Patent Publication Number: US-2016247633-A1

Title: Oxidant mixture for conjugated polymer synthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of and claims the priority benefit of U.S. application Ser. No. 13/951,470, filed on Jul. 26, 2013, now allowed, which claims the priority benefit of Taiwan application serial no. 101127060, filed on Jul. 26, 2012. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     1. Technical Field 
     The technical field relates to an electrolyte mixture, an electrolytic capacitor having the same and an oxidant mixture for conjugated polymer synthesis. 
     2. Background 
     Improving the electrolyte conductivity has long been one of the major topics in the development of an electrolytic capacitor. The electrolyte with a high conductivity can reduce the equivalent series resistance (ESR) of the electrolytic capacitor, so as to provide high-frequency low impedance and high reliability. A conductive polymer has a higher conductivity than an aqueous electrolyte or a solid organic semiconductor complex salt (e.g. tetracyanoquinodimethane (TCNQ) complex salt) used for conventional capacitors, and exhibits an adequate insulating property at high temperature. Therefore, such conductive polymer has become the mainstream of the solid electrolyte for existing electrolytic capacitors. 
     As compared to the conventional aqueous electrolyte, the conductive polymer as an electrolyte of an electrolytic capacitor provides low impedance and good thermal stability. However, the static capacitance of the electrolytic capacitor having the conductive polymer as an electrolyte is usually lower than that of the conventional aqueous electrolytic capacitor with similar size. The lower static capacitance has become the main drawback of the solid electrolytic capacitor. 
     SUMMARY 
     One of exemplary embodiments at least includes an oxidant mixture for conjugated polymer synthesis, and the oxidant mixture at least includes an oxidant, a polyether and a nitrogen-containing compound, or at least include the oxidant, the polyether and a nitrogen-containing polymer, or at least include the oxidant and a polyether compound with nitrogen-containing functional groups, wherein the oxidant mixture and a precursor of a monomer of a conjugated polymer are polymerized directly on a surfac of a dielectric layer. 
     Several exemplary embodiments accompanied with FIGURES are described in detail below to further describe the disclosure in details. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a process flow of a method of fabricating a solid electrolytic capacitor according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     One of exemplary embodiments provides a solid electrolytic capacitor, such as a solid electrolytic capacitor having a conductive polymer as an electrolyte, in which a conductive polymer mixture as a solid electrolyte is polymerized from a monomer of a conjugated polymer and an oxidant mixture. 
     The monomer of the conjugated polymer includes thiophene, a thiophene derivative, pyrrole, a pyrrole derivative, aniline, an aniline derivative, or a combination thereof. In an embodiment, the monomer of the conjugated polymer includes 3,4-ethylenedioxythiophene. 
     The oxidant mixture at least includes an oxidant, a polyether, and a nitrogen-containing compound or a nitrogen-containing polymer, or at least includes the oxidant and a polyether with nitrogen-containing functional groups. 
     The oxidant includes a ferric ion-containing salt, a copper ion-containing salt, or a persulfate. The ferric ion-containing salt includes ferric sulfate, ferric p-toluenesulfonate, ferric chloride, ferric nitriate, ferric perchlorate, or a combination thereof. The persulfate includes sodium persulfate, ammonium persulfate, or a combination thereof. 
     The polyether at least has a repeating unit structure represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein R is a linear or branched aliphatic structure, or a liner or branched aromatic structure; and n is from 1 to 1000. 
     The polyether includes polyethylene glycol (PEG), a polyethylene glycol copolymer, polyethylene oxide (PEO), a polyethylene oxide copolymer, polypropylene glycol (PPG), a polypropylene glycol copolymer, polyoxymethylene, a polyoxymethylene copolymer, polyphenylene oxide, a polyphenylene oxide copolymer, or a combination thereof. 
     The nitrogen-containing compound includes an imidazole compound, an imidazole derivative, an imidazoline compound, an imidazoline derivative, an urea compound, an urea derivative, an urethane compound, an urethane derivative, an imide compound, an imide derivative, an amide compound, an amide derivative, a pyridine compound, a pyridine derviative, a malamine compound, a malamine derivative, a triazole compound, a triazole derivative, or a combination thereof. 
     The nitrogen-containing polymer includes polyacrylamide, polyvinyl pyrrolidone, polyvinyl pyridine, polyethyleneimine, polyamide, polyimide, a secondary amine-containing polymer, a tertiary amine-containing polymer, a quaternary amine-containing polymer, or a combination thereof. 
     The amount ratio of components of the electrolyte mixture is not limited herein. In an embodiment, in order to provide better electrolyte properties, the monomer of the conductive polymer and the oxidant are in a molar ratio of 2.5:1 to 1:2.5. 
