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

Abstract

We propose a novel Si electrodeposition process using a liquid Zn electrode in molten KF–KCl. As the first step of the study, electrochemical measurement and electrolysis were conducted in a KF–KCl–K2SiF6 melt at 923 K. Cyclic voltammograms at a liquid Zn electrode showed the reduction currents due to Si–Zn formation around 0.8 V vs. K+/K. Si deposition was conducted by potentiostatic electrolysis at 0.75 V using liquid Zn in a BN crucible as an electrode. Crystalline Si was deposited not at the boundary between Zn and the molten salt, but at the bottom and side interfaces between Zn and the BN crucible, indicating that Si was electrodeposited via Si–Zn alloy formation. Galvanostatic electrolysis at −20 mA cm−2 with various electrical charges showed that the Si particle size increased with increasing charge, confirming the growth of crystalline Si. Finally, a mechanism of Si electrodeposition via Si–Zn alloying was discussed.