Institute of High-temperature Electrochemistry of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:
Yu. P. Zaykov, Professor, Director, e-mail: dir@ihte.uran.ru
A. V. Isakov, Junior Researcher
A. P. Apisarov, Researcher
O. V. Chemezov, Senior Researcher

Nowadays, silicon is widely used in electronic industry and metallurgy. Silicon nanomaterials can provide significant efficiency gains of anodes for lithium-ion electrochemical cells and photovoltaic cells. The main method of obtaining of high-purity silicon and silicon-based nanomaterials is a gas phase deposition. This method has a relatively high specific energy consumption and complex apparatus design. Therefore, it is urgent to develop new methods of silicon production. Electrolysis of molten salts is a promising method for production of silicon and silicon-based nanomaterials. Relatively cheap materials, such as K₂SiF₆ and SiO₂, can be used in this case as raw materials. Solutions of potassium hexafluorosilicate or silica in the mixture of alkali metal halides are promising electrolytes. In this paper, electrolytic deposition of silicon from the KF – KCl – K₂SiF₆ and KF – KCl – K₂SiF₆ – SiO₂ melts was investigated depending on the temperature, cathode current density and electrolyte composition. The process of silicon electrolysis was carried out in a laboratory scale cell with a high cathodic current yield (up to 93%). The composition and structure of the resulting deposits were studied using scanning electron microscopy, X-ray diffraction and X-ray analysis. This paper represents the results of the silicon electrolysis in molten KF – KCl – K₂SiF₆ and KF – KCl – K₂SiF₆ – SiO₂. Continuous layers and silicon nanowires were obtained by the electrolysis of halide and oxide-halide melts. Electron microscopy data and X-ray analysis revealed the influence of oxygen on the silicon cathode structure. It was found that the addition of silica to molten KF – KCl – K₂SiF₆ reduces the average grain size.

1. Nemchinova N. V., Klets V. E. Kremniy: svoystva, poluchenie, primenenie (Silicon: properties, obtaining, application). Irkutsk : Publishing House of Irkutsk State Technical University, 2008. 272 p.
2. Gerasimenko N. N., Parkhomenko Yu. N. Kremniy — material nanoelektroniki (Silicon — nanoelectronics material). Moscow : Tekhnosfera, 2007. 352 p.
3. Candace K. Chan, Peng H., Liu G., Mc Ilwrath K., Zhang X. F., Huggins R.A. and Cui Y. High-performance lithium battery anodes using silicon nanowires. Nature Nanotechnology. 2008. No. 3. pp. 31–35.
4. Stelzner Th., Pietsch M., Andra G., Falk F., Ose E., Christiansen S. Silicon nanowires-based solar cells. Nature Nanotechnology. 2008. Vol. 19. pp. 203–295.
5. O’Mara W. C., Herring R. B., Hunt I. P. Handbook of semicon ductor silicon technology. New Jersey : Noyes Publications, 1990. 795 p.
6. Givargizov E. I. Rost nitevidnykh i plastinchatykh kristallov iz para (Growth of fibrus and lamellar crystals from steam). Moscow : Nauka, 1977. 304 p.
7. Chemezov O. V., Batukhtin V. P., Apisarov A. P., Isakov A. V., Zaykov Yu. P. Sposob polucheniya nano- i mikrovolokon kremniya elektrolizom dioksida kremniya iz rasplavov soley (Method of obtaining of nanofibre and microfibre of silicon by electrolysis of silicon dioxide from salts‘ dissolutions). Patent RF, No. 2427526. Applied: June 01, 2012. Published: August 27, 2011.
8. Zaikov Yu. P., Redkin A. A., Apisarov A. A., Korzun I. V., Kulik N. P., Isakov A. V., Kataev A. A., Chemezov O. V. Silica solubility in molten fluoride-chloride electrolytes and density of KF – KCl – K₂SiF₆ – SiO₂ melts. Journal of chemical and engineering data. 2013. Vol. 58(4). pp. 932–937.
9. Frolenko D. B., Martemyanova Z. S., Valeev Z. I., Baraboshkin A. N. Elektrokhimiya — Russian Journal of Electrochemistry. 1992. Vol. 28, No. 12. pp. 1737–1745.
10. Frolenko D. B., Martemyanova Z. S., Baraboshkin A. N., Plaksin S. V. Rasplavy – Melts. 1993. No. 5. pp. 42–49.