     The amount ratio of components of the oxidant mixture, the molecular weight of the polyether, and the molecular weight of the nitrogen-containing polymer are not limited herein. In an embodiment, in order to provide an adequate liquid viscosity for the following reaction and fabrication of the capacitor, the amount of the polyether is not higher than 50 wt % of the oxidant mixture, the amount of an oxidant in the oxidant mixture is not higher than 70 wt % of the oxidant mixture. Besides, the nitrogen-containing compound or the repeating units of the nitrogen-containing polymer or nitrogen-containing functional groups of the nitrogen-containing polyether to the oxidant are in a molar ratio of no more than 2. 
     The conductive polymer mixture as a solid electrolyte polymerized from the monomer of the conjugated polymer and the oxidant mixture at least includes a conjugated polymer, a polyether and a nitrogen-containing compound, or at least includes the conjugated polymer, the polyether and a nitrogen containing polymer, or at least includes the conjugated polymer and a polyether with nitrogen-containing functional groups. 
     In the conductive polymer mixture as a solid electrolyte, the conjugated polymer includes polythiophene, a polythiophene derivative, polypyrrole, a polypyrrole derivative, polyaniline, a polyaniline derivative, or a combination thereof. 
     In the conductive polymer mixture as a solid electrolyte, the polyether and the nitrogen-containing compound are the same as those described above. 
     In an embodiment, the conductive polymer mixture as a solid electrolyte includes 10 wt % to 50 wt % of the conjugated polymer, 7 wt % to 40 wt % of the polyether, and 1.5 wt % to 10 wt % of the nitrogen-containing compound. In another embodiment, the conductive polymer mixture as a solid electrolyte includes 10 wt % to 50 wt % of the conjugated polymer, 7 wt % to 40 wt % of the polyether, and 1.5 wt % to 10 wt % of the nitrogen-containing polymer. 
     Other compounds can be added to the formulation and composition of the electrolyte mixture herein, so as to adjust properties to meet various requirements. For example, p-toluenesulfonic acid as a doping agent can be added to provide better conductive properties for the solid electrolyte mixture, or tetrahydrofuran (THF) can be added to improve processing or reaction properties. 
     As for the formulation and composition of the electrolyte mixture herein, the mixing sequence of components can be adjusted upon the actual requirement. For example, the polyether and the nitrogen-containing compound can be mixed with the monomer, and the oxidant is then added thereto to initiate the polymerization reaction. 
       FIG. 1  is a process flow of a method of fabricating a solid electrolytic capacitor according to an exemplary embodiment. 
     Referring to  FIG. 1 , in an embodiment, a method of fabricating a solid electrolytic capacitor includes implementing a step  10 , in which an anode aluminium foil with an Al 2 O 3  dielectric layer and a cathode aluminium foil are wound together with an interposed separator, so as to fabricate a solid electrolytic capacitor element. The solid electrolytic capacitor element is subjected to an electrochemical reforming, in which the surface of the metal electrode is oxidized by an electrochemical electrolysis reaction to form a metal oxide dielectric layer on the anode. 
     Thereafter, a step  20  is implemented to dip the solid electrolytic capacitor element in the monomer solution of the conjugated polymer and the oxidant mixture solution. 
     Afterwards, a step  30  is implemented to carry out a polymerization at elevated temperature, in which a polymerization reaction is accelerated with increasing temperature, so as to form a conductive polymer on the surface of the dielectric layer. The conductive polymer serves as an electrolyte mixture of the solid electrolytic capacitor. The elevated temperature up to 170° C. maximum is provided to ensure a complete polymerization. 
     Then, a step  40  is implemented to perform sealing and aging, in which the solid electrolytic capacitor element is encased in a case, sealed and aged. The case is an aluminium case, for example. The solid electrolytic capacitor element is sealed with rubber. The solid electrolytic capacitor is thus completed. 
     The solid electrolytic capacitor herein can be fabricated with other known methods and the fabricating method thereof is not limited by the said embodiment. 
     The oxidant mixture for conjugated polymer synthesis herein can effectively and synergistically increase the static capacitance of the fabricated solid electrolytic capacitor. 
     Example 1 
     An anode aluminium foil having an Al 2 O 3  dielectric layer formed through an electrochemical reaction at 41V and a cathode aluminium foil having a high surface area caused by electrochemical corrosion were wounded together with an interposed separator, so as to form a solid electrolytic capacitor element. Then, the capacitor element was put in an organic acid solution for an electrochemical reforming of the damaged Al 2 O 3  dielectric layer. The reforming capacitor element was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 1, respectively. A polymerization reaction was then accelerated at elevated temperature up to 170° C. maximum to ensure a complete polymerization. Thereafter, the capacitor element was encased in an aluminum case, sealed with rubber, and aged at 125° C. with an applied voltage of 16 V to lower the leakage current of the capacitor. A solid electrolytic capacitor of Example 1 was thus completely fabricated. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 1 were measured and listed in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 imidazole 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 2.99 
                 47.01 
                 Average 
                 168.15 
                 10.52 
                 5.13 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.67 
                 0.30 
                 2.82 
               
