ELECTROCHEMICAL DEPOSITION OF HIGH PURITY SILICON IN MOLTEN SALTS

摘要

Several approaches were tried in order to develop an electrochemical route for producing high purity silicon from molten salts. SiO_2, K_2SiF_6 and metallurgical silicon were used as the source of silicon. Molten electrolytes based on chloride (CaCl_2-NaCl) and fluoride (LiF-KF) at temperatures from 550 - 900°C were used. Transient electrochemical techniques were used to study the electrochemical behaviour of dissolved silicon species. Electrolysis experiments were carried out to deposit silicon. Silicon could be cathodically deposited and anodically dissolved in molten chloride and fluoride electrolytes. High electrorefining efficiency was obtained for many elements by using a liquid Si-Cu anode. The challenge was to reduce the contents of boron and phosphorus. The energy consumption was estimated to be less than 3 kWh/kg Si. Such a low energy requirement suggests that electrorefining by using repeated steps may be a promising way to produce silicon of solar grade quality.