [0247] 7 encapsulation (aluminium housing) [0248] 8 capacitor element (porous electrode material coated with dielectric and solid electrolyte and comprising the impregnation solvent) [0249] 9 rubber packing [0250] 10 lead wires