               
                 4 
                 50 
                 10 
                 2.99 
                 37.01 
                 Average 
                 246.08 
                 9.61 
                 2.92 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.86 
                 0.40 
                 1.22 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and imidazole to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 1. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 168 μF by addition of only imidazole to the oxidant solution; that is, imidazole alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and imidazole are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 246 μF; that is, the co-existence of polyethylene glycol and imidazole has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and imidazole can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively and synergistically enhanced. 
     Example 2 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 2, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 2. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 2 were measured and listed in Table 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                 2-methyl 
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 imidazole 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 3.60 
                 46.4 
                 Average 
                 181.07 
                 11.71 
                 3.21 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 3.17 
                 0.69 
                 1.88 
               
               
                 4 
                 50 
                 10 
                 3.60 
                 36.4 
                 Average 
                 250.14 
                 9.44 
                 4.03 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.93 
                 0.29 
                 2.68 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and 2-methyl imidazole to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 2. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is maintained at 181 μF by addition of only 2-methyl imidazole to the oxidant solution; that is, 2-methyl imidazole alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and 2-methyl imidazole are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 250 μF; that is, the co-existence of polyethylene glycol and 2-methyl imidazole has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and 2-methyl imidazole can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 3 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 3, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 3. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 3 were measured and listed in Table 3. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 urea 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 2.64 
                 47.56 
                 Average 
                 164.22 
                 10.91 
                 17.65 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.63 
                 0.31 
                 14.84 
               
               
                 4 
                 50 
                 10 
                 2.64 
                 37.56 
                 Average 
                 223.04 
                 9.87 
                 3.87 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.05 
                 0.38 
                 2.75 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and urea to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 3. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 164 μF by addition of only urea to the oxidant solution; that is, urea alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and urea are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 223 μF; that is, the co-existence of polyethylene glycol and urea has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and urea can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 4 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 4, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 4. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 4 were measured and listed in Table 4. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 urethane 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 7.82 
                 42.18 
                 Average 
                 175.81 
                 10.57 
                 35.73 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 4.15 
                 0.65 
                 26.33 
               
               
                 4 
                 50 
                 10 
                 7.82 
                 32.18 
                 Average 
                 230.37 
                 8.70 
                 1.91 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.60 
                 0.40 
                 0.91 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and urethane to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 4. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 176 μF by addition of only urethane to the oxidant solution; that is, urethane alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and urethane are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 230 μF; that is, the co-existence of polyethylene glycol and urethane has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and urethane can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 5 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 5, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 5. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 5 were measured and listed in Table 5. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 succinimide 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 8.70 
                 41.30 
                 Average 
                 163.77 
                 9.06 
                 14.89 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.35 
                 4.17 
               
               
                 4 
                 50 
                 10 
                 8.70 
                 31.30 
                 Average 
                 232.68 
                 9.01 
                 2.64 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 3.82 
                 0.23 
                 2.18 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and succinimide to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 5. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 164 μF by addition of only succinimide to the oxidant solution; that is, succinimide alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and succinimide are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 233 μF; that is, the co-existence of polyethylene glycol and succinimide has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and succinimide can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 6 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 6, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 6. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 6 were measured and listed in Table 6. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                 N-methyl 
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 acetamide 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 210.03 
                 9.51 
                 6.78 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.21 
                 0.38 
                 5.45 
               
               
                 3 
                 50 
                 — 
                 3.21 
                 46.79 
                 Average 
                 158.24 
                 9.55 
                 12.68 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.79 
                 0.47 
                 8.43 
               
