Electrodeposition of Silicon from the Low-Melting LiCl-KCl-CsCl-K₂SiF₆ Electrolytes

Abstract

The possibility of silicon electrodeposition from the low-melting LiCl-KCl-CsCl-K2SiF6 electrolytes has been studied. The stability of a silicon-containing additive was studied by cyclic voltammetry, and the rate constant of the chemical reaction of SiF4 release at a temperature of 827 K was calculated. It is determined that the constants of velocity values in the melt based on eutectic composition are 2 orders of magnitude higher, which indicates a higher rate of formation of volatile compounds. Cyclic voltammetry was also used to study the electrochemical behavior of K2SiF6 in the melts under study. It was found that the silicon electroreduction at the cathode is not reversible and proceeds in one 4-electron reaction. The diffusion coefficients calculated by the Matsuda-Ayabe equation were 3.28⸱10-5 and 0.72⸱10-5 cm2·s-1 at temperature of 753 and 823 K for each melt, respectively. According to the obtained voltammograms, the parameters for the silicon electrodeposition were selected. At a potential of -0.4 V vs QRE, dendritic silicon deposits were obtained.

Study of the Silicon Electrochemical Nucleation in LiCl-KCl-CsCl-K2SiF6 Melt

“…It was shown in Ref. 24 that in the melt of the eutectic composition (wt%) 30.3LiCl-15.3KCl-54.4CsCl, the concentration of silicon ions reaches equilibrium only 8 h after the melting of the mixture with 1 wt% K 2 SiF 6 . In this work, an electrolyte with a higher equilibrium concentration of silicon-containing ions (wt%) 8.7LiCl-9.8KCl-81.5CsCl+3K 2 SiF 6 was selected experimentally.…”

“…In our previous works, 24,25 a method was proposed for the electrodeposition of silicon from a molten LiCl-KCl-CsCl system at a temperature not exceeding 550 °C. The advantages of this system are the possibility of purification of salts by zone recrystallization and more thermal stability of silicon-containing ions in the melt.…”

Silicon Electrodeposition for Microelectronics and Distributed Energy: A Mini-Review

“…We carried out a series of experiments on silicon electrodeposition from low-fluoride systems based on mixtures of KCl, CsCl, and LiCl with additions of K2SiF6 and SiO2 in the temperature range 350 to 790 °С [32][33][34][35][36]. Due to the possibility of deep purification of chlorides by zone recrystallization [37], the proposed systems are suitable for use to obtain high-purity silicon.…”

“…As a result of the electrolysis of KCl-K2SiF6, KCl-K2SiF6-SiO2, KCl-CsCl-K2SiF6, and LiCl-KCl-CsCl-K2SiF6 melts, we obtained silicon deposits of various morphologies by varying the electrolysis parameters [32][33][34][35][36]. In particular, at a cathode current density of 20 to 150 mA cm −2 , silicon fibers (diameter 100-700 nm), tubes, and needles (diameter 100-400 nm) were obtained, the specific capacity of which after 15 cycles varied from 200 to 850 mAh g −1 .…”

Electrochemical Behaviors and Extraction of Ln(III) (Ln = La, Ce, Nd) Ions in LiCl–KCl–CsCl Eutectic Salts at Low Temperatures

“…However, the operating temperature of chloride salts requires that the salt be kept melted at all times, which imposes severe limitations on the equipment. , From the safety and economic point of view, lower operating temperatures are considered to be beneficial for reducing safety risks, saving costs, and facilitating the commercial application of the pyrochemical process. Therefore, compared with binary molten salts, the ternary eutectic salts LiCl–KCl–CsCl (mp = 538 K), which has a lower melting point compared to binary molten salts, has gradually attracted the attention of researchers in recent years. ,− As an ionic medium, the LiCl–KCl–CsCl eutectic was considered to have potential in the preparation of ammonia, and it can also be used for the preparation of semiconductor material Si. − It also shows sufficient potential to be used in spent fuel reprocessing processes. The electrochemical behaviors and the absorption spectra of Nd­(III) and Dy­(III) were studied in LiCl–KCl–CsCl. , The electrochemical behavior of U­(III) was also determined and metallic U was obtained by electrolysis in the range of 573–773 K. , In a word, the lower operating temperature of the LiCl–KCl–CsCl molten salt can greatly reduce the requirements of operating equipment, which is of great significance for the commercial application of the pyrochemical process. , …”