Electroreduction of silicon from the NaI–KI–K2SiF6 melt for lithium-ion power sources

Abstract

Silicon and silicon-based materials are increasingly used in microelectronics, metallurgy and power generation. To date, the active study aimed at the development of silicon materials to be used in devices for solar energy conversion, accumulation and storage is underway. In addition, silicon is a promising anode material for lithium-ion fuel cells. In the present paper, a possibility of silicon electroreduction from the NaI–KI–K2SiF6 melt in the argon atmosphere was studied. With this aim in view, the electrolysis of the NaI-KI-K2SiF6 melt with glassy carbon cathode was performed under galvanostatic and potentiostatic regimes at the temperatures from 650 to 750 °С. The morphology, phase and elemental analyses of the obtained silicon deposits were performed after their separation from the electrolytes by the ICP, SEM-EDX, XRD and Raman spectroscopy methods. Fiber and thread-like silicon samples of 60 to 320 nm in dimeter with admixture concentrations (mainly oxygen) from 1.2 to 4.6 wt.% were synthesized. The obtained samples were tested as possible Si/C composite anodes for lithium-ion power sources. The discharge capacity of such power sources after 30 cycles of lithiation-delithiation ranged from 440 to 565 mAh·g–1, and the coloumbic efficiency ranged from 89 to 91%.