Alkaline Chemical Polishing Combined with Silane Electrodeposition for Improving Etched Tunnel Distribution in Aluminum Foil

A combined pretreatment strategy involving alkaline chemical polishing and silane electrodeposition was proposed for regulating the surface state of aluminum foil and the formation of etched tunnels during DC tunnel etching. Electrochemical measurements and morphological characterization were used to evaluate the effects of this pretreatment on surface electrochemical activity and etched tunnel structure. The results showed that appropriate alkaline chemical polishing facilitated the removal of rolling-induced surface relief, improved the uniformity of surface electrochemical activity, and favored the uniform deposition of the silane film. In contrast, excessive polishing generated surface pits during the polishing process, and these preformed pits subsequently promoted tunnel merging during DC tunnel etching. Under the optimal processing conditions, the combined pretreatment significantly improved the distribution uniformity and dimensional consistency of etched tunnels and suppressed tunnel merging. Under the present testing conditions, the specific capacitance increased from 0.386 to 0.509 μF cm−2, corresponding to an improvement of approximately 31.9%. This work provides an effective approach for optimizing etched tunnel structure and improving the capacitance-related performance of aluminum capacitor foil.