Electrodeposition of Silicon from Molten KCl-K2SiF6 for Lithium-Ion Batteries

Abstract

In this paper we report characteristics and electrochemical properties of silicon fibers used as lithium-ion battery anode. All samples were synthesized by potentiostatic electrodeposition from molten KCl–K2SiF6. From molten KCl–CsCl–K2SiF6 deposition was carried out in galvanostatic mode. Despite the synthesis in inert atmosphere and absence of oxygen containing compounds in the melt resulting silicon after washing contains at least 15 at% oxygen. Silicon fibers synthesized at −250 mV (vs Si) were the thinnest with diameter as small as 100 nm; average fiber length increased with increasing overvoltage. Addition of CsCl to the melt results in decrease of the average fibers diameter. Silicon fibers synthesized at −250 mV (vs Si) in KCl–K2SiF6 melt showed the best cycling performance with capacity of 1030 mAh·g−1 at 0.2 A·g−1 discharge current and capacity of 715 mAh·g−1 after 10 cycles. Lithium diffusion coefficients calculated from galvanostatic intermittent titration technique (GITT) are common for silicon-based anode. The highest initial diffusion coefficient value of 6.68·10−11 cm2·s−1 was achieved for silicon synthesized from melt with addition of CsCl. Low capacity and rapid capacity fading for all samples can be caused by high silicon dioxide content, further treatment of synthesized silicon is necessary to achieve higher performance.