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.

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 .…”

Silicon electrowinning by molten salts electrolysis

“…Ag and Si are separated during the cooling process, where Ag is deposited on Ni. Si nanowires can also be electrodeposited in KCl-containing K 2 SiF 6 at temperatures below 800°C ( Trofimov et al, 2022 ). The morphology of the Si nanowires highly depends on the overpotential applied during the potentiostatic electrolysis.…”

Quantifying Aging-Induced Irreversible Volume Change of Porous Electrodes

“…Reversible active material volume change is known to be dependent on the lithium concentration [80][81][82][83][84][85] in the host material due to crystalline structure changes or phase changes, and can change during cycles, as is typical with graphite [86][87][88][89][90][91][92][93][94][95][96][97] based systems. In our previous work, we focused on predicting the cell level volume change utilizing both a constant molar volume change 26,34,38,40,41,[98][99][100] due to lithium intercalation into an active material, as well as an empirical function 35,42 governing the molar volume change of an active material due to lithium intercalation.…”