An electroplating apparatus for filling recessed features on a semiconductor substrate includes an electrolyte concentrator configured for concentrating an electrolyte having Cu2+ ions to form a concentrated electrolyte solution that would have been supersaturated at 20° C. The electrolyte is maintained at a temperature that is higher than 20° C., such as at least at about 40° C. The apparatus further includes a concentrated electrolyte reservoir and a plating cell, where the plating cell is configured for electroplating with concentrated electrolyte at a temperature of at least about 40° C. Electroplating with electrolytes having Cu2+ concentration of at least about 60 g/L at temperatures of at least about 40° C. results in very fast copper deposition rates, and is particularly well-suited for filling large, high aspect ratio features, such as through-silicon vias.