| Conductive polymer polypyrrole (PPy) was used as cathode materials for chip-typesolid aluminum electrolytic capacitors, in which the PPy cathode was prepared bychemical and electrochemical polymerization, a so-called “two-step method”. This studyhas investigated the effect of several key factors in the electrochemical polymerization stepon electrical properties of the capacitors. The key factors included solvent type ofelectrolyte, additives in electrolyte solution, electro-polymerization temperature, cathodicmaterials, etc. It was found that the best capacitor properties could be achieved byelectro-polymerization of PPy cathode at15℃in a water-based electrolyte solution with anadditive of4.0%PVA and by using carbon materials as cathode electrode. With suchimproved electrochemical system, average Cap value of the6.3V100μF capacitors wasincreased from92.9μF to104.7μF and average ESR was decreased from11.4m to7.3m.The capacitors prepared by the improved electrochemical system were tested forreliability such as storage life and durability etc. In addition, high frequency application,filter performance and noise cancellation, were also tested. The results indicated thatcapacitors in the experimental group were more stable than other groups under hightemperature storage, which demonstrated that PPy cathode made by the improved systemhad better thermal stability. The ESR of the experimental group were also more stableafter humidity test, and the post-tested value was only9.3m. After the1000h durabilitytest, capacitors in the experimental group remained higher Cap with less reduction andlower ESR with smaller rise. In the tests of filter performance and noise cancellation,capacitors were used as DC/DC converters or output capacitors in a switching powersupply. With the capacitors from the experimental group, the output ripple voltage wassignificantly improved. At a frequency of1MHz, the capacitors had reduced the noisescale from5.52mV to3.58mV. |
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