High purity Cu electrodeposition from a CuCl-1-Butylpyridinium chloride (BPC) ambient-temperature molten salt electrolyte has been investigated. In this study, silver was examined as an impurity. Ag did not electrodeposit in the Cu deposit and the Cu purity was 99.9999%, if the Ag(I) ion concentration was controlled to be less than 10 ppm in the 66.7mol%CuCl-33.3mol%BPC melt and less than 12ppm in the 44.0mol%CuCl-56.0mol%BPC melt. In addition, a method removal of the Ag(I) ion from the melt was studied. The method of refining by galvanostatic electrolysis at a large current density (25mA·cm−2) was effective, and the Ag(I) ion concentration in the melt decreased to lower than 9ppm. Furthermore, the codeposit of Cu with the N included in the BPC, which was the main content in the bath was also examined. The electrodeposition of N was not recognized.