               
                 4 
                 50 
                 10 
                 3.21 
                 36.79 
                 Average 
                 233.06 
                 8.88 
                 3.42 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.76 
                 0.36 
                 1.47 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and N-methyl acetamide to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 6. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 210 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 158 μF by addition of only N-methyl acetamide to the oxidant solution; that is, N-methyl acetamide alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and N-methyl acetamide are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 233 μF; that is, the co-existence of polyethylene glycol and N-methyl acetamide has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polyethylene glycol and N-methyl acetamide can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 7 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 7, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 7. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 7 were measured and listed in Table 7. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 7 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polypropylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 imidazole 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 185.63 
                 8.68 
                 17.67 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 3.05 
                 0.40 
                 18.68 
               
               
                 3 
                 50 
                 — 
                 2.99 
                 47.01 
                 Average 
                 168.15 
                 10.52 
                 5.13 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.67 
                 0.30 
                 2.82 
               
               
                 4 
                 50 
                 10 
                 2.99 
                 37.01 
                 Average 
                 218.42 
                 8.75 
                 38.68 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.92 
                 0.30 
                 35.84 
               
               
                   
               
               
                 *The molecular weight of polypropylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polypropylene glycol and imidazole to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 7. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 185 μF by addition of polypropylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 168 μF by addition of only imidazole to the oxidant solution; that is, imidazole alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polypropylene glycol and imidazole are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 218 μF; that is, the co-existence of polypropylene glycol and imidazole has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that the co-existence of polypropylene glycol and imidazole can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 8 
     Jeffamine® D230 (represented by formula I below) as a diamine compound available from Huntsman Corporation and succinic acid were mixed in a molar ratio of 5:4, and reacted completely under nitrogen at 160° C. Excessive acetic acid was added thereto, and the resulting solution was refluxed and reacted at the same temperature until the reaction was completed. The generated water and the remaining acetic acid were removed by heating under reduced pressure. Therefore, a polyether-amide copolymer having a molecular weight of 1500 (polyoxypropylene-amide in Table 8 represented by formula II below) was obtained. The copolymer was added to the oxidant solution according to the amount ratio of Table 8. 
     
       
         
         
             
             
         
       
     
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 8, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 8. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 8 were measured and listed in Table 8. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 8 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                 polyoxy- 
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polypropylene 
                 N-methyl 
                 propylene- 
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 acetamide 
                 amide 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                   
                   
                 — 
                 50 
                 Average 
                 180.14 
                 10.59 
                 9.57 
               
               
                   
                   
                   
                   
                   
                   
                 Std. 
                 1.77 
                 0.55 
                 4.30 
               
               
                 2 
                 50 
                 10 
                   
                   
                 40 
                 Average 
                 185.63 
                 8.68 
                 17.67 
               
               
                   
                   
                   
                   
                   
                   
                 Std. 
                 3.05 
                 0.40 
                 18.68 
               
               
                 3 
                 50 
                 10 
                 7.5 
                 — 
                 32.5 
                 Average 
                 224.63 
                 10.19 
                 3.71 
               
               
                   
                   
                   
                   
                   
                   
                 Std. 
                 2.65 
                 0.28 
                 1.72 
               
               
                 4 
                 50 
                 — 
                 — 
                 17.5 
                 32.5 
                 Average 
                 224.91 
                 9.58 
                 2.72 
               
               
                   
                   
                   
                   
                   
                   
                 Std. 
                 5.55 
                 0.37 
                 1.09 
               
               
                   
               
               
                 *The molecular weight of polypropylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polypropylene glycol and polyoxypropylene-amide copolymer to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 8. It is found that the static capacitance of the solid electrolytic capacitor is increased from 180 μF to 185 μF by addition of polypropylene glycol to the oxidant solution. However, when both polypropylene glycol and N-methyl acetamide are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is greatly enhanced from 180 μF to 224 μF. It is also found that when polyoxypropylene-amide is used instead of polypropylene glycol and N-methyl acetamide, the static capacitance of the solid electrolytic capacitor is still maintained at 224 μF. The results show that the addition of polyoxypropylene-amide or addition of both polypropylene glycol and N-methyl acetamide has the same effect on improvement of the static capacitance of the solid electrolytic capacitor. 
     In view of the results, a polymer formed from a polyether and a nitrogen-compound can function as polypropylene glycol and N-methyl acetamide mixed each other in the oxidant solution, both of which can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     Example 9 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 9, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 9. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 9 were measured and listed in Table 9. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 9 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 ferric 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 imidazole 
                 1-butanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 40 
                 — 
                 — 
                 60 
                 Average 
                 187.91 
                 12.64 
                 20.67 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.70 
                 0.49 
                 14.70 
               
