Effect of Chloride Ions on the Sparking Voltage of Working Electrolytes and Its Restraint Method

As we all know, chloride ions (Cl–) are major impurities that significantly influence the lifetime and degradation of the dielectric properties of working electrolytes in aluminum electrolytic capacitors. However, the exact destructive mechanism of Cl– on the working electrolytes remains unstudied. In this work, ppm NH4Cl is added to the working electrolytes to study the formation process of dense films of anodic alumina and the sparking voltage of electrolytes. As a result, nanopores and hemispherical shapes similar to the morphologies of the porous alumina film are found in the originally dense films of anodic alumina and the sparking voltage of electrolytes also decreases. The presence of Cl– leads to the generation of electronic current (Je) and oxygen gas evolution in the anodizing process, which could decrease the sparking voltage. The oxygen bubbles inside the dense films of anodic alumina result in the generation of nanopores and hemispherical shapes within them. When 1 wt % ethylene glycol borate polyester (BPE) is added to the NH4Cl electrolytes, the morphologies of nanopores and hemispherical shapes in the dense films disappear, which proves that BPE can not only restrain the generation of Je and oxygen gas evolution but also improve the sparking voltage.