## 4 Conclusions  
In this work, we studied the effect of cathode overvoltage and the addition of SiO\({}_{2}\) on the morphology of silicon electrolytic deposits obtained from KCl-K\({}_{2}\)SiF\({}_{6}\) and KCl-K\({}_{2}\)SiF\({}_{6}\)-SiO\({}_{2}\) melts at a temperature of 790 \({}^{\circ}\)C. Using scanning electron microscopy, it was shown that during electrolysis of the KCl-K\({}_{2}\)SiF\({}_{6}\) melt, nano-sized disordered fibers (300-400 nm in diameter) are formed on the cathode, while the addition of SiO\({}_{2}\) to the melt leads to an ordered growth of silicon deposit in the form of nano-sized needles and tubes (diameter 200-400 nm, length 30-60 \(\upmu\)m). At the same time, it was noted that an increase in cathode overvoltage during the electrolysis of the studied molten electrolytes has virtually no effect on the morphology and size of the deposit, which may be associated with the course of the process under the conditions of a slowed-down preceding chemical reaction of the silicon-containing ion dissociation.  
According to EDX analysis, the average oxygen content in silicon deposits obtained during the electrolysis of the KCl-K\({}_{2}\)SiF\({}_{6}\) melt was 2.1-4.3 wt.%, and in the deposits obtained during the electrolysis of this melt with the addition of SiO\({}_{2}\), the average oxygen content was 2.7-5.1 wt.%.  
Figure 7: Cycling performance and the coulombic efficiency of the Si/C made from silicon electrodeposited from (**a**) KCl–K\({}_{2}\)SiF\({}_{6}\) (samples 1–3) and (**b**) KCl–K\({}_{2}\)SiF\({}_{6}\)–SiO\({}_{2}\) (samples 4–6) at the cathode overvoltages of –0.1, –0.15, and –0.25 V. Diamonds-coulombic efficiency; squares-capacity.  
The resulting deposits were used for the manufacture of composite Si/C anode half-cells of lithium-ion batteries. All the synthesized samples have similar initial charge/discharge curves, although the capacity is different. Samples synthesized at 0.1 V show much lower capacity than the ones synthesized at 0.15 and 0.25 V overvoltage. Although the first cycle capacity of silicon synthesized with SiO\({}_{2}\) addition is lower than that of silicon obtained without additive, further cycling results in higher capacity and much higher capacity retention for all samples. For silicon deposited from KCl-K\({}_{2}\)SiF\({}_{6}\), the highest capacity value is 750 mAh-g\({}^{-1}\) with capacity retention of 46.6 % and coulombic efficiency of 92.7%. The best results are achieved for silicon synthesized from KCl-K\({}_{2}\)SiF\({}_{6}\)-SiO\({}_{2}\) at 0.15 V overvoltage; its capacity was 850 mAh-g\({}^{-1}\) after 15 cycles at a current of 200 mA-g\({}^{-1}\) and capacity retention of 74.5% with coulombic efficiency of 96.1%. Such differences in the capacity retention for the samples synthesized with and without SiO\({}_{2}\) addition is not clear and requires further investigation.  
Conceptualization, T.G. and A.S.; methodology; T.G., S.Z., N.L., A.L. and A.T.; validation, T.G. and A.S.; formal analysis, A.S. and A.T.; investigation, T.G., S.Z., N.L., A.L. and A.T.; writing--original draft preparation, T.G. and A.S.; writing--review and editing, T.G. and A.S.; supervision, A.S. and Y.Z.; project administration, A.T. and A.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. This work is performed in the frame of the State Assignment number 075-03-2020-582/1, dated 18 February 2020 (the theme number 0836-2020-0037). The authors declare no conflict of interest.