               
                 2 
                 40 
                 10 
                 — 
                 50 
                 Average 
                 211.86 
                 10.16 
                 5.05 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.79 
                 0.41 
                 4.26 
               
               
                 3 
                 40 
                 — 
                 2.39 
                 57.61 
                 Average 
                 174.35 
                 14.80 
                 10.98 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 2.77 
                 0.49 
                 6.09 
               
               
                 4 
                 40 
                 10 
                 2.39 
                 47.61 
                 Average 
                 236.29 
                 11.84 
                 2.33 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 4.69 
                 0.55 
                 1.58 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     The effect of polyethylene glycol and imidazole to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 9. It is found that the static capacitance of the solid electrolytic capacitor is increased from 187 μF to 211 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly reduced to 174 μF by addition of only imidazole to the oxidant solution; that is, imidazole alone in the oxidant solution does not improve the static capacitance of the solid electrolytic capacitor. However, when both polyethylene glycol and imidazole are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 236 μF. The results show that the co-existence of polyethylene glycol and imidazole can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. Besides, by comparison with Example 1, it is proved that the synergistic effect of the co-existence of polyethylene glycol and imidazole on improvement of the static capacitance of the solid electrolytic capacitor works in different solvent systems. 
     Example 10 
     A solid electrolytic capacitor element fabricated according to the manner of Example 1 was dipped in a monomer solution of 3,4-ethylenedioxythiophene (EDOT) and an oxidant solution listed in Table 10, followed by polymerization, sealing and charge aging with reference to the conditions of Example 1, so as to form a solid electrolytic capacitor of Example 10. The properties such as static capacitance, 100 kHz equivalent series resistance (ESR), leakage current (LC) of each solid electrolytic capacitor of Example 10 were measured and listed in Table 10. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 10 
               
             
            
               
                   
                   
               
               
                   
                 Composition of oxidant solution (wt %) 
                 Solid electrolytic capacitor properties 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 copper 
                   
                   
                   
                   
                 100 kHz 
                   
               
               
                   
                 p-toluene- 
                 polyethylene 
                   
                   
                 Capacitance 
                 ESR 
                 LC 
               
               
                 # 
                 sulfonate 
                 glycol* 
                 imidazole 
                 methanol 
                 (μF) 
                 (mΩ) 
                 (μA) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 50 
                 — 
                 — 
                 50 
                 Average 
                 10.12 
                 276.85 
                 0.93 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 3.62 
                 172.79 
                 0.20 
               
               
                 2 
                 50 
                 10 
                 — 
                 40 
                 Average 
                 5.21 
                 81.30 
                 4.93 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.99 
                 32.00 
                 0.42 
               
               
                 3 
                 50 
                 — 
                 4.20 
                 45.80 
                 Average 
                 13.28 
                 63.84 
                 1.64 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 1.17 
                 7.36 
                 0.69 
               
               
                 4 
                 50 
                 10 
                 4.20 
                 35.80 
                 Average 
                 93.25 
                 1.15 
                 2.03 
               
               
                   
                   
                   
                   
                   
                 Std. 
                 5.99 
                 0.12 
                 0.29 
               
               
                   
               
               
                 *The molecular weight of polyethylene glycol is 1000. 
               
            
           
         
       
     
     When the oxidant solution includes copper p-toluene-sulfonate, the effect of polyethylene glycol and imidazole to the solid electrolytic capacitor is shown in the solid electrolytic capacitor properties listed in Table 10. It is found that the static capacitance of the solid electrolytic capacitor is decreased from 10.12 μF to 5.21 μF by addition of polyethylene glycol to the oxidant solution. It is also found that the static capacitance is slightly increased to 13.28 μF by addition of only imidazole to the oxidant solution. However, when both polyethylene glycol and imidazole are present in the oxidant solution, the static capacitance of the solid electrolytic capacitor is increased up to 93.25 μF; that is, when the oxidant solution includes copper p-toluene-sulfonate, the co-existence of polyethylene glycol and imidazole has a synergistic effect on improvement of the static capacitance of the solid electrolytic capacitor. The results show that when the oxidant solution includes copper p-toluene-sulfonate, the co-existence of polyethylene glycol and imidazole can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     In view of the foregoing, when a polyether and a nitrogen-containing compound or a nitrogen-containing polymer are present in the oxidant solution, or when a polyether with nitrogen-containing functional groups is present in the oxidant solution, each of which can achieve an unexpected effect, and therefore the static capacitance of the solid electrolytic capacitor can be affectively enhanced. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.