Electrodeposition of Crystalline Si Using a Liquid Zn Electrode in Molten KF–KCl–K2SiF6

Abstract

In this study, we propose a novel Si electrodeposition method using a liquid Zn electrode in molten KF–KCl. Electrochemical measurements and electrolysis were conducted in a KF–KCl–K2SiF6 melt at 923 K. Cyclic voltammograms at a liquid Zn electrode revealed that the reduction currents at 0.75–1.0 V vs K+/K were attributed to the formation of Si–Zn liquid alloy. Additionally, Si was deposited through potentiostatic electrolysis at 0.75 V using liquid Zn in a boron nitride (BN) crucible as an electrode. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that deposited Si was located at the bottom and side of the interface between Zn and the BN crucible instead of at the interface between Zn and the molten salt, indicating the electrodeposition of Si attributed to Si–Zn liquid alloy formation. The obtained Si was confirmed to be the crystalline form by X-ray diffractometry, and the maximum grain size was approximately 2 mm. Galvanostatic electrolysis at –20 mA cm–2 with varying electrical charges showed that the Si grain size increased with increasing charge, confirming the growth of crystalline Si. Finally, the mechanism of Si electrodeposition on a Zn electrode through Si–Zn alloying was discussed.